Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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POLYISOCYANATE PARTICLES OF CONTROLLED PARTICLE SIZE AND PARTICLE SIZEDISTRI8UTION
D~SCRUPTION
The present invention relates to solid particles of polyiso~y~l~Les, in particular diisocyanates,
and more particularly diphellylll.e~ ne diiso.;y~lales (MDI), a method for the production
thereof and their use.
Polyisocyanates are well known in the art and are used extensively as raw materials, for
example in the production of polyurethanes.
Polyisocyanates cover a broad range of organic compounds having 2 or more isocyanate
groups. Such compounds may comprise aromatic and/or aliphatic groups. Examples of
polyiso~iy~les which are widely used include tolylene diisocyanates (ll~I), diphenylmeth~ne
diisocyanates (MDI), naph~h~l~n.o-1,5-diisocyanate (NDI), 1,6-hPY~m~thylene diisocyanate
(HDI), p-phenylenediisocyanate (PPDI), trans-cyclohexane- 1 ,4-diisocyanate (CHDI),
isophorone diisocyanate (IPDI) and tetramethylxylene diisocyanates (T~DI).
One of the most important polyisocyanates is MDI.
In order to obtain s~ti~f~ctQry storage stability and processing, h~n~lling and reaction
properties, modifications are brought about to the isocyanate species.
Modified forms of polyisocyanates are mainly liquefied products such as llimeri~ed or
trimerised forms of the polyisocyanates, or reaction products of polyisocyanates with
compounds co"~ isocyanate-reactive groups.
Some polyisocyanates, for example 4,4'-diphenylmethane diisocyanate, are already available
in the form of flakes, but these give rise to problems from a health and safety point of view
since they generate dust.
Also known is the use of finely-divided solid polyisocyanates, for example MDI-powders,
particularly in binders or adhesives (see e.g. US-A 4569982). These powders are produced by
~lo".;~;.,g a liquid stream. Hence, the droplets here have a broad particle size distribution, i.e.
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are polydispersed and have a tendency to coalesce. The result is that such powders generally
have a diameter of substantially less than I mm, are of irregular shape and have a large size
distribution.
In SU-A 145641 1 a method is described for producing solid spherical granules of 4,4'-MDI v
by pouring molten product dropwise into water and cooling whereupon the drops solidify and
form solid granules.
This method however results in the formation of urea-groups due to the reaction with water
and the presence of cignific~n~ ~mollntC 4,4'-MDI dimers, which are detrimental to the product
quality.
It has now been found that solid polyisocyanate particles can be produced which have a
controlled particle size and particle size distribution, and which are chemically virtually
identical to the starting material of which they are made.
In particular the flowability of such particles is much better, which allows easier and quicker
handling for storage or transport. Furtherrnore, the generation of dust by these particles is
considerably reduced and is below an acceptable level.
The present invention thus concerns solid polyisocyanate particles having a particle size
distribution index of less than 1.5. Preferably the particles are substantially free of inr~l1ced
impurities.
The term 'induced impurities' includes all reaction products formed through the reaction of
isocyanate-groups with isocyanate-reactive groups during the conversion of the polyisocyanate
starting material into particles which were not present in the starting material.
Such reaction products may be urethanes, allophanates, ureas, biurets, amides, carbodiimides
or uretonimines, or dimers or trimers of isocyanates.
The particle size distribution index (PSDI) is the ratio of the weight average particle size and
-
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the number average particle size~ the weight average particle size being
~wjD
~wj
wherein wi is the weight of the particles with inean fli~m~ter Dj,and the number average particle
size being
~nj
wherein nj is the number of particles with mean diameter Dj.
The term diameter as used herein is intended to include the main cross dimension of a particle.
Preferred polyisocyanate particles have a PSDI of less than 1.3. Most preferably the PSDI is
not more than 1.1.
The polyisocyanate particles of the present invention may have any shape~ but are preferably
spheroidal~ and most preferably spherical.
Polyisocyanate particles according to the invention may be one or more polyisocyanate species~
pl~r~ bly one or a mixture of congeneric species, e.g. oligomers, in particular one species, and
can be obtained from any organic polyisocyanate.
Useful polyisocyanates may be aliphatic~ cycloaliphatic, araliphatic, heterocyclic or aromatic.
Suitable polyisocyanates include, for example, hexamethylene diisocyanate, isophorone
diisocyanate, cyclohexane- I ,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate and p-
xylylene-diisocyanate .
Preferred polyisocyanates are aromatic polyisocyanates, for example phenylene diisocyanates,
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tolylene diisocyanates, I,5 -naphthylene diisocyanate and especially diphenylmethane
diisocyanate (MDI) based polyisocyanates like 4,4'-MDI, 2,4'-MDI or mixtures thereof and
polymeric MDI having an isocyanate functionality of more than 2.
A type of polyisocyanate with which it has been found particularly useful, is "pure" ~vIDI. .
The term "'pure" MDr is intended to include polyisocyanate compositions com~,. .sirlg at least
85%, preferably at least 95% and most preferably at least 99% by weight of 4,4'-~I.
Generally, "pure MDI" shows a strong tendency to dimerize. It is a particular advantage of this
invention that "pure MDI" particles according to the invention do not contain any in~lced
dlmer groups.
The polyisocyanate particles of the present invention generally have a r1i~mçter of from 0. I to
5 mm. The ~efe,.ed size largely depends on the application of the solid polyisocyanate
particles. For most applications a particle size of from I to 2.5 mm is prere--~d, 1.0 to 1.5 mm
being even more p-~ ed. Particles having a larger size tend to form 'pop-corns' and are less
pre~-, ed.
In a further aspect, the invention also relates to a method for the production of said
polyisocyanate particles which comprises subjecting molten polyisocyanates to a, preferably
vibrated, prilling treP,tmçnt.
Prilling operations are known from the production of o.a. fertilizers and are described in, for
example, EP-A 320.153. Further details on the prilling process can be found in e.g. EP-A
542545, EP-A 569162, EP-A 569163 and EP-A 570119, which are incorporated herein by
reference.
~n the prilling operation a molten material is caused to flow through at least one nozzle, which
is optionally vibrated, to form drops of the material which are cooled in a cooling medium to
give solid spheres or prills of the material.
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The cooling generally takes place in a tower where the drops fall down in a counter-current
fiow of a gas. Usually a plurality of nozles is used and the size of the drops largely depends
upon the size and type of the nozzles, the nature of the material being prilled and the rate of
flow of material through the nozzles.
The cooling me~lium is preferably not isocyanate-reactive and may be any inert gas. A
p,~ .ed gas is nitrogen. The choice of a suitable cooling medium and the cooling tenl~elal~lre
depend on the characteristics of the polyisocyanate starting material. For example, in the
production of particles from pure ~vIDI a temperature of-20 to -25 ~C is preferably employed.
Compared to other bulk particulate products the prilled products have a very narrow size
distribution.
Although the prilling treatment does generally not have a detrimental effect on the product
quality, usual additives such as stabilisers, anti-oxidants or pigments may be added to improve
such properties as storage and colour stability or oxidation resistance.
The polyisocyanate particles of the present invention can advantageously be used in the
production of polyisocyanate polyaddition products, such as foams, elastomers, coatings,
adhesives, se~l~ntc encapsulants or binders.
EXAMPLES
Examples 1-4
4 batches of pure MDI prills were produced on a pilot-scale prill tower by the process
generally described in EP-A 320. 153~ but here modified to meet the requirements for 4,4'-MDI
production. The feed rate of the melt was 25 kg/h and the cooling medium was liquid nitrogen.
Mostly a 6 hole plate was used.
A sample was taken from each batch and the PSDI was calculated. The results are shown in
tables I-IV.
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Table I: Hole si~: 650 rnicro~c (vibrated)
Sieve size% retained Median size Median No. of Percent in
(mm) on sizeby particle particles inrangeby
weight weight range (1 kg number
(.~rams) total)
<03 0.01
0.15 0 61.34 5.2
0.3 2.81
0.65 0.13 211.85 17.95
0.19
1.09 0.63 3.04 0.26
1.29 1.04 ~8~9.75 73.68
E~ ~54~ '.~ ~ ~ .. 3~ . ~ 3~'t"~ it~j~ ~ ~----1~
~ ~s~; ,r ~ ~ ~ ~ E;;~ ~ ~ l --¦
1.55 1.8 31.64 2.68
1.7 0.88
1.85 3.06 2.88 0.24
2 0
2.18 5 0 0
2.36 o
TOTALS 99.76 1,180.49
Weight average particle size = 1.3 mm
Number average particle size = 1.24 mm
PSDI= 1.048
,
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Table IT: Hole ~i7~: 650 micron.~ (unvibrated)
Sieve size% retained Median sizeMedian No. of Percent in
(mm) on sizeby particleparticles in rangeby
weight weight range (1 kg number
(~rams) total)
< 0.3 0.01
0.15 0 61.34 3.99
0.3 5.01
0.65 0.13 377.7 24.58
36.02
1.09 0.63 S75.86 37.47
t~
1.29 1.04 463.04 30.13
1.55 1.8 56.1 3.65
1.7 0.8
1.85 3.06 2.62 0.17
2 0
2.18 5 0 0
2.36 0
TOTALS 99.94 1,536.66
Weight average particle size = 1.215 mm
Number average particle size = 1.11 mm
PSDI = I .1
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Table rrI: Hole Si7~? 52Q rnicrorlc (vibrated)
Sieve size% retainedMedian size Median No. of Percent in
(m n) on size by particleparticles in range by
weight weight range (I kg number f
(~rams) total)
c 0.3 0.01
0.15 0 61.34 3
0.3 7.89
0.65 0.13 594.83 29.12
~ ~ t~ ~L 3 ~ Y
1.09 0.63 1,287.61 63.04
1.29 1.04 82.56 4.04
1.4 2.83
1.55 1.8 15.73 0.77
1.7 0.18
1.85 3.06 0.59 0.03
2 0
2.18 5 0 0
2.36 o
TOTALS 100.01 2.042.66
Weight average particle size = 1.1 mm
Number average particle size = 1.04 mm
PSDI= 1.058
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Table IV: Hole si7~: 1040 micron~ (vibrated)
Sieve size% retainedMedian sizeMedian No. of Percent in
(mm) on size by particle particles in range by
weight weight range (I kgnumber
(s~rams) total)
<03 0
0.15 0 0 0
0.3 0.71
0.65 0.13 53.53 15.36
0.75
1.09 0.63 11.99 3.44
1.18 1.02
1.29 1.04 9.84 2.82
1.4 3.92
1.55 1.8 21.79 6.25
1.7 64.57
1.85 3.06 211.14 60.58
2 20.13
2.18 5 40.23 3.41
2.36 8.9
2.52 7.73 11.51 0.98
TOTALS 100 348.52
Weight average particle size = 1.92 mm
Number average particle size = 1.8 mm
PSDI= 1.067
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Examples 5-6
Flowability of a range of prilled pure MDI batches was measured by weighing 250 g of frozen
prills and pouring it through a funnel into a cylinder of 42 mm ~ meter.
The average flow given in the tables V and VI is the average rate of 4 timed flows of batches
of frozen particles.
Table V
Target Prill Size (mm) Average Flow (.~/sec)
2.00 21.66
1.75 22.42
1.50 23.53
1.25 27.12
1.00 28.47
Table VI
Target Prill Size: 1.25 mm
% Prill at Tar~et Size Average Flo~ /sec)
50% - 60% 26.48
60~/o - 70% 26.69
70~,~0 - 80% 26.8
80~/o - 90% 27.23
90% - 27.15
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11
As can be seen from above Table V the flowability increases significantly with smaller particle
slze.
Table V I shows that for a given particle size the flowability increases with decreasing particle
size distribution (the higher the % prill at target size the narrower the particle size distribution).
A higher flowability enables quicker and easier drum filling and emptying operations.
Example 7
A chemical analysis was carried out for a batch of pure MDI prills and a batch of liquid pure
MDI starting material to demonstrate that the prilling process does not chernically alter the
MDI starting material.
Table VIT
% NCO% Dimer (GPC)% Oxidised MDI (GC-ECD)
Liquid pure MDI 33.21 0.034 3.69
Pure MDI prill 33.24 0.034 3.49
(GPC: Gel Permeation Chromatography; GC-ECD: Gas Chromatography - Electron Capture
Detector)
The chemical analysis shows little or no difference between the pure MDI prill and the liquid
MDI starting material. Thus, the prilling process does not chemically alter the MDI starting
material.
The gas chromatograms obtained for the prill and the liquid MDI appeared to be identical,
indicating that the prilling process does not introduce any further impurities to the starting
material.
