JPS61246373A - Pretreating agent and pretreatment of free-cutting steel prior to electroless plating - Google Patents

Abstract

PURPOSE:To clean and activate thoroughly the rugged surface part of a steel stock and to eliminate defective electroless plating by immersing the steel stock into a mixed bath prepd. by adding a metal cleaning and activating agent to a mixed acid base contg. a hydrochloric acid as a main agent and a sulfuric acid as assistant. CONSTITUTION:The mixed acid bath is prepd. by adding 1-5 g/l metal cleaning and activating agent contg. sodium gluconate as the main agent and contg. sulfanic acid, triethanol amine, acidic ammonium fluoride, etc., if necessary, to the mixed acid base mixed with 60-80 ml/l 35% hydrochloric acid 15-25 ml/l 98% sulfuric acid. The electroplating stock of the free-cutting steel is dipped into such bath for about 10 seconds. The rugged part an cavity, etc., on the surface of the steel stock are cleaned and activated by such treatment. The defective electroless plating is decreased according to the above-mentioned pretreatment. The reduction in the product cost and the improvement in the safety of the operation are made possible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electroless plating pretreatment agent and method for free-cutting steel, and particularly to an electroless plating pretreatment for cleaning and activating the surface unevenness of free-cutting steel. The present invention relates to agents and pretreatment methods.

[Conventional technology]

Conventionally, the process of electroless nickel plating of free-cutting steel is +1.
) Solvent degreasing (2) Alkaline degreasing -1 (3) Alkaline degreasing -2 (4) Activation by acid immersion (5) Electroless nickel plating (6) Chromic acid immersion (7) Draining treatment (8) Hot water washing ( 9) It goes through processes such as drying. The types of free-cutting steel that can be plated include: (11) Low-carbon sulfur free-cutting steel (2) Low-carbon lead super-free-cutting steel (3) Low-carbon tellurium super-free-cutting steel (4) Medium-carbon lead free-cutting steel Steel (5) High carbon lead tool steel etc. These include Cr as a chemical component of the structure.
There are differences in the presence/absence and content of Si, Mn, P, S, Pb, Te, Cr, etc., and the general characteristics are as follows. Both reduce machinability.

(U) Generally speaking, the more heterogeneous the weave, the better the machinability.

(c) S, Se, Te, Pb, and Bi to be contained in the steel.

Ag and the like give free machinability.

Among these, low-carbon lead ultra-free-cutting steel is mainly used for precision equipment parts that require cutting accuracy, such as shafts.

In addition, the acid used in the acid immersion treatment is only hydrochloric acid,
35% hydrochloric acid 50-80mj! /l, 98% sulfuric acid 10-4
0ml/1.50% hydrofluoric acid 0.3-1.0 m
l/j! Sometimes a mixture of these is used.

[Problem that the invention seeks to solve]

In the above-mentioned conventional electroless nickel plating of free-cutting steel, the problem was that as many as 10% of non-defective products were produced.

These areas with good mesh appearance are those in which certain parts of the film have adhesion, black stains, roughness, etc., and when these areas with good appearance are examined under a microscope, the following can be considered.

(b) The surface condition of the material in the well-developed area has large irregularities, and nests can also be seen in the surface structure of the material.

(b) Even in areas with good plating, irregularities and nests in the structure can be seen as described above, but their sizes are small.

(8) It is thought that the unevenness and cavities on the surface of the material are caused by the segregation of Pb, S, Te, etc. contained in the material.

(d) Next, due to acid treatment, the segregated areas become non-uniformly treated, and the solubility differs locally, resulting in sticky adhesion when acid treatment is insufficient, and black stains and roughness when acid treatment is excessive. It is considered that

(n) However, with current acid treatment, these blemishes do not occur all over the same unevenness or nests on the surface of the material, but only about half of them occur at most, and some do not. The reality is that the actual cause of poor metallurgy is not known, and there has been a desire for an immediate investigation into the cause of poor metallurgy and an improvement in the plating method.

[Means for solving problems]

The present invention was invented with the purpose of solving the above-mentioned problems and providing a pretreatment agent and method for electroless plating of free-cutting steel that performs pretreatment to prevent the occurrence of sticking defects.Specific means include: The main ingredient is hydrochloric acid, sulfuric acid is used as an auxiliary agent, and a metal cleaning activator is added and mixed.The metal cleaning activator has sodium gluconate as the main ingredient, and if necessary, sulfamic acid and triethanol It is constituted as an electroless plating pre-treatment agent for free-cutting steel characterized by adding and mixing an adjuvant selected from amines and acidic ammonium fluoride. Mix this as an agent to make a base acid, and add sodium gluconate as the main ingredient and sulfupmic acid as necessary.
A metal cleaning activator selected from triethanolamine and acidic ammonium fluoride is added and mixed to create an acid bath;
This method is a pretreatment method for electroless plating of free-cutting steel, which is characterized by immersing the electroless plated material steel in a nucleic acid bath for about 10 seconds to clean and activate the surface unevenness of the material steel.

[For production]

According to the present invention having the above structure, the pretreatment agent contains hydrochloric acid as a main subagent, sulfuric acid as an auxiliary agent, and a metal cleaning activator is added thereto. When used in processing), hydrochloric acid and sulfuric acid have a synergistic effect as a mixed acid to clean and activate the general surface of free-cutting steel.
The metal cleaning activator has a synergistic effect with the mixed acid, which has an activating effect on cleaning especially the unevenness and cavities on the surface of free-cutting steel. When pretreated free-cutting steel is coated with electroless nickel plating, the surface of the free-cutting steel, especially the uneven parts (holes, threads, etc.)
It is possible to provide good plating without any plating, stains, or roughness.

〔Example〕

Examples of the present invention will now be described in detail.

First, when we pick up a well-plated area from a conventional plated sample of free-cutting steel, we find (a) Peeling of the plating layer during polishing due to poor adhesion or poor adhesion in areas where the surface layer of the material is highly uneven.

(0) These recesses have large parts ranging from around 10 μm to 50 μm, and there is a possibility that the pre-treatment process agent seeped out from the nests of these recesses in the material, resulting in the failure.

(c) The plating sample shows streak-like marks along the drawing direction, and there is a possibility that drawing compound remains.

(=) Good results were seen in terms of appearance and appearance when pretreated using a commercially available powdered acid composition containing a fluoride salt instead of hydrochloric acid. This is thought to be due to the fact that the pretreatment chemical had little influence on the irregularities on the surface of the steel material, that is, the acid composition, which has activating power without being extremely acidic, brought about good results.

From the above considerations, the base acid is better than the currently used acid, and it is better to eliminate hydrofluoric acid, which is designated as a poisonous substance from the viewpoint of work environment and worker safety. In order to find a composition with excellent surface cleaning activation ability, the acids currently used (35% hydrochloric acid 50-80ml/A, 98% sulfuric acid 10
~40mj! .

50% hydrofluoric acid 0.3-1.0 ml/il
), extract only hydrochloric acid and sulfuric acid and use them as base acids.
35% salt #160-80ml/Il, 98% sulfuric acid 1
5 to 25 m 1 /l, and the process of selecting an additive to replace hydrofluoric acid, ie, a metal cleaning activator, will be described below.

The test pieces used were 5 each of low carbon sulfur free cutting steel (hereinafter referred to as Pb) and low carbon sulfur free cutting steel (hereinafter referred to as S) with a diameter of 5 cranes and a length of 10 cm. In accordance with the law:

<Step 1> Triflon cleaning (steam) - Alkaline degreasing (general alkaline degreasing agent 40 g/l, 60°C, 50 minutes) - Water washing - Acid immersion (room temperature 1 minute) - Water washing - Electroless nickel plating (general N
i-P electroless nickel plating agent 200ml/1l/
1. 85-90°C, 10 minutes) - Water washing - Rust prevention (potassium dichromate 10g/β.

60°C, 5 to 10 minutes) - Washing with water, drying - Judgment.

Judgment was made by visually observing the degree of occurrence of unplated areas.

The contents of the study are 70 ml/1 of 35% hydrochloric acid and 20 ml/1 of 98% sulfuric acid compared to the acids currently used.
As a result of adding various compounds to the base acid of il and comparing the plating finish based on the above test conditions, 0.4 ml of hydrofluoric acid (50%)! /L/sodium conate, sulfamic acid, acidic ammonium fluoride,
It was reproducibly found that glycerin was better than hydrofluoric acid at about 3 g/l.

Next, we will discuss the process under the following conditions with a slight modification.

Step 2> Triflon cleaning (hot bath -> cold bath - steam: 1 minute each) - Alkaline degreasing (general alkaline degreaser 70g/j!.

80°C, 4 minutes) - Water washing - Alkaline degreasing (general alkaline degreaser, 35 g/L 60'C, 8 minutes) - Water washing - Water washing -
Water washing - acid immersion treatment (greenhouse, 10 seconds) - water washing, water washing, water washing, water washing, electroless nickel plating (general N1-P electroless nickel plating agent 200mj!/j, 92±2℃, 16 minutes, 2~ Rocking every 3 minutes) - Water washing, water washing, water washing, monochromic acid treatment (potassium dichromate, 5 g/L, 60°C, 5 minutes)
- Water washing - Water washing - Water washing - Alcohol immersion (methanol, room temperature 30 seconds) - Drying (50 to 100°C) - Judgment (visual evaluation of the degree of non-plating).

The treatment test pieces were 10 pieces each of PB free-cutting steel and S free-cutting steel, and treated with 35% hydrochloric acid 70ml/It, 98% as described above.
% sulfuric acid 20 m It / l, hydrofluoric acid (50%) 0.4 mj! /j addition,
Sodium gluconate and sulfamic acid have a concentration of about 3 g/12, which is consistently better than hydrofluoric acid even if the processing conditions are changed.

Looking at these study results in detail, we find that when the acid immersion time is relatively long, 1 minute, sodium gluconate is dominant, and when the acid immersion time is short, 10 seconds, sulfamic acid tends to be dominant. It is clear that both sodium gluconate and sulfamic acid are good under both acid immersion conditions of 10 seconds and 1 minute.

When comparing sodium gluconate and sulfamic acid, sodium gluconate itself is neutral and easier to handle than sulfamic acid, which is an acidic substance. A study was conducted to further strengthen the surface activation ability of free-cutting steel by using sodium gluconate in combination with other compounds, using the above-mentioned process in which the acid immersion time was 10 seconds.

As a result, 70 mj of 35% hydrochloric acid! /l, 98% sulfuric acid 20
mj! /j! Sodium gluconate is good for PB free-cutting steel at 1-12 g/It, 1-9 g/L for S free-cutting steel, but 1-5 It was found that the best cleaning activation was achieved for both PB free-cutting steel and S free-cutting steel at g/6.

Also, 35% hydrochloric acid 70ml/12.98% sulfuric acid 20ml
When other compounds are further added in the concentration range of 1 to 5 g/12 sodium gluconate to the base acid of ml/12, sulfamic acid, ammonium acid fluoride,
Addition of 0.2 to 2 g/2 of each triethanolamine exhibits a synergistic effect with sodium gluconate, and a better plating finish can be obtained than when sodium gluconate is added alone.

To summarize the conditions for realizing the present invention, basically, the pretreatment agent for acid immersion in the pretreatment of electroless plating of free-cutting steel is hydrochloric acid as the base acid, and sulfuric acid as the base acid. is mixed as an auxiliary agent, and a metal cleaning activator consisting of sodium gluconate as the main agent and, if necessary, an auxiliary agent selected from sulfamic acid, acidic ammonium fluoride, and triethanolamine is added and mixed to this base acid. It consists of The hydrochloric acid and sulfuric acid used as the base acid are each concentrated acids, and the concentration grade of the concentrated acids is 30 to 39% hydrochloric acid, preferably 35% hydrochloric acid, and the minimum 95% sulfuric acid, preferably 98% sulfuric acid. shall be. In addition, the mixing ratio of hydrochloric acid and sulfuric acid in the base acid is 60 to 89 m as 35% hydrochloric acid.
l/l, preferably 70m7! /l, 15-25 ml t/II as 98% sulfuric acid, preferably 20 m
The blending ratio is 1/41.

With respect to the concentration range of hydrochloric acid and sulfuric acid as base acids, activation of the free-cutting steel surface cannot be achieved below the lower limit, and above the upper limit, etching of the material progresses and deterioration of the plating appearance occurs. Next, as a metal cleaning activator to be added to the base acid, sodium gluconate is the main ingredient, and sulfamic acid is added as necessary.

It consists of adjuvants selected from acidic ammonium fluoride and triethanolamine, but the main ingredient is sodium gluconate.
1-5 g/l and sulfamic acid.

For adjuvants selected from acidic ammonium fluoride and triethanolamine, add 0.2 to 2 g/It;
The total amount of main agent and auxiliary agent as a metal cleaning activator is 1 to 5 g.
/It.

Next, the pretreatment method for electroless plating of free-cutting steel is to create an acid immersion bath to which the base acid specified above and a metal cleaning activator are added, and to place the free-cutting steel as an electroless plating material in the acid bath. It consists of cleaning and activation of the free-cutting steel surface by immersion at room temperature (10-15°C) for 8 to 15 seconds, preferably 10 seconds.

Regarding the specific treatment, process examples have been explained above, but to add a supplementary explanation, the acid immersion bath according to the present invention can be constructed using a general lining tank or a synthetic resin tank. I can do things.

In use, the temperature is kept at room temperature (10 to 15°C), preferably constant (22°C), and kept warm by a heater or steam heating as necessary in winter. The material to be treated is usually stored in a stainless steel cage, degreased and washed with water in advance, and after being activated for cleaning in the acid immersion bath, it is removed from the bath, left in the air for 15 seconds, and then washed with water three times. In this water washing, an ultrasonic jet washer is used to wash and remove the processing agent from the uneven parts of the surface of the free-cutting steel material, especially the burrows.

After washing, drain the water, change the jig, and perform the electroless plating process as usual.

Comparative examples of the present invention will now be described in detail.

(Example 1 and Comparative Example 1) Based on the electroless plating steps 1 and 2,
The base acid used in the acid immersion bath is 35% hydrochloric acid 70md/l
, 98% hydrochloric acid was kept constant at 20 mA'/A', and hydrofluoric acid and sodium gluconate were compared as additive components. The comparison method is as follows: In step 1, 15 pieces each of Pb free-cutting steel and 15 S free-cutting steel were used. In process 2, 15 pieces of Pb free-cutting steel were used.
Ten free-cutting steels and ten S free-cutting steels were processed, and the degree of occurrence of non-plating was visually determined, and the number of non-defective products is shown in Table 1.

Compared to the currently used acid composition (Comparative Example 1), in Example 1, the number of non-defective products increased in both the plating processes of <Step 1> and <Step 2>, and the effect is recognized.

(Examples 2 to 7 and Comparative Example 1) Based on the electroless plating process (Step 2), the base acid used in the acid dipping bath was 35% hydrochloric acid 70ml/I! ,98%
The sulfur M20 m It / 1 was kept constant, and the additive components were hydrofluoric acid and sodium gluconate as the main ingredient, and a comparison was made of the combination composition with an adjuvant selected from sulfamic acid, acidic ammonium fluoride, and triethanolamine. went. The comparison method is 10 each for PB free-cutting steel and S free-cutting steel.
Plating was carried out based on the book removal process 2>, and the degree of non-plating was visually judged, and the number of non-defective products is shown in Table 2.

<Effects> According to the present invention having the above configuration, the pretreatment material is a base acid containing hydrochloric acid as a main ingredient and sulfuric acid as an auxiliary agent, and a metal cleaning life-saving agent added thereto. When used in pre-treatment (acid immersion treatment), hydrochloric acid and sulfuric acid have a synergistic effect as a mixed acid to clean and activate the general surface of free-cutting steel, and the metal cleaning activator has a synergistic effect with the mixed acid. In particular, the acid has a cleaning activation effect on the unevenness and cavities on the front surface of free-cutting steel, and the acid is not strong, and each characteristic exerts its effect individually. There are few negative effects. As a result, the present invention can significantly reduce the sticking quality of electroless plating, thereby streamlining quality factories and work processes, lowering product costs, and improving work safety.

Compared to the currently used acid composition (Comparative Example 1), it is clear that in Examples 2 to 7, the number of non-defective plated products increases based on the present invention, and the effect is recognized.

Claims (1)

[Scope of Claims] (1) Hydrochloric acid is used as a main ingredient, sulfuric acid is used as an auxiliary agent, and a metal cleaning activator is added and mixed therewith, and the metal cleaning activator is made of sodium gluconate as a main ingredient, and is mixed as necessary. A pretreatment agent for electroless plating of free-cutting steel, which is made by adding and mixing an adjuvant selected from sulfamic acid, triethanolamine, and acidic ammonium fluoride. (2) In the pretreatment agent, the hydrochloric acid is 35% hydrochloric acid 60%
ml/l~80ml/l, sulfuric acid is 98% sulfuric acid 15ml/l
1 to 25 ml/l, and the metal cleaning activator is added at an addition rate of 1 g/l to 4 g/l. Electrolytic plating pretreatment agent (3) Hydrochloric acid as the main ingredient and sulfuric acid as an auxiliary agent. Mix these to make a mixed acid base, and add sodium gluconate as the main ingredient and sulfamic acid, triethanolamine, acidic fluoride as necessary. An acid bath is created by adding and mixing a metal cleaning activator selected from ammonium chloride, and the electroless plated material steel is immersed in the acid bath for about 10 seconds to activate the cleaning activity on the uneven surface of the material steel. 1. A pretreatment method for electroless plating of free-cutting steel, characterized by: (4) In the pretreatment method, the mixed acid base is 35%
% hydrochloric acid 60ml/l ~ 80ml/l, 98% sulfuric acid 15ml
Claim 3, characterized in that the acid bath is constituted by a mixing ratio of l/l to 25 ml/l, and a metal cleaning activator at an addition rate of 1 g/l to 5 g/l. A pretreatment method for electroless plating of free-cutting steel described in .