PAPER SHEET MATERIAL WITH A PLASTIC-LIKE TACTILE EFFECT AND METHOD FOR THE PRODUCTION THEREOF

Description

The present invention relates to a paper sheet material with a plastic-like tactile effect and to the method for the production thereof.

Several types of paper having a plastic-like tactile surface effect have been present on the market for some time.

Such papers have application, for example, in the sector of packaging for high-end products.

One of the greatest drawbacks tied to the use of these papers is represented by their not always adequate suitability for being printed on precisely because of the surface treatments to which they are subjected in order to obtain the desired plastic-like tactile effect.

Among the surface treatments adopted, there are those based on compositions including kaolin and a polyurethane-based polymeric material, as well as silica or in any case a silicone product, to impart to the paper material the plastic-like tactile effect.

Such compositions are spread on the surface of a paper substrate.

Such surface treatments, in addition to risking impairing printability and print quality, may give rise to other drawbacks in the finished product, including a high cost and the difficulty of recycling.

The technical task of the present invention is thus to provide a paper sheet material with a plastic-like tactile effect and a method for the production thereof that enables the aforesaid technical drawbacks of the prior art to be overcome.

Within the scope of this technical task, one object of the invention is to provide a paper sheet material with a plastic-like tactile effect with adequate suitability for being printed on with high print quality.

Another object of the invention is to provide a paper sheet material with a plastic-like tactile effect that is easily recyclable.

Another object of the invention is to provide a paper sheet material with a plastic-like tactile effect that may be more easily produced.

The technical task, as well as these and other objects, are achieved according to the present invention by providing a paper sheet material comprising a paper substrate having a uniform coating layer on at least one face thereof, said coating layer having a composition comprising silica and/or a silicone product to impart to the paper material a plastic-like tactile effect and in addition a polymeric component and a mineral component, characterised in that said polymeric component includes a polyurethane-based polymeric material and a styrene acrylic-based polymeric material, and said mineral component includes kaolin and precipitated calcium carbonate.

Obviously, one or both faces of the paper substrate can have a respective coating layer.

It has been found that the combined provision of a polymeric component including at least one polyurethane-based polymeric material and a styrene acrylic-based polymeric material and a mineral component including kaolin and precipitated calcium carbonate imparts adequate printability to the paper sheet material.

The print quality also benefits from the fact that the precipitated calcium carbonate increases the degree of white, which enhances the brilliance of colours when, as is in general envisaged, coloured pigments are added to the composition.

The presence of the styrene acrylic-based polymeric material contributes to creating an ideal porosity for anchoring printing inks and significantly reduces ink drying times.

The present invention also discloses a method for producing a paper sheet material, comprising a step of making a paper substrate by means of a continuous machine for the production of paper, a step of preparing a composition comprising silica and/or a silicone product to impart to the paper sheet material a plastic-like tactile effect and in addition a polymeric component and a mineral component, characterised in that a polyurethane-based polymeric material and a styrene acrylic-based polymeric material are included in said polymeric component, and kaolin and precipitated calcium carbonate are included in said mineral component, and in that a uniform layer of said composition is applied by spreading on at least one face of said paper substrate.

Other features of the present invention are defined, moreover, in the subsequent claims.

The paper sheet material, as stated, comprises a paper substrate formed, for example, from cellulose fibres, at least one polymeric substance, suitable for imparting mechanical strength to the cellulose fibres (dry and wet), and an inorganic filler, suitable for imparting good characteristics of machinability and chemical stability to the material.

Preferably, the polymeric substance included in the paper substrate comprises one or more resins based on colophony and/or an alkyl ketene dimer and/or acetyl succinic acid and/or epichlorohydrin and/or carboxymethylcellulose.

Preferably, the inorganic filler is a mineral filler comprising one or more substances selected in the group consisting of carbonates, kaolins, talc, and mixtures thereof.

The paper substrate has, as stated, a uniform coating layer on at least one face thereof, having a composition comprising silica and/or a silicone product to impart to the paper material a plastic-like tactile effect.

The silica is preferably a colloidal silica.

The salient aspect of the invention consists in the composition of the coating layer, which further comprises a polymeric component and a mineral component, wherein the polymeric component includes a polyurethane-based polymeric material and a styrene acrylic-based polymeric material, and the mineral component includes kaolin and precipitated calcium carbonate.

The polyurethane-based polymeric material is preferably elastomeric.

The kaolin used preferably has a lamellar structure, but a calcined or non-calcined kaolin can also be used.

A dry weight ratio between the polyurethane-based polymeric material and the styrene acrylic-based polymeric material in the polymeric component comprised between 1 and 5 has been found to be advantageous.

A dry weight ratio between the kaolin and the precipitated calcium carbonate in the mineral component comprised between 1 and 10 has also been found to be advantageous.

A dry weight ratio between the mineral component and the polymeric component comprised between 1 and 10 has likewise been found to be advantageous.

Table 1 below shows the dry weight percentage composition of the mineral component and the dry weight ratio between kaolin and precipitated calcium carbonate in the mineral component, for five different cases of mineral component indicated as Cm1, Cm2, Cm3, Cm4 and Cm5.

Table 2 below shows the dry weight percentage of the polymeric component and the dry weight ratio between the polyurethane-based polymeric material and the styrene acrylic-based polymeric material, for five different cases of polymeric component indicated as Cp1, Cp2, Cp3, Cp4 and Cp5.

Table 3 below shows the dry weight percentage composition of the polymeric component and of the mineral component and the dry weight ratio between the mineral component and the polymeric component, for five different mixtures M1, M2, M3, M4 and M5 obtained by combining Cm1 with Cp1, Cm2 with Cp2, Cm3 with Cp3, Cm4 with Cp4 and Cm5 with Cp5.

Finally, a dry weight ratio between the mineral component and the silica and/or the silicone product comprised between 10 and 100 has been found to be advantageous.

The composition preferably further comprises at least one water-retaining material included among carboxymethyl cellulose, polyvinyl alcohol and casein.

A dry weight ratio between the mineral component and the water-retaining material comprised between 50 and 200 has been found to be advantageous.

Although various grammages can be imagined, a grammage of the paper substrate comprised between 360 and 420 g/m² has given very satisfactory results.

It is obviously not ruled out that the paper substrate can have a lower grammage, for example comprised between 90 and 360 g/m².

The coating layer, by contrast, is applied on the face of the paper substrate with a grammage comprised between 5 and 20 g/m².

The outer surface of the coating layer preferably has a smoothness as determined with a Bendtsen test apparatus comprised between 70 and 250 ml/min and a Cobb water absorption index comprised between 18 and 30 g/m².

The process for producing the paper sheet material is substantially the following.

The paper substrate is initially made in the form of a web in a known way with a continuous paper manufacturing machine.

Once the paper substrate has been produced, each face thereof to be coated is smoothed until a smoothness of about 70 ml/min, determined with a Bendtsen test apparatus, and a Cobb water absorption index of about 18 g/m² are obtained.

At this point, one prepares the composition to be applied, wherein the polymeric material can be used, for example, in the form of an aqueous dispersion that can be polymerised after application on the paper substrate.

At this point, a uniform coating layer is applied on the face of the paper substrate by spreading with a coating machine with an air knife or trailing blade.

The application envisages leaving an amount of composition equal to about 10 g/m² (dry amount) on the face of the paper substrate.

Subsequently, the paper substrate thus coated is heated to bring to completion the polymerisation of the polymeric component.

For this purpose, the coated paper substrate is brought into a hot air or infrared oven and treated at a temperature comprised between 100° C. and 250° C., for example 150° C., for a heating time comprised between 30 seconds and 4 minutes, for example 2 minutes.

The paper material is then cooled by means of a flow of cold air at less than about 10° C. Finally, the paper material is aerated with a flow of air at room temperature.

The paper sheet material with a plastic-like tactile effect thus conceived is susceptible of numerous modifications and variants, all falling within the scope of the inventive concept; furthermore, all the details may be replaced by technically equivalent elements.

The materials used, as well as the dimensions, may in practice be any whatsoever according to needs and the state of the art.