Substantially phosphate free acidic cleaner for plastics

An effective phosphate free and organic solvent free aqueous acidic cleaner for soiled plastic surfaces is a low foaming aqueous solution or dispersion that consists essentially of water and: PA1 (A) hydroxycarboxylic and/or dicarboxylic acid or acids; PA1 (B) nonionic surfactant; and, optionally, one or more of the following: PA1 (C) salts including anions of hydroxycarboxylic and/or dicarboxylic acid or acids, preferably anions of the same acid or acids as specified for part (A); and PA1 (D) a sufficient amount of hydrotrope material to produce a stable homogeneous solution or dispersion of components (A) through (C) in water; and PA1 (E) a sufficient amount of a biocidal material to inhibit growth of any bacteria and/or fungi that may be present in the composition.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to compositions and processes for cleaning 
engineering plastic surfaces. Surfaces that can be effectively cleaned 
according to this invention include, but are not limited to, polyester 
sheet molding compound ("SMC"); poly{vinyl chloride} ("PVC") homopolymers 
and copolymers; polyurethane and polyurea plastic surfaces such as those 
of objects made commercially by injection molding from these plastics; 
terpolymers of acrylonitrile, butadiene, and styrene ("ABS"); 
poly{phenylene oxide} ("PPO") and copolymers of "phenylene oxide" with 
other materials such as polyamides; polycarbonate ("PCO") polymers and 
copolymers; and thermoplastic polyolefins ("TPO"). The invention is 
particularly suited to cleaning plastics, more particularly SMC, that 
contain solid filler materials, especially those that are chemically 
alkaline, such as calcium carbonate. Common commercially available types 
of such SMC materials include PHASE ALPHA.TM. from Ashland Chemical Co., 
SL 1223.TM. from Eagle Picher Co., Type 7113.TM. from Gencorp, and RI 
9486.TM. from Rockwell International, Inc. 
The compositions of the invention are substantially or entirely free from 
phosphate and can be substantially or entirely free from volatile organic 
solvents as well, and are therefore less polluting than the now common 
commercial acidic cleaners for plastics. 
2. Statement of Related Art and Object of the Invention 
Numerous compositions and processes for cleaning plastic surfaces are 
currently known in the art. Most of them include acid, surfactant(s), and 
phosphates. In some locations, however, phosphates are forbidden or 
severely limited to avoid potential pollution and eutrophication of bodies 
of water that receive discharges of industrial waste water. Thus, 
compositions that contain little or no phosphate but are still effective 
cleaners have been sought. 
DESCRIPTION OF THE INVENTION 
General Principles of Description 
Except in the claims and the operating examples, or where otherwise 
expressly indicated, all numbers in this description indicating amounts of 
material or conditions of reaction and/or use are to be understood as 
modified by the word "about" in describing the broadest scope of the 
invention. Practice within the numerical limits stated is generally 
preferred. Also, unless expressly stated to the contrary: percent, "parts 
of", and ratio values are by weight; the term "polymer" includes 
"oligomer", "copolymer", "terpolymer", and the like; the description of a 
group or class of materials as suitable or preferred for a given purpose 
in connection with the invention implies that mixtures of any two or more 
of the members of the group or class are equally suitable or preferred; 
description of constituents in chemical terms refers to the constituents 
at the time of addition to any combination specified in the description, 
or as reduced or increased in amount in situ by acid-base reactions, and 
does not necessarily preclude chemical interactions among the constituents 
of a mixture once mixed; specification of materials in ionic form implies 
the presence of sufficient counterions to produce electrical neutrality 
for the composition as a whole (any counterions thus implicitly specified 
should preferably be selected from among other constituents explicitly 
specified in ionic form, to the extent possible; otherwise such 
counterions may be freely selected, except for avoiding counterions that 
act adversely to the objects of the invention); the term "mole" and its 
variations may be applied to elemental, ionic, and any other chemical 
species defined by number and type of atoms present, as well as to 
compounds with well defined molecules; an equivalent of acid is to be 
understood as the amount that would provide one gram atom of hydrogen 
atoms upon complete ionization; and an equivalent of the salt of such an 
acid is to be understood as the amount of the salt that requires the 
replacement of some other cations with one gram atom of hydrogen ions to 
regenerate the free acid. 
SUMMARY OF THE INVENTION 
One embodiment of a composition according to this invention, specifically a 
composition suited for direct use as such in cleaning plastic surfaces, 
which may be denoted hereinafter as a "working composition", is an acidic 
aqueous liquid solution that has a foam volume of not more than 25 
milliliters (hereinafter usually abbreviated "mL") from 150 mL of the 
composition when measured according to the test described below and that 
comprises, preferably consists essentially of, or more preferably consists 
of, water and: 
(A) hydroxycarboxylic and/or dicarboxylic acid or acids; 
(B) nonionic surfactant; and, optionally, one or more of the following: 
(C) salts including anions of hydroxycarboxylic and/or dicarboxylic acid or 
acids, preferably anions of the same acid or acids as specified for part 
(A); and 
(D) a sufficient amount of hydrotrope material to produce a stable 
homogeneous solution or dispersion of components (A) through (C) in water; 
and 
(E) a sufficient amount of a biocidal material to inhibit growth of any 
bacteria and/or fungi that may be present in the composition. 
Foaming potential for purposes of this description is measured by a test 
using 150 mL of cleaning composition, ready for actual use in cleaning, in 
a glass stoppered graduated cylinder with at least 250 ml capacity. The 
cylinder and its contents are brought to temperature equilibrium by any 
convenient method, usually a controlled temperature bath, and then are 
vigorously shaken up and down by hand, while upright with the stopper in 
place, ten times in quick succession. Immediately after this shaking is 
completed, the cylinder is placed upright on a horizontal table and the 
stopper is removed. A timer is started immediately after the stopper has 
been removed. The foam volume is determined from the graduations on the 
cylinder by noting the difference between the graduations at the top of 
the foam and at the top of the underlying liquid composition in the 
cylinder at a time 15.+-.1 seconds after the timer was started. 
Another embodiment of the invention is an aqueous concentrate that can be 
diluted with water only to produce, optionally after adjustment of pH by 
adding acid or base, a composition as given above ready for use as such in 
cleaning plastic surfaces. The term "water only" herein is intended to 
include water from normal domestic and industrial water supplies as well 
as deionized, distilled, or other specially purified water. 
A process according to this invention comprises contacting a soiled plastic 
surface with a suitable composition according to the invention as 
described above for a sufficient time at a sufficiently high temperature 
to achieve the desired amount of soil removal. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
Within the broadest scope of the invention, any organic acid made up of 
molecules of which each contains at least one carboxyl group and at least 
one hydroxyl or additional carboxyl group may be used for ingredient (A) 
above. Thus, for example, gluconic acid, hydroxyacetic acid, succinic 
acid, fumaric acid, potassium acid phthalate, tartaric acid, malonic acid, 
and citric acid could all be used. Preferably, component (A) is made up of 
molecules with not more than six carbon atoms each and with at least 
three, or more preferably, at least four, total --OH and --COOH groups per 
molecule. The most preferred acid for ingredient (A) is citric acid. In a 
working composition according to the invention, the concentration of the 
total of component (A) and component (C) when the latter is present 
preferably is, with increasing preference in the order given, not less 
than 0.4, 0.8, 1.2, 1.6, 2.0, 2.4, 2.8, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 
4.5, 4.6, 4.7, or 4.75 milliequivalents per kilogram (hereinafter usually 
abbreviated as "mEq/kg") and independently preferably is, with increasing 
preference in the order given, not more than 10, 9, 8, 7.5, 7.0, 6.5, 6.0, 
5.7, 5.4, 5.2, 5.1, 5.0, or 4.95 mEq/kg. 
Within the broadest scope of the invention, any conventional non-ionic 
surfactant that is water soluble or dispersible may be used for component 
(B). Preferred molecules for this component are generally those made by, 
or having a structure that could be made by, condensing fatty alcohols 
with suitable amounts of ethylene oxide, and optionally also with some 
propylene or other higher alkylene oxides, as generally known in the art. 
The hydrophile-lipophile-balance (hereinafter usually abbreviated as 
"HLB") value of component (B) independently preferably is, with increasing 
preference in the order given, not less than 6, 7, 8, 9, 9.5, 10.0, 10.5, 
10.7, 10.9, 11.1, 11.2, 11.3, 11.4, or 11.5 and independently preferably 
is, with increasing preference in the order given, not more than 18, 16, 
15, 14, 13, 12.7, 12.4, 12.2, 12.0, 11.9, 11.8, or 11.7. Independently, 
the concentration of component (B) in a working composition according to 
the invention preferably is, with increasing preference in the order 
given, not less than 0.21, 0.40, 0.60, 0.74, 0.87, 0.90, 0.95, 0.97, 1.00, 
1.03, 1.05, 1.07, 1.09, or 1.10 g/kg and independently preferably is, with 
increasing preference in the order given, not more than 10, 7, 4, 3.3, 
3.0, 2.6, 2.4, 2.2, 2.0, 1.8, 1.6, 1.5, 1.4, 1.3, or 1.2 g/kg. 
A hydrotrope is defined generally as a substance that increases the 
solubility in water of another material that is only partially soluble. 
Within the context of this specification, a hydrotrope is a material that 
increases the solubility in water, and more particularly in water 
containing substantial amounts of salts, of component (B) as defined 
above. Hydrotrope component (D) is usually preferred in the composition if 
there is a relatively large amount of salt present in the composition, 
salt which might otherwise tend to reduce the solubility of non-ionic 
detergents to a level where the ability of the composition to remove and 
disperse organic soils is less than is desirable. The presence of a 
hydrotrope, preferably an ammonium or alkali metal salt of a sulfonate of 
toluene, xylene, or cumene, makes possible the presence of relatively high 
amounts of both salt and nonionic surfactant in an aqueous solution. The 
most preferred hydrotrope is sodium cumene sulfonate. 
A concentration in grams per kilogram (hereinafter usually abbreviated 
"g/kg") of hydrotrope equal to from one quarter to three quarters of the 
concentration, or more preferably from 35 to 45% of the concentration, of 
salt component (C) present is generally preferred when component (C) is 
present, but a hydrotrope may also be useful in compositions even without 
component (C), to solubilize some or all of the nonionic surfactants in 
component (B). Thus, independently, especially when component (C) is not 
present in the composition, the amount of hydrotrope preferably is, with 
increasing preference in the order given, not less than 2, 4, 7, 12, 13, 
14, 15, 16, or 17 g/kg, and independently preferably is, with increasing 
preference in the order given, not more than 50, 40, 35, 30, 27, 24, 22, 
20, or 19 g/kg, of a total concentrate composition. 
As already noted above, one of the major objects of this invention is to 
avoid phosphate pollution. It is therefore increasingly more preferred 
that the compositions according to this invention contain no more than 2, 
1, 0.5, 0.25, 0.1, or 0.01 percent by weight of phosphate or other 
phosphorus containing anions produced by the ionization of phosphoric or 
condensed phosphoric acids. Similarly, to avoid air pollution and fire 
hazards, it is increasingly more preferred that the compositions according 
to this invention contain no more than 2, 1, 0.5, 0.25, 0.1, 0.07, 0.05, 
0.03, 0.02, or 0.01 percent by weight of organic materials with a boiling 
point lower than that of water or of other volatile organic compounds. 
The choice of pH and total acid content of a composition according to this 
invention generally requires some compromise between cleaning 
effectiveness and corrosive effect on the metal containers and/or other 
metal equipment generally used in connection with the cleaning process or 
for storing and transporting cleaning compositions. Lower pH and higher 
total acidity generally are favorable to consistency of cleaning and 
prolong the useful life of a cleaning composition, but these 
characteristics of the cleaning composition also promote corrosion, 
particularly of mild steel equipment which is in common commercial use in 
contact with the cleaning compositions. In order to select the optimum 
composition according to this invention it is therefore normally necessary 
to consider both cleaning effectiveness and corrosion risk. This will be 
illustrated in connection with the examples below. However, when corrosion 
is not a problem, considerably more acidic compositions according to the 
invention are highly effective. Thus, if corrosion is not a problem in the 
use of the compositions according to this invention, the pH value of a 
working composition preferably is, with increasing preference in the order 
given, not less than 1.0, 1.5, 1.7, 1.9, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, or 
2.7 and independently preferably is, with increasing preference in the 
order given, not more than 4.0, 3.7, 3.5, 3.3., 3.1, 3.0, or 2.9. On the 
other hand, when a working composition according to the invention is to be 
used in a mild steel container, the pH value of the working composition 
preferably is, with increasing preference in the order given, not less 
than 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, or 5.2 and independently 
preferably is, with increasing preference in the order given, not more 
than 6.1, 6.0, 5.9, 5.8, 5.7, 5.6, 5.5, 5.4, or 5.3. 
The major motive for providing a high buffer capacity in compositions 
according to the invention which are bufferred by the inclusion of 
optional component (C) as described above is to provide substantial 
consistency of cleaning effect as the composition is used, even when the 
pH of a working composition according to this invention is high enough to 
avoid serious corrosion of mild steel containers for the composition. This 
is particularly important when part of the cleaning involves removing 
alkaline types of soils, and also when the plastic being cleaned contains 
alkaline filler materials, such as the very commonly used calcium 
carbonate. In such cases, it eventually becomes advantageous to replenish 
the acid constituent of the composition as it is consumed during use. 
However, to minimize the frequency of such replacement needed, when the pH 
of a working composition is above 4.4, the bufferring capacity of the 
composition preferably is high enough to require, with increasing 
preference in the order given, at least 0.06, 0.10, 0.15, 0.19, 0.23, 
0.26, 0.27, 0.28, 0.29, or 0.30 milliequivalents of a strong base per 
liter of the composition must be added to raise the pH value of the 
composition by 0.1 pH unit. 
For practical reasons that will be apparent to those skilled in the art, it 
is strongly preferred to choose components for cleaning compositions 
according to this invention that have relatively low foaming 
characteristics at the temperature of actual use. In general, it has been 
observed that most compositions according to this invention, when measured 
by the test described above, will have large foam volumes at normal 
ambient temperatures, but that the amount of foam will decrease 
dramatically at some temperature below that normally used and preferred 
for cleaning. This is illustrated below in connection with the specific 
working examples. It is increasingly more preferred that the foam volume, 
measured as described above, of a composition for cleaning according to 
this invention be not more than 25, 20, 15, 12, 10, 8.0, 6.0, 5.0, 4.0, 
3.0, 2.0, 1.0 or 0.5 mL at the temperature of actual use for cleaning. If 
the temperature of intended use is not known, it is increasingly more 
preferred that the same values for foam volume not be exceeded at 
60.degree., 54.degree., 43.degree., or 32.degree. C. 
It is normally preferred that a concentrate according to the invention have 
a composition such that a solution of from 0.5 to 3%, or most preferably 
2%, by weight of the concentrate in water will be suitable for direct use 
for cleaning plastics as described above, possibly after pH adjustment as 
previously noted. 
Contacting between the surface and the liquid composition in a process 
according to the invention may be accomplished by any convenient method, 
such as immersing the surface in a container of the liquid composition, 
spraying the composition on the surface, or the like, or by a mixture of 
methods. Any temperature between just above the freezing point and just 
below the boiling point of the liquid cleaning composition may generally 
be used, with a temperature of 40.degree. to 70.degree. C. generally 
preferred and 50.degree.-60.degree. C. more preferred, with the preference 
strongly influenced by the reduction in the amount of foaming that has 
been observed at higher temperatures. At the preferred temperatures, a 
time of contact of from 20-120 seconds is generally preferred, with from 
45-75 seconds more preferred. 
After cleaning as described immediately above, it is generally preferred to 
rinse the cleaned surface with water to remove any residue of the cleaning 
composition before subsequent use or surface finishing of the cleaned 
plastic. Most preferably, at least the last such rinse should be with 
deionized or other purified water. Usually, the rinsed surface should then 
be dried before subsequent finishing treatments. Drying also may be 
accomplished by any convenient method, such as a hot air oven, exposure to 
infra-red radiation, microwave heating, or the like. 
The practice of this invention may be further appreciated from the 
following, non-limiting, working examples.

EXAMPLE 1 
For this example, a concentrate composition according to the invention was 
prepared from the following ingredients ("PBW"=parts by weight) by the 
following procedure: 20.0 PBW of citric acid was dissolved in 250 PBW of 
deionized ("DI") water. An amount of 13.0 PBW of 50% by weight of aqueous 
sodium hydroxide solution was added to this mixture with stirring until 
there was a uniform appearance throughout the solution. An amount of 5.0 
PBW of 60% by weight of aqueous fluotitanic acid was then added, again 
with stirring until there was a uniform appearance throughout the 
solution. To this mixture were then added in succession with stirring 200 
PBW of DI water, 25 PBW of sodium cumene sulfonate (commercially available 
as NAXONATE.TM. SC from Ruetgers-Neace Chemical Co., State College, Pa.), 
20.0 PBW of WITCONOL.TM. 1206 (a modified oxyalkylated alcohol, 
commercially available from Witco Corp., New York), 5.0 PBW of TRITON.TM. 
X-100 (octylphenoxy polyethoxy ethanol with a Hydrophile-Lipophile Balance 
of 13.5, commercially available from Rohm & Haas Co., Philadelphia), 5.0 
PBW of MAKON.TM. NF 12 (polyalkoxyIate on an aliphatic base, commercially 
available from Stepan Co., Northfield, Ill.), and 457 PBW of DI water. 
The concentrate as described immediately above was diluted with tap water 
to provide a 2% by weight amount of the concentrate in a composition for 
cleaning. This diluted composition was then adjusted with sodium hydroxide 
to give a pH of 5.2 and was tested for cleaning effect at 52.degree. C. 
with 75 seconds spraying contact on the soils and plastic substrates shown 
in Table 1, with the results also shown there. (The soils shown in Table 
1, which are representative of types of soil commonly encountered in an 
automobile manufacturing plant, were deliberately applied to the plastic 
test panels in a uniform manner for the purpose of these tests.) 
TABLE 1 
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CLEANING RESULTS WITH COMPOSITION OF 
EXAMPLE 1 
Effectiveness of Cleaning from: 
Soil Type PCO.sup.1 TPO.sup.2 PPO.sup.3 
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Mold release soap 
Clean Clean Clean 
Wax Trace left 
Part left Clean (WB) 
Lock lubricant 
Part left Not removed 
Clean (WB) 
Human skin oil 
Clean Clean Clean 
Motor oil Clean Not removed 
Clean (WB) 
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Footnotes for Table 1 
.sup.1 LEXAN .TM. from General Electric Co. 
.sup.2 Supplied by Republic Plastics Co. 
.sup.3 NORYL .TM. GTX 910 from General Electric Co. 
Other Notes for Table 1 
"Clean" means that the test panel was free from any visual evidence of th 
type of soil indicated and free from water breaks after rinsing with wate 
in the area of the test panel where the specified type of soil was presen 
before cleaning, except when followed by "(WB)", which indicates that 
water breaks were observable even though there was no visually detectable 
amount of soil remaining. 
The composition ready for cleaning use as described above was also tested 
for its corrosive effect on cold rolled mild steel panels 10 by 15 
centimeters in size. Panels were degreased in acetone, then dried and 
accurately weighed. Weighed panels were sprayed for 2 hours with the 
cleaning composition at 52.degree. C., then rinsed with DI water, dried, 
and again weighed accurately to determine weight loss. The average weight 
loss per panel on six panels was 0.27 grams, with an average deviation of 
0.04 grams. When the corrosion testing was repeated, except that less NaOH 
was added after dilution of the concentrate so that the initial pH was 
4.4, the average corrosion rate was about ten times higher. This higher 
corrosion rate is likely to be unacceptable, so that when using this 
particular embodiment of the cleaning composition according to this 
invention in a mild steel container, it is important to keep the pH above 
5. 
The buffering capacity of this composition is sufficiently high that at 
least 0.10 milliequivalents of strong base per liter of the composition 
must be added to raise the pH of the composition by 0.1 pH unit. 
EXAMPLE 2 
For this example, a concentrate composition according to the invention was 
prepared from the following ingredients by the following procedure: 60 PBW 
of a 50% by weight aqueous solution of gluconic acid was dissolved in 250 
PBW of deionized DI water. An amount of 11.0 PBW of 50% by weight aqueous 
sodium hydroxide solution was added to this mixture with stirring until 
there was a uniform appearance throughout the solution. To this mixture 
were then added in succession with stirring 205 PBW of DI water, 25 PBW of 
sodium cumene sulfonate, 20.0 PBW of WITCONOL.TM. 1206, 5.0 PBW of 
TRITON.TM. X-100, 5.0 PBW of MAKON.TM. NF 12, and 419 PBW of DI water. 
The concentrate as described immediately above was diluted with DI water to 
provide a 2% by weight amount of the concentrate in a composition suitable 
for cleaning. This composition was tested for its corrosive effect by 
immersing half of each of several corrosion test panels of the same type 
as used in Example 1 in a container of the cleaning composition initially 
at 60.degree. C. The panels remained in the cleaning composition 
overnight, but the temperature gradually declined to room temperature. 
Corrosive weight loss averaged only 0.033 grams per total panel 
equivalent. However, the buffering capacity of this gluconic acid 
containing composition is lower than that of the citric acid based 
composition of Example 1, so that it would not be expected to last nearly 
as long without replenishment in practical use. 
EXAMPLE 3 
For this example, a concentrate composition according to the invention was 
prepared from the following ingredients by the following procedure: 45 PBW 
of sodium citrate and 22 PBW of citric acid were dissolved in 660 PBW of 
DI water. An amount of 6.8 PBW of 50% by weight of aqueous sodium 
hydroxide solution was added to this mixture with stirring until there was 
a uniform appearance throughout the solution. To this mixture were then 
added in succession with stirring 27 PBW of sodium cumene sulfonate, 0.8 
PBW of sodium bisulfite (added for its biocidal effect), 86.0 PBW of DF 
16.TM. (a modified polyethoxylated alcohol nonionic surfactant with 
Chemical Abstracts Registry No. 68603-25-8, commercially available from 
Rohm & Haas Co.), and 152.4 PBW of DI water. 
To make a suitable composition for immediate use in cleaning, the 
concentrate described above may, for example, be diluted with tap or DI 
water to give a composition containing 2% by weight of the concentrate, 
and sufficient NaOH or citric acid added to this diluted composition to 
give a pH of 5.25.+-.0.25. As this composition is used for cleaning, the 
pH tends to rise, and most preferably additional citric acid is added, 
usually from aqueous solution, as necessary to keep the pH within the 
specified range. 
The foam volumes developed at various temperatures were measured by the 
method described above for a sample of a composition made by dissolving 
the concentrate prepared for this example in DI water to give a solution 
containing 2% of the concentrate by weight. The foam volumes found are 
shown in Table 2 below. The buffering capacity of this composition is 
sufficiently high that at least 0.30 milliequivalents of strong base per 
liter of the composition must be added to raise the pH of the composition 
by 0.1 pH unit. 
TABLE 2 
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FOAM VOLUMES FOR A COMPOSITION MADE BY 
DILUTING A CONCENTRATE ACCORDING TO 
EXAMPLE 3 
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Temperature, .degree.C.: 
21 27 31 37 43 49 60 
Foam Volume, mL: 
112 112 24 22 14 4 &lt;1 
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EXAMPLE 4 
This example illustrates compositions according to the invention without 
any component (C). The concentrate for this example had the following 
composition per kilogram: 47.5 g of anhydrous citric acid, 18.0 g of 
NAXONATE.TM. SC; 57.0 g of TRITON.TM. DF-16, 0.8 g of anhydrous sodium 
hydrogen sulfite, and the balance deionized water. A solution of 2% of 
this concentrate in water produces a highly effective working cleaner for 
plastics as generally described above.