JPH0138544B2 - - Google Patents

Description

Claim 1: Preparing a coating solution of a coating material capable of preventing polymer build-up in the form of a film, by the action on the coating solution of a vinyl chloride gas acting as a carrier for the coating material. Polymer build-up on the interior surface of a polymerization reaction vessel, comprising applying said coating material to the surface of said polymerization reaction vessel, and then polymerizing monomer while in constant contact with the coated interior surface of said reaction vessel. A method to virtually eliminate

2 Claim 1 in which the monomer is vinyl chloride
The method described in section.

3. The method of claim 1, wherein the coating material is present in the coating solution in an amount ranging from about 0.001 to 20.0% by weight.

4. The method of claim 1, wherein the vinyl chloride gas is at a temperature in the range of about 20<0>C to 100<0>C and a pressure of about 20 psig to 1000 psig.

5 The coating material is polyaminobenzene,
Polyhydric phenol, aminophenol, alkyl-
1. The polyaromatic amine according to claim 1, which is a polyaromatic amine produced by a condensation reaction of one or more compounds selected from the group consisting of substituted aminophenols, diphenylamines, and alkyl-substituted diphenylamines. Method.

6. The method of claim 5, wherein the coating solution is a solution of a polyaromatic amine in an organic solvent.

7. The method of claim 5, wherein the coating solution is an aqueous alkali metal hydroxide solution of a polyaromatic amine.

8. The coating solution of claim 7, wherein the coating solution comprises a dispersant selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, gelatin (calf skin), starch, and hydroxymethyl cellulose, which is operable in an aqueous medium. Method.

9. The coating solution consists of an aqueous alkali metal hydroxide solution containing a condensation product selected from the group consisting of self-condensates of one or more polyvalent phenols and self-condensates of polyvalent naphthols, and the polyvalent phenols are The method according to claim 1, wherein the method is selected from the group consisting of resormin, hydroquinone, catechol and phloroglucin.

10 The coating solution consists of an aqueous solution of tannin, the tannin being a hydrolyzable tannin,
2. The method of claim 1, wherein the tannin is selected from the group consisting of condensed tannins and ammonium tannate, and tannins complexed with metal ions.

11. The method according to claim 10, wherein the monomer is vinyl chloride.

12 The coating solution consists of an aqueous alkali metal hydroxide solution of an alkali-soluble dye, and the dye has -OH, -COOH, -SO ₃ H,
The method according to claim 1, which has one or more groups selected from the group consisting of and -SO ₃ Na.

13. The method of claim 12, wherein the dye is an ionic dye selected from the group consisting of acridine, azine, oxazine and thiazine.

14. The method of claim 1, wherein the coating solution comprises an organic solvent solution of a dye soluble in an organic solvent.

15. The method according to claim 14, wherein the dye is nigrosine and the solvent is dimethylformamide.

16 The coating solution consists of an aqueous solution of a water-soluble dye, said dye having a chemical structure of - COONa,
The method according to claim 1, which has one or more groups selected from the group consisting of -COOH, -SO ₃ H and -SO ₃ Na.

17. The method according to claim 1, wherein the monomers are vinyl chloride and vinyl acetate.

Background of the Invention In polymerization-type reactions, polymer deposits and build-up occur on the inner surface of the reactor, which not only impede heat transfer but also reduce productivity and adversely affect polymer quality. . This problem arises in commercial products of vinyl halides and vinylidene polymers and copolymers during homopolymerization or polymerization with other vinylidene monomers with terminal CH ₂ ═C groups or with polymerizable monoolefin monomers. It's a particularly tricky one. For example, in commercial preparations of vinyl chloride polymers, the polymer is usually prepared in the form of discrete, discrete particles by polymerization in an aqueous suspension system. When using such a system,
When used, the vinyl chloride and other comonomers are maintained in the form of small, separated droplets by the use of suspending agents and stirring. Once the reaction is complete, the resulting polymer is washed and dried. The reaction is usually carried out under pressure in a metal or glass-lined reactor equipped with a buffer and a high-speed stirrer. However, these polymerization systems are often not stable. Polymer build-up therefore forms on the interior surfaces of the polymerization reactor, including the buffle and stirrer. Clearly this polymerization build-up must be eliminated with the naturally deleterious consequences it causes.

In the past, various methods have been reported for removing polymer build-up from polymerization reactor surfaces, such as solvent cleaning and the use of various hydraulic mechanical reactor washers. Various methods have also been reported for reducing the amount and nature of polymer build-up formation on the surface, such as the use of various coatings on the surface prior to polymerization. In this regard, for example, US Pat. No. 3,669,946; 4,024,301;
See 4024330 and 4081248 etc. These various methods and coatings have given more than satisfactory results. However, efforts are constantly being made to find fundamental principles in preventing polymer build-up, especially from economic and environmental points of view.

Furthermore, given the size of commercial reactors, not only should a more dilute coating be used to reduce the cost, but also to dilute the color of that coating solution, since almost all known and useful coating solutions are colored. Work continues to find solutions. These coating solutions are applied to the reactor surfaces in a variety of ways, such as by brushing, smearing, watering, spraying, etc. onto the reactor. However, not only from the viewpoint of ease of operation and economy such as the size of commercially available products, but also from the viewpoint of application methods that substantially eliminate or substantially reduce the problem of discoloration and fading, coatings on the reactor surface have been developed. Efforts continue to be made to find fundamental ways to apply it.

SUMMARY OF THE INVENTION If the reaction vessel has previously been coated with a suitable coating on its internal surface, when the olefin monomer is polymerized therein,
It has been found that undesirable polymer build-up on the surfaces is virtually reduced and, in many cases, completely eliminated.
We have found that a variety of coating materials can be applied to reactor surfaces by application using vinyl chloride gas under pressure in the form of a mist of the coating material.
Examples of suitable coating materials for use in the present invention include linear or branched aromatic polyamines, self-condensing polyhydric phenols, tannic acid and tannate salts, a variety of alkali-soluble and water-soluble materials, either natural or synthetic. There are dyes that are soluble in organic solvents and dyes that are soluble in organic solvents. Due to the nature of the components of the coating and the method of application to the reactor surface of the present invention,
In this way it can be applied to the surface without opening the reactor giving a closed polymerization system. When olefin monomers are polymerized, the polymerization takes place in an aqueous polymerization medium that remains in contact with the coated surface throughout the polymerization reaction.

DETAILED DESCRIPTION In accordance with the present invention, a film or coating of coating material as defined and described below is applied to the internal surface of a polymerization reactor or vessel by means of gaseous vinyl chloride under pressure. be. In the text below
Although referred to as VCM, vinyl chloride gas under pressure is applied to the coating by picking up the coating solution at an aspirator valve or other suitable equipment, such as a vaporizer, and passing it through a suitable spray nozzle installed in the reactor. The substance forms a mist and coats the reactor surface. All exposed surfaces inside the reactor such as walls, stirrers, etc., in addition to the walls, are coated at the same time and in the same way, since the spray nozzles are arranged to cover the entire inner surface of the reactor. Ru. Furthermore, since the coating is in the form of a mist, all areas that may be difficult to obtain, such as blind spots or shadowed areas in the reactor, can likewise be uniformly coated using the present invention. . After the coating solution has been applied to the surface, the polymerization medium is introduced into the reactor and the reaction is initiated without the need for drying before introduction of the polymerization medium.

VCM gas flows through an aspirator or similar device. The equipment picks up the coating solution under pressures ranging from about 20 to 1000 psig. VCM pressure is dependent on the nature and viscosity of the coating solution being used as well as the spray system being used. Generally pressures in the range of about 80 to 250 psig are sufficient to give satisfactory results. As used in the present invention, the temperature of the VCM gas is typically about 20-100°C
within the range of Preferably, the temperature of the VCM gas is in the range of about 50-80°C.

The coating solution used in the present invention is usually an aqueous solution of the coating material, said solution being neutral, basic or acidic. For example, when using polyaromatic amines or polyhydric phenols as coating materials, aqueous solutions of alkali metal hydroxides are used therefor. The aqueous coating solution is preferably an organic solvent such as methanol and dimethylformamide. Organic solvents are particularly useful with water-insoluble systems such as dyes such as nigrosine. Regardless of the solvent used to create the coating solution, some, and sometimes all, of the solvent is vaporized as a result of the heat and pressure generated during the coating process. In any case, the coating material reaches all internal surfaces of the reactor in the form of a mist. As a result of the improved efficiency of the present coating method, the amount of coating material required has been significantly reduced. In fact, the amount of coating material required is reduced as it is no longer necessary to wash the reactor with water or other liquid solvents or non-solvents used for effluent removal and disposal of waste. are doing. The VCM gas used to coat the reactor is placed in the reactor and becomes part of the reaction medium, eliminating the need for its removal in terms of equipment or process. The amount of VCM gas is so small compared to the amount of monomer in the polymer charge that it has little or no effect on the balance of the polymerization recipe. Of course, the VCM gas can be removed if so desired, but for cost and environmental reasons it is best placed in the reactor.

Once the coating liquid has been prepared, it is fed into an aspirator or similar device where it is picked up by VCM gas. As previously pointed out, the coating material is introduced to the reactor surface in the form of a mist. Typically from about 0.001 to 0.001 by weight depending on the particular coating material and solvent used
Coating solutions with a concentration of coating material in the range of 20.0% are good. Approximately 0.05~ by weight
More preferred is a coating liquid in the 10.0% range.
The concentration and amount of coating solution used depends in large part on the type of coating material used, and to a certain extent on the system used to apply the coating. For example, when using a polyaromatic amine as the coating material, 8 ounces of a 1% solution by weight is sufficient to coat an 1100 gallon reactor using VCM gas. This is a significant advance over coating methods previously known in the art.

Many different coating materials capable of combating polymer build-up have been used to create coating solutions useful in practicing the methods of the present invention. In particular, these substances
It is a linear or branched aromatic polyamine or condensed polyhydric phenol. Polyaromatic amines are prepared by any one reaction alone, except for polyhydric phenols or one or more compounds selected from polyaminobenzenes, polyhydric phenols, aminophenols, alkyl-substituted diphenyl amines. Some examples of such polyaromatic amines can be mentioned. Examples include m-phenylenediamine (m-PDA) and resormine; m-PDA and p-aminophenol; p-PDA and hydroquinone;
Examples include toluene-2,4-diamine and resolmin; self-condensed m-PDA; reaction products of m-PDA, resolmin, and p-aminophenol. These polyaromatic amines are specifically shown and described in Morningstar and Kehe, US Pat. No. 4,024,330, issued May 17, 1977, and is incorporated herein. The invention also shows a method for preparing polyaromatic amines and applying them to the walls of reactors by means of solutions in organic solvents.

Witenhafer, Haehn, Cohen, 1977, 5
US Pat. No. 4,024,301, issued on May 17, 2003, describes a method for applying the linear or branched polyaromatic amines described above to the surface of a reactor using an aqueous solution of an alkali metal hydroxide. This patent is also incorporated herein.

U.S. patent issued March 28, 1978 by Cohen
4081248, applying to the reactor surface an aqueous alkali metal hydroxide coating solution containing a linear or branched polyaromatic amine as described herein and a dispersant that can be used in an aqueous medium. It describes how to do this. Useful dispersants so used are polyvinyl alcohol, polyvinylpyrrolidone, gelatin (calf skin), starch and hydroxypropyl methylcellulose. This patent is also incorporated herein.

Another class of coating materials that are very useful in substantially removing polymer build-up in polymerization reactors are self-condensing polyhydric phenols, which can also be used in the practice of the present process using VCM as a carrier. These coating materials are also introduced here, but according to Cohen
As shown and described in US Pat. No. 4,080,173, issued March 21, 1978. This invention also shows a method for producing self-condensing polyhydric phenols. The patent describes (1) a self-condensate of polyhydric phenols, or (2) a condensate of two or more polyhydric phenols, or (3) dissolved in an aqueous solution of an alkali metal hydroxide as the main component. A coating composition comprising a self-condensate of polyhydric naphthols has been applied to the reactor surface. The polyhydric phenols used to prepare the condensate are resormin, hydroquinone, catechol and phloroglucin.

Another class of materials suitable and used in the present process for application to the reactor surface to substantially eliminate polymer build-up is therefore another class of materials, such as tannins. It is an acidic tannin.
Tannins are divided into two main groups: hydrolysable tannins and condensed tannins. Tannins are usually fixed from extraction sources, ie trees or plants. Examples of hydrolysable tannins and their sources include Chinese gallic or tannic acid, myrovalantannin (nut), valonia tannin (acorn vine and barley), chestnut tree tannin (tree nut), ) davy davy tannin, (saya) etc. Examples of condensed tannins and their sources include oak tannins (tree bark), carrot tannins (tree bark),
Names include acacia tree tannin (tree bark), sumac tannin (leaf), quebratillo tannin (wood), redwood tannin (tree bark), and gambir tannin (leaf). Also useful are ammonium tannate and tannins combined with metal ions. Its tannins are due to Cohen
It is shown and described in US Pat. No. 4,105,840, issued Aug. 8, 1978, and is incorporated herein.

Another class of materials suitable for making coating solutions for application to reactor surfaces in accordance with the present method to substantially eliminate polymer build-up are various dyes. For example, alkali-soluble dyes that are dissolved in aqueous solutions of alkali metal hydroxides or ammonium hydroxides are described by Witenhafer, January 1978.
It is shown and described in US Pat. No. 4,068,059, issued on the 10th, and is incorporated herein. Alkali-soluble dyes contain one or more of the following radicals in their chemical structure: -OH, -
COOH, --SO ₃ H and --SO ₃ Na, and the radicals may be similar or different in any one dye structure. Azo dyes such as monoazo and polyazo dyes; metal-containing azo dyes; mordant dyes; pyrazolones; stilbene dyes, naphthol dyes, phenols, naphthols; anthraquinone dyes. ; diphenylmethane and triphenylmethane dyes; thiazoles, nitro dyes; xanthenes; benzoquinones and naphthoquinones; and soluble butt dyes such as indigoids and anthraquinoids. or,
Ionic dyes such as acridine, azine, oxazine and thiazine are also useful.

1977 under the name of Witenhafer as a further dye
There are water soluble dyes shown and described in pending Application Serial No. 807,958 filed June 20, 2006. These dyes contain one or more of the following radicals:-
Contains COONa, -COOH, -SO ₃ H and -SO ₃ Na. The dyes indicated in the above-mentioned applications are also incorporated herein by reference. In addition to the above dyes, dyes soluble in various organic solvents may be used, such as nigrosine, aniline black, etc., as shown, for example, in U.S. Pat.

A water-wet surface may be necessary to prevent polymer build-up in the reactor. When a metal or solid surface is not wet, liquids such as water thereby form droplets and do not run off into a smooth, uniform film. For example, common solid surfaces such as stainless steel become impermeable to water due to spontaneous contamination of the surface with organic materials upon contact with the atmosphere. The surface can be cleaned, for example with chromic acid or an abrasive cleanser, and becomes wettable with water. However, these are not sufficient answers. This is because the surface will not remain in that condition for a sufficiently long time, ie, longer than the duration of one polymerization reaction. That is, the surface must be recleaned after each polymerization cycle. It is therefore more desirable to apply a coating to a surface that becomes wet and resists the build-up of polymer thereon and remains that surface through multiple reaction cycles.

The wettability of solid surfaces can be measured. The angle formed between the lateral tangent of the droplet and the metal or glass surface is called the "contact angle" and the "theta"
It can be expressed as (θ). Furthermore, there is a critical surface tension that wets the solid surface as a measure of the wettability of the solid surface, and it is expressed as "γ _c ". The “γ _c ” is
Measured in dyn/cm. For a solid surface to be wetted, using water as the standard, θ is equal to or very close to 0, and ``γ _c' ' is
Must be 72 dyn/cm or higher.

More importantly, the coating material applied to the surface not only forms a wet surface, but also forms a continuous layer or film thereon that is not easily removed. The film or coating is attached to a solid or metal surface by adsorption and is often a single layer of coating material applied on the order of one molecule in thickness. These films with such thickness are invisible to the naked eye, thus further solving the previously mentioned coloration problem. Of course, thicker films will result if a coating solution is used that contains a higher solids content where the film or coating is visible to the naked eye. The film or layer formed by the coating composition applied to the surface by VCM gas according to the present invention is not removed by washing with water. That is, the coating or film is caused by agitation of the polymerization mixture in the reactor, when the agitated aqueous reaction medium is brought into contact with it;
It is resistant to removal from reactor surfaces.

Coating liquids useful in the present invention may include, if necessary,
It is also produced by a commonly used method using heat and stirring. Typically, temperatures in the range of about 0-100°C are suitable. Stirring is desirable to dissolve the coating material. When the concentration of the coating material is within the above range, the coating solution can be easily applied to the reactor surface by VCM gas through the nozzle installed in the reactor. Additionally, the molecular weight of the coating material influences its concentration of total solids in the coating solution or solution. Furthermore, these factors can alter the concentration of coating material in the coating solution.

It should be pointed out that the coating components used in the present invention work equally well on glass or metal surfaces such as stainless steel and the like. Although the exact mechanism for adhesion of the coating to the reactor surface is not known with certainty,
It is likely to involve some kind of electrical force or adsorption between the reactor surface and the coating material, especially with some coating solution. In any event, the coating components useful in the present invention are those that can substantially eliminate polymer build-up on the surface, with little, if any, polymer build-up occurring and no manual scraping operations required. It is of a "sand-like" nature that can be easily removed from the reactor surface. Avoidable polymer build-up is what is referred to as "paper-like"build-up; this type of build-up is very difficult to remove and is usually removed by hand or with a high-pressure jet of water or other liquid. It requires the use of In any case, the reactor must be opened to clean it, and doing so would allow the venting of unreacted monomers, such as vinyl chloride, into a health-hazardous atmosphere. That means you are doing it.

According to the present invention, multiple polymerizations are made during charging without opening the reactor by application of the coating with VCM gas. Although multiple charges are made without reapplying the surface, they should be done rapidly and preferably the reactor after every charge or every few charges to ensure a uniform and effective product. I've come to realize that it's good to reapply. This is most easily accomplished by application of the coating components with VCM gas through a spray nozzle as described above. If it is decided to reapply the reactor,
The reactor is drained and the internal surfaces are then rinsed with water via a spray nozzle to remove any loose polymer particles. Then the coating is applied by VCM gas. Thereafter, the reactor is charged in the usual manner with polymerization medium and polymerization components, and the polymerization reaction begins. Of course, it will be appreciated that even after each charge is polymerized, the reactor can be recoated as often as desired without opening the reactor. It should also be noted that due to the presence of the coating, no technical modification in the polymerization process is required. Furthermore, the use of internally coated reaction vessels of the present invention does not adversely affect the thermal stability or other physical and chemical properties of the polymers produced therein.

Although the present invention is specifically described with respect to the suspension polymerization of vinyl chloride, the process is similar to the dispersion, emulsion or suspension polymerization of polymerizable ethylenically unsaturated monomers where undesirable polymer build-up occurs. It makes me understand that it can also be applied to Examples of such monomers include vinyl bromide, other vinyl halides such as vinylidene chloride, and vinylidene halides, such as methyl methacrylate, ethyl acrylate, butyl acrylate, octyl acrylate, cyanoethyl acrylate, etc. Vinylidene monomers having at least one terminal CH ₂ =C group, such as acrylic esters of Styrene derivatives, vinylnaphthalene, including styrene, vinyltoluene, chlorostyrene, etc.; diolefins, including butadiene, isoprene, chloroprene, etc.; and mixtures of some types of these monomers with other copolymerizable vinylidene monomers; There are other types of vinylidene monomers known to those skilled in the art.

However, the present invention particularly provides that at least one end group of vinyl chloride, alone or one or more, can be copolymerized therewith in an amount of about 80% or more by weight, based on the weight of the monomer mixture.
It has been applied to suspension polymerization in mixtures with other vinylidenes having CH ₂ =C groups. Because polymer build-up is a problem in this area.

In the present invention, the polymerization process is generally carried out at temperatures ranging from about 0 to 100°C, depending on the particular monomers being polymerized. However, it is preferred to employ temperatures in the range of about 40-70°C. This is because at these temperatures polymers with the most beneficial properties are produced. The polymerization reaction time is about 2~
It changes to 15hr. For more volatile monomers,
The polymerization process is carried out under autogenous pressure, although superatmospheric pressures of 10 atmospheres or more are conveniently employed. Superatmospheric pressure is also employed for monomers with the necessary volatility at the reaction temperature, allowing reflux cooling of the reaction mixture.

Additionally, the polymerization process is accomplished utilizing full reactor technology. That is, the reaction vessel is completely filled with polymerization medium, which is maintained throughout the reaction by constant addition to it of an additional supplementary liquid containing water or monomer. Upon addition of some predetermined amount of liquid, the polymerization reaction is usually terminated by addition thereto of a quick stop liquid. The necessity of adding liquid is due to the volumetric contraction of the reaction medium produced by the conversion of the monomers of the polymerization phase.

Various coatings can be evaluated by visual observation, especially as illustrated in the specific examples described below.

To further explain the invention, the following specific example is given. However, it should be understood that this is merely illustrative and is not intended to be limiting. In the examples all parts and percentages are by weight unless otherwise indicated.

Example In this example an uncoated reactor was used to establish a control.
The reactor surface was cleaned with high pressure water before charging the polymerization components. Initially, 630 gallons of unmineralized water (52°C) was added with stirring to a reactor to which was added 72 pounds by weight of a 3% aqueous solution of hydroxypropyl methylcellulose. Then the reactor is closed and the mercury is removed without stirring.
I removed it to make it 25 inches. The catalyst was then added, which was 0.54 pounds of di-sec-butyl peroxydicarbonate as a 20% solution in hexane. Agitation was then started and 3000 pounds of vinyl chloride was added to the reactor. The reaction mixture was then heated to 52°C and the polymerization reaction was carried out at this temperature for 8.5 hours. During the course of the polymerization, unmineralized water was added at a rate of 0.27 gallons per minute to compensate for volume loss due to polymer formation. Polymerization is
Discontinued after 4 psig pressure drop or 8.5 hr. After removing the produced polymer, the reactor was flushed with water and three additional charges were subsequently made to the reactor in the same manner. Fourth
After the second charge, the reactor was tested for polymer build-up. All of the interior surfaces were heavily covered with polymer and papery build-up lumps or clumps. Therefore, the control reactor without coating on the internal surfaces was classified as "dirty."

Example In this example, the reactor was coated before the polymerization reaction took place therein. The coating solution used here consisted of 3 grams of Nigrosine Z1630 dissolved in 8 ounces of dimethylformamide. VCM gas was introduced into the reactor under a pressure of 150 psig through a spray nozzle installed in the reactor. Approximately 5 seconds after the VCM gas exits, the coating liquid is slowly added to the VCM gas stream and carried as a mist to the interior surfaces of the reactor. The coating operation was carried out for approximately 20 seconds, and upon completion, the reactor surface was rinsed with mineral-free water. (Note: This method is optional.) After the water wash, the reactor was charged using the example recipe and procedure. The reaction mixture was then heated to 52° C. and kept at this temperature throughout the polymerization reaction, which lasted for 8.5 hr. After this charge is over,
The polymer was removed and three additional charges were made in succession to the reactor in a similar manner. Before each additional charge the reactor surface was coated in the same manner as described above. For reactor testing, all surfaces were found to be clean and substantially free of polymer build-up after the fourth charge. There is almost no build-up, which means it is a soft, sand-like type that is easily removed with fingertip pressure. Improvements were demonstrated for the example uncoated or control reactors and there was no papery build-up.

Example In this example, the internal surfaces of the reactor were also coated with an aqueous alkali metal hydroxide solution of a self-condensed polyhydric phenol, resormine. Self-condensed resormin is covered by US Patent No. 4080173.
Manufactured according to the procedure given in . The concentration of the coating solution was prepared as follows.

15% Self-condensing resorumin 10% NaOH 75% Water (mineral-free) 20 c.c. of the above solution in 8 ounces of mineral-free water was used to coat the interior surfaces of the reactor. . The reactor was coated in the same manner as shown in the examples. Again, using the example polymerization recipe and procedure, four charges were made with water washing and coating of the internal surfaces after each charge. After the fourth charge and the polymer was removed, the reactor was tested and found to be in very good condition for polymer build-up. There was no papery buildup, just a few soft sandy spots that were easily removed. The condition of the reactor was much better than that of the control example.

Coating the interior surfaces of a polymerization reaction by this method not only virtually eliminates polymer build-up, but also allows less coating material to be used than ever before, providing a more economical coating method. That's true. According to this method, in the case of polymerization of vinyl chloride, p.
It is possible to operate a closed polymerization system, which has the advantage of reducing p.m. Numerous other advantages of the present invention will be apparent to those skilled in the art.

Although the invention has been described in its specific embodiments, certain modifications and equivalents may be made.
obvious to those skilled in the art,
It is intended to be included within the scope of the invention which may be limited only by the scope of the appended claims.