Antistatic agents for synthetic fibers

Antistatic agents for synthetic fibers comprising 5-50 weight percent of a specific type of quaternary ammonium alkyl phosphate containing 1 weight percent or less of by-product alkali metal halides and 50-95 weight percent of alkali metal salt of saturated alkyl phosphate have improved antistatic characteristics both in high and low humidity conditions, reduce the amount of deposits that fall off, yellowing by a heat treatment and generation of rust, and allow good coiling forms to be obtained.

This invention relates to antistatic agents for synthetic fibers. 
In general, static electricity presents problems to synthetic fibers not 
only in the manufacturing process of filament yarn and staple fiber, 
spinning process, weaving process and finishing process but also regarding 
products made from them. Static electricity impedes operations and lowers 
the quality of products by dishevelling and wrapping and producing fluff. 
It thus gives shocks to people, causes the clothes to stick and attracts 
dust particles. It is therefore necessary to use an antistatic agent with 
synthetic fibers but such an antistatic agent must be able to exhibit its 
effectiveness not only under a condition of high humidity but also when 
humidity is low. 
During the production of synthetic fibers, finishing oil which fall off and 
deposit themselves on the machines during each process present serious 
problems. During a spinning process, for example, the fibers may be caused 
to wrap around a draft rubber roller. If they fall off onto a guide or a 
trumpet, these machine parts must be cleaned more frequently. If they fall 
off onto a heater during a spinning-drawing process, tar will be 
generated. If they fall off onto a guide during a warping process, it will 
generate fluff and cause yarn breakage. As the processing speed is 
increased, the problems caused by the deposit become even more serious and 
this necessarily implies that antistatic agents to be applied to synthetic 
fibers must have the property of not falling off at a significant rate. 
The present invention relates to antistatic agents for synthetic fibers 
having this required characteristic. 
There are many types of surface active agents (cationic, anionic, non-ionic 
and amphoteric) serving as antistatic agents for synthetic fibers. Alkyl 
phosphates exhibit favorable antistatic properties under conditions of 
high and medium humidity, do not fall off very much, do not turn yellow by 
a heat treatment and do not rust much, but are not as effective as desired 
as an antistatic agent in low humidity situations. 
Quaternary ammonium salts such as trimethyl lauryl ammonium chloride, 
triethyl polyoxyethylene (3 mols) stearyl ammonium methosulfate, and 
tributyloctyl ammonium nitrate have also been used as antistatic agents. 
These quaternary ammonium salts are advantageous in that they exhibit 
favorable antistatic properties not only at high humidity but also at low 
humidity but they fall off, turn yellow by a heat treatment and generate 
rusts. 
These problems associated with quaternary ammonium salts, however, are 
thought to be caused by the counter anions of quaternary ammonium cations. 
In fact, if the counter anion is Cl.sup.-, rusting becomes a serious 
problem and if it is NO.sub.3.sup.- or CH.sub.3 SO.sub.4.sup.-, yellowing 
becomes serious. Earlier, quaternary ammonium salts with phosphate anion 
introduced as counter anion came to be considered (Japanese Patent Tokko 
45-573 and Tokkai 54-70223). These quaternary ammonium lower alkyl 
phosphates exhibit favorable antistatic properties both at high humidity 
and at low humidity and have the advantages of not turning yellow much by 
a heat treatment and not producing much rust, but have the problem of 
falling off significantly. 
It is therefore an object of the present invention to eliminate the 
aforementioned problems by providing antistatic agents for synthetic 
fibers which are capable of exhibiting favorable antistatic properties 
under both high and low humidity conditions and do not fall off, turn 
yellow by a heat treatment or rust much. 
An antistatic agent for synthetic fibers according to this invention 
comprises 5-50wt % of quaternary ammonium alkyl phosphates shown by the 
formula (I) or (II) below and not containing more than 1wt% of by-product 
alkali metal halides and 50-95wt% of alkali metal salts of saturated alkyl 
phosphate with 50% or more of alkyl groups with 18 or more carbon atoms: 
##STR1## 
where R.sup.1 and R.sup.3 are alkyl group or alkenyl group with 8-18 
carbon atoms, R.sup.2, R.sup.6, R.sup.7 and R.sup.8 are alkyl group with 
1-3 carbon atoms, R.sup.4 is hydrogen or alkyl or alkenyl group with 8-18 
carbon atoms, R.sup.5 is alkyl or alkenyl group with 7-17 carbon atoms, X 
is alkyl group with 1-3 carbon atoms or a group shown by -(AO).sub.q H, Y 
is alkyl group with 1-3 carbon atoms or a group shown by -(A'O).sub.r H, 
AO and A'O being the same respectively as OA and OA' in the formulas (I) 
and (II), q and r are integers in the range of 2-40 such that q+r=4-42, OA 
and OA' are a single oxyethylene or oxypropylene group or a block or 
random connected mixture thereof, l and m are each zero or an integer in 
the range of 1-20 such that l+m= 0-20, and n is 2 or 3. 
In the formulas (I) and (II), if the number of carbon atoms in R.sup.1 and 
R.sup.3 is less than 8 or that in R.sup.5 is less than 7, the amount of 
deposit increases. If the content of by-product alkali metal halides 
exceeds 1wt% with respect to the quaternary ammonium alkyl phosphate, 
there is increased yellowing by a heat treatment and rusting. For this 
reason and in particular for preventing rust, particular preferable 
content of alkali metal halides which is particularly preferable is 0.3wt% 
or less with respect to quaternary ammonium alkyl phosphate. 
Examples of quaternary ammonium alkyl phosphate of the present invention 
shown by the formula (I) or (II) include combinations of the following 
quaternary ammonium cations and phosphate anions. The quaternary ammonium 
cations may be trimethyloctyl ammonium cation, triethylstearyl ammonium 
cation, 
##STR2## 
where AO and A'O are the same as in (I), triethyl octanoic amidopropyl 
ammonium cation, etc. The phosphate anion may be polyoxyethylene (3 mols) 
lauryl phosphate anion, polyoxyethylene (10 mols) stearyl phosphate anion, 
octyl phosphate anion, etc. 
In the following, methods of producing quaternary ammonium alkyl phosphates 
of this invention will be explained. Because of their characteristic 
chemical structures, the quaternary ammonium alkyl phosphates of the 
present invention cannot be produced advantageously from a practical point 
of view by any of the conventional methods. There has been known a method, 
for example, of preventing alkali metal halides from being produced as 
by-products by direct reaction between tertiary amine and lower alkyl 
triester of phosphoric acid (Japanese patent Tokko 45-573 and Tokkai 
54-70223), but since triesters of phosphoric acid with a long-chain alkyl 
group have low reactivity with tertiary amines, they are not practical for 
the production of quaternary ammonium long-chain alkyl phosphates. 
According to another conventional method, an alkali metal salt of mono- 
and/or di-long-chain alkyl phosphate is reacted with mono-long-chain alkyl 
tri-short-chain alkyl ammonium halide by a salt exchange in water or an 
alcohol solvent such as methanol, isopropanol, etc. Quaternary ammonium 
alkyl phosphates are the produced by filtering inorganic by-product 
compounds such as alkali metal halides. Although this conventional method 
is popular for the production and refining of so-called complex salts 
which are combinations of anion and cation active agents, it is not 
appropriate for keeping the content of inorganic by-products to 1wt% or 
less because both the quaternary ammonium halide and the alkali metal salt 
of alkyl phosphate to be used contain long-chain alkyl groups and it is 
stoichiometrically difficult to carry out the salt exchange reaction for 
increasing their concentrations to relatively high levels in the range of 
10-50wt% in water or alcohol-type solvent which are required for 
industrial reasons. Accordingly, there will remain unused quaternary 
ammonium halides and alkali metal salts of alkyl phosphate and this makes 
it practically impossible to reduce the content of alkali metal halides to 
1wt% or less with respect to quaternary ammonium alkyl phosphates. 
Quaternary ammonium alkyl phosphates according to this invention can be 
produced by the method described below. First, tertiary amine shown by the 
following formula (1) or (2) is quaternalized by alkyl halide (with alkyl 
group given by R.sup.2 or R.sup.8 of (I) or (II)). Next, lower alcoholate 
of alkyl metal is used in the presence or absence of lower alcohol as 
solvent to exchange the halogen anions of the anion part with lower alcoxy 
anions, and after the alkali metal halides generated at this time as 
by-products are separated, mono- or di-alkyl phosphate shown by the 
following formula (3) is used to exchange the alcoxy anions: 
##STR3## 
where R.sup.1, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7 X, Y, l, m and 
n are as defined above. 
Examples of alkali metal alcoholate which may be used here include sodium 
methylate, sodium ethylate and potassium isopropoxide, but sodium 
methylate is industrially advantageous. Favorable results are obtained in 
view of the salt exchange reaction and the separation process thereafter, 
if lower alcohol such as methanol, ethanol and isopropanol is used as 
solvent. Thus, quarternary ammonium alkyl phosphates of the present 
invention are mixtures of mono alkyl phosphate and dialkyl phosphate of 
quarternary ammonium. 
Quaternary ammonium alkyl phosphates of the present invention can be used 
singly as an antistatic component of a finishing oil for synthetic fibers 
but there are situations in which they prove to be even more effective if 
used as an appropriate mixture with a conventional antistatic agent. For 
example, a mixture with an appropriate amount of quaternary ammonium alkyl 
phosphate added to an antistatic agent of alkyl phosphate type not only 
provides to synthetic fibers an antistatic property to such a degree that 
was totally unexpected from a single alkyl phosphate system but also 
prevents the wrapping and falling off and a good coiling form can be 
obtained. 
Representative examples of alkyl phosphate type antistatic agent of which 
the effectiveness can be significantly improved by the addition of an 
appropriate amount of quaternary ammonium phosphate of the present 
invention include alkali metal salts of saturated alkyl phosphate having 
as principal component alkyl group with 18 or more carbon atoms. In such a 
mixed system, the content of the quaternary ammonium alkyl phosphate of 
the present invention should be 5-50wt%. Although the optimum ratio 
varies, depending on the kinds of quaternary ammonium alkyl phosphate and 
alkali metal salt of alkyl phosphate, a particularly preferable range is 
5-20wt% of quaternary ammonium phosphate (that is, 95-80wt% of alkali 
metal salt of alkyl phosphate). The antistatic agents of this invention 
can be applied singly to synthetic fibers such as polyesters, 
polyacrylonitriles and polyamides or to their mixtures with natural and 
chemical fibers. The rate of application to such synthetic fibers 
(inclusive of mixed fibers) is generally 0.01-2wt% and preferably 
0.01-0.5wt%. They may be applied to filaments, a tow or staple fibers by a 
kiss-roll method, by dipping or by spraying either during or after a 
spinning process. They may also be applied to fiber products. 
In what follows, the present invention and its effects will be explained 
further in detail by way of examples and comparisons and it should be 
understood that these examples are not intended to limit the scope of this 
invention.

TEST NO. 1 
Synthesis of quaternary ammonium alkyl phosphate of this invention (Example 
A-1): 
One mol of phosphoric anhydride was added to three mols of octyl alcohol 
over a period of one hour at 60.degree.-70.degree. C. while stirring. They 
were allowed to react with each other at 70.degree. C. for three hours and 
a mixture of mono and dioctyl phosphate was obtained. Separately, 0.5 mol 
of octyl dimethylamine and 200 ml of methanol were set inside an autoclave 
and after the interior gas was replaced by nitrogen, 0.5 molar equivalent 
of methyl chloride was introduced for a reaction at 60.degree.-70.degree. 
C. for three hours to obtain octyltrimethyl ammonium chloride. To this was 
gradually added 96 g of 28% sodium methylate-menthanol solution (0.5 molar 
equivalent as sodium methylate) for salt exchange and the by-product 
sodium chloride was filtered away to obtain a methanol solution of 
octyltrimethyl ammonium methoxide. To this methanol solution was added 0.5 
mol of the aforementioned mixture of mono and dioctyl phosphate and after 
methanol was distilled away, it was diluted with water to obtain 50wt% 
aqueous solution of octyltrimethyl ammonium octyl phosphate (A-1). 
Other quaternary ammonium alkyl phosphates (A-2 through A-11 and B-1 
through B-16 except B-12; only those starting with the letter A are 
quaternary ammonium alkyl phosphates of this invention) were synthesized 
as follows. 
SYNTHESIS OF A-2 THROUGH A-11 
They were obtained by methods similar to the method for A-1. 
SYNTHESIS OF B-1 THROUGH B-8 
They were obtained by methods similar to the method for A-1. 
B-9 THROUGH B-12 
Conventionally available products were used. 
SYNTHESIS OF B-13 
This was done by heating to dissolve 347.5 g (1 mol) of stearyl trimethyl 
ammonium chloride and 334.7 g (1 mol) of sodium sesqui stearyl phosphate 
in 2000ml of a mixed solvent of isopropyl alcohol/water=95/5 (volume 
ratio). The solution was heated and stirred for one hour at 60.degree. C. 
and the deposited sodium chloride was filtered away by heating at 
45.degree.-50.degree. C. Isopropyl alcohol was distilled from the filtered 
solution thus obtained while heating under a reduced pressure and 
trimethyl stearyl ammonium stearyl phosphate with 80% of solid component 
was obtained. 
SYNTHESIS OF B-14 
This was done by dissolving with heat 347.5 g (1 mol) of stearyl trimethyl 
ammonium chloride and 668 g (1 molar equivalent) of 50% aqueous sodium 
sesqui stearyl phosphate in 2000 ml of isopropyl alcohol and 1000 ml of 
water and isopropyl alcohol was distilled away under azeotropy while the 
mixture was heated and stirred. Next, 1000 ml of isopropyl alcohol was 
added to dilute the solution and sodium chloride which deposited at 
35.degree.-40.degree. C. was filtered away. Isopropyl alcohol was 
distilled away by heating under a reduced pressure from the filtered 
solution which had been obtained and trimethyl stearyl ammonium stearyl 
phosphate with 80% of solid component was obtained. 
SYNTHESIS OF B-15 
This was obtained by a method similar to that for B-13. 
SYNTHESIS OF B-16 
This was obtained by a method similar to that for B-14. 
Each of the examples shown below (except B-12) is described as follows: (1) 
cation part (2) anion part (mixture of mono and di as in the case of 
aforementioned A-1, except B-9 through B-12), and (3) content of alkali 
metal halide (NaCl or KCl) with respect to effective components (weight 
percent, measured by the Volhard method except for B-9 through B-12). POE, 
POP and EO respectively stand for polyoxyethylene, polyoxypropylene and 
oxyethylene. 
A-1: (1) trimethyl octyl ammonium, (2) octyl phosphate, (3) 0.18 
A-2: (1) trimethyl octyl ammonium, (2) stearyl phosphate, (3) 0.14 
A-3: (1) trimethylstearyl ammonium, (2) octyl phosphate, (3) 0.14 
A-4: (1) trimethylstearyl ammonium, (2) stearyl phosphate, (3) 0.10 
A-5: (1) triethyl octanoic amido propyl ammonium, (2) POE (4 mols) octyl 
phosphate, (3) 0.20 
A-6: (1) triethyl octanoic amido propyl ammonium, (2) POE (15 mols) stearyl 
phosphate, (3) 0.24 
A-7: (1) triethyl stearoic amido propyl ammonium, (2) POE (2 mols)/POP (1 
mol) octyl phosphate, (3) 0.23 
A-8: (1) triethyl stearoic amido propyl ammonium, (2) POE (5 mols)/POP (1 
mol) stearyl phosphate, (3) 0.24 
##STR4## 
(2) octyl phosphate, (3) 0.63 
##STR5## 
(2) stearyl phosphate, (3) 0.27 A-11: (1) trimethyloctyl ammonium, (2) 
octyl phosphate, (3) 0.80 
B-1: (1) trimethylhexyl ammonium, (2) octyl phosphate, (3) 0.25 
B-2: (1) trimethylhexyl ammonium, (2) stearyl phosphate, (3) 0.20 
B-3: (1) trimethyloctyl ammonium, (2) butyl phosphate, (3) 0.34 
B-4: (1) triethyl butanoic amido propyl ammonium, (2) octyl phosphate, (3) 
0.75 
B-5: (1) triethylbutanoic amido propyl ammonium, (2) stearyl phosphate, (3) 
0.63 
B-6: (1) monomethyl dioctylbutanoic amido propyl ammonium, (2) butyl 
phosphate, (3) 0.01 
##STR6## 
(2) octyl phosphate, (3) 0.83 
##STR7## 
(2) butyl phosphate, (3) 0.72 B-9: (1) trimethyloctyl ammonium, (2) 
chloride 
B-10: (1) triethyloctylamidpropyl ammonium, (2) methosulfate 
##STR8## 
(2) nitrate B-12: (1) potassium lauryl phosphate 
B-13: (1) trimethylstearyl ammonium, (2) stearyl phosphate, (3) 2.10 
B-14: (1) trimethylstearyl ammonium, (2) stearyl phosphate, (3) 1.43 
B-15: (1) trimethyloctyl ammonium, (2) octyl phosphate, (3) 2.47 
B-16: (1) trimethyloctyl ammonium, (2) octyl phosphate, (3) 1.71 
The following measurements and evaluations were made regarding A-1 through 
A-11 and B-1 through B-16. 
MEASUREMENT OF ELECTRICAL RESISTANCE AND EVALUATION OF YELLOWING 
Staple fiber samples were prepared by applying 0.1% (effective weight 
percent) of each example by a spray method to polyester staple fibers 
(1.4-denier, 38 mm) and dried for one hour at 60.degree. C. These samples 
were left for 24 hours under the conditions of 25.degree. C. and 40%RH or 
25.degree. C. and 65%RH, and their electrical resistance was measured. 
They were also subjected to a heat treatment at 150.degree. C. for two 
hours and the degrees of their yellowing were observed and evaluated 
visually. 
MEASUREMENT OF ELECTROSTATIC CHARGE GENERATED BY FRICTION 
Pieces of refined woven acrylic cloth were immersed in 0.2% (effective 
weight percent) water solution of each example and then dried for one hour 
at 60.degree. C. They were left for 24 hours under the conditions of 
25.degree. C. and 40%RH and their static charges were measured by a rotary 
static tester. 
EVALUATION OF DEPOSIT THAT FALL OFF 
Staple fiber samples were prepared by applying 0.12% (effective weight 
percent) of each example by a spray method to polyester staple fibers 
(1.4-denier, 38 mm) and were left for 24 hours under the conditions of 
30.degree. C. and 70%RH. These samples were used and 10 kg of slivers 
manufactured by a carding engine was passed through a drawing frame. The 
deposits that fall off and become adhered to the trumpet to which the 
sliver is taken up were visually observed. Grades A through E were 
assigned in the increasing order of the amount of deposits, grade A being 
given if this amount is very small. 
EVALUATION OF RUSTING 
After washed knitting needles were immersed in 2% (effective weight 
percent) water solutions of individual examples, they were left for 24 
hours under the conditions of 20.degree. C. and 100%RH and the appearance 
of rust on each needle was visually observed and evaluated. 
The results of the above are shown in Tables 1 and 2. 
TABLE 1 
______________________________________ 
Resistance (.OMEGA.) 
Static 
A- 25.degree. C., 
25.degree. C., 
Charge 
De- 
No 40% RH 65% RH (V) posit Yellowing 
Rust 
______________________________________ 
1 1.2 .times. 10.sup.7 
8.8 .times. 10.sup.5 
100 A None None 
2 4.3 16 200 A None None 
3 5.7 33 170 A None None 
4 8.5 53 450 A None None 
5 3.2 13 180 A None None 
6 6.5 45 250 A None None 
7 6.3 43 210 A None None 
8 8.8 74 470 A None None 
9 1.3 9.0 100 A None Slight 
10 3.3 21 120 A None None 
11 1.5 8.5 100 A None Slight 
______________________________________ 
TABLE 2 
______________________________________ 
Resistance (.OMEGA.) 
Static 
B- 25.degree. C., 
25.degree. C., 
Charge 
De- 
No 40% RH 65% RH (V) posit Yellowing 
Rust 
______________________________________ 
1 1.0 .times. 10.sup.7 
11 .times. 10.sup.5 
110 E Slight 
None 
2 4.2 10 170 D None None 
3 3.2 9.5 100 E Slight 
None 
4 3.5 21 210 E None None 
5 4.7 3.5 350 D None None 
6 15 170 700 D None None 
7 1.3 12 100 E None None 
8 1.1 8.8 100 E None None 
9 3.5 22 210 D Present 
Great 
10 3.1 36 480 E Present 
Great 
11 7.7 44 400 E Present 
Great 
12 600 890 1400 A None None 
13 8.3 61 430 B Present 
Great 
14 8.4 59 400 A Slight 
Great 
15 1.1 17 90 E Slight 
Great 
16 4.0 15 360 D Slight 
Great 
______________________________________ 
TEST NO. 2 
Emulsions were prepared from individual finishing oil (sample of present 
invention 1-12 and comparison samples 1-9) having compositions (weight 
percent) shown in Tables 3 and 4 and fiber samples were produced by 
applying 0.15wt% of each by the spray method individually to polyester 
staple fibers (1.4-denier, 38 mm) and leaving for 24 hours under the 
temperature and humidity conditions shown in Tables 5 and 6. The following 
measurements were made and evaluated. The results of the test are shown in 
Tables 5 and 6. 
MEASUREMENT OF ELECTRIC RESISTANCE 
Measurements were taken as in Test No. 1. 
MEASUREMENT OF ROLLER WRAPPING 
Roving yarns produced from the fiber samples by using a roving frame were 
spun out of a spinning frame and the number of the fibers wrapped around 
the rubber roller (manufactured by Yamanouchi Rubber Company, hardness 82 
degrees) was counted. 
EVALUATION OF DEPOSITS 
Testing and evaluation were done as in Test No. 1. 
EVALUATION OF COILING FORM 
Samples were processed to drawing frame and the forms of the produced 
silver coils were evaluated and graded similarly into five levels from A 
(very good) to E (not good). 
TABLE 3 
______________________________________ 
(Samples of present invention) 
No. A-1 A-4 A-5 A-10 P-1 P-2 P-3 
______________________________________ 
1 5 95 
2 10 90 
3 10 90 
4 10 90 
5 15 85 
6 15 85 
7 20 80 
8 20 80 
9 30 70 
10 30 70 
11 40 60 
12 45 55 
______________________________________ 
TABLE 4 
______________________________________ 
(Comparison samples) 
No. A-1 A-4 B-15 B-16 B-13 B-3 P-1 P-2 P-4 P-5 
______________________________________ 
1 5 95 
2 10 90 
3 15 85 
4 30 70 
5 30 70 
6 10 90 
7 20 80 
8 30 70 
9 10 90 
______________________________________ 
In Tables 3 and 4, A-1 through A-10 and B-1 through B-16 are the same as 
previously defined. P-1, P-2 and P-3 are all potassium salts of saturated 
alkyl phosphate with octadecyl/hexadecyl=90/10, 85/15 and 65/35, 
respectively. P-4 and P-5 are respectively potassium hexadecyl phosphate 
and potassium dodecyl phosphate. 
TABLE 5 
______________________________________ 
(Samples of present invention) 
Wrapping Coiling 
Resistance (.OMEGA.) 
(times) Deposit Form 
25.degree. C., 
25.degree. C., 
30.degree. C., 
30 .degree. C., 
30.degree. C., 
No. 40% RH 65% RH 70% RH 70% RH 70% RH 
______________________________________ 
1 9.2 .times. 10.sup.7 
12.5 .times. 10.sup.5 
0 A A 
2 6.3 10.0 0 B B 
3 7.4 11.2 0 A A 
4 4.5 8.2 1 B B 
5 6.0 9.5 0 B B 
6 3.0 7.0 7 B C 
7 2.8 6.5 2 B B 
8 7.2 10.5 0 A A 
9 2.5 5.4 7 B B 
10 5.3 9.0 6 B B 
11 1.4 3.2 10 B C 
12 1.8 3.6 8 B C 
______________________________________ 
TABLE 6 
______________________________________ 
(Comparison samples) 
Resistance (.OMEGA.) 
25.degree. C., 
25.degree. C., 
Wrapping Coiling 
No. 40% RH 65% RH (times) Deposit 
Form 
______________________________________ 
1 9.0 .times. 10.sup.7 
11.8 .times. 10.sup.5 
7 C E 
2 6.0 9.6 10 C E 
3 6.2 9.0 12 D E 
4 2.0 5.2 15 D E 
5 4.9 8.8 20 E E 
6 8.3 10.3 18 B E 
7 2.1 5.1 15 C E 
8 1.0 2.8 17 C E 
9 6.2 8.9 7 D D 
______________________________________ 
Comparisons between Tables 1 and 2 and between Tables 5 and 6 clearly 
demonstrate that the finishing oil of the present invention described 
hereinabove exhibit superior antistatic characteristics both in high 
humidity and low humidity conditions, reduce the amount of deposits that 
fall off, yellowing by a heat treatment and generation of rust, and allow 
good coiling forms to be obtained.