Film comprising microfibrillated cellulose and products made therefrom

Abstract

The present invention is directed to a film comprising a base film which has been coated on at least one side with a coating that enhances gas and/or moisture barrier properties, wherein the base film comprises a fiber material and at least 60% by weight of said fiber material is microfibrillated cellulose, and the thickness of the coating is from 0.05 to 20 μm. The invention is also directed to products using said film. Such products are in particular packages suitable for sensitive objects that need to be packaged in a controlled or modified atmosphere. The film is also useful for other purposes, such as in the manufacture of balloons.

Claims

1. A film comprising: a base film which has been coated on at least one side with a coating that enhances gas and/or moisture barrier properties, wherein the base film comprises a fiber material and at least 60% by weight of said fiber material is microfibrillated cellulose, wherein the thickness of the coating is from 0.05 to 20 μm, per side of the base film, wherein the film is compostable, or biodegradable, or both, wherein the film is heat sealable, and wherein the coating comprises at least one component selected from a group consisting of: ethylene copolymers, acrylic polymers and copolymers, copolymers of styrene and butadiene, vinyl acetate polymers, polyvinyl alcohol, polylactic acid, poly-ethylene vinyl acetate, polyethylene vinyl chloride, polyvinylidene chloride, and mixtures thereof.

2. The film according to claim 1, wherein more than 80% of the coating applied has not penetrated deeper than 5 μm into the base film.

3. The film according to claim 1, wherein the film is not part of a laminate.

4. The film according to claim 1, wherein the coating has been carried out with a varnish which is UV or EB curable.

5. The film according to claim 1, wherein the coating has been carried out with a water-based varnish.

6. The film according to claim 1, wherein the coating has been applied by printing.

7. The film according to claim 1, wherein both sides of the base film have been coated.

8. The film according to claim 1, wherein the thickness of the coating is from 0.05 to 10 μm, per side of the base film.

9. A modified atmosphere package or controlled atmosphere package comprising: the film according to claim 1.

10. A balloon comprising: the film according to claim 1.

Description

DETAILED DESCRIPTION

(1) The microfibrillated cellulose used in the film according to the present invention can be prepared using methods known in the art.

(2) In one embodiment of the present invention, the base film is formed in a paper making machine or according to a wet laid production method, by providing a suspension onto a wire and dewatering the web to form an intermediate thin substrate or said base film. A suspension comprising microfibrillated cellulose is provided to form said base film.

(3) The microfibrillated cellulose content of the suspension may, according to one embodiment be in the range of from 60 to 99.9 weight-% based on the weight of solids of the suspension. In one embodiment, the microfibrillated cellulose content of the suspension may be in the range of 70 to 99 weight-%, in the range of 70 to 95 weight-%, or in the range of from 75 to 90 weight-%.

(4) Microfibrillated cellulose (MFC) shall in the context of the patent application mean a nano scale cellulose particle fiber or fibril with at least one dimension less than 100 nm. MFC comprises partly or totally fibrillated cellulose or lignocellulose fibers. The liberated fibrils have a diameter less than 100 nm, whereas the actual fibril diameter or particle size distribution and/or aspect ratio (length/width) depends on the source and the manufacturing methods.

(5) The smallest fibril is called elementary fibril and has a diameter of approximately 2-4 nm (see e.g. Chinga-Carrasco, G., Cellulose fibres, nanofibrils and microfibrils: The morphological sequence of MFC components from a plant physiology and fibre technology point of view, Nanoscale research letters 2011, 6:417), while it is common that the aggregated form of the elementary fibrils, also defined as microfibril (Fengel, D., Ultrastructural behavior of cell wall polysaccharides, Tappi J., March 1970, Vol 53, No. 3.), is the main product that is obtained when making MFC e.g. by using an extended refining process or pressure-drop disintegration process. Depending on the source and the manufacturing process, the length of the fibrils can vary from around 1 to more than 10 micrometers. A coarse MFC grade might contain a substantial fraction of fibrillated fibers, i.e. protruding fibrils from the tracheid (cellulose fiber), and with a certain amount of fibrils liberated from the tracheid (cellulose fiber).

(6) There are different acronyms for MFC such as cellulose microfibrils, fibrillated cellulose, nanofibrillated cellulose, fibril aggregates, nanoscale cellulose fibrils, cellulose nanofibers, cellulose nanofibrils, cellulose microfibers, cellulose fibrils, microfibrillar cellulose, microfibril aggregrates and cellulose microfibril aggregates. MFC can also be characterized by various physical or physical-chemical properties such as large surface area or its ability to form a gel-like material at low solids (1-5 wt %) when dispersed in water. The cellulose fiber is preferably fibrillated to such an extent that the final specific surface area of the formed MFC is from about 1 to about 300 m.sup.2/g, such as from 1 to 200 m.sup.2/g or more preferably 50-200 m.sup.2/g when determined for a freeze-dried material with the BET method.

(7) Various methods exist to make MFC, such as single or multiple pass refining, pre-hydrolysis followed by refining or high shear disintegration or liberation of fibrils. One or several pre-treatment step is usually required in order to make MFC manufacturing both energy efficient and sustainable. The cellulose fibers of the pulp to be supplied may thus be pre-treated enzymatically or chemically, for example to reduce the quantity of hemicellulose or lignin. The cellulose fibers may be chemically modified before fibrillation, wherein the cellulose molecules contain functional groups other (or more) than found in the original cellulose. Such groups include, among others, carboxymethyl (CM), aldehyde and/or carboxyl groups (cellulose obtained by N-oxyl mediated oxydation, for example “TEMPO”), or quaternary ammonium (cationic cellulose). After being modified or oxidized in one of the above-described methods, it is easier to disintegrate the fibers into MFC or nanofibrillar size fibrils.

(8) The nanofibrillar cellulose may contain some hemicelluloses; the amount is dependent on the plant source. Mechanical disintegration of the pre-treated fibers, e.g. hydrolysed, pre-swelled, or oxidized cellulose raw material is carried out with suitable equipment such as a refiner, grinder, homogenizer, colloider, friction grinder, ultrasound sonicator, fluidizer such as microfluidizer, macrofluidizer or fluidizer-type homogenizer. Depending on the MFC manufacturing method, the product might also contain fines, or nanocrystalline cellulose or e.g. other chemicals present in wood fibers or in papermaking process. The product might also contain various amounts of micron size fiber particles that have not been efficiently fibrillated. MFC is produced from wood cellulose fibers, both from hardwood or softwood fibers. It can also be made from microbial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources. It is preferably made from pulp including pulp from virgin fiber, e.g. mechanical, chemical and/or thermomechanical pulps. It can also be made from broke or recycled paper.

(9) The above described definition of MFC includes, but is not limited to, the new proposed TAPPI standard W13021 on cellulose nanofibril (CMF) defining a cellulose nanofiber material containing multiple elementary fibrils with both crystalline and amorphous regions.

(10) According to another embodiment, the suspension may comprise a mixture of different types of fibers, such as microfibrillated cellulose, and an amount of other types of fiber, such as kraft fibers, fines, reinforcement fibers, synthetic fibers, dissolving pulp, TMP or CTMP, PGW, etc.

(11) The suspension may also comprise other process or functional additives, such as fillers, pigments, wet strength chemicals, dry strength chemicals, retention chemicals, cross-linkers, softeners or plasticizers, adhesion primers, wetting agents, biocides, optical dyes, fluorescent whitening agents, de-foaming chemicals, hydrophobizing chemicals such as AKD, ASA, waxes, resins etc. Additives can also be added using a size press.

(12) The papermaking machine that may be used in the process according to the present invention may be any conventional type of machine known to the skilled person used for the production of paper, paperboard, tissue or similar products.

(13) Subsequent to the wet web being placed onto the wire, it is dewatered to form an intermediate thin substrate or film.

(14) The dewatering on wire may, according to one embodiment be performed by using known techniques with single wire or twin wire system, frictionless dewatering, membrane-assisted dewatering, vacuum- or ultrasound assisted dewatering, etc. After the wire section, the wet web is further dewatered and dried by mechanical pressing including shoe press, hot air, radiation drying, convection drying, etc. The film might also be dried or smoothened by soft or hard nip (or various combinations) calenders etc.

(15) According to one embodiment the wet web is dewatered by vacuum, i.e. water, and other liquids, is sucked from the furnish when it is placed on the wire.

(16) The film according to the present invention can be heated, for example in a conventional household oven. The film may contain additives that improve the resistance to heat. Further, the film may contain additives such as salts and/or metal oxides to improve the fire or flame resistance of the film, which may particularly useful when the film is used in the manufacture of a balloon.

(17) In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.