JP2000084996A - Manufacture of sealing thermoplastic resin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a suitable product particularly as a sealing film of a solar cell by annealing a resin film before lowering a temperature of the film to a softening point or lower of a thermoplastic resin, thereby reducing its contraction at the time of heating. SOLUTION: When a resin film is at a higher temperature than its softening point before a cooling step, the film is annealed by heating or the like as needed. The annealing is preferably conducted by maintaining the film in a temperature range higher by about 20 to 25 deg.C than the softening point for 1.0 to 2.0 min. In this case, the film 10 is conveyed via conveyors 12 for conveying the film with a plurality of rollers 11, and annealed by heating the film 10 during conveying by a heater 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermoplastic resin film for encapsulation, and particularly to EVA (ethylene-ethylene) which has a small shrinkage upon heating and is suitable for a solar cell encapsulation film.
The present invention relates to a method for producing a sealing thermoplastic resin film such as a vinyl acetate copolymer film.

[0002]

2. Description of the Related Art In recent years, solar cells which directly convert sunlight into electric energy have been attracting attention from the viewpoints of effective use of resources and prevention of environmental pollution, and their development has been promoted.

As shown in FIG. 2, a solar cell generally has an EVA film 3 between a glass substrate 1 and a back cover 2.
The silicon power generation element 4 is sealed by the sealing films A and 3B.

In such a solar cell, a glass substrate 1, an EVA film 3A for a sealing film, a silicon power generating element 4, an EVA film 3B for a sealing film, and a back cover 2 are laminated in this order, and the EVA is heated and melted. It is manufactured by bonding and integrating by crosslinking and curing.

In the production of such a solar cell, if the EVA films 3A and 3B for a sealing film are greatly shrunk at the time of heat crosslinking, the silicon power generation element 4 is damaged by the shrinkage.
The sealing EVA films 3A and 3B are required to have a small shrinkage at the time of heat crosslinking.

[0006] The EVA film as a sealing film of this solar cell is formed by a T-die method in which a molten resin is extruded from a die having a linear slit and rapidly cooled and solidified by a cooling roll or a water tank.

[0007]

However, the EVA film manufactured by the conventional T-die method cannot be said to have a sufficiently small shrinkage at the time of heat crosslinking, has a problem of damage to the silicon power generation element, and has a high quality. It was difficult to manufacture solar cells with good yield.

The present invention solves the above-mentioned conventional problems, and provides a method for producing a sealing thermoplastic resin film such as an EVA film for sealing, which has a small shrinkage upon heating and is particularly suitable as a sealing film for a solar cell. The purpose is to provide.

[0009]

The method for producing a thermoplastic resin film for sealing according to the present invention comprises a method for producing a thermoplastic resin film for sealing by molding a molten resin into a film and then cooling it. Before the temperature of the resin film falls below the softening point of the thermoplastic resin, the resin film is annealed.

According to the present invention, annealing is performed before the temperature of the thermoplastic resin film falls below the softening point of the thermoplastic resin. The amount of shrinkage during curing can be reduced.

The method of the present invention is particularly effective when the thermoplastic resin raw material is an EVA resin composition containing a crosslinking agent.

The annealing treatment in the present invention can be carried out by heating a resin film conveyed by a conveyor having a plurality of rollers by a heating means. By setting the peripheral speed of the roller on the side to be higher than the peripheral speed of the roller on the exit side so that a large tension is not applied to the resin film at the time of annealing, a favorable annealing effect can be obtained.

The sealing thermoplastic resin film formed in the present invention is particularly suitable as a sealing film for a solar cell.

[0014]

Embodiments of the present invention will be described below in detail.

In the present invention, for example, a molten resin is formed into a film by a conventional method such as a T-die method, and then cooled by a cooling roll or a cooling bath to produce a sealing thermoplastic resin film. Prior to the cooling step, when the resin film is at a temperature higher than its softening point, the resin film is annealed by heating as necessary.

This annealing treatment is preferably performed in a temperature range where the temperature of the resin film is higher by about 20 to 25 ° C. than the softening point.
It is preferable to maintain the resin film in a temperature range higher by about 20 to 25 ° C. than the softening point for 1.0 to 2.0 minutes.

An annealing method suitable for the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing an annealing treatment method suitable for the present invention. A resin film 10 is transported by a transport conveyor 12 which transports a film by a plurality of rollers 11, and the resin film 10 being transported is heated by a heater. An annealing process is performed by heating at 13.

In such an annealing process, it is preferable that a large tension is not applied to the resin film 10 during the annealing process, and the resin film 10 is heated in a loose state. In order to make the resin film 10 slackened, it is advantageous that the peripheral speed of the rollers 11 of the conveyor 12 is increased at the entrance and decreased at the exit.

For example, in the conveyor 12 shown in FIG. 1, the peripheral speed of the roller 11A on the entrance side is
The peripheral speed of the roller between the rollers 11A and 11B is an intermediate peripheral speed, and the peripheral speed of the roller gradually increases from the entrance side to the exit side. It is preferable to make it smaller.

When an EVA film is manufactured according to the present invention, the formed EVA film is heated at 70 to 75 ° C.
Over a period of 1.0 to 2.0 minutes.
The annealing treatment is preferably performed by maintaining the VA film at 60 to 80 ° C.

Next, an EVA resin composition suitable as a film forming raw material for producing an EVA film according to the present invention will be described.

The EVA resin according to the present invention preferably has a vinyl acetate content of 25% by weight or less. When the vinyl acetate content is less than 25% by weight, the water vapor transmission rate is too large, and it is difficult to obtain sufficient moisture proofness as a sealing film for a solar cell. However, an EVA resin having an excessively low vinyl acetate content has poor processability and an excessively high viscosity, so that the ability to follow a silicon power generation element during the production of a solar cell is poor. Therefore, the vinyl acetate content of the EVA resin is low. It is preferably at least 10% by weight.

The EVA resin used in the present invention is:
Melt flow rate is 0.7-20, especially 1.5-10
It is preferred that

The EVA resin composition used in the present invention has a cross-linking structure by adding a cross-linking agent for improving durability. The cross-linking agent generally generates radicals at 100 ° C. or higher. Organic peroxides are used, and those having a decomposition temperature of 70 ° C. or more with a half-life of 10 hours are particularly preferable in consideration of stability at the time of compounding. Such organic peroxides include, for example, 2,5-dimethylhexane;
2,5-dihydroperoxide; 2,5-dimethyl-2,5-di (t-butylperoxy) hexane; 3-
Di-t-butyl peroxide; t-dicumyl peroxide; 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne; dicumyl peroxide;
α'-bis (t-butylperoxyisopropyl) benzene; n-butyl-4,4-bis (t-butylperoxy) butane; 2,2-bis (t-butylperoxy) butane; 1,1- Bis (t-butylperoxy) cyclohexane; 1,1-bis (t-butylperoxy) 3,
3,5-trimethylcyclohexane; t-butylperoxybenzoate; benzoyl peroxide and the like can be used. The compounding amount of these organic peroxides is generally 5 parts by weight or less, preferably 1 to 3 parts by weight, based on 100 parts by weight of the EVA resin.

As a sealing film for a solar cell, a silane coupling agent can be added to the EVA resin for the purpose of improving the adhesion to the power generating element. Known silane coupling agents for this purpose, for example, γ-chloropropyltrimethoxysilane; vinyltrichlorosilane; vinyltriethoxysilane; vinyl-tris-
(Β-methoxyethoxy) silane; γ-methacryloxypropyltrimethoxysilane; β- (3,4-ethoxycyclohexyl) ethyltrimethoxysilane; γ-glycidoxypropyltrimethoxysilane; vinyltriacetoxysilane; γ-mercapto Propyltrimethoxysilane; γ-aminopropyltrimethoxysilane; N-β
-(Aminoethyl) -γ-aminopropyltrimethoxysilane and the like. The amount of the silane coupling agent is generally 5 parts by weight or less, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the EVA resin.

Further, the gel fraction of the EVA resin is improved,
A crosslinking aid can be added to the EVA resin to improve durability. Examples of the crosslinking auxiliary used for this purpose include known triaryl isocyanurate; trifunctional crosslinking auxiliary such as triallyl isocyanate;
Monofunctional crosslinking assistants such as K ester can also be mentioned. The amount of these crosslinking aids is generally equal to the amount of EVA resin 1
10 parts by weight or less, preferably 1 to 5 parts by weight with respect to 00 parts by weight
Parts by weight.

Further, for the purpose of improving the stability of the EVA resin, hydroquinone; hydroquinone monomethyl ether; p-benzoquinone; methylhydroquinone, and the like can be added. 5 parts by weight or less.

Further, if necessary, a coloring agent, an ultraviolet absorber, an antioxidant, a discoloration inhibitor and the like can be added in addition to the above. Examples of the coloring agent include inorganic pigments such as metal oxides and metal powders, and organic pigments such as azo-based, phthalocyanine-based, azo-based, acidic or basic dye-based lakes. UV absorbers include 2-hydroxy-4-octoxybenzophenone; benzophenones such as 2-hydroxy-4-methoxy-5-sulfobenzophenone; 2- (2'-hydroxy-5-methylphenyl) benzotriazole; Benzotriazoles; phenyl salicylate; pt-
There are hindered amines such as butylphenyl salicylate. As anti-aging agents, amines; phenols;
Bisphenyl type; hindered amine type, for example, di-t-butyl-p-cresol; bis (2,2,6,6
-Tetramethyl-4-piperazyl) sebacate.

To manufacture a solar cell using the EVA film formed according to the present invention, as shown in FIG. 2, a glass substrate 1, an EVA film 3A, a silicon power generation element 4,
The EVA film 3B and the back cover 2 are laminated, and 10
The heating and pressing may be performed at 0 to 150 ° C. and 1 atm for about 3 to 10 minutes.
B can be crosslinked to form a sealing film having excellent weather resistance. In this sealing, since the EVA film formed in the present invention has a small shrinkage at the time of heat crosslinking, damage of the power generation element can be prevented and a high quality product can be manufactured with high yield.

In the production of the solar cell, in order to surely prevent the damage of the power generating element, the EVA film when heated at about 140 to 160 ° C., which is the temperature of the heat crosslinking at the time of the production of the normal solar cell, is used. Although the shrinkage (shrinkage in the flow direction) is preferably 1.5% or less, according to the present invention, an EVA film having this shrinkage of 1.0% or less and having extremely small shrinkage during heat crosslinking is used. A film can be formed.

[0032]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 An EVA film was formed using an EVA resin composition having the following composition.

[EVA resin composition (parts by weight)] EVA resin (vinyl acetate content: 25% by weight, melt flow rate: 2.0): 100 Crosslinking agent: 1.5 Silane coupling agent: 0.2 Crosslinking aid Agent: 2.0 EVA film formed by ordinary T-die method at 75 ° C
During the above, annealing was performed according to the method shown in FIG.

As the conveyor 12, a roller having 12 rollers 11 arranged side by side is used.
When the peripheral speed of the roller 11A is 100, the peripheral speed of the roller 11A on the inlet side is 110,
The peripheral speeds of the rollers are 106 to 107, and the peripheral speeds of the three to four rollers following these rollers are 102 to 103. The peripheral speed of the rollers 11 gradually decreases from the inlet side to the outlet side. The peripheral speed was set to be as follows. Then, the EVA film 10 being transported by the transport conveyor 12 is heated by the heater 1.
The temperature was maintained at 70 ° C. or higher by heating at 3. This annealing was performed for 1.0 minute.

The EVA film after the annealing was cooled by a cooling roll and wound up by a winder.

The obtained EVA film was examined for shrinkage (shrinkage in the flow direction) when it was heated to 155 ° C., which is the heat crosslinking temperature at the time of manufacturing a normal solar cell.
%Met.

Comparative Example 1 An EVA film was formed in the same manner as in Example 1 except that the annealing treatment was not performed, and the shrinkage ratio was examined in the same manner. Rate.

From the results of the above Examples and Comparative Examples, since the EVA film formed by the present invention has a small shrinkage upon heat crosslinking, a high quality solar cell can be obtained by using this EVA film as a sealing film. It can be seen that it can be manufactured with good yield.

[0040]

As described in detail above, according to the method for producing a thermoplastic resin film for sealing of the present invention, the shrinkage during heat curing is small, and particularly, the sealing resin suitable for a solar cell sealing film. A plastic resin film can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of an annealing process according to the present invention.

FIG. 2 is a cross-sectional view illustrating a general solar cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Back cover 3A, 3B EVA film 4 Silicon power generation element 10 Resin film 11 Roller 12 Conveyor 13 Heater

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F201 AA10 AB03 AG10 AH33 AK07 AR06 BN01 BN07 BN11 BR06 BR33 4F207 AA10 AB03 AG01 AH33 AK07 AR06 KA01 KA17 KK51 KK52 KM16 KW33 KW50 5F061 AA01 BA03 CA22 CB02 DE03

Claims (5)

[Claims] 1. A method for producing a sealing thermoplastic resin film by molding a molten resin into a film and then cooling the same, wherein before the temperature of the resin film falls below the softening point of the thermoplastic resin. And a method for producing a thermoplastic resin film for sealing, comprising annealing the resin film. 2. The method according to claim 1, wherein the thermoplastic resin raw material is an EVA resin composition containing a crosslinking agent. 3. The sealing thermoplastic according to claim 1, wherein the annealing is performed by heating a resin film conveyed by a conveyor having a plurality of rollers by a heating means. A method for manufacturing a resin film. 4. The method for producing a thermoplastic resin film for sealing according to claim 3, wherein the peripheral speed of the rollers on the inlet side of the conveyor is higher than the peripheral speed of the rollers on the outlet side. 5. The thermoplastic resin film for sealing according to claim 1, wherein the thermoplastic resin film for sealing is a thermoplastic resin for a sealing film of a solar cell. Manufacturing method.