MANUFACTURE OF PACKAGING CONTAINERS

Abstract: To manufacture reinforced corrugated cardboard for use as a packaging container, one face of a core liner [A] which has been corrugated in a corrugater [2] is adhered to a side liner [B]. There is then applied to the corrugated core liner [A] firstly an aqueous solution of corn starch, by means of a coating apparatus [4], and secondly a reinforcing agent [D], by means of an applicator [5]. Another side liner [C] is then adhered to the corrugated core liner [A]. Score lines are formed in the resulting corrugated cardboard, by means of a scorer apparatus [7], before the reinforcing agent [D] has hardened.

Description: MANUFACTURE OF PACKAGING CONTAINERS This invention relates to a process of manufacturin 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 resist properties. Reference will he 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 ranufacturing process according to the present i.nvei-;tion; Figure t 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 5 is a cross-sectional view of part of another conventional packagine container. 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 lzill he 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 resistina 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. 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 h of the flap, but also on the sides a of the container as shown in Figures 1 and 2. It has been confire that in the manufacture of reinforced corrugated cardboard packaging containers, if reinforced corrugated cardboard manufactured by conventional manufacturing process is used, the necessary reinforceLrnent 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. 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. 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. 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. 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. 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. 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. 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. 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 900C. 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 app aratus 6. 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 600C to gelatinize it. When this adhesive agent is used, the reinforcing agent should be preheated to about 60"C or higher, preferably to 700C to 850C, taking into consideration its heat loss by radiation at the time of application of the reinforcing agent to the core liner. The invention is illustrated by the following Tests. Test 1 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 70cC 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 350C 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: Width of each of the liners used for the test: 407mm Paper quality: Front liner: C220 g/mê Core liner: SCP 160 g/m2 Back liner: K180 g/m2 Region applied with the reinforcing agent: 241 mm width on the centre line of the core liner Composition of the 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% based on the dry matter content of the yellow dextrin): 3.1 wt% kmount of the reinforcing agent applied: 35 g/m2 (Calculat ed in terms of solid matter) EMI7.1 <tb> replied <SEP> amount <SEP> (g) <tb> lsNlole <SEP> area <SEP> of <SEP> one <SEP> face <tb> (m2) <SEP> of <SEP> a <SEP> developed <tb> condition <SEP> of <SEP> the <SEP> pack <tb> aging <SEP> container <tb> Composition of the adhesive agent: Water: 77.9 wt% Yellow dextrin: 21.0 wt% Sodium hydroxide: 0.6 wt% Borax: 0.5 wt% Amount of the adhesive agent applied: 6 g/m2 (Calculated in terms of solid matter) Heating temperature in the heating plate apparatus: 170C t 5 Length of the heating zone in the heating plate apparatus: 12 m Table 1 EMI8.1 Temperature <SEP> of <SEP> Spply <SEP> Speed <SEP> Water <SEP> Content <tb> the <SEP> reinforc <tb> ing <SEP> agent <tb> <SEP> 35 C <SEP> 110 <SEP> m/minute <SEP> 15.0 <SEP> % <tb> <SEP> 70 C <SEP> 125 <SEP> m/minute <SEP> 11.3 <SEP> % <tb> It can be seen from the above that, when the reinforcing agent is previously heated to 60 C or more, preferably to 70 - 850C, 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. 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. 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. 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 (200C to 800C) for a corrugated cardboard manufacturing process. In order to meet these requirements, there may be used an aqueous solution comprising 40 t 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 facili tation of the application by spraying, dextrin is preferable. A reinforcing agent including 40 wt % to 60 t % 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. 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. 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 t 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 Shown below in Table 2 are the results of pressure strength tests on a reinforced corrugated cardboard packaging container produced in accordance with this ivention as compared with conventional products: Dimensions of the corrugated cardboard containers used for 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 in a strip of 60 mm width, including score lines Composition of the reinforcing agent: yellow dextrin: 41.6 wt% Waster: 55.2 wt% Surface active agent: 0.1 wt% Water resisting agent (6.7 wt% based on the yellow dextrin): 3.1 wt% Amount of the reinforcing agent applied: 40 g/mê (Calculated in terns of solid matter) EMI12.1 <tb> (Applied <SEP> amount <SEP> (g) <SEP> <tb> <SEP> Whole <SEP> area <SEP> (mê) <SEP> of <tb> <SEP> one <SEP> face <SEP> of <SEP> a <SEP> develo <tb> <SEP> ped <SEP> condition <SEP> of <SEP> the <tb> <SEP> packaging <SEP> container <tb> Composition of the adhesive agent: Water: 75.25 wt% Corn starch: 23.73 wt% Sodium hydroxide: 0.56 wt% Borax: 0,6 wt% Amount of the adhesive agent applied: 6 g/m2 (Calculated in terms of solid matter) EMI12.2 <tb> Applied <SEP> amount <SEP> (g) <tb> <SEP> Whole <SEP> area <SEP> of <SEP> one <tb> <SEP> 2 <SEP> <tb> <SEP> face <SEP> (m2) <SEP> of <SEP> a <SEP> develo-| <SEP> <tb> <SEP> ped <SEP> condition <SEP> of <SEP> the <tb> <SEP> packaging <SEP> container <tb> Table 2 EMI12.3 w <SEP> <tb> <SEP> Test <SEP> Items <tb> <SEP> Pressure <SEP> Deformation <tb> <SEP> Kind <SEP> of <SEP> Sample <SEP> ¯¯¯¯¯¯¯¯ <SEP> -- <tb> <SEP> Product <SEP> hy <SEP> the <SEP> present <tb> <SEP> invention <SEP> | <SEP> 246 <SEP> kg <SEP> 7.8 <SEP> mum <tb> <SEP> Conventional <SEP> product <SEP> No. <SEP> 1 <SEP> 1 <SEP> 215 <SEP> kg <SEP> 9 <tb> <SEP> Conventional <SEP> product <SEP> No. <SEP> 2 <SEP> l <SEP> 207 <SEP> kTh{M.5¯mm <tb> 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 Dimensions of the corrugated cardboard containers subjected to tests: 308 mm x 464 mm x 103 mm Paper quality: Front liner: K220 g/mê Core liner: S160 g/mê Back liner: K220 g/m2 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. 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. Table 3 EMI13.1 <tb> <SEP> Tested <SEP> Sample <SEP> -¯#¸sure <SEP> <SEP> Deformation <tb> Product <SEP> by <SEP> the <SEP> Present <tb> Invention <SEP> (X) <SEP> 662 <SEP> kg <SEP> 14 <SEP> mm <tb> Conventional <SEP> Product <SEP> No. <SEP> 1(Y) <SEP> 526 <SEP> kg <SEP> 15 <SEP> mm <tb> Conventional <SEP> Product <SEP> No. <SEP> 2(Z) <SEP> 431 <SEP> kg <SEP> 16 <SEP> 16 <SEP> mm <tb> 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. 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.

Claims: CLAIMS 1. A process of manufacturing reinforced corru aated cardboard for use in making a packaging container, which comprises adhering one face of a corrugated core liner to a side liner with an aqueous 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 - z0 wt % of processed starch, 40 -60 wt % of water, 0.1 wt 9. 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. 11 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 gelatinizino 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.

Inventors: ONO, MASAYUKI
Applicants: KABUSHIKI KAISHA TOMOKU
Application year: 1982
Main classification: B31F1
IPC codes: B31B1, B31F1, B31B45