Note: Descriptions are shown in the official language in which they were submitted.
396~- ~
- 1 - SL3 7 0
O~7E PART eRO8E~LINRABL~E HO~ NEI,T ;;
ADHEE;IVES
FIELD Oli' T~{E INVl~NTION
: The present invention relates to one part moisture ~ :
crosslinkable compositions based on polyolefinic silane
copolymers containing encapsulated siliane crosslinking
catalyst, methods for manufacturing to said compositions ~ :
and to said encapsulated crosslinking catalysts. ~ ~
.~:
, ~
BACXGROU~D OF T~E I~VEN~IO~
The polyolefin hot melt adhesive industry in the
United States alone has grown steadily from l00 million
pounds in 1970 to over 600 million pounds in l99l. Low
density polyethylene (LDP~) makes up approximately 25% of
the polyolefins used in hot melt formulations, while
ethylene-vinyl acetate (EVA) copolymer makes up most of
the rest. A typical polyole~in-based hot melt adhesive
is composed mainly of two or three components, namely,
polyole~in polymer (40-70 wt%), a modifying or tacki~ying
resin (30-40 wt%) and a petroleum wax (0-20wt%), wherein
the quantity and relative amount o~ each material is
2~396~.
- 2 - SL370
governed by the desired performance of the adhesive. The
polyolefin polymer forms the backbone of the adhesive and
provides strength and toughness. The Melt Index (MI) of
a thermoplastic polymer is a measure of melt viscosity,
wherein a high MI corresponds to a low viscosity.
Typically, for adhesive purposes, polyolefin polymers
with high melt index (MI) values of 100-2000 are required
to achieve desired adhesive properties. The modifying or
tackifying resin contributes surface wetting and tack,
while petroleum wax is used to lower melt viscosity,
reduce cost and control setting speed. Other additives
such as antioxidants, fillers, and the like known in the
hot melt adhesive art are also present to enhance certain
properties.
It is known that the thermoplastic nature of
existing uncrosslinked polrolefin-based hot melt
adhesives limits their heat resistance. Typically, the
polymers melt at <110C, which results in the destruction
of the strength and integrity of the adhesive. Shear
Adhesion Failure Temperatures (SAFT's) of existing
polyolefinic-based hot melt adhesive systems occur
_ <100C.
It is also known that polyamide and polyester-based
hot melt adhesives offer some, but limited, improvements
in temperature resistance due to their higher melting
points, although these materials are still thermoplastic,
not crosslinked, and have maximum SAFT's in the range of
180C. Further, these polymers, which are produced in
batch processes, are more expensive than polyolefins such
as LDPE and ethylene vinyl silane (EVS) copolymers which
are produced on reactors by continuous bulk
polymerization. It is known, therefore, that only
crosslinked hot melt adhesives offer real high
temperature and solvent resistance.
Reactive epoxy resins, acrylic resins, and
211396~ :
- 3 - SL370
polyurethanes, most commonly available in two-part
systems, have been developed to achieve this. However,
these materials tend to have cost and performance trade-
offs when compared to polyolefin based hot melt adhesive
compositions. For example, fast setting products tend to
sacrifice flexibility. Also, there are unfavourable
industrial hygiene issues associated with these
aforementioned reactive systems. For example, the
isocyanate groups in the polyurethane systems are
sensitizing agents.
At the present time, the major way to produce
crosslinked polyolefin-based hot melts is to subject the
finished article to ionizing radiation such as ~-rays or
electron beams. This irradiation offers a commercially
unfeasible proposition in most instances. Polyolefinic
silane copolymers such as ethylene-vinyl silane (EVS)
copolymers offer another means of crosslinking.
Polyolefinic silane copolymers harden or crosslink
in the pr~sence of water in a manner analogous to the
curing of silicone rubbers. Generally a silane
condensation catalyst is required although there are
reports where application of heat alone in air can induce
crosslinking (U.S. Pat. 3,225,018 - Zutty, issued Dec. 21
1965, U.S. Pat. 3,392,156 - Donaldson, issued July 9,
1968, and D.J. Bullen, G. Capaccio, C.J. Frye, T. Brock,
Brit. Polym. J., 21, 117-123, (1989).
There are five known factors which in~luence the
crosslinking of polyolefinic silane copolymers, namely,
1) catalyst concentration in the copolymer,
2) water concentration in the copolymer and external
to it,
3) temperature,
4) sample geometry, and -.
5) silane content
EVS crosslinking is reported to be first order with
.'~ . ' ': ' ' -' ~ ,,
i"i . ..
211396~
- 4 - SL370
respect to catalyst concentration and first order with
respect to water concentration in the polymer (A. K. Sen
et al, J. Appl. Polym. Sci., 44, 1153-1164, (1992).
Typical levels of residual water in EVS are 100 ppm or
less.
The effect of temperature on crosslinking in the
presence of catalyst can be approximated by the Arrhenius
relationship, the rate of crosslinking approximately
doubles with every 10C increase in temperature ( A. X.
Sen et al, J. Appl. Polym. Sci., 44, 1153-1164, (1992).
Sample geometry also plays a role by affecting the
time of diffusion of external environmental water into
the EVS copolymer. This environmental water in addition
to the residual water absorbed in the EVS at the point of
fabrication of the finished sample. The diffusion of
- environmental water into the sample is governed by ~ick's
Law of Diffusion which is:
Conc. of Water a (l/Thickness)2 ~ Conc. Gradient.
Therefore cure can be increased by increasing the
concentration of water outside the sample and by reducing
the sample cross-section.
The copolymerization of ethylene and vinyl silane in
a continuous bulk reactor to produce ethylene vinyl
silane copolymer is described in aforesaid USP's
3,~25,018, and 3,392,156, and U.S. Patent 4,297,310 - S.
Akutsu, et al, issued Oct. 27, 1981. Such EVS copolymers
contain the vinyl silane comonomer grouping in the range
of about 0.5 - 6 wt% based on the weight of the
copolymer. U.S. Patent No. 4,689,369 - Ishino et al,
issued August 25, 1987, describes cross-linkable
copolymers produced by the reactor polymerization of
silanes having an unsaturated and hydrolysable groups for
use in various molding fields, such as electric power
cables, pipes, tubes, films, and hollow and foamed
mouldings. Japan Kokai Tokkyo Koho JP 01,301,740 -
2113~
- 5 - SL370
Tachibana et al, filed May 31, 1988 describes heat
resistant hot melt adhesive compositions comprising
silane modified polyolefins, organotin silane
condensation catalysts, polyols, and, optionally,
tackifiers andtor waxes. One practical drawback
acknowledged in this application is that even at low
temperatures the crosslinking reaction starts once the
silane copolymer and catalyst are mixed. This has the
effect of seriously limiting the shelf life of the
composition. In order to achieve shelf-life the catalyst
must be packaged separately from the polyolefin silane
copolymer until near the time of application resulting in
a two-part adhesive.
There still remains a significant need in the hot
melt adhesive industry for shelf stable one-part adhesive
formulations which have improved solvent and higher
temperature resistance, wherein one-part compositions can
be placed in a single package and remain non-crosslinked
until used.
Encapsulation of various products has been
documented extensively. Gutcho has compiled a large
volume of patents which describe the encapsulation
processes for a wide variety of biologically active
ingredients. (M. Gutcho, Capsule Technology
Microencapsulation, Noyes Data Corp., 1972.)
A literature review of encapsulation techniques is
also set forth by Kondo (A. Kondo, Microcapsule
Processing and Technology, Ed. J.W. Van Valkenberg
1979.). In it he descrihes many examples of
encapsulation. One example of interest is the
encapsulation of an amine epoxy resin (tJ.S. Patent
3,167,602). In this example an amine epoxy resin curing
agent is encapsulated with a wax. These capsules are
then used in the preparation o~ one-liquid-type epoxy
adhesives. The encapsulation was accomplished by
~?
21~3~6~
- 6 - SL370
dropping the amine compound through a film of molten wax
which was floated on water at 70C. The amine drops are
encapsulated to a thickness of 70 to 100 microns and fall
through the water to cooler water at the bottom of the
tank where the wax solidifies. The recovered capsules
are stable for weeks at room temperature but release the
amine component when heated. This allows the amine to
then function as an epoxy curing agent.
Methods of encapsulation of active ingredients in a
polymer shell have been described for a variety of
applications, for example, for drug delivery (V.
Lenaerts, et al, Biomaterials, 5, 65-68, (1984).
Generally, the active ingredient is dissolved in a vinyl
monomer which is emulsified and then polymerized to ~orm
small polymeric particles containing the active
ingredient.
Encapsulation of chemical catalysts for use in EVS
crosslinking reactions by emulsion polymerization could
reasonably be anticipated to result in unacc~ptable
experimental results. Problems that could be anticipated
include reaction of the catalysts with the water used in
the emulsion, reaction of the catalysts with the vinyl
monomers, and reaction of the vinyl polymerization
catalysts with the silane condensation catalysts.
Another parameter critical to this invention relates
to the degree of damage to the catalyst containing
particles during their dispersion in the polyolefinic
sila~e copolymer. This factor, and the relative
compatibility of the silane condensation catalyst to the
encapsulating material vs the polyolefinic silane
copolymer, determines how well the catalyst is localized
in the encapsulent. The more complete the localization
of the catalyst the more shelf-stable the adhesive.
Ano~her anticipated factor is the m.p. and viscosity of
the silane condensation catalyst which would affect its
21~39~
- 7 -- SL370
diffusion mobility.
As a result of extensive investigations, we have
discovered novel, hot melt adhesive formulations which
are shelf-stable, yet, when momentarily melted during
application above defined temperatures described ;~
hereinbelow start crosslinking upon exposure to water. -
,:
BUMNARY OF THE :I:NVENTION
:
It is thus an object of the present invention to
provide novel one-part, shelf-stable adhesive
compositions comprising polyolefinic silane copolymers
mixed with silane condensation catalysts that are
encapsulated in such a manner that the catalysts are not
able to initiate crosslinking until the adhesive is
momentarily melted during application above the m.p. or
softening point of the material encapsulating the
catalyst.
It is a further object of the present invention to
provide methods of adhering a first substrate to a second
substrate by use of said hot-melt adhesive compositions.
It is yet a further object to provide novel
encapsulated silane condensation catalysts.
These and other advantages and objects of the
present invention will become apparent upon a reading of
the specification as a whole.
Benefits of encapsulating the silane condensation
catalysts can be realized if the material encapsulating
the catalyst melts above ~ 120C. The high MI
polyolefinic silane copolymers have crystalline melting
points <110C and we have found it possible to produce an
encapsulated catalyst that can be dispersed into the
polyolefinic silane copolymers below the m.p. of the
material encapsulating the catalyst. The catalyst
therefore remains localized within the encapsulent.
~.ir: .: ,.. . . .
2 ~ L 3 ~ 6 ~
- 8 - SL370
Hot melt adhesives, for example glue sticks, are
generally melted above 150C when applied to the
substrate. Therefore if the m.p. or softening point of
the encapsulating material is below this adhesive
application temperature the catalyst will be dispersed in
the adhesive and be able to initiate crosslinking.
Surprisingly, we have found that silane
condensation catalyst can be dissolved in vinyl monomer,
emulsi~ied, polymerized, recovered as a powder and be
mixed into polyolefinic silane copolymers below ~ 120C
to produce one part shelf-stable adhesive formulations
which, when momentarily melted during application above
the m.p. or softening point of the material encapsulating
the catalyst, crosslink upon exposure to moisture.
It is also generally practiced in the plastics
industry to introduce additives into polymer via the
masterbatch route. In this technique a concentrated
mixture of the additive is prepared in an inert polymer
carrier resin which is then letdown in the final product
to the desired concentration. It is generally desired to
use a masterbatch with similar melting and viscosity
characteristics as the final product to ensure proper
mixing of the additive.
Surprisingly, we have found that by compounding
silane condensation catalyst into materials which melt
above ~ 130C and grinding these materials into powders,
that these powders can be dispersed in polyolefinic
silane copolymers below ~ 120C to produce one component
shelf-stable adhesive formulation that, when momentarily
melted above the m.p. or softening point of the catalyst
containing powder, cro~slink upon exposure to moisture.
Accordingly, in one aspect the invention provides a
hot melt adhesive composition comprising an encap~ulated
silanol condensation catalyst, optionally a tackifier and
or wax, and a silane cross-linkable copolymer o~ the
~.: .,: : : . -
2~3~1
- 9 - SL370 ~ ~;
general formula~
~(CH2CH2)~(COM)y(~ER)w~
wherein TER is an ethylenically unsaturated monomer other
than ethylene; and
wherein COM is:
(CH2 CR
( CH2
(CHR2) n
Zm . :
Si(oR3)
and Z is -CO-O-CH2CH2-; m is 0 or 1; n is 0 or 1;
Rl=R2 is H or CH3; R3 is CH3 or C2Hs; x,y and w are
numerals,and x is greater than 50,
- ~
and 0.5 < (MMC~) y ~ 100 < 10.0; ~ ;~
2 0 [ 2 8--X + (MWO,~ Y ~ ( MWT~R ) W ]
and o< (MW~BR? W X 100 < 50;
[28-X + (MW""",)-Y + (MW1,ER)OW]
wherein MWC~ is the molecular weight of the comonomer,
MM~r is the molecular weight of the termonomer; ::
having a melt index greater than 100.
Preferably, the EVS copolymer has.a melt index (MI)
of greater than 200, and more preferably, greater than
400.
In one preferred aspec~t the invention provides a
composition as hereinabove defined wherein ~aid copolymer
is a graPt copolvmer of the general formula selected from
the group consisting of:
~ ., .. . .:
21~ 3~
- 10 - SL370
CH2 CH2 ) X ( CH2 I H ) y ( TER) w
I H2
jCH2
(R3 0) 3 Si
wherein R3 is CH3 or C2H5; TER is an ethylenically
10unsaturated monomer other than ethylene;
and ~CH2 C~2)x (CH2 fH)y (TER)W~
fH2
f-CH3
f=0
OCH2CH2CH2 Si (0 CH3) 3 ~ I :
2 0
and x, y and w are as hereinabove defined.
In a more preferred aspect the invention provides a
composition as hereinabove defined wherein said copolymer
has the general formula selected ~rom the group
consisting of~
~CH2 CH2)X(CH2 C Rl)y (TER)w ; :
Si (oR2) 3 . ; ~ ~ :
and ~:
~CH2 CH2)X (CH2 C Rl)y (TER)w~
1 . :~::
C0-O(CH2)3 Si(o C~I3)3
where Rl is H or CH3 and R2 is CH3 or C2H5; and TER, x, y,
and w are hereinabove defined; and wherein said copolymer
is prepared by radically polymerizing a polymerizable:~
monomeric mixture consisting essentially o~ ethylene and
at least one ethylenically unsaturated silane compound
selected ~rom the group consisting o~
vinyltrimethoxysilane, vinyltriethoxysilane and
methacryloxypropyltrimethoxysilane under a pressure
2~3~61
~ SL370
ranging from 1000 to 4000 kg/cm2, and containing said
silane compound in an amount of from 0.5 to 10 wt.%.
Most preferably, the ethylenically unsaturated
silane compound is vinyl trimethoxysilane.
Generally these copolymers are known as ethylene-
vinyl silane (EVS) copolymers.
The present invention in one aspect is based on the
surprising discovery that silane condensation catalysts
can be temporarily deactivated or localized by
encapsulation so that when the catalysts are compounded
into EVS copolymer at temperatures less than ~120C they
do not promote EVS crosslinking upon storage under
ambient conditions of temperature and humidity, but, when
these mixtures are heated momentarily above the m.p. or
softening point of the material encapsulating the
catalyst during application of the adhesive, ~he catalyst ~-
is released and starts promoting EVS crosslinking.
Yet a further aspect of the invention provides an
encapsulated silane condensation catalyst comprising
silanol condensation catalysts preferably selected from
the general classes of acidic compounds such as
carboxylic acids and basic compounds such as organic
titanates, and organic complexes or carboxylates of lead,
tin, cobalt, iron, nickel and zinc such as lead
naphenate, tetramethyl titanate, and dibutyltin dilaurate
encapsulated in a material softening or melting close to
or above, the so~tening or melting point of the E~S
copolymer in which it is mixed.
Encapsulating materials include any inert high
melting material compatible with EVS copolymers and
silane condensation catalysts and which can be prepared
as a fine powder preferably less than 48 mesh.
Methods of producing fine powder particles are well
known in the art and include grinding of solids or spray
drying of solutions or emulsions. Thus, the encapsulated
.;: ' ' .. ' . i . . ' ! : ,
2 1 ~ 3 9 6 1
- 12 - SL370
catalysts of use in the practice of the invention may be
obtained in fine powder form by such methods.
In one preferred aspect of the invention the
encapsulating material is prepared by the polymerization
of an emulsion of vinyl monomers containing silane
condensation catalyst to produce a powder of spherical
particles Ca. 1/3 ~m in diameter.
Such methods include a method of encapsulating the
silane condensation catalyst by dissolving or dispersing
the catalyst in monoethenically unsaturated monomer(s~,
emulsifying the monome~(s) containing catalyst in water
usually with the aid of surfactants or colloid
stabilizers, and polymerizing the monomer(s) by free
radical means at room temperature or above to produce an
emulsion of solid capsules. The emulsion is then dried
to yield free flowing powder of encapsulated silane
condensation catalyst.
An encapsulated silane condensation catalyst may be
further encapsulated with a second polymer to produce a
so-called core/shell capsule. This is accomplished by
adding another charge of monoethenically unsaturated
monomer(s) and optionally surfactants, coloidal
stablizers, and free radical catalyst, to the emulsion of
silane condensation catalyst capsules. This second
charge of monomer(s) coats the capsules and is
polymerized by free radical means at room temperature and
above to produce core/shell capsules.
The encapsulated catalyst is preferably encapsulated
with a material in alternative embodiments where the T8
or softening point of the polymer encapsulaking the
silane condensation catalyst is above the temperature at
which the capsules can be compounded into ~VS, generally
120C.
The monoethenically unsakurated monomers preferably
comprise mixkures of methacrylic acid (MA~) and methyl
- . -
21~ 3~1
- 13 - SL370
methacrylate (MMA), the silane condensation catalyst is
dibutyltin dilaurate (DBTDL), the surfactant is sodium
dodecyl sulphate, and the free radical initiator is
ammonium persulphate, wherein the polymerization
reactions are effected under nitxogen at 65-85C.
More preferably, the catalyst is encapsulated in a
so-called core/shell capsule. The monoethenically
unsaturated monomer used to make the capsule core polymer
is preferably styrene, the silane condensation catalyst
is an oligomer of dioctyl tin maleate (DOTM), the
urfactant is an ethoxylate of nonylphenol, and the free
radical initiator is a redox mixture of sodium
metabisulphite, ferric sulphate, and ammonium
persulphate. The reaction being carried out at 20C
under nitrogen.
The monoethenically unsaturated monomer used to make
the capsule shell polymer is acrylonitrile, and wherein
additional sodium metabisuphite and ammonium persulphate
is optionally added and reacted at 20-40C under
nitrogen.
In another preferred aspect of the invention, the
encapsulating material is a polymer compatible with EVS
which melts above the temperature at which the
encapsulated catalyst is compounded into the EVS-based
adhesive but which melts or softens below the application
temperature of the adhesive.
In yet another preferred aspect of the invention,
the encapsulating material is a solid compatible with ~VS
and the silane condensation catalyst which melts above
the temperature at which the encapsulated catalyst is
compounded into the EVS-based adhesive but which melts or
softens below the application temperature of the
adhesive.
Tackifiers of use in the practice of this aspect of
the invention are preferably selected from the general
~ 21 13961
- 14 - SL370
classes of resins, based on their chemical nature,
consisting of rosin, modified rosin, rosin derivatives,
hydrocarbon resins and terpene resins.
However, the person skilled in the art will know or
could readily determine without the need for undue
experimentation which tackifiers would be of value. By
way of guidance, wood resins, gum resins, tall oil
resins, hydrocarbon resin, and modified terpene resins as
described in "Handbook of Adhesives, page 562, are of use -
in the present invention. Examples of such tackifiers
are set forth in Table 1.
~A~E 1
_ _ _ _ : .
Ring and Ball
Softeniny Point
Trademark Tackifier Class (C) Acid Number l
_ I
Zonester 65 Rosin ester type 65C 78 ¦
i . _ I .
Sylvatac 140 Rosin ester type _ 139C 140
Nirez 1135 Terpene type i35C __
_ I : -.,
Nirez 2019 Terpene type 123C __ ~
_
20 STA-TAC B Hydrocarbon type100C __
_
Betaprene 255 Hydrocarbon type 132C __
I .
Zonatac 115 Hydrocarbon 115C __
Modified Terpene
I -
The relative amounts of ethylene vinyl silane (EVS)
and tackifying resin may be readily determined by the
skilled person in the adhesion art. Typically, the EVS
copolymer constitutes 30-95% w/w and the tacki~ier 5-70~
wlw .
21~396 ~i
- 15 - SL370
Th~ adhesive compositions may be made by compounding
the adhesive components above the softening temperature
of the material encapsulating the silane condensation
catalyst and then cooling the mixture to temperatures
below the softening temperature of the material
encapsulating the catalyst, generally <120C, before
compounding the catalyst capsules into the mixture.
The compositions of the invention as hereinbefore
defined may further comprise a diluent, carrier, adjuvant
and the like. Such a carrier is a petroleum wax present
in a concentration of 0-20% w/w. Petroleum waxes of use
in the compositions of the present invention have been
used in prior art hot melt adhesive compositions
comprising polyolefin polymer and tackifying resins to
reduce viscosity and cost.
The adhesive compositions according to the invention
are of use as hot melt adhesives with substrates within,
for example, the fields of paper laminates, cases,
cartons, book binding, labels, bags, textiles, carpet
seams, furniture, cans, tubes, drums and the like.
Accordingly, in a further aspect, the invention
provides a method of adhering a first substrate to a
second substrate, which method comprises applying a hot
melt adhesive composition according to the invention as
hereinbefore defined to either or both of said first
substrate and said second substrate and adhering said
substrates one to the other.
T~e various techniques of applying the composition
of the invention as hot melt adhesives fall within the
skill of the art.
.,, . ~, ,, . ~
21~396~ :
- 16 - SL370
DETAILED DE5C~IPTIO~ OF THE INVBNTION
The ethylene silane-crosslinkable copolymers o~ use
in the compositions of the present invention are
copolymers consisting essentially of ethylene and an
ethylenically unsaturated silane compound having a
hydrolyzable organic group.
The term "consisting essentially of" used herein
means that the ethylene copolymer can contain up to 50
wt% of copolymerizable monomers other than ethylene and
the ethenically unsaturated silane compound having a
hydrolyzable organic group. Examples o~ such optional ~ -~
monomers include ~-ole~ins such as propylene, hexane~
and 4-methylpentene-1; vinyl esters such as vinyl acetate
and vinyl butyrate; unsaturated organic acid derivatives
such as methyl acrylate, ethyl acrylatP and methyl
methacrylate; unsaturated aromatic monomers such as
styrene and ~-methylstyrene; and vinyl ethers such as
vinylmethyl ether and vinylphenyl ether. These optional
monomers can be present in the ethylene copolymer in any
forms, e.g. a graft form, a random form or a block form.
Ethylene and the unsaturated silane compound are
copolymerized under any conditions such that
copolymerization of the two monomers occur. More
specifically, those monomers are copolymerized under a
pressure of 500 to 10,000 kg/cm2, preferably 1,000 to
4,000 kg/cm~, and at a temperature of 100 to 400C,
preferably 150 to 350C, in the presence of a radical
polymerization initiator, optionally together with up to
about 50 wt% of a comonomer and a chain transfer agent.
The two monomers are brought into contact with each other
simultaneously or stepwise in a vessel or tube type
reactor.
In the copolymerization o~ ethylene and the
unsaturated silane compound, any radical polymerization
~ ':
~1~3~61
. - 17 - SL370
initiators, comonomers and chain transfer agents, which
are conventionally used in homopolymerization of ethylene
or copolymerization of ethylene with other monomers can
be used.
Examples of radical polymerization initiators
include (a) organic peroxides such as lauroyl peroxide,
dipropionyl peroxide, benzoyl peroxide, di-t-butyl
peroxide, t-butyl hydroperoxide, and t-butyl
peroxyisobutyrate; (b) molecular oxygen; (c) azo
lo compounds such as azobisisobutyronitrile and
azoisobutylvaleronitrile; and (d) peroxydicarbonates such
as n-butyl peroxydicarbonate, n-propyl peroxydicarbonate,
isopropyl peroxydicarbonate, and sec-butyl
peroxydicarbonate.
Examples of the chain transfer agent include (a)
paraf~inic hydrocarbons such as methane, ethane, propane,
butane and pentane; (b) ~-olefins such as propylene,
butene-1 and hexene-1; (c) aldehydes such as
formaldehyde, acetaldehyde and n-butylaldehyde; (d)
ketones such as acetone, methyl ethyl ketone and
cyclohexanone; (e) aromatic hydrocarbons; (f) chlorinated
hydrocarbons; and (g) hydrogen.
While the copolymer of use in the present invention
can be in the form of a normal copolymer of ethylene and
unsaturated organosilane copolymerized under high
pressure using a stirred autoclave reactor with free
radical initiators as hereinabove described, the
copolymer can also be of the form of a graft copolymer
prepared by graft polymerization of an unsaturated organo
silane onto polyethylene or copolymers of ethylene and
other monomers. While methods of making such copolymers
are known in the art, the copolymers of use in the
present invention are novel in having MI > 100.
Examples of silane condensation catalysts include:
(a) organometallic basic compounds particularly solids
` 2~L13~6~ ~
- 18 - SL370
such as oligomeric dialkyltin maleates and liquids such
as dibutyltin dilaurate; (b) organic titanates; (c)
acidic compounds such as carboxylic acids.
The catalyst encapsulating materials prepared by
emulsion polymerization of vinyl monomers consist
essentially of vinyl monomers emulsified using
surfactants and initiated using free radical or redox
initiators.
The catalyst may be encapsulated with any type of
polymer produced from any type of monoethenically
unsaturated monomer. Preferably the polymer may be
produced from any monomer or mixture of monomers such
that ideally the Tg of the resulting polymer is
approximately 125C. If the encapsulation is performed
below this temperature the particles may be further
coated with a higher Tg polymer. Typical monomers used
include vinyl aromatic compounds such as styrene, ring
substituted styrenes, which include vinyl toluene, 3,4-
dimethyl styrene, and p-isopropylstyrene. Acrylic acid
and methacrylic acid are also used. Alkyl methacrylic or
acrylic esters may also be used which commonly include
methyl methacrylate, methyl acrylate, ethyl acrylate,
butyl acrylate, ethyl hexyl acrylates, lauryl
methacrylate, and many others. Other monomers include
methacrylonitrile, acrylonitrile, vinyl chloride,
vinylidine chloride, vinyl acetate, etc.
As mentioned above the encapsulated catalyst may be
further encapsulated with a second polymer. This is
advantageous when the catalyst is encapsulated in a
polymer which possesses a Tg which is too low, when the
polymer does not effectively encapsulate the catalyst,
the polymer is not compatible with the EVS, or for other
reasons. The second polymer may be produced from any `~
monomer or mixture of monomers as listed in the paragraph
above such that ideally the T~ of the resulting polymer
~ ~:,~, . . . . . .
,1, "' ' ,
21139~ ~
- 19 - SL370
is approximately 125C. The requirements of monomers and
other conditions to produce such so called heterogeneous
core/shell polymers are well known and are aptly reviewed
by Lee and Rudin (S. Lee, A. Rudin, in "Polymer Latexes",
E.S. Daniels, E.D. Sudol, M.S. El-Aasser, Eds., ACS
Symposium Series 492, Washington, DC., 1992, P.234-254).
Chain transfer agents or bi- or polyfunctional
crosslinking monomers may also be used to enhance or
retard catalyst release. The chain transfer agents
decrease the molecular weight of the polymer increasing
the rate of catalyst diffusion from the particles while
crosslinking agents increase the molecular weight of the
polymer retarding the catalyst diffusion from the
particle. Typical examples of chain transfer agents
includemercaptoethanol, iso-octylmercaptopropanoate, or
carbon tetrachlorideO Typical crosslinking monomers are
ethylene dimethacrylate, allyl methacrylate, divinyl
benzene, 1,3-butanediol dimethacrylate, and the like.
Examples of ionic initiators commonly used for free
radical latex polymerizations are ammonium or potassium
persulphate. Hydrophobic nonionic initiators include
2,2-azobis (isobutyronitrile) and benzoyl peroxide.
Further diversity in initiators may be obtained by the
use of water soluble nonionic initiators such as tertiary
butyl hydroperoxide and hydrogen peroxide. The initiator
4,4-azo-bis-(4-cyanovaleric acid) in its acid state is
oil soluble but may be neutralized to become an ionic
water soluble initiator.
The above initiators are thermal initiators which
require heat to produce radicals. Redox systems offer
further ~reedom in that they allow for generation of free
radicals at lower temperatures. Tertiary butyl
hydroperoxide/sodium metabisulphite or potassium
persulphate/sodium bisulphite/iron II redox couples are
examples of this. Reactions in the presence of these
5t
i,,i, . . .
:
21139~ ~
- 20 - SL370 ~
initiators allow polymerizations to proceed at room
temperature. The concentrations of initiators typically
used are from 0.01 to 2% based on the weight of monomer.
Many types of surfactants commonly used in the art
of emulsion polymerization may be used. Typical,
although not exclusive, surfactants include
alkylbenzenesulphonates, such as sodium
dodecylbenzenesulphonate, and alkylsulphonates such as
sodiumdodecylsulphonate. Nonionic surfactants and
lo polymer stabilizers such as ethoxylated alkyl phenols,
poly(vinyl alcohol), and poly(acrylic acid) may also be
used.
Typical concentrations of surfactants used in the
encapsulation procedure are 0 to 10% based on the weight
of the monomer. When it is desirable to coat the
encapsulated catalyst with a second polymer to produce a
shell, less or no surfactant is added so that during
shell formation the new polymer formed resides on the
surface of existing particles instead of forming new
particles.
The catalyst encapsulating materials consisting of
powdered high melting polymers compatible with EVS
include, for example: (a) polypropylene; (b) ethylene-
propylene copolymer~; and (c~ any other polymer which
melts above the temperature at which the encapsulated
catalyst would be compounded into the EVS but melts below
the adhesive application temperature7
The catalyst encapsulating materials consisting of
powdered high melting solids compatible with EVS include,
for example: (a) glucose; (b) methylhydroquinone; and (c)
any other compatible solid which melts above the
temperature at which the encapsulated catalyst would be
compounded into the EVS, but which melts below the
adhesive application temperature.
The crosslinkable compositions of the present
~ ...
21~39~
- 21 - SL370
invention are sufficient if they have the above-described
compositions prior to kneading. For example, the
ingredients of the invention as hereinabove defined may
be prepared into the desired composition in a kneader.
Kneading can be conducted by conventional methods. Use
of an extruder is preferred. The kneaded product
containing an encapsulated silanol condensation catalyst
is applied in molten form above the softening or m.p. of
the encapsulent to adhere two substrates. The adhesive
then crosslinks upon exposure to water or water vapour.
The following description and examples are provided
to further illustrate the compositions of the present
invention, but are by no means intended as limiting.
DETAI~ED D~8CRIP~ION OF PREFERRED EMBODIMENT~
EVS copolymers of ethylene and vinyltrimethoxysilane
in pellet form maintained dry in water impermeable
packaging produced either by graft copolymerization or by
high pressure free radical polymerization were used in
the following experiments. The material produced ky high
pressure free radical polymerization is a new version of
AQUA-LINK~ (AT PLASTICS INC., Ontario Canada) produced
having MI of >100.
Hot melt adhesive formulations are mixed by heating
and stirring the components in closed or open vessels. ;; ;
Generally, this method would not work with crosslinkable
hot melt adhesive compositions, because once a
crosslinking catalyst was added, the adhesive would start
to cure and set-up in the pot. Even with encapsulated
catalysts described in this document it is inadvisable to
leave the encapsulated catalyst in the molten EVS
adhe~ive formulation for extended periods of time. Given
time, the catalyst could diffuse out of the encapsulent,
~, .
;",.. . . .
:~... , ~ , . .. ..
- 22 - 2113 9 6 ~ SL370
a phenomenon accelerated at higher temperatures.
The adhesive components are preferentially
compounded in a manner that minimizes the exposure of the
encapsulated catalyst to extended heat history above
-120C. The adhesive formulation containing encapsulated
catalyst can then be stored as a solid at ambient
conditions, or preferentially in packaging to minimize
moisture ingress into the adhesive, until the adhesive is
ready for use. As stated previously~ the rate of
crosslinking is dependent on the water content of the
adhesive. Minimizing water content will help prevent
premature crosslinking, especially once the adhesive is
melted.
Therefore, in order to minimize the heat exposure of
the encapsulated catalyst and also because some of the
tackifiers only melt above 120C, the EVS copolymer and
the other adhesive components were homogenized first
either on a roll mill, in a heated stirred pot, or in an
extruder. After this the adhesive formulation was cooled
below 120C and the encapsulated catalyst dispersed in
the adhesive formulation prior to fabricating the
adhesive into its final commercial shape and cooling the
adhesive to ambient temperature for storage prior to use.
Formulations containing regular non-encapsulated catalyst
and formulation containing no catalyst were used as
controls. The encapsulent softened at 129C as measured
by DSC.
% Gel values of the adhesive compounds were measured
one week and one month after compounding.
After compounding, the adhesives were collected and
immediately pressed into a 1.8mm thick 150mm x 180mm
plaque at 120C and 15000 kg pressure. These plaques
were then stored in a cabinet over saturated calcium
nitrate solution at 50% R.H. and ambient temperature. %
Gel values were measured over time to follow the cure of
~:!:: : ... . . .
2 ~ 6 ~
- 23 - SL370
the adhesive according to ASTM D2756 on powdered adhesive
packaged in stainless steel "teabags" and suspended in
boiling xylenes. These results are summarized in TABL~
2, using dibutyltin dilaurate silane conden~ation
catalystO
TABLE 2
- Cure of ~iah ~I EVS after ~illinc ~ 115C
Reg~lar Encal~sulat~d
10 AJubieDt Catalvst Catalvst
CurQ Ti~ 2 5 0 UI E VS with EVS with EV6
1 week 096 16% 0 . 796
1 month - 3696 18%
:.
After 1 week a portion of the plaque made with the
20 encapsulated catalyst and a portion of the plaque without -
catalyst were re-introduced on a roll mill at 180C,
above the softening point of the encapsulating material,
and milled for 2 minutes. After milling the compounds
were immediately pressed into plaques at 150C and 5000
25 kg. The plaques were stored for 1 week in a cabinet over
saturated calcium nitrate at 55% R.H. and ambient
temperature. The results are given in TABLE 3.
: ~ .
TABLE 3
Cure of ~iah ~I EV~ after ~illing @~800C
Enaa~ulated
nt Catal~t
Cur~ Ti~ 250 MI ~VB with EVS
1 week 0.6% 23.7%
The results shown in the Tables illustrate that
encapæulation of the catalyst in an appropriate material
and compounding the encapsulated catalyst into EVS at low
(~120C) temperatures below the melting or softening
point of the material encapsulating the catalyst produces
,,",, ~, ,
2~139~.
- 24 - SL370
shelf stable compounds that do not crosslink upon storage
for at least 1 week at ambient conditions, unlike EVS
compounds containing un-encapsulated catalyst. However,
when the compound containing the encapsulated catalyst is
melted at high temperatures above the softening or
melting point of the material encapsulating the catalyst,
then the catalyst is released and causes the EVS to
crosslink upon storage at ambient conditions.
The following examples are provided to illustrate
the embodiments of the invention.
EXAMP~ 1
Dibutyltin dilaurate (DBTDL) silane condensation was
encapsulated in a polymer via emulsion polymerization as
follows.
The polymer encapsulating the DBTDL ideally should
possess a softening point, or glass transition
temperature Tg of at approximately 125C so that the
encapsulated product can be blended into EVS at
approximately 120C without release of DBTDL. -~
Monomers were selected for encapsulatibn such that
the Tg of the resulting polymer would be 125C using the
Fox equation: ~ -
ltTg = wl/Tgl ~ w2/Tg2 ~ ~
where wl and w2 are the weight fraction6 of the polymer ~ -
and Tgl and Tg2 are the glass transition temperatures of
the respective polymers in degrees Kelvin.
0.75g sodium dodecyl sulphate surfactant was
dissolved in 375g deionized water. 25g DBTDL was added
to the mixture of monomers, 80 g methyl methacrylate
(MMA) Tg=105C and 20g methacrylic acid (MAA) Tg=228C.
This mixture was then added to the surfactant solution
and homogenized for 5 minutes using a high speed
disperser (~2000 rpm).
: :: ... ~ -, : , .
211396~
- 25 - SL370
The emulsion was transferred to a glass reactor
fitted with a mechanical stirrer and an overhead
condenser. The reactor was heated in an 85C water bath.
While heating the emulsion was stirred at ~400 rpm and
the initiator solution consisting of l.Og ammonium
persulphate in lng deionized water was added. The head
space in the reaction vessel was initially rapidly purged
with N2 for 1 minute and subsequently slow purged for the
remainder of the reaction.
When the reactor contents reached 70C (in about 7
minutes) the bath temperature was reduced to 65C to
control the reactor temperature. A maximum temperature
of 87C was reached in the reactor after 13 minutes from
the start of the reaction. The reactor contents were
allowed to react a further 5 minutes, then cooled to room
temperature.
The latex was poured onto a glass dish and allowed
to evaporate to dryness overnight. A fine white powder
resembling talcum powder was obtained. Another way of
isolating the product on a commercial saale would be to
pass the emulsion through a spray dryer.
EXAMP~E 2
.
The fine white powder from example 1 was analyzed
for tin content by neutron activation analysis and found
to contain 4.5~ tin. This corresponds to 25~ DBTDL, the
expected value.
The Tg of the encapsulated catalyst sample was
measured using differential scanning calorimetry (DSC)
using a Perkin Elmer DSC-4 System-~. The polymer had a
broad transition around 76C, another sharper transition
at 129C, and a broad transition from 167-179C.
Heterogeneous particles are composed of different
polymer types and thus are expected to produce more than
,.,j, ,~" ~ ir,, , ~ . , ," " , ~ , ~ "" ,,, ,, ";" " ., , ~ ", ~,,,
- 26 - 2~1396~ SL370
one measurable Tg. The lowest transition at 76C is
likely the Tg of the polymer plasticized with DBTDL. The
second transition at 129C is likely the T8 of
unplasticized polymer as confirmed by the Fox equation
calculation. The third transition is likely due to two
phenomena, the T~ of a MAA rich outer shell and an
exotherm due to loss of' surface due to coalescence.
(S.L. Bertha, R.M. Ikeda, J. Appl. Polym. Sci., 15 105
(1971)). Such structural heterogeneity is common.
This was confirmed using a melting point apparatus.
A small amount of material was placed in a capillary tube
and slowly heated using a Meltemp apparatus. The powder ~-~
became translucent at 160+5C. This was designated the
upper softening point.
~ -
EX~MPLE 3
The catalyst activity was tested by compounding the
following 3 samples on a laboratory two roll mill at
200C for 5 minutes:
: .
Sample #1) 250 MI EVS copolymer
Sample #2) 250 MI EVS copolymer
Regular DBTDL Catalyst masterbatch
Sample #3) 250 MI EVS copolymer
Encapsulated DBTDL Catalyst (Example 1)
Both samples #2 and #3 above were formulated to
contain 100 ppm Sn.
The samples were pressed into l.8mm x 150mm x 180mm
plaques in a press at 150C at 5000 kg pressure. The
plaques were cured by submerging in 90C water overnight.
%Gel values for the plaques were measured according to
ASTM D2756 on powdered sample packaged in stainless steel
"teabags" and suspended in boiling xylenes.
,.- : ' . ~ ', ., ~ :
-
i:
- 27 21~3961 SL370
~AMPLE %Gel
1 9-~i%
2 56.5%
3 52.2%
This proved the encapsulated catalyst was still
active.
E~AMPLE 4
: , :.,
In order to test if the encapsulated catalyst is
15: unable to promote EVS crosslinking if it is compounded
into EVS at low temperatures the following 3 samples were
compounded on a laboratory 2 roll mill at 115C for 2
minutes:
Sample #1) 250 MI EVS
Sample #2~ 250 MI EVS
Regular DB~DL catalyst masterbatch
Sample #3) 250 MI EVS
Encapsulated DBTDL catalyst (Example 1)
Both samples #2 and #3 were formulated to contain
100 ppm Sn.
The three samples were pressed into 1.8mm x 150mm x
180mm plaques at 120C and 15000 kg pressure. The
plaques were stored in a cabinet over saturated calcium
nitrate solution at 50i~ R.H. and ambient temperature for
one month. The ~Gel values were measured as described in
Example 3 and shown in TABLE 2.
Encapsulating the catalyst and compounding it into
EVS at low temperatures prevented the catalyst from
promoting EVS cure for at least 1 week.
After one week, portions o~ the uncured plaques from
Sample #1 and Sample #3 were then milled on a two roll
- 28 - 2113~6~ SL370
laboratory mill at 180C for 2 minutes. The milled
samples were pressed into plaques at 150C and 5000 kg
pressure and stored again in a cabinet over saturated
calcium nitrate at 50% R.H. and ambient temperature for
one week. The %Gel values were measured as described in
Example 3 and the results shown in TABLE 3.
Heating the EVS containing the encapsulated catalyst
above the upper softening temperature of the encapsulent
released the DBTDL catalyst into the EVS and allowed it
to promote crosslinking.
EXA~PLE S ~;
A solid silane condensation catalyst, an oligomer of -
dioctyltin maleate (DOTM), was compounded into
polypropylene of two different MI values on a laboratory
two roll mill under the conditions shown below~
8ANPLE FORMULA Condition~
5-1 90g 2 MI PP 190C mill
10g catalyst
5-2 90g 20 MI PP 185C mill
10g catalyst
:
The catalyst m.p. is -90C. These samples were
grbund in a Wiley mill to <48 mesh.
EXAMPLE 6
DOTM silane condensation catalyst was encapsulated
in a polymer via emulsion polymerization as follows.
1.5g of a 70~ solution of a 40 mole ethoxylate of
nonylphenol in water was dissolved in 345g of water. 20g
of DOTM was dissolved in 80g styrene monomer. This was
then added to the surfactant water solution under
.,, ,, . , . , ~ . . , . . . . . ,, ,. , , ~ ,
- 29 - 211396~ S~370
agitation.
The resulting emulsion was transferred to a glass
reactor fitted with a mechanical stirrer, an overhead
condenser and a thermometer. The temperature of the
reactor contents were maintained at 20~C using a
thermostated water bath. The emulsion was stirred at -
400 rpm. The head space was initially rapidly purged
with N2 for 1 minute and subsequently purged slowly for
the remainder of the reaction.
The initiator was a redox system consisting of
sodium metabisulphite, ferric sulphate, and ammonium
persulphate. A sodium metabisulphite solution, 1.0g in
10g water, was added to the reactor. A ferric sulphate
solution, .05g in 10g of water, wae then added. Finally
1.0g of ammonium persulphate dissolved in 10g of water
was added. After reacting for 1 hour, 1.0g of sodium
metabisulphite and 1.0g of ammonium persulphate were
again added and reacted for another hour. After reacting
for 2 hours 50% of the styrene had reacted as was
indicated by gravimetric analysis. At that time a
further 1.0g of sodium metabisulphite and 1.0g of
ammonium persulphate were again added along with 350g of
water and 100g of acrylonitrile monomer~ Within 10
minutes the reactor contents reached a maximum of 40C
indicating the reaction of the acrylonitrile. The
product was allowed to react of a further 30 minutes and
filtered to remove any coagulum.
The latex was poured into a glass dish and allowed
to dry overnight. A fine white powder was obtained.
EXAMPLE 7
A graft copolymer of low density polyethylene (LDPE)
and vinyltrimethoxysilane (VT~OS), designated EVS graft
zopolymer was prepared using a Berstorff ZE40 40mm co-
21~3~6~
- 30 - SL370
rotating twin screw extruder. The Berstorff extruder had
temperature zones set at 140-150-175-185-185-180-160-
115C (feed ~ die) and extruder speed at 150 rpm. A 400
MI LDPE (AT 193) was starve fed into the extruder to give
25 kg/hr output. A solution of ~7 wt% VulCup-R peroxide
in VTMOS was injected into the second zone of the
extruder at a rate of 10 g/min. This was monitored
through loss in weight of the VTMOS solution container.
The EVS graft copolymer was stranded through a water bath
and pelletized. The pellets were dried 1 hr in a forced
air oven at 50C and then sealed in a moisture barrier
foil pouch. The MI of the EVS graft copolymer was
measured by ASTM D1238 as 240 g/10 min. The ~ silane
content of the EVS graft copolymer was measured at ~2 wt%
by Fourier Transform Infrared (FTIR) Spectroscopy using
a calibration curve prepared from known standards of EVS
reactor copolymers.
While the invention has been described in detail and
with reference to specific embodiments thereof, it will
be apparent to one skilled in the art that various
changes and modifications can be made therein without
departing from the spirit and scope thereof.
