Note: Descriptions are shown in the official language in which they were submitted.
/- 1 3 3 8 6 5 2
Polyvinyl chloride (PVC) resins are used in
large quantities throughout the world. Typically
these PVC resins are produced by one of three
processes, suspension, emulsion or mass process.
Emulsion produced PVC is very small in particle size
such as 1 micron or less and is essentially
non-porous. The emulsion process uses a relatively
large amount of surfactants to make the small
particle resins. PVC resins produced by the mass
pirocess are much larger, having a weight average
particle size of from about 100 to 300 microns. The
mass resin is produced in a process which normally
does not use water and surfactants. The mass resin
does not have a pericellular membrane around the
particle. The absence of the pericellular membrane
offers some advantages such as a purer product and
faster uptake of plasticizer for a given porosity
value of a resin, although mass resins are known for
their low porosity.
This Application is a Division of Canadian
Patent Application S.N. 544,921, filed August 19, 1987.
By far the largest volume PVC resin is
produced by the suspension process. Suspension
produced PVC resins have about the same particle size
and the same end uses as does mass produced resin.
In the suspension process, surfactants such as
cellulose materials or partially hydrolyzed acetate
which is usually referred to as polyvinyl alcohol
(PVA) are used to suspend vinyl chloride monomer
droplets in water and the polymerization takes place
in the monomer droplet usually aided by a free
radical initiator.
In the suspension polymerization of PVC,
droplets of vinyl chloride monomer 30 - 150 microns
*
1 338652
-- 2
in diameter are dispersed in water by agitation and
aided by surfactants. A thin membrane is formed at
the water to monomer interface by dispersants such as
PVA. This membrane has been measured at 0.01 to 0.02
micron thick, and has been found to be a graft
copolymer of polyvinyl chloride and the
dispersant(s). Early in the polymerization,
particles of PVC deposit onto the membrane from both
the monomer and the water sides forming a skin
0.5 - 5.0 microns thick that can be observed on
grains sectioned after polymerization. Primary
particles which are about 1 micron in size deposit on--
the skin from the monomer side and water phase
polymerized PVC at about 0.1 micron in size deposits
on the water side of the membrane.
In suspension polymerization, droplets of
polymerizing PVC, 30 - 150 microns in size,
agglomerate to form particles or grains of 100 - 200
microns in diameter. With one droplet per particle
the shape is quite spherical. When several droplets
agglomerate to form one particle, the shape can be
quite irregular and knobby sometimes referred to as
popcorn shaped.
Suspension produced PVC particles desirably
have voids in the particle which is known as
porosity. These voids (porosity) form when the
various components of the particle agglomerate such
as the primary particles and droplets. Porosity is a
very important property of the resin because it not
only allows the polymerized resin to be easily
stripped of its residual monomer but also gives the
resin the ability to absorb large quantities of
plasticizers.
Not only is porosity important but also the
particle shape is important. Spherical particles
1 338652
-- 3
have several attributes such as fast extrusion and
high bulk density. However, an agglomerated highly
irregular particle has better ability to absorb
plasticizer quickly because of its irregular shape.
When PVC particles are desired for a
particular application which requires a "skinless" or
n low skin~ resin, then mass produced resin is usually
tthe resin of choice. A previous suspension process
was developed and is disclosed in U.S. Patent
3,706,722 to Nelson, et al, which produces resin
particles having ~low skin" features. The term "low
skin" as used herein refers to resin particles having-
less than 50% of their surface area as PVC as
measured by ESCA technique. This process is known as
a phase inversion process. In the early part of the
polymerization, the monomer is the continuous phase
and after about 10% conversion additional water is
added such as to make the water the continuous phase
and the monomer the discontinuous phase. This
process in essence runs a mass type polymerization up
to about 10% conversion and then inverts to a
suspension type polymerization. The resultant resin
particle, however, is a porous spherical shape
particle and not the more desirable porous
agglomerated irregular shape particle. Also, the
prior inversion process results in very heavy polymer
buildup on the internal surfaces of the
polymerization equipment. This buildup is sometimes
referred to as reactor fouling and is a highly
undesirable feature.
-- 4
1 3386~2
In accordance with the invention there is
provided an agitated aqueous suspension process for
producing porous, non-spherical, low-skin, agglomerated
polyvinyl chloride resin particles having a shape factor
of less than 0.85 comprising: polymerizing vinyl chloride
monomer in the presence of a dispersant system consisting
essentially of:
(a) from about 0.01 to about 0.03 part by weight
per 100 parts by weight monomer of an unneu-
tralized ion sensitive primary dispersant
capable of thickening water, and
(b) from about 0.1 to about 0.4 part by weight per
100 parts by weight monomer of a secondary
dispersant.
In particular, the present invention seeks to
produce PVC resins in particulate form which are non-
spherical, highly porous, friable and which are low-skin
resins.
In a particular embodiment the process
comprises polymerizing vinyl chloride monomer in an
agitated aqueous suspension wherein the aqueous medium
contains as the primary dispersant small amounts of at
least one ion sensitive dispersant capable of thickening
water and at least one secondary dispersant, wherein an
ionic material is charged to the polymerization medium at
from about 1% to 5% conversion of monomer to polymer and
the ionic material desorbs a substantial amount of the
ion sensitive primary dispersant off the monomer droplet,
thereby producing agglomerated, highly porous, friable,
PVC resin absent a continuous pericellular membrane.
A process to produce the low-skin resins of the
invention is provided. The low-skin process involves
using extremely low levels of from about 0.01 to about
0.03 part by weight per 100 parts by weight of polymeriz-
able monomer, of the water thickening primarydispersant(s) along with monomer-soluble secondary
dispersants.
1 338552
-- 5 --
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 is a photomicrograph of an
agglomerated, irregular shaped resin with a skin
essentially continuous over the resin particles'
surface. This Fig. 1 represents a standard pipe
grade suspension process produced PVC resin having a
skin. Fig. 1 is magnified 100 times actual size.
Figure 2 is a photomicrograph of a particle
o~ the resin of Fig. 1 magnified 500 times actual
size.
Figure 3 is a photomicrograph of an
agglomerated, non-spherical porous resin with a skin
essentially continuous over the resin particle
surface. This Fig. 3 represents a standard film
grade suspension process produced PVC resin. Figure
3 is magnified 100 times actual size.
Figure 4 is a photomicrograph of a particle
of the resin of Fig. 3 magnified 500 times actual
size.
Figure 5 iS a photomicrograph of an
agglomera~ed, non-spherical porous resin with
low-skin magnified 100 times. The resin in Fig. 5
was produced in E~ample 3.
Figure 6 is a photomicrograph of a resin
particle in Fig. 5 magnified 500 times actual size.
2 5 DETAILED DESCRIPTION
Polyvinyl chloride resin as used in this
invention means polyvinyl chloride homopolymers as
well as vinyl chloride polymerized with up to 50%,
preferably up to 20%, by weight of one or more other
vinylidene monomers having at least one terminal
CH2=C< grouping. Suitable comonomers that may be
polymerized with vinyl chloride are esters of acrylic
acid, for example, methyl acrylate, ethyl acrylate,
butyl acrylate, octyl acrylate, cyanoethyl acrylate,
and the like; vinyl acetate; esters of methacrylic
1 338~2
f; _
acid, such as methyl methacrylate, ethyl
methacrylate, butyl methacrylate, and the like;
styrene and styrene derivatives including ~-methyl
styrene, vinyl toluene, chlorostyrene; vinyl
naphthalene; diolefins including butadiene, isoprene,
chloroprene, and the like; and mixtures of any of
these types of monomers and other vinylidene monomers
c~opolymerizable therewith; and other vinylidene
monomers of the types known to those skilled in the
art. The amount of comonomer that can be polymerized
with vinyl chloride is a function of the choice of
comonomer, as is well understood by those skilled in --
the art. Preferably, the polyvinyl chloride polymers
of this invention are polyvinyl chloride
homopolymers. The invention will be described in
terms of a polyvinyl chloride homopolymer as the
preferred embodiment of this invention.
The process used to produce the novel resin
particles of this invention is an agitated aqueous
suspension process. In the process, water is the
polymerization medium and a vinyl monomer to water
ratio in the range of about 1.0:1.0 to 1.0:10.0 is
satisfactory. Preferably, a ratio in the range of
about 1.0:1.0 to 1.0:4.0 is employed.
An important feature of the process to
prepare the resin particles of this invention is the
dispersant system that is employed in the
polymerization reaction for the purpose of
stabilizing the dispersed monomer droplets. A
colloidal unstable system will result in what is
known as a solid charge, that is, the monomer
droplets will agglomerate into large chunks which are
unsuitable for use in normal PVC applications. A
dispersant system which will not allow any
agglomeration of monomer droplets will result in
1 338652
spherical particles. Such a process to produce
spherical particles is described in U.S. Patent
4,603,151. To obtain an agglomerated particle of
this invention requires a delicate balance of having
a few of the monomer droplets agglomerate but not
excessive agglomeration such as to result in
excessively large particles. An important component
o~ this process is an ion sensitive dispersant which
will thicken water. Examples of such thickeners and
how they are used are disclosed in U.S. Patent
3,620,988
The ion sensitive dispersants which will thicken
water are usually high molecular weight dispersants or
crosslinked dispersants which will thicken water at
concentrations of less than 2% in water, preferably
less than 0.2~, and more preferably less than 0.1%
concentration in water. Suitable ion sensitive
thickening dispersants include crosslinked
polyacrylic acid polymers, crosslinked ethylene malic
anhydride polymers, high molecular weight
uncrosslinked polyacrylic acid polymers and ethylene
malic anhydride polymers, and the like. The
invention will be explained in connection with a
substantially unneutralized crosslinked interpolymer.
A suitable ion sensitive thickener is a
substantially unneutralized crosslinked interpolymer
of one or more carboxylic acid monomers with a
polyunsaturated compound having a plurality of
terminally unsaturated polymerizable groups, for
example, a crosslinked polyacrylic acid polymer. The
crosslinking is responsible for making the
polyacrylic acid polymer incapable of forming a true
solution in water. In this regard, these polyacrylic
acid polymers are classified as being substantially
insoluble in water. Nevertheless, the structure of
- 8- 1 338652
the interpolymer must be such that it has enough
affinity-for water to swell appreciably in an aqueous
medium, thus thickening the water phase, but not to
the extent that it cannot be agitated rapidly.
Interpolymers that have little or no affinity for
water and do not swell to any measurable degree, are
not suitable for the purposes of the present
i~vention.
With respect to the crosslinked polymeric
dispersants used in making the resin of the
invention, the carboxylic acid monomers utilizable in
preparing the same are those which contain at least
one active carbon-to-carbon double bond in the
a, B-position with respect to a carboxyl group such
as
R" R"'
R'-C = C-COOH (1)
wherein R' is hydrogen or a -COOH group, and each of
R" and Rn' is a hydrogen or a monovalent substituent
group which is linked to one of the doubly bonded
carbon atoms. Carboxylic acids within this
definition include acids, such as acrylic acid,
wherein the double bond is terminal such as
CH2=C-COOH (2)
or the dicarboxylic acids such as maleic acid and
other anhydrides of the general structure
R-C-C=0
~ \0 (3)
R'-C-C=0
1 338b52
g
wherein R and R' are monovalent substituent groups
and especially those selected from the group
consisting of hydrogen and halogen groups and alkyl,
aryl, alkaryl, aralkyl, and cycloaliphatic radicals.
Included within the class of carboxylic
acids, shown by generic formula (1) above, are widely
divergent materials, such as the acrylic acids, such
ais acrylic acid itself, methacrylic acid, ethacrylic
acid, a- and B-chloro and bromo-acrylic acids,
10 crotonic acid, maleic acid, itaconic acid, and many
others.
Polymerizable carboxylic anhydrides include
any of the anhydrides of the above acids, including
mixed anhydrides, and those shown by generic formula
(3) above, including maleic anhydride, and others.
In many cases, it is preferred to copolymerize an
anhydride monomer with a comonomer, such as methyl
vinyl ether, styrene, ethylene, and the like.
It is preferred to employ polymeric
20 dispersants which are derived from polymers produced
by the polymerization of the a,B-monoolefinically
unsaturated carboxylic acids. The preferred
carboxylic acids are those derived from the acrylic
acids and a-substituted acrylic acids having the
general formula
R
CH2=C-COOH
wherein R is a monovalent substituent selected from
the group consisting of hydrogen, halogen, hydroxyl,
carboxyl, amide, ester, lactone, and lactam.
The most preferred polymeric dispersants are
those prepared from the lightly crosslinked
1 338652
-- 10 --
interpolymers of acrylic acid. These dispersants are
the most effective.
The crosslinking agents which may be
employed with any of the carboxylic monomers, or
5 mixtures thereof, may be any compound, not
necessarily monomeric in nature, containing two or
more terminal polymerizable CH2=C< groups per
molecule. Examples of this class of materials
include polyunsaturated-hydrocarbons, -polyethers,
10 -polyesters, -nitriles, -acids, -acid anhydrides,
-ketones, -alcohols and polyunsaturated compounds of
this class incorporating one or more of these and
other functional groups. Specifically, there may be
utilized divinyl benzene, divinyl naphthalene, ~
low-molecular weight and soluble polymerized dienes,
such as polybutadiene and other soluble homopolymers
of open chain aliphatic conjugated dienes, which
soluble polymers do not contain any appreciable
number of conjugated double bonds, and other
polyunsaturated hydrocarbons; polyunsaturated esters,
ester-amides and other ester derivatives, such as
ethylene glycol diacrylate, ethylene glycol
dimethacrylate, allyl acrylate, methylene
bisacrylamide, methylene bismethacrylamide,
triacrylyl triazine, hexallyl trimethylene
trisulfone, and many others; polyunsaturated ethers,
such as divinyl ether, diallyl ether, dimethyl allyl
ether, diallyl ethylene glycol ether, diallyl,
triallyl and other polyallyl ethers of glycerol,
butene-1,2-diol, l-phenyl-1,2,3-propanetriol, the
polyallyl, -vinyl and -crotyl polyethers containing
from two to seven or more of these or other alkenyl
ether groupings per molecule and made from polyhydric
alcohols, such as the carbohydrate sugars, and the
so-called ~sugar alcohols", including erythritol,
- ` -
1 338652
-- 11 --
pentaerythritol, arabitol, iditol, mannitol,
sorbitol, inositol, raffinose, glucose, sucrose, and
many others, and other polyhydroxy carbohydrate
derivatives, the corresponding polyalkenyl silanes,
such as the vinyl and allyl silanes, and others. Of
this large class of crosslinking agents, the
polyalkenyl polyethers of the carbohydrate sugars,
s~gar alcohols and other polyhydroxy carbohydrate
type derivatives containing from two to seven alkenyl
10 ether groups per molecule are particularly useful.
Such materials are easily prepared by a
Williamson-type synthesis involving the reaction of
an alkenyl halide, such as allyl chloride, allyl
bromide, methallyl chloride, crotyl chloride, and the
like, with a strongly alkaline solution of one or
more of the poly-hydroxy carbohydrate derivatives.
In the monomeric mixture, for making the
crosslinked polymers employed as primary dispersants
in the suspension polymerization process used in this
invention, the two essential monomeric materials
should be present in certain proportions, although
the exact proportions will vary considerably
depending on the characteristics desired in the
polymer. Small amounts of the polyalkenyl polyether
copolymerize quite readily with carboxylic monomers
and the crosslinking effect of the polyalkenyl
polyether on the carboxylic monomer is so strong that
as little as 0.1% by weight thereof, based on the
weight of the total ~ixture, produces a great
reduction in the water and solvent-solubility of the
resulting crosslinked polymer. When 0.1% to 4.0%,
more preferably 0.2p% to 2.5%, by weight of the
polyether is utilized, water-insoluble polymers are
obtained, especially with acrylic acids, which are
extremely water sensitive. Useful dispersants are
' - -
- 12 _ 1 338652
also obtained when 0.1% to 6.0%, and preferably 0.2%
to 5%, of the polyether is copolymerized with maleic
anhydride. In the dual copolymer, or two-compound
interpolymer, this means that the remainder of the
5 monomeric mixture will be the carboxylic monomer.
The monomeric proportions employed in the
production of multi-component interpolymers may vary
ih a somewhat similar manner. However, it is
generally desirable to utilize as much of the
carboxylic monomer or monomers and as little of the
other monomeric constituents as is consistent with
the desired water-insolubility and other properties.
In these interpolymers, therefore, the carboxylic
monomer or monomers should never be less than 25%,
and preferably not less than 40%, by weight of the
total monomeric mixture. Multicomponent
interpolymers may be made from monomeric mixtures
comprising from 25% to 95% of a carboxylic monomer,
such as acrylic acid, 0.1~ to 30~ of a polyalkenyl
polyether, such as a polyallyl polyether of sucrose,
and 5.0% to 74.9% of an additional monomer or
monomers. Preferred multi-component interpolymers
are the tripolymers resulting from the polymerization
of monomeric mixtures containing, respectively, from
40% to 95% by weight of acrylic acid, 0.20% to 2.5%
by weight of polyallyl polyether, such as that of
sucrose, and 4% to 59% of an additional monomer or
monomers, such as maleic anhydride, N-methyl
acrylamide, methyl vinyl ether, ethyl vinyl ether,
n-butyl vinyl ether, and the like, and mixtures of
maleic anhydride, a vinyl alkyl ether, such as vinyl
methyl ether, and a polyallyl polyether, in which the
sum of the moles of vinyl ether and polyallyl
polyether is substantially equivalent to the molar
quantity of maleic anhydride present. It should be
- 13 - 1 3386~2
borne in mind that in the above proportions, if a
maximum amount of two of the monomers are utilized,
that somewhat less than maximum amounts of the other
monomers must be utilized.
Suitable for use as additional monomers in
the production of multi-component interpolymers are
monoolefinic vinylidene monomers containing one
t~rminal CH2=C< group, such as styrene, the chloro
and ethoxy-styrenes, etc., acrylamide,
10 N-methyl-acrylamide, N,N-dimethyl acrylamide,
acrylonitrile, methacrylonitrile, methyl acrylate,
ethyl acrylate, 2-ethylhexylacrylate, methyl
methacrylate, vinyl acetate, vinyl benzoate, vinyl
pyridine, vinyl chloride, vinylidene chloride,
15 vinylidene chlorobromide, vinyl carbazole, vinyl
pyrrolidone, methyl vinyl ether, ethyl vinyl ether,
n-butyl vinyl ether, methyl vinyl ketone, ethylene,
isobutylene, dimethyl maleate, diethyl maleate, and
many others. In addition to the above monoolefinic
20 monomers, many of the divinyl dialkenyl or other
polyfunctional esters, amides, ethers, ketones, and
the like, may be used in the production of
multi-component interpolymers, especially those
polyfunctional monomers which nominally function as
25 crosslinking or insolubilizing monomers but which are
easily saponified and hydrolyzed to additional
hydroxyl, carboxyl and other hydrophilic groups. For
example, an interpolymer of acrylic acid and divinyl
ether is insoluble in water but upon standing
30 gradually goes into solution probably due to
hydrolysis and breaking of divinyl ether crosslinks.
The presence of strong alkali or acid speeds
dissolution. Spectroscopic analysis confirms the
presence in the polymers of non-carboxylic
35 hydroxyls. Similarly, diesters, such as diallyl
- 14 _ 1 3 3 8 6 5 2
maleate, ethylene glycol dimethacrylate, acrylic
anhydride, betaallyloxy acrylate, and many others,
are readily saponified or hydrolyzed by alkali or
acid with the introduction of additional hydroxyl
5 and/or carboxyl groups. Of the additional monomers,
N-methyl acrylamide, methyl vinyl ether, ethyl vinyl
ether and divinyl ether have been found particularly
useful in the production of ti.e substantially
unneutralized crosslinked interpolymers for use as
10 ion sensitive dispersants in the suspension
polymerization of vinyl monomers.
The amount of the water-insoluble
substantially unneutralized crosslinked interpolymer
useful as an ion sensitive dispersant, in the process
15 of making the novel resins of this invention will
vary in the range of about 0.01 parts by weight to
about 0.1 parts by weight, based on 100 parts by
weight of the monomer or monomers being polymerized.
Preferably, the amount used will be in the range of
about 0.02 parts by weight to about 0.06 parts by
weight per 100 parts by weight of monomer or monomers
being polymerized.
In the process to make the novel resins of
this invention, other secondary dispersants are
preferably employed, along with the ion sensitive
dispersant. Dispersants which tend to form a skin on
the resin particles~such as methyl cellulose and high
hydrolysis (above 70%) polyvinyl acetate should be
avoided. The secondary dispersants should be monomer
soluble and not fully soluble in water. For PVA
secondary dispersants, the higher the % hydrolysis,
the more water soluble the dispersant For example,
30% hydrolyzed PVA is monomer soluble and not water
soluble, 55% hydrolyzed PVA is very soluble in the
vinyl monomer but is also partially soluble in
- 15 - ~3386~
water. 72.5% hydrolyzed PVA is fully water soluble
and therefore not acceptable. The fully water
soluble dispersants will form a skin on the polymer
particle. Oil-soluble non-polyethylene oxide
5 containing secondary dispersants are suitable for use
in this invention. Suitable non-polyethylene oxide
containing secondary dispersants are those compounds
from the sorbitan ester family or the glycerol ester
or polyglycerol ester families, as well as the low
10 hydrolysis (less than 70%, preferably less than 60%,
and more preferably less than about 55%) polyvinyl
acetates, which do not contain polyethylene oxide
segments. As examples of such dispersants, there may
be named sorbitan trioleate, sorbitan tri-stearate,
15 sorbitan monooleate, sorbitan monopalmitrate,
glycerol monooleate, glycerol monostearate,
triglycerol monooleate, 50% hydrolyzed polyvinyl
acetate, and the like. A mixture of more than one of
these dispersants may be used. The function of the
secondary dispersants is to increase the porosity of
the polymer particles and to increase the colloidal
stability of the polymerization mixture. The
non-polyethylene oxide containing dispersant is used
at a level of from about 0.005 part by weight to
about 1.0 part by weight per 100 parts by weight of
monomer, preferably from about 0.1 part by weight to
about 0.4 part by weight per 100 parts by weight of
monomer. More than one secondary dispersant may be
used in this invention to achieve the secondary
dispersant level.
- The polymerization is initiated with a free
radical catalyst. The monomer-solublç or oil-soluble
catalysts that may be used in the polymerization
process of this invention are the alkanoyl, aroyl,
alkaraoyl, and aralkanoyl diperoxides and
1 3385~2
monohydroperoxides, azo compounds, peroxy ester,
percarbonates, and other free radical type
catalysts. As examples of such catalysts, there may
be named benzoyl peroxide, lauryl peroxide, diacetyl
5 peroxide, cumene hydroperoxides, methyl ethyl ketone
peroxide, diisopropylbenzene hydroperoxide,
2,4-dichlorobenzoyl peroxide, naphthoyl peroxide,
t-butyl perbenzoate, di-t-butyl perphthalate,
isopropyl percarbonate, acetyl cyclohexane sulfonyl
10 peroxide, disecondary butyl peroxydicarbonate,
5-butyl peroxyneodecanoate, di-normal propyl
peroxydicarbonate, azo-bis isobutyronitrile,
a,'-azodiisobutyrate, 2,2'-azo-bis-(2,4-dimethyl
valeronitrile), and many others. The particular free
radical catalyst employed will depend upon the
monomeric material(s) being polymerized, the
molecular weight and color requirements of the
polymer, the temperature of polymerization, etc.
Insofar as the amount of catalyst employed is
concerned, it has been found that an amount in the
range of about 0.005 parts by weight to about 1.00
parts by weight, based on 100 parts by weight of the
monomer or monomers being polymerized, is
satisfactory. However, it is preferred to employ an
amount of catalyst in the range of about 0.01 part by
weight to about 0.20 part by weight based on 100
parts by weight of monomer(s).
The suspension polymerization process of
this invention may be carried out at any temperature
which is normal for the monomeric material to be
polymerized. Preferably, a temperature in the range
of about 0C to about 100C is employed, more
preferably from about 40C to about 80C. In order
to facilitate temperature control during the
polymerization process, the reaction medium is kept
1 338652
in contact with cooling surfaces cooled by water,
brine, evaporation, etc. This is accomplished by
employing a jacketed polymerization reactor wherein
the cooling materials is circulated through the
5 jacket throughout the pblymerization reaction. This
cooling is necessary since most all of the
polymerization reactions are exothermic in nature.
It is understood, of course, that a heating medium
can be circulated through the jacket, if necessary.
The preferred process to produce resins of
this invention involves using an ionic material to
desorb the primary dispersant off the resin.
Suitable ionic materials are bases which will
neutralize the polyacrylic acid primary dispersant
15 and form a salt. Preferably, the ionic material is a
monovalent inorganic or organic base such as amines,
sodium hydroxide, ammonium hydroxide, potassium
hydroxide, lithium hydroxide, and the like. The most
preferred ionic material is sodium hydroxide.
20 Divalent and trivalent materials can crosslink the
polyacrylic acid primary dispersant and would
therefore not normally be chosen as the ionic
material. The preferred embodiment of this invention
will be described in terms of using sodium hydroxide
25 as the ionic material. The primary dispersant
protects the monomer droplets at the very early
stages of polymerization. Before the primary
dispersant can graft polymerize with the vinyl
chloride, NaOH is added to the polymerization
30 medium. The ion sensitive primary dispersant will
then swell in size and desorb off the droplet.
Protection of the droplet is accomplished after this
point by the increased size of the primary
dispersant. The NaOH must be added early in the
35 polymerization, usually from 0.5% to 5.0% conversion
1 3386~2
- 18 -
of monomer to polymer. If the NaOH is added at the
beginning or before about 0.5% conversion, the
primary dispersant will be desorbed off the droplet
too early and could result in an unstable
suspension. Preferably the NaOH is added at from 1%
to 3% conversion, more preferably 1% to 2%
conversion. Since the primary dispersant is desorbed
from the droplet and polymerization is continued
without a primary dispersant on the particle, the
resulting resin is essentially skin-free. Of course,
some primary dispersant can become attached to the
resin particle without departing from this invention
but there cannot be a continuous pericellular
membrane present as there is in normal suspension PVC
resin.
The amount of NaOH typically added is an
amount sufficient to raise the pH about 0.5 to 1.0
point. Usually the amount of NaOH needed to desorb
the primary dispersant is from about 0.0010 part by
weight to about 0.0100 part by weight per 100 parts
of monomer. More could be used but it would not
serve a useful purpose.
If an ion sensitive dispersant is used which
will thicken by lowering pH, then rather than adding
NaOH to desorb the dispersant, HCl could be used.
The HCl would work in the same fashion as described
above and should be added at similar low conversion
levels as described above.
An alternate process to produce the low skin
resins of this invention is to use extremely low
levels of the ion sensitive primary dispersant.
Levels of from about 0.01 to about 0.03 parts by
weight per 100 parts by weight of polymerizable
monomer should be used in this alternate method. If
these low levels are used, then it is not necessary
- 19 ~ 3 3 8 6 ~ ~
to use the NaOH to desorb the primary dispersant from
the monomer droplet. Secondary dispersants at levels
described above are used in this alternate method.
An additional alternate process to produce
the resins of this invention involves the use of a
combination of dispersants. The combination of
dispersants are non-polyethylene oxide containing
secondary dispersants such as sorbitan esters, for
example sorbitan monooleate and non-polyethylene
oxide containing dispersants such as low hydrolysis
PVA, and primary dispersant polyacrylic acid.
Sorbitan esters are effective porosifiers but in
amounts greater than 0.1 part they tend to be highly
destabilizing. It was also found that higher levels
of about 0.2 to 0.4 part of sorbitan ester would
prevent the formation of a skin by the primary
dispersant. It was also unexpectedly found that low
hydrolysis PVA (less than 70%, preferably less than
60%, more preferably less than about 55%) in amounts
of from about 0.1 to 0.3 part by weight would
counteract the destabilizing effect of sorbitan
ester.
- 20 _ 1 3 3 8 6 ~ 2
Reactor Charqinq Procedure
In the preferred process to produce
resins of this invention, a charging procedure similar
to the one disclosed in Canadian Patent Application
Serial No. 526,436, filed December 19, 1989, R. B.
Hawrylko, should be used. The procedure used is what
is known as a one poly floating method. The free
radical catalyst is first mixed with a solvent, which
is suitably selected from the group consisting of an
alcohol having at least 2 carbon atoms and a hydro-
carbon such as isopropyl alcohol, in the preferred
process. This technique of using a catalyst solution
and its added benefits are fully disclosed in the
above Canadian Patent Application. The polymerization
reactor charging procedure is explained in the steps
below.
(a) Charge water and ion sensitive primary
dispersant(s) capable of thickening water
to the polymerization vessel. The primary
dispersant(s) can be added as such but is
preferably added as a concentrated mixture
with water. The water and primary dis-
persant(s) may be premixed before charging
to the polymerization vessel. The charge
water is preferably demineralized water.
(b) Agitate the water and primary dispersant(s)
until the emulsion is formed.
(c) Reduce or stop the agitation such that non-
turbulent flow is achieved.
(d) Charge the monomer(s) to be polymerized to
the reactor vessel such that said monomer
floats as a top vinyl monomer layer on a
bottom emulsified thickened aqueous layer.
-~ -
1 338652
- 21 -
(e) Charge a solution comprising a solvent and
the free radical catalyst and optionally the
secondary dispersant(s) to the reactor. If
the secondary dispersant(s) are not combined
with the catalyst solution, then they should
have been premixed with the monomer before
adding to the reactor; the solvent has a
density equal to or less than the vinyl
10 ~ monomer being polymerized and the catalyst
in solution has a density less than l.Og/cc.
(f) Allow the catalyst solution to diffuse
through the monomer layer.
(g) Increase the agitation such that the entire
polymerization medium is emulsified.
(h) Conduct to polymerization until 1% to 2%
conversion is reached, then add NaOH to
desorb the primary dispersant from the
monomer droplet.
(i) Continue the polymerization until the de-
sired degree of polymerization is achieved.
An alternate charging method, known as the
two poly method, is to first add the monomer(s) to the
reactor together with the solution containing the
catalyst and secondary dispersant(s) The catalyst
solution could, of course, be premixed with the
monomer prior to adding to the reactor vessel, in
which case agitation would not be necessary after
adding to the reactor. This mixture is then agitated
thoroughly. The thickened water, which has been
previously made up by mixing the ion sensitive
thickening primary dispersant(s) with water, is
charged into the bottom of the reactor through a
bottom entry port. Agitation is then re-started and
35 polymerization conducted as above.
- 22 - 1 3 3 8 6 52
The catalyst could also be charged neat into
the water phase containing the primary dispersant.
If this method were used, then the catalyst would not
first be premixed with the solvent.
The polymer particles produced by the
present invention should have an average diameter by
weight greater than about 70 microns. The particles
c~uld have an average diameter up to 1000 microns but
normally, the polymer particles will have an average
10 diameter by weight less than about 300 microns.
Preferably, for most end uses, the polymer particles
will have a diameter in the range of about 100
microns to about 250 microns, most preferably from
about 125 microns to about 200 microns. Resins with
an average particle size by weight less than 70
microns tend to be dusty and build up static easily
such that they are less desirable.
The resin particles produced by this
invention are agglomerated non-spherical in shape. A
20 very good method to measure the spherical shape of
resins is to determine the shape factor by optical
procedures. The image of the particle is projected
onto a flat surface to provide a two dimensional
view. The shape factor of a particle is determined
by inscribing and circumscribing the resin particles
flat image with a circle. The ratio of the diameters
of the inscribed circle to the circumscribed circle
is the number known as the shape factor.
In the case of a perfect circle, the
inscribed and circumscribed circles would have the
same diameter and, therefore, the shape factor would
be unity (1.0). The more near the shape factor is to
1.0 the more spherical the particle.
The shape factor of the resin particles made
by this invention is less than about 0.85, preferably
1 3386~2
- 23 -
less than about 0.83, and more preferably less than
about 0.80.
The resin particles made by this invention
also have high porosity of from about 0.10 cc/g to
about 0.7 cc/g as measured using mercury
porosimeter. Preferably, the mercury porosity is
from about 0.30 cc/g to about 0.50 cc/g. Porosity is
mRasured according to ASTM D-2873 procedure.
Sometimes porosity is measured as DOP porosity, which
gives results about 0.02 cc/g higher than mercury
porosity values reported herein for the same resin.
The resins of this invention must also be --
low-skin. The terms low-skin and
skinless as used in this specification mean that the
resin does not have a continuous pericellular
membrane as does a typical PVC resin. There may be
discontinuous areas or spots of skin on the resin
surface but the resin would still be considered
skinless under the meaning used in this invention.
The term low-skin is used to refer to particles
having less than 50% PVC on their surface whereas the
term skinless refers to particles having 50% or
greater PVC on their surface.
One method to characterize skinless resins
is determine the composition of the surface of the
resin particle by use of XPS (ESCA) technique.
The surface will consist mainly of PVC
and seconary surfactants (porosifiers). This
- 24 - 1 3386~2
indicates that the particles have a significant
portion of holes in their skin, where said holes
allow the plasticizer to easily pass into and be
absorbed by the particle. ESCA is an acronym that
stands for electron spectroscopy for chemical
ajnalysis. The ESCA technique involves irradiating
the sample with X-rays from an X-ray tube. The
X-rays knock electrons out of the atoms that are on
the surface of the sample. The energy and number of
these electrons are measured. From that information
one can determine what elements are present. The
depth of analysis of ESCA is about 20 to 30 angstroms
which is about 5 or 6 monolayers of atoms on the
surface of a sample. One should keep in mind that
- the ESCA test conducts an analysis of the surface
visible to the ESCA. In a skinless or low skin
resin, pores are open to the surface, therefore the
X-rays are going into the pores and the results
reflect an analysis of the bottom of the pore as well
as the outermost surface of the resin particle. This
- explains to a great deal why the ESCA analysis of a
skinless resin shows the secondary dispersant
present. The secondary dispersant is believed to be
present on the primary particles which are visible
when looking into the pores.
Another method to determine if a resin is
skinless is to look at the resin under magnification
or take micro-photographs of resin particles and
observe if a continuous skin or pericellular membrane
exists. In a micro-photograph, an observer can see
into the internal area of the resin particles of this
invention. The high porosity, friable particles
- 25 - 1 33~6~2
appear like a sponge with many openings in the
surface of the resin particle. These openings allow
for fast plasticizer uptake and create a friable
particle which is easily broken down into smaller
units (primary particles).
The resin particles of this invention also
have a fast powder mix time as measured using a
torque rheometer according to ASTM D-6373. The resin
particles of this invention have a powder mix time of
less than about 400 seconds, preferably less than 300
seconds, more preferably less than 250 seconds.
The resins of this invention must also have
good friability. The friability value of a resin is
an indication of the relative ease with which grains
break down into agglomerates and finally to primary
particles. The lower a resin's friability value, the
more desirable the resin. High friability values are
known to relate to temporary fish-eyes and surface
roughness in flexible extrudates. Fish-eyes are
undesirable areas in a product, such as a film, which
are areas of non-uniformity. This is especially
important in powder e~trusion and high plasticizer
applications. One method to test PVC resin for
friability is to place a given amount of resin in a
mortar and grind the resin with a pestle. The better
the friability, the easier the resin particles will
break apart. The friability is then subjectively
graded on a scale of from 0 to 5, with 0 being very
friable and equivalent to the best known PVC for
friability. A level of 5 is equivalent to a high
quality film grade resin. Values between 0 and 5 are
rated as to how they compare with reference standards
which are blends of a O value resin and a 5 value
resin. The resins of this invention have a
friability value of about 2 or less, preferably they
- 26 - 1 3 3 8 6 5 2
have a friability value of 1 or less, and more
preferably they have a friability value of 0.
For reference, make up standards using
blends of Geon~ 92 (a skinless spherical PVC resin
produced by B.F.Goodrich according to the process of
U.S. Patent 3,706,722) and well known for its
excellent friability and Geon~ 30 (a high quality
f~lm grade PVC resin with a skin produced and sold by
B.F.Goodrich) as follows:
Reference Standard '0" is a mix of Geon 92:
100 parts and Geon 30: 0 parts.
Reference Standard "1" is a mix of Geon 92:
80 parts and Geon 30: 20 parts.
Reference Standard "2" is a mix of Geon 92:
60 parts and Geon 30: 40 parts.
Reference Standard "3~ is a mix of Geon 92:
40 parts and Geon 30: 60 parts.
Reference Standard "4~ is a mix of Geon 92:
20 parts and Geon 30: 80 parts.
Reference Standard "5" is a mix of Geon 92:
0 parts and Geon 30: 100 parts.
Compare the friability of the resin tested
to the friability of the reference standards. Choose
the standard which most closely corresponds to the
test resin and report that standard as the friability
of the test resin.
To further illustrate the present invention,
the following specific examples are given, it being
understood that this is merely intended in an
illustrative and not a limitative sense. In the
examples, all parts and percents are by weight unless
otherwise indicated.
1 338652
- 27 -
COMPARATIVE EXAMPLE 1
This Example is presented to demonstrate an
agglomerated, non-spherical resin having a skin.
F,igures 1 and 2 represent a standard production PVC
pipe resin having a skin and being agglomerated.
Figure 1 is a microphotograph showing a standard
suspension process produced PVC resin magnified 100
times actual size. Figure 2 is the same resin as is
in Figure 1 except one of the particles is magnified
500 times actual size. As can be seen, the resin has
an essentially continuous skin covering the resin
particle. The skin is a graft polymer of the
dispersant used with vinyl chloride. The shape
factor of the resin shown in Figures 1 and 2 is 0.76.
COMPARATIVE EXAMPLE 2
This Example is presented to demonstrate an
agglomerated, highly porous, non-spherical resin
having a skin. Figures 3 and 4 represent a standard
production PVC film grade resin having a skin and
being agglomerated and having higher porosity than
the resin of Example IV (Figures I and 2). Figure ~
is a magnification of 100, whereas Figure 4 is a 500
magnification of actual size. Although the resin is
porous, it can be seen that there exists an
essentially continuous skin covering the resin
particle.
- 28 - 1 3386~2
EXAMPLE 3 (INVENTION)
This Example is presented to show an alternate
method of producing low-skin resins of this invention
whereby low levels of the ion sensitive primary
dispersant are used and NaOH is not used to desorb the
primary dispersant. In this Example the following
polymerization recipe and conditions were used:
Inqredient Parts bY Weiqht
10 Vinyl chloride 100
Water (demineralized) 150
Polyacrylic acid dispersant 0.025
Low hydrolysis (55%) PVA 0.600
Di-secondary butyl peroxydicarbonate 0.022
15 Phenolic shortstop 0.010
An 1100 gallon reactor was used and the charging
procedure disclosed on pages 20-21 was employed, except
that NaOH was not used to desorb the polyacrylic acid
dispersant off the monomer droplets.
The resin produced was porous, low-skin,
agglomerated and non-spherical and had the following
properties:
Weight average particle size - 313 microns
Mercury porosity - 0.428 cc/g
Powder mix time - 246 seconds
From the microphotographs in Figures 5 and 6 it can be
seen that the particles of this Example are non-
spherical, agglomerated particles. Figure 5 is a
photomicrograph of this resin magnified 100 times actual
size. Figure 6 is a particle of Fig. 5 magnified to 500
times actual size. From Fig. 6 it can be seen that the
particle has low-skin, that is, there are significantly
large areas on the surface which have no skin and are
sponge-like in appearance. There are also areas which
have a skin on the surface of the particle. From Fig. 6
one can easily determine the difference in the degree of
skin between this low-skin particle and skinless
particles. The resin of this Example also exhibits
friability and fisheye levels.
- 29 -
- 1 338652
In all of the Examples which show the
polymerization processes of this invention, the reactor
buildup was from very low to none. This is in contrast
to the process of Nelson, et al, which gives very high
amounts of polymer buildup on the internal surfaces of
the polymerization equipment. The very nature of the
phase inversion process of Nelson, et al, is believed to
- be detrimental to keeping the polymerization equipment
clean. The process of this invention gives clean
reactors which are able to be used for several
polymerization runs before being shut down for cleaning.
The resins of this invention have many uses in
end product applications where PVC is used. Their
principal application is in film grade applications
because of their high porosity and friability. Anywhere
PVC resins are needed that require them to absorb a large
amount of plasticizer quickly, the resins of this
invention would be an excellent choice.
, .
~ f
