Film stack having an overlaminate film layer and a removable skin layer

Abstract

A film stack is described, particularly one comprising a base overlaminate film layer and a removable skin layer disposed on the base overlaminate film layer, which can prevent unintentional overstretching when the film stack is stretched together because the removable skin layer generates haze before the point where the base overlaminate layer is irreversibly damaged.

Description

[Background technology]

[0001] Film stacks including overlaminate film layers are used in graphics film applications to protect and impart durability to printed or imaged graphics films, particularly inks. The removable skin layer is an outer layer that can be peeled off by the user during or after application. Summary of the Invention

[0002] In one aspect, the present disclosure relates to a film stack. The film stack includes a base overlaminate film layer formed from a first material and having first and second major surfaces; a removable skin layer formed from a second material disposed on the first major surface of the base overlaminate film; and an adhesive layer disposed on the second major surface of the base overlaminate film. The base overlaminate film is transparent. The removable skin layer is stiffer than the base overlaminate film layer. The film stack can be stretched up to 30% elongation without causing irreversible damage to the base overlaminate layer.

[0003] In another aspect, the present disclosure relates to a film stack comprising a base overlaminate film layer and a removable skin layer disposed on a major surface of the base overlaminate film, wherein when the film stack is stretched, the removable skin layer provides a visible indication before irreversible damage to the overlaminate film layer occurs.

[0004] In yet another aspect, the present disclosure relates to a method for preventing overstretching while stretching a film stack, the method including: providing a film stack including a base overlaminate film layer and a removable skin layer disposed on the base overlaminate film layer, wherein when the film is in a stretched state, the removable skin layer becomes hazy before causing irreversible damage to the base overlaminate film layer; and stretching the film stack to or below the point at which the removable skin layer becomes hazy. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic cross-sectional side view of a film stack comprising a base overlaminate film layer and a removable skin layer. [Figure 2] FIG. 10 is a schematic cross-sectional side view of another film stack comprising two base overlaminate film layers and two removable skin layers. [Figure 3A] Schematic top view of an unstretched film stack, a film stack stretched to create haze in the removable skin layer, and a film stack with the hazy removable skin layer delaminated from the film stack to expose the underlying base overlaminate film layer. [Figure 3B] Schematic top view of an unstretched film stack, a film stack stretched to create haze in the removable skin layer, and a film stack with the hazy removable skin layer delaminated from the film stack to expose the underlying base overlaminate film layer. [Figure 3C] Schematic top view of an unstretched film stack, a film stack stretched to create haze in the removable skin layer, and a film stack with the hazy removable skin layer delaminated from the film stack to expose the underlying base overlaminate film layer. [Figure 4] 1 is a graph showing load force versus elongation for Example 3 (and its components) and Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0006]

[0003] Overlaminates are used in graphics films to protect or enhance the durability of the printed base graphics film. Overlaminates can provide physical protection, such as against abrasion or ambient conditions. Overlaminates can help extend the usable or optimal life of the printed graphics film product. Traditionally, overlaminates are laminated to the printed base graphics film during or after printing.

[0007] The outer surface of the overlaminate film can determine the overall appearance of the film stack to an observer. For example, a glossy outer surface (with little surface structure) provides a high percentage of specular to diffuse reflection, typically providing low haze and high clarity. Other desired outer surface structures may be desirable; for example, certain overlaminates may have a matte structure or other textured surface. For this reason, it is important to preserve and protect the surface properties of the overlaminate film. Surface scratches and other defects can affect the final appearance of the film stack and may be unpleasant for customers or observers. Therefore, a protective skin layer is typically provided on the surface of the film to be removed after lamination or final application, which may require squeegeeing or other physical contact that can damage the exposed surface.

[0008] Additionally, overlaminates can be thin and very conformable, and therefore difficult to handle. A removable skin layer can provide sufficient rigidity to facilitate handling. Traditionally, the removable skin layer can be removed once the overlaminate is laminated to the base graphics film, or after the combined film stack has been adhered to the desired surface or substrate.

[0009] Paper liners or polymeric materials are traditionally laminated to a base overlaminate film that is formed in a separate step. This typically requires an additional adhesive layer and attachment step, which can further complicate the manufacturing process. Alternatively, a temporary liner is provided on the front as protection during the installation step. The paper liner is opaque, preventing the graphics from being visible during installation.

[0010] Certain removable skin layers described herein may be formed through blown film molding or conventional extrusion processes and may be co-formed with the base overlaminate film, eliminating the need for a separate adhesive and / or thermal lamination process. Such removable skin layers may require a moderate peel force to separate the layer from the base overlaminate film while remaining securely attached throughout shipping, handling, and installation.

[0011] Figure 1 is a schematic cross-sectional side view of a film stack comprising a base overlaminate film layer and a removable skin layer. Figure 1 includes a film stack 100 comprising a base overlaminate film layer 110, a removable skin layer 120, a liner 130 with an optional release layer 132, a pressure-sensitive adhesive 140, and an optional tie layer 150.

[0012] The base overlaminate film layer 110 may be any suitable material and may be formed through any suitable process. In some embodiments, the base overlaminate film layer includes or is made from polyvinyl chloride. In some embodiments, the base overlaminate film layer includes polyurethane and cellulose acetate propionate or cellulose acetate butyrate. In some embodiments, the base overlaminate film layer includes or is made from polyester or copolyester. In some embodiments, the base overlaminate film includes or is made from an ionomer resin of a copolymer of ethylene and methacrylic acid. In some embodiments, the base overlaminate film layer includes or is made from ethylene vinyl acetate (EVA). In some embodiments, the base overlaminate film layer includes or is made from polycarbonate, polypropylene, or polystyrene. In some embodiments, the base overlaminate film layer includes or contains an elastomeric component. Polyamides and block copolymers containing polyamides may be suitable. A particular material or combination of materials may be selected for its physical, optical, and / or rheological properties. In some embodiments, the base overlaminate film layer may include two or more layers, and the two or more layers may include the same or different materials.

[0013] The base overlaminate film layer 110 may have any suitable thickness and may be formed by extrusion (such as melt extrusion or blown film molding). In some embodiments, the base overlaminate film layer 110 has a thickness of 25 micrometers to 100 micrometers. The base overlaminate film layer 110 may have a smooth or textured surface structure.

[0014] The removable skin layer 120 may be or may be formed from any suitable material. In some embodiments, the removable skin layer is stiffer than the base overlaminate film layer. In some embodiments, the removable skin layer 120 may be or include polypropylene. In some embodiments, the removable skin layer 120 may be or include any other suitable polymer, copolymer, or blend thereof. The removable skin layer 120 may have any suitable thickness, including from 10 micrometers to 150 micrometers. The thickness and material may be selected to provide sufficient stiffness to the film stack and maintain an adequate peel force for delamination. In some embodiments, the 90-degree peel force for delamination may be from 50 to 100 grams per inch (approximately 20 to 40 grams per centimeter). The removable skin layer may be extruded (melt extrusion or blown film), solution cast, or coated.

[0015] The removable skin layer 120 has a selected combination of material and thickness such that, when stretched, the skin layer rapidly develops haze. While many materials can develop stretch-induced haze, certain materials exhibit a rapid increase in haze at a certain stretch threshold. For example, stretching the skin layer from 0% to 30% can increase haze by 50 percentage points or more. In some embodiments, stretching the skin layer from 0% to 30% can increase haze by 60 percentage points or more. In some embodiments, stretching the skin layer from 0% to 30% can increase haze by 70 percentage points or more. In some embodiments, stretching the skin layer from 0% to 30% can increase haze by 80 percentage points or more. In some embodiments, stretching the skin layer from 0% to 30% can increase haze by 90 percentage points or more.

[0016] The liner 130 may be provided as part of the film stack 100 to protect the pressure-sensitive adhesive 140 from exposure to the elements, degradation, and unintended adhesion. The liner 130 also allows the film stack 100 to be configured, stored, and shipped as a roll without self-adhesion. The liner 130 may be any suitable material, generally including paper or a polymer such as polyethylene. In some embodiments, the liner 130 is coated or covered with an optional release layer 132, which may improve the smoothness and / or ease of separation between the liner and the pressure-sensitive adhesive. The optional release layer 132 may be silicone, wax, block copolymer, or any other suitable material. In some embodiments, the optional release layer 132 may be omitted or not necessary to provide the desired release characteristics.

[0017] A pressure-sensitive adhesive 140 is disposed between the liner 130 and the base overlaminate film layer 120. The pressure-sensitive adhesive 140 can be any suitable adhesive, including an acrylic adhesive, an epoxy, or an optically clear adhesive. Particularly for transparent or translucent base overlaminate films, the optical properties of the adhesive (typically high transmittance, low haze, and high clarity) can be important to maintain the overall appearance of the film during use. The pressure-sensitive adhesive can be extruded (melt extrusion or blown film), solution cast, or coated.

[0018] In some embodiments, the pressure-sensitive adhesive 140 may have sufficient structure to maintain its shape (i.e., not flow) over a range of exposed temperatures and humidity. In some embodiments, the adhesive may be fully or partially crosslinked. The adhesive may include pigments, dyes, or other colorants. In some embodiments, the adhesive may be 10 micrometers to 100 micrometers thick. In some embodiments, the adhesive may include partially embedded microbeads made from materials such as glass, ceramic, or polymer resins, or aggregates thereof held together with a suitable binder material. In some embodiments, the microbeads may be index-matched to the structured adhesive and / or may be transparent.

[0019] Because the base overlaminate film layer may not inherently bond well to the pressure-sensitive adhesive, some embodiments may include an optional tie layer 150. The tie layer, often referred to as a primer or prime layer, can be any suitable material or composition having any suitable thickness. The choice of tie layer is to ensure sufficient adhesion between the base overlaminate film layer and the pressure-sensitive adhesive (to prevent ply-bold failure). In some embodiments, the tie layer may include a polyamide or copolyamide. Certain materials may alternatively or additionally be useful as barrier layers to prevent migration of plasticizers, water, solvents, or other contaminants from the front surface of the film stack to the adhesive. The tie layer may be very thin, less than 10 micrometers thick, less than 6 micrometers thick, less than 5 micrometers thick, less than 4 micrometers thick, less than 3 micrometers thick, less than 2 micrometers thick, or even less than 1 micrometer thick. The tie layer may be solution-cast, coated, or even extruded or coextruded (with one or more of the other layers).

[0020] The film stack 100 as a whole can be stretched together to some extent without causing irreversible damage to the base overlaminate layer. In some embodiments, the film stack 100 can be stretched up to 30% elongation without causing irreversible damage to the base overlaminate layer. In some embodiments, the film stack 100 can be stretched up to 50% elongation without causing irreversible damage to the base overlaminate layer. In some embodiments, the film stack 100 can be stretched up to 100%, 200%, or more without causing irreversible damage to the base overlaminate layer. Stretchability aids in the application of such films to complex, curved, or channeled surfaces with minimal lift. However, all stretchable films have a limit beyond which they will undergo irreversible plastic deformation and ultimately break or tear. In some cases, the stress of an overstretched film will cause it to lift from the surface to which it is adhered. In some cases, the film may exhibit optical artifacts, such as haze.

[0021] It is important to avoid overstretching during use and installation. In embodiments described herein, the removable skin layer develops haze when the film stack is stretched at or before the base overlaminate layer is irreversibly optically or physically damaged. In some embodiments, the removable skin layer develops haze at or before any of the layers is irreversibly damaged.

[0022] Thus, the structures and stacks described herein can be useful because they provide a visual indicator to the installer or user that the base overlaminate film is approaching its recommended physical limit of elongation. Because the removable skin layer can be peeled off after application, the user can stop stretching at or near the point where haze is observed, continue installing the film after being warned that it is approaching the point of irreversible damage, and remove the skin layer with confidence that the underlying base overlaminate film layer has retained its optical and physical qualities.

[0023] In some embodiments, the film stack described herein can be laminated to a base graphics film (i.e., a colored or digitally printed decorative film) and the entire stack can still be stretched together. As described elsewhere, the entire film stack can have a recommended or safe stretch limit. In some embodiments, this can be 30%. In some embodiments, this can be 150%. In some embodiments, this can be 100%, 200%, or more. Similarly, the removable skin layer develops haze at or before the point where the base overlaminate layer and / or base graphics film are overstretched to the point of failure.

[0024] Figure 2 is a schematic cross-sectional side view of another film stack comprising two base overlaminate film layers and two removable skin layers. Film stack 200 is similar to film stack 100 of Figure 1, but Figure 2 shows an alternative construction in which two overlaminate base layers are formed and stored on a single liner layer. Film stack 200 comprises two removable skin layers 220, two base overlaminate film layers 210, two optional tie layers 250, two pressure-sensitive adhesive layers 240, and a single liner 230 that may or may not include a release coating on one or both surfaces.

[0025] Each component of Figure 2 is as described in connection with Figure 1, except that the manufacture of certain film stacks may be advantageously suited to an extrusion process. Forming two usable film sides on a single liner can provide more economical manufacturing, storage, and shipping with less waste. Additionally, when film stack 200 is stored or configured as a roll, removable skin layer 220 acts as a protective liner to minimize surface impressions or scratches on the base overlaminate film.

[0026] 3A-3C are schematic top views of an unstretched film stack (such as the film stack described and shown in conjunction with FIG. 1), a film stack that has been stretched to create haze in the removable skin layer, and a film stack with the removable skin layer in a hazy state delaminated from the film stack to expose the underlying base overlaminate film layer.

[0027] In a first step, Figure 3A shows a top view of the film stack with removable skin layer 320 visible. In some embodiments, removable skin layer 320 is substantially transparent or clear, allowing the surface of the underlying base overlaminate film to be seen through the top surface.

[0028] In the second step, FIG. 3B shows a top view of the stretched film stack with both the removable skin layer 320 and any underlying layers (such as the base overlaminate film 310). In some embodiments, this can be 130% or even 150% elongation. The removable skin layer is hazed by stretching. In some embodiments, developing haze means that the haze changes from unstretched to stretched by more than 50 percentage points. In some embodiments, developing haze means that the haze changes from unstretched to stretched by more than 60 percentage points. In some embodiments, developing haze means that the haze changes from unstretched to stretched by more than 70 percentage points. In some embodiments, developing haze means that the haze changes from unstretched to stretched by more than 80 percentage points. In some embodiments, developing haze means that the haze changes from unstretched to stretched by more than 90 percentage points. The underlying base overlaminate film does not develop haze and remains within its recommended stretch range for physical and optical integrity.

[0029] In the third step, Figure 3C shows a top view of the film stack with the removable skin layer being delaminated from the base overlaminate film layer. The removable skin layer 320 retains its haze but can be easily and cleanly removed to expose the underlying protected base overlaminate film 310. The skin layer can be removed before, during, or after final installation on the desired substrate. [Example]

[0030] [Table 1]

[0031] Preparation of Examples Examples 1-3 and Comparative Examples 1-5 were produced on a three-layer blown film line. The line had a customer-setup three-layer die with a 2-inch opening connected to three independent 3 / 4-inch Brabender single-screw extruders (Brabender GmbH & Co. KG, Kulturstrasse 49-55, 47051 Duisburg). Examples 4, 5, and 6, as well as Comparative Example 6, were produced on a seven-layer pancake stack die (Type LF-400 Coex 7-layer from Labtech Engineering). Airflow into the die was manually adjusted to achieve a blow-up ratio of approximately 2:1. The bubbles were then collapsed over an approximately 10-foot die, passed through rollers, and then wound onto a 3-inch core and wound up. The feed material was supplied by seven independent 20 mm diameter extruders (Labtech Scientific Single Screw Extruder Type LE20-30 / C HA).

[0032] The compositions of the examples and comparative examples are listed in the table below.

[0033] [Table 2]

[0034] [Table 3]

[0035] Test Method 90° peel force measurement The 90-degree peel test was performed using a peel tester (80-91 LAB MASTER Release & Adhesion Tester) manufactured by Testing Machines, Inc. (New Castle, DE 19720 USA). Samples were conditioned for at least 24 hours in a room at CTH (constant temperature of 73°F and 50% humidity). The conditioned samples were cut into 2.5 cm (TD, transverse direction) and approximately 30.5 cm (machine direction) strips. With the ionomer film side facing the adhesive, the samples were laminated to a metal plate using 3M Optically Clear Adhesive 8171, and the peel force to remove the peelable skin was measured. The 90-degree peel force (in grams) was measured at a speed of 120 inches / minute.

[0036] [Table 4]

[0037] Optical Haze Measurement The optical haze of the samples was measured using a Haze-Gard Plus haze meter commercially available from BYK Instruments (Columbia, Maryland 21046-2729, USA). Samples were cut to 38 mm x 127 mm (1.5 in x 5.0 in). Optical haze was measured on unstretched samples, and samples were stretched up to 30%. These samples were laminated to clear, 3 mm thick, 60 mm x 240 mm general-purpose acrylic panels using 3M Optically Clear Adhesive 8171 before measurement. The skin side was facing the air. The results are listed in the Haze Results Table below.

[0038] [Table 5]

[0039] Film Tensile Properties After conditioning the films in a CTH (constant temperature and humidity, 23°C and 50%) room for 24 hours, samples were cut to 38 mm x 127 mm (1.0 in x 5.0 in) in the machine direction. Testing was performed using an Instron (Model: EMSYSU 4242, Norwood, MA 02062) tensile machine at a crosshead speed of 12 in / min (304.8 mm / min) with a 2 in (50.8 mm) gap. Each of the examples could be stretched up to 150%.

[0040] 4 shows the load force (lbs / inch) versus elongation (%) for selected examples and example components. In the range of elongation (low levels) for handling and lamination, the skin layer 420 is stiffer than the overlaminate base layer 410. Similarly, the complete structure 440 (including the stiff skin layer) of Example 3 is stiffer than 430 of Comparative Example 5. In addition to the embodiments, the following aspects will be noted. (Appendix 1) 1. A film stack comprising: a base overlaminate film layer formed from a first material and having first and second major surfaces; a removable skin layer formed from a second material disposed on the first major surface of the base overlaminate film; an adhesive layer disposed on the second major surface of the base overlaminate film; the base overlaminate film layer is transparent; the removable skin layer is stiffer than the base overlaminate film layer; A film stack wherein the film stack is stretchable up to 30% elongation without causing irreversible damage to the base overlaminate layer. (Appendix 2) 10. The film stack of claim 1, wherein when the film stack is stretched together, the removable skin layer develops haze while the base overlaminate film layer remains transparent. (Appendix 3) 10. The film stack of claim 1, wherein the removable skin layer has a thickness of 10 micrometers to 150 micrometers. (Appendix 4) 2. The film stack of claim 1, wherein the film stack includes a tie layer between the adhesive layer and the base overlaminate film layer. (Appendix 5) 10. A roll of film comprising the film stack of claim 1, wherein the film stack is disposed on a liner. (Appendix 6) 10. The film stack of claim 1, wherein the first material and the second material are extrudable. (Appendix 7) 10. The film stack of claim 1, wherein the first material comprises polyvinyl chloride. (Appendix 8) 10. The film stack of claim 1, wherein the first material comprises polyurethane. (Appendix 9) 10. The film stack of claim 1, wherein the second material comprises polypropylene. (Appendix 10) 10. The film stack of claim 1, wherein the base overlaminate layer comprises an ionomer. (Appendix 11) 1. A film stack comprising: a base overlaminate film layer; a removable skin layer disposed on a major surface of the base overlaminate film; A film stack, wherein the removable skin layer provides a visible indication when the film stack is stretched before irreversible damage occurs to the base overlaminate film. (Appendix 12) 12. The film stack of claim 11, wherein the visible symptom is a sudden increase in haze. (Appendix 13) 13. The film stack of claim 12, wherein the abrupt increase in haze is an increase of at least 50 percentage points. (Appendix 14) 1. A method for preventing overstretching during stretching of a film stack, comprising: providing a film stack including a base overlaminate film layer and a removable skin layer disposed on the base overlaminate film layer, wherein when the film stack is stretched, the removable skin layer becomes hazy before causing irreversible damage to the base overlaminate film layer; stretching the film stack to or below the point at which the removable skin layer becomes hazy. (Appendix 15) 15. The method of claim 14, wherein stretching the film stack means stretching to 30% elongation. (Appendix 16) 12. The method of claim 11, wherein stretching the film stack means stretching to 50% elongation. (Appendix 17) 12. The method of claim 11, wherein stretching the film stack comprises stretching the film stack to a point where the removable skin layer increases its haze by 50 percentage points. (Appendix 18) 15. The method of claim 14, further comprising removing the skin layer. (Appendix 19) 15. The method of claim 14, further comprising the step of stretching the film. (Appendix 20) 20. The method of claim 19, comprising applying heat to the film.

Claims

1. 1. A film stack comprising: a base overlaminate film layer formed from a first material and having first and second major surfaces; a removable skin layer formed from a second material disposed on the first major surface of the base overlaminate film; an adhesive layer disposed on the second major surface of the base overlaminate film; the base overlaminate film layer is transparent; the removable skin layer is stiffer than the base overlaminate film layer; The film stack can be stretched to 30% elongation without causing irreversible damage to the base overlaminate layer, and when the film stack is stretched together, the removable skin layer exhibits an increase in haze of 50 percentage points or more from an unstretched state to a 30% stretched state.

2. 10. The film stack of claim 1, wherein the removable skin layer develops haze when the film stack is stretched together, while the base overlaminate film layer remains clear.

3. 10. The film stack of claim 1, wherein the removable skin layer has a thickness of from 10 micrometers to 150 micrometers.

4. The film stack of claim 1 , wherein the film stack includes a tie layer between the adhesive layer and the base overlaminate film layer.

5. 10. A roll of film comprising the film stack of claim 1, the film stack disposed on a liner.

6. The film stack of claim 1 , wherein the first material and the second material are extrudable.

7. The film stack of claim 1 , wherein the first material comprises polyvinyl chloride or polyurethane.

8. The film stack of claim 1 , wherein the second material comprises polypropylene.

9. The film stack of claim 1 , wherein the base overlaminate layer comprises an ionomer.

10. 1. A film stack comprising: a base overlaminate film layer; a removable skin layer disposed on a major surface of the base overlaminate film; When the film stack is stretched, the removable skin layer provides a visible indication before causing irreversible damage to the base overlaminate film, the visible indication being a sudden increase in haze of at least 50 percentage points.

11. 1. A method for preventing overstretching during stretching of a film stack, comprising: providing a film stack including a base overlaminate film layer and a removable skin layer disposed on the base overlaminate film layer, wherein when the film stack is stretched, the removable skin layer becomes hazy before causing irreversible damage to the base overlaminate film layer; stretching the film stack to or below the point at which the removable skin layer becomes hazy.

12. 12. The method of claim 11, wherein stretching the film stack means stretching to 30% elongation.

13. 12. The method of claim 11, wherein stretching the film stack comprises stretching the film stack to a point where the removable skin layer increases its haze by 50 percentage points.

14. The method of claim 11 including applying heat to the film.

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