WO2018005421A1

WO2018005421A1 - Visual filter life indicator comprising volatilizable material

Info

Publication number: WO2018005421A1
Application number: PCT/US2017/039396
Authority: WO
Inventors: Glen O. Gregerson; Kannan Seshadri
Original assignee: 3M Innovative Properties Company
Priority date: 2016-06-30
Filing date: 2017-06-27
Publication date: 2018-01-04
Also published as: TW201807684A

Abstract

A visual filter life indicator including a receptacle with an open end, a porous diffuser layer occlusively overlying the open end of the receptacle, and a visual indicator gel comprising a colorant and a volatilizable material disposed within the receptacle. The invention also relates to a method of visually monitoring the usable life of an air filter of a powered air- handling system, wherein the method comprises positioning a visual filter life indicator in an airflow path and visually observing the indicator to ascertain whether a surface of an indicating area of a visual indicator gel has receded from an indicia-bearing area of a major wall or a porous diffuser layer so that an indicating indicia is readily visible.

Description

VISUAL FILTER LIFE INDICATOR COMPRISING VOLATILIZABLE MATERIAL

Background

Filter life indicators are sometimes used in order that the end of the useful life of an air filter can be ascertained or estimated.

Summary

Herein is disclosed a visual filter life indicator that comprises a receptacle with a major open end, with a porous diffuser layer occlusively overlying the major open end of the receptacle. A visual indicator gel that includes colorant and that includes volatilizable material is disposed within the receptacle. These and other aspects of the invention will be apparent from the detailed description below. In no event, however, should this broad summary be construed to limit the claimable subject matter, whether such subject matter is presented in claims in the application as initially filed or in claims that are amended or otherwise presented in prosecution.

Brief Description of the Drawings

Fig. 1 shows a rear/side perspective view of an exemplary visual filter life indicator mounted on an exemplary air filter.

Fig. 2 is a rear/side perspective view of an exemplary visual filter life indicator.

Fig. 3 is a front/side perspective exploded view of an exemplary visual filter life indicator (with visual indicator gel omitted for clarity).

Fig. 4 is a side schematic cross-sectional view of a receptacle of an exemplary visual filter life indicator.

Fig. 5 is a magnified side schematic cross-sectional view of a portion of a receptacle of an exemplary visual filter life indicator.

Fig. 6 is a rear/side perspective view of an exemplary visual filter life indicator, after a period of use.

Fig. 7 is a magnified side schematic cross-sectional view of a portion of a receptacle of another exemplary visual filter life indicator.

Like reference numbers in the various figures indicate like elements. Some elements may be present in identical or equivalent multiples; in such cases only one or more representative elements may be designated by a reference number but it will be understood that such reference numbers apply to all such identical elements. Unless otherwise indicated, all figures and drawings in this document are not to scale and are chosen for the purpose of illustrating different embodiments of the invention. In particular the dimensions and shading gradations of the various components are depicted in illustrative terms only, and no relationship between the dimensions or appearance of the various components should be inferred from the drawings, unless so indicated. Although terms such as "top", bottom", "under", "over",

"outward", "inward", "up" and "down", and "first" and "second" may be used in this disclosure, it should be understood that those terms are used in their relative sense only unless otherwise noted. As used herein as a modifier to a property or attribute, the term "generally", unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within +/- 20 % for quantifiable properties). The term "substantially", unless otherwise specifically defined, means to a high degree of approximation (e .g., within +/- 10% for quantifiable properties) but again without requiring absolute precision or a perfect match. Terms such as same, equal, uniform, constant, strictly, and the like, are understood to be within the usual tolerances or measuring error applicable to the particular circumstance rather than requiring absolute precision or a perfect match.

The term "front" is used to denote the major side of a visual filter life indicator that comprises a porous diffuser layer bonded thereto. The term "rear" is used to denote the opposing major side. These terms are used purely for convenience of description and do not denote or necessitate any particular orientation in which the indicator is to be positioned for use. The term "lateral" as applied to a visual filter life indicator means any direction generally in the major plane of the visual filter life indicator; such directions may often coincide at least generally with a major plane of a diffuser layer that is present in the visual filter life indicator. Terms such as "upper" and "lower" have their conventional meaning with regard to the Earth's gravity.

Detailed Description

Disclosed herein is a visual filter life indicator 100. Indicator 100 is shown in one exemplary mode of use (mounted to an air filter 1) in Fig. 1, and is shown in greater detail in Figs. 2 and 3. Indicator 100 comprises a base 110 (as seen e.g. in Figs. 2 and 3) with a front side 104 and a rear side 102 and upper end 106 and a lower end 108, and comprising at least one receptacle 112 with a major closed end 114 and a major open end 116. The term "at least one receptacle" as used herein specifically allows the presence of any number (e.g. one, two three, four, or more) of receptacles as desired.

Indicator 100 further comprises a porous diffuser layer 140 (most easily visible in the exploded view of Fig. 3) that comprises area 143 that occlusively overlies the major open end 116 of receptacle

112. Receptacle 112 of base 110 and corresponding area 143 of diffuser layer 140 that overlies receptacle 112 combine to define a receptacle volume. A visual indicator gel 250 is disposed within receptacle 112. As shown in Fig. 3, in some embodiments a removable cover sheet 230 may be provided on the front side of diffuser layer 140, which cover sheet may be removed when indicator 100 is to be used.

Base 110 of indicator 100 may be provided in any suitable manner. In some embodiments, base

110 may be a unitary (integral) piece of molded thermoplastic organic polymer resin. Conveniently, in such embodiments receptacle 112 may be provided by forming (e.g., injection molding, thermoforming or vacuum-forming, etc.) the thermoplastic polymer resin to provide at least one thermoformed depression 128 in base 110. In such an arrangement, a rear terminus of depression 128 can provide the major closed end 114 of receptacle 112 and a major open end of depression 128 can provide the major open end 116 of receptacle 112. In some embodiments, receptacle 112 may take the form of a relatively shallow cavity or basin as illustrated in exemplary embodiment in Fig. 3. Such a receptacle may be significantly wider and/or longer (along at least one lateral dimension) than it is deep. In various embodiments, a receptacle may have a minimum depth (measured from major wall 113 to porous diffuser layer 140) of at least about 1, 2, 3, 4 or 5 mm. In further embodiments, a receptacle may have a maximum depth of at most about 20, 15, 12, 10, 8, 6 or 4 mm. In many embodiments, receptacle 112 may be elongated with a first end 118 and a second, opposing end 119 that are spaced apart along an elongated axis of the receptacle. In some embodiments, receptacle 112 may be tapered along its elongate axis so as to exhibit a greater cross-sectional area proximate second end 119 of the receptacle, and a smaller cross-sectional area 118 proximate first end 118 of the receptacle. In specific embodiments, a lateral width of the receptacle may be at least generally constant with the difference in cross-sectional area of the receptacle being due to receptacle 112 having a lesser depth at first end 118 and a greater depth at second end 119 (as in the exemplary design of Figs. 2 and 3). It will be appreciated that providing a tapered shape of receptacle 112 can enhance the ease with which indicator 100 can be inserted into and/or removed from an area with restricted space (e.g. a slot of a filter-receiving fixture of an air-handling unit).

In some embodiments, receptacle 112 may be defined at least in part by a major rear wall 113 that provides closed end 114 of receptacle 112. (Various minor sidewalls may also be provided, that combine with major wall 113 and porous diffuser layer 140 to define the above-mentioned receptacle volume). In some embodiments, at least one area of major wall 113 is an indicia-bearing area 151 that comprises at least one indicia 150, as discussed later in detail. In various embodiments, major wall 113 of base 110 may be at least translucent to visible light; in further embodiments it may be transparent to visible light. In specific embodiments, major wall 113 may transmit at least about 10, 20, 40, 80, 90, or 95 % of light (at a wavelength of approximately 520 nm) therethrough.

In some embodiments, base 110 may be impermeable. By this is meant that base 110 is at least substantially impermeable to volatilizable material that is present within receptacle 112. (This property may be provided by the material of base 110, by a material that provides a layer of base 110, or by several layers of base 110 in combination.) By substantially impermeable is meant that the ratio of the rate at which volatilizable material can leave receptacle 112 by passing through the material of the base, to the rate at which the volatilizable material can leave the receptacle by passing through porous diffuser layer 140 (as described below), is less than 0.001 (at 21°C).

A porous diffuser layer 140 is positioned (e.g., is attached to the front side 104 of base 110) so that an area 143 of diffuser layer 140 occlusively overlies major open end 116 of receptacle 112. In this context, to occlusively overlie means that substantially the only way that volatilizable material can exit receptacle 112 is by passing as a vapor through (the air-filled passages of) overlying area 143 of diffuser layer 140. In some embodiments, this may be achieved by bonding (by any suitable means, e.g. via adhesive bonding, heat-sealing, ultrasonic welding, etc.) diffuser layer 140 (e.g., rear surface 141 thereof) to one or more bonding areas 117 that partially or completely laterally surround receptacle 112. It may not be necessary that porous diffuser layer 140 is bonded to base 110 so as to provide a hermetic seal, although this can be done if desired. Rather, all that is needed is that any leakage pathway left by a non- hermetic seal should be sufficiently small that any loss of volatilizable material from receptacle 112 should be minimal during any initial storage period prior to use of indicator 100 (e.g., prior to a removable cover sheet 230 being removed).

Diffuser layer 140 is porous, defined herein as meaning that the layer comprises air-filled passageways (e.g., microperforations, interstitial spaces between fibers, interconnected air-filled cells of an open-celled foam, and the like) that extend completely through the diffuser layer from one major surface to another. (It is not necessary, however, that the passageways extend through the layer in a straight line, or along the shortest distance between the major surfaces.) Such air-filled passageways allow the passage of volatilized molecules therethrough in vapor form. Porous diffuser layer 140 will be distinguished from a layer that does not comprise porosity (i.e., a layer in which a small molecule, in order to pass through the layer, must solubilize in the solid material of the layer and then move therethrough by molecular diffusion through the solid material, rather than passing through air-filled passageways). In at least some embodiments, diffuser layer 140 may be at least substantially impermeable to liquids along any dimension thereof. A porous diffuser layer 140 of this type will be distinguished from e.g. wicking layers and the like that are often used e.g. to facilitate the movement of a liquid through the wicking layer to a location in which the liquid can be evaporated and/or to spread the liquid over a wider area so that is can be more rapidly evaporated.

Porous diffuser layer 140 may be conveniently provided as a sheet as shown in exemplary embodiment in Fig. 3. Such a sheet may be a film (e.g., a microperf rated film, with a microperforation being a through-hole having an average diameter of 400 microns or less), a knitted or woven material, etc. In particular embodiments, diffuser layer 140 is a nonwoven web. Such a sheet may thus comprise a number of specific through-holes that pass directly through the thickness of the sheet (e.g. in the case of a microperfbrated film); or, a sheet (e.g. a nonwoven web) may comprise tortuous paths (e.g., defined collectively by numerous fibers) through the thickness dimension thereof. Either arrangement (or any combination thereof) may be used as long as the ability to permit passage of vapors therethrough (and the ability to deny flow of liquids therethrough, if desired) is achieved. It will be appreciated that the size (e.g., diameter or effective diameter for circular or non-circular microperforations) or effective size of air- filled passages, as well as the chemical composition of the material of diffuser layer 140, may be chosen to achieve the desired combination of properties.

The microperforation size (and/or the effective size of a tortuous path) and/or density of microperfbrations/paths per unit area of diffuser layer 140 may be tailored to provide a desirable release rate of volatilizable material. Exemplary perforation sizes of microperfbrated films may be e.g. from about 10 to about 100 microns in diameter (or equivalent diameter in the case of non-circular or irregular microperforations). A nonwoven or woven diffuser layer 140 may be optimized e.g. by controlling fiber diameter, basis weight and solidity and/or thickness, to achieve the desired properties. Such nonwovens may be produced by different methods, such as spunbonding, meltblowing, wetlaying (papermaking methods), air-laying, composite methods such as spunbond-meltblown-spunbond (SMS), etc. Film materials and/or fibers of a woven or nonwoven fibrous layer may be chosen from any suitable material, e.g. polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polyester, polyurethane, and so on. Potentially suitable materials may be chosen from e.g. the materials available from Midwest Filtration (Cincinnati, OH) under the trade designation UNITHERM.

Surface treatments and the like may be used if desired to modify e.g. the surface energy of the microperforations, or of fibers that define a tortuous path. In particular embodiments, a diffuser layer 140 may be hydrophobic, e.g. by virtue of the composition of the material(s) that makes up the diffuser layer, by virtue of surface treatment, coating or the like that is provided on at least some surfaces of the diffuser layer, or by some combination of these. In some embodiments, a diffuser layer 140 may be oleophobic (again either through the composition of the material that makes up the diffuser layer, by a surface treatment or coating, or the like).

The ability of a porous diffuser layer 140 to allow passage of gases and vapors through the interstitial spaces thereof in order to completely pass through the thickness of the layer, may be characterized by any suitable parameter or test method. One convenient screening measurement that may correlate with the ability of a material to serve as a porous diffuser layer 140 is an air permeability test (a "Frazier" test) as performed using equipment of the general type supplied by the Frazier Precision Instrument Company (Hagerstown, MD). Such testing may be performed in general accordance with the methods outlined in ASTM Test Method D737-04 (2012), using 0.5 inches of water pressure drop, a 2.75 inch diameter opening and an 11 mm or 16 mm orifice. In various embodiments, porous diffuser layer 140 may exhibit an air permeability of at least about 100, 200 or 300 cubic feet per minute per square foot. In further embodiments, porous diffuser layer 140 may exhibit an air permeability of at most about 800, 600, 500, or 400 cubic feet per minute per square foot.

Potentially suitable candidate diffuser layers may be tested for their actual release of volatilizable material, e.g. using a representative visual indicator gel comprising volatilizable material, that is loaded into a receptacle of a visual filter life indicator comprising a base to which is attached a porous diffuser layer as disclosed herein. The indicator can be held in a controlled environment, exposed to a desired airflow and temperature (e.g. at 21°C, or at a higher temperature (e.g. 55°C) for accelerated testing), and the amount and rate of weight loss of volatilizable material can be monitored.

In some embodiments, at least one area of porous diffuser layer 140 (specifically, of area 143 of diffuser layer 140 that occlusively overlies open end 116 of receptacle 112) is an indicia-bearing area 144 that comprises at least one indicia 145, as discussed later in detail. In various embodiments, at least area 143 of diffuser layer 140 is at least translucent to visible light. That is, although diffuser layer 140 may scatter some light by virtue of its fibrous nature (e.g. in embodiments in which layer 140 is a nonwoven web), in various embodiments it may transmit at least about 10, 20, 40, 80, 90, or 95 % of light (at a wavelength of approximately 520 nm) therethrough. In further embodiments diffuser layer 140 may be transparent to visible light.

In some embodiments, a visual filter life indicator 100 as supplied to a user may comprise a removable cover sheet 230 that overlies porous diffuser layer 140 at least in area 143 where diffuser layer 140 overlies open end 116 of receptacle 112. In at least some embodiments cover sheet 230 may be impermeable in order to minimize or prevent any emission of volatilizable material from receptacle 112 until indicator 100 is ready to be used, at which time cover sheet 230 may be removed and disposed or recycled. By impermeable is meant that removable cover sheet 230 comprises at least one layer of material that provides (or, comprises layers that collectively provide) that sheet 230 is at least substantially impermeable to volatilizable material. By this is meant that the ratio of the rate at which volatilizable material can leave a receptacle by passing through cover sheet 230 (when cover sheet 230 is in place so as to occlusively overlie the receptacle), to the rate at which the volatilizable material can leave the receptacle by passing through diffuser layer 140 in the absence of cover sheet 230, is less than 0.001 (at 21°C). Any suitable material that is sufficiently impermeable (e.g. polyester film) may be used.

Cover sheet 230 may be removably bonded to diffuser layer 140 in any suitable way that allows at least a portion of cover sheet 230, or the entirety of cover sheet 230, to be removed (e.g., to be peeled away from diffuser layer 140) to expose at least area 143 of porous diffuser layer 140. In some exemplary embodiments, rear surface 231 of cover sheet 230 may comprise a pressure-sensitive adhesive (e.g., a removable or repositionable PSA) disposed thereon, that allows rear surface 231 of cover sheet 230 to be removably bonded to front surface 142 of diffuser layer 140. In some embodiments, (e.g. in the event that indicator 100 is supplied sealed within an impermeable container, such as a package fabricated from e.g. metallized polyester films) cover sheet 230 may not necessarily serve to seal receptacle 112 to prevent emission of volatilizable material. In such embodiments cover sheet 230 may e.g. serve primarily to protect porous diffuser layer 140 from physical damage, and/or may serve a decorative function. In such cases, cover sheet 230 may be made of any suitable material.

Visual indicator gel 250 is disposed within receptacle 112. By "gel" is meant a material that is at least semi-solid so that it will not exhibit viscous flow under the influence of gravity at 21°C. In some embodiments gel 250 may take the form of a solid slab, wafer, cake or puck. In particular embodiments, gel 250 may take the form of a wedge-shaped slab. In various embodiments, gel 250 may exhibit a viscosity at 2PC of at least about 250, 1000, 2000, 10000, or 50000 Poise. In additional embodiments, gel 250 may be formulated so as to remain at least semi-solid even during incidental exposure to elevated temperature as may be encountered during e.g. transportation in containerized shipping or storage an unairconditioned warehouse. In specific embodiments, gel 250 may exhibit a viscosity at 60°C of at least about 250, 1000, 2000, 10000, or 50000 Poise.

Visual indicator gel 250 comprises colorant. As used herein, the term colorant refers to any material or mixture (e.g. solution, blend, and so on) of materials that imparts a (non-white) color that is visually discernable to a human observer. (This and all references to a human observer refer to an adult human that has approximately 20:20 vision and has normal color vision (i.e., is not colorblind), observing an item in question from a distance of one meter in white light at a light level of 300 lux.) Colorant may be any suitable color, e.g. black, blue, purple, green, magenta, red, and so on. Material of visual indicator gel that does not exhibit sufficient color to be classified as a colorant will be termed diluent, as discussed in detail later herein.

Visual indicator gel 250 comprises volatilizable material. By volatilizable material is meant material that exhibits a boiling point of less than about 250 °C. In various embodiments volatilizable material exhibits a boiling point of less than about 200 or 150 °C. In further embodiments volatilizable material exhibits a boiling point of at least about 40, 60, 80, or 100 °C. In various embodiments volatilizable material exhibits a vapor pressure (at 21°C) of at least about 0.2, 0.5, 1.0, 2.0, 5, 10, 20, or 50 Pa. In further embodiments volatilizable material exhibits a vapor pressure (at 21 °C) of no more than about 100, 60, 40, 30, 15, or 5 Pa.

It is emphasized that terms such as "volatilize" and "volatilizable" broadly denote material that, when emitted from a receptacle of the visual filter life indicator, moves through porous diffuser layer 140 as molecules in vapor form, rather than in liquid or solid form (e.g. in the form of aerosol droplets, sprayed liquid or solid particles, and so on). The particular process by which volatilizable material is liberated from visual indicating gel 250 is not limited and may include e.g. evaporation, sublimation, or a mixture of the two. Still further, although the term "diffuser" layer has been used for convenience of description, this does not imply that the passage of volatilized molecules out of gel 250 and away from indicator 100 must occur strictly by molecular diffusion (e.g., Fickian diffusion). While such a mechanism may operate at least in part e.g. during passage of volatilized molecules through interstitial air spaces of a porous layer, such a mechanism is not required to be the only mechanism by which such material is emitted from indicator 100. In fact, in some embodiments molecular diffusion may not be the primary mechanism, e.g. it may be dominated by some other mechanism. For example, the rate of emission of volatilizable material from gel 250 may be significantly increased in the event that indicator 100 is exposed to airflow, in comparison to the emission rate when indicator 100 is positioned in quiescent air, as noted earlier.

In various embodiments, gel 250 comprises at least about 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, or 95 percent by weight of volatilizable material. In further embodiments, gel 250 comprises at most about 85, 75, 65, 55, 45, 35, 25, 20, 15, or 10 percent by weight of volatilizable material. Volatilizable material as disclosed herein does not encompass substances that may be present as trace components of other materials, and in particular does not encompass adventitious water as may be present in many materials.

In some embodiments, gel 250 comprises nonvolatilizable colorant compounded with volatilizable diluent. In some embodiments, gel 250 comprises volatilizable colorant compounded with nonvolatilizable diluent. In some embodiments, gel 250 comprises volatilizable colorant compounded with volatilizable diluent. Thus, in some embodiments colorant can itself be volatilizable material (and, in specific embodiments, may be the only volatilizable material present in gel 250). The term volatilizable colorant encompasses a single colorant material that is volatilizable, and also encompasses a mixture of colorant materials of which only a subset (e.g., one) may be volatilizable. The term volatilizable diluent encompasses a single diluent material that is volatilizable, and also encompasses a mixture of diluent materials of which only a subset (e.g., one) may be volatilizable. In some embodiments (e.g. when a nonvolatilizable diluent is used), the colorant of gel 250 may consist essentially of volatilizable material. In other embodiments (e .g. when a volatilizable diluent is used), the colorant of gel 250 may consist essentially of nonvolatilizable material. Similarly, in some embodiments (e.g. when nonvolatilizable colorant is used), the diluent of gel 250 may consist essentially of volatilizable material; in other embodiments (e.g. when volatilizable colorant is used), the diluent of gel 250 may consist essentially of nonvolatilizable material. When both volatilizable material and nonvolatilizable material are present in visual indicator gel 250, in some embodiments the ratio of the rate at which nonvolatilizable material exits a receptacle through porous diffuser layer 140 to the rate at which volatilizable material exits the receptacle through porous diffuser layer 140, is less than 0.001 at 21°C.

As noted above, the term colorant refers to any material or mixture of materials that imparts a non-white color that is visually discernable to a human observer. In some embodiments visual indicator gel 250 may comprise colorant that is volatilizable, for example, guaiazulene and like compounds. In some embodiments visual indicator gel 250 may comprise colorant that is nonvolatilizable. In such embodiments any suitable nonvolatilizable colorant (e.g. dye) may be used, chosen from a wide variety of available materials, e.g. azo dyes, aniline dyes, anthraquinone dyes, and so on. In some embodiments, nonvolatilizable colorant may be chosen from food-grade (e.g. FD&C) dyes. In some embodiments, nonvolatilizable colorant may comprise naturally-sourced (e.g. plant-derived) materials, such as e.g. cochineal, annatto, betanin, chlorophyllin, and so on. In some embodiments a nonvolatilizable colorant may exhibit a characteristic color that is accentuated or strengthened in the presence of a particular volatilizable diluent, so that as the volatilizable diluent is depleted from gel 250, the decreased concentration of the diluent in proximity to the colorant may cause the color to fade.

As noted above, the term diluent refers to any component of visual indicator gel 250 that is not a colorant. Diluent may provide a matrix for compounding of colorant thereinto. In some embodiments, colorant and diluent may be compounded with each other to form a solution (i.e., so that substantially no parcels of non-dissolved colorant are present). Diluent may be volatilizable or nonvolatilizable, as desired.

A nonvolatilizable diluent may include any suitable material or materials. In various embodiments, such a material may comprise one or more organic polymeric materials (e.g.,

compoundable polymeric resins), nonvolatilizable oils, greases and waxes, and so on. Such diluent may be chosen to provide that visual indicator gel 250 is in the form of an at least semi-solid material as noted above, in the typical temperature ranges at which indicator 100 is used (21°C can be used as a representative temperature for such purposes.) Exemplary organic polymers that may find use as nonvolatilizable diluent include e.g. olefinic copolymers, e.g. copolymers of polyethylene with ethylene methyl acrylate (for example the resins available from Exxon Mobil under the trade designations OPTEMA 120 and 220), ethylene vinyl acetate (EVA), or other copolymers containing other functional groups such as acids, esters, amides, acrylates, and the like. In addition, the organic polymer system could be comprised of styrene-isoprene-styrene segments or styrene -butadiene-styrene segments such as those seen in Kraton thermoplastic elastomer systems. Visual indicator gel 250 may comprise (either instead of, or in addition to, any nonvolatilizable organic polymer that may be present) any suitable inorganic material such as e.g. clay, fumed silica, diatomaceous earth, silica aerogels, and so on.

In some embodiments, diluent may be volatilizable; in such cases diluent may be able to exit receptacle 112 by passing through porous diffuser layer 140 in vapor form. In some embodiments, diluent may include one or more nonvolatilizable components and one or more volatilizable components. Any suitable volatilizable material may be included in volatilizable diluent of gel 250. In some embodiments, volatilizable diluent may be chosen from naturally-sourced (e.g. plant-derived rather than derived from e.g. petroleum or coal tar). In some embodiments, volatilizable diluent may be chosen from suitable terpenes and terpene derivatives. In some embodiments, volatilizable diluent may be chosen from so- called green-leaf volatilizable materials, terpenoids and the like. In some embodiments, volatilizable diluent may be chosen from commonly used oils such as cooking oils, vegetable oils, so-called carrier oils as used e.g. in aromatherapy, and the like. Potentially useful materials may be chosen from e.g. soybean oil, canola oil, castor oil, olive oil, peanut oil, almond oil, coconut oil, sesame oil, and extracts therefrom. (It will be appreciated that many such materials are characterized by a smoke point rather than a boiling point; for such materials a smoke point may be used as a proxy for a boiling point in regards to characterizing the volatilizability of the material).

Diluent of visual indicator gel 250 may comprise any ingredient as desired e.g. to desirably change the viscosity, rigidity or any other characteristic of gel 250. (Such ingredients may be nonvolatilizable or volatilizable.) Viscosity modifiers include plasticizers such as isopropyl myristate, heavy naphthenic oils, or other polymeric systems that may be branched, linear, dendritic, and so on. Tackifiers include Wingtack Plus and the like. If desired, one or more gelling agents may be used, e.g. wax esters such as those available from Croda, Edison, NJ under the trade designation SYNCROWAX, and acrylate containing polymers, such as those available from Air Products, Allentown, PA under the trade designation INTELLIMER. Some such components may be used to provide that visual indicator gel 250 is an oil-based gel. In some embodiments, visual indicator gel 250 may be an aqueous gel, which term generally encompasses gels that contain water e.g. along with other water-compatible diluents, and which may further include e.g. additives such as gelling agents or viscosifiers (e.g. polysaccharides, starches, alginates, carrageenan, and the like). Any such additives or components may serve e.g. to modify a property (e.g. viscosity) of visual indicator gel 250 at elevated temperature, e.g. in the case that the gel material is loaded into receptacle 112 in flowable form and is then allowed to cool to the range of 21°C to solidify to provide an at least semi-solid gel as defined herein.

In some embodiments, a volatilizable material of visual indicator gel 250 may comprise fragrance. In such embodiments, indicator 100 may thus serve two purposes; first, as a filter life indicator, and second, to impart a pleasing fragrance to an airspace (e.g. to a room of a building). Such fragrances are discussed in detail in PCT International Publication No WO2016011038 and in corresponding U.S. Provisional Patent Application No. 62/026112 entitled FRAGRANCE DISPENSER FOR AIR FILTER, both of which are incorporated by reference in their entirety herein. In some embodiments a volatilizable material of gel 205 may comprise materials that have both fragrant and colorant properties; i.e., many fragrant compounds may contain moities that render them colored. In such embodiments, the intrinsic color of fragrant compounds may be enhanced by the addition of complementary colorant materials (whether volatilizable or non-volatilizable). Such arrangements might enhance the baseline color intensity of the gel and/or provide increased contrast when in the indicative state.

Colorant (which again, may be a single colored material or a mixture of colored materials) can be mixed with diluent (which similarly may be a single material or a mixture of materials) in any desired ratio. In various embodiments, colorant may comprise at least about 0.2, 0.5, 1.0, 2.0, 5.0, 10.0, or 20.0 wt. % of visual indicator gel 250. In further embodiments, colorant may comprise at most about 80, 60, 40, 20, 10, or 5 wt. % of visual indicator gel 250. Colorant may be combined with diluent by batch mixing (e.g. in a planetary mixer), by compounding e.g. in an extruder or Brabender plastograph or a roller mill, or in general by any process that sufficiently homogenizes (e.g. co-dissolves) the colorant with the diluent to form gel 250 (or, to form a precursor that becomes gel 250 e.g. when cooled). The compounded mixture may be loaded into a receptacle. As noted, the compounded mixture may be heated to a temperature suitable to facilitate loading of the mixture into a receptacle and then cooled to achieve the final properties of the gel.

Visual indicator gel 250 will be present (e.g. as a tapered slab) within receptacle 112. In various embodiments, visual indicator gel 250 may occupy at least about 70, 80, 90, 95, or 98 volume percent of the receptacle volume. Gel 250 includes at least one, and often several, indicating areas each comprising a surface that (when indicator 100 is supplied to a user) abuts an indicia-bearing area of receptacle 112. Such an indicia-bearing area of receptacle 112 (that is abutted by an indicating area of gel 250) may be an area 151 of major wall 113; or it may be an area 144 of porous diffuser layer 140. In some embodiments, both major wall 113 and porous diffuser layer 140 may each comprise at least one indicia-bearing area.

Visual indicator gel 250 is disposed within receptacle 112 so that an indicating area of the gel abuts an indicia-bearing area of receptacle 112, e.g. in such manner that the surface of the indicating area of the gel is in intimate contact with an interior surface of an indicia-bearing area of a substrate of receptacle 112 of indicator 100. (In this context, a substrate of receptacle 112 may be e.g. a major wall 113 of base 110 or a porous diffuser layer 140.) This may be achieved, for example, by loading a precursor of gel 250 into receptacle 112 in flowable form so that the gel precursor wets out against the interior surface of the substrate at least in the indicia-bearing area of the substrate, and then allowing the precursor to harden (e.g. by cooling) so that it solidifies to form gel 250.

In some embodiments, an interior surface of a substrate (e.g. wall 113 or porous diffuser layer 140) of receptacle 112 of indicator 100 may be surface modified by any suitable means, to allow for better wetting and/or adhesion of gel 250 (or a precursor thereof). Possible methods include e.g. forming base 1 10 of a multilayer material (e.g. by multilayer extrusion) with a material of desirable wettability forming an interior surface of wall 113; by corona treatment; by application of a primer coating or layer; and so on. Moreover, in some embodiments gel 250 may include one or more materials (e.g. surfactants, wetting agents, etc.) that enhance the ability of gel 250 or a precursor thereof to wet against a desired interior surface of a substrate of indicator 100.

An indicating indicia of a substrate of receptacle 112 of indicator 100 will exhibit a color, and visual indicating gel 250 will comprise colorant, so that the indicating area(s) of visual indicating gel 250 will at least generally visually match the color of the indicating indicia when the surface of the indicating area of the gel is abutted against an interior surface of the indicia-bearing area of the substrate of indicator 100. By generally visually match is meant that the indicating indicia will not be clearly visible against the matching background color of the gel to a human observer at a range of 1 meter under conditions as specified earlier herein.

By way of specific example, referring to Fig. 4, an indicating indicia 150 of major wall 113 of indicator 100 will not be clearly visible when surface 251 of indicating area 253 of gel 250 is abutted against the interior (front) surface 1 15 of indicia-bearing area 151 of wall 113. That is, indicia will effectively disappear against the matching background provided by the gel.

Sufficient exposure of indicator 100 to airflow (e.g. after removing any cover sheet 230 therefrom) will cause volatilizable material (whether colorant, diluent, or both) to exit receptacle 112 through porous diffuser layer 140. With reference to Fig. 5, this can cause an air gap 252 to develop e.g. between a rear surface of the indicating area of the gel, and a front surface 1 15 of the indicia-bearing area 151 of the major wall 113 of indicator 100. At least some of the surface of the indicating area of the gel no longer being in intimate contact with the area of the wall that comprises the indicating indicia, the indicating indicia will become clearly visible. Depending e.g. on the percentage of visual indicating gel 250 that is in the form of volatilizable material, the depletion of volatilizable material may be such that the air gap may continue to grow with continued exposure to airflow. It is noted that the terminology of an air gap encompasses cases in which sufficient material of the visual indicator gel is removed such that an air gap extends generally, substantially, or essentially across the entire depth of the receptacle at a given location. It is also noted that Fig. 5 is an idealized representation; and, depending e.g. on how an indicator 100 is configured, depletion of volatilizable material may cause an air gap proximate major wall 113, an air gap proximate porous diffuser layer 140 (as discussed later in detail), or may cause air gaps in both locations. It will be appreciated that in embodiments in which the volatilizable material of visual indicator gel 250 includes only diluent, the indicia may become clearly visible primarily due to the development of an air gap between the indicia and the surface of the visual indicator gel. In embodiments in which the volatilizable material of visual indicator gel 250 includes colorant, the indicia may become clearly visible due to either or both of the development of an air gap and the visual indicator gel becoming less colored due to depletion of volatilizable colorant therefrom.

With reference to the exemplary design of Fig. 6, in some embodiments multiple indicating indicia 150, 150', and 150" may be provided (with only indicia 150 being visible in Fig. 6). One indicia (e .g., 150) may be located e.g. in a shallowest area of receptacle 112 so that this is the first indicating indicia that becomes visible upon depletion of volatilizable material. Other indicia may be located in areas of receptacle 112 that are configured so that these indicia only become visible after removal of increased amounts of volatilizable material from receptacle 112 (that is, after a longer exposure to an airflow). For example, in the exemplary design of Fig. 6, the first-revealed indicia 150 may read "80 %" (indicating e.g. that an air filter has 80 % of its usable lifetime left), with successive indicia 150', 150", and 150"' respectively reading 60 %, 40%, and 20 %. (A final indicia may read e.g. "Change Filter".)

It is noted that in some embodiments an indicia may be faintly visible to an observer even before any depletion of volatilizable material. Thus, the arrangements herein do not require that an indicia must be completely invisible prior before depletion of volatilizable material; all that is required is that the change in visibility of indicia with depletion of volatilizable material is sufficient that it will be apparent to an observer that a particular indicia has become clearly visible in contrast to its previous condition.

As noted previously, in some embodiments more than one receptacle 112 may be present. In some embodiments all such receptacles may be identical (e.g. in size and shape and in the amount of visual indicator gel disposed therein). In other embodiments such receptacles may be configured differently. For example, a first receptacle could be configured so that its indicia becomes visible at 80 % remaining lifetime, a second receptacle could be configured to reveal its indicia at 60 % remaining lifetime, and so on.

It will be appreciated that any or all of e.g. the taper of receptacle(s) 112, the amount of volatilizable material in gel 250, the volatility of that material, and the permeability of porous diffuser layer 140, may be manipulated alone or in combination, to tailor the response of visual filter life indicator 100 to coincide with the lifetime of an air filter with which the indicator is to be used. Such parameters may also take into consideration other factors such as e.g. the location in which the indicator is to be placed, the flowrate of the airstream in that location, the temperature of the airstream in that location, and so on. Although in the exemplary design shown in the Figures herein indicator 100 is configured so that a shallow end of the receptacle is proximate a lower end of the indicator, this does not have to be the case (as discussed below in regard to the exemplary design of Fig. 7). Nor does the indicator have to be configured and positioned so that a long axis of the receptacle is exactly vertical. In at least some embodiments, indicator 100 may be configured so that the rate of emission of volatilizable material from receptacle 112 is substantially greater when indicator 100 is exposed to airflow, than when indicator 100 is in quiescent air. Thus in such embodiments, the depletion of volatilizable material experienced by visual filter life indicator 100 may correspond to the time that indicator 100 is exposed to moving air (rather than corresponding to e.g. the total time that the indicator is exposed to air, whether moving or not). Thus, the reporting provided by visual filter life indicator 100 may correspond to the actual time in use of an air filter (i.e ., to the amount of time that the air filter was actually filtering moving air).

Although the discussions above have mainly concerned indicating indicia that are provided on major wall 1 13 of base 1 10 of indicator 100, in some embodiments one or more indicating indicia may be provided on porous diffuser layer 140 of indicator 100. It will be appreciated that even if layer 140 is e.g. a nonwoven which may be somewhat translucent due to its fibrous nature, layer 140 can be configured to be sufficiently light transmissive so that the above -discussed mode of operation (of color-matching when a surface of the indicator gel is abutted against a surface of layer 140, with, upon the development of an air gap, the color-matching disappearing to sufficient extent that the indicating indicia becomes visible) can take place. Thus as shown in idealized representation in Fig. 7, in some embodiments an indicating indicia 145 may be provided in an indicia-bearing area 144 of porous diffuser layer 140, such that development of an air gap 252 between front surface 254 of an indicating area 255 of visual indicator gel 250, and rear surface 141 of indicia-bearing area 144 of porous diffuser layer 140, can cause indicating indicia 145 to become visible. (It will be appreciated that in Fig. 7, a shallow end of receptacle 112 is positioned proximate an upper end 106 of indicator 100 rather than proximate a lower end 108 as in Figs. 1-6.) An indicating indicia 145 on porous diffuser layer 140 can be in addition to, or in place of, an indicating indicia 150 on major wall 113 of base 110.

Such options are in keeping with the aforementioned fact that in various embodiments an air gap may develop (upon depletion of volatilizable material from receptacle 1 12) proximate major wall 1 13, proximate porous diffuser layer 140, or both. It will be apparent that depending e.g. on the percentage of visual indicating gel that is comprised of volatilizable material and/or depending on the properties of the nonvolatilizable material that remains, the physical form taken by any visual indicating gel 250 that remains within receptacle 112 after depletion of at least some volatilizable material therefrom may vary widely. For example, in some embodiments a discrete air gap may form that is e.g. well defined and is located proximate e.g. major wall 113 or porous diffuser layer 140, as in the idealized representations of Figs. 5 and 7. In some embodiments the remaining visual indicating gel may take on a "Swiss cheese" appearance. Thus in various embodiments an air gap may be the result of visual indicator gel (e.g. slab) shrinking and receding bodily away from e.g. major wall 113; or, it may arise from local depletion of volatilizable material such that numerous small voids are formed near major wall 113, which voids gradually grow and/or coalesce to form an air gap sufficient to allow an indicia to become visible. (It will be appreciated that an air gap does not require that absolutely no visual indicator gel material can remain in contact with the indicia-bearing area of e.g. major wall 113.) Any such results are acceptable as long as there is sufficient separation of a large enough amount of an indicating area of the visual indicating gel, from an indicia of a substrate that defines receptacle 112, to allow the indicia to become visible so that indicator 100 can function as described herein. It will be appreciated that the fact that gel 2 0 is not a flowable liquid can advantageously provide that adjacent portions of gel 250 will not flow so as to fill a void or voids (e.g. an air gap) that develops due to emission of volatilizable material.

Indicating indicia may be provided e.g. by printing any suitable ink, dye or pigment, on any substrate (e.g. major wall 113 and/or porous diffuser layer 140) of indicator 100 as desired. Such an ink, dye or pigment may, but does not have to be, the same as an ink, dye or pigment that is included in visual indicating gel 250. All that is needed is sufficient color matching as discussed herein. In some embodiments, an indicating indicia may be provided in reversed type (e.g. a field of blue or black comprising therewithin an uncolored area in the shape of e.g. "60 %"). And, an indicating indicia does not necessarily have to include numerals and/or words. Rather, an indicia could simply be a symbol of any desired shape.

Indicator 100 may be used e.g. by removing the indicator from any packaging and then removing a cover sheet 230 from porous diffuser layer 140 if present. Indicator 100 may then be exposed to a stream of moving air that is motivated by a fan or blower and which stream of moving air is at least associated with an air filter whose usable lifetime it is desired to monitor. In some embodiments, indicator 100 may be placed in close proximity to (e.g. may be mounted to) an air filter as shown in the exemplary embodiment of Fig. 1. However, this may not be necessary. Rather, in some embodiments, indicator 100 need not be located physically near the air filter to be monitored, as long as the airflow experienced by indicator 100 is correlated with the airflow through the air filter (such that the reporting of the indicator is commensurate with the useable time of service of the air filter). For example, in some embodiments indicator 100 may be positioned proximate an air-emitting vent of a vehicle climate-control system or a building FFVAC system. (For example, an indicator could be attached to a register, grille or louver of such a vent.) Or, an indicator may be positioned proximate an intake (air-return) unit of a building HVAC system.

As noted, in some embodiments an indicator 100 may be positioned in proximity to (e.g., mounted on) an air filter e .g. of an HVAC unit. In particular embodiments, an indicator may be mounted upstream of such an air filter, e.g. with the "front" face of the indicator facing toward the upstream face 2 of the air filter. An indicator 100 may be mounted on an air filter by way of any suitable mechanism. Many such mechanisms may conveniently make use of a perimeter frame 3 of the air filter (such as made from cardboard, chipboard or the like) for such mounting. In some embodiments base 110 of indicator 100 may thus comprise a main body 111 that comprises the (at least one) receptacle 112; and, an extended portion 130 (as shown in exemplary embodiment in Fig. 2) that extends away from the main body.

Extended portion 130 may comprise any suitable mounting mechanism configured to mount (attach) to a perimeter frame of an air filter so as to position indicator 100 in the airstream immediately upstream of the air filter.

In some embodiments, an extended portion 130 may comprise pressure-sensitive adhesive to facilitate attachment of indicator 100 to any desired object or surface. Instead of or as an adjunct to an adhesive, extended portion 130 may comprise any mechanical mounting/attachment mechanism. For example, a small hole may be provided in extended portion 130 of base 110 of indicator 100, into which any suitable hook or post can be inserted. It will be understood that this is merely an example and that many mounting attachment systems may be used.

In some embodiments, an extended portion 130 of base 110 may generally comprise an L-shape with a first portion that extends from the main body of base 110 in a direction at least generally along a major plane of the main body of the base, and a second portion that extends from a terminus of the first portion and that is oriented at least generally orthogonally to the first portion.

In some embodiments, an extended portion 130 may comprise first and second portions as described above, and may further comprise a third portion that extends from a terminus of the second portion and that comprises a major plane that is oriented at least generally parallel to a major plane of the first portion. Such an extended portion 130 may thus generally comprise a U-shaped hook that allows indicator 100 to be hung from any desired object. (Similar arrangements may be achieved e.g. with a hook provided by a smoothly arcuate extended portion 130 rather than a U-shaped extended portion 130.) Although extended portion 130 and L-shaped and U-shaped variations are depicted e.g. in Fig. 1 with particular regard to mounting indicator 100 to e.g. a frame of a framed air filter, it will be appreciated any such extended portion 130 may be used to mount indicator 100 to any desired object (e.g. an airflow- emitting vent).

Indicator 100 may be produced in any desired manner. For example, a visual indicator gel 250 may be produced by compounding colorant and diluent (each of which, as noted, may be comprised of a mixture or solution of many different molecules and each of which may include volatilizable and/or nonvolatilizable material), e.g. at elevated temperature. The resulting product may then be loaded into receptacle 112 of base 110 (and, if loaded at elevated temperature, may then be allowed to cool, e.g. to form a solid slab). A porous diffuser layer 140 is bonded to the front side 104 of main body 111 of base 110. A removable cover sheet 230 may be removably bonded (e.g. by way of a PSA) to the front surface 142 of porous diffuser layer 140 if desired.

In some embodiments, porous diffuser layer 140 may provide a tapered face of receptacle 112. For example, a porous diffuser layer 140 may replace at least a portion of impermeable wall 113 of Fig. 3 (e.g. layer 140 may be bonded to an edge frame that extends from main body 111 of base 110 and that defines and surrounds an area that is occlusively overlain by porous diffuser layer 140). In such embodiments an impermeable wall may be provided in the position occupied by porous diffuser layer 140 in Fig. 3. Once produced, indicator 100 can be packaged in any suitable package. In particular embodiments the packaging material may be chosen (e.g., the packaging material may be a metallized polyester) to provide a sealed package from which minimal loss of volatilizable material may occur even over long-term storage and/or exposure to elevated temperatures. In some embodiments in which indicator 100 is packaged (i.e. sealed) within a packaging material with appropriate vapor-barrier properties, a cover sheet 230 may not need to exhibit significant vapor-barrier properties; in particular embodiments of this type, cover sheet 230 may be omitted from indicator 100.

List of Exemplary Embodiments

Embodiment 1 is a visual filter life indicator comprising: a base with a major wall and sidewalls that collectively define an open-ended receptacle; a porous diffuser layer that is mounted on a front side of the base and that occlusively overlies the open end of the receptacle, wherein an indicating indicia is provided on an indicia-bearing area of the major wall of the base and/or of the porous diffuser layer; and, a visual indicator gel that comprises colorant and that comprises volatilizable material, the indicator gel being disposed within the receptacle and including an indicating area comprising a surface that abuts an indicia-bearing area of the major wall of the base and/or a surface that abuts an indicia-bearing area of the porous diffuser layer.

Embodiment 2 is the visual filter life indicator of embodiment 1 wherein the visual indicator gel is adapted so that emission of volatilizable material from the receptacle due to air flow over the indicator causes an air gap to develop between at least a portion of a surface of the indicating area of the visual indicator gel and the indicia-bearing major area of the major wall of the base and/or the indicia-bearing major rear surface of the porous diffuser layer.

Embodiment 3 is the visual filter life indicator of any of embodiments 1-2 wherein the porous diffuser layer is an organic polymeric nonwoven web that exhibits an air permeability of from about 200 to about 800 cubic feet per minute per square foot.

Embodiment 4 is the visual filter life indicator of any of embodiments 1-3 wherein the porous diffuser layer is permeable to vapors but is at least substantially impermeable to liquids.

Embodiment 5 is the visual filter life indicator of any of embodiments 1-4 wherein the base is an impermeable unitary piece comprised of a molded thermoplastic organic polymeric resin and wherein the receptacle is provided by a molded depression in the base, wherein a terminus of the depression provides the major wall of the receptacle and wherein a major open end of the molded depression provides the major open end of the receptacle that is occlusively overlaid by the porous diffuser layer.

Embodiment 6 is the visual filter life indicator of any of embodiments 1-5 wherein the only pathway for volatilizable material to exit the receptacle is through the porous diffuser layer that occlusively covers the open end of the receptacle.

Embodiment 7 is the visual filter life indicator of any of embodiments 1-6 wherein the integral, molded base comprises a main body that comprises the receptacle and wherein the base further comprises an extended portion that extends away from the main body and that comprises a mounting mechanism. Embodiment 8 is the visual filter life indicator of any of embodiments 1-7 wherein the volatilizable material includes at least one volatilizable colorant that is compounded with at least one nonvolatilizable diluent.

Embodiment 9 is the visual filter life indicator of any of embodiments 1-7 wherein the volatilizable material includes at least one volatilizable diluent that is compounded with at least one nonvolatilizable colorant.

Embodiment 10 is the visual filter life indicator of any of embodiments 1-7 wherein the volatilizable material includes at least one volatilizable colorant that is compounded with at least one volatilizable diluent.

Embodiment 11 is the visual filter life indicator of any of embodiments 1-10 wherein the at least one indicating indicia of the major wall of the receptacle or of the porous diffuser layer exhibits a color and wherein the colorant of the visual indicating gel causes the indicating area of the visual indicating gel to at least generally visually match the color of the indicating indicia when the surface of the indicating area of the visual indicating gel is abutted against the indicia-bearing area of the major wall of the base or the indicia-bearing area of the porous diffuser layer.

Embodiment 12 is the visual filter life indicator of any of embodiments 1-11 wherein the receptacle is elongated with a first end and a second, opposing end that are spaced apart along an elongated axis of the receptacle, and wherein the receptacle is tapered so as to exhibit a greater cross- sectional area proximate the first end of the receptacle, and a smaller cross-sectional area proximate the second, opposing end of the receptacle.

Embodiment 13 is the visual filter life indicator of any of embodiments 1-12 further comprising an impermeable, removable cover sheet that overlies, and is removably adhesively bonded to, a front side of the porous diffuser layer.

Embodiment 14 is the visual filter life indicator of any of embodiments 1-13 wherein an indicating indicia is provided on an indicia-bearing area of the major wall of the base.

Embodiment 15 is the visual filter life indicator of any of embodiments 1-14 wherein an indicating indicia is provided on an indicia-bearing area of the porous diffuser layer.

Embodiment 16 is the visual filter life indicator of any of embodiments 1-15 wherein the visual indicator gel comprises fragrance.

Embodiment 17 is a method of visually monitoring the usable life of an air filter of a powered air- handling system, the method comprising: positioning a visual filter life indicator in an airflow path of a stream of moving air that is motivated by a fan of the powered air-handling system; if a removable cover sheet is present, detaching the removable cover sheet from a front side of the visual filter life indicator; and, visually observing the visual filter life indicator to ascertain whether a surface of an indicating area of a visual indicator gel has receded from an indicia-bearing area of a major wall of a base of the visual filter life indicator or from an indicia-bearing area of a porous diffuser layer of the visual filter life indicator so that an indicating indicia is readily visible. Embodiment 18 is the method of embodiment 17 wherein the visual filter life indicator is positioned in an airflow path that is proximate an air filter of a building HVAC system, proximate an air filter of a room air purifier, or proximate an air filter of a vehicle.

Embodiment 19 is the method of embodiment 18 wherein the visual filter life indicator is mounted to a perimeter frame of an air filter of a building HVAC system.

Embodiment 20 is the method of embodiment 17 wherein the visual filter life indicator is positioned in an airflow path that is proximate an air-exit or air-inlet of a building HVAC system.

Embodiment 21 is the method of embodiment 17, using the visual filter life indicator of any of embodiments 1-16.

It will be apparent to those skilled in the art that the specific exemplary elements, structures, features, details, configurations, etc., that are disclosed herein can be modified and/or combined in numerous embodiments. All such variations and combinations are contemplated by the inventor as being within the bounds of the conceived invention, not merely those representative designs that were chosen to serve as exemplary illustrations. Thus, the scope of the present invention should not be limited to the specific illustrative structures described herein, but rather extends at least to the structures described by the language of the claims, and the equivalents of those structures. Any of the elements that are positively recited in this specification as alternatives may be explicitly included in the claims or excluded from the claims, in any combination as desired. Any of the elements or combinations of elements that are recited in this specification in open-ended language (e.g., comprise and derivatives thereof), are considered to additionally be recited in closed-ended language (e.g., consist and derivatives thereof) and in partially closed-ended language (e.g., consist essentially, and derivatives thereof). Although various theories and possible mechanisms may have been discussed herein, in no event should such discussions serve to limit the claimable subject matter. To the extent that there is any conflict or discrepancy between this specification as written and the disclosure in any document incorporated by reference herein, this specification as written will control.

Claims

What is claimed is:

1. A visual filter life indicator comprising:

a base with a major wall and sidewalls that collectively define an open-ended receptacle;

a porous diffuser layer that is mounted on a front side of the base and that occlusively overlies the open end of the receptacle,

wherein an indicating indicia is provided on an indicia-bearing area of the major wall of the base and/or of the porous diffuser layer;

and,

a visual indicator gel that comprises colorant and that comprises volatilizable material, the indicator gel being disposed within the receptacle and including an indicating area comprising a surface that abuts an indicia-bearing area of the major wall of the base and/or a surface that abuts an indicia- bearing area of the porous diffuser layer.

2. The visual filter life indicator of claim 1 wherein the visual indicator gel is adapted so that emission of volatilizable material from the receptacle due to air flow over the indicator causes an air gap to develop between at least a portion of a surface of the indicating area of the visual indicator gel and the indicia-bearing major area of the major wall of the base and/or the indicia-bearing major rear surface of the porous diffuser layer.

3. The visual filter life indicator of claim 1 wherein the porous diffuser layer is an organic polymeric nonwoven web that exhibits an air permeability of from about 200 to about 800 cubic feet per minute per square foot.

4. The visual filter life indicator of claim 1 wherein the porous diffuser layer is permeable to vapors but is at least substantially impermeable to liquids.

5. The visual filter life indicator of claim 1 wherein the base is an impermeable unitary piece comprised of a molded thermoplastic organic polymeric resin and wherein the receptacle is provided by a molded depression in the base, wherein a terminus of the depression provides the major wall of the receptacle and wherein a major open end of the molded depression provides the major open end of the receptacle that is occlusively overlaid by the porous diffuser layer.

6. The visual filter life indicator of claim 1 wherein the only pathway for volatilizable material to exit the receptacle is through the porous diffuser layer that occlusively covers the open end of the receptacle.

7. The visual filter life indicator of claim 1 wherein the integral, molded base comprises a main body that comprises the receptacle and wherein the base further comprises an extended portion that extends away from the main body and that comprises a mounting mechanism.

8. The visual filter life indicator of claim 1 wherein the volatilizable material includes at least one volatilizable colorant that is compounded with at least one nonvolatilizable diluent.

9. The visual filter life indicator of claim 1 wherein the volatilizable material includes at least one volatilizable diluent that is compounded with at least one nonvolatilizable colorant.

10. The visual filter life indicator of claim 1 wherein the volatilizable material includes at least one volatilizable colorant that is compounded with at least one volatilizable diluent.

11. The visual filter life indicator of claim 1 wherein the at least one indicating indicia of the major wall of the receptacle or of the porous diffuser layer exhibits a color and wherein the colorant of the visual indicating gel causes the indicating area of the visual indicating gel to at least generally visually match the color of the indicating indicia when the surface of the indicating area of the visual indicating gel is abutted against the indicia-bearing area of the major wall of the base or the indicia-bearing area of the porous diffuser layer.

12. The visual filter life indicator of claim 1 wherein the receptacle is elongated with a first end and a second, opposing end that are spaced apart along an elongated axis of the receptacle, and wherein the receptacle is tapered so as to exhibit a greater cross-sectional area proximate the first end of the receptacle, and a smaller cross-sectional area proximate the second, opposing end of the receptacle.

13. The visual filter life indicator of claim 1 further comprising an impermeable, removable cover sheet that overlies, and is removably adhesively bonded to, a front side of the porous diffuser layer.

14. The visual filter life indicator of claim 1 wherein an indicating indicia is provided on an indicia- bearing area of the maj or wall of the base .

15. The visual filter life indicator of claim 1 wherein an indicating indicia is provided on an indicia- bearing area of the porous diffuser layer.

16. The visual filter life indicator of claim 1 wherein the visual indicator gel comprises fragrance.

17. A method of visually monitoring the usable life of an air filter of a powered air-handling system, the method comprising:

positioning a visual filter life indicator in an airflow path of a stream of moving air that is motivated by a fan of the powered air-handling system;

if a removable cover sheet is present, detaching the removable cover sheet from a front side of the visual filter life indicator;

and,

visually observing the visual filter life indicator to ascertain whether a surface of an indicating area of a visual indicator gel has receded from an indicia-bearing area of a major wall of a base of the visual filter life indicator or from an indicia-bearing area of a porous diffuser layer of the visual filter life indicator so that an indicating indicia is readily visible.

18. The method of claim 17 wherein the visual filter life indicator is positioned in an airflow path that is proximate an air filter of a building HVAC system, proximate an air filter of a room air purifier, or proximate an air filter of a vehicle.

19. The method of claim 18 wherein the visual filter life indicator is mounted to a perimeter frame of an air filter of a building HVAC system.

20. The method of claim 17 wherein the visual filter life indicator is positioned in an airflow path that is proximate an air-exit or air-inlet of a building HVAC system.