Technical Field
[0001] This invention relates to a method of cleaning a substrate. It particularly relates
to a method of cleaning fabric, especially for removal of stain from fabric.
[0002] The invention has been developed primarily for method of cleaning fabrics and will
be described hereinafter with reference to this application. However, it will be appreciated
that the invention is not limited to this particular field of use.
Background and Prior Art
[0003] Stains are localized soils on the fabrics that typically stand out due to colour
and appearance that is distinct from the rest of the fabric. One of the commonest
form of stains are foodstains, generally caused by accidental spilling of food materials
or by brushing of clothing items like necktie against a food item, or by contact of
food-laden cutlery and/or hands with an item of clothing.
[0004] Food stains are typically due to condiments like chilli or turmeric and food accompaniments
like tomato ketchup and mustard sauce etc. Food materials generally contain chromophoric
materials such as curcumin, carotenoids (such as lycopene, β-carotene, and oleoresin)
and the like, that give the food stains a characteristic bright colour. In most cases,
food materials also include oily or fatty materials making it more difficult to wash
the foodstains off with water. For example, pickles used in Asian eating habits, unlike
the ones used in European or American pickles, typically contain oil, chilli powder
and turmeric, and a layer of oil with bright yellow or reddish colour can be typically
seen floating on top. There is also a high likelihood of the area stained with food
material developing microbial contamination and/or unpleasant odour.
[0005] Often, the foodstains occur when the user does not have time or facility to clean,
i.e. during traveling, during business meetings or during working hours. Even if there
is time or facility to clean, the garment needs to be removed in order to clean the
stain effectively, causing inconvenience.
[0006] Conventional methods of cleaning with detergents, soaps and the like are relatively
less effective in removing food stains. Further, it is inconvenient and wasteful to
clean entire garment which is otherwise clean except for a small stained area.
[0007] Therefore, approaches for localized cleaning of stains or spot cleaning have been
explored in the past. Cleaning with bleaches or other oxidizing agents, though relatively
easy and effective, is likely to cause damage to fabrics and/or hands.
[0008] The approach of using solvents such as acetone or chlorinated solvents such as perchloroethylene
is fraught with safety and environmental concerns.
[0009] Method of removal of stains from a surface by contacting the surface with photocatalytic
materials followed by exposure to ultraviolet, visible or infrared irradiations have
therefore been explored in the past.
US20050227557 A1 (Li,
2005) discloses a method of making fabric with a photocatalyst, and in particular a manufacturing
method for applying the photocatalyst to a fabric, so that the fabric has functions
of sterilizing, deodorizing, self-cleaning, and anti-mildew when exposed to light.
It discloses a method of making fabric with photocatalyst comprising the following
steps. A length of fabric is cleansed with a water solution, and the solution on the
fabric is dehydrated to eliminate miscellaneous articles. A photocatalyst solution
comprising titania powder, acetone, resin and water is applied to the fabric and surplus
photocatalyst solution is eliminated, and the fabric is dried to solidify the photocatalyst
on the fabric.
[0010] This method requires use of organic solvents like acetone and binders like resins
in the photocatalyst solution for even application of the titania powder. Further,
the photocatalyst solution contains about 75-96.9 % water by weight, which must be
dried, a step which requires energy and time.
[0011] It is also known to use photosensitizers in combination with photocatalyst in cleaning
compositions.
[0012] US7141125 (Reckitt Benckiser,
2006) discloses a photocatalytic composition for cleaning including a photocatalytic material
and a photosensitizer, and a method of cleaning by applying a photocatalytic material
and a photosensitizer at a locus, for example on a surface. The residue combats soils
and/or undesired micro-organisms at the locus. The photocatalytic material is peroxo
modified titania, preferably in its anatase form, or peroxo modified titanic acid,
or a mixture thereof. The compositions are preferably alkaline.
[0013] The prior art methods using photocatalyst are relatively slow as these involve cleaning
compositions comprising a relatively large amount of water which requires relatively
long time for drying. In addition, such compositions comprising relatively large amount
of water, if applied to a fabric that is being worn by a user, cause unpleasant and
inconvenient wet sensation, besides sometime resulting into unwarranted spreading
of stains to previously unstained portions of the fabric. Thus there is an unfulfilled
need for a method for removing stain from a garment whilst the garment is being worn
by the user. There is a further need for a method that is relatively quick as compared
to prior art methods.
Objects of the Invention
[0014] It is an object of the present invention to overcome or ameliorate at least one of
the disadvantages of the prior art, or to provide a useful alternative.
[0015] One of the objects of the present invention is to provide a relatively fast method
of cleaning a substrate.
[0016] Another object of the present invention is to provide a method of cleaning a fabric.
[0017] Yet another object of the present invention is to provide a method of removing stains
from the fabric.
[0018] Present inventors have surprisingly found that contacting a substrate with fatty
acid and exposing the substrate to radiation results into faster and more convenient
cleaning of the substrate.
Summary of the Invention
[0019] According to the present invention, there is provided a method for cleaning a localized
stain from the fabric comprising the steps of:
- a) contacting at least 10 µg of C8-C30 fatty acid per cm2 area of the substrate, and;
- b) exposing the substrate to a radiation in ultraviolet, visible or infrared spectrum.
[0020] According to another aspect of the present invention, there is provided a cleaning
composition comprising from 70 to 99.99% by weight C8-C30 fatty acid and from 0.01
to 10% by weight a photocatalyst.
Detailed Description of the Invention
[0021] According to the present invention, there is provided a method for cleaning a substrate
comprising the steps of:
a. contacting at least 10 µg of C8-C30 fatty acid per cm2 area of the substrate, and;
b. exposing the substrate to a radiation in ultraviolet, visible or infrared spectrum.
Substrate
[0022] The substrate that can be cleaned using the method of the present invention includes
a fabric as well as hard surface such as metal, plastic, glass and the like. The substrate
is preferably fabric, more preferably a localized stained area of the fabric. When
the method is used for cleaning localized stained area from a fabric, it is not necessary
to contact the entire fabric with the fatty acid.
[0023] The term "area" as used herein means the apparent surface area of substrate that
is in contact with the fatty acid. For example, a swatch of fabric of square shape
with side equal to 10 cm has area of 100 cm
2.
Fatty acid
[0024] According to the present invention, fatty acid of chain length from 8 to 30, preferably
from 10 to 22, and more preferably from 12 to 18 is contacted with the substrate.
[0025] The amount of the fatty acid contacted with the substrate is at least 10 µg per cm
2 area of the substrate.
[0026] The amount of the fatty acid is preferably from 10 to 5000 µg, more preferably from
40 to 3000 µg, and most preferably from 40 to 1000 µg per cm
2 area of the substrate contacted.
[0027] The fatty acid can be saturated or unsaturated. However, unsaturated fatty acid is
preferred. Preferably, the iodine value of fatty acid is greater than 30, more preferably
greater than 60, most preferably greater than 90.
[0028] Fatty acid can be in a solid or liquid form. It is preferred that the fatty acid
used in the process of the present invention is liquid at room temperature.
[0029] The melting point of the fatty acid is preferably greater than 25 °C, more preferably
greater than 20 °C and most preferably greater than 10 °C.
[0030] When a solid fatty acid is used, it is preferably to mix it with a non-aqueous liquid
carrier. Suitable non-aqueous liquid carrier includes vegetable oil and C6-C10 alkanes.
Photocatalyst
[0031] The method of cleaning preferably comprises a step of contacting from 0.01 to 1 µg
photocatalyst per cm
2 area of the substrate. The amount of photocatalyst is preferably from 0.01 to 0.1
µg, more preferably from 0.01 to 0.04µg per cm
2 area of the substrate.
[0032] The step of contacting the substrate with the photocatalyst is preferably concurrent
with the step of contacting the substrate with C8-C24 fatty acid. It is further preferred
that the fatty acid and the photocatalyst are mixed together prior to contacting with
the substrate.
[0033] The photocatalyst is preferably selected from titanium dioxide, zinc oxide, stannic
oxide, ferric oxide, tungsten trioxide, cadmium sulphide, cadmium selenide, zinc sulphide,
or mixtures thereof.
[0034] It is particularly preferred that the photocatalyst is titanium dioxide. Titanium
dioxide exists in anatase, rutile and brookite crystalline forms, and any one of the
crystalline form of titanium dioxide can be used in the method of the present invention.
It is also possible to use a mixture of titanium dioxide of various crystalline forms.
It is particularly preferred that titanium dioxide is of anatase form.
Photosensitizer
[0035] The process of the present invention preferably comprises a step of contacting 0.005
to 0.1 µg photosensitizer per cm
2 area of the substrate. The amount of photosensitizer is preferably from 0.005 to
0.05 µg, more preferably from 0.005 to 0.02 µg per cm
2 area of the substrate.
[0036] The step of contacting the substrate with the photosensitizer is preferably concurrent
with the step of contacting the substrate with the photocatalyst. The photocatalyst,
the photosensitizer and the fatty acid are preferably mixed together prior to contacting
with the substrate.
[0037] The term photosensitizer as used herein means a chemical compound that readily undergoes
photoexcitation and then transfers its energy to other molecules, thus making the
reaction mixture more sensitive to light. Any photosensitizer can be used in the present
invention. Some non-limiting examples of photosensitizer include transition metal
complexes (like ruthenium complexes), porphyrins, phthalocyanines, coumarin, carboxylated
derivatives of anthracene, dyes and carbonyl compounds. It is particularly preferred
that the photosensitizer is selected from porphyrin, methylene blue, Rose Bengal or
benzophenone.
Water
[0038] Preferably, amount of water in contact with the substrate during the process is less
than 20 mg water per cm
2 area of the substrate. It is particularly preferred that the substrate is not contacted
with water during the process. When the substrate is a fabric, the weight ratio of
water to fabric is preferably less than 5, more preferably less than 2, and most preferably
less than 1. It is particularly preferred that the fabric is not contacted with water
during the process. The benefit of not contacting the fabric with water is that the
process can be used to remove a stain from a garment that is being worn by a user,
without causing unpleasant and inconvenient wet sensation, or without resulting into
unwarranted spreading of stains to previously unstained portions of the fabric. The
photocatalyst can be easily dispersed in the liquid fatty acid, or a non-aqueous liquid
carrier mixed with the fatty acid for uniform application on a substrate in absence
of water, and therefore the problem of patchy or non-uniform cleaning associated with
use of solid photocatalyst is obviated.
Solvent
[0039] The substrate may be contacted with an organic solvent during the process. Chlorinated
as well as non-chlorinated solvents such as chloroform, acetone or perchloroethylene
may be used. However, it is preferred that the substrate is not contacted with a solvent
during the process.
Soap and detergent
[0040] The method of present invention may involve a step of contacting the substrate with
soap or detergent. However, it is preferred that the substrate is not contacted with
soap or detergent during the process. The substrate may be washed with a cleaning
composition comprising soap or detergent after or prior to the process of the present
invention.
Radiation
[0041] The process of the present invention includes a step of exposing the substrate to
a radiation in ultraviolet, visible or infrared spectrum, after the step of contacting
the substrate with fatty acid.
[0042] Preferably, the radiation has a wavelength from 200 nm to 10000 nm. Source of radiation
that can be used includes uv-lamps, infrared lamps, fluorescent or incandescent lights,
and sunlight. It is particularly preferred that the substrate is exposed to sunlight.
Cleaning composition and forms
[0043] According to an aspect of the present invention, there is provided a cleaning composition
comprising from 70 to 99.99% by weight C8-C30 fatty acid and from 0.01 to 10% by weight
a photocatalyst.
[0044] According to a further preferred aspect, the cleaning composition further comprises
from 0.01 to 5% by weight a photosensitizer.
[0045] It is envisaged that the cleaning composition according to the present invention
can be used in any format that is convenient for contacting with the substrate. The
cleaning composition may be in form of solid, liquid, paste or a gel.
[0046] The solid cleaning composition is preferably in the form of powder, granules, or
a rigid abradable stick that can be conveniently contacted with a substrate. The cleaning
composition in stick format may comprise particulate filler material and binder materials.
[0047] The liquid cleaning composition is packaged preferably in a form that allows easy
dispensing, more preferably in a form that allows directed spraying of the liquid
cleaning composition on a substrate. The dispensing or spraying may be actuated by
mechanical action such as squeezing of a flexible packaging or by operating a piston
pump. Alternatively, the liquid cleaning composition may be packaged along with a
propellant carrier such as butane and stored in a pressurized container that allows
spraying of the liquid composition on the substrate.
[0048] The cleaning composition may be in form of a gel or a paste and packaged in squeeze-tubes
for easy dispensing.
Additional advantages of the process
[0049] The method for cleaning can be conveniently used to remove stains from a garment
whilst the garment is being worn by the user.
[0050] The method of the present invention provides an advantage of relative reduction in
malodour from a substrate.
[0051] The method of the present invention provides an advantage of relative reduction in
bacterial contamination of the substrate.
[0052] According to one aspect, the method offers benefit in cleaning a plastic substrate.
In particular, plastic food containers that have been tinged yellowish over period
of time, and which are difficult to clean by prior art methods, can be conveniently
and relatively quickly cleaned using the process of the present invention.
Examples
[0053] The invention will now be illustrated by way of examples. The examples are for the
purpose of illustration only and do not limit the scope of the invention in any manner.
[0054] Materials used in the examples are given below in Table 1:
Table 1 : Materials
Material (chemical name and trade name, if any) |
Source |
P25® - Titanium dioxide |
Degussa |
Oleic acid |
SD fine Chemicals |
Isostearic acid |
Fluka Chemicals |
Mineral oil, Light white oil |
Sigma |
SAFAL® - Sunflower Oil |
Karnataka co-op Oilseeds Growers Federation Ltd. |
Cobalt tetra phenyl porphyrin complex |
Aldrich Chem Co. |
SURF EXCEL® |
Hindustan Unilever Limited |
White cotton fabric |
Bombay Dyeing |
Lemon Pickle |
MTR® |
Red Chilli Powder |
Grocery shop |
Acetone (GR Grade) |
Merck |
Preparation of stained fabric swatches
Preparation of swatches prior to staining
[0055] 100% pure cotton white fabrics (ex Bombay Dyeing, India) were used in all the stain
degradation experiments. Prior to staining, they were washed five times and then ironed.
Washing was carried out in a top loading washing machine (Whirlpool) using a commercial
detergent, SURF EXCEL®. The washing protocol involved soaking the fabrics in SURF
EXCEL® at 3 g/L dosage (with the ratio of mass of liquid to the mass of fabric, or
the liquor to cloth ratio being approximately equal to 15) for 15 minutes followed
by a wash for 30 min and then by two rinses.
Preparation of Oleoresin extract
[0056] Oleoresin was extracted from red chilli powder using acetone. The extraction was
carried out till the residue became colourless. The residue was removed from the extract
by centrifugation. All the extracts were pooled together and the acetone was evaporated
using a rota evaporator to give a dark red gummy oleoresin. 200 µl Oleoresin extract
was dissolved in 5 ml of sunflower oil (SAFAL®), and this mix was used as a staining
solution.
Staining of fabric swatches
Pickle stains
[0057] 20 µL of the oil floating on top of the MTR® lemon pickle (pickle oil) was loaded
on to a 3.5 x 5.5 cm
2 cotton fabric. The stain was allowed to spread on the fabric for 5-10 minutes before
carrying out stain degradation experiments. The stain was circular in all cases and
the area was determined to be about 4.5 cm
2.
Oleoresin stains
[0058] The procedure given above for pickle stains was used except that 20 µL of oleoresin
staining solution was used instead of pickle oil.
Method of cleaning stains
[0059] Fatty acids were used for cleaning. Also, various cleaning compositions with or without
photocatalyst (P25®), with or without photosensitizer (Cobalt tetra phenyl porphyrin
complex, and fatty acid (either oleic or stearic acid), were made by mixing the ingredients.
Stained fabric swatches were contacted with the relevant composition by pipetting
out requisite amount on the fabric, and spreading with a glass rod, if required. The
fabric was then exposed to radiation in the solar light simulator (ATLAS CPS, intensity
= 3.9 mW/cm
2) in all the experiments, unless specified otherwise. In some experiments, the step
of exposure to radiation was eliminated and fabric swatches were stored in dark at
ambient temperature (between 20 to 30 °C).
Evaluation of cleaning efficacy and cleaning speed
[0060] The stain on the exposed fabrics was extracted at regular time intervals with 12
ml of acetone and the absorbance of extract was measured at 450 nm. Stain from area
of fabric unexposed to radiation was extracted with acetone and resulting extract
was used to determine the initial absorbance, A
0. From the initial absorbance, A
0 and the absorbance after t minutes of exposure, At, the percentage of stain remaining
on fabric was quantified using the following equation:

When At equalled zero, the stained area appeared to be visually clean. The time required
for A
t to equal zero, i.e. time required for complete degradation of the stain, was used
as a measure of speed of the cleaning process.
Contacting with fatty acid and exposing to radiation
[0061] The process according to the present invention was used in Example 1. Stained fabric
swatches prepared according to the method of staining described earlier were used
in the experiments. The processes of comparative examples 1-A and 1-B were outside
the scope of the present invention. The details are given in Table 2.
Table 2 Contacting with fatty acid and exposing to radiation
Example No |
Amount of isostearic acid contacted with fabric (µg/cm2) |
Exposure to radiation |
Time for complete degradation of oleoresin stain |
Time for complete degradation of pickle stain |
1 |
50 |
Yes |
25 min |
25 min |
1-A |
50 |
No |
> 2 days |
> 2 days |
1-B |
No |
Yes |
60 min |
30 min |
[0062] The time required for complete stain degradation is also tabulated in Table 2 above.
It is clear that the process of the present invention results in faster cleaning of
both oleoresin and pickle stains.
Effect of type of fatty acid on cleaning speed
[0063] Oleic acid, an unsaturated fatty acid (iodine value of 85-90) was used in Example
2 whilst isostearic acid, a saturated fatty acid (iodine value of 0) was used in Example
3. The details and the resulting cleaning speeds are tabulated in Table 3 below.
Table 3: Effect of degree of saturation of fatty acid on cleaning speed
Ex No |
Fatty acid and amount contacted with fabric (µg/cm2) |
Iodine value of fatty acid used |
Time for complete degradation of oleoresin stain (min) |
Time for complete degradation of pickle stain (min) |
2 |
Oleic acid, 50 |
85-90 |
20 |
20 |
3 |
Isostearic acid, 50 |
0 |
25 |
25 |
[0064] The above results demonstrate that unsaturated fatty acid provides faster cleaning
as compared to saturated fatty acid.
Effect of photocatalyst and amount of photocatalyst
[0065] In the process of Examples 4-7, stain is contacted with compositions comprising fatty
acid and a photocatalyst. In the process of Comparative Example 7-A, photocatalyst
is used in absence of fatty acid. In the process of Comparative Example 7-B, photocatalyst
is used in combination with water instead of fatty acid. The details are given in
Table 4.
Table 4: Effect of photocatalyst and amount of photocatalyst
Example No |
Substance contacted with fabric and its amount (µg/cm2) |
Time for complete degradation of pickle stain (min) |
4 |
Isostearic acid (50) + P25® (0.044) |
20 |
5 |
Oleic acid (50) + P25® (0.013) |
15 |
6 |
Oleic acid (50) + P25® (0.027) |
10 |
7 |
Oleic acid (50) + P25® (0.044) |
5 |
7-A |
P25® (0.044) |
* |
7-B |
P25® (0.044) + water (50) |
45 |
* Patchy or incomplete cleaning at 20 minutes |
[0066] Comparison of cleaning speed of Example 4 with Example 3 (results in Table 3), and
Examples 5-7 with Example 2 (results in Table 3) clearly demonstrates that cleaning
speed is enhanced by contacting the fabric with a photocatalyst. Examples 5-7 indicate
that cleaning is quicker as the amount of photocatalyst contacted with the stain is
increased. The process of Comparative Example 7-A results into patchy cleaning. Without
wishing to be limited by theory, it is believed that patchy cleaning that is observed
is due to the difficulty in uniformly applying the solid photocatalyst powder on the
stain. If the photocatalyst powder is dispersed in water to aid in uniform application,
as in the process of Comparative Example 7-B, the cleaning is slower.
Effect of amount of fatty acid
[0067] Examples 7-9 show the effect of amount of fatty acid contacted. Example 7 is reproduced
from Table 4 for convenience.
Table 5: Effect of amount of fatty acid
Example No |
Substance contacted with fabric and its amount (µg/cm2) |
Time for complete degradation of pickle stain(min) |
8 |
oleic acid (10) + P25® (0.044) |
15 |
9 |
oleic acid (20) + P25® (0.044) |
10 |
7 |
oleic acid (50) + P25® (0.044) |
5 |
[0068] The results indicate that the speed of cleaning is increased with the amount of fatty
acid contacted with the stain.
Effect of photosensitizer
[0069] In the process of Example 10, the stain is contacted with a composition comprising
fatty acid, photocatalyst and a photosensitizer. The composition used in the process
of Example 7 is similar to that used in Example 10, except that it does not comprise
a photosensitizer. The details are given in Table 6. Example 7 is reproduced from
Table 4 for convenience.
Table 6: Effect of photosensitizer
Example No |
Substance contacted with fabric and its amount (µg/cm2) |
Time for complete degradation of pickle stain (min) |
7 |
Oleic acid (50) + P25® (0.044) |
5 |
10 |
Oleic acid (50) + P25® (0.044) + cobalt tetra phenyl porphyrin complex (0.02) |
3 |
[0070] The results demonstrate the beneficial effect of addition of photosensitizer on the
speed of cleaning.
[0071] It will be appreciated that the examples clearly show the mode in which the process
of the present invention can be practiced. The examples also clearly demonstrate that
the process of the present invention is relatively quick and convenient process for
cleaning a substrate, particularly for stain removal from a fabric.