Note: Descriptions are shown in the official language in which they were submitted.
3 2~Z~353
TITLE
IMPROVED PRESSBOARD END PROCESS FOR ITS PREPARATION
DESCRIPTION
TECHNICAL FIELD
This inYention relates to an improved
aromatic polyamide pressboard having increased
resistance to compces6ion combined with relatively
: high oil absorption characteristics. the invention
al60 relate& to a proce6s for preparing the improved
pre6~board.
BACKGROUND OF THE INVENTION
Pressboa~d prepared prom cellulo6ic materials
has been known and commeccially used for many year6.
While the cellulosic pre66board is extremely u6eful.
its use at high tempecature it limited by the low
thecmal 6tability of cellulo~ic material6.
More cecently. aromatic eolyamide fiber6
US patent 3,063.966 and 3,133,138)~ fibrid~ (U.S.
patent 2,999,708) and paper tU.S. patent 3,756,908)
having excellent p~oper~ie6 at high temperature have
become known. Pre6sboard compri6ed of aromatic
polyamide fiber6 and fibrid6 i6 al60 known and can
readily be prepared using the 6ame erocedure~ used in
the preparation of cellulo~ic pre~6board.
Aromatic polyamide pre6~board has been found
to be u6eful in many aeplication6. For example, it
oil filled t~an~former~ it ha been found Jo have a
6uitably high oil absorption which contribute6 to good
electrical in6ulating propectie~. However, or 60me
u6e6, it i6 nece66ary that the pre6~board not only
HT-2400-A 35 have a 6uitably high oil ab60rption but al60 provide
~2~21 3~i;3
resistance to compression so that the pressboard can
provide suitable separation of electrically conducting
component. It has been found that compaction
processes as taught by the prior art either do not
provide p~essboard products having adequate re6i6tance
to compression, or that they do 60 only by providing a
pressboard product which doe6 not have adequate oil
absorption.
This invention provide6 an improYed aromatic
polyamide pLessboard having a combination of good
resistance to compression and adequate oil
absorption. This invention also provide6 a process
for the preparation of the improved pressboard.
BRIEF DESCRIPTION OF THE INVENTION
This invention provides a high density
pres6board comprised of 20-95~ by weight aromatic
polyamide fibrids and 80-5% by weight high temperature
resistant floc, said pressboard having a calculated
void volume of 13 to 28~ by volume of the pre6sboard,
a thicknes6 of 0.5 to 50 mm, a mercury intrusion
volume at low ~ur~ace~olume ,Vml, of les6 than 0.20
cm /g; a mercury intru6ion volume at high
surface/volume, Vmh, of 0.08 to 0.28 cm3/g, a oil
absorption by volume in cm3/g. VO, of 0.09 to 0.2B
and by weight 8-24~; and a total aYailable absorption
volume in cm3/g, Va, equal to the largest of the
values for Vml, Vmh, and VO: the ratio of V
to V~l being ae least 1.1; 6aid pre~board having a
compre6sion jet (as hereinafter defined) of greater
than 0.12 mm but no moee than O.5 mm. Preferably the
pre66board is compri6ed of 50-70% by weight aromatic
polyamide fibrid~ and 30-50% by weight high
temperature re6i6tant floc. Preferably ehe high
temperature re6istant floc consi~t6 of an aromatic
polyamide and the pres~board has a density of 1.00 to
0 2
Zi~5,3
1.20 g/cm3. Preferably the aromatic polyamide
fibrids and high temperature resistant floc consist
essentially of poly(m-phenylene
isophthalamide)(MPD-I). The pressboard preferably is
comprised of aromatic polyamide fibrids and bloc and
has a thickness of 1 to 10 mm, a density ox 1.02 to
1.17 g/cm3, most preferably 1.10 to 1.15 g/cm3.
The pressboard preferably ha a compres6ion set of
0.12 to 0.35 mm~ most preerably 0.20 to 0.30 mm.
The improved pressboard it prepared by a
pcocess whereby an aqueous 61urry having 0.1 Jo 2% by
weight total solids compri6ed of 20-95% by weight
aromatic polyamide fibrids and 80-5% by weight high
temperature re~i6tant floc having a length of 2 to lZ
mm., 6aid acomatic polyamide fibrid6 and high
temperature resistant floc having a melting point
higher than 3Z0C, the slurry i8 formed into a
watarleaf having a water content of 50-95% by weight,
the watecleaf i6 combined into multiple layers to form
20 a wet lap, the wet lap is pre66ed at 100 to 200C
under a pressure of 10 to 60 kg/cm2 to form a low
density pre~6board having a calculated void volume of
30 to 60% by volume of the pre66board, the low density
pres6board is dried, ultimately at 270-320C, until
2~ sub6tantially no further moisture is evolved and
finally pces~ed at 8 to 350 kg/cm2 at 270-3~0C.
Preferably the temperature i6 275-300C. Most
preferably, the final pre66ing i6 at 275-285C and the
pre6~Ure i8 15 to 70 kg/cm2. Pceferably the
30 prefi6board i6 cooled undec re6~raint. Preferably the
hiqh temperature resi6tant floc con~ist~ of an
aromatic polyamide. Preferably the aromatic polyamide
fibrids and the high temperature cesi6tant floc
con6i6t of poly~m-phenylene isophthalamide)~
~5
~2~2~35~
DETAILED DESCRIPTION OF T E INVENTION
Definitions
By "aromatic polyamide is meant non~usible
polyamides whecein the amide group, i.e., the
50 R
., .
- C - N -
radical where R is hydrogen or a 1-6 carbon alkyl
group, of each repeating unit is linked through the
nitrogen atom and the carbon atom to a carbon atom in
the cing of separate aromatic ring radicals. The term
"aromatic ring" is defined herein as a carbocyclic
ring possessing ee~onance.
By "aromatic polyamide fibrids~ meant
small, nongranular, nonrigid ibrous or film-like
particle6 of an aromatic polyamide having a melting
point higher than 320C. Two of their three
dimensions are of the order ox microns. Their
smallnes6 and suppleness allows them to be deposited
in phy6ically entwined configurations 6uch a are
commonly found in papers made from wood pulps.
Fibrids can be prepared by precipitating a solution of
the aromatic polyamide into a coagulant such as in
apparatus of the type disclosed in U.S. patent
3,018,091.
By "high temperature re6istant floc" is meant
short fiber6, typically having a length of 2 to lZ mm
and a linear density of 1-10 decitex, made of a
material having a melting point higher than 320C,
such as aromatic polyamides, aromatic
polyamide-imides, aromatic polyimides,
polybenzimidazoles, etc., or inorganic materials such
as glass, ceramic materials, alumina, etc. Other high
temperature resistant material6 such as mica may also
be pre6ent in rela~iYely finely subdivided form.
~.Z4 28~3
By aromatic polyamide floc" i6 meant 6hort
fibers cut from fibecs prepared by the proce~e6
described in U.S. patents 3,063,966, 3,133,13B,
3,767,756, and 3,869,430.
Conventional aromatic polyamide pre~sboard
may be prepared by feeding an aqueous 61urcy of MPD-I
fibrids and MPD-I floc to a cylinder paper forming
machine whereby water is removed and multiple layers
of fibrous mateEial having a water content of 50-95%
by weight of the wet sheet it built up to a wet lap of
the desired thickness The wet lap it cut f rom the
cylinder, laid flat and pressed at 100-200C, under a
pressure of 10-60 kg/cm . The resulting
conYentional pressboard usually ha a high oil
absorption of 20-50% by weight, a den6ity of about 0.7
to 0.9 gem a calculated void volume of about 35
to 50% by volume of the pressboard, mercury intru6ion
volume of about 0.30 to 0.50 cm3/g, both at low and
high 6urface/volume, a ratio of total available
ab60rption volume in cm3/g, Va, to the mercury
intru6ion volume at low surface/volume, Vml, of
about 1 and a compres6ion 6ee of 0.75 to 205 mm.
However, for 60me uses, 6uch a6 spacers used
in oil filled tran6former6, the comp~e~6ion 6et
desirably 6hould be not les6 than about 0.12 mm or
more than about 0.5 mm while maintaining an oil
ab60retion of at lea6t 8~. Pres6board with
compce6sion set value6 of lest than about 0.12 mm do
not have the combination of compressibility and
re6ilience nece~ary to maintain eroPer 6pacing of
electrical component in, e.g., t~an6former~.
Pre66board with compre6~ion 6et values greater than
0.5 mm likewise do not maintain proper spacing of
components.
2~3
The above desired properties are provided by
the product of this invention. It has been found that
when a low den6ity pressboard having a calculated void
volume of 30 to 60% prepared as described above is
further dried, ultimately at a temperature of
270-320C, until substantially no further moisture is
evolved and then pressed at 270-320C and a pre6sure
of 8 to 350 kg/cm2, preferably followed by cooling
under restraint, a pres~boald having the desired
properties is obtained. The drying i8 preferably
accomplished by step-wi~e increase in temperature.
Moisture evolution is facilitated by application and
release of light pressure. In general, the pre6sing
is preferably at 275-300C at 15 to 70 kg/cm2 or at
least 5 minute but thick product6 may require
pressing for longer times. More than one layer ox low
density pressboard may be combined during high
temperature pressing. In this case, longer pressing
times 6hould be employed. Preferably the high
temperature pres6ing should be above the glass
tran6ition temperature (~g) of the aromatic
polyamide comprising the fibridfi which in the case of
the prefereed poly(m-phenylene isophthalamide) fibrids
i6 about 275C.
It has been found that the proce6s described
above, wherein a wet lap i8 formed of multiple layers
of waterleaves having a water content of 50-95~ and
the wet lap is pressed at 100-200C under a pressure
of 10-60 kg/cm2 ts pcepare a low density pressboard
30 having a calculated void Yolume of 30-60%, and the low
density pressboard i8 then dried and pres6ed again at
270-320C under a pres6ure of 8-3~0 kg/cm , is
essential for obtaining a pressboard product
exhibiting good re6i6tance to compression as jell a6
35 adequate oil ab60rption. If the low density
~2~3~3
pressboard has a calculated void volume of less than
30%, the oil ab60rption ox the f inal pres6board
product tend6 to be very poor.
The pre6sboard of thi6 invention i8 u~e~ul in
clamping rings and in axial and radial 6pacer6 in oil
f illed electrical tran6formers.
Product of this invention have a calculated
void volume ox 13 to 28~ by volume of the pressboard,
mercury intrusion Yolumes at low surface/volume,
Vml, of less than 0.20 cm3/g and at high
surface~volume, Vmh, of 0.08 to 0.28 cm3/g, an oil
ab60rption by volume in cm3~g, VO, ox 0.08 to 0.28
and by weight of 8-24~ and a total available
absorption volume in cm3/g, Va, equal to the
lS largest of the value for Vml, V~h and VO, the
ratio ox Va to Vml being at least 1.1. Pressboard
having a calculated void volume of more than 28~ or a
ratio of Va to Vml of 1.0 generally exhibit6 poor
compres6ion set, while pre~6board having a calculated
20 void volume of le6s than 13~ or Vmh le66 than O.OB
cm3/g generally exhibits poor oil absorption. The
product6 of thi6 invention have Va values which are
quite different from Vml value6, the ratio of these
being at least 1.1 and a6 sigh a 4.
2s
TESTS
Density. Dry pre66board it cut into a
rectangular 6ample mea6uring at least 10 em x 10 cm (I
in x 4 in), preferably at least 20 cm x 20 cm t8 in x
30 8 in3, making sure that the ~orner6 are cut square 60
ehat the upper and lower faces of the 6ample are of
the Rame area and that the dimen~ion6 can be measured
accurately. The length and width of the rectangular
6ample are mea6ured to an accuracy of at lea6e 0.25 cm
~5 tO.l in). The thickne~6 of the rectangular sample ox
~2~5,~
pces6board i8 measured in at least ten places 6paced
6ubstantially equally apart around all sides of the
pressboard, away from the edges, using a micrometer
caliper which contacts the sample with 6urfaces having
a diameter of about 0.6 cm (0.25 in) at a pre~6ure of
about 0.1 kg/cmZ (about l.Z5 psi), to an accuracy of
at least 0.00025 cm (0.1 mil), averaging the ten
thickness measurements. The sample of pre~sboard is
then weighed to the nearest O.OOol g. The volume of
the sample of pressboard Vb is then calculated in
cm and the weight i5 divided by the volume to give
the density in g/cm3.
Calculated Void Volume. The void volume in
cm3, Vv, of a 6ample of the pres~board i6
detecmined from the relationship
Vb = Vm V~, or
VV = Vb - Vm. where
Vb is the volume of the pre6~board in cm3 a6
determined above, Vm i8 the total volume in cm3 of
20 all the materials comprising the pres6board, and Vv
is the retaining volume in cm3, which it taken as
the void volume. Vm is determined from the weight6
and densitie6 of each of the materials of which the
pre6sboard samele it made, calculated a follow6:
V = Wf I , where
1.38 g/cm I
Wf is the weight in g of the aromatic polyamide
fibrids in the pressboard 6ample, Wi it the weight
in g of the floc (including any other non-fibrid high
temperature re6i~tant ma~erial~ in the pre6~board
ample, and Pi it the density of the material of
which the floc is made tl.38 g~cm3 for MPD-I and
1.44 g~cm3 for polytp-phenyl~ne terephthalamide)~.
35 when there i6 more than one kind of floc (or other
~2428~3
high temperature resistant material such a6 mica),
Wi/pi i8 calculated as follow6:
Wi Wl , W2 +, . . Wn
Pi Pl P2 Pn
5 where i = 1, ..., n
The calculated void volume a6 a percentage volume,
Vv, i6 then calculated as follow6:
% Vv =11 m] x loo = V~ ox 100
In the case of a 100% MPD-I pcessboard 6ample having a
weight in g of ~b and a volume in
cm3 of Vb, and since for this case Ym = Wb
1.38 g a
the equation reduces to:
VV =Ll - Wb x 100
Vb~1.38 g/cm3
The calculated void volume it a mea~u~e of
all of the voids, both isolated void and
interconnected voids, in a sample of pressboard.
Oil Absorption. This test i6 carried out in
accordance with the method described by the
International Electrotechnical Commi66ion, IEC
Standard, Publication 641-~, First edition (1979),
"Specification for pres6board and pce6spaper for
electrical purposes, Part 2: Method6 of test," page6
29 and 31 (section 17), publifihed by Bureau Central de
la Commi6sion Electrotechnique Internationale Geneva,
Switzerland. The result it expre6sed Jo the neare6t
0.1% as a percentage by weight oil ab60rption on the
original ma66 of the pres~board 6ample tested. The
oil absorption by volume in cm3/g, VO, i6 when
calculated by dividing the percentage by weighe oil
ab60rption by the den6ity of ehe 6ample of
pre~6board. VO values are initially reported to the
28~3
same number of significant ~igure6 as the percentage
by weight oil absorption, then rounded to two decimal
places.
Compression Set. The pre6sboard to be te6ted
5 i6 cut into rectangular ~trip6 3.8 cm (1.5 in) wide X
5.1 cm (2.0 in) long and a sufficient number of the
6trips are tacked to make a 6tack approximately 5.1
cm (2.0 in) high. The tack of sample6 it placed in
an oven for 4~ hr~. at 110C, then taken from the oven
and placed in a conventional machine for testing
compressive properties, eguipped for constant rate of
crosshead movement and having a capacity of at least
10,000 kg (22,000 lb.) (e.g., the Tiniu~ Olsen
Universal Testing Machine, Model 60 SDT,
Servo-controlled, 60,000 lb. capacity, Super L U~M,
made by the Tiniu~ 016en Universal Testing Machine
Co., Inc., Easton Rd., Willow Grove, PA 19090 equipped
with a Model MM Flat Bed X-Y Recorder manufactured by
Houston Instrument6, Inc. and Tiniu6 Olsen Model D-2
and D-4 Deflectomer~ for accurately measuring the
deflection ox compre6sed 6ample6 at two different
chart magnifications. In carrying out the test, the
load i6 applied at the constant rate of 0.5 cm per
mix. (0.2 in. per min.) and relea6ed. A load of 680
kg (1,500 lb.), equivalent Jo 35 kg~cm2 (3,448 kPa:
500 p5i), i6 applied Jo the 6tack of samples, and the
load it the immediately released to a load of 13S kg
(300 lbs.). Thifi load, equivalent to 7 kg/cm~ (690
kPa; 100 p6i), it designated a the bedding pressure,
and the load i5 releafied to this bedding pres6ure
between each cycle. The stask of ~ample6 ifi next
cycled to 1361 kg (3,000 lb~.), equivalent to 70
kg~cm2 (6,B95 kPa: 1,000 psi), returning to the
bedding pre66ure. It it then cycled to 2,722 kg
(6,000 lb6.), equivalent to 141 kg/cm2 (13,790 kPa;
~24
2,000 psi), retucning to the bedding pre~ure.
Finally it is cycled to 4.082 kg (9,000 lb~.),
equivalent to 211 kg/cm2 (20,685 kPa: 3,000 pi
and back once more to the bedding pres6ure. The
compression set it taken as the lows in height in mm
(alternatively in mils) ox the stack of samples, as
measured by the deflectometer, upon the return to the
bedding pressure after the final cycle. It is
preferred to have the deflectomer reading6
coneinuously plotted on a chart 80 that the entire
sequence of cycle it displayed on a graph f or each
sample tested.
If the amount of sample material is limited,
the 3.~ em 5.1 cm rectangular 6trip6 are 6tacked to
a lesser height, preferably at least 2.55 cm ~1.0 in.)
high, and the deflection after the final cycle is
multiplied by the appropriate factor to scale the
re6ult to correspond to the result which would be
obtained fcom a tack 5.1 cm (2.0 in.) high.
Merc~Ey Intrusion Yolume In this
determination a conventional mercury poro6imeter
tAminco Mercury 60,000 pig max, Newport Scientific
Co., Inc., Silver Spring, MD 20910~ i6 employed to
determine the volume of mercury which Jan be forced
25 into the pores, or interconnected void6, of a porou6
6ample. To determine whether the 6urface area of a
given weight of the pre6~board ha an effect on the
volume of mercury which can be forced into it6 pore6,
determination are made both on low æur~ace~volume
30 samples and high ~urface/volume ~6ubdivided) ample
of the pres~board.
The nominal weight of each 6ample te6ted it
0.~ g. To prepare the low 6ucfaceivolume and high
6urface/volume 6ample6, an initial sample 61ightly
35 heavier than 0.6 g and preferably rectangular in shape
e 11
12
is cut from the pre~sboard to be tested. The initial
sample is then cut down in size ~e.g. with a pair of
side-cutter6) in a series of approximately 25 to 35
clean cuts stcaight through the pressboard near its
s edges to produce a corresponding number of ~ragment6.
leaving a preferably quadrilateral sample weighing
about 0.3 g which is taken as the sample for the low
~urface/volume measurement. This low surface/volume
sample should be of such shape that it will fit intact
in the penetrometer bulb (sample chamber) of the
porosimeter, if at all possible. If the sample it
very thin and a jingle piece weighing 0.3 g which will
fit in the penetrometer bulb cannoe be preparad, the
low ~urface/volume sample is prepared in the form of
two or even three eiece~ which will fit in the bulb.
The low sur~ace/volume sample is weighed to the
nearest 0.0001 g on glassine paper. A sufficient
number of the pres~board fragments, preferably about
25 eO 30, to weigh about 0.3 g are placed on gla~sine
paper (preferably they are collected on the glassine
paper as they are cut) a6 the high ~urface/volume
(subdivided) sample. The su~diYided sample is weighed
to the nearest O.OOOl g.
To conduct the determination, a weighed
sample iB placed in the open penetrometer bulb, after
which the bulb i6 capped and evacuated until the
vacuum gauge display6 a pres6ure of 50 microns of
mercury or lest. The filling device i6 then tilted
backward until it stop i6 reached, Jo thae the eip of
the penetrometer it immersed in mercury. The stopcock
on the filling device i8 gradually opened to admit air
to the 6y8te~ slowly, causing mercuLy to enter the
penetrometer bulb, zapping the tube to aid in wetting
the sample with mercury. After total weteing ha6 been
achieved, the filling device it returned to vertical
12
~z~
position. The penetLometer is then moved from the
vacuum chamber to the pressure chamber.
The pressure is then gradually increa6ed,
recording penetrometer reading6 at interval6 as the
S pressure increases. The equipment is customarily
provided with more than one pressure gauge, e.g.
recording maximum values of about 350 kg/cm (34
spa; S,000 pi) and about 4200 kg/cmZ (414 MPa:
60,000 psi), and if 60 the equipment it 6witched over
to the high pressure gauge at the appropriate time a6
the pressure increases. The penetrometer reading at
4200 kg/c~2 (414 MPa, 60,000 psi) i6 recorded at the
conclusion of the text. The meccury intrusion volume
at 4200 kg/cm2 is determined from the penetrometer
reading in accordance with the instcuceion6 provided
by the manufacturer of the equipment. For a
pacticular 6pecimen of pres6board, mercury intrusion
volume value6 in cm3/g (cm3 of mercury at 4200
kg/c~2 pressure per g of pre6sboard) are first
determined to four decimal places, then rounded and
finally reported Jo two decimal places both for the
low 6urface/volume and high 6urface/volume
(6ubdivided) 6a~ple6. If de6ired, graph6 of mercury
intrusion Yolume values oYer the entire pressure range
are constructed, based on the penetrometer reading6
taken at interval6 throughout the te6t. The mercury
intru6ion volume at low 6urface/volume it designated
by the 6ymbol, Vml, and the mercury intru6io~ volume
at high 6urfaoe/volume it de6ignated by the 6ymbol,
Vmh
Total Available Ab~orDtion Volume. The total
available ab60~ption volume, Va, of a pre~6board
sample it taken a being equal So the largest of the
value6 for Vml, V~h and VO (all ~alue6 prior to
rounding) fox the sample. For any given sample of
s 13
14
pressboard, Va is a measure of the volume in cm3
per g of the intecconnected voids in the sample which
are accessible to penetration by liquids.
The ratio, Va/Vml, is then calculated,
using values of Ya and Vml prior to rounding in
making the calculation. In reporting the ratio, it is
rounded to one decimal place. A value of this ratio
equal to or greater than 1.1 is indicative ox a
~tructu~e of limited oc partial accessibility ox
internal voids in the pressboard, a 6eructure
associated with good compression resistance of the
pressboa~d when the calculated void volume of the
pressboard is no more than 28%.
EXAMPLE 1
A. _Pceparation of "Standard Pres6board"
Filaments of poly(m-phenylene isophthalamide)
(MPD-I) having an inherent visco6ity of 1.5 were dry
spun from a solution containing 19~ MPD-I, 70%
dimethylacetamide tDMAc), gt calcium chloride, and 2~ -
water. On leaving the drying tower the a~-~pun
filaments were given a preliminary wa6h with water Jo
thaw they contained about 60t DMAc, 15% calcium
chloride, and 100-150S waxer, based on the weight of
dry polymer. The filaments were washed and drawn 4X
at 90C in a counter-current extraction-draw process
in which the calcium chlsride determined as chloride
content and DMAc contene were ceduced to about 0.1
and 0.5%, respectively. The filaments were
crystallized immediately after drawing by passing them
over hot roll6 at a temperature of about 340C. The
filament so produced had a linear density of 2.2
decitex ~2.0 denier), a tenacity of about 3.7 dN/tex
~4.2 g/denier), an initial modulus ox 70 dN/tex (79
gpd~ and an elongation of 34%. the filament6 were cut
to floc having a length of 3.4 mm ~0.135 in).
14
~Z42BS3
Fib~ids of MPD-I having an inherent viscosity
of 1.5 were prepared ~ub6tantially a6 described by
~ro~s in U.S. Patent 3,756,908, issued September 4,
1973, column 5 line 34-54, stopping short of the
refining step.
An aqueous slurry was prepared containing 1.0
wt. ibid and floc having a composition of 60% of
the above MPD-I fibrid~ and 40~ of the above MPD-I
floc. The slurry was held in an agitated vessel and
then pumped to a double disc refine (Beloit Jones
Model 3000 20-inch Double Disc refiner, made by the
Jones Division of the Beloit Corporation, Dalton,
Massachusetts 01226), equipped with refining discs
containing narrow bars and channels with surface
lS dams. The plate ox the refine were positioned with
a gap of 0.5 mm (20 mil6~ between the rotor and the
6tator plates. The roeor plates were operated at 900
rpm. After passing through the refiner, the filurry
was pasted through a second refiner under the tame
Z0 operating conditions. After the two passe through
the refiners the fib~id~ in the slurcy were well
reduced in size and well opened into fib~id films,
while the floc fiber were well di6tributed among the
ibrids. The 6 lurry made in this way was then diluted
ZS to approximately 0.1% by weight solid and fed to a
conventional cylinder wet paper-making machine upon
which a continuous sheet of wet paper wa6 made and
transferred Jo an endle~6 felt, the moi6ture content
being adjusted by fiuc~ion and pressure to about 400%
30 based on solids (80~ by weight cod on the wet
6heet). The weight of the olid~ in the wet paper was
approximately 36 g/m . The eontinuou~ wee 6hee~ way
next delivered to a forming roll, where it was wound
continuously on a cylindrical tube until it overlapped
about 70 time. A longitudinal cut was then made in
16
the layered paper and the entire thicknes6 of wet lap
(wet layered paper) was then removed and placed
between the platens of a hot press, the platen6 being
maintained at 140C and having been covered with wire
6c~een to facilitate moisture removal. The pre66 way
loaded at contact pressure, and the pre6sure was then
raised eo and maintained for one hour at 35 kq~cm2
(3450 kPa; 500 psi~ while the platens of the pre66
were maintained at 140C. The product, herein
designated as "Standard Pressboard", was a low density
aramid pre66board approximately 3.2 mm (lZ6 mils)
thick. It was found to have a density of 0.~2
g/cm3, a calculated void volume, % Yv, of 41~ by
volume of the pressboard, a co~pre6sion c of 2.13 em
(8~ mil6), and an oil absorption of 32.5%. V0 was
0.38 cm3~g, V~l was 0.38 cm3/g (rounded from
0.3791), and Vmh was 0.42 cm3/g (rounded from
0.4197) Va for this Standard Pces6board 6ample wa6
0.42 cm /g and the ratio V /V 1 way 1 1
B. Preparation of ComPression-Resistant Pre66board
A 30.5 cm X 30.5 cm (12 in X 12 in) square
sheet of the "Standard Pre66board" prepared a6 in Part
A above wa6 predried at 150C for at lea6t 2 hour6 and
then placed between the platen6 of a flat ere66
tMachine No. 9175-M, Wat60n Stillman Pres6 Divi6ion,
Farrel Company, Emhart Machinery Group, 25 Main St.,
An60nia, Connecticut 06401). With the plateRs
preheated to 280C and maintained at that temperature,
a pre6~ure of 19.5 kg~cm2 (1910 kPa; 277 p6i) wa6
appl;ed to the "Standard Pre6~board~' for a total of 20
minute, relea6ing the p~e~6ure for a few second and
then reapplying it aster a total ox 1. 2, 30 6, 12.
and 16 minute6 to permit e6cape of any trapped ga6es.
After a total of 20 minute6 of hot pce66ing, the
pre~sboard wa6 taken out hot, placed in another pre66
285~
17
at room temperature, and allowed to cool under a
pressure ox 2.~ kg/cm2 t276 kPa: 40 psi), jut
~ufficiènt to keep the pressboard flat while cooling.
The product. designated as "Sample lA", was an aramid
pre6sboard approximately Z.45 mm (96.5 mil6) thick
~hicknes~ range 2.35-2.53 mm). It was found to have
a density of 1.11 g/cm3, a % Vv of 20~, a
compre~6ion 6et of 0.30 mm (12 mils), and an oil
absorption ox 12.~ . V0 was 0.15 cm /g, Vml
0 way 0.15 cm /~ (rounded from 0.1502), and V was
mh
0.17 cm /g (rounded from 0.1700). Va for Sample
lA way 0.17 cm /g and the ratio Va/Vml was 1.1.
Another 6heet of predried "Standard
Pres6board" way subjected to the same procedure,
except that a pressule of 18.5 kg/cm2 (1813 kPa, 263
p6i~ was applied in the press for a total of 20
minutes at 2B0C. The product, designated as "Sample
lB", was approximately 2.5 mm (~8.7 mill) thick
(thickness range 2. 3a - 2.60 mm). It was found to
have a density of 1.08 g/cm3, a S Vv of 2Z%, a
compression set of 0~36 mm (14 mils), and an oil
ab60rption of 12.19%. V0 way 0.14 cm3/g, Vml
way 0.16 cm /g (rounded from 0.1551), and Vmh was
0.17 cm /g (rounded from 0.1743). Va for Sample
lB was 0.17 cm /g and the ratio Va/Vml was 1.1.
EXAMPLE Z
Two 46 cm X 122 cm (18 in x 48 in)
rectangular sheets of "Standard Press~oard", prepared
substantially as described in Paet A of Example 1 but
having a thickness of 3.0 mm (llB mils), were aligned
in a tack above and below a 46 cm x 122 cm 6heet of
1.6-mm thick "Standard Pres~board", similarly prepared
except what proportionately fewer overlap of wet
papeL were wound on ehe cylindrical coll in the
17
~2~3~i,3
18
~o~ming step. All of the 6heet6 were predried at
150C just beore worming the tack. The aligned
tack was then placed immediately in a hot press
having platens oil-heated to 280C (535F) and
subjected to three 2-minute cycle of contact pre66ure
(3.5 kg/cm2) at 2B0C followed by release of
pressure. A one-minute cycle of pre~6ure at 28
kg/cm~ (2758 kPa: 400 p6i) and quick relea6e way
hollowed by a one-minute cycle of pre6sure at 35
kg/cmZ and quick Eelease, after which pre66ure wa
applied at 35 kg/cmZ for fifteen minute6 while the
platens were maintained at 2~00C. The pre6sboard
product was taken out hot and placed under contact
pressure in a separate press, initially at room
temperature and water-cooled to ab60rb the heat of the
pressboard, to keep it flay while cooling. The
product, designated "Sample 2", wa6 an aramid
pressboard approximately 5.3 em thick (210 mils). It
was found to have a den6ity of 1.12 g~cm3, a % Vv
20 of 19%, a compre6sion 6et of 0.13 mm (5 mils), and an
oil ab60rpt on of 9.3%. V0 wa6 0.11 cm3~g, Vml
was 0.09 cm ~g (rounded from 0.0940), and Vmh wa6
0.17 cm ~g (rounded from 0.1665). Va for Sample 2
wa6 0.17 cm ~g and the ratio VaJVml wa6 1.8.
EXAMPLE 3
A 46 cm x 81 cm l in x 32 in) rectangular
6heet of 2.1-mm thick pre66board, prepared
~ubstan~ially like the "Standard Pre~6board" ox Part A
30 of Example I, except that proportionately fewer
overlap6 of wet paper weee u6ed, a placed without
predrying in a pre~6 equipped for electrical heating
and water cooling. Initially the pres6 wa6 at 66C
(150F) and contact pres6ure, about 3.5 kg/c~2 (345
35 kPa: 50 psi). the pre~6 wa6 heated over about 20
so
19
minutes under the tame contact pressure. with no
interval of pcessure release, to about Z80C (about
535E). The pressure was then increa6ed to 35
kg/cm (3~48 kPa; 500 psi) and maintained at that
pressure, with no relea6e of pres~u~e, for 12 ~inute6
while the pres6 way maintained at 280C. The
electrical heating way then discontinued and the pre6s
was then cooled back down to 66C with circulation of
cool water over a 20-minute period while the pressure
lO was maintained at 35 kg/~m2. The product,
designated "Sample 3", was an aramid pre~board
approximately 1.6 em ehick (64 mil6). lt way found to
have a density of 1.13 g/~m3, a % V~ of lB~, a
compce8sion 8et of 0.13 mm (5 mil6), and an oil
absorpt on of 9.32~. V0 way 0.11 cm3/g, Vml was
0.06 cm /g (rounded prom 0.0553), and Vmh was 0.14
cm /g (rounded from 0.1390). V or Sample 3 way
a
0.14 cm~/g and the ratio Va/Vml way 2.5.
EXAMPLE 4
Square ~heet6 of low density pre66board were
preeaced in sub6tantially the 6ame manner as the
"Standard Pressboard~' of Part A of Example l, with the
following exception6. Fibrids were refined and mixed
2S with f loc at the paper-making machine. Fifty 6hee~6
of wet paper were combined unto a wet lap and the
entire wet lap way jut into ~0-cm (8-in) square. In
pressing the 6quare~ of wet lap at 140C under a
pre~6ure of 35 kg/cm2, the pressure wa6 applied for
30 30 minute6 rather than ona hour. The low density
pre~6board 80 formed way 2.1 mm (81 mill thick and
had a den6ity of 0.88 g/cm3. It6 % Vv wa6 36~.
The low density pre66board was predried a lZ0C in an
oven for four hour6 and then placed between the
~5 platen6 of a flat pre6s preheated to 280~C a6 in
a 19
~4~28~
Part B ox Example I. Low pressure was applied briefly
at fiest, with three cycles ox celease of the ~re6sure
to permit escape of the trapped gasses followed by
reapplication ox the pre6sure. A pressure of 53
kg/cm2 (5171 kPa; 750 psi) was then applied or a
contact time of 1 minute, the hot pressboard finally
being cooled under r~&traint in a separate press. The
product, designated a "Sample 4A", was an aramid
pres~board 1.75 mm (69 mils) thick and had a density
ox 1.04 gem It6 % Vv was 25%. Vml way 0.15
cm3/g (rounded f rom 0.1542) and V~h was 0.17 cm /g
(rounded from 0.1712), The compLession set was 0.20 mm
(8.0 mils), the oil absorption was 15.9t by weight of
pressboard, and VO was 0.19 cm3/g. For Sample 4A,
Va was 0~19 cm /g and the ratio Va/V~l was 1.2.
Other 20-cm square 6heets of low density
pres~board were prepared in the tame manner, except
that the weight of the 601ids in the wet paper was
approximately 60 g/m2, the wet lap was formed from
ZO thirty sheets ox wet paper, and in the pressing step
the pres6ure was applied for 45 minutes rather than 30
minutes. The low density pres~board was 2.1 mm ~84
mil6) thick and had a density of 0.92 g/cm3. It S
V~ was 33~. The low dansity pre~sboard was p~edried
25 and hot pre6sed in the same manner as Sample 4A,
except that the pressure of 53 kg/cm2 wa6 applied
for a contact time of 10 mi~ute6. The product,
designated as Sample "~B", way an aramid pre~board
l.Q em t71 mil6) thick and had a den6ity of 1.15
30 g/cm3. Its % V~ was 17%. Vml was 0.05 cm3/g
(rounded prom 0.0486) and Vmh was 0.15 cm /g
Srounded from 0.1~52). The compre6sion 6et was 0.147
em (5.8 mils), the oil absorpeio~ wa6 9.7& by weight
of pre~board, and VO wa6 0.11 ~m3~g. For Sample
35 4B, Va wa6 0.15 cm /g and the ratio Va/Vml way 3Ø
i,3
EXAMPT,E 5
In a series of experiment, low density
pre6~board6 were made which contained varying ratios
of MPD-I fibrids and floc. the low density
pres~board6 were made in 6ubstan~ially the 6ame manner
as the "Standard Pre66board" of Part A of Example 1
with the following exceptions. Fibrid6 were refined
and then mixed with floc at the paper-making machine
in the proportion6 given below. Wet paper was
produced with the weight of the 601ids being
approximately 60 g/m2. Thirty sheets of wet paper
were combined into a wet lap which was cut into 20-cm
(8-in.~ ~quare6 and pre6sed.
In one experiment a mixture of 80S fibrids
and 20% floc having a cut length of 0.32 cm t0.125 in)
was used. The low density pressboard was prepared
under a pressure of 17.6 kg/cm2 (1724 kPa: 250 psi)
for 1.5 hr. at a temperature of 140C. It was
approximately 2.1 mm (82 mil6) thick and had a density
20 of 0.92 g/cm3. t Vv wa6 33~.
The low density pres6board way dried at lZ0C
for 4 hour6 and pre66ed at 280C~ under low pres6ure
at fir6t with brief cycles of release and
reapplication of pre66ure, then for 10 min. at 8.8
25 kg/cm2 (862 kPa; 125 pi he product. designated
"Sample SA". wa6 an aramid pre66board approximately
1.9 mm (73 mill) thick. had a den6ity of 1.04 g/cm3,
a compre~6ion jet of 0.21 mm (a.3 mils), an oil
absorption of 13.7% my weigh pre66board, and V0 was
30 0.16 cm3~g. % Vv for sample 5A was calculated a6
25%. Vml wa6 0.10 cm3/g trounded from O.og9o)~
Vmh way al60 0.10 cm /g rounded from 0.0996).
c 21
~z~
For sample SA Va was 0.16 cm3/g (the large6t of the
ml~ V0, and Vmh) and the ratio V /V wa$
1.6.
The procedure or preparing the low density
pressboard was repeated, except that a mixture ox 40
fibrids and 60% floc was used and that the pres6ure
applied was 35 kg/cmZ (3450 kPa; 500 psi) for a
period of q5 minutes at 140C. The low density
pres6board was approximately Z.6 mm (103 mils) thick
and had a density of 0.78 g/cm3. % Vv was 43%.
The low density pres6board was dried at 120C for 4
hours and pressed at 280C, under low pressure a
first with brief cycles of release and reapplication
of pressuce, then for 10 min. at a pres6ure of 53
kg/cm2 (5171 kPa3, finally being cooled under
ce~traint in a separate pre6~. The product,
designated "Sample 5B", was an aramid pres6board
approximately 2.0 mm (79 mils) thick, had a den6ity of
1-0? g/cm3, a compression jet of .15 mm (6.0 mil6),
an oil ab60rption of 17.1% by weight of pressboard,
and V0 was 0.20 cm3/g. % Vv was 26%. Vml wa6
0.17 cm /g (rounded from 0.16B3) and Vmh wa6 0.27
cm /g (rounded from 0.2673). For Sample SB, Va
was 0.27 cm /g and the eatio Va/Vml wa6 1.6.
The procedure for preparing the low den6i~y
pressboard was repeated again except that a mixture
of 20t fibeid6 and 80~ floc was u6ed and that the
pre~fiure applied way 35 kg/cm2 for a period of 45
~inute~ at 140C. The low density pres~board way
30 approximately 3.1 mm (123 mil6) thick and had a
den6ity Df 0.70 g/cm3. Vv for this low density
pres~board wa6 49~. The low density pressboard was
dried a6 de6cribed above and pres6ed at 280C, under
low pce~sure a fir6t with brief cycle of release and
35 reapplication of pres6ure, then for 10 min. at 79
2~
,3
23
kg/c~Z (7763 kPa: llZ5 p6i). The pcoduct, designaeed
"Sample 5C", wa6 an ara~id p~essboard applox~ately
2.1 em (84 thick, had a density of 1.03 g/cm3,
a compre~slon set of 0.35 mm (13.6 mils), an oil
absoLpeion of 12.1~ by weight of pres6board, and Y0
wa6 0.14 cm /g. Vv was 25%. V 1 way 0.16
cm3/q (rounded prom 0.1565) and Vmh wa 0.23
cm Jo (rounded prom 0.2342~. For Sample 5C, Va
was 0.23 cm g and ehe ratio Va~Vml was 1.5.
The procedure for preparing the low den6~ty
pres~board way repeated once more. except that a
mixture of 95~ fibrids and 5% floc way used and that
the pre66uLe applied was 17.6 kg/cm2 or a period of
1.5 hr ae 140C. The low density pressboard was
approximately 1.9 mm (75 mils) thick and had a density
ox 0.90 g/cm3. % Vv way 35~. The low density
pre66board was dried a6 de6cribed above and pressed at
280C, undee low pre6~ure at fic6t with brief cycles
of eelease and reapplication of pressure, then for 10
min at 8.8 kg/cm2. The product, de6ignated sample
5D~, was a aramid pre6sboard approximately 1.7 mm (68
mils) thick, had a density of 1.06 g~cm3, a
co~pres6ion 6et of 0.34 mm ~13.4 ifs an oil
ab60~ption of 11.7% by weight of pres6board, and V0
25 way 0.14 cm ~g. t Vv was 23~. Vml wa6 O.OS
cm3~g (rounded from 0.0459) and V~h was O.OB
cm3fg kounded from 0.0~05). For Sample SD, Va
- way 0.14 cm /g and the raeio Va/Vml wa6 3Ø
EXAMPLE 6
It a serie6 of experiments, low density
pre66board6 ba6ed partly on high-eemperature resistant
floc6 other than MPD-I flocs were made. The low
den6ity pres~board~ were made in sub~tant~ally the
3~ 6a~e wanner as the "Standard Pressboard" of Hart A of
23
' I
~24ZB53
24
non-MPD-I bloc way blended with MPD-I floc having a
cut length of 0.32 cm (0.125 in.) and the blend of
floc6 was mixed at the paper machine with refined
fibrids in the proportions given below. Wet paper was
5 produced with the weight of the solid6 being
approximately 60 g/m2. Thirty 6heets of wet eaper
were combined into a wet lap which was cut into 20-cm
(8-in.) squares and pressed undec the condition given
in ox. 1, Part A.
In one experiment, a mixture of 60% MPD-I
fibrid6, 20~ MPD-I floc, and 20% commercially
available poly(p-phenylene terephthalamide) (PPD-T)
floc having a linear den6ity of 1.67 decitex (1.5
denier) and a cut length of 0.32 cm (0.125 in.) wa6
used to ~repa~e an low density pre~6board having a
thickness of 2.9 mm (113 mill), a density of 0.83
cm ~g, and a % Vv of 41%. The low den6ity
pre~6board was dried at 120C for 4 hour6 and pressed
at 280C, under low pre~ure at first wieh brief
cycles of release and reapplication of pre66uee, then
at 53 kg/cm2 (5171 kPa; 750 psi) for 10 min., the
hot pre6sboard finally being cooled under re6traint in
a Reparate pre66. The product, de6ignated a6 "Sample
6A" wa6 a pre66board 2.2 mm (~6 mil6) thick having a
density of 1.10 g/cm3, a % Vv of 22t, a
compres6ion cet of 0.27 mm (lO.B ~il6), an oil
ab60cption of 10.8S by weight of pre~6board, and a
V0 of 0.13 cm3/g. Vml was 0.08 cm3/g trounded
from 0.0787) and Vmh wa6 0.12 cm3/g (rounded from
0.1151). Va for Sample 5A wa6 0.13 cm /g and the
ratio Va/Vml wa6 1.6.
In another experiment, a mixture of 60~ MPD-I
~ibrid~, 35~ ~PD-I floc, and So E-gla66 fiber floc
having a den6ity of 2.4 g/cm3 a linear den6ity of
3.3 decitex ~3 denier, and a cut length of 0.64 cm
c 24
~24 ;~
(0.25 in) was used to prepare an low density
pcessboard having a thickness of 2.2 mm (88 mils), a
density ox o.91 cm3/g, and a Vv 36~. The low
density pressboard was dried and pressed by the same
procedure described above for making Sample 6A, The
product, designated as "Sample 6B", was an
aramid/glass fiber pressboard 1.8 mm. (71 mils~ thick
having a density of 1.15 g/cm3~ a Vv of 20%, a
compression 6et of 0.18 mm (7 mils), an oil absorption
of 8.6% by weight ox pressboard and a VO of 0.10
cm /g. Vml was 0.06 cm3/g (rounded from 0.0576)
and Vmh was 0.14 cm3/g (rounded from 0.14Z4).
V~ for Sample 6B was 0.14 cm3/g and the ratio
Va/V~l was 2.5.
Control Sample Out6ide the Invention
(1) The procedure of Example 1, Part B, was
repeated, except that the pcessure was incLeased to 53
kg/cm2 (5171 kPa; 750 p6i), the press again being
~ain~ained at a eemperature of 280C. This product,
desiqnated as "Control 1" had an oil absorption of
only 2.03S. It was about 2.2 em (87 ) thick
(thickne6s range Z.14-2.31 mm) and had a density of
1.21 q/cm3, a % Vv of 12%, and a compre66ion set
25 of 0.30 mm (12 mils). VO way 0.023 cm3/g, Vml
was 0.04 cm /g (counded from 0.0~33), and Vmh was
0.09 c~3/g (rounded from 0.0889). For Control 1,
Va was 0.04 cm3/g and the ratio Va~Vml was
2.05.
(~) The procedure for preparing "Standard
Pressboard" a6 described it Example 1, Part I, was
repeated, except that the platens of the press were
heated to 200C and, after loading the preys at
contact pressure, the pre66ure wa6 raised Jo and
35 maintained at 60 kg/cm2 (5880 kPa; 850 pi for one
c 25
5,~
26
hour while the platens of the press were maintained at
200C. The product, designated as "Control 2", had a
high value of compres6ion 6et of 1.0 mm (40 mill). It
had a density ox 1.07 g/cm3, a ~Vv of 22~, and an
oil absorption of 9.59%. V0 was 0.11 cm3/g, V
was 0.17 cm /g (rounded from 0.1733 cm3/g~, and
V~h wa6 also 0.17 cm3/g (rounded from 0.1723).
For Control 2, Va way 0.17 cm3/g and the ratio
Va/Vml was 1Ø
(3A) ~ilament6 of MPD-I were prepared
substantially as described by Ross in U.S. Patent
3,756,908, Column 6, lines 11-23. The resulting high
modulus filaments were then cut to a floc hazing a
length of about 0.64 cm (0.25 in) and then slurried in
water to concentration of about 0.3~.
Pibrids of MPD-I were prepared sub6tantially
as described in column 5, lines 3~-57 of the same
patent. The refined fibrids were then diluted further
in water Jo a concentration of about 0.5%, and pas6ed
to a mixing "T" along with the above mentioned 61urry
of high modulus floc, at a ratio of fibrid to floc of
about 1.55 to 1.0 (60% fibrids and 40S floc). The
mixture was directed to the headbox of a ~ourdrinier
paper-making machine and then to a forming wire for
production of a wet 6heet. The wet 6heet way then
removed from the wire and pa6~ed through 6eeam heated
dryer can6 to reduce the moisture content of the hoe
to about 5~ or less. The paper way then wound on a
roll for further processing.
The paper waz removed from its roll, cut into
20-cm s8-in) 6quares, and then platen preyed to
produce 6a~ples of 2-ply paper 6ub~tantially a
de6cribed in column 7, line 6-11, of the 6ame
patent. The sample6 of 2-ply paper were pres6ed a
70.3 kg~cm2 (689.5 kPa; 1000 p~1) and 280C for one
26
i
~;~4~
minute. The resulting paper, designated a "Control
3A" had a thickness of about 0.25 mm (lO mils), a
density of absut O.B7 g/cm3, and a % Vv of 37% by
volume of the paper. Vml was 0.28 cm3/g (rounded
from 0.2B42) and Vmh was 0.18 cm3/g (rounded from
O.lBl8). The compression set way l.0 mm (40 mils),
the oil absorption was 35.3% by weight of paper, and
V0 way Of cm3/g. For Control 3A, Va was 0.41
cm /g and the ratio Va/Vml was l.S.
(3B) Filaments of MPD-I were prepared
substantially as described by Gross in U.S. Patent
3,756,908, column 5, lines 6B-75, and column 6. line6
1-7, resulting in low modulus filaments which were
then cut to a floc having a length of about 0.64 cm
~0.25 in) and s1urried in water to a concentration of
0.2~.
Fibrids of MPD-I were prepared as described
above for Control 3A and paper6 were prepared by
combining the fibrid and the low modulu6 floc at a
ratio of fibrid to floc of 1.5 to l.0 (60~ fibrid and
40% floc) in a wet 20-cm (8-in) squale hand6heet mold
(e.g., of the type made by Noble and Wood). Paper
made in this way are considered to be e6~entially the
6ame a6 papee~ made on a Fourdrinier paper machine.
The wet 6heets were removed from the lO0 mesh screen
of the hand6heet mold and dried on hot sheet dryer6 to
reduce the moi6ture content to about 5% or lest. The
~heet6 were then platen posed Jo produce samples of
2-ply paper. They were ere~sed at 70.3 kg~cm2
(689.5 kPa; lO00 p8i) and 260C for one minute.
The resulting paper, designated a6 "Control
3B" had a thickness of about 0.29 mm (ll mil6), a
den6ity of about 0.77 g/cm3, and a % Vv of 44t by
volume of the paper. Vml way 0.58 cm3~q (rounded
from 0.5787) and Vmh wa6 0.38 cm fg (rounded ffom
27
2~,3
28
0.3793). The compression et was 1.4 mm (54 mils),
the oil absorption was 49.9% by weight of the paper,
and V0 was 0.58 cm /g. For Control 3B, Va wa6
0.5a cm3/g and the ratio Va/Vml wa6 1Ø
(4) The procedure of Example 5 for preparing
Sample 5D was repeated, using a mixture of 95% fibrids
and 5% floc, except that the low density pre~sboard
was prepared by applying a pressure of 35 kg/cm2
(3450 kPa: 500 psi) for a period of 45 minute6 at
140C. The low density pressboard was approximately
1.7 mm (68 mils) thick and had a density of 1.00
g/cm3. % Vv was 2~. The low density pres6board
was dried at 120C for 4 hrs and pressed at 280C,
under low pres6ure at first with brie cycles of
release and Leapplication of pres6ure, then for 5 min
a 5.8 kg/cmZ. The product, designated "Control 4",
was an aramid pres~board approximately 1.6 mm (62
mil6) thick, had a density of 1.12 g/cm3, a
compre66ion set of 0.14 mm (5.5 ~il83, an oil
absorption of l by weight of pres6board, and V0
was 0.02 cm3/g. % Vv wa6 19~. Vml wa6 0.01
cm /q (rounded from 0.0141~ and Vmh was 0.02
cm Jg (rounded from 0.0173). For "Control 4", Va
way 0,02 cm3~g and the ratio Va~Vml was 1.2.
The properties and void parametec6 foc all of
the pre66board 6ample6 prepared a6 described in the
example, together with the control 6ample6, are
listed in the Table. the "Standard Pre66board"
(abbreviated Std. Pres~board~ sample of Part A ox
30 Example 1. is al80 listed. In the Table, the 6amples
are li6ted in descending order according to their
calculated void volume, % Vv.
28
5,3
h # O Of 0 0 O Us
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