Ink composition for indicating progress and completion of vulcanization of rubber products

An ink composition for indicating progress and completion of vulcanization of rubber articles comprising, per 100 parts by weight of the composition, PA0 (i) 0.01 to 10 parts by weight of at least one methine dye, PA0 (ii) 1 to 40 parts by weight of at least one member selected from the group consisting of rosin, rosin derivative, petroleum resin, phenol resin, xylene resin, alkyd resin, cumarone-indene resin, acrylic resin, epoxy resin, ketone resin and styrene-maleic acid resin, PA0 (iii) 0.5 to 50 parts by weight of at least one high molecular weight component selected from the group consisting of cellulose resin, polyvinyl butyral, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, polyamide, synthetic rubber and natural rubber, PA0 (iv) 30 to 80 parts by weight of at least one organic solvent capable of dissolving the components (ii) and (iii), and PA0 (v) 0.1 to 50 parts by weight of at least one halogenated organic acid.

This invention relates to an ink composition for indicating progress and 
completion of vulcanization of rubber products by the discoloration or 
fading of the composition. 
At present vulcanization of rubber products is carried out according to 
conditions for vulcanization such as time and temperature which are 
determined depending on the kind of rubber, the kind of vulcanizing agent, 
the shape and dimensions of rubber articles and so on. However, it is 
difficult to maintain uniformly the temperature in a vulcanization chamber 
of rubber articles. Further, rubber articles keep the appearance 
substantially unchanged during vulcanizing operation so that the operator 
can not directly detect, by visual inspection of individual rubber 
articles, whether the articles have been satisfactorily vulcanized. For 
these reasons, difficulty is entailed in preventing the production of 
defective rubber articles due to insufficient or excessive vulcanization. 
Moreover, such inadequate vulcanization poses problems concerning 
misvulcanized rubber articles, cumbersome inspection of rubber articles 
and consumption of more energy than is needed. 
It is an object of this invention to provide means for accurately 
indicating progress and completion of vulcanization of rubber articles. 
It is another object of the invention to provide means for preventing the 
loss of rubber articles due to insufficient or excessive vulcanization by 
accurately indicating completion of vulcanization of rubber articles. 
It is a further object of the invention to provide means for eliminating 
the time-consuming inspection of vulcanized rubber articles with simple 
visual inspection of the articles. 
It is a still further object of the invention to provide means for 
minimizing the waste of heat in vulcanization by adequately vulcanizing 
rubber articles. 
Other objects and features of this invention will become more apparent from 
the following description. 
The invention provides an ink composition for indicating progress and 
completion of vulcanization of rubber articles comprising, per 100 parts 
by weight of the composition, 
(i) 0.01 to 10 parts by weight of at least one methine dye, 
(ii) 1 to 40 parts by weight of at least one member selected from the group 
consisting of rosin, rosin derivative, petroleum resin, phenolic resin, 
xylene resin, alkyd resin, cumarone-indene resin, acrylic resin, epoxy 
resin, ketone resin and styrenemaleic acid resin, 
(iii) 0.5 to 50 parts by weight of at least one high molecular weight 
component selected from the group consisting of cellulose resin, polyvinyl 
butyral, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate 
copolymer, polyamide, synthetic rubber and natural rubber, 
(iv) 30 to 80 parts by weight of at least one organic solvent capable of 
dissolving the components (ii) and (iii), and 
(v) 0.1 to 50 parts by weight of at least one halogenated organic acid 
represented by the formula 
##STR1## 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 represent halogen, hydrogen, 
C.sub.1 -C.sub.4 alkyl, amino, nitro, hydroxyl, C.sub.1 -C.sub.4 alkoxy 
with the proviso that at least one of R.sub.1, R.sub.2, R.sub.3 and 
R.sub.4 is halogen: A.sub.1 and A.sub.2 are the same or different and 
represent hydrogen, --COOH or --SO.sub.3 H or, are combined together to 
form an anhydride when they are --COOH with the proviso that both A.sub.1 
and A.sub.2 are not hydrogen at the same time. 
Our research reveals that the ink composition comprising the five 
components (i) to (v) is high in adhesion to rubber articles to be 
vulcanized; the coating formed on the rubber articles is not easily 
separable from the article being vulcanized even if the article has 
changed its chemical and physical properties and shape by vulcanization; 
and the coating markedly discolors or fades after the article has been 
vulcanized at a specific temperature for a specific time, and that the 
present ink composition with such properties is able to accurately 
indicate completion of vulcanization of rubber articles. This invention 
has been accomplished based on these novel findings. 
According to this invention, at least one methine dye having one or more 
methine groups is used as the coloring component (i) for directly 
indicating progress and completion of vulcanization of rubber articles. 
Examples of methine dyes useful in the invention are classified below 
according to colors and Color Index numbers. 
(a) 
Methine dye: Basic Yellow 11, 12, 14, 22, 23, 28, 29, 33, 35, 40, 48, 49, 
51, 52, 53 
Cyanine dye: Basic Yellow 13 
Polymethine dye: Basic Yellow 21, 43, 44 
Azo-methine dye: Basic Yellow 24, 45 
(b) 
Methine dye: Basic Orange 21, 22, 27, 44, 46 
Azo-methine dye: Basic Orange 42 
(c) 
Methine dye: Basic Red 12, 13, 15, 27, 35, 36, 37, 48, 49, 52, 53, 66 
Cyanine dye: Basic Red 14, 68 
Azo-methine dye: Basic Red 45 
(d) 
Methine dye: Basic Violet 7, 15, 16, 40 
Cyanine dye: Basic Violet 39 
Polymethine dye: Basic Violet 20, 21, 27 
(e) 
Methine dye: Basic Blue 62, 69 
Among these methine dyes, preferred dyes are C.I. Basic Red 12, 13, 14, 15 
and 37, C.I. Basic Yellow 11 and 13, C.I. Basic Violet 15, etc. The 
coloring component (i) is used in an amount of 0.01 to 10% by weight, 
preferably 0.5 to 5% by weight, based on the composition. When the dye is 
used in lesser amount, the ink composition does not show clear color. With 
the dye employed in excess amount, the composition fails to distinctly 
discolor or fade, thereby failing to clearly indicate completion of 
vulcanization. 
These dyes are able to improve the water resistance of the composition when 
used as a kind of adduct prepared by bringing the dye into contact with 
phenolic resin or rosin or rosin derivative as disclosed in Japanese 
Patent No. 878644 (Japanese Examined Patent Publication No. 2324/1977). 
Useful resin components (ii) soluble in organic solvent include rosin, 
hydrogenated rosin, glycerin ester thereof, pentaerythritol ester thereof 
and like derivatives; dammar, shellac and like natural resins: petroleum 
resin: phenol-modified alkyd resin, styrenated alkyd resin, epoxy ester 
and like alkyd resins; rosin-modified phenolic resin and like phenolic 
resins; rosin-modified xylene resin, alkylphenol xylene resin and like 
xylene resins; coumarone-indene resin; acrylate or methacrylate polymer or 
copolymer and like acrylic resin; ketone resin; rosin-modified maleic acid 
resin, styrene-maleic acid copolymer; etc. Preferable examples of the 
resin component are rosin derivatives, petroleum resins, phenolic resins, 
ketone resins and styrene-maleic acid copolymers. Among the resins of the 
same kind, it is advantageous to use the resin having a higher softening 
point because the coating formed from such resin does not flow during 
vulcanization and articles formed with the coatings do not adhere each 
other. At least one of these resins is used as the resin component (ii) in 
an amount of 1 to 40% by weight, preferably 5 to 20% by weight, based on 
the ink composition. 
Usable as the high molecular weight component (iii) soluble in organic 
solvent are rubbers and synthetic resins capable of imparting elasticity 
to the coating. Examples of such rubbers are isobutylene rubber, isoprene 
rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, 
ethylene-propylene rubber, chloroprene rubber and like synthetic rubbers 
and natural rubber. Useful synthetic resins include methoxy cellulose, 
nitrocellulose, acetyl cellulose and like cellulose resins, polyvinyl 
butyral, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate 
copolymer, polyamide and like resins. At least one of them is used as the 
high molecular weight component (iii) in an amount of 0.5 to 50% by 
weight, preferably 5 to 20% by weight, based on the ink composition. The 
amounts of the resin component (ii) and the high molecular weight 
component (iii) to be used in this invention closely correlates to each 
other. Any one of the components (ii) and (iii) employed in lesser or 
excess amount leads to impaired adhesion of the ink composition to the 
rubber article, thereby causing likelihood of the coating being easily 
separated from the article during vulcanization. 
At least one of organic solvents usually used as the solvent for inks is 
usable as the organic solvent (iv). 
Examples of the organic solvents capable of dissolving the components (ii) 
and (iii) are shown below. 
(a) Aliphatic alcohols: ethanol, n-propyl alcohol, isopropyl alcohol, 
n-butyl alcohol, iso-butyl alcohol, n-amyl alcohol, n-hexyl alcohol, 
methyl amyl alcohol, 3-heptyl alcohol and the like. 
(b) Alicyclic alcohols: cyclohexyl alcohol, 2-methylcyclohexyl alcohol and 
the like. 
(c) Heterocyclic alcohols: furfuryl alcohol, tetrahydrofurfuryl alcohol and 
the like. 
(d) Aromatic alcohols: benzyl alcohol and the like. 
(e) Halogenated hydrocarbons: methylene chloride, chloroform, 
tetrachloromethane, ethylene chloride, trichloroethane, tetrachloroethane, 
dichloropropane, n-butyl chloride, ethylene bromide and the like. 
(f) Halogenated aromatic hydrocarbons: chlorobenzene, dichlorobenzene and 
the like. 
(g) Ethers: isopropyl ether, n-butyl ether, anisol, phenetol, 
epichlorohydrin, 1,4-dioxane, furfural, tetrahydrofuran, tetrahydropyran 
and the like. 
(h) Ketones: acetone, methyl ethyl ketone, methyl-isobutylketone, 
methyl-n-amyl ketone, methyl-n-hexyl ketone, diethyl ketone, 
acetonylacetone, mesityl oxide, phorone, isophorone, cyclohexanone, 
methylcyclohexanone, acetophenone and the like. 
(i) Ethylene glycol alkyl ethers: ethylene glycol monomethyl ether, 
ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene 
glycol isopropyl ether, ethylene glycol monobutyl ether, ethylene glycol 
dibutyl ether, diethylene glycol monobutyl ether and the like. 
(j) Hydrocarbons: n-pentane, iso-octane, n-hexane, n-decane, n-heptane, 
2,2-dimethylbutane, n-octane, cyclohexane, methylcyclohexane, decalin, 
benzene, toluene, xylene, ethylbenzene, diethylbenzene, cumene, 
amylbenzene, p-cymene, tetralin, p-menthane and the like. 
(k) Ethylene glycol alkyl esters: ethylene glycol monomethyl ether acetate, 
ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether 
acetate, diethylene glycol monoethyl ether acetate, diethylene glycol 
monobutyl ether acetate, diethylene glycol monoacetate and the like. 
(1) Esters: ethyl formate, n-butyl formate, ethyl acetate, n-propyl 
acetate, iso-butyl acetate, n-butyl acetate, n-amyl acetate, methoxybutyl 
acetate, cyclohexyl acetate, benzyl acetate, ethyl propionate, ethyl 
butyrate, ethyl hydroxy-iso-butyrate, n-butyl stearate, ethyl 
acetoacetate, methyl lactate, butyl lactate, methyl benzoate and the like. 
The amount of the organic solvent (iv) to be used is determined depending 
on the viscosity of the ink composition, the stability thereof in use and 
during storage, the drying rate thereof on application, etc. The organic 
solvent is employed in an amount of 30 to 80% by weight, preferably 40 to 
60% by weight, based on the ink composition. 
With this invention, at least one of halogenated organic acids and 
anhydrides thereof which do not volatilize or sublimate at the 
vulcanization temperature are incorporated in the ink composition to 
control the discoloration or fading of the colorant component (i) and to 
adjust the occurence of discoloration to the time for completion of 
vulcanization. The acid is used in an amount of 0.1 to 50 parts by weight, 
preferably 0.5 to 25 parts by weight, per 100 parts by weight of the ink 
composition. The halogenated organic acids are represented by the 
following formulas. 
##STR2## 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 represent halogen, hydrogen, 
C.sub.1 -C.sub.4 alkyl, amino, nitro, hydroxyl, C.sub.1 -C.sub.4 alkoxy 
with the proviso that at least one of R.sub.1, R.sub.2, R.sub.3 and 
R.sub.4 is halogen: A.sub.1 and A.sub.2 are the same or different and 
represent hydrogen, --COOH or --SO.sub.3 H or, are combined together to 
form an anhydride when they are --COOH with the proviso that both A.sub.1 
and A.sub.2 are not hydrogen at the same time. Preferable examples of 
halogenated organic acids and anhydride thereof are chlorophthalic 
anhydrides such as chlorophthalic anhydride, and tetrachlorophthalic 
anhydride, bromophthalic anhydrides such as bromophthalic anhydride, and 
tetrabromophthalic anhydride, 4-chlorobenzenesulfonic acid, 
2-fluoronaphthalenedisulfonic acid, 5-chlorosalicylic acid, 
2,3,4-trichlorobenzoic acid, etc. 
Further the ink composition of this invention may contain at least one of 
oil-soluble dyes and pigments which have high dispersibility in inks in 
order to give marked differences in color tone of the present ink between 
before and after vulcanization and to more accurately indicate completion 
of vulcanization. Examples of pigments useful in this invention are 
tianium dioxide, red iron oxide, ultramarine, chrome oxide, cadmium 
maroon, chrome orange, chrome yellow, cadmium yellow, Carmine 6B, 
Indanthrene Blue, Hansa Yellow, Alizarine Maroon, Phthalocyanine Green, 
Phthalocyanine Blue and Lake Red. These pigments are used in an amount of 
about 0.1 to about 50 parts by weight, per 100 parts by weight of the 
composition. Oil-soluble dyes are those generally known, such as 
phthalocyanine dyes, pyrazolone dyes, anthraquinone dyes, azo dyes, 
chromium complex dyes, etc. Examples of phthalocyanine dyes are Oil Blue 
BOS (trade mark, product of Orient Chemical Industries Ltd., Japan), 
Solvent Blue 55 (e.g. Neozapon Blue FLE, trade mark, product of BASF AG., 
West Germany), etc. Examples of pyrazolone dyes are Solvent Yellow 19 
(e.g. Vari Fast yellow 3104, trade mark, product of Orient Chemical 
Industries Ltd., Japan), Solvent Yellow 21 (e.g. Neozapon Yellow R, trade 
mark, product of BASF AG., West Germany), etc. Examples of anthraquinone 
dyes are Solvent Violet 14 (e.g. Oil Violet 732, trade mark, product of 
Orient Chemical Industries Ltd., Japan), etc. Examples of azo dyes afr 
Fast Orange RR (trade mark, product of Dainichi Seika Color & Chemicals 
Manufacturing Co., Ltd., Japan), etc. These dyes are used in an amount of 
about 0.01 to about 2 parts by weight, per 100 parts by weight of the 
composition. 
Known plasticizers such as dibutyl phthalate, dioctyl phthalate, tricresyl 
phosphate, etc. may be added in an amount of 2 to 10% by weight based on 
the combined weight of the resin component (ii) and the high molecular 
weight component (iii) to improve the properties of the coating formed 
from the components (ii) and (iii). 
At least one of surfactants, and like additives conventionally used in ink 
compositions may be incorporated into the ink composition of this 
invention. Examples of useful surfactants are nonionic surfactants, such 
as polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, 
polypropylene glycol-polyethylene glycol ether, fatty acid esters of 
polyethylene glycol, silicone-containing surfactants, fluorine-containing 
surfactants and the like. Examples of useful preservatives are sodium 
benzoate, potassium sorbate, pentachlorophenol sodium salt, phenol, etc. 
The ink composition of this invention can be prepared by various processes. 
For example, a methine dye (i) is dissolved in a portion of an organic 
solvent (iv) with stirring at a temperature ranging from room temperature 
to 80.degree. C. When a pigment is used, it may be dispersed therein at 
the same time. A resin component (ii) and a high molecular weight 
component (iii) are dissolved in the remaining portion of the organic 
solvent (iv) with stirring at room temperature to 80.degree. C. The two 
solutions thus prepared are mixed together, a halogenated organic acid (v) 
is added thereto and the mixture is stirred at 50.degree. to 80.degree. C. 
As a second choice, a dye (i) and a portion of a resin component (ii) are 
dissolved in a portion of an organic solvent (iv). The solution thus 
obtained is mixed with a solution of the remaining portion of the 
component (ii) and a high molecular weight component (iii) and a 
halogenated organic acid (v) in a remnant of the solvent. 
As a third choice, a solvent (iv) exellent in dissolving a dye (i) is mixed 
with another solvent (iv) which is able to dissolve a high molecular 
weight component (iii) in a high concentration. Then a dye (i), resin 
component (ii), high molecular weight (iii) and halogenated organic acid 
(v) are dissolved in the mixture of the two solvents.

This invention will be described below in more detail with reference to 
examples in which parts are all by weight. 
EXAMPLE 1 
An orange ink composition of this invention was prepared by using the 
following components. 
______________________________________ 
Vinyl chloride-vinyl acetate resin 
50 parts 
("Denka Vinyl #1000A", 
Denki Kagaku Kogyo Co., Ltd., Japan) 
Phenolic resin 70 parts 
("Tamanol 100S", 
Arakawa Chemical Co., Ltd., Japan) 
Isophorone 700 parts 
Toluene 400 parts 
Coloring agent 100 parts 
(50 parts of rubber and 
50 parts of pigment) 
C.I. Basic Yellow 11 30 parts 
Bromophthalic anhydride 120 parts 
______________________________________ 
The ink composition was applied to rubber hose which was then vulcanized at 
150.degree. C. for 25 minutes. The coating formed on the rubber article 
changed its color to red in 25 minutes. The inspection of the product 
revealed that it was satisfactorily vulcanized. 
The ink compositions prepared in this example and other examples to be 
described later were found to be easily applicable and highly adherent to 
rubber and the coating formed was found not to have been separated from 
the article during vulcanizing operation. 
EXAMPLE 2 
A red ink composition of this invention was prepared by uniformly mixing 
the following components. 
______________________________________ 
Petroleum resin 100 parts 
("Mitsui Hi-lets G-100X", 
Mitsui Petrochemical Co., Ltd., Japan) 
Butadiene rubber 60 parts 
("Nipol BR 1441", 
Nippon Zeon Co., Ltd., Japan) 
Ethylene glycol monoethyl ether 
150 parts 
Xylene 750 parts 
Oil soluble dye 1 part 
("Oil Blue #8", Chou Synthetic 
Chemical Co., Ltd., Japan) 
C.I. Basic Red 15 10 parts 
Chlorophthalic anhydride 5 parts 
Titanium oxide 270 parts 
______________________________________ 
The coating formed from the ink composition on rubber articles discolored 
to white by vulcanization of the articles at 145.degree. C. for 5 minutes, 
whereby it was able to clearly indicate the completion of vulcanization. 
EXAMPLE 3 
A purple ink composition was prepared by using the following components. 
______________________________________ 
Phenol resin 90 parts 
("Tamanol 100S", 
Arakawa Chemical Co., Ltd., Japan) 
Styrene-butadiene rubber 90 parts 
("Nipol 1006", 
Nippon Zeon Co., Ltd., Japan) 
Cyclohexanone 500 parts 
Xylene 500 parts 
Oil soluble dye 1 part 
("Selest Yellow GRN") 
C.I. Basic Violet 15 50 parts 
White pigment 250 parts 
("PAG 6806", Dainichi Color & 
Chemical Mfg. Co., Ltd., Japan) 
Tetrachlorophthalic anhydride 
50 parts 
______________________________________ 
The ink composition was applied to a surface portion of a rubber article 
which was then vulcanized at 140.degree. C. for 20 minutes. The coating 
formed from the ink composition discolored to yellow, thereby distinctly 
indicating the completion of vulcanization. 
EXAMPLE 4 
A purple ink composition was prepared by uniformly mixing the following 
components. 
______________________________________ 
C.I. Basic Red 35 1.5 parts 
("Diacryl Brilliant Pink R-N", 
Mitsubishi Kasei Kogyo K.K., Japan) 
Titanium oxide 25.0 parts 
Oil soluble dye 0.1 parts 
("SBN Blue-1", 
Hodogaya Chemical Co., Ltd., Japan) 
Rosin 20.0 parts 
("Rosin WW", Tokushima Seiyu K.K., Japan) 
Xylene 120.0 parts 
Toluene 280.0 parts 
Ethyl cellosolve 20.0 parts 
Styrene-butadiene rubber 20.0 parts 
("Nipol 1006", 
Nippon Zeon Co., Ltd., Japan) 
4-Chlorobenzenesulfonic acid 
10.0 parts 
______________________________________ 
The ink composition was applied to a rubber article which was then 
vulcanized at 145.degree. C. for 15 minutes, thereby changing the color of 
the coated layer of composition to blue. The vulcanization of the rubber 
article was found appropriate. 
EXAMPLE 5 
An orange ink composition consisting of the following components was 
prepared. 
______________________________________ 
C.I. Basic Orange 22 1.0 parts 
("Sumiacryl Orange R", 
Sumitomo Chemical Co., Ltd., Japan) 
Titanium oxide 20.0 parts 
Rosin-modified xylene resin 
25.0 parts 
("Nicanol A-70", Mitsubishi 
Gas Chemical Co., Ltd., Japan) 
Xylene 260.0 parts 
Ethyle acetate 20.0 parts 
Synthetic rubber 20.0 parts 
("EP-21", Nippon Synthetic 
Rubber Co., Ltd., Japan) 
Toluene 130.0 parts 
2-Fluoronaphthalenedisulfonic acid 
10.0 parts 
______________________________________ 
The coating formed from the composition on rubber articles changed its 
color from orange to white when the articles were vulcanized at 
160.degree. C. for 20 minutes. 
EXAMPLE 6 
A green ink composition was prepared using the following materials. 
______________________________________ 
C.I. Basic Blue 62 1.5 parts 
("Astrazon Blue 5RL", 
Bayer A.G., Germany) 
Acrylic resin 10.0 parts 
("Daikalac S-1235", 
Daido Kasei K.K., Japan) 
Methylcyclohexane 390.0 parts 
Phenolic resin 10.0 parts 
("Tamanol 1010R", 
Arakawa Chemical Co., Ltd., Japan) 
Yellow Pigment 25.0 parts 
("Hansa Yellow 10G", 
Hoechst A.G., Germany) 
Natural rubber 20.0 parts 
Methyl ethyl ketone 30.0 parts 
5-Chlorosalicylic acid 15.0 parts 
______________________________________ 
The ink composition was found to adequately indicate the vulcanization of 
rubber products by turning into yellow when the products were vulcanized 
at 145.degree. C. for 10 minutes. 
EXAMPLE 7 
A yellow ink composition was prepared by mixing the following materials. 
______________________________________ 
C.I. Basic Yellow 11 1.5 parts 
("Kayacryl Yellow 2GL", 
Nihon Kayaku, K.K., Japan) 
Titanium oxide 30.0 parts 
Rosin-modified maleic resin 
20.0 parts 
("Teskid MRG", Tokushima Seiyu K.K., Japan) 
Toluene 240.0 parts 
Ethyl cellosolve 20.0 parts 
Xylene 60.0 parts 
Methyl isobuthyl ketone 220.0 parts 
2,3,4-trichlorobenzoic acid 
20.0 parts 
______________________________________ 
The ink composition applied on the surface of a rubber article changed the 
color to white when the article was vulcanized at 160.degree. C. for 20 
minutes. 
EXAMPLE 8 
An orange ink composition of this invention was prepared by uniformly 
mixing the following materials. 
______________________________________ 
Ethanol 100 parts 
Toluene 900 parts 
Rosin 80 parts 
Yellow pigment (containing 50% 
90 parts 
of ethylene-propylene rubber) 
("Pigmotex Yellow 302E", 
Sanyo Color Co., Ltd., Japan) 
C.I. Basic Red 12 50 parts 
Tetrabromophthalic anhydride 
10 parts 
______________________________________ 
The coating formed from the ink composition discolored to yellow by 
vulcanization at 130.degree. C. for 10 minutes. 
EXAMPLE 9 
A red ink composition of this invention was prepared by uniformly mixing 
the following materials. 
______________________________________ 
Toluene 200 parts 
Xylene 800 parts 
Triethyl phosphate 100 parts 
Phenol resin 100 parts 
("Tamanol #526", 
Arakawa Chemical Co., Ltd., Japan) 
Styrene-butadiene rubber 70 parts 
("Nipol #2001", 
Nippon Zeon Co., Ltd., Japan) 
C.I. Basic Red 14 15 parts 
Oil soluble dye 1 part 
("Neozapon Blue FLE", BASF AG) 
Finely divided dispersible 
200 parts 
coloring agent 
("PAD-6701", Dainichi Color & 
Chemicals Mfg. Co., Ltd., Japan) 
Tetrabromophthalic anhydride 
100 parts 
______________________________________ 
The ink composition changed the color to white after vulcanization of 
rubber articles at 150.degree. C. for 20 minutes. 
EXAMPLE 10 
A number of ink compositions were prepared in the same manner as in Example 
9 except that the tetrabromophthalic anhydride was used in varying 
amounts. 
Table 1 given below shows the relationship between the amount of the 
tetrabromophthalic anhydride and the time required for the change of 
color. 
TABLE 1 
______________________________________ 
Tetrabromophthalic anhydride 
Discoloration 
Amount (part) 140.degree. C. 
150.degree. C. 
______________________________________ 
0 5 (min) 3 (min) 
20 7 4 
40 15 8 
60 22 12 
80 30 16 
100 (Ex. 8) 36 20 
200 78 42 
300 120 65 
______________________________________