WO2001032987A1

WO2001032987A1 - Moulded fibre products comprising modified starch and process for producing the same

Info

Publication number: WO2001032987A1
Application number: PCT/NL2000/000788
Authority: WO
Inventors: Harald John Kuiper; Benno Alexander Koopmans
Original assignee: Leopack B.V.
Priority date: 1999-11-01
Filing date: 2000-11-01
Publication date: 2001-05-10
Also published as: AU1739301A

Abstract

The present invention relates to a method for the manufacture of a moulded fibre article, said method comprising: a) providing a pulp mass; b) forming said pulp mass to provide a moulded fibre pre-form, in particular via a vacuum forming process; c) drying the moulded fibre pre-form thus obtained, d) optionally further processing the dried moulded fibre pre-form, such as by cutting, coating, colouring, printing; wherein, prior to step b), an additive is added to the pulp mass, said additive comprising at least one starch, starch derivative or starch degradation product, modified with at least one polymeric component. The invention also relates to moulded fibre products or articles obtained by said method.

Description

MOULDED FIBRE PRODUCTS COMPRISING MODIFIED STARCH AND PROCESS FOR PRODUCING THE

SAME

The present invention relates to moulded fibre products and their manufacture. More specifically, the invention relates to additives that can be incorporated into moulded fibre products during their manufacture and that provide advantages with respect to both the manufacturing process as well as the final articles obtained.

European patent 0 228 637 in the name of Chemische Fabrik Stockhausen discloses water soluble, kationic polyelectrolytes consisting of copolymers of acrylamide and dimethylaminopropylamide, that can be used as flocculants, in particular for sewage sludges resulting from waste water treatment.

The copolymers are powdery products, in which the dimethylaminopropylamide has been neutralised or quaternized with mineral acids, in which the quotient of the intrinsic viscosity of the copolymers divided by the molar ratio of acrylamide to dimethylaminopropylacrylamide is at least 200 ml/g, and in which the proportion of kationic monomers in the copolymer is between 4 and 80 mol. %.

For use as a flocculant, these copolymers are preferably used in the form of an aqueous solution containing 0.1 to 0.3 % dissolved powdery polymer.

EP 0 228 637 further relates to a process for the preparation of such water-soluble kationic polyelectrolytes, in which the dimethylaminopropylacrylamide monomers are first neutralized or quaternized with a mineral acid, after which the acrylamide monomers are added and the resulting monomeric mixture is copolymerized.

Other copolymers based on dimethylaminopropylacrylamide (DMAPAA) are for instance described in US-A-3,014,896, cited as prior art in EP 0 228 637. The non-prepublished German application DE 198 32 241.0 in the name of

Stockhausen GmbH, filed on July 17, 1998 describes the use of certain modified starches, obtained through the solubilisation ( Aufschluβ') of starch, starch derivatives or the degradation products thereof in aqueous solution with at least one kationic polymer, as retention agents for pigments, mineral fillers and fibrous fines in the manufacture of paper and cardboard.

In particular, the kationic polymer is a homopolymer or co-polymer containing at least 20% by weight of polymerised dialkylaminoalkyl(meth)acrylamide-units. The starch or starch derivative is preferably an anionic starch or starch derivative. The non-prepublished German application DE 198 32 241.0 also describes the preparation of these kationic polymer-modified starches.

Moulded fibre products and their manufacture are well known in the art. Generally, moulded fibre products are formed from a pulp mass, for instance a pulp mass obtained by milling a fibre-containing material into individual fibres in water or an aqueous medium using a pulper or beater, usually at elevated temperatures of about 30 - 70 °C.

The fibre containing starting material can be fibrous wood or similar materials, but is usually sorted or even unsorted recycled fibre material such as waste paper, cardboard, etc. (sometimes referred to as "secondary fibre"). The pulp mass thus obtained may then be treated to remove both coarse and fine particulate matter (such as solid wastes, plastics, etc.) and may also be treated to remove contaminants such as ink, adhesives, etc. The pulp may also be bleached, grinded/milled, subjected to de-inking, etc., and/or additives known per se may be added, such as couloring agents, paraffin, dewatering agents, retention agents, sizing agents, etc.. The fibrous slurry thus obtained is then formed into the final product article, i.e. by feeding the pulp mass to a mould forming process. In the high-throughput production of egg- trays and other packaging materials, usually a vacuum forming process is used, in which a suction mould (or in case of a two-part suction mould one half thereof) is submersed into the pulp mass, upon which a suitable amount of pulp is sucked onto the mould by application of a vacuum (usually through perforations in the mould).

The mould is then removed from the pulp mass, and the semi-formed article (hereinbelow referred to "pre-form") is separated/ejected from the mould (sometimes referred to as "kickoff) and is then preferably dried, e.g. at elevated temperatures, such as in an oven at about 100 - 300 °C, usually at about 150 - 250 °C. The dried moulded fibre article thus obtained may then be used as such (for instance in the case of egg trays) or optionally be subjected to further processing steps such as cutting, coating, colouring, printing etc..

This process can be used to manufacture a moulded fibre product of any desired shape or size, including egg trays, egg cartons, food trays and food containers, plant pots, as well as specialized (industrial) packaging materials, such as inner supports for packaging for consumer goods such as lightbulbs and electronic equipment. The latter may have highly complex shapes - designed using CAD-techniques- that are specifically adapted to the equipment or parts to be packaged, and that may also provide structural strength and/or impact resistance to the packaging. Increasingly, such moulded fibre packaging materials are replacing bulky polystyrene packaging.

Usually, manufacturing processes for moulded fibre products are carried out at high throughput, for instance using a process as schematically shown in Figure 1. This process uses a first set of suction moulds (2) placed on a first rotating carrier (1). The carrier (1) rotates so as to immerse the moulds (2) in the pulp mass (3) - fed into reservoir (4) from pulper (6) through line (5) - whereupon the moulds (2) take up the part of the pulp, e.g. as a result of suction applied to the mould. The pre-forms thus obtained are then transferred onto a second set of suction moulds (8) placed on a second rotating carrier (7), which transfers the pre-forms (9) onto a belt (10) which carries the pre-forms to drying oven (1 1). Using such equipment, egg trays may be produced in amounts of hunderds of units per minute or more.

In all moulded fibre applications, low production costs are of high importance. In view of this, manufacturers are constantly striving to improve the economy of the manufacturing process. At the same time, manufacturers are constantly striving to improve the properties of the final articles, such as stiffness, binding strength (resistance), etc.. These properties are not only important for relatively simple, high volume products such as egg trays or food containers, but also for the specialized packaging materials mentioned above.

For a further description of known processes for the manufacture of moulded fibre products, reference is made to for instance EP 0 650 543 and US-A-3,553,079. Object of the invention is therefore to provide an improved method for the manufacture of moulded fibre products. A further object is to provide moulded fibre products with improved properties.

It has now been found that the use - in the manufacture of moulded fibre products - of a specific class of additives offers a number of highly significant advantages, both with a view to the manufacturing process as well as the properties of the moulded fibre products obtained. In particular, the use of these additives allows for the production of moulded fibre articles with improved properties, and at lower cost per unit, compared to conventional manufacturing processes.

The additives used according to the invention comprise at least one starch, starch derivative or starch degradation product, in particular an anionic starch or starch derivative, that has been modified with at least one polymeric component, in particular a kationic polymeric component.

It was also found that highly preferred additives are the "PRAESTABOND® system" and "PRAESTABOND® system PK 880", available from Stockhausen GmbH. These additives contain as the kationic polymer the polymer "PK 880", also from Stockhausen

GmbH.

In a first aspect, the invention therefore relates to the use of a starch, starch derivative or starch degradation product that has been modified with at least one polymeric component, in the manufacture of moulded fibre products or articles.

The starch, starch derivative or starch degradation product is most preferably an anionic starch or starch derivative, and the polymeric component is preferably a kationic polymer, more preferably a kationic polymer based on dialkylaminoalkyl(meth)acrylamide units, as further described below. The anionic starch or starch derivative and the kationic polymer are preferably used in the form of an additive that is added to the pulp mass prior to the (vacuum) forming step thereof. Such an additive is preferably in the form of an aqueous solution, obtained by heating the anionic starch or starch derivative and the kationic polymer together in water or an aqueous medium, again as further described below. In a further aspect, the invention therefore relates to a method for the manufacture of a moulded fibre article, said method comprising: a) providing a pulp mass; b) forming said pulp mass to provide a moulded fibre pre-form, in particular via a vacuum forming process; c) drying the moulded fibre pre-form thus obtained, d) optionally further processing the dried moulded fibre pre-form, such as by cutting, coating, colouring, printing; said method being characterised in that, prior to step b), an additive is added to the pulp mass, said additive comprising at least one starch, starch derivative or starch degradation product, modified with at least one polymeric component.

The invention also relates to moulded fibre products or articles obtained by said method, and/or to moulded fibre products or articles that contain an additive as described herein. In this context, by containing is not only meant that such an additive is present (i.e. in a detectable amount) in the final moulded fibre product or article (as it usually will be), but also more generally that such an additive has been used in the manufacture of the moulded fibre product or article, i.e. that such an additive has been added to the pulp (mass) from which the moulded fibre product or article has been formed, e.g. by the aforementioned method. In yet another aspect, the invention relates to the use of (an additive containing) at least one starch, starch derivative or starch degradation product, modified with at least one polymeric component, in the manufacture of moulded fibre products or articles. The invention also relates to the use of at least one starch, starch derivative or starch degradation product, modified with at least one polymeric component, in the preparation of an additive for moulded fibre products or articles.

The starch or starch derivative can be a native starch such as potato, maize or cereal starch; a modified starch, such as starch degradation products including dextrins, chemically modified starches including substituted starches; and/or an anionic starch, including anonic starch esters or anionic starch ethers: and as such any starch, starch derivative, modified starch and/or anionic starch can be used. Examples of these and other suitable starches and starch derivatives are described in the non-prepublished German application DE 198 32 241.0.

Native starches, in particular native anionic starches, and anionic starch derivatives are especially preferred. Some commercially available examples of suitable starches are Cerestar Cbond™ (preferred) and Cerestar 0551 1.

The anionic starch or starch derivative is modified with a kationic polymer, for instance a kationic polymer based on monomers of (meth)acrylic acid and/or derivatives of (meth)acrylic acid. Most preferably, the kationic polymer is essentially as described in the non- prepublished German application DE 198 32 241.0, i.e. a kationic homopolymer or co- polymer based on dialkylaminoalkyl(meth)acrylamide-units, more preferably such a homopolymer or co-polymer that contains at least 20% by weight of such polymerised dialkylaminoalkyl(meth)acrylamide-units. For instance, these kationic polymers can contain at least 20% polymerised units of

(meth)acrylic acid amids with di-C|-C₂-alkylamido-C₂-C₆-alkylamines, present in protonated and/or quaternated form. These include protonated or quaternated, α,β-unsaturated, N- substituted carboxylic acids amids, such as dimethylaminoethyl-acrylamide or- metacrylamide, dimethylaminopropyl-acrylamide or -methacrylamidee, or N (N',N', 2',2"tetramethylaminoprolyl)-acrylamide or methacrylamide.

The kationic polymers can further contain all other monomeric units mentioned in the non-prepublished German application DE 198 32 241.0, such as ,β-unsaturated monomers, ethylenically unsaturated monomers, etc.. For the preparation of these kationic polymers, reference is again made to in the non-prepublished German application DE 198 32 241.0, as well as to EP-A-0 013 416 and EP-A-1 13 038.

The modified starches used as additives in the invention are also obtained essentially as described in the non-prepublished German application DE 198 32 241.0. Generally, this will involve converting the starch or starch derivative with the polymer in aqueous solution at a temperature of 70 - 130 °C, preferably 90 - 100 °C, optionally under elevated pressure. For instance, an aqueous solution of the starch (0.5 - 20 wt.% , preferably 2.0 - 10 wt.%) can be mixed -batch-wise or continuously- with an aqueous solution of the kationic polymer ( 0.1 - 2.0 wt.%, preferably 0.1 - 0.5 wt.%) in a ratio of 4: 1 to 25: 1 , preferably 10: 1 to 25: 1 most preferably 14: 1 to 20: 1 , whereupon the mixture is heated, for instance using a Jet-cooker. For instance, in order to obtain an additive for use in the invention, an aqueous solution/suspension of 1 - 10 wt.% , preferably 2.5 - 5 wt.% starch can be mixed in a Jet Cooker with an aqueous solution/suspension of 1 - 5 wt. %, preferably 2.5 - 5 wt. % polyacrylamide-component, to form a final solution/suspension, which can be added per se to the pulp mass prior to the mould forming step.

Optionally, further additives can then be added, such as those described in the non- prepublished German application DE 198 32 241, in the amounts indicated therein. However, for the purposes of the present invention, the modified starches and starch derivatives are preferably used as such. In the invention, the additive is added to or mixed with the pulp mass prior to the vaccum forming step, for instance by mixing it with the feed that -in the illustrative process shown in Figure 1- is fed to the vacuum forming step through line (5); or by adding it to reservoir (4). The additives will usually be added to the pulp mass in an amount of 0.1 - 5 %, preferably 0.5 - 2.5 % on a dry weight basis. Usually, as in known in the art, the pulp mass is prepared in the pulper (6) with a consistency of about 5,0 to 5,5 %. From the pulper, the pulp is then mixed with water to a consistency of about 3,5 to 4,5 %, to provide the so-called "thick pulp^'" ("dikstof). Prior to use in the forming machine, this "thick pulp" is then usually further diluted -i.e. in a suitable vessel- with water to provide the so-called "thin pulp" ("dunstof) with a consistency of about 1,0 to 1 ,2 %, which is used in the vacuum forming step(s). (Please note that the forming of the "thick pulp" and the "thin pulp", not shown in Figure 1 , will be incorporated into line (5))- According to the invention, the additive may be added to the pulp (mass) at any stage, i.e. to the pulper (6), to line (5), to reservoir (4); and/or to the starting pulp, to the thick pulp or to the thin pulp; or any suitable combination thereof.

However, it has been found that the greatest advantages, such as the highest increase in the stiffness of the final article, the best retention of the starch components and the highest solids content on the forming machine, are obtained when the additive is dosed to the pulp mass at a stage where the pulp has a consistency of about 3,5 - 4,5 % (i.e. to the "thick pulp").

For instance, it has been found that by adding 1,5 wt.% Praestabond to the "thick pulp" (3,5 - 4,5 % pulp consistency), the dry solids content on the forming machine can be (further) increased to 36 - 36,5 %. As a consequence, the amount of energy required for the forming machine (expressed as units of natural gas used by the forming machine per unit of time) can also be reduced, as less water needs to be evaporated from the pulp mass/pre-form. Also, the runnabilily of the forming machine can be (further) optimized, enabling the throughput of the forming machine to be (further) increased. Also, this may allow a (further) reduction of the production weight (e.g. the weight of each unit produced), while still retaining the desired quality and characteristics of the final product obtained; and/or a (further) reduction of the amount of expended energy, starting materials and/or (other) additives used.

The pulp mass is then formed in a manner known per se, and the pre-forms thus obtained are dried, usually in an oven at elevated temperatures of about 100 - 300 °C, usually about 150 - 250 °C. In general, in the drying step, the additives of the invention will allow the use of lower(ed) oven temperatures, compared to conventional moulded fibre processes, which reduces the energy requirements of the process.

The moulded fibre articles thus obtained may then be ready for use (for instance in the case of egg trays) and/or may optionally be processed further in a manner known per se, such as cutting, coating, coloring, printing etc.. The moulded fibre articles or products thus obtained form a further aspect of the invention.

The additives of the invention can be used with advantages in all moulded fibre products, as well as in all processes for the manufacture thereof. In particular, the additives can be used in high throughput - preferably - vacuum forming processes as described above, for instance using a "two rotor" machine as shown in Figure 1, or a "three rotor" machine; as well as in other mould or die forming processes for moulded fibre, in particular pressure forming processes. As mentioned above, such processes can be used for the manufacture of packaging materials, including egg trays, egg cartons, food trays, food containers, plant pots, as well as the specialized packaging materials (inner supports) described above.

The use of the additives of the invention may provide several advantages, relating both to the efficiency of the manufacturing process as well as the properties of the moulded fibre products obtained. These advantages may be obtained alone, but are usually obtained in combination, and inter alia comprise:

Improved runnabilty of the forming machines, including a reduction in the amount of "stickies" (i.e. materials that stick to the mould surfaces upon ejection of the pre-form) and in the amount of production waste. All this means that the time period between changing the mould for cleaning can be longer, which greatly improves the time-on-stream of the vacuum forming machines. It also means that the time and costs involved in cleaning the moulds is reduced, as well as the discharge from the mould cleaning process.

- The mould forming process can be run at higher throughput. - Decreased energy requirement for the forming and drying steps: the drying oven can be run at lower(ed) temperatures;

Improved stiffness. This allows the manufacturer to reduce the weight of the product per unit.

- Improved bending strength, both under conditions of low relative humidity (i.e. up to about 50 - 60%o), as well as conditions of high relative humidity (i.e. about 80% or more).

Increased solids content (expressed as dry weight) of the moulded fibre products. The increased stiffness and higher solids content - which allow for lower drying temperatures - also lead to improved appearance ("visual quality") of the final product, in particular of "white" products; - Generally improved product quality. This means that the process of the invention can be used with a pulp mass obtained from low-grade secondary fibre, such as unsorted or low grade waste paper, and still provide final products of desired quality.

The invention will now be illustrated by means of the non-limiting Example, as well as the Figure, which schematically shows a forming machine of the "two rotor" type.

Example 1 : Manufacture of egg trays. Egg trays were manufactured from a conventional secondary fibre pulp mass in a two rotor vacuum forming machine. The forming process was operated at conditions known per se for the industrial/commercial high throughput manufacture of egg trays.

According to the invention, PRAESTABOND™ system PK 880 - prepared as an aqueous solution/suspension according to the manufacturers instructions - was continously mixed with the pulp mass fed to the forming machine, in an amount corresponding to 2% on a dry weight basis.

After mould forming, the trays were dried in an oven at 240 °C and tested for bending strength (both under high and low humidity conditions), stiffness, as well as visual appearance. In these tests, the egg trays manufactured using the PRAESTABOND™ system PK 880 showed improved characteristics, compared to commercial egg trays made from the same pulp on the same forming machine at the same operating conditions.

"PRAESTABOND™ system" and "PRAESTABOND™ system PK 880" are trade names proprietary to Stockhausen GmbH.

Claims

C L A I M S

1. Method for the manufacture of a moulded fibre article, said method comprising: a) providing a pulp mass; b) forming said pulp mass to provide a moulded fibre pre-form, in particular via a vacuum forming process; c) drying the moulded fibre pre-form thus obtained, d) optionally further processing the dried moulded fibre pre-form, such as by cutting, coating, colouring, printing; said method being characterised in that, prior to step b), an additive is added to the pulp mass, said additive comprising at least one starch, starch derivative or starch degradation product, modified with at least one polymeric component.

2. Method according to claim 1, in which the additive comprises at least one anionic starch or starch derivative modified with at least one kationic polymer.

3. Method according to claim 2, in which the kationic polymer comprises at least one kationic homopolymer or co-polymer based on dialkylaminoalkyl(meth)acrylamide-units, more preferably such a homopolymer or co-polymer that contains at least 20% by weight of such polymerised dialkylaminoalkyl(meth)acrylamide-units.

4. Method according to any of the preceding claims, in which the kationic polymer is PK880 (Stockhausen GmbH) and/or in which the additive is the "PRAESTABOND® system" and/or the "PRAESTABOND® system PK 880"(Stockhausen GmbH).

5. Method according to any of the preceding claims, in which the additive is added to the pulp mass in the form of an aqueous solution/suspension, obtainable/obtained by mixing an aqueous solution/suspension of 1 - 10 wt.% , preferably 2.5 - 5 wt.% of the starch, starch derivative or starch degradation product with an aqueous solution/suspension of 1 - 5 wt. %, preferably 2.5 - 5 wt. % of the polymeric component.

6. Method according to claim 5,in which the aqueous solution is added to the pulp mass in an amount of 0.1 - 5 %, preferably 0.5 - 2.5 %, on a dry weight basis.

7. Method according to any of the preceding claims, for the manufacture of moulded fibre packaging materials, such as egg trays, egg cartons, food trays, food containers, plant pots and/or specialized packaging materials, such as an inner support for the packaging of consumer goods.

8. Use of an starch, starch derivative or starch degradation product, modified with at least one polymeric component, in the manufacture of moulded fibre products or articles.

9. Use according to claim 8, in which the starch, starch derivative or starch degradation product comprises at least one anionic starch, starch derivative or starch degradation product, and the at least one polymeric component comprises at least one kationic polymer.

10. Use according to claim 8 or 9, in which the kationic polymer comprises a kationic homopolymer or co-polymer based on dialkylaminoalkyl(meth)acrylamide-units, preferably a homopolymer or co-polymer based on dialkylaminoalkyl(meth)acrylamide-units that contains at least 20%> by weight of such polymerised dialkylaminoalkyl(meth)acrylamide- units.

11. Use according to any of claims 8 - 10, in which kationic polymer-modified anionic starch, starch derivative or starch degradation product is used in the form of an additive, said additive comprising an aqueous solution/suspension obtainable/obtained by mixing/heating an aqueous solution/suspension of 1 - 10 wt.% , preferably 2.5 - 5 wt.% of the starch, starch derivative or starch degradation product with an aqueous solution/suspension of 1 - 5 wt. %, preferably 2.5 - 5 wt. % of the polymeric component, at a temperature of 70 - 130 °C, preferably 90 - 100 °C, optionally under elevated pressure.

12. Use according to claim 1 1, in which the additive comprises "PRAESTABOND® system" and/or "PRAESTABOND® system PK 880" (Stockhausen GmbH), or an aqueous solution thereof.

13. Use according to any of the preceding claims, comprising adding the polymer- modified anionic starch, starch derivative or starch degradation product and/or the additive comprising the polymer-modified anionic starch, starch derivative or starch degradation product to a pulp mass prior to forming thereof.

14. Moulded fibre product or article, obtainable by the method of any of claims 1-7 and/or by the use of claims 8-13.

15. Moulded fibre product or article, containing at least one starch, starch derivative or starch degradation product, modified with at least one polymeric component; and/or containing at least one additive comprising at least one starch, starch derivative or starch degradation product, modified with at least one polymeric component.

16. Moulded fibre product according to claim 14 and/or 15, in the form of a packaging material, such as an egg tray, egg carton, food tray, food container, plant pot, and/or in the form of a specialized packaging material, such as an inner support for the packaging of consumer goods.

17. Use of a starch, starch derivative or starch degradation product, modified with at least one polymeric component, in the manufacture of an additive for moulded fibre products or articles.

18. Use according to claim 17, in which the starch, starch derivative or starch degradation product comprises at least one anionic starch, starch derivative or starch degradation product, and the at least one polymeric component comprises at least one kationic polymer.