DE102019131233A1 - Barrier layer for cellulose substrate - Google Patents

Abstract

The invention relates to a method for the production of coated substrates, in which a flowable, biodegradable and gas-tight first coating is applied to a cellulose-containing substrate Coating a second waterproof coating made of animal and / or vegetable waxes and / or lipids is applied.

Description

The invention relates to a process for the production of coated substrates, in which a flowable, biodegradable and gas-tight first coating is applied to a cellulose-containing substrate.

Packaging made of cellulose, in particular made of cast fiber, cardboard and paper are enjoying increasing popularity. Cellulose fibers are a frequently used material that is extremely easy to recycle. Recycled raw materials (wood, paper, etc.) are also ideal for the production of cellulosic packaging. The cellulose is processed, for example, in the fiber casting process. An aqueous pulp with cellulose fibers is produced from which the fibers are shaped. Using a simple scooping process, the water can be sucked off by a suction mold, with the cellulose fibers being deposited on the pore-provided surface of the suction mold. In the transfer process, the molded body formed by the suction mold is transferred to a transfer mold so that it is shaped from both sides. Additional thermal processing methods and pressing methods can be used, which increase the surface quality of the molded body. Alternatively, the cellulose can be processed into paper or cardboard and used as a packaging material.

It is known from the prior art to make cellulose-containing substrates essentially gas-tight by means of a coating. For this purpose, the substrates can e.g. with cellulose fibers, in particular microfibrils and / or nanofibrils made of cellulose, are coated.

Such coating processes are known from the publications EP 3 444 399 A1 , JP 2015 227517 A , JP 2012 011651 A , WO 2017 / 144009A1 , EP2529942B1 and WO 2017/072124 A1 . The substrates coated with cellulose fibrils are additionally coated with polymers such as polyethylene or polypropylene, but also with biodegradable polymers such as polylactic acid or polyvinyl alcohol.

The object of the invention is to produce a largely gas- and watertight packaging for packaging food, which is primarily made of natural raw materials.

According to the invention, this object is achieved in that a second waterproof coating composed of predominantly animal and / or vegetable waxes and / or lipids is applied to the first coating.

The second coating can contain, for example, at least 90% by weight of animal and / or vegetable waxes and / or lipids. The second coating can contain at least 70% by weight of animal and / or vegetable waxes.

The first coating and / or the second coating can be applied by spraying.

In other words, the sealing layer applied to the cellulose substrate can be made resistant to water and moisture by applying a layer of natural waxes and / or oils or fats. Natural waxes and / or lipids mainly consist of esters of fatty acids and, as oil-soluble products, are readily biodegradable according to the test method CEC-L-33-A-93. The entire coated packaging consequently consists mainly of cellulose fibers, possibly other natural components and natural lipids or waxes, and can therefore be disposed of in an environmentally friendly way, but can also be recycled.

• • Leinöl,
• • Carnaubawachs, und/oder
• • Bienenwachs.

In practice, the second coating can contain at least one of the following components:

• • Linseed oil,
• • Carnauba wax, and / or
• • beeswax.

Linseed oil is used to improve the malleability of the oil-wax mixture, which forms the second coating, and to minimize its brittleness after drying. Pharmaceutical, i.e. completely clarified, pure linseed oil should be used. Linseed oil is one of the few hardening oils and has been used for wood impregnation for centuries. A layer of linseed oil alone is open-pored, which means that some water and air can pass through, and is not suitable for permanently sealed food packaging.

Carnauba wax is a very hard, tropical wax with a high melting temperature (approx. 85-89 ° C). It has hardly any smell or taste of its own and is waterproof. It is very brittle when dry and hardens within seconds. Due to its hardness, it is also very resistant to abrasion. It is approved for food packaging and has long been used as a coating to increase the shelf life of, for example, mangos, sweets, etc.

Beeswax is an i.a. wax produced in Europe that is less hard than carnauba wax. When mixed with carnauba wax, beeswax helps reduce brittleness. It has hardly any inherent odor or taste and is also approved for use in connection with food. Its melting point is around 65 ° C.

• • 20 bis 30 Gew.-% Leinöl,
• • 40 bis 60 Gew.-% Carnaubawachs und
• • 30 bis 40 Gew.-% Bienenwachs.

In particular, the second coating can contain the following components:

• • 20 to 30% by weight linseed oil,
• • 40 to 60 wt .-% carnauba wax and
• • 30 to 40% by weight beeswax.

This mixture has the positive properties of the three components, i.e. high impermeability and abrasion resistance, a neutral smell or taste and high flexibility at ambient temperature. The coating properties of this mixture in combination with the underlying layer of cellulose microfibrils or cellulose nanofibrils is very well suited to meet the requirements for water resistance and gas tightness that are required for food packaging.

In practice, the flowable first coating solution for producing the first coating can have cellulose nanofibrils or microfibrils dissolved in water. Nanocellulose has cellulose microfibrils with a median diameter in a range from 30 to 100 nm and / or cellulose nanofibrils with a median diameter in a range from 5 to 20 nm. Industrially marketed cellulose fibrils are often a mixture of microfibrils and nanofibrils. In practice, a mixture of 2% by weight of nanocellulose in 98% by weight of water has proven itself for the first coating. If a higher cellulose content is selected, deformation of the fiber-containing substrate by the moisture can be reduced or avoided and the drying time shortened. In practice, a cellulose content of 2 to 10% by weight of the first coating solution is suitable.

However, there are other organic materials which, in a coating, increase the impermeability of a cellulose substrate to the penetration of gas. For example, casein powder can be mixed with water and denatured with calcium hydroxide. The casein increases the impermeability and mechanical strength of the substrate. Casein denatured with calcium hydroxide also becomes water repellent to some extent. It is also possible to denature the casein with baking soda, but this does not make it water-repellent. A coating with casein is particularly suitable for dairy products, the manufacture of which may produce casein. The strength-increasing effect of the casein coating enables the substrate to be used, for example, as a substitute for plastic, for example in the manufacture of disposable cutlery. Disposable cutlery can also be made from cellulose-coated substrates with a waterproof second layer. A casein coating can, however, significantly increase the strength, which e.g. is important in using the substrate to form a knife.

In practice, 30 g of casein powder were left to swell with 100 ml of water for about 8 to 10 hours, 30 g of calcium hydroxide were added and stirred. After another 50 ml of water had been added, the solution was sieved and used for coating. This coating can be applied after coating with cellulose fibers or as an alternative to coating with cellulose fibers. The first coating can also contain both cellulose fibers and casein.

Whey is also suitable as a component of the first coating. Whey can be denatured by heat (90 ° -100 ° C). Whey as part of the first coating also increases the strength of the coated substrate. The whey coating itself is not water-repellent and must therefore be made waterproof with the second coating.

Finally, gel-forming components such as agar agar (gelatine from algae) or psyllium husks (seed husks of the plantain species Plantago indica, Plantago afra) are suitable for adding to the first coating. Agar agar powder is e.g. for this purpose mixed with water and for 1 min. denatured at 100 ° C. When it cools, it hardens and gels. The gel can be applied to the substrate and forms a thin layer that closes the pores of the substrate, increases its strength and repels water.

A similar effect is achieved when ground psyllium husks are soaked in water and after approx. 20 minutes. Swelling is applied to the substrate.

As mentioned, the components of the first coating can be dissolved in water and applied at the same time. However, it is also possible to apply various components of the first, non-waterproof coating to the substrate in several application processes.

The first coating can first be dried before the second coating of natural waxes and lipids is applied. The water-containing first coating does not mix with the second coating of oil and wax, so that complete drying is desirable before the second coating is applied.

As mentioned at the beginning, the substrate itself is formed from cellulose fibers. In particular, the substrate can be produced as a thin-walled product using the fiber casting process with or without subsequent pressing or thermal molding.

• • eines Bechers;
• • eines Topfes;
• • eines Behälters;
• • eines Messers;
• • einer Gabel;
• • eines Löffels;
• • eines Tellers.

The substrate can have many different shapes, such as shape

• • a cup;
• • a pot;
• • a container;
• • a knife;
• • a fork;
• • a spoon;
• • a plate.

The substrate can serve as food packaging or as disposable crockery or cutlery. Particularly when used as disposable cutlery, the increased strength that can be achieved by the various components of the first coating is of considerable importance.

In addition, the aim is to produce a capsule into which a powder for preparing beverages, in particular ground coffee, is filled. Individually packaged portion packs for coffee are enjoying increasing popularity. Various packaging techniques are used for this. Pure aluminum packaging offers a high level of tightness and enables the coffee packaged in it to be stored for a long time. However, it also requires high energy consumption and high material costs in the manufacture of the packaging and leads to considerable amounts of waste. So-called coffee pods are coffee portions packed in cellulose fleece. This packaging weighs less and is more easily biodegradable than aluminum packaging. However, the pads lack tightness, so that the coffee packaged in them can be stored for less long or loses its aroma.

A coffee portion packaging consisting of a capsule consisting of the substrate described here has a high degree of tightness, which is much higher than that of a pad made of uncoated cellulose fiber. As a result, you can keep the coffee much longer. The capsule can be sealed with a cover layer consisting, for example, of a paper layer with the coating described above. This capsule consists solely of natural raw materials, namely cellulose and natural waxes and lipids, and can be easily disposed of or recycled.

To produce the capsule, a tray, that is to say a single-layer body with several depressions, can first be produced using the fiber casting process. This tray and the wells are first sprayed with the suspension with nanocellulose. After this first coating has dried, the mixture of waxes and oils, in particular 25% by weight of linseed oil, 50% by weight of carnauba wax and 25% by weight of beeswax, is applied as the second coating. This second coating can be sprayed or the substrate with the first coating can be dipped into this mixture, the wax / oil mixture then penetrating deep into the pores of the cellulose substrate with the first coating by heating and being evenly distributed. In this way, the tightness of the end product is increased.

The tray can also be re-pressed after the first coating has been sprayed on, in particular by means of a heated mold. This speeds up the drying process.

The waxes and lipids of the second coating are heated for application, e.g. to a temperature of 90 ° C in order to remain in the liquid state. The heated reservoir for the material of the second coating can be arranged in the immediate vicinity of a drying channel for the first coating. The nozzles for applying the second coating can also be heated. The second coating cools down in a short time (a few seconds) and hardens in the process. The food packaging can then be used.

The capsules, which are formed by the hollows in the tray, are then filled with the intended amount of coffee and then closed with a seal. The seal can consist of a paper layer which is also provided with a first coating made of nanocellulose and a second coating made of animal and / or vegetable waxes and / or lipids, so that it is gas-tight and water-resistant.

Sealing takes place using a tool that is precisely matched to the shape of the tray and that seals between the troughs filled with coffee on the cast fiber webs of the tray. The tool has approx. 5 mm wide metal webs that can be placed on the webs between the wells of the tray. The tool can be heated and pressed onto the tray with pressure, possibly in a counter-mold. The counter-shape makes it possible to apply the necessary pressure to the bars of the tray and holds the tray exactly in place in order to be able to carry out the sealing.

After sealing, the tray can be cut into individual capsules. It is also It is possible to cut larger sections with several capsules, which can then be separated either with scissors or by cutting on a perforation line that runs in a sealed web between two hollows of the tray.

It can be seen, however, that the coated substrate is also suitable for the packaging of other objects, in particular foodstuffs that have to be packaged in a largely gas-tight manner in order to preserve freshness. In particular, dried foods such as seasoning mixes or powders for making soups can be packaged in a beaker with such a coating. Substrates coated in this way can also be used as dinner plates or drinking cups, where they come into brief contact with water.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 3444399 A1 [0004]
• JP 2015227517 A [0004]
• JP 2012011651 A [0004]
• WO 2017/144009 A1 [0004]
• EP 2529942 B1 [0004]
• WO 2017/072124 A1 [0004]

Claims (15)

A method for the production of coated substrates, in which a flowable, biodegradable and gas-tight first coating is applied to a cellulose-containing substrate and this is solidified to form a coating, characterized in that a second waterproof coating of predominantly animal-based and / or vegetable waxes and / or lipids is applied. Procedure according to Claim 1 , characterized in that the second coating contains at least one of the following components: • linseed oil, • carnauba wax, and / or • beeswax. Procedure according to Claim 2 , characterized in that the second coating contains: • 20 to 30 wt .-% linseed oil, • 40 to 60 wt .-% carnauba wax and • 30 to 40 wt .-% beeswax. Method according to one of the preceding claims, characterized in that the flowable first coating has water and at least one of the following constituents: • cellulose fibers; • casein; • whey; • Agar Agar; • Psyllium husks. Procedure according to Claim 4 , characterized in that the first coating has nanocellulose dissolved in water with cellulose fibrils with a median diameter in a range from 30 to 100 nm and / or cellulose fibrils with a median diameter in a range from 5 to 20 nm. Method according to one of the preceding claims, characterized in that the cellulose content of the first coating is 2 to 10% by weight or more. Method according to one of the preceding claims, characterized in that the first coating is dried before the second coating is applied. Procedure according to Claim 7 , characterized in that the first coating is applied in two or more separate application processes. Procedure according to Claim 8 , characterized in that different compositions are applied in the application processes. Coated substrate made of cellulose, in which a biodegradable, first coating increases the gas tightness, characterized in that a second waterproof coating of predominantly animal and / or vegetable waxes and / or lipids is arranged on the first coating. Substrate after Claim 10 , characterized in that the second coating contains at least one of the following components: linseed oil; • carnauba wax; • beeswax. Substrate after Claim 11 , characterized in that the second coating contains: • 20 to 30 wt .-% linseed oil, • 40 to 60 wt .-% carnauba wax and • 30 to 40 wt .-% beeswax. Substrate according to one of the Claims 10 to 12 , characterized in that the first coating has at least one of the following components: cellulose fibers, in particular cellulose fibrils with a median diameter in a range from 30 to 100 nm and / or cellulose fibrils with a median diameter in a range of 5 to 20 nm; • casein; • whey; • Agar Agar; • Psyllium husks. Substrate according to one of the Claims 10 to 13 , characterized in that the substrate contains predominantly cellulose fibers. Substrate according to one of the Claims 10 to 14th , characterized in that it has the shape of at least one of the following items: • Cup; • Pot; • Container; • Knife; • Fork; • spoon; • Plate; • Coffee capsule.