Antifoams based on oil-in-water emulsions for the paper industry

Antifoams based on oil-in-water emulsions, in which the oil phase accounts for from 5 to 50% by weight of the emulsions and consists essentially of a mixture of PA1 (a) fatty esters of C.sub.12 -C.sub.22 -carboxylic acids with monohydric to trihydric C.sub.1 -C.sub.22 -alcohols, PA1 (b) polyglyceryl esters which are obtainable by at least 20% esterification of polyglycerols which contain at least 2 glyceryl units with at least one C.sub.12 -C.sub.36 -fatty acid and PA1 (c) fatty esters of C.sub.12 -C.sub.22 -carboxylic acids and polyalkylene glycols, the molecular weight of the polyalkylene glycols being up to 5,000 g/mol, and, if required, PA1 (d) long-chain alcohols, fatty esters of alcohols of at least 22 carbon atoms and C.sub.1 -C.sub.36 -carboxylic acids, distillation residues which are obtainable in the preparation of alcohols having a relatively large number of carbon atoms by oxo synthesis or by the Ziegler process and which may be alkoxylated, and/or PA1 (e) hydrocarbons having a boiling point above 200.degree. C. or fatty acids of 12 to 22 carbon atoms, are used for controlling foam in pulp digestion, in the beating of paper stock, in papermaking and in the dispersing of pigments for papermaking.

The present invention relates to antifoams for the paper industry, based on 
an oil-in-water emulsion, in which the oil phase accounts for from 5 to 
50% by weight of the emulsion and consists essentially of a mixture of 
esters of long-chain carboxylic acids and, if required, conventional 
hydrophobic compounds, such as alcohols of at least 12 carbon atoms, 
distillation residues which are obtainable in the preparation of alcohols 
having a relatively large number of carbon atoms by oxo synthesis or by 
the Ziegler process and which may be alkoxylated, and/or hydrocarbons 
having a boiling point above 200.degree. C. or fatty acids of 12 to 22 
carbon atoms. 
The prior unpublished European Patent Application No. 92113458.1 discloses 
antifoams for the paper industry, based on an oil-in-water emulsion, in 
which the oil phase accounts for from 5 to 50% by weight of the emulsion 
and contains 
(a) an alcohol of at least 12 carbon atoms, fatty esters of alcohols of at 
least 22 carbon atoms and C.sub.1 -C.sub.36 -carboxylic acids, 
distillation residues which are obtainable in the preparation of alcohols 
having a relatively large number of carbon atoms by oxo synthesis or by 
the Ziegler process and which may be alkoxylated, a mixture of the stated 
compounds and/or 
(b) a fatty ester of a C.sub.12 -C.sub.22 -carboxylic acid with a 
monohydric to trihydric C.sub.1 -C.sub.18 -alcohol and, if required, 
(c) a hydrocarbon having a boiling point above 200.degree. C. or a fatty 
acid of 12 to 22 carbon atoms 
in combination with 
(d) from 1 to 80% by weight of polyglyceryl esters which are obtainable by 
at least 20% esterification of a polyglycerol mixture comprising 
from 0 to 10% by weight of monoglycerol, 
from 15 to 40% by weight of diglycerol, 
from 30 to 55% by weight of triglycerol, 
from 10 to 25% by weight of tetraglycerol, 
from 0 to 15% by weight of pentaglycerol, 
from 0 to 10% by weight of hexaglycerol and 
from 0 to 5% by weight of polyglycerols having higher degrees of 
condensation 
with at least one fatty acid of 12 to 36 carbon atoms. These oil-in-water 
emulsions are efficient antifoams in papermaking even at above 35.degree. 
C., for example at from 50.degree. to 60.degree. C. In contrast, other 
known antifoams based on oil-in-water emulsions which are usually used in 
papermaking become less efficient when the temperature of the aqueous 
system to be defoamed increases to above 35.degree. C. At even higher 
temperatures, a more rapid decrease in the efficiency of the antifoams 
then occurs when the known oil-in-water emulsions are used. Since there is 
an increasing trend toward closed water circulations in the paper mills, 
the result is an increase in the temperature of the circulated water in 
papermaking, so that the efficiency of the antifoams used to date 
substantially decreases. 
It is an object of the present invention to provide antifoams which are 
still sufficiently efficient even at relatively high temperatures for the 
water circulations in the paper mills. 
We have found that this object is achieved, according to the invention, by 
antifoams for the paper industry, based on an oil-in-water emulsion, in 
which the oil phase accounts for from 5 to 50% by weight of the emulsion 
and consists essentially of the mixture of 
(a) fatty esters of C.sub.12 -C.sub.24 -carboxylic acids with monohydric to 
trihydric C.sub.1 -C.sub.22 -alcohols, 
(b) polyglyceryl esters which are obtainable by at least 20% esterification 
of polyglycerols which contain at least 2 glycerol units with at least one 
C.sub.12 -C.sub.36 -fatty acid and 
(c) fatty esters of C.sub.12 -C.sub.22 -carboxylic acids and polyalkylene 
glycols, the molecular weight of the polyalkylene glycols being up to 
5,000 g/mol, and, if required, 
(d) alcohols of at least 12 carbon atoms, fatty esters of alcohols of at 
least 22 carbon atoms and C.sub.1 -C.sub.36 -carboxylic acids, 
distillation residues which are obtainable in the preparation of alcohols 
having a relatively large number of carbon atoms by oxo synthesis or by 
the Ziegler process and which may be alkoxylated, a mixture of the stated 
compounds and/or 
(e) hydrocarbons having a boiling point above 200.degree. C. or fatty acids 
of 12 to 22 carbon atoms. 
Fatty esters of C.sub.12 -C.sub.22 -carboxylic acids with a monohydric to 
trihydric C.sub.1 -C.sub.22 -alcohol are used as components (a) of the oil 
phase of the antifoam emulsion. The fatty acids on which the esters are 
based are, for example, lauric acid, myristic acid, palmitic acid, stearic 
acid, arachidic acid and behenic acid. Palmitic acid or stearic acid is 
preferably used for the preparation of the esters. Monohydric C.sub.1 
-C.sub.18 -alcohols, e.g. methanol, ethanol, n-propanol, isopropanol, 
n-butanol, isobutanol, hexanol, decanol, palmityl alcohol and stearyl 
alcohol, as well as dihydric alcohols, such as ethylene glycol, propylene 
glycol, 1,6-hexanediol or 1,4-butanediol, and trihydric alcohols, such as 
glycerol, may be used for the esterification of the stated carboxylic 
acids. The polyhydric alcohols may be completely or partially esterified. 
This class of compounds also includes the naturally occuring vegetable and 
essential fatty esters, for example coconut oil, palm oil, soybean oil, 
rapeseed oil and olive oil, or various tallow varieties and oils of animal 
origin, for example beef tallow, lard, fish oil and whale oil. The 
compounds of the group (a) can be used in the form of individual defined 
esters or in the form of mixtures for the preparation of the oil phase of 
the antifoam emulsions and are present in the oil phase in an amount of 
from 1 to 90, preferably from 40 to 80, % by weight. 
Polyglyceryl esters which are obtainable by at least 20% esterification of 
polyglycerols which contain at least two glycerol units with at least one 
C.sub.12 -C.sub.36 -fatty acid are used as compounds of group (b). The 
polyglycerols on which the esters are based are esterified at least to 
such an extent that compounds which are virtually insoluble in water are 
formed. The polyglycerols are obtained in a conventional manner by 
alkali-catalyzed condensation of glycerol at elevated temperatures or by 
reacting epichlorohydrin with glycerol in the presence of an acidic 
catalyst (cf. for example Fette, Seifen, Anstrichmittel, 88th year, No. 3 
(1986), pages 101-106). As a rule, the two stated processes give product 
mixtures which contain polyglycerols having at least 2 glycerol units. The 
distribution of the individual polymers may vary depending on preparation. 
The polyglycerols usually contain from at least 2 to about 30, preferably 
from 2 to 12, polymerized glycerol units. For example, polyglycerols which 
contain the polymeric glycerols in the following amounts are commercially 
available: 
from 15 to 40% by weight of diglycerol, 
from 30 to 55% by weight of triglycerol, 
from 10 to 25% by weight of tetraglycerol, 
from 0 to 15% by weight of pentaglycerol, 
from 0 to 10% by weight of hexaglycerol and 
from 0 to 5% by weight of polyglycerols having a higher degree of 
condensation. 
Polyglycerols having at least 2 glycerol units are esterified with at least 
one fatty acid of at least 12 to 36, preferably 16 to 30, carbon atoms in 
the molecule. The degree of esterification of the OH groups in the 
polyglycerols is from at least 20 to 100%, preferably from 60 to 100%. The 
long-chain fatty acids used for esterification may be saturated or 
ethylenically unsaturated. Examples of suitable fatty acids are lauric 
acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic 
acid, oleic acid, hexadecanoic acids, elaidic acid, eicosenoic acids, 
docosenoic acids, such as erucic acid or prasidic acid, and 
polyethylenically unsaturated acids, such as octadecadienoic acids and 
octadecatrienoic acids, e.g. linoleic acid and linolenic acid, mixtures of 
the stated saturated carboxylic acids, mixtures of the stated unsaturated 
carboxylic acids and mixtures of the saturated and ethylenically 
unsaturated carboxylic acids as well as montanic acid. In addition to 
mixtures of the polyglycerols, the pure polymers which are at least 20% 
esterified, for example esters of diglycerol, triglycerol, tetraglycerol, 
pentaglycerol or hexaglycerol or esters of polyglycerols having a high 
degree of condensation, may also be used as compounds of component (b). 
The polyglyceryl esters are usually prepared in the presence of an acidic 
esterification catalyst, such as sulfuric acid, p-toluene-sulfonic acid, 
citric acid, phosphorous acid, phosphoric acid or hypophosphorous acid, or 
a basic catalyst, such as sodium methylate or potassium tert-butylate. 
The compounds of component (b) are present in the oil phase in an amount of 
from 1 to 80, preferably from 5 to 20, % by weight. 
Suitable components (c) of the oil phase are fatty esters of C.sub.12 
-C.sub.22 -carboxylic acids and polyalkylene glycols which have a 
molecular weight up to 5,000 g/mol. The carboxylic acids on which the 
esters are based have been stated above in the description of the 
component (a). Examples of suitable polyalkylene glycols are polyethylene 
glycol, polypropylene glycol and polybutylene glycol, as well as block 
copolymers of ethylene oxide and propylene oxide, of ethylene oxide and 
butylene oxide and of ethylene oxide, propylene oxide and butylene oxide. 
The copolymers may also contain the alkylene oxide as randomly distributed 
polymerized units. The molecular weight of the polyalkylene glycols is up 
to 5,000 g/mol. The polyalkylene glycols contain at least 2 polymerized 
alkylene oxide units, such as ethylene oxide units. Polyethylene glycols 
having molecular weights of from 200 to 1,000 and block copolymers of 
ethylene oxide and propylene oxide having a molecular weight of from 500 
to 2,000 g/mol are preferably used as esterification components for the 
fatty acids. Ethylene oxide and propylene oxide may be reacted in any 
ratio for the preparation of the block copolymers. 
The block copolymers and the random copolymers usually contain from 5 to 
50, preferably from 20 to 40, % by weight of ethylene oxide and from 50 to 
95, preferably from 60 to 80, % by weight of propylene oxide as 
polymerized units. The compounds of group (c) can be prepared by 
esterifying the abovementioned polyalkylene glycols with C.sub.16 
-C.sub.20 -carboxylic acids, such as palmitic acid or stearic acid, or 
alkylene oxides, e.g. ethylene oxide or a mixture of ethylene oxide and 
propylene oxide (random or in blocks), are subjected to an addition 
reaction with a C.sub.12 -C.sub.22 -carboxylic acid and the remaining free 
OH group of the polyetherester is then esterified with a C.sub.12 
-C.sub.22 -carboxylic acid. The long-chain carboxylic acid used for the 
esterification may be the same as or different from that which was 
subjected to the alkoxylation reaction. The fatty esters of component (c) 
are present in the oil phase in an amount of from 1 to 80, preferably from 
5 to 20, % by weight. 
In addition to the components (a), (b) and (c), the oil phase of the 
antifoam emulsions may also contain components usually used in antifoam 
mixtures. Examples of these are the compounds of group (d). These include 
alcohols of at least 12 carbon atoms, fatty esters of alcohols of at least 
22 carbon atoms and C.sub.1 -C.sub.36 -carboxylic acids, distillation 
residues which are obtainable in the preparation of alcohols having a 
relatively large number of carbon atoms by oxo synthesis or by the Ziegler 
process and which may be alkoxylated, and mixtures of the stated 
compounds. 
In particular, alcohols of at least 12 carbon atoms or mixtures of alcohols 
are used as component (d) of the oil phase of the oil-in-water emulsions. 
These are as a rule monohydric alcohols which contain up to 48 carbon 
atoms in the molecule. Such products are commercially available. However, 
fatty alcohols which have a substantially larger number of carbon atoms in 
the molecule may also be used as component (d). The alcohols of component 
(d) are either natural or synthetic alcohols. For example, lauryl alcohol, 
myristyl alcohol, cetyl alcohol, palmityl alcohol, stearyl alcohol, 
behenyl alcohol, oleyl alcohol, ricinyl alcohol, linoleyl alcohol and 
erucyl alcohol are suitable. 
Mixtures of alcohols, for example mixtures of (1) alcohols of 12 to 26 
carbon atoms and (2) alcohols of 28 to 48 carbon atoms, may also be used 
as component (d). 
The synthetic alcohols, which are obtainable, for example, by oxidation of 
aluminum alkyls by the Ziegler process, are saturated, straight-chain 
alcohols. Synthetic alcohols are also obtained by oxo synthesis. As a 
rule, mixtures of alcohols are obtainable. Distillation residues which are 
obtained in the preparation of the abovementioned alcohols by oxo 
synthesis or by the Ziegler process can also be used as component (d) of 
the oil phase of the antifoam emulsions. Alkoxylated distillation residues 
which are obtained in the abovementioned processes for the preparation of 
higher alcohols by oxo synthesis or by the Ziegler process are also 
suitable as component (d) of the oil phase of the antifoam emulsions. The 
oxyalkylated distillation residues are obtained by alkoxylating the 
distillation residues with ethylene oxide or with propylene oxide or with 
a mixture of ethylene oxide and propylene oxide by known methods. Up to 5 
ethylene oxide or propylene oxide groups undergo addition per OH group of 
the alcohol in the distillation residue. Preferably, from 1 to 2 ethylene 
oxide groups undergo addition per OH group of the alcohol in the 
distillation residue. 
Other suitable components (d) are fatty esters of alcohols of at least 22 
carbon atoms and C.sub.1 -C.sub.36 -carboxylic acids, for example montan 
waxes or Carnauba waxes. The compounds of component (d) are, if required, 
used in the oil phase of the antifoam emulsions in an amount of up to 80, 
preferably up to 10, % by weight, based on components (a), (b) and (c). 
The novel oil-in-water emulsions can, if required, contain a further group 
of conventional components of oil antifoams, ie. (e) hydrocarbons having a 
boiling point above 200.degree. C. or fatty acids of 12 to 22 carbon 
atoms. The compounds of group (e) are present in the oil phase in an 
amount of up to 50, preferably up to 20, % by weight, based on the 
components (a), (b) and (c). 
The novel antifoam emulsions are prepared by emulsifying the oil phase in 
the aqueous phase. To do this, either the components (a), (b) and (c) and, 
if required, (d) and/or (e) can be emulsified individually in the aqueous 
phase, or a mixture of the components (a), (b), (c) and, if required, (d) 
and/or (e) is first prepared and this mixture is then emulsified in the 
aqueous phase. The oil phase accounts for from 5 to 50% by weight of the 
oil-in-water emulsions, while the amount of the aqueous phase in the 
emulsions is from 95 to 50% by weight, the percentages by weight summing 
to 100. The oil phase consists essentially of the mixture of components 
(a) to (c) and, if required, (d) and/or (e). Owing to equilibria, however, 
the possibility of certain components of the aqueous phase also passing 
into the oil phase cannot be ruled out. However, the oil phase of the 
novel antifoam emulsions consists of at least 99% by weight of the 
components (a) to (c) and, if required, (d) and/or (e). 
To emulsify the oil phase in the aqueous phase, apparatuses in which the 
components of the emulsion are subjected to a strong shear gradient, for 
example dispersers, are required. In order to obtain particularly stable 
oil-in-water emulsions, the emulsification of the oil phase in the aqueous 
phase is preferably carried out in the presence of surfactants which have 
an HLB value of more than 6 (for the definition) of the HLB value, see W. 
C. Griffin, Journal of the Society of Cosmetic Chemists, 5 (1954), 
249-256). The surfactants are oil-in-water emulsifiers or typical wetting 
agents. Among the surfactants, it is possible to use anionic, cationic or 
nonionic compounds or mixtures of these compounds which are compatible 
with one another, for example mixtures of anionic and nonionic or of 
cationic and nonionic wetting agents. Substances of the stated type are, 
for example, sodium salts or ammonium salts of higher fatty acids, such as 
ammonium oleate or ammonium stearate, oxyalkylated alkylphenols, such as 
nonylphenol or isooctylphenol, which are reacted with ethylene oxide in a 
molar ratio of from 1:2 to 1:50, oxyethylated unsaturated oils, for 
example the reaction products of one mol of castor oil and from 30 to 40 
mol of ethylene oxide or the reaction products of one mol of sperm alcohol 
with from 60 to 80 mol of ethylene oxide. Preferably used emulsifiers are 
also sulfated oxyethylation products of nonylphenol or octylphenol, which 
are present as the sodium or ammonium salt of the corresponding sulfuric 
half-ester, or benzenesulfonic and alkylbenzenesulfonic acids and salts 
thereof. 100 parts by weight of the oil-in-water emulsions usually contain 
from 0.1 to 5 parts by weight of an emulsifier or of an emulsifier 
mixture. In addition to the abovementioned emulsifiers, protective 
colloids, such as high molecular weight polysaccharides and soaps, or 
other conventional additives, such as stabilizers, may be used in the 
preparation of the oil-in-water emulsions. For example, the addition of 
from 0.05 to 0.5% by weight, based on the total emulsion, of high 
molecular weight, water-soluble homo- and copolymers of acrylic acid, 
methacrylic acid, acrylamide or methacrylamide as a stabilizer has proven 
useful. The use of such stabilizers forms the subject of, for example, 
EP-B-0 149 812. 
By emulsifying the oil phase in the aqueous phase, oil-in-water emulsions 
which have a viscosity of from 300 to 3,000 mPa.s immediately after 
preparation and in which the oil phase has a mean particle size of less 
than 25 .mu.m, preferably from 0.5 to 15 .mu.m, are obtained. 
Although the mixtures of the components (a) and (b) or (a) and (c) alone 
have little efficiency as antifoams based on oil-in-water emulsions, 
surprisingly a synergistic effect occurs when a compound of component (b) 
is combined with compounds (a) and (c). The novel oil-in-water emulsions 
are used in the paper industry in aqueous systems in which the formation 
of foam, particularly at elevated temperatures, must be controlled, for 
example in pulp digestion, the beating of paper stock, papermaking with 
paper machines with closed circulations and the dispersing of pigments for 
papermaking. From 0.02 to 0.5, preferably from 0.05 to 0.3, part by weight 
of the oil-in-water antifoam emulsion is used per 100 parts by weight of 
paper stock in a foam-forming medium. 
When added to a paper stock suspension, the novel antifoams also effect 
deaeration and are therefore also used as deaerators in papermaking (in 
addition to the paper stock). They are also suitable as antifoams in the 
coating of the paper, where they are added to coating strips. The 
antifoams can also be used in the food industry, in the starch industry 
and in wastewater treatment plants for foam control. If they are added to 
the paper stock as a deaerator, the amounts used for this purpose are from 
0.02 to 0.5 part by weight per 100 parts by weight of paper stock. 
In the Examples which follow, parts and percentages are by weight. The mean 
particle size of the particles of the oil phase emulsified in water was 
determined with the aid of a Coulter counter. The K value of the polymers 
was determined in aqueous solution at 25.degree. C. and at a concentration 
of 0.5% by weight at pH 7 according to H. Fikentscher, Cellulose-Chemie 13 
(1932), 58-64 and 71-74.

EXAMPLE 1 
An oil-in-water emulsion in which the oil phase accounts for 29% by weight 
of the emulsion and has a mean particle size of from 2 to 10 .mu.m is 
prepared with the aid of a dispersant. 
The oil phase consists of the following components: 
(a) 18 parts of a glyceryl triester of C.sub.16 -C.sub.18 -fatty acids, 
(b) 5 parts of a polyglyceryl ester which is obtainable by esterifying a 
mixture of polyglycerols comprising 
27% of diglycerol, 
44% of triglycerol, 
19% of tetraglycerol and 
10% of polyglycerols having a higher degree of condensation 
with a C.sub.12 -C.sub.26 -fatty acid mixture, the degree of esterification 
being 60% and 
(c) 2 parts of a fatty ester which is obtainable by esterifying a C.sub.16 
-C.sub.18 -fatty acid mixture with a block copolymer of ethylene oxide and 
propylene oxide in a molar ratio of 3:7, having a molecular weight of 
1,200 g/mol. 
The aqueous phase consists of 3 parts of an emulsifier which is obtainable 
by subjecting 25 mol of ethylene oxide to an addition reaction of 1 mol of 
isooctylphenol and esterifying the adduct with sulfuric acid to give the 
half-ester, and one part of a copolymer of 70% of acrylamide and 30% of 
acrylic acid, having a K value of 270, 0.2 part of sodium hydroxide 
solution and 70 parts of water. 
The components (a), (b) and (c) are first heated to 110.degree. C. and then 
added to the aqueous phase heated to 80.degree. C., with dispersing. The 
oil-in-water emulsion obtainable in this manner has a viscosity of 540 
mPa.s at 20.degree. C. immediately after the preparation. 
COMATIVE EXAMPLE 1 
According to EP-A-0 140 812, an oil phase is first prepared by mixing the 
following components: 
23 parts of a mixture of fatty C.sub.12 -C.sub.26 -alcohols, 
5 parts of a glyceryl triester of C.sub.16 -C.sub.18 -fatty acids and 
1 part of a mineral oil (commercial white oil). 
The aqueous phase consists of: 
3 parts of an emulsifier which is obtainable by subjecting 25 mol of 
ethylene oxide to an addition reaction with 1 mol of isooctylphenol and 
esterifying the adduct with sulfuric acid to give the half-ester, 
1 part of a copolymer of 70% of acrylamide and 30% of acrylic acid, having 
a K value of 270, 
0.2 part of sodium hydroxide solution and 
65 parts of water. 
The oil phase described above is first heated to 110.degree. C. and is then 
added to the aqueous phase heated to 80.degree. C., with dispersing. The 
oil-in-water emulsion obtainable in this manner has a viscosity of 1,830 
mPa.s and a particle size of 2-10 .mu.m at 20.degree. C. immediately after 
the preparation. 
COMATIVE EXAMPLE 2 
Using the method stated in Example 1, an oil phase comprising 18 parts of 
the glyceryl ester of C.sub.16 -C.sub.18 -fatty acids (=components (a) 
according to the Example) and 7 parts of the polyglyceryl ester of 
component (b) of the Example is emulsified in the aqueous phase also 
stated in said Example. An oil-in-water emulsion which has a viscosity of 
760 mPa.s and a mean particle size of from 2 to 10 .mu.m at 20.degree. C. 
immediately after the preparation is obtained. 
COMATIVE EXAMPLE 3 
The procedure described in Example 1 is used, except that 18 parts of 
component (a) described there and 7 parts of component (c) described in 
the Example are used as the oil phase. An antifoam emulsion which has a 
viscosity of 920 mPa.s at 20.degree. C. and a mean particle size of from 2 
to 10 .mu.m immediately after the preparation is obtained. 
The oil-in-water emulsion obtained in the Example and the emulsions 
according to Comparative Examples 1 to 3 are tested with regard to their 
efficiency in a paper stock suspension. The efficiency of the antifoam 
emulsions is determined by measuring the foam value. The following 
procedure is used for this purpose: 
5 l of a 0.1% foam-forming paper stock suspension (groundwood) are 
circulated for 5 minutes in a trough consisting of transparent plastic. 
The amount of foam formed on the surface of the stock suspension is then 
measured with the aid of a grid on the wall of the trough in area units 
(cm.sup.2) and is expressed as the foam value for evaluating the 
efficiency of an antifoam. 
The paper stock suspension is circulated in the absence of an antifoam for 
5 minutes, a foam value of from 1,200 to 1,250 cm.sup.2 being obtained. By 
adding 2 mg/l of an effective antifoam (a total of 10 mg of solid) to the 
paper stock suspension, this value is substantially reduced, so that it is 
a measure of the efficiency of an antifoam. 
Testing of the antifoams: 
The temperature of the paper stock suspension described above is 50.degree. 
C., the temperature being kept constant to .+-.1.degree. C. during the 5 
minute test. 
The efficiency of the antifoam is expressed as a percentage of residual 
foam R: 
##EQU1## 
where F.sub.e is the foam value measured after the addition of an antifoam 
and F.sub.O is the foam zero value, ie. the value measured in the absence 
of an antifoam. In this terminology, the smaller R the better the 
antifoam. 
The following results are obtained: 
______________________________________ 
% residual foam 
______________________________________ 
Example 23 
Comparative Example 
1 34 
2 40 
3 63 
______________________________________