DE1810030A1 - Process for the treatment of a copper protective layer with an underlying, reflective silver layer - Google Patents

Description

Patent attorney Dipl.-Phys. Gerhard Liedl 8 Munich 22 Steinsdorfstr. 21-22 Tel. 29 84

B 3924

ASAHIGLASSCO., LTD. 2-14, Marunouchi, Chiyoda-ku, Tokyo / JAPAN

Method for treating a copper protective layer with a underlying, reflective silver layer.

The invention relates to a method for treating a copper protective layer with an underlying, reflective silver layer, the protective copper layer is created by chemical reduction on a reflective Silver layer, which is arranged on a glass plate, is formed.

H / K

It is known from American patents 2,664,363, 2,720,487 and 2,768,944 to form a protective copper layer on a reflective silver layer which is arranged on a glass plate. In these known methods, the procedure is such that a copper sulfate solution and a suspension of finely divided metal are brought into action on the reflective layer. This method, which is referred to below as the Cu-Back method, is well suited to avoid any damage to the reflective silver layer. With this method it is also possible to produce a mirror with a sufficient reflectivity, whereby even a thin silver layer can be formed. This is advantageous in that silver is very expensive, so that costs can be saved by using a thin layer of silver. The .. Cu-Back process is particularly advantageous if. The copper sulphate solution contains an acidic substance - such a solution is hereinafter referred to as acidic copper sulphate solution - as described in the American patents 2,726,487 and 2,768,44 , according to which either phosphoric acid or sulfuric acid ate aanr © Smtetans in Aawea-

So that eifis cilisa®

are referred to as "pin holes" and as an "orange effect" when it comes to varnishes are known. This creates corrosion spots in the silver layer, therefore the silver layer is not adequately protected.

The "pin holes" are less present when the thickness of the copper protective layer increases. It is obvious, however, that the thickness of the copper protective layer has certain upper limits for reasons of economy are set. For practical reasons there is a certain limit In terms of the thickness of the copper layer, however, it is very difficult, if not impossible, to avoid all "pin holes". As a rule, the thickness of the copper layer is in a range from 40 to 20OmR. It is thus extremely difficult to form a protective copper layer at the same time is thin and also has no "pin holes". The Cu-Back process also has the following disadvantage. If an acidic copper sulphate solution is used to produce a protective copper layer, this solution must be used Formation of the layer can be washed out completely. If the washing is incomplete is, the silver layer is gradually decomposed by the residue of acid. For reliable protection against decomposition it is necessary that Wash the protective copper layer carefully with distilled water. This washing requires a relatively high expenditure of time and money.

Based on the aforementioned prior art, the object of the invention is to avoid the disadvantages of the known processes, in particular the Cu-Back process and to enable the production of a copper protective layer, which has no "pin holes". Furthermore, according to the invention

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Washing of the copper protective layer either simplified or completely ' can be omitted, with the quality of the copper protective layer should be improved. According to the invention, this object is achieved by that the copper protective layer is treated with a chromating solution containing chromic acid, dichromic acid, chromates and / or dichromates.

If the copper protective layer is exposed to a corrosive atmosphere there is point-wise corrosion. It is assumed that the cores of corrosion originate from small imperfections in the layer, which so are small that they are invisible to the naked eye. These little flaws are the aforementioned "pin holes".

The number of corrosion nuclei depends on the type of atmosphere that the Copper protective layer is exposed. The stronger the number, the bigger it is is the corrosive effect of the atmosphere. The change in the number of "pin holes" can be explained by the following hypothesis.

As mentioned above, a very thin layer of copper has a Thickness from 40 to 200ητμ several latent defects, which indicate disturbances in the alignment of the copper atoms as well as other perturbations. These latent defects and voids have a practical effect as "pin holes", which are responsible for the cores of corrosion, if the layer is exposed to a corrosive atmosphere.

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The mentioned flaws and defects are of various shapes and sizes Type.

With type A there is a practical effect (actual flaws) even with weak corrosive influences, e.g. when spraying distilled water for 25 seconds with subsequent drying. With type A “defects actually show up if the layer is somewhat thicker exposed to corrosive conditions, e.g. if left standing in a solution of NaCl (30 g / l) for 48 hours at room temperature, With type A “actual flaws only show up if the copper layer exposed to very strong corrosive conditions. This is the case, for example, when the copper layer is in contact with a filter paper is brought, which is impregnated with an aqueous solution that

60 g / l NaCl, 10 g / l potassium ferricyanide and 1.2 cm / l concentrated aqueous Contains ammonia, the exposure time being 5 minutes at room temperature amounts to.

If thus the copper protective layer of a weak corrosive atmosphere is exposed arise from the latent defects of type A-actual Defects (i.e. 'pin holes *'). When the atmosphere is normal or high has a corrosive effect, the latent defects of types A and A «, or Aj, A "and A" to actual defects, i.e. H. converted to "pin holes". The above hypothesis explains why the number of "pin, Holes "is greater when the corrosive effect of the atmosphere, which is the Copper layer is exposed, becomes stronger.

00 9823/1758

Due to the chromating treatment according to the invention, the latent defects and defects of type A to type A ₃ and higher are eliminated, so that one treated according to the invention. Copper protective layer does not have any "pin holes" even with extremely strong corrosive effects,

Why the washing when performing the chromating treatment according to the invention can come in omission is not fully clarified. It will, however, assumed that the "removal" of the latent defects and the resulting increased corrosion resistance of the protective layer is the reason for this, Another explanation can also be that the copper layer and / or the Acid can be immobilized by the chromating treatment.

Although, as mentioned above, the real reasons are not entirely are cleared up, it should be noted, however, that by the invention Treatment of the process step of washing can be omitted completely. The treatment according to the invention can even be used achieve greater corrosion resistance of the protective layer than with a extremely careful washing according to known procedures.

When the method according to the invention is carried out in practice, the reflective silver layer is deposited on the glass plate in a vacuum. The glass plate is carefully washed with pure water, e.g. B. distilled water, washed and then treated _{with a dilute solution of SnCl 0.} The concentration of this solution is preferably between 0.1 and 1%. the

009823 / 1.7 68 392Φ

Treatment of the glass plate with the SnCl ₂ solution, which is referred to below as the inactivation treatment, improves the binding force between the glass and the silver layer. To form the silver layer, a solution containing a silver salt and ammonia in amounts of approx. 5 to 25 grams or approx. 10 to 50 grams - AgNO ₃ and NH ₄ OH - is used (the above weight data refer to an amount of 1 liter). This silver salt solution is 30 to 60% of the stoichiometric amount of a solution of a reducing agent - z. B. Rochelle Salt, Saccharic! or formaldehyde added. The mixture is poured onto a glass plate, the silver salt being reduced so that firmly adhering metallic silver forms on the glass plate, which results in the reflective silver layer. After the glass plate has been silvered, the silver layer is washed and treated with an acidic copper sulfate solution and a suspension of finely divided metal, a protective copper layer being formed on the glass plate. The methods described in US Pat. Nos. 2,720 and 2,768,944 can be used for this purpose.

The finely divided metal is said to have a reducing effect on the copper ions have, westialb any of the metals listed below in Can be used: Zn, Fe, Cd, Ni, Co, Cr, W, Mo, Mn. It can alloys of these metals are also used. The fine and small particles of the metal are evenly mixed with water for the preparation a suspension in an amount of 6 to 12 grams per liter. The suspension is applied to the silver layer simultaneously with the acidic copper sulfate solution sprayed on. The preferred volume used for the

3 2

spray is 20 ms each 30 cm nro dm.

ORIGINAL INSPECTED

The acidic copper sulfate solution is a solution containing 50 to 240 grams of copper sulfate (CuSo ₄ ° 5 H ₂ O) and 5 to 20 grams of an acidic substance per

Liter contains. The aforementioned acidic substance can be any organic or inorganic acid, e.g. B. phosphoric acid, sulfuric acid, tartaric acid, oxalic acid, formic acid. Salts such as e.g. Ammonium persulfate, come into use. Sulfuric acid and ammonium sulfate are particularly preferred.

The amount of acidic copper sulphate solution is chosen so that the proportion is 4 of CuSO; in the solution is 5 to 10 times as large as the stoichiometric Amount related to the finely divided metal in the suspension. If the Suspension and the solution at the same time on the silver-plated glass plate in the the aforementioned amounts - i.e. approx. 20 to 60 cm and 20 to 60 cm per 1 dm Silver layer - when sprayed on, a protective copper layer forms in a thickness of approx. 45 to 100

The copper protective layer formed in this way is then treated with a Chromierungs ™ solution treated, the chromic acid, dichromic acid, chromates and / or bichromates contains.

Preferred chromates and bichromates are the alkali metal salts or ammonium salts of chromic acid © and DicSiromsäwre _s such as. B. Sodium chromate, Kaliumctiroraat, Ammoniumcferomatj, Kalramdictiromat ,, Natrtamdichromat, Ammoiu'umdichromat etc.

3924 00-9823 / 1758

The concentration of the chromating solution is in the range of 0.01 to 80 grams per liter, preferably in a range from 0.1 to 20 grams per liter. A range from 0.1 to is particularly preferred 2 grams per liter. The treatment time is too long if the concentration is too low. The copper film is dissolved when the concentration of Solution is too high. In both cases there are disadvantages =

The chromating solution preferably does not contain any strong acids, such as Sulfuric acid and hydrochloric acid. If a strong acid is present, a value of 0.01 N or less should be observed, a solution which contains a large amount of a strong acid, it causes deterioration in the quality of the copper layer. The presence of nitric acid is particularly harmful.

It is preferred according to the invention, for the purpose of chromating with the copper layer provided product either immerse in the chromating solution or the chromizing solution on the protective copper layer to spray on. When immersed, the time required is in

approx.
an area about 1 to 100 seconds ago. When spraying is 4as

3 2

Required spray volume approx. 5 to 50 cm per dm of copper layer. Although a larger spray amount is favorable per se, there is, however, the disadvantage here of higher costs.

009823/1760

The copper protective layer can be treated with water before the chromating treatment getting washed. However, washing with water can also be carried out after the chromating treatment. Even though, as mentioned above, an additional washing can be carried out, but this is by no means to achieve the success aimed for according to the invention absolutely necessary.

According to the invention, good results are also achieved when the Chrome plating immediately after manufacturing a product according to the known Cu-Back ^ process takes place, which is followed by drying - without washing connects.

Further details and features of the invention are from the following Description of preferred embodiments apparent.

example 1

A glass plate is carefully washed with distilled water and treated with a 0.3% aqueous solution of SnCIL. Then becomes a

3 Mixture of one liter of a solution A and 500 cm of a solution B ^j

3 2

poured onto the glass plate in an amount of 5 cm per dm, whereby a reflective silver layer with a thickness of 55 κιμ is formed.

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Solution A: silver salt (ζ. B. AgNOJ 23 g / l

Ammonia (NH ₄ OH) 36 g / l

Solution B: sugar 10 g / l

Tartaric acid 1.4 g / l.

The reflective silver layer is with 25 cm of a solution C and

3
27 cm of a solution D sprayed, a copper protective layer with a thickness of 87 ητμ is generated.

Solution C: CuSO ₄ - 5 H ₃ O 100 g / l

(NH ₄ ) ₂ S ₂ O ₈ 10 g / l

Solution D: Zn powder (300 mesh and less) θ g / l.

Without washing, the copper-plated product is immersed in a chromating solution containing 5 g / l chromic acid - CrO ₃ . It is immersed for 5 seconds, followed by drying.

A filter paper with a impregnated aqueous solution containing 60g / l NaCi, 10 g / l potassium ferricyanide

3
and 1.2 cm / l of concentrated aqueous ammonia. The impres-

009823/1758

- id -

nated filter paper is brought into contact with the copper layer and left at room temperature for 5 minutes. There will be no Damage or impairment of the reflective silver layer was found.

Example 2

With the same corrosion test, a product that looks eteomized is fairly heavily corroded ₉ with 34 corrosion points per dm / although the copper layer had been carefully washed off with distilled water for about 20 days. '

A silver-plated glass plate with an Ehromier & en Küpferschichtj the similar as in Example 1, we are generally immersed in an aqueous solution, the 30 grams of NaCÄpr © liter © isMlt. The plate will be repeated 48 hours at room temperature © IngeteuetiiLis there are no impairments whatsoever (spots).

In contrast Merssu becomes a
15 seconds with distilled
ie it show up

00 9823/17 68

Example 3

A silver-plated glass plate protected by copper is, as in example 1, chromed and left to stand in air for two days. This shows that the gloss of the protective copper layer of the is the same as it is immediately after the production according to the Cu-Back method can be observed. In the case of a product in which the protective copper layer is washed with distilled water for approx. 25 seconds and in which chrome plating has not taken place, a black discoloration shows up in two days, although the silver layer has no effect is.

A similar product, on which distilled water for about 5 seconds 100 shows that it has been sprayed on and subsequently dried

2
Corrosion points per dm - the reflective silver layer - after 2 days.

Example 4

A mixture of 1 liter of solution A and 500 cm of solution B is poured onto a glass plate covered with distilled water carefully

0098 23/1758

washed and treated with a 0.1% solution of SnCl _2.

3 2

It is applied in an amount of 5 cm per 1 dm. poured onto the glass plate, a reflective silver layer having a thickness of 50 m ^ obtained will.

Solution A: Silver salt (AgNO ₃ ) 18 g / l Ammonia (NH ₄ OH) 32 g / l NaOH 14 g / l Solution B: sugar 10 g / l Tartaric acid 1.4 g / l

The reflective silver layer is coated with 30 cm of a solution C at the same time

3 2

and with 30 cm of a solution D - based on 1 dm - sprayed, whereby one receives a protective copper layer with a thickness of 94 ΐημ ·.

Solution C: CuSO ₄ -OH ₂ O 120 g / l

H ₂ SO ₄ 7 g / l

Solution D: Fe, finely divided 10 g / l (300 mesh sizes or less)

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-Id-

Without washing with water, an aqueous layer is applied to the copper protective layer Solution of potassium dichromate (1 g / l, CrO ₃ ) in an amount of approx. 3 cm

sprayed on per dm, followed by drying.

A strong coding effect is produced by the fact that the copper layer is brought into contact with a filter paper which is covered with

is impregnated with an aqueous solution containing 60 g / l NaCl, 10 g / l potassium ferricyanide and 1.2 cm / l concentrated aqueous ammonia. The whole is left to stand at room temperature for 5 minutes. It there are no impairments of the reflective silver layer. (Stains).

A product made in the same way, but in which the process step of chalking is omitted, is made with distilled water sprayed for about 30 seconds. After the corrosion test, they show

ο 20 corrosion spots per dm.

Example 5

A silver-plated glass, which has a chromed copper protective layer - similar to Example 4 - is immersed in an aqueous solution of NaCl (30 g / l) immersed for 48 hours. There are no impairments (stains) on the product.

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In the case of a non-chromed product, which is only made with distilled water sprayed for 20 seconds show on immersion

2
50 corrosion spots per dm within 6 hours.

Example 6

A silver-plated glass protected by a copper layer, which has been chrome-plated in the same manner as described in Example 4, is exposed to the atmosphere for 2 days. At the end of this time, the layer shows the same gloss as immediately after production by the Cu-Batk process.

In contrast to this, a cropping layer produced in the same way shows However, which is not chromed, but only with distilled water during Sprayed for 30 seconds and subsequently dried, blackening after two days, although the silver layer remains intact.

A similar copper protective layer that was treated with distilled water during Has been sprayed for 5 seconds and dried, shows after two days un-

2
40 corrosion spots per dm. .

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Example 7

A glass plate is carefully washed with distilled water and treated with a 0.05% solution of SnCl «. 5 cm of a mixed solution consisting of 1 liter of solution A is poured onto the glass plate

and 500 cm of solution B. A reflective silver layer is obtained with an average thickness of 54 m μ.

Solution A: ■ silver salt (AgNO ₃ ) 20 g / l Ammonia (NH ₄ OH) 35 g / l NaOH 15 g / l Solution B: sugar 10 g / l Tartaric acid 1.4 g / l

The following solutions are simultaneously applied to the reflective silver layer C and D sprayed on in an amount of 40 cm per dm each, with a copper protective layer with a thickness of 120 πμ is formed.

Solution C: CuSO ₄ . 5 H ₃ O 100 g / l

(NH ₄ ) ₂ S ₂ O ₈ 15 g / l

Solution D: Zn finely divided 9.3 g / l

(300 mesh sizes and less)

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Without washing, the protective copper layer is dissolved in a solution of sodium chromate (2 g / l, CrOJ immersed for 3 seconds and dried.

A strong corrosive effect is produced by the fact that the copper layer is brought into contact with a filter paper for 5 minutes at room temperature, which is impregnated with an aqueous solution which is 60 g / l NaCl, 10 g / l potassium ferricyanide and 1.2 cm 1 concentrated, contains aqueous ammonia. The silver layer shows no impairments and remains completely spotless. In contrast, one shows similar Produced copper layer, which is not chromed, but only has been sprayed with distilled water for approx. 30 seconds,

ο
approx. 20 corrosion points per dm if the same corrosive influence

is available.

Example 8

A silver-plated glass plate that resembles a chrome-plated copper protective layer which has according to Example 7 is immersed in an aqueous solution of NaCl (30 g / l) for 48 hours. Again, there is no staining whatsoever observed. In contrast to this, a copper layer that is not chromed, but only treated with distilled water for 5 seconds

has been washed, approx. 40 corrosion points per dm after a 6 hour period Immersion.

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Example 9

A silver-plated glass plate with a copper layer - see Example 7 - is left to stand in the air for 2 days. The shine of the copper protective layer remains completely unchanged. In contrast, a Copper layer formed in the same way, but instead of chroming, washing off with distilled water for 30 seconds was carried out, blackening in 2 days, although the silver layer was not affected. If a similarly formed copper layer is washed with distilled water for 5 seconds, 30 points of corrosion per dm appear after a period of 2 days.

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Claims (5)

Claims 1. Method of treating a copper protective layer with one underneath lying, reflective silver layer / which is on a suitable carrier, in particular glass, is arranged, characterized in that on the copper protective layer a chromating solution is applied which contains chromic acid, dichromic acid, chromates and / or dichromates. 2. The method according to claim 1, characterized in that the chromating solution is a dilute solution containing chromic acid, dichromic acid, chromates and / or dichromates in an amount of 0.1 to 20 grams each Liter contains. 3. The method according to claim 1 or 2, characterized in that the Chromating solution does not contain a strong acid. 4. The method according to one or more of the preceding claims, characterized in that an acidic copper sulphate solution which contains sulfuric acid is used in the production of the protective copper layer. 5. The method according to claim 4, characterized in that the copper sulfate solution Contains ammonium persulphate. 009823/1758