Note: Descriptions are shown in the official language in which they were submitted.
1057911
Background of the Invention
This invention relates to transparent paper, particularly
to improved transparent paper formed of a mixture of synthetic
pulp and natural pulp.
Heretofore, transparent papers composed of natural
pulp such as glassine papers have been practically used.
However, those transparent papers have various disadvantages
in practical use owing to the use of heavlly beaten natural pulp.
One of the greatest disadvantages is that the conventional
transparent papers ar e very sensitive to moisture or water and
tend to cause stretching, curl and corrugation. The conventional
transparent papers are not therefore suitable for offset printing in which
damping water is used and for the secondary processing with
an aqueous coating composition. The conventional transparent
papers further have such a disadvantage that the blister phenomenon
occurs when heated because they have a relatively high equilibrium
moisture and a high bulk density owing to a high hydration of pulp.
In addi~ion, in the preparation of such ~ conventional transparent
papers, it is necessary to use pulp which can be beaten easily
and some special beating conditions are required in connection
with the structure of a beating device in order to accelerate
hydration of pulp as highly as possible. Furthermore, the heavy
beating results in a decrease in freeness of pulp which in turn
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restricts the paper making speed.
Recently, Japanese Laid-Open Patent Publication No.
35, 608 of 1974 disclosed an improved method for making transparent
paper in which polyethylene fibers or polypropylene fibers are mixed
with wood pulp to form paper and then a heat at a temperature
above the melting point of the resins which constitute the above
fibers andapressure are applied to the resultant paper. However,
such poly a!-olefin fibers have a poor dispersibility in water,
and accordingly it is difficult to obtain a uniform texture of paper.
In addition, since the action is carried out by heating under pressure
the paper at a temperature above the melting point of the resins
which constitute the fibers, the transparency of the poly c~olefin
fiber part is too high compared with that of natural pulp part and
consequently it is extremely difficult to obtain a sheet having
a uniform transparency. The transparent paper including
poly d-olefin fibers has poor affinity to water, therefore, it can hardly
be used for offset prLing and secondary processing with
an aqueous coating composition, though it has an improved dimensional
stability. Further, upon the transparentizing treatment with
heat and pressure, it tends to adhere to a heating roll to
form a piling of poly ~-olefin fibers thereon.
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10579~1
An object of the invention is to provide a novel
transparent paper which at least partly mitigates the above
disadvantages of the conventional transparent paper and pro-
vides various new advantages which have heretofore never been
obtained with conventional transparent papers.
Another object of the invention is to provide an
improved transparent paper which is formed of a mixture of
synthetic pulp of a polyvinyl alcohol-acrylonitrile copolymer
and an acrylonitrilestyrene copolymer with natural pulp.
The invention will become apparent from the following
detailed description.
The present invention provides transparent paper
obtained by moistening a fibrous matrix in the form of a sheet
material so as to have a moisture content within the range -
of 5 to 40% and then pressing the thus moistened sheet material
with press means having a press surface temperature of 130C
to 250C, said fibrous matrix consisting essentially of:
a) 6 to 60 parts by weight on dry basis of synthetic
pulp formed from stable fibres having a length of
1.0 to 25 mm and having a self-bondable microfibril
structure of pulp fibres having a diameter of 0.01
to 5 microns at their minimum dimensions and a length
at least five times their average diameter, the
synthetic pulp having a f~eeness of 50 to 600 cc
CSF and being of a blended polymer system which
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10579~
consists essentially of
5 to 40% by weight of polyvinyl alcohol- ~
acrylonitrile copolymer comprising a poly- ;
vinyl alcohol component which has an average
degree of polymerization of 500 to 3400 and
is chemically bonded to an acrylonitrile
component, the polyvinyl alcohol component
content being 20 to 80% by weight, and the
polyvinyl alcohol-acrylonitrile copolymer
being dispersed in 60 to 95~ by weight of
acrylonitrilestyrene copolymer in which
the acrylonitrile component content is 5 to
45% by weight; and
b) 94 to 40 parts by weight on dry basis of natural
pulp .
The polyvinyl alcohol-acrylonitrile copolymer is
hereinafter referred to as "PVA-AN copolymer" and the
acrylonitrile-styrene copolymer is hereinafter referred to
as "AN-S copolymer".
In the PVA-AN copolymer,-polyvinyl alcohol is
hereinafter referred to as "PVA" which is the hydrophilic
component and acrylonitrile is hereinafter referred to as
"AN" which is a hydrophobic component are chemically bonded
to each other, for example, either in the form of a graft
1057911
copolymer or in the form of a block copolymer. Preferably,
the PVA-AN copolymer is a graft copolymer.
If desired, the blended polymer system may further
include unreacted PVA in an amount of 23% or less by weight
and/or an acrylonitrile polymer in an amount of 35~ or less
by weight each with respect to the total amount of the blended
polymer system.
The PVA-AN graft copolymer can be obtained by
aqueous heterogeneous polymerization or solution homogeneous
polymerization. The average degree of polymerization of
PVA iS preferably within the range of 600 to 1800. The degree
of saponification of PVA is preferably 60~ or more. The
polymerization of PVA with AN to form a graft copolymer may
be carried out by dissolving PVA in a solvent for poly-
merization, for example, dimethyl sulfoxide;
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mixing and dissolving 25 to 500% by weight (based on the amount of
PVA) of AN in the resultant PVA solution; and polymerizing them
with use of a catalyst for polymerization, for example, persulfate
at a room temperature or at a relatively low temperature such as 70~C
or below. The final product after this^polymerization, may
include a PVA-AN graft copolymer, unreacted PVA and polyacrylonitrile.
In the reaction for obtaining the PVA-AN copolymer,
a small amount of an AN polymer which is not bonded to the
hydrophilic component and an unreacted hydrophilic component
which is not bonded to AN may be produced as by-products.
However the existence of those by-products in the blended polymer
system would be harmless so far as the system includes the PVA~AN
copolymer and the AN-S copolymer in the before mentioned
amounts, respectively. Accordingly it is unnecessary to remove
those by-products from the final product of polymerization for
obtaining the PVA-AN graft copolymer . What is important
is that the AN component and PVA component are chemically
- bonded to each other and the copolymer has the before mentioned
PVA content, whereby it becomes possible to impart an excellent
hydrophilic property, an excellent dispersibility in water and
an excellent self-adhesive property to the resultant synthetic pulp.
When the AN component and the PVA component are simply blended
and exist in the system, it is impossible to impart such
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', characteristics to the resultant synthetic pulp.
.
There may be an alternative polymerization method in which
AN is added to an aqueous solution of PVA and then polymerization
is c`arried out. The PVA-AN graft copolymer which is produced
by this method can be isolated by reprecipitation and then filtration.
The PVA content in the graft copolymer should be within
the range of 20 to 80% by weight, preferably within the range of
35 to 65% by weight. In case the PVA content is less than 20% by
weight, the molecular weight of the grafted polyacrylonitrile
component would become too large, impairing the processability and
impeding the development of the hydrophilic property of the res~ltant
synthetic pulp. On the other hand, if the PVA content exceeds
80% by weight, when the resultant fiber or pulp is made into an
aqueous slurry, PVA would flow out into water and the slurry
would cause foams which become obstacles to beating and paper making.
The use of PVA having an average degree of polymerization
of less than 500 will result in decrleasing the water resistance of the
paper. On the other hand, if the average degree of polymerization
of PVA used exceeds 3400, the hydrophilic property of the resultant
fiber will be degraded and fibrillation will not be carried out smoothly,
and accordingly the synthetic pulp having desired properties would
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never been obtained.
In preparing the PVA-AN copolymer, in addition to AN,
less than 40 mol% of a vinyl monomer other than AN, but which
is copolymerizable with AN, for example, vinyl acetate, methyl
acrylate, styrene and vinyl chloride, may also be copolymerized.
The AN content in the AN-S copolymer used in the invention
should be within the range of 5 to 45% by weight, preferably,
within the range of 15 to 40% by weight. When this AN content
exceeds 45% by weight, the compatibility of the AN-S copolymer
with the PVA-AN copolymer would be too high, impairing the forms or
characteristics of the resultant fibrils, On the other hand,
whenthe AN content is less than 5% by weight, the solubility of
the AN-S copolymer in a solvent (dimethyl sulfoxide) is reduced,
and accordingly a spinnable concentrated solution of the blended
copolymers cannot be formed. Therefore, the uniform synthetic
pulp cannot be obtained.
The AN-S copolymer whi~h is used in the invention can be
prepared through the utilization of any of conventional techniques
of random copolymerization such as an aqueous heterogeneous
polymerization and a mass polymerization.
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The blended polymer system for the synthetic pulp
according to the invention comprises 5 to 40% by weight of a PVA-AN
copolymer and 60 to 95% by weight of such an AN-S copolymer.
If the amount of the PVA-AN copolymer is less than 5% by
weight, it is difficult to fibrillate the fibers by beating, and
the fibers will have only low hydrophilic property. When such
synthetic pulp is mixed with wood pulp to make a paper, the paper
having excellent physical properties could not be obtained.
On the o ther hand, if the amount of the PVA-AN copolymer
exceeds 40% by weight, both the water resistance and the dimensional
stability to moisture of the resultant paper would be decreased.
It is not desirable that the amount of AN-S copolymer
is less than 60% by weight because the coagulation ability of the
fibers in a coagulation bath is reduced,
The blended polymer system for the synthetic pulp is
never limited to those consisting of said two copolymers only.
The system may contain unreacted PVA and an AN polymer produced
as by-products in the process of the graft copolymerization
and may further contain another acrylonitrile polymer.
A greater part of unreacted PVA are removed in the state of
an aqueous slurry in the process of making fibers and pulp.
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However, the amount of PVA in the blended polymer system
initially prepared should not exceed 23% by weight. If the amount
o:E unreactéd PVA exceeds 23% by weight, it will cause to produce
foams in the aqueous slurry.
The amount of the AN polymer in the b lended system prepared
should not exceed 35% by weight. If the AN polymer amount exceeds
35% by weight, the excessive fibrillation would be caused.
i
As to the addition of an AN polymer to the blended polymer
system, a separately prepared linear polymer may be used.
One having a molecular weight of about 20, 000 to 100, 000 is preferable,
It may contain the aforementioned vinyl monomers which can be
used in the gr~ copolymerization as a copolymerizable component
in such an amount within the range not exceeding 40 mol %.
Among the methods for preparing synthetic pulp from the
above mentioned blended composition, there are included a method
of beating fibers produced from the above system and a method
for preparing pulp materials directly from the blended polymer
composition .
As methods for producing fibers, there may be included
a flush spinning method and an emulsion flush spinning method
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lV5791~
in addition to the conventional spinning methods such as a wet
spinning method, a dry wet spinning method and a phase separation
spinning method. Among them the wet spinning method is most
preferable. A further explanation of the wet spinning method
will be given below.
The composition including the PVA-AN copolymer and
the AN-S copolymer is dissolved in a solvent such as dimethyl sulfoxide.
This solution is then wet spun by a conventional method into an
aqueous spinning bath, for example, an aqueous solution of
dimethyl sulfoxide containing up to the maxirnum of 80 % by weight
of dimethyl sulfoxide to produce an undrawn water-containing gel
filament. Such undrawn filament may be drawn in a hot water
j ~ath or in an atmosphere of steam. Further, the drawn filament
may be subjected to a heat treatment for fixing its length or
relaxing in a ho.t water bath or in an atmosphere of steam.
A draw ratio is preferably more than -3.0,but this is not
intended to limit the scope of the present invention. The use
of the undrawn filament is not harmful to achieve the objects of the,
invention. However, in the case of using the undrawn filament,
it is necessary to pay close attention to handle it because the undrawn
filament has a low strength.
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1~57911
.
Referring to the heat treatment for relaxation, a
, relaxation ratio is preferably more than 45%, but this is not
intended to limit the scope of the invention. By such procedures,
a fine pulp having a good dispersibility is easily obt~ined. - When
the draw ratio is not more than 3. O, the filament which is
subjected to such heat treatment is rather cut than fibrillated
in the process of beating. However, when the beating is
carried out without subjecting the filament to the hest treatment,
the objects of t~ invention can be achieved with the draw ratio
being not more than 3. O.
What is important is that the above fibrious material
consists of a hydrophilic component (PVA-AN graft copolymer)
and a hydrophobic component (AN-S copolymer) and that the
hydrophilic component is dispersed in the hydrophobic component
and exists in the form of being arranged as an independent phase
in the direction of the fiber axis.
1, .
Such fibrous material is easily fibrillated by beating,
and accordmgly a pulp or pulp like material having an excellent
hydrophilic property, a dispersibility in water~ and a self-adhesive
property can be obtained.
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1057911
The obtained filaments are then be cut into staple fibers
having a length of 1. 0 to 25 mm.
Instead of the aforementioned heat treatment prior to the
process of cutting, fibers may be subjected to a heat treatment
in a hot water or in an atomosphere of steam. In such a case,
it is desirable that the temperature for the treatment is within
the range of 90 to 120C and treatment time is within the range
between 30 seconds and 8 minutes, however, those are not
intended to limit the scope of the invention .
The fibers which are obtained according to th- above
method can easily be fibrillated by means of beating which
is usually applied to wood pulp, and may be made into pulp having
an excellent dispersibility in water.
The above staple fibers are made into an aqueous
dispersion having a concentration of 1 to 20% by weight
and subjected to a beating treatment by use of the conventional
beating devices such as beaters, refiners, PFI mills and ball mills.
The synthetic fiber prepared according to the invention
has a self-bondable microfibril structure. The pulp part icles
are entangled each other by the microfibrils. Each of tke fibers
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1057911
may have a diam'eter of 0. 01 to 5 microns, preferably 0. 05
to 3. 0 microns, at its minimum dimension portion. The
length of each of t-he fibers may be more than five times, preferably
twenty times, the average diameter.
The synthetic pulp may be solely or partly of a latent
microfibril structure. The term "latent microfibril structure"
refers to fibrous material itself obtained according to the invention,
or to the fibrous material a part of which is crushed in the process
of beating andis ;present in the form of microfibrils. Namely,
the latent microfibril structure is a precursor which can be
entirely converted to the microfibrils with sufficient beating.
When the beating with use of ~he conventional beating devices is
carried out to such an extent that the beaten fibrous materials
become suitable for forming a paper like sheet, a greater part of the
pulp material is occupied by the microfibril structure. In the
process of beating, powder like minute particles which are smaller
in size than the above microfibrils may be produced as by-products,
but those are not essential to the invention.
When the minimum di~nension of the above microfibril structure
does not meet such requirements that t~he diameter is at least
O. 01 microns and the length is more than five timesthe average diameter.
the entanglement of the pulp particles is degraded, and accordingly
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lV5791~
the strength and texture of the resultant paper are impaired.
Since the pulp material of the invention contains the
microfibril structures and the latent microfibril structure~,
the freeness of the pulp can be controlled at wlll by varying the
beating conditions. In addition, a paper having an excellent
wet strength is obtained without any additives such as binder
since the microfibrils have the self-adhesive property.
The structure of the synthetic pulp prepared according to
the invention may be defined by a freeness which is determined
according to Japanese Industrial Standard JIS P-8182 with use of
Canadian Standard Freeness testing machine. The freeness
of the pulp material of the invention should be within the range
of 50 to 600 cc, preferably within the range of 100 to 400cc.
When the freeness is less than 50cc, the tear strength of the resultant
paper is lowered and the paper making speed is lowered to such
an extent that the paper making is substantially impossible.
On the other hand, the freeness exceeds 600cc, the pulp loses
the paper making ability, and a paper having a good texture,
a good surface uniformity and good physical pPoperties is not
obta ined .
The tranSparent paper according to the invention
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is obtained by subjecting a sheet comprising 6 to 60 parts by weight
on dry basis of the above synthetic pulp and 94 to 40 parts by
weight on dry basis of natural pulp to a transparentizing
treatment with moisture, heat and pressure.
f
As the natural pulp, wood pulp is most preferably used,
but other natural pulp such as one which is prepared from bast
fibers or animal fibers may also be used.
If the amount of the synthetic pulp is less than 6 parts by weight,
the resultant base sheet is not sufficient for Fractical use in the
respects to its transparency, wet-strength, tensil strength,
folding strength, and dimensional stability, though these properties
of the base sheet are improyed when compared with a transparent
base sheet consisting of the conventional natural pulp only. On the
other hand the amount of the synthetic pulp exceeds 60 parts by weight,
the mechanical strength becomes uneven, especially the tear strength
and the folding strength are reduced. Preferably, the sheet
is formed of 10 to 50 parts by weight of synthetic pulp and 90 to 50
parts by weight of natural pulp.
The synthetic pulp and the natural pulp mixed in the
above proportions are made into a sheet with use of a conventional
wet system paper making machine. In the process of the paper
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lOS7~11
making, the conventional additives such as sizing agents, fixing agents,
releasing agents, antistatic agents, fillers and dyestuffs may be
added to the system.
.
Application in the paper making process of starch, polyvinyl
alcohol, carboxymethyl cellulose, sodium alginat~, solutions or
emulsions of synthetic resins or conventional transparentizing
agents may also be carried out by size-pressing, impregnation or coating.
.
The weight of the resultant sheet material may be controlled
within the range 25 to 200 g/m, but this is not intended to limit the
scope of the invention.
.
According to the invention it is possible to obtain a high
transparency without using a heavily beaten pulp which is used
to make a conve~ntional transparent paper Heretofore,
it has been necessary to use a heavily beaten pulp having a CSF
(Canadian Standard Freeness) of 50 to 150 cc to make conventional
transparent paper. However, according to the invention,
an excellent transparency can be o'otained with use of usually
or slightly beaten pulp. Therefore, the disadvantages inherent
with use of the heavily beaten natural pulp, such as a decrease
in the rate of paper making, a decrease in physical properties such
as dimensional stability, tear strength and folding strength
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~OS7~11
and the generation of blister phenomenon can be avoided
a cc ord ing to the invention .
The thus obtained sheet materi~l is then transparentized
by moistening the sheet to a moisture content within the range of
5 to 40%, and then passing it through a pressure equipment
having a surface temperature of above 130C to impart heat
and pressure. The moisture content is given by the following
formula
Weight of water contained in the sheet
Moi~ture content = X100
Weight of the sheet containing water
If the moisture content is less than 5%, a uniform transparency of the
sheet is not obtained. While, when the moisture content exceeds
401O, the physical strength of the sheet is reduced, causing
adhesion to the roll of the pressure equipment and making troubles
such as a break. Among the typical moistening methods,
there may be included a method of coating water by coater,
a method of spraying water and a so-called electrostatic
moistening method. In the moistening process, various additives
such as sizing agents, releasing agents, antistatic agents;
dystuffs and transparentizing agents may be added to water.
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~057911 - -
For the pressing treatment any conventional means
such as a super calender and a machine calender, an eguipment
having two rolls which form a nip, and a hot press type eq-llipment
may be utilized.
In the process of transparentizing treatment with use
of those equipments the sheet material is pressed at least one time
by a pressure equipment having a surface temperature of 130C or
above, whereby a desired transparency of the sheet is obtained
However, in view of 'the fact that the synthetic polymers which
constitute the synthetic pulp are decomposed at about 250C,
it is necessary to be careful so as not to raise the temperature
of the sheet to above 250C. The pressure which is applied to the sheet
material.- is controlled at will depending on the thickness of the
sheet, the mixing ratio of pulps and the condition of moistening.
But it may be usually within the range of about 100 to 500 kg/cm,
preferably about 120 to 400 kg/cm.
!
The transparent paper according to the invention has
such various advantages as described below, as compared
with conventional transparent paper such as glassine paper
or transparent paper formed of poly ~t olefin fibers and wood pulp.
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The synthetic pulp described can be uniformly dispersed
in the sheet in the form of microfibrils having numerous micro voids
and has hydrophilic moieties in itself. Therefore, the water
contained in the sheet functions as a plasticizer not only for
natural pulp but also for synthetic pulp. In addition, when the
sheet is subjected to the treatment with heat and pressure, the
water contained in the sheet is removed accompanying air which
is filled in the micro voids, whereby an inherent clarity of
the polymers which constitute the synthetic pulp are developed
effectively, and accordingly an excellent transparency is
obta ined .
The equilibrium moisture (at 20C, 60% RH) of the
untreated sheet material of the invention varies with the mixing
ratio of synthetic pulp, for example, it is about 6 % when the
sheet consists of 10 parts by weight of synthetic pulp and 90 parts
by weight of natural pulp, and it is about 4 % when the sheet consists
of 60 % by weight of synthetic pulp and 40% by weight of natural pulp.
When it is intended to obtain a desired transparency, it is found
that there is such a relation between the mixin-g -ratio of synthetic
pulp and the moisture content that an increase in the amount of
synthetic pulp saves the moisture content. Therefore, when the
mixing ratio of synthetic pulp is 60 %, it is sufficient for achieving
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1057911
the effect that the moisture content is at least 5 %. When the
mixing ratio of synthetic pulp is 10 %, the moisture content is
preferably more than 20 %.
As is understood from the abovê descriptions, the
transparent paper according to the invention has following advantages:
(a) It has a uniform and high transparency.
(b) It has excellent physical properties such as a tensile
strength and a folding strength.
(c) It has an excellent stability to moisture or water,
whereby the disadvantages such as curl, stretching
and corrugation can be avoided.
(d) The blister phenomenon which occurs when it is heated
can be avoided.
(e) It is suitable for various uses such as offset printing
use and secondary processing use.
(f) It offers various advantages in preparation such as an
- increase of ,the rate of paper making, a reduction
of beating treatment and a simplified transparentizing
treatment .
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lOS7911 - :
This invention includes not only a sheet which is wholly
transparentized but also a sheet which is partly transparentized .
The transparency of the resultant paper may be controlled
at will according to its use. For example, it is generally
controlled at more than 50 % u~hem the paper is used for a master
for duplication. For a tracing paper or a paper for plotter,
it is controlled at more than 60 %. And it is controlled at more
than 80 % when the paper is used for a glassine paper.
The transparency is given by the following formula:
Transparency = 100 - (value of opacity)
wherein the value of opacity is measured by Hunter reflectometer
according to JIS P-8138.
The invention will be further illustrated by reference
to the following examples, however, the invention is not limited
to those examples but includes wide variations.
Unless otherwise indicated, parts and % signify parts by
weight and % by weight, respectively.
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10579~
Exa mple
A PVA-AN graft copolymer in which the ratio of PVA to
AN i6 50/50 was obtained by grafting AN to PVA having a degree
of polymerization of 1400 according to a~n ordinary radical polymerization
method with use of persulfate salt as a catalyst.
I
An AN-S copolymer in which the ratio of AN to styrene
is 24/76, having an intrinsic viscosity of 0. 54 (determined in MEK
at 30C ) was obtained according tOa conventional suspension
polyme r ization .
One part by weight of the above PVA-AN graft copolymer
and 4 parts by ~veight of the above AN-S copolymer were diss`olved in
15 parts by weight of dimethyl sulfoxide (hereinafter referred to as
"DMSO") to obtain a 25% spinning solution.
A wet spinning with that solution was carried out in a water/
DMSO (45/55) bath from a spinning nozzle having a diameter of
0. 08mm to obtain a continuous filament having a denier of 7 and a PVA
content of 10% . The draw ratio was 2 times. Thus obtained filament
was cut into staple fibers having a length of about 10mm and the fibers were
then beaten with use of a single discrefiner under the conditions of
a pulp concentration of 3 % and the clearance of 50 mic:rons to obtain
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1057911
a synthetic pulp (A) whose CSF was 200cc. The a verage
diameter of the fibrils was 8 microns, the minimum diameter
in a fibril was 0. 5 microns and the ratio of the length by the average
diameter was about 50.
Separately, bleached broad-leaved wood kraft pulp (L)
having a CSF of 480cc, bleached needle-leaved wood pulp (N)
having a CSF of 350cc, heavily beaten bleached needle-leaved
wood kraft pulp (N') having a CSF of lOOcc and heavily beaten
bleached broad-leaved wood kraft pulp (L') having a CSF of 120cc
were prepared. The above synthetic pulp (A) and the natural pulp
(L) (N) (L') (N') were formed intoa sheet witha manual paper-
making sheet machine (with 80 mesh metal screen) manufactured
by Toyo Seiki Co., Ltd. according to the formulations shown
in the following Table 1.
As a control, a bleached needle-leaved wood kraft
pulp (N') having a CSF of lOOcc and a bleached broad-leaved
wood kraft pulp (L') having a CSF of 120cc were mixed with
the above synthetic pulp (A) to form a sheet under the condition
shown in Table 1 in the same manner as in th~ above.
The moisture contents of the thus obtained dry sheets were
controlled as shown in Table 1 by applying water to the sheets with
a wire wound coating rod. Then, the sheets were subjected
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lOS'7911
to a transparentizing treatment in which the sheets were made to
pass through a nip of a two stack pressure equipment provided with an
elastic roll and a hard chrome plated metal roll (surface temperature
at 150C) under the linear pressure of 135 kg/cm for four times
in all, reversing the sheet upside-down. Various characteristics
of the obtained transparent papers are shown in Table 1.
The transparent papers obtained according to the invention were
superior in the paper making ability, the transparency, the
physical properties and the secondary processability, compared
with that of Control. The transparent paper according to the
invention had a good balance of quality.
Example 2
Two kinds of filam~ts having PVA contents of 30% and 10%
respec~ively, were made by a conventional spinning method
similarto that described in Example 1 froma 25% solution in
DMSO of a mixture of one part by weight of a PVA-AN copolymer
obtained by grafting AN to PVA having a degree of polymerization
of 1800 according to an ordinary radical polymerization method
with uæe of persulfate salt as a catalyst in which the ratio of PVA/AN
is 80/20, with 1. 67 and 7 parts respectively by weight of an
AN-S copolymer having an intrinsic viscosity of 0. 65 determined
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105~91~L
in MEK at 30C which is obtained by a conventional suspension
polymerization method, in which the ratio of AN/styrene is
30/70. The draw ratio was 3. 5 times and each of the
obtained two kinds of filaments had a denier of 5. The filamen~s
were cut into staple fibers having a length of about 3 mm and the
staple fibers were then beaten in the same manner as in Example 1,
respectively, to obtain two kinds of synthetic pulp. One was
a synthetic pulp (B) whose PVA content was 30% and having a CSF of 195 cc,
and the other was a synthetic pulp (C) whose PV~ content was 10%
and having a CSF of 240 cc.
The average diameter of the fibrils having a PVA content
of 30% was 2 microns, the minimum diameter in the fibril
was 0. 2 microns and the ratio of the length by the average .
diameter was about 90, and the average diameter of the fibrils
having a PVA content of 10 % was 4 microns, the minimum diame~er
in the fibril was 0. 3 microns and the ratio of the length
by the average diameter was about 70.
Separately, a bleached needle-leaved wood kraft
pulp (N"~ having a CSF of 280cc and a bleached broad-leaved
wood kraft pulp ~L") having a CSF of 450cc were prepared.
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1(~5791~
A sheet was formed with use of the above synthetic pulps
(B) and (C) and natural pulps (N' ')and (L' ' ) in the same manner
as in Example 1 under the condition as shown in Table 2.
The moisture content of the resultant sheet was adjusted at the
value shown in Table 2 in the same manner as in Example 1.
Then, the sheet was made to pass through the two stack calender
which was used in Example 1 under the conditions of the surface
temperature of the roll at 140C and t~e linear pressure at
220kg/cm for four times in all, reversing the sheet upside-down,
to obtain a transparent paper. The properties of the
resultant transparent papers are shown in Table 2.
Example 3
Two kinds of filaments having PVA contents of 7 % and
20% respective;Ly, were made by a wet spinning method similar
to that disclosed in Example 1 from a 25% solution in DMSO of
a mixture of one part of a PVA-AN graft copolymer obtained
by grafting AN to PVA having a degree of polymerization
of 1100 according to an ordinary radical polymerization method
with use of persulfate salt as a catalyst in which the ratio of
PVA/AN was 60/40, with 7. 57 and 2 parts, respectively,
- 28 -
1057911
of an AN-S copolymer having an intrinsic vi scos ity ()f 0. ~5 determined
in MEK at 30C which was obtained by a conventional mass
polymerization method, in which the ratio ofAN/styrene
was 20/80.
The obtained tWG kinds of filaments had the same denier
of 10. Those filaments were cut into staple fibers having a length
of about 5 mm and the staple fibers are then beaten in the same
manner as in Example 1 to obtain two kinds of synthetic pulp.
One was a synthetic pulp (D) whose PVA content was 7% having
a CSF of 230cc, and the other was a synthetic pulp (E) whose
PVA content was 20% having a CSF of 200cc. The average
diameter of the fibrils having a PVA content of 7 % was 13 microns,
the minimum diameter in the fibril was 0. 8 microns and the
ratio of the length by the average diameter was about 45, and the
average diameter of the fibrils having a PVA content of 20 %
was 8 microns, the minimum diameter in the fibril was 0. 5 microns
and the ratio of the length by the average diameter was about 55.
Separately, the same bleached needle-leaved wood kraft pulp (N) -
and bleached broad-leaved wood kraft pulp (L) as in E~ample 1
were prepared. The above synthetic pulps (~) and (E) and
natural pu1ps (N) and (L) were mixed in such proportions
as shown in Table 3 to form a dry sheet with a Fourdrinier test
machine manufactured by Mitsubishi Kakoki Co., Ltd. at the
- 29 -
lOS7911
paper making rate of 20m/min.
The moisture content of the resultant sheets were
adjusted at the value shown in Table 3 by water coating
with use of a pilot coater. Then, the sheets were made to pass
through 4 nips of a super calender which was provided with
alternatively arranged chilled rolls having a highest surface temperature
of 160C and cotton rolls under the linear pressure at 220kg/cm
to obtain transparent papers. The properties of the resultant
transparent papers are shown in Table 3.
Control 3
A transparent paper was obtained in the same manner
as in Example 1-4 except that a commercially available pulp
prepared from poly 0(-olefin fiber was used instead of the synthetic
pulp (A) which was used in Example 1-4, and that the adjustment
of moisture content was not carried out. The transparency
of the resultant transparent paper was only 60 %. Besides,
a macroscoplc unevenness of transparency was remarkably
appreciated. The offset printabilities of the above
transparent paper and that of the transparent paper obtained
in Example 1-4 were examined, respectively. The transparent
paper of Example 1-4 showed a good ink acceptability and gave
a good result in printing. On the contrary, the transparent
- 30 -
1057911
paper obtained in this control showed a poor ink acceptability due to its
poor water absorbability, and microscopic white-spots were remarkably
appreciated .
Example 4
A continuous filament having a denier of 7 and having a PVA
content of 7 % was prepared by a conventional spinning method similar
to that in EKample 1 from a 25% solution in DMSO of a mixture of
one part of a PVA-AN graft copolymer obtained by grafting AN
to PVA having a degree of polymerization of 2600 according to an
ordinary radical polymerlzation method with use of persulfate salt as a
catalyst, in which the ratio of PVA/AN was 30/70, with 3. 29
parts of an AN-S copolymer having an intrinsic viscosity of 0. 54
determined in ME K at 30C which was obtained by a usual suspension
polymerization method, in which the ratio of AN/styrene was 24,/76.
The obtained filament was cut into staple fibers having a length
of about 10 mm and then the staple fibers Iwere beaten in the same
manner as in Example 1 to obtain a synthetic pulp (F)
having a CSF of 280cc. The average diameter of the fibrils was
13 microns, the minimum diameter in the fibril was 0. 8 microns and
the ratio of the length by the average diameter was about 45.
-31-
105791~
The bleached needle-leaved wood kraft pulp tN) and the
bleached broad-leaved wood kraft pulp (L) which were used in
Example 1 were mixedw~hthe above synthetic pulp (F) in
such propl3rtions as shown in Table 4. The resultant mixed
pulp was made into two sheets with a Fourdrinier test machine
manufactured by Mitsubishi Kakoki Co., Ltd. at a rate of
20 m/min. The moisture contents of the resultant dry
sheets were controlled at the value shown in Table 4 by-spraying
3 % aqueous solution of glycerin as a plasticizer with use
of a spray-type damping equipment attached to a pilot coater.
Then, the sheets were made to pass through 4 nips of a super
calender provided with alternatively arranged chilled rolls
having a highest surface temperature of 150C and cotton rolls
under the linear pressure of at most 200kg/cm to obtain
a transparentized papers, The properties of the obtained
transparent papers are shown in Table 4. The transparent
papers obtained in Example 4 showed excelIent properties
having a good balance of quality. To the contrary, the
transparent paper obtained in Control 4 had an undesirable
texture due to its poor dehydration property, and showed a poor ' t
workability in super calendering due to its poor tear strength and folding
strength and showed a bad ink acceptability in offset printing,
Furthermore, the corrugation~ of the resultant transparent
- 32 -
A
1~)5793LiL
paper were appreciated.
:E~ample 5
A continuous filament having a PVA content of 28 % was
made by-a wet spinning method similar to that described in Example 1
from a 25% solution in DMSO of a mixture of one part of a
reaction product obtained by grafting AN to PVA having a degree
of polymerization of 1800 according to an ordinary radical
polymerization method with use of persulfate salt as a catalyst,
which consisted of 74 % by weight of PVA-AN copolymer (75/25),
(20% by weight of unreacted PVA and 6 % by weight of a homogenous
acrylonitrile polymer, with 1. 7 parts of an AN-S copolymer
(havingan intrinsic visoosity of 0.71 determined in MEKat 30C)
which was obtal~ned by a conventional suspension polymerization method,
in which the ratio of AN/styrene . was 15/85. The obtained
filament having a denier of 7 was cut into staple fibers having
a length of about 5mm and the staple fibers were then beaten
in the same manner as in Example 1 to obtain a synthetic pulp (G)
having a CSF of 240cc. The average diameter of the
fibrils was 4 microns, the minimum diameter in a fibril was 0 3
microns and the ratio of the length by the average diameter
was about 70.
10~7911
Separately, a bleached needle-leaved wood kraft
pulp (N"') having a CSF of 550cc a bleached broad-leaved
wood pulp (L"') having a CSF of 620cc were prepared,
The above synthetic pulp (G) and the natural pulps (N"') and
(L"') were mixed and made into two sheets under the conditions
shown in Table 5. As a Control, a sheet composed of the above
natural pulps (N"') and (L"') only was prepared under the condition
shown in Table 5.
The moisture contents of the resultant sheets were adjusted
at the values shown in Table 5 by coating a 0. 3 % aqueous solution
containing sodium chloride as an antistatic agent on one side
surface of the sheet with use of a wire wound coating rod.
Then the sheets were made to pass through a two stack type
calender provided with an elastic roll and a hard chrome plated
metal roll (surface temperature at 150C) four times under
linear pressure of 210kg/cm, reversing both sides of sheets,
to obtain transparentized papers. The properties of the resultant
papers are shown in Table 5.
The transparent papers obtained in this Example were
superior to that obtained in Control in the respects of the
transparency, the physical properties and the secondary
processability. The properties of the transparent papers
- 34 -
!
1~57911
according to the invention transcended those which the glassine
paper should possess.
Example 6.
A continuous filament having a PVA content of 10%
was made by a wet spinning method similar to that disclosed
in E xample 1 from 25% solution in DMSO of a mixture of one part
of a PVA-AN graft copolymer obtained by grafting AN to PVA
having a degree of polymerization of 800 according to a conventional
radical polymerization with use of persulfate salt as catalyst,
in which the ratio of PVA/AN was 40/60, with 3 parts of AN-S
copolymer havingan intrinsic viscosity of 0.75 determined
n MEK at 30C and having a ratio of AN/styrene at 20¦80, which
was obtained by a common suspension polymeri zation method.
The draw ratio was 2. 0 times.
The resultant filament having a denier of 10 was cut
into staple fibers having a length of about 5 mm, and the staple fibers
were then beaten in th e same manner aæ in Example 1 to obtain
a synthetic pulp (H) having a CSF of 260 cc. The average
diameter of the fibrils was 7 microns, the minimum
-35-
,1
~
10579~1
diamer in the fibril was 0. 5 microns and the ratio of the length
by the average diameter was about 50.
The same bleached needle-leaved wood kraft pulp (N"')
and bleached broad-leaved wood kraft pulp (L"') as those
which used in Example 5 were prepar ed.
The above synthetic pulp and natural pulps (N"') and
(L"') were mixed at the mixing ratio shown in Table 1) and then
made into three sheets with use of a commercially available
Fourdrinier paper machine provided with a wire cloth having
a width of 1975mm, at a paper-making rate
of 50 m/min.
As a control, a sheet composed of the above natural
pulps (N"') and (L"') only was prepared in the same manner as
the above.
The moisture contents o~ each sheet thus prepared
was adjusted at the value shown in Table 6 by coating a 0. 2 %
aqueous solution containing a commercially available wax emulsion
as a releasing agent with a commercially available bar coater.
Then, each sheet was made to pass 16 nips of a super calender
provided with alternatively arranged chilled rolls having a highest
-~6
1~)579~
surface temperature of 160C and cotton rolls under the
linear pressure of at most 400 kg/cm to o'btain a transparentized
paper, The properties of the resultant transparent papers
are shown in Table 6.
It was clearly appreciated that the transparent papers
obtained in this :Example showed an excellent transparency
and excellent properties having a good balance of q uality
with increasing the mixing ratio of synthetic pulp even when
the moisture content was relatively low. On the contrary, the
sheet composed of natural pulp only which was obtained in Control
had an insufficient transparency though, it was treated at high moisture
content .
.
.- I
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- 37 -
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1t)579~L1
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Note:
1) Talc filler (~): The amount of ash in a dry p~per
determined according to Japanese
. Industrial Standard JIS P-8128
2) Oxidized starch siz,e press:
The amount of coating g/m2 on dry
basis
3) Dehydration rate:
Time required for dehydration of 10~
of pulp dispersion on a 80 mesh metal
screen of a manual paper-making
sheet machine having a width of 20 cm
and a length of 25 cm
4) Transparéncy (~) = 100 - value of opacity by Hunter
reflectometer (JIS P-8138)
5) Air permiability was measured by High Pressure Gurley
Densometer (ASTM D726-58, method B)
6) Breaking length was measured according to JIS P-8113
7? Tear factor was determined according to JIS P-8116
: 8) Folding strength was measured by MIT according to
JIS P-8115
. tensile strength of re~etted p~per
9) Breakinglength (Km)= (K~ xDOO
` drybasis weight (g/m2~ xpaperwidth
. . wherein the tensile strength of
. re`wetted pap~r.ls measured by JIS P-8135,
the dry basis weight is given by.
JIS P-8111, and the paper width is
15 mm as defined in JIS P-8135.
.
. -40-
1~)579~
10) Expansion in water was measured with a Fenchel
expansion meter after dipping the sheet in water
at 20C for 5 minutes.
The above note for each of the items in Table 1
also applied to Tables 2 to 6.
-41-
105 7
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