DE2437953A1 - METHOD AND COMPOSITION FOR TREATMENT OF PLASTIC SUBSTRATES BEFORE PLATING - Google Patents

Description

PATE NTAN WALTE

dr. ing. H. NEGENDANK (-1973) dipl.-ing. H. HAUCK Dipl.-Phys. W. SCHMITZ DiPJWNG. E. GRAALFS · DiPt ₁ -ING. W. WEHNERT

HAMBURG-MUNICH DELIVERY ADDRESS HAMBURG 36 · WEÜEH WAIL 41

TEI .. Se 74 28 AND 36 4 115 TEIjEGR. NEGKDAPATENT HAMBURG

OXY METAL INDUSTRIES CORPORATION Munich iö. mozartsth. 23

TEL. S 88 05 80

F. O. Box 20201 TEtEGH. NEGEDAPATBNT Munich Detroit. Michigan 48220 / USA HAMBURG, July 31, 1974

Method and composition for treating plastic substrates before placement

It is known to use plastic parts prior to electroless plating and subsequent electroplating with a sequence of To treat process steps that basically involve the etching of the plastic surface with an aqueous acidic Solution that contains hexavalent chromium ions, one or more water rinses, neutralize with a dilute one organic acid, such as hydrochloric acid, further water rinses, contacting the substrate surface with one acidic tin-palladium coraplex, an additional one Water flushing, accelerating the activated plastic surface and thereafter includes one or more water washes prior to electroless nickel plating.

To carry out the acceleration - on this step is the invention directed in particular - has already been proposed after activation and before metallization a Solution to use the excess tin (II)

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Removed hydroxide from the substrate surface. Typical examples Such solutions include dilute acids such as perchloric acid, sulfuric acid or phosphoric acid, as well as alkaline ones Materials such as sodium hydroxide, sodium carbonate or Sodium pyrophosphax.

It has also already been found that a slight controllable acceleration (acceleration) with the help an acidic reacting dilute palladium chloride solution can be carried out after activation. It was, however also "found the effectiveness of the mentioned AccelBrator solution is hindered by trace amounts of hexavalent chromium ions that cause the Has substrate as a result of the previous etching. In order to improve this condition, it has been proposed to remove the contamination the accelerator solution by hexavalent chromium ions by the periodic addition of a suitable source of tin (II) ions to control and in this way a conversion of hexavalent chromium into trivalent chromium.

In all of these publications, however, could not be in any If the tin (H) hydroxide is almost completely removed, resulting from the water rinse following activation, and at the same time almost no removal of the palladium hydroxide also formed by the water rinse can be carried out successfully, toie mentioned, are the palladium ions due to their catalytic heat

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ORIGINAL INSPECTED

potentiales "in the subsequent electroless plating step necessary.

The present invention is particularly directed to a method and an effective composition with which the surfaces of a polymeric substrate can be accelerated after their activation and before electroless placement, the accelerator solution the removal of the tin (II) ions, which together with the palladium are deposited during the activation, promotes, and wherein the accelerator has the property of activating the contacts of the immersion frames made of stainless steel, so that an electroless plating of a metal is formed thereon, which has a catalytic effect on the subsequent electroless plating.

The accelerator solution provided by the invention basically comprises particular molar concentrations of an inorganic acid, of metal salts which are able to be reduced to the metallic state by a surface made of iron or stainless steel and which are selected from group VIII B of the periodic table are with the exception of iron, and a compound capable of ionizing and generating fluoride ions, preferably monovalent negative fluoride ions. More precisely, the inorganic acid is relatively dilute hydrochloric acid, hydrofluoric acid, oleic acid, or oleic acid, or their equivalents, or mixtures thereof.

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gen. A preferred metal salt that meets the conditions mentioned is nickel chloride, although cobalt chloride is also Ruthenium chloride or any salt from the platinum group of the periodic table that has a lower reduction potential possessed as iron, can be used. A presently preferred source of the fluoride ions is sodium fluoride or sodium hydrogen fluoride, though also through the use of ammonium hydrogen fluoride, ammonium fluoride, lithium fluoride, potassium hydrogen fluoride, Fluorosilicic acid or hydrofluoric acid can achieve satisfactory results.

If the teaching of the invention is followed, excess Stannous hydroxide resulting from the activation step and the result of a hydrolysis reaction, if the plastic part is rinsed with water after activation, from the microscopic cavities in the polymer surface removed.

During the water rinse, hydrolysis of the palladium chloride also occurs with the subsequent formation of Palladium hydroxide. The Palladiutnions practice in the following electroless nickel plating has a catalytic effect off, while the tin (II) ions do not have a catalytic effect. According to the invention, the selective removal of the tin (II) ions achieved by the palladium ions that under carefully controlled time and temperature conditions

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_ 5 -

2A37953

a solution is used, which is preferably relatively dilute hydrochloric acid, nickel chloride hexahydrate and Includes sodium bifluoride.

In a typical chemical placement process, one polymeric plastic substrate, the plastic part is first removed from surface dirt, e.g. in an aqueous alkaline Soak solution cleaned, the cleaned part is then brought into contact with oineui organic solvent, the either a single-phase system or an emulsion of water and organic solvent, after which a thorough The part is rinsed with water. The part is then brought into contact with an aqueous, acidic solution which contains hexavalent chromium ions in order to etch the plastic surface in this way, after which an or multiple rinses are made in water and / or solutions that contain chromium-reducing or chroai-extracting agents. Then the substrate surface is brought into contact with an acidic reacting tin-palladium complex, generally the a palladium chloride, tin (II) chloride and diluted Hydrochloric acid-containing activator is, after which the polymeric substrate is carefully rinsed. Then, according to the invention, the activated plastic surface is accelerated, where particular molar concentrations of an inorganic acid, a metal salt of main group VIIIB des Periodic table with the exception of iron, which is capable of being transformed into a metallic state by means of iron or stainless steel reduced to ground, and a compound that is able to ionize and fluoride ions, i.e. monovalent negative

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tive fluoride ions, to generate, find use. the electroless plating is usually done thereafter a 'water rinse and immersion or other contact Bring the subs stepped if he has a surface with a chemical Plating solution, which is a reducible salt of the Surface of metal to be deposited, such as tfickel, lobalt, Copper, o.a. contains, completed. The metallized surface is then rinsed with water and then stands available for conventional electroplating.

The acceleration of a substrate surface after activation is of course known. Carrying out this Step is based on the assumption that during the activation of the substrate not only palladium or another catalytic material to form the necessary initiation points (initiating foci) for the reduction of i-metal ions is deposited in the electroless plating solution, but also tin (II) ions and / or other impurities that are also present in known activation solutions, are also deposited on the substrate surface or at least adhere to this, and that more precisely, during the water rinse after the activation step Hydrolysis of bladium (II) chloride and tin (H) -ChI oride takes place, which are entrained in microscopic cavities in the surface of the polymeric substrate. These Tin (II) ions in the form of tin (II) hydroxide as well

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other impurities have a disruptive effect on the subsequent metal deposition, just like adhering hexavalent chromium ions left over from etching. This removal of contaminants is the primary task of a normal accelerator solution. The problem is to promote the removal of these impurities preferentially at the palladium hydroxide points which become points to be catalyzed after reduction. The known BeSchTe ₁ uniger solutions have proven to be quite effective in removing tin (II) ions; however, their use is critical as they must be carefully controlled so as not to remove excessive amounts of palladium and thus hinder the successful performance of electroless plating.

According to the invention it was found that when using an accelerator solution, which consists of an inorganic Acid in an amount of about 0.025 to 1.00 hol, a metal salt, that is in leave, by iron or stainless Steel to be reduced to its metallic state and which comes from group VIII B of the periodic table, with Except- from iron, in an amount of about 0.002 to 0.2 mol and a compound that is able to ionize and to generate monovalent negative fluoride ions and the

put together.

In an amount of about 0.004-0.6 moles, the above-mentioned problems and disadvantages of the prior art methods the technology can be almost completely eliminated. More precisely,

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the invention removes excess tin (II) hydroxide quickly removed, leaving the palladium hydroxide behind and can perform an important catalytic puncture in electroless plating. In addition, the here described door procedure the contacts of the hanging parts stainless steel activated, that is, they are cleaned so as to have almost no adsorbed metal oxides such as trace amounts of tin, and that on the frame contacts catalytic metal in the form of reduced nickel or Cobalt, depending on the Group VIII B salt used, remains. The invention also enables the almost complete removal of the tin (III) hydroxide colloid (Sn [ohJ,) obtained by oxidation of tin (II) hydroxide by the presence of oxygen in the air or in the aqueous solution caused by agitation in the Flush, arises.

An exemplary activation solution comprises about 200 mg / _{l palladium chloride (PdCl 2} ), about 13 g / l SnCl ₂ and 100 g / l hydrochloric acid. It is believed that essentially the reaction product listed below is formed when these materials are combined:

^S n ^C1 3

^S n ^C1 3

Pd

^S n ^C1 3

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2A37953

It is believed that during the flush that follows activation, too

PdCl ₄ ⁼ and S _n Ol ₄ "" + HCl
form.

The water apparently reacts during the rinse also with the palladium (II) chloride and tin (II) chloride mentioned in the following way:

PdCl - + 2H "0 - * Pd (OH) ₀ + 4HCl SnCl ₄ = + 2H ₂ O - ^ Sn (OH) ₂ + 4HCl.

Tin (II) hydroxide has almost the same degree of solubility as palladium hydroxide. Obviously from this The previous attempts to accelerate the activated plastic surface by means of a thinned one failed Dissolution of an acid or an alkali metal unsuccessful.

As will be described in the examples below, a preferred accelerator solution contains about 10 to 30 g per liter of hydrochloric acid or a general concentration range of 3 to about 10 volumes, although this range is not always critical, 1/2 to 40 g per liter of nickel chloride hexahydrate and about 1/4 to 2 g per liter of sodium bifluoride (FaHF ₂ ). However, fluoroboric acid (HBF.) With approximately the same concentration or sulfuric acid with approximately the same concentration can also be used for the acid. The nickel chloride hexahydrate can also by

509815/1109

Cobalt chloride hexahydrate, ttuthenium chloride or any other compound from the platinum group of the periodic table which has a lower reduction potential than iron. As a source of fluoride ions, ammonium hydrogen fluoride (NH.HFp), sodium fluoride (HaF), lithium fluoride, potassium fluoride (KF), _{fluorosilicic acid (H 2} SiFg hydrofluoric acid (HF) or any other compound that is able to ionize and monovalent negative The time to effect an effective acceleration of the activated plastic substrate is normally between about 30 seconds and 30 minutes. The temperature range is about 115 to HO ⁰ F. The temperature range is about 115 to HO 0 F.

With the method according to the invention and the erfindungsgeraässen Composition can be a variety of plastics, such as polypropylene, phenols, epoxy and polysulfone polymers as well as copolymers such as acrylonitrile butadiene styrene (ABS) or other plastics that can be chemically plated. Particularly good results have been obtained with ABS and a polymer that is a combination of a polyaryl ether, of ABS and a polysulfone and marketed by Uniroyal Inc. under the trademark ARYLON will.

A series of experiments in which the composition according to the invention was applied was carried out as follows.

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An acidic accelerator containing 15 g / l hydrochloric acid and 1 g / l of nickel chloride hexahydrate, 200 ppm of divalent tin in the form of stannous chloride were added. An immersion time of about 30 seconds with a temperature of about 125 "to 130 ° F were in the coating of the substrate and dead zones or a lack of continuity formed by the electrolessly deposited metal established. However, when about 2 g / l sodium bifluoride was added, the normal effect of the Accelerator solution can be restored. As above. is carried out, part of the divalent tin hydroxide that is retained on the plastic surface while the ..assorspülung or the supply of air to tetravalent Tin hydroxide oxidizes. Usually one would expect that the hydrochloric acid dissolves the tin hydroxide, but the colloidal tetravalent tin hydroxide reacts relatively slowly with the dilute hydrochloric acid present in the accelerator. When the concentration of hydrogen chloride acid is increased, not only the tin hydroxides but also palladium are removed, which acts as a catalyst for the electroless plating is required. According to the invention, relatively small amounts of monovalent negative fluoride ions promote the rapid removal and dissolution of the colloidal tetravalent tin hydroxide. In addition, nickel ions have an effect or other metal ions that are able to penetrate an iron or stainless steel surface in their metallic State to be reduced, i.e. metal salts from the group

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VIII B of the periodic table with the exception of iron, as Catalysts for electroless nickel and lead if they added to the acidic accelerator for immersion deposition on the stainless steel contacts. In this "way" the contacts stay active, and it can Nickel can be electrolessly deposited on them as well as on the parts, resulting in a lower and more uniform contact resistance results.

In another experiment, an acidic accelerator containing 15 g / l of hydrochloric acid and 1 g / l of nickel chloride hexahydrate contained about 1 ppm of tetravalent tin colloid, which was obtained by dissolving 1.45 g of SnCl. 5HO made in 500 ml of distilled water was added. This solution / ms ö to 12 hours resistant before tin (III) hydroxide particles precipitated v as an insoluble precipitate. Widespread dead zones were found, but when 2 g / L sodium bifluoride was added, the normal functioning of the solution was restored. The subsequent addition of up to 5,000 ppm of tetravalent tin colloid did not interfere with the effectiveness of the acidic accelerator.

In another experiment, an accelerator that 15 g / l hydrochloric acid, 1 g / l nickel chloride hexahydrate and 1.84 g / l ammonium hydrogen fluoride, about 500 ppm added to tetravalent tin colloid. The examined plastic parts had an excellent plating quality.

^{ity on} 509815/1109

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'2 ^ 37953

opened.

IiS further tests were carried out. In the first experiment the accelerator contained 15 g / l HCl, 0.65 g / l Hi ¹ and 1.0 g / l MCl ₂ .6H ₂ O. In a second experiment it consisted of 15 g / l HCl, 40 g / l ITiCl ₂ .6H ₃ O and 1.84 g / l ammonium hydrogen fluoride. The plating quality of the parts was excellent in both trials.

It has been found that at this point in the process cycle there is an important condition that was not previously has been recognized. If with a hanging rack or an attachment that has a large number of adjacent Plastic parts, as is common practice, the metallized plastic parts do not have a relatively low value and have a uniform electrical resistance value with respect to the frame or the mounting in conventional solutions they are electro-plated in a very special way. Those parts that have a low having electrical resistance between their surface and the frame are plated very quickly, while those Parts that have a high resistance between their surfaces and the frame, with a noticeable reduced initial speed. It follows that those parts where the plating rather begins, soon a much higher surface current density

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exhibit

than those with whom the movement slowly sets in.

As a result, it can happen that the effective electrical resistance for the induced bipolar charge distribution on the surface of a part with high resistance is considerably less than that resulting from the direct circuit connection to the cathodic pole of the power supply for electroplating results. From this it follows on the basis of elementary physics that certain surface areas the metallized plastic parts are anodic with respect to the electrolyte and that the one thereon metallic coating is dissolved electrolytically. .As a result of this sequence of events, certain parts on the device in its metallic coating after the full electroplating streaks, dead zones, or poor plating. That such high and Non-uniform "part-frame resistances" occur when only an inorganic acid is used as an accelerator as is the case with the known processes, is shown in the attached Table 1. Therefore practice in the present invention the metal salt selected from group VIII B of the periodic table, excluding iron is and is able to be reduced to its metallic state by an iron or stainless steel surface to become, the function of being a metallic on the stainless steel contacts by immersion deposition Provide a film that acts catalytically on the deposition of the subsequent electroless plating step and

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this promotes the electrical resistance between the plastic surface and the frame or the fastening to a low and uniform value. The effectiveness of this procedure is determined by the shown in the attached Table II results, in which the results on the installation of the present j'finding shown in the entire process cycle are.

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TABLE I.

electrical resistance in ohms

investigated accelerator part on part · ,, -,,,

n "" +. "- n ^ t τ" 4 ^ contact

11.5 g / l HCl 22 14 8

129 ⁰ F. 5000 14 4986

30.6 g / l 117 ⁰ F. 60 sec.

Part on
frame part
alone 22nd 14th 5000 14th 24 14th 5000 14th 21 12th 18th 14th 16 14th

90 see. 24 14 10

4986 9 4 2

31.5 g / L HCl 5000 11 4989

plus 18.4 g / l HBF ₄

83 ⁰ F. 30 see.

32 -1 16 26th ¹ O 5ü 68 10 13th 24 11 9 20th 11 6th 19th 13th 13th 25th 12th 4988 5000 12th 4988 5000 12th 14th 26th 12th 4988 5000 12th 158 170 12th 27 40 13th

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- 17 -

11.5 g / l HCl 0.5
NiCl g / i
₂ .6H, , 0 130 ° 60 sec.

11.5 g / l HCl 0.140 g / l PdCl ₂

60 see.

18 g / l HCl 1 g / l CoCl ₂ .6H ₂ O

90 see.

TABLE II resistance in ohms electrical part
alone Contact leuniger part · on
frame 9 1 10 8th 1 9 9 1" 10 9 1 10 9 2 11 9 O 9 6th O 6th 12th 4th 16 12th 10 22nd 12th 2 1-4 12th O 12th 12th 2 14th 13th 1 14th 14th 1 15th 8th 3 11 9 O 9 9 3 12th 10 O 10 10 1 11 10 O 10 9 1 10

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- Ϊ8 -

TABLE II - Porting

electrical resistance in ohms

investigated accelerator

22.5 g / l HCl 4 g / l NiGl ₂ .6H ₂ O

134 ⁰ F.
30 see.

15 g / 1 HGl 1 g / l NiCl ₂ .6H ₂ O

1 g / l NH ₄ HF ₂

30 see.

Part on
frame part
alone Contact 14th 10 4th 16 10 6th 15th 11 13th 11 IV) 15th 10 5 11 10 1 10 10 • 0 7th 7th 0 7th 7th 0 ti 8th 0 y ü . 1 11 9 2 8th 8th 0 10 9 1

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ORIGINAL INSPECTED

From the foregoing, it can be seen that the invention provides an accelerator solution and a method of treating a liquid substrate disclosed with this solution, in deran application excess tin (II) ions on rapid V / ei se can be effectively removed while at the same time the palladium ions for the more catalytic! Exposure to electroless plating. Furthermore is determined by the presence of ITickelions or others Metal ions, which act as a catalyst for electroless nickel, a dip deposition on the stainless steel contacts keeping them in an active state and the electroless nickel deposition on the contacts as well allows the parts and in this way makes a low and uniform contact resistance possible. The accelerator and the method of the invention can be used with a variety of plastic parts. As mentioned there are a number of substituents for the inorganic acid as well as variations in the metal salts, which must be able to be reduced to their metallic state by means of iron or stainless steel surfaces and which are normally from Group VIII B des Periodic table, excluding iron, are selected. In addition, many compounds have been mentioned that are capable are to ionize and generate fluoride ions. These and other changes can of course be carried out, without deviating from the inventive teaching.

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Patent claims

Claims (1)

Claims; 1. Method of treating a polymeric plastic substrate prior to plating a surface, characterized by the steps of: etching the substrate in one aqueous acidic bath, activation of the substrate surface by contact with an acidic tin-palladium complex activating agent, Rinsing the activated surface with an aqueous medium, while doing so tin and palladium hydroxides are formed on the surface and accelerate the activated and rinsed surface with a solution containing an inorganic acid, a metal salt that is capable of being replaced by an iron Surface to be reduced to the metallic state and that from group VIII B of the periodic table, excluded Iron, is selected and comprises a compound capable of ionizing and generating fluoride ions, thereby producing almost all of the tin hydroxide without affecting the catalytic properties of the remaining Palladium hydroxide is removed quickly. 2. The method according to claim 1, characterized in that the inorganic acid is present in a molar concentration of 0.25 to 1.00, that the metal salt in a molar concentration of about 0.002 to 0.2 and the compound used as the source - the Έ1 uoridionon acts, in a molar ', η concentration of about 0.004 to O ₁ C is present. 509815/1109 ²¹ 3. The method according to claim 1, characterized in that the inorganic acid is selected from that group is that of hydrochloric acid, sulfuric acid, hydrofluoric acid or mixtures thereof. 4. The method according to claim "1, characterized in that the compound capable of ionizing and generating fluoride ions is selected from that group is made up of sodium hydrogen fluoride, ammonium hydrogen fluoride, Sodium fluoride, potassium hydrogen fluoride, potassium fluoride, Lithium fluoride, fluorosilicic acid and hydrofluoric acid. 5. The method according to claim 1, characterized in that the metal salt which is capable of being reduced to the metallic state is selected from that group which consists of nickel or cobalt chloride hexahydrate and ruthenium chloride. 6. Method of treating a polymeric plastic substrate -before plating a surface, characterized by the following steps: etching the substrate in an aqueous acidic bath, activation of the substrate surface by contact with an acidic tin-palladium complex Activating agent, rinsing the activated surface with an aqueous medium, wherein on this way tin and palladium hydroxide on the surface - 22 . 509815/1109 " ²² " 2 ^ 37953 are formed, and accelerate the activated and rinsed surface with a solution containing about 10 to 30 g per liter of HCl, about 1/2 to 40 pounds per liter of KiCl, .6H, .O and contains about 1/4 to 2 g per liter of NaHPp. 7. The method according to claim 6, characterized in that the substrate is about 30 seconds during the acceleration with the solution. to 3 minutes is kept in contact and that the solution is kept at a temperature of about 115 to HO ⁰ P. 8. The method according to claim 1, characterized in that daü the polymeric plastic substrate from that group is selected from acrylonitrile butadiene styrene, polypropylene, phenolic, epoxy and polysulfone plastics consists. 9. Composition for treating a polymeric plastic substrate before plating a surface and after etching, activating and rinsing, characterized in that that they are inorganic acid, a metal salt capable of being reduced to the metallic state and that from group VIII Ξ of the periodic table, • excluding iron, and a compound capable of ionizing and generating fluoride ions , ent., holds. - 23 509815/1109 ORIGINAL INSPECTED 10. Composition according to claim 9, characterized in that da2 the inorganic acid in a molar concentration of about 0.25 to 1.00, the metal salt in a molar concentration Concentration of about 0.002 to 0.2 and the compound that acts as the source of the fluoride ions in one raolar concentration of about 0.004 to 0.6 is present. 11. Composition according to claim 9, characterized in that dai the inorganic acid is selected from that group is derived from hydrochloric acid, sulfuric acid, Borofluoric acid or mixtures thereof. 12. The composition according to claim 9, characterized in that the compound which is able to ionize and generate fluoride ions is selected from the group consisting of sodium hydrogen fluoride, ammonium hydrogen fluoride, sodium fluoride, potassium hydrogen fluoride, potassium fluoride, luminous fluoride, fluorosilicic acid and hydrofluoric acid . Yj. A composition according to claim 3, characterized in that, as <.z the i-Ietallsalz, which is able to be reduced to the metallic state selected from the group that consists of nickel or cobalt chloride hexahydrate and ruthenium chloride. - 24 5 0 9 8 15/1109 14. Composition for treating a polymeric plastic substrate before plating a surface and after etching, activating and rinsing, characterized in that it contains 10 to 30 g per liter of HCl, about 1/2 to 40 g per liter of NiGIp.6HpO and about Contains 1/4 to 2 g per liter of NaHF ₂ . 15. Composition according to claim 14, characterized in that the NaHIV is replaced by an equivalent amount of EF . 509815/1109