A wetness indicating hot-melt adhesive which changes color quickly in response to the presence of moisture is disclosed which contains 20 to 70 wt. % of polymer, 35 to 100 wt. % of which is water sensitive polymer; 27 to 60 wt. % of organic acid which is selected from a high acid number fatty acid or a combination of a high acid number fatty acid and other high acid number organic acids; 0 to 30 wt. % of water soluble wax and a wetness indicating agent which changes the color of the composition rapidly in response to moisture therein.

FIELD OF THE INVENTION 
This invention relates to wetness indicators. More specifically this 
invention concerns wetness indicating hot-melt adhesion compositions. 
BACKGROUND OF THE INVENTION 
Hot melt adhesives are well known. Generally, hot-melt adhesives are 
applied by melting the adhesive composition and applying a coat of the 
molten adhesive layer on a substrate. The coated material is then cooled 
to harden the adhesive layer and is ready for storage. Among the hot-melt 
adhesives that have been found useful and economically important are 
remoistenable hot-melt adhesives and remoistenable pressure-sensitive 
hot-melt adhesives. 
Water activatable adhesives applied from water-based media are commonly 
used as envelope-flap adhesives, postage-stamp adhesives, binding tapes, 
sealing tapes, diapers and the like. Now, remoistenable hot-melt adhesives 
can be used for similar applications. For such use, it is desirable that 
the hot-melt coating be capable of storage without blocking, i.e. adhering 
due to activating of the adhesive of combination of ambient humidity, 
temperature and contact pressure. In addition, the dried adhesive, when 
contacted with water, must be uniformly activated and capable of 
developing an adherent bond between the coated surface and an uncoated 
surface. The hot-melt characteristics of the formulations are also 
important. The adhesive should have good pot life, at least 30-40 hours at 
usual application temperatures of about 350.degree. F., as well as low 
viscosity characteristics at these temperatures, and the viscosity of the 
hot-melt should be substantially constant during the pot-life of the 
hot-melt. 
As a result of previous work in this field, a water activatable adhesive 
which has excellent non-blocking and water activatable adhesive 
characteristics, and also excellent hot-melt characteristics has been 
found, as disclosed in U.S. Pat. No. 4,325,851. 
Pressure sensitive hot-melt adhesives are useful for the adhesive coating 
of labels, cloth patches and the like. A water soluble pressure-sensitive 
hot-melt adhesive composition with excellent adhesive properties has been 
disclosed in U.S. Pat. No. 4,331,576. Labels comprised of this water 
soluble pressure-sensitive hot-melt adhesive composition adhere 
permanently to substrates under normal conditions; on the other hand, when 
wet, such labels can be removed readily without damage to the substrate. 
Non-pressure sensitive hot-melt adhesives have been used as the adhesive 
medium for multiline construction of disposable baby and adult diapers, 
sanitary napkins and hospital bed pads. In this construction the adhesive 
is applied in longitudinal, parallel or bead multi-lines to laminate a 
polyolefin film which forms the outer shell to tissues or non-woven 
substrates. It is often desirable to know if it is wet and thus a hot melt 
adhesive used in this capacity, and yet signaling the presence of water by 
a color change is invaluable. 
An example of a non-pressure sensitive water based latex adhesive which 
when dry, signals the presence of water by a color change is taught in 
U.S. Pat. No. 4,231,370, issued to Mroz et al. According to this 
disclosure a flexible pH-change/color wetness indicator is coated on a 
surface portion of the product, which is visible through the cover member, 
and which retains sharp edge definition of the coated surface portion when 
wetted, for example, by urine. Such a coating includes a 
pH-change/color-change type material dispersed in a polymer latex matrix 
composed of styrene/2-ethylhexyl-acrylate copolymer, vinyl 
acetate/ethylene copolymer and polyvinyl acetate. To obtain a suitable pH, 
sufficient acid buffering means, such as phosphoric acid must be used; 
this is a harsh acid which could conceivably hurt a child. 
It is a disadvantage of the broadly similar prior art Mroz et al 
composition, that the adhesive material can only be obtained by 
evaporation from a water-based latex composition. This means that 
equipment must be provided during the manufacture of the Mroz et al 
product which can release the water present. Also such problems as 
foaming, and proper wetting of the substrate must overcome, all resulting 
in a more expensive manufacturing process of the Mroz et al formula. It is 
another disadvantage that any color change of the Mroz et al composition 
takes a very long time to take effect, e.g. of the order of 3 minutes, as 
can be seen, for example, from FIGS. 3 and 4 of the Mroz et al patent. 
Further, the time required for the color change in the Mroz et al 
composition is dependent on the thickness of the coating, as well as the 
pH of the wetting composition; the thicker the coating and the lower the 
pH, the slower the color change. 
It is often desirable to know quickly, by visual inspection, whether a 
substrate has become wet. For example, it is desirable to know when a 
diaper has become wet, but the wetness of a diaper which is plastic 
coated, or which is worn under a water proof panty, is not readily 
determined by visual inspection. 
SUMMARY OF THE INVENTION 
An object of the present invention is the provision of a hot-melt adhesive 
composition which is capable of indicating the presence of water therein. 
Another object of the present invention is the provision of a hot-melt 
adhesive composition which changes color in response to wetness. 
A further object of the present invention is the provision of a hot-melt 
adhesive which changes color rapidly when wet. Another object of the 
present invention is the provision of a hot melt adhesive coating which 
changes color rapidly when wet, independent of the thickness of the 
coating and substantially independent of the pH of the wetting 
composition. 
A particular object of the present invention is the provision of a hot-melt 
adhesive composition which is effective to show quickly that a diaper has 
become wet. 
These and other objects are accomplished by the present invention. 
A wetness indicating composition has been discovered which adheres 
substantially to any substrate, and which provides immediate recognition, 
by visual inspection, that the substrate has become wet. 
According to the invention, the wetness indicating composition is composed 
of a hot-melt adhesive composition and a wetness indicating agent which 
causes the composition to change color in response to the presence of 
water in the composition. 
The wetness indicating hot-melt adhesive composition of the invention 
comprises: 
(A) 20 to 70 wt.% of total polymer components, said polymer components 
comprising 35 to 100 wt.% of water sensitive polymer selected from vinyl 
pyrrolidone homopolymer, vinyl pyrrolidone/vinyl acetate copolymer or a 
mixture thereof, any balance comprising at least one polymer selected from 
the group consisting of ethylene vinyl acetate copolymer, ethylene/acrylic 
acid copolymer and polyamide; 
(B) 27 to 60 wt.% of an acidic composition selected from 
(a) at least one free monobasic saturated or unsaturated fatty acid having 
an acid number above 137 or 
(b) 15 to 50 wt.% of the fatty acid in combination with 10 to 55 wt.% of at 
least one other organic acid having an acid number above 130; 
(C) 0 to 30 wt.% of a water soluble wax; and 
(D) a wetness indicating agent capable of causing the composition to change 
color in response to the presence of moisture in the composition, in an 
amount effective to provide the composition with a readily visible color 
when wet, which is distinct from the color of the dry composition. 
In a particular embodiment of the invention, a device, such as a label, 
tape, or plastic, which can be coated with a hot-melt, is coated with the 
wetness indicating hot-melt adhesive composition of the invention. 
Another embodiment of the invention is a diaper which contains the wetness 
indicating hot-melt adhesive composition of the invention. 
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION 
The polymer component of the wetness indicating hot-melt adhesive 
composition of the invention is based on water sensitive resin which is 
selected from vinyl pyrrolidone homopolymer (VP) and vinyl 
pyrrolidone/vinyl acetate copolymer (VP/VA) and mixtures thereof. In the 
copolymer, the proportion of the monomer components ranges from 3:1 to 1:3 
by weight of each monomer moiety. Within this range the flow points of the 
copolymer are satisfactory for the hot-melt formulations of this 
invention. 
A satisfactory copolymer in the solid state is marketed by GAF Corp. (NYC, 
N.Y., USA) under the trade name PVP/VA S630. This is a 60/40 VP/VA 
copolymer. Other polymers of different proportions are commercially 
available with most being marketed in solution form by GAF (USA) and BASF 
(W. Germany). A useful vinyl pyrrolidone homopolymer is marketed by BASF, 
under the tradename Luviskol. Products in solution form require removal of 
the solvents before or during the preparation of the hot-melt. The water 
sensitivity of these copolymers provides the water activatable or water 
sensitive property of the final adhesive formulation, when coated on the 
substrate. 
Optionally, one or more additional polymers compatible with VP or VP/VA may 
be included in the adhesive composition of the invention. For example, 
ethylene/vinyl acetate copolymer (E/VA), ethylene/acrylic acid copolymer 
(E/AA) and polyamides (PA) are compatible with VP and VP/VA, and useful in 
the present formulations. 
Such ethylene/vinyl acetate copolymers are marketed by several companies 
such as duPont (Delaware USA) under the "Elvax" trade name. The vinyl 
acetate content of these copolymers suitable for inclusion in the 
formulations of this invention ranges from about 17 to 29%. Preferred are 
the copolymers at the lower end of the range, as they are the most 
compatible with the VP/VA copolymers. The Elvax 410 series copolymer 
having a VA content of 17.5 to 18.5% is most preferred; it has a melt 
index (ASTM D 1238) of 455-550. The E/VA copolymer, unlike the VP/VA 
copolymer, is not water sensitive. It has been used as a major polymer 
component in direct sealing hot-melt adhesives, that is, in adhesives 
where the melt is applied and the surfaces joined before the melt 
solidifies. 
Ethylene/acrylic acid copolymers suitable for use in the present 
compositions are produced by Allied Chemical Co. under the Allied Chemical 
trade name. Allied Chemical Co. does not provide the copolymer ratios, but 
indicates the acid number to be between 40 and 75 for these specialty 
products. 
The polyamide can be either of low amine number type (10-28) or of high 
acid number (80-140). The lower amine polyamide is produced by Emery Inc., 
while the high acid number polyamide is produced by Crosby Inc. of Los 
Angeles. 
The total polymer content of the compositions of the invention may range 
from 20 to 70 wt.%, of which 35 to 100 wt.% is VP or VP/VA, and any 
remainder is selected from another polymer or copolymer such as E/VA, 
E/AA, PA and a combination thereof. More preferably, the compositions of 
the invention contain about 30 to 65 wt.% of total polymer. It is also 
more preferable that at least 50 wt.% of the polymer components be VP/VA, 
VP, or a combination thereof. 
Fatty acids useful for the present invention are liquid aliphatic straight 
chain free fatty acids. Other high acid number (more than 130) organic 
acids such as high acid number rosin, hydrogenated rosin or tall oil may 
be used in conjunction therewith. 
Commercial liquid fatty acids may be blended with each other or with other 
high acid number organic acids including rosin and tall oil products. The 
acids, when mixed, should be able to withstand 350.degree. F. for 48 hrs., 
without any serious chemical degradation as evidenced by color or odor. 
High acid number fatty acids, which contain at least 14 carbon atoms, when 
used alone, i.e. without other types of organic acids, may be present in 
an amount of 27 to 60 wt.%, depending on the desired characteristic of the 
adhesive. Alternately, when used in combination with other high acid 
number organic acids, the fatty acids may be present in an amount of 15 to 
50 wt.%, while the other organic acids make up the remaining acid 
requirements, i.e. 10 to 55 wt.%. 
When a pressure sensitive hot-melt adhesive is desired, it is preferable 
that the fatty acid should be used in an amount of 27 to 60 wt.%, more 
preferably 35 to 50 wt.% of the composition. It is also preferable that 
the proportion of fatty acid to total polymer in the composition be from 
1:2 to 2:1. For example at a weight range of 13 or 14 wt.% of fatty acid 
alone, the desired results are not achieved; a composition with this 
proportion of acid components is suitable as a remoistenable hot-melt 
adhesive only, but will not produce any change in color. 
If desired, waxy materials selected from solid water soluble, waxy, 
polyethylene glycols or polyoxyethylene glycols (PEG) may be included in 
the wetness indicating adhesive composition of the invention in an amount 
up to 30 wt.% of the invention to modify the physical properties of the 
composition. Commercial water soluble solid PEG waxes range in molecular 
weight from about 4,000 to about 20,000 and are marketed by Union Carbide 
under the Carbowax trade name; equivalent materials are available from 
other sources. 
As the wetness indicating agent, a material which is compatible with the 
instant compositions, or VP and VP/VA polymers in particular, and which is 
capable of changing the color of the adhesive composition quickly when the 
adhesive composition is wet, compared to the color of the dry adhesive 
composition, may be used in the present wetness indicating adhesive 
composition. Acid-base indicators, which change color in response to a 
change in pH, are preferred, because they change color rapidly, and those 
providing a change to a bright, vivid color are generally most preferred. 
Other materials which change color in response to water may be used as the 
wetness indicating agent, such as dyes which are substantially invisible 
in the dry composition, which quickly become a vivid color when wet. An 
example of such a material is the blue dye Calcocid Blue 2G made by 
American Cyanamide Corp. 
Acid-base indicators for use in the present compositions are those which 
change color at a pH in the range of about 3 to 7, such as Ethyl Red, 
Bromophenol Blue (made by Eastman Kodak), or Bromocresol Green mixed with 
Bromophenol Blue; Bromophenol Blue is particularly preferred. The wetness 
indicating agent is used in an amount effective to provide the composition 
with a readily visible color when the composition is wet, and of course, 
the readily visible color must be easily distinguishable from the color of 
the dry composition; generally about 0.05 to 0.1 wt.% pf indicator, based 
on the weight of the composition, is adequate. 
Optional components of the compositions of the invention include 
antioxidants, which may be added in an amount of about 0.05 to 0.1 wt.%, 
rosins, such as Sylvatac 95, (made by Sylvachem Corp.), plasticizer, such 
as Dantocol, surfactants, essential oils and perfumes and similar special 
purpose additives common in this art, and are within the ambit of the 
invention. 
Compared to compositions of the prior art, color change in the composition, 
according to the present invention, is very fast, and substantially 
independent of the thickness of the composition of the coating applied to 
a substrate and of pH range within certain limits of the wetting 
composition. Thus a change in color is obtained within 5-30 seconds. This 
can be faster, depending of the shape of the beadline.

The following examples of the invention are for the purpose of illustrating 
representative compositions preferred for specific uses, and it must be 
realized that no single formulation is satisfactory for all substrates. 
All proportions are by weight unless otherwise indicated. 
EXAMPLE 1 
The antioxidant, Irganox 1010 (manufactured by Ciba-Geigy) in an amount of 
0.1 wt.% and about 0.05 wt.% Bromophenol Blue were mixed with the other 
nonpolymer components until uniform, with heating and then the polymer was 
added with continued heating at a temperature of about 
160.degree.-177.degree. C. with stirring until dissolved. 
The proportion of fatty acid and polymer components was as follows: 
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Fatty acid (Emersol 871) 36 wt. % 
Ethylene/acrylic acid copolymer (AC-580) 
18 wt. % 
Vinyl pyrrolidone/vinyl acetate copolymer 
100 wt. % 
(Gantron PVP) to make up 
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This adhesive product can be applied to a substrate, such as a polyethylene 
film, in an amount sufficient to cause the polyethylene film to adhere to 
another substrate, such as absorbent, non-woven material. When the 
absorbent material is wet, the adhesive product immediately turns bright 
blue. 
EXAMPLES 2-6 
These examples have been prepared as described in Example 1, and contain 
0.1 wt.% of the antioxidant, Irganox 1010, 0.07 wt.% of the pH indicator 
Bromophenol Blue, as well as polymer, water soluble wax, and fatty acid in 
the amounts shown in Table 1. 
In these examples the following material have been used. 
Polymer: Gantron S630; vinyl pyrrolidone/vinyl acetate copolymer 
Fatty acid: Emersol 871 in Examples 2-4 and 6 Emersol 150 in Example 5 
Water soluble wax: Carbowax 4000 
TABLE 1 
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EXAMPLE 
Component 2 3 4 5 6 
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Polymer 40 40 54.6 54.6 20.0 
Fatty acid 50 40 27.3 27.3 53.3 
Water sol. wax 
10 20 18.1 18.1 26.7 
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The hot-melt of examples 2-5 forms an adhesive film on a substrate such as 
paper, polyethylene or polypropylene, which is light yellow in color. When 
wet, the film turns bright blue immediately. Example 6 is a light yellow 
gel, which changes to a bright blue color in response to wetness. 
EXAMPLE 7 
In combination with 0.1 wt.% of the antioxidant, Irganox 1010 and 0.07 wt.% 
of Bromophenol Blue, the following components were mixed under the 
conditions described in Example 1. 
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Pyrrolidone homopolymer (Luviskol K-30) 
30.00 wt. % 
Ethylene/vinyl acetate copolymer (Elvax 410) 
20.00 wt. % 
High acid no cpd., i.e. fatty acid (Emersol 871) 
100.00 wt. % 
to make up 
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This product forms an adherent film, light yellow in color, on a substrate 
such as paper, polyethylene, or polypropylene, which turns bright blue 
immediately when wet with water. 
EXAMPLES 8-10 
The formulation in Table 2, plus 0.1 wt.% of the antioxidant Irganox 1010 
and 0.07 wt.% of the pH indicator, Bromophenol blue, yield products which 
form light yellow colored, adherent films on substrates such as paper, 
polyethylene, polyester non-woven fibers, and polypropylene. The films are 
effective to cause the substrate to adhere to another material, and become 
bright blue in color in response to contact with a wet paper towel. 
TABLE 2 
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EXAMPLE 
Component 8 9 10 
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Vinyl pyrrolidone/vinyl 
40 36.3 45.5 
acetate copolymer (Gantron) 
Ethylene/vinyl acetate 
10 18.2 18.2 
copolymer (Elvax 410) 
Fatty acid (Emersol 871) 
50 45.5 36.3 
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