Note: Descriptions are shown in the official language in which they were submitted.
SPECIFICATION
108Z088
This invention relates to a novel reinforced corrugated
paper board and a method for producing the same.
A large variety of reinforced corrugated boards are
known which have been made of wood pulp containing thermosetting
resin material such as melamine-formaldehyde resins or epichloro-
hydrin resins. It has been also known to reinforce the
corrugated paper board by impregnating the paper board with
paraffin or su~thetic resins, or by using a thick, multiwalled
or resin-impregnated paper board as an inner fluted member.
These and other prior art attempts have not, heretofore,
been successful because of the use of special adhesive for
lamination with liner sheet, insufficient wet strength or
incapability of being processed by conventional corrugate
machines.
A paper made of a mixture of wood pulp and thermoplastic
resin is known. This paper, however, has not been used to any
great extent'for making corrugated boards because the
thermoplastic resin contained therein would melt and deposit'
onto the pre-heating rollers or corrugating rollers when the
paper is processed by a conventional corrugate machine, or it
requires the use of a special adhesive for laminating with
the outer liner membex.
~Q~e r~r
It is a primary object of the prc~e~ invention to provide
a reinforced corrugated paper board which can be manufactured
by means of a conventional corrugate machine.
According to the present invention, a reinforced corrugated
paper board is provided comprising an inner fluted member and
an outer liner laminated to at least one side of said inner
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108;~088
fluted member. Said inner fluted member is made by using a
conventional papermaking machine to form a multiwall paper
board comprising an inner layer of a mixture of cellulose pulp
containing about 20% to about 50% by weight of thermoplastic
resin fibres based on the dry mixture, and two outer layers of
cellulosic pulp free of thermoplastic fibres each formed onto
the opposite surfaces of said inner layer. The multiwall
sheet material is incorporated together into a unitary, fluted
inner member during the processing of the material by a conven-
tional corrugating machine as it passes through the nips betweenpreheating rollers and corrugating rollers successively under
pressure at an elevated temperature.
The thermoplastic resin fibres which may be used for
this purpose are polyethylene, polyamide, polyvinyl alcohol,
polyvinylchIoride, polystyrene and acrylic resin fibres. At
a content of the resin substantially less than that specified, -~-
improvement in physical properties of the fluted member such
as adhesion with wood pulp fibres, wet strength or absorption
of water will be insufficient. The cellulose pulp which may
be used as the primary component of the inner layer may be any
cellulosic pulp conventionally used for the production of
corrugated paper board such as semichemical pulp, waste paper
pulp or mixtures thereof.
The outer layers to be formed on the both surfaces
of the inner layer may be of the same type of cellulosic pulp
as used in the inner layer but do not contain the thermoplastic
resin. Each of the outer layers has a sheet weight from about
20 to 50 g/m2. At a sheet weight less than 20 g/m2, the
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thermoplastic resin in the inner layer will difuse onto the
outer layers during the processing and thus deposit on the
drying cylinders of paper machine, preheating rollers or
corrugating rollers of corrugate machine, whereas a sheet
weight greater than 50 g/m2 decreases wet strength of the
inner sheet member to be corrugated.
The wet strength of the outer layer of the fluted member
t/~e~n7osett~
may be increased by incorporating a e~#~K~-~d~resin
material such as melamine-formaldehyde resin or epichlorohydrine
resin into the outer layer.
The multiwall sheet material to be processed into the
fluted member may be formed in conventional manner using, for
example, an ultraformer machine into a wet sheet r dehydrating
the wet sheet between two sheets of felt and then drying on-
a drying cylinder. ~s the sheet has not sufficiently been
heated and pressed, the resulting sheet does not have a su~ficient
strength for use as the inner fluted member as such.
One of particular advantages of this invention resides
in the fact that the strength of the multiwall sheet may be
remarXably improved during the processing by a conventional
corrugate machine by pressing the sheet at a temperature
higher than the softening point, preferably higher than the
melting point of the thermoplastic resin. This hot-press
treatment is effected by passing the sheet between the nips
of oppositely rotating pre-heating rollers or oppositely rotating
corrugating rollers.
This processing will be described in detail by making
reference to the accompanying drawings, wherein FIG. 1 is a
schematic view of the system for making the corrugated board
of the present invention, and FIG. 2 is a longitudinal cross- -
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sectional view of the corrugated board of this invention
Referring now to FIG. l, there is shown schematically
the corrugate machine system as it is used to produce the fluted
member and then laminate the same to a single sheet of outer
liner at one side thereof. The multiwall sheet material F to
be corrugated is fed from the unwind station (not shown) toward
a pre-heating roller l, passes around the roller and is heated
at a temperature of about 190C. The heated sheet is then
moistenèd at moistener 2 and fed toward oppositely rotating
corrugating rollers 3, 3. The corrugating rollers are centrally
heated at a temperature of about 160C. The sheet F passes
through the nip between the corrugating rollers 3, 3 under
a linear nip pressure from about 30 to about 40 kg/cm where
the sheet is fluted. Onto the crests of the fluted sheet on
one of rotably engaging corrugating rollers 3 are applied a
liquid pa~te such as starch paste by a doctor-roller 5 which
is po~itioned adjacent to said one roller 3.
~ scraper 4 rotatably mounted adjacent to the doctor
roller 5 removes any excess of the paste solution on the doctor
roller 5. A sheet of outer liner R is fed from its unwind
station toward a pair of pre-heating rollers and he~ated at a
predetermined temperature. The sheet then proceeds through the
nip between one of corrugating rollers 3 and a pressure roller 7
which is positioned adjacent to said roller 3 where two sheets
F and R are laminated together. The resulting corrugated paper
board comprises a fluted mem~er made from the multiwall
sheet F and an outer liner F bonded on only one side of the
fluted member. It will be apparent to those skilled in the
art, however, that another outer liner may be laminated on the
opposite side of the fluted member to produce the corrugated
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board as shown in FIG. 2 in cross-section by providing with an
additional laminating station similar to the first laminating
station in the down stream of the first station.
The finished corrugated board is taken up by a pair of
take-up conveyers 9 through a guide roller 8.
The resultant corrugated board is shown in FIG. 2 in
cross-section. In this embodiment the corrugated board includes
an inner fluted member 11 and two layers of outer liner 12,
12 bonded to the fluted member 11 at each crest lla of the member
11. The inner fluted member 11 is made of a unitary laminated
multiwall sheet material comprising an inner layer llb and - -
outer layers llc on both side of the inner layer llb. The
inner layer llb contains at least 15% by weight of a thermoplastic
resin and the balance of cellulosic pulp, preferably semichemical
or waste paper pulp. Typically the inner layer contains
about 30% by weigkt of polyethylene short fibers in a waste
paper pulp and has a sheet weight of 170 g/m . The outer
layer contains a waste paper pulp of the same type as used in
the inner layer and 0.4% by weight of a wet strength additive
_such as modified polyamide-epichloro-hydrine resin. Each
outer layers llc are formed onto the opposite sidesjof the
inner layer llb at a sheet weight of 40 g/m .
The outer liner 12 of the corrugated board may be a
water-proof, conventional one such as JIS K-320 and is
laminated to the fluted member 11 at each crest thereof with
a conventional adhesive such as starch.
It will be appreciated from the foregoing description
that the corrugated paper board of the present invention may
be manufactured in conventional manner using conventional
corrugate machines without need for any change on the processing
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or the system as the thermoplastic resin is present only in
the inner layer of the fluted member and will not diffuse onto
the surface of outer cellulosic layer during the processing of
the starting multiwall sheet by the corrugate machine. The
starting sheet may be produced in conventional manner using a
conventional paper machine and the layers of web may be incorporated
together into a unitary sheet simultaneously when the sheet
is processed in the corrugate machine for shaping the sheet
into the fluted member.
The following example serves to illustrate the present -
invention and should not be construed us limiting its scope.
EXAMPLE
Preparation of starting sheet material
Waste paper pulp was mixed with 30~ by weight, calcula*ed
for the mixture, of polyethylene short staple fiber (Mitsui
Zellabach Co., Ltd. SWP-E400, m.p. 131C, 0.9 mm long). The
mixture was used as the material of the inner layer. The
material of the outer layer contained 0.4% by weight of a
modified polyamide-epichlorohydrine resin in waste paper pulp.
These materials were formed into a multiwall web sheet
comprising a first outer layer, two inner layers and a second
outer layer successively using an ultraformer paper machine and
dried. Each of the outer layers had a sheet weight of 40 g/m2
A and each of two inner layers had a sheet we ght of 85 g/m2
respectively. The web-forming speed was 7.~ m/minute. The
sheet weight of the entire layers was 250 g/m2.
The resultant sheet was pressed at a temperature of 140C -~
at a pressure of 50 kg/cm for 5 seconds.
A control paper sheet was prepared at the same sheet
weight as above from waste paper pulp only. The characteristics
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of the above two sheets are shown in Table 1.
Table 1
Present invention Control 1
Sheet weight, g/m2 242 252
dry 9.4 6.0
Burst, Kg/cm2 wet 7.5 2.2
wet/dry 79.5% 36.6%
Ring crush, kg dry 58.1 42.6
wet 14.3 4.6
wet/dry 24.6% 10O7%
The data in Table 1 were measured according to JIS-
P8126 wherein "dry" is for the sample stored at 20c at 65~
RH for 24 hours and "wet" is for the sample immersed in water
at 20C for 1 hour.
Preparation of corruqated paPer board
The resulting starting sheet material produced by the
above process was fed to a corrugate machine (Mitsubishi
Lungston Co., Ltd., 2200 mm width) to shape into a fluted member.
The surface temperature of the preheating roller was 190C and
the linear nip pressure between the corrugating rollers was 40
kg/cm.
An outer liner of JIS K-320 was laminated onto both
sides of the fluted member with starch paste to obtain a
finished corrugated paper board.
The above procedure was repeated to produce control 2
except that a multiwall paper board made of waste paper pulp
having a sheet weight of 250 g/m2 was used as the material of
the fluted member. control 3 was produced by repeating the
above procedure except that the multiwall paper board made
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of waste paper pulp having a sheet weight of 250 g/m as
the material of the fluted member and an outer liner of JIS
K-220 were used and the resulting corrugated board was
impregnated with liquid paraffin at a take-up amount of 45%.
The characteristics of the resultant corrugated paper
board in comparison with controls are shown in Table 2.
Table_2
Present invention Control 2 Control 3
10Flat crush Strength; dry101.8 65.1 83.5
kg/5 in2 wet 22.5 5.7 16.9
End crush strength, dry 13.5 10.7 8.9
kg/5 cm wet 2.1 0.2 1.6
It is to be understood that various modifications and
substitutions may be made by those skilled in the art without
- ~ departing from the novel ~ and scope of the invention.
