Patent Application
20230084783
The invention relates to a method for manufacturing two-sided laminated cardboard, wherein on both sides of an intermediate cardboard layer a first outer layer and a second outer layer, respectively, are laminated. According to the invention the first outer layer and/or the second outer layer can be manufactured from various materials, such as for example paper, cardboard or synthetic material. The invention further relates to two-sided laminated cardboard manufactured by such a method.
From practice a method is known according to the pre-characterizing portion of the appended independent claim 1, i.e. a method for manufacturing two-sided laminated cardboard, wherein on both sides of an intermediate cardboard layer a first outer layer and a second outer layer, respectively, are laminated, and wherein during said laminating:
the intermediate layer is conveyed in a conveying direction through a laminating apparatus;
the first outer layer is glued together with the upper side of the intermediate layer by means of a rotating upper roller under exertion of a first torque, and the second outer layer is glued together with the lower side of the intermediate layer by means of a rotating lower roller under exertion of a second torque;
a measuring roller measures a measured band tension, in the conveying direction, of the intermediate layer being conveyed;
for the purpose of a taut running of the intermediate layer, the intermediate layer being conveyed is kept at a pre-determined constant operational band tension in the conveying direction in dependence of said measured band tension and in dependence of said pre-determined constant operational band tension; and
for the purpose of counteracting concaveness or convexness, in the conveying direction, of the two-sided laminated cardboard to be manufactured, band tensions of the first outer layer and the second outer layer are controlled.
An important parameter in the production and processing of laminated cardboard is the degree into which a cardboard is lying flat. A bad flatness degree of a cardboard hampers the conveyance of the cardboard in processing machines, as well as the conveyance of the eventual product.
Laminated cardboard can unintentionally be curved (concaveness/convexness) in conveying direction (MD), in transverse direction (CD) or in a direction in-between MD and CD (Warp). For preventing concaveness or convexness in the transverse direction CD in case of outer laminating layers made from paper, control in CD commonly takes place by controlling fiber direction of the laminating papers and by symmetry in humidity level of the laminating papers and the intermediate cardboard layer.
For preventing concaveness or convexness in MD (the conveying direction), control in MD commonly takes place by controlling the band tensions of the laminating papers by means of brakes at the unrolling of the laminating papers. Herein, however, some adverse side effects occur, which is explained as follows. The adhesive applicator, which is situated between the unroller and the laminating press, increases the band tensions dependent on various factors. Controlling the band tensions for controlling the flatness can change the adhesive application instruction, while controlling the adhesive application instruction on its turn changes the band tensions again. At higher band tensions and thin outer paper layers there is increased risk of band breakage of the wet outer paper layers having been glued. Low band tension, on the other hand, can cause loss of grip at the spreader roll, which results into pleats.
It is an object of the invention to provide an alternative solution for preventing concaveness or convexness, in the conveying direction, of the two-sided laminated cardboard to be manufactured, wherein the occurrence of the above-mentioned adverse side effects is counteracted.
For that purpose the invention provides a method according to the appended independent claim 1, as well as a two-sided laminated cardboard according to the appended independent claim 2.
Hence, the invention provides a method for manufacturing two-sided laminated cardboard, wherein on both sides of an intermediate cardboard layer a first outer layer and a second outer layer, respectively, are laminated, and wherein during said laminating:
the intermediate layer is conveyed in a conveying direction through a laminating apparatus;
the first outer layer is glued together with the upper side of the intermediate layer by means of a rotating upper roller under exertion of a first torque, and the second outer layer is glued together with the lower side of the intermediate layer by means of a rotating lower roller under exertion of a second torque;
a measuring roller measures a measured band tension, in the conveying direction, of the intermediate layer being conveyed;
for the purpose of a taut running of the intermediate layer, the intermediate layer being conveyed is kept at a pre-determined constant operational band tension in the conveying direction in dependence of said measured band tension and in dependence of said pre-determined constant operational band tension; and
for the purpose of counteracting concaveness or convexness, in the conveying direction, of the two-sided laminated cardboard to be manufactured, band tensions of the first outer layer and the second outer layer are controlled;
characterized in that
in said controlling of said band tensions of the first outer layer and the second outer layer:
a torque addition sum of the first torque and the second torque is controlled towards a pre-determined constant value of said torque addition sum, said pre-determined constant value being obtained from experience; and
a torque difference between the first torque and the second torque is controlled towards a pre-determined value of said torque difference, said pre-determined value of said torque difference being obtained from experience, while maintaining said controlling of said torque addition sum towards said pre-determined constant value of said torque addition sum.
Concisely worded, the invention therefore relates to a concaveness/convexness control in the conveying direction, wherein said concaveness/convexness control is based on applying a torque difference control for the upper and lower rollers while keeping the total torque of the torques of both rollers equal.
According to this torque difference control, wherein total torque is kept equal, it is for example possible to increase the first torque of the upper roller and simultaneously decrease the second torque of the lower roller by a same value, whereby the upper first outer layer is glued to the intermediate layer with decreased MD tension, and the lower second outer layer is glued to the intermediate layer with increased MD tension. This difference in tension results into a bulging correction for counteracting an undesirable concave shape of the 3-layered end product. Conversely, the first torque of the upper roller can be decreased and the second torque of the lower roller can be simultaeously increased by a same value, whereby the upper first outer layer is glued to the intermediate layer with increased MD tension, and the lower second outer layer is glued to the intermediate layer with decreased MD tension. This tension difference results into a hollowing correction for counteracting an undesirable convex shape of the 3-layered end product. Such simultaneous, but mutually opposite, ways of controlling the upper roller and the lower roller, make that the total of the two torques of the two rollers remains equal.
Thanks to using the torque difference control, wherein total torque is kept equal, the invention provides an effective corrective flatness control, wherein a corrective control action has no consequences for band running and band tension of the intermediate cardboard layer, and wherein the pleat and breakage risk of the glued outer layers is minimized.
Hereinafter the invention is further elucidated with reference to a non-limiting example embodiment, and with reference to the schematical
For the purpose of a taut running of the intermediate layer 2 the intermediate layer 2 is kept at the pre-determined constant operational band tension T in the conveying direction MD. This is controlled in dependence of the band tension measured by the measuring roller 23 and in dependence of the pre-determined constant operational band tension T.
For the purpose of counteracting concaveness or convexness in the conveying direction MD of the two-sided laminated cardboard 1 to be manufactured, the band tensions of the first outer layer 11 and the second outer layer 12 in the conveying direction MD are controlled. Therein, the addition sum Q1+Q2 of the first torque Q1 and the second torque Q2 are controlled towards the pre-determined constant value Q. In other words, the control is such that eventually Q1+Q2=Q applies. Therein, also the torque difference between the first torque Q1 and the second torque Q2 is controlled towards the pre-determined value ΔQ of said torque difference, while maintaining said controlling of said torque addition sum towards said pre-determined constant value Q. As seen in
Q1+Q2=(½Q+½ΔQ)+(½Q−½ΔQ)=Q, and
Q1−Q2=(½Q+½ΔQ)−(½Q−½ΔQ)=ΔQ.
It has appeared that, thanks to using this “torque difference control, wherein total torque is kept equal”, a practically realizable and effective corrective flatness control is obtained, wherein a corrective control action has no consequences for band running and band tension of the intermediate cardboard layer, and wherein the pleat and breakage risk of the glued outer layers is minimized.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2024873 | Feb 2020 | NL | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NL2021/050087 | 2/10/2021 | WO |
