Heat sealable barrier material for food and non-food packaging

Abstract

The present invention relates to a heat-sealable barrier material comprising a carrier substrate; and a barrier coating arranged on at least one side of the carrier substrate, wherein the barrier coating is composed of polyvinyl alcohol (PVOH) and / or ethylene-vinyl alcohol copolymer (EVOH) and further comprises tannin in an amount of 5 wt.% to 25 wt.%, based on the total weight of the barrier coating.

Description

[0001] The present invention relates to a heat-sealable barrier material for packaging in the food and non-food sectors, as well as a process for its production.

[0002] Packaging products and containers made of cellulosic materials, such as paper and cardboard, are used for packaging beverage containers, frozen foods, cereals, and a variety of other food and non-food consumer goods. This often requires improved barrier properties, including an oil, grease, water, and / or moisture vapor barrier. For this purpose, the paper or cardboard is coated or treated with coatings made of waxes, polymers, fluorocarbons, and the like. Polyvinyl alcohol is particularly suitable as a barrier coating to achieve optimal and safe barrier properties against fats, oils, oxygen, and flavors.

[0003] To seal a package or form a container, such as a cup, the plastic coatings can be firmly and permanently bonded together using heat sealing. Heat sealing requires a heat source warm enough to melt the plastic coating and a pressure unit that presses both package halves together.

[0004] However, barrier coatings made of polyvinyl alcohol have the disadvantage that high sealing temperatures of 200 ± 20°C are required for a secure seal. These high sealing temperatures can cause problems with temperature-sensitive products, such as chocolate. The high temperatures also cause problems for the heat-sealing machines themselves, as they operate at their upper temperature limits, leading to frequent failures. Furthermore, the high temperatures reduce the cycle rate because the sealing time per seam is increased.

[0005] The present invention is therefore based on the technical object of providing a heat-sealable barrier material in which the sealing temperature of the barrier coating is reduced.

[0006] The above-described object is achieved by the embodiments of the present invention characterized in the claims. In particular, the invention provides a heat-sealable barrier material comprising: a carrier substrate; and a barrier coating disposed on at least one side of the carrier substrate, wherein the barrier coating is composed of polyvinyl alcohol (PVOH) and / or ethylene-vinyl alcohol copolymer (EVOH) and further comprises tannin in an amount of 5 wt.% to 25 wt.%, based on the total weight (100 wt.%) of the barrier coating.

[0007] The heat-sealable barrier material according to the invention not only allows goods to be packaged more gently, but also increases the cycle frequency of the packaging machines. The low sealing temperatures also lead to energy savings on the packaging machines.

[0008] The heat-sealable barrier material according to the invention comprises at least one carrier substrate. The carrier substrate gives the packaging its shape.

[0009] The carrier substrate preferably comprises cellulose fibers, and the proportion of cellulose fibers is preferably greater than or equal to 90 wt.%, based on the total mass of the carrier substrate and determined as an oven-dry mass fraction. Paper or a paper substrate is more preferably used as the carrier substrate.

[0010] In the context of the present invention, the term "paper" means paper with a weight per square meter of ≤ 150 g / m 2< , preferably ≤ 100 g / m 2< , particularly preferably ≤ 80 g / m 2< .

[0011] According to the invention, an uncoated paper substrate or a non-surface-treated coating base paper substrate is particularly preferably suitable as the carrier substrate. For the purposes of the present invention, an uncoated paper substrate is understood to mean a paper substrate that does not comprise any layers applied by coating. However, it may optionally comprise layers that are not or have not been applied by coating. Thus, an uncoated paper substrate may be prepared and comprise, for example, a starch-impregnated surface or a starch layer (preferably applied to the side of the carrier substrate opposite the intermediate layer or barrier layer, i.e., the "back" of the carrier substrate). For example, the back of a paper substrate may be coated with a starch layer, preferably modified starch, particularly preferably modified corn starch.A backside coating can improve the properties of the resulting barrier material. For example, it is possible to create a backside-printable barrier material.

[0012] For the purposes of the present invention, a coated paper substrate is understood to mean a paper substrate comprising one or more layers applied by coating, in particular a two-, three-, four-, or multi-layer paper substrate. Possible layers of such a coated paper substrate include functional layers and structure-forming layers (such as leveling layers for smoothing the surface).

[0013] For the purposes of the present invention, a non-surface-treated coating base paper substrate is understood to mean a paper substrate that is uncoated and unprepared. Non-surface-treated coating base paper exhibits particularly good recyclability and particularly good environmental compatibility. Non-surface-treated coating base paper is typically not treated in a size press. Alternatively, the coating base paper can already be provided with an intermediate layer, for example, in the form of a precoat, using a coating device integrated into the paper machine.

[0014] The heat-sealable barrier material according to the invention comprises at least one barrier coating arranged on at least one side of the carrier substrate, wherein the barrier coating is composed essentially of polyvinyl alcohol (PVOH) and / or ethylene-vinyl alcohol copolymer (EVOH), preferably polyvinyl alcohol, and further comprises tannin according to the invention. The barrier coating imparts the packaging its preferred barrier effect against fats, oils, oxygen, and flavors, as well as its heat-sealability.

[0015] The barrier coating preferably has a layer thickness in the range of 1 to 20 µm, more preferably in the range of 2 µm to 15 µm, and particularly preferably in the range of 3 µm to 10 µm. If the layer thickness is within the range defined above, the barrier coating has an excellent barrier effect against fats, oils, oxygen, and flavors, as well as excellent heat sealability.

[0016] The barrier coating of the barrier material according to the invention preferably comprises polyvinyl alcohol. The polyvinyl alcohol according to the invention serves as a binder and simultaneously as a sealing compound in the barrier coating, whereby the polyvinyl alcohol can be modified and / or unmodified, preferably consisting of unmodified polyvinyl alcohol and mixtures thereof.

[0017] Preferably, the polyvinyl alcohol has a viscosity of ≤ 9 mPa*s, more preferably ≤ 7 mPa*s, in a 4% aqueous solution at 20°C. The measurement is carried out according to DIN 53015 "Dynamic viscosity of Newtonian liquids using the Höppler falling ball viscometer."

[0018] Furthermore, the polyvinyl alcohol is preferably crosslinked, especially crosslinked. A suitable crosslinking agent can be selected from the group consisting of formaldehyde, glyoxal, zirconium compounds, including ammonium zirconium(IV) carbonate and zirconium(IV) carbonate, polyamidoamine epichlorohydrin resins, boric acid, and dihydroxybis(ammonium lactato)titanium(IV), with glyoxal being particularly used for this purpose.

[0019] Due to crosslinking, in particular crosslinking, the barrier material according to the invention has improved stability.

[0020] In a preferred embodiment, the proportion of polyvinyl alcohol is more than 50 wt.%, more preferably more than 73 wt.%, and particularly preferably more than 83 wt.%, based on the total mass of the barrier coating. If the proportion of polyvinyl alcohol is below the above minimum, the barrier coating has insufficient barrier effect against fats, oils, oxygen, and flavors, as well as insufficient heat sealability.

[0021] The barrier coating of the barrier material according to the invention comprises tannin. In the context of the present invention, the term "tannin" refers to polyhydroxyphenols. The tannin according to the invention serves to reduce the sealing temperature of the barrier coating. Furthermore, the tannin imparts antiviral and antibacterial properties to the barrier coating. The tannin can be present in salt-free form or in salt form, for example, as a sodium salt.

[0022] According to the present invention, the tannin content is in the range of 5 wt.% to 25 wt.%, based on the total mass of the barrier coating. In a preferred embodiment, the tannin content is in the range of 10 wt.% to 20 wt.%, and more preferably in the range of 13 to 17 wt.%, based on the total mass of the barrier coating. If the tannin content is below the above-defined range, the sealing temperature of the barrier coating is not sufficiently reduced. If the tannin content is above the above-defined range, this has a negative effect on the barrier effect against water, fats, oils, oxygen, and flavors.

[0023] In a preferred embodiment, the barrier material has an intermediate layer comprising inorganic pigments, which is arranged between the carrier substrate and the barrier coating.

[0024] In addition to the inorganic pigments, the intermediate layer preferably comprises at least one synthetic polymer as a binder; more preferably, the synthetic polymer is styrene-butadiene latex.

[0025] Preferably, a "binder : pigment ratio" within the intermediate layer is in the range of 3:7 to 1:9, based on the mass fractions (in %) of binder or pigment.

[0026] Pigment in the intermediate layer.

[0027] In a preferred embodiment, the intermediate layer has a basis weight of 2 to 20 g / m 2< , more preferably of 5 to 15 g / m 2< , and particularly preferably of 7 to 12 g / m 2< .

[0028] A further aspect of the present invention relates to a process for producing a heat-sealable barrier material, comprising the steps: (i) providing a carrier substrate; and (ii) applying a barrier coating, wherein the barrier coating is composed of polyvinyl alcohol and / or ethylene-vinyl alcohol copolymer and further comprises tannin in an amount of 5 wt.% to 25 wt.%, based on the total weight of the barrier coating, to at least one side of the carrier substrate.

[0029] According to the present invention, the inventive method comprises step (i) of providing a carrier substrate. All of the above statements regarding the carrier substrate in the barrier material according to the invention also apply to the inventive method for producing the barrier material according to the invention.

[0030] According to the present invention, the process according to the invention comprises step (ii) of applying a barrier coating comprising polyvinyl alcohol and tannin to at least one side of the carrier substrate, wherein the tannin content is in the range of 5 wt.% to 25 wt.%, based on the total mass of the barrier coating. All of the above statements regarding the barrier coating in the barrier material according to the invention also apply to the process according to the invention for producing the barrier material according to the invention.

[0031] In a preferred embodiment, step (ii) is divided into substeps (iia) to (iic), wherein substeps (iia) to (iic) are characterized as follows: (iia) providing or preparing a barrier coating composition comprising polyvinyl alcohol and tannin, (iib) applying the barrier coating composition from step (iia) to at least one side of the carrier substrate so that a barrier coating is formed, and (iic) drying and / or crosslinking the barrier coating formed in step (iib).

[0032] In a preferred embodiment, the method for producing according to the invention additionally comprises the following step (iii), which is carried out before step (ii): (iii) applying an intermediate layer comprising inorganic pigments to at least one side of the carrier substrate to which the barrier coating is applied,

[0033] All the above statements regarding the intermediate layer in the barrier material according to the invention also apply to the process according to the invention for producing the barrier material according to the invention.

[0034] In a further preferred embodiment, the above-mentioned step (iii) is divided into sub-steps (iiia) to (iiic), wherein the sub-steps (iiia) to (iiic) are characterized as follows: (iiia) providing or producing an interlayer composition comprising inorganic pigments, (iiib) applying the interlayer composition from step (iiia) to the at least one side of the carrier substrate to which the barrier coating is applied, so that an interlayer is formed, and (iiic) drying and / or crosslinking the interlayer formed in step (iiib).

[0035] Within the scope of the present invention, various techniques for applying layers or coatings and layer compositions or coating compositions are known to those skilled in the art. These techniques, referred to as "coating," include, for example, blade coating, film press coating, cast coating, curtain coating, doctor blade coating, air knife coating, or spray coating. Air knife coating and doctor blade coating are preferred according to the invention.

[0036] Within the scope of the present invention, various techniques for "drying and / or crosslinking" layer compositions or coating compositions are known to the person skilled in the art.

[0037] In a preferred embodiment of the manufacturing process according to the invention, the barrier coating is applied to the carrier substrate within five days, more preferably within three days, and particularly preferably within one day after manufacturing. This allows the sealing temperature to be further reduced compared to barrier coatings that are stored for longer than five days prior to application.

[0038] A further aspect of the present invention relates to a method for heat sealing a barrier material according to the invention, comprising the following steps: (i) Providing the barrier material according to the invention, (ii) placing the provided barrier material according to the invention on top of each other so that the surface lies on the surface of the barrier coating, (iii) pressing the barrier material lying on the surface under the action of heat so that the barrier coating is heated to the molten state at least in the part lying on the surface, (iv) reducing the contact pressure and the action of heat so that the layer brought into the molten state cools down.

[0039] A further aspect of the present invention relates to the use of the barrier material according to the invention as a packaging material and / or for packaging a product. The use of the barrier material according to the invention prevents the penetration of fats, oils, oxygen, and aromas, thus advantageously protecting the packaged product. Furthermore, the product can be packaged gently due to the reduced heat-sealing temperature.

[0040] A further aspect of the present invention relates to the use of tannin to reduce the melting temperature of polyvinyl alcohol and / or ethylene-vinyl alcohol copolymer in a barrier coating of a heat-sealable barrier material, wherein the tannin content in the barrier coating is in the range of 5 wt.% to 25 wt.%. All of the above statements regarding the barrier material according to the invention also apply to the application according to the invention for reducing the melting temperature.

[0041] Due to the reduced heat sealing temperature, the present invention is particularly advantageous for temperature-sensitive foods, for example in the area of ​​chocolate as well as chocolate-filled and chocolate-coated foods, but also for other temperature-sensitive foods or even temperature-sensitive non-food goods.

[0042] The figures show: FIG. 1shows the strength (in N) of sealed seams on barrier coatings with different tannin contents (Examples 1 to 3 and Comparative Example 1) at various sealing temperatures. The strength was measured directly after hot tack using the Labormaster HCT laboratory sealing device with integrated force measurement at a peel speed of 6 m / min. FIG. 2 shows the strength (in N) of sealed seams on barrier coatings with different tannin contents (Examples 1 to 3 and Comparative Example 1) at various sealing temperatures. The strength was measured 4 days after heat sealing (cold tack) using the Labormaster HCT laboratory sealing device with integrated force measurement at a peel speed of 6 m / min. Examples

[0043] The following examples serve to illustrate the present invention, but are not limited thereto. Example 1:

[0044] Tannin, dissolved in water, is mixed with a 25% NaOH solution to adjust the pH to 7. This solution is then metered into a solution of polyvinyl alcohol (Mowiol 6-98), Metolat 700, Agitan 351, and water. 42% Cartabond TSI is metered into this solution to obtain a barrier coating liquid. The barrier coating liquid is applied to the precoated side of a paper with a basis weight of 50 g / m² as the carrier substrate using an Erichson Multicoater RK 303 laboratory coating machine with a doctor blade system and dried. The barrier coating has a basis weight of 4 g / m² and a tannin content of 10 wt.%, based on the total mass of the barrier coating.

[0045] The dried barrier material is placed coated barrier side to coated barrier side, and a sealing seam is created using flat sealing jaws measuring 1 x 6 cm, using the Labormaster HCT 3200 laboratory sealing device with a sealing time of 0.3 seconds at different temperatures. The strength (in N) of the sealing seam, measured in the Labormaster HCT with integrated force measurement at a pull-off speed of 6 m / min in relation to the sealing temperature, is shown in the Figures 1 and 2 The Figure 1 the strength (in N) of the sealing seam immediately after sealing (hot tack) and the Figure 2 the strength (in N) of the sealed seam after a standing time of 4 days (cold tack). Example 2:

[0046] Production of a barrier material as defined in Example 1, wherein the tannin content is 15 wt.%, based on the total mass of the barrier coating. A seal is produced using the laboratory sealing device Labormaster HCT 3200 with a sealing time of 0.3 seconds at different temperatures. The measured strength (in N) of the seal is shown in the Figures 1 and 2 shown. Example 3:

[0047] Production of a barrier material as defined in Example 1, wherein the tannin content is 20 wt.%, based on the total mass of the barrier coating. A seal is produced using the laboratory sealing device Labormaster HCT 3200 with a sealing time of 0.3 seconds at different temperatures. The measured strength (in N) of the seal is shown in the Figures 1 and 2 shown. Comparison example 1:

[0048] Production of a barrier material as defined in Example 1, without the presence of tannin. A seal is made using the laboratory sealing device Labormaster HCT 3200 with a sealing time of 0.3 seconds at different temperatures. The measured strength of the seal is shown in the Figures 1 and 2 shown.

[0049] As from FIGS. 1 and 2 As can be seen, the addition of tannin to the barrier coating advantageously reduced the heat-sealing temperature. A tannin content of 15 wt.% and 20 wt.%, based on the total mass of the barrier coating, proved particularly advantageous. In all examples, good seal strength was achieved both immediately after heat sealing (hot tack) and four days after (cold tack). Comparison example 2:

[0050] Preparation of a barrier material as defined in Example 1, wherein the barrier coating composition was left to stand for 6 days in the laboratory at room temperature without stirring in a closed vessel before the barrier coating composition was applied to the carrier substrate and dried. Comparison example 3:

[0051] Preparation of a barrier material as in Example 2, wherein the barrier coating composition was allowed to stand for 6 days after preparation before the barrier coating composition was applied to the carrier substrate and dried. Comparison example 4:

[0052] Preparation of a barrier material as in Example 3, wherein the barrier coating composition was allowed to stand for 6 days after preparation before the barrier coating composition was applied to the carrier substrate and dried.

Claims

1. A heat-sealable barrier material comprising a carrier substrate; and a barrier coating disposed on at least one side of the carrier substrate, wherein the barrier coating is composed of polyvinyl alcohol and / or ethylene-vinyl alcohol copolymer, preferably polyvinyl alcohol, and further comprises tannin in an amount of 5 wt.% to 25 wt.%, based on the total weight of the barrier coating.

2. Heat-sealable barrier material according to claim 1, wherein the carrier substrate comprises cellulose fibers, and the proportion of cellulose fibers is greater than or equal to 90% by weight, based on the total mass of the carrier substrate.

3. Heat sealable barrier material according to claim 1 or 2, wherein the polyvinyl alcohol is selected from the group consisting of unmodified polyvinyl alcohol and mixtures thereof.

4. Heat-sealable barrier material according to one of claims 1 to 3, wherein the polyvinyl alcohol in a 4% aqueous solution at 20°C has a viscosity of ≤ 9 mPa*s, measured according to DIN 53015.

5. Heat-sealable barrier material according to one of claims 1 to 4, further comprising an intermediate layer comprising inorganic pigments arranged between the carrier substrate and the barrier coating.

6. Heat-sealable barrier material according to claim 5, wherein the inorganic pigment is calcined kaolin.

7. A method for producing a heat-sealable barrier material, comprising the steps of: (i) providing a carrier substrate; and (ii) applying a barrier coating, wherein the barrier coating is composed of polyvinyl alcohol and / or ethylene-vinyl alcohol copolymer and further comprises tannin in an amount of 5% to 25% by weight, based on the total weight of the barrier coating, to at least one side of the carrier substrate.

8. A method of manufacturing according to claim 7, further comprising the following step (iii), which is carried out before step (ii): (iii) applying an intermediate layer comprising inorganic pigments to the at least one side of the carrier substrate to which the barrier coating is applied.

9. A method of manufacture according to claim 7 or 8, wherein the barrier coating is applied to the carrier substrate within four days after manufacture.

10. Use of the heat-sealable barrier material according to any one of claims 1 to 6 as packaging material.

11. Use of tannin to reduce the melting temperature of polyvinyl alcohol and / or ethylene-vinyl alcohol copolymer in a barrier coating of a heat-sealable barrier material, wherein a proportion of the tannin in the barrier coating is in the range of 5 wt% to 25 wt%.

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