U.S. patent number 3,708,263 [Application Number 05/106,739] was granted by the patent office on 1973-01-02 for method for continuous sterilization at low temperature.
Invention is credited to Raymond M. G. Boucher.
United States Patent |
3,708,263 |
Boucher |
January 2, 1973 |
METHOD FOR CONTINUOUS STERILIZATION AT LOW TEMPERATURE
Abstract
An automatic method and apparatus to continuously surface
sterilize at temperatures below 75.degree. C any objects, parts or
components made of metal or heat sensitive materials. Said method
consists of treating materials first in a synergistically active
chemical solution in an ultrasonic tank, then of rinsing in a
second ultrasonic tank. The final step consists of drying the
processed material in a sterile atmosphere. The three different
processing steps take place in a matter of minutes inside a laminar
flow positive pressure clean or white room. The apparatus
continuously delivers sterile parts or instruments ready for
packaging and sealing. Sterilized parts or instruments are not
physically or chemically affected by the process and do not contain
dissolved corrosive or toxic compounds.
Inventors: |
Boucher; Raymond M. G. (New
York, NY) |
Family
ID: |
22312993 |
Appl.
No.: |
05/106,739 |
Filed: |
January 15, 1971 |
Current U.S.
Class: |
422/20;
422/36 |
Current CPC
Class: |
A61L
2/025 (20130101); A61L 2/18 (20130101) |
Current International
Class: |
A61L
2/18 (20060101); A61l 013/00 (); A61l 001/00 ();
A61l 003/00 () |
Field of
Search: |
;21/12R,54A,DIG.2,12A,58,54R ;134/1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
947,699 |
|
Jan 1964 |
|
GB |
|
947,700 |
|
Jan 1964 |
|
GB |
|
Primary Examiner: Richman; Barry S.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. The process of sterilizing sensitive materials such as plastic
or the like comprising contacting the material to be treated with a
chemical solution comprising an aqueous solution of from 0.05 to 5
percent by volume glutaraldehyde and from 1 part per million to 2
percent by volume of dimethyl-sulfoxide and ultrasonic waves
simultaneously at temperatures below 75.degree. C.
2. A continuous process of synergistically destroying all surface
micro-organisms including pathogens, viruses and spores on metal or
heat sensitive materials such as plastic or the like, comprising
contacting the material to be treated with a chemical solution
comprising an aqueous solution of from 0.05 to 5 percent by volume
glutaraldehyde and from 1 part per million to 2 percent by volume
dimethylsulfoxide and ultrasonic waves simultaneously at
temperatures below 75.degree. C, subsequently treating the material
with a rinsing solution and ultrasonic waves simultaneously at
temperatures below 75.degree. C and finally drying the material at
temperatures below 75.degree. C.
3. The process of claim 2, wherein the material to be treated is
first submerged in said chemical solution while said material to be
treated and said chemical solution is being treated with ultrasonic
waves, subsequently said material to be treated is submerged in a
rinsing solution while said material to be treated and said rinsing
solution is being treated with ultrasonic waves and finally drying
said material to be treated.
4. The process of claim 2, wherein the rinsing solution is sterile
water.
5. The process of claim 2, wherein all the steps take place in a
sterile atmosphere.
6. The process of claim 2, wherein the chemical solution has a pH
of between 2 to 8.5.
7. The process of claim 2, wherein the chemical solution contains a
buffer to adjust the pH from between 7 and 8.5.
8. The process of claim 2, wherein the chemical solution is
submitted to a high intensity ultrasonic field whose normal
frequency is from between 8 kHz and 900 kHz.
9. The process of claim 2, wherein the chemical solution is
submitted to an ultrasonic field having an intensity of at least 10
watts per liter.
10. The process of claim 2, wherein the material is treated in the
chemical solution at a temperature of between 15.degree. and
70.degree. C.
11. The process of claim 2, wherein the rinsing solution is
submitted to a high intensity ultrasonic field whose normal
frequency is from between 8 kHz and 300 kHz.
12. The process of claim 2, wherein the intensity of the ultrasonic
field on the rinsing solution is greater than 10 watts per
liter.
13. The process of claim 2, wherein the temperature of the rinsing
solution is between 45.degree. and 70.degree. C.
14. The process of claim 2, wherein the material to be treated is
dried at a temperature at between 70.degree. and 75.degree. C.
15. The process of claim 2, wherein the material is treated with
the chemical solution and ultrasonic waves, the rinsing solution
and ultrasonic waves and the drying operation for from 2 to 30
minutes each, respectively.
16. The process of claim 2, wherein the material being treated is
exposed to ultraviolet light while being dried.
17. The process of claim 2, wherein the rinsing solution also
contains up to 0.1 percent by volume of a surface active agent.
18. The process of claim 17, wherein the surface active agent is a
cationic surface active agent.
19. The process of claim 18, wherein the cationic surface active
agent is a quaternary ammonium salt.
Description
This invention relates to a continuous sterilization method at low
and medium temperatures to process heat sensitive materials such as
hospital and medical plastic made disposables or delicate
electro-optical devices such as bronchoscopes or cytoscopes which
cannot be autoclaved. Today hospitals, clinics and practitioner
offices use a large number of disposables made of heat sensitive
materials. Among these items are syringes, suction catheters,
feeding and urinary drainage tubes, sutures, masks, nebulizer
tubes, surgical gloves, etc. To sterilize these heat sensitive
materials before, during or after packaging, most of today's
manufacturers use low temperature gas sterilization. This is at the
moment the only practical method to handle low softening point
plastics, but, as well known, this method has numerous drawbacks
and limitations. Although several aerosols, vapours and gases (see
C. R. Philipps, Disinfection, Sterilization and Preservation, pg.
669 Lea and Febiger, Philadelphia, 1968) have been suggested in the
past for gaseous sterilization, ethylene-oxide is the only chemical
used on a large scale for industrial and medical applications. The
advantages of ethylene-oxide sterilization lie not in the speed,
simplicity, or economy of the treatment but rather in the fact that
many types of materials are sterilized with least damage to the
material itself when this technique is used. Among the drawbacks of
this method is the acute inhalation toxicity of this gas. Cases of
acute human exposures with nausea, vomiting, and mental
disorientation have been reported in the technical literature (R.
E. Joyner, Archiv. Environ Health, vol. 8, 700-710, May 2, 1964).
As little as 3 percent of ethylene-oxide vapor in the air will
support combustion and will have explosive violence if confined.
When mixed with carbon dioxide (90% CO.sup.2) or various
fluorinated hydrocarbons the resulting mixture can in turn be mixed
with air in all proportions without any risk of explosion. However,
these mixtures are very slow acting compared to pure ethylene
oxide. The humidity of the air or gas mixture is another important
factor to take into consideration. Ethylene oxide sterilization is
most rapid at about 30 to 40 percent relative humidity and
decreases as the relative humidity approaches 100 percent. Highly
desiccated micro-organisms are slow to respond to ethylene oxide
sterilization. Ethylene oxide is a very active chemical (alkylating
agent) and it sometimes alters the characteristics of the processed
material. A note of warning has been sounded, for instance, in the
sterilization of foodstuffs. It has been shown (E. A. Hawk and O.
Mickelsen, Science, vol. 121, no. 3143, 442-444, Mar. 1955) that
various vitamins and amino acids were attacked by ethylene oxide.
More recently a food additive amendment to the Food, Drug and
Cosmetic Act discouraged the use of ethylene oxide due to the
presence of traces of toxic ethylene glycol which is one of the
by-products of the hydrolyzation of this chemical.
When processing certain organic materials (such as plastics) it has
been found that ethylene oxide is often soluble and may remain in
large amount after sterilization. Up to 4 percent ethylene oxide
has been detected by C. R. Philipps after gas sterilization of
rubber. Laboratory personnel have received chemical burns by
donning rubber shoes only 1 hour or so after they were sterilized.
More recently R. B. Roberts (MSR Fourth Quarter, page 3, 1968)
warned that ethylene oxide residues on surgical supplies could harm
medical personnel as well as patients. On rubber gloves, they can
burn the hands; and on tubes carrying blood, they will damage red
blood cells. Endotracheal tubes which are not properly aerated can
cause tracheitis or tissue necrosis. As a result of these
observations it was recommended that surgical plastic devices stand
at least 5 days at room temperature or 8 hours at 120.degree. F
before use. Since already the time requested for ethylene oxide
sterilization is not negligible (for instance a 180 minute cycle at
30.degree.C) an additional long deaeration period often renders
this method very expensive. It precludes anyway the development of
a continuous process for sterile packaging.
Special problems (see D. A. Gunther, J. R. Nelson, G. W. Smith,
Contam. Contr. vol. VIII, No. 8, 9-12, Aug. 1969) are also
encountered in ethylene oxide bulk sterilization of disposable
articles such as catheters, irrigation sets, intravenous kits,
syringes etc. Most of these items are being packaged in clear
plastic film, such as hermetically sealed polyethylene. When a
sealed polyethylene package is placed in the environment of a
permeable sterilizing gas mixture, the gases will permeate the
polyethylene unit they reach an equilibrium. This occurs when the
concentrations of the permeating gases become equal on the inside
and on the outside of the package. Since the residual air within
the package is trapped it also contributes to increase the pressure
inside the package. Thus, when the permeating gases reach
equilibrium, the total pressure in the package may become greater
than the outside pressure. This often results in package "swelling"
or even rupture. To cope with this problem various pressure cycles
are imposed upon the processed load. The pressure decrease is also
programmed to coincide with the pressure decrease within the
package as the permeable gases permeate out during the final stage
(post-diffusion period). This means a lengthy operation which can
last up to 8 hours when including water vaporization time, ethylene
oxide exposure and gas evacuation.
Despite all the above mentioned drawbacks, ethylene oxide
sterilization is the only technique used today at industrial scale
to "batch process" medical and hospital disposables. Other
non-thermal techniques of surface sterilization have been tried at
laboratory scale (particles radiation, electro-magnetic radiations)
but they always were too inefficient (long contact time required),
expensive or delicate to handle for industrial scale processing.
For instance ultraviolet (at 2,650 A, 2,350 A and 2,537 A for
instance) irradiation can be under certain conditions quite
effective to destroy bacteria, vegetative cells or spores. The
energy level required to kill Bacillus Subtilis spores for instance
is said to be around 22,000 microwatt/sec/cm.sup.2. The difficulty
with ultraviolet radiation as a sterilizing agent is that it has a
very low penetrating power and micro-organisms are easily shielded
from it by soil or other materials through which it cannot
penetrate. The presence of agglomerates or "shadow zones" greatly
limits the use of this technique for surface sterilization of odd
shaped devices. In addition certain organic materials and plastics
are quite susceptible (polymerization or molecular degradation) to
high intensity UV irradiation. The same disadvantage exists when
one uses radioactive sources, such as cobalt 60 (gamma radiation)
or Xrays. The energy imparted by electrons, Xrays and gamma rays
results in ionizations (Compton effect) within the absorbed
material. This has a lethal effect on the majority of spores
according to dosage rate, presence of oxygen or protective
compounds, physiological state of the micro organisms, water
content and temperature. To achieve complete sterilization for
instance of Bacillus megaterium spores (A Tallentire, and E. L.
Powers, Rad Res, 20, 270-287, 1963) large doses of energy
(5.10.sup.5 Rad) are needed and this means potential damage to the
irradiated material. More recently the synergistic effect produced
by combining heat and radiation (Contamination Control, 20-22, Feb.
1970) gave some hope of improving operational conditions.
Unfortunately, if the method provides a reduction in irradiation
time requirements (from 40 to 12 hours) at 105.degree. C it does
not seem to give encouraging results at temperatures below
105.degree. C.
It is therefore an object of the present invention to provide a
method to surface sterilize laboratory, medical, dental devices and
heat sensitive disposables in a matter of minutes rather than
hours.
It is also an object of the present invention to surface sterilize
within a short time period at low and medium temperatures within
the 15.degree. to 70.degree. C temperature range.
It is a further object of this invention to quickly "surface
sterilize" heat sensitive instruments and components in a
continuous process, which includes dipping the load of contaminated
objects in an ultrasonic bath synergistically activated by a
sporicidal agent, rinsing it in a second bath with sterile water,
drying it at a temperature below 75.degree.C inside an ultraviolet
tunnel and conveying the sterile material directly to the packaging
machine. All said automatic operations taking place in a germs- and
particles-free "white" room atmosphere.
It is a further object of this invention to continuously
surface-sterilize heat sensitive materials, tools, instruments or
components without leaving an amount of absorbed or dissolved
chemical which could create a toxicity problem when the processed
part is in contact with the human body.
It is a further object of this invention to continuously sterilize
heat sensitive materials in a manner such that none of the
physical, chemical, mechanical or structural characteristics of the
sterilized products will be altered during processing.
Other objects, advantages, features and uses of our invention will
be apparent during the course of the following discussion. To aid
in the understanding of the present invention, the potential
contribution of large amplitude sonic and ultrasonic waves to the
mechanism of sterilization in liquid phase when used alone or in
combination with chemicals such as glutaraldehyde or alkalynized
glutaraldehyde will first be reviewed briefly.
Although a little complex at first sight, the physical action of
sonic or ultrasonic waves can be brought into play in four major
ways; namely, through large variations of pressure, motion, heat
degradation or electrical phenomena. The acoustic energy is
transmitted through the liquid by the back and forth motion of the
molecules along the direction of propagation. This produces
alternate adiabatic compressions and rarefactions, together with
corresponding changes in density and temperature.
In the case of a planar acoustic wave transmitted through a liquid
like water at an intensity of 10 watt/cm.sup.2, one can calculate
that the water molecules will oscillate with a motion amplitude of
the order of 3 microns (assume the emission frequency equal to 20
kHz). The molecular accelerations at the end of the molecular
excursions will be 5,000 times greater than the acceleration due to
gravity and considerable pressure changes (a few atmospheres) will
occur at any given point in the liquid twenty thousand times each
second. Since the pressure is increased and decreased alternately,
it is understandable that during the negative pressure phase a
point may be reached at which the natural cohesive forces of the
liquid will be overcome. Then a new phenomenon known as
"cavitation" takes place. It corresponds to the formation and rapid
collapse of small cavities through the entire liquid. According to
the energy density level the cavities are filled with gas or vapor.
In the latter case, their collapse produces very large amplitude
shock waves (up to several hundred atmospheres) with local
temperature up to a few hundred degrees centigrade or more.
Electrical discharges are also believed to occur during the
collapsing phase, this is called the sonoluminescence effect.
Due primarily to the effects of electrical discharges (ionization),
"hot" points in the liquid, and sharp pressure waves gradients, the
molecular bonds of water will be severed and free radicals OH and H
will then be produced.
Chemically active hydroxyl radicals and hydrogen atoms will be
available in the water solution to trigger several types of
chemical reactions which may lead to bactericidal compounds such as
water peroxide. (See I.E. Elpiner, Ultrasound, pg. 20, Chapter 2,
Consult. Bur. ed. New York 1964). If other chemicals are present in
the water such as glutaraldehyde, other molecular bond breakages
could take place which would favor for instance the combination of
aldehyde radicals with cells amino groups. With carbontetrachloride
one will observe, for instance, the production of free chlorine
(S.P. Liu, Chlorine Release Test for Caviation Activity
Measurements, Journal of Acoustical Society of America, Vol. 38,
No. 5, 817-826, Nov. 1965) and with potassium iodide the liberation
of iodine (D. E. Goldman and G. R. Ringe, Determination of Pressure
Nodes in Liquids, J. Acous. Soc. Am., Vol. 21, 270, 1949). It is
known that alkyl and aryl halides in aqueous suspension, irradiated
at low frequency, are hydrolysed to produce a halide ion and the
corresponding hydroxyl compound or ether (A. E. Crawford,
Ultrasonic Engineering, pg. 212, Chapter 9, London, Butterworths
Sci. Publ. 1955). The production of highly bactericidal compounds
such as ozone can also be the result of low frequency sonic
irradiation of oxygen saturated water. (M. Haissinsky and A.
Mangeot, Nuovo Cimento, 4:5, 1086, 1956). Nitrous acid, nitric acid
and nitrogen oxides can also be detected in small amounts during
the insonation of water saturated with air or nitrogen.
It can be said that low frequency (8 to 300 kHz) high energy
density (higher than 10 watts/liter) acoustic emissions may alone
produce free radicals, atoms, ions or new chemicals with strong
bactericidal or sporicidal powers. Beside the production of new
chemicals or active radicals which could be toxic to most
pathogens, viruses or spores it is important to consider in detail
the other physical mechanisms which may affect the life of
unicellular or multicellular micro-organisms under ultrasonic
irradiation.
Large amplitude sonic and ultrasonic waves, inside the frequency
range previously stated, will considerably modify the ion exchange
processes through the cell membranes. This modification of the
diffusional process through inert or living membranes is well known
in the art. Along these lines there is, for instance, the early
work of J. H. Rees (Mast. Thesis, Mass. Inst. Techn., 1948) on the
influence of low frequency insonation (10 to 30 kHz) on the
dialysis constant. The enhanced membrane diffusion observed during
insonation can be interpreted as the complex result of the
radiation pressure, the acoustic pressure and cavitation on the
motion of individual ions or molecules. Each ion or molecule
receives a supplementary amount of energy in a high intensity
acoustic field, and it "boosts" its level of activity. This could
be, for instance, an extra "push" due to the passage of fast
travelling cavitation shock waves resulting from the collapse of a
resonant bubble. (I. Schmid, Acustica, 9:4, 321-326, 1959). But the
effect of acoustic waves on the membrane structure must also be
carefully considered. The enormous localized pressure waves which
can rip apart metal particles during intense vapourous cavitation
can indeed loosen macromolecular structures, such as the cell walls
of water-borne micro-organisms. By so doing, pressure waves
associated with the acoustic field can change the permeability of
the walls and membranes of living cells. This would explain, for
instance, why low frequency (8 - 300 kHz) high energy density
(above 10 watts/liter) ultrasound waves increase the sensitivity of
micro-organisms to disinfectants. It has been shown, for instance,
a few years ago (I. E. Elpiner, Gigiena I Sanit, USSR, 7:26, 1958)
that the sterilization of aqueous suspensions of E. Coli previously
irradiated at 20-25 kHz requires much lower concentration of
bactericides than the treatment of the same type of unirradiated
suspensions.
One can conclude that ultrasonic irradiation of contaminated
liquids at low frequency, high intensity, and with reasonable
contact time may lead either to the production of compounds which
would be toxic to the micro-organisms in contact with the liquid
phase (through reaction at the active sites) or to cells structure
modifications which will be lethal to the same micro-organisms.
Whatever the micro-organisms destruction mechanism is, ultrasonic
irradiation alone would rarely achieve a hundred percent kill. This
is understandable when one remembers that positive results can be
observed in practice only with huge amount of acoustic energy and
long exposure times (often several days).
It has been found in accordance with one aspect of the present
invention that a combination of liquid borne ultrasonic energy with
the chemical action of a glutaraldehyde solution provides an
extremely fast kill of pathogen bacteria, viruses, vegetative
cells, bacterial spores and spores. Such fast bactericidal and
sporicidal action takes place in a matter of minutes (1 to 30
minutes) thus enabling the continuous treatment of contaminated
parts when they are submerged during the right time period in the
ultrasonically activated solution of glutaraldehyde.
When using batches of hundred disposable syringes artifically
contaminated with Bacillus Subtilis (ATCC 6051) or Clostridium
sporogenes (ATCC 7955) it was found that a 6 minutes contact time
in a 1 percent solution of glutaraldehyde (pH5) at a temperature of
54.degree. C would give 100 percent kill. The ultrasonic bath was
operated at a nominal frequency of 20 kHz while the density of
acoustic energy corresponded to approximately 15 watts per liter.
The average number of micro-organisms per syringe was one million
before treatment. All other things being equal, a higher bath
temperature (70.degree. C) would reduce treatment time to less than
4 minutes.
It was also found that the sporicidal effect remained the same when
pH varied between 2 and 7 at the above mentioned temperatures, all
other experimental conditions being identical.
It was also found that the same bactericidal and sporicidal
activity was displayed for ultrasonically irradiated solutions (1
and 2 percent) buffered by suitable alkalinating agents to a pH of
7.5 to 8.5. In this latter case it was discovered that under the
experimental conditions hereabove defined it was possible to
decrease the 100 percent kill contact time down to 8 minutes at a
temperature as low as 25.degree. C.
It was also found that higher ultrasonic frequencies (250 kHz for
instance) could also provide total destruction of spores on the
contaminated syringes with a slightly longer exposure (30 minutes
at 25.degree. C) time in a 2 percent solution of alkalinized
glutaraldehyde. In all cases the bactericidal and sporicidal
mechanisms seem to be the result of a synergistic phenomenon
between the chemical and ultrasonic energy since the killing effect
of the combined agents is always greater than the sum of the two
agents acting separately.
It was also found that the synergistic bactericidal and sporicidal
activity can be accelerated by adding traces of dimethyl sulfoxide
to the glutaraldehyde solution in the ultrasonic tank. For
instance, as previously mentioned, a batch of 100 disposable
syringes artifically contaminated with Bacillus Subtilis (ATCC
6051) were sterilized after a 6 minutes contact in a 1 percent
solution of glutaraldehyde (pH5) at 54.degree. C. The same batch of
syringes under identical conditions were sterilized in only 3
minutes when adding between 1 and 10 parts per million of
dimethylsulfoxide to the activated solution in the ultrasonic
tank.
This important time reduction could be due to a faster penetration
of activated chemical molecules or radicals through the spores
cortex. The above described experiments took place at a nominal
frequency of 20 kHz while the average density of acoustic energy in
the tank oscillated between 15 and 20 watts per litter.
It was also found that the concentration of glutaraldehyde could be
greatly decreased when operating at higher temperatures in the
60.degree. to 70.degree. C range. For instance, at 70.degree.C a
0.1 percent concentration of glutaraldehyde (pH 4.7) enables the
complete sterilization of contaminated disposable syringes in 5 to
6 minutes, thus providing results equal to those obtained with a 1
percent glutaraldehyde solution at 54.degree.C. In all these
experiments, the acoustic energy density in the tank remained
constant (around 15 to 20 watts/liter). The nominal frequency was
kept at 20 kHz.
The method of surface sterilization, object of the present
invention, consists of a three step system. The first step consists
of dipping the contaminated objects in an ultrasonic bath heated at
a temperature comprised between 25.degree. and 70.degree.C and
filled with a glutaraldehyde solution (maximum concentration 5
percent). The objects to be sterilized are contained in a tray (or
trays) made of perforated metal or plastic. Said tray is submerged
in the activated ultrasonic solution and moves slowly under the
influence of a "carrier-conveyor" system. The contact time into the
activated ultrasonic solution varies according to the nature of the
contaminant and the bath temperature, but it is in general
comprised between 2 and 30 minutes.
When the irradiated tray leaves the ultrasonic tank which contains
the glutaraldehyde solution traces of this chemical may remain
absorbed on the wet processed parts. From analytical data
(spectroscopy) the glutaraldehyde content of the sterilized parts
is always less than one thousandth (1/1,000) of the original amount
present in the processing tank. This means a quantity far below any
potentially dangerous toxicity level. However, to decrease this
content down to a few gammas (parts per million) a second
ultrasonic tank is used with sterile water into which the tray is
dipped during a few minutes at a temperature comprised between
54.degree. and 70.degree.C. This second ultrasonic tank which
performs a thorough washing operation of any remaining traces of
glutaraldehyde is the second step of the continuous sterilization
process object of the present invention. The last step consists of
a drying operation (a few minutes) into a medium temperature
tunnel. Said tunnel contains several powerful ultraviolet lamps
(intensity 10 watts/square foot) to maintain sterile surface
conditions while the warm stream of filtered air is injected in the
tunnel countercurrent to the direction of the moving tray (or
trays). The filtered air temperature is calculated to maintain at
all times a maximum temperature in the 54.degree. to 70.degree. C
range inside the processed solid parts. Residence time (a few
minutes) in the tunnel is the same as the exposure time in the
ultrasonically activated solution tank and in the following washing
tank.
FIG. 1 is a vertical cross-sectional side view of the three
apparatuses (synergistic bath, cleaning tank and dryer) which are
needed to apply the method object of the invention.
FIG. 2 is a vertical cross-sectional front view of the dryer-oven
taken along the line 2--2 as seen in FIG. 1.
As can be seen in FIG. 1, the system to continuously sterilize heat
sensitive parts consists of an ultrasonic tank 3 which contains the
sterilizing agents, said ultrasonic tank being followed by a second
ultrasonic tank 4 which rinses and eliminates most of the chemicals
absorbed on the processed material, said ultrasonic rinsing tank
being followed by a drying tunnel or oven 5 equipped with a
sporicidal source (ultraviolet lamps, microwave source,
radiant.gamma. or X rays source).
The heat sensitive material 6 to be processed is placed into trays
of perforated metal or plastic baskets 7 which are suspended
through a hook 8 to a standard moving chain-wheel device 9 guided
by a rail support 10. The latter is designed in such a way that the
basket will be submerged at a few inches distance of the liquid/air
interface when the basket enters the areas above the ultrasonic
tanks 3 and 4.
The ultrasonic tanks 3 and 4 are in general of the same type and
they have the same dimensions to insure identical contact time for
the processed material in the liquid phases. The ultrasonic tank
will consist for instance of a stainless steel parallel-epipedic
tank 11 whose lateral walls (one or several of them according to
the type of operation) contain a heating element 12 (electrical
resistance, infrared, microwave, or dielectric, for instance. To
the bottom of the tank are fastened one or several standard
electroacoustic transducers 13 (piezo ceramic, ferrite or
magnetostrictive types) which irradiate in and upward manner and
create a high intensity ultrasonic field 14. To successfully apply
the process object of the present invention, the acoustic energy
density in the two tanks 3 and 4 must be greater than ten watts of
irradiated acoustic energy per liter.
The frequency of emission of the transducer elements in the first
tank 3 must also be comprised between 8 kHz and 900 kHz while the
frequency range in the rinsing tank 4 is restricted to the 8 kHz to
300 kHz region. Also located in the lower section below each tank
bottom is a power-generator G to drive the transducers array with
associated cooling and automatic frequency tuning or impedance
matching devices. The standard power generator could be packaged
separately and placed at a remote location since this will not
affect the proper functioning of the transducers. As shown in FIG.
1, the ultrasonic generator is activated from the main line
alternative current (120 or 220 volts, 60 cycles) through an
electrical connector 15. Each ultrasonic tank is equipped with a
draining-valve system arrangement 16. The first ultrasonic tank 3
is provided with an opening 17 which enables introducing fresh
sporicidal agent into the tank. An electric pump 18 introduces
automatically the active chemicals at the right dosage and
concentration into the filtered water main line 19. In the first
tank 3, the active cavitating solution will contain, for instance,
a solution 20 of glutaraldehyde whose concentration will be
comprised between 0.05 and 5 percent volume. Optionally and
according to the type of micro-organisms to be destroyed, a certain
amount of dimethylsulfoxide could be added (concentration lower
than 2 percent in volume). The temperature in the first tank 3
could vary between 15.degree. and 70.degree. C according to
solution pH and to the type of irradiated micro-organisms. In most
current applications for spores destruction, the first tank is
operated around 54.degree. C. The speed of the basket conveyor
system is adjusted to allow an average contact time in the
sterilizing solution comprised between 2 and 30 minutes according
to the type of application. The second ultrasonic tank 4 whose
function is to rinse away most of the chemicals absorbed on the
sterilized parts or components originally contains germ free water
21 with small amount of (less that 0.1 percent) surface active
agents such as cationic surface active agents or quaternary
ammonium salts. The second ultrasonic tank is always operated at a
temperature comprised between 45.degree. and 70.degree. C which
corresponds to maximum cavitation activity (L. D. Rosenberg,
Ultrasonic News, 16 -20, 4th quarter 1960).
After the sterilizing and rinsing operations, the baskets which
contain the sterile equipment enter into the drying tunnel 5. The
length of the drying tunnel is the same as the length of each one
of the two ultrasonic tanks 3 and 4, thus providing the same
contact time in the liquids and the dryer. The dryer tunnel 5, as
shown in FIG. 1, is only one of the possible embodiments of the
type of dryer apparatus to be used in our invention. As shown in
FIG. 2, the dryer tunnel in this example is of circular shape with
a slit longitudinal opening 22 at the top to allow the continuous
motion of the hooks 8 to which the basket 7 are attached. Three
openings 23 at the bottom of the tunnel are provided to introduce
warm filtered air into the tunnel. Warm air could be conveyed
through a piping system communicating with a central source of warm
filtered air, or it could be provided by means of individual
blowers 24 equipped with an internal heating element 25. The air
could be drawn directly from the processing room and filtered at
the blower inlet 26. The temperature inside the dryer tunnel is
adjusted for each application (taking into account convection,
conduction and radiation thermal effects) in such a manner that the
maximum temperature of the parts at the time they leave the tunnel
is always below 70.degree. to 75.degree. C. This objective can be
achieved through the use of various forms of thermal energy such as
infrared, dielectric or electromagnetic (microwaves) heating. Since
the baskets which enter the dryer-tunnel 5 are sterile and contain
sterile material, it is necessary to sterilize the tunnel
atmosphere to avoid the deposition of airborne bacteria or spores.
To insure such a protection during the final drying phase we
already mentioned that we use warm filtered air. As a supplementary
protection, the dryer tunnel is equipped with powerful ultraviolet
lamps. In FIGS. 1 and 2, three such ultraviolet lamps 27 are shown
spaced each at 120.degree. from the other. These ultraviolet lamps
could, for instance, be of the Hanovia type 94A-1 which emits 7.3
watts of UV energy at the 2,537 A wave length. They will insure
complete destruction of airborne bacteria and spores during
processing time in the tunnel. A transformer 28 is shown connected
to one of the ultraviolet lamps. The basket 29 which leaves the
tunnel, contains dry, sterilized parts or components with traces of
chemicals far below toxicity level. At no time does the temperature
of parts reach a level higher than 70.degree. - 75.degree. C. Such
parts and components are ready to be fed manually or automatically
to a packaging machine under sterile conditions.
Also not shown in FIGS. 1 and 2, but obvious to a person skilled in
the art, the entire system described in FIGS. 1 and 2 is enclosed
inside a positive pressure clean or white room equipped with high
retention ULTRA HEPA filter modules. Horizontal laminar flow clean
rooms (class 100) of the type manufactured by Agnew-Higgins could
be used to operate the continuous sterilization system hereabove
described. With a view to increasing the efficiency of the white
room for bacteria and spores control, additional mobile LETHERAY
high intensity UV air sterilizers could be added inside the white
room specially in the vicinity of transfer points i.e., between
tank 4 and tunnel 5, or between tunnel 5 exit and the packaging
sealing machine).
Without departing from the frame work of the present invention, it
must be well understood that, according to the desired results, the
present invention can be applied to variable load sizes of heat
sensitive materials at different temperatures within the specified
15.degree. - 70.degree. C range or at multiple gas pressures above
the irradiated liquid, and that, still without departing from the
scope of the invention, the structural details of the described
apparatuses, the dimensions and the shapes of their members (such
as the ultrasonic tank configuration) and their arrangement (the
position of ultraviolet tubes inside the dryer tunnel, for
instance) may be modified, and that certain members may be replaced
by other equivalent means (electrical heating elements replaced,
for instance by infrared radiant panels).
The teachings of the invention may be practiced within the
following parameters:
First Step:
contact time in the sterilizing solution: 2 to 30 minutes
Glutaraldehyde concentration: 0.05 to 5 percent in volume
Glutaraldehyde solution pH: 2 to 8.5
Dimethylsulfoxide concentration: less than 2 percent in volume
Acoustic energy density in liquid: higher than 10 watts/liter
Emission Frequency: 8 to 900 kHz
Temperature range in liquid: 15.degree. to 70.degree. C
Second Step:
Contact time in rinsing solution: 2 to 30 minutes
Concentration of surface active agents less than 0.1 percent in
volume
Acoustic energy density in liquid: higher than 10 watts/liter
Emission Frequency: 8 to 300 kHz
Temperature range in liquid: 45.degree. to 70.degree. C
Third Step:
Contact time in dryer tunnel: 2 to 30 minutes
Temperature inside tunnel: adjusted to a maximum of 70.degree. to
75.degree. C in the processed material leaving the dryer
* * * * *