Moulding of regenerated cellulose films into shaped structures

Abstract

According to an example aspect of the present invention, there is provided a method for manufacturing shaped structures from regenerated cellulose films by rewetting and heat moulding.

Description

MOULDING OF REGENERATED CELLULOSE FILMS INTO SHAPEDSTRUCTURESFIELD

[0001] The present invention relates to deep draw type moulding of regenerated cellulose films to produce shaped structures.BACKGROUND

[0002] Alternative materials are constantly being developed in order to replace the existing plastic materials in for example food and other packaging and coating solutions. Sustainable cellulose-based materials provide a promising starting point.

[0003] Food casings made from regenerated cellulose have been known for an extended period of time and can be made by using methods well known to those skilled in the art. In particular, xanthate viscose is made by treating cellulose from cotton, wood, or other plant fibre with alkali followed by dissolving in carbon di-sulphide. The resulting viscose is then extruded through a die to form a tube. The resulting tube is then regenerated, usually by passing it through a coagulating bath containing coagulating materials such as sodium sulphate, and sulphuric acid. The casing is then dried. US-patents 2,999,756 and 3,835,113 describe such processes in detail.

[0004] US-patent 5,952,064 relates to a tubular film, which may be used for encasing food, comprising a material, which has been regenerated from a solution of cellulose and dried. US-patent 4,857,201 on the other hand discloses a method for improving the solute selectivity of cellulose or cellulosic membranes used for the separation of organic mixtures, said method comprising the steps of drying a water wet cellulose or cellulosic membrane, rewetting the dried membrane, and redrying the membrane. However, these documents fails to disclose reshaping wetted regenerated cellulose film by moulding.

[0005] There is a need for a novel technology of producing shaped structures from regenerated cellulose films for answering to the growing needs of sustainable coating and packaging industry.SUMMARY OF THE INVENTION

[0006] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0007] According to an aspect of the present invention, there is provided a method for manufacturing shaped structures from regenerated cellulose films.

[0008] This and other aspects, together with the advantages thereof over known solutions are achieved by the present invention, as hereinafter described and claimed.

[0009] The method of the present invention is mainly characterized by what is stated in the characterizing part of claim 1.

[0010] The shaped structure of the present invention is mainly characterized by what is stated in the characterizing part of claim 7.

[0011] Considerable advantages are obtained by means of the invention. The invention provides solutions for replacing plastic in food or other packaging solutions. It enables after-orientation or film stretching and orientation in a separate second phase. It can also be used in combination with water webs, which can be activated with water. The rewetting water may also act as a carrier for functional components contributing for example in heat-sealing, cross-linking and enhancing the water tolerance. In addition, moulding can be carried out by using existing tools and machinery at converters commonly used for carton board moulding. Furthermore, the three-dimensional shaped structure can be manufactured in a different location (such as close to the end-use location) than the film manufacturing, which improves the logistics and reduces related costs.

[0012] Next, the present technology will be described more closely with reference to certain embodiments.EMBODIMENTS

[0013] The present technology provides means for producing three-dimensional shaped structures from regenerated cellulose films via rewetting and heated moulding.

[0014] FIGURE 1 is a chart showing the tensile strengths (MPa) of the dry film, film rewetted with water and film rewetted with water and glycerol.

[0015] FIGURE 2 is a chart showing the Young’s modulus (MPa) of the dry film, film rewetted with water and film rewetted with water and glycerol.

[0016] FIGURE 3 is a chart showing strain at break (%) of the dry film, film rewetted with water and film rewetted with water and glycerol.

[0017] FIGURES 4-6 are photos showing shaped structures according to different examples.

[0018] FIGURE 7 shows the mechanical properties (Tensile strength (MPa), measured in MD, and Strain (%)) in pilot line films plasticized for 2 mins with 10 % glycerol. Tensile strength for 90 % RH and 1 min in water decreased by 38 % and 46 % respectively compared to 50 % RH. Strain for 90 % RH and 1 min in water increased by 5 % and 22 % respectively compared to 50 % RH.

[0019] The present invention is based on re-softening phenomenon, which occurs once regenerated cellulose film is subjected to water after film drying. This softening causes the film to become more strainable and less brittle, allowing it to be shaped by using a moulding tool such as male-female mould combination used in deep draw type converting applications.

[0020] According to one embodiment of the present invention, the present method for manufacturing shaped structures from regenerated cellulose films comprises at least the following steps: rewetting the regenerated cellulose film with water, applying the rewetted film into or in between a heated mould(s), and solidifying the film into the shaped structure via evaporation of moisture in the heated mould(s).

[0021] In the present context, the regenerated cellulose film can be produced forexample by the method described in patent application WO 2009 / 135875 Al.

[0022] In one embodiment of the present invention, the rewetting water is used as a carrier for functional components, such as glycerol or any other multihydroxy polyol, which may be utilized for example in heat-sealing and cross-linking purposes and for enhancing the water tolerance of the formed shaped structure. For example, glycerol was herein used as a functional component as 10% glycerol / water solution by dipping a film into bath for 60 seconds. Glycerol enhanced strain at break in comparison of only rewetting in water. Tensile strength and modulus were maintained at higher level when compared of dipping in glycerol / water mixture than only in water.

[0023] According to one embodiment of the present invention, the rewetting is carried out by spraying, dipping, steaming or coating.

[0024] Typically, cellulose film materials when manufactured correctly elongates around 20%. By rewetting the regenerated cellulose film according to the present invention, the elongation can be doubled to 40% without essentially compromising ductility, which enables the moulding into intact permanent shapes.

[0025] Thus, according to one embodiment of the present invention, the elongation (i.e. strain at break) of the regenerated cellulose film is higher compared to a non-rewetted cellulose film, preferably at least 30%, and more preferably around 40% after the rewetting step.

[0026] According to one embodiment of the present invention, the film is applied onto a mouldable cellulose-based paper or carton board.

[0027] A cellulose-based shaped structure comprising rewetted, moulded and dried regenerated cellulose film belongs to a scope of the present invention.

[0028] One embodiment of the present invention is a cellulose-based shaped structure, which comprises rewetted, moulded and dried regenerated cellulose film on a mouldable cellulose-based paper or carton board.

[0029] A further embodiment of the present invention is a cellulose-based shaped structure, which consists of rewetted, moulded and dried regenerated cellulose film.

[0030] According to one embodiment of the present invention, the cellulose film ofthe cellulose-based shaped structure has a thickness between 20 and 100 pm.

[0031] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0032] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0033] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.INDUSTRIAL APPLICABILITY

[0034] The present invention is industrially applicable in for example cellulose- based coating and packaging industry. The described method can be used for manufacturing coated paper or carton plates, cups, bottles, cutlery, food casings and such.EXAMPLESIn first example, a regenerated cellulose film was manufactured using a pilot machine intended for manufacturing of stand alone films from dissolved cellulose solutiuon. Here, a stand alone film was manufactured from cellulose solution (Biocelsol dissolving method) having solids content of 6.56 % and ball drop viscosity (ball dropping time for 200 mm; Dpipe= Dbaii=l / 8”, 130 mg; modified ASTM D1343-95) of 60 s at 20 °C. The solution was casted on a rotating Teflon coated steel cylinder using a slot die. Wet thickness after casting was 600 ± 20 microns. The cylinder transports the dissolved cellulose solution into regeneration bath (10 wt% sulphuric acid) and was further guided into washing bath. From washing bath film was immersed into plastization bath for 60 seconds and later placed on drying jigs, which prevented film shrinkage and providing isotropic character for the film. Finished film having a thickness of 51 microns was stored at standard conditions (50%RH, 23 °C) until used.A film blank was immersed into water bath for 60 seconds. Right after the films was placed between a male-female mould pair shaped as hemisphere with diameter of 85 mm. The shape was formed be pressing to moulds together and solidified to shape placing the forced sample in oven at 104 °C overnight (see figure 4). The mould requires approximately 13 % of strain.In second example, a film blanck was immersed into water bath again for 60 seconds. Right after the film was placed between a male-female mould pair shaped as a six pill dosage tray with a single pill dimensions of (L2.3xW1.3xD) mm. The shape was formed be pressing to moulds together and solidified to shape placing the forced sample in oven at 104 °C overnight. The shape was stretched to dimensions of (L2.6 x W1.5 x D) mm (see figure 5).In third example, a film blank was immersed into water / glycerol (10 wt% of glycerol) bath again for 60 seconds. Right after the film was placed between a male-female mould pair shaped as tray with two square shapes on the bottom part. The shape was formed be pressing to moulds together and solidified to shape placing the forced sample in oven at 104 °C overnight (see figure 6). The mould requires approximately (LI 4% x W17%) of strain.In fourth example, a regenerated cellulose film was manufactured using a pilot machine intended for manufacturing of stand-alone films from dissolved cellulose solution. Here, a stand-alone film was manufactured from cellulose solution (Biocelsol dissolving method) having solids content of 6.80 % and ball drop viscosity (ball dropping time for 200 mm; Dpipe=Dball=l / 8”, 130 mg; modified ASTM D1343-95) of 67 s at 20 °C. The solution was casted on PET substrate in contact with a rotating steel cylinder using a slot die. Wet thickness casting was 400 ± 20 microns. The cylinder transports the dissolved cellulose solution into regeneration bath (10 wt-% sulphuric acid) and was further guided into a washing bath. From the washing bath film was cut and immersed into plasticization bath (10& glycerol / water mixture) for 60 seconds manually offline. Following plasticization film (approx. 180 x 25 cm) was placed on drying jigs, which prevented film shrinkage and provided isotropic character for the film.Finished film having a thickness of approximately 50 microns was stored at standard conditions (50 % RH, 23 °C) until used. Film mechanical properties (strength, Young's modulus, strain at break) were evaluated using Floyd ES 5 Universal Test Machine (AMETEK, USA) equipped with a 100 N load cell. The width of the specimens was 15 mm, and the film thickness for each specimen was measured and recorded as the average of two measurements. The tests were performed with a crosshead speed of 5 mm / min and the clamp span was set to 50 mm. Film specimens were pre-conditioned in three methods: 1) standard conditions (50 % RH, 23 °C), 2) conditioned in humidity cabinet for 24 hours at 90 % RH, 23 °C and 3) immersed into water bath (23 °C) for 60 seconds prior to measurements.Mechanical properties are shown in Figure 7. Immersion into water bath results in more significant increase in strain at break than elevated relative humidity. Strain at break for specimen conditioned at 90 % RH and 60 seconds in water increased by 5 % and 22 % respectively compared to specimen conditioned at 50 % RH.CITATION LISTPatent literatureUS 2,999,756US 3,835,113 US 5,952,064US 4,857,201WO 2009 / 135875 Al

Claims

CLAIMS:

1. A method for manufacturing shaped structures from regenerated cellulose films, characterized in comprising at least the following steps: rewetting the regenerated cellulose film with water, applying the rewetted film into or in between a mould(s), and solidifying the film into the shaped structure via evaporation of moisture in the mould(s).

2. The method according to claim 1, characterized in that the solidification of the film into the shaped structure and evaporation of moisture is carried out by applying heat in temperature between 50 and 110 °C.

3. The method according to claim 1 or 2, characterized in that the rewetting water is used as a carrier for functional components, such as glycerol.

4. The method according to any preceding claims, characterized in that the rewetting is carried out by spraying, dipping, steaming or coating.

5. The method according to any of the preceding claims, characterized in that elongation of the regenerated cellulose film is higher compared to a non-rewetted cellulose film, preferably at least 30%, and more preferably around 40% after the rewetting step.

6. The method according to any of the preceding claims, characterized in applying the film onto a mouldable cellulose-based paper or carton board.

7. A cellulose-based shaped structure, characterized in comprising rewetted, moulded and dried regenerated cellulose film.

8. The cellulose-based shaped structure according to claim 7, characterized in comprising rewetted, moulded and dried regenerated cellulose film on a mouldable cellulose-based paper or carton board.

9. A cellulose-based shaped structure, characterized in consisting of rewetted, moulded and dried regenerated cellulose film.

10. The cellulose-based shaped structure according to any of claims 7 to 9, characterized in that the cellulose film has a thickness between 20 and 100 pm.

11. The cellulose-based shaped structure according to any of claims 7 to 10, characterized in being manufactured according to a method of any of claims 1 to 6.

12. Use of the cellulose-based shaped structure according to any of claims 7 to 11 in food or other packaging applications, for example as plates, cups, bottles, cutlery and food casings.

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