JP2013093422A - Back sheet for solar battery, and solar battery module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a back sheet for a solar battery which keeps an excellent adhesiveness between an easily stickable layer and an adhesive layer adjacent to the easily stickable layer even in a situation such that it is in a humid and hot environment over an extended period of time.SOLUTION: The back sheet for a solar battery comprises: a base material including a biaxially stretched polyester film; and an easily stickable layer which is provided on at least one side of the base material and which includes a binder including a thermoplastic resin having, in its molecule, a carboxy group, a cross-linked structure part originating from a carbodiimide crosslinking agent, and a wax including an ester of higher fatty acid and higher alcohol in a range of 1.0 mass% to 20 mass% to the total mass of the easily stickable layer.

Description

  The present invention relates to a solar cell backsheet and a solar cell module.

  Polyester is applied to various uses such as electrical insulation and optical uses. Among these, solar cell applications such as a sheet for protecting the back surface of a solar cell (so-called back sheet) have attracted attention as electrical insulation applications in recent years.

  On the other hand, polyester usually has many carboxy groups and hydroxyl groups on its surface, and tends to undergo a hydrolysis reaction under environmental conditions where moisture exists, and tends to deteriorate over time. For example, the installation environment in which solar cell modules are generally used is an environment that is constantly exposed to wind and rain, such as outdoors, and is exposed to conditions where hydrolysis reaction is likely to proceed. Therefore, polyester is applied to solar cell applications. Sometimes, it is an important property that the hydrolyzability of polyester is suppressed.

By the way, the solar cell element is generally covered with a sealing material using an ethylene / vinyl acetate copolymer (EVA) resin. In order to protect the solar cell, it is important that the back sheet adheres to the sealing material and supports the sealing material including the solar cell element. Therefore, it is preferable that the adhesiveness between the back sheet and the sealing material is high.
For example, by performing surface treatment such as corona treatment or flame treatment on the surface of the backsheet, it is possible to temporarily improve the mutual adhesion, but the adhesiveness decreases due to changes over time after the surface treatment, The processed backsheet may cause blocking.
For this reason, a functional layer capable of providing adhesion to the sealing material, a so-called easy-adhesion layer, may be formed on the back sheet. In this case, the back sheet having the easy-adhesive layer is required to exhibit the function of the easy-adhesive layer while expressing the original function of the back sheet.

  As a technology related to the above situation, a polyester film and a coating thereon are provided for the purpose of providing adhesion and adhesion to EVA as a sealing material while having excellent mechanical properties, heat resistance and moisture resistance. The resin film is formed by applying a coating liquid to a film, and the coating liquid contains 10 to 100% by weight of the crosslinking agent (A) per 100% by weight of the solid content. An easy-adhesive polyester film for use is disclosed (for example, see Patent Document 1).

JP 2006-152013 A

  However, in the film described in Patent Document 1, when an easy-adhesive layer and a functional member such as a white film are bonded together with an adhesive, the easy-adhesive layer and an adhesive layer adjacent to the easy-adhesive layer Since the adhesiveness of the solar cell element was insufficient, it was insufficient to support the sealing material including the solar cell element, and the original function of the backsheet for protecting the solar cell could not be sufficiently exhibited.

  The present invention has been made in view of the above, and a solar cell backsheet excellent in adhesiveness between an easy-adhesive layer and an adhesive layer adjacent to the easy-adhesive layer even under a long-term wet heat environment, and An object of the present invention is to provide a solar cell module capable of obtaining stable power generation performance over a long period of time, and to achieve the object.

The present invention relates to a wax in which an easy-adhesive layer containing a binder containing a thermoplastic resin having a carboxy group in the molecule and a crosslinked structure portion derived from a carbodiimide crosslinking agent further contains an ester of a higher fatty acid and a higher alcohol It has been achieved on the basis of the knowledge that the easy-adhesive layer becomes soft and sticky by containing the styrene.
Specific means for achieving the above object are as follows.

  <1> A base material containing a biaxially stretched polyester film, a binder provided on at least one surface of the base material, and containing a thermoplastic resin having a carboxy group in the molecule, a crosslinked structure portion derived from a carbodiimide crosslinking agent, And an easy-adhesive layer containing a wax containing an ester of a higher fatty acid and a higher alcohol in the range of 1.0% by mass to 20% by mass with respect to the total mass of the easy-adhesive layer. It is a back sheet.

  <2> The back sheet for a solar cell according to <1>, wherein the wax has a freezing point of 60 ° C to 150 ° C.

  <3> The solar cell according to <1> or <2>, wherein the wax includes an ester of a higher fatty acid having 13 to 30 carbon atoms and a monovalent or divalent higher alcohol having 25 to 35 carbon atoms. It is a back sheet for.

  <4> Any one of the items <1> to <3>, further including an adhesive layer containing a polyurethane-based resin on the surface opposite to the base material among the surfaces of the easy-adhesive layer. It is a solar cell backsheet as described in one.

  <5> A transparent substrate on which sunlight is incident, a solar cell element disposed on one side of the substrate, and a surface of the solar cell element disposed on the side opposite to the side on which the substrate is disposed. 1> to the solar cell backsheet according to any one of <4>.

ADVANTAGE OF THE INVENTION According to this invention, the solar cell backsheet excellent in the adhesiveness of an easily bonding layer and the adhesive bond layer adjacent to an easily bonding layer can be provided also in the wet heat environment over a long period of time. Also,
ADVANTAGE OF THE INVENTION According to this invention, the solar cell module which can obtain the stable electric power generation performance over a long term can be provided.

<Back sheet for solar cell>
The back sheet for solar cell of the present invention includes a base material including a biaxially stretched polyester film, a binder provided on at least one surface of the base material, and a thermoplastic resin having a carboxy group in the molecule, and a carbodiimide crosslinking agent. Easy-adhesive layer containing a crosslinked structure part derived from the above and a wax containing an ester of a higher fatty acid and a higher alcohol in a range of 1.0% by mass to 20% by mass with respect to the total mass of the easy-adhesive layer And is configured.
Hereinafter, “a wax containing an ester of a higher fatty acid and a higher alcohol” is also referred to as a “specific wax”, and in the present invention “a binder containing a thermoplastic resin having a carboxy group in the molecule, a crosslinked structure portion derived from a carbodiimide crosslinking agent” And an “adhesive layer containing a wax containing an ester of a higher fatty acid and a higher alcohol” is also referred to as a “specific easy adhesive layer”. In addition, a base material including a biaxially stretched polyester film may be simply referred to as a “base material”.

  The specific easy-adhesion layer has a crosslinked structure portion derived from a carbodiimide cross-linking agent in which a binder containing a thermoplastic resin having a carboxy group in the molecule is cross-linked by a carbodiimide cross-linking agent, and the specific wax includes a binder and a carbodiimide It is thought that it exists in the bridge | crosslinking body with a crosslinking agent, between a binder, and a binder, or exists in the surface of a specific easily-adhesive layer.

The conventional easy-adhesion layer has adhesiveness between the easy-adhesion layer and the adjacent layer by containing an adhesive or adhesive component. However, solar cell backsheets are often placed in an environment where they are exposed to direct sunlight and exposed to rain, and in such a moist heat environment, adhesive or sticky components deteriorate and adhesion over a long period of time. It was difficult to maintain sex.
On the other hand, the specific easy-adhesion layer has a specific wax by providing a flexibility to the specific easy-adhesion layer by the presence of the specific wax between the binder and the carbodiimide cross-linking agent or between the binder and the binder. It is thought that stickiness will occur. Such adhesiveness is considered to improve the adhesion between the adhesive layer and the specific easy-adhesion layer when the adhesive layer is adjacent to the specific easy-adhesion layer.
In addition, as an aspect in which the adhesive layer is adjacent to the specific easy-adhesive layer, an adhesive is applied to the specific easy-adhesive layer (for example, coating with an adhesive-containing coating solution), or a white color to which an adhesive is applied A mode in which a functional member such as a member is bonded to the specific easy adhesion layer so that the adhesive side and the specific easy adhesion layer face each other is conceivable.

  Furthermore, since the specific wax containing an ester of a higher fatty acid and a higher alcohol is excellent in water repellency to repel water, the specific wax is contained in the specific easy-adhesive layer, so that the surface of the specific easy-adhesive layer It is considered that the specific easy-adhesion layer can be protected from moisture such as rain water and moisture.

From the above, the layer adjacent to the specific easy-adhesion layer is formed by providing the solar cell backsheet with the specific easy-adhesion layer on at least one surface of the base material including the biaxially stretched polyester film. When is an adhesive layer, it is considered that the adhesion between the specific easy-adhesion layer and the adhesive layer is excellent, and such adhesiveness can be maintained even in a long-term wet heat environment.
Hereinafter, the easy-adhesion layer (specific easy-adhesion layer) which comprises the solar cell backsheet of this invention, a base material, and the layer which the solar cell backsheet may have as needed are demonstrated.

[Easily Adhesive Layer (Specific Easy Adhesive Layer)]
The easy-adhesion layer (specific easy-adhesion layer) in the present invention includes at least a binder containing a thermoplastic resin having a carboxy group in the molecule, a crosslinked structure portion derived from a carbodiimide crosslinking agent, and a higher fatty acid and a higher alcohol. A wax containing a specific ester (specific wax) is contained. Moreover, content of the easily-adhesive layer of specific wax is the range of 1.0 mass%-20 mass% with respect to the total mass of an easily-adhesive layer.
As long as the effects of the present invention are not impaired, a surfactant, fine particles, and the like may be further contained.

-Wax (specific wax)-
The wax contained in the specific easy-adhesion layer is not particularly limited as long as it contains an ester of a higher fatty acid and a higher alcohol. Generally, the wax is solid at room temperature (for example, 25 ° C.) and is liquid when heated. It becomes. For example, natural wax extracted from minerals such as animals, plants, or petroleum, or synthetic waxes such as polyethylene wax can be used.
More specifically, animal waxes include, for example, beeswax, spermaceti, ibota wax, and plant waxes include, for example, carnauba wax, palm wax, sugarcane wax, wood wax, rice bran wax, and mineral wax. Examples include montan wax.

Among the above, the specific wax preferably has a freezing point of 60 ° C to 150 ° C. When the freezing point is 60 ° C. or higher, the specific easy-adhesion layer is less likely to be tacky (not easily sticky) at room temperature (for example, 25 ° C.), and is prevented from being difficult to handle as a film. When the freezing point is 150 ° C. or lower, tackiness is likely to occur.
The freezing point of the specific wax is more preferably 60 ° C to 120 ° C.
As the higher fatty acid, a fatty acid having 13 to 30 carbon atoms is preferable, and examples thereof include serotic acid and palmitic acid. As the higher alcohol, an alcohol having 25 to 35 carbon atoms is preferable, for example, myricyl alcohol. As the alcohol, monovalent or divalent alcohol is usually used, and more preferably monovalent.

  Among waxes having an ester of a free fatty acid having a freezing point of 60 ° C. to 150 ° C. and a higher fatty acid having 13 to 30 carbon atoms and a higher alcohol having 25 to 35 carbon atoms, in particular, serotic acid or palmitic acid and myricyl alcohol And the like, that is, carnauba wax mainly composed of mysilyl cellotate or palm wax mainly composed of misilyl palmitate. The main component means that the content ratio in the total mass of the wax exceeds 50% by mass.

  As described above, the content of the specific wax in the easy-adhesion layer is 1.0% by mass to 20% by mass with respect to the total mass of the specific easy-adhesion layer. If the content of the specific wax in the easy-adhesive layer is not 1.0% by mass or more, the adhesion between the specific easy-adhesive layer and the adhesive cannot be obtained. The layer strength of the layer cannot be maintained, and the stickiness of the specific easily adhesive layer cannot be suppressed. The content of the specific wax in the easy-adhesive layer is preferably 3.0% by mass to 15% by mass with respect to the total mass of the specific easy-adhesive layer.

As described above, the specific easy-adhesion layer contains a specific wax in the binder or the crosslinked binder, so that the specific easy-adhesion layer is resistant to moisture, and even in a long-term wet heat environment, the easy-adhesion layer and the easy-adhesion layer The adhesive layer adjacent to the surface is excellent in adhesiveness, but also has the effect of improving the scratch resistance of the specific easily adhesive layer.
Conventionally, a wax was sometimes used to obtain the scratch resistance of the layer, but the content of the wax was usually less than 1% by mass relative to the total mass of the layer. This is because if the amount of wax is 1% by mass or more, the layer becomes too flexible and it is difficult to maintain the strength and shape of the layer, and the layer surface is sticky.
However, the specific easy-adhesive layer in the present invention has a strong cross-linking structure of a binder containing a thermoplastic resin having a carboxy group in the molecule and a carbodiimide cross-linking agent, and is excellent in layer strength. Even if the content is increased, it is possible to suppress the specific easily adhesive layer from becoming too soft and damaging the strength and shape. Therefore, the specific wax of 1% by mass or more as described above can be contained in the specific easily adhesive layer.

When the specific easy-adhesion layer is formed using the coating liquid for forming the specific easy-adhesion layer, the specific wax is dispersed in water in order to uniformly disperse the specific wax in the specific easy-adhesion layer. The resulting emulsion is preferably added to the coating solution.
The specific wax may be synthesized or a commercially available wax may be used. A commercially available wax can be obtained as an emulsion in which a specific wax is dispersed in water. Examples of commercially available waxes include, for example, Cellosol 524 manufactured by Chukyo Yushi Co., Ltd. [main component; myricyl serotate, CH ₃ (CH ₂ ) ₂₄ COO (CH ₂ ) CH ₃ , freezing point 82 ° C., solid content 30%], etc. Is mentioned.

-Binder-
The binder contained in the specific easily adhesive layer includes a thermoplastic resin having a carboxy group in the molecule.
The thermoplastic resin is excellent in flexibility and contributes to the flexibility or tackiness of the specific easy-adhesive layer, and thus the adhesiveness.
Because the thermoplastic resin has a carboxy group in the molecule, it is highly reactive with the carbodiimide crosslinking agent and can form a strong cross-linked body, so the specific easy-adhesion layer has layer strength and hydrolysis resistance. It is considered that (weather resistance) is excellent.
The thermoplastic resin having a carboxy group in the molecule constituting the binder is not particularly limited as long as it is generally used. Specific examples include (meth) acrylic resins, polyesters, ethylene-acrylic acid ester copolymer resins, and mixtures thereof.

Among these, a (meth) acrylic resin is more preferable from the viewpoint of durability (layer strength). The (meth) acrylic resin means either an acrylic resin or a methacrylic resin, or both.
Specific content of the binder in the easy adhesion layer is preferably in the range of ^{0.01g / m 2 ~5g / m 2} , the range of 0.03g ^{/ m 2} ~3g ^/ m 2 is particularly preferred. When the amount of the binder is 0.01 g / m ² or more, a better adhesive force is obtained, and when it is 5 g / m ² or less, a better surface shape is obtained.

-Crosslinked structure part derived from carbodiimide crosslinking agent-
The specific easy-adhesion layer contains a crosslinked structure portion derived from a carbodiimide crosslinking agent.
As described later, the specific easy-adhesion layer uses the specific easy-adhesion layer forming composition containing at least the binder, the specific wax, and the carbodiimide crosslinking agent as described above for forming the specific easy-adhesion layer. Can be formed. The composition for forming a specific easy-adhesive layer may be used as a coating liquid for forming a specific easy-adhesive layer by, for example, dissolving in a solvent such as water.
The carbodiimide cross-linking agent in the composition for forming a specific easy-adhesive layer reacts with the binder, and when the specific easy-adhesive layer is formed, the specific easy-adhesive layer is a cross-linked structure portion that cross-links the binder and the binder. Contains. Such a crosslinked structure part is a structure part derived from a carbodiimide crosslinking agent.

Binders containing thermoplastic resins that are rich in reactivity with carbodiimide crosslinkers and excellent in flexibility are cross-linked by carbodiimide crosslinkers, so that the specific adhesive layer is hydrolyzed even in wet and heat environments. It becomes an easily adhesive layer which is difficult and has flexibility.
Furthermore, if an acrylic resin having excellent durability is used as the thermoplastic resin having a carboxy group in the molecule, it is considered that the layer strength is further enhanced.

  Since the carbodiimide cross-linking agent also reacts with the terminal carboxy group of the biaxially stretched polyester film that is the base material in the present invention, for example, the specific easy-adhesive layer forming coating liquid described above is applied to the base material and specified. When the easy-adhesive layer is formed, the binder in the specific easy-adhesive layer and even the biaxially stretched polyester film are cross-linked, and a cross-linked structure portion derived from the carbodiimide cross-linking agent can be formed. Therefore, the specific easy-adhesion layer and the substrate are easily adhered to each other due to the crosslinking between the binder in the specific easy-adhesion layer and the biaxially stretched polyester film. Further, it is considered that such cross-linking makes it difficult for moisture to enter between the base material and the specific easy-adhesion layer, and the weather resistance of the base material can be maintained.

  Examples of the carbodiimide crosslinking agent constituting the crosslinked structure portion derived from the carbodiimide crosslinking agent include carbodiimide compounds that can be contained in the PET film that is the base material of the present invention described above. Specifically, the polyfunctional carbodiimide is is there.

  The polyfunctional carbodiimide is preferably a polycarbodiimide having a polymerization degree of 3 to 15. The polycarbodiimide generally has a repeating unit represented by “—R—N═C═N—” or the like, and the R represents a divalent linking group such as alkylene or arylene. Examples of such a repeating unit include 1,5-naphthalenecarbodiimide, 4,4′-diphenylmethanecarbodiimide, 4,4′-diphenyldimethylmethanecarbodiimide, 1,3-phenylenecarbodiimide, 2,4-tolylenecarbodiimide, 2,6-tolylenecarbodiimide, a mixture of 2,4-tolylenecarbodiimide and 2,6-tolylenecarbodiimide, hexamethylenecarbodiimide, cyclohexane-1,4-carbodiimide, xylylenecarbodiimide, isophoronecarbodiimide, dicyclohexylmethane-4, 4'-carbodiimide, methylcyclohexanecarbodiimide, tetramethylxylylene carbodiimide, 2,6-diisopropylphenylcarbodiimide and 1,3,5-triisopropylbenzene-2 Such as 4-carbodiimide and the like.

  Only 1 type may be sufficient as the carbodiimide crosslinking agent which a specific easily bonding layer contains, and 2 or more types may be sufficient as it.

The content of the crosslinked structure portion derived from the carbodiimide crosslinking agent in the specific easy-adhesive layer is preferably determined in consideration of the mass ratio with the thermoplastic resin having a carboxy group in the molecule in the binder described above. However, 5 mass%-50 mass% are preferable with respect to the binder total mass in a specific easily-adhesive layer, More preferably, they are 20 mass%-40 mass%. When the content of the crosslinked structure portion is 5% by mass or more, a good crosslinking effect can be obtained, and the strength reduction or adhesion failure of the specific easily adhesive layer hardly occurs. When the adhesive layer is formed from a coating solution, the pot life of the coating solution can be kept longer.
In addition, content of the crosslinked structure part derived from the carbodiimide crosslinking agent in the specific easy-adhesion layer is the total mass of the composition for specific easy-adhesion layer formation in the composition for specific easy-adhesion layer (specific easy adhesion). When the composition for forming an adhesive layer is a coating liquid for forming a specific easily adhesive layer, it corresponds to the content of the carbodiimide crosslinking agent relative to the total solid content of the coating liquid.

-Other ingredients-
The specific easy-adhesion layer may contain various additives within a range that does not impair the object of the present invention. Examples of such additives include surfactants, ultraviolet absorbers, light stabilizers, and antioxidants.

-Method for forming characteristically easy-adhesive layer-
The specific easy-adhesion layer is composed of a binder containing a thermoplastic resin having a carboxy group in the molecule, a carbodiimide crosslinking agent, and a composition for forming a specific easy-adhesion layer containing at least a specific wax. A layer can be formed by applying to at least one surface of the containing substrate. When providing an undercoat layer to be described later between the base material and the specific easy-adhesive layer, after forming the undercoat layer on the base material, the specific easy-adhesive layer is formed on the formed undercoat layer. What is necessary is just to provide a composition.

  The composition for forming a specific easy-adhesive layer may further contain various additives, or may contain a coating solvent to form a coating liquid (a coating liquid for forming a specific easy-adhesive layer). The coating solution may be an aqueous system using water as an application solvent, or a solvent system using an organic solvent such as toluene or methyl ethyl ketone. Among these, from the viewpoint of environmental burden, it is preferable to use water as a solvent. A coating solvent may be used individually by 1 type, and may mix and use 2 or more types. Examples of preferable coating solvents include water, water / methyl alcohol = 95/5 (mass ratio), and the like.

  Further, as described above, when using the specific easy-adhesion layer forming coating solution, the specific wax added to the specific easy-adhesion layer forming coating solution is an emulsion in which the specific wax is dispersed in water. It is preferable to add to the coating liquid for forming a specific easy-adhesive layer. The emulsion in which the specific wax is dispersed in water can be prepared by mixing the specific wax, water, and a known surfactant.

Various coating methods such as slit coating, ink-jet method, spin coating, cast coating, roll coating, screen printing, etc. are applied as methods for applying the specific adhesive layer forming composition onto the substrate (or undercoat layer). Can be given.
Before applying the coating solution to the base material (or undercoat layer), the surface of the base material (or undercoat layer) is subjected to acid etching treatment with a mixed solution of chromic sulfate, flame treatment with a gas flame, ultraviolet irradiation treatment. Surface treatment such as corona discharge treatment or glow discharge treatment may be performed.

The thickness of the specific easy-adhesive layer is not particularly limited, but is preferably 0.01 μm to 5.0 μm, and preferably 0.02 μm to 3.0 μm.
The specific easy-adhesion layer may be composed of a single layer, or may be a multilayer of two or more layers. When the specific easy-adhesion layer is a multilayer, the total thickness of the specific easy-adhesion layer composed of multiple layers is preferably 0.01 μm to 8.0 μm.

[Undercoat layer]
The solar cell backsheet of the present invention may have an undercoat layer between the specific easy-adhesion layer and a substrate containing a biaxially stretched polyester film described later.
The undercoat layer is generally used to increase the adhesion between the specific easily adhesive layer and the substrate. In the present invention, as described above, the biaxially stretched polyester film constituting the base material and the thermoplastic resin having a carboxy group in the molecule constituting the binder in the specific easy-adhesion layer form a crosslinked structure. Adhesion can be imparted, but by having an undercoat layer, adhesion is improved and further hydrolysis resistance is obtained.
The undercoat layer is composed of a binder containing an acrylic resin, a crosslinked structure portion derived from a carbodiimide crosslinking agent, and inorganic fine particles from the viewpoint of adhesion between the specific easily adhesive layer and the substrate as described above. It is preferable.

-Binder containing acrylic resin-
The binder contained in the undercoat layer only needs to contain at least an acrylic resin, and may further contain a resin other than the acrylic resin.
The binder in the undercoat layer contains a carboxy group that reacts with a carbodiimide crosslinking agent, which will be described later, and contains at least an acrylic resin with excellent durability, so that it is crosslinked by the carbodiimide crosslinking agent and exposed to rain outdoors. It can be a layer having excellent durability even in a humid heat environment.

  As an acrylic resin, what is necessary is just an acrylic resin obtained using a well-known acrylic monomer. An acrylic monomer other than the acrylic monomer can also be included as a copolymerization component. Examples of such an acrylic monomer include (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl ( (Meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, n-hexyl (meth) acrylate, 2- Ethylhexyl (meth) acrylate, acetoxyethyl (meth) acrylate, phenyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2- (2-methoxyethoxy) ethyl (meth) acrylate , Cyclohexyl ( Acrylate), benzyl (meth) acrylate, diethylene glycol monomethyl ether (meth) acrylate, diethylene glycol monoethyl ether (meth) acrylate, diethylene glycol monophenyl ether (meth) acrylate, triethylene glycol monomethyl ether (meth) acrylate, triethylene glycol mono Ethyl ether (meth) acrylate, dipropylene glycol monomethyl ether (meth) acrylate, polyethylene glycol monomethyl ether (meth) acrylate, polypropylene glycol monomethyl ether (meth) acrylate, monomethyl ether (meta) of a copolymer of ethylene glycol and propylene glycol ) Acrylate, N, N-dimethylaminoethyl Meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate.

  Examples of other resins that can be used in combination include polyester, urethane resin (polyurethane), acrylic resin (polyacryl), olefin resin (polyolefin), vinyl alcohol resin (polyvinyl alcohol), and silicone resin.

  The acrylic resin contained in the undercoat layer may be only one type or two or more types. Moreover, only 1 type may be sufficient as the other resin which can be used together with an acrylic resin, and 2 or more types may be sufficient as it.

The binder content in the undercoat layer is preferably determined in consideration of the mass ratio with the carbodiimide crosslinking agent described later, but is preferably 0.005 g / m ^{2 to} 0.1 g / m ² . The effect of this invention can be improved more by making content of a binder into the said range.

  Moreover, when using resin other than an acrylic resin together, it is preferable that content of the acrylic resin in all the binders contained in an undercoat layer is 70 mass% or more with respect to the total binder mass, and 80 mass%. More preferably. Furthermore, it is preferable that all the binders contained in the undercoat layer are acrylic resins.

-Crosslinked structure part derived from carbodiimide crosslinking agent-
The undercoat layer contains a crosslinked structure portion derived from a carbodiimide crosslinking agent.
As will be described later, the undercoat layer can be formed by drying a coating film obtained by applying a coating solution for forming the undercoat layer onto the substrate of the present invention. In the coating liquid for forming the undercoat layer, it is necessary to contain at least a binder containing the acrylic resin described above, a carbodiimide crosslinking agent, and inorganic fine particles described later. When the carbodiimide crosslinking agent in the coating solution reacts with the acrylic resin in the binder to form an undercoat layer, the undercoat layer contains a crosslinked structure portion that crosslinks the binder and the binder. Such a crosslinked structure part is a structure part derived from a carbodiimide crosslinking agent.
When the binder containing the acrylic resin having excellent durability is crosslinked, the undercoat layer becomes a layer having excellent durability even in a wet heat environment.

  Moreover, since the carbodiimide crosslinking agent in the undercoat layer also reacts with the terminal carboxy group of the biaxially stretched polyester film constituting the base material, the binder in the undercoat layer and the biaxially stretched polyester film are also crosslinked. And having a crosslinked structure portion derived from a carbodiimide crosslinking agent. Crosslinking between the binder and the biaxially stretched polyester film in the undercoat layer greatly contributes to excellent adhesion between the easily adhesive layer and the substrate. In addition, it is considered that moisture is less likely to enter between the base material and the easy-adhesion layer due to the cross-linking of the highly durable binder in the undercoat layer and the biaxially stretched polyester film, and the weather resistance of the base material is maintained. It is done.

The carbodiimide crosslinking agent constituting the crosslinked structure portion derived from the carbodiimide crosslinking agent contained in the undercoat layer is the same as the carbodiimide crosslinking agent constituting the crosslinked structure portion derived from the carbodiimide crosslinking agent contained in the specific easy-adhesive layer Is mentioned.
The carbodiimide crosslinking agent contained in the undercoat layer may be only one type or two or more types.

  The content of the crosslinked structure portion derived from the carbodiimide crosslinking agent in the undercoat layer is preferably determined in consideration of the mass ratio with the acrylic resin in the binder described above, and satisfies the formula (1) described later. It is preferable that

  The content of the crosslinked structure portion derived from the carbodiimide crosslinking agent in the undercoat layer corresponds to the amount contained in the coating liquid for forming the undercoat layer. Therefore, the content of the carbodiimide crosslinking agent in the coating solution for forming the undercoat layer is preferably set in an amount determined from the formula (1) described later.

-Inorganic fine particles-
The undercoat layer contains inorganic fine particles.
When the undercoat layer contains inorganic fine particles, the adhesion between the base material and the easy-adhesion layer of the solar cell backsheet can be increased.
The inorganic fine particles that can be contained in the undercoat layer are not particularly limited, and examples thereof include clay, mica, titanium oxide, tin oxide, calcium carbonate, carion, talc, wet silica, dry silica, colloidal silica, calcium phosphate, barium sulfate, and alumina. And zirconia.

Among these, silica (including wet, dry, and colloidal), titanium oxide, alumina, and tin oxide are preferable, and tin oxide or silica is preferable because of a small decrease in adhesion when exposed to a wet heat atmosphere. Among these, tin oxide is particularly preferable.
Tin oxide has a relatively large particle shape and relatively high surface properties compared to silica, and tends to form complex particles by forming secondary particles and tertiary particles. As a result, it is considered that the bond between the tin oxide particles and the binder resin is held stronger than that of the silica particles.

  In addition, the undercoat layer is formed by coating on the substrate of the present invention using a coating solution containing an acrylic resin, tin oxide, and a carbodiimide crosslinking agent. It has been found that the adhesion to the substrate is particularly excellent.

The inorganic fine particles that can be contained in the undercoat layer may be one type or two or more types, but when two or more types of inorganic fine particles are used, at least one of them is preferably tin oxide. The main component is preferably tin oxide. Here, the main component means that the tin oxide has a mass exceeding 50% by mass with respect to the total mass of the inorganic fine particles in the undercoat layer, and the ratio of the tin oxide to the total mass of the inorganic fine particles is: It is preferably 70% by mass or more, and more preferably 90% by mass or more.
The inorganic fine particles that can be contained in the undercoat layer are particularly preferably one type of tin oxide.

The content of the inorganic fine particles in the undercoat layer is preferably 50% by mass to 500% by mass with respect to the total mass of the binder in the undercoat layer. At this time, it is preferable that the inorganic fine particles contain tin oxide as a main component.
When the content of the inorganic fine particles in the undercoat layer is 50% by mass or more with respect to the total mass of the binder in the undercoat layer, the weather resistance and the adhesion between the easily adhesive layer and the base material Can be improved.

In general, when the content of the inorganic fine particles is a high concentration of 100% by mass or more with respect to the total mass of the binder contained in the same layer, the adhesion between adjacent layers tends to be impaired. However, since it has excellent adhesiveness due to the combination of the binder, carbodiimide cross-linking agent, and inorganic fine particles contained in the undercoat layer, the inorganic fine particles can be increased in concentration and can be contained up to 500% by mass. In particular, the combination of an acrylic resin, a carbodiimide crosslinking agent, and tin oxide is particularly excellent in the adhesion between the easy-adhesive layer and the base material of the present invention. Even if the content of the inorganic fine particles with respect to the binder is 500% by mass, the adhesion between the easily adhesive layer and the substrate of the present invention is excellent.
When the content of the inorganic fine particles with respect to the binder is 500% by mass or less, the undercoat layer is unlikely to become powdery, and the adhesion between the easily adhesive layer and the substrate of the present invention is hardly impaired.

  The content of the inorganic fine particles in the undercoat layer is more preferably 100% by mass to 400% by mass and 150% by mass to 300% by mass with respect to the total mass of the binder in the undercoat layer. Further preferred.

  The particle size of the inorganic fine particles is not particularly limited, but is preferably about 10 nm to 700 nm, more preferably about 20 nm to 300 nm from the viewpoint of adhesion. Moreover, there is no restriction | limiting in particular in the shape of microparticles | fine-particles, and things, such as a spherical form, an indefinite form, and a needle shape, can be used.

-Formula (1)-
The back sheet for a solar cell of the present invention has a mass ratio X (carbodiimide crosslinking agent / carbodiimide crosslinking agent / acrylic resin) where the acid value of the acrylic resin in the undercoat layer is A and the equivalent amount of the carbodiimide crosslinking agent is B. It is preferable that the acrylic resin) satisfies the following formula (1) between the product AB (= A × B) of A and B.
(0.8AB) / 56100 <X <(2.0AB) / 56100 (1)

The acid value A of the acrylic resin is the number of mg of potassium hydroxide required to neutralize free fatty acids present in 1 g of the acrylic resin.
The equivalent amount B of carbodiimide crosslinking agent is the number of grams of carbodiimide compound containing 1 mol of carbodiimide groups.

  In the formula (1), “56100” represents a value (56.1 × 1000 = 56100) obtained by multiplying the weight average molecular weight 56.1 of potassium hydroxide (KOH) used for measurement of the acid value of the acrylic resin by 1000. “AB / 56100” represents the ratio of the acrylic resin to the carbodiimide crosslinking agent in which the number of moles of acid in the acrylic resin is equal to the number of moles of carbodiimide groups in the carbodiimide crosslinking agent.

  The carbodiimide equivalent B of the carbodiimide crosslinking agent is preferably 200 to 500.

-Surfactant-
The undercoat layer may further contain a surfactant.
Examples of the surfactant include known surfactants such as anionic and nonionic surfactants. The content of the surfactant in the subbing layer is ^{preferably 0.1mg / m 2 ~15mg / m 2} , more preferably ^{0.5mg / m 2 ~5mg / m 2} .
Since the coating liquid for forming the undercoat layer contains a surfactant in an amount within the above range, it is possible to satisfactorily form a layer while suppressing the occurrence of repellency, thereby further enhancing the effects of the present invention. Can do.

-Other additives-
The undercoat layer may contain various additives as long as the object of the present invention is not impaired. Examples of such additives include ultraviolet absorbers, light stabilizers, and antioxidants.

-Formation method of undercoat layer-
The undercoat layer comprises a coating solution for forming an undercoat layer containing a binder, a cross-linking agent, inorganic fine particles, a coating solvent, and other components included as necessary so as to have the above-described content. It is formed by applying to at least one surface.
As a coating method, for example, a known coating method such as a gravure coater or a bar coater can be used.
The coating solution may be an aqueous system using water as an application solvent, or a solvent system using an organic solvent such as toluene or methyl ethyl ketone. Among these, from the viewpoint of environmental burden, it is preferable to use water as a solvent. A coating solvent may be used individually by 1 type, and may mix and use 2 or more types. Examples of preferable coating solvents include water, water / methyl alcohol = 95/5 (mass ratio), and the like.
Before applying the coating solution to the substrate of the present invention, the substrate surface is subjected to acid etching treatment with a mixed solution of chromic sulfate, flame treatment with a gas flame, ultraviolet irradiation treatment, corona discharge treatment, glow discharge treatment, etc. The surface treatment may be performed.

The thickness of the undercoat layer is not particularly limited, but is preferably 0.2 μm to 8.0 μm, and preferably 0.5 μm to 6.0 μm.
The undercoat layer may be composed of a single layer of only one layer, or may be a multilayer of two or more layers. When the undercoat layer is a multilayer, the total thickness of the undercoat layer composed of the multilayer is preferably 0.2 μm to 8.0 μm.

[Other layers]
The solar cell backsheet only needs to have the above-mentioned specific easily adhesive layer on at least one surface of the base material. Furthermore, the solar cell backsheet has a design property on the reflective layer that reflects sunlight and the solar cell backsheet. There may be provided a functional layer that provides various functionalities, such as a colored layer to be provided and a gas barrier layer that prevents intrusion of water and gas.
The reflective layer only needs to contain, for example, a white pigment such as titanium oxide, and the colored layer generally contains a black pigment, a blue pigment, or the like. A white PET sheet may be used as the reflective layer.
The gas barrier layer only needs to contain, for example, an inorganic oxide, an inorganic nitride, an inorganic oxynitride, an inorganic halide, an inorganic sulfide, and the like. Aluminum foil may be used as the gas barrier layer. Water vapor permeability of the gas barrier layer as the (moisture permeability), 1 × ¹⁰ is preferably ^{1 g / m 2 · d~1 ×} 10 -5 g / m 2 · d, 1 × 10 2 g / m 2 · d~1 It is more preferable that it is * 10 < ^-4 > g / m < ² > * d.

The functional layer may be a coating layer using a coating liquid for forming a functional layer on the surface of the specific easy-adhesion layer, or may be a vapor deposition layer by vapor deposition, or a functional member sheet. However, since the specific easy-adhesion layer is excellent in adhesiveness to the adhesive, in the present invention, the specific easy-adhesion layer functions by interposing the adhesive layer between the specific easy-adhesion layer and the functional layer. It is preferable to form a functional layer (functional member sheet).
Specifically, an adhesive is applied to the specific easy-adhesive layer of the solar cell backsheet of the present invention to form an adhesive layer, and then a functional member sheet is bonded to the functional member sheet. An example is a method in which an adhesive is applied in advance to form an adhesive layer, the adhesive layer side is opposed to the specific easy-adhesive layer, and the specific easy-adhesive layer and the functional member sheet are bonded.

-Adhesive layer-
As mentioned above, when the solar cell backsheet has a functional layer, the solar cell backsheet is on the side opposite to the substrate of the surface of the easy-adhesive layer (specific easy-adhesive layer). It is preferable that the surface further has an adhesive layer containing an adhesive.
Adhesives contained in the adhesive layer include two-component curing type, solvent type, solventless type, aqueous type, two-component solvent type, one-component solventless type, two-component solventless type, emulsion type, etc. Adhesives, polyether adhesives, mixed adhesives of polyether and polyurethane, mixed adhesives of polyester and polyurethane, mixed adhesives of polyester and isocyanate, aromatic polyester adhesives, aliphatic Examples thereof include a polyester-based adhesive, an aromatic polyether-based adhesive, an aliphatic polyether-based adhesive, a polyester-based adhesive, an isocyanate-based adhesive, and a polyurethane-based adhesive. A polyester-based adhesive containing a polyurethane-based resin is preferable.
That is, the adhesive layer is preferably an adhesive layer containing a polyurethane resin.
The dry thickness of the adhesive layer is preferably 0.5 μm to 8 μm, more preferably 1 μm to 5 μm.

In the solar cell backsheet of the present invention, the specific easy-adhesion layer contains a binder, a crosslinked structure portion derived from a carbodiimide crosslinking agent, and a specific wax. Excellent adhesion between the easy-adhesive layer and the adhesive layer adjacent to the easy-adhesive layer.
Therefore, the solar cell backsheet of the present invention has a high elongation at break in a moist heat environment. For example, the breaking elongation retention before and after the acceleration test after standing for 48 hours in an environment of 120 ° C. and a relative humidity of 100% (also referred to as 100% RH) is in the range of 20% to 90%.
Specifically, the breaking elongation retention is calculated as follows.
First, the elongation at break is measured by a method based on JIS-K7127 for the solar cell backsheet before the acceleration test and the solar cell backsheet after the acceleration test. The breaking elongation of the back sheet for a solar cell before acceleration test L _before, when the breaking elongation of the back sheet for a solar cell after the acceleration test was _after L, is calculated from the following formula (L).
Breaking elongation retention ratio [%] = ( _after L / _before L) × 100 Formula (L)

[Base material including biaxially stretched polyester film]
The solar cell backsheet of the present invention has a base material containing a biaxially stretched polyester film.
Biaxial stretching refers to stretching an unstretched film in a certain direction (direction A) and then stretching in a direction different from direction A (usually a direction perpendicular to direction A), and the polyethylene terephthalate film has two directions. It means that it is stretched. Therefore, the biaxially stretched polyester film is a polyester obtained by stretching a polyester in a biaxial direction to form a film.
Although the biaxial direction is not particularly limited, as will be described later, the biaxially stretched polyester film generally transports the polyester, which is a long unstretched film, in the length direction while transporting the unstretched film (MD). Stretched in the machine direction (Machine Direction) and in the direction perpendicular to the transport direction of the unstretched film (TD; Transverse Direction).

  The biaxially stretched polyester film used for the substrate is not particularly limited as long as the polyester is stretched in the biaxial direction to form a film, but from the viewpoint of hydrolysis resistance (weather resistance) of the substrate, the pre-peak temperature However, it is preferable to be controlled within a range described later.

-Pre-peak temperature measured by differential scanning calorimetry (DSC)-
The substrate preferably has a pre-peak temperature measured by differential scanning calorimetry (DSC) of 225 ° C to 235 ° C.
“Pre-peak temperature measured by differential scanning calorimetry (DSC)” refers to the peak that appears first when differential scanning calorimetry (DSC) is performed on a substrate containing a biaxially stretched polyester film. The temperature generally corresponds to the highest film surface temperature (heat setting temperature) of the polyester film at the time of heat setting in which the polyester is stretched and then heated with the stretching tension applied.
In the present invention, the pre-peak temperature is a value obtained by a conventional method using a differential scanning calorimeter [manufactured by Shimadzu Corporation, DSC-50].

  When the specific peak adhesive layer or undercoat layer is formed on the base material, the pre-peak temperature of the base material is 225 ° C. or higher. Adhesion with the adhesive layer (or undercoat layer) can be complemented. Moreover, a hydrolysis-resistant fall can be suppressed because the pre-peak temperature of a base material is 235 degrees C or less.

-Thermal shrinkage-
Furthermore, the thermal contraction rate (heating condition: heating at 150 ° C. for 30 minutes) of the substrate of the present invention is preferably 2.0% or less. As will be described later, the heat shrinkage rate is adjusted to the above range by controlling the heating temperature (T _heat setting and / or T _{heat relaxation} ) in each step of heat setting and / or heat relaxation in the transverse stretching step. Can do.
Polyester generally has a larger thermal expansion coefficient and hygroscopic expansion coefficient than glass, and therefore tends to be stressed by changes in temperature and humidity, and tends to cause cracks and peeling of layers. When the thermal contraction rate of the base material of the present invention is within the above range, it is possible to prevent the specific coating layer applied and formed on the base material of the present invention from cracking.

The heat shrinkage rate is more preferably 1.0% or less, and further preferably 0.5% or less.
The heat shrinkage in the present invention is the shrinkage of the polyester film before and after the treatment at 150 ° C. for 30 minutes (unit%; = film length after treatment / film length before treatment × 100).

-Base material thickness-
The thickness of the substrate is preferably 50 μm to 350 μm, more preferably 75 μm to 320 μm, and even more preferably 75 μm to 290 μm.
Next, the manufacturing method of a base material is demonstrated in detail.

<Manufacturing method of substrate>
The base material of the present invention may be manufactured by a base material manufacturing method including at least a stretching step of stretching the polyester in the biaxial direction, but the physical properties of the pre-peak temperature of the polyester after biaxial stretching are preferable as described above. From the viewpoint of controlling to be within the range, it is preferable to produce the substrate by the method for producing a substrate of the present invention shown below.
Hereafter, the manufacturing method of the base material of this invention is demonstrated concretely.

The base material manufacturing method of the present invention includes a film forming step in which a polyester raw material is melt-extruded into a sheet shape, cooled on a casting drum to form a polyester film, and the formed polyester film is longitudinally stretched in the longitudinal direction. And at least a longitudinal stretching step and a lateral stretching step for laterally stretching the polyester film after the longitudinal stretching in a width direction perpendicular to the longitudinal direction.
The transverse stretching step includes a preheating step of preheating the polyester film after longitudinal stretching to a temperature at which the polyester film can be stretched, and a stretching step of stretching the preheated polyester film in a transverse direction by applying tension in the width direction orthogonal to the longitudinal direction. A heat setting step of heating and fixing the maximum reachable film surface temperature of the polyester film after the longitudinal stretching and the transverse stretching in a range of 220 ° C. to 260 ° C., and the heat-set polyester film It is configured by providing a heat relaxation step for heating and relaxing the tension of the polyester film and a cooling step for cooling the polyester film after the heat relaxation.

  In the film forming step, the polyester raw material is melt-extruded into a sheet and cooled on a casting drum (also called “chill roll” or “cooling roll”) to form a polyester film.

The method of melt-extruding the polyester raw material and the polyester raw material are not particularly limited, but the intrinsic viscosity can be set to a desired intrinsic viscosity by a catalyst used for synthesis of the polyester raw material resin, a polymerization method, or the like.
The polyester raw material will be described.

(Polyester raw material)
The polyester raw material is not particularly limited as long as it is a raw material for the polyester film and contains polyester, and may contain a slurry of inorganic particles or organic particles in addition to the polyester. In addition, the polyester used as the raw material of the polyester melt-extruded by the extruder is also referred to as a polyester raw material resin or simply as a raw material resin. The polyester raw material resin may contain a titanium element derived from a catalyst.
The kind of polyester raw material resin contained in the polyester raw material is not particularly limited.
It may be synthesized using a dicarboxylic acid component and a diol component, or a commercially available polyester may be used.

When synthesizing a polyester raw material resin, for example, (A) a dicarboxylic acid component and (B) a diol component can be obtained by an esterification reaction and / or a transesterification reaction by a well-known method.
(A) Examples of the dicarboxylic acid component include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalonic acid Aliphatic dicarboxylic acids such as ethylmalonic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, isosorbide, cyclohexanedicarboxylic acid, decalin dicarboxylic acid, and the like, terephthalic acid, isophthalic acid, phthalic acid, 1,4- Naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 4,4′-diphenyl dicarboxylic acid, 4,4′-diphenyl ether dicarboxylic acid, 5-sodium sulfo Isophthalic acid, phenyl ether Boy carboxylic acid, anthracene dicarboxylic acid, phenanthrene carboxylic, 9,9'-bis (4-carboxyphenyl) a dicarboxylic acid or its ester derivatives such as aromatic dicarboxylic acids such as fluorene acid.

  (B) Examples of the diol component include fats such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol. Diols, cycloaliphatic dimethanol, spiroglycol, isosorbide and other alicyclic diols, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis (4-hydroxyphenyl) ) Diol compounds such as aromatic diols such as fluorene.

As the (A) dicarboxylic acid component, at least one kind of aromatic dicarboxylic acid is preferably used. More preferably, the dicarboxylic acid component contains an aromatic dicarboxylic acid as a main component. A dicarboxylic acid component other than the aromatic dicarboxylic acid may be included. Examples of such a dicarboxylic acid component include ester derivatives such as aromatic dicarboxylic acids.
“Containing aromatic dicarboxylic acid as a main component” means that the proportion of aromatic dicarboxylic acid in the dicarboxylic acid component is 80% by mass or more.
Moreover, it is preferable that at least one kind of aliphatic diol is used as the diol component (B). The aliphatic diol can contain ethylene glycol, and preferably contains ethylene glycol as a main component.
The main component means that the proportion of ethylene glycol in the diol component is 80% by mass or more.

<Method for producing solar cell backsheet>
The back sheet for solar cell of the present invention includes a base material including a biaxially stretched polyester film, a binder provided on at least one surface of the base material, and a thermoplastic resin having a carboxy group in the molecule, and a carbodiimide crosslinking agent. Is not particularly limited as long as it is a method capable of producing a laminate having a crosslinked structure portion derived from the above and an easy-adhesive layer containing a wax containing an ester of a higher fatty acid and a higher alcohol. The method demonstrated in the formation method of an easily bonding layer (specific easily bonding layer) is mentioned. That is, a binder containing a thermoplastic resin having a carboxy group in the molecule, a carbodiimide cross-linking agent, and a composition for forming a specific easy-adhesive layer containing at least a specific wax, at least a base material including a biaxially stretched polyester film By applying to one surface, a layer can be formed.
From the viewpoint of ease of layer formation, controllability of the layer thickness, etc., it is preferable to apply the specific easy-adhesive layer forming composition on the substrate as a coating liquid to form the specific easy-adhesive layer. The solar cell backsheet of the present invention is preferably manufactured by the following method for manufacturing a solar cell backsheet of the present invention.

  The manufacturing method of the solar cell backsheet of the present invention is derived from a carbodiimide cross-linking agent containing a thermoplastic resin having a carboxy group in the molecule on at least one surface on a substrate including a biaxially stretched polyester film. Easy adhesion by applying a coating solution for forming an easy-adhesive layer (coating solution for forming a specific easy-adhesive layer) containing a crosslinked structure part, a wax containing an ester of a higher fatty acid and a higher alcohol, and a coating solvent. An easy-adhesive layer (specific easy-adhesive layer) forming step of applying and forming a layer (specific easy-adhesive layer) is configured.

  In order to increase the adhesion between the easy-adhesive layer (specific easy-adhesive layer) and the substrate, the method for producing a back sheet for a solar cell of the present invention includes at least one of the substrates including a biaxially stretched polyester film. The surface of the undercoat layer is formed by applying a coating solution for forming an undercoat layer containing a binder containing an acrylic resin, a crosslinked structure portion derived from a carbodiimide crosslinking agent, inorganic fine particles, and a coating solvent. A coating layer forming step, a binder containing a thermoplastic resin having a carboxy group in the molecule, a crosslinked structure portion derived from a carbodiimide cross-linking agent, a wax containing an ester of a higher fatty acid and a higher alcohol, and a coating solvent Easy-adhesive layer (specific easy-adhesive layer) formation by applying an easy-adhesive layer (specific easy-adhesive layer) by applying an adhesive layer-forming coating liquid (specific easy-adhesive layer-forming coating liquid) And extent, may be a method configured to have a.

The method for producing a back sheet for a solar cell of the present invention further includes an adhesive layer forming step of forming an adhesive layer by applying an adhesive on the easily adhesive layer (specific adhesive layer) formed by coating. You may have.
Further, the adhesive layer forming step may be a layer in which the functional member sheet is bonded in advance. That is, in the adhesive layer forming step, the side of the functional member sheet to which the adhesive has been applied is pasted on the easily formed adhesive layer (specific easy adhesive layer) that has been applied. The adhesive layer / functional layer simultaneous forming step of simultaneously forming the adhesive layer and the functional layer (functional member sheet) on the easy adhesive layer (specific easy adhesive layer) may be used.
But the manufacturing method of the solar cell backsheet of this invention does not have an adhesive bond layer and a functional layer simultaneous formation process, but sticks a functional member sheet | seat on an adhesive bond layer after an adhesive bond layer formation process. The aspect which further has a functional layer formation process of attaching and forming a functional layer may be sufficient.

  The details of the coating liquid used in each step, that is, the coating liquid and coating method for forming the specific easy-adhesive layer, and the coating liquid and coating method for forming the undercoat layer are as described. As described above, before applying the coating liquid to the base material or the undercoat layer, the surface of the base material or the undercoat layer is subjected to an acid etching treatment with a mixed solution of chromic sulfuric acid, a flame treatment with a gas flame, Surface treatment such as ultraviolet irradiation treatment, corona discharge treatment, and glow discharge treatment may be performed.

<Solar cell module>
A solar cell module generally includes a solar cell element that converts light energy of sunlight into electric energy, a transparent substrate on which sunlight is incident, and the polyester film of the present invention described above (back sheet for solar cell). It is arranged between them. As a specific embodiment, a power generating element (solar cell element) connected by a lead wiring for taking out electricity is sealed with a sealing agent such as ethylene / vinyl acetate copolymer (EVA) resin, Etc., and a transparent substrate such as the above, and the polyester film (back sheet) of the present invention may be sandwiched and bonded together.

  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.

  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” and “%” are based on mass.

[Example 1]
(Manufacture of base materials)
The base material of the base film for solar battery back sheets was formed by the following procedure.
First, a polyethylene terephthalate (PET) having an inherent viscosity of 0.66 polycondensed using Ti as a catalyst was dried to a moisture content of 50 ppm or less and used as a PET raw material (PET raw material 1). The moisture content of PET is a value measured at 25 ° C. using a trace moisture meter (Karl Fischer method).

The obtained PET raw material 1 was supplied to an extruder whose temperature was set to 280 ° C. to 300 ° C., and melt kneaded in the extruder.
The molten resin was discharged from a die onto a chill roll (cooling roll) electrostatically applied to obtain an unstretched film (amorphous base). The obtained amorphous base was stretched (longitudinal stretch) in the transport direction (MD) of the amorphous base. Then, it extended | stretched (widthwise extending | stretching) to the width direction (TD) orthogonal to MD, and heat-fixed at 240 degreeC, and obtained the PET base material 1 of thickness 210 micrometers. The PET substrate 1 was subjected to differential scanning calorimetry (DSC) using a differential scanning calorimeter [manufactured by Shimadzu Corporation, DSC-50], and the pre-peak temperature of the PET substrate 1 was measured. Met.

The thickness of the PET substrate 1 was determined as follows.
Using a contact-type film thickness meter (manufactured by Anritsu Co., Ltd.) with respect to the PET substrate 1, 50 points were sampled at equal intervals over 0.5 m in the longitudinally stretched direction (longitudinal direction of the PET substrate 1). After sampling 50 points at equal intervals (50 equal parts in the width direction) over the entire width of the PET substrate 1 in the film width direction (direction perpendicular to the longitudinal direction), the thicknesses of these 100 points were measured. The average thickness of these 100 points was determined and used as the thickness of the PET substrate 1.

(Formation of undercoat layer and easy adhesion layer)
The obtained PET substrate 1 was conveyed at a conveyance speed of 105 m / min, and corona discharge treatment was performed on both sides of the PET substrate 1 under the condition of 730 J / m ² .

-Formation of undercoat layer-
After applying the following undercoat layer coating solution (1) to the dry surface of 142 mg / m ² by a bar coating method on one side of a PET substrate 1 subjected to corona discharge treatment, The coating film 1 was dried at 160 ° C. for 1 minute to form an undercoat layer.

-Preparation of undercoat layer coating solution (1)-
-Polyacrylic binder (binder) 21.5 parts [manufactured by Toa Gosei Chemical Co., Ltd., Jurimer ET-410, solid content 30%]
Carbodiimide compound (carbodiimide crosslinking agent) 3.9 parts [Nisshinbo Chemical Co., Ltd., Carbodilite V-02-L2, solid content 20%]
Surfactant A 15.0 parts [manufactured by Sanyo Chemical Industries, 1% aqueous solution of NAROACTY CL-95]
・ Inorganic filler (inorganic fine particles) 40.0 parts [Mitsubishi Materials Electronics Chemical Co., Ltd., S-2000, tin oxide 20% aqueous solution]
・ Distilled water added so that the total is 1,000 parts

  Components of the above composition were mixed to prepare an undercoat layer coating solution (1) for forming an undercoat layer.

-Formation of an easily adhesive layer-
On the obtained undercoat layer, so that the dry mass is 30.9 mg / m ^2, after obtaining the coating film 2 was applied by the following easy adhesion layer coating solution (1) bar coating, The easy-adhesion layer was formed by drying the coating film 2 at 170 degreeC for 1 minute.

-Preparation of easy-adhesion layer coating solution (1)-
-10.0 parts of polyacryl binder (thermoplastic resin having a carboxy group in the molecule) [manufactured by Toagosei Co., Ltd., Jurimer ET-410, solid content 30%]
-Carbodiimide compound (carbodiimide crosslinking agent) 2.0 parts [Nisshinbo Chemical Co., Ltd., Carbodilite V-02-L2, solid content 20%]
Carnauba wax (Wax 1; specific wax) 1.33 parts [Main component: Myricyl serotate, CH ₃ (CH ₂ ) ₂₄ COO (CH ₂ ) ₂₉ CH ₃ , freezing point 82 ° C.,
Chukyo Yushi Co., Ltd., Cellosol 524, solid content 30%]
Surfactant A 15.0 parts [manufactured by Sanyo Chemical Industries, 1% aqueous solution of NAROACTY CL-95]
・ Distilled water added so that the total is 1,000 parts

The component of the said composition was mixed and the easily bonding layer coating liquid (1) for easily bonding layer formation was prepared.
Hereinafter, the “thermoplastic resin having a carboxy group in the molecule” is also referred to as “specific thermoplastic resin”.

As described above, a solar cell backsheet 1 was obtained in which an undercoat layer and an easy-adhesion layer (specific easy-adhesion layer) were laminated on one side of the PET base material 1 in this order from the PET base material 1 side.
Table 1 shows the component constitution of the undercoat layer and the easily adhesive layer. In the “easy-adhesive layer” column, the amounts shown in the “wax” and “mass ratio” columns are the mass ratio [%] to the total solid content in the easy-adhesive layer.

<Evaluation of solar battery back sheet>
The solar cell backsheet 1 was used to evaluate adhesion and scratch resistance.

[1. Adhesion evaluation)
Using the adhesive, the adhesion between the easily adhesive layer of the solar battery backsheet 1 and the adhesive layer adjacent to the easily adhesive layer was evaluated.
First, two samples having a length of 120 mm and a width of 50 mm were cut out from the solar battery backsheet 1. A sample cut out from the solar cell backsheet 1 is referred to as a test sample (A).
Next, a peel test film provided with an easy-adhesive layer was prepared in the same manner except that the thickness of the base film was 120 μm, and two samples having a length of 120 mm and a width of 50 mm were cut out. A sample cut out from the peel test film is referred to as a test sample (B).

  A urethane-based adhesive [Mitsui Chemicals, Takelac A1143 / Takenate A50 (9 parts by mass / 1 mixture) mixed] is applied to the surface of the easy adhesion layer of the test sample (A) at a thickness of 5 μm, and the test sample (B ), And then allowed to stand at 40 ° C. for 5 days, cured and adhered to obtain an adhesion sample.

The obtained adhesive sample was cut to a width of 20 mm, and the test sample (A) side and the test sample (B) side of the cut adhesive sample were each gripped according to JIS K6854-2 (1999), and 100 mm A 180 ° peel test was conducted by pulling in the opposite direction at a speed of / min.
The 180 ° peel test was performed on each of the adhesion sample before the acceleration test and the adhesion sample after the acceleration test that was allowed to stand for 48 hours in an environment of 105 ° C. and 100% RH.
At this time, the peel force was continuously measured, and the maximum value was obtained from the continuously measured values. This test was performed on three adhesion samples, and the maximum value was measured for each. And the average value of the three measured maximum values is obtained as the adhesive force between the easy-adhesive layer of the solar cell backsheet 1 and the adhesive (adhesive layer), and the easy-adhesive layer in the solar cell backsheet 1 It was used as an index of adhesion between the adhesive layer and the adhesive layer. The evaluation results are shown in Table 1.
In addition, the evaluation result about the adhesion sample before an acceleration test was shown in the A column of the “adhesiveness” column, and the evaluation result about the adhesion sample after the acceleration test was shown in the B column of the “adhesion” column.

Based on the obtained adhesive strength, “adhesiveness” was evaluated according to the following evaluation criteria. Those practically acceptable are those classified into levels 3 to 5.
5; Sample that breaks without peeling off interface 4; Peeling force 20N or more 3; Peeling force 15N or more and less than 20N 2; Peeling force 10N or more and less than 15N 1; Peeling force Less than 10N or peeling occurred during accelerated test

[2. (Scratch resistance evaluation)
The scratch resistance evaluation was performed by a scratch test in which the surface of the easily adhesive layer of the solar battery backsheet 1 was scratched at a speed of 1 cm / second using a sapphire needle having a tip diameter of 0.1 mm. At this time, the load for pressing the sapphire needle against the polymer sheet was continuously changed from 0 g to 100 g. Each surface of the polymer sheet after scratching the polymer sheet was observed with an optical microscope, and the lowest load [g] at which scratches were observed was used as a scale for evaluating scratch resistance.
The larger the value of the minimum load [g] at which scratches are observed, the better the scratch resistance.

“Scratch resistance” was evaluated according to the following evaluation criteria. Those practically acceptable are those classified into levels 3 to 5.
5; Minimum load at which scratches are observed is 80 g or more 4; Minimum load at which scratches are observed is 60 g or more and less than 80 g 3; Minimum load at which scratches are observed is 40 g or more and less than 60 g 2 ; The minimum load at which scratches are observed is 20 g or more and less than 40 g 1; The minimum load at which scratches are observed is less than 20 g

[Example 2]
In the production of the PET substrate 1 used in Example 1, the heat setting temperature of the unstretched film (non-crystal base) was changed from 240 ° C. to 225 ° C., and the thickness after stretching was 125 μm. A PET substrate 2 having a thickness of 125 μm was obtained. As a result of measuring the pre-peak temperature for the PET substrate 2 by the same method as for the PET substrate 1, it was 214 ° C.
Next, in the production of the solar cell backsheet 1, except that the PET base material 2 was used instead of the PET base material 1, and the basecoat layer coating liquid (2) was used instead of the basecoat layer coating liquid (1). Similarly, the solar cell backsheet 2 of Example 2 was manufactured.
About the obtained solar cell backsheet 2, adhesiveness and damage resistance were evaluated by the same evaluation method and evaluation criteria as the solar cell backsheet 1, and the evaluation results are shown in Table 1.

-Preparation of undercoat layer coating solution (2)-
-Polyacrylic binder (binder) 21.5 parts [manufactured by Toa Gosei Chemical Co., Ltd., Jurimer ET-410, solid content 30%]
Carbodiimide compound (carbodiimide crosslinking agent) 3.9 parts [Nisshinbo Chemical Co., Ltd., Carbodilite V-02-L2, solid content 20%]
Surfactant A 15.0 parts [manufactured by Sanyo Chemical Industries, 1% aqueous solution of NAROACTY CL-95]
・ Surfactant B 7.5 parts [manufactured by NOF Corporation, 1% aqueous solution of Lapisol A-80]
・ Inorganic filler (inorganic fine particles) 40.0 parts [Mitsubishi Materials Electronics Chemical Co., Ltd., S-2000, tin oxide 20% aqueous solution]
・ Distilled water added so that the total is 1,000 parts

  Components of the above composition were mixed to prepare an undercoat layer coating solution (2) for forming an undercoat layer.

Example 3
In the production of the solar cell backsheet 1 of Example 1, Example 3 was carried out in the same manner except that the following easy-adhesion layer coating solution (2) was used instead of using the easy-adhesion layer coating solution (1). The solar cell backsheet 3 was manufactured.
The obtained solar cell backsheet 3 was evaluated for adhesion and scratch resistance by the same evaluation method and evaluation criteria as those for the solar cell backsheet 1, and Table 1 shows the evaluation results.

-Preparation of easy-adhesion layer coating solution (2)-
・ Polyacryl binder (specific thermoplastic resin) 10.0 parts [manufactured by Toa Gosei Chemical Co., Ltd., Jurimer ET-410, solid content 30%]
-Carbodiimide compound (carbodiimide crosslinking agent) 2.0 parts [Nisshinbo Chemical Co., Ltd., Carbodilite V-02-L2, solid content 20%]
Palm wax (wax 2; specific wax) 1.33 parts [main component: myricyl palmitate, CH ₃ (CH ₂ ) ₁₄ COO (CH ₂ ) ₂₉ CH ₃ , freezing point 100 ° C.,
Solid content 30%]
Surfactant A 15.0 parts [manufactured by Sanyo Chemical Industries, 1% aqueous solution of NAROACTY CL-95]
・ Distilled water added so that the total is 1,000 parts

  The component of the said composition was mixed and the easily bonding layer coating liquid (2) for easily bonding layer formation was prepared.

Example 4
In the production of the solar cell backsheet 1 of Example 1, the following easy-adhesion layer coating solution (3) was directly applied without applying the undercoat layer coating solution (1) and the easy-adhesion layer coating solution (1). A solar battery back sheet 4 of Example 4 was produced in the same manner except that it was applied.
The obtained solar cell backsheet 4 was evaluated for adhesion and scratch resistance by the same evaluation method and evaluation criteria as those for the solar cell backsheet 1, and Table 1 shows the evaluation results.

-Preparation of easy-adhesion layer coating solution (3)-
-Polyacrylic binder (specific thermoplastic resin) 43.0 parts [manufactured by Toagosei Chemical Co., Ltd., Jurimer ET-410, solid content 30%]
Polyolefin binder (thermoplastic resin) 130.0 parts [Unitika Ltd., Arrow Base SE1013N, solid content 20%]
-Carbodiimide compound (carbodiimide crosslinking agent) 65.0 parts [Nisshinbo Chemical Co., Ltd., Carbodilite V-02-L2, solid content 20%]
-Carnauba wax (Wax 1; specific wax) 10.0 parts [Main component: Myricyl cellotate, CH ₃ (CH ₂ ) ₂₄ COO (CH ₂ ) ₂₉ CH ₃ , freezing point 82 ° C,
Chukyo Yushi Co., Ltd., Cellosol 524, solid content 30%]
・ Acrylic resin beads [manufactured by Soken Chemical Co., Ltd., MR-2G] 0.6 parts ・ Surfactant A 50.0 parts [manufactured by Sanyo Chemical Industries, Ltd., 1% aqueous solution of NAROACTY CL-95]
Surfactant C 50.0 parts [manufactured by Fuji Film Fine Chemical Co., Ltd., sodium 1,2- {bis (3,3,4,4,5,5,6,6,6 nanofluorohexylcarbonyl)} ethane 1% aqueous solution of sulfonate
・ Distilled water added so that the total is 1,000 parts

  The component of the said composition was mixed and the easily bonding layer coating liquid (3) for easily bonding layer formation was prepared.

Example 5
In the production of the solar cell backsheet 4 of Example 4, the solar cell backsheet 5 of Example 5 was produced in the same manner except that the PET substrate 2 was used instead of the PET substrate 1.
The obtained solar cell backsheet 5 was evaluated for adhesion and scratch resistance by the same evaluation method and evaluation criteria as those for the solar cell backsheet 4, and Table 1 shows the evaluation results.

[Comparative Example 1]
In the production of the solar cell backsheet 1 of Example 1, instead of using the easy-adhesion layer coating solution (1), the following easy-adhesion layer coating solution (101) was used in the same manner as in Comparative Example 1. Solar cell backsheet 101 was manufactured.
About the obtained solar cell backsheet 101, adhesiveness and damage resistance were evaluated by the same evaluation method and evaluation criteria as the solar cell backsheet 1, and the evaluation results are shown in Table 1.

-Preparation of easy-adhesion layer coating solution (101)-
・ Polyacryl binder (specific thermoplastic resin) 10.0 parts [manufactured by Toa Gosei Chemical Co., Ltd., Jurimer ET-410, solid content 30%]
-Carbodiimide compound (carbodiimide crosslinking agent) 2.0 parts [Nisshinbo Chemical Co., Ltd., Carbodilite V-02-L2, solid content 20%]
Fatty acid (wax 101; comparative wax) 2.22 parts [Freezing point 55 ° C., manufactured by Chukyo Yushi Co., Ltd., Cellosol 920, solid content 18%]
Surfactant A 15.0 parts [manufactured by Sanyo Chemical Industries, 1% aqueous solution of NAROACTY CL-95]
・ Distilled water added so that the total is 1,000 parts

  The component of the said composition was mixed and the easily bonding layer coating liquid (101) for easily bonding layer formation was prepared.

[Comparative Example 2]
In the production of the solar cell backsheet 1 of Example 1, Comparative Example 2 was carried out in the same manner except that the following easy-adhesion layer coating solution (102) was used instead of using the easy-adhesion layer coating solution (1). The solar cell backsheet 102 was manufactured.
The obtained solar cell backsheet 102 was evaluated for adhesion and scratch resistance by the same evaluation method and evaluation criteria as those for the solar cell backsheet 1, and the evaluation results are shown in Table 1.

-Preparation of easy-adhesion layer coating solution (102)-
・ Polyacryl binder (specific thermoplastic resin) 10.0 parts [manufactured by Toa Gosei Chemical Co., Ltd., Jurimer ET-410, solid content 30%]
Epoxy compound (epoxy crosslinking agent) 40.0 parts [manufactured by Nagase ChemteX Corporation, Denacol EX-614B, solid content 1%]
Carnauba wax (Wax 1; specific wax) 1.33 parts [Main component: Myricyl serotate, CH ₃ (CH ₂ ) ₂₄ COO (CH ₂ ) ₂₉ CH ₃ , freezing point 82 ° C.,
Chukyo Yushi Co., Ltd., Cellosol 524, solid content 30%]
Surfactant A 15.0 parts [manufactured by Sanyo Chemical Industries, 1% aqueous solution of NAROACTY CL-95]
・ Distilled water added so that the total is 1,000 parts

  The component of the said composition was mixed and the easily bonding layer coating liquid (102) for easily bonding layer formation was prepared.

[Comparative Example 3]
In the production of the solar cell backsheet 1 of Example 1, instead of using the easy-adhesion layer coating solution (1), the same procedure was used except that the following easy-adhesion layer coating solution (103) was used. Solar cell backsheet 103 was manufactured.
The obtained solar cell backsheet 103 was evaluated for adhesion and scratch resistance by the same evaluation method and evaluation criteria as those for the solar cell backsheet 1, and Table 1 shows the evaluation results.

-Preparation of easy-adhesion layer coating solution (103)-
・ Polyacryl binder (specific thermoplastic resin) 10.0 parts [manufactured by Toa Gosei Chemical Co., Ltd., Jurimer ET-410, solid content 30%]
-Carbodiimide compound (carbodiimide crosslinking agent) 2.0 parts [Nisshinbo Chemical Co., Ltd., Carbodilite V-02-L2, solid content 20%]
-Carnauba wax (Wax 1; specific wax) 0.13 parts [Main component: Myricyl cellotate, CH ₃ (CH ₂ ) ₂₄ COO (CH ₂ ) ₂₉ CH ₃ , freezing point 82 ° C.,
Chukyo Yushi Co., Ltd., Cellosol 524, solid content 30%]
Surfactant A 15.0 parts [manufactured by Sanyo Chemical Industries, 1% aqueous solution of NAROACTY CL-95]
・ Distilled water added so that the total is 1,000 parts

  The component of the said composition was mixed and the easily bonding layer coating liquid (103) for easily bonding layer formation was prepared.

  As shown in Table 1, the solar cell backsheet 101 of Comparative Example 1 has insufficient adhesion between the easy-adhesive layer and the adhesive layer adjacent to the easy-adhesive layer under a long-term wet heat environment. Met. On the other hand, the solar cell backsheets 1 to 5 of the examples all have excellent adhesiveness between the easy-adhesive layer and the adhesive layer adjacent to the easy-adhesive layer even in a long-term wet heat environment. I understand that.

(Example 6 to Example 10)
3 mm thick tempered glass, EVA sheet (SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.), crystalline solar cell, EVA sheet (SC50B manufactured by Mitsui Chemicals Fabro Co., Ltd.), Examples 1 to The solar cell backsheet produced in Example 5 was superposed in this order, and it was bonded to EVA by hot pressing using a vacuum laminator (manufactured by Nisshinbo Co., Ltd., vacuum laminating machine), so that a crystalline solar cell module 1 ~ 5 were made. At this time, the solar cell backsheet was disposed such that the easy-adhesive layer was in contact with the EVA sheet, and adhesion was performed by the method described below.

-Adhesion method-
Using a vacuum laminator, vacuum was applied at 128 ° C. for 3 minutes, and then pressure was applied for 2 minutes to temporarily bond. Thereafter, the main adhesion treatment was performed in a dry oven at 150 ° C. for 30 minutes.

  When the solar cell modules 1 to 5 produced above were operated for power generation, they all showed good power generation performance as solar cells.

Claims (5)

A substrate comprising a biaxially stretched polyester film;
A binder provided on at least one surface of the base material, including a binder containing a thermoplastic resin having a carboxy group in the molecule, a crosslinked structure portion derived from a carbodiimide crosslinking agent, and a wax containing an ester of a higher fatty acid and a higher alcohol. An easy-adhesive layer contained in a range of 1.0% by mass to 20% by mass with respect to the total mass of the easy-adhesive layer;
A solar cell backsheet.   The solar cell backsheet according to claim 1, wherein the wax has a freezing point of 60C to 150C.   The solar cell backsheet according to claim 1 or 2, wherein the wax contains an ester of a higher fatty acid having 13 to 30 carbon atoms and a monovalent or divalent higher alcohol having 25 to 35 carbon atoms.   The sun according to any one of claims 1 to 3, further comprising an adhesive layer containing a polyurethane-based resin on a surface of the easy-adhesive layer opposite to the substrate. Battery backsheet.   A transparent substrate on which sunlight is incident, a solar cell element disposed on one side of the substrate, and a side opposite to the side of the solar cell element on which the substrate is disposed. A solar cell module comprising: the solar cell backsheet according to any one of items 4 to 9.