Process for suspension polymerization of vinyl chloride in a reactor equipped with a reflux condenser and a modified brumaging impeller

The present invention provides a process for producing vinyl chloride resin in suspension polymerization of vinyl chloride monomer by the use of a polymerization reactor equipped with a reflux condenser using an improved brumagine-type impeller equipped with auxiliary blade/s, and polymerization is started in a range of 0.8 to 1.0 of the water/monomer ratio, polymerization temperature is raised to 3.degree. to 10.degree. C. at polymer conversion being not more than 50 weight percent, with water being added in the course of polymerization not more than making up for the volumetrical contraction resulting from the progress of polymerization so that upon completion of polymerization the water/monomer ratio is controlled in a range of 1.0 to 1.4. The polyvinyl chloride resin obtained by the present process is superior in quality such as high bulk density and little fish eye with high productivity.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for producing vinyl chloride 
resin, and more particularly to a process for producing vinyl chloride 
resin high in polymerization productivity, high in bulk density and with 
less fish eye by the use of a polymerization reactor equipped with a 
reflux condenser. 
2. Description of the Prior Art 
In the production of vinyl chloride resin it is often the case that a 
reflux condenser is used for improving productivity as well as for 
energy-saving but this is accompanied by problems that suspension 
polymerization under cooling by a reflux condenser often causes an 
increased porosity in the particle interior and affected smoothness of the 
particle's surface and the resulting deterioration of the filling property 
causes lowering of the bulk density and an increase of fish eye. As to 
bulk density, it is well known that it is correlated with vinyl chloride 
resin's productivity in processing and lowering of bulk density is known 
to cause lowering of extruder's output to thus result in aggravation of 
productivity in processing. As means of improving polyvinyl chloride's 
bulk density there is known, for instance, a method of adding vinyl 
chloride monomer in the course of polymerization (Japanese Laid-Open Pat. 
App. No. 97679/75) but the vinyl chloride resin obtained by this process 
is known to have many fish eyes and, moreover, the residual monomer in the 
resin is difficult to remove. 
Meanwhile, the market's need for less fish eye of vinyl chloride resin 
(hereinafter referred to as "PVC") has been getting more severe year after 
year and general tendency is that fish eye of PVC plasticized with a high 
polymer plasticizer of relatively low plasticizing ability and high 
viscosity such as of polyester series is being taken up as problematic. In 
order to solve the problem of fish eye, it is recommended to prevent 
formation of low-porosity particles caused by low dispersion frequency 
through best possible improvement of dispersion-coalescence frequency of 
monomer droplets and also to improve the homogeneity of particles in the 
polymerized system through local monomer addition polymerization due to 
monomer condensed in the reflux condenser taking place in the top layer of 
polymer suspension through inhibition of bubbling in the middle stage of 
polymerization and thereafter. When a reflux condenser is used, gas 
generating from the monomer droplets are contained in the polymer 
suspension to result in lower homogeneity attainable by stirring and 
results in aggravation of fish eye through bubbling phenomenon in which 
polymer particles form a floating creamy layer on the polymer suspension 
in the middle stage of polymerization and thereafter. 
Further, when the bubbling phenomenon is marked, there is caused another 
problem that the polymer suspension overflows into the reflux condenser 
and its piping to cause deposition of scales to adversely affect the 
product's quality, also causing lowering of the heat-removing capacity of 
the reflux condenser and seriously affecting the safety control of the 
producing process. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a process for producing 
PVC by the use of a polymerization reactor equipped with a reflux 
condenser safe from the above-mentioned problems of the conventional 
process, higher in bulk density and with less fish eye. 
Another object of the present invention is to provide a process for 
producing PVC with less fish eye by the use of a high polymer plasticizer. 
Still another object of the present invention is to provide a process for 
producing PVC with less bubbling phenomenon, being capable of increasing 
the monomer charge without risk of suspension overflowing into the piping 
and the interior of reflux condenser and shortened in the time required 
for polymerization, these together resulting in a high productivity of 
PVC. 
Further objects and features of the present invention will be apparent from 
a reading of the following description. 
After their intensive studies the present inventors discovered to complete 
the present invention that the above objects can be accomplished by 
controlling the water/monomer ratio within a fixed range, modifying the 
polymerization temperature in the course of polymerization and further by 
the use of special stirring blades.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to a process for producing PVC wherein in 
suspension polymerization of vinyl chloride monomer and other monomers 
capable of copolymerizing therewith by the use of a polymerization reactor 
equipped with a reflux condenser in the gas phase portion of the 
polymerization reactor or outside the polymerization reactor stirring 
blades are used, each thereof being a by rumagine-type impeller with an 
auxiliary blade inclined with respect to the level rotary direction 
standing on the outer surface of a main blade attached to the tip thereof, 
the water/monomer ratio of initial charging is controlled in a range of 
0.8-1.0, polymerization is conducted in the first stage of polymerization 
to not more than 50 weight percent in polymer conversion, then the second 
stage of polymerization is conducted at a temperature 3.degree.-10.degree. 
C. higher than the polymerization temperature in the first stage, with 
water being added continuously or intermittently in the course of 
polymerization not more than making up for the volumetrical contraction 
resulting from the progress of polymerization so that upon completion of 
polymerization the water/monomer ratio is controlled in a range of 
1.0-1.4. 
Normally it is known that the degree of lowering of a resin's bulk density 
when a reflux condenser is used increases with increasing quantity of heat 
removed by the reflux condenser (hereinafter referred to as "Qrc") and as 
in the present invention (1) to set the water/monomer ratio at the time of 
initial charging small (i.e. increasing the charge amount of vinyl 
chloride monomer) and (2) to shift the polymerization temperature from a 
low to high level, both means enhancement of the generation of heat in the 
course of polymerization. Meanwhile, there is a certain innate limit to 
the heat removing capacity by a reactor jacket it is inevitable to 
increase Qrc of the reflux condenser, this supposed to be counter to the 
desired increase of bulk density. Surprisingly, however, the present 
inventors discovered that these two technical means enable substantial 
increase of Qrc without causing lowering of the bulk density and even 
marked increase of the bulk density could be hoped for, and thus completed 
this invention. 
Brumagine-type impellers are rational means of stirring for use in 
suspension polymerization of vinyl chloride being capable of high-speed 
spinning requiring no large driving force and high in shearing effect but 
it was supposed to be relatively less capable of producing a vertical flow 
and problematic for homogeneous stirring of the system desired. 
The marked improvement of PVC with regard to fish eye by the use of the 
stirring blades of the present invention is attributable to not only 
improved stirring efficiency and resultant dispersion-coalescence 
frequency in the early stage of polymerization and improved homogeneity of 
particles in the polymerization system but also to the stirring blades' 
capability to produce vertical flow and vortex suction effect which is 
effective for preventing the bubbling phenomenon characteristic owing to 
use of the reflux condenser as well as for improving homogeneity of 
polymer suspension. 
The stirring blades of the present invention are described below under 
reference to the appended drawings showing their embodiments. 
FIG. 1 is a plane view of the stirring blades of the present invention and 
FIG. 2 is a front view of the main blade thereof. In these figures, the 
main blade 3 is attached to the supporting portion 2 extending in the 
normal direction from the vertical shaft 1 (Brumagine-type impeller is 
normally in such a construction.). On the outer surface of the main blade 
3 an auxiliary blade 4 is attached at a given inclination. 
FIGS. 3 through 14 are perspective views showing the alternative 
embodiments of the main blade 3 and auxiliary blade 4 of the present 
invention. 
In the present invention the auxiliary blade 4 is set at a given angle of 
inclination to the level rotary direction, that is, an angle of elevation 
or depression (.alpha.). The angle of inclination is not particularly 
specified but generally preferred range is 5.degree.-30.degree.. If it is 
less than 5.degree. no sufficient vertical flow can be generated to result 
in insufficient general stirring effect, while when it is more than 
30.degree., it is likely to result in generation of too vigorous vertical 
flow, this causing too much power consumption and also an excessive 
dispersion with a risk of abnormal polymerization 
The area of each auxiliary blade 4 is preferred to be in a range of 20-60% 
of the area of the main blade 3. If it is less than 20% the effect 
produced by the use of the auxiliary blade (shearing effect, stirring 
effect) is insufficient, whereas when it is more than 60%, too much power 
consumption results as well as an excessive dispersion with a risk of 
abnormal polymerization. Furthermore, scales are likely to deposit and a 
lot of effort and time are required for removal thereof. 
The auxiliary blade 4 is not necessarily set perpendicular to the main 
blade 3 and inclined attachment within a range of 45.degree.-135.degree. 
is acceptable. The number of auxiliary blades is not specified either. It 
may be properly decided according to the size of the main blade 3 but 
normally 1-2 of them per one main blade will give a favorable result. 
The shape of the auxiliary blade 4 is not particularly specified either, 
and as shown in the drawings it may be rectangular, rhombic or triangular 
if it has a specified surface area. It need not be formed to cover the 
entire width of the main blade 3 and may as well be interrupted. Its 
thickness, too, is not particularly specified and may be properly decided 
according to the sizes of the main blade 3 and auxiliary blade 4 etc. When 
more than one auxiliary blade are set to one main blade, they are not 
necessarily of the same shape and dimensions and those of different shapes 
and dimensions may as well be used. 
The auxiliary blade 4 may be welded to the main blade 3 to be monoblock 
therewith or prepared separately and secured together by mechanical means 
such as bolting. 
The present invention features setting the water/monomer ratio at the time 
of initial charging within a range of 0.8-1.0 and controlling the 
water/monomer ratio upon completion of polymerization within a range of 
1.0-1.4, preferably within a range of 1.0-1.2, by adding water 
continuously or intermittently in the course of polymerization with care 
not to exceed the volumetrical contraction resulting from the progress of 
polymerization. 
The addition of water is to be done continuously or intermittently to make 
up for the volumetrical contraction resulting from progress of 
polymerization, but it is preferred to be done continuously when stability 
of the product's quality, controllability of inside temperature and 
desired prevention of bubbling etc. are taken into consideration. 
The volumetrical contraction resulting from progress of polymerization 
(.DELTA. V) is the quantity calculated by the following formula. 
EQU .DELTA.V=(Monomer charging).times.(Conversion).times.[(1/monomer 
density)-(1/1.4)] 
When the water/monomer ratio at the time of initial charging is less than 
0.8, coarse particles generate, while when it is in excess of 1.0, reduced 
is the bulk density increasing effect. 
When the water/monomer ratio upon completion of polymerization is less than 
1.0, particle size becomes rough and bulk density tends to get lower, 
whereas, when the amount of water added should be more than enough to make 
up for the volumetrical contraction, it results in increase of slurry 
volume in the polymerization system to result in extreme cases in 
overflowing of the polymer slurry into the piping or the interior of the 
reflux condenser to cause deposition of scales and this results in 
deterioration of quality (fish eye). Hence, the water/monomer ratio upon 
completion of polymerization should be not more than 1.4, preferably not 
exceeding 1.2. 
Further, the present invention features that polymerization is conducted in 
the first stage to not more than 50 weight percent in terms of polymer 
conversion and polymerization in the second stage is conducted at a 
temperature 3.degree.-10.degree. C. higher than in the first stage. The 
conversion when the polymerization temperature is changed is not more than 
50 weight percent, preferably 10-50 weight percent and more preferably 
15-50 weight percent. If it is less than 10 weight percent, fish eye tends 
to increase, while, when it is in excess of 50 weight percent, bulk 
density increasing effect is reduced. 
As other monomers which can be copolymerized with vinyl chloride in the 
process of the present invention there are cited, for instance, olefins 
such as ethylene and propylene, vinyl esters such as vinyl acetate and 
vinyl stearate, (meth)acrylate esters such as methyl acrylate and methyl 
methacrylate, esters or anhydrides of acids such as maleic acid and 
fumaric acid, nitrile compounds such as acrylonitrile and vinylidene 
compounds such as vinylidene chloride. 
As polymerization initiators used in the process of the present invention, 
there are included initiators normally used for suspension polymerization 
of vinyl chloride namely organic peroxides such as lauroyl peroxide, 
3,5,5-trimethylhexanoyl peroxide, t-butyl peroxypivalate, t-butyl 
peroxyneodecanoate, di-isopropyl peroxydicarbonate, di-2-ethylhexyl 
peroxydicarbonate and acetyl cyclohexylsulfonyl peroxide, and azo 
compounds such as .alpha., .alpha.'-azobis-isobutylonitrile and .alpha., 
.alpha.'-azobis-2,4-dimethyl valeronitrile. These are used signly or in 
combination with two or more. 
As suspending agents used in the process of the present invention are cited 
known suspending agents such as partially saponified polyvinyl alcohol, 
vinyl acetate-maleic anhydride copolymer, styrene-maleic anhydride 
copolymer, polyvinyl pyrolidone, gelatine, starch, methyl cellulose, 
hydroxypropyl methylcellulose and polyethylene oxide either alone or in 
combination but of these, preferred are partially saponified polyvinyl 
alcohol and/or hydroxypropyl methylcellulose in quality, polymerization 
stability etc. Preferred dose of the above-mentioned suspending agent is 
0.01-1 weight part per 100 weight parts of vinyl chloride monomer, 
although there is no particular limit to it. 
In the process of the present invention it is also possible to use a 
molecular weight adjusting agent. 
The initiator, suspending agent and molecular weight adjusting agent etc. 
may be added at once to the polymerization system at the beginning of 
polymerization and it is as well possible to add them in portions in the 
course of polymerization. 
The polymerization temperature in the process of the present invention may 
normally be in a range of 40.degree.-75.degree. C., although there is no 
particular limit to it. 
According to the present invention, it is possible to conduct suspension 
polymerization by the use of a polymerization reactor equipped with a 
reflux condenser for production of PVC high in bulk density with less fish 
eye and it is also possible to increase the monomer charge without risk of 
suspension overflowing into the piping or the interior of reflux 
condenser, which along with shortening of the polymerization time enables 
sizable improvement of productivity, the industrial significance of the 
present invention being thus remarkable. 
Hereafter examples of the present invention are given as well as control 
examples but these mean no limitation of the present invention. 
In the description below evaluation of the product's quality was made by 
the following methods. 
Bulk density: According to JIS K-6721. 
Particle size distribution: Sifting and shaking method. 
Porosity: Porosity was determined by the use of mercury compression type 
porosimeter of Aminco Inc., U.S.A. (Model 5-7118) through measurement of 
the volume of mercury pressed in per 100 g PVC at an absolute pressure of 
31-1011 psi (pore size 0.17-5.8 .mu.m). 
Fish eye: 100 weight parts of PVC obtained by polymerization, 50 weight 
parts of plasticizer [PN 250 (adipic acid-type polyester: molecular weight 
approx. 2,000), maker: Adeca Argus Inc.], 3 weight parts of tribase, 0.5 
weight parts of stearic acid, 0.4 weight parts of titanium dioxide and 0.2 
weight parts of carbon black were mixed, after still-standing for 3 hours 
the mixture was milled through 8 inch rolls at 150.degree. C. (sheet 
thickness: 0.2 mm). Sheets were cut out after 8 minutes and 10 minutes of 
milling and the number of transparent particles (fish eyes) per 5 
cm.times.5 cm sheet were counted. 
EXAMPLE 1 
90 weight parts of water having dissolved in it 0.07 weight parts of 
partially saponified polyvinyl alcohol were charged into a polymerization 
reactor 1.7 m.sup.3 in capacity provided with Brumagine-type impeller 
having attached thereto auxiliary blades as shown in FIG. 8 and also 
equipped with a reflux condenser having a heat transfer area of 5 m.sup.2, 
0.024 weight parts of di-2-ethylhexyl peroxy-di-carbonate and 0.024 weight 
parts of t-butyl peroxy-neodecanoate were added as initiators, 100 weight 
parts of vinyl chloride monomer (682 kg) was charged after deaeration, the 
temperature was raised to 54.degree. C. (polymerization temperature in the 
first stage) for polymerization to start, flow of cooling water was 
started through the reflux condenser when the polymer conversion reached 
3% and polymerization was conducted with Qrc being adjusted to 27,500 
kcal/hr from the 30 minutes on after the start of flowing cooling water. 
When the polymer conversion has reached 35%, the polymerization 
temperature was raised to 59.degree. C. (polymerization temperature in the 
2 nd stage) and polymerization was continued with Qrc readjusted to 40,000 
kcal/hr, the operation of the reflux condenser was stopped when the inside 
pressure lowered 1 kg/cm.sup.2 from the steady pressure corresponding to 
the polymerization temperature in the 2nd stage to recover the 
unpolymerized monomer, the slurry was then dehydrated and dried in a 
fluidized bed drier for PVC to be obtained. From immediately after the 
start of polymerization, water was continuously added at a constant rate 
by the use of a reciprocating pump all through the period of 
polymerization so that the water/monomer ratio at the start of recovery 
(upon completion of polymerization) was adjusted to 1.1 (total amount of 
water added: 20 weight parts). 
The resulting PVC was quite satisfactory with regard to bulk density and 
fish eye as shown in Table 1 with no indication of polymer suspension 
overflowing into the reflux condenser. 
EXAMPLE 2 
Polymerization was conducted in the same way as Example 1 except that the 
auxiliary blades were changed to what are shown in FIG. 13 and the 
resulting polymer was dehydrated and dried. 
The resulting PVC was satisfactory with regard to bulk density and fish eye 
as shown in Table 1 with no indication of polymer suspension overflowing 
into the reflux condenser. 
EXAMPLE 3 
Polymerization was conducted in the same way as Example 1 except that the 
polymerization temperature was changed when the conversion reached 50% and 
the polymer was dehydrated and dried. 
The resulting PVC was satisfactory with regard to bulk density and fish eye 
as shown in Table 1 with no indication of overflowing of polymer 
suspension into the reflux condenser. 
EXAMPLE 4 
Polymerization was conducted in the same way as Example 1 except that the 
polymerization temperature in the first stage was adjusted to 52.degree. 
C. and that in the second stage to 62.degree. C. and the Qrc of the reflux 
condenser at the polymerizing temperatures in the first and second stages 
were adjusted to 22,500 kcal/hr and 47,500 kcal/hr respectively and the 
polymer was dehydrated and dried. 
The resulting PVC was satisfactory with regard to bulk density and fish eye 
as shown in Table 1 with no indication of overflowing of polymer 
suspension into the reflux condenser. 
EXAMPLE 5 
Polymerization was conducted in the same way as Example 1 except that the 
water/monomer ratio at the time of initial charging was adjusted to 1.0 
without changing total charging volume and 651 kg of vinyl chloride 
monomer was charged and water was added so that the water/monomer ratio at 
the time of starting recovery of unpolymerized monomer was adjusted to 1.4 
(total amount of water added: 40 weight parts) and Qrc at the 
polymerization temperatures in the first and second stages were adjusted 
to 26,500 kcal/hr and 38,000 kcal/hr respectively and the polymer was 
dehydrated and dried. 
The resulting PVC was satisfactory with regard to bulk density and fish eye 
as shown in Table 1 with no indication of overflowing of polymer 
suspension into the reflux condenser. 
CONTROL EXAMPLE 1 
Polymerization was conducted in the same way as Example 1 except that 
ordinary Brumagine-type impeller was used with no auxiliary blade. The 
resulting PVC contained a lot of fish eyes. The result is shown in Table 
1. 
CONTROL EXAMPLE 2 
Polymerization was conducted in the same way as Example 1 except that the 
polymerization temperature was changed when the conversion reached 60%. 
The resulting PVC was low in bulk density. 
CONTROL EXAMPLE 3 
Polymerization was conducted in the same way as Example 1 except that the 
polymerization temperature was set at 57.degree. C. for both first and 
second stages and Qrc was adjusted to 34,000 kcal/hr. The resulting PVC 
was low in bulk density. 
CONTROL EXAMPLE 4 
Polymerization was conducted in the same way as Example 1 except that the 
polymerization temperature in the first stage was set at 49.5.degree. C. 
and that in the second stage at 65.degree. C. and Qrc at the 
polymerization temperatures in the first and second stages was adjusted to 
17,000 kcal/hr and 51,000 kcal/hr respectively. The resulting PVC had a 
lot of fish eyes. 
CONTROL EXAMPLE 5 
Polymerization was conducted in the same way as Example 1 except that the 
water/monomer ratio at the time of initial charging was adjusted to 0.7 
without changing total charging volume rate and 755 kg of vinyl chloride 
monomer was charged and water was added so that the water/monomer ratio at 
the time of starting recovery was adjusted to 1.1 (total amount of water 
added: 40 weight parts) and Qrc at the polymerization temperatures in the 
first and second stages were adjusted to 30,000 kcal/hr and 44.000 kcal/hr 
respectively. The resulting PVC contained a lot of coarse particles. 
CONTROL EXAMPLE 6 
Polymerization was conducted in the same way as Example 1 except that the 
water/monomer ratio at the time of initial charging was adjusted to 1.1 
without changing total charging volume (charged quantity of vinyl chloride 
monomer: 622 kg) and water was added so that the water/monomer ratio at 
the time of starting recovery was adjusted to 1.4 (total amount of water 
added: 30 weight parts) and Qrc at the polymerization temperatures in the 
first and second stages were adjusted to 25,400 kcal/hr and 36,000 kcal/hr 
respectively. The resulting PVC was low in bulk density. 
CONTROL EXAMPLE 7 
Polymerization was conducted in the same way as Example 1 except that 
ordinary Brumagine-type impeller without any auxiliary blade were used, 
the water/monomer ratio at the time of initial charging was adjusted to 
1.2 without changing total charging volume (charged quantity of vinyl 
chloride monomer: 600 kg) and no water was added in the course of 
polymerization and Qrc was adjusted to 30,000 kcal/hr throughout the 
polymerization. The resulting PVC was low in bulk density and had a lot of 
fish eyes. 
CONTROL EXAMPLE 8 
120 weight parts of water having dissolved in it 0.07 weight parts of 
partially saponified polyvinyl alcohol was charged into a polymerization 
reactor 1.7 m.sup.3 in capacity provided with ordinary Brumagine-type 
impeller without any auxiliary blade, 0.024 weight parts of 
di-2-ethylhexyl peroxy-di-carbonate and 0.024 weight parts of t-butyl 
peroxyneodecanoate were added as initiators, 100 weight parts of vinyl 
chloride monomer (600 kg) was charged after deaeration, the temperature 
was raised to 57.degree. C. for polymerization to start, unpolymerized 
monomer was recovered when the inside pressure lowered 1 kg/cm.sup.2 from 
the steady pressure corresponding to the polymerization temperature, then 
slurry was dehydrated and dried in a fluidized bed drier for PVC to be 
obtained. In the course of polymerization no addition of water was made 
and no reflux condenser was used. The resulting PVC was 0.525 in bulk 
density and contained 75 fish eyes at 8th minute and 23 at 10th minute. 
TABLE 1 
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Example Control Example 
1 2 3 4 5 1 2 3 4 5 6 7 8 
__________________________________________________________________________ 
Reflux condenser 
Used 
" " " " " " " " " " " Not 
used 
Auxiliary blade 
FIG. 
FIG. 
FIG. 
" " None 
FIG. 
" " " " None 
None 
8 13 8 8 
Shape Rec- 
" " " " None 
Rec- 
" " " " None 
None 
tang. tang. 
Number/one main 
2 " " " " None 
2 " " " " None 
None 
blade 
Angle/elevation (.alpha.) 
20 " " " " None 
20 " " " " None 
None 
Area % against 
30 " " " " None 
30 " " " " None 
None 
main blade/aux. blade 
Water/monomer ratio 
Time/initial charging 
0.9 " " " 1.0 0.9 " " " 0.7 1.1 1.2 " 
Start of recovery 
1.1 " " " 1.4 1.1 " " " 1.1 1.4 1.2 " 
Initial charge/ 
monomer 
(kg) 682 " " " 651 682 " " " 755 622 600 " 
Water added (wt. %) 
20 " " " 40 20 " " " 40 30 -- -- 
Polymerizing 
temp. (.degree.C.) 
1st stage 54 " " 52 54 " 54 57 49.5 
54 54 57 57 
2nd stage 59 " " 62 59 " 59 57 65 59 59 57 57 
Time of changing 
35 " 50 35 " " 60 -- 35 35 35 -- -- 
temp. (Conversion %) 
Qrc (kcal/hr) 
1st stage 27500 
" " 22500 
26500 
27500 
27500 
34000 
17000 
30000 
25400 
30000 
-- 
2nd stage 40000 
" " 47500 
38000 
40000 
40000 
34000 
51000 
44000 
36000 
30000 
-- 
Particle size 
distribution (%) 
60 mesh on 0 0 0 0 0 0 0 0 0 17 0 0 0 
60-100 mesh 
21 23 22 20 19 20 19 20 22 51 15 12 11 
100-145 mesh 
63 61 63 63 62 65 65 64 63 30 72 70 68 
145-200 mesh 
14 15 13 16 17 13 15 15 15 2 12 17 20 
200 mesh pass 
2 1 2 1 2 2 1 1 1 0 1 1 1 
Porosity cc/100 g 
24.5 
24.3 
24.7 
24.0 
25.0 
24.0 
26.0 
25.5 
21.5 
-- 26.0 
27.5 
25.0 
Bulk density 
0.535 
0.536 
0.530 
0.538 
0.530 
0.535 
0.515 
0.513 
0.545 
-- 0.519 
0.500 
0.525 
Fish eye 
(piece/5 cm .times. 5 cm) 
8th minute 73 76 70 75 68 352 70 68 250 -- 66 325 75 
10th minute 
19 21 15 20 17 130 14 15 100 -- 13 125 23 
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