TITLE

VERSATILE PRINTABLE TOPLINER

TECHNICAL FIELD

The present invention relates to a topliner that can be printed, either before or after being laminated, through digital printing and at least one of flexography printing (commonly known as flexo printing) and offset printing, as well as to its method of production and its use in digital printing, flexo printing or offset printing. Further, the present invention relates to a packaging material comprising said topliner, as well as a method to produce such a packaging material.

PRIOR ART

Topliner is the fibrous board that is used in the manufacture of corrugated or solid cardboards by lamination onto the outer layers of the cardboard.

In the case of corrugated cardboard, the topliner is laminated directly onto the corrugated material (open fluting material) or onto another topliner of a corrugated construction (closed fluting material), whereas in the case of solid cardboard, the topliner is laminated onto a solid core cardboard.

A typical lamination process is the reel-to-reel corrugator process, where the corrugated cardboard is formed by gluing different liner materials together. The topliner may also be laminated onto sheets of corrugated material in a so-called sheet lamination process or for lamination to solid board. Typically starch based or water based dispersion liquid adhesives are used, which have the disadvantage of wicking into the cardboard material and causing, on the one hand, the so-called "washboarding" effect (rippling of the surface of the topliner) and, on the other hand, the use of more adhesive than would be necessary, to account for the amount of absorbed and therefore "lost" adhesive.

For all lamination processes the topliner may either be printed before lamination (pre-print) or after lamination (post-print).

Nowadays, flexo printing is the most common printing technique in the field of corrugated cardboard and consequentially has the highest market share. It is mainly applied in large scale production since the costs per print unit are lower for bigger print runs. In some cases, offset printing may be used also in the field of corrugated cardboard, but the market share for offset printing is low compared to flexo printing.

Currently, digital ink jet printing has a small market share in the overall field of cardboard applications but this share is growing significantly, in particular in food contact applications such as trays or packaging where water based inks are preferred. Digital printing is particularly interesting both for small print jobs and for print jobs with integrated variable data printing were each unit can have a different printing.

Inkjet printers are available for digital post-print of the laminated corrugated constructions and for digital pre-print of the topliner, which is then laminated on a corrugator or in a sheet lamination process. One of the major advantages of digital pre-print in comparison to flexo pre-print is the possibility of easily combining different print jobs on a single pre-printed topliner reel, which is then laminated on a corrugator, because digital printing does not require changing a print plate to change the print image.

Thus, as a further advantage, the print job change broke and downtime can be reduced significantly for the corrugated material production when using digital printing, especially for print jobs with a low number of print units.

The coexistence of several printing techniques in the industry leads to inefficiency in the sense that on the one hand, producers of topliners must cater to the various technical needs of the market using several and incompatible printing techniques, while cardboard producers must keep an ample inventory of different topliners to be able to provide the needed end-consumer cardboard that is ordered. Alternatively, in order to reduce the need for keeping multiple topliners in stock, it is possible to "upgrade" a topliner optimized for flexo printing to a topliner that can reasonably be printed via digital printing by applying a primer coating optimized for ink jet printing inks on top of the topliner optimized for flexo printing. This allows keeping only one paper quality (optimized for flexo printing) in stock for both printing techniques, but increases the cost of digital printing since these primer coatings are very expensive.

While in theory, the problem of optimizing an ink receptive coating layer in order to provide acceptable printing results for both flexo and digital printing seems that it could be solved in one and the same ink receptive layer, given that both flexo and inkjet printing inks are water based, in real world practice the ink fixing agents required for the inkjet printing inks have been found to interfere with water-based flexo inks by destabilizing them and leading to deposits in the flexo printing stations.

There exists thus a need to provide a solution to the above problems, in which market needs of cardboard producers like corrugated cardboard or solid cardboard producers and end- consumers can be addressed more efficiently.

SUMMARY OF THE INVENTION

The present invention provides a topliner, that may be used in digital printing and at least one of flexo printing and offset printing, be it in pre- or post-printing, and which allows for more efficient manufacture of printed cardboard, either corrugated or not corrugated.

It is an object of the present invention to provide a topliner comprising a fibrous substrate, said fibrous substrate having two sides, a first ink receptive coating layer and a second ink receptive coating layer, wherein the first ink receptive layer is optimized for offset and/or flexographic printing and wherein the second ink receptive coating layer is optimized for receiving inkjet printing inks, characterized in that, the first ink receptive coating layer is located on one side of the fibrous substrate, and the second ink receptive coating layer is located on the opposite side of the fibrous substrate.

In an embodiment of the topliner of the present invention, the second ink receptive coating layer comprises a ink fixing agent and optionally a pigment, wherein if present, preferably the pigment is comprised in an amount of at least 45 weight percent, based on the total dry weight of the second ink receptive coating layer.

In a further embodiment of the topliner of the present invention, the first and the second ink receptive coating layer comprise a pigment, preferably the same pigment.

It is further an object of the present invention to provide a packaging material, in particular a boxboard or containerboard, comprising a topliner as described above.

It is also an object of the present invention to provide a process for producing a topliner according to the above, wherein the process includes the steps of:

- providing a fibrous substrate, preferably having a grammage of from 70 to 190 g/m2;

- applying a first ink receptive coating layer on one side of the fibrous substrate,

- applying a second ink receptive coating layer on the other side of the fibrous substrate, wherein the first and second ink receptive coating layer are preferably applied using a size press, film press, blade coater or curtain coater.

It is further an object of the present invention to provide a packaging material, in particular a boxboard or containerboard, comprising a topliner as described above laminated to a packaging material precursor.

It is another object of the present invention to provide a process for producing a packaging material, in particular a boxboard or corrugated cardboard, wherein the process includes the steps of: providing a topliner as described above; laminating, using a liquid adhesive, a side of the topliner to a packaging precursor, wherein the ink receptive coating layer on the side of the topliner that is laminated to the packaging precursor is not printed, and hardening the liquid adhesive to form a packaging material.

It is further an object of the present invention to provide a use of a topliner as described above in a packaging material as described above or in a process for producing a packaging material as described above.

Further embodiments of the invention are laid down in the dependent claims.

DESCRIPTION OF PREFERRED EMBODIMENTS

It is an object of the present invention to provide a topliner comprising a fibrous substrate, a first ink receptive coating layer and a second ink receptive coating layer, wherein the first ink receptive layer is optimized for offset and/or flexographic printing and wherein the second ink receptive coating layer is optimized for receiving inkjet printing inks, characterized in that, the first ink receptive coating layer is located on one side of the fibrous substrate, and the second ink receptive coating layer is located on the opposite side of the fibrous substrate.

The topliner according to the present invention can be used in inkjet printing, and at least one of flexo printing and offset printing, by orienting the topliner accordingly and exposing the corresponding ink receptive coating layer to the printer, as needed.

Suitable fibrous substrates that may be used in the topliner of the present invention may have a grammage of from 70 to 190 g/m ² , preferably of from 80 to 135 g/m ² .

The fibrous substrate may comprise, and may be produced by providing papermaking furnish comprising, hardwood fibers, softwood fibers, or a combination of hardwood and softwood fibers. The fibers may be derived from hardwood and softwood via the kraft or sulfite pulping process, and may be bleached or unbleached. Alternatively, the fibers may be derived from hardwood and softwood using mechanical, chemical or thermomechanical pulping methods. In one embodiment of the topliner according to the present invention, the fibrous substrate comprises a mixture of sulfate pulp and sulphite pulp, which pulps may be independently bleached or unbleached.

The fibers may be virgin fibers or may be recycled fibers, or a mixture of both.

The fibrous substrate may comprise other conventional materials known in the art of paperboard and cardboard production, such as starch, fillers, sizing chemicals and reinforcing polymers can also be included in the papermaking raw materials.

In an embodiment of the topliner of the present invention, the second ink receptive coating layer comprises an ink fixing agent and optionally a pigment. Usually, an ink receptive layer that is suitable for digital printing must comprise a digital printing primer layer free from pigments and which comprises an ink fixing agent. One reason for the absence of pigments is that the digital printing primer is often applied through fine nozzles in the same fashion as the ink that is deposited on the substrate - the pigments would clog and deteriorate the nozzle orifices. Thus, the second ink receptive layer differs in that respect from existing primer layers used in digital printing. The inclusion of a pigment into the second ink receptive layer is therefore not required perse in the second ink receptive coating layer, but leads to several advantages:

During the lamination step of the process to produce a cardboard, be it laminating the topliner directly onto the corrugated material (open fluting material) or onto another topliner of a corrugated material construction (closed fluting material), or be it laminating the topliner onto a solid core cardboard, the inclusion of pigment allows the use of less adhesive. The reason for less adhesive being needed during the lamination step is that the second ink receptive coating layer, by virtue of the pigment contained in it, also acts as a barrier layer against the liquid adhesive and minimizes penetration of the liquid adhesive into the bulk of the topliner, reducing washboarding and consequently reducing the amount of liquid adhesive needed.

It is noted that washboarding is even further amplified during post-printing, i.e. when the adhered topliner is printed on, instead of it being printed before the lamination step.

As an added value, using the pigment in the second ink receptive coating layer allows to reduce the amount of ink fixing agent in the second ink receptive coating layer, which is needed in the second ink receptive coating layer for correctly bonding the water-based inks used in digital printing and which drives the cost of the topliner up.

In another embodiment of the topliner of the present invention, the second ink receptive coating layer comprises an ink fixing agent and is essentially free of pigment.

The first ink receptive coating layer, which is optimized for offset and/or flexo printing, comprises one or more binders, one or more pigments as well as one or more additives.

Suitable binders that may be used in the first ink receptive coating layer may be chosen among starch, polymer latexes and polymer solutions. Suitable polymer latexes may be styrene butadiene latex or styrene acrylate latex. Suitable polymer solutions are PVOH solutions.

Suitable pigments that may be used in the first ink receptive coating layer may be pigments known in the art of paper coatings, in particular mineral pigments such as ground calcium carbonate, precipitated calcium carbonate, clay or kaolin, talc and the like.

Suitable additives that may be used in the first ink receptive coating layer may be additives such as rheology additives, surface tension additives, crosslinking additives and optical brightening additives.

The dry coating weight of the first ink receptive coating layer may be of from 1.5 to 15 g/m ² , or of from 1.5 to 5 g/m ² .

The second ink receptive coating layer, which is optimized for digital printing, comprises one or more ink fixing agent, optionally one or more pigments, one or more binders as well as optionally one or more additives. The application of the second ink receptive coating layer allows the producer of cardboard to omit a separate, and costly, application of a dedicated primer coating for digital inkjet printing printing, since the topliner, if oriented correctly, allows for its use as-is in digital inkjet pre- or post-printing.

Suitable ink fixing agents agents that may be used in the second ink receptive coating layer may be salts comprising metal ions such as for example Mg, Ca or Na, or other metal ions. In general, salts comprising metal ions may be comprised in the second ink receptive layer in an amount of at least 1 weight percent or of from about 1 to about 25 % weight percent, in an amount of at least 2 weight percent or from about 2 to 5 weight percent, based on the total dry weight of the second ink receptive coating layer or the total dry weight of the combined amounts of binder and pigment.

Suitable binders that may be used in the second ink receptive coating layer may be chosen among starch, polymer latexes and polymer solutions. Suitable polymer latexes may be styrene butadiene late or styrene acrylate latex. Suitable polymer solutions are PVOH solutions.

Suitable pigments that may be used in the second ink receptive coating layer may be pigments known in the art of paper coatings, in particular mineral pigments such as ground calcium carbonate, precipitated calcium carbonate, clay or kaolin, talc and the like.

Suitable additives that may be used in the second ink receptive coating layer may be additives such as rheology additives, surface tension additives, crosslinking additives, anti foaming agents, dyes, and optical brightening additives.

The second ink receptive coating layer may or may not comprises a pigment, since the pigment is not necessarily required for digital printing, and in particular inkjet printing. In the case where no pigment is comprised, the second ink receptive coating layer comprises one or more ink fixing agent and one or more binders, and optionally one or more additives, with the one or more binder being preferably comprised in an amount of more than 50 weight percent, more preferably more than 75 weight percent and up to 95 weight percent, based on the total dry weight of the second ink receptive coating layer

In a preferred embodiment of the second ink receptive coating layer not comprising a pigment, the binder may be starch and is preferably starch and/or the second ink receptive coating layer not comprising a pigment has dry coating weight of about 1 to 2.5 g/m ² .

In the case where the second ink receptive coating layer comprises a pigment the second ink receptive coating layer comprises one or more ink fixing agent, one or more pigments, one or more binders, and optionally one or more additives. In a preferred embodiment of the second ink receptive coating layer comprising a pigment, the one or more binder is preferably comprised in an amount of less than 50 weight percent, more preferably less than 45 weight percent or of from 5 to 45 weight percent, even more preferably in an amount of less than 25 weight percent or 5 to 25 weight percent, based on the total dry weight of the second ink receptive coating layer and/or the one or more pigment is comprised in an amount of more than 45 weight percent, more preferably in an amount of 45 to 90 weight percent, even more preferably in an amount of more than 70 weight percent or of 70 to 90 weight percent, based on the total dry weight of the second ink receptive coating layer.

In the case where the one or more binder is comprised in an amount of less than 25 weight percent or of 5 to 25 weight percent, based on the total dry weight of the second ink receptive coating layer and/or the one or more pigment is comprised in an amount of more than 70 weight percent or of 70 to 90 weight percent, based on the total dry weight of the second ink receptive coating layer, the dry coating weight of second ink receptive coating layer is preferably in the range of about 1 to 5 g/m ² or 5 to15 g/m ² _.

In an embodiment the one or more binder is comprised in an amount of 40 to 49 weight percent, based on the total dry weight of the second ink receptive coating layer and/or the one or more pigment is comprised in an amount of 40 to 49 weight percent, based on the total dry weight of the second ink receptive coating layer, the dry coating weight of second ink receptive coating layer is preferably in the range of about 1 to 2.5 g/m ² _.

The dry coating weight of the second ink receptive coating layer may in general be of from 1 to 15 g/m ² orof from 1 to 5 g/m ²

It is understood that, even though the first and second ink receptive coating layer share most of their components such as binders, pigments and additives, the first and second ink receptive coating layer may differ in the amounts of said components since each ink receptive coating layer will be optimized to a receive a different printing ink , and in particular to receive the printing ink via specific printing techniques. It is understood that a person skilled in the art will be able to adjust the composition and the physical-chemical properties of the ink receptive layers to a particular type of ink and/or printing technique requirement on the basis of his or her common general knowledge.

In a further embodiment of the topliner of the present invention, the first and the second ink receptive coating layer may or may not comprise a pigment, and if present, may preferably comprise the same pigment.

When both first and second ink receptive coating layer comprise a pigment, the ink receptive layer that is not printed and that is in contact with the liquid adhesive during lamination of the topliner to the cardboard precursor material acts as a barrier layer against the liquid adhesive and wicking of the liquid adhesive into the bulk of the topliner, reducing washboarding and the amount of liquid adhesive needed.

The liquid adhesive used during the lamination is generally an aqueous liquid adhesive. The adhesive agent within the liquid adhesive may be chosen, for example, from starch or glue.

It is also an object of the present invention to provide a process for producing a topliner according to the above, wherein the process includes the steps of:

- providing a fibrous substrate, preferably having a grammage of from 70 to 190 g/m2;

- applying a first ink receptive coating layer on one side of the fibrous substrate,

- applying a second ink receptive coating layer on the other side of the fibrous substrate, wherein the first and second ink receptive coating layer are preferably applied using a size press, film press, blade coater or curtain coater.

The step of applying the first ink receptive coating layer on one side of the fibrous substrate may be carried out on-line in a paper machine or may be carried out off-line, after production of the fibrous substrate in a dedicated coater of the above-mentioned type.

In a preferred embodiment of the process for producing a topliner, the first ink receptive coating layer is applied in an amount of 1.5 to 15 g/m ² ; or of 1.5 to 5 g/m ² .

In a preferred embodiment of the process for producing a topliner, the second ink receptive coating layer is applied in an amount of 1.5 to 15 g/m ² ; or of 1.5 to 5 g/m ² .

It is further an object of the present invention to provide a packaging material, in particular a boxboard or containerboard, comprising a topliner as described above, laminated to a packaging material precursor. The packaging material may be printed, in case the topliner comprised in the packaging material was pre-printed or in case the topliner comprised in the packaging material was printed after the lamination of the topliner, or the packaging material may be not printed.

In general, only one side of a packaging material is printed and thus it is understood that the topliner will be laminated to at least one of the sides of a packaging material precursor. However, there exist applications where the both sides of a packaging material are printed and thus it is understood that a topliner may then be laminated to each one of both sides of a packaging material precursor. In one embodiment of a packaging material, one side of the packaging material exhibits a topliner according to the present invention such that the first ink receptive coating layer is facing the packaging precursor material and the opposite side exhibits a topliner according to the present invention such that the second ink receptive coating layer is facing the packaging precursor material, This allows to provide a packaging material that is printed, or that may be printed, by flexo or offset printing on one side and with inkjet printing on the opposite side.

Thus, the packaging material can be formed into a container, where the exterior surface is printed by flexo or offset printing with a generic print image and the interior surface is printed by inkjet printing with a personalized print image.

The packaging material precursor will depended on the packaging material to be produced.

In the case where the packaging material is a boxboard, the packaging precursor material may be a solid core cardboard, which may comprise one cardboard sheet or more cardboard sheets bonded to each other. The cardboard sheets may have different compositions with respect to the type of pulp fiber used, depending on the intended use of the packaging material. The solid core cardboard may further comprise one or more coating layers that are in general applied during the production of the solid core cardboard to impart a given functionality.

In one embodiment of the packaging material, the packaging material may be a boxboard. In particular, the packaging material may be folding boxboard, also referred to as FBB, solid bleached board also referred to as SBB, solid unbleached board, also referred to as SUB, or white-lined chipboard also referred to as WLC, GD, GT or UD.

In one embodiment of the packaging material, the boxboard includes a solid core cardboard as the packaging material precursor and at least one topliner according to the present invention.

In one embodiment of the packaging material, the boxboard includes a solid core cardboard as the packaging material precursor and one topliner according to the present invention, which topliner according to the present invention is adhered to one side of the solid core cardboard. It is understood that in addition to the topliner according to the present invention, the boxboard may include one or more standard liner(s), which standard liner(s) may be adhered to the solid core cardboard of the boxboard and adhered to a topliner according to the present invention and/or may be adhered to the solid core cardboard on the side opposite the side where the topliner according to the present invention is adhered.

Examples of a cross-section of such a packaging material would be:

"2-layer" boxboard:

'3-layer" boxboard:

'4-layer" boxboard:

In one embodiment of the packaging material, the boxboard includes two topliners according to the present invention, where one topliner is adhered to each side of the boxboard. It is understood that in addition to the two topliner according to the present inventions, the boxboards may include one, two, or more standard liners, which standard liner(s), which standard liner(s) may be adhered to the solid core cardboard of the boxboard and adhered to a topliner according to the present invention.

Examples of a cross-section of such a packaging material would be:

"3-layer" boxboard:

In the case where the packaging material is a corrugated fiberboard, the packaging precursor material may be a corrugated medium, or containerboard, i.e. a material consisting of a standard liner bonded to a corrugated medium on one side or a material consisting of a standard liner bonded to a corrugated medium on each side. The standard liner and the corrugated medium may have different compositions with respect to the type of pulp fiber used, depending on the intended use of the packaging material. The standard liner and corrugated medium may further comprise one or more coating layers that are in general applied during the production of the solid core cardboard to impart a given functionality.

In one embodiment of the packaging material, the packaging material may be a corrugated fiberboard, which includes at least one topliner according to the present invention and a corrugated medium, or fluting, where said topliner is adhered to one side of the corrugated medium. The packaging material may or may not include further a standard liner, i.e. a standard liner that is not coated with a first and second ink receptive coating layer, on the side opposite the side where the topliner according to the present invention is adhered to the corrugated medium. Two examples of a cross-section of such a packaging material would be:

"3-layer" corrugated fiberboard:

"2-layer" corrugated fiberboard:

In one embodiment of the packaging material, the packaging material may be a corrugated fiberboard, which includes at least one topliner according to the present invention, one or more standard liner, and a corrugated medium, or fluting, where the topliner according to the present invention is adhered to a standard liner adhered to one side of the corrugated medium. The packaging material may or may not include further standard liners, e.g. a standard liner that is not coated with a first and second ink receptive coating layer, on the side opposite the side where the topliner according to the present invention is adhered to the standard liner adhered to one side of the corrugated medium. Two examples of a cross- section of such a packaging material would be:

"4-layer" corrugated fiberboard:

"3-layer" corrugated fiberboard:

In one embodiment of the packaging material, the packaging material may be a corrugated fiberboard, which includes two topliners according to the present invention and a corrugated medium, or fluting, where each topliner is adhered to one of the side of the corrugated medium. One examples of a cross-section of such a packaging material would be:

"3-layer" corrugated fiberboard:

In one embodiment of the packaging material, the packaging material may be a corrugated fiberboard, which includes two topliners according to the present invention and a corrugated medium, or fluting, where at least one topliner according to the present invention is adhered to a standard liner adhered to one side of the corrugated medium, or where each topliner according to the present invention is adhered to a standard liner adhered to one of the two sides of the corrugated medium. Two examples of a cross-section of such a packaging material would be:

’4-layer" corrugated fiberboard:

"5-layer" corrugated fiberboard:

It is further an object of the present invention to provide a process for producing a packaging material, in particular a boxboard or corrugated cardboard, wherein the process includes the steps of: providing a topliner as described above; laminating, using a liquid adhesive, a side of the topliner to a packaging precursor, wherein the ink receptive coating layer on the side of the topliner that is laminated to the packaging precursor is not printed, and hardening the liquid adhesive to form a packaging material.

The process for producing a packaging material according to the present invention may be carried out on a paper machine in-line or may be carried out by first providing the packaging material precursor, for example on a corrugator, and then laminating the topliner to the packaging material precursor.

The ink receptive coating layer on the side of the topliner that is laminated to the packaging precursor is not printed exhibits a barrier function against the liquid adhesive and thus allows to reduce the amount of liquid adhesive needed for sufficient adhesion and further allows to reduce washboarding on the printed, or to be printed, side of the topliner that is opposite the side of the topliner that is laminated to the packaging precursor.

In an embodiment of the process for producing a packaging material according to the present invention, the process includes further the steps of: before to the step of laminating the topliner to the packaging material precursor, printing one among the first ink receptive coating layer and the second ink receptive coating layer. In another embodiment of the process for producing a packaging material according to the present invention, the process includes further the steps of: after the step of laminating the topliner to the packaging material precursor, printing the ink receptive coating layer of the topliner that is opposite the side of the topliner that is laminated to the packaging precursor.

It is further an object of the present invention to provide a use of a topliner as described above in a packaging material as described above or in a process for producing a packaging material as described above.

LIST OF REFERENCE SIGNS none