Note: Descriptions are shown in the official language in which they were submitted.
O~Z. ~ 51
MANUFACTU~E OF COPOLYMERS OF ETHYLENE
The invention ~elates to a process for the manufackure o~ co~
polymers of ethylene which çontain, as copolymerizçd units, more
than 60 per cent by weight of ethylene, from 1 to 20 per cent by
weight of tert.-butyl acrylate and/or tert.-butyl methacrylate and
I
from ~ to 10 per cen~ by weight of acrylic acid and/or methacrylic
acid, by copolymerization of ethylene and tert -butyl acrylate
and/or tert.-buty~ methacrylate at from 200 to 350C at pressures
above 800 atmospheres.
~ ~rench Yatent 1,596~991 discloses a process for the manufac-
ilO~ ture o~ ethylene copolymers whiqh contain, as copolymerized units,
; a predominant amount of ethylene, an alkene-carboxylic acid of 3 to
12~carbon atoms, minor ~mounts of alkenes of 3 to 8 carbon atoms
and, optionallyg esters of alkenecarboxylic acids of ~ to 12 carbon
atoms with secondary alkanols of 3 to 8 carbon atoms or tertiary
alkanpls of 4 to 8 carbon atoms, and/or further monomers which are
copolymerlzable with ethylene. The copolymers are manufactured by
copolymerizing monomer mixtures of ethylene, an ester of an alkene-
carboxyli¢ acid of ~ to 12 carbon atoms with a secondary alkanol of
3 to~8 carbon atoms or a tertiary alkanol of ~ to 8 carbon atoms
ZO and~ optionally~ further monomers which are copolmyerizable with
ethyleneJ at pressures of from 100 to 8,ooo atmospheres, and at
`~ from 110 to 350C using catalyt,ic amounts of free radical initia-
tors. The temperature in the reactor must be at least sufficiently
high that the secondary or tertiary ester groups in the polymer
o.z 31J351
pyr^~yze partially or completely. Free carboxylic acid groups are
then obtained in the polymer, an alkene being eliminated.
However, the homogeneity of the products manufactured by the
said process is unsatisfactary. This phenomenon is particularly ob-
~ectionable if the polymers are used as hot-melt adhesivqs, because
very thin films are required for this purpose, Irregularities in
the hot-melt adheslve ~ilm (holes~ specks) are a considerable dis-
advantage because they ~educe the adhesion at the interface between
the hot-melt adhesive and the material to be honded (eg. polyethylene
or metals). If ~he bonded areas are subjected to substantial stressJ
the materials bonded to one another can separate~ for example where
the film contains specks. Inhomogeneous films of these polymers give
considerable technical difficulties when used in the manufacture of
laminates.
A further disadvantage o~ the conventional process is that the
copolymer content and melt index of the products obtained show con-
siderable variation.
~i It is an ob~ect of the present i~vention to modify the pro-
cess described above so that homogeneous ethylene copolymers are
~20 obtained in which the copolymer content and melt index show little
variation. It is a further ob~ect that the ethylenq copolymers should
be çapable of conversion to very thin films which do not exhibit
ob~ectionable irregularities.
~ç have found that these objects are achieved, according to
the invention, by passing the reaction mixture, obtained after
the polymerization~ into a zone in which the pressure is below 500
atmos~heres and the temperature is from 200 to 250C, the mean re-
sidence time of the reaction mixture in the zone belng from 2 to
10 minutes.
In a preferred embodiment of the process9 the temperature of
the reaction mixture in the high pressure isolation zone, which is
from 200 to 250C, is not allowed to vary by more than ~ 2C.
Acqording to the invention, substantially more homogeneous
-2-
0.~ 31,351
ethylene copolymers are obtained than by the conventional pro-
cess.
The ethylene employed for the polymerlzation should be at
least 98 per cent pure. tert.-Butyl acrylate and tert.-butyl meth-
acrylate are commercially available. The ethylene copolymers, which
contain~ as copolymerized units, a predominant amount of ethylene,
from 1 to 10 per cent by we~ght of acrylic acid and/or methacrylic
acid and ~rom 1 to 20 per cent by weight of tert.-butyl acrylate
and~or tert.-butyl methacrylate, are manufactured in conventional
equipment, eg. autoclaves or tubul~r reactors. It has proved par-
ticularly advantageous to carry out the process continuously. Pre-
ferably, the polymerization is qarried out in tubular reactors,
cf. Ullmanns Encyklopadie der technischen Chemie, 3rd Edition,
Urban and Schwarzenberg~ Berlin-Munich 1963, Volume 14~ page 139.
The polymerization of the monomer mixture is carried out at pres-
sures above 800 atmospheres, 4s a rule, pressures of up to 3,000
atmospheres are used, but the polymerization can also be carried
out at pressures of up to 8,ooo atmospheres. The polymerization
temperature is from 200 to 350C and preferably from 280 to 330Co
Ethylene is copolymerized with tert.-butyl acrylate~ tert.-
butyl methacrylate or a mixture of both acrylates in the presence
of free radical initiators. By free radical polymerization initia-
tors are to be understood catalysts which can also be used for
the high pressure homopolymeriæation of ethylene. For exampleJ
oxygenJ ad~antageously in amounts of from 10 to 200 molar ppm,
based on the ethylene to be polymerizqd, may be used. Peroxides and
other compounds which form free radicals may also be used, as
well as mixtures of peroxides having different decomposition points,
hydroperoxidesJ and mixtures o~ oxygen and peroxides and/or hydro-
peroxides. Examples of peroxides and hydroperoxides are tert.-
butyl peroxypivalate, di~tert.-butyl peroxide, tert,-butyl hydro-
peroxide, tert.-butyl perbenzoate, p-menthane hydroperoxide and
dilauroyl peroxide. Compounds such as azoisobutyrodinitrile are
-3-
~ O.Z. 31,351
a'~o included under free radical polymerization initiators
In a special embodiment Or the process according to the in-
vention, conventional polymqrization regulators are used. By means
of these ~t is possible to vary the melt index of the ethylene co-
polymers produced. Examples of suitable regulator~ are hydro~en,
~etoneS, alcohols, ethers and normal and branched hydrocarbons;
propylene, methyl ethyl ketone and propionaldehyde are used pre-
ferentially. In general, from 0.2 to 5 mole per cent of the poly-
merization regulators, based on the ethylene to be polymerized, are
employed.
The copolymerization of the ethylene with tert.-butyl acrylate
or tert.-butyl methacrylate can also be carried out in the presence
of other compounds whioh are copolymerizable with ethylene. Examples
of suitable çomonomers are vlnyl esters derived from saturated carb-
oxylic acids of 3 to 8 carbon atoms, other acrylic acid esters and
methacrylic acid esters, fumaric acid esters and maleic acid esters.
The polymerization is in general carried out in the absence
of a solvent. The small amou~ts of an inert solvent, eg. benzene,
petroleum or other inert solvents, in which the polymerization
initiators are dissolve~, are negligible compared to the other ma-
terials employed. If oxygen is used ~s the polymerization intiator,
no solvent whatsaever is necessary.
At the e~d Or the polymerization reactor, the temperature of
the reaction mixture is in general above 285C. The reaction mix-
ture is then passed into a cooling zone where it is cooled to from
200 to 250C. This step may either be carried out under the pres-
sure at which the polymerization is carried out, or after letting
down the reaction mixture3 at ~ressures below 500 atmospheres. Im-
mediately aftqr the cooling treatment, the reaction mixture is fed
; ~0 into a high pressure product isolation zone in which it ls kept
at a temperature of from 200 to 25QC which preferably varies by
at most ~ 2C, and where it undergoes partial pyrolysis. This con-
verts the copolymerized tert.-butyl acrylate units or tert.-butyl
--4--
oOZ. 31y351
me~acrylate units partially into acrylic acid units or methacrylic
acid units, with elimination of isobutyleneO The temperature of
the reaction mixture in the pyrolysis zone pre~erably does not va-
ry by more than -~ 2C. If the temperature variation in this zone
is greater, the pyrolysis o~ the tert.-butyl acrylate or tert,-bu-
tyl methaorylate units becomes uncontrolled and inhomogeneous pro-
ducts are obtained. The mean residence time o~ the reaction mix-
ture in the pyrolysis zone is in general rrom 2 to 10 minutes. The
mean residence time is the time for which the copolymer formed re-
mains in the reactor zone in which a pressure below 500 atmospheresand a temperature of from 200 to 250C prevails. The mean residence
time is defined by the ratio of the volume of the apparatus to the
mean volume of product which has passed through the volume o~ the
apparatus per unit tlme. The pressure in the pyrolysis zone is in
general from 50 to 500 atmospheres. However~ the pyrolysis can al-
so be carried out at lower pressures or under reduced pressure, eg.
at from 1 to 50 mm Hg. According to the inventionl homogeneous co-
polymers are obtained, which contain, as copolymerized units9 more
; than 60 per cent by weight of ethylene, from l to 10 per cent by
weight of acrylic acid and/or methacrylic acid and ~rom l to 20 per
cent by weight of tert,-butyl acrylate and/or tert.-butyl meth-
acrylate. The ethylçne copolymers manufactured by the process of
the invention are homogeneous and are used~ above allg as hot-melt
adhesives, eg. ~or metals, ceramics, paper, textilesg plastics,
; wood, glass and the like. For example, in contrast to polyethylene,
the copolymers can easily be colored or printed with most conven-
tional dyes. When blended with polyole~ins, the copolymers give
mixtures which can also be printed and dyed. Since the ethylene
copolymers manufactured according to the invention are homogeneous~
they can easily be converted to thin, homogeneous films which are
employed as hot~melt adhesive films. The melt index o~ the ethyl-
ene copolymers manufactured according to the invention is from
0.1 to 50, preferab}y from 1 to 20, g/10 min. (determined ac-
~ O~Z ~351cord~ to ASTM D 123~-65 T at from 190~ under a load of 2v16 kg)o
The Examples which follow illustrate the inventionO The poly-
merization apparatus is a tubular reactor as conventional~y employed
for continuous high-pressure polymerizationO The ratio of the dia-
meter of the reaction tube to its length is 1020,000. The reaction
tube is surrounded by a jacketing tube which contains a heat trans
fer medium. The reaction tu~e is divided into two zones which can be
heated independently of one another, the first zone extending over
two-fifth~ of the length of the tube and the second over the remain-
ing three-fifths of the length of the reaction tubeO ~t the end of
the reaction tube there is a valve which serves both to regulate
the pressure in the polymerization space and also to discharge the
reaction productl This valve is followed by a ~acketed tube in which
the reaction mixture which has left the reaction tube is cooled to
a temperature of from 200 to a maximum of 250~o The pressure in
this zone is less than 500 atmospheres. At this temperature~ the re
action mixture is then passed into a high pressure product isola-
tion zone or high pressure separator, in which the pressure is ap-
proximately the same as in the preceding jacketed tubeO In this zone,
the polymer obtained in the reaction tube is separated from the non-
polymerized monomers. The mean residence time of the reaction mix-
ture9 obtained from the polymerizationJ after having been cooled to
from 200 to 250C~ is from 2 to 10 minutesO ~rom the high pressure
product lsolation zone the polymer~ which still contains small amounts
of monomer, is passed to a low pressure product separator at pres-
sures of less than 10 atmospheres, and from this latter separator
the polymer is fed to an extruder. The non-polymerized monomers are
recycled to the reactor, via a conventional separator system for re
movlng materials which are liquid under normal conditionsO The amount
of these components removed from the c~rculation system is only suf-
ficient to ensure a stationary state when the reactor is operatlng
continuously.
In the Examples, parts are by weightO
-6;
3La~ f~ o zO ~ 51
EXAMPIE, 1
A mixture whioh consists of 10,000 parts of ethylene, 270 parts
of tert.-butyl acrylate and 14 molar ppm of` oxygen, based on ethyl-
ene, is compressed to 2,200 atmospheres and fed to the reaotor de-
scribed above. The heat transfer medium in zones I and II of the re
actor jacket is kept at 200C during the polymerizationO As a re-
sult of the exothermicity of the reaction" the reaction mixture
reaches peak temperatures of 300C in both the reaction zones~ The
mean residence time of the reaction mixture in the reactor is 50
seconds.
The polymer is cooled to 250C under a pressure of ;500 at-
mospheres and is left under a pressure of 270 atmospheres at 250C
in the high pressure separator which is downstream from the reactor.
The temperature in the high pressure separator is kept constant so
that the maximum deviation is -~ 2C. The mean residence time of the
ethylene copolymer in the high pressure separator is 10 minutes.
1,850 parts of an ethylene copolymer which contains ~7 per cent by
weight of tert.-butyl acrylate and 508 per cent by weight of acrylic
acid, as copolymerized units, are obtained. The ethylene copolymer
has a melt index (190C/2.16 kg) of 7.1 g~10 mins and a density (ac
cording to DIN 53,479/7.2) of 0.927~ g/cm3, and exhibits good ho-
mogenelty and gives films having good properties.
EXAMPI~E 2
The procedure described in Example 1 is followed but the poly-
merization is carried out under a pressure of 29300 atmospheres~ As
a result of the exothermicity of the reaction, the reaction mixture
reaches peak temperatures of 315C. The polymer is cooled to 210C
under a pressure of 300 atmospheres and is then transferred direct-
ly to the high pressure separator in which it is kept for 8 minutes
at a pressure OI 280 atmospheres and at 210C9 with a maximum de-
viation of + 2Cc 1,900 parts of an ethylene copolymer containing
~0 7.8 per cent by weight of ter~ -butyl acrylate and ~iOO per cent by
weight of acrylic acidj as copolymerized unitsi are obtairled, The
--7--
6'~L~f~
OoZo ~1 9351
eth~ene copolymer has a melt index (190C/2016 kg) of 7~4 g/10
mins and a density of 0.9269 g/cm~, and exhibits good homogeneity
and gives films having good properties~
EXAMPLE 3
The procedure described in Example 2 is ~ollowed but the po-
lymer is pyrolyzed at 2~0C lnstead o~ 210Co The temperature of
the polymer in the pyrolysis zone is kept constant and deviates by
at most + 2C. 1,900 parts of an ethylene copolymer containing
6.6 per cent by wei~ht of tert.-butyl acrylate and 4~1 per cent
by weight of acrylic acid are obtainedO The ethylene copolymer has
a melt index (190C/2.16 kg) of 8.0 g/10 mins and a density (accord-
ing to DIN 53,479/7.2) of 0.9271 g/cm3) and exhibits good homoge-
neity and gives films having good properties.
COMPARATIVE EXAMPLE 1
A mixture of 10,000 parts of ethyleneJ 270 parts of tert -
` butyl acrylate and 14 molar ppm of oxygen, based on ethylene, ispolymerized by the method described in Example 1~ under a pressure
of 2,200 atmospheres. The polymerization conditions are the same
as those stated in Example 1. In modification of Example 19 the
polymer is not cooled and instead is transferred direct to a pro-
duct separator in which it remains for 60 seconds at ~10Co The
temperature fluctuates by about +10 CO An ethylene copolymer which
is inhomogeneous and unsuitable for the manufacture of thin hot-
melt adhesive films is obtained. Various samples of the product
whioh were taken show that the composikion varies; egO, from 7.0
to 9.0 per cent by weight of acrylic acid, and a melt index (190C/
2.16 kg) of from 4.5 to 8.8 g/10 mins, are found The copolymerized
tert.-butyl acrylate is pyrolyzed completely under the stated
conditions.
COMPARATIVE EXAMPLE 2
A mixture whioh consists of 10,000 parts of ethylene and
~00 parts of tert.-butyl acrylate and is compressed to 29~00 a~-
~0 mospheres is fed to the reactor desoribed in Example 1, The poly-
--8--
~6~ oOzO ~1,351
meri ~tion is carried out in the presence of ~0 ppm of oxygen~ Thetemperature o~ the heat transfer medium is 180C in zone I and 200C
in zone II. As a result of the exothermicity of the reaction, the
reaction mixture reaches a maximum temperature of 270C in both
zones. The residenae time during polymerization is 60 seconds, The
reaction mixture is then le~t for 50 seconds ln t}le product sepa-
rator at 320 C under a pressure of 280 atmospheres~ 13 900 parts of
an ethylene copolymer which contains ~rom 7.5 to 9,6 per cent by
weight o~ acrylic acid as copolymerized units are obtainedO The co-
polymerized tert.-butyl acrylate is pyrolyzed completely under the
above conditions. The ethylene copolymer obtained is very inhomo-
geneous and is unsuitable for the manufacture o~ hot-melt adhesive
fil~s.
The homogeneity of t~ ethylene copolymersJ referred to in the
Examples, was determined on 40/u thick films~ The films were pre-
pared by extruding the ethylene copolymer, obtained in the various
ExamplesJ at a material temperature of 150C~ The draw off speed is
6.5 m/minute, the ~rost line 250 mm and the blow-up ratio is 1.2.
The extruded tubular film passes through an optical instrument which
1:
;i20 continuously measures inhomogeneities in the film. The measurement
covers a 5 cm zone of the lay-flat film which passes through it and
which is 23 cm wide. Each inhomogeneity in the film (specks, clots,
~ish-eyesj generates an electrical pulseO The number of pulses,
~ which corresponds to the number of specks, is counted over a period
;~ of measurement of, eg., 400 seconds (corresponding to the scanning
of a film area of 4,3 m2). By varying the sensitlvity setting used
for the measurement, the inhomogeneities can be divlded into 3 groups,
namely
I speck sizç from 0.5 to 1 mm
II speck size from 1 to 2 mm
III speck size greater than 2 mmO
The results are summarized in the TableO
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~ o.z. ~ 51
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