EP3253918B1 - Light packaging paper for food having improved resistance to fats - Google Patents

Description

FIELD OF THE INVENTION

The invention relates to a paper for packaging food. In particular, it relates to a paper which, despite its low basis weight, by combining special paper properties with a coating of nanoparticles of a biopolymer has sufficient resistance to the penetration of fats and oils and yet is readily recyclable and toxicologically safe.

BACKGROUND AND PRIOR ART

Food packaging paper has many different and sometimes contradictory requirements. A first function of the packaging paper is that it protects the packaged food from environmental influences. This requires at least some mechanical strength and chemical resistance to typical environmental influences. A second function is that the wrapping paper should also protect the environment from the effects of the packaged food with which it may come into contact. Above all, this requires sufficient resistance to the penetration of fats, oils and water through the wrapping paper. In addition, the packaging paper for food should have a defined resistance to the penetration of water vapor, to prevent the food from drying out too quickly.

Since packaging paper for food is very often used only once, it makes sense for ecological reasons if the packaging paper can be recycled as easily as possible or, if it is not disposed of properly, at least biodegradable.

For the same reason, it is also desirable that the packaging paper for food has the lowest possible basis weight, so that little raw materials must be used for production and the amount of waste resulting from the disposal of the packaging paper, is relatively low.

Typically, the requirements of a high or defined resistance to the penetration of fats and oils, as well as the good recyclability or biodegradability in combination with a low basis weight of the packaging paper contradict each other.

A known from the prior art method for the production of packaging papers, which achieve a very good resistance to the penetration of fats, oils and water or water vapor, is to coat a base paper on one side with polyethylene, for example in an extrusion process. Because of this coating, such a paper can not be recycled or only with great effort. Therefore, this method satisfies the requirement of reusability or biodegradability only insufficiently.

Another method known in the art for producing packaging papers which achieve very good resistance to the penetration of fats, oils and water is to coat the paper with certain fluorochemical substances. In particular, polyfluorinated organic compounds, and especially fluorotelene alcohols, CF ₃ (CF ₂ ) _n (CH 2) _m OH with n = 1.2,..., In particular with n = 5 or n = 7, and m = 0.1, 2, ..., 10, in particular with m = 0.1 or 2, have proven themselves for this application. The use of these substances may lead to contamination with perfluorooctanoic acid (PFOA, C ₈ HF ₁₅ O ₂ ), which accumulates in the human body and is regulated by the EU REACH Regulation ( Registration, Evaluation, Authorization of Chemicals ). is classified as toxic for reproduction, carcinogenic and toxic. For this reason alone polyfluorinated organic compounds are not desirable as part of a packaging paper and in particular not as part of a packaging paper for food. In addition, such papers are also hardly recyclable.

Many attempts to coat a packaging paper for food with substances of predominantly biological origin, so that in addition to good recyclability or biodegradability even a high resistance to the penetration of fats, oils and water is achieved, were not successful, because of the high resistance to Penetration of fats, oils and water, which the coating with polyethylene or the use of polyfluorinated organic compounds offers, could not be achieved, in particular not for packaging paper with a low basis weight.

In other attempts to coat the packaging paper with petroleum-based waxes, it was possible to achieve a high resistance to the penetration of fats, oils and water but the requirement of good recyclability or biodegradability is again insufficiently met. In addition, these based on petroleum products waxes in turn are ecologically disadvantageous.

In WO 2015/180699 describes a paper containing nanoparticles of a biopolymer. These nanoparticles, in particular, increase the dry strength of the paper, so that a higher proportion of recycled fibers can be used, which brings ecological benefits. In addition, the nanoparticles increase the resistance to fats and oils. However, the papers described in this patent application are comparatively heavy, over 60 g / m ² , and substantial amounts of nanoparticles are required, usually at least 6 g / m ² , to achieve sufficient strength. In addition, the use of perfluorooctanoic acid is further described as beneficial, and despite all these measures, no resistance to fats and oils exceeding a kit level of 5 is achieved.

Therefore, there is still a great need in the industry to have a wrapping paper that, with good strength, requires little use of raw materials, completely dispenses with the use of organic fluorine compounds and yet has a high resistance to fats and oils.

SUMMARY OF THE INVENTION

The present invention has for its object to provide a packaging paper for food, which has a low basis weight, provides a sufficiently high resistance to the penetration of fats and oils and can be easily recycled or biodegraded.

This object is achieved by a packaging paper according to claim 1 and by a manufacturing method according to claim 14. Advantageous developments are specified in the dependent claims.

The packaging paper according to the invention has a weight per unit area of from 20 g / m ² to 50 g / m ² , comprises pulp fibers and one or more fillers, the total amount of fillers being between 5% and 20% by weight, based on the weight of the filler Packaging paper is. Furthermore, the wrapping paper comprises a sizing agent contained in such an amount that on both sides a relative water absorption capacity, expressed by the quotient of the Cobb ₆₀ value determined according to ISO 535: 2014 and the basis weight of 0.4 to 0.7 results.

Furthermore, the packaging paper according to the invention has on at least one side a coating which comprises nanoparticles of a starch, the packaging paper containing between 1 g / m ² and 6 g / m ^{2 of} the said nanoparticles, and the packaging paper contains no compounds of the structure CF ₃ (CF ₂ ) _n (CH ₂ ) _m X, where n = 5 or n = 7 and m = 0,1 or 2 and X is a hydroxy group (X = OH) or a carboxy group (X = COOH), or at most a proportion of such compounds in the total weight of the packaging paper, which does not exceed 0.1 ‰, and it has a resistance to fats and oils of 6 to 12, described by the kit level according to TAPPI T559 cm-12, if in this test at least one side coated with said nanoparticles is exposed to the test liquids. In preferred embodiments, however, this resistance to fats and oils is achieved on both sides.

In the prior art, it is believed that the water absorption capacity of a packaging paper should be low in order to achieve a sufficient barrier effect. The packaging paper should therefore be water repellent. This ensures on the one hand that water can not penetrate quickly through the packaging paper and on the other hand ensures that water-based coating solutions remain on the surface of the packaging paper.

However, the inventors have surprisingly found that the water absorption capacity should not be as small as possible, but that it is for the overall function of the paper in combination with said nanoparticles of considerable advantage, if it is within a certain narrow range of values. The inventors have found that in this narrow range of values, it is possible to optimally distribute a water-based coating material between the surface and the volume of the packaging paper and achieve high barrier effects despite the low basis weight, so that less coating material is required.

Furthermore, the inventors have found that this does not depend on the absolute water absorption capacity, as measured, for example, according to ISO 535: 2014 and expressed as Cobb ₆₀ value in g / m ² , but rather that the water absorption capacity in With respect to the basis weight of the packaging paper is suitably selected. For this purpose, the relative water absorption capacity is defined as a dimensionless ratio from the Cobb ₆₀ value according to ISO 535: 2014 and the basis weight according to ISO 536: 2012. For example, if the Cobb ₆₀ value is 15 g / m ² and the basis weight is 35 g / m ² , then the relative water absorption capacity is 15/35 ≈ 0.428. The invention relates to water-suspended nanoparticles of a starch as coating material and the experiments show that largely independent of the basis weight With a relative water absorption capacity between 0.4 and 0.7, preferably between 0.4 and 0.6, an optimal distribution of nanoparticles of a starch in the packaging paper can be achieved, so that the finished packaging paper, if it contains the nanoparticles of a starch in an amount containing only 1 g / m ² to 6 g / m ² , already reached Kit Level after TAPPI T559 cm-12 of at least 6. This represents a first significant advantage of the invention. In addition, can be completely dispensed with the use of unwanted organic fluorine compounds, which are commonly used as a barrier against fats and oils, which is another advantage of the invention, especially in terms of environmental aspects.

It is also an essential aspect of the invention that the relative water absorption capacity of both sides of the paper in the above-mentioned range is from 0.4 to 0.7, and preferably from 0.4 to 0.6. This is contrary to the expectations of the prior art because the absolute and relative water absorption capacity of the coated side of a paper is generally smaller than that of the uncoated side, while it is important for the invention that the water absorption capacity be independent of any coating in the stated range lies.

The packaging paper according to the invention has a basis weight between 20 g / m ² and 50 g / m ² . In general, the basis weight will be as low as possible to save on raw materials, but then the barrier effect against fats and oils will be reduced, so that a preferred range for the weight per unit area is between 25 g / m ² and 40 g / m ² . The basis weight of a paper can be measured according to ISO 536: 2012.

The packaging paper according to the invention comprises pulp fibers. In principle, all known from the prior art pulp fibers come into question, with which the usually required technical properties, such as sufficient tensile strength, can be achieved. In the context of the invention, it has proved to be advantageous if the pulp fibers are sulphate pulp fibers and comprise 25% by weight to 75% by weight of long fibers and 25% by weight to 75% by weight of short fibers, the percentages being based on Refer to mass of pulp fibers. Long fiber sulphate pulp can be obtained, for example, from spruce or pine, while the short fiber pulp can be obtained, for example, from birch, beech or eucalyptus. The use of pulp fibers from other plants, such as flax, hemp, sisal, abacá, ramie, jute, kenaf or esparto grass is also possible and can for achieving a particularly high tensile strength (flax, hemp, sisal, abaca) or a high paper volume (esparto grass ) make sense.

Also fibers of regenerated cellulose, such as modal fibers or lyocell fibers, can be used, but worsen the biodegradability. Fibers made of thermoplastics such as polyethylene or polypropylene can also be used, especially if a heat sealability is required. Of course, however, these fibers also deteriorate biodegradability.

In general, the pulp fibers will be bleached because the packaging paper is then white and often printed. Alternatively, the pulp fibers, or at least a portion thereof, may be unbleached. The wrapping paper will then have a light brown to dark brown color. The use of unbleached pulp fibers can be beneficial if environmental aspects of the packaging paper are of particular importance.

Less preferred are recycled fibers, which are recovered primarily from waste paper because such fibers are often contaminated by substances that are undesirable in food packaging. These include, for example, mineral oil-based saturated hydrocarbons (MOSH) and mineral oil-based aromatic hydrocarbons (MOAH). In a preferred embodiment of the packaging paper, therefore, it contains no or almost no recycled fibers, in particular not those from waste paper. In a very particularly preferred embodiment, the above-mentioned pulp fibers are not recycled, ie completely, or at least 95 wt .-% virgin pulp .

The packaging paper according to the invention comprises fillers. The proportion of fillers in the packaging paper is rather low and is between 5 wt .-% and 20 wt .-% based on the mass of the finished packaging paper. In the production of paper in general, but especially of packaging paper, the skilled person is anxious to choose the filler content as high as possible, because it achieves a higher whiteness, higher opacity and lower costs for the packaging paper. At present, the trend in papermaking is towards increasingly higher filler contents, which may well be 40% by weight or higher. However, the inventors have found that for the purposes of the invention, a comparatively low filler content is of crucial importance. The reason for this is that a high filler content gives the paper a porous structure, which degrades the barrier effect. For this reason, the filler content is in each case between 5 wt .-% and 20 wt .-%, but preferably between 5 wt .-% and 15 wt .-%.

As fillers different fillers can be used. These include, for example, especially carbonates, such as precipitated or geologically degraded calcium carbonate or magnesium carbonate; Metal oxides, such as titanium dioxide or magnesium oxide; metal hydroxides, such as magnesium hydroxide or aluminum hydroxide; and silicates such as kaolin and talc. The use of mixtures of these fillers is compatible with the invention.

For example, titanium dioxide can be used as a single filler or in a blend to increase opacity and whiteness. Because titanium dioxide is particularly effective in this regard, with equal whiteness and opacity, the overall filler content, and thus the basis weight, can be reduced and a low porosity structure advantageous for the purposes of the invention can be provided.

Due to the high price of titanium dioxide, it is also possible to replace part of the titanium dioxide with other fillers, so-called extenders , which, in combination with titanium dioxide, enhance its action. For a mass unit of titanium dioxide that is to be replaced by an extender , however, several mass units of the extender must be used. Examples of suitable extenders are calcined kaolin, aluminum hydroxide (Al (OH) ₃ ) or precipitated amorphous silicates.

For example, kaolin or talc may also be used as the sole filler or in a mixture to increase the smoothness of the packaging paper and affect the porous structure. As a result, the printability can be improved and a limited barrier effect can be achieved.

For the barrier effect of the packaging paper according to the invention, it is essential that nanoparticles of one starch are applied to the packaging paper such that the finished packaging paper contains between 1 g / m ² and 6 g / m ^{2 of} the nanoparticles. This amount is sufficient to achieve a good resistance to fats and oils, a so-called kit level of 6 to 12, measured according to TAPPI T559 cm-12. The amount of nanoparticles of a starch in the packaging paper is preferably between 1.5 g / m ² and 5.5 g / m ² and very particularly preferably between 1.5 g / m ² and 5 g / m ² .

The preparation of nanoparticles of a starch suitable for the invention is exemplary in WO 2008/022127 . WO 2010/065750 and WO 2011/084692 described. In the cited patents, however, the nanoparticles are mainly used to improve the printability. The starches suitable for the preparation of the nanoparticles include, for example, potato starch, corn starch, wheat starch, rice starch or tapioca starch. In general, starches with a high amylopectin content, in particular those with a content of at least 90%, preferably at least 95%, of amylopectin are generally suitable.

The average size of the nanoparticles is between 1 nm and 500 nm, preferably between 10 nm and 400 nm and particularly preferably between 40 nm and 200 nm.

In addition to the components essential for the packaging paper according to the invention, the packaging paper may contain further components.

These include sizing agents, such as alkyl ketene dimers (AKD), alkenylsuccinic anhydride (ASA) or rosin glues. These sizing agents render the packaging paper hydrophobic and are necessary to adjust the relative water absorption capacity of the packaging paper to the value required by the invention. The amount of sizing agent required for this purpose can be determined by the skilled person on the basis of his experience or determined by experiments. The sizing agent may be added in bulk or applied to the surface during the manufacture of the packaging paper. When added in bulk, the sizing agent is already contained in the headbox in the suspension. This type of sizing is also referred to as "bulk sized" in the present disclosure and is preferred. Additionally or alternatively, however, the sizing agent can also be applied to the surface, for example in a size press of a paper machine.

If it is desired that the wrapping paper be particularly water-resistant, it may also contain wet strength agent, which significantly increases the strength of the wrapping paper when wet. A well-suited wet strength agent is polyaminopolyamide-epichlorohydrin (PAE). As an indication, PAE can be used in an amount of 2 kg per ton of packaging paper.

Another optional component of the packaging paper may be starch, which explicitly does not mean the nanoparticles of a starch. Thickness can be added to the wrapping paper to increase its dry strength. Here, too, the skilled person will be able to choose the required amount based on experience and can take a quantity of 5 kg per ton of wrapping paper as a guide.

In the case where only one side of the packaging paper is coated with one nanoparticle of one thickness, the other side may be coated with ordinary thickness to prevent the packaging paper from bulging as the moisture changes because the two sides of the packaging paper become wet upon moistening stretching differently. For the further processing of the packaging paper, in particular the printing, it is important that the packaging paper does not buckle.

The packaging paper according to the invention may contain, in addition to the fillers, pigments or dyes. For example, yellow, red, brown or black iron oxides or carbon particles can be used to give the paper a color other than white. Pigments can also be understood as meaning metal particles or plastic particles which give the paper a particular color or a special luster. In particular, the use of gold leaf is conceivable for particularly high-quality packaging paper.

Dyes which can preferably be used are those which can be processed in an aqueous composition, but which do not dissolve appreciably from the packaging paper upon contact with food, so that the foodstuff is not contaminated. UV resistance can also play a role in the choice of dye.

The packaging paper according to the invention can also be printed. In many cases, food packaging papers are printed with trademarks, logos, company names, synopsis, or other information. For this purpose, it is possible to use all printing methods known from the prior art and customary for packaging papers for foodstuffs, in particular gravure printing, flexographic printing or digital printing.

The packaging paper can be printed on one, one or both sides. When printing on only one side, preferably one side of the packaging paper is coated with the nanoparticles of one thickness and the other side is printed. The side coated with nanoparticles of a starch side is then preferably facing the food.

Other components of the packaging paper, as they are necessary for example for the production of the paper, the skilled person can choose suitable. These include, for example, retention aids, crosslinking agents, dispersing agents, defoamers or biocides. In general, when using these components, as well as all of the aforementioned components of the packaging paper, the statutory provisions must be taken into account.

In packaging papers for foodstuffs, in particular those which have a high resistance to fats and oils, fluorine compounds are very frequently used in the prior art. These include a class of compounds having the general formula CF ₃ (CF ₂ ) _n (CH ₂ ) _m X, the so-called fluorotelomer alcohols, when X is a hydroxy group (X = OH) or fluorinated or perfluorinated carboxylic acids when X is a carboxy group ( X = COOH). N can assume the values n = 1,2, ... and m the values M = 0,1,2, ..., 10.

Of particular importance are fluorotelene alcohols with n = 5 or n = 7 and m = 0.1 or 2 and X = OH, and the perfluorooctanoic acid with n = 6, m = o and X = COOH.

It is an essential object and a significant advantage of the packaging paper according to the invention that such fluorine compounds are not contained in the packaging paper. In this context, "not containing" means that they are not contained in an amount that significantly contributes to the barrier effect against fats or oils. However, it is conceivable and still compatible with the invention that traces of such fluorine compounds are contained, which have come about through contamination, for example by contact with other non-inventive packaging papers. In any case, the proportion of such fluorine compounds to the total mass of the packaging paper should not exceed 0.1 ‰.

Another property of the packaging paper essential to the invention is its water absorption capacity. The absolute water absorption capacity is determined according to ISO 535: 2014 and given as Cobb ₆₀ value ("Cobb ₆₀ ") in g / m ² . After determining the basis weight of the packaging paper ("FLG") in g / m ² according to ISO 536: 2012, the relative water absorption capacity can be calculated from this by the ratio Cobb ₆₀ / FLG. Since the Cobb ₆₀ value for both sides of the packaging paper can be determined separately, each side of the packaging paper is assigned a relative water absorption capacity. It has been found to be essential for the invention that the relative water absorption capacity of both sides is similar and lies between 0.4 and 0.7, preferably between 0.4 and 0.6. The inventors assume that only in this value range can an optimal distribution of the aqueous coating composition and thus of the nanoparticles in the packaging paper be achieved. This optimum distribution ensures high resistance to greases and oils with comparatively low application rates and low grammage of the packaging paper.

Another essential characteristic of the packaging paper according to the invention is its resistance to the penetration of fats and oils. This property is quantified according to the method described in TAPPI T559 cm-12. 12 different test liquids are applied to the paper, sorted and numbered according to their tendency to penetrate paper from 1 to 12. The liquids are tested in ascending order, and the number of the last liquid that did not penetrate the paper defines the resistance to fats and oils, which is referred to as kit level. The kit level can therefore assume values from 0 to 12. In order to achieve adequate resistance to greases and oils in packaging papers for common foods, the kit level should be at least 6 and not more than 12, preferred is a kit level of 6 to 10, which is already sufficient for the vast majority of all applications and very particularly preferred is a kit level from 6 to 8.

In the TAPPI T559 cm-12 test, the side of the packaging paper coated with nanoparticles of one starch should face the test liquids. If both sides of the packaging paper are coated with nanoparticles of one thickness, the Kit Level must be in the range of 6 to 12 for each of the two sides of the packaging paper. However, the kit levels of the two sides may differ and kit levels in the preferred tighter intervals may therefore appear in only one side of the packaging paper in any combination, while the kit level for the other side may be outside the preferred interval, but in any case between 6 and 12 must be.

The kit level can be primarily influenced by the amount of nanoparticles of one starch in the packaging paper, with a higher order amount also leading to a higher kit level. Further measures which the person skilled in the art can take to adjust the kit level for the purposes of this invention include the choice of the type and amount of sizing agent, the milling of the pulp fibers and paper-compacting measures such as calendering. For all these measures, however, the specifications regarding the relative water absorption capacity must be observed.

Another aspect of the invention, which is optional but may provide further advantages in terms of raw material usage and barrier action against fats and oils, is the choice of a particular low air permeability. The inclusion of the coating composition in the paper structure is also determined by the porous structure of the packaging paper. One method of evaluating the porous structure of the packaging paper is Gurley's air permeability, which can be measured according to ISO 5636-5: 2013. In this case, a pressure difference between the two sides of the packaging paper is applied and measured how long it takes for a certain volume of air, typically 100 cm ³ , has flowed through a defined area of the paper. The air permeability according to Gurley is given in seconds. A high Gurley value in seconds means low air permeability and vice versa, a low value in seconds means high air permeability. The air permeability can be influenced in particular by the grinding of the pulp in papermaking and by the choice of the type, amount and average particle size of the filler or of the filler mixture and is therefore a parameter which the person skilled in the art can set in certain areas.

For the purposes of the invention, Gurley's air permeability may be used to denote the barrier effect provided by the nanoparticles of starch and the paper structure to adjust even better. The air permeability according to Gurley will preferably be between 1000 s and 10000 s, more preferably between 2000 s and 8000 s. This is a significantly lower air permeability than known from the prior art packaging papers for food, which usually have a Lufbellässigkeit according to Gurley from 50 s to 500 s. In general, Gurley's air permeability is not significantly dependent on the direction of gas flow through the paper, so the specified limits apply regardless of the direction of flow. In fact, experiments by the inventors have shown that Gurley's air permeability has an independent meaning for the purposes of increasing resistance to oils and fats in the sense that, in all other essential parameters considered here, identical papers have less air permeability Gurley offers better resistance to fats and oils. In preferred packaging papers, care is therefore taken to ensure that the air permeability according to Gurley is at least 1000 s, preferably at least 2000 s.

The thickness of the packaging paper is between 20 .mu.m and 60 .mu.m, preferably between 25 .mu.m and 50 .mu.m. The thickness can be measured according to ISO 534: 2011 on a single layer.

The tensile strength of the packaging paper is generally important for the manufacture and use as packaging paper. The tensile strength is usually different in the machine direction and transverse direction of the paper. In the machine direction, the tensile strength should be between 1 kN / m and 5 kN / m, preferably between 2 kN / m and 4 kN / m. In the transverse direction, the tensile strength is generally lower, which is not a problem because the load is applied in many processing processes, especially in the machine direction. The transverse tensile strength should be between 0.5 kN / m and 4 kN / m, preferably between 1 kN / m and 3 kN / m.

The elongation at break of the packaging paper is also important. A sufficient elongation at break is required in order to be able to partially compensate for differences in speed in the course of the packaging paper in processing machines. The elongation at break is different in the machine direction and transverse direction of the packaging paper and should be between 1% and 3% in the machine direction and between 2% and 6% in the transverse direction.

Tensile strength and elongation at break can be determined according to ISO 1924-2: 2008.

The preparation of the packaging paper according to the invention can be carried out entirely by means of the devices known from the prior art, for example using a Fourdrinier paper machine.

The application of the coating composition can then be carried out using a coating device known from the prior art. This can be, for example, the film or size press in a paper machine, or else a separate application device for coating, such as a blade coater or rod coater. The application of the coating composition can also be done by printing the packaging paper.

The application of the coating composition to the packaging paper takes place at least on one side, preferably on the top side of the packaging paper. However, it is possible for a particularly high resistance to greases and oils to coat both sides of the packaging paper. If both sides of the packaging paper are coated, the applied type and amount of nanoparticles of a starch may differ between the two sides, but in total the applied amount of nanoparticles of a starch for the packaging paper according to the invention as mentioned above must be between 1 g / m ² and 6 g / m ² amount.

The order of the coating composition on the packaging paper should preferably be made on the entire surface of one side of the packaging paper, because areas excluded from the application will not have sufficient resistance to greases and oils. However, it is possible to exclude areas from the order which ensure that they do not come into contact with the packaged food because, for example, they are lost to other components of the packaging. In a particular embodiment of the invention, the coating composition may be applied to the packaging paper on one side in a pattern and on the other side in an approximately complementary pattern such that each point of the packaging paper is coated with the nanoparticles of a starch on at least one side of the packaging paper. The term "approximately" may mean that the two patterns overlap slightly, so that under no circumstances does a partial area of the packaging paper remain on both sides without a coating due to the production tolerances.

The order of the coating composition can also be such that the amount of nanoparticles of a starch changes over the surface of the packaging paper. For example, less or no coating composition could be applied in areas of the packaging paper that are known to have little contact with the food. These areas can have any shape, the compatible with the procurement procedure. As a result, for example, the need for nanoparticles of one thickness can be reduced.

The coating composition preferably comprises at least water and nanoparticles of a starch. The level of nanoparticles of a starch in the coating composition may vary and will depend on the amount of nanoparticles to be applied to the paper as well as the rheological requirements of the application process. Also, the available capacity in the subsequent drying of the packaging paper may play a role in the choice of coating composition. The coating composition contains between 10% and 40% by weight of nanoparticles of a starch, preferably between 20% and 35% by weight, each based on the weight of the coating composition.

For the requirements of the nanoparticles of a starch, their size and their manufacturing processes, the information given above applies.

The coating composition may contain other components. These include, for example, the aforementioned components of the packaging paper, such as fillers, pigments, dyes and sizing agents, but also crosslinking agents.

In a preferred embodiment of the invention, the coating composition may contain talc or kaolin or a mixture thereof, wherein the amount of talc and kaolin in total may be between 30% and 65% by weight based on the weight of the nanoparticles. These fillers can increase the resistance to fats and oils because of the shape of their particles.

The preparation of the coating composition is preferably carried out according to the instructions of the manufacturer of the nanoparticles of a starch.

After application of the coating composition, the packaging paper is preferably dried. For the drying process known from the prior art can be used, for example by infrared radiation, hot air or contact with a heated drying cylinder, microwaves or combinations thereof.

Other processing such as printing, cutting, embossing or folding may be carried out according to the requirements of the end use of the packaging paper.

The following exemplary embodiments are intended to demonstrate the advantages of the packaging paper according to the invention.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

shows a Table 1, are summarized in the properties of packaging papers according to the invention and comparative examples not according to the invention.

Fig. 2

shows a Table 2, in the other properties of the packaging papers of Fig. 1 are summarized.

DESCRIPTION OF SOME EMBODIMENTS AND NOT ACCOMPANYING EMBODIMENTS

From blends of long fiber and short fiber pulp (Table 1, "Long fiber" and "Short fiber" columns) and various fillers (Table 1, column "Fillers") several papers were reported in Tables 1 and 2 of Fig. 1 or 2 denoted by AL, wherein in Tables 1 and 2, the same letters in the column "Paper" denote the same paper. The papers A, K and L are non-inventive papers which serve as comparative examples, while the papers BJ are packaging papers according to the invention.

The percentages of long fiber pulp and short fiber pulp relate to the weight of the fiber composition, the percentages of the fillers are based on the basis weight of the packaging paper.

The papers were sized in the mass with alkyl ketene dimer (AKD) depending on the requirements of the Cobb ₆₀ value. On the papers BE, G, H, K and L, an aqueous composition containing 33% by weight nanoparticles of a corn starch was applied to the top in the film press of the paper machine. For paper A, no coating was applied, for paper F it was applied to both sides and for paper J to the wire side. The amount of nanoparticles of the starch is given in Table 1 column "Nanoparticles". Table 1, column "Coating", indicates which side or sides of the paper are coated, where "OS" is the top and "SS" is the screen side of the paper.

In all single-side coated papers, ie, BE and GL, normal strength in a small amount of 0.1 g was additionally / m ² applied to 0.5 g / m ² on the uncoated side in order to prevent a curvature of the wrapping paper. After application of the coating composition The papers were dried, conditioned according to ISO 187 at 23 ° C and 50% relative humidity and then carried out measurements.

The basis weight of each packaging paper was determined according to ISO 536: 2012 and is given in Table 1 in the column "Basis Weight". The weight per unit area is between 25.4 g / m ² and 46.3 g / m ² .

The Cobb ₆₀ value, Table 2, column "Cobb ₆₀ ", the wire side ("SS") and the top ("OS") was measured according to ISO 535: 2014 for papers BL and the quotient of the basis weight of Table 1 Cobb ₆₀ Value and basis weight calculated for each side of the paper. It is given in Table 2, column "Relative water absorption capacity".

Gurley air permeability was determined according to ISO 5636-5: 2013, with the air always flowing from the top to the screen side. The measurement results are given in Table 2, column "Air permeability (Gurley)".

The resistance to greases and oils was determined several times according to TAPPI T559 cm-12 for the coated side or the coated sides for the papers B-L, respectively. The result is shown in Table 2, column "Kit Level". As a comparison, a measurement was also made on both sides of the uncoated paper A.

Furthermore, the tensile strength and elongation at break were determined according to ISO 1924-2: 2008 in the machine direction and transverse direction, respectively. The results are not detailed, but were always between 1.3 kN / m and 4.6 kN / m for the machine direction tensile strength, while lying between 0.9 kN / m and 2.4 kN / m in the transverse direction , This tensile strength is sufficient for easy further processing in any case.
The machine direction elongation was between 1.3% and 2.6% and between 2.9% and 5.8% in the transverse direction. These values are sufficient for easy further processing.

By means of non-inventive, uncoated paper A with a kit level on each side between 0 and 2, it can be seen that a coating of the paper with the nanoparticles of a starch is in any case required in order to obtain a significant resistance to fats and oils.

The papers according to the invention of the embodiments B to E show for different basis weights of 25.4 g / m ² to 45.9 g / m ² that with a relative water absorption capacity of 0.44 to 0.63 and a quantity of nanoparticles of the strength of 1.7 g / m ² to 5.1 g / m ^2, a sufficient resistance to oils and fats, expressed by the kit level, of 6-8 can be achieved.

The paper of embodiment F according to the invention shows a very high-quality packaging paper with a basis weight of 46.3 g / m ² and titanium dioxide in the filler mixture. This gives the paper a high opacity and whiteness. The paper F is coated on both sides with nanoparticles of the starch and therefore has a very high resistance to oils and fats, expressed by the kit level, from 9 to 11.

A comparison of the papers D and G according to the invention shows that the two papers are very similar in terms of their basis weight with 38.8 g / m ² and 38.5 g / m ² . Otherwise, they do not differ in any significant parameters apart from the air permeability which is for Gurley paper D 6685 s and Gurley paper G 8320 s. Paper D thus has the higher air permeability and resistance to oils and fats expressed by the kit level of 6-7, while the paper G reaches a kit level of 7-8. This shows that a low air permeability and thus a high value in seconds according to Gurley for the resistance to oils and fats, regardless of other properties can be beneficial.

The inventive paper of embodiment H explores the limits of the invention and shows only a resistance to fats and oils with a high relative water absorption capacity of 0.62 (OS) and 0.67 (SS) and a high air permeability of 1224 s according to Gurley. expressed by the kit level, from 5-6. Thus, this packaging paper is just fine for use as packaging paper for foodstuffs.

The paper of embodiment J of the invention demonstrates the invention for an alternative fiber mixture, consisting of 70 wt .-% long-fiber pulp and 30 wt .-% short fiber pulp, each based on the mass of the fiber mixture, and a low filler content of 5 wt .-% based on the mass of the packaging paper. In addition, the coating is applied in contrast to all other embodiments on the screen side. Despite all these modifications, the wrapping paper achieves resistance to fats and oils expressed by the kit level of 6-7. This, in combination with the other embodiments, shows that the relative water absorption capacity and the air permeability are of particular importance separately as well as in combination in order to achieve a high resistance to oils and greases.

The non-inventive papers K and L is a very little sized paper (K) whose relative water absorption capacity of 0.82 to 0.90 is too high to realize the invention and a very strong sized paper (L ), whose relative water absorption capacity of 0.20 to 0.25 is too low to realize the invention. Both papers achieve a kit level of at most 5, despite the fact that at least 4 g / m ^{2 of} the nanoparticles have been applied. These two non-inventive embodiments also show the particular importance of the relative water absorption capacity for the resistance to fats and oils.

Claims (15)

1. Packaging paper for food, with a basis weight from 20 g/m² to 50 g/m², comprising cellulose fibers and one or more filler materials, in which the total amount of filler materials is between 5 % by weight and 20 % by weight with respect to the weight of the packaging paper, wherein the packaging paper

   • comprises a sizing agent, which is contained in such an amount that on both sides a relative water absorption of 0.4 to 0.7 is achieved, wherein the relative water absorbency is defined as the ratio of the Cobb₆₀ value, determined in accordance with ISO 535:2014, to the basis weight,

   • has a coating on at least one side, which comprises nanoparticles of a starch, wherein the coating contains between 1 g/m² and 6 g/m² of said nanoparticles,

   • does not contain any compounds with the structure CF₃(CF₂)_n(CH₂)_mX, wherein n=5 or n=7 and m=0, 1 or 2 and X is a hydroxyl group (X=OH) or a carboxyl group (X=COOH), or the proportion of such compounds with respect to the total mass of the packaging paper is less than 0.1 ‰, and

   • which has a resistance against grease and oil of 6 to 12, described by the Kit Level in accordance with TAPPI T559 cm-12, wherein in the test in accordance with TAPPI T559 cm-12, the at least one side coated with said nanoparticles is exposed to the test liquids.
2. Packaging paper according to claim 1, in which the basis weight is between 25 g/m² and 40 g/m².
3. Packaging paper according to claims 1 or 2, in which the cellulose fibers are sulfate pulp fibers and comprise 25% by weight to 75% by weight long fibers and 25% by weight to 75% by weight short fibers, with respect to the mass of the cellulose fibers.
4. Packaging paper according to claim 3, in which the long fiber pulp is sourced from one or more of the plants spruce, pine, flax, hemp, sisal, abaca, ramie, jute and kenaf and/or the short fiber pulp is sourced from one or more of the tree species birch, beech and/or eucalyptus.
5. Packaging paper according to one of the preceding claims, in which the pulp is bleached, or in which the pulp is unbleached and/or in which said cellulose fibers are completely, but at least to 95% by weight with respect to the pulp mass, formed by virgin fibers.
6. Packaging paper according to one of the preceding claims, in which the total amount of filler materials is between 5% by weight and 15% by weight with respect to the weight of the packaging paper.
7. Packaging paper according to one of the preceding claims, in which the one or more filler materials is selected from the group consisting of carbonates, in particular precipitated or geologically sourced calcium carbonate or magnesium carbonate; metal oxides, in particular titanium dioxide or magnesium oxide; metal hydroxides, in particular magnesium hydroxide or aluminum hydroxide; and silicates, in particular kaolin and talc.
8. Packaging paper according to one of the preceding claims, in which the filler materials comprise a combination of titanium dioxide and an extender, which in combination with titanium dioxide enhances its effect, wherein the extender is preferably formed by calcined kaolin, aluminum hydroxide (Al(OH)₃), a precipitated, amorphous silicate or a combination thereof.
9. Packaging paper according to one of the preceding claims, in which the amount of nanoparticles of a starch in the packaging paper is between 1.5 g/m² and 5.5 g/m², preferably between 1.5 g/m² and 5 g/m², and/or in which the nanoparticles are sourced from one or more of the following starches: potato starch, corn starch, wheat starch, rice starch or tapioca starch.
10. Packaging paper according to one of the preceding claims, in which the mean size of the nanoparticles is between 1 nm and 500 nm, preferably between 10 nm and 400 nm and particularly preferably between 40 nm and 200 nm, and/or in which the sizing agent is preferably formed by an alkyl ketene dimer (AKD), an alkenyl succinic anhydride (ASA) or a resin size.
11. Packaging paper according to one of the preceding claims, which further contains one or more of the following components:

    • a wet strength agent, which is suitable for increasing the wet strength of the packaging paper, in particular polyamine polyamide epichlorhydrin,

    • starch, which is not present in the form of nanoparticles, wherein, in the case in which the packaging paper is coated with the nanoparticles of a starch on only one side, the starch is applied to the other side of the packaging paper,

    • pigments or dyes, in particular yellow, red, brown or black iron oxides or carbon particles, or

    • gold foil, and/or

    which is coated with the nanoparticles of a starch on only one side, and which is printed on the other side, wherein during use, the side coated with nanoparticles of a starch preferably faces the food.
12. Packaging paper according to one of the preceding claims, in which the relative water absorbency of both sides is between 0.4 and 0.6, and/or which has a resistance against grease and oil of 6 to 10, preferably of 6 to 8, described by the Kit Level in accordance with TAPPI T559 cm-12, wherein in the test in accordance with TAPPI T559 cm-12, the at least one side coated with said nanoparticles is exposed to the test liquids and/or wherein the Gurley air permeability is between 1000 s and 10000 s, preferably between 2000 s and 8000 s.
13. Packaging paper according to one of the preceding claims, wherein the thickness is between 20 µm and 60 µm, preferably between 25 µm and 50 µm, and/or wherein the tensile strength in machine direction is between 1 kN/m and 5 kN/m, preferably between 2 kN/m and 4 kN/m and/or wherein the tensile strength in cross direction is between 0.5 kN/m and 4 kN/m, preferably between 1 kN/m and 3 kN/m and/or wherein the elongation at break in machine direction is between 1% and 3% and between 2% and 6% in cross direction.
14. Process for the manufacture of a packaging paper according to one of the preceding claims, in which the nanoparticles of a starch are applied as component of a coating composition

    • during the manufacture of the packaging paper in a paper machine, in particular in a film press or size press, or

    • onto a preliminary paper in an application device which is separate from the paper machine,

    wherein the coating composition contains at least water and said nanoparticles, and wherein the coating composition contains between 10% by weight and 40% by weight, preferably between 20% by weight and 35% by weight of said nanoparticles, each with respect to the weight of the coating composition.
15. Process according to claim 14, in which the coating composition further contains talc and/or kaolin, of which the total mass corresponds to 30% to 65% by weight of the mass of said nanoparticles, and/or in which the coating composition is applied to the packaging paper on one side in the form of a pattern, and in which preferably, the coating composition is applied to the other side in an at least approximately complementary pattern, so that every section of the packaging paper is coated with the nanoparticles of a starch on at least one side of the packaging paper.

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