Note: Descriptions are shown in the official language in which they were submitted.
MET~OD OF PRODUCING MEDIUM-GRADE COATED PAPER CONTAINING HIGH-YIELD PULPS
FOR WEB OFFSET PRINTING
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to a method of producing medium-grade
coated paper for web offset printing, the base paper of which contains high-
yield pulps. More particularly, it relates to a method of producing medium-
grade coated paper for web offset printing, having a reduced tendency toward
heat-set roughening.
2. Descrip~ion of the Prior Art.
Recently, the importance of coated paper for printing as a medium for
magazines, advertising, catalogs and other publications, is again being
recognized. Particularly, the demand for coated paper of grades Nos. 3,4
and 5 (hereinafter referred to as "med:ium-grade coated paper") has been
increasing rapidly because of the need of reducing the weight and cost of
pflper. The trend to lighter weight publication grades is pointed out in
various articles, for example, in an article by James P. Hanson, Pulp and
P~per magazine, May 1977, pages 74-76. The various grades are identified on
page 74. Generally, medium-grade coated paper i8 widely used in the field
of light-weight pflper of 45 to 80 g/m2as compared with high-grade (grade
No. I or No. 2) coated paper wllich does not contain high-yield pulps. There-
fore, to compensate for the reduction of opacity resulting from the decrease
of the basis weight of the paper and to reduce the cost of paper, the base
paper of medium-grade coated paper contains one or more of ~he high-yield
pulps set out below in an amount equal to between 5~to and 100% by weight of
its pulp composition. The high-yield pulps, and the designation of each,
are as follows:
mechanical pulp MP
stone-ground pulp SGP
pressure stone-ground pulp PSGP
refiner-ground pulp RGP
thermo-mechanical pulp TMP
-1- ``.~
chemi-mechanical pulp CMP
chemi-thermo-mechanical pulp CTMP
chemi-ground pulp CGP
semi-chemical pulp SCP
In many cases~ medium-grade coated paper, because of its purposes and
applications, is subjected to web offset printing, which is high-speed
printing. In the web offset printing process the stream of hot gases
employed in the dryer section to heat-set and/or dry the printing ink i6 -
liable to produce unfavorab~e phenomena of blistering and heat set roughening
that are not seen in other printing processes such as sheet offset printing,
rotogravure printing and letter press printing. These ~henomena are serious
disadvantages exerting unfavorable results in the printed paper.
Blistering is seen both in high-grade and ~edium-grade coated papers,
and has been found to be attributable to the fact th~t, in a hot drying
process conducted immediately after the web offset printing, moisture remain- ¦
ing in the base paper is instantaneously evaporated by heat exceeding lOO C
and the expanded vapor pushes up the paper surface. A number of methods for
eliminating such blistering have been provided.
Heat-set roughen.ing, a phenomenon wherein the paper surfaces become rough
after web offset printing, is seen only in medium-grade coated paper, not in
high-grade coated paper. Neither the causes of such heat-set roughening nor
remedies therefor as yet have been disclosed. Heat-set roughening is con-
sidered to be the most difficult technical problem in the manufacture of
medium-grade coated paper for web offset printing.
The inventors have continued a study for 8 long period of time with a
view of reducing heat-set roughening. As a result, it has been found that
even if fiber bundles, shives and the like of high-yield pulps, which
previously were considered to be the main cause of heat-set roughening, are
removed from the pulp composition, heat-set roughening still occurfi when ~he
coating composition on both surfaces is above 16 g/m~, and this tendency is
accentuated when the co~ting composition has been applied by means of a
blade coater. Further study has revealed that heat-set roughening i9
attributable to the essential difference in properties between high-yield
,
; 2
,~
~ ~.45Zl~
pulps and chemical pulps contained in the base paper. That is, the causes of
heat-set roughening are as follows- under drying and ~inishing conditions
of coated paper required for obtaining the same smoothness and gloss, the
high yield pu]ps in the base paper contain more moisture than the chemical
pu]ps therein, and thererore in a hot drying process in web offset printing
the moisture, not only in shives of the high-yield pulps but also in single
fiber pieces, thereof evaporates instantaneously; furthermore, the fibers of
the high-yield pulps are very rigid and their bonding strength is small~
On the basis of this finding, the inventors have made ~urther study not
onlv of the base paper but also of the coating composition in order to reduce
heat-set roughening in medium-grade coated paper for web offset printing. As
a res~llt, the inventors have successfully obtained medium-grade coated paper
in which heat-set roughening is reduced, by employing a base paper containing
high-yield pulps having a certain fiber length distribution and by employing
coatin& compositions containing certain natural ground calcium carbonate in fl
limited proportion.
BRIEF SUMMARY OF INVENTlON
lt is an object of the present invention to provide a method of producing
medium-grade coated paper for web offset printing, in which the heat-set
roughening tendency of the paper has been reduced.
It is another object of the present invention to provide a method of
producing medium-grade coated paper of excellent quality at a low cost.
These and Gther objects have been attained by A method which comprises
applying a co~ting composition to both surfaces of a base paper,
- said coating ccmposition containing natural ground calcium carbonate
with a specific surface area of from 1.5 m2/g to 5 m2/g under the
following conditions:
(i) when said specific surface area is from 1.5 m2/g to 2.5 m2/g;
said natural ground calcium carbonate is employed in a proportion
of from 10% to (9OS-125)~, by weight of the total pigment content,
where "S" represents the specific surface area (m2/g of the
calcium carbonate used; and
(ii) when said specific surface are~ is from 2.5 m2/g to 5 m2/g; said
natural ground calcium carbonate is employed in a proportion of
~ ~ frcm 10~ to 100~, by weight, of the total pigm~nt content'
5~
the upper limit of the percent by weight of calcium carbonate to the
total pigment content in ~i) being estflblished by the relationship
(90S-125)%,
- said base paper containing one or more high-yield pulps in an amount
equal to 10% to 100% by weight of the fiber content thereof, and one
or more chemicsl pulps in an amount equal to O% t~ 90% by weight of the
fiber content thereof,
- said high-yield pulp(s) being below 30% by weight in the total of ehe
fiber fractions retained on ~ 12-mesh screen, a 24-mesh screen and ',
a 42-mesh screen, when the fiber fraction analysi6 ia performed in
accordance with the "Method of Screening Test of Paper Pulp" set
forth in JIS P8207,
-- the combined totul weight of these three fiber fractions
being hereinafter referred to as the "42-mesh fiber fraction
content".
Other and further ob~ects and advantages of the invention will appear
more fully from the following description.
BRIEF D~SCRIPTION OF THE DRAWING
! l`he flttached drawing shows the relationship between the specific surface
¦ area and proportion of natural ground calcium carbonate used as a pigment in
a coating co~position. In the present invention, the specific surface area
and proportion of natural ground calcium carbonate are selected from the
shadowed portion in this drawing.
DETAILED DESCRIPTION
The high-yield pulps used in the present invention are conventional
high-yield pulps such as MP (SGP, ~GP, TMP or the like), CMP (CTMP or the
like~ or SCP, and consist of unbleached pulps, semi-bleached pulps and/or
bleached pulps which are widely used in newsprint paper, paper board~ medium-
grade paper, medium-grade coated paper, groundwood paper, etc. Selectively
used in the present invention are high-yield pulps which, irrespective of
their kinds, are below 30% and preferably below 20~/o~ or more preferably below
10%~ in the 42-mesh fiber fraction content. ~igh-yield pulps generally used
... . .
. ~ .
~S~
in paper making have 42-mesh fiber fraction contents as follows: flpprox.
25 to 4C% for SGP, approx. 30 to 60/o for RGP, and approx. 35 to 75% for TMP.
In the present invention, high-yield pulps are adapted to have the above-
mentioned 42-mesh fiber fraction contents of less than 30% by properly
adjusting the manufacturing conditions of the high-yield pulps, refining
conditions. screening conditions, post refining conditions, etc. Particularly
high-yield pulps with a 42-mesh fiber fraction content of below 5/O are the
most pre~ferable because they combine with a certain coating composition of~
the present invention to reduce heat-set roughening very remflrkably. If the
42-mesh fiber fraction content is too low, however, the yield of pulps i6
reduced and additional power rates are required for refining, post refining,
etc. Therefore, the 42-mesh fiber fraction content is adjusted according to
the desired qua]ity of the medium-grade coated paper, the proportion of
high-yield pulps used, the composition of the coating composition, etc.
Among high-yield pulps having said 42-mesh fiber fraction content, it
is preferable to employ a high-yield pulp which is below 80%, and preferably
helow 70~/~. in the nmo~ t by welght o~ the fiber fraction passing through a
150-mesh screen (hereinafter referred to flS the "belo~ 150-mesh fiber
fraction content") because it effectively reduces the heat-set roughening
and prevents blistering. The below 150-mesh fiber fraction content is
determined according to test method JIS P8207. ~hen more than one kind
of high-yield pulp is used in the present invention, the 42-mesh fiber
fraction content and the below 150-mesh fiber fraction content are determined
aEter the high-yield pulps are mixed together. Llgnin is sometimes removed
from high-yield pulps by oxidation or deoxidization. Because in such cases
the high-yield pulps become like chemical pulps, heat-set roughening is
reduced, but the original objects to improve opaclty and reduce paper cost
by using high-yield pulps cannot be attained. Therefore, such treatment is
preferably limited to such an extent that the high-yield pulps show
brightness of below 80% when determined by means of a Hunter mult$purpose
reflectometer, and this applies also to the case of bleached wflste paper.
The b3se paper of medium-grade coated paper used ~n the present inven-
tion contains said high-yield pulps at least 10% by weight, and is produced
.
'~t'~ I
~45~1~
.
as follows: The high-yield pulps are mixed with chemical pt~lp, waste paper
pulp, broke pulp, etc. and, according to need, with auxiliary agents such RS
filler, si~e, retention aid, paper strengthening agent, dyestuff, alum, piech
control agent, anti-foaming agent, etc. Then the thus prepared paper-
making ~urnish wllich can be either flt sn acid pH or alkaline pH is made lnto
paper by means of a regular single-wire or double-wire paper machine. Alka-
line paper making is preferable frcm t~.te po mt of view of re-utiliz~tg t~te
broke. If necess~ry, it is possible to apply starch, pdlyvinyl alcohol,
polyacrylamide or the like as a surface size by me~ns of a size press, gate
roll coater or th'e like in the paper making process.
The coating composition applied to the base paper thus obtained contains
pigments and adhesives as its principal ingredients in the same manner as
conventional coating compositions. In the present invention, the coating
composition contains natural ground calcium carbonate, having a specific
surface area of 1.5 m~/g to 5 ml/g, in the proportion of 10 to 1007~, by
weight, of the total pigment content. When the specific surfflce area of the
natural ground calcium carbonate is 1.5 to 2.5 m~/g, the upper limit of the
proportion thereof is (9OS-125)% by weight of the total pigment content.
("S" represents the specific surface area of the natural ground calcium
carbonate).
If natural ground calcium carbonate having a specific surface area of
less than 1.5 m~/g is used or if natural ground calcium carbon~te having a
specific surface area of 1.5 m~/g to 2.5 m~/g is used in excess of the
flforesaid range, heat- set roughening is reduced bùt the smoothness of coated
surfaces is seriously affected, printed matter obtained being lnferior in
printed surface smoothness and ink gloss in spite of the reduction of heat-
set roughening. Consequently, in the present invention, nfltural ground
calcium carbonate having a specific surface area of 1/5 m~/g and 8reater is
uscd ~ithin the aforesaid range. In t~te case of natural ground calcium carbonat~
having a specific surface area of greater than 5 m~/g, ink gloss and printed
stlrfAce strength flre reduced, and therefore lt is necessary to increflse the
amount of adhesives in the coating composition, which results in a rise in
production cost and an increase of heat-set roughening. Consequently, in the
2~
present invention, natural ground calcium carbonate having a specific surface
area of less than 5 m~/g is used.
Natural ground cfllcium carbonate is made as follows: Limestone, sparite,
micrite, marble, calcite, natural chalk or the like, is ground into fine
particles one to several times by a dry or wet process by mechanical means
such as a crusher, pebble mill, hammer mill, micron mill, ball mill, jet mill,
attritor, sand mill, attrition mill, etc., and is, as required, classified
by air elutriation, hydraulic elutriation, etc., and is further condensed
`and dried. Natural ground calcium carbonate for paper coating thus obtained
in the forrn of a slurr~ or dry pawder is used ill the present invention.
Particularly, it is preferable to use natural ground calcium carbonate
adapted to satisfy formula (1) below, more preferably formula (2) below, as
disclosed in Japanese Patent LaidOpen Publications No. Sho 53-81709, Sho
53-40462, etc., by being mechanically ground by a wet process, either ron-
tinuously or batch by batch, by means of a sand mill, attrition mill,
attritor, agitation mill, etc., with natural or synthetic particles, not
exceeding approx. 5 mm in diameter, such AS Ottawa sand, glass beads, ceramic
beads, silicate beads, zirconium beads, etc., as a medium of grinding,
(hereinafter referred to as "sand mill treatment").
p ~ 5 + N - - - - - - - - - - (1)
I = N
; 0 8 + N - (2)
where "N" represents the specific surface area (m /g) before
sand mill treatment, and
"P" represents the specific surface area (m /g) after
, sand mill treatment.
~ A coating composition containing such natural ground calcium carbonate,
adapted, by said sand mill treatment, to have a specific surface area of
! greater than 2 m2/g,is excellent in fluidity and water retention, snd free
from streaks and even if such natural ground calcium carbonate is used ln a
high proportion of above 20V/o by weight of the total pigment content, coflted
~ surface smoothnes.s, printed surface smoothness and ink gloss are maintained
; in good condition.
1,
, ~ , -7-
,~ I
.
Pigments contained, along with said natural ground calcium carbonate,
in the coating composition of the present invention may be conventional
pigments for paper coating such as kaolin, clay, barium sulfate, precipitated
calcium carbonate, aluminum hydroxide, satin white, titanium dioxide,
calcium sulfite, zinc sulfate, plastic pigment, etc. mixed according to
their respective properties. It is to be understood that these are merely
by way of example, and pigments used in the present invention are not
limited to those listed. In the present invention, one kind, or more than
one kind, of adhesive is chosen, according to the des1red paper quality,
from conventional adhesives for paper coating such as the following:
natural adhesives including casein, soyabean protein, yeast protein, starch,
oxidized starch, esterified starch, etherified starch, cationic starch,
other modified starches and cellulose derivatives; and synthetic resin
adhesives including conjugate diene copolymer latexes such as ~tyrene-
butadiene copolymer and methyl methacrylflte-butadiene copolymer, acrylic
polymer latexes such as polymer or copolymer of acrylic and/or methacrylic
acid ester, po~yvinyl acetate latexes such as ethylene-vinyl acetate co-
polymer, and other alkali non-sensative or alkali sensitive synthetic resin
emulsions. Generally~ adhesives are used in a range of 5 to 25 parts by
weight of solids to lOO parts of pigment by weight. However, it is
desirable to use adhesives in a range of lO to ~0 parts by weight of solids
thereto in order to obtain excellent smoothness, opacity, paper glo9s and
ink gloss by increasing coating weight and to reduce heat-set roughening.
It is of course possible to mix the coating composition, as required, with
auxiliary agents such as dispersants, flow modi~iers, anti-foaming agents,
dyestuffs, lubricants, insolubilizers and water-retention agents,which are
used in conventional coating compositions.
In the present invention, the base paper is single-coated or muleiple-
coated on both surfaces with said coating composition by means of an on-
machine or off-machine coater so that the total coating weight on both 6ur-
faces is abo~e 5 g/n- . The makeup of the coating composition on each surface
and that of the coating composieion forming each layer in multiple coating may
be changed suitably. Coating may be done by any process and by means of any
,;: `~)
~52~L
of conventional coating machines, for instance, as follows: an air knife
coater, roll coater, puddle-type or inverted blade coater with bevel or bent
blade, Bill blade coater, twin blade coater and Champflex coater.
Among these coating machines, blade coaters have been preferred in
producing high-quality coated papers because they give smoother coated
surfaces. However, if the blade coaters are used in producing medium-
grade coated paper for web offset printing, the possibility of heat-set
roughening increases particularly when the coating weight total on both
surfaces is above 16 g/m', because the pigments in the coating composition
are liable to show orientation and the vapor permeability of the coating
layers is decreased. Consequently, to obtain medium-grade coeted paper
without heat-set roughening by means of the blade coaters, it has been
generally considered necessary, for instance, to reduce coating weight at
tlle sacrifice of paper quality including paper gloss, smoothness and ink
gloss~ or to decrease moisture in the product considerably. However,
according to the present invention, it is not necessary to take such
measures as decreasing moisture in the product even when a coating weight
total for both sur~aces is above 24 g/m2and it is possible to finish
medium-grade coated paper for web offset printing having excellent paper
gloss, smoothness ~nd ink gloss by means of finishing machines such as a
machine calendar, super calender and gloss calender.
It is not clear why such advantages are obtained, but it is surmised
that this is because a very good balance is maintained between the quality
of medium-grade coated paper, such as paper gloss, smoothness and ink gloss,
and the reduction of heat-set roughening owing to the improvement in vapor
permeability, by applying the coating composition, containing natural ground
calcium carbonate with a certain specific surface area in a limlted propor-
tion, onto the base paper which has reduced heat-set roughening by containing
high-yield pulps with a certain fiber length distribution.
Thus, according to the present invention, it is possible to reduce
heat-set roughening and to obtain medium-grade coated paper of excellent
quality for web offset printing. Furthermore, particularly when the coating
composition contains natural ground calcium carbonate above 20% by weight
.
3~3
of the total pigment content thereof, coated psper with high brightness can
be obtained; therefore it is possible to put a larger quantity of low-
priced high-yield pulps into the base paper and to produce medium-grade
light-weight coated paper having good opacity at very low cost.
The present invention will now be described in detail with reference
to examples. It is to be understood that the present invention is not
limited to the examples. In the examples, "parts" or '~/OIl (percent) means
"parts" or "%" by weight unless otherwise stated.
Example l
Base paper of 40 g/m~ for medium-grade coated paper was obtained from
a paper-making furnish comprising 1 part rosin size, 3 parts alum and 5 parts
talc filler being respectively added to a pulp suspension consisting of
15 parts SGP~ adapted, by post refining, to have a 42-mesh fiber fraction
content of 4% and a below 150-mesh fiber fraction content of 67%, 65 parts
of coniferous bleached kraft pulp (hereinafter referred to as '~BKP)
t-aving a Can.ldian StandArd Freeness thereinafter referred to as ~'CSF") of
550 CC alld 20 parts deciduous or hardwood bleached kraft pulp (hereinafter
referred to ns "LBKP") hflving a CSF of 450 CC. (The "parts" of pulp given
in this and the following examples are parts by weight on a bone dry basi8).
A coating composition of 60% solids was obtained by dispersing 15 parts
natural ground calcium carbonate with a specific surface area of 1.6 m /g
(Super 1700" made by Maruo Calcium Co., Japan) and 85 parts kaolin ("UW-90"
supplied by Engelhard Minerals & Chemicals Corporation, USA) in water with
0.2 part sodium polyacrylate as dispersant so as to give a solid matter
concentration of 65%, 3nd further adding thereto an aqueous suspension of
cooked oxidized starch ('~S-3800" made by Nippon Shokuhin ~flko KK, Japan) in
an amount to providè lO parts ,r solid matter and adding styrene-butadiene
copolymer latex ("JSR-0697"4nade by Japan Synthetic Rubber Co., Ltd, Japan)
in an amount to provide 7 parts of solid matter. The coating composition
was applied to said base paper by means of a blade coater so as to give a dry
coating weight (total for both surfaces) of 24 g/m~ . Then the paper was
dried and finished on a supercalender. Thus, medium-grade coated paper of
64 g/m~ was obtained. The medium-grade coated paper was subjected to paper
quality tests, the results of which are shown in Table 1.
1 - 4 inclusive. qhe terms bearing these superscript numerals are all
trademarks.
.,j ..,
,,.,"", -10-
~ 5~
The specific surface area of the natural ground calcium carbonate was
measured as follows by means of a powder surface area tester of the air
permeability type (made by Shimadzu-Corp. Japan): A 3g sample was put into
a sample tube 1 cm x 2 square cm and the specific surface area was calculated
from the time required for 20 cc air to pass through it in a 600 mm water
column. (In all of the following examples, the specific surface area of
natural ground calcium carbonate was measured in this way).
In Comparative Example 1, medium-grade coated paper was obtained in
the same way as in Example 1 except that the proportions of natural ground
calcium carbonate and ~aolin in the coating composition were changed to 30
parts and 70 parts respectively. The medium-grade coated paper thus obtained
was subjected to the same paper quality tests, the results of which are
shown in Table 1.
E~ample 2
Base paper for medium-grade coated paper was obtained in the same way
as in Example 1 except that the pulp composition consisted of 35 part8 RGP
adapted to have a 42-mesh fiber fraction content of 9% and a below 150-mesh
fiber fraction content of 51%, 4~ parts NBKP having a CSF of 550 CC and 25
parts LBKP having a CSF of 450 CC~
A coating colllposition was obtained in the same wsy ~s in Example 1
except that 40 pflrts natural ~round calcium carbonate with a specific surface
area of 1.9 m~/g. ("Escalon 2000" ~rom Sankyo Seihun KK., Japan) and 60 parts
kaolin ("HT Clay" sold by EMC, ~SA) were used as pigments. The coating
composition was applied to said base paper and dried in the same wsy 8S in
Example 1. The coated paper was finished by means of a supercalender to
obtain medium-grade coated paper. The medium-grade ~oated paper thus obtain-
ed was subjected to paper quality tests, the results of which are ~hown ln
Table 1.
In Comparative Example 2~ medium-grade coated paper was obtained in the
same way as in Example 2 except that the 42-mesh fiber raceion content of
RGP ~as 35%. The medium-grade coated paper thus obtained was sub~ected to
paper quality tests, the results of which are shown in ~able 1.
* Trademark
** Trademark
- 11-
~L~52 ~L
.
Example 3
Base paper ~or medium-grade coated paper W8S obtained in the same way
as in Example 1 except that the pulp fiber composition consisted of 35 parts
TM~ adapted to have a 42-mesh fiber fraction content of 9% and a below 150-
mesh fiber fraction content of 42%, 32.5 parts NB~P having a CSF of 550 CC
and 32.5 parts LBKP having a CSF of 450 CC. Natural ground calcium carbonate
with a specific surface area of 1.5 m~/g ("Softon 1500" made by Bihoku
~unka Co., Japan) was processed to have a specific surface area of 2.1 m~/g
by dispersing it in water by means of a turbine type agitator with 0.2%
sodium polyacrylate as dispersant so as to give a solid matter concentration
of 70%, and by grinding the slurry thus obtained by means of a sand grinder
(model "32G" made by Igarashi Kikai Seizo Co., Ltd.,Japan) at a speed of
1,000 rpm and a flow of 400 liters per hour, and with glass beads of
approx. 2.5 mm average diameter as a medium of grinding. A coating com-
position was obtained in the same way as in Example 1 except that 50 parts
natural ground calcium carbonate thus obtained and 50 parts kflolin
**
t"Hydrasheen 90" supplied by Huber Corporation, USA) were used as pigments.
The coating composition was applied to said base paper and dried in the
same way as in Example 1.
The coated pflper was finished by means of a supercalender to ob~ain
medium-grade coated paper. The medium-grade coated paper thus obtained was
subjected to paper quality tests, the results of which are shown in Tsble 1.
In Comparative Example 3, medium-grade coated paper was obtained in the
same way as in Example 3 except that the pigments in the coating composition
consisted of 75 parts of the natural ground calcium carbonate thus obtRined
and 25 parts kaolin. The medium-grade coated paper thus obtained was sub-
jected to paper quality tests, the results of which are shown in Table 1.
Example 4
Base paper of 35 g/m~ for medium-grade coated paper was obtained fr~m a
paper-making furnis'n con-prising 0.5 part rosin si7e, 3 parts fllum, 3 parts
kaolin filler and 0.3 part paper strengthening agent of polyacrylamide resin
being respectively added to a pulp suspension consisting of 30 parts T~
adapted to have a 42-mesll fiber fraction content of 25% and a below 150-mesh
* Trademark -1 2 -
** Trademark
~5~
fiber fraction content of 35%, 20 parts SGP which was the sflme as used in
Example 1 and 50 parts NBKP which was also the same as used in Example 1.
Natural ground calcium carbonate with a specific surface area of 1.5
m~/g ("Softon 1500" made by Bihoku Funka Co., Japsn) was adapted to have a
specific surface area of 2.3 ma/g by dispersing it in water with a disper-
sant so as to give a solid matter concentration of 60%J and by treating the
slurry thus obtained by means of an attrition mill using silicate besd6 of
approx. 1 mm average diameter. A coating composition was obtained in the ~
same way as in Example 1 except that 75 parts of the nfltural ground calcium
~arbonate thus obtained and 25 parts kaolin ("UW-90" supplied by EMC, USA)
were used as pigments. The coating composition was applied to said base
paper and dried in the same way as in Example 1. The coated paper was
finished by means of a supercalender to obtain medium-grade coated paper.
The medium-grade coated paper thus obtained was subjected to paper quality
tests, the results of which are shown in Table 1.
In comparative Example 4, medium--grade coated paper was obtained in the
same way as in Example 4 except that the pigment in the coating composition
consisted of 100 parts of the thlls obtained natural ground calcium carbonate.
The medium-grade coated paper thus obtained was subjected to paper quality
tests, the results of which are shown in Table 1.
Example 5
Base paper for medium-grade coated paper was obtained in the same way
as in ~xample 1 except that the pulp composition consisted of ~0 parts RGP
adapted to have a 42-mesh fiber fraction content of 25% and a below 150-mesh
fiber fraction content of 50%, 20 parts KBKP having a CSF of 550 CC and 60
parts LBKP having a CSF of 450 CC. Natural ground calcium carbonate with a
specific surface area of 0.1 m~/g was adapted to have a specific surface
area of 3 m~/g by dispersing it in water with 1~0% sodium polyacrylate as
dispersant so as to give a solid matter concentration of 70%, and by treat-
ing the slurry thus obtained by means of a sand mill. A coating composition
was obtained in the same way as in Example 1 except that 100 parts natural
ground calcium carbonate thus obtained was used as a pigment. The coating
-13-
~S~
composition WQS applied to said base paper and dried in the same way es in
Example l The coated paper was finished by means of a supercalender to
obtain medium-grade coated paper. The medium-grade coated paper thus ob-
tained was subjected to paper quality tests, the results of which are shown
in Table 1.
In Comparative Example 5 medium-grade coated paper was obtained in the
same way as in Example 1 except that the pigment in the coating composition
consisted of lO0 parts kaolin. The medium-grade coated paper thus obtained
was subjected to paper quality tests, the results of which are shown in
Table l.
Example 6
Base paper for medium-grade coated paper was obtained in the same way
as in Example l except that the pulp composition consisted of 70 parts SGP
adapted to have a 42-mesh fiber fraction content of 5~/0 and a below 150-mesh
fiber fraction content oE 55% and 30 parts NBKP having a CSF of 550 CC.
Natural ground calcium carbonflte with a specific surface area of 0.03 ma/g
was adapted to have a specific surface area of 4.5 m?/g by dispersing it in
water with 0~6~/o sodium polyacrylate ancl 0.2% tetrasodium pyrophosphate as
dispersants so as to gi~re a solid matter concentration of 73%, and by
treating the slurry thus obtained by means of a horizontal type sand mill
(~bynami~ made by Willy A. Bachofen AG, West Germany).
A coating composition with a solid matter concentration of 58%, com-
prising 100 parts natural ground calcium carbonate thus obtained, adhesives
of 5 parts (solid matter) oxidized starch as an aqueous slurry and 12 parts
(solid matter) of styrene-butadiene copolymer latex ("SN 304" made by
Sumitomo Naugatuch Co., Ltd., Japan), some dyestuff, some anti-foaming agent
and some insolubilizer, was applied to said base paper by means of a blade
coater so as to give a dry coating weight total for both surfaces of 26 g/m~.
Then, the paper was dried, and finished on a supercalender to obtain medium-
grade coated paper. The medium-grade coated paper thus obtained was sub~ected
to paper quality tests, the results of which are shown in Table l.
ln Comparative Example 6 medium-grade coated paper was obtained in the
* TradOEk -14-
** Trademark
2~
same wfly as in Example 2 except that the pigments in the coating composition
consisted of 50 parts precipitated calcium carbonate ('~Z" made by Shiraishi
Kogyo KK, Japan~ and 50 parts kaolin ("Hl Clay" supplied by EMC, USA). The
medium-grade coated paper thus obtained was subjected to paper quality tests,
the results of wl-ich are shown Ln Table 1.
Example 7
~ edium-grade coated paper was obtained in the same way as in Example 1
except that the pulp composition consisted of 35 parts RGP adapted to have
a 42-mesh fiber fraction content of 15% and a below 150-mesh fiber fraction
content of 50%, and 65 parts LBKP having a CSF of 500 CC, and that the pig-
ments in the coating composition consisted of 40 parts natural ground
calcium carbonate adapted my means of an attritor to have a specific surface
area of 2.5 m /g and 60 parts kaolin (HT Clay" supplied by ~MC, USA). The
medium-grade coated paper thus obtained was put to paper quality tests, the
results of which are shown in Table 1.
In Comparative Example 7 medium-grade coated paper was obtained in the
same way as in Example 1 except that the papermaking furnish comprlsed 1
part rosin size, 3 parts alum, 0.2 part polyacrylamide resin and 5 parts
talc being respectively added to a pu:Lp suspension conslsting of 50 parts
SGP adapted, by post refining, to have a 42-mesh fiber fraction content
of 0% and a below 150-mesh fiber fraction content of 85%, and 50 parts
NBKP having a CSF of 550 CC. The medium-grade ~oated paper thus obtained
was subjected to paper quality tests, the results of whlch are shown in
Table 1
Example 8
Base paper of 50 g/m~ for medium-grade coated paper was obtained from
a papermaking furnish comprising 0.05 part size of alkylketene dimer
("Hercon 40" made by Dic Hercules Co, Japan), 0.05 part fixing agent of
polyamide epichlorhYdrin ("Kymene" made by Dic Hercules Co., Japan), 1.0
pa~t paper strengthening agent of cationic starch and 3 parts filler of
natural ground calcium carbonate being respectively added to a pulp fiber
composition consisting of 30 parts SGP adapted to have a 42-mesh fiber
fraction content of 20% and a below 150-mesh fil~er fraction content of 45~/
* Trademark -15-
** Trad~ark
*** Trademark
11~5~1~
55 parts NBKP having a CSF of 550 CC and 15 parts L~KP hflving a CSF of
450 CC.
A coating composition was obtained in the same way as in E~ample 1
except that the pigments therein consisted of 30 parts natural ground calcium
carbonate the specific surface area of which ~as chsnged from 1 m~/g to
4 m~/g by treatment at a concentration of 65% by means of an attrition mill,
50 parts kaolin ("HT Clay" supplied by EMC, USA) and 20 parts aluminum
hydroxide ("Higilite H-42" made by Showa Denko KK, Japan)~ The coating ~
composition was applied to said base paper and dried in the same way as in
Example 1. The coated paper was finished by means of a supercalender to
obtain medium-grade coated paper. The medium-grade coated paper thus
Obtailled W3S subiected to paper quality tests, the results of which are
shown in Table l.
As seen from Table 1, medium-grade coated paper obtained in each of the
inventive Examples was satisfactory arld well-balanced in heat-set roughening,
printed surface smoothness, ink gloss, picking and blistering as compared
with medium-grade coated paper in any Comparative Example.
The results of the paper quality tests shown in Table 1 were
obtained as follows:
(1) Gloss: Gloss was measured at an angle of incidence
of 75 by means of a specular gloss meter.
(2) Heat-set roughening; By means of an RI printing
tester made by Akira Industry Co. 9 Japan; l cc ink
for web offset printing was distributed, and both
surfaces of the medium-grade coated paper were
printed therewith. Immediately after that, the
paper was dried by heating both surfaces at a
temperature of 200~ G, and heat-set rou~hening on
both surfaces was visually measured.
(3) Printed surface smoothness; ~he same procedure was
taken as in (2) above except that the heating temp-
erature was 150 C. The smoothness of the printed
surfaces was visually measured.
* Trademark
~3 - 1
~9L5'~
(4) Ink Gloss: The ink gloss of the printed matter
obtained in (3) above was visually measured.
(5) Picking: The medium-grade coated psper was printed
with ink having a high tack value by means of an
RI printing tester. Picking was visually measured.
(6) Blistering: The same procedure ~as taken as in (2)
except that the heating temperature was 250~C.
Blistering was visually measured.
(7) Evaluation: Tl)e results of the visual measurements
in (2) to (6) are represented in Table I by the
following four relative valuations:
........ Very good
D .......... Good
........ Poor
X .......... Very Poor
Throughout the specification and claims, the fiber fractions are
those determined in accordance with the '~ethod of Screening Test of Paper
Pulp" set forth in ~IS P8207.
As many apparently widely different embodiments of this invention
mfly be made without departing from the spirit and scope thereof, it is to
be understood that the invention is not limited to the speciflc embodiments
thereof except as defined in the appended claims.
17-
~L~452~
TABLE 1
. . Heat-Set Printed Inh ~
Example ~loss ~oughen- Surfaee GlossPicking Blistering .
No. ing Smoothness _ . . _ .
1 60 O 0 0 q 0
2 50 O 0 0 ~ 0
3 58 O O ~ a o --
4 48 a a a - o o
42 n o o a o
6 50 a ~ o o o
7 54 O n o
8 57 O 0 D a
. . _ _
Comparative
Examp]e
_-- ~, _ _ _ _
I 50 O ~ ~ ~ P .
2 46 X X X ~ .
3 8~3
4 88 ~ ~ ~ ~]
X X _ ~ ~
6 55 C) a ~ x ~
7 60 O D A X
