Disclosed is an anti-plating agent for use in hot-dip plating process, having the following two kinds of composition. The composition of the first kind includes an alkali silicate; boric acid, and alkali hydroxide, magnesia and/or magnesium hydroxide, titania and/or titanium hydroxide, and at least one compound selected from a group consisting of alumina, aluminium hydroxide and alumina zol. The composition of the second kind includes an alkali silicate, boric acid, alkali hydroxide, magnesia and/or magnesium hydroxide, alumina and/or aluminium hydroxide, and at least one kind of titanium oxide and titanium complex oxide and/or at least one kind of zirconium oxide and zirconium complex oxide. These anti-plating agents have a good anti-plating effect and permit an easy separation of the coating film and, hence, can suitably be used in one-side hot-dip plating of steel sheets.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an anti-plating agent for use in the 
production of one-side plated steel sheet or strip by hot-dip process. 
2. Description of the Prior Art 
Recently, in the field of the steel sheet to be used for automobiles, 
domestic electric equipments, building materials and the like, it has been 
eagerly demanded to produce a so-called one-side plates steel sheet by 
plating only one side of a steel sheet to give the sheet a sufficiently 
high corrosion resistance and, at the same time, to improve the 
weldability of the sheet. 
One-side plated sheet can be produced by the electroplating process, but 
the electroplating process is low in the plating speed and high in the 
production cost of the sheet. Therefore, the hot dip process is 
advantageously used in the production of the one-side plates steel sheet 
on a large scale. 
There have hitherto been proposed various methods in the production of 
one-side plates steel sheet by the hot-dipping process. For example, the 
following methods are known in the production of zinc-plated steel sheet, 
that is, a method wherein two steel sheets are superposed and welded at 
the edge, and the welded steel sheets are plated, and then the welded edge 
is cut off; a method wherein molten zinc is plated on only one side of a 
steel sheet by the roll coating method, curtain-flow coating method or 
other particular method; a method wherein plating is effected on both 
sides of the steel sheet and then the plating layer on one side is removed 
by an electrolysis or grinding; a method wherein an anti-plating agent is 
applied beforehand on one side of the steel sheet and is removed after the 
plating; and a method wherein the plating is effected on only one side of 
the steel sheet by elevating or protruding the surface of the bath by 
means of ultrasonic wave or an electromagnetic pump. 
These known methods, however, are generally impractical to carry out and 
raise the cost of production uneconomically. For these reasons, only few 
of them are put into production in the commercial scale. 
As the conventional one-side zinc plating methods employing anti-plating 
agent, the following technics have been known. Namely, Japanese patent 
application publication No. 7,112/64 discloses the use of water-glass, 
while Japanese patent application publication No. 4,204/64 teaches the use 
of an aqueous slurry of a mixture of CaO, MgO and alkali metaborate. 
Japanese patent laid-open No. 48.029/78 teaches the use of an aqueous 
slurry consisting mainly of alkali metal silicate and ammonium silicate, 
while Japanese patent application publication No. 8,101/76 discloses a 
plating prohibitor consisting essentially of a silicon resin. The use of 
an aqueous slurry of scale-like synthetic silicon compound is disclosed in 
Japanese patent laid-open No. 64,026/79. Also, U.S. Pat. No. 3,121,019 
discloses the use of alkali earth metal oxides. 
These methods, however, still have the following drawbacks. That is, in the 
continuous hot-dip metal plating process, wherein a steel sheet with an 
anti-plating film coated thereon is annealed in reducing atmosphere 
(usually at 700.degree. C.) just before the plating by the hot-dipping, 
the anti-plating film coating the sheet surface decomposes or partly 
exfoliates from the steel sheet surface during the annealing. It is, 
therefore, difficult to completely prevent one side of the sheet from 
being plated. Moreover, the steel is sometimes oxidized in the air after 
plating, and a troublesome step is required in order to reduce or 
mechanically remove the oxide. Further, the film formed on one side of the 
steel sheet by the coating agent is generally poor in the peeling 
property, and it is almost impossible to remove the film completely 
without deteriorating the appearance of the steel sheet surface. In 
addition, the removal of the film is usually expensive. 
As the anti-plating agents which can effectively prevent the plating and 
attaching of molten metal onto the coating layer while exhibiting good 
peeling property, the present inventors have already proposed an aqueous 
slurry containing four constituents: namely, magnesia, boric acid, an 
alkali and alkali silicate, in Japanese patent laid-open No. 146,730/77. 
Subsequently, the inventors proposed in Japanese Patent Laid-open No. 
119,157/80 and aqueous slurry of 5-component system containing, in 
addition to the four constituents mentioned above, titania or titanium 
hydroxide. 
These anti-plating agents, however, still suffered the following drawbacks. 
Namely, in the continuous hot-dip zinc plating method having the step of 
annealing in a reducing atmosphere in advance to the plating, the zinc 
attaches to the coating layer of the anti-plating agent when the speed of 
pulling out of the steel from the molten zinc bath is too high or when the 
annealing is conducted at a temperature above the A.sub.1 transformation 
temperature aiming at achieving a higher workability of the zinc-plated 
steel sheet. The attaching of the zinc to the coating layer causes not 
only the wasteful use of the zinc but also a contamination of the 
production line due to peeling off of the zinc when the steel sheets move 
along the path of the production line. 
OBJECT OF THE INVENTION 
Accordingly, a first object of the invention is to provide an anti-plating 
agent consisting of an aqueous slurry containing one element selected from 
the group consisting of the previously proposed five elements of magnesia, 
boric acid, alkali, alkali salt of silicic acid, titania and titanium 
hydroxide, with at least one additive selected from a group consisting of 
alumina, aluminium hydroxide and an alumina zol, thereby to make it 
possible to produce one-side plated steel sheets while preventing 
effectively the plating on the side coated by the anti-plating agent, as 
well as deposition of molten metal onto the surface of the coating layer, 
and ensuring a good peeling of the film after the baking. 
A second object of the invention is to provide an anti-plating agent 
consisting of an aqueous slurry which is formed by adding alumina or 
aluminium hydroxide to alkali silicate, boric acid, hydroxide of alkali 
metal, magnesia and/or magnesium hydroxide and further adding oxide or 
complex oxide of titanium and/or oxide or complex oxide of zirconium, 
thereby to make it possible to produce one-side plated steel sheets while 
preventing effectively the plating on the side of the steel sheet coated 
by the anti-plating agent, as well as deposition of molten metal onto the 
surface of the coating film, and ensuring a good peeling of the film after 
the baking. 
SUMMARY OF THE INVENTION 
According to one aspect of the invention, there is provided an anti-plating 
agent consisting of a 6-component aqueous slurry containing at least one 
of magnesia and magnesium hydroxide, an alkali silicate (M.sub.2 
O.nSiO.mH.sub.2 O, m being an alkali metal), boric acid, hydroxide of 
alkali metal, at least of titania and titanium hydroxide, and at least one 
of alumina, aluminium hydroxide and alumina zol. 
According to another aspect of the invention, there is provided an 
anti-plating agent consisting of an aqueous slurry which is prepared by 
adding to water, major constituents including alkali silicate, boric acid, 
hydroxide of alkali metal, magnesia and/or magnesium hydroxide; alumina 
and/or aluminium hydroxide and at least one titanium oxide and/or titanium 
complex oxide and/or at least one zirconium oxide or zirconium complex 
oxide. In this specification, the terms "titanium oxide" and "complex 
titanium oxide" are used to mean TiO.sub.2, SrTiO.sub.3, BaTiO.sub.3, 
Mg.sub.2 TiO.sub.4 and CaTiO.sub.3. Also, the term "zirconium oxide" and 
"zirconium complex oxide" are used to mean ZrO.sub.2, ZrSiO.sub.3, 
CaZrO.sub.3 and BaZrO.sub.3. 
According to the invention, the mean particle size of each constituent of 
the anti-plating agent is limited as follows, for the reasons which will 
be described later. Namely, the mean particle size of magnesia or 
magnesium hydroxide is preferably selected to range between 0.01 and 1 
.mu.m, while the mean particle sizes of alumina or aluminium hydroxide, 
oxide and complex oxide of titanium and oxide and complex oxide of 
zirconium are preferably selected to fall within the range of between 0.1 
and 100 .mu.m.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A description will be made hereinunder as to how a one-side plated steel 
sheet is produced by hot dipping using an anti-plating agent in accordance 
with the invention, before turning to the detailed description of the 
embodiments. 
An aqueous slurry having the above-described composition is applied to one 
side of a steel sheet after a sufficient degreasing of the steel sheet 
surface. Then, the steel sheet surface is dried preferably at a 
temperature not higher than 20.degree. C. The application of the 
anti-plating agent, i.e. the aqueous slurry, may be made by any known 
method and tool such as roll type applicator, Spray type applicator, brush 
or the like. The amount of application of the agent is 5 to 300 g/m.sup.2 
in the state after the drying. The selection of the amount of application 
of the agent is important because a too small amount may cause an 
imperfect coating while a too large amount may cause a cracking in the 
coating film in the course of the drying, both of which will impede the 
perfect prevention of plating. As stated before, the drying should be made 
preferably at a temperature not higher than 200.degree. C. to evaporate 
the water content of the anti-plating agent, in order to maintain s 
reducing atmosphere in the subsequent annealing step and in order to avoid 
cracking and separation of the coating film which may, for otherwise, be 
caused by an abrupt heating to a high temperature. 
After forming a uniform coating film on one side of the steel sheet, the 
steel sheet is subjected to an annealing conducted at about 700.degree. to 
900.degree. C., as in the case of ordinary continous hot dip process and, 
then cooled down to a temperature approximating the bath temperature which 
is 460.degree. C. in the case of zinc plating, before the steel is dipped 
in the plating bath. Meanwhile, the coating film is partly fluidized and 
becomes glassy by the heat applied during the annealing, and is changed 
into a solid coat during cooling or dipping, thereby to effectively 
prevent the molten metal from contacting the coated steel sheet surface in 
the bath. The steel sheet pulled out from the plating bath has been plated 
only at one side thereof, while the other side is not plated but is coated 
by the coating film. This coating film of antiplating agent has an 
extremely low wettability to the molten metal is observed on the coating 
film surface after pulling out from the bath. There may be, however, an 
attaching of dross, although such an attaching takes place only seldom. It 
is, therefore, advisable to subject the steel sheet to a gas wiping 
immediately after the plating, preferably with an annealing gas such as 
butane, propane or the like gas. It proved also that the coating film 
plays, thanks to its extremely fine and minute structure, the role of an 
insulator which prevents the ambient air from contacting the steel sheet 
surface under the cover thereby to perfectly eliminate the undesirable 
oxidation of that surface by the air. 
After the completion of the plating, it is necessary to remove the coating 
film from the steel sheet. When the anti-plating agent of the invention is 
used, such a removal can easily be made simply by quenching the steel 
sheet from a temperature higher than 100.degree. C. in the case of the 
first-mentioned agent and from a temperature higher than 200.degree. C. in 
the case of the anti-plating agent mentioned second. The quenching may be 
made before the solidification of the plating aiming also at an adjustment 
of the spangle size or may be made after the solidification. It is also 
possible to effect the quenching after reheating the steel sheet which is 
once cooled down gradually. 
As the way of quenching, immersion in water is easy and effective. An 
experiment showed that, by effecting the quenching in water, the coating 
film is completely separated from the steel sheet surface and, in 
addition, the steel sheet surface revealed after the separation of film is 
not oxidized at all, so that it is possible to obtain an unplated rolled 
surface as it is. The separation and removal of the coating film can be 
made easily by other measure than the described immersion in water, e.g. a 
repeated slight bending, grinding or polishing. It is possible to obtain a 
perfect one-side plated steel sheet, by subjecting the steel sheet to a 
rinsing by water and final finishing washing by a light brushing, after 
the removal of the coating film. 
According to the first form of the invention, it is possible to remarkably 
eliminate the undesirable deposition of the molten metal to the coating 
film of the anti-plating agent, which has been experienced in the prior 
art when the speed of pulling out of the steel sheet is too high or when 
the annealing is made at a too high temperature, so that a perfect 
one-side plated steel sheet can easily be obtained. 
The above-described advantage is obtained for the first time by the 
development of the novel anti-plating agent of the invention. The most 
remarkable effect was obtained when the anti-plating agent is an aqueous 
slurry prepared by dissolving or dispersing the following matters in the 
water: 10 g of MgO (a part or whole of MgO may be substituted by 
Mg(OH).sub.2 of the same molecule number), 1 to 30 g of aqueous solution 
of alkali silicate as the residual of heat-dehydration (M.sub.2 
O.nSiO.sub.2, n=0.5 to 4), 1 to 30 g of boric acid as H.sub.3 BO.sub.3, 
0.1 to 20 g of alkali as MOH; 1 to 10 g of titania as TiO.sub.2 (a part or 
whole of TiO.sub.2 may be substituted by titanium hydroxide of the same 
molecule number); and 1 to 10 g of alumina as Al.sub.2 O.sub.3 (a part or 
whole of Al.sub.2 O.sub.3 may be substituted by aluminium hydroxide or 
alumina zol of the same molecule number). 
The first embodiment of the invention will be described in detail 
hereinunder through specific practical examples. 
EXAMPLE 1) 
An aqueous slurry was prepared by dispersing the following substances in a 
suitable amount of water: 10 g of MgO; 10 g of water glass (4.5 g as 
Na.sub.2 O.2SiO.sub.2); 4 g of NaOH; 6 g of H.sub.3 BO.sub.3 ; 2 g of 
TiO.sub.2 ; and 3 g of Al.sub.2 O.sub.3. This aqueous slurry was applied 
by a roll applicator to one side of a cold-rolled steel which had been 
cleaned by an ordinary alkali degreasing and rinsing by water. The amount 
of application was about 50 g/m.sup.2 in the state after the drying. After 
the application, the steel sheet was subjected to a low-temperature drying 
which was conducted at 150.degree. C. for 1 minute in an oven opened to 
the atmosphere and then to an annealing which was conducted at 700.degree. 
for 2 minutes in the atmosphere consisting of 10%H.sub.2 and 90%N.sub.2 
and further to a cooling down to 530.degree. C. in the same atmosphere. 
The steel sheet was then dipped in a plating bath of molten zinc. 
The composition of the plating bath was 0.18% Al-Zn. The temperature of the 
bath and the dipping time were 465.+-.5.degree. C. and 3 seconds, 
respectively. After the plating, the steel sheet was pulled out from the 
plating bath and a gas wiping was conducted with N.sub.2 gas to adjust the 
amount of the plating. Then, when the sheet temperature came down to about 
300.degree. C., the steel sheet was quenched by immersion in water of 
about 20.degree. C. The steel sheet after the plating operation was plated 
only at its one side while the other side was completely coated by the 
coating film os the anti-plating agent. The coating film was separated and 
removed from the steel sheet surface. Subsequently, the steel sheet was 
rinsed with water and brushing followed by drying by means of a blower. In 
consequence, a one-side plated steel sheet was obtained to have one side 
uniformly plated with zinc of about 150 g/m.sup.2 and the other side which 
was the clean cold-rolled surface. 
(EXAMPLE 2) 
An aqueous slurry was prepared by dissolving or dispersing the following 
substance in suitable amount of waer: 14.5 g of Mg(OH).sub.2 ; 10 g of 
aqueous solution of kalium silicate (6 g as K.sub.2 O.SiO.sub.2), 6 g of 
KOH; 5 g of H.sub.3 BO.sub.3 ; 3 g of TiO.sub.2 and 4 g of Al(OH).sub.3. 
This slurry was applied in the same manner as Example 1 and the steel 
sheet applied with this aqueous slurry was treated under the same 
condition as Example 1. As a result, a perfect one-side plated steel sheet 
was obtained as in the case of Example 1. 
(EXAMPLE 3) 
A plurality of one-side plated steel sheets were produced using 
anti-plating agent of compositions shown in Table 1. Three different 
annealing temperatures of 700.degree. C., 750.degree. C. and 850.degree. 
C. were employed. Also, two different pulling out speeds of 40 mpm and 60 
mpm were used. Then, a test was conducted to investigate how the 
deposition of molten zinc and the easiness of removal of the coating film 
of the anti-plating agent are affected by the change of annealing 
temperature and the change of the pull out speed, the result of which is 
shown in Table 1. In Table 1, the deposition of zinc and easiness of 
removal of the coating layer are evaluated as follows. 
(1) deposition of zinc 
O: almost no deposition of molten zinc to the surface of coating film of 
anti-plating agent 
.DELTA.: molten zinc deposited to a part of coating film 
X: molten zinc deposited to whole surface of coating film 
(2) easiness of separation and removal of anti-plating agent 
O: complete separation 
.DELTA.: partly separated 
X: no separation at all 
As will be clearly seen from Table 1, the use of the anti-plating agent of 
the invention ensures almost no deposition of molten zinc to the surface 
of the antiplating coating film and an easy separation of the coating film 
by water-cooling or repeated slight bending, even when the annealing 
temperature is elevated and even when the speed of pulling out from the 
molten zinc bath is increased to 60 mpm. 
TABLE 1 
__________________________________________________________________________ 
deposition peel of 
molten zinc 
anti-plating 
annealing 
pull-out 
pullout 
agent film 
temp. speed 
speed by water 
No. composition of anti-plating agent (g) 
(.degree.C.) 
40 mpm 
60 mpm 
cooling 
by 
__________________________________________________________________________ 
bending 
prior art 
MgO water 
NaOH 
H.sub.3 BO.sub.3 
700 X X O O 
glass 750 X X O O 
(1) 10g 10g 4g 6g 850 X X O O 
prior art 
MgO water 
NaOH 
H.sub.3 BO.sub.3 
TiO.sub.2 700 O .DELTA. 
O O 
glass 750 .DELTA. 
X O O 
(2) 10g 10g 4g 6g 3g 850 X X O O 
present 
MgO water 
NaOH 
H.sub.3 BO.sub.3 
TiO.sub.2 
Al.sub.2 O.sub.3 
700 O O O O 
invention glass 750 O O O O 
(1) 10g 10g 4g 6g 3g 3g 850 O O O O 
MgO water 
KOH H.sub. 3 BO.sub.3 
TiO.sub.2 
Al.sub.2 O.sub.3 
700 O O .DELTA. 
O 
glass 750 O O O O 
(2) 10g 10g 6g 5g 5g 6g 850 O O O O 
Mg(OH).sub.2 K.sub.2 O.SiO.sub.2 
NaOH 
H.sub.3 BO.sub.3 
Ti(OH).sub.4 
Al(OH).sub.3 
700 O O .DELTA. 
O 
750 O O .DELTA. 
O 
(3) 14g6g 5g 7g 4g 8g 850 O O O O 
Mg(OH).sub.2 K.sub.2 O.SiO 
NaOH 
H.sub.3 BO.sub.3 
Ti(OH).sub.4 
Al(OH).sub.3 
700 O O O O 
750 O O O O 
(4) 14g6g 4g 6g 2g 4g 850 O O O O 
__________________________________________________________________________ 
In the anti-plating agent in accordance with the second form of the 
invention, the alkali silicate, boric acid and the alkali metal hydroxide 
mainly serve to prevent the plating and also to prevent oxidation of the 
steel sheet after the plating. On the other hand, the prevention of 
deposition of the molten metal onto the coating film surface is achieved 
mainly by magnesia or magnesium hydroxide, alumina or aluminium hydroxide, 
and oxide and/or complex hydroxide of titanium and/or zirconium. 
Particularly, the addition of alumina or aluminium hydroxide, and oxide 
and/or complexed oxide of titanium and zirconium completely eliminates the 
undesirable deposition of molten metal onto the coating film surface and 
facilitates the separation of the coating film, which have been 
experienced in the known anti-plating agents proposed by the present 
applicant when the speed of pulling out from the molten metal bath is too 
high or when the annealing temperature is too high, thereby to ensure a 
superior quality of the one-side plated steel sheet. 
The highest effects or prevention of plating, prevention of deposition of 
molten metal to the coating film surface and facilitation of separation of 
the baked film were obtained when the anti-plating agent was prepared by 
adding selective components B to common components A in accordance with 
the following examples B-1 to B-3. 
______________________________________ 
(A) common components (weight part) 
alkali silicate 0.5 to 30 
boric acid 0.5 to 30 
alkali metal hydroxide 0.5 to 20 
one or both of magnesia 
and magnesium hydroxide 1 to 30 
one or both of alumina 
and aluminium hydroxide 1 to 20 
(B) selective component (weight part) 
(B-1) at least one kind of titanium oxide 
and/or titanium complex oxide 
1 to 20 
(B-2) at least one kind of zirconium oxide 
and/or zirconium complex oxide 
1 to 20 
(B-3) at least one kind of titanium oxide 
and/or titanium complex oxide 
1 to 20 
at least one kind of zirconium oxide 
and/or zirconium complex oxide 
______________________________________ 
Preferably, the mean particle size of the magnesia and magnesium hydroxide 
is selected to range between 0.01 and 1 .mu.m. It is also preferred that 
alumina and aluminium hydroxide, and oxides and complex oxides of titanium 
and zirconium have mean particle sizes which fall within the range of 
between 0.1 and 100 .mu.m. Mean particle size of magnesia and magnesium 
hydroxide less than 0.01 .mu.m is impractical because such a small 
particle size permits a secular change of the aqueous slurry and 
solidification of the same, although superior effects of prevention of 
plating, prevention of deposition of molten metal and easiness of 
separation of coating film are obtainable even with such small particle 
size. On the other hand, the effect of prevention of plating is decreased 
and the separation of the coating film is made difficult when the mean 
particle size is increased beyond 1 .mu.m. 
Mean particle sizes of alumina and aluminium hydroxide, and oxides and 
complex oxides of titanium and zirconium less than 0.1 m permits the 
formation of numerous pin holes in the surface of the baked surface to 
deteriorate the anti-plating effect and to cause an oxidation of the steel 
sheet surface. Also, the tendency of secular change of the aqueous slurry 
as the anti-plating agent is promoted by such small particle size. To the 
contrary, when the mean particle size exceeds 100 .mu.m, the peeling of 
the baked film is deteriorated and the application of the aqueous slurry 
by the roll applicator, spray and so forth is made difficult. 
By selecting the composition ratio of the antiplating agent as stated above 
while determining the mean particle sizes of the magnesia, magnesium 
hydroxide, alumina, aluminium hydroxide and oxides and complexed oxides of 
titanium and zirconium as stated above, it is possible to obtain a 
one-side plated steel sheet with superior effecs of prevention of plating, 
prevention of deposition of molten metal on the coating film and easiness 
of separation of the baked film. 
Practical examples of the anti-plating agent in accordance with the second 
form of the invention will be explained hereinunder. 
(EXAMPLE 1) 
An aqueous solution was prepared by dissolving or dispersing the following 
substances on suitable amount of water: 10 g of MgO; 10 g of water glass 
(4.5 g as Na.sub.2 O.2SiO.sub.2); 4 g of NaOH; 6 g of H.sub.3 BO.sub.3 ; 2 
g of BaTiO.sub.3 and 3 g of Al.sub.2 O.sub.3. The slurry was applied onto 
one side of a steel sheet which had been cleaned by ordinary alkali 
degreasing and rinsing by water, using a roll applicator by an amount of 
about 50 g/m.sup.2 in the state after drying. The steel sheet was then 
dried for 1 minute at a low temperature of 150.degree. C. in an oven 
opened to the atmosphere, and was subjected to an annealing conducted for 
2 minutes in an atmosphere consisting of 10%H.sub.2 +90%N.sub.2, followed 
by a cooling down to 530.degree. C. in the same atmosphere. The steel 
sheet was then dipped in a molten zinc plating bath of 0.18%Al-Zn for 
plating with zinc. The bath temperature and the dipping time were 
465.+-.5.degree. C. and 3 seconds, respectively. The steel was pulled out 
from the bath and was wiped by a gas wiper while it is still held just 
above the bath, for adjusting the amount of zinc attaching thereto. Then, 
when the steel sheet temperature was lowered to about 300.degree. C., the 
steel sheet was immersed in water of about 20.degree. C. for quenching. 
The steel sheet after the plating was plated at its one side while the 
other side was completely coated by the anti-plating coating film. The 
coating film, however, could easily be separated by the quenching in the 
water. The steel sheet was then rinsed by water and was subjected to a 
brushing following by drying by means of a blower. In consequence, a 
one-side plated steel sheet was obtained to have one side uniformly plated 
with zinc at a rate of about 150 g/m.sup.2 while the other side presented 
clean cold-rolled surface. 
(EXAMPLE 2) 
An aqueous slurry was prepared by dissolving or dispersing the following 
substances in suitable amount of water: 14.5 g of Mg(OH).sub.2 ; 10 g of 
aqueous solution of kalium silicate (6 g as K.sub.2 O.SiO.sub.2); 6 g of 
KOH; 5 g of H.sub.3 BO.sub.3 ; 3 g of ZrSiO.sub.3 and 4 g of Al(OH).sub.3. 
A zinc plating was conducted in the same manner as Example 1 using the 
above-mentioned aqueous slurry as the anti-plating agent. The plated steel 
sheet was slightly bent in water (one-time bending at 30.degree.) to 
separate the coating film. The steel sheet was then subjected to rinsing 
by water, brushing and drying by a blower. In consequence, a perfect 
one-side plated steel sheet plated only at one side with zinc was obtained 
as in the case of Example 1. 
(EXAMPLE 3) 
An aqueous slurry was prepared by dissolving or dispersing the following 
matters in suitable amount of water: 20 g of MgO; 15 g of water glass; 10 
g of H.sub.3 BO.sub.3 ; 8 g of NaOH; 3.5 g of TiO.sub.2 ; 5 g of 
Al(OH).sub.3 and 5 g of ZrO.sub.2. A plating was conducted under the same 
condition as Example 1 using the above-mentioned aqueous slurry as the 
anti-plating agent. In consequence, a perfect one-side zinc plated steel 
sheet was obtained equally to the case of Example 1. 
(EXAMPLE 4) 
The stability or resistance to secular change of the aqueous slurries was 
examined with various conventional compositions and compositions in 
accordance with the invention of the anti-plating agent, while varying the 
particle sizes of the constituents. The test was conducted using these 
anti-plating agents while employing two different annealing temperatures 
of 750.degree. C. and 850.degree. C. and two different pull-out speeds of 
40 mpm and 60 mpm, to check for the anti-plating effect, deposition of 
molten zinc to the coating film layer and the easiness of separation of 
the baked film, the result of which is shown in Table 2. The method of 
evaluation of the property is shown in Table 3. 
As will be clearly seen from Table 2, the use of the anti-plating agents of 
the invention ensures almost no deposition of the molten zinc onto the 
surface of the coating film of the anti-plating agent and an easy 
separation of the coating film by bending, even when the annealing 
temperature is increased and the speed of pulling out is increased to 60 
mpm. 
Although the preferred embodiments have been described with specific 
reference to the case of hot dip zinc plating on one side of a steel 
sheet, it will be clear to those skilled in the art that the anti-plating 
agent of the invention can equally be applied to the hot dip plating 
process with Al, Zn-Al, Sn, Pb, Pb-Sn and the like material. 
3 TABLE 2 
mean mean secular particle particle stability deposition of size 
of size of of agent anneal- molten zinc peeling* MgO or MgO or in 
aqueous ing temp. pull-out 60 anti-plating of coating No. composition of 
anti-plating agent (g) Mg(OH) Mg(OH) slurry state .degree.C. speed 40 
mpm power film 
prior art water MgO NaOH H.sub.3 BO.sub.3 0.05 O 750 X X O O 
glass (1) 10 10 4 6 850 X X O O prior art water MgO NaOH H.sub.3 
BO.sub.3 TiO.sub.2 0.5 0.5 O 750 X O O glass (2) 10 10 4 6 3 
850 X X O O prior art K.sub.2 O.SiO.sub.2 MgO NaOH H.sub.3 BO.sub.3 
TiO.sub.2 5 1.0 O 750 X X (3) 8 10 4 8 5 850 X X X prior art 
meta MgO 750 X X X X bolic sodium silicate (4) 6 21 
850 X X X X prior art amino 750 X X O sodium silicate (5) 10 
850 X X O prior art water 750 X X X X glass (6) 10 
850 X X X X 
mean mean secular deposition of particle particle stability molten 
zinc size of size of of agent annealing pull-out peeling* MgO or 
MgO or in aqueous temp. speed 40 60 anti-plating of coating No. compositi 
on of anti-plating agent (g) Mg(OH).sub.2 Mg(OH).sub.2 slurry state 
.degree.C. mpm mpm power film 
present water MgO NaOH H.sub.3 BO.sub.3 Al.sub.2 O.sub.3 TiO.sub.2 
10 0.05-30 O 750 O O .DELTA. .DELTA. invention glass (1) 10 10 4 6 3 3 
850 O O .DELTA. X present water MgO NaOH H.sub.3 BO.sub.3 Al.sub.2 
O.sub.3 TiO.sub.2 0.005 0.5-70 X 750 O O O O invention glass (2) 10 10 
4 6 3 3 850 O O O O present K.sub.2 O.SiO.sub.2 MgO NaOH H.sub.3 
BO.sub.3 Al.sub.2 O.sub.3 TiO.sub.2 0.8 1-70 O 750 O O O O invention 
(3) 8 12 6 8 3 3 850 O O O O present K.sub.2 O.SiO.sub.2 MgO NaOH 
H.sub.3 BO.sub.3 Al.sub.2 O.sub.3 BaTiO.sub.3 0.1 1-30 O 750 O O O O 
invention (4) 12 14 9 10 2 6 850 O O O O present water MgO KOH 
H.sub.3 BO.sub.3 Al(OH).sub.3 ZrO.sub.2 0.9 0.1-1 O 750 O O O O 
invention glass (5) 20 22 10 14 5 3 850 O O O O present water MgO 
KOH H.sub.3 BO.sub.3 Al.sub.2 O.sub.3 ZrSiO.sub.3 TiO.sub.2 0.05 0.8-50 
O 750 O O O O invention glass (6) 8 11 5 3 1 2 3 850 O O O O present 
K.sub.2 O.SiO.sub.2 Mg(OH).sub.2 NaOH H.sub.3 BO.sub.3 Al(OH).sub.3 
CaZrO.sub.3 Mg.sub.2 TiO.sub.4 0.02 0.2-80 O 750 O O O O invention (7) 
15 16 3 6 8 3 4 850 O O O O present water Mg(OH).sub.2 NaOH H.sub.3 
BO.sub.3 Al(OH).sub.3 TiO.sub.2 CaTiO.sub.3 0.5 0.5-20 O 750 O O O O 
invention glass (8) 16 13 6 9 1 3.5 2 850 O O O O present water MgO 
KOH H.sub.3 BO.sub.3 Al.sub.2 O.sub.3 TiO.sub.2 Mg.sub.2 TiO.sub.4 
BaZrO.sub.3 0.05 0.2-30 O 750 O O O O invention glass (9) 11 12 5 7 2 3 
1 1 850 O O O O present water MgO Mg(OH).sub.2 NaOH H.sub.3 BO.sub.3 
Al.sub.2 O.sub.3 TiO.sub.2 0.01 10-50 O 750 O O O O invention glass 
(10) 25 10 5 10 16 2 3 850 O O O O present K.sub.2 O.SiO.sub.2 MgO 
NaOH H.sub.3 BO.sub.3 Al(OH).sub.3 Mg.sub.2 TiO.sub.4 5 10-30 O 750 O 
O .DELTA. X invention (11) 5 20 15 23 3 3 850 O O .DELTA. X present 
water MgO NaOH H.sub.3 BO.sub.3 Al(OH).sub.3 Al.sub.2 
O.sub.3 SrTiO.sub.3 ZrO.sub.2 0.08 1-60 O 750 O O O O invention glass 
(12) 18 18 3 9 0.5 4 3 1 850 O O O O present water MgO KOH H.sub.3 
BO.sub.3 Al(OH).sub.3 CaTiO.sub.3 TiO.sub.2 ZrSiO.sub.3 0.5 0.1-1 O 750 
O O O O invention glass (13) 15 10 7 13 10 10 4 5 850 O O O O 
*one time bend in water (bending angle 30.degree.) 
TABLE 3 
______________________________________ 
Evaluation Method 
Evaluation 
stability peeling 
of anti-plating 
deposition of 
anti-plating of baked 
aqueous slurry 
molten zinc effect film 
______________________________________ 
no change over 
almost no deposi- 
no temper color 
perfect 
10 days tion of zinc on 
and no deposi- 
peeling 
baked film surface 
tion of Zn on 
steel surface 
changed in 
attaching of zinc 
temper color partly 
5 to 6 days 
to a part of baked 
on a part of peeled 
film surface steel surface 
changed in 
zinc attached to 
temper color and 
no 
several hours 
whole surface of 
Zn deposition on 
peeling 
baked film steel surface 
______________________________________ 
As will be seen from the foregoing description, by using the anti-plating 
agent in accordance with the invention, it is possible to eliminate the 
undesirable decomposition and peeling off of the anti-plating coating film 
which were often experienced in the prior art during annealing, so that 
the plating on the other side of the steel sheet is perfectly prevented. 
In addition, the steel sheet surface revealed after the removal of the 
coating film is never oxidized nor changed in state and held in the name 
state as that presented before the plating, in contrast to the prior art 
in which the steel sheet surface is oxidized or changed in the state after 
the removal of the coating film.