[0001] This invention relates to a process of manufactur- in reinforced corrugated cardboard
for use in making packaging containers such as carton boxes, and more particularly
relates to a process of manufacturing packaging containers made of reinforced corrugated
cardboard and having improved pressure resisting properties.
[0002] Reference will be made in the following description to the accompanying drawings
in which:
Figure 1 is a partially cut-away perspective view of a preferred reinforced corrugated
cardboard packaging container produced according to the present invention;
Figure 2 is a section view taken along line II-II of Figure 1;
Figure 3 is a schematic diagram illustrating a preferred manufacturing process according
to the present invention;
Figure 4 is a diagram showing the results of pressure resisting tests in regard to
the relationships between the pressure strength and the deformation of cardboard containers;
Figure 5 is a perspective view of a conventional packaging container; and
Figure 6 is a cross-sectional view of part of another conventional packaging container.
[0003] Corrugated cardboard packaging containers are widely used for various packaging applications
because they are light in weight and strong in mechanical strength. However, when
the commodities to be contained therein are heavy and the corrugated cardboard packaging
containers containing the commodities are piled one upon another, there is the danger
that the pressure applied to the containers will be beyond the limit of the pressure
resisting strength of the corrugated cardboard itself, whereby deformation or breakage
of the packaging containers will take place. For this reason, as disclosed in Japanese
Utility Model Laid-Open Application 52-84427, it has been proposed that the pressure
resisting strength of a packaging container be improved by applying a reinforcing
agent to the core of the corrugated cardboard forming the four side portions of the
body of the packaging container.
[0004] However, in use of such containers, of which side portions have been reinforced,
when such containers containing heavy commodities are piled one upon another, the
score line portions b thereof are crushed by pressure, as shown in Figure 6, and additionally
the flaps c thereof crumple inside the side portions a, as shown in Figure 5, so that
the interior dimensions of the container are decreased to such an extent that the
container becomes unsuitable for reuse or is liable to break at the score line portions
b. In view of the above, it has been proposed, in Japanese Utility Model Application
53-12420, that the reinforcement treatment be carried out not only on the score line
portions b of the flap, but also on the sides a of the container as shown in Figures
1 and 2.
[0005] It has been confirmed that in the manufacture of reinforced corrugated cardboard
packaging containers, if reinforced corrugated cardboard manufactured by conventional
manufacturing process is used, the necessary reinforcement cannot be fully attained.
Thus, in a conventional process of manufacturing reinforced corrugated cardboard,
a reinforcing agent is applied to a sheet of cardboard, the reinforced cardboard is
then formed by pressing into a corrugated core liner, thereafter front and back liners
are adhered to both faces of the liner to obtain reinforced corrugated cardboard,
thereafter the reinforced corrugated cardboard is scored so that score lines are formed
in the cardboard, and a packaging container is then formed.
[0006] When the score lines are thus formed, since the reinforcing agent of the core liner
has been earlier hardened by heating and drying by means of a preheater and by heating
during the corrugation, the portions of the corrugated cardboard reinforced with the
reinforcing agent are crushed and its structure is destroyed on forming the score
lines therein by the scorer, so that when these portions are subjected to pressure
when the containers are piled one upon another, these portions are bent as shown in
Figure 6, and the purpose of reinforcing of the score lines is meaningless.
[0007] The present invention provides a process of manufacturing of a reinforced corrugated
cardboard type packaging container in which the score line portions are reinforced
without fail and its resistance to pressure is improved to overcome the shortcomings
in the prior art. According to the present invention, a corrugated core liner is adhered
at one face to one side liner with an aqueous solution comprising or mainly composed
of corn starch, and then the other face of the corrugated core liner is applied with
an aqueous solution comprising or mainly composed of corn starch and thereafter is
further applied with a reinforcing agent and thereafter the same is adhered to another
side liner, and then the two side liners and the corrugated core liner are heated
to form reinforced corrugated cardboard, and before completion of hardening of the
reinforcing agent score lines for a packaging container are formed in the reinforced
region of the reinforced corrugated cardboard.
[0008] One example of a process of manufacturing reinforced corrugated cardboard according
to this invention will now be explained with reference to Figure 3. As shown in this
Figure, a sheet A for a core liner is heated and dried by a preheater 1 and is press-formed
into a corrugated core liner by corrugator 2. At the same time, there is applied thereto
an adhesive agent comprising an aqueous solution mainly composed of corn starch, by
a coating apparatus 3, this agent being applied to the crests of one face of the corrugated
core liner A. Thereafter the corrugated core liner A is adhered to one side liner
B, which is previously heated and dried by a preheater 8. Thereafter, to the corrugated
core liner A, there is applied an aqueous solution mainly composed of corn starch,
by a coating apparatus 4, this solution being applied to the crests of the other face
of the corrugated liner A. Thereafter, a reinforcing agent D is applied by an applicator
5, partially in the region in which score lines for forming a packaging container
are to be formed later.
[0009] The corrugated core liner A is then adhered to another side liner C, so that a sheet
of reinforced corrugated cardboard E is formed, this corrugated cardboard being heated
by a heating plate apparatus 6 to increase the stickness of the bonding agent.
[0010] Thereafter, the reinforced corrugated cardboard E is continuously fed to a slitter-scorer
apparatus 7 and is formed with score lines F, before completion of the hardening of
the reinforcing agent D applied to the reinforced corrugated cardboard E as above,
and also is cut to any desired width and form.
[0011] Thus, since the reinforcing agent D has not hardened at the time of forming the score
lines b in the cardboard E by the scorer apparatus 7, the score lines are formed in
the reinforced region of the reinforced corrugated cardboard without crushing and
destroying the structure of that region.
[0012] The above description with reference to Figure 3 is limited to the case in which
the reinforcing agent D is applied to the core liner only in the region thereof in
which score lines are to be formed. However, the reinforcing agent D may be applied
not only to the foregoing region thereof but also to additional regions thereof corresponding
to the whole of the four side walls of the packaging container to be formed.
[0013] The adhesive agent used in this invnetion is an aqueous solution mainly composed
of corn starch. It may be gelatinized, and is usually applied to the corrugated core
liner A in a viscous condition at a temperature of 70°C to 90°C.
[0014] Also, according to this invention, the adhesive agent may be used in the form of
an aqueous solution of corn starch at the time of application thereof to the corrugated
core liner, and thereafter may be gelatinized by heating the core liner and both the
side liners, such as by use of the heating plate apparatus 6.
[0015] As described above, in manufacturing a packaging container made of the reinforced
corrugated cardboard, according to this invention, the step of applying the reinforcing
agent to the core liner is an additoinal step as compared to the steps of a conventional
process of manufacturing corrugated cardboard. When applying the reinforcing agent,
if the application temperature of the reinforcing agent is low, the heating time necessary
for strengthening the mutual bonding of the laminate members A, B, C by the heating
plate apparatus 6 is prolonged. Particularly, when the aqueous solution mainly composed
of corn starch is applied to the core liner and thereafter is gelatinized by heating
for effecting the mutually bonding of the laminate members A, B, C, and when a reinforcing
agent of a low temperature is applied onto the aqueous solution, the heating time
has to be extended for gelatinization of the said solution. This results in a lowering
in the production efficiency of reinforced corrugated cardboard. This problem can
be overcome by preheating the reinforcing agent and then applying this preheated reinforcing
agent to the core .liner. In particular, when the aqueous solution mainly composed
of corn starch is applied to the core liner and thereafter is heated to gelatinize
it, it is preferable to use a reinforcing agent which has been preheated above the
gelatinization temperature of the aqueous solution. For instance, as such adhesive
agents, there may be used a Stein-Hall formulation, which is of such a kind that an
aqueous solution mainly composed of corn starch is heated to approximately 50°C to
60°C to gelatinize it. When this adhesive agent is used, the reinforcing agent should
be preheated to about 60°C or higher, preferably to 70°C to 85°C, taking into consideration
its heat loss by radiation at the time of application of the reinforcing agent to
the core liner.
[0016] The invention is illustrated by the following Tests.
Test 1
[0017] In the course of manufacturing reinforced corrugated cardboard, to the core liner,
while being supplied in one direction as shown in Figure 3, there was applied the
foregoing aqueous solution of the adhesive agent, and then the foregoing reinforcing
agent in succession and along the longitudinal direction of the core liner. One sample
of reinforced corrugated cardboard was manufactured by applying a reinforcing agent
previously heated to 70
cC to a core liner supplied at a speed of 110 m/minute, and another sample of reinforced
corrugated cardboard was manufactured by applying a reinforcing agent previously heated
to 35°C to a core liner supplied at a speed of 125 m/minute. After the lapse of one
hour after manufacturing the two samples, the water content of each of the two samples
was measured, and the results are shown in the following Table 1. Other particular
items are described below:

[0018] It can be seen from the above that, when the reinforcing agent is previously heated
to 60°C or more, preferably to 70 - 85°C, and is applied, the supply speed of the
core liner to the heating plate apparatus can be increased and also the water content
in the reinforced corrugated cardboard manufactured can be decreased so that the time
for complete bonding of the core liner to the side liner can be reduced, resulting
in an improvement in the manufacturing efficiency. ,
[0019] It is self-evident that the reinforcing agent should not harden at the temperature
of the heated plate of the apparatus 6. If, after the reinforcing agent is applied
to the core liner A, it is difficult for the adhesive agent to attach to the core
liner A, so that the strength of the bond between the core liner A and the surface
liner C is reduced. Therefore, it is preferable to apply the reinforcing agent D after
the application of the adhesive agent to the core liner A. Accordingly, it is preferable
to use a reinforcing agent able to sufficiently penetrate into the core liner A to
which the adhesive agent has already been applied. Furthermore, for the purpose of
partially reinforcing only the score line portions at the time of forming a packaging
container, it is preferable to use a reinforcing agent which is suitable for application
by spraying.
[0020] As a result of the study of reinforming agents, it has been found that a reinforcing
agent comprising chemically treated or processed starch, water, a surface active agent,
and a water resisting agent for starch is especially suitable as the reinforcing agent
used in this invention. Preferably, such a reinforcing agent comprises 60 wt % to
40 wt % of the processed starch, 40 wt % to 60 wt % of water, 0.1 wt % or less of
the surface active agent, and a water resisting agent for starch in an amount which
is 6 wt % or more relative to the solid content of the processed starch.
[0021] It is desirable that the reinforcing agent have as high concentration as possible
and as low a water content as possible so as not to deform the corrugations of the
core liner when the reinforcing agent is applied to the core liner, and that it have
so low a coefficient of viscosity as to facilitate application thereof by spraying.
This coefficient is preferably 100 cps or less (BH type viscosimeter at 20 rpm) at
the temperature (20°C to 80°C) for a corrugated cardboard manufacturing process.
[0022] In order to meet these requirements, there may be used an aqueous solution comprising
40 wt% to 60 wt% of processed starch and 60 wt % to 40 wt % of water. As for the processed
starch, dextrin, oxidized starch or the like may be used, but in view of the strength
of the coating film formed on the core liner by application of the reinforcing agent,
and of facilitation of the application by spraying, dextrin is preferable.
[0023] A reinforcing agent including 40 wt % to 60 wt % of the processed starch meets the
above described requirements, but because of its comparatively high concentration,
it is somewhat unfavourable in respect of the penetration into the core liner. In
order to shorten the time for penetration into the core liner a surface active agent
is added. As for the surface active agent, a dialkyl sulphosuccinate ester, an alkylnaphthalene
sulphonate ester, or the like, is preferably used. In particular, a dialkyl sulphosuccinate
ester is preferably used because it has defoaming properties effective in preventing
uneven coating on the core liner caused by foaming of the reinforcing agent when the
reinforcing agent is applied by spraying. When the amount of the surface active agent
exceeds 0.1 wt %, appreciably improved mechanical strength cannot be observed; rather
foaming becomes easier at the time of the spraying, so that a uniform coating on the
core liner cannot be produced.
[0024] Thus, in order to accelerate penetration of the reinforcing agent into the core liner,
a surface active agent is added, but at the same time the hygroscopic properties of
the core liner coated with the reinforcing agent are increased. Thus, the water content
of the corrugated cardboard is increased to, for example, 12 wt% to 13 wt%, so that
its mechanical strength is reduced. Therefore, in order to increase its resistance
to moisture and maintain its mechanical strength, a water resisting agent for starch
is added to the reinforcing agent in an amount based on the amount of the processed
starch.
[0025] As for the water resisting agent for starch, trimethoxy methyl melamine or the like
are preferably used. A preferred amount of the water resisting agent for starch is
6 wt % to 10 wt% based on a solid component, i.e. the dry matter content of the processed
starch. By the addition of 6 wt % or more of the water resisting agent for starch,
non-reinforced corrugated cardboard which has a 70% residual strength can be increased
in its residual strength. However, by the addition of an amount thereof exceeding
10%, no appreciable increase in the residual strength is obtained, but rather the
chemical reaction of the water resisting agent with the processed starch does not
take place and the water resisting agent for starch is liberated. Test 2
[0027] Conventional product No. 1 is one produced by applying the reinforcing agent to the
core liner before feeding the core liner to the corrugator, and conventional product
No. 2 is one made of non-reinforced corrugated cardboard.
Test 3
[0028] Dimensions of the corrugated cardboard containers subjected to tests:
308 mm x 464 nm x 103 mm
[0029] Paper quality:

[0030] Region applied with the reinforcing agent:
Applied onto the whole area of the four sides of the container and onto a width of
30 mm including the score lines of the flaps thereof.
[0031] The composition of the reinforcing agent and the amount thereof applied were the
same as in Test 2. The composition of the adhesive agent and the amount thereof applied
were the same as in Test 2. The results are given in Table 3.

[0032] Conventional products No. 1 and No. 2 are the same as in Test 2. The relationships
between the loads applied to the corrugated containers and the amounts of deformation
thereof in Test 3 are given in Figure 4.
[0033] As is clear from the above, according to this invention, a corrugated core liner
and both side liners are adhered together by an adhesive agent comprising an aqueous
solution composed mainly of corn starch, so that even in the case where the reinforcing
agent is applied to the core liner after the adhesive agent has been applied to the
core liner, the reinforcing agent can penetrate sufficiently into the core liner and
does not hamper the adhering of the core liner and the side liner, and consequently
reinforced corrugated cardboard excellent in presusre resting strenght can be produced.
Further, according to this invention, the score lines for the packaging container-are
scored before the reinforcing agent hardens, so that the structure of the score line
region thereof is not destroyed and reinforced corrugated cardboard packaging containers
having improved pressure resisting properties can be made. The process of this invention
can be carried out easily and simply by incorporating the reinforcing in any conventional
existing corrugator.
1. A process of manufacturing reinforced corrugated cardboard for use in making a
packaging container, which comprises adhering one face of a corrugated core liner
to a side liner with an aoueous solution comprising corn starch; applying to the other
face of the corrugated core liner (a) an aqueous solution comprising corn starch and
thereafter (b) a reinforcing agent; adhering another side liner to said other face
of the core liner; heating the two side liners and the corrugated core liner to form
reinforced corrugated cardboard; and, before completion of the hardening of the reinforcing
agent, forming score lines for a packaging container in the reinforced region of the
reinforced corrugated cardboard.
2. A process as claimed in claim 1, wherein the reinforcing agent comprises 60 - 40
wt % of processed starch, 40 -60 wt % of water, 0.1 wt % or less of a surface active
agent, and a water resisting agent for starch in an amount of 0.6 wt % or more based
on the solid content of said processed starch.
3. A process claimed in claim 1 or 2, wherein, after application to the corrugated
core liner of the aqueous solution comprising corn starch and the reinforcing agent,
the reinforcing agent is preheated above the gelatinizing temperature thereof.
4. Reinforced corrugated cardboard manufactured by a process as claimed in claim 1,
2 or 3.
5. A packaging container made of reinforced corrugated cardboard as claimed in claim
4.