some materials are not very compatible with ink, printing processes. ex. polypropylene surface...
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SURFACE TREATMENT• Some materials are not very compatible with ink, printing processes. Ex. Polypropylene• Surface energy is an important factor in terms of wetting behavior of the material• When material is exposed to ink, it might not spread on the material as required• We have to change the surface energy of the material so that we can modify our surface in terms of its appearence
CORONA TREATMENT
Used for increasing the surface energy Exploits the corona effect Result of this treatment is usually better adhesion and
better wettability properties Usually employed in film production Its effect degrades over time, that is why inking or
printing is done after corona treatment
Corona treatment is a surface modification technique that uses a low temperature corona discharge plasma to impart changes in the properties of a surface. The corona plasma is generated by the application of high voltage to sharp electrode tips which forms plasma at the ends of the sharp tips.
CORONA TREATMENT Electromagnetic field is produced by magnetic field
generator Film winded on a roll goes under the corona generators Excited species in the air modifies the surface Important parameters are voltage, pressure of the air,
sample/electrode geometry
FLAME TREATMENT Again used for wetting and printing purposes Usually used for polyolefin surfaces Basic apparatus: Flame generators and mold holding the
material Flames located at certain points scans the material for the
time of treatment Scan time, material-flame distance, flame temperature
are important in this treatment
PLASMA TREATMENT Introduction of plasma to the surface Process resembles corona discharge Has to be done in a vacuum chamber for a better
homogeneity in gaseous mixture Anode and cathode are used to form plasmas Plasmas generated modify surface via increasing surface
activity in micro level
PLASMA, PRINCIPLES AND APPLICATIONS
PLASMA TREATMENT There are two types of plasma treatment Cold Plasma vs Hot Plasma Temperature of plasma is very high at atmospheric
pressure This can be utilized in melting of a powder to be used as a
coating. This is called hot plasma treatment It is usually used for deposition of coatings
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FUNCTIONALIZATION OF POLYMER SURFACES
Functionalization occurs by chemical interaction of plasma produced species - ions, radicals and photons with the surface.
· Example: H abstraction by O atom enables affixing O atoms as a peroxy site.
· Increase surface energy increase wettability.
Process treats the top few layers.
Wettability on PE film with 3 zones of treatment.
Courtesy: http://www.polymer-surface.com
(a)(b)
(c)
· Pulsed atmospheric filamentary discharges (coronas) routinely treat commodity polymers like poly-propylene (PP) and polyethylene (PE).
SURFACE MODIFICATION OF POLYMERS
· Filamentary Plasma 10s – 200 mm
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PRIMER ON SURFACE CHEMISTRY
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Polypropylene structure
Functional groups are when treated in O2 containing plasmas:
Alkyl Alkoxy Carbonyl Alcohol Peroxy Acid
R R-O R=O R-OH R-OO O=R-OH
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PRIMER ON SURFACE CHEMISTRY
· Ratio of O, OH, O2 and O3 fluxes determine surface composition.
· Magnitude of fluxes and residence time determines importance of surface-surface reactions.
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· Polymer surfaces are continuously treated at web speeds of a few m/s with residence times in plasma of up to a few ms.
· Non-air gas mixtures are often “forced flowed” through gap to customize radicals to surface.
FORCED GAS FLOW AND WEB MOVEMENT
Gas Flow
LAB MADE INDUCTIVE COUPLED PLASMA
There are two types of ICP geometries: planar and cylindrical. In planar geometry, the electrode is a coil of flat metal wound like a spiral. In cylindrical geometry, it is like a helical spring.When a time-varying electric current is passed through the coil, it creates a time-varying magnetic field around it, which in turn induces azimuthally electric currents in the rarefied gas, leading to the formation of a plasma. Argon is one example of a commonly-used rarefied gas.
Plasma technologies in Plasma lab
Used for biocompatible materials (polymers, composites, artificial blood vessel, etc.)• sterilization • functionalization
PLASMAS USED IN PLASMA LAB
For medical purposes the inductively coupled oxygen plasma is used. Typical parameters of weakly ionized fully dissociated oxygen plasma • Electron temperature 5 eV• Electron density 1015 m-3
• Positive ion density 1015 m-3 • Degree of dissociation up to 100%• Neutral gas kinetic temperature about 50C• Density of O atoms depends on pressure• Density of O atoms often over 1021 m-3
Plasmas are created in oxygen,
hydrogen, nitrogen and argon
AFM investigations of biological samples
Atomic Force Microscope (AFM) (left) and image of Staphylococcus aureus (right).
Plasma functionalization of organic materials
oxygen plasma
Surface polymer
C-OH
C-O COOH C=O
Polar groups on a polymer surface cause a dramatic increase of surface wettability.
Reactive particles from oxygen plasma are incorporated on the surface forming O-rich functional groups.
Surface wettability is measured by water drop
The contact angle of a water drop on a polymer surface versus plasma treatment time
untreated
treated 0.5s
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6Treatment time (s)
Con
tact
ang
le (°
)
Appearance of functional groups is best analysed by X-ray photoelectron spectroscopy (XPS = ESCA)
sample
X-ray source
Elec
tron
dete
cto
r
Photo-electrons
hn
Instrument PHI-TFA Principle
Appearance of functional groups is monitored by XPS
010020030040050060070080090010001100
Binding enegy (eV)
Inte
ns
ity
(a
rb. u
nit
s)
untreated
plasma treated
afterglow treated
C
1sO
1s
O K
LL
S 2
s
S 2
p
O K
LL
O K
LL
O 1
sO
1s
C
1s
C
1s
S 2
s
S 2
p
S 2
s
S 2
p
Survey spectra of PES (poly(ether sulfones)) polymer before (bottom) and after different plasma treatment (middle and top).
280 285 290 295 300 Binding Energy (eV)
Inte
nsi
ty (
arb
. u
nit
s)
A
B
D
280 285 290 295 300 Binding Energy (eV)
Inte
nsi
ty (
arb
. u
nit
s)
A
B
C
D Untreated PES
Plasma activated PES (1s)
A … C-C or C-H
B … C-O
C … C=O
D … O=S=O
High resolution C 1s peak
c cO oI II
ION BEAM TREATMENT Ion assisted vs ion implantation Ion implantation is a process in which ion beam is
introduced directly to the surface Ion assisted treatment is to target species which will then
form a coating on the surface Apparatus includes ion gun and closed system
METALLİZATİON Used in coatings whose material can be found in liquid
form and evaporates easily. Ex. Aluminium Electron gun hits the coating material in liquid form Evaporated material is coated on the polymeric film Beam emitted has to be controlled
OTHER TYPES In surface treatment, UV, laser, X-ray could also be
employed Their main impact is to maintain cross-linking on the
surface Closed system is required because the process has to be
precise Properties like diffusion coefficient, permeability,
adhesion can be modified
CHEMİCAL MODİFİCATİONS In the treatment of polymeric surfaces, chemical
composition of polymer surfaces can be modified either by direct chemical reaction with a given solution (wet treatment) or by the covalent bonding of suitable macromolecular chains to the sample surface (grafting).
WET TREATMENT Wet treatments were the first surface modification
techniques used in order to improve surface properties of polymers.
Hot chromic acid was used to oxidize polyolefins Specific solutions were prepared in order to exploit
specific liquid-polymer interaction. The effectiveness of the treatment depends on the
interaction of the different modification mechanisms
WET TREATMENT Polymer surfaces are rarely homogeneous. When the surface composition is constant
throughout the surface, amorphous and crystalline domains are present on it.
Wet treatment is not homogeneous on the surface.
TECHNİQUES Sodium etching of fluoropolymers Oxidizing treatment based on chromic acid
solutions Hydrolysis of polyesters etc.
ETCHİNG OF FLUOROPOLYMERS Etching is a process of preparing the surface of a
fluoropolymer insulated wire or tubing for bonding to another material.
The etching process is used on PTFE, FEP and PFA fluoropolymers.
PTFE has superb thermal, electrical and chemical resistance characteristics.
PTFE the choice in applications such as coating of non-stick frying pans.
ETCHİNG OF FLUOROPOLYMERS The chemical structure of PTFE results in a non-polar,
non-wettable surface. The etching process strips a layer of fluorine atoms
from the surface and leaves the carbon atoms with a deficiency of electrons.
When the altered surface is exposed to the atmosphere, oxygen and hydrogen restore some of the electrons forming a surface that will accept bonding.
ETCHİNG OF FLUOROPOLYMERS The effectiveness of etching is measured by calculating the change in
surface wettability. θ = contact angle
SURFACE OXİDATİON AND ETCHİNG Surface treatment of various polymers by oxidizing
solutions was developed as a result of the low metal-to-polymer adhesion.
In the early studies and papers that were written, the problem was handled only in a physical manner.
Later studies, mainly following the development of the surface sensitive analytical techniques, considered also the chemical side of the problem.
REASONS Removing completely, or to prevent formation of, what
are often referred to as weak boundary layers. Protecting the adherend surfaces before bonding. Producing a specific adherend surface topography,
thereby altering the surface profile, and possibly increasing the bondable surface area, that is, to roughen the surface.
HYDROLYSİS The attack of a nucleophilic agent, such as a base,
on an electron-deficient carbon atom, has been exploited in several different classes of polymers in order to improve their surface properties.
HYDROLYSİS Hydrolysis of PET by hot
sodium hydroxide attack is the oldest and most used technique which increases the number of hydrophilic groups, improves the moisture-related properties.
FUNCTİONALİZATİON The aim of the functionalization of polymer surfaces is
to create a surface layer of well-defined functional groups.
In this way one can create polymeric surfaces of controlled properties or a rigid substrate of controlled chemical reactivity.
SURFACE GRAFTING In surface grafting, the aim is to achieve
chemical modification of the surface by the covalent bonding of new macromolecules on top of the substrate.
Fundamental step in grafting is the creation of reactive groups on the substrate surface.
SURFACE GRAFTİNG It can either be done chemically or by
irradiation (ionizing radiation, UV light and glow discharge).
This grafting-coupling technique is sometimes followed but it is more common to contact the activated surface with a suitable monomer, so that a growing chain starts from the activated site.
REFERENCES http://www.markelcorporation.com/material10.html http://www.devicelink.com/mddi/archive/05/10/006.
html http://pubs.acs.org/cgi-bin/abstract.cgi/jpchax/1994/9
8/i47/f-pdf/f_j100098a046.pdf?sessid=6006l3 http://www.kobelco.co.jp/p108/p14/sfe05.htm http://www.adhesivestoolkit.com/Docu-Data/SurfaceP
reTreatment.xtp http://www.sciencedirect.com