Note: Descriptions are shown in the official language in which they were submitted.
1067Z4~
FIELD OF THE INVEN~ION
This invention relates to a new process for
producing pulp-forming particles of a thermally stable
~ynthetic polymer having very good sheet-formability,
and a synthetic paper-like sheet prepared therefrom and
- having superior thermal stability, impregnating ability,
texture uniformity and electrical insulation.
BAC~GROUND OF THE INVENTIO~
Wood pulp has been best known as pulp for paper-
making, and a great maJority of electrically insulating
- sheets heretofore in use are papers from wood pu~p. ~he
wood pulp papers, however, have a serious defect of hav-
ing poor thermal stability, and their thermal stability
is far from that required for reducing the size and
weight of electric machinery such as motors or trans-
formers.
Recently, pulp-forming particles of synthetic
pol~mers have attracted much attention as materials for
electrically insulating sheets because of their superior
2~ thermal stability and electrical insulation. For example,
United States Patent 2,999,788 discloses pulp-forming
particles composed of a synthetic polymer. A sheet formed
: from the pulp-forming particles disclosed in this patent,
however, is unsuitable as an electrical insulating sheet
2~ because of its insufficient impregnating abilit~. In
G/~ ~o~ye
J addition, since water drainin6 from a sheet-forming screen
. . .
is poor at the time of sheet forming, the resulting sheet
has a no~-uniform texture. It is difficult therefore to
29 obtain a sheet having a uniform thic~ness, and the resulting
-- 2 --
1067Z44
sheet has insufficient electriGal insulation. Especially
when it is desired to reduce the size and weight of
electric machinery such as motors and transforemers,
the electricahy insulating sheet used should have not
only superior thermal stability and impregnating ability,
but also a uniform texture. These requirements cannot
be sufficiently met when the pulp-forming particles
disclosed in the above patent are used.
British Patent Specification No. 1,129,097
discloses a high tempera~ure-resistant structure suit-
able for electrical insulation which is composed of an
intertwined mixture of mica particles and substantially
unfused aromatic polyamide fibrids. However, the aromatic
polyamide fibrids used in this patent cause poor water
drainage from the sheet-forming screen, and cannot afford
a sheet of uniform texture. - -
It is an obaect of this invention to provide
pulp-forming particles which have good sheet-formability
and permit good water drainage from a sheet-forming screen,
and can afford synthetic paper-like sheets having a good
uniformity of texture and superior thermal stability, im-
pregnating ability and electrical insulation.
SUMMARY 0~ THE INVENTION
~he present invention provides a process for
preparing pulp-forming particles, which comprises adding
a solution of a thermally stable aromatic nitrogen-
containing polymer selected from the group consisting of
aromatic polyamides and nitrogen-containing polyhetero-
cyclic compounds in an aqueous organic solvent consisting
~067Z44
of an organic solvent and water to a precipitant consisting of an
amide-type solvent for the polymer and water with stirring, there-
by to form a dispersion containing pulp-forming particles of said
polymer, the water content of the polymer solution being 1 to 10%
by weight based on the total amount of the aqueous organic sol-
vent, and the polymer and the concentration of said amide-type
solvent in the precipitant being 15 to 48% by weight when the poly-
mer is the aromatic polyamide, and 40 to 75% by weight when the
polymer is the nitrogen-containing polyheterocyclic compound; and
heating the resulting pulp particles to 30 - 90C in the presence
of at least 2 parts by weight, per part by weight of the pulp
particles, of said aqueous solvent and said precipitant.
The invention further provides a synthetic paper-like
sheet composed of the pulp-forming particles prepared by the above
process and thermally stable staple fibers.
DETAILED DESCRIPTION OF THE INVENTION
A method has already been known to provide pulp-forming
particles by adding a solution of a synthetic polymer in an organic
solvent to a precipitant with stirring. However, the pulp-forming
particles produced by the conventional methods have the defect that
water drainage from the sheet-forming screen is poor, and a sheet
of uniorm texture is difficult to obtain (in the present applica-
tion, this defect is expressed as "poor sheet-formability"). We
have unexpectedly found that the presence of a specified amount
~1 to 10% by weight~ of water ~n the polymer solution markedly
106729~4
improves the sheet-formability of the pulp-forming particles and the
electrically insulating properties of synthetic paper-like sheets
prepared from the pulp-forming particles. It has generally been
thought that the presence of water in a solution of a polymer in an
organic solvent should desirably be avoided since it causes a reduc-
tion in the solubility of the polymer and results in an unstable
solution. In view of this fact, it is surprising that the superior
advantage mentioned above can be obtained by using an aqueous organic
solvent containing a fairly large amount of water.
When the water content of the solution is less then 1% by
weight there is insufficient effect of the water addition, and when
it exceeds 10% by weight, the solution becomes exceedingly unstable.
The preferred water content of the solution is 3 to 9% by weight.
We have further found that a proper choice of the preci-
pitant markedly improves the sheet-formability of the pulp-forming
particles and the electrical insulating properties of synthetic
paper-like sheets made therefrom. Based on this finding, we knew
that when the polymer used is the aromatic polyamide, a precipi-
tant composed of water and 15 to 48% by weight, preferably 30 to 45%
by weight, of the amide-type solvent should be used, and when the
polymer used is the nitrogen-containing polyheterocyclic compound,
a precipitant composed of water and 40 to 75% by weightJ preferably
60 to 70% by weight, of the amide-type solvent should be used.
1067Z44
When the concentration of the amide-type solvent in the precipi-
tant is smaller than the lower limit of the above concentration
range, the resulting pulp-forming particles become coarser and
larger rod-like particles, and their sheet-formability is very much
deteriorated. Consequently, synthetic paper-like sheets made from
these particles have poor electrical insulation. On the other hand,
when the concentration of the amide-type solvent exceeds the upper
limit of the above-specified range, the pulp-forming particles
flocculate into a mass, and their sheet-formability is exceedingly
reduced. Thus, synthetic paper-like sheets prepared from these pulp-
forming particles have po0r electrical insulation.
We have further ~ound for the first time that when pulp-
forming particles obtained by adding the polymer solution to the
stirred precipitant to precipitate the polymer are heated to a
temperature of 30 to 90C, preferably to 35 to 70C, in the presence
of at least 2 parts by weight, preferably at least 5 parts by weight,
more preferably at least 30 parts by weight, per part by weight of
the pulp-forming particles ~solid), of the aqueous organic solvent
and precipitant, the sheet-formability of the pulp-forming part-
icles can be markedly enhanced. The upper limit of the total amount
of the aqueous organic solvent and the precipitant to be present is
not critical. However, the lower limit of this amount is critical,
and when the amount of the aqueous organic solvent and the precipitant
is less then 2 parts by weight per part by weight
-- 6 --
1067244
of the pulp-forming particles, the heat-treatment renders the pulp-forming
particles leather-like or massy, and makes subsequent operations such as
washing, beating and sheet-forming troublesome. The heat-treatment tempera-
ture is also important. When the temperature is lower than 30 C, sheet-
formability is poor. With increasing treatment temperature the required heat-
treatment time becomes correspondingly reduced, but when the temperature
exceeds 90C, the appropriate treatment time becomes so short that a uniform
quality of the pulp-forming particles cannot be maintained.
The present invention is based on the above three new discoveries,
and one of the most important advzntages of the present invention is to
provide pulp-forming particles having superior sheet-formability. The mean
specific filtration resistance value measured by the method to be described
is a very good measure for evaluating the sheet-formability of the pulp-
forming particles. When the pulp-forming particles have a mean specific
filtration resistance of 5 x 108 to 100 x 108 cm/g, they have acceptable
sheet-formability. When the mean specific filtration resistance exceeds
100 x 10 cm/g, water drainage from the sheet-forming screen becomes poor,
and it is difficult to obtain sheets having a very uniform texture. On the
other hand, when it is smaller than 5 x 108 cm/g, water draining is too fast
and the paper texture is deteriorated.
The invention is described in greater detail below.
Thermally stable aromatic nitrogen-containing polymer
The aromatic polymer used as a starting polymer in this invention
means a polymer in which a considerable portion of the main chain is composed
B -7-
~067Z44
of an aromatic ring. The thermally stable polymer used as a starting
polymer means a polymer which has a softening point of at least 155 C,
preferably at least 250C, and in respect of which properties, such as tensile
strength, elongation, dielectric constant, degree of polymerization and color,
will not undergo great change on exposure to temperatures of at least 155C,
preferably at least 180C, in air for long periods of time. The thermally
stable aromatic nitrogen-containing polymer used in this invention is either
an aromatic polyamide or a nitrogen-containing polyheterocyclic compound.
Preferably, the polymer used in the present invention is a polymer which has
a solubility of at least 3% by weight, preferably at least 5% by weight, in
organic solvents at room temperature and forms a stable solution. The
aromatic polyamides and nitrogen-containing polyheterocyclic compounds are
known, and examples of the thermally stable aromatic nitrogen-containing
polymers used in the present invention are shown below.
1. Aromatic polyamides
(1) Polyamides formed by condensation between dicarboxylic acids con-
taining an aromatic ring (preferably, highly active derivatives such as acid
halides) and diamines containing an aromatic ring. For example, they are
homopolymers derived from one kind of dicarboxylic acid such as terephthalic
acid or isophthalic acid and one kind of diamine such as m-phenylenediamine,
4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl methane or
-8-
J 1067Z44
xylylene diamine, or copolymers derived from the dicarbo-
xylic acid component and the diamine component either
one or both of which consist of at least two kinds of
compounds.
Typical examples include poly(m-phenylene iso-
phthalamide), poly(m-xylylenediamine terephthalamide)? poly
(N-methyl p-phenylene terephthalamide), and a copolyamide
of m-phen~lene diamine, isophthalic acid and terephthalic
acid.
1~ (2) Polyamides obtained by condensing aminocarboxylic
acids containing an aromatic ring preferably after they
have been activated. ~hey may be homopolymers derived
from one kind of aminocarboxylic acid such as p- or m- ~
aminobenzoic acid, or p--aminomethylbenzoic acid, or copoly-
mers derived from at least two kinds of the aminocarboxylic
acid. A condensation product of p-aminobenzoic acid is
a typical example~ - -
(3) Copolyamides obtained by copolymerizing (1) and
(2) above. A polyamide obtained by condensing m-phenylene-
diamine, isophthaloyl chloride and p-aminobenzoyl chloride
hydrochloride.
2. ~itrogen-containing polyheterocyclic compounds
(1) Aromatic polyamideimides
Polyamideimides containing a recurring unit of
the following formula
0 0
-HN-C- ~ -C~N
--C'
O
9 ~
1067Z4~
wherein R is ~ or - ~ - X -
O
- in which X is -0-, -S02-, -C--, or a lower
alkylene groupO
The polyamideimides may contain an inert substituent such
as a methyl group, an alkoxy group or a halogen atom.
(2) Aromatic polyamide hydrazides containing
a Fecurring unit of the following formula
O O
" "
- C - ~ - C - NE~H_
These ~olymers may contain an inert substituent such as a
methyl group, an alkoxy group or a halogen atom
(3) Aromatic polyamide imidazoles containing a
recurring unit of the following formula
.
0 H
H~- C - ~ ~C - R -
wherein R is the same as defined in (l) above.
These polymers may contain an inert substituent such as
a methyl group, an alkoxy group or a halogen atom.
(4) Aromatic polyimides containing a recurring
unit of the following formula
O O
Il 11
~C ~ , C\
- N I 1I N - R --
`C '~/~C~
Il 11 .
'O O
-- 10 --
~06724~ .
wherein R is the same as defined in (1) above.
These polymers may contain an inert substitu~nt such as
- a methyl group, an alXoxy group or a halogen atom.
(5) Aromatic polyazoles
~xamples are polybenzimidazole, polybenzoxazole
and polybenzothiazole. These polymers may contain an
inert substituent such as a methyl group, an alkoxy group
or a halogen atom.
R ~70/y~e~ o ~ c~ Z.~ o ~7
~LJ (6) Polyguinazolinedione, pol~bcn~o~adi~one,
pGlyquinazolone, and polyquinoxaline.
(7) Polythiazole, polyoxazole, polyoxadiazole,
polyhydantoin, and polyparabanic acid.
(8) Polymers containing a recurring unlt of
- the following formula
-
- O O
H~-- C - ~ C - NH - R -
C - OH
O
wherein R is the same as defined i~ (1) aboveO
These polymers are precursors of polyamideimidesO
(9) Aromatic polyhydrazides and aromatic
polyurea. The compounds (8) and (9) are considered as
precursors, but are also included within the definition
of the nitrogen-containing polyheterocyclic compounds
used in the present inventionO It is also possible to
use polymers obtained by copolymerizing the precursor
(8) or (9) with an aromatic dicarboxylic acid such as
iSophthalic acld or terephthalic acid, benzophenonetetra-
-- 11 --
- 106724~
carboxylic anhydride, or pyromellitic anhydride.
Preferred aromatic polyamides used in the
present invention are poly(m phenylene isophthalamide)
and poly(m-phenylene isophthalamide terephthalamide) 9
and preferred nitrogen-containing polyheterocyclic
compounds are aromatic polyamideimides~ Polyamide-
imides containing a recurring unit of the following
formNla
O O
~ C -,~,_ C ~
~ C ,N - R
- _ O
wherein R is -- ~ - X -- ~ - in which
X is a lower alky]ene group, preferably
a methylene grou~,
are especially preferredO
PolYmer solutions
In the process of this invention, the above
thermally stable aromatic nitrogen-containing polymer
is dissolved in an agueous organic solvent consisting
of an organic solvent and water to form a polymer solu-
tion. The water content of the polymer solution should
be 1 to 10% by weight, preferably 3 to ~/0 by weight,
based on the total amount of th-e polymer, organic
solvent and waterO Suit~ble organic solvents include
N-methyl-2-pyrrolidone~ N,N-dimethyl formamide, N,N-
dimethyl acetamide, dimethyl sulfoxi~e, hexamethyl
phosphorylamide-, and tetramethylurea. These solvents
can-be used either singly or in admixture of two or moreO
- 12 -
1067Z44
If desired, an inorganic salt such as calcium chloride
or lithium chloride may be added to the above organic
solvent to increase its polymer solubilizing powerO
~he polymer conc~ntration in the solution
differs according to the type and the degree of polymer-
ization of the polymer, but generally, ranges from 2 to
- 15% by weightO
It is not altogether necessary to add to the
solution a finely divided solid inorganic substance
which does not substantially react with the solution and
is insoluble in the solutionO This is however preferred
in order to further improve the electrical insulation and
thermal stability of sheets made from the resulting
polymer solutionO Micas having good electrical insula-
- tion and thermal stability are preferred as the solid
inorganic substanceO Spherical flaky substances such
as asbestos, glass flakes, quartz powder, talc, kaolin,
alumina, and calcium sulfate are also preferred. The
amou~t of the solid inorganic substance that may be added
is 50 to 900/0 by weight, preferably 100 to 400% by weight,
based on the weight of the polymerO
When the solid inorganic substance is to be
added to the polymer solution, it is preferred to dis-
perse it therein as uniformly as possibleO ~xamples of
preferred devices used for this purpose are an Attritor
(a product of Mitsui Miike Seisakusho COD~ Ltdo) and a
T.K. Homomixer (a product of Tokushu Eika Kogyo CoO, Ltdo)o
Various methods c~n be used in the present in-
vention-for including water in the polymer solutionO
1067244
For example, it is preferred to employ a method which comprises
mixing the solvent with a required amount of water, adding the
polymer to the mixture, and stirring the entire mixture to form a
solution. The polymer to be added to the mixture may be in the form
of a solid such as a powder or granule, or a highly concentrated
solution. When the polymer is a solid, it is possible to cause a
part or the whole of the required amount of water to be absorbed
by or adhere to the polymer, and then to mix the polymer with the
solvent.
When the polymer is obtained by solution polymerization,
a part or the whole of the required amount of water may be added
during or before the polymerization so long as it does not adver-
sely affect the polymerization.
The required amount of water may also be added after
dissolving the polymer in the solvent to a certain polymer concen-
tration. When the addition of water causes a local precipitation
of the polymer, it is necessary to dissolve the polymer completely
in the solvent by a proper measure such as the prolongation of the
mixing-stirring time or the heating of the solution.
As previously stated, the presence of a predetermined
water in the polymer solution offers an advantage of improving the
sheet-formability of the resulting pulp-forming particles and the
electrical insulation of the resulting sheet. Since the polymer
solution used in the process of this invention contains a fairly
large amount of water, the water content of the polymer solution does
not appreciably change by mois~re absorption in subsequent handling
of the polymer solution. This offers another advantage that the
- 14 -
` 1067Z44
degree of undersirable fluctuations in the quality of pulp-forming
particles caused by such fluctuations in the water content of the
polymer solution is far smaller than in a conventional process using
a substantially anhydrous polymer solution, and therefore, the process
steps can be very easily controlled.
Preparation of the pulp-forming-~articles
When the polymer solution prepared as mentioned above is
added to a stirred precipitant composed of an amide-type solvent for
the polymer and water, the polymer precipitates to yield pulp-
forming particles. The concentration of the amide-type solvent in
the precipitant is 15 to 48% by weight, preferably 30 to 45% by
weight, when the polymer is the aromatic polyamide, and 40 to 75%
by weight, preferably 60 to 70% by weight, when the polymer is the
nitrogen-containing polyheterocyclic compound. Preferably, the
polymer solution is added while the precipitant is stirred at high
speed to bring about a shearing action or beating action on the
polymer solution and simultaneously to extract the solvent from it.
The amide-type solvent used in the present invention
includes, for example, N,N-dimethyl formamide, N,N-dimethyl acetamide,
N-methyl-2-pyrrolidone, N-acetyl-pyrrolidone, N-methyl-caprolactam,
N-acetyl-caprolactam, hexamethyl-phosphorylamide, and tetramethylurea.
Of these, a solvent composed mainly of N-methyl-2-pyrrolidone is
preferred.
In the process of this invention, it is preferred to use
the same amide-type solvent to dissolve the polymer and for forming
the precipitant.
~067Z44
Heat-treatment of pulp-orming partlcles
The pulp-forming particles so prepared are then heat-
treated at a temperature of 30 to 90C, preferably 35 to 70C, in the
presence of at least 2 parts by weight, preferably at least 5 parts
by weight, more preferably at least 30 parts by weight, per part
by weight of the pulp-forming particles (solid content), of the
aqueous organic solvent and precipitant used. The pulp-forming
particles may be heat-treated either as dispersed in liquid or as
fabricated into a web form. For example, when the polymer solution
is added to a stirred precipitant in a preciptator, the polymer
precipitates to yield pulp-forming particles. Since these pulp-
forming particles are dispersed in~a liquid composed of the aqueous
organic solvent and the precipitant and the dispersion has sufficient
flowability, it can be directly transferred to a heater such as a
double-walled heater and continuously heat-treated there. AlternativelyJ
the dispersion can be transferred to a tank equipped with a heating
device, and heat-treated there batchwise. When, on the other hand,
the amount of the aqueous solvent and precipitant is relatively small
and a dispersion having flowability cannot be obtained (for example,
when a greater portion of the liquid is separated by filtration of
the above dispersion), the pulp-forming particles, to which the
remainder of the liquid has adhered, are processed into a web form,
and the resulting web-like pulp-forming particles having adhered there-
to the aqueous organic solvent and the precipitant are passed
- 16 -
~067Z44
..
between heated rolls to heat-treat them. Suitable heat-
treatment times differ according to the type of the
polymer? the type of the precipitant, and particularly
the heating temperature~ But the heat-treatment time is
usually several seconds to several hours. Generally, the
heat treatment time is preferably shorter with higher
- heat-treating temperaturesO The optimum heat-treatment
time should be selected so that a preferred mean specific
filtration resistance valùe can be obtained. This can be
easily determined experimentally by those skilled in the
art.
Production_of ~y~nthetic ~a~er-like sheets from ~ul~-formin~
particles
Paper-like sheets of excellent quality can be
obtained by subjecting a mixture of the pulp-forming par-
ticles prepared by the process of this invention with
thermally stable staple fibers to a sheet-forming processO
- Conveniently, the sheet formation from this mixture is
- carried out by the wet method using a paper machine of the
~ourdrinier or cylinder type as in conventional-papermaking
from wood pulpo
The staple fibers may be of any thermally stable
staple fibers, and include, for example, the follo~lingO
(1) Staple fibers of the same aromatic poly-
amides as hereinbefore described~
(2) ~taple fibers of the same nitrogen-containing
polyheterocyclic compounds.
(3) Staple fibers of the same precursors of
nitrogen-containing polyheterocyclic-compounds as described
.
-- 17 --
1067Z44
hereinabove (the polymers ~8) and (9) mentioned above under paragraph 2).
(4) Staple fibers of polyphenylene oxide or polyarylene oxides.
~ 5) Staple fibers of aromatic polyesters.
Examples of the aromatic polyesters are as follows:
(a) Polyethylene-2,6-naphthalate and/or polyethylene-2,7-
naphthalate.
(b) Copolyesters containing at least 85 mole% of an ethylene-
2,6-naphthalate unit and/or an ethylene-217-naphthalate unit, preferably
copolyesters using an aromatic dicarboxylic acid as an acid component.
(c) (i) Mixed polyesters containing polyethylene-2,6-
naphthalate and/or polyethylene-2,7-naphthalate.
(ii) Mixed polyesters containing a copolyester containing
at least 85 mole% of an ethylene-2,6-naphthalate and/or an ethylene-
2,7-naphthalate unit.
(d) Polyethylene terephthalate.
(e) Copolyesters containing at least 85 mole% of an ethylene
terephthalate unit, preferably copolyesters using an aromatic dicar-
boxylic acid as an acid component.
(f) (i) Mixed polyesters containing polyethylene terephthalate.
(ii) Mixed polyesters containing a copolyester containing
at least 85 mole% of an ethylene terephthalate unit.
(6) Staple fibers of inorganic compounds, such as glass
fibers, asbestos fibers, rock wool, slag wool,
~067Z~14
. .
fused silica fibers, bauxite fibers, boron fibers, potassium
titanate fibers, magnesia fibers, and whiskers of alumina
- or silicon nitride.
(7) ~atural fibers such as cellulose fibers,
regenerated cellulose fibers, and cellulose acetate fibers.
0f the above staple fibers, fibers from polymers
may be made of the same or different polymer as or from
that which constitutes the polymer solutionO
The denier size of each of the individual staple
fibers is 0. 5 to 10 denier, preferably lo 5 to 300 denierO
The length of the staple fibers differs according to the
single fiber denier, but is generally 1 to 10 mm, prefer-
ably 3 to 8 mmO
The sheet thus obtained from the pulp forming
15 particles of this invention contains the pulp--forming
particles in an amount of 20 to 95% by weight, preferably
40 to 60% by weight, based on the weight of the sheetO
When the amount of the pulp-forming particles is
less than 20% by weight, the properties of the sheet, such
as dielectric strength, tensile strength and elongation
become poorO When the amount of the pulp-forming particles
is larger than 95/0 by weight, the impregnating ability,
tensile strength and elongation of the sheet become poorO
The wet sheet prepared is dried, and heated
25 under pressure by means of a-hot press or heated rolls,
etc. to afford a synthetic paper-like sheet cf excellent
quality. ~he heating temperature somewhat differs accord-
ing, for example, to the crystallinity and the degree of
polymerization of the pulp--forming particles and staple
- 19 -
1067244
fibers, but suitable heating temperatures are llO to 320C.
At temperatures below 110C, the pressing is insufficient
and a tough sheet cannot be obtained. On the other hand,
at temperatures higher than ~20C, the polymer portions
of the pulp-forming particles completely melt-adhere to
one another and become film~like, and the sheet obtained
lacks flexibility. ~hus, temperatures outside the above-
specified range are not preferredO ~he pressure also
differs somewhat according to the crystallinity and the
degree of polymerization of the pulp-forming particles,
and is preferably not more than 200 Kg/cm~O When the
pressure is above 200 Kg~cm2, the polymer portions of the
pulp-forming particles completely melt adhere to one ano--
ther especially at elevated temperatures and become film-
likeO ~hus, the resulting sheet lacks flexibility~
- The following ~xamples and Comparative ~xamples
- illustrate the present inventionO ~he various properties
described in these examples were measured by the following
methods.
Logarithmic viscosity (~ lh)
.. , 1 ~
Measured at 30C for a soiution of the sample
polymer dissolved in N-methyl-2-pyrrolidone in a concentra-
tion of 0.5 g/100 mol~
Dielectric stren~th
Measured in accordance with JIS C 2111 using an
alternate current voltage.
Impre~natabilit~ (permeabilit~)
The sample cut in a circular shape with a
diameter of 2 cm is made afloat on the surface of an
.
.
- --r~
` 1067Z44
insulating oil (JIS No. 1), and the time required until
the insulating oil permeates onto the surface of the
sample is measured.
Texture uniformit~
~he surface condition of the sample sheet is
visually observed. Also, the condition of the sheet is
visually observed through light rays of the visible
region. Thus, the texture uniformity of the sheet is.
evaluated and rated on a scale of good and poor.
Mean specific filtration resistance
Into a glass tube having an inside diameter of
34 mm and a length of 130 cm and equipped with a stopper
and a 200-mesh wire screen at its bottom, a 0.5% aqueous
suspension of pulp-forming particles is placed up to a
- 15 height of 120 cm from the surface of the wire screen.
The stopper is removed, and the liquid surface level
descreasing with time is measuredO ~he mean specific
- - filtration resistance is calculated from the following
- equationO
Mean specific ,p x g x b
filtration resistance ~ --~
~ x c x Ho
wherein
~: the density of water ( ~ cm3)
g: the gravity, the acceleration 980 (cm~sec2)
b: the discharge water resistance (sec)
~: the viscosity of water ( ~cm,secO)
c: the concentration of the pulp suspension ( ~cc)
-Ho: the initial liquid surface level 120 (cm)
- 21 -
1067Z44
- ~ .
~he discharge water resistance (b) is determined
- in the following manner. Let the liquid surface level
after the ~apse Oftseconds from the beginning of the liquid
level decrease by the removing of the stopper be H, and
the value of H/ko be x. A graph is prepared by plotting
t and (x - ~n x - 1) (where ~n represents natural logarithm)O
Except for ve,ry small values of t, a straight line is ob-
tained. ~he inclination of this line is b, and with regard
B to this straight line ortion, the relation t=b(x -~nx
i0 is establishedO
~xample 1
Preparation of a ~ol~mer solution
~rimellitic anhydride and 4,4'-diaminodiphenyl
~ methane were condensed in a molar ratio of 2:1 in N-
methyl-2-pyrrolidone to form a bis-imide compoundO ~he
bis-imide compound was reacted with 2 moles, per mole of
the 4,4'-diaminodiphenylmethane, of trimellitic anhydride
and 3 moles, per mole of the 4,4'-diaminodiphenylmethane,
of 4,4'-diphenylmethane diisocyanate to from a solutlon
containing 2,~/o of polyamideimide (having a logarithmic
viscosity in N-methyl-2-pyrrolidone of 0.73) in the N-
methyl-2-pyrrolidone (solution A)o
Separately~ 190 parts of deionized water was added
to 2,~50 parts of N-methyl-2-pyrrolidone~ and 418 parts of
a mica powder having a particle size, measured by the
Andreasen pipette method, of 400 to 1,000 mesh was addedO
The mixture was then stirred for 40 minutes by means of
a T.K. Homomixer (a product of Tokushu Kika Kogyo Co., Ltd.)
to form a mixture consisting of N~methyl-2-pyrrolidone,
- ~2 -
~067244
water and mica (mixed solution B).
gOO parts of the solution A was added to 2958
- parts of the mixed solution B, and they were stirred
until a homogeneous solution consisting of the polyamide
imide, N-methyl-2-pyrrolidone, water and mica was obtained
(solution C). ~he concentration of the polyamideimide in
the solution C was 60 ~/o by weight, and its water content
was 5.~/o by weight (the above weight percentages were
calculated with the omission of the amount of the mica).
PreParation of a nreci~itant
30 Parts of water was added to 70 parts of N-
methyl-2-pyrrolidone, and the mixture was simply stirred
to form a precipitantO
- Pre~aration of ~ul~-forming ~a~ticle~ -
A continuous precipitator of the in-line mixer
type consisting of a combination of a stator equipped with
a buffle and a turbine vane-type rotor and equipped with a
feed inlet for the precipitant and the polymer solution and .
an opening for discharging a pulp-forming particle slurry
after precipitation was charged simultaneously with 005
- E ~min. of solution C and 5 Kg/min. of the precipitant,
and the resulting slurry of pulp-forming particles was
discharged out of the discharge openingO At this time,
the temperature of the precipitant was adjusted to ~5C,
and the temperature of the solution C, to 35C The
speed of the rotor was adjusted to 5,000 rpm~
Heat-treatmert
~ ive liters of the resulting-slurry of pulp-
forming particles was placed in a 7-liter tank, and stirred
- 23 -
'1067Z44
,~o sse c~
at a speed of about 60 rpm. Warm water was flow~
into a jacket attached to the tank to heat-treat
the slurry at a temperature of 60C for 5 minutes.
After the heat-treatment, the pulp--forming particle
slurry was placed in a centrifugal separator and a
- greater portion of the precipitant was separated as
a filtrate. ~hen, deionized water was fed to wash
the pulp--forming particles sufficientlyO The result-
ing pulp-forming particles had a mean spec~fic filtra-
tion resistance of 33 x 108 cm/gO
Sheet formin~
An aqueous dispersion containing 2016 g
(solids content) of the resulting pulp-formirg
particles and poly(m-phenylene isophthalamide) fibers
with a single fiber denier of 2 denier and a fiber
length of 7 mm (CONEX, a registered trademark for a
product of Teijin Limited) was processed on a TAPPI
~ 0~7 ~ ~e
standard sheet machine. Water drninin'~ from the wire
screen was good, and the pulp-forming particles ex--
~o hibited good sheet-formability. The resulting sheet
had good uniformity of texture. The staple fiber
content of the sheet was 20% by weightO
The wet sheet was hot-pressed at 230C and
200 K ~cm2 to form a sheet having a thickness of 113
microns. The sheet had a dielectric strength of 29
KV/mm, an impregnatability of 800 sec/mm, a tensile
strength of 3.7 Kg/cm2 and an elongation of 6.0%.
The sheet was immersed in a silicone oil
at 240C for lOOO hours. ~ut its above properties
- 24 -
1067Z44
..
scarcely changed, and its termal stability was good.
Comparative Exam~le 1
Pulp-forming particles and sheets were
prepared in the same way as in Example 1 except
that the amount of water in solution B was varied
as shown in ~able 1. ~he properties of the sheets - -
obtained were measured and the results are shown in
Table 1.
.
1067Z44
~able 1
Amount of Mean ~ .
water specific .
. filtration Dielectric Impregnat .
Run . resistance Texture strength ability
No. Parts 0/~ (x 108 cm/g) uniformity (KV/mm) (sec/mm)
_ _ _ . ~ __
1 0 0 . 4 Poor 4O1 800
. __ . _ ~ __
2 15 0.46 4 . Poor 9 7 830
3 381 _ 10.5 4 . Poor _ _9-3 . 7 _ _
~he polymer precipitated upon addition of
4 485.6 13.0 the solution A to the mixed so'ution B,
. ~ _ and solution C could not be formed.
__
In Run ~oO 1 in which no water was added to the
polymer solution and in Run NoO 2 in which the amount of
water added was too small, the pulp-forming particles in
- the slurry flocculated to form a massO Thus, they had a
~er~ low mean specific filtration resistanceO me result-
ing sheet had an exceedingly uneven surface, and poor pro-
. perties, especially poor dielectric strengthO
On the other hand, in Run No. 3 where the amount
of water was too large, the precipitation rate was so fast
that the pulp-forming particles formed had a large size,
and had a very low mean specific filtration resistance.
A sheet from these pulp-forming particles had a rough
surface and lnsufficient dielectric s.rengthO In Rhn
~o. 4 in which the amount of water was further increased,
it was impossible to form a solution corresponding to
solution C in Example 1, and subsequent operations failedO
It can be appreciated that in Example 1 in accord-
ance with this invention, the pulp-forming particles had
- 26 -
106724~
a far higher mean specific filtration resistance, and the
resulting sheet had f~r superior uniformity of texture
- and electrical insulation, than in these comparative runs.
ExamPle 2
5 g of a powder of poly(m-phenylene isophthal-
amide terephthalamide) obtained by interfacial polymeri--
zation and having a logarithmic viscosity of 109 (iso-
phthaloyl chloride/terephthaloyl chloride = 97/3 (molar
ratio)~ was dissolved in a solvent consisting of 95 g of
N-methyl-2-pyrrolidone and 6 g of water (the water content
of the solution was 5066% by weight), and then 9.8 g of
- the same mica as used in Example 1 was addedO ~his mixed
solution was introduced into a precipitant composed of 550 g
of water and 450 g of N-methyl-2-pyrrolidone stirred at high
speed in a home blender (National MX-130~ Type, a registered
trademark) to form a slurry of pulp-forming particles. ~he
resulting slurry was transferred into a flask, and heat-
treated at 60Co for 5 minutesO ~he slurry was then subjected
to a centrifugal separator to separate it into the precipi-
tant and the pulp-forming particles. Ihe precipitant
remaining adhered to the pulp-forming particles was removed
by washing with a large quantity of waterO The resulting
pulp-forming particles had a mean specific filtration re-
sistance of 35 x 108 cm/g.
An aqueous dispersion containing 204~ g (solids
content) of the resulting pulp-forming particles and 0~27 g
of the same aromatic polyamide fibers as used in Example
1 having a single fiber denier of 2.0 denier and a length
of 5 mm was processed on a TAPPI standard sheet machine.
- 27 -
1~67Z44
~he wet sheet obtained was dried, and hot-pressed at
200 Eg~cm2 by means of a press whose surface temperature
was held at 250C. to form a sheet havin~ a thickness of
about 105 microns. ~he sheet had a staple fiber content
e
5 Of 10% by weight. In the sheet formation, water drnining
from the wire screen was fast, and the sheet-formability
of the puip-forming particles was good. The resulting sheet
had excellent uniformity of texture.
The sheet obtained had a dielectric strength of
49.7 EV/mm, an impregnatability of 5800 sec/mm, a tensile
strength of 400 Kg/mm2 and an elongation of 5.~/00 When the
sheet was allowed to stand in air at 270C. for 7 days,
the above properties scarcely changed. ~he sheet was sub-
- stantially free from coloration, and proved to have good
thermal stabilityO
~ or comparison, the above procedure was repeated
except that water was not added in forming the polymer
solution. ~he resulting sheet had a dielectric strength of
32 EV/mm which was insufficient for a sheet containing only
20 10% by weight of staple fibers~ -
- Example ~
Pre~aration of pol~mer solution
A polymer solution C having a polyamideimide
concentration of 6.1% by weight and a water content of
5.6% by weight was prepared in the same way as in ~xample
1 except that the polyamideimide used to form solution
A had a logarithmic viscosity of 0~75; in the preparation
of mixed solution B, 1423 parts of ~-methyl-2-pyrrolidone,
115 parts of deionized water and 232 parts of a mica powder
- 28 -
1067Z44
were mixed; and that the solution.C was prepared by mix-
ing 1770 parts of the mixed solution B and 500 parts of
the solution Ao
Preparation of pre~ tant
N-Methyl-2-pyrrolidone was mixed with water to
form three precipitants having an N-methyl-pyrrolidone .
concentration of 45, 60, and 70/0 by weight respectivelyO
Using the three precipitants, pulp-forming
- particles were formed and heat-treated in the.same way as
in Example 1 except that the speed of the rotor in the
precipitator was changed to 7100 rpm, and the temperature
of the precipitant was adjusted to 34Co ~heets were pre-
pared from the pulp-forming particles and poly(m-phenylene
isophthalamide) fibers in the same way as in Example 2 ex-
cept that the pressing of the sheet was effected at 230Co
and 200 Kg/cm2 and the thickness of the resulting sheets was-.
100 micronsO
~he properties of the pulp-forming particles and
the sheets were measured, and the results are shown in
Table 2
. able 2
_.. .
- Concent- ~ean specific .
ration of filtration Uniformity Dielectric.
Run the precipitant resistance of strength
NoO (wt.%) (x 108 cm/g) texture(KV/mm)
1 45 _ Good 47.5
2 60 - 53 Good 52O0
3 70 42 Good 51 o O
- 29 -
- 1067Z4~
~ hese three kinds of sheets were allowed to
stand in air at 210C. for 1000 hours, but their pro-
perties scarcely changed~ When they were dipped in a
silicone oil at 240Co for 1000 hours, they were scarcely
colored, and their tensile strength and elongation were
not deteriorated appreciably. ~heir thermal stability
were also good.
Compara i e_Example 2
~xample 3 was repeated except that the concent-
ration of N-methyl-2-pyrrolidone in the precipitant was
- changed to 0, 10, 30, 77, and 90% by weight respectivelyO
- ~he properties of the resulting pulp-forming particles and
sheets were measured, and the results are shown in ~able ~O
Table ~_ ~
Concent- Mean specific
ration of the filtration Uniformity Dielectric
Run precipitant resist~nce of stren~th
NoO (wt.%) (x 10~ cm/g) texture(KV7mm)
_. ___. __ ._ .
1 _ 3 Poor 80 8
2 10 - - Poor lloO
. . . _ _
3 30 _ Poor 18 0 3
4 77 _ _ _ _ Poor 5O9
Pbulpiforming particles could not be
~ . ._. _
In Runs Nos. 1 to 3 in which the concentration of
N-methyl-2-pyrrolidone in the precipitant was too low, the
pulp-forming particles were of a rod-like shape with a large
size, and thus had a very low mean specific filtration re-
sistance. ~he resulting sheets had a low dielectric strength.
- 30 -
' '''~F
1067244
In Runs Nos. 4 and 5 the N-methyl-2-pyrrolidone
concentration of the precipitant was too higho In Run
No. 4, the pulp-forming particles flocculated and had a
very low mean specific filtration resistance, and the
resulting sheet had a low dielectric strength. In Run
No. 5, the concentration of the solvent was higher than
in Run No. 4,, and the precipitation of polymer hardly
occurred, and it was impossible to obtain pulp-forming
particles.
Example 4
60 Parts of a powder of poly(m-phenylene iso-
phthalamide) obtained by interfacial pol~merization a~d
having a logarithm;c viscosity of 1~83 was dispersed in a
solvent consisting of 940 parts of N-methyl-2-pyrrolidone
and 65 parts of water and cooled to 5C. (the solution
- had a water content of 6.1% by weight), and 111 parts of
a mica powder having a particle diameter, as measured by
the Andreasen pipette method, of 400 to 1000 mesh was addedO
~he mixture was then heated to about 40C. to dissolve the
polymer completelyO
On the other hand, N-methyl-2-pyrrolidone was
- mixed with water to make three kinds of precipitants having
an N-methyl-2-pyrrolidone concentration of 20, 30 and 40%
by weight respectivelyO
A continuous precipitator of the inline mixer type
consisting of a cylindrical stator having a diameter of
40 mm and a rotor with two turbine vane-like blades and
including openings for the polymer-solution and the pre-
cipitant and an opening for discharging the resulting
- 31 -
106724~
slurry of pulp-forming particles was charged with 0.5 Kg/
min. of the polymer solution and 5 Kg/min. of the pre-
cipitant at the same time, and the resulting slurry of
pulp-forming particles was taken out from the dischaxge
opening. ~t this time, both the precipitant and the poly-
mer solution were maintained at a temperature of 20C.
~he speed of the rotor was adjusted to 9,000 rpmO
The resulting pulp-forming particles were heat-
treated in the same way as in E~ample lo
An aqueous dispersion containing 2016 g (solids
content) of the resulting pulp-forming particles and 0O54 g
of poly(m-phenylene isophthalamide) fibers (CONEX, a re-
gistered trademark, a product of ~eijin ~imited) having a
single fiber denier of 2 denier and cut to a length of 5 mm
was processed on a ~APPI standard sheet machine, dried, and
pressed at 300Co and 200 Eg/cm2 to form a sheet having a
thickness of about 120 microns. ~he sheet had a staple fiber
content of 20% by weightO The properties of the pulp-form-
ing particles and the sheets were measured, and the results
are shown in ~able 4O
_able 4
Concentra- _ _
tion of the filtration Dielectric Tensile
Run precipitant resis~ance Uniformity strength streng~h
No. (wto%) (x 10 cm/g) of texture (KV/mm) (Kg/cm )
1 20 _ Good 34 _.___
2 30 37 Good 40 5-3
3 40 2 Good 36 5~4
_ _ _ __ ______
- 32 -
106~244
- ~he three sheets were allowed to stand in air
at 270C. for 7 days~ But the above properties of the
sheets hardly changedO ~he degree of coloration of the
sheets was low, and their thcrmal stability was good.
_mParati e Example_~
Example 4 was repeated except that the N-methyl-
2-pyrrolidone concentration of the precipitant was changed
to 0, 10 and ~/o by wei~ktO The properties of the result-
ing pulp-forming particles and sheets were measured, and
the results are shown in ~able 5
~able_5
_, __ _ ~_
Concentra- Mean
tion of the filtration Dielectric Tensile
Run precipitant resis~ance Uniformity strength streng~h
No. (wto%) (x 10 cm/g) of texture (KV/mm) (Kg/cm )
_____ _ . __. .__ _ ,
1 0 4 Poor lOoO 4O0
_ _ . _ . _~ ,
2 10 4 Poor 22O5 3.8
_._ _ ____._ , ____ __ ~ __
3 50 2 Poor 14.9 4O3 -
_ _ _ _
In Runs Nos. 1 and 2 in which the concentration
of N-methyl-2-pyrrolidone of the precipitant was too low,
the resulting pulp-forming particles were of a rod-like
shape with a large size and had a very low mean specific
filtration resistance. Ihe resulting sheet had a low
dielectric resistanceO
In Run No~ 3 in which the concentration of N-
methyl-2-pyrrolidone was too high, the pulp-forming par-
ticles flocculated and had a very low mean specific
,
~067Z4~
filtration resistanceO ~he sheet had a low dielectric
resistance.
Exam~le ~
By the same method as in Example l, a 2~/~ by
weight solution of polyamideimide with a logarithmic
viscosity of 0.78 in N-methyl-2-pyrrolidone was prepared.
- ~he resulting solution was diluted with N-methyl-2-pyr-
rolidone and water to form a solution having a polymer
concentration of 6% by weight and a water content of 6% by
weightO A slurry of pulp-forming particles was prepared by
the same method as in Example 1 using a mixture of 60 parts
of N-methyl-2-pyrrolidone and 40 parts of water as a pre-
cipitant, except that the temperatures of the precipitant
and the polymer solution were adjusted to 1~Co ~ and the
speed of the rotor was adjusted to 7100 rpmO
~he resulting slurry of pulp-forming particles
was heat-treated by the same method as in Example l at vary-
~ ing heating temperatures for varying periods as shown in
Table 6. In Run No. 7 in ~able 6 in which the heat-t~ atmen~
r~ ~D~ec~ 0,~
--20 temperature was adjusted to 95C., steam was flowcd in a
tank jacket for heating.
~heets were prepared from the resulting pulp-
forming particles and aromatic polyamide staple fibers in
the same manner as in Example 2 except that the pressing
f the sheets was performed at 1700C. and 200 Kg/cm2 to
form sheets with a thickness of about 170 microns.
I~he properties of the pulp-forming particles and
sheets were me~sured, and the results are shown in ~ble
6.
-- 34 --
1067244
Table 6
Heat-treatment
conditions Mean
_ _ specific
~empera- filtration Dielectric
Run tu~e ~ime resis~ance Uniformity strength
No. ( CO) (min) (x 10~ cm/g) of texture (KV/mm)
1 Untreated 211 Poor 5800
2 40 60 98 Good 6503
_ . _ ____ ____ . . ___ __._
3 50 20 _ ~ 9 Good 64 9
4 _ _ __ _ 5 53 Good 69.8
_ 7 5 12 Good 5708
6 ~ 271440 205 Poor 58.3
7 95 00~ 4 Poor 2708
~ . _
In Table 6, Runs Nos. 1, 6 and 7 are comparative
runs. In Run No. 6, the pulp-forming particles had an ex-
cessively high mean specific filtration resistance becauseof the low heating temperature, although the treatment was
B carried out for as long as 24 hoursO Consequently, water
Jro~ ~ ~g e
dr~irirg from the wire screen was poor at the time of sheet
forming, and the resulting sheet had poor uniformity of
texture. In Run NoO 1, no heating was performed, and the
results were the same as in Rhn No. 6. On the other hand,
in Rhn No. 7, the heat-treatment temperature was high, and
the pulp-forning particles flocculated and melt-adhered
and had a very low mean specific filtration resistanceO ~he
resulting sheet had a very uneven surface and low di-
electric strength.
- 35 -
1067Z44
Runs Nos. 2 to 5 were in accordance with the
process of this invention. ~he resulting pulp-forming
particl.es had a suitable mean specific filtration re-
sistance, and the resulting sheets had good uniformity
of texture and dielectric strengthO
ExamPle 6
- . 6 Parts of poly(m-phenylene isophthalamide)
obtained by interfacial polymerization and having a loga-
rithmic viscosity of 1.8 was dissol~ed in a solvent con-
sisting of 94 parts of N-methyl-2-pyrrolidone and 6 parts
of water (the solution had a water content of 5066% by
weight), and then 11.1 parts of a mica powder having a
particle size, as determined by the Andreasen pipette
method, of 400 to lOO meshO
On the other hand, a precipitant consisting of
40 parts of N-methyl-2-pyrrolidone and 60 parts of water
was preparedO In the same way as in ~xample 5, a slurry of
- pulp-forming particles ~Jas prepared, heat-treated and washedO
~he mean specific filtration resistances of the resulting
pulp-forming particles are shown in Table 70
In the same way as in ~xample 5, sheets were
formed from the resulting pulp-forming particles, dried,
and hot-pressed at 250 Eg/cm20 ~he sheets had a thickness
of about llO micronsO ~he texture uniformity and dielectric
strength of the sheets were measured, and the results are
shown in ~able 7.
- 36 -
1067244
Table 7
Treatment _ _ _ _
conditio ns ¦ Mean
T filtration Dielectric
empera- Tim resistanceUniformity resistance
NRuOn tu~OrC.) ~min ) (x 108 cm/g) of texture ~KV/mm)
_
1 Untreated 159 Poor 51.4
_--50 _ ~_ ~_
3 70 2 50 Good 50.0
4 27 1440 _ 151 Poor ¦ 52.1
5 95 0.3 3 Poor I 18.3
Runs Nos. 1, 4 and 5 were comparison runs. In Run No. 4,
the mean specific filtration resistance of the pulp-forming particles
was too high in spite of the 24-hour treatment, and since water
drainage from the wire screen was poor at the time of sheet forming,
the resulting sheet had poor uniformity of texture. The sheet had
a good dielectric strength on an average, but individual values varied
widely. In Run No. 1 in which no heating was performed, the results
were substantially the same.
In Run No. 5 in which the heat-treatment temperature was too
high, the pulp-formlng particles flocculated and adhered and had very
low mean specific filtration resistance. The resulting paper had a
rough surface and a markedly low dielectric strength.
In Runs Nos. 2 and 3 which were in accordance with the pro-
cess of this invention, the pulp-forming particles had a suitable
mean specific filtration resistance, and
- 37 -
1067244
the resulting sheets had good uniformity of texture and
dielectric stren~thO
~,.
.
'.'
' :,
.~
1,:
Z`
, ~ .
'~ .
,
., .
- 38 -
