Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 95130720 218 7 316 pCTlU895103°81
HIGH TEMPERATURE RESISTANT ANTISTATIC
PRESSURE-SENSITIVE ADHESIVE TAPE
Background of the Invention
Field of the Invention
The invention relates to pressure-sensitive adhesive
' tape constructions which are useful for masking printed
circuit boards (PCBs) at the high temperatures associated
with wave soldering operations. These adhesive tapes,
which comprise ionically conductive polymeric
microparticulate adhesive formulations, provide tapes
extremely resistant to tribocharging, thereby protecting
electronic components from static charge buildup. In
addition, the adhesive masking tape, upon removal from a
PCB, does not contaminate the surface of the board with
adhesive residue.
Description of the Art
The process of wave soldering is commonly used for
permanently attaching electronic components to printed
circuit boards. Various methods are used to mask or
cover areas of the board during the wave soldering
attachment process where solder is not desired. It is
known, for example, to achieve such masking by use of
self-adhesive tapes based on high-temperature-resistant
polyimide film coated with a silicone-based adhesive.
However, the removal of such tapes from the surface of
electronic assemblies causes tribocharging accompanied by
static charges which can damage sensitive electronic
components and cause contamination of the printed
circuits by silicone.
Electrically conductive tapes are also useful for -
the masking purpose. Electrically conductive tapes do
' not tribocharge as readily as those made from insulating
materials such as silicones. The use of conductive
WO 95130720 218 7 31 b PCT/US95/03381
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tapes, in assembly operat-ions, therefore, will reduce the
failure rate of electronic components.
Several different types of conductive tape are=known
for use. at ambient temperatures. United States patents
3,104,985, 3,832,598 and 4,749,612 describe adhesive
tapes with a coating of.carbon black in a binder which is
taught to dissipate electrostatic charges. Various
patents also disclose multiple layer tape structures
wherein one-of the layers, usually a buried layer, is
electrically conductive.
For example, Japanese Patent Publication J 63012681-
A discloses a tape with an intermediate, antistatic
polymer layer situated between a polyolefin support and a
rubber adhesive layer.
European Patent Publication EP- 0422919-A2 discloses
a tape having a layer of conductive particles or
conductive foil surrounded by binder, situated between a
polymer film support and a silicone adhesive. The use of
a high temperature film support, po-lyimide, combined with
silicone binder and adhesive, is stated to yield a tape
which will perform well as a-wave solder masking tape at
temperatures unsuitable for earlier antistatic tapes,
i.e., this tape will survive-in a wave solder bath for up
to 5 seconds at 250°C.
Antistatic or conductive tapes which rely on the use
of conductive particles require high loading of these
particles.for sufficient electrostatic charge-
neutralization. The effect of the conductive particles
must be active at the surface of an otherwise-insulative
adhesive for static free masking of electronic
assemblies. Charge transfer to the underlying layer of
conductive particles requires a conductive pathway
through the adhesive. However, high particulate loading
often leads to loss of adhesion and undesirable transfer
of contaminating material. This problem must be balanced
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against the use of additional polymeric binder which may
electrically insulate adjacent conductive particles and
thus cause increased tribocharging while reducing
transfer-.
The need for balance between particle loading and
polymeric binder could be avoided with an inherently
conductive adhesive layer. However, there is no known
disclosure of a wave solder masking tape using an
inherently conductive adhesive in direct contact with the
printed circuit board. Whether conductive in nature or
not, most non-silicone adhesives will not survive the
wave soldering process, and are thus not useful for such
an application.
The current inventors have discovered an inherently
conductive adhesive useful at the high temperatures
required by wave solder baths. When coated onto a highly
temperature resistant material bearing a specific primer
thereon, a tape construction is provided which is useful
for wave soldering applications without the problems of
previously disclosed wave solder masking tapes.
Adhesive tapes of the invention comprise sonically
charged acrylic microparticulate adhesives. Polymeric
microparticles having polymer-electrolytes on the surface
of each polymer particle provide conductive particles
which are useful as antistatic adhesive compositions.
Surprisingly such adhesives exhibit high temperature
resistance when placed in a wave solder bath.
Particulate adhesives are also known in the art, and
have been coated on a variety of substrates and used
primarily in applications requiring a low level of
adhesion, e.g., repositionability. Such spheres and
their use in aerosol adhesive systems having
repositionable properties are disclosed in U.S. Pat. No.
3,691,140 (Silver). These microparticles are prepared by
aqueous suspension polymerization of alkyl acrylate
WO 95!30720 218 7 315 P~'f1~1S95103381
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monomers and ionic comonomer, e.g:, sodium methacrylate,
in the presence of an emulsifier. The use of-a water-
soluble, substantially oil-insoluble ionic comonome~-is
r
critical to preventing coagulation or agglomeration of
the microparticles. However, particulate adhesives
disclosed in the prior art have all-been useful as
repositionable adhesives for such applications as
Post-It'M brand notes, and other removable items.
Pressure-sensitive tapes made with this type of adhesive
are likely to be considered unsuitable for use as
antistatic tapes due to their lack of conductivity, and
ease ofremoval. Further; acrylic adhesives are
typically not considered to be heat resistant in nature.
Adhesive tapes of the invention provide antistatic
tapes which are extremely effective in dissipating
electrostatic charge and may be used in sensitive
applications without worry about adhesive transfer.
Summary of the Invention
The invention provides a high-temperature resistant,
antistatic, pressure-sensitive adhesive tape comprising a
polymeric film support bearing a primer which causes a
non-tribocharging, microparticulate adhesive to strongly
adhere to the backing. This tape has the capacity to
survive immersion in molten solder, at-elevated
temperature, essentially unchanged for periods of up to 5
seconds, preferably up to 20 seconds.
More specifically, the-invention provides a heat-
resistant anti-static pressure-sensitive adhesive tape
comprising a substrate having opposing surfaces, at least
one surface bearing thereon, a microparticulate adhesive
having an average diameter of atleast 1 micrometer,-
wherein the microparticles have a surface bearing thereon
an ionic conductive material formed from a polymer
b
electrolyte base polymer, and at least one ionic salt
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selected from the group consisting of salts of alkali metals
and salts of alkaline earth metals, said adhesive being
adhered to said substrate by means of a primer composition,
said primer comprising at least one phenolic resin and at
least one rubbery compound,
said adhesive tape surviving in a wave-solder bath
for at least 5 seconds.
According to one aspect of the present invention,
there is provided a heat-resistant anti-static pressure-
sensitive adhesive tape comprising a substrate having
opposing surfaces, at least one of said surfaces bearing
thereon an acrylic microparticulate adhesive wherein the
microparticles have an average diameter of 1 to
250 micrometers, wherein the microparticles have a surface
bearing thereon an ionic conductive material formed from a
polymer electrolyte base polymer and at least one ionic salt
selected from the group consisting of salts of alkali metals
and salts of alkaline earth metals, said adhesive being
bonded to said substrate by means of a primer, said primer
comprising at least one phenolic resin and at least one
rubbery compound, said adhesive tape being capable of
surviving immersion in molten solder at 260°C for at
least 5 seconds.
According to another aspect of the present
invention, there is provided a heat-resistant anti-static
pressure-sensitive adhesive tape described herein, wherein
said at least one phenolic resin is a phenol-formaldehyde
resin.
According to still another aspect of the present
invention, there is provided a heat-resistant anti-static
pressure-sensitive adhesive tape described herein, wherein
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said primer coating comprises at least one rubbery compound
selected from the group consisting of a butyl rubber, an
acrylonitrile-butadiene copolymer, an acrylonitrile-
butadiene-styrene copolymer, a styrene-butadiene-styrene
copolymer, a styrene-ethylene butylene-styrene copolymer,
polychloroprene, polybutadiene, polyisoprene, and a styrene-
isoprene-styrene copolymer.
According to yet another aspect of the present
invention, there is provided a heat-resistant anti-static
pressure-sensitive adhesive tape described herein, wherein
said primer coating comprises a mixture of acrylonitrile-
butadiene-styrene copolymer and polychloroprene.
According to a further aspect of the present
invention, there is provided a heat-resistant anti-static
pressure-sensitive adhesive tape described herein, wherein
said microparticulate adhesive comprises a polymer of
monomers comprising: a) at least 70 parts of at least one
alkyl (meth)acrylate or vinyl ester, b) correspondingly, up
to 30 parts of at least one polar monomer, to make 100 parts
monomer, and wherein said ionic conductive material
comprises a polymer electrolyte formed from a polymer
electrolyte base polymer selected from the group consisting
of polyethylene oxide, polyphenylene oxide, polyphenylene
sulfide, polyethylene sulfide, polyethyleneimine,
polypropylene oxide, polybutylene oxide, polybutylene
sulfide, and polybutylene imine, said polymer electrolyte
base polymer is added in an amount of from 0.1 part to
10 parts per 100 parts monomer.
According to yet a further aspect of the present
invention, there is provided a heat-resistant anti-static
pressure-sensitive adhesive tape described herein, wherein
said ionic conductive material comprises from 0.01 moles to
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moles of at least one salt of an alkali metal or alkaline
earth metal per mole of the polymer electrolyte base
polymer.
According to still a further aspect of the present
5 invention, there is provided a heat-resistant anti-static
pressure-sensitive adhesive tape described herein, wherein
said salt is selected from the group consisting of LiCl,
LiN03, LiCF3S03, LiS09, LiOH, KOH, NaSCN, NaI, BaS03CF3, and
NH40H .
10 According to another aspect of the present
invention, there is provided a heat-resistant anti-static
pressure sensitive adhesive tape described herein, wherein
the at least one alkyl (meth)acrylate comprises one of more
component selected from the group consisting of isooctyl
(meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl
(meth)acrylate, isoamyl (meth)acrylate, isodecyl
(meth)acrylate, and butyl (meth)acrylate, the at least one
vinyl ester comprises one or more component selected from
the group consisting of vinyl 2-ethylhexanoate, vinyl
caproate, vinyl laurate, vinyl pelargonate, vinyl hexanoate,
vinyl propionate, vinyl decanoate, and vinyl octanoate, and
the at least one polar monomer comprises one or more
component selected from the group consisting of N-vinyl-2-
pyrrolidone, N-vinyl caprolactam, acrylonitrile, vinyl
acrylate, diallyl phthalate, acrylic acid, methacrylic acid,
itaconic acid, an hydroxyalkyl acrylate, a cyanoalkyl
acrylate, an acrylamide, and a substituted acrylamide.
According to yet another aspect of the present
invention, there is provided a heat-resistant anti-static
pressure-sensitive adhesive tape described herein, wherein
said substrate is selected from the group consisting of
polyimide, polyphenylene sulfide, heat-treated non-woven
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material, fiberglass, metallized polymeric film, ceramic
sheet material, and metal foil.
According to yet another aspect of the present
invention, there is provided a heat-resistant anti-static
pressure-sensitive adhesive tape described herein, wherein
said substrate is polyimide.
Preferably, the heat-resistant anti-static
pressure-sensitive adhesive tape of the invention comprises
an adhesive polymer of monomers comprising:
a) at least 70 parts of at least one alkyl
(meth)acrylate or vinyl ester,
b) correspondingly, up to 30 parts of at least one
polar monomer, to make 100 parts monomer,
and wherein said ionic conductive material comprises a
polymer electrolyte formed from a polymer electrolyte base
polymer, said polymer electrolyte base polymer added in an
amount of from 0.1 part to 10 parts, said adhesive being
adhered to said substrate by means of a primer composition,
said primer comprising at least one phenolic formaldehyde
resin and at least one rubbery compound selected from the
group consisting of butyl rubbers, acrylonitrile-butadiene,
acrylonitrile-butadiene-styrene copolymers, styrene-
butadiene-styrene, styrene-ethylene butylene-styrene,
polychloroprene, polybutadiene, polyisoprene, styrene-
isoprene-styrene, and mixtures thereof,
said adhesive tape surviving in a wave-solder bath
for at least 10 seconds.
As used herein, these terms have the following
meanings.
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1. The term "polymer electrolyte base polymer" means
a polymer which is capable of forming a polymeric species
containing electron donating atoms which may be associated
with acceptor atoms during formation of the microparticle.
2. The term "polymer electrolyte functional unit"
means the group containing the electron donating species.
The term "microparticle" means a particle
having a diameter of from 1 micrometer to 250
micrometers.
4- The term "tribocharging" means electrostatic
charge generation associated with friction or separation
between separable surfaces.
5. The term "droplet" means the liquid stage of
the microparticles prior to the completion of
polymerization.
6. The term "cavity" means a space within the
walls of a droplet or microparticle when still in the
suspension or dispersion medium prior to drying, and thus
containing whatever medium was used.
7. The term "void" means an empty space completely
within the walls of a polymerized microparticle.
g_ The term "hollow"means containing at least one
void or cavity.
g. The term "solid" means voids or cavity-free.
10. The term alkyl (meth)acrylate means an alkyl
acrylate or alkyl methacrylate.
11. The term "modified surface" means a surface
which has been subjected to a priming, coating or
treatment such as chemical or radiation treatment such
that the original properties of the surface have been
changed.
As used herein, all parts, percents, and ratios are
by weight, unless specifically stated otherwise.
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Detailed Description of the Invention
Alkyl acrylate or methacrylate monomers useful in
preparing the microparticles and conductive pressure-
sensitive adhesives for use in tapes of this invention
are those monofunctional unsaturated acrylate or
methacrylic esters of non-tertiary alkyl alcohols, the
alkyl groups of which have from 4 to about 14 carbon
atoms. Such acrylates.are oleophilic, water
emulsifiable, have limited water solubility, and as
homopolymers, generally have glass transition
temperatures below about -20°C. Included within this
class of monomers are, for example, isooctyl acrylate, 4-
methyl-2-pentyl acrylate, 2-methylbutyl acrylate, isoamyl
acrylate, sec-butyl acrylate, n-butyl acrylate, 2-
ethylhexyl acrylate, isodecyl methacrylate, isononyl
acrylate, isodecyl acrylate, and the like, singly or in
mixtures.
Preferred acrylates include isooctyl acrylate,
isononyl acrylate, isoamyl acrylate, isodecyl acrylate,
2-ethylhexyl acrylate, n-butyl acrylate, sec-butyl
acrylate, and mixtures thereof. Acrylate or methacrylate
or other vinyl monomers which, as homopolymers, have
glass transition temperatures higher than about -20°C,
e.g., tert-butyl acrylate, vinyl acetate, and the like,
may be utilized in conjunction with one or more of the
acrylate or methacrylate monomers provided that the glass
transition temperature of the resultant polymer is below
about -20°C. When methacrylate monomer is the sole alkyl
acrylate utilized, a crosslinking agent, infra, must be
included.
Useful vinyl ester monomers are those which form
homopolymers having glass transition temperatures below
about 10°C. Such esters comprise 2 to 14 carbon atoms,
and includes such monomers as vinyl 2-ethylhexanoate,
WO 95/30720 ? ~ g 7 3 ~ 6 PCTIUS95103381
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vinyl caprate, vinyl laurate,vinyl pelargonate, vinyl
hexanoate, vinyl propionate, vinyl decanoate, vinyl
octanoate, and the like.
r
Useful polar monomers include moderately polar
monomers such as N-vinyl-2-pyrrolidone, N-vinyl
a
caprolactam, acrylonitrile, vinyl acrylate, ahd diallyl .
phthalate, as well as strongly polar monomers such as
acrylic--acid, methacrylic acid, itaconic-acid,
hydroxyalkyl acrylates, cyanoalkyl acrylates,
acrylamides, substituted acrylamides. When more than one
polar monomer is used, mixtures may include monomers-
having similar or unlike polarities, e.g., one moderately
polar and one strongly polar monomer or two monomers from-
one group.
The conductive microparticles and the pressure-
sensitive adhesives made therefrom comprise at least 70
parts by weight of at least one alkyl (meth)acrylate
ester or vinyl ester and correspondingly, up to 30 parts
by weight of one or more polar monomers.
Polymer electrolyte base polymers suitable for-use
include polyethylene oxide, polyphenylene oxide,
polyphenylene sulfide, polyethylene sulfide,
polyethyleneimine, polypropylene oxide, polybutylene
oxide, polybutylene sulfide, polybutylene imine, and the
like. Polyethylene oxide is preferred. Useful amounts
of the polymer electrolyte base polymer in microparticles
of the invention range from 0.1 part to 10 parts,
preferably from 1 part to 5 parts, based on LDO parts
monomer weight.
The conductive properties of. the polymeric
microparticles may be further enhanced by the addition of
ionic salts to adhesive compositions which contain the
microparticles. It is believed that the ionic salts
become associated with the electron donatinggroups
present in the amorphous polymer domains.
WO 95130720 2 ~ ~ 7 3 i ~ PCTlUS95103381
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Salts used for this purpose include salts of alkali
metals, and alkaline earth metals, including but not
limited to, NaI, NaSCN, BaCF3Sos, NaBr, NaC109, LiCl,
LiN03, L1CF3SO3, LiS04, LiOH and KOH. Lithium salts are
preferred for the present invention, especially lithium
nitrate.
Microparticles may v~e prepared by various
emulsification processes, which are varied depending on
whether hollow or solid microparticles are desired.
Aqueous suspensions of hollow microparticles may be
prepared by a "two-step" emulsification process which
first involves forming a water-in-oil emulsion of an
aqueous solution of polax- monomers) in oil phase
monomer,--i.e., at least cne (meth)acrylate or vinyl ester
monomer, with a polymer electrolyte base polymer, using
an emulsifier having a lcw hydrophilic-lipophilic balance
(HLB) value. Suitable emulsifiers are those having an
HLB value below about 7, prefer<:bly in the range of about
2 to about 7. Examples cf-such emulsifiers include
sorbitan monooleate, sorbitan trioleate, and ethoxylated
oleyl alcohol such as Brij'M 93, available from Atlas
Chemical Industries, Inc.
J
WO 95!30720 2 J g ~ 3 ~ a PCTIUS95103381
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Thus, in this first step, oil phase monomer(s),
polymer electrolyte base polymer, emulsifier, a free-
radical initiator, and, optionally, a crosslinking
r
monomer or monomers as defined below are-combined, and an
aqueous solution of all or a-portion of the polar
monomers) is agitated and poured into the oil phase
mixture to form a water-in-oil emulsion. The polymer
electrolyte base polymer may be added to either the-oil -
phase or the water-phase. A thickening agent, e.g.~-
methyl cellulose may also be included in theaqueous
phase of the water-in-oil emulsion. In the s-econd step,
a water-in-oil-in-water emulsion is formed by dispersing
the water-in-oil emulsion of_the first step into an
aqueous phasecontaining an emulsifier-having-an HLB
value above about 6. The aqueous phase may also contain
any portion of -the polar monomers) which-was not added
in step-one. Examples of such-emulsifiers include
ethoxylated sorbitan monooleate, ethoxylated-lauryl
alcohol, and alkyl sulfates. In both steps, when an
emulsifier is-utilized, its concentration should be-
greater than its critical-micelle-concentration, which is
herein defined as the minimum concentration of emulsifier
necessary for the formation of micelles, i.e.,sub-
microscopic aggregations of emulsifier molecules.
Critical micelle concentration is slightly different for
each emulsifier; usable concentrations ranging from 1.0 x
10-' to about 3.0 moles/liter. Additional detail
concerning the preparation of water-in-oil-in-water,-
emulsions, i.e., multiple emulsions, may be found in
various literature references, e.g., Surfactant Systems:
Their Chemistry, Pharmacy, & Biology, (D. Attwood and A.
T. Florence, Chapman & Hall-Ztd, New York City, 1983).
The final process step of this method involves-the
application of heat or radiation to initiate
polymerization of the monomers. Useful initiators are
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those which are normally suitable for free radical
polymerization of acrylate or vinyl ester monomers and
which are oil-soluble and of-very low solubility in
water. However, when the polar monomer is N-vinyl
pyrrolidone, the use of benzoyl peroxide as the initiator
is recommended.
Examples of such initiators include azo compounds,
hydropex-oxides, peroxides, and the like, and
photoinitiators such as benzophenone, benzoin ethyl
ether, and 2,2-dimethoxy-2-phenyl acetophenone.
Use of a water-soluble polymerization initiator
causes formation of substantial amounts of-latex. The
extremely small particle size of latex particles renders
any significant formation of latex undesirable. The
initiator is generally used in an amount ranging from
0.01 percent up to 10 percent by weight of the total
polymerizable composition, preferably up to 5 percent.
Aqueous suspensions of hollow conductive
microparticles may also by prepared by a "one-step"
emulsification process. comprising aqueous suspension
polymerization of at least one alkyl (meth)acrylate ester
monomer or vinyl ester monomer and at least one polar
monomer and a polymer electrolyte base polymer in the
presence of at least one emulsifier capable of producing
a water-in-oil emulsion inside the droplets which is
substantially stable during emulsification and
polymerization.- As in the two-step emulsification
process, the emulsifier is utilized in concentrations
greater than its critical micelle concentration. In
_ 30 general, high HLB emulsifiers are required, i.e.,
emulsifiers having an HLB value of at least about 25,
will produce stable cavity-containing droplets during the
polymerization, and are-suitable for use in this one-step
process. Examples of such emulsifiers include
alkylarylether sulfates such as sodium alkylarylether
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sulfate; e.g., TritonT"' W/30, available from Rohm and
Haas, alkylarylpolyether sulfates such as
alkylarylpoly(ethylene oxide)- sulfates, preferably those
A
having up to about 4 ethyleneoxy repeat units, and alkyl
sulfates such as sodium lauryl sulfate, ammonium lauryl
r
sulfate, triethanolamine lauryl sulfate, and sodium
hexadecyl sulfate, alkyl ether sulfates such as ammonium
lauryl ether sulfate, and-alkylpolyether-sulfates such as
alkyl poly-(ethylene oxide) sulfates, preferably those
having up to about 4 ethyleneoxy units. Alkyl sulfates,
alkyl ether sulfates, alkylarylether sulfates-and
mixtures thereof are-preferred as they provide a maximum
void volume per micraparticle for-a minimum amount of
surfactant. Nonionic emulsifiers, e.g:, SiponicTM Y-500-
70 (ethoxylated oleyl alcohol), commercially-available
from Alcolac, Inc, and PluronicTM P103 (a block copolymer
of polypropylene oxide and polyethylene oxide
commercially from BASF Corporation) can be utilized alone
or in conjunction with anionic emulsifiers. Polymeric
stabilizers may also be present but are not necessary.
The composition may also contain a crosslinking
agent such as a multifunctional -(meth)acrylate, e.g:,
butanediol diacrylate or hexanediol diacrylate, or other
multifunctional crosslinker such as divinylbenzene. When
used, crosslinker(s) is (are) added at a level of up to 1
percent, preferably up to 0.5 percent, of the total-
polymerizable composition.
Solid microparticles also useful in tapes of the
invention may be made by a similar one-step process
comprising aqueous suspension polymerization-of at least -
one alkyl (meth)acrylate ester monomer or vinyl ester
monomer, at least one polar monomer and a polymer - -
electrolyte base polymer in the presence of an-suspension
stabilizer. St is not necessary to use a high HLB
WO 95!30720 6
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PCT/US95/03381
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emulsifier because the droplets formed
need not be
cavity-containing droplets. Examples
of such useful
lower HLB emulsifiers include ammonium
lauryl sulfate
such as Standapol'M A, available
from Hercules and other-
s steric or-electrosteric polymeric
stabilizers such as
9
(poly)vinyl alcohol, polyacrylic
acid, polymethacrylic
acid, polyacrylamide, polyvinyl pyrrolidone,
polyvinyl
methylether, and the like.
Microsphere preparation may be modified
by
withholding the addition or alloy
part of the polymer
electrolyte base polymer, and polar
monomers until after
polymerization of the oil phase is
initiated; however,
the components must be added to the
polymerizing mixture
prior to 100$ polymer conversion.
. Discrete conductive polymeric microparticles
may
also be prepared via suspension polymerizations
disclosed
in U.S. Pat. No. 3,691,140, US 4,166,152,
US 4,636,432,
US 4,656,218, and US 5,045,569, for
preparing adhesive
compositions.
The conductive microparticles-are
normally tacky,
elastomeric, insoluble but swellable
in organic solvents,
and small, typically having diameters
of at least 1
micrometer, preferably in the range
of 1 to 250
micrometers, more preferably from
about 1 to 50
micrometers. -They may be solid,
contain a single void,
or multiple voids.
Following polymerization, an aqueous
suspension of
the microparticles is obtained which
is stable to
agglomeration or coagulation under
room temperature
conditions. The suspension may have
non-volatile solids
contents of from 10 to 50 percent
by weight. Upon
prolonged standing, the suspension
separates into two
phases, one phase being aqueous and
substantially free of
polymer, the other phase being an
aqueous suspension of
conductive microparticles. Where
high I-ZLB emulsifiers -
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are used the droplets have one or more cavities which,
upon drying, become voids. Both phases may contain a
minor portion of small latex particles. Decantation of
A
the microparticle-rich phase provides an aqueous
suspension having a non-volatile solids content on the
P
order of about 40-SO percent which, if shaken with water,
will readily redisperse. -
The adhesion properties-of the microparticles-iday be
altered by addition of tackifying resin and/or
plasticizer. --Preferred tackifiers for use herein include-
hydrogenated rosin esters commercially available from
companies such as Hercules Inc., under such trade names
as ForalT"' 65, ForalT"' 85, ForalTM 105, and Tacolyn'iM.
Other useful tackifiers include those based on t-butyl
styrene. Useful plasticizers include dioctyl phthalate,
2-ethyl hexyl phosphate, tricresyl phosphate, and the
like.
It is also within the scope of this invention to
include various other components to the adhesives used in
tapes of the invention, such as pigments, fillers,
including additional conductive fillers, stabilizers; or
various polymeric additives.
Tapes of the invention may be produced by coating
microparticle-containing compositions of the invention
onto a variety of high-temperature resistant primed
substrates. Suitable substrates includepolymeric-films
such as polyimide and poly-phenylene sulfide, heat-
treated non-wovens, fiberglass, metallized polymeric
film, ceramic sheet-material, metal foils, etc. The
substrate, or tape backing, as it is sometimes called,
must be able to withstand temperatures of at -least 200°C
and preferably about 260°C, without degrading or
releasing the adhesive from the surface.
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The surfaces) bearing the microparticulate adhesive
thereon are primed surfaces. Primers useful in tapes of
the invention comprise at least one phenolic resin and at
least one rubbery component.
Useful rubbery components include natural rubbers
a
such as butyl rubbers, and various synthetic compounds,
including but not limited to, acrylonitrile-butadiene,
acrylonitrile-butadiene-styrene copolymers, styrene-
butadiene-styrene, styrene-ethylene butylene-styrene,
polychloroprene, polybutadiene, polyisoprene, styrene-
isoprene-styrene, and mixtures thereof. Preferred
primers contain mixtures of two or more rubbery
compounds, such as acrylonitrile-butadiene
and
,
polychloroprene.
Useful phenolic resins, include but are not limited
to, phenol formaldehyde resin, available commercially
from Union Carbide under- the trade names UCAR BKR-2620,
and UCAR CK-1635, novolak resins and the like, and
mixtures thereof. Preferred primers contain from 40 to
120, preferably from 40 to 100 parts of phenolic resin
per 100 parts of rubbery compound.
The primer may further comprise additives such as
tackifying agents, antioxidants, colorants, viscosity
adjusting agents, solvents and other conventional
additives, which may be used in such amounts as are known
in the art.
Preferred tackifying agents include hydrogenated
rosin esters, include those available from Hercules under
such trade names as Piccolyte'M, Foral"~
Pental
nTM
and
,
y
,
the like.
Preferred primers include from 15 to 100 parts of
tackifier.
Coating of the adhesive and the primer may be
carried out by conventional methods such as knife
coating, Meyer bar coating, and other conventional means
WO 95130720 , L 18 7 316 PC'TJU595103381
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known in the art for coatingadhesives such as use of an
extrusion die.
The tape may be commercialized in roll-form, or may
a
be divided into segments for-sale, such as strips or
labels. Additionally, the adhesive may be provided
between two substrates, e.g., the adhesive is coated onto
a polyimide substrate, which may be provided on a low
adhesion backsize or other easily removable surface for
individual use.
These and other aspects of the invention are
illustrated by the following_examples which should not be
viewed as limiting in scope=
Glossary
IOA Isooctyl Acrylate
AA Acrylic Acid
PEO Polyethylene Oxide
PEO (750) Acrylate terminated PEO having a MW
of about 750)
BPER 70~ Benzoyl Peroxide, Lucidol'M 70
PEODMA Polyethylene Oxide Dimethacrylate
[(PEO)sDMA]
1,6 HDDA 1,6 Hexanedinl Diacrylate
ALS Ammonium Lauryl Sulfate-
Standapol'!M A Ammonium Lauryl Sulfate from Hercules
Santivar A Antioxidant di-tertiary amyl
hydroquinone
PiccolyteT"'
5115 Polyterpene resin (tackifier)
ZirexTM Zinc Resinate (tackifier) '
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Phenolic Resins:
CK-1635 Phenol-Formaldehyde Resin, also
designated CK-1635 UCAR, manufactured
by Union Carbide
BKR-2620 Phenol-Formaldehyde Resin, also
designated BKR-2620 UCAR,
manufactured by Union Carbide.
Test Methods
Tribocharging Measurements of Antistatic Coatings
The separation of materials which have been
laminated to each other causes the generation of
electrical charge on the surfaces which were previously
in contact. It is possible to calculate the magnitude of
the electrical charge as a measure of volts generated.
Voltages were conveniently measured using a 3M 711
Charge Analyser, available from Minnesota Mining and
Manufacturing Co. This equipment includes a voltage
sensor, mounted in a suitable enclosure. The enclosure
is provided with a digital read-out of voltage measured
with respect to a stainless steel plate which is
horizontally disposed and insulatively attached above the
enclosure. Static charge development may be measured for
adhesive tapes of the invention by laminating the tape
with its adhesive face in contact with the surface of the
stainless steel plate.
A strip of tape, 1.0" wide x 6.0" long is applied to
the upper surface of the stainless steel plate using a 3
1b roller. The steel plate is then grounded to zero the
digital display. Next, a free end of the tape is grasped
and using a uniformly applied force, the tape is peeled
away from the surface of the steel plate at a rate of 1.0
ft/sec. The voltage developed on the steel plate is
displayed via digital read-out. After this reading is
noted, the detector is zeroed by grounding the steel
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plate. The tape which was previously peeled frDm the
steel plate, is-next positioned as close as possible. to
the steel plate without touching it. A second reading of
0
voltage is displayed which represents the voltage
residing on the surface of the tape.
It is possible to determine the voltage generated
during separation of adhesive tapes of the invention from
a printed circuit board by attachment of a suitable board
to the surface of the stainless steel plate.- Adhesive
tape is then attached to the-circuit board us.~ng the
procedure.described previously for the steel plate. Upon
peeling the tape from th= circuit board a voltage reading
is displayed which reflects the charge generated on the
surface of the circuit beard_ ,-Following the-process of
zeroing the instrument,-by grounding, the residual charge
on the tape is measured by positioning the peeled tape in
close proximity to the steel-plate.
Tribocharging during unwind of a roll of !.ape is
also measured using the 3?rI 711 Charge Analyser. In_this
case a length of tape approximately 1.0 ft. long is,
unwound from a roll of adhesive tape but not removed from
it. When the unwound length is placed in close proximity
to the previously grounded steel plate, a voltage reading
is displayed which represents the magnitude of the charge
on the tape.
Adhesive Transfer _
With tapes of the current invention it ~is important
to prevent adhesive transfer from the tape onto the
surface of electronic assemblies which are subject to
wave soldering. The test measures the ability of the
tape to maintain a strong bond between film support and -
adhesive even at the elevated temperature of molten
solder-. _
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A tape sample (2.5 cm x 7.6 cm) is applied with its
adhesive in contact with the surface of a 4.45 cm x lOcm
section of dust-free printed circuit board (PCB). A
small portion of the tape overlaps an edge portion of the
PCB to facilitate subsequent removal. Pressure from a 3
s
1b roller assures consistent application of the tape
samples. These test pieces are then positioned in a
molten solder bath so that the tape is held below the
surface of the solder for a desired length of time.
1O After removal from the solder bath, the test pieces
are allowed to cool to rowm temperature. The free end of
the tape is grasped and .irawn away from the edge of the
PCB. Observation is made to determine if the adhesive
separates from the film rapport, thereby leaving an un-
wanted residue on the surface of the PCB.
xamples
Preparations ef Microparticles
_Example 1
Acrylic acid (5.4g), polyethylene oxide acrylate
(PEO 750) (13.5q), PEODMA (O.ISg) and 70$ benzoyl
peroxide (0.99g) were dissolved in isooctyl acrylate
(223.2g). This solution was added to an aqueous solution
of surfactant. The surfactant solution comprised
StandapolT"sA, available from Hercules, (8.4g) dissolved
in de-ionized water (360g). An emulsion of the isooctyl
acrylate solution in the aqueous solution was produced by
high shear mixing using an Omni mixer at setting 5.
Mixing was continued until the average particle size of
the oily droplets was approximately 3Etm. Size was
determined using an optical microscope.
The resulting oil-in-water emulsion was charged to a -
1-liter resin reactor equipped with four baffles, a
paddle stirrer and a suitable heat source, such as a
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heating mantle. With continuous stirring at a rate of
400 rpm, the reactor and contents were heated to 60°C.
At this point the reactor was degassed with
0
nitrogen. A reaction proceeded in the absence of oxygen.
This was allowed to continue for a period of 22 hours
J
while both temperature and stirring rate were maintained.
The resulting aqueous suspension contained insoluble
particles of approximately SEun in diameter.
Example 2. .... _. .m.
Primer Composition for Polyimide Substrate
Ingred. Parts ~ solids
Butadiene/Acrylonitrile 75.00 parts 25.63
Neoprene W. 25.00 parts 8.54
Phenolic Resin BKR-2620 19.90 parts 6.8
Santivar A 3.95 parts 1.35
Piccolyte 5115 - 49.67 parts 16.97
Zirex 49.67 parts 16.97
Phenolic Resin 69.43 parts 23.73
Methyl Ethyl Ketone 329.57 parts
iso-Propanol 60.00 parts
Toluene - 621.00 parts
PhVSical Properties.,. __., _r, .
S.G. of Solids 1.065 S.G. of Solution 0.884
# per Gallon 7.370 ~ Comb. RHC Soln. 7-.67
~ Comb. RHC on Solids 34.17 ~ Theoretical Solids22.45
Preparation of Primer Solufion Materials .
Butadiene/Acrylonitrile 75.00 parts 5.755 ,.
NeopreneTM W. 25.00 parts -- 1.918
Phenolic Resin BKR-2620 19.90 parts 1.527
Santivar'""- A 3. 95 darts 0. 303~-
Piccolyte'M SlIS 49.67 parts 3.811$
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PCTIUS95/03381
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Zirex'M 49.67 parts 3.811$
Phenolic Resin 69.43 parts 5.328$
Methyl Ethyl Ketone 329:57 parts 25.290$
iso-Propanol 60.00 parts 4.604$
Toluene 621.00 parts 47.652$
The resins, tackifiers and antioxidant, indicated
above, are dissolved in a mixed solvent comprising methyl
ethyl ketone, iso-propanol and toluene to provide a
primer coating for film supports. Conventional churns,
equipped withstirrers, or similar equipment may be used
for primer solution preparation. The solution is
inspected for clarity and filtered if necessary.
Example 3
Adhesive Coatin Composition
Adhesives 100 parts
Lithium Nitrate 0.40 parts
Lithium Hydroxide 0.28 parts
Ammonium Hydroxide 0.60 parts
Benzotriazole2 0.05 parts
Thickener (QA 708)' 0.30 parts
' 40$ solids suspension of Ex. 1
Z 10$ soln, in 1:1 IPA/Water
3 50$ soln. in IPA
To 100 parts of the adhesive, prepared as previously
described, was added a combination of lithium salts, to
. 30 increase ionic conductivity, ammonium hydroxide for pH
adjustment, benzotriazole for corrosion inhibition and a
thickener to improve coating characteristics. Each of
the additional ingredients was slowly stirred into the
adhesive composition and thoroughly mixed prior to
coating.
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Example 4
Tape Preparation Using A Primer Coating
The high temperature resistant, antistatic adhesive
tape of the present invention was prepared by coating
suitable film supports with a primer, which, after
drying, was over-coated with a layer of the antistatic
adhesive composition.
The primer composition was used as previously
described or with addition of 0.5 parts of benzotriazole
corrosion protection agent. A knurled roll applied a
coating of primer on a 20 ~.~m (1 mil) filled polyimide
(Kapton) film. The coated film was dried at 180°F for 1
min. with a resulting primer coating weight of 0.003
gm/sq. ft.
A 75 ~zm (3 mil) film of adhesive was then coated
over the primer layer then dried for 3 mins. at 110°C
(230°F) .
Examples 5-lOC
Tape Properties
The electrical and adhesive properties of tapes including
the invention are presented in the following table.
Examples 5, C6 and C7 were tested at 10$ relative
humidity while samples 8, C9 and C10 were tested at a0°
relative humidity.
Examples 5 and 8 are tapes of the current invention.
Examples C6 and C9 comprise a commercially available tape
known as 3M ##92 Tape which has a silicone adhesive.
Examples C7 and C10 are a commercially available tape
known as 3M #1205.
Note that only the tapes of the invention exhibit
both lack of adhesive transfer and low tribocharging.
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Tape ConductivityTribocharge Adhesive
Identity Ohms/sq. Volts Transfer*
(3M Tester...$711)
Unwind Removal from
PC Board
Ex. S 4.8 X 109 3.0 35 No transfer
Ex. 6C 1.3 x 101 >2000 670 No transfer
Ex. C7 2.7 x 10'5 ,1919 680 > 30B Transfer
Ex. B 2.7 x 108 2 4 No transfer
Ex. 9C 2.3 x lOlA 1311 - 581 No transfer
I Ex. C10 5.8 x 1015 1223. 566 > 30~ Transfer
I
* Adhesive transfer was measured at 287°C (550°F) with
tape samples dipped into molten solder for 5 seconds.
