Packaging material comprising a starch-based barrier coating and coating composition and process for producing the same

Abstract

A starch-based coating compound for packaging materials, in particular for paper, pasteboard or cardboard, wherein the starch has a molecular weight in the range of 800,000 to 50,000,000 g/mol, preferably in the range of 800,000 to 20,000,000 g/mol. The coating compound is used for surface-sealing packaging materials, to prevent the passage of mineral oil contaminants from the packaging material into packaged goods. The subject disclosure furthermore relates to a multi-layer packaging material, which is produced using the coating compound, and to a method for producing said packaging material.

Claims

1. A multi-layer packaging material, comprising: a planar substrate selected from the group consisting of paper, pasteboard and cardboard as carrier layer, and at least one starch-based barrier layer, which is applied to the planar substrate, wherein the barrier layer comprises: at least one starch comprising a weight average of the molecular distribution M.sub.w in the range of 0.8 million to 50 million g/mol, 0-70% by weight of at least one plasticizer, wherein the plasticizer portion is based on starch plus plasticizer, 0-50% by weight of at least one polymeric additive, wherein the portion of the polymeric additive(s) is based on starch plus polymeric additive, 0-5% by weight of an additive or of an additive mixture, based on the dry mixture, and, optionally, water bound in the barrier layer.

2. The packaging material according to claim 1, wherein the barrier layer is obtained from a coating compound comprised of: the at least one starch, 0-70% by weight of the at least one plasticizer, wherein the plasticizer portion is based on starch plus plasticizer, 0-50% by weight of the at least one polymeric additive, wherein the portion of the polymeric additive(s) is based on starch plus polymeric additive, 0-5% by weight of the additive or of the additive mixture, based on the dry mixture, and water, wherein the at least one starch of the coating compound is present in dissolved form and has a weight average of the molecular weight distribution M.sub.w in g/mol in the range of 0.8 million to 50 million, and the lower limit as well as the upper limit for the portion of the at least one starch in the coating compound in % by weight, based on starch and plasticizer and water, is provided in dependence on the molecular weight M.sub.w of the starch by: TABLE-US-00003 M.sub.w million g/mol 0.8 1 1.5 2 2.3 2.5 2.8 3 6 7 8 9 10 12 15 20 lower 14.4 14.1 13.3 12.6 12.2 11.9 11.5 11.1 6.7 5.2 3.7 2.5 2.4 2.2 2.1 1.7 limit upper 40.6 40.3 39.6 38.8 38.5 38.1 37.7 37.4 32.9 31.4 30.0 28.5 27.0 24.0 19.6 12.2 limit wherein the lower and upper limits for the portion of the at least one starch comprising a weight average of the molecular weight distribution M.sub.w, which lie between the values or outside of the values of the above Table, are obtained by means of linear interpolation or by means of linear extrapolation.

3. The packaging material according to claim 2, wherein the at least one starch in the coating compound comprises tapioca starch, pea starch, potato starch or any mixture thereof.

4. The packaging material according to claim 2, wherein an amylose content of the at least one starch in the coating compound is in the range of 0 to less than 60% by weight.

5. The packaging material according to claim 2, wherein the coating compound comprises at least 5% by weight of the at least one plasticizer.

6. The packaging material according to claim 2, wherein the at least one plasticizer of the coating compound comprises a plurality of plasticizers, wherein at least 5% of each one of the plurality of plasticizers are represented in the combination.

7. The packaging material according to claim 2, wherein the coating compound comprises maximally 30% by weight of the at least one polymeric additive.

8. The packaging material according to claim 2, wherein the at least one polymeric additive of the barrier layer comprises xanthan and/or polyvinyl alcohol.

9. The packaging material according to claim 2, wherein the at least one starch of the coating compound is selected from the group consisting of tapioca starch, pea starch and potato starch, and the starch is a hydroxypropylated starch comprising a molecular weight in million g/mol of 1 to 20 wherein the plasticizer content of the coating compound in % by weight, based on starch and plasticizer, is in the range of 0-45%, and the starch content of the coating compound in % by weight, based on starch and water and plasticizer, is in the range of 14 to 35%.

10. The packaging material according to claim 1, wherein the barrier layer is applied to an outer surface of the planar substrate, which corresponds to the rear side of the packaging material and thus to the inside of a packaging, which is to be created.

11. The packaging material according to claim 1, wherein the planar substrate additionally comprises a precoat which is arranged between the substrate surface and the barrier layer.

12. A packaging comprising the multi-layer packaging material according to claim 1, wherein the barrier layer forms the inside of the packaging.

13. The packaging material according to claim 1, where the at least one starch comprising a weight average of the molecular distribution M.sub.w in the range of 0.8 million to 20 million g/mol.

14. The packaging material according to claim 11, wherein the precoat is a mineral precoat.

15. The packaging material according to claim 8, further comprising 0.01 to less than 2.5% by weight of the xanthan and/or 1 to 30% by weight of the polyvinyl alcohol.

16. The packaging material according to claim 15, further comprising 1 to 10% by weight of the polyvinyl alcohol.

17. The packaging material according to claim 1, wherein the barrier layer further comprises polyvinyl alcohol in % by weight, based on starch and polyvinyl alcohol, present in the range of 1 to 30.

18. The packaging according to claim 12, comprising further layers in addition to the barrier layer.

Description

BRIEF DESCRIPTION OF THE FIGURE

(1) FIG. 1 shows, schematically, a coating system according to the prior art, as it is common in the finishing of paper.

ANALYTIC METHODS

(2) Determining the Application Weight

(3) A paper having a known surface is dried in a circulating air oven at 130° C. for 15 min and is then weighed. The surface weight of the untreated paper can be obtained in g/m.sup.2 from the weight and the known surface.

(4) A coated paper having a known surface is dried in the same manner and is weighed and the surface weight of the coated paper is thus obtained in g/m.sup.2. The surface weight of the coating is obtained in g/m.sup.2 from the difference of the two surface weights.

(5) Determining the Molecular Weight M.sub.w

(6) M.sub.w is understood to be the weight average of the molecular weight distribution.

(7) If the starch is present in the form of powder, the starch is suspended in water with a concentration of 3% of dry substance. This suspension is then heated up in a mini autoclave to 150° C. by being stirred and is held there for 20 min. The solution obtained in this manner is then cooled down to approximately 60° C., is thinned to 0.3%, and is filtered with a 0.005 mm membrane filter. The filtered solution is then measured with GPC-MALLS (gel permeations chromatography with multi-angle laser light scattering).

(8) If the starch is to be analyzed with regard to its molecular weight in a barrier layer on a paper, the following 2 methods can be used to obtain the starch solution.

(9) 1) The starch is scraped off the paper by means of a scalpel or it is abraded using a fine abrasive paper. The powdery material obtained thereby can be transferred into a solution, as is present for the above-described starch, which is present in the form of powder, in the same manner.

(10) 2) In the alternative, the barrier layer can be analyzed together with the paper. For this purpose, the material is cut into pieces of approx. 2*2 mm, is suspended in the autoclave and is stirred at room temperature overnight. The same process as described above for starches in the form of powder is then carried out. In response to the filtration, however, a coarse filter is used first, so as to filter out the insoluble paper components. Due to the fact that common papers can already include starch even without a barrier layer, a reference measurement is made, if necessary, with the uncoated paper or a reference measurement is made with the paper, from which the barrier layer was removed mechanically, respectively. An assessment can then be made from the reference measurement, which components are to be attributed to the barrier and which components are to be attributed to the paper during the GPC-MALLS analysis.

(11) An Alliance 2695 separation module from Waters, a DRI detector 2414 from Waters, a MALLS detector Dawn-HELEOS from Wyatt Technologie comprising a wavelength of 658 nm and a K5 flow-through cell were used for the measurements. A SUPREMA gel column set was used for the GPC column, exclusion limits S30000 with 10E8-10E6, S1000 with 2E6-5E4, S100 with 1E5-1E3. Eluent: DMSO with 0.09 m NaNO.sub.3. Temperature: 70° C. Evaluation: Astra software 5.5.0.18. A refractive index increment do/dc of 0.068 was used for the calculation.

MODES FOR CARRYING OUT THE INVENTION

EXAMPLE 1

(12) Starch: Hydroxypropylated pea starch comprising M.sub.w=4,500,000 g/mol

(13) Formulation: (unless specified otherwise, all quantities refer to the total formulation) 18.0% by weight of starch dry 10.2% by weight of glycerin, corresponds to 36.17% by weight of glycerin, based on starch and glycerin, and 71.8% by weight of water 100% by weight total

(14) The mixture was cooked in a batch cooker comprising an anchor stirrer at 95° C. for approximately 45 min, so that a clear, homogenous solution comprising a solids content of 28.2% was created. This solution had a viscosity of 370 mPas at 50° C.

(15) Paper: 230 g/m.sup.2, without rear side coating

(16) Coating aggregate: combo blade comprising flat doctor 20mm (0.8 bar contact pressure)

(17) Web speed: 350 m/min

(18) Application weight dry: 9.6 g/m.sup.2

(19) Drying setting: IR heater (65%), dry air: 160° C. (12 m drying section)

(20) Quick test with spray oil showed a significant reduction of the permeability for hydrocarbons.

EXAMPLE 2

(21) Starch: hydroxypropylated pea starch comprising M.sub.w=4,500,000 g/mol

(22) Formulation: (unless specified otherwise, all quantities refer to the total formulation) 17.8% by weight of starch dry 1.9% by weight of PVA (88% hydrolyzed, dynamic viscosity of 8 mPas at a 4% solution and 20° C.) 7.3% by weight of glycerin, corresponds to 29.0% by weight of glycerin, based on starch and glycerin, and 72.8% by weight of water 99.8% by weight total

(23) The mixture was cooked in a batch cooker comprising an anchor stirrer at 95° C. for approximately 45 min, so that a clear, homogenous solution comprising a solids content of 27.0% was created. This solution had a viscosity of 260 mPas at 50° C. 0.2% by weight of a commercially available wetting agent was added to the mixture, so as to obtain a stable curtain in response to the curtain coating.

(24) Paper: 230 g/m.sup.2, comprising a coating according to example 1

(25) Coating aggregate: curtain coater

(26) Web speed: 100 m/min

(27) Application weight dry: 11 g/m.sup.2

(28) Drying setting: IR heater (65%), dry air: 160° C. (12 m drying section)

(29) A measurement of the mineral oil migration from the cardboard through the coating was carried out in the style of method DIN14338 (so-called “Tenax method”) and resulted in a barrier effect of 99.1% for MOSH and MOAH. After creasing and folding the paper, a barrier effect of 98.2% was obtained.

EXAMPLE 3

(30) Starch: hydroxypropylated pea starch comprising M.sub.w=20,960,000 g/mol

(31) Formulation: (unless specified otherwise, all quantities refer to the total formulation) 8.6% by weight of starch dry 0.2% by weight of PVA (98% hydrolyzed, dynamic viscosity of 40 mPas with a 4% solution and 20° C.) 4.6% by weight of glycerin, corresponds to 34.84% by weight of glycerin, based on starch and glycerin, and 86.6% by weight of water 100% by weight total

(32) The mixture was cooked in a batch cooker comprising an anchor stirrer at 95° C. for approximately 45 min, so that a clear, homogenous solution comprising solids content of 13.4% was created. The solution had a viscosity of 600 mPas at 40° C.

(33) Paper: commercially available folding box cardboard comprising 329 g/m.sup.2, comprising a coating according to example 1

(34) Coating aggregate: roll doctor C50, 1 bar contact pressure

(35) Web speed: 200 m/min

(36) Application weight dry: 8 g/m.sup.2

(37) Drying setting: IR heater (80%), dry air: 260° C. (12 m drying section)

(38) Quick test with spray oil showed a significant reduction of the permeability for hydrocarbons.

EXAMPLE 4

(39) Starch: hydroxypropylated pea starch comprising M.sub.w=20,960,000 g/mol

(40) Formulation: (unless specified otherwise, all quantities refer to the total formulation) 7.2% by weight of starch dry 0.2% by weight of PVA (98% hydrolyzed, dynamic viscosity of 40 mPas with a 4% solution and 20° C.) 3.9% by weight of glycerin, corresponds to 35.14% by weight of glycerin, based on starch and glycerin, and 88.5% by weight of water 99.8% by weight total

(41) The mixture was cooked in a batch cooker comprising an anchor stirrer at 95° C. for approximately 45 min, so that a clear, homogenous solution comprising solids content of 11.3% by weight was created. This solution had a viscosity of 320 mPas at 37° C. 0.2% by weight of a commercially available wetting agent was added to the mixture.

(42) Paper: the coated paper from example 3

(43) Coating aggregate: curtain coater

(44) Web speed: 100 m/min

(45) Application weight dry: 11.7 g/m.sup.2

(46) Drying setting: IR heater (60%), dry air: 250° C. (12 m drying section)

(47) The migration measurement for MOSH/MOAH resulted in a barrier effect of 97.4%. After creasing and folding, a barrier effect of 96.0% was obtained.

EXAMPLE 5

(48) Starch: hydroxypropylated pea starch comprising M.sub.w=170,000 g/mol

(49) Formulation: (unless specified otherwise, all quantities refer to the total formulation) 29.6% by weight of starch 10.8% by weight of glycerin, corresponds to 26.8% by weight of glycerin, based on starch and glycerin, and 59.6% by weight of water 100% by weight total

(50) The mixture was cooked in a batch cooker comprising an anchor stirrer at 95° C. for approximately 45 min, so that a clear, homogenous solution comprising a solids content of 40.4% was created. This solution had a viscosity of 1080 mPas at 43° C.

(51) Paper: raw cardboard comprising 250 g/m.sup.2

(52) Coating aggregate: roll doctor (20 mm smooth, contact pressure 0.8 bar)

(53) Web speed: 250 m/min

(54) Application weight dry: 12.8 g/m.sup.2

(55) Drying setting: IR heater (60%), dry air: 150° C. (12 m drying section)

(56) A second coating with the same starch solution was applied to the obtained coating (by adding 0.2% of wetting agent):

(57) Coating aggregate: curtain coater

(58) Web speed: 200 m/min

(59) Application weight dry: 8.6 g/m.sup.2

(60) Drying setting: IR heater (30%), dry air: 160° C. (8 m drying section)

(61) Migration measurements for MOSH/MOAH determined a barrier effect of just under 30%. SEM picture of the coating showed numerous tears comprising a width of a few micrometers.

LIST OF REFERENCE NUMERALS

(62) 1 raw paper roll 1′ coated paper roll 2 raw paper web 2′ paper web (coated) 3 guide rollers 4 coating device 5 application roller 6 coating sump 7 doctor 8 dryer 9 hot air dryer 10 paper web 11 application aggregate/blade coater 12 roll doctor 13 spraying device 14 steam shower 15 IR dryer