Patent Grant
9797096
This application is a 371 of PCT/EP2013/068347 filed 5 Sep. 2013.
The present invention generally relates to a method and apparatus of manufacturing food wrap paper. Particularly, though not exclusively, the present invention relates to a method and apparatus of manufacturing fast food wrap paper with basis weight of 25.5 g/m2 to 34 g/m2.
Fast food is often wrapped in relatively thin paper that is coated so as to mitigate penetration of grease into the structure of the paper and excessive passing through of vapour so as to mitigate loss of opacity and cooling of hot food. Such a wrap paper is typically produced in three major stages. First, a base paper is produced to have a fair opacity. To this end, TiO2 particles are mixed to the pulp. Second, in an off-line process, one side of the base paper is waxed or polyethylene coated. Third, the paper is cut into sheets and packaged into boxes that are suited for end-user's needs.
The coating is made by applying heated wax or polyethylene in an off-line coating station onto a running paper web. The hot coating is in a molten form and thus adheres uniformly to the base paper and forms a barrier layer. The coating layer is relatively thin and light in comparison to the base paper being coated and thus in part cools down by itself to solid state as heat transfers from the coating to the base paper. When the coating is in the solid state, the coated paper is ready to be rolled in or cut into sheets and boxed.
Food wrap papers are produced with different specifications for different needs: hamburger wrap paper, for instance, is typically made of paper having basis weight of 25 g/m2 to 33 g/m2 including a few g/m2 coating. French fries, on the other hand, are typically produced with significantly heavier base paper. Generally, the lighter the base paper, the more prone the paper is for web breaks, holes, wrinkles and other quality defects.
In papermaking, the capacity of paper production lines is constantly being increased as far as possible in order to reduce unit costs and thus to enhance efficiency of the production. The capacity can be effected in a number of ways, such as: increasing production rates (e.g. broader web, faster run speed), reducing down-time (faster grade changes, less web breaks, faster resumption of production after web-breaks) and reducing proportion of production that falls below quality requirements. Paper machines are notoriously expensive production units with which risks are not willingly taken if not absolutely necessary. For example, with the light-weight base paper for hamburger wrap, on-line coating is instantly un-attractive to a skilled person: the paper web is weak and prone for breaking especially when wetted by coating. The off-line coating wax and polyethylene are not suited for on-line coating. In on-line production they would form sticky deposits that accrue and kind of burn onto drying cylinders and rolls. Such stains may ultimately require grinding of cylinders or rolls.
It is an object of the invention to enhance the efficiency of the production of food wrap paper with basis weight of 25.5 g/m2 to 34 g/m2. Another object of the invention is to additionally or alternatively reduce the amount of additives and/or energy needed for production of such food wrap paper. Yet another object of the invention is to additionally or alternatively reduce defects in such food wrap paper.
According to a first example aspect of the invention there is provided a method for manufacturing food wrap paper, comprising:
According to a second example aspect of the invention there is provided a paper making apparatus, comprising:
Different non-binding example aspects and embodiments of the present invention will be presented in following detailed description and in appended dependent claims. It should be appreciated that corresponding embodiments may be freely applied to other embodiments and example aspects.
Some example embodiments of the invention will be described with reference to the accompanying drawings, in which:
In the following description, like reference signs denote like elements.
The paper machine 100 further comprises a pressing section 120 and a drying section 130 that remove water from paper web 112. The drying section is divided into two or more sub-sections 132, 134, 136 surrounding one or more paper treatment units such as surface treatment stations 140, 150 and middle calender 160. The paper machine 110 also comprises a finishing section 170. The finishing section 170 comprises, in this example, a machine calendar 172.
It is to be understood that each of the described sections are on-line units. In other words, these units operate on paper while it is being formed in the paper machine, or the paper is not transferred on a machine roll or winder roll, for example, to off-line processing.
The forming section 110 is implemented using commercially available parts such as headbox, foils, plastic or metallic wires and suction boxes. The forming section may aim at producing symmetric z-distribution of particles e.g. with a gap former or asymmetric z-distribution of particles e.g. using a fourdrinier wire. The forming section 110 as well as other main parts of the paper machine are configured using ordinary paper making knowledge considering the paper grade in question and available resources. The paper web is formed according to an example embodiment substantially without added opacifying chemicals. Substantially without added opacifying chemicals means in this context that opacifying chemicals are not intentionally added. Some opacifying chemicals may yet end up into the paper web from the source materials.
The drying section 130 typically comprises a number of steam-heated drying cylinders. A typical paper machine has some tens of drying cylinders, one or more of which may be of so-called Yankee cylinder type for also glazing the side of the paper web that contacts with the cylinder. The drying section 130 can also comprise infrared, air blow boxes, or any other elements. For control of cross-direction moisture profile of the paper web 112, the drying section 130 may also comprise a cross-directionally profiling moistening device.
In the example embodiment illustrated by
The paper machine 100 also comprises in one example embodiment one or more machine calendars before one or more sizing or coating stations.
In this document, sizing and coating may be used interchangeably unless expressly otherwise stated, as the difference is often somewhat indefinite.
The drying section 130 may be entirely within a single hood. Alternatively, the drying section 130 may be formed of physically more distinct sections distributed into two or more hoods.
A skilled paper maker knows how to implement the normal parts of a paper machine that operate as known in the art. Hence, the structure and operation relating to surface treating of the paper web 112 will next be described in further detail. The example embodiment shown in
The machine calendar can be configured to flatten the paper web to target thickness or caliber. The target thickness is selected in some example embodiments from: a range of 30 μm to 38 μm; a range of 33 μm to 35 μm; and 34 μm. In thickness of 33 μm to 35 μm, preferably, 34 μm, the food wrap paper produced by the method may be perceived best suited for wrapping fast food such as hamburgers: dead-fold stiffness high enough to stay wrapped while still sufficiently thin to enable convenient wrapping also when wrapped multiple rounds around an object to be packaged. The calendering may help in packaging desired number of sheets in boxes of a predetermined size. Moreover, the calendering can be used to enable forming heavier and stronger base paper for barrier coating while achieving the target thickness.
In
A second unit 220 is provided, for instance, as a moisture measurement or moisture profiling station or as an applicator roll, curtain, short-dwell, air-doctor, size press or spray coating or sizing unit for applying coating or sizing material directly onto the paper web 112.
Alternatively or additionally to sizing or coating at the second unit 220, the system 200 can be configured to apply a film transfer layer on one or two nip rolls 230a, 230b with respective sizing or coating material application adjusters 240a, 240b. The sizing or coating material application adjusters 240a, 240b may comprise one or more jets, nozzles or mouths for output of the sizing or coating material and one or more amount limiters such as rods, blades, dosing rolls (as known from multi-roll sizers or coaters), and/or air-doctors for instance.
The surface treatment material and application amounts may differ between the different sides 112a, 112b. It is not even necessary in all embodiments to perform any surface treatment on both sides 112a and 112b of the paper web 112.
The first side 112a can be surface treated with a barrier material while the second side 112b can be left untreated. The barrier material is selected in some example embodiments from any one or more of the following: polymer dispersions, polyolefins, PVA, CMC, starch, PCL, PLA Chitosan, talcum, clay, lattices, CaCO3, NFC, xylane, and hemicellulose.
In an example embodiment, the viscosity of the barrier material is adjusted by use of one or more viscosity modifiers. The viscosity modifiers comprise, for example, any of carboxymethyl cellulose, polyvinyl alcohol or synthetic thickeners.
In an example embodiment, the surface tension of the barrier material is adjusted by use of one or more wetting agents. The wetting agents comprise, for example, any of surfactants.
In an example embodiment, the second side 112b is sized or coated for curl control, water control and/or penetration support purpose using any of the known compositions for this purpose.
The nip rolls 230a, 230b are configured to press the surface treatment material at least partly through the respective surface of the paper web 112 into the structure of the paper web when the paper web 112 travels through the nip.
The barrier material can be heated to a temperature high enough to bind the barrier material onto the paper web so as to avoid subsequent peeling of the barrier material.
In an example embodiment, the nip is temperature controlled e.g. by circulation of temperature control fluid inside one or both nip rolls 230a, 230b and/or by use of electric heating elements. The temperature control comprises, depending on circumstances and the example embodiment, cooling, heating or as needed cooling or heating. The temperature in the nip can thus be adjusted to a level in which the barrier material adheres to the paper web.
The barrier material can also or alternatively be heated by one or more drying elements.
Adhering to the paper web may refer to forming a sufficiently strong and strongly attached a layer to withstand subsequent processing without peeling off from the paper web. Preferably the temperature of the nip is kept low enough to avoid excessively losing viscosity of the barrier material in order to avoid or mitigate some staining problems. Such problems might otherwise prevent or hinder commercially reasonable online surface treatment of the paper web 112 with the barrier material.
The nip load and nip rolls are configured suitably for the used surface treatment material and for the desired properties of the paper web 112. In this case, the surface treatment is performed such that desired total basis weight is attained, when taking into account any other surface treatment processes performed with the paper machine 100. The desired total basis weight is e.g. 25.5 g/m2 to 34 g/m2 when measured in balance moisture. By measuring in balance moisture reference is made to normal paper testing conditions i.e. 23° C., 50% relative humidity, normal air pressure.
The nip rolls 230a, 230b may belong to a size press.
In an example embodiment, the barrier material is cooled before applying onto the first side of the paper web in the on-line surface treating. The barrier material is cooled e.g. to a temperature of 15° C. to 25° C. before applying onto the first side of the paper web in the on-line surface treating.
The on-line surface treating is performed in one example embodiment with the barrier material such that the melting point of staining components in the barrier material is sufficiently separated from the temperature in which the barrier material is brought onto the paper web. The temperature separating can be provided by controlling at least one of the composition of the barrier material and the temperature of the barrier material when measured at the moment of applying onto the surface of the paper web.
The paper web 112 is processed in one example embodiment in two surface treatment phases so that two layers of barrier material, i.e. a first layer and a second layer, are sequentially applied on the first side 112a of the paper web 112. The barrier material may be let to cure or dry between sequential on-line surface treatment phases such that previously applied barrier material inhibits penetration of water in subsequent applying of barrier material into the base paper web.
The two-phase surface treatment advantageously reduces water load on the paper web 112 and thus reduces momentary impairment of the tensile strength of the paper web. The better the tensile strength, the smaller the risk of paper breaks and of spreading wet or poorly cured or dried surface treatment material onto subsequent drying rolls or other hot parts of the paper machine 100. Moreover, the two-phase surface treatment enables use of barrier materials of different compositions and/or different water content in the different layers.
For example, the first layer can be produced to a greater basis weight than the second layer. The first layer can be produced to a basis weight that is 1 to 3, preferably 2, times the basis weight of the second layer, when in balance moisture. The first layer can be produced to a basis weight of 0.3 g/m2 to 4.5 g/m2 when in balance moisture. The second layer can be produced to a basis weight of 0.3 g/m2 to 3 g/m2 when in balance moisture. The first and second layers can be produced to a combined basis weight of 1 g/m2 to 4.5 g/m2 and preferably 3 g/m2 when in balance moisture.
In an example embodiment, the first layer is formed to contain one or more opacifying chemicals so that desired opacity is attained for the manufactured wrap paper. The opacifying chemicals can be selected e.g. from a group consisting of: TiO2; kaolin; clay; talcum; CaCO3; and any composition comprising any one or more thereof.
Opacifying chemicals need not be added to the barrier material with which the second layer is formed. Concentration of opacifying chemicals in the second layer is thus in one example embodiment less than half or less than tenth of that in the first layer. By omitting opacifying chemicals, the second layer may become less porous than the first layer. Moreover, by containing opacifying chemicals substantially solely in the first layer, total amount of opacifying chemicals may be reduced for a given desired opacity level.
After each surface treatment phase, the paper web 112 can be guided and dried with contactless elements such as one or more blow boxes 250 and/or infrared dryers 260 to an extent that enables contacting processing without excessively disturbing surface treated surface or surfaces of the paper web 112. Alternatively, a sufficiently long free span may be provided to let the paper web 112 cure and/or dry before contacting parts of the paper machine 100. Using contactless support and/or drying elements can yet help to reduce total length of the product line, increase water removal capacity and/or reduce length of free spans and thus reduce web break risks.
In embodiments in which only one side of the paper web 112 is surface treated at a given station by applying sizing or coating material such as the barrier material, the paper web 112 can be supported from the side that is not sized or coated by that station.
It shall be understood that
Various embodiments have been presented. It should be appreciated that in this document, words comprise, include and contain are each used as open-ended expressions with no intended exclusivity.
The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments of the invention a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented in the foregoing, but that it can be implemented in other embodiments using equivalent means or in different combinations of embodiments without deviating from the characteristics of the invention.
Furthermore, some of the features of the afore-disclosed embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/068347 | 9/5/2013 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2015/032432 | 3/12/2015 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6531196 | Aho et al. | Mar 2003 | B1 |
| 20070000568 | Bohme et al. | Jan 2007 | A1 |
| Entry |
|---|
| International Search Report for PCT/EP2013/068347 dated Apr. 24, 2014. |
| Number | Date | Country | |
|---|---|---|---|
| 20160194831 A1 | Jul 2016 | US |
