Patent Application
20240059937
The present invention relates to an adhesive delivery system. In particular, the present invention is a system for delivering an adhesive to a shaped surface.
Die cut or laser cut adhesives are widely used as optical and/or bonding layers in electronic and automotive displays. With the increased trend of displays in both consumer electronics and automotive becoming more complex and taking new shapes, such as being non-flat or curved, various materials and manufacturing methods need to be developed to apply adhesives onto the shaped surface. Adhesives used in electronic displays are generally provided with a release liner on each surface to protect the adhesive until the adhesive is ready for use. The release liners used to apply the adhesive in electronic displays have typically been rigid and dimensionally stable.
To laminate the adhesive to a surface, various methods can be used. In one method, a roller laminator is used to laminate adhesive to 2D and 2.5D (curved on 2 opposite edges) display surfaces. In this method, a light release liner is removed from the adhesive and one edge of the adhesive is aligned with the mating edge of the display layer surface. Aided by the support of a rigid heavy release liner, a roller then applies the adhesive precisely to the display surface. Another method to laminate an adhesive onto a display surface is to use a vacuum laminator. In this method, the adhesive is secured to an applicating surface and aligned above the display layer surface. The adhesive is then applied to the display surface under surface pressure in a vacuum environment.
While rigid liners provide effective support to an adhesive when laminating to 2D and 2.5D surfaces, they can present some issues when laminating an adhesive to 3D surfaces due to potential large deformation required to conform and stress that can buckle the liner material. One solution to the buckling problem is to use a less rigid liner or to reduce the rigidity of the process liner with heat during the lamination process; however, this can create quality problems at each step of the manufacturing process. When a less rigid liner is used, the adhesive and liner are pulled over the display surface in a vacuum and adhered. Traditional liners can wrinkle as parts of the liner are pulled to and over the curved corners of the display surface. While the less rigid liners allow for shaping to a curved surface, they can be limiting in that they must have enough rigidity to support the adhesive during the coating, converting, and assembly processes.
In one embodiment, the present invention is an adhesive delivery system including a conformable film having top and bottom faces, an adhesive releasably coated on at least a portion of the top face of the conformable film, and a light release liner adhered to the adhesive side opposite the conformable film.
The invention may be further illustrated by reference to the accompanying drawings wherein:
The adhesive delivery system of the present invention is particularly useful in the field of electronic display manufacturing. For a planar film to conform uniformly to a three-dimensional curved surface, the film will bend, stretch and/or compress as it contacts the mating surface, which can create stress both in the film and surface substrate. The deformation strain of the film can generate stresses that exceed its yield strength where if the stress is then released, the deformation strain does not fully recover, which is defined as plastic deformation. If the strain is recovered, then the material is typically considered elastic or viscoelastic where the strain recovers with time. Materials such as polyurethane will recover strain significantly better than polypropylene films, for example, when strain levels exceed about 10%. If strain deformation is held fixed, the stress level can relax. If a stress is maintained, the material can also generate creep strain, where the material continues to deform with time. Creep can occur at any given strain level when stress is present. In one embodiment, the conformable film is conformable to three-dimensional (3D) electronic display layer surfaces. As such, when the adhesive is applied to a display layer surface using the conformable film, the adhesive conforms to the surface uniformly, without wrinkles or optical distortion.
The adhesive delivery system 10 of the present invention, as shown in the figures, includes a heavy release liner 12 having a top face 14 with release properties and a bottom face 16, an adhesive 18 coated on at least a portion of the top face 14 of the heavy release liner 12, and a light release liner 20 releasably adhered to the adhesive 18 opposite the heavy release liner 12. The heavy release liner 12 is a two-layer peelable construction and includes a conformable film 22 and a rigid liner 24 which may also be employed as a rigid frame carrier 26 for the conformable film 22. The rigid frame carrier 26 is attached to and covers at least a portion of the conformable film 22. The rigid frame carrier 26 is formed of material substantially more rigid than the conformable film 22 to provide rigidity to the delivery system 10, particularly after removal of the light release liner 20. The rigid frame carrier 26 may be permanently or releasably attached to the conformable film 22. In the embodiments shown in
In one embodiment, the heavy release liner 12 includes a thin, stretchable, conformable film 22 having a surface treated with a release coating and a rigid frame carrier 26. In one embodiment, the release coating can include, but is not limited to: silicone, fluoropolymer, or hydrophobic alkyl acrylate. Where the rigid liner 24 supporting the conformable film 22 is also the rigid frame carrier 26 (as shown in
In one embodiment, the rigid frame carrier 26 includes a window 28 around the adhesive 18 so that the entirety of the conformable film 22 contacting the adhesive 18 is free to conform to the surface unencumbered during the lamination process. In another embodiment, the present invention also offers the advantage of strategically locating the rigid frame carrier 26 on the conformable film 22 behind certain areas of the adhesive 18 to control strain of the conformable film 22 and adhesive 18 as desired. By controlling strain, optical defects can be reduced.
The adhesive delivery system 10 of the present invention is useful in connection with any conformable film 22 having an adhesive coating 18 on it. In one embodiment, the adhesive 18 may have a heavy bond to the conformable film 22 and a light bond to another optical film, such as an OLED display, such that the conformable film 22 may be adhered to the OLED to aid in a 3D shaping or laminating process where the adhesive/conformable film substrate is subsequently removed.
Light release liners 20 which are suitable for use in the adhesive delivery system 10 of the present invention can be made of materials including, but not limited to: polyester, polyethylene, polyurethane, polypropylene or composites of such. In one embodiment, the light release liner is coated with release agents such as fluorochemicals or silicones. For example, U.S. Pat. No. 4,472,480, which is hereby incorporated by reference, describes low surface energy perfluorochemical liners. In one embodiment, the light release liner 20 can include, but is not limited to: polyester films and polyolefin films coated with silicone release materials. Examples of commercially available silicone coated release liners include, but are not limited to: RFO2N liner, commercially available from SKC Haas, Korea; LN75 liner, commercially available from Nan Ya Plastics Corp., Taiwan, and those sold by Loparex, located in Cary, North Carolina.
The conformable film 22 of the present invention has a true stress/strain slope that does not exceed about 60 MPa, particularly does not exceed about 40 MPa, and more particularly does not exceed about 20 MPa, from 0 to 100% true strain and has no appreciable plastic (or permanent) deformation. This slope is similar to Young's Modulus for elastic materials, which can be defined as E=σ/ε, where E is Young's modulus, σ is the uniaxial engineering stress or uniaxial force per unit fixed area, and E is the uniaxial engineering strain, or proportional deformation (change in length divided by original length. For large deformation cases, engineering strain does not accurately describe the deformation state and true strain is then defined. True strain is the integral of the change in length divided by length integrated from the original part length which simplifies to the natural logarithm of the engineering strain incremented by 1 unit. For small strains (<1%) engineering strain is like true strain. For 3D lamination cases, true strain can exceed about 50%. True stress is defined like engineering stress except the area is no longer fixed. The slope limit is defined for the conformable material as the slope itself may not be constant. Both E and σ have units of pressure, while E is dimensionless. For a given amount of percent true strain on the conformable film, the true stress should not exceed the value limited by the slope (ex. 100% true strain should not exceed about 40 MPa).
The conformable film 22 is formed from materials having the desirable properties of resiliency and transparency for release liners. In one embodiment, the conformable film 22 is translucent or transparent polymeric films. In one embodiment, the conformable film 22 can include, but is not limited to: polyurethane, polyethylene, polypropylene, polyvinyl chloride, polyacrylate, and combinations thereof.
In one embodiment, the conformable film 22 of the present invention includes a low adhesion coating or surface on the adhesive contact side. The low adhesion coating may be applied by applying a release coating or by adding release additives in the conformable film resin prior to it being casted or extruded as a thin film. In one embodiment, the low adhesion coating on the adhesive facing side is compatible both with the adhesive and the rigid frame carrier bonding method. The low adhesion coating, if present, on the side opposite the adhesive is compatible with the rigid frame carrier bonding method.
The primary considerations in choosing any low adhesion coatings or treatments according to the present invention are their release characteristics and their compatibility with the bond between the rigid frame carrier 26 and the conformable film 22 and between the adhesive 18 and the conformable film 22.
The rigid frame carrier 26 suitable for use in the adhesive delivery systems 10 of the present invention can be made materials including, but not limited to: polyurethane, polyester, polyethylene, polypropylene, or composites of such. In one embodiment, the rigid frame carrier is coated with release agents such as fluorochemicals or silicones. For example, U.S. Pat. No. 4,472,480, which is hereby incorporated by reference, describes low surface energy perfluorochemical liners. In one embodiment, the rigid frame carrier 26 is coated with low adhesion adhesive layer. In such way, the frame carrier can be bonded to the flexible, conformable liner to provide the support of handling during coating, lamination process. In one embodiment, the rigid frame carrier can include, but is not limited to: polyurethane films, polyolefin films, and even paper. Examples of commercially available silicone coated release liners include, but are not limited to: RFO2N liner, commercially available from SKC Haas, Korea; LN75 liner, commercially available from Nan Ya Plastics Corp., Taiwan, and those sold by Loparex, located in Cary, North Carolina.
In one embodiment, the material used to supply the rigid frame carrier 26 for the delivery system 10 is substantially more rigid than the conformable film 22 to prevent the conformable film 22 from wrinkling and controlling undesirable strain of the adhesive 18 during application. The material used for the rigid frame carrier 26 may have a controlled bond to the conformable film 22. In one embodiment, the rigid frame carrier material 26 may be adhesive coated to create a bond to the conformable film 22. In another embodiment, the rigid frame carrier material 26 may also be bonded to the conformable film 22 by extruding the conformable film resin onto the rigid frame carrier material. In yet another embodiment, the rigid frame carrier material 26 may also be heat-sealable to the conformable film, with or without the low adhesion coating, for the purpose of manufacturing the adhesive delivery system 10. In general, materials for the rigid frame carrier 26 can include, but are not limited to: polyester films, polycarbonate films, poly(methyl)methacrylate films, acrylonitrile butadiene styrene films, polypropylene films, polyurethane films, polyethylene terephthalate films, polyoxymethylene films, and combinations thereof.
Other combinations of release liners and adhesives are contemplated for use with embodiments according to the present invention. Those skilled in the art will be familiar with the processes of testing a new adhesive against different liners or a new liner against different adhesives to arrive at the combination of qualities desired in a final product. The considerations pertinent to the selection of a silicone release liner can be found in Chapter 18 of the Handbook of Pressure Sensitive Adhesive Technology, Van Nostrand-Reinhold, 1982, pp. 384-403. U.S. Pat. No. 4,472,480 also describes considerations pertinent to the selection of a perfluoropolyether release liner.
Release liners are available from a variety of manufacturers in a wide variety of proprietary formulations. Those skilled in the art will normally test those release liners in simulated use conditions against an adhesive of choice to arrive at a product with the desired release characteristics.
In one embodiment, the adhesive 18 is an optically clear transfer adhesive having high flow/creep at elevated temperatures of about 65° C., low initial tack at room temperature, and sufficient adhesive properties for the display electronics and automotive industries. As used herein, the term “optically clear” refers to a material that has a haze of less than about 6%, particularly less than about 4% and more particularly less than about 2%; a luminous transmission of greater than about 88%, particularly greater than about 89%, and more particularly greater than about 90%; and an optical clarity of greater than about 98%, particularly greater than about 99%, and more particularly greater than about 99.5% when cured. Typically, the clarity, haze, and transmission are measured on a construction in which the adhesive is held between two optical films, such as poly(ethylene terephthalate) (PET). The measurement is then taken on the entire construction, including the adhesive and the substrates. Both the haze and the luminous transmission can be determined using, for example, ASTM-D 1003-92. The optical measurements of transmission, haze, and optical clarity can be made using, for example, a BYK Gardner haze-gard plus 4725 instrument (Geretsried, Germany). The BYK instrument uses an illuminant “C” source and measures all the light over that spectral range to calculate a transmission value. Haze is the percentage of transmitted light that deviates from the incident beam by more than 2.5°. Optical clarity is evaluated at angles of less than 2.5°. Typically, the PCOCA is visually free of bubbles.
The adhesive 18 can achieve high flow/creep at elevated temperatures of about 65° C., low initial tack at room temperature, and sufficient adhesive properties for the display electronics and automotive industries. The adhesive 18 may be activated to achieve the properties described above in any manner known to those of skill in the art. In one embodiment, the adhesive 18 is a pressure sensitive adhesive (PSA). The PSA may have lower tack, stronger molecular interaction (such as, hydrogen bonding), and high modulus at room temperature. In one embodiment, the adhesive 18 is a heat activated adhesive. In one embodiment, the adhesive 18 acts like a film (e.g. plastic sheet) when laminated and through an ultraviolet dosage, the film turns viscoelastic and into a pressure sensitive adhesive. In one embodiment, the adhesive 18 is a chemical activated adhesive that includes an additive that reacts with the adhesive, very slowly building adhesion as the reaction takes place. In one embodiment, the adhesive 18 can include a silicone that is at the surface of the adhesive 18. The presence of silicone would make the initial adhesion low, thus allowing the adhesive to be reworkable (i.e., peeled off) if there are lamination defects. Over time, the silicone will migrate into the bulk of the adhesive and therefore become tacky to the glass, and build higher adhesion to the glass. In one embodiment, the adhesive 18 may be a tacky pressure sensitive layer but with embodied structures to achieve repositionability and slip properties. In one embodiment, the adhesive 18 may be a tacky pressure sensitive adhesive, but with non-tacky domains to help slip or repositionability. The non-tacky domains may have similar refractive indices with the adhesive layer. The non-tacky domains may be a heat active adhesive formulation.
In one embodiment, the laminating temperature of the adhesive 18 is between about 40° C. to about 150° C., particularly between about 40° C. and about 100° C., more particularly between about 50° C. and about 80° C., and most particularly about 65° C.
Creep is a measurement of how much the adhesive 18 will deform when a given pressure or stress is applied. It would be expected that the higher the creep strain percentage, the more likely the adhesive will “flow” into a 3D shape when laminating pressure is applied. In one embodiment, the adhesive 18 has a creep strain percentage at about 25° C. of between about 0 and about 100%, particularly between about 2 and about 75%, and more particularly between about 2 and about 50%. In one embodiment, the adhesive 18 has a creep strain percentage at about 65° C. of between about 65 and about 800%, particularly between about 85 and about 600%, and more particularly between about 100 and about 500%.
In one embodiment, the adhesive 18 has a glass transition temperature (Tg) of between about −20° C. and about 150° C., particularly between about −15° C. and about 100° C., and more particularly between about −5° C. and about 85° C.
The storage modulus is a measure of the elastic nature of the adhesive 18. The higher the value, the more film like and the higher tendency for the adhesive to have low tack, which can be better for slipping. In one embodiment, the adhesive 18 has a storage modulus at about 25° C. of between about 1E+4 and about 1E+9 Pa, particularly between about 1E+5 t and o about 1E+8 Pa, and more particularly between about 5E+5 and about 5E+7 Pa. In one embodiment, the adhesive 18 has a storage modulus at about 65° C. of between about 1E+2 and about 1E+6 Pa, particularly between about 1E+3 and about 1E+6 Pa, and more particularly between about 1E+4 and about 1E+6 Pa.
The loss modulus is the measure of the viscosity properties of the adhesive 18. The higher the loss modulus, the more the adhesive behaves as a liquid. In one embodiment, the adhesive 18 has a loss modulus at about 25° C. of between about 1E+3 and about 1E+9 Pa, particularly between about 1E+4 and about 1E+8 Pa, and more particularly between about 1E+5 and about 5E+7 Pa. In one embodiment, the adhesive 18 has a storage modulus at about 65° C. of between about 1E+3 and about 5E+6 Pa, particularly between about 1E+4 and about 1E+6 Pa, and more particularly between about 1E+4 and about 1E+5 Pa.
The tan delta of the adhesive 18 is the loss modulus divided by the storage modulus. The tan delta can help describe the “flow” of the adhesive. A high tan delta generally means higher flow, along with more “liquid like” properties. In one embodiment, the adhesive has a tan delta at about 25° C. of between about 0.01 and about 2.5, particularly between about 0.1 and 2.2, and more particularly between about 0.4 and 1.5. In one embodiment, the adhesive has a tan delta at about 65° C. of between about 0.1 and about 3, particularly between about 0.25 and 3, and more particularly between about 0.5 and 2.5.
The adhesive 18 of the present invention also has a peel adhesion of at least about 100 g/cm, particularly at least about 500 g/cm and more particularly at least about 1000 g/cm based on ASTM 3330 when cured. If the peel adhesion of the adhesive 18 is too low, the adhesive 18 will fail and may cause an article including it to come apart (i.e., delaminate). An adhesive may fail in a number of ways.
In one embodiment, the adhesive 18 is imparted with a microstructure pattern to prevent wet out on substrates at room temperature. At elevated temperatures, the adhesive will wet out. The microstructure can function to facilitate air bleed during wet out. The microstructure can be imparted onto the adhesive 18 either by coating directly onto a structured backing or transferring after coating to a structured backing. This structured backing will act as the light and heavy release liner of the transfer adhesive. The heavy release liner will be conformable to the shape of the surface to be covered to reduce buckling of the liner and adhesive during lamination.
In one embodiment, the adhesive 18 is a multi-layer composite. The multi-layer construction includes at least two layers of adhesives with different properties. For example, a thin, less tacky adhesive skin layer and a PSA core layer. The less tacky adhesive layer provides the ability to “slip” during the lamination process, and the thick PSA core can provide efficient flow during the lamination process.
The delivery system 10 of the present invention includes a release on both sides of the conformable film 22—release with the adhesive 18 and release with the rigid frame carrier 26. Or, in some embodiments, the rigid frame carrier 26 is applied to the conformable film 22 as part of the die cutting process versus using the rigid liner 24 as the rigid frame carrier substrate 26. In the case of bonding the rigid frame carrier 26 during the converting process, a strong bond will be created and will have a different set of requirements than the bond if the conformable film 22 is extruded onto the rigid frame carrier 26.
Examples of combinations providing suitable carrier bonding are presented in the examples below, but it is contemplated that many other combinations will also satisfy the requirements for the apparatus and method according to the present invention.
As discussed above, the adhesive delivery system 10 includes a conformable film 22 having a controlled release surface on the top face of the conformable film 22 and a controlled release surface on the bottom surface of the conformable film 22, an adhesive 18 adhered to the top surface of the conformable film 22, a rigid frame carrier 26 adhered to either the top or bottom surface of the conformable film 22, and a light liner 20 attached to the exposed surface of adhesive 18. In one embodiment, the rigid frame carrier 26 is attached to the conformable film 22 with an extrusion melt bond or heat seal bond. Optionally, a window portion 28 can be cut out of the rigid frame carrier 26, creating a frame and a window exposing a portion of the face of the conformable film 22. The rigid frame carrier 26 provides rigidity to the conformable film 22 after the light liner 20 is removed from the delivery system 10. As described above, the low adhesion coating between the liner and the adhesive 18 is compatible with the bond between the rigid frame carrier 26 and the conformable film 22. Various methods of manufacturing the adhesive delivery system 10 of the present invention are discussed below.
In
In practice, the conformable film 22 and the rigid frame carrier 26 are needed to conform the adhesive 18 to the shaped surface 40 and carry with it the adhesive 18 for lamination. In one embodiment, the adhesive 18 and conformable film 22 are pushed onto the surface to be bonded with a puck 36. In cases where the adhesive 18 includes a textured surface, the microstructure on the adhesive 18 facilitates slip for alignment during lamination and air bleed.
Various methods can be used to optically bond an adhesive 18 of the delivery system 10 to a shaped surface 40. One method uses lamination equipment operating under vacuum to eliminate trapped air.
In one embodiment, the puck 36 is formed of silicone. Soft silicon pucks will compress during film tension prior to lamination resulting in displacement. This will result in edge contact of the adhesive 18 prior and prevent wet out in corners of the shaped surface 40. As shown in
In some embodiments, the resulting laminates can be optical elements or can be used to prepare optical elements. As used herein, the term “optical element” refers to an article that has an optical effect or optical application. The optical elements can be used, for example, in electronic displays, architectural applications, transportation applications, projection applications, photonics applications, and graphics applications. Suitable optical elements include, but are not limited to, glazing (e.g., windows and windshields), screens or displays, cathode ray tubes, and reflectors.
Exemplary optically clear substrates include, but are not limited to: a display panel, such as liquid crystal display, an OLED display, a touch panel or a cathode ray tube, a window or glazing, an optical component such as a reflector, polarizer, diffraction grating, mirror, or cover lens, another film such as a decorative film or another optical film.
Representative examples of optically clear substrates include glass and polymeric substrates including those that contain polycarbonates, polyesters (e.g., polyethylene terephthalates and polyethylene naphthalates), polyurethanes, poly(meth)acrylates (e.g., polymethyl methacrylates), polyvinyl alcohols, polyolefins such as polyethylenes, polypropylenes, and cellulose triacetates. Typically, cover lenses can be made of glass, polymethyl methacrylates, or polycarbonate.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/059514 | 10/9/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62914157 | Oct 2019 | US |
