Highly durable surface-conditioning agent

The present invention provides a highly durable surface-conditioning agent for use in a pretreatment step for a phosphate coating treatment of metallic materials, which is an aqueous solution comprising 1 to 50 ppm of titanium ion, 50 to 1,000 ppm or phosphate ion, 50 to 400 ppm of tripolyphosphate ion and 20 to 1,500 ppm of carbonate ion, with a tripolyphosphate ion/titanium ion weight ratio of 10 to 100, and having a pH of 8.5 to 10.0.

FIELD OF THE INVENTION 
The present invention relates to a highly durable surface-conditioning 
agent for use in a pretreatment for a phosphate coating treatment of a 
metallic material. 
BACKGROUND ART 
Automotive bodies, household electric appliances and the like are produced 
by molding metallic materials, such as steel sheets and galvanized steel 
sheets, into metallic moldings, followed by coating and assembling, etc. 
The coating of such metallic moldings includes various steps, namely the 
steps of degreasing, surface conditioning, chemical conversion treatment, 
electrodeposition coating, among others. 
The surface-conditioning treatment is a treatment required for enabling, in 
the next phosphate coating treatment step, rapid formation of uniform and 
high-density coatings consisting of phosphate salt crystals all over the 
metal surface. It generally comprises immersing metallic moldings in a 
surface-conditioning bath to thereby cause formation of phosphate crystal 
nuclei on the metal surface. 
The surface-conditioning ability of a surface-conditioning agent results 
from the titanium phosphate colloid contained in the surface-conditioning 
agent. The titanium phosphate colloid by nature tends to undergo 
dissolution or aggregation with the lapse of time, hence be progressively 
deteriorated. 
In the case of surface-conditioning agents, techniques have been 
investigated for stabilizing the titanium phosphate colloid by pII 
adjustment and other means to thereby avoid the degradation of colloidal 
character or the unsatisfactory surface conditioning resulting from the 
colloid becoming a suspension. 
Japanese Kokai Publication Hei-02-83202 discloses a method for preparing 
activated titanium phosphate having stable surface conditioning ability 
and suited for zinc phosphating. Said method comprises preparing activated 
titanium phosphate for zinc phosphating from a titanium (IV) compound and 
at least one member selected from the group consisting of an 
orthophosphoric acid compound, a polyphosphoric acid compound and a 
metaphosphoric acid compound and can give a surface-conditioning agent 
having stable surface-conditioning ability as compared with the prior art 
surface-conditioning agents showing greatly varying surface-conditioning 
ability among batches even when prepared under certain specified reaction 
conditions. 
The surface-conditioning agent obtained by said method, however, still has 
drawbacks. For instance, the pH control in surface-conditioning baths is 
difficult, hence it is difficult to obtain a stable titanium phosphate 
colloid, and this is disadvantageous in particular in dipping treatment 
which requires a stable surface-conditioning agent in large quantities 
over a long period of time. 
Japanese Kokoku Publication Sho-58-55229 discloses a surface-conditioning 
agent for zinc phosphating which comprises titanium ion, phosphate ion, 
pyrophosphate ion and carbonate ion. This surface-conditioning agent is 
characterized in that the pH is prevented from decreasing by the addition 
of a carbonate ion-providing carbonic acid compound and the titanium 
phosphate colloid is stabilized by the addition of pyrophosphate ion and 
that the surface-conditioning ability can be stably exhibited over a long 
period of time. Another feature is that said composition is advantageous 
in dipping treatment in which a, particular requirement is long-period 
stability, since the pH can easily be controlled by addition of a carbonic 
acid compound. 
However, the pyrophosphate ion used there is not sufficient in its property 
as a metal chelating agent capable of stabilizing titanium phosphate 
colloid and said surface-conditioning agent cannot be said to be a 
surface-conditioning agent having good durability. 
SUMMARY OF THE INVENTION 
In view of the state of the art mentioned above, it is a primary object of 
the present invention to provide a surface-conditioning agent having 
excellent surface-conditioning ability and high durability. 
The highly durable surface-conditioning agent of the present invention is a 
highly durable surface-conditioning agent for use in a pretreatment step 
for a phosphate coating treatment of metallic materials, which is an 
aqueous solution comprising 1 to 50 ppm of titanium ion, 50 to 1,000 ppm 
of phosphate ion, 50 to 400 ppm of tripolyphosphate ion and 20 to 1,500 
ppm of carbonate ion, with a tripolyphosphate ion/titanium ion weight 
ratio of 10 to 100, and having a pH of 8.5 to 10.0. 
DETAILED DESCRIPTION OF THE INVENTION 
The highly durable surface-conditioning agent of the present invention 
causes titanium phosphate colloid to adhere to the surface of a metallic 
material such as iron or zinc and thereby promotes, in the next phosphate 
coating treatment, the formation of chemical conversion coatings with the 
aid of said colloid as crystal nuclei, leading to formation of good 
chemical conversion coatings. 
The highly durable surface-conditioning agent of the present invention 
comprises 1 to 50 ppm of titanium ion, 50 to 1,000 ppm of phosphate ion, 
50 to 400 ppm of tripolyphosphate ion and 20 to 1,500 ppm of carbonate 
ion. 
When the concentration of said titanium ion is less than 1 ppm, the colloid 
to serve as crystal nuclei is insufficient. At concentrations exceeding 50 
ppm, no extra effect than the desired effect can be obtained, hence they 
are uneconomical. Thus, the above range is critical. 
The source of said titanium ion is not limited to any particular species 
but includes, among others, titanium sulfate and titanium oxide. 
When the concentration of said phosphate ion is less than 50 ppm, the 
colloid to serve as crystal nuclei is insufficient. At concentrations 
exceeding 1,000 ppm, no extra effect than the desired effect can be 
obtained, hence they are uneconomical. Thus, the above range is critical. 
The source of said phosphate ion is not limited to any particular species 
but includes, among others, phosphoric acid; alkali metal 
dihydrogenphosphates such as sodium dihydrogenphosphate; ammonium 
dihydrogenphosphate; dialkali metal hydrogenphosphates such as disodium 
hydrogenphosphate: diammonium hydrogenphosphate; trialkali metal 
phosphates such as trisodium phosphate; and triammonium phosphates. 
At concentrations below 50 ppm, said tripolyphosphate ion as a metal 
chelating agent cannot stabilize the colloid effectively, hence fine 
chemical conversion coatings cannot be formed in the next phosphate 
coating treatment. At concentrations exceeding 400 ppm, said ion reacts 
with the metallic material surface to form tripolyphosphate compounds, 
inhibiting the formation of chemical conversion coatings. The above range 
is thus critical. 
The source of said tripolyphosphate ion is not limited to any particular 
species but includes, among others, alkali metal salts of 
tripolyphosphoric acid such as sodium tripolyphosphate, etc. 
When the concentration of said carbonate ion is less than 20 ppm, no 
substantial buffering effect can be produced and the pH is allowed to 
lower, and tripolyphosphate compounds are formed by the reaction of said 
tripolyphosphate ion with the metallic material surface, whereby the 
formation of chemical conversion coatings is inhibited. At concentrations 
exceeding 1,500 ppm, the formation of chemical conversion coatings is 
inhibited. The above range is thus critical. 
As a result of adjustment of the carbonate ion concentration to the range 
mentioned above, the highly durable surface-conditioning agent of the 
present invention is maintained at pH 8.5 to 10.0 and the colloid is 
stabilized. 
The source of the bicarbonate ion is not limited to any particular species 
but includes, among others, carbonic acid; alkali metal acid carbonate 
such as sodium acid carbonate; and ammonium acid carbonate. 
The source of said carbonate ion is not limited to any particular species 
but includes, among others, carbonic acid; alkali metal carbonates such as 
sodium carbonate; and ammonium carbonate. 
In accordance with the present invention, the (tripolyphosphate 
ion)/(titanium ion) weight ratio is within the range of 10 to 100. When 
said ratio is less than 10, the colloid is unstable and tends to aggregate 
and the resulting surface-conditioning agent loses durability. When said 
ratio exceeds 100, the colloid is dissolved and the resulting 
surface-conditioning agent lacks durability. The above range is thus 
critical. A preferred range is 20 to 40. 
The level of addition of said tripolyphosphate ion can suitably be selected 
depending on the hardness of water. When, for instance, the hardness of 
water is high, said tripolyphosphate ion chelates metal ions contained in 
water and therefore its proportion of said tripolyphosphate ion which can 
effectively chelate the colloid decreases, hence the level of addition 
thereof should preferably be increased. 
The highly durable surface-conditioning agent of the present invention has 
a pH of 8.5 to 10.0. 
At a pH below 8.5, said tripolyphosphate ion will react with the metallic 
material surface to form a tripolyphosphate compound, inhibiting the 
formation of chemical conversion coatings. At a pH above 10.0, the colloid 
tends to dissolve, thus becomes unstable. A preferred pH range is 9.0 to 
9.5. 
In the practice of the present invention, sodium pyrophosphate may 
additionally be used for further stabilization of the colloid and for 
forming fine chemical conversion coatings in the next phosphate coating 
treatment. 
In the practice of the present invention, at least one member selected from 
the group consisting of sodium carbonate and sodium bicarbonate may 
additionally be added for the purpose of obtaining a more marked buffering 
effect. 
The present invention, which has the above constitution, enables highly 
durable surface conditioning as compared with the conventional 
surface-conditioning agents, providing an even, uniform and dense chemical 
conversion coating in the next phosphate coating treatment step.

BEST MODE FOR CARRYING OUT THE INVENTION 
The following reference examples and Examples illustrate the present 
invention in further detail, but are by no means limitative of the scope 
of the invention. 
REFERENCE EXAMPLE 
Preparation of Titanium Materials 
Titanium material A: A mixture of 7.0% of titanium sulfate, 72.9% of 
anhydrous disodium hydrogenphosphate and 20.1% of water was heated at 
100.degree. C. to 120.degree. C. with stirring until the water content 
became not more than 1.5% (about 2 hours). The powder obtained was 
designated as titanium material A. The content of titanium in the titanium 
material A was 1.68% by weight. 
Titanium material B: A mixture of 11.0% of titanium sulfate, 68.6% of 
anhydrous disodium hydrogenphosphate and 20.4% of water was heated at 
100.degree. C. to 120.degree. C. with stirring until the water content 
became not more than 1.5% (about 2 hours). The powder obtained was 
designated as titanium material B. The content of titanium in the titanium 
material B was 2.65% by weight. 
EXAMPLES 1 & 2 AND COMATIVE EXAMPLES 1 TO 3 
The titanium materials, anhydrous sodium pyrophosphate, anhydrous sodium 
tripolyphosphate, sodium carbonate and sodium bicarbonate were mixed 
together in the proportions shown in Table 1 and stirred well to give each 
condensed surface-conditioning agent. Baths were prepared by adding water 
to each surface-conditioning agent to a concentration of 0.1% (w/v) and 
stirring the resulting mixture well. The thus-prepared 
surface-conditioning agents were evaluated by the method mentioned below, 
and the results obtained are shown in Table 1. 
(Evaluation Method) 
Each surface-conditioning agent prepared as described above was exposed 
under the following treatment load every day immediately following the 
time of bath preparation. 
(1) Aeration 
200 liters of air/liter of a surface-conditioning agent (using an air 
pump). 
(2) Metal treatment 
Cold-rolled steel sheet (SPC) 0.42 m.sup.2 /liter of surface-conditioning 
agent (contact time: 20 seconds); 
Galvanized steel sheet (SGAC) 0.42 m.sup.2 /liter of surface-conditioning 
agent (contact time: 20 seconds). 
On the 10th day after bath preparation, zinc phosphating was performed and 
the chemical conversion coating on each steel sheet was observed and the 
durability of each surface-conditioning agent was evaluated. 
(Zinc Phosphating) 
Each cold-rolled steel sheet (SPC) (70.times.150.times.0.8 mm), degreased 
beforehand, was immersed in each surface-conditioning bath just after bath 
preparation and after 10 days of the above loading treatment at room 
temperature. After 1 minute of immersion, the bath liquid was drained off 
and the steel sheet was immediately subjected to the chemical conversion 
treatment by the dipping method using a zinc phosphating solution 
(Surfdyne SD2500, product of Nippon Paint) at 40.degree. C. for 2 minutes, 
and then washed with water and dried. 
In Table 1, the symbol .largecircle. indicates that a uniform and dense 
zinc phosphate coating (crystal diameter of the zinc phosphate coating: 1 
to 3 .mu.m) was formed. The symbol .DELTA.indicates that a zinc phosphate 
coating (crystal diameter of the zinc phosphate coating: 3 .mu.m or more) 
was formed with a hiding effect. The symbol x indicates that an 
insufficient hiding effect and/or yellow rust was observed and the crystal 
diameter of the zinc phosphate coating was not less than 3 .mu.m. 
TABLE 1 
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Comparative 
Example Example 
1 2 3 1 2 
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Formulation (%); 
Titanium material A 
40.0 26.6 40.0 -- -- 
Titanium material B 
-- -- -- 52.6 52.6 
Anhydrous disodium hydrogenphos- 
15.0 43.4 30.0 -- -- 
phate 
Anhydrous sodium pyrophosphate 
-- -- -- 36.1 -- 
Anhydrous sodium tripolyphosphate 
30.0 15.0 30.0 -- 18.0 
Sodium carbonate 15.0 10.0 -- 11.3 10.0 
Sodium bicarbonate 
-- 5.0 -- -- 19.4 
Concentration (ppm) 
in 0.1% (w/v) surface-conditioning 
agent; 
Titanium ion 6.7 4.5 6.7 13.9 13.9 
Phosphate ion 277.6 450.9 444.9 
303.1 
303.1 
Condensed phosphate ion 
206.4 103.2 206.4 
236.1 
123.8 
Carbonate ion 84.9 55.6 -- 64.0 195.2 
Pyrophosphate ion/titanium ion 
-- -- -- 17.0 -- 
Tripolyphosphate ion/titanium ion 
30.8 22.9 30.8 -- 8.9 
pH of 0.1% surface-conditioning 
10.0 9.5 8.5 9.7 9.5 
agent 
Results cf chemical conversion 
treatment; 
Just after bath preparation 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
After 10 days .largecircle. 
.largecircle. 
.DELTA. 
X .DELTA. 
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