Note: Descriptions are shown in the official language in which they were submitted.
Yal
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Method of Removing Mold From Plastic Bottles and Mold
Removing Additive
Backaround of the Invention
In many countries, bottles such as soft drink bottles are
repeatedly cleaned and reused. The used bottles are passed
through a bottle-washing apparatus which cleans the bottle,
permitting it to be refilled and reused. Both plastic and
glass bottles are subject to reuse.
Due to the physical characteristics of glass versus plastic
bottles, the two are treated somewhat differently. Glass
bottles are subjected to a highly alkaline wash containing
2-411 sodium hydroxide at a temperature of generally 70 C or
higher. This is quite effective in removing most soils.
One soil which is particularly difficult to remove is mold.
Mold tightly adheres to the surface of bottles, both plastic
and glass, and is relatively difficult to remove. Mold can
be removed from glass bottles by simply operating at
temperatures above 60 C, which is typically done. But with
plastic containers, this is not possible. At temperatures
higher than 60 C, most plastic containers will shrink.
Further, higher temperatures and higher alkalinity promote
stress cracking which is unsightly and eventually can cause
the bottle to leak or break open. Certain surfactants also
promote stress cracking. Other harsh chemicals such as
bleaches will remove mold. But these would corrode the
equipment and therefore are unacceptable. EDTA is currently
used to enhance mold removal. However, this is not always
totally effective.
Compounding the problem of mold removal is the fact that its
mechanism of attachment to a surface is not completely
understood. It is believed that a protein and/or a
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glycoprotein is involved in the attachment, but the exact
chemical nature of this attachment, as well as the physical
nature of this attachment, are not completely understood.
Suuunary of the Invention
It is an object of the present invention to provide an
additive for a bottle-washing apparatus which effectively
removes mold from the surface of plastic articles such as
bottles without destroying the plastic article.
More particularly, the present invention is premised upon the
realization that an alkaline wash solution which includes an
effective amount of a complex phosphate, in combination with
a suitable surfactant, either nonionic or anionic, will
effectively remove mold from plastic surfaces at temperatures
less than 60 C. This, in turn, permits the removal of mold
from the plastic surface without destruction of the plastic
container.
More particularly, the present invention is premised on the
realization that the removal of mold is enhanced by the
further addition of an effective amount of a phosphonate
which is also useful in the cleaning of the bottle. In a
preferred embodiment, the bottle-washing solution will also
include a chelating agent such as sodium gluconate, sodium
glucoheptonate, or sodium boroheptonate. Although gluconates
are considered to be less effective at milder alkalinities,
it provides a significant improvement in mold removal in this
system. These combined components provide an extremely
effective bottle-washing solution which outperforms
currently-used bottle washing formulations in the removal of
mold from plastic surfaces. Further, the formulation of the
present invention, even with the added surfactant, does not
further promote stress cracking relative to commercially
available formulations. Although formulated primarily for
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plastic containers, this formulation will also assist in
removal of mold from glass containers as well.
The objects and advantages of the present invention will be
further appreciated in light of the following detailed
description and drawing description in which:
Brief Description of Drawing
The Figure is a graph showing the test results of Example 2
demonstrating mold removal from bottles in a commercial
bottle washing apparatus.
Detailed Description
The present invention is a method and solution for cleaning
reusable plastic bottles and is particularly directed at mold
removal. The reusable plastic bottles cleaned according to
the present invention can be formed from many different
plastics. Most reusable plastic bottles are currently formed
from polyesters such as polyethylene terephthalate,
polybutylene terephthalate, polyethylene naphthalate, and
polycarbonate. Basically any reusable plastic bottle which
can be subjected to an alkaline wash is suitable for use in
the present invention.
By way of background, bottle washing apparatuses generally
include three or four sections. The bottles are introduced
into the machine and supported throughout the washing process
by individual holders or pockets. Bottles are initially
directed to a prerinse section which is designed to remove
large particles and labels. In this section water and
residuals from the cleaning process are directed at the
bottles as they are introduced into the machine.
Next, the bottles are conveyed to a cleaning or soaking
section where they are soaked in a caustic solution at an
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elevated temperature, generally no higher than 60 C for
plastic bottles such as PET bottles. After 7 to about 30
minutes (generally 9-11 minutes) in the soaking section the
bottles are taken to a warm rinse and then to a final potable
water rinse. The final rinse is then reused for the
subsequent initial prerinse.
The cleaning or soaking solution is a caustic solution.
Generally this contains 0.5 to 5.00, and preferably 1.0 to
3.0%, sodium hydroxide for PET containers. This acts to clean
the bottles and dissolve metals such as metal foils of the
label and the closure rings. This caustic solution also, in
combination with temperature and contact time, renders the
bottles commercially sterile. However, at caustic
concentrations greater than 3% stress cracking of the plastic
bottles is excessive.
In addition to the caustic, the soaking solution will include
an additive to enhance mold removal. The mold-removing
additive is a combination of complex phosphates, surfactants,
and preferably chelating agents, particularly gluconates and
related agents, as well as threshold water conditioners such
as the phosphonates. The additive itself is formed in a
concentrated stable aqueous solution or a premixed powder
which is formulated with the above components in a proportion
to provide for effective use concentration of all the
components when added.
Generally the soaking solution in the bottle washing
apparatus, i.e., at use concentration, should have 1000 to
2500 ppm of the complex phosphates. Complex phosphates
include the common polyphosphates. Particular phosphates
which can be employed include sodium tripolyphosphate,
potassium tripolyphosphate, sodium potassium
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tripolyphosphate, tetrapotassium, pyrophosphate, and
tetrasodium pyrophosphate, as well as others.
5
In addition to the complex phosphate, the wash solution
must include an effective amount of a surfactant, either an
anionic surfactant, a nonionic surfactant, an amphoteric
surfactant, or a mixture thereof. It is important that the
surfactants be selected so that they do not promote stress
cracking of the plastic bottles. The most effective
nonionic surfactants are the polyalkoxylated fatty alcohols
and the polyethoxylated straight chain alcohols. These are
also preferred since they contribute to foam control.
Commercially available alkoxylated alcohol surfactants
include Makon" NF 12, Plurafac" LF 221, Plurafac- LF 223,
PlurafacTM LF 431, PolytergentTa SLF18, and TritonT" DF12, a
modified polyethoxylated alcohol. Other suitable nonionics
include alkyl polyglycosides such as TritonT" BG10, Triton"
CGIO, and EO - P0 block copolymers such as IndustrolT" N-3.
Suitable anionics include sodium C14 - C16 alpha olef in
sulfonates such as BiotergeTM AS-40, alkyl aryl sulfonates,
carboxylated alcohols such as PolytergentTm CSI, alkali
metal salts of phosphate esters such as TritonT" H66, alkali
metal alkanoates such as Monatrope" 1250, fatty alcohol
polyglycol ether carboxylic acids such as AkypoTy LF4,
dioctylsulfosuccinate such as MonawetT" M070, modified
ethoxylates such as MonaTm NF 10 and Triton- DF 20, and
alkali metal xylene sulfonates such as EltesolT" PX93.
Suitable amphoterics include alkyl and alkyl alkoxy
iminodiproprionates such as lauryl iminodiproprionate and
isodecyloxypropyl iminodiproprionate sold under the
trademark Alkali surfactant.
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Generally 200-1000 ppm surfactant will be used in the soaking
solution. The upper limit is determined by economics.
Concentrations greater than 1000 ppm provide little added
benefit. A blend of surfactants may be preferred to reduce
stress cracking and improve efficiency.
In addition to the phosphate and surfactant, the formulation
optionally includes 500-1000 ppm of an organic phosphonate.
Typically used organophosphonates include aminotrimethylene
phosphonic acid, 1-hydroxyethylene (1,1 diphosphonic acid),
hexamethylenediaminetetramethylene phosphonic acid,
diethylenetriaminepentamethylene phosphonic acid, and
phosphonobutanetricarboxylic acid. These assist not only in
mold removal, but also carry over to the rinse section of the
bottle washer to provide threshold water conditioning in that
section, reducing scale.
Finally, the present invention can also include one or more
chelating agents. Suitable chelating agents are the
gluconates and comparable compositions. Particular chelating
agents include sodium gluconate or gluconic acid, sodium
glucoheptonate, and sodium boroheptonate. These should be
present in the wash solution at a concentration of from 500
ppm to 2000 ppm.
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The concentrated formulation can be stated in terms of a
ratio of parts by weight actives. The mold removing
composition of the present invention will generally include
from 10 to 25 parts by weight of the complex phosphate, 2 to
10 parts by weight of the surfactant, and optionally but
preferably 5 to 10 parts by weight of the phosphonate, and 5
to 20 parts by weight of the chelating agent, which is
preferably sodium gluconate. Said surfactant is desirably
either an anionic surfactant selected from alkylaryl
sulfonates, C14-C16 alpha olefin sulfonates and alkyl
sulfosuccinates, or a nonionic surfactant selected from
polyalkoxylated fatty alcohols and polyethoxylated straight
chain alcohols. Most preferred surfactant for use in said
composition is iminodipropionate. If said composition is
formulated as a liquid, it will also include an amount of
caustic liquid to maintain an alkaline pH. The balance of the
product would then be water. Generally, it is desirable to
have as high an actives content as possible. With the present
formulation, an actives content of 40o to 50o can be
achieved.
Table 1 shows three different liquid formulations of the
present invention. With liquid formulations, each of the
individual components is simply combined with water. The
order of addition is not significant. These are blended until
a stable solution is formed.
1 I
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Table 1
Raw Materials Formula 1 Formula 2 Formula 3
Soft Water 50.87 51.07 53.24
Sodium Gluconate 7.0 7.0 7.0
DequestT" 2000 3.0 3.0 3.0
Caustic Liquid 50% 2.0 2.0 2.0
KTPP Liquid 50 27.13 27.13 27.13
PlurafacTM LF221 1.0 0.32
(Nonionic 95%) (0.95) (0.30)
PlurafacTM LF223 1.0 0.31
(Nonionic 98%) (0.98) (0.30)
TritonT" BG 10
(Nonionic 70%)
AkypoT" LF4 (Anionic 2.0 2.0 2.0
900) (1.8) (1.8) (1.8)
EltesolT" PX93 7.0 6.8 5.0
An amount of the concentrated composition is added to the
soaking solution to provide an acceptable level of actives in
30 the soaking solution. Generally, the use concentration will
be 0.5 to 1.501 with 1.25o preferred.
The present invention is illustrated by way of the following
non-limiting examples showing preferred methods of practicing
35 the invention.
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EXAMPLE 1
In order to test the bottle washing composition of the
present invention, and to compare this with commercially-
available additives, actual consumer bottles containing mold
colonies were collected. Approximately 50% of the moldy
bottles had greater than 10 mold colonies. These were then
passed through a bottle washing apparatus under identical
conditions with different standard soaking solutions and mold
removal results were compared. Initially, 2.8% sodium
hydroxide was used by itself. This cleaned 360 of the
bottles, but left 260 of the bottles with greater than 10
mold colonies. Two commercially available products were
tested, each with 2.801 NaOH and a commercially available
additive. These cleaned 46o and 54% of the bottles,
respectively, both leaving 24% with greater than 10 mold
colonies. 0.25% w/v sodium tripolyphosphate (1720 ppm) was
then added to the solution containing the commercially
available product. This, in turn, cleaned 56% of the bottles
and left 12% with greater than 10 mold colonies. To this
solution was then added 0.02% w/v surfactant (200 ppm
alkoxylated alcohol). With this combined solution of sodium
hydroxide, sodium tripolyphosphate and surfactant, 60% of the
bottles were cleaned leaving only 6% of the bottles with
greater than 10 mold colonies.
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EXAMPLE 2
In a second study, consumer bottles containing mold colonies
were collected and separated into 7 groups. The Figure is a
graph depicting the seven groups. The first group was not
5 washed and contained 23o bottles with greater than 10 mold
colonies (negative control). A second group was sent through
a bottle washing solution with 2.8% sodium hydroxide
(standard control). This cleaned 42% of the bottles and left
23% with greater than 10 mold colonies. Two commercially
10 available products listed at RPB and MR were again tested
with 2.8% NaOH. These cleaned 51% and 46% of the bottles,
respectively, leaving greater than 10 mold colonies in 270
and 18%, respectively. Formula 3, listed as "X" in the
Figure, was then added to the sodium hydroxide at 0.4%
concentration. This resulted in 46a of the bottles being
cleaned with 17a of the bottles left with greater than 10
mold colonies. The concentration was then increased to 0.80,
resulting in 51% of the bottles being cleaned and 21%
containing more than 10 mold colonies. Finally, at 1.250
concentration, 65% of the bottles were cleaned, with 13% of
the bottles having more than 10 mold counts.
These tests were all relatively severe and they were not
expected to achieve 100o cleaning or 100% mold removal. The
results shown by Formula 3 were considered significantly
better than commercially available products, particularly at
the 1.25% concentration level.
These test results indicate that the sodium tripolyphosphate,
in combination with the nonionic surfactant, is particularly
effective at removing mold, and that the Formula 3 is a
significant improvement over the combination of sodium
tripolyphosphate and nonionic surfactant by itself. Further,
test results indicated that the addition of Formula 3, in
spite of the use of the surfactant, promoted less stress
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cracking than other commercial additives. Thus, the present
invention provides better mold removal and promotes less
stress cracking than commercially available products.
Exemplary dry formulations which are useful in assisting mold
removal are listed below, as well as an indication of mold
removal efficacy in laboratory studies:
POWDERS
Material: Weight Percent
STPP, granular 45.00
SKTP, granular 63.00
Sodium gluconate 25.00 25.00
Dequest 2016D 6.00 6.00
Makon NF 12 6.00
Soda Ash 15.00
Poly Tergent SLF-18 6.00
Poly Tergent CS-1 3.00
Mold Removal 90-10001 10001
W/w additives 0.40 0.401
NaOH 2.80a 1.50o
Other exemplary liquid formulations are listed below.
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LIQUIDS
Material: ----------------- Weight Percent----------------
Water, soft 74.75 74.50 68.50 49.75 68.10 70.30 70.50 69.20
KTPP, 60% 24.00 24.00 30.00 40.00
solution
Sodium 7.00 7.00 7.0 5.0
gluconate
Triton DF12 0.25 0.25
Triton DF 16 0.25
Alkali 1.00 1.25 1.25
Surfactant
Sodium Xylene 10.00
Sulfonate,
40% solution
Mona NF 10 0.25
Inustrol N-3 1.50
NaOH, 50% 2.00 2.00 2.0 4.0
liquor
Dequest 2000 3.00 3.00 3.0 3.30
SKTP, 12.00 12.00 12.00 12.50
granular
PolyTergent 1.40 2.00 1.00
SLF-18
PolyTergent 3.00 2.00 3.00
CS-1
Makon NF-12
Monatrope
1250
Alkenyl 3.40 2.30 3.50 2.00
Carboxy
Sulfonate
Use at t v/v 1.70 1.70 1.40 1.00 0.40 1.00 0.40 1.50
% mold 90- 100 100 100 90-
removal 100 100
% NaOH 2.80 1.5 1.50 1.50
Each of these significatly enhance mold removal in an
alkaline bottle washing solution.
