Paper sheet material with a glittering and reflective surface appearance

Abstract

The paper sheet material comprises a paper substrate, and a treatment layer applied to at least one surface of said paper substrate to impart a glittering and reflective appearance to said surface, said surface treatment layer being characterised in that it is formed from a dispersion including a dispersed phase comprising mica granules and a transparent binding dispersing phase comprising a polyurethane resin.

Description

[0001] PAPER SHEET MATERIAL WITH A GLITTERING AND REFLECTIVE SURFACE

[0002] APPEARANCE

[0003] DESCRIPTION

[0004] The present invention relates to a paper sheet material with a glittering and reflective surface appearance and to the method for the production thereof.

[0005] Numerous types of paper having a glittering and reflective surface effect have been present on the market for some time.

[0006] Such papers have application, for example, in the packaging industry and in the advertising industry.

[0007] 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 glittering and reflective effect.

[0008] Among the surface treatments adopted, there are those based on dispersions in which the dispersed phase consists of mica granules of varying dimensions and the dispersing phase consists of suitable natural and / or synthetic binders.

[0009] Such surface treatments, in addition to risking impairing printability, may pose other drawbacks, including the not always adequate effectiveness of the binders used, which may lead to defects in the finished product, such as, for example, a certain non-uniformity in the surface appearance imparted.

[0010] The technical task of the present invention is thus to provide a paper sheet material with a glittering and reflective surface appearance and a method for the production thereof that enables the aforesaid technical drawbacks of the prior art to be overcome.

[0011] Within the scope of this technical task, one object of the invention is to provide a paper sheet material with a glittering and reflective surface appearance with adequate suitability for being printed on.

[0012] Another object of the invention is to provide a paper sheet material with a glittering and reflective surface appearance that is uniform and lasts over time.

[0013] Yet a further object of the invention is to provide a paper sheet material with a glittering and reflective surface appearance that may be produced in a simple and repeatable manner using well-established techniques.

[0014] 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 and a treatment layer applied to at least one surface of said paper substrate to impart a glittering and reflective appearance to said surface, said surface treatment layer being characterised in that it is formed from a dispersion including a dispersed phase comprising mica granules and a transparent binding dispersing phase comprising a polyurethane resin.

[0015] The invention also discloses a process for manufacturing a paper sheet material, characterised by making a paper substrate by means of a continuous paper manufacturing machine, and applying a treatment layer to at least one surface of said paper substrate to impart a glittering and reflective appearance to said surface of said paper substrate, wherein said treatment layer includes a dispersion including a dispersed phase comprising mica granules and a transparent binding dispersing phase comprising a polyurethane resin.

[0016] Other features of the present invention are defined, moreover, in the subsequent claims.

[0017] The treatment layer may obviously be applied to only one or also both main surfaces of the paper sheet material.

[0018] The treatment layer may optionally be formed by a coating.

[0019] One of the most advantageous aspects of the invention consists in the reliance on a polyurethane resin to be used as a binder in the dispersing phase of the dispersion. The use of the polyurethane resin has surprisingly been found to be particularly suitable due to the fact that it performs a closure action on the treated surface, which is thus more homogeneous and consequently more suitable for the application of homogeneous layers of printing inks and, at the same time, due to the fact that it increases the binding power over the mica granules and consequently improves the quality and durability of the surface treatment.

[0020] The binding dispersing phase of the dispersion can advantageously further comprise at least one synthetic styrene acrylic and / or styrene butadiene latex.

[0021] It has been found that the use, in the dispersing phase of the dispersion, of a number comprised between 2 and 4 parts by weight of the synthetic latex for every part by weight of the polyurethane resin optimises the binding effect.

[0022] The mica granules in the dispersed phase of the dispersion have dimensions comprised between 2 and 300 pm.

[0023] It has surprisingly been found that the use of mica granules of large dimensions, particularly comprised between 150 and 300 pm, also improves the glittering and reflective effect without impairing printability.

[0024] The dispersion preferably has between 5 and 50% by weight of the dispersed phase.

[0025] The dispersed phase can be devoid of pigments or include coloured pigments and / or kaolin in addition to the mica granules.

[0026] The treatment layer has a grammage comprised between 5 and 15 g / m2, preferably comprised between 8 and 10 g / m2.

[0027] The treatment layer further has a viscosity comprised between 120 and 400 cP at 6 RPM, preferably comprised between 150 and 350 cP at 6 RPM.

[0028] The treatment layer is applied in an amount comprised between 1 and 5 % by weight of the paper material. The paper substrate comprises 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.

[0029] 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.

[0030] 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.

[0031] The process for manufacturing the aforesaid paper sheet material comprises making a paper substrate by means of a continuous paper manufacturing machine, and applying the treatment layer to at least one surface of the paper substrate to impart thereto a glittering and reflective appearance.

[0032] In order to favour the polymerisation of the polyurethane resin, the paper sheet substrate can be subjected to heating in an infrared or hot air oven.

[0033] Two possible compositions of the paper sheet material are shown below by way of example.

[0034] EXAMPLE 1

[0035] Paper sheet material

[0036] -paper substrate: 95% by weight

[0037] -treatment layer in the form of a coating: 5% by weight of which the paper substrate is of a type and composition known in the prior art, whereas the coating has the composition shown below.

[0038] Coating

[0039] Dispersing phase: 90% by weight of the dispersion, of which -polyurethane resin: 20% by weight

[0040] -synthetic styrene acrylic latex: 70%

[0041] -additives: 10%

[0042] Dispersed phase: 10% by weight of the dispersion, of which

[0043] -mica granules: 100% by weight

[0044] EXAMPLE 2

[0045] Paper sheet material

[0046] -paper substrate: 98% by weight

[0047] -treatment layer in the form of a coating: 2% by weight of which the paper substrate is of a type and composition known in the prior art, whereas the coating has the composition shown below.

[0048] Coating

[0049] Dispersing phase: 60% by weight of the dispersion, of which

[0050] -polyurethane resin: 30% by weight

[0051] -synthetic styrene butadiene latex: 60%

[0052] -additives: 10%

[0053] Dispersed phase: 40% by weight of the dispersion, of which

[0054] -mica granules: 75% by weight

[0055] - coloured pigments and kaolin: 25% by weight

[0056] The paper sheet material with a glittering and reflective surface appearance 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.

[0057] The materials used, as well as the dimensions, may in practice be any whatsoever according to needs and the state of the art.

Claims

CLAIMS A paper sheet material comprising a paper substrate and a treatment layer applied to at least one surface of said paper substrate to impart a glittering and reflective appearance to said surface, said surface treatment layer being characterised in that it is formed from a dispersion including a dispersed phase of between 5 and 50% by weight comprising mica granules having dimensions comprised between 2 and 300 pm, preferably between 150 and 300 pm, and a transparent binding dispersing phase comprising a polyurethane resin and at least one synthetic styrene acrylic and / or styrene butadiene latex, said dispersing phase of said dispersion having from 2 to 4 parts by weight of said synthetic latex for every part by weight of said polyurethane resin. The paper sheet material according to the preceding claim, characterised in that said dispersed phase also includes coloured pigments and / or kaolin. The paper sheet material according to any preceding claim, characterised in that said treatment layer has a grammage comprised between 5 and 15 g / m2. A process for manufacturing a paper sheet material, characterised by making a paper substrate by means of a continuous paper manufacturing machine, and applying a treatment layer to at least one surface of said paper substrate to impart a glittering and reflective appearance to said surface of said paper substrate, wherein said treatment layer includes a dispersion including a dispersed phase of between 5 and 50% by weight comprising mica granules having dimensions comprised between 2 and 300 m, preferably between 150 and 300 pm, and a transparent binding dispersing phase comprising a polyurethane resin and at least one synthetic styrene acrylic and / or styrene butadiene latex, said dispersing phase of said dispersion having from 2 to 4 parts by weight of said synthetic latex for every part by weight of said polyurethane resin.