Specification
Title of Invention: Composition for encapsulant film comprising ethylene/alpha-olefin copolymer and encapsulant film comprising same
technical field
[One]
Cross-Citation with Related Applications
[2]
This application claims the benefit of priority based on the Korean Patent Application 2020-0046029 dated April 16, 2020, and all contents disclosed in the documents of the Korean patent applications are incorporated as a part of this specification.
[3]
[4]
technical field
[5]
The present invention relates to a composition for an encapsulant film comprising an ethylene/alpha-olefin copolymer having high volume resistance and light transmittance, and an encapsulant film using the same.
[6]
background
[7]
As global environmental problems and energy problems are becoming more and more serious, solar cells are attracting attention as a means of generating energy that is clean and not depleted. When solar cells are used outdoors, such as on the roof of a building, it is common to use them in a module form. Cell encapsulant / crystalline solar cell element crystalline solar cell element / solar cell encapsulant / solar cell module protective sheet (back side protective member) are laminated in this order and manufactured. On the other hand, in order to obtain a thin-film solar cell module, the thin-film solar cell element/solar cell sealing material/solar cell module protective sheet (back side protection member) is laminated in order and manufactured.
[8]
As the above-described solar cell sealing material, an ethylene/vinyl acetate copolymer, an ethylene/alpha-olefin copolymer, or the like is generally used. Moreover, since long-term weather resistance is calculated|required in a solar cell sealing material, the light stabilizer is normally contained as an additive. Moreover, in consideration of the adhesiveness of the front surface side transparent protective member thru|or the back surface side protective member represented by glass, a silane coupling agent is also normally contained in a solar cell sealing material.
[9]
Specifically, an ethylene/vinyl acetate copolymer (EVA) sheet has been widely used because of its excellent transparency, flexibility, and adhesion. Ethylene/vinyl acetate copolymer (EVA) films are widely used because of their excellent transparency, flexibility, and adhesion. However, when the EVA composition is used as a constituent material of a solar cell sealing material, there is a concern that components such as acetic acid gas generated by decomposition of EVA may affect the solar cell element.
[10]
Moreover, with the recent spread of photovoltaic power generation, large-scale power generation systems, such as mega solar, are progressing, and there is also a movement to increase the system voltage for the purpose of lowering transmission loss or the like. As the system voltage rises, the potential difference between the frame and the cell increases in the solar cell module. That is, the frame of the solar cell module is generally grounded, and when the system voltage of the solar cell array becomes 600V to 1000V, in the module with the highest voltage, the potential difference between the frame and the cell becomes 600V to 1000V of the system voltage as it is, and the high voltage In this authorized state, power generation will be maintained during the day. In addition, compared to the sealing material, the glass has a low electrical resistance, and a high voltage is generated between the glass and the cell through the frame. That is, under the power generation situation during the day, in the series-connected modules, the potential difference between the cell and the module and between the cell and the glass surface increases sequentially on the ground side, and the potential difference of the high voltage of the system voltage is maintained in the largest place. Among the solar cell modules used in such a state, an example of a module using a crystalline-based power generation device in which the output is greatly reduced and the PID (abbreviation for Potential Induced Degradation) phenomenon occurs has also been reported. Therefore, in order to solve this problem, a higher volume resistivity is calculated|required of the solar cell sealing material which is in direct contact with a solar cell element.
[11]
Volume resistivity or resistivity (ρ), also known as electrical resistance, is defined as the electrical resistance between opposite sides of 1 m3 of a material, this volume resistance being reproducible within a predetermined range in all of the above applications and being a permanent molded product It is important to obtain In the field of electrical insulation materials for high-voltage power cables, high-pressure processed low-density polyethylene, cross-linked polyethylene, and the like have been widely used due to their excellent electrical properties. One of the difficulties with high voltage power cables is the power loss that occurs during power transmission. Reduction of power loss is the most important requirement to be satisfied. Reduction of power loss can be achieved by enhancing the high voltage properties of the insulating material, in particular the volume resistance. However, the insulating material for a power cable is heated to a high temperature (about 90° C.) by heat generated by passing an electric current in the vicinity of the inner conductor, but is maintained at room temperature in the vicinity of the outer conductor. Conventional polyethylene shows a significant drop in volume resistance as the temperature rises. Therefore, polyethylene exhibits a significant drop in volume resistance in the vicinity of the inner conductor through current flow.
[12]
As such, it is still necessary to develop an ethylene/alpha-olefin copolymer that has excellent volume resistance and can be usefully used as a material requiring high insulation properties such as solar cell encapsulants.
[13]
[14]
[Prior art literature]
[15]
[Patent Literature]
[16]
Korean Patent Publication 2018-0063669
[17]
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[18]
It is an object of the present invention to provide a composition for an encapsulant film that includes an ethylene/alpha-olefin copolymer having a wide crystallinity distribution while maintaining a narrow molecular weight distribution, thereby exhibiting high volume resistance and excellent insulation.
[19]
Another object of the present invention is to provide a method for preparing the composition for an encapsulant film and an encapsulant film prepared by using the composition for an encapsulant film.
[20]
means of solving the problem
[21]
In order to solve the above problems, the present invention provides a composition for an encapsulant film comprising an ethylene/alpha-olefin copolymer satisfying the following conditions (a) to (d).
[22]
(a) a density of 0.85 to 0.89 g/cc;
[23]
(b) having a molecular weight distribution of 1.5 to 2.3;
[24]
(c) the melting temperature is 85° C. or less; and,
[25]
(d) the free volume proportional constant (C 2 ) derived from the following equations 1 and 2 is 600 or less;
[26]
[Equation 1]
[27]

[28]
In Equation 1 above,
[29]
η O (T) is the viscosity (Pa s) of the copolymer measured by ARES-G2 (Advanced Rheometric Expansion System) at an arbitrary temperature T (K),
[30]
η 0 (T r ) is the viscosity (Pa s) of the copolymer measured by ARES-G2 at the reference temperature T r (K),
[31]
a T is a shift factor of an arbitrary temperature T (K) with respect to the reference temperature T r (K), and is obtained from Equation 1 above,
[32]
[Equation 2]
[33]

[34]
In Equation 2 above,
[35]
C 1 is an inverse constant of free volume,
[36]
C 2 is the free volume proportionality constant (K),
[37]
C 1 and C 2 are intrinsic constants of the ethylene/alpha-olefin copolymer, and are obtained from Equation 2 above.
[38]
[39]
In addition, the present invention provides an encapsulant film comprising the composition for the encapsulant film.
[40]
Effects of the Invention
[41]
The composition for an encapsulant film of the present invention uses an ethylene/alpha-olefin copolymer having a low free volume due to a high crystallinity distribution, and thereby exhibits excellent volume resistance and light transmittance for various uses in the field of electrical and electronic industries widely available as
[42]
Modes for carrying out the invention
[43]
Hereinafter, the present invention will be described in more detail to help the understanding of the present invention.
[44]
The terms or words used in the description and claims of the present invention should not be construed as being limited to their ordinary or dictionary meanings, and the inventor appropriately defines the concept of the term in order to best describe his invention. Based on the principle that can be done, it should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention.
[45]
[46]
[Composition for Encapsulant Film]
[47]
The composition for an encapsulant film of the present invention is characterized in that it includes an ethylene/alpha-olefin copolymer satisfying the following conditions (a) to (d).
[48]
(a) a density of 0.85 to 0.89 g/cc;
[49]
(b) having a molecular weight distribution of 1.5 to 2.3;
[50]
(c) the melting temperature is 85° C. or less; and,
[51]
(d) the free volume proportional constant (C 2 ) derived from the following equations 1 and 2 is 600 or less;
[52]
[Equation 1]
[53]

[54]
In Equation 1 above,
[55]
η O (T) is the viscosity (Pa s) of the copolymer measured by ARES-G2 (Advanced Rheometric Expansion System) at an arbitrary temperature T (K),
[56]
η 0 (T r ) is the viscosity (Pa s) of the copolymer measured by ARES-G2 at the reference temperature T r (K),
[57]
a T is a shift factor of an arbitrary temperature T (K) with respect to the reference temperature T r (K), and is obtained from Equation 1 above,
[58]
[Equation 2]
[59]

[60]
In Equation 2 above,
[61]
C 1 is an inverse constant of free volume,
[62]
C 2 is the free volume proportionality constant (K),
[63]
C 1 and C 2 are intrinsic constants of the ethylene/alpha-olefin copolymer, and are obtained from Equation 2 above.
[64]
[65]
The present invention relates to a composition for an encapsulant film having high volume resistance and excellent electrical insulation properties. Specifically, the ethylene/alpha-olefin copolymer contained in the composition for an encapsulant film of the present invention is used as a catalyst by mixing the transition metal compound represented by Formula 1 and Formula 2 during preparation, and the transition metal represented by Formula 1 Due to the structural characteristics of the catalyst, it is difficult to introduce an alpha-olefin-based monomer to the compound, which tends to produce a high-density copolymer, and the transition metal compound represented by Formula 2 can introduce a large amount of alpha-olefin. A low-density polymer (elastomer) can also be prepared, and the two transition metal compounds have different copolymerizability for incorporating an alpha-olefinic monomer when used alone.
[66]
The ethylene/alpha-olefin copolymer prepared by using their mixed composition as a catalyst is a copolymer having both a low-density region in which a large amount of alpha-olefinic monomer is mixed and a high-density region in which a small amount of alpha-olefin-based monomer is incorporated. Since the crystallinity distribution is wide and contains a small amount of free volume, the composition for an encapsulant film of the present invention using the same has excellent electrical insulation properties because of low charge mobility.
[67]
[68]
The ethylene/alpha-olefin copolymer contained in the composition for an encapsulant film of the present invention is a low-density polymer having a density in the range of 0.85 to 0.89 g/cc, wherein the density may mean a density according to ASTM D-792. have. More specifically, the density may be 0.850 g/cc or more, 0.860 g/cc or more, 0.870 g/cc or more, 0.875 g/cc or more, and 0.890 g/cc or less, 0.880 g/cc or less.
[69]
If the density is out of the above range, there may be a problem in that the volume resistance or light transmittance of the ethylene/alpha-olefin copolymer is lowered.

Claims
[Claim 1]
A composition for an encapsulant film comprising an ethylene/alpha-olefin copolymer satisfying the following conditions (a) to (d): (a) a density of 0.85 to 0.89 g/cc; (b) having a molecular weight distribution of 1.5 to 2.3; (c) the melting temperature is 85° C. or less; And, (d) the free volume proportional constant (C 2 ) derived from the following equations 1 and 2 is 600 or less; [Equation 1] In Equation 1, η O (T) is the viscosity (Pa·s) of the copolymer measured by ARES-G2 (Advanced Rheometric Expansion System) at an arbitrary temperature T (K), and η 0 (T r ) is the viscosity (Pa s) of the copolymer measured by ARES-G2 at the reference temperature T r (K), and a T is the transfer factor of an arbitrary temperature T (K) with respect to the reference temperature T r (K). (Shift Factor) obtained from Equation 1, [Equation 2] In Equation 2, C 1 is a free volume inverse proportional constant, C 2 is a free volume proportional constant (K), and C 1and C 2 is an intrinsic constant of the ethylene/alpha-olefin copolymer, which is obtained from Equation 2 above.
[Claim 2]
The method according to claim 1, The free volume proportional constant (C 2 ) Will be 300 to 550, the composition for the encapsulant film.
[Claim 3]
The method according to claim 1, The molecular weight distribution is 1.8 to 2.2, the encapsulant film composition.
[Claim 4]
The method according to claim 1, wherein the ethylene / alpha-olefin copolymer is a melt index (MI 10 , 190 °C, 10 kg load condition) value to the melt index (MI 2.16 , 190 °C, 2.16 kg load condition) melt flow index (MFRR) , Melt Flow Rate Ratio, MI 10 /MI 2.16 ) is 8.0 or less, the composition for the encapsulant film.
[Claim 5]
The method according to claim 1, The crystallization temperature of the ethylene / alpha-olefin copolymer is 70 ℃ or less, the composition for an encapsulant film.
[Claim 6]
The method according to claim 1, The melt index (MI 2.16 , 190 ℃, 2.16 kg load condition) of the ethylene / alpha-olefin copolymer is 0.1 to 50 dg / min, the composition for an encapsulant film.
[Claim 7]
The method according to claim 1, The weight average molecular weight of the ethylene / alpha-olefin copolymer is 40,000 to 150,000 g / mol, the composition for the encapsulant film.
[Claim 8]
The method according to claim 1, wherein the alpha-olefin is propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1 -Dodecene, 1-tetradecene, 1-hexadecene, and 1-eicosene comprising at least one selected from the group consisting of, the composition for the encapsulant film.
[Claim 9]
The composition for an encapsulant film according to claim 1, wherein the alpha-olefin is contained in an amount of greater than 0 and 99 mol% or less compared to the copolymer.
[Claim 10]
The method according to claim 1, wherein it further comprises at least one selected from the group consisting of a crosslinking agent, a crosslinking aid, a silane coupling agent, an unsaturated silane compound, an amino silane compound, a light stabilizer, a UV absorber, and a heat stabilizer. composition.
[Claim 11]
An encapsulant film comprising the composition for an encapsulant film of any one of claims 1 to 10.
[Claim 12]
A solar cell module comprising the encapsulant film of claim 11 .