U.S. patent application number 11/208187 was filed with the patent office on 2006-03-09 for perfluoroelastomer articles having good surface properties.
Invention is credited to Kaori Iwamoto, Bunichi Rai, Shinichi Sogo.
Application Number | 20060051570 11/208187 |
Document ID | / |
Family ID | 35457410 |
Filed Date | 2006-03-09 |
United States Patent
Application |
20060051570 |
Kind Code |
A1 |
Iwamoto; Kaori ; et
al. |
March 9, 2006 |
Perfluoroelastomer articles having good surface properties
Abstract
Cured perfluoroelastomer articles are disclosed which have
improved surface characteristics. The articles are coated with a
thin durable film comprising a fluorocarbon telomer which reduces
surface stickiness, while maintaining the sealing properties of the
article.
Inventors: |
Iwamoto; Kaori;
(Utsunomiya-shi, JP) ; Rai; Bunichi; (Tokyo,
JP) ; Sogo; Shinichi; (Tsuduki-ku, JP) |
Correspondence
Address: |
DUPONT PERFORMANCE ELASTOMERS L.L.C.
PATENT RECORDS CENTER
4417 LANCASTER PIKE, BARLEY MILL PLAZA P25
WILMINGTON
DE
19805
US
|
Family ID: |
35457410 |
Appl. No.: |
11/208187 |
Filed: |
August 19, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60607103 |
Sep 3, 2004 |
|
|
|
Current U.S.
Class: |
428/336 ;
427/372.2; 428/422; 526/247; 526/250 |
Current CPC
Class: |
C08J 2327/12 20130101;
C08J 2327/18 20130101; C08J 2427/00 20130101; Y10T 428/265
20150115; Y10T 428/31544 20150401; C08J 7/0427 20200101; C08J 7/043
20200101 |
Class at
Publication: |
428/336 ;
526/247; 526/250; 428/422; 427/372.2 |
International
Class: |
C08F 16/24 20060101
C08F016/24; B32B 27/00 20060101 B32B027/00 |
Claims
1. A cured perfluoroelastomer article for use as a vacuum seal in a
high temperature environment, said article having a surface coated
with a film comprising a fluorocarbon telomer having a weight
average molecular weight between 1000 and 10000.
2. A cured perfluoroelastomer article of claim 1 wherein said
perfluoroelastomer comprises copolymerized units of
tetrafluoroethylene, a perfluorinated vinyl ether and a cure site
monomer.
3. A cured perfluoroelastomer article of claim 2 wherein said
perfluoroelastomer comprises copolymerized units of 53.0-79.6 mole
percent tetrafluoroethylene, 20.0-46.6 mole percent
perfluoro(methyl vinyl ether) and 0.4-1.5 mole percent
nitrile-containing cure site monomer.
4. A cured perfluoroelastomer article of claim 1 wherein said
fluorocarbon telomer is polytetrafluoroethylene.
5. A cured perfluoroelastomer article of claim 1 wherein said
fluorocarbon telomer has a weight average molecular weight between
2000 and 4000.
6. A cured perfluoroelastomer article of claim 1 wherein said film
has a thickness between 0.1 and 20 microns.
7. A cured perfluoroelastomer article of claim 6 wherein said film
has a thickness between 3 and 10 microns.
8. A process for making a cured perfluoroelastomer article for use
as a vacuum seal in a high temperature environment, said process
comprising: A. coating a cured perfluoroelastomer article with a
dispersion comprising i) a fluorocarbon telomer having a weight
average molecular weight between 1000 and 10000 to for a wet-coated
perfluoroelastomer article; B. drying said wet-coated
perfluoroelastomer article to form a dry-coated perfluoroelastomer
article at a temperature below 200.degree. C.; and C. heating said
dry-coated perfluoroelastomer article to a temperature and for a
sufficient period of time whereby said fluorocarbon telomer melts
and forms a film on said perfluoroelastomer article.
9. A process for making a cured perfluoroelastomer article of claim
8 wherein said drying step B) is at a temperature between
20.degree. and 25.degree. C.
10. A process for making a cured perfluoroelastomer article of
claim 8 wherein said heating step C) is at a temperature between
290.degree. and 320.degree. C. for more than 5 minutes.
11. A process for making a cured perfluoroelastomer article of
claim 8 wherein said perfluoroelastomer comprises copolymerized
units of tetrafluoroethylene, a perfluorinated vinyl ether and a
cure site monomer.
12. A process for making a cured perfluoroelastomer article of
claim 8 wherein said fluorocarbon telomer is
polytetrafluoroethylene.
13. A process for making a cured perfluoroelastomer article of
claim 8 wherein said film formed in step C) has a thickness between
0.1 and 20 microns.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/607,103 filed Sep. 3, 2004.
FIELD OF THE INVENTION
[0002] This invention relates to perfluoroelastomer articles for
use as vacuum seals in high temperature environments, said articles
having good surface lubricity. More specifically, this invention
relates to cured perfluoroelastomer articles coated with a thin
film of a composition comprising a fluorocarbon telomer having a
weight average molecular weight between 1000 and 10000.
BACKGROUND OF THE INVENTION
[0003] Perfluoroelastomers have achieved outstanding commercial
success and are used in a wide variety of applications in which
severe environments are encountered, in particular those end uses
where exposure to high temperatures and aggressive chemicals
occurs. For example, these polymers are often used in seals for
aircraft engines, in oil-well drilling devices, and in sealing
elements for industrial equipment used at high temperatures.
[0004] The outstanding properties of perfluoroelastomers are
largely attributable to the stability and inertness of the
copolymerized perfluorinated monomer units that make up the major
portion of the polymer backbones in these compositions. Such
monomers include tetrafluoroethylene and perfluorinated vinyl
ethers. In order to develop elastomeric properties fully,
perfluoroelastomers are typically crosslinked, i.e. vulcanized. To
this end, a small amount of cure site monomer is copolymerized with
the perfluorinated monomer units. Cure site monomers containing at
least one nitrile group, for example
perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene, are especially
preferred. Such compositions are described in U.S. Pat. Nos.
4,281,092; 4,394,489; 5,789,489; and 5,789,509.
[0005] In certain end use applications, a cured perfluoroelastomer
article may undesirably adhere to the surface of other materials
that are in contact with it, particularly if the perfluoroelastomer
article and other material are forcibly held in contact for a long
period of time at elevated pressures and temperatures, and then
cooled. It may be difficult, or impossible, to easily remove the
perfluoroelastomer article from contact with the other material
without damaging the perfluoroelastomer article, other material, or
both. Also, the perfluoroelastomer article may be undesirably
pulled from the groove in which it is seated when the article is
being separated from a surface to which it has adhered. Thus, there
is a need for perfluoroelastomer articles that have an improved,
less sticky surface.
[0006] Kishino et al. (U.S. Pat. No. 5,763,068) disclose
fluororesin-coated fluoroelastomer articles. In contrast to
perfluoroelastomers, fluoroelastomers contain copolymerized units
of at least one monomer which is either partially fluorinated (such
as vinylidene fluoride), or non-fluorinated (such as propylene).
The articles are made by first blending uncured fluoroelastomer
with up to 50 parts fluororesin; shaping the blend into an article
and curing it; coating the cured article with an aqueous
fluororesin dispersion; drying the coated article; and finally
heating the article above the melting point of the fluororesin in
order to form a durable fluororesin film coating. However, blending
a high level of fluororesin with a fluoroelastomer or
perfluoroelastomer typically reduces the physical properties of
cured articles produced from such blends, especially if the
articles are used in a high temperature environment. Compression
set resistance and elongation are particularly adversely effected.
Heating fluoroelastomer articles to a temperature of about
300.degree. C. or higher, in order to melt the fluororesin, may
further degrade the physical properties of the articles.
[0007] Tarney et al. (WO 02/20650) disclose fluoropolymer coated
perfluoroelastomer articles which have good physical properties and
a low stick surface. However, in demanding applications which
require excellent high vacuum sealing performance, Tarney's
articles may leak due to the nature of the surface coating.
[0008] EP 1403348 A1 discloses perfluoroelastomer parts which are
coated with a thin film of a polysiloxane-urethane oligomer. Such
parts have both a low stick surface and good sealing performance at
moderate operating temperatures. However, at operating temperatures
above about 250.degree. C., the surface becomes sticky.
[0009] Thus, there is a need for perfluoroelastomer articles that
have an improved, less sticky surface at operating temperatures
above 250.degree. C. and which have excellent sealing performance
in high vacuum applications such as in some semiconductor
manufacturing equipment.
SUMMARY OF THE INVENTION
[0010] An aspect of this invention is a cured perfluoroelastomer
article having a surface coated with a film comprising a
fluorocarbon telomer having a weight average molecular weight
between 1000 and 10000.
[0011] Another aspect of this invention is a process comprising:
[0012] A. coating a cured perfluoroelastomer article with a
dispersion comprising i) a fluorocarbon telomer having a weight
average molecular weight between 1000 and 10000 to for a wet-coated
perfluoroelastomer article; [0013] B. drying said wet-coated
perfluoroelastomer article to form a dry-coated perfluoroelastomer
article at a temperature below 200.degree. C.; and [0014] C.
heating said dry-coated perfluoroelastomer article to a temperature
and for a sufficient period of time whereby said fluorocarbon
telomer melts and forms a film on said perfluoroelastomer
article.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Perfluoroelastomers are polymeric compositions having
copolymerized units of at least two principal perfluorinated
monomers. Generally, one of the principal comonomers is a
perfluoroolefin while the other is a perfluorovinyl ether.
Representative perfluorinated olefins include tetrafluoroethylene
and hexafluoropropylene. Suitable perfluorinated vinyl ethers
include those of the formula
CF.sub.2.dbd.CFO(R.sub.f'O).sub.n(R.sub.f''O).sub.mR.sub.f (I)
where R.sub.f' and R.sub.f'' are different linear or branched
perfluoroalkylene groups of 2-6 carbon atoms, m and n are
independently 0-10, and R.sub.f is a perfluoroalkyl group of 1-6
carbon atoms.
[0016] A preferred class of perfluorinated vinyl ethers includes
compositions of the formula
CF.sub.2.dbd.CFO(CF.sub.2CFXO).sub.nR.sub.f (II) where X is F or
CF.sub.3, n is 0-5, and R.sub.f is a perfluoroalkyl group of 1-6
carbon atoms.
[0017] Most preferred perfluorinated vinyl ethers are those wherein
n is 0 or 1 and R.sub.f contains 1-3 carbon atoms. Examples of such
perfluorinated ethers include perfluoro(methyl vinyl) ether and
perfluoro(propyl vinyl) ether. Other useful monomers include
compounds of the formula
CF.sub.2.dbd.CFO[(CF.sub.2).sub.mCF.sub.2CFZO].sub.nR.sub.f (III)
where R.sub.f is a perfluoroalkyl group having 1-6 carbon atoms,
m=0 or 1, n=0-5, and Z=F or CF.sub.3. Preferred members of this
class are those in which R.sub.f is C.sub.3F.sub.7, m=0, and n=1.
Additional perfluorinated vinyl ether monomers include compounds of
the formula
CF.sub.2.dbd.CFO[(CF.sub.2CFCF.sub.3O).sub.n(CF.sub.2CF.sub.2CF.sub.2O).s-
ub.m(CF.sub.2).sub.p]C.sub.xF.sub.2x+1 (IV) where m and n=1-10,
p=0-3, and x=1-5. Preferred members of this class include compounds
where n=0-1, m=0-1, and x=1.
[0018] Additional examples of useful perfluorinated vinyl ethers
include
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)O(CF.sub.2O).sub.mC.sub.nF.sub.2n+1
(V) where n=1-5, m=1-3, and where, preferably, n=1.
[0019] Preferred perfluoroelastomer copolymers are comprised of
tetrafluoroethylene and at least one perfluorinated vinyl ether as
principal monomer units. In such copolymers, the copolymerized
perfluorinated vinyl ether units constitute from about 15-50 mole
percent of total monomer units in the polymer.
[0020] The perfluoroelastomer further contains copolymerized units
of at least one cure site monomer, generally in amounts of from
0.1-5 mole percent. The range is preferably between 0.3-1.5 mole
percent. Although more than one type of cure site monomer may be
present, most commonly one cure site monomer is used and it
contains at least one nitrile substituent group. Suitable cure site
monomers include nitrile-containing fluorinated olefins and
nitrile-containing fluorinated vinyl ethers. Useful
nitrile-containing cure site monomers include those of the formulas
shown below. CF.sub.2.dbd.CF--O(CF.sub.2).sub.n--CN (VI) where
n=2-12, preferably 2-6;
CF.sub.2.dbd.CF--O[CF.sub.2--CFCF.sub.3--O].sub.n--CF.sub.2--CFCF.sub.3---
CN (VII) where n=0-4, preferably 0-2; and
CF.sub.2.dbd.CF--[OCF.sub.2CFCF.sub.3].sub.x--O--(CF.sub.2).sub.n--CN
(VIII) where x=1-2, and n=14.
[0021] Those of formula (VIII) are preferred. Especially preferred
cure site monomers are perfluorinated polyethers having a nitrile
group and a trifluorovinyl ether group. A most preferred cure site
monomer is CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2CN
(IX) i.e. perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene) or
8-CNVE.
[0022] Other cure site monomers include olefins represented by the
formula R.sub.1CH.dbd.CR.sub.2R.sub.3, wherein R.sub.1 and R.sub.2
are independently selected from hydrogen and fluorine and R.sub.3
is independently selected from hydrogen, fluorine, alkyl, and
perfluoroalkyl. The perfluoroalkyl group may contain up to about 12
carbon atoms. However, perfluoroalkyl groups of up to 4 carbon
atoms are preferred. In addition, the cure site monomer preferably
has no more than three hydrogen atoms. Examples of such olefins
include ethylene, vinylidene fluoride, vinyl fluoride,
trifluoroethylene, 1-hydropentafluoropropene, and
2-hydropentafluoropropene, as well as brominated olefins such as
4-bromo-3,3,4,4-tetrafluorobutene-1 and bromotrifluoroethylene.
Alternatively, or in addition to copolymerized units of cure site
monomers, cure sites of bromine or iodine-containing end groups may
be introduced onto the perfluoroelastomer polymer chain by the
reaction of bromine or iodine-containing chain transfer agents
during polymerization.
[0023] Another type of cure site monomer which may be incorporated
in the perfluoroelastomers employed in this invention is
perfluoro(2-phenoxypropyl vinyl ether) and related monomers as
disclosed in U.S. Pat. No. 3,467,638.
[0024] An especially preferred perfluoroelastomer contains
53.0-79.6 mole percent tetrafluoroethylene, 20.0-46.6 mole percent
perfluoro(methyl vinyl) ether and 0.4 to 1.5 mole percent
nitrile-containing cure site monomer.
[0025] When the perfluoroelastomer has copolymerized units of a
nitrile-containing cure site monomer, a cure system based on an
organotin compound can be utilized. Suitable organotin compounds
include allyl-, propargyl-, triphenyl- and allenyl tin curatives.
Tetraalkyltin compounds or tetraaryltin compounds are the preferred
curing agents for use in conjunction with nitrile-substituted cure
sites. The amount of curing agent employed will necessarily depend
on the degree of crosslinking desired in the final product as well
as the type and concentration of reactive moieties in the
perfluoroelastomer. In general, about 0.5-10 parts by weight per
100 parts elastomer (phr) of curing agent can be used, and 14 phr
is satisfactory for most purposes. It is believed that the nitrile
groups trimerize to form s-triazine rings in the presence of curing
agents such as organotin, thereby crosslinking the
perfluoroelastomer. The crosslinks are thermally stable, even at
temperatures of 275.degree. C. and above.
[0026] A preferred cure system, useful for perfluoroelastomers
containing nitrile-containing cure sites, utilizes
bis(aminophenols) and bis(aminothiophenols) of the formulas
##STR1## and tetraamines of the formula ##STR2## where A is
SO.sub.2, O, CO, alkylene of 1-6 carbon atoms, perfluoroalkylene of
1-10 carbon atoms, or a carbon-carbon bond linking the two aromatic
rings. The amino and hydroxyl or thio groups in formulas XII and
XIII above are adjacent to each other on the benzene rings and are
interchangeably in the meta and para positions with respect to the
group A. Preferably, the curing agent is a compound selected from
the group consisting of
4,4'-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis(2-aminophenol);
4,4'-sulfonylbis(2-aminophenol); 3,3'-diaminobenzidine; and
3,3',4,4'-tetraminobenzophenone. The first of these is the most
preferred and will be referred to as bis(aminophenol) AF. The
curing agents can be prepared as disclosed in U.S. Pat. No.
3,332,907 to Angelo. Bis(aminophenol) AF can be prepared by
nitration of
4,4'-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]-bisphenol
(i.e. bisphenol AF), preferably with potassium nitrate and
trifluoroacetic acid, followed by catalytic hydrogenation,
preferably with ethanol as a solvent and a catalytic amount of
palladium on carbon as catalyst. The level of curing agent should
be chosen to optimize the desired properties of the vulcanizate. In
general, a slight excess of curing agent over the amount required
to react with all the cure sites present in the perfluoroelastomer
is used. Typically, 0.5-5.0 parts by weight of the curative per 100
parts of elastomer is required. The preferred range is 1.0-2.0
phr.
[0027] Peroxides may also be utilized as curing agents,
particularly when the cures site is a nitrile group or an iodine or
bromine group. Useful peroxides are those which generate free
radicals at curing temperatures. A dialkyl peroxide or a
bis(dialkyl peroxide) which decomposes at a temperature above
50.degree. C. is especially preferred. In many cases it is
preferred to use a ditertiarybutyl peroxide having a tertiary
carbon atom attached to peroxy oxygen. Among the most useful
peroxides of this type are
2,5-dimethyl-2,5-di(tertiarybutylperoxy)hexyne-3 and
2,5-dimethyl-2,5-di(tertiarybutylperoxy)hexane. Other peroxides can
be selected from such compounds as dicumyl peroxide, dibenzoyl
peroxide, tertiarybutyl perbenzoate, and
di[1,3-dimethyl-3-(t-butylperoxy)butyl]carbonate.
[0028] Generally, about 1-3 parts of peroxide per 100 parts of
perfluoroelastomer is used. Another material which is usually
blended with the composition as a part of the peroxide curative
system is a coagent composed of a polyunsaturated compound which is
capable of cooperating with the peroxide to provide a useful cure.
These coagents can be added in an amount between 0.1 and 10 parts
per 100 parts perfluoroelastomer, preferably between 2-5 phr. The
coagent may be one or more of the following compounds: triallyl
cyanurate; triallyl isocyanurate; tri(methylallyl)isocyanurate;
tris(diallylamine)-s-triazine; triallyl phosphite; N,N-diallyl
acrylamide; hexaallyl phosphoramide; N,N,N',N'-tetraalkyl
tetraphthalamide; N,N,N',N'-tetraallyl malonamide; trivinyl
isocyanurate; 2,4,6-trivinyl methyltrisiloxane; and
tri(5-norbornene-2-methylene)cyanurate. Particularly useful is
triallyl isocyanurate.
[0029] Other curatives suitable for vulcanizing perfluoroelastomers
having nitrile cure sites include ammonia, the ammonium salts of
inorganic or organic acids (e.g. ammonium perfluorooctanoate) as
disclosed in U.S. Pat. No. 5,565,512, and compounds (e.g. urea)
which decompose to produce ammonia as disclosed in U.S. Pat. No.
6,281,296 B1.
[0030] Depending on the cure site monomers present, it is also
possible to use a dual cure system. For example,
perfluoroelastomers having copolymerized units of
nitrile-containing cure site monomers can be cured using a curative
comprising a mixture of a peroxide in combination with an organotin
curative and a coagent. Generally, 0.3-5 parts of peroxide, 0.3-5
parts of coagent, and 0.1-10 parts of organotin curative are
utilized.
[0031] Additives, such as fillers (e.g. carbon black, barium
sulfate, silica, aluminum oxide, aluminum silicate, and titanium
dioxide), stabilizers, plasticizers, lubricants, and processing
aids typically utilized in perfluoroelastomer compounding can be
incorporated into the compositions of the present invention,
provided they have adequate stability for the intended service
conditions.
[0032] Cured (i.e. vulcanized or crosslinked) perfluoroelastomer
articles employed in this invention are made by shaping and then
crosslinking the above perfluoroelastomer compositions. Curing may
be induced by heat or by radiation. The article may subsequently be
post cured at elevated temperatures for a period of time.
[0033] After extensive research, a polymeric coating composition
has been found that provides perfluoroelastomer articles with both
low surface stickiness and good sealing properties when used at
operating temperatures in the region of 250.degree. C. to
330.degree. C. The durable films which coat the perfluoroelastomer
articles employed in this invention are comprised of fluorocarbon
telomers having a weight average molecular weight between 1000 and
10000, preferably between 2000 and 4000. Such telomers typically
have a peak softening point between 290.degree. C. and 310.degree.
C. Examples of fluorocarbon telomers that may be employed in this
invention include, but are not limited to polytetrafluoroethylene
(PTFE), and copolymers of tetrafluoroethylene such as PFA and FEP.
PTFE is preferred.
[0034] In the process of this invention, the uncured fluorocarbon
telomer is applied as a dispersion to a cured perfluoroelastomer
article. Liquids, including water and organic solvents, may be used
to form the dispersion. The dispersion typically comprises between
1 and 20 weight percent fluorocarbon telomer, based on the total
weight of the dispersion. The dispersion may also contain minor
amounts of other ingredients such as surfactants, pH buffers, etc.
Commercially available telomer dispersions are available under the
trade names DuPont.TM. DryFilm performance dispersions, Daikin
Lubron PTFE lubricants, and Central Glass Cefral Coat.
[0035] The cured, perfluoroelastomer article may be coated with
fluorocarbon telomer dispersion by any means commonly employed in
the art such as by dipping, spray coating, or by contacting with an
applicator. Coating thickness is typically 0.1 to 20 microns,
preferably 3 to 10 microns. Generally, the thicker the coating, the
less sticky the resulting perfluoroelastomer article. However, as
the coating thickness increases, the article's ability to form a
good (i.e. non-leaking) seal decreases, so the two properties must
be balanced for a particular end use application.
[0036] The wet-coated article thus produced is then dried to remove
most of the liquid. Drying may be done at any temperature less than
the temperature where the fluorocarbon telomer melts. Care must be
taken not to dry the coating too quickly. Otherwise, bubbles may
form in the coating, which when burst, may result in large
non-coated areas on the surface of the article. Typically, drying
is done in air at room temperature (20.degree. C.-25.degree.
C.).
[0037] The dry-coated article thus produced is then heated to a
temperature where the fluorocarbon telomer melts and forms a film.
Typically, this will be at a temperature between 290.degree. C. and
320.degree. C. for more than 5 minutes. One skilled in the art will
recognize that this heating step must be controlled so that the
coated part is not subjected to a high temperature for a time
sufficient to cause unacceptable thermal degradation to the telomer
film or to the perfluoroelastomer article. The maximum temperature
and exposure time depends on the particular fluorocarbon telomer
and perfluoroelastomer article. It is not necessary that the
resulting film be a continuous film of uniform thickness in order
for the resulting perfluoroelastomer article to have a greatly
improved surface with little or no stickiness. The physical
properties of the film-coated articles of this invention have
comparable physical properties to non-coated perfluoroelastomer
articles.
[0038] To improve the durability (i.e. adhesion) of the film onto
the surface of a cured perfluoroelastomer article, the surface of
the article may preferably be pre-treated, i.e. prior to
application of the dispersion, to increase surface area. Examples
of suitable surface treatments for use in this invention include,
but are not limited to roll flow, sanding, grinding, and plasma or
chemical etching. Roll flow refers to a process wherein a cured
perfluoroelastomer article and abrasive particles are agitated in a
container for a period of time in order to increase the surface
area of the article via introduction of microscopic pits, cracks
and the like onto the surface. Sanding and plasma or chemical
etching increases the article's surface area by similar means.
Preferably, the surface is also cleaned with an appropriate solvent
to remove contaminants such as mold release agents, lubricants,
oils, etc.
[0039] The fluorocarbon telomer film coated perfluoroelastomer
articles of this invention are useful in many end use applications
such as those involving high temperatures (i.e. 250.degree. C. to
330.degree. C.), high vacuums (i.e. pressures of 0.1-10.sup.-5 Pa)
and harsh chemical or plasma environments wherein it is undesirable
for the perfluoroelastomer articles to stick to the surfaces of
materials with which the articles are in contact. Examples of such
end use applications include semiconductor manufacturing equipment
and the chemical process industry.
EXAMPLES
Test Method
Sticking Force
[0040] Stickiness was measured on type AS-214 o-rings. An o-ring
was compressed 25% in a jig between two stainless steel plates. The
jig was then placed in an air oven for 16 hours at 300.degree. C.
Afterwards, the jig was removed from the oven and allowed to cool
at room temperature for 3 hours. The plates were then attached to
an Instron and the force required to pull the plates apart was
measured. A sticking force less than 150 N was acceptable and
greater than 150 N unacceptable.
Helium Leak Test
[0041] A film-coated type AS-214 o-ring was used in a jig to form a
seal between a chamber fillable with helium and a chamber under
vacuum. The o-ring was compressed 25%. The vacuum chamber was
connected to a ULVAC HELIOT 301 Helium Leak Detector. The test was
run by measuring the elapsed time between when helium was
introduced into the helium chamber and when it was detected at the
rate of at least 10.sup.-10 Pa m.sup.3/sec by the He detector. An
elapsed time of greater than 30 seconds was acceptable, between 30
seconds and 15 seconds marginal, and less than 15 seconds,
unacceptable.
Example 1
[0042] The cured perfluoroelastomer articles employed in this
Example were type AS-214 o-rings made from a perfluoroelastomer
comprising copolymerized units of tetrafluoroethylene,
perfluoro(methyl vinyl)ether and
perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene). In addition to
perfluoroelastomer, o-rings contained 6.5 phr TiO.sub.2 and 3 phr
SiO.sub.2.
[0043] O-rings were spray coated with DuPont.TM. Teflon.RTM. finish
851 K-02730, a dispersion (5.5 weight percent solids in DuPont.TM.
Vertrel.RTM. HFC 43-10 solvent) of polytetrafluoroethylene having a
weight average molecular weight of 3000. The coated o-rings were
dried in air at room temperature for a few minutes. These
dry-coated o-rings were then baked in an air oven at 310.degree. C.
for 10 minutes to yield fluorocarbon telomer film-coated
perfluoroelastomer articles of this invention. The coated o-rings
were washed with water. Film thickness was 5 microns.
[0044] Comparative coated o-rings were made by the same procedure,
except either DuPont.TM. DryFilm 2000 (weight average molecular
weight of 40,000) or an FEP (weight average molecular weight of
100,000) was used in place of the Teflon.RTM. 851 K-02730.
[0045] Sticking force of the film-coated perfluoroelastomer o-rings
was measured according to the Test Method. The results for the film
coated o-rings of the invention averaged 120 N for 3 o-rings
tested. Comparative o-rings coated with the DryFilm 2000 had a
sticking force of 200 N and comparative o-rings coated with FEP had
a sticking force of 510N. The sticking force of a control (i.e. not
coated) perfluoroelastomer o-ring was measured as 275 N.
[0046] The sealing ability of three other film-coated o-rings of
the invention prepared above was measured by the He leak test
method. The average elapsed time was 60 seconds. Comparative
o-rings coated with the DryFilm 2000 had an elapsed time of 60
seconds and comparative o-rings coated with FEP had an elapsed time
of 0 seconds. The elapsed time of a control (i.e. not coated)
perfluoroelastomer o-ring was 60 seconds.
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