Note: Descriptions are shown in the official language in which they were submitted.
- P~ 26752
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~his in~ention rel~te~ to polyester production
and in particular to the production o~ linear aromatic
polyesters.
Such polyesters are normally produced by first
forming ~ monomeric ester b~ esterification of an
aromatic carboxylic acid, e~g. terep~thalic acid, with a
gl~col (so called direct esterification) or an ester
` interch nge reaction by reacting a glycol with a dialkyl
ester o~ ~he acid, e.g. dimethyl te~ephthalate. ~he
"mo~omer",e.g. bis(~-hydrox~ alkyl) terephthalate,is
then polyconde~ed. ~he prese~t inventio~ is concer~ed
with the direct esterificatio~ process.
The pol~condensatio~ reaction is normally conducted
in the prese~ce o~ a catalyst such as a germanium or an
`1 15 antimon~ compou~d.
Germanium compounds~are particularly useful as
~; they generally give polyester6 of improved colour
compared with the use of antimon~ compounds but it has
, :
been foun~ that the use of a combination of germa~ium
a~d ant~mo~ compounds give p~rticularly good polyesters.
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Ger~a~ium dioxide i8 the most commonl~ used
germanium catalyst but the most readil~ obtainable
.
form thereo~, viz hexagonal crystalline~germanium
, : ~
dioxide,is only poorly soluble in the reaction medium.
Various methods have been proposed ~or improving its
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solubility and, in particular, it has been proposed, in British Patent 1,197,
004, to make an alkaline solution of the crystalline germanium dioxide in a
glycol. :
In the direct esterification process it is conventional practice to
utilise a base, such as sodium hydroxide, as a softening point stabiliser :
(see British Patent 782,036).
We have found that if the alkaline germanium dioxide/glycol solution :
is present during the esterification process, polyesters of enhanced softening
;; point and improved colour are obtained compared with processes wherein simply
10 a base is used as a softening point stabiliser and the germanium dioxide solu- :.
tion is added after the esterification process has taken place. ;;
. Accordi.ngly we provide a process for the production of polyethylene
` terephthalate which comp~ises: ta) esterifying terephthalic acid with ethy- ~ .
- lene glycol at an elevated temperature; and ~b) polycondenslng the product of :
. ~a}, without isolation, under reduced pressure and ln the presence of antimony
trioxide in amount 100 to 1000 parts per million by weight of the terephthalic
.
. acid originally present; step ~a) being carried out in the presence of a ~:
~ solution of germanium dioxide in alkal~i metal hydroxide and ethylene glycol~
,; , ~ the amount of germanium dioxide being 10 to 200 parts per~million by welght
based on the amount of terephthalic acid present at the start of the reaction
and the amount of the~alkali metal hydroxide being: ~i) greater than the equi-
' ~ ~:: valent per mole of germanium dioxide; (ii) greater~than 0.5 gram equivalents
.:`, per million grams of the dicarboxylic acid~ and (iii) less than the greater -~ .
,' ;.~ ':'.:'
. 1 o twice the equivalent per mole of germanlum dioxide and 2,5 gram equivalents : -~
,", ~ . . ,
: per million grams of~the dicarboxylic:acid. : ~
In a preferred~embodiment~ there lS provided a process for the produc- .:
: tlon of~polyethylene~terephthalate which comprlses: ~a~ esterifying terephtha- ..
lic acid:~with ethylene glycol at an~elevated temperature; ~b) polycondensing ~ ; :
the product of ~a), without lsolation, under reduced pressure and in the pre~
30~ sence of~antimony trloxide in :amount~100 to 1000 parts per million by weight
of the terephthallc acid originally present; step ~a) being carried out in the .. :
pre:sence of a solutlon o~ germanium dioxide in sodium hydroxide and ethylene
~ :. l :
~ 76~
glycol, the amount of germanium dioxide being 10 to 200 parts per million by
weight based on the amount of terephthalic acid present at the start of the
- reaction and the amount of the sodium hydroxide be:ing: (i) greater than 38.2
parts by weight per 100 parts by weight of germanium dioxide; ~ii) greater than
20 parts by weight per million parts by weight of the terephthalic acid; ~iii)
less than the greater of 76.4 parts by weight per ]L00 parts by weight of ger-
manium dioxide and 100 parts by weight per million parts by weight of terephth-
alic acid.
It is important that at least one equivalent of the alka:li metal
hydroxide is used for each mole of germanium dioxide in order to ensure that the
latter is dissolved. Thus, when using sodium hydroxide, for each :L00 parts by
weight of germanium dioxide, at least 38.2 parts of sodium hydroxide should be
~; used. In place of sodium hydroxide, hydroxides of other alkali metals, e.g.
lithium, potassium, rubidium and caesium may be employed. However~ for econo-
mic reasons, sodium hydroxide is preferred.
We have found that the addition of too much of the alkali metal hy-
droxide adversely affects the colour of the product and so we prefer to use
less than 2, particularly less than 1.5, equivalents per mole of germanium di~
oxide.
The amount of germanium dioxide used is 10 to 200 parts per million
parts by weight of the terephthalic acid. However, where small amounts, i.e.
at the lower end of this range, of germanium dioxide are used~ more than 2
equivalents of alkali metal hydroxide may be used for each mole of germanium
dioxide. Thus, the amount of alkali metal hydroxide is preferably within the
ange 0.5-2.5, preferably 0.75-2.0, gram equivalents per million grams of the :
dicarboxylic acid, i.e. for sodium hydroxide 20-100, preferably 30-80, parts
per million parts by weight of dicarboxylic acid.
The amount of ethylene glycol used to form the germanium catalyst
solution should be sufficient to ensure dissolution of the germanium dioxide
and alkali metal hydroxide.
The amount of antimony trioxide used as additional polycondensation
catalyst should be sufficient to ensure an acceptable polycondensation rate is
_4_ ;-
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768~
obtained The amount used ;s in the range 100-1000, preferably 200-750, parts
per million parts by weight of terephthalic acid orlginally present. The
antimony trioxide is generally added after completion of the esterification
reaction and then, while maintaining the reaction medium at an elevated temp-
erature, the prevailing pressure reduced to effect polycondensation.
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Pf 26752
~ 4~6~
Other additives commonly employed in polyester
manufacture may be added at a suitable stage in the
process, generally before or during the polgcondensation
reaction. Examples of such additives are phosphorus
compounds, such as o~yacids of phosphorus, e.g.
phosphoric or phosphorous acids, or salts or esters
thereof, dyeing assistants, delus1tra~ts, fillers,
optical whiteners, dyes, pigments and chain ex~enders.
The esterification reaction is conducted at an
ele~ated temperature, generally in the range 200~280C,
~- generally under ele~ated pressure, with removal of
water by distillation.
The polycondensation reaction is generally conducted
at a temperature in the range of 250-300C under a
reduced pressure, generally less than 30 mm of mercur~,
with removal of the evolred glycol.
The invention is particularly suited to the
~; production of polyesters for ~ibre or film manufacture.
~he inventio~ is illustrated by the ~ollowing
e~amples wherein all parts and percentages are
,
expressed by weight~
(Examples I, II and IV are comparative).
Example I ~ -
60.5 part~of terephthalic acid and 38 8 parts
; 2~5~ ethylene~glycol were esterified under a pre~Burs of
.
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P~ 26152
768~
40 psi at a temperature of 240C i.n the presence of
0.0035 parts sodium hydroxide. 0.07 parts triphenyl
phosphate stabiliser were then added after
esterification, followed by 0.0035 parts of
: 5 amorphous germanium dioxide and 0.021 ~arts antimony
: trioxide were added as polycondensation catalyst.
Polycondensa~ion was completed by raisi~g the
. temperature to 290C and applying a vacuum of 0.1 mm .
of mercury~ ~he resultant polymer had an intrinsic : .
~ 10 viscosity (IY) - as measured on a 1% solution in -~
: o-chlorophenol at 25C - of 0.658, a yellowness of
30 units and softening point of 255.4C. ~he
yellowness figure quoted is a measurement uf the colour
of the sample obtained on a "colormaster" dif~erential
.1 15 colorimeter. ~he higher the yellowness figure, the
poorer the colour of the polymer.
: : Exam~e II : :
-~ Polymer was made as described in Example I but
.. ~ instead of amorphous germanium dioxide, 0.0035 parts
hexagonal germanium dioxlde dissolved in an ethylene
glycol solution containing 0.0014 parts sodium
hydroxide were added after esterification together
~wlth the:antimon;~ trioxide as polycondensation catalyst.
he resultant~polymer~had~an IV Or 00694~, a yellowness
:: of~40 units `and a softening point of 255.1C. . ;
. .
P~ 26752
~47~3
; Example III
60.5 parts terephthalic acid and 38.8 part~
; .
ethylene glycol were esterified under the conditions
deQcribed in Example I but i~ the presence o~ 0.00~5
5 parts hexagonal germanium dioxide dissolved in ~n
ethylene gl~col solution containillg the 0.0035 part~
sodium hydroxide. 0.07 parts triphenyl phosphate
:
~tabiliser and 0.021 parts antimony trioxide catalyst
were added a~ter esterification and polycondensation
. ~,
completed as in ~xamplea I and II. ~he polymer
.. ..
of IV 90682 ga~e a yellowne~s o~ 27 unit~ and a
sortanin~ point of 256~7Co
~, Example IV
86.5 parts terephthalic acid and 42 p~rts ethylene
glycol we~e esterified at a temp~erature o~ 241C and
~: J ~ a~ pre~ure o~ 2~8 atmospheres in~the presence of
0.005 part~ sodium hydroxide.; 0.21 part~ triphenyl
~ : :
phosphate as ~tabiliser and 0.005 parts he~agona1
germani~m dioxide, dis~oIved~in an~eth~lene glycol
~ ~olution containing 0.002 parts sodium h~droxide, and
0.03 part3 antimo~y trioxide as po1ycondensation
~,~ catalyst were then added. Polycondensation was
completed~by~rai~ing~the tomperature to 290a and~
decreasing the pr~sQure to 0.1 mm mercur~ pressure.
Pf 26752
6~
~he polymer had a~ IV of 0~658, a yellowness of
32 units and softening point of 25B.8C.
., ~Z
86.5 parts terephthalic acid and 42 part~i ethylene
glycol were esterified at a temperature of 241C
and pressure of 2.8 atmospheres in the presence o~ :
0.005 parts hexago~al germanium di~Dxide di~solved in
an ethylene gl~col solution containing 0.005 parts
sodium hydroxide. 0.21 parts triphenylphosphate and
0.03 parts a~timony trioxide were added a~ter
esterification and the polycondensation was co~pleted
~ as in Example IV. ~he polymer had a~ IV of 0.645,
:1 yellow~ess of 25 units and softening point 259~2C --
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