Gas plasma treatment for water and oil proofing of fabrics and paper

An improved method for imparting water and oil repellent surface properties to fabrics or paper includes pretreatment in a low pressure oxygen plasma in the presence of water vapor followed by plasma polymerization of methane in a high frequency glow discharge carried out in the same treatment chamber. The resultant polymer film formed on the material surface resists separation from the treated material even after prolonged immersion in water. The method is characterized by use of low cost and readily available starting monomer, by use of a single treatment unit for all stages of the process, reduced energy requirements and treatment time, and improved results over conventional processes.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to surface treatments for textiles and paper 
products for imparting resistance to impregnation by liquid to the treated 
materials, and in particular is directed to gas plasma treatments for that 
purpose. 
2. State of the Prior Art 
The production of high quality textiles or paper calls for efficient 
methods for imparting soil-resistance to the textile or paper materials. 
Polymer surface coatings have been used to this end. Currently practiced 
methods of coating a paper surface with such a film involve at least seven 
distinct stages: 
synthesis of a monomer; 
polymerization of the monomer with formation of intermediate or end 
polymer; 
preparation of a film forming solution; 
cleaning of the surface or application of a bonding agent to the surface; 
application of the coating; 
drying of the coating; 
solidification of the coating. 
The basic disadvantages of these methods include the large number of stages 
involved in the process as well as unevenness and excessive thickness of 
the resultant coating, which leads to a change in the appearance of the 
treated material. 
Japanese patent 63-75002 describes treatment in an impulse or pulsed 
discharge in an atmosphere comprising the gases CH.sub.4, C.sub.2 H.sub.6 
or C.sub.4 H.sub.10 for increasing the durability and thermal stability of 
ferromagnetic layers of magnetic tapes. This method cannot be applied to 
fabrics because the film formed during the process changes the appearance 
of the treated surface. 
Another prior method of achieving film plasma polymerization, described in 
U.S. Pat. No. 4,188,426, includes treatment in a glow discharge of 
per-fluoro-cyclo-butane or hexafluoroethane to reduce the friction 
coefficient and to improve the surface hydrophobia of organic and 
inorganic substrates (e.g. polyethylene films, metals). This method also 
cannot be applied to fabrics because the film formed during the process 
changes the appearance of the treated surface. In addition, the use of 
fluoro containing monomers is contraindicated by ecological 
considerations. 
A known method of water and oil repellent finishing of textiles, described 
in USSR Patent 1,158,634, includes plasma treatment in a glow discharge in 
an atmosphere of inorganic gases, followed by treatment with a fluoro 
containing acrylic monomer in gas phase. The first stage of the process 
can cause additional destruction of archival documents when the documents 
interact with the gas that creates the plasma. The second stage forms too 
rough a film. 
Another prior method of plasma formation of a thin film on the surface of 
polymer material, described in Japanese Patent 62-132940, includes: 
1. plasma treatment in a glow discharge in an atmosphere of 
H.sub.2,CO,N.sub.2,O.sub.2 gases; 
2. plasma polymerization; and 
3. treatment in hydrogen plasma. 
The first stage is used to improve adhesion of the film surface for the 
subsequent polymerization stage. This first stage lasts from 20 sec to 30 
minutes of time and can cause additional destruction of archive documents 
when the documents interact with the gas that creates the plasma. 
A prior method described in USSR patent 642550 for treatment of rubber 
articles includes, treatment in a glow discharge; immersion in an emulsion 
of polytetra-fluoro-ethylene; and treatment by glow discharge. The 
application of fluoro-containing monomers is an ecologically detrimental 
feature of this method. 
Japan patent 62-260836 describes a surface plasma polymerization treatment 
of glass or synthetic sponges, including treatment in a glow discharge in 
an atmosphere of nitroethane or nitropropane. This method cannot be 
applied fabrics or paper because the film formed by the process changes 
the appearance of the treated surface. Also, use of nitro-compounds is 
ecologically undesirable. 
Patents of Japan 62-132940; EPW--Japan, 0177364; Japan, 61-221236; Japan; 
and USSR 1158634 describe pretreatment of materials in a plasma of 
inorganic gas for 40 sec. to 20 minutes to purify and activate surfaces 
for subsequent processing. As a result, polymer films deposited by a 
subsequent polymerization stage adhere better to the treated material 
surfaces. However, in some instances satisfactory treatment results 
require discharge power levels which are harmful or destructive to the 
material being treated. 
A prior method of depositing a thin surface film by a plasma polymerization 
process (Japanese patent 62-132940) includes treatment in a glow discharge 
of H.sub.2, CO, N.sub.2 or O.sub.2 at p=0.05-5 Torr, t=30 sec--20 min, 
power 5-50 KWt; then a plasma polymerization stage, followed by plasma 
treatment in hydrogen. The film obtained by this method is characterized 
by improved durability, but changes the appearance of the treated surface 
and physico-mechanical properties of materials. 
Japanese patent 61-22136 discloses a method of surface preparation before 
coating of polyolefine articles which includes the steps of treatment by a 
fluoro-organic solvent, staining in a glow discharge of oxygen, and 
coating. The film obtained by this method is characterized by improved 
strength to peeling and water resistance. Use of fluoro-containing solvent 
however is an ecologically undesirable feature of this method. 
What is needed is a method for imparting liquid resistant surface 
properties to fabrics and paper products which do not alter the appearance 
nor physically damage the treated material, which involves a minimum of 
processing of the item, which can be safely used on various materials, 
which is not ecologically damaging, and which is simple and dependable. 
SUMMARY OF THE INVENTION 
The present invention is an improved method for applying a durable water 
and oil-repellent finish to textile fabrics, fibers and paper materials. 
The finish obtained includes a thin polymer coating formed by plasma 
polymerization on the surface of the material. The polymer coating does 
not alter the appearance nor the physical and mechanical properties of the 
treated materials. 
The novel method includes a first, surface preparation and activation stage 
before the second or plasma polymerization stage. The surface of the 
subject material is first treated in a low temperature plasma of an 
inorganic gas, preferably oxygen gas. The concentration of active 
components in the plasma is increased by addition of water vapor at a 
concentration is between 0.05 and 0.5% to the oxygen gas, resulting in 
superior activation and preparation of the surfaces with shortened 
treatment times as compared to treatment with dry gas. This makes the 
activation process more economical and commercially attractive. 
According to this improved method, textile fabrics and paper products are 
exposed to a low temperature plasma of methane gas at a pressure of 
between 0.01 and 10 Torr, input power generator frequency of 1-40 MHz at a 
specific discharge power of 0.003 to 3.0 Wt/cm.sup.3, for 30 sec to 3600 
sec The materials may be first exposed to a low pressure oxygen plasma 
before exposure to the methane gas plasma. Water vapor to a concentration 
of between 0.05 to 0.5% may be added to the oxygen plasma. Exposure to the 
oxygen plasma takes place at a pressure of 0.01 to 10 Torr, with input 
power generator frequency of 1 to 40 MHz at specific discharge power of 
0.003 to 3.0 Wt/cm.sup.3, for a treatment time ranging from 3.0 sec to 60 
sec. 
The presently preferred method for imparting water and oil repellent 
surface properties to materials including textile fabrics and paper 
products comprises the steps of first exposing the materials to a low 
pressure oxygen plasma including water vapor at a concentration of between 
0.05 to 0.5%, at a pressure of 0.01-10 Torr, input power generator 
frequency of 1 to 40 MHz with specific discharge power of 0.003 to 3.0 
Wt/cm.sup.3, for a treatment time ranging from 3.0 sec to 60 sec; and then 
exposing the materials to a low temperature plasma of methane gas at a 
pressure of between 0.01 and 10 Torr, input power generator frequency of 1 
to 40 MHz at a specific discharge power of 0.003 to 3.0 Wt/cm.sup.3 for 30 
sec to 3600 sec.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The novel method includes a first, surface preparation and activation stage 
and a second, plasma polymerization stage. 
The surface of the subject material is first treated in a low temperature 
oxygen plasma. Atomic oxygen, ozone and other highly reactive particles 
are formed in an oxygen plasma. The concentration of these components 
determines the speed and depth of the surface activation and treatment 
process. The addition of water vapor has been found to intensify the 
surface activation process in inorganic gas plasmas when water vapor 
concentration is between 0.05 and 0.5%. A further increase in water vapor 
concentration however is counterproductive as it hinders the surface 
activation process and can lead to extinction of the glow discharge. 
Addition of water vapor in concentrations of 0.05-0.5% during the 
pretreatment stage has been found to achieve activation of the surfaces of 
the subject material, before polymerization, at a lower specific power of 
the gas discharge and in a shorter time than with dry gas. In addition, 
after polymerization, the wetting angle is increased and surface energy of 
the treated material is decreased, and stronger bonding of the polymer 
film occurs, so that the polymer films do not separate from the substrate 
material even following prolonged immersion in water. 
The plasma polymerization generally includes processes occurring in the 
gaseous phase (i.e., in the plasma volume), and processes taking place on 
the surface being treated. In electrical glow discharges generated under 
low pressure, the main activation process involves collisions of free 
electrons accompanied by dissociation of the monomer: 
EQU CH.sub.4 +e.fwdarw.CH.sub.3 +H+e 
EQU CH.sub.4 +e.fwdarw.CH.sub.2 +H.sub.2 +e 
and by ionization of the formed free radicals: 
EQU CH.sub.3 +e.fwdarw.CH.sub.3 +2e 
EQU CH.sub.3 +e.fwdarw.CH.sub.2 +2e 
Under low pressure conditions the main recombination process involves 
surface phenomena. Energy is released in the course of recombination, 
including kinetic energy of the ions and the ionization energy of the 
same. The energy released leads to the formation of so-called growth 
centers on the surface being treated: 
EQU surface e+CH.sub.3.sup.+ .fwdarw.CH.sub.3 +growth center 
Formation of polymer film on the surface can be described by the following 
reactions: 
EQU Growth center+CH.sub.3 .fwdarw.polymer 
EQU Growth center+CH.sub.2 .fwdarw.polymer+growth center 
Formation of the polymer can be understood to include formation of the 
building blocks in the gas phase, and completion of polymer formation on 
the surface being treated. 
Use of methane as the sole starting monomer in the plasma polymerization 
stage leads to formation of a polymer film consisting of considerably 
branched carbon chains, which results in advantageous surface film 
properties. It is important to this type of treatment that the new surface 
characteristics obtained be stable over long periods of time. Films formed 
by methane plasma polymerization are characterized by high adhesion to the 
substrate. This is attributed to the absence of reaction capable groups in 
methane, which results in the plasma polymerization proceeding at a 
relatively slow rate. Films formed by methane plasma polymerization are 
further characterized by low permeability to air and water, and strong 
hydrophobic properties. For a 1000 Angstrom film thickness, the 
permeability is 7.57.times.10.sup.-13 cm.sup.3 /cm.sup.2 sek.cm.h.c. That 
is significantly lower than the permeability of polymer films obtained by 
conventional methods (polyethylene--9.times.10.sup.-9 ; 
polyvinilchloride--5.times.10.sup.-11). 
The gas plasmas used in this treatment process are generated in a low 
pressure glow discharge. A main characteristic of this type of plasma is 
its non-isotermicity: Te&gt;&gt;Ti=Tg, where 
Te--temperature of electrons, 
Ti--temperature of ions, 
Tg--temperature of gas. 
Typically: Te=30,000K; ; Tg=375K 
The apparatus employed for the low pressure plasma treatment is 
schematically illustrated in FIG. 1 of the attached drawing. The plasma 
treatment is as follows. Material to be processed, indicated by the 
numeral 1, is placed in a vacuum chamber 2. Three gas bottles 4, 
separately containing the gases used in the process, are connected through 
suitable valves and conduits to the chamber 2. The chamber 2 is evacuated 
by means of vacuum pump 3 until the interior pressure of chamber 2 reaches 
0.01 Torr. The vacuum system then is flushed with oxygen gas from one of 
bottles 4, and the chamber is again evacuated. Oxygen gas and water vapor 
are then fed, in metered amounts, into the system to a pressure from 0.01 
to 10.00 Torr. Two cylindrical electrodes 6 are mounted to the exterior of 
the chamber 2 in axially spaced apart relationship. A high frequency 
electrical power generator 5 connected between the electrodes 6 lights a 
plasma generating glow discharge in the chamber 2 between the electrodes. 
The preferred specific power of the discharge is between 0.003 to 3 
Wt/cm.sup.3, and the discharge is sustained for 3 to 60 seconds. Power to 
the electrodes is then turned off. The chamber 2 is evacuated to a 
pressure of 0.01 Torr, and the vacuum system is flushed with methane from 
another of bottles 4. Methane gas is then fed to chamber 2 to a pressure 
of 0.01 tp 10 Torr. Power is again applied to the electrodes 6 to light 
the glow discharge. The specific power of the discharge is between 0.003 
to 3 Wt/cm.sup.3, and the discharge is sustained for 30 to 3600 seconds. 
Both power generator and vacuum pump are then turned off, the chamber 2 is 
brought to atmospheric pressure, and the treated material 1 is removed 
from the chamber by opening end closure 7. The cylindrical electrodes may 
be replaced by electrode plates diametrically opposed on the exterior of 
the cylindrical chamber 2. 
Fabrics and paper treated by this process acquire water and oil repellent 
properties. It was found that the absorption time for water drops placed 
on a treated surface is greater than its evaporation time on that surface. 
The degree of surface activation of treated fabrics can be evaluated by 
measurement of capillary absorption of the samples, as set forth in Tables 
1-3. 
Comparison of three types of paper before and after plasma-chemical 
treatment showed that the strength characteristics of the samples are 
practically unaffected by the thin polymer layer deposited on their 
surface. The strength characteristics of treated samples were found 
substantially unchanged after thermal and ultraviolet aging of the 
samples. Deformation characteristics of initial and treated paper samples 
were found to be practically the same. Consequently, application of a thin 
polymer layer does not affect strength and deformation characteristics of 
the paper substrate, but leads, however, to virtual loss of capillary 
absorption of the treated material. 
EXAMPLE 1 
A 150.times.150 mm sample of woolen fabric with specific density 495 g/mm 
is placed in the discharge chamber 2 with external cylindrical electrodes 
6. Air is extracted to a pressure of 0.01 Torr. Oxygen with water vapor 
added to a concentration of 0.1% is fed into the chamber to a pressure of 
0.5 Torr. A glow discharge is ignited by supplying high frequency voltage 
(13.56 MHz) to the electrodes 6 with a specific power discharge of 0.15 
Wt/cm.sup.3. The discharge is extinguished after 30 sec, and gas is 
evacuated from the chamber to a pressure of 0.01 Torr. This is followed by 
the introduction of methane into the system a pressure of 0.5 Torr. The 
glow discharge is again ignited by supplying high frequency voltage (13.56 
MHz) to the electrodes with a specific power discharge of 0.15 
Wt/cm.sup.3. The discharge is extinguished after 450 sec.; vacuum pumping 
is stopped, air is admitted into the system and the sample 1 is taken out 
of the discharge unit. The sample is then subjected to testing after 
treatment. The wetting angle measurements were performed within 10 min. 
after finishing the plasma polymerization treatment. 
The oil repellent score of the sample after treatment was measured as 120. 
A drop of water placed on the sample did not spread after several hours, 
and gradually evaporated. The sample elongation before break in the wet 
state of the treated sample was 23.2%, increased from 19% for the dry 
untreated sample and 21% for the treated sample. Water column resistance 
increased from 0 to 190 cm after treatment. In other words, the untreated 
initial sample wets with water and oil practically at once. The treated 
sample shows water and oil repellent properties. 
Separation of the polymer film from the sample material did not occur after 
the sample was boiled in water for one hour. The mechanical strength and 
deformation properties of the sample remained unchanged. 
EXAMPLE 2 
A sample of sulfite paper (containing sizing agents: high-resin glue--0.5%, 
alumina--0.5%; cooling filler--25%) was placed in the discharge unit 2 
with external cylindrical electrodes 6, but specific power of electrical 
discharge was adjusted to 0.75 Wt/cm.sup.3 (for both stage 1 and 2 of the 
treatment process, and treatment by plasma polymerization proceeded for 
360 sec as in Example 1. 
The following properties of the sample were determined in accordance with 
methods known and accepted in the paper industry: 
tensile strength and stretching; 
tear resistance; 
deformation in wet state; 
whiteness of spherical photometer. 
Paper durability was estimated according to the stability of its strength 
characteristics following thermal (@T=100+3 deg. C.) aging for 30 days and 
exposure to ultra violet radiation on both sides under a UV lamp for 60 
min. 
Comparison of strength and deformation characteristics of treated paper 
samples (before and after thermal and UV aging) showed that these 
characteristics are substantially unaffected by the thin polymer layer, 
which however leads to virtual loss of capillary absorption of the treated 
material. Capillary absorption of the untreated sample was 36 mm/10 min. 
The treated sample had no absorption. The wetting angle of the treated 
sample was 115 degrees. After the sample was kept in the water for one 
month neither separation of the film nor change of sample properties 
occurred. 
EXAMPLE 3 
A sample of woolen fabric with density 540 g/m.sup.2 was placed in the 
discharge unit 2 with parallel electrodes diametrically opposed on the 
chamber exterior, and treated under conditions the indicated in example 2, 
but the specific power of the electrical discharge was adjusted to 1.5 
Wt/cm.sup.3 (for both stage 1 and 2 of the process). The pretreatment or 
activation stage 1 proceeded for 3 sec. and the polymerization stage 2 
proceeded for 120 sec. 
The longitudinal elongation before break of a 50.times.100 mm sample when 
dry increased, as a result of treatment, from 9.5% (untreated sample) to 
11.0%, and from 15.2 (untreated sample) to 16.4% when wet. 
Water resistance of the untreated sample was 260 cm in water. Water 
resistance of the sample treated in plasma was 420 cm in water. A drop of 
water placed on the sample did not spread over the surface after several 
hours, gradually evaporating. The oil repellent score was 120. The colors 
of fabric did not fade after exposure to ultraviolet radiation. 
EXAMPLE 4 
A sample of newsprint paper (containing sulfate unbleached cellulose--25%, 
white pulp mass--75%, filler--not more than 5%) was placed in the 
discharge unit 2 with external cylindrical electrodes 6, and treated under 
the conditions indicated in example 2, but the frequency of electrical 
discharge was adjusted to 6.25 MHz. 
Mechanical properties of the treated sample were not degraded after thermal 
and UV aging. Time of absorption of a water drop for the untreated sample 
was 3 sec. The treated sample showed no capillary absorption. The 
absorption time for water is greater than its evaporation time on the 
treated surface. The wetting (contact) angle of water was 110 degrees. 
After thermal and UV aging these characteristics were unchanged. These 
surface characteristics of the treated sample do not deteriorate, and the 
polymer coating on the treated surface does not separate from the sample 
after immersion of the sample in water. 
TABLE 1 
______________________________________ 
EFFECT OF WATER VAPOR CONCENTRATION ON 
INTENSITY OF SURFACE ACTIVATION UNDER 
FIXED TREATMENT CONDITIONS 
Capillary 
Specific Power 
Time of Treat- Absorption 
Wt/cm3 ment Sec (H.sub.2 O) % 
mm/10 min 
______________________________________ 
0 initial 0 0 21 
0.3 60 0 24 
0.3 60 0.05 26 
0.3 60 0.1 28 
0.3 60 0.15 30 
0.3 60 0.2 31 
0.3 60 0.3 30 
0.3 60 0.4 27 
0.3 60 0.5 25 
0.3 60 0.6 21 
______________________________________ 
The added water vapor activates the plasma process and increases the 
capillary absorption of the treated sample compared to results obtained b 
existing methods. As seen from the table, the maximum activation was 
obtained at (H.sub.2 O) = 0.2 to 0.25% concentration. 
TABLE 2 
______________________________________ 
EFFECT OF TREATMENT TIME ON SURFACE 
ACTIVATION AT MOST EFFICIENT CONCENTRATION 
OF WATER VAPOR AND FIXED SPECIFIC POWER 
Capillary 
Specific 
Time of Absorption at Capillary 
Power Treatment (H.sub.2 O) = 0.0 Absorption 
Wt/cm3 Sec. mm/10 min (H.sub.2 O), % 
mm/10 min 
______________________________________ 
0 initial 
0 21 0 21 
0.15 10 21.5 0.2 22.5 
0.15 20 22 0.2 24.5 
0.15 30 22.5 0.2 26 
0.15 40 23 0.2 28 
0.15 50 23.5 0.2 29 
0.15 60 24 0.2 30 
______________________________________ 
TABLE 3 
______________________________________ 
EFFECT OF SPECIFIC POWER OR SURFACE 
ACTIVATION AT MOST EFFICIENT 
CONCENTRATION OF WATER VAPOR 
AND FIXED TREATMENT TIME 
Capillary 
Specific 
Time of Absorption Capillary 
Power Treatment mm/10 min Absorption 
Wt/cm3 Sec at (H.sub.2 O) = 0.0 
(H.sub.2 O), % 
mm/10 min 
______________________________________ 
0 0 21 0 21 
initial 
0.003 10 21 2.0 23 
0.5 10 21 2.0 25 
1.0 10 22 2.0 26.5 
1.5 10 23 2.0 28 
2.0 10 24 2.0 29 
2.5 10 25 2.0 30 
3.0 10 26 2.0 30.5 
______________________________________ 
Addition of water vapor in .05-.5% concentration allows surface activatio 
before polymerization at a lower specific power and in a shorter time tha 
activation with dry gas. This makes the activation process more 
economical. 
TABLE 4 
______________________________________ 
EFFECT OF POLYMERIZATION TREATMENT TIME 
ON PROPERTIES OF PAPER 
Time of Capillary Contract 
Specific Polymeri- Absorp- Angle of 
Power zation tion Water, 
Wt/cm3 sec. mm/10 min Degrees 
______________________________________ 
Sulphate 
0 0 37 -- 
Paper initial 
0.5 15 15 74 
0.5 20 5 83 
0.5 30 0 106 
0.5 60 0 112 
0.5 3600 0 108 
0.5 3600 0 
0.5 3700 0 115 
______________________________________ 
TABLE 5 
______________________________________ 
EFFECT OF SPECIFIC POWER DURING POLYMER- 
IZATION STAGE ON PROPERTIES OF PAPER 
Contact 
Time of Specific Capillary Angle of 
Polymeriza- Power Absorption 
Water 
tion Sec. Wt/cm3 mm/10 min Degrees 
______________________________________ 
Newsprint 
0 initial 0 49 -- 
600 0.002 24 68 
600 0.0025 7 85 
600 0.003 0 95 
600 0.5 0 97 
600 1.0 0 103 
600 2.0 0 107 
600 3.0 0 112 
600 3.0 0 109 
600 3.5 0 113 
______________________________________