Multilayer products processed wet-on-wet

Abstract

A wet-on-wet coating process is provided to produce a multilayer article. A first coating material and a second coating material are sequentially applied to a structured substrate surface to form a skin layer directly on the structured substrate surface and a bulk layer on the skin layer. The conformability of the skin layer can be adjusted to provide desired surface and bulk properties.

Description

Background Art

[0001] Applicators are widely used in multi-layer coating processes to deliver a wide range of fluids to a continuous web to form a multi-layer coated article. Fluids can be applied using a single-layer coating process so that the fluids are applied sequentially, with each layer completing steps such as drying, curing, etc. before the next layer is applied. Summary of the invention

[0002] Briefly, in one aspect, the present disclosure describes a method. The method includes conveying a substrate from a first coating applicator to a second coating applicator along a web path, the substrate including a structured surface, the structured surface including a pattern of structured features; applying a first coating fluid from the first coating applicator to the structured surface of the substrate to form a skin layer directly on the pattern of structured features; applying a second coating fluid from the second coating applicator to the skin layer to form a second coating layer directly on the first coating layer, the second coating fluid being different from the first coating fluid; and solidifying the first coating layer and the second coating layer to form a double-layer coating including a skin layer and a bulk layer. The residence time between applying the first coating fluid and applying the second coating fluid is controlled to adjust the conformability of the skin layer on the structured surface.

[0003] On the other hand, the present disclosure describes a multilayer coated article. The article includes: a substrate, the substrate includes a first major surface and a second major surface opposite to each other, the first major surface includes a microstructured surface, the microstructured surface includes a pattern of structured features, the pattern of structured features includes one or more rising walls, the one or more rising walls each extend from a raised end to a lower end opposite to the raised end, each rising wall connects the raised surface at the raised end and the corner at the lower end; and a double-layer coating, the double-layer coating is disposed on the first main microstructured surface of the substrate. The double-layer coating includes a skin layer directly disposed on the microstructured surface of the substrate. The skin layer has a greater thickness on the corner than on the raised surface. The body layer is directly disposed on the skin layer.

[0004] Various advantages are obtained in exemplary embodiments of the present disclosure. One such advantage of exemplary embodiments of the present disclosure is that the conformability of the skin coating layer on the structured surface can be controlled by residence time and / or other environmental factors. Thus, the resulting dual-layer coating can exhibit different surface and bulk coating properties for desired applications.

[0005] Various aspects and advantages of the exemplary embodiments of the present disclosure have been summarized. The above summary of the invention is not intended to describe each illustrated embodiment or every implementation of the current certain exemplary embodiments of the present disclosure. The following drawings and detailed description more specifically illustrate certain preferred embodiments using the principles disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present disclosure may be more fully understood by considering the following detailed description of various embodiments of the present disclosure in conjunction with the accompanying drawings, in which:

[0007] Figure 1 is a schematic diagram of a coating apparatus according to an exemplary embodiment of the present disclosure.

[0008] Figure 2A is a cross-sectional view of a wet skin layer coated on a surface of a microstructured web according to one embodiment.

[0009] Figure 2B is a cross-sectional view of a wet-on-wet multi-layer coated article according to one embodiment.

[0010] Figure 2C is through Figure 2B A cross-sectional view of a multi-layer coated product formed by solidifying the product.

[0011] Figure 2D is a cross-sectional view of a wet-on-wet multi-layer coated article according to another embodiment.

[0012] Figure 2E is through Figure 2D A cross-sectional view of a multi-layer coated product formed by solidifying the product.

[0013] Figure 3 is a cross-sectional view of a multi-layer coated article bonded to a film.

[0014] Figure 4A This is an atomic force microscope (AFM) image of Comparative Example C1.

[0015] Figure 4B This is an AFM image of Example E1.

[0016] Figure 5A This is an AFM image of Comparative Example C2.

[0017] Figure 5B This is an AFM image of Example E2.

[0018] Fig. 6A is an AFM image of Example E3A.

[0019] Figure 6B yes Figure 5A An enlarged partial view of an image.

[0020] Figure 6C yes Figure 5A An enlarged partial view of an image.

[0021] Fig. 7A is an AFM image of Example E3B.

[0022] Figure 7B yes Fig. 6A An enlarged partial view of an image.

[0023] Figure 7C yes Fig. 6A An enlarged partial view of an image.

[0024] Fig. 8A is an AFM image of Example E3C.

[0025] Figure 8B yes Fig. 7A An enlarged partial view of an image.

[0026] Figure 8C yes Fig. 7A An enlarged partial view of an image.

[0027] Fig. 9 is a graph of dry thickness of the epidermal coating versus residence time.

[0028] Fig. 10A is an AFM image of Example E5A.

[0029] Fig. 10B is an AFM image of Example E5B.

[0030] Fig.11 is a cross-sectional view of a microstructured web surface.

[0031] Fig. 12A is a cross-sectional view of a wet-on-wet multilayer coating on a flat web substrate.

[0032] Fig. 12B is through Fig. 12A Cross-sectional view of a multilayer coating on a flat web substrate solidified from an article.

[0033] In the accompanying drawings, like reference numerals indicate like elements. Although the above drawings, which may not be drawn to scale, illustrate various embodiments of the present disclosure, other embodiments may also be envisioned, as indicated in the detailed description. In all cases, the presently disclosed disclosure is described by representation of exemplary embodiments rather than by express limitations. It should be understood that many other modifications and embodiments may be devised by those skilled in the art that fall within the scope and spirit of the present disclosure. DETAILED DESCRIPTION

[0034] For the following Glossary of defined terms, these definitions shall govern throughout this application, unless a different definition is provided in the claims or elsewhere in the specification.

[0035] Glossary

[0036] Certain terms are used throughout the specification and claims, which, although mostly well known, may require some explanation. It should be understood that:

[0037] The term "coating fluid" refers to a fluid having a combination of interfacial properties and viscosity such that the fluid will not dewet from the web surface after being spread on the surface during transmission through the coating station. Examples of coating fluids that can be coated by the present disclosure are monomers, oligomers, solutions of dissolved solids, solid fluid dispersions, fluid mixtures, and emulsions. Such fluids are used to produce a wide variety of functional coatings on webs, including release coatings, low adhesion coatings, primer coatings, adhesive coatings that respond to electromagnetic radiation or electric or magnetic fields, protective coatings, optically active coatings, and chemically active coatings. Exemplary coating fluids are further described in U.S. Pat. No. 5,527,578 (Mazurek et al.), U.S. Pat. No. 5,858,545 (Everaerts et al.), U.S. Pat. No. 6,007,914 (Joseph et al.), and PCT Publication No. WO 00 / 02966 (Kesti et al.), all of which are incorporated herein by reference.

[0038] By using orientation terms such as "atop," "on," "over," "overlying," "uppermost," "below," and the like, with respect to the positions of various elements in the disclosed coated articles, we refer to the relative position of the elements with respect to a horizontally disposed, upwardly facing substrate. However, unless otherwise indicated, the present invention is not intended that the substrate or article should have any particular spatial orientation during or after manufacture.

[0039] By using the term "overlying" to describe the position of a layer relative to a substrate or other element of an article of the present disclosure, we refer to the layer as being on top of the substrate or other element, but not necessarily adjacent to the substrate or other element.

[0040] The term "about" or "approximately" with respect to a value or shape means + / -5% of that value or property or feature, but explicitly includes the exact value. For example, a viscosity of "about" 1 Pa-sec means a viscosity from 0.95 Pa-sec to 1.05 Pa-sec, but also explicitly includes a viscosity of exactly 1 Pa-sec. Similarly, a "substantially square" perimeter is intended to describe a geometric shape having four side edges, wherein the length of each side edge is 95% to 105% of the length of any other side edge, but also includes geometric shapes in which each side edge has exactly the same length.

[0041] The term "substantially" with respect to a property or feature means that the property or feature is exhibited to a greater extent than the opposite side of the property or feature is exhibited. For example, a "substantially" transparent substrate refers to a substrate that transmits more radiation (e.g., visible light) than it does not transmit (e.g., absorbs and reflects). Thus, a substrate that transmits more than 50% of visible light incident on its surface is substantially transparent, but a substrate that transmits 50% or less of visible light incident on its surface is not substantially transparent.

[0042] As used in this specification and the accompanying embodiments, the singular forms "a", "an", and "the" include plural referents unless the content clearly indicates otherwise. Thus, for example, reference to a fine fiber comprising "a compound" includes a mixture of two or more compounds. As used in this specification and the accompanying embodiments, the term "or" is generally used in its sense including "and / or" unless the content clearly dictates otherwise.

[0043] As used in this specification, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (eg, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.8, 4, and 5).

[0044] Unless otherwise specified, all numerals of the expression amount or composition, characteristic measurement, etc. used in this specification and embodiment should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise specified, the numerical parameters shown in the above specification and the attached embodiment list can vary according to the desired characteristics sought to be obtained by those skilled in the art using the teaching content of the present disclosure. At the very least, and without attempting to limit the application of the principle of equivalents to the scope of the embodiment protected by the claims, each numerical parameter should be interpreted at least according to the reported significant digits and by applying the usual rounding method.

[0045] Various exemplary embodiments of the present disclosure will now be described with specific reference to the accompanying drawings. Various modifications and changes may be made to the exemplary embodiments of the present disclosure without departing from the spirit and scope of the present disclosure. Therefore, it should be understood that the embodiments of the present disclosure are not limited to the exemplary embodiments described below, but should be controlled by the limiting factors shown in the claims and any equivalents thereof.

[0046] In the present disclosure, a wet-on-wet coating process for producing a multilayer coating is provided. A first coating fluid and a second coating fluid are sequentially applied to a structured substrate surface to form a first coating layer directly on the structured substrate surface and a second coating layer on the first coating layer. The conformability of the first coating layer can be adjusted to provide desired surface and bulk coating properties. In addition to coating functions, the wet-on-wet coating process described herein can also be used to improve coating limitations typically encountered in single-layer die coating methods and dry lamination methods for multilayer coating constructions.

[0047] See now Figure 1 , illustrates a schematic diagram of a coating apparatus 100 for performing the method of the present disclosure according to some embodiments. The coating apparatus 100 includes a web path for conveying a web 2 from a first coating applicator 110 to a second coating applicator 120. A first coating fluid is applied from the first coating applicator 110 to a structured surface 22 of the web 2 to form a skin layer directly on a pattern of structured features on the web 2. A second coating fluid is applied from the second coating applicator 120 to the skin layer to form a bulk layer directly on the skin layer. The second coating fluid is different from the first coating fluid. For example, the second coating fluid may have a different composition, a different chemical phase, or a material property that can be used to distinguish a solidified bulk layer from a solidified skin layer. The web path may include various rollers 11, 13, 15, 17 and / or other mechanisms to convey the web 2 at a predetermined linear speed along the longitudinal direction D. In some embodiments, it is preferred to select a suitable web transport mechanism that does not contact structured surface 22 of web 2 in the web path between first coating applicator 110 to second coating applicator 120 .

[0048] exist Figure 1 In the depicted embodiment, the first coating applicator 110 includes a slot die 112 that engages the web 2 in a free span path 114 between the support rollers 13 and 15. The slot die 112 includes one or more die holes or channels through which the first coating fluid can flow toward the structural surface 22 of the web 2, wherein the one or more channels are arranged in the longitudinal or cross-web direction. The die coating process for applying the first coating fluid can be referred to as a pre-metered coating process. For example, the first coating applicator 110 may include a pump and a control system for the pump. The pump can provide a predetermined flow rate of the first coating fluid. The predetermined flow rate and other factors (such as, for example, web speed) can largely define the wet coating thickness of the epidermis layer. The pump can be, for example, a high-bandwidth precision pump that is fluidly connected to the input port of the die body.

[0049] It should be understood that the first coating applicator 110 can be any suitable applicator for applying a thin fluid layer to the web surface. Suitable first coating applicators may include, for example, fluid bearing die coating applicators, gravure coating applicators, Meyer rod coating applicators, rod coating applicators, slot die coating applicators, curtain coating applicators, slide coating applicators, notched rod coating applicators, air knife coating applicators, blade coating applicators, blade coating applicators, dip coating applicators or roller coating applicators. Exemplary applicators are described in the following: for example, "Liquid Film Coating", edited by Kistler SF and Schweizer PM. Springer Dordrecht (Springer, Dordrecht) 1997, pp. 401-462, 539-571, 637-672 and 735-768.

[0050] exist Figure 1 In the embodiment depicted in the drawings, the second coating applicator 120 includes a slot die 122 engaged with a support roller 124. The slot die 122 includes one or more die holes or channels through which the second coating fluid can flow toward the support roller 124, wherein the one or more channels are arranged in the longitudinal or transverse direction. The die coating process for applying the second coating fluid can be referred to as a pre-metered coating process. For example, the second coating applicator 120 may include a pump and a control system for the pump. The pump can provide a predetermined flow rate of the second coating fluid. The predetermined flow rate and other factors (such as, for example, web speed) can largely define the thickness of the second coating layer. The pump can be, for example, a high-bandwidth precision pump that is fluidly connected to the input port of the die body.

[0051] It should be understood that various configurations of slot dies may be applied herein. Exemplary slot dies are described in, for example, U.S. Patent No. 7,846,504 (Maier et al.). It should also be understood that the second coating applicator 120 may be any suitable applicator for coating the second coating fluid on the web surface 22, which has been covered by the epidermis of the first coating fluid. Suitable second coating applicators may include, for example, slot die coating applicators, slide coating applicators, curtain coating applicators, roller coating applicators, gravure coating applicators, or notched rod coating applicators.

[0052] exist Figure 1In the depicted embodiment of , the first coating applicator 110 and the second coating applicator 120 are separated by a distance L as measured along the machine direction web length between the respective coating zones of the first coating applicator 110 and the second coating applicator 120. In other words, after the first coating fluid is applied from the first coating applicator 110 to the web surface 22 to form the skin layer, the web 2 is conveyed along the web path a distance L to reach the coating zone of the second coating applicator 120, wherein the second coating fluid is applied to the skin layer to form the bulk layer.

[0053] The web is conveyed at a certain speed between the first coating applicator 110 and the second coating applicator 120 along this web path, and the speed is called the line speed or coating speed. The time spent by the web from the coating area of ​​the first coating applicator 110 to the coating area of ​​the second coating applicator 120 refers to the residence time T between the first coating and the second coating. This residence time T can be calculated by dividing the distance of the web path L by the line speed. The residence time T can be determined by considering a wide range of coating factors, including, for example, the physical constraints of the web speed, the coating applicator, and the drying rate of different formulations within the thickness limit. In some embodiments, the distance L can be in the range of, for example, 0.01m to 20m, 0.1m to 20m, 0.1m to 10m, or 0.2m to 5m. In some embodiments, the residence time T between the first coating and the second coating can be in the range of, for example, 0.001 seconds to 200 seconds, 0.01 seconds to 200 seconds, 0.01 seconds to 100 seconds, or 0.1 seconds to 30 seconds.

[0054] In some embodiments, the first coating applicator 110 and the second coating applicator 120 may be mounted on separate coating stations. In some embodiments, the first coating applicator 110 and the second coating applicator 120 may be mounted on a single coating station. The distance between the first coating applicator 110 and the second coating applicator 120 may be adjustable by any suitable mechanism.

[0055] See again Figure 1, after applying the second coating fluid from the second coating applicator 120 to the skin layer to form the bulk layer directly on the skin layer, the fluid coating on the web surface 22 is solidified to form a dry double-layer coating including a skin layer and a bulk layer corresponding to the first coating fluid and the second coating fluid, respectively. In some embodiments, the fluid coating can be solidified by a curing process, which may refer to chemical crosslinking such as by exposure to any form of radiation, heating, or subjecting it to a chemical reaction that causes the material to harden or increase in viscosity (e.g., at ambient temperature or under heating conditions). Suitable curing conditions are well known in the art, including, for example, heating, using visible light or ultraviolet (UV) light, electron beam irradiation, and the like. Alternatively, "solidification" can be caused by removing the solvent during drying without (e.g.) polymerization or crosslinking.

[0056] The present disclosure has discovered that the coating thickness and uniformity of the first coating layer (skin layer) and the second coating layer (bulk layer) can affect the performance attributes of the dual-layer coated article. The first coating applicator and the second coating applicator (such as Figure 1 The first coating applicator 110 and the second coating applicator 120 shown can control the wet coating thickness applied to the web surface 22. After the solvent or volatile materials are removed during the solidification step, the dry thickness of the skin layer and the bulk layer is obtained. Although the articles of interest in the present disclosure have a microstructured web surface 22, it is convenient to refer to the theoretical wet thickness assuming that the web surface is flat, such as Fig. 12A Under these ideal conditions, a wet-on-wet coating method is applied to a web 1 having a flat web surface 21, wherein the first coating fluid 31 has a value of t w The second coating fluid 33 forms a layer of wet thickness 533 on top of the wet first coating fluid. Since the coating can shrink during the solidification step (due to evolution of solvents, monomers or other substances), the dry thickness can be significantly less than the wet thickness for each layer. For convenience, consider again an idealized web 1 with a flat surface 21, Fig. 12B A skin layer 31' having a dry thickness 531' and a body layer 33' having a dry thickness 533' are shown, and these layers may be composed of Fig. 12A The solidification of the wet coating state exemplified in FIG.

[0057] Prior to solidification, the ratio of the average wet thickness of the epidermis layer to the average wet thickness of the bulk layer is, for example, in the range of about 0.01 to about 1.0, about 0.03 to about 0.5, or about 0.05 to about 0.2. It should be understood that in some embodiments, the epidermis layer may have a local wet thickness greater than the local wet thickness of the bulk layer. In some embodiments, the epidermis layer may have an average wet thickness greater than the average wet thickness of the bulk layer. The double-layer coating may have a dry thickness in the range of, for example, about 10 microns to about 250 microns, or about 12 microns to about 75 microns.

[0058] The first coating fluid for forming a skin layer or "wetting layer" on the web surface 22 may include one or more adhesives, such as a pressure sensitive adhesive (PSA) and optional additional components, depending on the desired properties of the skin layer. An exemplary pressure sensitive adhesive (PSA) for the skin layer may include a copolymer prepared from polymerized isooctyl acrylate, acrylamide, and a silicon-containing monomer.

[0059] In some embodiments, the first coating fluid may include monomers dissolved in an inert organic solvent and polymerized using a suitable free radical initiator that can be activated thermally or photochemically. Forming the skin layer from the first coating fluid may include evaporating the solvent therefrom after the first coating fluid is applied to the web surface 22.

[0060] The properties of the adhesive skin layer can be designed so that it is easy to peel from the web surface 22, thereby facilitating the separation of the skin layer from the web surface 22 with little or no damage to the body layer. The properties of the skin layer can also be designed so that an article (e.g., an adhesive graphic) having a backing bonded to the body layer can be temporarily repositioned. The skin coating layer can be designed so that the article is temporarily repositionable with little or no change in the bulk adhesive properties of the body layer. This can be demonstrated by a low initial peel adhesion (bonding strength) of the article to the article, followed by an increase in the peel adhesion over time. For example, it may be used in an article to exhibit an initial peel adhesion that is about 20% or more lower than that of an article without a skin layer. The skin layer can also be designed so that the body layer does not stick to itself once the substrate is removed.

[0061] In some embodiments, the second coating fluid may include a pressure sensitive adhesive (PSA) and optional additional components, depending on the desired properties of the coating formed. Forming a coating layer or film from the second coating fluid may include evaporating a solvent of the second coating fluid after coating, or cooling if the second coating fluid includes a hot melt pressure sensitive adhesive (PSA). Forming a film from the second coating fluid may also include curing the components in the fluid, such as using heat, UV or other sources of radiation energy to initiate a reaction between the crosslinking agent and the polymer or oligomer components. Any combination of these is also available.

[0062] The properties of the film or body layer can be designed so that it forms a predetermined minimum peel adhesion for a particular article. For example, an application may require that the body layer cannot be removed from the article after a period of time or can only be removed under strict conditions such as high heat or solvents that dissolve the layer. Such articles may include paint replacement films for automobiles. Alternatively, an application may require that the film be removable after a short period of time, such as paint masking tape on windows, or removable after a longer period of time, such as a protective film on a display device.

[0063] A variety of additional components may be included in the first coating fluid or the second coating fluid to achieve the desired properties of the corresponding epidermis or body layer. For example, tackifying resins and plasticizers may be used to adjust the adhesion of the epidermis or body layer. Tackifying resins may include rosin, polyterpene resins, phenolic resins, and coumarone-indene resins, and may be used in an amount of up to about 150 parts by weight based on 100 parts by weight of the silicon-containing pressure sensitive adhesive (PSA).

[0064] Plasticizers may include aromatic hydrocarbons, paraffins, and naphthenic extender oils, and may be used in an amount up to about 50 parts by weight based on 100 parts by weight of the silicon-containing pressure sensitive adhesive (PSA). Pigments, fillers, glass beads, stabilizers, crosslinking agents, etc. may also be added.

[0065] The second coating fluid for forming the bulk layer is different from the first coating fluid for forming the epidermis layer. In some embodiments, the second coating fluid may have a higher viscosity than the first coating fluid. For example, the first coating fluid may have a viscosity in the range of about 0.5 cP to about 300 cP at a shear rate of 100 1 / s, optionally about 5 cP to about 100 cP at a shear rate of 100 1 / s. The viscosity ratio at a shear rate of 100 1 / s between the first coating fluid and the second coating fluid is, for example, in the range of about 0.0001 to about 1, optionally about 0.001 to about 0.5.

[0066] In the present disclosure, the first coating fluid (skin layer) includes a solvent component, such as, for example, an organic solvent, water, a monomer, etc. In some embodiments, the first coating fluid and the second coating fluid may contain corresponding polymers that are soluble in the same solvent (such as, for example, ethyl acetate). In the case where both polymer systems are soluble in the same solvent, undesirable large-scale phase separation in some embodiments can be avoided. The present disclosure observes that large-scale phase separation can occur when the first coating fluid for the skin layer includes a solvent that is immiscible with the solvent of the second coating fluid for the bulk polymer.

[0067] In some embodiments, the bulk layer formed by solidifying the second coating fluid may exhibit a lower glass transition temperature (Tg) than the skin layer formed by solidifying the first coating fluid. In some embodiments, the bulk layer may have an average thickness of at least 10 microns; and include an acrylate pressure-sensitive adhesive with a Fox Tg of up to -30°C. The skin layer may have an average thickness of up to 25 microns. The ratio of the average thickness of the bulk layer to the average thickness of the skin layer is at least 2: 1. The skin layer may include an adhesive with a Fox Tg of -20°C to +50°C. PCT Publication No. WO 2019 / 123180 (Agent Case No. 80030WO003, Yarusso et al.) describes a double-layer adhesive with a high Tg at the bonding surface, which is incorporated by reference.

[0068] The major surface 22 of the web 2 coated with the first coating fluid may have a textured or structured surface. An exemplary web having a textured or structured surface may be a release liner. The textured or structured surface will impart a shape to the coating layer or layers thereon. One useful shape may be a web formed by, for example, FIG. 2A to FIG. 2E Two or more flat surfaces separated by at least one groove or channel shown. Textured surfaces include those having random roughness, random shape patterns, ordered roughness, ordered shape patterns, or combinations thereof. Structured surfaces include microstructured surfaces, such as those provided by microstructured release liners. Microstructured surfaces generally include microstructures having at least two lateral dimensions (i.e., dimensions within the film plane) less than 1.4 mm (55 mils), such as prepared as described in US6,197,397 (Sher et al.), US6,123,890 (Mazurek et al.), US6,838,142B2 (Yang et al.), US6,838,150B2 (Mazurek et al.), etc. The microstructured surface may include a pattern of structured features having a feature height in the range of, for example, about 100 nm to about 1 mm. For example, the microstructured surface can include a range of shapes, including ridges, columns, pyramids, hemispheres, and cones, and / or they can be protrusions or depressions with flat, pointed, truncated, or rounded portions, all of which can have angled or perpendicular sides relative to the plane in which the surface lies. The microstructured surface can have an irregular pattern of intersecting channels such as linear channels or forming a grid, or a combination thereof. The microstructured surface can impart substantially continuous open circuits or grooves to the first and / or second coating layer.

[0069] For purposes of this disclosure, a structure on a microstructured web surface may be characterized as a raised surface supported by walls that transition into corners toward the base of the structure. Fig.11As shown, the structured surface 22 of the web 2 may include one or more raised features 222 characterized by a raised surface 222a supported by a substantially vertical riser 224. The riser 224 extends from a raised end to a lower end and transitions from the raised surface 222a at the raised end to a sharp corner 223 at the lower end adjacent to the base of the raised feature 222. The structured surface 22 may also include one or more curved raised features 322 having a raised surface 322a along a riser 324 that gradually changes in slope and a smooth corner 323 at the base of the feature. The riser 324 extends from a raised end to a lower end and transitions from the raised surface 322a at the raised end to a corner 323 at the lower end. In addition, the structured surface 22 may include one or more recessed features 422 having a raised surface 422a adjacent to a riser 424 that transitions toward the base of the structure to a corner 423. Rising wall 424 extends from the raised end to the lower end and transitions from raised surface 422a at the raised end to corner 423 at the lower end. Complex structured surfaces can have composite features that are combined and extended based on the geometric descriptions provided herein.

[0070] See again Figure 1 , the first coating fluid and the second coating fluid are sequentially applied to the structured surface 22 of the web 2 to form a skin layer and a bulk layer directly on the skin layer, respectively. In the present disclosure, the residence time between applying the first coating fluid and applying the second coating fluid can be controlled to adjust the conformability of the skin layer on the surface of the structured web. This FIG. 2A to FIG. 2E Further examples are given in .

[0071] like Figure 2A As shown, via a first coating applicator (e.g., Figure 1The first coating applicator 110 of the present invention applies the first coating fluid 32 to the structured surface 22 of the web 2 to form a skin layer of the first coating fluid 32. The first coating fluid may have a relatively lower viscosity and a lower surface tension than the second coating fluid, so that the first coating fluid can "saturate" the structured surface 22 of the web 2. For applying a single layer of fluid to a substrate, if the surface tension of the fluid is less than the surface energy of the substrate, the fluid will properly wet the substrate. If not, the force applied along the surface of the fluid may cause it to "bead up" and form droplets. The structured surface 22 includes a pattern of structured features, which can further help the first coating fluid 32 saturate the structured surface 22. The pattern of structured features includes one or more raised features 222 separated by grooves 224. The structured features on the structured surface 22 may have, for example, an average feature height / depth of about 0.1 microns to about 1000 microns, about 1 micron to about 200 microns, about 2 microns to about 100 microns, or about 10 microns to about 50 microns. The first coating fluid 32 may have a sufficient wet thickness to fill the recesses 224 and cover the raised features 222, or may have a wet thickness less than that required to fill the recesses 224 and cover the raised features 222, but be applied in such a manner that it conformally covers both the recesses 224 and the raised features 222.

[0072] After applying the first coating fluid 32 to the structured surface 22 of the web 2 via the first coating applicator to form a skin layer of the first coating fluid 32, the web 2 is transported from the first coating applicator to a second coating applicator (e.g., Figure 1 A second coating applicator 120 is provided, wherein a second coating fluid 34 is applied to the skin layer 32 on the structured surface 22 of the web 2 via the second coating applicator, such as Figure 2B and Figure 2D Then the fluid coating on the web 2 is solidified to form a double-layer coating, as shown. Figure 2C and Figure 2E shown.

[0073] During the transfer of the web 2 from the first coating applicator to the second applicator, the skin layer of the first coating fluid 32 on the structured surface 22 of the web 2 may begin to solidify or evaporate, and the thickness of the layer may begin to shrink. At the same time, the skin layer may begin to dewet from the raised features of the structured surface 22 and accumulate in the corners. The residence time between applying the first coating fluid and applying the second coating fluid, as well as one or more environmental factors, may be controlled to adjust the conformability of the skin layer on the structured web surface.

[0074] At relatively low residence time T1, the skin layer can have good conformability around structured features, such as Figure 2B and Figure 2C As shown. Figure 2B , when the second coating fluid 34 is applied over the skin layer of the first coating fluid 32, the raised surfaces 222a of the raised features 222 of height h are still covered by the first coating fluid 32. The second coating fluid 34 and the first coating fluid 32 on top of the pattern of structured features can be described by a repeating unit 240 that repeats across the web surface 22 defined by an area 241 that includes a portion of a smaller area 242 that characterizes the fractional area coverage of the raised features 222. After solidification, the first coating fluid 32 forms a continuous skin layer 32' that directly covers the structured surface 22, as shown in FIG. Figure 2C The skin layer 32' has a dry thickness 238' near the corner 223 of the structured feature that is greater than the dry thickness 236' on the raised surface 222a. The continuous body layer 34' covers the continuous skin layer 32', which substantially conforms to the structured surface 22.

[0075] As the residence time increases from T1 to T2, there is less coating on the raised features of the structured web surface and more accumulation on the corners, e.g. Figure 2D and Figure 2E As shown. Figure 2D In the embodiment depicted in FIG. 1 , when the second coating fluid 34 is applied over the skin layer of the first coating fluid 32, the first coating fluid 32 substantially dewets from the raised surfaces of the raised features 222. After solidification, the first coating fluid 32 forms a substantially discontinuous skin layer 32″ that resides primarily in the grooves 224 separated by the raised features 222, as shown in FIG. Figure 2E As shown. On the corners 223 of the structured features, the first coating fluid 32 can accumulate and contribute to the increase in dry thickness of the skin layer 32 ″. The continuous body layer 34 ″ covers the skin layer 32 ″ in the grooves 224 and the raised features 222 .

[0076] In some embodiments, the residence time T1 can be controlled, for example, in the range of 0.001 seconds to 30 seconds. The residence time T2 can be controlled, for example, in the range of 1 second to 200 seconds.

[0077] In some embodiments, when the substrate moves from the first coating applicator to the second coating applicator, one or more environmental factors can be controlled to adjust the conformability. The environmental factors can include, for example, at least one of temperature, ambient radiation, vapor pressure, etc.

[0078] In some embodiments, when the substrate moves from the first coating applicator to the second coating applicator, one or more fluid properties of the first coating liquid can be controlled to adjust the conformability. The one or more fluid properties of the first coating liquid can include, for example, at least one of viscosity, surface tension, solid percentage, or volatility of the solvent. In some embodiments, conformability can be further controlled by adjusting the surface properties of the web, including, for example, surface energy, surface microstructure features (e.g., size, sharp edges, etc.), sub-scale roughness, electrostatic charge, chemically reactive functional groups, polarity, etc.

[0079] In some embodiments, controlling the dwell time can include at least one of: (i) controlling the web speed to move the substrate from the first coating applicator to the second coating applicator, or (ii) controlling the distance between the first coating applicator and the second coating applicator.

[0080] After solidification, the formed two-layer coating includes a bulk layer / skin layer configuration on the structured web surface.The two-layer coating can have a dry thickness in the range of about 10 microns to about 250 microns, optionally about 12 microns to about 75 microns.

[0081] In some embodiments, the bulk layer may have an average thickness of at least 10 microns. In certain embodiments, the bulk layer may have an average thickness of at least 20 microns, at least 30 microns, or at least 50 microns and at most 150 microns, at most 125 microns, at most 100 microns, at most 75 microns, or at most 50 microns.

[0082] In some embodiments, the continuous / discontinuous skin layer may have an average thickness that is less than the characteristic height of the structured surface. In some embodiments, the continuous / discontinuous skin layer may have an average thickness of at most about 25 microns. In certain embodiments, the continuous / discontinuous skin layer may have an average thickness of at most 20 microns, at most 12 microns, at most 10 microns, at most 8 microns, at most 6 microns, at most 4 microns, or at most 2 microns.

[0083] In some embodiments, the ratio of the average thickness of the continuous / discontinuous skin layer to the average thickness of the bulk layer may be, for example, in the range of about 0.005 to about 0.5, about 0.01 to about 0.3, or about 0.01 to about 0.06. The ratio of the average thickness of the bulk layer to the average thickness of the continuous / discontinuous skin layer is at least 2:1. In certain embodiments, the ratio of the average thickness of the bulk layer to the average thickness of the continuous / discontinuous skin layer is at least 3:1, at least 4:1, at least 5:1, at least 10:1, at least 20:1, at least 50:1, or at least 70:1. In certain embodiments, the ratio of the average thickness of the bulk layer to the average thickness of the continuous / discontinuous skin layer is at most 300:1, at most 200:1, at most 100:1, or at most 50:1.

[0084] In some embodiments, the body layer shows a lower glass transition temperature than the epidermis.Compared with the debonding power of the lower Tg adhesive of the independent basic body layer, the relatively thin epidermis comprising the higher Tg adhesive provides the increase of the debonding power required for adhesive and substrate separation.In addition, the lower Tg adhesive of the body layer provides necessary conformability for good substrate wetting and energy dissipation, and will lack this conformability in the higher Tg adhesive of the independent superimposed epidermis.These composite characteristics can make the observed bonding performance (that is, tearing force / resistance) of the adhesive article of the present disclosure significantly improved.

[0085] In some embodiments, the double-layer coating may include a diffusion interface between the epidermis and the bulk layer, the diffusion interface having a thickness of, for example, about 0.1 microns to 10 microns, about 0.2 microns to 5 microns, or about 0.5 microns to 3 microns. Although not wishing to be bound by theory, the inventors believe that such a diffusion interface may be obtained by the wet-on-wet process described herein. The polymers in the first coating fluid for the epidermis and the second coating fluid for the bulk layer may have a certain degree of mobility through the depth of the coating, including the ability to interact or migrate at the interface of the two layers. Interdiffusion of polymers into adjacent layers may also occur during the solidification process (e.g., drying). In addition, the blended polymer materials in the diffusion interface region may generate a smooth characteristic gradient from one layer to the next, or a complex morphology such as in the case of phase separation of the polymer materials. The present disclosure finds that significantly more interactions and interdiffusions may occur between the high Tg epidermis and the low Tg bulk layer. FIG. 10A to FIG. 10B The cross-sectional AFM phase image in will provide a visual representation of the diffusion interface, which will be further described below.

[0086] The present disclosure provides methods for preparing two-layer adhesives in which the surface characteristics of the adhesive can be tuned to highly desirable performance attributes of adhesives, particularly PSAs.The two-layer adhesives described herein can be used in a variety of applications. Figure 3A single application of adhesive to a graphic film is illustrated. Article 40 includes a vinyl film 41 having a printed surface 411. Vinyl film 41 is attached to a double layer of adhesive 42 via an optional primer 43 on the side of a body layer 421. The skin layer 422 of the double layer of adhesive 42 is in direct contact with the structured surface 22 (e.g., release liner) of the substrate 2. The conformability of the skin layer 422 on the structured surface 22 and thus the surface properties of the adhesive after the release liner is removed can be controlled according to the methods described herein.

[0087] In some embodiments, the vinyl film 41 is loaded with TiO2 pigment to give it a solid white color that controls the white point of the product. The primer 43 is loaded with carbon black, which helps to provide opacity to the product. The primer 43 also serves as a permanent bond between the film 41 and the adhesive 42.

[0088] The first coating fluid and the second coating fluid can be particle-carrying fluids loaded with various particles to provide multiple functions. In some embodiments of graphic film applications, the first coating fluid used to form the skin layer 422 can be loaded with carbon black. The second coating fluid used to form the bulk layer 421 can be loaded with one or more pigments, optionally including TiO2. This can improve the bulk opacity and white point of the final product by independently controlling the skin layer to target adhesion and tear performance metrics while loading the bulk adhesive with pigments.

[0089] List of Exemplary Embodiments

[0090] It should be understood that any of Embodiments 1 to 21 and Embodiments 22 to 29 may be combined.

[0091] Embodiment 1 is a method, the method comprising:

[0092] moving a substrate along a web path from a first coating applicator to a second coating applicator, the substrate comprising a structured surface including a pattern of structured features;

[0093] applying a first coating fluid from the first coating applicator onto the structured surface of the substrate to form a first coating layer directly on the pattern of structured features;

[0094] applying a second coating fluid from the second coating applicator onto the first coating layer to form a second coating layer directly on the first coating layer, the second coating fluid being different from the first coating fluid; and

[0095] solidifying the first coating layer and the second coating layer to form a double-layer coating including a skin layer and a bulk layer,

[0096] The residence time between applying the first coating fluid and applying the second coating fluid is controlled to adjust the conformability of the skin layer on the structured surface.

[0097] Embodiment 2 is a method according to embodiment 1, further comprising: controlling one or more environmental factors to adjust the conformality as the substrate moves from the first coating applicator to the second coating applicator.

[0098] Embodiment 3 is a method according to embodiment 2, wherein the one or more environmental factors include at least one of temperature, ambient radiation, or vapor pressure.

[0099] Embodiment 4 is a method according to any one of embodiments 1 to 3, which also includes: when the substrate moves from the first coating applicator to the second coating applicator, controlling one or more fluid properties of the first coating liquid to adjust the conformality.

[0100] Embodiment 5 is a method according to embodiment 4, wherein the one or more fluid properties of the first coating liquid include at least one of viscosity, percent solids, or volatility of solvent.

[0101] Embodiment 6 is a method according to any one of embodiments 1 to 5, wherein controlling the residence time comprises at least one of: (i) controlling the web speed so that the substrate moves from the first coating applicator to the second coating applicator, or (ii) controlling the distance between the first coating applicator and the second coating applicator.

[0102] Embodiment 7 is a method according to any one of embodiments 1 to 6, wherein the second coating fluid has a higher viscosity than the first coating fluid.

[0103] Embodiment 8 is a method according to embodiment 7, wherein the first coating fluid has a viscosity in the range of about 0.5 cP to about 300 cP at a shear rate of 100 1 / s, optionally about 5 cP to about 100 cP at a shear rate of 100 1 / s.

[0104] Embodiment 9 is a method according to embodiment 7 or 8, wherein the viscosity ratio between the first coating fluid and the second coating fluid at a shear rate of 100 1 / s is in the range of about 0.0001 to about 1, optionally about 0.001 to about 0.5.

[0105] Embodiment 10 is a method according to any one of embodiments 1 to 9, wherein the ratio of the first coating layer average wet thickness to the bulk layer average wet thickness is in the range of about 0.01 to about 1.0, optionally about 0.05 to about 0.2.

[0106] Embodiment 11 is a method according to any one of embodiments 1 to 10, wherein the dual-layer coating has a dry thickness in the range of about 10 microns to about 250 microns, optionally about 12 microns to about 75 microns.

[0107] Embodiment 12 is a method according to any one of embodiments 1 to 11, wherein the ratio of the average dry thickness of the skin layer to the average dry thickness of the bulk layer is in the range of about 0.01 to about 0.3, optionally about 0.01 to about 0.06.

[0108] Embodiment 13 is a method according to any one of embodiments 1 to 12, wherein the dual-layer coating includes a diffusion interface located between the skin layer and the bulk layer, the diffusion interface having a thickness of about 0.2 microns to about 5.0 microns.

[0109] Embodiment 14 is a method according to any one of embodiments 1 to 13, wherein the bulk layer exhibits a lower glass transition temperature than the skin layer.

[0110] Embodiment 15 is a method according to any one of embodiments 1 to 14, wherein the structural features have a feature height or depth of about 2 microns to about 100 microns, optionally about 10 microns to about 50 microns.

[0111] Embodiment 16 is a method according to any one of embodiments 1 to 15, wherein at least one of the first coating fluid and the second coating fluid comprises one or more particle-carrying fluids.

[0112] Embodiment 17 is a method according to embodiment 16, wherein the first coating fluid further comprises carbon black.

[0113] Embodiment 18 is a method according to embodiment 16 or 17, wherein the second coating fluid further comprises one or more pigments, optionally, the pigments comprise TiO2.

[0114] Embodiment 19 is a method according to any one of embodiments 1 to 18, wherein the first coating applicator includes at least one of the following: a fluid bearing die coating applicator, a gravure coating applicator, a rod coating applicator, a slot die coating applicator, a curtain coating applicator, a slide coating applicator, a notched rod coating applicator, an air knife coating applicator, a blade coating applicator, a scraper coating applicator, a dip coating applicator or a roller coating applicator.

[0115] Embodiment 20 is a method according to any one of embodiments 1 to 19, wherein the second coating applicator comprises at least one of the following: a slot die coating applicator, a slide coating applicator, a curtain coating applicator, a roller coating applicator, a gravure coating applicator or a notched rod coating applicator.

[0116] Embodiment 21 is a method according to any one of embodiments 1 to 20, wherein the second coating applicator is pre-metered.

[0117] Embodiment 22 is a multi-layer coated article comprising:

[0118] A substrate comprising a first major surface and an opposing second major surface, the first major surface comprising a microstructured surface, the microstructured surface comprising a pattern of structured features, the pattern of structured features comprising one or more rising walls, the one or more rising walls each extending from a raised end to a lower end opposite the raised end, each rising wall connecting a raised surface at the raised end and a corner at the lower end; and

[0119] a double-layer coating disposed on the microstructured surface of the substrate,

[0120] The double-layer coating comprises:

[0121] A skin layer disposed directly on the microstructured surface of the substrate, wherein the skin layer has a greater thickness on the corners than on the raised surfaces; and

[0122] A body layer is directly disposed on the skin layer.

[0123] Embodiment 23 is an article according to embodiment 22, wherein the skin layer is a continuous layer substantially covering the microstructured surface.

[0124] Embodiment 24 is an article according to embodiment 23, wherein the skin layer substantially conformally covers the microstructured surface of the substrate.

[0125] Embodiment 25 is the article of any one of embodiments 22 to 24, wherein the skin layer is a discontinuous layer separated by the raised surface.

[0126] Embodiment 26 is an article according to any one of embodiments 22 to 25, wherein the ratio of the average dry thickness of the skin layer to the average dry thickness of the body layer is in the range of about 0.01 to about 0.3, optionally about 0.01 to about 0.06.

[0127] Embodiment 27 is an article according to any one of embodiments 22 to 26, wherein the dual-layer coating includes a diffusion interface located between the skin layer and the bulk layer, the diffusion interface having a thickness of about 0.2 microns to about 5.0 microns.

[0128] Embodiment 28 is an article according to any one of embodiments 22 to 27, wherein the body layer exhibits a lower glass transition temperature, Tg, than the skin layer.

[0129] Embodiment 29 is an article according to any one of embodiments 22 to 28, wherein the dual-layer coating includes one or more particle-carrying layers.

[0130] The operation of the present disclosure will be further described with reference to the examples described in detail below. These examples are provided to further illustrate various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications may be made and still fall within the scope of the present disclosure.

[0131] Example

[0132] These embodiments are for illustrative purposes only and are not intended to unduly limit the scope of the appended claims. Although the numerical ranges and parameters showing the broad scope of the present disclosure are approximate values, the numerical values ​​shown in the specific examples are recorded as accurately as possible. However, any numerical value inherently contains certain errors, and the standard deviation existing in its respective test measurements will inevitably cause such errors. At the very least, and without attempting to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be interpreted based on the reported significant digits and by applying conventional rounding methods.

[0133] Materials Summary

[0134] Unless otherwise indicated, all parts, percentages, ratios, etc. in the examples and the remainder of this specification are by weight. Table 1 provides the naming conventions, material properties, and references used to describe each material used in the following examples.

[0135] All web materials used in the examples were four-layer release liners with a paper core, a polyethylene layer on the back side and a micro-embossed polyethylene layer with a silicone release coating on the front side. Details of the microstructure geometry of the two different web materials are listed in the table below.

[0136] Table 1

[0137]

[0138] The coating fluids used in the examples are described below as Formulation A, Formulation B, Formulation C, and Formulation D. Table 2 provides a brief summary of material descriptions and properties for reference. For the purposes of these descriptions, the term "percent" or "pph" refers to the weight parts of a component such as a tackifier or crosslinker based on 100 parts by weight of the PSA polymer in the formulation.

[0139] Description of Formulation A: A stock solution was prepared by mixing the (meth)acrylate monomer material mentioned in US 9,102,774 B2, acrylic acid and acrylamide in a ratio of 90 / 7 / 3 with 0.25% VAZO-67 initiator and ethyl acetate in a 1 liter bottle. The mixture was then divided into two bottles. The bottles were purged with nitrogen, sealed, and placed in a water bath, stirred, at 65° C. for 24 hours. The material was further diluted from 39.8% solids to 10% solids by adding ethyl acetate.

[0140] Description of Formulation B: A stock solution was prepared by mixing 160 g butyl acrylate, 10 g acrylic acid, 30 g N-vinyl pyrrolidone, 30 g vinyl acetate, 290 g ethyl acetate, 10 g isopropanol, and 0.5 g VAZO-67 initiator in a 1 liter bottle. The mixture was then split into two bottles and each bottle was purged with nitrogen, sealed, and placed in a water bath, stirred, at 65°C for 24 hours. The material was further diluted to 10% solids by adding ethyl acetate.

[0141] Formulation C Description: An acrylic pressure-sensitive adhesive solution (described as Adhesive Solution 1 in U.S. Pat. No. 5,296,277 (Wilson et al.) and containing 0.14 parts per hundred (pph) of bisamide and 16 parts per hundred of a tackifier) ​​was prepared at 38.5% solids. The tackifier used was Terpene Phenol, purchased from Kraton Corporation, Houston, TX as "SYLVARES" TP2019. (See WO2019 / 193501, Table 1, A1)

[0142] Formulation D Description: An acrylic pressure sensitive adhesive solution (described as Adhesive Solution 1 in US Pat. No. 5,296,277 (Wilson et al.) and containing 0.14 parts per hundred (pph) of bisamide) was prepared at 35% solids.

[0143] Table 2

[0144]

[0145]

[0146] Test Method

[0147] The following test methods were used to evaluate some of the embodiments of the present disclosure.

[0148] Sample preparation for cross-sectioned adhesive films :

[0149] Cross-sectioning of the multilayer adhesive coating was performed using cryosectioning. The microstructured liner tended to delaminate during sample preparation. These liners were therefore removed and the samples were thinly embedded in Struers Specifix epoxy (cured overnight at room temperature and then cryosectioned at close to -60°C using a Leica EM UC6).

[0150] AFM (Atomic Force Microscope)

[0151] Atomic force microscopy (AFM) in tapping mode is used to characterize cross-sectional layers. Atomic force microscopy (AFM) consists of a flexible microcantilever and a sharp tip attached to the free end of the microcantilever. The sharp AFM tip can be brought into contact with the sample and scanned in a raster pattern to generate a high-resolution three-dimensional image of the sample surface. The technology is based on the interaction force between the tip and the sample surface, which causes the cantilever to deflect when it is swept across the surface. The cantilever deflection is monitored using a laser deflection technique, in which a laser beam is reflected from the back of the cantilever and detected by a photodiode. A piezoelectric scanner is used to accurately control the movement of the tip in the vertical and lateral directions. The topographic information is obtained by using the photodiode signal as a control parameter of the feedback mechanism. In the tapping mode AFM, the flexible tip / cantilever assembly oscillates at a resonant frequency close to the cantilever, and the two main signal outputs are the topography (height) and phase images. The amplitude of the vertical oscillation is the input parameter of the feedback loop for generating the topographic image. The phase shift measured as the phase difference between the photodiode output and the driving excitation signal is monitored to generate a phase image. Phase images are used for visualization purposes. Phase signals are usually related to a complex contribution set from surface material properties (dissipation, elasticity, adhesion), surface topography and are therefore difficult to interpret quantitatively. Darker areas in the phase image correspond to materials with lower stiffness, while brighter areas correspond to materials with higher stiffness. All AFM images are obtained from BrukerDimension ICON AFM system. The AFM tip used is an OTESPA-R3 silicon tip with a nominal spring constant of 42 N / m, a resonant frequency between 200 kHz and 400 kHz, and a nominal tip radius of curvature of 7 nm.

[0152] Viscosity measurement

[0153] The coating fluids were characterized using a Discovery hybrid rheometer (TA Instruments) with a Peltier concentric cylinder instrument geometry, where a bob (28 mm diameter) rotated at a controlled rate while immersed in approximately 25 mL of the analyzed coating fluid contained in a close-fitting cup (30 mm diameter). The instrument software (TA Instruments) was used to specify a flow chart to measure shear viscosities ranging from 0.1 1 / s to 1000 1 / s of shear rate. During each measurement, the temperature was maintained at 23°C. For each coating fluid in Table 2, the viscosity values ​​recorded at a shear rate of 100 1 / s are reported.

[0154] Glass transition temperature (Tg)

[0155] Fox glass transition temperature (Tg) is a value calculated using the Fox equation. The calculation is based on a weighted average of the individual homopolymer glass transition values. For a copolymer made from n different monomers, the inverse of the Tg of the copolymer is equal to the sum of the weight fractions of each component divided by the Tg of that particular component. That is, for a copolymer made from n components, 1 / Tg of the copolymer is equal to (weight fraction of component 1 ÷ Tg of component 1) + (weight fraction of component 2 ÷ Tg of component 2) + (weight fraction of component 3 ÷ Tg of component 3) + … + (weight fraction of component n ÷ Tg of component n).

[0156] Coating equipment and processes

[0157] The double-layer coating embodiments and comparative examples have similar Figure 1 The coating process is performed on a homemade coating system configured with a coating device 100 of the present invention. In each embodiment, a first coating fluid is applied from a first coating applicator to form a skin layer on the structured surface of a web substrate. The wet-on-wet coating method involves applying a second coating fluid from a second coating applicator to the skin layer to form a bulk layer directly on the skin layer. The web travels from the first coating applicator to the second coating applicator during a limited time (referred to as the residence time between coatings), which affects the double-layer coating characteristics as described in the following embodiments. In these cases, the residence time is controlled by changing the web speed, but the distance separating the first coating applicator and the second coating applicator can also be used as a suitable control mechanism.

[0158] The web coated with the fluid layer was conveyed into a four-zone convection drying oven with a temperature profile of 120 / 140 / 180 / 200° F. The web speed was controlled during the drying process to achieve the desired drying time within the convection oven zones. After drying, the solidified coating samples were carefully collected to allow cross-sectional analysis with AFM.

[0159] Dry lamination (Comparative Examples C1 to C2) Wet-on-wet (Examples E1 to E2) Two-layer adhesive

[0160] Example C1

[0161] This example describes a two-layer adhesive constructed on a microstructured web surface using different coating and solidification steps for the bulk and skin layer adhesives. In the first step, a Figure 1 The skin layer coating was prepared on a coating system configured with a coating apparatus 100 of . Adhesive coating formulation A was coated onto microstructured web material A at a wet thickness of 21 microns using a slot die coating process applied to a free span web path at 0.13 meters per second. The coated web was conveyed to a four-zone convection drying oven with a temperature profile of 120 / 140 / 180 / 200°F, with a drying time of approximately 19 seconds in each oven zone, and then collected on web material A as a sample of the solidified skin layer coating.

[0162] As a second step, an adhesive bulk layer was prepared by applying Formulation C using a hand-drawn notched bar applicator to deposit a wet coating thickness of approximately 100 microns on a 50 micron thick PET film. The coating of Formulation C was placed in a batch oven at 180F for 10 minutes and then collected as a sample of the solidified bulk layer coating on the PET film.

[0163] Finally, a 12 cm wide, 3.5 kg weighted lamination roller was manually applied at room temperature to evenly laminate the skin layer sample to the body layer sample. This dry lamination process produced a two-layer adhesive construction in which the adhesive body layer and skin layer were bonded between the PET film and the web material A.

[0164] The solidified samples were cross-sectioned and analyzed using AFM (method described in previous text) for coating characterization with submicron resolution of the bilayer configuration, demonstrating that Figure 4A A distinct interface between the adhesive bulk layer and the skin layer is shown. AFM imaging reveals accumulation of skin layer coating near the corners of microstructural features on web material A. Thus, if a coating of the same wet coating thickness and solids content had been solidified on an idealized web with a flat surface, the solidified skin layer coating thickness varies significantly along the topography of the web microstructure, resulting in local thicknesses exceeding twice the expected dry thickness (2.1 microns).

[0165] Example C2

[0166] This example describes a two-layer adhesive constructed on a microstructured web surface using the method in Example C1. In this case, web material B was used in the first coating step with the skin layer sample coated with Formulation A. The body layer sample was prepared in a separate hand-painted coating step of Formulation C as described in Example C1 and then laminated to the skin layer sample. The coating rate, thickness and drying conditions were controlled to be equivalent to Example C1.

[0167] Similar to Example C1, AFM analysis showed a clear interface between the adhesive bulk layer and the skin layer, such as Figure 5A Also consistent with the dry lamination process of Example C1, the skin layer appears excessively near the corners of the microstructural features on web material B, resulting in significant local thickness variations in the topography of the skin layer along the web surface.

[0168] It was determined that the microstructural features imparted in the two-layer adhesive by the web material B typically wrinkled or collapsed when the web material was removed during sample preparation for AFM analysis. Figure 5A The fidelity of the microstructured shapes is shown, but the failure does not interfere with the analysis regarding excessive skin layer accumulation near the corner area. In the case where the skin layer is substantially conformal to the same material and sample preparation method (see Example E2), the fidelity of the microstructured features is greatly improved. Therefore, it is concluded that the conformability of the skin layer helps stabilize the microstructured features in the absence of a supporting web material.

[0169] Example E1

[0170] This example describes a two-layer adhesive construction where the bulk layer and skin layer are applied using a similar Figure 1 The adhesive coating formulation A was coated on the microstructured web surface by a wet-on-wet coating method on a coating system of a coating apparatus 100 of FIG. Adhesive coating formulation A was deposited as a skin layer of 21 microns wet thickness onto microstructured web material A using a slot die coating method applied to a free span web path at 0.51 meters per second. After the skin layer was coated, the adhesive was deposited at a distance of approximately 1.5 meters (see FIG. 1 ). Figure 1 The web was conveyed to the bulk layer coating applicator at L in the figure, resulting in a residence time of about 3 seconds between coating steps. A slot die with a backup roller was used at the bulk layer coating applicator to apply adhesive formulation C on top of the skin layer at a wet thickness of 100 microns. The coated web was then conveyed to a four-zone convection drying oven with a temperature profile of 120 / 140 / 180 / 200°F, with a drying time of approximately 19 seconds in each oven zone, and then collected on web material A as a sample of the solidified two-layer adhesive (bulk layer and skin layer).

[0171] The solidified samples were cross-sectioned and analyzed using AFM (method described in previous text) for coating characterization with submicron resolution of the bilayer configuration, demonstrating that Figure 4B A clear interface between the adhesive bulk layer and the skin layer is shown. Although AFM imaging provides clear contrast between the bulk and skin layer domains, the interface between the adhesive layers is no longer present in Example C1. Figure 4A In contrast, the wet-on-wet coating method featured in this embodiment produces a diffuse interface feature that is characterized by Figure 4B This is shown by the gradual transition between the skin layer and the bulk layer in FIG. 1 , which indicates the blending of the adhesive polymers in this transition region.

[0172] AFM analysis revealed a skin layer that was highly conformal to the microstructural topography of Web Material A. For example, the local thickness of the skin layer near the corners of the microstructured web was within 20% of the expected dry thickness (2.1 microns) for coatings with the same wet coating thickness and solids content on an idealized web with a flat surface. This characteristic of the two-layer construction provides a sharp contrast to Example C1, where the skin layer coating was excessively accumulated near the corner areas.

[0173] Example E2

[0174] This example describes a two-layer adhesive constructed on a microstructured web surface using the wet-on-wet coating method of Example E1. In this case, web material B was used as a substrate for skin layer deposition of Formulation A and subsequent bulk layer coating of Formulation C. A web speed of 0.13 meters per second was used in this example, transporting the web a distance of approximately 1.5 meters between coating steps (see Figure 1 The coating thickness and drying conditions were controlled to be equivalent to Example E1.

[0175] Similar to Example E1, Figure 5B The AFM images shown reveal a substantially conformal skin layer along the microstructural topography of Web Material B, in contrast to the excessive skin layer accumulation found in Comparative Example C2 (see Figure 4B ). In addition, the AFM sample preparation did not produce failure modes associated with microstructure shrinkage or collapse, which was common for the less conformable two-layer adhesive samples prepared in Example C2. Thus, in this case, microstructure feature stability and fidelity were greatly improved, with the skin layer being substantially conformable through process control of the wet-on-wet coating method.

[0176] Dwell time

[0177] Example E3

[0178] Examples E3A to E3C describe two-layer adhesive constructions prepared using the wet-on-wet coating method described in Example E1 with varying residence times between the skin layer and body layer coating applicators. In these examples, the length of the web path between coating steps was fixed at approximately 1.5 meters (see Figure 1 The web speed was controlled to achieve different desired residence time values. The coating thickness and drying conditions were set to be the same for each case. Formulation A was deposited as a skin layer at a wet thickness of 21 microns onto microstructured fibrous web material A, and formulation B was subsequently applied as a bulk layer at a wet thickness of 100 microns. The fluid-coated web was conveyed to a four-zone convection drying oven with a temperature profile of 120 / 140 / 180 / 200°F, with a drying time of approximately 19 seconds in each oven zone.

[0179] Table 3 lists the web speed and corresponding residence time values ​​for Examples 3A to 3C. In addition, the table summarizes the corresponding AFM images for each Example with measured values ​​of the skin layer thickness near the raised surface of the microstructured features and adjacent corner regions.

[0180] Table 3 also introduces the epidermal conformability index R t , the skin conformity index is defined by the ratio of the dry thickness of the skin along the characteristic raised surface relative to the thickness of the skin in the adjacent corner region. If the skin is initially substantially flat in the wet two-layer coating (before drying), then it may be expected that the skin will be locally thinned at the characteristic raised surface relative to the adjacent corner region, such as Figure 2A As shown in Figure 2. In this scenario, less of the coating fluid volume resides above the microstructured raised surface relative to the adjacent areas, resulting in a thinner skin layer along the feature raised surface as the coating dries and solidifies. Assuming no flow redistribution during drying and that the fluid and solid densities are approximately equivalent, the mass balance for the skin layer coating can be used to roughly estimate the ratio R of the dry skin thickness along the feature raised surface relative to the dry skin thickness of the adjacent corner area. t In other words, assuming an initially flat wet coating curve, the calculated R t The value (expressed by Equation 1 below) represents the maximum skin layer conformability index that allows for a given skin layer wet thickness on a given microstructured web.

[0181]

[0182] In Equation 1, h is the microstructure feature height, and A is the fractional area coverage of the microstructure raised features on the web surface (corresponding to Figure 2B The ratio of 242 to 241 shown), and t w is the theoretical wet thickness of the coating when applied to a flat surface (corresponding to Fig. 12A Table 3 lists the calculated R t value (using Equation 1) and the measured R t value.

[0183] Table 3. Properties corresponding to Examples 3A to 3C

[0184]

[0185] exist Fig. 9 The skin thickness data are plotted in to illustrate the trend of skin depletion from feature protrusion surfaces and accumulation near corners with increasing residence time. Fig. 9 Also included is a curve labeled "Theoretical" which represents the expected dry thickness of the skin layer if it were coated on a flat surface. The following section contains a more detailed description of the two-layer adhesives prepared by wet-on-wet coating conditions in Examples E3A through E3C.

[0186] Example E3A

[0187] Example E3A is the same as Example E1. AFM analysis is used to analyze the entire feature area ( Fig. 6A ) and in the corner area ( Figure 6B ) and raised surfaces ( Figure 6C ) is shown in an enlarged view near the bottom of the figure. Fig. 6A The wide view in demonstrates that the conditions of Example E3A produce a continuous skin layer that substantially conformally covers the microstructural features on the surface of Web Material A.

[0188] In the image Figure 6B and Figure 6C The enlarged view shown in 2 reveals that the skin layer is locally thinned at the characteristic raised surface relative to the adjacent corner area, which would be expected if the skin layer was initially substantially flat in the wet two-layer coating (before drying), as shown in FIG. Figure 2A As described in the text above, Formula 1 describes the theoretical conformality index R t As the ratio of the skin layer dry thickness along the feature raised surface relative to the skin layer dry thickness in the adjacent corner region. Interpolated values ​​for this example (h = 13 microns, A = 0.2, and tw = 2.1 microns) predict R t The value is 0.44. Based on the measurement of coating thickness (from Figure 6B and Figure 6C ) t The value of 0.52 is reasonably close to the prediction considering the assumptions of the relatively simple theoretical model.The agreement between theory and measurement demonstrates that the process conditions used in Example E3A approximately achieve the maximum conformality index.

[0189] Example E3B

[0190] AFM analysis is used to analyze the entire feature area ( Fig. 7A ) and in the corner area ( Figure 7B ) and raised surfaces ( Figure 7C ) is used to characterize the double-layer adhesive. Fig. 7A The wide view in confirms that the conditions of this example produce a continuous skin layer that covers the microstructural features on the surface of Web Material A, but it does not have the same conformal properties of Example E3A. Enlarged Image ( Figure 7B and Figure 7C ) reveals that the skin layer becomes thinner at the characteristic convex surface and accumulates more skin layer material near the adjacent corner area. t The value is 0.34, which indicates that the skin layer is less conformable than in Example E3A. This result indicates that some flow redistribution of the skin layer occurs during the longer residence time between the first coating step and the second coating step in this example (6 seconds residence time) relative to Example E3A (3 seconds residence time).

[0191] Example E3C

[0192] AFM analysis is used to analyze the entire feature area ( Fig. 8A ) and in the corner area ( Figure 8B ) and raised surfaces ( Figure 8C ) is used to characterize the double-layer adhesive. Fig. 8A The wide view in shows that the conditions of this embodiment produce a discontinuous skin layer that does not completely cover the microstructural features on the surface of the web material A. The enlarged image ( Figure 8B and Figure 8C ) reveals that the epidermis does not extend to the characteristic raised surface, but accumulates in the adjacent corner area to a more significant extent than in Example E3B. In this case, R t The value of 0 reflects the discontinuous nature of the skin layer not being present (zero thickness) at the raised surfaces of the microstructured features. Thus, due to the longer dwell time between the first and second coating steps in this example (12 second dwell time) relative to Example E3B (6 second dwell time), the skin layer does not conformally follow the microstructured surface.

[0193] Diffusion interface

[0194] Example E4A

[0195] This embodiment describes a two-layer adhesive construction where the body layer and skin layer are applied during a single pass similar to Figure 1The adhesive coating formulation B was coated on the microstructured web surface by a wet-on-wet coating method on a coating system of a coating apparatus 100 of FIG. Adhesive coating formulation B was deposited as a 21 micron wet thickness skin layer onto microstructured web material B at 0.15 meters per second using a Meyer rod coating method applied to a free span web path. After the skin layer was coated, the adhesive was deposited at a distance of approximately 0.9 meters (see FIG. Figure 1 L) The web was conveyed to the bulk layer coating applicator, resulting in a residence time of about 6 seconds between coating steps. A slot die with a backup roller was used at the bulk layer coating applicator to apply adhesive formulation D on top of the skin layer at a wet thickness of 84 microns. The coated web was then conveyed to a four-zone convection drying oven with a temperature profile of 120 / 140 / 180 / 200°F, with a drying time of approximately 24 seconds in each oven zone, and then collected on web material B as a sample of the solidified two-layer adhesive (bulk layer and skin layer).

[0196] AFM analysis similar to Example E1 was used to characterize the samples of the double layer structure with submicron resolution, such as Fig. 10A shown. Fig. 10A The AFM images shown provide clear contrast between the bulk and skin layer domains, but do not appear to have the characteristics of a distinct interface between the adhesive layers observed in Example C1 (see Figure 4A ), nor does it have the smooth diffusion interface transition obtained from the conditions in Example E1 (see Figure 4B ). In contrast, this embodiment generates a complex adhesive topography at the diffuse interface, where polymer from the bulk layer appears as submicron domains encapsulated within the skin layer adhesive. The diffuse interface, which is 1 to 2 microns thick, follows the topography of the microstructured web. Near the corner regions, the skin layer thickens substantially, creating a clear transition from the bulk layer to the diffuse interface (encapsulated bulk layer polymer) to the skin layer primarily adjacent to the microstructured web.

[0197] Example E4B

[0198] This example describes a two-layer adhesive constructed on a microstructured web surface using the wet-on-wet coating method in Example E4A. In this case, web material B was used as a substrate for the deposition of a skin layer of Formulation B at a wet thickness of 56 microns. A subsequent bulk layer coating of Formulation D was deposited on top of the fluid skin layer at a wet thickness of 74 microns. The web speed, dwell time between coating applicators, and drying conditions were controlled to be equivalent to Example E4A.

[0199] AFM analysis is used to characterize samples with bilayer structures with submicron resolution, such as Fig. 10B As shown. Similar to Example 4A, Fig. 10BThe AFM images in 4A show a complex adhesive topography at the diffuse interface, where polymer from the bulk layer appears as submicron domains encapsulated within the skin layer adhesive. The diffuse interface, which is 1 to 2 microns thick, follows the topography of the microstructured web. The skin layer of this example is substantially thicker than that of Example 4A, resulting in a more pronounced transition from the diffuse interface (encapsulated bulk layer polymer) to the skin layer primarily near the base of the microstructured features.

[0200] References throughout this specification to "one embodiment", "certain embodiments", "one or more embodiments" or "an embodiment", whether or not the term "exemplary" is included before the term "embodiment", mean that the particular features, structures, materials or characteristics described in conjunction with the embodiment are included in at least one embodiment of certain exemplary embodiments of the present disclosure. Therefore, phrases such as "in one or more embodiments", "in certain embodiments", "in one embodiment" or "in an embodiment" appearing throughout this specification do not necessarily refer to the same embodiment in certain exemplary embodiments of the present disclosure. Furthermore, specific features, structures, materials or characteristics may be combined in any suitable manner in one or more embodiments.

[0201] Although this specification has described certain exemplary embodiments in detail, it should be understood that those skilled in the art can easily think of changes, modifications and equivalents of these embodiments after understanding the above. Therefore, it should be understood that the present disclosure should not be unduly limited to the exemplary embodiments shown above. In particular, as used herein, the numerical range expressed by the end value is intended to include all numerical values ​​contained in the range (for example, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4 and 5). In addition, all numbers used herein are considered to be modified by the term "about".

[0202] In addition, all publications and patents cited herein are incorporated herein by reference in their entirety, just as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. Various exemplary embodiments have been described. These and other embodiments are within the scope of the following claims.

Claims

1. A method, comprising: moving a substrate along a web path from a first coating applicator to a second coating applicator, the substrate comprising a structured surface including a pattern of structured features; applying a first coating fluid from the first coating applicator onto the structured surface of the substrate to form a first coating layer directly on the pattern of structured features, wherein the first coating fluid comprises a first polymer; applying a second coating fluid from the second coating applicator onto the first coating layer to form a second coating layer directly on the first coating layer, the second coating fluid being different from the first coating fluid, wherein the second coating fluid includes a second polymer; as well as solidifying the first coating layer and the second coating layer to form a double-layer coating including a skin layer and a bulk layer, wherein the bulk layer has a lower glass transition temperature than the skin layer; and wherein the residence time between applying the first coating fluid and applying the second coating fluid is controlled to achieve a diffusion interface having a thickness of 0.2 microns to 5.0 microns between the skin layer and the bulk layer, the diffusion interface comprising submicron domains of the second polymer encapsulated within the first polymer. 2 . The method of claim 1 , wherein the second coating fluid has a higher viscosity than the first coating fluid. 3 . The method according to claim 2 , wherein the first coating fluid has a viscosity in the range of 0.5 cP to 300 cP at a shear rate of 100 1 / s. 4 . The method according to claim 2 , wherein a viscosity ratio between the first coating fluid and the second coating fluid at a shear rate of 100 1 / s is in the range of 0.001 to 0.

5. 5 . The method of claim 1 , wherein a ratio of an average wet thickness of the first coating layer to an average wet thickness of the bulk layer is in a range of 0.01 to 1.

0. The method according to claim 1 , wherein the ratio of the average dry thickness of the skin layer to the average dry thickness of the bulk layer is in the range of 0.01 to 0.

3.

7. The method of claim 1, wherein the structural features have a feature height or depth of 2 microns to 100 microns.

8. The method of claim 1, wherein at least one of the first coating fluid and the second coating fluid comprises one or more particle-carrying fluids.

9. The method of any one of claims 1-8, wherein the body layer comprises an acrylate pressure sensitive adhesive having a glass transition temperature of at most -30°C, and the skin layer comprises an adhesive having a glass transition temperature of -20°C to 50°C.

10. A multi-layer coated article, comprising: A substrate comprising a first major surface and an opposing second major surface, the first major surface comprising a microstructured surface, the microstructured surface comprising a pattern of structured features, the pattern of structured features comprising one or more rising walls, the one or more rising walls each extending from a raised end to a lower end opposite the raised end, each rising wall connecting a raised surface at the raised end and a corner at the lower end; and a dual-layer coating disposed on the microstructured surface of the substrate, The double-layer coating comprises: a skin layer comprising a first polymer and disposed directly on the microstructured surface of the substrate, wherein the skin layer has a greater thickness on the corners than on the raised surfaces; a bulk layer comprising a second polymer and disposed directly on the skin layer, the bulk layer having a lower glass transition temperature than the skin layer; and A diffusion interface between the skin layer and the bulk layer has a thickness of 0.2 microns to 5.0 microns, the diffusion interface comprising submicron domains of a second polymer encapsulated within the first polymer.

11. The article of claim 10, wherein the skin layer is a continuous layer covering the microstructured surface.

12. The article of claim 10, wherein the skin layer is a discontinuous layer separated by the raised surfaces.

13. The article of claim 10, wherein the ratio of the average dry thickness of the skin layer to the average dry thickness of the body layer is in the range of 0.01 to 0.

3.

14. The article of claim 10, wherein the dual-layer coating comprises one or more particle-carrying layers.

15. The article of any one of claims 10-14, wherein the body layer comprises an acrylate pressure sensitive adhesive having a glass transition temperature of at most -30°C, and the skin layer comprises an adhesive having a glass transition temperature of -20°C to 50°C.

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