Product Introduction

Topcoat treatment on zinc-based plating
Nippon Hyomen Kagaku Kabushiki Kaisha R & D center

Introduction
Most of the zinc and zinc alloy plating in Japan areFeatures

finalized by chemical conversion coating, but there are also

Aqueous organic-mineral topcoat

specifications to apply topcoat coating treatment after・Be most commonly used for zinc plating.

chemical conversion coating treatment. Although the・Can be selected by required friction coefficient.

purpose of the topcoat treatment varies, the following are・Can be diluted with water and easy to handle.

mentioned as the main ones:・Can be treated with the same level of equipment as the・Improvement of corrosion resistancepost-treatment of zinc plating.

・Adjustment and improvement of fastening

Aqueous inorganic silica type topcoat
・Provide high heat resistance of the film.

characteristics of fastening parts

・Provide the almost same coefficient of friction as the・Improvement of treatment appearance
・Prevention and reduction of galvanic corrosion inchemical conversion coating.
・Can be diluted with water and easy to handle.

composite materials, etc.
Though the popularization rate of topcoat at present in the・Can be treated with the same level of equipment as thepost-treatment of zinc plating.

country is not high, it is considered that the demand will
increase in future mainly for the above-mentioned purpose.

1

・Be not suitable for bending or caulking processing.
Nonaqueous organic-mineral topcoat
・Provide both heat resistance and flexibility of theProduct Summarycoating.

We have a lineup of an aqueous organic-mineral topcoat,an aqueous inorganic silica type topcoat, and a nonaqueous・Form a tough coatings by siloxane bonding.

organic-mineral topcoat as topcoats for zinc-based plating

・Be used in explosion protection equipment.

(Table 1).
Product nameTR-705

Solvent
AqueousClassification
Organic-mineral

Coefficient of friction-ColorClear

TR-701

Aqueous

Organic-mineral

0.08 to 0.13

Clear

TR-700

Aqueous

Organic-mineral

0.12 to 0.18

Clear

TR-108

Aqueous

Organic-mineral

0.14 to 0.20

Clear

TR-735T

Aqueous

Organic-mineral

0.24 to 0.30

Clear

TR-740

Aqueous

Organic-mineral

0.20 to 0.25

BlackTR-170

Aqueous

Inorganic silica

0.30 to 0.40

Clear

TR-712

Aqueous

Inorganic silica

0.30 to 0.40

Clear

TR-720

Nonaqueous

Organic-mineral

0.24 to 0.30

Clear

Remarks
For Rack
For barrel
Low friction typeFor barrel
For barrelHigh corrosion resistance typeFor rack or barrelHigh friction typeFor barrelHigh Temperature resistant typeHigh corrosion resistance of the inner nonplated partLow-cost typeHigh corrosion resistance of the inner nonplated partHigh corrosion resistance type

Table 1: Topcoat Lineup*In addition to the above lineup, the company is also licensing and marketing COVENTYA's FINIGARD.
202010301 JASCO Nippon Hyomen Kagaku Kabushiki Kaisha 1

[Product Introduction] Topcoat treatment on zinc-based plating

the conventional zinc-based plating, it can be realized

Mechanisms
This paper explains the mechanism of corrosion

corrosion resistance improvement and improvement ofresistance improvement and friction coefficient adjustment

fastening

characteristics by performing additionally.

using aqueous organic-mineral topcoat most often used in

Therefore, it is a technical with a high possibility thatthe topcoat for zinc-based plating as an example. Figure 1

demand will increase in the future for the purpose of raisingshows a film structure model when an aqueous organic-

the level of the current specification and stabilizing themineral topcoat is treated on zinc plating.

quality.
Especially, the application to fastening parts such as volts

Base resin

Inorganic binder

is effective, but the selection of the product according to theWax

targeted friction coefficient is necessary.
Topcoat layer
0.5 to 2μm
Passivation layer
Approximately 0.5μm
Zinc plating layer
5 to 10μm

Literature
1: Hideo Susa; J. Surf. Finish. Soc. Jpn. Vol.70, No. 8, pp.
388-393 (2019)

Figure 1: Aqueous Organic-mineral Topcoat on Zinc Plating
Although the passivation layer is for suppressing thecorrosion progress of the zinc plating layer, it also functions
as a primer for strengthening the adhesion between the zincplating layer and the topcoat layer in addition to this function.
The topcoat layer has a thickness of approximately 0.5 to2μm, depending on the treatment method, and has a structurein which an inorganic binder and wax are dispersed in thebase resin.
Corrosion resistance is improved by the covering effect of
the topcoat layer which is firmly adhered to the zinc plating
layer via the passivation layer.
The inorganic binder contributes to the thickening of thetopcoat layer and the improvement of the film strength. As aresult, it leads to enhanced corrosion resistance.
Wax contributes to adjust of coefficient of friction offastening parts, etc. Target coefficient of friction can beobtained by adjusting the type and amount of wax added.
Although the passivation layer on the zinc-based plating
has an iridescent color because it is very thin, iridescentcolor disappears by the topcoat layer is added to this, themetalic color of the plating itself becomes visible. For
example, in many cases, zinc-nickel alloy plating subjected
to trivalent chromium chemical conversion treatment has a
blue color, but the iridescent color disappears due to the
topcoat treatment, resulting in a color tone similar to that ofstainless steel.

In closing
Topcoat treatment without changing the process itself of202010301 JASCO Nippon Hyomen Kagaku Kabushiki Kaisha 2