Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
  • G01N31/22—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators
  • G01N31/222—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators for investigating moisture content

Definitions

• the present invention relates to humidity paper indicators used for indicating the absorbent capacity of a desiccant material or more generally for evidencing the humidity conditions of the ambient in which the indicator is placed.
• Humidity paper indicators industrially used are prepared by impregnating paper sheets of various sizes with humidity-sensitive substances.
• Indicating labels are also used in order to indicate the desiccant activity of the material; furthermore, they are used during packaging of products based on desiccant clay, white silica gel, allumina and molecular sieves and more generally for all those desiccant materials which show no evident colour differences between their maximum activity and depletion of the desiccant power.
• a portion of the area of the indicating labels commonly used in industry is impregnated with a cobalt chloride solution. This area changes colour from blue to pink depending on the humidity present in the medium in which the label is placed; the colour change is reversible and thus allows the label to be regenerated for further use.
• the concentration of the cobalt chloride solution used for colouring the indicating labels determines the sensitivity to the various humidity contents.
• the colour change should ideally be marked and easily distinguishable even with low relative humidity concentrations. Disclosure of the invention
• the present invention relates to humidity indicators comprising a support impregnated with copper salts.
• These salts can be copper chloride, copper bromide, copper iodide or copper fluoride. More generally, copper (II) halides, obtained by using either the pure salts or a mixture of salts containing the Cu + ion with a generic anion and salts containing the chloride, bromide and iodide ions with any cation, may be used.
• the above described mixture can be added with salts whose anions form with copper (II) cations coloured salts, such as sulfates, nitrates, chromates, permanganates and the like, which act as coloured background for a better chromatic evaluation of the humidity.
• salts whose anions form with copper (II) cations coloured salts, such as sulfates, nitrates, chromates, permanganates and the like, which act as coloured background for a better chromatic evaluation of the humidity.
• Organic or inorganic dyes acting as a colour background enhancing the colour contrast indicating the change of humidity conditions may also be used.
• the described salts may be mixed to provide solutions used for impregnating the support material, which is immersed therein.
• the paper material impregnated with the mixture of the invention acts as humidity indicator.
• An indicating label is obtained by using a paper support.
• the humidity-sensitive active principle have different colours depending on the humidity they are exposed to and on the water content of the chemical environment of the active principle. Such feature allows to prepare humidity- indicating labels which, according to the concentration of the active principle impregnating the paper, are more o less sensitive to humidity concentration and change colour, thereby indicating when the humidity threshold value they have been calibrated for has been exceeded.
• the values of humidity to which the indicator is sensitive may be evaluated through the colour changes of the impregnated area.
• the solution of copper salts, colour synergistic salts and background dyes of the invention may be used for impregnating parts of the materials used in the field of desiccants, such as non-woven fabrics or any material constituting the sachets containing the desiccants, in order to indicate the desiccant power of the sachet.
• the components of the humidity indicator of the invention are therefore:
• an active ingredient consisting of a copper halide, in particular copper chloride, copper bromide, copper iodide or copper fluoride;
• synergists which increase the colour of the active principles in both dry and humid conditions, and may either increase or decrease the sensitivity of the impregnated material to the relative humidity to which it is exposed;
• synergistic products include alkali and alkaline-earth metal salts, salts of transition elements, some of them being hygroscopic or deliquescent, in particular magnesium, sodium, lithium, calcium, potassium, barium, iron chlorides, bromides, fluorides and iodides, as well as potassium, lithium, calcium, magnesium, sodium and iron nitrates, dichromates and sulfates.
• Examples of anions introduced in the form of synergistic salts, which, in the presence of copper (II) ions, provide a background coloration to the area impregnated with the solution, thereby modifying the coloration caused by the active principle alone are bromides, dichromates, nitrates and sulphates.
• Dyes used in mixture with the above described substances include synthetic organic dyes, natural dyes, mineral dyes, vegetable dyes and pigments or mixtures thereof.
• the most suitable colours for the use according to the invention are red, which may provide more or less intense shades of pink, the chromatic scales of blue (in particular light blue), green and violet or the chromatic scales deriving from the mixture of the three primary colours.
• the indicating labels of the invention are obtained by soaking or spraying a paper support with aqueous-alcoholic or aqueous solutions containing the copper ion, the synergistic salts and the dyes according to the present invention.
• the paper is then dried with a jet of hot air or by heating in a normal oven at about 60°C for the time required.
• Tests have been carried out on solutions having various concentrations of the copper halide active principles alone or combined with the other synergistic salts, in mixture with different types of dyes in order to control the colour change as a function of the humidity to which the paper should be sensitive.
• the amount of dye used is a function of the desired background colour; the pink shade typical of cobalt indicators when exposed to humid medium may be reproduced by using the dye.
• Water or a water-ethanol mixture may be used for dissolving the components; alternatively, other solvents inducing solubilization of the used salts and dyes may be employed.
• the described solutions may be used on a number of different paper supports, or on natural fabrics, synthetic non-woven fabrics and in general on those fabrics used for preparing desiccant sachets, with application of a humidity indicating drop.
• copper bromide with synergistic salts containing bromides, such as sodium bromide without the addition of dyes, indicating labels may be obtained, following immersion, which have dark/black colour when placed in medium with humidity below a fixed value, whereas change to colourless or pale light blue when exposed to humidity above such fixed value.
• Example 1 1.5 g of copper chloride dihydrate + 3.0 g of magnesium chloride hexahydrate in 100 ml of water-alcohol mixture (70% water and 30% alcohol). No dyes are added.
• the dye can be selected from:
• the resulting indicator will be yellow/green when dry and light blue when humid.
• the resulting indicator will be yellow/orange when dry and pink when humid. Finally, if the selected background is light green, the resulting indicator will be yellow/green when dry and light green when humid.
• synergistic salts containing the chloride ion increases the chromatic contrast of the label obtained by impregnation and the use of different salts and amounts may result in different sensitivities to humidity. Similar results can be obtained by replacing magnesium chloride, potassium chloride or sodium chloride with other synergistic salts containing the chloride ion, such as lithium chloride or any metal chloride.
• a dye provides an increase in the contrast and different sensitivities of the indicator to relative humidity. Sensitivity to humidity of the label is evidenced by the change in colour from yellow when dry to the paper background colour when humid.
• a number of solutions (water/alcohol) of the active ingredient combined with other halide synergistic salts were prepared, in order to evaluate the different colours of the indicating labels prepared by impregnating them with the solutions.
• the procedure described above was followed, then the effects obtained by impregnation of the paper supports were tested.
• the indicators obtained by immersion in the solutions A, B and C, after drying with a jet of hot air or by heating in oven at 60/70°C, have more intense dark colour that those obtained with the solution D which contains no synergistic salts.
• the different sensitivities to atmospheric humidity and the different shades of colours deriving from the presence of synergists containing the chloride ion (A) or the bromide (B, C) ion may be evaluated.
• salts containing the bromide ion form copper bromide in solution, they can be used to obtain brown shades, whereas salts containing the chloride ion increase the yellow colour thus obtaining dark shades.
• the described solution may be diluted to obtain all the dark/black shades and different sensitivities to humidity.
• sodium bromide or any other salt containing the bromide ion, can be used as the synergistic salt.
• the same results are obtained directly starting from copper bromide.
• the dark/black colour is strengthened to obtain black.
• humidity indicators can be obtained with brown colour up to the yellow/brown colour typical of indicators obtained using solutions containing chlorides.
• Examples of said solutions are: A) 1.7 g of copper bromide + 100 ml of water.
• Solutions B and C provide indicating labels which have stronger dark colour in dry conditions than those obtained using solution A.

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Citations (6)

• 2000
  • 2000-12-01 IT IT2000MI002599 patent/IT1319669B1/it active
• 2001
  • 2001-11-28 EP EP01998819A patent/EP1340073A1/en not_active Withdrawn
  • 2001-11-28 AU AU2002221903A patent/AU2002221903A1/en not_active Abandoned
  • 2001-11-28 WO PCT/EP2001/013880 patent/WO2002044712A1/en not_active Application Discontinuation

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