Process for the preparation of reaction products of natural resinic acids and formaldehyde

Process for the manufacture of resinous products which comprises PA0 (a) reacting in a first step, at least one natural resinic acid with 7.5 to 12% by weight, referred to the weight of the natural resinic acids, of a polymeric formaldehyde at a superatmospheric pressure and at a temperature of from 100.degree. to 200.degree. C., PA0 (b) in a second stage, increasing the temperature to at least 200.degree. C., but by at least 20.degree. C., and continuing the reaction at atmospheric pressure to yield a partial esterified product having an acid number of 115 to 135, PA0 (c) reacting the reaction product obtained from (b) at a temperature of at least 200.degree. C. with an amount of an alkaline-reacting calcium compound sufficient to yield a partial calcium salt having a calcium content of from 3.5 to 4% by weight, referred to the weight of the reaction product; PA0 (d) neutralizing any residual calcium compound by the addition of from 10 to 50% by weight, relative to the weight of the calcium compound added, of a saturated monocarboxylic acid having from 1 to 6 carbon atoms, at a temperature of at least 200.degree. C. and simultaneously completing the salt formation by reaction to yield a reaction product having an acid number of from 20 to 40, the product PA0 (e.sub.1) then being isolated or PA0 (e.sub.2) being admixed with up to 5% by weight of natural resinic acids after at least one of stages (b) to (d), and a printing ink containing said products.

This invention relates to a process for the preparation of partial esters 
and partial salts of reaction products of natural resinic acids and 
formaldehyde, and to the use thereof. 
The development of very high-speed printing machines and the trend to 
print, but only on papers which are normally or only slightly coated, but 
also increasingly on uncoated papers make especially high demands on the 
quality of gravure printing inks for such use. These are required to be 
not only stable, so that they may be stored even when incorporating red, 
blue and yellow pigments and change their colouration as little as 
possible, but also to exhibit good pigment wetting, to dry quickly and 
give the print good durability and a high gloss. 
The reaction of rosin with formaldehyde with the intention of simply 
converting the acid and low-melting natural resinic acids into 
higher-melting and more neutral products has been described. It is also 
known that in the preparation of resinates, especially zinc resinates, 
such reaction products are more resistant to "blocking," that is, to signs 
of crystallisation, compared with melts of natural resinic acids reacted 
directly with metal compounds. The reaction of melts of balsam rosin 
firstly with paraformaldehyde and then either with calcium acetate or 
calcium hydroxide at 275.degree. to 290.degree. C. has also been 
described. In this case, however, only resins with an acid number of 5 are 
obtained, which are not soluble in toluene, but are still just capable of 
swelling. These resins are therefore not suitable for gravure printing. A 
further disadvantage of this process is that, despite modification of the 
rosin with paraformaldehyde, it is not possible to prevent "blocking" from 
occurring following the addition of zinc oxide after brief reaction, so 
that it is no longer possible to incorporate calcium hydroxide, as shown 
by the Examples of this publication. 
Although some other Examples describe the preparation of resinates obtained 
without "blocking", these have melting points of only 74.degree. to 
93.degree. C. and are completely turbid. 
According to one feature of the present invention there is provided a 
process for the manufacture of resinous products which comprises 
(a) reacting, in a first stage, at least one natural resinic acid with 7.5 
to 12, preferably 8 to 10% by weight of a polymeric formaldehyde referred 
to the weight of natural resinic acid, at a superatmospheric pressure and 
at a temperature of 100.degree. to 200.degree. C.; 
(b) in a second stage, increasing the temperature to at least 200.degree. 
C., but by at least 20.degree. C., and continuing the reaction at 
atmospheric pressure to yield a partially esterified product having an 
acid number of 115 to 135; 
(c) reacting the reaction product obtained from (b) at a temperature of at 
least 200.degree. C., preferably at a temperature not lower than that used 
in (b), with an amount of an alkaline calcium compound sufficient to yield 
a partial calcium salt having a calcium content of 3.5 to 4% by weight 
referred to the weight of the reaction product; and 
(d) neutralising any residual calcium compound by the addition of 10 to 50% 
by weight, relative to the calcium compound added, of a saturated 
monocarboxylic acid having from 1 to 6 carbon atoms, and preferably acetic 
acid, at a temperature of at least 200.degree. C. and simultaneously 
completing salt formation to yield a reaction product having an acid 
number of 20 to 40. 
The products manufactured according to the process of the invention are 
distinguished by especially favourable properties for use as printing-ink 
binders, especially for inks intended for use in toluene gravure printing. 
Such products are soluble in toluene, do not "block" during their 
preparation and do not contain any undesired portion of unreacted metal 
compounds. The products generally have a melting point of at least 
130.degree. C. (capillary method) and a viscosity of 50 to 600, preferably 
70 to 400 mPa.s (50% toluene/20.degree. C.). 
Natural resinic acids which may be used in the process of the invention 
are, for example, rosin, especially balsam rosin, root resins, tall oil 
resin, either individually or in admixture. 
The partial esterification of stages (a) and (b) is effected by 
esterification by the carboxyl groups of the natural resinic acid with the 
methylol groups obtained from the reaction with the polymeric 
formaldehyde. 
The proportion of polymeric formaldehyde which may be used in the process 
according to the invention, for example in the form of trioxan, preferably 
paraformaldehyde, should be kept in stage (a) within the range specified 
in order to obtain a product having the desired properties, in particular 
to obtain products having a sufficiently high melting point. 
Stage (a) of the process is preferably effected at a pressure of 2 to 10 
bars, preferably 3 to 6 bars. In many cases, however, stage (a) may be 
carried out at a superatmospheric pressure outside this range. 
Advantageously, the reaction of stage (a) is carried out at a temperature 
of 125.degree. to 200.degree. C., preferably up to 180.degree. C.; in 
stages (b) and (c) at a temperature of 200.degree. to 280.degree. C., 
preferably at 200.degree. to 260.degree. C.; and in stage (d) at a 
temperature of 200.degree. to 260.degree. C. 
The reaction of stage (c) is generally carried out using calcium oxide 
and/or calcium hydroxide, preferably in the form of a suspension thereof 
in a suitable solvent. Suspension results in a homogeneous distribution 
and therefore complete reaction. Solvents which may be used for this 
purpose are, for example high-boiling media, such as xylene, white spirit, 
turpentine, mineral oils having a boiling range of up to 280.degree. C., 
resinic oils having an acid number of less than 20, such as those used in 
the preparation of natural resinic acids modified with phenol resin, as 
well as terpene phenol distillates with an acid number of less than 1, as 
used in the preparation of terpene phenol resins. 
The reaction of the carboxylic acid in stage (d) may also be carried out in 
the presence of a solvent, preferably the same solvent as is used for 
suspending the calcium compounds used in step (c). The reaction with the 
carboxylic acid, especially acetic acid, causes not only conversion of 
unreacted calcium compounds into the corresponding salt, but also serves 
simultaneously to control the viscosity of the product. Any unreacted 
carboxylic acid does not necessarily need to be removed, since it does not 
have a disadvantageous effect on the properties of the final product. 
It is also possible, in a further stage (e) of the process of the invention 
to mix or to modify with up to 5% by weight of natural resinic acids, 
products which are obtained with higher viscosities than those desired, in 
order thereby to achieve products with the desired viscosity. Stage (e) 
may take place with or without a chemical reaction. In the former case, 
the natural resinic acid is advantageously added after stage (b) and/or 
after stage (d), although it is also possible to do this after stage (c). 
At the temperatures applied thereafter or at the temperature at which the 
resinic acid is added after stage (d), e.g. at 200.degree. to 250.degree. 
C., modification takes place by reaction. 
The products according to the invention have considerably higher melting 
points than the natural resinic acids used as starting materials. They are 
very soluble in aromatic hydrocarbons, especially in toluene. Since they 
also have very good wetting properties on pigments, they are preeminently 
suitable as binding agents for toluene gravure printing inks. As such, 
they show rapid drying, a high gloss, high colour strength and good 
durability on coated and uncoated paper. Thus according to a further 
aspect of the present invention there is provided a printing ink 
composition, preferably a gravure printing ink composition, containing a 
reaction product obtained from the process of the present invention. 
Especially advantageous is the behaviour in storage of toluene gravure 
printing inks prepared with yellow pigments, because they not only remain 
generally stable in respect of their viscosity, but also show 
substantially less tendency to turn green than commercial resinates.

The following Examples serve to illustrate the process according to the 
invention and printing inks produced from the products thereof. In the 
Examples, unless specified otherwise, T represents parts by weight and % 
represents % by weight. The viscosity values always relate to a 50% 
toluene solution/20.degree. C. The melting points (Mp) were determined by 
the capillary method. 
EXAMPLES 
For stage (a), the natural resinic acids or mixtures thereof are melted; 
paraformaldehyde is added to the mixture heated to 100.degree. to 
120.degree. C., the mixture being brought to the desired temperature with 
stirring in a pressure vessel. When the reaction is complete stage (b) is 
effected at atmospheric pressure and the mixture is heated to above 
200.degree. C. for partial esterification, water containing formaldehyde 
being evaporated off. 
The following Table 1 gives a summary of stages (a) and (b). The acid 
numbers given were determined by means of methanolic potassium hydroxide. 
Table 1 
______________________________________ 
Example 1 2 3 4 5 
______________________________________ 
Starting materials 
Portuguese rosin (T) 
3000 3000 2400 -- -- 
Mp. 65.degree. C., Acid No. 165 
American root resin (T) 
-- -- -- 3000 -- 
Mp. 62.degree. C., Acid No. 162 
American tall oil 
resin (T) -- -- 600 -- 3000 
Mp. 58.degree. C., Acid No. 160 
Paraformaldehyde (T) 
225 300 300 255 360 
Stage a) - Reaction at superatmospheric pressure. 
Temperature 160.degree. C. 
+ + + + + 
Maximum pressure (bars) 
3.5 4.8 3.8 4.2 5.6 
Minimum pressure (bars) 
1.8 2.5 2.2 2.0 2.8 
Reaction time (4 h) 
+ + + + + 
Stage b) - Partial esterification at atmospheric pressure. 
Reaction 1h/250.degree. C. 
+ + + + + 
Yield (T) 3070 3100 3060 3080 3125 
Melting point (Mp) (.degree.C.) 
80 82 81 78 85 
Acid Number 127 122 123 126 115 
______________________________________ 
As indicated in Table 1, after stages (a) and (b) the melting point is 
already increased in comparison with that of the starting resinic acids 
with a simultaneous lowering of the acid number. 
The following Examples illustrate the further processing in stages (c) to 
(d): 
600 T of a sample according to Examples 1 to 5 is reacted in stage c) with 
calcium oxide or calcium hydroxide, optionally in suspension in a solvent, 
and in stage (d) with acetic acid (99%), optionally together with the same 
organic solvent as in stage (c). Table 2 gives a summary of Examples 1a to 
5d and the products obtained. 
1a--15 minutes after the addition of calcium oxide (not in suspension) the 
acetic acid is added dropwise and the mixture is heated to 220.degree. to 
260.degree. C. until the acid number has fallen to approximately 35. After 
removal of the volatile fractions under reduced pressure the reaction 
product is obtained. 0.9 T of calcium oxide were not reacted. 
1b--This Example is effected as in Example 1a, but with a suspension of 
calcium oxide and with acetic acid in xylene. Despite the rather higher 
quantity of calcium oxide the latter is reacted completely owing to its 
homogeneous distribution in the solvent. 
The products of Examples 1a and 1b yield quick-drying printing inks with a 
high gloss, good colour strength and good hold-out on coated and natural 
resin paper. 
2a--The sample from Example 2 is melted. 1 hour after the addition of the 
calcium hydroxide suspension the acetic acid is added at 250.degree. C. 
The process is continued as in Example 1a. 
3a to 5d--The solvent for the calcium hydroxide suspension according to 
Example 3a is mineral oil having a boiling range of 240.degree. to 
270.degree. C., for Examples 3b, 4b and 5b to 5d is a distillate (acid 
number=0) obtained from the preparation of terpene pnenol resins, and for 
Examples 4a and 5a is a resin oil (acid number=12) obtained from the 
preparation of natural resinic acids modified with phenol resin. In 
Examples 5c and 5d natural acids are added additionally after stage d). 
5V (Comparison Example to 5b)--In this Comparison Example the addition of a 
carboxylic acid is omitted. Consequently, the viscosity of the final 
product is considerably higher than that of the final product of Example 
(5b). 
Table 2 
__________________________________________________________________________ 
1 2 3 4 
Example a b a b a b a b 
__________________________________________________________________________ 
Stage c) 
Temp. (.degree.C.) 
220-260 
220-260 230-260 
230-260 
230-260 
230-260 
CaO (T) 32 33 -- -- 16 -- -- -- 
Ca(OH).sub.2 (T) 
-- -- 39 41 20 41 39 41 
Organic -- 33 30 60 35 30 30 30 
Solvent(T) 
(xylene) (turp- 
(white- 
(miner- (resin 
entine) 
spirit) 
al oil) oil) 
Stage d) (+e) 
Acetic acid 
10 15 10 15 15 17 10 15 
(T) 
Organic -- 15 10 20 15 12 10 15 
Solvent (T) 
Natural 
resin (T) 
-- -- -- -- -- -- -- 
Final Product 
603 600 597 595 605 600 603 595 
(T) 
Melting point 
(T) 140 143 137 147 140 147 139 144 
Acid Number 
35 33 27 25 30 26 24 24 
Viscosity 
70 110 125 300 150 305 120 273 
(50% toluene 
20.degree. C.) (mPa.s) 
__________________________________________________________________________ 
V Comparison 
5 Comparison Sample 
Example a b 5b c d A B 
__________________________________________________________________________ 
Stage c) 
Temperature 
230-260 
230-260 
230-260 230-260 
230-260 
(.degree.C.) 
CaO (T) -- -- -- -- -- 
Ca(OH).sub.2 (T) 
39 41 41 41 -- 
organic 30 30 30 30 -- 
solvent (T) 
(resinic 
(as 4b) 
(as 4b) (as 4b) 
oil) 
Stage d) (+e) 
Acetic acid 
(T) 10 15 -- 15 15 
Organic 
Solvent (T) 
10 15 -- 15 15 
natural 
resin (T) 
-- -- -- 20 30 
Final Product 
Melting point592 594 616 624 -- -- 
(.degree.C.) 
150 154 148 147 146 134 141 
Acid Number 
22 20 23 23 21 43 49 
Viscosity 
(50% toluene 
220 558 954 340 200 90 270 
20.degree. C.) (mPa.s) 
__________________________________________________________________________ 
Printing Test 
(a) Preparation of the printing inks 
The final products according to the previous Examples were dissolved in 
toluene and mixed with suitable pigments. For red inks, 20% red pigment 
was added; for blue inks, 16% blue pigment; and for yellow inks, 12% 
yellow pigment were added. 100 T of 50% toluene solutions were mixed with 
enough toluene to give an efflux time of 17 seconds in a DIN 4-mm beaker. 
Discussion of the Results of Table 3 
(a) and (b) red inks 
The following Table 3 shows that all inks of type (a) and (b) (with the 
exception of Example 4a) dry at least as quickly as the ink from the 
comparison resin considered, but on average more quickly. With all the 
Examples the gloss is more favourable than that of the Comparison 
Examples. Also, durability on paper is at least equivalent to that of the 
Comparison Example and in most cases it is superior thereto. The stability 
in storage of the red inks corresponds to that of the Comparison Example. 
(c) blue inks 
With the exception of Example 5c which has the same drying characteristics 
as the Comparison Example, all the other Examples show more rapid drying 
with a markedly improved gloss. Durability on paper is better in all cases 
than with the Comparison Example. Stability in storage is also more 
favourable. 
Table 3 
__________________________________________________________________________ 
Compa- Compa- 
rison rison 
resin resin 
1a 1b 2a 3a 4a A 2b 3b 4b 5a 5c 5d B 
__________________________________________________________________________ 
a) Red inks from bin- 
b) Red inks from binding 
ding agents of vis- agents of viscosity 
cosity 70-150mPa.s 150-400 mPa.s 
DIN 4-mm efflux time 
17 16.9 
17.1 
17 16.9 
17.1 16.9 
17.2 
17 17.3 
17.1 
17 16.9 
of inks/25.degree. C./S 
Drying of 36.mu.m wet 
40 38 36 37 45 40 35 36 37 40 41 42 43 
layer on coated paper/s 
Gloss 85 79 81 86 90 73 75 72 70 74 80 82 60 
Durability of 6.mu.m wet 
layer thickness on coated 
paper[60g/m.sup.2 ] 
as comparison ink A B 
+ + - - - + - - - - + + + 
ink 
better than ink A B 
- - + + + + + + + - - 
worse than ink A B 
- - - - - - - - - - - 
DIN 4-mm efflux time 
19.4 
19 19.2 
18.9 
19.5 
19.3 18.6 
18.9 
18.4 
18.7 
18.7 
18 18.8 
after 14 days/24.degree. C./s 
__________________________________________________________________________ 
Compa- Compa- 
rison rison 
resin resin 
2b 3a A 3b 4b 5c B 
__________________________________________________________________________ 
c) Blue inks 
DIN 4-mm efflux time 
17.1 
16.9 
17 17 17 17.1 
17.1 
of inks/25.degree. C./S 
Drying of 36.mu.m wet 
40 42 43 40 42 45 45 
layer on coated paper 
Gloss 74 70 63 64 65 70 55 
Durability of 6.mu.m wet 
layer thickness on coated 
paper [60g/m.sup.2 ] 
as comparison A B 
- - + - - -- + 
ink 
better than ink A B 
+ + - + + + - 
worse than ink A B 
- - - - - - - 
DIN 4-mm efflux time 
20.3 
20.5 
21 20 19 19.8 
20.6 
after 14 days/24.degree. C./s 
__________________________________________________________________________ 
(d) yellow inks 
Improved durability on paper is also obtained with yellow inks. To test 
stability in storage, a portion of the yellow inks were stored in a 
refrigerator and the major portion in screw-cap bottles for 7 days at 
40.degree. C. After a further day of storage at room temperature, the inks 
stored under refrigeration and the inks stored at 40.degree. C. were 
applied next to one another to coated paper with a wet-layer thickness of 
12 .mu.m by means of a wire coil and then assessed for their tendency to 
turn green. Also, the efflux time in a DIN 4 mm beaker at 25.degree. C. 
was determined. 
The results for the yellow inks are summarised in the following Table 4. 
Table 4 shows that the products prepared according to the invention as 
binding agents provide the yellow printing inks with not only better 
stability in storage, but also better stability of colouration. 
Table 4 
______________________________________ 
Com- 
parison 
resin 
Example 
1a 1b 2a 2b 3a 3b 4a 4b 5a 5d 5e 
A B 
______________________________________ 
d) yellow inks 
DIN 4- 
mm ef- 
flux time 
32 28 30 27 30 26 28 26 30 33 36 44 48 
of inks/ 
25.degree. C./s 
Turning 
green of 
inks: 
Slight 
+ + + + + + + + + + + - - 
Marked 
- - - - - - - - - - - + + 
Strong 
- - - - - - - - - - - + - 
______________________________________ 
It is not intended that the examples given herein should be construed to 
limit the invention thereto, but rather they are submitted to illustrate 
some of the specific embodiments of the invention. Resort may be had to 
various modifications and variations of the present invention without 
departing from the spirit of the discovery or the scope of the appended 
claims.