INDICATOR LOADED THERMO-SENSITIVE CAPSULES

TECHNOLOGICAL FIELD

The invention generally concerns thermo-sensitive capsules and matrices comprising same for reporting thermal variations in electric circuits.

BACKGROUND

Electrical fires that involve electrical failure or malfunction are responsible for a significant number of fires that develops in residential homes or industrial facilities, causing significant economic damage and casualties. Many of the electrical fires seem to be initiated because of damaged wires, damaged accessories and loose contacts in electrical cabinets. The malfunction causes an increase in the temperature of the equipment, leading to a fire.

Early detection of malfunctions enables to maintain the system before a fire is set and thus prevents casualties and economic damage.

One approach is to use thermal imaging to detect irregular temperature increases in electrical cabinets. While thermal imaging is highly sensitive and can detect a very small increase in the temperature, this method however can be implemented as a periodic service only, while the failure development can occur between one thermal survey to another; therefore in practicality, this method cannot provide a continuous early detection of fire.

Another approach includes the use of various smoke and heat sensors that provide alert when exposed to smoke or a temperature increase in the ambient environment. Such sensors do not provide an early indication, but rather usually after the fire has already occurred, therefore cannot provide an early indication of a malfunction.

Heat-sensitive odor-emitting components are also utilized. An odor emitting material, such as an alcohol, is sealed into a resin capsule, a resin tape, or a resin tube, and this is mounted on a site where heat generation is expected. Upon heat generation, the capsule melts, and the odor emitting material is released. The odor emitting material could be detected directly by a person, or by means of a gas detector. This method could provide an early detection of overheating, however difficult to be implemented widely, on all electrical components in an electrical cabinet. Other existing technologies make use of containers loaded with a volatile agent that is released upon exposure to certain temperatures. The volatile agents are single compound materials, such as liquid alcohols and ketones, loaded in a capsule sealed with a metallic material that melts at a predetermined temperature, thereby allowing release of the volatile agent.

Similarly, a matrix of a volatile agent may be dispersed in a material that melts at a certain temperature and allows diffusion out of the agent.

Shape memory seals are also used to construct such alarm units. These open the capsule when exposed to a temperature that changes its shape.

JPH0666646 describes a heat-sensitive smell producing microcapsule which can notify the temperature conditions even at a limited local point, quickly and easily, while selecting the temperature freely. The heat-sensitive smell producing microcapsules encapsulate an admixture of a smelling substance and a thermally fusible composition within a shell. The thermally fusible composition begins to fuse at a specific temperature. When the volatile smelling substance is admixed with the thermally fusible composition, the thermally fusible composition begins to fuse when the atmospheric temperature exceeds the specific temperature and the smelling substance evaporates. The shell suppresses the evaporation of the smelling substance effectively and preserves the smelling substance for a long term until fusion of the thermally fusible composition.

JP2008224475 describes a temperature sensing system for detecting a temperature rise of the device that is housed inside a box fixed volume having a predetermined ventilation and vapor the temperature rise in the apparatus in a container where the gas release hole is formed and it turned into to accommodates a gas generating material which generates a gas is constituted by sealing with a sealing material to melt the gas discharge hole at a predetermined temperature, the temperature sensing which is installed in said device housed within the box and the element is placed in the box, a gas detecting element that detects the concentration of the gas in the atmosphere in the box, based on the output of the gas detecting element, the degree to which the gas is increased per unit time temperature sensing system comprising an increase calculation unit that calculates an increase in degree, a determination section for determining whether or not the increase is not less than a predetermined threshold.

JPH05157633 describes a gas discharging device for detecting abnormal high temperature of various equipment, such as cable connecting sections, electric parts, electric facilities, mechanical facilities, buildings. The device is a gas discharging device for detecting temperature which discharges such a gas that can be detected with a gas detector as the temperature of a section to be detected rises and has a coated substrate with a hole section for fitting and supporting a seal which is made of a material having high heat conductivity and supports the substrate. The substrate is coated with a coating agent containing a low-boiling point compound which gasifies when the temperature rises.

CN101069073 describes an aroma-generating container of the heat reaction type wherein an aroma generator is contained in a container provided with an aroma divergence port and the aroma divergence port is sealed with a sealing agent that melts at a definite temperature.

WO2004093942 describes a shell containing a substance and a shape memory material activator configured to be deformed in response to only a single action such as temperature change and to subsequently create a path through the shell where its content is exposed.

US6,843,199 provides a technology which is intended to correct malfunction and disadvantages known and associated with the use of capsules or microcapsules comprising indicator materials, as known in the art. The technology disclosed provides a housing mainly made of an inorganic material, the housing encases an odorous material and is designed to operate at rather high temperatures.

BACKGROUND ART

[1] JPH0666646

[2] JP2008224475

[3] JPH05157633

[4] CN101069073

[5] WO2004093942

[6] US6,843,199

SUMMARY OF THE INVENTION

As a person of skill in the art would realize, existing alarm systems for use in electric cabinets suffer from several drawbacks, such as, limited ability to provide reliable early alarm and are thus better defined as providing post-fire alarm, periodic detection, specific systems for specific electric cabinet, etc. Present views in the pertinent field suggest avoiding use of capsules or microcapsules comprising indicator materials in such applications (see for example [6]).

Against existing knowledge and in order to overcome many of the drawbacks and malfunctions known for and associated with existing alarm systems, the inventors have developed a unique family of capsules, films, compositions and elements for use in construction of alarm systems that can provide an effective and sensitive early indication of an increase in a temperature in an electric cabinet. The alarm systems of the invention exhibit improved characteristics, such as high sensitivity, high reliability (substantially no false alarms), high compatibility (to different electric cabinets), durability and sustainability.

The inventors of the present invention have developed capsules (microcapsules), films, compositions and elements for use in construction of such alarm systems, which can be easily pre-formed and stored for use upon demand; and which may be easily implemented to any electrical system (e.g., electric cabinet), e.g., fit to different electric elements with different designs, concomitant with a high performance and reliability.

Thus, in a first aspect of the invention, there is provided a capsule (microcapsule) for use in the construction of an alarm system, the capsule comprising a core containing at least one releasable indicator material and a solid shell enclosing the core and comprising a thermo-sensitive material (pore-forming material) being a solid at a first temperature and capable of undergoing a phase transformation or decomposition (e.g., erosion) at a second higher temperature (or at a higher temperature) to thereby allow material communication between the core and the surrounding (the thermo- sensitive material is a pore-forming material for achieving holes, pores or channels through the shell material).

In another aspect, the invention provides a capsule for use in construction of an alarm system, the capsule comprising a core containing at least one releasable indicator material and a solid shell enclosing the core; the solid shell comprising a thermo- sensitive material being a solid at a first temperature and capable of undergoing a phase transformation or decomposition (e.g., erosion) at a second higher temperature (or at a higher temperature) to thereby allow release of an amount of said releasable indicator material. Further provided is a capsule for use in construction of an alarm system, the capsule comprising a core and a solid shell enclosing the core;

-the core containing at least one releasable indicator material;

-the solid shell comprising a thermo-sensitive material being a solid at a first temperature and capable of undergoing a phase transformation or decomposition at a second higher temperature, to thereby permit material communication between the core and the surrounding (formation of holes, pores or channels through the shell material); wherein said at least one releasable indicator material is configured to exit (or be released or burst out) from said core at said second temperature or at a higher temperature.

The capsules used in accordance with the invention are typically spherical particles in the micro-scale. The capsules are selected amongst microcapsules. The population of capsules may include capsules of various sizes and shapes; some may be microcapsules, some may be nano-capsules, some may be spheres and others may be non-spherical.

Thus, the invention provides a family of novel capsules, e.g., microcapsules which hermetically contain at least one releasable indicator material which can exit the capsule only when the thermo-sensitive material (which the shell of the capsules comprises) undergoes a phase change (e.g., melts) or undergoes decomposition (e.g., via erosion), resulting in the formation of holes, pores or channels within the capsules' shells. These holes, pores or channels as will be further explained below, extend the full thickness of the shell, from the core of the capsules (namely the capsules center where the at least one material is contained) outwards to the capsules' environment. Thereby, the at least one material may exist the capsule and cause the alarm to go on.

At a normal operating temperature, namely at a temperature typically measured in, e.g., closed electric systems or other systems in which the capsules of the invention may be implemented, taking into consideration one's ability to control environmental temperatures at a variety of locations and during different seasons, at or around 50°C (e.g., a range between 50 and 70°C), as further disclosed herein, the capsules contain at least one releasable indicator material, which may be a gaseous material, a liquid material or a solid material, as a single material, as a mixture of materials, or loaded onto or adsorbed onto a different (e.g., carrier) material, and which cannot escape the capsule through the capsule shell. At such a normal operating temperature (e.g., a range between 50 and 70°C), the shell material enclosing the at least one releasable indicator material is a solid material comprising a plurality of thermo- sensitive pore-forming material region(s), which are locations on or within or disperse in the shell coat and which hold a thermo-sensitive solid (e.g., at times in the form of material particulates) material. Once the temperature increases above a certain pre-defined threshold temperature, e.g., 70°C, the thermo-sensitive pore-forming materials undergo a phase change, decomposition, erode or otherwise clear out of the shell material, leaving behind holes, pores or channels, which permit evacuation or release of the at least one releasable indicator material.

Depending on, inter alia, the intended use, the selection of materials making up the capsules, the at least one releasable indicator material may be selected to remain in the capsules at the threshold temperature in a non-volatile form, exhibiting diminished or limited release. In such cases, the at least one releasable indicator material may be configured or engineered to evaporate (have a higher volatility) or escape the capsule upon further increase in the temperature to a higher temperature; thereby limiting the number false negative alarms.

In other cases, the at least one releasable indicator material is selected to have volatility sufficient to escape the capsules at the threshold temperature (namely at the temperature at which the thermo-sensitive material undergoes phase change or decomposition).

In still other cases, the at least one releasable indicator material is selected to have volatility sufficient to increase pressure inside the capsule to assist in the capsule opening or in the melting or decomposition of the pore-forming material in the shell.

As used herein, in reference to a material "capable of undergoing a phase transformation " , the invention refers to the ability of the material, e.g., a thermo- sensitive material to alter its phase upon experiencing a certain temperature(s). In other words, at a certain (first) temperature the thermo-sensitive material is at a certain (first) material phase (being typically solid) and at another (second) higher temperature the thermo-sensitive material undergoes a transformation to another (second) material phase (semi-solid or liquid or gel, or gas). The modification from one phase to another phase may be upon experiencing a certain (different) temperature, e.g., by increasing the temperature of the environment. The "phase" or "material phase" encompasses any form of a material form that upon certain conditions (e.g., temperature) alters to another form. The term encompasses material association (material associated to another material versus unassociated state), material state (solid versus liquid versus gas), crystalline state (crystal versus amorphous), and others. In some embodiments, the material phase is the material state, selected from solid, liquid and gas.

Capsules of the invention may be of any form. In some cases, the capsules are core/shell materials constructed of a core in which the at least one releasable indicator material is held (or contained). In other cases, the capsules may be spheres containing the at least one releasable indicator material. In yet other cases, the capsules may be constructed of an adsorbent material holding the at least one releasable indicator material and coated with an external film or shell. Notwithstanding the form of the capsules, they may be of any shape and size.

In some embodiments, the capsules are selected to hold a volume ranging from about 1 microliter to 1 ml to milliliter of the at least one releasable indicator material, in any form, e.g., in solid or adsorbent form.

The material from which the capsule walls or shells are made depends, inter alia, on the final utility and detection parameters. Generally speaking, the shell material is selected to be heat stable at any temperature below 70°C. In other words, at a temperature above 70°C, the shell material and/or the pore-forming material embedded in said shell material may begin to undergo phase change or decomposition, e.g., erosion.

The capsule shell is in the form of a continuous material surrounding the at least one releasable indicator material contained in the capsule core and preventing its leakage or release therefrom. To assist in the controlled sensitivity to a temperature increase, the shell material is formed with a plurality of pore-forming seeds or particles or regions which are selected of materials that undergo phase change or decomposition at a temperature above 70°C. In some embodiments, the pore-forming seeds or particles or regions are selected of materials that undergo phase change or decomposition at a temperature above 65°C, above 70°C, above 75°C, above 80°C, above 85°C, above 90°C or above 95°C. Thus, as used herein, the threshold temperature above which the capsule shell begins to undergo a phase change, decomposition, erode or otherwise clear out of the shell material, leaving behind holes, pores or channels, which permit evacuation or release of the at least one releasable indicator material, is between about 60°C and 70°C. In some embodiments, the threshold temperature is between about 65 °C and 70°C.

In some embodiments, the pore-forming seeds or particles or regions are selected of materials that undergo phase change or decomposition at a temperature between 60°C and 80°C, or between 65°C and 80°C, or between 70°C and 80°C, or between 60°C and 70°C, or between 60°C and 90°C, or between 70°C and 90°C, or between 80°C and 90°C.

In cases where the at least one releasable indicator material is adsorbed onto a carrier or an adsorbent material such as a sponge material or a hydrogel, e.g., made of polyurethane, nylon or any other polymer, the carrier or adsorbent material may be coated with a shell of, e.g., a polymeric material that contains the pore-forming particles. It should be noted that such a technology allows simple preparation of the detection capsules, as coating of a loaded carrier or adsorbent, e.g., sponge material can be achieved by spraying or dipping of the coating solution. These capsules are less sensitive to leaking as the indicator material is held within the carrier or adsorbent, e.g., sponge, matrix and only when the coating is disrupted by heat the material significantly evaporates.

The capsule shell may comprise one to several materials layers, each layer may or may not be the same vis-a-vis material content, thickness, structure, incorporation of other materials, sensitivity to heat, etc.

The capsule wall or shell material is selected to be impermeable to the at least one releasable indicator material and to any external material, such as humidity, which at the normal operating temperature may cause degradation or disruption of the shell.

In some embodiments, the shell material is of or comprises a polymeric material.

In some embodiments, the polymeric material is selected from polymers that melt at temperatures above 100°C.

In some embodiments, the polymeric material is selected amongst hydrophilic or hydrophobic polymeric materials.

In some embodiments, the polymeric materials are selected from olefinic polymers such as polyethylene, polypropylene and copolymers and terpolymers thereof.

In some embodiments, the polymeric material is selected from polymers and copolymers of monoolefinic hydrocarbons having at least two carbon atoms, e.g., copolymers of ethylene, propylene, various butenes, pentenes and hexenes, as well as halogenated olefin derivatives.

In some embodiments, the polymeric materials are selected from copolymers of ethylene and ethyl acrylate; vinyl polymers comprising one or more monomers selected from vinyl aryls, e.g., styrene, o-phenylstyrene, m-phenylstyrene, p-phenylstyrene, o- methylstyrene, m-methylstyrene, p-phenylstyrene, o-methoxy styrene, m- methoxy styrene, p-methoxystyrene, o-nitrosytrene, m-nitrostyrene, p-nitrostyrene, and the like; vinyl and vinylidene halides, e.g., vinyl chloride, vinylidene chloride, vinylidene bromide, and the like; vinyl esters e.g., vinyl acetate, vinyl propionate, vinyl butyrate, vinyl chloroacetate, vinyl benzoate, and the like.

In some embodiments, the polymeric material is selected from vulcanized rubbers such as cyclized or isomerized rubber, rubber hydrochloride, polybutadiene rubbers (e.g., Gr-S and nitrile rubber), polychloroprene and copolymers, polysulphide rubbers, polyisobutylene and the butylrubbers, the various polyethylenes, e.g., chlorosulphonated polyethylene rubbers, polytetrafluorethylene, polystyrene, polyvinylcarbazole and polyacenaphthylene, indene and coumaroneindene resins, polyvinyl acetate, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl formal, polyvinyl acetal, and polyvinyl butyral, polyvinyl chloride, vinyl chloride-vinyl acetate copolymers polyacrylonitrile, vinyl chloride-acrylonitrile copolymers, polyvinylidene chloride and its copolymers, polymethyl methacrylate and related polyacrylates, ketone aldehyde polymers and polyacrylate rubbers.

In some embodiments, the polymeric material is selected amongst polycarbonates; cellulose-based materials, e.g., cellulose acetate, cellulose triacetate, cellulose acetate butyrate, cellulose propionate, ethyl cellulose, and the like; polyamides; polyesters, e.g., polyethylene terephthalate, polyethylene isophthalate, poly(ethylene-2,7-naphthamate), polybutylene terephthalate, polypropylene terephthalate, copolymers thereof and the like; chlorinated polyethylene, chlorinated polyvinyl chloride, polyfluoroethylene, polytrifluorochloroethylene, polyhexafluoropropylene, copolymers thereof.

In some embodiments, the polymeric material is selected from polyurethanes, polysulfones, polyacetals, halogenated olefins, and phenoxy resins.

In some embodiments, the polymeric material is selected amongst thermoplastic materials. In some embodiments, the polymeric material is selected amongst polyamides.

In some embodiments, the polymeric material is selected amongst polyolefins.

In some embodiments, the polymeric material is selected amongst polyesters.

In some embodiments, the polymeric material is selected amongst nylon 6, nylon 6,6, nylon 6,10, nylon-11, and materials based on any of the foregoing.

In other embodiments, the polymeric material is selected from polyethylene, polypropylene, poly(vinyl chloride), Nylon 66, poly(ethylene terephthalate), poly(methyl methacrylate) and polymers with alkyl methacrylates such as ethyl methacrylate, butyl methacrylate, hexyl methacrylate and other hydrophobic acrylates or methacrylates, polyurethanes silicones and ethyl cellulose.

In some embodiments, the polymeric material is used as a composite of the polymer with at least one additional material (additive). In some embodiments, the at least one additive is selected amongst inorganic solids that reduce diffusion of indicator gas from the capsule and increase the mechanical strength of the capsule, e.g., oxides of Mn, Mg, Zn, Ti, P and Ca.

In some embodiments, the oxides are selected from MnO, MgO, ZnO, Ti(¾, phosphate salts, and CaSO/ _t .

In some embodiments, the additive is selected amongst talc, microcrystalline cellulose, poly(methyl methacrylate) beads and glass beads.

In some embodiments, the additive may be selected from alumina, aluminum hydrates, feldspar, talc, calcium carbonates, clay, carbon black, quartz, novaculite, and other forms of silica, kaolinite, bentonite, garnet, saponite, beidellite, calcium oxide, wollastonite, calcium hydroxide, fibers selected from glass fibers, metal fibers, carbon fibers, jute, hemp, sisal or organic polymeric fibers.

In some embodiments, the additive may be selected from antistatic agents, plasticizers, lubricants, nucleating agents, impact modifiers, colorants, heat and light stabilizers.

In some embodiments, the polymeric shell is decorated, embedded with or comprises regions comprising or consisting of at least one thermo-sensitive pore- forming materials, which upon an increase in the temperature undergo phase change or decomposition and open pore channels in the polymeric shell. The pore-forming material may be in a particulate form and may be dispersed in the shell in any amount and in any distribution pattern so long as the pores formed upon increase in the temperature permit material communication from the core of the capsules to their surroundings or cause partial or total rapture of the capsule shell and subsequent release of the at least one releasable indicator material.

Further, in some embodiments, the particles of the pore-forming material are selected based on their size to permit control over the amount of the indicator material released from the core and the mechanism by which the holes or pores are formed.

As used herein, the "thermo-sensitive material" or "pore-forming material" is a material which undergoes a phase change or decomposition (e.g., by erosion) and thereafter removal or displacement from the shell material; to thereby leave behind holes, pores or channels through which the at least one releasable indicator material may leak out, be released or burst out.

In some embodiments, formation of pores or holes in the shell material occurs via melting of the thermo-sensitive pore-forming material at its melting temperature or at a higher temperature.

To achieve release of the at least one releasable indicator material from within the capsules, complete removal of the pore-forming material is not necessary. Partial removal may suffice, as long as a high degree of porosity is achieved. In some embodiments, at least 50%, 60%, 70%, 80%, 90% or 95% (by weight) of the pore- forming material is removed following phase change or decomposition. In some embodiments, the entire pore-forming material is removed or displaced.

In some embodiments, the content of the pore-forming material in a polymeric shell is from about 1 to about 40% w/w, depending, inter alia, on the particle size of the pore-forming material and melting properties, the thickness of the sealant or the capsule shell and the desired rate of release of the indicator vapors.

In some embodiments of the invention, the shell material comprises the thermo- sensitive pore-forming material, optionally in the form of particles, in an amount which is at least 1% by weight of the shell material, at least 10%, at least 30% or at least 40% of the shell material, to allow immediate release of the indicator gas through the capsule.

In some embodiments, the shell material comprises the thermo-sensitive pore- forming material, optionally in the form of particles, in an amount which is at least 1 % by weight of the releasable indicator material. In some embodiments, the pore-forming material is selected from small organic molecules and organic salts and alloys.

In some embodiments, the pore-forming material is a metal alloy. In some embodiments, the alloy is based on a metal selected from Bi, In and Sn. In some embodiments, the alloy is a Bi-based alloy. In some embodiments, the alloy is Bi:In:Sn. In some embodiments, the alloy is Bi:In:Sn having a melting temperature of above 60°C or above 70°C or above 80°C. In some embodiments, the alloy is Bi:In:Sn at a 57:26:17 ratio. In some embodiments, the alloy is Bi:In:Sn at a 54:30:16 ratio.

In some embodiments, the pore-forming material is a material that upon heating generates C(¾. In some embodiments, the material is benzoyl peroxide or carbamate peroxide.

In other embodiments, the pore-forming material is a material that upon heating generates N ₂ . In some embodiments, the material is azobis-isobutironitrile.

In some embodiments, the pore-forming material is an organic salt. Non-limiting examples of organic salts include bis(octapentadienyl) germanium, Ge(C5l¾)2; triphenyl bismuth Bi(Ph)3; Gallium chloride, GaCl ₃ ; phosphomolybdic acid octacoshydrate (H ₇ [P(Mo ₂ 0 ₇ ) ₆ ]-28H ₂ 0); Barium hydroxide octahydrate, Ba(OH) ₂ - 8H ₂ 0; cyclopentadienyldicarbonyl (methyl)iron(II), CH ₃ Fe(CO) ₂ CsH5; antimonium iodide, Sbls; samarium (II or III) nitrate hexahydrate, Sm(N0 ₃ )2- 6¾0; sodium pyrophosphate decahydrate, Na4P ₂ 0 ₇ - IOH2O and niobium fluoride, NbFs.

In some embodiments, the pore-forming material is an organic material selected from acrylamide, acetoacetyl alanine, acetylamide, naphthalene, tristearin, waxes and fats that melt at the desired temperature for pore formation.

The at least one releasable indicator material which is contained in the core of a capsule according to the invention (either as such or adsorbed onto another material) is typically an organic or inorganic material that may be implemented at any physical phase. In some embodiments, the at least one releasable indicator material is a solid at room temperature. In some embodiments, it is a solid material at the normal operating temperature of the system in which the capsules are implemented. In some embodiments, it is a solid at temperatures between 70° and 100°C.

The solid releasable indicator material may be a molecular solid, e.g., iodine and naphthalene, or a salt or composition of materials that decompose into a detectable agent (or agents) such as ammonium carbonate or iodine. The releasable indicator material is selected to be sufficiently volatile to escape or leak out or be released or burst out from the capsule core once pores are formed in the capsule shell or once the shell has been disrupted. The releasable indicator material is stable under ambient conditions (and under the normal operating temperature) and is released (or undergoes a change enabling release) under certain other conditions. In some embodiments, the release is carried out by vaporization of the releasable indicator material. Therefore, in some embodiments, the at least one releasable indicator material is a vaporizable material (volatile material). The vaporizable material may be a material that evaporates readily at a predetermined temperature above the normal operating temperature, as defined. In some embodiments, the vaporizable material is a material having a high vapor pressure at a predetermined temperature above the normal operating temperature, as defined.

To achieve detection of the releasable indicator material, once released from the capsule, it is not necessary to cause complete release of the capsule. Depending on the intended application, the capsules are engineered and configured to enable release of at least 50%, 60%, 70%, 80%, 90% or 95% (by weight) of the material. In some embodiments, the entire releasable indicator material is released.

The releasable indicator material is selected to be easy to handle during storage in the capsules, environmentally safe, evaporable under the application conditions and detectable by the sensor at a desired concentration in air, at part-per-million (ppm) levels or below.

In some embodiments, the at least one releasable indicator material is selected amongst C2-C6 alcohols, C2-C6 mercaptans, C ₆ -Ci2 hydrocarbons, C2-C6 ketones, C2-C6 aldehydes, C2-Q2 alkenes, C2-Q2 alkyne, Cs-Cs cyclic alkanes, C ₁ -Q2 hydrocarbons haloalkanes, Ce-Cu aromatic molecules, nitroxides, NO, H2S, SO2, SF6, ammonia, fluorinated short hydrocarbons (Freons), solid iodine, chlorine, bromine and organic or inorganic salts.

In some embodiments, the at least one releasable indicator material is an inorganic salt. In some embodiments, the inorganic salt is iodide salts such as KI and Nal, mixed with an oxidizing agent, such as CUSO4 or iron sulfate, which upon heating form iodine vapors. In some embodiments, the at least one releasable indicator material is an organic salt. In some embodiments, the organic salt is ammonium carbonate that upon heating releases ammonia.

In some embodiments, the at least one releasable indicator material is a material which releases iodine vapors.

In some embodiments, the at least one releasable indicator material is a material which releases ammonia vapors.

In some embodiments, the at least one releasable indicator material is an aromatic material. In some embodiments, the aromatic material is naphthalene or acetophenone.

The at least one releasable indicator material may be a single material or a combination of several materials. The material may be in a form of pro-indicator, wherein the molecule is part of another material or is in the form of a molecule which upon exposure to heat, or to another molecule, such as oxygen or moisture, generates the indicator material(s). Such systems may be, for example, azo-bis-isobutyronitrile (AIBN) that upon application of heat degrades to form isobutylene and nitrogen. Another example is a mixture of iron sulfide and acid that upon contact generate H ₂ S.

The at least one releasable indicator material may be encapsulated as a free solid or liquid in a capsule shell or adsorbed onto a porous polymer or sponge or complexed onto a polymer or a small molecule. A single molecule or mixture of molecules may be encapsulated.

The capsules of the invention may be implemented for use in a continuous material matrix which may be of any material, provided that the capsules are partially or fully exposed to the environment such that an increase in the temperature may be directly sensed.

The capsules may be applied directly onto any potential hot-spot, namely at any point where an increase of temperature may occur due to loose wire connections of otherwise any electric malfunction. The application may be via any method of application known in the art, including spraying a formulation comprising the capsules onto or in the vicinity of a hot-spot or by gluing the particles onto or in the vicinity of a hot spot.

Thus, the invention further provides a formulation comprising a plurality of capsules according to the invention and at least one carrier. The capsules may be dispersed in a propellant or a solvent such as water, optionally further containing an adhesive material, as defined, and applied as spray onto a hot spot.

Further provided is an adhesive formulation comprising the capsules and at least one adhesive material. The at least one adhesive material may be any binder or material that can cause irreversible association of the capsules to a substrate on or in the vicinity of a hot spot. In some embodiments, the adhesive material is selected amongst epoxies, cyanoacrylates, urethanes and acrylic adhesives. In some embodiments, the adhesive material is selected from cyanoacrylate; casein glue; cement glues; resin glues such as epoxy resins, acrylic resins, phenol formaldehyde resins, polyvinyl acetate (PVA) and polyvinyl pyrrolidone (PVP); Canada balsam; pastes such as latex pastes; polyethylene hot melt; acrylonitrile; cellulose nitrate; polyurethane, polyvinyl chloride (PVC), and others.

The amount of a formulation comprising capsules of the invention which is applied onto a hot spot is controlled by the time and degree of application and is related, inter alia, to the volume of distribution of the indicator molecules. Where the capsules are dispersed in an adhesive carrier, the content of capsules may be 50% or 60% of the total content (wt).

For any mean of application, the capsules should remain intact in the carrier or the adhesive material. Once applied, a film is formed comprising a plurality of capsules which are at least partially surface exposed so that thermo-sensing may be possible.

Thus, the invention further provides a film comprising at least one releasable indicator material for use in an alarm system, the releasable indicator material being in a form of a plurality of capsules at least partially exposed on a surface region of said film, each capsule comprising a core and a solid shell enclosing the core; the core containing the releasable indicator material; the solid shell comprising a thermo-sensitive material being a solid at a first temperature and capable of undergoing a phase transformation or decomposition (e.g., erosion) at a second higher temperature to thereby allow material communication between the core and the surrounding therethrough (formation of holes, pores or channels through the shell material).

In another aspect the invention provides a solid matrix for use in the construction of an alarm system, the matrix embedding at least partially a plurality of capsules containing a releasable indicator material; each capsules having a solid shell comprising a thermo-sensitive material (pore-forming material) at a first temperature and capable of undergoing a phase transformation at a second higher temperature; the thermo- sensitive material being configured to undergo erosion (or material removal) at said second temperature or at a higher temperature to thereby allow material communication between the capsules cores and the surroundings (the thermo-sensitive material is a pore -forming material for achieving formation of channels through the shell material, pores).

In some embodiments, the thermo-sensitive material is configured to undergo erosion (or material removal) at said second temperature or at a higher temperature to thereby allow release of an amount of said releasable indicator material.

In some embodiments, the at least one releasable indicator material is configured to exit (or be released or burst out) from said cores at said second temperature or at a higher temperature.

The invention further provides a surface associated with a plurality of capsules, each capsule comprising a core and a solid shell enclosing the core; the core containing the releasable indicator material; the solid shell comprising a thermo-sensitive material being a solid at a first temperature and capable of undergoing a phase transformation at a second higher temperature; the thermo-sensitive material configured to undergo erosion (or material removal) at said second temperature or at a higher temperature to thereby allow material communication between the core and the surrounding.

The carrier may additionally function as an adhesive agent, enabling adhesion to a hot spot.

The invention further provides an element comprising a film of the invention, or a plurality of capsules of the invention associated, optionally via at least one carrier material (matrix material or adhesive) with a substrate of said element.

As stated above, a film of capsules of the invention may be formed on any surface. As the capsules are intended for use as indicators in electric cabinets to alarm an increase in a normally operated electric circuit and provide an early indication that certain conditions have been created to facilitate spontaneous ignition, the film is formed or associated with a hot spot or on a surface in its vicinity. Thus, in a first implementation of the invention, a film or an element comprising a plurality of capsules of the invention may be attached or associated with each end of an electrical wire or component. Thus, the invention further provides an electric wire or electric component associated with a film or an element comprising a plurality of capsules of the invention.

Further provided is an electric circuit comprising at least one electric wire or component, said wire or component being associated with an element or capsules of the invention. In some embodiments, a film comprising the capsules is formed at at least one end of the wire, the wire end being suited for assembly into or with a further wire or component in the circuit.

In some embodiments, each of the wires in said circuit is associated at at least one end with a film or an element comprising capsules of the invention.

In some embodiments, each and every wire is associated with an element or film of capsules at every end thereof.

The electric circuit is typically housed in an electric and/or electronic enclosure (housing or cabinet) such as, for example, phone exchange cabinets, enclosures for folding multiplex equipment for transmitting phone or data signals, electric cabinets and others. Such enclosures or housings or cabinet structures may comprise numerous heat- generating elements or features which increase the temperature within the enclosure to above room temperature (above 25 °C). Thus, the enclosure is typically maintained at a normal operating temperature which is unique to the specific enclosure and which depends, inter alia, on the size of the enclosure, its location, degree of thermal ventilation, number of electric wires, number of electrical connections, etc. Once an element within the enclosure malfunctions or connectivity becomes loose, the temperature within the enclosure may increase, necessitating early detection. Thus, for an efficient detection of any increase in the operating temperature of such an enclosure, capsules, or film or element according to the invention may be appended to or associated with any one component in the enclosure or its vicinity. To provide early detection, the enclosure further comprises a sensor for detecting the evolution of the at least one releasable indicator material in the enclosure and optionally an alarm and/or a shut off system for notifying or shutting down, respectively, the malfunction operation of the enclosure.

The release of the at least one releasable indicator material from capsules of the invention is electronically detected by a sensor element positioned in the vicinity of a plurality of wires or components in the enclosure. In some embodiments, the sensor is adapted and configured to go on when a predefined amount or volume of the at least one releasable indicator material is detected.

The sensor may be selected amongst infrared point sensors, ultrasonic sensors, electrochemical gas sensors, and semiconductor sensors. All may be utilized for detecting a wide range of gases at ppm levels and can be found in industrial plants, refineries, waste-water treatment facilities, vehicles, and homes.

The invention further provides a capsule loaded with a vaporizable indicator or precursors thereof for producing an indicator, sealed or composed of a polymer composition, attached to a hot spot that upon exposure to a pre-determined temperature between 50 and 120°C opens up to release the loaded indicator.

In some embodiments, the capsule is made from polymers and compositions or metallic materials and combination thereof. In some embodiments, the polymer composition seal is composed of a continuous polymer or adhesive containing a porogen (pore-forming material) or porogens that melt or modify upon exposure to a pre-determined temperature which allow the release of the containing indicator.

In some embodiments, the porogen is composed of a metallic alloy, organic or inorganic compounds or mixtures thereof. In further embodiments, the progens is selected amongst alloys containing Bi:In:Sn at a 57:26:17 that melt at 79°C and the 54:30: 16 alloy that melt at 81°C. lternatively, the porogen may be in the form of salts, for example: bis(octapentadienyl) germanium, Ge(CsHs)2; triphenyl bismuth, Bi(Ph)3; Gallium chloride, GaCi ₃ ; phosphomolybdic acid octacoshydrate (H ₇ [P(Mo ₂ 0 ₇ ) ₆ ]-28H ₂ 0); Barium hydroxide octahydrate, Ba(OH) ₂ - 8H ₂ 0; cyclopentadienyldicarbonyl (methyl)iron(II), CH ₃ Fe(CO)2CsH5 that melts at 78°C; antimonium iodide, Sbls; samarium(II or III) nitrate hexahydrate, Sm(N0 ₃ )2- 6H20; sodium pyrophosphate decahydrate, Na4P2C - IOH2O and niobium fluoride, NbFs that melts at 80°C. In some embodiments, the porogen is selected amongst organic compounds such as naphthalene, tristearin and waxes.

In some embodiments, the coating that seals the indicator or precursors of the indicator or indicators is a polymer composition that melts at a pre-determined temperature to allow release of the indicator. The polymer compositions may be copolymers of alkyl methacrylates or acrylates, aliphatic polyesters made from, for example, propylene glycol and succinic acid and adipic acid. Polymeric plastics include but not limited to: polyethylene terephthalate (PET), polyethylene (PE), polypropylene, polyvinyl chloride (PVC), polycarbonate, polyvinyl acetate, ABS and combination thereof. The polymer plastic compositions may include addition of fillers, plasticizers, carbon, minerals, colorants and combination thereof.

The capsule of the invention may contain a volume of from 5-1000 microliters. The wall thickness of the capsule may be in the range from a few microns to about 1000 microns and may be made of a single or multilayer or from a single or multiple polymers and additives.

Also provided is a film composition containing a component that melt at the desired temperature and form holes across the film to allow compounds cross the membrane. The temperature trigger for opening up the capsule is a compound added to the polymer plastic or glue that melt at the desired temperature.

The invention further provides a polymer composite containing a porogen that upon exposure to a temperature between 50-100°C, forms pores to allow gas to diffuse through the polymer. In some embodiments, the porogen is a metallic or an organic molecule that melts at a desired temperature.

The invention further provides a solid (at room temperature) indicator composed of a single compound or two or more compounds that upon exposure to a desired temperature between 50-100°C releases the indicator in a gas form.

The invention further provides a capsule made from an envelope loaded with an indicator composition that is sealed with a polymer composite disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1A-E provides illustrations of systems according to some embodiments of the invention.

In Fig. 1A a general system according to the invention is illustrated, wherein an electric cabinet contains at least one wire (step 1) associated with a film of the invention. At about 80°C the indicator is released (step 2) from the film and is detected by a gas sensor. Only ppm levels of the indicator are necessary for the gas sensor to go off and alarm the thermal increase (step 3).

In Fig. IB three optional applications of a film of the invention are depicted. The first is a clip-on application wherein an element according to the invention is attached or associated with the end of a wire at a potential hot-spot. The second is a film formed at the potential hot-spot by spraying a formulation according to the invention or in the form of a gel. The third option is a thread.

In Fig. 1C a cross-section view of a threaded capsule is depicted. In the figure: 1. Outside isolated shield; 2. Indicator material; 3. Metal shield; 4. Sealing plug; 5. Electrically conductive material; 6. Electrically conductive plastic shield; 7. Electrically conductive connection area; 8. Electrical element; and 9. Plug pressing area.

In Fig. ID a clip-on application is depicted. In the figure: 1. Plastic clips; 2. Plastic hinge; 3. Sealing plug; 4. Indicator material; 5. Outside plastic shield; 6. Electrically conductive plastic shield; 7. Electrically conductive material; and 8. Electrical element.

In Fig. IE a device applied by spraying is depicted. In the figure: 1. Adhesive material/coating; 2. Capsule shell; 3. Indicator material; 4. Electrically conductive plastic shield; 5. Electrically conductive material; and 6. Electrical element.

Figs. 2A-D present microscopic images (12 zoom) of polyurethane films (thickness = 0.42 mm) containing 10 (Fig. 2A, 2C) or 20 wt% (Fig. 2B, 2D) of alloy (Bi:In:Sn at a 57:26:17 w/w ratio, melting point 79°C) before (Fig. 2A, 2B) and after heating (Fig. 2C, 2D). Images were taken by Nikon SMZ 25 microscope. Films were heated at 85 °C for 15 minutes and cooled to room temperature for SEM analysis. After heating the particles are less ordered in the film.

DETAILED DESCRIPTION OF THE INVENTION

The inventors of the present invention have developed capsules (microcapsules), films, compositions and elements for use in construction of such alarm systems, which can be easily pre-formed and stored for use upon demand; and which may be easily implemented to any electrical system (e.g., electric cabinet), e.g., fit to different electric elements with different designs, concomitant with a high performance and reliability. Certain methods for forming devices and elements of the invention and certain system embodiments of the invention are generally depicted in Figs. 1A-E.

Example 1: Preparation of films containing alloy as porogen

Films were prepared by dissolving segmented polyurethane (PU, Pellethane) in tetrahydrofuran to form a viscous solution (10-20% w/w) and alloy composed of Bi:In:Sn at a 57:26: 17 w/w ratio, melting point 79°C) was added and mixed well before spreading the viscous solution onto a film cast. The cast was allowed to evaporate at room air to form these uniform films. The films were evaluated microscopically before and after heating to about 85°C for 10 minutes (Figs. 2A-D). Uniform distribution of particles throughout the films is noticed and increase in density with the increase in % alloy added.

The melting temperature of the alloy was checked by Differential Scanning Calorimetry (DSC) for the alloy only and the alloy mixed in polyurethane film (PU: The melting points of each of the two samples were the same. This indicates that the mixture with the polymer did not have an effect on the melting point of the alloy. These films were placed in diffusion cells to determine the effect of temperature on the diffusion through the films. In the lower chamber, iodine particles were placed and a 1 % solution of starch was placed onto the upper chamber on the film. No color change was seen when remain at room temperature. However, when heated to about 80°C, blue-colored water was observed in the upper chamber, which intensified shortly after heating. This experiment demonstrates the porogenic effect of the alloy in the film. Similar results were obtained when an organic porogen, such as acrylamide, was used.

Example 2: Encapsulation of iodine into capsules

Iron or aluminum capsules were prepared to fit an electric wire where the capsule is made like a sleeve that has an opening in the center to allow insertion of the electric wire or a capsule with hemisphere structure that can be mounted onto a wire. Both containers are open in the top of the device with a free volume of about 100 microliters. To these capsules, 50 mg of powder of pure solid iodine was added and the open side was sealed with a two-component commercial epoxy glue containing increasing amounts of alloy (0, 10, 20, 30 and 40% w/w of 15 micron round particle size, alloy composed of Bi:In:Sn at a 57:26: 17 w/w ratio, melting point 79°C). The iodine loaded containers (10 for each type) were placed in a 60°C oven and change in the weight of the capsules or iodine leak was monitored weekly for 30 days. For all containers, no change in weight was found and no iodine release was determined by immersing the devices in amylose solution and following the formation of blue color which indicate iodine release. When placing the containers in a 80 ± 5°C oven, most of the 30% alloy containing epoxy seal disrupted within 2 minutes to release its iodine content as brown cloud. Containers sealed with epoxy containing 0 and 10% alloy remain sealed even after one week.

To better understand the seal required, epoxy seals in depth of approximately 1 and 2 mm (40 and 80 mg total amount per seal) were prepared and placed in oven as above. All sealed containers of both types remain sealed when stored at a 70oC oven for one week. However, at 80oC, the 1 mm seal containing 30% alloy, disrupted in less than 1 minute.

In a further study, powder of iodine complexed in polyurethane (Pellethane) or Nylon 6,6 particles (50% content, prepared by immersing the polymer particles in a KModine aqueous solution or placing them in a container containing high content of iodine vapors for 24 hours) were loaded in the containers as above and sealed with 30 or 40% alloy epoxy glue as above. The sealed containers remain stable for one week at a 70°C oven, however, when the oven temperature increased to 80°C iodine was immediately released as a brown cloud. Similarly, iodine paste in mineral oil (50% iodine content) was loaded in the containers using a syringe which allows easy loading and stability.

Envelopes made of epoxy glue loaded with 30% alloy with a wall thickness of 1 mm loaded with iodine powder or iodine complexed in polymer particles described above remain stable for one week at 60°C and disrupted at 80°C to release its iodine content as vapor. It should be noted that envelopes prepared from various polymers, including: polyurethanes, silicones, EVA and ethyl cellulose, were not stable in keeping the iodine and deteriorated with time with iodine molecules diffusing out the envelop while damaging the envelope. Epoxy glues from different sources were effective in sealing iodine.

The stability and release of iodine in real electric cabinet was determined in a custom made electric cabinet of the size 110x80x30 cm, equipped with wires, heating elements, heat sensors, RI camera and a sensor for iodine vapor detection at a level of 1- 20 ppm. This cabinet is also equipped with a sensor to determine ammonia at 2-40 ppm (needed for the next experiment).

In a separate experiment, the ability of naphthalene to serve as porogen instead of the alloy, 30% w/w naphthalene powder was added to epoxide glue and tested for release of ammonia or iodine. Naphthalene was as effective as the alloy as porogen. However, naphthalene is easy to evaporate and thus stability of the device for years under environmental conditions should be confirmed. Two other organic molecules were tested as prorogens, acrylamide and acetoacetyl alanine which melt at temperatures in the range of 80-85°C. These porogens when loaded in the epoxide composition did not affect the epoxy curing or strength and remain stable in a 70°C oven for more than 2 weeks but formed pores when the temperature was increased to above 80°C.

Example 3: Ammonia releasing devices

Salts containing ammonia, including: ammonium carbonate, ammonium bicarbonate, ammonium sulfite, ammonium chloride, ammonium sulfate, ammonium citrate and more, were tested as potential for releasing ammonia when heated that can be detected. Only ammonium carbonate, ammonium bicarbonate and ammonium sulfite released an appreciable amount of ammonia when heated. An appreciable amount of ammonia was also released when these ammonium salts were mixed with a base such as sodium hydroxide and sodium carbonate.

Ammonium carbonate powder, 50-80 mg, was loaded in the containers described in Example 1 and sealed with epoxy resin containing 30 or 40% alloy or acrylamide powder and placed in a 70°C oven for one week. The loaded containers remain stable and did not change in weight during this period. However, when the temperature was increased to 80-85°C, detectable amounts of ammonia were release within minutes. 5-40 ppm ammonia were detected in the testing cabinet. Unlike iodine, the selection of polymers for sealing the containers loaded with ammonium carbonate is wide as the salt is stable and does not attack polymers.

In a further experiment, 2 mm beads made by compression of ammonium carbonate powder using a compression molder and a suitable die. The beads were dip coated with a THF solution of Pellthene, common segmented polyurethane, containing 20% alloy. Coatings of 0.1 and 0.3 mm were obtained. When exposed to 40°C no weight loss was detected for one week.

Example 4: stabilization of ammonium carbonate in oils

Ammonium carbonate is a volatile compound that tends to decompose at temperatures below 50°C. Although encapsulation in a suitable capsule of the salt protects the compound from escaping the capsule, special capsules with thick shell are needed. In this experiment, fine powder of ammonium carbonate was mixed in castor oil, mineral oil and silicone oil to for a white pasty material that can be injected. The mixtures were loaded in an open glass vial and placed in an oil bath at 40, 60 and 80°C and the weight loss was determined at certain time points. As reference, fine powder of ammonium carbonate was placed in a glass vial and placed at the same temperatures. The results are given in Table 1:

Table 1: weight loss of ammonium carbonate samples when placed in oven at

60 and 80°C.

Mineral oil was found the best medium to stabilize ammonium carbonate. This mixture has an advantage to be used for easy loading capsules or containers with this indicator.

Example 5: preparation of microcapsules

Microcapsules loaded with indicator precursors are prepared by coating powders of the indicator or its precursors with a polymer coating by pan coating. However, due to the different shape and size of the pure salts (ammonium carbonate, potassium iodide, and ammonium chloride) a non-uniform coating is obtained, although for practical use these coated articles are suitable for temperature sensitive indicator release.

More uniform coated particles are prepared by absorbing a concentrated solution of heat stable precursor for the indicator (ammonium chloride, potassium iodide, CuSO/t, ammonium acetate, etc) into porous microparticles and evaporation of the solvent (water or water mixtures) by freeze-dry or air evaporation. The microcapsules were then coated with a polymer containing a porogen or a polymer that melt at the desired temperature, i.e. 80°C. In a typical experiment, commercially available dry hydrogel beads of different sizes (used for retaining water in plants or hydrogels made from crosslinked hydroxyl ethyl methacrylate) where placed in a concentrated solution of ammonium chloride (30% w/v in water) and allowed to swell. After 20 hours, the swollen beads (can absorb 10 times solution per the dry bead) are lyophilized or put in the oven to evaporate the water. The spherical dry particles are coated with polyurethane containing 20% w/w alloy or acrylamide that melt at 80°C by either pan coating or by dip coating where the dry beads are placed in a pan coating device and a solution of the Pellethane (5% in THF) containing 20 %w/w fine powder of alloy is sprayed onto the dry beads while mixing in the spinning pan container. The thickness of the coating is determined by the amount of polymer solution sprayed onto the particles. Another possibility is coating with a polymer that melt or change its properties at the desired temperature, for example copolymers of alkyl methacrylates or copolymers of butylene-succinate-adipate (Biotechnol. J. 2010, 5, 1149-1163), that can be selected based on their melting point. These polymers are soluble in common solvents, dichloromthane, chloroform, ethyl acetate or tetrahydrofuran (THF). These polymers are coated onto the beads by pan coating, fluidized bed or other coating systems used in the pharmaceutical industry. This method for making microbeads loaded with indicator precursors can be used for a single agent such as ammonium chloride that upon mixing with another compound forms the indicator. Thus, potassium iodide, KI, is loaded in the beads and mixed with a powder of cupper or iron sulfate (CuSO/t) where upon the exposure of the KI from the beads at the desired temperature and interaction of KI with the oxidizing agent (CuSO/t), iodine vapors are formed. The beads or the polymer coating may be loaded with a colorant where upon disruption at the desired temperature, the site of application is marked with a color that allows identification of the hot spot releasing the indicator. An alternative method for making uniform particles loaded with indicator salts is by interface polymerization-encapsulation. In this method, a concentrated aqueous solution of the agent to be encapsulated, i.e. ammonium acetate, KI, CuSO/ _t , containing dissolved radical source such as ammonium persulfate and surfactants such as Tween and Span. This aqueous solution was dispersed into silicon oil containing methacrylate monomers such as methyl, ethyl or butyl methacrylate. The mixture was vigorously mixed to form a uniform dispersion. The mixing was continued while surface polymerization is taking place. After 3 days mixing at room temperature, the particles were separated and left to dry at room air to result in methacrylate capsules loaded with the desired salt.

The particles of one component were mixed in a solution or dispersion that contain the second component which upon contact form the indicator gas. For example, particles loaded with KI are mixed in a non-aqueous dispersion or CUSO4 and sprayed or paint onto a hot spot which upon heating to 80°C, the coating of the KI particles disrupt and the KI interacts with the CUSO4 to form iodine vapors that are detected by the iodine sensor.

Example 6: Disruption of capsule by accumulation of internal pressure

A metallic capsule as described in Example 2, was loaded with the indicator precursors along with a pressure forming agent in an amount that upon heating at a desired temperature, i.e. 80°C, disrupt the capsule seal to allow evaporation of the indicator/s.

In a typical experiment, 60 mg of ammonium carbonate is loaded in the metallic capsule and 5 mg of benzoyl peroxide powder is added to the capsule. The capsule is sealed with epoxide glue at a thickness of 1 mm that allows disruption of the capsule upon heating at 80°C due to the accumulation of carbon dioxide within the capsule that apply pressure on the seal until disruption.

Example 7: Preparation of microcapsules

Highly porous Polystyrene beads, porous PMMA beads, Carbopol powder, porous silica microparticles or polyurethane microparticles of a particles size in the range of 200-1000 microns, are immersed in a concentrated solution of NaOH or KI or ammonium chloride for 24 hours. The socked particles are isolated by light centrifugation or decantation and lyophilized to form particles that are loaded with either NaOH or KI or ammonium chloride. The flowing particles are added into a temperature controlled pan coating and polyurethane or ethylene vinyl acetate in dichloromethane dispersion containing 20% w/w of fine powder of 15 micron in size 79°C melting alloy. The uniform dispersion is sprayed onto the rotating particles while solvent is evaporating out. The free flowing capsules retain the incorporated agents. These particles are mixed with the complementary salt that upon heating at 80°C are exposed to mix with the complementary reagent to form the indicator in situ. Thus, when particles loaded with NaOH are mixed with ammonium chloride at room temperature, no ammonia is formed. However, upon heating the mixture to 80°C, ammonia is released due to the reaction between the based and ammonium chloride.

Example 8: Iodine loaded sponges

Adsorption of Iodine onto the PU Sponges in the Solution: 10 round PU sponge units, with each unit containing an average weight of 4g, 9 cm diameter, and 6 mm thickness were immersed in 1 liter solution containing 50g of elemental iodine. The PU sponges were kept in the solution with shaking at room temperature for 24, 48, and 72 hours to reach equilibrium. The solvents examined for the adsorption of iodine were hexane, chloroform, ethanol and water. Solutions in which elemental iodine was not completely dissolved were kept to reach dissolution / adsorption equilibrium. A potassium iodide aqueous solution was prepared by dissolving in water (Lugol). The PU sponges were carefully squeezed and dried at room temperature in a fuming hood for 24 hours.

Iodine adsorption on PU Ssponges Using Ssublimation Pprocess: Iodine impregnation on the PU sponges without solvents was tested by sublimation process. The PU sponges with the above mentioned specifications were placed in desiccators containing elemental iodine with no direct contact between the PU sponges and the elemental iodine. The diffusion rate of iodine vapor into the PU polymers was controlled by varying the temperature using a heating plate with an oil bath.

The percentage of iodine captured by each of the PU sponges (from the solution that was calculated by dividing the iodine content of each complex by the initial related polymer carrier Iodine content) was determined by dissolving 50 mg of sponge sample in 20 mL ethanol followed by titration with 0.1 volumetric solutions of sodium thiosulfate.

EVA Coatings on Iodinated PU Sponges: Different sets of iodinated PU sponges with one or two layers of coating were prepared using a pressurized spray mechanism with 5% (w/w) EVA in chloroform in the fuming hood; they were then left for drying. The weight of the EVA coated on the IPU sponges was measured by the difference in weight before and after spraying. The effect of EVA coatings on the porosity size of IPU sponges was studied using a light microscope. EVA coating did block the iodine evaporation from loaded sponges. Heat pore forming alloy 15 micron size powder was added at 10% loading per EVA polymer and sprayed onto the sponges to form a seal that if disrupted when heated to 80°C while releasing the iodine molecules. Particles of 50 microns or films at any shape are loaded with iodine and coated for use as indicator. These iodine containing polymers can be farther loaded in a retaining capsule that upon heating burst and release the iodine content.

Examples 9: Capsules prepared from plastic for aluminum foil welded or glued with a polymer that melt at a desired temperature, for example 80°C.

Plastic films or metal based foils of different thicknesses are welded or glued into capsules of the appropriate size (3x5x1 mm) by welding or gluing using a composition that melt at 80°C.

Tubes made of aluminum or cupper foil of 2-5 mm diameter and 20-50 micron wall thickness where cut into 4 mm tubes and glued or welded with a polymer composition that melt at 80°C. These capsules were loaded with the marker solvent (isopropanol, butanol, etc) either during production of capsule or injected into the sealed capsule. The capsule was mounted onto the hot spot using glue that melt above 100°C.

For the above capsules, high temperature glues and welding compositions can be used, however, a certain opening sealed with low temperature composition suitable for rapid melting and release of its content upon reaching 80oC.

Glues that adhere to metal surface and polymer surface are commercially available, they are based on acrylic polymers, epoxides and even silicon. Example 10: release of ammonia from heating of ammonium sulfite

Ammonium sulfite powder or past in mineral oil (50% w/w) were loaded in plastic or metal capsule at an amount of 50 to 100 mg and sealed with epoxide glue containing 40% w/w porogen (alloy or acrylamide). Upon heating at temperature above the melting temperature of the porogen, ammonia was released.