This invention relates to a new process for making adhesives and sealants
made from monohydroxylated diene polymers. More specifically, the invention relates
to such a process wherein the normally insoluble photoinitiator is incorporated
into the polymer in a very fine micro emulsion.
Background of the Invention
The use of and a process for making novel epoxidized monohydroxylated
polydienes in UV curable adhesive and sealant and compositions is described in U.S.
Patent 5,776,998. The polymers are combined with other ingredients such as a tackifying
resin to make them suitable for adhesive and sealant products. A photoinitiator
is included in the combination to promote UV curing (crosslinking) of the composition.
A prior art method for making such materials involved blending the components in
a nonaqueous solvent such as tetrahydrofuran (THF) and then casting adhesive films
from the solution. THF was used because the particular commercial photoinitiator
(mixed triaryl sulfonium hexafluoroantimonate salts in propylene carbonate) selected
was not otherwise soluble in the adhesive formulation but was soluble in THF. After
the adhesives were solvent cast, the THF was evaporated to leave the photoinitiator
adequately dispersed in the remaining adhesive film to initiate effective UV curing
upon exposure to UV light.
For many applications, the use of nonaqueous solvents is undesirable
because of environmental hazards and the cost of nonaqueous solvent removal and
a nonaqueous solvent itself. U.S. Patent 5,776,998 described a nonaqueous solvent-free
process for dispersing the same and other photoinitiators in an epoxidized monohydroxylated
diene polymer formulation so that an effectively cured adhesive or sealant is produced
without the problems of the solvent. The process involved mixing the components
without a nonaqueous solvent under high shear conditions in a high shear mixer at
a shear rate of at least 38,000 S-1 or in a sonicator at a power density
of at least 4 watts per milliliter.
The process of U.S. 5,776,998 was able to achieve fine dispersions
having droplet sizes of less than 10 micron diameter as described in the patent.
In fact, the best dispersions produced by the method of the patent were able to
achieve dispersions having a droplet size of approximately one-half micron diameter.
As described in the patent, good UV cured adhesive and sealant products could be
produced with the dispersions produced by the mixing method described in the patent.
Experience with these dispersions (emulsions) has shown that it is
very important to have a very small particle size photoinitiator emulsion. Those
photoinitiator emulsions that appear by to be about 0.5 micron diameter are much
more beneficial than emulsions at 1 or more micron diameter. The very fine emulsions
allow almost instant curing when used at levels as low as 0.04 to 0.10 weight percent
(wt%) active initiator based on the entire adhesive formulation. In addition to
the obvious advantage of needing less of what is the most expensive component of
the formulation, the very low levels allow the final cured formulation to have the
greatest degree of heat stability. The lower the amount of residual acid, generated
by the UV exposure of the photoinitiator, the less bond breakage occurs in the gel
A preferred method of introducing the photoinitiator emulsion to the
formulation has been to first make a concentrated emulsion of the photoinitiator
in one of the components of the formulation, and then add it as the last component
of the formulation. Pre-making the photoinitiator concentrate has several advantages.
First, it allows the photointiator emulsion to checked before use. Second, it allows
the emulsion to be prepared at another site where the needed equipment is located.
Third, it allows a much smaller amount of material be processed on the sonifier
or very high shear equipment, thus reducing equipment size. Fourth, it allows an
accurate amount of photoinitiator to be easily added to the formulation. Most often
the photoinitiator concentrate has been a 5 wt% emulsion of tri-aryl sulfonium hexafluoroantimonate
salt in KRATON LIQUID® Polymer L-1203 (mono-ol polymer) prepared by sonication.
Sometimes it has been a 5 wt% emulsion of the same salt in KRATON LIQUID® Polymer
L-207 (epoxidized mono-ol polymer) prepared by sonication.
Several improvements in the photoinitiator concentrate and its production
have become apparent from working with industry. First, there has been a strong
need to be able to produce the emulsion on lower shear, more readily available equipment
than a sonicator or very high shear rotor/stator equipment. Second, when the photoinitiator
emulsion concentrate is made ahead of time or at another location, an important
feature of the emulsion concentrate is its shelf stability under storage and shipping
conditions. It is very important to make dispersions which have the least tendency
to agglomerate and increase in particle size, for the reasons stated above. Increased
stability has been greatly desired. Third, there has always been
the need to make the smallest droplet size emulsion to extract maximum cure for
the minimum usage.
Summary of the Invention
This invention relates to a process for producing an ultraviolet curable
adhesives, coating or sealant composition, comprising a monohydroxylated epoxidized
polydiene block copolymer comprised of at least two different diene monomers, wherein
at least one is a diene monomer which yields unsaturation suitable for epoxidation
and wherein the polymer contains from 0.5 to 4.0 milliequivalents of epoxy per gram
of polymer, and optionally other formulating ingredients, said process comprising
mixing the epoxidized polymer and optional formulating ingredients with a photo
initiator which is insoluble in the polymer and without any non-aqueous solvent,
under low shearing conditions at a shear rate of less than 38,000 s-1
in a medium to high speed mixer, with a blade tip speed of from 200 to 2000 centimeters
per second, at a temperature from 25 to 130°C.
The process involves mixing the above polymer or the polymer with
one or more other formulating ingredients together with an insoluble photoinitiator
which is preferably selected from the group consisting of triaryl sulfonium salts.
The mixture is subjected to relatively low shear mixing conditions in a medium to
high speed mixer at a temperature from 40 to 100°C.
This process is highly suited for making stable cationic photoinitiator
concentrations, usually consisting of only the photoinitiator and the epoxized mono-ol
polymer, that are added to adhesive, coating, sealant, etc. formulations to effect
rapid UV cure. The dispersed photoinitiator droplets are less than 1 micron in diameter,
preferably 0.5 micron or less, and preferably uniformly distributed in the emulsion
Detailed Description of the Invention
Polymers containing ethylenic unsaturation can be prepared by copolymerizing
one or more olefins, particularly diolefins, by themselves or with one or more alkenyl
aromatic hydrocarbon monomers. The copolymers may, of course, be random, tapered,
block or a combination of these, as well as linear, star or radial.
In general, when solution anionic techniques are used, copolymers
of conjugated diolefins, optionally with vinyl aromatic hydrocarbons, are prepared
by contacting the monomer or monomers to be polymerized simultaneously or sequentially
with an anionic polymerization initiator such as group IA metals, preferably lithium,
their alkyls, amides, silanolates, naphthalides, biphenyls or anthracenyl derivatives.
The monohydroxylated polydienes are synthesized by anionic polymerization of conjugated
diene hydrocarbons with these lithium initiators. This process is well known as
described in U.S. Patents Nos. 4,039,593 and Re. 27,145 which descriptions are incorporated
herein by reference. Polymerization commences with a monolithium initiator which
builds a living polymer backbone at each lithium site.
Conjugated diolefins which may be polymerized anionically include
those conjugated diolefins containing from about 4 to about 24 carbon atoms such
as 1,3-butadiene, isoprene, piperylene, methylpentadiene, phenylbutadiene, 3,4-dimethyl-1,3-hexadiene,
4,5-diethyl-1,3-octadiene and the like. Isoprene and butadiene are the preferred
conjugated diene monomers for use in the present invention because of their low
cost and ready availability.
The monohydroxylated polydiene polymer of the present invention has
the structural formula
wherein A and B are polymer blocks which may be homopolymer blocks of conjugated
diolefin monomers or copolymer blocks of conjugated diolefin monomers. Generally,
it is preferred that the A blocks should have a greater concentration of more highly
substituted aliphatic double bonds than the B blocks have. Thus, the A blocks have
a greater concentration of di-, tri-, or tetra-substituted unsaturation sites (aliphatic
double bonds) per unit of block mass than do the B blocks. This produces a polymer
wherein the most facile epoxidation occurs in the A blocks.
The A blocks have a molecular weight of from 500 to 4,000, and preferably
1000 to 3000, and the B blocks have a molecular weight of 2000 to 10,000, preferably
3000 to 6000. x and y are 0 or 1. Either x or y must be 1, but only one at a time
can be 1. Either the A or the B block may be capped with a miniblock of polymer,
50 to 1000 molecular weight, of a different composition, to compensate for any initiation,
tapering due to unfavorable copolymerization rates, or capping difficulties. These
polymers may be epoxidized such that they contain from 0.5 to 4 milliequivalents
(meq) of epoxy per gram of polymer.
Diblocks falling within the above description are preferred. The overall
molecular weight of such diblocks prior to hydrogenation and epoxidation may range
from 2500 to 14,000, preferably 3000 to 7000. For example, where I represents isoprene,
B represents butadiene, and a slash (/) represents a random copolymer block, the
diblocks may have the following structures:
Blow vinyl -Bhigher vinyl-OH I-B-OH I-I/B-OH
These diblocks are advantageous in that they exhibit a good viscosity for preparing
photoinitiator concentrates. It is preferred that the hydroxyl be attached to the
butadiene block because the epoxidation proceeds more favorably with isoprene and
there will be a separation between the functionalities on the polymer. This produces
a more unique surfactant-like molecule than can also cure on both ends. KRATON LIQUID®
L-207 is a hydrogenated and epoxidized I-B-OH polymer that is available in commercial
quantities. It falls within the preferred range for the I and B blocks. Its overall
molecular weight prior to epoxidation and hydrogenation is about 5400 to 6600.
Epoxidation of the base polymer can be effected by reaction with organic
peracids which can be preformed or formed in situ. Suitable preformed peracids include
peracetic and perbenzoic acids. In situ formation may be accomplished by using hydrogen
peroxide and a low molecular weight fatty acid such as formic acid. These and other
methods are described in more detail in U. S. Patents 5,229,464 and 5,247,026 which
are herein incorporated by reference. The amount of epoxidation of these polydiene
polymers ranges from 0.5 to 4 milliequivalents of epoxide per gram of polymer. Lower
levels are desirable to avoid overcure. Above 4 meq/g, the rigidity, crosslink density,
cost, difficulty of manufacture, and polarity of the polymer (so as to not accept
certain monohydroxy diene polymer and to dissolve the photoinitiator) are too high
to provide benefit. The preferred amount of epoxidation is 1 to 3 meq/g and the
most preferred amount of epoxidation is the amount on KRATON LIQUID® L-207 polymer,
about 1.4 to 2.0 meq/g. The most preferred amount best balances rate of cure against
overcure and better maintains compatibility with a variety of formulating ingredients
commonly used with polydiene based adhesives. Additionally it produces excellent
photointiator emulsions. Epoxidation can cause the molecular weight and the viscosity
of the diblock to increase somewhat due to dimer and trimer formation. This is not
detrimental to the invention.
The molecular weights of linear polymers or unassembled linear segments
of polymers such as mono-, di-, triblock, etc., arms of star polymers before coupling
are conveniently measured by Gel Permeation Chromatography (GPC), where the GPC
system has been appropriately calibrated. For anionically polymerized linear polymers,
the polymer is essentially monodisperse (weight average molecular weight/number
average molecular weight ratio approaches unity). For low molecular weight functionalized
polymers, especially if they become slightly polydisperse because of dimer and trimer
formation, the number average molecular weight should be calculated from the chromatograph.
For materials to be used in the columns of the GPC, styrene-divinylbenzene gels
or silica gels are commonly used and are excellent materials. Tetrahydrofuran is
an excellent non-aqueous solvent for polymers of the type described herein. A refractive
index detector may be used. Calibration of the GPC can done by measuring the number
average molecular weight by proton NMR first on several polymers of the same type.
If desired, these block copolymers can be partially hydrogenated.
Hydrogenation may be effected selectively as disclosed in U.S. Patent Reissue 27,145
which is herein incorporated by reference. The hydrogenation of these polymers and
copolymers may be carried out by a variety of well established processes including
hydrogenation in the presence of such catalysts as Raney Nickel, noble metals such
as platinum and the like, soluble transition metal catalysts and titanium catalysts
as in U.S. Patent 5,039,755 which is also incorporated by reference. The polymers
may have different diene blocks and these diene blocks may be selectively hydrogenated
as described in U.S. Patent 5,229,464 which is also herein incorporated by reference.
Partially unsaturated hydroxylated polymers are useful for further functionalization
to make the epoxidized polymers of this invention. The partial unsaturation preferably
is such that 0.5 to 4 meq of aliphatic double bonds suitable for epoxidation remain
on the polymer. If epoxidation is done before hydrogenation, then it is preferred
that all remaining aliphatic double bonds be hydrogenated.
The binders of this invention may be cured by cationic means using
acid catalysts but are preferably cured by means of ultraviolet or electron beam
radiation. Radiation curing utilizing a wide variety of electromagnetic wavelengths
is feasible. Either ionizing radiation such as alpha, beta, gamma, X-rays and high
energy electrons or non-ionizing radiation such as ultraviolet, visible, infrared,
microwave and radio frequency may be used. A complete description of how this irradiation
may be accomplished is found in commonly assigned U. S. Patent 5,229,464 which is
herein incorporated by reference.
When using radiation it is necessary to employ a photoinitiator to
initiate the crosslinking reaction. For the practice of this invention, the photoinitiator
must be in a liquid form and insoluble in at least one of the polymers of this invention.
All of the sulfonium salt initiators currently available are in liquid form (they
are dissolved in propylene carbonate) and appear to be substantially insoluble in
the most preferred polymer of this invention. They are also very suitable for emulsification.
On the contrary, all or most of the iodonium salt photoinitiators currently available
have at least some solubility in the polymers of this invention because of the alkyl
chains they bear or the cation used, and are not suitable for the invention. These
may be added to the adhesive or sealant formulations as supplemental additives provided
they do not destabilize the emulsion. Useful photoinitiators for emulsification
include the following triarylsulfonium hexafluoroantimonate salts: Cyracure UVI-6974
(mixed triaryl type) available from Union Carbide, UVE-1014 (mixed triaryl type)
available from Von Roll Isola, ADEKA Optimer SP-170 from Asahi Denka Kogyo K.K.,
and Sarcat CD1010 from Sartomer. The following arylsulfonium hexafluorophosphate
salts also are suitable for emulsification, although they are not as desirable because
of their slower cure. Cyracure UVI6990 from Union Carbide, UVE-1016 from Von Roll
Isola, ADEKA Optimer SP-150 from Asahi Denka Kogyo K.K., and Sarcat CD1011 from
Sartomer. Some of the soluble iodonium photoinitiators include Sarcat CD-1012 from
Sartomer, Rhodorsil R-2074 from Rhodia, (4-octyloxyphenyl)-phenyl-iodonium hexafluoroantimonate
or phosphate, and (4-decyloxyphenyl)-phenyl-iodonium hexafluoroantimonate or phosphate.
The onium salts can be used alone or in conjunction with a photosensitizer
to respond to long wavelength UV and visible light. Examples of photosensitizers
include thioxanthone, anthracene, perylene, phenothiazione, 1,2-benzathracene coronene,
pyrene and tetracene. The dispersion/emulsions of the present invention may contain
up to 40% by weight and more of the photoinitiator.
According to the present invention, the insoluble photoinitiators
described above can be dispersed in the polymers described above, optionally with
other ingredients such as tackifying resins, to produce a composition which is radiation
curable without the necessity for a non-aqueous solvent. The polymer, optional resin,
and photoinitiator are mixed together in mixing equipment under high speed but medium
shear mixing conditions.
The mixing is accomplished at a blade tip speed of from 200 to 2000
cm/sec. If the mixing speed is less than about 200, then some of emulsified droplets
can be greater than 1 micron in diameter, which slows the initial cure, and decreases
the self-life of the product. If the mixing speed is roughly more than about 2000
cm/sec, then unnecessary heat is being produced. Unremoved heat energy raises the
temperature of the emulsion and this tends to negate any potential advantageous
effect of higher tip speed. The cut off top tip speed is not a well-defined value.
It is more suggestive of what speed is expected to produce more heat than can be
practically removed in a production situation. Blade tip speed is determined by
the diameter of the disk (blade, impeller) and the shaft rpm. Commercial high-speed
dispersers can provide up to 5000 ft/min (2540 cm/sec).
The preferred tip speed for this invention is 300 to 1500 cm/sec,
and the most preferred is 800 to 1200 cm/sec. The temperature during mixing can
range from 25°C to 130°C, preferably 40°C to 100°C, most preferably 50°C to 80°C.
At a temperature higher than 130°C, too many of the particles tend to be above 1
micron in diameter. The emulsion concentrates appears to be microemulsions, at least
when not being made near the limiting bottom speed and the limiting upper temperature
of the invention. Typically a microemulsion has an upper phase transition temperature
where the microemulsion is no longer stable and the droplets become large. With
the emulsion concentrates of this invention, the phase change temperature is not
sharp, but gradual, perhaps because of the high viscosity/molecular weight of the
polymer used or because of the special functionality of the polymeric "surfactant"
being used. When excess temperature damages the emulsion, the "microemulsion" of
this invention can easily be reformed by allowing the temperature to drop and simply
Examples of mixing equipment in which the present invention can be
carried out be would most commonly available equipment that can deliver the blade
tip speed and which have some heating and cooling capacity. One example which is
preferred for use herein is a Hockmeyer mixer which is a high speed disk disperser
normally used at shear rates well below 1000 sec-1 for mixing paint and
pigment dispersion. High-speed dispersers are described in Paint Flow and Pigment
Dispersion by Temple C. Patton, published in 1979 by John Wiley & Sons.
They are generally operated in laminar flow and certainly are not capable of producing
the turbulent conditions of as high as 10,000 sec-1 shear
The equipment may also have a lid to restrict UV light exposure. Other
enhancements include a vacuum kettle for defoaming and restricting UV light, a second
slower mixing element to premix the components to avoid initial overheating, and
additional shafts, each with its own disk, to aid in the movement of the viscous
material to the high speed blade zone.
The process of this invention appears to create very stable microemulsions
of the initiators. The micro emulsion droplet sizes are mostly less than 0.5 micron
and most of them are at least initially too small to detected at using optical microscopy,
with white light, at 2000X, in transmission mode. Generally, such optical microscopy
can only resolve particles at 1 micron or larger. The presence of particles or structures
less than 1 micron in diameter can still be detected by observing pseudo particles
(fuzzy light and dark spots) which result from light being scattered or refracted
by the small initiator droplets or by agglomerates of small droplets. As the size
becomes even smaller (believed to be at about 0.5 micron) or the bunching of small
droplets ceases, nothing can be detected. Attaining 0.5 micron droplet size and
less, with uniform distribution of the droplets, is very important to achieving
good UV cure of the final composition and the best shelf-life for the photoinitiator
emulsion concentrates. The presence of the droplets and their distribution when
these small sizes are reached can only be detected by much more sophisticated equipment.
A Leica TSC confocal laser scanning microscope can be used in reflected mode to
image such emulsion particles.
It is common practice to add an adhesion promoting or tackifying resin
that is compatible with the polymer, generally from 20 to 400 parts per hundred
parts of polymer. A common tackifying resin is a diene-olefin copolymer of piperylene
and 2-methyl-2-butene having a softening point of about 95°C. This resin is available
commercially under the tradename Wingtack® 95 and is prepared by the cationic
polymerization of 60% piperylene, 10% isoprene, 5% cyclopentadiene, 15% 2-methyl-2-butene
and about 10% dimer, as taught in U.S. Patent No. 3,577,398. Other tackifying resins
may be employed wherein the resinous copolymer comprises 20-80 weight percent of
piperylene and 80-20 weight percent of 2-methyl-2-butene. The resins normally have
ring and ball softening points as determined by ASTM method E28 between about 80°C
Hydrogenated resins are normally used when the polymer itself is hydrogenated.
Useful hydrogenated resins include the Regalrez@ resins from Hercules which are
manufactured by selective hydrogenation of base resins polymerized using styrenic-based
comonomers. The degree of hydrogenation ranges form 30% to 100%. Softening points
vary from 18 to 140°C. Other useful resins include the Regalite® resins which
are manufactured by selective hydrogenation of base resins polymerized from mixed
aromatic monomer feed steams. Softening points vary from 90-125°C. The Regalite®
T and V resins are also useful. So are the Arkon® P series resins from Arakawa.
Other useful resins include polyterpene resins and liquid resins such as Adtac LV
and Piccolyte® S25 from Hercules.
Aromatic resins may also be employed as tackifying agents, provided
that they are compatible with the particular polymer used in the formulation and
do not appreciably interfere with UV light transmission or solubility balance of
the photoinitiator droplets. Normally, these resins should also have ring and ball
softening points between about 80°C and 115°C although mixtures of aromatic resins
having high and low softening points may also be used. Useful resins include coumarone-indene
resins, polystyrene resins, vinyl toluene-alpha methylstyrene copolymers and polyindene
Optional components of the present invention are stabilizers which
inhibit or retard heat degradation, oxidation, skin formation, and color formation.
Stabilizers are typically added to the commercially available compounds in order
to protect the polymers against heat degradation and oxidation during the preparation,
use and high temperature storage of the composition.
Adhesives are frequently thin layers of sticky compositions which
are used in protected environments (adhering two substrates together). Therefore,
unhydrogenated epoxidized polymers will usually have adequate stability so resin
type and concentration will be selected for maximum stickiness without great concern
for stability, and pigments will usually not be used.
Sealants are gap fillers. Therefore, they are used in fairly thick
layers to fill the space between two substrates. Since the two substrates frequently
move relative to each other, sealants are usually low modulus compositions capable
of withstanding this movement. Since sealants are frequently exposed to the weather,
the hydrogenated epoxidized polymers are usually used. Resins and plasticizers will
be selected to maintain low modulus and minimize dirt pick-up. Fillers and pigment
will be selected to give appropriate durability and color. Since sealants are applied
in fairly thick layers, non-aqueous solvent content is as low as possible to minimize
The materials used in the following examples include:
1. KRATON LIQUID® Polymers L-1203A and L-1203B are both hydrogenated polybutadiene
mono-ols wherein a hydroxyl group is located at one end of the molecule. A has number
average molecular weight of 3750 and B has a number average molecular weight of
2. KRATON LIQUID® Polymer L-1302 is a hydrogenated isoprene-butadiene block
copolymer having a number average molecular weight of about 6400.
3. KRATON LIQUID® Polymer L-207 is identical to Polymer L-1302 except that
it is epoxidized, mostly in the isoprene block, such that about 1.7 meq of epoxy
per gram of polymer are present on the polymer.
4. UVI-6974 is a photoinitiator made by Union Carbide which is triaryl sulfonium
5. UVE-1014 is a photoinitiator from Von Roll Isola USA, Inc., which is triaryl
sulfonium hexafluoroantimonate, it is interchangeable with the UVI-6974.
6. SP-170 is a photoinitiator from Adeka, believed to be similar to UVI-6974.
7. Regalite® R-91 is a hydrogenated mixed aromatic tackifying resin made
by Hercules by selective partial hydrogenation of base resin polymerized from mixed
aromatic monomer feed streams. It has a R & B softening point of 88°C.
In most of the experiments below, the mixing was carried out in a
Hockmeyer lab/pilot sized 2 horsepower mixer. The 2 horsepower unit is capable of
mixing about 1 to 4 gallons of paint or adhesive formulations and has a single shaft
with a 4 inch diameter flat toothed blade attached (in some experiments, an alternative
4 inch diameter blade consisting of 3 flat surfaces welded together by two sets
of fins between the 3 surfaces was used), a single speed electric motor, and a belt
and pulley system to control the shaft speed. The mixer is capable of delivering
continuous shaft speeds between 600 and 1900 rpm.
A lab 77 watt electric mixer equipped with a small impeller was also
used. The shaft rpm could be varied between about 650 rpm and 1850 rpm. The diameter
of the impeller blade was 1.5 inch.
The primary microscope used was a top of the line (vintage 1980's)
Zeiss microscope equipped with, white light, a Plan 100/1.25 oil objective, a Miroimage
Video Systems AutomatiCan A106A video, a Sony Triniton high resolution color video
monitor, and a Toshiba HC-1200A color video printer. This microscope can not clearly
resolve photoinitiator droplets smaller than about 1 micron diameter, but can detect
the presence of droplets or droplet associations below 1 micron. Droplets and associated
droplets smaller than about 0.5 micron cannot be detected. Also used was a very
modern Leica TSC confocal laser scanning microscope was used in reflected mode to
image such emulsion particles. The microscope was equipped with a 63X oil immersion
lens. The lens had a 0.4 micron depth of focus and a lateral resolution of 0.15
micron. This microscope can detect droplets as small as about 0.2 micron diameter.
It was used, when available, observe the detail of the microemulsions that are cannot
be seen with the Zeiss microscope. A short scan time was used because the motion
of the droplets in the liquid medium caused the droplets to look fuzzy.
Example 1 (Comparative)
This experiment shows the limitations of the prior art procedure as
described in U.S. Patent 5,776,998 for making a photoinitiator dispersion. A 50
gram batch of photoinitiator emulsion was prepared in the sonicator used in the
'998 patent, a Branson 450 sonifier, using UVI-6974 photoinitiator and both L-1203A
and L-1203B polymers in separate experiments. 2.5 grams of the photoinitiator and
47.5 grams of the polymer were weighed into a small bottle, heated in an over to
135°C, and then sonified for one minute and cooled. The results are shown in Table
1 below for the two polymers. As can be seen and as discussed in the '998 patent,
an emulsion with small droplet size was achieved using L-1203A. L-1203A had a higher
molecular weight (and viscosity) than L-1203B. The emulsion effected a fast cure
in an adhesive formulation. On the other hand, the emulsion formed using L-1203B
had easily seen droplets using the Zeiss with droplets as large as 2.5 micron and
even larger when heat aged. It was very ineffective in the same formulation for
causing UV cure, as seen below. This behavior is typical of what we have observed
with these photoinitiator emulsions. Larger droplets seen using the Zeiss, correspond
to poorer UV cure. This example also demonstrates the importance of having a certain
minimum molecular weight/viscosity to help stabilize the photoinitiator emulsion
concentrate. The sonication should be expected to instantaneously make made very
small droplets when using L-1203B as well as with L-1203A. The fact that they were
not observed suggests they could not remain stable even for the time it took for
the dispersion to cool and make the photomicrographs because the viscosity was too
low to retard the droplet-droplet collisions.
Testing for Cure:ABL-20720.2820.28L-1203A23.2123.21Regalite R9154.9554.955wt% emulsion made with L-1203A1.6005wt% emulsion made with L-1203B (no heat or re-sonication)01.60UV curing*As soon as film coolsCured to touchGoo, no cureAfter 4 days at room temperatureCured to touchNot cured to touch, some dark cure developingAfter 21 days at room temperatureCured to touchCured to touch
* The adhesives were applied to 2 mil, corona treated, Mylar film
preheated to 60°C, and immediately UV cured with a 300 watt/inch Fusion H bulb,
dose was 200mJ/cm2.
Example 2 (Comparative)
As another comparative example, the apparent problem of too low a
continuous phase viscosity was investigated by trying to sonify UVI-6974 into a
tackifying resin that is typical of those used in adhesives for cationic UV cure
using this type of polymer. Regalite® R-91 resin has a lower molecular weight
(Mn is about 600) than Polymer L-1203B (Mn = 3500) and at
room temperature it is a solid. 2.0 grams of UVI-6974 and 38.0 grams of Regalite®
R-91 tackifying resin were added to a small glass bottle, heated to 135°C, and sonicated
for 1.5 minutes. A sample was removed and placed on a microscopic slide and a cover
slip placed over it. It immediately solidified. The rest was poured onto release
paper which caused it to solidify almost immediately. Although the mixture was very
low in viscosity during the sonication stage, and very small droplets may have formed
instantaneously, most of the dispersed photoinitiator was in large droplets. See
the results shown in Table 2 below wherein the Zeiss detectable emulsion droplet
size ranged from 0.5 up to 2.4 micron.
A small amount of UVI-6974 photoinitiator (5 percent of the mixture)
was dispersed into L-207 epoxidized polymer using the Hockmeyer mixer described
above.. The polymer was transferred into a stainless steel pot and warmed in a 100°C
oven. The pot was placed on a hot plate under the mixture and heated to 135°C using
the hot plate and low speed mixing. Once the mixture was at 135°C, the shaft speed
was increased to 1800 rpm. While at 1800 rpm, the photoinitiator was added slowly
over about 10 minutes. The mixture was mixed another 10 minutes at 1800 rpm while
maintaining the temperature of the batch at about 135°C. The mixer was turned off
and a small sample was taken and observed with the Zeiss microscope. The droplets
of the photoinitiator were in the 0.5 to 1.0 micron range desired, as reported in
Table 3 below. Two hours later, the batch temperature had decreased to 65°C. At
that point, another sample was taken and observed under the microscope. No change
could be observed. The particle size, number, and distribution looked the same.
The droplet size and distribution continued to look about the same as obtained when
making a dispersion of the photoinitiator by the sonication method.
A micro emulsion normally has an upper temperature limit above which
the micro emulsion breaks. Often that temperature is in the 70 to 100°C range. Speculating
that the interaction between the photoinitiator and the L-207 polymer might have
some special significance in this case, perhaps even to be suitable for micro emulsion
formation, the mixer was turned back on. The speed was quickly (about three minutes)
dialed up to 2050 rpm. This was too fast for the belt/pulley system to handle and
the drive belt flew off the pulley and broke. Unfortunately, the mixer had only
been on for three minutes when the belt broke. However, this was advantageous since
there was little time for the temperature to rise significantly above 65°C. A sample
was taken from the pot, without any great expectations because of the short mixing
time, for microscopy. Surprisingly, even with only the extremely short mixing time,
the emulsion was improved dramatically. Almost none of the photoinitiator droplets
could be seen with the Zeiss microscope. Apparently, a much finer emulsion had been
made than those previously achieved by sonication and temperature appeared to be
a critical factor.
With a Hockmeyer mixer or similar equipment, the L-207 polymer could
be mixed well at a temperature as low as 65°C without temperature buildup, apparently
because of lower shear, yet a much finer and probably more stable emulsion could
be made. The Hockmeyer mixer was run under conditions of laminar flow. Under laminar
flow conditions, the maximum shear rate, R, is equal to the tip speed, expressed
in cm/se, divided by the separation distance between the disk and the bottom of
the mixing tank, also given in cm. Normal distance between the disk and the bottom
of the tank to produce a normal flow pattern is 0.5 to 1.0 times the disk diameter,
which corresponds to 5.08 cm to 10.16 cm for a 4 inch blade. Therefore, the maximum
shear rate seen in the each mix is approximately the tip speed divided by 5.08 cm.
As a final test to check the usefulness of this particular emulsion,
a small amount was added to a pressure sensitive adhesive (the active photoinitiator
was 0.04 percent by weight of the formulation) and the warm adhesive was exposed
to UV light. The adhesive cured nearly instantaneously. It was cured completely
to the touch within 20 seconds after the brief exposure.
In this experiment, an alternative blade was used for the Hockmeyer
mixer. This was a 4 inch diameter blade consisting of three flat surfaces welded
together by two sets of fins between the three surfaces. The manufacturer's literature
suggests that this blade arrangement provides somewhat increased shear over that
of the other blade.
The three polymers, L-1302, L-207, and L-1203, were compared for their
ability to disperse the insoluble photoinitiator UV-6974. The photoinitiator was
dispersed in each of the polymers using increasing speed as shown in Table 4 below.
As seen from the table, only L-207 was effective in producing a very fine droplet
sized emulsion. The droplets produced were actually too small to be observed using
the Zeiss microscope. The emulsion appeared to be more akin to a micro emulsion
than any regular emulsion formed by the application of very high shear. The other
two polymers produced coarse emulsions which are commercially unacceptable. They
would result in slow cure and would have a very short lifetime because the larger
droplets would quickly assimilate the remaining smaller droplets and that would
prevent cure. The triple ring blade was suitable for making the good, extremely
small emulsions using the insoluble photoinitiator and Polymer L-207 but did not
appear to be as effective as the simpler flat blade used previously. The flat blade
produces somewhat less shear and somewhat more mixing action and appears more suitable
for making the extremely fine dispersions which are the desired result of the present
The triple ring blade was removed and replaced with the toothed flat
blade used earlier. Two of the emulsions (-69 and -70) of Example 4 were weighed
into a pot at a ratio of 5 parts of the emulsion with L-207 and 95 parts of the
emulsion with L-1302. The blend was heated to 60°C and then mixed for 20 minutes
at 1800 rpm. A small sample was removed and examined for droplet size. The presence
of just five parts of the L-207/photoinitiator dispersion was enough to radically
improve the emulsion (as compared against the L-1302 emulsion of Example 4) as shown
in Table 5 below. In a second experiment, additional L-207 emulsion was added to
the pot to yield a new blend ratio of 20 parts of that emulsion and 80 parts of
the L-1302 emulsion. Starting from 60°C again, the blend was mixed at 1800 rpm for
20 minutes. The resulting emulsion was so improved that it looked indistinguishable
from the 100 percent L-207/photoinitiator emulsion of Example 4 as can be seen in
Table 5 below. This shows that the interaction of the L-207 with the photoinitiator
is special enough that only 20 percent of the available polymer in emulsion concentrate
has to be L-207. Again, the small sized emulsion occurring at a low mixing temperature
suggests that a micro emulsion was occurring.
To further define the most desirable mixing temperature for making
the L-207/photoinitiator special emulsion, batches were made using 60°C and 90°C
as the mixing temperatures. The results are shown in Table 6 below. Clearly, it
can be seen that 90°C is an acceptable temperature but that it is not as good as
60°C. The results in the table also continue to show that better emulsions are formed
by mixing at high shaft speeds (greater blade tip speed) as long as the temperature
can be controlled.
Using the old sonication method, emulsions at greater than 5 percent
weight loading of the photoinitiator were very unstable and unsuitable for commercial
use. In the present example, emulsions of the photoinitiator and Polymer L-207 were
prepared at 5, 20, and 40 percent weight photoinitiator loading. The results of
the experiment are described in Table 7 below. In the table, it is seen that excellent
emulsions can be prepared at all three of the loadings and that the emulsions are
very stable at room temperature. When the emulsions are stored at 70°C for a week,
it appears that there is benefit to using the 5 percent loading as these results
show that the elevated temperature emulsion stability is increased at lower loading,
i.e., 5 percent > 20 percent > 40 percent. However, the temperature by the
end of the mixing increased as a function of photoinitiator loading. At 40 percent
loading, the temperature reached 88°C by the end of the mixing and this has already
been shown to be less desirable than 60°C in a previous example. It is likely that
had a pot been constructed with a cold water jacket or cooling coils, a temperature
of 60°C or possibly less could have been maintained and the 70°C stability check
samples may have looked considerably better. The concentrates that were affected
by the heat aging should be completely restorable to their original condition simply
by re-mixing them as instructed by this invention.
This example contains a comparison of the sonication method of the
'998 patent to the method which is the subject of the present invention. A 4000
gram batch of the emulsion of the present invention was prepared on the Hockmeyer
mixer equipped with a flat toothed 4 inch diameter blade. 3800 grams of L-207 polymer
were added to the stainless steel pot and heated up to 65°C. The mixer was set to
approximately 600 rpm and 200 grams of photoinitiator UVE-1014 were slowly added.
After the addition was complete, the mixer speed was increased to about 1950 rpm
and the batch was mixed for 20 minutes. Air cooling was used and the final batch
temperature reached 79°C. The mixer was turned off and the batch was filled into
amber containers for storage.
A 50 gram batch of photoinitiator emulsion was prepared on the sonicator
described above using UVE-1014 and L-207 polymer in the following manner. 2.5 grams
of the photoinitiator and 47.5 grams of the polymer were weighed into a small bottle,
heated in an oven to 135°C, and then sonified for 1 minute. The mixture was allowed
to cool for 2 minutes and then resonified for an additional minute. The maximum
temperature reached was 187°C. Double sonication was used because the viscosity
of the L-207 polymer is sufficiently high such that it is visually obvious that
a single sonication for 1 minute does not make a uniform mixture. Also, a 50 gram
batch of emulsion was made using the same photoinitiator and Polymer L-1203 in a
similar way, except that only a single 1 minute sonication cycle was needed because
of the lower viscosity of the L-1203 polymer. The maximum temperature reached was
171°C. The three batches were examined using optical microscopy. The results are
shown in Table 8 below. It can be seen that the method of the present invention
produces droplets which are much smaller than the droplets produced by the prior
art sonication method.
A 5% emulsion photoinitiator concentrate was made using EKP-206 epoxidized
mono-ol polymer and UVE-1014 as the initiator. EKP-206 is not an example of the
present invention because it contains polymerized styrene in the second block. It
has about 1.5 meq/g of epoxy. EKP-206 is much more viscous than L-207 at room temperature
because it has a higher glass transition temperature, but near 100°C and higher
is similar to that of L-207 because it about the same molecular weight. It was expected
that it would be more difficult to keep the temperature in the most preferred range
of the invention, which is 50° to 80°C. As in several of the previous examples,
the Hockmeyer high speed disperser was used. 3800 grams of EKP-206 were added stainless
steel container and warmed in an oven to about 60°C. The container was placed under
the Hockmeyer equipped with the 4 inch flat blade placed into the liquid and stirred
at 625 rpm. When the material was stirring well, at a temperature of 69°C, 200 grams
of UVE-1014 was added over 5 minutes. The mixture was mixed for 20 minutes, mixing
was stopped briefly and a sample was taken for microscopy, the speed was increased
to about 1200 rpm and the mixture was mixed another 20 minutes, the mixer was stopped
briefly and a sample was taken. The mixing speed was then increased to about 1800
rpm and mixed another 20 minutes and then mixing was stopped. The final temperature
of the emulsion was 84°C. The table below shows details the conditions and shows
the Zeiss microscopy results. An emulsion of droplet size required by the present
invention could not be made. Because the droplets are so large and therefore so
few are photographed, the photomicrographs taken offer insufficient evidence to
even assert that particle size is decreasing with increase tip speed.
Different low shear mixing equipment was used in this example. The
equipment was the lab 77 watt electric stirring motor equipped with a lab type 3
vanes (rounded) impeller blade where the 3 vanes are flat but turned at fixed an
angle to the liquid. The diameter of circular pattern the spinning blade produces
was 1.5 inches. 95 grams of L-207 were weighted into a Pyrex beaker, warmed and
placed on a hot plate under the mixer and mixed until a temperature of 66°C was
achieved at the minimum speed for the mixer of 650 rpm. 5.0 grams of UVE-1014 were
added, and the mixing was continued for 20 minutes. The mixer was stopped briefly
and a sample for microscopy was taken. The mixer was increased to the maximum speed
it could produce under the load, 1650 rpm, and the emulsion was mixed for another
30 minutes. The beaker was removed from the mixer and the bottom and sides were
inspected to make sure that none of the photoinitiator had not been mixed in. An
excellent emulsion concentrate of the invention was obtained at the higher mixing
speed. The emulsion formed at the lower speed was considered of borderline quality,
just outside the scope of invention when judged by droplet size under the Zeiss
microscope. See the table below.
A counter example was prepared in as identical a means as possible
using L-1203 polymer. 95 grams of L-1203 were added to a Pyrex beaker, placed under
the same mixer, and heated and mixed until the temperature of the polymer was 65C.
5.0 grams of UVE-1014 were added and mixed for 20 minutes at the minimum speed the
mixer would run, this time measure at 650 rpm. The mixer as briefly stopped and
a sample was taken for microscopy. The sample was very clear to the naked eye, indicating
that either the photoinitiator was sitting on the bottom of the beaker or the emulsion
formed was very course. The mixer was restarted and the speed mixture was mixed
for 20 minutes at the maximum speed obtainable from the mixer, in this case 1850
rpm. The final mixing temperature was 67°C. An emulsion of small size, such as delivered
by the present invention, was not formed. See the table below.
Verfahren zur Herstellung einer durch ultraviolette Strahlung härtbaren Klebstoff,
Beschichtungs- oder Versiegelungszusammensetzung, umfassend ein monohydroxyliertes
epoxidiertes Polydienblock-Copolymer, bestehend aus wenigstens zwei verschiedenen
Dienmonomeren, worin wenigstens eines davon ein Dienmonomer ist, das eine Ungesättigtheit
ergibt, die für eine Epoxydierung geeignet ist und worin das Polymer von 0.5 bis
4.0 Milliäquivalente Epoxyharz pro Gramm Polymer enthält, und wahlweise andere Formulierungsbestandteile,
wobei das Verfahren das Mischen des epoxidierten Polymers und der optionalen Formulierungsbestandteile
mit einem Photoinitiator umfasst, der in dem Polymer unlöslich ist und ohne ein
nicht-wässriges Lösungsmittel unter niedrigen Scherbedingungen und bei einer Scherrate
von weniger als 38,000 s-1 in einem Medium durch einen Hochgeschwindigkeitsmischer
mit einer Rührgeschwindigkeit an der Schaufelspitze von 200 bis 2000 cm/s bei einer
Temperatur von 25 bis 130°C.
Verfahren nach Anspruch 1, worin die Rührgeschwindigkeit an der Schaufelspitze
von 300 bis 1500 cm/s beträgt.
Verfahren nach Anspruch 1, worin die angelegte Schergeschwindigkeit weniger
als 10,000 s-1 beträgt.
Verfahren nach Anspruch 1, worin die Temperatur von 40 bis 100°C beträgt.
Verfahren nach Anspruch 1, worin das Polymer ein Diblockpolymer aus Isopren
und Butadien ist, worin der Isoprenblock den größten Teil der Epoxidierung
enthält und die Hydroxylgruppe sich am Ende des Butadienblocks befindet.
Verfahren nach Anspruch 5 worin das Polymer ein Molekulargewichtzahlenmittel
von 2500 bis 14,000 aufweist.
Verfahren nach Anspruch 6, worin das Polymer 1 bis 3 Milliäquivalente Epoxidharz
pro Gramm Polymer aufweist.
A process for producing an ultraviolet curable adhesive, coating or sealant
composition, comprising a monohydroxylated epoxidized polydiene block copolymer,
comprised of at least two different diene monomers, wherein at least one is a diene
monomer which yields unsaturation suitable for epoxidation and wherein the polymer
contains from 0.5 to 4.0 milliequivalents of epoxy per gram of polymer, and optionally
other formulating ingredients, said process comprising mixing the epoxidized polymer
and optional formulating ingredients with a photo initiator which is insoluble in
the polymer and without any non-aqueous solvent, under low shearing conditions at
a shear rate of less than 38,000 s-1 in a medium to high speed mixer,
with a blade tip speed of from 200 to 2000 centimeters per second, at a temperature
from 25 to 130°C.
The process of claim 1 wherein the blade tip speed is from 300 to 1500 cm/sec.
The process of claim 1 wherein the applied shear rate is less than 10,000 s-1.
The process of claim 1 wherein the temperature is from 40 to 100°C.
The process of claim 1 wherein the polymer is a diblock polymer of isoprene
and butadiene wherein the isoprene block contains most of the epoxidation and the
hydroxyl group is on the end of the butadiene block.
The process of claim 5 wherein the polymer has a number average molecular weight
of 2500 to 14,000.
The process of claim 6 wherein the polymer has from 1 to 3 milliequivalents
of epoxy per gram of polymer.
Procédé de production d'une composition d'adhésif, de revêtement ou de produit
de scellement durcissant aux ultraviolets, comprenant un copolymère bloc de polydiène
époxydé monohydroxylé, composé d'au moins deux monomères diènes différents, où au
moins l'un est un monomère diène procurant une insaturation appropriée à l'époxydation,
et où le polymère contient de 0,5 à 4,0 milliéquivalents d'époxy par gramme de polymère,
et éventuellement d'autres ingrédients de formulation, ledit procédé comprenant
le mélange du polymère époxydé et d'éventuels ingrédients de formulation avec un
photoinitiateur qui est insoluble dans le polymère et sans solvant non aqueux, dans
des conditions de faible cisaillement avec un taux de cisaillement de moins de 38
000 s-1 dans un mélangeur à vitesse moyenne à élevée, avec une vitesse
d'extrémité de pale de 200 à 2 000 centimètres par seconde, à une température de
25 à 130°C.
Procédé selon la revendication 1, dans lequel la vitesse d'extrémité de pale
est de 300 à 1 500 cm/s.
Procédé selon la revendication 1, dans lequel le taux de cisaillement appliqué
est de moins de 10 000 s-1.
Procédé selon la revendication 1, dans lequel la température est de 40 à 100°C.
Procédé selon la revendication 1, dans lequel le polymère est un polymère dibloc
d'isoprène et de butadiène dans lequel le bloc isoprène contient la majorité de
l'époxydation et le groupe hydroxyle se trouve à la fin du bloc butadiène.
Procédé selon la revendication 5, dans lequel le polymère a une moyenne numérique
de poids moléculaire de 2 500 à 14 000.
Procédé selon la revendication 6, dans lequel le polymère possède de 1 à 3 milliéquivalents
d'époxy par gamme de polymère.