DE4445193C2 - Coated paper / cardboard with low permeability for gaseous substances and their use - Google Patents

Description

The invention relates to a coated paper or cardboard for Packaging purposes, which has a low permeability to gaseous Has substances, in particular water vapor and / or oxygen and in the Barrier layers no ethylene homopolymer or halogen containing polymers or Copolymers such as e.g. B. contains polyvinylidene chloride and its use.

Packaging materials based on paper or cardboard, the gas impermeable Having coatings has long been state of the art. From the GB-PS 11 89 395 it is known to apply barrier layers on paper substrates, which as Pigment kaolin and as film-forming binder PVC, vinylidene chloride copolymers, Vinyl acetate homopolymer and vinyl acetate copolymers contain the oxygen to reduce permeability. The layers are made up of aqueous dispersion the backing paper applied.

DE-OS 15 69 337 describes a packaging material that is on paper, Glassine or foils as the carrier material has barrier layers, which cyclized rubber, a waxy material and a heat sealable contain film-forming polymer or a polymer mixture. Among the polymers are called ethylene / acrylate copolymers. The coated material is low Permeability to water vapor.

DE 15 46 441 C3 is directed to packaging paper, which is made from aqueous Dispersion applied barrier to reduce water vapor permeability. The barrier layer contains a mixture of polyethylene and a thermoplastic elastomeric polymer, the polymer being a is hydrolyzed copolymer of ethylene and an acrylic acid ester.

DE 40 26 040 A1 describes a plastic-coated paper / cardboard on which a polyamide barrier layer is applied by extrusion. As  Adhesion promoter is used with a coextruded layer made of an ethylene terpolymer Ethylene acrylic acid ester and maleic anhydride as comonomers or one Ethylene / acrylic acid copolymers with 3-9% comonomer content.

Laminates are known from WO 92/11952 A1, in which on carrier materials at least on one surface a metal layer and at least on one Surface of a layer of a vinylidene chloride copolymer is present. As Carrier materials are plastics, regenerated cellulose and paper. As Metals are called Fe, Cu, Al, Ti and their alloys, whereby aluminum is particularly preferred.

From DE 30 24 259 C2 is a metal-coated paper with low air and Moisture permeability known. There is a layer of one on a backing paper ionomeric resin from film-forming copolymers of ethylene and acrylic acid or Methacrylic acid and then a 10-100 nm thick metal layer applied. The Metal layer can still be covered with a protective layer.

The object of the present invention is to provide a packaging material with paper or To create cardboard as a carrier material that has a low gas permeability has, in particular for water vapor and / or oxygen, but not the Polymers containing environmentally harmful chlorine or in paper recycling contains problematic ethylene homopolymers in existing barrier layers.

This object is achieved by a coated paper or a coated cardboard with low permeability for gaseous substances with barrier layers of film-forming polymers applied to a carrier paper or cardboard, with the exception of polyvinyl chloride, polyvinylidene chloride or their copolymers and ethylene homopolymer, whereby on one of the main surfaces of the carrier paper or cartons arranged, in a quantity of 3-20 g / m² (dry weight applied first layer of film-forming polymers) one or more 10 nm to 200 nm thick metal layer (s) and / or metal oxide layer (s) and / or SiO _x layer ( en), where x is a number from 0.5 to 2, is (are) deposited and there is a covering layer of film-forming polymers applied in an amount of 0.02 to 2.0 g / m² (dry weight), characterized that the two layers of the film-forming polymer one or more copolymer (s) or graft copolymer (s) from ethylene un d contain α, β-ethylenically unsaturated bonds and monomers containing carboxyl groups, or carboxylated styrene-acrylate copolymer or carboxylated or non-carboxylated acrylate polymer or mixtures thereof as the main constituent of the film-forming polymer in the form in which the carboxyl groups are not in salt form. The amount of the top layer applied is preferably 0.5 to 15 g / m 2.

The layers of the film-forming polymers can additionally still contain pigments and usual auxiliary substances. Main ingredient of the film-forming polymer means that the layer is 70-100% by weight, preferably 90-100% by weight of the copolymer of Ethylene and comonomers with α, β-ethylenically unsaturated bonds and carboxyl group (s) and / or carboxylated styrene / acrylate copolymer and / or carboxylated or non-carboxylated Acrylate polymer based on film-forming polymer contains.

The further subclaims are directed to preferred embodiments of the invention and the use of the coated paper / cardboard as packaging material for moisture and / or oxygen sensitive products, e.g. B. food, cosmetic articles or medical products.

The inventive, at least three-layer composite coating of two layers with film-forming polymers and one in between arranged thin metal or metal oxide layer becomes a very low gas permeability of the coated Material reached. For water vapor, it is max. 5 g / m² and day, determined according to DIN 53 122 at 23 ° C and 100% relative Humidity. The water vapor permeability is preferably below 3 g / m² and day. It was also found that the oxygen permeability the coated according to the invention  Backing materials is very low and under 10 cm³ / m² day bar at 23 ° C and 75% relative humidity (DIN 53380, part 3, draft). This locking effect is with Total application weight of the composite coating of 5-30 g / m², preferred 8-20 g / m² achieved.

Surprisingly, it was found that ethylene-acrylic acid copolymers in particular and / or ethylene-methacrylic acid copolymers and / or carboxylated styrene Acrylic acid copolymer and / or carboxylated or non-carboxylated Acrylate polymer in combination with metal or metal oxide layers between the plastic layers are arranged, water vapor and / or oxygen result in permeability that is at least as good or better than that Barrier effect of the known layers of ethylene homopolymer or chlorine-containing Polymers.

The usual base paper, cardboard and real Parchment with basis weights of 30 g / m² to 500 g / m², preferably 50 g / m² up to 250 g / m², suitable. The surface of the paper to be coated should preferably have a low roughness and thus a high smoothness, such as. B. for machine-smooth coating base papers or coated base papers.

The metal layer or metal oxide layer or SiO _x layer with a thickness of 10 nm-200 nm, preferably 20 nm to 100 nm, can be processed by simple or multiple thermal vapor deposition or other conventional physical vapor deposition (PVD process), for example cathode sputtering of suitable metals, or in the case of metal oxides, applied to the precoated substrate in a reactive atmosphere. Suitable metals are, for example, aluminum, nickel, copper, zinc or their alloys; suitable oxides are e.g. As aluminum oxide or silicon oxide (SiOx), where x = 0.5 to 2, and mixed oxides of the metals.

In the case of metal layers, the layer preferably has a specific one Surface resistance of less than 10 ohms / cm². That is very particularly preferred Metal layer made of aluminum or aluminum alloys.

Deposition of such layers by thermal evaporation or sputtering under reduced pressure is a coating technique which is well known to the person skilled in the art, and in the present case it is possible to work under the usual conditions in order to achieve the layer thickness according to the invention. The layer can also be formed by multiple deposition. In the case of multiple deposition, the same or different metals and / or metal oxides and / or SiO _{x can be} deposited.

Both, the first and the top layer, contain as the main component of the film-forming polymers from one or more copolymer (s) or graft copolymer (s) Ethylene and α, β-ethylenically unsaturated bonds and carboxyl groups having monomers. The content of the comonomer containing carboxyl groups can, based on the weight of the copolymer, 5 to 30% by weight, preferably 15 to 25% by weight, most preferably about 20% by weight. Especially preferred comonomers are acrylic acid and methacrylic acid. But it can also Ethylene copolymers with other copolymerizable carboxyl-containing Comonomers can be used, such as. B. crotonic acid, maleic acid, fumaric acid.

Instead of or in combination with this copolymer, carboxylated ones can also be used or non-carboxylated acrylate copolymers and / or carboxylated styrene Acrylate copolymer can be used in the two layers. The carboxylated Styrene-acrylic acid copolymers or carboxylated acrylate polymers are preferred have an acid number in the range from 5 to 100, preferably 10 to 50.

It is also possible to have different ones in the first layer and the top layer to use or combine the above-mentioned film-forming polymers.  

The film-forming copolymers can be extruded from the melt Paper / cardboard can be applied. However, application is particularly preferred from aqueous dispersion and subsequent drying of the coating. The watery Dispersions of these copolymers preferably have an alkaline pH Range that can be achieved for example by adding NH₄OH.

The formation of the barrier layers can also be thinned by repeated application Layers are made to the desired thickness.

The barrier layer (s) according to the invention, which as the main constituent of the contains film-containing polymer (s), can also contain up to 60% by weight, based on the layer weight, one or more pigment (s) or one or more filler (s) contain, with platelet-shaped pigments are preferred. examples for flaky pigments are kaolin, bentonite, talc. But it can also TiO₂, SiO₂, chalk and others known for the coating of paper Pigments are used or used.

In the case of the application of the barrier layer from aqueous dispersion Pigments are added to the aqueous polymer dispersion, optionally in predispersed form. By using pigment (s), the suitability of the (s) Coated papers / cardboard for waste paper recycling have a positive influence. Further Auxiliaries as are customary for processing can be used. These include e.g. B. lubricants, anti-foaming agents, viscosity regulators, antistatic agents, Dispersing agents, anti-settling agents and dyes. The use of larger ones Amounts of waxes or fats should be avoided in order to introduce the paper / cardboard according to the invention to facilitate the waste paper cycle.

Together with that for the formation of the composite coating according to the invention essential special film-forming polymers already mentioned can still so that compatible other film-forming polymers can also be used. As another In principle, a large number of film-forming polymers for the barrier layers are suitable of polymers that are selected on the basis of the properties to be achieved.  

Of the other polymers or copolymers are ethylene homopolymer, Polyvinyl chloride, polyvinylidene chloride or their copolymers excluded. This additional further film-forming polymers / copolymers can be selected be made of water-soluble film-forming polymers such as polyvinyl alcohol, Polyacrylic acid, or from plastic dispersions consisting of (Meth) acrylic ester copolymers, styrene-butadiene copolymers, styrene-acrylate copolymers, styrene-butadiene-acrylonitrile copolymers, vinyl acetate (co) polymers.

If the first layer to be applied contains such a polymer, it is necessary to that this layer can be metallized or vaporized with metal oxide. For this is one to produce as hole-free as possible layer on the carrier material, on the The surface of the evaporated or sputtered material adheres well and chemically is not changed.

If the top layer contains such a polymer, layers are from 1 g / m² to 20 g / m² (dry weight), which are heat sealable, with good adhesion to the steamed layer preferred. The cover layers are still to protect the evaporated layer provided.

On the top layer, printing, painting z. B. with a nitrocellulose or polyurethane varnish can be applied as well as an adhesive or Laminating adhesive for subsequent lamination of the coated material be applied with another paper or cardboard, e.g. B. a pressure sensitive adhesive Polyacrylate or polyvinyl acetate or e.g. B. a conventional polyurethane lamination adhesive.

The barrier papers / boxes according to the invention are suitable for packaging sensitive goods, especially food that z. B. before water vapor or Oxygen or both should be protected. For this, from the Barrier paper packaging are produced, in particular the  Coating inside, that is attached to the packaged goods. In this case, a Packaging z. B. by sealing the outer film-forming layer against itself yourself or another packaging material. The protection of the packaged goods is however also given if the coating on that facing away from the packaged goods Paper side is attached.

Furthermore, the paper / cardboard can be covered with one or both sides Coatings, e.g. B. paint or printing, provided or with others Papers or boxes must be laminated.

By using the barrier paper / cardboard according to the invention with excellent barrier properties for gases you get packaging that can be produced inexpensively, fat-resistant, aroma-tight, heat-sealable and are resistant to kinks and folds. Neither occurs when packaging food sensory influence on the packaged goods. Through the metallization with z. B. Aluminum is obtained with light-tight packaging with or without metallic Appearance, depending on the choice of the top layer. By using metal oxides as thin interlayer, transparent coatings can be obtained.

The barrier papers are environmentally neutral and can be left without residues and without Burn occurrence of halogen-containing gases. They are especially for that Waste paper recycling suitable without additional measures, especially at Use of pigments. The coatings of the invention Ethylene copolymer can also e.g. B. at pH <10 and elevated temperature (<40 ° C) be redispersed, the paper fibers being released for the recycling of waste paper.  

Measurement methods

Water vapor permeability:
The water vapor permeability WDD was determined according to DIN 53122 part 2. Deviating from the climatic conditions specified there, 23 ° C and 100% relative humidity was chosen. Values are obtained in g of water per m² and day. The coating side of the samples faced the dry nitrogen stream.

Oxygen permeability

The oxygen permeability (OxTr) in cm³ / m² day bar became according to DIN 53380 part 3 (draft) determined at 23 ° C and 75% relative humidity. The coating side the samples were turned to the nitrogen flow.

transparency

The visual transparency of the samples was determined using a McBeth TD densitometer 528 (Wratten filter No. 106).

Surface resistance / layer thickness of the metallization

The surface resistance / sheet resistance was measured using a 4-point measurement with 1 V, 5 mm electrode spacing examined. The layer thickness is obtained from electron microscopic investigations (Verpackungsrundschau 44 (1993), 4, 23. . . 28).

The invention is described in more detail using the following examples:  

Examples Example 1 (comparative example)

A machine-smooth coating base paper of 70 g / m² becomes watery with a 25% ammoniacal dispersion of an ethylene-acrylic acid copolymer with a Acrylic acid content of 20% by weight (e.g. Tecseal E 712 from Trüb-Chemie) using a Roll doctor blade coated and dried at 130 ° C for 2 min in a drying cabinet.

The dry film is 10 g / m². The barrier against water vapor and Oxygen is insufficient (see Table 1).

Example 2 (comparative example)

As described in Example 1, the test is carried out with a dry film application of 20 g / m² carried out. The barrier effect against water vapor is despite the high Plastic application relatively bad (Table 1), the barrier effect against oxygen insufficient.

Example 3 (comparative example)

The experiment from Example 2 is carried out with an aqueous styrene-butadiene dispersion (e.g. Styrofan dispersion DS 2306 (50%) from BASF). In a dry film application of 10.4 g / m² is the barrier effect against water vapor and oxygen low (Table 1).

Example 4 (comparative example)

The coated paper from Example 3 is on the coated side High vacuum with an aluminum layer of approx. 70 nm into one Surface resistance of 1 ohm / cm² evaporated. A top layer of 10 g / m² Dry film application (Styrofan DS 2306) is then applied to the metallization upset. The water vapor and oxygen barrier effect is opposite Example 3 improved, but still insufficient (Table 1).  

Example 5

A machine-smooth coating base paper of 70 g / m² is made with a 25% ammoniacal dispersion of pH = 9 of an ethylene-acrylic acid copolymer with an acrylic acid content of 20% by weight (e.g. Tecseal E 712 from Trüb-Chemie) a roller doctor blade and coated at 130 ° C for 2 min in a drying cabinet dried. The dry film application of the first layer is 10 g / m². On the coated side of the paper is aluminum in a layer thickness of approx. 80 nm and a surface resistance below 1 ohm / cm² evaporated in vacuo. A covering layer with a dry film application of 10 g / m² applied, which has the same composition and in the same way how to apply the first layer. The barrier paper obtained points excellent barrier effect against water vapor and oxygen (Table 1).

Example 6

The experiment is carried out as described in Example 5, but with a Dry film application of the first layer of 20 g / m², which is achieved by applying twice 10 g / m² was obtained.

The barrier paper obtained has an excellent barrier effect against water vapor and oxygen (Table 1).

Example 7

A machine-smooth coating base paper of 60 g / m² becomes watery ammoniacal dispersion of pH = 9.5, consisting of a mixture of one Ethylene-acrylic acid copolymers (20% by weight acrylic acid) with commercially available powdered talc in a ratio of 60:40 (based on solids) by means of a Coating machine coated. The coating mass with a solids content  35% is applied to the paper with a roller and shortly thereafter using a roller squeegee or an air brush to the desired order quantity dosed. The paper coated in this way is used in several hot air dryer sections Dried 100 ° C to 130 ° C to a final moisture content of 4.5%. Of the Dry film application of this first layer is 6 g / m². On the coated side of the paper is aluminum in a layer thickness of 60 nm and one Surface resistance of 1 ohm / cm² in a vacuum metallizer for vapor-deposited sheet materials from the Leybold company. On the aluminum layer is a top layer with a dry film application of 4 g / m² in the same way and Way applied like the first layer. The barrier paper obtained demonstrates a total order of 10 g / m² excellent barrier effect against Water vapor and oxygen (Tab. 1). The paper can do this without any problems Waste paper recycling can be fed.

Example 8

The coating of the machine-smooth coating base paper of 60 g / m² is carried out as in Example 7. However, the first layer is different from Example 7 with a dry film application of 13 g / m² by double coating with 6.5 g / m² applied, the top layer by coating with a Dry film application of 11 g / m² applied. The barrier paper obtained points excellent, compared to Example 7 even further improved blocking effect against Water vapor and oxygen on (Tab. 1). The paper can do this without any problems Waste paper recycling can be fed.  

Example 9

A coated coating base paper of 67 g / m 2 becomes aqueous with a 32% strength ammoniacal dispersion with pH = 9.0 of an ethylene-acrylic acid copolymer with an acrylic acid content of 20% by weight (e.g. Tecseal E 799 from Trüb-Chemie) a roller doctor blade and coated at 130 ° C for 2 min in a drying cabinet dried. The dry film application is 16 g / m². On the coated side of the Paper becomes aluminum in a layer thickness of approx. 80 nm in a vacuum evaporated. A heat-sealable top layer is also applied to the aluminum layer a dry film application of 7 g / m² from an aqueous dispersion of a carboxylated Acrylate copolymers (glass transition temperature -5 ° C, acid number 25, solid 48%), to which small amounts of defoamers and antiblocking agents have been added, upset. The barrier paper obtained has an excellent barrier effect against water vapor (Tab. 1) and is heat sealable at approx. 120 ° C with the Coating side against paper or coating side against coating page.

Example 10

A 60 g / m² real parchment paper is made as in Example 9 with a first layer aqueous dispersion of a carboxylated styrene-acrylate copolymer (glass over temperature 22 ° C, acid number 65, solids 46%) at 10 g / m² dry film coated and then metallized with aluminum. On the The metal layer is then a dry film application of 10 g / m² of the same carboxy gelled styrene-acrylate dispersion applied. The barrier paper obtained points excellent barrier effect against water vapor (Table 1) and is at 120 ° C heat sealable.  

Example 11

The coated and metallized paper from Example 5 is on the metal layer with a top layer of an ethylene-methacrylate acid copolymer with a 15% methacrylic acid content from aqueous ammonical dispersion at pH 10 coated with a roller doctor blade and at 120 ° C for 2 min in a drying cabinet dried. The dry application of the top layer is 10 g / m². The received Barrier paper is heat sealable at 120 ° C and exhibits excellent Barrier effect against water vapor (Tab. 1).

Table 1

Measured values for the examples

Claims (10)

1. Coated paper / cardboard with low permeability for gaseous substances with barrier layers of film-forming polymers applied to the carrier paper or cardboard, with the exception of polyvinyl chloride, polyvinylidene chloride or their copolymers and ethylene homopolymer, whereby arranged on one of the main surfaces of the carrier paper or cardboard, in an amount of 3 to 20 g / m² (dry weight) applied first layer of film-forming polymers one or more 10 nm to 200 nm thick metal layer (s) and / or metal oxide layer (s) and / or SiO _x layer (s), where x is a number from 0.5 to 2, is (are) deposited and there is a covering layer of film-forming polymers applied in an amount of 0.02 to 20 g / m² (dry weight), characterized in that the two layers of the film-forming polymer one or more copolymer (s) or graft copolymer (s) of ethylene and α, β-ethylenically unsaturated bonds and carboxyl group containing monomers, or carboxylated styrene-acrylate copolymer or carboxylated or non-carboxylated acrylate polymer or mixtures thereof as the main component of the film-forming polymer in the form in which the carboxyl groups are not in salt form. 2. Coated paper / cardboard according to claim 1, characterized, that the applied amount of the top layer is 0.5 to 15 g / m².   3. Coated paper / cardboard according to claim 1, characterized, that the comonomer of ethylene acrylic acid and / or methacrylic acid is. 4. Coated paper / cardboard according to claim 1 or 3, characterized, that the first layer or the top layer as film-forming (s) Polymer (s), based on film-forming polymer (s), 70 to 100% by weight ethylene (meth) acrylic acid copolymer and / or carboxylated Styrene-acrylate copolymer and / or carboxylated or non-carboxylated acrylate polymer and 0 to 30% by weight of one or several film-forming polymers or copolymers from styrene-acrylate copolymers, styrene-butadiene copolymers, Styrene-butadiene-acrylonitrile copolymers, (meth) acrylate ester copolymers, Vinyl acetate (co) polymers, polyacrylic acid and Contains polyvinyl alcohol. 5. Coated paper / cardboard according to one of claims 1 to 4, characterized, that the first layer and / or the top layer 0 to 60 wt.% based on the total weight of the layer, one or more pigment (s) or contains one or more filler (s). 6. Coated paper / cardboard according to claim 1, characterized, that the copolymer of ethylene and α, β-ethylenically unsaturated Bonds and carboxyl-containing monomers 5 to Contains 30% by weight of this comonomer. 7. Coated paper / cardboard according to claim 5, characterized, that as a pigment or filler a platelet-shaped pigment is available.   8. Coated paper / cardboard according to claim 1, characterized, that the metal layer (s) or metal oxide layer (s) from one Metal and / or metal oxide of Al, Cu, Ni, Zn or their alloys exists. 9. Coated paper / cardboard according to claim 1, characterized, that the metal layer has a specific surface resistance of <10 ohms / cm². 10. Use the coated paper / cardboard after one of claims 1 to 9 for packaging moisture and / or oxygen sensitive material.