U.S. patent application number 15/566439 was filed with the patent office on 2018-04-19 for surface modification of silicones.
The applicant listed for this patent is Dow Corning Corporation. Invention is credited to Michael BACKER, Hans Peter WOLF.
Application Number | 20180104889 15/566439 |
Document ID | / |
Family ID | 53298783 |
Filed Date | 2018-04-19 |
United States Patent
Application |
20180104889 |
Kind Code |
A1 |
BACKER; Michael ; et
al. |
April 19, 2018 |
SURFACE MODIFICATION OF SILICONES
Abstract
A process for modifying a silicone elastomeric-based surface of
an article where the coefficient of friction (COF) of the silicone
elastomeric-based surface is generally reduced by at least 5% is
disclosed. The process comprises subjecting the silicone
elastomeric-based surface of the article to vacuum ultraviolet (UV)
radiation.
Inventors: |
BACKER; Michael; (Mainz,
DE) ; WOLF; Hans Peter; (Liederbach, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dow Corning Corporation |
Midland |
MI |
US |
|
|
Family ID: |
53298783 |
Appl. No.: |
15/566439 |
Filed: |
April 14, 2016 |
PCT Filed: |
April 14, 2016 |
PCT NO: |
PCT/EP2016/058245 |
371 Date: |
October 13, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 59/16 20130101;
D06N 2209/108 20130101; D06M 10/10 20130101; B64D 17/02 20130101;
D06M 15/715 20130101; D06N 3/128 20130101; B29C 2791/006 20130101;
B60R 2021/23533 20130101; D06N 3/0036 20130101; B60R 21/235
20130101; C08L 83/00 20130101; D06N 2211/00 20130101; C08J 7/123
20130101; D06N 3/0006 20130101; B60R 2021/23514 20130101; D06N
3/0081 20130101; D06N 2211/268 20130101; D06M 15/3568 20130101;
D06N 3/0059 20130101 |
International
Class: |
B29C 59/16 20060101
B29C059/16; C08J 7/12 20060101 C08J007/12; C08L 83/00 20060101
C08L083/00; D06N 3/12 20060101 D06N003/12; D06N 3/00 20060101
D06N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2015 |
GB |
1506589.9 |
Claims
1. A process for modifying a silicone elastomeric-based surface of
an article, said process comprising: subjecting the silicone
elastomeric-based surface of the article to vacuum ultraviolet
radiation; wherein the coefficient of friction of the silicone
elastomeric-based surface is reduced by at least 5%.
2. The process according to claim 1, wherein the silicone
elastomeric-based surface of the article consists of silicone
elastomer.
3. The process according to claim 2, wherein the silicone elastomer
is the reaction product of a hydrosilylation or peroxide cure of an
alkenyl-functional organopolysiloxane and a Si--H functional
organopolysiloxane.
4. The process according to claim 1, wherein the article is a
molded article made of silicone elastomer.
5. The process according to claim 4, wherein the molded article is
a case for an electronic device, an optical device, a medical
device, a sport and leisure device, or a toy.
6. The process according to claim 4, wherein the molded article is
formed by extrusion.
7. The process according to claim 4, wherein the molded article
comprises tubing.
8. The process according to claim 4, wherein the molded article is
a car part or a case for an electronic device and wherein the
silicone elastomer is overmolded over at least part of the
article.
9. The process according to claim 1, wherein the article is a
silicone elastomer coated article.
10. The process according to claim 1, wherein the article is
coated, overmolded, molded or extruded, and is subsequently
subjected to vacuum ultraviolet radiation.
11. The process according to claim 1, wherein the vacuum
ultraviolet radiation is performed using an excimer lamp.
12. The process according to claim 1, wherein the vacuum
ultraviolet radiation is performed using a low-pressure mercury
lamp.
13. The process according to claim 1, wherein the vacuum
ultraviolet radiation is performed on a conveyor belt.
14. An article having a silicone elastomeric-based surface, which
surface is modified by the process according to claim 1.
15. The article according to claim 14, wherein the silicone
elastomeric-based surface has a modified surface layer of less than
1 mm in thickness.
16. The article according to claim 14, wherein the article is a
molded silicone article free of a non-silicone elastomeric coating
layer.
17. (canceled)
18. A case for an electronic device or an optical device or a
medical device or a sport and leisure device or a toy formed by the
process according to claim 1.
Description
[0001] This invention relates to modifying the surface of a
silicone article and to silicon articles having a modified surface.
In particular we have found that the surface of a silicone article
can be modified to reduce the coefficient of friction of the
silicone surface. Silicones, for example silicone elastomers, are
resilient, impact resistant, mouldable and resistant to heat,
moisture and chemicals. Silicone elastomers may be electrically
insulating. In some instances, silicone elastomers may be used for
the manufacture of moulded articles such as casings. Moulded
silicone elastomers have a surface which is soft but tend to pick
up dust and may even be tacky. For uses such as casings for
electronic devices, for example hand held electronic devices, the
silicone elastomer surface has generally been coated or covered
with a harder plastics material.
[0002] US-A-2013/0037207 describes a method for adhering a hard
silicone resin and a substrate, the method comprising the steps of:
applying excitation treatment to a surface of a hard silicone
resin; juxtaposing and pressurizing the surface and a substrate;
and adhering the hard silicone resin and the substrate.
[0003] US-A-2010/304133 describes a method for producing a
transparent resin plate in which a resin substrate is covered with
a hard-coat layer, comprising: forming said hard-coat layer out of
silicone polymer by a wet method; irradiating a region of the
hard-coat layer with vacuum ultraviolet rays from an ultraviolet
light source, wherein the vacuum ultraviolet layers have a
wavelength less than 200 nm, and wherein only said region is
reformed, by exposure to the irradiation, into a hardened film
mainly composed of silicon dioxide.
[0004] K. Efimenko et al in J. Colloid and Interface Science 254,
306-315 (2002) describe surface modification of a
polydimethylsiloxane (PDMS) elastomer by UV and UV/ozone treatment,
for use for example in soft lithography.
[0005] V-M. Graubner et al in Macromolecules 2004, 37, 5936-5943
describe photochemical modification of crosslinked PDMS by
irradiation at 172 nm. Irradiation results in a large increase in
surface free energy and surface oxidation of the polymer.
[0006] P. Swiderek et al in Macromol. Mater. Eng. 2012, 297,
1091-1101, describe crosslinking of thin liquid PDMS layers by
H.sub.2 radio frequency plasma treatment, by Xe.sub.2 excimer VUV
irradiation and by low energy electron beam.
[0007] A process according to the present invention for modifying a
silicone elastomeric based surface of an article is characterised
in that the coefficient of friction of the silicone surface is
reduced by at least 5% by subjecting the article to vacuum
ultraviolet (VUV) radiation.
[0008] The invention includes an article having a silicone
elastomeric based surface, which surface is modified by the above
process and having a reduction of coefficient of friction reduced
by at least 5%.
[0009] Ultraviolet (UV) light is an electromagnetic radiation with
a wavelength from 400 nm to 10 nm, shorter than that of visible
light but longer than X-rays. By vacuum ultraviolet (or VUV)
radiation we mean radiation of wavelength 120 to 200 nm.
[0010] The article having a silicone elastomeric based surface can
be a molded article made of a silicone elastomer or of a silicone
elastomeric based composition, that is, a blend of a silicone
elastomer with a compatible polymer, or a silicone elastomer
containing a particulate filler. The article can for example be
moulded by injection moulding, blow moulding, compression moulding
or extrusion.
[0011] The article having a silicone elastomeric based surface can
be an article in which a silicone elastomer or a silicone
elastomeric based composition has been overmoulded over at least
part of the article, or eventually over the entire external surface
of the article.
[0012] Alternatively the article having a silicone elastomeric
based surface can be a silicone elastomer coated article. The
article may be a textile or fabric such as nylon or polyester; a
reinforced textile such as silicone elastomer reinforced textile; a
silicone elastomer based article. In such events, the surface
modification does not alter the silicone elastomeric properties of
the final silicone elastomer coated article.
[0013] Further articles which may be coated by a silicone
elastomeric based surface can be exemplified by various metals,
thermoplastic plastics, thermosetting plastics, rubbers such as
silicone rubbers and so forth, backing fabrics, electronic parts
and components, and light-emitting elements.
[0014] The vacuum ultraviolet treatment according to the invention
preferably takes place after any curing reaction of the silicone
elastomer or of the silicone elastomer based composition, and after
the silicone elastomer or the silicone elastomer based composition
has been shaped by moulding or coating. The vacuum ultraviolet
treatment can advantageously be a post-treatment of a finished
article produced from a silicone elastomer or from a silicone
elastomer based composition.
[0015] Silicone elastomers may be prepared by curing an
alkenyl-functional organopolysiloxane and a Si--H functional
organopolysiloxane. The alkenyl-functional organopolysiloxane and
the Si--H functional organopolysiloxane can be cured in the
presence of a hydrosilylation catalyst or in the presence of a
peroxide catalyst.
[0016] The alkenyl-functional organopolysiloxane generally has at
least two alkenyl groups per molecule, for example vinyl, hexenyl,
allyl, butenyl, pentenyl, or heptenyl groups. Silicon-bonded
organic groups in the alkenyl-functional organopolysiloxane other
than the alkenyl groups may be exemplified by methyl, ethyl,
propyl, butyl, pentyl, hexyl, or similar alkyl groups; or phenyl,
tolyl, xylyl, or similar aryl groups; or hydroxyalkyl groups such
as HOCH.sub.2CH.sub.2-- or groups derived from ethylene glycol or
propylene glycol such as HOCH.sub.2CH.sub.2O(CH.sub.2).sub.3-- or
HOCH.sub.2CH(CH.sub.3)O(CH.sub.2).sub.3--. All or part of the
alkenyl-functional organopolysiloxane may have a predominantly
linear molecular structure and can for example comprise an
.alpha.,.omega.-vinyldimethylsiloxy polydimethylsiloxane, an
.alpha.,.omega.-vinyldimethylsiloxy copolymer of
methylvinylsiloxane and dimethylsiloxane units, and/or an
.alpha.,.omega.-trimethylsiloxy copolymer of methylvinylsiloxane
and dimethylsiloxane units. The alkenyl-functional
organopolysiloxane can optionally additionally comprise a branched
organopolysiloxane containing alkenyl units.
[0017] The Si--H functional organopolysiloxane generally has at
least two, and preferably has at least 3, Si-bonded hydrogen atoms
per molecule. It can for example be a low molecular weight
organosilicon resin or a short or long chain organosiloxane
polymer, which may be linear or cyclic. The Si--H functional
organopolysiloxane may for example have the general formula
##STR00001##
wherein R.sup.4 denotes an alkyl or aryl group having up to 10
carbon atoms, and R.sup.3 denotes a group R.sup.4 or a hydrogen
atom, p has a value of from 0 to 20, and q has a value of from 1 to
70, and there are at least 2 or 3 silicon-bonded hydrogen atoms
present per molecule. R.sup.4 can for example be a lower alkyl
group having 1 to 3 carbon atoms, such as a methyl group. Examples
of suitable Si--H functional organopolysiloxanes include
trimethylsiloxane end-blocked polymethylhydrosiloxanes,
dimethylhydrosiloxane end-blocked methylhydro siloxane,
dimethylsiloxane methylhydrosiloxane copolymers and
tetramethylcyclotetrasiloxane. A mixture of more than one of these
materials can be used.
[0018] The molar ratio of Si--H groups in the organopolysiloxane
(B) to aliphatically unsaturated groups in the organopolysiloxane
(A) is preferably at least 1:1 and can be up to 8:1 or 10:1. For
example the molar ratio of Si--H groups to aliphatically
unsaturated groups is in the range from 1.3:1 to 5:1.
[0019] The hydrosilylation catalyst (C) is preferably a platinum
group metal (Group VIII of the Periodic Table) or a compound
thereof. Platinum and/or platinum compounds are preferred, for
example finely powdered platinum; a chloroplatinic acid or an
alcohol solution of a chloroplatinic acid; an olefin complex of a
chloroplatinic acid; a complex of a chloroplatinic acid and an
alkenylsiloxane; a platinum-diketone complex; metallic platinum on
silica, alumina, carbon or a similar carrier; or a thermoplastic
resin powder that contains a platinum compound. Catalysts based on
other platinum group metals can be exemplified by rhodium,
ruthenium, iridium, or palladium compounds. For example, these
catalysts can be represented by the following formulas:
RhCl(PPh.sub.3).sub.3, RhCl(CO)(PPh.sub.3).sub.2,
Ru.sub.3(CO).sub.12, IrCl(CO)(PPh.sub.3).sub.2, and
Pd(PPh.sub.3).sub.4 (where Ph stands for a phenyl group).
[0020] Further examples of hydrosilylation catalysts include cobalt
complexes containing terdentate pyridine di-imine ligands such as
(.sup.MesPDI)CoN.sub.2 and (.sup.MesPDI)CoCH.sub.3; and metal
terpyridine complexes such as
bis(trimethylsilyl)iron(11)terpyridine.
[0021] A silicone elastomer can be prepared from the
alkenyl-functional organopolysiloxane and Si--H functional
organopolysiloxane by curing in the presence of the hydrosilylation
catalyst typically at a temperature in the range 20 to 200.degree.
C., alternatively 50 to 190.degree. C., alternatively 80 to
190.degree. C. Curing can for example take place in a mould to form
a moulded silicone article. The composition comprising the
alkenyl-functional organopolysiloxane, the Si--H functional
organopolysiloxane and the catalyst can for example be injection
moulded to form an article, or the composition can be overmoulded
by injection moulding around an article.
[0022] Examples of peroxide catalysts include benzoyl peroxide,
4-monochlorobenzoyl peroxide, dicumyl peroxide, tert-butyl
peroxybenzoate, tert-butylcumyl peroxide, tert-butyloxide,
2,5-dimethyl-2,5-di-tert-butylperoxyhexane, 2,4-dichlorobenzoyl
peroxide, di-t-butylperoxy-diisopropylbenzene,
1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,
2,5-di-tert-butylperoxyhexane-3,2,5-dimethyl-2,5-bis(tert-butylperoxy)
hexane, or cumyl-tert-butylperoxide. These catalysts can be used
individually or in combinations of two or more.
[0023] A silicone elastomer can be prepared from the
alkenyl-functional organopolysiloxane and Si--H functional
organopolysiloxane by curing in the presence of the peroxide
catalyst at a temperature in the range 50 to 200.degree. C. Curing
can for example take place in a mould to form a moulded silicone
article by injection moulding or overmoulding.
[0024] An alternative type of silicone elastomer which benefits
from surface modification according to the invention is a high
consistency elastomer comprising a polyorganosiloxane gum having a
viscosity of 1000 Pas or more at 25.degree. C. Unless otherwise
indicated all viscosity values given herein were measured at
25.degree. C. The polyorganosiloxane gum can for example have
terminal silanol groups and be cured with a peroxide catalyst or
can have alkenyl terminal groups and be cured by a Si--H functional
organopolysiloxane and a hydrosilylation catalyst. High consistency
elastomers are generally too stiff to be injection moulded but can
be moulded and cured by compression moulding, for example at a
temperature in the range.
[0025] The silicone elastomer composition can contain a filler or
can be unfilled. The filler can be a reinforcing filler such as
silica or modified silica. Suitable other fillers include ground
quartz, ground cured silicone rubber particles, carbon black, glass
microspheres and calcium carbonate. The amount of filler can for
example be up to 75% by weight of the silicone elastomer
composition.
[0026] The silicone elastomer composition may further comprise a
silane, for example an organofunctional silane or organofunctional
siloxane oligomer. Examples of organofunctional groups which can
usefully be present in the silane include olefinically unsaturated
groups such as alkenyl groups, for example vinyl, allyl,
1-propenyl, isopropenyl, or hexenyl groups, or acrylate or
methacrylate groups. Examples of suitable unsaturated silanes
include 3-methacryloylpropyl trimethoxysilane, 3-methacryloylpropyl
triethoxysilane, vinyltrimethoxysilane or vinyltriethoxysilane.
[0027] The silicone elastomer composition may comprise other
additives known in the art. Such additives include but are not
limited to pigments, adhesion promoters, curing retarders, extender
fillers, heat resistance improvers, heat stabilizers, flame
retardants, inhibitors, chain extenders, plasticisers, electrically
conductive fillers, thermally conductive fillers. Further additives
include dyes, rheological modifiers, fungicides, biocides, UV
stabilizers, water scavengers,
[0028] Examples of pigments include iron oxide, colcothar, titanium
dioxide, zinc oxide, carbon black.
[0029] Examples of adhesion promoters include organic titanium
compounds such as organic titanic acid esters; metal chelate
compounds such as a titanium chelate compound, an aluminum chelate
compound, and a zirconium chelate compound; alkoxysilanes such as
aminoalkylalkoxy silanes, mercapto-alkylalkoxy silanes, epoxy
group-containing organoalkoxysilanes, acryloxy group-containing
organoalkoxysilane, and methacryloxy group-containing
organoalkoxysilanes; and organopolysiloxanes containing an epoxy
group, an alkenyl group and an alkoxy group in one molecule;
isocyanurates containing silicon groups such as
1,3,5-tris(trialkoxysilylalkyl) isocyanurates; reaction products of
epoxyalkylalkoxy silanes such as 3-glycidoxypropyltrimethoxysilane
with amino-substituted alkoxysilanes such as
3-aminopropyltrimethoxysilane and optionally alkylalkoxy silanes
such as methyl-trimethoxysilane. epoxyalkylalkoxy silane,
mercaptoalkylalkoxy silane, and derivatives thereof.
[0030] Examples of curing retarders include acetylene compounds
such as 1-ethynyl-1-cyclohexanol, 2-methyl-3-butyn-2-ol,
3,5-dimethyl-1-hexyn-3-ol, 3,5-dimethyl-1-octyn-3-ol and
2-phenyl-3-butyn-2-ol; enyne compounds such as
3-methyl-3-penten-1-yne and 3,5-dimethyl-3-hexen-1-yne; triazoles
such as benzotriazole; phosphines; mercaptanes; and hydrazines.
[0031] Examples of extender fillers include quartz powder,
diatomaceous earth, calcium carbonate, magnesium carbonate.
[0032] Examples of heat resistance improvers include cerium oxide,
cerium hydroxide, iron oxide, carbon black, iron carboxylate salts,
cerium hydrate, titania, barium zirconate, cerium octoates,
zirconium octoates, and porphyrins.
[0033] Examples of flame retardants include carbon black, aluminum
trihydrate, hydrated aluminium hydroxide, silicates such as
wollastonite, platinum and platinum compounds.
[0034] Examples of chain extenders include SiH-endcapped
polydimethylsiloxane.
[0035] Examples of plasticisers include unreactive short chain
siloxanes such as polydimethylsiloxane having terminal
triorganosiloxy groups wherein the organic substituents are, for
example, methyl, vinyl or phenyl or combinations of these groups,
generally having a viscosity of from about 5 to about 100,000 mPas;
dialkyl phthalates wherein the alkyl group may be linear and/or
branched and contains from six to 20 carbon atoms such as dioctyl,
dihexyl, dinonyl, didecyl, diallanyl and other phthalates; adipate,
azelate, oleate and sebacate esters, polyols such as ethylene
glycol and its derivatives, organic phosphates such as tricresyl
phosphate and/or triphenyl phosphates, castor oil, tung oil, fatty
acids and/or esters of fatty acids. Further examples of
plasticisers include mineral oil fractions comprising linear
(n-paraffinic) mineral oils, branched (iso-paraffinic) mineral oils
and/or cyclic (naphthenic) mineral oils, mineral oil fractions
comprising linear (n-paraffinic) mineral oils, branched
(iso-paraffinic) mineral oils and/or cyclic (naphthenic) mineral
oils.
[0036] Examples of electrically conductive fillers include carbon
black, metal particles such as silver particles, metal oxide
fillers such as titanium oxide powder whose surface has been
treated with tin and/or antimony, potassium titanate powder whose
surface has been treated with tin and/or antimony, tin oxide whose
surface has been treated with antimony, and zinc oxide whose
surface has been treated with aluminium.
[0037] Examples of thermally conductive fillers include metal
particles such as powders, flakes and colloidal silver, copper,
nickel, platinum, gold aluminium and titanium, metal oxides,
particularly aluminium oxide (Al.sub.2O.sub.3) and beryllium oxide
(BeO); magnesium oxide, zinc oxide, zirconium oxide; Ceramic
fillers such as tungsten monocarbide, silicon carbide and aluminium
nitride, boron nitride and diamond.
[0038] Silicone elastomers may be characterized by their hardness
(DIN 53505 Shore A), by their tensile strength and elongation at
break (DIN 53504-S1), and their tear-propagation resistance (ASTM
D624B).
[0039] Various methods may be used to expose surfaces to VUV
radiation.
[0040] Vacuum ultraviolet irradiation can be performed inside a
vessel which is evacuated or which is filled with an inert gas such
as argon, helium, xenon, neon or nitrogen. Vacuum ultraviolet
irradiation may be performed in ambient conditions, but may also be
performed in oxygen controlled atmosphere, typically with a level
of oxygen below 2%. Vacuum ultraviolet irradiation can for example
be performed at atmospheric pressure in an atmosphere of nitrogen
containing 1% oxygen by weight. The source of vacuum ultraviolet
irradiation can for example be a Xe.sub.2* excimer lamp emitting
incoherent light at a wavelength of 172 nm corresponding to a
photon energy of 7.2 eV and spectral bandwidth of 14 nm. An example
of such a lamp is Xeradex.RTM. vacuum ultraviolet Excimer Lamp
supplied by Osram GmbH. The distance between the lamp outer rim and
the silicone surface can for example be from 1 to 30 cm. The
irradiation energy density can for example be between 20 and 200
Jcm.sup.-2. The irradiation duration can for example be 1 to 2000
seconds.
[0041] As an example, irradiation by VUV light may be performed as
follows: inside a vessel filled with an inert gas at atmospheric
pressure with an O.sub.2 admixture of 1%. A Xe.sup.2 excimer lamp
(Xeradex.RTM. VUV excimer Lamp; Osram GmbH) emitting incoherent
light at a wavelength of 172 nm corresponding to a photon energy of
7.2 eV and spectral bandwidth of 14 nm may be used as radiation
source. The irradiation energy density between 104 and 46
Jcm.sup.-2 may be varied by changing the distance between the lamp
outer rim and sample surface from 1 to 30 mm. The irradiation
duration may be of 900 s.
[0042] An alternative source of vacuum ultraviolet radiation is
BlueLight high power Excimer systems from Heraeus Noblelight GmbH.
These are doped mercury/amalgam lamps available with various peak
spectral lines, for example 185 nm and 254 nm.
[0043] Excimer lamps exist of different kinds emitting over the
spectra of 120 to 240 nm, such as Ar.sub.e*, Kr.sub.2*, Xe.sub.2*
emitting at 126, 146, 172 nm respectively. For example, the 172 nm
radiation of a Xe.sub.2 dielectric barrier discharge may be used to
remove polymers, activate surface bonds, adjust wetting angles,
induce metallization and chemical vapor deposition (CVD) and
directly dissociate molecular oxygen.
[0044] Another method includes a 30-W deuterium lamp facility. The
average intensity of the 30-W deuterium lamp was approximately 2.2
equivalent Suns (2.4.times.10-5 W/cm.sup.2); the intensity of the
lamp naturally drops off at 200 nm; and exposures were done at a
vacuum pressure <10.sup.-5 torr (where 1 torr=133,322 Pa), with
54 cm between the lamp and the center of the sample plate which was
perpendicular to the beam. The VUV lamp radiation passed through a
magnesium fluoride end-window which provided a lower cut-off
wavelength of 115 nm. A cesium iodide (CsI) phototube was used to
measure the lamp's intensity.
[0045] A further method includes an atomic oxygen (AO) facility
which produces VUV radiation (with a peak intensity at 130 nm) with
an MgF.sub.2 lens to block AO. The dose of VUV radiation in the AO
facility may be qualitative, with more time in the facility defined
as "more" radiation. The AO facility uses a radio frequency power
supply to create an oscillating electrical potential between two
plates in the presence of a partial pressure of air, thereby
generating oxygen-rich plasma. Molecules of O.sub.2 are broken to
produce atomic oxygen, and the movement of electrons between energy
levels in excited oxygen atoms produces VUV radiation. Specimens to
receive only VUV in the AO facility were placed in a protective
fixture with an MgF.sub.2 lens covering the top mating surface of
the specimen. These MgF.sub.2 lenses are transparent to VUV. By
covering specimens with MgF.sub.2 and protecting them from AO, one
may determine if the VUV present affects the surface properties of
the silicone elastomeric based article.
[0046] Yet another method comprises an exposure of vacuum
ultraviolet light between 200 mJ/cm.sup.2 and 1500 mJ/cm.sup.2.
Typically, the wavelength of the exposure vacuum ultraviolet light
may be 172 nm. Examples of apparatus include vacuum ultraviolet
exposure apparatus UVS-1000SM, from USHIO INC.
[0047] The irradiation may be carried out in a static or moving
mode, such as on a conveyor belt.
[0048] The vacuum ultraviolet radiation generally reduces the
coefficient of friction of the silicone elastomeric based surface
by at least 5%, alternatively by at least 10%, alternatively by at
least 15%, alternatively by at least 30%, alternatively by at least
50%.
[0049] The dynamic coefficient of friction of the cured coating may
be measured according to DIN 53357:1986-11 test method, potentially
with a modification using a 200 g sledge.
[0050] The coefficient of friction may be measured according to
ISO8295:1995(E) standard, providing for both static and dynamic
coefficient of friction.
[0051] The coefficient of friction may be measured according to
ASTM D1894-01 standard, Standard Test Method for Static and Kinetic
Coefficients of Friction of Plastic Film and Sheeting, providing
for both static and dynamic coefficient of friction. The methods by
ASTM D1894-01 and ISO8295:1995 are not technically equivalent.
[0052] The coefficient of friction may be determined as follows:
crosslinked silicone elastomer foils (80.times.30 mm) of thickness
2 mm are fastened to a metal slider using a weight of 190 g and a
contact area of 24 cm.sup.2, and drawn at a velocity of 100 cm/min
over a steel plate. The coefficient of friction p is calculated
from the following formula: p=frictional force/weight.
[0053] The vacuum ultraviolet radiation also modifies the feel of
the silicone surface when it is handled or held; the surface is
perceived as less sticky or less tacky.
[0054] The vacuum ultraviolet radiation only modifies or affects a
thin layer at the upper surface of the silicone elastomeric based
material. The depth or thickness of the modified surface layer of
the silicone elastomeric based material is generally less than 1 mm
thick, alternatively less than 500 nm thick, alternatively less
than 100 nm thick, alternatively less than 800 nm thick,
alternatively less than 50 nm thick, alternatively less than 10 nm
thick. The bulk properties of the silicone elastomeric based
material, such as the flexibility and tensile and flexural
strength, elongation at break, transparency, are not substantially
altered by the vacuum ultraviolet radiation. The vacuum ultraviolet
radiation reduces the coefficient of friction of the silicone
elastomeric based surface and improves the surface feel of the
article without modifying bulk physical properties of the silicone
elastomer article such as flexibility or impact strength.
[0055] The surface modification of the silicone elastomeric based
material is permanent in time, that is, it does not disappear with
time and does not wear off upon use. By permanent, it is meant that
the surface modification will last at least as long as the article
is in use. This permanent effect of the surface modification of the
silicone elastomeric based material is advantageous over other
methods to treat surfaces, such as plasma treatment.
[0056] The article having a silicone elastomeric based surface can
be a part or component of an electronic, electrical, optical,
medical or communication device. The article having a silicone
elastomeric based surface can be used in the electronics industry,
the automotive industry or in lighting or in medical
applications.
[0057] The invention has particular advantages for wearable items
such as watch bracelets, GPS bracelets, and temple tips and nose
pads for sunglasses, reading glasses and other spectacles. These
items can be moulded from a silicone elastomeric composition. The
improved surface feel achieved by reducing the coefficient of
friction of a silicone elastomeric based surface makes such items
more comfortable to wear for prolonged periods.
[0058] The invention also has particular advantages for hand held
electronic devices such as cellphones (mobile phones). A casing for
a hand held electronic device can be moulded from a silicone
elastomeric composition or can be formed from another material
overmoulded with a silicone elastomeric composition surface layer.
The surface feel of a device having a silicone elastomeric based
surface modified by the process of the invention is less sticky
than an unmodified silicone elastomeric based surface and may be
perceived as more attractive than a hard plastics casing. The
casing of an electronic device molded from a silicone elastomeric
composition and modified by the process of the invention does not
need to be coated or covered with a harder plastics material.
[0059] The invention is useful for other electronic device parts
and components such as casings for tablet and laptop computers,
keyboard keys, touch pads, keyboard palm rests
[0060] In medical applications, silicone elastomer articles which
can advantageously be modified by the process of the invention
include tubing, membranes, seals and prosthetics and other moulded
parts. The benefits of having a reduced coefficient of friction
include reduced friction in skin contact applications in
orthopaedics; tube handling and low dust pick up in tubing; soft
touch comfort for face masks and low dust pick up in
anaesthesia/respiratory devices; printed surface protection in
keypads; reduced stickiness of silicone parts in assembly.
[0061] In lighting systems cured silicone elastomeric compositions
may be highly transparent, flex-resistant, resistant to bending and
heat. The transparency and/or the refractive index of the material
typically should not be affected by bending or heat. Perception of
dust pick up or tackiness may be an issue. Reducing the coefficient
of friction of a cured silicone elastomer material while
maintaining its transparency and flexibility, is advantageous for
the lighting application. In lighting systems, the article having a
silicone elastomeric based surface may be an optical member or
component that is transparent to light, e.g., visible light,
infrared, ultraviolet, far ultraviolet, x-ray, laser, and so forth;
may be an optical member or component for devices involved with
high energy, high output light; may be a thin film or superfine
optical member or component or may be an optical member or
component of very small size. Optical components include
collimators, optical waveguides, optical films, solar concentrators
with any sorts of shapes and any sorts of surface micro-structures,
such as, e.g., Fresnel lens, micro-facets or sand-blasted effect
that are used for controlling the light output for application in
lighting.
[0062] In the automotive industry silicone elastomeric compositions
can be used for steering wheel skins, gear knobs, grip handles, arm
rests, interior skin, car mats (such as cup holder, bin, and glove
box mats), small knobs, switches, and larger parts such as glove
box panels, dashboards, or door panels. Further automotive
applications include weather insulation seals, such as mirror seals
and interior and exterior window seals. Such articles can be
moulded or overmoulded from a silicone elastomeric composition.
[0063] In a further application, the automotive industry uses
silicone elastomer compositions as fabric coatings for air bags.
Subjecting the air bag or the coated fabric to vacuum ultraviolet
radiation according to the invention reduces the coefficient of
friction of the silicone elastomeric based surface so that the air
bag opens more readily when inflated. The vacuum ultraviolet
radiation treatment does not negatively affect the gas barrier
properties of the coated air bag or the pressure retention of the
air bag. Additional benefits may include ease of folding, space
saving compared to hard topcoat, heat shield.
[0064] Silicone elastomeric compositions generally have high
resistance to impact, to heat, to water, to solvents and to
chemicals, and are used in various applications such as ducts and
cable insulation, hoses, boots, bellows, gaskets, liquid line
components and air ducts; architectural seals; furniture
components; packaging components such as seals, bottles, bottle
closures, cans and cups; cookware parts and accessories such as
baking tools, baking molds or baking forms; and sporting and
leisure goods such as rackets, bike parts; footwear soles, and
toys. Any of these articles can be subjected to vacuum ultraviolet
radiation according to the invention to reduce the coefficient of
friction of the silicone elastomeric based surface.
[0065] The present invention also provides for the use of vacuum
ultraviolet radiation to reduce the coefficient of friction of the
silicone elastomeric based surface of 1) a silicone elastomer
article or of 2) a silicone elastomer coated article by at least
5%.
[0066] The present invention further provides for the use of an
article treated by the process described above as a case for an
electronic device or an optical device or a medical device or a
sport and leisure devices or a toy.
EXAMPLES
[0067] Silicone elastomer (or silicone rubber) pieces were prepared
from commercially available liquid silicone rubber compositions,
Xiameter.RTM. RBL-9200-30 LSR, Xiameter.RTM. RBL-9200-50 LSR and
Xiameter.RTM. RBL-9200-70 LSR. These compositions represent
general-purpose injection-molding materials, which are suitable for
a wide range of typical silicone rubber applications. The digits
30, 50 and 70 indicate the Shore A hardness of the cured materials
obtained from these compositions. Typically, these compositions are
provided in two parts form (parts A and B), which are combined
prior to curing (reacting).
[0068] Equivalent amounts of the Part A and B of the individual LSR
have been mixed, de-aired and poured into a 202.times.108.times.32
mm (L.times.W.times.H) mold and press-cured for 10 min at
120.degree. C. The cured plates have been then irradiated with a
low pressure mercury lamp (wavelength 185 nm and 254 nm) of type
Heraeus Noblelight, Soluva 4.20 VUV Modul (UV Intensity 140 mW/cm2,
for a wave length of 254 nm, at distance of 10 mm; providing for an
irradiation area of 230.times.140 mm), for either 3 min or 5 min
respectively.
[0069] The cured plates (with and without irradiation) have been
tested for change in coefficient of friction. The results are
listed in Table 1.
[0070] The static and dynamic coefficients of friction were
measured using a Zwick device, set up according to ISO8295 from
Jan. 10, 1995, where a sliding reinforcing plate is moved along the
test specimen and friction is measured. The parameters were set as
follows: sliding trail of 300 mm length and 150 mm width, a
moveable device of 200 g having a Teflon surface, moving at a speed
of 150 mm/min, with a force of 200 N.
[0071] The coefficients of friction, both static and dynamic are
evidenced to be reduced by more than 10% of the initial value, and
even more than 50% when comparing the untreated materials and the
materials that were irradiated for 5 minutes. The untreated
materials Comparative examples 1 and 2 have defects in sliding
because the surface is not slippery and some friction and
elasticity interaction prevent the moving device from sliding
smoothly on the surface.
TABLE-US-00001 Irradiation Static Dynamic time coefficient of
coefficient of (seconds) friction friction Comparative RBL-9200-30
0 15.8* (high (10.0 s)- example 1 variability) defects in sliding
Example 1 RBL-9200-30 180 7.5 4.8 Example 2 RBL-9200-30 300 1.9 2.2
Comparative RBL-9200-50 0 15.1* (high (8)-defects in example 2
variability) sliding Example 3 RBL-9200-50 180 1.3 1.5 Example 4
RBL-9200-50 300 1.8 0.3 Comparative RBL-9200-70 0 9.4 6.8 example 3
Example 5 RBL-9200-70 180 3.0 2.1 Example 6 RBL-9200-70 300 0.7
1.0
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