Conformable Shielding Film

Abstract

A method for thermoforming a rigid film structure includes applying a rigid film structure to a mold and heating the rigid film structure until it conforms to the mold. The rigid film structure includes a rigid polymer film layer, a light management film layer, and a shielding film layer. The shielding film includes polymethyl methacrylate (PMMA), and the shielding film layer contacts the surface of the mold.

Description

[Background technology]

[0001] Many businesses and other organizations use external signs made from molded or thermoformed laminates of rigid films. Rigid films used for thermoforming often include polyvinyl chloride (PVC) combined with other substrates, such as polycarbonate. Generally, thermoforming a rigid film to create a sign or other rigid structure involves applying the film or several materials laminated together to the surface of a mold, heating the mold, and using a vacuum to draw the film to the mold surface. The mold is then cooled, allowing the newly formed shape to be removed from the mold.

[0002] In some instances, the surface of the mold scratches the surface of the laminated material with which it comes into contact. This is especially true when a light management film layer (which is often much thinner than the rigid polymer substrate to which it is laminated) comes into contact with the surface of the mold. As a result, it can be very difficult to produce high-quality thermoformed structures, and the resulting thermoformed article can be scratched, resulting in both visual and functional defects. Summary of the Invention

[0003] The present disclosure solves problems associated with thermoformed rigid film structures for various applications, such as illuminated signs. Highly illuminated signs have a convex exterior surface, with the light source located on the concave or interior side of the sign. Highly illuminated signs are also colored or include some kind of light management feature. This color or feature is achieved by laminating a thinner piece of film to one side of a thicker rigid film and then thermoforming the rigid film structure. It is often preferable to laminate the light management film layer to the side of the rigid film that forms the interior of the illuminated sign. Because the more durable, thicker rigid film is on the exterior of the sign in this structure, the sign has improved lifespan and weatherability, and can withstand sunlight, rain, heat, snow, and exposure better than thinner light management films.

[0004] At the same time, however, the thermoforming process is typically more efficient when thermoforming rigid film structures with a "male" mold (a mold with primarily convex features) as opposed to a "female" mold (with primarily concave features). This is because it is easier to draw a heated film onto a convex mold surface than to obtain a precise conformance of the heated film to a concave mold surface. In addition, a concave mold may result in mold surface textures being more likely to remain on the resulting thermoformed article. Molds with primarily concave features may also be more expensive to maintain for repeated use.

[0005] To achieve optimal thermoforming of lighted signs, the color control layer is internal to the sign and primarily convex molds are used to thermoform the sign, but this requires the thinner color control layer to come into contact with the mold surface, which often results in damage to the layer and therefore visual and functional defects in the finished product.

[0006] The present disclosure solves this problem by providing the benefits of efficiently thermoforming rigid film structures while minimizing damage to the light-modulating layer of the structure. The present disclosure also provides a method of thermoforming a rigid film structure using a mold, which provides improved weather resistance by allowing the rigid film structure to be thermoformed onto the convex surface of the mold. The present disclosure also allows for easier alignment of the rigid film structure, primarily against the convex mold surface, by allowing the user to position the desired portion of the rigid film structure directly against the convex surface of the mold. Rigid film structures according to the present disclosure also provide improved durability during thermoforming, as the rigid polymer film can form the exterior of the sign and be exposed to the weather and elements, thereby preventing other layers from being exposed.

[0007] In one example, the present disclosure provides a method for thermoforming a rigid film structure. The method includes applying a rigid film structure to a mold and heating the rigid film structure until it conforms to the mold. The rigid film structure includes a rigid polymer film layer, a light management film layer, and a shielding film layer. The shielding film includes polymethyl methacrylate (PMMA), and the shielding film layer contacts a surface of the mold.

[0008] In another example, the present disclosure provides a rigid film structure for use in a thermoforming process, the rigid film structure comprising a rigid polymer film layer, a light management film layer, and a shielding film layer, the shielding film layer comprising polymethyl methacrylate (PMMA), The shielding film layer is configured to contact a surface of a mold, and the rigid film structure conforms to the shape of the mold when heated.

[0009] In some examples, the stiff polymer film layer comprises at least one of polycarbonate, acrylic, polyethylene terephthalate, and polyethylene terephthalate glycol.

[0010] In some examples, the method further includes applying a vacuum to the side of the male mold opposite the rigid film structure.

[0011] In some examples, the light management film layer is a vinyl film.

[0012] In some examples, the light management film layer further includes a printed ink layer.

[0013] In some examples, the light management film layer is light transmissive.

[0014] In some instances, the light management film layer acts as a diffuser.

[0015] In some examples, the shielding film layers are optically inactive.

[0016] In some examples, the shielding film layer is made of polymethyl methacrylate.

[0017] In some examples, the shielding film layer has a thickness of less than 100 micrometers.

[0018] In some examples, the shielding film layer has a thickness of less than 100 micrometers. [Brief explanation of the drawings]

[0019] A more complete understanding of the present invention can be obtained from the following detailed description considered in conjunction with the accompanying drawings.

[0020] [Figure 1] 1 illustrates a cross section of a rigid film structure that can be used for thermoforming in accordance with the present disclosure.

[0021] [Figure 2] 1 shows a cross section of a rigid film structure conforming to the surface of a mold having predominantly convex features.

[0022] [Figure 3] The defects identified in the evaluation criteria of the examples are shown.

[0023] [Figure 4A] 1 shows a schematic of the experimental set up for the laminated materials and mold. [Figure 4B] 1 shows a schematic of the experimental set up for the laminated materials and mold. [Figure 4C] 1 shows a schematic of the experimental set up for the laminated materials and mold.

[0024] [Figure 5A] The thermoforming results of E1 are shown. [Figure 5B] The thermoforming results of E1 are shown.

[0025] [Figure 6A] The thermoforming results of CE1 are shown. [Figure 6B] The thermoforming results of CE1 are shown.

[0026] Structural changes may be made and the embodiments shown and described herein utilized without departing from the scope of the present invention. The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, the use of a number to refer to a component in a given figure is not intended to limit the component in another figure bearing the same number. DETAILED DESCRIPTION OF THE INVENTION

[0027] 1 shows a cross section of a rigid film structure 100 that can be used for thermoforming in accordance with the present disclosure. Rigid film structure 100 includes a rigid polymer film layer 110, a light management film layer 120, and a shielding film layer 130. In some examples, rigid film structure 100 may include additional layers, and in some examples, light management film layer 120 and shielding layer 130 may be a single film layer.

[0028] The rigid polymer film 110 may comprise various polymers, such as polycarbonate, acrylic, polyethylene terephthalate, and polyethylene terephthalate glycol, or any combination thereof. The rigid polymer film 110 is typically thicker than both the light management film layer 120 and the shielding layer 130 and is rigid so that it cannot be manually stretched and will substantially maintain its shape unless modified by heating to a softening, melting, or flow temperature. The rigid polymer film 110 can have a range of thicknesses. For example, the rigid polymer film 110 can have a thickness of about 1 mm, about 2 mm, about 2.5 mm, about 3 mm, about 3.5 mm, about 4 mm, or about 5 mm, or a range between any two of the foregoing thicknesses.

[0029] The rigid polymer film 110 can have a range of melting points or temperatures required to thermoform the rigid polymer film 110. For example, temperatures of 250°F, 275°F, 300°F, 325°F, 350°F, 375°F, 400°F, 425°F, or 450°F, or temperatures ranging between any two of the aforementioned temperatures, can be used to thermoform the rigid polymer film 110 or rigid film structure 100.

[0030] In some examples, the rigid polymer film 110 is transparent or optically inert, allowing the light management film 120 to be visible through the rigid polymer film 110 .

[0031] The light management film 120 may be a cast or calendered polymer film. The light management film 120 may be a vinyl or non-vinyl film. Examples of film types consistent with the present disclosure include films made from various polymers or polymer blends, such as polyurethane, polyester, polyamide, polyolefin, polystyrene, polycarbonate, polyacrylate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, and fluoropolymers. Commercially available films consistent with the present disclosure include 180mC 3M™ Controltac™ Graphic Film with Comply™ Adhesive and SV480mC 3M™ Envision™ Print Wrap Film.

[0032] Light management film 120 can have various features that affect the transmission (or reflection) of light incident on rigid film structure 100. For example, light management film 120 can be light transmissive and can act as a diffuser to improve the distribution of light across the surface of a sign formed from rigid film structure 100. Light management film 120 can be structured to include features such as lenses or light extraction features. Light management film 120 can also include a printed ink layer. The printed ink layer can have a single color, a pattern, or an image visible through rigid film 110. The printed ink layer can be printed by various methods, such as inkjet printing, gravure printing, or screen printing.

[0033] Light management film layer 120 can have a range of thicknesses. For example, light management film layer 120 can have a thickness of about 25 μm, about 50 μm, about 75 μm, about 100 μm, about 125 μm, about 150 μm, about 175 μm, about 200 μm, or a range between any two of the aforementioned thickness values.

[0034] Shielding film layer 130 can be made from a variety of materials, including, but not limited to, polymethyl methacrylate (PMMA). In some examples, shielding film layer 130 consists solely of PMMA. PMMA has been found to have rare and surprisingly effective protective properties when applied to or included in rigid film structure 100 to protect light modulating layer 120 from damage caused by contact with a mold, particularly a mold having a convex surface.

[0035] In some examples, the shielding film layer 130 is optically inactive such that it does not modulate or affect the transmission of light through the shielding film layer 130 before it reaches and passes through the light regulating layer 120.

[0036] The shielding film layers 130 may be relatively thin, for example, in some instances, the shielding film layers have a thickness of less than 150 micrometers, less than 125 micrometers, less than 100 micrometers, less than 75 micrometers, or even less than 50 micrometers, or have a thickness ranging between any two of the aforementioned thicknesses.

[0037] The rigid polymer film 110, light management film 120, and shielding film layer 130 can be laminated together using a pressure-sensitive adhesive between each layer. For example, the light management film 120 can have an adhesive layer (such as a pressure-sensitive adhesive) on a major side that is covered by a removable liner. When the rigid film structure 110 is made, the liner can be removed and the light management layer 120 can be adhered to the rigid polymer film 110. Similarly, the shielding film 130 can have an adhesive layer on one side and a removable liner covering the adhesive layer. The liner can be removed from the adhesive coating on the shielding film 130 and the shielding film 130 can be adhered to the light management film 120 on the opposite side of the rigid polymer film 110.

[0038] In another example, the light management film 120 can be laminated to the shielding film 130 in a roll-to-roll lamination process, and the laminated product can then be adhered or laminated to the stiff polymer film 110 .

[0039] FIG. 2 shows a cross-sectional view of a rigid film structure 200 conforming to the surface of a mold 210 having primarily raised features 212. In FIG. 2, the rigid film structure 200 includes a rigid polymer film 220, a light management film 230, and a shielding film 240. The rigid film structure is applied to the surface of the mold 210 such that the shielding film 240 contacts the surface of the mold 210. The mold 210 is heated, and as a result of the heating, the rigid film structure 200 softens, or in some instances, melts or flows. In some instances, the mold 210 can have an opening that allows a vacuum to be applied to the surface of the mold opposite the surface to which the rigid film structure 200 is applied. In these instances, the vacuum then draws the softened rigid film structure into conformance and contact with the surface of the mold. [Example] Film laminates were made and thermoformed with and without the shielding film. The resulting forms were inspected for defects. These examples are for illustrative purposes only and are not meant to limit the scope of the appended claims. The following abbreviations are used herein: in = inches, cm = centimeters, °C = degrees Celsius, °F = degrees Fahrenheit. [Table 1] Test Method Visual Inspection Test Thermoformed parts were evaluated for visual defects using a sign face light box. The white LED used in the light box was positioned at a 99-inch 2 (639cm 2 The average luminous emittance over the surface area of ​​the sign diffuser was set to 2351 lux. procedure: 1. The backside of the thermoformed parts was visually evaluated (see evaluation criteria). 2. The thermoformed part was placed on a light box with the front side facing out. The front side of the part was visually evaluated in reflected light (see evaluation criteria), including the top, sides, and a 0.5 inch (1.27 cm) landing area below the sides (the flat area that is typically covered when the thermoformed part is attached to a sign), as well as downweb, crossweb, and at an oblique angle. 3. The LEDs on the light box were turned on and the thermoformed part was used to mask the areas of the light box surface not covered by the part, ensuring that all light was blocked. The front side of the part was evaluated in transmitted light, including the top, sides, and a 0.5 inch (1.27 cm) landing area below the sides, and from downweb, crossweb, and at an oblique angle (see evaluation criteria). 4. The thermoformed part failed the visual inspection test if any of the evaluation criteria were observed. 5.Evaluation criteria: Physical defects such as cracks, holes, bubbles, wrinkles, melting, burning, or contamination. ii. Shadows, bubbles, or unevenness caused by lifting of the film after thermoforming, including lifting of the translucent portion from the substrate (air bubbles, caused by improper surface creation of the substrate before application, or by the mold not releasing), and / or lifting between film layers (shadows, within the structure). iii. Non-uniformity of color saturation between the top and sides of the part (i.e., the top appears much darker than the sides, and the coloring on the sides appears irregular). Each of the evaluation criteria is shown in FIG. (Example) All substrates were dried, cleaned, and applied using the recommended thermoforming film application procedure specified in 3M Thermoforming Instruction Bulletin 5.16 (3M Company, St. Paul, MN). The molds used to prepare the examples were constructed from MDF (medium density fiberboard). The mold geometry was a 2.25 inch (5.71 cm) deep trapezoidal frustum with an 8 inch x 8 inch (20.3 cm x 20.3 cm) base and a 6.75 inch x 6.75 inch (17.1 cm x 17.1 cm) top. The four sides of the mold were designed to allow for evaluation of various draft angles and edge shapes. Sides A and B had a 6.4 degree draft angle and a 0.25 inch (0.64 cm) edge radius. Sides C and D had a 20 degree draft angle and a 9 / 32 inch (0.71 cm) edge radius. One of the corners was rounded, approximately 2 inches (5.08 cm) from the top surface of the mold, with a 20 degree draft angle to the base of the rounded corner when viewed from the top. The mold is shown in Figures 4A and 4B. Figure 4C shows the laminated layers. The film that contacted the mold was the barrier film layer (the backside of the resulting thermoformed part). The substrate was on the outermost surface of the laminate (the frontside of the resulting thermoformed part). Example 1 (E1) Using the 3M Translucent Thermoforming Instruction Bulletin 5.16 (3M Company, St. Paul, MN) procedure for film application, B1, D1, and T1 were laminated to S1. The construction was then placed on top of the mold and thermoformed at 380°F to 420°F (193°C to 215°C). E1 was evaluated and passed the visual inspection test, successfully protecting D1 and T1. E1 had no ruptures, bubbles, burns, or tear defects, achieving essentially perfect moldability or repeatability of the mold. The results are shown in Figure 5 and Table 2 below. Example 2 (E2) B1, D2, and T1 were laminated to S1 using the same process used for E1. The structures were thermoformed at 380°F to 420°F (193°C to 215°C). E2 was evaluated and passed the visual inspection test, successfully protecting D2 and T1. E2 achieved perfect moldability or repeatability with no ruptures, bubbles, burns, or tear defects. The results are shown in Table 2 below. Example 3 (E3) B2, D2, and T1 were laminated to S2 using the same process used for E1. The structures were thermoformed at 360°F to 385°F (182°C to 196°C). E3 was evaluated and passed the visual inspection test, successfully protecting D2 and T1. E3 achieved perfect moldability or repeatability with no ruptures, bubbles, burns, or tear defects. The results are shown in Table 2 below. Example 4 (E4) Using the same process used for E1, B2, D2, and T1 were laminated to S3. The structures were thermoformed at 360°F to 385°F (182°C to 196°C). E4 was evaluated and passed the visual inspection test, successfully protecting D2 and T1. E4 achieved perfect moldability or repeatability with no ruptures, bubbles, burns, or tear defects. The results are shown in Table 2 below. Example 5 (E5) B1 and T1 were laminated to S1 using the same process used for E1. The construction was thermoformed at 380°F to 420°F (193°C to 215°C). E5 was evaluated and passed the visual inspection test, successfully protecting T1. E5 achieved perfect moldability or repeatability with no ruptures, bubbles, burns, or tear defects. The results are shown in Table 2 below. Comparative Example 1: No shielding film (CE1) D2 and T1 were laminated to S1 using the same process used for E1. The structures were thermoformed at 380°F to 420°F (193°C to 215°C). CE1 failed the visual inspection test. CE1 had rupture, burn, and tear defects. The results are shown in Figure 6 and Table 2 below.

Table 2

Claims

1. 1. A method of thermoforming a rigid film structure comprising, in order, a rigid polymeric film layer, a light management film layer, and a protective film layer, comprising: applying the rigid film structure to a mold from the protective film layer side; heating the rigid film structure; applying a vacuum to a space between the protective film layer of the rigid film structure and the mold; Including, the protective film layer comprises polymethyl methacrylate (PMMA); The method wherein only the protective film layer contacts the surface of the mold.

2. The method of claim 1 , wherein the rigid polymeric film layer comprises at least one of polycarbonate, acrylic, polyethylene terephthalate, and polyethylene terephthalate glycol.

3. The method of claim 1 , wherein the light management film layer is a vinyl film.

4. The method of claim 1 , wherein the light management film layer further comprises a printed ink layer.

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