Patent Publication Number: US-2023143337-A1

Title: A thermoforming machine and method

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates to a thermoforming machine and method. Such thermoforming may for example be used in the process of laminating a functional multi-layer film on an optical article such as an ophthalmic lens by use of increased pressure and temperature. 
     BACKGROUND OF THE DISCLOSURE 
     By “functional film”, what is meant is a film providing the optical article with at least one feature among a hard coat, anti-scratch properties, an antireflective coating, a polarizing film, a tint, a mirror or a filter for specific wavelengths, anti-shock, anti-smudge, anti-fog, self-healing, self-cleaning or antistatic properties, etc. 
     By “laminating” a film on an optical article, what is meant is the operation involving the deposition of a film on a surface of the optical article to be laminated. The lamination operation is usually performed by first providing the film disposed onto a carrier. The film and the carrier are then compressed onto the surface to be laminated, by applying a difference of pressure between a side of the carrier having both the film and the optical article and the other side, or by applying a force from the optical article side. 
     An adhesive, e.g. a pressure sensitive adhesive, is generally previously disposed on the face of the film which is intended to be pressed onto said surface so as to maintain the film on said surface. 
     In alternative processes, the adhesive is positioned onto the optical article prior to pressing the film onto the optical article and/or the film is pressed onto the optical article without being fixed to a carrier, but for example by directly applying pressure on the film or using a stamp or a blown membrane or balloon. 
     In the field of optical article manufacturing, the film lamination process generally requires pre-processing or “forming” the consumable or laminate complex, in order to shape the film with a given curvature, so as to comply with and match the curvature of the surfaced prescription ophthalmic lens to laminate better than a flat film, be it the convex or concave side of the lens. 
     To laminate a lens, in order to induce a desired curvature with a custom radius into a film complex or consumable  10  as shown in  FIG.  1   , the consumable  10  comprising a carrier  12  and a film patch  14  glued to the carrier  12 , the consumable  10  is usually clamped and inflated by thermoforming.  FIG.  2    shows from top to bottom three successive phases of the thermoforming of the consumable  10  of  FIG.  1   . 
     When thermoforming, uniform heat distribution is desired within the member being thermoformed i.e. within the patch  14  in  FIG.  2   . 
     In addition, it is desirable to maintain a controlled pressure within the thermoforming chamber. 
     When introducing heated air into the thermoforming chamber, the heated air flow is directional and is directed towards the patch in order to heat it by convection. The temperature of the air must be maintained in a predetermined range, e.g. between 100 and 115 degrees Celsius, depending on the desired sag or curvature for the film to laminate. 
     If the air simply flows towards the center of the patch and heats it from the center outwards, this will result in a large temperature gradient within the film, the area of the film below the air flow being hotter than the other areas. This is unsuitable for thermoforming. 
     SUMMARY OF THE DISCLOSURE 
     An object of the disclosure is to overcome the above-mentioned drawbacks of the prior art. 
     To that end, the disclosure provides a thermoforming machine comprising a thermoforming chamber having at least one heated air inlet through which heated air flows into the thermoforming chamber at a controlled pressure, wherein the air inlet cooperates with a heated air flow distribution regulator located in the thermoforming chamber and through which the heated air flows out of the thermoforming chamber at a predetermined temperature, the regulator comprising a heated air flow regulating mask receiving heated air flow, having a plurality of flow restricting elements providing different air flow restrictions. 
     This makes it possible to reduce the temperature gradients in the member being thermoformed during thermoforming, resulting in significantly improved precision in the curvature of that member. 
     The disclosure also provides a thermoforming method using a thermoforming machine as succinctly described above, for giving a predetermined curvature to a film to be applied on an optical article, the film being placed below the mask so as to be centered with respect to the mask, wherein heated air flows from the heated air inlet into the thermoforming chamber at a controlled pressure and flows out of the thermoforming chamber at a predetermined temperature by passing through the heated air flow regulating mask, thus generating uniform heat distribution within the film, until the predetermined target curvature is obtained. 
     The disclosure further provides an optical article comprising a front face and a rear face, wherein at least one of the front and rear faces is coated by a film thermoformed by implementing a thermoforming method as succinctly described above. 
     The disclosure further provides an assembly comprising a thermoforming machine and a film and/or film patch and/or active film and/or adhesive to be thermoformed by the thermoforming machine, the thermoforming machine comprising a thermoforming chamber having at least one heated air inlet through which heated air flows into the thermoforming chamber at a controlled pressure, wherein 
     the air inlet cooperates with a heated air flow distribution regulator located in the thermoforming chamber and through which the heated air flows out of the thermoforming chamber at a predetermined temperature, the regulator comprising a heated air flow regulating mask receiving heated air flow, having a plurality of flow restricting elements providing different air flow restrictions, 
     in an embodiment for the assembly, the film and/or film patch and/or active film and/or adhesive has a non-circular predetermined shape and the plurality of flow restricting elements have a same or similar geometry as the predetermined shape of the film and/or film patch and/or active film and/or adhesive, alternatively the film and/or film patch and/or active film and/or adhesive has a predetermined shape and the plurality of flow restricting elements is distributed both in the center of the heated air flow regulating mask and on a predetermined number of concentric shapes, the concentric shapes having a same geometry as the predetermined shape of the film and/or film patch and/or active film and/or adhesive. 
     In the context above, the non-circular predetermined shape of the film and/or film patch and/or active film and/or adhesive corresponds to the smallest feature between the film, a contour of the thermoforming chamber which imposes the shape of the thermoforming, and a possible patch present within the film; said patch being destined to be thereafter transferred on an ophthalmic lens. 
     In the context above, a non-circular shape means that more than 3% or preferably more than 5% of the effective surface of the film and/or film patch and/or active film and/or adhesive is present out of the biggest inscribed circle that could be inscribed within the shape of the patch. The effective surface of the film patch in this context corresponds to the surface of the film patch excluding one or more possible handling flaps or strips. 
     As the method, the optical article and the assembly according to the disclosure have the same advantages as the thermoforming machine, they are not repeated here. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the description provided herein and the advantages thereof, reference is now made to the brief descriptions below, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts. 
         FIG.  1    is a schematic view of a prior art consumable to be thermoformed. 
         FIG.  2    is a set of three schematic views showing successive phases of the prior art thermoforming of the consumable of  FIG.  1   . 
         FIG.  3    is a schematic view of a thermoforming machine according to the disclosure, in a particular embodiment. 
         FIG.  4    is a schematic view of an air flow regulating mask comprised in a thermoforming machine according to the disclosure in a particular embodiment. 
         FIG.  5    is a set of two schematic cross-section views of an air flow regulating mask comprised in a thermoforming machine according to the disclosure in a particular embodiment. 
         FIG.  6    is a schematic view of an air flow regulating mask comprised in a thermoforming machine according to the disclosure in a particular embodiment and of a corresponding film patch comprised in an assembly according to the disclosure in a particular embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     In the description which follows, although making and using various embodiments are discussed in detail below, it should be appreciated that as described herein are provided many inventive concepts that may embodied in a wide variety of contexts. Embodiments discussed herein are merely representative and do not limit the scope of the disclosure. It will also be obvious to one skilled in the art that all the technical features that are defined relative to a process can be transposed, individually or in combination, to a device and conversely, all the technical features relative to a device can be transposed, individually or in combination, to a process and the technical features of the different embodiments may be exchanged or combined with the features of other embodiments. 
     The terms “comprise” (and any grammatical variation thereof, such as “comprises” and “comprising”), “have” (and any grammatical variation thereof, such as “has” and “having”), “contain” (and any grammatical variation thereof, such as “contains” and “containing”), and “include” (and any grammatical variation thereof such as “includes” and “including”) are open-ended linking verbs. They are used to specify the presence of stated features, integers, steps or components or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps or components or groups thereof. As a result, a method, or a step in a method, that “comprises”, “has”, “contains”, or “includes” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. 
     As shown in  FIG.  3   , a thermoforming machine  30  according to the disclosure comprises a thermoforming chamber  32 . 
     The thermoforming chamber  32  has at least one heated air inlet  34  through which heated air flows, from an air inlet  31  at room temperature through an inline heating pipe  33 , into the thermoforming chamber  32  at a controlled pressure. To that end, the thermoforming chamber  32  may comprise a back pressure regulating diaphragm  36  and a pressurized air inlet  38  for back pressure regulation. The thermoforming chamber  32  may further comprise a thermocouple  35  for controlling the temperature. It further enables to control processes for reaching or maintaining a predetermined temperature. 
     The heated air inlet  34  cooperates with a heated air flow distribution regulator  40  located in the thermoforming chamber  32 . The heated air flows through the air flow distribution regulator  40  out of the thermoforming chamber  32  at a predetermined temperature. The heated air flow distribution regulator  40  enables to control a distribution of the air flow within the thermoforming chamber  32 . As the air flow is heated air, it thus enables to control the temperature distribution within the chamber. Indeed, the air flow being heated prior to entering the thermoforming chamber  32 , the air flow temperature is controlled and predetermined easily. Further, controlling the temperature within the thermoforming chamber  32  becomes linked with controlling a heated air flow rate within the thermoforming chamber  32 . 
     According to an embodiment of the disclosure, the heated air flow distribution regulator  40  is oriented toward an opening in the thermoforming chamber  32  which is destined to be closed by the film to be thermoformed. 
     In a further embodiment, the heated air flow distribution regulator  40  is positioned relatively parallel to the above-mentioned opening, or so that the film prior to thermoforming is essentially parallel to the heated air flow distribution regulator  40  if the film to be thermoformed is essentially flat prior to thermoforming. 
     According to the disclosure, the regulator  40  comprises a heated air flow regulating mask  42  receiving heated air flow and having a plurality of flow restricting elements  44  shown in  FIG.  4   , providing different air flow restrictions. 
     In an embodiment, the plurality of flow restricting elements  44  are distributed in such a manner from the periphery to the center of the mask  42  that a first one of the flow restricting elements  44  restricts the air flow less than a second one of the flow restricting elements  44 . 
     This results in reduced direct air flow in the periphery of the patch, which balances the effect of the indirect air flow heating, caused by heated air flowing from the center of the patch to its periphery. Thus, uneven heating is avoided. 
     For example, the size of the above-mentioned first one of the flow restricting elements  44  may be larger than the size of the above-mentioned second one of the flow restricting elements  44 . 
     In an embodiment, the first flow restricting element  44  is closer to the center of the mask than the second flow restricting element  44 . 
     In another embodiment, conversely, the second flow restricting element  44  is closer to the center of the mask than the first flow restricting element  44 . 
     In the particular embodiment shown in  FIG.  4   , the plurality of flow restricting elements  44  is distributed on a predetermined number of concentric circles  46 , the center of which is the center of the mask  42 . In addition, at least one flow restricting element  44  may be provided in the center of the mask  42 . 
     The circle is a non-limiting example of geometry which may be replaced by another shape. In another embodiment, the plurality of flow restricting elements  44  is distributed on a predetermined number of concentric contours, which may be related to the shape of the patch  14 , such as an ellipse-like shape, as illustrated in  FIG.  6   . 
     In the particular embodiment shown in  FIG.  4   , the flow restricting elements  44  located on a same shape of the concentric shapes, i.e. on a given one and the same circle of the concentric circles  46  in that non-limiting example, have the same size. Moreover, the flow restricting elements  44  located on a same shape of the concentric shapes, i.e. on a given one and the same circle of the concentric circles  46  in that non-limiting example, may be equidistant from each other. 
     By way of non-limiting example, the number of concentric shapes may be 5 and the value of the angular sector between two adjacent flow restricting elements  44  on a same shape may be between 9° and 60°, in particular about 9° for the outermost concentric shape and about 60° for the centermost concentric shape. 
     In an embodiment, at least two concentric shapes are such that the above-mentioned angular sector is greater for the concentric shape closer to the center of the mask  42 . 
     In the particular embodiment shown in  FIG.  4   , the flow restricting elements  44  are circular openings. By way of non-limiting example, the diameters of the openings may be between 1 mm and 10 mm, in particular about 1 mm for the openings of the outermost concentric shapes and about 10 mm for an opening at the center of the concentric shapes. 
     However, the flow restricting elements  44  may have any other geometry such as square, rectangular, triangular, elliptic, a contour similar to the patch shape, etc. and may have any appropriate dimensions. 
     In an embodiment, the heated air flow distribution regulator  40  may have a flat surface. 
     In an embodiment, the heated air flow distribution regulator  40  may have a curved surface. 
     Moreover, the flow restricting element  44  may have a variable volume. In other words, the volume of a given element  44 , e.g. the volume of the opening in a given element  44 , may be different from the volume of the opening in another element  44  in the same regulator  40 . Besides, the air flow can be controlled by the size of the cross-section area of the flow restricting elements  44 , because a small cross-section area may cause significant friction, but the air flow can also be controlled by the depth or height of the flow restricting elements  44  and/or by the form of the air path through the flow restricting elements  44 .  FIG.  5    shows two non-limiting examples of the mask  42  in cross-section. In the example on the right of  FIG.  5   , one of the elements  44  has a path with air flow changing directions and the flow restricting elements  44  have a variable volume. 
     A thermoforming method using a thermoforming machine as described above makes it possible to give a predetermined curvature to a film to be applied on an optical article. 
     The film is placed below the mask  42  so as to be centered with respect to the mask  42 . Fixing the film below the mask  42  enables sealing of the thermoforming chamber  32 . 
     Then, heated air flows from the heated air inlet  34  into the thermoforming chamber  32  at a controlled pressure into an initial pressure zone  50  of the thermoforming chamber  32  (see zone  50  in  FIG.  3   ) and, at a predetermined low threshold pressure, begins to flow out of the thermoforming chamber  32  through the heated air flow distribution regulator  40 , at a predetermined temperature, by passing through the mask  42 , thus generating uniform heat distribution within the film, until the predetermined target temperature is reached, the target temperature depending on the material and/or on the desired final curvature or sag of the film. 
     Once the target temperature is obtained, the back pressure regulating diaphragm  36  used to control the pressure increases the pressure, for example by 0.03 bar/s, up to for example 5 bar, either in the upper, heating chamber, or in a lower chamber, if any. 
     The pressure increases until the target thermoforming curvature is obtained or until the maximum allowed pressure (predetermined high threshold pressure) is reached. 
     The back pressure mechanism maintains the pressure within the thermoforming chamber  32  by introducing pressurized air above the back pressure regulating diaphragm  36 , through the pressurized air inlet  38 . If the pressure inside the thermoforming chamber  32  surpasses the back-pressure on the diaphragm  36 , the diaphragm  36  opens and releases air from within the thermoforming chamber  32 , thus reducing the pressure. This enables control of the pressure within the thermoforming chamber  32  throughout the process, while maintaining constant flow of heated air from the heated air inlet  34 , at a controlled temperature. 
     By way of non-limiting example, the temperature may be comprised between 100° C. and 140° C. and is preferably 120° C. 
     By way of non-limiting example, the pressure may be comprised between 0.2 bar and 8 bar, preferably between 0.5 bar and 6 bar. 
     Depending on the dimensions of the thermoforming chamber  32 , the heated air may have a flow rate comprised between 20 l/min and 160 l/min and is preferably 60 l/min. 
     Alternatively, the pressure in the thermoforming chamber  32  may be maintained at atmospheric pressure. In such a case, increased pressure for forming may be applied on the film from the opposite side, where the film patch faces downwards, the pressure from below introducing a convex shape suited for front-side lamination. 
     At least one of the front and rear faces of an optical article such as an ophthalmic lens may be coated by a film thermoformed in the various manners described above. 
     In an embodiment of an assembly according to the present disclosure, comprising a thermoforming machine as described above and a film and/or a film patch and/or an active (functional) film and/or an adhesive to be thermoformed by the thermoforming machine, where the film and/or the film patch and/or the active film and/or the adhesive has a predetermined shape, the flow restricting elements  44  comprised in the heated air flow regulating mask  42  may have a geometry identical to, or similar to, or at least reminiscent of the geometry of the shape of the film and/or of the film patch and/or of the active film and/or of the adhesive. 
       FIG.  6    illustrates a non-limiting example of such flow restricting elements  44  (shown on the right of the drawing). 
     As shown in  FIG.  6   , the contour of the set of flow restricting elements  44  has a geometry that approximately matches the geometry of the shape of the film patch  14 . 
     In that particular example, the concentric shapes are not circular, but elliptic, as shown by the concentric ellipses  46 ′. Two of the concentric ellipses  46 ′ are shown in dashed lines, the dashed lines having been added on the drawing for better showing the concentric ellipses  46 ′. 
     In that particular embodiment, the concentric shapes are the concentric ellipses  46 ′ and approximately match the film patch  14  (shown on the left of the drawing). 
     In addition, as also shown in the non-limiting example of  FIG.  6   , each of the flow restricting elements  44  is itself an ellipse. 
     However, the features relating to the elliptic or circular or other geometry of the flow restricting elements  44  themselves and/or the concentric circles  46  resp. ellipses  46 ′ and/or the similarity between the shape of the film patch  14  and the contour of the set of flow restricting elements  44  may be present, either in separate embodiments, or in combination with one another in one or several embodiment(s). 
     In an embodiment, the thermoforming method described above may use an assembly as described above, for giving a predetermined curvature to a film to be applied on an optical article, the film being placed below the mask so as to be centered with respect to the mask. Heated air may flow from the heated air inlet into the thermoforming chamber at a controlled pressure and flow out of the thermoforming chamber at a predetermined temperature by passing through the heated air flow regulating mask, thus generating uniform heat distribution within the film, until the predetermined target curvature is obtained. 
     Although representative systems and methods have been described in detail herein, those skilled in the art will recognize that various substitutions and modifications may be made without departing from the scope of what is described and defined by the appended claims.