A Method for the coding of absorbent material

The present invention provides a process for marking a diaper fabric which comprises applying to the fabric one or more images by means of an ink jet printing technique during the fabrication of the diaper from its component materials. Preferably, the invention is used to apply a fluid indicator fluid to that face of the impervious layer to be in contact with the absorbent layer during the manufacture of the composite diaper fabric, the other face of the absorbent layer being that which is to be directly or indirectly in contact with a wearer of the diaper. It is also preferred that the indicator fluid comprise a water-soluble dyestuff whereby the indicator is rendered mobile upon contact with a fluid. The invention further provides a diaper having an image formed thereon, preferably on that face of the impervious layer in contact with the absorbent layer, which image comprises a series of dots configured to form the desired image, preferably the image is formed from a water-soluble dyestuff.

The present invention relates to the coding of absorbent materials, notably 
to the marking of manufacturing and other codes on a diaper, particularly 
to provide a fluid mobile marking to indicate when the diaper has been 
wetted. 
In the production of diapers, a layer of an absorbent material such as a 
flocked, felted or needled fabric, tissue or reticulated material or 
cotton wool-like material is combined with an impervious material, the 
absorbent layer being designed to absorb urine and other body fluids from 
the person wearing the diaper and the outer layer being designed to 
prevent escape of these from the absorbent layer into the environment. 
Whilst the final form of the finished diaper may differ from manufacturer 
to manufacturer, the above construction of the diaper fabric is common to 
substantially all designs of diaper and is produced by similar techniques. 
It would be desirable to be able to print date, quality control and other 
manufacturing codes on each batch of diaper fabric and to give each 
individual diaper the manufacturer's brand name or other indicia to aid 
marketing of the diapers. However, the lengths of material which are to be 
combined to form the composite diaper fabric travel at high speeds and it 
would be necessary to ensure accurate registration of the printing with 
the fast moving material so that the printed images occur at the desired 
location on each diaper. This is difficult and any relative movement 
between the printing head and the material being printed would cause 
blurring of the image. Furthermore, the fluffy nature of the absorbent 
layer would cause major problems due to fluff contamination of the 
printing head. It has been therefore been proposed to use pre-printed 
material carrying random images on the material so as to avoid the need 
for accurate registration between the various components used to make up 
the diaper fabric. However, this requires that a production line be 
designated to a given product or that the operation of that line must be 
interrupted to change from one feed of pre-printed material to another 
where it is desired to change the image in the diaper fabric being 
produced. 
We have found that ink jet printing tehniques provide an advantageous 
method for marking quality control codes and the like onto a diaper during 
its manufacture, notably onto the inner face of the impervious layer of 
the diaper fabric. An ink jet printer is a non-contact type of printer and 
reduces problems due to fluff contamination and snagging of the material 
being printed with the print head which occur with contact type printers 
as used hitherto. Furthermore, an ink jet printer produces an image which 
can be readily altered without the need to close down a printing line to 
change printing plates and the like, thus enabling a manufacturer to vary 
the image produced to suit a purchaser's individual requirements and to 
switch between one image and another at will without having to stop the 
diaper fabric production line. The print head for an ink jet printer is 
compact and therefore can readily be incorporated into a diaper fabric 
production line without disruption of the layout of the line or 
iterference with other operations in the production line. Furthermore, an 
ink jet printer can operate at high speeds to secure accurate positioning 
of the image on a fast moving component of the diaper fabric immediately 
prior to that component being incorporated into the diaper fabric, thus 
reducing the problems of registration of the image with the diaper fabric.

Accordingly, the present invention provides a process for marking a diaper 
which comprises applying one or more images to one or more components of 
the diaper by means of an ink jet printing technique. The Figure 
illustrates the method steps of the claimed invention. Preferably, the 
invention is used to apply an indicator fluid to that face of the 
impervious layer of a composite diaper fabric to be in contact with the 
absorbent layer, the other face of the absorbent layer being that which is 
to be directly or indirectly in contact with a wearer of the diaper. 
Preferably, such application takes place during the process of manufacture 
of the composite diaper fabric rather than during the fabrication of the 
individual components for subsequent use in the manufacture of the 
composite fabric. It is also preferred that the indicator fluid contain a 
water-soluble dyestuff and that the indicator fluid be rendered mobile 
upon contact with a bodily fluid. 
The invention further provides a diaper fabricated from a composite fabric 
having an image formed thereon, preferably on that face of the impervious 
layer in contact with the absorbent layer, which image comprises a series 
of dots configured to form the desired image. Preferably the image is 
formed from a water-soluble dyestuff. 
The invention can be applied to all types of diaper and to form any desired 
image on the diaper. Thus, the invention can be applied in the manufacture 
of incontinence pads, as well as to diapers for infants. The term diaper 
is therefore used herein to denote in general a composite construction 
comprising a liquid impervious layer having in association therewith a 
fluid absorbent layer adapted to be in contact directly or indirectly with 
a wearer of the diaper, the construction being in sheet, strip or pad form 
and intended for use upon the person. The term diaper fabric is used 
herein to denote this construction prior to cutting or otherwise forming 
the individual diapers therefrom. 
The fluid applied to the diaper fabric can be one which is visible under UV 
light or one which carries magnetic particles to provide an image which 
can be scanned by a magnetic sensor for use in quality control or other 
manufacturing control operations. However, the invention is of special use 
in the application of a dyestuff to the diaper fabric to provide an image 
which can be used for marketing purposes and/or to provide an indicator 
which disperses or intensifies and/or changes in colour to indicate when 
the diaper has been wetted by the wearer. For convenience, the invention 
will be described hereinafter in terms of this preferred use and in terms 
of a diaper which comprises an absorbent layer comprising a 
cotton-wool-like cellulosic material as the absorbent material encased in 
a water permeable casing such as non-woven, felted, needled or similar 
tissue-like material, and a sheet plastic material mounted on one side of 
the absorbent layer to provide an outer impervious layer. 
The diaper fabric can be manufactured by any suitable method. This will 
usually comprise bringing together lengths of the absorbent material, the 
casing for that material and the impervious layer on a continuous basis to 
form the basic diaper fabric. This is then subjected to such other 
treatments, eg. folding the fabric to adopt the desired configuration, 
applying side fastenings and so on, as may be required to form the 
individual diapers. The present invention is not restricted to any 
specific method by which the diaper fabric is formed nor its subsequent 
treatment and these can be of conventional nature. As indicated above, the 
invention is preferably applied to the material of the impervious layer as 
this is or is about to be incorporated with the other components into the 
composite diaper fabric. 
The present invention therefore further provides in a diaper fabrication 
process a printer station located in association with the feed of one or 
more of the component materials for the diaper fabric and adapted to apply 
a fluid to the material by means of an ink jet printer. In the preferred 
embodiment of the invention, the printing station is located on the feed 
path of the impervious material so that it forms an image on that face of 
the material which is to be in contact with the absorbent layer in the 
composite diaper fabric. Thus, when the impervious material is combined 
with the absorbent layer or with the components used to form that layer to 
give the diaper fabric, the image is located between the impervious and 
absorbent layers and is protected from smearing or abrasion during 
subsequent handling or use by the impervious layer, but is visible through 
that layer. 
The image can be formed by any suitable ink jet printing technique. Thus, 
the image can be formed using an on-demand printer in which droplets of 
ink are dispensed from an array of nozzles located across the line of 
travel of the fabric. Each nozzle is fed with ink, usually under pressure, 
through a valving means, eg. a solenoid valve. The sequence of operation 
of the valves is controlled by a micro-processor or the like so that they 
are actuated in the desired order to emit droplets to form the desired 
image. Typical of suitable ink jet printers of this type for present use 
are those sold by Willett Printos Limited as LCP printers. 
Alternatively, the ink is dispensed continuously through a nozzle as a 
discrete single jet which passes through a charge electrode. The stream of 
ink is excited by applying a vibration thereto to break the stream up into 
substantially uniform droplets, eg. by exciting a piezo-electric crystal 
in contact with the ink. The charged droplets are passed through an 
electric field which causes the droplets to be deflected away from their 
natural flight path. The extent of deflection is controlled by the charge 
applied to the droplet and/or the strength of the deflecting field. Thus, 
the flight path of each droplet can be controlled so that it falls upon 
the desired location on the impervious material or into a catcher 
mechanism or gutter where it is desired that no image be printed with that 
droplet. Droplets falling into the gutter are re-cycled for re-use. 
Typical of such printers are those available as Willett Printos 1600 
printers. 
Other suitable ink jet printers include those in which the ink composition 
is drawn from the nozzle by electrostatic forces to give charged droplets 
which can be guided as described above; those where the droplets are drawn 
through the nozzles by capillary action; and those where the ink 
composition is heated within the printing head immediately adjacent the 
nozzle so as to form a vapour bubble which expels the ink through the 
nozzle. 
The above forms of printer are characterised in that they are non-contact 
printers and hence do not crush or otherwise affect the structure of the 
diaper fabric nor do they present an obstruction to the free passage of 
material past the printing station. The operation of the printer can be 
closely synchronised with the movement of the substrate upon which 
printing is to take place. Hence, accurate registration of the printed 
images with the impervious material or the diaper fabric can be achieved, 
even where the speed of travel of the material being printed varies. 
The image which is formed can be selected at will by the operator so as to 
identify a batch of diaper fabric for manufacture or quality control 
purposes. However, it is preferred that images be formed at appropriate 
intervals on the impervious material so that each individual diaper 
carries an image printed thereon which will vary when the diaper is wetted 
by a body fluid. The images formed by an ink jet printer are characterised 
by being composed of a number of dots, whereas conventional contact 
printing techniques, such as are proposed in for example U.S. Pat. No. 
4,022,211, give continuous images which readily smudge if there is not 
complete co-ordination between the fabric being printed and the printing 
plattern. 
The indicator fluid used to form the image can be of any suitable 
composition, for example it can be a solvent or water based ink. 
Preferably, the ink composition is one which is rendered mobile upon 
subsequent contact with body fluids so that the image forms a smudge 
visible through the outer impervious plastics layer when the wearer wets 
the diaper. This smudge provides a simple and effective indicator that the 
diaper has been wetted by the wearer. Alternatively, the ink composition 
can be one which develops a colour or intensifies and/or changes colour 
when contacted with a body fluid. It is therefore preferred that the 
indicator composition contain a physiologically acceptable water-soluble 
dyestuff, notably one which is a food grade material. The optimum 
composition for application to the diaper fabric will depend upon the 
intensity of colouration required both when dry and when wetted, and can 
be readily determined in each case. It is a further advantage of the use 
of an ink jet printer that the ink composition can be readily changed 
merely by using a secondary printing head without the need to halt the 
diaper fabrication process. 
As indicated above, the composite diaper fabric can be subjected to further 
treatment to form the individual diaper units. It is also within the scope 
of the present invention to give the printed component one or more 
subsequent treatments before it is incorporated into the diaper fabric. 
Thus, the printed image can be dried to avoid the risk of smudging as the 
overall diaper fabric is built up or it can be printed with other images. 
The invention will now be illustrated by the following Examples in which 
all parts and percentages are given by weight: 
Example 1 
A diaper fabric comprising an absorbent layer 1 of cotton wool-like 
material encased in a needled tissue like cellulosic material 2 and having 
an outer sheet polyethylene plastics impervious layer 3 was formed by 
feeding webs of the individual components through a conventional high 
speed diaper manufacturing line shown diagrammatically in the accompanying 
drawing. A Willett Printos 1600 continuous ink jet printer head 4 was 
located over the sheet feed of the polyethylene sheet so as to print dot 
matrix images thereon 16 dots high. 
The printer head comprised a nozzle 5 fed with an ink composition to form a 
jet of fluid issuing from the nozzle. This jet was broken up into a series 
of discrete mono-sized and substantially uniformly spaced apart droplets 6 
by excitement with a piezoelectric crystal acting on the ink. 
At or above the point at which the jet broke up into droplets, was mounted 
a charge electrode 7 which applied a varying charge to the droplets. The 
charged droplets passed between a pair of charged deflection plates 8 
which generated an electric field which caused the droplets to deflect 
from their free flight path by an amount which depended upon the charge 
carried by the droplet. The extent of deflection determined the position 
at which the droplet was deposited on the polyethylene web 3 and hence the 
image formed. Where it was desired not to deposit a droplet on the 
polyethylene sheet the droplet was not given a charge and followed its 
free flight path into a gutter or other catching means 9 which intercepted 
the path of the droplet. The droplets caught in the gutter were recycled 
for re-use. 
The printer 4 used an ethanol based ink composition containing a food grade 
water-soluble blue dyestuff. The resultant diapers each possessed a 
clearly visible blue image formed from a series of dots on the inner 
surface of the polyethylene layer 3. 
When worn by a small child, the image could be seen without removing the 
diaper. When the child wetted the diaper, the image became smudged and 
provided a clearly visible indication of when the diaper needed changing. 
Example 2 
The process of Example 1 was repeated except that the ink composition was a 
water/ethanol based composition containing a polymeric binder to provide a 
composition which rapidly dried upon application to the polyethylene 
sheet. When the printed image from such a composition was wetted, the 
dyestuff dispersed and the image faded in the wetted area. 
Example 3 
The process of Example 1 was repeated except that the coloured dyestuff was 
replaced with a colourless but UV fluorescent agent. The resultant image 
on the diaper fabric could be read under UV illumination for quality 
control purposes but did not give an image which could be detected by a 
user under normal conditions.