Patent Application
20070240813
Disclosed herein are processes for forming a multilayer film and the films formed thereby.
Embossing processes have been utilized to provide surface structures in a film. For example, embossing processes have been utilized to provide film surface structures that include angled, cubic patterns to direct, diffuse, or polarize light. Films with these surface structures are used in backlight displays, signs, microfluidic devices, electronic devices, and elsewhere.
Current embossing processes utilize a separate carrier layer to support the film during the embossing process. Basically, the film is disposed onto the carrier layer. The film, which is at a temperature above its glass transition temperature, is forced against a pattern (e.g., embossing belt or embossing drum), which comprises surface features that are a negative image of the features desired. As the heated film is forced against the pattern, the film flows into the surface features. The film is then cooled below its glass transition temperature to freeze the positive of the surface features into the film, and removed from the pattern. The film must then be stripped from the carrier layer. Removal of the carrier layer, however, may damage the surface features on the film.
There is a continual need for more efficient processes and systems for embossing films.
Disclosed herein are processes for forming a multilayer film and the films formed thereby.
In one embodiment, the process for forming a multilayer film comprises disposing a supportive layer adjacent to an imprinting layer and imprinting microstructures in the imprinting layer as the multilayer film passes between a heated roller and a compression roller, wherein the imprinting layer has an imprinting temperature that is lower than the supportive layer melting temperature. During processing, the multilayer film is free of a removable carrier layer. The supportive layer has a supportive layer glass transition temperature that is greater than or equal to about 15° C. higher than the imprinting layer glass transition temperature and/or the supportive layer has a supportive layer melting temperature that is greater than or equal to about 15° C. higher than an imprinting layer melting temperature.
In another embodiment, the process for forming a multilayer film comprises: heating an imprinting layer to an imprinting layer temperature and imprinting microstructures in the imprinting layer to form a multilayer film comprising the imprinting layer and a supportive layer. The supportive layer physically contacts the compression roller during processing. The supportive layer has a supportive layer glass transition temperature that is greater than or equal to about 15° C. higher than the imprinting layer glass transition temperature and/or the supportive layer has a supportive layer melting temperature that is greater than or equal to about 15° C. higher than an imprinting layer melting temperature.
The above described and other features are exemplified by the following figures and detailed description.
Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:
Referring to
Supportive layer 16 supports imprinting layer 14 during the embossing process. As a result, the material of supportive layer 16 has a higher glass transition temperature than the material of imprinting layer 14. During processing, supportive layer 14 is softened (e.g., heated above its glass transition temperature (Tg)). Since layer 16 has a higher glass transition temperature (Tg) and/or higher melting temperature (Tm) than layer 14, layer 16 can maintain its structural integrity during the embossing of layer 14. Supportive layer 16 can comprise a material having a Tm and/or Tg that is sufficiently different than the Tm and/or Tg (respectively) of the layer 14 material such that, under the embossing conditions, layer 16 retains it structural integrity, and supports layer 14. For example, the Tm and/or Tg of the material of layer 16 can be greater than or equal to about 15° C. higher than the Tm and/or Tg (respectively) of the material of layer 14, or more specifically, greater than or equal to about 30° C. higher than the Tm and/or Tg (respectively) of the material of layer 14, or, yet more specifically, greater than or equal to about 45° C. higher than the Tm and/or Tg (respectively) of the material of layer 14.
Imprinting layer 14 can comprise any material that can be embossed and that provides the desired mechanical and optical properties. If imprinting layer 14 is not compatible with supportive layer 16 (e.g., will not sufficiently bond thereto to prevent delamination), layer(s) can be disposed between the imprinting layer 14 and the supportive layer 16 to attain the desired mechanical properties.
In one embodiment, the imprinting layer glass transition temperature is less than or equal to about 115° C. and the supportive layer glass transition temperature is about 135° C., or, more specifically, layer 14 has a glass transition temperature of less than or equal to about 105° C., while layer 16 has a glass transition temperature of greater than or equal to about 140° C. For example, the layer 14 comprises polycarbonate and polyester, or, more specifically, layer 14 comprises a polycarbonate-polyester copolymer such that layer 14 has a glass transition temperature of about 90° C. to about 105° C. (e.g., XYLEX®, commercially available from General Electric Plastics, Pittsfield, Mass.). Meanwhile, layer 16 comprises polycarbonate having a glass transition temperature of about 140° C. to about 150° C. (e.g., LEXAN®, commercially available from General Electric Plastics, Pittsfield, Mass.).
First and second hoppers 40, 42 are provided to route plastic stock material to the extruder(s). Specifically, material forming imprinting layer 14 is fed into hopper 40, and material forming supportive layer 16 is fed into hopper 42. These hoppers can feed extruder(s) 44, 46, that feed co-extrusion die 48 that forms the layered film 18. In other embodiments, the layers 14, 16 can be separately formed, disposed adjacent to one another (with additional layer(s) optionally disposed therewith) to form the layered film 18, and then processed similar to the co-extrusion layers.
From the extrusion device 20, the layered film 18 passes through calendaring device 22, cooling station 24, and onto embossing belt 110. Calendaring device 22 can be employed to control the thickness of the layered film 18, and optionally to impart a desired surface finish to the surface of the layered film 18 (e.g., to the supportive layer 16). Calendaring device 22 comprises calendaring rollers 100 and 102 that form a nip 104 that can be maintained at a desired nip pressure. Layered film 18 is fed through the nip 104. The roller 102 can provide a surface finish such as a polish finish, a matte finish, or a velvet finish.
When the layered film 18 is routed through the nip 104, calendaring rollers 100 and 102 provide a selected pressure to the multilayer film to compress the film to a selected thickness. The thickness of the multilayer film and the imprinting and supportive layers can be selected for materials employed, processing requirements, and the end-use requirements. The thickness of the multilayer film can be about 0.025 millimeters (mm) to about 2 mm, or, more specifically, about 0.1 mm to about 1 mm, and still more specifically, about 0.15 mm to about 0.5 mm. The thickness of imprinting layer 14 can be sufficient to receive the desired surface features, e.g., thicker than the largest surface feature. The thickness of the supportive layer 16 is variable based upon the size of the imprinting layer, cost considerations, and so forth, and is sufficient to provide the desired structural integrity to the imprinting layer during processing. For example, the thickness can be greater than or equal to about 0.025 mm.
After being processed by the calendaring device 22, the layered film 18 can be routed to a cooling station 24 that can cool the layered film 18 to below the supportive layer glass transition temperature. The cooling station 24 can comprise a forced air cooling device (e.g., in which fans force cooled air over surface(s) of the layered film 18), liquid cooling device, other thermal exchanging devices, as well as combinations comprising at least one of the foregoing. Depending upon the process design, the layered film 18 can be cooled to a temperature below the supportive layer glass transition temperature yet above the imprinting layer glass transition temperature, or to a temperature below the imprinting layer glass transition temperature. If the supportive layer 16 is not coextruded with the other layer(s), depending upon the temperature of any extruded layer(s), the cooling station 24 may be eliminated from the system. Once below the glass transition temperature of layers 14, 16.
In an alternative exemplary embodiment, each layer 14, 16 can be separately formed into a sheet and then disposed adjacent to one another to form a layered film with other optional layer(s) therebetween possible. Layers 14, 16 can be attached together (e.g., laminated) before or during the embossing process. For example, can be aligned together prior to the embossing process by routing the imprinting and supportive layers through a roll lamination device. The roll lamination device can heat one or both of the layers 14, 16 to above their glass transition temperature, and can apply a pressure to join the layers 14, 16. The supportive layer can then be cooled to enable it to provide the desired structural integrity to the imprinting layer during embossing.
Optionally, the multilayer film can be preheated with heater(s) prior to contacting the belt and/or prior to contacting the roller 116. Once at the desired thermal condition (e.g., the imprinting layer is heated to an imprinting layer temperature that enables the desired imprinting), the layered film 18 passes through the embossing station 26 which embosses surface structures into layer 14. The imprinting temperature can be greater than or equal to 10° C. lower than both the supportive layer melting temperature and the supportive layer glass transition temperature, or, more specifically, greater than or equal to 20° C. lower than both the supportive layer melting temperature and the supportive layer glass transition temperature.
In yet another embodiment, the supportive layer can be formed and introduced to a nip between calendaring rolls as the imprinting layer can be extruded into the nip to form the imprinting layer onto the supportive layer or can be a heated layer introduced to the nip on the supportive layer, and to imprint the desired surface features onto the supportive layer. Since the supportive layer has a higher Tm and/or Tg than the imprinting layer, it maintains its structural integrity, supports the imprinting layer during processing, and can have a desired surface texture on a side opposite the imprinting layer.
Embossing station 26 can include an embossing belt 110, a hot roller 112 (e.g. a heated roller), a cold roller 114 and compression rollers 116, 118, 120, 122, 124. Embossing belt 110 comprises the surface structures to be embossed into layer 14. This belt assists in heating and transporting the layered film 18. Embossing belt 110, a continuous belt disposed around the rollers 112 and 114, can be formed from a metal (e.g., nickel, iron, copper, cobalt, and so forth), and so forth, as well as combinations comprising at least one of the foregoing, such as martensitic, ferritic, and austenitic stainless materials, nickel titanium alloy, and the like. Embossing belt 110 has a surface 130 comprising an embossing pattern 132. For example, the embossing pattern 132 can be microstructures such as light-reflecting elements such as cube-corners (e.g., triangular pyramid), trihedral, hemispheres, prisms, ellipses, tetragonal, grooves, channels, microlenses, and others, as well as combinations comprising at least one of the foregoing.
The embossing belt 110 is disposed around rollers 112 and 114 and is operably coupled to the rollers 112, 114 such that the rollers induce embossing belt 110 to advance to various locations of embossing station 26 at a selected speed. The hot roller 112, which can be internally heated, can be capable of heating the embossing belt 110 and the imprinting layer 14 above the imprinting layer glass transition temperature and/or other heater(s) can be employed to attain the desired temperature, while the cold roller 114 is capable of cooling the multilayer film 12 to below the glass transition temperature of imprinting layer 14.
In addition to the rollers 14, 16, thermal exchange device(s) can be employed with the system. For example, additional heaters can be used before or during the embossing (e.g., before roll 112 or adjacent roll 112), and/or additional cooling device(s) can be employed after the compression roll 124.
Nips are formed between the heated roller 112 and compression rollers 116, 118, 120, 122, 124, enabling the provision of selected pressures to the multilayer film 18. The pressure forces the film, and especially the first surface 14, into the embossing belt 110, to emboss the microstructures into the imprinting layer 14. Rollers 116, 118, 120, 122, and 124, along with rollers 112, and 114 are manufactured from metals (e.g., copper, aluminum, iron), metal alloys (e.g., martensitic, ferritic, and austenitic stainless materials), as well as polymeric materials (e.g., ethylene propylene diamine monomer based rubber (EPDM), silicone). The external surface of the rollers can comprise a coating to enhance the properties of the roller (e.g., chromed, nitrided, nickel coated, polytetrafluoroethylene (PTFE) coated).
Compression rollers 116, 118, 120, 122, 124 are illustrated in
In an alternative exemplary embodiment, the microstructures can be disposed on a calendaring roller (e.g., directly or on a sleeve around the roller). Here, the supportive layer 16 can be introduced to a nip between the calendaring rollers wherein the imprinting layer 14 is extruded into the nip such that the imprinting layer 14 is disposed on the calendering roll comprising the microstructures. Here, the supportive layer 16 would provide the support to the imprinting layer 14 as the imprinting layer 14 coats the supportive layer 16 and as the microstructures are formed into the imprinting layer 14 as it cools to below its glass transition temperature.
After the surface structures are formed in layer 14, the belt transports multilayer film 12 to cold roller 114, and optionally past a cooling station (not shown). Cold roller 114 removes heat from multilayer film 12. Multilayer film 12 is then transferred from cold roller 114 to an uptake roller 28. Multilayer film 12 can then be stored or can then be transported to another location for further processing.
Since multilayer film 12 is embossed without using a separate carrier film (e.g., polyester films such as those sold under the MYLAR®, manufactured by Dupont Corporation, Wilmington, Del.), there is no need to remove the separate carrier film from multilayer film 12. This simplifies the process, and reduces material and equipment costs. Also, since the carrier film is not stripped from the multilayer film, there is a reduction in damaged and scrapped multilayer films due to damage of the microstructures during stripping. Additionally, since the supportive layer 16 can be in direct contact with calendaring roll(s), a desired surface finish can be disposed and maintained on the surface of the supportive layer 16.
The present process enables the production of an embossed multilayer film without the use of a removable carrier layer. The supportive layer, which is a portion of the final multilayer film, has a melting temperature (Tm) and/or glass transition temperature (Tg) that is substantially higher than the Tm and/or Tg of the imprinting layer such that the supportive layer can provide structural integrity to the imprinting layer during imprinting of surface features into the imprinting layer. Due to this temperature difference, surface features and/or texture on the supportive layer can be maintained throughout the formation of the multilayer film. Hence, multilayer films that were produced using a carrier layer did not have surface features and/or texture on the film second side; the features were not retained through the imprinting process. This process eliminates the need for a carrier layer, eliminates damage caused by the separation of the carrier layer from the formed film, and enables two sided texturing and/or imprinting of a multilayer film.
Multilayer films produced with the present process can be employed various multilayer film applications. These films can be used in any application where the control and/or adjustment of light is desired (e.g., reflected, diffused, collimated, and so forth). Exemplary applications include displays (e.g., back lit displays), signs, labels, and so forth. The multilayer film can be formed as a diffusing film, collimating film, and/or polarizing film.
The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The term “combination” is intended to include, as applicable, mixtures, blends, reaction products, alloys, and the like. If ranges are disclosed, the endpoints of all ranges directed to the same component or property are inclusive and independently combinable (e.g., ranges of “up to about 25 wt. %, or, more specifically, about 5 wt. % to about 20 wt. %,” is inclusive of the endpoints and all intermediate values of the ranges of “about 5 wt. % to about 25 wt. %,” etc.). The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity).
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
