Note: Descriptions are shown in the official language in which they were submitted.
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1 CONDITIONING OF CAPROLACTAM POLYMERS
FOR ELECTROLESS PLATING
Background of the Invention
The present invention relates to electroless plating
of caprolactam polymers in particular, to provide a surface
uniformly receptive to electrolessly deposited nickel a~d
15 coppar.
The beneits of electroless plated, non-conductive
articles, particularly plastic articles, are well known.
In the finished product, the desirable characteristics of
the plastic and the metal are combined to offer thereby
~; 20 the technical and aesthetic advantages of each.
Polymeric substrates are conventionally plated by
pre-etching the surface by contact with an aqueous
~ solution of at least one organic co~,pound active for
: conditioning the surface of the plastic, then etching with
2 a strong oxidizing acid or base, seeding the surface with
a noble metal catalyst, e.g., a palladium chloride
solution, then immersing the seeded surface in an auto-
: catalytic electroless solution where an initial coating of a
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conductive metal, e.g., coppeX o~ nickel~ ~s established by
chemical depo~ition. The metal deposit acts as a buss to allow
a thicker coating of metal to be huilt up electrolytically.
Attempts to adapt conventional procedures for electroless
plating of polymers to polyamides by us have resulted in a
failure to achieve a uniform adherent coat of metal. Having
found conventional electroless plating procedures ineffective,
a quest was initiated to discover a procudure to enable uniform
coating of polyamides with electroless deposited metals.
SUMMARY OF THE INVENTION
It has now been found that electroless plating of
caprolactam polymers, particularly filled caprolactam polymers,
can be realized by contacting a caprolactam polymer substrate
with an aqueous solution comprising at least one acetic acid
compound of the formula:
`` O .
, X3C-C ~
OH
.
wherein each X is independently selected from the group consisting
of hydrogen~ hydroxyl and halogen and in which the acetic acid
; compound is present in a concentration sufficient to tender the
caprolactam substrate receptive to a noble metal catalyst.
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1 This is followed by seeding the surface with a
metal electroless plating catalyst selected from solutions
of noble metal ions and colloidal suspansions or dispersions
of noble or non-noble metal particles.
Following seeding and activation of the metal catalyst
by conventional means, the surface can be uniorml~ plated
with electroless copper or nickel.
Contact time in the organic acid etch is normally from
about 10 seconds to 15 minutes at room temperatures.
10 Concentration of the acetic acid compound is normally
at least about 3 percent ~y weight of solution up to
solution saturation, preferab~y from about 5 to about
60 percent by weight.
In carrying out the process, an alkali solution having
~5 a pH of at least about~ 10, may be used to condition the
substrate and if used, is pre~erably employed at a temper-
ature from about 1~0F to the boiling point of the solutio~
or the softening point of the plastic, whichever is less,
preferably 170 to about 200F at contact times r~nging
20 from about O.S to about 20 minutes or more, depending
on temperature and alkali concentra~ion. Conc~n~ration
is normally from about 2 percent by weight of solution
to solution saturation, preferably from about 10 to about
50 percent by weight. It is preferred to employ a solution
25 of an alkali metal hydroxide such as sodium or potassium
hydroxide.
In conductin~ the process of the invention, the
article may be pre~conditioned by contacting the article
in an aqueous solution of an organic solvent, preferably
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1 an alkali soluble organic solvent for the caprolactam polymer
in a concentration up to about 2 percent by weight,
preferably up to about I percent by weight. Ethylene glycol,
phenolic compounds such as chlorophenol, cresols and salts
5 thereof are presently preferred. The so~vent may be contained
in its own bath or included in the alkali solution so
long as the alkali does not hydrolyze or otherwise degrade
the organic solvent. The solvent serve~ to soften the plastic
to acid etch. Contact with the solvent solution is prior
10 to contact with the acid etch and may be, if used, be
prior to contact with the alkali solu~ion.
In addition, the substrate after contact with the
solution of the acetic acid compound may be further
conditioned to remove surface debris of the etching
lS by contact with acidic to basic wash.
De~ailed Description
According to the present invention, there is provided
a process which enables uniform electroless deposition of
~0 metals onto substrates formed from caprolactam polymers,
typically filled substrates.
The process of the invention requires contacting the
caprolactam article with an etch solution comprising an
organic acid compound containing from 2 to about 10 carbon
2 atoms and having a solubility in waker of at leas~ 3
percent by weight of the solution, and con~act is for
a time sufficient to render the surface uniformly receptive
to a me~al ca~alyst~ It is preferred to use a solution
of an acetic acid compound as def ined ~elow~
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1 As part of the process measures, water rinsing with
deionized water is performed for good housekeeping between
each s~ep. The substrate may be pre-treated with a dilute
solution of solvent for the polyamide, preferably an alkali
5 soluble solvent, to soften the -~urface of the substrate
to promote etch. The solvent for the polyamid~ may be
. contained in a ~eparate bath or part of the alkaline
solution, as herein defined.
In addition, the substrates may be contacted with an
acidic or basic solution subsequent to etch to remove
debris ]?resent on the surface of the substrate.
.. .
The caprolactam polymers to be conditioned are known
as Nylon 6~
The essential step of the process is contact of the
caprolactam substance with an organic etch containing
preferably at least one acetic acid compound. The presently
preferred etch is one comprisi.ng at least about 3 percent by
weight of solution, preferably 5 ~o about 65 percent by
weight, and more preferably, from about 10 to about 25
percent by weight of solution o~ at least one acetic acid
compound of the formula:
. ' .
.
. X3C-~ ~
OH
, .
where each X is independently hydroxyl, hydrogen or
halogen9 with halogen pre~erred~ Contact is at room
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12398-JPG
1 temperature, although elevated temperatures may be
employed. Contact times range from about 10 seconds to
15 minutes or more and are for a time sufficient to etch
the surface of the amide to a degree that it becomes
5 uniformly receptive to seeding by a metal electroless plating
catalyst.
Among the acetic acid compounds which may be used
there may be mentioned trichloracetic acid, acetic acid,
hydroxyacetic acid, dichloracetic acid, chloracetic acid,
10 fluoracetic acid, difluoracetic acid, trifluoracetic acid,
L bromacetic acid, dibromacetic acid and the like. Tri-
chloroacetic acid is presently preferred.
An optional step o~ the prncess is contacting the
caprolactam substrate with an aqueous alkaline solution having
1 a pH of at least 10 to condition the surface prior to contact
with the acid etch. It is pre~;ently preferred that the
a1kaline solution contain at least one alkali metal hydroxide,
such as sodium and/or potassium hydroxide. The alkali
employed should be present in a concentration from about
2 2 percent to solution saturation, preferably from about
10 to about 50 percent by weight. Solut~on temperature
is maintained from about 150~F to the lesser of the boiling
~j point of the solution and the softening point of the
caprolactam substrate, preferably from a temperature of
¦ 2 about 170F to 200F~ Contact time may vary from about
¦ 0.5 to 20 minutes or more, depending upon temperature
and the alkali concentration, although it has been found
I that prolonged immersions will not damage the substrate.
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1 Besides the alkali metal hydroxides, there may be employed
alkaline compounds such as sodium metasilicate, trisodium
phosphate, sodium carbonate and the like, used alone and/or
in combination with an alkali metal hydroxide.
There may also be employed as part of the process, a
separate bath used alone; preceding or following the alkaline
conditioner or included in the alkaline conditioner, of
a solvent for the surface of th~ caprolactam to soften
the surface to aid attack by the alkali and~or the etch.
Typically, concentration of the solvent is up to about
2 percent by weight, preferably up to about 1 percent
by weight. A wide variety of solvents for polyamides
may be used. The presently preferred solvents are ethylene
glycol, phenols such as chlorophenol, cresols and the
like, and salts thereof. It is presently preferred to
precede the acid etch by contact with the solution of the
solvent whether or not an alkaline conditioner is used.
The solvent erves to soften the surface of the caprolactam
substrate to promote conditioning and/or etching.
In addition, subsequent to etch the caprolactam substrate
may be brought into contact with an acid or alkaline solution
of either an organic or inorganic base to cleanse ~he
surface of debris, i.e., filler and/or degradated resin~
Such solations are normally maintained at room temperature,
although elevated temperatures may be employed.
Concentrations are in the range up to about 20 percent
by weight, preferably up to about 10 percent by weight.
Functional acids include hydrochloric acid, sulfuric acid,
phosphoric acid, nitric acid, formic acid, acetic acid
7~-9 7
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and the like. There may also be employed the alkaline
solution used for conditioni,ng as well as salt solutions~
such as solutions of borax and ammonium bifluoride. The
concentration is that which,will enhance surface finish
without de-tracting from the ability of etched surface to
accept a metal catalyst.
Whether or not the cleansing treatment is employed,
; the article is rinsed in water, usually deionized water,
and seeded with a metal electroless plating catalyst contained
in an ~U~QU~ medium. The catalyst may be noble or non-noble
metal based. The use of a noble metal catalyst contained
;' in an aqueous medium is preferred. By a noble metal catalyst
contained in an aqueous mediu,m,there is meant an ionic
solution or colloidal suspension of the free metals. Colloidal
suspensions are preferred. The noble metals include gold,
platinum and palladium, with palladium preferred. Suitable
non-noble metal catalysts are described in 'U.S. Patent
3l958,~48 assigned to the same assignee as this application.
A suitable ionic bath is one containing palladium
chloride in a concentration of about 0.2 grams per liter
solution and 3 ml of concentrated hydrochloric acid per
; liter of solution. Following seeding, the palladium can be
reduced to the free metal state by immersion in a bath of
, a reducing agent such as dimethyl amine borane.
Colloidal suspensions of noble metals are described
in U.S. Patent 3,011,~20 to C. R. Shipleyl Jr. The
presently preferred colloidal suspension is one which is about
1.7 molar in hydrochloric acid ~LCl~. Such suspensions
` are colloidal in nature in which the noble metal colloid
- 8 -
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is maintained in suspension by a protective colloid,- i~e.
stannic acid colloids. Follo~ing seeding, the colloid is
removed by immersion in an acidic or alkaline accelerator
solution to remove the protective colloid and expose the
absorbed noble metal.
Although less preferred, there may also be employed
a seeding method which involves contacting the etched
article with a sensitizing solution containing stannous
chloride followed by immersion in an activator solution,
such as a palladlum chloride solution, where the ionic
palladium is reduced to the free metal on the surface of
the substrate.
Suitably activated, the article may be electrolessly
; plated by conventional means. Electroless copper and
nickel formulatlons, such as those described in UOS~
Patents 3,011,920 and 3,874,072 may be employed. Electro-
less copper solutions and typically based on a Soluble
copper salt, such as copper sulfate, a complexing agent
for the cupric ion such as Rochelle salt, an alkali hydroxide
for adjustment of pH, a carbonate radical as a buffer and
a reducing agent for the cupric ion such as formaldehyde.
Following electroless plating, the substrate may be
electrolytically plated by conventional means, with copper,
nickel, gold, silver, chromium and the like to provide the
~5 desired finish on the article.
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12398:JPG
1 Example
An article molded of Capron(TM) XPM-1030, a filled
Nylon 6, manufactured and sold by ~llied Chemical Corpora-
tion, was contacted with a 15 percent by weight to volume
aqueous solution of trichloracetic acid solution maintained
at room temperature for 5 minutes. After rinsing in deionized
water, the article was seeded by contact with a propriet~ry
colloidal tin-palladium catalyst, as described in U.S.
Patent 3,011,920, at an acid molarity of about 1.7. An
alkaline accelerator was used to expose the palladium metal.
The catalyst was maintained at about 120F and the accelerator
at about 105F. The seeded article was electrolessly plated
using CupositlTM) PM-990, manufactured and sold by the
Shipley Company. The electroLess plating solution was
maintained at room temperaturle.
Following alectroless plating, the article was rinsed
in deionized water, soaked in an alkaline cleaner, passed
to a reverse current cleaner, an acid dip, ~right acid
`l copper and nickel electrolytic plating solutions, and finally
¦ 20 to a chromium plating solution.
¦ The plated article was subjected to a cycle test to
~i determine adhesion performance under thermal stress
conditions~ In this test, the plated article was maintained
at a temperature of 180F for 1 hour, then cooled to and
maintàined at room temperature for 30 minutes then cooled
to -20F and maintainad at that temperature for 1 hour.
The cycle test was passed.
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