Note: Descriptions are shown in the official language in which they were submitted.
1tJ~(~3~3
This invention is a composition for sheets,
fllms, coatings, containers or trays comprising a blend
of polyethylene terephthalate (as defined herein) and a
terpolymer of ~thylene, vinyl ester and acrylic or
methacrylic acid.
In the prior art, unmodified polyethylene tere-
phthalate has been used in making shaped and other arti-
cles which utilize its toughness, its formability, its
durability and its chemically and biologically inert
behavior. For some uses, however, such unmodlfled poly~
ethylene terephthalate has properties or deflciencies
which make it unsuitable.
Accordingly, specialized blends have been
developed to meet particular needs. For example, poly-
ethylene terepht.halate with copolymer~ of ~ -oleflns
and vinyl esters have been developed to enhance mechanic~l
properties, such as hardness, lmpact strength, tou~hness
and abrasion reslstance.
According to the present invention, there ls
provided a composition for sheets, films, coatings or
containers comprising a blend of polyethylene tereph-
thalate wlth a polymeric additive that ls malnly but no~
entirely based on ethylene, characterized in that the
blend includes, by weight, 99 to 95% polyethylene tereph-
I thalate and 1 to 5% of a terpolymer of at least 65% ethy-
¦ lene wlth (a) at least 5% of a vinyl ester of
a 1-6 carbon saturated monobasic aliphatlc carboxylic
acld and (b) 0.1 to 10% of acrylic and/or methacrylic
~cl~. It iB prcferred to uee 3% of the terpolymer.
Preferred vinyl esters are the vinyl esters of 1 to 4
- 2 -
~.
,
., .,.,
1040338
car~on saturated monobaslc aliphatic carboxylic acids,
especially vinyl acetate; preferred quantity of vinyl
ester in the terpolymer is at least 12~, especially 20
to 30%. Preferred quantity of acrylic or methacrylic
acid in the terpol~-mer is 0.5% to 7%, especially ~.5%
to 3%. The most preferred terpolymer consists of 72%
ethylene, 27% vlnyl acetate and 1% methacrylic acid.
Sheets made from the polyethylene terephthalate/
terpolymer blends of this invention have been round to
be particularly useful for making thermoformed trays of
greater toughness and with greater freedom from embrittle-
ment or sagging after heating, at temperatures up to
, about 200C., for example, as compared to trays of un-
modlfied polyethylene terephthalate or of polyethylene
terephthalate with prevlously used modifiers. Other
beneflts which arise from these sheets as used ln thermo-
formed structures or trays include more rapld crystalli-
zatlon, providing better form stability in newly-formed
structures, as well as improved mold release and forming
properties. Further, we have found that trays made
uslng sheets of such polyethylene terephthalate/terpolymer
blends may be formed in known vacuum thermoforming equip-
ment at a reduced cycle time, as compared to trays made
using sheets of known blends or of unmodified polyethylene
terephthalate.
The requirements for a satisfactory, versatile
tray are that it should permit cooking of its contents
up to about 200C., and should have thermal stability
and not become too brittle or be prone to cracking upon
heating. Further, it should not become distorted upon
heatlng.
_ 3 _
lQ4~33~3
Previou~ly lt ha~ been the practlce to rorm
tray~ of heat-~ealable polymer~, ~uch a~ vlnyl~ ~nd
olefln~, to facllltate ~ecurlng lld~ thereon, but these
iln general do not po~se~-the thermal ~tablllty requlred
for reheatlng ~ood~. Formed tray~ of alumlnum foll have
been employed, but these lack verJatlllty ln that they
are unJultable ~or u~e ln mlcrowave oven~, for example,
Compo~itlonJ accordlng to the pre~ent lnventlon
have been found u~eful ln the form of cooklng contalnerJ
or tray~ for packaglng rood and for Jub~equent cooklng
and reheatlng Or rood,.
Terpolymer~ wlthln the ~cope of tho~e userul
ln the pre~ent lnventlon lnclude tho~e de~crlbed ln
detall ln U.S. Patent 3 215 678 to Adelman et al. The
degree o~ improvement in propertle~ obtalned by thlJ
lnventlon appear~ to be relatlvely ln~en~ltlve to
varlatlon Or the melt lndex o~ the terpolymer u~ed ln
thl~ lnventlon.
Polyethylene terephthalate whlch can be u~ed ln
the blend of thl~ lnventlon lnclude~ (a~ polymer~ whereln
at lea~t 97~ o~ the polymer contaln~ the repeatlng ethyle~e
terephthalate unlt~ Or the rormula:
i. O O
-0CH2CH20C ~
wlth the remalnder belng mlnor amount~ of e~ter-rormlng
component~, and (b~ copolymer~ o~ ethylene terephthalate
whereln up to 10 mole percent o~ the copolymer 1~ pre-
pared from the monomer unlt~ o~ dlethylene glycol; pro-
pane-1,3-dlol; butane-1,4-diol; polytetramethylene glycol;
polyethylene glycol; polypropylene glycol; 1,4-hydroxy-
i 30 methylcyclohexane; and the llke, ~ub~tltuted for the
,~ ,
1 ~1 --4--
,,
~. ,
1()4V338
glycol molety in the preparation of the copolymer and/or
l~ophthallc; blbenzoic; naphthalene 1,4- or 2,6-dlcarboxyllc;
adlplc; sebacic; decane-l,lO-dicarboxylic acid; and the like,
- substituted for the acid moiety in the preparation of the
copolymer.
Specific limits on the amount of comonomer are
governed by the polymer glass transltion temperature since
lt has been fou~d that copolymers havlng a glass transl-
tlon temperatu~e below about 50C. generally have reduced
mechanical properties. Thls generally corresponds to the
additlon of no more than 10 mole percent comonomer. One
exceptlon to thls ls the additlon of blbenzolc acld where
,
the copolymer ~lass transltlon temperature remalns above
50~C. even when the copolymer contalns more than 10 mole
percent blbenzoic acid. Other exceptlons will be obvlous
to the artlsan. alass transitlon temperature~ are a~
determined using standard differentlal scannlng calorl-
metry technlques.
l In the compositlons of thls lnventlon the poly-
¦ 2~ ethylene terephthalate may contaln from 0.1 to 1.5% by
weight of afinely divided inert mineral solld ~ubstance,
or a nucleating agent. Calcium carbonate, aluminum
~lllcates and talc are examples of sultable nucleatlng
agents. If deslred, the polyethylene terephthalate may
contaln a nucleating agent and opaclfylng agent, 8uch as
tltanlum dloxlde. Preferably, the polyethylene tereph-
thalate contalns 1% talc and 1.5% tltanlum dloxlde. The
inherent viscosity of the blend composltion preferably ls
,
from 0.70 to 0.95 and for a shaped article therefrom,
~; 30 inherent viscosity preferably is from 0.65 tc 0.85.
: . .
. ~
, .. . . . . .
()338
used herein, inherent vlsco~lty i8 b~ed on
1% concentration of polymer ln a 75/25 welght percent
~olutlon of trlfluoroacetlc acld/methylene chlorlde,
respectively, at 30C. and i8 computed uslng the formula
n~tur~l log (vl~co~lty of ~olution)
Inherent Vl~co~lty = viscosity o~ ~olvent
where C i8 the concentratlon ~xpre~ed ln grams oi poly-
mer per lO0 milllllterJ of ~olution.
In preparlng the compo~ltion~ o~ the pre~ant
lnvention, the component~ ~hould be pre-dried at tempera-
ture~ and pre~ures such a8 to obtain maximum drying
whlle avoldlng agglom¢ratlon. They may be blended by
meterlng the indlvldual ~tream~ lnto a ~lngle or twin
~crew extruder ~hlch serve~ to melt and mix the components,
The blend, thus mlxed and melted, may then be extruded by
known method~.
Sheet~, lncludlng ca~t amorphou~ ~heet~, or
fllm~ made from the blend~ o~ the ln~tant inventlon may
be prepared by kno~n ~methods and devlce~, e.g., as ln
U.S. Patent 2 823 421 to ~carlett,
~ny number Or thermoformlng method~ and devlce~
may be u~ed whereln a ~heet, sultably clamped, 1~ drawn
or pu~hed lnto a mold u~lng the vacuum whereby ~uch ~heet
take~ the ~hape o~ the lnner ~urrace Or the mold whlch lt
; 1~ brought lnto contact wlth to form the molded artlcle
or contalner. The method~ may lnclude (l) stralght
i,! vacuum formlng (2~ drape formlng (3~ match-mold formlng
(4) ~llp-ring formlng (5~ plug-assl~t vacuum formlng
(6~ plug-a~slst pressure formlng (7~ ~nap-vacuum forming
` .
--6--
, ~
1~3'~ 3~
, . . .
(8~ blllo~ rormlng (9~ trapped-~heet, contact-heat pre~-
- ~ure rormlng and (10~ preheat, plug-a~cl~t pre~ure ~orm-
'.f' ' lng,
Mean~ and dctail~ ror Juch thermo~ormlng may be
` found ln copendlng Canadlan Patent ~ppllcatlon 193 039, ~ led
February 20, 1974.
, Improvement~ brought abcut by the ln~tant lnve-
ntlon may be note~ by rererrlng to the rollo~lng T~ble I:
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--8--
. 1~14~3338
; The drawing i9 a graph comparing impact strengths
of sheets made from a polyethylene terephthalate/terpolymer
blend of thls lnvention with ~heets made from a polyethylene
terephthalate/cop~lymer blend at various lnherent visc~sities,
, The polyethylene terephthalate/terpolymer blend
sheets tested contained 96~ polyethylene terephthalate
and 3% of the terpolymer which consisted of 72% ethylene,
27% vinyl acetate, and 1% methacrylic acid, while the poly-
ethylene terephthalate/copolymer blend sheets contained
96% polyethylene terephthalate and 3% of the copolymer
which consisted of 72~ ethylene and 28~ vinyl acetate,
Both the polyethylene terephthalate/terpolymer and poly-
ethylene terephthalate/copolymer blends contained 1
talc,
In making the sheets tested, the polyethylene
terephthalate/terpolymer and polyethylene terephthalate/
copolymer blends were extruded onto a co~led surface,
after whlch the a~orphous sheets formed thereby were
strlpped from the sur~ace, These sheets were then brought
lnto contact with a heated surface and crystallized at
150C for 100 seconds, Such sheets, after crystalliza-
tlon, were then tested at room temperature using a Gardner
impact tester, The results of these tests appear in the
graph whlch clearly shows the lmprovements ln impact
strengths brought about by the instant invention,
The following Example and Table II also show
tray forming and tray durability improvements brought
about by this inventlon,
Example
SAmple~ o~ polyethylene terephthalRte ~ere
~)4()338
blended ~ith a terpolymer Or 72~ ethylene, 27~ vlnyl
acetate and 1% methacryllc acid and compared to poly-
ethylene terephthalate samples blended wlth a copolymer
of 72% ethylene and 28% vinyl acetate with respect to
tray formability ar.d durability after oven heating.
All samples contained 96% polyethylene terephthalate,
3% of the terpolymer or copolymer, and 1% talc, all
by weight based on the total weight of the blend.
The samples were prepared from carefully drled
components, melt blended in a screw extruder and cast
onto a cooled quench roll to form amorphous sheets. The
amorphous sheets, ranging in thickness from 325 to 450
microns, were evaluated for formabillty by preheatlng the
~heet from 8 to 10 seconds to a temperature from 90 to
100C., and formlng ln a heated vacuum rormlng mold.
Mold cycle tlmes and mold temperatures varled as ~hown
ln Table II.
Formabillty, or moldlng quallty, lncludlng con-
formatlon to the mold cavity, the unirormlty Or the llp
Or the formed tray, and the ease Or mold release were
evaluated with results as shown ln Table II.
The perrormance Or the rormed tray wlt~, respect
to toughness or brlttleness (l.e., durablllty) were evalu-
ated after oven heating for 15 mlnutes at 200C., wlth
results also as shown in Table II.
In thls durablllty evaluatlon the trays were
licked wlth a flnger after such oven heatlng and coollng
to room temperature and, as Table II shows, trays formed
from sheets of polyethylene terephthalate blended wlth the
terpolymer were "tough" and undamaged whlle trays Or sheets
made using the copolymer were 80 "brlttle" they shattered
at the point of impact.
-- 10 --
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--12--
