U.S. patent application number 11/794353 was filed with the patent office on 2007-11-22 for encapsulating material for solar cell.
This patent application is currently assigned to DuPont-Mitsui Polychemicals Co., Ltd.. Invention is credited to Koichi Nishijima, Akira Yamashita.
Application Number | 20070267059 11/794353 |
Document ID | / |
Family ID | 36614905 |
Filed Date | 2007-11-22 |
United States Patent
Application |
20070267059 |
Kind Code |
A1 |
Nishijima; Koichi ; et
al. |
November 22, 2007 |
Encapsulating Material for Solar Cell
Abstract
Encapsulating material for solar cells which facilitates
fabricating solar cell modules and has excellent transparency, heat
resistance, flexibility, etc., and a solar cell modules. More
specifically, the present invention provides encapsulating material
for solar cells comprising a non-crystalline or low-crystalline
a-olefin-based copolymer or its composition (I). In a preferred
embodiment, the aforementioned copolymer or its composition (I) is
a resin composition (C) containing 50 to 100 parts by weight of
non-crystalline .alpha.-olefin polymer (A) meeting the following
requirements: (a) the .alpha.-olefin having 3 to 20 carbon atoms is
not less than 20 mol %, (b) practically no melt peak as measured by
a differential scanning calorimeter is observed, and (c) the Mw/Mn
is not more than 5, and 50 to 0 parts by weight of crystalline
.alpha.-olefin polymer (B) (the total of (A) and (B) being 100
parts by weight).
Inventors: |
Nishijima; Koichi;
(Ichihara-shi, JP) ; Yamashita; Akira;
(Chiyoda-ku, JP) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
DuPont-Mitsui Polychemicals Co.,
Ltd.
5-2, Higashi-Shimbashi 1-chome
Minato-ku, TOKYO
JP
105-7117
Mitsui Chemicals Fabro, Inc.
2-6, Kudan-kita 4-chome
Chiyoda-ku, TOKYO
JP
102-0073
|
Family ID: |
36614905 |
Appl. No.: |
11/794353 |
Filed: |
December 27, 2005 |
PCT Filed: |
December 27, 2005 |
PCT NO: |
PCT/JP05/23882 |
371 Date: |
June 28, 2007 |
Current U.S.
Class: |
136/256 |
Current CPC
Class: |
C08K 5/34924 20130101;
C08K 5/14 20130101; C08L 23/0815 20130101; C08L 23/10 20130101;
Y02E 10/50 20130101; C08L 2312/00 20130101; C08K 5/34924 20130101;
C08K 5/14 20130101; C08L 2203/206 20130101; C08L 2666/06 20130101;
C08L 2666/06 20130101; C08L 23/02 20130101; C08L 2205/02 20130101;
C08L 23/0815 20130101; C08L 2312/00 20130101; H01L 31/048 20130101;
C08L 23/14 20130101; C08L 23/02 20130101; C08L 2203/206 20130101;
H01L 31/0481 20130101; C08L 23/10 20130101 |
Class at
Publication: |
136/256 |
International
Class: |
C08L 23/00 20060101
C08L023/00; H01L 31/04 20060101 H01L031/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2004 |
JP |
2004-381061 |
Dec 28, 2004 |
JP |
2004-381109 |
Claims
1. Encapsulating material for solar cells comprising a
non-crystalline or low-crystalline .alpha.-olefin-based copolymer
or its composition (I).
2. Encapsulating material for solar cells according to claim 1,
wherein the aforementioned non-crystalline or low-crystalline
.alpha.-olefin-based copolymer or its composition (I) is resin
composition (C) containing 50 to 100 parts by weight of
non-crystalline .alpha.-olefin polymer (A) meeting the following
requirements (a) through (c) and 50 to 0 parts by weight of
crystalline .alpha.-olefin polymer (B) (the total of (A) and (B)
being 100 parts by weight): (a) a polymerization unit based on
.alpha.-olefin having 3 to 20 carbon atoms is not less than 20 mol
%; (b) practically no melt peak as measured by a differential
scanning calorimeter is observed; (c) the Mw/Mn is not more than
5.
3. Encapsulating material for solar cells according to claim 2,
wherein the propylene polymerization unit of the aforementioned
non-crystalline .alpha.-olefin polymer (A) is not less than 30 mol
%.
4. Encapsulating material for solar cells according to claim 2,
wherein the aforementioned non-crystalline .alpha.-olefin polymer
(A) is a polymer produced by use of a metallocene catalyst.
5. Encapsulating material for solar cells according to claim 2,
wherein the aforementioned crystalline .alpha.-olefin polymer (B)
is a propylene homopolymer or a copolymer of propylene and another
.alpha.-olefin.
6. Encapsulating material for solar cells according to claim 2,
wherein the aforementioned resin composition (C) is a composition
having JIS A hardness of 40 to 100.
7. Encapsulating material for solar cells according to claim 1,
wherein the aforementioned copolymer or its composition (I) is a
non-crystalline or low-crystalline .alpha.-olefin copolymer (D)
having a crystallinity of not higher than 40% as measured by use of
X rays.
8. Encapsulating material for solar cells according to claim 7,
wherein the Shore D hardness of the aforementioned non-crystalline
or low-crystalline .alpha.-olefin-based copolymer is not higher
than 60.
9. Encapsulating material for solar cells according to claim 1,
wherein at least one kind selected from among cross-linking agents,
cross-linking accelerators, silane-coupling agents, antioxidants,
ultraviolet absorbers and light stabilizers is compounded to the
aforementioned copolymer or its composition (I).
10. Encapsulating material for solar cells according to claim 1,
wherein the storage elastic modulus at 150.degree. C. of the
aforementioned copolymer or its composition (I) is not lower than
10.sup.3 Pa.
11. Encapsulating material for solar cells according to claim 1,
wherein the haze of the aforementioned copolymer or its composition
(I) at the thickness of 0.5 mm is not higher than 10%.
12. Encapsulating material for solar cells according to claim 1,
which is in the form of sheet.
13. A solar cell module which is obtained by using the solar cell
encapsulating material as defined in claim 1.
14. A solar cell module according to claim 13, wherein the solar
cell encapsulating material layer is cross-linked.
15. Encapsulating material for solar cells according to claim 2,
wherein the storage elastic modulus at 150.degree. C. of the
aforementioned copolymer or its composition (I) is not lower than
10.sup.3 Pa.
16. Encapsulating material for solar cells according to claim 2,
wherein the haze of the aforementioned copolymer or its composition
(I) at the thickness of 0.5 mm is not higher than 10%.
Description
TECHNICAL FIELD
[0001] The present invention relates to an encapsulating material
for solar cells in solar cell modules and solar cell modules using
the encapsulating material. More specifically, the present
invention is concerned with encapsulating material for solar cells
having excellent transparency, heat resistance, flexibility and
other properties that makes the formation of solar cell modules
easy.
BACKGROUND ART
[0002] Hydraulic power generation, wind power generation and
photovoltaic power generation which make use of inexhaustible
natural energy and help reduce carbon dioxide and improve other
environmental problems are getting into the limelight. Out of
these, the spread of photovoltaic power generation has been making
remarkable progress in recent years as the performance of solar
cell modules in power generation efficiency and other respects has
been making marked improvements while on the other hand their
prices have been declining and the national and local governments
has been promoting the business of introducing photovoltaic power
generation systems for household use. However, further spread of
photovoltaic power generation will require further cost reductions,
and to this end research is being continued night and day to work
on the improvement of power generation efficiency.
[0003] A solar cell module is generally a package formed by
protecting a solar cell comprising such solar cell element as
silicon, gallium-arsenic and copper-iridium-selenium with a top
transparent protective material and a bottom protective substrate
material, with the solar cell and the protective materials fixed by
use of an encapsulating material. For this reason, any
encapsulating material for solar cells is required to have
satisfactory transparency so that power generation efficiency will
be increased. Encapsulating material for solar cells is also
required to have heat resistance so that any troubles such as the
flow or deformation of the encapsulating material will not occur
even when the temperature rises during the use of the solar cell
module. Furthermore, in recent years, as the wall thickness of
solar cell element is becoming smaller, encapsulating materials
having excellent flexibility are also sought after.
[0004] At present, an ethylene-vinyl acetate copolymer having a
high vinyl acetate content is used for the encapsulating materials
for solar cells in solar cell modules from the viewpoint of
flexibility, transparency and other properties. However, because of
its inadequate heat resistance, it is necessary to use organic
peroxide additionally for such ethylene-vinyl acetate copolymer.
For this reason, it is necessary to use a two-step process in which
a sheet-like encapsulating material is first prepared from an
ethylene-vinyl acetate copolymer containing an organic peroxide and
then a solar cell element is sealed with the sheet thus obtained.
In the step of making the sheet, it is necessary to mold the sheet
at such low temperature that will not cause the decomposition of
the organic peroxide and as a result it is impossible to increase
the extrusion rate. On top of that, in the step of sealing the
solar cell element, it is commonly necessary to carry out a
time-consuming two-step bonding process which comprises a step of
preliminarily bonding the solar cell over several minutes to score
of minutes by use of a laminator and then a step of firmly bonding
it over scores of minutes to one hour in an oven at a high
temperature at which the organic peroxide is decomposed.
Consequently, it is troublesome and requires much time to produce a
solar cell module, which in turn constitutes a factor in increasing
the manufacturing cost.
[0005] Reference 1: Japanese Patent Publication SHO 2-40709
DISCLOSURE OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0006] The present invention provides encapsulating material for
solar cells showing excellent transparency, heat resistance,
flexibility and other properties. The present invention provides
encapsulating material for solar cells which without requiring the
use of any organic peroxide makes possible a significant
improvement in the efficiency in the production of solar cell
modules and a substantial reduction in the manufacturing cost of
solar cell modules.
[0007] The use of the non-crystalline or low-crystalline
.alpha.-olefin-based copolymer of the present invention or its
composition (I) makes it possible to provide encapsulating material
for solar cells that will prevent an occurrence of such troubles as
the flow or deformation of the encapsulating material and an
impairment of the appearance of the solar cell even when the
temperature rises during the use of the solar cell module.
Specifically, the present invention makes it possible to provide
encapsulating material for solar cells which shows a melting point
of not lower than 85.degree. C., a storage elastic modulus of not
less than 10.sup.3 Pa at 150.degree. C., Shore D hardness of not
more than 60, and haze at a thickness of 0.5 mm of not more than
10%.
[0008] The present invention also provides an embodiment in which
the non-crystalline or low-crystalline .alpha.-olefin-based
copolymer or its composition (I) is a copolymer comprising ethylene
as the main component and is cross-linked by the compounding of a
cross-linking agent. In this case as well, such non-crystalline or
low-crystalline .alpha.-olefin-based copolymer or its composition
makes it possible to form encapsulating material for solar cells
layer showing excellent flexibility and provide encapsulating
material for solar cells that makes a reduction in the wall
thickness of the solar cell possible.
[0009] The present invention provides a solar cell module using the
solar cell encapsulating material of the present invention.
MEANS TO SOLVE THE PROBLEMS
[0010] The present invention provides encapsulating material for
solar cells comprising a non-crystalline or low-crystalline
.alpha.-olefin-based copolymer or its composition (I).
[0011] The present invention provides encapsulating material for
solar cells as claimed in claim 1, wherein the aforementioned
copolymer or its composition (I) is resin composition (C)
containing 50 to 100 parts by weight of non-crystalline
.alpha.-olefin polymer (A) meeting the following requirements (a)
to (c) and 50 to 0 parts by weight of crystalline .alpha.-olefin
polymer (B) (the total of (A) and (B) being 100 parts by weight):
[0012] (a) The polymerization unit based on .alpha.-olefin having 3
to 20 carbon atoms is not less than 20 mol %. [0013] (b)
Practically no melt peak as measured by a differential scanning
calorimeter is observed. [0014] (c) The Mw/Mn is not more than
5.
[0015] The present invention also provides encapsulating material
for solar cells as claimed in claim 1., wherein the aforementioned
copolymer or its composition (I) is a non-crystalline or
low-crystalline .alpha.-olefin copolymer (D) having a crystallinity
of not higher than 40% as measured by use of X rays.
[0016] Encapsulating material for solar cells, wherein at least one
kind of additives selected from among cross-linking agents,
cross-linking aids, silane-coupling agents, antioxidants,
ultraviolet absorbers and light stabilizers is compounded to the
aforementioned copolymer or its composition (I) is a preferable
embodiment of the present invention.
[0017] Encapsulating material for solar cells, wherein the storage
elastic modulus at 150.degree. C. of the aforementioned copolymer
or its composition (I) is not lower than 10.sup.3 Pa is a
preferable embodiment of the present invention.
[0018] The present invention also provides a solar cell module that
can be obtained by using any of the aforementioned solar cell
encapsulating materials.
[0019] The present invention also provides a solar cell module,
wherein the aforementioned solar cell encapsulating material layer
is cross-linked.
EFFECT OF THE INVENTION
[0020] The present invention provides encapsulating material for
solar cells having excellent transparency, heat resistance,
flexibility and other properties.
[0021] The present invention provides encapsulating material for
solar cells which without requiring the use of any organic peroxide
makes possible a significant improvement in the efficiency in the
production of solar cell modules and a substantial reduction in the
manufacturing cost of solar cell modules.
[0022] According to the present invention, the use of the
non-crystalline or low-crystalline .alpha.-olefin-based copolymer
of the present invention or its composition (I) makes it possible
to provide encapsulating material for solar cells that will prevent
an occurrence of such troubles as the flow or deformation of the
encapsulating material and an impairment of the appearance of the
solar cell even when the temperature rises during the use of the
solar cell module.
[0023] The present invention provides a solar cell module using the
solar cell encapsulating material of the present invention which
shows excellent performance.
BEST EMBODIMENTS OF THE INVENTION
[0024] An explanation is given of encapsulating material for solar
cells comprising the non-crystalline or low-crystalline
.alpha.-olefin-based copolymer of the present invention or its
composition (I).
[0025] Given below are preferable examples of the non-crystalline
or low-crystalline .alpha.-olefin-based copolymer of the present
invention or its composition (I). As the first example, resin
composition (C) containing 50 to 100 parts by weight of
non-crystalline .alpha.-olefin polymer (A) meeting the following
requirements (a) through (c) and 50 to 0 parts by weight of
crystalline .alpha.-olefin polymer (B) (the total of (A) and (B)
being 100 parts by weight) can be cited: [0026] (a) The
polymerization unit based on .alpha.-olefin having 3 to 20 carbon
atoms is not less than 20 mol %. [0027] (b) Practically no melt
peak as measured by a differential scanning calorimeter is
observed. [0028] (c) The Mw/Mn is not more than 5.
[0029] The non-crystalline .alpha.-olefin polymer (A) that is used
in the present invention is a polymer containing not less than 20%,
preferably not less than 30%, of the monomer unit based on an
.alpha.-olefin having 3 to 20 carbon atoms, with the content of all
monomer units taken as 100 mol %. If the aforementioned content of
the monomer unit is too low, polymer (A) may show inferior
transparency and bleed resistance in some cases. Especially in the
light of heat resistance and transparency, a polymer having the
propylene unit content of not less than 30%, preferably not less
than 50%, particularly preferably not less than 80%, is preferably
used. Examples of the aforementioned .alpha.-olefin having 3 to 20
carbon atoms include straight-chain .alpha.-olefins such as
propylene, 1-butene, 1-pentene, 1-hexene 1-heptene, 1-octene,
1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene,
1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene,
1-octadecene, 1-nanodecene and 1-eicocene and branched
.alpha.-olefin such as 3-methyl-1-butene, 3-methyl-1-pentene,
4-methyl-1-pentene, 2-ethyl-1-hexene and 2,2,4-trimethyl-1-pentene.
These may be used in combination of two more of them.
[0030] The non-crystalline .alpha.-olefin polymer (A) may contain
monomer units other than the .alpha.-olefins having 3 to 20 carbon
atoms. As examples of such monomers, ethylene, polyen compounds,
cyclic olefins and vinyl aromatic compounds, for example, may be
cited. The content of such monomer is preferably not higher than 70
mol %, more preferably not higher than 50 mol %, particularly
preferably not higher than 20 mol %, wherein the total content of
all monomer in the non-crystalline .alpha.-olefin polymer refers as
100%.
[0031] The non-crystalline .alpha.-olefin polymer (A) is preferably
propylene homopolymer, propylene-ethylene copolymer, copolymer of
.alpha.-olefin other than propylene and propylene, copolymer of
.alpha.-olefin other than propylene, propylene and ethylene, more
preferably propylene homopolymer, propylene-ethylene copolymer,
propylene-1-butene copolymer, propylene-1-hexene copolymer,
propylene-ethylene-1-butene copolymer, propylene-ethylene-1-hexene
copolymer, further preferably propylene-1-butene copolymer,
propylene-ethylene-1-butene copolymer, most preferably
propylene-1-butene copolymer. The aforementioned polymers may be
used singly or in combination of not less than two of them.
[0032] The non-crystalline .alpha.-olefin polymer (A) is a polymer
whose melt peak is not practically observed when tested by a
differential scanning calorimeter (DSC). A polymer whose melt peak
is observed shows unsatisfactory transparency in some cases.
[0033] For the non-crystalline .alpha.-olefin polymer (A), an
.alpha.-olefin polymer whose molecular weight distribution (Mw/Mn),
a ratio between the weight-average molecular weight (Mw) and
number-average molecular weight (Mn) which are measured by
gel-permeation chromatography (GPC) with the standard polystyrene
used as the molecular weight standard substance, is not more than
5, preferably 1 to 4, is also used. If an .alpha.-olefin polymer
whose molecular weight distribution is too large, the bleed
resistance, transparency or other properties may be unsatisfactory
in some cases.
[0034] The non-crystalline .alpha.-olefin polymer (A) having such
properties as mentioned above can be manufactured by the slurry
polymerization process, solution polymerization process, mass
polymerization process, gas-phase polymerization process, etc.
using a metallocene catalyst. Examples of such metallocene catalyst
include those metallocene catalysts disclosed in Japanese Laid-open
Patent Applications SHO 58-19309, SHO 60-35005, SHO 60-35006, SHO
60-35007, SHO 60-35008,SHO 61-130314, HEI 3-163088, HEI 4-268307,
HEI 9,12790, HEI 9-87313, HEI 10-508055, HEI 11-80233 and Japanese
publication of International Application HEI 10-508055. As a
particularly preferably example of the manufacturing process using
a metallocene catalyst, a process disclosed in European Patent
Publication No.1211287 can be cited.
[0035] In the present invention, the crystalline .alpha.-olefin
polymer (B) which can be used together with non-crystalline
.alpha.-olefin polymer (A) is a polymer or copolymer of an
.alpha.-olefin having 2 to 10 carbon atoms whose crystallinity as
measured by use of X rays is not lower than 30%. In view of the
compatibility with non-crystalline .alpha.-olefin polymer (A),
transparency, heat resistance, etc., the use of propylene
homopolymer or random copolymer of propylene and another
.alpha.-olefin at a low ratio is preferable. Examples of the
.alpha.-olefin in such random copolymer include .alpha.-olefins
having 2 to 10 carbon atoms such as ethylene, 1-butene,
4-methyl-1-pentene, 1-hexene and 1-octene. Out of these, ethylene
and/or 1-butene is preferable. The random copolymer preferably has
the above .alpha.-olefin content of not higher than 10 wt %. The
aforementioned propylene homopolymer or random copolymer of
propylene is a homopolymer or random copolymer preferably showing a
melt peak of 120.degree. C. to 170.degree. C., particularly
preferably 150.degree. C. to 170.degree. C., as measured by a
differential scanning calorimeter (DSC) from the viewpoint of heat
resistance.
[0036] Such propylene homopolymer or random copolymer of propylene
and another .alpha.-olefin at a low ratio can be produced by
polymerizing propylene or copolymerizing propylene and
.alpha.-olefin in the presence of a stereoregular olefin
polymerization catalyst containing a titanium- or metallocene-based
transition metal compound component, an organic aluminum component,
and as required, an electron donor, a support, etc.
[0037] The solar cell encapsulating material of the present
invention uses resin composition (C) which comprises 50 to 100,
preferably 60 to 99, more preferably 70 to 95, parts by weight of
the aforementioned non-crystalline .alpha.-olefin polymer (A) and
50 to 0, preferably 40 to 1, more preferably 30 to 5, parts by
weight of the aforementioned crystalline .alpha.-olefin polymer (B)
(the total of (A) and (B) being 100 parts by weight). For resin
component (C), the kinds and compounding ratios of (A) and (B)
should be preferably so selected that it will show a melt peak (as
measured by a differential scanning calorimeter) of 120.degree. C.
to 170.degree. C., preferably 150.degree. C. to 170.degree. C.,
which is attributable to crystalline a-olefin polymer (B), storage
elastic modulus at 150.degree. C. of not lower than 10.sup.3 Pa,
JIS A hardness of 40 to 100, preferably 50 to 90, and haze of not
higher than 10%, preferably not higher than 5%, at the sheet
thickness of 0.5 mm.
[0038] As the second preferable example of the non-crystalline or
low-crystalline .alpha.-olefin-based copolymer of the present
invention or its composition (I), the non-crystalline or
low-crystalline .alpha.-olefin-based copolymer (D) whose
crystallinity as measured by use of X rays is not higher than 40%
can be cited.
[0039] The non-crystalline or low-crystalline .alpha.-olefin-based
copolymer (D) which is used as the encapsulating material of the
present invention is a copolymer having rubber properties which
uses not less than two kinds of .alpha.-olefin having 2 to 10
carbon atoms as the components and shows crystallinity of not
higher than 40% (0 to 40%) as measured by the X-ray diffraction
method. From the viewpoint of heat resistance, a copolymer showing
crystallinity of approximately 1 to 40%, such as a copolymer
falling under the category of what is called low-crystalline
copolymers, is preferably used rather than a completely
non-crystalline copolymer. However, any copolymer comprising
ethylene as the main component that is compounded with an organic
peroxide may be of the completely crystalline type (crystallinity:
0).
[0040] A representative example of such copolymer (D) is a
copolymer which comprises ethylene or propylene as the main
component, one or two or more other .alpha.-olefins having 2 to 10
carbon atoms as the accessory components and as required a small
amount of diene monomer.
[0041] Examples of the copolymers comprising ethylene as the main
component include those copolymers which contain a 50 to 90 mol %,
preferably 70 to 85 mol %, ethylene polymerization unit, a 50 to 10
mol %, preferably 30 to 15 mol % polymerization unit of
.alpha.-olefins other than ethylene, and as required not higher
than 2 mol %, preferably not higher than 1 mol %, diene monomer
polymerization unit. Examples of such ethylene-based copolymers
include ethylene-propylene copolymer, ethylene-1-butene copolymer,
ethylene-4-methyl-1-pentene copolymer, ethylene-1-hexene copolymer,
ethylene-1-octene copolymer, ethylene-propylene-dicychlopentadiene
copolymer, ethylene-propylene-5-ethylydene-2-norbornene copolymer,
and ethylene-propylene-1,6-hexadiene copolymer. Out of these,
ethylene-propylene copolymer, ethylene-propylene-diene copolymer or
ethylene-1-butene copolymer are particularly preferable.
[0042] Furthermore, examples of the copolymers comprising propylene
as the main component include those copolymers which contain a 70
to 95 mol %, preferably 72 to 90 mol %, propylene polymerization
unit, and a 5 to 30 mol %, preferably 10 to 28 mol % polymerization
unit of .alpha.-olefins other than propylene. Examples of such
propylene-based copolymers include propylene-ethylene copolymer and
propylene-1-butene copolymer.
[0043] For the aforementioned non-crystalline or low-crystalline
.alpha.-olefin-based copolymer (D), those .alpha.-olefin-based
copolymers which have a melt flow rate (MFR) of 0.1 to 50,
preferably 0.5 to 20, g/10 minutes, as measured at 230.degree. C.
under a load of 2,160 g by the method based on ASTM D-1238 is
preferably used from the viewpoint of moldability, mechanical
strength and other properties.
[0044] When the aforementioned non-crystalline or low-crystalline
.alpha.-olefin-based copolymer (D) is a copolymer comprising
ethylene as the main component, it can be manufactured by
copolymerizing ethylene and other .alpha.-olefins in the presence
of a vanadium catalyst comprising a soluble vanadium compound and
an organic aluminum halide, or metallocene catalyst comprising a
metallocene compound such as a cyclopentadienyl-coordinated
zirconium compound and an organic aluminumoxy compound.
Furthermore, in the case of a copolymer comprising propylene as the
main component, it can be manufactured by copolymerizing propylene
and other .alpha.-olefins in the presence of a stereoregular olefin
polymerization catalyst containing a transition metal compound
component such as a high-activity titanium catalyst component or a
metallocene catalyst component, an organic aluminum component, and
as required an electron donor, a support, etc.
[0045] In using the .alpha.-olefin-based copolymer of the present
invention as encapsulating material for solar cells, other polymers
and various additives may be compounded to it as required. Specific
examples of such additives include cross-linking agents,
cross-linking aids, tackifiers, silane coupling agents, ultraviolet
absorbers, hindered phenol-based and phosphite-based antioxidants,
hindered amine-based light stabilizers, light diffusion agents,
fire retardants, pigments (white pigment, for example), and
anti-discoloration agents. In the present invention, there is
normally no need for compounding a cross-linking agent or a
cross-linking aid to the non-crystalline or low-crystalline
.alpha.-olefin-based copolymer or its composition (I). However, if
a high degree of heat resistance is required, a cross-linking agent
or a cross-linking agent and an aid may be compounded. The
compounding of these makes it possible to cross-link the
non-crystalline or low-crystalline a-olefin-based copolymer or its
composition (I) with the encapsulating material incorporated into a
solar cell in such manner that the encapsulating material is in
contact with the solar cell and to endow the solar cell with such
heat resistance that will prevent the encapsulating material from
melting and flowing when the solar cell is used at high
temperature, while maintaining the transparency of the
encapsulating material layer.
[0046] For usable cross-linking agents, organic peroxides the
decomposition temperature (a temperature at which the half-life
period is one hours) of which is 70.degree. C. to 180.degree. C.,
particularly 90.degree. C. to 160.degree. C. are preferably used.
Examples of such organic peroxides include tertiary butyl peroxy
isopropyl carbonate, tertiary butyl peroxy acetate, tertiary butyl
peroxy benzoate, dicumyl peroxide, 2,5-dimethyl-2,5-bis(tertiary
butyl peroxy)hexane, ditertiary butyl peroxide,
2,5-dimethyl-2,5-bis(tertiary butyl
peroxy)hexine-3,1,1-bis(tertiary butyl peroxy)-3,3,5,-trimethyl
cyclohexane, 1,1-bis(tertiary butyl peroxy)cyclohexane,
methylethylketone peroxide, 2,5-dimethylhexyl-2,5-bisperoxybenzoate
tertiary butyl hydroperoxide, p-methane hydroperoxide, benzoyl
peroxide, p-chlorobenzoyl peroxide, tertiary butyl
peroxyisobutylate, hydroxyheptyl peroxide, and dichlohexanon
peroxide. An optimum compounding ratio of a cross-linking agent
varies with the types of cross-linking agent, but a ratio of 0.1 to
5 parts by weight, particularly 0.5 to 3 parts by weight, per 100
parts by weight of the non-crystalline or low-crystalline
.alpha.-olefin-based copolymer or its composition (I) is
effective.
[0047] Cross-linking aids are effective in accelerating
cross-linking reaction and raising the degree of the cross-linking
of a non-crystalline .alpha.-olefin-based copolymer comprising
ethylene as the main component. As specific examples of
cross-linking aids, poly unsaturated compounds such as polyallyl
compounds and poly(meth)acryloxy compounds can be cited. More
specific examples include polyallyl compounds such as triallyl
isocyanurate, triallyl cyanurate, diallyl phthalate, diallyl
fumarate and diallyl maleate, poly(meth)acryloxy compounds such as
ethylene glycol diacrylate, ethylene glycol dimethacrylate and
trimethlol propane trimethacrylate, and divinyl benzene. It is
effective for cross-linking aids to be compounded at a ratio of
approximately 0.5 to 5 parts by weight to 100 part by weight of the
non-crystalline or low-crystalline .alpha.-olefin-based copolymer
or its composition (I).
[0048] Silane coupling agents are useful for improving the adhesion
of the encapsulating material to the protective materials, solar
cells, etc. As examples of silane coupling agents, compounds having
hydrolysable groups such as the alkoxy group as well as unsaturated
groups of the vinyl group, acryloxy group and methacryroxy group,
the amino group and the epoxy group can be cited. Specific examples
of silane coupling agents include
N-(.beta.-aminoethyl)-.gamma.-aminopropyltrimethoxy silane,
N-(.beta.-aminoethyl)-.gamma.-aminopropylmethyidimethoxy silane,
.gamma.-aminopropyltriethoxy methoxy silane,
.gamma.-glycidoxypropyltrimethoxy silane, and
.gamma.-methacryloxypropyl triethoxy silane. A silane coupling
agent is preferably compounded at a ratio of 0.1 to 5 parts by
weight against 100 parts by weight of the non-crystalline or
low-crystalline .alpha.-olefin-based copolymer or its composition
(I).
[0049] As examples of the ultraviolet absorbers that can be added
to the solar cell encapsulating material of the present invention,
benzophenon-based, benzotriazol-based, triazine-based, salicyclic
ester-based and many other types can be cited. Examples of
benzophenon-based ultraviolet absorbers include
2-hydroxy4-methoxybenzophenone,
2-hydroxy-4-methoxy-2'-carboxybenzophenone,
2-hydroxy-4-octoxybenzophenone,
2-hydroxy-4-n-dodecyloxybenzophenone,
2-hydroxy-4-n-octadecyloxybenzophenone,
2-hydroxy-4-benzyloxybenzophenone,
2-hydroxy4-methoxy-5-sulfobenzophenon,
2-hydroxy-5-chlorobenzophenone, 2,4-dihydroxybenzophenone,
2,2'-dihydroxy-4-methoxybenzophenone,
2,2'-dihyroxy-4-4'-dimethoxybenzophenone, and
2,2'-4,4'-tetrahydroxy benzophenone.
[0050] Examples of benzotriazol-based ultraviolet absorbers include
hydroxyphenyl-substituted benzotriazol compound, such as
2-(2-hydroxy-5-methylphenyl) benzotriazol,
2-(2-hydroxy-5-t-butylphenyl) benzotriazol,
2-(2-hydroxy-3,5-t-dimethyl phenyl) benzotriazol,
2-(2-methyl-4-hydroxyphenyl) benzotriazol,
2-(2-hydroxy-3-methyl-5-t-butylphenyl) benzotriazol,
2-(2-hydroxy-3, 5-di-t-amylphenyl) benzotriazol and
2-(2-hydroxy-3,5-di-t-butylphenyl) benzotriazol. Furthermore,
examples of triazine-based ultraviolet absorbers include
2-[4,6-bis(2,4-dimethylphenyl)]-1,3,5-t-triazine-2-il]-5-(octyloxy)phenol-
, and 2-(4,6-diphenyl-1,3,5-tiazine-2-il)-5-(hexyloxy)phenol.
Examples of salicyclic ester-based absorbers include
phenylsalicylate and p-octylphenylsalicylate. The compounding
amount of an ultraviolet absorber is preferably 0 to 2 parts by
weight per 100 parts by weight of the non-crystalline or
low-crystalline .alpha.-olefin-based copolymer or its composition
(I).
[0051] Solar cell modules can be fabricated by using of the solar
cell encapsulating material of the present invention and by fixing
the solar cell element with top and bottom protective materials. As
examples of such solar cell modules, various types can be cited. As
examples of such solar cell modules, the following can be cited: a
solar cell module in which a solar cell element is sandwiched on
both sides by means of an encapsulating material in such manner as
a top transparent protective material/encapsulating material/solar
cell element /encapsulating material/bottom protective material, a
solar cell module having such structure that an encapsulating
material and a top transparent protective material are formed on a
solar cell element formed on the inner circumference of the bottom
substrate protective material, and a solar cell module in which an
encapsulating material and a bottom transparent protective material
are formed on a solar cell element formed on the inner
circumference of the top transparent protective material, such as
an amorphous solar cell element formed by sputtering or the like on
the transparent fluororesin-based protective material.
[0052] As examples of solar cell s elements , a wide variety of
solar cells elements can be cited, including solar cells based on
silicon such as single-crystal silicon, polycrystal silicon and
amorphous silicon and solar cells based on III-V-Group and
II-VI-Group compounds such as gallium-arsenic,
copper-indium-selenium and cadmium-tellurium.
[0053] As examples of the top protective material making up solar
cell modules, glass, acrylic resin, polycarbonate, polyester,
fluorine-containing resin, etc. can be cited. The bottom protective
material is a single-layer or multi-layer sheet made of metal or
various thermoplastic resin film, including metals such as tin,
aluminum and stainless steel, inorganic materials such as glass,
and single-layer or multi-layer protective materials made of
polyester, inorganic compound vapor deposition polyester,
fluorine-containing resin and polyolefin, for example. Primer
treatment may be done to top and/or bottom protective materials in
order to improve their adhesion with the encapsulating
material.
[0054] The solar cell encapsulating material of the present
invention is used normally in the form of a sheet approximately 0.1
to 1 mm in thickness. The solar cell encapsulating material in the
form of a sheet can be manufactured by the sheet forming method
known to the public using a T-die extruder, calendering equipment,
and other equipment. For example, a cross-linking agent,
cross-linking aid, silane coupling agent, ultraviolet absorber,
antioxidant, light stabilizer, etc., which are added as required
are dr.gamma.-blended in advance with a non-crystalline or
low-crystalline .alpha.-olefin-based copolymer or its composition
(I), fed from the hopper of a T-die extruder, and extruded to form
a sheet. Needless to say, at the time of such dry-blending, some or
all of the additives may be used in the form of masterbatch.
[0055] In the case of the first specific example of the
non-crystalline or low-crystalline .alpha.-olefin-based copolymer
of the present invention or its composition (I), encapsulating
material for solar cells in the form of a sheet which comprises
resin composition (C) can be manufactured by the sheet forming
method known to the public using a T-die extruder, calendering
equipment. For example, such an encapsulating material can be
formed by dry-blending crystalline .alpha.-olefin polymer (B), a
silane coupling agent, an ultraviolet absorber, an antioxidant, a
light stabilizer and other additives with non-crystalline
.alpha.-olefin polymer (A) as required and feeding them from the
hopper of a T-die extruder to extrude a sheet. It goes without
saying that it is possible to melt and mix non-crystalline
.alpha.-olefin polymer (A) and crystalline a-olefin polymer (B) in
advance or to produce composition (C) of both .alpha.-olefin
polymers by consecutive polymerization. At the time of such
dry-blending, some or all of the additives may be used in the form
of masterbatch.
[0056] In the case of the second specific example of the
non-crystalline or low-crystalline .alpha.-olefin-based copolymer
of the present invention or its composition (I), for example, a
cross-linking agent, cross-linking aid, silane coupling agent,
ultraviolet absorber, antioxidant, light stabilizer, etc., which
are added as required are dry-blended in advance with a
non-crystalline or low-crystalline .alpha.-olefin-based copolymer
(D), fed from the hopper of a T-die extruder, and extruded to form
a sheet. Needless to say, at the time of such dry-blending, some or
all of the additives may be used in the form of masterbatch.
Furthermore, in the T-die extrusion or calendaring, it is also
possible to use a resin composition obtained by melting and mixing
some or all of the additives together with the non-crystalline or
low-crystalline .alpha.-olefin-based copolymer or its composition
(I) beforehand by use of a single-screw extruder, twin-screw
extruder, Banbury mixer, kneader, etc.
[0057] In the manufacture of a solar cell module, it is possible to
form a module of a structure as described above by the method same
as the conventional method in which a sheet of the encapsulating
material for solar cell of the present invention is prepared in
advance and is press-bonded at a temperature at which the solar
cell encapsulating material melts. In this case, if any organic
peroxide is not compounded to the solar cell encapsulating
material, the molding of a sheet of the solar cell encapsulating
material can be carried out with high productivity at high
temperature, and it is possible to complete the formation of a
module in a short time and high temperature without having to go
through a two-step bonding process in the formation of a module.
Moreover, if a method in which a solar cell and the top protective
material or the bottom protective material are laminated by
extrusion-coating the solar cell encapsulating material of the
present invention is adopted, there is no need to bother to mold a
sheet, and it becomes possible to produce a solar cell module in a
single step. Therefore, the use of the solar cell encapsulating
material of the present invention makes it possible to improve
productivity in the manufacture of modules substantially
[0058] In the case of compound a peroxide to the solar cell
encapsulating material, what has to be done is only to bond the
solar cell encapsulating material tentatively to the solar cell and
the protective materials at a temperature at which the
cross-linking agent will not decompose but the encapsulating
material for solar cell of the present invention will melt and then
raise temperature to carry out the bonding of them adequately and
the cross-linking of the non-crystalline or low-crystalline
.alpha.-olefin-based copolymer. In this case, in order to ensure
that a solar cell module with satisfactory heat resistance showing
the melting point (DSC method) of the solar cell encapsulating
material of not lower than 85.degree. C. and showing with the
storage elastic modulus at 150.degree. C. being not lower than 103
Pa, the cross-linking of the non-crystalline or low-crystalline
.alpha.-olefin-based copolymer should preferably be carried so that
the gelation percent will be 50% to 98%, preferably 70% to 95% (by
immersing 1 g of the sample in 100 ml of xylene, heating it for 24
hours at 110.degree. C. and measuring the mass percent of the
undissolved filtrate filtrated through a 20-mesh wire netting).
Therefore, what has to be done is only to select those formations
of the additives which meet these conditions and to select the
types and compounding amounts of the additives, for example,
properly.
EXAMPLES
[0059] Given below is a detailed explanation of the present
invention using Examples. The present invention is not limited in
any way by these Examples.
[0060] The physical properties of the present invention were
determined by the following methods:
[0061] (1) Storage Elastic Modulus (E')
[0062] A 2-mm press-molded sheet was prepared under the conditions
of 15 minutes at 150.degree. C., and the storage elastic modulus of
the sheet was determined at 150.degree. C. under the following
conditions:
[0063] Equipment: DVE-V4 available from UBM
[0064] Testing mode: Pulling
[0065] Sample size: 30 mm.times.5 mm
[0066] Frequency: 10 Hz
[0067] Rate of temperature rise: 3.degree. C./min
[0068] Amplitude of vibration: 2 .mu.m
[0069] (2) Haze, Total Light Transmission
[0070] A 0.5-mm sheet was sandwiched with two sheets of 3-mm blue
glass and laminated for 15 minutes at 150.degree. C. by use of a
vacuum laminating machine. The haze and total light transmission
were measured by a method based on JIS K7105.
[0071] (3) 600 Slanting Test
[0072] A 0.5-mm sheet was sandwiched with a 3-mm blue glass plate
and an aluminum plate and laminated for 15 minutes at 150.degree.
C. by use of a vacuum laminating machine. The sample slanted at 600
at 100.degree. C. and then was observed for 500 hours as to whether
the sheet would melt and be brought into slippage from the
glass.
[0073] (4) Gel Percent
[0074] A 1-mm press-molded sheet was prepared under the conditions
of 30 minutes at 150.degree. C., and approx. 1 g of the sheet was
cut off and weighed accurately. The samples was immersed in 100 cc
of xylene and treated for 24 hours at 110.degree. C. After
filtration, the residues were dried and weighed accurately. The gel
percent was calculated by dividing the weight of the residues by
the weight measured before the treatment.
Example 1
[0075] A sheet 0.5 mm in thickness was prepared at a processing
temperature of 160.degree. C. by use of a profile extruder (screw
diameter: 40 mm; L/D=26; screw full flight: CR=2.6), using a resin
composition comprising 85 parts by weight of a non-crystalline
propylene polymer and 15 parts by weight of crystalline
polypropylene (trade name: Toughcellene T3512; available from
Sumitomo Chemical Co.; melt peak as measured by a differential
scanning calorimeter; 158.degree. C., JIS A hardness: 56). The
physical properties of the resultant sheet were measured. Results
are shown in Table 1. TABLE-US-00001 TABLE 1 Physical properties
Measurement value Haze (%) 6.8 Total light transmission (%) 83.2
Storage elastic modulus (Pa) at 150.degree. C. 1.0 .times. 10.sup.6
60.degree. slanting test (100.degree. C. .times. 1000 hrs) No
slippage/do discloration
Example 2
[0076] A sheet 0.5 mm in thickness was prepared at a processing
temperature of 160.degree. C. by use of a profile extruder (screw
diameter: 40 mm; L/D=26; screw full flight: CR=2.6), using a
non-crystalline or low-crystalline propylene-butene copolymer (PBR)
(available from Mitsui Chemicals, Inc.; a non-crystalline or
low-crystalline .alpha.-olefin-based copolymer; trade name: TAFMER
XR110T; melt flow rate (ASTM D1238): 3.2 g/10 min (190.degree. C.),
6.0 g/10 min (230.degree. C.); melting point: 110.degree. C.; Shore
D hardness: 56). The physical properties of the resultant sheet
were measured. Results are shown in Table 2.
Example 3
[0077] A sheet 0.5 mm in thickness was prepared by the same method
as described in Example 1 except that a mixture of the
propylene-butene-1 copolymer and an alicyclic tackifier (trade
name: Alcon AM-1; available from Arakawa Chemical Co.; softening
point: 125.degree. C.) in a weight ratio of 90:10 was used in place
of the propylene-butene-1 copolymer of examplel. The physical
properties of the resultant sheet were measured. Results are shown
in Table 2.
Example 4
[0078] A sheet 0.5 mm in thickness was prepared at a processing
temperature of 100.degree. C. by use of a profile extruder (screw
diameter: 40 mm; L/D=26; screw full flight: CR=2.6), using a
mixture of 100 parts by weight of a non-crystalline or
low-crystalline etylene-butene copolymer (EBR) (available from
Mitsui Chemicals, Inc.; a non-crystalline or low-crystalline
.alpha.-olefin-based copolymer; trade name: TAFMER A4085; melt flow
rate (ASTM D1238): 3.6 g/10 min (190.degree. C.), 6.7 g/10 min
(230.degree. C.); melting point: 72.degree. C.; JIS A hardness:
84), 1.5 parts by weight of
2,5-dimethyl-2,5-di(t-butylperoxy)hexane as a cross-linking agent,
and 2 parts by weight of triallylisocyanurate as a cross-linking
aid. The physical properties of the resultant sheet were measured.
Results are shown in Table 2.
Example 5
[0079] A sheet 0.5 mm in thickness was prepared by the same method
as described in Example 4 except that the amount of the
cross-linking agent was 1.2 parts by weight and the use of the
cross-linking accelerator was omitted. The physical properties of
the resultant sheet were measured. Results are shown in Table
2.
Example 6
[0080] A sheet 0.5 mm in thickness was prepared by the same method
as described in Example 5 except that a non-crystalline or
low-crystalline etylene-propylene copolymer (EPR) (available from
Mitsui Chemicals, Inc.; a non-crystalline or low-crystalline
.alpha.-olefin-based copolymer; trade name: TAFMER P0275; melt flow
rate (ASTM D1238): 2.5 g/10 min (190.degree. C.); melting point:
30.degree. C.; JIS A hardness: 56) was used in place of the
ethylene-butene-1 copolymer. The physical properties of the
resultant sheet were measured. Results are shown in Table 2.
TABLE-US-00002 TABLE 2 Example 2 Example 3 Example 4 Example 5
Example 6 Composition EBR 100 100 (parts by weight) EPR 100 PBR 100
90 Tackifier 10 Cross-linking agent 1.5 1.2 1.2 Cross-linking aid 2
Physical properties Haze (%) 5.8 3.8 1.8 1.9 2.8 Total light 87.1
87.2 90.4 90.4 90.1 transmission (%) Gelation percent (%) -- -- 92
82 80 Storage elastic 1.1 .times. 10.sup.5 8.5 .times. 10.sup.4 8.5
.times. 10.sup.4 7.9 .times. 10.sup.4 3.2 .times. 10.sup.4 modulus
(Pa) 60.degree. slating test No slippage/ No slippage/ No slippage/
No slippage/ No slippage/ discoloration discoloration discoloration
discoloration discoloration
POSSIBLILITY OF INDUSTRIAL USE
[0081] The encapsulating material for solar cell that is provided
by the present invention is encapsulating material for solar cells
showing excellent transparency, heat resistance, flexibility,
etc.
[0082] In the encapsulating material for solar cell that is
provided by the present invention the use of an organic peroxide is
not essential. For this reason, the encapsulating material for
solar cell makes it possible to improve productivity in the solar
cell module manufacturing process remarkably and reduce the solar
cell module manufacturing cost substantially.
[0083] The encapsulating material for solar cell that is provided
by the present invention has high storage elastic modulus at
150.degree. C., low haze and proper hardness. This makes it
possible to avoid troubles such as the flow or deformation of the
solar cell encapsulating material and an impairment of the
appearance even when the temperature rises during the use of the
solar cell module obtained from the solar cell encapsulating
material.
[0084] Furthermore, if a copolymer using ethylene as the main
component is selected for the non-crystalline or low-crystalline
.alpha.-olefin-based copolymer and a cross-linking agent is
compounded to such copolymer, there will be no such advantage in
the manufacturing process as described above but it will be
possible to form encapsulating material for solar cells layer
exhibiting excellent flexibility. This will make it possible to
fully cope with modules of smaller wall thickness.
[0085] According to the present invention, the use of the solar
cell encapsulating material of the present invention provides a
solar cell module showing excellent performance.
* * * * *