Color-developing phenolic-aldehyde composition for pressure-sensitive recording sheet material and process for the preparation thereof

Disclosed is a color-developing composition for pressure-sensitive recording sheet material of the self-contained type comprising (A) 100 parts by weight of a copolymer obtained by reacting a p-alkylphenol having an alkyl moiety of from 1 to 12 carbon atoms and phenol with formaldehyde and (B) from 1 to 20 parts by weight of a hindered phenolic compound selected from phenols having an alkyl, alkylene or hydroxyl substituent radical in at least the 2- or 6-position, or both, of the benzene ring and derivatives thereof, the copolymer and the hindered phenolic compound being homogeneously dissolved in mutual solution. The hindered phenolic compound is either added to the starting materials for the preparation of the copolymer or, at the end of the copolymerization reaction, added to the resulting copolymer and dissolved homogeneously in mutual solution.

BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
This invention relates to improved color-developing compositions for 
pressure-sensitive recording sheet material of the single-sheet type. 
(b) Description of the Prior Art 
Pressure-sensitive recording sheet materials are generally divided into two 
groups: the double-sheet and the single-sheet type. Pressure-sensitive 
recording sheet materials of the double-sheet type comprise a first sheet 
(generally known as "coated back sheet") coated with microcapsules 
containing an electron donative organic compound (commonly called 
"pressure-sensitive dye") dissolved in a non-volatile and hydrophobic 
organic solvent and a second sheet (generally known as "coated front 
sheet") coated with an aqueous coating composition containing an electron 
attractive color developer, these sheets being disposed with the coated 
surfaces thereof facing each other. On the other hand, pressure-sensitive 
recording sheet materials of the single-sheet type (commonly called 
"self-contained papers") comprise a single sheet having one surface coated 
both with a layer of microcapsules and with a layer of color developer. 
In the above-described pressure-sensitive recording sheet materials are 
used one or more pressure-sensitive dyes selected from (1) 
triphenylmethane dyes such as Crystal Violet Lactone, (2) methylene blue 
dyes such as Benzoyl Leucomethylene Blue, (3) fluoran dyes such as 
Rhodamine Lactam, (4) leucoauramine dyes, (5) spiropyran dyes, and the 
like. 
On the other hand, the electron attractive color developers used therein 
include (1) inorganic solid acids such as acid clay and activated clay, 
(2) certain phenol-formaldehyde polymers, (3) metallic salts of 
substituted salicylic acids, and the like. Among these color developers, 
certain phenol-formaldehyde polymers and particularly 
p-phenylphenol-formaldehyde polymers are widely used in pressure-sensitive 
recording sheet materials of the double-sheet type because of (1) their 
excellent color-developing performance, (2) the good application 
properties (or rheological properties) of the aqueous coating color 
prepared therefrom and (3) the good water resistance of the sheets coated 
therewith. 
In the prior art, however, it was quite impractical to use such 
p-phenylphenol-formaldehyde polymers as the color developer for 
pressure-sensitive recording sheet material of the single-sheet type 
because they tend to cause a remarkable degree of backgrounding (or 
spontaneous color development) during manufacture and/or handling. 
The present inventors have previously proposed the use of certain 
p-alkylphenol-phenol-formaldehyde copolymers as the color developer for 
pressure-sensitive recording sheet material of the single-sheet type. They 
are copolymers obtained by reacting one or more p-alkylphenols having the 
general formula 
##STR1## 
where R is an alkyl radical containing from 1 to 12 carbon atoms, and 
phenol with formaldehyde in the presence of an acid catalyst, and are now 
finding wide acceptance. 
When used as the color developer for pressure-sensitive sheet material of 
the single-sheet type, the above-described 
p-alkylphenol-phenol-formaldehyde copolymers show great advantages such as 
(1) excellent color-developing performance, (2) good resistance to 
staining by moist heat (or a low degree of spontaneous color development), 
and (3) good resistance to yellowing by light. However, these copolymers 
and self-contained papers fabricated therewith are still liable to 
yellowing by air oxidation. Thus, there is an eager desire for an 
improvement which can solve this problem. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a novel improved 
color-developing composition for pressure-sensitive recording sheet 
material of the single-sheet type. 
It is another object of the present invention to provide an improved 
color-developing composition for pressure-sensitive recording sheet 
material of the single-sheet type which composition is significantly 
improved in resistance to yellowing during storage and in an oxidizing 
atmosphere. 
It is still another object of the present invention to provide an improved 
color-developing composition for pressure-sensitive recording sheet 
material of the single-sheet type which composition has excellent 
color-developing performance, good resistance to staining by moist heat, 
and good resistance to yellowing by light. 
It has now been discovered that these objects of the present invention are 
accomplished by a color-developing composition comprising a 
p-alkylphenol-phenol-formaldehyde copolymer and a phenol having an alkyl, 
alkylene or hydroxyl substituent radical in at least 2- or 6-position, or 
both, of the benzene ring (hereinafter referred to as "hindered phenolic 
compound"), both ingredients being homogeneously dissolved in mutual 
solution. 
DETAILED DESCRIPTION OF THE INVENTION 
According to the present invention, there is provided a color-developing 
composition for pressure-sensitive recording sheet material of the 
self-contained type comprising (A) 100 parts by weight of a copolymer 
obtained by reacting at least one p-alkylphenol selected from the group 
consisting of compounds having the general formula 
##STR2## 
where R is an alkyl radical containing from 1 to 12 carbon atoms, and 
phenol with formaldehyde and (B) from 1 to 20 parts by weight of a 
hindered phenolic compound selected from the group consisting of phenols 
having an alkyl, alkylene or hydroxyl substituent radical in at least the 
2- or 6-position, or both, of the benzene ring and derivatives thereof, 
the copolymer and the hindered phenolic compound being homogeneously 
dissolved in mutual solution. 
The above-described composition is pulverized and then subjected to wet 
milling in the presence of a surface active agent. To the resulting 
aqueous suspension are added various ingredients required to provide the 
characteristics desired for pressure-sensitive recording sheet materials. 
The aqueous coating color so prepared is applied on the 
microcapsule-bearing surface of coated back sheets and then dried to 
obtain self-contained papers. 
The p-alkylphenol used in the present invention may be any of the 
para-substituted phenols in which the substituent radical is a C.sub.1 
-C.sub.12 alkyl radical. For example, p-cresol, p-ethylphenol, 
p-iso-propylphenol, p-sec-butylphenol, p-tert-butylphenol, 
p-tert-amylphenol, p-cyclohexylphenol, p-sec-hexylphenol, p-n-octylphenol, 
p-tert-octylphenol, p-nonylphenol, p-tert-dodecylphenol and the like are 
all usable. However, p-alkylphenols having a C.sub.4 -C.sub.10 alkyl 
radical are preferred. A desired p-alkylphenol-phenol-formaldehyde 
copolymer can be obtained by mixing one or more such p-alkylphenols with 
phenol and reacting them with formaldehyde in the presence of a catalyst. 
Among others, p-tert-octylphenol is most preferred in view of its 
color-developing performance and particularly its initial color-developing 
ability. The p-alkylphenol may include small amounts of isomers and 
homologues which have been produced in the course of its synthesis. 
The formaldehyde used in the present invention may be supplied from any of 
the source materials, such as formalin, paraformaldehyde and the like, 
which can generate formaldehyde under the reaction conditions. The 
catalyst used in the present invention may be any of the well-known 
catalyst for the synthesis of phenol-formaldehyde polymers, such as 
sulfuric acid, p-toluenesulfonic acid, phosphoric acid, hydrochloric acid, 
trichloroacetic acid, oxalic acid, sodium hydroxide, ammonia and the like. 
However, hydrochloric acid and oxalic acid are preferred in view of the 
color of the resulting copolymer. 
In the p-alkylphenol-phenol-formaldehyde copolymers used in the present 
invention, the molar ratio of the p-alkylphenol to the phenol ranges from 
0.3 to 5 and preferably from 0.5 to 3. The molar ratio of the formaldehyde 
to the combined amount of the p-alkylphenol and the phenol (hereinafter 
referred to as "F/P ratio") ranges from 0.6 to 1.0. Generally, as the F/P 
ratio increases, the softening point (as measured according to ASTM 
E28-58T) of the condensation product is elevated and the color-developing 
performance thereof is degraded. In the preparation of a particular 
p-alkylphenol-phenol-formaldehyde copolymer, the F/P ratio should be 
chosen so that the softening point thereof ranges from 70.degree. to 
120.degree. C. and preferably from 80.degree. to 120.degree. C. and most 
preferably from 90.degree. to 110.degree. C. If the softening point is 
below 70.degree. C., difficulty will be encountered in pulverizing 
operation and in the preparation of an aqueous suspension, while if it is 
above 120.degree. C., the color-developing performance (particularly, the 
color-developing rate) will be degraded to an impractical level. 
The hindered phenolic compounds, which are used in the present invention in 
order to improve the discoloration behavior of the 
p-alkylphenol-phenol-formaldehyde copolymer (that is, in order to 
substantially prevent yellowing thereof) during storage and in an 
oxidizing atmosphere, include phenols having an alkyl, alkylene or 
hydroxyl radical or radicals in at least the 2- or 6-position, or both, of 
the benzene ring and derivatives thereof. Specifically, these hindered 
phenolic compounds can be classified into three groups: [A] 
2,6-di-tert-butylphenol derivatives, [B] di- or triphenol derivatives, and 
[C] other phenol derivatives. 
[A] The 2,6-di-tert-butylphenol derivatives include: (I) unsubstituted, 
p-alkyl-substituted and p-hydroxyalkyl-substituted phenols such as 
2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol, 
2,4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-p-ethylphenol, 
3,5-di-tert-butyl-4-hydroxybenzyl alcohol, and the like; (II) 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(alkylthio)-1,3,5-triazines 
such as 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis-(n-butylthio)-1,3,5-triazin 
e, 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(n-octylthio)-1,3,5-triazine 
, 6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(tert-octylthio)-1,3,5-tria 
zine, 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(n-nonylthio)-1,3,5-triazine 
, and the like; (III) esters and amides of 
(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid such as dodecyl 
3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl 
3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,2'-thiodiethyl bis 
[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,6-hexanediol 
bis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 
N,N'-hexamethylene-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide), 
pentaerythrityl tetrakis 
[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the like; (IV) di- 
and triphenols having tert-butyl substituent radicals in both of the 2- 
and 6-positions of the benzene ring with respect to the phenolic hydroxyl 
group, such as 2,2'-(3,5-di-tert-butyl-4-hydroxyphenyl)propane, 
4,4'-cyclohexylidene-bis(2,6-di-tert-butylphenol), 
1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 
4,4'-methylene-bis-(2,6-di-tert-butylphenol), 
4,4'-thio-bis(2,6-di-tert-butylphenol), and the like; and (V) other 
2,6-di-tert-butylphenol derivatives such as 
2,6-di-tert-butyl-4-dialkylaminophenols, 
(3,5-di-tert-butyl-4-hydroxyphenyl)alkyl phosphates, 
tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, and the like. 
[B] The di- and triphenol derivatives (excluding the compounds of subgroup 
[A](IV)) include, for example, 4,4'-thio-bis(3-methyl-6-tert-butylphenol), 
2,2'-thio-bis(di-sec-amylphenol), 
2,2'-thio-bis(4-methyl-6-tert-butylphenol), 
2,2'-thio-bis(4,6-di-tert-butylresorcinol), 
4,4'-butylidene-bis(3-methyl-6-tert-butylphenol), 
2,2'-methylene-bis(3-methyl-6-tert-butylphenol), 
2,2'-methylene-bis(4-ethyl-6-tert-butylphenol), 
1,1,3-tris(2-methyl-4-hydroxy-5-tert:butyl)butane, and the like. 
[C] The other phenol derivatives include, for example, 
3-methyl-6-tert-butylphenol, 2,4-di-tert-butylphenol, 
2,5-di-tert-butyl-p-cresol, butylhydroxyanisole, catechol, 
p-tert-butylcatechol, 4,6-di-tert-butylresorcinol, 
4,6-di-tert-amylresorcinol, 2,4-di-tert-butyl-.alpha.-naphthol, and the 
like. 
Although these hindered phenolic compounds are all effective in preventing 
the p-alkylphenol-phenol-formaldehyde copolymer of the present invention 
from yellowing during storage, the 2,6-di-tert-butylphenol derivatives 
have been found to be more effective. Among the 2,6-di-tert-butylphenol 
derivatives, 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(alkylthio)-1,3,5-triazines 
and particularly 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(n-octylthio)-1,3,5-triazine 
as well as esters of (3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid and 
particularly octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate are 
exceptionally effective. 
The discoloration behavior of p-alkylphenol-phenol-formaldehyde copolymers 
and self-contained papers fabricated therewith is presumed to be 
attributable to the colored products of oxidation reactions caused, during 
storage, by oxygen or oxidizing agents present in air. However, since the 
real cause for yellowing cannot be determined in most cases, no effective 
countermeasures have been taken in the past. 
Moreover, the copolymers having phenol radicals in the molecule show a 
strong tendency to yellowing during storage, as compared with 
p-alkylphenol-formaldehyde polymers. Furthermore, the tendency becomes 
much stronger in the pH range (pH 8-9) commonly used for aqueous coating 
color. 
The hindered phenolic compounds used in the present invention are known to 
be useful as oxidation inhibitors for general-purpose plastics such as 
polyethylene, polypropylene and polystyrene; synthetic rubbers such as 
styrene-butadiene rubber, isoprene rubber and ethylene-propylene rubber; 
polyurethanes; polycarbonates; polyamides; polyacetals; and the like. 
However, since the hindered phenolic compounds come under the same 
category as the above-described p-alkylphenol-phenol-formaldehyde 
copolymers, it has been utterly unknown in the past that these compounds 
are useful as yellowing inhibitors for phenol-formaldehyde polymers and 
particularly as yellowing inhibitors for pressure-sensitive recording 
sheet materials having applied thereto a considerable amount of 
phenol-formaldehyde polymer in the form of finely-divided particles. 
In the fabrication of self-contained papers, a hindered phenolic compound 
as defined above, together with a p-alkylphenol-phenol-formaldehyde 
copolymer as defined above, is applied to sheets of paper. There are a 
number of possible methods of doing this: (1) An aqueous suspension of the 
p-alkylphenol-phenol-formaldehyde copolymer is prepared and then mixed 
with a separately prepared aqueous suspension of the hindered phenolic 
compound to form an aqueous coating color. Alternatively, (2) the hindered 
phenolic compound is added to the p-alkylphenol-phenol-formaldehyde 
copolymer and the resulting mixture is suspended in water by wet milling. 
Alternatively, (3) a resinous composition comprising the 
p-alkylphenol-phenol-formaldehyde copolymer and the hindered phenolic 
compound dissolved homogeneously in mutual solution is prepared and then 
suspended in water. 
According to these three methods, self-contained papers containing the same 
hindered phenolic compound in an equal amount were fabricated and then 
examined for resistance to yellowing during storage and in an oxidizing 
atmosphere. As a result, the method (3) has been found to be the most 
effective in improving resistance to yellowing. The results obtained with 
the methods (1) and (2) are less desirable than those obtained with the 
method (3). 
Thus, when self-contained papers are fabricated by the combined use of a 
p-alkylphenol-formaldehyde copolymer and a hindered phenolic compound, a 
satisfactory improvement in resistance to yellowing is produced not by a 
mere uniform mixture of finely-divided particles of the 
p-alkylphenol-phenol-formaldehyde copolymer and finely-divided particles 
of the hindered phenolic compound, but by finely-divided particles of a 
composition comprising the p-alkylphenol-phenol-formaldehyde copolymer and 
the hindered phenolic compound dissolved homogeneously in mutual solution. 
The resinous compositions of the present invention, which comprise a 
p-alkylphenol-phenol-formaldehyde copolymer and a hindered phenolic 
compound dissolved homogeneously in mutual solution, can be prepared 
according to the following procedure: p-Alkylphenol and phenol are reacted 
with formaldehyde or a source material of formaldehyde at a temperature of 
from 70.degree. to 180.degree. C. for a period of from 1 to 10 hours in 
the presence of a suitable catalyst. If formalin or paraformaldehyde is 
used as the source material of formaldehyde or if a small amount of water 
is added to the reaction system, the reaction temperature can disirably be 
controlled through the medium of the boiling point (100.degree. C.) of 
water. After the reaction carried out for a predetermined period of time, 
the water is removed under normal pressure and then under reduced 
pressure. On completion of the reaction, the reaction mixture is cooled to 
obtain a colorless or light-colored and transparent resin. 
A hindered phenolic compound is either added to the starting materials for 
the preparation of the copolymer or, after removal of the water, added to 
the resulting copolymer. The hindered phenolic compound is used in an 
amount of from 1 to 20 parts by weight per 100 parts by weight of the 
p-alkylphenol-phenol-formaldehyde copolymer. If the amount of the hindered 
phenolic compound is less than 1 part by weight, no sufficient improvement 
in resistance to yellowing will be produced, while if it is greater than 
20 parts by weight, no further improvement in resistance to yellowing will 
be noted and economical losses will result. 
Thus, the color-developing compositions of the present invention, which 
comprise a p-alkylphenol-phenol-formaldehyde copolymer and a hindered 
phenolic compound dissolved homogeneously in mutual solution, exhibit 
improved resistance to yellowing during storage and in an oxidizing 
atmosphere, in addition to the excellent color-developing performance, 
good resistance to staining by moist heat, and good resistance to 
yellowing by light that are possessed by the copolymer. 
Accordingly, self-contained papers fabricated with a color-developing 
composition of the present invention are very excellent in overall 
characteristics and significantly improved in commercial value. 
In order to further illustrate the present invention, the following 
examples and controls are given. In these examples and controls, the 
measurement of the softening point of a copolymer, the preparation of an 
aqueous suspension of a color-developing composition, the preparation of 
an aqueous coating color, the fabrication of self-contained papers, the 
determination of the color-developing rate, and the evaluation of 
resistance to yellowing during storage, to yellowing by NO.sub.x, and to 
staining by moist heat were carried out according to the following 
procedures. 
[Measurement of the Softening Point of a Copolymer] 
The softening point of a p-alkylphenol-phenol-formaldehyde copolymer was 
measured at a heating rate of 5.degree. C./min. according to ASTM E28-58T 
(Softening Point by Ring and Ball Apparatus). 
[Preparation of an Aqueous Suspension of a Color-developing Composition] 
A composition comprising a p-alkylphenol-phenol-formaldehyde copolymer and 
a hindered phenolic compound, or a p-alkylphenol-phenol-formaldehyde 
copolymer alone, was pulverized. Then, 80 g of the resulting fine powder 
of 50-mesh size, 6.4 g of a polymeric polycarboxylic acid type surface 
active agent (comprising a 25% aqueous solution of "Carribon B" 
manufactured and sold by Kao-Atlas Co., Japan), and 113.6 g of water were 
mixed in a sand grinding mill to form an aqueous suspension of white 
particles having an average diameter of 2.0.mu.. 
[Preparation of an Aqueous Coating Color] 
Using the above-described aqueous suspension, an aqueous coating color was 
prepared according to the following formulation. 
______________________________________ 
Solid 
Amount Content 
(parts by 
(parts by 
Ingredient 
weight) weight) Notes 
______________________________________ 
Aqueous 253 106.3 
Suspension 
Kaolin 545 545 
Calcium 100 100 
Carbonate 
50% Aqueous Disper- 
Latex 130 65 sion of Dow 636 
20% Aqueous Solution 
of MS-3600 (manufactured 
Oxidized Starch 
475 95 and sold by Nihon Shoku- 
hin Kako Co., Japan) 
Water 775.3 
Total 2278.3 911.3 
______________________________________ 
[Fabrication of Self-contained Papers] 
Coated back sheets were prepared by coating sheets of paper (having a basis 
weight of 40 g/sq.m.) with a layer of microcapsules containing Crystal 
Violet Lactone. Then, using a Mayer bar, the above-described aqueous 
coating color was applied to the microcapsule-bearing surface of the 
coated back papers so as to give a dry-coat weight of 5.5 g/sq.m. Thus, 
self-contained papers designed to produce a blue color were obtained. 
[Determination of the Color-developing Rate] 
A self-contained paper fabricated as above was placed between two sheets of 
quality paper and imprinted with an electrically-operated typewriter to 
develop a cobalt blue color. The reflectance of the self-contained paper 
was measured by means of Model TSS Hunter Colorimeter (manufactured and 
sold by Toyo Seiki Co., Japan) equipped with an amber filter. This 
measurement of the density of the developed color was made both 1 minute 
and 20 hours after imprinting. Then, the initial color-developing range 
(J.sub.1) and the ultimate color-developing rate (J.sub.2) were calculated 
from the following equations: 
##EQU1## 
where I.sub.0, I.sub.1 and I.sub.2 are the reflectances observed before 
imprinting, 1 minute after imprinting, and 20 hours after imprinting, 
respectively. With both the initial and the ultimate color-developing rate 
higher values represent more desirable results. 
[Resistance to Yellowing During Storage] 
(A) A self-contained paper fabricated as above (but not yet subjected to 
color development) was stuck on a wall of a room not exposed to direct 
sunlight and allowed to stand for 2 months. Using Model TSS Hunter 
Colorimeter equipped with a blue filter, the reflectance of the 
self-contained paper was measured before and after testing. Then, the 
degree of yellowing during storage was expressed in terms of the retention 
of whiteness (Q) defined by the following equation: 
EQU Q=(M.sub.2 /M.sub.1).times.100 (%) 
where M.sub.1 and M.sub.2 are the reflectances observed before and after 
testing, respectively. 
(B) In order to accelerate yellowing during storage and examine the degree 
of yellowing during storage at elevated temperatures, a self-contained 
paper fabricated as above was placed in a Geer oven thermostated at 
50.degree. C. and allowed to stand for 10 days. Using a blue filter, the 
reflectance of the self-contained paper was measured before and after 
testing. Then, the degree of yellowing during storage was expressed in 
terms of the retention of whiteness (P) defined by the following equation: 
EQU P=(L.sub.2 /L.sub.1).times.100 (%) 
where L.sub.1 and L.sub.2 are the reflectances observed before and after 
testing, respectively. 
In these procedures (A) and (B), greater values for the retention of 
whiteness (Q) or (P) represent less degrees of yellowing of the coated 
surface, thus indicating that the quality of the self-contained paper is 
so high as to retain a high degree of whiteness even after long-term 
storage under practical conditions. 
[Resistance to Yellowing by NO.sub.x ] 
Pressure-sensitive recording sheet materials using a phenol-formaldehyde 
polymer as color developer are known to undergo yellowing during storage 
in an oxidizing atmosphere such as NO.sub.x. Accordingly, the degree of 
yellowing in an atmosphere of NO.sub.x (which is a typical oxidant gas) 
was examined according to JIS-1055 (Procedure for Testing the Fastness of 
Dyed Materials and Dyestuffs to Nitrogen Oxide Gas). A self-contained 
paper fabricated as above (but not yet subjected to color development) was 
placed in a sealed container and exposed to nitrogen oxide gas for 50 
minutes. Using a blue filter, the reflectance of the self-contained paper 
was measured before and after testing. Then, the degree of yellowing by 
NO.sub.x was expressed in terms of the retention of whiteness (R) defined 
by the following equation: 
EQU R=(N.sub.2 /N.sub.1).times.100 (%) 
where N.sub.1 and N.sub.2 are the reflectances observed before and after 
testing, respectively. 
Greater values for the retention of whiteness (R) represent less degrees of 
yellowing in an oxidizing atmosphere such as NO.sub.x, thus indicating 
that yellowing of the self-contained paper is prevented during long-term 
storage under practical conditions. 
[Resistance to Staining by Moist Heat] 
A self-contained paper fabricated as above was placed in a chamber kept at 
a temperature of 40.degree. C. and a relative humidity of 90%, and allowed 
to stand for 16 hours. Using an amber filter, the reflectance of the 
self-contained paper was measured before and after testing. Then, the 
degree of staining by moist heat (or the degree of spontaneous color 
development under high-temperature and high-humidity conditions) was 
expressed in terms of the retention of whiteness (T) defined by the 
following equation: 
EQU T=(S.sub.2 /S.sub.1).times.100 (%) 
where S.sub.1 and S.sub.2 are the reflectances observed before and after 
testing, respectively. 
Greater values for the retention of whiteness (T) represent less degrees of 
spontaneous color development under high-temperature and high-humidity 
conditions. If the degree of staining by moist heat is on such a level as 
shown in the following examples and controls, the problem of spontaneous 
color development will not arise in case of practical application using an 
air-knife coater.

EXAMPLE 1 
A mixture of 180 g of p-tert-butylphenol, 75.2 g of phenol, 15 g of 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(n-butylthio)-1,3,5-triazine 
, 137.8 g of 37% formalin, and 3.4 g of 15% hydrochloric acid was allowed 
to condence for 8 hours with water being refluxed. Thereafter, the water 
was removed by heating the mixture at temperatures up to 170.degree. C. 
under normal pressure and then under reduced pressure. On completion of 
the reaction, 290 g of a light-brown and transparent resinous composition 
having a softening point of 101.degree. C. was obtained. 
EXAMPLE 2 
A mixture of 180 g of p-tert-butylphenol, 75.2 g of phenol, 20 g of 
octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (manufactured 
and sold by Ciba-Geigy Co. under the trade name of Irganox 1076), 137.8 g 
of 37% formalin, and 3.4 g of 15% hydrochloric acid was allowed to 
condense for 8 hours with water being refluxed. Thereafter, the water was 
removed by heating the mixture at temperatures up to 170.degree. C. under 
normal pressure and then under reduced pressure. On completion of the 
reaction, 295 g of a light-brown and transparent resinous composition 
having a softening point of 100.degree. C. was obtained. 
Control 1 
The procedure of Example 1 was repeated except that the octadecyl 
3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate was omitted. As a result, 
275 g of a light-brown and transparent 
p-tert-butylphenol-phenol-formaldehyde copolymer having a softening point 
of 102.degree. C. was obtained. 
EXAMPLE 3 
A mixture of 287 g of p-tert-octylphenol, 63 g of phenol, 67.5 g of 80% 
paraformaldehyde, 17.5 g of 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(n-octylthio)-1,3,5-triazine 
(manufactured and sold by Ciba-Geigy Co. under the trade name of Irganox 
565), and 5.0 g of oxalic acid dihydrate was allowed to condense for 10 
hours with water being refluxed. Thereafter, the water was removed by 
heating the mixture at temperatures up to 165.degree. C. under normal 
pressure and then under reduced pressure. On completion of the reaction, 
384 g of a pale-yellow and transparent resinous composition having a 
softening point of 100.degree. C. was obtained. 
EXAMPLE 4 
A mixture of 232.5 g of p-tert-octylphenol, 67.5 g of phenol, 134.8 g of 
37% formalin, and 4.0 g of 30% hydrochloric acid was allowed to condense 
for 6 hours with water being refluxed. Thereafter, the water was removed 
by heating the mixture at temperatures up to 170.degree. C. under normal 
pressure and then under reduced pressure. Thus, a pale-yellow and 
transparent resin having a softening point of 102.degree. C. was obtained. 
The resin was maintained at 150.degree. C. with stirring, during which 20 
g of 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(n-octylthio)-1,3,5-triazine 
was added thereto and dissolved therein homogeneously. On cooling to room 
temperature, 338 g of a pale-yellow and transparent resinous composition 
having a softening point of 101.degree. C. was obtained. 
EXAMPLE 5 
The procedure of Example 4 was repeated except that the 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(n-octylthio)-1,3,5-triazine 
was replaced by 20 g of 
tetrakis[methylene-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane. 
As a result, 340 g of a pale-yellow and transparent resinous composition 
having a softening point of 100.degree. C. was obtained. 
Control 2 
A mixture of 232.5 g of p-tert-octylphenol, 67.5 g of phenol, 134.8 g of 
37% formalin, and 4.0 g of 30% hydrochloric acid was allowed to condense 
for 6 hours with water being refluxed. Thereafter, the water was removed 
by heating the mixture at temperatures up to 170.degree. C. under normal 
pressure and then under reduced pressure. On cooling to room temperature, 
318 g of a pale-yellow and transparent 
p-tert-octylphenol-phenol-formaldehyde copolymer having a softening point 
of 102.degree. C. was obtained. 
TABLE 1 
__________________________________________________________________________ 
Evaluation of Performance 
Resistance to Yellowing 
During Storage 
Color- Retention Resistance 
Resistance 
developing 
of White- to Yellowing 
to Staining 
Rate ness (Q) 
Retention of 
by by Moist 
Type of P-Alkyl- Ulti- 
After Stor- 
Whiteness(P) 
NO.sub.x 
Heat 
phenol-phenol- Initial 
mate 
age in a 
After Stor- 
Retention 
Retention 
formaldehyde Type of Hindered 
Value 
Value 
Room for 2 
age at 50.degree. C. 
Whiteness 
of 
Copolymer Phenolic Compound 
(J.sub.1) 
(J.sub.2) 
Months 
for 10 Days 
(R) Whiteness 
__________________________________________________________________________ 
(T) 
p-tert-Butylphenol- 
6-(4-Hydroxy-3,5-di-tert- 
Ex. 1 
phenol-formalde- 
butylanilino)-2,4-bis(n- 
17.0 
44.4 
98.5 97.2 76.3 62.1 
hyde Copolymer 
butylthio)-1,3,5-triazine 
p-tert-Butylphenol- 
Octadecyl 3-(3,5-di-tert- 
Ex. 2 
phenol-formalde- 
butyl-4-hydroxyphenyl)- 
17.0 
44.3 
96.2 94.1 75.2 62.0 
hyde Copolymer 
propionate 
p-tert-Butylphenol- 
Con- 
phenol-formalde- 
Not used 17.2 
44.5 
90.3 87.0 70.1 61.8 
trol 1 
hyde Copolymer 
p-tert-Octylphenol- 
6-(4-Hydroxy-3,5-di-tert- 
Ex. 3 
phenol-formaldehyde 
butylanilino)-2,4-bis(n- 
23.0 
40.6 
97.4 95.2 75.2 63.0 
Copolymer octylthio)-1,3,5-triazine 
p-tert-Octylphenol- 
6-(4-Hydroxy-3,5-di-tert- 
Ex. 4 
phenol-formaldehyde 
butylanilino)-2,4-bis(n- 
22.7 
40.4 
97.8 96.3 74.2 62.8 
Copolymer octylthio)-1,3,5-triazine 
p-tert-Octylphenol- 
Tetrakis methylene-(3,5- 
Ex. 5 
phenol-formaldehyde 
di-tert-butyl-4-hydroxy- 
22.8 
40.7 
92.3 92.5 74.8 62.2 
Copolymer phenyl)propionate methane 
p-tert-Octylphenol- 
Con- 
phenol-formaldehyde 
Not used 23.3 
40.5 
89.4 86.2 69.6 63.8 
trol 2 
Copolymer 
__________________________________________________________________________ 
EXAMPLE 6 
The procedure of Example 4 was repeated except that the 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(n-octylthio)-1,3,5-triazine 
was replaced by 20 g of 4,4'-thio-bis(3-methyl-6-tert-butylphenol). As a 
result, 340 g of a pale-yellow and transparent resinous composition having 
a softening point of 100.degree. C. was obtained. 
EXAMPLE 7 
The procedure of Example 4 was repeated except that the 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(n-octylthio)-1,3,5-triazine 
was replaced by 18 g of 4,6-di-tert-amylresorcinol. As a result, 338 g of 
a pale-yellow and transparent resinous composition having a softening 
point of 102.degree. C. was obtained. 
EXAMPLE 8 
The procedure of Example 4 was repeated except that the 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(n-octylthio)-1,3,5-triazine 
was replaced by 22 g of 2,4,6-tri-tert-butylphenol. As a result, 342 g of 
a pale-yellow and transparent resinous composition having a softening 
point of 101.degree. C. was obtained. 
Control 3 
The procedure of Example 4 was repeated except that the 
6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(n-octylthio)-1,3,5-triazine 
was replaced by 15 g of N,N'-diphenyl-p-phenylenediamine. As a result, 335 
g of a dark-gray and transparent resinous composition was obtained. 
TABLE 2 
__________________________________________________________________________ 
Evaluation of Performance 
Resistance to Yellowing 
During Storage 
Resistance 
Resistance 
Color- Retention to Yellowing 
to Stain- 
developing 
of by ing by 
Rate Whiteness 
Retention of 
NO.sub.x 
Moist Heat 
Ulti- 
(Q) After 
Whiteness(P) 
Retention 
Retention 
Type of p-Alkyl- Initial 
mate 
Storage in 
After Stor- 
of of 
phenol-phenol-form- 
Type of Hindered 
Value 
Value 
a Room for 
age at 50.degree. C. 
Whiteness 
Whiteness 
aldehyde Copolymer 
Phenolic Compound 
(J.sub.1) 
(J.sub.2) 
2 Months 
for 10 Days 
(R) (T) 
__________________________________________________________________________ 
p-tert-Octylphenol- 
4,4'-Thio-bis(3-methyl-6- 
Ex. 6 
phenol-formaldehyde 
tert-butylphenol) 
22.9 
40.5 
91.4 89.9 71.8 62.4 
Copolymer 
p-tert-Octylphenol- 
Ex. 7 
phenol-formaldehyde 
4,6-Di-tert-amylresorcinol 
23.0 
40.4 
90.4 90.3 73.1 62.3 
Copolymer 
p-tert-Octylphenol- 
2,4,6-Tri-tert-butyl- 
Ex. 8 
phenol-formaldehyde 
phenol 22.8 
40.6 
91.9 92.8 76.5 62.5 
Copolymer 
p-tert-Octylphenol- 
N,N'-Diphenyl-p- 
Con- 
phenol-formaldehyde 
phenylene-diamine 
20.8 
39.9 
70.8 68.2 69.2 60.8 
trol 3 
Copolymer 
__________________________________________________________________________