WO1996027494A1

WO1996027494A1 - Production of double-ply corrugated paperboard

Info

Publication number: WO1996027494A1
Application number: PCT/KR1995/000097
Authority: WO
Inventors: Do Wook Kim; Ki Jeong Kim
Original assignee: Daeyoung Packing Co., Ltd.
Priority date: 1995-03-06
Filing date: 1995-07-31
Publication date: 1996-09-12
Also published as: KR0181564B1; AU3122095A; KR960033731A

Abstract

A method of and an apparatus for producing a high strength double-ply corrugated paperboard including multiple-ply corrugated mediums (11a, 21a) laminated together between liners (12a, 22a) such that they are completely in contact with each other or partially in contact with each other at intervals to form a space therebetween for every corrugation, thereby capable of exhibiting a high compressive strength while having a small thickness to minimize the packaging size, and effectively absorbing outside shock applied to the package to keep the packaged goods more safe. The method includes the steps of forming a single-faced downward-corrugated paperboard (13) and a single-face upward-corrugated paperboard (23), preheating the paperboards, sensing positions of corrugations of the preheated paperboards, coating an adhesive on the corrugated mediums of the position-determined paperboards, guiding the adhesive-applied paperboards to a heating plate; and pressing the paperboards against each other at a desired pressure during the paperboards pass over the heating plate.

Description

Production of double-ply corrugated paperboard

Technical Field

The present invention relates in general to paperboards used for packaging goods and, more particularly, to a method of and an apparatus for producing a high strength double-ply corrugated paperboard including upper and lower liners and multiple-ply corrugated mediums disposed between the liners, thereby capable of exhibiting a high compressive strength while having a small thickness to minimize the packaging size, and effectively absorbing outside shock applied to the package to keep the packaged goods more safe.

Background Art

As well known to those skilled in the art, various fragile goods needing to be handled with care, for example expensive bottled cosmetics, electronic and electric products such as television sets, are conventionally packaged using rigid boxes with shock-absorbing materials. The above shock-absorbing materials are used for absorbing the outside shock applied to the packaged goods and thereby protect the goods from the shock.

In the prior art, both expanded polystyrene formed according to the contours of the goods to be packaged and cardboard mounts folded into given shapes or partially cut out sufficient enough to hold the goods in the package boxes are generally used as shock-absorbing materials. When the goods to be packaged are heavy goods such as refrigerators, the packaging materials for such goods need to be provided with both excellent shock absorption and rigidity sufficient enough to absorb the outside shock and to bear the weight of the heavy goods. In order to achieve the above object, the package boxes for such heavy goods are preferably bottomed with wooden pallets.

The expanded polystyrene used as a shock-absorbing material has an advantage in that it is easily formed and suitable for mass production. However, the expanded polystyrene is breaks easily and induces static electricity. Therefore, the expanded polystyrene not only causes environmental contamination due to its broken pieces, but also is scarcely used for packaging precision goods due to the static electricity. Otherwise stated, use of the expanded polystyrene as the shock-absorbing material is limited as it remarkably reduces the expected life of the packaged goods.

The cardboard mounts folded into given shapes or partially cut out sufficient enough to hold the goods in the package boxes are problematic in that they are not suitable for mass production. Furthermore, the above cardboard mounts have inferior durability and generate paper dust while packaging the goods. Due to the inferior durability as well as the paper dust, the above cardboard mounts may exert a bad influence upon the expected life of the packaged goods. In order to rectify the above problems, package cases formed using pulp molds have been recently proposed and used. However, the above package cases need to be formed using individual molds even when the cases are produced on a small scale. As the molds should be produced by highly skilled workers one by one, the package cases are problematic in that it is very difficult to produce the cases. Another problem of the above package cases is resided in that they are expensive.

As people are recently becoming environmentally conscious, used packaging materials need appropriate treating to prevent them from causing environmental contamination. However, it has been noted that treatment of various plastic packaging materials such as expanded polystyrene is very difficult as the above plastic packaging materials can not be recycled. The above plastic packaging materials will cause environmental contamination and exert a bad influence upon the ecosystem when they are simply discarded. Therefore, environmentally conscious people tend to avoid using such plastic packaging materials. Thus, demand for the above plastic packaging materials is reduced. Disclosure of the Invention

It is, therefore, an object of the present invention to provide a high strength corrugated paperboard in which the above problems can be overcome and which has an improved structure suitable for not only reliably protecting the packaged goods, but also improving durability of the packaging paper sheet.

It is another object of the present invention to provide a double-ply corrugated paperboard having a value- added structure including multiple-ply corrugated mediums laminated together between the liners such that they are completely in contact with each other or partially in contact with each other at intervals to form a space therebetween for every corrugation, thereby capable of exhibiting a high compressive strength while having a small thickness to minimize the packaging size.

It is a further object of the present invention to provide a cheap and regenerable corrugated paperboard which is not made of materials causing environmental contamination, but made of regenerable paper, and which can be produced through an automatic process.

In order to accomplish the above objects, the present invention provides a method for producing a double-ply corrugated paperboard comprising the steps of: bonding a continuous corrugated medium to one surface of a continuous liner having opposite surfaces such that corrugations of the corrugated medium face downward, thereby forming a single-faced downward-corrugated paperboard; bonding another continuous corrugated medium to one surface of another continuous liner having opposite surfaces such that corrugations of the another corrugated medium face downward, thereby forming a single-faced upward-corrugated paperboard; preheating the paperboards; sensing positions of corrugations on the preheated paperboards, namely, numbers of the corrugations in a pitch control-synchronized manner such that facing corrugations of the paperboards can keep their accurate relative positions at which they can be completely in contact with each other or partially in contact with each other to define a space therebetween for every corrugation; coating an adhesive on the corrugated mediums of the position-determined paperboards; guiding the adhesive-applied paperboards to a heating plate; and pressing the paperboards against each other at a desired pressure during the paperboards pass over the heating plate.

In accordance with an embodiment of the present invention, the step of sensing the numbers of corrugations comprises the step of controlling feeding speeds of the paperboards such that two corrugations of the upward- corrugated paperboard are fed per one corrugation of the downward-corrugated paperboard.

In accordance with another embodiment of the present invention, the step of sensing the numbers of corrugations comprises the step of controlling feeding speeds of the paperboards, which have the same corrugation pitch, but different corrugation heights, such that the corrugations of the paperboards are sensed in a ratio of 1 : 1. Alternatively, the step of sensing the numbers of corrugations comprises the step of controlling feeding speeds of the paperboards, which have the same corrugation pitch and height, but different curvatures, such that the corrugations of the paperboards are sensed in a ratio of 1 : 1.

The present invention also provides an apparatus for producing a double-ply corrugated paperboard comprising: single-faced downward-corrugated paperboard forming means adapted to receive a first medium and a first liner respectively from a first medium supply roll and a first liner supply roll, to corrugate the first medium and to bond the first, corrugated medium to the first liner such that corrugations of the corrugated first medium face downward, thereby forming a single-faced downward- corrugated paperboard; single-faced downward-corrugated paperboard forming means adapted to receive a second medium and a second liner respectively from a second medium supply roll and a second liner supply roll, to corrugate the second medium and to bond the second, corrugated medium to the second liner such that corrugations of the corrugated second medium face upward, thereby forming a single-faced upward-corrugated paperboard; a tension roll and pre-heating means both arranged downstream each of the downward- and upward- corrugated paperboard forming means and adapted to apply a constant tension to the corresponding corrugated paperboard being continuously fed under a condition that its corrugations face to those of the other corrugated paperboard; adhesive coating means adapted to continuously coat an adhesive on facing surfaces of the corrugated mediums of the paperboards; corrugation number sensing means disposed between paths of the paperboards and adapted to count numbers of the facing corrugations of the paperboards; and a heating plate and pressing belt means both adapted to press the adhesive-applied paperboards at a desired pressure while heating them, thereby bonding them together.

Brief Description of Drawings

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view illustrating an apparatus for producing a double-ply corrugated paperboard in accordance with the present invention; FIG. 2 is a schematic view illustrating a single- faced corrugated paperboard forming station included in the apparatus of the present invention; and

FIGS. 3A to 3C are sectional views respectively illustrating paperboards produced in accordance with a paperboard producing method of the present invention wherein

FIG. 3A shows a double-ply corrugated paperboard structure including a pair of corrugated mediums with different corrugation pitches, FIG. 3B shows a double-ply corrugated paperboard structure including a pair of corrugated mediums with the same corrugation pitch, but different corrugation heights, and

FIG. 3C shows a double-ply corrugated paperboard structure including a pair of corrugated mediums with the same corrugation pitch and height, but different curvatures.

Best Mode for Carrying out the Invention

FIGS. 1 and 2 illustrate an apparatus for producing a continuous paperboard in accordance with the present invention, respectively.

As shown in FIGS. 1, the apparatus for producing a continuous double-ply corrugated paperboard includes a first single-faced corrugated paperboard forming station 10 and a second single-faced corrugated paperboard forming station 20. The first single-faced corrugated paperboard forming station 10 receives a medium 11a and a liner 12a from a medium supply roll 11 and a liner supply roll 12, respectively, corrugates the medium 11a, and then bonds the corrugated medium 11a to one surface of the liner 12a, thereby forming a single-faced corrugated paperboard 13. Similarly, the second single-faced corrugated paperboard forming station 20 receives a medium 21a and a liner 22a from a medium supply roll 21 and a liner supply roll 22, respectively, corrugates the medium 21a, and then bonds the corrugated medium 21a to one surface of the liner 22a, thereby forming a single-faced corrugated paperboard 23. In the illustrated case, the corrugated medium 11a is bonded to the lower surface of the liner 12a whereas the corrugated medium 21a is bonded to the upper surface of the liner 22a.

Each of the first and second single-faced corrugated paperboard forming stations 10 and 20 includes a pair of corrugator rollers 14 and 15 adapted to guide the corresponding medium 11a or 21a therebetween and to corrugate the medium to have a desired wave, an adhesive coating roller 16 arranged on one side of the upper corrugator roller 15 and adapted to uniformly coat an adhesive on one surface of the medium, and a drum type heater 18 disposed over the upper corrugator roller 15 and adapted to bring the liner 12a or 22a fed from its liner supply roll into contact with the corrugated medium 11a or 21a passing over the corrugator roller 15.

As shown in FIG. 2, the adhesive coating roller 16, which applies an adhesive to one surface of the corrugated medium 11a or 21a on one side of the upper corrugator roller 15, is preferred to be dipped in an adhesive storage tank 17 filled with the adhesive. As the adhesive coating roller 16 rotates, the adhesive thereon is rapidly transferred to the corrugated medium 11a or 21a.

Alternatively, another adhesive coating means may be used. For example, a nozzle-attached plate construction may be used which includes a plurality of nozzles aligned in a line with one another. In this case, selected one of the nozzles are opened depending on the shape of the corrugated medium so that the width and space of adhesive coatings on the corrugated medium can be optionally adjusted. A separate dipping roller 16a may be provided which is dipped in the adhesive storage tank 17. In this case, the adhesive coating roller 16 is arranged between the dipping roller 16a and the upper corrugator roller 15 so that it can transfer the adhesive from the dipping roller 16a to the corrugated medium 11a or 21a on the upper corrugator roller 15. In this case, it is possible to more uniformly apply the adhesive to the corrugated medium 11a or 21a. The first and second single-faced corrugated paperboard forming stations 10 and 20 produce the single- faced corrugated paperboard 13 in which the corrugated medium is bonded to the lower surface of the liner and the single-faced corrugated paperboard 23 in which the corrugated medium is bonded to the upper surface of the liner, respectively. In a subsequent station, the upper corrugated paperboard 13 is laminated on the lower corrugated paperboard 23.

The corrugator rollers 14 and 15 are vertically arranged to engage with each other such that a regular wave of the medium 11a or 21a is continuously formed. The upper corrugator roller 15 is provided at its outer corrugated surface with a plurality of suction holes (not shown) arranged along each groove of the roller 15. When the medium 11a or 21a to be bond to the liner 12a or 22a passes between the corrugator rollers 14 and 15, it is in close contact with the corrugated surface of the corrugator roller 15 by a strong suction applied thereto through the suction holes so that it can maintain its desired wave shape.

Of factors determining the dimensions of the corrugator rollers 14 and 15 required for producing a desired double-ply corrugated paperboard, the most important one is the ratio between the corrugation pitch of the lower corrugations and the corrugation pitch of the upper corrugations. This corrugation pitch ratio determines the shock absorptivity and durability of the final product, namely, the double-ply corrugated paperboard. For example, where a double-ply corrugated paperboard in which its upper corrugations have a corrugation pitch corresponding to 2 times that of its lower corrugations is to be produced, as shown in FIG. 3A, it is required to use, for the first and second forming stations 10 and 40, two different sets of corrugator rollers 14 and 15 having a diameter ratio of 1 : 2. Where a double-ply corrugated paperboard having upper and lower corrugations with the same corrugation pitch is to be produced, as shown in FIG. 3B or 3C, it is required to use, for the first and second forming stations 10 and 40, two sets of corrugator rollers 14 and 15 having a diameter ratio of 1 : 1. In this case, a variety of shock absorption effects can be expected by varying the corrugation shape and the corrugation height. Downstream the first and second single-faced corrugated paperboard forming stations 10 and 20, tension rolls 31 and pre-heating units 30 are arranged to feed corresponding single-faced corrugated paperboards 13 and 23 at a constant speed while applying a certain tension to the paperboards 13 and 23, respectively.

The tension rolls 31, which adjust the feeding speed of each corresponding paperboard 13 or 23 by applying a tension to the paperboard, are arranged on both sides of each corresponding pre-heating unit 30 serving to pre-heat the corresponding paperboard to a temperature required for the bonding. It is preferred that the tension rolls 31 is controlled in speed by a corrugation number sensing unit 32 which will be described later.

Adhesive coating units 33 are disposed downstream the pre-heating units 30 to continuously or intermittently apply an adhesive to the corrugated mediums 11a and 21a of the single-faced corrugated paperboards 13 and 23, respectively so that the facing waves of the paperboards 13 and 23 can be bonded together. The corrugation number sensing unit 32 is also provided between paths of the paperboards 13 and 23 to count the number of corrugations of each paperboard. A heating plate 34 and a pair of press belts 35 are arranged downstream the pre-heating units 33.

Where a double-ply corrugated paperboard, in which its upper corrugations have a corrugation pitch corresponding to 2 times that of its lower corrugations, is to be produced, the corrugation number sensing unit 32 should control the feeding speeds of the upper and lower paperboards such that two lower corrugations are fed per one upper corrugation. Pitches of the corrugations can be accurately controlled by counting every pitch of the upper corrugated paperboard 11a and every pitch of the lower corrugated paperboard 21a by the sensors, respectively, operating data generated by the sensors every counting time, and controlling the tension rolls 31 on the basis of a phase difference based on the result of the operation. Alternatively, this may be achieved by continuously checking the cross-sections of the paperboards 11a and 21a at intervals of 1/1,000 to 1/10,000 second by a super-high speed camera (image), and controlling the tension rolls 31 on the basis of an instant corrugation phase difference obtained from the result of the checking.

Preferably, the adhesive coating unit 33 has the same construction as the adhesive coating roller 16 which is shown in FIG. 2.

The single-faced corrugated paperboards 13 and 23 applied with the adhesive on their corrugated mediums are fed through a gap defined between the press belts 35 and pressed against each other by a uniform pressure provided by the press belts 35 while being heated by the heating plate 34. Thus, a double-ply corrugated paperboard of a good quality exhibiting both the shock absorptivity and the durability can be produced.

Now, operation of the apparatus having the above- mentioned arrangement in accordance with the present invention will be described. As the first single-faced corrugated paperboard forming station 10 receives the medium 11a and the liner 12a respectively from the medium supply roll 11 and the liner supply roll 12, it corrugates the medium 11a and then bonds the corrugated medium 11a to the liner 12a, thereby forming the single-faced corrugated paperboard 13. At this time, the corrugated medium 11a is bonded to the lower surface of the liner 12a such that its corrugations faces downward.

Simultaneously, another single-faced corrugated paperboard 13 is formed in the second single-faced corrugated paperboard forming station 20 by bonding the corrugated medium 21a to the upper surface of the liner 22a such that its corrugations faces upward. These paperboards 13 and 23 are then guided in one direction by guides 19 respectively arranged at the exits of the forming stations 10 and 20 so that their facing corrugations can keep their accurate relative positions at which they can be completely in contact with each other or partially in contact with each other to defined a space therebetween.

Thereafter, the upper and lower single-faced corrugated paperboards 13 and 23 pass over the pre-heating units 30, respectively. By the pre-heating units 30, the paperboards 13 and 23 are sufficiently pre-heated at their surfaces.

The pre-heated paperboards 13 and 23 then pass over the corrugation number sensing unit 32 which serves to sense positions of corrugations on each paperboard so that the facing corrugations of the paperboards 13 and 23 can keep their accurate relative positions at which they can be completely in contact with each other or partially in contact with each other to define a space therebetween. After completing the determination of the corrugation positions, the single-faced corrugated paperboards 13 and 23 are coated with an adhesive on their corrugated mediums 11a and 21a. The adhesive-applied paperboards 13 and 23 are then fed to the nip between the press belts 35. As the paperboards 13 and 23 pass through the nip between the press belts 35, they are pressed against each other by the press belts 35 while being heated by the heating plate 34. Accordingly, the paperboards 13 and 23 are firmly bonded together. Thus, a desired double-ply corrugated paperboard with a high strength is produced. Where a double-ply corrugated paperboard in which its upper corrugations have a corrugation pitch corresponding to 2 times that of its lower corrugations is to be produced, as shown in FIG. 3A, it is required to use, for the first and second forming stations 10 and 20, two different sets of corrugator rollers 14 and 15 having a corrugation pitch ratio of 2 : 1 so that two lower corrugations can be formed per one upper corrugation. In this case, the feeding speeds of the paperboards 13 and 23 are controlled such that two corrugations of the lower paperboard 23 are fed per one corrugation of the upper paperboard 13 at the step of sensing the number of corrugations through the corrugation number sensing unit 32.

In this case, each valley of the lower corrugated medium 12a having a larger corrugation pitch overlaps with two successive crests of the upper corrugated medium 11a having a smaller corrugation pitch. When this double-ply corrugated paperboard is subjected to a load from the outside, each valley of the lower corrugations is pushed toward the valley defined between the corresponding crests of the upper corrugations. Simultaneously, the crests of the upper corrugations are pushed into the corresponding valley of the lower corrugations. When the load is released before the elastic limit of the upper and lower corrugated mediums 101 and 104, the strain is completely removed so that the corrugated mediums 11a and 12a can return to their original states, respectively. In this case, accordingly, the double-ply corrugated paperboard can have a durable shock absorptivity.

Where a double-ply corrugated paperboard having upper and lower corrugations with the same corrugation pitch, but with different corrugation heights is to be produced, as shown in FIG. 3B, it is required to use, for the first and second forming stations 10 and 20, two different sets of corrugator rollers 14 and 15 having a corrugation pitch ratio of 1 : 1, but having different corrugation heights. In this case, the corrugator rollers 14 and 15 of the first and second forming stations 10 and 20 produce continuous upper corrugations and continuous lower corrugations having the same corrugation pitch, but different corrugation heights, respectively. The corrugation number sensing step should involve the upper and lower single-faced corrugated paperboards having the same corrugation pitch, but different corrugation heights in a corrugation pitch ratio of 1 : 1 so that corresponding upper and lower corrugations are bonded together such that they faces to each other. When this double-ply corrugated paperboard is subjected to a shock from the outside, the shock is primarily absorbed by spaces which are defined between the upper and lower corrugated mediums 11a and 21a by virtue of corrugation height difference. For a higher shock, it is secondarily absorbed by the lower corrugated medium 21a of the double- ply corrugated paperboard. Thus, the shock absorption is effectively achieved.

Where a double-ply corrugated paperboard having upper and lower corrugations with the same corrugation pitch and the same corrugation height is to be produced, as shown in FIG. 3C, two identical sets of corrugator rollers 14 and 15 having the same corrugation pitch and the same corrugation height are used for the first and second forming stations 10 and 20, respectively. In this case, however, it is required to form corrugations constituted by alternating crests and valleys both having different curvatures at their peaks from each other so that the upper and lower corrugations have spaces defined between each valley and each crest overlapping with the valley. Here, the valleys are corrugation portions bonded to the corresponding liner at their peaks. In this case, a variety of shock absorption effects can be expected by varying the corrugation shape and the corrugation height. As apparent from the above description, the double- ply corrugated paperboard according to the present invention includes two corrugated mediums laminated together such that they are completely in contact with each other or partially in contact with each other at intervals to form a space therebetween for every corrugation. In such a laminated structure, the facing double-ply corrugated medium exhibit the elasticity and the shock absorptivity at opposite surfaces thereof. Accordingly, the double-ply corrugated paperboard has an internal shock absorptivity provided by its paper material as well as a durability and a stiffness both provided by the waves of its corrugated mediums. In terms of the weight, the paperboard of the present invention is considerably light, as compared to conventional wood or synthetic resin pallets. In this regard, the present paperboard has a convenience in use. There is also an advantage that no accident occurs due to a carelessness in handling. Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

As apparent from the above description, the present invention provides a double-ply corrugated paperboard produced by bonding a corrugated medium to the lower surface of a liner and another corrugated medium to the upper surface of another liner, thereby forming facing upper and lower single-faced corrugated paperboards, preheating the paperboards, sensing positions of corrugations on the paperboards such that the facing corrugations of the paperboards can keep their accurate relative positions at which they can be completely in contact with each other or partially in contact with each other to define a space therebetween, coating an adhesive on the corrugated mediums of the paperboards, guiding the adhesive-applied paperboards to the heating plate, and pressing the paperboards against each other at a certain pressure during the paperboards pass over the heating plate. In accordance with the present invention, the paperboard is entirely made of regenerable paper other than materials causing an environmental contamination. In accordance with the present invention, a plurality of corrugated mediums may be provided between upper and lower liners of the paperboard such that adjacent ones of the corrugated mediums are completely in contact with each other or partially in contact with each other at intervals to define a space therebetween for every corrugation. Accordingly, it is possible to increase the compressive strength of the paperboard and yet maintain a small thickness of the paperboard. By virtue of this advantage, it is possible to provide high value-added paperboards capable of effectively achieving a minimized packaging size. Once the paperboard of the present invention is used for its packaging purpose, it may be reused as shock absorbing materials for packaging after it is collected. In this regard, the present paperboard is a high value- added product. Therefore, the present invention can greatly reduces the expense of the packaging material and contributes to the protection of environment and the reuse of the resource. Since the present paperboard can effectively absorb a shock applied from the outside to a packaged content, it can keep the packaged content more safe.

Claims

Claims :

1. A method for producing a double-ply corrugated paperboard comprising the steps of: bonding a continuous corrugated medium to one surface of a continuous liner having opposite surfaces such that corrugations of the corrugated medium face downward, thereby forming a single-faced downward-corrugated paperboard; bonding another continuous corrugated medium to one surface of another continuous liner having opposite surfaces such that corrugations of the another corrugated medium face downward, thereby forming a single-faced upward-corrugated paperboard; preheating the paperboards; sensing positions of corrugations on the preheated paperboards, namely, numbers of the corrugations in a pitch control-synchronized manner such that facing corrugations of the paperboards can keep their accurate relative positions at which they can be completely in contact with each other or partially in contact with each other to define a space therebetween for every corrugation; coating an adhesive on the corrugated mediums of the position-determined paperboards; guiding the adhesive-applied paperboards to a heating plate; and pressing the paperboards against each other at a desired pressure during the paperboards pass over the heating plate.

2. The method in accordance with claim 1, wherein the step of sensing the numbers of corrugations comprises the step of controlling feeding speeds of the paperboards such that two corrugations of the upward-corrugated paperboard are fed per one corrugation of the downward-corrugated paperboard.

3. The method in accordance with claim 1, wherein the step of sensing the numbers of corrugations comprises the step of controlling feeding speeds of the paperboards, which have the same corrugation pitch, but different corrugation heights, such that the corrugations of the paperboards are sensed in a ratio of 1 : 1.

4. The method in accordance with claim 1, wherein the step of sensing the numbers of corrugations comprises the step of controlling feeding speeds of the paperboards, which have the same corrugation pitch and height, but different curvatures, such that the corrugations of the paperboards are sensed in a ratio of 1 : 1.

5. The method in accordance with any one of claims 1 to 4, wherein the step of bonding the paperboards together comprises the steps of: counting every pitch of the downward-corrugated paperboard and every pitch of the upward-corrugated paperboard by sensors, respectively; operating data generated by the sensors every counting time; and controlling tension rolls, which respectively adjust feeding speeds of the paperboards, on the basis of a phase difference based on the result of the operation, whereby pitches of the corrugations are more accurately controlled.

6. The method in accordance with any one of claims 1 to 4, wherein the step of bonding the paperboards together comprises the steps of: continuously checking the cross-sections of the paperboards at intervals of 1/1,000 to 1/10,000 second by a super-high speed camera; and controlling tension rolls, which respectively adjust feeding speeds of the paperboards, on the basis of an instant corrugation phase difference obtained from the result of the checking.

7. An apparatus for producing a double-ply corrugated paperboard comprising: single-faced downward-corrugated paperboard forming means adapted to receive a first medium and a first liner respectively from a first medium supply roll and a first liner supply roll, to corrugate the first medium and to bond the first, corrugated medium to the first liner such that corrugations of the corrugated first medium face downward, thereby forming a single-faced downward- corrugated paperboard; single-faced downward-corrugated paperboard forming means adapted to receive a second medium and a second liner respectively from a second medium supply roll and a second liner supply roll, to corrugate the second medium and to bond the second, corrugated medium to the second liner such that corrugations of the corrugated second medium face upward, thereby forming a single-faced upward- corrugated paperboard; a tension roll and pre-heating means both arranged downstream each of the downward- and upward-corrugated paperboard forming means and adapted to apply a constant tension to the corresponding corrugated paperboard being continuously fed under a condition that its corrugations face to those of the other corrugated paperboard; adhesive coating means adapted to continuously coat an adhesive on facing surfaces of the corrugated mediums of the paperboards; corrugation number sensing means disposed between paths of the paperboards and adapted to count numbers of the facing corrugations of the paperboards; and a heating plate and pressing belt means both adapted to press the adhesive-applied paperboards at a desired pressure while heating them, thereby bonding them together.

8. The apparatus in accordance with claim 7, wherein each of the single-faced corrugated paperboard forming means comprises: a pair of vertically arranged corrugator rollers adapted to guide the corresponding medium therebetween and to corrugate the guided medium to have a desired wave; an adhesive coating roller arranged on one side of the upper one of the corrugator rollers and adapted to uniformly coat an adhesive on one surface of the corrugated medium; and a drum type heater disposed over the upper corrugator roller and adapted to bring the corrugated medium into contact with the corresponding liner.

9. The apparatus in accordance with claim 6, wherein the corrugator rollers are vertically arranged to engage with each other such that a regular wave of the corresponding medium is continuously formed, and the upper corrugator roller is provided at an outer corrugated surface thereof with a plurality of suction holes arranged along each groove thereof, the suction holes serving to maintain the corrugated shape of the corrugated medium until the corrugated medium is bonded to the liner.

10. The apparatus in accordance with claim 7, wherein the tension roll is controlled in speed by the corrugation number sensing means.

11. The apparatus in accordance with any one of claims 7 to 10, wherein the downward- and upward- corrugated paperboard forming means form continuous downward and upward corrugations such that the upward corrugations have a pitch corresponding to two times that of the downward corrugations, and the corrugation number sensing means controls feeding speeds of the downward- and upward-corrugated paperboard such that two downward corrugations are fed per one upward corrugation.

12. The apparatus in accordance with claim 11, wherein the downward- and upward-corrugated paperboard forming means form continuous downward and upward corrugations such that the upward corrugations have the same pitch as the downward corrugations, but have a different height from the downward corrugations, and the corrugation number sensing means controls feeding speeds of the downward- and upward-corrugated paperboard such that the downward and upward corrugations are sensed in a ratio of 1 : 1.

13. The apparatus in accordance with claim 11, wherein the downward- and upward-corrugated paperboard forming means form continuous downward and upward corrugations such that the downward and upward corrugations have the same pitch and height, but have different curvatures between each crest peak thereof and each valley peak thereof boned to the corresponding liner so that the overlapping corrugations define continuous spaces therebetween.

14. The apparatus in accordance with claim 12, further comprising sensors for counting every pitch of the downward-corrugated paperboard and every pitch of the upward-corrugated paperboard, respectively, operating data generated every counting time, and controlling the tension rolls on the basis of a phase difference based on the result of the operation, respectively, whereby pitches of the corrugations are more accurately controlled.

15. The method in accordance with claim 12, further comprising a super-high speed camera for continuously checking the cross-sections of the paperboards at intervals of 1/1,000 to 1/10,000 second, and controlling each tension roll on the basis of an instant corrugation phase difference obtained from the result of the checking, whereby pitches of the corrugations are more accurately controlled.