The invention relates to a method for processing plastic material as defined in the preamble of claim 1 and to the processed plastic material as defined in the preamble of claim 8.

Known from the prior art are many different plastic-based materials.

Also known from the prior art are electrically charged note sheets and the like formed from plastic-based material that can be attached on different bases by means of the electrical charge. In addition, known from the prior art are different sticker- and adhesive-surfaced note sheets formed from plastic- and paper-based materials, the problem of which is that the sticker or adhesive surface easily leaves a mark on the base on which it has been attached.

The problem in the plastic-based materials known from the prior art is that they are difficult to be printed. Plastic-based material cannot be conventionally printed by the generally known printing methods because the printing ink cannot be adhered and absorbed in the plastic-based material, whereby the printing ink will not dry and the impression becomes messy and staining. In addition, spreading the printing ink on the surface of a plastic material often provides a waving effect in the material, whereby the material becomes cockled.

From EP 2289695 is known an electrostatic adsorbable sheet. From WO 01/030588 is known adherent plastic notes. From EP 0328353 is known a method for providing a substrate with a writing surface. From EP 0789281 is known a liquid toner printable thermoplastic film.

An objective of the invention is to eliminate the drawbacks referred to above and to disclose a new type of a method for processing plastic material. Another objective of the invention is to disclose a new type of plastic material that is suitable to be printed by the known printing methods.

The method and the plastic material according to the invention are characterized by what has been presented in the claims.

The invention is based on a method for processing plastic material in order to print the plastic material. According to the invention, at least one surface of the plastic material is coated with at least one coating mixture that contains a pigment and a binder and an alcohol to provide a coating layer and to increase pore volume to the surface of the plastic material, and the plastic material is selected so as to be able to receive an electrical charge, and the plastic material is charged electrically before coating or after coating, and the plastic material is provided onto a carrier material. Preferably, at least one surface of the plastic material is coated with at least one coating layer.

In addition, the invention is based on the corresponding processed plastic material. According to the invention, the plastic material selected so as to be able to receive an electrical charge is processed by coating at least one of its surfaces with at least one coating mixture that contains a pigment and a binder and an alcohol to form a coating layer and to increase pore volume on the surface of the plastic material. The plastic material is has been charged electrically before coating or after coating. The plastic material is provided onto a carrier material.

The invention is specifically based on the coating of plastic material, such as a plastic web, sheet or the like, so as to provide a good base for printing in order to print the plastic material by any printing technique. The invention is based on the basic idea of providing increased pore volume to the surface of the dense plastic material and absorbing the printing ink better and faster in the surface of the plastic material. In addition, the invention is based on the processing of electrically charged or electrically chargeable plastic material so that the plastic material will be easily printable by a desired printing technique.

Electrically charged plastic material in this context refers to electrically charged material that is self-adhesive by virtue of the electrical charge. Electrically chargeable plastic material in this context refers to electrically chargeable material that is self-adhesive after generation of the electrical charge.

The purpose of the coating layer that is formed from a coating mixture is, in the context of this invention, to act as a printing ink adhesion basis in which the printing ink is absorbed and adhered irrespective of the printing method. The coating layer must be functional in home printing as well as in industrial printing. Each coating layer may be formed from the same coating mixture. Alternatively, at least one coating layer is formed from a. different coating mixture than the rest of the coating layers. In one embodiment, the surface of the plastic material is provided with a first and a second coating layer, and the second coating layer is formed from a different coating mixture than the first coating layer.

In one embodiment of the invention, the coating mixture contains 5 to 80 w-% of the binder, in one embodiment 10 to 30 w-% of the binder.

In one embodiment of the invention, the coating mixture contains 30 to 70 w-%, in one embodiment 40 to 60 w-%, of alcohol.

In one embodiment of the invention, the binder is selected from the group of latex, starch, protein, e.g. casein, adhesive, resin and their combinations.

In one embodiment of the invention, the coating mixture contains an additive and/or a filler. The filler may have been selected from the coating mixture fillers known per se.

In one embodiment of the invention, the coating mixture contains an additive, such as a rheology modifier, e.g. CMC, to modify the rheology, e.g. to raise the viscosity. In one embodiment, the coating mixture contains less than 1.5 w-%, in one embodiment approximately 1 w-%, of the additive for raising the viscosity.

In one embodiment, the additives may include other suitable and desired additives, e.g. colorants, auxiliary pigments, strength improving agents, plasticizers, lubricants, wet strength improving agents, dispersing agents, defoamers and/or optical brighteners or other agents required by the purpose of use.

In one embodiment of the invention, the pigment is selected from the group of mineral-based pigments, calcium carbonates, such as PCC and GCC, kaolin, talc, gypsum, titanium dioxide, organic pigments, e.g. plastic pigments, cellulose-based pigments and their different combinations. In one embodiment, the employed pigment is a combination of several pigments to obtain the best properties, e.g. lightness, porosity, printing ink absorption, runnability, opacity, gloss, bulk etc. for the coating layer.

In one embodiment, the size of the pigment particles in the coating mixture is less than 10, µm, preferably 0.2 to 5 µm, in the coating of the plastic material.

In one embodiment, the amount of coating in the coating layer on the surface of the plastic material ranges from 1 to 40 g/m², in one embodiment from 5 to 10 g/m², in one embodiment from 10 to 20 g/m², in one embodiment is at least 20 g/m² and in one embodiment from 20 to 30 g/m². Preferably, the thickness of the coating layer depends on the employed printing method and the employed amount of ink. Preferably, the coating layer acts as an absorber for the solvent in the printing ink. Preferably, the thickness of the coating layer is defined so as to prevent a heat shock effect during printing on the surface of the plastic material, e.g. in laser printing.

In one embodiment of the invention, the plastic material is precoated with a preliminary mixture before coating the plastic material with the coating mixture. Coating with the preliminary mixture and the coating mixture may be effected substantially in the same process or sequentially in a two-step process or in completely different processes. In one embodiment, the preliminary mixture contains a pigment and a binder. In one embodiment, the preliminary mixture contains latex but not substantially a pigment. In one embodiment, the preliminary mixture has substantially the same composition as the coating mixture but may have a coarser particle size distribution. In one embodiment, the preliminary mixture includes an additive. By precoating, it is possible to improve the adhesion and spreading of the coating mixture on the surface of the plastic material. In one embodiment, the amount of precoating is approximately 1 to 5 g/m². In one embodiment, the size of the pigment particles in the preliminary mixture is less than 10 µm, preferably 1 to 5 µm.

In one embodiment, the plastic material is selected from any suitable plastics and their different combinations. In one embodiment, the plastic material is selected so as to be able to receive an electrical charge. In one embodiment, the plastic material is polypropylene or a derivative thereof. The plastic material may be present in the form of a web, film, sheet or the like.

In one embodiment of the invention, the plastic material is electrically chargeable. In one embodiment, the plastic material is charged electrically. In one embodiment, the plastic material is charged electrically before coating. This way, the surface of the plastic material is provided with surface energy, which improves spreading of the coating mixture on the surface of the plastic material and its adhesion on the surface of the plastic material. In one embodiment, the plastic material is charged electrically after coating. In one embodiment, the electrical charging is effected by means of a corona treatment.

In one embodiment, the amount of the electrical charge provided to the plastic material depends on the thickness and thereby the weight of the coating layer. In one embodiment, the electrical charge must be raised as the weight of the material increases.

In one embodiment of the invention, the plastic material is provided onto a carrier material. The carrier material facilitates the processing of the plastic material. Preferably, the plastic material can be separated from the carrier material when it is being brought into use and is to be attached to a desired position and to a desired base. As the plastic material is separated from the carrier material, the electrical charge of the plastic material is activated and the plastic material can be attached to the desired base.

In one embodiment of the invention, an insulation layer is provided between the plastic material and the coating layer. By the insulation layer, the plastic material can be protected e.g. in the printing from the effect of heat and heat shocks.

The plastic material may be formed by any method and/or device known per se. The plastic material may be of any color, and it may be monochromatic or patterned. The surface of the plastic material may be modified, e.g. grooved.

In one embodiment, the plastic material is coated by blade coating, spray coating, rod coating, film transfer coating, curtain coating, offset machine, rotogravure machine or flexographic press or their different combinations. In one embodiment, the plastic material is coated by blade coating. In one embodiment, the plastic material is coated by spray coating. In one embodiment, the precoating and actual coating of the plastic material can be effected by the same coating method or alternatively by different coating methods.

In one embodiment, the coated plastic material is dried after coating or between the different coating steps.

In one embodiment of the invention, the coated plastic material is used in printing selected from the group of: offset printing, digital printing, laser printing, inkjet printing and their combinations.

The plastic material can be colored and/or patterned in connection with the manufacture, coating and/or printing of the plastic material. The plastic material according to the invention can be manufactured with a mat or glossy surface.

The material according to the invention can be used as note sheets, memos, posters, decorative material, interior decoration material, window decorations or in equivalent purposes of use. The material according to the invention can be used in households, offices, commerce or other desired applications.

The plastic material according to the invention is not dependent on the printing method, but the coated plastic material can be printed by any printing technique.

The coating layer according to the invention absorbs the printing ink, whereby the surface of the plastic material becomes tack-free practically immediately after printing.

The plastic material according to the invention provides new possibilities for use. The plastic material according to the invention can be used as such or e.g. as combined material with another material.

Another advantage of the invention is that the coated plastic material is inexpensive to manufacture, and the desired material can also be manufactured in small batches.

In the following section, the invention will be described with detailed examples of its embodiments.

Coating mixtures according to the invention were formed in the tests and spread on the surface of an electrically charged polypropylene material. The electrically charged polypropylene material was used to form electrically charged, self-adhesive note sheets.

The coating compositions contained as a pigment 50 w-% of calcium carbonate, GCC (HC-60), and as a binder 10 w-% of latex. The coating mixture consisted mainly of round and coarse calcium carbonate particles, the size of which ranged from 0.2 to 5 µm. In addition, the coating mixtures contained approximately 1 w-% of CMC and 40 w-% of water and, in some cases, 1 to 2 w-% of alcohol.

Before coating, the polypropylene material was charged electrically by a corona treatment to form a self-adhesive plastic film and precoated by a preliminary mixture that contained latex. The precoating was provided to the surface of the polypropylene by approximately 3 g/m².

The polypropylene material was coated with the coating mixtures by sheet blade coating to form a coating layer on the surface of the polypropylene material. The amount of the coating layer was approximately 20 g/m². Blade coating is a coating method that is known per se and is not described in more detail in this connection. The coating mixtures were well spread on the surface of the polypropylene material.

The precoating and coating of the polypropylene material were effected in sequential steps.

The coated polypropylene materials were printed by different printing methods; inkjet, laser printing and digital printing technique.

Coating mixtures according to the invention were formed in the tests and spread on the surface of an electrically charged polypropylene material.

The coating mixtures contained as a pigment 35 w-% of calcium carbonate, GCC (HC-60), and as a binder 30 w-% of resin. The coating mixture consisted mainly of round and coarse calcium carbonate particles, the size of which ranged from 0.2 to 5 µm. In addition, the coating mixtures contained approximately 30 to 40 w-% of alcohol.

The polypropylene material was coated with the coating mixtures by film transfer coating to form a coating layer on the surface of the polypropylene material. The amount of the coating layer was approximately 15 g/m². The coating mixtures were well spread on the surface of the polypropylene material.

Precoating and two surface coatings of the polypropylene material were effected in sequential steps.

The coated polypropylene materials were printed by different printing methods; inkjet, laser printing and digital printing technique.

Coating mixtures according to the invention were formed in the tests and spread on the surface of an electrically charged polypropylene material. The polypropylene material was provided by lamination onto paperboard that acted as a carrier material.

The coating mixtures contained as a pigment 20 w-% of calcium carbonate, GCC (HC-60), and as a binder 40 w-% of resin. The coating mixture consisted mainly of round and coarse calcium carbonate particles, the size of which ranged from 0.2 to 5 µm. In addition, the coating mixtures contained approximately 1 w-% of a plasticizer, e.g. calcium stearate, and 40 w-% of alcohol.

The polypropylene material was coated with the coating mixtures by sheet blade coating to form a coating layer on the surface of the polypropylene material. The amount of the coating layer was approximately 10 g/m2. The coating mixtures were well spread on the surface of the polypropylene material.

Precoating and coating of the polypropylene material were performed sequentially.

The coated polypropylene materials were printed by different printing methods; inkjet, laser printing and digital printing technique.

It was discovered that large pore volume and large pores wherein the printing ink was well absorbed were provided in all tests to the surface of the plastic material by the tested coating mixtures. In addition, the printing ink was well adhered to the coating layer, and the surface of the coated material was practically immediately tack-free.

It was discovered that the invention provides for the easy printing of plastic material without staining. In addition, in additional tests it was discovered that a plastic material that is suitable to be printed was provided using many different coating mixture ratios.

The method for processing plastic material and the processed plastic material according to the invention are suitable in different embodiments to be used in different printing purposes.

The invention is not limited merely to the examples referred to above; instead, many variations are possible within the scope of the inventive idea defined by the claims.