U.S. patent application number 14/831266 was filed with the patent office on 2017-02-23 for solutions of organic salts as pretreatments for plastic prior to etching.
The applicant listed for this patent is MacDermid Acumen, Inc.. Invention is credited to Roderick D. Herdman, Trevor Pearson, Craig Robinson.
Application Number | 20170051410 14/831266 |
Document ID | / |
Family ID | 58051689 |
Filed Date | 2017-02-23 |
United States Patent
Application |
20170051410 |
Kind Code |
A1 |
Pearson; Trevor ; et
al. |
February 23, 2017 |
Solutions of Organic Salts as Pretreatments for Plastic Prior to
Etching
Abstract
A method of preparing a plastic substrate to accept metal
plating thereon is described. The method includes the steps of
pretreating the plastic substrate by contacting the plastic
substrate with an aqueous electrolyte comprising an organic salt to
raise the surface energy of the plastic substrate. Thereafter, the
plastic substrate can be etched and metal plated.
Inventors: |
Pearson; Trevor; (West
Midlands, GB) ; Robinson; Craig; (West Midlands,
GB) ; Herdman; Roderick D.; (Staffordshire,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MacDermid Acumen, Inc. |
Waterbury |
CT |
US |
|
|
Family ID: |
58051689 |
Appl. No.: |
14/831266 |
Filed: |
August 20, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 18/24 20130101;
C23C 18/2086 20130101; C23C 18/22 20130101 |
International
Class: |
C23C 18/20 20060101
C23C018/20; C23C 18/24 20060101 C23C018/24 |
Claims
1. A method of treating a plastic substrate to accept metal plating
thereon, the method comprising the steps of: a) pretreating the
plastic substrate by contacting the plastic substrate with an
aqueous electrolyte comprising an organic salt; and thereafter b)
etching the treated plastic substrate with an etchant.
2. The method according to claim 1, wherein the etchant is a chrome
based etchant.
3. The method according to claim 1, wherein the etchant is
chrome-free.
4. The method according to claim 1, wherein the organic salt
comprises an ionic liquid and combinations thereof.
5. The method according to claim 4, wherein the ionic liquid
comprises an imidazolium compound having the formula: ##STR00002##
wherein R1 and R3 are each, independently of one another, an
organic radical having from 1 to 20 carbon atoms, R2, R4 and R5 are
each, independently of one another, an H atom or an organic radical
having from 1 to 20 carbon atoms, X is an anion and n is 1, 2 or
3.
6. The method according to claim 5, wherein the imidazolium
compound is selected from the group consisting of
1,3-dimethylimidazolium methylsulfate, 1,3-dimethylimidazolium
hydrogensulfate, 1,3-dimethylimidazolium dimethylphosphate,
1,3-dimethylimidazolium acetate, 1-ethyl-3-methylimidazolium
methylsulfate, 1-ethyl-3-methylimidazolium hydrogensulfate,
1-ethyl-3-methylimidazolium thiocyanate,
1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium
methanesulfonate, 1-ethyl-3-methylimidazolium diethylphosphate,
1-(1-butyl)-3-methylimidazolium methylsulfate,
1-(1-butyl)-3-methylimidazolium hydrogensulfate,
1-(1-butyl)-3-methylimidazolium thiocyanate,
1-(1-butyl)-3-methylimidazolium acetate,
1-(1-butyl)-3-methylimidazolium methanesulfonate, 1-(1-do
decyl)-3-methylimidazolium methylsulfate,
1-(1-dodecyl)-3-methylimidazolium hydrogensulfate,
1-(1-tetradecyl)-3-methylimidazolium methylsulfate,
1-(1-tetradecyl)-3-methylimidazolium hydrogensulfate,
1-(1-hexadecyl)-3-methylimidazolium methylsulfate or
1-(1-hexadecyl)-3-methylimidazolium hydrogensulfate, and
combinations of one or more of the foregoing.
7. The method according to claim 4, wherein the ionic liquid
comprises 2-hydroxyethylammonium formate or methyltributylammonium
methylsulfate.
8. The method according to claim 6 or 7, wherein the ionic liquid
comprises at least one of 1-ethyl-2-methylimidazolium acetate and
methyltributylammonium methylsulfate.
9. The method according to claim 1, wherein the aqueous electrolyte
comprises less than 50% by weight of the organic salt.
10. The method according to claim 9, wherein the aqueous
electrolyte comprises less than 30% by weight of the organic
salt.
11. The method according to claim 10, wherein the aqueous
electrolyte comprises less than about 20% by weight of the organic
salt.
12. The method according to claim 1, further comprising the step of
degreasing and cleaning the plastic substrate prior to step a).
13. The method according to claim 1, wherein the plastic substrate
comprises an acrylonitrile-butadiene-styrene copolymer of
acrylonitrile-butadiene-styrene-polycarbonate.
14. The method according to claim 1, wherein the plastic substrate
is contacted with the aqueous electrolyte by spraying or by
immersion.
15. The method according to claim 1, wherein the aqueous
electrolyte is maintained at a temperature of between 0.degree. C.
and about 120.degree. C.
16. The method according to claim 1, wherein the plastic substrate
is contacted with the aqueous electrolyte for a period of time
sufficient to raise the surface energy of the plastic
substrate.
17. The method according to claim 16, wherein the plastic substrate
is contacted with the aqueous electrolyte for between about 30
seconds and about 10 minutes.
18. The method according to claim 1, wherein more than 4 molecules
of water per ion of organic salt are available for solvation.
19. The method according to claim 18, wherein more than 9 molecules
of water per ion of organic salt are available for solvation.
20. The method according to claim 19, wherein more than 10
molecules of water per ion of organic salt are available for
solvation.
21. The method according to claim 1, further comprising the step of
rinsing the substrate after step a) and before step b).
22. The method according to claim 21, wherein the rinsing step is
carried out for between about 30 seconds and about 5 minutes.
23. The method according to claim 22, wherein the rinsing step is
carried out for about 1 minute to about 3 minutes.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to an improved
method of pretreating a non-conductive substrate in a plastic
metallization process.
BACKGROUND OF THE INVENTION
[0002] It is well known to plate non-conductive substrates, (i.e.
plastics) with metal for a variety of purposes, including for
decoration and for the fabrication of electronic devices. An
example of a decorative use is for automobile parts such as trim.
Examples of electronic uses include printed circuits, wherein metal
plated in a selective pattern comprises the conductors of the
printed circuit board, and metal plated plastics used for EMI
shielding. ABS resins are among the most commonly plated plastics
for decorative purposes while phenolic and epoxy resins are among
the most commonly plated plastics for the fabrication of printed
circuit boards.
[0003] There are typically many stages involved in the plating of
plastics. A typical processing sequence for preparing plastics for
subsequent plating thereon includes the following steps:
[0004] (1) etching the substrate with a chromic acid etching
solution;
[0005] (2) neutralizing the etched surface with a chrome
neutralizing solution;
[0006] (3) activating the etched surface using a colloidal
palladium tin activator;
[0007] (4) removing tin with an accelerating step; and
[0008] (5) depositing a layer of electroless copper or electroless
nickel followed by electrolytic copper and/or nickel plating.
[0009] For the durability of metal layers deposited on the plastic
substrate surfaces, it is important that the metal layers exhibit
sufficient adhesion to the surface. In order to achieve this
adhesion, the plastic surface is typically treated by roughening or
etching to provide a suitable surface to accept metal plating
thereon. Etching the plastic provides mechanical adhesion of the
subsequent metallic coatings and provides a suitable surface for
the adsorption of the palladium colloid catalyst which is typically
applied in order to catalyze deposition of the initial metallic
layer from an autocatalytic nickel or copper plating process.
[0010] The initial etching of the plastic surfaces is a critical
element of the overall process. However, only certain types of
plastic components are suitable for plating. One of the most common
types of plastic for electroplating is
acrylonitrile/butadiene/styrene (ABS) or a blend of this material
with polycarbonate (ABS/PC). ABS consists of two phases--a
relatively hard phase consisting of an acrylonitrile/styrene
copolymer and a softer polybutadiene phase.
[0011] Currently, this material is etched almost exclusively using
a mixture of chromic and sulfuric acids, which is highly effective
as an etchant for both ABS and ABS/PC. The polybutadiene phase of
the plastic contains double bonds in the polymer backbone, which
are oxidized by the chromic acid, thus causing complete breakdown
and dissolution of the polybutadiene phase exposed at the surface
of the plastic which gives an effective etch to the surface of the
plastic.
[0012] However, a significant problem with the traditional chromic
acid etching step is that chromic acid is a recognized carcinogen
and is increasingly regulated, requiring that wherever possible,
the use of chromic acid be replaced with safer alternatives. The
use of a chromic acid etchant also has well-known and serious
drawbacks, including the toxicity of chromium compounds which makes
their disposal difficult, chromic acid residues remaining on the
polymer surface that inhibit electroless deposition, and the
difficulty of rinsing chromic acid residues from the polymer
surface following treatment. Additionally, hot hexavalent chromic
acid solutions are naturally hazardous to workers. Burns and upper
respiratory bleeding are common in workers routinely involved with
these chrome etch solutions.
[0013] Early attempts to replace the use of chromic acid to etch
plastic typically focused on the use of permanganate ions as an
alternative to chromic acid. The use of permanganate was described
by U.S. Pat. No. 4,610,895 to Tubergen et al., the subject matter
of which is herein incorporated by reference in its entirety.
Later, the use of permanganate was described in combination with an
ionic palladium activation stage as set forth in U.S. Pat. Pub. No.
2005/0199587 to Bengston, the subject matter of which is herein
incorporated by reference in its entirety. The use of permanganate
solutions in combination with perhalo ions (such as perchlorate or
periodate) was described, for example in U.S. Pat. Pub. No.
2009/0092757 to Satou, the subject matter of which is herein
incorporated by reference in its entirety. Finally, International
Publication No. WO2009/023628 to Schildman et al., the subject
matter of which is herein incorporated by reference in its
entirety, described the use of permanganate ions in the absence of
alkali metal or alkaline earth metal cations.
[0014] However, all of these attempts to etch plastic using
permanganate ions were not capable of producing etch
characteristics which match those obtained by the use of chromic
acid and the stability of these etch solutions was also poor,
resulting in the formation of manganese dioxide sludge.
[0015] As a result, none of these processes proved satisfactory for
various economic, performance and/or environmental reasons and none
of these processes have achieved commercial success or been
accepted by the industry as suitable replacements for chromic acid
etching.
[0016] U.S. Pat. Pub. No. 2013/0186774 to Pearson et al., the
subject matter of which is herein incorporated by reference in its
entirety, describes the use of trivalent manganese in combination
with strong sulfuric acid to etch plastics, such as ABS and ABS/PC
plastics. As described therein, trivalent manganese can readily be
produced by electrolysis at low current density of divalent
manganese ions in a strong acid solution, and a solution of
trivalent manganese ions in a strongly acidic solution is capable
of etching ABS and is a suitable replacement for chromic acid
etching solutions. In addition, related U.S. Pat. Pub. No.
2013/0186862 to Pearson et al., the subject matter of which is
herein incorporated by reference in its entirety, describes that
that it is possible to increase the amount of manganese that can be
dissolved in the bath by replacing a portion of the sulfuric acid
with another acid, such as methane sulfonic acid in which the
manganese ions may be more soluble. The additional acid must have
both the necessary stability against oxidation and the ability to
increase the solubility of manganese ions. Finally, related U.S.
Pat. Pub. No. 2013/0186861 to Pearson et al., the subject matter of
which is herein incorporated by reference in its entirety,
describes the use of vitreous carbon and lead as electrodes in the
system for producing a manganese(III)-based etchant.
[0017] One of the differences between the use of these
manganese(III)-based etching solutions as compared with the chromic
acid etching solutions of the prior art is that it was found that
it is necessary in most situations to pre-treat the plastic prior
to etching to raise its surface energy. Thus, most processes
require the use of a pretreating solvent to raise the surface
energy of the surface to a sufficient degree to provide good
adhesion of the subsequently applied metal plating layer
thereto.
[0018] Various solvents have been investigated for modifying the
surface of the plastic substrate and raise its surface energy,
including, for example, butyrolactone and diglyme. However,
butyrolactone is a controlled substance due to its tendency to
hydrolyze to gamma hydroxybutyric acid which is a controlled drug,
and diglyme is also heavily regulated due to its mutagenic and
hepatotoxic properties. Another issue with the use of these
materials is that they are only marginally effective on some
moldings and grades of ABS. Based thereon, additional research is
needed to provide new pretreatment compositions that are capable of
providing a good result and that are less toxic than the solvents
previously used.
[0019] Thus, there remains a need in the art for an improved method
of preparing a plastic substrate to accept metal plating thereon
that overcomes the deficiencies of the prior art.
SUMMARY OF THE INVENTION
[0020] It is an object of the present invention to improve adhesion
of a metal layer plated on a plastic substrate.
[0021] It is another object of the present invention to improve the
adhesion of a metal layer plated on an ABS or ABS/PC substrate.
[0022] It is another object of the present invention to provide an
improved method of preparing a plastic substrate to accept metal
plating thereon.
[0023] It is still another object of the present invention to
provide an improved method of pre-treating a plastic substrate that
is compatible with chrome and chrome-free etchants.
[0024] To that end, in one embodiment, the present invention
relates generally to a method of treating a plastic substrate to
accept metal plating thereon, the method comprising the steps
of:
[0025] a) pretreating the plastic substrate by contacting the
plastic substrate with an aqueous electrolyte comprising an organic
salt; and thereafter
[0026] b) etching the treated plastic substrate with an
etchant.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The present invention relates generally to a method of
treating a plastic substrate to accept metal plating thereon, the
method comprising the steps of:
[0028] a) pretreating the plastic substrate by contacting the
plastic substrate with an aqueous electrolyte comprising an organic
salt; and thereafter
[0029] b) etching the treated plastic substrate with an
etchant.
[0030] The inventors of the present invention have discovered that
if ionic liquids, comprising an organic salt having a melting point
of less than 100.degree. C. at 100 bar, are diluted in a suitable
solvent, the ionic liquid dissociates into an aqueous solution of
the corresponding organic salt in solution. This aqueous
electrolyte based on the ionic liquid is compatible with parts
which are subsequently to be processed with a chrome or chrome-free
etchant and is capable of raising the surface energy of the
underlying plastic substrate so as to allow for the plastic
substrate to be adequately treated with a chrome or chrome-free
etchant. Chrome-free etchant means that no chrome containing
compounds are intentionally added to the etch solution and chrome
concentration due to contaminants in the etch solution is less than
1 ppm.
[0031] By definition, ionic liquids are salts that melt at low
temperatures (typically less than about 100.degree. C.) and which
are made up exclusively of ions. In other words, an ionic liquid is
a liquid salt that consists of ions and ion pairs.
[0032] Ionic liquids are typically composed of heterocyclic organic
cations and various anions and have unique properties including
non-volatility, non-flammability, and a wide temperature range for
the liquid phase. The molecular weight of most ionic liquids is
typically less than about 2000 g/mol, and may be less than about
1500 g/mol, or even less than about 750 g/mol.
[0033] In one embodiment, the compositions of the present invention
may be based on imidazolium compounds. Particularly preferably
imidazolium compounds include imidazolium compounds of the
formula:
##STR00001##
[0034] wherein R1 and R3 are each, independently of one another, an
organic radical having from 1 to 20 carbon atoms, R2, R4 and R5 are
each, independently of one another, an H atom or an organic radical
having from 1 to 20 carbon atoms, X is an anion and n is 1, 2 or
3.
[0035] Examples of imidazolium compounds include, for example,
1,3-dimethylimidazolium methylsulfate, 1,3-dimethylimidazolium
hydrogensulfate, 1,3-dimethylimidazolium dimethylphosphate,
1,3-dimethylimidazolium acetate, 1-ethyl-3-methylimidazolium
methylsulfate, 1-ethyl-3-methylimidazolium hydrogensulfate,
1-ethyl-3-methylimidazolium thiocyanate,
1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium
methanesulfonate, 1-ethyl-3-methylimidazolium diethylphosphate,
1-(1-butyl)-3-methylimidazolium methylsulfate,
1-(1-butyl)-3-methylimidazolium hydrogensulfate,
1-(1-butyl)-3-methylimidazolium thiocyanate,
1-(1-butyl)-3-methylimidazolium acetate,
1-(1-butyl)-3-methylimidazolium methanesulfonate,
1-(1-dodecyl)-3-methylimidazolium methylsul fate,
1-(1-dodecyl)-3-methylimidazolium hydrogensulfate,
1-(1-tetradecyl)-3-methylimidazolium methylsulfate,
1-(1-tetradecyl)-3-methylimidazolium hydrogensulfate,
1-(1-hexadecyl)-3-methylimidazolium methylsulfate or
1-(1-hexadecyl)-3-methylimidazolium hydrogensulfate, and
combinations of one or more of the foregoing.
[0036] In another embodiment, the aqueous electrolyte may contain
ionic liquids such as 2-hydroxyethylammonium formate or
methyltributylammonium methylsulfate (MTBS) alone or in combination
with imidazolium compounds.
[0037] Particularly preferred examples, include, but are not
limited to 1-ethyl-2-methylimidazolium acetate and
methyltributylammonium methylsulfate (MTBS).
[0038] In the process described herein, the ionic liquid or similar
organic salt is diluted with water or any non-ionic solvent that is
able to decompose the ionic liquid and produce an aqueous
electrolyte comprising an organic salt without having deleterious
effects on the substrate. Thus, the present invention is not
directed to an ionic liquid for pre treating the plastic substrate
but is instead directed to the use of an aqueous electrolyte that
contains an organic salt. As used herein an organic salt is the
ions that result from mixing an ionic liquid with a solvent such as
water.
[0039] The composition of the present invention may further
comprise additional solvents, pH adjusters, buffers, thickeners,
co-solvents such as glycerol, propylene carbonate, isopropanol and
glycol ethers, and surface active agents for modifying the surface
tension of the solution, by way of example and not limitation.
[0040] As described herein, the aqueous electrolyte solutions of
the present invention are prepared by diluting an ionic liquid or
other suitable organic salt with a solvent that is capable of
decomposing the organic salt. In a preferred embodiment, the
composition comprises less than 50% by weight of the organic salt,
more preferably less than 30% by weight of the organic salt diluted
with water, and most preferably less than about 20% by weight of
the organic salt. In one embodiment, the composition described
herein includes about 10 to about 20% by weight of the organic salt
in an aqueous solution of water and/or another suitable
solvent.
[0041] Prior to contacting the plastic substrate with the aqueous
electrolyte composition described herein, the substrate may be
cleaned and degreased.
[0042] Thereafter, the cleaned and degreased plastic substrate is
contacted with the aqueous electrolyte of the invention. The
contacting time of the plastic substrate with the aqueous
electrolyte as well as the contacting temperature (i.e. the
temperature at which the aqueous electrolyte is maintained) will
vary depending on the substrate being treated and the composition
of the aqueous electrolyte.
[0043] In a preferred embodiment, the plastic substrate is
contacted with the aqueous electrolyte at a temperature of between
0.degree. C. and about 120.degree. C., more preferably at a
temperature of between about 40.degree. C. to about 100.degree. C.
The aqueous electrolyte can be contacted with the plastic substrate
by various means including immersion or spraying. In a preferred
embodiment, the plastic substrate is contacted with the aqueous
electrolyte by immersing the plastic substrate in the aqueous
electrolyte.
[0044] The plastic substrate is contacted with the aqueous
electrolyte for a period of time sufficient to raise the surface
energy of the plastic substrate. Thus the contacting time may be
between about 30 seconds and about 10 minutes, more preferably
between about 1 minute and about 5 minutes. The surface energy of
ABS test panels was found to be 30-32 dynes/cm without the use of
the current invention prior to etching and when treated for 5
minutes at 50.degree. C. using an aqueous electrolyte of the
current invention on ABS test panels prior to etching, the surface
energy was increased to 32-36 dynes/cm.
[0045] After being contacted with the aqueous electrolyte, the
plastic substrate is optionally but preferably rinsed to remove any
aqueous electrolyte remaining on the surface. The rinsing step is
preferably carried out using a water rinse. The rinsing step may
preferably be carried out for between about 30 seconds and about 5
minutes, more preferably for between about 1 minute to about 3
minutes and may be accomplished by spraying or immersion.
[0046] Once the plastic substrate has been contacted with the
aqueous electrolyte described herein under suitable conditions to
raise the surface energy of the plastic substrate and then rinsed,
it may then be contacted with an etchant as described for example
in U.S. Pat. Pub. No. 2013/0186774 to Pearson et al., the subject
matter of which is herein incorporated by reference in its
entirety.
[0047] Examples of the current invention as compared to prior art
examples are shown below. All chemistry used to carry out these
experiments is available from MacDermid Inc.
Comparative Example 1
Chrome Etch
[0048] Alkaline cleaner (2 minutes, 60 C)
Rinse
[0049] Chrome etch (9 minutes, 68 C)
Rinse
[0050] Chrome Neutraliser (Macuplex 9338, 2 minutes, 50 C)
Rinse
[0051] Acid Dip (Hydrochloric acid, 2 minutes at room temperature)
Activator (Mactivate 360, 3 minutes, 30 C)
Rinse
[0052] Accelerator (Ultacel 9369, 2 minutes, 50 C)
Rinse
[0053] Electroless nickel (Macuplex J64, 7 minutes, 30 C)
Rinse
[0054] Acid Copper plate (Cumac Optima, 90 minutes, 3.5 A/dm2)
Rinse and dry
[0055] Peel strength tested according to ASTM B533 using an Instron
Peel Test instrument.=9.8 N/cm
Example 1
Pretreatment Using the Current Invention Prior to Chrome Etch
[0056] Alkaline cleaner (2 minutes, 60 C)
Rinse
Pretreatment (200 g/1 MTBS, 5 Minutes, 50 C)
Rinse
[0057] Chrome etch (9 minutes, 68 C)
Rinse
[0058] Chrome Neutraliser (Macuplex 9338, 2 minutes, 50 C)
Rinse
[0059] Acid Dip (Hydrochloric acid, 2 minutes at room temperature)
Activator (Mactivate 360, 3 minutes, 30 C)
Rinse
[0060] Accelerator (Ultacel 9369, 2 minutes, 50 C)
Rinse
[0061] Electroless nickel (Macuplex J64, 7 minutes, 30 C)
Rinse
[0062] Acid Copper plate (Cumac Optima, 90 minutes, 3.5 A/dm2)
Rinse and dry
[0063] Peel strength tested according to ASTM B533 using an Instron
Peel Test instrument.=14.6 N/cm
Comparative Example 2
Chrome-Free Etch
[0064] Alkaline cleaner (2 minutes, 60 C)
Rinse
Pre-Treatment (10% v/v Propylene Carbonate, 5% v/v
Gammabutyrolactone in Water, 2 Minutes at 35 C)
Rinse
[0065] Manganese(III) etch solution (15 minutes, 68 C)
Rinse
[0066] Chrome Neutraliser (Macuplex 9338, 2 minutes, 50 C)
Rinse
[0067] Acid Dip (Hydrochloric acid, 2 minutes at room temperature)
Activator (Mactivate 360, 3 minutes, 30 C)
Rinse
[0068] Accelerator (Ultacel 9369, 2 minutes, 50 C)
Rinse
[0069] Electroless nickel (Macuplex J64, 7 minutes, 30 C)
Rinse
[0070] Acid Copper plate (Cumac Optima, 90 minutes, 3.5 A/dm2)
Rinse and dry
[0071] Peel strength tested according to ASTM B533 using an Instron
Peel Test instrument.=1.9 N/cm
Example 2
Pretreatment Using the Current Invention Prior to Chrome-Free
Etch
[0072] Alkaline cleaner (2 minutes, 60 C)
Rinse
Pretreatment (500 g/l MTBS, 5 Minutes, 50 C)
Rinse
[0073] Manganese(III) etch solution 15 minutes at 68 C
Rinse
[0074] Chrome Neutraliser (Macuplex 9338, 2 minutes, 50 C)
Rinse
[0075] Acid Dip (Hydrochloric acid 2 minutes at room temperature)
Activator (Mactivate 360, 3 minutes at 30 C)
Rinse
[0076] Accelerator (Ultacel 9369, 2 minutes, 50 C)
Rinse
[0077] Electroless nickel (Macuplex J64, 7 minutes, 30 C)
Rinse
[0078] Acid Copper plate (Cumac Optima, 90 minutes, 3.5 A/dm2)
Rinse and dry
[0079] Peel strength tested according to ASTM B533 using an Instron
Peel Test instrument.=6.0 N/cm
Example 3
Pretreatment Using the Current Invention with Chrome-Free Etch
[0080] Alkaline cleaner (2 minutes, 60 C)
Rinse
Pretreatment (200 g/1 MTBS, 5 Minutes, 50 C)
Rinse
[0081] Manganese(III) etch solution 15 minutes at 68 C
Rinse
[0082] Chrome Neutraliser (Macuplex 9338, 2 minutes, 50 C)
Rinse
[0083] Acid Dip (Hydrochloric acid 2 minutes at room temperature)
Activator (Mactivate 360, 3 minutes at 30 C)
Rinse
[0084] Accelerator (Ultacel 9369, 2 minutes, 50 C)
Rinse
[0085] Electroless nickel (Macuplex J64, 7 minutes, 30 C)
Rinse
[0086] Acid Copper plate (Cumac Optima, 90 minutes, 3.5 A/dm2)
Rinse and dry
[0087] Peel strength tested according to ASTM B533 using an Instron
Peel Test instrument.=7.3 N/cm
[0088] This set of experiments was carried out using increasingly
dilute ionic liquid. Surprisingly, it was found that even at a
dilution of 20% of the ionic liquid in water, excellent adhesion
was obtained following etching in both chrome and chrome-free
etchant solutions. In each case an ABS substrate was immersed in an
aqueous solution containing the ions of an organic salt for 5
minutes at 50.degree. C. The substrates were then briefly rinsed
and then etched in an etchant. The substrates were then
electrolessly plated with copper, in each case, the adhesion of the
metal plates was excellent.
[0089] The act of diluting the ionic liquid converted the ionic
liquid into an aqueous electrolyte solution of an organic salt in
water, so it is no longer an ionic liquid. The transition between
an ionic liquid and a solution of an organic salt in water depends
on the solvation number for the ions in solution. The generally
accepted definition of an ionic liquid is simply an ionic salt
consisting only of ions above its melting point. In this state, the
ions which were held in the crystal lattice become mobile.
[0090] If we take sodium chloride as an example, it becomes an
ionic liquid above its melting point of 801.degree. C. At room
temperature, a 5.35M solution in water is readily obtained.
However, this would never be described as an ionic liquid. At this
concentration, the solution contains 260 g/kg of sodium chloride so
1 kg of this solution would contain 740 g/kg of water or 41.1 moles
of water and 4.44 moles of sodium chloride (8.88 moles of ions). It
can be inferred from that in this case, every ion will have 9
molecules of water available for solvation. Of course, in the case
of an organic ionic liquid, the solvation number will be different,
but is likely to be lower than 9 because larger ions are less
polarizing than smaller ones.
[0091] If we consider methylttibutylammonium methylsulfate (MTBS)
which has a molecular mass of 317, it is simple to calculate the
amount of molecules of water available per ion versus
concentration. At a concentration of about 50% MTBS, there were
will be more than 10 molecules of water available per ion of MTBS.
This would certainly be considered to be an electrolyte solution,
and not an ionic liquid. Above this concentration, the
interpretation is somewhat less clear-cut, but almost certainly any
concentration of MTBS below 70% (4 molecules of water per ion)
would be considered to be an aqueous electrolyte solution rather
than an ionic liquid.
[0092] As described herein, it has been unexpectedly found that
ionic liquids that are sufficiently diluted to produce an aqueous
electrolyte containing an organic salt can be beneficially used to
pretreat an ABS or ABS/PC plastic substrate prior to etching the
plastic substrate with a chrome or chrome-free etchant. It is
unexpected that these dilute solutions would have this desirable
effect in raising the surface energy of the plastic substrate. In
addition, it was surprisingly found the aqueous electrolyte can
contain a concentration of the organic salt of less than about 20%.
Additionally, it was found that at concentrations of less than
about 60%, the aqueous electrolyte solution is very easy to rinse
from the plastic surface and thus short rinse times can be
utilized.
[0093] Once the plastic substrate has been contacted with the
pretreating composition, it is then contacted with an etch solution
as described in related Pat. Pub. No. 2013/0186774 to Pearson et
al., the subject matter of which is herein incorporated by
reference in its entirety. By using the process described herein,
very high adhesion values can be obtained between the underlying
plastic substrate and the metal layer that is plated thereon.
[0094] Thereafter, additional steps may be undertaken to obtain a
sufficiently adherent metalized plastic substrate.
[0095] It should also be understood that the following claims are
intended to cover all of the generic and specific features of the
invention described herein and all statements of the scope of the
invention that as a matter of language might fall therebetween.
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