Note: Descriptions are shown in the official language in which they were submitted.
1 1~$~ 1
Process for the production of a polychloroprene adhesive
having an improved pot-life
.
l This inveI1tion rel~tes to a process for the
production of an adhesive basecl on polychloroprene
which may be obtain~d by the continuous
polymerisation of chloroprene in aqueous emulsion in
the presence o~ small quantities o~ an emulsifier.
Tl1e polymerisation o~ chloroprene in aqueous
emulsion has long been known and is carried out on an
industrial scale (c~ or example, Encyclopedia o~
Polymer Science and Technology, Vol. 3, pages 705-730,
Interscience, 1965). This radically controlled
polymerisation process takes place very quickly and is
accompanied by vigorous evolution of heat. Rapid
dissipation o~ the heat of polymerisation is dif~icult
par-ticwlarly when it is in-tended to maintain a low
l~ polymerisation temperature and presupposes a very
efficient cooling system.
Numerous proposals have been put ~orward in the
pate~1t literature with a view to meeting the stringen-t
demands which are imposed both upon the polymer and upon
the adhesives producea therefrom. However, di~icultios
are encountered in the reproducible production of
polychloroprenes having a uniformly high quality level.
Aceordingly, it is preferred in practice both for this
reason and for economic reasons to polymerise chloroprene
in a continuous polymerisation plant.
For the produetion of adhesives, polychloroprene
is dissolved in suitable solven-ts. The flow properties
of the adhesives change during storage, whieh is
- refleeted in partieular in an increasing solution
viseosity and whieh leads to a considerable deterioration
in processibility. ~hese disadvantages may be obviated,
for example, hy masticating the polymer on mixing rolls.
Unfortunately~ this proeess is time-consuming and
expensive.
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1 I-t is known -that the raw material and mixillg
properties of the polymeLs ~lepend upon the composi-tion
o -the eluulsifiers and t~le concerltrations thereof in
-the aqueous emulsion. Altllough a high emulsi~ier
conten-t increases the polymerisa-tion ~elocity and
impro~es the stabili-ty of the latex, it has an adverse
effect upon crucial product properties o-E the adhesives,
such as stability in storage and pot-life.
Accordingly, it would be desirable to reduce
the emulsifier content during polymerisation. As is
kno~n, however, the polymerisation ~elocity decreases
wi~h reduced emulsi~ier content (F. Holscher,
Dispersionen synthetischer Hochpolymer [Dispersions of
Synthetic ~igh Polymers], Part 1, Properties, Production
and Testing, Springer-Verlag, Berlin~Heidelberg-New
York, 1969, pages 81 et ~ ~lere polymerisation is
carried out continuously, this means a lower monomer
~ conversion in the polymerisation plant for the same
; residence time. The monomer conversion may be increased
for the same polymerisation temperature either by a
-~ longer residence time of the emulsion in the polymerisation
plant or by using larger amo~mts of activator. In
either case, reductions in product quality are inevitable.
The mean residence time ~Vz) of the polymerising
chloroprene in the reactor cascade is crucially importan-t
;~ if polymerisa-tion is to take place uni~ormly without
interruption and if the polymer is -to have uniformly
good properties, It is determined in accordance with
` the following simple formula:
v Lh]
.'. ~
where in
Vz is the residence time ~h);
Vk is the sum of the reactor capacities o~ the
; 35 polymerisation plant (m3); and
L is the quantity of late~ ~ormed per hour (m~/h).
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~:;
1 1555~1
1 In a cascac~e of 7 reactors, V~ is normally from
2 to 4 hours. When the ~ lsion has a long residence
time in the corl-tinuous ins-tallation (Vz~5 hours), i.e.
whe n the polymerisation reaction takes place slowlyt
so-called "popcorn" polymer is formed in addi-tion -to the
required chloroprene polymer. Popcorn polymer consists
of highly cross-linked products which are insoluble in
organic solvents. Once popcorn seeds have ~ormed, they
grow quickly under the effect of au-to-catalysis,
res~lting in blockages in the polymerisation plant,
e~cessive conversion levels and~ hence, in the formation
o~ polymers charac-terised by highly fluctuating
properties.
I~, lly contrast, the residence time is too short
(Vz~2 hours) the heat of polymerisation is difficult to
~issipate and proclucts having unfavourable raw material
and vulcanisate properties are formed. Accordingly, the
continuous inter-ference-~ree polymerisation of chloroprene
to form produc-ts o~ high quality is only possible within
; 20 a certa-ln residence tim~ range.
This continuous polymerisation o~ chloroprene is
known and has been described, for example, in U.S. Patent
B Nos~? 2,394,291 and 2,8~1,842.
In order to reach the same reaction velocity in
continuous polymerisation as in batch polymerisation, it
is either necessary to use more emulsifier or, as
~escribed in U.S. Patent No. 2,~94,291, to introduce
considerably more activa-tor solution. However, this
leads to the formation of deposits in the polymerisation
and degassing tract o~ the polymerisation plant.
Accordingly, continuous interference-free
polymerisation in the presence of low concentrations o~
emulsifier is not possible. Neither does the contimlous
; polymerisation o~ chloroprene by means of an emulsi~ier
system o~ salts of disproportionated abietic acid,
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~ ~55~1
l fat-ty acid and non-ionic e~ulsifiers, as described in
D~-OS No 2,520,339, produce the required result
because the non-ionic eululsifiers slow down the
polymerisation reaction and the above-mentioned adverse
e~fects oocur
Gerluan Of~enlegungsschrift Nos. 2,047,44g and
2,047~450 describe processes for the production of
polychloroprene latices rich in solids. In these
processes, adequate colloidal stability o~ the latex
during polymerisation is only achieved when a combination
of 3 emulsi~iers and dispersants in precisely defined
concen-tration ranges is used. ~o obtain adequate latex
stability, it is essential that, in addi-tion to the
polymeric fatty acids, no less than from 1.5 to 2.0
parts, by weight, of a condensation product of naphthalene
sulphonic acid and ~ormaldehycle per lOO parts, by weight,
of chloroprene and no more than l.5 parts, by weight,
of a disproportionated abietic acid should be added.
However, these latices cannot be worked-up in-to the solid
rubber, ~or example, by low temperature coagulation.
However, products obtained by electrolyte
precipitation undergo serious discolouration during drying.
Accordingly, it was surprising to ~ind that it is possible,
without adding polymeric fatty acids and in the presence
o~ small quantities of condensa-tion products o~ naphthalene
sulphonic acids and ~ormaldehyde, to improve latex
stability during the continuous polymerisation reaction,
considerably to lengthen the operating time o~ the
polymerisation plant (even where the mixture has a low
3o water content) and to obtain latices which may readily
be worked-up, ~or e~ample by low temperature coagulation,
providing the sodium hydroxide normally used is replaced
by potassium hydroxide or by mi~tures of o-ther alkali
B metal hydroxides, such as LiO~,- ~ and CsOH, and the
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1 15558 ~
-- 5
l Na-salts of -the elnulsifiers are replaced by the potassium
salts thereo~. The reaction velocity of the continuous
polymerisation of chloroprene in the presence of lo~
concentrations of emulsifier may be adequately controlled
by the choice oE the mixture of di~erent alkali metal
hydroxides and the concentration thereof in the mixture.
Stable latices are obtained in this way and, a~ter
working-up into the adhesive, give produc-ts having
considerably impro~ed raw material and mixing properties.
Accordingly~ the presen-t invention relates to a
process ~or the continuous polymerisation o~ chloroprene,
which may contain up to 30~0, by weight, of one or more
comonomers, to form polymer latices in an aqueous
alkaline emlllsion con-taining from 0.2 to 1.5 parts, by
weight, preferably from 0.4 to 0.9 parts, by ~eigh-t, of
~OE per 100 parts, by l~eigh-t, of monomer and potassium
salts o~ emulsi~iers, such as from 2 5 to ~ 1 parts, by
weight, of disproportionated abie-tic acid, and from 0.3
to l.O parts, by weight, of condensation products o~
naphthalene sulphonic acid and formaldehyde. In the
emulsion, which contains from 90 to 150 parts, by weight,
preferably from lOO to 130 parts, by weight, of water
- per lOO partsJ by weight'of monomer, up to 60~, by
~ weight, of the potassi~ ions may be replaced by other
;~ ~ 25 alkali metal ions~ such as Li~ or Na~. The exact
'~ concentration of potassium ions which must be present
depends upon the average residence time of the polymerising
~' ch'loroprene in the cascade of reactors, upon the
concentration of emulsifiers and upon the ~ater content
of the mi~ture, although it may readily be determined
by those skilled in the art. The process according to
the present invention may 'be aclvantageously applied hoth
in the batch polymerisation and in the continuous
polymerisation of chloroprene, the ndvantages thereof
being particularly apparent in the continuous polymerisation
o~ chloroprene.
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~ ~558 ~
-- 6
the practical application oP the process
according to the present invention, chloroprene may be
polymerised on i-ts o~n or may be replaced in a
proportion of up to ~0~0 by another compound
copolymerisa~le with chloroprene, such as monovinyl
compo~lnds (e.~. acrylonitrile, methacrylonitrile, vinylidene
chloride, ~-chloroacrylonitrile, methacrylic acid esters
and acrylic acid esters), vinyl-substituted aromatic
compounds (e.g.styrena and vinyl toluenes) and conjugated
diene compounds (e.g. 1,3-butadiene and 1-chloro,1,3-butadiene).
The polymerisation reaction is carried out in
aqueous alkaline emulsion in the presence oP radical
initiators. Suitable emulsi~ier systems are potassium
salts oP water-soluble satura-ted or unsaturated monocarboxylic
acids, ~or e~ample disproportionated resinic acids,
optionally in admix-ture with Patty acicls, SUCtl as oleic
ac~d and coconut oil fatt~ acids, The emulsifiers are ~enerally
added in quantities o~ from 2.5 to 4.l parts, by weight,
prePerably from 2~8 to 3 5 parts, by weight, based on
lO0 parts, by weight 9 of monomer.
Condensation products o~ naphthalene sulphonic
acid and ~ormaldehyde are also used as additional
emulsifiers. In this connection, it has been ~ound to be
desirable to add from 0.3 to l.0 part, by weight,
prePerably Prom 0.4 to 0.8 part, by weight, of this surface-
active compound per lO0 parts, by weight of monomer. It
is precisely in cases where the mi~ture has a low water
content that latex stability may be additionally
increased by adding ~rom O.l to 0.5 part oP sodium
hexametaphosphate~ ~
Chain-trans~er agents 3 such as alkyl mercaptans
or dialkyl xanthogen disulphides, are added Por the
purpose o~ regulating molecular weight. The quantity in
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1 15~58 ~
l ~hich tlle mercap~all~ for e~ample dodecyl mercaptan, is
used influences the molecular weight o~ the polymer
-formel1. The average molecular weig~lt o~ the polymer
decreases with increaSincJ addition of mercaptan,
as reflected in the alling Mooney viscosity
of the produots.
The reaction product has a favourable Mooney
range for further processing when the mercaptan is added
in quantities of fro~ O.l to 0.3 part, by weight, per
lO0 parts, by weigh-t, of monomer~
The q~lantities o~ chain-transfer agents required
to obtain a required polymer viscosity may readily be
determined by those skilled in the art~
If the e~ulsifier system according to the
present invention is llsed9 the emulsion has to be adjusted
to a pH above lO, pre~erably from ll -to 13.5.
The polymerisation reaction is initia-ted by the
; addition of known polymerisation initia-tors. Suitable
initiators are radical-forming compounds, such as alkali
metal persulphates, hydrogen pero~ide and organic
peroxides, such as cumene hy~ropero~ide or benzoyl
peroxide, or co~binations of peroxides with reducing
agents, such as formamidine sulphinic acid.
The monomer conversion should not e~ceed 85go and
is normally from 60 to 80~o.
The temperature prevailing during the polymerisa-tio~
reaction may be from 0 to 30~C, preferably from lO to
20C. Polymerisation is terminated by the addition of
inhibitors, such as phenothiazine. Residual unreacted
monomer may be removed by steam distillation. The p~
of the alkaline latex is reduced to 5 to 7,
preferably to 6.0 to 6.5, using dilute acetic acid and
the polymer is isolated from this e~ulsion, for e~anple
by low temperature coagulation, and dried as described,
~or example, in Chem. Engng. Progr. 43, 391 (l974) and
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1 in German Patent No. 1,051,506. Hol~ever, working-up
~ay also be carried out by other con~entional methods,
as described, for e~ample, in German Patent No. 1,111,804.
The production of polychloroprene solutions and
5 0~ a~lesives based on these solutions is carriecl out by
kno~ methods o~ the type described, for example, in
German Offenlegungsschrift No. 1,200,988.
The present in~ention is illustrated by the
following EYamples.
EX~MPLE 1 (Comparison ~Yample)
The a~ueous phase (W) and the monomer phase ~M)
are introduced in a constant ratio (through a measuring
and control system) together with the activator phase
(A) into the first reactor o~ a polymerisation cascade
consisting of 7 identical reactors each having a ~olume
of 50 litres. ~he average resi1enoe time per reactor is
30 minutes. ~Reactors of the type described in German
Offenlegungsschri~t No. 2,650,714 were used).
20 chloroprene 100.0 parts, by weight
n-dodeoyl mercaptan 0.13 part, by weight
phenothiazine 0. ols part, by weight
~ (W) = aqueous ~ase:
;~ deionised water 150.0 parts, by weight
25 sodium salt of a disproportionated
abietic acid 6.o parts, by weight
sodium salt of a condensation
product o~ naphthalene sulphonic
acid and formaldehyde 0.7 part, by weight
30 caustic soda o.63 part, by weight
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il5S~8~L
_ 9 _
1 (A) = ac-tiva~ ase:
1~ by weight fo~dine su1phinic acld 0.07 part, by weight
potassium persulphate 0.05 part, by weight
an-thraquinolle-2-sulphonlc ac1d-~a 0.005 part, by -weight
The reac-tion begins in the first reactor of the
cascade at an internal temperature of 15C. ~æt~rnal
cooling dissipates the heat of polymerisation liberated
and reduces the polymerisation temperature to 10C. The
reaction is terminated at a monomer conversion of 80~ by
the addition of phenothiazine. The residual monomer is
removed from the polymer by steam distillation and, after
the p~ has been reduced to 6.o, -the polymer late~ is
coagulated and isolated on cooling rollsO The coagulated
polymer is friable and may only be dried with difficulty.
The polymer has a Mooney viscosi-ty (ML 4) of 100 units.
After a polymerisation time of 4 days, the polymerisation
cascade is run down. 10 kg of polymeric deposits have
collected in the reactors over this period.
EXA~PLE 2 (Comparison Eæample)
Reduction o-f the emulsifier concentra-tion.
PoLymerisation is carried out in the same way as
in Comparison Example 1, but using an aqueous phase which,
instead of 6.o parts, by weight, contains 3.2 parts, by
weight, of the sodium salt of a disproportionated abietic
acid. The polymerisation reaction takes place slowly and
the required monomer conversion of 80% canno-t be reached,
even by a considerably greaterinput of activator (cf.
Table 1). After it had been in progress for 2~ hours,
the polymerisation reaction had to be terminated because
the pipe system between the reactors is blocked by
deposi-ts. 42 kg of coagulate were removed from the
installation.
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1 EX.~IPLE 3 (Comparison ~xample)
Reduction o~ the water content of the mix-ture.
The procedure is as in Example 1, except tha-t,
instead of 150 parts, by ~eight, the aqueous pllase now
con-tains 120 parts, ~y weight, o~ water Polymerisation
is terminated a~ter 4 days. 22 kg of polymeric deposits
have collected in the reactors. The first deposits are
~ormed in the latex after storage ~or 3 days. The pH
o~ the latex cannot be reduced -to pH 6.0 for working-up
because the polymer actually coagulates and precipitates
at pE 7. Accordingly, the polymer is isolated at pH
7.4. The dried polymer has a Mooney YiSCosity ML 4 of
95 units.
EX~MPLE 4 (Comparison Example)
Lower concentrations of water and emulsifier in the mixture.
The procedure is as in ~xample 1, except that the
emulsifier content is reduced to 4 parts, by weight, and
the water content to 110 parts, by ~eight. The monomer
conversion is only 551do despite a high consumption of
aotivator. Polymerisa-tion is terminated after 18 hours.
46 kg of deposi-ts have collected in the reactors.
(KOH as the alkali component)
The procedure is as described in Example 1, e~cept
that the sodium hydroxide in -the aqueous phase (W) is
replaced by equimolar quantities of potassium hydroxide.
Despite a lower consumption o~ activator, the polymerisation
reaction takes place more uni~ormly and, even a~ter a
polymerisation time of 8 days, the reactors do not contain
any deposits. The polymer has a Mooney viscosity ML ~ o~
103 units.
EXAMPLE 6
-
Reduction of the emulsifier concentration.
The procedure is as in Example 2, except that the
sodium hydroxide is replaced by equimolar quantities of
potassium hydroxide. The monomer conversion of 80do is
Le A 20 ~13
11~5581
- 11 -
l reacl1ed Yi-th a lo~ consumption of activator. A~ter a
polymerisation time o~ 8 days, the reactors do not
contain any deposits. The polymer has a Mooney viscosity
ML 4 of lO0 units.
ElYAMPLE 7
Reduction of the water content in the mixture.
The procedure is as in Example 3, except that the
sodium hydro~ide is replaced by equimolar quantities of
potassium hydroxide. After a polymerisation time o~ 8
days, the reactors contain 4 kg of deposits. The polymer
has a kIooney viscosity ML 4 of 98 units.
EXAMPL~ 8
Lower concentrations o~ water and emulsifier in the mixture
The procedure is as described in Example 4, except
that the sodium hydro~ide is repl~ced by equimolar
quantities of potassium hydroxide. A~ter a polymerisation
time o~ 8 days, the reactors contain l kg o~ deposlts.
The late~ is stable in storage and may be coagulated and
isolated on cooling rolls at p~ 6. The coagulated
polymer is elastic and easy to dry. The polymer has a
Mooney viscosity ML 4 of lOl units.
EX~IPLE 9
Lower concentrations of water and emulsifier in the mi~ture
and replacement of the sodium ions by potassium ions
The procedure is as in Example 8, except that the
sodium salts of the emulsifiers are replaced by equimolar
quantities o~ potassium salts. Despite a lower consumption
of activator, the polymerisation reaction takes place
without any problems and, after a polymerisation time of 8
,o days, the polymerisation vessels do not contain any deposits
The latex is worked-up in the same way as described in
Example 8. The polymer has a Mooney viscosity ML-4 of
104 units.
Le A 20 113
_ .... . _
~ 155~ 1
- 12 -
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Le A 20 113
1 155581
1 As shown in E~amples 1 to &; a reduction in the
emulsifier concentration (Example 2) or a lower water
content in the mi~tllre (~æample 3) or both (E~ample 4)
leads, in the presence of Na~ ions, to heavy deposits
in the polymerisation vessels and to premature termination
of the continuous polymerisation process The required
monomer conversion is reached with difLiculty, if at
- all. Even partial replacement o~ the Na~ ions by
ions (Examples 5 to 8) is su~-~icient to eliminate
these di~iculties. Storable latices which are easy
~ to work-up are obtained. Where the Na~ ions are
; completely replaced by ~ ions in the mi~ture (Eæample 9),
the required monomer conversion is easily reached despite
a low consumption of activator. The continuous
polymerisation plant may be operated for prolonged
periods completely free from deposits.
E.YAMPLE 10
Pot-life
25 g o~ the polychloroprene produced in ~xamples
1, 3 and 5 to 9 were dissolved with stirring ~laboratory
stirrer, 600 r.p.m.) in 125 g o~ a solvent mi~æture o~
ethyl acetate7pe~roleum 65/95 and toluene (ratio, by weight,
2:2:1). The thus-obtained adhesives were diluted to a
viscosity of 1.5 Pas, as measured at 20C using a Brookfield
B 25 LVT viscosimeter (No. 4 spindle, 30 r.p.m.), by addition
of further qu ntities of the same solvent miæture. 7.5 g
of Desmodur RF were thoroughly mi~ed with the
resulting solution and the viscosity o~ this adhesive
mi~ture was determined in ~0 seconds using a Brookfield
LVT ~iscosimeter (No. ~ spinale, 60 r.p.m.). The bottle
was then stored at 20C/65~ relative humidity and the
increase in the viscosity o~ the mi~ture was determined
by hourly measurement using the Brook~ield LVT viscosimeter
until a 50~ increase in the initial viscosity had been
obtained .
Le A 2O 113
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Le A 2o 113
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