Note: Descriptions are shown in the official language in which they were submitted.
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¦~ BACKGROUMD OF THE INVENTION
¦ Field of the Invent~on
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! This invention deals with aqueous ink compOSitiotlS
i for use in capillary type writing instruments which contain
'jultrafine particles of colloidal silica to reduce skin sta~ning,
feathering and penetration of ink into paper.
Description of the Prior Art
Staining of skin and feathering and strike-through on
soft papers by dye residuum has long been a problem with the use
of ink writing instruments. Products devPloped primarily for
the children's market, usually pens or marking devices ha~ing
'` fiber, felt, or porous plastic type writing poin~s, are an
example of a situation where product abuse can be foreseen and
liwhere significantly reduced skin staining would be desirable
and competitively advantageous.
ll Among the ~arious prior art patents which have included !
iliinely divided silica or other minerals as a writing instrument
~ink ingredient is U.S. 3,074,800 which uses microscopic particles ¦
' of silica gel mixed with a wax to yield a plastic thixotropic
I'ink havin~ a reduced tendency to flow around a s~atic ball point
when the pen is not being used. The non-aqueous ink compositions '
which are disclosed are described as having a viscosity of
1000 to 3000 poises at 68F and would hence be unsuitable for
'~use in capillary type writing instruments.
25 1l The use of bento~ite as an anti-settling agent for
! pigments in quick drying marking inks is disclosed in U.S.
¦2,684,303. ~ince pigments rather than water soluble dyes are
employed to impart color to the compositions, skin staining and
¦paper feathering are not a problem.
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U.S. 3,073,707 teaches the use of clays and in
particular kaolin to regulate the thickness of hydrophilic
printing ink compositions to facilitate the application of
such inks to the printing press.
SUMMARY OF THE INVENTION
The present invention comprises an aqueous ink com-
position adapted for use in Gapillary type writing instru-
ments comprising an acid dye in combination with colloidally
dispersed, non-agglomerated particles of a surface-hydroxylated
silica.
DETAILED ~E~CRIPTION OF THE INVENTION
One means of limiting dye-skin and dye-paper inter-
action is by the mechanical means of preventing physical con-
tact. Colloidal ultrafine particles, in particular, colloidal
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dispersions of non-agglomerated particles of surface-~r~s-
o~,l~e~ silica of e~ceptionally small diameter are commer-
cially available in a variety of sizes and are stable at high
solids concentration. We have discovered that utilization of
such ultrafine particles in aqueous formulations based upon
acid dyes which normally stain skin and paper leads to reduced
aGI 50 r p~ io-n,
staining presumably by preferential ~b~4~ ~i~ association
of the dye on the ultrafine surface. The macroscopic size of
the particle, relative to the dye molecule, reduces the likeli-
hood of both dye penetration and absorption on skin and paper.
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Capillary type writing instruments employ a variety
of types of fiber, felt, and porous plastic writing points.
Felt is a fabric of natural and/or synthetic fibers worked
together by pressure, heat, or chemical action without
weaving or knitting. The fibers tend to be arranged in a
random fashion. When felt is used as a writing point, the
ink is conveyed through the interstices between the individual
fibers by capillary action.
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,~ A second type of capillary writing point is made by
bonding together a bundle of parallel strands of either natural
or synthetic fibers to form capillary pathways between the
~jbundles leading to the writing poin~. The fibrous point is
" made by setting a bundle of parallel strands of synthetic fibers
in a desired relation by drawlng the bundle through a heat-
setting zone to establish dimensions in cross-section of the
' final object and to create longitudinally extending channels.
The strength of the point can be subsequently increased by im-
mersion in a dilute resin solution followed by heating to
evaporate the solvent and cure the resin.
Another type of capillary writing point is made by
extrudîng and melt drawing an acrylic or other suitable polymer
1~ a~d ~hen reforming the internal portions of the extruded body
'by a comp~essive drawing operation to obtain channels of the
desired si~e. The writing point thus formed has a longitudinally
ext~nding, axial, ink-conveying channel and circumaxqal, spaced,
ink-conveying chalmels, the axial channel having a cross-sectional~
, area equivalent to a circle with a diameter between two and four
~ mils. The longitudinal channels of the rods serve tQ deliver
ink to the writing point by means of capillary action.
' In each of the above cases, the ink is Eed from a
reservoir to the WTiting surface by means of the writing point.
~j The reservoir which feeds the writing point may be either a
!~ container of liquid ink or a bundle of fibers saturated with
Il ink. Since the capillary channels of such wrlting instruments
i' are quite small sometimes being less than 1.0 mil in diameter,
llit is necessary that the ink formula~ions to be used have a
jl,sufficiently low viscosity to permit capillary flow~ It has
3Q 1l been typical in the past to avoid ink formulations containing
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insoluble particulate lng~edients to reduce the risk of clogging
~l the capillary passages.
il Many of the better ink formulations for use in capillar~
1 flow writing instruments comprise aqueous based compositions
,I containing water soluble acid dyes as the color imparting in-
¦ gredient. Such formulations, however, have the disadvantage
that they may tend to feather on the surface of ~he writi~g
paper and to stain heavily if inadvertently applied to the skin
i of the user. We have found that both of these disadvantages
' can be reduced if from 1.0 to 20.0% of colloidally dispersed,
` non-agglomerated particles of a surface-hydroxylated silica
having an average particle si~e of 2 to lOOm~, preferably 10 to
'I 25m~, is added to the ink formula~ion prior to its being used to
,j fill the reservoir of the writing-instrument. To pre~ent reaction'
~I with the charged silica particles, the dyes for use in the prac- !
il tice of our invention should be limited to acid dyes, i.e.
those dyes possessing one or more sulfonate groups attached to
an aromatic nucleus and which can be classified according to
I their che~ical structure into ten different categories:
i! nitro, nitroso, monoazo, monoazo (metallized), disazo triphenol-
Il methane, xanthene, anthraquinone, azine, and quinoline. The
¦ amount of dye used will, of course, vary with the nature and
'I color of the inX to be produced but should constitute from
¦I about 0.5% to about 15~ by weight of the total ink composition.
1~ While an aqueous solution of a water soluble acid dye and the
1 silica will produce an acceptable inX, it is preferred to in-
¦! clude one or more polyhydric alcohols in the ink formulation
to control viscosity and improve line characteristics. Poly-
'I hydric alcohols useful in the invention include alkylene glycols, ,
!I polyalkylcne ~lycols, mono- and di-alkyl ethers of polyhydrlc
I alcohols, and trihydric alcohols. Thc preferred alcohols are
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' glycerin and ethylene glycol, and mixtures thereof. The total
il amount of polyhydric alcohol employed in the compositions of the
1 invention ~ay be varied within wide limi~s as dictated by the
!~ viscosity considerations of the final composition bearing in
S ij mind that viscosity will be controlled in part by the identity
',j of the dyes employed in the relative proportions of such dyes
and the colloidal silica. In general, the polyhyclric alcohol
component of the invention should constitute from about 1.0%
to about 50.0% by weight.
'- If desired, it is also possible to add other optional
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ingredients typically used in water based inks such as benzo- !
I' triazole as a corrosion inhibitor and a preservative such as
'll methyl parasept.
.~ The inks can be produced by the simple operation of
l mixing and dissolving the ingredients in any suitable way, it
being preferred that the ink components be held at 55C with
constant stirring for two hours after their initial mixing.
The prepared ink is then incorporated in any of the conventional
capillary writing instrument types described above using well
'known procedures. ~or example, the ink may be iniected into
the end of the reservoir opposite the writing point in a pre- ¦
viously assembled porous point pen by means of a syringe. An
alternative procedure described in U.S. Patent 3,581,378 is to
!jfirst saturate a fibrous reservoir with the ink for~ulation
ijfollowed by insertion into the barrel of the porous point pen.
In order to illustrate typical and preferred ink compositions
'lembodying the present invention, the following examples are
!l included.
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EXAMPLE I
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¦ An ink composition having the following formulatio~
was prepared.
l In~redient % by Wei~ht
Color Index Acid Red 289 ~.0
¦I Methyl parasep~ 0.25
il Propyl parasept 0.15
1. Propylene glycol 8.0
Il Glycerin 7.0
o !i ~olloidal silica (avg. particle size--13m~) 8.0
Water q.s. to 100
' Procedure: The colloidal silica used was a commercial aqNeous
B !1 dispersion (Ludox HS-40, du Pont) available at a 40% solids
~! content. The above ingredients less the colloidal silica and
!! its accompanying water werecombined and heated to 55C for two
llhours with constant stirring. The solution was allowed to cool
¦l to room temperature, at which time the colloidal silica dis- i
persion was slowly added with stirrlng. After filtering, the
j ink formulation was charged into writing instruments having
j writing tips formed of closely packed polyester fiber strands.
i The skin staining potentlal of the composition of
Example I was compared with a control composition not containing
Il the colloidal silica by applying samples of both inks with li
¦Icotton swabs to the palm of a hand followed by a 30-minute drying ¦
l¦period. After that time a portion of each stain was scrubbed
with a commercially available toilet soap for 15 seconds and
a comparative evaluation of the two stains made. Such comparison ¦
of the composition of this example and its control composition
l¦showed that while the control left a medium palmar stain after
Isoap scrubbing, the composition containing the colloidal silica
¦left a light stain.
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I EXAMPLE II
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¦ A writing ink composition having the following for~-
¦ ulation was prepared.
Ingredient 1O by ~ei~h~
¦I Color Index Acid Blue 9 (C.I. #42090) 2.0
Methyl parasept 0-25
Propyl parasept 0.15
~j Propylene glycol ~-
~l Glycerin 7.0
!i Colloidal silica (avg. particle siæe--13m~ 6.0
li ~ater q.c;. to 100
~; Procedure: The colloidal silica used was a co~mercial aqueous
B ,I dispersion (Ludox HS-a, du Pont) available at a 30% solids
' contents. The above ingredients less the colloidal silica and
lS ?! its accompanying water were combined and heated to 55C fo~ two
hours with constant stirring. The solution was allowed to cool
,I to room temperature, at which time the colloidal silica dis-
i! persion ~as slowly added with stirring. After filtering, the
t ink formulation was charged into writing instruments having
iI writing tips formed of closely packed polyester fiber strands.
¦j Evaluation of the composition of Example II with a
~¦ si~ilar control not containing colloidal silica exhibited re-
! duced staining.
¦~ The ink co~positions of Examples I and II were loaded
, into felt tipped marking instruments to check their delivery
performance under marking-use conditions. It was i~ediately
obser~ed that a reduction in feathering occurred when compared
l with compositions not containing the colloidal silica. Spot
! tests of ten ~1 o each ink delivered onto filter paper gave
¦ a spot diameter of 13 mm for a control composition versus 11 mm
ior the formula~ions of Examples I and II. Using uncoated
groundwood 60 lb. paper, strike-through also appeared to be
¦ 1~8s with the inks of the invention. This was verified by
¦ taking vertical ~ections of the paper and mieroseopic examination.
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IlEXAMPLE XII
!~ A l~riting ink composition having the following formula- !
¦Ition was prepared.
l Ingredient % by Wei~ht
! Color Index Acid Red 52 (C.I.#45100) 0.5
ilColor Index Acid Blue 9 ~C,I.#42090) 2.0
IMethyl parasept 0.25
I¦Propyl parasept 0.15
I Propylene glycol 8~0
¦IGlycerin 7~0
~IlColloidal silica ~avg. particle size--7m~) 7.5
jlWater q.s. to 100
!!,Procedure: The colloidal silica used was a co~mercial aqueous '
I B !I dispersion (Ludox SM-30, du Pon~ available at a 30% solids
!llevel. The above ingredients less the colloidal silica and
its accompanying water were combined and heated to 55C for two
Ijhours with constant stirring. The solution was allowed to cool
',Ito room temperature, at which time the colloidal silica dis-
llpersion was slowly added with stirring. After filtering, the
,link formulation was charged into writing instruments having
ilwriting tips formed of closely packed polyester fiber strands.
I~EXAMPLE IV
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A writing ink compos~tion having the following
formulation was prepared.
l Ingredient % by Weight
Color Index Acid Blue 9 (C.I.#42090) 2 0
Color Index Acid Yellow 1 ~C.I.#10316) 1 0
~Methyl parasept 0.25
IPropyl parasept 0.15
Propylene glycol 8.0
Glycerin 7
Colloidal siLica (avg. particle size--13m~) 6 0
¦Water q.s. to 100
¦Procedure: The colloidal silica used was a commercial aqueouR
dispersion ~Ludox HS-40, du Pont) available at a 40% solids
,content. The above ingredients less the colloidal silica and ,,
its accompanying water were combined and heated to 55C for two
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hours with constant stirring. The solution was allowed to cool
i t~ room temperature, at which time the colloidal silica dis-
I persion was slowly added with stirring. After filtering, the
!l ink formulation was charged into writing instruments having
j writing tips formed of closely packed polyester fiber strands.
i EXAMPLE V
I A writing ink composition having the following
formulation was prepared.
~ Ingredient V/o by Weight
! Color Index Acid Blue 9 (C.I.#42090~ 2.0
Methyl parasept 0.25
' Propyl parasept 0.15
, Propylene glycol 8.0
I Glycerin 7.0
j'l Colloidal silica (avg. particle size--13m~3 8.0
Water q.s. to 100
Procedure: The colloidal silic~ used was a commercial aq~eous
dispersion (Ludox HS-40, du Pont) available at a 40% solids
licontent. The above ingredients less the colloidal silica and
,l its accompanying water were combined and heated to 55C for two
hours with constant stirring. The solution was allowed to cool
to room temperature, at which time the colloidal silica dis- !
persion was slowly added with stirring After filtering, the I .
~¦ink for~ulation was charged into writing instruments having
!Iwriting tips formed of closely packed polyester fiber strands.
Evaluation of the inks described in Examples III, IV,
and V with control compositions not containing the colloidal
Ijsilica ingredient showed that whereas the control composition
¦llgave dark polymer staining, the modified inks were judged
Ivir~ually stain-free after soap scrubbing.
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