NL2008872C2 - Biodegradable composite paper materials. - Google Patents

Description

BIODEGRADABLE COMPOSITE PAPER MATERIALS FIELD OF THE INVENTION

The present invention relates to a biodegradable multilayered paperboard 5 composite for folding cartons. The present invention further relates to a process for the manufacture of such composite materials, and to containers comprising the novel composite materials.

BACKGROUND OF THE INVENTION

Laminated paperboard materials are ubiquitously used. They are usually 10 multiply composites prepared by lamination of cartonboard with aluminium foil or optionally metallised polymeric materials, such as polyethylene terephthalate (PET) or similar polyesters, or polyolefins, which provide the composite material with a highly glossy surface, as for instance disclosed in US-A-3,972,467, GB-A-1218042 or US-A-3,416,411. Recent approaches to make such materials biodegradable 15 typically involve the use of biodegradable polymers instead of the PET, as for instance the laminate disclosed in US-A-6312823.

For metallised folding box applications, usually a cartonboard grade referred to as white back Folding Box Board, also referred herein as GD 1, GD 2, GC1 and GC2, in line with DIN 19303 is employed, which typically is a white back multiply 20 construction prepared from layers of mechanical pulp sandwiched between layers of bleached chemical pulp, which are kaolinite pigment coated on the outside layer. GC refers to virgin fibre board, while GD contains recycling fibres.

The white back cartonboard is usually an off-machine cast coated cartonboard, which has been calendered by highly polished chromium plated 25 cylinder to give a very high gloss and/or coloured finish. Typically, such cartonboards, which is at least single-sidedly coated with a kaolinite coating, and of a grammage of 160 to 350 grams per square meter (g/m2)are employed, onto which a vacuum metallised PET foil of typically 12 pm thickness is laminated with a suitable adhesive.

The role of the cartonboard in such composites is largely to provide 30 mechanical properties, such as stiffness at a given flexibility and printability, which requires the use single-sidedly coated cartonboard of a sufficiently high thickness.

While ubiquitously employed, the metallised polyester foil/cartonboard composites are however not easily, or not at all biodegradable, while also not recyclable due to the differing nature of its components. Yet further, as polyester 2 material is typically based on petrochemicals, the material is not sustainably long term available. Yet further, the cardboard is required to be a sufficiently high thickness, since the mechanical strength of the material is largely dictated by the stiffness of the cardboard component, while the polyester foil primarily increases 5 tensile strength. However, the PET surface, due to the inherent low surface tension, may cause issues during overprinting.

Accordingly, there remains the need for a composite material for flexible coating, which is overprintable, but also fully biologically degradable, as well as fully recyclable.

10 SUMMARY OF THE INVENTION

The present invention relates to a biodegradable multilayer laminate for flexible product packaging, comprising: a cardboard layer; and (b) a non-woven base material layer comprising cellulosic material, further comprising a metal layer having a thickness of in the range of from 10 to 250 nm deposited on a first surface, wherein 15 the non-woven base material layer is laminated to the cardboard layer on a second, non-metalized surface.

The present invention further pertains to a process for preparing a multilayered cardboard material for folding box packaging according to any one of claims 1 to 7, comprising the steps of: i) applying a metal layer by vacuum vapour 20 deposition on a non-woven substrate, and ii) laminating a cardboard substrate to the non-woven substrate on the non-metalized surface; and to the materials and boxes thus obtainable.

The cardboard layer according to the invention preferably has a gram mage in the range of from 200 to 500 g/m2 according to ISO EN536.

25 Short Description of the Figures

Figure 1 depicts the layer built-up of a preferred embodiment of the subject invention. Herein, a laminate (1) is composed of a cardboard layer 13, an intermediate bonding layer 14, a paper layer 12 and a metal layer 11.

Detailed Description of the Invention 30 The present invention provides for laminates that are not only biodegradable, but at the same time also permit to reduce the laminated weight due to the higher inherent stiffness at lower layer thickness; it allows easy embossing, provide for a high scratch resistance due to the higher surface hardness of the paper layer. It further also allows the use of easily obtainable grades of carton board and/or paper 3 that do not require extensive bleaching and can use more recycled fibres, thereby improving the environmental foot print of such materials, as exemplified by the use of thin GK carton board instead of thicker GD or GC1/S or GC2/S grade carton boards.

The non-woven sheetlike substrate (b) preferably is a single side coated sheet-5 like non-woven cellulosic material, or a double side coated sheet-like non-woven cellulosic material, more preferably C1/S and C2/S paper or cardboard. The non-woven material preferably comprises a cellulosic material, preferably paper of cardboard.

The non-woven sheetlike substrate preferably comprises a layer of paper or 10 other cellulose-based material. The layer preferably has a grammage of from 20 to 134 g/m2, preferably from 30 to 130 g/m2, more preferably from 40 to 70 g/m2, yet more preferably of from 45 to 65 g/m2, and most preferably of from 50 to 55 g/m2.

The paper or other cellulose-based material may be unbleached, or bleached, and preferably is coated. It may further carry one or more coating layers, but 15 preferably only has been coated with a kaolinite (clay) coating prior to the metalizing step.

Typical coated paper materials include so-called C/1S and C/2S papers, which is used to indicate on which side of a particular paper a coating is applied. C/1S indicates "coated on one side." C/2S indicates "coated on two sides”.

20 The paper material preferably is approved for use with the food materials to be packaged, such as by FDA approval. The front side, i.e. the side facing the outside of the container, may advantageously be printed in conventional offset, flexo or gravure print.

The metal layer preferably is deposited by a physical vapour deposition process 25 onto the non-woven base material prior to the lamination.

Paper or carton or card board bulk density can typically be calculated by dividing the grammage by the caliper (also known as base weight, and thickness respectively). The latter are term typically used in the pulp and paper industry to denote a measure of mass of the product per unit of area for a type of paper or 30 paperboard.

The term "bulk density" is not used in its traditional sense of mass per unit volume. "Paper density", rather, is a measure of the area density.

In the pulp and paper industry, it is common to set a commercial paper machine to produce paper to a target paper density. Paper density can also be used to 4 distinguish paper from paperboard as the latter usually has a grammage greater than 134 g/m2. whereas paper has a grammage of 134 g/m2 or below.

Typically, the cardboard according to the present invention has a grammage in 5 the range of from 200 to 500 g/m2, preferably in the range of from 250 to 400 g/m2, as determined according to ISO EN536, and expressed in grams per square metre.

The caliper or thickness of the card board is preferably in the range of from 200 to 600 pm, more preferably in the range of from 225 to 575 pm, as measured according to EN 20534, and expressed in micrometres. The cardboard layer is 10 preferably an unbleached, cost-efficient cardboard, such as GK (“Graukarton” = grey cartonboard) unbleached card board. Such materials are known as GK unlined grey board, or calendered GK unlined grey board. The overall bulk density of the cardboard material according to the invention is preferably in the range of from 1.0 to 4.0, as determined according to EN 20534.

15 The choice of layer combinations imparts flexibility in the manufacturing of a laminated material according to the invention. In some cases, it may be desired to have the more natural appearance of a more brownish coloured cardboard towards the inside, whereby an unbleached paper may be chosen also for the second, outer paper layer.

20 The vacuum deposited metal typically adheres to the surface of the non- woven material. The resulting metal coating thickness typically is in a range of from 40-3000 Angstrom, preferably at least 50, more preferably at least 100 Angstrom, but may generally be in the range of from 10 to 250 nm.

The metal layer preferably comprises aluminium. Other metals or alloys may 25 be employed where desired, with aluminium being the most preferred.

The non-woven material typically is coated prior to printing. Preferably the material is coated prior to the metallizing step, and the metal layer then coated with a topcoat prior to overprinting.

The application process of the coating to a substrate is preferably done by 30 means of one or more optionally engraved cylinders, ensuring the right amount of drying energy and humidification steps are applied to the substrate. The machine may use corona treatment to regulate the surface energy of the substrate prior to coating. The engraved cylinder(s) are preferably housed in a closed chamber, more preferably in overpressure, and advantageously use doctor blades for the application.

5

The application may be performed in a single, double, or multiple layers, preferably in a single or double layer.

The above described laminate structure may also comprise one or more additional layers wherein these layers may independently comprise a further barrier 5 coating, and an adhesive or tie material.

The non-woven sheetlike substrate preferably is laminated to the cardboard layer. This may advantageously be achieved by the use of an intermediate bonding layer.

The intermediate bonding layer may be an adhesive layer or coating, either 10 solvent borne, water borne, such as highly biodegradable adhesive materials, e.g. starch based adhesives, or neat. Preferably, according to a particularly cost-efficient and simple embodiment of the laminated material, the intermediate bonding layer is a layer of an extrusion laminated thermoplastic polymer, preferably a heat melt polyolefin copolymer, e.g. a coextrudable polyethylene copolymer that is also 15 biodegradable.

The present invention further relates to a process for preparing a multilayered cardboard material for folding box packaging, comprising the steps of: i) applying a metal layer by vacuum vapour deposition on a non-woven substrate, and ii) laminating a cardboard substrate to the non-woven substrate on the non-metalized 20 surface. Preferably, the non-woven base material is a single sidedly coated sheetlike non-woven cellulosic material, or a double side coated sheet-like non-woven cellulosic material. It may comprise fibrous material such as tissue, paper or cardboard.

The non-woven base layer is preferably subjected to a high vacuum 25 metallization process to coat the exposed coating layer surface with a thin metallic surface of a metal. In this high vacuum metalizing process, the metal is vaporized and deposited on the substrate. Aluminium is particularly well suited for this invention, but other metals such as silver, tin, zinc, gold, platinum, titanium, gold, lead, nickel and tantalum, as well as alloys thereof, such as chromium titanium may also 30 preferably be employed.

The metallic layer may serve a number of functions besides its decorative purpose, since it creates a brilliant metallic surface. Applicants have found that the combination of a first coating layer according to the invention, followed by the metal 6 layer serves as a barrier coating which permits a simple paper MVTR and OTR values that are otherwise not achievable for coated paper materials.

The deposited metal adheres to the surface of the first coating. The resulting metal coating thickness typically is in a range of from 40-3000 Angstrom, preferably 5 at least 50, more preferably at least 100 Angstrom, but may generally be in the range of from 10 to 250 nm.

The resulting metal-coated substrates may be prone to oxidation, which may cause adherence problems in subsequent treatments and applications, for instance label printing. Furthermore, the surface is prone to scratching or damages.

10 Accordingly, in order to convert the metallised substrate obtained in step i) into an easily overprintable substrate, a topcoat, mostly a clear coat, may advantageously be applied to the metallised substrate in optional step iii). Suitable clear coats are for instance disclosed in US3,677,792 and WO00/77300. Preferably, the metallised substrate may be subjected to calendaring to increase smoothness 15 prior to, after the base coat application, or after the metallization step. The prefarbly highly overprintable top coat is applied to the surface of the metallic layer to enhance its printability and to reduce potential corrosion. The top coat may be a solvent based coating, a water based coating or otherwise based coating. The topcoat is chosen such that it preferably does not affect the metal layer, the base coat, or the substrate 20 in any significant way, thus avoiding for instance delamination or corrosion of the metal layer.

The application process of the coating to a substrate is preferably done by means of one or more optionally engraved cylinder(s), ensuring the right amount of drying energy and humidification steps are applied to the substrate. The machine 25 may use corona treatment to regulate the surface energy of the substrate prior to coating. The engraved cylinder(s) are preferably housed in a closed chamber, more preferably in overpressure, and advantageously use doctor blades for the application. The application may be performed in a single, double, or multiple layers, preferably in a single or double layer.

30 The topcoat preferably provides the sheet with physical characteristics that result in a final sheet having the desired characteristics of good appearance, high gloss, high metal adhesion, satisfactory printability, high wet rub, high dry and wet flexibility, and other factors such as low wet expansivity, curl stability, corrosion resistance, excellent ink retention, and/or short wash off/deglueing. Yet further, the 7 topcoat should be overprintable, i.e. allow application of printing inks in any suitable printing process, without causing compatibility issues or defaults, such as wetting problems. The overprintability of topcoats is an important issue in the area of packaging and labelling in applications such as ink printing, hot foil stamping and 5 thermal transfer printing.

Clear coats usually applied for metallized substrates are known to be difficult to overprint, due to the inherent low surface tension, and the potential presence of waxes and silicone additives as flowing aids and/or defoamers in the formulations. Accordingly, the top coat employed in the present process is overprintable, i.e. 10 providing good adhesion to inks when printed onto the topcoat and properly cured, and substantially without surface defects.

The top coat typically has a dry thickness of between 10 pm and 0.5 pm, preferably less than 5 pm, more preferably less than 4 pm, and most preferably less than 3 pm. The top coat preferably has a dry thickness of at least 0.5 pm, more 15 preferably at least 0.6 pm, and most preferably at least 0.7 pm. The top coat typically is applied at a solids content of between 6 and 0.5 g/m2, preferably between 3 and 0.6 g/m2, more preferably between 2 and 0.85 g/m2. The process further comprises overprinting the metal layer of top coat, either after lamination or, before; which is typically employed to print brand and product names, as well as techyncial 20 specifications onto the packaging.

The process further preferably comprising cutting, embossing and/or perforating the thus obtained sheetlike structure.

The thus obtainable cut-outs may be folded to obtain one or more folded packaging boxes. The present invention also relates to the use of a substrate or 25 packaging according to the invention for the preparation of folding boxes. The term folding boxes herein refers to any kind of packaging that involves folding up a sheetlike sturcure, e.g. rectangular boxes, such as for medication or personal hygiene products and/or banderols such as those for food and bottle packaging.

Those skilled in the art will appreciate that the invention described herein is 30 susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

Claims (18)

A biodegradable multi-layer laminate for a flexible packaging of products, comprising: (a) a cardboard layer; and (b) a non-woven layer of base material comprising cellulose material, and furthermore provided with a metal layer having a thickness in the range of 10-250 nm and deposited on a first surface, the non-woven layer base material on the cardboard layer is laminated on a second, non-metallized surface. 10 The laminate of claim 1, wherein the cardboard layer has a specific density that is in the range of 200-500 g / m2 in accordance with ISO EN536. 3. Laminate according to claim 1 or claim 2, wherein the metal layer comprises aluminum and alloys thereof. 4. Laminate according to any one of the preceding claims, wherein the metal layer was deposited on the non-woven base material by using a physical vapor deposition method, and this before the lamination. 20 A laminate according to any one of the preceding claims, wherein the non-woven material is a one-sided, sheet-shaped, non-woven cellulosic material, or a two-sided, sheet-shaped, non-woven cellulosic material. The laminate of claim 5, further comprising an overprintable top coating layer on the metal layer. A laminate according to any one of the preceding claims, wherein the non-woven layer of base material has a specific density of 20-80 g / m2. 30 A laminate according to any one of the preceding claims, wherein the metallized layer of base material is laminated to the cardboard layer by using an intermediate adhesive layer. The laminate according to claim 8, wherein the intermediate adhesive layer comprises a thermal adhesive based on a solvent or based on water. A method for preparing a multi-layer cardboard material for a packaging folding box according to any one of claims 1-8, comprising the steps of: i. applying a metal layer to a non-woven sheet-shaped material by using a vacuum vapor deposition; and ii. laminating a cardboard substrate to the non-woven material on the non-metallized surface. The method of claim 10, wherein the non-woven material is one-sided, sheet-shaped, non-woven cellulosic material, or is a two-sided, sheet-shaped, non-woven cellulosic material. 12. A method according to claim 11, wherein the non-woven material contains fibrous material such as fabric, paper, or cardboard. The method of any one of claims 10-12, wherein the metal comprises aluminum, alloys, and / or combinations thereof. A method according to any of claims 10-13, further comprising applying a top coating layer to the metallized side of the non-woven material as obtained in step i). 15. Method as claimed in any of the claims 10-14, further comprising overprinting the top coating layer. A method according to any one of claims 10-15, further comprising cutting, punching, and / or perforating the thus obtained sheet-like structure. The method of claim 16, further comprising folding the cut, punched, and / or perforated material to obtain a folded package box. 18. Use of a substrate or of a package according to any one of claims 1-9, for preparing folding boxes.