DE1191518B - Phosphate-containing coating compounds for air filters - Google Patents

Description

Phosphate-containing coating compositions for air filters The invention relates to new, thickened, thixotropic phosphate gel masses, which are used to coat filter materials are suitable for dust in air filters.

Industrial air filters contain porous filter media or mats, through which the air is passed.

The filter medium is with a stable, non-volatile liquid coated, which traps the dust particles as they pass through the filter, creating it is prevented that these are again entrained in the air flow. It surrenders however, due to the loss of this liquid coating during use a reduction in the cleaning capacity of the filter. The liquid can from the filter medium due to the high air velocities that occur, for example in diesel engine filters. Furthermore, if the filter medium exists consists of tightly wound round coils, as it has recently been developed automatic exchange filters is the case, there is a risk of the liquid coating is squeezed out.

So far, these losses have been avoided by using the fluid a semi-soluble resin or other gelling agent. However These resin-liquid masses suffer a drop in viscosity for those in diesel engine filters occurring temperatures. If gel-forming agents, for example finely divided Silica, are used in amounts up to 70% based on that Mixture, usually required for satisfactory thickening. At a Such an amount of silica in the liquid can clog the spray nozzles and associated filters commonly used to cover the mat will occur. In addition, the mixture becomes thicker due to aging the syneresis, which reduces the ability to capture the dust particles. Syneresis can also occur during storage, causing the liquid is separated from the gel structure. The separated liquid then pulls out of the Matte addition, creating a higher concentration of gel solids on the surface remains behind the mat. The overall effect is always a loss of capacity for filtering dust.

The invention results in filter media coated with liquid for use in filters for high air velocity and in automatic filters. The viscous liquids according to the invention can easily be sprayed onto filter mats and they do not squeeze out when the mats are wound tightly on rollers are.

The stable gelled liquids also sweat for filter mats according to the invention do not separate during storage, nor do they separate when increased Temperatures.

The improved coating compositions for filters according to the invention contain a tri-organic phosphate of the general formula where n is a number between 0 and 1 and the alkyl radical contains 1 to 8 carbon atoms and the aryl radical is derived from tar acid, 0.5 to 5 percent by weight of practically pure fumed silicon dioxide with a particle size not above 0.025 p and 0.1 to 2, 5 percent by weight of a surface-active agent from the group of nonionic surface-active agents, cationic surface-active agents, polyglycols and / or water.

These coating compounds represent stable, thickened liquids, which can be easily sprayed on without clogging filters and nozzles; and they have no tendency to form a liquid exudate which is derived from the Filter mat can be separated.

By mixing the organic phosphate with finely divided pyrogenic Silica and certain surfactants become considerably less Silica required than was previously thought necessary for the Increase the viscosity of the liquid up to the desired range. Furthermore it was found that the gelled liquid under close to spray conditions under lying circumstances is surprisingly fluid. Thus, tricresyl phosphate can according to Invention to a viscosity in the range from about 10,000 to more than 50,000 cP (measured gelled or thickened in a Brookfield viscometer at 6 rev / min), and yet this same liquid has a viscosity down to about 200 cP for spray purposes (measured with a rheometer that corresponds to spray conditions).

It is believed that the effect of the coating on the filter mat to capture the dust particles is based on that of wetting. If a thin Layer of dust that has been trapped by the liquid will carry the particles through Leakage of the liquid covered by the layer.

So in a short time that will be a few seconds to a few minutes can, the first layer of dust completely wetted by the liquid, and the liquid is again open to the dust contained in the air.

Heretofore, the concentration of the thickener was in the coating so high that the dust collection capacity of the filter dropped sharply. According to the invention has the mass, although its viscosity is very high, has a sufficient wetting capacity, to seep through and wet the dust already trapped, and is on top of this Way to catch additional amounts of dust particles. Expressed differently this means that the mass is sufficiently viscous to remain on the filter mats, and that nevertheless the capacity of the liquid to capture dust particles is not significant is decreased.

Another aspect of the invention is that draining the fluid from the mat can be prevented by syneresis. As already As stated above, this phenomenon causes the liquid to separate from the solid component of the gel and finally of the filter mat, so that a very thick substance with high solids content remains. This peeling diminishes the wetting properties and the dust collection capacity of the remaining gel considerable. It was found that by adding a small amount of a soluble resinous material such as cellulose acetate butyrate to organic phosphate prior to the addition of the fumed silica, this stripping was further reduced will. If so, the organic phosphate first with cellulose acetate butyrate is thickened, there is very little loss of separated liquid from the gel on. It also increases the need for silica in this way continued to decrease.

The degree of physical distribution of the silica and the surfactant in the organic phosphate affects the viscosity the liquid. The viscosities get somewhat with a high speed mixer higher than with an ordinary stirrer; Ball mills or roller mills can also can be used to make satisfactory dispersions.

Elevated temperatures should be avoided during the dispersion stage as the heat can adversely affect the gel structure. Normally the mixing operation is carried out at room temperature.

That for the production of the highly viscous masses according to the invention The silicon dioxide used is of the type known as "fumed silicon dioxide". It is made by adding almost pure silicon tetrachloride with water in the Vapor phase is reacted with the production of silicon dioxide and hydrogen chloride. The silica produced in this way is a very pure powder of purity on the order of 990 /, and has a particle size of no more than about 0.025 in. Fumed silicas are currently commercially available available with particle sizes as low as about 0.007. Preferably has the pyrogenic Silica has a particle size of about 0.015 to 0.020, u.

As surface-active agents are nonionic surface agents, for example polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan tristearate and sorbitan monostearate, as well as cationic surfactants, such as. B. alkyltrimethylammonium chloride, Dialkyldimethylammonium chloride, octadecenyltrimethylammonium chloride and tetraethylammonium bromide, extremely effective in increasing the body content of organic phosphate mass.

Polyglycols such as B. the polyethylene glycols and polypropylene glycols, are suitable surfactants according to the invention. Strangely enough is one of the most effective surfactants in small amounts of water. The presence a small amount of water in silica-gelled organic phosphates increases the thickness of the gel up to 35 times the thickness, as it is only with phosphate and Silica occurs alone. If an anionic surfactant is used there must be a small amount of water.

If desired, mixtures of different surface-active substances can also be used Funds are used. All of these treated with surfactants In gels, the thickening effect is stable for many days.

About 0.5 to 50% fumed silica by weight of the entire mixture are sufficient to produce gelled liquids necessary; preferably 1 to 2.5 01o is sufficient to make excellent gels to obtain.

If the liquid phosphate was first thickened with resin, that lies Amount of silica required preferably in the range of about 0.5 to 1.5010. In the case of the pre-thickened liquids, about 1.5 to 3.5% cellulose acetate butyrate resin, based on the weight of the total mixture, added.

This area is sufficient to make stable gels and around to prevent substantial losses through Syneresis. From the surfactant is an amount ranging from about 0.1 to 2.5 percent by weight of the total mixture generally sufficient to achieve useful gels. Preferably will 0.5 to 20% surfactant used.

Possess the triorganic phosphates useful in accordance with the invention the general formula 0 (alkyl - 0 P ¼ 0 - aryl) 3n where n is a number between 0 and represents 1, the alkyl radical has 1 to 8 carbon atoms and the aryl radical derived from tar acids. The term "tar acids" includes acids which with dilute sodium hydroxide solution from tars, such as. B. coal tar, wood tar and lignite tar, can be extracted. Raw tar acid extracts generally contain phenol, ortho-cresol, meta-cresol, para-cresol and the six isomeric xylenes, and they can are fractionated, resulting in different proportions of these products. With the expression »Tricresylphosphata are esters made from phosphoric acid and a mixture which includes alkylphenols known as cresylic acid, and those from coal tar, Wood tar or petroleum distillates.

Suitable alkyl radicals include methyl, ethyl, propyl, isopropyl, Butyl, amyl, isohexyl and ethylhexyl radicals and many more. Preferably there is the phosphate from tricresyl phosphate.

The following examples serve to further illustrate the invention, without limiting them.

All parts and percentages are based on weight.

Example 1 Tricresyl phosphate with a specific gravity of 1.194 was made with a commercially available cellulose acetate butyrate having a butyryl content of about 48 0 / o and an acetyl content of about 60 / o at 1100 C mixed so that a 2 weight percent solution resulted. To 98.5 parts of this solution were 1.0 part of fumed silica and 0.5 part of polyoxyethylene sorbitan monooleate added. A Waring mixer was used to disperse the additives at room temperature used. The Brookfield viscosity of this mixture (using the viscometer Model LVF with spindle no. 4) was 17,000 cP at 6 rev / min. and 5400 cP at 60 Rev./min., Generally working according to ASTM method D 1824 61 T.

The mixture was subjected to a high shear force by being through two standard nozzles under constant pressure. The Castor-Severs rheometer viscosities were 580 cP with a 1.58 mm nozzle and 460 cP with a 3.17 mm nozzle at a pressure of 2.1 kg / cm2 and a shear stress of 18036 and 33900 dyn / cm2. The amount of the pressed material was 113.1 g / min. at the nozzle of 1.58 mm and 1764 g / min. at the nozzle of 3.17 mm. These measurements were made under stress performed close to that of a spray gun, generally by the ASTM method D1823 61T was worked with the exception that the nozzles indicated above and prints were applied.

A second sample of the above mixture having a Brookfield viscosity of 18700 cP at 6 rev / Min. And 4400 cP at 60 rev./min. became in an uncoated Given paper cups for 14 days.

The percentage of material lost due to exudation by the Paper fiber was 0.4%. From this experiment it follows that the syneretic Loss over a long period of time is completely negligible.

As a measure of the wetting capacity of this pre-thickened gelled Liquid was a drop of the liquid in contact with a sheet of glass with a thin layer of finely powdered clay.

The time during which a 1 mm wide strip of the clay wets was about 453 minutes.

Because the average thickness of a single layer of dust is only a few microns this wetting time is extremely short for practical purposes.

Example 2 Tricresyl phosphate was made in a three-roll paint mill using the same silica and surfactant as in Example 1 mixed.

The mixture contained 95.5 parts of the phosphate liquid, 2.0 parts of the surfactant and 2.5 parts of silica. The measured as in Example 1 Brookfield viscosities were 49,000 at 6 rpm and 6,700 at 60 rpm. The viscosities obtained with the Castor-Severs rheometer were also 220 cP the 1.58mm nozzle and 240 cP with the 3.17mm nozzle.

The wetting effect of this mixture was determined using the method with the wetted clay, as described in Example 1, measured. A 1 mm strip of the clay was wetted in about 40 seconds.

The viscosity of this mixture was also at various determined elevated temperatures.

The following Brookfield viscosities were determined using the LVF no. 4-spindle at 60 rev / min. The results are compared with a commercially available coating composition thickened with a typical resin. Tempe- With Silica Thickened With Resin rature gelled liquid liquid, viscosity o C viscosity (cP) 30 6250 7850 40 6563 5250 50 6875 3120 60 6812 1125 70 6563 125 80 6000 100 Example 3 Brookfield viscosities (LVF # 4 spindle) of silica gelled tricresyl phosphate mixed with other surfactants were determined using a high speed mixer to make the following mixtures. The viscosities of these blends are compared to those of two blends that did not contain a surfactant. Mass ABCDE comparison Tricresyl phosphate ... ... 96.0 95.5 95.5 95.5 95.5 97.5 * 96.0 Silica ............... 4.0 2.5 2.5 2.5 2.5 2.5 4.0 Polyoxyethylene sorbitan monooleate 1.0 - - - - - - Water ... .......... ..... . - 1.5 - - - - - Tetraethylammonium bromide ... - - 2.0 - - - - Sorbitan monostearate (25% aqueous Dispersion) ............... - - - 2.0 - - - Polyethylene glycol (molecular weight 400) ................ - - - - 1.5 - - Viscosity (cP) 6 rev / min. ..............> 100,000 25,000 30,000 44,000 24,000 700 - 60 rev / min. ..............> 10 000 3 600 3 350 7 000 4 100 450 450 When these compositions were sprayed onto filter mats, they exhibited excellent dust cleaning properties, the mats maintaining their dust cleaning properties for long periods of time.

Example 4 Further coating compositions gelled with pyrogenic silicon dioxide were prepared from commercially available tricresyl phosphate which originated from cresylic acid with a content of about 100% xylene, methyl diphenyl phosphate and 2-ethylhexyl diphenyl phosphate. The masses and the Brookfield viscosities (LVF No. 4 spindle) of these mixtures are listed in the table below. Mass ABC Tricresyl phosphate .... | 95.5 | - | - Methyldiphenyl phosphate - 95.5 - 2-ethylhexyldiphenyl- phosphate .......... - - 95.5 Silica ....... 2.5 2.5 2.5 Polyoxyethylene sorbitan monooleat ......... 2.0 2.0 2.0 Viscosity (cP) 6 rev / min. .... | 49 000 | 9 500 | 12,000 60 rev / min. .... 6 700 1 500 2050 Claims: 1. Phosphate-containing coating compositions for air filters, characterized by a content of a triorganic phosphate of the formula where n is a number between 0 and 1, the alkyl radical has 1 to 8 carbon atoms and the aryl radical is derived from tar acids, 0.5 to 5 percent by weight of a practically pure fumed silicon dioxide with a particle size not above 0.025μ and 0.1 to 2 , 5 percent by weight of a surfactant such as nonionic surfactants, cationic surfactants, polyglycols and / or water.

Claims (1)

2. coating composition according to claim 1, characterized in that the organic phosphate consists of tricresyl phosphate and fumed silicon dioxide has a particle size of 0.015 to 0.20 µ. 3. coating composition according to claim 2, characterized in that further 1.5 to 3.5 weight percent cellulose acetate butyrate is present. ~~~~~~~~ Considered drawn pamphlets: U.S. Patents Nos. 2,347,031, 2,620,044; British U.S. Patent No. 553,735.