Acid washing of polyamide

Abstract

A method for pickling polyamide, the method comprising step a) contacting the polyamide with an acid pickling solution comprising - a mixture of at least two inorganic acids - MHF2, wherein M is a base ion or an ammonium ion - a monocarboxylic acid having 1 to 5 carbon atoms b) contacting with an organic solvent having 1 to 10 carbon atoms, wherein steps a) and b) are performed sequentially or simultaneously.

Description

[0001] The present invention relates to a method for pickling polyamide prior to metallization and a pickling solution for this purpose.

[0002] Before metallizing the polyamide surface, the polyamide surface must be acid-washed to allow the metal layer to adhere.

[0003] Typical metal-coated (electroplated) plastics are acrylonitrile-butadiene-styrene copolymer (ABS) and ABS polycarbonate (ABS-PC). They are used in decorative elements, switches, display elements, etc., for example in automobiles.

[0004] For both decorative and technical reasons, polyamide (PA) plastic surfaces are often coated with a suitable metallic layer. Polyamide (PA) is used in automotive engineering, for example, to provide sufficient strength for door handles and other safety-related components due to its specific properties. In this context, the desired decorative and valuable characteristics are emphasized through the bonding of the metallic coating.

[0005] For the durability of the metal layer deposited on a polyamide surface, sufficient adhesive strength on the polyamide surface is crucial. To achieve this adhesive strength, it is common practice in the prior art to roughen / swell the polyamide surface before the corresponding metal deposition to ensure sufficient adhesive strength of the deposited metal layer. Various methods for this purpose are known in the prior art. Typically, the polyamide surface is treated with a pickling solution containing chromium (VI) and fluoride, followed by metallization. This chromium-sulfuric acid-based pickling solution can, for example, contain, a 1:1 weight ratio of chromium (VI) oxide and sulfuric acid.

[0006] Typical polyamide pickling solutions contain compounds containing chromium (VI). However, chromium (VI) compounds are suspected of being carcinogenic, therefore the handling of these compounds must strictly comply with environmental protection and occupational safety regulations. REACH is expected to ban the commercial use of chromium (VI) within the European Union.

[0007] Therefore, the object of the present invention is to provide a method for acid-washing polyamide components that overcomes at least some of the aforementioned disadvantages, particularly the absence of chromium compounds.

[0008] This task is accomplished by an acid-washing method for polyamide, the method comprising the following steps:

[0009] a) Contacting the polyamide with an acid pickling solution, the acid pickling solution comprising

[0010] -A mixture of at least two inorganic acids

[0011] -MHF2, where M is a base ion or an ammonium ion.

[0012] - Monocarboxylic acids having 1 to 5 carbon atoms

[0013] b) Contact with organic solvents having 1 to 10 carbon atoms, wherein

[0014] Steps a) and b) are performed sequentially or simultaneously.

[0015] The compositions of the present invention can acid-wash polyamides for subsequent metallization without chromium, especially chromium (VI).

[0016] The preferred pickling solution is one that is essentially free of chromium, especially with a chromium content of ≤1 mg / L.

[0017] In this method, the surface of the polyamide (e.g., a polyamide component) is roughened, creating tiny cavities. Strong inorganic acids can also break amide bonds.

[0018] In one embodiment of the invention, the pickling solution contains two inorganic acids, a fluoride source, and a monocarboxylic acid. After pickling, the pickling product is contacted with an organic solvent.

[0019] In another embodiment, contact with the acidic pickling solution and contact with the organic solvent occur simultaneously.

[0020] Suitable inorganic acids, especially typical inorganic acid salts, phosphoric acid, sulfuric acid, and nitric acid, with hydrochloric acid and phosphoric acid being preferred.

[0021] Sodium bifluoride, potassium bifluoride, and ammonium bifluoride are particularly suitable sources of fluoride.

[0022] Suitable monocarboxylic acids include formic acid, acetic acid, propionic acid, or mixtures thereof.

[0023] Suitable organic solvents having 1 to 10 carbon atoms include, for example, n-butanol, isobutanol, tert-butanol, isopropanol, n-propanol, and ethylene glycol ethers, such as 1-methoxy-2-propanol, 2-butoxyethane-1-ol, 2-(2-butoxyethoxy)ethanol, 2-(2-methoxyethoxy)ethanol, dipropylene glycol methyl ether, and mixtures thereof. The compound preferably has 3 to 8 carbon atoms. Preferably, the organic solvent is selected from alcohols and ethers.

[0024] A suitable concentration is, for example,

[0025] - An inorganic acid mixture with a concentration of 1 to 5 mol / L in the pickling solution.

[0026] -5 to 50 g / L MHF2

[0027] -50 to 300 g / L of monocarboxylic acids

[0028] -Optional organic solvents of 30 to 100 g / L.

[0029] Volume was measured at 23°C.

[0030] The mixture of two inorganic acids may contain each acid independently in the range of 0.5 to 3 mol / L, preferably with a total concentration of 1 to 4 or 2 to 4 mol / L.

[0031] Contact with polyamide should be carried out in a suitable manner at a temperature typically between 20 and 50°C. The suitable contact time is approximately 3 to 15 minutes.

[0032] When performing the method of the present invention, it is not always necessary to move the pickling solution or the product in the pickling solution. In some embodiments, the pickling solution or the product is stirred in the pickling solution.

[0033] It is recommended to perform at least one rinsing step after pickling before continuing.

[0034] In many cases, performing a two-rinse step is beneficial. A particularly suitable method is to perform a first hot rinse at a temperature above 25°C, followed by a cold rinse at room temperature. The appropriate temperature range for the hot rinse step is 30 to 40°C.

[0035] For both hot and cold rinse steps, the rinse solution may contain surfactants to improve surface wetting. Hot rinse steps may also include surfactants, while cold rinse steps may not. Typical exposure times during rinsing steps are 3 to 10 minutes.

[0036] One or more rinsing steps can also be performed as alkaline rinsing steps to neutralize the surface. During hot rinsing steps, the washing solution can be agitated by injecting air. Cold rinsing steps are generally performed without agitating the bath solution.

[0037] A typical further step is contact with a catalyst to deposit a metal nucleus on the pickled surface. Such methods are known to those skilled in the art and can also be used on the pickled surfaces described in this invention. Common metals used for this purpose are, for example, palladium, platinum, silver, or ruthenium. They are typically contacted with the pickled surface as colloids. Methods where the deposition of the metal nucleus is affected by both acids and alkalis are known.

[0038] The copper or nickel layer is then typically metallized by electroless plating, usually through reduction with a copper or nickel metal salt. Other electroless plating deposition methods are also known in principle, such as those for depositing cobalt, copper / nickel, nickel / cobalt, or gold layers. In some embodiments, an ammonium-free electroless nickel plating method is used.

[0039] Metallization can be performed without external current, followed by coating with another layer, which is also known to those skilled in other plastics fields.

[0040] Therefore, preferably, the method of the present invention includes the following steps:

[0041] - Pickling with the pickling solution of the present invention

[0042] - Separation of metal cores using catalysts

[0043] - Chemical plating to deposit the first metal layer, and

[0044] - If necessary, deposit additional metal layers.

[0045] Another object of the present invention is to provide an acid pickling solution containing...

[0046] -A mixture of at least two inorganic acids

[0047] -MHF2, where M is a base ion or an ammonium ion.

[0048] - Monocarboxylic acids having 1 to 5 carbon atoms.

[0049] Another object of the present invention is to use the pickling solution to pickle polyamides, especially PA6.

[0050] Figure 1 This is an SEM image of Embodiment 1 of the present invention.

[0051] Figure 2 These are SEM images of comparative examples.

[0052] This embodiment will explain the invention in more detail:

[0053] Example 1: Pickling

[0054] Components treated with an acid pickling solution containing the following components

[0055] -HCl 37%-ig: 150ml / L

[0056] -H3PO4 85% -ig: 100ml / L

[0057] 2-(2-Butoxyethoxy)ethanol: 50 ml / L

[0058] -Ammonium bifluoride: 35g / L

[0059] - Formic acid: 100ml / L

[0060] - The rest: water

[0061] Pickle at 40℃ for 5 minutes.

[0062] The acid-washed polyamide has a size of 3dm. 2 PA6M40 sample.

[0063] For comparison, the same polyamide was pickled with commercial chromium (VI) pickling solution (CrO3 380 g / l, H2SO4 380 g / l).

[0064] Two SEM images from the embodiments and comparative examples of the present invention are shown below. Figure 1 and Figure 2 As shown.

[0065] It can be seen that the surface structures have suffered varying degrees of damage. At this level, the differences in quality are practically impossible to assess.

[0066] Example 2: Rinsing and Activation

[0067] First, the surface was rinsed at 35°C with air agitation for 5 minutes, then cooled at room temperature for 2 minutes without agitation or the addition of a wetting agent, and activated at 40°C for 4 minutes with a catalyst containing 40 mg / L palladium. The amount of palladium deposited on the surface was then measured. The polyamide value etched in this invention is >0.3 mg / dm³. 2 The value of the comparison product was 0.3 mg / dm³. 2 A higher palladium loading is beneficial for the chemical deposition of additional layers.

[0068] Example 3: Chemical Plating Deposition

[0069] In the next step, the resulting product is coated using a nickel solution deposited without an external current.

[0070] Example 4: Analysis

[0071] In the pull-off test according to DIN 53494, the product of this invention achieves a pull-off strength of >15 N / cm, while the comparative product achieves a pull-off strength of 8 N / cm. Determining the pull-off force of the metal layer on galvanized plastic parts according to this standard allows for comparative evaluation of methods and investigation of the influence of method parameters on smooth, flat specimens. The peel force, as defined in this standard, is the force (N) required to peel a 25 mm wide strip of 40 μm thick copper layer perpendicular to the specimen surface.

[0072] Use a product obtained from ATO as another comparative product. Process it as follows:

[0073] -400ml / l PA expansion concentrate and 130ml / l PA conditioning agent, 40℃-5 minutes.

[0074] Rinse at 40°C for 8 minutes.

[0075] Then rinse with cold water for 2 x 4 minutes.

[0076] The remaining steps are the same. Here, only a nickel layer with a peel strength of 6.9 N / cm can be obtained.

[0077] Current results indicate that, despite the use of environmentally friendly chromium-free pickling solutions, adhesion levels superior to those of existing technologies were achieved.

[0078] Example 5: Changes in Solvent

[0079] The types of solvents vary as shown below.

[0080] Surface energy is measured by measuring the contact angle of a solid surface, according to DIN 55660-2.

[0081] Use Krüss Advance software.

[0082]

[0083] Subsequently, rinsing, activation, and subsequent deposition were performed as described above. After activation, the palladium loading was measured, and after deposition, adhesion was monitored over a period of time. Finally, an impact test (100°C for 1 hour, followed by quenching) was performed, repeated up to 3 times, and a visual evaluation was conducted.

[0084]

[0085] Impact testing revealed variations in coating stability; depending on the application, it can be adapted to the application without repeated testing.

[0086] Example 6: Correlation of Components

[0087] These experiments were conducted using 2-(2-butoxyethoxy)ethanol as a solvent.

[0088] Designation Surface free energy (mN / m) Dispersion mN / m Polarity mN / m Free of HCI 47,42 40,09 7,33 "free of H3PO4" 59,76 44,55 15,22 without CH2O2 55,32 40,09 15,24 Free of LM 55,56 44,23 11,33 without NH4HF2 66,63 45,74 20,89

[0089] Similar to Example 5, further analysis was performed:

[0090]

[0091] Example 7: Concentration Changes

[0092]

[0093]

Claims

1. A pickling method of a polyamide, the method comprising the steps of a) contacting a polyamide with a pickling solution, the pickling solution comprising A mixture of at least two inorganic acids MHF2, wherein M is an alkali metal ion or an ammonium ion Monocarboxylic acids having 1 to 5 carbon atoms wherein the pickling solution does not comprise a hexavalent chromium compound; and wherein the concentration in the pickling solution is 1 to 5 mol / l of a mixture of mineral acids 5 to 60 g / l of MHF2 50 to 300 g / L of monocarboxylic acids b) contacting with an organic solvent having 1 to 10 carbon atoms, wherein steps a) and b) are performed sequentially or simultaneously.

2. The method according to claim 1, wherein the inorganic acid is hydrochloric acid, phosphoric acid, sulfuric acid, nitric acid.

3. The method according to claim 1 or 2, wherein the organic solvent is selected from n-butanol, iso-butanol, tert-butanol, iso-propanol, n-propanol and glycol ethers, or mixtures thereof.

4. The method according to claim 1 or 2, wherein the MHF2 is NaHF2, KHF2, or mixtures thereof.

5. The method according to claim 1 or 2, wherein the monobasic carboxylic acid is formic acid, acetic acid, propionic acid, or mixtures thereof.

6. The method according to claim 1 or 2, wherein the pickling solution comprises the organic solvent in a concentration of 30 to 100 g / l.

7. The method according to claim 1 or 2, wherein the contacting is performed at 20 to 50 °C.

8. The method according to claim 1 or 2, wherein the contacting is performed for 3 to 15 minutes.

9. The method according to claim 1 or 2, wherein at least one rinsing step is performed after pickling.

10. The method according to claim 1 or 2, the method is followed by a step of contacting the pickled polyamide with a catalyst.

11. The method according to claim 10, the method is followed by a step of electroless nickel plating.

12. A pickling solution, the pickling solution comprising A mixture of at least two inorganic acids MHF2, wherein M is an alkali metal ion or an ammonium ion monocarboxylic acids having 1 to 5 C atoms; wherein the pickling solution does not comprise a hexavalent chromium compound; and wherein the concentration in the pickling solution is 1 to 5 mol / l of a mixture of mineral acids 5 to 60 g / l of MHF2 50 to 300 g / l of monocarboxylic acid.

13. The pickling solution according to claim 12, further comprising an organic solvent having 1 to 5 C atoms.

14. The pickling solution according to claim 13, wherein the pickling solution comprises the organic solvent in a concentration of 30 to 100 g / l.

15. The pickling solution according to claim 12 or 13, wherein the inorganic acid is selected from the group consisting of hydrochloric acid, phosphoric acid, sulfuric acid and nitric acid.

16. The pickling solution according to claim 12 or 13, wherein the inorganic acid comprises hydrochloric acid and phosphoric acid.

17. Use of the pickling solution according to any one of claims 12 to 16 for pickling a polyamide.

Images