U.S. patent application number 14/184011 was filed with the patent office on 2015-08-20 for treatment for electroplating racks to avoid rack metallization.
This patent application is currently assigned to MacDermid Acumen, Inc.. The applicant listed for this patent is MacDermid Acumen, Inc.. Invention is credited to Roshan V. Chapaneri, Roderick D. Herdman, Alison Hyslop.
Application Number | 20150233011 14/184011 |
Document ID | / |
Family ID | 53797590 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150233011 |
Kind Code |
A1 |
Herdman; Roderick D. ; et
al. |
August 20, 2015 |
Treatment for Electroplating Racks to Avoid Rack Metallization
Abstract
An electroplating rack for supporting non-conductive substrates
during an electrodeposition process is described. The
electroplating rack is coated with a non-conductive material, such
as a PVC plastisol. The electroplating rack is treated with a
non-aqueous solution comprising a metallization inhibitor prior to
the electrodeposition process to inhibit rack plate up when using
etchants that do not contain chromic acid.
Inventors: |
Herdman; Roderick D.;
(Staffordshire, GB) ; Chapaneri; Roshan V.;
(Coventry, GB) ; Hyslop; Alison; (Birmingham,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MacDermid Acumen, Inc. |
Waterbury |
CT |
US |
|
|
Assignee: |
MacDermid Acumen, Inc.
Waterbury
CT
|
Family ID: |
53797590 |
Appl. No.: |
14/184011 |
Filed: |
February 19, 2014 |
Current U.S.
Class: |
205/183 ;
204/297.06; 427/430.1 |
Current CPC
Class: |
C23C 18/163 20130101;
C25D 17/08 20130101 |
International
Class: |
C25D 17/08 20060101
C25D017/08; C23C 28/00 20060101 C23C028/00 |
Claims
1. An electroplating rack for supporting non-conductive substrates
during a plating process, wherein the electroplating rack is at
least partially coated with a non-conductive material; and wherein
the electroplating rack is treated with a non-aqueous solution
comprising a metallization inhibitor.
2. The electroplating rack according to claim 1, wherein the
electroplating rack is at least partially coated with a PVC
plastisol.
3. The electroplating rack according to claim 1, wherein the
metallization inhibitor is at least substantially insoluble in
aqueous media.
4. The electroplating rack according to claim 3, wherein the
metallization inhibitor is an organic compound comprising sulfur in
a -2 valency.
5. The electroplating rack according to claim 3, wherein the
metallization inhibitor comprises a transition metal salt of a
di-substituted dithiocarbamate or a tetra-substituted thiuram
sulfide.
6. The electroplating rack according to claim 5, wherein the
metallization inhibitor is selected from the group consisting of
zinc dimethyl-dithiocarbamate, zinc diethyldithiocarbamate, zinc
dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, zinc
dibenzyldithiocarbamate, zinc pentamethylenedithiocarbamate,
tellurium diethyldithiocarbamate, nickel dibutyl dithiocarbamate,
nickel dimethyldithiocarbamate, zinc diisononyldithiocarbamate,
tetrabenzylthiuram disulfide, mercaptobenzothiazole, mercaptothiazo
line, mercaptobenzimidazole, mercaptoimidazole,
mercaptobenzoxazole, mercaptothiazole, mercaptotriazole,
dithiocyanuric acid, trithiocyanuric acid, and combinations of one
or more of the foregoing.
7. The electroplating rack according to claim 6, wherein the
metallization inhibitor comprises nickel dibutyl dithiocarbamate or
tetrabenzylthiuram disulfide.
8. The electroplating rack according to claim 1, wherein the
non-aqueous solution comprises a non-aqueous solvent, wherein the
non-aqueous solvent is non-volatile and is capable of dissolving an
effective amount of the metallization inhibitor.
9. The electroplating rack according to claim 8, wherein the
non-aqueous solvent is selected from the group consisting of
butylene carbonate, propylene carbonate, ethylene carbonate,
dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate,
propyl lactate, gammabutyrolactone, ethyl 3 -ethoxypropionate and
diethyleneglycol monomethyl ether acetate, ethyleneglycol
monomethyl ether acetate, ethyleneglycol monoethyl ether acetate,
diethyleneglycol monoethyl ether acetate, diethyleneglycol
mono-n-butyl ether acetate, propyleneglycol monomethyl ether
acetate, propyleneglycol monoethyl ether acetate, is
propyleneglycol monopropyl ether acetate, propyleneglycol monobutyl
ether acetate, dipropyleneglycol monomethyl ether acetate,
dipropyleneglycol monoethyl ether acetate, glycol diacetate, and
combinations of one or more of the foregoing.
10. The electroplating rack according to claim 9, wherein the
non-aqueous solvent comprises ethyl 3-ethoxypropionate, n-propyl
lactate, gamma-butyrolactone, or combinations of one or more of the
foregoing.
11. A method of treating an electroplating rack used for supporting
non-conductive substrates during a plating process, wherein the
electroplating rack is at least partially coated with with PVC
plastisol, the method comprising: a) contacting the electroplating
rack with a non-aqueous solution comprising a metallization
inhibitor; b) mounting non-conductive substrates to the
electroplating rack that has been contacted with the non-aqueous
solution comprising a metallizaton inhibitor; and c) etching the
non-conductive substrates supported on the electroplating rack with
an etchant that does not contain chromic acid.
12. (canceled)
13. The method according to claim 11, wherein the electroplating
rack is contacted with the non-aqueous solution by immersing the
electroplating rack in the non-aqueous solution.
14. The method according to claim 11, wherein the metallization
inhibitor is at least substantially insoluble in aqueous media.
15. The method according to claim 14, wherein the metallization
inhibitor is an organic compound comprising sulfur in a -2
valency.
16. The method according to claim 14, wherein the metallization
inhibitor comprises a transition metal salt of a di-substituted
dithiocarbamate or a tetra-substituted thiuram sulfide.
17. The method according to claim 16, wherein the metallization
inhibitor is selected from the group consisting of zinc
dimethyl-dithiocarbamate, zinc diethyldithiocarbamate, zinc
dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, zinc
dibenzyldithiocarbamate, zinc pentamethylenedithiocarbamate,
tellurium diethyldithiocarbamate, nickel dibutyl dithiocarbamate,
nickel dimethyldithiocarbamate, zinc diisononyldithiocarbamate,
tetrabenzylthiuram disulfide, mercaptobenzothiazole,
mercaptothiazoline, mercaptobenzimidazole, mercaptoimidazole,
mercaptobenzoxazole, mercaptothiazole, mercaptotriazole,
dithiocyanuric acid, trithiocyanuric acid, and combinations of one
or more of the foregoing.
18. The method according to claim 17, wherein the metallization
inhibitor comprises nickel dibutyl dithiocarbamate or
tetrabenzylthiuram disulfide.
19. The method according to claim 11, wherein the non-aqueous
solution comprises a non-aqueous solvent, wherein the non-aqueous
solvent is non-volatile and is capable of dissolving an effective
amount of the metallization inhibitor.
20. The method according to claim 19, wherein the non-aqueous
solvent is selected from the group consisting of butylene
carbonate, propylene carbonate, ethylene carbonate, dimethyl
carbonate, diethyl carbonate, ethylmethyl carbonate, propyl
lactate, gamma-butyrolactone, ethyl 3-ethoxypropionate and
diethyleneglycol monomethyl ether acetate, ethyleneglycol
monomethyl ether acetate, ethyleneglycol monoethyl ether acetate,
diethyleneglycol monoethyl ether acetate, diethyleneglycol
mono-n-butyl ether acetate, propyleneglycol monomethyl ether
acetate, propyleneglycol monoethyl ether acetate, propyleneglycol
monopropyl ether acetate, propyleneglycol monobutyl ether acetate,
dipropyleneglycol monomethyl ether acetate, dipropyleneglycol
monoethyl ether acetate, glycol diacetate, and combinations of one
or more of the foregoing.
21. The method according to claim 20, wherein the non-aqueous
solvent comprises ethyl 3-ethoxypropionate, n-propyl lactate,
gamma-butyrolactone, or combinations of one or more of the
foregoing.
22. The method according to claim 11, wherein the non-aqueous
solution comprises about 5 g/L to about 40 g/L of the metallization
inhibitor.
23. The method according to claim 22, wherein the non-aqueous
solution comprises about 10 g/L to about 25 g/L of the
metallization inhibitor.
24. The method according to claim 23, wherein the non-aqueous
solution comprises about 15 g/L to about 20 g/L of the
metallization inhibitor.
25. The method according to claim 13, wherein the non-aqueous
solution is maintained at a temperature of between about 25.degree.
C. and about 75.degree. C. during the time that the electroplating
rack is immersed in the non-aqueous solution.
26. The method according to claim 25, wherein the non-aqueous
solution is maintained at a temperature of between about 35.degree.
C. and about 65.degree. C. during the time that the electroplating
rack is immersed in the non-aqueous solution.
27. The method according to claim 13, wherein the electroplating
rack is immersed in the non-aqueous solution for between about 1
minute and about 60 minutes.
28. The method according to claim 27, wherein the electroplating
rack is immersed in the non-aqueous solution for between about 2
minute and about 30 minutes.
29. (canceled)
30. The method according to claim 11, further comprising the steps
of: a) activating the surface of the non-conductive substrates by
immersing the electroplating rack with the non-conductive
substrates mounted thereon into a solution comprising colloidal
palladium/tin or ionic palladium; b) immersing the electroplating
rack containing the etched and activated non-conductive substrates
mounted thereon in an electroless metallization bath to
electrolessly deposit metal thereon; and c) electroplating the
non-conductive substrates to plate metal thereon, wherein the
treated coated portion of electroplating rack remains free of the
electrolessly deposited metal.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a method of
treating electroplating racks used for supporting non-conductive
substrates during a metallization step.
BACKGROUND OF THE INVENTION
[0002] For many years, processes have been available to facilitate
the deposition of electrodeposited metals onto plastic substrates.
Typically, the process involves the steps of: [0003] 1) Etching the
plastic in a suitable etching solution such that the surface of the
plastic becomes roughened and wetted so that the subsequently
applied deposit has good adhesion; [0004] 2) Activating the surface
of the plastic using a colloidal or ionic solution of a metal
(usually palladium) capable of initiating the deposition of an
autocatalytically applied metal coating (e.g., copper or nickel);
[0005] 3) Depositing a thin layer of autocatalytically applied
metal; and [0006] 4) Carrying out electrodeposition of metal onto
the metallized plastic substrate. Typically, layers of copper,
nickel and/or chromium will be applied to produce the finished
article.
[0007] The most widely used plastic substrates are
acrylonitrile/butadiene/styrene copolymers (ABS) or ABS blended
with polycarbonate (ABS/PC). These materials are readily formed
into components by the process of injection molding. ABS comprises
a relatively hard matrix of acrylonitrile/styrene copolymer and the
butadiene polymerizes to form a separate phase. It is this softer
phase of polybutadiene (which contains double bonds in the polymer
backbone) which may be readily etched using various techniques.
[0008] Traditionally, the etching has been carried out using a
mixture of chromic and sulfuric acids operated at elevated
temperature. The chromic acid is capable of dissolving the
polybutadiene phase of the ABS by oxidation of the double bonds in
the backbone of the polybutadiene polymer, which has proven to be
reliable and effective over a wide range of ABS and ABS/PC
plastics. However, the use of chromic acid has become increasingly
regulated because of its toxicity and carcinogenic nature. For this
reason, there has been considerable research into other means of
etching ABS plastics and a number of approaches have been suggested
to achieve this.
[0009] For example, acidic permanganate is capable of oxidizing the
double bonds in the polybutadiene. Chain scission can then be
achieved by further oxidation with periodate ions. Ozone is also
capable of oxidizing polybutadiene. However, ozone is extremely
dangerous to use and highly toxic. Likewise, sulfur trioxide can be
used to etch ABS, but this has not been successfully achieved on a
typical plating line. Other examples of techniques for etching ABS
plastics are described in U.S. Pat. Pub. No. 2005/0199587 to
Bengston, U.S. Pat. Pub. No. 2009/0092757 to Sakou et al., and U.S.
Pat. No. 5,160,600 to Gordhanbai et al., the subject matter of each
of which is herein incorporated by reference in its entirety.
[0010] More recently, it has been discovered that ABS and ABS/PC
plastic can be etched in a solution containing manganese(III) ions
in strong sulfuric acid as described 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.
[0011] In order to plate plastic components, they are attached to
plating racks which transmit the electrical current to the
sensitized and metallized plastic components. The racks are
typically at least partially coated with a non-conductive material
to prevent the rack from being entirely covered with metal during
the electroplating process, and the most common rack coating is a
PVC plastisol. The use of chromic acid in the etching stage prior
to activation is effective in modifying the surface of the
plastisol coating so that it is resistant to metallization after
being coated with a palladium activator (usually a colloid of
palladium and tin). When chromic acid is replaced with other
etching techniques, for example, using processes containing
permanganate or manganese (III), the plastisol coating of the
plating rack becomes coated with the activator and subsequently
becomes coated with a layer of either nickel or copper in the
electroless plating stage. Thus, a major problem with all of the
currently known methods that do not utilize chromic acid is that
rack coatings tend to become plated in the subsequently electroless
plating stage. This phenomenon is known as "rack plate up" and is a
major problem with any form of chrome-free etching technology.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to inhibit rack
plate up in the process of electroplating non-conductive
substrates.
[0013] It is another object of the present invention to inhibit
rack plate up in the process of electroplating non-conductive
substrates in which the non-conductive substrates are etched using
a chrome-free etchant.
[0014] It is still another object of the present invention to
provide a treatment for electroplating racks used for supporting
non-conductive substrates during the electroplating process.
[0015] To that end, in one embodiment, the present invention
relates generally to an electroplating rack for supporting
non-conductive substrates during an electrodeposition process,
[0016] wherein the electroplating rack is at least partially coated
with a non-conductive material; and
[0017] wherein the electroplating rack is treated with a
non-aqueous solution comprising a metallization inhibitor.
[0018] In another embodiment, the present invention relates
generally to a method of treating an electroplating rack used for
supporting non-conductive substrates during an electrodeposition
process, wherein the electroplating rack is at least partially
coated with a non-conductive material, the method comprising:
[0019] contacting the electroplating rack with a non-aqueous
solution comprising a metallization inhibitor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The present invention allows for the treatment of
electroplating racks used for the purpose of supporting
non-conductive substrates during a metallization step. The method
described herein allows for the effective activation of plastics
that have been etched without the use of chromic acid while
avoiding the common problem of rack "plate up" which occurs when
chromic acid free etchants are used for the initial roughening of
the plastic. In addition, the present invention relates generally
to the catalysis and subsequent metallization of plastics such as
ABS and ABS/PC plastics that have been etched in process solutions
that do not contain chromic acid and without problems of "plate up"
on at least partially coated racks.
[0021] In one preferred embodiment, the method generally comprises
the steps of: [0022] 1) Immersing a rack partially coated with
non-conductive material in a solution containing a metallization
inhibitor; [0023] 2) Rinsing and drying the rack; [0024] 3)
Mounting the parts to be metallized on the rack; [0025] 4) Etching
the plastic components mounted on the treated racks in etching
solutions that do not contain chromic acid (including, for example,
etching solutions based on permanganate or manganese (III); [0026]
5) Activating the surface of the plastic by immersing the plating
racks in a solution comprising colloidal palladium/tin or ionic
palladium; [0027] 6) Immersing the rack in an accelerating process
to remove protective tin oxides from the surface (in the case of
colloidal palladium/tin activation) or immersing the rack in a
reducing process to form palladium metal on the surface (in the
case of ionic palladium); [0028] 7) Immersing the racks containing
the etched and activated parts in a metallization bath to
chemically deposit either nickel or copper onto the surface of the
activated part; and [0029] 8) Electroplating the parts, typically
by plating copper, nickel and/or chromium.
[0030] Thus, in one embodiment, the present invention relates
generally to an electroplating rack for supporting non-conductive
substrates during an electrodeposition process,
[0031] wherein the electroplating rack is at least partially coated
with a non-conductive material; and wherein the electroplating rack
is treated with a non-aqueous solution comprising a metallization
inhibitor.
[0032] As described herein, the electroplating rack is typically
coated with a PVC plastisol, or another non-conductive
material.
[0033] The non-aqueous solution generally comprises about 5 g/L to
about 40 g/L of the metallization inhibitor, more preferably about
15 g/L to about 25 g/L of the metallization inhibitor, and most
preferably about 10 g/L to about 20 g/L of the metallization
inhibitor.
[0034] The non-aqueous solution is preferably maintained at a
temperature of between about 25.degree. C. and about 75.degree. C.,
more preferably a temperature of between about 35.degree. C. and
about 65.degree. C., during the time that the electroplating rack
is immersed in the non-aqueous solution. In addition, the
electroplating rack is immersed in the non-aqueous solution for a
period of time sufficient to treat the PVC plastisol coated rack to
avoid rack plate on. That is the electroplating rack is preferably
immersed in the non-aqueous solution for between about 1 minute and
about 60 minutes, more preferably for between about 2 minute and
about 30 minutes.
[0035] The inventors of the present invention have found that
metallization inhibitors that are substantially soluble in aqueous
media are unsuitable for the process described herein because they
tend to slowly leach into subsequent process solutions and prevent
metallization of the parts. Preferably, the metallization inhibitor
is at least essentially insoluble in aqueous media. Thus, the
solution containing the metallization inhibitor is a non-aqueous
solution.
[0036] Suitable water insoluble metallization inhibitors are
generally organic compounds comprising sulfur in a -2 valency and
include, but are not limited to, transition metal salts of
di-substituted dithiocarbamates and tetra-substituted thiuram
sulfides. Suitable dithiocarbamates include, for example, zinc
dimethyl-dithiocarbamate (ZDMC), zinc diethyldithiocarbamate
(ZDEC), zinc dibutyldithiocarbamate (ZDBC), zinc
ethylphenyldithiocarbamate (ZEPC), zinc dibenzyldithiocarbamate
(ZBEC), zinc pentamethylenedithiocarbamate (Z5MC), tellurium
diethyldithiocarbamate, nickel dibutyl dithiocarbamate, nickel
dimethyldithiocarbamate, and zinc diisononyldithiocarbamate.
Preferred tetra-substituted thiuram sulfides include, for example,
tetrabenzylthiuram disulfide, mercaptobenzothiazoles,
mercaptothiazolines, mercaptobenzimidazoles, mercaptoimidazoles,
mercaptobenzoxazoles, mercaptothiazole, mercaptotriazole,
dithiocyanuric acid, and trithiocyanuric acid. Combinations of one
or more of the metallization inhibitors may also be sued. In a
preferred embodiment, the metallization inhibitor comprises nickel
dibutyl dithiocarbamate or tetrabenzylthiuram disulfide.
[0037] Suitable non-aqueous solvents include, but are not limited
to butylene carbonate, propylene carbonate, ethylene carbonate,
dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate,
propyl lactate, gamma-butyrolactone, ethyl 3-ethoxypropionate and
diethyleneglycol monomethyl ether acetate, ethyleneglycol
monomethyl ether acetate, ethyleneglycol monoethyl ether acetate,
diethyleneglycol monoethyl ether acetate, diethyleneglycol
mono-n-butyl ether acetate, propyleneglycol monomethyl ether
acetate, propyleneglycol monoethyl ether acetate, propyleneglycol
monopropyl ether acetate, propyleneglycol monobutyl ether acetate,
dipropyleneglycol monomethyl ether acetate, dipropyleneglycol
monoethyl ether acetate, glycol diacetate, by way of example and
not limitation.
[0038] The solvent mixture must be capable of dissolving an
effective amount of the metallization inhibitor, be readily rinsed
off treated racks, and be preferably non-volatile and safe to
handle with regards to its toxicology and flammability. In
addition, the solvent mixture should cause no damage to the rack
coating. It has been found that solvents that are very readily
water-soluble can have difficulty in dissolving water-insoluble
metallization inhibitors and thus do not give an effective
inhibition of metallization. However, substantially water insoluble
solvents that readily dissolve the inhibitors and provide a better
degree of inhibition can cause a greater degree of attack on the
rack coating and are also more problematic to rinse off the rack
after treatment.
[0039] The degree of attack on the rack coating is related to the
degree of diffusion of the metallization inhibitor into the surface
of the rack coating, and the choice of solvents is therefore
critical to the success of the process.
[0040] The metallization inhibitor described herein can be readily
applied to racks during the normal treatment cycle to remove
unwanted metallic deposits from the tips of the contact points.
[0041] The invention will now be illustrated with reference to the
following non-limiting examples:
Comparative Example 1
[0042] An ABS test panel and a new PVC plastisol coated test piece
were processed through a standard pretreatment sequence comprising
the following stages: [0043] 1) Etch the test pieces in a solution
containing 400 g/L of chromic acid, 350 g/L of sulfuric acid and
0.1 g/L of perfluorooctylsulfonic acid (8 minutes at 65.degree.
C.); [0044] 2) Rinse; [0045] 3) Subject the test pieces to a
reducing stage comprising an aqueous solution of hydroxylamine
hydrochloride and hydrochloric acid; [0046] 4) Rinse; [0047] 5)
Immerse the test pieces in a solution of 30% hydrochloric acid as a
pre-dip before activation; [0048] 6) Immerse the test pieces in a
conventional palladium/tin activator (MacDermid Macuplex D34C) for
3 minutes at 30.degree. C.; [0049] 7) Rinse; [0050] 8) Immerse the
test pieces in a conventional accelerator solution (MacDermid
Ultracel 9369) for 2 minutes at 50.degree. C.; [0051] 9) Rinse; and
[0052] 10) Immerse the test pieces in an electroless nickel process
designed for plating on plastic applications (MacDermid Macuplex
J64) for 7 minutes at 30.degree. C.
[0053] Following this treatment, the test pieces were examined. It
was found that the ABS test panel was fully covered in electroless
nickel with no apparent voids. Subsequent electroplating of this
test panel gave full coverage and good adhesion. The PVC plastisol
coated test piece showed no coverage of the electroless nickel.
Repeated cycling of ABS and PVC test pieces through steps 1-10
continually showed full electroless nickel coverage of ABS and no
electroless nickel coverage of the PVC.
Comparative Example 2
[0054] An ABS test panel and a new PVC plastisol coated test piece
were processed through a pretreatment sequence comprising the
following stages: [0055] 1) Immerse the test pieces in a solvent
predip comprising 100 mL/L of propylene carbonate and 50 mL/L of
gamma-butyrolactone for 2 minutes at 35.degree. C.; [0056] 2)
Rinse; [0057] 3) Etch the test pieces in a solution comprising 12.5
M sulfuric acid containing 0.04 M manganous sulfate and 0.02 M of
manganese(III) ions at 68.degree. C. for 20 minutes; [0058] 4)
Rinse; [0059] 5) Subject the test pieces to a reducing stage
comprising an aqueous solution of ascorbic acid; and [0060] 6)
Carry out stages 4 to 10 of Comparative Example 1.
[0061] Following this treatment, the test pieces were examined. It
was found that the ABS test panel was fully covered in electroless
nickel with no apparent voids. Subsequent electroplating of this
test panel gave full coverage and good adhesion. The PVC plastisol
coated test piece showed significant coverage of the electroless
nickel which was observed to cover between 10% and 50% of the
surface area. This would be expected to cause considerable problems
in commercial practice. Repeated cycling of ABS and PVC plastisol
coated test pieces through steps 1-6 continually showed full
electroless nickel coverage of ABS and increasing amounts of
electroless nickel coverage of the PVC plastisol coated test
piece.
Comparative Example 3
[0062] An old PVC plastisol coated test piece which had been cycled
hundreds of times in a production facility using hexavalent
chromium treatment solutions, was leached for several hours in hot
water to remove any remaining hexavalent chromium on the surface
(the inventors have determined that this leaching effectively
eliminates any metallization inhibition provided by hexavalent
chromium in the PVC plastisol).
[0063] An ABS test panel and the old PVC plastisol coated test
piece were processed through stages 1-6 of Comparative Example
2.
[0064] Following this treatment, the test pieces were examined. The
ABS test panel was fully covered in electroless nickel with no
apparent voids. Subsequent electroplating of this test panel gave
full coverage and good adhesion. The PVC plastisol coated test
piece showed full coverage of the electroless nickel over the
entire surface of the plastisol test piece. This would be totally
unacceptable in commercial practice.
Comparative Example 4
[0065] A new PVC plastisol coated test piece was treated as
follows: [0066] A. Immerse the plastisol coated test piece in gamma
butyrolactone for 10 minutes at 65.degree. C.; [0067] B. Rinse and
dry the test piece.
[0068] An ABS test panel and the treated PVC plastisol coated test
piece were processed through the following stages: [0069] 1)
Immerse the test pieces in a solvent predip comprising 100 mL/L of
propylene carbonate and 50 mL/L of gamma-butyrolactone for 2
minutes at 35.degree. C.; [0070] 2) Rinse; [0071] 3) Etch the test
pieces in a solution comprising 12.5 M sulfuric acid containing
0.04 M manganous sulfate and 0.02 M of manganese(III) ions at
68.degree. C. for 20 minutes; [0072] 4) Rinse; [0073] 5) Subject
the test pieces to a reducing stage comprising an aqueous solution
of ascorbic acid; and [0074] 6) Carry out stages 4 to 10 of
Comparative Example 1.
[0075] Following this treatment, the test pieces were examined. It
was found that the ABS test panel was fully covered in electroless
nickel with no apparent voids. Subsequent electroplating of this
test panel gave full coverage and good adhesion. The PVC plastisol
coated test piece showed significant coverage of the electroless
nickel which was observed to cover between 10% and 50% of the
surface area. There was no apparent difference observed between the
PVC plastisol coated test piece that had been treated in a solvent
versus a PVC plastisol coated test piece that had not been treated
in a solvent.
[0076] These comparative examples illustrate the problems
associated with rack plate-up when chrome-free pretreatment
sequences are utilized and demonstrate that old used PVC plastisol
surfaces are more prone to metallization than new PVC plastisol
surfaces when hexavalent chromium is absent. Comparative Example 4
demonstrates that a solvent treatment without the inhibitor has no
effect.
Example 1
[0077] A new PVC plastisol coated test piece was treated as
follows: [0078] A. Immerse the plastisol coated test piece in a
solution of gamma butyrolactone containing 20 g/L of nickel
dibutyldithiocarbamate for 10 minutes at 65.degree. C.; [0079] B.
Rinse and dry the test piece.
[0080] An ABS test panel and the treated PVC plastisol coated test
piece were processed through the following stages: [0081] 1)
Immerse the test pieces in a solvent predip comprising 100 mL/L of
propylene carbonate and 50 mL/L of gamma-butyrolactone for 2
minutes at 35.degree. C.; [0082] 2) Rinse; [0083] 3) Etch the test
pieces in a solution comprising 12.5 M sulfuric acid containing
0.04 M manganous sulfate and 0.02 M of manganese(III) ions at
68.degree. C. for 20 minutes; [0084] 4) Rinse; [0085] 5) Subject
the test pieces to a reducing stage comprising an aqueous solution
of ascorbic acid; and [0086] 6) Carry out stages 4 to 10 of
Comparative Example 1.
[0087] Following this treatment, the test pieces were examined. It
was found that the ABS test panel was fully covered in electroless
nickel with no apparent voids. Subsequent electroplating of this
test panel gave full coverage and good adhesion. In addition, the
PVC plastisol coated test piece showed no coverage of the
electroless nickel.
[0088] Repeated cycling of ABS and the treated PVC plastisol test
piece through steps 1-6 continually showed full electroless nickel
coverage of ABS and no electroless nickel coverage of the treated
PVC plastisol coated test piece up to 3 cycles. After 3 cycles,
approximately 10% of metallization was visible on the PVC
plastisol. At this stage, the PVC plastisol coated test piece was
treated in the inhibitor solution for a second time and then
repeatedly cycled through stages 1 through 6 again. No
metallization was found on the treated PVC plastisol for at least
another 3 cycles, while full electroless nickel coverage was
obtained on the ABS test piece. The appearance of the PVC plastisol
was still satisfactory with little or no change from its original
appearance.
Example 2
[0089] A new PVC plastisol coated test piece was treated as
follows: [0090] A. Immerse the plastisol coated test piece in a
solution of ethyl 3-ethoxypropionate containing 20 g/L of nickel
dibutyldithiocarbamate for 30 minutes at 42.degree. C.; [0091] B.
Rinse and dry the test piece.
[0092] An ABS test panel and the treated PVC plastisol coated test
piece were processed through stages 1-6 as described in Example
1.
[0093] Following this treatment, the test pieces were examined. It
was found that the ABS test panel was fully covered in electroless
nickel with no apparent voids. Subsequent electroplating of this
test panel gave full coverage and good adhesion. The treated PVC
plastisol coated test piece showed no coverage of the electroless
nickel.
[0094] Repeated cycling of the ABS and treated PVC plastisol coated
test pieces through steps 1-6 as described in Example 1 continually
showed full electroless nickel coverage of ABS and no electroless
nickel coverage of the treated PVC plastisol up to 4 cycles.
[0095] The appearance of the PVC plastisol was still satisfactory
but was softer than the original coating.
Example 3
[0096] A new PVC plastisol coated test piece was treated as
follows: [0097] A. Immerse the plastisol coated test piece in a
solution of n-propyl lactate and ethyl 3-ethoxypropionate
containing 10 g/L of tetrabenzylthiuram disulfide for 10 minutes at
40.degree. C.; [0098] B. Rinse and dry the test piece.
[0099] An ABS test panel and the treated PVC plastisol coated test
piece were processed through stages 1-6 as described in Example
1.
[0100] Following this treatment, the test pieces were examined. It
was found that the ABS test panel was fully covered in electroless
nickel with no apparent voids. Subsequent electroplating of this
test panel gave full coverage and good adhesion. The treated PVC
plastisol coated test piece showed no coverage of the electroless
nickel.
[0101] Repeated cycling of the ABS and treated PVC plastisol coated
test pieces through steps 1-6 described in Example 1 continually
showed full electroless nickel coverage of ABS and no electroless
nickel coverage of the treated PVC plastisol up to 6 cycles. After
6 cycles, a small amount of metallization was visible on the PVC
plastisol. At this stage, the PVC plastisol coated test piece was
treated in the inhibitor solution for a second time and then
repeatedly cycled through steps 1 to 6 as described in Example 1
again. No metallization was found on the PVC plastisol for at least
another 6 cycles, while full electroless nickel coverage was
obtained on the ABS test piece.
[0102] The appearance of the PVC plastisol was still satisfactory,
with little or no change from its original appearance.
Example 4
[0103] A new PVC plastisol coated test piece was treated as
follows: [0104] A. Immerse the plastisol coated test piece in a
solution of ethyl 3-ethoxypropionate containing 10 g/L of
tetrabenzylthiuram disulfide for 30 minutes at 40.degree. C.;
[0105] B. Rinse and dry the test piece.
[0106] An ABS test panel and the treated PVC plastisol coated test
piece were processed through stages 1-6 as described in Example
1.
[0107] Following this treatment, the test pieces were examined. It
was found that the ABS test panel was fully covered in electroless
nickel with no apparent voids. Subsequent electroplating of this
test panel gave full coverage and good adhesion. The treated PVC
plastisol coated test piece showed no coverage of the electroless
nickel.
[0108] Repeated cycling of the ABS and treated PVC plastisol coated
test pieces through steps A and B above and then through steps 1-6
as described in Example 1 (i.e. with the PVC plastisol being
treated in the inhibitor solution prior to each etch and
metallization cycle) continually showed full electroless nickel
coverage of ABS and none or minimal electroless nickel coverage of
the treated PVC plastisol up to 10 cycles. After 10 cycles, a small
amount of metallization was visible on the PVC plastisol.
[0109] The appearance of the PVC plastisol was satisfactory, but
was softer than the original coating.
Example 5
[0110] An old plastisol test piece which had been cycled hundreds
of times on a production facility using hexavalent chromium
treatment solutions, was leached for several hours in hot water to
remove any remaining hexavalent chromium on the surface.
[0111] The old PVC plastisol coated test piece was treated as
follows: [0112] A. Immerse the plastisol coated test piece in a
solution of n-propyl lactate and ethyl 3-ethoxypropionate
containing 10 g/L of tetrabenzylthiuram disulfide for 5 minutes at
40.degree. C.; [0113] B. Rinse and dry the test piece.
[0114] An ABS test panel and the treated PVC plastisol coated test
piece were processed through stages 1-6 as described in Example
1.
[0115] Following this treatment, the test pieces were examined. It
was found that the ABS test panel was fully covered in electroless
nickel with no apparent voids. Subsequent electroplating of this
test panel gave full coverage and good adhesion. The treated PVC
plastisol coated test piece showed no coverage of the electroless
nickel despite being a very well used and aged coating with a
cracked and roughened surface.
[0116] Repeated cycling of the ABS and treated PVC plastisol coated
test pieces through step A and B above and then through steps 1-6
as described in Example 1 (for this example, the plastisol coating
was treated in the inhibitor solution prior to each etch and
metallization cycle) continually showed full electroless nickel
coverage of ABS and no electroless nickel coverage of the treated
PVC plastisol up to 25 cycles.
Example 6
[0117] A new PVC plastisol coated test piece was treated as
follows: [0118] A. Immerse the plastisol coated test piece in a
solution of n-propyl lactate and ethyl 3-ethoxypropionate
containing 10 g/L of tetrabenzylthiuram disulfide for 2 minutes at
40.degree. C.; [0119] B. Rinse and dry the test piece.
[0120] An ABS test panel and the treated PVC plastisol coated test
piece were processed through stages 1-6 as described in Example
1.
[0121] Following this treatment, the test pieces were examined. It
was found that the ABS test panel was fully covered in electroless
nickel with no apparent voids. Subsequent electroplating of this
test panel gave full coverage and good adhesion. The treated PVC
plastisol coated test piece showed no coverage of the electroless
nickel.
[0122] Repeated cycling of the ABS and treated PVC plastisol coated
test pieces through steps A and B above and then through steps 1-6
as described in Example 1 (for this example, the plastisol coating
was treated in the inhibitor solution prior to each etch and
metallization cycle) continually showed full electroless nickel
coverage of ABS and no electroless nickel coverage of the treated
PVC plastisol up to 25 cycles.
[0123] The appearance of the PVC plastisol was still satisfactory,
with little or no change from its original appearance.
* * * * *