Manufacturing process of a laminated polymeric product

Abstract

A manufacturing process of, and the relative laminated, polymeric semi-finished product are disclosed, the laminated, polymeric semi-finished product having in-depth aesthetic features, including at least two mutually welded layers by a lamination process with heat and/or pressure addition, wherein at least one of the layers is a thermoplastic material, in which the following steps are provided: providing a cohesion layer 100-500 micron thick, consisting of thermoplastic polyurethane, featuring in-depth aesthetic patterns; providing polymeric sheets with materials having a softening temperature above the one of the cohesion layer; and laminating at least one of the polymeric sheets at least partly transparent or translucent with the cohesion layer, by heat and/or pressure addition suitable to reach the softening of the cohesion layer featuring aesthetic patterns.

Claims

1. A manufacturing process of a laminated, polymeric semi-finished product having patterned features, the process comprising: providing a cohesion layer, 100-500 micron thick and consisting of thermoplastic polyurethane (TPU), the cohesion layer obtained by any of wet-block and dry block processes, and featuring in-depth patterns; providing polymeric sheets, formed of materials having a softening temperature higher than a softening temperature of said cohesion layer, at least one of said polymeric sheets being at least partly transparent or translucent; and laminating the at least one of said polymeric sheets to said cohesion layer, with heat and/or pressure addition suitable to reach a softening of said cohesion layer.

2. The process of claim 1, wherein said polymeric sheets are based on one of the polymeric materials of the group consisting of polyamide (PA), polyurethane (PU), polyethereimides (PEI), cellulose propionate (CP), polyurethane-polyurea, thermosetting polyurethane, polycarbonate (PC), polymethil metacrylate (PMMA), acrylonitryl butadien styrene (ABS), polyethylene (PE), styrene-acrylonitryl (SAN), acrylonitryl-styrene-acrylate (ASA), mixtures of polycarbonate and acrylonitryl butadien styrene (PC/ABS), PVC, polybutylenteraphtalate (PBT), PBT/ASA, and ASA/PC.

3. The process of claim 1, wherein said laminating is carried out at a temperature of between 40 and 220 C., and with pressures from 1 kg/cm.sup.2 to 100 kg/cm.sup.2.

4. A layered semi-finished polymeric product, provided with in-depth patterns, comprising: at least two layers, mutually welded to each other by lamination with heat and/or pressure addition, wherein a first layer of said at least two layers is a cohesion layer (F1) consisting of thermoplastic polyurethane (TPU) obtained by any of wet-block and dry block processes, and featuring in-depth patterns, wherein a second layer of said at least two layers is a polymeric sheet, wherein said cohesion layer has a softening temperature that is lower than a softening temperature of said polymeric sheet, and wherein said polymeric sheet in contact with the cohesion layer (F1) is at least partly transparent or translucent.

5. The product of claim 4, wherein said polymeric sheet are based on one of the polymeric materials of the group consisting of polyamide, polyurethane, cellulose propionate, polycarbonate, polymethyl metacrylate (PMMA), acrylonitryl butadien styrene (ABS), polyethylene (PE), styrene-acrylonitryl (SAN), acrylonitryl-styren-acrylate (ASA), mixtures of polycarbonate and acrylonitryl butadien styrene (PC/ABS), PVC, polybutylenteraphtalate (PBT), PBT/ASA, and ASA/PC.

6. The process of claim 2, wherein said laminating is carried out at a temperature of between 40 and 220 C., and with pressures from 1 kg/cm.sup.2 to 100 kg/cm.sup.2.

7. The process of claim 3, wherein the heat addition occurs at a temperature higher than 100 C.

8. The process of claim 6, wherein the heat addition occurs at a temperature higher than 100 C.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Further characteristics and advantages of the process and the product according to the invention will become more apparent from the following detailed description of preferred embodiments thereof, given by way of example and illustrated on the accompanying drawings, in which:

(2) FIG. 1 is a schematic perspective view of an exemplary laminate composed of an intermediate layer of thermoplastic polyurethane and two transparent outer layers;

(3) FIG. 2 is a schematic perspective view of an exemplary laminate composed of an intermediate layer of thermoplastic polyurethane and two outer layers of which only one transparent;

(4) FIG. 3 is a schematic perspective view of an exemplary laminate composed of an intermediate layer of thermoplastic polyurethane and two outer layers of which one translucent and the other one shaded.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(5) A sheet of plastic material is produced, in a per se known manner, by means of a lamination of several planar layers of different materials. By lamination, in the context of the present application, is meant any process suitable to bond a plurality of layers formed by individual foils of plastic material, which can be different or the same, but different in terms of technical performance or aesthetic appearance.

(6) In the following it will be described some preferred methods for obtaining the lamination, but generally said methods make use of heat and pressure addition to melt one or more of the component layers, in order to obtain an intimate adherence or even a chemical bond with the adjacent layers, and to produce a stable sheet in which the individual layers are permanently bonded to each other, while avoidingat least in normal operating conditionsa delamination between the various layers.

(7) According to the invention, at least one of these intermediate layers F1 is a thermoplastic polyurethane-based semi-finished product, which has been conferred an aesthetic value with an in-depth pattern, using one of viable processes on a thermoplastic material, which is preferably block processing, co-extrusion and co-injection, that allow to define aesthetic patterns in deep into the material, thus giving a durable and very much appreciated aesthetic featuring to the material.

(8) This intermediate layer F1 of thermoplastic polyurethane (TPU) is produced with one of the methods just described, possibly applying aesthetic featuring through an overprint, and then allowing it to cool and possibly storing it. The thickness of this layer is preferably between 100 and 500 microns.

(9) According to the invention, it constitutes a support for an aesthetic pattern and, at the same time, an effective binder element for the lamination process, taking advantage of the inherent qualities of thermoplastic polyurethanes, whichdue to the chemical properties and to the relatively low melting point (between 80 and 220 C.)are able to effectively act as bonding agent for a plurality of different plastic polymeric materials. Therefore, according to the invention, this thermoplastic polyurethane layer having aesthetic features is going to constitute a reference element for the lamination with other layers of different materials, which are then selected only by virtue of their technical performance, as long as they have a sufficient transparency (on the whole area of the semi-finished product or on its own suitably selected portion) to allow the external exploitation of the aesthetic features of the interlayer of thermoplastic polyurethane.

(10) The laminating process according to the invention provides then to couple the plastic polyurethane layer having aesthetic features with a sheet of other technical plastic material, or between two films/sheets of semi-finished plastic material FL1 and FL2 (FL1 refers to the upper top sheet of the package and FL2 refers to the lower base sheet of the package), each with a thickness preferably comprised between 500 microns and 1 cm.

(11) If the thermoplastic polyurethane layer F1 is particularly thin, for example about 100 microns, it can be supplied temporary coupled to a release paper: in this case, one can expect a light laminating step of the layer F1 on a first sheet FL1, before removing the release paper, and subsequently a second step of laminating with the other sheet FL2.

(12) The plastic sheets FL1 and FL2that can be laminated by means of the interposition of the intermediate TPU layer having aesthetic featuresare preferably selected from the group consisting of polymers such as polyamide (PA), polyurethane (PU), polyethereimides (PEI), cellulose propionate (CP), polyurethane-polyurea, thermosetting polyurethane, polycarbonate (PC), polymethil metacrylate (PMMA), acrylonitryl butadien styrene (ABS), polyethylene (PE), styrene-acrylonitryl (SAN), acrylonitryl-styrene-acrylate (ASA), mixtures of polycarbonate and acrylonitryl butadien styrene (PC/ABS), PVC, polybutylenteraphtalate (PBT), PBT/ASA, ASA/PC.

(13) It is also known that a plasma treatment, applied on the surface of certain polymers being in contact with the thermoplastic polyurethane sheet, can improve the adhesion: for example, advantageous results are obtained with some polyamides (Polyamide 6.6), PBT, PS, PP.

(14) The two plastic sheets FL1 and FL2, opposing and adhering to the intermediate layer of laminated TPU having aesthetic features, can be formed from the same polymer or from two different polymers (for example, a cellulose propionate sheet and a polyamide sheet). Based on the final application of the product or of the structure to be obtained (for example, the frame for glasses), at least one of the two sheets FL1 or FL2 must have at least a transparency or translucency featurepossibly on a geometrically defined portion thereoffor making evident the aesthetic pattern of the underlying intermediate layer of TPU; in some cases, to improve and make more evident the aesthetic connotation of the layer F1 of TPU, both the sheets FL1 and FL2 have characteristics, optionally at least partial, of transparency/translucency.

(15) The sheets FL1 and FL2 can also have aesthetic features or characteristic multichromatic properties, but this is not essential in the teaching provided herein. As non-limiting examples, in FIG. 2 a laminate is illustrated in which the top sheet FL1 is transparent while the base sheet FL2 is opaque, for example it is homogeneously coloured, while FIG. 3 illustrates a laminate in which the top sheet FL1 is shaded while the base sheet FL2 is translucent with a uniform colour. The shades on the most external sheets FL1 and FL2 may also be obtained by an extrusion process or by inserting a pigment filler or by using a dyeing process (known in the eyeglass sector as dipping, i.e., an immersion dyeing, which is shaded).

(16) The package consisting of at least three layers FL1, FL2 and F1and possibly other more outer layers, whether or not including an additional thermoplastic polyurethane interlayer having aesthetic featuresis placed, according to a first embodiment, in a plane press where, by means of pressure and heat addition, a laminate of the final thickness from 1050 microns to about 2 cm is obtained.

(17) The lamination heat can also be supplied by other techniques, such as a high-frequency or friction heating process.

(18) In this press process, the temperature is typically lower than the softening temperature of the materials which make up the outer sheets FL1 and FL2, but suitable to lead to softening (without excessive fluidization, as is also explained below) of the intermediate layer of TPU.

(19) The heating, cooling and pressure conditions, as well as the time duration of the various processing cycles, therefore, depend on factors such as:

(20) Type and thickness of the polyurethane layer F1;

(21) Type and thickness of the polymer used for the other layers FL1 and FL2.

(22) The bonding between the various layers of the package mainly depends on the softening temperature of the polyurethane layer F1, which, in addition to the aesthetic function, acts as a binding agent (hot melt adhesive). For this reason, the package must comprise one polyurethane layer F1, which hasas mentioned abovea softening temperature lower than, or equal to, that of the polymers used for the other surrounding layers FL1 and FL2; in this way, the bonding of the laminate is ensured while avoiding the deformation of the individual components. Said softening must be sufficient to obtain a package (FL1, F1, FL2) that is difficult to be delaminated, but avoiding to reach an excessive fluidity that would compromise the stability and consistency of the aesthetic pattern of the polyurethane sheet F1.

(23) The conditions should therefore be selected on the basis of a trade-off on the specific composition chosen.

(24) Usual temperatures with thermoplastic materials are between 40 and 220 C., preferably above 100 C., with pressures of about 1 kg/cm.sup.2 to 100 kg/cm.sup.2, however, inversely proportional to the process temperature (too high pressure along with high temperatures are to be avoided, in order to not decompose the coherence of the aesthetic patterns), and reduced residence times of about 1 minute to 10 hours.

(25) By way of example, below it is reported an experimental test of a process carried out for forming a package consisting of:

(26) A first top layer FL1 of polyamide (commercial product Trogamid TR90) 2000 microns thick;

(27) An intermediate layer F1 of thermoplastic polyurethane (for example, an aliphatic polyurethane) obtained by block process with a damask aesthetic effect in the thickness of 200 microns;

(28) A second base layer FL2 of polyamide (commercial product Trogamid TR 90) 2000 microns thick.

(29) The base sheet FL2 was obtained by injection moulding of a polyamide, with surfaces clean and free from surface contamination, and was placed horizontally on a plane; on said sheet FL2 a sheet was laid having a thickness of 200 microns of the intermediate layer F1 of thermoplastic polyurethane having aesthetic features and, on top of this, the top sheet FL1 of polyamide with surfaces clean and free from surface contamination.

(30) The package thus obtained was placed between two chrome-plated sheets, within a plane of a press. Thereafter, pressure and heat have been applied, with the following specifications: temperature 130 C., pressure of 5 kg/cm.sup.2 for a time of 10 minutes.

(31) The laminated product, once cooled, was cut and milled in the shape of a front frame of eyeglasses by means of conditions known to any eyeglass manufacturer.

(32) The product thus obtained was excellent both in terms of technical performance, and of the aesthetic effect achieved. In particular, while ensuring the usual strength and stiffness performance, it was possible to produce eyeglasses with low thickness and provided with a typical thinness of the profiles, achieving advantageous results in technical (lightness) and aesthetic (new light lines) terms.

(33) The semi-finished product of the invention is not obtained only by a press lamination, as indicated above. In alternative embodiments, it is provided that the lamination is carried out with other types of welding: for example, as indicated above, in certain conditions an ultrasonic or vibration/friction welding can be used.

(34) In certain conditions, an intermediate layer of thermoplastic polyurethane (F1) having a thickness greater than 500 microns is not recommended because it could be a hindrance to subsequent processing, such as polishing. In fact, when the hardness of interlayer of TPU (F1) is lower than the hardness of the other adjacent layers, a mechanical processing on the perimetral edges of the laminate can lead to differentiated wear of the materials, resulting in the formation of an unwanted meniscus in the side surface, which tends to accumulate the processing material (abrasive pastes) and to produce triggering points for possible de-laminations of the semi-finished product.

(35) The semi-finished product according to the invention is very effective and fully satisfies the objects stated in the preamble. Through the production of thermoplastic polyurethane sheets featuring in-depth decorations and aesthetic effects (in particular obtainable by a block process), it is possible to have a lamination layer that gives both the desired aesthetic effect and the binder function in a laminate composed of sheets with various polymeric materials, which thus confer the desired technical performance to the semi-finished product.

(36) A further advantage deriving from the selection of an intermediate layer based on thermoplastic polyurethane, concerns the fact that it is unnecessary to provide the use of specific glues and adhesives to bind the laminate layers to each other. This implies the elimination of additional costs, practical difficulties and, above all, does not adversely affect the dimensional stability of the laminate: indeed, the thermoplastic polyurethane has dimensional deformations close to 0%, as well as having a flexibility that allows it to match and to follow the curvatures imposed by the outer sheets FL1 and FL2 in all classic processes in the eyewear sector, including thermoforming processes.

(37) Still, in the case of a laminate obtained with TPU and very high performance polymers, such as Nylon, in the production of eyeglass processes for the definition of the structural cores could been even avoided, so as to simplify the production of the laminated eyewear.

(38) Finally, providing the aesthetic component in an interlayer advantageously protects all the aesthetic effects from any wear or chemical attack belonging to the external environment.

(39) It is however understood that the invention is not limited to the particular embodiments illustrated above, which represent only non-limiting examples of its scope, but that numerous variants are possible, all within the reach of a skilled in the art, without thereby departing from the scope of the invention.

(40) Though the lamination techniques described above are only some of those viable, also other processing modes could be advantageously used, still exploiting the aesthetic qualities and the binding function of the intermediate layer of thermoplastic polyurethane. Furthermore, the lamination can take place not only between rectangular sheets, but also between already semi-finished sheets, for example blanks of eyeglass front frames or temples.

(41) Still, the thermoplastic polyurethane sheet having aesthetic features can also be laminated with other support materials, such as paper, cardboard or thin sheets of wood or other materials.

(42) Finally, as already mentioned above, it is not excluded that the laminating process can produce a semi-finished product in which a thermoplastic polyurethane layer having aesthetic features remains on the outside of the semi-finished product.