JP6029518B2 - Polyvinyl acetal film - Google Patents

Description

  The present invention relates to a polyvinyl acetal film that can be finely adjusted in position at the time of lay-up, and is less likely to shrink and flow out of resin from an end when laminated.

  A solar cell module used for photovoltaic power generation generally has a plurality of solar cells between a light-transmitting protective member such as a glass plate and a glass plate or other hard back plate (cover plate or back sheet). Are connected in series. Since solar cells are extremely fragile, in solar cell modules, it is widely performed to place solar cells between a protective member and a back plate in a state where the solar cells are sealed with an adhesive resin sealing material. .

As a sealing material for solar cells, it is known to use a sheet made of an ethylene-vinyl acetate copolymer containing a crosslinking agent made of an organic peroxide (see, for example, Patent Documents 1 and 2). . However, the ethylene-vinyl acetate copolymer has a problem that acetic acid is generated by hydrolysis or thermal decomposition, and the generated acetic acid causes corrosion of metal parts such as electrodes and conductive wires (connections) in the solar cell module. Furthermore, in the case of this conventional technique, an ethylene-vinyl acetate copolymer sheet as a sealing material is laminated (laminated) with the inner surface of a translucent protective member, the inner surface of a solar cell, the back plate, and the like. The process of heating and pressurizing is usually employed, but since it is necessary to perform lamination while advancing the crosslinking reaction of the ethylene-vinyl acetate copolymer sheet, it is possible to achieve a shortened manufacturing process that has been required in recent years. Have difficulty.
Further, when a thermosetting resin is used as the sealing resin, it is difficult to simultaneously control the embedding and curing of the solar battery cell.

Moreover, it is known to use the film which consists of polyvinyl butyral as a sealing material for photovoltaic cells (for example, refer patent document 3). Polyvinyl butyral has an advantage that it is less susceptible to corrosion of metal members in solar cell modules than ethylene-vinyl acetate copolymer because it has only a small amount of vinyl acetate units that generate an acid component, and it is a thermoplastic resin. Polyvinyl butyral has a high viscosity at the flow start temperature, so there is less concern that the resin will flow out of the glass edge during the production of the solar cell module and contaminate the device and the glass surface. -It can be advantageously used in a method of manufacturing a solar cell module by a two-roll process.
Furthermore, since polyvinyl butyral film has high strength and excellent adhesion to glass and penetration resistance, it is also used as an intermediate film for automobile windshields and safety laminated glass for buildings (for example, patents). (Ref. 4).
However, the conventional polyvinyl butyral film for sealing solar battery cells and the polyvinyl butyral film for safety glass interlayer film are used for the adhesion between the polyvinyl butyral films at the time of manufacturing the solar cell module or the safety glass. , It is easy to make close contact with other members, it is difficult to fine-tune the position when laying up the polyvinyl butyral film on a member such as glass, and the polyvinyl butyral film is accurately laid up in place with good workability There is a problem that it is difficult to do. In addition, the conventional polyvinyl butyral film is likely to shrink when heated and pressurized, and when the polyvinyl butyral film shrinks, in the solar cell module, the position of the solar battery cell, the occurrence of unsealed portions, the generation of voids, Decrease in the adhesive strength between the polyvinyl butyral sealing material and other members such as a glass plate is likely to occur. With laminated glass, misalignment between the glass to be bonded, generation of bubbles at the bonded portion, Generation | occurrence | production of the location which does not exist, generation | occurrence | production of a space | gap, the fall of the adhesive strength of a glass plate and a polyvinyl butyral intermediate film, etc. occur easily.

JP 58-023870 A Japanese Patent Laid-Open No. 6-177412 JP 2006-013505 A Japanese Patent No. 3101778 International Publication No. 03/033583 EP 1356683 Specification

Hiroshi Ashiya, “Introduction to Polarizing Microscopes for Polymer Materials First Edition”, Agne Technology Center, Inc., 2001, p. 85-91

The object of the present invention is to make fine adjustment of the lay-up position easily when laying up (stacking) on glass or other members, which is unlikely to cause close contact between films or other members. It is possible to provide a polyvinyl acetal film that can be accurately laid up at a predetermined position and that is less likely to shrink or flow out of resin from the end portion even when heated.
Furthermore, the objective of this invention is providing the sealing material for solar cells which consists of a polyvinyl acetal film which has an above-described characteristic, and the intermediate film for laminated glasses.
And the objective of this invention is providing the solar cell module and laminated glass using the polyvinyl acetal film which has an above described characteristic.

When the present inventors have continued various studies to achieve the above-mentioned object, a film generated when a polyvinyl acetal film is used as a sealing material for manufacturing a solar cell module or an intermediate film for laminated glass is used. It has been found that the close contact and the close contact with other members such as a glass plate are caused by the physical properties of the surface of the polyvinyl acetal film.
It was also found that the shrinkage of the polyvinyl acetal film that occurs when heated is based on a structural difference or physical property difference in the thickness direction of the film.
Therefore, as a result of further investigation based on those findings, the two surface sides of the polyvinyl acetal film form a skin layer having a predetermined birefringence, and the core portion between the two skin layers is more than the skin layer. A polyvinyl acetal film having a specific three-layer structure having a low specific birefringence could be produced. And when the solar cell module was manufactured using the obtained polyvinyl acetal film as a sealing material, and when the laminated glass was manufactured using the polyvinyl acetal film as an intermediate film, the polyvinyl acetal film is between films. And adhesion to other members such as a glass plate is difficult to occur, and when the polyvinyl acetal film is laid up on another member such as a glass plate, fine adjustment of the position is extremely easy, and heating is also performed. However, it was found that shrinkage and resin outflow from the end portion are less likely to occur, and further studies were made based on these findings to complete the present invention.

That is, the present invention
(1) A polyvinyl acetal film formed using a polyvinyl acetal having a vinyl alcohol unit content of 8 to 30% by mass, and a core layer C is present between two outer skin layers A and B And having the following formulas (I) , (II) and (IV) :
Δn _MDA ≧ Δn _MDB (I)
Δn _MDB −Δn _MDC ≧ 0.1 × 10 ⁻³ (II)
Δn _MDA <3.5 × 10 ^-3 (IV)
(In the above formula, Δn _MDA is the birefringence index of skin layer A in the machine flow direction, Δn _MDB is the birefringence index of skin layer B in the machine flow direction, and Δn _MDC is the birefringence index of core layer C in the machine flow direction. Show.)
Is a polyvinyl acetal film characterized by satisfying

And this invention,
( 2 ) one or both of the following formulas (V) and (VI);
Δn _MDA / Δn _TDA = 0.5 to 3.0 (V)
Δn _MDB / Δn _TDB = 0.5 to 3.0 (VI)
(In the above formula, Δn _MDA is the birefringence index of skin layer A in the machine flow direction, Δn _MDB is the birefringence index of skin layer B in the machine flow direction, and Δn _TDA is perpendicular to the machine flow direction of skin layer A. (The birefringence index, Δn _TDB indicates the birefringence index in the direction perpendicular to the machine flow direction of the skin layer B.)
The polyvinyl acetal film of ( 1 ), which further satisfies the following:
( 3 ) Melt tension of 0.5 to 2.5 cN when discharged in a strand form at a rate of 45 mm / sec from a circular die having a diameter of 1 mm under heating and melting at 200 ° C. and taken up at a rate 5 times the discharge rate The polyvinyl acetal film of (1) or (2) , which is formed from a polyvinyl acetal or a polyvinyl acetal composition having
It is.

Furthermore, the present invention provides
( 4 ) A solar cell encapsulant comprising the polyvinyl acetal film of any one of (1) to ( 3 );
( 5 ) A solar cell module comprising the solar cell encapsulant of ( 4 ) above;
It is.

And this invention,
( 6 ) An interlayer film for laminated glass comprising the polyvinyl acetal film of any one of (1) to ( 3 ); and
( 7 ) Laminated glass comprising the interlayer film for laminated glass of ( 6 ) above;
It is.

  The polyvinyl acetal film of the present invention is less likely to adhere between films and other members such as a glass plate, and when the polyvinyl acetal film of the present invention is laid up (laminated) on another member such as a glass plate Fine adjustment of the position is extremely easy. Therefore, by using the polyvinyl acetal film of the present invention as a sealing material for solar cells, an interlayer film for laminated glass, etc., the polyvinyl acetal film of the present invention can be accurately placed at a predetermined position of a member such as a glass plate with good workability. Thus, a high quality solar cell module, laminated glass and the like can be manufactured with high productivity.

  The polyvinyl acetal film of the present invention hardly shrinks even when heated. Therefore, when the polyvinyl acetal film of the present invention is used as a sealing material for solar cells, an interlayer film for laminated glass, etc., positional deviation between members, generation of unsealed portions, generation of voids, polyvinyl butyral sealing The adhesive strength between the stopper or the intermediate film and another member such as a glass plate is hardly reduced, and various products such as a solar cell module and laminated glass can be manufactured smoothly.

The polyvinyl acetal film of the present invention is less likely to cause resin outflow from the end of a glass plate or the like during the production of a solar cell module or laminated glass, and less likely to stain the device or the glass surface, and does not require a crosslinking step. It can be advantageously used in a method of manufacturing a solar cell module or laminated glass by a roll-to-roll process.
Furthermore, the polyvinyl acetal film of the present invention has high strength and is excellent in adhesion to members such as a glass plate and penetration resistance.

FIG. 1 shows the birefringence (Δn _MDA ) of the skin layer A, the birefringence (Δn _MDB ) of the skin layer B, and the birefringence (Δn) of the core layer C in the machine flow direction (length direction) of the polyvinyl acetal film. It is the schematic which shows the collection method of the sample at the time of measuring _MDC ). FIG. 2 shows the birefringence (Δn _TDA ) of the skin layer A, the birefringence (Δn _TDB ) of the skin layer B, and the birefringence of the core layer C in the direction (width direction) perpendicular to the machine flow direction of the polyvinyl acetal film. It is the schematic which shows the collection method of the sample at the time of measuring a rate ((DELTA) _nTDC ).

The present invention is described in detail below.
The polyvinyl acetal film of the present invention has a three-layer structure in which a skin layer A and a skin layer B are respectively provided on both surfaces (outside) of the film, and a core layer C exists between the two skin layers A and B. Have.
In the polyvinyl acetal film of the present invention, the thickness of each of the skin layer A and the skin layer B is not particularly limited, but is, for example, 5% or less with respect to the total thickness of the polyvinyl acetal film (5% from the surface layer of the film). Skin layer A and skin layer B have a higher birefringence than the core layer C portion.
In the present invention, the thickness of the core layer C refers to a remaining portion obtained by subtracting the total thickness of the skin layer A and the skin layer B on both surfaces from the total thickness of the polyvinyl acetal film.
For example, when the thickness of the skin layer A and the skin layer B is 3% of the total thickness of the polyvinyl acetal film, the thickness of the core layer C existing inside the skin layer A and the skin layer B is It becomes 94% of the thickness of the whole film.

When the birefringence in the machine flow direction of the polyvinyl acetal film (line direction and length direction when continuously forming the polyvinyl acetal film) (hereinafter referred to as “length direction (MD)”) is measured, skin layer A The birefringence in the length direction (MD) of the skin and the birefringence in the length direction (MD) of the skin layer B may be the same or different. , Skin layer having a larger birefringence in the length direction (MD) [skin layer in which the birefringence in the length direction (MD) is greater than or equal to the birefringence in the length direction (MD) of the other skin layer ] Is a skin layer A, and a skin layer having a birefringence in the length direction (MD) equal to or lower than the birefringence in the length direction (MD) of the skin layer A is defined as a skin layer B.
That is, in the polyvinyl acetal film of the present invention, the skin layer A and the skin layer B have a relationship represented by the following formula (I).
Δn _MDA ≧ Δn _MDB (I)
[In the formula, Δn _MDA represents the birefringence in the length direction (MD) of the skin layer A, and Δn _MDB represents the birefringence in the length direction (MD) of the skin layer B. ]

The polyvinyl acetal film of the present invention in which the skin layer A and the skin layer B have the relationship of the above formula (I) satisfies the following formulas (II) and (IV) .
Δn _MDB −Δn _MDC ≧ 0.1 × 10 ⁻³ (II)
Δn _MDA <3.5 × 10 ^-3 (IV)
[In the formula, Δn _MDA is the birefringence in the length direction (MD) of skin layer A, Δn _MDB is the birefringence in the length direction (MD) of skin layer B, and Δn _MDC is the length direction of core layer C. The birefringence of (MD) is shown. ]

The polyvinyl acetal film of the present invention has a difference (Δn _MDB ) between the birefringence index (Δn _MDB ) in the length direction (MD) of the skin layer B and the birefringence index (Δn _MDC ) in the length direction (MD) of the core layer C. −Δn _MDC ) needs to satisfy the above formula (II), that is, 0.1 × 10 ⁻³ or more, preferably 0.15 × 10 ⁻³ or more, More preferably, it is × 10 ⁻³ or more.
The difference (Δn _MDB −Δn _MDC ) between the birefringence index (Δn _MDB ) in the length direction (MD) of the skin layer B and the birefringence index (Δn _MDC ) in the length direction (MD) of the core layer C is 0.1. If it is smaller than × 10 ⁻³ , adhesion between polyvinyl acetal films and adhesion to other members are likely to occur, and when the polyvinyl acetal film is laid up on a glass plate or other member (when stacked, laminated) Fine adjustment of the position becomes difficult, and it becomes difficult to accurately lay up the polyvinyl acetal film with good workability.

The upper limit of the difference (Δn _MDB −Δn _MDC ) between the birefringence index (Δn _MDB ) in the length direction (MD) of the skin layer B and the birefringence index (Δn _MDC ) in the length direction (MD) of the core layer C is Although not particularly limited, the difference (Δn _MDB −Δn _MDC ) between the birefringence index (Δn _MDB ) in the length direction (MD) of the skin layer B and the birefringence index (Δn _MDC ) in the length direction (MD) of the core layer C ) As a result, the difference (Δn _MDA −Δn _MDC ) between the birefringence index (Δn _MDA ) in the length direction (MD) of the skin layer A and the birefringence index (Δn _MDC ) in the length direction (MD) of the core layer C is If it becomes too large, in the solar cell module, the position of the solar cell, the occurrence of unsealed portions, the generation of voids, the decrease in the adhesive strength between the polyvinyl acetal sealing material and other members, etc. are likely to occur. In laminated glass, misalignment between the glass to be bonded, generation of bubbles at the bonded part, Generation of non-existent location of film, generation of voids tends to decrease and become liable to occur in the bonding strength between the glass plate and the polyvinyl acetal intermediate film.
From this point, the difference (Δn _MDB −Δn _MDC ) between the birefringence index (Δn _MDB ) in the length direction (MD) of the skin layer B and the birefringence index (Δn _MDC ) in the length direction (MD) of the core layer C The difference (Δn _MDA −Δn _MDC ) between the birefringence (Δn _MDA ) in the length direction (MD) of the skin layer A and the birefringence (Δn _MDC ) in the length direction (MD) of the core layer C is It is preferably 3.3 × 10 ⁻³ or less, and more preferably 2.3 × 10 ⁻³ or less.

The polyvinyl acetal film of the present invention satisfies the above formulas (I) and (II) from the viewpoint of preventing the shrinkage of the polyvinyl acetal film, and further includes the following formula (IV) :
Δn _MDA <3.5 × 10 ^-3 (IV)
[In the above formula, Δn _MDA represents the birefringence of the skin layer A in the length direction (MD). ]
Is satisfied . From this point, the birefringence (Δn _MDB ) in the length direction (MD) of the skin layer B of the polyvinyl acetal film is also preferably less than 3.5 × 10 ⁻³ .

In the polyvinyl acetal film of the present invention, the birefringence index (Δn _MDC ) in the length direction (MD) of the core layer C is represented by the following formula (III);
Δn _MDC ≦ 0.2 × 10 ⁻³ (III)
In particular, Δn _MDC is preferably 0.15 × 10 ⁻³ or less, more preferably 0.1 × 10 ⁻³ or less.
If the birefringence index (Δn _MDC ) in the length direction (MD) of the core layer C becomes too large, the polyvinyl acetal film shrinks when the polyvinyl acetal film is laminated (superposed) on another member and heated. As a result, in the solar cell module, the positional deviation of the solar cells, the generation of unsealed portions, the generation of voids, the decrease in the adhesive strength between the polyvinyl acetal sealing material and other members, etc. are likely to occur. Therefore, misalignment between the glass to be bonded, generation of bubbles at the bonded portion, generation of a portion where no intermediate film exists, generation of voids, decrease in adhesive strength between the glass plate and the polyvinyl acetal intermediate film, etc. are likely to occur. Tend to be.
From the viewpoint of production, the birefringence (Δn _MDC ) in the length direction (MD) of the core layer C is preferably 0.001 × 10 ⁻³ or more, and 0.01 × 10 ⁻³ or more. It is more preferable that
From the viewpoint of adhesion prevention and shrinkage prevention at the time of laminating the polyvinyl acetal film, the birefringence (Δn _MDA ) of the skin layer A in the length direction (MD) and the length direction (MD) of the skin layer B of the polyvinyl acetal film The birefringence (Δn _MDB ) is preferably 0.1 × 10 ⁻³ or more and less than 3.5 × 10 ⁻³ , and is 0.2 × 10 ^{−3 to} 3.0 × 10 ⁻³ . It is more preferable that it is 0.5 × 10 ^{−3 to} 2.5 × 10 ⁻³ .

Further, the polyvinyl acetal film of the present invention satisfies the above formulas (I), (II) and (IV) or formulas (I) to (IV), and further includes any of the following formulas (V) and (VI). Satisfying either or both is preferable from the viewpoint of preventing shrinkage.
Δn _MDA / Δn _TDA = 0.5 to 3.0 (V)
Δn _MDB / Δn _TDB = 0.5 to 3.0 (VI)
[In the above formula, Δn _MDA is the birefringence in the length direction (MD) of skin layer A, Δn _MDB is the birefringence in the length direction (MD) of skin layer B, and Δn _TDA is the length of skin layer A. Birefringence in the direction perpendicular to the direction (MD) (width direction (TD)), Δn _TDB denotes the birefringence in the direction perpendicular to the length direction (MD) of the skin layer B (width direction (TD)) . ]
In particular, the polyvinyl acetal film of the present invention can more effectively prevent shrinkage when heated, so the birefringence (Δn _MDA ) in the length direction (MD) of the skin layer A and the length direction of the skin layer A The ratio (Δn _MDA / Δn _TDA ) of the birefringence index (Δn _TDA ) in the direction (width direction (TD)) [hereinafter referred to as “width direction (TD)”] perpendicular to (ND), and the length of the skin layer B The ratio (Δn _MDB / Δn _TDB ) between the birefringence index (Δn _MDB ) in the length direction (MD) and the birefringence index (Δn _TDB ) in the width direction (TD) of the skin layer B is 0.5 to More preferably, it is in the range of 2.0.

Further, in the polyvinyl acetal film of the present invention, in addition to the above formula, the birefringence (Δn _TDC ) in the width direction (TD) of the core layer C is preferably 0.2 × 10 ⁻³ or less, It is more preferably 0.15 × 10 ⁻³ or less, and further preferably 0.1 × 10 ⁻³ or less. When the birefringence index (Δn _TDC ) in the width direction (TD) of the core layer C is too large, shrinkage is likely to occur when the polyvinyl acetal film is heated. Misalignment, generation of unsealed parts, generation of voids, decrease in adhesive strength between the polyvinyl acetal sealing material and other members, etc., and when used in the production of laminated glass, the glass to be bonded There is a tendency that misalignment between them, generation of bubbles at the bonded portion, generation of a portion where no intermediate film is present, generation of voids, decrease in adhesive strength between the glass plate and the polyvinyl acetal intermediate film, and the like.
From the viewpoint of manufacturing, the birefringence (Δn _TDC ) in the width direction (TD) of the core layer C is preferably 0.001 × 10 ⁻³ or more, and 0.01 × 10 ⁻³ or more. More preferably.

Here, the birefringence (Δn _MDA , Δn _MDB and Δn _MDC ) in the length direction (MD) and the width direction (TD) of the skin layer A, skin layer B and core layer C of the polyvinyl acetal film in the present invention. The refractive indexes (Δn _TDA , Δn _TDB and Δn _TDC ) are those measured by the following method.

[Measurement of birefringence (Δn _MDA , Δn _MDB , Δn _MDC ) and birefringence (Δn _TDA , Δn _TDB and Δn _TDC ) in the length direction (MD) of the polyvinyl acetal film]
(1) The birefringence (Δn _MDA , Δn _MDB , Δn _MDC ) in the length direction (MD) and the birefringence in the width direction (TD) of the skin layer A, skin layer B, and core layer C of the polyvinyl acetal film Δn _TDA , Δn _TDB and Δn _TDC ) were measured by the following methods (2) and (3) with reference to the method described in Non-Patent Document 1.
(2) Measurement of birefringence (Δn _MDA , Δn _MDB , Δn _MDC ) in the length direction (MD):
(I) The size of MD × TD = 2 mm × 10 mm from the central portion in the width direction (TD) of the film at an arbitrary position in the length direction (MD) of the polyvinyl acetal film, as shown in FIG. A thin strip was cut out, and the strip was sandwiched between PET films having a thickness of 100 μm on both sides, and was further sandwiched between wooden frames and attached to a microtome apparatus.
(Ii) Next, as shown in FIG. 1B (PET film and wooden frame are not shown), the strips collected above are spaced 20 μm in parallel with the length direction (MD) of the strips. And sliced 20 pieces for observation (MD × TD = 2 mm × 20 μm) shown in FIG. From the slice pieces, three slice pieces having a smooth slice surface and no slice thickness unevenness were selected, each was placed on a slide glass, sealed with a cover glass and a sealing liquid, and the slice thickness was measured with an eyepiece micrometer. . The observation was performed in a visual field of 10 times the eyepiece and 20 times the objective (total 200 times).

(Iii) Next, the cover glass is moved so that the slice surface can be observed, the slice piece is tilted as shown in FIG. 1 (d), and the same place where the thickness is measured in (ii) is the extinction position + 45 °. It was confirmed that the retardation was 1 wavelength or less from the interference light on the slice surface under white light illumination using a Belek compensator attached to a diagonal microscope.
(Iv) The light source was changed to sodium D line (monochromatic light with a wavelength of 589 nm), the angle knob of the Belek compensator was rotated so that the center of the black stripe was at the crosshair in the center of the field of view, and the rotation angle a was read . Next, the angle knob was rotated in the opposite direction to move one wavelength, and the angle b was read so that the center of the black stripe was at the cross line in the center of the visual field. This operation was repeated 4 times, and the average value of 4 times in total for the angles a and b was used as a reading value.
(V) determine the resulting a, compensation values from two angles of b i = (a-b) / 2 ( provided that a> b) ^{above, f (i) = sin 2} i × (1 + 0.204sin 2 i) is multiplied by the optical constant C unique to the Berek compensator to obtain the retardation R [R = f (i) × C], divided by the measured thickness to obtain the birefringence, and the same measurement is performed three times ( n = 3), and the average value was defined as the birefringence (Δn). At that time, the birefringence (Δn _MDA ) in the length direction (MD) of the skin layer A and the birefringence (Δn _MDB ) in the length direction (MD) of the skin layer B are determined from the outermost surface of the polyvinyl acetal film. Measurement was made at a depth of 1 μm, and the birefringence index (Δn _MDC ) in the length direction (MD) of the core layer C was measured at the central position of the film thickness (the central position of the slice surface).

(3) Measurement of birefringence (Δn _TDA , Δn _TDB and Δn _TDC ) in the width direction (TD):
(I) The size of MD × TD = 10 mm × 2 mm from the center in the width direction (TD) of the film at an arbitrary position in the length direction (MD) of the polyvinyl acetal film as shown in FIG. A thin strip was cut out, and the strip was sandwiched between PET films having a thickness of 100 μm on both sides, and was further sandwiched between wooden frames and attached to a microtome apparatus.
(Ii) Next, as shown in (b) of FIG. 2 (PET film and wooden frame are not shown), the strips collected above are parallel with the width direction (TD) of the strips at intervals of 20 μm. Slicing was performed to produce 20 slices for observation (MD × TD = 20 μm × 2 mm) shown in FIG. From the slice pieces, three slice pieces having a smooth slice surface and no slice thickness unevenness were selected, each was placed on a slide glass, sealed with a cover glass and a sealing liquid, and the slice thickness was measured with an eyepiece micrometer. . The observation was performed in a visual field of 10 times the eyepiece and 20 times the objective (total 200 times).

(Iii) Next, the cover glass is moved so that the slice surface can be observed, the slice piece is tilted as shown in FIG. 2 (d), and the same place where the thickness is measured in (ii) above is the extinction position + 45 °. It was confirmed that the retardation was 1 wavelength or less from the interference light on the slice surface under white light illumination using a Belek compensator attached to a diagonal microscope.
(Iv) The light source was changed to sodium D line (monochromatic light with a wavelength of 589 nm), the angle knob of the Belek compensator was rotated so that the center of the black stripe was at the crosshair in the center of the field of view, and the rotation angle a was read . Next, the angle knob was rotated in the opposite direction to move one wavelength, and the angle b was read so that the center of the black stripe was at the cross line in the center of the visual field. This operation was repeated 4 times, and the average value of 4 times in total for the angles a and b was used as a reading value.
(V) determine the resulting a, compensation values from two angles of b i = (a-b) / 2 ( provided that a> b) ^{above, f (i) = sin 2} i × (1 + 0.204sin 2 i) is multiplied by the optical constant C unique to the Berek compensator to obtain the retardation R [R = f (i) × C], divided by the measured thickness to obtain the birefringence, and the same measurement is performed three times ( n = 3), and the average value was defined as the birefringence (Δn). At that time, the birefringence (Δn _TDA ) in the width direction (TD) of the skin layer A and the birefringence (Δn _TDB ) in the width direction (TD) of the skin layer B were 1 μm from the outermost surface of the polyvinyl acetal film. The birefringence (Δn _TDC ) in the width direction (TD) of the core layer C was measured at the depth position, and was measured at the center position of the film thickness (center position of the slice surface).

The polyvinyl acetal film of the present invention must be formed using a polyvinyl acetal having a vinyl alcohol unit content of 8 to 30% by mass, and the vinyl alcohol unit content is 10 to 22% by mass. It is preferably formed using polyvinyl acetal, and more preferably formed using polyvinyl acetal having a vinyl alcohol unit content of 12 to 18% by mass.
In the polyvinyl acetal that forms the polyvinyl acetal film, if the content of the vinyl alcohol unit is too small, problems such as a decrease in the mechanical strength of the polyvinyl acetal film and poor adhesion to the substrate occur, while the content of the vinyl alcohol unit. If the amount is too large, the hygroscopicity of the polyvinyl acetal film becomes high, and corrosion of the metal due to absorbed water, a decrease in insulation, peeling of the polyvinyl acetal film from the base material, and the like are likely to occur.
Here, the “vinyl alcohol unit” referred to in the present specification is not acetalized, but remains in the polyvinyl acetal with the hydroxyl group-containing structural unit represented by the formula “—CH ₂ —CH (OH) —”. In this specification, “the content (% by mass) of vinyl alcohol units” refers to the content (% by mass) measured according to JIS K6728: 1977.

The production method of the polyvinyl acetal for forming the polyvinyl acetal film of the present invention is not particularly limited as long as the content of the vinyl alcohol unit is 8 to 30% by mass. It can manufacture by making it react and acetalize.
The polyvinyl alcohol polymer used for the production of polyvinyl acetal is produced by saponifying a polymer (polyvinyl ester) obtained by polymerizing a vinyl ester monomer and changing the ester group in the polymer to a hydroxyl group. be able to.

  Examples of vinyl ester monomers that can be used in the production of polyvinyl esters include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, and vinyl caprylate. , Vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate and the like, and one or more of these can be used. Among them, the polyvinyl ester is preferably polyvinyl acetate obtained by polymerizing vinyl acetate.

  In addition, the polyvinyl ester, particularly polyvinyl acetate, may have a structural unit derived from another polymerizable monomer, if necessary, as long as the gist of the present invention is not impaired. Examples of the other monomers include α-olefins such as ethylene, propylene, n-butene, and isobutylene; acrylic acid or a salt thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate. Acrylates such as n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid or salts thereof; methyl methacrylate, methacryl Methacrylic acid such as ethyl acetate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate ester Acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl acrylamide, diacetone acrylamide, acrylamide propane sulfonic acid or its salt, acrylamidopropyldimethylamine or its salt or quaternary salt, N-methylol acrylamide or its Acrylamide derivatives such as derivatives; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid or salts thereof, methacrylamidepropyldimethylamine or salts or quaternary salts thereof, N-methylolmethacrylamide or the like thereof Methacrylamide derivatives such as derivatives; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether Vinyl ethers such as ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; Examples include vinylidene halides such as vinylidene and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or salts thereof, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate, and the like. And having structural units derived from one or more of these. When the polyvinyl ester, particularly polyvinyl acetate, has a structural unit derived from another monomer, the content is preferably less than 20 mol% with respect to all the structural units constituting the polyvinyl ester. More preferably, it is less than%.

  The saponification reaction of polyvinyl ester (especially polyvinyl acetate) is not particularly limited and can be performed in the same manner as in the past. For example, an alcoholysis method using an alkali catalyst or an acid catalyst, a hydrolysis method, etc. can be applied, Among them, a saponification reaction using methanol as a solvent and a caustic soda (NaOH) catalyst is simple and preferably employed.

The polyvinyl acetal film of the present invention has a polymerization degree in the range of 100 to 3000, more preferably 500 to 2500, particularly 1000 to 2000, and a saponification degree of 95 mol% or more, further 98 mol% or more, particularly 99 mol%. It is formed by using a polyvinyl acetal obtained by acetalizing the polyvinyl alcohol polymer as described above, so that the moldability when producing a polyvinyl acetal film is excellent, and the mechanical properties of the polyvinyl acetal film are It is preferable from the viewpoint of improving the corrosion resistance of the metal member.
Here, the degree of polymerization of the polyvinyl alcohol polymer in this specification refers to the degree of polymerization measured according to JIS K 6726: 1994. After re-saponifying and purifying the polyvinyl alcohol polymer, It is obtained from the intrinsic viscosity measured in water.
In addition, the saponification degree of the polyvinyl alcohol polymer in the present specification is the sum of the structural units (typically vinyl acetate units) that can be converted into vinyl alcohol units by saponification and the vinyl alcohol units of the polyvinyl alcohol polymer. It means the ratio (mol%) of the number of moles of the vinyl alcohol unit to the number of moles, and can be measured according to the description of JIS K 6726: 1994.

Examples of aldehydes for acetalizing polyvinyl alcohol polymers with aldehydes to form polyvinyl acetals include, for example, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, valeraldehyde, isovaleraldehyde, pivalaldehyde, and capron. Examples include aldehyde, heptaldehyde, caprylaldehyde, pelargonaldehyde, caprinaldehyde, undecylaldehyde, laurinaldehyde, tridecylaldehyde, myristic aldehyde, pentadecylaldehyde, palmitic aldehyde, stearyl aldehyde, tolyl aldehyde, naphthaldehyde, etc. . The polyvinyl acetal which forms the polyvinyl acetal film of the present invention can be obtained by acetalizing a polyvinyl alcohol polymer with one or more of the aldehydes described above.
If necessary, the polyvinyl acetal for forming the polyvinyl acetal film of the present invention contains a small proportion of polyfunctional aldehydes and aldehydes having a functional group other than aldehyde groups (preferably all aldehydes) together with the aldehydes described above. And acetalized polyvinyl alcohol polymer may be used.

  Among them, the polyvinyl acetal forming the polyvinyl acetal film of the present invention is preferably a polyvinyl acetal obtained by acetalizing a polyvinyl alcohol polymer with an aldehyde compound having 1 to 12 carbon atoms, and the polyvinyl alcohol polymer is a carbon number. More preferably, it is a polyvinyl acetal acetalized with an alkyl aldehyde compound of 1 to 6, more preferably a polyvinyl acetal obtained by acetalizing a polyvinyl alcohol polymer with an alkyl aldehyde compound having 1 to 4 carbon atoms. Polyvinyl butyral obtained by acetalizing a base polymer with butyraldehyde is particularly preferable. A film formed using polyvinyl butyral has excellent mechanical properties and is suitable for the production of solar cell modules and laminated glass.

The acetalization method of the polyvinyl alcohol polymer for obtaining the polyvinyl acetal is not particularly limited, but in order to industrially produce the polyvinyl acetal in large quantities, the polyvinyl alcohol polymer is used at a high temperature, for example, 90 ° C or more. A method in which a polyvinyl alcohol polymer aqueous solution is prepared in advance by sufficiently dissolving in water at a temperature and an aldehyde is reacted under acidic conditions in an aqueous solution in which the polyvinyl alcohol polymer is uniformly dissolved is preferably employed. The
In this case, the concentration of the polyvinyl alcohol polymer in the aqueous polyvinyl alcohol polymer solution is preferably 5 to 40% by mass, more preferably 5 to 20% by mass, and still more preferably 8 to 15% by mass. If the concentration of the polyvinyl alcohol polymer is too low, the productivity of the polyvinyl acetal may be deteriorated. On the other hand, if the concentration of the polyvinyl alcohol polymer is too high, stirring becomes difficult during the reaction. Gelation may occur due to hydrogen bonding between the molecules of the coalescence, and the reaction may be spotted.

As the catalyst for acetalization by reacting aldehydes under acidic conditions in an aqueous solution of a polyvinyl alcohol polymer, any of inorganic acids and organic acids can be used. For example, nitric acid, sulfuric acid, Mention may be made of inorganic acids such as hydrochloric acid and carbonic acid, and organic acids such as acetic acid and paratoluenesulfonic acid. Among them, an inorganic acid is preferably used because a sufficient reaction rate can be obtained and washing after the reaction is easy, and hydrochloric acid, sulfuric acid and nitric acid are more preferably used. The concentration of the acid catalyst in the reaction system depends on the type of acid catalyst used. In the case of hydrochloric acid, sulfuric acid, and nitric acid, 0.01 to 5 mol of these acids are used with respect to 1 liter of an aqueous solution of the polyvinyl alcohol polymer. It is preferable to add at a ratio of 0.1 to 2 mol.
If the acid concentration in the aqueous solution of the polyvinyl alcohol polymer is too low, the reaction rate becomes slow, and it may take a long time to obtain a polyvinyl acetal having the desired degree of acetalization and physical properties. On the other hand, when the concentration of the acid in the aqueous solution of the polyvinyl alcohol polymer is too high, it becomes difficult to control the reaction, and an aldehyde trimer is easily generated.

  The order of addition of the aldehydes and the catalyst when acetalizing by reacting the aldehydes with the polyvinyl alcohol polymer is not particularly limited, and can be performed by a conventionally known method. For example, the polyvinyl alcohol polymer A method of adding an aldehyde after adding the above-mentioned acid catalyst to an aqueous solution, a method of adding an acid catalyst after adding an aldehyde to an aqueous solution of a polyvinyl alcohol polymer, an aldehyde in an aqueous solution of a polyvinyl alcohol polymer And a method of simultaneously adding an acid catalyst, a method of adding an aqueous solution of a polyvinyl alcohol polymer to a solution containing an aldehyde and an acid catalyst, and the like. At that time, the addition of the aldehydes and the addition of the acid catalyst may be performed at one time or may be performed in a plurality of times.

  The acetalization of the polyvinyl alcohol polymer with aldehydes is preferably performed in a temperature range of 0 to 80 ° C. Among them, the reaction is performed at a relatively low temperature of 0 to 40 ° C., particularly 5 to 20 ° C. until the polyvinyl acetal particles are precipitated, and then the temperature is higher than that in order to complete the reaction after the polyvinyl acetal particles are precipitated. For example, when the reaction is further carried out at a temperature of 50 to 80 ° C., particularly 65 to 75 ° C., a porous polyvinyl acetal that can be easily washed can be produced with good productivity, which is more preferable. If the reaction temperature is too high, the polyvinyl acetals may be fused together, making it difficult to obtain porous polyvinyl acetal particles.

  The polyvinyl acetal particles obtained as described above are preferably porous in order to efficiently remove the remaining acid catalyst and aldehydes. In order to obtain porous polyvinyl acetal particles, in addition to the adjustment of the reaction temperature described above, the viscosity of the reaction solution, the stirring speed, the shape of the stirring blade, the shape of the reaction vessel, the reaction speed, the method of adding the catalyst and aldehydes It is good to adjust.

The polyvinyl acetal obtained as described above is decomposed with an acid in the presence of water to produce aldehydes, and therefore it is preferable to remove unreacted aldehydes or remove acid.
In general, it is preferable to perform an acid removal treatment after removing aldehydes from the viewpoint of efficiently removing unreacted aldehydes.
As a method of obtaining polyvinyl acetal with a low content of unreacted aldehydes, for example, a method of completing the reaction under conditions where the reaction rate of aldehydes is high, a solvent such as water or a water / alcohol mixed solvent is sufficient. And a method of chemically treating aldehydes.

  Examples of the method for removing the acid contained in polyvinyl acetal include a method of washing polyvinyl acetal particles with an aqueous solution of an alkali compound, a method of washing with a large amount of water, and the like. Examples of the alkali compound used at that time include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and amine compounds such as ammonia, triethylamine, and pyridine. More than seeds can be used. From the viewpoint of coloring prevention, an inorganic metal hydroxide is preferable, and an alkali metal hydroxide is more preferably used from the viewpoint of hardly adversely affecting the adhesion to glass.

The polyvinyl acetal after removing the acid preferably has an alkali titer value of 0.1 to 30, and more preferably has an alkali titer value of 1 to 20. When the alkali titer value of the polyvinyl acetal is too low, the hydrolysis resistance is lowered. On the other hand, when the alkali titer value is too high, the polyvinyl acetal film is easily colored.
In addition, the alkali titer value of polyvinyl acetal in this specification represents the quantity (mL) of hydrochloric acid aqueous solution with a density | concentration of 0.01 mol / L required for alkali titration (neutralization) of polyvinyl acetal 100g.

The polyvinyl acetal film of the present invention is an acetate group represented by a vinyl acetate unit [formula: —CH ₂ —C (H) (— O—CO—CH ₃ ) —] measured according to JIS K6728: 1977. It is preferable that the content of unsaponified units having a vinyl acetal is 5% by mass or less based on the mass of the polyvinyl acetal, and the content of vinyl acetate units is 2% by mass or less. More preferably, it is formed using a polyvinyl acetal having a vinyl acetate unit content of 1% by mass or less. When the content of vinyl acetate units in polyvinyl acetal is high, vinyl acetate units generate acetic acid that corrodes metal parts by thermal decomposition or hydrolysis by moisture, as well as olefin bonds in polyvinyl acetal by elimination of acetic acid. It becomes easy to produce and color.

  In addition, the polyvinyl acetal that forms the polyvinyl acetal film of the present invention is a content of chlorine ions, sulfate ions, and nitrate ions derived from the acid catalyst used for acetalization (when a plurality of ions are contained, the total content thereof) ) Is preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 20 ppm or less. Since these strong acid ions cause corrosion of metal members used in solar cell modules and the like, the smaller the content thereof, the better.

  The polyvinyl acetal which forms the polyvinyl acetal film of the present invention may be a polyvinyl acetal obtained by treating a polyvinyl alcohol polymer with an aldehyde to be acetalized or acetalizing with a treatment with an aldehyde. Further, it may be a crosslinked or partially crosslinked polyvinyl acetal. As the crosslinked or partially crosslinked polyvinyl acetal, for example, a part of the hydroxyl group in the vinyl alcohol unit remaining in the polyvinyl acetal is a polyfunctional compound such as a polyaldehyde compound, a polyisocyanate compound, a polyepoxy compound, or a polycarboxylic acid anhydride. And a polyvinyl acetal that is crosslinked or partially crosslinked by reacting with a hydroxyl-reactive compound (hydroxyl-reactive crosslinking agent).

The polyvinyl acetal film of the present invention may be formed from a polyvinyl acetal alone without containing other components other than the polyvinyl acetal, or a polyvinyl acetal containing a component other than the polyvinyl acetal such as a plasticizer in the polyvinyl acetal. It may be formed from a composition.
Among these, since the polyvinyl acetal film of the present invention can be produced with good moldability and good productivity, the polyvinyl acetal film of the present invention is preferably formed from a polyvinyl acetal composition containing a plasticizer.

The kind of plasticizer to be blended with polyvinyl acetal is not particularly limited. For example, triethylene glycol-di (2-ethylhexanoate), tetraethylene glycol-di (2-ethylhexanoate), di- (2- Butoxyethyl) -adipic acid ester, di- (2-butoxyethyl) -sebacic acid ester, di- (2-butoxyethyl) -azeleic acid ester, di- (2-butoxyethyl) -glutaric acid ester, di- ( 2-butoxyethyl) -phthalic acid ester, di- (2-butoxyethoxyethyl) -adipic acid ester, di- (2-butoxyethoxyethyl) -sebacic acid ester, di- (2-butoxyethoxyethyl) -azeleic acid Ester, di- (2-butoxyethoxyethyl) -glutaric acid ester, di- (2-butoxy) Toxiethyl) -phthalic acid ester, di- (2-hexoxyethyl) -adipic acid ester, di- (2-hexoxyethyl) -sebacic acid ester, di- (2-hexoxyethyl) -azeleic acid ester, di- (2-hexoxyethyl) -Glutaric acid ester, di- (2-hexoxyethoxyethyl) -adipic acid ester, di- (2-hexoxyethoxyethyl) -sebacic acid ester, di- (2-hexoxyethoxyethyl) -azeleic acid ester, Examples include di- (2-hexoxyethoxyethyl) -glutaric acid ester and 1,2-cyclohexanedicarboxylic acid-diisononyl ester, and one or more of these can be used. Among them, a plasticizer having a total number of carbon and oxygen constituting the plasticizer molecule higher than 28 is preferably used because it has low volatility and can be laminated at a high temperature. For example, triethylene glycol-di (2-ethylhexanoate), tetraethylene glycol-di (2-ethylhexanoate), di- (2-butoxyethoxyethyl) -adipate , Di- (2-butoxyethoxyethyl) -sebacic acid ester, 1,2-cyclohexanedicarboxylic acid-diisononyl ester, and the like. Among these, triethylene glycol-di (2-ethylhexahexadiene) is used since a desired plasticizing effect can be obtained in a small amount without deteriorating the corrosion prevention characteristics of the solar cell encapsulant or the interlayer film for laminated glass. Noate) and 1,2-cyclohexanedicarboxylic acid-diisononyl ester are more preferably used.
When forming the polyvinyl acetal film of this invention from the polyvinyl acetal composition containing a plasticizer, 15-50 mass parts is preferable with respect to 100 mass parts of polyvinyl acetals, and 20-40 masses. Part is more preferred.

The polyvinyl acetal composition forming the polyvinyl acetal film of the present invention may be one kind of an antioxidant, an ultraviolet absorber, an adhesive strength modifier, an anti-blocking agent, a pigment, a dye, a functional inorganic compound, or the like, if necessary. You may contain 2 or more types.
When the polyvinyl acetal film of the present invention is formed from a polyvinyl acetal composition containing an antioxidant, examples of the antioxidant include a phenol-based antioxidant, a phosphorus-based antioxidant, and a sulfur-based antioxidant. 1 type, or 2 or more types, such as these, can be contained. Among these, phenolic antioxidants, particularly alkyl-substituted phenolic antioxidants are preferably used.
When the polyvinyl acetal film of the present invention is formed from a polyvinyl acetal composition containing an antioxidant, the content of the antioxidant is 0.001 to 5 parts by mass with respect to 100 parts by mass of the polyvinyl acetal. It is preferable that it is 0.01-1 mass part.

When the polyvinyl acetal film of the present invention is formed from a polyvinyl acetal composition containing an ultraviolet absorber, for example, one kind of a benzotriazole ultraviolet absorber, a hindered amine ultraviolet absorber, a benzoate ultraviolet absorber, or the like Two or more kinds can be contained.
When the polyvinyl acetal film of the present invention is formed from a polyvinyl acetal composition containing an ultraviolet absorber, the content of the ultraviolet absorber is 10 to 50,000 ppm based on the mass of the polyvinyl acetal. Preferably, it is 100-10,000 ppm.

When the polyvinyl acetal film of the present invention is formed from a polyvinyl acetal composition containing an adhesive strength modifier, for example, it contains one or more of the adhesive strength modifiers disclosed in Patent Document 5. Among them, alkali metal salts and / or alkaline earth metal salts of organic acids are preferable, and in particular, one or both of potassium acetate and magnesium acetate are more preferably used.
When the polyvinyl acetal film of the present invention is formed from a polyvinyl acetal composition containing an adhesion modifier, the content of the adhesion modifier is 1 to 10,000 ppm based on the mass of the polyvinyl acetal. It is preferably 5 to 1,000 ppm, more preferably 10 to 300 ppm.
The optimal content of the adhesive strength modifier varies depending on the type of the adhesive strength modifier, the use of the polyvinyl acetal film, the application location, and the like, but the adhesive strength of the polyvinyl acetal film to the glass is described in Patent Document 5. In the Pummel test, it is generally preferable to adjust the numerical value to be in the range of 3 to 10, and particularly when high penetration resistance is required, the numerical value is in the range of 3 to 6. It is more preferable to adjust it to be, and when high prevention of glass scattering is required, it is more preferable to adjust the numerical value to be in the range of 7-10. When high glass scattering prevention performance is required for the polyvinyl acetal film, it is also a useful method not to add an adhesive strength modifier.

  When the polyvinyl acetal film of the present invention is formed from a polyvinyl acetal composition containing a functional inorganic compound, examples of the functional inorganic compound include a light reflecting material, a light absorbing material, a thermal conductivity improving material, and an electrical property. An improved material, a gas barrier property improving material, a mechanical property improving material or the like can be used.

  The thickness of the polyvinyl acetal film of the present invention is not particularly limited, but in general, the thickness is preferably 0.38 to 2.28 mm from the viewpoint of sealing performance, shortening of the cycle time of the laminating process, and the like. More preferably, it is 0.50 to 1.52 mm. If the polyvinyl acetal film is too thin, it will be difficult to sufficiently fill (seal) the space around the solar cells and functional units when used as a solar cell sealing material, while the polyvinyl acetal film is thick. If it is too high, the cost of the polyvinyl acetal film itself tends to be high, and the cycle time of the laminating process tends to be long, leading to a reduction in productivity.

When the polyvinyl acetal film of the present invention is discharged in a strand form at a speed of 45 mm / second from a circular die having a diameter of 1 mm under heating and melting at 200 ° C. and taken up at a rate 5 times the discharge speed, 0.5 to It is preferably formed from a polyvinyl acetal or a polyvinyl acetal composition having a melt tension in the range of 2.5 cN, and from the polyvinyl acetal or the polyvinyl acetal composition in which the melt tension is in the range of 0.6 to 2.0 cN. More preferably, it is formed from a polyvinyl acetal or a polyvinyl acetal composition having a melt tension in the range of 0.7 to 1.5 cN.
Here, the above-mentioned melt tension (melt tension) in the present specification refers to the melt tension of polyvinyl acetal itself when the polyvinyl acetal film is formed from polyvinyl acetal alone containing no other additive. When the film is formed from a polyvinyl acetal composition obtained by adding some additive to polyvinyl acetal, it refers to the melt tension of the polyvinyl acetal composition forming the film.
When a polyvinyl acetal or a polyvinyl acetal composition having a melt tension exceeding 2.5 cN is used, it is difficult to stably form a polyvinyl acetal film. On the other hand, when the polyvinyl acetal film is formed from a polyvinyl acetal having a melt tension of less than 0.5 or a polyvinyl acetal composition, when the polyvinyl acetal film is used for manufacturing a solar cell module, laminated glass, etc., the polyvinyl acetal The film melt flows out from between the substrates such as glass plates, and the finish of the solar cell module and the laminated glass tends to be poor, and the manufacturing equipment is contaminated and it takes time to clean it. Tends to decrease. The melt tension depends on the degree of polymerization of polyvinyl acetal and the amount of plasticizer contained in the polyvinyl acetal composition.

The polyvinyl acetal film of the present invention may have a flat surface or may have irregularities on the surface. When unevenness is provided on the surface of the polyvinyl acetal film, deaeration can be enhanced when the polyvinyl acetal film is laminated on a glass plate or other member in order to produce a solar cell module, laminated glass or the like.
When providing unevenness on the surface of the polyvinyl acetal film, a conventionally known method can be employed, for example, a method of providing a melt fracture structure by adjusting extrusion conditions, a method of imparting an embossed structure to the extruded film, and the like. .

The method for producing the polyvinyl acetal film of the present invention is not particularly limited, and any one capable of producing a polyvinyl acetal film having a three-layer structure consisting of skin layer A / core layer C / skin layer B and satisfying the requirements defined in the present invention. You may manufacture by the method of.
Among them, the polyvinyl acetal film of the present invention is smoothly produced by the following method.

[The suitable manufacturing method of the polyvinyl acetal film of this invention]
Using the polyvinyl acetal or the polyvinyl acetal composition, a polyvinyl acetal film is produced by melt extrusion using an extruder.
At that time, as a polyvinyl acetal or a polyvinyl acetal composition (hereinafter sometimes collectively referred to as “polyvinyl acetal (composition)”) which is a raw material for producing a film, a diameter of 1 mm is obtained by heating and melting at 200 ° C. When discharged from a circular die at a speed of 45 mm / second in a strand shape and taken up at a rate 5 times the discharge speed, a melt tension of 0.5 to 2.5 cN, and further a melt of 0.6 to 2.0 cN Polyvinyl acetal (composition) having a tension, particularly a melt tension of 0.7 to 1.5 cN is preferably used.
The temperature of the polyvinyl acetal (composition) during extrusion (melt kneading and the resin temperature at the die portion) is preferably 150 to 250 ° C, and more preferably 180 to 230 ° C. If the temperature of the polyvinyl acetal (composition) is too high, decomposition of the polyvinyl acetal occurs and the content of volatile substances increases. On the other hand, if the temperature of the polyvinyl acetal (composition) is too low, the polyvinyl acetal (composition) contains Volatile substances originally contained are difficult to volatilize, and the content of volatile substances is also increased. In order to efficiently remove the volatile substance from the polyvinyl acetal (composition), it is preferable to remove the volatile substance by reducing the pressure from the vent port of the extruder.

  In producing a polyvinyl acetal film by melt extrusion using an extruder, the average lip gap (average lip clearance) of the die is adjusted to 100 to 135% of the thickness of the finally obtained polyvinyl acetal film. After the polyvinyl acetal (composition) is melt-extruded from the die, it is immediately cooled in a water bath at a temperature of 10 to 40 ° C., and then subjected to a heat treatment (relaxation treatment) at 30 to 70 ° C. in a non-tensioned state without applying tension. By this, at least the above formulas (I) to (III) defined in the present invention are satisfied, and optionally one or more of the above formulas (IV), (V) and (VI) A satisfactory polyvinyl acetal film of the present invention having a three-layer structure consisting of skin layer A / core layer C / skin layer B can be obtained. it can.

  In a die used for extrusion molding, each of the tip portions of two members arranged to face each other with a gap therebetween to form a slit serving as an extrusion port is generally called a lip. “Die lip gap” refers to the gap between two lips facing each other. In the production of the polyvinyl acetal film, either a T-die method using a flat die or an inflation method using a circular die can be adopted. Among them, the T-die method using a flat die is used in a water bath of a film extruded from the die. It is preferably employed because it can be rapidly cooled.

Because the lip gap of the die is not always the same over the entire width direction of the die slit (in the case of a flat die) or the entire circumference (in the case of a circular die), there may be some differences In the present invention, the average value of the measured values measured every 1 cm in the width direction of the slit of the flat die or the average value of the measured values measured every 1 cm over the entire circumference of the circular slit of the circular die is taken. Average lip gap ”.
The measurement of the lip gap at each position of the die slip is, for example, by using a metal plate of a predetermined thickness and sequentially trying how many metal plates can be stacked and inserted into the lip at the measurement position. It can be measured.
For the adjustment of the lip gap, a die in which the lip gap is fixed in advance may be used, or when it is required to adjust the lip gap appropriately depending on conditions, such a configuration in which such a lip gap adjusting means is provided. No. of dice may be used. Lip opening adjustment means include manual adjustment means using a die bolt, heat bolt method, robot method, lip heater method, automatic adjustment means using a piezoelectric element method, etc. Among these, versatility for thermoplastic resins Therefore, the automatic adjustment means by the heat bolt method is preferable.

In the production of the polyvinyl acetal film of the present invention, it is important to keep the average lip gap of the die during film formation in the range of 100 to 135% as described above with respect to the thickness of the finally obtained polyvinyl acetal film. It is preferable to make it the range of 110-125%, and it is more preferable to set it as the range of 115-120%.
By setting the average lip gap of the die to the specific range described above, the pressure applied to the surface of the polyvinyl acetal film is in an appropriate range. Therefore, the skin layer satisfying the specific formula defined in the present invention is a polyvinyl acetal film. Formed on both sides.
When the lip gap of the die exceeds 135% with respect to the thickness of the finally obtained polyvinyl acetal film, the pressure applied to the surface of the film is small. Therefore, when used for manufacturing a solar cell module or laminated glass, fine adjustment of the position at the time of layup tends to be difficult. On the other hand, if the lip gap of the die is less than 100% with respect to the thickness of the finally obtained polyvinyl acetal film, a large pressure is applied to the film surface. There is a possibility that the refractive index becomes too high and a polyvinyl acetal film that easily contracts is obtained.

  It is important that the polyvinyl acetal film melt-extruded from the die is quenched in the above-described 10-40 ° C. water bath, thereby stabilizing the layer structure of the skin layer and the core layer. The temperature of the water bath is more preferably 20 to 30 ° C. If the temperature of the water bath is too high, it takes time to stabilize the layer structure, and the formation of the skin layer may be hindered. On the other hand, if the temperature of the water bath is too low, the tension applied to the polyvinyl acetal film increases, and the birefringence in the length direction (MD) becomes too high, and the polyvinyl acetal film is likely to shrink.

Furthermore, in order to relieve the stress of the polyvinyl acetal film after cooling, it is necessary to perform heat treatment without applying tension (without tension), and the temperature (relaxation temperature) of this heat treatment is 30 to 70 ° C. described above. Is important, and it is preferably 30 to 60 ° C. When the relaxation temperature is too high, the adhesion of the polyvinyl acetal film surface becomes strong, while when the relaxation temperature is too low, the polyvinyl acetal film is easily contracted.
The heat treatment time (relaxation time) is preferably 1 to 90 minutes, more preferably 5 to 60 minutes, and further preferably 10 to 45 minutes.

The polyvinyl acetal film of the present invention may be used as it is or may be used by laminating two or more sheets depending on the application, purpose of use and the like.
The use in particular of the polyvinyl acetal film of this invention is not restrict | limited, For example, it can use as a sealing material at the time of manufacturing a solar cell module, an intermediate film for laminated glass, etc.

When the polyvinyl acetal film of the present invention is used as a solar cell sealing material, the configuration and type (type) of the obtained solar cell module are not particularly limited, and may be a solar cell module manufactured using the sealing material. Any may be used.
Although not limited at all, the polyvinyl acetal film of the present invention is, for example, a solar cell such as a surface-side transparent protective member / surface sealing material / solar battery cell / back surface sealing material / back surface side protection member. Solar cell encapsulant having a configuration sandwiched between both sides by an encapsulant, front side transparent protective member / solar cell / encapsulant / back side protective member having a configuration such as a solar cell encapsulant, front side It can be used as a solar cell sealing material having a configuration such as transparent protective member / sealing material / solar cell / back surface side protective member.

  The solar battery module in the solar battery module manufactured using the polyvinyl acetal film of the present invention as a sealing material is not particularly limited. For example, silicon-based materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, gallium arsenide, CIGS Various types of solar cells such as III-V and II-VI group compound semiconductor systems such as cadmium and tellurium, organic systems such as dye sensitization, and organic thin films can be used.

  Moreover, as said surface side transparent protection member which comprises a solar cell module, plates or sheets, such as glass, an acrylic resin, a polycarbonate, polyester, a fluorine-containing resin, can be used, for example. Further, as the above-described back surface protection member constituting the solar cell module, for example, a single or multilayer sheet such as a metal or various thermoplastic resin films can be used, and specifically, for example, tin, aluminum, stainless steel, etc. A single-layer or multi-layer sheet such as a metal such as steel, an inorganic material such as glass, a polyester, an inorganic vapor-deposited polyester, a fluorine-containing resin, or a polyolefin can be used.

  The manufacturing method when manufacturing a solar cell module using the polyvinyl acetal film of the present invention as a sealing material is not particularly limited, and a manufacturing method similar to the conventional method can be adopted. Melting temperature of the polyvinyl acetal film in a state where the sealing material sheet made of the polyvinyl acetal film of the invention is sandwiched between the front surface side transparent protective member and the solar battery cell and / or between the solar battery cell and the back surface side protective member. Or it can manufacture by the method of crimping | bonding at the temperature beyond it.

When using a vacuum laminator apparatus at the time of manufacture of a solar cell module, any of the vacuum laminator apparatuses conventionally used at the time of manufacture of a solar cell module can be used. When manufacturing a solar cell module using a vacuum laminator device, a method of laminating and pressing at a temperature of 100 to 200 ° C., particularly 130 to 170 ° C. under a reduced pressure of 1 to 30000 Pa is preferably employed.
Moreover, when using a vacuum bag or a vacuum ring at the time of manufacture of a solar cell module, 130-170 degreeC under the pressure of about 20000 Pa using the vacuum bag or vacuum ring described in patent document 6, etc., for example. A solar cell module can be manufactured by laminating and pressure bonding.

  Moreover, when manufacturing a solar cell module using a nip roll, for example, after pre-bonding by performing the first pressure bonding at a temperature lower than the flow start temperature of the polyvinyl acetal forming the polyvinyl acetal film, it is higher than that. When the second pressure bonding is performed at a condition close to the flow start temperature and the second preliminary bonding is performed or the final bonding is performed, and then the final bonding is not performed (when the first and second bonding are temporary bonding) For example, a method of further autoclaving (final adhesion) may be employed. Specifically, for example, the sealing material composed of the polyvinyl acetal film of the present invention is heated to 30 to 100 ° C. with an infrared heater or the like, and laminated on the surface side transparent protective member, the solar battery cell, the back side protective member, etc. When the first pre-adhesion is performed by compressing and degassing with a roll, and then the final adhesion or the second pre-adhesion is performed by pressing with a roll heated to 50 to 150 ° C. When the final adhesion is not performed Further, for example, a method of producing a solar cell module by autoclaving at a temperature of 130 to 155 ° C. for about 2 hours under a pressure of about 1 to 1.5 MPa can be employed.

  The solar cell module manufactured by using the polyvinyl acetal film of the present invention as a sealing material is used as a member such as a window, a wall, a roof, a solarium, a soundproof wall, a show window, a balcony, or a handrail that is irradiated with sunlight. The light energy irradiated from the sun can be converted into electric power by using or attaching to those places, or by using it as a partition glass member such as a conference room, a home appliance or the like. Moreover, it can also utilize as a solar power plant by installing the solar cell module using the sealing material which consists of a polyvinyl acetal film of this invention in large quantities.

  In addition, the laminated glass produced using the polyvinyl acetal film of the present invention as an intermediate film is excellent in penetration resistance, impact resistance, and sound insulation, and also when glass breaks, it is difficult for glass to scatter. It can be effectively used as security glass for buildings. Moreover, the laminated glass which uses such a polyvinyl acetal film of the present invention as an intermediate film by making the polyvinyl acetal film of the present invention contain an ultraviolet absorber, an infrared absorber, or the like, or giving a predetermined coloring or decoration, In addition to the properties of penetration resistance, impact resistance, sound insulation, and anti-scattering properties of glass, it also functions as an ultraviolet or infrared absorbing glass or decorative glass.

EXAMPLES Hereinafter, although an Example etc. demonstrate this invention further in detail, this invention is not limited to the Example shown below.
In the following examples, the degree of polymerization of the polyvinyl alcohol polymer before acetalization with butyraldehyde, the content of vinyl alcohol units and the content of vinyl acetate units in polyvinyl butyral, as described above, are in accordance with JIS K 6726: 1994. Year (degree of polymerization), measured according to JIS K6728: 1977 (contents of vinyl alcohol units and vinyl acetate units).

Further, in the following examples, the birefringence (Δn _MDA , Δn _MDB , Δn _MDC ) in the length direction (MD) of the skin layer A, skin layer B and core layer C of the polyvinyl butyral film and the skin layer of the polyvinyl butyral film The birefringence (Δn _TDA , Δn _TDB , Δn _TDC ) in the width direction (TD) of A, skin layer B and core layer C was measured by the method described above.
The following measuring equipment was used.
* Polarizing microscope: “OPTIPHOTO POL” manufactured by Nikon Corporation
* Eyepiece micrometer: manufactured by Nippon Optical Co., Ltd. * Belek Compensator: manufactured by Olympus Corporation

Moreover, the melt tension of the polyvinyl butyral composition used for the production of the polyvinyl butyral film was measured by the following method.
[Melt tension of polyvinyl butyral composition for film production]
The polyvinyl butyral composition is heated to 200 ° C. and melted, and the polyvinyl butyral composition at 200 ° C. is discharged in a strand shape from a circular die having a diameter of 1 mm at a speed of 45 mm / second to a speed 5 times the discharge speed (225 mm The melt tension (melt tension) at the time of the take-up was measured using “Rheological 5000” manufactured by CEAST (hereinafter, the melt tension measured by this method is simply referred to as “melt tension”). is there).

  Using the polyvinyl butyral film obtained in the following example as a sealing material for solar cell modules or an intermediate film for laminated glass, a vacuum laminator (module laminator) (for research and development) manufactured by Nisshinbo Mechatronics Inc. is used. When the solar cell module or laminated glass is manufactured, the position of the polyvinyl butyral film can be finely adjusted when it is laid up on the glass plate. The spillability was evaluated according to the following evaluation criteria.

[Evaluation criteria for ease of fine adjustment of position during layup]
○: The polyvinyl butyral film does not adhere to the glass plate, the polyvinyl butyral film can be easily moved on the glass plate, and the arrangement position of the polyvinyl butyral film during layup can be easily finely adjusted.
X: The polyvinyl butyral film is easily adhered to the glass plate, and it is difficult to finely adjust the arrangement position of the polyvinyl butyral film at the time of layup.

[Evaluation criteria for shrinkage of polyvinyl butyral film when thermocompression bonded]
○: The polyvinyl butyral film does not shrink when heated and pressurized, and the space between the front surface side transparent protective member (glass plate), the solar battery cell, and the back surface side protective member (glass plate) is completely formed by the polyvinyl butyral composition. Without gaps or unsealed parts (in the case of a solar cell module), or an intermediate film formed from a polyvinyl butyral composition between two glass plates does not cause gaps or non-adhesive parts Fully filled.
X: Shrinkage of the polyvinyl butyral film occurs when heated and pressurized, and the space between the surface side transparent protective member (glass plate), the solar battery cell, and the back side protective member (glass plate) is formed by the polyvinyl butyral composition. It is not completely sealed, and there is a gap or unsealed part in the contact part between the polyvinyl butyral film and any of the front surface side transparent protective member (glass plate), solar cell and back surface side protective member (glass plate). (In the case of a solar cell module), or there is a space or no space between the intermediate film formed from the polyvinyl butyral composition and one or both of the two glass plates on both sides. .

[Evaluation criteria for outflow from end of polyvinyl butyral film when thermocompression bonded]
○: A polyvinyl butyral film is laid up (arranged) between the front surface side transparent protective member (glass plate) and the solar cell and between the solar cell and back surface side protective member (glass plate), and heated and pressed. When a solar cell module is produced, or when a laminated glass is produced by laying up (arranging) a polyvinyl butyral film between two glass plates, there is no outflow of the polyvinyl butyral composition from the edge of the glass plate. .
X: A polyvinyl butyral film is laid up (arranged) between the front surface side transparent protective member (glass plate) and the solar cell and between the solar cell and the back surface side protective member (glass plate), and heated and pressed. When a solar cell module is produced, or when a laminated glass is produced by laying up (arranging) a polyvinyl butyral film between two glass plates, the polyvinyl butyral composition flows out from the edge of the glass plate. ing.

<< Example 1 >> [Production of polyvinyl butyral film (a)]
(1) Polyvinyl butyral obtained by acetalizing polyvinyl alcohol having a polymerization degree of 1700 with butyraldehyde (vinyl alcohol unit content = 19% by mass, vinyl acetate unit content = 1% by mass) and 75 parts by mass and triethylene glycol-di A polyvinyl butyral composition was prepared by mixing 25 parts by mass of (2-ethylhexanoate) at 25 ° C.
It was 0.6 cN when the melt tension of this polyvinyl butyral composition was measured by the above-mentioned method.
(2) Using the polyvinyl butyral composition obtained in (1) above, using a twin screw extruder (screw diameter 40 mm), a die [T die, lip width = 400 mm, average lip gap = 0 .91 mm (120% of the thickness of the finally obtained film)], extruded at a temperature of 220 ° C. and a discharge rate of 240 kg / hr of the polyvinyl butyral composition at the time of extrusion, and then 30 ° C. The film was quickly cooled in a water bath, then removed from the water bath, heat-treated at 40 ° C. for 30 minutes in a non-tensioned state to relieve stress, and a 0.76 mm thick polyvinyl butyral film [hereinafter referred to as “polyvinyl butyral film ( a) ") was produced.
(3) Birefringence (Δn _MDA , Δn _MDB , Δn _MDC ) in the length direction (MD) of the skin layer A, skin layer B, and core layer C of the polyvinyl butyral film (a) obtained in (2) above In addition, the birefringence (Δn _TDA , Δn _TDB , Δn _TDC ) in the width direction (TD) of the skin layer A, skin layer B, and core layer C was measured by the method described above, and as shown in Table 1 below. It was.

<< Example 2 >> [Production of polyvinyl butyral film (b)]
(1) Using the same polyvinyl butyral composition used in Example 1, using a twin screw extruder (screw diameter 40 mm), a die [T die, lip width = 400 mm, average lip gap = 0.84 mm (110% of the thickness of the finally obtained film)] was extruded into a film under the conditions of a polyvinyl butyral composition at the time of extrusion at a temperature of 220 ° C. and a discharge rate of 240 kg / hr. Quenched in a water bath at 0 ° C., then removed from the water bath and heat-treated at 30 ° C. for 30 minutes in a non-tensioned state to relieve the stress. A 0.76 mm thick polyvinyl butyral film [hereinafter this film is referred to as “polyvinyl butyral ( b) "was produced.
(2) Birefringence (Δn _MDA , Δn _MDB , Δn _MDC ) in the length direction (MD) of the skin layer A, skin layer B, and core layer C of the polyvinyl butyral film (b) obtained in (1) above In addition, the birefringence (Δn _TDA , Δn _TDB , Δn _TDC ) in the width direction (TD) of the skin layer A, skin layer B, and core layer C was measured by the method described above, and as shown in Table 1 below. It was.

<< Example 3 >> [Production of polyvinyl butyral film (c)]
(1) When obtaining polyvinyl butyral obtained by acetalizing polyvinyl alcohol having a polymerization degree of 1700 with butyraldehyde (vinyl alcohol unit content = 19 mass%, vinyl acetate unit content = 1 mass%), 1 mass% Glutaraldehyde (crosslinking agent) was added to produce partially crosslinked polyvinyl butyral.
75 parts by mass of the partially crosslinked polyvinyl butyral thus obtained and 25 parts by mass of triethylene glycol di (2-ethylhexanoate) were mixed at 25 ° C. to prepare a polyvinyl butyral composition.
The melt tension of this polyvinyl butyral composition was measured by the method described above and found to be 1.5 cN.
(2) Using the polyvinyl butyral composition obtained in (1) above, using a twin screw extruder (screw diameter 40 mm), a die [T die, lip width = 400 mm, average lip gap = 0 .91 mm (120% of the thickness of the finally obtained film)], extruded at a temperature of 220 ° C. and a discharge rate of 240 kg / hr of the polyvinyl butyral composition at the time of extrusion, and then 30 ° C. The film was rapidly cooled in a water bath, then removed from the water bath, and heat-treated at 40 ° C. for 30 minutes in a non-tensioned state to relieve the stress. Thus, a 0.76 mm thick partially crosslinked polyvinyl butyral film [hereinafter referred to as “polyvinyl butyral” Film (c) "] was produced.
(3) Birefringence (Δn _MDA , Δn _MDB , Δn _MDC ) in the length direction (MD) of the skin layer A, skin layer B, and core layer C of the polyvinyl butyral film (c) obtained in (2) above In addition, the birefringence (Δn _TDA , Δn _TDB , Δn _TDC ) in the width direction (TD) of the skin layer A, skin layer B, and core layer C was measured by the method described above, and as shown in Table 1 below. It was.

<< Comparative Example 1 >> [Production of polyvinyl butyral film (d)]
(1) Using the same polyvinyl butyral composition used in Example 1, using a twin screw extruder (screw diameter 40 mm), a die [T die, lip width = 400 mm, average lip gap = The film was extruded from 0.745 mm (98% of the thickness of the finally obtained film) into a film under the conditions of a temperature of 220 ° C. and a discharge rate of 240 kg / hr of the polyvinyl butyral composition at the time of extrusion. Quenched in a water bath at 0 ° C., then removed from the water bath to produce a 0.76 mm thick polyvinyl butyral film (hereinafter referred to as “polyvinyl butyral film (d)”) without heat treatment for stress relaxation. did.
(2) Birefringence (Δn _MDA , Δn _MDB , Δn _MDC ) in the length direction (MD) of the skin layer A, skin layer B, and core layer C of the polyvinyl butyral film (d) obtained in (1) above In addition, the birefringence (Δn _TDA , Δn _TDB , Δn _TDC ) in the width direction (TD) of the skin layer A, skin layer B, and core layer C was measured by the method described above, and as shown in Table 1 below. It was.

<< Comparative Example 2 >> [Production of polyvinyl butyral film (e)]
(1) Using the same polyvinyl butyral composition used in Example 1, using a twin screw extruder (screw diameter 40 mm), a die [T die, lip width = 400 mm, average lip gap = 1.06 mm (139% of the thickness of the finally obtained film)] was extruded into a film under the conditions of a temperature of 220 ° C. and a discharge rate of 240 kg / hr of the polyvinyl butyral composition at the time of extrusion. The film was naturally cooled in air at 0 ° C. and then heat-treated at 70 ° C. for 30 minutes in a non-tensioned state to relieve the stress. Was manufactured.
(2) Birefringence (Δn _MDA , Δn _MDB , Δn _MDC ) in the length direction (MD) of the skin layer A, skin layer B, and core layer C of the polyvinyl butyral film (e) obtained in (1) above In addition, the birefringence (Δn _TDA , Δn _TDB , Δn _TDC ) in the width direction (TD) of the skin layer A, skin layer B, and core layer C was measured by the method described above, and as shown in Table 1 below. It was.

Example 4 [Production of solar cell module]
(1) Two glass plates of length × width × thickness = 350 mm × 350 mm × 3.2 mm were prepared as a front surface side transparent protective member and a back surface side protective member.
Also, solar cells ("RSC150SF-1 / 1" manufactured by Kyocera Corporation) (size: vertical x horizontal = 150 mm x 155 mm) are arranged in a rectangular shape with 2 vertical x 2 horizontal and connected in series. One set was prepared.
(2) The polyvinyl butyral film (a) produced in Example 1 was cut into a size of length × width = 350 mm × 350 mm to prepare two film pieces for a sealing material.
(3) On the surface side transparent protective member (glass plate) prepared in the above (1), one piece of the polyvinyl butyral film piece prepared in the above (2) is laid up (laminated and superposed). The ease of fine adjustment of the layup position was evaluated according to the evaluation criteria described above, and as shown in Table 2 below.
(4) On the surface-side transparent protective member (glass plate) obtained in (3) above, the photovoltaic cell set prepared in (1) above is placed on the layup of the polyvinyl butyral film piece. The remaining film piece prepared in (2) above is further stacked on top, and a back surface side protection member (glass plate) is stacked thereon, and the surface side transparent protection member (glass plate) / film piece / solar cell. A laminate composed of a cell set / film piece / back side protection member (glass plate) was produced.
(5) The laminate produced in (4) above is housed in a vacuum laminator (module laminator) “LAMINATOR 1522N” manufactured by Nisshinbo Mechatronics Inc., heated at 160 ° C. for 15 minutes under a reduced pressure of 100 Pa, and then 50 kPa. The solar cell module was manufactured by holding at 160 ° C. for 15 minutes.
When the solar cell module obtained by this was observed visually and the shrinkage | contraction property of the polyvinyl butyral film and the outflow property from an edge part were evaluated according to the above-mentioned evaluation criteria, it was as shown in Table 2 below.

<< Example 5 >> [Production of laminated glass]
(1) Two glass plates of length × width × thickness = 350 mm × 350 mm × 3.2 mm were prepared.
(2) The polyvinyl butyral film (b) produced in Example 2 was cut into a size of length × width = 350 mm × 350 mm to produce one film piece for an intermediate film.
(3) On the one glass plate prepared in (1) above, the film piece prepared in (2) above is laid up, and the evaluation criteria described above for ease of fine adjustment of the layup position at that time Was evaluated as shown in Table 2 below.
(4) The other glass plate prepared in (1) above is overlaid on the glass plate obtained in (3) above, and the glass plate / film piece / glass. A laminate consisting of plates was produced.
(5) The laminate produced in (4) above is housed in the same vacuum laminator used in Example 4, heated at 160 ° C. for 15 minutes under a reduced pressure of 100 Pa, and then at 15 at 50 kPa and 160 ° C. Laminated glass was produced by holding for a minute. The obtained laminated glass was visually observed, and the shrinkability and the outflow from the end of the polyvinyl butyral film were evaluated according to the above-described evaluation criteria. The results were as shown in Table 2 below.

Example 6 [Production of solar cell module]
(1) As the film piece for the sealing material, except that two pieces of film obtained by cutting the polyvinyl butyral film (c) obtained in Example 3 into a size of length × width = 350 mm × 350 mm were used. The same operation as in Example 4 was performed to manufacture a solar cell module.
In that case, evaluation mentioned above about the ease of fine adjustment of the lay-up position at the time of laying up the film piece produced from the polyvinyl butyral film (c) on the surface side transparent protection member (glass plate) When evaluated according to the standard, it was as shown in Table 2 below.
(2) Moreover, when the solar cell module obtained by said (1) was observed visually and the shrinkage | contraction property of the polyvinyl butyral film and the outflow property from an edge part were evaluated according to the above-mentioned evaluation criteria, following Table 2 It was as shown in.

Example 7 [Production of Solar Cell Module]
(1) Two polyvinyl butyral films (a) obtained in Example 1 were superposed and pressed under conditions of a temperature of 25 ° C. and a pressure of 5 MPa to produce a laminated polyvinyl butyral film having a thickness of 1.52 mm. .
(2) Examples except that two film pieces obtained by cutting the laminated polyvinyl butyral film obtained in (1) above into a size of length x width = 350 mm x 350 mm were used as the film pieces for the sealing material. The same operation as 4 was performed to manufacture a solar cell module.
At that time, on the surface-side transparent protective member (glass plate), the evaluation criteria described above for the ease of fine adjustment of the lay-up position when one film piece produced from the laminated polyvinyl butyral film was laid up Therefore, when evaluated, it was as shown in Table 2 below.
(3) Moreover, when the solar cell module obtained by said (2) was observed visually and the shrinkage | contraction property of the polyvinyl butyral film and the outflow property from an edge part were evaluated according to the above-mentioned evaluation criteria, following Table 2 It was as shown in.

<< Comparative Example 3 >> [Production of solar cell module]
(1) As the film piece for the sealing material, except that two film pieces obtained by cutting the polyvinyl butyral film (d) obtained in Comparative Example 1 into a size of length × width = 350 mm × 350 mm were used. The same operation as in Example 4 was performed to manufacture a solar cell module.
In that case, evaluation mentioned above about the ease of the fine adjustment of the layup position at the time of laying up the film piece produced from the polyvinyl butyral film (d) on the surface side transparent protection member (glass plate) When evaluated according to the standard, it was as shown in Table 2 below.
(2) Moreover, when the solar cell module obtained by said (1) was observed visually and the shrinkage | contraction property of the polyvinyl butyral film and the outflow property from an edge part were evaluated according to the above-mentioned evaluation criteria, following Table 2 It was as shown in.

<< Comparative Example 4 >> [Production of solar cell module]
(1) As the film piece for the sealing material, except that two pieces of film obtained by cutting the polyvinyl butyral film (e) obtained in Comparative Example 2 into a size of length × width = 350 mm × 350 mm were used. The same operation as in Example 4 was performed to manufacture a solar cell module.
At that time, the evaluation described above for the ease of fine adjustment of the layup position when one film piece prepared from the polyvinyl butyral film (e) is laid up on the surface side transparent protective member (glass plate). When evaluated according to the standard, it was as shown in Table 2 below.
(2) Moreover, when the solar cell module obtained by said (1) was observed visually and the shrinkage | contraction property of the polyvinyl butyral film and the outflow property from an edge part were evaluated according to the above-mentioned evaluation criteria, following Table 2 It was as shown in.

  As can be seen from the results in Tables 1 and 2, the polyvinyl butyral films of Examples 1 to 3 that satisfy the above-described formulas (I) to (III) defined in the present invention are used for manufacturing solar cell modules. When used as an encapsulant, and when used as an intermediate film in the production of laminated glass, there is no adhesion to members such as glass plates, and fine position adjustment can be performed well during layup It is possible to produce high-quality solar cell modules and laminated glass with good workability and good productivity, with no shrinkage, and no resin outflow from the end of a member such as a glass plate. Can do.

  The polyvinyl acetal film of the present invention can be finely adjusted in position very easily at the time of lay-up, and is less likely to shrink during lamination, and further, the resin does not easily flow out from the end of a member such as a glass plate. When used in the manufacture of various products such as battery modules and laminated glass, it is extremely useful because it can shorten the time during layup, improve workability, and improve product yield.

Claims (8)

A polyvinyl acetal film formed by using a polyvinyl acetal having a vinyl alcohol unit content of 8 to 30% by mass, wherein the core layer C is present between two outer skin layers A and B. Having the structure and having the following formulas (I), (II) and (IV):
Δn _MDA ≧ Δn _MDB (I)
Δn _MDB −Δn _MDC ≧ 0.1 × 10 ⁻³ (II)
Δn _MDA <3.5 × 10 ^-3 (IV)
(In the above formula, Δn _MDA is the birefringence index of skin layer A in the machine flow direction, Δn _MDB is the birefringence index of skin layer B in the machine flow direction, and Δn _MDC is the birefringence index of core layer C in the machine flow direction. Show.)
It consists of a polyvinyl acetal film satisfying the above. A polyvinyl acetal film formed by using a polyvinyl acetal having a vinyl alcohol unit content of 8 to 30% by mass, wherein the core layer C is present between two outer skin layers A and B. Having the structure and having the following formulas (I), (II) and (IV):
Δn _MDA ≧ Δn _MDB (I)
Δn _MDB −Δn _MDC ≧ 0.1 × 10 ⁻³ (II)
Δn _MDA <3.5 × 10 ^-3 (IV)
(In the above formula, Δn _MDA is the birefringence index of skin layer A in the machine flow direction, Δn _MDB is the birefringence index of skin layer B in the machine flow direction, and Δn _MDC is the birefringence index of core layer C in the machine flow direction. Show.)
An interlayer film for laminated glass, comprising a polyvinyl acetal film satisfying the requirements. The polyvinyl acetal film which forms the sealing material for solar cells is either or both of the following formulas (V) and (VI):
Δn _MDA / Δn _TDA = 0.5 to 3.0 (V)
Δn _MDB / Δn _TDB = 0.5 to 3.0 (VI)
(In the above formula, Δn _MDA is the birefringence index of skin layer A in the machine flow direction, Δn _MDB is the birefringence index of skin layer B in the machine flow direction, and Δn _TDA is perpendicular to the machine flow direction of skin layer A. (The birefringence index, Δn _TDB indicates the birefringence index in the direction perpendicular to the machine flow direction of the skin layer B.)
The solar cell encapsulant according to claim 1 , further satisfying The polyvinyl acetal film forming the interlayer film for laminated glass is one or both of the following formulas (V) and (VI):
Δn _MDA / Δn _TDA = 0.5 to 3.0 (V)
Δn _MDB / Δn _TDB = 0.5 to 3.0 (VI)
(In the above formula, Δn _MDA is the birefringence index of skin layer A in the machine flow direction, Δn _MDB is the birefringence index of skin layer B in the machine flow direction, and Δn _TDA is perpendicular to the machine flow direction of skin layer A. (The birefringence index, Δn _TDB indicates the birefringence index in the direction perpendicular to the machine flow direction of the skin layer B.)
The interlayer film for laminated glass according to claim 2 , further satisfying: When the polyvinyl acetal film that forms the sealing material for solar cells is discharged in a strand form at a speed of 45 mm / second from a circular die having a diameter of 1 mm under heating and melting at 200 ° C., and taken up at a speed five times the discharge speed. polyvinyl acetal or is formed from a polyvinyl acetal composition, sealing material for a solar cell according to claim 1 or 3 having a melt tension of 0.5～2.5CN. When the polyvinyl acetal film forming the interlayer film for laminated glass is discharged in a strand form at a speed of 45 mm / second from a circular die having a diameter of 1 mm under heating and melting at 200 ° C., the film is taken out at a speed 5 times the discharge speed. The interlayer film for laminated glass according to claim 2 or 4 , which is formed from a polyvinyl acetal or a polyvinyl acetal composition having a melt tension of 0.5 to 2.5 cN. A solar cell module provided with the sealing material for solar cells of any one of Claims 1, 3, and 5 . Laminated glass comprising the interlayer film for laminated glass according to any one of claims 2, 4, and 6 .

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