Monitoring System Based on Etching of Metals

Abstract

Compositions, devices and processes related to etching of a very thin layer or fine particles of a metal are disclosed for monitoring a variety of parameters, such as time, temperature, time-temperature, thawing, freezing, microwave, humidity, ionizing radiation, sterilization and chemicals. These devices have capabilities of producing a long and sharp induction period of an irreversible visual change. The devices are composed of an indicator comprising a very thin layer of a metal (e.g., polyester film having an extremely thin, e.g., about one hundred Angstroms layer of aluminum) and an activator, e.g., a reactant, such as water, water vapor, an acid, a base, oxidizing agent or their precursors, which is capable of reacting with the said indicator. The indicator retains its opacity and metallic luster, e.g., silvery white, mirror like finish of aluminum layer for a long time. The activator destroys the indicator layer including the naturally formed oxide layer. The indicator layer does not have a matrix/binder. As the device becomes transparent from being highly opaque, any color, message or image printed under it become visible at a pre-determined time, thus making the device self reading. A sealing tape or large label made from an activator and an indicator can be used for sealing boxes and monitoring self-life of perishables inside it. Ink formulations composed of a metal powder and a proper activator can be used for monitoring several sterilization processes, such as sterilization with steam. When water is used as an activator, a thin layer of metals, such as that of aluminum can be used as steam sterilization or humidity indicator. The process can also be used for making patterns, printing plates, electronic circuits and RFIDs (radio frequency identification devices).

What is claimed is: 
     
         1 . A sterilization indicating system comprising a substrate having a metal indicator layer composed of a metal on its surface, and a layer of an activator or a precursor of said activator;
 wherein the thickness of the metal indicating layer if from 10 Angstroms to 0.01 mm, and wherein the metal indicator layer is destroyed when exposed to a sterilant to cause an irreversible change in opacity, reflectivity or electrical conductivity of the metal indicator layer;   wherein the sterilant is humidity, ionizing radiation, steam, ethylene oxide, plasma, formaldehyde, dry heat, hydrogen peroxide or a mixture thereof;   wherein the metal is aluminum, tin, zinc, copper, magnesium or iron; and   wherein the activator or the precursor is selected from the group consisting of carboxylic acids, carboxylic acid salts, phenols, polyols, amines, amine salts, halide salts and thiocyanate salts.   
     
     
         2 . The sterilization indicating system of  claim 1  wherein the metal indicator and the activator or its precursors are in a form of particles in a binder. 
     
     
         3 . The sterilization indicating system of  claim 1  further comprising a protective layer. 
     
     
         4 . The sterilization indicating system of  claim 1  wherein the metal indicator has an oxide layer. 
     
     
         5 . The sterilization indicating system of  claim 1  further comprising a patterned layer of a barrier material, wherein when the system? is activated, the barrier material protects certain areas selected by the pattern on the metal indicator layer, allowing the remaining metal indicator layer to create a message or at least one conductive path for an electronic device, or a metal pattern. 
     
     
         6 . The sterilization indicating system of  claim 5  further comprising at least one electronic chip or component connected to the conductive path. 
     
     
         7 . The sterilization indicating system of  claim 1  which has at least one message which appears as in color, word or symbol. 
     
     
         8 . The sterilization indicating system of  claim 1  which further comprises a system wherein an additional one or more layers are added to the system, wherein the additional layers are selected from a layer permeable to activator, a wedge shape layer permeable to activator, a reactive layer, a destroyable or degradable barrier layer, an expiration indicating layer, a tamper indicating layer, an activation indicating layer, a message or image creating layer, a separating layer, a removable layer, a disappearing layer, an activatable layer, a microencapsulated layer or a thermally printable layer. 
     
     
         9 . The sterilization indicating system of  claim 1  comprising an activator layer, said activator layer comprising an activator, or a precursor to said activator; and a permeable layer; wherein the time required for a change in the indicator layer or activation energy of the system is varied or adjusted by changing one or more of the parameters selected from the group consisting of: thickness of the activator layer; thickness of the metallic indicator layer; thickness of the permeable layer; concentration of the activator; concentration of the precursor; concentration of an additive in the activator; concentration of an additive in the permeable layer; nature of a solvent, surfactant or a catalyst; nature of the activator layer; nature of the indicator layer; nature of the permeable layer; nature of the additive; and nature of a reaction accelerator or retarder. 
     
     
         10 . A sterilization indicating system comprising a substrate having a metal layer on its surface;
 wherein the metal layer is composed of a metal or its alloy, with or without a naturally formed oxide layer, and optionally (a) an activator or its precursor, and (b) a polymeric binder, and   wherein the metal layer is capable of being destroyed when exposed to one or more sterilants selected from humidity, water, steam, ethylene oxide, aldehydes, oxidizing agents, plasmas of vapors or gases, dry heat and ionizing radiation, causing an irreversible change in opacity, reflectivity or electrical conductivity of the metal layer.   
     
     
         11 . The sterilization indicating system of  claim 10 , wherein the metal layer is (a) a continuous layer, or (b) particles dispersed in a polymeric binder layer, preferably the sterilization indicating system further has one or more layers selected from the group of an activator in the polymeric binder layer, a precursor for an activator in the polymeric binder layer and a polymeric protective layer; wherein said polymeric layers are permeable to the sterilant. 
     
     
         12 . The sterilization indicating system of  claim 10 , wherein the metal is selected from alkali metals, alkaline earth metals, transition metals, post transition metals, lanthanides and actinides metals and their alloys, preferably the metal is selected from aluminum, tin, zinc, copper, manganese, magnesium, nickel, cobalt, iron, indium, silver and their alloys; 
     
     
         13 . The sterilization indicating system of  claim 10 , wherein the activator or its precursor is selected from the group consisting of a base, acid, salt, chelate, organometallic, halide, oxide, nitrate, nitrite, phosphate, phosphite, phosphonate, silicate, sulfate, bisulfate, sulfite, sulfide, bisulfide, sulfonate, cyanate, cyanide, thiocyanate, acetylacetonate, carboxylate, percarboxylate, carbonate or bicarbonate, a mono, di and trivalent cation of a metal, cation of nitrogen, sulfur, alcohol, amide, amine, carbamate, ester, halocarbon, ketone, nitro, nitroso, oxime, phenol, urea, urethane and a mixture thereof. 
     
     
         14 . The sterilization indicating system of  claim 13  wherein the activator or its precursor is selected from the group consisting of ammonium bromide, ammonium thiocyanate, calcium chloride, copper chloride, copper ammonia complexes, lithium acetylacetonate, lithium chloride, lithium formate, potassium acetate, potassium benzoate, potassium bromide, potassium chloride, potassium ferrocyanide, potassium ferrocyanide, potassium formate, sodium acetate, sodium bicarbonate, sodium bromide, sodium carbonate, sodium cyanate, sodium diethyldithiocarbamate, sodium iodide, sodium metasilicate, sodium nitrate, sodium sulfite, sodium tetrafluoroborate, sodium tetraborate, sodium thiocyanate, sodium thiosulfate, tetraethylammonium bromide, tetrabutylammonium bromide, zinc chloride and a mixture thereof. 
     
     
         15 . The sterilization indicating system of  claim 10  which further comprises a system wherein an additional one or more layers are added to the indicating system, wherein the additional layers are selected from a layer permeable to activator, a wedge shape layer permeable to sterilant, a reactive layer, a destroyable or degradable barrier layer, an expiration indicating layer, a tamper indicating layer, an activation indicating layer, a message or image creating layer, a separating layer, a removable layer, a disappearing layer, an activatable layer, a microencapsulated layer or a thermally printable layer. 
     
     
         16 . The sterilization indicating system of  claim 10  wherein a time, temperature, time-temperature or activation energy required for a change in opacity or conductivity of the metal layer is varied or adjusted by changing one or more of the parameters selected from: thickness of the activator layer, thickness of the metal or the metal alloy layer, thickness of the metal oxide or the metal alloy oxide layer, thickness of the permeable layer, concentration of an additive, nature of a solvent, surfactant and a catalyst, nature of the metal or the metal alloy, nature of metal oxide or metal alloy oxide, nature of the permeable layer, nature of the additive and nature of a reaction accelerator and retarder. 
     
     
         17 . The sterilization indicating system of  claim 10  wherein the system is capable of providing an induction period caused by the destruction of the metal layer, the naturally formed oxide layer or both the metal and the oxide layers, which destruction is measured by a delay in a visual indication or change in conductivity of the metal or metal alloy layer. 
     
     
         18 . The sterilization indicating system of  claim 10  which has one or more messages in color, word, number, barcode or symbol on one or both the sides of the metal layer. 
     
     
         19 . The sterilization indicating system of  claim 18  which contains at least two messages wherein a first message of said two messages does not start to appear at a same time as a second message of said two messages, preferably a first appearing message indicates a status or quality of an item before a sterilization treatment of the item and a second appearing message alone or in combination with the first appearing message indicates a status or a quality of the item after the sterilization treatment, most preferably the first appearing message indicates un-doneness, not-processed, non-usability, non-acceptability, untreated, unexposed or non-sterile and the second appearing message alone or in combination with the first appearing message indicates doneness, processed, usability, acceptability, treated, exposed or sterile. 
     
     
         20 . The sterilization indicating system of  claim 10 , wherein the metal layer is an antenna of a RFID having at least one readable RFID electronic chip and at least a portion of the antenna or the whole antenna is covered with a layer of an activator or a precursor for an activator. 
     
     
         21 . The sterilization indicating system of  claim 10  comprising a sterilization indicating ink composition;
 wherein said ink comprises particles of a metal or its alloy, with or without a naturally formed oxide layer, a binder permeable to a sterilant, and water or an organic material; 
 wherein when the particles of the metal or its alloy are capable of being destroyed when exposed to a sterilant, causing an irreversible change in opacity, reflectivity, or electrical conductivity of the metal or the metal alloy. 
 
     
     
         22 . A process for making a sterilization indicating system comprising:
 forming a metal layer on a surface of a substrate wherein the metal layer is composed of a metal or its alloy, with or without a naturally formed oxide layer, and optionally (a) an activator or its precursor, and (b) a polymeric binder;   wherein when the metal layer is exposed to one or more sterilants, the metal layer is destroyed;   wherein the sterilants are selected from the group consisting of humidity, water, steam, ethylene oxide, aldehydes, oxidizing agents, plasmas of vapors or gases, dry heat and ionizing radiation causing an irreversible change in opacity, reflectivity or electrical conductivity of the metal layer.