EP1340073A1 - Humidity paper indicators with coloured support - Google Patents

Abstract

A humidity indicator comprising a support coloured or impregnated with a copper halide or other salts capable of releasing Cu++ ions and halide ions and one or more dyes.

Description

HUMIDITY PAPER INDICATORS WITH COLOURED SUPPORT

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. Technological Background

Humidity paper indicators industrially used are prepared by impregnating paper sheets of various sizes with humidity-sensitive substances.

These indicators are used in a number of fields for indicating the humidity conditions present inside packagings and pointing out any penetration of humidity inside products, articles, apparatuses which need protection during transportation. 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.

In Amendment XXV of European Directive 67/548, the cobalt chloride used hitherto in the field of desiccant materials in non-woven fabrics, inside blue silica gel or on labels as a humidity indicator has been relabelled and reclassifϊed.

The consequences of this regulation include a series of warnings as regards the handling and use of products containing inorganic cobalt salts.

Since, in indicating labels, the coloration is given by cobalt chloride at a certain concentration, the problem arises of identifying one or more components capable of replacing cobalt chloride in its function as a substance capable of changing colour according to the humidity conditions.

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. 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.

For example, by exposing the label in a climatic chamber and varying the relative humidity, 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.

Depending on the concentrations of the active principle and of the synergist in the mixture used for the impregnation, a material that is more or less sensitive to humidity can be obtained.

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;

- optional 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;

- organic and inorganic dyes, whose colours act on the shades obtained when using only the synergists and the active principles, improving the resulting chromatic contrast. Examples of 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.

It is generally possible to prepare humidity-indicating labels starting from mixtures containing less than 10 g per litre of the active principles and the same amount by weight of the synergist, up to the using solutions containing 5 times the amount of active principle and 7 times the amount of synergist containing halide ions.

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.

Using as active ingredient 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.

The following examples illustrate the invention in greater detail. Example 1 A) 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. B) 1.5 g copper chloride dihydrate + 3.0 g of magnesium chloride hexahydrate + 100 ml of water-alcohol solution + dye. The dye can be selected from:

• light blue so as to give background colour Reference Pantone 317 U, or

• red so as to give background colour Reference Pantone 196U, or • green so as to give background colour Reference Pantone 331U or 365U.

C) 1.5 g copper chloride + 3.0 g of sodium chloride + 100 ml of water- alcohol solution + dye as preferred.

D) 1.5 g copper chloride + 3.0 g of potassium chloride + 100 ml of water- alcohol solution + dye as preferred.

In particular, if the selected background is light blue, the resulting indicator will be yellow/green when dry and light blue when humid.

On the other hand, if the selected background is pink, 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.

The use of these 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.

The use of 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.

The label exposed to certain humidity conditions will still have yellow colour, whereas beyond a defined humidity value it will change to the background colour due to the dye. It is therefore evident that said label will be calibrated for indicating the humidity value at which it undergoes colour change from its colour when dry to its colour when humid. Example 2 The effect of other synergistic halides will now be tested in the presence of the same active ingredient copper chloride and of the same background, coloured for example in red.

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.

A) 1.2 g copper chloride dihydrate + 3.6 g of magnesium chloride hexahydrate + 100 ml of water/alcohol solution + red dye.

B) 1.2 g copper chloride + 5 g of potassium bromide + 100 ml of water/alcohol solution + red dye.

C) 1.2 g copper chloride + 5 g of sodium bromide + 100 ml of water/alcohol solution + red dye.

D) 1.2 g copper chloride + 100 ml of water/alcohol solution.

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. Furthermore, 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.

In particular, since 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.

By varying the amounts or the proportions between active ingredient, synergist and dye, colour changes may be modulated to increase the sensitivity of the indicator and to obtain different colours of the indicator in dry or humid conditions. Example 3

An indicating label was immersed in a solution of 2 g of copper sulfate pentahydrate + 3 g of potassium bromide in 100 ml of aqueous mixture. The colour of the labels in dry conditions is dark/black.

The described solution may be diluted to obtain all the dark/black shades and different sensitivities to humidity.

Analogously, 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. In this case, in the presence of synergistic salts based on the bromide ion, the dark/black colour is strengthened to obtain black.

Again, by impregnation with copper bromide and synergistic chloride salts, humidity indicators can be obtained with brown colour up to the yellow/brown colour typical of indicators obtained using solutions containing chlorides.

The addition of dyes to the solutions used improves the chromatic sensitivity to humidity.

Examples of said solutions are: A) 1.7 g of copper bromide + 100 ml of water.

B) 1.7 g of copper bromide + 1 g of potassium bromide + 100 ml of water.

C) 1.7 g of copper bromide + 1 g of sodium bromide + 100 ml of water. D) 1.7 g of copper bromide + 1 g of sodium bromide + 100 ml of water + dye as preferred. The dye can be selected from: • light blue so as to give background colour Reference Pantone

317U, or

• red so as to give background colour Reference Pantone 196U, or

• dye green so as to give background colour Reference Pantone 331U or 365U. E) 1.7 g of copper bromide + 1 g of magnesium chloride hexahydrate + 100 ml of water + dye as preferred.

The differences in the colour of the indicating label impregnated with the solutions consisting of the active ingredient copper bromide alone (A) were compared with those of labels obtained by impregnation with the solutions B, C, D, E.

Solutions B and C provide indicating labels which have stronger dark colour in dry conditions than those obtained using solution A.

With the solution D, the improvements induced by the dye may be observed. Using the solution E, the differences induced by both the dye and the chloride ion synergist are observed, with the corresponding changes of the indicator shades.

Claims

1. A humidity indicator comprising a support coloured or impregnated with a copper halide or other salts capable of releasing Cu⁺⁺ ions and halide ions, and one or more dyes.

2. A humidity indicator as claimed in claim 1, further containing synergistic salts.

3. A humidity indicator as claimed in claim 1 or 2, in which the copper halide is selected from copper chloride, bromide, iodide or fluoride.

4. A humidity indicator as claimed in claim 3, in which the copper halide is copper bromide or copper chloride.

5. A humidity indicator as claimed in any one of claims 1 to 4, in which said support is a solid material.

6. A humidity indicator as claimed in claim 1, in which said support is paper, a natural fabric or a non- woven fabric.

7. A humidity indicator as claimed in any one of claims 2 to 6, in which the synergistic salts are selected from magnesium, sodium, lithium, calcium, potassium, barium and iron chlorides, bromides, fluorides, iodides, nitrates, dichromates, sulfates.

8. A humidity indicator as claimed in any one of the above claims, in which dyes are selected from synthetic organic dyes, natural dyes, vegetable dyes, mineral dyes, and coloured pigments or mixtures thereof, preferably colours selected from red, green, light blue or mixtures of the three primary colours red, yellow and blue.

9. A humidity indicator as claimed in any one of the above claims, in which dyes are mixed in solution with the active ingredient and the synergists, or the dye is placed directly on the paper as a background causing a pink, light blue or light green colour.