U.S. patent application number 11/830580 was filed with the patent office on 2008-01-31 for biocidal roofing granules, roofing products including such granules, and process for preparing same.
Invention is credited to Alexandra Dekoninck, Van Nhan Nguyen, Sophie Vanpoulle.
Application Number | 20080026183 11/830580 |
Document ID | / |
Family ID | 35431263 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080026183 |
Kind Code |
A1 |
Vanpoulle; Sophie ; et
al. |
January 31, 2008 |
BIOCIDAL ROOFING GRANULES, ROOFING PRODUCTS INCLUDING SUCH
GRANULES, AND PROCESS FOR PREPARING SAME
Abstract
Biocidal roofing granules include a mineral core covered with an
outer layer of mesoporous silica including photocatalytic
nanoparticles of anatase titanium dioxide as a biocide and an
optional organic biocide.
Inventors: |
Vanpoulle; Sophie;
(Gentilly, FR) ; Nguyen; Van Nhan; (Paris, FR)
; Dekoninck; Alexandra; (Ezanville, FR) |
Correspondence
Address: |
PAUL AND PAUL
2000 MARKET STREET
SUITE 2900
PHILADELPHIA
PA
19103
US
|
Family ID: |
35431263 |
Appl. No.: |
11/830580 |
Filed: |
July 30, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/FR2006/050296 |
Apr 4, 2006 |
|
|
|
11830580 |
Jul 30, 2007 |
|
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|
Current U.S.
Class: |
428/143 ;
427/212 |
Current CPC
Class: |
C09C 1/0081 20130101;
E04D 2001/005 20130101; Y10T 428/24388 20150115; C09C 3/006
20130101; Y10T 428/2438 20150115; C09C 3/08 20130101; C09C 3/12
20130101; E04D 13/002 20130101; C01P 2006/14 20130101; Y10T
428/24372 20150115; C09C 3/063 20130101; A01N 25/12 20130101; C01P
2006/12 20130101; A01N 25/34 20130101; A01N 25/12 20130101; A01N
43/80 20130101; A01N 25/34 20130101; A01N 43/80 20130101 |
Class at
Publication: |
428/143 ;
427/212 |
International
Class: |
B05D 7/00 20060101
B05D007/00; E01F 9/04 20060101 E01F009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 30, 2007 |
FR |
05 50 899 |
Apr 7, 2005 |
FR |
05 50 889 |
Claims
1. Biocidal roofing granules comprising: a mineral core; and an
exterior coating covering the mineral core; and at least one
biocidal photocatalytic metal oxide; the exterior coating including
at least one porous layer having a network of pores formed therein;
and the porous inorganic layer containing the at least one biocidal
photocatalytic metal oxide in the network of pores.
2. Biocidal roofing granules according to claim 1, wherein the at
least one porous layer comprises an inorganic material selected
from the group consisting of silica, alumina, zirconia and titania,
and mixtures thereof.
3. Biocidal roofing granules according to claim 2, wherein the at
least one porous layer has an average pore diameter of between 1 nm
and 100 nm.
4. Biocidal roofing granules according to claim 1, wherein the at
least one porous layer has a total pore volume of at least
0.5.times.10.sup.-3 cm.sup.3/g and less than 0.1 cm.sup.3/g for
pores having an average diameter less than 100 nm.
5. Biocidal roofing granules according to claim 4, wherein the at
least one porous layer has a total pore volume of between
0.7.times.10.sup.-3 cm.sup.3/g and 1.times.10.sup.-2 cm.sup.3/g for
pores having an average diameter less than 76 nm.
6. Biocidal roofing granules according to claim 1, wherein the at
least one porous layer has an average thickness no greater than
about 40 .mu.m.
7. Biocidal roofing granules according to claim 1, wherein the at
least one porous layer has an average thickness between about 0.5
.mu.m and 10 .mu.m.
8. Biocidal roofing granules according to claim 1, wherein the at
least one porous layer has an average thickness between about 1
.mu.m and 5 .mu.m.
9. Biocidal roofing granules according to claim 1, wherein the
photocatalytic metal oxide is selected from the group consisting of
photocatalytic titanium oxide, photocatalytic copper oxide,
photocatalytic vanadium oxide, and photocatalytic zinc oxide, and
mixtures thereof.
10. Biocidal roofing granules according to claim 9 further
comprising at least one metal selected from the group consisting of
Pt, Au, Os, Pd, Ni, Sn, Cu, Fe, Mn, Rh, Nb, and Ru, and mixtures
thereof.
11. Biocidal roofing granules according to claim 1, wherein the
photocatalytic metal oxide comprise from about 0.1 to 10 percent by
weight of the exterior covering.
12. Biocidal roofing granules according to claim 1, wherein said
granules further comprise a second biocidal composition selected
from the group consisting of inorganic biocides and organic
biocides.
13. A process for preparing biocidal roofing granules, the process
comprising: (a) providing a mineral core; (b) preparing a
gel-forming inorganic coating medium; (c) providing at least one
biocidal photocatalytic metal oxide; (d) coating the mineral core
with the inorganic sol; (e) forming a porous coating layer on the
mineral core from the inorganic sol, the porous coating layer
having a pore network; and (f) disposing the at least one
photocatalytic metal oxide in the pore network.
14. A process according to claim 13 wherein the gel-forming
inorganic coating medium is selected from the group consisting of
silica sol-gels, colloidal silica media, colloidal zirconia media,
colloidal titania media, and colloidal alumina media
15. A process according to claim 13 wherein the coating medium is
an aqueous suspension prepared from at least one precursor selected
from the group consisting of alkylsilanes, alkoxysilanes, zirconium
oxychloride, zirconium alkoxides, titanium chloride, titanium
alkoxides, aluminum chloride, aluminum alkoxides, sodium silicate,
potassium silicate, pyrogenic silica, pyrogenic alumina, pyrogenic
titania, pyrogenic zirconia, and mixtures thereof.
16. A process according to claim 15 wherein the at least one
precursor is selected from the group consisting of
tetramethoxysilane, tetraethoxysilane, and methyl
triethoxysilane.
17. A process according to claim 13, wherein the coating medium
further comprises the at least one biocidal photocatalytic
material.
18. A process according to claim 13 wherein the biocidal roofing
granules further comprise a second biocidal composition selected
from the group consisting of inorganic biocides and organic
biocides
19. A process according to claim 13 wherein the porous coating
network is formed by drying the coating medium.
20. A process according to claim 13 wherein the coating medium
further comprises at least one sacrificial template material.
21. A process according to claim 20 wherein the sacrificial
template material is selected from the group consisting of
multiblock polyalkylene oxide materials, polyvinyl alcohol, and
quaternary ammonium salts.
22. A process according to claim 20 wherein the sacrificial
template material is a
polyethyleneoxide-polypropyleneoxide-polyethyleneoxide triblock
material.
23. A process according to claim 20 wherein the sacrificial
template material is cetyl trimethylammonium bromide.
24. A process according to claim 19 wherein the coating medium is
dried out at a temperature between about 10 and 100.degree. C.,
preferably between 20 and 80.degree. C.
25. A process according to claim 13, wherein the coating medium
further includes a sacrificial template material, and wherein
forming the porous network comprises calcining the sol at a
temperature from about 200.degree. C. to 1000.degree. C., before
disposing the at least one photocatalytic metal oxide in the porous
network.
26. A process according to claim 25 wherein the sacrificial
template material is an organic polymer.
27. A process according to claims 13 wherein the at least one
photocatalytic metal oxide is disposed in the porous inorganic
layer by applying a suspension of the at least one photocatalytic
material in a liquid carrier material to the porous inorganic
layer, and evaporating the carrier material.
28. A roofing shingle including roofing granules according to claim
1.
29. A roofing shingle according to claim 28 wherein the mass of
roofing granules per unit of area is between about 0.5 and 2.5
kg/m.sup.2.
30. A roofing shingle according to claim 29, wherein the roofing
granules including the at least one photocatalytic metal oxide
comprise from about 0.1% to 10% by weight of the total weight of
roofing granules.
31. A roofing product including a biocidal coating, the roofing
product comprising: a base material; and an exterior coating
covering the base material; the exterior coating including at least
one porous layer having a network of pores formed therein; the
porous inorganic layer containing at least one biocidal
photocatalytic metal oxide in the network.
32. A roofing product according to claim 31, wherein the at least
one porous layer comprises an inorganic material selected from the
group consisting of silica, alumina, zirconia and titania, and
mixtures thereof.
33. A roofing product according to claim 31, wherein the porous
layer has an average pore diameter of between 1 nm and 100 nm.
34. A roofing product according to claim 31, wherein the at least
one porous layer has a total pore volume of at least
0.5.times.10.sup.-3 cm.sup.3/g and less than 0.1 cm.sup.3/g for
pores having an average diameter less than 100 nm.
35. A roofing product according to claim 31, wherein the at least
one porous layer has a total pore volume of between
0.7.times.10.sup.-3 and 1.times.10.sup.-2 cm.sup.3/g for pores
having an average diameter less than 76 nm.
36. A roofing product according to claim 31, wherein the at least
one porous layer has an average thickness no greater than about 40
.mu.m.
37. A roofing product according to claim 31, wherein the at least
one porous layer has an average thickness between about 0.5 .mu.m
and 10 .mu.m.
38. A roofing product according to claim 31, wherein the at least
one porous layer has an average thickness between about 1 .mu.m and
5 .mu.m.
39. A roofing product according to claim 31, wherein the
photocatalytic metal oxide is selected from the group consisting of
photocatalytic titanium oxide, photocatalytic copper oxide,
photocatalytic vanadium oxide, and photocatalytic zinc oxide, and
mixtures thereof.
40. A roofing product according to claim 31 further comprising a
metal selected from the group consisting of Pt, Au, Os, Pd, Ni, Sn,
Cu, Fe, Rh, Nb, and Ru, and mixtures thereof.
41. A roofing product according to claim 31, wherein the
photocatalytic metal oxide comprise from about 0.1 to 10 percent by
weight of the exterior covering.
42. A roofing product according to claim 31, wherein the biocidal
coating further comprises a second biocidal composition selected
from the group consisting of inorganic biocides and organic
biocides.
43. A roofing product according to claim 31, wherein the base
material is selected from the group consisting of roofing shingles,
roofing membranes and roofing granules.
44. A process for preparing roofing materials, the process
comprising: (a) providing a base material; (b) preparing a
gel-forming inorganic coating medium; (c) providing at least one
biocidal photocatalytic metal oxide; (d) coating the base material
with the inorganic coating medium; (e) forming a porous coating
layer on the mineral core from the inorganic coating medium, the
porous coating layer having a pore network; and (f) disposing the
at least one photocatalytic metal oxide in the pore network.
45. A process according to claim 44 wherein the gel-forming
inorganic coating medium is selected from the group consisting of
silica sol-gels, colloidal silica media, colloidal zirconia media,
colloidal titania media, and colloidal alumina media
46. A process according to claim 44 wherein the coating medium is
an aqueous suspension prepared from at least one precursor selected
from the group consisting of alkylsilanes, alkoxysilanes, zirconium
oxychloride, zirconium alkoxides, sodium silicate, potassium
silicate, titanium chloride, titanium alkoxides, aluminum chloride,
aluminum alkoxides, pyrogenic silica, pyrogenic alumina, pyrogenic
titania, pyrogenic zirconia, and mixtures thereof.
47. A process according to claim 46 wherein the at least one
precursor is selected from the group consisting of
tetramethoxysilane, tetraethoxysilane, and methyl
triethoxysilane.
48. A process according to claim 46, wherein the coating medium
further comprises the at least one biocidal photocatalytic metal
oxide.
49. A process according to claim 46 wherein the porous coating
network is formed by drying the coating medium.
50. A process according to claim 46 wherein the coating medium
further comprises at least one sacrificial template material.
51. A process according to claim 50 wherein the sacrificial
template material is selected from the group consisting of
multiblock polyalkylene oxide materials, polyvinyl alcohol, and
quaternary ammonium salts.
52. A process according to claim 50 wherein the sacrificial
template material is a
polyethyleneoxide-polypropyleneoxide-polyethyleneoxide triblock
material.
53. A process according to claim 50 wherein the sacrificial
template material is cetyl trimethylammonium bromide.
54. A process according to claim 46 wherein the coating medium
further comprises a second biocidal composition selected from the
group consisting of inorganic biocides and organic biocides.
55. A process according to claim 46 wherein the coating medium is
dried out at a temperature between about 10 and 100.degree. C.
56. A process according to claim 55 wherein the coating medium is
dried out a temperature between about 20 and 80.degree. C.
57. A process according to claim 55 wherein the coating medium
comprises a sacrificial template and the sacrificial template
material comprises an organic polymer.
58. A process according to claim 55 wherein the at least one
photocatalytic metal oxide is disposed in the porous inorganic
layer by applying a suspension of the at least one photocatalytic
material in a liquid carrier material to the porous inorganic
layer, and evaporating the carrier material.
59. A process according to claim 46 wherein the base material is
selected from roofing shingles, roofing membranes and roofing
granules.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation-in-part of
International Application No. PCT/FR2006/050296, filed Apr. 4,
2006, and designating the United States, which application claims
the priority of French Patent Application No. 05 50 899 filed Apr.
7, 2005.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention refers to roofing granules and roofing
products having biocidal activity.
[0004] 2. Brief Description of the Prior Art
[0005] Asphalt shingles are conventionally used in the United
States and Canada as roofing and siding materials.
[0006] Asphalt shingles can be classified into two types of
shingles according to the nature of the reinforcement. "Organic"
shingles contain cellulose or wood fiber as a thick fiber felt.
"Glass fiber" shingles contain a nonwoven mat of glass fibers held
together by a binder that is insoluble in water.
[0007] In the manufacture of organic shingles, a continuous web of
organic fiber felt is fed from a supply roll to an accumulating
device made up of several rollers, and then immersed in a first
liquid asphalt bath having a temperature of about 250.degree. C.
After leaving the first liquid asphalt bath, the felt passes
through a second accumulating device so that the felt can absorb
excess asphalt and cool slightly. The so-impregnated felt is then
coated with molten asphalt on each of its two faces, which
ultimately become respectively the upper and lower faces of the
web. Roofing granules are distributed on the upper face, and an
anti-adhesive agent, for example, talc, is applied to the lower
face. The resulting web passes between the rollers of a cold
calendar so as to partially embed the roofing granules in the hot
asphalt layer on the upper face of the web, and the subsequently
cooled product is collected in the form of rolls or of sheets cut
to the desired dimensions.
[0008] Except for the first stage of impregnation, which is
omitted, the manufacture of the glass fiber shingles is carried out
in the same way.
[0009] In the shingle, the asphalt functions principally to make
material impervious to water. It is also used to support the
granules and to give strength to the material. The highly ductile
character of the asphalt-impregnated felt makes it possible to
obtain a flexible product. In general, the longevity of the shingle
increases with the quantity of asphalt employed.
[0010] The roofing granules, in general formed from mineral
materials, serve to provide the shingle with durability. They
protect the asphalt from the effects of the solar radiation (in
particular from the degradative effects of ultraviolet rays) and of
the environment (wind, precipitation, pollution, and the like), and
contribute to better reflection of incident radiation. The granules
moreover are typically colored, naturally or artificially by way of
the application of pigments, to meet the aesthetic requirements of
the user.
[0011] However, it is not unusual to see unattractive green, brown
or black spots appearing on the surface of asphalt shingles of
buildings located in temperate climates. These spots are due to
micro-organisms, mainly algae of the Gloeocapsa genus which benefit
from conditions favorable to their growth found in temperate
climates. These conditions include heat, moisture and nutrients.
The essential biogenic salts may be provided by the mineral
granules themselves, but also may be supplied by organic matter
which settles on the shingles. The unattractiveness of these spots,
all the more noticeable when the color of the shingle is a light
one, is not the only disadvantage. In addition, the resulting
darkening of the surface causes an increase in the absorption of
the solar radiation, which in turn reduces the effectiveness of the
shingles as thermal insulation, and decreases its service life.
[0012] To address this problem, algae-contaminated shingles can be
treated with suitable biocides. However, the complete elimination
of the algae is difficult, and requires the treatment of the entire
building, including seemingly healthy surfaces. Even by using a
powerful biocide such as sodium hypochlorite, the prophylactic
effect is not permanent, because the roof is subsequently scrubbed
by weather-borne water. Moreover, certain green algae particularly
resistant to biocides can re-colonize previously treated surfaces,
thus requiring additional treatments, at regular intervals, to
limit their reappearance.
[0013] Other methods known to prevent the appearance of the
undesirable algae growth are based on the incorporation of
algaecide in the shingle. For example, it has been suggested that
granules include metal compounds in the form of zinc oxide or
sulfide (U.S. Pat. No. 3,507,676), or copper oxide (U.S. Pat. No.
5,356,664), or that a mixture copper oxide and zinc oxide (U.S.
Patent Publication 2002/0258835 and U.S. Patent Publication
2002/0255548) be incorporated in the asphalt.
[0014] It has also been suggested to disperse a granular or
pulverulent material containing an algaecide on the surface of the
shingle (JP-A-2004162482).
[0015] U.S. Pat. No. 6,245,381 suggests adding a biocide in the
form of salt or of chelate starting from Cu.sup.2+, Zn.sup.2+ and
Sn.sup.2+ ions complexed with an organic binder anion in asphalt
during the manufacture of the shingle.
[0016] Another approach has been to employ photocatalytic particles
as biocidal agents. The photocatalytic effect has been employed to
provide self-cleaning glass and other ceramic materials. For
example, U.S. Pat. No. 6,037,289 discloses a substrate provided
with photocatalytic anatase titanium dioxide that is at least
partially crystalline, and has a mean size of between 5 and 80 nm.
The coating can include an inorganic binder, such as an amorphous
or partially crystalline oxide, or mixture of oxides, such as
oxides of silicon, titanium, tin, zirconium or aluminum, which can
serve as a matrix for the photocatalytic titanium oxide.
Alternatively, a partly organic binder can be used, such as a
binder based on epoxide-containing alkoxysilanes. Similarly, U.S.
Pat. No. 6,465,088 discloses a substrate such as a glass or
acrylate glazing material covered with a photocatalytic coating
including crystallized particles having photocatalytic properties
and a mineral binder comprising at least one oxide of a metal
having photocatalytic properties. U.S. Pat. Nos. 6,569,520 and
6,881,702 disclose a photocatalytic composition and method for
preventing algae growth on building materials such as roofing
granules. A plurality of photocatalytic particles, such as anatase
titanium dioxide, is dispersed in a silicate binder to form an
exterior coating for a substrate such as a roofing granule or
concrete surface. At least a portion of some of the photocatalytic
particles is exposed on the surface of the coating.
[0017] There is a continuing need to prevent the appearance of
undesirable algae growth on roofing shingles and other roofing
materials.
SUMMARY OF THE INVENTION
[0018] In one aspect, the present invention provides biocidal
roofing granules comprising a mineral core and an exterior coating
covering the mineral core. The exterior coating includes at least
one porous layer having a network of pores formed therein, and the
porous inorganic layer contains at least one biocidal
photocatalytic metal oxide in the network of pores. Preferably, the
at least one porous layer is a mesoporous layer. Optionally, the
exterior coating also includes at least one non-photocatalytic
metal oxide, and/or at least one biocidal organic compound to
limit, or to prevent, the growth of micro-organisms, in particular
the growth of algae. The present invention also provides a process
for preparing such biocidal roofing granules. The present invention
also provides roofing products, including roofing shingles which
include such biocidal roofing granules.
[0019] In another aspect, the present invention provides roofing
products including a biocidal coating, such as roofing shingles.
These roofing products according to the present invention comprise
a base material, such as a conventional roofing shingle, and an
exterior coating covering the base material. The exterior coating
includes at least one porous layer having a network of pores formed
therein; and the porous inorganic layer contains at least one
biocidal photocatalytic metal oxide in the network. Optionally, the
exterior coating also includes at least one non-photocatalytic
metal oxide, and/or at least one biocidal organic compound to
limit, or to prevent, the growth of micro-organisms, in particular
the growth of algae. The present invention also provides a process
for preparing such roofing products.
[0020] Preferably, the at least one porous layer comprises an
inorganic material selected from the group consisting of silica,
alumina, zirconia and titania, and mixtures thereof.
[0021] It is also preferred that the porous layer have an average
pore diameter of between 1 nm and 100 nm. Preferably, the at least
one porous layer has a total pore volume of at least
0.5.times.10.sup.-3 cm.sup.3/g for pores having an average diameter
less than 100 nm, and that the total pore volume is less than 0.1
cm.sup.3/g for pores having an average diameter less than 100 nm.
More preferably, the at least one porous layer has a total pore
volume of between 0.7.times.10.sup.-1 and 1.times.10.sup.-1
cm.sup.3/g for pores having an average diameter less than 76 nm.
Preferably, the at least one porous layer has an average thickness
no greater than about 40 .mu.m, more preferably no greater than 20
.mu.m, and still more preferably the at least one porous layer has
an average thickness between 0.5 .mu.m and 10 .mu.m, and even more
preferably, the at least one porous layer has an average thickness
between 1 .mu.m and 5 .mu.m.
[0022] It is preferred that the at least one photocatalytic metal
oxide be selected from the group consisting of photocatalytic
titanium oxide, photocatalytic copper oxide, photocatalytic
vanadium oxide, and photocatalytic zinc oxide, and mixtures
thereof. Photocatalytic titanium dioxide is especially preferred.
The at least one photocatalytic metal oxide can be optionally
dispersed in the at least one porous layer in combination with a
metal such as Pt, Au, Os, Pd, Ni, Sn, Cu, Fe, Mn, Rh, Nb, or Ru,
for example.
[0023] Preferably, the at least one photocatalytic metal oxide
comprises from about 1 to 60 percent by weight of the at least one
porous layer. Preferably, the at least one photocatalytic metal
comprise from about 1 to 20 percent by weight of the exterior
covering including the at least one porous layer.
[0024] In the biocidal granules according to the invention, the
mineral core serves as a support for the porous layer, which
includes the at least one photocatalytic metal oxide. The at least
one photocatalytic metal oxide provides an antimicrobial or
biocidal effect. In addition, the porous layer forms, to some
extent, a reservoir for the at least one optional additional
biocide, such as an organic biocidal compound or an inorganic
biocidal compound, which can thus diffuse towards outside. In the
roofing products including a biocidal coating, the porous layer
provides similar functions as a carrier for the at least one
photocatalytic metal oxide and as a reservoir for the optional at
least one additional biocide.
[0025] Because of the antimicrobial effect of the at least one
photocatalytic metal oxide, it is possible to reliably control the
growth of micro-organisms.
[0026] Preferably, the at least one photocatalytic metal oxide
comprises from about 1 to 60 percent by weight of the at least one
porous layer. Preferably, the at least one photocatalytic metal
comprise from about 1 to 20 percent by weight of the exterior
covering including the at least one porous layer.
[0027] The optional at least one organic or inorganic biocidal
compound further increases the flexibility and usefulness of this
approach, permitting the controlled release of the organic biocidal
compound, so that the roofing products can be tailored to specific
local conditions.
[0028] The porous layer comprises an inorganic material, preferably
an oxide of a metal or a metalloid, and is more preferably selected
from the group consisting of silica, alumina, zirconia and titanium
oxide, and mixtures thereof. Preferably, the porous layer comprises
silica.
BRIEF DESCRIPTION OF THE FIGURES
[0029] FIG. 1 is a schematic illustration of a first type of
biocidal roofing granule according to the present invention.
[0030] FIG. 2 is a schematic illustration of a second type of
biocidal roofing granule according to the present invention.
[0031] FIG. 3 is a schematic illustration of a third type of
biocidal roofing granule according to the present invention.
[0032] FIG. 4 is a photograph showing a comparison of the
photocatalytic effect of biocidal roofing granules according to the
present invention with control granules.
[0033] FIG. 5 is a photograph of roofing shingle of the present
invention illustrating the photocatalytic activity of a mesoporous
coating on the shingle.
[0034] FIG. 6 is a graph showing the photocatalytic effect of two
embodiments of roofing granules according to the present
invention.
[0035] FIG. 7 is a graph showing the photocatalytic effect of an
embodiment of roofing granules according to the present
invention.
[0036] FIG. 8 is a graph showing the photocatalytic effect of an
embodiment of roofing granules according to the present
invention.
DETAILED DESCRIPTION
[0037] Preferably, the at least one porous layer is mesoporous. By
"mesoporous" is meant having an average pore diameter from about 5
nm to about 50 nm.
[0038] As used in the present specification, the strength in color
space E is defined as E=(L.sup.2+a.sup.2+b.sup.2).sup.1/2, where L,
a, and b are the color measurements for a given sample using the
1976 CIE Lab color space. The total color difference .DELTA.E is
defined as
.DELTA.E=(.DELTA.L.sup.2+.DELTA.a.sup.2+.DELTA.b.sup.2).sup.. . .
where .DELTA.L, .DELTA.a, and .DELTA.b are respectively the
differences in L, a and b for two different color measurements.
[0039] Referring now to the drawings, in which like reference
numerals refer to like elements in each of the several views, there
are shown schematically in FIGS. 1-3 examples of biocidal roofing
granules according to the present invention.
[0040] FIG. 1 is a schematic representation of a first type of
biocidal roofing granule 10 of the present invention. FIG. 1
schematically illustrates a biocidal granule 10 including an inert
mineral core particle 12 covered with a mesoporous coating layer 14
composed of an inert porous inorganic matrix 16 and at least one
photocatalytic metal oxide 18 contained therein and at least
partially protruding through the exterior surface of the mesoporous
coating layer 14.
[0041] FIG. 2 is a schematic representation of a second type of
biocidal roofing granule 20 of the present invention. FIG. 2
schematically illustrates a biocidal granule 20 including an inert
mineral core particle 22 covered with a color coating layer 24,
which in turn is covered with an outer mesoporous coating layer 26
composed of an inert porous inorganic matrix 28 and at least one
photocatalytic metal oxide 30 contained therein and at least
partially protruding through the exterior surface of the mesoporous
coating layer 26.
[0042] FIG. 3 is a schematic representation of a third type of
biocidal roofing granule 40 of the present invention. FIG. 3
schematically illustrates a biocidal granule 40 including an inert
mineral core particle 42 covered with a color coating layer 44,
which in turn is covered with an inner mesoporous coating layer 46,
which in turn is covered with an outer mesoporous coating layer 50
composed of an inert porous inorganic matrix 52 and at least one
photocatalytic metal oxide 54 contained therein and at least
partially protruding through the exterior surface of the outer
mesoporous coating layer 50. The biocidal granule 40 also includes
at least one organic biocide or inorganic biocide distributed in
the pore network of the inner mesoporous coating layer 46 and the
outer mesoporous coating layer 50.
[0043] The mineral core can consist of any chemically inert matter,
which can be used as support to the at least one porous inorganic
layer, and having moreover mechanical properties enabling the
mineral core to resist the various operations implemented during
the manufacture of the asphalt shingles. For examples, the mineral
core can be formed from materials available in the natural state,
such as talc, granite, siliceous sand, andesite, porphyry, marble,
syenite, rhyolite, diabase, quartz, slate, basalt, sandstone, and
marine shells, as well as material derived from recycled
manufactured goods, such as bricks, concrete, and porcelain.
[0044] The mineral core can be provided as granules, generally
obtained by crushing above mentioned materials and sifting of the
products obtained, having a size of particle, taken in its greatest
dimension, ranging between about 0.2 and 3 mm, preferably between
about 0.4 mm and 2.4 mm, and more preferably about 1 mm. The
mineral core can have a form approaching that of a sphere, but it
can also have the shape of a plate, i.e. of a relatively planar
element of little thickness compared to its surface.
[0045] Preferably, the mineral core has a low porosity, defined in
particular as having an average pore volume less than about
1.times.10.sup.-3 cm.sup.3/g measured for pores having an average
diameter of less than 70 nm.
[0046] Preferably, the average mass of the particles forming the
mineral core generally lies between about 0.05 mg and 15 mg, and
preferably between about 0.3 mg and 7 mg.
[0047] Before being covered by the at least one porous exterior
inorganic layer, the mineral core can undergo one or more
operations to provide a color coating, in particular by the
application of one or more layers of colored coating including a
binder, such as an alkali metal silicate, and one or more compounds
of the color desired, for example selected among the pigments of
metallic oxides and the carbon black. The techniques for
application of such colored layers are well-known in the roofing
granule art. The colored coating layer can also include at least
one non-photocatalytic metal oxide, such as copper oxide, zinc
oxide, or a mixture thereof, as an optional additional biocidal
material.
[0048] In addition, the mineral core can be covered with one or
more intermediate coating layers between the mineral core and the
at least one porous exterior inorganic layer. These intermediate
coating layers can be formed from a binder, such as an alkali metal
silicate binder, such as sodium silicate or potassium silicate, and
at least one non-photocatalytic metal oxide, such as copper oxide,
zinc oxide, or a mixture thereof, as an optional additional
biocidal material. Preferably, such intermediate coating layers are
provided between the mineral core and the color coating layer.
[0049] Further, the mineral core can be covered with one or more
intermediate porous coating layers between the mineral core and the
at least one porous exterior inorganic layer. The at least one
intermediate porous coating layers can serve as a reservoir for the
optional at least one organic biocide.
[0050] The biocidal granules can comprise moreover at least one
blocking coating layer covering in whole or in part the at least
one intermediate porous layer. The blocking coating layer functions
to delay the diffusion of the optional organic biocide from the
intermediate porous coating layer. Although the blocking coating
layer is permeable to the optional organic biocide, the blocking
coating layer preferably has a porosity less than that of the
subjacent porous layer containing the optional organic biocide.
Preferably, the porosity of the blocking coating layer is less by
at least 20%, and more preferably less than 50%, than that of the
intermediate coating porous layer containing optional organic
biocide.
[0051] The blocking coating layer can comprise inorganic material,
for example of comparable nature to that which constitutes the at
least one intermediate porous layer, or in the alternative, the
blocking coating layer can comprise organic material, preferably an
organic polymeric material such as a polyacrylate, polyurethane, or
silane-terminated polyurethane or fluoropolymer.
[0052] The outermost coating layer covering the mineral core is
preferably the at least one porous layer which includes the at
least one photocatalytic metal oxide. This at least one outer
porous layer preferably has an average pore diameter ranging from
about 1 nm to 100 nm, and more preferably between about 2 nm and 50
nm. It is especially preferred that the average pore diameter of
this at least one outer porous layer be about 5 nm.
[0053] The at least one outer porous layer preferably has a total
pore volume of at least about 0.5.times.10.sup.-3 cm.sup.3/g for
pores less than 100 nm in average diameter, and preferably less
than about 0.1 cm.sup.3/g for pores less than 100 nm in average
diameter. Preferably, the at least one outer porous layer has a
total pore volume ranging from about 0.7.times.10.sup.-3 cm.sup.3/g
to 1.times.10.sup.-2 cm.sup.3/g for pores less than about 76 nm in
average diameter. More preferably, the at least one outer porous
layer has a total pore volume of about 1.25.times.10.sup.-3
cm.sup.3/g for pores less than about 76 nm in average diameter.
[0054] The specific surface of the at least one outer porous layer
is preferably greater than about 1 m.sup.2/g, preferably, the
specific surface area of the porous layer is from about 1.25
m.sup.2/g to 100 m.sup.2/g.
[0055] The at least one outer porous layer has an average thickness
with most equal to about 20 .mu.m, preferably ranging between 0.5
and 10 gm, advantageously between 1 and 5 .mu.m. The outer porous
layer can be made up of one or more sublayers, preferably from 1 to
3 sublayers, with each such sublayer having a thickness of from
about 1 .mu.m to 2 .mu.m.
[0056] The optional organic biocide, which can be provided in the
optional at least one intermediate porous inorganic layer, can be
selected from organic compounds known to limit or prevent the
development of micro-organisms. For example, the at least one
optional biocide can be an aldehyde, a condensate of formaldehyde,
a triazine, a phenol, an ester of carbonic acid, an amide, a
carbamate, a thiocarbamate, a thiocyanate, a dibenzamidine, a
derivative of pyridine, a triazole, a thiazole, an isothiazolone
such as the isothiazolin-3-one, an N-haloalkylthio compound, or a
mixture of these compounds. Preferred organic biocides are
isothiazolin-3-ones, in particular, 2-n-octyl-4-isothiazolin-3-one
(OIT), and 4,5-dichloro-2-(n-octyl)-4-isothiazolin-3-one
(DCOIT).
[0057] Such optional organic biocides include optional organic
biocides, such as aldehyde, triazine, phenol, amide, carbamate,
thiocarbamate, thiocyanate, dibenzamidine, triazole, thiazole,
isothiazolone, N-haloalkylthiozolone, and mixtures thereof.
[0058] The amount of the optional organic biocide in the granule
depends on the nature and the characteristics of intermediate
inorganic porous layer(s), in particular the thickness and of the
volume of pores available. In general, the quantity of biocide can
be up to about 4 percent by weight of the granule, preferably up to
about 2.5 percent, and more preferably up to about 1 percent.
Depending on the thickness of the at least one porous layer, the
biocide can also be coated outside the at least one porous layer,
and the quantity of biocide can be up to about 10 percent by weight
of the granule, preferably up to about 8 percent by weight of the
granule.
[0059] The present invention also provides a process for preparing
biocidal roofing granules. This process includes the steps of
providing a mineral core, preparing a gel-forming inorganic coating
medium, providing at least one biocidal photocatalytic metal oxide,
coating the mineral core with the gel-forming inorganic coating
medium, forming a porous coating layer on the mineral core from the
sol of inorganic precursor material, the porous coating layer
having a pore network; and disposing the at least one
photocatalytic metal oxide in the pore network.
[0060] The gel-forming inorganic coating medium can be a
gel-forming inorganic sol. Preferably, the gel-forming inorganic
coating medium is a sol selected from the group consisting of
silica sol-gels, colloidal silica media, colloidal zirconia media,
colloidal titania media, and colloidal alumina media.
[0061] In one embodiment of the present invention, the biocidal
roofing granules are prepared by treating the mineral core with a
sol of inorganic precursor ready to form the porous layer. The sol
includes an inorganic precursor material, a template material for
forming the pore network, and the at least one photocatalytic metal
oxide.
[0062] Formation of the porous inorganic material from the
inorganic precursor material by the sol-gel method is well-known in
the art. As is understood in the art, a "sol" is a dispersion of
colloidal particles dispersed in a liquid; and by "gel" is a
network of polymeric chains. Conventionally, the sol-gel method as
applied to film formation on a target surface is understood to
include the steps of forming a sol of colloidal particles of
inorganic precursor material dispersed in a liquid carrier;
applying the sol of colloidal particles to surface to be covered
(i.e. film deposition); gelling the mixture on the surface so as to
form a three-dimensional network of colloidal particles and a
network of pores (i.e. a xerogel), and eliminating the liquid phase
to obtain a thickening or the chemical stabilization of the network
of pores and formation of a film on the surface to be covered. The
physics and chemistry of the sol-gel method are reviewed in C.
Jeffrey Binker et al., Sol-Gel Science (Academic Press, Boston
1990), incorporated herein by reference. The sol of inorganic
precursor material can also include a sacrificial template
material, which is removed after film formation to provide the pore
network. In the absence of a template material, control of the size
and extent of aggregation of the colloidal particles of inorganic
precursor material during film deposition, and control of the
relative rates of condensation and evaporation of the liquid
carrier, determines the characteristics of the pore network so
formed, including the pore volume of the coating layer, the pore
size, and the surface area of the pores. Conversely, when a
template material is included in the sol of inorganic precursor
material, the nature and amount of the template material affect the
characteristics of the pore network obtained. For example, in the
present process, templated mesoporous silica films or coating
layers are synthesized through a solution phase process involving
the association of a surfactant or block copolymer templating
material with silica precursor materials that occurs during
evaporation of the solvent employed. During film formation, it is
believed that a liquid crystalline structure having nano-scale
periodicity is formed. This structure is subsequently solidified by
condensation of the silica precursor material, and the templating
material is subsequently removed to provide the pore structure,
such as by calcination or extraction.
[0063] According to one presently preferred embodiment, the
biocidal granules of the present invention are obtained by treating
a substrate of mineral core with a sol including the inorganic
precursor, then drying at a temperature ranging between 20 and 80
degrees C., preferably between 40 and 70 degrees C., and more
preferably between 50 and 65 degrees C. This embodiment makes it
possible to obtain in a single stage a granule with microporous
coating layer, that is, a coating layer having a pore diameter
ranging between about 0.5 and 2 nm, and preferably about 1 nm.
[0064] According to another presently preferred embodiment, the
biocidal granules are obtained in a multiple step process, the
process comprising treating the substrate or mineral core with a
sol of inorganic precursor including a templating material or
structuring agent to form a coating layer on the surface of the
substrate, and subsequently calcining the coating layer at a
sufficient temperature to eliminate the structuring agent.
[0065] In one aspect of the process of the present invention, the
substrate employed is simply the mineral core, and a single
mesoporous coating layer is formed on the surface of the substrate.
In this case, the sol includes both the inorganic precursor
material and the at least one photocatalytic metal oxide as well as
a templating material. In this case the templating material can be
removed by calcination at an elevated temperature. Templating
materials that are removable by calcination at an elevated
temperature include organic surfactants as well as organic polymers
and block copolymers.
[0066] In another aspect of the process of the present invention,
the substrate employed is a conventional colored roofing granule,
and a single mesoporous coating layer is formed on the surface of
the colored roofing granule. In this case, the sol includes both
the inorganic precursor material and the at least one
photocatalytic metal oxide as well as a templating material. In
this case, the templating material can be removed by calcination at
an elevated temperature.
[0067] In yet another aspect of the process of the present
invention, the substrate employed is an algae-resistant roofing
granule, and a single mesoporous coating layer is formed on the
surface of the algae-resistant roofing granule. Algae-resistant
roofing granules typically include at least one non-photocatalytic
algaecidal metal oxide, preferably copper oxide and/or zinc oxide,
in at least one coating layer on their mineral cores.
Algae-resistant roofing granules are disclosed, for example, in
U.S. Pat. Nos. 3,507,676, 4,092,441, 5,356,664, 6,124,466 each
incorporated herein by reference. In this case, the sol includes
both the inorganic precursor material and the at least one
photocatalytic metal oxide as well as a templating material. In
this case, the templating material can be removed by calcination at
an elevated temperature.
[0068] In another aspect of the process of the present invention,
the substrate employed, which can be a mineral core, a conventional
colored roofing granule, or an algae-resistant roofing granule, is
covered with a sodium ion barrier layer prior to application of the
single mesoporous coating layer to the surface of the substrate. As
is known in the art, sodium ions tend to interfere with or "poison"
the beneficial photocatalytic action of the at least one
photocatalytic metal oxide. The preparation and deposition of
sodium ion barrier coating is disclosed, for example, in U.S. Pat.
Nos. 6,362,121 and 6,465,088, each incorporated herein by
reference.
[0069] In still another aspect of the process of the present
invention, the substrate employed, which can be a mineral core, a
conventional colored roofing granule, or an algae-resistant roofing
granule, or a substrate including a sodium ion barrier layer, is
first coated with one or more initial or inner mesoporous coating
layers, which may optionally include the at least one
photocatalytic metal oxide. Preferably, however, in this aspect of
the process of the present invention, the one or more inner
mesoporous layers does not include the at least one photocatalytic
metal oxide, and is instead provided to increase the ultimate
thickness of the mesoporous network on the exterior of the
substrate. In this case, the sol includes both the inorganic
precursor material and the at least one photocatalytic metal oxide
as well as a templating material. In this case, the templating
material can be removed by calcination at an elevated temperature.
In this case, an optional organic biocide can be introduced into
the porous network subsequent to formation of the pore network.
Since it is preferred that the at least one photocatalytic metal
oxide be present in the outermost layer of the biocidal particles,
this aspect of the process of the present invention provides for a
porous network to serve as a reservoir for the optional organic
biocide, while reducing the proportion of the at least one
photocatalytic metal oxide present in the interior of the porous
network, and thus making more efficient use of the at least one
photocatalytic metal oxide.
[0070] In another aspect of the present invention, the substrate
comprises a roofing material, such as the upper or outer surface of
a roofing shingle surfaced with roofing granules, such as
conventional colored roofing granules, algae-resistant roofing
granules, or a mixture thereof, or such a roofing material covered
with an optional initial or inner mesoporous layer, and an outer
mesoporous coating layer is formed on the substrate. In this case,
the sol for producing the outer mesoporous coating includes both
the inorganic precursor material and the at least one
photocatalytic metal oxide as well as a templating material. In
this case the templating material cannot be removed by calcination
at an elevated temperature, because the roofing material typically
includes bituminous material which could be degraded, damaged or
destroyed by exposure to temperatures sufficient to calcine the
templating material. In this case, the templating material is
preferably selected so that the templating material can be removed
by an alternative method. For example, a surfactant material that
is removable from the porous network by an extraction method can be
chosen as the templating material. In the alternative, the
templating material can be a templating material that is
photocatalytically degradable, and is photocatalytically degraded
by the at least one photocatalytic metal oxide, such as titanium
dioxide, embedded in the at least one porous inorganic layer.
[0071] By structuring agent (or template), is understood an organic
material promoting the creation of pores in the inorganic matter
network. This organic material can be broken up by calcination at a
temperature greater than about 200.degree. C., and preferably less
than about 100.degree. C., advantageously ranging between about
400.degree. C. and 700.degree. C., and more preferably at about
450.degree. C.
[0072] Example of structuring agents or templating materials
include organic polymers such as copolymers, such as
poly(alkyleneoxide) block copolymers, and in particular,
poly(oxyethylene)-(oxypropylene)-(oxyethylene) triblock copolymers,
and quaternary ammonium salts such as cetyltrimethylammonium
bromide.
[0073] Examples of block copolymer structuring agents are
amphiphilic poly(alkylene oxide) block copolymers including
triblock copolymer in which relatively hydrophilic blocks, such as
linear poly(oxyethylene) blocks extend from either end of a central
linear hydrophobic block, such as a poly(oxypropylene) block or a
poly(oxybutylene) block. Preferably, the hydrophilic blocks have a
degree of polymerization of at least 5 and the central hydrophobic
block has a degree of polymerization of at least 30. The use of
triblock copolymers as templating agents is discussed, for example,
in D. Zhao et al., Science, 279 (1998) 548-552, incorporated herein
by reference.
[0074] Examples of surfactant structuring agents include
cetylpyridinium chloride, cetylpyridinium bromide,
cetyltrimethylammonium chloride, cetyltrimethylammonium bromide,
cetyldimethylethylammonium bromide, stearyltrimethylammonium
chloride, stearyltrimethylammonium bromide,
myristyltrimethylammonium chloride, myristyltrimethylammonium
bromide, lauryltrimethylammonium chloride, lauryltrimethylammonium
bromide, decyltrimethylammonium chloride, decyltrimethylammonium
bromide, and mixtures thereof.
[0075] The proportion of the structuring agent or templating
material employed depends on the degree of desired degree of
porosity and the desired pore size. In general, the structuring
agent comprises from about 20 to 80% of the weight of the inorganic
precursor, and preferably 40 to 70% of the weight of the inorganic
precursor.
[0076] When an optional organic biocide is to be introduced into
the porous network, the selection of the structuring agent used to
form the porous network should be determined by taking into
consideration the size of optional organic biocide molecule to be
introduced into the pores. Preferably, the size of the pores is
greater then the size of the optional organic biocide molecule.
[0077] The process of the present invention makes it possible to
obtain a mesoporous layer of porosity containing pores having an
average diameter ranging between about 2 and 50 nm, and preferably
having an average diameter of less than 10 nm.
[0078] In a first alternative, the optional organic biocide is
applied in the form of a solution to the exterior porous inorganic
layer. Preferably, the solution includes both the optional organic
biocide and a volatile solvent, preferably a volatile organic
solvent. The volatile solvent is removed after application of the
solution to porous layer, for example by evaporation according to
any known method. Examples of volatile organic solvents that can be
employed include alkanes, in particular cyclohexane, alcohols, in
particular ethanol, ketones, in particular acetone, and chlorinated
compounds, in particular methylene chloride. Water based organic
solvent azeotropes with suppressed boiling points can also be
employed. The biocide solution can be applied by spraying, or by
immersing the substrate including the porous layer in the solution
including the optional organic biocide.
[0079] In a second alternative, the optional organic biocide is
included in a sol containing the inorganic precursor, which can be
the same or differ from that which is used to obtain the porous
inorganic layer on the substrate. Preferably, the substrate
including the porous inorganic layer is immersed in the sol
including the optional organic biocide, and the solvent is
subsequently removed by drying.
[0080] When a sol is employed in the process of the present
invention, the sol can be prepared in any manner known in the art
sufficient to provide a gel-forming sol material that can be
further processed into a mesoporous inorganic coating. For example,
the sol can be a silica sol prepared by an ion exchange technique
such as by passing sodium silicate through an proton-exchanging
ion-exchange column, a silica sol prepared by an organic reaction
technique, such as by mixing tetraethoxysilane and ethanol followed
by the addition of base, by an inorganic reaction technique, such
as by mixing solutions of ammonium chloride and sodium silicate or
potassium silicate followed by removal and the electrolyte and
redispersion of the sol, and the like.
[0081] When a sol is employed in the process of the present
invention, the sol is preferably an aqueous suspension prepared
from one or more organic precursors selected from alkylsilanes, and
alkoxysilanes, including tetralkoxysilanes such as
tetramethoxysilane (TMOS), tetraethoxysilane (TEOS),
tetra-n-propoxysilane, tetra-n-butaoxysilane, and
tetrakis(2-methoxyethoxy)silane; organotrialkoxysilanes such as
methyltriethoxysilane (MTEOS), methyltrimethoxysilane, methyl
tri-n-propoxysilane, phenyl triethoxysilane, and vinyl
triethoxysilane, siloxane oligomers such as hexamethoxydisiloxane,
and octamethoxytrisiloxane; aluminum alkoxides such as aluminum
tributoxide, titanium alkoxides such as titanium tetraethoxide and
titanium tetraisopropoxide, zirconium alkoxides such as zirconium
tetraethoxide, aluminum chloride, zirconyl chloride, and the like.
Conventionally, the sol is treated with acid, preferably at a
temperature ranging between about 20 and 100.degree. C. and in the
presence of an alcohol such as ethanol, for sufficient length of
time to obtain the conversion of the inorganic precursor into
corresponding metallic oxide.
[0082] In the alternative, when a sol is employed in the present
invention, the sol can be prepared by dispersing a pyrogenic
material in a suitable liquid medium. Examples of pyrogenic
materials include pyrogenic silica made by flame oxidation such as
those available under the Aerosil and Cab-O-Sil trademarks,
pyrogenic titania, pyrogenic alumina, pyrogenic zirconia, and
mixtures thereof. By "pyrogenic material" is meant a material
generated during a high energy process, such as in a furnace at an
elevated temperature, in a flame, in a laser beam, in a particle
beam such as an electron beam, in a plasma, or the like. Examples
of suitable liquid media include water and other polar solvents. In
addition, the sol can be prepared from a combination of one or more
pyrogenic materials and at least one organic precursor, such as
alkylsilanes, and alkoxysilanes, including tetralkoxysilanes such
as tetramethoxysilane (TMOS), tetraethoxysilane (TEOS),
tetra-n-propoxysilane, tetra-n-butaoxysilane, and
tetrakis(2-methoxyethoxy)silane; organotrialkoxysilanes such as
methyltriethoxysilane (MTEOS), methyltrimethoxysilane, methyl
tri-n-propoxysilane, phenyl triethoxysilane, and vinyl
triethoxysilane, siloxane oligomers such as hexamethoxydisiloxane,
and octamethoxytrisiloxane; aluminum alkoxides such as aluminum
tributoxide, titanium alkoxides such as titanium tetraethoxide and
titanium tetraisopropoxide, zirconium alkoxides such as zirconium
tetraethoxide, aluminum chloride, zirconyl chloride, and the
like.
[0083] In another aspect, the present invention provides biocidal
mesoporous polymeric coatings. The preparation of mesoporous
polymeric coating materials is disclosed, for example, in U.S. Pat.
No. 6,537,703, incorporated herein by reference.
[0084] In the alternative, powder coating materials can be employed
to provide a porous exterior coating on the roofing granules or
roofing products, or as a base coating for a mesoporous coating
layer including at least one biocide. Powder coating materials are
typically dry, solid powder materials that include a polymeric
resinous binder with a melting temperature above ambient
temperature and optional pigments, extenders, flow control agents,
and/or other additives. Powder coating materials or compositions
for use in the present invention preferably include both a
polymeric binder and at least one biocidal material.
[0085] Suitable powder coating material should have excellent
outdoor durability; a melting temperature for application of
between 66 degrees C.-204 degrees C. (150 degrees F.-400 degrees
F.); and low viscosity upon melting to completely impregnate the
tie-layer in a relatively short period of time. By "low viscosity"
is meant a viscosity of from about 50 centipoise to 3000
centipoise.
[0086] Examples of suitable powder coating compositions include
thermoplastic and thermoset powder coating compositions.
Thermoplastic powder coating compositions are frequently employed
to provide coating of at least about 250 microns. Thermosetting
powder coating compositions are frequently employed to provide
thinner coatings, such as coatings with a thickness of from about
20 to 80 microns. Suitable powder coating polymeric materials
include, but are not limited to, acrylic and related copolymers,
polyesters, polyamides, epoxies, polyolefin and its alloys,
polypropylene, acid containing polyolefins such as polyethylene
acrylic acid or polyethylene methacrylic acid, polyvinyl chloride,
polyester block amide, ethylene chlorotrifluorethylene, or
polyvinylidene fluoride. Examples of thermosetting materials
include epoxy, polyester, and acrylic thermosetting materials.
Examples of thermoplastic materials include polyamide,
polyethylene, polypropylene, polyvinyl chloride, polyester, and
polyvinylidene fluoride thermoplastic materials.
[0087] Preferably, a powder coating composition having good
exterior durability and weatherability characteristics is employed.
Examples of powder coating compositions providing coatings with
good exterior durability include thermoplastic polyester
compositions, thermoplastic polyvinylidene fluoride compositions,
thermosetting polyester compositions such as hydroxyalkylamide
polyesters, thermosetting epoxy resin compositions, thermosetting
epoxy-polyester hybrid coating compositions, thermosetting
polyester-triglycydyl isocyanurate compositions, thermosetting GMA
acrylic compositions, thermosetting acrylic urethane compositions,
and thermosetting polyester urethane compositions.
[0088] Powder coating compositions for use in the present invention
are preferably provided with at least one biocidal material. In
addition, powder coating compositions for use in the preparative
process of the present invention can include other components, such
as curing agents or hardeners, extenders, and additives such as
thixotropes, flow modifiers, and the like.
[0089] The biocidal granules of the invention can be used to
control the development of micro-organisms in particular of algae
in roofing material to limit the appearance of unappealing blotches
and spots on the roofing materials. The roofing material can be an
organic asphalt shingle, containing fibers of wood or cellulose, or
a glass fiber reinforced shingle or roofing membrane.
[0090] The coating compositions used in preparing the biocidal
granules can include other components, such as conventional metal
oxide colorants of the type employed in the manufacture of roofing
granules, solar heat-reflective pigments such as titanium dioxide,
other biocidal materials, and the like.
[0091] The biocidal granules prepared according to the process of
the present invention can be employed in the manufacture of
biocidal roofing products, such as biocidal asphalt shingles, using
conventional roofing production processes. Typically, bituminous
roofing products are sheet goods that include a non-woven base or
scrim formed of a fibrous material, such as a glass fiber scrim.
Bituminous roofing products are typically manufactured in
continuous processes in which a continuous substrate sheet of a
fibrous material such as a continuous felt sheet or glass fiber mat
is immersed in a bath of hot, fluid bituminous coating material so
that the bituminous material saturates the substrate sheet and
coats at least one side of the substrate. Thus, the substrate is
coated with one or more layers of a bituminous material such as
asphalt to provide water and weather resistance to the roofing
product. The reverse side of the substrate sheet can be coated with
an anti-stick material such as a suitable mineral powder or a fine
sand. The upper side of the roofing product is typically coated
with mineral granules to provide durability, reflect heat and solar
radiation, and to protect the bituminous binder from environmental
degradation. The roofing granules are typically distributed over
selected portions of the upper side of the substrate, and the
bituminous material serves as an adhesive to bind the roofing
granules to the sheet when the bituminous material has cooled.
[0092] The biocidal granules of the present invention can be mixed
with conventional roofing granules, and the granule mixture can be
embedded in the surface of such bituminous roofing products using
conventional methods. The biocide granules can be mixed with
untreated granules to comprise about 10 percent by weight of the
total granule weight, and preferably, less than 10 percent by
weight.
[0093] Alternatively, biocidal granules of the present invention
can be substituted for conventional roofing granules in the
manufacture of bituminous roofing products to provide those roofing
products with resistance to biological discoloration and
degradation. One or more classes of the biocidal granules can be
applied sequentially to the roofing product surface, followed by
application of conventional roofing granules. In one embodiment of
the process of the present invention, a first class of biocidal
granules is first applied to the surface of the roofing product,
followed by application of a second class of biocidal granules,
followed finally by application of conventional roofing granules.
In another embodiment, one or more classes of the biocidal granules
can be pre-mixed and applied simultaneously to the surface of the
roofing product. In another embodiment of the present invention, a
mixture of two or more classes of biocidal granules is first
applied to the surface of the roofing product, followed by
application of conventional roofing granules. Given the order of
application, any excess granules that are not successfully embedded
in the surface of the roofing product are likely to be conventional
granules. Thus, the order of application of these embodiments of
the process of the present invention is likely to permit more
precise loading of the roofing product surface with the classes of
biocidal granules than otherwise. In another embodiment of the
present invention, biocidal granules may be employed to cover a
substantial portion of, or substantially all of the roofing product
surface, or of the exposed portion of the roofing product
surface.
[0094] The roofing product sheet can be cut into conventional
shingle sizes and shapes (such as one foot by three feet
rectangles), slots can be cut in the shingles to provide a
plurality of "tabs" for ease of installation and aesthetic effects,
additional bituminous adhesive can be applied in strategic
locations and covered with release paper to provide for securing
successive courses of shingles during roof installation, and the
finished shingles can be packaged. More complex methods of shingle
construction can also be employed, such as building up multiple
layers of sheets in selected portions of the shingle to provide an
enhanced visual appearance, or to simulate other types of roofing
products. Release strips can also be strategically applied to the
shingles so as to line up with sealing adhesive so that stacked
shingles can be packaged without the need for separate release
paper covers for the additional adhesive. It will be noted that the
roofing product sheet can also be retained in substantially larger
format sizes such as, for example 3 feet by 30 feet or more for
membrane or roll roofing product applications.
[0095] The bituminous material used in manufacturing roofing
products according to the present invention is derived from a
petroleum processing by-product such as pitch, "straight-run"
bitumen, or "blown" bitumen. The bituminous material can be
modified with extender materials such as oils, petroleum extracts,
and/or petroleum residues. The bituminous material can include
various modifying ingredients such as polymeric materials, such as
SBS (styrene-butadiene-styrene) block copolymers, resins, oils,
flame-retardant materials, oils, stabilizing materials, anti-static
compounds, and the like. Preferably, the total amount by weight of
such modifying ingredients is not more than about 15 percent of the
total weight of the bituminous material. The bituminous material
can also include amorphous polyolefins, up to about 25 percent by
weight. Examples of suitable amorphous polyolefins include atactic
polypropylene, ethylene-propylene rubber, etc. Preferably, the
amorphous polyolefins employed have a softening point of from about
130 degrees C. to about 160 degrees C. The bituminous composition
can also include a suitable filler, such as calcium carbonate,
talc, carbon black, stone dust, or fly ash, preferably in an amount
from about 10 percent to about 70 percent by weight of the
bituminous composite material.
[0096] In asphalt shingles, the mass of roofing granules per unit
of area generally lies between 0.5 and 2.5 kg/m.sup.2, preferably
between 1 and 2 kg/m.sup.2.
[0097] The examples which follow make it possible to illustrate the
invention without however limiting it.
EXAMPLE 1
a) Preparation of the Granules
[0098] Base granules having the following characteristics are
employed:
[0099] White colored roofing granules (Product No. 93, commercially
available from CertainTeed Corporation) having a white color
coating (2.7% by weight titanium oxide) are used as the base
granules with an average diameter of 1 mm, and average mass of 1.26
mg, a specific surface BET of 0.37 m.sup.2/g, and a total pore
volume (diameter<69 nm) of 6.07.times.10.sup.-4 cm.sup.3/g.
[0100] A sol is prepared using 22.3 ml of tetraethoxysilane (TEOS
from Aldrich-Sigma, 99%); 22.1 ml of an ethanolic solution of 10%
v/v of 2-n-octyl-4-isothiazolin-3-one (OIT; 0.2 M); and 9 ml of
hydrochloric acid to give a pH of 1.25. The sol is subjected to
hydrolysis at 60 degrees C. for 1 hour.
[0101] 50 g of base granules are immersed in the sol for 15
minutes. The resulting suspension is filtered and the granules are
washed with water, and are dried at 60.degree. C. for 2 hours. The
resulting biocidal granules included 0.7% by weight OIT (as
determined by thermogravimetry).
b) Preparation of Roofing Material
[0102] A test sample of roofing material is prepare by depositing
on an aluminum plate (L=10 cm; W=3.75 cm) a plaque prepared from a
mixture of asphalt (32% in weight) and of calcium carbonate (68% in
weight) about the same size as the aluminum plate and having a
thickness of 1.6 mm. The test sample is heated at 150 degrees C.,
and a granule mixture is distributed on asphalt (1.61 kg/m.sup.2),
and partially embedded in the asphalt using a roller with a 14 cm
diameter (3 passages). The granule mixture includes untreated
granules (90% in weight), and biocidal granules prepared as
described in a) above (10% in weight).
c) Biocidal Activity
[0103] The biocidal activity of the biocidal granules is measured
as follows:
[0104] Gloeocapsa sp. (UTEX LB 795) is cultivated in flasks of 1
liter containing 500 ml of Allen medium, under constant
ventilation, at 22 degrees C., under fluorescent light (340-380
nm). The culture is agitated (50-70 RPM; 5 to 10 minutes) at
regular intervals (3 or 4 days). After 20 days of culture, the
medium contains about 1.times.10.sup.6 spores/ml.
[0105] The medium containing the spores is atomized on samples of
test sample, on the face containing the granules at a distance of
approximately 4 cm. Each sample is placed in a Petri dish (relative
moisture higher than 80%) laid out in a drying oven at 22 degrees
C. under the above mentioned conditions of illumination. The
samples receive a quantity of sufficient Allen medium daily to
ensure the survival of the algae.
[0106] Counting of living cells is carried out via fluorescence
microscopy (enlargement .times.200). 10 measurements distributed on
the whole of the surface of the sample are taken. From these
measurements, the rate of survival=(number of alive cells at time
T/number of alive cells to T=0).times.100 is calculated. The
results appear in the Table 1, which indicates the rate of survival
of the cells for various times of incubation in the presence of
biocidal granules according to the invention (Example 1) and of
untreated granules (control).
EXAMPLE 2
[0107] The process of Example 1 is repeated with the following
modifications as follows.
[0108] Preparation of the Granules
[0109] A sol containing 17.8 g of methyltriethoxysilane (MTEOS,
Aldrich-Sigma), 5.4 g of hydrochloric acid (pH 2.5) and 13.8 g of
ethanol is prepared. The hydrolysis of the sol is carried out at
ambient temperature (25.degree. C.) over 2 hours.
[0110] 10 ml of sol and 20 ml of an ethanolic solution containing
1.864 g of polyether triblock (ethylene oxide) 73--(propylene
oxide) 28--(ethylene oxide) 73 (Pluronic PE6800 marketed by BASF)
are mixed to provide a coating material.
[0111] 50 g of the untreated granules of Example 1 are plunged in
the coating mixture for 15 minutes. The resulting suspension is
filtered and the granules are calcined in a furnace under the
following conditions:
[0112] To calcine the granules, the temperature is elevated from 25
degrees C. to 100 degrees C. over a 30 minutes period, and
maintained at 100 degrees C. for 2 hours. The temperature is then
elevated from 100 degrees C. to 150 degrees C. over a 15 minute
period, and maintained at 150 degrees C. during 2 hours. The
temperature is then raised from 150 degrees C. to 175 degrees C.
over a 15 minute period and maintained at 175 degrees C. for 2
hours. The temperature is then raised from 175 degrees C. to 200
degrees C. over a 10 minute period, and then raised from 200
degrees C. to 300 degrees C. over a 300 minute period, and
maintained at 300 degrees C. for 1 hour. The temperature is then
raised from 300 degrees C. to 450 degrees C. over a 150 minute
period, and maintained at 450 degrees C. for 1 hour.
[0113] The cooled calcined granules are submerged in the sol of
Example 1 and are treated under the same conditions.
[0114] The granules show the following characteristics-- [0115]
surface BET: 1.66 m.sup.2/g [0116] total volume of pores
(diameter<76 nm): 1.25.times.10.sup.-3 cm.sup.3/g [0117]
thickness of the porous layer: 2 .mu.m [0118] content of OIT
(measured by thermogravimetry): 0.7% in weight.
[0119] The results of measurements of the biocidal activity appear
in Table 1.
EXAMPLE 3
[0120] Example 2 is repeated except that the amount of OIT is
increased to 0.4% by weight. The results of measurements of the
biocidal activity appear in Table 1.
EXAMPLE 4
[0121] Granules are prepared as in Example 2. After calcination and
cooling, the granules are submerged in a solution of OIT with 10%
v/v in cyclohexane for 4 days at the ambient temperature (20-25
degrees C.). The resulting mixture is filtered and the resulting
biocidal granules are washed with cyclohexane and then dried at 60
degrees C. for 2 hours. The dried granules contain 2.52% in weight
of OIT. TABLE-US-00001 TABLE 1 Rate of survival (%) T = 5 days T =
8 days T = 14 days T = 19 days Ex. 1 2.17 0 0 0 Ex. 2 0.8 0 0 0 Ex.
3 6.46 0 0 0 Control 51.11 34.22 27.11 31.55 Reference 4.91 0 0
0
[0122] The granules of the Examples 1 to 3 prepared according to
the process of the present invention exhibit a biocide activity
shown by a rate of algae survival which is less than for the
control not containing a biocide. The rate of survival of the algae
is strongly reduced after 5 days and is vanished after 8 days of
incubation.
[0123] This survival rate is comparable to that obtained by using a
mixture of granulated particles containing 10% of copper oxide
loaded granules (Algae Block.TM. Copper Roofing Granules marketed
by 3M) ("Reference" in Table 1).
EXAMPLE 5
[0124] Granules are prepared as follows:
[0125] A sol A containing 10 g of tetraethoxysilane (TEOS,
Aldrich-Sigma), 4.3 g of hydrochloric acid (pH 2.5) and 8.34 g of
ethanol is prepared. The hydrolysis of the sol is carried out at 60
degrees C. for 1 hour.
[0126] A solution B of 3.85 g of 3.85 g of polyether triblock
(ethylene oxide) 73---(propylene oxide) 28--(ethylene oxide) 73
(Pluronic PE or EP 6800, BASF) in 40.29 g of ethanol is
prepared.
[0127] The solution A is added to solution B, followed by addition
of 33.33 g of 15% aqueous dispersion of titanium oxide
nanoparticles (S5-300A from Millennium, used as received)
[0128] 50 g of the untreated granules of Example 1 are plunged in
the coating mixture for 15 minutes. The resulting suspension is
filtered and the coated granules are calcined in a furnace under
the following conditions:
[0129] To calcine the granules, the temperature is elevated from 25
degrees C. to 100 degrees C. over a 30 minutes period, and
maintained at 100.degree. C. for 2 hours. The temperature is then
elevated from 100 degrees C. to 150 degrees C. over a 15 minute
period, and maintained at 150 degrees C. during 2 hours. The
temperature is then raised from 150 degrees C. to 175 degrees C.
over a 15 minute period and maintained at 175.degree. C. for 2
hours. The temperature is then raised from 175 degrees C. to 200
degrees C. over a 10 minute period, and then raised from 200
degrees C. to 300 degrees C. over a 300 minute period, and
maintained at 300 degrees C. for 1 hour. The temperature is then
raised from 300 degrees C. to 450 degrees C. over a 150 minute
period, and maintained at 450 degrees C. for 1 hour.
EXAMPLE 6
[0130] The process of Example 5 was repeated, except that roofing
granules having a white colored coating (Product No. 93,
commercially available from CertainTeed Corporation) were
substituted for the uncoated natural roofing granules of Example 5.
The white granules included a rhyolite mineral as the base material
coated with an exterior white color coating including pigment grade
rutile titanium oxide as a pigment and a binder comprising sodium
silicate and clay.
COMPARATIVE EXAMPLE 1
[0131] The process of Example 5 was repeated, except that the
titanium dioxide was omitted, to provide natural granules having a
mesoporous coating layer on their surface.
[0132] In order to confirm and quantify the mesoporous surface
layer on the roofing granules, the pore surface area was measure
using a BET apparatus. The results of the measurements are provided
in Table 2 below, and confirm the presence of the mesoporous layer
on the granules, in that the specific surface area of the granules
with the mesoporous layer is five to ten times greater than that of
the control (natural granules). TABLE-US-00002 TABLE 2 Specific
Total adsorbed surface Pore specific volume (cm.sup.3/g) Granules
area (m.sup.2/g) volume (cm.sup.3/g) (B.J.H., C = 0.75) Natural
granules 0.37 6 .times. 10.sup.-4 -- Example 5 2.13 6 .times.
10.sup.-3 10.0 Example 6 1.70 3.6 .times. 10.sup.-3 4.9 Comparative
Ex. 1 1.66 1.2 .times. 10.sup.-3 --
[0133] In order to test the photocatalytic effect of the added
photocatalytic metal oxide, a qualitative test was carried out by
studying the photocatalytic degradation of the organic red dye
rhodamine 6G under ultraviolet light. A solution of 0.04 g/l of
rhodamine in water was sprayed on the granules of Example 5,
Comparative Example 1, and a control consisting of natural
granules, and dried. The samples were then exposed to ultraviolet
light for one hour, and the resulting granules were photographed as
shown in the grayscale image of FIG. 4. The granules in the upper
portion of the photograph were coated with a photocatalytic coating
according to the present invention (Example 5), sprayed with the
rhodamine solution and exposed to ultraviolet light. The granules
have natural grey color, visible in the original color photograph.
The granules in the lower left portion of the photograph were
coated with a photocatalytic coating and sprayed with the rhodamine
solution, but were not exposed to ultraviolet light. These granules
have a pronounced pink color, visible in the original color
photograph from which the grayscale image was derived. The granules
in the lower right portion of the photograph were sprayed with
rhodamine solution and exposed to ultraviolet light. These granules
also have a pronounced pink color, visible in the original color
photograph. These results show that the photocatalytic coating was
effective in photodegrading the rhodamine dye applied, while the
control showed no degradation qualitatively in the absence of the
photocatalyst. This is a qualitative test to visualize the
photocatalytic activity of granules treated with titanium dioxide.
This test could otherwise become quantitative if the same volume of
rhodamine solution and same weight of granules were used. The
difference in the intensity of the pink color between the samples
can be measured from such photographs. Another qualitative method
is described in Example 7.
EXAMPLE 7
[0134] A conventional roofing shingle (commercially available from
CertainTeed Corporation), having roofing granules partially
embedded in the upper asphalt surface, was immersed in an
ultrasonic bath filled with water and cleaned ultrasonically for 15
minutes. The water was replaced with ethanol, and the shingle was
cleaned ultrasonically in ethanol for another 15 minutes. The
shingle was then dried for 20 minutes at 80 degrees C.
[0135] A solution "A" of 9.9 g of tetraethoxysilane (0.0475 M),
8.34 g of ethanol, and 4.29 g (0.238 M) of water are stirred for
one hour at 60 degrees C., until the mixture becomes
transparent.
[0136] A solution "B" of 3.85 g of cetyltrimethylammonium bromide
(CTAB, Aldrich) in 40.29 g of ethanol is prepared.
[0137] Solution "A" is added to solution "B", followed by addition
of 22.33 g of a 15 percent by weight aqueous suspension of titanium
dioxide nanoparticles (S5 300A, Millennium Chemicals, used as
received), to provide a coating sol having a molar ratio of
titanium to silicon of 1.32 and a CTAB to silicon molar ratio of
0.2.
[0138] The roofing shingles are immersed in the coating sol for 15
minutes, and subsequently dried at 80 degrees C. for two hours to
eliminate residual ethanol.
[0139] To test for the presence of photocatalytic metal oxide in a
mesoporous coating, the resulting coated shingle was sprayed with a
solution of 0.04 g/l rhodamine in water. Half the shingle was then
exposed to ultraviolet radiation from a mercury lamp (50 W/m.sup.2
measured with monochromatic sensor at 365 nm) for 10 minutes. A
photograph of the shingle is reproduced in FIG. 5. The left side of
the shingle in FIG. 5 was exposed to ultraviolet radiation, and the
appearance of the left side of the shingle in the original color
photograph shows that the rhodamine dye has been degraded, while
the right side was not exposed, and the right side of the shingle
appears pink in color in the original color photograph.
[0140] The ultraviolet radiation from the mercury lamp employed
corresponds to an average global power integrated over the UV-A
range (315-400 nm) of 50 W/m.sup.2. By comparison, exterior UV-A
radiation in cloudy weather is about 30 W/m.sup.2 and sunny summer
weather provides about 60 W/m.sup.2 of UV-A radiation.
[0141] To test for the effectiveness of the photocatalytic metal
oxide in either of the mesoporous coatings, the resulting coated
shingles were sprayed with a solution of 0.04 g/l rhodamine in
water. Half of each of the shingles was then exposed to ultraviolet
radiation from a mercury lamp (50 W/m.sup.2 measured with
monochromatic sensor at 365 nm) for up to 370 minutes. The change
in E as measured for rhodamine treated shingles versus shingles
that had not been sprayed with the rhodamine solution is reported
as a function of time of exposure in Table 3, as is the calculated
percentage degradation of the rhodamine, for CTAB-templated
mesoporous coating, as well as for PE 6800-templated mesoporous
coating. The percent degradation of the rhodamine is plotted as a
function of time in FIG. 6. The results suggests that pore
structure created by the polyethylene oxide template material
provides somewhat better access of the rhodamine to the
photocatalytic metal oxide, in that the rhodamine is degraded
somewhat more rapidly in the PE 6800-templated mesoporous coating.
TABLE-US-00003 TABLE 3 Time (min) Template 0 18 30 45 60 90 120 180
270 370 CTAB .DELTA.E 20.05 9.83 8.32 6.91 5.61 4.31 3.81 2.56 1.13
0.71 Percent 0.00 50.97 58.50 65.54 72.02 78.50 81.00 87.23 94.36
96.46 degradation PE6800 .DELTA.E 27.40 17.28 11.29 7.73 5.66 3.89
3.54 3.00 1.95 1.66 Percent 0.00 36.93 58.80 71.79 79.34 85.80
87.08 89.05 92.88 93.94 degradation
EXAMPLE 8
[0142] Typically a mesoporous layer can be obtained on roofing
granules by a sol-gel process using surfactant PE 6800 or CTAB to
create an ordered porosity in the layer. Both PE 6800 and CTAB are
soluble in aqueous alcohol solution. After thermal treatment at 400
degrees C., the porous layer obtained typically has a specific
surface area in the range of 1.7 m.sup.2/g to 3 m.sup.2/g. In order
to eliminate the use of alcohol or other organic solvents, a porous
layer is formed from colloidal silica and polyvinyl alcohol
(Mw=10.sup.4-10.sup.5 g/mole) as follows:
[0143] A solution of tetraethoxysilane (5 ml, TEOS 99%, Aldrich) in
aqueous 0.1 M hydrochloric acid (35 ml) is prepared at 60 degrees
C., and 3.3 ml of ammonium hydroxide (1M) is added to yield
colloidal silica. After one hour of stirring to promote maturation
of the colloidal silica, 6 g of a suspension of titanium dioxide
nanoparticles (30 wt %, 2730X, Degussa) is added to the colloidal
silica, followed by addition of 38 ml of an aqueous dispersion of
polyvinyl alcohol (20,000 g/mole, 5.5 wt % solution). Roofing
granules are then immersed in the resulting sol and dried, or the
sol is sprayed directly on roofing shingles. Roofing granules
coated with the sol are then dried at 80 degrees C. for 24 hours
and subsequently calcined at 450 degrees C. for one hour. The
roofing shingles coated with the sol are subsequently dried at 80
degrees C. for 24 hours. The polyvinyl alcohol serves to increase
the layer thickness of the mesoporous coating, and also to increase
the porosity obtained after thermal treatment of the roofing
granules.
[0144] The use of polyvinyl alcohol is not necessary to have a
photocatalytic effect of granules. By consequence, a photocatalytic
solution can be obtained without adding of polyvinyl alcohol. The
porosity of layer can be provided by the space between colloidal
silica particles.
[0145] A discoloration test (with rhodamine solution) was carried
out on shingles samples treated with colloidal silica embedded
titanium dioxide (without adding polyvinyl alcohol). The results of
this test are given in table 4 and FIG. 7 (for .DELTA.E variation).
TABLE-US-00004 TABLE 4 Time (min) .DELTA.E UV-A .DELTA.E (%
degradation) 0 17.83 0.00 5 15.29 14.27 10 13.30 25.41 15 10.75
39.70 20 9.77 45.24 25 8.59 51.82 30 7.48 58.05 40 5.84 67.24 60
5.17 71.02 90 4.03 77.43 120 3.53 80.20 240 2.97 83.34 360 3.14
82.40
[0146] The variation of a* can also be monitored using the
calorimetric test. As rhodamine has pink color, a* is thus the most
varied when the sample is exposed under UV-A. Table 5 gives the
variation of a* values for the same sample obtained in Table 4.
These values are plotted in FIG. 8. TABLE-US-00005 TABLE 5 Time
(min) a* .DELTA.a* (% degradation) 0 16.65 0 5 14.07 15.50 10 12.08
27.43 15 9.48 43.04 20 8.44 49.29 25 7.23 56.58 30 6.32 62.06 40
4.73 71.61 60 3.96 76.22 90 2.77 86.36 120 2.20 86.81 240 0.90
94.57 360 0.70 95.80
[0147] In effect, it is more interesting to follow the variation of
a* rather than .DELTA.E because a* relate directly to the pink
color of rhodamine.
[0148] Various modifications can be made in the details of the
various embodiments of the processes, compositions and articles of
the present invention, all within the scope and spirit of the
invention and defined by the appended claims.
* * * * *