JP2012071502A - Method of manufacturing ethylene-vinyl acetate copolymer (eva) sheet for solar cell sealing materials - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an annealing treatment method which can reduce heat shrinkage while nearly keeping a sheet width and a thickness.SOLUTION: A method of manufacturing an ethylene-vinyl acetate copolymer sheet for solar cell sealing materials comprises extruding the molten ethylene-vinyl acetate copolymer (EVA) from a T die 12, cooling it in a polishing roll 13c to mold a sheet 3, passing through a double belt press device 17 having a heating region at least in a part inside a region from an inlet port to an outlet, and winding after cooling the sheet immediately after moving from the region of the downstream side in the heating region of the double belt press device or the double belt press device.

Description

  The present invention relates to a method for producing an ethylene-vinyl acetate copolymer (EVA) sheet, and more particularly, to a method for producing an EVA sheet having a small shrinkage during heating and suitable as a sealing material for solar cells.

2. Description of the Related Art Conventionally, solar cells that directly convert sunlight into electric energy have attracted attention and are being developed from the standpoints of effective use of resources and prevention of environmental pollution. In general, as shown in FIGS. 3A and 3B, the solar cell includes a glass surface side sealing material sheet 3 a and a back sheet surface side sealing material sheet 3 b between the glass substrate 1 and the back sheet 2. The solar cell 4 is sealed. (Hereinafter, the glass surface side sealing material sheet 3a and the back sheet surface side sealing material sheet 3b may be collectively referred to as sealing material sheets 3a and 3b).
For example, in the case of a crystalline silicon type solar cell that is the mainstream as a solar cell module, as shown in FIG. 3A, a glass substrate 1 and an ethylene-vinyl acetate copolymer (hereinafter, ethylene-vinyl acetate copolymer is expressed as EVA). The glass sheet side encapsulant sheet 3a, the solar battery cell (silicon power generation element) 4, the EVA back sheet surface side encapsulant sheet 3b, and the back sheet 2 are laminated in this order, and a vacuum laminator is used. A solar cell module bonded without bubbles as shown in FIG. 3-2 is produced by heating and melting the EVA sealant sheets 3a and 3b made of EVA by crosslinking and curing by crosslinking. The

  In the manufacture of such a solar cell module, if the shrinkage at the time of heating the sealing material sheets 3a, 3b made of EVA is large, the silicon power generation element 4 may be damaged due to the shrinkage deformation. Therefore, the encapsulant sheets 3a and 3b made of EVA are required to have small shrinkage during heating. Furthermore, in recent years, the thickness of silicon power generation elements has been reduced to around 100 μm due to the effective use of crystalline silicon resources and the demand for cost reductions for the spread of solar cell modules. There is an increasing demand for reducing heat shrinkage (hereinafter, sometimes referred to as heat gain).

  The EVA sheet used as a sealing material sheet of this solar cell is formed by a T-die method in which molten EVA is extruded from a T-die having a linear slit and rapidly cooled and solidified by a cooling roll. The outline will be described with reference to FIG. FIG. 1 is a diagram showing components of a sheet forming apparatus that continuously forms an EVA sheet 3 to form a winding roll. Note that FIG. 1 shows only main parts, and a frame, an intermediate roll, and the like for fixing the twin-screw extruder 11 and the T-die 12 are omitted. In FIG. 1, EVA is melt-kneaded with a crosslinking agent and other additives in a twin-screw extruder 11, extruded into a sheet shape with a T-die 12, cooled and solidified with polishing rolls 13 a to 13 c, and formed into a solid sheet. At that time, a concavo-convex pattern is formed by engraving on the surface of the polishing roll 13b, and the concavo-convex shape is transferred to the sheet during cooling and solidification. This uneven shape has a function of providing cushioning properties so as not to break the silicon power generation element in the process of being heated and compressed by being laminated toward the surface in contact with the silicon power generation element when the solar cell module is manufactured. The EVA sheet 3 that has exited the polishing rolls 13 a to 13 c passes through the annealing treatment device 14. With this annealing processing apparatus 14, the thermal distortion of the EVA sheet 3 is reduced. As shown in FIG. 2, the annealing apparatus 14 heats the sheet by arranging a number of far infrared heaters 15 to heat the EVA sheet 3 in a non-contact manner, or by conveying the sheet onto a heated roll. A roll method is known (for example, Patent Documents 1 and 2). After passing through such an annealing apparatus 14, the in-line inspection device 31 inspects the presence or absence of foreign matter and the like, and then the sheet is wound up by the winder 32.

  However, in the case of the heat treatment by the non-contact heater as shown in FIG. 2, when the sheet 3 is conveyed between the conveying rolls 16, the sheet 3 tends to shrink in the width direction and the traveling direction due to the heat shrinkage stress generated in the sheet. The force works and the sheet shrinks. Therefore, the sheet width changes at the entrance and exit of the heat treatment furnace. Also, the sheet may be torn between the conveying rolls in terms of shrinkage in the traveling direction. Conventionally, in order to alleviate the contraction force, the speed of each transport roll 16 is individually adjusted, and the transport speed is decreased toward the downstream. When shrinkage occurs in the width direction and running direction in the heat treatment process in this way, it becomes difficult to adjust the sheet width, and the required product width cannot be obtained, or the thickness increases due to shrinkage in the width direction and running direction. There is a problem that it is difficult to adjust the thickness of the T-die 12.

JP 2000-084996 A JP 2010-100032 A

  However, according to the knowledge of the present inventors, in the manufacturing method as described in Patent Document 1, the sheet shrinks before and after the annealing process, and the width and thickness of the sheet change. In view of the amount of change, the width and thickness of the sheet extruded from the T-die had to be adjusted. In addition, the shrinkage and thickness change may have a distribution in the width direction. In that case, it is necessary to adjust the thickness distribution by predicting the distribution in the width direction in the T die, which is an extremely difficult adjustment. End up.

  As described above, in the prior art, it is difficult to adjust the thickness distribution with the T die that corrects the width shrinkage and the thickness change in the annealing process.

  In view of the problems of the conventional technology as described above, an object of the present invention is to provide an annealing method that can reduce heat yield while substantially maintaining the sheet width and thickness.

In view of the above-described problems of the prior art, the present inventors have intensively studied a method for reducing heat yield in which changes in sheet width and thickness do not easily occur. As a result, the above-described object has been achieved. That is,
(1) Double belt press having melted ethylene-vinyl acetate copolymer (EVA) extruded from a T die, cooled with a polishing roll to form a sheet, and having a heating region in at least a part of the region from the inlet to the outlet Ethylene for solar cell encapsulating material, wherein the sheet is cooled and wound immediately after passing through a device and cooling the sheet immediately after exiting the double belt press device or a region downstream of the heating region of the double belt press device -Manufacturing method of a vinyl acetate copolymer sheet.
(2) The manufacturing method of the ethylene-vinyl acetate copolymer (EVA) sheet for solar cell sealing materials as described in said (1) using the double belt press apparatus by which the double belt surface processed the mold release property.
(3) The solar cell sealing according to (1) or (2), wherein the double belt press device has a cooling region downstream of a heating region, and heats and cools a sheet within the double belt press device. The manufacturing method of the ethylene-vinyl acetate copolymer sheet for materials.
(4) The solar cell sealing according to any one of (1) to (3), wherein the temperature of the heating region of the double belt press device is + 10 ° C. or higher and + 30 ° C. or lower of the melting point of the ethylene-vinyl acetate copolymer. The manufacturing method of the ethylene-vinyl acetate copolymer sheet for materials.
(5) The ethylene-vinyl acetate copolymer for solar cell encapsulating material according to any one of (1) to (4), wherein the passage time of the heating region of the double belt press device is 20 seconds or more and 1 minute or less. Sheet manufacturing method.
(6) The ethylene-vinyl acetate copolymer for solar cell sealing material according to any one of (1) to (5) above, wherein embossing is performed on at least one surface of the sheet immediately after exiting the double belt press device ( EVA) Sheet manufacturing method.
(7) The ethylene-vinyl acetate copolymer for a solar cell encapsulant according to any one of (1) to (5), wherein the belt surface of the double belt press device is subjected to a roughening process. Sheet manufacturing method.

  Generally, an ethylene-vinyl acetate copolymer that is excellent in light transmittance and moisture resistance, has good adhesion to glass, and is excellent in cost is mainly used as a sealing material for a solar cell module. The ethylene-vinyl acetate copolymer is a copolymer synthesized from ethylene and vinyl acetate, but the EVA, which is the main raw material resin of the EVA sheet applied in the present invention, has a vinyl acetate (VA) content. It is preferable that it is 20-35 mass%. When it is larger than 35% by mass, the water vapor transmission rate is increased, and the moisture permeability required as a sealing material for solar cells may not be ensured. Moreover, since resin is too hard as it is less than 20 mass%, a silicon power generation element may be cracked in the manufacturing process of a solar cell module. The EVA used in the present invention preferably has a melt flow rate of 2 to 50 g / 10 min.

  In the resin composition containing EVA used in the present invention, a crosslinking agent is added as an additive for improving heat resistance to give a crosslinked structure. Generally, the crosslinking agent has a temperature of 100 to 120 ° C. or more. An organic peroxide is used that begins to initiate the crosslinking reaction. Examples of such an organic peroxide include 2,5-dimethylhexane; 2,5-dihydroperoxide; 2,5-dimethyl-2,5-di (t-butylperoxy) hexane; -T-butyl peroxide; t-dicumyl peroxide; 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne; dicumyl peroxide; α, α'-bis (t-butylperoxide Oxyisopropyl) 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, etc. it can. The compounding amount of these organic peroxides is generally 5 parts by mass or less, preferably 0.5 to 2 parts by mass with respect to 100 parts by mass of EVA.

  Furthermore, a crosslinking aid can be added to EVA as an additive for improving the crosslinking rate of EVA and improving heat resistance. Examples of crosslinking aids provided for this purpose include trifunctional crosslinking aids such as triallyl isocyanurate; triallyl isocyanate as well as monofunctional crosslinking aids such as NK esters. it can. The amount of these crosslinking aids is generally 5 parts by mass or less, preferably 1 to 3 parts by mass with respect to 100 parts by mass of EVA.

  Moreover, it is common to add a silane coupling agent to EVA as an additive for improving the adhesive force with glass or a power generation element as a sealing film of a solar cell. Known silane coupling agents for this purpose are, for example, γ-chloropropyltrimethoxysilane; vinyltrichlorosilane; vinyltriethoxysilane; vinyl-tris- (β-methoxyethoxy) silane; γ-methacryloxy. Propyltrimethoxysilane; β- (3,4-ethoxycyclohexyl) ethyltrimethoxysilane; γ-glycidoxypropyltrimethoxysilane; vinyltriacetoxysilane; γ-mercaptopropyltrimethoxysilane; γ-aminopropyltrimethoxysilane N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane and the like can be mentioned. The compounding amount of these silane coupling agents is generally 5 parts by mass or less, preferably 0.1 to 1 part by mass with respect to 100 parts by mass of EVA.

  Furthermore, hydroquinone; hydroquinone monomethyl ether; p-benzoquinone; methyl hydroquinone and the like can be added as additives for improving the stability of EVA, and the amount of these is generally 3 masses per 100 mass parts of EVA. Or less.

  Furthermore, if necessary, an ultraviolet absorber, an antioxidant, a light stabilizer, and the like can be added as additives other than those described above. Examples of ultraviolet absorbers include 2-hydroxy-4-octoxybenzophenone; benzophenones such as 2-hydroxy-4-methoxy-5-sulfobenzophenone; 2- (2′-hydroxy-5-methylphenyl) benzotriazole Benzotriazoles; phenyl salsylates; hindered amines such as pt-butylphenyl salsylates. Antiaging agents include amines; phenols; bisphenyls; hindered amines, such as di-t-butyl-p-cresol; bis (2,2,6,6-tetramethyl-4-piperazyl). ) Sebacate.

  In the present invention, as shown in FIG. 4, such EVA and additives are melt-kneaded by a twin-screw extruder 11, extruded from a T-die 12, and cooled and solidified by polishing rolls 13 a and 13 c to form an EVA sheet 3. To do. In order to reduce the thermal distortion of the EVA sheet 3 generated during the cooling and solidification, the EVA sheet 3 is annealed, and then inspected for the presence of foreign matter by the in-line inspector 31 and then rolled by a winder. Take up around. In this annealing treatment, after the EVA sheet 3 is once heated to the melting point or higher, the EVA sheet 3 is kept at a high temperature for a predetermined time or more, thereby relaxing the EVA molecular orientation in the EVA sheet 3 and reducing thermal strain. effective.

  In the present invention, the T-die method refers to a method of forming a flat sheet or film by extruding molten resin from a flat die. Since a flat die has a wide shape in accordance with the sheet width to be extruded, it becomes a T shape when attached to an extruder, and is collectively called a T die.

  In the present invention, the polishing roll 13 is composed of a plurality of rolls for sandwiching and pressing a sheet-like molten resin extruded from the T-die 12 with a pair of rolls to simultaneously form the thickness and surface property of the sheet. This is a sheet conveying apparatus. Each configured roll includes a mechanism that is adjusted to a temperature suitable for cooling and shaping of the molten resin, and a mechanism that can adjust the gap between the rolls and the pressurizing pressure.

  In the present invention, as shown in FIG. 5, the double belt press device sandwiches a resin sheet between a pair of upper and lower metal belts 18 a and 18 b, and appropriately adjusts the temperature and pressure of the belt at each conveyance position of the sheet. By conveying a sheet, it refers to an apparatus that heats and forms the sheet by pressurizing and heating the sheet (in some cases, cooling in the same apparatus). By heating the sheet while restraining the EVA sheet with two belts, the EVA sheet 3 can be maintained while maintaining the dimensional accuracy while suppressing the deformation in the plane direction due to the thermal contraction during the sheet heating and the deformation in the thickness direction. Annealing treatment is possible.

  In the present invention, in order to reduce thermal distortion of the sheet, it is necessary to have a heating region for heating the sheet to an appropriate temperature in at least a part of the region from the sheet inlet to the outlet of the double belt press device. There is. In this heating, it is efficient to heat the sheet by contact heat transfer at the contact portion between the metal belt and the sheet, and the target function is achieved by the method of heating the metal belt. The heating of the metal belt includes a method of heating a roll that conveys the metal belt with a medium, a method of heating a radiant heat by bringing a heater close to the belt, and a method of heating by the principle of electromagnetic induction. Moreover, in this invention, the temperature of a heating area | region refers to the temperature from which a sheet | seat becomes the highest temperature in the said heating area | region. Furthermore, the passage time of the heating region refers to a time during which the melting point of EVA becomes + 10 ° C. or higher while the EVA sheet is conveyed in the double belt press apparatus. Further, it is more desirable that there is an area for cooling so that the sheet temperature is lower than the temperature in the heating area in the area downstream of the heating area and the exit of the double belt press apparatus. In this cooling, it is only necessary to have a function of reducing the sheet temperature to below the melting point of EVA + 10 ° C. so that the sheet coming out from the outlet of the double belt press apparatus does not bend and deform due to its own weight. In addition, if the EVA sheet is wound in a high temperature state, blocking may occur between the layers of the wound sheet roll. Therefore, in the region from the exit of the double belt press device to the winding device, the sheet has a melting point of −30 ° C. It is desirable to have the cooling roll 21 for cooling so that it may become the following.

  In the present invention, the releasability treatment on the surface of the double belt means that the EVA sheet is easily peeled off from the belt at the outlet of the double belt press device and is released on the surface of the belt so that it can be smoothly conveyed to the next step. This means coating the surface of the belt with a high-hardness material such as a fluorine-based resin or a silicone-based resin, or using a ceramic material with high hardness.

  Further, the embossing in the present invention means that the conveyance roll and the EVA sheet are adhered downstream from the double belt press apparatus, or the EVA sheet and the conveyance roll are not blocked by the take-up roll body. The process which gives the uneven | corrugated shape to the EVA sheet surface so that a contact area and the contact area of EVA sheets may become as small as possible.

  Moreover, the roughening process in this invention refers to the process which provides the uneven | corrugated shape to the belt surface of a double belt apparatus in order to transfer the uneven | corrugated shape to the EVA sheet surface. Examples of the surface roughening method include sand blasting, etching, engraving, and the like, but there is no particular limitation as long as it can be processed into a predetermined surface roughness.

  Moreover, according to the preferable form of this invention, the surface roughness Rz of the said sheet | seat surface is 3-20 micrometers, and the sheet | seat with which the unevenness | corrugation is evenly distributed is preferable.

  As described above, when the heat treatment is performed by a double belt press apparatus, the heat treatment can be performed in a continuous manner, the continuity of heating in the traveling direction (longitudinal direction) of the sheet, and the uniform temperature of the entire heating surface. The property becomes favorable. When the double belt press device continuously performs heating and cooling in one belt press machine, the running stability of the sheet on the downstream side of the belt press device is increased, and the dimensional accuracy and film thickness accuracy are improved. And since it cools, applying a pressure after a heating, it can maintain the orientation state of a molecular chain easily, and can reduce heat yield more reliably.

  Further, when the heating temperature of the double belt press apparatus is + 10 ° C. or higher and + 30 ° C. or lower of the melting point of EVA and the cooling temperature is the melting point + 10 ° C. or lower, the stress in the sheet is relieved with an appropriate resin viscosity during heating. In addition, since the sheet can be carried out of the apparatus with an appropriate resin viscosity at the time of cooling, an EVA sheet having a high dimensional accuracy and a low heat yield can be obtained more reliably.

  According to the present invention, it is possible to provide an annealing method capable of reducing heat yield while maintaining the sheet width and thickness substantially, and a sheet having low heat yield can be manufactured by a production process with good reproducibility, and adjustment loss is shortened. it can.

It is the schematic diagram which showed an example of the manufacturing method of the conventional EVA sheet | seat for solar cell sealing materials. It is the schematic diagram which showed an example of the manufacturing method of the conventional EVA sheet | seat for solar cell sealing materials. It is the schematic diagram which showed the member structure of the solar cell module. It is the schematic diagram which showed the member structure of the solar cell module. It is the schematic schematic which showed an example of the manufacturing method of the EVA sheet | seat for solar cell sealing materials of this invention. It is the schematic diagram which showed an example of the double belt press apparatus used for the manufacturing method of the EVA sheet | seat for solar cell sealing materials of this invention. It is the schematic schematic which showed an example of the manufacturing method of the EVA sheet | seat for solar cell sealing materials of this invention.

  Hereinafter, the manufacturing method of the ethylene-vinyl acetate copolymer (EVA) sheet | seat for solar cell sealing materials of this invention is demonstrated, referring drawings.

FIG. 4 is a schematic view of a sheet film forming apparatus showing one embodiment of the production method of the present invention. FIG. 4 shows only the main part, and a part of the frame and the transport roll for fixing the structure are omitted. Note that components having the same or equivalent functions as those of the conventional example are denoted by the same reference numerals, and detailed description thereof is omitted.
4 includes a twin-screw extruder 11 that melts and kneads EVA and additives at a high temperature, a T-die 12 that extrudes the kneaded molten resin into a sheet, and cools the extruded high-temperature sheet. Polishing rolls 13a and 13c that are solidified and formed into a solid sheet are provided. The EVA sheet 3 thus formed is sent to the double belt press device 17 and conveyed while being sandwiched by the double belt press device 17 while being reheated by the belt 18 heated in advance. The EVA sheet 3 is cooled to an appropriate temperature by the cooling roll 21 immediately after leaving the double belt press device 17 and then sent to a subsequent process.

  Further, the heat treatment of the EVA sheet 3 in the double belt press apparatus unit 17 will be described in detail. For the heat treatment, it is preferable to use a belt press type that can uniformly heat the EVA sheet. The belt press type here means one having a structure in which a sheet is sandwiched between the belts to be pressure-bonded. In such a belt press type, since the belt can be moved at a constant speed by the drive drums 19 and 20, continuous heat treatment can be performed. The double belt press device 17 used for the heat treatment is not particularly limited as long as it has the above structure. For example, a hydraulic double belt press machine using a press for pressurization, a roll double using a press roll. A belt press machine, a belt gripping type belt press machine, a rot cure, or the like can be used, but a roll type double belt press machine is preferred because of the flexibility of gap adjustment.

  In the present invention, the heat yield at 80 ° C. of the EVA sheet after the heat treatment is 20% or less, and a heat yield of 0 to 15% is particularly preferable. If this heat yield exceeds 20%, the solar cell position may be shifted due to the shrinkage deformation of the EVA sheet when the solar cell module is manufactured, particularly when a thin solar cell of 120 μm or less is handled. May end up.

  Moreover, it is preferable that a double belt press apparatus performs heating and cooling continuously within one double belt press apparatus. Further, the temperature at the time of hot rolling is preferably a temperature of EVA melting point + 10 ° C. or higher and + 30 ° C. or lower, more preferably EVA melting point + 15 ° C. or higher and + 25 ° C. or lower. In order to promote relaxation of thermal distortion, a temperature of EVA melting point + 10 ° C. or higher is preferable, and a temperature of EVA melting point + 30 ° C. or lower is preferable in order to maintain the thickness and width of the sheet even in a pressed state. In the present specification, the melting point of EVA refers to an endothermic peak value temperature in a temperature rising process in DSC measurement.

  The temperature during cooling is preferably the melting point of EVA + 10 ° C. or lower, more preferably the melting point or lower and the melting point−30 ° C. or higher. That is, the above temperature condition is preferable in order to convey the EVA sheet after the heat treatment while maintaining the restrained state of the sheet to the downstream process of the sheet while suppressing deformation due to tension.

  More preferably, the roll between the most upstream heating drum 19 and the most downstream cooling drum 20 may be provided with a temperature adjusting mechanism for changing the temperature stepwise. For example, a method of providing a pressure roll that pushes the belt from the inside of the belt between the most upstream drum and the most downstream drum and adjusting the temperature of the pressure roll is given as an example. FIG. 5 is a schematic diagram of an example of the apparatus. Pressure belts 22a and 22b are provided on the inner side of the belt, and the pressure of the pressure roller 22a is adjusted by adjusting the pressure of the pressure air cylinder 23. The pressure applied to the contact surfaces of 18b can be adjusted. Further, it is preferable that the pressure rollers 22a and 22b have a structure in which the roller temperature can be adjusted by a medium circulation structure for temperature adjustment. With this temperature adjustment structure, the temperature of the belts 18a and 18b at each position can be adjusted, and the temperature of the EVA sheet 3 can be adjusted as appropriate. The number of pressure rolls is not particularly limited, but is usually preferably about 10 to 30. Further, it is preferable to make the gap constant by setting the biting angle of the pressure roll to 0 °. Here, the biting angle means the angle of the belt surface with respect to the traveling horizontal direction of the EVA sheet, and the belt surface indicates a region where the EVA sheet is sandwiched.

  Moreover, it is preferable that the time for which the sheet is heated by the double belt press device 17 is 20 seconds or more during which the sheet is maintained at the melting point + 10 ° C. or higher. The EVA sheet starts to soften when the melting point is higher than the melting point, but according to the knowledge of the inventors, thermal strain is more easily relaxed in the temperature range of the melting point + 10 ° C. or higher. As a guideline for the heating time of the double belt press device, the distance from the position contacting both the heated upper and lower belts to the peeling position, that is, the distance from the center axis of the most upstream drum to the center axis of the most downstream drum is the sheet. It is preferable that the time for transporting is 20 seconds or more and 1 minute or less. If it is less than 20 seconds, the sheet is cooled without sufficiently relaxing the thermal strain in the EVA sheet, and the thermal strain may remain. Further, if the time is longer than 1 minute, the heat yield can be sufficiently reduced, but the length of the belt becomes longer and the equipment becomes expensive.

  Further, the EVA sheet 3 that is sticky at high temperature is easily peeled off from the belts 18a and 18b on the surfaces of the belts 18a and 18b, and the belt surfaces have releasability so that the belts can be smoothly conveyed to the next step. Well, it has been subjected to a treatment to improve the releasability by coating with fluorine resin or silicone resin, which is a heat resistant material, or by thermal spraying high hardness ceramic material etc. preferable. In particular, a fluorine-based resin or a silicone-based resin is more preferable because release processing can be realized at a relatively low cost by coating on the belt surface.

  The surface of the belt that contacts the sheet should be roughened. Since EVA sheets are sticky particularly at high temperatures, they may be in close contact with a guide roll that contacts and conveys the sheet, and may be difficult to peel off, or may be blocked between sheets when wound on a take-up roll body. Therefore, it is preferable that at least one surface of the EVA sheet is embossed so as to provide unevenness so that the contact area with the contacting sheet is as small as possible. Since the EVA sheet is softened when it is heat-treated with a double belt press apparatus and the belt surface shape is transferred, the belt surface is preferably roughened in the range of 1 to 30 μm in Rz. In particular, Rz of 10 to 30 μm is more preferable because the cushioning property when contacting the solar cell at the time of manufacturing the solar cell module can be improved. However, since roughening of Rz = 10 μm or more becomes difficult by general sandblasting or the like, engraving is preferably performed on the belt surface in the sense of intentionally designing cushioning properties. Further, it is preferable to perform this roughening treatment on both the upper and lower belt surfaces, since the peelability can be improved regardless of whether the contact surface with the conveying roll is on the upper or lower surface of the sheet.

  Moreover, you may process the embossing process of an EVA sheet immediately after a double belt press apparatus. FIG. 6 is a schematic diagram showing an example of the method. A sheet heated by a double belt press is conveyed at a high temperature and is nipped between an embossing roller 24 and an embossing counter roller 25, thereby embossing. The surface shape of the processing roller 24 is transferred to the EVA sheet 3. Then, after the EVA sheet 3 is cooled by passing through the cooling roll 21, it is conveyed to a winder.

  Furthermore, when processing into a solar cell module, the sheet surface that comes into contact with the solar battery cell can be processed with a deeper embossing process so that a relatively deep unevenness process can be processed. More preferable for the purpose of making it difficult to occur. For this purpose, it is preferable to form a deep uneven shape of Rz = 10 μm or more on the surface of the belt 18a or 18b of the double belt press device or the embossing roller 24 by engraving or the like. In the case of the present invention, since the EVA sheet 3 is embossed by the double belt press device 17 or later, the polishing roll 13b subjected to expensive engraving as described in the background art and FIG. Alternatively, it is possible to use a polishing roll 13c that has been subjected to a mild satin treatment.

  By producing an EVA sheet using the heat treatment method by the double belt press apparatus of the present invention described above, an EVA sheet having low heat yield and good dimensional accuracy can be produced. In addition, by applying the EVA sheet manufactured in this way to the manufacture of a crystalline solar cell module, it is possible to provide a solar cell manufacturing process with a good yield, in which cell displacement and cracking are difficult to place.

The measurement method used in this example is shown below.
(1) Sheet thickness The thickness of 20 points in the width direction of the molded EVA sheet was measured with the following measuring instrument, and the average thickness, maximum thickness, and minimum thickness were determined.
Measuring instrument: Mitsutoyo Thickness Gauge (Type 547-301)
(2) Heat gain (heat shrinkability)
A flat square test piece having a side of 120 mm was cut out from the obtained EVA sheet. Two parallel straight lines were drawn on the test piece with an interval of 100 mm in the running direction during manufacture (hereinafter abbreviated as MD direction).

Next, the test piece was immersed in warm water heated to 80 ° C., and after 60 seconds, the EVA sheet was taken out from the warm water to remove moisture on the sheet surface.
An interval A (mm) between two straight lines drawn on the test piece was measured with a caliper at five points, a heat shrinkage rate was calculated based on the following formula, and an average value was obtained.

Heat yield (%) = 100 × (100−A) / 100
Example 1
EVA sheet A was manufactured using the manufacturing apparatus schematically shown in FIG. The schematic structure of the double belt press device 17 is the same as that shown in FIG. Specifically, EVA (vinyl acetate content: 28% by mass, melt flow rate: 15 g / 10 min, melting point: 71 ° C.) 100 parts by mass, t-butylperoxy-2-ethylhexyl monocarbonate (1 hour half-life (Temperature: 119 ° C.) A resin composition comprising 0.5 part by mass, 0.1 part by mass of 2,6-di-t-butyl-4-methylphenol and 0.3 part by mass of 2-hydroxy-4-methoxybenzophenone. The biaxial extruder 11 was supplied, melt-kneaded at 100 ° C., and the EVA sheet was extruded from the T-die 12 connected to the biaxial extruder 11 and held at 105 ° C. The T die has a lip width of 1300 mm and a lip gap of 1.0 mm.

  The EVA sheet was cooled and solidified by polishing rolls 13a and 13c maintained at 20 ° C. The sheet temperature when the EVA sheet was discharged from the T die was 107 ° C. The sheet width at this time was 1150 mm, and the sheet conveying speed was 10 m / min.

Next, the EVA sheet 3 was conveyed to the double belt press device 17, and the sheet 3 was supplied so that the sheet was sandwiched between the two belts 18a and 18b. The main structure of the double belt press apparatus 17 is as follows.
(1) Double belt ・ Material, thickness: made of stainless steel, 1 mm
・ Width: 1500mm
-Surface roughness (Rz 10-point average roughness): Upper belt 12 μm, Lower belt 6 μm
(2) Driving drum ・ Diameter, surface length: diameter 500 mm, surface length 1600 mm
・ Drum center axis distance: 5.5m
(3) Pressure roller-Diameter, surface length: diameter 100 mm, surface length 1600 mm
-Arrangement pitch: 200mm
・ Each roller pressing force: 1kN
In the double belt press device 17, the temperature of the uppermost drive drum 19 and the pressure rollers 22a and 22b were adjusted to 100 ° C., and the temperature of the most downstream drive drum 20 was adjusted to 60 ° C. At this time, the temperature of the surface of the stainless steel belt 18 transported on each drive drum was 94 ° C. on the upstream drum and 67 ° C. on the downstream drum.

The sheet obtained by heat-treating the EVA sheet 3 through the double belt press device 17 was cooled by the cooling roll unit 21 and wound up. The sheet temperature immediately after winding was 28 ° C. The EVA sheet thus obtained had an average thickness of 0.52 mm, a maximum value of 0.54 mm, and a minimum value of 0.50 mm. The heat yield in the MD direction of the sheet was 11%.
(Comparative Example 1)
In FIG. 4, the EVA sheet was wound up in the same manner as in Example 1 except that the sheet conveyed from the polishing roll 13 was wound without passing through the double belt press device 17. The sheet temperature immediately after winding was 25 ° C. The EVA sheet thus obtained had an average thickness of 0.55 mm, a maximum value of 0.56 mm, and a minimum value of 0.54 mm. The heat yield in the MD direction of the sheet was 60%.
(Comparative Example 2)
In FIG. 3, an EVA sheet was obtained in the same manner as in Example 1 except that the sheet conveyed from the polishing roll 13 was passed through an annealing apparatus 14 using a far infrared heater and wound up. At this time, the maximum temperature of the sheet passing through the annealing apparatus was 85 ° C., and the EVA sheet 3 was passed through the annealing apparatus 14 for 30 seconds.
The sheet obtained by heat-treating the EVA sheet 3 through the annealing apparatus 14 was cooled by the cooling roll unit 21 and wound up. The sheet temperature immediately after winding was 33 ° C. The EVA sheet thus obtained had an average thickness of 0.59 mm, a maximum value of 0.67 mm, and a minimum value of 0.52 mm. Further, the sheet width was 1150 mm, which was the same as that in Example 1 before the annealing treatment, but contracted to 1020 mm after the annealing treatment. The heat yield in the MD direction of the sheet was 28%.

  The present invention is very suitable for a method for producing an ethylene-vinyl acetate copolymer (EVA) sheet for a solar cell encapsulant, but it can also be applied to other sheets, webs such as films, and the like. The application range is not limited to these.

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Back sheet 3 EVA sheet 3a Glass surface side sealing material sheet 3b Back sheet surface side sealing agent sheet 4 Solar cell 5 Aluminum frame 6 Wiring box 11 Biaxial extruder 12 T die 13a Polishing roll (on the surface) Without engraving)
13b Polishing roll (with engraving on the surface)
13c Polishing roll (no engraving on the surface)
14 Annealing treatment device 15 Far-infrared heater 16 Conveying roller 17 Double belt press device 18 Steel belt 18a Upper steel belt 18b Lower brake belt 19 Upstream drive drum 20 Downstream drive drum 21 Cooling roller 22 Pressure roller 22a Upper pressure roller 22b Lower pressure roller 23 Pressure cylinder 24 Embossing roller 25 Embossing counter roller 31 Inline inspection device 32 Winder 33 Gear pump 34 Sheet conveying direction

Claims (7)

The melted ethylene-vinyl acetate copolymer is extruded from a T die, cooled with a polishing roll to form a sheet, passed through a double belt press apparatus having a heating region in at least a part of the region from the inlet to the outlet, An ethylene-vinyl acetate copolymer for a solar cell encapsulant, wherein the sheet is cooled and wound after the region downstream of the heating region of a double belt press device or after exiting the double belt press device Sheet manufacturing method. The manufacturing method of the ethylene-vinyl acetate copolymer sheet for solar cell sealing materials of Claim 1 using the double belt press apparatus by which the double belt surface was processed by the mold release property. The said double belt press apparatus has a cooling area | region downstream of a heating area | region, and heats and cools a sheet | seat within the double belt press apparatus, The ethylene-vinyl acetate for solar cell sealing materials of Claim 1 or 2 A method for producing a copolymer sheet. 4. The ethylene-vinyl acetate for solar cell encapsulant according to claim 1, wherein the temperature of the heating region of the double belt press device is not lower than + 10 ° C. and not higher than + 30 ° C. of the melting point of the ethylene-vinyl acetate copolymer. A method for producing a copolymer sheet. 5. The method for producing an ethylene-vinyl acetate copolymer sheet for a solar cell encapsulant according to claim 1, wherein the passing time of the heating region of the double belt press device is 20 seconds or more and 1 minute or less. The manufacturing method of the ethylene-vinyl acetate copolymer sheet for solar cell sealing materials in any one of Claims 1-5 which performs embossing to at least one surface of the sheet | seat immediately after leaving the said double belt press apparatus. The method for producing an ethylene-vinyl acetate copolymer sheet for a solar cell encapsulant according to any one of claims 1 to 5, wherein the belt surface of the double belt press device is subjected to a roughening process.

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