Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
r
~ 2020571
Attorney Docket No.: 327410-2790 ~ ~
:
The present invention relates to additives for middle
distillates, and particularly diesel fuels, which additives hinder the
settling of paraffin crystals in the fuels and improve their
filterability, and to middle distillates containing such additives.
The resort of the petroleum consuming industries to supplies
of, in part, lower quality has intensified extant problems in
petroleum production or has pushed these problems for the first ~`
time into conscious scrutiny. ;
The content of paraffin in petroleum oils and petroleum
products must also be seen from this point of view. The
paraffins crystallize on cooling, whereby the ability of the oils
or oil products to flow is reduced at low temperatures and can
~;cease~entirely at a sufficiently low temperature. On heating,
;the orystallized paraffins generally go back into solution in the
oil matrix.
Technology has developed additives, the so-called "pour
point"~reducers (the "Pour Point Temperature" is that at which -
- the oil just still flows, cf. DIN 51597), which effectively `
reduce the "pour point" even at concentrations between 0.05 and -~
1 peraent by weight (cf. Ullmanns EncYclo~adie der technischen
ChemLe,~4th edltion, Vol. 20, Verlag Chemie, 1981).
~ , . ,
In~practice, primarlly ethylene-vinyl acetate copolymers ` ~-`
(EVA copolymers) have been used as flow improvers for middle
disti~llates. In EP-A }13,581 is taught the addition of - -
addltives comprising copolymers of ethylene and of the vinyl ~;
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ester of a carboxylic acid having 1 - 4 carbon atoms and a
molecular weight (number average) of 1000 to 6000 as a flow
improver for a petroleum fuel, the 20 percent and 90 percent
distillation points of which differ within a temperature region
of 65 to 100 Centigrade degrees, and/or as a flow improver for a
;.
distillate fuel the 90 percent distillation point and boiling
point of which differ by 10 to 20 Centigrade degrees, that is for
the so-called "narrow boiling distillates". The additive for
this purpose can also be a mixture of two copolymers.
This published patent application, following the example of
U.S. 3,048,479, selects according to the principle that
nucleation of the paraffin wax is promoted by means of one of the
copolymers ("nucleator") and that by means of the other copolymer
the crystal growth of the paraffin is to be hindered ("growth
arrestor"). Concretely, this European patent publication in both
cases uses ethylene-vinyl acetate copolymers.
EP-A 254,284 relates to a method for improving the fIow of ~ ~
petroleum oils and petroleum oil distillates by the addition of ~ .
mixtures of an ethylene-vinyl acetate-diisobutylene terpolymer
and an ethylene-vinyl acetate copolymer. The terpolymer
preferably has a molecular weight M~ of 500 - 10,000 and ;~
preferably contains in the side chains 6 to 20 CH3 groups, per
100 CH2 groups, whlch do not derive from the acetate; the EVA
copolymer preferably has a molecular weight M~ from 500 to 10,000 ~;`
" -
a~d contains 2 to 10 CH3 groups per 100 CHz groups. -
Flow improvers for petroleum oils or petroleum oil
distillates are also known from DE-A 35 01 384, which improvers ~-
contain two copolymers, namely an ethylene-vinyl acetate
copolymer with a vinyl acetate content of 25 - 35 percent by
' ~. `~ ' .
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weight and a viscosity of 200 - 1500 mPa s (at 140C) and an
ethylene-propene-vinyl acetate copolymer also containing 25 - 35
percent by weight of vinyl acetate and having a viscosity of
200 - 1500 mPa s.
JP-B 62 119 296 (Chem. Abstr. 107, 80830m) describes a flow
improver for fuel oils which on the one hand contains a copolymer
of ethylene with at least one carboxylic acid vinyl ester having ;
a molecular weight less than 1100 and, on the other hand, a
copolymer of ethylene with a carboxylic acid vinyl ester having ;~;
a molecular weight in the region from 500 - 10,000. ~-;
Additives having a pour-point improving effect for gasoline,
kerosene, and fuel oils and comprising EVA are also proposed in
JP-B 58 194 988 (cf. Chem. Abstr. 100, 177634u). These are
additives containing from 2 to 98 percent of ethylene-vinyl ;~
ester copolymers and, for the remainder, ethylene-vinyl acetate
copolymer or acrylic acid ester-ethylene copolymer, inter alia. -~
In an older publlcation (DE-A 20 48 308), the addition of an
ethylene-vinyl acetate copolymer in the form of a mixture is
recommended, for example of one part by weight of a copolymer
havlng~a~ moleoular weight of 3000 and three parts of a copolymer
having a molecular weight of 9000. Graft copolymers of long
. ~
chain esters of (meth)acrylic acid onto ethylene-vinyl acetate
copolymers are!recommendedi in DE-A 37 25 059 as flow improveis
for mlddle~distillates.
As follows from the publications describing the state of the `
: ~
~art, mixtures of ethylene-vinyl ester copolymers of different
types are recommended as oil additives, whereby the flow
improvlng properties of the additives are specially emphasized.
The concept of using mixtures is, however, insufficient to enable ~ ` ;
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, .. . .. .. ............ ......... ......... ..... ....... .. .. . . ..... . . . .. .. . . . .. . .
-` 202~71
the derivation therefrom of ready, concrete rules for industrial
purposes. Understandably, the type and kind or origin of the
oils or oil products play a critical role. On the other hand,
not only the composition, but also the molecular weight, of a
polymeric additive is of decisive influence on its specific
efficacy. The problem which is at the root of the present
invention is to put additives for middle distillates at the
disposal of the petroleum industry. The problem especially
concerns diesel fuels, with particular emphasis on "high final
boiling" diesel fuels. The aforementioned problem particularly
is to provide additives which hinder the settling of paraffin
crystals at low temperatures and which improve the filterability
of the petroleum oil products.
As is usual in the petroleum industry, by "middle - -
distillates" is understood those fractions which usually include ~; ~
.~
gas oils (boiling range 170C - 350C, particularly 225C - 350C
Terminal Boiling Point according to ASTM 2892), diesel fuels,
airoraft turbine fuels, and heating oils. In general, those
fractlons boiling in the range above 170C, preferably above
225C, are~included in this category (cf. Winnacker-Kuchler, -~ `
Chemische Technoloqie, 4th edition, Carl Hanser Verlag, Munich
1981). In particular, the use of the additives of the invention
is directed to "high final boiling" diesel fuels. By this term,
... . ..
the~skil~led artisan meane generally diesel fuels having boiling
end~points greater than 380C and a difference between the
bolling end point and the 90 percent distillation point greater -~
~ - ~,, ~ : , .
than 30 Centigrade degrees. ~ -
The additives according to the invention serve particularly
as flow improvers for middle distillates which contain more than ~ -~
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0.5 percent by weight of alkanes having a chain length of C25 or
greater, especially such middle distillates having a boiling
point (at 760 mm pressure) above 360C.
The additives according to the present invention comprise:
~ ) 20 - 95 parts by weight of an ethylene-vinyl acetate
copolymer or of an ethylene-vinyl acetate terpolymer having a
specific viscosity, ~ ~/c, = 6 - 50 ml/g (measured at 25C in
xylene), a vinyl acetate content of 25 - 35 percent by weight,
and a degree of branching of 3 to 15 CH3 groups per 100 CH
groups, and
B) 1 - 80 parts by weight of an ethylene-vinyl acetate copolymer
having a melt viscosity index (MFI) of 20 to lOOO g/10 min and a vinyl
...., ~ . ~
acetate content of 15 - 35 percent by weight, and
C) 0 - 75, preferably 1 - 70, and particularly 5 - 66,
. . ...
parts by weight of a polyalkyl (meth)acrylate having 6 - 26,
preferably 8 - 24, carbon atoms in the alkyl portion.
In case component A) is present as a terpolymer, it is a
copolymer of 20 - 35 percent by weight of vinyl acetate, 50 to 70
percent by weight of ethylene, and S to 15 percen~ by weight of a ~ ~
third monomer selected from the group of olefins, especially from ~ '
the alkyl dienes, represented for example by diisobutylene or
isobutylene, or from the alkenes having more than 2 carbon atoms,
exemplified by propene.
The preparation of the individual components of ethylene-
vinyl acetate copolymer and terpolymers according to A) and B) is
as already discussed -- state of the art. (Cf. DE-A 36 16 056;
EP-A 99 646, or DE-A 19 14 756.) Preparation advantageously -
~takes place by copolymerization of the monomer in an autoclave at
temperatures from 80C - 150C and pressures from 5 - 16 mPa s in -
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the presence of free radical initiators such as peroxides and in
suitable inert organic solvents.
The solvents fall into the following groups:
i) kerosene (boiling range 180C - 210C)
ii) gas oils (boiling range 225C - 350C; cf. DIN 51567)
iii) paraffin based oils, consisting of
Fraction 1 (boiling range 250C - 275C/normal
pressure) at density dl5 less than
0.825)
Fraction 2 (boiling range 275C - 300C/53 mbar)
at density d~g less than 0.876
iv) naphthene based oils, consisting of
Fraction 1 (boiling range 250C - 275C/normal ;
pressure) at density dlS greater than
0.860) ~ ~;
Fraction 2 (boiling range 275C - 300Ct53 mbar) -
at density dl5 greater than 0.934
(cf. Winnacker-Kuchler, Chemische Technoloaie, 4th edition,
Vol.6, 570, Carl Hanser Verlag, Munich 1982; Ullmanns
~, .
Encvclopadie er techn. Chemie, 4th Edition, Vol. 10, pp 624 -
625~, Verlag Chemie). Representatives of this type, useful ~ ;
~; according~to the inventions, are commercially available, for
example. A measured viscosity of ~ /c of 6 - 50 ml/g
corresponds~roughly to a molecular weight Mw of about 1000 -
~10,000. A melt viscoslty index (MFI) of 20 - 1000 corresponds
approximately to a molecular weight Mw of 20,000 - 10,000. The
last mentioned, higher molecular weight ethylene-vinyl acetate
. . -. :.
~ copoIymers thus are of the same type as commercial hot melt ~ -
:: .: ,., ~ :
~ ~ adhesives. ~ ` ~
:
The analytical determinations (molecular weight, etc.) for
;; ethylene-vinyl acetate copolymer can be carried out according
~;~ Brauer et al., Chem. Techn. 24, 630 - 635 (1977). The
determination of viscosity, ~ /c, is performed according to
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DIN 1342, DIN 51562, DIN 7745, ASTM D2857. See also,
Kirk-Othmer, Encyclopedia of Chemical TechnoloqY, 3rd Edition,
Vol. 18, pp 207-228, J. Wiley, New York 1982). `~
The preparation of the polyalkyl (meth)acrylate, C), can
follow in a known manner by (free radical) polymerization from ~;
the known monom~rs of the formula I
CH2 = C - C - ORz
R o
wherein R1 stands for hydrogen or methyl and R2 for an optionally ;~
~ . . . ..
branched alkyl group having 6 - 26, preferably 8 - 24,
particularly 12 - 20, carbon atoms.
The preparation of the polyalkyl (meth)acrylate is
preferably performed by means of solution polymerization and in a
particular manner proceeding in the presence of components A) ~`~
or/and B). As solvents, those pertinent materi~ls mentioned
earlier in which the monomers dissolve and which will permit
polymerLzation at an elevated temperature, are suitable, for
example. As a guide value, a boiling point of at least 50C at
760~mm~can~be;mentioned. Thus, the solvents fall, for example,
among~the~h~ydrocarbons such as kerosene (boiling range 180C -
21~0~C~), oils having a naphthene base, oils having a paraffin ~ ;~
base, or the gas oils, as mentioned earlier. ~ -
In general', the conditions are so chosen that the polymer
formed stand& in a weight ratio to the solvent of 80 : 20 to
20 : 80, preferably 60 : ~40 to 25 : 75. As a rule of thumb, a
~: ~
weight ratio of solvent to polymer of 1 : 1 can be given.
In carrying out the polymerization of the monomers of
formula I, one can proceed as follows:
Thc monomers of formula I are warmed in the solvent to a
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temperature above 50C in a suitable polymerization vessel -~
equipped with a stirrer, reflux condenser, and thermometer.
Suitably, an inert gas like nitrogen or argon or helium is
suitably first introduced over a certain period of time, for
example an hour, and then further processing is under an inert
atmosphere. The polymerization is initiated with free radical
initiators known per se, preferably of the lipophilic type,
particularly per-compounds such as butyl perpivalate and tert.-
butyl peroctoate. The amount of initiator added is usually in
the range from 0.1 to 2 percent by weight calculated on the
monomers (cf. H. Rauch-Puntigam, Th. Volker, AcrYl- und
MethacrYlverbindungen. Springer Verlag 1967).
For control of the molecular weight, chain transfer agents,
e.g. the known sulfur chain transfer agents, particularly
mercaptans such as dodecyl mercaptan, can be added in the usual
amounts of 0.5 - 5 percent by weight calculated on the monomers.
- ~ :
A~period of about 4 - 16 hours can usually be taken as the ~
~duration of the total polymerization time. The polymer can be ~ ~-
isolated in a known fashion, for example by precipitation, but
sultably it is arranged so that further processing can be in
solut~ion.
The polymerization of the monomers of the formula I in the
~presence of ethylene-vinyl acetate copolymers or terpolymers can,
n principle, be~aarried out in the same fashion:
The solution of polymers A) and B) in the solvents is
~adYantageously promoted by warming, particularly to temperatures
ln~the range of 90C + 10 C, with stirring. Further, the
monomers of formula I plus initiator are advantageously added
during the reaction, advantageously using a dosing pump, under an
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~ 2020~71
inert atmosphere at an elevated temperature, taking into
consideration the decomposition temperatures (up to about 90 C) of
the initiators used, and within a certain time period, for example
2 + 1/2 hours. Advantageously at the end of monomer addition,
initiator is again added in an amount of about 5 - 15 percent of the
amount already added. As a rule, the total polymerization time can
be estimated at about 4 - 16 hours.
The additives of the invention are as a rule available for
use as relatively concentrated polymer solutions in the solvents
mentioned. In general, the content of polymer in the concentrates
is 20 to 80 percent by weight. They are advantageously added to the
oils or fractions whose flowability or filterability is to be
improved in such amounts that these contain 10 to 1000 ppm,
preferably 50 to 500 ppm, of the polymer additives according to the
invention.
The positive effect of the additives of the invention is
particular}y outstanding when used in middle distillates, above all
in middle distillates which contain more than 0.5 percent by weight
of n-alXanes having chain lengths of 25 or more C-atoms, and
especially in such middle distillates whose boiling point is above
230-C at 760 mm pressure.
Above all, the superior ability of the polymer mixtures of
the invention to hinder wax settling are demonstrated to their full
degree oniy in diesel fuéls containing largé amounts of long chain
n-a}kanes, as described above. For the most part, these are "high
final boiling" diesel fuels to a lesser extent those are diesel
fuels with normal boiling behavior. In contrast, in many diesel
fuels~ containing small amounts of long chain alanes, the flow
improving properties become more evident than those hindering wax
settling.
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One of the goals behind the present invention is to make
available additives which will hinder wax settling as well as
showing a flow improving effect, at least for important segments
of the entire range of middle distillates if not over the entire
range itself. This goal could, surprisingly, be reached by the
polymer combination according to the invention of components A),
B), and, optionally, C). The excellent storage stability of ~ :;
concentrated forms of the additive of the invention, especially
in the presence of component C), is particularly to be
:. ,
emphasized. It is remarkable in this connection that the
advantage of an improved storage stability is not associated with
a general decrease in efficacy. ~:
A better understanding of the present invention and of its
many advantages will be had by referring to the following -~
Examples, given by way of illustration. :
Determination of the viscosity ~ ~/c is carried out
according to DIN 1342, DIN 51562, and DIN 7745. Determination of
the melt viscosity takes place according to DIN 53735 or ASTM
1268-62T.
I. Pre~aration of the Additives of the Invention from the
Components A), B), and o~tionally C).
General Directions:
The ethylene-vinyl acetate copolymers and optional
poLyalkyl (meth)acrylates, in the mixing ratios given in the
individual Examples, are dissolved in kerosene (boiling point
aooc - 220C) over a period of 2 hours by stirring at 80C. The
amount of kerosene is so chosen that 50 percent solutions result
in:each case.
The following Examples 1 - 8 are prepared using the
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,., ~
~ ,
following ethylene-vinyl acetate copolymers or terpolymers, all
of which had a degree of branching between 3 and 15 CH3 groups
per 100 CH2 groups~
VA-A1 = ethylene-vinyl acetate-diisobutylene terpolymer
(61 : 28 : 11, ~ ~/c (xylene, 25C) = 16 ml/g)
EVA-A2 = ethylene-vinyl acetate copolymer, VA-content = 32 -
wt.-%, ~ ~/c (xylene, 25C) = 19 ml/g
EVA-B3 = ethylene-vinyl acetate copolymer, 28 wt-% VAi, MFI
150 g/10 min
EVA-B4 = ethylene-vinyl acetate copolymer, 28 wt.-% VA, MFI
400 g/10 min
EVA-B5 = ethylene-vinyl acetate copolymer, 28 wt.-% VA, MFI
800 g/10 min
EVA-~6 = ethylene-vinyl acetate copolymer, 19 wt.-% VA, MFI
12 g/10 min i;~
EVA-B7 = ethylene-vinyl acetate copolymer, 18 wt.-% VA, MFI `
150 g/10 min -~
Exam~le ComPOSitiOn (Parts bY Weiqht)
1 50 pts. EVA-A1 + 50 pts. EVA-B3
2 66 pts. EVA-A2 + 34 pts. EVA-B4
3 50 pts. EVA-A1 + 50 pts. EVA-B5
4 80 pts. EVA-A1 + 20 pts. EVA-B3
50 pts. EVA-A2 + 50 pts. EVA-B3
6 95 pts. EVA-A1 + 5 pts. EVA-B6
7 ~ 90 pts. EVA-A1 + 10 pts. EVA-B7
8 !`70 pts.~iEVA-A1~+ 20 pts. EVA-B5 + llO pts. PAMA~C1
(see Example 10)
Example 9 --
712.5 g of EVA-A1 and 37.5 g of EVA-B6 are dissolved by
stirring in 750 g of kerosene (180C - 210C) at 90C in a round
bottomed vessel equipped wîth a blade stirrer and reflux
aondenser. Subsequently, a mixture of 1500 g of iso-ClO- -
methacrylate and 22.5 g of tert.butyl peroctoate is added at
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90C over a period of 2 hours under a nitrogen atmosphere to the
already-present solution by means of a dosing pump. At the end
of the addition, a further l.S g of tert.-butyl peroctoate are
added. The total polymerization time is 16 hours. The product
contains a total of 75 percent of polymer, flows at room
temperature [~Ot, ( 40C) = 4500 mPa s], and is cloudy white. --~
., ~
The solidification point is at ~5C. In contrast to the
procedure in Ex~mple ~, wherein PAMA [polyalkyl ;~
(meth)acrylate is admixed with EVA polymers, this Example shows
polymerization of the alkyl (meth)acrylate monomers in the
presence of the EVA copolymer. The product of this Example
consists of 47.5 parts of EVA-A1, 2.5 parts of EVA-B6, and 50
parts of polyisodecyl methacrylate.
Following Example 10 describes the preparation of component
C), more specifically identified herein as PAMA C1.
Exiample 10
600 g of tallow methacrylate and 600 g of a naphthene based
~oil havlng a viscosity of 1.2 mmZ/s at 100 C are warmed to 75C
in a~2-liter four-necked flask. Nz is introduced for 1 hour,
then lS g of docecyl mercaptan and 4.8 g of t-butyl perpivalate
are added. After 4 hours 1.2 g of t-butyl perpivalate are again
added. After 12 hours the polymerization is completed.
~,~/c (20C, CHCl3) = 10 ml/g
Conversion: 98.7 percent.
II. Flow Improvinq Effect of the Additives.
The flow improvers according to Example 1 - 9 were added to
a~series of products from the range of middle distillates. The
products, designated DK1 to DK7, are described below: ~
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2020~71 : ~
DK 1 is diesel fuel from an English refinery
DK 2 is diesel fuel from a German refinery
DK 3 is diesel fuel from a German refinery
DK 4 is diesel fuel from a French refinery
DK 5 is diesel fuel from a Greek refinery
DK 6 is diesel fuel from a German refinery
DK 7 is diesel fuel from a German refinery
::
In the following Table, the Cold Filter Plugging Point . ~.
(CFPP) determined according to DIN 51428 or J. of the Institute ; ~
of Petroleum, 52 (510) is given. ~;
DK Content of Content of CFPP End Boiling
n-alkanes n-alkanes Point
C > 25 ( C ) ~ C ) ;: ~
17 % 0.8 % + 2 390 ;. . -
2 22 % 0.9 % + 2 377
3 14 % 0.6 % - 3 37
4 14 % 0.9 % + 2 382
S 24 % 1.8 % + 10 395
6 17 % 0.9 ~ + 3 400
7 : 15 % 0.7 % + 2 391
The amounts of additive added refer in each case to amounts
of the 50 percent solutions of Example 1 - 8 or the 75 percent ~ :
solution of Example 9,~which solutions were heated before ! ' ~ '
~additlon.~ For comparison, 50 percent solutions, in kerosene, of
individual ethylene-vinyl acetate copolymers were similarly added
.
:~: to the various diesel fuels, DK. ::
~ '
:
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,,~
DK 1 ~ .
Example Amount added (ppm)
100 200 300
1 - 9 - 12 - 13
3 - 13 - 15
- 12 - 14
9 - 7 - 9 - 10
. . ;.
Compn. EVA-A1 - 7 -9 - 10
Compn. EVA-A2 - 10
.
DK 2
Example Amount added (ppm)
150 250 500
1 - 4 - 10 - 11 ;~
2 - 9 - 10 ~-
~ ~ . :.
3 . - 11
Compn, EVA-A1 ~ - 1 - 7 - 9
DR:3~
Example ~ Amount added (ppm)
50 , 100 300 . 400
~ - 13 - 16 - 17 - 17
2~ 3 ~ ;- 15 ' - 15 - 16
, :-. , ~ , - ~ .~ , , , : : : :
Compn~ EVA-Al ~ - 11 - 12 - 13 - 15 ~ :
Compn~ EVA-B3~ - 3 : - 10 - 14 ~:
~ : ~: : . :
:Example Amount added (ppm)
: :50 100 200 400
Compn. EVA-A1 ~ 3 + 0 - 2
, : ,: ,
:~ : ~ , . ~ .;
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2020~71 ~:
DK 5
Example Amount added (ppm)
200 400 500
1 + 4
8 + 5 - 4 ~ 4 ~'
Compn. EVA-A1 + 6
Compn. EVA-A2 + 6
DK 6 ,:
Example Amount added (ppm)
200 500
.:
4 - 2
- 3
8 - 12 - 14
Compn. EVA-A1 - 2
Compn. EVA-A2 - 1
DK 7
Example Amount added (ppm)
100 150
6 - 16
: ,
, .
7 - 14 - 16
9 - 15 - 17
Compn. EVA-A1 - 8 - 12
Compn.~EVA-A2 - 10 - 13
III. "Wax Antisettling", Effect.
Samples of DK containing additive are put into graduated 20
ml measuring cylinders and cooled to a temperature 5 Centigrade
degrees below the cloud point (CP). Subsequently, the settling
of~paraffin~crystals is observed as a function of time and is
reported~in percent sedimentation. The determination of the
Cloud Point (CP) is according to DIN 51597. Again, comparisons ~ ;
with sample~s containing individual ethylene-vinyl acetate
. ~: ~:: ,.:
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001-03-12
2020571 ~ ~
additives are made.
DK 1: Amount added 500 ppm; T = - 1C; CP = + 4C
ExamPle Sedimentation after 100 hours
1 5 %
3 6 % ;
9 5 %
7 %
Compn. EVA-Al 40 %
Compn. EVA-A2 80 %
~'
DK 2: Amount added 250 ppm; T = - 3C; CP = + 2C
Example Sedimentation after
30 hours 95 hours
9 45 % 64 %
1 52 % 64 %
2 53 % 68 %
~- 3 51 % 63 %
Compn. EVA-Al 72 % 80 %
,
DK 3: Amount added 200 ppm; T = - 8C; CP = - 3C
Example Sedimentation after
30 hou~rs 80 hours
2 % 7 %
; 2~ 4 % 10 %
Compn. EVA-Al 68 % 74 % ~ ~ -
DK~4:~ Amount added 100 ppm; T = - 3C CP = + 2C
Example ~ ~ Sédimentation after
50 hours 100 hours 140 hours `~
2 % 5 % 7 %
3~ 1 % 3 % 4 %
9~ ~` 4 % 7 % 10 %
Compn.~EVA-Al11 % 35 % 65 ~
~ ,
~, ~; '' ''
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DK 6: Amount added 500 ppm; T = - 1C; CP = + 4C
Example Sedimentation after
_ 60 hours 170 hours .
8 2 % 11 %
Compn. EVA-Al 10 % 55 %
Compn. EVA-A2 70 % 90 %
' ;:,
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