Abstract:
An antislipping composition for a fastener having a head portion, comprising a crosslinked polymer prepared by the polymerization of an olefinic unsaturated carboxylic acid and a compound represented by a general formula (1) given below ##STR1## where R is a hydrogen atom or a methyl group, and the sum of 1, m and n is larger than 0 and not larger than 500, except that where R is a hydrogen atom and n is zero, l+m is not 1, a liquid medium containing at least one compound selected from the group consisting of glycol ethers and glycerin, and silicon carbide particles having acute corner portions.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an antislipping composition for a fastener having a head portion such as a bolt or a screw, particularly, to a composition which permits easily fastening or detaching the fastener with an ordinary tool such as a driver or a torque wrench even where a groove or a corner of the head portion is collapsed. The expression &#34;fastener having a head portion&#34; used herein represents a fastener to which force applied to a tool is transmitted through the head portion such as a bolt or a screw in fastening or detaching the fastener. 
     A fastener having a head portion such as a bolt or a screw is widely used in various fields. Where a groove or a corner of the head portion is collapsed, it is necessary to cut a new groove in the head portion or use a special tool in fastening or detaching the fastener. Such a special tool is not available in the general family. In such a case, the fastener must be forcedly fastened or detached using, for example, a cutting pliers. Under the circumstances, it is of high importance to develop a technique which permits easily fastening or detaching the fastener, even if a groove or a corner of the head portion of the fastener is collapsed. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an antislipping composition for a fastener having a head portion, comprising particles having a predetermined shape and a predetermined hardness, and a predetermined liquid medium which permits imparting fluidity to the composition and which exhibit low toxicity. 
     According to an aspect of the present invention, there is provided an antislipping composition for a fastener having a head portion, comprising: 
     a crosslinked polymer prepared by the polymerization of an olefinic unsaturated carboxylic acid and a compound represented by a general formula (1) given below: ##STR2## where R is a hydrogen atom or a methyl group, and the sum of 1, m and n is larger than 0 and not larger than 500, except that where R is a hydrogen atom and n is zero, l+m is not 1; a liquid medium containing at least one compound selected from the group consisting of glycol ethers and glycerin, and 
     silicon carbide particles having acute corner portions. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The antislipping composition of the present invention contains particles having a predetermined shape and a predetermined hardness. Silicon carbide particles having acute corner portions are used in the present invention as such particles. Where the particles contained in the composition are spherical or do not have acute corner portions, it is impossible to achieve a desired object. Specifically, where a screw or a bolt whose groove or corner in the head portion is collapsed is fastened or detached by an ordinary tool such as a driver, the groove or corner of the head portion is not mechanically caught by the tool. The mechanical catching is not achieved either where the particles have a low hardness, resulting in failure to achieve a desired object. 
     The particles contained in the composition are required to have acute corner portions, as pointed out above. The term &#34;acute corner portion&#34; denotes that the edges of the particles have acute angles. However, it is not necessary for all the edge portions of the particles to have acute angles. The silicon carbide particles having acute corner portions, which are specified in the present invention, can be obtained by pulverizing a crystalline silicon carbide. There are other particles having acute corner portions such as aluminum oxide particles. However, aluminum oxide does not exhibit a sufficiently high hardness, resulting in failure to achieve a desired object, as already pointed out. 
     It is desirable for the silicon carbide particles contained in the antislipping composition of the present invention to have a maximum particle size not larger than 300 μm and to include at least 60% by weight of particles having a particle size of at least 50 μm. The requirement of &#34;a maximum particle size not larger than 300 μm and at least 60% by weight of the particles having at least 50 μm&#34; represents particles falling within a particle size range of #80 to #180 defined in Particle Size Distribution of Coarse Grains of Abrasives in JIS (Japanese Industrial Standards) R6001. Where the head portion of a fastener is coated with an antislipping composition containing silicon carbide particles having a particle size exceeding 300 μm, it is difficult to mount correctly a tool such as a driver or a torque wrench to the head portion of the fastener, with the result that the force applied to the tool is not transmitted to the head portion of the fastener. On the other hand, where silicon carbide particles do not include at least 60% by weight of particles having a particle size of at least 50 μm, the groove or corner of the head portion of the fastener is not mechanically caught by the tool, resulting in failure to achieve a desired object. More preferably, the silicon carbide particles should fall within the particle size range of #100 and #150 specified in JIS R6001. 
     The silicon carbide particles should preferably be contained in the composition in an amount of 20 to 50% by weight of the composition. The amount smaller than 20% by weight is insufficient for allowing the groove or corner in the head portion of the fastener to be mechanically caught by the tool. On the other hand, if the amount of the silicon carbide particles is larger than 50% by weight, the fluidity of the composition is lowered, resulting in failure for the composition to enter a small clearance between groove or corner in the head portion of the fastener and the tool such as a driver or a torque wrench. More preferably, the silicon carbide particles should be contained in an amount of 30 to 40% by weight. 
     The antislipping composition of the present invention also contains a liquid medium containing at least one compound selected from the group consisting of glycol ethers and glycerin. Glycol ethers are effective for imparting a fluidity to the antislipping composition. Where the composition contains a glycol ether, fluidity is imparted to the composition to allow the composition to enter easily a small clearance to produce a desired effect in addition to the operability of the composition is improved. The glycol ethers effectively used in the present invention include, for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, ethylene glycol mono-tert-butyl ether, and 3-methyl-3-methoxybutanol. These compounds can be used singly or in the form of a mixture of some of these compounds. The most preferred glycol ether is 3-methyl-3-methoxybutanol. 
     In the present invention, glycerin can be used in place of or together with the glycol ethers exemplified above. It was certainly known to use ethylene glycol or propylene glycol as a liquid medium in an antislipping composition containing solid particles. However, ethylene glycol exhibits toxicity and, thus, should be handled carefully, making it undesirable for the antislipping composition used in the general family to contain ethylene glycol. 
     Also, ethylene glycol and propylene glycol were found to be poor and substantially equal to each other in the fluidity-imparting capability. On the other hand, compositions containing glycol ethers and/or glycerin exhibit excellent fluidity, as apparent from Examples described herein later. 
     Glycol ethers used in the present invention are also effective for preventing freezing. Further, since glycol ethers can be mixed with water at an optional mixing ratio, the fluidity of the composition can be controlled easily over a wide range. It is desirable for the content of glycol ether and/or glycerin to be 5 to 20% by weight of the composition. If the content is lower than 5% by weight, it is impossible to obtain sufficient effects of imparting fluidity to the composition and preventing the composition from being frozen. If the content exceeds 20% by weight, however, the fluidity of the composition is rendered excessively high, leading to a low viscosity of the composition. As a result, the silicon carbide particles fail to be stably kept dispersed in the composition. More preferably, the composition should contain 7.5 to 15% by weight of glycol ethers and/or glycerin. 
     The antislipping composition of the present invention also contains a crosslinked polymer. The crosslinked polymer, which is a carboxyvinyl polymer, is prepared by the polymerization of an olefinic unsaturated carboxylic acid and a compound represented by the general formula (1) given previously. The olefinic carboxylic acid has at least one active carbon-to-carbon olefinic double bond and at least one carboxyl group, and includes, for example, acrylic acid, methacrylic acid, itaconic acid, chloroacrylic acid, cyanoacrylic acid, α-phenyl acrylic acid, α-benzyl acrylic acid, crotonic acid, maleic acid, fumaric acid, and sorbic acid. Preferably, acrylic acid and methacrylic acid should be used as the olefinic unsaturated carboxylic acid. 
     For preparing the compound represented by general formula (1), alcohols having a molecular weight of about 150 to 1000 are used preferably as the starting materials. 
     The olefinic unsaturated carboxylic acid and the compound of formula (1) are polymerized and crosslinked to form a carboxyvinyl polymer. The polymerization should desirably be carried out in the presence of a catalyst within a solvent capable of dissolving both the olefinic unsaturated carboxylic acid and the compound of formula (1) and incapable of dissolving the resultant copolymer. For example, toluene, benzene, n-hexane, ethyl acetate, etc. can be used as the solvent. The azo type, peroxide type or redox type radical polymerization initiator can be used as the copolymerization catalyst. The specific compounds used as the catalyst include, for example, azo-bisisobutyronitile, 2,2&#39;-azobis(2,4-dimethylvaleronitrile), 2,2&#39;-azobis(2,4-dimethyl-4-methoxyvaleronitrile, benzoyl peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, persulfate, a combination of persulfate and percarbonate, and a combination of persulfate and sulfite. The polymerization temperature, which is naturally dependent on the kinds of the catalyst, monomers, etc., should desirably be 30° to 90° C. in general. 
     Polyacrylates neutralized in advance are generally available on the market as thickeners. However, the conventional thickeners, if used in the present invention, are contained in the composition in a linearly stretched state. As a result, webbing is brought about to cause the composition to exhibit a viscosity having a so-called strong-knees and, thus, a good workability cannot be obtained. To overcome this difficulty, the carboxyvinyl polymer is used in the present invention to control appropriately the viscosity of the antislipping composition. The molecules of the carboxyvinyl polymer are contained in the composition in the shape of an aegagropilas or a coil. The particular condition is considered to prevent webbing and to provide a good workability of the composition. It should be noted that, if the carboxyvinyl polymer is neutralized with an alkali, it is possible to obtain a neutral or alkaline antislipping composition having a good workability. Preferably, sodium bicarbonate should be used for neutralizing the polymer, though a known alkali can be used for the neutralization. 
     The content of the carboxyvinyl polymer should desirably be 2 to 5% by weight of the composition. If the polymer content is less than 2% by weight, the silicon carbide particles are precipitated. If the polymer content is higher than 5% by weight, however, the viscosity of the composition is rendered excessively high, resulting in failure to obtain a good workability. Where the carboxyvinyl polymer is neutralized with sodium bicarbonate, the amount of the neutralizing agent should desirably be 0.2 to 2.0% by weight of the composition. If the amount of the neutralizing agent is smaller than 0.2% by weight, the silicon carbide particles are precipitated. If the amount exceeds 2.0% by weight, however, the viscosity of the composition is rendered excessively high, resulting in failure to obtain a composition having a good workability. 
     In the antislipping composition of the present invention, it is desirable for the liquid medium to contain water and a rust inhibitor in addition to sodium bicarbonate used as a neutralizing agent. In order to prevent the silicon carbide particles from being precipitated with time within the composition, it is desirable to add sodium bicarbonate as a neutralizing agent of the carboxyvinyl polymer so as to control appropriately the viscosity of the antislipping composition. Ammonia water or sodium hydroxide is generally known as a neutralizing agent. However, these known neutralizing agents, which emit a strong odor and constitute strong alkali, must be handled very carefully and, thus, are not desirable. On the other hand, sodium bicarbonate is free from the above-noted problems and, thus, can be handled easily. In addition, sodium bicarbonate is cheap and can be added directly, making it easy to use sodium bicarbonate in manufacturing the antislipping composition of the present invention. It is desirable to use sodium bicarbonate in a minimum amount required for neutralizing the carboxyvinyl polymer. 
     Known rust inhibitors can be used in the present invention as far as the inhibitor is compatible with the composition of the present invention. Specifically, the rust inhibitors used in the present invention include, for example, organic acids such as benzoic acid, alkenyl succinate, esters such as propyl benzoate, alkylamines such as alkanolamine, nitrites of amines, carboxylates of amines, and mineral oils. These rust inhibitors can be used singly or in the form of a mixture of these compounds. It is desirable to add the rust inhibitor in an amount of 0.1 to 5% by weight of the antislipping composition. 
     In preparing the composition of the present invention, for example, carboxyvinyl polymer is dissolved in a mixed liquid consisting of water and at least one of 3-methyl-3-methoxybutanol and glycerin, followed by neutralizing the polymer with sodium bicarbonate so as to adjust the viscosity of the resultant solution at a desired level. Then, silicon carbide particles and a rust inhibitor are added to the solution while stirring the solution to prepare a desired composition having these solid components uniformly mixed therein. The fluidity of the composition, which can be determined as desired, should desirably be about 15 to 50 Pa·s at 20° C. in general. 
     If the composition of the present invention is applied to the head portion of a fastener having a head portion such as a bolt or a screw, the fastener can be fastened easily by an ordinary tool such as a driver or a torque wrench without collapsing the groove or corner in the head portion of the fastener. Also, where the groove or corner in the head portion of the fastener is collapsed, the fastener can be detached easily by the ordinary tool if the head portion is coated with the composition of the present invention. 
    
    
     EXAMPLE 1 
     HIVISWAKO 103 (trade name of carboxyvinyl polymer manufactured by Wako Pure Chemical Industries, Ltd.) and sodium bicarbonate were dissolved in water, followed by adding 3-methyl-3-methoxybutanol to the resultant solution to obtain a viscous liquid. Further, DENSIC #60 (trade name of silicon carbide particles manufactured by Showa Denko K. K.) and RUSMIN W-50 (trade name of a rust inhibitor manufactured by Kyoeisha Chemical Corporation) were added to the resultant viscous liquid to obtain a sample of composition of Example 1. A homogenizer AM-7 manufactured by Nihonseiki Kaisha Ltd. was used for mixing and dissolving the components. 
     EXAMPLES 2 TO 5 
     Samples for these Examples were prepared as in Example 1, except for the particle size of the silicon carbide particles used. 
     EXAMPLES 6 TO 9 
     Samples for these Examples were prepared as in Example 1, except for the amount of the silicon carbide particles used. 
     EXAMPLES 10 TO 14 
     Samples for these Examples were prepared as in Example 1, except for the amount of 3-methyl-3-methoxybutanol used. 
     EXAMPLES 15 TO 18 
     Samples for these Examples were prepared as in Example 1, except that glycerin was used in varied amounts in place of 3-methyl-3-methoxybutanol used. 
     EXAMPLES 19 AND 20 
     Carboxyvinyl polymer (HIBISWAKO 103) and sodium bicarbonate were dissolved in water, followed by adding 3-methyl-3-methoxybutanol (Example 19) or glycerin (Example 20) to the resultant solution to obtain samples for these Examples. A homogenizer AM-7 referred to previously was used for dissolving the components. The viscosities of the viscous samples for these Examples were measured, and a thixotropic index denoting the viscosity properties was calculated on the basis of change in viscosity with the number of rotations of a viscometer. 
     EXAMPLES 21 TO 28 
     Samples for these Examples were prepared as in Example 1, except for the amount of carboxyvinyl polymer used. 
     COMPARATIVE EXAMPLES 1 TO 3 
     Samples for these Comparative Examples were prepared as in Example 1, except that the silicon carbide particles used in Example 1 were replaced by other materials. 
     COMPARATIVE EXAMPLES 4 TO 8 
     Samples for these Comparative Examples were prepared as in Example 1, except that ethylene glycol was used in place of 3-methyl-3-methoxybutanol used in Example 1. 
     COMPARATIVE EXAMPLE 9 
     A sample for this Comparative Example was prepared as in Example 20, except that the amount of water used was 500 parts by weight and that glycerin used in Example 20 was not used in this Comparative Example. 
     COMPARATIVE EXAMPLE 10 
     A sample for this Comparative Example was prepared as in Example 20, except that ethylene glycol was used in this Comparative Example in place of glycerin used in Example 20. 
     COMPARATIVE EXAMPLES 11 AND 12 
     Samples for these Comparative Examples were prepared as in Example 1, except that carboxyvinyl polymer used in Example 1 was replaced by other materials. 
     The samples for these Examples and Comparative Examples were evaluated as follows: 
     Evaluation 1: 
     A head portion with a collapsed groove of a screw was coated with each of the samples. Then, the screw was detached and fastened with a driver to evaluate the effect produced by the sample compositions, with the results as shown in Tables 2, 3 and 5. The compositions of these samples are also shown in these Tables. The evaluations are given in these Tables by symbols given below: 
     ⊚: excellent; ◯: effective; 
     Δ: slightly effective: x: not effective 
     Evaluation 2: 
     Each of the samples was filled in a container provided with a nozzle, and evaluated the squeezing property, thixotropic property, webbing property, and dispersion stability of the sample as discharged from the nozzle. Tables 2, 3, 4 and 5 show the results. The evaluations are given in these Tables by symbols given below: 
     ⊚: excellent; ◯: effective; 
     Δ1: low in effect of improving dispersion stability; 
     Δ2: low in effect of improving thixotropic property; 
     Δ3: low in effect of improving squeezing property; 
     x1: poor in dispersion stability; 
     x2: not effective in respect of thixotropic property; 
     x3: incapable of squeezing; 
     x4: webbing from nozzle. 
     The raw materials used in the Examples and Comparative Examples are summarized in Table 1. 
     
                       TABLE 1______________________________________Raw material  Manufactures Trade name______________________________________silicon carbide         Showa Denko  DENSIC #60 ˜particles     K.K.         #220Aluminum oxide         Showa Denko  MORUNDUMparticles     K.K.         #120 (Brown                      Fused                      Alumina                      MORUNDUM)Carboxyvinyl  Wako Pure    HIVISWAKOpolymer       Chemical     103         Industries,         Ltd.Polysodiumacrylate         NIPPON       AQUALIC IH-N         SHOKUBAI Co.         Ltd.Rust inhibitor         KYOEISHA     RUSMIN W-50         CHEMICAL         CORPORATIONSand particles         Nihon Ceraway                      DAURAREC NChaving obtuse Kaisha Co.,corners       Ltd.Silica-alumina         JAPAN FILLITE                      FILLITE 52/7micro hollow  Co. Ltd.spheres______________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________   particle size defined   in JIS R6001            Example 1                 Example 2                      Example 3                           Example 4                                Example 5__________________________________________________________________________DENSIC #60    #60     35.0 #80    #80          35.0#120   #120               35.0#180   #180                    35.0#220   #220                         35.0MORUNDUM #120DAURAREC NCFILLITE 52/7HIVISWAKO 103    1.0  1.0  1.0  1.0  1.0sodium bicarbonate            1.0  1.0  1.0  1.0  1.0water            51.5 51.5 51.5 51.5 51.5RUSMIN W-50      1.5  1.5  1.5  1.5  1.53-methyl-3-methoxybutanol            10.0 10.0 10.0 10.0 10.0Evaluation 1     Δ                 ◯                      ⊚                           ◯                                ΔEvaluation 2     ◯                 ◯                      ◯                           ◯                                ◯__________________________________________________________________________   particle size defined   in JIS R6001             Example 6                  Example 7                         Example 8                              Example 9__________________________________________________________________________DENSIC #60    #60 #80    #80#120   #120      10.0 20.0   50.0 60.0#180   #180#220   #220MORUNDUM #120DAURAREC NCFILLITE 52/7HIVISWAKO 103     1.0  1.0    1.0  1.0sodium bicarbonate             1.0  1.0    1.0  1.0water             76.5 66.5   36.5 26.5RUSMIN W-50       1.5  1.5    1.5  1.53-methyl-3-methoxybutanol             10.0 10.0   10.0 10.0Evaluation 1      Δ                  ◯                         ◯                              ΔEvaluation 2      ◯                  ◯                         ◯                              ◯__________________________________________________________________________     particle size defined              Comparative                      Comparative                            Comparative     in JIS R6001              Example 1                      Example 2                            Example 3__________________________________________________________________________DENSIC #60  #60 #80  #80#120 #120#180 #180#220 #220MORUNDUM #120      35.0DAURAREC NC                35.0FILLITE 52/7                     35.0HIVISWAKO 103      1.0     1.0   1.0sodium bicarbonate 1.0     1.0   1.0water              51.5    51.5  51.5RUSMIN W-50        1.5     1.5   1.53-methyl-3-methoxybutanol              10.0    10.0  10.0Evaluation 1       × ×                            ×Evaluation 2       ◯                      ◯                            ◯__________________________________________________________________________ 
    
     
                                           TABLE 3__________________________________________________________________________    Example 10          Example 11                Example 12                      Example 13                            Example 14__________________________________________________________________________3-methyl-3-    5.0   7.5   15.0  20.0  25.0methoxybutanolglycerinethyleneglycolHIVISWAKO 103    1.0   1.0   1.0   1.0   1.0sodium   1.0   1.0   1.0   1.0   1.0bicarbonatewater    56.5  54.0  46.5  41.5  36.5RUSMIN W-50    1.5   1.5   1.5   1.5   1.5DENSIC #120    35.0  35.0  35.0  35.0  35.0Evaluation 1    ◯          ◯                ◯                      ◯                            ◯Evaluation 2    ◯          ⊚                ⊚                      ⊚                            Δ1__________________________________________________________________________      Example 15            Example 16                    Example 17                          Example 18__________________________________________________________________________3-methyl-3-methoxybutanolglycerin   5.0   10.0    20.0  25.0ethyleneglycolHIVISWAKO 103      1.0   1.0     1.0   1.0sodium     1.0   1.0     1.0   1.0bicarbonatewater      56.5  51.5    41.5  36.5RUSMIN W-50      1.5   1.5     1.5   1.5DENSIC #120      35.0  35.0    35.0  35.0Evaluation 1      ◯            ◯                    ◯                          ◯Evaluation 2      Δ2            ◯                    ◯                          Δ1__________________________________________________________________________    Comparative          Comparative                Comparative                      Comparative                            Comparative    Example 4          Example 5                Example 6                      Example 7                            Example 8__________________________________________________________________________3-methyl-3-methoxybutanolglycerinethylene 5.0   10.0  20.0  25.0  30.0glycolHIVISWAKO 103    1.0   1.0   1.0   1.0   1.0sodium   1.0   1.0   1.0   1.0   1.0bicarbonatewater    56.5  51.5  41.5  36.5  31.5RUSMIN W-50    1.5   1.5   1.5   1.5   1.5DENSIC #120    35.0  35.0  35.0  35.0  35.0Evaluation 1    ◯          ◯                ◯                      ◯                            ◯Evaluation 2    ×2          ×2                ◯                      ◯                            ×1__________________________________________________________________________ 
    
     
                                           TABLE 4__________________________________________________________________________                       Comparative                             Comparative           Example 19                 Example 20                       Example 9                             Example 20__________________________________________________________________________water           400.0 400.0 500.0 400.03-methyl-3-methoxybutanol           100.0glycerin              100.0ethylene glycol                   100.0HIVISWAKO 103   5.0   5.0   5.0   5.0sodium bicarbonate           5.0   5.0   5.0   5.0Viscosity (Pa · s)     2 rpm 150.0 400.0 170.0 330.0BH type viscometer     4 rpm 110.0 286.0 110.0 240.0Rotor No. 7    20 rpm 29.6  91.0  60.0  86.8thixotropic index     2 rpm/20 rpm           5.07  4.40  2.83  3.80     4 rpm/20 rpm           3.71  3.14  1.83  2.74__________________________________________________________________________ 
    
     
                                           TABLE 5__________________________________________________________________________              Example                   Example                         Example                              Example                                    Example    COMPONENTS              21   22    23   24    25__________________________________________________________________________HIVISWAKO 103    carboxyvinyl polymer              1.0  2.0   5.0  6.0   0.1AQUALIC IH-N    sodium polyacrylateSMECTITE SWN    hydrophilic smectitesodium bicarbonate                       0.1DENSIC #120        35.0 35.0  35.0 35.0  35.0water              52.0 51.5  48.5 47.5  53.3RUSMIN W-50        1.5  1.5   1.5  1.5   1.53-methyl-3-methoxybutanol              10.0 10.0  10.0 10.0  10.0Evaluation 1       ◯                   ◯                         ◯                              ◯                                    ◯Evaluation 2       Δ1                   ◯                         ◯                              Δ3                                    Δ1__________________________________________________________________________              Example                   Example                        Example                             Comparative                                   Comparative    COMPONENTS              26   27   28   Example 11                                   Example 12__________________________________________________________________________HIVISWAKO 103    carboxyvinyl polymer              0.2  2.0  2.5AQUALIC IH-N    sodium polyacrylate      2.0SMECTITE SWN    hydrophilic smectite           2.0sodium bicarbonate 0.2  2.0  2.5DENSIC #120        35.0 35.0 35.0 35.0  35.0water              53.1 49.5 48.5 51.5  51.5RUSMIN W-50        1.5  1.5  1.5  1.5   1.53-methyl-3-methoxybutanol              10.0 10.0 10.0 1.5   1.5Evaluation 1       ◯                   ◯                        ◯                             ◯                                   ◯Evaluation 2       ◯                   ◯                        Δ3                             ×4                                   ×1__________________________________________________________________________ 
    
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalent.