WO2014130507A1

WO2014130507A1 - Multi-layer optically clear adhesives, foams, transfer tapes, and articles comprising such adhesives

Info

Publication number: WO2014130507A1
Application number: PCT/US2014/017045
Authority: WO
Inventors: Chan U. Ko; Prakash Mallya
Original assignee: Avery Dennison Corp
Current assignee: Avery Dennison Corp
Priority date: 2013-02-22
Filing date: 2014-02-19
Publication date: 2014-08-28
Anticipated expiration: 2015-08-22

Abstract

The present invention relates to a multilayer adhesive. The adhesive can comprise two or three layers. A two-layer adhesive comprises a soft adhesive layer and a firm adhesive layer adjacent the soft adhesive layer. A three-layer adhesive has a first soft adhesive layer, a second soft adhesive layer, and a firm adhesive layer disposed in between the first and second soft adhesive layers. The adhesive can be an optically clear adhesive. The configuration of the adhesive layers provides an adhesive with a high degree of flexibility and strength. Multilayered optically clear adhesives can be used with electronic screens, touch pads, mirrors, and other electronic applications.

Description

MULTI-LAYER OPTICALLY CLEAR ADHESIVES, FOAMS,

TRANSFER TAPES, AND ARTICLES COMPRISING SUCH ADHESIVES

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims the benefit of U.S. Provisional Patent Application No. 61/768,086 filed February 22, 2013, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The present invention provides ad hesives, such as pressu re sensitive adhesives, including optically clear ad hesives. The invention also relates to articles employing such adhesives. The adhesive is useful in various applications including, but not limited to, adhering su bstrates together, a nd is particularly useful for adhering an optically clear su bstrate to an article, e.g., adhering a display screen or panel to form electronic devices including but not limited to, cellular devices, smart phones, ta blet applications, etc.

BACKGROUND

[0003] Optically clear adhesives are used to bond together a clear su bstrate to another su bstrate in a pplications where it is desira ble that the optical clarity of the su bstrate not be impaired or diminished by the adhesive. In some applications, including for electronic devices, an optically clear adhesive is used to secure a display screen to the electronic device. In addition to provid ing sufficient optical clarity or transparency, the adhesives must provide sufficient adhesive strength to bond the articles together and prevent detachment. Often, adhesives that exhibit excellent adhesion are not reworkable and the film can tear or stretch upon attempting to reposition or adjust the position of the clear substrate (e.g., the display screen) on the device. Firmer adhesives can allow for better repositionability, but such adhesives may result in air gaps between corners or non-planar regions between the adhesives. Thus, in many situations, if the clear substrate is not positioned perfectly or there are any air gaps between the adhesive and the substrate, the entire substrate (e.g., the display screen) must be discarded. This can be extremely expensive, especially for electronic applications.

SUMMARY

[0004] The difficulties and drawbacks associated with previously known optically clear adhesives and practices associated with optically clear adhesives are addressed in the present multilayered adhesive.

[0005] In one aspect, the present invention provides a multilayered adhesive having two layers. The adhesive comprises a soft optically clear adhesive (OCA) layer and a firm optically clear adhesive layer.

[0006] In another aspect, the present invention provides a multilayered adhesive comprising a first soft optically clear adhesive layer, a firm optically clear adhesive layer, and a second soft optically clear adhesive layer, where the firm optically clear adhesive layer is disposed in between the first and second soft optically clear adhesive layers.

[0007] An additional aspect of the invention is a two-layer optically clear adhesive that is used in an electronics application.

[0008] An additional aspect of the invention is a three-layer optically clear adhesive that is used in an electronics application. [0009] The combination of the soft adhesive layer with the firm adhesive layer, and optionally with another soft adhesive layer provides an adhesive with excellent properties. While providing a soft adhesive with good flow or wetting properties to avoid air gaps or bubbles, the adhesives have sufficient strength such that they can be repositioned or reworkable in adhering substrates together. The adhesives can be removed as one piece without tearing or substantial stretching of the adhesive. The adhesives can also provide easier handling than other typical softer adhesives, including easier processing such as die-cutting. The adhesives can also exhibit sufficient softness to provide cushioning or impact absorption properties.

[0010] These and other aspects of the invention will be more fully understood by referring to the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a schematic side view of a multilayered adhesive construction in accordance with an embodiment of the present invention;

[0012] FIG. 2 is a schematic side view of a multilayered adhesive construction in accordance with an embodiment of the present invention;

[0013] FIG. 3 is a schematic side view of a multi-layered optically clear adhesive in relation to an optically clear su bstrate;

[0014] FIG. 4 is a schematic side view of a two layered adhesive in relation to substrate; and

[0015] FIG. 5 is a schematic side view of a three layer adhesive in relation to substrate.

[0016] Unless otherwise indicated, the illustrations in the above figures are not necessarily drawn to scale. DETAILED DESCRIPTION

[0017] The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.

[0018] The apparatuses and methods disclosed in this application are described in detail by way of various embodiments, examples, and with reference to the figures. Unless otherwise specified, like numbers in the figures indicate references to the same, similar, or corresponding elements throughout the figures. It will be appreciated that modifications to disclosed and described examples, arrangements, configurations, components, elements, apparatuses, methods, materials, etc., can be made and may be desired for a specific application. In this disclosure, any identification of specific shapes, materials, techniques, arrangements, etc., are either related to a specific example presented or are merely a general description of such a shape, material, technique, arrangement, etc. Identifications of specific details or examples are not intended to be, and should not be, construed as mandatory or limiting unless specifically designated as such.

[0019] The present invention provides a multilayered adhesive. In one embodiment, the adhesive can be an optically clear adhesive (OCA). The adhesive comprises a first, uppermost adhesive layer comprising a soft adhesive, and a second layer adjacent and beneath the first adhesive layer that comprises a firm adhesive, where the soft adhesive layer and the firm adhesive can have a hardness property such that the hardness property of the soft adhesive layer is lower than the hardness property of the firm adhesive. That is, the soft adhesive layer is softer than the firm adhesive layer. In one embodiment, the adhesive comprises a first soft adhesive layer, a second soft adhesive layer, and a firm adhesive layer disposed between the first and second soft adhesive layers. In one embodiment, the adhesive comprises two layers, a soft optically clear adhesive layer and a firm optically clear adhesive layer adjacent the soft adhesive layer. In another embodiment, the adhesive comprises three layers, a first soft optically clear adhesive layer, a second soft optically clear adhesive layer, and a firm optically clear adhesive layer disposed between the first and second soft adhesive layers.

[0020] In one embodiment, the hardness property of the adhesive layers is chosen from the glass transition temperature of the adhesive layer, the modulus of the adhesive layer, or a combination thereof. In a two-layer adhesive composition, the uppermost soft adhesive layer has a glass transition temperature, a modulus, or both that is less than the glass transition temperature, modulus, or both of the firm adhesive layer. In a three-layer adhesive, the first and second soft adhesive layers independently have a glass transition temperature, or both that is less than the glass transition temperature, the modulus, or both of the first adhesive layer. In a three-layer adhesive, the properties of the first and second soft adhesive layers can be the same or different. In one embodiment, the second soft adhesive layer has a glass transition temperature, a modulus, or both that is higher than that of the first adhesive layer.

[0021] FIG. 1 illustrates an embodiment of a two layer adhesive construction. A multilayered adhesive 100 comprises a soft adhesive layer 110 and a firm adhesive layer 120 adjacent the soft adhesive layer. In one embodiment, the soft and firm adhesive layers are optically clear adhesives.

[0022] FIG. 2 illustrates an embodiment of a three layer adhesive construction. A multilayered adhesive 200 comprises a first soft adhesive layer 210, a second soft adhesive layer 220, and a firm adhesive layer 230 disposed between the first and second adhesive layers. In one embodiment, each of the soft adhesive layers and the firm adhesive layer are optically clear adhesives.

[0023] The adhesives for the respective layers can be selected as desired to provide an adhesive with properties suitable for an intended application. The soft adhesive layer(s) can comprise a material chose from acrylic based or non-acrylic based materials. Acrylic based adhesives comprise acrylic monomers. The term "acrylic monomer" refers to any monomer in the class of free-radical polymerizable monomers that includes acrylic acid, methacrylic acid, acrylamide, methacrylamide, acrylonitrile, and derivatives thereof. Non-limiting examples include alkyl (meth)acrylates, hydroxyalkyl (meth)acrylates, alkyl (meth)acrylamides, alkyl di(meth)acrylates, ethylenically unsaturated carboxylic acids, epoxy (meth)acrylates (e.g., glycidyl (meth)acrylate), ethoxylated (meth)acrylates, cyanoacrylates, etc. Also included are acrylic-, (meth)acrylamido-, and (meth)acrylonitrile-terminated macromers.

[0024] Alkyl (meth)acrylates are well known and commonly used in the preparation of acrylic PSAs. Nonlimiting examples include methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, nonyl, decyl, undecyl, and dodecyl acrylate, and the corresponding methacrylates. Cyclic acrylates and methacrylates, e.g., cyclohexyl acrylate, isobornyl acrylate, are also included. (Meth)acrylates with 4-12 carbon atoms per alkyl group are considered "soft" monomers, and form copolymers with lower glass transition temperatures (Tg's) than so-celled "hard" monomers, e.g., methyl (meth)acrylate, ethyl methacrylate, etc.

[0025] Non-limiting examples of hydroxyalkyl (meth)acrylates include hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), and hydroxypropyl acrylate.

[0026] Non-limiting examples of alkyl (meth)acrylamides include acrylamide, methacrylamide, N-methylol (meth)acrylamide, N-ethanol acrylamide, Ν,Ν-dimethyl (meth)acrylamide, N-t-butyl acrylamide, octyl-acrylamide, etc.

[0027] Non-limiting examples of alkyl di(meth)acrylates include dimethylaminoethyl di(meth)acrylate, 1,6-hexanediol diacrylate, diethyleneglycol di(meth)acrylate, triethyleneglycol di (meth)acrylate, etc.

[0028] Non-limiting examples of ethylenically unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, beta-carboxyethyl acrylate (beta-CEA), and higher oligomers of acrylic acid. [0029] (Meth)acrylic-, (meth)acrylamido-, and (meth)acrylonitrile-terminated macromers are rubber or acrylic polymers of small to medium chain length (N_w from about 2,000 to 25,000) terminated with a (meth)acrylic, (meth)acrylamido, or (meth)acrylonitrile functional group or for example, adhesives sold under the trade name K ATON. The preparation of (meth)acryl-terminated ethylene-propylene and ethylene/butylene macromers and their use in preparing acrylic-rubber hybrid graft copolymers are described in U.S. Pat. No. 5,625,005, which is incorporated by reference herein.

[0030] The term "non-acrylic monomer" refers to a free-radical polymerizable monomer having a vinyl or other ethylenically unsaturated group, other than acrylic monomers. Non-limiting examples include allylic monomers, styrenic monomers (e.g., styrene, alpha-methyl styrene, t-butyl- styrene, 4-methoxy-styrene, 3-ethyl-styrene, 4-ethyl-styrene, and 1,4- or 1,3 divinyl-benzene), N-vinyl lactams (e.g., N-vinyl pyrrolidone), vinyl pyridine, vinyl esters (e.g., vinyl acetate, vinyl butyrate, vinyl propionate, vinyl isobutyrate, vinyl valerate, and vinyl versitate), sodium vinyl sulfonate, and dialkyl maleates and fumarates (e.g., dioctyl maleate, di-ethylhexyl fumarate, etc.).

[0031] In one embodiment, the soft adhesive layer can comprise rubber based adhesives. It will be appreciated that rubber based adhesives may not be particularly suitable for applications requiring an optically clear adhesive because rubber based adhesives typically have a high haze and are yellowish in color. Such adhesives, however, may be suitable for other applications where advantages of the present adhesives constructions can be beneficial. In one embodiment, rubber based adhesives may be suita ble for bonding to a substrate having a low surface energy.

[0032] The rubber based adhesive can be a natural or synthetic rubber material. For example, the rubber based pressure-sensitive adhesive can comprise natural and/or synthetic elastomeric polymers based on synthetic or natural rubber, such as natural rubber (polyisoprene), polybutadiene, synthetic polyisoprene, random styrene-butadiene (SB) polymers, SB block copolymers, multi-armed and repeating SB copolymers. Styrene-isoprene-styrene, styrene-butadiene-styrene, styrene-butadiene, and styrene-isoprene copolymers, block, random, or multi-armed copolymers, and blends and mixtures thereof may also be used. Examples of suitable rubber based adhesive include, but are not limited to, those described in U.S. Pat. No. 5,290,842, the entire disclosure of which is incorporated herein by reference.

[0033] Adhesives suitable for use in the soft adhesive layer include, but not limited to, rubber based adhesives, which typically contain relatively mobile ingredients. The mobile ingredients of these adhesives normally consist of oils, resins, tackifiers, or other organic molecules added during the adhesive formulation process. However, as can be appreciated by one of skill in the art, such mobile ingredients may also be of natural origin or may result as a byproduct of the manufacturing process. In addition, such mobile ingredients may also result from degradation of one or more components of the adhesive formulation during processing or use.

[0034] Migration of these mobile ingredients may result in the adhesive layer losing some of its adhesive strength, since many of these mobile ingredients are added to enhance adhesion. Thus, it is generally desirable to confine migratory mobile species to their original environment within the construction.

[0035] Examples of mobile ingredients used in rubber-based adhesive formulations include, but are not limited to, hydrogenated aromatic resins wherein a significant portion of the benzene rings are converted to cyclohexane rings (e.g., the REGALREZ family of resins manufactured by Hercules of Passaic, New Jersey, and the ARKON family of resins manufactured by Arakawa Chemical of Chicago, III.); hydrogenated polycyclic resins (e.g., ESCOREZ 5300, 5320, 5340, and 5380 manufactured by Exxon of Irving, Tex.); and plasticizer oils (e.g., SHELLFLEX 371 manufactured by Shell of Houston, Tex., and KAYDOL mineral oil manufactured by Witco of Greenwich, Conn.). [0036] An extended list of acrylic and non-acrylic monomers used to prepare PSAs is found in Appendix 15A of the Handbook, at pages 444-450, incorporated by reference herein and attached hereto as Appendix I.

[0037] The hardness properties of the adhesive layer can be defined by the glass transition temperature of the adhesive layer, the modulus of the adhesive layer, or both.

[0038] The properties of the soft adhesive layer(s) can be selected as desired for a particular purpose or intended use. In one embodiment, the adhesive of the soft adhesive layer(s) have a glass transition temperature (Tg) of about -5 ^QC or less; about -10 ^QC or less; even about -20 ^QC or less. In one embodiment the adhesive of the soft adhesive layer has a glass transition temperature of about -5 5C to about -20 5C; about -10 to about -15 ^C; -5 to about -10 ^C; even about -15 to about -20 ^QC. Here as elsewhere in the specification and claims, numerical values can be combined to form new and non-disclosed ranges.

[0039] In one embodiment, the adhesive for the soft adhesive layers can have a modulus (G') of about 1 x 10^s dyne/cm² to about 3 x 10^s dyne/cm² (about 10 kPa to about 30 kPa); from about 1.2 x 10^s dyne/cm² to about 2.8 x 10^s dyne/cm² (about 12 kPa to about 28 kPa); from about 1.5 x 10^s dyne/cm² to about 2.5 x 10^s dyne/cm² (about 15 kPa to about 25 kPa); even from about 1.7 x 10^s dyne/cm² to about 2.2 x 10^s dyne/cm² (about 17 kPa to about 22 kPa).

[0040] In embodiments comprising first and second soft adhesive layers, the first and second soft adhesive layers can be formed from the same or different adhesive compositions, and can have the same or different properties. In one embodiment, the second soft adhesive layer (the lower most adhesive layer) has a hardness that is greater than the corresponding hardness property of the first soft adhesive layer but less than the corresponding property of the firm adhesive layer.

[0041] In one embodiment, the soft adhesive layer is optically clear. As used herein, the term "optically clear adhesive" refers to a material that has a luminous transmittance of greater than about 99 percent, a haze of less than about 1 percent, Typically, the adhesive may be visually free of bubbles. In one embodiment, the optically clear adhesive can have a luminous transmittance of about 99.2 percent or greater, 99.5 percent or greater, 99.7 percent or greater, 99.9 percent greater, even 100 percent.

[0042] The soft adhesive layer can have a thickness as desired for a particular purpose or intended application. In one embodiment, the soft adhesive layer has a thickness of from about 1 micron to about 150 micron; from about 10 micron to about 10 micron to about 125 micron; from about 25 micron to about 100 micron; even from about 50 micron to about 75 micron. It will be appreciated that the adhesive for the soft adhesive layer does not have to be an optically clear adhesive where optically clarity is not a concern. In such embodiments, the adhesive can have a transmittance less than 99%.

[0043] The firm adhesive layer can comprise an adhesive material chosen from an acrylic based adhesive, a rubber based adhesives, synthetic block copolymers, etc. The firm adhesive layer is provided such that it has one or more properties that render it to be firmer or harder than the soft adhesive layer(s). Acrylic based adhesives for the firm adhesive can comprise acrylic based monomers as described above with respect to the soft adhesive and can also include a sufficient number of hard monomers such as, for example, methyl (meth)acrylate, ethyl methacrylate, etc.

[0044] In one embodiment, the firm adhesive layer can also act as a barrier layer that can prevent migration of the migratory species present in the soft adhesive layer(s) or be substantially resistant to other materials such as plasticizers. Suitable acrylic-based pressure-sensitive adhesives that can act as a barrier layer include those that comprise polymers of acrylic monomers, polymers of methacrylic monomers, and copolymers, blends, or mixtures thereof, which may include smaller amounts of non-acrylic monomers such as vinyl acetate and other vinyl esters, styrene and substituted styrenes, fumarates, maleates, vinyl lactams, and any other olefinic unsaturated monomers which copolymerize with acrylate and methacrylate. For example, polymers of the following monomers, and copolymers, blends, or mixtures thereof may also be used to form suitable barrier layers: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, isohexyl acrylate, cyclohexyl acrylate, isooctyl acrylate, 2- ethyl hexyl acrylate, decyl acrylate, lauryl acrylate, stearyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, isohexyl methacrylate, cyclohexyl methacrylate, isooctyl methacrylate, 2-ethyl hexyl methacrylate, decyl methacrylate, lauryl methacrylate, stearyl methacrylate, and isobornyl methacrylate.

[0045] Acrylic-based polymer resins can be applied using a variety of techniques, most preferably as a 100% solid via hot melt, solvent, or emulsion coating, or as a syrup followed by irradiation polymerization, or by any other means known to those of skill in the art. These polymer compositions can be used in their commercially available form, or as modified with physically compatible plasticizers and tackifiers, such as rosin-based, hydrocarbon, or terpene-phenolic resins.

[0046] In one embodiment, the adhesive of the firm adhesive layer(s) have a glass transition temperature (Tg) of about 5 ^QC or greater; 10 ^QC or greater; 15 ^QC or greater; 20 ^QC or greater; even 25 ^QC or greater. In one embodiment the adhesive of the soft adhesive layer has a glass transition temperature of 5 to 25 ^c, 10 to 20 even 12 to 15 ^c. It will be appreciated that the adhesive for the soft adhesive layer does not have to be an optically clear adhesive where optically clarity is not a concern. In such embodiments, the adhesive can have a transmittance less than 99%.

[0047] In one embodiment, the firm adhesive has a modulus (G') of about 2 x 10^s dyne/cm² to about 4 x 10^s dyne/cm² (about 20 kPa to about 40 kPa); from about 2.2 x 10^s dyne/cm² to about 3.8 x 10^s dyne/cm² (about 22 kPa to about 38 kPa); even from about 2.5 x 10^s dyne/cm² to about 3.5 x 10^s dyne/cm² (about 25 kPa to about 35 kPa). Here as elsewhere in the specification and claims, numerical values can be combined to form new and non-disclosed ranges.

[0048] The firm adhesive layer can have a thickness as desired for a particular purpose or intended application. In one embodiment, the firm adhesive layer has a coat weight of from about 1 micron to about 150 micron; from about 10 micron to about 125 micron; from about 25 micron to about 100 micron; even from about 50 micron to about 75 micron. It will be appreciated that the adhesive for the soft adhesive layer does not have to be an optically clear adhesive where optically clarity is not a concern. In such embodiments, the adhesive can have a transmittance less than 99%.

[0049] In one embodiment, the firm adhesive layer is optically clear. As used herein, the term "optically clear adhesive" refers to a material that has a luminous transmittance of greater than 99 percent, a haze of less than about 1 percent. Typically, the optically clear adhesive may be visually free of bubbles. In one embodiment, the optically clear adhesive can have a luminous transmittance of about 99.2 percent or greater, 99.5 percent or greater, 99.7 percent or greater, 99.9 percent greater, even 100 percent.

[0050] The firm adhesive layer desirably maintains optical clarity, bond strength, and resistance to tearing over the lifetime of the article in which it is used.

[0051] As described above, the individual layers can exhibit su bstantial optical clarity or transparency. The overall adhesive construction further exhibits excellent optical clarity such that it can be used in optical applications. In one embodiment, the adhesive construction has haze value of about 1 percent or less; about 0.9 percent or less, about 0.7 percent or less; about 0.5 percent or less; even about 0.1 percent or less.

[0052] The adhesives are capable of adhering to a wide variety of surfaces. In one embodiment, the protective films are capable of adhering to and removable from surfaces such as stainless steel, painted steel, polycarbonate, rigid polypropylene, and chrome plated surfaces. [0053] In one embodiment, the adhesives are suitable for adhering to low surface energy surfaces. In one embodiment, the adhesive can be applied to, and exhibit the adhesion characteristics described herein, when adhered to a surface having a surface energy of about 50 dynes per centimeter or less; about 45 dynes per centimeter or less; about 40 dynes per centimeter or less; even about 35 dynes per centimeter or less. In one embodiment, the surface has a surface energy of from about 5 dynes per centimeter to about 50 dynes per centimeter; about 10 dynes per centimeter to about 45 dynes per centimeter; about 15 dynes per centimeter to about 40 dynes per centimeter; even about 20 dynes per centimeter to about 35 dynes per centimeter. Here as elsewhere in the specification and claims, numerical values can be combined to form new and non-disclosed ranges. In one embodiment, the soft adhesive layer exhibits good adhesion to substrates having a low surface energy. The ability to adhere to a low energy surface can be a property of the soft adhesive layer (for two layer constructing) or the second as lower most soft adhesive layer (in three layer constructing).

[0054] The adhesive layers can be formed by any suitable method. Nonlimiting examples of conventional PSA coating methods include slot die, air knife, brush, curtain, extrusion, blade, floating knife, gravure, kiss roll, knife-over-blanket, knife-over-roll, offset gravure, reverse roll, reverse smoothing roll, rod, and squeeze roll coating. The adhesive composition can be coated on a release liner (e.g., a silicone-coated paper or film), air-or oven-dried, and then laminated to a flexible backing, i.e., a facestock. Alternatively, the adhesive can be coated directly on a facestock, dried, and then protected with a release liner. Self-wound tapes also can be prepared, e.g., by coating he adhesive on one side of a rape facestock. (The other side of the facestock is silicone-coated or otherwise treated so the tape can be wound up on itself without blocking.)

[0055] The adhesive layers can be separately coated onto a facestock or release liner, dried, and then laminated together. In another embodiment, the adhesive layers can be sequentially coated by coating a first adhesive layer, and then coating the next desired adhesive layer over the first adhesive layer prior to complete drying of the first adhesive layer. The adhesive construction can then be fully cured or dried after coating the respective layers.

[0056] In one embodiment, the adhesive layers can be coated simultaneously or near- simultaneously using a slide coating, multilayer die-coating, or die/slide combination coating. In one embodiment, the adhesive layers can be coated using a multi-layer die such as that described in U.S. Patent No. 5,993,961, the disclosure of which is incorporated by reference herein in its entirety.

[0057] The adhesive construction can be coated onto a release liner. Any release liner suitable for the chosen adhesive may be used. For pressure sensitive adhesives, release liners may be coated papers or films, and super calendared paper, for example. Coating materials suitable for release liners include, for example, silicone-based and fluorine-based materials, or any other material that has the desired releasing properties, for example, waxes and carbamates. The release liner can include a suitable release coating on one or both sides so as to allow the adhesive to be wound upon itself during storage.

[0058] The present adhesives with the upper soft adhesive layer, a firm adhesive layer adjacent the upper soft layer, and optionally another, lower soft adhesive layer adjacent the firm adhesive layer exhibits excellent properties. The adhesives exhibit excellent adhesion but have a sufficient strength such that the adhesives are reworkable without tearing or stretching. The strength of the adhesive also provides the adhesives with excellent handling properties and allows for them to be die cut (as compared to conventional soft adhesives). Additionally, the soft adhesive outer layer provides an adhesive that exhibits sufficient flow such that the adhesive can accommodate non-planar surfaces without any significant gaps or air pockets forming between the non-planar surface and the adhesive.

[0059] The multilayered adhesives can be used to adhere one substrate to another and are particularly suitable to adhere an optically clear substrate to another substrate. The adhesive can be attached to any suitable substrate. In one embodiment, the adhesive can be attached to a backing layer or facestock material. In one embodiment, the backing layer can be chosen from a polymeric material such as a polyolefinic facestock, vinyl facestock, a polyester facestock, a polyurethane facestock, etc. Examples of suitable facestock materials include, but are not limited to, polyethylene, polypropylene, polybutylene, polymers of ethylene-propylene diene monomers, polyurethane foams, etc. Thus, in one aspect, the adhesive can be used to form a tape like construction with a suitable backing.

[0060] In still other embodiments, the adhesives can be used to adhere a first substrate to a second substrate, where the first substrate is panel or film. In one embodiment, the adhesives are particularly suitable for adhering a panel suitable as screen or display in an electronic device to a body of an electronic device. Suitable materials for the screen include acrylic or glass based substrates. The panel or screen can be a display panel, a liquid crystal display, a touch panel, a window, a mirror, a lens, etc. The substrate layer may provide flexibility, optical transmission, mechanical strength, and anti-glare functions.

[0061] The adhesive articles of the invention can be used with a wide variety of display overlays. Such display overlays include flexible overlays (e.g., thin films made of a suitable plastic material) and rigid overlays (e.g., panels made of glass or a suitable plastic material). The display overlay can be unframed or can be equipped with a frame or other bezel. Representative display overlays include microlouvered privacy filters, antireflection films, polarizing films, diffusers, colored filters, electromagnetic shields, scratch or smudge resistant films, low surface energy films and touch-sensitive panels.

[0062] The adhesive articles and display overlays can be used on a wide variety of information displays including, but not limited to, multi-character and especially multi-line displays such as LCDs, plasma displays, electroluminescent displays, front and rear projection displays, cathode ray tubes ("CRTs") and signage. The adhesive articles and display overlays of the invention can also be used on single-pixel or binary displays such as individual light emitting diodes ("LEDs"), signal lamps and switches. The adhesive articles and display overlays can be used on illuminated or non-illuminated displays. The invention has particular utility for displays whose information display area is in the form of a viewing screen having a viewing surface that is susceptible to damage during normal use.

[0063] The adhesives can be used in a variety of portable and non-portable information display devices including notebook computer displays, computer monitors, personal digital assistants ("PDAs"), cell phones (including combination PDA/cell phones), touch-sensitive screens, wrist watches, car navigation systems, global positioning systems, depth finders, calculators, electronic books, CD or DVD players, televisions (e.g., projection televisions), instrument gauges, instrument panel covers, signage such as graphic displays (including indoor and outdoor graphics, bumper stickers, and the like), and reflective sheeting. These information display devices can have planar viewing faces or non-planar viewing faces (e.g., the curved face of a typical CRT). Usually the display overlay will be positioned on the viewing face of the information display device so that it overlies or substantially overlies all of the information display area.

[0064] The invention thus may facilitate installation, removal, or replacement of display overlays on a display. In particular, the adhesives with the upper soft adhesive layer, a firm adhesive layer adjacent the upper soft layer, and optionally a second, lower soft adhesive layer adjacent the firm adhesive layer exhibits excellent properties. The adhesives are reworkable and can be repositioned without the adhesive tearing or stretching, which can reduce the number of articles that have to be discarded.

[0065] The present adhesives are also particularly suitable for applications where one substrate is substantially non-planar. For example, in some electronic applications, a display panel can contain a bezel around a portion of the display panel substrate. The present adhesives, having an upper, soft adhesive layer allow for wetting out around the bezel area such that the soft adhesive layer sufficiently adheres to the panel without generating any gaps or bubbles between the substrate and the adhesive.

[0066] Referring to FIG. 3, an article 300 comprises a substrate 310 (such as, for example, a display panel or clear substrate) and an adhesive 330 to be adhered to the substrate. The substrate 310 includes a bezel 320 around the periphery of the substrate. The bezel 320 can be a layer of ink or some other material as desired for a particular purpose or intended use. The adhesive 330 comprise a multi- layered adhesive in accordance with aspects of the present invention, and is provided such that a soft adhesive layer will contact the underlying surface of the substrate 310 and the bezel area 320.

[0067] FIG. 4 illustrates an embodiment of a two-layer adhesive article. Article 300' has two-layer adhesive 100 adhered to a panel 310 having a bezel 320. The adhesive 100 includes the soft adhesive layer 110 and the firm adhesive layer 120. The soft adhesive layer 110 is adhered to the under surface of the substrate 310 and the bezel 320. The firm adhesive layer 120 can then be adhered to another substrate to attach the substrate 310 to a substrate of interest.

[0068] FIG. 5 illustrates an embodiment of a three-layer adhesive article. Article 300" has three-layer adhesive 200 adhered to a panel 310 having a bezel 320. The adhesive 200 includes the soft adhesive layer 210, soft adhesive layer 220, and the firm adhesive layer 230. The adhesive layer 210 is adhered to the under surface of the substrate 310 and the bezel 320. The soft adhesive layer 220 can then be adhered to another substrate to attach the substrate 310 to a substrate of interest.

[0069] Many other benefits will no doubt become apparent from future application and development of this technology.

[0070] All of the features disclosed in the specification, including the claims, abstract, and drawings, and all of the steps in any method or process disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in the specification, including the claims, abstract, and drawings, can be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0071] The foregoing detailed description of the present invention is provided for purposes of illustration, and it is not intended to be exhaustive or to limit the invention to the particular embodiments disclosed. The embodiments may provide different capabilities and benefits, depending on the configuration used to implement the key features of the invention. Accordingly, the scope of the invention is defined only by the following claims.

Claims

CLAIMS What is claimed is:

1. An adhesive construction comprising:

a first adhesive layer comprising a soft adhesive composition;

a second adhesive layer adjacent the first adhesive, the second adhesive comprising a firm adhesive material, where the first adhesive and the second adhesive each have a hardness property, and the hardness property of the first adhesive layer is lower than the hardness property of the second adhesive layer.

2. The adhesive of claim 1, wherein the hardness property is the glass transition temperature, the modulus, or both the glass transition temperature and the modulus.

3. The adhesive of claim 1, wherein the first adhesive has a glass transition temperature of about -5° C or less.

4. The adhesive of claim 1, wherein the first adhesive has a glass transition temperature of about -5° C to about -20° C.

5. The adhesive of any of claims 1 to 4, wherein the second adhesive has a glass transition temperature of about 5° C or greater.

6. The adhesive of claims 1 to 4, wherein the second adhesive layer has a glass transition temperature of about 5° C to about 25° C.

7. The adhesive of any of claims 1 to 5, wherein the first adhesive has a modulus of about 1 x 10^s dyne/cm² to a bout 3 x 10^s dyne/cm².

8. The adhesive of any of claims 1 to 5, wherein the second adhesive has a modulus of about 2 x 10^s dyne/cm² to about 4 x 10^s dyne/cm²

9. The adhesive of any of claims 1 to 8, wherein the first adhesive layer comprises an acrylic based adhesive, a rubber based adhesive, or a combination of two or more thereof.

10. The adhesive of any of claims 1 to 9, wherein the first adhesive layer comprises polyisoprene, polybutadiene, styrenebutadiene polymers, styrene-butadiene block copolymers, multi- armed repeating styrene-butadiene copolymers, styrene-isoprene-styrene polymers, styrene- butadienestyrene polymers, styrene-isoprene polymers, styreneisoprene block copolymers, and multi- armed repeating styrene-isoprene copolymers, or a combination of two or more thereof.

11. The adhesive of any of claims 1 to 10, wherein the second adhesive layer comprises an adhesive comprising a monomer chosen from methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, isohexyl acrylate, cyclohexyl acrylate, isooctyl acrylate, 2-ethyl hexyl acrylate, decyl acrylate, lauryl acrylate, stearyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, isohexyl methacrylate, cyclohexyl methacrylate, isooctyl methacrylate, 2-ethyl hexyl methacrylate, decyl methacrylate, lauryl methacrylate, stearyl methacrylate, and isobornyl methacrylate, or a combination of two or more thereof.

12. The adhesive of any of claims 1 to 11, wherein at least one of the first and second adhesive layers is optically clear adhesives.

13. The adhesive of any of claims 1 to 12 comprising a third adhesive layer disposed adjacent the second adhesive layer and opposite the first adhesive layer, the third adhesive layer having at least one hardness property, the at least one hardness property of the third adhesive layer being less than that of the second adhesive layer.

14. The adhesive of claim 11, wherein the third adhesive has a glass transition temperature of about -5° C or less.

15. The adhesive of any of claims 11 to 14, wherein the third adhesive has a modulus of about 1 x 10^s dyne/cm² to about 3 x 10^s dyne/cm²

16. The adhesive of any of claims 13 to 15, wherein the at least one hardness property of the third adhesive layer is less than that of the second adhesive layer, but greater than that of the first adhesive layer.

17. The adhesive of any of claims 11 to 16, wherein the third adhesive layer is an optically clear adhesive.

18. The adhesive of any of claims 1 to 17, wherein the second adhesive layer is a barrier layer.

19. An adhesive tape comprising a facestock and the adhesive article of any of claims 1 to

18.

20. The adhesive tape of claim 19, wherein the facestock is chosen from a polyolefin, a vinyl material, a urethane material, an ester material, or a combination of two or more thereof.

21. The adhesive tape of claim 19, wherein the facestock is a foam material.

22. An article comprising a first substrate adhered to a second substrate by an adhesive of any of claims 1 to 18.

23. The article of claim 22, wherein the first substrate is an optically clear substrate, and the first adhesive layer is adhered to a lower surface of the first substrate.

24. The article of claim 23, wherein the first substrate comprises a bezel on at least a portion of the lower surface of the substrate, and the first adhesive layer is adhered to the lower surface of the substrate and the bezel.

25. The article of any of claims 22 to 24, wherein the article is an electronic device, and the first substrate comprises a display panel, a liquid crystal display, a touch panel, a window, a mirror, a lens, or a combination of two or more thereof.