Note: Descriptions are shown in the official language in which they were submitted.
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WEAR RESISTANT IMAGE PRINTING ON LATEX SURFACES
FIELD OF THE INVENTION
The printing of rubber articles made from rubber latex.
DISCUSSION OF THE PRIOR ART
The printing of rubber articles made from rubber latex, in particuiar
natural rubber latex, is well known in the art. Balloons have been printed
using natural rubber solutions in mineral spirits. These solutions yield a print10 which can be easily removed by common household detergents and
chemicals.
Ink systems for latex rubber, in particular natural latex articles and,
more specifically, latex rubber gloves require a degree of chemical resistance
15 not found commercially today. Rubber gloves commonly are exposed to a
variety of household chemicals including detergents, bleach, ammonia, oils
and grease, polishes, disinfectants, etc. Any decorative system for rubber
gloves should be resistant to these common materials. It would therefore
be desirable to provide a decorative technique which comprises a printing
20 system for the surface of such rubber articles wherein the printed image is
resistant to common household chemicals.
SUMMARY OF THE INVENTION
There is provided a method for printing images on a latex rubber
25 surface which comprises applying an ink con~aining natural or synthetic
rubber, pigment dispersion, and a solvent medium, in particular an
aromatically unsaturated solvent medium for said rubber.
A critical feature of the invention is the presence of an agent capable
30 upon cure, of forming a chemi~,ally and abrasion resistant, tough flexible
structure integrating the rubber of said base coat, where it is present, the
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rubber of the ink, together with the pigment therein, and the rubber of the
latex surface, in at least one of the base coat and the ink. The mechanism
if this integration is not fully understood, but its creation of a surprising level
of resistance thereby is unquestionably novel.
The preferred integrating agent is, suitably an aryl diisocyanate.
Where the rubber containing ink is used over a base coat of natural rubber
in such a solvent, the aryl diisocyanate may be either in the base coat or the
ink.
1 0
A base coat of natural rubber in such a suitable solvent is required,
where the rubber in the ink is synthetic rubber. The integrating agent, such
as an aryl diisocyanate may be either in the base coat or the ink. However,
a portion of the solvent may be replaced by a terpene, a terpenoid or a high
15 boiling ketone suitably having a boiling point over 1 20~C, such as
isophorone or the like.
The efficacy of the printing may be improved by certain pre- and post-
printing steps. One such additional step, is heating the printing surface.
20 Another, highly desirable, added step, is placing a base coat upon the
printing s~rfass that r~el~es th~ irnag~, !n crle embodim~t of the processj
this base coat is allowed to dry to tackiness before the image is printed. As
stated above, this base coat comprises natural rubber in an aromatically
unsaturated solvent.
. . . ~ . ,,
The ink as well as the base coat may be applied using a number of
common printing techniques including: gravure printing, flexo printing,
screen printing, and pad printing. Pad printing however, has been found to
be superior for the inventive purposes, such as: printing individual rubber
30 articles like rubber gloves.
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DESCRIPTION OF THE PREFERRE~D EMBODIMENTS
There is provided a method and a formulation for printing images on
latex rubber surfaces. It is desirable that the weight amount of the aryl
diisocyanate is between 0.5 and 3.0 times that of the total rubber in
5 solution within the ink or within the base coat where used or both. The
rubber may be natural rubber or synthetic rubber. Suitably, the diisocyanate
is selected from the group consisting of toluene -, methylene diphenyl- and
polymeric methylene diphenyl diisocyanates, and mixtures thereof.
The rubber in the ink may be natural rubber or synthetic rubber such
as neoprene rubber or blends thereof. For good printing, the ink, at printing
time, should have a viscosity at 20~C of between 800 and 3000 cps. The
use of synthetic rubber in the ink is preferred over natural rubber since its
chemical resistance is greater. However natural rubber, when mixed with
15 aryl diisocyanate will provide sufficient resis~ivity. Aryl diisocyanate whencured per se will form a hard brittle product, In the presence of rubber, it
becomes integrated therewith to yield a flexible, tough, and chemically
resistant structure or matrix, that provides the unique printing product
associated with this invention.
Inks containing the diisocyanate should be promptly used after
mixing, suitably withir~ 10 hours of preparation.
Prior art printing solvents generally use mineral spirits, such as:
25 aliphatic or alicyclic hydrocarbons. In contrast, the solvents used in the inks
and precoat of the invention, are aromatically, unsaturated solvents.
Aliphatic esters of aromatic acids, or higher liquid aromatic hydrocarbons are
preferred. Especially suitable, is methyl naphthalene. The latter may, under
certain conditions, be partially replaced with terpenes, or terpenoids, such
30 as: dilimonene, or high boiling ketones, such as: isophorone. The methyl
naphthalene, however, is preferred. Glidsol 90, manufactured by SCM
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Glisol Organics, 210 Summit Ave., Montvale NJ 07645, is a terpene
formulation that is especially preferred. Terpenes and terpenoids can be
used in the base coat, but this is not preferred. It should be noted, that
commercial methyl naphthalene, is in fact, a complex mixture containing
5 dimethyl naphthalene, ethyl methyl naphthalene, and other heavy, fractional
coal tar components.
The actual amounts of rubber, solvents, and pigments used in the
printing formulations of this invention, may vary quite substantially
10 depending on the desired consistency and drying speed. The desired inl<
viscosity range at 20~C., is approximately between 800 and 3,000 cps.
Approximately between 5 and 40 wt% of pigment is contained in the ink
composition.
The image to be printed on a latex rubber surface in accordance with
the ink formulation of this invention, is not particularly dependent upon any
conventional printing method. Stability of the image is improved by the
additional step of heating the printed surface. Suitably, the heating is
accomplished in a temperature range of from approximately 95 to 130~C.
20 for 10 to 20 minutes, or approximately frorn 190 to 230~C. for 3 to 8
seconds .
Heat curing can increase the chemical and abrasive resistance of the
printed ink image to the commonly used, household cleaner, Pine Sol~. A
25 simple test of ink image endurance is to rub the printed image with a pad
impregnated with Pine Sol at recommended, household detergent strength.
Resistance of Neoprene, and natural rubber-containing inks of this invention,
are capable of withstanding 35 to 100 rubs. This is achievable with the
inventive ink formulations due to the presence of the aryl diisocyanate,
30 which as aforementioned, intimately embeds within the rubber molecules.
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The resistance of the printed image may also be improved by certain
pre-, and post-printing steps. Washing the surface of the article with water
and surfactant, followed by drying; or just washing the surface with a
hydrocarbon solvent, will improve the printing process. The washing
5 procedure, however, is not recommended for gloves containing flock on
their inner surfaces. Heating the printed irnage for approximately 3 to 6
seconds at approximately between 1 90-220~C., is helpful.
One of the unusual, and totally unexpected aspects of this invention,
10 is the ability of the printed image product to become increasingly resistant
to chemical attack and abrasion with time. It has been observed that while
the printed image product is contact stable immediately after the initial
heating step, the resistance to chemical abrasion continues to build towards
a maximum over an extended period at ambient temperature. Testing
15 reveals that the printed image product reaches maximum efficacy between
20 and 60 days after printing. This slow cure does not pose a marketing
problem, however, because the mean time between manufacture and the
arrival at the point of sale of a typical printed latex rubber glove, is usuallyabout 75 days.
Printed image stability is also improved by placing a base coat upon
the surface receiving the printed image. l~he base coat is applied and
allowed to dry until tacky. The image is then printed upon the tacky base
coat surface. The base coat can comprise natural rubber in an aromatically
25 unsaturated solvent. Suitably, this base coat also contains an aryl
diisocyanate, in an approximate weight amount of between 0.5 and 3.0
times that of the rubber. in solution.
One method of printing an image on a latex rubber surface includes
30 preparing a clear base coat solution, comprising natural rubber of
approximately one to ten parts by weight in an aromatic hydrocarbon
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solvent of approximately 45 to 50 parts by weight. This clear base coat
solution is then admixed with a premixed moiety comprising an aromatic
hydrocarbon solvent of approximately between 2 to 15 parts by weight
containing an aryl diisocyanate of approximately 1 to 30 parts by weight.
5 The above admixture is then mixed with a pigment having an approximate
weight of between 0.3 to 5.0 times that of the rubber in solution. The
components of this formulation, viz., the clear coat, the premix, and the
pigment, are mixed at ambient temperature, and then printed upon the latex
rubber surface preferably within 10 hours of the mixing.
A generally preferred method of printing an image on a latex rubber
surface comprises the step of applying a base coat to the rubber surface
containing natural rubber in approximate range by weight of between 5 to
15 parts in a solvent approximatély ranging in weight between 80 to 120
15 parts, and an aryl diisocyanate ranging in weight between 0 to 45 parts.
The image is then printed onto the base coat utilizing an ink whose
formulation comprises natural or synthetic rubber in approximately 1 to 10
parts by weight; a rubber solvent in the approximate weight of between 30
to 60 parts; a pigment of approximately 0.3 to 5.0 times the weight of the
20 rubber; and an aryl diisocyanate in the weight range of approximately 0 to
30 parts.
The rubber solvent in the aforesaid formulation can be an aromatic
hydrocarbon, a terpene, a terpenoid, a ketone boiling above 1 20~C., or a
25 mixture thereof. The rubber solvent in the base coat may be an aromatic
hydrocarbon solvent comprising approximately 60 to 90 parts by weight, a
terpene, or terpenoid solvent in approximate weight of between 0 to 60
parts. The rubber solvent in the ink may be an aromatic hydrocarbon
solvent comprising approximately 30 to 50 parts by weight, and a terpene
30 or terpenoid solvent of approxin,alely 0 to 30 parts by weight.
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Various combinations of base coat and ink compositions are within
the scope of the present invention. In one embodiment, the ink comprises
synthetic rubber in approximately 1 to 10 parts by weight; an aromatic
hydrocarbon solvent in about 30 to 80 parts by weight; and a pigment that
5 is 0.3 to 5 parts by weight. The base coat can comprise natural rubber in
approximate weight of between 5 to 15 parts; an aromatic hydrocarbon
solvent in approximately 80 to 120 parts by weight; and an aryl
diisocyanate in approximate weight of between 1 to 45 parts.
In another embodiment the ink comprises synthetic rubber in
approximate weight of between 1 to 10 parts; an aromatic hydrocarbon
solvent of approximately 30 to 60 parts by weight; a pigment in
approximate weight of between 0.3 to 5.0 parts; and an aryl diisocyanate
approximately 1 to 30 parts by weight. The base coat can comprise natural
15 rubber approximately 5 to 15 parts by weight in an aromatic hydrocarbon
solvent comprising approximately 80 to 120 parts by weight.
In a further embodiment the ink comprises synthetic rubber in about
1 to 10 parts by weight; an aromatic hydrocarbon solvent approximately 15
20 to 60 parts by weight; a terpene, or terpenoid solvent in approximate weight
range of 5 to 40 parts; and a pigment approximately 0.3 to 5.0 parts by
weight. The base coat comprises natural rubber approximately between 5
to 15 parts by weight; an aromatic hydrocarbon solvent in an approximate
weight range of between 80 to 120 parts; and an aryl diisocyanate of about
25 1 to 45 parts by weight.
In yet another embodiment the ink comprises synthetic rubber in
~ approximate weight range of 1 to 10 parts; an aromatic hydrocarbon solvent
of about 15 to 60 parts by weight; a terpene, or terpenoid solvent of
30 approximately 5 to 40 parts by weight; a pigment in a weight range of
between 0.3 to 5.0 parts, and an aryl diisocyanate in approximate weight
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of between 1 to 30 parts. The base coat comprises natural rubber from
approximately 5 to 15 parts by weight in an aromatic hydrocarbon solvent
of about 80 to 90 parts by weight.
It is to be reiterated, that the aromatic hydrocarbon of choice in the
above formulations, is commercial grade methyl naphthalene.
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EXAMPLES
Printing Methodology
.
A series of printing stations each comprise pad printer. The printing
stations are aligned to provide sequential processing. A first printing station
is charged with the base coat, and the pigmented printing ink is charged to
the second printing station. A number of colors may be printed by placing
additional pad printing stations in line all subsequent to the first base coat
10 printer. It has been found that improved results are obtained by not
allowing the base coat to thoroughly dry before the pigmented ink is applied .
A slight base coat tackiness should remain as the rubber glove passes under
subsequent print stations. Heat is applied to the print surface by contact
heating with a teflon coated aluminum plated heater to an approximate
15 temperature of 21 5~C. for five seconds. The heating procedure assists in
the cure of the printing ink, which effects its ability to resist chemical attack
and abrasiom
Additional improvement is obtained by placing the rubber gloves in an
20 oven heated to 1 20~C for approximately fifteen minutes~
Stability Test
A test was developed to compare the ability of ink formulations to
25 withstand exposure to common household chemicals. It was found that
Pine Sol~, manufactured by IMFC by Clorox Co., Oakland, CA, most readily
attacked rubber ink systems. A 50% solution of Pine Sol~ in water was
~ applied to a commercial paper towel. The saturated paper towel was rubbed
across the print surface applying moderate hand pressure. The number of
30 rubbing cycles that would erase the image was recorded. Each rubbing
cycle consisted of a back-and-forth rubbing motion comprising 4 cm. in
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length. As an example, a printed image that comprises a balloon ink was
found to disappear in as little as one cycle.
In the subsequent Tables of Results, certain abbreviations are used:
5 SMRL: Standard Malaysian Rubber Light ( Latex); Alcan Rubber & Chemical
Inc., New York NY
DABCO T-12 (Dibutyltin Dilaurate): Air Products & Chemicals Inc.,
Allentown PA
PAPI 2021: polymethylene polyphenyl isocyanate mfg. by Dow Chemical
10 Company, Plastics Div., Midland Ml.
Di-XXXX Pigments: 25% Pigment, 75% Dinonyl Phthalate; Mfg by Cardinal
Color Inc., Paterson NJ 07524
NEOPRENE GW: Dupont Co., Elastomer Div., Wilmington DE
STALITE S: R.T. Vanderbilt, Norwalk, CT
1 5
Solutions were prepared using a Versamix mixer model MW5 of one
gallon capacity obtained from Ross & Co., Long Island, N. Y. Mixing was
accompllshed using a slow agitation speed setting for five days.
As used in these Tables of Result$ and the claims herein, the term:
''parts '' ~fers ~ parts by ~eight ~,~t prcpcrtio~s. Th~ tota! for ar,y
composition may be more or less than 100.
Example I
A printing ink is prepared as follows:
- PARTS
Neoprene GW 1 7.0
Methyl Naphthalene # 5 41.33
Limonene 145 41.33
Pigment Dispersion: Blue Di-61 12 20.0
30 Agerite Stalite 0.34
Total 1 20
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An image was imprinted upon a latex surface using the above
formulation. The aforementioned rubbing test was performed using pads
impregnated with Pine Sol~. The test was conducted 12 days after printing.
5 The printed image was air cured. Only one rub was required to remove the
image.
- Example ll
In the ink formulation given in Example 1, 17 parts of PAPI 2020 were
10 added to the ink.' After printing an image upon a latex surface, a Pine sol~
test was performed after 12 days. The printed image was air cured at
ambient. It required 6 rubs to erase the image.
Example !ll
15 A base coat is prepared as follows:
PARTS
Std. Malaysian Rubber Light (SMRL) 8.85
Dabco T12__ __ _ _ __0.6_ __
Methyl Naphthalene #5 91.15
.. . .
Total 1 00.57
The above base coat was applied to a natural rubber surface just prior
to application of the ink shown in Example ll. A Pine sol~ rubbing test was
performed after 12 days. It took approximately between 12 to 22 rubs to
25 remove the printed image. This test was additionally performed using a cure
of 60 days. The image required 40 rubs for removal.
Example IV Natural rubber ink
To the composition of Example lll was added
PAPI 2020 8 parts
Blue Di-6 1 1 2 20 parts
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The Pine sol~ rubbing Test was performed after the printed image was
allowed to cure for 9 days. The image was removed after 16 rubs.
Example V
An ink of Example IV was applied over a base coat of Example lll.
The Pine sol rubbing test was performed after 9 days cure of the
printed image. It took 36 rubs to remove the printed image.
Example Vl
10 Further Test resùlts: STANDARD 4 COLOR RUBBER INK FORMULATIONS
CLEAR BLACK YELLOW RED BLUE BASE
Me.Naphthalene
#5 44.9
SMRL 4.8
Dabco T-12 -- - 0.3
TOTAL 50.0
Clear 50.0 50.0 50.0 50.0 50.0
Yellow Dl-4225 0 10.0 ' 0 0 0
Red Dl-2023 0 0 10.0 0 0
Blue-DI 6112 0 0 0 10.0 0
Black Dl-9017 4.0 0 0 0 0
Me.Naphthalene 9.3 4.3 4.3 9.3 4.3
#5
PAPI(202t ) - - 4.3- 4.3 4.3 4.3 4.3
TOTAL PARTS 67.6 68.6 68.6 73.6 58.6
All colours printed together in a design pattern.
Cure time: 60 days. Pine sol test: More than 40 rubs to failure
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Example Vll
NATURAL RUBBER INKS - NO BASE
1-92 A-92 B-92 H-92
SMRL 4.425 4.425 4.425 4.425
Methyl Naphthalene #5 45.58 45.58 45.58 45.58
DABCO T-12 0.3 0.3 0.3 0 3
Methyl Naphthalene #5 --- 0.5 3.0 15.0
IPremix)
~ PAPI 2020 (Premix) --- 0.5 3.0 15.0
Blue Dl-6112 10.0 10.0 10.0 10.0
TOTAL PARTS 60.306 61.305 66.305 90.305
% SMRL NR-PAPI 2020 ---
Ratio 8.85: 1.0 1.48: 1.0 0.3: 1.0
1 5 PINE SOL TEST
RESULTS (time of
cure/rubs to failure)
5 DAYS 6 6 12 3
15 DAYS 9 15 16 15
30 DAYS 10 . 20 20 20
Air Cure, Hot Stamp,
200~C., 3 sec
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Example Vlll
NATURAL RUBBER INK WITH BASE COAT
base coat A-92 B-9Z H-92
SMRL 4.425 4.425 4.425 4.425
Methyl Naphthalene #5 45.58 45.58 45.58 45.58
DABCO T-12 0.3 0.3 0.3 0.3
Methyl Naphthalene ~5 --- 0.5 3.0 15.0
(Premix)
PAPI 2020 (Premix) --- 0.5 3.0 15.0
Blue Dl-6112 10.0 10.0 10.0
TOTAL PARTS 50.306 61.305 66.305 90.305
% SMRL NR-PAPI 2020 --- 8.85:1.0 1.48:1.0 0.3:1.0
Ratio
1 5 PINE SOL TEST
RESULTS (time of
cure/rubs to failure)
5 DAYS 12 18 15
15 DAYS 34 36 19
30 DAYS 30 35 30
Air Cure, Hot Stamp,
200~C., 3 sec
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Example IX
STANDARD NEOPRENE INK FORMULATIONS
CLEAR BLACK YELLOW RED BLUE BASE
Methyl
Naphthalene #5 44.9
N atural
Rubber,SMRL 4.8
Dabco T-12 0.3
(Clear) 50 0 50 0 0 0 0
1 0 Methyl 24.80
Naphthalene #5
Limonene 145 16.53
Neoprene GW 8.50
Agerite Stalite S 0.17
1 5 (Neoclear) 50.0 0 50.0 ,50.0 50.0 50.0
Yellow Dl-4225 0 10.0 0 0 0
Red Di-2023 0 0 10.0 0 0
Blue Dl-6112 0 0 0 10.0 0
Black Dl-9017 4.0 0 0 - 0
Methyl 8.6 8.6 8.6 8.6 4.3
Naphthalene #5
PAPI ) 0 0 0 0 4.3
TOTAL PARTS 62.6 68.6 68.6 68.6 58.6
The above inks were printed together in a design pattern over a base
coat as described in the second portion of Example Vlll above.
Curing Time was 60 days. A rubbing Pine sol~ test required 40 rubs
to remove the printed image.
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16
Example X
AIR CURE, HOT STAMP, 200~C., 3 sec.
BASE COAT:
SMRL 8.85
5 Methyl Naphthalene #5 91.15
DABCO T-1 2 O. 6
TOTAL 100. 6
J-100 L-100 N-100
Neoprene GW ,............. 8.5 8.5 8.5
Methyl Naphthalene #5 20.67 20.67 20.67
Limonene 145 20.67 20.67 20.67
Age Rite Stalite S 0.17 0.17 0.17
Blue Dl-6112 10.0 - 10.0 10.0
Methyl Naphthalene #5 (Premix) 1.0 6.0 12.0
1 5. PAPI 2020 (Premix) 1.0 6.0 12.0
TOTAL PARTS 62.01 72.01 84.01
Neoprene-PAPI 2020 8.85:1.0 1.42:1.0 0.71:1.0
PINE SOL TEST RESULTS
Irubs to ~ailure)- 2 days 11 20 12
12 days 11 20 22
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Example Xl
NATURAL/SYNTHETIC RUBBER INK BLENDS
A-133 B-133 C-133
SMRL 1.0
Methyl Naphthalene #5 10 4.0
PAPI-2020 0.33 0.23 0.19
Blue Dl-6112 0.1 4.0 3.33
Isophorone 4.0
1 0 D-Limonene 4.0
Cyclohexanone 4.0 10.0
Neoprene GW 4.0
Hypalon 20 3.33
Butyl Cellosolve Acetate 3.33
1 5 TOTAL PART5 11.43 20.23 20.17
Hypalon DupontTM- Chlorosulphonated Polyurethane Rubber (CSM
Rubber)
G=Blend 75% B-133, 25% A-133 = Neoprene/ Natural Rubber
H-Blend 75% C-133, 25% A-133 = Hypalon/ Natural Rubber
B and C printed over Base G and H no base
B-133 C-133 G-133 H-133
Pine -Sol Test
(time of cure/rubs to
2 5 failure)
6 Days 10 7 ~ 4
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18
Since other modifications and changes varied to fit particular
operating requirements and environments will be apparent to those skilled
in the art, the invention is not considered limited to the examples chosen for
5 purposes of disclosure, and covers all changes and modifications which do
not constitute departures from the true spirit and scope of this invention.
Having thus described the invention, what is desired to be protected
by Letters Patent is presented in the subsequently appended claims.
