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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to multicomponent solvents formulated for use as
cleaning agents and diluents with low or no toxicity and non-flammable or
non-combustible characteristics. More particularly, the present invention
relates to multicomponent solvents formulated to be miscible with oil-,
and resin-based paints, but is not limited thereto. The solvents of the
present invention act as cleaners of, and thinners for, such paints, with
minimal effect on the desired properties of the paint, while maintaining
the noted safety features.
2. Description of The Prior Art
In the field of solvents, and, in particular, paint solvents used to thin
or otherwise dilute the paint resin or binder, there has been a long
history of use of compounds and compositions with less-than-desirable
health and safety characteristics. Of course, the hazards of such solvents
were not well known and in any case, suitable, inexpensive alternatives
were few and far between. The situation remains basically the same today.
As a result, solvents that were used long ago continue to remain in use.
Specifically, there exists in primary use today thinning compounds known
generically as turpentine and "mineral spirits." Both compounds have
desirable properties in that they are miscible with many
commercially-available oil-based paints and they are relatively
non-hazardous. That characterization is of course dependent upon comparing
those solvents with suitable alternatives.
There are several methods used to define a satisfactory solvent. Two of the
more widely-used techniques include the Kauri-butanol test, conducted
under American Society of Testing and Materials (ASTM) D-1133, and a
Solubility Parameter evaluation. The Kauri-butanol test provides a
relative measure of the solvency of a compound or mixture when that
compound or mixture is added to a standard solution of kauri resin in
butanol. For the most part, the higher the value, the greater the
solvating capacity of the solvent. In general, a kauri-butanol (K.sub.B)
value of less than 32 indicates a compound with poor solvency
characteristics, at least for oil-based resins, while a K.sub.B value
above 90 indicates good solvency for such resins.
The measure of the solvency characteristics of a compound or mixture under
the solubility parameter evaluation is actually a determination based upon
the inherent characteristics of the material rather than its interaction
with another compound. The solubility parameter is based on the heat of
vaporization of the material, a property available in the appropriate
technical literature for many solvents. This parameter is perhaps more
useful in determining the relative solvency of a wider array of compounds
than is the kauri-butanol test. Under this measure, a high value tends to
indicate a solvent suitable for use with polar compounds, while a lower
number tends to indicate that the solvent can be used to dilute non-polar
compounds. Water, for example, has a solubility parameter of 23.4, while
mineral spirits has a value of 6.9.
Another measure of the suitability of a particular solvent with a
particular resin is its evaporation rate. This rate determines the speed
with which a solvent-thinned paint, for example, will dry after
application. Depending upon the desired drying rate for the resin, one
solvent may be more useful than another. In general, a highly-evaporative
solvent will produce faster resin drying. Of course, that drying rate is a
function of temperature. It should also be noted that those solvents with
relatively high evaporation rates, such as mineral spirits, also tend to
have lower flash points and therefore present flammability hazards.
Of the two paint solvents most commonly used, turpentine and mineral
spirits, turpentine was the first one in wide use. Turpentine is an
essential oil of the naturally-occurring terpene family, consisting
principally of alpha-pinene. Broadly stated, its characteristics include:
1) good miscibility with an array of commonly-used paint resins; 2) a
suitable evaporation rate, providing sufficient time to easily apply the
resin and a reasonable drying time; 3) a flash point (the temperature at
which the vapor space just above the compound will ignite) that is higher
than offer available solvents; and 4) an odor that is not completely
unpleasant. However, in spite of the noted advantages, there are problems
with turpentine, including its flash point (only about 90.degree. F.) and
an undesirable level of toxicity, that have made the search for
substitutes an urgent one.
For a number of years mineral spirits have been used as substitutes for
turpentine-primarily on the basis of lower cost and greater availability,
rather than on any improvement in flash point or toxicity. The solubility
parameter associated with mineral spirits is slightly less than that of
turpentine (6.9 versus 8.1) though well within the values evidencing
suitable solubility for oil-based resins. Mineral spirits (or white
spirits) is a term used to designate a wide class of petroleum-based
aliphatic-hydrocarbon solvents in the C10-C15 range that boil at
temperatures greater than 300.degree. F. Due to the abundance of
petroleum, lower-priced mineral spirits have, to a great extent, replaced
turpentine as oil-based-paint solvents. Of course, in the generic class of
petroleum-based solvents there are a range of compounds with varying
characteristics. In spite of their noted usefulness in providing good
thinning for oil-based paints, there is a continuing push to reduce direct
human contact with hydrocarbons generally, given recent observations that
such compounds tend to be carcinogenic.
In addition to mineral spirits, there are the lighter aliphatics, such as
the hexanes and octanes that evaporate more quickly and/or are more
compatible with particular resins. To a certain extent, these compounds
may make up a fraction of the generic mineral spirits solvent. However, in
some specific cases they may be used directly as solvents in and of
themselves. A wide range of aromatic hydrocarbons, including toluene and
xylene, are also considered useful solvents, particularly for oil-based
paints that have aromatics as constituents. Of course, the hazards
associated with these aromatics are at least as well-known as those
observed with the other hydrocarbons. In fact, enactment of the Clean Air
Act of 1990 has restricted the use of such solvents, among many others. As
a result, they are little used as thinners or cleaners by private
individuals. Nevertheless, on occasion, they do make up at least a small
portion of the mixtures used as thinners, including those designated as
mineral spirits.
In spite of the well-known hazards associated with the aliphatic and
aromatic hydrocarbon solvents, including their relatively-low flash
points, they continue to be used as thinners and cleaners for a variety of
paints. Of course, these solvents, along with turpentine, are inadequate
for paints that are not oil- or resin-based--typically the
cellulose-derived materials known generically as lacquers (resins derived
from plants and fossilized material). As a result, other solvents are used
to perform the same functions undertaken by the noted compounds and
mixtures. For example, the solvents used to thin shellacs (insect-produced
resins) are alcohol-based, the solvents commonly used to thin
nitrocellulosic substances are esters. Ketones are often used as solvents
for acrylic and vinyl resins. Again, while useful in thinning and cleaning
a range of resins, these various oxygenated solvents suffer the same
deficiencies associated with turpentine, mineral spirits, and the other
hydrocarbon solvents. Those deficiencies are, primarily, unacceptable
levels of toxicity and low flash points. It has been observed that mixing
relatively dissimilar solvents, such as combining a hydrocarbon with an
oxygenated solvent, can result in a single solvent mixture with average
solubility and evaporation rate, useable with dissimilar resin types.
However, such mixtures may still suffer the deficiencies of the individual
constituents.
As noted, one principal concern with a wide array of solvents involves the
possibility that the vapor space above the particular liquid will ignite
under certain conditions. In order to support such ignition, a sufficient
quantity of the solvent's vapor must be present in combination with
oxygen. One measure used to define the temperature at which a combustible
mixture of oxygen with the vapor of a particular solvent will support
ignition is the flash point. The flash point is the temperature at which
the solvent's vapor pressure is sufficient to produce a flame in the
present of an ignitor. Low flash points generally indicate a greater
likelihood that ignition will occur. Generally, they also indicate that
evaporation will occur sooner than with high-flash-point solvents. Under
U.S. Department of Transportation standards, a solvent is considered: 1)
flammable if it has a flash point below 135.degree. F.; 2) non-flammable,
but combustible if it has a flash point in the range 135.degree.
F.-175.degree. F.; and 3) non-combustible if it has a flash point greater
than 175.degree. F. In simple terms under these definitions, a flammable
compound is one that can ignite under ambient conditions that can occur
naturally and that are to be expected during transport, while a
combustible compound is one that can ignite under unlikely but possible
transportation conditions. There are some suitable oil-based solvents that
can be considered non-flammable, such as heavy aliphatic- and
aromatic-hydrocarbons. Even fewer can be considered non-combustible.
One attempt at fixing the flammability problem noted for many solvents
involved the use of chlorinated and/or fluorinated hydrocarbons either as
substitutes for those earlier solvents, or as constituents in mixtures
containing the earlier solvents. The high flash points of these
halogenated hydrocarbons, which include methylene chloride and
trichloroethylene, among others, translate into a significant reduction in
the flammability of the solvent. However, the commonly-used halogenated
hydrocarbons are generally considered to be more toxic than the earlier
solvents. In fact, many are deemed to be carcinogenic. Moreover, the
deleterious affect of the highly-volatile chlorinated solvents, and
chlorofluorocarbons in particular, on the ozone layer is well documented.
Apart from this failed attempt to provide solvents with both good solvating
characteristics for resins of interest and low-, or non-flammability, the
toxicity of such compounds has always been considered at first an unknown,
and then later, a necessary evil. Toxicities of many substances, including
solvents, are most commonly defined either by their Threshold Limit Value
(TLV) or by LD50 Test results. TLV is the quantity of a compound that a
person can be exposed to over a given period of time without adverse
health effects. The time period is typically defined as an 8-hour work day
and the values are measured in parts of the vapor of the compound per
million parts of air containing the vapor, at standard temperature and
pressure. Under Occupational Safety & Health Administration regulations, a
low TLV number (e.g., less than 100 ppm) indicates a toxic compound,
whereas a high TLV (e.g., greater than 100 ppm) indicates reduced
toxicity. Turpentine, for example, has a TLV of 100 ppm, while mineral
spirits have TLV values higher than that.
The LD50 Test, on the other hand, involves the introduction of the compound
into a living organism, by ingestion, inhalation, injection, or the like,
and observation of whether death occurs within a specified period of time.
While a variety of organisms may be evaluated, one of the more commonly
used is a laboratory white rat. Under the Federal Hazardous Substance Act
(FHSA), a substance is considered toxic if at least one-half of the rats
in a test die within ten days of receiving the substance and they have
received at least five grams per kilogram of the animal's body weight. Of
course, when at least half die within the noted time period after
receiving less than five grams/kilogram, the substance is also deemed to
be toxic. If fewer than half the rats die over the ten-day period after
receiving at least 5 grams/kilogram, the substance is, by FHSA definition,
non-toxic. Typically, the number of rats observed in a test group is ten.
A further characteristic considered to be important by paint thinner
users--particularly those users who work in close proximity to the paint
source, such as artists, for example--is the odor of the mixture in use.
At first that may not seem to be a significant factor, in light of
flammability and toxicity concerns. However, when one is exposed to an
offensive odor for an extended period of time, that characteristic becomes
increasingly significant. Therefore, many prior-art solvents, while
effective thinners and cleaning agents, either are simply too offensive,
or they require the addition of odor maskers--generally compounds that are
compatible with the particular solvent and that also provide a not
unpleasant odor. One such substance commonly used in masking is
d-limonene, a naturally-occurring compound in the same terpene family as
turpentine. It has a lemon odor and solvating characteristics for some
natural resins. However, it does have a flash point slightly below that of
turpentine.
Therefore, there exists a need for solvents that can be used to improve the
applicability, or "spreadability," of resins, and oil-based paints in
particular, on surfaces of interest; that is, solvents--as well as solvent
mixtures--that can be used to thin such resins without significantly
affecting the ultimate properties of the dried resins. Of course, an
accompanying feature of such solvents is the ability to use them to clean
items in contact with the undried resins when the solvents are used in
excess.
Further, there exists a need for such solvents with evaporation rates that
are compatible with the drying of the particular resins. In other words,
such solvents must not evaporate too quickly so as to cause the resins to
crack upon drying; nor must they evaporate too slowly so as to prevent
drying of the resins. There also exists a need for such solvents with very
little, if any, unpleasant odor emissions, particularly when the resin to
be thinned is used in close quarters.
Still further, there exists a need for such solvents with low-, or
no-toxicity, as defined under standards such as TLV ratings or LD50
values. Yet further, there exists a need for such solvents with all of the
above-noted characteristics as well as having a composition that renders
them non-flammable or, ideally, non-combustible.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide solvents suitable as
thinners and cleaners for a wide array of resins--oil-based paints in
particular--with little, if any, effect on the characteristics of such
resins. Such suitability to be defined by the miscibility and observed
compatibility of the formulated solvents with such resins, as well as the
solvents' effect on the drying rate of the resins. It is also an object of
the present invention to provide solvents with the noted characteristics
and that also produce little, if any, unpleasant odor emissions,
particularly for resins located in close proximity to the user. It is yet
another object of the present invention to provide solvents with the noted
characteristics and that are further deemed to be non-toxic. It is still
another object of the present invention to provide solvents with all of
the above-noted characteristics and that are yet further rated as
non-flammable or non-combustible. There is no single solvent compound of
which the inventor is presently aware that: 1) is soluble with oil-based
resins in particular; 2) has a desirable evaporation rate for good drying
of the resin after application; 3) meets generally-accepted standards for
compounds that can be defined as having low-, or no-toxicity; and 4) is
defined as non-flammable or non-combustible. There are many solvents with
two or three of these characteristics, but none with all four.
The noted and other objectives are achieved in the present invention
through the novel combination of a plurality of known compounds. The
particular goal of the present invention is to first start with a solvent
known to be compatible with an array of oil-based resins commonly used by
artists, painters, and other individuals who work in close proximity with
the resin mixture that is in use. That is not to say that the solvent
formulations to be described will be useful only in those fields; rather,
the original research on the subject of the invention was conducted with
such people in mind. It has been observed, however, that the benefits of
the formulations of the present invention extend to other solvent users.
Next, the negative characteristics associated with such known solvents
are, in effect, "diluted" to acceptable levels without dilution of the
desirable solubility and evaporative characteristics noted.
It has been discovered through much experimentation that a variety of
co-solvents and/or fillers will act as suitable diluents. Of course, the
extent of their use is dependent upon the starting solvent. Initially, the
present invention involves starting with no more than 60% by weight of a
propylene carbonate compound, an ethylene glycol ether compound, a
propylene glycol ether compound, or alternatively, a propyl-ether acetate
compound as the primary solvent. These starter solvent compound groups,
while having low evaporation rates relative to other potential solvent
starters, have good solubility with a wide variety of resin systems,
particularly the cellulose-based resins. This can be said for the
mono-ethylene and the mono-propylene as well as multiple ethylenes and
propylenes of both compound types. Particular glycol groups to be used
include ethylene glycol monomethyl ether, diethylene glycol monomethyl
ether, ethylene glycol monobutyl ether, diethylene monobutyl ether,
propylene glycol phenyl ether, dipropylene glycol N-propyl ether propylene
glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene
glycol monopropyl ether, propylene glycol monobutyl ether, and dipropylene
glycol monobutyl ether. Carbitol groups including the butyl carbitols and
methyl carbitols are also considered suitable starters. It has been
observed that several of the propylene glycols available from Dow Chemical
Corp., Midland, Mich., under the Dowanol.RTM. tradename have been found to
be suitable starter solvents. It is important to note that these starter
solvents have relatively high flash points, indicating non-flammable
characteristics. However, most of them fail to meet the LD50 Test
standards for non-toxicity. Those that do not fail are generally
unacceptable in terms of solubility with commonly-available resin systems
and/or have very slow evaporation rates. Many aliphatic esters and ketones
have also been reviewed as possible starter solvents; however, they have
low flash points, relatively-high toxicity, and they give off particularly
unpleasant odors.
In order to overcome deficiencies in the starter solvent compounds set out
above, a number of other fillers and/or "co-solvents" are added to the
particular starter solvent selected. The co-solvents can be defined as
those compounds that are actively involved in the reduction of resin
viscosity by effectively "dissolving" the resin in the solvent to form a
homogeneous mixture. The fillers, on the other hand, have properties
similar to the resin system, such as viscosity and compatibility with
other compounds, but they do not act to dissolve the resin. It is to be
noted that a compound may act as a filler for one or a number of types of
resins, while also acting as a solvent for others. Thus, in considering a
compound for solvency it is necessary to select compounds that will
enhance the applicability of the resin, without sacrificing, to a great
extent, the resins' drying rates. In considering a filler, the basis for
acceptability is that of not hindering the desired application
characteristics while at the same time acting to bring the complete
solvent mixture to 100% by weight. Ideally, a solvent formulation would
include compounds that alternatively acted as co-solvents and fillers,
dependent upon the resin system used. As a basis for evaluating the
mixtures produced, the applicability and drying characteristics of
turpentine- and mineral-spirits-thinned resins were used as standards.
To that end, and first regarding co-solvents for the starter solvents
described above, many different types can be used--in particular, some
petroleum-derived hydrocarbons, because of their low cost and
compatibility with oil-based resins. Isoalkenes have been found useful,
due to the varying evaporation rates associated with the compounds in that
class of hydrocarbons. They also give off little odor. However, due to the
health concerns noted regarding hydrocarbons in general, they must be
limited to less than 10% by weight of a total solvent mixture. The
isoalkane identified as Isopar L.TM., available from the Exxon Company
USA, Houston, Tex., has been found a suitable co-solvent in that regard.
Isoalkanes of the type corresponding to Isopar L.TM. are the C.sub.10
-C.sub.12 isoalkanes. Isoalkanes of the type corresponding to Isopar L.TM.
are the C.sub.10 -C.sub.12 isoalkanes. In addition, alkyl acetates such as
the isodecyl acetates available from the Exxon Corporation under the
Exxate.TM. tradename, including, but not limited to, Exxate 1000.TM., as
well as the oxy-alcohol esters and N-methyl pyrrolidone and their
equivalents are also well-known suitable co-solvents. It has been noted
that N-methyl pyrrolidone is compatible with a wide array of solvents and
resins, including some water-based materials. It and its analogues are
particularly useful in solvent mixtures used for many types of resins.
Compounds that have been evaluated to act as fillers for solvents used to
reduce the viscosities of oil-based resins include propylene glycol,
dipropylene glycol and propylene carbonate. To a limited extent these
compounds do not affect the applicability of the resin in solution. They
are beneficial in that they have compatible evaporation rates, low-, or
no-toxicity, and they are non-flammable. It has been determined that for
such resins the glycols described may be as much as 40% by weight of the
total solvent formulation.
A number of alcohols have also been evaluated as suitable fillers. As
noted, fillers can alternatively act as solvents, dependent upon the
particular resin. This is particularly true for alcohols. It is well known
that for shellacs and ethylcellulose, alcohols can be used to reduce resin
viscosity for enhanced applicability, and so they act more as solvents.
Furthermore, the alcohols are suitable as fillers for the oil-based resins
in that they have suitable evaporation rates. Particular alcohols deemed
to be useful in this application include isopropyl alcohol and ethyl
alcohol. Of course, it is to be understood that denatured alcohol is not
to be used, given its poisonous effects. In addition, it has been observed
that alcohols used as fillers with the starter solvents noted must be
limited to no more than 20% by weight of the mixture.
Another filler type to be used is the group of compounds known generally as
oxidizing oils. Of course, it is well known in the field of artists' paint
formulations that the term oxidizing oils describes those
naturally-occurring oils that are sometimes referred to as vegetable oils.
They are useful with oil-based resins and alkyds. Specific oxidizing oils
include safflower, poppyseed, linseed, and sunflower, among others. These | | |
