EP4624657A1

EP4624657A1 - Wax-free twist wrapper

Info

Publication number: EP4624657A1
Application number: EP24167635.2A
Authority: EP
Inventors: Alessio BROCCANELLO; Simone VEZZÙ
Original assignee: Sappi Papier Holding GmbH
Current assignee: Sappi Papier Holding GmbH
Priority date: 2024-03-28
Filing date: 2024-03-28
Publication date: 2025-10-01
Anticipated expiration: 2044-03-28
Also published as: ES3062368T3; EP4624657C0; EP4624657B1; WO2025202157A1

Abstract

A wax-free printable twist wrapper having a grease resistance value of 4, or of from 4 to 12, when measured according to TAPPI Test method T559, and comprising, or consisting of, a paper substrate comprising a mixture of at least one hardwood pulp and at least one softwood pulp, said mixture having a degree of Schopper-Riegler between 35 and 50, preferably 35 and 40, and comprising at least 40 % by weight of at least one hardwood pulp, a print receiving layer on one side of the paper substrate, said print receiving layer comprising at least one binder and at least one clay pigment, and a barrier layer on the other side of the paper substrate, wherein said printable twist wrapper has a moisture content of from 5% to 15% and has a density of 1 g/cm3 or more.

Description

TECHNICAL FIELD

The present invention relates to a process for the manufacture of a wax-free twist wrapper, which may be further printable.

PRIOR ART

Sweet treats such as candies, candied fruits, caramels, toffees, chocolates and other sweets are often provided in single portions for individual consumption and packaged in a wrapper. In the context of this invention, the term "wrapper" means a paper which is suitable to be used for wrapping.
Traditionally, such wrappers have been based on paper that is imbibed in, or impregnated with, wax or a wax-like substance. The resulting waxy surface of the wrapper avoids strong adhesion of the potentially sticky candy to the wrapper and on the other hand forms a barrier layer against the sometimes greasy or oily sweets, such as chocolate-coated confections, packed therein. However, the waxy surface also makes the wrapper nearly impossible to print, which is why a wrapper must be printed prior to it being waxed. As a result, such wrappers are first provided as printable precursor wrappers, then printed on and finally waxed. This adds cost as these two separate converting steps are separated and generally not performed simultaneously. The wrapper according to the invention can advantageously replace wax solutions and plastic solutions.
When packaging sweets in conventional wrapper, the sweets are first enveloped a larger sheet of wrapper and the wrapper is the twisted at one or both ends to close the wrapper. At industrial production rates, the forces that are applied via a packaging apparatus to the ends of the wrapper are considerable, and accordingly a certain fraction of packages will have defects, which may range from a tear in the wrapper or a cracking of the print on the wrapper in the region of, or the region surrounding, the twisted portion of the wrapper.
While plastic films are printable, exhibit barrier properties and have good mechanical properties that avoid tearing during packaging, they are considered undesirable as twist wrappers because they cannot be recycled easily and because they are generally sourced from petrochemical products. On the other hand, paper-based twist wrappers that are waxed are not easily printed and cannot be recycled because of the high wax content they exhibit.
It is therefore desirable to provide a twist wrapper that is easily printable, which exhibits good mechanical properties, especially when twisted, and which exhibits good barrier properties while being easily recyclable. Furthermore, the twist wrapper should ideally be able to be used at high throughput, i.e. at speeds in excess of 1 500 candy pieces per minute, or even in excess of 2 000 candy pieces per minute.

SUMMARY OF THE INVENTION

The present invention provides a twist wrapper that is easily printable, which exhibits good mechanical properties, especially when twisted, and which exhibits good barrier properties while being easily recyclable, as well as a method to produce such a twist wrapper.
The twist wrapper according to the present invention is free of wax or wax-like substances impregnation that interfere with the printing and/or recycling of the twist wrapper, and provides printability, barrier properties, and recyclability via an alternative structure. Furthermore, the wrapper can only be printed (and requires no waxing) before being used as twist wrapper.
It is thus a first object of the present invention to provide a process for the manufacture of a wax-free printable twist wrapper having a grease resistance value of 4 or more, or of from 4 to 12, when measured according to TAPPI Test method T559, comprising the steps of:

forming a paper substrate from a paper furnish comprising paper pulp, in a paper machine, wherein the paper pulp in the paper furnish is obtained by refining a mixture of at least one hardwood pulp and at least one softwood pulp to a degree of Schopper-Riegler between 30 and 50, preferably between 35 and 40, said mixture comprising at least 40 % by weight of at least one hardwood pulp,
coating the paper on one side with a print receiving layer, said print receiving layer comprising at least one binder and at least one clay pigment,
coating the paper on the opposed side with a barrier layer to form a printable twist wrapper precursor having a moisture content of less than 5% by weight,
increasing the moisture content of the printable twist wrapper precursor to a value of more than 5% by weight, based on the weight of the printable twist wrapper precursor,
densifying the printable twist wrapper precursor and decreasing the moisture content of the printable twist wrapper precursor, such as to form a printable twist wrapper having a moisture content of from 5% to 15% and having a density of 1 g/cm³ or more, wherein preferably decreasing the moisture content is carried out at a temperature of between 75 °C and 130 °C.

It is a second object of the present invention to provide a wax-free printable twist wrapper, which may be obtained by the process according to the first object of the present invention, the wax-free printable twist wrapper having a grease resistance value of 4 or more, or of from 4 to 12, when measured according to TAPPI Test method T559 and comprising, or consisting of,

a paper substrate comprising a mixture of at least one hardwood pulp and at least one softwood pulp, said mixture having a degree of Schopper-Riegler between 35 and 50, preferably 35 and 40, and comprising at least 40 % by weight of at least one hardwood pulp,
a print receiving layer on one side of the paper substrate, said print receiving layer comprising at least one binder and at least one clay pigment, and
a barrier layer on the other side of the paper substrate,
wherein said printable twist wrapper has a moisture content of from 5% to 15% and has a density of 1 g/cm³ or more.

It is a third object of the present invention to provide a use of a wax-free printable twist wrapper according to the second object of the present invention, for twist wrapping, preferably double-twist wrapping, of a confection such as, but not limited to, hard candy or chocolate-covered confections, for example, in said wax-free printable twist wrapper.
Further embodiments of the invention are laid down in the dependent claims.

DESCRIPTION OF PREFERRED EMBODIMENTS

The process for the manufacture of a wax-free printable twist wrapper having a grease resistance value of 4 or more, or of from 4 to 12, more when measured according to TAPPI Test method T559, according to the first object of the present invention comprises the steps of:

forming a paper substrate from a paper furnish comprising paper pulp, in a paper machine, wherein the paper pulp in the paper furnish is obtained by refining a mixture of at least one hardwood pulp and at least one softwood pulp to a degree of Schopper-Riegler between 30 and 50, preferably 35 and 40, said mixture comprising at least 40 % by weight of at least one hard wood pulp,
coating the paper on one side with a print receiving layer, said print receiving layer comprising at least one binder and at least one clay pigment,
coating the paper on the opposed side with a barrier layer to form a printable twist wrapper precursor having a moisture content of less than 5% by weight,
increasing the moisture content of the printable twist wrapper precursor to a value of more than 5% by weight, based on the weight of the printable twist wrapper precursor,
densifying the printable twist wrapper precursor and decreasing the moisture content of the printable twist wrapper precursor, such as to form a printable twist wrapper having a moisture content of from 5% to 15% and having a density of 1 g/cm³ or more, wherein preferably decreasing the moisture content s carried out at a temperature of between 75 °C and 130°C.

In the step of forming a paper substrate from a paper furnish comprising paper pulp, in a paper machine, wherein the paper pulp in the paper furnish is obtained by refining a mixture of at least one hardwood pulp and at least one softwood pulp to a degree of Schopper-Riegler between 30 and 50, preferably 35 and 40, said mixture comprising at least 40 % by weight of at least one hard wood pulp. The main requirements for use as a twist wrapper are both grease resistance and tearing strength. Conventional grease resistance papers have Schopper-Riegler (°SR) value typically of more than 70. So, the SR value between 30 and 50 according to the present invention is not typical for grease resistance papers. On the one hand, pulp refining is generally expensive in terms of time and energy (and thus less economical), and in order to increase effectiveness, the use of papers having rather low Schopper-Riegler (°SR) is appreciated. However, to achieve grease resistance, in conventional grease resistance papers, the high SR value is key. On the other hand, for use as a twist wrapper, it is equally important for the paper to exhibit good tearing strength. Tearing strength is affected negatively as the Schopper-Riegler (°SR) value increases. It is therefore a challenge to decrease the SR value in order to increase tear strength, but at the same time, to balance the other properties in such way that the grease resistance could be achieved at the same time. Because twist wrappers are often printed, another challenge is to provide good flex-crack resistance, meaning that a print receiving layer and the print on it will not crack during or after twisting of the wrapper.
It is also noted, that the furnish comprising a mixture of softwood and hardwood has a technical effect of improving the mechanical resistance of the wrapper. In a way the furnish comprising a mixture of soft- and hardwood contributes also to the final TAPPI value; the effect is due to the limited penetration of the coating inside the paper.
In a preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the paper substrate according to the invention advantageously has a weight of between 35 gsm and 50 gsm. In a preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the paper substrate according to the invention advantageously has a weight of between 42 and 48 gsm.
In another preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the paper substate (i.e the still uncoated twist wrapper) has a weight of about from 25 gsm to 45 gsm, preferably of from 30 to 40 gsm. The weight, or grammage, of the paper substrate may be determined according to ISO 536, at 23 °C and 50% rel. humidity.
The paper machine may be, for example, a Fourdrinier paper machine. It will be apparent to the person of ordinary skill in the art of papermaking that other type of paper machines may be used as well.
It is understood that the paper pulp is obtained by refining a mixture of at least one hardwood pulp and at least one softwood pulp having a degree of Schopper-Riegler below 30 to a degree of Schopper-Riegler between 30 and 50. The mixture of at least one hardwood pulp and at least one softwood pulp may be refined at low or high consistency. Refining may be carried out in a refiner such as for example in a double-disc refiner, conical disc refiner of or in a conical refiner. It is understood that the furnish may further comprise further solids that are useful in paper production, in addition to mixture of at least one hardwood pulp and at least one softwood pulp. For instance, the furnish may further comprise pigments, additives, sizing agents or inorganic fillers such as for example calcium carbonate.
In a preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the mixture of at least one hardwood pulp and at least one softwood pulp has a degree of Schopper-Riegler of 35 to 50, more preferably from 35 to 45, preferably 35 and 40.
The hardwood pulp may be sourced from hardwoods such as for example birch, eucalyptus or blends of both.
The softwood pulp may be sourced from softwoods such as for example spruce, pine, or blends of both.
In general, in the manufacture of a wax-free printable twist wrapper, according to the first object of the present, the hardwood and softwood pulps are both preferably chemical pulps, such as Kraft pulp, sulfite pulp or dissolving pulp. In a preferred embodiment, the hardwood and softwood pulps are bleached hardwood and softwood pulps. Consequently, in a much-preferred embodiment of the manufacture of a wax-free printable twist wrapper, according to the first object of the present invention, both hardwood and softwood pulps are bleached chemical pulps, such as for example Bleached Softwood Kraft (BSK) and Bleached Hardwood Kraft (BHK).
In the mixture of at least one hardwood pulp and at least one softwood pulp, at least 40 % by weight are formed by the at least one hardwood pulp, and preferably at least 50 % by weight are formed by the at least one hardwood pulp. When at least 40% by weight are formed by the at least one hardwood pulp, the mixture of at least one hardwood pulp and at least one softwood pulp provides for a paper substrate and/or wax-free printable twist wrapper that has excellent mechanical properties.
In the step of coating the paper on one side with a print receiving layer, said print receiving layer comprising at least one binder and at least one clay pigment, a print receiving layer composition is applied to the paper substrate, where the print receiving layer composition is applied as liquid or slurry. Coating the paper on one side with a print receiving layer may be carried in the paper machine or may be carried out outside the paper machine in a separate coating device. While in principle, the coating the paper on one side with a print receiving layer may be carried out in either the paper machine, in particular in the forming section of the paper machine, or may be carried out outside the paper machine in a separate coating device, it has been found that coating the paper on one side with a print receiving layer is advantageous, in terms of process flexibility, because the application the print receiving layer in the paper machine frees up coating capability in an ensuing coating step outside the paper machine in a coating device. Thus, in a preferred embodiment the step of coating the paper on one side with a print receiving layer is carried out in the paper machine, in particular in the forming section.
The print receiving layer that is coated on one side of the paper comprises at least one binder and at least one clay pigment. The binder may be, for example a polymer binder such as a copolymer of styrene. Known copolymer of styrene are, for example, styrene butadiene copolymer or styrene acrylic copolymer. The clay pigment may be, for example, a kaolin.
In a preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the binder is a polymer binder such as a copolymer of styrene and more preferably is a styrene butadiene copolymer.
In a preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the clay pigment is a kaolin.
The print receiving layer composition is normally applied as liquid or slurry and will thus comprise the polymer binder in a liquified form, most commonly in the form of an emulsion or a dispersion. Likewise, the clay pigment will be suspended in the print receiving layer composition. It is understood that the print receiving layer composition may further comprise other components in addition to the binder and the pigment, such as for example biocides, dispersants, rheology modifiers and such.
In the step of coating the paper on the opposed side with a barrier layer to form a printable twist wrapper precursor having a moisture content of less than 5% by weight, a barrier layer composition is applied to the opposed side of the paper substrate, where the barrier layer composition is applied as liquid or slurry, and comprises a barrier polymer in a liquified form, most commonly in the form of an emulsion or a dispersion. Coating the paper on the opposed side with a barrier layer may be carried in the paper machine or may be carried out outside the paper machine in a separate coating device. In any case, the barrier layer is formed by drying the paper substrate coated with the barrier layer composition extensively to a moisture content of less than 5% by weight, to remove water from the barrier layer composition and enhance film formation of the barrier polymer comprised in the barrier layer composition. While in principle, the coating the paper on the opposed side with a barrier layer may be carried out in either the paper machine, in particular in the forming section of the paper machine, or may be carried out outside the paper machine in a separate coating device, it has been found that coating the paper on the opposed side with a barrier layer in a coating device is advantageous, in terms of barrier performance, because the application the barrier layer in the coating device allows a pre-coating of the paper substrate on the opposed side with a precoat layer the paper in the paper machine in a coating device. The precoat layer smoothens the roughness of the paper substrate and is applied in the paper machine. Also, precoat have a technical effect of improving the application quality when a barrier layer is applied, which means more uniform surface with less pinholes in the barrier layer. In a preferred embodiment of the present invention, the precoat layer has a weight of, between 1 gsm and 4 gsm. It is noted that when a precoat layer is comprised in the twist wrapper, the thickness of the paper substrate may be reduced accordingly. Thus, in one embodiment, the thickness of the twist wrapper is unaffected by the presence of a precoat layer. This may be because the combined thickness of the precoat layer and the paper substrate corresponds to the thickness of the paper substrate when no precoat layer is applied or because the combined thickness of the precoat layer and the barrier layer corresponds to the thickness of the barrier layer when no precoat layer is applied. Stated alternatively, the "added" thickness of a precoat layer, may in some embodiments, be absorbed by the adjoining layer, i.e. either the paper substrate layer of the barrier layer.
Thus, in a preferred embodiment of the step of coating the paper on opposed side with a barrier layer, the step of coating the paper on the opposed side with a barrier layer is carried out in a coating device, more preferably onto a precoat layer on the opposed side of the paper substrate, which precoat layer is applied in the paper machine, in particular in the forming section.
The precoat layer coated on the opposed side of the paper substrate comprises preferably a precoat composition, which composition may comprise copolymers of styrene, polymers, or copolymers of polyvinyl alcohol, or microfibrillated cellulose. For instance, the precoat layer may essentially consist of polyvinyl alcohol or of microfibrillated cellulose in some embodiments.
The twist wrapper has a grease resistance value of 4 or more, or of from 4 to 12, when measured according to TAPPI Test method T559. It is understood that the grease resistance value of the twist wrapper is determined by applying a plurality of testing liquids on the barrier layer of the twist wrapper, i.e. on the side of the wax-free printable twist wrapper bearing the barrier layer. The procedure is identical in the case where the wax-free printable twist wrapper includes a precoat layer or a print layer.
The twist wrapper has a grease resistance value of 4, or of from 4 to 12, and preferably has a grease resistance value of 5, or of from 5 to 12, and more preferably has a grease resistance value of 6, or of from 6 to 12, when measured according to TAPPI Test method T559.
In the step of increasing the moisture content of the printable twist wrapper precursor to a value of more than 5% by weight based on the weight of the printable twist wrapper precursor, the moisture content of the printable twist wrapper precursor is increased by the addition of water to the printable twist wrapper precursor. Adding water to the printable twist wrapper precursor can be achieved via sprinkling or spraying a water mist onto the printable twist wrapper precursor. The purpose of increasing the moisture content of the printable twist wrapper precursor is primarily that of preparing the printable twist wrapper precursor for the subsequent step of densification and drying. Densification is more efficiently achieved on a damp paper and drying the paper to a moisture content of between 5% and 15% requires that the paper comprises a certain "reservoir" of humidity prior to drying. Thus, the moisture content of the printable twist wrapper precursor may be increased to a value of more than 5% by weight when the target moisture in the final printable twist wrapper precursor should be approx. 5% by weight. On the other hand, the moisture content of the printable twist wrapper precursor may be increased to a value of more than 10% by weight when the target moisture in the final printable twist wrapper precursor should be approx. 10% by weight, and so on. Therefore, in some embodiments of the first object of the present invention, the moisture content of the printable twist wrapper precursor may be increased to a value of more than 5, 8, 11, 14, 15 or more % by weight. It was found that increasing moisture content can have an advantageous effect on resistance to twisting; twist wrappers having high moisture will be more flexible; by increasing the moisture one avoids a dry wrapper which will be more brittle.
It should be understood that the increase of the moisture content of the printable twist wrapper precursor to a value of more than 5% by weight based on the weight of the printable twist wrapper precursor is due to the step of coating the paper on opposed side with a barrier layer, which requires drying the barrier layer composition, and thus necessarily the underlying paper substrate, as well as the barrier layer, to a moisture of less than 5%.
In the step of densifying the printable twist wrapper precursor and decreasing the moisture content of the printable twist wrapper precursor, such as to form a printable twist wrapper having a moisture content of from 5% to 15% and having a density of 1 g/cm³ or more, the densification may be carried out via any suitable densification means suitable for paper manufacturing, such as nip rolls, single rolls and so on. The decreasing of the moisture content of the printable twist wrapper precursor may equally be carried out using any drying means suitable for paper manufacturing, such as hot air blowers, IR radiators, heated rolls and so on. While the step of densifying the printable twist wrapper precursor and decreasing the moisture content of the printable twist wrapper precursor may be carried out by either first drying and then densifying or densifying and then drying, both may also be carried out simultaneously. On one hand, a moisture content of from 5% to 15% provides the printable twist wrapper with a suitable suppleness and flexibility that is needed when wrapping a confection at high speeds on a wrapper machine. Furthermore, when adjusting the moisture content between 5% and 15%, the occurrence of blocking during the unwinding of reels of twist wrapper can be avoided. Increasing moisture content above 15% is possible, but not preferable, because it may result in blocking, as well as problems with unwinding the twist wrapper - paper may stick and then also cause runnability issues with printing at the final user side.
Thus, in a preferred embodiment of the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the step of densifying the printable twist wrapper precursor and decreasing the moisture content of the printable twist wrapper precursor is simultaneously achieved by supercalendering the printable twist wrapper precursor. Supercalendering is achieved by passing the printable twist wrapper precursor through the nips of a supercalender. Supercalendering is further useful to increase the gloss of the printable twist wrapper and increase the smoothness of the printable twist wrapper. Supercalendering improves stiffness, but does not contribute significantly to the barrier properties.
Decreasing the moisture content may be carried out at any temperature, and may in some cases be supplemented by the application of an under-pressure or vacuum, but is preferably carried out at a temperature of between 75° and 130 °C, especially when carried out at atmospheric pressure.
Densifying is carried out by subjecting the printable twist wrapper precursor to pressure across the thickness of the printable twist wrapper precursor, which linear pressure may be in the range 180 N/mm to 280 N/mm.
In a preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the process comprises further the steps of:

prior to coating the paper substrate on the opposed side with a barrier layer, coating the paper substrate on the opposed side with a precoat layer.

In a preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the printable twist wrapper has a weight of from 30 g/m² to 60 g/m², and preferably has a weight of from 35 g/m² to 50 g/m².
In a preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the print receiving layer has a weight of from 3 g/m² to 11 g/m², preferably of from 4 g/m² to 7 g/m² and more preferably of from 2 g/m² to 6 g/m² and/or wherein the barrier layer has a weight of from 0.5 g/m² to 8 g/m², preferably of from 1 g/m² to 6 g/m², more preferably of from 2 g/m² to 5 g/m².
In a preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the mixture of at least one hardwood pulp and at least one softwood pulp comprises at least two and preferably two softwood pulps.
In a preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, the barrier polymer comprised in the barrier layer, or in the barrier layer composition, are chosen among polymers or copolymers of styrene or polymers or copolymers of polyvinyl alcohol, preferably among polymers or copolymers of vinyl alcohol. In a more preferred embodiment, the barrier layer comprises, or essentially consists, of a barrier polymer that is a polymer or copolymer of vinyl alcohol such as polyvinylalcohol (PVOH). In another preferred embodiment, the barrier layer comprises, or essentially consists, of a barrier polymer that is a polymer or copolymer of vinyl alcohol such as ethylene vinyl alcohol (EVOH). The barrier layer may comprise a mix of two or more barrier polymers. Other latex layers may be also suitable as the component of the barrier polymer.
In a preferred embodiment of the process for the manufacture of a wax-free printable twist wrapper according to the first object of the present invention, after the step of densifying the printable twist wrapper precursor and decreasing the moisture content of the printable twist wrapper precursor, the wax-free printable twist wrapper has a thickness of from 3 µm to 8 µm.
The wax-free printable twist wrapper, according to the second object of the present invention, which may be obtained via the above process according to the first object of the present invention, having a grease resistance value of 4, or of from 4 to 12, when measured according to TAPPI Test method T559, comprises, or consists of,

a paper substrate comprising a mixture of at least one short fiber wood pulp and at least one long fiber wood pulp, said mixture having a degree of Schopper-Riegler between 35 and 50, preferably 35 and 40, and comprising at least 40 % by weight of at least one short fiber wood pulp,
a print receiving layer on one side of the paper substrate, said print receiving layer comprising at least one binder and at least one clay pigment, and
a barrier layer on the other side of the paper substrate,
wherein said printable twist wrapper has a moisture content of from 5% to 15% and has a density of 1 g/cm³ or more.

In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the mixture of at least one hardwood pulp and at least one softwood pulp has a degree of Schopper-Riegler of 35 to 50, more preferably from 35 to 45, preferably 35 and 40.
The hardwood pulp may be sourced from hardwoods such as for example birch and eucalyptus, or mixtures of both.
The softwood pulp may be sourced from softwoods such as for example spruce and pine, or mixtures of both.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the hardwood and softwood pulps are both preferably chemical pulps, such as Kraft pulp, sulfite pulp or dissolving pulp. In a preferred embodiment, the hardwood and softwood pulps are bleached hardwood and softwood pulps. Consequently, in a much-preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, both hardwood and softwood pulps are bleached chemical pulps, such as for example Bleached Softwood Kraft (BSK) and Bleached Hardwood Kraft (BHK).
In the mixture of at least one hardwood pulp and at least one softwood pulp, at least 40 % by weight are formed by the at least one hard wood pulp, and preferably at least 50 % by weight are formed by the at least one hard wood pulp. When at least 40 % by weight are formed by the at least one hard wood pulp, the mixture of at least one hardwood pulp and at least one softwood pulp provides for a paper substrate and/or wax-free printable twist wrapper that has excellent mechanical properties.
The print receiving layer comprises at least one binder and at least one clay pigment, and is generally coated onto the paper substrate as a print receiving layer composition, where the print receiving layer composition is a liquid or slurry. Coating the paper on one side with a print receiving layer may be carried in the paper machine or may be carried out outside the paper machine in a separate coating device. While in principle, the coating the paper on one side with a print receiving layer may be carried out in either the paper machine, in particular in the forming section of the paper machine, or may be carried out outside the paper machine in a separate coating device, it has been found that coating the paper on one side with a print receiving layer is advantageous, in terms of process flexibility, because the application the print receiving layer in the paper machine frees up coating capability in an ensuing coating step outside the paper machine in a coating device. Thus, in a preferred embodiment the step of coating the paper on one side with a print receiving layer is carried out in the paper machine, in particular in the forming section.
The print receiving layer composition is normally applied as liquid or slurry and will thus comprise the polymer binder in a liquified form, most commonly in the form of an emulsion or a dispersion. Likewise, the clay pigment will be suspended in the print receiving layer composition. It is understood that the print receiving layer composition may further comprise other components in addition to the binder and the pigment, such as for example biocides, dispersants, rheology modifiers and such.
The print receiving layer on one side of the paper substrate comprises at least one binder and at least one clay pigment. The binder may be, for example a polymer binder such as a copolymer of styrene. Known copolymer of styrene are, for example, styrene butadiene copolymer or styrene acrylic copolymer. The clay pigment may be, for example, a kaolin.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the clay pigment is a kaolin.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the print receiving layer comprises a mixture of two or more clay pigments, and/or wherein the binder is preferably chosen from chosen among polymers or copolymers of styrene. In a more preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the binder is a polymer binder such as a copolymer of styrene and more preferably is a styrene butadiene copolymer.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the wax-free printable twist wrapper further comprises a precoat layer on the other side of the paper substrate, between the paper substrate and the barrier layer. More specifically, both precoat layer and barrier layer are located on the same, "opposed" side of the paper substrate, i.e., on the opposite side of the paper substrate that is the side of the print receiving player. The precoat layer, as its name implies, is applied prior to coating the paper substrate on the opposed side with a barrier layer, coating the paper substrate on the opposed side with a precoat layer. This smoothens the surface of the paper substrate and allows to better form a barrier layer that is free of defects such as pinholes, when compared to a directly coating the barrier layer on the opposed side of the paper substrate. Nonetheless, directly coating the barrier layer on the opposed side of the paper substrate can equally provide a functional grease barrier.
The precoat layer may comprise, or consist of, copolymers of styrene, polymers, or copolymers of polyvinyl alcohol, or microfibrillated cellulose. For instance, the precoat layer may essentially consist of polyvinyl alcohol or of microfibrillated cellulose in some embodiments.
The wax-free printable twist wrapper according to the second object of the present invention comprises a barrier layer on the other side of the paper substrate. The barrier layer serves among others, as a barrier against oil and grease, and thus confers a grease resistance value of 4 or more, or of from 4 to 12 when measured according to TAPPI Test method T559, to the twist wrapper.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the barrier polymer is chosen among polymers or copolymers of styrene or polymers or copolymers of polyvinyl alcohol, and preferably is a polymer or copolymer of vinyl alcohol. For instance, the barrier layer may comprise, or essentially consist of, polyvinylalcohol.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the printable twist wrapper has a weight of from 30 g/m2 to 60 g/m2, and preferably has a weight of from 35 g/m2 to 50 g/m2. Thus, the wax-free printable twist wrapper according to the second object of the present invention is a light paper, when compared to commercially available waxed wrappers that are heavily impregnated with wax.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the print receiving layer of the printable twist wrapper has a weight of from 3 g/m2 to 11 g/m2, preferably of from 4 g/m2 to 7 g/m2.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the barrier layer of the of the printable twist wrapper has a weight of from 0.5 g/m2 to 8 g/m2, preferably of from 1 g/m2 to 6 g/m2, more preferably of from 2 g/m2 to 5 g/m2.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the mixture of at least one hardwood pulp and at least one softwood pulp comprises at least two and preferably two softwood pulps. When at least two softwood pulps are included in the mixture of soft- and hardwood pulps, the mechanical properties of the twist wrapper can be balanced. The first softwood functions to enhance the tensile strength and the other softwood functions to enhance tearing strength, for examples. A person skilled in the art, may be able to adjust the proportion between the at least two softwood such as to balance the mechanical properties to a particular range.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the printable twist wrapper has a thickness of from 3 µm to 8 µm. In addition to being a rather light, the wax-free printable twist wrapper according to the second object of the present invention is also thin, which positively influences the flex-crack resistance of the twist wrapper.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the print receiving layer comprises an ink image, printed preferably using gravure printing, but also with flexographic techniques. One advantage of the wax-free printable twist wrapper according to the second object of the present invention is that it may be printed immediately prior to the wrapping of a confection because it is free of a wax impregnation. Waxes are inert materials that and the wax from the impregnation will make printing on a waxed wrapper nearly impossible, which is why the conventional wrappers are printed prior to wax impregnation. This however means that when using such pre-printed wrappers, it must carefully be considered what the planned amount of wrapper will be, to on one hand avoid waste of surplus wrapper and on the other hand to avoid to run into shortages of wrapper. The wax-free printable twist wrapper according to the second object of the present invention can be provided as ready-to-use wrapper that can easily be printed on demand, because it has already the barrier properties and the printability that are required.
In a preferred embodiment of the wax-free printable twist wrapper according to the second object of the present invention, the printable twist wrapper has a tensile strength in machine direction (MD), when measured according to ISO 1924-2 of between 55 and 65 N/15mm and/or has a tensile strength in cross direction (CD), when measured according to ISO 1924-2 of between 25 and 35 N/15mm, and/or has a elongation at break in machine direction (MD), when measured according to ISO 1924-2 of between 1,5 and 2 %, and/or has a elongation at break in cross direction (CD), when measured according to ISO 1924-2 of between 6,5 and 7.5 %, and/or has an Elmendorf tearing force in machine direction (MD), when measured according to ISO 1974 of between 210 and 250 mN, and/or has an Elmendorf tearing force in cross direction (MD), when measured according to ISO 1974 of between 210 and 250 mN.

EXPERIMENTAL DATA

A series of wax-free printable twist wrappers (Wrapper 1, 2, 3, 4, 5)were obtained by forming a paper substrate from a mixture of hardwood pulp and softwood pulp comprising at least 40% hardwood pulp, which mixture was refined until a degree of between 35 and 45 Schopper-Riegler was reached. To each paper substrate, a print receiving layer comprising a binder and a clay pigment was coated on the bottom side, in-line in the paper machine.
Then, different barrier coatings were applied to the top side of each of the paper substrates (PVOH, EVOH, CMC, starch, a mixture of PVOH/EVOH) and the thus coated precursor paper substrates were dried to a moisture content of less than 5% to form the respective barrier layers, having a weight of between 1 and 6 gsm. After being re-moisturized to increase the moisture content of the precursor paper substrate to more than 5% and subsequently being supercalendered in a 9-nip supercalender to decrease the moisture via heat to a value between 7% to 12% and to increase the density via pressure to more than 1 g/cm³.

The wax-free printable twist wrappers described above according to the invention were subjected to multiple tests to determine the tensile strength, the elongation at break as well as the tearing strength in both machine (MD) and cross direction (CD), and the average values obtained from the wrappers are compared to a commercially available, conventional wax-impregnated and printed twist wrapper in the below table. As can be seen from the below results, a wax-free printable twist wrappers according to the invention emulate the mechanical properties of a conventional waxed and printed twist wrapper. The results are summarized in Table 1.

Table 1

Feature	Unit	Method	Commercial waxed & printed twist wrapper	Average (std)
Grammage	g/m²	ISO 536	55	44.8 (0.87)
Tensile Strength (MD)	N/15 mm	ISO 1924-2	45,6	49.4 (7.83)
Tensile strength (CD)	N/15 mm	ISO 1924-2	30,5	27.4 (4.28)
Elongation @ break (MD)	%	ISO 1924-2	1,5	1.8 (0.11)
Elongation @ break (CD)	%	ISO 1924-2	6,5	6.9 (0.50)
Tearing (Elmendorf) (MD)	mN	ISO 1974	231	210.8 (22.30)
Tearing (Elmendorf) (CD)	mN	ISO 1974	230	235.4 (13.33)

As can be seen, on average, the wax-free printable twist wrappers according to the present invention, even at weights below the 50 gsm, are equivalent or superior in terms of tensile strength, elongation at break as well as tearing strength in both machine (MD) and cross direction (CD), when compared to a commercially available wax-impregnated printed twist wrapper having a significantly higher weight of about 55 gsm.
The wax-free printable twist wrappers according to the present invention could be used in a commercial setting for wrapping hard candy on a Theegarten EK4 machine at a speed of 2000 pcs/min or more, as a "plug-in" substitute for commercially available printed & waxed wrapper papers.

Claims

A process for the manufacture of a wax-free printable twist wrapper having a grease resistance value of 4 or more, or of from 4 to 12 when measured according to TAPPI Test method T559, comprising the steps of:
- forming a paper substrate from a paper furnish comprising paper pulp, in a paper machine, wherein the paper pulp in the paper furnish is obtained by refining a mixture of at least one hardwood pulp and at least one softwood pulp to a degree of Schopper-Riegler between 30 and 50, preferably 35 and 40, said mixture comprising at least 40 % by weight of at least one hardwood pulp,

- coating the paper substrate on one side with a print receiving layer, said print receiving layer comprising at least one binder and at least one clay pigment,

- coating the paper substrate on the opposed side with a barrier layer to form a printable twist wrapper precursor having a moisture content of less than 5% by weight, and subsequently,

- increasing the moisture content of the printable twist wrapper precursor to a value of more than 5% by weight, based on the weight of the printable twist wrapper precursor,

- densifying the printable twist wrapper precursor and decreasing the moisture content of the printable twist wrapper precursor, such as to form a printable twist wrapper having a moisture content of from 5% to 15%, preferably of from 7% to 12%, and having a density of 1 g/cm³ or more, wherein preferably decreasing the moisture content s carried out at a temperature of between 75 °C and 130 °C.
The process for the manufacture of a wax-free printable twist wrapper according to claim 1, comprising further the steps of:
- prior to coating the paper substrate on the opposed side with a barrier layer, coating the paper substrate on the opposed side with a precoat layer.
The process for the manufacture of a wax-free printable twist wrapper according to claim 1 or 2, wherein said printable twist wrapper has a weight of from 30 g/m² to 60 g/m², and preferably has a weight of from 35 g/m² to 50 g/m², and preferably wherein the print receiving layer has a weight of from 3 g/m² to 11 g/m², preferably of from 4 g/m² to 7 g/m² , preferably of from 2 g/m² to 6 g/m², and/or wherein the barrier layer has a weight of from 0.5 g/m² to 8 g/m², preferably of from 1 g/m² to 6 g/m², more preferably of from 2 g/m² to 5 g/m².
The process for the manufacture of a wax-free printable twist wrapper according to any of the preceding claims, wherein the mixture of at least one hardwood pulp and at least one softwood pulp comprises at least two and preferably two softwood pulps.
The process for the manufacture of a wax-free printable twist wrapper according to any of the preceding claims, wherein said barrier layer comprises, or substantially consists of, a barrier polymer chosen among polymers or copolymers of styrene or polymers or copolymers of polyvinyl alcohol, preferably among polymers or copolymers of vinyl alcohol, and more preferably is a polyvinyl alcohol.
The process for the manufacture of a wax-free printable twist wrapper according to any of the preceding claims, wherein after the step of densifying the printable twist wrapper precursor and decreasing the moisture content of the printable twist wrapper precursor, the wax-free printable twist wrapper has a thickness of from 3 µm to 8 µm.
A wax-free printable twist wrapper having a grease resistance value of 4, or of from 4 to 12, when measured according to TAPPI Test method T559, and comprising, or consisting of,
a paper substrate comprising a mixture of at least one hardwood pulp and at least one softwood pulp, said mixture having a degree of Schopper-Riegler between 35 and 50, preferably 35 and 40, and comprising at least 40 % by weight of at least one hardwood pulp,

a print receiving layer on one side of the paper substrate, said print receiving layer comprising at least one binder and at least one clay pigment, and

a barrier layer on the other side of the paper substrate,

wherein said printable twist wrapper has a moisture content of from 5% to 15% and has a density of 1 g/cm³ or more.
The wax-free printable twist wrapper according to claim 7, wherein the wax-free printable twist wrapper further comprises a precoat layer on the other side of the paper substrate, between the paper substrate and the barrier layer.
The wax-free printable twist wrapper according to claim 7 or 8, wherein said printable twist wrapper has a weight of from 30 g/m² to 60 g/m², and preferably has a weight of from 35 g/m² to 50 g/m², and preferably wherein the print receiving layer has a weight of from 3 g/m² to 11 g/m², preferably of from 4 g/m² to 7 g/m² and/or wherein the barrier layer has a weight of from 0.5 g/m² to 8 g/m², preferably of from 1 g/m² to 6 g/m², more preferably of from 2 g/m² to 5 g/m².
The wax-free printable twist wrapper according to any one of claims 7 to 9, wherein the mixture of at least one hardwood pulp and at least one softwood pulp comprises at least two, and preferably two softwood pulps.
The wax-free printable twist wrapper according to any one of claims 7 to 10, wherein the barrier layer comprises, or substantially consists of, a barrier polymer, wherein said barrier polymer is preferably chosen among polymers or copolymers of styrene or polymers or copolymers of vinyl alcohol, and preferably is a polymer or copolymer of vinyl alcohol, preferably barrier polymer comprises or is substantially a polyvinyl alcohol.
The wax-free printable twist wrapper according to any one of claims 7 to 11, wherein it has a tensile strength in machine direction (MD), when measured according to ISO 1924-2 of between 55 and 65 N/15mm and/or has a tensile strength in cross direction (CD), when measured according to ISO 1924-2 of between 25 and 35 N/15mm, and/or has a elongation at break in machine direction (MD), when measured according to ISO 1924-2 of between 1,5 and 2 %, and/or has a elongation at break in cross direction (CD), when measured according to ISO 1924-2 of between 6,5 and 7.5 %, and/or has an Elmendorf tearing force in machine direction (MD), when measured according to ISO 1974 of between 210 and 250 mN, and/or has an Elmendorf tearing force in cross direction (MD), when measured according to ISO 1974 of between 210 and 250 mN.
The wax-free printable twist wrapper according to any one of claims 7 to 12, wherein said printable twist wrapper has a thickness of from 3 µm to 8 µm.
The wax-free printable twist wrapper according to any one of claims 7 to 13, wherein the print receiving layer comprises an ink image, printed preferably using gravure technique.
Use of a wax-free printable twist wrapper obtained according any one of claims 1 to 6, for twist wrapping, preferably double-twist wrapping, of a confection in said wax-free printable twist wrapper.