Note: Descriptions are shown in the official language in which they were submitted.
6~36
Background o~ the Inven-tion
In blow molding processes, molten resin must form
into stable parisons for a time long enough to permit a mold
to enclose the parison. If these molten resins do not possess
suf~icient "melt strength" or melt viscosity, the parisons
will tend to elongate or draw under their own weight and either
not be blow moldable or result in blow molded articles which
have non-uniform wall thicknesses, low surface gloss, poorly
defined sample shape, and a large number of pitmarks.
Polymers such as polyesters, polyamides, polyethers,
and polyamines when melted generally form thin liquids naving
low melt viscosities and poor melt strengths. These low melt
viscosity materials are unsuited or are only poorly suited for the
manufacture of extruded shapes, tubes, deep drawn articles, and
large blow molded articles. In order to overcome this disadvantage
and to convert these polymers to a form better suited for the above-
mentioned manufacturing techniques it is known to add compounds
to the plastics which will increase their melt viscosities.
The materials which are added to increase the melt viscosity
of the plastics are generally cross-linking agents, as described,
for example, in United States Patent 3,378,532. Such cross-linking
agents may be added during the condensation reaction by which the
plastics are formed, and/or to the plastics after their formation
(prior to, or during their melting). Examples of cross-linking
agents which may be added to the plastics after their formation
and before or after their melting in order to increase the melt
viscosity include compounds containing at least two epoxy or
isocyanate groups in the molecule, organic phosphorus compounds,
peroxides, bishaloalkylaryl compounds, and polyesters o~ carbonic
acid.
-- 2 --
~ o~9~53'6
These known_cross linking agents which are added to
increase the melt viscosity of the polymer are not completely
satisfactory. They may, for instance, cause an excessively
rapid and large increase in viscosity or form reaction products
which have an adverse influence on the quality of the plastics.
Furthermore, the results obtained with the use of these known
cross-linking agents are not always uniform or reproducible.
For example, when polyesters of carbonic acid are used to
increase the melt viscosity, the degree of viscosity increase is
generally dependent not only upon the amount of additive used
but also upon its molecular weight and on the stage of the
polycondensation reaction at which the addition takes place.
Besides having sufficient melt viscosity or "melt
strength", polymers which are to be used in blow molding and
related applications should also possess sufficient die swell,
i.e., the molten polymer should expand as it is released from
the extrusion die. This die swell is important for blow
molding applications since (a) the larger the diame-ter of
; the extruded polymer, the easier it is for air to be blown into
the parison, and (b) the greater the die swell the greater the
expansion of-the molten polymer to fit the particular mold.
Polyesters having low intrinsic viscosities are
particularly difficult to blow mold. The prior art illustrates
the use of nurnerous additives to modify various properties of
polyesters. For example~ United States Patent 3,376,272 discloses a
processforthe preparation of branched chain, high molecular
weight thermoplastic polyesters having a multiplicity of linear
non-cross.ilinked polyester branched chains from dicarboxylic
acid anhydrides, monoepoxides, and an alcohol compound by
reacting these compounds at a temperature below 150C. However,
1~9~36
the polyesters described in this patent are formed from s.nhyariaes
and are therefore not crystalline. Non-crystalline pol~Jmers tend
to take longer time to set up in a mola and thus are not suitea
or are only poorly suited for blow molding and related applica-
tions.
As indicated above, compounds containing epoxy groups
in the molecule have been used to increase the melt viscosity
of polyesters (see, for example, United States Patent 2,830,031).
But although the use of epoxies as cross-linking agents for
polyesters is known, little appears known about the use of
epoxies as reactants which promote the branching (and hence
increase the "melt strength") but not the cross-linking of
polyesters.
United States Patent 3,547,873 disclosesthe prcduction of
thermoplastic molding compositions from linear saturated polyesters
and polyfunctional epoxides. This process, however, also yields
products which lack the melt strength ana die swell necessary
for blow molding applications.
Polyisocyanates have also been used to increase the melt
viscosity of polymers such as polyesters. For example, United States
Patent 2,333,639 aiscloses the reaction of low intrinsic viscosity,
low molecular weight polyesters with polyisocyanates (e.g.,
a diisocyanate) at temperatures up to 300C to form higher
intrinsic viscosity, higher molecular weight, fusible polyesters,
but this process results in relatively low melting, linear, soft
amorphous polyesters with poor melt viscosity and poor die swell
properties.
-- 4 --
gL~g~S36
United States Patent 3,304,286 discloses the xeaction of a poly-
ester with a polyisocyanate such as diisocyanate. However, this process
yields products having straight chain non-branched structures. These products
thus lack the melt strength and die swell needed for blow molding applications.
Furthermore, United States Patent 3,692,744 discloses the pre-
paration of polyester molding materials which can be injection lded by
having present in the polyes~erifica~ion mixture, besides the terephthalic
acid and diol con~onents, 0.05 to 3 moles percent, based upon the acid
component, of a compound containing at leas$ three ester forming groups such
as a polycarboxylic acid, a polyhydric alcohol, or a hydroxy carboxylic acid.
The use of epoxy or isocyanate compounds is not disclosed, however.
The search has continued foT improved processes for preparing
polymers having increased melt strength. The present invention has resulted
from that search.
It would be advantageous to avoid or substantially alleviate the
above problems of the prior art.
In particular~ it would be advantageous to have a process for
preparing impToved polymer compositions having improved melt strength and
die swell characteristics.
It would be advantageous to have a process for preparing improved
polymer compositions useful in blow molding and profile extrusion
applications.
It would be advantageous to have the improved polymer compositions
prepared by these processes.
It would also be advantageous to have an improved polymer molding
pxocess utilizing these new polymers.
In one aspect, the present invention provides a process for pre-
paring branched chain thermoplastic polymers having increased melt strength
which are useful in ext~usion applications. This process comprises reacting
at least one thermoplastic polymer which is in the molten state and which
~L~3~6~36
is capable of reaction with an epoxy or isocyanate functionality, wi~h at
least one branching agent selected from the gTOUp consisting of epoxy con-
taining at least two epoxy groups per molecule of epoxy branching agent, and
isocyanate containing greater than two isocyanate groups per molecule of
isocyanate branching agent, to produce branched chain thermoplastic polymers
having a melt strength ratio of Tl/T2 of less than about 2.0 at 235 C.
In another aspect~ the pxesent in~ention provides the melt strength
improved thernoplastic polymers produced by this process.
In still another aspect, there is provided an improved molding
process which comprises ~orming a melt of the above-described melt strength
improved thermoplastic polymer into a desi~ed article and cooling the molten
polymer.
According to a particular embodiment of the present invention there
is provided a process for preparing branched chain thermoplastic polyesters
of incTeased melt strength useful in extIusion applications, which pTOCeSS
comprises reacting a~ least one thermoplastic polyester capable of reaction
with an epoxy or isocyanate functionality, said polyester being in the
molten state, with at least one branching agent selected from the group con-
sisting of epoxy containing at least two epoxy groups per lecule of epoxy
branching ag~nt and isocyanate containing greater than two isocyanate groups
per molecule of isocyanate branching agent to pYo~uce said branched chain
ther~oplastic polyesters having a melt strength ratio of Tl/T2 of less than
about 1.8 at 235 C.
The present invention also provides a process for preparing
branched chain polybutylene terephthalate having increased melt strength
and useful in ex~rusion applications which process comprises reacting from
about 95 to about 99% by weight polybutylene terephthalate in the molten
state, with from about 1 to about 5% by weight of at least one branching
agent selected from the group consisting of epoxy containing at least two
epoxy groups per molecule of epoxy branching agent, and isocyanate containing
~ 653~
greater than two isocyanate groups per molecule of isocyanate branching a~ent
wherein said reaction is carried out at a temperature of from about 220 to
about 280C and at substantially atmospheric pressure to produce said
branched chain polybutylene terephthalate having a melt strength ratio of
Tl/T2 of less than about 1.6 at 235C.
The present invention according -to a further aspect provides a
branched chain, improved melt strength thermoplastic polymer suitable fo~
extrusion applications and having a melt strength ratio of Tl/T2 of less
than about 2.0 at 235C wherein said branched chain polymer comprises ~he
reaction product of at least one thermoplastic polymer capable of reaction
with an epoxy or isocyanate functionality and at least one branching agent
selected from the group consisting of epoxy containing at least two epoxy
groups peT molecule of epoxy branching agent and isocyanate containing
greater than two isocyanate groups per molecule of isocyanate branching agent.
The present invention further provides a branched chain, improved
melt stTength thermoplastic polyester suitable for extrusion applications and
having a melt strength ratio of Tl/T2 of less than about 1.6 at 235C wherein
said branched chain ther plastic polyester CompTises the reaction pToduct
of from about 95 to about 99% by weight of at least one saturated ~hermo-
plastic polyester having carboxylic acid end functional groups and capable
o~ reaction with an epoxy or isocyanate functionality, and from about l to
about 5% by weight of at least one branching agent selected from the group
consisting of epoxy containing at least two epoxy groups per lecl~le of
epoxy branching agent and iso yanate containing greater than two isocyanate
gxoups per molecule of isocyanate branching agent.
The eSseDCe of the present invention is the discovery that when
thermoplastic polymers in a molten state are chemically reacted with the
particularly defined epoxy or isocyanate branching agents as described above,
the molten, the~moplastic polymer product possesses increased melt strength.
The polymers prepared according to the process of the present invention also
have improved die swell characteristics, i.e., a~ter extrusion of the
-6a-
., .~,
~ ;5i36
molten polymer through an orifice having a particular diameter,
the diameter of -the extruded polymer may increase up to about
-two or three times the diameter of the extrusion orifice.
Description of the Preferred Embodiments
As indicated hereinabove, the process of the present
invention comprises reacting molten polymer with an epoxy or
isocyanate branching agent to form an improved polymer having
increased melt strength.
Any thermoplastic polymer which contains functional groups
capable of reacting with the epoxy or isocyanate branching agent
may be used in the process of the present invention. Such functional
groups include carboxyl, amine, hydroxyl, epoxy, and isocyanate
groups. Thermoplastic polymers include polyesters, polyamides,
and allyl alcohol/styrene copolymers. Saturated thermoplastic
polyesters are preferred.
The term "thermoplastic" polyrner is meant to incluae all
polymers which soften when exposed to sufficient heat and which
return to their original condition when cooled to room temperature.
Thermoplastic polyesters are preferred polymers for use
in the present process. Saturated thermoplastic polyesters are
particularly preferred and include saturated aliphatic/aromatic
polyesters and wholly aromatic polyesters. The term "saturated"
polyester is meant to include all polyesters which do not contain
ethylenic unsaturation in the polymer chain. The saturated,
thermoplastic polyesters may be halogenated, i.e., contain
halogen (e.g., bromine and/or chlorine) substitution in the
polyester chain. The use of halogenated polyesters is particularly
desirable when products having decreased flammability are desired.
-- 7 --
iS36
The saturated thermoplastic polyesters useful in the
present invention may be formed in a multitude of ways well kno~
to those skilled in this art. These saturated thermoplastic
polyesters may be prepared from dihydric alcohols and dicarboxylic
acids or the dialkyl esters of dicarboxylic acids wherein the
alkyl groups may contain from one to seven carbon atoms.
Typical dihydric alcohols include aromatic dihydric alcohols
such as bisphenol A [i.e., 2,2-bis(4-hydroxyphenyl)propane],
phenolphthalein, 4,4'-sulfonyl diphenol,resorcinol, hydroquinone,
catechol, naphthalene diols, stilbene bisphenol, 4,4'-diphenylether
diphenol, and mixtures thereof, and aliphatic dihydric alcohols
such as saturated dihydric alcohols having from 2 to 4 carbon
atoms, and mixtures thereof.
Halogenated dihydric alcohols may also be employed.
Suchhal0genated dihydric alcohols include, for example,
tetrabromobisphenol A, tetrachlorobisphenol A, 2,2'-[isopropyli-
denebis(2,6-dichloro-p-phenylene)], and 2,2-bis[3,5-dibromo-
4-(2-hydroxyethoxy)phenyl]propane.
Typical aromatic carboxylic acids include, for example,
phthalic acid (including isophthalic and terephthalic), hydroxy-
benzoic acid, and mixtures thereof.
Typical polyesters useful herein include the linear
polyesters of an aromatic dicarboxylic acid reacted with a
saturated aliphatic or cycloaliphatic diol~ particularly poly~
ethylene terephthalate, polypropylene terephthalate, polybutylene
terephthalate, poly-1,3-cyclobutane terephthalate, polypentylene
terephthalate, polycyclohexane-1,4-dimethylol terephthalate,
poly-1,5-pentane diol terephthalate, and polyneopentylglycol
terephthalate.
3~i
Typical wholly aromatic thermoplastic polyesters incluae
the reaction product of bisphenol A, isophthalic or terephthalic
acids or mixtures (50/50 or 60/40 mole %) of isophthalic and
terephthalic acids. Such polyesters may additionally contain
minor amounts of a saturated aliphatic dihydric alcohol having
from 2 to 4 carbon atoms. Halogenated wholly aromatic thermo-
plastic polyesters include for example, the-reaction product of
tetrabromobisphenol A, and a 50-50 mole ratio of isophthalic
and terephthalic acid (and optionally, a minor amount of ethylene
glycol).
Polypropylene terephthalate, polybutylene terephthalate,
and mixtures thereof as well as mixtures of polyethylene
terephthalate and polybutylene terephthalate are particularly
preferred polyesters.
In the process of the present invention, the thermoplastic
polymer is reacted with an epoxy branching agent containing at
least two epoxy groups per molecule of epoxy branching agent or
with an isocyanate branching agent containing greater than two
isocyanate groups per mo]ecule of isocyan~te branching agent
whereby high melt strength, substantially non-cross lin~ed
thermoplastic polymers are formed.
Epoxy branching agents useful in the present invention
include epoxy molecules having two or more epoxy groups per
epoxy molecule. Thus, di-, tri-, or more highly substituted
epoxies may be used. Halogenated epoxies (i.e., those substituted
with e.g., bromine and/or chlorine) may also be used, especially
,~,",' ~
,
i53~i
when flame retardant properties are desired. Mixtures of two
or more epoxies may be used as well as epoxies containing minor
(i.e., less than about 25% by weight) amounts of impurities as
long as the impurities do not affect the reaction between the
thermoplastic polymer and the epoxy.
The epoxy resins utilized in the present invention are
most commonly prepared by the condensation of bisphenol A
(4,4'-isopropylidene diphenol) and epichlorohydrin. Also, other
polyols, such as aliphatic glycols and novolac resins may be reacted
with epichlorohydrin for the production of epoxy resins suitable
for use in the instant process provided resinous products are
selected which possess the requisite flow properties.
In a preferred embodiment of the invention epoxy resins
are selected which possess terminal epoxide groups and are
condensation products of bisphenol A and epichlorohydrin of the
following formula:
c~2~~c~_c~o~l~ -~ - t
O- CH2 - CH - CH2
-- 10 --
S36
where n varies between zero and a small number less than about
10. When n is zero, the resin is a very fluid light-colorea
material which is essentially the diglycidyl ether of bisphenol
A. As the molecular weight increases, the viscosity of the
resin also generally increases. Accordingly, the particularly
preferred liquid epoxy resins generally possess an n value
averaging less than about 1Ø Epoxy novalacs, as well as
epoxy cycloaliphatics may also be selected. Illustrative examples
by standard trade designations of particularly useful commercially
available epoxy resins include: Epi-Rez* 508, Epi-Rez* 510,
Epi-Rez* 520, Epi-Rez* 530, Epi-Rez* 540, Epi-Rez* 550, and Epi-Rez*
5155 (Celanese Coatings Company); DER* 332, and DE~T* 438 (Dow
Chemical Company); Epon* 828, and Epon* 1031 (Shell Chemical
Company); and ERLA* 2256 (Union Carbide). Other epoxies useful
in the present process include cyclohexane diepoxide, cyclopentane
diepoxide, and butane diol diglycidyl ether.
A particularly preferred epoxy isthe diglycidyl ether
of bisphenol A.
Polyisocyanates useful in the present invention contain
greater than two isoscyanate groups per molecule and thus include
tri-, tetra-, and pentaisocyanates. Typical polyisocyanates
include polyphenylene polyisocyanate, triphenylmethane
triisocyanate, benzene triisocyanate, aliphatic and cyclo-
aliphatic polyisocyanates, and naphthalene triisocyanate.
A particularly preferred polyisocyanate is polyphenylene poly-
isocyanate.
Mixtures of two or more branching agents may be used as
long as the particular branching agents in the mixture are
compatible with each other --i.e., do not reduce reactivity
or branching.
*Trademark; epoxy resin - 11 -
. . .
.~!
;S36
The amounts of thermoplastic polymer and epoxy orisocyanate branching agent used in the present invention may vary
widely, although generally from about 75 to about 99.99, typic-
ally from about 90 to about 99.9, and preferably from about 95 to
about 99% by weight polymer, and generally from about 0.01 to
about 25, typically from about 0.1 to about 10, and preferably
from about 1 to about 5% by weight branching agent may be
employed. The expressed percentages are by weight of the total
reaction mixture (i.e., total weight of thermoplastic polymer
and branching agent).
Other additives, both polymeric and non-polymeric,
such as flame retardants, lubricity agents, dyes, antioxidants,
and inorganic fillers (such as glass) may be employed as long
as these additives do not interfere with the reaction between
the thermoplastic polymer and the branching agent. Such
additives may generally be present in amounts up to about 10
by weight of the total reaction mixture.
When an epoxy branching agent is employed in the
present invention, it is necessary to add to the reaction mixture
a catalyst or reaction initiator. Such catalysts or reaction
initiators include aliphatic and aromatic amines, particularly
tertiary amines, amine adducts, acids, acid anhydrides, aldehyde
condensation products, and Lewis acid type catalysts, such as
boron trifluoride. Particularly preferred catalysts or reaction
initiators which produce improved products are disclosed in
copending Canadian patent application Serial No. 266,401
(corresponding to United States Patent No. 4,101,601, issued
on July 18, 1978).
. ~ ~12
;536
When an isocyanate branching agent is employed in tbe present in-
vention, a catalyst or reaction initiator is not generally needed since such
reactions proceed at an acceptable rate in the absence of catalysts.
The thermoplastic polymer and branching agent may be blended in any
convenient manner as long as they are in contact for a period of time suffi-
cient for chemical reaction to take place. Thus, the improved melt strength
; polymers of the present invention may be prepared by coating the thermoplastic
polymer with a solution of the branching agent in a soivent in which the
branching agent is soluble and the polymer is insoluble. The solvent should
be substantially non-reactive toward the reactants and products of the reac-
tion. Such solvents include hydrocarbons (such as methylene chloride) and
ketones. The coated polymer may be allowed to air dry and then may be heated
to the temperature at which reaction between the thermoplastic polymer and
branching agent takes place.
The reactants may also be prepared by blending the branching agent
with solid polymer chip and then feeding this mixture to a melt screw extruder
(such as a Werner-Pfleiderer ZSK twin screw extruder) which is at a temper-
ature high enough to cause the polymer to melt and thus enable reaction be-
tween the thermoplastic polymer and branching agent to take place.
Alternatively, the thermoplastic polymer may be milled until fully
rnolten in a plastograph (such as a C.W. Brabender Rolle Type plastograph) at
temperatures high enough to melt the polymer. When the polymer is in the
molten state, the branching agent may be introduced directly into the polymer
until a melt viscosity of generally greater than about 10,000, typically
greater than about 20,000, and preferably greater than about 60,000 poise is
achieved.
~; In this specification, the term "melt viscosity" refers to
the viscosity of the polymer in a molten or fused state. Melt viscosity
- is measured by dyna~ic viscosity evaluation in a rheometrics viscometer
30 at 240 C. Such a measurement may be obtained by placing a sample in a rheo-
lC,~6~3~
meter and heating to 240C. The melt viscosity may be obtained by plotting
dynamic viscosity versus frequency.
The present process may be carried out at subatmospheric, atmos-
pheric, or superatmospheric pressures, al-though substantially atmospheric
pressures are preferred.
The present process may be carried out at any temperature which is
such that the thermoplastic polymer will remain in the molten sta-te for a
period of time sufficient to enable reaction between the thermoplastic polymer
and the branching agent to take place. However, the temperature should not
be high enough to decompose the thermoplastic polymer. At atmospheric pres-
sure, the reaction may be carried out a-t temperatures of generally from about
150 to about 350, typically from about 180 to about 300, and preferably from
about 220 to about 280 C.
The reaction between the thermoplastic polymer and the branching
agent may be conducted generally in any environment. However, because of the
sensitivity of certain branching agents, catalysts, and polymers to the pres-
ence of water, the reaction is preferably carried out in the substantial
absence of water. Sufficient quantities of water tend -to destroy the activity
of certain catalysts as well as tha-t of certain of the branching agents, and
to degrade the polymers. It is also often desirable to conduct the reaction
in the substantial absence of oxygen gas. Thus, the reaction is preferably
carried out in dry nitrogen, helium, and/or argon.
The molten thermoplastic polymer and the branching agent must be
in contact for a sufficient period of time for chemical reaction to take
place. ~eaction progress may be monitored in various ways. For example,
when polyesters or polymers containing carboxylic acid end groups are reacted
with the branching agent, the progress of the reaction may be monitored by
observing the decrease in the carbo~Jlic acid end groups (CEG) with time.
When no further decrease in CEG takes place, reaction has ceased.
P~eaction rate, of course, is a function of temperature, but in the
- 14 -
~653~i
present invention a reaction time of generally from about 45 to about 150,
typically from about 60 to about 130, preferably from about 90 to about 120
seconds (melt screw extruder) may be employed. Because mixing does not take
place to as great a degree in a plastograph as in a melt screw extruder, re-
action times in a plastograph are generally somewhat longer. When an epoxy
branching agent is employed in the absence of a catalyst, significantly
longer reaction times are required.
The process of the present invention may be carried out in a batch,
semi-continuous, or continuous manner, as desired.
It should be noted that in the process of the present invention, a
chemical reaction is actually occurring between the thermoplastic polymer and
the branching agent. This reaction is evidenced by an increase in melt
strength as well as an increase in the intrinsic viscosity (I.V.). When
polyesters or compounds containing carboxylic acid end groups are reacted
with the branching agents, the chemical reaction is also evidenced by a con-
comitant decrease in CEG level.
The increase in melt strength and concomitant increase in I.V. re-
sult from chain branching of the thermoplastic polymer, ~Jhich chain branching
occurs when the polymer and branching agent are reacted as described herein-
above.
As indicated hereinabove, the present process provides thermo-
plastic polymers having increased melt strength. These increased melt
strength thermoplastic polymers are useful for extrusion applications. Such
applications include pipe, film, and blow molding uses such as inblow mold-
ing bottles.
Melt strength may be measured by extruding a six-inch strand of
thermoplastic polymer through a constant drive index apparatus at a temper-
ature high enough to keep the polymer molten (generally about 235 C). Melt
strength (~S) may be defined as follows:
~1
, ....
~96536
MS
T2
wherein the time required to extrude a polymer s-trand three inches (Tl) from
the base of the melt index barrel i5 determined and without interruption the
time required to extrude the same polymer to six inches is determined. The
difference between the total time at six inches and the time at three inches
is computed to give T2.
A melt strength value of from about l.0 to about 2.6 is desirable
when the material is to be used in extrusion applications. Ideally, a value
of l.0 is desired since this would mean that the second three-inch segment
extruded at the same rate as the first segment.
For polymers with poor or low melt strengths, the second segment is
extruded much more rapidly than the firs-t segment, resulting in a Tl/T2 ratio
significantly greater than lØ
Thus, polymers having poor or very low melt strengths have rather
large values of Tl/T2. By saying that certain polymers have "no melt
strength" is meant that the second segment of the six-inch strand is extruded
so rapidly that T2 cannot be measured.
The term "high melt strength polymers" refers to polymers having a
ratio of Tl/T2 approaching the ideal value of l.0, and the terms "poor" or
"low melt strength polymers" refer to polymers having comparatively large
Tl/T2 ratios. Polymers having "no melt strength" have so small a T2 value
;~ that the melt strength cannot be measured.
The melt strength of a polymer depends upon the particular polymer
; employed as well as the temperature. However, the improved melt strength
polymers of the present invention have melt strengths of generally less than
about 2.0, typically less than about 1.8, and preferably less than about 1.6
at 235C.
The improved melt strength polymers of the present invention also
have improved die swell characteristics. Die swell may be described as the
, ~ ,
653~
increase in diameter which takes place when the molten polymer is released
from an extrusion die. As the polymer moves through the die, the entangle-
ments and branches of the polymer chains are deformed or displaced from their
equilibrium positions. This represents a storage of elastic energy. As the
polymer is released from the die, this energy is regained by a return of the
entanglements and branches to their equilibrium positions. This results in
die swell.
The diameter of the improved melt strength polymers of the present
invention may increase up to about -two or three times the diameter of the ex-
trusion orifice. Die swell is important for blow molding applications since(a) the larger the diameter of the extruded polymer, the easier it is for air
to be blown into the melt, and (b~ the greater the die swell, the greater the
expansion of the polymer to fit the particular mold.
The improved melt strength polymers of the present invention also
have increased intrinsic viscosities. The "intrinsic viscosity" of the poly-
mers of the present invention may be conveniently determined by the equation
I.V. = lim In
c~o c
wherein Nr is the "relative viscosity" obtained by dividing the viscosity of
a dilute solution of the polymer by the viscosity of the solvent employed
(measured at the sarne temperature)~ and c is the polymer concentration in the
solution, expressed in grams per 100 milliliters. The intrinsic viscosity of
the improved polymers of the present invention in o-chlorophenol at 25 C is
generally from about o.85 to about 1.7, -typically from about 0.90 to about
1.65 and preferably from about 0.95 to about 1.6 poise.
As indicated hereinabove, when polyesters or polymers containing
carboxylic acid end groups are reacted with the branching agents, the extent
of reaction may be determined by measuring the change in the number of micro-
equivalents of carboxylic acid end groups per gram of polymer. By "carbox-
ylic acid end groups" is meant the number of carboxylic acid end groups
@~
~96536
present in the polymer, measured in microequivalents per gram of pol~Jmer.The number of carboxylic acid end groups may be measured by dissolving the
polymer in a 70/30 mixture of o-cresol/chloroform solvent and potentiometri-
cally titrating the solution with tetrabutylarnmonium hydroxide. When poly-
esters or polymers containing carboxylic acid end functional groups are re-
acted with the branching agent, these improved melt strength polymers may
contain generally less than about 65, typically less than about 60, and pref-
erably less than about 55 microequivalents of carboxylic acid end groups per
gram of polymer.
The present invention is further illustrated by the following ex-
amples. All parts and percentages in the examples as well as in the speci-
fication and claims are by weight unless otherwise specified.
EXA~LE I
This Example illustrates the preparation of a highly branched,
thermoplastic polyester useful in blow molding.
Forty-seven and one-half grams (95 weight percent) of polybutylene
terephthalate having 62 milliequivalents of carboxylic acid end groups per
kilogram of polybutylene terephthalate are added to a C.W. Brabender Rolle
type plastograph. The polybutylene terephthalate is then heated to a temper-
ature of 250 C such that only the molten polymer is present. At this time,
2.5 grams (5 weight percent) of the diglycidyl ether of bisphenol-A are
added. After 30 minutes, the molten polybutylene terephthalate is removed
from the plastograph and cooled to room temperature.
The melt viscosity of the unmodified polybutylene terephthalate
as measured by a rheometer is 1,000 poise and the molecular weight is 44,168.
The melt viscosity of the polybutylene terephthalate as modified by the di-
glycidyl ether of bisphenol-A is go,oob poise and its molecular weight is
44,870. The modified polybutylene terephthalate is fusible and substantially
thermoplastic.
A cornparison of the intrinsic viscosity (I.V.), n~ber of csrbox-
- 18 -
~/
5~i
ylic acid end groups (CEG), and melt strength (MS) of bot~l t'ne unmodifiea ana
modifiea polybutylene terephthalate (PBT) is inaicatea in Table I below:
TABLE I
-
Property Unmodified PBT Modified PBT
I.V. 0.75 0.97( )
C.E.G. 85 50
M.S. not measurable ( ) 1.5
(1) The present invention also provides a method for increasing the I.V. of
PBT as indicated by the increase from 0.75 to 0.97 when modified with the
branching agent.
(2) MS could not be measured in this case because the molten polymer had such
a poor MS that it drippea.
EXAMPLE II
This Example illustrates the preparation of a highly branchea,
thermoplastic polyester useful in blow molding, using polyethylene terephthal-
ate reacted with polyphenylene polyisocyanate.
; Forty-eight grams of polyethylene terephthalate having 60 milli-
equivalents of carboxylic acid end groups per kilogram of polyethylene tere-
phthalate are adaed to a C.W. Brabenaer Rolle type plastograph. The poly-
ethylene terephthalate is heatea to a temperature of 270 C such that only
molten polymer is present. At this time, 2.0 grams of polyphenylene poly-
;~ isocyanate (averaging more than two isocyanate groups per molecule) are added
to the molten polyethylene terephthalate at 270C. After 5 minutes the molten
; 15 polyet'nylene terep'nthalate is removed from the plastograph and cooled to room
temperature.
The melt viscosity of the unmodified polyethylene terephthalate is
9,000 poise and its molecular weight is 46,ooo whereas the melt viscosity of
the polyet'nylene terephthala-te as modifiea in accordance with the process of
the present invention is 98,ooo poise ana its molecular weight is ~7,200.
The modified polyethylene terephthala-te is fusible and substantially thermo-
plastic.
-- 19 --
,~,
;5;~6
A comparison of the I.V., CEG, and MS of both the unmodified and
modified polyethylene terephthalate (PET) is indicated in Table II belou:
TABLE II
_ . _ . ... _ . _ . _ .
Property Unmodified PETModified PET
IV 1.0 1.2
CEG 76 40
~S 4.6 1.1
EXAMPLE III
This Example illustrates the preparation of a bighly branched,
thermoplastic polyester useful in blow molding, using polybutylene tere-
phthalate reacted with triphenylmethane triisocyan-ate.
Forty-nine grams of polybutylene terephthalate having 65 milli-
equivalents of hydroxyl end groups per kilogram are added to a C.W. Brabendar
Rolle type plastograph. The polymer i8 heated to 250 C and when all the
polymer is molten, one gram of triphenylmethane triisocyanate is added.
After seven minutes, the molten polymer is removed and cooled to room temper-
ature.
The modified polybutylene terephthalate is fusible and substantially
thermoplastic and has a melt viscosity of 95,000 poise and a molecular weight
of 46,ooo. The melt viscosity of a polybutylene terephthalate formed in the
same manner without the triphenylmethane triisocyanate branching agent has a
melt viscosity of 1,000 poise and a molecular weight of 44,000.
A comparison of the I.V., CEG and MS of both the unmodified and
modified PLT is indicated in Table III below:
TABLE III
Property Unmodified PBTModified PBT
IV O.gO 1.1
CEG 68 39
5.0 ~.2
_ 20 -
~9~5~
E ~ ~LE IV
This Example illustrates the use of a catalyst (triphenyl pbos-
phine) to increase the rate of the reaction of Example III.
The same procedure as in Example III is employed except that 0.5
grams of triphenyl phosphine are added to the molten polybutylene terephal-
ate at the same -time as the triphenylmethane -triisocyanate. The same re-
sults are obtained in half the reaction time.
EXAMPLE V
This Example illustrates the preparation of a highly branched,
thermoplastic polyester useful in blow molding, by employing polybutylene
terephthalate pellets coated with polyphenylene polyisocyanate.
Forty-nine grams of polybutylene terephthalate having 65 milli-
equivalents of hydroxyl end groups per kilogram are coated with a solution
of polyphenylene polyisocyanate in methylene chloride with the result that,
when the methylene chloride is evaporated, there is provided polybutylene
terephthalate pellets coated with about 1.5 weight percent polyphenylene
polyisocyanate. These coated pellets are treated as in Exarnple III with
similar results.
The polymer melts obtained in accordance with the present invention
have a uniform viscosity of a sufficien-tly high value to be outstandingly
suited for use in fabrication techniques for production of articles, as, for
example, extrusion, particularly blow molding. With the use of tbe melt vis-
cosity increasing additives in accordance with the presen-t invention~ an ex-
cessively rapid increase in viscosity is avoided. Furthermore, the invention
has the additional advantage that the additives used in accordance thereof
are completely compatible with the polymers so that they distribute them-
selves quite uniformly in the melted mass.
The polymers with the increased melt viscosity in accordance with
the present invention may be worked up without difficulty into extruded
shapes of all types, such as tubes or rods, into large blown bodies, as well
- 21 -
/j
~L~96~i3~
as sheets for blow molding, vacuum molding, deep-drawing, ana the like.
The improved melt strength polymers of the present invention have
improved tensile strength, percent elongation, flexural strength, flexural
modulus, tensile modulus, and Rockwell hardness as indicated in Table IV
5 below (the polybutylene terephthalate is modified as in Example III).
TABLE IV
Property (1) Unmodified PBT Modified PBT
Tensile Strength 7400 790G
Percent Elongation 5.9 8.2
Flexural Strength 10,900 13,100
Flexural Modulus 3.72 x 105 4.19 X 105
Tensile Modulus 3.66 x 105 4.21 x 105
Rockwell Hardness-"m" 58 74
. .
(1) As determined on specimens which were injection molded on a 2.5 oz.
:~ Stubbe Screw injection molding machine under the conditions listed in
Table V below:
TABLE V
Nozzle Temperature ( C) 241
Barrel Temperature ( C) 235
Mold Temperature (C) 54
RPM (Screw) 85
Cycle (Seconds) 22
- EXAMPLE VI
The various polyesters formed in Examples I to V are each utilized
in the blow-molding of a 2.2 inch diameter, 3.3 inch high barrel shape aero-
sol container.
Blow molding of melt viscosity increased polyesters is accomplished
by cha-rging -the polymer to a 2.5 inch multi-station rotary blow molder at
241 C, and the pol~ner is processed under the conditions listed in Table VI
~Dg653~
below:
TABLE_VI
Screw (RPM) ~5
Back Pressure (psi) 1600
Blow Pressure (psi) 120
Cornpression Rate 3.5/1
The blow molded articles formed from the polyesters of Examples I
through V which have been modified with a branching agent are well-formed, of
uniform thickness, have high gloss and no pitmarks. The blow molded articles
formed from the various cornparative polyesters of the Examples which are not
modified with the branching agent, however, are not blow moldable and conse-
quently are poorly formed, have nonuniform walls, and are generally rather
rough.
A comparison of the branched modified polyester of the present in-
vention with unmodified (non-branched) polyesters with respect to certain
properties of blow molded articles are given in Table VII below:
TABLE VII
Blow Molded Property Modified Polyester Unmodified Polyester
Wall Thickness uniform variable
Surface Gloss high low
Internal Roughness none poor
Pinch-Off Weld good poor
Pitmarks none many
Shape good poorly defined
The principles, preferred embodiments, and modes of operation of the
present invention have been described in the foregoing specification. The in-
vention which is intended to be protected herein, however, is not to be con-
strued as limited to the particular forms disclosed, since these are to be
regarded as illustrative rather than restrictive. Variations and changes may
be made by those skilled in the art without departing from the spirit of the
invention.
