Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/50—Sympathetic, colour changing or similar inks
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
  • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
  • G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
  • G01N21/81—Indicating humidity

Definitions

• the invention relates to humidity indicators subjected to antistatic surface treatments and printed with particular graphic solutions which use inks with dissipative characteristics.
• the entire surface of the humidity indicators thus obtained is dissipative, and they are useful to measure the humidity present in environments which require protection against humidity and electrostatic discharges, or contact with materials sensitive to electrostatic discharges.
• the humidity indicator cards used to indicate the humidity present in industrial packing are manufactured by impregnating the paper with particular substances that change colour when a given humidity level is reached, such as cobalt salts and in particular CoCl 2 , copper salts such as CuCl 2 , CuBr 2 , and others.
• the indicator cards can be calibrated to measure a wide range of environmental humidity by varying the concentration of salts in the paper or substrate.
• Fibreglass, plastic, fabric or Tyvek can be used instead of paper.
• said materials can be used as media suitable to make desiccant bags with both a dehydrating and a humidity-indicating function. Said desiccant bags present an area that changes colour when a given humidity level is exceeded, or rather when the desiccant properties of the bag are depleted. All the materials used to make humidity indicators, such as paper, fabrics, non-woven fabrics, Tyvek, polymer media and fibreglass, act as electrical insulators and are electrostatically charged in the absence of humidity.
• Humidity indicator cards and the humidity indicators currently on the market in general, therefore cannot be used in direct contact with products that need to be protected against both humidity and electrostatic discharges. This situation often occurs in the case of the packing used in the electronic industry, in which both humidity indicators and desiccant salts are used, reducing the relative humidity to under 5% shortly after the packing is closed.
• the environmental conditions in which humidity indicators operate are consequently particularly restrictive, requiring:
• the present invention solves said problems.
• special types of printing ink with dissipative characteristics have been used to solve this problem, together with particular graphic solutions which dissipate the electrostatic charges that form on the medium in the presence of low humidity levels in areas in which antistatic substances cannot be used.
• the surface resistance of the material must be between 10 4 and 10 11 ⁇ , while its resistivity must be between 10 5 and 10 12 ⁇ in order to give dissipative characteristics as defined in the technical specifications used in the industry.
• the electrostatic charges must be dissipated in less than two seconds when the material is discharged (more commonly known as being "earthed"). This measurement is performed on material conditioned for 72 hours at 12% relative humidity and 23 0 C.
• the electronic components must be stored in hermetically sealed packaging in direct contact with desiccant bags able to reduce the relative humidity to under 5%, as established by reference standard JEDEC J-STD-033A. Antistatic humidity indicators must therefore be dissipative even at a relative humidity level of under 5%, so as not to damage components sensitive to electrostatic discharges.
• the humidity indicator devices on the market are constituted by a medium on which substances that change colour in the presence of humidity are deposited. If the medium is constituted by paper, said device is called a "humidity indicator card".
• the generic humidity indicator card presents an area (1) impregnated with substances that change colour in the presence of humidity. This area is bounded by printed zones (2), while the remainder of the card has the natural colour of the paper and possibly a printed logo and instructions (3).
• a humidity indicator card is preferably considered dissipative if the surface resistance of the material is in the acceptance range all over its surface (Zone (1)+Zone (2)+Zone (3)).
• the zones of said indicator cards in which substances that change colour in the presence of humidity (3) are not deposited can be rendered antistatic on the surface by using quaternary ammonium salts with the formula N + R1R2R3R4.
• X " wherein R1-R4, which are equal or different, represent alkyl groups C1-C20, possibly substituted by hydroxy, alkenyl, benzyl, phenyl, alkylamidoalkyl or alkenylamidoalkyl groups, and X is a halide, nitrate or sulphate anion, or a mixture thereof.
• Polyglycols or polyols such as glycerol or esterified polyols such as monoglycerides, diglycerides and triglycerides and their derivatives can be used for the same purpose.
• substances such as glycerol are deposited on the surface of the humidity indicator, they make the surface antistatic, and when they are mixed with other antistatics, they produce synergic and improved effects.
• Glycerol and polyols in general also demonstrate a synergic and improving effect on performance when they are mixed with printing varnishes containing graphite and carbon black; the surface resistance of a sheet of paper printed with these varnishes is in the dissipative material range.
• the surface can be rendered dissipative by crisscrossing it with thin transverse lines or squares printed with an ink containing graphite, carbon black or silver.
• the preferred medium for making a humidity indicator is paper, preferably impregnated with copper or cobalt salts.
• At least one quaternary ammonium salt as defined above preferably having one of groups R1-R4 selected from among an alkyl or alkylamidoalkyl group, having 6 to 20 carbon atoms such as stearamidopropyldimethyl-2- hydroxyethylammonium nitrate, can be used as a particularly efficient antistatic agent on a paper medium.
• quaternary ammonium salts which are particularly advantageous as antistatics, wherein at least one of groups R1-R4 is an alkenyl or alkenylamidoalkyl group which has 6 to 18 carbon atoms and contains at least two conjugated double bonds, such as the salt known by the trade name of ethyldimethyl soya alkyl ethyl sulphate, can be used on the indicator medium constituted by Tyvek or certain non- woven fabrics.
• quaternary salts of the first type are preferred when the material that constitutes the medium of the humidity indicator card is selected from among cellulose, viscose, ABS and polyacrylates, whereas quaternary salts with conjugated unsaturations are preferred when the substrate of the humidity indicator card is selected from among fabrics manufactured with spunbonded technology (Tyvek ® ), multicomponent fabrics containing polyethylene and polyethylene-terephthalate in which the short fibre is held together by fusion (without added binder), or multicomponent fabrics, polyethylene terephthalate, polypropylene or Nylon 6, manufactured with a continuous- fibre filament and multilayer structure.
• the two types of quaternary salt can advantageously be mixed together.
• the dissipative characteristics of the indicator card must also be extended to the areas (1) impregnated with substances that change colour in the presence of humidity, and it has been found that this can be achieved by using inks containing graphite, carbon black or silver powder.
• inks containing graphite, carbon black or silver powder When these products, which are present on the market for particular applications, are used to print a surface, it becomes conductive or dissipative, depending on the composition of the varnish, the regularity and type of surface substrate, and the printing quality.
• Objects introduced into environments which require protection against electrostatic discharges must not be conductive, but dissipative.
• the indicator cards according to the invention have the dual function of indicating the humidity present in the packaging and not causing electrostatic discharges in the packaging.
• the surface resistance of the whole indicator area is between 10 4 and 10 11 ⁇ , so the humidity indicators obtained with the technologies described have dissipative characteristics.
• the choice of making the entire surface of the indicator dissipative by using a printing varnish containing graphite and carbon black or silver is a simple, effective solution compared with the risk of incompatibility between antistatic substances and humidity-indicating substances, or with the use of substrates containing conductive fibres.
• surface treatment is not influenced by the presence of adhesives in the paper that bind the short fibres.
• Printing can also be performed with dissipative ink on any type of paper or non-woven fabric (NWF), regardless of the technology used to make it.
• NWF non-woven fabric
• this technology is a surface treatment, it allows the use of a correct quantity of graphite designed to control the dissipation of electrostatic charges.
• the varnishes used to print the paper can be modified to obtain printing, and consequently surfaces, with dissipative surface characteristics. If the use of a varnish causes excessively conductive printing, acrylic resins or fatty resins can be added to the varnish to reduce the surface conductivity of the printed page and obtain dissipative characteristics.
• the varnishes can be rendered dissipative by direct addition of graphite, carbon black or silver powder, or polyols such as glycerol.
• One or more substances with colours in the UV or visible light spectrum can be added to the quaternary antistatic agents and polyols; examples are fluorescein and its derivatives such as aminofluorescein, "alkyl substituted perylene dye”, “alkyl substituted naphthalimide dye”, or products known by the trade names fluorescent perylene green, fluorescent perylene orange, fluorescent perylene yellow, fluorescent perylene red and fluorescent naphthalimide violet.
• both the customer and the manufacturer can perform a colorimeter test to check that the treatment has been performed on the humidity indicator, independently of direct measurement of the characteristics of the sample.
• Dyeing the covering with a mixture of antistatic and a dye detectable under UV light produces humidity indicators of the same colour as the original medium, and a UV lamp can be used to check whether the treatment has been given evenly.
• a quaternary antistatic compound which is coloured in the UV or visible spectrum can also be used. It has been found that humidity indicators with dissipative characteristics can be obtained by treating the surface of the medium, by spraying or an equivalent technique, with solutions or suspensions of antistatic agents in a wide range of concentrations, which are not critical in themselves, depending on the speed of the manufacturing process and the composition of the covering material.
• the quantity of substance deposited per surface unit of the covering being equal, the increase in concentration of quaternary antistatic, used alone or in a mixture, improves the dissipative performance of the indicator surface. Moreover, depending on the composition of the medium used, the structural characteristics of the surface and the treatment system, it has been found that it may be necessary to treat 1 square decimetre of covering with at least 0.5 g of solution at a concentration of 10%-90% in weight of quaternary antistatic, glycerol, or mixtures thereof.
• the concentration of graphite in the varnish can range between 5% and 50% in weight, in the presence of quantities of acrylic resin or fatty resins ranging between 10% and 50%.
• glycerol or polyglycols used in various concentrations in weight in ink improve the dissipative characteristics of the printed surface, presenting a synergic effect with the antistatic action of the graphite or conductive materials contained in the varnish with which the treatment is performed.
• these results can be obtained by using paper with a smooth, compact surface and a printing process that produces a compact, even print.
• the surface thus printed presents dissipative characteristics which would have been insulating in the absence of glycerol.
• Treatment with glycerol or polyglycols can also be performed after the printing process, and presents similar synergic effects and improvement in the surface antistatic characteristics.
• the treatment was performed by spraying 0.3 g of a hydroalcoholic solution containing 35% in weight of ethyldimethyl soya alkyl ethyl sulphate.
• the indicator thus obtained was enclosed for 72 hours in heat-sealed steamproof packaging containing desiccant bags.
• the humidity indicator was thus dehydrated, and the internal humidity level in the packaging proved to be under 5%. Under these conditions, the antistatic treatment was found to make the indicator dissipative even in the presence of low humidity levels.
• the surface of the untreated zone (1) has insulating characteristics, which can be cancelled out if the card is printed with a dissipative or conductive ink able to give the printed surface dissipative characteristics.
• EXAMPLE 2 A dense lattice was traced on both sides of the card using an ink described by the manufacturer as "conductive black”. The lines were printed with ink having dissipative characteristics, one-tenth of a millimetre thick, with the sides of the indicator joined, and approx. 3 mm apart: this graphic solution, together with the use of a conductive ink, rendered the printed surface dissipative.
• the sample thus produced presented a surface resistance in the range of dissipative materials after 72 hours' conditioning in an environment with a humidity level of under 5%.
• the humidity indicator card proved to be dissipative all over its surface, including the area impregnated with substances that change colour in the presence of humidity.
• the surface resistance of a humidity indicator card that uses this kind of graphic solution falls into the conformity range of dissipative materials due to the use of a conductive ink, together with other factors such as the compactness and smoothness of the paper surface and the homogeneity and continuity of the printing.
• This printing technology can replace or be additional to treatment with quaternary ammonium salts and glycols.
• Humidity indicators which use as substrate a special paper based on short viscose fibres and PET fibres, with a polyacrylic as binder, were surface treated.
• a first humidity indicator was treated with 0.3 g per square decimetre of a 25% solution of ethyldimethyl soya alkyl ethyl sulphate
• a second humidity indicator was treated with an equal quantity of stearamidopropyldimethyl-2-hydroxyethylammonium nitrate
• a third indicator was treated with 0.3 g per square decimetre of a 25% mixture in weight of equal parts of said two antistatics.
• Humidity indicators can be rendered dissipative all over their surface by employing a printing process that uses dissipative inks.
• Inks which impart insulating characteristics to the surface on which they are printed are available on the market. Inks which give surfaces conductive characteristics are also available, but the surface resistance of the zones printed with the humidity indicator is affected not only by the type of ink (conductive or insulating), but also by the type of medium (paper, Tyvek etc), the structure, porosity and surface continuity of the material used to make the humidity indicator, and the type and quality of printing. For example, offset printing technology does not always produce a quality level sufficient to deposit the necessary amount of conductive ink on the surface and consequently obtain sufficient dissipative characteristics under the dry conditions in which the humidity indicator is required to operate.
• Dissipative humidity indicators have been produced by printing the surface of the indicator with inks able to give it dissipative characteristics and using lined or squared graphics or negative printing, ie. white lettering on an all-black background.
• Dissipative inks were obtained by introducing 30% in weight of micronised graphite paste with a particle size of between 0.05 and 5 microns into an offset printing ink.
• a humidity indicator was printed with an ink obtained by mixing 30 g of graphite paste at a concentration of 35% with 70 g of offset printing ink. The indicator was printed on both sides, paying particular attention to the quality and continuity of printing. The indicator was placed in closed, heat-sealed packaging for 72 hours, so that the humidity level in the packaging fell to below 5%, as under real conditions. The measurements demonstrate that the surface characteristics of the indicator are dissipative.
• the surface of the paper is not always smooth and easily printed; for test purposes, a second card, made from cellulose-based absorbent paper with a neutral pH, such as DEO paper made by the Cordenons paper mill, was printed with a conductive ink for offset printing machines.
• the measurements demonstrated that the surface characteristics of the indicator covering were not dissipative, although a conductive ink was used.
• This experiment proves that the characteristics and quality of printing can require the use of a particularly conductive ink which makes up for the problems caused by printing on a non-uniform surface.
• An improvement in the characteristics of the ink can be obtained by adding 10 to 60% glycerol; particularly good results were obtained with a 30% glycerol mixture.
• the surface of the card proved to be dissipative, and the surface resistance was lower than if only glycerol-free ink had been used.
• An increase in the concentration of graphite, carbon black or glycerol in the ink is directly proportional to the increase in surface conductivity of the printed product.
• an increase in the concentrations of the components of the ink, such as resins increases the surface resistance. If these parameters are adjusted, black ink can be given the dissipative characteristics required to print the graphics that enable electrostatic charges to be dissipated throughout the area of the humidity indicator.
• These humidity indicators can be used in environments that require protection against electrostatic discharges. Surface resistance was measured by applying a voltage of 100 V. The electrostatic charge decay time was measured in an environment with under 12% R/H and 23 0 C; the sample was charged with 1100-1200 V, and the time taken to reach 100 V, after contact was established between the bag and earth, was measured. The same measurements can be repeated at 12% R/H and 23 0 C, with similar results.
• bags which present charge decay times of under 2 seconds, and surface resistance of between 10 4 and 10 n or resistivity between 10 5 and 10 12 can be considered dissipative.

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Citations (3)

• 2005
  • 2005-03-11 IT ITMI20050390 patent/ITMI20050390A1/it unknown
• 2006
  • 2006-02-16 WO PCT/EP2006/001397 patent/WO2006094610A1/en not_active Application Discontinuation

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