Patent Grant
7897558
This invention relates to a unique combination of two or more alkylated cyclic siloxanes and glycol ethers as solvents characterized as low-volatile organic or non-volatile organic compositions with flash points above 140° F., and vapor pressures of less than seven millimeters of mercury (7 mm Hg.).
Solvent cleaners are known for their excellent cleaning ability, quick drying, metal compatibility, and low surface tension to facilitate penetration. Unfortunately, some solvents are known also for the air pollution they cause (as volatile organic compounds or VOC), toxicity, flammability, and incompatibility with plastics.
The use of volatile organic compounds (VOC) solvents has been discouraged due to their deleterious effect on the environment. Regulations have been promulgated to accelerate the phase-out of environmentally destructive solvents.
The Environmental Protection Agency (“EPA”) promulgates rules and regulations regarding environmental concerns such as VOCs. EPA has defined VOC's to include volatile compounds of carbon which promote atmospheric photochemical reactivity. Thus, there is a need to reduce the use of conventional VOC solvents and it is apparent that there is a need for solvents which have little or no VOC content.
The old specification P-D-680 solvent, commonly called Stoddard solvent or mineral spirits, contains petroleum fractions that are complex mixtures of aliphatic hydrocarbons, but may contain some aromatics and olefinics. P-D-680 contains hazardous air pollutants (HAP's) and VOC's, and causes health and environmental concerns. The revision to MIL-PRF-680 eliminated the HAP's, but MIL-PRF-680 still covers a petroleum-based solvent containing the same amount of VOC's as P-D-680. Since P-D-680 was first written, these solvents have been specified for general cleaning to remove oil and grease from aircraft and engine components and from ground support equipment.
There are several alternatives to the P-D-680/MIL-PRF-680 solvents: water-based, semi-aqueous, and solvent-based cleaners. Water-based cleaners contain detergents to remove grease and oil and may be used hot and/or with various forms of agitation (spray or ultrasonic). Disadvantages include flash rusting, embrittlement of high strength steel and poor cleaning efficiency. Semi-aqueous cleaning processes incorporate not only detergents, but also solvents to improve effectiveness. Some products contain solvents emulsified in water while others contain water-rinsable solvents. A significant disadvantage to semi-aqueous cleaners is their susceptibility to separation. Solvent-based cleaners, however, continue to be used in effective, low cost cleaning processes. In order to retain the capability of solvent cleaning, a new type of solvent is needed to meet the HAP and VOC requirements.
Under Title III of the 1990 Clean Air Act (CAA) amendments, the U.S. Environmental Protection Agency (EPA) has established emissions standards for categories and sub-categories of sources that emit or have the potential to emit listed HAPs. In addition, under the proposed rule, MIL-PRF-680 will no longer be allowed in solvent degreasing operations in the SCAQMD. If a substitute material or process is not authorized, the Aircraft Intermediate Maintenance Detachment (AIMD) at Lemoore and other maintenance facilities will not be able to perform specific maintenance requirements in accordance with NAVAIR technical manuals. Since MIL-PRF-680 is the only material authorized by the applicable maintenance manuals to clean flight critical parts, an approved alternative for MIL-PRF-680 is necessary to meet the new environmental regulations.
To meet the new regulations, NAVAIR's Aircraft Materials Laboratory at Patuxent River, Md., recently tested several commercial products. As a result, a new specification MIL-PRF-32295 entitled “Cleaner, Non-Aqueous, Low-VOC, HAP-Free solvents,” was developed to provide environmentally friendly cleaners to the Department of Defense (DoD) services. The new specification requires that a solvent must be free of HAPs, must contain no more than 25 grams per liter of VOC's, must be effective on grease and oil, must not contain ozone-depleting substances (non-ODS), must be non-toxic, must be compatible with metals and non-metals, and must be safe to use. In addition, the Aerospace National Emission Standards for Hazardous Air Pollutants (NESHAP) states that immersion-cleaning solvents must have vapor pressures less than seven millimeters of mercury (7 mm Hg.), and wipe cleaning solvents must have vapor pressures less than 45 mm Hg. MIL-PRF-32295 classifies low vapor pressure solvents (less than 7 mm Hg) as Type I and moderate vapor pressure solvents (less than 45 mm Hg) as Type II. This invention will meet the requirements of MIL-PRF-32295 Type II specification. Products of this invention qualify to be used to clean weapon systems across DoD maintenance facilities as an alternative to MIL-PRF-680.
The present invention relates to solvent compositions characterized as low-volatile organic or non-volatile organic solvents. The non-volatile (non-VOC) organic solvents consist essentially of a unique combination of at least one or more alkylated cyclicsiloxanes having from 5 to 8 repeating siloxane units wherein said alkyl or alkylated substituents have from 1 to 6 carbon atoms, and at least one alkylated cyclicsiloxane having 3 or 4 repeating siloxane units wherein said alkyl or alkylated substituents have 1 to 4 carbon atoms, and at least one glycol alkyl ether. These non-volatile organic cyclicsiloxane solvents are further characterized as having flash points above 140° F. and vapor pressures of less than seven millimeters of mercury (7 mm Hg.).
The present invention relates to organic compositions consisting essentially of low-volatile (low-VOC) or non-volatile (non-VOC) compounds. These organic compositions are further characterized as having flash points above 140° F., and have vapor pressures of less than seven millimeters of mercury (7 mm Hg.).
The organic compositions are particularly useful as non-volatile (non-VOC) solvents and consist essentially of about 50 to 70 and more particularly 55 to 65 parts by weight of at least one alkylated cyclicsiloxane having from 5 to 8 repeating siloxane units wherein said alkylation or alkyl substituents have from 1 to 6 linear or branched carbon atoms including, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, and from about 20 to 40 and more particularly 25 to 35 parts by weight of at least one alkylated cyclicsiloxane having 3 or 4 repeating siloxane units wherein said alkylation or alkyl substituents have from 1 to 4 linear or branched carbon atoms including, for example, methyl, ethyl, propyl, isopropyl, butyl, and isobutyl, and from about 5 to 15 and more particularly 8 to 12 parts by weight of at least one glycol alkyl ether wherein said alkyl substituent has 4 to 8 branched or linear carbon atoms. The alkylation of the cyclicsiloxanes can be derived from alkyl compounds that are branched or linear and are either all the same or different alkyl compounds. It is important that the alkyl groups of the glycol alkyl ethers have at least four carbon atoms derived from the same or different alkyl compounds.
Typical examples of the cyclicsiloxanes having 5 to 8 repeating siloxane units, and the cyclicsiloxanes having 3 or 4 siloxane units include, for example, tetramethylcyclotetrasiloxane, 1,3,5,7-tetraethylcyclotetrasiloxane, 1,3,5,7,9-pentamethylcyclopentasiloxane, 1,3,5,7,9-pentaethylcyclopentasiloxane octamethyl cyclotetrasiloxane, decamethyl pentacyclosiloxane. Particularly suitable is a mixture or blend of octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane and a diethylene glycol monoalkyl ether. The glycol alkyl ethers particularly include the monoalkyl ethers of diethylene glycol, triethylene glycol, tetraethylene glycol, and the lower molecular weight polyethylene glycol alkyl ethers wherein the alkyl group must have at least four (4) branched or linear carbon atoms.
The following are specific examples illustrating the cyclicsiloxane glycol ether compositions of this invention.
I. Cleaning Efficiency
The cleaning efficiency test for the cyclosiloxane solvents (Navsolve cleaner) of this invention was conducted in accordance with MIL-PRF-32295 specification (test Method 4.5.9) as described below.
Preparation of test specimens. Stainless steel coupons 1 by 2 by 0.05 inches (25 by 50 by 1.3 mm) shall be polished with 240 grit aluminum oxide abrasive paper or cloth and solvent wiped with isopropyl alcohol. Coupons shall be weighed (weight=W1), coated on one side with 20-25 mg of soil, then reweighed (weight=W2). Soils to be tested were as follows:
Test procedure. Fresh solvent was used for each soil tested. Each test coupon was cyclically immersed and withdrawn from a 150-ml beaker containing 100 ml of the cleaner at a rate of 20 cycles per minute for 5 minutes. Each coupon shall then be dried for 10 minutes at 140±4° F. (60±2° C.), cooled to room temperature, and reweighed (weight=W3). Cleaning efficiency for the cleaner was calculated as follows for each coupon:
% Cleaning efficiency=(W2−W3)/(W2−W1)×100
The test result for each soil shall be the average of three coupon cleaning efficiencies.
II. Volatile Organic Compounds (VOC) Analysis
The VOC content for the cyclosiloxane solvents of this inventin (Navsolve cleaner) was measured in accordance with MIL-PRF-32295 Specification (SCAQMD Method 313-06). The VOC analysis for the cyclosiloxane solvents (Navsolve cleaner) was found as 4.0 g/l; the VOC content for MIL-PRF-680 is more than 750 g/l.
III. Total Immersion Corrosion Test
The total immersion corrosion test for the cyclosiloxane solvents (Navsolve cleaner) was conducted in accordance with the requirements of MIL-PRF-32295 specification (ASTM F483) and gave the following results:
IV. Sandwich Corrosion Test
The sandwich corrosion test for the cyclosiloxane solvents (Navsolve cleaner) was conducted in accordance with MIL-PRF-32295 specification requirements (ASTM F1110); the product met the requirements successfully. The following aluminum alloys were used in conducting the sandwich corrosion test:
Aluminum SAE 250/4
Aluminum SAE 250/5
Aluminum SAE 250/12
Aluminum SAE 250/13
V. Flash Point
The flash point of flammable liquid is the lowest temperature at which it can form an ignitable mixture in air. The flash point for the cyclosiloxane solvents (Navsolve cleaner) was measured in accordance with MIL-PRF-32295 specification (ASTM D-56) and found as 141° F. To avoid the flammability problems, the flash point for the solvent must be 140° F. or higher. The flash point property is essential for solvent cleaner selection to ensure worker safety and health protection.
VI. Hydrogen Embrittlement Test
The hydrogen embrittlement test was conducted in accordance with MIL-PRF-32295 specification (ASTM F519); using cadmium-plated AIS14340, type 1a specimens. Each specimen was stressed by applying a load equivalent to 45 percent of notch fracture strength. The notch was immersed in the cleaner for the duration of the test (150 hours). The cyclosiloxane solvent of this invention (Navsolve cleaner) met the requirements successfully.
Advantages and New Features
To meet the new environmental regulations, it is essential to identify and validate effective, safe, and environmentally friendly products for cleaning applications. The advantages of the cyclosiloxane solvent (Navsolve cleaner) are listed below:
The following is a list of the ASTM standard test used to obtain the data set forth in Tables I and II.
While various embodiments of the invention have been disclosed, the specific composition and methods described herein are not intended to limit the scope of the invention.
The invention described herein was made by employees of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5942007 | Berndt et al. | Aug 1999 | A |
| 7569652 | Kennedy et al. | Aug 2009 | B2 |
| 7576170 | Perry et al. | Aug 2009 | B2 |
| 7579495 | Perry et al. | Aug 2009 | B2 |
