JP5740236B2 - Film and manufacturing method thereof - Google Patents

Description

  The present invention relates to a film useful as a back sheet for a solar cell module and a method for producing the film.

  Generally, a solar cell module has a transparent filling material (hereinafter also referred to as a sealing material) / solar cell element / sealing material / back sheet (on a glass or front sheet on a light receiving surface side on which sunlight is incident). (Hereinafter also referred to as BS) has a structure in which they are stacked in this order. Specifically, the solar cell element is generally configured to be embedded in a resin (sealing material) such as EVA (ethylene-vinyl acetate copolymer) and further to be attached with a protective sheet for solar cell. The Moreover, as this protective sheet for solar cells, conventionally, a polyester film, particularly a polyethylene terephthalate (hereinafter referred to as PET) film has been used.

  However, the solar cell protective sheet, especially the solar cell backsheet (BS), which is the outermost layer, is expected to be placed in an environment exposed to outdoor wind and rain for a long period of time. Therefore, excellent weather resistance is required.

  Here, polyester films such as PET, which are also used as a back sheet for solar cells, have excellent heat resistance, mechanical properties, chemical resistance, and the like. There is still room for improvement from the viewpoint of hydrolyzability. Thus, as a technique for improving the hydrolysis resistance of a polyester film, for example, a technique of blending a terminal sealing material such as polycarbodiimide with polyester has been proposed (for example, see Patent Documents 1 to 3 below).

  However, even with the technique using these polycarbodiimides as the end-capping agent for polyester, the improvement in hydrolysis resistance has not been sufficient. Moreover, there was no suggestion in these documents about a measure for further improving the hydrolysis resistance.

JP-A-8-73719 JP 2009-155479 A JP 2010-235824 A

  As described above, when the polyester film is exposed to a wet heat atmosphere under an environment such as being exposed to wind and rain outdoors, the polyester film becomes more brittle and the durability to breakage is reduced. . As a result of intensive studies by the inventors, when the polyester film is placed under high humidity and high temperature, moisture enters the interior of the polyester film at low density, and plasticizes the amorphous part. It was found to increase the mobility of molecules. Furthermore, the amorphous part having increased molecular mobility is hydrolyzed using the proton at the carboxyl group terminal of the polyester as a reaction catalyst. Thus, it was found that the hydrolyzed polyester having a low molecular weight further increased in molecular mobility and progressed in crystallization, and as a result, the embrittlement of the film progressed and the durability against breakage decreased. Thus, improving hydrolysis resistance is one of the important issues particularly for polyester films used in solar cell modules. Moreover, when using a polyester film for the back sheet | seat etc. of a solar cell module, it is calculated | required that adhesiveness with other layers, such as a sealing material, is high besides the viewpoint of weather resistance, such as hydrolysis resistance. From this viewpoint, having an excellent surface shape is also a preferable element for the polyester film.

  The present invention has been made in view of the above circumstances, and the problem to be solved by the present invention is to provide a film having excellent hydrolysis resistance and a good surface shape, and a method for producing the same. It is.

[Ｒ₁、Ｒ₂、Ｒ₃、Ｒ₄は、それぞれ独立に、炭素数１〜７のアルキル基あるいは水素原子を表す。ｎは繰返し単位数を示す。]
［６］ 前記ポリマー構造単位Ａおよび前記ポリマー構造単位Ｂの少なくとも一方が、ポリ（１，３，５−トリイソプロピルフェニレン−２，４−カルボジイミド）、ポリ（１，５-ジイソプロピルフェニレン-２、４-カルボジイミド）、１，３，５−トリイソプロピルフェニレン−２，４−カルボジイミドと１，５-ジイソプロピルフェニレン-２、４-カルボジイミドのランダム共重合物に由来する［１］〜［５］のいずれか一項に記載のフィルム。
［７］ 前記ポリエステルがポリエチレンテレフタレートである［１］〜［６］のいずれか一項に記載のフィルム。
［８］ ポリエステルと、数平均分子量１０００〜４０００の第一のポリカルボジイミドおよび数平均分子量１８０００以上の第二のポリカルボジイミドと、を反応させてポリマーを合成する合成工程と、
前記合成工程によって合成された前記ポリマーを成膜してフィルムを形成するフィルム形成工程と、
を含むフィルムの製造方法。
［９］ 前記合成工程によって、前記ポリエステルの分子末端に前記第１のポリカルボジイミドが結合した部位と、前記ポリエステルの分子末端に前記第２のポリカルボジイミドが結合した部位が形成される［８］に記載のフィルムの製造方法。
［１０］ 前記フィルム形成工程によって形成された前記フィルムを延伸する延伸工程をさらに含む［８］または［９］に記載のフィルムの製造方法。
［１１］ 前記延伸がニ軸延伸である［９］に記載のフィルムの製造方法。
［１２］ ＭＤ配向度［Δｎ（ｘ−ｚ）］とＴＤ配向度［Δｎ（ｙ−ｚ）］がいずれも０．１４以上である[１１] に記載のフィルムの製造方法。
［１３］ 前記延伸工程において、前記フィルムに熱処理を施す［１０］〜［１２］のいずれか一項に記載のフィルムの製造方法。
［１４］ 前記延伸工程において、前記熱処理を施した前記フィルムを、長手方向（ＭＤ）及び幅方向（ＴＤ）の両方向について熱緩和処理を施す［１３］に記載のフィルムの製造方法。
［１５］ 前記第一のポリカルボジイミドの数平均分子量が３０００〜４０００である［８］〜［１４］のいずれか一項に記載のフィルムの製造方法。
［１６］ 前記第一のポリカルボジイミドおよび前記第二のポリカルボジイミドの少なくとも一方が、下記一般式（１）で表される構造単位を有する［８］〜［１５］のいずれか一項に記載のフィルムの製造方法。

[Ｒ₁、Ｒ₂、Ｒ₃、Ｒ₄は、それぞれ独立に、炭素数１〜７のアルキル基あるいは水素原子を表す。ｎは繰返し単位数を示す。]
［１７］ 前記第一のポリカルボジイミドおよび前記第二のポリカルボジイミドの少なくとも一方が、ポリ（１，３，５−トリイソプロピルフェニレン−２，４−カルボジイミド）、ポリ（１，５-ジイソプロピルフェニレン-２、４-カルボジイミド）、１，３，５−トリイソプロピルフェニレン−２，４−カルボジイミドと１，５-ジイソプロピルフェニレン-２、４-カルボジイミドのランダム共重合物から選ばれる［８］〜［１６］のいずれか一項に記載のフィルムの製造方法。
［１８］ 前記ポリエステルがポリエチレンテレフタレートである［８］〜［１７］のいずれか一項に記載のフィルムの製造方法。
［１９］ 前記ポリエステルのカルボン酸価が２０eq/ton以下である［８］〜［１８］のいずれか一項に記載のフィルムの製造方法。
［２０］ 前記ポリエステルのカルボン酸価が１５eq/ton以下である［８］〜［１８］のいずれか一項に記載のフィルムの製造方法。
［２１］ ［８］〜［２０］のいずれか一項に記載の製造方法により製造されるフィルム。
［２２］ ［１］〜［７］および［２１］のいずれか一項に記載のフィルムに、ＣＯＯＨ、ＯＨ、ＳＯ₃Ｈ、ＮＨ₂及びその塩から選ばれる少なくとも一つの官能基を含む層を積層したフィルム。 As a result of intensive studies, the present inventors have found that a film having a good surface shape can be obtained by producing a film using a polymer having a specific structure, and having excellent hydrolysis resistance. It came to provide this invention which has the following structures.
[1] A film containing a polymer,
The polymer has a polymer structural unit containing a —N═C═N— structure and a —N═C (R) —NH— structure in the main chain (provided that the main chain contains no ester bond, R represents a polyester structure bonded to a C atom at one end), and
The polymer structural unit includes a polymer structural unit A having a number average molecular weight of 1000 to 4000 excluding R and a polymer structural unit B having a number average molecular weight of 18000 or more excluding R. To film.
[2] The film according to [1], wherein the polymer structural unit includes a portion bonded to another polymer structural unit via a polyester structure represented by R.
[3] The film according to [1] or [2], wherein the polymer structural unit has OH or COOH at the other end of the polyester structure represented by R.
[4] The film according to any one of [1] to [3], wherein the number average molecular weight of the polymer structural unit A excluding the R is 3000 to 4000.
[5] The film according to any one of [1] to [4], wherein at least one of the polymer structural unit A and the polymer structural unit B has a structural unit represented by the following general formula (1).

[R ₁ , R ₂ , R ₃ and R ₄ each independently represents an alkyl group having 1 to 7 carbon atoms or a hydrogen atom. n represents the number of repeating units. ]
[6] At least one of the polymer structural unit A and the polymer structural unit B is poly (1,3,5-triisopropylphenylene-2,4-carbodiimide), poly (1,5-diisopropylphenylene-2, 4 -Carbodiimide), any of [1]-[5] derived from a random copolymer of 1,3,5-triisopropylphenylene-2,4-carbodiimide and 1,5-diisopropylphenylene-2,4-carbodiimide The film according to one item.
[7] The film according to any one of [1] to [6], wherein the polyester is polyethylene terephthalate.
[8] A synthesis step of synthesizing a polymer by reacting polyester with a first polycarbodiimide having a number average molecular weight of 1000 to 4000 and a second polycarbodiimide having a number average molecular weight of 18000 or more,
A film forming step of forming a film by forming the polymer synthesized by the synthesis step; and
Manufacturing method of including film.
[9] In the step [8], the synthesis step forms a part where the first polycarbodiimide is bonded to the molecular terminal of the polyester and a part where the second polycarbodiimide is bonded to the molecular terminal of the polyester. The manufacturing method of the film of description.
[10] The method for producing a film according to [8] or [9], further including a stretching step of stretching the film formed by the film forming step.
[11] The method for producing a film according to [9], wherein the stretching is biaxial stretching.
[12] The method for producing a film according to [11], wherein the MD orientation degree [Δn (x−z)] and the TD orientation degree [Δn (yz)] are both 0.14 or more.
[13] The method for producing a film according to any one of [10] to [12], wherein the film is subjected to a heat treatment in the stretching step.
[14] The method for producing a film according to [13], wherein in the stretching step, the film subjected to the heat treatment is subjected to a thermal relaxation treatment in both the longitudinal direction (MD) and the width direction (TD).
[15] The method for producing a film according to any one of [8] to [14], wherein the number average molecular weight of the first polycarbodiimide is 3000 to 4000.
[16] As described in any one of [8] to [15], at least one of the first polycarbodiimide and the second polycarbodiimide has a structural unit represented by the following general formula (1). A method for producing a film.

[R ₁ , R ₂ , R ₃ and R ₄ each independently represents an alkyl group having 1 to 7 carbon atoms or a hydrogen atom. n represents the number of repeating units. ]
[17] At least one of the first polycarbodiimide and the second polycarbodiimide is poly (1,3,5-triisopropylphenylene-2,4-carbodiimide) or poly (1,5-diisopropylphenylene-2). 4-carbodiimide), 1,3,5-triisopropylphenylene-2,4-carbodiimide and 1,5-diisopropylphenylene-2, 4-carbodiimide random copolymers selected from [8] to [16] The manufacturing method of the film as described in any one.
[18] The method for producing a film according to any one of [8] to [17], wherein the polyester is polyethylene terephthalate.
[19] The method for producing a film according to any one of [8] to [18], wherein the polyester has a carboxylic acid value of 20 eq / ton or less.
[20] The method for producing a film according to any one of [8] to [18], wherein the polyester has a carboxylic acid value of 15 eq / ton or less.
[21] A film produced by the production method according to any one of [8] to [20].
[22] A layer containing at least one functional group selected from COOH, OH, SO ₃ H, NH ₂ and a salt thereof on the film according to any one of [1] to [ 7 ] and [21]. Laminated film.

  ADVANTAGE OF THE INVENTION According to this invention, it is excellent in hydrolysis resistance and can provide the film which has a favorable planar shape, and its manufacturing method. The film of the present invention is particularly useful as a back sheet for solar cells.

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

<Film production method>
The method for producing a film of the present invention comprises at least a polyester, a first polycarbodiimide having a number average molecular weight of 1000 to 4000, and a second polycarbodiimide having a number average molecular weight of 18000 or more to react with each other at the end of the polyester. A synthesis step of synthesizing a polymer including a portion to which at least one selected from the first polycarbodiimide and the second polycarboimide is bonded, and forming the film by forming the polymer synthesized by the synthesis step A film forming step.

(Synthesis process)
In the method for producing the film, the synthesis step includes at least (1) polyester, (2) first polycarbodiimide having a number average molecular weight of 1000 to 4000, and (3) second polycarbodiimide having a number average molecular weight of 18,000 or more. And synthesizing a polymer containing a site in which at least one selected from the first polycarbodiimide and the second polycarboimide is bonded to the terminal of the polyester.

When the oligomeric terminal blocking agent such as first polycarbodiimide is blended into the polyester, it acts much the end groups of the polyester, acid value derived from the number of such initial terminal COOH groups of the polyester (Acid Value; less , Sometimes referred to as “AV” for short). However, even when only such oligomeric polycarbodiimide is used, the reaction rate constant of the hydrolysis of the polyester cannot be sufficiently reduced. On the other hand, when a high-molecular end-capping agent is used as in the case of the second polycarbodiimide, the polyester AV degradation ability is not sufficient, but the polyester hydrolysis rate constant can be lowered. However, when these first polycarbodiimide and second polycarbodiimide are combined in a polyester, the AV of the polyester can be greatly reduced even when the oligomeric polycarbodiimide is used alone. Furthermore, the reaction rate constant of the hydrolysis of the polyester can be sufficiently reduced. The effect of achieving both low AV and low reaction rate constants is not clear, but the addition of the oligomeric first polycarbodiimide makes the polymer-based second polycarbodiimide sufficiently It is presumed that this was due to diffusion and an improved reaction rate.

  Further, when the first polycarbodiimide and the second polycarbodiimide are combined in the polyester as described above, there is an advantage that the adhesion to the film having active protons is improved when the film is formed. Although this effect is not clear, it is presumed that the polymer-based second polycarbodiimide that forms a crosslinked structure with more polyester in the molecule is localized near the film surface. .

-Polyester-
The polyester has a —COO— bond or a —OCO— bond in the middle of the polymer. The terminal group of the polyester is an OH group, a COOH group, or a group in which they are protected (OR ^X group, COOR ^X group (R ^X is an arbitrary substituent such as an alkyl group)), and an aromatic dibasic acid Alternatively, it is preferably a linear saturated polyester synthesized from an ester-forming derivative thereof and a diol or an ester-forming derivative thereof, and examples of the polyester include 2009-155479 and JP-A 2010-235824. Those described in the publication can be used as appropriate.

  Specific examples of the linear saturated polyester include polyethylene terephthalate (PET), polyethylene isophthalate, polybutylene terephthalate, poly (1,4-cyclohexylenedimethylene terephthalate), polyethylene-2,6-naphthalate, of which polyethylene terephthalate Alternatively, polyethylene-2,6-naphthalate is particularly preferable from the viewpoint of the balance between mechanical properties and cost.

  The polyester may be a homopolymer or a copolymer. Further, the polyester may be blended with a small amount of another type of resin such as polyimide. Moreover, you may use crystalline polyester which can form anisotropy at the time of a fusion | melting as said polyester.

  The terminal carboxyl group content (resin carboxylic acid value) in the polyester is preferably 20 eq / ton or less, more preferably 15 eq / ton or less, relative to the polyester. When the carboxyl group content is 20 eq / ton or less, hydrolysis resistance can be maintained, and a decrease in strength when subjected to wet heat aging can be suppressed small. The lower limit of the content of the terminal carboxyl group is desirably 10 eq / ton or more from the viewpoint of maintaining the adhesiveness with a layer (for example, a white layer) formed on the film of the present invention on which a polymer described later is formed. The terminal carboxyl group content in the polyester can be adjusted by polymerization catalyst species, polymerization time, and film forming conditions (film forming temperature and time). The carboxyl group content is H.264. A. Pohl, Anal. Chem. 26 (1954) 2145, and can be measured by a titration method. Specifically, the polyester is dissolved in benzyl alcohol at 205 ° C., a phenol red indicator is added, and titrated with a solution of sodium hydroxide in water / methanol / benzyl alcohol to determine the carboxylic acid value (eq / ton) can be calculated.

  The terminal hydroxyl group content in the polyester is preferably 120 eq / ton or less, more preferably 90 eq / ton or less, based on the polyester. When the hydroxyl group content is 120 eq / ton or less, the reaction between the polycarbodiimide and the hydroxyl group is suppressed, and the carboxyl group reacts preferentially and the carboxylic acid value can be further reduced. The lower limit of the hydroxyl group content is preferably 20 eq / ton from the viewpoint of adhesion to the upper layer. The hydroxyl group content in the polyester can be adjusted by polymerization catalyst species, polymerization time, and film forming conditions (film forming temperature and time). The terminal hydroxyl group content may be a value measured by 1H-NMR using a deuterated hexafluoroisopropanol solvent.

  The intrinsic viscosity (IV) of the polyester is 0.5 to 0.5 from the viewpoint of setting the intrinsic viscosity after film formation to a preferable range described later and the stirring property at the time of synthesis with polycarbodiimide described later. 0.9 dl / g is preferable, 0.55 to 0.85 dl / g is more preferable, and 0.6 to 0.85 dl / g is particularly preferable.

  The molecular weight of the polyester is preferably a weight average molecular weight (Mw) of 5000 to 30000, more preferably 8000 to 26000, and particularly preferably 12000 to 24000 from the viewpoints of heat resistance and viscosity. As the weight average molecular weight of the polyester, a value in terms of polymethyl methacrylate (PMMA) measured by gel permeation chromatography (GPC) using hexafluoroisopropanol as a solvent can be used.

  The polyester can be synthesized by a known method. For example, polyester can be synthesized by a known polycondensation method or ring-opening polymerization method, and any of transesterification and direct polymerization can be applied.

  When the polyester resin used in the present invention is a polymer or copolymer obtained by a condensation reaction mainly comprising an aromatic dibasic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof , An aromatic dibasic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof can be produced by an esterification reaction or an ester exchange reaction, and then a polycondensation reaction. Moreover, the carboxylic acid value and intrinsic viscosity of the polyester can be controlled by selecting the raw material and reaction conditions. In order to effectively advance the esterification reaction or transesterification reaction and polycondensation reaction, it is preferable to add a polymerization catalyst during these reactions.

  As the polymerization catalyst for polymerizing the polyester, Sb-based, Ge-based, and Ti-based compounds are preferably used from the viewpoint of suppressing the carboxyl group content to a predetermined range or less, and Ti-based compounds are particularly preferable. In the case of using a Ti-based compound, an embodiment in which polymerization is performed by using the Ti-based compound as a catalyst in a range of 1 ppm to 30 ppm, more preferably 3 ppm to 15 ppm is preferable. When the proportion of the Ti-based compound is within the above range, the terminal carboxyl group can be adjusted to the following range, and the hydrolysis resistance of the polymer substrate can be kept low.

  Examples of the synthesis of polyester using a Ti compound include Japanese Patent Publication No. 8-301198, Japanese Patent No. 2543624, Japanese Patent No. 3335683, Japanese Patent No. 3717380, Japanese Patent No. 39797756, Japanese Patent No. 3996226, Japanese Patent No. 3997866, Japanese Patent No. 39968671, The methods described in Japanese Patent No. 40000867, Japanese Patent No. 4053837, Japanese Patent No. 4127119, Japanese Patent No. 4134710, Japanese Patent No. 4159154, Japanese Patent No. 4269704, Japanese Patent No. 431538, and the like can be applied.

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

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

-Polycarbodiimide-
The polycarbodiimide is a compound having a structure (carbodiimide group) represented by (—N═C═N—). For example, the organic isocyanate is heated in the presence of an appropriate catalyst to decarboxylate. It can be produced by reaction. In the synthesis step in the present invention, a first polycarbodiimide having a number average molecular weight of 1000 to 4000 and a second polycarbodiimide having a number average molecular weight of 18000 or more are used. The number average molecular weight of polycarbodiimide is determined by applying polycarbodiimide powder to a single solvent selected from chloroform, tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP) and hexafluoroisopropanol (HFIP), or to a mixed solvent of two or more. The number average molecular weight obtained from the polystyrene standard can be used by dissolving and measuring the curve of the molecular weight distribution curve using GPC.

  If the number average molecular weight of the first polycarbodiimide is less than 1000, the volatility is high, so the desired carboxylic acid value is high and the reaction rate constant is also high. On the other hand, if the number average molecular weight of the first polycarbodiimide exceeds 4000, the mobility of the polymer chain is low and the reactivity is poor, so that the initial carboxylic acid value becomes high. The number average molecular weight of the first polycarbodiimide is preferably 1000 to 4000, more preferably 1500 to 4000, and particularly preferably 3000 to 4000 from the viewpoints of volatility and reactivity.

  If the number average molecular weight of the second polycarbodiimide is less than 18000, the volatility increases and the degree of decrease in the reaction rate constant decreases. The upper limit of the second polycarbodiimide is not particularly limited as long as the effect of the present invention is not impaired, but is preferably 30000 or less from the viewpoint of the mobility of the polymer chain. The number average molecular weight of the second polycarbodiimide is preferably 18000 to 30000, more preferably 18000 to 28000, from the viewpoints of volatility and polymer chain mobility.

  The polycarbodiimide can be selected from compounds obtained by polymerizing aliphatic diisocyanates, alicyclic diisocyanates, aromatic diisocyanates and mixtures thereof. Specific examples of the polycarbodiimide include poly (1,6-hexamethylenecarbodiimide), poly (4,4′-methylenebiscyclohexylcarbodiimide), poly (1,3-cyclohexylenecarbodiimide), poly (1,4-cycloheximide). Silenecarbodiimide), poly (4,4′-dicyclohexylmethanecarbodiimide), poly (4,4′-diphenylmethanecarbodiimide), poly (3,3′-dimethyl-4,4′-diphenylmethanecarbodiimide), poly (naphthylenecarbodiimide) ), Poly (p-phenylenecarbodiimide), poly (m-phenylenecarbodiimide), poly (tolylcarbodiimide), poly (diisopropylcarbodiimide), poly (methyl-diisopropylphenylenecarbodiimide), poly (1,3,5- Polycarbodiimides such as (riisopropylbenzene) polycarbodiimide, poly (1,3,5-triisopropylbenzene and 1,5-diisopropylbenzene) polycarbodiimide, poly (triethylphenylenecarbodiimide), poly (triisopropylphenylenecarbodiimide), etc. be able to. Further, as a commercial product, “STABAXOL” manufactured by Rhein Chemie Japan Co., Ltd. can be used. Specifically, examples of the first polycarbodiimide include stabuxol P (molecular weight 3000 to 4000, manufactured by Rhein Chemie Japan), LA-1 (molecular weight about 2000, manufactured by Nisshinbo Chemical Co., Ltd.). Examples of the second polycarbodiimide include stavaxol P400 (molecular weight: about 20000, manufactured by Rhein Chemie Japan) and STABILIZER9000 (molecular weight: about 20000, manufactured by Rhein Chemie).

  The polycarbodiimide is preferably a compound obtained by polymerizing aromatic diisocyanate, and is preferably a polycarbodiimide having a unit structure represented by the following general formula (1).

[Ｒ₁、Ｒ₂、Ｒ₃、Ｒ₄は、それぞれ独立に、炭素数１〜７のアルキル基あるいは水素原子を表す。ｎは繰返し単位数を示す。]

[R ₁ , R ₂ , R ₃ and R ₄ each independently represents an alkyl group having 1 to 7 carbon atoms or a hydrogen atom. n represents the number of repeating units. ]

  Examples of the polycarbodiimide having a unit structure represented by the general formula (1) obtained by polymerizing aromatic diisocyanate include poly (1,3,5-triisopropylphenylene-2,4-carbodiimide), poly (1 , 5-diisopropylphenylene-2,4-carbodiimide) and copolymers thereof can be preferably used.

  The first polycarbodiimide and the second polycarbodiimide include diisocyanate (for example, 2,4,6-triisopropylphenyl 1,3-diisocyanate) and phospholene oxide (for example, 3-methyl-1-phenyl-2- Phosphorene oxide) can be synthesized by heating. The number average molecular weight of polycarbodiimide can be controlled by selecting the amount of each material added and the reaction time.

-Polymer synthesis-
In the synthesis step, at least selected from the first polycarbodiimide and the second polycarboimide at the terminal of the polyester by mixing and reacting the first polycarbodiimide and the second carbodiimide with the polyester. A polymer is synthesized that contains the sites where one species is attached. At this time, in the reaction mixture (in the mixture in which a plurality of polymer molecules coexist), the portion where the first polycarbodiimide is bonded to the terminal of the polyester molecule and the terminal of the polyester molecule which is the same or different from the polyester molecule The site | part with which the 2nd polycarbodiimide couple | bonded is mixed. Synthesis of the polyester and the first and second polycarbodiimides may be performed by melt-mixing them or by mixing them in a solution state. In addition, when melt-mixing, for example, using a twin-screw extruder, or a polyester (so-called master batch) containing a polycarbodiimide compound at a relatively high concentration at the time of molding such as injection molding is chipped into an aromatic polyester polymer. It is also possible to employ a method of mixing in a state such as, and then melt-molding. The synthesis can also be performed by solid phase polymerization. The solid phase polymerization refers to, for example, a polymerization method in which a polymer is put into a vacuum resistant container, the inside of the container is evacuated, and the reaction is performed while stirring.
For example, as reaction conditions (melting conditions) in a twin-screw extruder, the temperature is usually 170 ° C. to 250 ° C., the pressure is 0.1 MPa to 30 MPa, and the time is about 0.1 minutes to 20 minutes. Moreover, as conditions for solid phase polymerization, the temperature is usually 170 ° C. to 240 ° C., and the time is about 0.1 minutes to 60 minutes.

  In the synthesis step, the content ratio (mass basis) of the total amount of polyester / first and second polycarbodiimides is preferably 99.99 / 0.01 to 90/10 from the viewpoint of crying and heat resistance. .95 / 0.05 to 95/5 is more preferable, and 99.9 / 0.1 to 99/1 is particularly preferable. In addition, the content ratio (mass basis) of the first polycarbodiimide / second carbodiimide in the synthesis step is preferably 1/99 to 99/1 from the viewpoint of volatility and reactivity, and 10/90 to 90/10. Is more preferable, and 30/70 to 70/30 is particularly preferable.

As described above, examples of the terminal group of the polyester include OH group, COOH group, and groups in which these are protected (OR ^X group, COOR ^X group). For example, when polycarbodiimide is bonded to the COOH (COOR ^x ) end group of polyester, the following bonding site (1) is formed.

Further, for example, when polycarbodiimide is bonded to the OH group (OR ^X group) end of the polyester, the following bonding site (2) is formed.

  In the synthesis step, these bonds are continuously formed to form a network structure. That is, by reaction of the polyester with the first polycarbodiimide and the second polycarbodiimide, the terminal of the polyester and the carbodiimide group in the first polycarbodiimide and the second polycarbodiimide are bonded, as described above, A polymer having a site in which at least one selected from the first polycarbodiimide and the second polycarboimide is bonded to the terminal of the polyester is synthesized.

--New polymer--
Among the polymers, a polyester, both are bound polymer of the first polycarbodiimide and second polycarbodiimide is a novel polymer. That is, the novel polymer has a polymer structural unit containing a —N═C═N— structure and a —N═C (R) —NH— structure in the main chain (provided that an ester bond is not present in the main chain). And R represents a polyester structure bonded to a C atom at one end.), And the polymer structural unit is a polymer having a number average molecular weight of 1000 to 4000 excluding R It is a polymer containing a structural unit A and a polymer structural unit B having an average molecular weight of 18000 or more in a portion excluding the R. In the said polymer, it is preferable that the said polymer structural unit contains the site | part couple | bonded with the other said polymer structural unit through the polyester structure represented by said R. That is, in the novel polymer, for example, the unit structure A corresponding to the first polycarbodiimide and the unit structure B corresponding to the second polycarbodiimide are bonded to both ends of the polyester. Can have a structure. At this time, the same unit structures may be bonded via a polyester structure represented by R. In addition, the polymer has the —N═C (R) —NH— structure in which OH or COOH is bonded to the other end of the polyester structure represented by R, that is, bonded to the polymer unit structure at one end. In addition, the other terminal group may have a polyester structure which is an OH group or a COOH group. When such a novel polymer is schematically represented, the following structure is obtained.

That is, the polymer shown in the schematic diagram includes a —N═C═N— structure and a —N═C (R1) —NH— structure in the main chain, and a number average molecular weight of a portion excluding the R1. Is a polymer structural unit A having a molecular weight of 1000 to 4000, an N—C═N— structure and a —N═C (R 2) —NH— structure in the main chain, and the average molecular weight of the portion excluding the R 2 is 18,000 or more polymer structural units B. In the schematic diagram, R1 and R2 each represent a polyester structure. In the schematic diagram, the polymer unit structure A and the polymer unit structure B are bonded to both ends thereof via R1 in the unit structure A. Furthermore, in the said schematic diagram, the polymer unit structure B has -N = C (R) -NH- structure which has a polyester structure whose other terminal group is a COOH group.
The terminal carboxyl group content (resin carboxylic acid value) in the polymer synthesized in the synthesis step is preferably 20 eq / ton or less, more preferably 15 eq / ton or less, based on the total amount of the polymer. When the carboxyl group content is 20 eq / ton or less, hydrolysis resistance can be maintained, and a decrease in strength when subjected to wet heat aging can be suppressed small. Moreover, generation | occurrence | production of a micro foreign material can be suppressed and the film excellent in surface shape can be produced. The lower limit of the content of the terminal carboxyl group is preferably 1 eq / ton from the viewpoint of maintaining adhesiveness with a layer (for example, a white layer) formed on the film of the present invention on which a polymer described later is formed. The carboxyl group content is H.264. A. Pohl, Anal. Chem. 26 (1954) 2145, and can be measured by a titration method. Specifically, the polymer is dissolved in benzyl alcohol at 205 ° C., a phenol red indicator is added, and titration is performed with a water / methanol / benzyl alcohol solution of sodium hydroxide. / ton) can be calculated.

  The molecular weight of the polymer synthesized in the synthesis step is preferably a weight average molecular weight (Mw) of 6,000 to 5,000,000, more preferably 10,000 to 2,000,000, from the viewpoint of film uniformity. Is particularly preferred. As the weight average molecular weight of the polymer, a value in terms of polymethyl methacrylate (PMMA) measured by gel permeation chromatography (GPC) using hexafluoroisopropanol as a solvent can be used.

  The glass transition temperature (Tg) of the polymer synthesized in the synthesis step is preferably 20 ° C. to 200 ° C., more preferably 30 ° C. to 160 ° C., and 40 ° C. to 120 ° C. from the viewpoint of heat resistance. It is particularly preferable that the temperature is C. The glass transition temperature of the polymer can be measured with a differential scanning calorimeter (DSC) or the like.

(Film forming process)
The polymer synthesized in the synthesis step is formed into a film in the film formation step. In the film formation step, the polymer (melt) synthesized in the synthesis step is passed through a gear pump or a filter, and then extruded through a die to a cooling roll, which is cooled and solidified (unstretched). Can be formed. The extruded melt can be brought into close contact with the cooling roll using an electrostatic application method. Under the present circumstances, the surface temperature of a cooling roll can be about 10 to 40 degreeC.

(Stretching process)
The (unstretched) film formed by the film forming step can be subjected to a stretching treatment in the stretching step. In the stretching step, the film that has been cooled and solidified with a cooling roll (unstretched) is preferably stretched in one or two directions, and more preferably stretched in two directions. Stretching in the two directions (biaxial stretching) includes stretching in the longitudinal direction (MD: Machine Direction) (hereinafter also referred to as “longitudinal stretching”) and stretching in the width direction (TD: Transverse Direction) (hereinafter referred to as “lateral stretching”). "). The longitudinal stretching and lateral stretching may each be performed once, or may be performed a plurality of times, and may be simultaneously performed longitudinally and laterally.
The stretching treatment is preferably performed at a 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. to Tg + 30 ° C.

A preferable draw ratio is 280% to 500%, more preferably 300% to 480%, and further 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. Either vertical (MD) or horizontal (TD) may be increased. The draw ratio here is determined using the following equation.
Stretch ratio (%) = 100 × {(Length after stretching) − (Length before stretching)} / (Length before stretching)

For example, the biaxial stretching treatment is performed once or twice or more in the longitudinal direction at (Tg ₁ ) ° C. to (Tg ₁ +60) ° C. which is the glass transition temperature of the film, and the total magnification becomes 3 to 6 times. Then, it can be applied at (Tg ₁ ) ° C. to (Tg + 60) ° C. so that the magnification is 3 to 5 times in the width direction.

  The biaxial stretching process can be stretched in the longitudinal direction using two or more pairs of nip rolls with increased peripheral speed on the outlet side (longitudinal stretching), and both ends of the film are gripped by chucks and are orthogonally crossed (longitudinal). In the direction perpendicular to the direction) (lateral stretching).

  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 the heat treatment, crystallites can be generated, and mechanical properties and durability can be improved. The film may be subjected to heat treatment at about 180 ° C. to 210 ° C. (more preferably, 185 ° C. to 210 ° C.) for 1 second to 60 seconds (more preferably 2 seconds to 30 seconds).

In the stretching step, a heat relaxation treatment can be performed after the heat treatment. The heat 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 film. The various conditions in the thermal relaxation treatment are preferably treatment at a temperature lower than the heat treatment temperature, and preferably 130 to 205 ° C. Moreover, as for the said heat relaxation process, it is preferable that both MD and TD are 1 to 12%, and, as for the thermal contraction rate (150 degreeC) of a film, 1 to 10% is still more preferable. For heat shrinkage (150 ° C), 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, and fixed at one end to an oven adjusted to a temperature of 150 ° C. The other end is left free for 30 minutes, and then the distance between the gauge points is measured at room temperature. This length is defined as L (mm), and the heat shrinkage rate is obtained by the following formula using the measured value. Can do.
150 ° C. heat shrinkage (%) = 100 × (300−L) / 300
Further, when the thermal contraction rate is positive, it indicates shrinkage, and negative indicates elongation.

<Film>
The film of the present invention contains a polymer having a specific structure. The polymer has a polymer structural unit containing a —N═C═N— structure and a —N═C (R) —NH— structure in the main chain (provided that the main chain contains no ester bond, R represents a polyester structure bonded to a C atom at one end), and the polymer structural unit is a polymer structural unit A having a number average molecular weight of 1000 to 4000 excluding R And a polymer structural unit B having a number average molecular weight excluding R of 18000 or more.
The film of the present invention can be produced by the production method of the present invention described above. That is, the film of the present invention includes the polymer synthesized in the synthesis step. Although the thickness of the film of this invention changes with uses, when using as a back seat | sheet for solar cells, it is preferable that they are 25 micrometers-300 micrometers, and it is more preferable that they are 120 micrometers or more and 300 micrometers or less. When the thickness is 25 μm or more, sufficient mechanical strength is obtained, and when the thickness is 300 μm or less, it is advantageous in terms of cost.

The film of the present invention is preferably stretched, and more preferably biaxially stretched. The MD orientation degree and the TD orientation degree of the film of the present invention are each preferably 0.14 or more, more preferably 0.155 or more, and particularly preferably 0.16 or more. When the degree of orientation is 0.14 or more, the restraint property of the amorphous chain is improved (the mobility is lowered), and the heat and humidity resistance is improved. The MD and TD orientation degrees are x, y of a biaxially oriented film in an atmosphere at 25 ° C. using an Abbe refractometer, a monochromatic light sodium D-line as a light source, and methylene iodide as a mounting liquid. , Z-direction refractive index is measured, MD orientation degree: Δn (x−z), TD
; It can calculate from (DELTA) n (yz).

  In addition, the intrinsic viscosity (IV) of the film of the present invention is set from the viewpoint of setting the intrinsic viscosity after being formed as a film in a preferable range described below, and from the viewpoint of agitation during synthesis with polycarbodiimide described below. 0.55-0.9 dl / g is preferable, 0.6-0.85 dl / g is still more preferable, and 0.62-0.82 dl / g is especially preferable.

As described above, a film excellent in hydrolysis resistance can be produced by the production method of the present invention described above. The film obtained by the production method of the present invention can be suitably used as a protective sheet (back sheet) for a solar cell module as described later, and can also be used for other applications.
The film of the present invention can also be used as a laminate provided thereon with a coating layer containing at least one functional group selected from COOH, OH, SO ₃ H, NH ₂ and salts thereof. Since the film of this invention contains the polymer synthesize | combined in the said synthetic | combination process, it is excellent in adhesiveness with the layer which has the above functional groups.

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

[Example 1]
1. Preparation of polyester resin-step (A)-
4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol were mixed for 90 minutes to form a slurry, which was continuously supplied to the first esterification reactor at a flow rate of 3800 kg / h. Next, an ethylene glycol solution of a citric acid chelate titanium complex ("VERTEC AC-420", manufactured by Johnson Matthey) in which citric acid is coordinated to Ti metal is continuously supplied to the first esterification reaction tank. While stirring at an internal temperature of 250 ° C., the reaction was carried out with an average residence time of about 4.3 hours to obtain an oligomer. At this time, the citric acid chelate titanium complex was continuously added so that the amount of Ti added was 9 ppm in terms of element. The acid value of the obtained oligomer was 550 eq / ton.

The obtained oligomer was transferred to a second esterification reaction tank and reacted by stirring at a reaction tank temperature of 250 ° C. and an average residence time of 1.2 hours to obtain an oligomer having an acid value of 180 eq / ton. The inside of the second esterification reaction tank is divided into three zones from the first zone to the third zone. From the second zone, an ethylene glycol solution of magnesium acetate is added, and the amount of Mg added is 75 ppm in terms of element. Then, from the third zone, an ethylene glycol solution of trimethyl phosphate was continuously supplied so that the addition amount of P was 65 ppm in terms of element. The ethylene glycol solution of trimethyl phosphate was prepared by adding a 25 ° C. trimethyl phosphate solution to a 25 ° C. ethylene glycol solution and stirring at 25 ° C. for 2 hours (phosphorus compound content in the solution: 3 .8% by mass).
As a result, an esterification reaction product was obtained.

-Process (B)-
The esterification reaction product obtained in the step (A) was continuously supplied to the first polycondensation reaction tank. Next, polycondensation (ester exchange reaction) is carried out with an average residence time of about 1.8 hours while stirring the esterification reaction product at a reaction temperature of 270 ° C. and a reaction tank pressure of 20 torr (2.67 × 10 ⁻³ MPa). It was.

Next, the obtained reaction product was transferred from the first polycondensation reaction tank to the second double condensation reaction tank. Thereafter, the reaction product was stirred in the second double condensation reaction tank at a reaction tank temperature of 276 ° C. and a reaction tank pressure of 5 torr (6.67 × 10 ⁻⁴ MPa), and the residence time was about 1.2 hours. (Transesterification reaction).

Subsequently, the reaction product obtained by the transesterification reaction is further transferred from the second double condensation reaction tank to the third triple condensation reaction tank. In this reaction tank, the reaction tank temperature is 278 ° C. and the reaction tank pressure is 1. While stirring at 5 torr (2.0 × 10 ⁻⁴ MPa), the reaction (transesterification reaction) was carried out under the condition of a residence time of 1.5 hours. Carboxylic acid value: 24 eq / ton, IV (intrinsic viscosity): 0.65 dl / G reaction product (polyethylene terephthalate (PET)) was obtained.

Furthermore, the obtained PET was heat-treated at 210 ° C. for 30 hours under a reduced pressure of 50 Pa using a rotary vacuum polymerization apparatus. Thereafter, nitrogen gas at 25 ° C. was allowed to flow into the vacuum polymerization apparatus, and the pellet was cooled to 25 ° C. to obtain a polyester resin having a carboxylic acid number of 14 eq / ton and IV of 0.75 dl / g.

<Evaluation of polyester resin>
Using the obtained polyester resin, the carboxylic acid value was measured by the following method.

(Acid value of resin (terminal COOH group amount))
About the obtained polyester resin, H.M. A. Pohl, Anal. Chem. 26 (1954) 2145, the amount of terminal COOH groups was measured by a titration method. Specifically, the polyester resin was dissolved in benzyl alcohol at 205 ° C., a phenol red indicator was added, and titration was performed with a water / methanol / benzyl alcohol solution of sodium hydroxide.

2. Film production-extrusion (synthesis process, film formation process)-
99.7 parts of the obtained polyester resin described above was put into a hopper of a biaxial kneading extruder having a diameter of 50 mm by a main feeder, and polycarbodiimide (1) (stavaxol P400 (molecular weight about 20000, line chemi 0.2 parts) and 0.1 part of polycarbodiimide (2) (Stavaxol P (molecular weight 3000-4000, manufactured by Rhein Chemie Japan)) were added and melted and extruded at 280 ° C. The extruded melt (melt) was passed through a gear pump and a filter (pore diameter: 20 μm), and then extruded from a die to a 20 ° C. cooling roll to obtain an amorphous sheet. The extruded melt was brought into close contact with the cooling roll using an electrostatic application method. In addition, the additive was not volatilized or decomposed during the extrusion (such as smoke or odor).

-Stretching (biaxial stretching process)-
The unstretched film extruded and solidified on the cooling roll was sequentially biaxially stretched by the following method to obtain a polyester film having a thickness of 175 μm.
<Stretching method>
(A) Longitudinal stretching The unstretched film was passed between two pairs of nip rolls having different peripheral speeds and stretched in the longitudinal direction (conveying direction). The preheating temperature was 90 ° C., the stretching temperature was 90 ° C., the stretching ratio was 3.5 times, and the stretching speed was 3000% / second.
(B) Transverse stretching The longitudinally stretched film was stretched laterally under the following conditions using a tenter.
<Conditions>
-Preheating temperature: 100 ° C
-Stretching temperature: 110 ° C
-Stretch ratio: 4.2 times-Stretch speed: 70% / second

-Heat fixation / thermal relaxation-
Then, the stretched film after finishing longitudinal stretching and lateral stretching was heat-set under the following conditions. Further, after heat setting, the tenter width was reduced and heat relaxation was performed under the following conditions.
<Heat setting conditions>
・ Heat fixing temperature: 200 ℃
・ Heat setting time: 2 seconds <thermal relaxation conditions>
-Thermal relaxation temperature: 195 ° C
-Thermal relaxation rate: 5%

-Winding-
After heat setting and heat relaxation, both ends of the polyester film were trimmed by 10 cm. Then, after extruding (knurling) with a width of 10 mm at both ends, it was wound up with a tension of 25 kg / m. The width was 1.5 m and the winding length was 2000 m.
As described above, the biaxially oriented polyester film of Example 1 (hereinafter also referred to as “sample film”) was produced. The obtained sample film had a good surface shape with no spots or wrinkles.

<Evaluation of polyester film>
Using the sample film obtained in Example 1, the following measurement was performed.
The obtained results are shown in Table 2 below.

(Heat shrinkage)
-150 ° C heat shrinkage-
A sample having a measurement direction of 350 mm and a width of 50 mm was cut out, marked at 300 mm intervals in the vicinity of both ends in the longitudinal direction of the sample, fixed at one end in an oven adjusted to a temperature of 150 ° C., and left at the other end for 30 minutes. After 30 minutes, this was taken out of the oven, the distance between the gauge points was measured at room temperature, and this length was defined as L (mm). Using these measured values, the thermal shrinkage rate was determined by the following formula.
150 ° C. heat shrinkage (%) = 100 × (300−L) / 300
Moreover, the thermal contraction rate measured the value of MD direction (longitudinal direction) and TD direction (lateral direction) of the film. Each measured value is an average value of measured values at the center (C) in the width direction and near both ends (F, B). Further, when the thermal contraction rate is positive, it indicates shrinkage, and negative indicates elongation.

(Degree of orientation)
The Abbe refractometer was used, the monochromatic light sodium D line was used as the light source, and the refractive index in the x, y, and z directions was measured in a 25 ° C. atmosphere using methylene iodide as the mounting liquid.
The degree of orientation of MD and TD was Δn (x−z) and Δn (y−z), respectively, and the degree of orientation was calculated.

(Carboxylic acid value of film (terminal COOH amount))
The sample film is completely dissolved in a mixed solution of benzyl alcohol / chloroform (= 2/3; volume ratio), phenol red is used as an indicator, and this is titrated with a standard solution (0.025NKOH-methanol mixed solution). The carboxylic acid value (eq / ton) corresponding to the film acid value was calculated from the quantification.

(Break elongation half-life (hr))
The breaking elongation retention half-life was evaluated by subjecting the polyester film obtained in Example 1 to a storage treatment (heat treatment) at 120 ° C. and a relative humidity of 100%. The breaking elongation (%) shown was evaluated by measuring a storage time at which the breaking elongation (%) shown by the polyester film before storage was 50%.
It shows that the hydrolysis resistance of a polyester resin composition and the polyester film obtained using this is excellent, so that break elongation retention half-life is long.

(Volatile)
Sensory evaluation of smoke and odor generated from the die of the twin screw extruder was performed, and volatility was evaluated according to the following criteria.
<Standard>
○: No smoke or odor was generated.
Δ: Smoke was not generated, but odor was generated. ×: Smoke and odor were generated.
Those having poor volatility had an epoxy compound attached to the film surface, which deteriorated the film performance such as a strange odor and surface unevenness.

(Surface shape)
The obtained polyester film was visually observed, and the surface condition was visually evaluated according to the following criteria.
<Standard>
○: No wrinkles or irregularities were observed and the surface condition was good.
Δ: Some wrinkles or irregularities were partially observed.
X: Wrinkles or irregularities were observed on the entire surface.

(Reaction rate constant)

<Standard>
A: Less than 1.3 × 10 ⁻⁶ tоn / mоl / hr ○: 1.30 × 10 ⁻⁶ tоn / mоl / hr or more, less than 1.35 × 10 ⁻⁶ tоn / mоl / hr Δ: 1.35 × 10 ⁻⁶ tоn / mоl / hr or more, 1.40 × 10 ⁻⁶ tоn / mоl / hr or less ×: 1.40 × 10 ⁻⁶ tоn / mоl / hr or more, 1.45 × 10 ⁻⁶ tоn / mоl / Less than hr XX: 1.45 × 10 ^-6 tоn / mоl / hr or more

[Examples 2 to 22 and Comparative Examples 1 to 11]
In Example 1 described above, the polyester resin and the first and second polycarbodiimides used in “2. Production of Film” were appropriately changed according to Table 1 below, and the production conditions were changed according to Table 1. The film of each Example and the comparative example was obtained like Example 1 except having carried out. In Example 21, only a longitudinal stretching was performed to obtain a uniaxially stretched film. In Example 22, an unstretched film was obtained without stretching. The carboxylic acid value and intrinsic viscosity (IV) of the polyester can be controlled by appropriately adjusting the polymerization conditions, the solid phase polymerization temperature, and the time.

In Table 1, polycarbodiimide (monocarbodiimide) is as follows.
-Starbazole P400: Polycarbodiimide, number average molecular weight of about 20000, manufactured by Rhein Chemie Japan Co., Ltd.-Starbazole P: Polycarbodiimide, number average molecular weight of 3000, manufactured by Rhein Chemie Japan Co., Ltd.-Carbodilite HMV-8CA: Polycarbodiimide, number average Molecular weight about 3000, manufactured by Nisshinbo Chemical Co., Ltd.)
STABILIZER 9000: polycarbodiimide, number average molecular weight of about 20000, manufactured by Rhein Chemie)
-Starvacol P100: polycarbodiimide, number average molecular weight of about 10,000, manufactured by Rhein Chemie Japan Co., Ltd.)
-Starbazole I: Monocarbodiimide, number average molecular weight 360, manufactured by Rhein Chemie Japan Co., Ltd.-Production Example 1: Polycarbodiimide, number average molecular weight of about 1400
Production Example 2: Polycarbodiimide, number average molecular weight of about 18000
Production Example 3: Polycarbodiimide, number average molecular weight of about 28000
Production Example 4: Polycarbodiimide, number average molecular weight of about 1000
Production Example 5: Polycarbodiimide, number average molecular weight of about 50,000
Production Example 6: Polycarbodiimide, number average molecular weight of about 14,000
Production Example 7: Polycarbodiimide, number average molecular weight of about 900
Production Example 8: Polycarbodiimide, number average molecular weight of about 17000

  In Table 1, Production Examples 1 to 6 produced polycarbodiimide as follows.

(Production Examples 1-6)
1000 parts of 2,4,6-triisopropylphenyl 1,3-diisocyanate and 10 parts of 3-methyl-1-phenyl-2-phospholene oxide were heated to 120 ° C. over 1 hour, and then the temperature was The polycarbodiimide of Production Example 1 was synthesized by performing the reaction for 20 hours without change. The number average molecular weight (Mn) of the polycarbodiimide obtained from GPC was found to be 1400. Moreover, the addition amount and reaction time were controlled suitably, and the polycarbodiimide of the manufacture examples 2-6 which has the number average molecular weight of the said Table 1 was synthesize | combined by the same method.

  As can be seen from the results in Table 2, the films of the examples had good reaction rate constants and also had good elongation at break half life (hydrolysis resistance) of 160 hr or more. Further, the film of the example also had a good surface shape.

3. Production of Back Sheet for Solar Cell A back sheet for solar cell was produced using the polyester films produced in Examples 1 to 18 and Comparative Examples 1 to 13.
First, the following (i) reflective layer and (ii) easy-adhesion layer were coated in this order on one side of the polyester films prepared in Examples 1 to 18 and Comparative Examples 1 to 13.

(I) Reflective layer (colored layer)
Various components having the following composition were mixed and subjected to a dispersion treatment for 1 hour using a dynomill type disperser to prepare a pigment dispersion.
<Prescription of pigment dispersion>
・ Titanium dioxide: 39.9 parts (Taipeke R-780-2, manufactured by Ishihara Sangyo Co., Ltd., solid content: 100% by mass)
・ Polyvinyl alcohol: 8.0 parts (PVA-105, manufactured by Kuraray Co., Ltd., solid content: 10%)
・ Surfactant (Demol EP, manufactured by Kao Corporation, solid content: 25%) ・ ・ ・ 0.5 part ・ Distilled water ・ ・ ・ 51.6 parts

Next, using the obtained pigment dispersion, various components having the following composition were mixed to prepare a coating solution for forming a reflective layer.
<Prescription of reflection layer forming coating solution>
-The above-mentioned pigment dispersion ... 71.4 parts-Polyacrylic resin aqueous dispersion ... 17.1 parts (Binder: Jurimer ET410, manufactured by Nippon Pure Chemical Industries, Ltd., solid content: 30% by mass)
Polyoxyalkylene alkyl ether 2.7 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Oxazoline compound (crosslinking agent) ... 1.8 parts (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass)
・ Distilled water: 7.0 parts

The reflective layer-forming coating solution obtained above was applied to each polyester film with a bar coater and dried at 180 ° C. for 1 minute, and (i) a reflective layer (white) with a titanium dioxide coating amount of 6.5 g / m ^2. Layer).

(Ii) Easy-adhesive layer The components of the following composition are mixed to prepare an easy-adhesive layer coating solution, and this is applied to the binder layer so that the binder coating amount is 0.09 g / m ² (i) It was applied to. Then, it was made to dry at 180 degreeC for 1 minute, and (ii) the easily bonding layer was formed.
<Composition of coating solution for easy adhesion layer>
・ Polyolefin resin aqueous dispersion: 5.2 parts (carboxylic acid-containing binder: Chemipearl S75N, manufactured by Mitsui Chemicals, solid content: 24% by mass)
Polyoxyalkylene alkyl ether 7.8 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Oxazoline compound: 0.8 part (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass)
Silica fine particle aqueous dispersion 2.9 parts (Aerosil OX-50, manufactured by Nippon Aerosil Co., Ltd., solid content: 10% by mass)
・ Distilled water ... 83.3 parts

  Next, on the surface of the polyester film opposite to the side on which the (i) reflective layer and (ii) easy-adhesive layer are formed, the following (iii) undercoat layer, (iv) barrier layer, and (v) An antifouling layer was applied sequentially from the polyester film side.

(Iii) Undercoat layer Various components having the following composition were mixed to prepare a coating solution for an undercoat layer, this coating solution was applied to a polyester film, dried at 180 ° C. for 1 minute, and an undercoat layer (dry coating amount: about 0.1 g / m ² ) was formed.
<Composition of coating solution for undercoat layer>
・ Polyester resin: 1.7 parts (Vaironal MD-1200, manufactured by Toyobo Co., Ltd., solid content: 17% by mass)
Polyester resin: 3.8 parts (Sulphonic acid-containing binder: Pesresin A-520, manufactured by Takamatsu Oils & Fats Co., Ltd., solid content: 30% by mass)
Polyoxyalkylene alkyl ether: 1.5 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
Carbodiimide compound: 1.3 parts (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content: 10% by mass)
・ Distilled water ... 91.7 parts

(Iv) Barrier layer Subsequently, a vapor deposition film of silicon oxide having a thickness of 800 mm was formed on the surface of the formed undercoat layer under the following vapor deposition conditions to obtain a barrier layer.
<Deposition conditions>
Reaction gas mixture ratio (unit: slm): hexamethyldisiloxane / oxygen gas / helium = 1/10/10
・ Vacuum degree in the vacuum chamber: 5.0 × 10−6 mbar
・ Vacuum degree in the deposition chamber: 6.0 × 10 −2 mbar
・ Cooling ・ Electrode drum power supply: 20kW
-Film transport speed: 80 m / min

(V) Antifouling Layer As shown below, a coating solution for forming the first and second antifouling layers is prepared, and a first antifouling layer coating solution and a second antifouling layer are formed on the barrier layer. The coating liquid for layers was applied in this order, and a two-layer antifouling layer was applied.

<First antifouling layer>
-Preparation of coating solution for first antifouling layer-
Components in the following composition were mixed to prepare a first antifouling layer coating solution.
<Composition of coating solution>
Seranaate WSA1070 (manufactured by DIC Corporation) 45.9 parts Oxazoline compound (crosslinking agent) 7.7 parts (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25% by mass )
・ Polyoxyalkylene alkyl ether: 2.0 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
・ Pigment dispersion used in the reflective layer: 33.0 parts ・ Distilled water: 11.4 parts

-Formation of first antifouling layer-
The obtained coating solution was coated on the barrier layer so that the binder coating amount was 3.0 g / m ² and dried at 180 ° C. for 1 minute to form a first antifouling layer.

-Preparation of coating solution for second antifouling layer-
Components in the following composition were mixed to prepare a second antifouling layer coating solution.
<Composition of coating solution>
Fluorine-based binder: Obligard (manufactured by AGC Co-Tech Co., Ltd.) ... 45.9 parts Oxazoline compound ... 7.7 parts (Epocross WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25 mass) %: Crosslinking agent)
・ Polyoxyalkylene alkyl ether: 2.0 parts (Naroacty CL95, manufactured by Sanyo Chemical Industries, solid content: 1% by mass)
-The pigment dispersion prepared for the reflective layer ... 33.0 parts-Distilled water ... 11.4 parts

-Formation of second antifouling layer-
The prepared coating solution for the second antifouling layer is applied onto the first antifouling layer formed on the barrier layer so that the binder application amount is 2.0 g / m ² , and the mixture is applied at 180 ° C. for 1 minute. A second antifouling layer was formed by drying.

  As described above, a back sheet having a reflective layer and an easy adhesion layer on one side of the polyester film and having an undercoat layer, a barrier layer, and an antifouling layer on the other side was produced.

(Adhesion)
The obtained back sheet was subjected to storage treatment (heat treatment) under the conditions of 120 ° C. and relative humidity of 100%, and the adhesion after 60 hours was evaluated by a tape peeling test. The tape peeling test was carried out by cutting in a grid and evaluated according to the following criteria. The results are shown in Table 2 above.
○: No peeling.
Δ: Peeling of less than 10% was observed.
X: Peeling of 10% or more was recognized.

  As can be seen from Table 2, the back sheet using the film of the example had good adhesion.

4). Production of Solar Cell Using the back sheet produced as described above, a solar cell power generation module was produced by bonding to a transparent filler so as to have the structure shown in FIG. 1 of JP-A-2009-158952. At this time, it stuck so that the easily-adhesive layer of a backsheet might contact the transparent filler which embeds a solar cell element.

5. Overview Evaluation of Solar Cell The polyester films of Comparative Examples 6 to 7 and 12 to 13 had a poor surface shape, and defects were caused when they were bonded to the solar cell element. On the other hand, the polyester films of Examples 1 to 18 and Comparative Examples 1 to 5 and 8 to 11 were able to produce solar cells with good surface conditions and no defects. Examples 7 to 8 and Examples 16 to 17 also had a slightly poor surface shape, but were not at a level causing problems as solar cells.

Claims (22)

A film comprising a polymer,
The polymer has a polymer structural unit containing a —N═C═N— structure and a —N═C (R) —NH— structure in the main chain (provided that the main chain contains no ester bond, R represents a polyester structure bonded to a C atom at one end), and
The polymer structural unit includes a polymer structural unit A having a number average molecular weight of 1000 to 4000 excluding R and a polymer structural unit B having a number average molecular weight of 18000 or more excluding R. To film.   The film according to claim 1, wherein the polymer structural unit includes a portion bonded to another polymer structural unit via a polyester structure represented by R.   The film according to claim 1 or 2, wherein the polymer structural unit has OH or COOH at the other end of the polyester structure represented by R.   The film according to any one of claims 1 to 3, wherein the number average molecular weight of the polymer structural unit A excluding the R is 3000 to 4000. The film according to any one of claims 1 to 4, wherein at least one of the polymer structural unit A and the polymer structural unit B has a structural unit represented by the following general formula (1).

[R ₁ , R ₂ , R ₃ and R ₄ each independently represents an alkyl group having 1 to 7 carbon atoms or a hydrogen atom. n represents the number of repeating units. ]   At least one of the polymer structural unit A and the polymer structural unit B is poly (1,3,5-triisopropylphenylene-2,4-carbodiimide), poly (1,5-diisopropylphenylene-2,4-carbodiimide). 6, derived from a random copolymer of 1,3,5-triisopropylphenylene-2,4-carbodiimide and 1,5-diisopropylphenylene-2,4-carbodiimide. the film.   The film according to any one of claims 1 to 6, wherein the polyester is polyethylene terephthalate. A synthesis step of synthesizing a polymer by reacting polyester with a first polycarbodiimide having a number average molecular weight of 1000 to 4000 and a second polycarbodiimide having a number average molecular weight of 18000 or more;
A film forming step of forming a film by forming the polymer synthesized by the synthesis step; and
Manufacturing method of including film. 9. The film according to claim 8, wherein the synthesis step forms a site where the first polycarbodiimide is bonded to the molecular end of the polyester and a site where the second polycarbodiimide is bonded to the molecular end of the polyester. Manufacturing method . The method for producing a film according to claim 8 or 9, further comprising a stretching step of stretching the film formed by the film forming step. The method for producing a film according to claim 9, wherein the stretching is biaxial stretching. The method for producing a film according to claim 11, wherein the MD orientation degree [Δn (x−z)] and the TD orientation degree [Δn (yz)] are both 0.14 or more.   The manufacturing method of the film as described in any one of Claims 10-12 which heat-processes to the said film in the said extending process.   The method for producing a film according to claim 13, wherein in the stretching step, the film subjected to the heat treatment is subjected to a thermal relaxation treatment in both the longitudinal direction (MD) and the width direction (TD).   The number average molecular weight of said 1st polycarbodiimide is 3000-4000, The manufacturing method of the film as described in any one of Claims 8-14. The manufacturing method of the film as described in any one of Claims 8-15 in which at least one of said 1st polycarbodiimide and said 2nd polycarbodiimide has a structural unit represented by following General formula (1).

[R ₁ , R ₂ , R ₃ and R ₄ each independently represents an alkyl group having 1 to 7 carbon atoms or a hydrogen atom. n represents the number of repeating units. ]   At least one of the first polycarbodiimide and the second polycarbodiimide is poly (1,3,5-triisopropylphenylene-2,4-carbodiimide), poly (1,5-diisopropylphenylene-2, 4- A carbodiimide), 1,3,5-triisopropylphenylene-2,4-carbodiimide and a random copolymer of 1,5-diisopropylphenylene-2,4-carbodiimide according to any one of claims 8 to 16. The manufacturing method of the film of description.   The method for producing a film according to any one of claims 8 to 17, wherein the polyester is polyethylene terephthalate.   The method for producing a film according to claim 8, wherein the polyester has a carboxylic acid value of 20 eq / ton or less.   The method for producing a film according to claim 8, wherein the polyester has a carboxylic acid value of 15 eq / ton or less.   The film manufactured by the manufacturing method as described in any one of Claims 8-20. The film according to any one of claims 1 to 7 and 21, were COOH, OH, SO ₃ H, a layer containing at least one functional group selected from NH ₂ and salts thereof and laminated film.