EP3047068B1 - Packaging material with a starch-based barrier coating and coating mass and method for producing the same - Google Patents

Description

TECHNICAL AREA

The invention relates to a packaging material with a starch-based barrier coating, a process for the preparation of a packaging material with a starch-based barrier coating, a starch-based coating composition and their use for the surface sealing of packaging materials.

STATE OF THE 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 of A. Vollmer et al. from the year 2011 (Eur Food Res Technol (2011) 232: 175-182 ) were 119 samples of dry foods from different Packaging types are examined for their mineral oil saturated hydrocarbons (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 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 dated 09 December 2009. The publication, available at http://www.bfr.bund.de/de/fragen and reply to mineraloel uebergaengen from packaging materials on Lebensmittel-50470.html , provides short-term options for the exclusion of the Direct contact of recycled paper and board with dry foods with high specific surface area proposed by use of inner bags (eg PET films) with barrier effect.

However, such additional inner packaging is not desirable on the one hand for economic reasons, as they make the packaging more expensive, and on the other hand, they are unecological because 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 impurities can be 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.

Other approaches include the use of multi-layer laminates and the application of barrier layers to the inside of cardboard packaging to prevent the migration of mineral oil contamination through the gas phase. It offers manufacturers of paper and cardboard packaging, in particular folding boxboard and corrugated cardboard 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.

In the WO13076241A2 It is proposed to use aqueous dispersions based on polyvinyl acetate for producing a coating on film-shaped substrates for reducing the diffusion of oily substances from packaging into foodstuffs 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. Moreover, the use of a synthetic, poorly biodegradable coating tarnishes the reputation of carton packaging as an ecologically highly advantageous packaging solution. Since such coatings are also relatively expensive, there is still a need for cost-effective, ecologically meaningful coating compositions with a good barrier effect.

Starch-based coatings are known in the paper industry. These are used, for example, in the paper coating in coating colors to give cardboard 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. Thus, for example, a 10% starch solution at 40 ° C have a viscosity of> 5,000 mPas and is therefore not useful in conventional brushing. Therefore, partially degraded starches are usually used with average molecular weights of M _w <<1'000'000 g / mol in order to keep the viscosity of the starch solution and thus of the coating composition in a manageable framework at higher solids contents (for example a 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.

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.

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

PRESENTATION OF THE INVENTION

The object is solved 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.

Another aspect of the invention relates to a process for producing this packaging material.

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.

Furthermore, the invention relates to the use of a starch-based coating composition for surface sealing of packaging materials in order to prevent or reduce the migration of, for example, contained in the packaging material lipophilic impurities in the packaged goods. 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 include linear, cyclic and aromatic hydrocarbons, in particular MOSH and / or MOAH.

As a natural polymer from renewable resources, starch has the distinct advantage that the price is low and the environmental balance is positive compared to synthetic products. 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 in the form of a solution with long-chain, ie high molecular weight, starch molecules is used, which can be applied efficiently with a high solids content to a suitable substrate or a carrier layer of a packaging material, preferably on paper, board or cardboard, and then on the film is filmed into a coherent barrier layer or a coherent barrier film.

This barrier layer substantially restricts or prevents the migration of lipophilic contaminants from the package or packaging into the packaged product. It has surprisingly been found that long-chain starch types can be usefully used for coating and the use of long-chain starch types in the barrier coating also leads to significantly better mechanical properties and barrier properties of the coating.

The coating composition of the invention is used as a solution, preferably as an aqueous solution, the solids content of which contains starch as the main component. The barrier effect depends crucially on obtaining a full-coverage barrier coating that is virtually free of imperfections (eg pinholes) and that the barrier coating is flexible and non-sticky so that the multilayer packaging material thus obtained, for example the coated paper, can be removed by means of the In the packaging industry customary creasing and folding techniques can be processed without the barrier coating is thereby significantly damaged or impaired. This is the only way to ensure that the packaged goods, for example the packaged foodstuffs, are adequately protected against the entry of the above-mentioned contaminants, even during prolonged storage periods.

The coating composition according to the invention is based on starch. The lower the molecular weight of the starch used, the more brittle the starch or the barrier film produced therefrom, even at higher plasticizer contents. Brittle films are unusable as a barrier because they break easily or crack and thus allow the passage of impurities. On the other hand, the viscosity of starch in solution increases massively with the molecular weight of the starch used. The viscosity in solution is primarily dominated by the largest starch macromolecules. However, in order to be able to apply the starch to a packaging material, for example a paper, economically, a low viscosity of the composition used for coating is desired. In the case of high molecular weight starches, the viscosity of the solution can be achieved by using a low solids content which correlates with a high water content of the solution. However, this water must be dried away at high cost in the production of packaging materials.

The way out of this situation opens up the inventive approach in which particularly advantageous compositions for the coating of packaging materials have been developed.

coating

The coating composition according to the invention is obtained from a coating composition which comprises the constituents mentioned below for the coating composition, it being possible to use for the at least one starch any starch having a molecular weight M _w of at least or more than 0.8 million g / mol. The starch (s) and optionally further existing solid and / or liquid additives are typically stirred into an aqueous solution, preferably in water. The terms coating composition and coating composition differ in that the coating composition in the sense of the present patent application means the composition which can be directly used for coating or in which the starch is already present in dissolved form.

Unless otherwise indicated, the abbreviation M _w always denotes the weight average molecular weight.

• mindestens eine Stärke,
• 0-70 Gew.-% Weichmacher,
• 0-50 Gew.-% eines polymeren Zusatzstoffs oder mehrerer polymerer Zusatzstoffe,
• 0-5 Gew.-% eines Additiv oder einer Additivmischung, und

The inventive starch-based coating composition comprises

• at least one strength,
• 0-70% by weight of plasticizer,
• 0-50% by weight of a polymeric additive or of several polymeric additives,
• 0-5 wt .-% of an additive or an additive mixture, and

Water.

Unless otherwise indicated, the present patent application states that all stated amounts of starch are based on the sum of the proportions of starch plus plasticizer plus water. Accordingly, the softener components are based on the sum of starch plus plasticizer. The proportion of the polymeric additive (s) is based on the sum of starch plus polymeric additive. The proportion of the additive (s) is based on the dry mixture or composition.

The proportion of water is understood as the remainder to 100 wt .-%, wherein a filler, if any, is not taken into account in the calculation.

The starch is present in ready-to-use, finished coating mass in dissolved form.

According to one possible embodiment of the present invention, the coating composition consists of the at least one starch, the proportion of which, based on starch, plasticizer and water, being determined in accordance with Table 1 explained below, being 0-70% by weight of at least one plasticizer. 50 wt .-% of at least one polymeric additive, 0-5 wt .-% of at least one additive, and a residue of water to 100 wt .-%.

The lower limit for the molecular weight M _w of at least one starch in millions of g / mol (= 10 ⁶ g / mol = million g / mol) is 0.8, preferably 1.0, more preferably 1.5, more preferably 2 , 0, more preferably 2.25, even more preferably 2.5, even more preferably 2.75, most preferably 3.0.

The upper limit for the molecular weight M _{w of} the at least one starch in millions of g / mol in the coating composition is about 20, preferably 15, more preferably 12, even more preferably 10, even more preferably 9, even more preferably 8, even more preferably 7, most preferably 6. In another embodiment, the upper limit for the molecular weight M _{w of} the at least one starch may be more than 20 million g / mol, preferably in the range of more than 20 to 50 million g / mol.

The proportion of starch in wt .-% in the coating composition, based on starch and plasticizer and water, is dependent on the molecular weight M _{w of} the starch and is represented by the following Table 1.

The lower limit of the amount of starch in wt% for the respective molecular weights is given in Table 1 on line A1, a preferred lower limit on line A2, an even more preferred lower limit on line A3, an even more preferred lower limit on line A4, one more more preferred lower limit on line A5, an even more preferred lower limit on line A6, an even more preferred lower limit on line A7, most preferably on line A8.

The upper limit of the amount of starch in wt% for the respective molecular weights is given in Table 1 on line B1, a preferred upper limit on line B2, an even more preferred upper limit on line B3, an even more preferred upper limit on line B4, one more more preferred upper limit on line B5, an even more preferred upper limit on line B6, an even more preferred upper limit on line B7, most preferred is the upper limit according to line B8.

The lower and upper limits for the amount of molecular weight starch between or outside the values of Table 1 can be obtained by linear interpolation or by linear extrapolation. For starches having a molecular weight M _w of more than 20 million g / mol, preferably in the range of more than 20 million g / mol to 50 million g / mol, the values can be obtained by linear extrapolation. Table 1: Starch content in wt .-% depending on M <sub> w </ sub> in million g / mol Million g / mol 0.8 1 1.5 2 2.3 2.5 2.8 3 6 7 8th 9 10 12 15 20 A1 14.4 14.1 13.3 12.6 12.2 11.9 11.5 11.1 6.7 5.2 3.7 2.5 2.4 2.2 2.1 1.7 A2 16.0 15.7 15.0 14.2 13.9 13.5 13.1 12.7 8.3 6.8 5.3 3.9 3.3 2.3 2.1 1.9 A3 17.3 17.0 16.2 15.5 15.1 14.7 14.4 14.0 9.6 8.1 6.6 5.1 3.6 2.5 2.3 2.0 A4 18.3 18.0 17.2 16.5 16.1 15.8 15.4 15.0 10.6 9.1 7.6 6.1 4.7 2.7 2.5 2.2 A5 19.1 18.8 18.1 17.4 17.0 16.6 16.3 15.9 11.4 10.0 8.5 7.0 5.5 3.0 2.8 2.3 A6 19.9 19.6 18.9 18.1 17.7 17.4 17.0 16.6 12.2 10.7 9.2 7.8 6.3 3.3 3.0 2.5 A7 20.6 20.3 19.5 18.8 18.4 18.0 17.7 17.3 12.9 11.4 9.9 8.4 6.9 4.0 3.3 3.0 A8 21.1 20.9 20.1 19.4 19.0 18.6 18.3 17.9 13.5 12.0 10.5 9.0 7.5 4.6 3.7 2.7 B8 32.8 32.5 31.8 31.1 30.7 30.3 29.9 29.6 25.1 23.7 22.2 20.7 19.2 16.3 11.8 4.4 B7 34.1 33.8 33.0 32.3 31.9 31.6 31.2 30.8 26.4 24.9 23.4 21.9 20.5 17.5 13.1 5.7 B6 35.1 34.8 34.1 33.3 33.0 32.6 32.2 31.9 27.4 25.9 24.5 23.0 21.5 18.5 14.1 6.7 B5 36.7 36.4 35.7 34.9 34.6 34.2 33.8 33.5 29.0 27.5 26.1 24.6 23.1 20.1 15.7 8.3 B4 38.0 37.7 36.9 36.2 35.8 35.5 35.1 34.7 30.3 28.8 27.3 25.8 24.4 21.4 17.0 9.6 B3 39.0 38.7 38.0 37.2 36.9 36.5 36.1 35.7 31.3 29.8 28.3 26.9 25.4 22.4 18.0 10.6 B2 39.9 39.6 38.8 38.1 37.7 37.4 37.0 36.6 32.2 30.7 29.2 27.7 26.3 23.3 18.9 11.5 B1 40.6 40.3 39.6 38.8 38.5 38.1 37.7 37.4 32.9 31.4 30.0 28.5 27.0 24.0 19.6 12.2

The erfindungsmässe coating composition may further contain one or more fillers. The proportion of filler (s) is not taken into account in the calculation of the 100% by weight. Rather, the filler is added in addition to the 100 wt .-%.

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 in each case means the entire water, ie the water supplied plus the water, which is present in the substances, such as starch, as moisture / bound. Unless stated otherwise, the term wt .-% always means weight fraction per part by weight.

Viscosity and pH of the coating compositions

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

The upper limit of the viscosity in mPas is 5,000, preferably 3,000, more preferably 2,500, even more preferably 2,200, even more preferably 2,000, even more preferably 1,800, even more preferably 1. 600, most preferably 1'500.

Most preferably, the viscosity of the coating composition is in the range of 200 to 1000 mPas.

If the viscosity is too low, the use of coating compositions based on starch results in too low a coating weight and thus an excessively thin barrier coating or barrier layer. If the viscosity is too high, the use of coating compositions based on starch results in an excessively high application weight and / or controlled, uniform application is 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 ,

Strength

For the coating composition, the coating composition and the coating, in principle any starch or any mixtures thereof can be used as the starch with regard to the origin and the preparation. 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 origin, root starches, such as potato starches or tapioca starches, are preferred. Particularly preferred is tapioca starch. Tapioca starch 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 strength is native, i. unmodified state used. Hereby useful properties can be obtained at low cost.

In a further preferred embodiment, substituted starches, such as starch esters and starch ethers, are used, such as, for example, hydroxypropylated or acetylated starches. These modifications lead to particularly high elasticity of the barrier coating or the barrier layer, 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 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 starch is a non-crosslinked starch or a mixture of non-crosslinked starches.

In a preferred embodiment, substituted 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 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 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 result in a reduced extensibility of the barrier coating being able to lead.

The amylose content of the starch (s) in wt .-% is preferably> = 0, more preferably> 0.5, more preferably> 0.7, more preferably> 1, even more preferably> 2.5, most preferably> 5. Too low levels of amylose may result in reduced stretchability 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 starches having 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, very particularly 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 starches are permitted which are approved for applications for contact with food.

The strength in the coating composition is solved. For the purposes of the present patent application, a starch is considered as dissolved if, when viewed in a polarizing microscope, at least 80%, preferably at least 90%, preferably at least 95%, preferably at least 97%, more preferably at least 99% of the starch granules are in the swollen state and are no longer birefringent.

Preferably, at least 10%, more preferably more than 30%, even more preferably more than 50%, even more preferably more than 70% and even more preferably more than 90% of these starch granules have burst or have already broken down into fragments.

Even more preferably, all starch granules are substantially disintegrated. Most preferably, the dissolved starch is a true molecular solution in which the starch granules are completely destructured, that is, destroyed, and no longer are any fragments of starch granules. The dissolved form of starch is typically obtained in aqueous systems by the following measures: boiling the starch, particularly with a jet cooker, heating to a temperature above the gelatinization temperature, dissolving extruded amorphous starch, using pregelatinized starch. When dissolved, the starch grains first absorb water and gelatinize. Gelatinized starch granules easily break down into fragments under shear and these can 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. The degree of destructuring of the starch granules can be determined and determined by simple light microscopic observation, for example at 200 × magnification. Preferably, the starch is stained with iodine.

Molecular weight of the starch

In order to enable the required mechanical properties of the barrier coating, a high molecular weight M _{w of} the starch is a prerequisite. The at least one starch used to formulate the coating composition therefore has a molecular weight M _w in millions of g / mol of at least 0.8, preferably 1.0, more preferably 1.5, even more preferably 2.0, even more preferably 2.25, even more preferably 2.5, more preferably 2.75, most preferably 3.0.

An upper limit for the at least one starch for formulating the coating composition generally does not exist. The reason for this is that at very high molecular weights, such as> 20 million g / mol, the starch macromolecules are mechanically unstable. In the usual treatment methods, the mass is stirred while cooking the starch, and the shear that occurs in this case is already sufficient to break the macromolecules, whereby a molecular weight M _w of <20 million g / mol can quickly result. Typically, at the usual stirring rates, molecular weights M _w of about 15 million g / mol or even 12 million g / mol.

Nevertheless, for the formulation of the coating composition according to a preferred embodiment, starches are used whose upper limit of molecular weight M _{w is} in millions of g / mol, preferably 20, more preferably 15, even more preferably 12, even more preferably 10, even more preferably 9, even more preferably 8 more preferably 7, most preferably 6. As the molecular weight decreases, the preparation of the coating composition becomes easier and, finally, lower viscosities are obtained.

softener

Suitable plasticizers are in principle all plasticizers listed in the prior art for starch and any mixtures thereof. Unless otherwise specified, the term plasticizer in the present application is intended to include a plasticizer and mixtures of plasticizers.

A low level of plasticizer leads to embrittlement of the barrier layer 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. Preferably, polyols are used, such as glycerin, sorbitol, maltitol, erythritol, xylitol, mannitol, galactitol, tagatose, lactitol, maltulose, isomalt, maltol, etc., but also various sugars, such as sucrose / sucrose, maltose, trehalose, lactose, lactulose , Galactose, fructose, etc., as well Monosaccharides 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 plus plasticizer, is 70, preferably 60, more preferably 55, more preferably 50, even more preferably 46, most preferably 42.

The lower limit of the plasticizer content of the coating composition in% by weight, based on starch plus plasticizer, in one embodiment is 0. According to further embodiments, the lower limit for the plasticizer content of the coating composition in% by weight, based on starch plus plasticizer, is preferred 5, more preferably 10, more preferably 15, even more preferably 20, even more preferably 25, even more preferably 28, even more preferably 31, even more preferably 32.5, most preferably 33.5.

The limits for the plasticizer content of the barrier layer 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 110 ° 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 are used. The proportion of plasticizers which fulfill this condition in the total plasticizer content of the coating composition 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 a reduced tendency to migrate from the barrier coating into the substrate of the packaging material, for example the paper. By migrating the plasticizers, the barrier coating loses flexibility.

In preferred embodiments, a combination of at least 2 plasticizers is used, 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%. 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.

Modifying polymers

In addition to the starch or starch mixture having a molecular weight M _w of at least 800,000 g / mol, which is not included in the polymeric additives or modifying polymers mentioned in this section, the coating composition may optionally be admixed with at least one further polymeric additive to modify the mechanical properties of the barrier coating or barrier layer advantageously, in particular in order to increase their flexibility, and to improve the processability of the coating composition. Furthermore, these modifying polymers contribute to an increase in the solids content.

Suitable modifying polymers are in principle all hydrophilic substances and mixtures thereof, 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 modifying polymers are hydrocolloids and gums, such as galactomannans, such as guar gum or locust bean gum; Cellulose derivatives, in particular cellulose ethers; Pectins, especially rhamnogalacturonans and protopectins; dextrans; xanthan; zymosan; Seaweed hydrocolloids such as alginates, agar-agar, agarose, carrageenan and carrageenans; furcellaran; Hydrocolloids off Lichens, such as lichenin 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; Starch having a molecular weight M _w of less than 800,000 g / mol and any combinations thereof.

In preferred embodiments, the maximum level of modifying polymer or modifying polymers of the coating composition, as well as in the barrier coating, in weight percent, based on starch plus modifying polymer, is 50, more preferably 40, even more preferably 30, even more preferably 20 more preferably 10, more preferably 5, even more preferably 2.5, most preferably 1.5.

If present, the minimum amount of modifying polymer or modifying polymers of the coating composition, as well as in the barrier coating, in weight percent, based on starch plus modifying polymer, is 0.01, preferably 0.05, more preferably 0.1, even more preferably 0.3, more preferably 0.6, even more preferably 0.8, most preferably 1.0. Since the modifying polymer is an optional component, the minimum amount may also be 0% by weight.

According to preferred embodiments, xanthan gum is used as a modifying polymer, since xanthan gum also can particularly effectively prevent the sedimentation of suspended solids in the coating composition, such as fillers, and optionally residues of starch granules. A maximum proportion of <2.5% by weight of xanthan as modifying polymer 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. Xanthan gum may be used in particular in combination with any one or more of the aforementioned starches. In particular, any combination with the other components, ie, plasticizers, polymeric additives, fillers, additives, lecithin and fatty acids according to the invention are also included.

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

Preference is also given to using polyvinyl alcohol (PVA) since PVA not only 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, more preferably> 10, most preferably> 15.

In a preferred embodiment, the maximum level of PVA in weight percent based on starch plus PVA is 40, more preferably 30, even more preferably 20, even more preferably 15, even more preferably 10, even more preferably 7, even more preferably 5, most especially 4. The minimum proportion of PVA in% by weight is 0, preferably 0.1, more preferably 0.3, even more preferably 0.6, even more preferably 1, even more preferably 1.5, even more preferably 2, very particularly preferably 3 PVA may be used in particular in combination with any one or more of the aforementioned starches. In particular, any combination with the other components, ie plasticizers, polymeric additives, fillers, additives, lecithin and fatty acids according to the invention are also included.

The aforementioned ranges for xanthan and PVA are, of course, to be understood as forming a proportion of the modifying polymers if one or both components are present or the modifying polymer contains only xanthan and / or PVA. The quantitative ranges for xanthan and PVA are therefore not to be understood as being additive to the abovementioned general quantitative ranges for the modifying polymer (s).

The limits for the modifying polymer content of the barrier coating correspond to the limits for the proportion of modifying polymer in the coating composition.

filler

The filler component of the coating composition or of the barrier coating is all components which are virtually insoluble in water or are present in the coating composition, as well as in the barrier coating, in the form of particles, such as, for example, pigments, glass particles, soot particles, mineral particles such as titanium dioxide, Talc, carbonates. The filler component is mathematically subtracted from the formulas, as it is not essential to most functional components of the formulation whether a filler component is present or not. Unless otherwise indicated and nothing else is obvious, therefore, the percentages by weight relating to the composition of the barrier coating in the following embodiments mentioned as particularly preferred in each case relate to the proportions without an optionally additionally present filler component.

Regardless, the proportion of the filler component in wt .-% in the dry barrier layer, so here the total mass of starch and optional components, but without water, at <50, more preferably <30, more preferably <20, more preferably <10, even more preferably, <5 most preferably <3. The flexibility of the barrier coating is especially reduced at higher levels of filler.

If present, the minimum weight percent filler component 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.

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

additives

The coating composition of the invention may further optionally comprise one or more additives. Thus, for example, the following additives can be used as further components of the coating composition: surfactants, such as ionic or nonionic surfactants, wetting agents, defoamers, stabilizers, dyes, other polymers than those 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.

Water content and solids content of the coating composition

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

The proportion of water for the formulation of or in the coating composition results arithmetically from the difference of 100% by weight minus the sum of the percentages by weight of all components other than the fillers.

• Bevorzugt ist die Stärke eine hydroxypropylierte Erbsenstärke mit einem Molekulargewicht in Millionen g/mol im Bereich von 1 bis 20, vorzugsweise von 2,5 bis 10. Der Weichmacher ist bevorzugt Glycerin. Der Weichmachergehalt in Gew.-%, bezogen auf Stärke und Weichmacher, liegt im Bereich von 0 - 45, vorzugsweise von 15 bis 37, der Stärkegehalt, bezogen auf Stärke und Wasser und Weichmacher, liegt im Bereich von 14 bis 35 Gew.-%. Die Beschichtungsmasse umfasst bevorzugt außerdem einen Anteil an PVA von 1 bis 30 Gew.-%, vorzugsweise 1 bis 20 Gew.-%, noch bevorzugter 1 bis 10 Gew.-%.

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 the processability of the coating composition:

• Preferably, the starch is a hydroxypropylated pea starch having a molecular weight in millions of g / mol ranging from 1 to 20, preferably from 2.5 to 10. The plasticizer is preferably glycerin. 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 starch and water and plasticizer, is in the range of 14 to 35 wt .-% , The coating composition preferably also comprises a proportion of PVA of 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

Of these compositions, particularly suitable barriers will be included if the barrier layer is preferably applied in two passes, For each pass preferably a basis weight (dry) of 5 to 15 g / m ^{2 is} applied.

Comparable results are obtained when a hydroxypropylated tapioca starch or a hydroxypropylated potato starch is used instead of the hydroxypropylated pea starch. The proportion of the starch in the coating composition is determined as described above according to Table 1. The above-mentioned preferred upper and lower limits for the amount of starch also apply.

According to a further preferred embodiment, the starch is a hydroxypropylated tapioca starch having a molecular weight in millions of g / mol in the range from 1 to 20, preferably from 2.5 to 10. The plasticizer is preferably glycerol. 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 starch and water and plasticizer, is in the range of 14 to 35 wt .-% , The coating composition preferably also comprises a proportion of PVA of 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

According to a further preferred embodiment, the starch is a hydroxypropylated potato starch having a molecular weight in millions of g / mol in the range from 1 to 20, preferably from 2.5 to 10. The plasticizer is preferably glycerol. 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 starch and water and plasticizer, is in the range of 14 to 35 wt .-% , The coating composition preferably also comprises a proportion of PVA of 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

From these compositions too, particularly suitable barriers are included if the barrier layer is preferably applied in two passes, wherein a basis weight (dry) of 5 to 15 g _/ m ² is preferably applied on each pass.

In another aspect, the present invention relates to the use of a starch-based coating composition or coating composition for Surface sealing of packaging materials to prevent or reduce the migration of lipophilic contaminants contained in the packaging material, such as mineral oil residues, in particular MOSH and / or MOAH.

• mindestens eine Stärke mit einem Molekulargewicht M_w im Bereich von 800'000 bis 20'000'000 g/mol,
• 0-70 Gew.-% Weichmacher, wobei der Weichmacheranteil auf Stärke plus Weichmacher bezogen ist,
• 0-50 Gew.-% eines polymeren Zusatzstoffs oder mehrerer polymerer Zusatzstoffe, wobei der Anteil des/der polymeren Zusatzstoffe auf Stärke plus polymerer Zusatzstoff bezogen ist,
• 0-5 Gew.-% eines Additiv oder einer Additivmischung, bezogen auf die trockene Mischung, und

The coating composition used comprises

• at least one starch having a molecular weight M _w in the range from 800,000 to 20,000,000 g / mol,
• 0-70% by weight of plasticizer, the plasticizer content being based on starch plus plasticizer,
• 0-50% by weight of a polymeric additive or of several polymeric additives, the proportion of the polymeric additive (s) being based on starch plus polymeric additive,
• 0-5 wt .-% of an additive or an additive mixture, based on the dry mixture, and

Water, wherein the at least one starch is present in dissolved form.

With regard to the plasticizer, the polymeric additives, the additives and also optionally present filler reference is made to the above statements.

With regard to the origin of the starch and the molecular weight M _{w of} the starch, reference is also made to the above statements. In a preferred embodiment, the lower limit and the upper limit for the proportion of the at least one starch in the coating composition in wt .-%, based on starch, plasticizer and water, depending on the molecular weight M _{w of} the at least one strength is given by: M _w million g / mol 0.8 1 1.5 2 2.3 2.5 2.8 3 6 7 8th 9 10 12 15 20 Lower limit 14.4 14.1 13.3 12.6 12.2 11.9 11.5 11.1 6.7 5.2 3.7 2.5 2.4 2.2 2.1 1.7 Upper limit 40.6 40.3 39.6 38.8 38.5 38.1 37.7 37.4 32.9 31.4 30.0 28.5 27.0 24.0 19.6 12.2 and wherein the lower and upper limits for the proportion of said starch at molecular weights intermediate between the values of the table can be obtained by linear interpolation. Further preferred limits can be found in Table 1 above. All coating compositions disclosed above represent particularly preferred embodiments for the use according to the invention.

barrier layer

• mindestens eine Stärke mit einem Gewichtsmittel der Molekulargewichtsverteilung M_w in g/mol von 0,8 Millionen bis zu 20 Millionen,
• 0-70 Gew.-% Weichmacher, wobei der Weichmacheranteil auf Stärke plus Weichmacher bezogen ist,
• 0-50 Gew.-% eines polymeren Zusatzstoffs oder mehrerer polymerer Zusatzstoffe, wobei der Anteil des/der polymeren Zusatzstoffe auf Stärke plus polymerer Zusatzstoff bezogen ist,
• 0-5 Gew.-% eines Additiv oder einer Additivmischung, bezogen auf die trockene Mischung, und

gegebenenfalls Wasser, welches in der Barriereschicht gebunden ist.The inventive starch-based barrier layer comprises

• at least one starch with a weight-average molecular weight distribution M _w in g / mol of 0.8 million up to 20 million,
• 0-70% by weight of plasticizer, the plasticizer content being based on starch plus plasticizer,
• 0-50% by weight of a polymeric additive or of several polymeric additives, the proportion of the polymeric additive (s) being based on starch plus polymeric additive,
• 0-5 wt .-% of an additive or an additive mixture, based on the dry mixture, and

optionally water which is bound in the barrier layer.

The barrier layer according to the invention may further comprise fillers. In this case, the sum of all components contained in the barrier layer, with the exception of the optionally contained fillers, gives 100 wt .-%. If present, the proportion of filler is additionally added to the coating composition.

With regard to the plasticizer, the polymeric additives and the additives as well as the optionally also present filler reference is made to the above statements.

With regard to the origin of the starch and the molecular weight M _{w of} the starch, reference is also made to the above statements.

Water content of the barrier layer

Part of the water of the coating composition may be bound in the solidified barrier layer. The remaining water is lost mainly in the drying of the packaging material. 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 Wt%, more preferably at most 5 wt%, and most preferably at most 3 wt%.

The finished, dried barrier layer is preferably solid and not sticky.

grammage

As the basis weight increases, the barrier effect of the barrier coating increases. The surface of paper, 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. For price reasons, rougher papers are also used in the packaging industry and a good barrier layer is also obtained with 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.

The upper limit of 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 17, even more preferably 16, even more preferably 15, most preferably 14. The thinner the application, the less likely blistering and pinholes are 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.

It has surprisingly been found that the barrier layers according to the invention are or remain flexible even on the packaging material. This is surprising since a per se flexible starch film, when applied to a paper, can often lose a lot of flexibility. If, for example, a casting material based on starch is poured onto a Teflon film and dried, then a soft and flexible film can be obtained. However, applying the same casting compound to a paper can result in a hard, inflexible film that already cracks even without mechanical stress. Since starch films usually require a level of plasticizer to be soft and flexible and not brittle, one might suspect that the film on the paper loses plasticizer to the paper and this is the reason for the embrittlement of a per se flexible starch film. On the other hand, said embrittlement was not always observed. Surprisingly, it was found that the flexibility increases significantly with the molecular weight from about 800'000 g / mol. This is already a very high molecular weight in the world of macromolecules and it would have been expected that at such high molecular weights, the flexibility would decrease rather than increase as the entanglement of the macromolecules increases with molecular weight, thereby making it difficult to slide the macromolecules one upon another. The flexibility of the starch film on the paper continued to increase as the molecular weight continued to increase.

Furthermore, the barrier layers obtained according to the invention are characterized in that they are nationwide and have no defects, such as in the form of pinholes. Pinholes or blisters typically result from the drying of the applied coating composition. After the coating composition has been applied to the paper, part of the coating composition is absorbed by the nearest paper layers. During drying, the coated paper side is treated with infrared radiation and / or hot air. The surface of the coating dries faster than the underlying layers, forming a barrier against the vapor in the area of the surface, which wants to escape from the lower layers. This leads to the formation of vapor bubbles, which eventually burst open and lead to defects in the barrier layer. The thicker the layer, the more difficult it is to avoid such blisters. Particularly problematic is the part of the coating mass which has been absorbed by the paper and has penetrated more or less deeply into the paper. Even with very slow and thus uneconomic drying blisters and Pinholes can still arise. Surprisingly, it has been found that the tendency to form blisters and pinholes decreases with increasing molecular weight of the starch. This behavior is attributed to the fact that with increasing molecular weight, the low shear viscosity increases with molecular weight and thus a corresponding casting material is much less able to penetrate into the porous paper.

packing material

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

substratum

The barrier coating is applied to a flat substrate, which is suitable as packaging material. The sheet-like substrate is preferably a paper, a cardboard or a cardboard. Unless otherwise mentioned, in the context of the present patent application the term paper should always also include cardboard. 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 narrower sense as well as cardboard and paperboard.

Particularly preferred papers are used as a substrate for the packaging material or as a carrier material for the barrier coating, which are permitted under food law and thus can be used as food packaging.

The barrier coating is applied to the back side of the substrate, ie the side which forms the inside of the packaging in the finished packaging. This results from the fact that a barrier with respect to the interior of the packaging or the packaged goods present therein should be obtained. The backs of papers suitable for packaging are typically rough, while those for most a printing provided front pages are relatively 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 on the front side of the substrate, so the outside of the finished package, further, known in the art coatings or printed. 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, further layers may comprise on packaging material according to the invention.

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.

Barrier layer applied to the substrate

The applied barrier layer consists of at least one layer. The barrier layer is thus produced or applied in at least one application (passage, line). According to a preferred embodiment of the present invention, 2 jobs are made with the application mass being dried therebetween. Also 3 and more orders are possible, whereby 2 orders are preferred, and 3 orders are preferred before 4 orders.

method

1. a) Bereitstellen eines flächigen Substrats, welche vorzugsweise ein Material ausgewählt aus der Gruppe, bestehend aus Papier, Pappe und Karton umfasst,
2. b) Bereitstellen der erfindungsgemäßen Beschichtungsmasse
3. c) Auftragen der Beschichtungsmasse von Schritt b) auf mindestens eine Seite des flächigen Substrats und Bilden einer Schicht auf dem flächigen Substrat, und
4. d) Erhöhen der Temperatur zum Trocknen und Verfestigen der aufgetragenen und zu einer Schicht umgeformten Beschichtungsmasse.

The method according to the invention for producing the multilayer packaging material comprises the following steps:

1. a) providing a flat substrate, which preferably comprises a material selected from the group consisting of paper, cardboard and cardboard,
2. b) providing the coating composition according to the invention
3. c) applying the coating composition of step b) to at least one side of the planar substrate and forming a layer on the planar substrate, and
4. d) raising the temperature to dry and solidify the coated and layered coating.

The coating composition according to the invention can be provided by mixing the powdery starch present in a liquid phase, the liquid phase having at least water, preferably at least water and plasticizer. The resulting suspension is then heated or "boiled" to a temperature above the gelatinization temperature. For example, the suspension may be used at atmospheric conditions, i. at a temperature of <100 ° C, or it is cooked at temperatures> 100 ° C, for example at 130 ° C with a jet cooker.

Optionally, instead of cooking starch, i. Starch that must be cooked to develop viscosity, also precooked starch, such as pregelatinized starch. However, since a starch kitchen is typically present in the paper industry by default, it is more advantageous to use the cheaper cooking strength.

During cooking, the starch granules absorb water and the partially crystalline structure of the starch grain is converted into an amorphous, strongly swollen structure Starch grain can absorb a multiple of its own weight of water, but initially present as a suspended particle. If the starch grain is maximally swollen, then the highest viscosity results. The higher the temperature at which the starch is cooked, the longer it is cooked and the more intensively the mixture is sheared, for example by a mixer, the more the swollen starch grain decomposes. First, it breaks down into fragments, which in turn disintegrate into smaller fragments, until finally a true molecular solution is created. During this transition from maximally swollen starch granules to the molecular solution, the viscosity is significantly reduced without the molecular weight having to decrease. Since the lowest possible viscosities are desired, it is advantageous if the starch is cooked to the extent that more or less a molecular solution has formed, which is typically the case when cooking with the jet cooker and using shear. If precooked starch is used, the cooking process is unnecessary, but it is advantageous to shear the mixture mechanically, for example by intensive stirring, in order to break down the starch granules and, if possible, to obtain a true solution of the starch macromolecules.

When cooking, as well as during the subsequent cooling phase and, if appropriate, storage time, care must be taken that the pH is within a range where no chemical degradation of the starch takes place, which occurs at a pH of> 4, preferably> 5, even more preferably> 6, more preferably> 6.5. Ideally, the pH is in the range of 7.

The starch composition prepared in this way can then be applied to the paper with the desired weight per unit area using the methods known in the paper industry. While typical coatings in the paper industry are applied to the front of the paper, for a barrier layer, the coating is applied to the back of the paper.

Application of the coating mass

Methods of applying liquids to sheet substrates are well known. The coating can be done in various ways: for example, the barrier mass may be painted, printed, cast, sprayed, rolled or otherwise planar and applied 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 mass is applied by brushing or pouring. Known and suitable coating methods are, for example, blade coating, knife coating and size press.

A particularly suitable casting method is curtain coating, in which case good barrier coatings with comparatively low application quantities could be obtained in particular.

Preferably, the barrier coating is prepared in more than one stroke. 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.

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 the first application is obtained as a backsize immediately following the production of the paper 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 may be applied to the paper, paperboard or paperboard, or may have been previously applied, for example, by the papermaker, on the one hand serving to remove the water from the coating mass hampering the subsequent barrier layers from penetrating into the paper, cardboard or board and, on the other hand, smoothing the surface to be coated. Especially with paper that is very absorbent, such a precursor offers significant advantages. 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 the 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. A starch-based pre-coat differs from the barrier layer according to the invention in that the pre-coat does not have all the features according to the invention of the barrier layer, ie, for example, has starch with a different molecular weight distribution and / or a different proportion than indicated in Table 1.

The preferred weight average molecular weight distribution M _w of the starch used in the pre-coat in g / mol is> 500,000, preferably> 1,000,000, preferably> 2,000,000, preferably> 2,500,000, more preferably> 3 '000'000, most preferably>4'000'000.

With respect to the solids content and plasticizer content of the precoat mass of dissolved starch, what has already been mentioned previously 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 for the basis weight of the precoat is 1, preferably 2, more preferably 3, and most preferably 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 papermaker is around 100-1,000 m / min, which is a speed of 1.7-17, for the heavier papers preferably used as a substrate for the barrier coating 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 to the paper at an elevated temperature.

In a preferred embodiment, the temperature in ° C. of the coating composition when applied to the paper is> 20, more preferably> 30, more preferably> 35, even more preferably> 40, most preferably> 45.

The upper limit of the application temperature is dependent, for example, on the composition of the coating composition, but results unambiguously for the person skilled in the art inter alia from the abovementioned requirements on the viscosity and thus the spreadability of the coating composition.

Pretreatment of the paper

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

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.

Drying of the paper

The coated with the coating composition paper can be dried with the usual in the paper industry drying process. In particular, infrared (IR) radiators and hot air hoods are 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 part of the drying process is performed 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.

A common device for painting, in particular of paper and cardboard, as in the prior art, is in Fig.1 shown schematically. 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 IR jet heater 8 and a hot air drying system 9. The web is guided by so-called guide rollers 3. The web can roll from one 1 unwound and rolled after drying again on such a l' become. However, this is not absolutely necessary: painting, for example, can also be an intermediate step in a multistage, continuous process.

For example, the coating composition may be applied to the substrate surface by knife coating, blading, casting, rolling, spraying, printing, or other methods suitable for applying liquid compositions. In FIG. 1 is an example of a common execution of a coating unit 4 outlined. 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 1', without sticking.

For drying the coated paper web, the drying processes known in the paper industry, such as, for example, those based on infrared radiation and hot air or drying by means of hot rolls, are suitable.

• Figur 1 zeigt schematisch eine Streichanlage gemäss dem Stand der Technik, wie sie in der Veredelung von Papier üblich ist.

Brief explanation of the figure:

• FIG. 1 shows schematically a coating system according to the prior art, as is customary in the finishing of paper.

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 grammage of the coated paper is in g / m ² receive. 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

M _w is understood to mean 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 in a mini-autoclave with stirring up to 150 ° C and held there for 20 min. Subsequently, the solution thus obtained 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).

1. 1) Die Stärke wird vom Papier mit einem Skalpell abgekratzt oder sie wird mit einem feinen Schleifpapier abgeschliffen. Das dabei erhaltene puderartige Material kann in gleicher Art in eine Lösung überführt werden wie für die oben beschriebene in Pulverform vorliegende Stärke.
2. 2) Alternativ kann die Barriereschicht zusammen mit dem Papier analysiert werden. Dazu wird das Material in Stücke von ca. 2*2 mm zerschnitten, im Autoklaven suspendiert und über Nacht bei Raumtemperatur gerührt. Dann wird wie oben für pulverförmige Stärke beschrieben verfahren. Bei der Filtration wird jedoch zuerst ein grober Filter verwendet, um die unlöslichen Papierbestandteile abzufiltrieren. Da übliche Papiere auch ohne eine Barriereschicht bereits Stärke enthalten können, wird gegebenenfalls eine Referenzmessung mit dem unbeschichteten Papier gemacht bzw. eine Referenzmessung mit dem Papier von dem die Barriereschicht mechanisch abgelöst worden ist. Aus der Referenzmessung kann dann beurteilt werden, welche Bestandteile bei der GPC-MALLS Analyse der Barriere und welche dem Papier zuzurechnen sind.

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 the starch solution.

1. 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 for the starch described above in powder form.
2. 2) Alternatively, the barrier layer can be analyzed along with the paper. For this purpose, the material is cut into pieces of about 2 * 2 mm, 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 Waters Alliance 2695 Separation Module, Waters DRI detector 2414, Dawn-HELEOS Dawn-HELEOS MALLS detector with 658 nm wavelength and 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 1E5 - 1 E3. Eluent: DMSO with 0.09m 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.

WAYS FOR CARRYING OUT THE INVENTION example 1

Starch: Hydroxypropylated pea starch with M _w = 4 500 000 g / mol Recipe: (all quantities are based on the total formulation unless otherwise stated) 18.0% by weight Thickness dry 10.2% by weight Glycerol, corresponds to 36.17 wt .-% glycerol, based on starch and glycerol, and 71.8% by weight of water 100% by weight total

The mixture was cooked in a batch cooker with an anchor stirrer at 95 ° C for about 45 minutes, resulting in a clear, homogeneous solution with a solids content of 28.2%. This solution had a viscosity of 370 mPas at 50 ° C.
Paper: 230 g / m ² , without backsheet
Coater: combi-blade with squeegee 20mm (0.8 bar contact pressure) Web speed: 350 m / min
Dry coat weight: 9.6 g / m ²
Drying setting: IR emitter (65%), dry air: 160 ° C (12 m drying distance)

Quick test with spray oil showed a significant reduction in permeability to hydrocarbons.

Example 2

Starch: Hydroxypropylated pea starch with M _w = 4 500 000 g / mol Recipe: (all quantities are based on the total formulation unless otherwise stated) 17.8% by weight Thickness dry 1.9% by weight PVA (88% hydrolyzed, dynamic viscosity of 8 mPas at 4% Solution and 20 ° C) 7.3% by weight Glycerol, corresponds to 29.0 wt .-% glycerol, based on starch and Glycerine, and 72.8% by weight of water 99.8% by weight total

The mixture was boiled in a batch cooker with an anchor stirrer at 95 ° C. for about 45 minutes to give a clear, homogeneous solution with a solids content of 27.0%. This solution had a viscosity of 260 mPas at 50 ° C. 0.2% by weight of a commercial wetting agent was added to the mixture in order to obtain a stable curtain during curtain coating.
Paper: 230 g / m ² , with a coating according to Example 1
Coater: Curtain Coater
Web speed: 100 m / min
Dry coat weight: 11 g / m ²
Drying setting: IR emitter (65%), dry air: 160 ° C (12 m drying distance)

A measurement of the mineral oil migration from the board through the coating was carried out in accordance with method DIN14338 (so-called "Tenax method") and showed a barrier effect of 99.1% for MOSH and MOAH. After creasing and folding of the paper, a barrier effect of 98.2% was obtained.

Example 3

Starch: Hydroxypropylated pea starch with M _w = 20 960 000 g / mol Recipe: (all quantities are based on the total formulation unless otherwise stated) 8.6% by weight Thickness dry 0.2% by weight PVA (98% hydrolyzed, dynamic viscosity of 40 mPas at a 4% solution and 20 ° C) 4.6% by weight Glycerol, corresponds to 34.84 wt .-% glycerol, based on starch and Glycerine, and 86.6% by weight of water 100% by weight total

The mixture was boiled in a batch cooker with an anchor stirrer at 95 ° C. for about 45 minutes to give a clear, homogeneous solution with a solids content of 13.4%. This solution had a viscosity of 600 mPas at 40 ° C.
Paper: Commercially available carton box with 329 g / m ² , with a coating according to Example 1
Coater: roller squeegee C50, 1 bar contact pressure
Web speed: 200 m / min
Dry coat weight: 8 g / m ²
Drying setting: IR emitter (80%), dry air: 260 ° C (12 m drying distance)

Quick test with spray oil showed a significant reduction in permeability to hydrocarbons.

Example 4

Starch: Hydroxypropylated pea starch with M _w = 20 960 000 g / mol Recipe: (all quantities are based on the total formulation unless otherwise stated) 7.2% by weight Thickness dry 0.2% by weight PVA (98% hydrolyzed, dynamic viscosity of 40 mPas at a 4% solution and 20 ° C) 3.9% by weight Glycerol, corresponds to 35.14 wt .-% glycerol, based on starch and Glycerine, and 88.5% by weight of water 99.8% by weight total

The mixture was boiled in a batch cooker with an anchor stirrer at 95 ° C. for about 45 minutes, resulting in a clear, homogeneous solution with a solids content of 11.3%. This solution had a viscosity of 320 mPas at 37 ° C. To the mixture was added 0.2% by weight of a commercial wetting agent.
Paper: the coated paper of Example 3
Coater: Curtain Coater
Web speed: 100 m / min
Dry application weight: 11.7 g / m ²
Drying setting: IR emitter (60%), dry air: 250 ° C (12 m drying distance)

The migration measurement for MOSH / MOAH gave a barrier effect of 97.4%. After creasing and folding a barrier effect of 96.0% was obtained.

Example 5

Starch: Hydroxypropylated pea starch with M _w = 170 000 g / mol Recipe: (all quantities are based on the total formulation unless otherwise stated) 29.6% by weight Strength 10.8% by weight Glycerol, corresponding to 26.8 wt .-% glycerol, based on starch and Glycerine, and 59.6% by weight of water 100% by weight total

The mixture was boiled in a batch cooker with an anchor stirrer at 95 ° C. for about 45 minutes, resulting in a clear, homogeneous solution with a solids content of 40.4%. This solution had a viscosity of 1080 mPas at 43 ° C.
Paper: Cardboard box with 250 g / m ²
Coater: roller blade (20 mm smooth, contact pressure 0.8 bar)
Web speed: 250 m / min
Dry coating weight: 12.8 g / m ²
Drying setting: IR emitter (60%), dry air: 150 ° C (12 m drying distance)

• Streichaggregat: Curtain Coater
• Bahngeschwindigkeit: 200 m/min
• Auftragsgewicht trocken: 8,6 g/m²
• Trocknungseinstellung: IR-Strahler (30%), Trockenluft: 160°C (8 m Trockenstrecke)

A second coating was applied to the resulting coating with the same starch solution (with addition of 0.2% wetting agent):

• Coater: Curtain Coater
• Web speed: 200 m / min
• Dry coat weight: 8.6 g / m ²
• Drying setting: IR emitter (30%), dry air: 160 ° C (8 m drying distance)

Migration measurements for MOSH / MOAH revealed a barrier effect of almost 30%. SEM images of the coating showed numerous cracks a few microns wide.

LIST OF REFERENCE SIGNS

1

Rohpapierrolle

1'

coated paper roll

2

base paper

2 '

Paper web (coated)

3

guide rolls

4

coater

5

applicator roll

6

String swamp

7

doctor

8th

desiccation

9

Heissluftrockung

10

paper web

11

Application Aggregate / Blade Coater

12

roll doctor

13

sprayer

14

steam blow

15

IR drying

Claims (21)

1. An aqueous coating compound, comprising

   - at least one starch,

   - 0-70% by weight of at least one plasticizer, wherein the plasticizer portion is based on starch plus plasticizer,

   - 0-50% by weight of at least one polymeric additive, wherein the portion of the polymeric additive(s) is based on starch plus polymeric additive,

   - 0-5% by weight of an additive or of an additive mixture, based on the dry mixture, and

   - water, characterized in that

   the starch of the coating compound is present in dissolved form and has a weight average of the molecular weight distribution M_w in g/mol in the range of 0.8 million to 50 million, preferably in the range of 0.8 million to 20 million, and the lower limit as well as the upper limit for the portion of the starch in the coating compound in % by weight, based on starch and plasticizer and water, is provided in dependence on the molecular weight M_w of the starch by: M_w million g/mol 0.8 1 1.5 2 2.3 2.5 2.8 3 6 7 8 9 10 12 15 20 lower limit 14.4 14.1 13.3 12.6 12.2 11.9 11.5 11.1 6.7 5.2 3.7 2.5 2.4 2.2 2.1 1.7 upper limit 40.6 40.3 39.6 38.8 38.5 38.1 37.7 37.4 32.9 31.4 30.0 28.5 27.0 24.0 19.6 12.2 wherein the lower and upper limits for the portion of the starch comprising a weight average of the molecular weight distribution M_w, which lie between the values or outside of the values of the above Table, are obtained by means of linear interpolation or by means of linear extrapolation.
2. The coating compound according to claim 1, wherein the starch comprises tapioca starch, pea starch, potato starch or any mixture thereof, in particular substituted tapioca starch, substituted pea starch, substituted potato starch or any mixture thereof.
3. The coating compound according to claim 1 or 2, wherein the amylose content of the 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.
4. The coating compound according to any one of claims 1 to 3, wherein the plasticizer content is at least 5% by weight, preferably at least 10% by weight, more preferably at least 15% by weight.
5. The coating compound according to any one of claims 1 to 4, wherein the coating compound comprises at least 2, preferably at least 3 plasticizers, wherein at least 5%, preferably at least 10%, most preferably at least 15% of the individual plasticizers are represented in the combination.
6. The coating compound according to any one of claims 1 to 5, wherein the coating compound in % by weight comprises maximally 30% by weight, preferably maximally 20% by weight, of one or a plurality of polymeric additives.
7. The coating compound according to any one of claims 1 to 6, wherein the polymeric additive comprises xanthan and/or polyvinyl alcohol, preferably comprising a portion of 0.01 to less than 2.5% by weight of xanthan and/or 1 to 30% by weight, preferably 1 to 10% by weight of polyvinyl alcohol.
8. The coating compound according to any one of claims 1 to 7, wherein the at least one starch is selected from the group consisting of tapioca starch, pea starch and potato starch, and the starch is a hydroxypropylated starch comprising a molecular weight in million g/mol of 1 to 20, preferably of 2.5 to 10, wherein the plasticizer content in % by weight, based on starch and plasticizer, is in the range of 0-45%, preferably in the range of 15 to 37, and the starch content in % by weight, based on starch and water and plasticizer, is in the range of 14 to 35%, and optionally a portion of polyvinyl alcohol in % by weight, based on starch and polyvinyl alcohol, is present in the range of 1 to 30, preferably 1 to 20, more preferably 1 to 10.
9. A use of a starch-based coating compound for sealing the surface of packaging materials to prevent the migration of lipophilic contaminants from the packaging material into the packaged good, wherein the coating compound comprises

   - at least one starch comprising a weight average of the molecular weight distribution M_w in the range of 0.8 million to 50 million g/mol, preferably in the range of 0.8 million to 20 million g/mol,

   - 0-70% by weight of at least one plasticizer, wherein the plasticizer portion is based on starch plus plasticizer,

   - 0-50% by weight of at least one polymeric additive, wherein the portion of the polymeric additive(s) is based on starch plus polymeric additive,

   - 0-5% by weight of an additive or of an additive mixture, based on the dry mixture, and

   - water.
10. The use according to claim 9, wherein a coating compound according to any one of claims 1 to 8 is used.
11. The use according to claim 9 or 10, wherein the barrier layer obtained from the coating compound has a surface weight in g/m² in the range of 3 to 80 g/m².
12. The use according to any one of claims 9 to 11, wherein the surface sealing takes place by applying two successive coats, and the application weight per coat is in the range of 4 to 17 g/m².
13. A multi-layer packaging material, comprising
    a planar substrate selected from the group consisting of paper, pasteboard and cardboard as carrier layer, and
    at least one starch-based barrier layer, which is applied to the planar substrate, wherein the barrier layer comprises

    - at least one starch comprising a weight average of the molecular weight distribution M_w in the range of 0.8 million to 50 million g/mol, preferably in the range of 0.8 million to 20 million g/mol,

    - 0-70% by weight of at least one plasticizer, wherein the plasticizer portion is based on starch plus plasticizer,

    - 0-50% by weight of at least one polymeric additive, wherein the portion of the polymeric additive(s) is based on starch plus polymeric additive,

    - 0-5% by weight of an additive or of an additive mixture, based on the dry mixture, and, optionally, water bound in the barrier layer.
14. The packaging material according to claim 13, wherein the barrier layer is obtained from a coating compound according to any one of claims 1 to 8.
15. The packaging material according to claim 13 or 14, wherein the barrier layer is applied to an outer surface of the planar substrate, which corresponds to the rear side of the packaging material and thus to the inside of a packaging, which is to be created.
16. The packaging material according to any one of claims 13 to 15, wherein the planar substrate additionally comprises a precoat, preferably a mineral precoat, which is arranged between the substrate surface and the barrier layer.
17. A packaging comprising the multi-layer packaging material according to any one of claims 13 to 16 and optionally further layers, wherein the barrier layer forms the inside of the packaging.
18. A method for producing a multi-layer packaging material according to any one of claims 13 to 16, comprising the steps

    a) providing a planar substrate, which is selected from the group consisting of paper, pasteboard and cardboard and which can optionally have a precoat,

    b) providing a coating compound according to any one of claims 1 to 8,

    c) applying the coating compound of step b) to at least one side of the planar substrate and forming a layer on the planar substrate, and

    d) increasing the temperature for drying and solidifying the applied coating compound, which has been shaped to form a film.
19. The method according to claim 18, wherein the coating compound in step c) is applied by means of curtain coating.
20. The method according to claim 18 or 19, wherein the method prior to step c) additionally comprises the application of a precoat, preferably a mineral precoat.
21. A packaging material, which can be obtained according to the method according to any one of claims 18 to 20.

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