Note: Descriptions are shown in the official language in which they were submitted.
33303
The present invelltil~rl relates to a process lo r the l~&r~t~F~et.t~ of paper,
particularly o f piper useful as the intermediate layer medium o F
corrugated paper board, and to the thy s resulting product.
To is known that the corrugated paper boards in their simplest Form, consist of
three layers, namely two outer layers, forming the Faces of Lye paper hoard
and called "liners", and an intermediate, corrugated layer known in the
related art as the "medium".
In the case of the five layer corrugated paper boards, there are provided two
layers of corrugated "medium" paper, each one being interposed between two
layers of "liner".
It is also known that, owing to the main use of the corrugated paper boards in
the packing field the most significant properties of the single component
layers, for an evaluation as a whole of the corrugcltr -i paper boards are the
crushirlg strength (also known as the "Concord"), the water and the
wet strength.
In the past the "medium" papers were manufactured from straw, but such a
technology is being almost worldwide abandoned, both because the straw
handling costs became too much heavy, (particularly with respect to the
transportation and the involved labor) and owing to the pollutiorl problems
of the industrial effluents deriving from such a raw material.
Presently the "medium" papers are produced according to technologies which
can be essentially no Furred to two classes of raw materials:
a) "medium" paper produced from mixtures of particles or chips of wood
cooked by chemical processes (80%) and waste paper (20%); these
papers are also called "semichernical" papers (or papers from serniche-
mica pulp and are increasingly expensive due to the prevalence of a
valuable materia~such as the wood.) "medium" papers produced from mixtures of waste paper which are
improved by surface treatment of the resulting paper with
starches or resins, the-so-called "flutings" being thus obtained.
In this case too, apart -from the lower quality o f the resulting paper, the
~33~3~3
manufacturing costs are increased no-t only due to the raw mat-
trial being used, but also mainly owing to the additional
operations required.
It is enough to observe that the starch is added to
the paper in the already substantially dried condition, as
coming out of the drying section, in the form of a thin sun-
race layer, applied by a water solution having a concentration
of about 2%, whereby the treated paper must be -thereafter dried
again with a relevant energy consumption.
Lastly, generally in the paper industry the effluent
waters resulting from the treatment of the wood particles
(also known as the "black lookers constitute a very serious
lo problem Fran the point of view of the pollution and their treatment greatlyaffects the manufacturing costs The present invention provides a pro-
cuss for the manufacturing of paper, particularly "medium" paper for
corrugated paper board, which allows less valuable raw material to be
used with the proper-ties of crush resistance and water repellency being
maintained at the same level or, the type and concentration of raw
materials being the same, allows the aforesaid properties to be improved.
In particular, the present invention provides such
a process which, in the case of the "semi chemical" papers, and
the physical and mechanical properties being the same,
particularly the crush strength being the same, allows the con-
tents of wood pulp to be reduced.
Again, the present invention provides a process of
-the aforesaid type which in the case of "fluting" paper,
allows the crush strength to be increased by about 20%.
The present invention still further provides a pro-
cuss for the manufacturing of improved paper products, such as
cardboard, wherein the "stiffness" is a qualitatively import
lent feature.
7 _ 3 _
. . .
33~3
According -to the present invention there is provided
a process for the manufacturing of paper, particularly medium
paper for corrugated board, in which the paper, in the drying
stage and having a content of dry matter of between
pa -
~Jf~;333~
I C3 E?.IIl!(I with I)I;JCI~ Lyle s VOW cowlick tl~rlt~ to a vclllle
() f to Lo ` I ) to to my Ir):)tr31 ill l, Wylie I 1 itch littoral
thy' rl)r)l.Ol)t'; of Only rnal.l-rial ill Ill! pull all lot filial'; of Oily malt31`ial ill
file blrlck lyres crier the cnrlcentra~ion it of bitterly 50:L() anti 92:L0, anti
eye lily or l)I?t~Vt3c~11 I lo) a I L).
Irk thief prerelrt?(i ellll)odilnent of tune process of the inventiorl the concentrated
black liquor, bore Lye application to tot? pulper, is ~iul)plt3rnented with a small
pursuant of alcohols preferably polyvinyl alcohol.
it hats Zen fount that tile property of the black liquors owe improvincJ
lht3 properties us Life treated paper i s thus enllal-lced.
AccorfJill(~ to a foreteller embodiment of the invention, Whitehall thought black licluors
are to be Usual for tile treallTlerlt of colnured papers, even of light colors,
tl1eY Con ICKY l)reV;OUSIY tre-lte(j IVY ~arLj;ll Why ten jn9 aloud !;UI)St3C1Ur?I1t deluge for
instarlcl~ lay rr~e~lrl~i I I i,- a pot so krlowrl Iflallrlt3l
It has bell in fact surprisingly Furled that the black liquors which to date hadno use or had a limited use in differerlt technical Fields arid were only a
problem from the point of view of the pollution of the effluent waters of
paper rnarlllfilcLurirlg industries, whorl are applied as a thin layer Lo the paper
bunk Intel proville~l theft they are r)reviollsly concentraLe-l It a cnrltellts of
at least So of dry material, preferably 30 to 50~, allow the following
results to be Asheville:
I) In thought kiwi of thought sernichl3rnical papers, (owe of wood pulps and owe of
waste plier pulp), the crush strenc~trl (Concord) is increase d by more
thrill owe whereby tot? US? of semichelnical paper of lower grams per
styler meter is perrrlitte(l to obtain corrugated paper board having the
aureole crusllil-lg strength.
2) i~lterllatively, in tile case o f the serrlicllelnical papers, the relic
Barlow wood pull) and waste paper plop can be chilrlgr?cl~ sassing for
to 3 I 3(1:~) Lo) I , tllr l~llysicill all I~(3lni(~ lo us
partirulrlrly Life crllsllirlg strt?rlgth, briny l-n-aintairlrd urlvarit3cl. Theeconolrlical advarltage is sol f-evidellt, i f attention is paid to thy? fact
that by the waste paper plop an ecollomy of 30 to owe with respect to
I 3
the wood pulp is achieved.
3) In the case of the "fluting" papers, wherein to date
the necessary crushing strength is obtained by applying starch
or resins, there is not only achieved a saving of energy (in
the previously statewide sense) and of raw materials, since
starches and resins are more expensive than the black liquors,
but also better results are obtained as regards the increase
of the crushing strength. In this embodiment it is preferable
that -the concentration of the black liquors is higher, of the
order of 40 Jo 50%.
4) In the case of paper products in which the "stiffness"
effect is important as regards the quality and thus the price
of the product, as for instance cardboards for industrial pack-
ins, or the Nanette layers, therefore an improved product
can be obtained at a lower cost.
5) By the process of the invention there are again incus-
tribally acceptable the plants for the manufacturing of paper
and cellulose from straw, since the problem of the effluent
and of the resultant pollution is advantageously solved.
Several at-tempts have been made in -the past to reuse
or recycle the black liquors, those attempts only involving
the addition of the black liquors to the aqueous suspension
ox fires before the forming of the paper sheet without any
previous concentration step. These attempts were essentially
useless since. although an increase of grams per square meter
occurred, the physical and mechanical properties of the result-
in paper became worse. The fully surprising feature of -the
process of the invention is that by coating the paper, already
dried to an optimum value of residual moisture content, with
the black liquors, also previously concentrated, the resulting
product is qualitatively and significantly improved.
In this connection, the field tests demonstrated
that a difference of the moisture content of 20 -to 30% is
5 -
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:~33~
necessary to ensure the desired results. Otherwise stated,
if the residual moisture content of the paper is about 30%
it will be enough that the black liquors are concentrated to
not more than 50% to obtain the optimum results.
Tests of the crushing strength have been carried
out, of type known as Flat Crush Test (FIT), on corrugated
paper board comprising an outer liner of raft paper of 125
g/sq.m a medium semi chemical paper of 130 g/sq.m., and an
inner layer of liner paper of 125 g/sq.m.
Four samples (samples A) of corrugated paper board
in which the medium layer had not been treated with black
liquors, and four samples (samples B) of the same corrugated
paper board in which the medium paper had been treated with
10~ concentrated black liquors were subjected to the FIT with
following results:
A B
average weight ~48 4~8
FIT crushing 1~1 188
the percent increase of the crushing strength in this case was
higher than 24~.
Without imposing undue limitations to the present in-
mention a plausible hypothesis is that the black liquors,
owing to the concentration step, acquire the faculty of cry-
tallizing and polymerizing (depending on the nature of -the
components), onto the surface of the paper being treated,
thus giving the already mentioned ~Istiffness~l effect, semi-
far to or greater than the traditional treatment agents, but
with the previously mentioned advantages.
In this connection it seems reasonable to suppose
that the better results, as obtained with the black liquors,
can be attributed to a greater compatibility with the fiber
substances which are treated therewith.
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333~3
For the preparation of the hack liquors to be used
for the present invention there is carried out the washing
and squeezing of the wood particles or chips after the comma-
eel cooking the operation being repeated the most suitable
number of times. Like treatment is carried out on the pulp
obtained from the beating operation as effected on the alone-
said chips, the resulting black liquors being recovered and
combined.
lo As the black liquors useful for the present invent
lion there are contemplated not only those resulting from
semi chemical and chemical cooking treatments of annual or
multi annual plants, as by-products of the paper and/or cell-
lose manufacturing, but also the black liquors which are
purposely produced from plants or wastes of annual and multi-
annual plants such as straws of various nature and canes)
saw mill wastes, vine-shoots, sawdust and generally wood
flour.
In the latter case these raw materials are comma-
gaily treated with either acidic or basic solutions, the
chemical treatment being effected to obtain the maximum yield
of black liquors, whereas cellulose or hemicellulose also
useful in the paper industry J are obtained as the byproducts.
he black liquors are then passed to a concentration
plant, comprising two or more stages (depending on the sought
concentration degree.
Clearly, the higher is the resulting concentration,
the more economical is the use of the resulting black liquors,
since the energy consumption for the drying of the treated
paper will be lower.
As already mentioned, for the invention, a concentra-
lion degree of 5% is sufficient.
,.,~
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Elowever, especially when "fluting" papers are to
be treated, it is convenient to bring the concentration of
the black liquors to values of I to 50%.
The black liquors are produced in the plants for
the manufacturing of chemical or semi chemical paper starting
from wood. They can be used again in the same paper mill or
even in paper mills producing "fluting" paper, namely from
waste paper pulp. In the latter case, of course, the con-
c~ntration of the black liquors is adjusted to at least 35
to 40% for transport saving.
The resulting black liquors, having greater or lesser
viscosity and consistency, depending on the concentration
degree, are coated onto the paper during its drying step, by
means of coating rollers, or of any other suitable device
depending on the type of black liquors.
The coating of the paper can take place onto one
or both surfaces, or between one sheet and the other in the
case of doubled paper, cardboard or paper board, by using known
coupling, coaling and impregnating machines.-
It has been further assessed that the addition of
alcohols (particularly polyvinyl alcohol) even in small per-
cent ages of the order of 0.2-0.3% by weight referred to the
weight of -the paper, to the concentrated black liquors, causes
their behavior, as an additive for the improvement of the
basic qualities of the treated paper, to be enhanced.
Lastly, as already assessed in the tests, the verge-
table source of the black liquors must be selected as a function
of the mainly desired results.
For instance, whereas the black liquors obtained from
multi annual plants by semi chemical or soda/sulfate cooking
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.. . .. .. . . . . . . . .. .
~'~333~3
mainly yield an improvement of the crushing strength, -those
obtained from annual plants (straw and the like) by the same
cooking treatments mainly yield an improvement of the burst-
in strength, whereby the former is more advantageous for
the treatment, of papers to be used for "medium", whereas the
latter is useful for the "liners".
Lastly, the bisulfite type cooking of multi annual
plants gives black liquors qualitatively increasing the crush-
in strength and the bursting strength without any of thought improvements substantially Prevailing with respect to
the other.
The invention also provides the papers and paper board
when obtained by the process of the present invention since,
the content of wood pulp being the same, show better properties
of crushing strength and resistance to moisture.
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