LUMINESCENT MEMBRANE AND MAKING PROCESS OF THE SAME

The present invention relates to a luminescent membrane and a making process of the same, of the type specified in the preamble of the first claim.

In particular, the invention relates to a membrane adapted to be used, for example, in clothing, footwear, saddlery, helmets, coatings for bottle caps, flame-protective clothing, the use of coloured sheets for wrapping or packaging (various items as well as food), the veneering of furnishing surfaces such as, for example, furniture, or as a protective coating for machinery or the like. Similar membranes are described, for example, in patent application EP-A-3156224.

Different types of luminescent membranes are currently known and described, for example, in patent applications US-A-2004/0202850 and US-A-2008/0305310. These membranes have the particularity of lighting up and shining in a light-free environment and/or when they are excited by an external light striking the surface itself.

Patent application WO-A-2016/204636 discloses a process for producing a reflective photoluminescent coating by using a reflective photoluminescent powder paint.

The paint is therefore made of polyester, polyurethane, epoxy or mixed resin, adhesive substances, additives, phosphorus, and reflective glass beads, and undergoes a step of electrostatic dry spraying onto a substrate.

After annealing, the paint acquires the ability to react to the light it is exposed to, and therefore the coating is able to show its coloured pigments when there is light, and become phosphorescent when there is no light.

Patent application US-A-4623579, instead, describes an article comprising outer coupled layers of a thermoplastic resin between which a decorative layer is arranged, the latter comprising a composition comprising a colouring component having a phosphorescent dye and a fluorescent dye and a binding material resin. The binding material can be selected from polyester, polyurethane and acrylic polymers and copolymers, with a mixture of butadiene-acrylonitrile rubber and polyurethane composition.

The composite article is prepared by coating two resin films with the composition described above, followed by contacting the films on the coated surfaces and applying heat and pressure to bind them together so as to form the decorative composite article.

The described prior art has a few major drawbacks.

In particular, the above-described materials do not allow the luminescence or fluorescence characteristics to be maintained for a long time in the absence of light. Moreover, they do not simultaneously guarantee luminescence both in light and dark conditions.

Therefore, all the articles or the membranes described comprise expensive materials when compared to the purposes for which they are intended.

In addition, the structures constituting the above-mentioned devices are complex and/or need many additives in order to obtain, for example, the required luminescence characteristics.

The physical characteristics are accompanied by the costs and the complexity of the implementation procedures for obtaining the same.

In this context, the technical task underlying the present invention is to devise a luminescent membrane and a process of making the same, which are capable of substantially obviating at least some of the above-mentioned drawbacks. Within the scope of said technical task, a major object of the invention is to obtain a luminescent membrane capable of maximizing efficiency, yet reducing costs and complexity.

In particular, a major object of the invention is to provide a membrane, which is capable of maintaining luminescence for a long time in a light-free environment and capable of maintaining visibility effects even in the presence of light.

Another major object of the invention is to provide a process of manufacturing the luminescent membrane, which is simple and inexpensive.

The technical task and the specified objects are achieved by means of a luminescent membrane and a process of making the same as claimed in the appended claim 1 . Preferred embodiments are described in the dependent claims.

The features and advantages of the invention will be apparent from the detailed description of preferred embodiments of the invention, with reference to the accompanying drawings, in which:

Fig. 1 shows a diagram of the plant suitable for implementing the process according to the invention.

Fig. 2 shows the cross-section of a membrane according to the invention; and

Fig. 3 is a top view of a membrane according to the invention.

In the present document, the measures, values, shapes and geometric references (such as perpendicularity and parallelism), when associated with terms like "about" or other similar terms such as "almost" or "substantially", are to be understood as unless measurement errors or inaccuracies due to production and/or manufacturing defects and, especially, unless a slight difference from the value, measure, shape, or geometric reference with which it is associated. For example, these terms, if associated with a value, preferably indicate a difference not exceeding 10% of the value itself.

Furthermore, when used, terms such as "first", "second", "higher", "lower", "main" and "secondary" do not necessarily identify an order, a priority relationship or a relative position, but can simply be used to distinguish more clearly the different components from each other.

The measurements and the data reported in this text are to be considered, unless otherwise indicated, as carried out in the International Standard Atmosphere ICAO (ISO 2533).

With reference to the Figures, the luminescent membrane according to the invention is indicated as a whole by the numeral 1.

The membrane 1 preferably comprises a main film 3.

If the membrane 1 is a multilayer membrane, it may further comprise a secondary film 2 identifying, for example, the inner layer of the membrane 1 , which is adapted to contact an object to be coated or the skin.

In the case in which the secondary film 2 is present, the membrane 1 comprises an adhesive layer 4 interposed between the main film 3 and the secondary film 2 and adapted to integrally bond the main film 3 and the secondary film 2 together. Alternatively, the main film 3 and the secondary film 2 can be connected to each other by seams or the like.

Preferably, the secondary film 2 is a layer of refractive material, which is preferably a flexible and membrane material known per se and used, for example, in reflective safety vests or jackets for road use. Alternatively, the secondary film 2 is a polymeric layer comprising refractive portions or particles. Alternatively, the secondary film 2 is an elastic fabric or the like. Suitably, either one of the main film 3 and the secondary film 2 is pierced. In particular, the pierced film is the film that in the final use of the fabric will be arranged towards the outside, and preferably towards the main film 3. Consequently, both films 2 and 3 are visible from the outside (Fig. 3). The holes preferably have a diameter ranging from 0.5 cm to 5 cm, and the percentage of holes on the total surface is suitably between 10% and 60%.

The main film 3 preferably consists of a polyurethane resin main layer 3d and may comprise a base layer 3e.

Preferably, the main film 3 has a total thickness preferably ranging from 10 pm to 300 pm, and more preferably from 50 g/m ² to 150 g/m ² .

Preferably, the main layer 3d is a luminescent layer and further comprises luminescent particles consisting of luminescent oxides.

The luminescent oxides can, for example, consist of MAI2O4 where M is one or more metals selected from calcium, strontium and barium oxide, which can be inhibited with europium acting as a luminescence activator and may optionally contain other activators such as lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium or tin and bismuth as co-activators, as in SrAl204 (EU ²⁺ , Dy ³⁺ ).

Alternatively, they may consist of (M'xM' _y )Al204, where x+y=1 and I and M" are, for example, different from each other and selected from calcium, strontium and barium oxide, which can be inhibited by europium acting as an activator and may optionally contain other activators such as, for example, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium or tin and bismuth as co-activators; or Mi _-x Al204-x (where M is at least one metal selected from calcium, strontium and barium, or wherein M comprises magnesium and at least one metal selected from calcium, strontium and barium, where x is not zero and preferably has a value of between 0.3 and 0.6, the oxide can be inhibited by europium as the activator and may optionally contain other activators such as lanthanum,

cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium or tin and bismuth as the co-activators; or still LnB03, where Ln is at least one rare-earth element; M ₄ Ah ₄ 025, wherein M is one or more metals selected from calcium, strontium and barium oxide, which can be inhibited with europium as the activator and may optionally contain other activators such as lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium or tin and bismuth as co- activators; S AI15O25; M(ll)i-xEU(ll)xM(lll)pEU(lll)qTB(lll)rBgOi6 where M(ll) is at least one divalent metal selected from barium, strontium, lead and calcium, M (III) is selected from lanthanum, gadolinium, yttrium, cerium, lutetium and bismuth, with 0<x<0.2, and p, q, and r being different from zero, strictly comprised between -1 and 1 such that p+q+r=1 ; Lm-xTbxMgBsOio where Ln may comprise rare-earth elements or yttrium and 0<x<1 ; M5(i-a)Eu5a ²⁺ Si4X6 where M may be Ba-i-bSrb, with 0<b<0.1 , 0≤a<0.2 and X is Ch-cBr _c where 0≤c≤1 ; Lai _-x Sm _x OBr where 0<x≤0.1 ); ZnO: Zn; ZnO:Ga ₂ 0 ₃ :Bi; CaTi0 ₃ :Pr ³⁺ ; La ₂ Ti0 ₅ :Pr ³⁺ ; La ₂ Ti ₂ 07:Pr ³⁺ ; (La,Pr) ₂ Ti ₂ 0 ₇ ; (La,Yb,Pr) ₂ Ti ₂ 0y; YB0 ₃ :(Eu ³⁺ , Tb ³⁺ , Gd ³⁺ ); Y ₃ B0 ₆ :Eu ³⁺ , LnBOs (inhibited with Eu ³⁺ , Tb ³⁺ , Pr ³⁺ or Tm ³⁺ , inhibited or co-inhibited with Ce ³⁺ or Gd ³⁺ and Eu ³⁺ , Tb ³⁺ , Pr ³⁺ , Tm ³⁺ or Pr ³⁺ ); Ln ₃ B06 (inhibited with Eu ³⁺ , Tb ³⁺ , Pr ³⁺ or Tm ³⁺ , inhibited or co- inhibited with Ce ³⁺ or Gd ³⁺ and Eu ³⁺ , Tb ³⁺ , Pr ³⁺ , Tm ³⁺ or Pr ³⁺ ); Ln(B0 ₂ ) ₃ (inhibited with Eu ³⁺ , Tb ³⁺ , Pr ³⁺ or Tm ³⁺ , inhibited or co-inhibited with Ce ³⁺ or Gd ³⁺ and Eu ³⁺ , Tb ³⁺ , Pr ³⁺ , Tm ³⁺ or Pr ³⁺ ); Si0 ₂ (inhibited with rare-earth elements), Si0 ₂ :(Sm ³⁺ , Al ³⁺ ); AI(2-x-y)(Y,Ln)x03: yM where M may be Cr ₂ 03, V2O5, NiO, WOs, CuO, FeO, Fe ₂ Os and Ln can be Er, La, Yb, Sm, Gd and mixtures thereof, and 0.48<x<1.51 and 0.007<y<0.2); AI2O3 (inhibited with rare-earth elements).

The layer 3 is also preferably fluorescent because the main layer 3d is loaded with fluorescent particles of a known type or because it is coated with a fluorescent coating of a known type.

The main layer 3d preferably comprises one or more underlayers, suitably 3 or 4 underlayers, each of which is made by coating, for example hot coating, with polyurethane resins. In detail, it has an external underlayer 3a; an internal underlayer 3b interposed between the external underlayer 3a and, if present, the secondary film 2, and integrally bonded to the secondary film 2; and, preferably, an intermediate underlayer 3c interposed between the underlayers 3a and 3b.

The external underlayer 3a comprises a mixture of polyurethane resins with characteristics suitable for resisting to external agents and suitably providing "touch" features (surface relief effects).

The internal underlayer 3b and the intermediate underlayer 3c comprise a mixture of polyurethane resins reinforcing the first one with additives to yield technical features and optional pigmentation by means of dichromatic effects.

The underlayers 3a, 3b, 3c all mainly consist of polyurethane resins and may also contain luminescent oxides in any possible combination.

For example, each one of, or one or two selected from the underlayers 3a, 3b, 3c may contain luminescent oxides.

Preferably, the intermediate underlayer 3c comprises luminescent oxides, and at least one of, or both the underlayers 3a, 3b does/do not comprise luminescent oxides and may comprise polyurethane mixtures or have characteristics similar to the secondary film 2, and therefore comprise refractive particles that maintain the above described phosphorescent characteristics unchanged.

In detail, the main layer 3d preferably comprises total luminescent oxide concentrations ranging between 1 % and 80% of the final dry weight of the film, more preferably between 20 and 70%, more preferably between 40 and 60%, more precisely, it is, for example, in an amount of about 50% of the final dry weight of the film.

Preferably, the luminescent oxide is in the form of a powder. Therefore, the granular particles constituting the powder have, for example, dimensions between 25 pm and 350 pm, more preferably between 100 pm and 250 pm.

The base layer 3e is preferably made of fabric or other materials and may not be present. It is used to give better mechanical characteristics to the main film 3.

Alternatively, the main film 3 can be exclusively composed of the main layer 3d.

An adhesive underlayer 3f is suitably present between the main layer 3d and the base layer 3e for integrally bonding the main layer 3d and the base layer 3e together.

It is made of suitably cross-linked polyurethane.

If the secondary film 2 is included in the membrane 1 , interposed between the secondary film 2 and the main film 3, and in particular between the secondary film 2 and the internal underlayer 3b, the multilayer membrane 1 has an adhesive layer 4 integrally bonding the secondary film 2 and the underlayer 3b together.

The above-described multilayer membrane 1 is innovatively manufactured through a novel manufacturing process 10.

The process 10 for the membrane 1 comprises a transfer process and summarily provides a coating process, including manufacturing the main film 3 by coating a transfer paper 5 with at least one polyurethane solution; and, if applicable, connecting said main film 3 to a secondary film 2 for manufacturing the membrane

I when the membrane 1 is a multilayer membrane; and detaching the membrane 1 , i.e. the main film or the assembly of the main film 3 with the secondary film 2 from the transfer paper 5.

The transfer paper 5 is wound on a roll 5a and moved by one or more traction rollers

I I arranged at the end of the processing, along a processing line 10a preferably arranged along a horizontal plane, i.e. parallel to the gravitational gradient.

The coating process comprises at least one step of coating with a coatable, hence preferably liquid mixture of polyurethane resins, i.e. a mixture made of one or more polyurethane resins diluted with a solvent such as DMF (dimethylformamide) or water.

These polyurethane resins, as said, comprise luminescent oxides preferably of the type, according to the configurations and in the percentages as described above. Said luminescent oxides are appropriately inserted and preferably mixed in the coatable polyurethane resins prior to the coating of said coatable mixture.

The polyurethane resins optionally further comprise the components required for making the film 3 fluorescent, these components being known per se.

The coating step provides, in succession, a substep of depositing the polyurethane mixture; a distribution substep in which an adjusting blade distributes the mixture, resulting in an almost uniform thickness thereof; and a substep of drying the polyurethane mixture adapted to evaporate the solvent.

In particular, the manufacturing process 10 provides three or four consecutive coating steps, i.e. a first coating step 20 adapted to provide the external underlayer 3a by coating the transfer paper 5 with a first polyurethane mixture 20a; a second coating step 30 adapted to provide the intermediate underlayer 3c by coating the external underlayer 3a with a second polyurethane mixture 30a; and a third coating step 40 adapted to provide the internal underlayer 3b by coating the intermediate underlayer 3c with a third polyurethane mixture 40a.

The first polyurethane mixture 20a, the second polyurethane mixture 30a, and the third the polyurethane mixture 40a consist of polyurethane suitably added with additives and optionally with pigments.

The first coating step 20 comprises a first depositing substep 21 ; a first distribution substep 22; and a first drying substep 23.

In the first substep 21 , the first mixture 20a is deposited by gravity on the transfer paper 5, which, by continuing to advance along the processing direction 10a, reaches a first adjusting blade 22a virtually parallel to the transfer paper 5.

At this point the distribution substep 22 begins, in which the first blade 22a spreads out, over the transfer paper 5, the first mixture 20a, thus resulting in a uniform thickness. Preferably, the distance between the first adjusting blade 22a and the transfer paper 5, and therefore the thickness of the first polyurethane mixture 20a are substantially comprised between 5 pm and 1000 pm.

After passing the first adjusting blade 22a, the paper 5 and the first mixture 20a cross, over a period of time substantially between 30 s and 60 s, a first drying oven 23a where they are subjected to the first drying substep 23.

The first oven 23a has a temperature substantially comprised between 50°C and 200°C so that the solvent of the first mixture 20a fully evaporates, thus leaving, integral with the paper 5, the polyurethane resin of the first mixture 20a constituting the external underlayer 3a.

The assembly of the transfer paper 5 with the external underlayer 3a, once it has come out of the drying oven 23a, undergoes the second coating step 30 which, similarly to the first step 20, provides a second depositing substep 31 ; a second distribution substep 32; and a second drying substep 33.

During the second depositing substep 31 , the second mixture 30a is deposited by gravity on the external underlayer 3a, and in the second distribution substep 32 a second adjusting blade 32a spreads out the second blade 32a over the external underlayer 3a.

In particular, the second adjusting blade 32a, by being substantially parallel to the transfer paper 5 and having a distance from the paper substantially comprised between 5 pm and 1000 pm, defines a uniform thickness of the appropriate value for the second mixture 30a.

Subsequently, the transfer paper 5, the external underlayer 3a, and the second mixture 30a cross, in about 30 s to 60 s, a second drying oven 33a which, by having a temperature substantially comprised between 50°C and 200°C, allows complete evaporation of the solvent, thus leaving the resin of the second mixture 30a, and therefore the intermediate underlayer 3c, fixed on the external underlayer 3a.

Once the second coating step 30 is completed, the third coating step 40 begins, also comprising a third depositing substep 41 wherein the third mixture 40a is deposited by gravity on the intermediate underlayer 3c; a third distribution substep 42 wherein a third adjusting blade 42a, substantially parallel to the transfer paper 5 and arranged at a distance from the paper 5 substantially comprised between 5 pm and 1000 pm, distributes, over the intermediate underlayer 3c, the third mixture 40a, thus resulting in a uniform thickness; and a third drying substep 43 in which the transfer paper 5, the underlayers 3a and 3c, and the third mixture 40a cross, in a time substantially comprised between 30 s and 60 s, a third drying oven 43a which, by having a temperature comprised between 50°C and 200°C, evaporates the solvent of the third mixture 40a, thus leaving the resin of the second mixture 40a, and therefore the internal underlayer 3b, fixed on the intermediate underlayer 3c. At this point the main layer 30 is completely formed.

The coating step is followed by the gluing step, which glues the main layer 3d to the support layer 3e.

Preferably, the gluing step comprises an additional coating step 50 in which the adhesive underlayer 3f is formed on the main layer 3d, and in particular on the internal underlayer 3b; and an adhesion step 60 in which the multilayer membrane 1 is formed by gluing the support layer 3e to the main layer 3d. The adhesion step 60 occurs after the additional coating step 50, so that the adhesive underlayer 3f acts as a glue between the two materials.

The additional coating step 50 comprises an additional depositing substep 51 , wherein the gluing mixture 50a is deposited, preferably by gravity, on the main film 3, and more precisely on the internal underlayer 3b.

The gluing mixture 50a comprises a polyurethane adhesive and a solvent, suitably DMF or water.

Subsequently, the additional coating step 50 comprises a distribution substep 52 wherein an adjusting blade 52a, parallel and spaced from the paper 5, distributes the gluing mixture 50a defining a uniform thickness through it; and, finally, a drying substep 53 wherein the transfer paper 5, the main film 3, and the gluing mixture 50a cross, in a time span of about 30 s to 60 s, a drying oven 53a which, by having a temperature comprised between 50°C and 200°C, evaporates the solvent of the gluing mixture 50a, thus leaving an adhesive layer 4 fixed to the internal underlayer 3b.

Once the additional coating step 50 is completed, the process comprises the adhesion step 60.

The support layer 3e is wound on an additional roll adapted to be contacted with and laid on the adhesive underlayer 3f, which then bonds it by gluing it to the main layer 3d, thereby providing the main film 30.

At this point, a piercing step 70 is preferably carried out, wherein one of the main film 3 and the secondary film 2, preferably the main film 2, is pierced.

This piercing step 70 comprises using known punching machines adapted to make holes with dimensions, in terms of diameter if the holes are circular, preferably as previously indicated.

The piercing step 70 allows at least part of the non-pierced film, preferably the secondary film 2, to be visible from the outside.

The last step is the gluing step 80, which glues the secondary film 2 to the main film 3. In particular, the secondary film is glued onto the support layer 3e. The gluing takes place via the adhesive layer 4 of the known type, for example a calender, or by stitching or the like.

The manufacturing process 10 for making a membrane 1 , finally, can comprise an adjustment step in which the distance of one or more of the blades 22a, 32a and 42a, 52a from the transfer paper 5 is changed so as to change the thickness of at least one of the underlayers 3a, 3b, and 3c or of the adhesive layer 4.

The invention provides significant advantages.

In fact, the membrane 1 is highly luminescent due to the use of luminescent oxides within the main film 3.

Therefore, the membrane 1 is highly efficient when placed in a light-free environment.

In addition, the membrane 1 may comprise refractive material in at least one alternate layer of the main film 3, and therefore maintains high brightness and efficiency even when in the presence of light.

Moreover, the membrane 1 has technical and aesthetic characteristics, which are stable overtime, therefore ensuring an optimal and lasting efficiency.

This aspect has been obtained thanks to both the particular manufacturing process 10, which, by providing the underlayers 3a, 3b and 3c by means of coating, ensures their firm anchoring to the secondary film 2, and the adhesive layer 4, which tightly bonds the main film 3 to the secondary film 2.

Another advantage is the reduction of waste and production reject, which would require complex and expensive disposal operations, and therefore the reduced environmental impact of the manufacturing process.

Another advantage is that the process allows both the use of sheets of a few microns and the use of sheets of several millimetres (hence also rigid and non-windable sheets), and also made of a different material.

In fact, by taking a paper sheet 5 having incisions, it is possible to obtain a main film 3, and in particular an external layer 3a, which, as it is obtained by coating, transfers and therefore reproduces these incisions.

The invention is susceptible of variations falling within the scope of the inventive concept.

In particular, the support layer 3e may not be present and the secondary film 2 may be glued to the main film 3 by a process similar to the gluing described between the main layer 3d and the support layer 3e. In this case, the adhesive layer 4 is identical and made identically to the adhesive underlayer 3f previously described.

All details are replaceable by equivalent elements, and the materials, shapes and dimensions may be any materials, shapes and dimensions.