Note: Descriptions are shown in the official language in which they were submitted.
BA~KGROUND OF THE INVENTION
It is known that certain plastic materials have found
some application in the ovenware field. For e~ample, polymethyl-
pentene has been used for injection molded trays which can be used
in the preparation of foods. Polysulfone has also been employed
in food handling applications. However, no satisfactory material
has been found possessing utility over the wide ranges of condi-
tions and of demands which are encountered in the provision of
cook-in containers, or ovenware, which can be used in either
thermal ovens or microwave ovens.
In addition to the obvious necessity for a material
which can withstand the temperatures met in the heat source used
for cooking, a material must provide a unique combination of a
number of other characteristics before ovenware fabricated from
the material can be successfully employed in the preparation of
food. The material must have good electrical properties. It must
be able to undergo severe thermal shocks in that ovenware prepared
from it must be capable of going from conditions of extreme cold
to high temperatures in relatively brief periods of time. The
material must have good hardness and impact strength and possess
high tensile and flexural trength. It must also be resistant to
boiling water and to ad~erse e~fects from immersion in detergents.
In the area of food related properties the material
must impart to the ovenware fabricated from it resistance to
staining by a wide variety of foodstuffs. It must provide a
surface affording good antistick properties, ready releasability
for the food which it contains. It must not emit or give off any
volatile matter and it must not have any extractable constituent~
And in addition to meeting all of the foregoing requirernents,
articles prepared from it must present a pleasing appearance~
'iS ;r
SUMMARY OF THE PRESENT INVENTION
Ovenware meeting the stringent demands of the cook-in
container market is provided by fabrica~ing the ovenware articles
from a plastic material based upon wholly aromatic polyesters,
more particularly, upon oxybenzoyl polyesters.
The wholly aromatic polyesters employed in accordance
with the present invention consist of combinations of repeating
units of one or more of the following formulae:
~ ~X~n ~/ c __oc~3 (Xln ~ ~\ co~
P--q
I II
10 ~ ~ ~X)n ~ ~ ~ ~ ~ co -
- - r - - s
III IV
oc ~ ~ co _o ~3 o
t u
O VI
where x is O, S,~c-, NH, or SO2
and n is o or 1 and the total of the integers p+q+r~stt~u,
in the moieties present is from about 3 to about 800.
Combinations of the above units include union of the
carbonyl group of Formulae I, II, IV and V with the oxy group
of Fo.rmulae I/ III, IV and VI. In the most general combi.nation
all units of the above formulae can be present in a single co-
polymer. The simplest embodiment would be homopolymers of units
I or IVo Other combinations include mixtures of unlts Il and III,
II and VI, III and V, V and VI, and I and IY.
The location of the functional groups are preferably
in the parar (l,4~ positions. They can also be located in ortho
(l,2) position to each other. With respect -to the napthalene
moiety the most desirable locations of the functional groups are
l,4; l~5 and 2,6. Such groups can also be in the ortho position
to each other.
The symbols p, q, r, s, t and u are integers and
indicate the number of moieties present in -the polymer. The total
(p+q+r+s~t~u) can vary from 30-~00 and, when present, the ratio
of q/r, q/u, t/r, t/u, q~t/r. q+t/r+u and t/r+u can vary from
about lO/ll to about ll/lO with most prefèrable ratio being lO/lO.
Exemplary of materials from which the moieties of
Formula I may be obtained are p-hydroxybenzoic acid, phenyl-p-
hydroxybenzoate, p-acetoxybenzoic acid and isobutyl-p-acetoxy-
benzoate. Those from which the moie~y of Formula II is derivableinclude terephthalic acid, isophthalic acid, diphenyl tere~
phthalate, diethyl isophthalate, methylethyl terephthalate and
the isobutyl half ester of terephthalic acid. Among the compounds
from which the moiety of Formula III results are p,p'-bisphenol;
p,p'-oxybisphenol; 4,4'-dihydroxybenzophenone; resorcinol, and
hydro~uinone. Inspection will show which of these materials are
also suitable for supplyiny the moieties of Formulas VI-VIII.
Example of monomers represented by Formula IV are
6-hydroxy-l-naphthoic acid, 5-acetoxy-l-napthoic acid and phenyl
5-hydroxy-l-naphthoate. Monomers representing ~ormula V include
l,4-napthalenedicarboxylic acid, l,5-napthalenedicarboxylic acid
and 2,6-napthalenedicarboxylic acid. The diphenyl esters or
dicarbonyl chlorides of these acids can also be used. Examples
of monomers representative of Formula VI are, l,4~dihydroxy~
naphthalene, 2,6-diacetoxynaphthalene, and 1,5-dihydroxynaphtha-
lene.
Particularly preferred for use in the practice of the
present invention are plastic materials based upon oxybenzoyl
polyesters.
The oxybenzoyl polyesters useful in the present
invention are generally those repeating units of Formula VI:.
O ~= C ~
where p is an integer of from about 3 to about 600.
One preferred class of oxybenzoyl polyesters are those
of Formula VII:
(VII)
._
Rl o ~) 11 ~ o~2
P
wherein Rl is a member selected from the group consisting of
benzoyl, lower alkanoyl, or preferably hydrogen, wherein R2 is
hydrogen, henzyl, lower alkyl, or preferably phenyl and p is an
integer from 3 to 600 and preferably 30 to 200. These values of
~ correspond to a molecular weight of about 1,000 to 72,000 and
preferably 3,500 to 25,000.
Another preferred class of oxybenzoyl polyesters are
copolyesters of recurring units of Formulas VII, VIII and IX:
(VIII) o ~ o
~C - I J C
_ ~ q
__ _
(IX) _ o ~ ( (X) ~ ~ O
n _ r
wherein X is - O or - SO2 - m is 0 or 1: n is 0 or 1: q:r =
10:15 to 15:10; p:q = 1:100 to 100:1; p + q -~ r = 3 to 600 and
preferably 20 to 200. The carbonyl groups of the moiety of
Formula I or III are linked to the oxy groups of a moiety of
Formula I or IV; the oxy groups of the moiety of Formula I or IV
are linked to the carbonyl groups of the moiety of Formula I or
III.
The preferred copolyesters are those of recurring units
of Formula X;
(X) ~
C ~ C-O ~C -O ~ ~ O
The synthesis of these polyesters is described in detail
in U.S. Paten-t 3,637~595 entitled "P-Oxybenzoyl Copolyesters".
The polyesters useful in the present invention can also
be chemically modified by various means such as by inclusion in
the ~olyester of monofunctional reactant~ such as benZoic acid or
tri - or hi~her functional reactant5 such as trlmesic acid o~
cyanuric chloride. The benzene ring3 in the~e polyeste~s a~e p~~
ferably unsubstitu~ed ~ut can be substituted with non~interferrin~
substituen~.s,examples of which include among othe~ halogen ~uch
as chlorine or bromine, lower alkoxy such a.s methoxy and low~
alkyl such as methyl.
The oxybenzoyl polyesters useful in the present invention
can be employed with various fillers of types and in amounts which
do no-t ma~erially affect -th desired properties. ~xamples of
suitable fillers include among others glass fibers,polytetra-
fluoroethylene, pigments,fillers and polyimides.
The invention is further illustrated by the following
examples in which all parts and percen~ages are by weight unless
otherwise indicated. These nonlimi~ing examples are illustrative
of certain embodiments designed to teach those skilled in th~ art
how to practice the invention and to represent the best mode
contemplated for carrying out the inven-tion.
EXAMPLE I
250 ~ of a mixture consisting of 40~ o-terphenyl and
60~ m-terphenyl i5 ~harged il~tO a four-neclced, round bottom flask
fitted with a stirrer, a nitrogen inlet, a thermometer and a dis-
tilling head leading to a condenser. The distilling head is ex-
ternally wound with electrical resistance heating wire in order
that it may ~e heated and a hea~ing mantle is provided ~o heat the
f~ask and its contentsO Tl~e contents of the flask are melted by
heating to dbout 60C.~ whereupon 68 g of ~acetoxybenzoic acid
are added with stirring. ~`he entire condensation is carried out
with constant stirring and with a slow flow of nitroyen through the
flask to provide a non-oxidizing atmosphere. The distilling head
is heated to about 120C and the mixture in the flask is heated
to about 340C, polyester preci~itation startinc3 to occur at
about 3P0C. The distilling head ~emperature is then raised ~o
about 18QC to avoid refluxing of the distillata and/ox ~olid~
ification thereof in the distilling head, and the mixtu~ th~
flask is held at about 340~C for about 12 hour~. A total O~
25.5 g of distillate is collected, consisting primarily ~f aCetic
acid, the remainder being primarily terphenyl liquid heat t~ans~er
medium. It is observed tha-t 25 g of this distillate are coll~cted
within 35 minutes after the temperature of 340C h~ bee~ reached,
indicating that the polym~ri2ation is already approaching com-
pletion within this time.
The resulting mix~ure is cooled to 80~, becoming qui-te
viscous. ~out 200 ml of acetone are added slowing and ~he mixture
is filtered to recover the polyester precipitate. The polyester
is extracted overnight with acetone in a Soxhlet extractor to
remove any residual ter~henyl liquid hea~ transfer medium and is
then dried in vacuu~ for 3 hours at 110C. A yield of 43 g (96%
of theory) of p-oxybenzoyl polyester powder is obtained.
~he product was infusible and upon being held at 400C
in air it exhibited a weight loss of only 0.83~ per hour. Differ-
ential thermal analysi~ revealed an endotherm, during heatinc~, at
329-343C, with a peak at 336C and a corresponding exo~herm ~urinc~
cooling, evidencing a reversible crystalline tran~ition, ~hi~
~eve~sible tran~ition was also evidenced by a marked change ~hich
occurred in the X-ray ~owder diffraction pattern u~on heating the
product to about 340C, the original ~attern ~ein~ resumed upon
coolill~J.
In the X-ray ~owder diffraction pattern of the product
at roon~ temperature, usincJ monochromatic co~per K alpha radiation,
the large numbe.r and the sharpness of the diffrac-tion lines indi-
cates that the polyes~er is hi~hly crystalline.
The use of a liquld heat transfer.medium is esserltial
to the method employed. *he liquid must be inert, i.e it mu~t ~e
non-reactive with the p-acetoxybenzoic acid monomer and th~ conden-
sation products ther~of under the condition~ ~mployed. ~h~ liq~id
must also be high boiling, having a boiling point unde~ th~ condi-
tions employed which is at least as high a~ the hig~e~t temp~tu~
to which the reaction mixture iB heated, and convenl~ntly ~mewhat
higher so that refluxing may be avoided. It will be appa~ent ~ha$
the heat transfer medium need no~ be liquid at room tempe~ature,
but it should preferably have a melting point below that o~ the
monomer (about 180C). A wide variety of materials has ~een found
to be suitable as liquid hea~ transfer media including, for example
o-terphenyl, m-terphenyl, p-terphenyl and mixtures oE two or msre
thereof 5uch dS employed in the example; partially hydrogenated
terphenyls SUc}l as th~se commercially available under ~he trade
mark Therminol~ 66; and a eutectic mixture of 73O5% diphenyl oxide
and 26.5% dip}lenyl suc}l as that which is co~nercially available as
~owthermR A heat tr~nsfer medium. O~her suitable liquid heat
ransfer media include diphenoxybip}lenyls and mixtures thereof
uch as those disclosed in U. S. Pat. 3,406,207-
--3--
~X~MPI.E 2
This example illustrates the synthesis of a copolyesteruseful in the present invention.
The following quantities of the following ingredients
are combined as indicated.
Quantity
I~em Ingredient Grams Moles
A P-hydroxybenzoic Acid 138
B Phenyl acetate 170 1.25
C Therminol 77 500 __
D Diphenyl Terephthalate 318
E llydrogen Chloride
F ~3ydroquinone 111 1.~1
G Therminol 77 500 --
Items A - D are char~3ed to a four-necked, round bottom
flask fitted with a ~hermometer, a stirrer, a combined ni-trogen
and HCl inlet ~nd an outlet connected to a condenser. Nitrogen is
passed slowly through the inlet. The flask and its contents are
heated to 180C whereupon ~Cl is bubbl~d through the reaction mi~-
ture. The outlet head t~mperature i5 kept at 110 - 120C by
external heating during the p-hydroxy~enzoic acid, phenyl acetate
ester exchange reaction.
The flask and its contents are stirred a-t 180C ior
6 hours whereupon the HCl is shut off, the outlet head tempe~ature
rai~ed to 180 - 190C and the nlixture ~ irred at 220C for 3,5
hGurs. Up to this point, 159 grams of dis~illate are collected in
the ~ondenser. Item F is then added and the temperature gradually
increased from 220C to 320C over a period of 10 hours ~10C/hr)~
~tirring is continu~d at 320C or 16 hours and then for three
additional hours at 340C to form a slurry~ The total amount o~
distillate, consisting of phenol, acetic acid and phenyl acetate,
amounts to 384 g. Item G is added and the r~acti~n mixture per-
5 mitted to cool to 70C. Acetone (750 ml~ is added and the slurryfiltered, the solids are extrac~ed in a Soxhlet with acetone to
remove i~ems C and ~. The solids are dried in vacuo at 110C
overnight wher~upon the resultant copolyester 1320 y/ 89.2 percent
of theory) is ~ecoYered ~ a granular powder.
The oxybenzoyl polyesters~ discussed generally in the
earlier part o~ thi~ specification and specifically illust~ated
in Examples 1 to 5, can be molded according to conventional
techniques to p.roduce the ovenware articles of the present inve~-
tion. Additives ~uch a~ are conventionally employed in moldi~
compositions can be incorporated p~ior to mo~ding ~or th~ir ~co~
nized purpose. UnSo Pat~. No. 3,884,876 and 399~0~7~9 di~cl~emolding procedures for oxybenzoyl polye~ers Which CDUld be a~aPted
for the fabrication of ovenware.
EXAMPLE 3
20 518 parts of isophthallc acid, 1,557 ~)arts of tereph-
thalic acid, 5,175 parts of para-hydroxybenzoic acid, 6,885 parts
of acetic anhydride and 2,325 ~arts of p,p'-bis~)henol are mixed
together and refluxed ~or 17 hours, dt a temperatllre of about 180
C, after which the reflux condenqer is replaced with a distilling
head and the temperature is raised to 345C over a period of 1 and
1/4 hours. The reaction mixture is stirred ~hroughout the heatin~
period, being particularly actlvely mixed during the period in
--10--
which the temperature is being raise~ to 345C. I'h~ yield of
polyn~er is 8,020 parts and 8,010 parts of distillate are recovered.
The contents of the reaction vessel are removed, cooled and ground
to pa~ticle si~es in the 20 to 160 mesh range, U~S. Standard Sieve
S Seri~S. ~he resin made is of a molecular weight in -the 5,030 -
20,000 rang , with an average weight in about the middle of Ruch
range. The product is estimated to b~ about 50% crystalline.
~ he resin particles are held unde~ vacuum illu~ra~ively
at an elevatPd tempexature ak an absolute pres~ure of abou~ 100 mm
10 o;f mercury for eigh~ hs:~urs and recove:re~ a~ a ~:rarlula~ powde~ .
EXAMPLE 4
The following quantities of the following ingredi0nt~
are comhined as indicated.
Quantity
It~m Ingrèdient ~rams Moles
A Terephthalic Acid 291 1.75
B P-Hydroxybe~zoic Acid 483 3.50
C p,p'-biphenol 325 1~75
D Acetic Anhydride 755 7.40
Items.A~D are heated to 145C and refluxed overnight.
The reflux conden~er is removed an~ a distilling head put i~ placeO
The mixture is heated with stirring at a rate of 20C/hour t~
300C and the contents oE the reac~or removed. ~t ~hi~ point about
92-94~ of the theoretical ace~ic aci~ i8 collec~ed. The pr~p~lyme~
is ground up and advanced as in Example 3. employing a tempe~ature
of about 250-350C.
EXAMPL~ 5
~uantity
Item Ingredient Grams Moles
A p~ droxybenæoic Acid 276. (2.00)
B Terephthaloyl Chloride 203 l.0
C Trimesic Acid 8~4 0.040
D Therminol 66 1274
E p,p'-~iphenol 186 l.0
F Acetic Anhydride 224.6 2.2
Items A-~ are heated to 130C and h~ld one hou~, Th~
reaction is exothermic and care i5 ~a~en to maintain t~mperature
at 130C. The contents are then he~ted at 155C for one hour and
180C f or 4 hours . The mixture is then cooled to 150C and item
E added whereby the temperature is ~urther reduced to 140C. Item
:IS F is then added. ~his Inixture is then refluxed one hour at 155C
ancl t:he reflux condenser replaced by ~ di~tlllation cQl~nn. While
distilling the ac~ic acid formed, the contents of the reactor are
heated to 3~0C and h~l~ 3 hours. Tlle suspended polymer is cooled
to 250C and the mix-ture passed th~ou~Jh a filter. The solid m~ter-
ial is work~d with trichloroethylene to remove the heat transferfluid. The dried Jowder is advancPd further in vacuum as in
Example 3.
In order to demonstrate the un.ique suitabllity of oxy-
bPn~oyl polyester~ for ~he fabrication of ovenware, -~h~ ~ollowin~
tests were carri~d out on various ltems of pla~tlc ove~wa~e~ such
as bowls, cups, etcO0 which we~e ~abricated from oxy~enæoyl poly-
esters, polysulfone, polybutylene terephthal~te, polyp~opylene
polycarbonate alld a therrno~et polyester.
-12~
EXAM~L~ 6
q'hermal (Electric) Oven "No Load" Test
~he plastic article was placed in a glass container on
the sh~lf 5 1/~ inches from bottom of the oven. The oven ~empera-
ture was s~t and the ov~n allowed to heat up from room temperature.
The plastic article was allowed to ~tay 1/2 hour in the oven or to
failure, if sooner.
~he following results were ~oted. A cup cut ~rom a
muffin pan fabricated from a thermoset polyester resin emitted an
odor within 15 minutes and began to smoke in 30 minu~es at an oven
ternperature of 410F. A 2-inch strip cut from a bacon tray
fabricated from a polysulfone resin softened in 15 minute3 and
became totally distorted at an oven temperature of 410Fo
2-inch strip from a roasting tray fabricated from a ~olycarbona~e
resin softened, sagged and became totally distorted in 1~ minutes
at an oven tem~erature ~f 410F. ~ bowl made fxom polypr~pylene
resin melted flat within 10 rninutes at an oven temperature of
410F. A casserole dish fabrlca~ed ~rom polybu~ylene terephthalate
~egan to smoke in 5 n~inutes and emitted detectable odor but did
not become distorted in 30 nlislutes at a temperature of 410~. A
bowl fa~ricated from an oxyb~nzoyl polyester, in accordance with
the present invelltion, showed no sign of damage after 1 hour at
an oven temperature of 500~
EXA~IPLE 7
Microwave Oven - "No I.oad" Test
In conducting this test, the plas-tic object was placed
in ~he center of the rnicrowav~ oven directly on the gLass tray.
The plastic article was hea~ed at full power for 20 minut2s or to
failure, if sooner.
The followlng results were noted. A cup cut from a
muf~in ~an fabricated from a filled thermo5et polyester emitted
a sligh~ odor wi~hin 17 minutes, but otherwise showed no sign 4f
damage. A 9-~nch cake pan fdbric~ted from polypropylene ~how~d
no damage other than a ~oftening O~ the bottom where the rim con
tacted the hot glasq tray. A cup cut from a muffin pan fabricate~
from poly~utylene terephthalate had a hole burned in the 8ide and
bottom within 11 minute~ roastin~ rack fabricated f~om
polycarbonate resin showed a di~torted ~p~t, 1 inch in diameter i~
the middle of the rack. A bacon roaster ~abricated ~om ~ poly-
sulfone udel resin ~howed no damage O~ any kind. A ~owl ~abrlc-
ated from a clear polysulfone udel ~esin exhibited a di~coloration
within the surface at the bottom of the bowl. A bowl ~abr~cated
from an oxybenzoyl polyester showed no sign of damag~ of any kind.
EXAMPLE 3
Oil Resistance - Microwave Oven Test
In conducting this test, a layer of Wesson oil was
poured in the plastic vesselO The vessel was centered on the
glass tray in the microwave oven. After varying periods at high
power, the vessel was removed and examined.
The following resul~s were noted~ ~ bowl fabricated
from a polypropylene resin showed s~reaking below ~he oil line
within 6 minutes (severe at 9 minutes). After washing these were
shown to be blister~ which readily peeled away in ~lbrous ~txands
A bowl f~brica~ed from a polysulfone resin exhibited s ~eaking
below the oil within 6 minute~ whirh wa~ readily seen. ~ter
washing, blister~, cracks and a "~u~n" ~pot in ~he bottom o~ the
howl were observed. A cup cut from a muffin pan ~ab~icat~d ~o~
polybutylene terephthalate at 5 mi~tes' exposure showed the ~ide
3~ wall at its juncti.on wi~h the bo~tom bursting and allowing
oil to flow o~t. A slight darkening ~elow the oll was re5istant
to soap and water. A bowl fabricated from an oxybenzoyl polyester
exhibited no observable damage after 20 minutes. The bowl washed
clean without stain.
EXAMPLE 9
Freezer To Oven-Thawing-Warming Test
In carrying out this test the plastic containers were
loaded with approximately 100 g of Chili (Shop-Ri~e~ canned chili
con carne~ and frozen overnight in the freezer section of a
refrigerator. The plastic containers were then placed in a tray
in a 425F preheated oven and allowed to remain until the contents
were bubbling. If the container failed, it was removed sooner.
The following results were noted. A bowl fabricated
from a polypropylene resin had melted to the level of the food
after 8 minutes. No thawing had taken place. A bowl fabricated
from a polysulfone resin after 27 minutes had a distortion at
the lip. At 33 minutes the bowl was soft and distorted. The food
was warm, not hot. The bowl cleaned well with no staining. A
cook pan fabricated from polybutylene terephthalate had distorted
sides after 12 minutes. At 20 minutes the article was cornpletely
out of shape and the food was not warm. The pan was fairly easy
to clean but showed slight staining. A cook pan fabricated from
a thermoset polyester took 35 minutes' time to heat the food. The
pan was hard to clean. There was a slight stain. A bowl fabricated
from an oxybenzoyl polyester showed no damage after 40 minutes to
bubbling. The bowl cleaned easily with no staining.
EXAMPLE 10
Stain And After-Odor Test (Barbecue Sauce)
In conducting this test barbecue sauce (Kraft) was
placed in a 1/2 inch layer on the bottom of the plastic containerO
The container was then placed in a 400F preheated oven for 1/2
hour. At this time the sauce was thick, dark, and crusty. After
cooling the container was washed with soap and water using a
Dobie pad. The container was examined for a stain line and was
.~.
4~
judged to be stained i~ 15 minutes ~urther washing could no
remove evidence of the stain. The container wa~ then returnea
to the oven for 15 minu~e~, removed and smelled while hot~ any
unusual odor was noted.
s The follow.ing r~sults were noted. A cup cut ~rom a
mu~fin pan ~abricat~d from a thermo~et polyester exhibit~d a
severe yellow stain. ~n after~odor of barbecue sauce wa~ detected.
A cup cu~ ~rom a ~uffin pan fabricated ~rom polybutylene
terephthalate exhi~ited a severe yellow stain. An after-odor was
present, although no~ identified, which could be polymer. A bowl
fabricated from a polysuLfone resin emitted a slight deteetable
odor. A bowl fabricate.l from an oxybenzoyl polye~ter showed no
stain nor after-odor.
The polyes~er Ltems employed in the tests ~et forth in
Examples 6 to 10 wexe fal)ricat~d from the polyester o~ Exampl~ 3.
Similar tests ~arr.i~d out on the items ~abricat~d from
~he polyesters of Examples 1l 2, 4 and 5 gave compa~abl~ ~xcellent
results.
-16-
