U.S. patent application number 10/276351 was filed with the patent office on 2003-08-21 for method for the treatment of work pieces with a palladium colloid solution.
Invention is credited to Brandes, Mariola, Dyrbusch, Brigitte, Middeke, Hermann.
Application Number | 20030155250 10/276351 |
Document ID | / |
Family ID | 7642432 |
Filed Date | 2003-08-21 |
United States Patent
Application |
20030155250 |
Kind Code |
A1 |
Middeke, Hermann ; et
al. |
August 21, 2003 |
Method for the treatment of work pieces with a palladium colloid
solution
Abstract
The invention relates to a method for the treatment of work
pieces with a palladium colloid solution by bringing the work
pieces into contact with the colloid solution, palladium being
recovered after the use of the colloid solution. This is achieved
by separating palladium colloid particles from the colloid liquid
by means of a molecular filter. With this method it is easy to
continuously and largely completely separate palladium from the
spent processing solutions without investing large amounts of
chemicals, energy and time. The spent processing solution may
especially be worked up after separation of the part of the
solution containing palladium such that palladium can be recovered
completely and be reused for further processing.
Inventors: |
Middeke, Hermann; (Ming Yue
Yilu, CN) ; Brandes, Mariola; (Berlin, DE) ;
Dyrbusch, Brigitte; (Berlin, DE) |
Correspondence
Address: |
John F McNulty
Paul & Paul
2900 Two Thousand Market Street
Philadelphia
PA
19103
US
|
Family ID: |
7642432 |
Appl. No.: |
10/276351 |
Filed: |
April 21, 2003 |
PCT Filed: |
May 4, 2001 |
PCT NO: |
PCT/EP01/05064 |
Current U.S.
Class: |
205/163 ;
205/166 |
Current CPC
Class: |
B01D 61/145 20130101;
B01D 61/027 20130101; C23C 18/1617 20130101; C25D 21/20
20130101 |
Class at
Publication: |
205/163 ;
205/166 |
International
Class: |
C25D 005/54; C25D
005/56 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2000 |
DE |
100242391 |
Claims
1. Method for the treatment of work pieces with a palladium colloid
solution, comprising the method step of bringing the work pieces
into contact with the colloid solution, wherein after treatment of
the work pieces with the palladium colloid solution palladium is
recovered from said solution by a method comprising the following
method steps: bringing the palladium colloid solution into contact
with a molecular filter and separating palladium colloid particles
contained in the palladium colloid solution from said solution by
means of the molecular filter.
2. Method according to claim 1, wherein the molecular filter has an
exclusion pore size of from 200 Dalton to 10.000 Dalton.
3. Method according to claim 2, wherein the molecular filter has an
exclusion pore size of at least 500 Dalton.
4. Method according to claim 3, wherein the molecular filter has an
exclusion size of at least 2.000 Dalton.
5. Method according to any of the preceding claims, wherein the
molecular filter is made of a material, selected from the group
comprising polysulfones, perfluorinated polymers and ceramics.
6. Method according to any of the preceding claims, further
comprising the following method steps: a. bringing the work pieces
into contact with the colloid solution for activating the work
pieces; b. after the activating treatment has been carried out
removing the colloid solution adhering to the surfaces of the work
pieces from the surfaces with a rinsing liquid; c. pressing the
rinsing liquid through the molecular filter, the liquid having
passed through the molecular filter being a permeate liquid and the
liquid not having passed through the molecular filter being a
concentrate liquid; d. producing a palladium colloid solution by
using the concentrate liquid and adding suitable replenishment
agents to the concentrate liquid in appropriate amounts.
7. Method according to claim 6, wherein the colloid solution is
removed from the surfaces of the work pieces by spraying the
surfaces with a rinsing liquid after the activating treatment has
been carried out.
8. Method according to any of the preceding claims, wherein
palladium is recovered from a hydrochloric palladium colloid
solution stabilized with tin.
9. Method according to claim 8, wherein the palladium colloid
solution is mixed with a hydrochloric acid solution prior to
separating the colloid particles from the palladium colloid
solution with the molecular filter.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for the treatment
of work pieces with a palladium colloid solution, preferably to a
method for the treatment with a hydrochloric palladium colloid
solution being stabilized with tin.
BACKGROUND OF THE INVENTION
[0002] For the electroplating of work pieces the surfaces thereof
must first be treated to render them electrically conductive if the
work pieces have electrically nonconducting surfaces. For this
purpose the work pieces are dipped into a solution containing
colloidal palladium. The palladium particles thereupon adsorbed on
the surfaces serve as activators for initiating electroless metal
deposition, which results in the production of an electrically
conductive layer on the surface of the work pieces. This conductive
layer may afterwards be electroplated with any metal. This process
may for example be applied to the production of printed circuit
boards and of sanitary appliances, metallized parts for automotive
industry and of furniture mountings, especially for chromium
plating of plastics parts.
[0003] If work pieces provided with electrically nonconducting
surfaces are treated and thereafter are removed from the activating
solution, the solution partly adheres to the surfaces of the
pieces. This adhering solution is normally rinsed off with
water.
[0004] If conventional procedures are applied for activating work
pieces, a solution containing colloidal palladium with a palladium
concentration of from 50 to 100 mg/l palladium is typically
employed. In general therefore about 5 mg palladium are adsorbed to
plastics parts having a geometrical surface area of 1 square meter.
This amount is required for activating the plastics surfaces. If
the work pieces to be treated are removed from the respective
treatment station, however, about 0.2 liter activating solution are
left on each square meter of the surface of the work pieces, this
remaining solution being dragged out. For this reason from about 10
to about 20 mg palladium are lost per square meter of surface area
of the work pieces by drag out from the activating solution,
rinsing-off of the work pieces' surfaces and by transferring this
liquid to the waste water treatment.
[0005] Palladium containing activating solutions are also used for
direct plating on electrically nonconducting surfaces without using
electroless plating methods. In this case the adsorbed layer
containing palladium is converted into an electrically conducting
layer, which may be used to directly electrodeposit metal on an
activated nonconducting surface. For this purpose a higher
concentration of the palladium colloid particles of about 200 mg
palladium per liter solution is required.
[0006] Drag out of palladium from the activating solution amounts
to about 50 mg/m.sup.2 if conventional direct plating procedures
are applied. By making use of appropriate measures, for example by
preceding adsorption of polyelectrolytic compounds on the
nonconducting surfaces, adsorption of the palladium particles may
be enhanced considerably to about 50 mg/m.sup.2 surface area of the
work pieces. All the same still about 50% of the employed palladium
is lost due to drag out. Only 50% are still available for
electroplating of the work piece surfaces.
[0007] For example it is known to recover palladium from processing
solutions.
[0008] In U.S. Pat. No. 4,078,918 a process for recovering
palladium from various materials is disclosed, the materials
containing dissolved or non-dissolved palladium. The materials are
first treated with an oxidizing agent in order to destroy organic
components if necessary and are then treated with ammonium
hydroxide to form ammine complexes. The palladium complexes being
formed are then reduced by means of ascorbic acid, thereby
precipitating palladium from the processing solution, which may
finally be separated by filtration.
[0009] Further a process for recovering palladium from solutions
containing colloidal Pd/SnCl.sub.2 is disclosed in "Reclamation of
Palladium from Colloidal Seeder Solutions" in Chem. Abstr.,
1990:462908 HCAPLUS, these solutions usually serving as a
pretreatment agent in an electroless plating process. In this
procedure the solution is aerated for 24 hours, thereby coagulating
palladium from the solution. The precipitate formed is then
separated, dried and processed further.
[0010] A method for precipitating palladium from a solution by
adding metallic tin to this solution at a temperature of 90.degree.
C. is described in "Recovery of Palladium and Tin Dichloride from
Waste Water Solutions of Colloidal Palladium in Tin Dichloride" in
Chem. Abstr., 1985:580341 HCAPLUS.
[0011] A further process for recovering palladium from spent
catalytic colloidal palladium baths is disclosed in U.S. Pat. No.
4,435,258, these baths being used for activating nonconductive
surfaces for subsequent electroless metallization. The activating
solutions are worked up by dissolving colloidal palladium by adding
an oxidizing agent to the solution, for example hydrogen peroxide,
thereby forming a true solution, subsequently heating the solution
to destroy residual hydrogen peroxide and afterwards precipitating
palladium at a cathode by electrodepositing palladium.
[0012] Finally a process for recovering palladium from
Pd/SnCl.sub.2 solutions is described in "Recovery of the Colloidal
Palladium Content of Exhausted Activating Solutions Used for the
Current-Free Metal Coating of Resin Surfaces" in Chem. Abstr.,
1976:481575 HCAPLUS. In this case palladium is precipitated by
adding concentrated nitric acid to the solution and separated by
filtrating.
[0013] The known methods for treating the work pieces with a
palladium colloid containing solution are complicated and
expensive.
[0014] The problem of the present invention therefore consists in
avoiding the disadvantages of the known methods and especially in
finding a method to treat work pieces with a palladium colloid
solution which may be carried out easily. Only small amounts of
additional chemicals shall be required for performing the method.
Moreover the method shall be carried out with low expense of energy
and time.
SUMMARY OF THE INVENTION
[0015] The method according to the invention serves to treat work
pieces with a palladium colloid solution by bringing the work
pieces into contact with the colloid solution.
[0016] For continuous operation of the method, after treatment of
the work pieces with the palladium colloid solution, palladium is
recovered from said solution by a method comprising
[0017] bringing the the palladium colloid solution into contact
with a molecular (membrane) filter and
[0018] separating palladium colloid particles contained in the
palladium colloid solution from said solution by means of the
molecular filter.
[0019] Preferably the invention relates to the treatment of work
pieces with a hydrochloric palladium colloid solution being
stabilized with tin.
[0020] It is possible by carrying out the method according to the
invention under continuous operation to largely separate palladium,
especially palladium colloid particles, from spent palladium
processing solutions with low expenditure of chemicals, energy and
time. It is especially possible to work up the spent processing
solutions after separating the palladium containing part of the
solution from the spent solution in order to recover and reuse
palladium completely.
[0021] As compared to the method for recovering palladium from
colloidal Pd/SnCl.sub.2 solutions, as descibed in Chem. Abstr.,
1990:462908 HCAPLUS, the method according the present invention
advantageously leads to complete separation of palladium between
the concentrate part and the permeate part of the liquid. In
contrast with this new method the known method suffers from the
fact that a considerable part of palladium is oxidized to bivalent
soluble palladium during the precipitation method. Therefore
palladium cannot be separated entirely from the solution by
filtration. For this reason palladium is lost partly due to the
recovery method.
[0022] Furthermore in contrast to the method described in Chem.
Abstr., 1985:580341 HCAPLUS, the method according to the present
invention advantageously does not require considerable expenditure
of additional chemicals, such as for example of metallic tin, as
well as of additional energy and time for heating the colloid
solution as is the case if the known method would be carried
out.
[0023] The method according to the invention also has the
additional advantage to be a single-stage recovery method. This is
in contrast to the method as described in U.S. Pat. No.4,435,258.
Therefore the method according to the invention is very easy to
perform. Furthermore palladium can be removed essentially
completely from palladium containing solutions, whereas, if the
method as described in U.S. Pat. No. 4,435,258 is used, only a very
low current yield may be achieved when the palladium concentration
is low which is normally the case after prolonged electrolysis
time. Therefore complete removal of palladium is very complicated
oder not at all possible if this known method is used.
[0024] Furthermore in contrast to the method as described in Chem.
Abstr., 1976:481575 HCAPLUS, the method according to the invention
is especially suited for continuous operation. The method described
in this prior art document moreover does not manage without
additional chemicals.
[0025] Colloidal palladium activating solutions contain palladium
particles which are surrounded by a protective coating (protective
colloid). Experiments using high-resolution electron microscopy
(HREM) and atomic force microscopy (AFM) have shown that the
palladium particles have a diameter of at least 2.5 nm.
Surprisingly the size distribution is extremely narrow: It has
proven that no considerable deviations from the mean particle size
of 2.5 nm occurs in solutions containing colloidal palladium that
are usually used to activate nonconductor surfaces.
[0026] Normally colloid solutions are acidic and very often contain
hydrochloric acid. Further they often contain chloride ions and if
necessary bivalent and tetravalent tin or organic polymeric
stabilizers and reducing agents. With the exception of polymers,
which are used in very small amounts, all other components
contained in these solutions are ionic. It is guessed that these
ionic components are considerably smaller in size than the
palladium particles.
[0027] For this reason it was surprising that palladium particles
can be removed selectively and completely from these colloid
solutions with appropriate molecular filters having different
porosity though tin at the same time is present at a high
concentration (typically more than 70-fold of the palladium
concentration) and moreover tin compounds are known to form colloid
solutions being difficult to filtrate. It has also been known that
tin compounds are predominantly present in the palladium particles
so that selective separation of the palladium particles from tin
was not to be expected at all with this method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] For performing ultrafiltration or nanofiltration various
types of membranes made of various materials are known that can be
used for carrying out the present invention. For example molecular
filters made of polysulfones, especially polyethersulfones (PES),
perfluorinated polymers and ceramics made advantageously be
applied. For the selection of the type to be used for carrying out
the present invention it has proven that it depends only on a
sufficient stability of the membrane material towards the liquid to
be treated, for example the activating solution which may contain
up to 15 wt.-% hydrochloric acid. Surprisingly it has further been
found out that the porosity of the molecular filter is not critical
at all for the performance of separation of the palladium particles
from the liquid if a molecular filter is chosen with an exclusion
pore size of from 200 Dalton to 10.000 Dalton, since in this case
the palladium particles completely remain in the concentrate
liquid.
[0029] In order to separate the palladium colloid particles
molecular filters are used that preferably have an exclusion pore
size of from 200 Dalton to 10.000 Dalton.
[0030] If a molecular filter with an exclusion pore size of less
than 200 Dalton is used, palladium is still able to pass through
the filter membrane, but in this case a considerable amount of tin
compounds is held back by the membrane.
[0031] Therefore under these conditions separation efficiency of
palladium particles versus tin compounds is very low. If molecular
filters are used that have an exclusion pore size of considerably
more than 10.000 Dalton, the palladium particles pass through the
membrane. Therefore in this case the palladium particles can no
longer be separated from the residual liquid and its components,
namely the tin compounds. The range of from 200 Dalton to 10.000
Dalton therefore is an optimum with respect to the selectivity of
separation of palladium particles from the other components of the
solution to be treated, namely the tin compounds. An exclusion pore
size of at least 500 Dalton is especially preferred. Most
advantageous has proven an exclusion pore size of at least 2.000
Dalton. These further lower limits of the range represent preferred
embodiments of the present invention, presenting an even better
selectivity of separation between palladium particles and tin
compounds under the circumstances mentioned.
[0032] The molecular filters are preferably made of a material,
selected from the group comprising polysulfones, especially
polyethersulfones (PES), perfluorinated polymers, for example
polytetrafluorethylene (for example TEFLON.RTM., trade name of
DuPont de Nemours), and ceramics. These materials are sufficiently
chemically resistant towards the strongly acidic solutions
containing hydrochloric acid.
[0033] Observations and investigations made in favor of the present
invention have led to the conclusion that it is possible to recover
palladium particles from liquids, especially from rinsing liquid s,
by means of molecular filters. For this purpose the following
method steps are carried out:
[0034] a. The work pieces are brought into contact with the colloid
solution for activating the work pieces.
[0035] b. After the activating treatment has been carried out the
colloid solution adhering to the surfaces of the work pieces is
removed from the surfaces with a rinsing liquid.
[0036] c. The rinsing liquid is pressurized und thus led through
the molecular filter, the liquid being led through the molecular
filter being a permeate liquid and the liquid not being led through
the molecular filter being a concentrate liquid.
[0037] d. Preferably a palladium colloid solution is produced by
using the concentrate liquid and adding suitable replenishment
agents to the concentrate liquid in appropriate amounts.
[0038] After activating treatment has been carried out the work
pieces, preferably made from nonconducting material, are rinsed
with a rinsing liquid in an appropriate device. Rinsing is
preferably performed by spraying in order to minimize the volume of
rinsing liquid. Prior to separating the colloid particles from the
liquid by means of the molecular filter hydrochloric acid can be
added to the solution even during spraying the rinsing liquid to
the work pieces. If a sufficient amount of hydrochloric acid is
added to the liquid, the tin compounds contained in the liquid do
not hydrolyze so that cloudiness does not occur and precipitates
are not formed due to these compounds. Subsequently the rinsing
liquid is pressed through the selective molecular filter membrane
by means of a pressurized pump, the membrane holding back the
palladium particles und letting pass the rinsing liquid, especially
rinsing water, and all other components contained in the rinsing
liquid. The permeate liquid can then be led to waste water
treatment.
[0039] The palladium being held back and present as a homogeneous
metal dispersion concentrate can be used to produce an activating
solution. According to the composition of the concentrate tin(II)
or tin(IV) salts and hydrochloric acid in higher or lower amounts
are to be added to the concentrate liquid. In another alternative
the palladium held back may be dissolved und be used as a solution,
for example a palladium chloride solution, in order to produce an
activating solution or alternatively to use this solution for any
other purpose.
[0040] For clarification of the method according to the present
invention reference is made to FIG. 1, which shows a schematic
drawing of an apparatus, that may be used for carrying out the
ultrafiltration or nanofiltration of a palladium colloid
solution.
[0041] After treatment in the palladium colloid solution has been
cariied out the work pieces (not shown) are transferred to a
spraying container 1 in which the work pieces are held vertically
and are rinsed by spraying rinsing water to the pieces. Spraying is
carrier out by using spray nozzles 2 which are located are the
lateral side walls of the rinsing spraying container 1. The water
being sprayed to the surfaces of the work pieces wet the surfaces
of the work pieces so that the colloid solution is rinsed off the
surfaces. For this purpose used rinsing liquid Z from a further
rinsing station is used, in which the work pieces being rinsed in
this spraying container 1 will be rinsed again with rinsing liquid.
The spent rinsing liquid is led to the spray nozzles 2 via a
pipeline 4 by means of a pump 3. The liquid will only be sprayed
into the spraying container 1 if work pieces are present in this
container 1. Regulation of the rinsing liquid is performed by means
of a valve 5 which only allows the liquid to pass to the container
1 is work pieces are to be treated.
[0042] The rinsing liquid running down at the surfaces of the work
pieces and containing colloid solution due to the rinsing treatment
accumulate at the bottom of the rinsing container 1. This liquid is
removed from the rinsing container 1 via a pipeline 6.
[0043] Concentrated hydrochloric acid contained in the container 7
is admixed via a further pipeline 8 to the rinsing liquid coming
out from the container 1, thereby lowering the pH of the rinsing
liquid. Due to this lowering cloudiness does not occur and
precipitates do not form in the rinsing liquid though tin compounds
are present in the liquid.
[0044] The rinsing liquid made acidic with hydrochloric acid is
afterwards led to the molecular filter unit 10 via a pump 9. A
filter membrane is arranged inside the molecular filter 10. The
liquid present in the region in front of the filter membrane in the
molecular filter is pumped in a circuit (not shown). Therefore the
colloid particles are permanently in motion in the region in front
of the filter membrane, so that the pores of the membrane may not
be clogged (cross-flow).
[0045] The part of the liquid that has passed through the filter
membrane represents the permeate liquid P. The part of the liquid
that has not passed through the filter membrane represents the
concentrate liquid K. This part K is intermittently or continuously
removed from the filtration unit 10.
[0046] In the following examples are given to more clearly describe
the present invention:
EXAMPLE 1
[0047] By means of cross-flow technique a solution containing 200
mg/l colloidal palladium, 330 ml/l hydrochloric acid (37 wt.-%) and
34 g/l tin (as a mixture of tin(II)-chloride and tin(IV)-chloride)
was pressed through a filter membrane made from
polyvinylidenfluorides (PVDF) with an exclusion pore size of 6.000
Dalton at a pressure of 10 bar (.DELTA.10.sup.6Pa). The permeate
liquid that had passed through the filter membrane was colorless
and clear without any cloudiness. The concentrate liquid remained
black due to the colloidal palladium particles. It was found out
that the flux through the filter membrane diminished after a few
minutes because the colloid had entered the membrane.
EXAMPLE 2
[0048] The experiment of example 1 was repeated by using a membrane
made of polysulfone (PES). This membrane had an exclusion pore size
of 1000 Dalton. The flux through this membrane was less than that
experienced from example 1 though the same pressure was applied (10
bar .DELTA.10.sup.6Pa). However a decrease of flux during the
experiment, which lasted 1 hour, could not be detected.
EXAMPLE 3
[0049] Since a larger pore size would allow a higher flux, the
experiment was repeated with a membrane with an exclusion pore size
of 55.000 Dalton. In this case the filtrate (permeate) liquid was
also black. This pointed at the fact that colloidal metal could
pass the membrane.
EXAMPLES 4-6
[0050] Example 1 was repeated with three further membranes which
were made from PVDF. The exclusion pore size of these three
membranes were 250 Dalton, 400 Dalton and 6.000 Dalton,
respectively.
[0051] After execution of the separation of the palladium particles
from the liquid the concentrations of palladium, tin(II), tin(IV)
and hydrochloric acid were determined and the total tin content was
calculated from the tin(II) and tin(IV) concentrations. The results
are given in table 1. Moreover in this table the ratios of the tin
concentration in the concentrate liquid to the tin concentration in
the permeate liquid as well as the respective ratio for the
hydrochloric acid concentations are given.
[0052] The data presented in table 1 indicate that the total amount
of palladium remains in the concentrate liquid irrespective of the
exclusion pore size of the membranes, whereas no palladium could be
detected in the permeate liquid. Furthermore the ratios for the tin
concentrations and for the hydrochloric acid concentrations drop as
the exclusion pore size increases. This points at the fact that
these substances arrive easier into the permeate liquid and remain
to a smaller extent in the concentrate liquid as the exclusion pore
size increases. By using a membrane with an exclusion pore size of
6.000 Dalton the concentrate liquid therefore contained the lowest
amount of tin and hydrochloric acid.
1 TABLE 1 Size Exclusion Limit: Size Exclusion Limit: Size
Exclusion Limit: 250 Dalton 400 Dalton 6,000 Dalton Original
Concentration Permeate Concentrate Ratio Permeate Concentrate Ratio
Permeate Concentrate Ratio Palladium 198,5 mg/l 0 mg/l 190,0 mg/l 0
mg/l 398,5 mg/l 0 mg/l 229,0 mg/l Tin (II) 27,0 g/l 12,7 g/l 24,1
g/l 22,3 g/l 27,4 g/l 23,4 g/l 10,6 g/l Tin (IV) 7,0 g/l 7,1 g/l
5,5 g/l 10,9 g/l 9,3 g/l 7,3 g/l 12,5 g/l Tin, tot. 34,0 g/l 19,8
g/l 29,6 g/l 1,50 33,2 g/l 36,7 g/l 1,11 30,7 g/l 23,1 g/l 0,75
Hydro- 332,2 ml/l 207,0 ml/l 324,0 ml/l 1,57 313,3 ml/l 334,0 ml/l
1,07 318,0 ml/l 302,0 ml/l 0,95 chloric Acid
[0053] Reference Numerals:
[0054] 1 rinsing container
[0055] 2 spray nozzles
[0056] 3 pump
[0057] 4 pipeline
[0058] 5 valve
[0059] 6 pipeline
[0060] 7 container for hydrochloric acid
[0061] 8 pipeline
[0062] 9 pump
[0063] 10 membrane filtration unit
[0064] Z rinsing liquid
[0065] p permeate liquid
[0066] K concentrate liquid
* * * * *