CARDBOARD WITH EDGE SEALED WITH MIXTURE OF HOT-MELT ADHESIVE AND WAX

Abstract

Cardboard with edges sealed by a mixture of hot-melt adhesive and wax includes two surface sheets and an intermediate core material. The surface sheets have a pair of corresponding edges that form an edge opening therebetween communicating with the interstitial spaces in the cardboard and sealed by an edge-sealing structure in the interstitial spaces. The edge-sealing structure includes a primer layer formed by an adhesive mixture and a sealing layer formed by a sealing mixture. The adhesive mixture is made by mixing the hot-melt adhesive with the wax, adhesively bonds the surface sheets and the intermediate core material together, and forms the primer layer with voids and providing a porous supporting surface to be coated with the sealing mixture. The sealing mixture is less adhesive than the adhesive mixture and fills up the voids in the primer layer. Thus, the cardboard achieves waterproofness and thermal and acoustic insulation at low cost.

Claims

1. Cardboard with edges sealed with a mixture of a hot-melt adhesive and wax, wherein the cardboard comprises a first surface sheet, a second surface sheet, and an intermediate core material provided between the surface sheets; the intermediate core material has a top side and a bottom side each forming at least one interstitial space with a corresponding one of the surface sheets; the surface sheets have a pair of corresponding edges that form an edge opening therebetween; and the edge opening is in communication with the interstitial spaces; the cardboard being characterized in that the interstitial spaces are provided therein with an edge-sealing structure for sealing the edge opening, the edge-sealing structure comprising: a primer layer, formed by an adhesive mixture, and the adhesive mixture made by mixing the hot-melt adhesive with the wax, wherein the hot-melt adhesive makes up 10% to 65% by weight of the adhesive mixture, the adhesive mixture is applied to the edge opening to adhesively bond the surface sheets and the intermediate core material together, and the adhesive mixture when cured forms the primer layer with a plurality of voids; and a sealing layer, formed by a sealing mixture, and the sealing mixture made by mixing the hot-melt adhesive with the wax, wherein the hot-melt adhesive makes up 5% to 40% by weight of the sealing mixture, the hot-melt adhesive in the sealing mixture has a lower weight percentage than the hot-melt adhesive in the adhesive mixture such that the sealing mixture is less adhesive than the adhesive mixture, and the sealing mixture is applied to the primer layer to fill up said voids in the primer layer that correspond to the edge opening, thereby forming the sealing layer.

2. The cardboard of claim 1, wherein the hot-melt adhesive makes up 30% to 65% by weight of the adhesive mixture.

3. The cardboard of claim 2, wherein the hot-melt adhesive makes up 5% to 30% by weight of the sealing mixture.

4. The cardboard of claim 1, wherein the edge-sealing structure has a thickness ranging from 1 cm to 5 cm.

5. The cardboard of claim 2, wherein the edge-sealing structure has a thickness ranging from 1 cm to 5 cm.

6. The cardboard of claim 3, wherein the edge-sealing structure has a thickness ranging from 1 cm to 5 cm.

7. The cardboard of claim 4, wherein the first surface sheet has an outer side coated with the wax to form a waterproof layer.

8. The cardboard of claim 5, wherein the first surface sheet has an outer side coated with the wax to form a waterproof layer.

9. The cardboard of claim 6, wherein the first surface sheet has an outer side coated with the wax to form a waterproof layer.

10. The cardboard of claim 7, wherein the cardboard is a corrugated cardboard, the intermediate core material has a corrugated configuration and extends in a wavy manner in a direction defined as a corrugation direction, and the edge of the cardboard, along which the edge opening is located, is parallel to the corrugation direction.

11. The cardboard of claim 8, wherein the cardboard is a corrugated cardboard, the intermediate core material has a corrugated configuration and extends in a wavy manner in a direction defined as a corrugation direction, and the edge of the cardboard, along which the edge opening is located, is parallel to the corrugation direction.

12. The cardboard of claim 9, wherein the cardboard is a corrugated cardboard, the intermediate core material has a corrugated configuration and extends in a wavy manner in a direction defined as a corrugation direction, and the edge of the cardboard, along which the edge opening is located, is parallel to the corrugation direction.

13. The cardboard of claim 10, wherein the cardboard has another edge, which is perpendicular to the corrugation direction and is formed with a corrugation-direction opening, the corrugation-direction opening is also in communication with the interstitial spaces, and the interstitial spaces are provided therein with another said edge-sealing structure adjacent to the corrugation-direction opening.

14. The cardboard of claim 11, wherein the cardboard has another edge, which is perpendicular to the corrugation direction and is formed with a corrugation-direction opening, the corrugation-direction opening is also in communication with the interstitial spaces, and the interstitial spaces are provided therein with another said edge-sealing structure adjacent to the corrugation-direction opening.

15. The cardboard of claim 12, wherein the cardboard has another edge, which is perpendicular to the corrugation direction and is formed with a corrugation-direction opening, the corrugation-direction opening is also in communication with the interstitial spaces, and the interstitial spaces are provided therein with another said edge-sealing structure adjacent to the corrugation-direction opening.

16. The cardboard of claim 13, wherein the second surface sheet has an outer side provided with a buffer layer.

17. The cardboard of claim 14, wherein the second surface sheet has an outer side provided with a buffer layer.

18. The cardboard of claim 15, wherein the second surface sheet has an outer side provided with a buffer layer.

19. The cardboard of claim 16, wherein the buffer layer is made of expandable polyethylene (EPE).

20. The cardboard of claim 17, wherein the buffer layer is made of expandable polyethylene (EPE).

21. The cardboard of claim 18, wherein the buffer layer is made of expandable polyethylene (EPE).

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0011] The working principle, structural features, and objectives of the present invention can be better understood by referring to the following detailed description of an illustrative embodiment in conjunction with the accompanying drawings, in which:

[0012] FIG. 1 schematically shows a piece of conventional corrugated cardboard;

[0013] FIG. 2 schematically shows the structure of a piece of corrugated cardboard according to the present invention; and

[0014] FIG. 3A to FIG. 3C schematically show how the edge-sealing structure of the present invention is formed.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention provides cardboard having edges sealed with a mixture of a hot-melt adhesive and wax. Referring to FIG. 2 and FIG. 3A for a preferred embodiment of the present invention, the cardboard 2 at least includes a first surface sheet 21 (For example, kraft paper), a second surface sheet 22, and at least one intermediate core material 23. The intermediate core material 23 is provided between the surface sheets 21, 22 and is bent or curved (in the case where the cardboard 2 is a corrugated cardboard, the intermediate core material 23 may be composed of a stack of one to three layers of curved or corrugated paper) such that each of the top and bottom sides of the intermediate core material 23 forms at least one interstitial space 20 (referred to as air columns between the core material 23 and the surface sheets 21, 22) with the corresponding surface material 21, 22. The surface sheets 21, 22 have a pair of corresponding edges that form an edge opening 201 therebetween. The interstitial spaces 20 are in communication with the edge opening 201.

[0016] According to the present invention, the interstitial spaces 20 are provided therein with an edge-sealing structure 3 for sealing the edge opening 201. The edge-sealing structure 3 includes a primer layer and a sealing layer. The primer layer is formed by an adhesive mixture 31 and the sealing layer is formed by a sealing mixture 32. The adhesive mixture 31 is made by mixing a hot-melt adhesive with wax, wherein the hot-melt adhesive may be low-density polyethylene (LDPE) or ethylene vinyl acetate (EVA) but is not limited to the foregoing. For example, the hot-melt adhesive may be a mixture of different hot-melt adhesives. The wax may be a soft microcrystalline wax or a fully refined wax but is also not limited to the foregoing. To easily identify the compositions of the cardboard 2 claimed in this application, FIGS. 2 to 3C use sloping lines, grid lines, and dots thereon for clearly referring to the sealing mixture 32, the waterproof layer 24 coated on the outer side of the first surface sheet 21, and the adhesive mixture 31 of the cardboard 2, respectively, which vary in wax content. The core feature of the present invention is to incorporate such properties of the hot-melt adhesive as adhesiveness and not being absorbable by the intermediate core material 23 and the waterproofing property of the wax into the edge-sealing structure 3. As long as the hot-melt adhesive and the wax satisfy the above property requirements, their constituent materials may be adjusted as needed.

[0017] The details and arrangement of the edge-sealing structure 3 are described below regarding FIG. 2 and FIGS. 3A to 3C. The hot-melt adhesive in the adhesive mixture 31 constitutes 10% to 65%, preferably 30% to 65%, by weight of the adhesive mixture 31. After heating and mixing the hot-melt adhesive and wax making up the adhesive mixture 31, the resulting mixture is filled into the interstitial spaces 20 through the edge opening 201 by spray coating and is thus adhesively bonded to, and hence located between, the surface sheets 21, 22 and the intermediate core material 23. In consequence, the surface sheets 21, 22 and the intermediate core material 23 are adhesively bonded together and form a single unit. The adhesive mixture 31 is so adhesive that a plurality of voids 310 are formed in a central portion of the adhesive mixture 31 due to surface tension when the adhesive mixture 31 attaches to the inner sides of the surface sheets 21, 22, and that therefore the adhesive mixture 31 forms the porous primer layer in the edge opening 201 as shown in FIG. 3B. The shape, size and number of voids in the primer layer are dependent on the quantity of hot melt adhesive in the adhesive mixture; microscopic appearance of the primer layer could range from a fibrous structure resembling spider webs to a mushy structure resembling melted marshmallows.

[0018] The sealing mixture 32 is also made by mixing the hot-melt adhesive with the wax, wherein the hot-melt adhesive constitutes 5% to 40%, preferably 5% to 30%, by weight of the sealing mixture 32. The weight percentage of the hot-melt adhesive in the sealing mixture 32 is lower than that of the hot-melt adhesive in the adhesive mixture 31 such that the sealing mixture 32 is less adhesive and more fluid than the adhesive mixture 31. The sealing mixture 32 is spray-coated on the primer layer (the adhesive mixture 31) to fill up at least the voids 310 in the primer layer (the adhesive mixture 31) that correspond to the edge opening 201 (see FIGS. 3B and 3C), thereby forming the sealing layer that seals the edge opening 201 of the cardboard 2 in a watertight manner. In this preferred embodiment of the present invention, the sealing mixture 32 covers the entire outer side of the primer layer (the adhesive mixture 31), i.e., the side facing the edge opening 201 (see FIG. 2), as a waterproof structure coated on the primer layer.

[0019] The adhesive mixture 31, which is more adhesive than the sealing mixture 32, can adhere tightly to the inner sides of the surface sheets 21, 22 such that the wax in the adhesive mixture 31 will not be adsorbed by the surface sheets 21, 22. This technical feature enables the porous primer layer to be formed in the interstitial spaces 20 and be coated with the sealing mixture 32 to solve the problem of the prior art that, as stated in Description of Related Art and shown in FIG. 1, the interior of the edge opening 101 of the conventional corrugated cardboard cannot be coated with wax. In addition, with the sealing mixture 32 being less adhesive than the adhesive mixture 31 and hence capable of evenly covering and seeping into the primer layer to fill up the voids 310, the primer layer (the adhesive mixture 31) and the sealing mixture 32 jointly form a perfectly watertight double-layer protective structure that ensures moisture resistance of the cardboard 2 by preventing moisture from penetrating the surface sheets 21, 22 or the intermediate core material 23 through the edge opening 201.

[0020] Apart from enhancing moisture resistance of the cardboard 2, the edge-sealing structure 3 contributes to higher thermal insulation and heat resistance. Also, the edge-sealing structure 3 adds little to the weight of the cardboard 2 and allows the cardboard 2 to be transported with ease and folded into corrugated boxes of various shapes or specifications without difficulty. Besides, the edge-sealing structure 3 is easy to implement, for a manufacturer only must arrange two spray nozzles sequentially on a machine configured for conveying the cardboard 2, and the edge-sealing structure 3 can be rapidly formed by spray-coating the edge opening 201 with the adhesive mixture 31 and the sealing mixture 32 one after the other.

[0021] While the cardboard 2 in the preferred embodiment described herein is implemented as corrugated cardboard, i.e., with the intermediate core material 23 having a corrugated configuration, the edge-sealing structure 3 is applicable to and can form a watertight protective layer in all cardboard structures that are formed by multiple layers of paper materials and that have voids in the edges. Furthermore, once the edge-sealing structure 3 is formed in the cardboard 2, the cardboard 2 can be folded either manually or by a machine to form a corrugated box. As the process of scoring a piece of cardboard at different positions to facilitate folding into a corrugated box is well known in the art, a description of the scoring process is omitted herein.

[0022] In the preferred embodiment of the present invention, referring to FIG. 2, the top side of the cardboard 2 (i.e., the outer side of the first surface sheet 21) may be further coated with the wax to form a waterproof layer 24. After the cardboard 2 is folded into a corrugated box, the waterproof layer 24 constitutes the outer side of the corrugated box to protect the box against dampness and moisture.

[0023] Moreover, once the waterproof layer 24 is formed on the top side of the cardboard 2 by coating the top side with wax and allowing the wax to solidify, a buffer layer 25 may be additionally provided on (For example, adhesively bonded with glue or a hot-melt adhesive to) the outer side of the second surface sheet 22. After the cardboard 2 is folded into a corrugated box, the buffer layer 25 constitutes the inner side of the corrugated box (i.e., the side facing the goods in the box). The buffer layer 25 may be a pad made of a foamed material such as expandable polyethylene (EPE). EPE is anti-static, impact-resistant, shock-absorbent, resistant to deformation, recyclable, and therefore helpful in improving thermal, electrical, and acoustic insulation of the cardboard 2 (and of the corrugated box made thereof).

[0024] To make the cardboard 2 even more resistant to impact, the buffer layer 25 may be formed by multiple layers of foamed materials. For example, based on the densities of the foamed materials used, the second surface sheet 22 may be adhesively bonded with a high-density foamed material, a medium-density foamed material, and a low-density foamed material (For example, EPE), in that order. The thickness of the multilayer buffer layer 25 may range from 2 cm to 6 cm. This buffer layer 25 can greatly increase the structural strength and pressure-bearing capacity (together with thermal and acoustic insulation) of the cardboard 2 so that a corrugated box formed by the cardboard 2 is less likely to deform, tear, or break when subjected to external impact.

[0025] Referring again to FIG. 2, the direction in which the intermediate core material 23 extends in a wavy manner is referred to as the corrugation direction of corrugated cardboard. The edge opening 201 is formed along an edge of the cardboard 2 that is parallel to the corrugation direction, whereas a corrugation-direction opening 202 is formed along an edge of the cardboard 2 that is perpendicular to the corrugation direction. Both the edge opening 201 and the corrugation-direction opening 202 are in communication with the interstitial spaces 20. In the preferred embodiment of the present invention, the edge-sealing structure 3 is preferentially provided in the edge opening 201, which is more open and hence more susceptible to moisture than the corrugation-direction opening 202. To achieve thorough water tightness, an additional edge-sealing structure 3 may be provided, in the same way as described above, in a portion of the interstitial spaces 20 that is adjacent to the corrugation-direction opening 202. When all the edges of the cardboard 2 are sealed by their respective edge-sealing structures 3, air circulation between the interior of the cardboard 2 and the outside is cut off to provide even higher thermal insulation, which is advantageous to the transport of seafood, fresh produce, wine, flowers, and other goods that need to be thermally insulated during transportation.

[0026] According to actual measurement conducted by the inventor of the present invention, an edge-sealing structure 3 created by the method disclosed herein can form a perfectly watertight protective layer when its thickness is about 1 to 5 cm (For example, the thickness D1 of the adhesive mixture 31 is 1 to 2 cm, and so is the thickness D2 of the sealing mixture 32). It can therefore be inferred that the hot-melt adhesive and the wax are not required in large quantities. Compared with the conventional approach of submerging an entire piece of cardboard in wax, the present invention features a significant reduction in cost so that corrugated boxes can achieve higher resistance to moisture at lower cost than those made of the conventional corrugated cardboard.

[0027] Aside from being folded into corrugated boxes for use in freight transport, the cardboard 2 of the present invention may function as a building material as well. Thanks to the edge-sealing structure 3, the waterproof layer 24, and the buffer layer 25, the cardboard 2 performs well in terms of waterproofness, thermal and acoustic insulation, impact resistance, and pressure bearing while staying lightweight, and this combination of advantageous properties allows the resulting building material to be used flexibly (For example, to impart thermal insulation and moisture resistance to a wall of a building).

[0028] The embodiment described above is but a preferred one of the present invention and does not impose limitation on the technical features of the invention. All equivalent changes based on the technical contents disclosed herein and readily conceivable by a person of ordinary skill in the art should fall within the scope of the present invention.