Smoothly bendable board

Abstract

A smoothly bendable board including a middle layer, a first outer layer attached to the middle layer and a second outer layer attached to the middle layer is disclosed. The second outer layer has a lower bending stiffness according to ISO 5628 than the first outer layer such that the smoothly bendable board is outwardly bendable only in a direction towards which the second layer faces. A method for producing a smoothly bendable board is also disclosed.

Claims

1. A smoothly bendable board comprising a middle layer, a first outer layer attached to the middle layer and a second outer layer attached to the middle layer, wherein the middle layer is a corrugated layer comprising flutes, wherein the second outer layer is selected from the group consisting of a fine paper, a supercalendered paper, a machine-glazed paper, a newsprint, a machine-finished paper, a metal foil, and a metalized film, and a laminate of any two or more thereof, wherein the bending stiffness of the second outer layer is chosen according to the equation $\begin{array}{cc}{\mathrm{EI}}_{\mathrm{second}\mathrm{outer}\mathrm{layer}}<\frac{SCT.Math.{\lambda }^2}{4{\pi }^2},& \left(\mathrm{Equation}2\right),\end{array}$ such that each section of the second outer layer exhibits buckling according to $\begin{array}{cc}\mathrm{Pk}=\frac{4{\pi }^2\mathrm{EI}}{{\lambda }^2},& \left(\mathrm{Equation}1\right)\end{array}$ where EI.sub.second outer layer is the bending stiffness of the second outer layer, SCT is the second outer layer's compression strength according to the short-span compressive test according to ISO 9895, λ is the length between two peaks of the flutes of the middle layer of smoothly bendable board and Pk is the buckling force required to buckle the second outer layer, and wherein the second outer layer has a lower bending stiffness according to ISO 5628 than the first outer layer such that the smoothly bendable board is outwardly bendable only in a direction towards which the second layer faces, where the direction is essentially perpendicular to the flutes of the middle layer, such that the first outer layer of the smoothly bendable board becomes convex after bending, and wherein the smoothly bendable board passes a bending test comprising bending a test piece of the smoothly bendable board 180° around a pipe having a diameter in the range of 102 mm.

2. The smoothly bendable board according to claim 1, wherein the first outer layer is selected from the group consisting of a liner, paper, plastic, a laminate of any two or more thereof, and a composite of any two or more thereof.

3. The smoothly bendable board according to claim 1, wherein the first outer layer is made up of one of a fine paper, supercalendered paper, machine-glazed paper, greaseproof paper, newsprint or machine-finished paper, liner, metal foil, metalized film, a composite material or a laminate of any two or more of fine paper, supercalendered paper, machine-glazed paper, greaseproof paper, newsprint or machine-finished paper, liner, metal foil, metalized film or a composite material.

4. The smoothly bendable board according to claim 1, wherein the corrugated middle layer comprises any of the flute sizes A, B, C, E, F, G or K or a combination of any of the flute sizes A, B, C, E, F, G or K.

5. The smoothly bendable board according to claim 1, wherein the second outer layer is newsprint.

6. The smoothly bendable board according to claim 5, wherein the first outer layer is made up of one of a fine paper, supercalendered paper, machine-glazed paper, greaseproof paper, newsprint or machine-finished paper, liner, metal foil, metalized film, a composite material or a laminate of any two or more of fine paper, supercalendered paper, machine-glazed paper, greaseproof paper, newsprint or machine-finished paper, liner, metal foil, metalized film or a composite material.

7. The smoothly bendable board according to claim 6, wherein the first outer layer is newsprint.

8. A method for producing a smoothly bendable board according to claim 1, comprising middle layer, a first outer layer and a second outer layer, the method comprising: attaching the first outer layer to the middle layer, producing a single-face board; and attaching the second outer layer to the middle layer, wherein the second outer layer is selected from the group consisting of a fine paper, a supercalendered paper, a machine-glazed paper, a newsprint, a machine-finished paper, a metal foil, and a metalized film, and a laminate of any two or more thereof, wherein the middle layer is a corrugated layer comprising flutes, the bending stiffness of the second outer layer is chosen according to the equation $\begin{array}{cc}{\mathrm{EI}}_{\mathrm{second}\mathrm{outer}\mathrm{layer}}<\frac{SCT.Math.{\lambda }^2}{4{\pi }^2},& \left(\mathrm{Equation}2\right),\end{array}$ such that each section of the second outer layer exhibits buckling according to $\begin{array}{cc}\mathrm{Pk}=\frac{4{\pi }^2\mathrm{EI}}{{\lambda }^2},& \left(\mathrm{Equation}1\right),\end{array}$ where EI.sub.second outer layer is the bending stiffness of the second outer layer, SCT is the second outer layer's compression strength according to the short-span compressive test according to ISO 9895, λ is the length between two peaks of the flutes of the middle layer of smoothly bendable board and Pk is the buckling force required to buckle the second outer layer, and wherein the second outer layer has a lower bending stiffness according to ISO 5628 than the first outer layer such that the smoothly bendable board is outwardly bendable only in a direction towards which the second layer faces, where the direction is essentially perpendicular to the flutes of the middle layer, such that the first outer layer of the smoothly bendable board becomes convex after bending.

9. The method according to claim 8, the method further comprising: using an initially curved single faced board curved in the direction towards which the first layer faces, and arranging the initially curved single faced board to be flat before attaching the second outer layer.

10. The method according to claim 8, the method further comprising: attaching the first outer layer to the middle layer, producing a single-face board; arranging the single-face corrugated board such that it is curved in a direction towards which the second layer faces; and attaching the second outer layer to the curved corrugated middle layer.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1a schematically shows a single face corrugated board according to prior art;

(2) FIG. 1b schematically shows a double face corrugated board according to prior art;

(3) FIG. 2a schematically shows a smoothly bendable board according to an embodiment of the invention in a flat state;

(4) FIG. 2b schematically shows a smoothly bendable board according to an embodiment of the invention being outwardly bent in a direction towards which the second layer faces and perpendicular to the flutes of the corrugated middle layer;

(5) FIG. 3 schematically shows the concept of buckling of the second outer layer.

DETAILED DESCRIPTION OF DRAWINGS

(6) In the drawings, like features have the same reference numbers.

(7) FIG. 1a schematically discloses a single face corrugated board 1 according to prior art. The single face corrugated board 1 includes a first outer layer 2 attached to a corrugated layer 3 including flutes. The single face corrugated board 1 does not exhibit a significant amount of stiffness as it is intended to be wrapped around fragile objects made of for instance glass or porcelain.

(8) FIG. 1b schematically discloses a double face corrugated board 4 according to prior art. The double face corrugated board 4 includes besides the first outer layer 2 and the corrugated layer 3 including flutes a second outer layer 5. The second outer layer 5 is of the same kind as for the first outer layer 2 aiming at giving the double face corrugated board 4 a high degree of stiffness and strength as it is intended for packaging. At the same time it is not bendable to a high degree without deforming.

(9) FIG. 2a schematically discloses a smoothly bendable board 6. The smoothly bendable board 6 includes a first outer layer 2, a middle layer 3, and a second outer layer 5 made of a material with a lower bending stiffness than the first outer layer 2. Although the smoothly bendable board in FIG. 2 shows a corrugated middle layer 3, the middle layer 3 is not limited to a corrugated layer.

(10) The following description also applies to a smoothly bendable board having a middle layer made up of, for instance, a thermoformed core. When corrugated middle layer is stated it is conceivable to have a thermoformed core instead. The first outer layer 2 and the second outer layer 5 of the smoothly bendable board 6 may be either a single layer or a laminate of two or more layers having the above mentioned characteristics. The outer layers may also be coated or laminated together with another layer such as a film to achieve barrier properties such as barrier against moisture, water vapour, grease, aroma, oxygen, or migration of volatile substances such as components of mineral oil and free radical from UV-ink or other volatile substances. The corrugated layer 3 including flutes may include a single layer of fluting or two or more layers of fluting where each layer may have the same flute size or different flute sizes.

(11) The first outer layer 2 and the second outer layer 5 may have a surface suitable for printing as is known in the art.

(12) FIG. 2b schematically shows the smoothly bendable board 6 being outwardly bent in a direction towards which the second layer 5 faces and perpendicular to the flutes of the corrugated middle layer 3. The low bending stiffness of the second outer layer 5 in combination with the high bending stiffness of the first outer layer 2 makes this possible. The same characteristics make it difficult for the smoothly bendable board 6 to bend in the opposite direction without deforming one or more of the layers 2, 3 or 5.

(13) The smoothly bendable board 6 shown in FIG. 2b is manufactured by applying a second outer layer 5 to a single face corrugated board, such as one shown in FIG. 1a. The second outer layer 5 is applied to the single face corrugated board by means of starch glue, melt adhesive or any other kind of fastening means suitable for attaching a layer to a fluting layer. The fastening means may contain other functional components, for example to achieve barrier properties according to what has been mentioned earlier.

(14) The second outer layer is generally applied while the single face corrugated board is placed flat on a surface. In order to ensure that the smoothly bendable board 6 stays flat it may be suitable to use an initially curved single faced corrugated board in the direction of the corrugated middle layer 3, and arrange it to be flat before attaching the second outer layer 5. It will then be more difficult for the smoothly bendable board 6 to spontaneously bend in the direction towards which the second layer faces. By using this production method, it is possible to add bending resistance (in the direction towards the second outer layer) to the material.

(15) The smoothly bendable board 6 shall be possible to bend into a radius which corresponds to less than the minimum radius that standard corrugated board can be bent into. After bending of the smoothly bendable board 6 there shall be no creasing, i.e. folding of the first outer layer 2 of the board. The first outer layer 2 of the smoothly bendable board 6 becomes convex after bending. In FIG. 2, the buckling of the second outer layer 5 is not present for illustrative reasons. The concept of buckling is shown in FIG. 3.

(16) FIG. 3 shows a close up of the smoothly bendable board 6 in FIG. 2b. In FIG. 3, the first outer layer displays a smooth and continuous radius without creasing. The corrugated middle layer 3 includes a number of peaks 7 facing the second outer layer 5 and a number of valleys 8 facing the first outer layer. Between the peaks 7 the second outer layer includes sections 9. One condition to get a smooth and continuous radius is that the second outer layer 5 should buckle between each peak 7 of the corrugated middle layer 3 when the material is subjected to bending in the bendable direction. When each section 9 of the second outer layer 5 exhibits buckling, the bending can be distributed across each section of the material. In FIG. 3, the size of the buckling of the second outer layer is shown for illustrative purposes and may vary depending on, for instance, the degree of bending and the choice of materials.

(17) The concept of buckling is described in more detail above.

(18) When the smoothly bendable board 6 is exposed to bending the material in the second outer layer 5 will start to buckle between the tops 7 of the corrugated middle layer 3 if the bending stiffness of the second outer layer 5 is low enough.

(19) In order to test the minimum radius that the smoothly bendable board can be bent to without getting material damage, a special test rig has been developed. The test rig includes six pipes with a smooth surface having the diameters 102 mm, 75 mm, 34 mm, 33 mm, 20 mm and 12 mm. The pipes can be made of metal and are mounted onto a base such as a beam or a table for stability.

(20) The width of the test pieces of all boards is 105 mm, i.e. the size of an A4 paper cut in two halves. The length of the test pieces is 297 mm, i.e. the length of an A4 paper. All test pieces are conditioned according to ISO 187 (pre-conditioned at 30% RH, 23 degrees C., and thereafter conditioned at 50% RH, 23 degrees C.).

(21) A selected test piece is first bent around the largest pipe and thereafter visually inspected to detect any damages to the material. The test piece is bent 180°, i.e. such that both ends of the test piece point in the same direction. If no damage is visually detectable, the test piece is bent around the second largest pipe and evaluated in the same way. This procedure is repeated using a smaller pipe diameter until the material is damaged by the bending process or until the material successfully passes bending around the smallest 12 mm pipe. In addition to testing the different types of smoothly bendable corrugated board, a selection of carton board grades is chosen. In addition to the PE-laminated corrugated board, the 483E grade (E-flute used for outdoor displays, 610 g/m2 where the fluting is laminated onto liner+PE-layer+MG-paper) is tested.

(22) Table 1 illustrates the result of the bending test. OK! means that no damage is seen visually. Fail! means that damage such as kinks is seen visually in any of the outer layers. A * before the grade indicates that the board was made according to an embodiment of the invention.

(23) TABLE-US-00001 TABLE 1 Smoothly bendable corrugated board and carton board tests for minimum bending radius, *indicates that the board is made according to an embodiment of the invention. 102 75 43 33 20 12 Grade mm mm mm mm mm mm *C-flute between OK! OK! OK! OK! OK! OK! EK 165 + News print 45 *B-flute between OK! OK! OK! OK! OK! OK! EK 125 + News print 45 *E-flute between OK! OK! OK! OK! OK! OK! EK 125 + News print 45 *G-flute between OK! OK! OK! OK! OK! OK! EK 125 + News print 45 MCK 600 WLC OK! OK! FAIL! Kasu 300 GC1 OK! OK! FAIL! MCK 450 GT4 OK! OK! FAIL! Invercote Creato OK! OK! OK! OK! OK! FAIL! 240 Invercote Duo OK! OK! OK! FAIL! 450 Incada Exel 240 OK! OK! FAIL! Eco-Print 300 OK! OK! OK! OK! FAIL! GT3 483E FAIL!

(24) As can be seen from table 1, all smoothly bendable boards according to embodiments of the invention are able to bend to a radius that is smaller than conventional boards without exhibiting visual damage to any of the outer layers. As can be seen in table 1, the 483E grade fails already at the 102 diameter pipe.

(25) Reference signs mentioned in the claims should not be seen as limiting the extent of the matter protected by the claims, and their sole function is to make claims easier to understand.

(26) As will be realised, the invention is capable of modification in various obvious respects, all without departing from the scope of the appended claims. Accordingly, the drawings and the description thereto are to be regarded as illustrative in nature, and not restrictive.