This is a continuation-in-part of U.S. Patent Applicatio Serial No. 07/628,568, filed December 17, 1990.

FIELD OF THE INVENTION

The present invention relates to ink compositions applied to substrates, and in particular to inks comprised of a mixture of polyurethane and an air-curable, oil-based ink applied directly to a substrate.

BACKGROUND OF THE INVENTION

A coating is a clear over-print applied to a press sheet to improve the overall glossiness and provide abrasion resistance to the printed image. Today's printing industry demands high gloss, high abrasion resistant coatings, for example as dust jackets for books, for advertising brochures, and food packaging.

Coatings are applied in-line on-press as an extra press unit, off-line on coating or varnishing machines, or in-line followed by off-line to achieve the greatest effect. Coatings are applied locally to selected image areas with conventional offset lithographic techniques on press, or with blanket cut-outs on coating machines.

Coatings may also be applied over the entire sheet with offset blankets either on-press or on a coating machine.

The term "varnishing" is still used to define in-line coating using printing units to apply a coating to a localized area. Occasionally, the term is also used to differentiate creative, special-effect coating from production coating. Varnishing originally referred to coating with a boiled linseed oil varnish, applied on-press as if the varnish were a clear ink. Although varnish increased gloss and rub-resistance, anti-setoff powder used in printing decreased the gloss and rub-resistance. In some cases, varnish actually decreased gloss.

In general, there are two types of coatings presently used by the printing industry; "aqueous" coatings and "UV" coatings, neither of which has proven wholly satisfactory. Aqueous (acrylic) and ultraviolet (UV) coatings have over the years, however, come to replace varnish as the primary coating mediums for over-

printing.

An aqueous (acrylic) coating is a water-soluble, thermoplasti polymer coating that requires heat and air to dry or harden th coating. Aqueous coatings are 60% solvent, (water and alcohol) much of which escapes in the coating and drying process, along wit some of the gloss. Once applied and dried under infrared heat aqueous coatings harden instantly, but because they ar thermoplastics they can be softened with reapplication of heat.

A UV coating is a monomer coating that requires ultra viole energy to dry or harden the coating. UV coatings have a photo initiator which start the ultraviolet hardening process. U coatings are solventless, which means that once applied and drie under ultraviolet energy UV coatings harden instantly and are no susceptible to softening.

Although aqueous and UV coatings have improved the level o gloss and abrasion resistance over previously used coatings, acrylic and UV coatings are not without problems. For example, aqueous coatings will not adhere to a previous UV coating. Als aqueous coatings are less glossy and less rub-resistant than U coatings. Aqueous coatings have a tendency to "reactivate" on the sheet, for example, when stored in a warm warehouse, which can cause the sheets to stick together and ruin the job.

UV coatings are more expensive than aqueous coatings, requiring special expensive equipment and ultraviolet lights, which require workers to wear protective clothing and goggles. UV coatings have a tendency to crack when a printed sheet is folded, and cannot be printed over once applied to a substrate. Also, UV coatings typically require special catalysts and other additives to impart an acceptable coating.

In general, the prior art coatings are not especially useful in many different applications for which coatings are required, such as hot- and cold-food packaging. Often, coatings of the prior art exhibit low gloss, poor scratch resistance, poor waterproofing, heat and cold sensitivity, and adherence problems relative to the substrate. Frequently the coatings of the prior art do not significantly minimize the tendency for ink colors to fade. Also,

these prior art coatings do little to improve the otherwise dul colors of ink printed on recycled paper. Accordingly, it would b useful to develop a coating for printed substrates that eliminate or reduced most or all of the above-noted problems experienced wit the prior art coatings.

In general, inks comprise a mixture of pigment, vehicle, an additives. The pigment is what gives ink its color. The vehicl typically comprises a rosin-based resin, an oil, and/or a petroleu distillate. The oils may be vegetable, petroleum or rubber-based The additives include driers, anti-skinning agents and waxes.

Most recently, soybean oil, a vegetable oil, has been gainin acceptance as an alternative to petroleum oils in the manufactur of printing inks. Soybean oil-based printing inks have been use for both black and color printing since about 1987. Black soy ink are typically 70-80% soybean oil and color soy inks generally hav a lower oil content by weight, including a larger proportion o pigment than the black inks.

Soybean oil-based printing inks are considered to b environmentally advantageous relative to petroleum-based inks. So ink produces less vapors, known as "volatile organic compounds" o "V.O.C.'s", which are regulated by the EPA. Petroleum-based ink often have a 25-40% V.O.C. rating whereas soy ink V.O.C. rating are typically less than 10%, often in the 2-4% range, and in som cases even 0%. Soy ink is also biodegradable than petroleum-base inks.

The quantity of soybean oil used in inks varies, dependin upon manufacturer and the end use of the ink. Newspaper ink generally use greater than 50% by weight soybean oil, sheet-fe printers use about 20-40% soybean oil, magazine inks use 10-15 soybean oil and business forms are typically printed with ink containing about 40% soybean oil by weight. These percentages ar based on the non-pigment portion of the ink.

Despite its growing acceptability, soybean oil-based inks hav not yet realized their full potential as a replacement fo petroleum-based inks. One of the concerns of soybean oil-base inks is the tendency for these inks to dry more slowly than th

petroleum-based inks. This tendency to dry more slowly makes s inks less attractive to commercial printers with high volume hea set presses. The soybean oil-based links also tend to ha inferior dry-back characteristics, adversely affecting pri quality, as the ink tends to dry back into the sheet, bei absorbed by the sheet as it dries. Soy inks also frequentl exhibit inferior scratch resistance. Accordingly, a significan advance in the art could be realized if a soybean oil-based in could be developed that experienced faster drying than conventiona soybean oil-based inks and achieved better dry-back and scratc resistance than conventional soybean oil-based inks.

It is an object of the present invention to provide a non aqueous coating that is waterproof and highly abrasion resistant It is a further object of the present invention to provide coating that imparts improved gloss to a substrate.

It is yet another object of the present invention to provid a coating which protects against fading of colors over which th coating is applied.

It is another object of the present invention to provide coating which is insensitive to hot and cold temperature extremes.

It is still another object of the present invention to provid a coating which brightens ink or other pigments over which th coating is applied.

It is a further object of the present invention to allo coating and/or printing over surfaces which normally cannot b adhered to.

It is another object of the present invention to provide coating which is quick- rying.

It is still another object of the invention to provide an oil- based ink that experiences improved drying properties, including faster drying and improved dry-back.

It is yet another object of the invention to provide an oil- based ink that exhibits increased yield.

It is a further object of the invention to provide an oil- based ink that yields improved scratch resistance.

SUMMARY OF THE INVENTION

According to the present invention, it has unexpectedly be found that a coating for printed and other substrates comprisi a mixture of polyurethane and a clear-coat varnish, without a catalysts or additives, produces a waterproof coating that stable in both hot and cold environments, and imparts great scratch resistance and gloss relative to prior art coatings. T coating dries relatively rapidly and produces improved col enhancement and fade resistant relative to prior art coatings.

In a preferred embodiment of the invention, polyurethane a clear-coat varnish are present in a weight ratio of about 1:16 1:10 and most preferably about 1:12. Because the coating is no aqueous, it imparts waterproof properties that are not availab from the aqueous coatings. The coating does not, however, requi the expensive ultraviolet equipment required for the UV coating

In another embodiment of the invention polyurethane is mix directly with oil-based ink, imparting improved properties to t ink,_

In yet another embodiment of the invention, a coating polyurethane/varnish is applied to the printed substrate print with the polyurethane/ink composition.

Still another embodiment of the present invention incorporat polyurethane into an air-curable oil or rubber-based i composition. In one preferred embodiment, a soybean oil petroleum oil-based ink composition includes from 1% to 50 polyurethane by weight based on the total weight of the ink prio to polyurethane addition. The ink experiences improved dry-bac even at levels as low as 1% polyurethane by weight.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 illustrates an infrared spectrograph for varnis alone.

Figure 2 illustrates an infrared spectrograph for polyurethan alone.

Figure 3 illustrates an infrared spectrograph for varnish wit polyurethane according to a preferred embodiment of the presen invention.

Figure 4 illustrates an infrared spectrograph of proces

yellow ink with polyurethane according to a preferred embodime of the present invention.

Figure 5a-f illustrates dry-back results of preferr embodiments of the invention, comparing ink containing polyurethane to ink containing polyurethane.

DETAILED DESCRIPTION OF THE INVENTION One embodiment of the present invention comprises a no aqueous composition for use as a waterproof coating, which stable in both hot and cold environments. Preferably, t composition comprises a mixture of a polyurethane and a clear-coa varnish. As used herein, the term "polyurethane" refers to any o the various polymeric materials known as polyurethane. By way o example, but not limitation, a polyurethane material that has bee used with success in the present invention comprises a product b the name ZAR®GL0SS, manufactured by United Gilsonite Laboratories of Scranton, Pennsylvania. Another suitable polyurethane i manu acture .by Minwax, of Montvale, New Jersey, and is sold a clear gloss polyurethane.

The ZAR®GL0SS product comprises approximately 45% by weigh mineral spirits and 50% by weight modified polyurethane resin, an less than about 5% kerosene.

It is, of course, contemplated to be within the scope of th invention that it would be possible to mix polyurethane resi directly with the varnish, or the ink, or to use other polyurethan mixtures, either with or without a mineral spirit carrier, as woul be appreciated by those skilled in the art.

As used herein, the term "varnish" refers to any oleoresinou varnish that may be used in the printing industry. Varnishe suitable for coatings are known, and include, for example thos described in U.S. Patent No. 2,412,592, incorporated by referenc herein. "Clear coat varnish" is a well-known term used an understood by those skilled in the printing industry. By way of example, but not limitation, a varnish that has proven useful in connection with the present invention includes that known by the name ALGLOSS OVERVARNISH, product code P017, manufactured by Algan,

Inc. of Chagrin Falls, Ohio. Also, overprint varnish sold by Ca Inc. of Denver, CO has proven effective in compositions of t present invention.

In a preferred embodiment of the invention, approximately o part of polyurethane, by weight, is mixed with approximately 10 16 parts of varnish by weight to produce a non-aqueous coati which may be applied directly to the inked sheet. Most preferabl one part by weight polyurethane to twelve parts by weight varni is used. If the ratio of varnish to polyurethane goes much bel 10, the polyurethane tends to form a layer which interferes wi providing an acceptable coating. If the ratio goes much above 1 the improved results of the present invention becomes le pronounce .

Surprisingly, it has been found that when this coating applied and dried, the resulting coated substrate exhibits superi gloss, abrasion resistance, color enhancement and fade resistan relative to prior art coatings.

The use of polyurethane generally in connection with coatin is not new. Hille, et al. U.S. Patent No. 4,496,675 discloses aqueous dispersion based on a polyurethane synthetic resin. Thi dispersion includes a hydrolyzed shellac as a second bind component. However, this coating is aqueous, and must b manufactured by hydrolyzing the shellac, by heating the compositio in water in the presence of bases to prepare the aqueous solution Such a coating would not hold up to the waterproof requirements o the present invention. Haas et al., U.S. Patent No. 4,775,558 discloses polyurethanes combined with other materials, such a linseed oil. However, the art has failed to recognize th unexpectedly superior coating properties achieved using th critical limitations taught by the present invention, wherein onl 1 part by weight polyurethane is used with 10 to 16, and mos preferably 12, parts by weight of varnish as a waterproof coatin composition exhibiting high gloss and scratch resistance. Example 1

A coating of the present invention was prepared by thoroughl mixing one part ZAR®GL0SS polyurethane by weight with 12 parts b

weight of ALGLOSS OVERVARNISH. A light reflection test w conducted using paper substrate printed with dense black ink. T same ink batch was used for all test pieces, and the lig reflectivity test was conducted according to industry accept practice, which includes illuminating the test piece at a 60° ang and measuring the amount of light reflected from the test pie using a gloss meter. In each case, the coating applied to the te piece was allowed to dry before testing.

Table I below discloses the comparative light reflecti results of uncoated paper (Sample A) a coating of the prior a (varnish only. Sample B) and the coating of the present inventio (Sample C). As illustrated, the coating of the present inventio provides far superior light reflective properties than either th uncoated or varnished surfaces. This is particularly surprising in that only about 8% (wt. ) of the Sample C composition by weigh comprised polyurethane (only 4% on polyurethane solids basis), ye Sample C exhibited over 58% better gloss than the varnish coatin alone. Sample B.

Table I Liσht Reflection Test - Polyurethane/Varnish Coating Sample . % Light Reflected

A Dense Black Only 48.5%

B Dense Black with Varnish 48.5% C Dense Black With

Polyurethane/Varnish 77.5% It has been found that the coating of the present inventio produces a high-gloss coating which dries in approximately 2 hours, requiring non heated dryers. However, if heated driers ar used, it would be possible to apply a thicker coating, resultin in even higher gloss. The coating produced is scratch resistant, and requires no special coater or tower-type baking oven. Th coating can be run on a small duplicator offset press, a larg offset press or a letter press.

The coating of the invention is applied in the same manner as ink except the entire surface is coated. No special mixing is required, but the polyurethane and varnish should be thoroughly

mixed prior to application.

The coating of the present invention protects again ultraviolet rays, enriches colors of printed materials, bonds surfaces that normally cannot be overprinted, such as UV coating and brightens ink on recycled paper. Significantly, the coati of the present invention imparts waterproof properties to t substrate, an important consideration for food packagin Additionally, the coating on the present invention has been fou not to be affected by heat or cold. Example 2

A sunlight test was used to determine the present invention ability to prevent ultraviolet fading. The test pieces we printed with a yellow-green ink, which has a high tendency to fad and set in a sunny window for approximately three weeks. Each the test pieces was partially covered to provide a control col for comparison. The three test pieces included an uncoated shee a sheet coated with a UV coating, and a sheet coated with a coati of polyurethane/varnish as described in Example 1. Upon inspecti at the conclusion of the test, the uncoated sheet experienc almost complete color loss, while the UV coated sheet exhibit some fading, as clearly indicated by a strong contrast li separating the exposed and unexposed portions of the sheet. T sample coated with the polyurethane/varnish coating of the prese invention exhibited the least amount of fading, as the li separating the exposed surfaces from the unexposed surfaces w barely discernible. Example 3

Cardstock used for food packaging was coated with t polyurethane/varnish coating of Example 1 and placed in a freez for 7 weeks. No frost penetration or water damage to t underlying substrate was visible after this time period. When th type of coated sheet is placed under running tap water, no wat penetration to the substrate occurs, and water rolls quickly o the surface.

Although the precise mechanism whereby the polyurethane a

varnish interact, when used in the preferred ratios, is n precisely understood, it is believed that the polyurethane a varnish combine chemically in some way, producing a coati yielding the superior properties of the present invention. An spectrum has been run on the coating of the present inventio indicating that the combined polyurethane and varnish comprise product which is different from the polyurethane and varnis individually. See Figures 1-4.

In another embodiment of the invention polyurethane is adde directly to an oil-based ink in an amount of 1:100 to 1:1 parts b weight polyurethane to oil-based ink. As used herein, the ter "oil-based ink" is intended to embrace inks containing vegetabl oil, petroleum oil and/or rubber-based inks of all kinds. It ha unexpectedly been found that by adding the polyurethane to the oil based ink in this way the ink adheres to a previously coated job The polyurethane also acts as a tack reducer, and enables reds blues and violets to withstand heat application withou reactivation (fading) or bronzing. The polyurethane in tur brightens the ink pigment and imparts higher gloss to the finishe print. Furthermore, it has been found that the ink dries harde and more quickly, with less setoff, and better release than th same ink without polyurethane. Also, the polyurethane and in mixture produces a smoother solid with less ink (higher yield) an protects against fading. Example 4

The same polyurethane/varnish coating as used in Example 1 wa employed, except in this example, one part of polyurethane per 1 parts of oil-based dense black ink, by weight, (from the same in batch used in Example 1) was used. Three test pieces were run, Sample D, which was the polyurethane/ink alone, Sample E, which was the polyurethane/ink overcoated with varnish only, and Sample F, which was the polyurethane/ink overcoated with the polyurethane/varnish coating of Example 1. The results are shown in Table II, which shows that the polyurethane, when added to the ink, increases reflectivity slightly over the ink without

polyurethane shown in Sample A of Table I. Also as shown in Tabl II, when the test piece was varnished, (Sample E) reflectivit actually dropped, but was improved significantly (35.8%) b overcoating with the polyurethane/varnish coating of the presen invention (Sample F) .

It has been found that when the ink contains polyurethane, i is possible to print on substrates that will not normally accep ink. For example, we have unexpectedly found that th polyurethane, when added to rubber-based inks, permits these ink to print on surfaces, such as enamel, to which such links normall do not adhere.

Table II Light Reflectivity Test - Polyurethane in Ink Sample % Light Reflected

D Dense Black Only 50.4%

E Dense Black With Varnish 49.2%

F Dense Black With

Polyurethane/Varnish 66.8%

Example 5

A sheet of paper having a UV coating was printed with the sam type of ink as described in Sample F of Example 4 above. The in remained on the surface, and after drying, adhered to the surfac and could not be rubbed off. The same UV coated paper was printe with a standard ink, that is, not containing polyurethane, and wa allowed to dry. The resulting ink smeared off the sheet when dr with little hand pressure.

In a preferred method of practicing the present invention th ink to which polyurethane has been added, preferably in quantitie of about one to fifty parts polyurethane per one-hundred parts ink by weight, is printed on a substrate, followed by the applicatio of a polyurethane/varnish coating (of the type described in Exampl 1). After the coating is applied, the printed substrate is allowe to cure in conventional manner, for example by air-drying o through heated drying if desired. However, it has bee surprisingly found that drying times for the present invention hav

been reduced from typically 24-48 hours to only 2-1/2 hours.

The coatings of the present invention are useful on a variet of printable substrates including paper, cardboard, liner-board card-stock, wood, metal, mineral substrates, enamel, plastics cellophane and foil. Example 6

A Southerland Rubber Tester was used to test the abrasio resistance of the coatings of the present invention. A coatin similar to that described in Example 1 was applied to variou substrates under various conditions as set forth in Table III indicating extremely good abrasion resistance.

Table III

Substrate Pound Test No. Strokes Abrasion 100# Gloss Enamel 2

100# Gloss Enamel 4

10 Pt. Coated Board Stock

10 Pt. Coated 50 Light Scuff Mark Board Stock

Cambell Board Stock

Poly Board Stock 4

1266 Board Stock 4

1061 Board Stock 4

Recycled Board 4

It is preferred in practicing the present invention that oil- based inks be used, taking advantage of the non-aqueous nature of the coating.

Optionally, following the curing of the coating used according

to the present invention, it is possible to coat the printe substrate with a UV coating, using conventional methods. Example 7

In another embodiment of the invention, an air-curable in composition consisting of a mixture of an oil-based ink an polyurethane in a weight ratio of polyurethane to ink of abou 1:100 to about 1:1 was prepared. Figures 5a-f show the results o (a) dry-back tests run using an ink containing petroleum oil an no polyurethane, which had an 8 point dry-back; (b) an in containing one part polyurethane by weight to 70 parts petroleu oil-based ink having a 4 point dry-back; (c) an ink containing on part polyurethane to 40 parts petroleum oil-based ink having a 4. point dry-back; (d) an ink containing one part polyurethane to parts petroleum oil-based ink having a 5 point dry-back; (e) an in containing one part polyurethane to two parts petroleum oil-base ink having a 3 point dry-back; and (f) an ink containing one par polyurethane to one part petroleum oil-based ink having a 1.7 poin dry-back. All parts in this example are on a weight basis, and th same oil-based black ink was used in all examples illustrated i Figures 5a-f. As Figures 5a-f and this Example 7 indicates, addin as little as about 1.4% by weight polyurethane to an oil-based in composition can improve the dry-back dramatically, in this case by 50%.

A normal, or generally acceptable dry-back measure is 5-1 points. It is highly preferred, however, to have less dry-back and zero dry-back is especially desirable. In general, the highe the dry-back, the lower the density of the printed ink, when dry and the more ink needed to bring the density up to desired levels We have unexpectedly found, as evidenced by visual comparison, tha the polyurethane-containing inks of the invention can experienc zero dry-back, and in some cases actually experience negative dry back, that is, a higher density when dry than when wet on th substrate.

The inks tested in Figures 5a-f proved to have better ru characteristics than the same inks in which no polyurethane wa

added. These results further establish the advantages of t present invention.

In addition to petroleum-based inks, the invention may al be used with vegetable oil-based inks, such as soy ink. A bonafi soy ink must use soybean oil as its only vegetable oil ingredien except for trace amounts of tung oil, chinawood oil, etc.

The minimum acceptable content of soybean oil in soy inks, a set by the American Soybean Association, varies according to th type of ink:

Minimum Soybean Type Oil Content* soy news inks 55 percent soy sheet-fed inks 20 percent soy forms inks 40 percent soy heat-set inks 10 percent

*of the non-pigment portion of the ink, by weight.

We have found that the benefits of the invention, includin improved dry-back, (better density), faster drying, and reduced in consumption (higher-yield) can be realized by mixing polyurethan with soybean oil-based inks, having at least 10% by weight soybea oil exclusive of pigment in the ink prior to the addition o polyurethane. Soybean oils containing about 10-90% by weigh soybean oil exclusive of the pigment can be advantageously use according to the present invention simply by mixing a quantity o polyurethane with the soybean ink prior to use. We have found tha a lower limit on the advantages of the invention is reached a about 1% by weight polyurethane based on the oil-based ink. Th upper limit, if one exists, appears to be dictated more b viscosity concerns; the example of Figures 5e and 5f were found to lose viscosity to the point that body-gum additives would need to be added in order to use those inks on a sheet-fed press. However, these viscosity limitations are primarily economic considerations. A typical, commercially available soybean oil-based ink contains the following components: soybean oil, pigment, resins, and waxes.

The air-curable ink compositions of the present invention a advantageous in that they do not require the significant equipme expenditure required for the radiation-curable (UV) i compositions. As used herein, the term "air-curable" is intend to embrace inks and coatings which may be dried or cured witho aid of radiation, such as ultraviolet radiation. Additionally, t use of polyurethane reduces drying times and produces better dry back than is possible in oil-based inks not containing t polyurethane. While the precise mechanism is not fully understood it is believed that the polyurethane gives better penetration t the substrate, allowing a thinner ink film to be applied, producin quicker drying and reduced consumption relative to inks no incorporating the polyurethane. Example 8

Sheet fed oil-based ink was mixed with polyurethane in a rati of 1 part polyurethane to 16 parts, ink, by weight, based on th total weight of the ink prior to mixing. The following Table I summarizes the results. The ink with polyurethane experienced n "bronzing", while the ink without polyurethane experience bronzing, which is a frequent problem with red and blue inks. Th ink containing polyurethane exhibited less setoff and better dryin time than the ink without polyurethane. The ink used in Table I was Warm Red #82/660, National Printing Ink, Marietta, Georgia.

Table IV

As Table IV illustrates, the ink containing polyurethan exhibited a 63% higher yield then the same ink with n

polyurethane. The other data in Table IV, including PU (% wat pickup) demonstrate that the ink composition of the prese invention exhibits properties generally recognized as acceptabl by ink users and manufacturers. The lower conductivity of th invention relative to the ink with no polyurethane, is generall recognized as preferred by ink manufacturers. Example 9

Soy ink sold under the name SOYA, by national Printing Ink Marietta, Georgia, was mixed with polyurethane in a ratio of on part polyurethane to 16 parts soy ink, by weight. Four ink colors black, blue, yellow, and red, were mixed with polyurethane. Th resulting ink compositions were tested for dry-back. The result are shown in Table V. Each of the figures in Table V represents densitometer average reading for ten samples for each color.

Table V

The densitometer readings indicate that the addition of polyurethane to soy ink unexpectedly results in kink compositions having a higher density when dry than when wet. Dry-back is determined by subtracting the dry densitometer reading from the wet densitometer reading. Thus, the present invention not only produces ink with near zero dry-back, (blue), but actually negative dry-back, in the cases of the black, yellow, and red inks. Example 10

Rub tests have shown that, in addition to having better dry- back, the soy inks containing polyurethane are more scratch resistant than soy inks without polyurethane. A black, sheet-fed

process soybean ink was rub tested against the same ink containi 1 part polyurethane to 16 parts ink by weight, using a Southerla Rub Tester. Although both inks showed scratching, the i containing polyurethane showed better scratch resistance than t ink containing no polyurethane. These same inks were tested f dry-back. The results are shown in Table VI. As these resul indicate, the soybean ink containing polyurethane experienced le dry-back than the ink without polyurethane.

Table VI

The invention has been described herein in terms of particul embodiment, which are representative and illustrative only. T particular examples serve to illustrate my invention, but not lim same, the invention being defined more generally by the followi claims and their equivalents. While many objects and advantag of the invention have been set forth, it is understood that t invention is defined by the scope of the following claims, not the objects and advantages.