Method for producing a paper having improved imperviousness to grease and oil, paper produced, and use thereof

Abstract

The present invention relates to a method for producing a paper having improved imperviousness to grease and oil, comprising the steps of: (a) providing a paper having a first and a second surface; (b) applying an aqueous solution onto the first surface, wherein the aqueous solution comprises approximately 10 to 50 wt.% collagen hydrolysate and at least approximately 0.1 wt.% of a plasticiser; (c) drying the aqueous solution in order to obtain a coating comprising collagen hydrolysate and plasticiser on the first surface.

Description

[0001] Process for producing a paper with improved grease and oil resistance, produced paper and its use

[0002] The present invention relates to a process for producing a paper with improved grease and oil resistance.

[0003] The invention further relates to a paper with improved grease and oil resistance, which is produced according to this method, and to the use of the paper as packaging material.

[0004] The use of paper as a packaging material, or as a component of packaging materials, has long been known. In this respect, paper has the fundamental advantage over most other packaging materials in that it is biodegradable and easily recyclable. On the other hand, however, paper has the disadvantage that it is very easily penetrated or permeated by hydrophobic substances such as oils and fats, which severely limits or even eliminates the usability of pure paper packaging for corresponding products, especially for fatty or oily foods.

[0005] To avoid this problem, packaging made from various composite materials is known in which the paper is provided with a barrier layer for fats or oils. These barrier layers are usually based on synthetic polymers, particularly fluorine-containing polymers or siloxane compounds, which generally exhibit poor or no biodegradability. The use of such packaging is therefore extremely disadvantageous in terms of environmental pollution, particularly marine pollution, and recycling is often only possible to a limited extent or with increased effort. The invention is therefore based on the object of proposing a process for producing a paper with improved grease and oil resistance, wherein the paper produced is biodegradable.

[0006] This object is achieved according to the invention by a method which comprises the steps:

[0007] (a) providing a paper having a first and a second surface;

[0008] (b) applying an aqueous solution to the first surface, the aqueous solution comprising about 10 to about 50 wt.% collagen hydrolysate and at least about 0.1 wt.% of a plasticizer;

[0009] (c) drying the aqueous solution to obtain a coating comprising collagen hydrolysate and plasticizer on the first surface.

[0010] Surprisingly, it has been shown that coating a paper surface with collagen hydrolysate results in a relatively high oil and grease resistance of the paper.

[0011] Collagen hydrolysate is a hydrolysis product of the animal structural protein collagen. Collagen hydrolysate is completely biodegradable and harmless to health, so that paper produced using the process according to the invention not only fully meets the biodegradability requirement but is also suitable as a packaging material, especially for food.

[0012] Furthermore, it was found that the papers produced according to the invention also have a very high gloss and excellent printability, depending on the embodiment.

[0013] The improved grease and oil resistance of the paper produced according to the invention means improved resistance to hydrophobic substances in general. These include, in particular, vegetable and animal fats and oils, i.e., triglycerides, which are solid (fats) or liquid (oils) at room temperature. This is particularly relevant for use as food packaging. However, the resistance is also improved against hydrophobic substances based on synthetic or mineral oil, which is relevant, for example, for use as packaging material for cosmetics.

[0014] The grease and oil resistance of paper can be quantified in particular with the so-called KIT test, according to the test protocol T 559 cm-12 of the TAPPI (Technical Association of the Pulp and Paper Industry).

[0015] When using paper as a packaging material, it is necessary that the appropriate grease and oil resistance is maintained even after mechanical stress on the paper associated with the packaging process (i.e., bending, folding, and / or creasing the paper). Interestingly, the inventors discovered that even the addition of a relatively small amount of plasticizer to the aqueous solution of collagen hydrolysate applied in step (b) of the process according to the invention results in the grease and oil resistance of the produced paper being largely maintained even after such mechanical stress.It is assumed that, after drying the aqueous solution in step (c) of the process according to the invention, the collagen hydrolysate forms a substantially continuous coating on the surface of the paper, with the brittleness of this coating being reduced by the addition of plasticizer. Thus, cracks in the coating under mechanical stress, which lead to a reduction in grease and oil resistance, are prevented or reduced.

[0016] Suitable plasticizers are known in the art and include, in particular, those plasticizers frequently used in combination with gelatin, e.g., in the production of soft capsules. The plasticizer is preferably selected from sugar alcohols, in particular from glycerol, sorbitol, or mixtures thereof.

[0017] The paper produced in step (a) of the process according to the invention is typically a paper based on cellulose, mechanical pulp, and / or recycled paper. These technical raw materials for paper production are all based on cellulose, with cellulose consisting predominantly of cellulose and mechanical pulp additionally containing a proportion of lignin.

[0018] The paper used in the present invention is fundamentally unlimited in terms of basis weight. Thus, the invention explicitly encompasses thicker materials such as cardboard and paperboard, although for the sake of simplicity, only the term "paper" is used here, regardless of the basis weight. Typically, the paper has a basis weight of approximately 60 to approximately 200 g / m². 2 preferably from approx. 80 to approx. 150 g / m 2 , more preferably from approx. 90 to approx. 120 g / m 2This corresponds to the basis weight of papers that are usually used as packaging material (but also, for example, as writing paper).

[0019] According to the invention, the aqueous solution applied to the first surface of the paper comprises approximately 10 to approximately 50 wt.% collagen hydrolysate. It has been shown that a collagen hydrolysate concentration in this range results in an aqueous solution that not only has a viscosity favorable for application, but that the viscosity of the solution is then also relatively independent of the shear forces. In contrast, aqueous solutions with a higher concentration of collagen hydrolysate exhibit pseudoplastic behavior, i.e., a decreasing viscosity with increasing shear forces. Lower concentrations of collagen hydrolysate, in turn, have the disadvantage that larger application quantities of the solution and longer drying times are required.

[0020] The aqueous solution preferably comprises approximately 20 to approximately 45 wt.% collagen hydrolysate, more preferably approximately 30 to approximately 40 wt.% collagen hydrolysate. This concentration has been shown to be particularly advantageous for applying the aqueous solution to the surface of the paper.

[0021] The collagen hydrolysate used in the process according to the invention is typically produced by chemical or enzymatic hydrolysis of collagen-containing animal starting materials. The animal starting material is preferably selected from the skin or bones of vertebrates, in particular cattle, pigs, or sheep. Particularly preferred is the production of the collagen hydrolysate by enzymatic hydrolysis of gelatin, in particular using one or more endopeptidases.

[0022] Collagen hydrolysate typically exists as a mixture of peptides with a specific molecular weight distribution, whereby this molecular weight distribution can be influenced by the respective hydrolysis conditions (in particular by the enzymes used, hydrolysis time, temperature, and pH). The collagen hydrolysate typically has an average molecular weight of approximately 500 to approximately 25,000 Da, preferably approximately 1,000 to approximately 12,000 Da, and more preferably approximately 2,000 to approximately 6,000 Da. These figures always refer to the weight-average molecular weight, which is determined by gel permeation chromatography.

[0023] A collagen hydrolysate with an average molecular weight of approximately 3,000 Da can be used with particular advantage within the scope of the invention. Such a collagen hydrolysate is marketed, for example, by the applicant, GELITA AG, in the form of a 50% solution under the name NOVOTEC® CP800.

[0024] As an alternative to enzymatic hydrolysis, the collagen hydrolysate can be produced by recombinant gene expression within the scope of the invention. By using natural collagen sequences, particularly from cattle or pigs, and expressing them in genetically modified cells (e.g., yeast, bacteria, or plant cells, especially tobacco), products can be produced that are essentially identical to the hydrolysis products of the corresponding collagen-containing raw materials. This makes it possible, among other things, to obtain a narrower or precisely specified molecular weight distribution.

[0025] In addition to the collagen hydrolysate, the aqueous solution also contains plasticizers, such as glycerin. As described above, a small proportion of approximately 0.1% by weight of plasticizer is often sufficient to reduce the brittleness of the coating formed and significantly improve the grease and oil resistance of the produced paper, even after mechanical stress. The aqueous solution can also contain higher proportions of plasticizer, such as up to approximately 5% by weight, although the properties of the produced paper are no longer significantly improved by significantly higher proportions. The aqueous solution preferably comprises approximately 0.5 to approximately 1.5% by weight of plasticizer, more preferably approximately 0.8 to approximately 1.2% by weight.

[0026] Even though collagen hydrolysate already has good water solubility and processability at room temperature, it is preferred within the scope of the invention if the aqueous solution is applied at a solution temperature of approximately 40 to approximately 60 °C, more preferably approximately 45 to approximately 55 °C. It has been shown that the aqueous solution in this temperature range, especially with the above-mentioned preferred concentrations of collagen hydrolysate, has a viscosity favorable for application to the paper surface.

[0027] The aqueous solution can be applied in step (b) of the process according to the invention using various application methods known from the prior art, such as spraying, rolling, or doctoring. Devices for applying the aqueous solution using a doctor blade or blade are known in the paper industry, for example, as so-called coating units.

[0028] Further preferred application methods, which are also known from the paper industry, include applying the aqueous solution by means of a film press, a size press or contactless by means of curtain coating (curtain coating experience).

[0029] The proportion of collagen hydrolysate and plasticizer (and optionally other additives) as well as the application quantity of the aqueous solution determines the basis weight of the coating obtained after drying. The application quantity is advantageously selected so that, after drying, the basis weight of the coating comprising collagen hydrolysate and plasticizer is approximately 8 to approximately 20 g / m 2 results, preferably from about 9 to about 15 g / m 2 , more preferably from about 10 to about 12 g / m 2 When applying the aqueous solution using a doctor blade, a corresponding application quantity can be achieved, for example, with a doctor blade spacing of approximately 15 to approximately 30 pm.

[0030] The drying of the aqueous solution in step (c) of the process according to the invention is advantageously carried out at a temperature of approximately 30 to approximately 70°C, preferably approximately 40 to approximately 60°C, more preferably approximately 45 to approximately 55°C. Therefore, it is advantageous if the aqueous solution already has a corresponding or similar temperature upon application, as described above.

[0031] In addition to the collagen hydrolysate and the plasticizer, the aqueous solution can optionally contain other additives to further improve the properties of the produced paper or to adapt it to specific requirements. Among other things, this can influence the printability, ink fixation, and wet strength of the paper. Such additives can be selected, in particular, from pigments dispersed in the aqueous solution, binders such as starch, polyvinyl alcohol, or gelatin, crosslinking agents such as tannins, and / or other additives such as sizing agents.

[0032] According to an advantageous embodiment of the invention, the aqueous solution comprises dispersed pigments, preferably selected from carbonates, silicates, bentonites, or kaolin. Platelet-shaped embodiments of such pigments are particularly suitable. These pigments can, under certain circumstances, further improve the grease and oil-proofing of the paper by further impeding the transport of the fat- or oil-containing substance through the barrier layer.

[0033] In a further preferred embodiment, the aqueous solution comprises additional binders, such as modified starches, polyvinyl alcohol, or a combination thereof. In particular, cationized or anionized variants of such binders can lead to a further enhanced barrier function of the paper coating. The barrier function can also be enhanced by other additives known from paper production, such as sizing agents.

[0034] In addition to the barrier effect of the paper produced according to the invention against fats and oils, a certain barrier effect against water, water vapor, and / or various gases can also be achieved by adding a crosslinking agent. Various crosslinking agents are known that chemically crosslink collagen hydrolysate and, if present, a binder. Biodegradable crosslinking agents, such as various tannins, are preferred.

[0035] Finally, the selection and composition of the paper used as raw material also contributes to the density and barrier function of the paper product manufactured according to the invention. The density of the raw paper plays a decisive role here. This can be increased by equipment commonly used in the paper industry, such as calenders.

[0036] There is a correlation between the density of the starting paper and the composition and application quantity of the aqueous solution in the process according to the invention. For example, by combining a dense base paper with the above-mentioned additives, the application weight of the coating on the base paper can be further reduced. In many cases, it is sufficient to coat one of the surfaces of the paper using the process according to the invention, namely the surface that comes into contact with hydrophobic substances when used as a packaging material, for example, with an oily or fatty food. However, it is also possible within the scope of the invention to produce a paper that has improved grease and oil resistance on both sides. In this case, the process further comprises the steps:

[0037] (b2) applying an aqueous solution to the second surface, wherein the aqueous solution comprises about 30 to about 50 wt.% collagen hydrolysate and at least about 0.1 wt.% of a plasticizer;

[0038] (c2) drying the aqueous solution to obtain a coating comprising collagen hydrolysate and plasticizer on the second surface.

[0039] Steps (b) and (b2), as well as (c) and (c2), can each be carried out simultaneously, in particular using a suitable device (e.g., a film or size press) to apply the aqueous solution to both surfaces of the paper simultaneously. Alternatively, steps (b2) and (c2) can be carried out after steps (b) and (c).

[0040] The present invention further relates to a paper with improved grease and oil resistance, which is obtainable by the process according to the invention. The advantages and preferred embodiments of the paper according to the invention have already been explained in connection with the process according to the invention.

[0041] The paper according to the invention exhibits improved grease and oil resistance compared to the paper used in the process, i.e., before application of the coating containing collagen hydrolysate and plasticizer. Grease and oil resistance can be quantified, in particular, using the KIT test according to TAPPI test protocol T 559 cm-12. This test yields a KIT value of 1 to 12. The higher the KIT value, the better the paper's grease and oil resistance.

[0042] The paper according to the invention preferably has a KIT value of 10 or more, more preferably 11 or more. Due to the addition of plasticizer, the KIT value of the paper according to the invention is not significantly affected by mechanical stress such as bending or folding.

[0043] The present invention further relates to the use of the paper according to the invention as a packaging material, in particular for packaging oily or fatty foods or cosmetics. For example, the paper according to the invention can be used as a packaging material for chocolate or similar products.

[0044] Surprisingly, the improved grease and oil resistance of the paper according to the invention is maintained even at temperatures above 200°C. Thus, the process according to the invention and the paper according to the invention are also suitable for high-temperature applications, e.g., for food packaging in which the food in question is heated and / or cooked, particularly in an oven. Examples of this are baked goods that are baked by the consumer in such packaging.

[0045] In this context, the invention also relates to the use of the paper according to the invention as baking paper.

[0046] These and other advantages of the invention are explained in more detail with reference to the following examples. Examples

[0047] In a series of tests, the grease and oil resistance of papers produced according to the invention was investigated using the KIT test according to the TAPPI test protocol T 559 cm-12, before and after mechanical stress.

[0048] The starting paper used was a standard office paper with a basis weight of 100 g / m 2 used.

[0049] The coating was carried out with aqueous solutions, each containing 40 wt.% of a collagen hydrolysate with an average molecular weight of approximately 3,000 Da (NOVOTEC® CP800), as well as different amounts of the plasticizer glycerol of 0.87 wt.%, 2.61 wt.% and 4.35 wt.%.

[0050] The aqueous solution was applied to the surface of the paper with a doctor blade spacing of 20 pm. The paper was then dried at 50 °C and conditioned overnight at 22 °C. The coating application rate after drying was between 12 and 14 g / m 2 .

[0051] The grease and oil resistance of the coated papers was determined on the one hand without any mechanical stress, and on the other hand after mechanical stress on the paper by rolling it up and unrolling it with a radius of approximately 1 to 2 cm.

[0052] When determining the KIT test, 12 defined test solutions are applied dropwise to the surface of the paper and removed after 15 seconds. The highest number of test solutions that did not cause any visible darkening on the paper during this 15-second period corresponds to the test result for that paper. The test was repeated 10 times for each paper, and the mean values ​​were calculated. The results are shown in Table 1. Table 1

[0053] The results show, firstly, that all papers produced according to the invention have a KIT value of 11 or 12 before mechanical stress (rolling), which generally represents a very high grease and oil resistance.

[0054] The high grease and oil resistance is largely maintained even after mechanical stress (rolling), which is primarily due to the influence of the plasticizer (here, glycerin), which counteracts any deterioration of the coating caused by rolling. It is noteworthy that a relatively small amount of 0.87 wt.% plasticizer is sufficient for this effect, and increasing the amount does not provide any further benefit.

[0055] As a comparative example, the same starting paper was coated with an aqueous solution of 40 wt.% collagen hydrolysate (NOVOTEC® CP800) that contained no plasticizer. The application rate, drying, mechanical stress, and KIT test were carried out as in the inventive examples. The results are shown in Table 2. Table 2

[0056] In contrast to the examples according to the invention, the KIT value of the paper coated without plasticizer drops significantly from 10 to 8 due to the mechanical stress.

[0057] In another experiment, the heat resistance of a paper coated with collagen hydrolysate was investigated. For this experiment, an aqueous solution of 40 wt.% collagen hydrolysate (NOVOTEC® CP800) was applied to the surface of a base paper suitable for the production of baking paper, using a doctor blade spacing of 20 μm. The paper was then dried at 50 °C and conditioned overnight at 22 °C. The coating applied after drying was approximately 10 g / m 2 .

[0058] For the coated paper, KIT values ​​of 10 to 12 were measured using the test procedure described above.

[0059] To assess the temperature resistance of the coating, the paper was heated in an oven for one hour at 220 °C and 250 °C, respectively. This resulted in a slight brown color compared to the base paper (more pronounced at 250 °C than at 220 °C), but no smoke or burning odor was observed. Repeating the KIT test after heating and cooling the paper still yielded high KIT values ​​in the range of 10 to 12. This demonstrates that the grease and oil resistance of the paper, provided by the collagen hydrolysate, is maintained even at high temperatures.

Claims

P atentansp ü che Process for producing a paper with improved grease and oil resistance, comprising the steps: (a) providing a paper having a first and a second surface; (b) applying an aqueous solution to the first surface, the aqueous solution comprising about 10 to about 50 wt.% collagen hydrolysate and at least about 0.1 wt.% of a plasticizer; (c) drying the aqueous solution to obtain a coating comprising collagen hydrolysate and plasticizer on the first surface. The method according to claim 1, wherein the plasticizer is selected from sugar alcohols, in particular from glycerol, sorbitol, or mixtures thereof. The method according to claim 1 or 2, wherein the paper is a paper based on cellulose, mechanical pulp, and / or waste paper. The method according to any one of the preceding claims, wherein the paper has a basis weight of approximately 60 to approximately 200 g / m 2preferably from about 80 to about 150 g / m 2 , more preferably from approx. 90 to approx. 120 g / m 2 . Method according to one of the preceding claims, wherein the aqueous solution comprises approximately 20 to approximately 45 wt.% collagen hydrolysate, preferably approximately 30 to approximately 40 wt.% collagen hydrolysate. Method according to one of the preceding claims, wherein the collagen hydrolysate is produced by chemical or enzymatic hydrolysis of collagen-containing animal starting materials, preferably from skin or bones of vertebrates, in particular from cattle, pigs or sheep. Method according to one of claims 1 to 5, wherein the collagen hydrolysate is produced by recombinant gene expression. Method according to one of the preceding claims, wherein the collagen hydrolysate has an average molecular weight of about 500 to about 25,000 Da, preferably from about 1,000 to about 12,000 Da, more preferably from about 2,000 to about 6,000 Da. Method according to one of the preceding claims, wherein the aqueous solution comprises up to about 5 wt.% plasticizer, preferably about 0.5 to about 1.5 wt.%, more preferably about 0.8 to about 1.2 wt.%. Method according to one of the preceding claims, wherein the application of the aqueous solution takes place at a temperature of the solution of about 40 to about 60 °C, preferably of about 45 to about 55 °C.Method according to one of the preceding claims, wherein the aqueous solution is applied by spraying, rolling, doctoring, by means of a coating device, a film press, a size press, or by means of curtain coating. Method according to one of the preceding claims, wherein the application quantity of the aqueous solution is selected such that, after drying, the basis weight of the coating comprising collagen hydrolysate and plasticizer is approximately 8 to approximately 20 g / m. 2 results, preferably from about 9 to about 15 g / m 2 , more preferably from about 10 to about 12 g / m 2 . A method according to any one of the preceding claims, wherein the drying of the aqueous solution is carried out at a temperature of about 30 to about 70 °C preferably from about 40 to about 60 °C, more preferably from about 45 to about 55 °C. The process according to any one of the preceding claims, wherein the aqueous solution further comprises further additives, which are in particular selected from pigments dispersed in the aqueous solution, binders such as modified starches, polyvinyl alcohol or gelatin, crosslinking agents such as tannins, and / or further additives such as sizing agents. The process according to any one of the preceding claims, further comprising the steps: (b2) applying an aqueous solution to the second surface, wherein the aqueous solution comprises about 30 to about 50 wt.% collagen hydrolysate and at least about 0.1 wt.% of a plasticizer; (c2) drying the aqueous solution to obtain a coating comprising collagen hydrolysate and plasticizer on the second surface. The process according to claim 15, wherein steps (b) and (b2) and (c) and (c2) are each carried out simultaneously, or wherein steps (b2) and (c2) are carried out after steps (b) and (c). Paper with improved grease and oil resistance, obtainable according to the process according to any one of the preceding claims. The paper according to claim 17, wherein the first surface of the paper has a KIT value of 10 or more, preferably of 11 or more, determined according to the TAPPI test protocol T 559 cm-12. Use of the paper according to claim 17 or 18 as packaging material, in particular for packaging oily or fatty foods or cosmetics. Use of the paper according to claim 17 or 18 as baking paper. * * *

Images