GB2112707A - Method of manufacturing reinforced corrugated cardboard intended for forming a packaging container - Google Patents

Abstract

A method of manufacturing reinforced corrugated cardboard for forming a packaging container, comprises the steps of joining together by adhesive (3) a corrugated core (A) and a first liner (B) for one face of the core, applying an adhesive (4) and then a reinforcing agent (5) to the other face of the corrugated core liner and joining a second outer liner (C) to said other face of the corrugated core to form reinforced corrugated cardboard. Before the reinforcing agent is allowed to harden score lines are formed by means (7) in the cardboard in regions where the reinforcing agent has been applied. The cardboard can then be folded to form a packaging container. The adhesive may be an aqueous solution mainly composed of corn starch and the reinforcing agent may be composed of processed starch, water, a surface active agent and a water resisting agent for the starch. <IMAGE>

Description

SPECIFICATION Method of manufacturing reinforced corrugated cardboard intended for forming a packaging container This invention relates to a method of manufacturing reinforced corrugated cardboard intended for forming a packaging container, such as a carton, box or the like.

Reference will first be made to Figures 5 and 6 of the accompanying drawings, in which: Figure 5 is a partly cut-away perspective view of a conventional packaging container, and Figure 6 is a diagrammatic cross-sectional view of a part of another conventional packaging container.

Corrugated cardboard packaging containers are widely used for various packaging applications because they are light in weight and are strong in mechanical strength. But when commodities to be contained therein are heavy in weight and the containers containing the commodities are piled upon one another, there is a danger that the pressure applied to the containers is beyond the limit of the pressure resisting strength possessed by the corrugated cardboard itself and consequently deformation or breakage of the packaging container takes place. For this reason, as can be seen in Japanese Utility Model published Application No.

52-84427, it has been proposed that the pressure resisting strength of a packaging container is improved by applying a reinforcing agent to the core of the corrugated cardboard forming the four sides of the body of the packaging container.

However, when using containers of which the side portions are reinforced and when such containers containing heavy commodities are piled upon one another, score line portions b thereof are crushed by pressure as shown in Figure 6, and additionally flaps cthereof cave in 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 re-use or is liable to be broken at the score line portions b. In view of this, a reinforced corrugated cardboard packaging container has been proposed as can be seen in Japanese Utility Model Application No. 53-12420, where reinforcement treatment is applied not only to the sides of the container but also to the score line portions of the flap.

It has been confirmed that in manufacturing of the reinforced corrugated cardboard packaging container, if the reinforced cardboard manufactured by a conventional reinforced corrugated cardboard manufacturing method is used, the object of the reinforcement cannot be fully attained. Namely, the conventional method of manufacturing reinforced corrugated cardboard is such that a reinforcing agent is previously applied to a sheet of cardboard which is then corrugated by pressing into a corrugated core liner and thereafter the front and back liners are adhered respectively to both side surfaces thereof to obtain reinforced corrugated cardboard.

Thereafter, score lines are formed in the cardboard thereby to form a packaging container.

When the score lines are thus formed, since the reinforcing agent of the core liner has been earlier hardened through heating and drying by a pre-heater and through heating during corrugation forming, 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 a scorer, so that when these portions have pressure applied in the stacked condition of the containers, they are bent as shown in Figure 6 and so the reason for reinforcing the score lines becomes pointless.

According to the present invention, there is provided a method of manufacturing reinforced corrugated cardboard intended for forming a packaging container, the method including the steps of joining together by adhesive a corrugated core liner and a first outer liner for one side of the core liner, applying an adhesive and then a reinforcing agent to the other side of said corrugated core liner, joining a second outer side liner to said other side of said corrugated core liner to form reinforced corrugated cardboard and, before completion of hardening of said reinforcing agent, forming score lines in regions where said reinforcing agent has been applied.

Four a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to Figures 1 to 4 of the accompanying drawings, in which: Figure 1 is a partly cut-away perspective view of a reinforced corrugated cardboard packaging container produced according to the present invention, Figure 2 is a diagrammatic sectional view taken along the line ll-ll in Figure 1, Figure 3 is a schematic diagram to explain the steps of the present method, and Figure 4 is a diagram showing the result of pressure resisting tests on different cardboard containers to ascertain the relationships between the pressure strength and deformation.

One example of a method of manufacturing reinforced corrugated cardboard intended for forming a packaging container according to the invention will first be explained with reference to Figure 3.

A sheet for a core liner A is heated and dried by a preheater 1 and is press-formed into a corrugated core liner by a core-forming corrugator 2 and at the same time is applied with an adhesive agent by a pasting apparatus 3 to the peaks of one side surface of the corrugated core liner A. Thereafter, the adhesive coated side of the corrugated core liner A is adhered to one side liner B which has been previously heated and dried by a pre-heater 8. The peaks of the other side surface of the corrugated core liner A are then coated with an adhesive agent by a pasting apparatus 4 and thereafter are further coated with a reinforcing agent D by a reinforcing agent applicator 5 partially to regions in which score lines are to be formed later for forming the packaging container.

The corrugated core liner A is then adhered to another side liner C, so that a sheet of reinforced corrugated cardboard D is formed, which is then heated by a heating plate apparatus 6 to increase the adhesive strength of the adhesive agent.

The reinforced corrugated cardboard E is then continuously fed to a slitter-scorer apparatus 7 which forms score lines F as shown in Figure 2 before completion of hardening of the reinforcing agent D previously applied to the reinforced corrugated cardboard E as above. The cardboard is also cut in any desired width and form at this stage.

Thus, since the reinforcing agent D is not yet hardened at the time of forming the score lines F in the cardboard E by the scorer apparatus 7, the score lines can be formed in the reinforced region of the reinforced corrugated cardboard without crushing and destroying the structure of that region.

In the foregoing example, the reinforcing agent D has been applied to the region in which score lines are later to be formed, so that there is produced a packaging container as shown in Figure 1. However, application ofthe reinforcing agent D need not be limited to that region but it may be applied also to such regions including regions which are to be formed later into the sides a of the body of the packaging container.

The adhesive agent used is an aqueous solution mainly composed of corn starch and is gelatinised and is applied to the corrugated core liner A in viscous condition at a temperature of 70"C to 90"C.

Also, the adhesive agent is used in the form of an aqueous solution of corn starch at the time of application thereof to the corrugated core liner and thereafter the same is gelatinised by the heating of the core liner and both the side liners by the heating plate apparatus 6.

With the application of the reinforcing agent, if the application temperature of the reinforcing agent is low, the heating time necessary for strengthening the mutual bonding of those laminated members A, B, C by the heating plate apparatus 6 has to be prolonged. Particularly when the aqueous solution mainly composed of corn starch is applied to the core liner and thereafter is gelatinised by heating for securing the mutual bonding of the laminated members A, B, C and when the reinforcing agent of a low temperature is applied to the aqueous solution, the heating time has to be extended for gelatinisation of the solution. This results in lowering in the production efficiency of the reinforced corrugated cardboard. Accordingly, this problem can be removed by preheating the reinforcing agent and then applying the preheated agent to the core liner.

Especially in the case where the aqueous solution mainly composed of corn starch is applied to the core liner and thereafter is heated to be gelatinised, it is preferable to use the reinforcing agent after preheating it to above the gelatinisation temperature of the aqueous solution. As an example of such an adhesive agent, a Stein-Hall formulation may be used which is of such a kind that an aqueous solution mainly composed of corn starch is heated to approximately 500C to 60"C to be gelatinised.When this adhesive agent is used, the reinforcing agent should be preheated to about 60"C or higher than that, preferably to between 70"C and 85"C, considering its heat radiation loss at the time of application of the reinforcing agentto the core liner.

In the method of manufacturing of the corrugated cardboard, the following tests as to how the change in pre-heating temperature of the reinforcing agent has influence on efficiency of the manufacturing of the corrugated cardboard were carried out as follows.

Two corrugated cardboard samples for comparison tests were manufactured in such respective conditioning that, in the first case, the reinforcing agent was preheated to 70"C and was applied to the core liner adhered to one side liner and the core liner adhered to the other side liner was supplied at a supply speed of 125 m/min to the heating plate apparatus and, in the second case, the reinforcing agent was preheated to 35"C and was applied to the core liner adhered to one side liner, and the core liner adhered to the other side liner was supplied at a supply speed of 110 m/min to the heating plate apparatus.

Other test conditions were as follows: Width of each liner to be tested: 407 mm Paper quality: Front liner C220g/m2 Core liner SCP160g/m2 Rear liner K180g/m2 Region applied with the reinforcing agent: Width of 241 mm at the central portion of the core lin er Composition of the Yellow dextrin 41.6 wt.% reinforcing agent: Water 55.2 wt.% Surface active agent 0.1 wt.% Water resisting agent (Corresponding to 6.7 wt.% per the dry matter of yellowdextrin) 3.1 wt.% Applied amountofthe reinforcing agent: 359/m2 (converted to dry matter) Amount of application = 9.

All area of one side surface m2 of a developed condition of the container Composition ofthe adhesive agent: Water 77.9% Yellow dextrin 21.0 wt.% Sodium hydroxide 0.6 wt.% Borax 0.5 wt.% Applied amount of the adhesive agent: 6g/m2 (converted to dry matter) Heating temperature of the heating plate apparatus: 170 C+5 Length of the heating region of the heating plate apparatus: 12 m Respective water contents of the two resultant corrugated cardboard samples were measured after one hour after manufacture thereof.The results are shown in the following table.

Temperature of reinforcing agent Supply speed Water content 35"C 110mimic 15.0% 70"C 125m/min 11.3%

It can be understood from the above results that, when the reinforcing agent is preheated to 600 or higher than that, preferably to between 70 and 85"C and is applied to the core liner, the supply speed to the heating plate apparatus can be increased and also the water content of the corrugated cardboard produced can be decreased and so the affixing of the core liner to the other side liner can be completed rapidly.

It will be appreciated that the object of the present invention cannot be attained by using any reinforcing agent having such a property that it is hardened under the temperature conditions of the heating plate apparatus 6. If, after the reinforcing agent is applied to the core liner A, the adhesive agent is applied to that core liner A, it makes the adhesive agent difficult to attach to the core liner A so that bonding between the core liner A and the other surface line C becomes bad. Therefore, it is preferable to apply the reinforcing agent Dafter application of the adhesive agent to the core liner A.

Accordingly, it is preferable to use any reinforcing agent having such a property as 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 the packaging container, it is preferable to use any reinforcing agent which is suitable for application by spraying.

As a result of study of reinforcing agents it has been confirmed 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 for the reinforcing agent used in the present method.

Such a reinforcing agent can comprise 60% to 40% by weight of process starch, 40% to 60% by weight of water, 0.1% by weight or less of surface active agent, and a water resisting agent for starch which is 6% by weight or more in proportion to a solid content of the process starch.

For this reinforcing agent, it is important that it is in as high a concentration as possible and is as low in water content as possible so as not to deform the corrugation of the core liner when the reinforcing agent is applied to it. It is also important that it is as low in coefficient of viscosity as to facilitate application thereof by spraying and its coefficient is preferably 100 cps or less (BH typeviscometer at 20 rpm) under the temperature condition (20"C to 80"C) for the corrugated cardboard manufacturing process.

In order to meet these requirements, there is used an aqueous solution thereof comprising 40% to 60% by weight of processed starch and 60% to 40% by weight of water. As for the processed starch, dextrin, oxidised starch orthe like are used, for example, but in view of the strength of a coating film formed on the core liner by application of the reinforcing agent, and of facilitation of the application by spraying, dextrin is preferable.

The reinforcing agent including 40% to 60% by weight of the processed starch meets the above described requirements, but because of a comparatively high concentration, it is somewhat infavourable in penetrating into the core liner, so that in order to shorten the time for penetration into the core liner a surface active agent is added. The surface active agent can be, for example, a dialkyl sulphosuccinate ester or an alkylnaphthalene sulphonate ester but especially a dialkyl sulphosuccinate ester is preferably used because it has a defoaming property that is effective in preventing an uneven coating on the core liner caused by foaming of the reinforcing agent when the reinforced agent is applied by spraying.Even when the added amount of the surface active agent exceeds 0.1% by weight, appreciably improved mechanical strength cannot be observed and rather foaming becomes easier at the time of the spraying application, so that a uniform coating on the core liner cannot be produced.

Thus, in order to accelerate penetration of the reinforcing agent into the core liner, the surface active agent is added, but at the same time a hygroscopic property of the core liner coated with the reinforcing agent is increased and, if it is left as it is, the water content of the corrugated cardboard is increased to 12% to 13% weight, so that its mechanical strength is lowered. Therefore, in order to increase its resistance to moisture and maintain its mechanical strength, the water resisting agent for starch is added in proportion to the amount of the processed starch.

As for the water resisting agent for starch, for instance, trimethoxymethyl melamine is used. The additional amount of water resisting agent for starch is 6% to 10% by weight on the basis of a solid component, that is, the dry matter of the processed starch, and by an additional amount of 6% by weight 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, if the additional amount thereof exceeds 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 proceed and the water resisting agent for starch is liberated.

Shown below are the results of pressure strength tests on a reinforced corrugated cardboard packaging container produced in accordance with the method according to the present invention as compared with conventional products.

Test 2 Dimensions of the corrugated cardboard containers subjected to the tests: 365 mm X 255 mm X 236 mm Paper quality: Front liner: C210 g/m2 Core liner: S215 g/m2 Back liner: C180 g/m2 Region applied with the reinforcing agent: Applied region in a strip form of 60 mm width including scored lines Composition of reinforcing agent: Yellow dextrin 41.6 wt.% Water 55.2 wt.% Surface active agent 0.1 wt.% Water resisting agent (Corresponding to 6.7 wt.% per the dry matter of yellow dextrin): 3.1 wt.% Applied amount of the reinforcing agent: 40 g/m2 (Converted to dry matter) Amount of application g.

All area of one side surface m2 of a developed condition of the container Composition of the adhesive agent: Water 75.25 wt.% Corn starch 23.73 wt.% Sodium hydroxide 0.56wt.% Borax OA6 wt.% Applied amount of the adhesive agent: 6 g/m2 (Converted to dry matter)

Test Items Pressure Deformation Kind of Sample Product by the present invention 246 kg 7.8 mm Conventional product No. 1 215 kg 9.0 mm Conventional product No. 2 207 kg 9.5 mm The conventional product No. 1 was one produced by applying the reinforcing agent to the core liner before feeding the core liner to the corrugator, and the conventional product No. 2 was one made of non-reinforced corrugated cardboard.

Test 3 Dimensions of the corrugated cardboard containers subjected to the tests: 308 mm X 464 mm X 103 mm Paper quality: Front liner: K220 Core liner: S160 Back liner: K220 Region coated with the reinforcing agent: Coating on all areas of the four sides of the container and on a width of 30 mm including the second lines of the flaps thereof.

The composition of the reinforcing agent and the applied amount thereof and the composition of the adhesive agent and the applied amount thereof were the same as in Test 2.

Test Items Pressure Deformation Tested Say Sample Product by the present invention X 662 kg 14 mm Conventional Product No. 1 Y 526 kg 15 mm Conventional Product No. 2 Z 431 kg 16 mm The conventional products Nos. 1 and 2 were the same as in Test 2.

The relationships between the loads applied to the corrugated containers and deformation amounts thereof in Test 3 are shown in Figure 4.

As will be clear from the foregoing description, with the present process, one side liner and the corrugated core liner are adhered together by the corrugator and then that corrugated liner has an adhesive agent applied to it and then has a reinforc ing agent applied to it. Thereafter, the opposite side liner is adhered to form reinforced corrugated cardboard and, before completion of hardening of the reinforcing agent, score lines are formed in the reinforced region of the reinforced corrugated cardboard, so that a reinforced corrugated cardboard packaging container which is improved in resistance to pressure can be provided, without destroying the structure ofthescore line portions.

Additionally, performance of the present method can be carried out by incorporating a reinforcing agent coating apparatus in a conventional existing corrugator.

Claims (9)

1. A method of manufacturing reinforced corrugated cardboard intended for forming a packaging container, the method including the steps of joining together by adhesive a corrugated core liner and a first outer liner for one side of the core liner, applying an adhesive and then a reinforcing agent to the other side of said corrugated core liner, joining a second outer side liner to said other side of said corrugated core liner to form reinforced corrugated cardboard and, before completion of hardening of said reinforcing agent, forming score lines in regions where said reinforcing agent has been applied.

2. A method as claimed in claim 1, wherein said first outer liner is adhered to said corrugated core liner by a corrugator which has formed said corrugated core liner.

3. A method as claimed in claim 1 or 2, wherein said adhesive is an aqueous solution mainly composed of corn starch.

4. A method as claimed in any one of the preceding claims, wherein, after the step of joining said second outer side liner to said other side of said corrugated core liner, the reinforced corrugated cardboard is heated to increase the adhesive strength of said adhesive agent.

5. A method as claimed in any one of the preceding claims, wherein said reinforcing agent is composed of 60 to 40% by weight of processed starch, 40 to 60% by weight of water, 0.1% by weight or less of surface active agent and 0.6% by weight or more of water resisting agent for starch, based on the solid content of said processed starch.

6. A method as claimed in any one of the preceding claims, wherein said reinforcing agent is preheated above its gelatinising temperature before it is applied to said other side of said corrugated core liner.

7. A method of manufacturing reinforced corrugated cardboard intended for forming a packaging container, substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

8. Reinforced corrugated cardboard intended for forming a packaging container, the cardboard having been made by the method as claimed in any one of the preceding claims.

9. A packaging container made of reinforced corrugated cardboard as claimed in claim 8.