WO2022219526A1

WO2022219526A1 - A multilayered moulded product and method for the preparation thereof

Info

Publication number: WO2022219526A1
Application number: PCT/IB2022/053422
Authority: WO
Inventors: Isto Heiskanen; Kaj Backfolk
Original assignee: Stora Enso Oyj
Current assignee: Stora Enso Oyj
Priority date: 2021-04-12
Filing date: 2022-04-12
Publication date: 2022-10-20
Anticipated expiration: 2023-10-12

Abstract

The present invention relates to a multi-layered moulded product comprising at least one bulky layer (A) comprising fibres and having a density of 100-700 kg/dm3, and at least one high-density layer (B) comprising fibres and at least 20 wt% highly-refined cellulose calculated on the total weight of said high-density layer, and having a density ≥700 kg/dm3, wherein the high-density layer (B) is arranged on at least one side of a bulky layer (A), or between two bulky layers (A).

Description

A MULTILAYERED MOULDED PRODUCT AND METHOD FOR THE PREPARATION THEREOF

FIELD OF THE INVENTION

The present invention concerns a multi-layered moulded product and a method of making the said product.

TECHNICAL BACKGROUND

During recent years there has been an increased awareness of the impact of packaging material on the environment and there is a demand for materials that cause less harm to the environment than petroleum-based plastics. Lignocellulose or cellulose-based fibers have a special potential, as the most abundant renewable natural polymers on earth, and the availability of methods for preparing large volumes on an industrial scale, often presented in the forms of chemical or mechanical pulp with disintegrated cellulosic fibers. Moulded cellulosic pulp provides for an environmentally friendly packaging material that is recyclable, compostable and biodegradable.

While there is a demand for environmentally friendly packaging products, especially single-use food packaging products, a known problem with wet moulded pulp products is that it has proven to be difficult to provide barrier properties. Packages for food requires adequate grease resistance, or water repellence properties, or both. To impart such properties to a moulded article of cellulose, a surface treatment or coating method is often required. In addition, the coating should preferably have properties that not only improves the properties but also facilitates the manufacturing of the moulded articles without compromising repulpability and recyclability. Prior art discloses ideas to provide desired properties to the moulded products, e.g. post-coating the moulded product with barrier coating layer, or to add functional chemicals such as AKD to the furnish to hydrophobize the material.

A moulded product formed by cellulose fibres provided with a layer of a lignophenol derivative and a surface layer of a microfibrillated cellulose has been disclosed in JP200513322 (Showa Marutsutsu Co Ltd). JP2018062718A (Daio Paper Corp) presents manufacturing of a cellulose nanofibre moulded component. An acoustic diaphragm prepared by immersing a substrate in a liquid dispersion of microfibrillated pulp and depositing the pulp on the substrate by suction is disclosed in US5473121A (Sony Corporation). SE541435 (Stora Enso) presents a process for spraying microfibrillated cellulose (MFC) onto a moulded article to provide the article with a coating layer. The addition of MFC to a wet moulded pulp may on one hand improve strength properties and smoothness, but on the other hand increase drainage time and therefore production costs associated with dewatering and drying. Also, current moulding techniques lead to a rough surface on the end-product, reducing barrier function and resulting in a need of high amounts of chemical additives.

There is a need for cellulose-based, surface treated or coated moulded articles where the coating preferably has properties that not only improves the product properties but also facilitates the manufacturing of the moulded articles as well as repulpability and recycling. SUMMARY OF THE INVENTION

An object of the present disclosure is to provide a multilayered moulded product and a method of making the said product, which overcomes or mitigates at least some of the disadvantages of such products in the prior art.

It has been found that using a multilayer approach may speed up the manufacturing process and provide a more efficient use of cellulose.

In such a multilayer approach, a high-density layer comprising highly refined cellulose is positioned on at least one side of a bulky layer comprising cellulose thus creating a multilayer moulded product.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1A illustrates the moulding of a bulky layer (A);

Fig. IB illustrates the moulding of a high-density layer (B); and

Fig. 1C illustrates a multilayered product, wherein a high-density layer (B) is positioned on the inside of a bulky layer (A).

DETAILED DESCRIPTION OF THE INVENTION One aspect of the present invention is a multilayered moulded product comprising at least one bulky layer (A) comprising cellulose fibers and having a density of 100-700 kg/dm³, and at least one high- density layer (B) comprising fibres and at least 20 wt% highly refined cellulose, as calculated on the total fiber weight of said high-density layer, wherein the high-density layer (B) has a density ³700 kg/dm3 and is arranged on at least one side of a bulky layer (A).

In one aspect of the invention, said bulky layer (A) has a density between 200 - 700 kg/dm³, or more preferably 250 - 600 kg/dm³. Another aspect of the present invention is a process for the preparation of a multilayered moulded product comprising fibers, wherein the process comprises providing at least one bulky layer (A) comprising cellulose fibres and having a density of 200-700 kg/dm³; providing at least one moulded high-density layer (B) having a density ³700 kg/dm³, such as between 700 - 1400 kg/dm³, comprising fibres and at least 20 wt% highly refined cellulose as calculated on the dry weight of said high-density layer, and joining the bulky layer (A) to the high-density layer (B).

According to one aspect of the process for preparation of a multi layered product according to the invention, each of the provided bulky layer (A) and moulded high-density layer (B) respectively has a dry content of at least 15wt%, preferably at least 30wt%.

Preferably, each of the two layers (A) and (B) are moulded layers comprising a 3D shape.

According to one aspect of the invention, each of the two layers (A) and (B) is wet moulded separate from each other before being joined into a multi-layered product.

According to one aspect of the invention, each of the two layers (A) and (B) are provided as free-standing and self-supporting structures i.e. not necessarily supported by any mould to retain the shape, and are joined together to form the multi-layered moulded product. A free-standing moulded structure (A) and (B) preferably has a dry content of at least 30wt%, preferably at least 40wt%. It is advantageous to manufacture the high-density layer (B) by means of wet moulding into a separate structure (i.e. separate from the bulky layer (A)) before joining it to a bulky matching layer (A) because it is possible to obtain an even (high-density) layer void of any pin-holes, which thus provides a reliable functionality (such as barrier properties) across its entire surface.

The bulky layer (A) comprising fibres, such as natural fibres, such as lignocellulose fibres or cellulose fibres, according to the present invention, can be moulded using methods known in the art. In the production of moulded pulp layers, formation moulds typically descend in a vat filled with pulp. A vacuum then sucks the pulp mixture onto the formation moulds. The formation moulds may contain a stainless steel mesh, which ensures an even vacuum through the mould and provides for an even distribution of the pulp over the mould surface. Moulded layers produced in this way typically have a rough surface. As used herein, the term moulded article encompasses a wet, semidry, dry moulded article as well as an interim product.

The bulky layer (A) may be moulded in a female mould or a male mould. Fibres used in the bulky layer (A) can be, for example, lignocellulose fibres derived from wood or agriculture sources. It can also be recycled fibre such as deinked pulp. Other examples of pulps included are kraft pulp, dissolving pulp, CTMP, TMP, NSSC, reinforcement pulps, cellulose fines, sulphite pulps, pulps obtained from e.g. organosolv processes. The pulp can further be unbleached or bleached or even coloured. Preferably the suspension used to form the bulky layer (A) comprises at least 5wt% or preferably at least 10wt% or more preferably at least 15wt% such as 15-90 wt% pre- consumer waste or reject. Said reject is free from PFAS i.e. per- and polyfluoroalkyl substances. Said reject contains preferably less than 1 wt% wet strength additives. Said reject is preferably free from NIAS (non-intentionally added substances). Said reject is preferably thermo-chemically treated in at least one step in order to reduce microbial activity and to allow reduced amount of biocides.

The bulky layer (A) and/or the high-density layer (B) may further contain process and performance chemicals. Example of process chemicals are e.g. drainage chemicals, slip or lubricants, wet strength chemicals, and fillers. Example, of performance chemicals are such that affects the final end product properties such as hydrophobicity (AKD, ASA, Rosin sizes, SMA, waxes preferably <15 kg/tn), wet strength (various resins e.g. PAE), strength (polysaccharides such as starches or cellulose derivatives), rub resistance, oil and grease resistance (barrier chemicals esp. PVOH of derivatives thereof, cellulose derivatives), electrostaticity (metal salts), printability (Metal salts, cationic polymers, pigments), etc. Some of the additives can improve both process and performance.

The bulky layer (A) should preferably be low density, bulky and designed for providing rigidity and stiffness at low material usage.

One desired feature of the bulky layer (A) is that it is permeable such that the high-density layer (B) can be applied on the partly dried bulky layer (A).

According to some examples, the grammage of the bulky layer (A) is 50-500 g/m² or more preferably 50-400 and most preferably 50-350 g/m². According to a preferred aspect of the present invention, the high density layer (B) comprises a highly refined pulp with degree of Schopper Riegler of 70-94.

According to one aspect of the invention, the high-density layer of the moulded product of the present invention comprises at least 20wt% highly refined pulp based on the total fiber weight of the high-density layer (B), or more preferably between 50-99 wt%, based on the total fiber weight of the high-density layer.

According to one aspect of the invention, the highly refined pulp has been prepared in presence of at least one polysaccharide co-additive at a concentration between 0.1-20 wt%. The preferred polysaccharide is cellulose derivative such as sodium carboxymethyl cellulose.

According to some examples, the grammage for the high-density layer (B) is 5-100 g/m², more preferably 5-80 g/m² and most preferably 5-60 or 5-50 g/m².

An advantage according to the inventive approach is quick and easy drainage and dewatering. Also, concentrating barrier chemicals to the high-density layer (B) will be more efficient than if adding barrier chemicals to the bulky layer (A). Both the bulky layer (A) and the high-density layer (B) can comprise process or functional chemicals.

Using highly refined cellulose/highly refined pulp in said high-density layer (B) provides rigidity to the moulded end product. A further advantage of using highly refined pulp is that it may act as a barrier especially against greases and fats but also e.g. aroma or gases. If combining with other performance chemicals, barrier properties can be further improved.

The high-density layer (B) may be made in a different moulding unit than the bulky layer (A). Such a solution would e.g. allow for use of different furnishes upon manufacturing.

In one embodiment of the present invention, the moulding of the bulky layer (A) may be carried out in a female mould, and the high- density layer (B) is moulded in a male mould. In another embodiment, the moulding of the high-density layer (B) is made in a female mould and the bulky layer (A) is made in a male mould.

When using male and female moulds, the male mould part as inserted in the female mould part may form a slot between said moulds, wherein said slot the multi-layered moulded product would fit.

As an example, the bulky layer (A) is dewatered to at least >5 wt% and more preferably >10 wt% and most preferably 15-85 wt%. Thus, when sufficiently dewatered, most of the water is drainage from the structure and a second layer (i.e. layer (B)) can be applied.

As an option, the bulky layer (A) will also have high wet strength so it can be dipped in a second solution without dissolving or contaminating such a second furnish.

In another embodiment of the present method, the moulded high- density layer (B) may be placed onto one side of the bulky layer (A) while the bulky layer (A) is still in the mould. A vacuum may still be applied to the mould with the bulky layer (A) when the high-density layer (B) is placed onto the bulky layer (A). In a further embodiment, the moulded bulky layer (A) may be placed onto one side of the high-density layer (B) while the high-density layer (B) is still in its mould. A vacuum may still be applied to the mould with high-density layer (B) when the bulky layer (A) is placed onto the high-density layer (B).

The dry content of the moulded article according to the present invention may be more than 50% by weight, such as more than 60% by weight, more than 70% by weight, more than 80% by weight or more than 90% by weight.

In one embodiment of the present invention the bulky layer (A) is at least partly dried prior to applying at least one high-density layer (B) thereon.

In one embodiment of the invention, the moulded article is, at least partly, being dried or dewatered after that at least one high-density layer (B) has been applied to at least one bulky layer (A).

In one embodiment of the present invention, the contact angle of a water drop placed on the surface of the coated moulded article is more than 60° such as more than 80° or more than 90°. The contact angle can be determined using methods known in the art.

In one embodiment of the present invention, the oil and grease resistance according to the KIT method is at least 6 or more preferably at least 8 such as between 8-12 (KIT Standard ISO 16532- 2). Definitions

It is to be understood that "cellulose fibers" referred to herein corresponds to material comprising natural cellulose-based fibers and/or lignocellulose fibres, including aqueous pulp compositions and/or fiber-based sheet or web materials. Any cellulosic fibers known in the art, including cellulose fibers if any natural origin, such as those derived from vegetable pulp or agricultural-based pulp, can be used in cellulose fiber material. Non-limiting examples of cellulose fibers suitable for use in this invention are cellulose fibers derived from softwoods such as pines, firs and spruces, as well as fibers derived from eucalyptus, bagasse, bamboo and other ligneous and cellulose sources.

A cellulose fibre is significantly longer than it is wide. Cellulose fibres can have a mean width of 10 to 50pm. The fibre length of softwood can be from 2.5 to 4.5 mm, while hardwood can have a fibre length from 0.7 to 1.6 mm, and Eucalyptus from 0.7 to 1.5 mm. However, the fibre length can vary considerably with different growing place, etc. The cellulose fibres in the material disclosed herein can have a length from 0.1 mm to 65 mm, from 0.1 mm to 10 mm, or 0.5 mm to 65 mm, or from 0.5 mm to 10 mm, or from 0.5 mm to 7 mm. The fibre lengths may provide different mechanical characteristics to the material. Due to the length of fibres, they can entangle with each other and impart fibre to fibre interbonds that bring strength to the material. The aspect ratio, i.e. the ratio of the fibre length to the fibre width, of the cellulose fibres in the material according to the present invention can be at least 10, at least 25, at least 50, at least 75, or at least 100. The aspect ratio can be up to 6500, or preferably up to 2000. It is also to be understood that said "highly refined pulp" / "highly refined cellulose" is cellulose refined to an SR value in the range of 70-94, preferably in the range of 70-90, and wherein the cellulose fibers have a length of <1 mm. The Schopper-Riegler value can be obtained through the standard method defined in EN ISO 5267-1. This SR value is determined for a pulp, with or without additional chemicals, thus the fibers have not consolidated into a film or started any hornification or such. To determine the Schopper Riegler value it is preferable to take a sample just after the disintegration when consistency is relatively low. The skilled person understands that paper making chemicals, such as retention agents or dewatering agents, have an impact on the SR value. The SR value specified herein, is to be understood as an indication but not a limitation, to reflect the characteristics of the material itself.

An advantage of highly refined pulp is that it has high surface area and provides better strength due to presence of long fibers. Also, it has very low infiltration behaviour, believed by the inventors to be important for enabling a layered structure.

Claims

1. A multi-layered moulded product comprising at least one bulky layer (A) comprising fibres and having a density of 100-700 kg/dm³, and at least one high-density layer (B) comprising fibres and at least 20 wt% highly-refined cellulose calculated on the total weight of said high-density layer, and having a density ³700 kg/dm³, wherein the high-density layer (B) is arranged on at least one side of a bulky layer (A), or between two bulky layers (A).

2. A multi-layered product according to claim 1, wherein the fibres in the bulky layer (A) are lignocellulose fibres.

3. A multi-layered product according to claim 1, wherein the fibres in the high-density layer (B) are lignocellulose fibres.

4. A multi-layered product according to any one of the previous claims, wherein the bulky layer (A) has a density between 200 - 700 kg/dm³, or more preferably 250 - 600 kg/dm³.

5. A multi-layered product according to claim 3 or 4, wherein the high-density layer (B) comprise at least 50 wt% highly refined cellulose.

6. A multi-layered product according to claim 1, wherein the high- density layer (B) further comprise drainage chemicals, slip or lubricants, wet strength chemicals, and fillers.

7. A process for manufacturing of a multi-layered moulded product, wherein the process comprises providing at least one bulky layer (A) comprising fibres and having a density of 100-700 kg/dm³, providing a wet moulded high-density layer (B) comprising fibres and at least 20 wt% highly refined cellulose as calculated on the total weight of said high-density layer, and position the bulky layer (A) and the moulded high-density layer (B) together thus creating a multi-layered product.

8. A process according to claim 7, wherein the bulky layer (A) is provided by wet moulding.

9. A process according to claim 7, wherein the high-density layer

(B) comprises at least 50 wt% highly refined cellulose.

10. A process according to claim 7, wherein the high-density layer (B) is formed in a different moulding unit than the bulky-layer (A).

11. A process according to any one of claims 7-10, wherein said high- density layer has a density ³700kg/dm³.

12. A process according to any one of claims 7-11, wherein the bulky layer (A) and the high-density layer (B) respectively are moulded separately from each other before being joined to each other to form a multi-layered product.

13. A multi-layered product prepared according to the process in claim 7.