Aqueous composition for wet sanding of dried paint, plastics, and the like

An aqueous liquid composition containing glycerin and polyethylene glycol with a molecular weight in the range of about 400 to about 1000, and, optionally, additional surfactant, is an excellent liquid auxiliary for wet sanding and produces a sanding mud that can easily be removed by washing with water, even after drying.

FIELD OF THE INVENTION 
This invention relates to an aqueous liquid composition that is 
substantially free from volatile organic compounds ("VOC") and is useful 
directly as, or can be diluted with water to make a liquid useful directly 
as, the liquid auxiliary for wet sanding of organic surfaces such as the 
surfaces of various structural plastics and plastic sheet materials, 
including but not limited to polyolefins, polycarbonate esters, 
polyacetals, polyamides, filled thermosetting polyesters, and the like and 
also such organic surfaces as dried and/or cured paint, lacquer, primer, 
and like protective coating materials that comprise an organic binder and 
usually also pigment and/or dye and optionally fillers. 
BACKGROUND OF THE INVENTION AND RELATED ART 
In order to achieve the desired degree of surface finishing quality, it is 
often necessary to smooth or polish the surface of plastics and of dried 
and/or cured coatings of paints and like materials, particularly 
intermediate coats that are to be covered by another coating of paint or 
lacquer. This smoothing and/or polishing is most commonly accomplished by 
abrasive finishing or sanding, using an abrasive such as silicon carbide, 
garnet, iron oxide, or aluminum oxide, either in the form of a coated 
abrasive in which the abrasive grits are attached to some flexible backing 
or in a slurry of the abrasive grits with some liquid. If a coated 
abrasive is used, it is customary to utilize a liquid auxiliary during the 
sanding operation, in order to achieve optimum surface quality and avoid 
the generation of excessive dust, which would at best be annoying, and at 
worst could be seriously hazardous, to workers performing the sanding; 
dust could also damage wet protective coating materials on processed parts 
in the vicinity of the sanding operation by settling on the wet coatings 
and thereby making the surface rough when it is desired to be smooth. 
Therefore, whether a coated abrasive or a slurry is used initially, by the 
completion of the sanding operation the smoothed surface is normally 
covered with a mixture of a liquid carrier and suspended finely divided 
abrasive and solid organic particles. This mixture is commonly called 
"sanding mud" or simply "mud" in the abrasive art. 
Before subsequent finishing operations, the sanding mud normally should be 
removed from the surface. Water or a water based rinse liquid is usually 
used to accomplish this removal, and sometimes power washing of the rinse 
liquid is used to assist in removing the sanding mud. In many instances, 
not even power washing will satisfactorily remove the sanding mud, so that 
hand rubbing or wiping, with substantial expense that would preferably be 
avoided, is required in order to achieve adequate surface quality. 
In many instances in the prior art, a mixture of isopropyl alcohol 
(hereinafter often abbreviated "IPA") or a conventional dishwashing 
detergent liquid and water has been used as the sanding liquid auxiliary; 
water without any special additive is also frequently used. These types of 
liquid auxiliary have proved to be at least moderately satisfactory when 
the sanding mud formed in the course of using it is promptly washed away 
after completion of sanding. However, in certain assembly line 
manufacturing operations, it has been found that the time between sanding 
and washing is long enough for the sanding mud formed during use of these 
types of liquid auxiliary to dry sufficiently to resist ready removal by 
rinsing, or even by power washing, with water. Even in manufacturing 
operations where such drying does not occur during operation under most 
conditions, it can still occur during interruptions of normal processing 
conditions, such as occur during rest periods for the operators, which may 
include as much as two-thirds of the time in a day in single worker shift 
operations, or as a result of mechanical malfunctions of the operations. 
Also, IPA is of course a regulated VOC. Accordingly, a major object of 
this invention is to provide a superior aqueous liquid auxiliary for 
sanding that is substantially free from VOC's and is readily removed by 
water rinsing, even after substantial times of exposure to normal ambient 
air. Another object is to provide a technically satisfactory aqueous 
liquid auxiliary containing only ingredients that are harmless to human 
skin, in view of the virtual practical impossibility of preventing contact 
between the liquid auxiliary used in wet sanding by hand and the skin of 
the workers performing the sanding. Other objects will be apparent from 
the description below. 
DESCRIPTION OF THE INVENTION 
Other than in the operating examples and claims, or where otherwise 
expressly indicated, all numbers expressing conditions of use or 
quantities of ingredients used herein are to be understood as modified in 
all instances by the term "about" in describing the broadest aspects of 
the invention. Practice within the numerical limits given is generally 
preferred, however. Also, unless expressly stated to the contrary: percent 
values are by weight; 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, 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; and 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 stated objects of the invention. 
SUMMARY OF THE INVENTION 
One major embodiment of the present invention is a sanding liquid auxiliary 
composition that comprises, preferably consists essentially of, or most 
preferably consists of, water and: 
(A) from 1.0 to 50%, preferably from 5.0 to 25%, more preferably from 10.0 
to 20%, or still more preferably from 13.0 to 18.0%, of dissolved polyol 
molecules selected from the group consisting of molecules that include 
from 2-6 carbon atoms and at least two-thirds as many hydroxyl groups as 
carbon atoms, preferably with no other atoms than carbon, hydrogen, and 
oxygen, independently preferably with at exactly as many hydroxyl groups 
as carbon atoms, most preferably glycerin; and 
(B) from 0.5 to 40%, preferably from 0.8 to 16%, more preferably from 1.0 
to 10%, or still more preferably from 2.0 to 6.0%, of dissolved hydroxy 
terminated polyoxyethylene (also called "polyethyleneglycol") having a 
weight average molecular weight in the range from 200 to 4000, preferably 
in the range from 300 to 1900, or more preferably in the range from 400 to 
1000; and, optionally, 
(C) from 0.01 to 5%, preferably from 0.1 to 4%, or more preferably from 0.5 
to 2.5% total of surfactant not within the scope of components (A) and 
(B), preferably alkylpolyglucoside surfactant. 
An alkyl polyglucoside is a compound of the formula I: 
EQU R.sup.1 O(G).sub.n (I), 
where R.sup.1 is a monovalent organic moiety containing from one to 30 
carbon atoms; G represents a divalent moiety (except for one monovalent 
terminal moiety) derived from a reducing saccharide containing 5 or 6 
atoms by removing hydrogen atom(s) therefrom; and n is a number having an 
average value from 1 to 6. 
Compositions as described immediately above are "working" compositions, 
i.e., they are suitable for direct use as an auxiliary by application to 
an organic surface before the surface is sanded. A composition of the 
invention can also be provided as a concentrate intended for dilution with 
water before use. Other embodiments of the invention include a process of 
using a composition according to the invention for a sanding liquid 
auxiliary and a sanding process using a composition according to the 
invention as liquid auxiliary. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
Preferably all the ingredients of the compositions according to the 
invention are selected from materials with well-established harmlessness 
to human skin. Hypoallergenic materials such as glycerin and alkyl 
polyglucosides are especially preferred for this reason among others. 
Preferably the ratio by weight between component (A) and component (B) in a 
composition according to this invention is within the range from 30:1 to 
1:1, more preferably within the range from 10:1.0 to 2.0:1.0 
Preferably a composition according to the invention does not substantially 
swell or dissolve the organic solid to be sanded. This property can 
conveniently be checked by placing a few drops of the composition on a 
sample of the surface to be sanded, allowing the drops to remain in place 
on the surface for at least eight hours, and then rinsing off the 
composition and examining the surface for visible damage. Most preferably, 
no change in the surface to be sanded is observable with the unaided eye 
after this test. In some cases, however, a faint haziness is observable in 
the tested surface after such an extended test, without any significant 
harm to the performance of the composition that causes the haze in 
practical use. Compositions that leave the surface to be sanded visibly 
swollen, blistered, and/or tacky are preferably avoided. 
Individual components can be tested in the same way as described above for 
the compositions, if the individual components are liquid, or in 
concentrated solutions if the components are solids at the intended 
sanding temperature. Most surfactants tested have been found to promote 
swelling of the surfaces to be sanded, but alkyl polyglucosides are 
exceptional in lacking any such detrimental tendency. If a surfactant is 
needed or preferred in the composition, therefore, this class of 
surfactants is preferred. 
The most common reason for using a surfactant is to promote spreading of 
the liquid auxiliary over the surface to be sanded. The amount of 
surfactant used, if any, preferably is sufficient to cause a contact angle 
between the liquid auxiliary and the surface to be sanded that is, with 
increasing preference in the order given, no more than 95, 35, 20, 12, or 
6, degrees. 
The amount of liquid auxiliary material needed for effective sanding can 
not be exactly specified, but it can readily be determined by those of 
ordinary skill in the art, taking account of the amount of sanding to be 
done and the nature of the substrate being sanded, with some slight 
experimentation possibly being required. It is believed that the minimum 
amount of active substances (i.e., components (A), (B), and (C) if used) 
in the liquid auxiliary needed for effective operation according to the 
invention may be correlated with the surface area of sanding swarf 
produced, analogously to the well known phenomenon of the "oil demand" of 
paint pigment particles. As a general guideline, however, for a working 
liquid. auxiliary composition containing 20% of active ingredients, an 
amount of liquid auxiliary corresponding to at least 25 milliliters ("ml") 
per square meter ("m.sup.2 ") of surface to be sanded is preferred, an 
amount of at least 125 ml/m.sup.2 is more preferred, and an amount of at 
least 350 ml/m.sup.2 is still more preferred, when the surface is sanded 
with abrasive grits having a standard grading size of 400 to 600 
(corresponding to median particle sizes from 30 to 15 microns). For more 
or less concentrated liquid auxiliaries, the amount of liquid auxiliary 
can be adjusted accordingly to provide the same amount of active 
ingredient per unit area of surface sanded. 
Polyethylene glycols sold by Dow Chemical Company under the trade name of 
POLYGLYCOL E and by BASF under the trade name PLURACOL are among those 
useful in the practice of the invention and readily available. 
Polyethylene glycols have the formula H(OCH.sub.2 CH.sub.2).sub.n OH, and 
those where n on average is in the range of about 4 to about 11 are most 
useful for component (B) of a composition according to the invention. In 
the commercially available polyethyleneglycols the trade name is usually 
followed by a number which corresponds to the average molecular weight of 
the product, and this convention is followed herein, using the generally 
art recognized abbreviation "PEG" for polyethyleneglycols, instead of the 
specific trade name. For example, for PEG 400, n=8.2-9.1, and the 
molecular weight, which is to be understood herein as weight average 
molecular weight, would be about 400. 
Component (C) when used is preferably selected from nonionic and/or 
amphoteric (also called "ampholytic") surfactants only. Commercial 
surfactants such as TRITON.RTM. DF-54 (modified polyethoxy adduct), 
TRITON.RTM. DF12 (modified polyethoxylated linear alcohol); Triton.RTM. 
DF-16 (a terminated ethoxylated linear alcohol), products of Union Carbide 
Corporation; MAKON.RTM. NF-12 (an alkylphenoxypolyoxyethylene alcohol) 
manufactured by Stepan Company; and PLURONIC.RTM. L62 (a polyoxyethylene 
polyoxypropylene block copolymer) manufactured by BASF Wynadotte 
Corporation are examples of nonionic surfactants that can be used for 
component (C). Typical useful amphoteric surfactants include the following 
commercially available products: MONATERIC.RTM. CyNa50, a 50% active 
solution of the sodium salt of 2-caprylic-1-(ethyl beta oxypropionic 
acid)-imidazoline by Mona Industries, and ALKAWET.RTM. LF, a proprietary 
amphoteric surfactant blend manufactured by Lonza. However, as already 
noted, the most preferred surfactants are the (nonionic) alkyl 
polyglucosides, which are commercially available from Henkel Corporation 
under the trade name APG.RTM.. 
As already noted briefly above, the process according to this invention is 
most useful when some time elapses between the completion of sanding and 
the removal of the sanding mud from the sanded surface. With increasing 
preference in the order given, therefore, it is preferred that a process 
according to this invention include a time delay of at least 0.5, 1.0, 
2.5, 4.6, 7.1, 12.0, 20, or 30 minutes between the completion of sanding 
and the beginning of rinsing to remove sanding mud from the sanded surface 
.

The practice of the invention can be further appreciated from the following 
nonlimiting examples and comparison examples. 
EXAMPLES GROUP I 
Three working compositions according to the invention were prepared with 
the ingredients shown in Table 1. 
TABLE I 
______________________________________ 
Percent of Ingredient in Example No.: 
Ingredient 1 2 3 
______________________________________ 
Glycerine 18.0 14.0 13.0 
PEG 400 2.0 -- 1.0 
PEG 1000 -- 4.0 5.0 
MONATERIC .RTM. 
-- 2.0 -- 
CyNa50 
APG .RTM. 325 
-- -- 1.0 
______________________________________ 
The composition of Example 1 remains as a bead when placed on a typical 
dried primer coat surface, having an estimated contact angle of at least 
90.degree.. The composition of Example 2 spreads spontaneously over the 
same surface, having a contact angle not much more than 0.degree.. The 
composition of Example 3 is intermediate in wetting power between the 
other two. 
All three compositions were tested on panels precoated with U04AD045 gray 
primer from BASF Corporation and on other panels precoated with 
"80.degree. Gloss" RIM primer from PPG Corp. When ten drops of each 
formulation (having a total volume of 0.5 ml) were applied to a surface 
area of 5 square centimeters on each panel, excellent sanding lubrication 
was achieved when sanding with 3M Type 286 L Grit 400 Waterproof coated 
abrasive paper. The sanding mud was allowed to stand for 8 hours in air at 
43.degree. C. and 60% relative humidity ("RH"). The sanding mud from 
Example 1 was very quickly washed away from the PPG primer with ordinary 
rinsing only, but a slight amount of sanding mud was left on the other 
panels tested after such ordinary rinsing, with the least amount left on 
panels with the formulation of Example 1 and the most with the formulation 
of Example 2. The sanding mud from all these tests was readily removed by 
conventional power washing, using a 2% concentration of CO.RTM. Plastic 
Cleaner 2501 in water at 57.degree. C. for a contact time of 60 seconds 
("sec" ), followed by 30 sec rinse with ambient temperature tap water and 
a second 30 sec rinse with ambient temperature deionized water, and 
finally blowing dry with compressed air. 
All the formulations were separately tested for attack on the substrates, 
without doing any abrasive finishing, under exposure for 8 hours at 
49.degree. C. and 25% RH. The only evidence of attack on the substrate was 
a very slight slick remnant on the BASF primer with the formulation of 
Example 1. 
EXAMPLE AND COMISON EXAMPLE COMPONENTS GROUP II 
In this group, various candidate components were tested for possible damage 
to substrates. A few drops of each component were placed on the surface of 
test substrates as described further below and allowed to stand for 8 
hours in air at 49.degree. C. and 25% RH; then the residue of the liquid 
auxiliary was rinsed away with 60 seconds of water spraying. The 
substrates tested and their identifying numbers are: 
1. U04AD045 gray primer from BASF Corporation 
2. Premix gray SMC primer from Siebert-Oxidermo Corporation 
3. XENOY.TM. polycarbonate/polyester blend plastic from General Electric 
4. Red Spot Paint Company type 206LE 2K Polyurethane Topcoat, white 
5. "80.degree. Gloss" RIM primer from PPG Corporation. 
The components tested and their identifying abbreviations (in parentheses) 
are: APG.RTM. 225 (Apg2) and APG.RTM. 325 (Apg3) from Henkel Corp.; PEG 
400 (P400), PEG 1000 (P 1000), and PEG 6000 (P 6000); glycerine (GLYC); 
Triton.RTM. DF-16 (DF-16); MAKON.RTM. NF-12 (NF-12); MONATERIC.RTM. CyNa50 
(MON) and PLURONIC.RTM.L63 (PLU). The results are shown in Table 2. Only 
glycerine, APG.RTM. surfactants, and PEG 1000 were generally free from any 
evidence of damage when applied in full strength as in this test, but many 
of the other components listed can be used in the amounts preferred for 
working compositions according to the invention, without causing any 
unacceptable damage to the surfaces sanded. 
TABLE 2 
______________________________________ 
Com- Evidence of Damage on Substrate No.: 
ponent 
1 2 3 4 5 
______________________________________ 
Apg2 trace none none none none 
Apg3 none none none none none 
P 400 flat, shiny haze whitish raised area 
whitish raised damage raised 
raised area 
area bump 
P 1000 
nm nm nm nm none 
P 6000 
nm nm nm nm none, but 
dried mud 
difficult to 
remove 
GLY nm nm nm nm none 
DF 16 slick shiny haze whitish bump 
raised damage raised 
area bump 
MON trace trace haze slight raised area 
damage raised area 
NF 12 glossy glossy, haze raised area 
raised area 
raised slightly 
damage 
slick raised 
PLU glossy glossy, raised raised area 
raised area 
raised slightly 
area 
slick raised 
______________________________________ 
Note for Table 2: 
"nm" means not measured. 
COMISON EXAMPLES GROUP II 
The commercially available dishwashing detergents DAWN.RTM., DOVE.RTM., 
IVORY CLEAR.RTM., and JOY.RTM. were tried at 2% active ingredient 
concentration in water as wet sanding auxiliary liquids under the same 
general conditions as described in Groups I and II. All of them proved 
substantially ineffective in producing sanding muds that could easily be 
removed after 8 hours drying. If used as supplied, with about 20% active 
ingredients, or at any concentration down to about 2.5%, these commercial 
liquid detergents are too viscous to perform satisfactorily as sanding 
auxiliaries for wet sanding with fine coated abrasive such as Grit 400.