U.S. patent application number 10/420168 was filed with the patent office on 2003-11-13 for optical elements comprising a polyfluropolyether surface treatment.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Clear, Susannah C., Elsbernd, Cheryl S., Flynn, Richard M., Pellerite, Mark J..
Application Number | 20030211287 10/420168 |
Document ID | / |
Family ID | 24805220 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030211287 |
Kind Code |
A1 |
Pellerite, Mark J. ; et
al. |
November 13, 2003 |
Optical elements comprising a polyfluropolyether surface
treatment
Abstract
The present invention relates to optical elements comprising
fluorochemical surface treatments. The invention further relates to
materials such as retroreflective sheetings, pavement markings and
beaded projection screens comprising a binder and the surface
treated optical elements. The fluorochemical surface treatment is
substantially free of perfluoroalkyl groups having more than four
carbon atoms. Preferably, the surface treatment is a
polyfluoropolyether-based compound comprising at least one polar
group or polar group-containing organic radical.
Inventors: |
Pellerite, Mark J.;
(Woodbury, MN) ; Clear, Susannah C.; (Cottage
Grove, MN) ; Elsbernd, Cheryl S.; (Woodbury, MN)
; Flynn, Richard M.; (Mahtomedi, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
24805220 |
Appl. No.: |
10/420168 |
Filed: |
April 21, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10420168 |
Apr 21, 2003 |
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09698434 |
Oct 27, 2000 |
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Current U.S.
Class: |
428/142 ;
428/421 |
Current CPC
Class: |
Y10T 428/252 20150115;
Y10T 428/24388 20150115; C08G 65/007 20130101; Y10T 428/2991
20150115; Y10T 428/2996 20150115; C09D 171/02 20130101; Y10T
428/3154 20150401; Y10T 428/254 20150115; G02B 5/128 20130101; Y10T
428/31544 20150401; Y10T 428/25 20150115; Y10T 428/24364 20150115;
Y10T 428/2995 20150115; Y10T 428/2438 20150115; C03C 12/02
20130101; Y10T 428/2998 20150115 |
Class at
Publication: |
428/142 ;
428/421 |
International
Class: |
B32B 001/00 |
Claims
What is claimed is:
1. An optical element having a surface treatment comprising a
polyfluoropolyether compound having at least one polar group or
polar group-containing organic radical.
2. The optical element of claim 1 wherein the polyfluoropolyether
compound has the general formula R.sub.f-[X].sub.y wherein R.sub.f
is a monovalent or divalent perfluoropolyether group, X is a polar
group or polar group-containing organic radical, and y ranges from
1 to 2.
3. The optical element of claim 2 wherein R.sub.f comprises one or
more repeating units selected from the group comprising
--C.sub.nF.sub.2n)--, --(C.sub.nF.sub.2nO)--, --(CF(Z))--,
--(CF(Z)O)--, --(CF(Z)C.sub.nF.sub.2nO)--,
--(C.sub.nF.sub.2nCF(Z)O)--, --(CF.sub.2CF(Z)O)--, and combinations
thereof; wherein the average n value ranges from 1 to 4 and Z is a
perfluoroalkyl group, an oxygen-substituted perfluoroalkyl group, a
perfluoroalkoxy group, or an oxygen-substituted perfluoroalkoxy
group having 1 to about 4 carbon atoms and 1 to about 4 oxygen
atoms.
4. The optical element of claim 2 wherein X is selected from the
group comprising carboxylic acid, sulfonic acid, phosphonic acid,
carboxylate salt, sulfonate, phosphonate, phosphate esters,
ammonium salts, amine, amide, alkyl amide, alkyl aryl amide, imide,
sulfonamide, hydroxymethyl, thiol, ester, silane, polyoxyalkyene,
organic radicals substituted with one or more of said polar groups,
and mixtures thereof.
5. The optical element of claim 2 wherein the polyfluoropolyether
compound is selected from the group comprising the general
formulas: i) X--(CF.sub.2O(CF.sub.2O).sub.m(C.sub.2F.sub.4O
).sub.pCF.sub.2)--X; ii)
C.sub.3F.sub.7O(CF(CF.sub.3)C.sub.2O).sub.pCF(CF.sub.3)--X; and
iii) X--CF.sub.2O(C.sub.2F.sub.4O).sub.mCF.sub.2--X wherein m and p
each independently range from 0 to 50 with the proviso that m and p
are not both 0 and X is a polar group or polar group-containing
organic radical selected from the group comprising
CONH(CH.sub.2).sub.3Si(OMe).sub.3, CONH(R) wherein R is an alkyl
radical having 1 to 8 carbon atoms, CONHCH.sub.2CH.sub.2Ph,
CO.sub.2NH.sub.4, CH.sub.2NH.sub.2,CO.sub.2H, CH.sub.2OH,
CO.sub.2CH.sub.3 and combinations thereof.
6. The optical element of claim 2 wherein the polyfluoropolyether
compound has the general formula: i)
X--(CF.sub.2O(CF.sub.2O).sub.m(C.sub.2F.sub.4- O).sub.pCF.sub.2)--X
wherein X is CONH(CH.sub.2).sub.3Si(OMe.sub.3; CO.sub.2H,
CO.sub.2NH.sub.4, and mixtures thereof; ii)
C.sub.3F.sub.7O(CF(CF.sub.3)CF.sub.2O(.sub.pCF(CF.sub.3)--X wherein
X is CO.sub.2H, CO.sub.2NH.sub.4 and mixtures thereof, wherein m
ranges from 0 to 50 and p ranges from 0 to 50, with the proviso
that m and p are not both 0.
7. The optical element of claim 1 wherein the number average
molecular weight of the polyfluoropolyether compound ranges from
about 400 to about 10,000 g/mole.
8. The optical element of claim 7 wherein the number average
molecular weight of the polyfluoropolyether compound is greater
than about 1000 g/mole.
9. The optical element of claim 7 wherein the number average
molecular weight of the polyfluoropolyether compound is greater
than about 2600 g/mole.,
10. The optical element of claim 7 wherein the number average
molecular weight is less than about 8,000 g/mole.
11. The optical element of claim 1 wherein the percent float in
heptane is at least about 90%.
12. An optical element having a surface treatment comprising a
fluorochemical compound at a concentration of less than about 100
ppm wherein the percent float in heptane is at least about 90%.
13. An optical element having a surface treatment comprising a
fluorochemical compound having the general formula
(C.sub.nF.sub.2n+1)--X wherein n ranges from 1 to 3 and X is a
polar group or polar group-containing organic radical.
14. An optical element having a surface treatment comprising a
fluorochemical compound having the general formula
(C.sub.nF.sub.2n+1)--X wherein n ranges from 1 to 4 and X is a
polar group or polar group-containing organic radical; and wherein
said compound is free of heavy metals and transition metals.
15. The optical element of claim 14 wherein X is selected from the
group comprising sulfonic acids and salts thereof; sulfonamides,
sulfonimides and salts thereof; amides, silanes and mixtures
thereof.
16. A method of coating optical elements comprising the steps of:
a) providing an aqueous surface treatment comprising at least one
fluorocarbon compound wherein said compound is free of
perfluoroalkyl groups having more than four carbon atoms; and b)
coating optical elements with said composition; and c) drying, said
composition.
17. The method of claim 16 wherein said fluorocarbon compound has
the general formula (C.sub.nF.sub.2n+1)--X wherein n ranges from 1
to 4, m ranges from 0 to 4, and X is a polar group or polar
group-containing organic radical.
18. The method of claim 16 wherein said aqueous composition is
substantially free of heavy metals and transition metals.
19. The method of claim 16 wherein said aqueous composition
comprises up to about 30 wt-% of a cosolvent with respect to the
total weight of the solution.
20. A pavement marking comprising a liquid binder and a multitude
of the optical elements of claim 1.
21. A pavement marking comprising a liquid binder and a multitude
of the optical elements of claim 13.
22. A pavement marking comprising a liquid binder and a multitude
of the optical elements of claim 14.
23. The pavement marking of claim 20 wherein the optical elements
are embedded in the binder at a depth of about 40-70% of their
diameters.
24. The pavement marking of claim 21 wherein the optical elements
are embedded in the binder at a depth of about 40-70% of their
diameters.
25. The pavement marking of claim 22 wherein the optical elements
are embedded in the binder at a depth of about 40-70% of their
diameters.
26. A reflective sheeting comprising: a) a top coat layer having an
exposed surface; b) a binder layer disposed on the exposed surface
of the top coat layer; c) a multitude of the optical elements of
claim 1 disposed on the binder layer; d) a space coat layer
disposed on the binder layer; and e) a reflective layer disposed on
the space coat layer.
27. A reflective sheeting comprising: a) a top coat layer having an
exposed surface; b) a binder layer disposed on the exposed surface
of the top coat layer; c) a multitude of the optical elements of
claim 13 disposed on the binder layer; d) a space coat layer
disposed on the binder layer; and e) a reflective layer disposed on
the space coat layer.
28. A reflective sheeting comprising: a) a top coat layer having an
exposed surface; b) a binder layer disposed on the exposed surface
of the top coat layer; c) a multitude of the optical elements of
claim 14 disposed on the binder layer; d) a space coat layer
disposed on the binder layer; and e) a reflective layer disposed on
the space coat layer.
29. The reflective sheeting of claim 26 wherein the optical
elements are embedded in the binder at a depth of about 40-70% of
their diameters.
30. The reflective sheeting of claim 27 wherein the optical
elements are embedded in the binder at a depth of about 40-70% of
their diameters.
31. The reflective sheeting of claim 28 wherein the optical
elements are embedded in the binder at a depth of about 40-70% of
their diameters.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to optical elements comprising
fluorochemical surface treatments. The invention further relates to
materials such as retroreflective sheetings, pavement markings and
beaded projection screens comprising a binder and the surface
treated optical elements. The fluorochemical surface treatment is
substantially free of perfluoroalkyl groups having more than four
carbon atoms. Preferably, the surface treatment is a
polyfluoropolyether-based compound comprising at least one polar
group or polar group-containing organic radical.
BACKGROUND OF THE INVENTION
[0002] Beaded projection display screens, retroreflective sheeting
used in the manufacture of roadway signs, and retroreflective
paints typically include optical elements adhered through the use
of a binder. In the case of beaded projection display materials,
the optical elements are microscopic glass beads that act as lenses
to collect projected light from the rear of the screen and focus it
to relatively small spots, near the surfaces of the microspheres.
The foci are approximately in the areas where the optical elements
contact a front support layer. In other retroreflective materials,
the optical elements act as lenses which focus the light onto a
reflector (metal mirror of diffusely reflecting pigment) and once
the light has been reflected off the reflector the microspheres
again act as lenses to resend the light back toward the incoming
light source. In order to contribute the desired retroreflective
property, however, it is important that a layer of glass
microspheres be present on the surface of the binder layer.
[0003] As discussed in U.S. Pat. No. 3,222,204, ordinary glass
beads tend to sink into the uncured liquid binder layer. In
instances wherein the individual beads are not entirely submerged,
the optical properties of the bead can also be impaired by the
binder wetting out the bead surface and spreading on the exposed
bead surface. To address this problem, U.S. Pat. No. 3,222,204
teaches coating the glass beads with a thin surface coating of an
oleophobic fluorocarbon sizing agent. At column 5, lines 61-75,
this reference states that, "Aqueous treating solutions of
fluorocarbon chromium coordination complexes are preferred and are
described in U.S. Pat. Nos. 2,662,835 (Dec. 15, 1953) and 2,809,990
(Oct. 15, 1957) and 2,934,450 (Apr. 26, 1960). The complex may be
made by reacting chromyl chloride with a fluorocarbon
monocarboxylic acid (having a highly fluorinated terminal chain or
tail containing 4 to 10 carbon atoms) in an isopropanol vehicle
that serves as both a solvent and reducing agent, the chromium to
acid mole ratio being in the range of 2:1 to 5:1. The resultant
green-colored isopropanol solution of the complex is diluted with
water at the time of use. The fluorocarbon acid preferably has 6 to
8 fully fluorinated (perfluorinated) carbon atoms in the terminal
fluorocarbon chain or tail." Specific working examples include
chromium coordination complexes of perfluorooctanoic acid and
N-ethyl-N-perfluorooctanesulfonyl glycine.
[0004] U.S. Pat. No. 4,713,295 teaches coating glass beads with a
mixture of substances. The mixture comprises a first substance
which if used alone would tend to make the beads hydrophobic while
leaving them oleophilic and a second substance which if used alone
would tend to make the beads both hydrophobic and oleophobic. "For
the best results, it is preferred to use a second substance which
is an anionic fluorocarbon compound, and optimally, said second
substance is a fluoro-alkyl-sulphonate, for example a
fluoro-alkyl-sulphonate in which the alkyl has a long chain (C14 to
C18)." (See Column 4, lines 8-13). The exemplified hydrophobic and
oleophobic substance is a potassium fluoroalkyl-sulphonate (for
example FC129 from 3M). (See column 5, lines 50-52) FC 129 is a
potassium fluoroctyl sulphonyl-containing compound.
SUMMARY OF THE INVENTION
[0005] The fluorocarbon surface treatment of the present invention
is substantially free of perfluoroalkyl groups having more than 4
carbon atoms. The present inventors have identified various
fluorocarbon derivatives that lack the previously preferred 6 to 8
carbon and longer fully fluorinated tail. Although the terminal
fluorocarbon tail is considerably shorter, or absent, the surface
treatments of the present invention are surprisingly effective in
obtaining the desired floatation properties combined with the
desired adhesion with the binder.
[0006] In one embodiment, the present invention is an optical
element having a surface treatment comprising a polyfluoropolyether
compound having at least one polar group or polar group-containing
organic radical. The polyfluoropolyether compound has the general
formula R.sub.f-[X].sub.y wherein R.sub.f is a monovalent or
divalent polyfluoropolyether group, X is a polar group or polar
group-containing organic radical, and y ranges from 1 to 2. R.sub.f
comprises one or more repeating units selected from the group
comprising --(C.sub.nF.sub.2n)--, --(C.sub.nF.sub.2nO)--,
--(CF(Z))--, --(CF(Z)O)--, --(CF(Z)C.sub.nF.sub.2nO)--,
--(C.sub.nF.sub.2nCF(Z)O)--, --(CF.sub.2CF(Z)O)--, and combinations
thereof; wherein the average n value ranges from 1 to 4 and Z is a
perfluoroalkyl group, an oxygen-substituted perfluoroalkyl group, a
perfluoroalkoxy group, or an oxygen-substituted perfluoroalkoxy
group having 1 to about 4 carbon atoms and 1 to about 4 oxygen
atoms. The polar group or polar group-containing organic radical,
X, is preferably selected from the group comprising carboxylic
acid, sulfonic acid, phosphonic acid, carboxylate salt, sulfonate,
phosphonate, phosphate esters, ammonium salts, amine, amide, alkyl
amide, alkyl aryl amide, imide, sulfonamide, hydroxymethyl, thiol,
ester, silane, polyoxyalkyene, organic radicals substituted with
one or more of such polar groups, and mixtures thereof.
[0007] Preferred polyfluoropolyether surface treatments have the
general formulas
X--(CF.sub.2O(CF.sub.2O).sub.m(C.sub.2F.sub.4O).sub.pCF.sub.2)---
X, C.sub.3F.sub.7O(CF(CF.sub.3)CF.sub.2O).sub.pCF(CF.sub.2)--X, and
X--CF.sub.2O(C.sub.2F.sub.4O) .sub.mCF.sub.2--X; wherein m and p
each range from 0 to 50 with the proviso that m and p are not both
0 and X is a polar group or polar group-containing organic radical
comprising CONH(CH.sub.2).sub.3Si(OMe).sub.3, CONH(R) wherein R is
an alkyl radical having 1 to 8 carbon atoms,
CONHCH.sub.2CH.sub.2Ph, CO.sub.2NH.sub.4, CH.sub.2NH.sub.2,
CO.sub.2H, CH.sub.2OH, CO.sub.2CH.sub.3 and combinations thereof.
Further, the polyfluoropolyether compounds having the general
formula X--(CF.sub.2O(CF.sub.2O).sub.m(C.sub.2F.sub.4O).sub.p-
CF.sub.2)--X wherein X is CONH(CH.sub.2).sub.3Si(OMe).sub.3;
CO.sub.2H, CO.sub.2NH.sub.4 and mixtures thereof; and
(C.sub.3F.sub.7O(CF(CF.sub.3)C- F.sub.2O).sub.p(CF(CF.sub.3)--X
wherein X is CO.sub.2H, CO.sub.2NH.sub.4, and mixtures thereof;
wherein m and p each range from 0 to 50 with the proviso that m and
p are not both 0, have demonstrated 100% float at loading levels of
about 100 ppm and less.
[0008] The number average (Mn) molecular weight of the
polyfluoropolyether compound preferably ranges from about 400 to
about 10,000 g/mole. Mn is preferably greater than about 1000
g/mole and more preferably greater than about 2000 g/mole. Mn is
preferably less than about 8,000 g/mole.
[0009] In another embodiment, the present invention is an optical
element having a surface treatment comprising a fluorochemical
compound having the general formula (C.sub.nF.sub.2n+1)--X wherein
n ranges from 1 to 3 and X is a polar group or polar
group-containing organic radical.
[0010] In another embodiment, the present invention is an optical
element having a surface treatment comprising a fluorochemical
compound having the general formula (C.sub.nF.sub.2n+1)--X wherein
n ranges from 1 to 4, X is a polar group or polar group-containing
organic radical and the surface treatment is free of heavy metals
and transition metals.
[0011] In embodiments wherein the surface treatment has the general
formula (C.sub.nF.sub.2n+1)--X, X is preferably selected from the
group comprising sulfonic acids and salts thereof; sulfonamides,
sulfonimides and salts thereof; amides, silanes, and mixtures of
such surface treatments.
[0012] The surface treated optical elements of the invention
preferably exhibit a percent float in heptane of at least about
90%.
[0013] In another embodiment the present invention is an optical
element having a surface treatment comprising a fluorochemical
compound at a concentration of less than about 100 ppm based on the
weight of the optical elements wherein the percent float in heptane
is at least about 90%.
[0014] In another aspect, the present invention is a method of
coating an optical element comprising providing an aqueous surface
treatment comprising at least one fluorocarbon compound wherein
said compound is free of perfluoroalkyl groups having more than
four carbon atoms, coating said composition on optical elements,
and drying said composition. The aqueous composition preferably
comprises no more than 30 wt-% of a cosolvent with respect to the
total weight of the solution.
[0015] The invention further relates to reflective articles such as
pavement markings, reflective sheeting, and projection screens
comprising a binder and the surface treated optical elements of the
invention. The optical elements are embedded in the binder surface
at a depth of about 40 to 60 percent of their diameters.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention relates to optical elements such as
glass beads coated with a fluorocarbon surface treatment. The
terminology "optical element" refers to a material having a
particle size ranging from about 25 to 1000 microns and having a
refractive index ranging from about 1.5 to about 2.3 and higher.
"Surface treatment" refers to the presence of a fluorochemical
comprising one or more C.sub.1 to C.sub.4 fluoroalkyl and/or one or
more C.sub.1 to C.sub.4 fluoroalkylene fragments on the surface of
the optical elements. The presence of such can be detected by means
of x-ray photoelectron spectroscopy (XPS) or time of flight
secondary ion mass spectroscopy.
[0017] The optical elements have at least one dimension that is no
larger than 2 millimeters and preferably no larger than 250
microns. The optical elements may be in the form of any shape such
as granules, flakes and fibers. However, spheroidal glass elements,
denoted as "glass beads", "beads" and "microspheres" hereinafter
are preferred for materials such as retroreflective articles (e.g.
retroreflective sheetings, pavement markings and beaded projection
screens).
[0018] During the manufacture of retroreflective materials, optical
elements are fixed in place by means of a liquid binder. Optical
elements have a density or specific gravity several times that of
the liquid binder, causing the optical elements to sink into the
liquid binder layer, rather than float on the surface.
[0019] Preferred properties of optical elements will be described
herein with respect to glass beads. Ordinary glass beads typically
have a density of about 2.5 and a refractive index of about 1.5.
"High index" beads refers to beads having a density of about 3.5
and a refractive index of about 1.9, whereas "super high index"
typically refers to beads having a density of about 5 and a
refractive index of about 2.3 or higher. The diameter of the glass
beads typically ranges from a few microns to approximately 2500
microns and is preferably from about 25 to 1000 microns.
[0020] In addition to having the desired particle size and
refractive index, the glass beads are typically transparent. The
term transparent means that when viewed under an optical microscope
(e.g., at 100.times. ) the microspheres have the property of
transmitting rays of visible light so that bodies beneath the
microspheres, such as bodies of the same nature as the microspheres
can be clearly seen through the microspheres, when both are
immersed in oil of approximately the same refractive index as the
microspheres. The outline, periphery or edges of bodies beneath the
microspheres are clearly discernible. Although the oil should have
a refractive index approximating that of the microspheres, it
should not be so close that the microspheres seem to disappear as
would be the case for a perfect match.
[0021] The optical elements may comprise microspheres that are
ceramic. In general, ceramic microsphere optical elements are
comprised of metal oxides that are substantially colorless.
Suitable metal oxides include Al.sub.2O.sub.3, SiO.sub.2,
ThO.sub.2, SnO.sub.2, TiO.sub.2, Y.sub.2O.sub.3 and ZrO.sub.2 with
the oxides of zirconium, silicon, and titanium being preferred. The
ceramic microspheres can exhibit a range of properties, depending
on the kind and amounts of the various metal oxides employed as
well as the method of manufacture. Preferred, however, are dense
microspheres having substantially no open porosity that have an
average hardness greater than sand.
[0022] Additional information concerning the desired properties for
various end-uses and methods of manufacture of microspheres (e.g.
sol-gel process), can be found in U.S. Pat. Nos. 3,493,403;
3,709,706 and 4,564,556; incorporated herein by reference. Glass
beads suitable for use as optical elements in the invention are
also commercially available from Flex-O-Lite Corporation, Fenton,
Mo. and Nippon Electric Glass, Osaka, Japan.
[0023] The optical elements of the invention are coated with a
surface treatment that alters the floatation properties of the
optical element in the liquid binder. "Float" and derivations
thereof, described in the context of glass beads, refers to the
beads assuming a position wherein slightly more than half of each
bead is submerged. The liquid binder preferably contacts the
embedded beads only up to 5 to 30.degree. above their equators. The
floatability of the glass beads can be affected to some extent by
the particle size, particle size distribution, surface chemistry
and chemical make-up of the particular glass. beads as well as the
chemical make-up, density, and viscosity of the binder. In general,
however, only about 10% or less of the glass beads tend to float in
heptane test liquid in the absence of an effective surface
treatment.
[0024] The position that the glass beads attain relative to the
undisturbed binder due to the surface treatment assists the
anchoring of the beads in the ultimate dried or solidified binder
coating. The glass beads are preferably embedded to about 40-70%,
and more preferably to about 40-60% of their diameters. The beads
are adequately exposed providing a sphere-lens having a large
optical aperture relative to its size. During the drying or
solidification of the binder, there is some shrinkage of the binder
film. However, the beads remain bonded with the centers of the
floated beads being approximately equidistant from the underlying
back surface of the binder layer or the top surface of the
base.
[0025] In addition to the improvement in floatation of the optical
elements, it is also important that the surface treatment does not
adversely affect the adhesion of the optical elements with the
liquid binder. The adhesion can be evaluated in several ways and
will be described herein with respect to a preferred optical
element, glass beads. The initial adhesion can subjectively
determined by estimating the depth to which the embedded glass
beads have sunk into the binder after curing. The glass beads are
preferably embedded to a depth of about 40-70%, and more preferably
to about 40-60% of their diameters. Another way of evaluating
adhesion is accelerated aging evaluations. A piece of cured glass
bead-embedded binder is conditioned in boiling water for 24 hours.
After conditioning, the glass beads are preferably embedded to the
same extent as prior to conditioning and the individual glass beads
are difficult to remove with a dissection probe. Yet another way to
evaluate the effect of the binder on adhesion is comparative
tensile testing. A uniform slurry of binder and untreated glass
beads at a ratio of about 1 to 3 is drawn down into a film having a
thickness of about 0.4 mm. A second slurry of binder and surface
treated glass beads employing the same ratio of ingredients and
film thickness is prepared. After the samples are fully cured, the
samples are conditioned for 24 hours in water at ambient
temperature. Tensile testing is conducted with a 1" wide sample
employing a 2" gap at a rate of 0.5 inches/minute. The stress at
break of the sample comprising the surface treated beads is about
the same as or preferably greater than the control sample,
comprising untreated beads (.gtoreq.about 90% of the standard
deviation of the average value). Any one of the previously
described methods is typically sufficient to determine whether the
surface treatment adversely affects the adhesion of the glass beads
with the liquid binder. Preferably, however, all three of the
evaluations are conducted.
[0026] The optical elements are coated with a fluorochemical
compound having at least one fluoroalkyl and/or fluoroalkylene
linkage having 1 to 4 carbon atoms and at least one polar group or
polar group-containing organic radical. The fluorochemical surface
treatment is substantially free of relatively long chain
perfluoroalkyl groups, having 6 or more carbon atoms.
"Substantially free" refers to at least about 90 wt-% of the
surface treatment comprising C.sub.1 to C.sub.4 fluoroalkyl and/or
C.sub.1 to C.sub.4 fluoroalkylene segments. Preferably, less than
about 1 wt-% of the fluoroalkyl and fluoroalkylene segments contain
more than 4 carbon atoms. Most preferably, only trace impurities of
fluoroalkyl and fluoroalkylene segments containing more than 4
carbon atoms are present.
[0027] The fluorochemical surface treatment is preferably a
polyfluoropolyether compound having at least one polar group or
polar group-containing organic radical. The polyfluoropolyether
compound has the general formula R.sub.f-[X].sub.y wherein R.sub.f
is a, monovalent or divalent polyfluoropolyether group, X is a
polar group or polar group-containing organic radical and y ranges
from 1 to 2.
[0028] The polyfluoropolyether group (R.sub.f) can include linear,
branched, and/or cyclic structures, that may be saturated or
unsaturated, and substituted with one or more oxygen atoms. The
polyfluoropolyether group is preferably a perfluorinated group
(i.e., all C--H bonds are replaced by C--F bonds). More preferably,
R.sub.f includes one or more perfluorinated repeating units
comprising --(C.sub.nF.sub.2n)--, --(C.sub.nF.sub.2nO)--,
--(CF(Z))--, --(CF(Z)O)--, --(CF(Z)C.sub.nF.sub.2nO)--,
--(C.sub.nF.sub.2nCF(Z)O)--, --(CF.sub.2CF(Z)O)--, and combinations
thereof, wherein the average value for n ranges from 1 to 4. In
these repeating units, Z is a perfluoroalkyl group, an
oxygen-substituted perfluoroalkyl group, a perfluoroalkoxy group,
or an oxygen-substituted perfluoroalkoxy group, all of which can be
linear, branched, or cyclic, that may be saturated or unsaturated,
and substituted with one or more oxygen atoms. The pendant groups Z
preferably have about 1 to about 4 carbon atoms and 0 to about 4
oxygen atoms with the proviso that each perfluoroalkylene linkage
has 4 or fewer contiguous carbon atoms. Examples of
polyfluoropolyethers containing polymeric moieties made of these
repeating units are disclosed in U.S. Pat. No. 5,306,758
(Pellerite).
[0029] For the monovalent polyfluoropolyether group, the terminal
groups can be (C.sub.nF.sub.2n+1)--, (C.sub.nF.sub.2n+1O)--,
(Y'C.sub.nF.sub.2nO)--, or (Y'C.sub.nF.sub.2n+1O)-- wherein Y' is
H, Cl, or Br, for example. Preferably, these terminal groups are
perfluorinated. In these repeating units or terminal groups, the
average value for n is 1 or more, preferably about 1 to about 4 and
more preferably about 1 to about 3. A preferred approximate average
structure for a monovalent polyfluoropolyether group is
C.sub.3F.sub.7O(CF(CF.sub.3)CF.sub.2O).sub.p- CF(CF.sub.3)--
wherein an average value for p is 1 to about 50. As synthesized,
these compounds typically include a mixture of oligomers. The
approximate average structure is the approximate average of the
mixture of oligomers.
[0030] Preferred approximate average structures for divalent
polyfluoropolyether groups include
--CF.sub.2O(CF.sub.2O).sub.m(C.sub.2F.- sub.4O).sub.pCF.sub.2-,
--CF(CF.sub.3) (OCF.sub.2CF(CF.sub.3)).sub.mO(C.su-
b.nF.sub.2n)O(CF(CF.sub.3)CF.sub.2O).sub.pCF(CF.sub.3)-- wherein
the value for n ranges from 2 to 4,
--CF.sub.2O(C.sub.2F.sub.4O).sub.pCF.sub.2-, and
--(CF.sub.2).sub.3O(C.sub.4F.sub.8O).sub.p(CF.sub.2).sub.3--,
wherein an average value for m is 0 to about 50 and an average
value for p is 0 to about 50, with the proviso that both in and p
cannot be 0 in the same group. Of these, particularly, preferred
approximate average structures are
--CF.sub.2O(CF.sub.2O).sub.m(C.sub.2F.sub.4O).sub.pCF.sub.2- and
--CF.sub.2O(C.sub.2F.sub.4O).sub.pCF.sub.2-.
[0031] A wide variety of polar groups or polar group-containing
organic radicals, X, are suitable provided such functional
end-group(s) serve an intended purpose of binding the surface
treatment to the optical elements and not adversely affecting the
adhesion between the binder and the optical elements. Additionally,
since the perfluoro tail is hydrophobic, the polar group or polar
group-containing organic radical also permits the making of dilute
emulsions, solutions, and dispersions for treating the optical
elements. The polar group or polar group containing radical may be
anionic, nonionic, cationic, or amphoteric. In general, the more
commonly employed polar groups or polar group-containing organic
radicals for aqueous delivery of the treatment solution include
organic acids, particularly carboxylic acid, sulfonic acid and
phosphonic acid; carboxylate salts, sulfonates, phosphonates,
phosphate esters, ammonium salts, amines, amides, alkyl amides,
alkyl aryl amides, imides, sulfonamides, hydroxymethyl, thiols,
esters, silanes, and polyoxyalkyenes, as well as other organic
radicals such as alkylene or arylene substituted with one or more
of such polar groups. The polyfluoropolyether compound may have any
one of these polar groups or polar group-containing organic
radicals or any combination thereof. For enhanced water solubility
and ease of processing, the polyfluoropolyether based surface
treatment having an acid group is preferably converted to the
corresponding salt by neutralization with an appropriate base for
embodiments wherein the molecular weight (Mn) is greater than about
1000 g/mole. Other suitable functional groups are known from U.S.
Pat. No. 3,810,874 issued May 14, 1974, incorporated herein by
reference.
[0032] The number of repeat units in the polyfluoropolyether group
(R.sub.f) combined with the molecular weight of the polar organic
group is sufficient to form a compound having a number average
molecular weight (Mn) ranging from about 200 g/mole to about 20,000
g/mole. Preferably, Mn is at least about 400 g/mole and less than
about 15,000 g/mole, more preferably less than about 10,000 g/mole,
and most preferably about 8,000 g/mole or less. Further, the number
average molecular weight of the polyfluoropolyether compound is
preferably greater than about 1,000 g/mole and more preferably
greater than about 2,000 g/mole. It is surprising that oligomeric
species several times larger in molecular weight than the
previously preferred perfluorooctyl based compounds can effectively
be employed as a surface treatment without compromising adhesion of
the optical elements to the binder.
[0033] Preferred surface treatments include those
polyfluoropolyether based compounds having the general formulas
X--(CF.sub.2O(CF.sub.2O).sub.-
m(C.sub.2F.sub.4O).sub.pCF.sub.2)--X,
C.sub.3F.sub.7O(CF(CF.sub.3)CF.sub.2- O).sub.pCF(CF.sub.3)--X, and
X--CF.sub.2O(C.sub.2F.sub.4O).sub.pCF.sub.2-X- ; wherein m and p
each range from 0 to 50 with the proviso that m and p are not both
0 and X is one or more polar groups or polar group-containing
organic radicals comprising CONH(CH.sub.2).sub.3Si(OMe).- sub.3,
CONH(R) wherein R is an alkyl radical having 1 to 8 carbon atoms,
CONHCH.sub.2CH.sub.2Ph, CO.sub.2NH.sub.4, CH.sub.2NH.sub.2,
CO.sub.2H, CH.sub.2OH and CO.sub.2CH.sub.3. In particular, the
compounds having the general formula
X--(CF.sub.2O(CF.sub.2O).sub.m(C.sub.2F.sub.4O).sub.pCF.s- ub.2)--X
wherein X is CONH(CH.sub.2).sub.3Si(OMe).sub.3; CO.sub.2H,
CO.sub.2NH.sub.4 and mixtures thereof, and
(C.sub.3F.sub.7O(CF(CF.sub.3)C- F.sub.2O).sub.n(CF(CF.sub.3)--X
wherein X is CO.sub.2H, CO.sub.2NH.sub.4 and mixtures thereof; have
demonstrated 100% float at relatively low concentrations, ranging
from about 50 ppm to about 100 ppm based on the weight of the
optical elements.
[0034] The polyfluoropolyether compound may be prepared with known
techniques.
[0035] A preferred polyfluoropolyether based surface treatment is
poly(hexafluoropropylene oxide) having a carboxylic acid group
located on one chain terminus, commercially available from Dupont,
Wilmington, Del. under the trade designation "Krytox". "Krytox" 157
FS is available in three relatively broad molecular weight ranges,
2500 g/mole (FSL), 3500-4000 g/mole (FSM) and 7000-7500 g/mole
(FSH), respectively for the low, medium and high molecular weights.
The low and medium molecular weight grades are preferred for
aqueous delivery of the surface treatment. Other suitable
polyfluoropolyether compounds include those under the trade
designation "Fomblin" Z-DIAC, "Fluorolink" C and "Fluorolink" 7004,
commercially available from Ausimont USA, Thorofare, N.J.
[0036] Although polyfluoropolyether based compounds are preferred,
other fluorochemical compounds bearing short chain perfluororalkyl
segments are also suitable for use as a surface treatment for
optical elements. Such fluorochemical compounds have the general
formula (C.sub.nF.sub.2n+1)-[X] wherein n ranges from 1 to 4 and X
is a polar group or polar group-containing organic radical.
Preferably, n ranges from 2 to 4 and more preferably n ranges from
3 to 4. Although perfluorobutyric acid does induce the desired
floatation in heptane, the use of such and similar derivatives is
typically avoided in view of the difficulty in handling such
chemicals. The polar group or polar group-containing organic
radical may be any of the polar groups or polar group-containing
organic radicals previously described for the polyfluoropolyether
based surface treatment or a mixture of such surface treatments.
Preferred, however, are fluorochemical derivatives having polar
groups or polar group-containing organic radicals that are
substantially free of heavy metals and transition metals (trace
impurities only). Representative surface treatments include those
having polar groups or polar group-containing organic radicals such
as sulfonic acids and salts thereof (e.g. C.sub.4F.sub.9SO.sub.3H,
C.sub.4F.sub.9SO.sub.3Li, C.sub.4F.sub.9SO.sub.3K); sulfonamides,
sulfonimides and salts thereof (e.g.
(C.sub.4F.sub.9SO.sub.2).sub.2NH, (C.sub.4F.sub.9SO.sub.2).sub.2NK;
and silanes (e.g. (CF.sub.3).sub.2CFO(CH.sub.2).sub.3SiCl.sub.3).
Such fluorochemical derivatives are known in the art and can be
prepared with known techniques. In general, the best results were
obtained with compounds contaning heptafluoropropyl or
nonafluorobutyl groups. Further, the acids tend to exhibit higher
percent float on a more consistent basis than their corresponding
salts.
[0037] The surface treatment comprises any one or any mixture
thereof of the previously described compounds wherein the compound
or mixture of compounds is substantially free of perfluororalkyl
groups having 6 or more carbon atoms. The surface treatment may be
a single polyfluoropolyether based compound, a single fluoroalkyl
based compound having 1 to 4 carbon atoms, a mixture of two or more
polyfluoropolyether compounds, a mixture of two or more fluoroalkyl
based compounds, each having 1 to 4 carbon atoms; as well as
mixtures of one or more polyfluoropolyether based compounds with
one or more fluoroalkyl based compounds, each having 1 to 4 carbon
atoms. Further, each individual compound has at least one polar
group or polar group-containing organic radical.
[0038] The surface treatment is present on the optical elements in
an amount sufficient such that greater than about 50% of the
optical elements float in heptane. Preferably, the surface
treatment improves the floatability such that greater than about
80% of the optical elements float in heptane and more preferably
about 90-100% of the optical elements float in heptane.
[0039] The amount of fluorochemical derivative employed for coating
the optical elements typically ranges from about 5 ppm to about
1000 ppm with respect to the weight of the optical elements. A
preferred fluorochemical compound is one that contributes the
desired floatation at minimum concentrations. The amount of
fluorochemical derivative is usually about 600 ppm or less,
preferably about 300 ppm or less, more preferably about 150 ppm,
even more preferably about 100 ppm, and most preferably about 50
ppm or less. Typically, the overall coating thickness of the
surface treatment of the present invention is greater than about 15
Angstroms, preferably, greater than about 20 Angstroms, and more
preferably, greater than about 50 Angstroms. Thicker coatings can
be obtained if desired, although it is preferred that the coating
thickness be no greater than about 500 Angstroms, more preferably,
no greater than about 300 Angstroms, and most preferably, no
greater than about 150 Angstroms thick. Excessive concentrations of
surface treatment can result in agglomeration of the optical
elements. Such limits can be determined by routine experimentation
and in some instances the agglomeration can be reduced by the use
of flow control agents.
[0040] The fluorochemical compositions described herein for use as
surface treatment for optical elements are typically liquids. The
surface treatments are combined with various solvents to form
emulsion(s), solution(s) or dispersion(s). The emulsion(s),
solution(s), and dispersion(s) are then further diluted in order to
deliver the desired concentration. It is assumed that negligible
amounts of the diluted surface treatment are lost and substantially
all of the surface treatment present in the emulsion, solution or
dispersion is deposited on the optical elements. Hence, the
concentration (ppm) based on the weight of the optical elements
being coated with the emulsion, solution, or dispersion is
approximately equal to the amount retained on the optical elements
upon evaporation of the solvent. Although aqueous emulsions,
solutions, and dispersions are preferred, up to about 50% of a
cosolvent such as methanol, isopropanol, or methyl perfluorobutyl
ether may be added. Preferably, the aqueous emulsions, solutions,
and dispersions comprise less than about 30% cosolvent, more
preferably less than about 10% cosolvent, and most preferably the
aqueous emulsions, solutions, and dispersions are substantially
free of cosolvent. The aqueous surface treatment is coated on the
optical elements typically by combining the optical elements with
the minimum volume of aqueous surface treatment to uniformly coat
the optical elements and then drying the coated elements. Although
aqueous delivery is preferred, the surface treatment could also be
applied from 100% organic solvent as well as by other techniques
such as vapor deposition.
[0041] In addition to the surface treatment of the invention, the
optical elements may comprise one or more additional surface
treatments such as adhesion promoters and flow control agents that
reduce particle agglomeration. Various silanes such as
3-aminopropyltriethoxysilane are commonly employed as adhesion
promoters, whereas methacrylato chromic chloride, commercially
available from Zaclon Inc, Cleveland, Ohio under the trade
designation "Volan" is a typical flow control agent.
[0042] The surface treated optical elements of the invention can be
employed for producing a variety of reflective products or articles
such as pavement markings, retroreflective sheeting, and beaded
projection screens. Such products share the common feature of
comprising a liquid binder layer and embedding a multitude of
optical elements into the binder surface followed by solidifying
the binder to retain the optical elements in place. In the pavement
markings, retroreflective sheeting, and beaded projection screens
of the invention, at least a portion of the optical elements will
comprise the surface treated optical elements of the invention.
Typically, the majority of, and preferably substantially all, the
optical elements employed in the manufacture of the reflective
products will comprise the surface treated optical elements of the
invention.
[0043] Various known binder materials may be employed including
various one and two-part curable binders, as well as thermoplastic
binders wherein the binder attains a liquid state via heating until
molten. Common binder materials include polyacrylates,
methacrylates, polyolefins, polyurethanes, polyepoxide resins,
phenolic resins, and polyesters. For reflective paints the binder
may comprise reflective pigment. For reflective sheeting, however,
the binder is typically transparent. Transparent binders are
applied to a reflective base or may be applied to a release-coated
support, from which after solidification of the binder, the beaded
film is stripped and may subsequently be applied to a reflective
base or be given a reflective coating or plating.
[0044] There are several types of retroreflective articles in which
the surface treated optical elements may be used such as exposed
lens (e.g. U.S. Pat. Nos. 2,326,634 and 2,354,018), embedded lens
(e.g. U.S. Pat. No. 2,407,680), and encapsulated lens (e.g. U.S.
Pat. No. 4,025,159) retroreflective sheeting. Retroreflective
articles can be prepared by known methods including a method
comprising the steps of: (i) forming a top coat on a release coated
web (e.g. coating a solution of hydroxy-functional acrylic polyol
and aliphatic polyfuntional isocyanate onto a release-coated paper
web and then curing by conveying the coating through an oven at
about 150.degree. C. for about 10 minutes); (ii) coating the
exposed surface of the top coat with a liquid binder (e.g. coating
a solution comprising an oil-free synthetic polyester resin and a
butylated melamine resin); (iii) drying the binder to form an
uncured tacky bead-bond layer; (iv) cascade-coating onto the
bead-bond layer a plurality of glass microspheres forming a
monolayer of embedded glass microspheres; (v) curing the
bead-containing bead-bond layer to a non-tacky state (e.g. by
heating to 150.degree. C.); forming a space coat layer over the
bead-containing bead-bond layer (e.g. coating a 25% solids solution
comprised of a polyvinylbutyral resin and a butylated melamine
resin in a solvent and curing at 170.degree. C. for about 10
minutes); (vi) applying a reflective layer over the space coat
layer (e.g. vapor deposition of aluminum metal at a thickness of
about 100 nm); and stripping away the release-coated web. An
adhesive layer is typically applied to the reflective layer (e.g.
by coating a 0.025 mm thick layer of an aggressive acrylic
pressure-sensitive adhesive onto a silicone-treated release liner
and pressing the adhesive against the reflective layer).
[0045] A The surface treated optical elements are also useful in
pavement marking materials. The optical elements can be
incorporated into coating compositions that generally comprise a
film-forming material having a multiplicity of optical elements
dispersed therein. The surface treated optical elements may also be
used in drop-on applications for such purposes as highway lane
striping in which the optical elements are simply dropped onto wet
paint or hot thermoplastic and adhered thereto.
[0046] One typical pavement marking sheet is described in U.S. Pat.
No. 4,248,932. This sheet material is a prefabricated strip adapted
to be laid on and secured to pavement for such purposes as lane
dividing lines and comprises a base sheet, such as a soft aluminum
foil which is conformable to a roadway surface; a top layer (also
called the support film or binder film) adhered to one surface of
the base, sheet and being very flexible and resistant to rupture;
and a monolayer of surface treated optical elements such as
transparent microsphere lens elements partially embedded in the top
layer in a scattered or randomly separated manner. The pavement
marking sheet construction may also include an adhesive (e.g.,
pressure sensitive, heat or solvent activated, or contact adhesive)
on the bottom of the base sheet. The base sheet may be made of an
elastomer such as acrylonitrile-butadiene polymer, polyurethane, or
neoprene rubber. The top layer in which the surface treated
microspheres are embedded is typically a polymer such as vinyl
polymers, polyurethanes, epoxies, and polyesters. Alternatively,
the surface treated microsphere lenses may be completely embedded
in a layer of the pavement marking sheet.
[0047] Pavement marking sheets may be made by processes known in
the art (see e.g. U.S. Pat. No. 4,248,932), one example comprising
the steps of: (i) coating onto a base sheet of soft aluminum (50
micrometers thick) a mixture of resins (e.g., epoxy and
acrylonitrile butadiene elastomer mixture), pigment (TiO.sub.2) and
solvent (e.g., methyl ethyl ketone) to form the support film; (ii)
dropping onto the wet surface of the support film ingredients a
multiplicity of the surface treated optical elements of the
invention; and curing the support film at 150.degree. C. for about
10 minutes. A layer of adhesive is then usually coated on the
bottom of the base sheet.
[0048] Pigments or other coloring agents may be included in the top
layer in an amount sufficient to color the sheet material for use
as a traffic control marking. Titanium dioxide will typically be
used for obtaining a white color; whereas, lead chromate will
typically be used to provide a yellow color.
[0049] A rear projection screen is a sheet-like optical device
having a relatively thin viewing layer that is placed at an image
surface of an optical projection apparatus. Rear projection screen
displays comprising glass microspheres embedded in an opaque matrix
are known from U.S. Pat. No. 2,378,252, for example. Generally, the
size of the microspheres is less than about 150 microns. For
maximum brightness, the microspheres have an index of refraction of
less than about 1.8 and preferably from about 1.45 to about 1.75. A
plurality of the surface treated glass microspheres are attached to
and are in intimate contact with a major surface of a transparent
substrate. Alternatively, a diffusion layer can be formed by
coating an optically inhomogeneous material as a separate layer
onto the transparent substrate prior to application of the opaque
binder and microspheres. Rear projection screens are prepared by i)
providing a substrate (e.g. polyester , polycarbonate) having an
opaque binder disposed thereon (e.g. acrylate loaded with carbon
black to make it opaque); and ii) applying the surface treated
glass microspheres under conditions effective to produce
microspheres in optical contact with the substrate and embedded in
the opaque matrix.
[0050] In some useful embodiments of the invention, a specular
reflective means is provided by a layer of metal (e.g. aluminum)
vapor-deposited on the surface treated microspheres. Another useful
specular reflective means is a dielectric reflector which comprises
one or more layers of a transparent material behind the
microspheres, each layer having a refractive index of about 0.3
higher or lower than that of the adjacent layer or beads and each
layer having an optical thickness corresponding to an odd numbered
multiple of about 1/4 wavelength of light in the visible range.
More detail on such dielectric reflectors is found in U.S. Pat. No.
3,700,305.
[0051] The invention is further illustrated by the following
examples.
[0052] Test Methods
[0053] 1. Heptane Floatation--A single layer of optical elements
was spread on a clean inverted pint paint can lid. Heptane was
slowly introduced with a syringe or dropper at the edge of the lid
until it overflows. The percentage of optical elements floating was
estimated visually. In the absence of indicating otherwise, the
beads were tested within 24 hours of being coated with the surface
treatment.
[0054] 2. Initial Adhesion--A polyurethane liquid binder having the
following components was prepared:
1 27 parts Rutile titanium dioxide pigment (commercially available
from Dupont, New Johnsonville, TN under the trade designation
Tipure R-960") 25 parts polyester polyol (commercially available
from Union Carbide Corp., Danbury, CT under the trade designation
"Tone 0301") 50 parts aliphatic polyisocyanate (commercially
available from Bayer Corp., Pittsburgh, PA under the trade
designation Desmodur N-100)
[0055] The binder was drawn down on a paper liner at thickness of
0.4 mm. Immediately thereafter, a plurality of the indicated glass
beads were cascaded over the binder, maximizing the number of
adhered beads per surface area of binder. The bead coated binder
was then cured in an oven (100.degree. C. for 30 minutes is
typically sufficient for the polyurethane binder). The bead-coated
binder film was examined under a microscope. The sample passes when
the optical elements are embedded to about 40-70% of their
diameters.
[0056] 3. Accelerated Aging Adhesion--A1/4" by 1" piece of cured
bead-coated binder film, prepared for the Initial Adhesion Test, is
placed in a flask of boiling water for 24 hours. The aged sample is
then inspected under a microscope to determine whether the optical
elements remain embedded. The sample passes when the sample appears
approximately the same as the initial sample and the beads are
difficult to remove with a dissection probe.
[0057] 4. Coefficient of Retroreflection (RA), in cd/Lux/m.sup.2,
was measured at an entrance angle of -4.0 degrees and an
observation angle of 0.2.degree. according to Procedure B of ASTM
Standard B 809-94a. The photometer used for the measurements is
described in U.S. Defensive Publication No. T987,003.
[0058] In general, the R.sub.F-[X]Y polyfluoropolyethers used in
the examples had the following structures:
[0059] "Structure A" is
X--CF.sub.2O(CF.sub.2O).sub.m(C.sub.2F.sub.4O).sub- .pCF.sub.2X
(<m> and <p> .about.10-12)
[0060] "Structure B" is
C.sub.3F.sub.7O(CF(CF.sub.3)CF.sub.2O).sub.pCF(CF.- sub.3)--X
[0061] "Structure C" is
X--CF.sub.2O(C.sub.2F.sub.4O).sub.mCF.sub.p--X
[0062] A perfluoropolyether diol having Structure C wherein
X=CH.sub.2OH, and Mn.about.1250 was prepared as described in U.S.
Pat. No. 5,266,650 (Example 1). A perfluoropolyether diamine having
Structure A wherein X=CH.sub.2NH.sub.2 was prepared as described in
U.S. Pat. No. 3,810,874 (Example 14). The other perfluoropolyether
starting compounds employed in the examples were commercially
available. The source of these compounds as well as the structure
and number average molecular weight is depicted in the following
Table I.
2TABLE I Trade Supplier, Designation Location Structure X Mn
"Fomblin " Z- Ausimont USA, A CO.sub.2CH.sub.3 .about.2000 DEAL
Thorofare, NJ "Fomblin" Z- Ausimont USA, A CO.sub.2H .about.2100
DIAC Thorofare, NJ "Fluorolink" C Ausimont USA, A CO.sub.2H
.about.2200 Thorofare, NJ "Krytox" 157 Dupont, B CO.sub.2H
.about.2500 FSL Wilmington, DE "Krytox" 157 Dupont, B CO.sub.2H
.about.3500-4000 FSM Wilmington, DE "Krytox" 157 Dupont, B
CO.sub.2H .about.7000-7500 FSH Wilmington, DE "Fluorolink" Ausimont
USA, * CO.sub.2H .about.700 7004 Thorofare, NJ *monofunctional
C.sub.3 perfluoropolyether, exact structure unknown
[0063] Optical Elements
[0064] Different type's of reflective beads were employed to
evaluate the effectiveness of the surface treatment of the
invention. Type 1 reflective glass beads had an index of refraction
of 2.3 and an average diameter of 71 microns. Type 2 reflective
glass beads had an index of refraction of 2.3 and an average
diameter of 56 microns. Both the Type 1 and Type 2 beads are
representative of optical elements commonly used for reflective
sheeting. The Type 1 and Type 2 glass beads had a density of about
4.6 and are composed of barium, titanium and zinc oxides as
described in U.S. Pat. No. 3,493,403. Type 3 reflective glass
beads, commercially available from Nippon Electric Glass, Osaka,
Japan under the trade designation "K-68", had an index of
refraction of 2.2. The "K-68" beads are also available having a
silane pretreatment (Type 3--pretreated). Type 4, Type 5, and Type
6 reflective glass beads are representative of optical elements
commonly employed for reflective paint (e.g. pavement markings).
The Type 4 and Type 5 glass beads were obtained from Flex-O-Lite
Corporation, Fenton, Mo. Type 4, having the trade designation "831"
had an average diameter of 65 microns and an index of refraction of
1.9. Type 5 had an index of refraction of 1.5 and a size gradation
that complies with the American Association of State Highway and
Transportation Officials designation M 247-81. Type 6 glass beads
had an average diameter of 200 microns, an index of refraction of
1.75 and were prepared according to the teaching of U.S. Pat. No.
4,564,556.
[0065] For Examples 1-32 and 38-51, the optical elements were
surface treated by charging a 25 g sample of the indicated bead
type into a round-bottom flask. A sufficient amount (8-10 ml) of
the indicated solvent (deionized water, methanol, isopropanol,
dichloromethane or HFE 7100-methyl perfluorobutyl ether, obtained
from Minnesota Mining & Manufacturing "3M" Company, St. Paul,
Minn.) was added to cover and wet out the beads. The
perfluoropolyether derivative was then added, as a dilute (usually
1 wt %) solution, in an amount to provide the desired treatment
level, 50-600 ppm based on the weight of the reflective beads. Most
of the solvent was removed by rotary evaporation. The beads were
heated in a forced-air oven at 120.degree. C. for 30 min (for
samples treated out of organic solvent) or 2 hr (for samples
treated out of water, in which case the rotary evaporation step was
omitted.) The dried beads were then tested in the heptane float
test as described above.
[0066] Examples 1-17 of Table II depict the percent float of Type 1
reflective beads that were surface treated with various
perfluoropolyether acid salts solutions employing the solvent
indicated in column 2 and the concentration (loading) of
perfluoropolyether indicated in column 3. Each of the indicated
perfluoropolyether carboxylic acid derivatives were converted to
the corresponding salt by first diluting a sample of the
perfluoropolyether carboxylic acid (generally 1-2 g) to 10 wt % in
methanol in a screw-top vial. For the "Fomblin", "Fluorolink" C,
and "Krytox" 157 FS perfluoropolyether acids, the dilution yielded
a cloudy, two-phase mixture. The mixture was shaken while a
solution of concentrated ammonium hydroxide or 10 wt % potassium
hydroxide in water was added dropwise until the mixture clarified,
leaving a foamy solution. For "Fomblin" Z-DIAC and "Krytox" 157
FSL, the resulting solutions of ammonium salts were clear. For
"Fluorolink" C and "Krytox" 157 FSM, and the potassium salt of
"Krytox" 157 FSL, the neutralized salt solutions were slightly
hazy. The neutralized ammonium salt mixture of "Krytox" 157 FSH,
was hazy and only partially translucent. The mixture did not foam
upon shaking and exhibited some phase separation after standing at
room temperature overnight. Each solution was then diluted further
to 1 wt % with additional methanol prior to application to the
reflective beads as surface treatments. Comparative A is a solution
of 31.5 wt % N-ethyl-N-perfluorooctanesulfony- lglycine chromium
complex in isopropanol, prepared as described according to U.S.
Pat. No. 2,809,990 (Example 1). The solution was diluted with
methanol to 1 wt % solids. The percent float is reported in Table
II. The results demonstrate that 100% bead float can be obtained
lower concentrations of perfluoropolyether treatment than with the
prior art N-ethyl-N-perfluorooctanesulfonylglycine chromium
complex.
3TABLE II % Float of Beads Treated with Perfluoropolyether
Carboxylic Acid Salts Loading Perfluoropolyether Acid Salt Solvent
(ppm) % Float Ex. 1 - "Krytox" 157 FSL NH.sub.4.sup.+ Water 150
.about.100 Ex. 2 - "Krytox" 157 FSL NH.sub.4.sup.+ Water 100
.about.100 Ex. 3 - "Krytox" 157 FSL NH.sub.4.sup.+ Water 50
.about.100 Ex. 4 - "Krytox" 157 FSL NH.sub.4.sup.+ Methanol 150
.about.100 Ex. 5 - "Krytox" 157 FSM NH.sub.4.sup.+ Water 150
.about.100 Ex. 6 - "Krytox" 157 FSM NH.sub.4.sup.+ Methanol 150
.about.100 Ex. 7 - "Krytox" 157 FSH NH.sub.4.sup.+ Water 150
.about.100 Ex. 8 - "Krytox" 157 FSH NH.sub.4.sup.+ Methanol 150
.about.100 Ex. 9 - "Krytox" 157 FSL K.sup.+ Water 150 .about.100
Ex. 10 - "Krytox" 157 FSL K.sup.+ Methanol 150 .about.100 Ex. 11 -
"Krytox" 157 FSL K.sup.+ Methanol 300 .about.100 Ex. 12 - "Fomblin"
Z-DIAC NH.sub.4.sup.+ Water 50 .about.100 Ex. 13 - "Fomblin" Z-DIAC
NH.sub.4.sup.+ Water 100 .about.100 Ex. 14 - "Fomblin" Z-DIAC
NH.sub.4.sup.+ Water 150 .about.100 Ex. 15 - "Fomblin" Z-DIAC
NH.sub.4.sup.+ Methanol 150 .about.100 Ex. 16 - "Fluorolink" C
NH.sub.4.sup.+ Water 150 .about.100 Ex. 17 - "Fluorolink" C
NH.sub.4.sup.+ Methanol 150 .about.100 Comparative A Water 50
.about.50 Comparative A Water 100 .about.80 Control - No Surface
Treatment Water 0 <10 Control - No Surface Treatment Methanol 0
<10
[0067] A solution of 1 wt % "Fluorolink" 7004 carboxylic acid in
methanol was prepared. Type 1 beads were coated in the same manner
as previously described. Table III depicts the % float obtained
with this acid-terminated perfluoropolyether, employing the solvent
indicated in column 1 and the concentration (loading) indicated in
column 2.
4TABLE III % Float of Beads Treated with "Fluorolink" 7004
Carboxylic Acid Solvent Loading (ppm) % Float Ex. 18 - Methanol 150
.about.60 Ex. 19 - Methanol 300 .about.100 Ex. 20 - Water 150
.about.100 Control - Water 0 <10 Control - Methanol 0 <10
EXAMPLES 21-23
[0068] A perfluoropolyether derivative having Structure A wherein
X=CONH.sub.2 (Ex. 21) was prepared by bubbling ammonia gas through
a sample of "Fomblin" Z-DEAL (Structure A wherein
X=CO.sub.2CH.sub.3), until infrared analysis indicated complete
replacement of ester with amide. Perfluoropolyether derivatives
having Structure A wherein X=CONH(n-C.sub.6H.sub.13) (Ex. 22),
Structure A wherein X=CONHCH.sub.2CH.sub.2Ph (Ex. 23), and
Structure A wherein
X=CONHCH.sub.2CH.sub.2CH.sub.2Si(OCH.sub.3).sub.3 (Ex. 24), were
prepared by titration of "Fomblin" Z-DEAL with, respectively,
n-hexylamine, 2-phenylethylamine, and
3-aminopropyltrimethoxysilane. The reaction was monitored by
infrared analysis to confirm complete replacement of ester with
amide. These derivatives were used without further purification or
removal of byproduct methanol. The perfluoropolyether bis(amides)
(Ex. 21-23) were dissolved in methanol to make three 1 wt %
solutions. Each solution was then used to treat Type 1 reflective
beads employing methanol as the solvent, using the procedure
described above. The loading level was 150 ppm. All three samples
exhibited .about.100% bead float in the float test, while a control
sample treated with methanol exhibited <10% float.
EXAMPLE 24-31
[0069] Each of the perfluoropolyether derivatives depicted in Table
IV were diluted in HFE 7100 to make 1 wt % solutions. These
solutions were used to treat Type 1 or Type 2 beads in additional
HFE 7100 or isopropanol as solvent (per column 3), in the same
manner as described above. Comparative Examples B & C are
perfluoropolyether oils having Structure B and X=F (no polar
group). The Comparative Examples were diluted to 1 wt % in HFE 7100
and in additional HFE 7100 to obtain the desired treatment level.
The bead type, solvent type, concentration (loading), and percent,
float are shown in Table IV as follows. The results demonstrate the
importance of the polyfluoropolyether structure having a polar
group or polar group-containing organic radical for use in the
invention as a surface treatment.
5TABLE IV % Float of Beads Treated with Perfluoropolyether
Derivatives Bead Loading Perfluoropolyether Derivative Type Solvent
(ppm) % Float Ex. 24- Structure A, X = 1 HFE 7100 100 .about.100
CONHCH.sub.2CH.sub.2CH.sub.2Si(OCH.sub.3).sub.3 Ex. 25 - Structure
C, X = 1 HFE 1700 150 .about.100 CH.sub.2OH Ex. 26 - Structure C, X
= 1 HFE 1700 300 .about.100 CH.sub.2OH Ex. 27 - "Fomblin" Z-DEAL 2
Isopropanol 600 .about.100 Ex. 28 - Structure A, X = 2 Isopropanol
600 .about.100 CH.sub.2NH.sub.2 Ex. 29 - "Krytox" 157 FSL 2
Isopropanol 600 .about.100 Ex. 30 - "Krytox" 157 FSM 2 Isopropanol
600 >90 Ex. 31 - "Krytox" 157 FSH 2 Isopropanol 600 >80
Comparative B - "Krytox" 1514 1 HFE 7100 150 <5% Comparative B -
"Krytox" 1514 1 HFE 7100 300 <5% Comparative C - "Krytox" 1645 1
HFE 7100 150 <5% Comparative C - "Krytox" 1645 1 HFE 7100 300
<5% Control (no surface treatment) 1 -- 0 <10 Control (no
surface treatment) 1 -- 0 <10
EXAMPLE 32
[0070] The perfluoropolyether diamine derivative having Structure A
wherein X=CH.sub.2NH.sub.2 was diluted to 1 wt % in methanol in a
screw top vial, yielding a hazy, two-phase mixture. The mixture was
shaken while adding 1N HCl solution dropwise until the mixture
clarified, leaving a clear, foamy solution. The mixture was diluted
further with deionized water to obtain a solution of the
perfluoropolyether bis (amine hydrochloride) salt in 3:1 (w/w)
water:methanol. Appropriate amounts of this 0.25% solution were
then added to samples of Type 1 beads to obtain loadings of 100,
300, and 600 ppm. The samples were oven dried as described
previously, and tested for % float. The 100 ppm concentration
resulted in .about.75% float, whereas the 300 and 600 ppm
concentrations resulted in .about.100% float.
EXAMPLES 33-36
[0071] A surface treatment solution was prepared by adding 20 g of
"Krytox" 17 FSL to 180 g methanol in a 500 ml Erlenmeyer flask
equipped with magnetic stirring. While stirring vigorously,
concentrated ammonium hydroxide aqueous solution was added dropwise
(about 0.6 g) until the cloudy, two-phase mixture became clear,
indicative of a single-phase, homogeneous solution. 1.322 g of the
homogeneous solution was diluted with 8.68 g of deionized water.
Four type of beads were surface treated by hand mixing 50 grams of
each bead type with 0.675 ml of the diluted solution. The coated
beads were dried at 90.degree. C. in a forced air oven. The percent
float was determined and is reported in Table IV as follows.
6TABLE V % Float of Beads Treated with Perfluoropolyether
Carboxylic Acid Salts Bead Type % Float Ex. 33 - Type 3 .about.100
Ex. 34 - Type 3 (pretreated) .about.100 Ex. 35 - Type 4 .about.100
Ex. 36 - Type 5 .about.100
EXAMPLE 37
Aqueous Delivery of Krytox 157FSL Acid without Cosolvents
[0072] An 8 oz screw-top jar was charged with approximately 0.03 g
"Krytox" 157 FSL acid and 60 g deionized water. The jar was capped
and shaken to yield a cloudy, coarse, unstable emulsion. Type 1
reflective beads (200 g, .about.150 ppm perfluoropolyether acid
treatment were added, and the mixture was shaken vigorously to wet
out the beads. When the beads were allowed to settle, the
supernatant liquid was seen to have clarified. The sample was dried
in a forced air oven at 120.degree. C. for 3.5 hr. After cooling,
the beads were tested and found to give .about.100% float. The
beads were retested after storage of the surface treated beads at
room temperature for 48 hours. The beads continued to exhibit
.about.100% float.
[0073] Table VI depicts other fluorochemical surface treatments
that are substantially free of long chain perfluoroalkyl groups.
These surface treatments were used to coat Type 1 beads in the
manner previously described with the exception that Example 46
employed the Type 2 beads.
7TABLE VI % Float of (C.sub.nF.sub.2n+1)-[X] Fluorochemical Surface
Treatments Loading Surface Treatment Solvent (ppm) % Float Sulfonic
Acids & Salts Ex. 38 - C.sub.4F.sub.9SO.sub.3H Methanol 300
.about.100 Ex. 39 - C.sub.4F.sub.9SO.sub.3H Methanol 150 .about.100
Ex. 40 - C.sub.4F.sub.9SO.sub.3H Water 150 .about.100 Ex. 41 -
C.sub.4F.sub.9SO.sub.3Li Methanol 300 .about.100 Ex. 42 -
C.sub.4F.sub.9SO.sub.3Li Methanol 150 .about.100 Ex. 43 -
C.sub.4F.sub.9SO.sub.3Li Water 150 .about.90 Sulfonimides &
Salts Ex. 44 - (C.sub.4F.sub.9SO.sub.2).sub.2NH Methanol 300
.about.100 Ex. 45 - (C.sub.4F.sub.9SO.sub.2).sub.2NH Methanol 150
.about.100 Ex. 46 - (C.sub.4F.sub.9SO.sub.2).sub.2NH Water 150
.about.100 Ex. 47 - (C.sub.4F.sub.9SO.sub.2).sub.2NK Isopropanol
600 >90 Fluorinated Acids Ex. 48 - n-C.sub.3F.sub.7CO.sub.2H
Methanol 300 >90 Fluoroalkyl Silane Ex. 49 -
(CF.sub.3).sub.2CFO(CH.s- ub.2).sub.3SiCl.sub.3 CH.sub.2Cl.sub.2
150 .about.100 Ex. 50 -
(CF.sub.3).sub.2CFO(CH.sub.2).sub.3SiCl.sub.3 CH.sub.2Cl.sub.2 300
.about.100 Ex. 51 - (CF.sub.3).sub.2CFO(CH.sub.2).sub.3SiCl.sub.3
CH.sub.2Cl.sub.2 600 .about.100 Comparative A Methanol 300
.about.100 Control - No Treatment -- -- .about.10-20
[0074] Adhesion testing was conducted on some of the surface
treated glass beads. Type 6 glass beads were pretreated with 600
ppm of 3-aminopropyltriethoxysilane commercially available from OSI
Specialties, Danbury, Conn. under the trade designation "Silquest
A-1100". The "Krytox" 157 FSL NH.sub.4.sup.+ surface treatment was
prepared as previously described. Ten wt-% solutions of
"Fluorolink" C and "Fluorolink" 7004 were prepared with isopropanol
and ethanol, respectively. The solutions were further diluted with
water to obtain the desired treatment level. Type 6 beads were
coated with the surface treatment indicated in column 1 at the
treatment level indicated in column 2 in the manner previously
described. Table VII depicts the % Float, Initial Adhesion,
Accelerated Aging Adhesion, and the Coefficient of Retroreflection
(RA).
8TABLE VII Initial Ad- Accelerated Surface Loading % hesion Aging
RA Treatment (ppm) Float (%) (pass/fail) (cd/lux/m.sup.2) Control*
(none) 0 0 .about.95 ** .62 Control (none) 0 0 .about.95 ** .98 Ex.
52 "Krytox" 50 .about.95 .about.40 Pass 8.47 157 FSL NH.sub.4.sup.+
Ex. 53 50 .about.95 .about.40 Pass 8.79 "Fluorolink" C Ex. 54 50
.about.80 .about.55 Pass 8.29 "Fluorolink 7004" * no "Silquest
A-1100" ** Could not be determined since the beads were embedded to
95%
* * * * *