Patent Application
20250179737
The use of paper as a packing material, or as a component of packing materials, has long been known. In this regard, paper has the fundamental advantage over most other packing materials that it is biodegradable and readily recyclable. On the other hand, however, paper has the disadvantage that it is very easily penetrated or passed through by hydrophobic substances such as oils and greases, which severely restricts or rules out the usability of packing made entirely from paper for such products, in particular greasy or oily foodstuffs.
To obviate this problem, packing made from various composite materials in which the paper is provided with a barrier layer for greases or oils is known. These barrier layers are usually based on synthetic polymers, in particular fluoropolymers or siloxane compounds, which generally have poor biodegradability or none at all. The use of such packing is thus extremely disadvantageous from the point of view of environmental pollution, including in particular marine pollution, and even re-use is often only possible to a limited extent or at great expense.
The present invention relates to a method for manufacturing a paper having improved impermeability to grease and oil.
The invention further relates to a paper having improved impermeability to grease and oil that has been manufactured by this method, and to the use of the paper as packing material.
The object of the invention is thus to propose a method for manufacturing a paper having improved impermeability to grease and oil, wherein the paper that is manufactured is biodegradable.
According to the invention, this object is achieved by a method that comprises the following steps:
Surprisingly, it has been found that coating a paper surface with collagen hydrolysate results in a relatively high impermeability of the paper to oil and grease.
Collagen hydrolysate is a hydrolysis product of the animal structural protein collagen. Collagen hydrolysate is completely biodegradable and is harmless to health, so a paper manufactured by the method according to the invention not only entirely meets the requirement for biodegradability but is also suitable as a packing material in particular for foodstuffs.
Moreover, it has been found that the papers manufactured according to the invention also have, depending on the configuration, very high gloss and excellent printability.
Improved impermeability to grease and oil of the paper manufactured according to the invention means improved impermeability to hydrophobic substances in general. These comprise in particular vegetable and animal fats and oils, that is to say triglycerides that are solid (fats) or liquid (oils) at room temperature. This has particular relevance for use as a packing for foodstuffs. However, the impermeability is likewise improved in relation to hydrophobic substances with a synthetic basis or those based on mineral oil, which has relevance for example for use as a packing material for cosmetics.
The impermeability of paper to grease and oil may in particular be quantified using the so-called kit test, corresponding to TAPPI (Technical Association of the Pulp and Paper Industry) test protocol T 559 cm-12.
When paper is used as a packing material, it is necessary for the corresponding impermeability to grease and oil to be retained even after the paper has undergone a mechanical load that is entailed in the packing process (that is to say on bending, folding and/or crumpling of the paper). In this regard, interestingly, the inventors have found that the addition of even a relatively small quantity of plasticizer to the aqueous solution of collagen hydrolysate applied in step (b) of the method according to the invention has the result that the impermeability of the manufactured paper to grease and oil is indeed retained for the most part after a mechanical load of this kind. It is assumed from this that, after the aqueous solution has dried in step (c) of the method according to the invention, the collagen hydrolysate forms a substantially uninterrupted coating on the surface of the paper, wherein the brittleness of this coating is reduced by the addition of plasticizer. Thus, cracks in the coating in the course of the mechanical load that result in a decrease in the impermeability to grease and oil are prevented or reduced.
Suitable plasticizers are known from the prior art and comprise in particular plasticizers that are frequently used in combination with gelatine, for example in the manufacture of soft capsules. Preferably, the plasticizer is selected from sugar alcohols, in particular glycerol, sorbitol or mixtures of these.
The paper provided in step (a) of the method according to the invention is typically a paper based on chemical pulp, mechanical pulp and/or waste paper pulp. These industrial raw materials for papermaking are all based on cellulose, wherein chemical pulp comprises predominantly cellulose and mechanical pulp additionally contains a proportion of lignin.
Fundamentally, the paper used within the scope of the present invention is not limited in respect of its weight per surface area. Thus, the invention explicitly also comprises relatively thick materials such as cardboard and paperboard, even though for the sake of simplicity only the term “paper” is used here, regardless of the weight per surface area. Typically, the paper has a weight per surface area of from approximately 60 to approximately 200 g/m2, preferably from approximately 80 to approximately 150 g/m2, more preferably from approximately 90 to approximately 120 g/m2. This corresponds to the weight per surface area of papers that are conventionally used as packing material (but also for example that of writing paper).
According to the invention, the aqueous solution that is applied to the first surface of the paper comprises from approximately 10 to approximately 50 weight % of collagen hydrolysate. It has been found that a concentration of collagen hydrolysate in this range not only gives an aqueous solution having a viscosity favorable to application but that the viscosity of the solution is in that case also relatively independent of shear stresses. By contrast, aqueous solutions having a higher concentration of collagen hydrolysate are subject to shear thinning, that is to say their viscosity decreases as shear stresses increase. Lower concentrations of collagen hydrolysate, in turn, have the disadvantage of requiring larger quantities of the solution to be applied and longer drying times.
Preferably, the aqueous solution comprises from approximately 20 to approximately 45 weight % of collagen hydrolysate, more preferably from approximately 30 to approximately 40 weight % of collagen hydrolysate. It has been found that this concentration is particularly advantageous for the application of the aqueous solution to the surface of the paper.
The collagen hydrolysate that is used in the method according to the invention is typically produced by chemical or enzymatic hydrolysis of starting materials of animal origin containing collagen. The starting material of animal origin is preferably selected from the skin or bones of vertebrates, in particular of cattle, pigs or sheep. The production of collagen hydrolysate by the enzymatic hydrolysis of gelatine, in particular using one or more endopeptidases, is particularly preferred.
Collagen hydrolysate is typically in the form of a mixture of peptides of a particular molecular weight distribution, wherein this molecular weight distribution may be affected by the respective conditions of hydrolysis (in particular by the enzymes used, duration of the hydrolysis, temperature and pH value). The collagen hydrolysate typically has an average molecular weight of from approximately 500 to approximately 25,000 Da, preferably from approximately 1,000 to approximately 12,000 Da, more preferably from approximately 2,000 to approximately 6,000 Da. These values relate in each case to the weight-average molecular weight, which is determined by gel permeation chromatography.
Particularly advantageously, within the scope of the invention a collagen hydrolysate having an average molecular weight of approximately 3,000 Da may be used. A collagen hydrolysate of this kind is sold for example by the Applicant, Gelita AG, in the form of a 50% solution under the name of NOVOTEC® CP800.
As an alternative to enzymatic hydrolysis, within the scope of the invention the collagen hydrolysate may be produced by recombinant gene expression. By using natural collagen sequences, in particular from cattle or pigs, and the expression of these in genetically modified cells (such as yeasts, bacteria or plant cells, in particular tobacco), products that are substantially identical to the hydrolysis products of the corresponding collagen-containing raw materials may be produced. Here, it is possible among other things to obtain a relatively narrow or precisely predetermined molecular weight distribution.
In addition to the collagen hydrolysate, the aqueous solution also comprises plasticizers such as glycerol. As described above, frequently even a small proportion of approximately 0.1 weight % of plasticizer is sufficient to reduce the brittleness of the coating that is formed and to significantly improve the impermeability of the paper that is manufactured to grease and oil, even after it has undergone a mechanical load. The aqueous solution may also comprise higher proportions of plasticizer, such as up to approximately 5 weight %, although significantly higher proportions do not substantially further improve the properties of the paper that is manufactured. Preferably, the aqueous solution comprises from approximately 0.5 to approximately 1.5 weight % of plasticizer, more preferably from approximately 0.8 to approximately 1.2 weight %.
Even though collagen hydrolysate already has good water solubility and processability at room temperature, within the scope of the invention it is preferred if the aqueous solution is applied at a temperature of the solution of from approximately 40 to approximately 60° C., more preferably from approximately 45 to approximately 55° C. It has been found that in this temperature range, in particular using the above-mentioned preferred concentrations of collagen hydrolysate, the aqueous solution has a viscosity that is favorable to application to the paper surface.
Application of the aqueous solution in step (b) of the method according to the invention may be performed using various application methods known from the prior art, such as by spraying, using a roller or scraping. Devices for applying the aqueous solution by scraper or blade are known in the paper industry, for example as so-called coaters.
Further preferred application methods that are likewise known from the paper industry comprise application of the aqueous solution by a film press, a size press or, without contact, a curtain-coating method.
The proportion of collagen hydrolysate and plasticizer (and optionally further additives) and the quantity of aqueous solution applied give the weight by surface area of the coating that is obtained after drying. Favorably, the quantity applied is selected such that after drying the result is a weight by surface area of the coating that comprises collagen hydrolysate and plasticizer of from approximately 8 to approximately 20 g/m2, preferably from approximately 9 to approximately 15 g/m2, more preferably from approximately 10 to approximately 12 g/m2. If the aqueous solution is applied by scraper, a corresponding application quantity can be achieved for example with a scraper spacing of from approximately 15 to approximately 30 μm.
Drying of the aqueous solution in step (c) of the method according to the invention is favorably performed at a temperature of from approximately 30 to approximately 70° C., preferably from approximately 40 to approximately 60° C., more preferably from approximately 45 to approximately 55° C. Given this, it is favorable if the aqueous solution is already at a corresponding or similar temperature at the time of application, as described above.
In addition to the collagen hydrolysate and the plasticizer, the aqueous solution may optionally comprise further additives, in order to further improve the properties of the paper that is manufactured or to adapt them to particular requirements. Among other things, this may have an effect on the printability, ink fixing and wet strength of the paper. Additives of this kind may in particular be selected from pigments dispersed in the aqueous solution, binders such as starch, polyvinyl alcohol or gelatine, crosslinking agents such as tannins, and/or further additives such as sizing agents.
According to an advantageous embodiment of the invention, the aqueous solution comprises dispersed pigments which are preferably selected from carbonates, silicates, bentonites or kaolin. Particularly suitable here are platelet configurations of such pigments. These pigments may in some circumstances further improve the impermeability of the paper to grease and oil by further impeding the transport path of the greasy or oily substance through the barrier layer.
In a further preferred embodiment, the aqueous solution comprises additional binders such as modified starches, polyvinyl alcohol or combinations of these. In particular, cationized or anionized variants of such binders may result in further enhancement of the barrier function of the paper coating. Further additives known from papermaking, such as sizing agents, may also intensify the barrier function.
In addition to the barrier action in relation to greases and oils by the paper that is manufactured according to the invention, a certain barrier action in relation to water, water vapor and/or different gases may also be achieved by the addition of a crosslinking agent. Various crosslinking agents are known that bring about chemical crosslinking of collagen hydrolysate and where applicable a binder contained in the solution. Preferred here are biodegradable crosslinkers such as various tannins.
Finally, the selection and composition of the paper that is used as the raw material also contributes to the impermeability or barrier function of the paper product manufactured according to the invention. Here, the impermeability of the raw paper has a relevant effect. This may be enhanced by assemblies that are conventional in the paper industry, such as calenders.
Here, there is an interaction between the impermeability of the starting material paper and the composition and applied quantity of the aqueous solution in the method according to the invention. For example, the combination of an impermeable base paper and the above-mentioned additives may allow the weight of coating applied to the base paper to be further reduced.
In many cases, using the method according to the invention it is sufficient to coat one of the surfaces of the paper, namely the surface which, during use as a packing material, comes into contact with hydrophobic substances such as an oily or greasy foodstuff. However, it is also possible within the scope of the invention to manufacture a paper which has improved impermeability to grease and oil on both sides. In this case, the method further comprises the following steps:
Steps (b) and (b2) may be carried out simultaneously and steps (c) and (c2) may be carried out simultaneously, in particular with the aid of a suitable device (such as a film or size press), in order to apply the aqueous solution to both surfaces of the paper at the same time. As an alternative, steps (b2) and (c2) may be carried out after steps (b) and (c).
Further, the present invention relates to a paper having improved impermeability to grease and oil which is obtainable by the method according to the invention. The advantages and preferred embodiments of the paper according to the invention have already been explained in conjunction with the method according to the invention.
The paper according to the invention has an improved impermeability to grease and oil by comparison with the paper used for the method, that is to say before the coating containing collagen hydrolysate and plasticizer has been applied. The impermeability to grease and oil may in particular be quantified using the kit test in conformance with the TAPPI test protocol T 559 cm-12, wherein this test gives as the result a kit value of from 1 to 12. The higher the kit value, the greater the impermeability of the paper to grease and oil.
The paper according to the invention preferably has a kit value of 10 or above, more preferably 11 or above. As a result of the addition of plasticizer, the kit value of the paper according to the invention is not substantially impaired by a mechanical load such as bending or folding.
Further, the present invention relates to the use of the paper according to the invention as a packing material, in particular for packing oily or greasy foodstuffs, or cosmetics. For example, the paper according to the invention may be used as a packing material for chocolate or similar products.
Surprisingly, the improved impermeability of the paper according to the invention to grease and oil is retained even at temperatures above 200° C. Thus, the method according to the invention and the paper according to the invention are also suitable for high-temperature applications, that is to say for example for the packing of foodstuffs in which the foodstuff concerned is heated and/or cooked, in particular in an oven. Examples of this are baked goods that are baked by the consumer in a corresponding pack.
In this connection, the invention thus also relates to the use of the paper according to the invention as a baking paper.
These and further advantages of the invention are explained in more detail with reference to the examples below.
In a series of tests, the impermeability of papers manufactured according to the invention to grease and oil was investigated using the kit test in conformance with the TAPPI test protocol T 559 cm-12, before and after they underwent a mechanical load.
As the starting material paper, a conventional office paper with a weight per surface area of 100 g/m2 was used.
Coating was performed using aqueous solutions each containing 40 weight % of a collagen hydrolysate having an average molecular weight of approximately 3,000 Da (NOVOTEC® CP800) and having different quantities of the plasticizer glycerol, namely 0.87 weight %, 2.61 weight % and 4.35 weight %.
The aqueous solution was in each case scraped onto one surface of the paper with a scraper spacing of 20 μm, and then the paper was dried at 50° C. and conditioned overnight at 22° C. The quantity of coating applied was between 12 and 14 g/m2 after drying.
The impermeability of the coated papers to grease and oil was determined on the one hand without a mechanical load, and on the other after the paper had undergone a mechanical load by being rolled up to a radius of approximately 1 to 2 cm and unrolled again.
During determination using the kit test, 12 defined test solutions were applied to the surface of the paper using a dropper, and were then removed again after 15 seconds. The largest number of such test solutions that caused no visible darkening on the paper during this period of 15 seconds is the test result for this paper. The test was repeated ten times for each paper and the values averaged. The results are shown in Table 1.
First, the results show that all the papers manufactured according to the invention have a kit value of 11 or 12 before undergoing the mechanical load (rolling), which in general represents a very high impermeability to grease and oil.
The high impermeability to grease and oil is also retained to a very large extent after a mechanical load (rolling), which is in particular attributable to the effect of the plasticizer (in this case glycerol), which counters impairment of the coating as a result of being rolled up. It is notable here that even the relatively small quantity of 0.87 weight % of plasticizer is sufficient for this effect, and increasing the quantity does not bring about any further advantage.
As a comparative example, the same starting material paper was coated with an aqueous solution of 40 weight % of collagen hydrolysate (NOVOTEC® CP800) containing no plasticizer. The quantity applied, drying, mechanical load and method by which the kit test was carried out were as in the examples according to the invention. The results are shown in Table 2.
Unlike the examples according to the invention, the kit value of the paper coated with no plasticizer falls significantly, from 10 to 8, as a result of the mechanical load.
In a further test, the heat resistance of a paper coated with collagen hydrolysate was investigated. For this purpose, an aqueous solution of 40 weight % of collagen hydrolysate (NOVOTEC® CP800) was scraped onto the surface of a raw paper suitable for manufacturing baking paper, with a scraper spacing of 20 μm. Then the paper was dried at 50° C. and conditioned overnight at 22° C. The quantity of coating applied was approximately 10 g/m2 after drying.
For the coated paper, kit values of 10 to 12 were measured using the test method described above.
For assessment of the heat resistance of the coating, the paper was heated in an oven for one hour, to 220° C. and to 250° C. respectively. This resulted in slight browning by comparison with the raw paper (more pronounced at 250° C. than at 220° C.), but no smoke developed and there was no smell of burning.
When the kit test was repeated after heating and cooling of the paper, the result was once again high kit values in the range of 10 to 12. This shows that the impermeability of the paper to grease and oil that was brought about by the collagen hydrolysate is retained even at high temperatures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 119 507.4 | Aug 2022 | DE | national |
This patent application is a continuation of International Patent Application No. PCT/EP2023/071461, filed on Aug. 2, 2023, which claims the benefit of German Patent Application No. 10 2022 119 507.4, filed on Aug. 3, 2022, each of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2023/071461 | Aug 2023 | WO |
| Child | 19042770 | US |
