EP3044368A1

EP3044368A1 - Packaging material having a barrier coating based on starch, and coating mass, method, and device for producing such a barrier coating

Info

Publication number: EP3044368A1
Application number: EP14761645.2A
Authority: EP
Inventors: Rolf Müller; Federico Innerebner
Original assignee: Innogel AG
Current assignee: Innogel AG
Priority date: 2013-09-10
Filing date: 2014-09-09
Publication date: 2016-07-20
Also published as: US20160222592A1; CA2923974A1; WO2015036391A1

Abstract

The invention relates to a new packaging material having a starch-based barrier coating, which packaging material is characterized in that the barrier coating comprises 30 to 90 wt% of starch after a possibly present filler component has been deducted, wherein at least 20% of the starch has an average molecular weight of at least 500,000 g/mol, preferably at least 1,000,000 g/mol, and at least 20 wt% of the starch in the barrier coating is in the form of gelatinized starch particles. A fraction of 0 to 70 wt% of plasticizer in the barrier coating and a weight per unit area in the range of 3 to 80 g/m², especially preferably between 12 and 40 g/m², allow for the creation of a mechanically stable barrier coating, which, for example on the inside of cardboard packagings, effectively prevents the diffusion of non-polar hydrocarbons and hydrocarbon derivatives and thus protects the packaged foods against contamination. The new packaging material is simple and economical to produce at high process speeds and has the additional advantage that the new packaging material can be recycled without limitation and meets possible legal requirements related to foods.

Description

Packaging material with a starch-based barrier coating, and coating composition, method and apparatus for producing such a barrier coating

TECHNICAL AREA

The invention relates to a packaging material having a starch-based barrier coating, a process for producing a starch-based barrier coating packaging material, a starch-based coating composition, its use for surface sealing of packaging materials, and an apparatus for producing the multi-layered packaging material of the present invention.

PRIOR ART In 2009, the Cantonal Laboratory Zurich in scientific publications drew attention to the problem of the migration of mineral oils from cardboard packaging to so-called "dry" foods. This problem arises in particular with recycled cardboard packaging. The main sources of mineral oil contamination were identified as the printing inks from the newspaper industry, as well as the printing inks used to print cardboard packaging. Because the migration mainly takes place via the gas phase, it can not be ruled out, even when using virgin fiber cardboard, that mineral oil residues from secondary packaging or neighboring packaging enter the food. In a publication by A. Vollmer et al. from 201 1 (Eur Food Res Technol (201 1) 232: 175-182), 1 19 samples of dry foodstuffs from different packaging types were analyzed for their mineral oil saturated hydrocar- bon (MOSH). In addition to these saturated chain and cyclic hydrocarbons (MOSH), the aromatic hydrocarbons (MOAH) in the form of mixtures of predominantly alkylated aromatic hydrocarbons as relevant impurities play an important role. Foods without additional packaging take up up to 70% of the MOSH and a large part of the MOAH from the packaging via the gas phase (migration). The mineral oil contamination thereby exceeds the maximum permissible values many times over. Additional inner packaging made of paper or polyethylene (PE) could not limit the mineral oil migration according to this study. However, the authors concluded that inner packaging made of polypropylene (PE), acrylate-coated PE, polyethylene terephthalate (PET) or aluminum-coated films effectively prevented MOSH migration to dry foods for at least 3 months.

The German Federal Institute for Risk Assessment (BfR) has already reached similar conclusions in its Opinion No. 008/2010 of 9 December 2009. In the publication, see http://www.bfr.bund.de/de/fragen und Antworten As regards short-term options for action, the exclusion of direct contact of recycled paper and board with dry foods having a large specific surface area by using inner bags (eg PET films) with barrier effect is proposed as short-term options for action. However, such additional inner packaging is on the one hand not desirable for economic reasons, since they make the packaging more expensive and on the other hand, they are unecological, since they increase the volume of waste.

The paper industry is therefore trying to tackle the problem of mineral oil contamination in the packaging sector with further approaches. On the one hand, attempts are being made to eliminate sources of pollution by using fresh board material and mineral oil-free printing inks. In this way, the Contaminants are avoided. The abandonment of the use of recycled paper, however, is ecologically and economically extremely disadvantageous.

Cleaning the waste paper prior to board production would also be a convenient way to prevent the mineral oil contamination of the food. In order to meet the migration limits, it will probably be necessary to remove up to 99% of the mineral oil from the waste paper. However, there is still a lack of suitable large-scale technical procedures and, in addition, it is already foreseeable that it will be an extremely cost- and resource-intensive solution.

Further approaches include the use of multi-layer laminates and the application of barrier layers on the inside of cardboard packaging to prevent the migration of mineral oil pollution through the gas phase. It offers manufacturers of paper and cardboard packaging, in particular folding carton boxes and corrugated liners, the opportunity to react quickly to the existing need for new packaging solutions without having to forego the ecologically most sensible use of recycled paper.

W013076241 A2 proposes using aqueous dispersions based on polyvinyl acetate for producing a coating on film-like substrates for reducing the diffusion of oily substances from packaging into foods and medical devices. However, the barrier layer based on polyvinyl acetate is not soluble in water and thus interferes with the recycling of a cardboard treated in this way in recycling processes currently in use. In addition, the use of a synthetic, poorly biodegradable coating tarnishes the reputation of carton packaging as an ecologically highly advantageous packaging solution. Moreover, since such coatings are comparatively expensive, there is still a need for cost-effective, ecologically sensible coating compositions with a good barrier effect.

Also known in the paper industry are starch-based coatings. These are used, for example, in the paper coating in coating colors to cardboard To give more strength or to improve the paper properties such as reducing dust and smoothing surfaces for better printability.

Starch develops a high viscosity when cooking in solution even at low solids content. For example, a 10% strength solution at 40 ° C. may have a viscosity of> 5,000 mPas and is therefore not usable in conventional brushing methods. Therefore, partially degraded starches are usually used with average molecular weights of M _W "0000000 g / mol, in order to keep the viscosity of the starch solution and thus of the coating mass within a manageable range at higher solids contents (eg 50% starch solution with a viscosity of <3 '000 mPas at 40 ° C). Starch coatings of such degraded, degraded or partially degraded starches are relatively brittle and break easily in the manufacture of cardboard packaging. In particular, the mechanical stresses during folding and grooves of the cardboard do not withstand such coatings, so that unwanted defects in the coating caused by the turn mineral oil residues can migrate into the packaged food. Such compositions are therefore not useful as a barrier coating, since the coating must be flexible in order to be grooved and folded into folding cartons, for example, during processing of the coated packaging material.

Methods for coating paper and cardboard are generally known to the person skilled in the art. A common device for painting, in particular of paper and cardboard, as in the prior art, is shown schematically in Figure 1. Essential components of such a device for coating a web 2 are the coating unit 4 and the subsequent drying device, usually consisting of an I R jet heater 8 and a hot air drying system 9. The web is guided by so-called guide rollers 3. The web can unwound from a roll 1 and rolled after drying again on such a V. However, this is not absolutely necessary: painting, for example, can also represent an intermediate step in a multi-stage continuous process. For example, the coating composition can be applied to the substrate surface by knife coating, blading, spraying, spraying, printing or other methods suitable for applying liquid compositions. In FIG. 1, a typical embodiment of a coating unit 4 is shown by way of example. About an applicator roll 5, which runs through a so-called swamp sump 6, the coating is applied to the paper. With a squeegee or a blade (blade) 7, the excess coating is stripped off. The coated web 2 'is passed over the drying 8, 9 and thereby dried so that it can be re-formed in a retractor to a paper roll V without sticking. Thus, the requirements for the mechanical properties and the barrier effect of the coating are in contradiction to the requirements imposed by the coating process. This problem is currently not solved satisfactorily.

It is therefore an object of the invention to provide improved compositions for the coating of packaging materials which can be used in an economically sensible manner, can be applied efficiently and inexpensively to flat substrates and at the same time have an outstanding barrier property.

Furthermore, it is an object of the present invention to provide an improved method for coating paper and a device suitable therefor.

PRESENTATION OF THE INVENTION

These objects are achieved by the features of the independent claims. Preferred embodiments are given in the dependent claims.

According to a first aspect, the present invention relates to a multilayer packaging material comprising a planar substrate and at least one starch-based barrier layer applied thereto. The invention further relates to a coating composition which is suitable for producing the packaging material according to the invention and is preferably used for the production of the packaging material.

Another aspect of the invention relates to a method for producing this packaging material and to a device which is suitable for carrying out this method.

Furthermore, the invention relates to the use of a starch-based coating composition for the surface sealing of packaging materials in order to prevent or reduce the migration of lipophilic impurities, for example, contained in the packaging material into the packaged product. The coating compositions according to the invention are preferably used for this purpose.

Lipophilic impurities in the context of the present invention include mineral oil impurities resulting, for example, from residues of printing inks in recycled paper. The impurities comprise linear, ring-shaped and aromatic hydrocarbons, in particular MOSH and / or MOAH.

The process according to the invention for producing a packaging material with a starch-based barrier coating or barrier layer differs substantially from known processes in that a coating composition of high molecular weight in the form of a suspension of starch particles is applied to a substrate to be coated and the suspension on the substrate with the aid of hot steam, preferably of water vapor, which may optionally contain further constituents, gelatinized "in situ" and thus solidified into a barrier coating. The result of this is that the coating on the substrate in the finished state, in a preferred embodiment, has interconnected particles of more or less strongly destructured starch granules and thus differs clearly from starch coatings which are produced from dissolved starch.

As a natural polymer from renewable resources, starch has the distinct advantage that the price compared to the synthetic products low and the environmental footprint is positive. Another advantage is that starch is already established in the paper industry and does not pose a disruptive factor in existing recycling processes.

According to the present invention, a coating composition is used in the form of a low-viscosity suspension of granular starch, which may contain long-chain or high-molecular starch molecules, which are coated efficiently with high solids content on a suitable substrate or a carrier layer of a packaging material, preferably on paper or cardboard can and then by heat, preferably by steam, more preferably steam, gelatini- sated and filmed. The application of the starch composition in the form of a suspension makes it possible to combine a high solids content in the application composition with a relatively low viscosity as required for brushing with simultaneous use of preferably undegraded, ie long-chain starch types. It has surprisingly been found that long-chain types of starch, in particular in the form of a suspension, can be usefully used for coating and the use of these long-chain types of starch in the barrier coating also leads to significantly better mechanical properties of the coating. The average molecular weights M _{w of} the starches used according to the invention should be at least 500O00 g / mol, preferably at least 1 000 000 g / mol. In this case, the abbreviation M _w in the present patent application always denotes the weight-average molecular weight.

The coating composition of the invention is a suspension whose solids content contains starch as the main component. It is within the meaning of the invention that these suspended starch particles are gelatinized, ie gelatinized, by the external action of heat and moisture immediately after application to the substrate ("in situ") to form a coherent barrier coating, which inhibits the migration of lipophilic impurities, In particular, MOSH (Mineral Oil Saturated Hydrocarbons) and MOAH (Mineral Oil Aromatic Hydrocarbons), in which packaged goods are substantially restricted or completely prevented, are critically dependent on obtaining a full-coverage barrier coating that is virtually free of imperfections. Pinholes), and that the barrier coating is flexible and non-sticky so that the paper industry standard creasing and folding techniques can be processed without the barrier coating is significantly damaged or impaired. Only in this way can it be ensured that the packaged foodstuffs are adequately protected against the passage of the mineral oil components, even during prolonged storage periods. The main component of the coating composition according to the invention is starch. For the purposes of the invention, starch is used in at least one coating operation, ie in at least one layer of the barrier coating or barrier layer whose average molecular weight M _{w is} at least 500O00 g / mol, preferably at least 1 000 Og / mol and particularly preferably at least 200 O00 g / mol. agrees with GPC-MALLS). The average molecular weights are determined by GPC-MALLS (gel permeation chromatography with multi-angle laser light scattering) after pressure cooking the starch at 150 ° C in a closed autoclave. The "in situ" gelatinization according to the invention in combination with the use of aqueous coating compositions with a high content of high molecular weight starches makes it possible to use readily processable, low-viscosity coating compositions which have a relatively low water content, such that the amounts applied to achieve the desired layer thicknesses / amounts of starch Water quantity can then be dried off with the available systems customary in the paper industry without having to make high investments for more efficient drying sections The following further advantages are explained which entail the reduction of the amount of water applied to the paper substrate to be coated. Not only in terms of additional investment costs, if the amount of water that needs to be dried off is kept as low as possible, the lower the molecular weight, the more brittle it becomes the strength, even at higher plasticizer levels. On the other hand, the viscosity of starch in solution increases massively with the molecular weight of the starch. The viscosity in solution is primarily dominated by the largest starch macromolecules. This means that even a 10% solution of desired large starch macromolecules can give a viscosity of> 5,000 mPas. However, to apply the starch to the paper, a lower viscosity is desired. So to apply appropriate high molecular weight starch macromolecules in sufficient quantity on the paper, would be Solutions with at least 90% water content necessary. In order to achieve the same layer thickness with a 10% solution as with a 50% solution, around 10 times more water is needed. Water that needs to be dried away at a high cost. In order to obtain a 50% pourable starch solution, the starch must be very much degraded and then its mechanical properties are far from the required properties.

A way out of this situation opens up the inventive approach of not applying the starch as a solution to a packaging material to be coated, for example a paper, but to use at least a portion of the starch in the aqueous coating composition in the form of non-gelatinized, suspended starch granules. However, with the use of such granular starch, it must be ensured that the starch is released from the grains at least partially on the substrate, i. the starch is gelatinized so that the large starch macromolecules it contains can be effective. In order to be able to gelatinize the starch granules, sufficient water must be present and the granules must be heated to the gelatinization temperature. In the process, water diffuses into the grains and, under the influence of the water, a phase transformation takes place in the starch grain, whereby the partially crystalline structure transforms into an amorphous structure. Since a lot of water is absorbed by the starch granules, even a thin mass solidifies. In a two-dimensional application, a film with a certain strength is obtained. Subsequent drying results in the suitable barrier film.

Native starch is in the form of starch granules. These grains are birefringent in the polarizing microscope. It is well known to those skilled in the art that starch granules can be gelatinized, for example, in aqueous solutions. When gelatinizing the starch grains absorb water and sources significantly. Gelatinized starch grains also burst and, for example, shatter easily into fragments under shear, which can then dissolve completely until a true molecular solution is formed. The transition from non-swollen starch through gelatinized starch granules to dissolved starch can be subdivided into the following stages: Step 1: the crystallinity of the starch is at most partially destroyed, in the polarizing microscope

Level 1.1: no more than 5% of the grains no longer birefringent

Level 1.2: 5 - 10% of the grains no longer birefringent

Stage 1.3: 10 - 20% of the grains no longer birefringent

Level 1.4: 20 - 30% of the grains no longer birefringent

Stage 1.5: 30 - 40% of the grains no longer birefringent Stage 2: the crystallinity of the starch is substantially destroyed, are in the polarizing microscope

Stage 2.1: 40 - 50% of the grains no longer birefringent

Stage 2.2: 50 - 60% of the grains no longer birefringent

Level 2.3: 60 - 80% of grains no longer birefringent

Level 2.4: 80 - 100% of the grains are no longer birefringent

Level 3: at most 5% of the grains are birefringent Level 3.1: and 1 - 10% of the grains have burst

Stage 3.2: and 10 - 20% of the grains have burst

Stage 3.3: and 20 - 30% of the grains have burst

Stage 3.4: and 30 - 50% of the grains have burst

Level 3.5: and 50 - 70% of the grains have burst

Level 3.6: and 70 - 100% of the grains have burst

Thickened starch granules are characterized in that the starch granules have cracks on the surface and / or the previously relatively smooth surface has been significantly deformed (eg crumpled surface). In addition to starch particles which are still present as whole grains, starch particles which have decomposed into fragments may also be present. The starch granules as well as the fragments are still recognizable as entities. Step 4: No birefringence is observed, the starch grains are substantially destroyed

Stage 4.1: there are still fragments of starch granules, the starch is largely dissolved before stage 4.2: the starch is completely dissolved

In the context of the present patent application, a granular starch is referred to as a starch which is at most destructured up to stage 1 .5. The starch is preferably destructured at most up to stage 1 .4, more preferably up to stage 1 .3, even more preferably up to stage 1 .2 and most preferably at most up to stage 1 .1. Starches having one of these levels of destructuring may also be referred to as non-gelatinized starches.

Strengths of the destructuring stages 2 and 3 are for the purposes of the present invention as gelatinized starch or gelatinized starch particles. Gelatinized starches thus have a degree of destructuring in the range of at least level 2.1 to at most level 3.6. Levels 2.2, 2.3 and 2.4 each represent even more preferred lower limits in ascending order. Levels 3.5, 3.4, 3.3, 3.2 and 3.1 each represent even more preferred upper limits in descending order.

A dissolved starch is destructured at least up to level 4.1. According to a particularly preferred embodiment of the present invention, the dissolved starch is present as a true molecular solution.

The degree of destructuring of the starch particles can be easily determined from the above gradations in the polarizing microscope, for example at 200 × magnification.

Unless otherwise stated, the present patent application states that all plasticizer components are based on the sum of starch plus plasticizer. The proportion of thickening agent (s) is based on the sum of starch plus based on. The proportion of the additive (s) is based on the dry mixture or composition. Unless otherwise indicated, the term wt .-% always means weight fraction per part by weight.

coating

The aqueous coating composition according to the invention comprises, after subtracting an optionally present filler component, the following proportions of components: a) 10-75% by weight of granular starch, b) optionally <50% by weight of dissolved starch, c) 0-70 % By weight of plasticizer, the plasticizer content being based on starch plus plasticizer, d) 25-90% by weight of water, said coating composition having a viscosity in the range of 50-5000 mPas at 40 ° C., as described in more detail below measured with a Brookfield viscometer at a rotational speed of 100rpm. The strength is the sum of granular and dissolved starch. In the context of the present invention, the weight proportions of the substances mean in each case the dry substances and not the substances in their commercial form in which they contain a certain water content as moisture. The water content refers to all the water, i. the supplied water plus the water that is present in the fabrics as moisture. The proportions of the components of the disclosed compositions, except for the filler (s), are always chosen so that the sum is 100% by weight.

According to one embodiment of the invention, the coating composition of the components a) to d) with the abovementioned proportions and a or more of the thickeners defined below with the stated proportions.

According to a further embodiment of the invention, the coating composition consists of the components a) to d). The coating composition can be used directly for coating the substrate.

Viscosity and pH of the coating compositions

The lower limit of the viscosity of the coating compositions according to the invention in mPas measured at 40 ° C. with a Brookfield viscometer at 100 rpm is 50, preferably 70, more preferably 100, most preferably 150.

The upper limit of the viscosity in mPas is 5Ό00, preferably 3Ό00, more preferably 2,500, more preferably 2Ό00, even more preferably 1 1 800, even more preferably 1 1 600, most preferably 1 1 500.

If the viscosity is too low, the use of a starch-based coating material will result in too low a coating weight and thus an excessively thin barrier coating. If the viscosity is too high, the application of a starch-based coating masses will result in an excessively high application weight or a controlled uniform application will be disproportionately impaired.

The pH of the coating composition according to the invention is preferably> 4, preferably> 5, preferably> 6, more preferably> 6.5, most preferably> 6.7 and on the other hand preferably <10, preferably <9, preferably <8.5 ,

According to a further aspect, the present invention relates to the use of the above-described coating composition for the surface sealing of packaging materials in order to prevent the migration of lipophilic substances contained in the packaging material. len impurities such as mineral oil residues, in particular MOSH and / or MOAH to prevent or reduce.

In particular, the coating composition according to the invention is used for surface sealing of inner sides of packaging.

barrier layer

The barrier coating or barrier layer according to the invention comprises, after subtracting an optionally present filler component (which is defined precisely below), the following components: a) 30-100% by weight of starch, b) 0-70% by weight of plasticizer, the amount of plasticizer is based on starch plus plasticizer, where c)> 20% by weight of the starch has a molecular weight M _w of> 1000000 g / mol, and d)> 20% by weight of the starch in the barrier coating in the form of gelatinized Starch particles are present, and e) the barrier coating has a weight per unit area of 5 to 80 g / m ² . Gelatinized starch particles

In the barrier coating applied to a substrate,> 20% by weight, preferably> 30% by weight, more preferably> 50% by weight, even more preferably> 70% by weight, even more preferably> 90% by weight even more preferably> 95% by weight, most preferably> 99% by weight of the starch in the form of gelatinized starch particles. The Tinned starch particles contribute to advantageous mechanical properties, such as the flexibility of the coating, in particular if there are good moving macromolecules between the particles, which are selected from the thickening agents. The gelatinized starch particles of the barrier layer emerge from the granular starch used in the coating composition. In other words, the gelatinized starch or gelatinized starch particles of the barrier layer have a higher degree of destructuring than the granular starch used in the coating composition. As gelatinized starch particles or gelatinized starch, a starch is preferably designated in which at least 40%, preferably at least 50%, more preferably at least 60%, even more preferably at least 80% of the starch granules are no longer birefringent. Gelatinized starch particles or gelatinized starch also includes starch in a state where at most 5% of the starch granules are birefringent, and wherein at least 1%, preferably at least 10%, more preferably at least 20%, even more preferably at least 30%, even more preferably at least 50% even more preferably at least 70% of the starch granules have burst.

Molecular Weight of Starch To enable the required mechanical properties of the barrier coating, the fraction of the largest macromolecules is of particular relevance. Therefore, it should be> 20 wt .-%, preferably> 30 wt .-%, more preferably> 40 wt .-%, more preferably> 50 wt .-%, most preferably> 60 wt .-% of the thickness of the barrier coating, a molecular weight M _w of> 1 O00O00g / mol. In a preferred embodiment,> 20%, preferably> 30%, more preferably> 40%, even more preferably> 50%, most preferably> 60%, by weight of the barrier coating thickness have a molecular weight M _w of> 2,000,000 g / mol. In a further preferred embodiment,> 20 wt .-%, preferably> 30 wt .-%, more preferably> 40 wt .-%, more preferably> 50 wt .-%, most preferably> 60 wt .-% of the starch Barrier coating have a molecular weight M _w of> 3,000,000 g / mol. In a further preferred embodiment,> 20 wt .-%, preferably> 30 wt .-%, more preferably> 40 wt .-%, more preferably> 50 wt .-%, most preferably> 60 wt .-% of the starch Barrier coating have a molecular weight M _w of> 5O00O00g / mol.

In a further preferred embodiment,> 20 wt .-%, preferably> 30 wt .-%, more preferably> 40 wt .-%, more preferably> 50 wt .-%, most preferably> 60 wt .-% of the starch Barrier coating have a molecular weight M _w of>10'000'000g / mol.

As already mentioned above, the average molecular weight M _{w of} the starches used is at least 500 o00 g / mol, preferably at least 1 000 000 g / mol. It has proved to be advantageous if this weight average molecular weight distribution M _w of the barrier coating thickness in g / mol is more than 50000, preferably> 10000, more preferably> 2 000, more preferably> 2 ^, 500 000, even more preferred > 3Ό00Ό00, more preferably> 4Ό00Ό00, more preferably> 5Ό00Ό00, even more preferably> 7Ό00Ό00, most preferably> 10ΟΟΟΌΟΟ.

The upper limit of the average molecular weight M _{w of} the starches used, in particular the granular starch, is basically not limited except by the natural conditions. Preferably, the upper limit is 50 million g / mol. Since in the production processes according to the present invention the starch molecules used are practically not degraded in terms of their molecular weight, the abovementioned information on the molecular weights of the starch in the barrier coatings can also be transferred to the coating compositions. Here in particular, the information relates to the granular starch used, which is found in the coating as gelatinised starch particles.

grammage

As the basis weight increases, the barrier effect of the barrier coating increases. The surface of papers, board and cardboard is not really smooth, but has a more or less pronounced roughness - a kind of mountain and valley landscape - on. In order to obtain a good barrier effect, the valleys must first be filled up and the layer should then cover even the highest mountain peaks. Since rougher papers are also used in the packaging industry for price reasons and a good barrier layer should also be obtained in these papers, it is necessary that thicker barrier coatings can be applied. The best possible barrier effect and rougher papers therefore require a larger order quantity or a larger basis weight. But this also increases the material and process costs, in particular since thick layers can only be obtained by repeated application of coating material, with the applied layer in each case having to be dried in between. In addition, the flexibility of the barrier coating is reduced with increasing thickness.

The upper limit for the basis weight (dry matter) of the barrier in g / m ² is therefore 80, preferably 70, more preferably 60, more preferably 55, more preferably 50, even more preferably 45, even more preferably 40, more preferably 35, more preferably 30, most preferably 25.

On the other hand, the lower limit for the basis weight of the barrier in g / m ² is 3, preferably 5, more preferably 7, more preferably 9, most preferably 10. Granular starch

Granular starch refers to a starch in which at least 60%, preferably at least 70%, more preferably at least 80%, even more preferably at least at least 90%, more preferably at least 95%, most preferably about 100% of the starch granules are birefringent. The starch granules lose their birefringent character during gelatinization, which is due to the semi-crystalline structure of the starch granules. Thus, birefringent is synonymous with non-gelatinized. Double-breaking starch granules absorb water only to a very limited extent, hardly swell and behave like solid particles. They hardly produce viscosity. Only after heating to the gelatinization temperature do the starch granules absorb water and swell strongly, and then produce very pronounced viscosity.

The upper limit for the proportion of the granular starch in the coating mass in% by weight, after deduction of an optionally present filler component, is at most 75, preferably at most 70, preferably at most 65, more preferably at most 60, even more preferably at most 56, more preferably at most 53, even more preferably at most 49, most preferably at most 47. The lower limit for the proportion of granular starch in the coating composition in wt .-%, after deduction of an optionally present filler component, is at least 10, preferably at least 15, preferably at least 20, more preferably at least 25, even more preferably at least 28, even more preferably at least 31, most preferably at least 34. The preferred weight average molecular weight distribution M _{w of} the granular starch in g / mol is included > 500Ό00, preferably> 1 Ό00Ό00, preferably> 2Ό00Ό00, preferably>2'500Ό00,preferably> 3Ό00Ό00, preferably> 4Ό00Ό00, preferably> 5Ό00Ό00, preferably> 7Ό00Ό00, most preferably> 10Ό00Ό00.

In principle, with regard to the origin and the preparation, any granular starches or mixtures thereof can be used as granular starch. They can be used, for example, in the native state as well as in the physically and / or chemically / enzymatically modified state.

With regard to the origin, root starches, such as, for example, potato starches or tapioca starches are preferred, since these are compared with starches of other origins low Gelatinisierungstemperaturen and the solidification or gelation of the coating composition to a barrier coating therefore already at low temperatures is possible. Particularly preferred is tapioca brand. Tapioca brand is colorless and tasteless and there are no known genetically modified variants of tapioca starch. More preferred is pea starch, since it has been found to have particularly good film-forming properties.

In a preferred embodiment, the granular starch is native, i. unmodified state used. Hereby useful properties can be obtained at low cost. In a further preferred embodiment, substituted granular starches, such as starch esters and starch ethers, are used, for example hydroxypropylated or acetylated starches. These modifications lead to a particularly high elongation capacity of the barrier coating, which is an important advantage in the groove and folding of the barrier coating. Alternatively, oxidized starches are used. Particularly preferred are hydroxypropylated starches.

In a further preferred embodiment, crosslinked granular starches are used, in particular crosslinked starch esters or crosslinked starch ethers, for example starch phosphates and starch adipates. Preferably, the crosslinking is weak. Such starches are commercially available. By increasing the molecular weight associated with crosslinking, improved mechanical properties are obtained. Particularly preferred are crosslinked hydroxypropylated starches, in particular weakly crosslinked hydroxypropylated starches. For ease of processing, non-crosslinked hydroxypropylated starches are preferred. According to another embodiment of the present invention, the granular starch is an uncrosslinked starch or a mixture of non-crosslinked starches.

In a preferred embodiment, substituted granular tapioca starch is used, in particular hydroxypropylated tapioca starch. Preferably crosslinked substituted tapioca starch, such as hydroxypropylated starch phosphate. In a further preferred embodiment, substituted granular pea starch is used, in particular hydroxypropylated pea starch. Preferably cross-linked substituted pea starch, such as hydroxypropylated starch phosphate. The amylose content of the granular starch (s) in% by weight is preferably <60, more preferably <50 even more preferably <40, even more preferably <37, even more preferably <35. It has been found that high amylose contents lead to reduced elongation capacity Barrier coating can lead.

The amylose content of the granular starch (s) in% by weight is preferably> = 0, more preferably> 0.5, more preferably> 0.7, even more preferably> 1, even more preferably> 2.5, very particularly preferably > 5. Too low amylose contents can lead to a reduced elasticity of the barrier coating.

According to preferred embodiments, no so-called "waxy" starches are used in the coatings according to the invention and the coating compositions.

Further preferred are granular starches with a dextrose equivalent (DE) of <3, more preferably <1, most preferably <0.7, even more preferably <0.5, even more preferably <0.2, even more preferably <0.1, most preferably <0.05. The dextrose equivalent of a polysaccharide mixture refers to the percentage of reducing sugars in the dry matter. It corresponds to the amount of glucose (= dextrose), which would have the same reducing power per 100 g of dry matter. The DE value is a measure of how far the polymer degradation has taken place. At high DE values, poor mechanical properties are obtained. The dextrose equivalent is determined according to ISO standard 5377. According to preferred embodiments of the invention, granular starches approved for food contact applications are used.

Dissolved starch The coating composition may optionally also comprise dissolved starch. The dissolved form of starch in aqueous systems is typically obtained by the following means well known to those skilled in the art: cooking the starch, especially with a jet cooker, heating to a temperature above the gelatinization temperature, dissolving extruded amorphous starch, using pregelatinized starch. Dissolved starch may be in the form of a true molecular solution, as defined above, but fragments of destructured starch granules may also be present. Gelatinized starch granules easily break down into fragments under shear and then dissolve completely. Even after prolonged cooking, the gelatinized starch granules disintegrate into fragments, eventually creating a true molecular solution. With the Jet Cooker, a molecular solution is obtained very quickly.

Dissolved starch, as well as the thickening agents mentioned below, can be used to increase the viscosity of the coating composition and to modify the barrier coating self-shingles. Their use is optional according to the present invention.

As regards suitable starches and preferred types, essentially the same statements apply to the dissolved starches as to the granular starches. Exceptions are the limitations to molecular weight. Dissolved starch may also have a lower molecular weight than granular starch. So dissolved starch can be used according to an embodiment, also short-chain starch having a molecular weight M _w of less than 500Ό00 g / mol.

The proportion of the dissolved starch in the coating composition in% by weight, after deduction of an optional filler component, is preferably <50, more preferably <40, more preferably <30, even more preferably <20, even more preferably <15 more preferably <10, more preferably <7, most preferably <5.

The lower limit of the proportion of the dissolved starch in the coating mass in% by weight, after deduction of an optionally present filler component, according to one embodiment is 0. The lower limit may also be 0.5% by weight more preferably 1% by weight, more preferably 2% by weight, most preferably 3% by weight, each after deduction of any optional filler component.

Water content of the coating composition Water is important for adjusting the viscosity of the coating composition and for the gelatinization after the conversion of the coating composition into a barrier coating. The higher the water content of the coating composition, the lower its viscosity, and the lower the gelatinization temperature required. On the other hand, a high water content makes drying difficult, as more water has to be removed from the barrier coating.

The upper limit for the water content of the coating composition in% by weight, after deduction of an optionally present filler component, is 90, preferably 85, more preferably 80, more preferably 75, more preferably 72, even more preferably 69, The lower limit for the weight percent water content of the coating composition, after deduction of any optional filler component, is 25, preferably 30, more preferably 35, more preferably 40, even more preferably 44, even more preferably at 47, more preferably at 51, most preferably at 53.

Part of the water in the coating mass may be bound in the solidified barrier layer. The remaining water is lost during the drying of the packaging material and subsequent storage. The maximum water content of the barrier layer in the finished packaging material immediately after the production is at most 25% by weight, preferably at most 20% by weight, more preferably at most 15% by weight, even more preferably at most 10% by weight, still more preferably at most 7% by weight .%, more preferably at most 5% by weight, still more preferably at most 3% by weight.

Solids content of the coating composition In coatings of paper, the skilled person speaks of solids content rather than water content, the two properties are of course directly linked. The solids content defines the sum of all components, including any fillers, other than water. The solids content of a sample can be determined by simple differential weighing of the sample before and after drying. For this purpose, the samples are dried, for example, in a commercial drying oven for 10-60 minutes at 130 ° C. In order to determine the solids content of the coating composition on the substrate, ie in the packaging material, a piece of coated substrate is used as the sample.

The lower limit for the solids content of the coating composition in% by weight, after deduction of an optionally present filler component, is 10, preferably 15, more preferably 20, more preferably 25, even more preferably 28, most preferably 34 The upper limit for the solids content of the coating composition in% by weight, after deduction of an optionally present filler component, is 75, more preferably 70, more preferably 65, even more preferably 60, even more preferably 56, even more preferably 53, even more preferable at 49, most preferably at 47.

Softeners Suitable plasticizers are in principle all plasticizers listed in the state of the art for starch and any mixtures thereof. A low level of plasticizer leads to embrittlement of the barrier coating at low humidity, while a high plasticizer content leads to stickiness and a soft material of low elongation at high humidity. Plasticizers can be used singly or in mixtures of different plasticizers. Preference is given to using polyols, for example glycerol, sorbitol, maltitol, erythritol, xylitol, mannitol, galactitol, tagatose, lactitol, maleate cellulose, isomalt, maltol, etc., but also various sugars such as sucrose / sucrose, maltose, trehalose, lactose, lactulose, galactose, fructose, etc., as well as mono- and oligosaccharides. Glycerol is particularly preferred as a plasticizer. Water is also a plasticizer for starch, but is not included in the plasticizers and taken into account separately.

The upper limit of the plasticizer content of the coating composition in% by weight, based on starch (granular starch plus dissolved starch) plus plasticizer, is 70, preferably 60, more preferably 55, more preferably 50, even more preferably 46, The lower limit for the plasticizer content of the coating composition in% by weight, based on starch (granular starch plus dissolved starch) plus plasticizer, in one embodiment is 0. In such embodiments, therefore, the coating composition according to the invention comprises, except for impurities which are not unavoidable , no plasticizer. According to preferred embodiments, the lower limit in% by weight is 5, preferably 10, more preferably 15, more preferably 20, more preferably 25, even more preferably 28, even more preferably 31, even more preferably 32, 5, most preferably 33.5, each based on starch (granular starch plus dissolved starch) plus plasticizer.

The limits for the plasticizer content of the barrier coating correspond to the limits for the plasticizer content of the coating composition.

In preferred embodiments, plasticizers having a maximum melting temperature of 150 ° C (for the anhydrous plasticizer), preferably 125 ° C, more preferably 1 10 ° C, even more preferably 95 ° C, most preferably 70 ° C are used. The proportion of these plasticizers in the total plasticizer content is in wt .-%> 50, preferably> 70, more preferably> 80, most preferably> 90. With decreasing melting temperature of the plasticizer whose softening effect increases.

In a preferred embodiment, plasticizers having a molar mass in g / mol of> 90, preferably> 120, preferably> 140, preferably> 150, most preferably> 160 used. The proportion of plasticizers which fulfill this condition in the total plasticizer content is in wt .-%> 10, preferably> 20, more preferably> 30, most preferably> 40. With increasing molecular weight of the plasticizer decreases its migration ability, the plasticizer then has So to migrate a reduced tendency from the barrier coating in the paper. By migrating the plasticizers, the barrier coating loses flexibility.

In preferred embodiments, a combination of at least 2 plasticizers is used, preferably of at least 3 plasticizers, in which combination the individual plasticizers are represented by at least 5%, preferably at least 10%, most preferably at least 15%. Two isomeric plasticizers are considered as different plasticizers. The combination of plasticizers can reduce the tendency of individual plasticizers to crystallize. Upon crystallization, the softening effect disappears.

Thickener A thickening agent or a mixture of thickening agents may be added to the coating composition in order to adjust the viscosity of the coating composition to a desired value and to maintain the homogeneity of the coating composition, in particular to prevent sedimentation of the granular starch and thus the production process of the barrier coating to simplify. In addition, thickeners are advantageously used to modify the mechanical properties of the barrier coating, in particular to increase their flexibility.

Suitable thickeners are in principle all hydrophilic substances and mixtures thereof which increase the viscosity, in particular hydrophilic polymers and preferably those from vegetable sources. Preferably, this polymer contains polar groups such as hydroxyl groups, carboxyl groups or ionic groups, such as carboxylate or sulfonate groups.

Examples of thickening agents are hydrocolloids and gums such as galactomannans such as guar gum or locust bean gum; Cellulose derivatives, in particular cellulose loseether; Pectins, especially rhamnogalacturonans and protopectins; dextrans; xanthan; zymosan; Seaweed hydrocolloids such as alginates, agar-agar, agarose, carrageenan and carrageenans; furcellaran; Lycopene hydrocolloids such as Lichenine and Isolichenine or hydrocolloids as exudates of wood such as tragacanth (Astragalus gum), karaya gum, gum arabic, kutira gum; inulin; Latex; chitin; chitosan; gellan; collagen; Gelatin; Casein and any combinations thereof.

Dissolved starch can be used for the same functionality as the thickeners, but is not included in the thickening and treated separately in the context of the present invention.

In preferred embodiments, the maximum level of thickener in the coating composition, as well as in the barrier coating, is in weight percent based on starch plus thickener 50, more preferably 40, even more preferably 30, even more preferably 20, even more preferably 10, even more preferably 5 , more preferably 2.5, most preferably 1, 5.

If present, the minimum proportion of coating composition thickener, as well as the barrier coating, in weight percent, based on starch plus thickener, is 0.01, preferably 0.05, more preferably 0.1, even more preferably 0, 3, more preferably 0.6, more preferably 0.8, most preferably 1, 0. Since the thickening agent is an optional component, the minimum amount may also be 0% by weight.

According to preferred embodiments, xanthan gum is used as thickener, since xanthan gum can particularly effectively prevent the sedimentation of suspended starch particles. A maximum proportion of <2.5% by weight of xanthan as thickening agent of the coating composition and of the barrier coating has proved to be particularly advantageous in further embodiments. The minimum amount of xanthan in% by weight is 0, preferably 0.01, more preferably 0.05, even more preferably 0.1. The thickener xanthan gum can be used in particular in combination with one or more of any of the aforementioned granular starches. In particular, any combination with the other grains Components, ie dissolved starch, plasticizers, fillers and additives according to the invention also included.

In a further preferred embodiment, water-soluble cellulose derivatives are used, for example methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, hydroxyethylmethylcellulose or hydroxypropylmethylcellulose.

Preference is furthermore given to using polyvinyl alcohol (PVA) since PVA not only produces viscosity and stabilizes the coating composition, but also improves the mechanical properties of the barrier coating, in particular its flexibility. Preferably PVA is used with a degree of hydrolysis of> 70%, more preferably of> 75%, even more preferably> 80%, most preferably> 85%. Also preferred is a degree of hydrolysis of <99%, more preferably of <98%, most preferably <96%. Preferably, a 4% solution of the PVA at 20 ° C. according to DIN 53015 has a viscosity in mPas of> 3, preferably> 5, more preferably> 7, even more preferably> 10, most preferably> 15.

In a preferred embodiment, the maximum amount of PVA in weight percent, based on the dry coating composition, after subtracting the optional filler component is 40, more preferably 30, even more preferably 20, even more preferably 15, even more preferably 10, even more preferably 7 , more preferably 5, most preferably 4. The minimum amount of PVA in wt.% is 0, preferably 0.1, more preferably 0.3, even more preferably 0.6, even more preferably 1, even more preferably 1.5 more preferably 2, most preferably 3. PVA may be used in particular in combination with one or more of any of the aforementioned granular starches. In particular, any combination with the other components, that is to say dissolved starch, plasticizers, fillers and additives are also included according to the invention.

The aforementioned ranges for xanthan and PVA are, of course, to be understood as meaning that if one or both components are present, they form a proportion of the thickener or the thickener contains only xanthan and / or PVA. The quantity ranges for xanthan and PVA are therefore not additive to understand the above general amount ranges for the thickener.

The limits for the proportion of thickener of the barrier coating correspond to the limits for the proportion of thickener of the coating composition. filler

The filler component of the coating composition or of the barrier coating is any constituent which is virtually insoluble in water or in the form of particles in the coating composition, as well as in the barrier coating, such as pigments, glass particles, soot particles, mineral particles, such as titanium dioxide, talc, carbonates. It should be noted here that starch particles are never counted in the context of the present invention to the fillers, not even the birefringent starch granules. The filler component is usually deducted mathematically in the formulations, since it is not essential for most functional components of the recipe, whether a filler component is present or not. Unless otherwise stated and nothing else is obvious, therefore, the percentages by weight with respect to the composition of the barrier coating in the following always refer to the proportions without the filler component.

The proportion of the filler component in wt .-% is in the dry barrier coating at <70, preferably <50, more preferably <30, more preferably <20, more preferably <10, more preferably <5 most preferably <3. The filler component must at the gelatinization also be heated and therefore requires in this step a higher energy input. The flexibility of the barrier coating is v. A. reduced at higher levels of filler.

The limits for the proportion of filler of the barrier coating correspond to the limits for the proportion of filler in the coating composition. The proportion of filler (s) is not taken into account in the calculation of the 100% by weight of the components of the coating composition. Rather, the filler is added in the formulation of the composition in addition to the 100% by weight of the other components. In the Determination of the solids content / basis weight of the barrier layer, however, is taken into account.

If present, the minimum amount of filler component in weight percent in the dry barrier layer is 0.1, more preferably 0.2, even more preferably 0.5, even more preferably 0.8, most preferably 1.0. Since the filler component is an optional component, the minimum level may also be 0% by weight.

additives

For example, the following additives can be used as further components of the coating composition: surface-active substances, such as, for example, ionic or nonionic surfactants, wetting agents, defoamers, stabilizers, dyes, other polymers than the already mentioned, biocides, pH regulators, thixotropic agents ,

The proportion of the additive or additives, based on the dry coating composition, is 0 to at most 5% by weight. The proportion is preferably <3, more preferably <2, even more preferably <1, most preferably <0.7. If present, the minimum level of additive (s) is preferably 0.1% by weight.

The limits for the additive content of the barrier coating correspond to the limits for the additive content of the coating composition. Lecithin and fatty acids

The coating composition according to the invention and thus the barrier layer may also optionally contain lecithin and / or fatty acids.

The lecithin is preferably soy lecithin. Lecithin reduces the water sensitivity of the barrier layer, in particular, the toughness is increased at low humidity. The lower limit of the lecithin content in the coating composition or the barrier layer in% by weight, based on the starch, is 0, preferably 0.01, more preferably 0.05, even more preferably 0.1. The upper limit of the lecithin content in the coating composition or the barrier layer in% by weight, based on the starch, is 10, preferably 7, more preferably 5, even more preferably 4, even more preferably 3.

For the fatty acids, fatty acids are preferred. Stearic acid is particularly preferred. Fatty acids reduce the water sensitivity of the barrier layer, in particular, the stickiness is increased at high humidity.

The lower limit of the fatty acid content in the coating composition or the barrier layer in% by weight, based on the starch, is 0, preferably 0.01, more preferably 0.05, even more preferably 0.1. The upper limit of the fatty acid content in the coating composition or the barrier layer in% by weight, based on the starch, is 10, preferably 7, more preferably 5, even more preferably 4, even more preferably 3.

The following compositions of the coating composition have proved to be particularly suitable for providing a barrier layer with regard to the mechanical properties and / or the barrier effect of the barrier layers obtained therefrom and to the processability of the coating composition:

Preferably, the starch is a hydroxypropylated pea starch having a molecular weight in millions of g / mol in the range of preferably 1 to 20, preferably 2.5 to 10. The plasticizer content in wt .-%, based on starch and plasticizer, is in the range of 0 - 45%, preferably from 15 to 37%, the starch content, based on the formulation without optional filler, is in the range of 25 to 65 wt .-%, preferably from 30 to 50 wt.%. The coating composition preferably contains a proportion of PVA of from 1 to 30% by weight, preferably from 1 to 20% by weight, more preferably from 1 to 10%. The barrier layer is preferably applied in two passes, wherein a basis weight (dry) of 3, preferably 4, more preferably 5 to 15 g / m ^{2 is} applied for each pass. The plasticizer is preferably glycerin. Instead of the hydroxypropylated pea starch, it is also possible to use a hydroxypropylated tarioca starch or a hydroxypropylated potato starch.

According to another preferred embodiment of the coating composition, the starch is a hydroxypropylated tapioca starch having a molecular weight in millions of g / mol in the range of preferably 1 to 20, preferably 2.5 to 10. The plasticizer content in wt .-%, based on starch and Plasticizer, is in the range of 0-45%, preferably from 15 to 37%, the starch content, based on the formulation without optional filler, is in the range of 25 to 65 wt .-%, preferably from 30 to 50 wt.% , The coating composition preferably contains a proportion of PVA of 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 1 to 10%. The barrier layer is preferably applied in two passes, wherein a basis weight (dry) of 3, preferably 4, more preferably 5 to 15 g / m ^{2 is} applied for each pass. The plasticizer is preferably glycerin. According to a further preferred embodiment of the coating composition, the starch is a hydroxypropylated potato starch, having a molecular weight in millions of g / mol in the range of preferably 1 to 20, preferably from 2.5 to 10. The plasticizer content in wt .-%, based on starch and Plasticizer, is in the range of 0-45%, preferably from 15 to 37%, the starch content, based on the formulation without optional filler, is in the range of 25 to 65 wt .-%, preferably from 30 to 50 wt.% , The coating composition preferably contains a proportion of PVA of from 1 to 30% by weight, preferably from 1 to 20% by weight, more preferably from 1 to 10%. The barrier layer is preferably applied in two passes, wherein a basis weight at each passage (dry) of 3, pre- preferably 4, more preferably 5 to 15 g / m ² is applied. The plasticizer is preferably glycerin.

packing material

The packaging material according to the invention is multi-layered and comprises a planar substrate as carrier layer and at least one on the flat substrate provided barrier layer, which is composed and constructed as explained above.

According to a preferred embodiment, the finished, dried barrier layer is solid and not sticky. The packaging material according to the invention can be obtained by the process according to the invention which is described in detail below.

substratum

The barrier coating is applied to a flat substrate, which is suitable as packaging material. Preferred packaging materials are papers. Papers suitable as a barrier coating substrate have a basis weight in g / m ² of preferably <800, more preferably <600, even more preferably <500, even more preferably <400, most preferably <380. On the other hand, m ² is preferably> 30, more preferably> 50, more preferably> 70, even more preferably> 90, even more preferably> 110, most preferably> 120. Paper is understood to mean paper in the strict sense as well as cardboard and paperboard. Whenever paper is used below, cardboard should always be included. Particularly preferred papers are used as a substrate for the barrier coating, which are used as food packaging, in particular in the form of folding boxes. The barrier coating is applied to the back side of the papers, which results from the fact that a barrier to the interior of the packaging should be obtained. The backs of papers suitable for packaging are typically rough, while the fronts most often intended for printing are comparatively smooth. However, papers with rather smooth backs are preferred, since smooth surfaces can be finished much easier with good barrier coatings. A smoother reverse side can be obtained for example by means of a pre-coat. The precursor means a layer which is applied to the paper substrate before the barrier layer. The precoat can already be applied to the paper manufacturer. The packaging materials according to the invention can have or be printed on the front side of the substrate, ie the outside of the finished packaging, further coatings known to the person skilled in the art. In any case, the barrier layer does not form the outside of the finished package, but is arranged so that it delimits the surface substrate, so the carrier material from the interior of the package and thus of the packaged goods contained in the package. If desired, the packaging material according to the invention may comprise further layers.

According to a further aspect, the present invention also relates to packaging, in particular folded packages, which can comprise or be produced from the packaging material according to the invention. Here, the starch-based barrier layer does not form the outside of the package.

method

The method according to the invention for producing the multilayer packaging material comprises the following steps: a) provision of a planar substrate, which is preferably selected from the group consisting of paper, cardboard and paperboard, b) provision of a coating mass,

c) applying the coating composition of step b) to at least one

Side of the sheet substrate and forming a layer on the sheet substrate, and

d) raising the temperature to dry and solidify the coated and layered coating.

The coating composition according to the invention is a suspension with granular starch suspended therein. This suspension is gelatinized in situ on the substrate and dried. All coating compositions or coating compositions according to the invention which are explained in the present application can preferably be used or used in the process according to the invention. Application of the coating mass

Methods of applying liquids such as suspensions to sheet substrates are well known. The coating can be done in various ways: e.g. the barrier coating may be painted, printed, cast, sprayed, rolled or otherwise applied evenly and evenly. The necessary for the formation of an effective barrier layer thickness can be applied in one or more passes.

In a preferred embodiment, the barrier or coating composition is applied by brushing or glazing. Known and suitable coating methods are, for example, blade coating, knife coating and size press. A particularly suitable casting method is curtain coating, it being possible in particular to obtain good barrier coatings with comparatively low application rates.

Preferably, the barrier composition is prepared / applied in more than one line. Particularly preferably, the coating is produced in 2 coating passes between which the substrate web does not necessarily have to be rolled up again. Surprisingly, a better barrier is obtained when a barrier layer of a given basis weight of eg 20 g / m ^{2 is applied} in 2 passes, eg 10 g / m ^{2 being} applied, instead of one pass where 20 g / m ^{2 is} applied become.

For a smooth paper, a sufficient barrier coating can be obtained in 1 or 2 passes. For a rough paper, 2 to 4 strike passes may be necessary.

The upper limit of the basis weight (dry matter) in g / m ² for a single application is preferably 30, preferably 25, more preferably 20, more preferably 18, more preferably 16, even more preferably 15, most preferably 14. The thinner the application, the less blistering and pinholes can be expected, and the easier it is to dry the coating. The lower limit of the basis weight (dry matter) in g / m ² for a single application is preferably 3, preferably 4, more preferably 5, more preferably 6, even more preferably 7. The thicker the coating, the better The cover of the paper and the more effective the barrier becomes. In a preferred embodiment, a first barrier layer or a first application for the barrier layer is obtained in-line with a paper machine. That is, the first job is obtained as a backsize immediately after the paper is made on the fresh paper without the paper web having been previously rolled up. The second job is then done elsewhere after the paper web has been rolled up with the first job.

In a preferred embodiment, a precoat can be applied to the paper, paperboard or paperboard or pre-applied, for example by the papermaker, which on the one hand serves to hinder the water from the coating composition of the following barrier layers into the substrate Paper to penetrate the cardboard or cardboard and on the other hand smoothes the surface to be coated. Especially with paper that is highly absorbent, such a precursor offers significant advantages, because it makes the water of the coating composition better available for the gelatinization of the granular starch. Preferably, the precoat also has properties that reduce the migration of aliphatic and aromatic hydrocarbons.

For a precoat, it is possible to apply masses used in the paper industry to improve the surfaces, in particular in order to reduce surface roughness, improve printability and machinability. So a mineral precoat, such as a carbonate precursor be used. On the other hand, a primer may also be applied with a starch-based compound.

In a particularly preferred embodiment, this precoat is prepared with a precoat mass of dissolved starch. With regard to the starches and starch types suitable for this purpose, the statements already made to describe the granular starch apply. A starch-based primer is different from the original The barrier layer according to the invention is characterized in that the precoat does not have all the features according to the invention of the barrier layer, that is to say for example contains no gelatinized starch particles in the stated quantitative range.

The preferred weight average molecular weight distribution M _w of the dissolved starch used in the preamplifier in g / mol is> 500Ό00, preferably> 1Ό00Ό00, preferably> 2,000,000 preferably> 2,500,000, more preferably> 3Ό00Ό00, most preferably> 4Ό00Ό00.

With regard to the solids content and plasticizer content of the precoat mass of dissolved starch, what has already been mentioned in the sections "solids content of the coating composition" and "plasticizer" also applies.

The upper limit for the basis weight in g / m ² is 30, preferably 25, more preferably 20, most preferably 15.

The lower limit of the basis weight of the precoat is 1, preferably 2, more preferably 3, and bevorzugtesten at 5 g / m ^2. One or more, preferably 2, 3 or 4, layers of the coating composition according to the invention, as explained in detail above, can then be applied to the precoat.

speed

The speed with which the paper web to be coated is moved at the paper manufacturer is around 100-100 m / min for the heavier papers, which are preferably used as the substrate for the barrier coating, which is a speed of 1.7 to 17 m / s corresponds. Most processes are in the range of 200 - 800 m / min. In the further processing of papers, such as in a coater, sometimes lower speeds are used. The barrier coating according to the invention can be produced at industrial speeds in a continuous process. Temperature of the coating mass

It is advantageous if the coating composition is applied at an elevated temperature to the substrate to be coated, preferably the paper. The higher this temperature is, the lower the temperature increase necessary in the subsequent gelatinization, and therefore the faster the gelatinization can be achieved.

In a preferred embodiment, the temperature in ° C. of the coating composition when applied to the substrate, preferably the paper, is> 20, more preferably> 30, more preferably> 35, even more preferably> 40, most preferably> 45 Coating mass is too high, it will solidify before application due to gelatinization and is then no longer useful for a coating. The upper limit of the application temperature depends on the composition of the coating composition, but results for the skilled person but clearly from the aforementioned requirements for the viscosity and thus the spreadability of the coating composition.

If the coating composition is heated slowly and its viscosity is measured, the viscosity of the coating composition decreases continuously until a viscosity minimum at the temperature Tv is reached, whereafter the viscosity rises at first slowly, then very quickly. The viscosity minimum characterizes the ideal temperature of the coating composition. Due to the low viscosity of the job is facilitated, or the highest possible solids content can still be processed, on the other hand, then only a minimum increase in temperature is required to gelatinize the coating composition. The viscosity minimum of the coating composition depends primarily on the starch used. For native starches, Tv is 60 ° C for potato starch and tapioca starch, 75 ° C for corn starch, 80 ° C for wheat starch, Waxy corn starch for pea starch and 65 ° C for pea starch. When the starches are substituted, such as hydroxypropylated, the indicated temperatures are reduced by 10 ° C. Preferably, when applied in ° C, the temperature of the coating composition is in the range of Tv with the upper limit: <20, more preferably <7, even more preferably <5, most preferably <3 above Tv and the lower limit is <20, more preferably <15, more preferably <1 1, even more preferably <7, even more preferably <5, most preferably <3 below Tv.

Pretreatment of the paper

An advantageous effect can be obtained when the coating composition is applied to a preheated paper, wherein the paper can be heated, for example, with infrared radiators. The heat from the paper can then also be used to heat the applied coating composition.

In a preferred embodiment, therefore, the paper is heated so that immediately before application of the coating, the side facing the coating has a temperature in ° C of> 30, more preferably> 40, more preferably> 50, even more preferably> 60, even more preferably> 70 , most preferably> 80. A particularly advantageous effect can be obtained if the side of the paper facing the coating is heated to such an extent immediately before the application of the coating that at least the lowermost, ie directly to the paper, portions of the granular starch of the applied coating composition are already heated by the heat Gelatinize at least partially from the paper and thus solidify. As a result, the penetration of water from the coating composition into the paper is made more difficult because in the gelatinized layer the water is bound much more strongly than in the applied suspension. The gelatinized portions at the boundary between the applied coating composition and the paper surface act as a boundary layer during the manufacturing process against the penetration of water into the paper. As a result, the subsequent drying is greatly facilitated, the process can be accelerated and the formation of blisters is counteracted.

In a particularly preferred embodiment, the surface of the paper facing the coating is at a temperature above Tv in ° C of> 5, still more preferably> 10, more preferably> 15, even more preferably> 20, even more preferably> 25, even more preferably> 30, most preferably> 35.

Apparatus for in situ gelatinization of the coating composition In the case of in situ gelatinization, the coating composition applied to the paper substrate is heated on the paper. Preferably, the coating composition is heated above 50 ° C, more preferably at least 60 ° C, even more preferably at least 70 ° C, more preferably at least 80 ° C, even more preferably at least 90 ° C, even more preferably at least 100 ° C , It has been found that the IR radiation heaters customary in the drying devices of the paper industry are insufficient for in situ gelatinization of the coating composition according to the invention, since the heating energy is introduced too slowly and at least some of the water required for the gelatinization evaporates, before sufficient gelatinization can be obtained. Particularly affected is the top layer of the barrier coating, which dries most quickly. By the usual heating units thus no suitable barrier coating can be formed.

According to the present invention, this problem is solved in the in situ gelatinization of the starch by arranging before the generally customary drying means by means of which steam, preferably water vapor, is applied to the coated surface. By condensation of the vapor on the coated surface, a high energy is released very quickly and distributed due to the good thermal conductivity of water to the coating composition. It has been shown that suitable steam can be applied in particular with a steam blower. Steam boxes are used in the paper industry for the rewetting of paper webs. For the purposes of the present invention, a corresponding construction can be used if it fulfills the following criteria. In a preferred embodiment, the steam supplied to the steam blow box has a temperature in ° C of> 105, more preferably> 110, more preferably> 1-15, even more preferably> 120, most preferably> 125. The upper limit of the steam temperature in ° C is preferably <200, preferably <180, more preferably <170, even more preferably <160, most preferably <150.

In a preferred embodiment, the vapor that escapes from the steam blower has a temperature in ° C of> 100, more preferably> 101, more preferably> 103, most preferably> 105, so that the vapor does not condense until it reaches the substrate , In a preferred embodiment, the steam delivered from the steam box has a temperature in ° C of <150, more preferably <140, even more preferably <130, even more preferably <125, even more preferably <120, most preferably <1-15 , At too high a temperature, the vapor may not cool sufficiently to condense on the substrate. Preferably, this vapor is dry saturated, i. it is close to the condensation limit, but contains no condensate.

In a preferred embodiment, for each g / m ^{2 of} the coating composition, a vapor amount in g / m ² of> 0.02, more preferably> 0.04, more preferably> 0.06, even more preferably> 0.07, even more preferably> 0.08, most preferably> 0.09 deposited on the substrate or condensed. As the amount of steam increases, the gelation is accelerated and the degree of gelatinization increases. Water which is applied to the coating composition before the application of the vapor, for example with a spray device, is likewise calculated here for the coating composition.

In a preferred embodiment, for each g / m ^{2 of} the coating composition, a vapor amount in g / m ² of <50, more preferably <25, more preferably <10, even more preferably <5, even more preferably <3, even more preferably <1, still more preferably <0.7, most preferably <0.5. As the amount of steam decreases, the amount of water condensate that must then be dried away is reduced, thus speeding up and simplifying drying. Water, which is before the application of the steam fes is applied to the coating composition is also calculated here to the coating composition.

The steam should be distributed as evenly as possible over the entire coating surface. The technical requirements for the construction of a steam box that meets these conditions are known in the art.

Thanks to the aforementioned teaching on compositions and process parameters, surprisingly within a few hundredths of a second complete gelatinization and thus solidification of the coating composition on the substrate could be achieved, ie in situ gelatinization, where a low-viscosity aqueous liquid was converted into an elastic solid virtually instantaneously the water of the coating composition is bound therein.

By allowing in situ gelatinization of the starch by application of a suitable water vapor within such a short period of time, the problem was simultaneously solved or at least significantly alleviated that water from the coating mass substantially penetrates into the porous paper. On the other hand, such water absorbed by the paper is otherwise absent during gelatinization and, on the other hand, poses a problem in the drying of the barrier coating. It would take a relatively long and efficient drying cycle to dry such deep water, and even with relatively gentle and slow drying of this water under the already established barrier coating easily vapor bubbles, which break up the barrier coating by blistering / blistering and thus essentially destroying the barrier effect.

Sprayer It has been found that particularly good results can be obtained by spraying the coating on the paper with water prior to the application of steam, which can be done, for example, with a spray bar containing a series of spray nozzles containing the required water is distributed finely and evenly on the coated web. It should be as even as possible Water film on the coating material, which facilitates the subsequent gelatinization and leads to particularly good barrier coatings, probably by the top layer of the coating composition is protected from premature dehydration. In a preferred embodiment, an amount of water in g / m ² of <10, more preferably <7, more preferably <5, even more preferably <3, most preferably <1 is sprayed per m ^{2 of} substrate. The finer the sprayed water droplets, the less water is needed.

In a preferred embodiment, the temperature of the water being sprayed is in ° C at> 30, more preferably> 40, more preferably> 50, even more preferably> 60, even more preferably> 70, most preferably> 80.

As the temperature of the sprayed-on water increases, the coating mass is heated and subsequently a faster gelatinization is made possible. At higher temperatures, the uppermost layer of the coating composition is at least partially gelatinized and thus solidified by the hot or hot sprayed-on water. The sprayed-on water then forms a particularly effective protective film against drying, since it can hardly penetrate into the coating composition. Such a superficial water film is then very easy and fast to dry with the usual drying methods that are used after the vapor deposition. In particular, blistering can be avoided even with rapid drying.

desiccation

The coated with the coating composition paper can be dried with the usual in the paper industry drying process. Here are mainly IR lamps and hot air hoods used. It is customary that the side of the paper is treated with IR or hot air on which a layer to be dried has been applied. In a preferred embodiment, however, at least a part of the drying process is carried out so that the other side of the Paper is treated with IR or hot air (to which no layer to be dried has been applied).

In a further preferred embodiment, in at least part of the drying process, both sides are treated simultaneously with IR or hot air. The advantage of these preferred methods is that the formation of blisters and pinholes can be more easily suppressed and thus better barriers are available.

Brief explanation of the figures

The invention will be explained in more detail with reference to embodiments in conjunction with the drawings. Show it:

Figure 1 schematically shows a coating system according to the prior art, as is customary in the finishing of paper, and

Figure 2 schematically a device according to the invention, in which only in the

Representation for simplicity, for example, from Fig. 1 prior art device parts for rolling and guiding the paper and are omitted for drying. Analytical methods

Determination of the order weight

A paper of known area is dried in a convection oven at 130 ° C for 15 min and then weighed. From the weight and the known area, the basis weight of the untreated paper in g / m ² can be obtained. A coated paper of known area is dried and weighed in the same manner and thus the basis weight of the coated paper in g / m ^{2 is} obtained. The basis weight of the coating in g / m ^{2 is} obtained from the difference between the two basis weights.

Determination of the molecular weight M _w The Mw is the weight average molecular weight distribution.

If the starch is in the form of a powder, the starch is suspended in water at a concentration of 3% dry matter. This suspension is then heated up to 150 ° C. in a mini-autoclave with stirring and heated there for 20 minutes. hold. Subsequently, the resulting solution is cooled to about 60 ° C, diluted to 0.3% and filtered with a 0.005 mm membrane filter. The filtered solution is then measured by GPC-MALLS (gel permeation chromatography with multi-angle laser light scattering). If the starch in a barrier layer on a paper is to be analyzed for its molecular weight, the following two methods can be used to obtain a starch solution.

1) The starch is scraped off the paper with a scalpel or it is sanded with a fine sandpaper. The powdery material thus obtained can be converted in the same way into a solution, as described above for powder present in powder form.

2) Alternatively, the barrier layer can be analyzed along with the paper. For this purpose, the material is cut into pieces of about 2 ^* 2mm and suspended in an autoclave and stirred overnight at room temperature. Then proceed as described above for powdered starch. However, in filtration, a coarse filter is first used to filter off the insoluble paper components. Since conventional papers can already contain starch even without a barrier layer, a reference measurement is optionally made with the uncoated paper or a reference measurement with the paper from which the barrier layer has been mechanically removed. From the reference measurement can then be judged which components in the GPC-MALLS analysis of the barrier and which are attributable to the paper.

Measurements were taken using a Waters Alliance 2695 Separation Module, a Waters 2414 DRI Detector, a Dawn-HELEOS MALLS detector from Wyatt Technology with a wavelength of 658 nm, and a K5 flow cell. For the GPC column a SUPREMA gel column set was used, exclusion limits S30000 with 10E8-10E6, S1000 with 2E6 - 5E4, S100 with 1 E5 - 1 E3. Eluent: DMSO with 0.09 m NaNO ₃ . Temperature: 70 ° C. Evaluation: Astra Software 5.5.0.18. It was calculated with a refractive index increment dn / dc of 0.068. Recovery of starch particles from the coating of the packaging material

The barriers prepared contain gelatinized starch particles. These starch particles can be separated, for example, by dissolving the barrier at 70 ° C. for 30 minutes at a stirring speed of less than 60 revolutions per minute of the soluble constituents (these are in particular plasticizers, soluble starch, optionally thickeners) and their quantitative fraction at the barrier can thus be measured.

Recovery Method # 1 In a preferred embodiment, the minimum amount in weight percent of the starch in the barrier that can be recovered after dissolving the barrier at 70 ° C for 30 minutes and a stirring speed of less than 60 revolutions per minute, 30, preferably 40, more preferably 50, even more preferably 55, even more preferably 60, even more preferably 65, most preferably 70%. Recovery Method No. 2

In a further preferred embodiment, the proportion of the mass is determined, which can be recovered after dissolving the barrier at 70 ° C for 30 min and a stirring speed of less than 60 revolutions per minute, and based on the mass of the barrier. The determination according to this definition is simpler than that according to recovery method no. 1, because it can be applied even if the composition of the barrier is not known exactly. The minimum weight percent of the mass that can be recovered is 25, preferably 35, more preferably 40, even more preferably 45, most preferably 50. PROCEDURES FOR CARRYING OUT THE INVENTION FIG. 2 schematically shows the arrangement of the devices for producing the starch coating according to a preferred embodiment of the present invention. In principle, it does not matter how the starch-containing coating is applied to the paper web 10. A blade coater 1 1 with roller blade (profiled or smooth) 12 has proved to be advantageous, but other applicators can be used. Also advantageous as the application has proven by means of a curtain coater. According to the invention, a spray device 13 for application of the water and a steam blower box 14 is arranged between the application unit 1 1 and IR drying 15, which serve in addition to the IR radiation gelatinize the gelatinisieren the applied, unverkleisterte starch and to form a homogeneous film , The position of sprayer and steam box should be in close proximity to the application unit.

Example 1 :

A suspension consisting of 37% by weight (hereinafter referred to in each case by weight percent based on the dry weight, unless otherwise stated) of a hydroxypropylated pea starch (M _w = 19Ό00Ό00 g / mol), 18 wt .-% Gly- Cerin (99.5% strength) and 45% water are homogenized at room temperature in a mixer with an anchor stirrer and placed in a coating device in which sedimentation of the particles is prevented by continuous circulation of the mass. The suspension has a viscosity of 200 mPas at 24 ° C, a measured solids content of 52% and a pH of 7.7. The substrate used is the back of a commercial folding carton with a basis weight of 230 g / m ² and a roll width of 60 cm. At a machine speed of 150 m / min, the starch mass was applied via a combi-blade coater with a profiled roller blade (profile C35, 0.8 bar squeegee pressure). Immediately after the application was by means of a spray strip surface water sprayed onto the surface coated with a throughput of 12 g / m with saturated steam which has been brought to the surface by means of steam blower ² and immediately thereafter, the starch was coated, gelatinized. The steam had a temperature of about 120 ° C and was operated so that the throughput was about 30 g / m ^{2 of} steam. Following the steam box, the paper web was adjusted to the usual settings in the paper finishing by means of gas-IR heating and subsequent hot-air drying dried. The drying plant consisted of 4 gas IR radiant heaters, followed by 3 dry hoods with hot air. The performance and temperature of the drying units were adjusted so that the paper surface at the measuring points between the drying elements as high as possible temperature, but not more than 1 10 ° C showed. Drying conditions:

The carton could then be rolled up and did not stick. The basis weight of the dry coating was determined by differential weighing to 10 g / m ² .

A quick test with spray oil showed a significantly reduced wetting of the board surface with oil compared to the uncoated board surface.

Example 2:

As in Example 1, however, two strokes of 10 g / m ^{2 were} applied. A test with spray oil showed even more reduced wetting of the coated board surface. By means of a migration measurement, the barrier effect against MOH (mineral oil hydrocarbons) with less than 35 C atoms was determined by the coated board to be> 90%.

For migration measurement, it should be noted that there is currently no standardized measurement method, but the results of different measurement methods harmonize surprisingly well. The% data relate to the ratio by which the amount of MOSH and MOAH compared to the uncoated green cardboard is reduced. was changed. A description of a method can be found in: K. Fiseier, K. Grob in 'Packaging Technology and Science', 2012 Vol.25, issue 5, p.285-301).

Example 3: A suspension was mixed at 30-35 ° C. from 34.9% by weight of starch (hydroxypropylated tapioca starch, M _W = 190000 g / mol), 13.7% by weight of glycerol (99.8%) , 3.5% by weight of polyvinyl alcohol (with a viscosity of 8 mPas, degree of hydrolysis 88%) and 47.9% by weight of water with an overall viscosity of 1670 mPas at 34 ° C. The suspension was placed in a combi-blade coater where it was circulated to ensure homogeneity.

The suspension was coated at a web speed of 120 m / min with a 20 mm squeegee at a squeegee pressure of 0.6 bar on a commercial carton box with a basis weight of 350 g / m ² . Immediately after brushing, about 18 g / m ^{2 of} water were applied over a flat area by means of a water spray bar. Immediately thereafter hot, saturated steam at a throughput of about 35 g / m ^{2 was} blown flat onto the 60 cm wide paper web onto the coating with the aid of a steam-blow box 1 17 ° C. The web surface had a temperature of about 90 ° C after the steam box. Subsequently, the coating was passed through a drying plant with 4 gas IR radiant heaters, followed by 3 drying hoods with hot air. The performance and temperature of the drying units were adjusted so that the paper surface at the measuring points between the drying elements as high as possible temperature, but not more than 1 10 ° C showed.

Drying conditions:

IR emitter: Leis1 2 3 4 Hot air 1 2 3 device: 80% drying hoods Number of heating blocks 4/4 4/8 1/8 2/8 Temp. ° C 170 200 180 on / max.

The carton could then be rolled up and did not stick. The basis weight of the dry coating was determined by differential weighing to 13 g / m ² .

With the same suspension, a cover coat was applied to the already coated roll again under the same conditions, except that the squeegee pressure was increased to 1.5 bar. The applied basis weight was measured to be 8.5 g / m ² .

The total coating had a basis weight of 21 g / m ² .

Two samples of the coated carton were each subjected to a migration test for MOSH / MOAH, with a pattern previously grooved (1 x 90 °) in the center. The test showed that the barrier effect in the grooved pattern was only reduced by about 1.5% compared to the un-grooved cardboard.

Example 4:

Before coating with a suspension of particulate starch, a precoat was prepared with dissolved starch. The starch solution had the following composition of in weight%: 17.8% starch (hydroxypropylated easily degraded pea starch, M _w = 4'500O00g / mol), 9.5% glycerol (99.8% pure), 72.7% Water. The mixture was stirred cold and cooked in the jet cooker to form a clear solution. This had at 55 ° C a viscosity of 1 180 mPas (Brookefield viscometer).

The precoat was applied to the Combi-Blade with a roller blade (20 mm squeegee, 0.8 bar squeegee pressure) at a machine speed of 350 m / min on a 230 g / m ² heavy carton. The coating weight after drying was determined to be 9.6 g / m ² . Drying conditions:

To this precursor with a suspension consisting of 34.5% by weight of starch (HP tapioca starch, M _w = 19O00O00g / mol), 18% glycerol (99.8%), 3.5% PVA (with a viscosity of 8 mPas , Degree of hydrolysis 88%) and 44% water applied to topcoat. The suspension had a viscosity of 1510 mPas and a pH of 7.0 at 29 ° C. It was applied with a 20 mm squeegee at 2.5 bar contact pressure and a machine speed of 150 m / min. With the spray bar about 7 g / m ^{2 of} water were sprayed. The settings of the steam box were the same as in Example 3. The coated web surface had a temperature of 89 ° C immediately after the steam box. The coating weight was determined after drying to 8.6 g / m ² .

Drying conditions:

Example 5: (Comparative Example) A starch solution was prepared by boiling in a jet cooker with the following composition in% by weight: 25.7% starch (degraded, hydroxypropylated pea starch, M _w = 170,000 g / mol), 1 1, 8% glycerol (99.8%) ig), 62.5% water. The solution had a Brookefield viscosity of 990 mPas at 33 ° C and a pH of 7.9. With a profiled roller blade (C40) a line of 14 g / m ^{2 was} applied and dried at a machine speed of 200 m / min.

Drying conditions:

On this primer, a cover coat with a basis weight of 9.5 g / m ^{2 was applied} via a curtain coater at 170 m / min. The starch solution used to had the following composition in% by weight: 24.4% starch (degraded, hydroxypropylated pea starch, M _w = 170,000 g / mol), 1 1% glycerin (99.8% pure), 1% polyvinyl lyvinyl alcohol (with a viscosity of 40mPas, degree of hydrolysis 98%), 63.6% water. The solution had a Brookefield viscosity of 920 mPas at 45 ° C and a pH of 7.9.

Drying conditions:

IR emitter: Leis1 2 3 4 Hot air 1 2 3 device: 60% drying hoods

Number of heating blocks 8/8 3/8 2/8 2/8 Temp. ° C 280 280 255

In the test, the coating showed little barrier to hydrocarbons. SEM images of the surface showed good coverage of the surface with the barrier layer, but numerous cracks in the layer. The cracking was attributed to the high degree of degradation of the starch used.

Example 6: (Comparative Example)

A suspension consisting of 34.5 wt .-% starch (HP tapioca starch, M _w = 1, 9 ^* 10 ⁷ g / mol), 18% glycerol (99.8%), 3.5% PVA (with a viscosity of 8 mPas, degree of hydrolysis 88%) and 44% water were mixed. The suspension had a viscosity of 1810 mPas and a pH of 7.0 at 32 ° C. The suspension was applied in the Combiblade coater with a squeegee 20 mm at 1, 5 bar squeegee pressure on a commercial carton box with 250 g / m ² basis weight. No steam box was used, the web was passed through the dryer immediately after the coater and dried with the following settings: Drying conditions:

The spray test showed only an insignificant improvement in the barrier effect compared to the raw board. SEM images of the coated surface showed that still the granular structure of the starch was visible and no filming of the starch mass took place.

LIST OF REFERENCE SIGNS

1 ro paper roll

r coated paper roll

2 raw paper web

2 'paper web (coated)

3 guide rollers

4 coating device

5 application roller

6 prank swamp

7 squeegee

8 drying

9 hot air drying

10 paper web

1 1 application unit / blade coater

12 roller blade

13 spray device

14 steam box

15 IR drying

Claims

claims

A starch-based barrier coating material for inhibiting the diffusion of non-polar hydrocarbons and / or hydrocarbon derivatives, the packaging material comprising: a sheet substrate, preferably selected from the group consisting of paper, paperboard and cardboard, as a backing layer, and

at least one starch-based barrier layer applied to the planar substrate, wherein the barrier layer is characterized in that

the barrier layer, after deduction of an optionally present filler component, comprises 30-100% by weight of starch, where at least> 20% of the starch has an average molecular weight M _w of at least 1 × 100 000 g / mol, and

> 20% wt .-% of the starch in the barrier layer in the form of gelatinized starch particles, and the barrier layer, based on starch plus plasticizer, 0 - 70 wt .-% plasticizer, and the barrier layer in the dry mass has a basis weight in the range of 3 - has 80 g / m ² .

The packaging material according to claim 1, wherein the barrier layer is applied to a surface of the sheet substrate which corresponds to the back of the packaging material and thus to the inside of a package to be produced, the substrate preferably having paper weights of g / m ² in the range of 30 to 800 is.

3. Packaging material according to claim 1 or 2, wherein more than 50 wt .-% of the thickness of the barrier layer has a molecular weight M _w of> 2Ό00Ό00 g / mol.

4. Packaging material according to one of claims 1 to 3, wherein in the barrier layer> 25 wt .-%, preferably> 30% wt .-% and particularly preferably> 35

Wt .-% of the starch is in the form of gelatinized starch particles.

The packaging material according to any one of claims 1 to 4, wherein the thickness of the barrier layer, preferably the gelatinized starch particles, tapioca starch, pea starch, potato starch or any mixture thereof, preferably substituted tapioca starch, substituted pea starch, substituted potato starch or any mixture thereof, comprises / include.

6. The packaging material according to claim 5, wherein the barrier layer contains the starch or the starches in a proportion of 30 to 100 wt .-%, after deduction of an optionally present filler component.

7. Packaging material according to one of claims 1 to 6, wherein the plasticizer content in the barrier layer in wt .-%, based on starch plus Weichma- rather, at least 5 wt .-%, preferably at least 10 wt .-% is.

8. Packaging material according to one of claims 1 to 7, wherein the barrier layer in wt .-%, based on starch plus thickener, at most 50 wt .-%, preferably at most 30 wt .-%, thickener comprises.

9. The packaging material according to claim 1, wherein the thickener comprises xanthan and / or polyvinyl alcohol, preferably in a proportion of 0.01 to <2.5% by weight xanthan and / or 1 to 30% by weight, preferably 1 to 10 wt .-%, polyvinyl alcohol.

10. Packaging material according to one of claims 1 to 9, wherein the sheet-like substrate additionally comprises a pre-coat, preferably a mineral precoat, which is arranged between the substrate surface and the barrier layer.

1 1. A process for producing a multilayer packaging material having a starch-based barrier layer comprising the steps of a) providing a sheet substrate which is preferably selected from the group consisting of paper, paperboard and cardboard, and which optionally has a precoat,

b) providing a coating mass,

c) applying the coating composition of step b) to at least one

Side of the sheet substrate and forming a layer on the sheet substrate, and

d) raising the temperature to dry and solidify the applied and formed into a layer coating composition, characterized in that the coating composition is a suspension having suspended therein granular starch and this suspension is gelatinized on the substrate in situ and dried.

12. The method of claim 1 1, wherein the temperature in ° C of the coating composition when applied to the substrate at least 20, preferably at least 50, more preferably at least 60, and / or the temperature during application, based on the temperature Tv at the the coating composition has its viscosity minimum within the following limits: <1 1 above Tv and <15 below Tv.

13. The method of claim 1 1 or 12, wherein at least the surface to be coated of the substrate is heated prior to application of the coating composition, so that at least the surface during application has a temperature in ° C of> 30 and / or this temperature in ° C. preferably> 5 above Tv of the coating composition.

14. The method according to any one of claims 1 1 to 13, wherein on the coated surface before drying steam, preferably steam, is applied.

15. The method according to any one of claims 1 1 to 14, wherein the coating composition is sprayed with water prior to the application of the vapor.

16. Packaging material according to one of claims 1 to 10, obtainable by the method according to one of claims 1 1 to 15.

17. Coating composition for packaging materials, in particular for paper, cardboard or cardboard, the coating composition comprising: a) 10-75% by weight of granular starch,

b) 0-50% by weight of dissolved starch,

c) 0-70% by weight of plasticizer,

d) 25-90 wt .-% water, wherein the preferred weight average molecular weight distribution M _{w of} the granular starch is> 500Ό00, and

the coating composition at 40 ° C has a viscosity in the range of 50-30000 mPas. 18. Coating composition according to claim 17, wherein the weight average molecular weight distribution M _{w of} the granular starch is at least 1 Ό00Ό00 g / mol, preferably at least 2Ό00Ό00 g / mol or more.

A coating composition according to claim 17 or 18, wherein the coating composition comprises tapioca starch, pea starch, potato starch or any mixture thereof, preferably substituted tapioca starch, substituted pea starch, substituted potato starch or any mixture thereof.

A coating composition according to any one of claims 17 to 19, wherein the granular starch, tapioca starch, pea starch, potato starch or any mixture thereof, preferably substituted tapioca starch, substituted pea starch, substituted potato starch or any mixtures thereof.

21. A coating composition according to any one of claims 17 to 20, wherein the amylose content of the granular starch is in the range of 0 to less than 60% by weight, preferably in the range of more than 0.5 to less than 35% by weight. 22. Coating composition according to one of claims 17 to 21, wherein the plasticizer content is at least 5 wt .-%, preferably at least 10 wt .-%, more preferably at least 15 wt .-%.

23. The coating composition according to claim 17, wherein the coating composition comprises at least 2, preferably at least 3 plasticizers, wherein in the combination the individual plasticizers are represented by at least 5%, preferably at least 10%, most preferably at least 15% , 24. A coating composition according to any one of claims 17 to 23, wherein the coating composition in wt .-%, based on the total starch plus thickening agent, at most 50 wt .-%, preferably at most 30 wt .-%, thickener. 25. Coating composition according to one of claims 17 to 24, wherein the thickener xanthan and / or polyvinyl alcohol, preferably in a proportion of 0.01 to <2.5 wt .-% xanthan and / or 1 to 30, preferably 1 to 10 Wt .-%, polyvinyl alcohol. 26. Use of the coating composition according to any one of claims 17 to 25 in a method according to any one of claims 1 1 to 15.

27. Use of a starch-based coating composition for sealing the surface of packaging materials in order to prevent the migration of lipophilic impurities from the packaging material into the packaged product, wherein the coating composition is a suspension with granular starch suspended therein.

28. Use according to claim 27, wherein a coating composition according to any one of claims 17 to 25 is used.

29. An apparatus for producing a multilayer packaging material having a starch-based barrier layer according to any one of claims 1 to 10 or 16, the apparatus comprising:

- means for applying a coating composition to a flat substrate, and

Means for drying the coated substrate, the apparatus being characterized in that before the means for drying means for in situ gelatinization are arranged, with the aid of which steam can be applied to the coated surface, said means preferably comprising a steam blow box.

30. The apparatus of claim 29, wherein a spray device for spraying the coated surface is arranged in front of the device for applying steam.