JPH05504919A - Improved method for removing coatings from easily damaged substrates and useful jetting media - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] 5. Field of invention for improved method for removing coatings from scratched substrates and propellant media useful therefor This invention describes a method and method for removing coatings from easily damaged gold straw and composite surfaces or similar substrates. This invention relates to a propellant medium useful for this purpose.

Background of the invention Coatings ( It is often desirable to clean or remove coatings. such purpose Numerous techniques are known for coating surfaces such as paints, sealants, lacquers, etc. Cleaning or removal of coatings ranges from mechanical iH polishing to chemical applications. granite walls and Hard durable surfaces like heavy steel plating can withstand harsh blasting like sandblasting Can be cleaned or removed using abrasive techniques. More delicate surfaces should be used to prevent substrate stains. A less invasive treatment is required.

Civilian airlines and military authorities routinely remove paint and pond impressions from the exteriors of modern airplanes. It takes a lot of money to remove or polish the material. These surfaces are made of lightweight aluminum or other metal alloys or composites, which are relatively soft and do not resist paint or paint. The coating must be removed with care to avoid excessive polishing or chemical damage. this Such damage can lead to vI-destructive damage in extreme cases.

5. Sandblasting is used to remove coatings from scratched metal and composite surfaces such as aircraft. Various improved peeling techniques similar to those have been proposed. Propellant media useful for such purposes It is preferable that the body (blasti mouth g media) meet the following criteria.

1. Relatively non-aggressive (Mohs hardness of approximately 2.0-3.0); 2. Different the availability of various particle size distributions for the treatment of substrates; 3. Free-flowing under high humidity conditions and over a wide range of air pressures and media flow rates; 4. #7 Water soluble to facilitate separation of insoluble paints and resins and facilitate waste disposal. be non-polluting and non-polluting.

Carr U.S. Pat. No. 4.731.125 (granted March 15, 1988) The use of plastic media for jet cleaning of scratched metal and composite surfaces is indicated. Ru. However, such materials are relatively expensive and their use poses waste disposal problems. Wake up vine.

Heavy carbon as a spray medium for removing coatings from five-scarred surfaces such as aircraft parts Sodium chloride has also been proposed. Baking soda easily meets criteria 1, 2 and 4 above. This makes it an ideal choice for such media. Thus, this one is relatively It is non-aggressive (2.5 on the Mohs scale) and available in a variety of particle sizes. , water soluble and commonly used in sewage treatment plants to adjust alkalinity and pH. Usually used. The mild abrasive properties of sodium bicarbonate can be used, for example, for tooth polishing. Already used in wood. For example, U.S. Pat. No. 3.882.638, 3.97 2.123, 4゜174, 571, 4.412.402, 4.21 No. 4.871, No. 4.462.803, No. 4.482.322, No. 4.48 No. 7.582, No. 4.492.575, No. 4°494, No. 932 and No. 4.5 See No. 22.597.

The raw disadvantage of using sodium bicarbonate as a propellant is that it cannot be compressed or The important thing is that there is a tendency to form a cake due to exposure to high humidity conditions. That's true. This is intense in commercial jet finishing operations, where the compressed air flow is substantially damp. air is saturated, i.e. has a relative humidity of greater than 90%, and the air compressor Contains oily filth from sir. In addition, commercially available sodium bicarbonate is Inherently poor flow properties due to particle size distribution and crystalline shape.

Adding flow aids to improve flow and anti-caking properties of sodium bicarbonate It has been known. Thus, in baking formulations and dental air jet prophylactic media, It was previously proposed to combine sodium bicarbonate with calcium phosphate (TCP). ing. The addition of such materials improves the flow and anti-caking properties of the bicarbonate. death However, TCP-treated sodium bicarbonate has a shelf life of 3 to 6 months at room temperature. This is because the TCP absorbs moisture until it is saturated, after which the product condenses.

It is therefore an object of the present invention to media) and the provision of such media to sensitive metals. An object of the present invention is to provide a method for removing a film from the surface of a composite material. Let's use it The bicarbonate propellant media is free-flowing and has a long shelf life under adverse commercial jetting conditions. The propellant is grown under a wide range of well-regulated high flow rates and air pressures at high temperatures. It can be used as a body. Other objects and advantages of the invention are as follows: It should be obvious.

Summary of the invention According to this invention, the injection medium has an average particle size of approximately 100 to 500 microns. crystalline water-soluble heavy carbon, preferably within the range of 250 to 300 microns. The sodium acid particles are preferably at least about 12% O based on the weight of the bicarbonate. or about 0.2-3% hydrophobic silica in admixture with a flow/anti-caking agent. A high velocity flowing stream, preferably a substantially saturated compressed air stream, under a pressure of 1O-150psi We present a method for removing coatings from 5-scarred substrates, which consists of spray finishing the 5-scarred surface with provide

The relatively large particle size of bicarbonate removes corrosive substances from the substrate without damaging the substrate. It has been found to be quite effective in removing products as well as other coatings. child This means that smaller particles have a larger effective surface area as a propellant than larger particles. Contradicts conventional wisdom that it is a more effective cleaning agent. Moreover, most known In spray applications, the faster the feed rate of the spray material, the higher the production rate, i.e. the faster the coating removal. Leaving is faster. However, when using crystalline bicarbonate within the above particle sizes, Efficiently, it takes 1 minute with a regular sandblasting machine using a 0.5 inch diameter nozzle. Economic production rates can be achieved with feed rates of about 3 to 4 pounds per feed. this speed In the following, significantly increasing the bicarbonate injection medium feed rate results in little increase in production rate. stomach.

According to another feature of the invention, by adding hydrophobic silica to the injection medium, Contains no flow aid or, like TCP, contains flow aids such as hydrophilic warp. Significantly better flow properties than comparison media. Additionally, hydrophobic with bicarbonate propellant Those containing silica flow aids have significantly longer, virtually indefinite shelf lives and are commercially available. Excellent resistance to the high relative humidity of commercial compressed air streams.

It is preferable to use crystalline sodium bicarbonate as an abrasive in the propellant of this invention. Yes. However, other water-soluble bicarbonates, such as potassium bicarbonate, It is contemplated that potash metals and ammonium bicarbonate may be used as well. Therefore, The following description refers to the preferred crystalline sodium bicarbonate-containing propellant media. However, this invention also encompasses propellant media containing water-soluble crystalline bicarbonate abrasives as well. It will be understood that it is included.

Hydrophobic silica can be mixed with hydrophilic silica as a flow aid in dental prophylactic abrasive media. It was used in the Such media operate under dramatically different conditions than commercial jetting media. applied in Thus, the dental prophylactic medium has a particle size of approximately 65-70 microns. Contains bicarbonate particles with a Through a 1/16-1732 inch nozzle under the pressure of a laboratory compressed air supply machine, It is applied at a rate of about 3 g per minute.

Most importantly, such an air supply machine is practically not saturated with moisture, and the inherent characteristics of applying commercial propellant media at high throughput in saturated compressed air jet streams. There are different flow and caking problems.

The propellant medium of this invention is a mixture of hydrophobic silica particles, e.g. For example, it consists essentially of sodium bicarbonate. Different from known hydrophilic adhesive strength The hydrophobic silica is substantially free of non-hydrogen-bonded silanol groups and absorbed water.

One preferred hydrophobic glue available for the propellant media is Aerosil ) R972, a product available from Degussa AG. child It is a pure condensed nolicorn dioxide aerosol with silano on its surface. Approximately 75% of the ru groups are chemically reacted with dimethyldichlorosilane, and the product is , approximately 0.7+nmol of chemically bonded methyl groups per 100 m' of surface area. Contains approximately 1% carbon. The particles are between about 10 and 40 nanometers. It varies in diameter and has a specific surface area of about 110 m”/H. It can be made by flame hydrolysis of mosquitoes. More details: Angew, Chem, 72.744 (+960), F-PS 1.368.765 and DT-AS 1 163, 784. Further details regarding these materials can be found in 19 Included in Degussa AG's technical report in August 1986, "Basic properties and applications of Erosil" There is.

The hydrophobic silica particles are present in the crystalline sodium bicarbonate propellant at least about 0.2%. and is mixed in a proportion of up to about 3% (by weight).

Crystalline bicarbonate particles can have any desired diameter within the range of about 100 to 500 microns. It may be of uniform particle size. The propellant is used to remove paint from the exterior of the aircraft. crystalline bicarbonate grains having an average particle size of about 250-300 microns when It is preferable to use children.

The propellant thus configured is suitable for use on five scratch-resistant metals, such as the exterior surfaces of aircraft, such as aluminum. Cleaning or deliquifying aluminum or aluminum metal or composite substrates Even though it's Yoigetsu. Composites that can be treated with this jetting medium are matrix e.g. Contain fibers such as glass strands and graphite for reinforcement with epoxy resin. Consists of things.

Such a propellant medium is suitable for commercial pressure air streams, i.e., substantially humid and saturated (9 0% relative humidity or higher) and is suitable for streams containing oily contaminants from compressors. It is preferable to use A water stream is added to the media/air stream to cool the workpiece and remove dust. Formation can be controlled or film removal rates are somewhat reduced. bicarbonate/sparse The aqueous silica propellant is about 1-10 pounds per minute, preferably about 3-4 pounds per minute. approximately 10-150 ps from a 1/4 inch or larger injection nozzle at a flow rate of Can be applied at an air pressure of i.

According to the invention, as set out above and in more detail below, The propellant medium used is non-caking, has an excellent shelf life, and is free-flowing. be. Therefore, this product is suitable for removing coatings from the surfaces of 5-corrosive metals and composites. Therefore, it can be easily used in commercial jetting operations.

Brief description of the drawing Figure 1 shows a clad aluminum sample with visible corrosion on the surface and penetrating the cladding. This is an electron scanning micrograph of the strike panel before spray finishing.

Figure 2 shows a clad aluminum test panel cleaned by the method of the present invention. This is an electron scanning micrograph. Corrosion byproduct or metal surface 1! Removed without damage It is obvious that the second one was removed.

Figure 3 shows the use of different feed rates of bicarbonate propellant with different average particle sizes. This is a graph comparing the production speeds obtained.

Detailed description of preferred embodiments The following examples show five flow characteristics (example: high production rate) for the injection media of this invention. (Examples 2 and 3). In the examples, all parts and parts are shown unless otherwise indicated. Cents are by weight and all humidity is 0F.

Example 1 Two crystalline sodium bicarbonate samples (each with an average grain size of approximately 250-300 microns) one of which was mixed with 0.5% Erosil R-972 hydrophobic silica. The mixture was used as a media in standard sandblasting equipment. The equipment is manufactured in the United States, Numit AccuStrip System manufactured by Schmidt of Hyuston, KS 0, connected to a 6-way foot-plus pot and an 800 cfm compressor. , a 5-inch nozzle diameter and a Thompson valve.

The Blastbot was equipped with a scale that allowed it to measure the average flow rate.

Each bicarbonate formulation utilizes moisture-saturated, room-temperature compressed air and blasts into the plastpot. A pressure of 60 psig was injected through the nozzle through the media.

Crystalline sodium bicarbonate particles without hydrophobic silica flow aids intermittently flow, rapidly clogging the nozzle and preventing further flow. The replenished flow is maintained. I couldn't hold it.

Crystalline bicarbonate-hydrophobic silica formulations change from 1 bond to 5 bonds per minute. The system was flowed continuously for over 65 hours at a controlled drop rate. Due to this No flow problems were observed.

Example 2 2' x 2' x 0.032 inch thick aluminum test panel treated with water, washed with phosphoric acid solution, rinsed with water, treated with Allodane corrosion inhibitor, Rinse and clean with a final water rinse. Apply epoxide braker and The mixture was air-dried for 8 hours. A polyurethane paint is then applied and the panels are left to dry for 7 days. It was dry. It was then aged in an air oven at 210°F for 96 hours. paint and plastic The target thickness of the immer was 2 mm.

Suitable orifice spray to regulate the flow rate of various sodium bicarbonate propellant media I put it in a plastic pot with a lid. The propellant is 99.5% sodium bicarbonate. (different particle sizes) and 0.5% dirosyl E972 hydrophobic acid.

Set the nozzle pressure to 60 psi and bring the media to a sufficient differential pressure to give the desired delivery rate. did.

I Water pressure was 200 psi and flow rate was 0.5 gal/min. processed product The plasto nozzle angle made with was set to 60°. Increase the media supply amount from 2 to 41!　 Changed to bs/+++in.

The time for complete depainting of the panel was recorded.

The bicarbonate production rate and average particle size for each medium were as follows.

(micron) (ft, 2/m1n>crystalline NaFfCOz 275 2. 2 Compressed NaHCOz 390 1.0 Particle size, Miku a) 65, 90, 150.250 Production speed (when removing paint while) Supply amount 21b, /min O, 751, 31, 41, 6 Supply amount 3I! b, /mi n 1.0 1.7 1.8 2.0 Supply amount 4fb, /min +, 2 1.9 2.0 2.2 This data is summarized in Figure 3 and shows that the song sl or 21 bs/min , curve 2 is 3 A' b/min, and curve 3 is 4 l b/min.

This data corresponds to the large average particle size of sodium bicarbonate (150 and 250 microns). more effective at all feed rates than those containing small particles. Show that something is true.

Economical production is achieved at an average flow rate of approximately 3 pounds per minute; at high feed rates, production It is also clear that there is little improvement in speed.

Example 3 Crystalline sodium bicarbonate and Erosil with an average particle size of approximately 250-300 microns The injection medium described in Example 1, which is mixed with 0.5% of R-972 hydrophobic silica, is granulated. Compressed bicarbonates ranging from 120 meshes to +40 meshes were added to the same hydrophobic film. A comparison was made with a propellant mixed with a similar amount of liquor auxiliary (0.5%). Each The medium was used to depaint aluminum test panels as described in Example 2. It was used for The maximum production rate obtained with each medium was determined and is shown in the table below. The table is , injection containing crystalline sodium bicarbonate from a medium containing compressed sodium bicarbonate This shows that there is an improvement in production speed when using a medium.

Injection media abrasive average particle size Production rate (microns) (ft, 2/m1 n) Crystalline NaHCOi 275 2.2 Compressed NaHCOz 390 1, 0 From the above disclosure, it can be seen that the present invention can remove paint or paint from the surface of a five-scratch (sensitivity) substrate. Method for cleaning or removing coatings and propellants containing crystalline sodium bicarbonate useful therein It will be understood that it is something that provides a body. Example in the preferred embodiment above Various modifications may be made to the plast process and injection medium shown without departing from the scope of the invention. It will be understood that it can be done. The previous description is therefore illustrative and limited. It should be understood that it is not a thing.

Figure 1 jlTIn, L (mif, ft2/#suOU summary The propellant is water soluble and crystalline with an average particle size of 100-500 microns. 5-scratch metal consisting of a mixture of bicarbonate particles and a hydrophobic silica flow/anti-caking agent and propellant media and methods for removing coatings from composite surfaces.

international search report

Claims (10)

[Claims] 1. From the group consisting of alkali metal bicarbonate and ammonium bicarbonate as propellant medium For selected water-soluble and crystalline bicarbonate ions, the amount of carbonate ions average particle size Brush sensitive surfaces with a high-velocity flow stream containing particles of 100 to 500 microns. A method for removing coatings from surfaces of easily damaged metals and composite materials. 2. The flowing stream is a substantially saturated compressed air stream under a pressure of 10 to 150 psi. 2. The method of claim 1. 3. A jet stream is applied to the treated surface at a rate of 1 to 10 bonds of bicarbonate per minute. 2. The method of claim 1. 4. The bicarbonate particles have an average particle size within the range of 250-300 microns The method of claim 1. 5. 2. The method of claim 1, wherein the bicarbonate is sodium carbonate. 6. The propellant medium contains a hydrophobic silica flow/anti-caking agent containing 0.2-3% of bicarbonate ( 2. The method of claim 1, comprising: weight). 7. The hydrophobic silica is substantially free of non-hydrogen-bonded silanol groups and absorbed water. 7. The method of claim 6. 8. Water soluble selected from the group consisting of alkali metal bicarbonate and ammonium bicarbonate crystalline bicarbonate particles with a particle size of 100 to 500 microns; Mixing with 0.2-3% (by weight) of hydrophobic silica flow/anti-caking agent bicarbonate A propellant for removing coatings from the surfaces of sensitive metals and composite materials. 9. The bicarbonate is sodium bicarbonate, and the hydrophobic silica has non-hydrogen-bonded silanol groups. 9. The propellant medium of claim 8, which is substantially free of absorbed water. 10. The bicarbonate has an average particle size within the range of 250-300 microns. The injection medium according to claim 8.