METHOD FOR DYEING NYLON FILAMENTS

METHODE DE TEINTURE DES FILS NYLON

English Abstract

A method for dyeing nylon filaments for use in
wear-indicating toothbrushes includes immersing a batch of a first
nylon filament for between 10 minutes and 80 minutes in an
aqueous solution containing between 0.01% and 0.19% weight to
volume of Indigotine dye, said solution having a pH between 1
and 7 and having a temperature between 50°C and 90°C, the dye
penetrating into the filament to color an outer cross-sectional
region and not penetrating into an inner cross-sectional
region of the filament; removing the batch of the
first nylon filament from the solution, and repeating the
steps for a batch of a second nylon filament, reusing the same
solution.

French Abstract

Procédé permettant de teindre des filaments de nylon destinés à être utilisés pour indiquer l'usure des brosses à dents. Dans ce procédé on plonge une charge d'un premier filament de nylon pendant environ 10 à 80 minutes dans une solution aqueuse contenant environ entre 0,01 % et 0,19 % en poids par rapport au volume de colorant indigotine, le pH de cette solution se situant entre 1 et 7 et sa température étant comprise entre 50 C et 90 C. Le colorant pénètre dans le filament pour colorer une zone externe en coupe transversale mais ne pénètre pas dans une zone interne en coupe transversale dudit filament. On retire la charge de premier filament de nylon de la solution et on recommence ces étapes pour une charge d'un deuxième filament de nylon, en utilisant de nouveau la même solution.

Claims

6
CLAIMS:
1. A method of dyeing and affixing nylon
filaments to toothbrushes, comprising:
(a) immersing a first batch of a nylon filament
for between 10 minutes and 80 minutes in an
aqueous solution comprising between 0.01% and
0.05% weight to volume of Indigotine dye,
said solution having a pH between 2.5 and
4.5, and having a temperature between 70°C
and 85°C, said Indigotine dye consistently
penetrating into said nylon filament to color
an even outer cross-sectional region of said
nylon filament, and not penetrating into an
inner cross-sectional region of said nylon
filament;
(b) removing the first batch of said nylon
filament from said solution to provide a
first dyed nylon filament having said outer
cross-sectional region colored with said
Indigotine dye and said inner cross-sectional
region not colored with said Indigotine dye;
(c) affixing said first dyed nylon filament to
the head of a first toothbrush;
(d) repeating steps (a), (b), and (c) for a
second batch of a nylon filament and a second
toothbrush, reusing the same said solution,
to provide first and second toothbrushes each


7

having the same amount of said Indigotine dye
consistently penetrating into said nylon
filament to color evenly the same outer
cross-sectional region of said nylon filament
in each toothbrush.
2. The method of claim 1 comprising the
additional step of repeating steps (a), (b), and (c) for a
third batch of a nylon filament and a third toothbrush, reusing
the same said solution, to provide first, second and third
toothbrushes each having the same amount of said Indigotine dye
consistently penetrating into said nylon filament to color
wenly the same outer cross-sectional region of said nylon
filament in each toothbrush.
3. The method of claim 2 comprising the
additional step of repeating steps (a), (b), and (c) for a
fourth batch of a nylon filament and a fourth toothbrush,
reusing the same said solution, to provide first, second,
third, and fourth toothbrushes each having the same amount of
said Indigotine dye consistently penetrating into said nylon
filament to color evenly the same outer cross-sectional region
of said nylon filament in each toothbrush.
4. The method of claim 1, wherein step (a) is
performed at atmospheric pressure.
5. The method of claim 1, wherein said nylon
filaments have an average diameter of between 0.127 and 0.356
mm (0.005 inches and 0.014 inches).


8

6. The method of claim 1, wherein said nylon
filaments are monofilaments.
7. The method of claim 1, wherein said first
batch of said nylon filament is immersed in said aqueous
solution for less than 60 minutes.
8. The method of claim 1, wherein said first
batch of said nylon filament weighs at least 4.8 kg (10 lbs.).

Description

W'D 92/22699 PCT/US92/04589
'109935
- 1 -
METHOD FOR DYEING NYLON FILAMENTS
The invention relates to filaments for
toothbrushes .
Breuer et al., U.S. Pat. No. 4,802,255
describes nylon monofilaments that include at least two
colored regions, one of which is provided by a dye.
The monofilaments are included in the bristles of
toothbrushes and, as the toothbrush is used by the
owner, the color intensity of the dyed region changes
in response to wear, providing an indication of when
the toothbrush should be replaced. Breuer et al. lists
six food dyes or colorants that can be used to dye the
monofilaments including Indigotine (FD&C Blue No. 2),
and in col. 4 broadly describes the conditions that can
be used for dyeing. Breuer et al. also provides a
number of specific examples of dyeing procedures,
including three (examples 4-6) in which Indigotine is
used as the dye.
The specific dyeing procedures described by
Breuer et al. were for laboratory samples. However, to
produce a sufficient amount of dyed filaments for
commercial toothbrushes, a procedure is needed that can
be used for dyeing large amounts of filaments. The
procedure should be cost-efficient and, of course,
should produce nylon filaments that have a consistent
level of dye penetration.
In general, the invention is a method for



WO 92/22699 PCT/US92/04589
2~.~g93~
- 2 -
dyeing batches of nylon filaments for toothbrushes. As
used herein, a batch is at least two pounds of nylon
filament. The method includes immersing a batch of a
first nylon filament for between 10 minutes and 80
minutes in an aqueous solution containing between .O1%
and 0.1% weight to volume of Indigotine dye. The
solution should have a pH between 1 and 7, and should
have a temperature between 50'C. and 90'C. While the
nylon filament is immersed, the dye penetrates into an
outer cross-sectional region but not into an inner
cross-sectional region. The batch of the first nylon
filament is removed from the solution, and can be used
for bristles in a wear-indicating toothbrush. The same
procedure is repeated for a batch of a second nylon
filament, reusing the same solution. Preferably, the
same solution is then used for dyeing additional
batches. In the preferred method, the aqueous solution
contains between 0.01% and 0.05% weight to volume of
Indigotine dye; the solution has a pH of between 2.5
and 4.5; and the temperature of the solution is between
70'C. and 85°C. Preferably, the dyeing step is
performed at atmospheric pressure and takes less than
60 minutes, and the nylon filaments have a diameter of
between 0.005 inches and 0.014 inches.
The method can be used to produce commercial
quantities of nylon filaments for use in wear-
indicating toothbrushes in a cost-effective manner.
For example, the procedure can be used on 10-40 lb.
batches of nylon filaments, and even on batches
weighing 100 lbs or more. Importantly, the same
solution can be reused at least once, and even up to
five or six times, and still produce filaments in which
the Indigotine dye has penetrated an even, consistent
cross-sectional area. The method is easy to carry out,
safe, and provides a stable dye solution.



WO 92/22699 PCT/US92/04589
210935
- 3 -
Other advantages of the invention will be
apparent from the description of the preferred
embodiment thereof, and from the claims.
Dyed wear-indicating nylon monofilaments,
toothbrushes including such monofilaments, and the way
the toothbrushes are made are described in detail in
Breuer et al.
The dyeing solution used in the method of the
invention contains between 0.01% and 0.1% weight to
to volume Indigotine. If too much Indigotine is used, too
much dye penetrates too far into the filament. If too
little dye is used, too little dye may penetrate, and
the solution may not be reusable because the initial
batch of filament may absorb the limited quantifiy of
dye present.
The temperature of the solution should be
between 50'C. and 90'C. Too high a temperature results
in water quickly evaporating off, resulting in the dye
becoming more concentrated, and the dye being taken up
too fast, making the degree of penetration more
difficult to control. Too low a temperature results in
too slow a dye uptake.
The dyeing process preferably is done at
atmospheric pressure, to avoid the necessity of using
large pressurized equipment in a plant.
Indigotine is an acid stable dye, and the
solution should be acidic.
The volume of dyeing solution should be large
enough so that the first batch of filament does not
absorb such a high percentage of the dye in the
solution that the solution cannot be reused to dye a
second batch.
The nylon filaments, most preferably
monofilaments, should be of the diameter commonly used
in toothbrushes, most preferably 0.008 or 0.009 inch.




. 4 21 49935
The nylon filament should be immersed in solution long
enough to get adequate dye penetration of the outer cross-
sectional diameter of the filament to provide good wear-
indicating characteristics. Preferably, the immersion time
should be as limited as possible, and should be less than 1
hour.
A detailed description of the most preferred method is
provided below, beginning with a description of the equipment
and solutions used, followed by the procedure.
The dyeing step is performed in a 633 gallon WhitingT"'
stainless steel tank having side dimensions of 30" x 40" x
130".
The dyeing solution used in the tank includes 633
gallons of distilled water; 7.7 liters of glacial acidic acid;
and 555 g of 1000 pure Indigotine. The temperature of the
solution is maintained at 75°C. + 1.5°C.
Two 633 gallon rinse tanks also are used. The first
tank is filled with tap water. The second tank is filled with
tap water mixed with 1.5 liters of Dow CorningT"' #24 silicone
emulsion.
The monofilament used is an eight foot long, 0.008 inch
diameter WytexT"" 6.12 S nylon hank (bundle) weighing
approximately 10 pounds. The hank should be siliconed,
annealed, wet, and combed prior to dyeing, according to
standard procedures. The hank should not be dried prior to
use.




4a ~ 1 0 9 9 3 5
Dyeing Procedure
1) Completely submerse four hanks in the dye
solution.
2) Set timer for 45 minutes.
3) Lift and resubmerse hanks every 1.5 minutes to
permit circulation of dye between filaments.



WO 92/22699 ~ 10 9 9 3 5 PCT/US92/04589
- 5 -
4) After 45 minutes, remove hanks and
transfer to the first rinse tank. Rinse
by dipping 4 to 5 times.
5) Transfer the to the second rinse tank.
Continue rinsing by dipping another 4 to
5 times. This rinse will restore the
finish lost during the dyeing process.
6) Recomb hanks and continue with the normal
drying and wrapping process.
7) Repeat the procedure 4 times for
additional batches of hanks, using the
same solutions. The dye solution and
first rinse are changed after 5 hanks
have been dyed: the second rinse solution
is replaced daily.
Optionally, the above procedure can be modified by
immersing set of hanks for 30 minutes in a dyeing
solution heated to 80'C. ~ 1.5'C. In addition, the
procedure can be used to dye 10 hanks at a time, as
opposed to four hanks.
Other embodiments are within the claims.