Technical Field of the Invention This invention relates to topcoats for printing media. More specifically, the invention relates to topcoats which improve the anchorage and therefor the adhesion of a toner to a facestock with laser printing.

Background of the Invention Laser printing and photocopy technologies use toner which is fused to the print media, such as paper, film, etc. The laser heats the toner, melting and fusing it to the paper. The image is written onto an electrostatically charged photo-conductor by a laser. The photo-conductor loop carries the charged image to the developers where toner is deposited onto the image loop, and subsequently transferred to the base sheet. The substrate plus toner is passed through a fuser roll to impregnate the image onto the sheet.

Printers can be distinguished based on the position of the fusing roll relative to the unfused toner. In'back-side'fusion architecture, heat passes from the unprinted side of the sheet to the toner on the topside of the substrate; whereas, the fuser is placed directly over the toner in front fusing architectures.

The polymeric binder in toner, being the major component, largely dictates the thermal properties and fusing efficiency of the toner. For monochrome equipment, the binder is typically polystyrene based, or a hybrid thereof. Whereas, color print technology, in general, uses polyester based resins. While the fundamental technology and architecture of traditional

monochrome (black/white/gray scale) and color laser printers show several commonalties, the specifics of fusing mechanisms and chemical compositions of the toners require substantially unique solutions and approaches toward the development of color toner receptive layers.

One area, where the degree of toner fusion is greatly impacted, is the thickness of the base stock, e. g. print media. This is especially important for base stock at least about 5 mil, or even totaling 7 mil or greater in thickness.

For color laser printing, toner anchorage and fusion failure may occur.

Some of the key factors that may have lead to the failures: (1) Toner thermal transitions: The monochrome polystyrene based toner, in general, does not have a distinct melting transition. Fusion occurs over the entire viscoelastic zone. Whereby, color toner has well defined glassy and melting transitions to properly fuse to the substrate.

(2) Surface energy, functionality, and polarity: The monochrome topcoats tested were polystyrene-hybrids, which have significantly lower surface energies and polarities than the polyester resins in color toner.

There is a large degree of incompatibility between the polystryene based topcoat resins and color toner.

Furthermore, secondary colors, i. e. red, green, and blue are achieved by layering the primary toners, thereby increasing the amount of toner to be fused on color prints as opposed to monochrome/gray scale images.

There is a need for a coating composition which provides improved toner fusion. It is also desirable to have a coating composition which is aqueous.

Summary of the Invention This invention relates to toner receptive topcoats having improved fusion and anchorage of color toners. The formulations comprise a polymeric binder and, optionally, at least one functional additive. In one embodiment, the invention relates to an aqueous topcoat composition comprising a major amount of a solvent and a minor amount of a polymeric binder in order to

obtain a toner adhesion rating of greater than or equal to about 1 5 g, or greater than or equal to about 17, or greater than or equal to about 20 in the BYK-Gardner test. The invention also relates to printable substrates having a topcoat which improves the adhesion of the toner. Methods of making the topcoated printable substrate is also included herein. The topcoats provide increased toner anchorage, especially color toner anchorage. The topcoat is particularly effective in providing improved toner anchorage to thick facestocks.

Brief Description of the Drawings Fig. 1 is a schematic representation of the laser imaging process using front fusing.

Fig. 2 is a schematic representation of the laser imaging process using back fusing.

Detailed Description of the Preferred Embodiments As described above the topcoats are binders which improve the anchorage of the toner for laser printing. The topcoats have a solvent, such as water and a binder, such as a polymeric binder. The topcoats, optionally include one or more functional additives. These functional additives are those affecting thermal and rheological properties. The topcoats improve the toner anchorage on the printable substrate.

Fig. 1 represents a typical laser printer assembly 10, which has color toner components 11 which are"written"onto an electrostatically charged photo-conductor 12 by a laser 13. The photo-conductor 12 carries the charged the toner where it is deposited to the base sheet 14. The substrate plus toner is passed through at least one fuser roller 15 to impregnate the image onto the sheet. Fig. 2A, is a schematic of a backside fuser assembly,

where toner components 11 on substrate 14 are passed by fuser roller 15 whereby the toner components are melted and adhered to the substrate. Fig.

2B, is a schematic of a front side fuser assembly, where toner components 11 on substrate 14 are passed by fuser roiler 15 whereby the toner componets are melted and adherred to the substrate.

The topcoats are useful on printable substrate. These substrates include polymeric film and paper substrates. Examples of useful substrates include all paper substrates, including label stock, printer paper stock, card stock, and metallized paper, and film substrates, such as those used as the facestocks of labels and color transparencies. The facestocks may be paper or polymer film facestocks known to those in the art. The printable substrate may also be those used in multilayer laminates, such as label stock. These printable substrates may be any thickness, such as label stock, which may have a thickness of about 2 to about 4 mils. In one embodiment, the printable substrate is part of a laminated structure having a facestock which is printable, a pressure sensitive adhesive and a release liner on the pressure adhesive. The thickness of the laminated structure may be the same thickness printable substrates discussed herein.

In one embodiment, the topcoats are particularly useful on thick facestocks. Thick facestocks are those having thicknesses of at least about 5 mils, or at least about 6 mils, or even greater than about 7 mils. In one embodiment, the facestocks typically have a thickness greater than 7, or greater than 7.3, or greater than 7.5 mils. In one embodiment, the topcoat is used on post card or business card stock. The polymer film facestock may be any of those used in the art and include those which have multiple layers.

Table A contains examples of useful facestocks.

Table A

Paper Source Caliper Porosity Opacity Smoothness (Basis Weight) (mil) Tappi T538 Wausau Bright 8.5 28 97 n/a White(65#) Wausau Color 7.2 38 98 111/119 Copy (60#) Wausau Exact 8 20 98 163/168 Opaque Smooth White (65#) The printable substrates are coated with a coating composition which comprises a major amount of a solvent and a binder. The solvent may be any of those know in the topcoating arts. The solvents include water, alcools (such as lower alcools, those having up to about eight carbon atoms, including methanol, ethanol and the like), ketones (such as lower ketones, including acetone, methyl, ethyl ketone, and the like), aldehydes (such as lower aldehydes, including ethanal, butanal, and the like), n- vinylpyrrolidinone, etc. In one embodiment, the solvent is water and the compositions are aqueous compositions. The solvent is present in an amount of at least about 50%, or at least about 60%, or at least about 65% or at least about 70% by weight.

As stated above the coating composition is placed on the printable substrate and forms a topcoat. The topcoat of the facestock generally has a thickness of about 0.1 to about 0.8 mil, or about 0.3 to about 0.5 mil. The topcoat may be applied directly to the facestock or may be connected to the facestock through an intermediate layer, such as a tie layer.

The topcoat is composed, in one aspect, solely of at least one binder.

The binders include those polymers which improve the anchorage of the

toner, such as polyesters, sulfonated polyesters, polyvinyl acetates, polyvinyl pyrrolidinone, etc. Combinations of such binders may be used. The binders are present in the coating composition at a minor amount. In one embodiment, the binder is present in an amount from about 3% to about 45%, or from about 5% to about 40%, or from about 10% to about 35%, or from 12% to about 30% by weight. Here and elsewhere in the specification and claims, the range or ratio limits may be combined.

In one embodiment, the polyesters are prepared by reacting at least one polycarboxylic acid or ester, such as a dicarboxylic acid or ester with at least one polyol, such as a diol. The dicarboxylic acid may be aliphatic, alicyclic or aromatic. Examples of such acids include are: oxalic acid, malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, dodecanedioic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, phthalic acid, isophthalic acid,, terephthalic acid, 2,5-norbornene dicarboxylic acid, diglycolic acid, thiodipropionic acid, 4,4'-sulphonyldibenzoic acid, 2,5-naphthalene dicarboxylic acid and 2,6-naphthalene dicarboxylic acid. These dicarboxylic acid monomers may be employed by themselves or as combination of at least two dicarboxylic acid monomers. Among these monomers include phthalic acid, isophthalic acid and terephthalic acid.

The diols include aliphatic, alicyclic and aromatic diols. The diol component of the polyester includes cycloaliphatic diols having 6 to 20 carbon atoms or aliphatic diols having 3 to 20 carbon atoms. Examples of such diols include ethylene glycol; propylene glycol, 1,3-propanediol, 2- methyl-1,3-propanediol, 2,2-dimethyl- 1,3-propanediol (neopentylglycol), 2-ethyl-2-butyl-1, 3-propane diol(neopentylglycol), 2-ethyl-2-butyl-1, 3-propanediol, 2-ethyl-2-isobutyl-1,3-

propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 2,2,4,4-tetramethyl- 1,3-cyclobutanediol, p-xylylenediol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, hexaethylene glycol, heptaethylene glycol, octaethylene glycol, nonaethylene glycol, decaethylene glycols, 2,2,4- trimethyl-1-1, 3-pentanediol, hydroxypivalyl hydroxypivalate, dipropylene glycol, 1,1 0-decanediol, hydrogenated bisphenol A, and mixtures thereof. In one embodiment, the diols include diethylene glycol; neopentyl glycol, cyclohexanedimethanol, 2-ethyl-2-butyl-1, 3-propanediol, 2,2,4-trimethyl-1,3- pentanediol, hydroxypivalyl hydroxypivalate, and 2-methyl-1, 3-propanediol.

In another embodiment, the binder is a sulfonated polyester or sulfopolyester. These polyesters are generally prepared by the partial polycondensation reaction of one or more of the above dicarboxylic acids or esters, one or more polyester and a sulfonate containing aromatic dicarboxylic acid. The degree of sulfonation in the polyester is typically between 0.1 and 30 mol percent, and or between 0.2 mol percent and 1 5 mol percent of the repeating polymer units. The molecular weights of the polyols are, for example, an Mw from about 400 to about 1,800, and Mn of from about 200 to about 1,400 and an Mw from about 700 to about 1,400 and an Mn from about 400 to about 1,100.

The aromatic nucleus of the difunctional aromatic monomer may addition carry an--S03 M group. The aromatic monomers include benzene, naphthalene, anthracene, diphenyl, oxydiphenyl, sulphonyidiphenyl and methylenediphenyl nuclei. Examples of difunctional aromatic monomers additionally carrying an--S03 M group which may be mentioned are sulphoisophthalic acid, sulphoterephthalic acid, sulphophthalic acid and 4- sulphonaphthalene-2, 7-dicarboxylic acid. In one embodiment, the

compositions that are the subject-matter of the invention employ copolymers based on isophthalate/sulphoisophthalate. In enother embodiment, the invention employs copolymers obtained by condensation of diethylene glycol, cyclohexanedimethanol, isophthalic acid and sulphoisophthalic acid. Such polymers are sold, for example, under the trade name EASTMAN AQ by Eastman Chemical Products.

The glycols employed are ethylene glycol and at least one branched chain glycol, preferably neopentyl glycol. At least two dicarboxylic acids are utilized. They are independently chosen from the group consisting of sulfoarylene dicarboxylic acids such as 3-sulfophthalic acid, 4-sulfophthalic acid, 5-sulfophthalic acid, sulfoterephthalic acid, 4-sulfonapthalene-2,7- dicarboxylic acid, 5. (4-sulfophenyl) isophthalic acid, 5- (4-sulfoisophthalic sulfophenoxy) isophthalic acid, 5- (2-sulfoethyl) isophthalic acid, and 5- sulfoisophthalic acid, with the latter preferred; alkyl or alkoxy substituted meta-or para-arylene dicarboxylic acids such as 5-methyl isophthalic acid.

Sulfonated polyesters that are useful for preparing the compounds of this invention are described in U. S. Pat. Nos. 4,480,085,4,543,315; 4,401,743; and EP 0,462,704, all of which are incorporated herein by reference.

In another embodiment, the binder is a polyvinyl acetate. The polyvinyl acetate is typically a homopolymer or copolymer of vinyl acetate and an olefin having from about 2 to about 8 carbon atoms, such as ethylene, propylene or butylene. Examples of these binders includes Vinac XX210, a polyvinyl acetate homopolymer.

In another embodiment, the topcoat is prepared with functional additives. Each functional additives may be present in an amount up to about 20%, or up to about about 15%, or up to about 8% by weight. The lower limait for the fucntional additive is, in one embodiment, 0.1 %, or 0.2% by

weight. In another embodiment, the functional additives are typically present in an amount from about 1 % to about 14% by weight. The functional additives are mixed with the binder and applied to the facestock. The functional additive may be at least one thermal regulator, defoamer, surfactant, plasticizer and dispersing aid. Such functional addition additives include waxes which include micronized hydrocarbon wax of Micro Powders, Inc. and Jonwax 26, Jonwax 120 (available from S. C. Johnson and Sons, Inc., Racine, Wisconsin 43403, U. S. A.), or Vanwax 35 (available from Vantage, Garfield, N. J. 07026); surfactants such polyethylene glycols such as Carbowaxs 400 and Surfynol 104 or Surfynol 440 (available from Air Products and Chemicals, Allentown, Penna. 18105), Carbowet 990 (available from Vantage), and Aerosol TO-75 (available from American Cyanamid, Wayne, N. J. 07470); defoamers such as Drewplus L4764 (Air Products) and Foamaster 111 (Henkel Corporation); thermal regulators such as Silojet P-405 (an amorphous precipitated silica of Grace Davison); cobinders, such as Flexthane 620 (aqueous polyurethane mulsion of Air Products; plasticizers, such as Paraplex G-54 (polyester plasticizer of C. P. Hall Corp.); biocides; pH stabilizers; thickeners such as Acrysol RM-825 (available from Rohm & Haas, Philadelphia, Penna. 19105); and the like.

The following examples relate to topcoat formulations. Unless otherwise indicated, the amounts and ratios are by weight. The temperature is in degrees Celsius, and the pressure is atmospheric. All weights and percentages are based upon dry weight measurements. The materials of Table 1 are used to prepare the topcoat formulations of Table 2.

Table 1

Trade Chemical Class Source Name Eastman Aqueous Dispersible Polyester Eastman Chemical AQ35S Resin Eastman Aqueous Dispersible Polyester Eastman Chemical AQ38S Resin Eastman Aqueous Dispersible Polyester Eastman Chemical AQ55S Resin Vinac Polyvinyl Acetate Homopolymer Air Products XX210 FineTone Polyester Reichhold Chemical 382ES MSP 250-Micronized Hydrocarbon Wax Micro Powders, Inc. 50 Carbital 95 Calcium Carbonate Dispersion Frankiin Industrial Silojet P-Amorphous precipitated silica Grace Davison 405 Syloid Amorphous Precipitated Silica Grace Davison 74X6500 Plasthall Polyester Plasticizer The C. P. Hall Corp 7055 NeoRez Aqueous Polyurethane Emulsion Air Products 9320 Carbowax Polyethylene glycol surfactant Union Carbide 400 Drewplus Defoamer Drew Industrial Flexthane Aqueous Polyurethane Emulsion Air Products 620 Paraplex G-Polyester Plasticizer The C. P. Hall Corp. 54

The topcoats formulations of Table 2 are prepared as follows: (1) Example &num 1-23 The appropriate amounts of deionized water (Table 2) and Drewplus L474 (approximately 1 drop for every 267 gram of final batch weight) are charged to a suitable stainless steel beaker. The system is heated to 45°C under constant agitation. Once the temperature has stabilized, Component A (Table 2) is added, stepwise, at a rate of 5 grams per minute while maintaining a temperature of 45-50°C during the inclusion process. Once the addition of Component A is complete, the system is maintained at 45-50°C for an additional 15-60 minutes allowing for complete dispersion of Component A. The mixture is passed through a 150/1 filtration screen and cooled to room temperature. While stirring the dispersion at room temperature, Component B (Table 2), if present, is added at a rate of 0.25 gram per minute. Once addition of Component B is complete, the system is stirred for an addition 15 minutes. Component C (Table 2), if present, is then added in one pass to the stirring formulation and agitated for 15 minutes. Once all components have been thoroughly mixed, the final formulation is filtered through a 200Su screen.

(2) Example #24:

Deionized water (Table 2) is charged to a suitable stainless steel vessel.

Component A (Table 2) is added in one aliquot and stirred for five minutes under mild agitation. Subsequently, Component B (Table 2) is added in one pass to Component A. The resulting mixture is agitated for an addition 15 minutes.

(3) Example #25: 2-Butanone (57.4%, Table 2) is added to an appropriate stainless steel container. Component A (Table 2) is added at a rate of 160 grams per minute to the stirring solvent. The system is stirred for an additional 10 minutes following the completion of the Component A addition. Component C (Table 2) is added at a rate of 3.3 grams per minute, and the system is stirred for 10 minutes.

Table 2

Ex # Component Component Component % % % % A B C A B C Water 1 Eastman MSP 250-Plasthall 20.5 2.2 2.3 75.0 AQ35S 50 7050 2 Eastman MSP 250-Carbowax 22.4 2.1 2.3 73.2 AQ35S 50 400 _ 3 Eastman Carbital 95 Plasthall 22.8 2.2 2.3 72.8 AQ35S 7050 4 Eastman Silojet P-Plasthall 21.4 0.0 2.7 75.9 AQ35S405 7050 5 Eastman Silojet P-NeoRez 21.3 0.6 1.1 77.1 AQ35S405 9320 6 Eastman Silojet P-None 21.9 0.6 0.0 77.5 AQ35S 405 7 Eastman None Plasthall 21.5 0.0 2.3 76.2 AQ35S 7050 8 Eastman None None 24.0 0.0 0.0 76.0 AQ35S 9 Eastman Syloid Plasthall 13.6 1.0 1.5 83.8 AQ38S74X6500 7050 10 Eastman Syloid Drewplus 13.7 1.0 1.0 84.3 AQ38S74X6500 L474 11 Eastman Syloid None 13.8 1.7 0.0 84.6 AQ38S 74X6500 12 Eastman Carbital 95 None 14.4 3.2 0.0 82.5 AQ38S

13 Eastman Silojet P-Vinac 71.4 AQ38S405 XX210 14 Eastman Silojet P-None 13.8 1.7 0.0 84.5 AQ38S 405 15 Eastman Silojet P-None 14.7 1.7 0.0 83.6 AQ38S 405 16 Eastman Silojet P-None 13.3 4.7 0.0 82.0 AQ38S 405 17 Eastman Silojet P-None 13.9 0.6 0.0 85.5 AQ38S 405 18 Eastman None Flexthane 13.0 0.0 2.8 84.2 AQ38S 620 19 Eastman None None 14.0 0.0 0.0 86.0 AQ38S 20 Eastman Syloid None 14.8 1.6 0.0 83.6 AQ55S 74X6500 21 Eastman Carbital 95 Plasthall 14.5 0.7 2.4 82.4 AQ55S 7050 22 Eastman Carbital 95 None 14.5 2.4 0.0 83.1 AQ55S 23 Eastman Silojet P-Flexthane 13.6 1.7 3.1 81.6 AQ55S 405 620 24 Vinac Carbital 95 None 22.5 2.5 0.0 75.0 XX210 25 FineTone None Paraplex G-38.2 0.0 4.4 *57.4 382ES 54 * 2-Butanone was substituted for water in Example #25

The above topcoats are applied to the facestock discussed below. The toner anchorage is determined using the following equipment and test methods for the formulations of Table 2.

Printers: (1) HP Color LaserJet 5 by Hewlett Packard (2) SC-1275 by Lexmark Toner Adhesion Testing: BYK-Gardner Balance Beam Scrape Adhesion and Mar Tester SG-8101 as specified according to ASTM D-2197 Print Methods: (1) All prints are made on Plain Paper Mode (2) Unless otherwise specified, all prints are tested from the HP Color LaserJet 5 are taken following an appropriate warm-up period.

In general, this consists of printing no less than three pages of standard copy paper prior to introduction of the test materials.

(3) No warm-up period is necessary for the Lexmark SC-1275.

Toner Anchorage Testing Procedure: (1) All samples are tested using the BYK Gardner SG-8101 with a steel rod stylus, part #SG-8104, available from BYK Gardner.

(2) All samples are printed from the HP Color LaserJet5 were tested at the leading and trailing edges (3) Leading and trailing edges scrape values are not reported for samples printed using the Lexmark SC-1275.

Table 3: BYK-Gardner Toner Adhesion Results on Non-topcoated Substrates BYK-Gardner Test Results Paper Source Caliper HP Color Laser HP Color Laser Lexmark Jet 5 Jet 5 SC1275 (Basis Weight) (mil) Leading Edge Trailing Edge (gramForce) (gramForce) (gramForce) Champion Chambril 8.5 10 10 20 (180g) Wausau Color Copy 7 10 10 20 (155g) Wausau Opaque 8 20 10 20 Cover (180g) Finch Text (155g) 7 20 10 10 Table 4: BYK-Gardner Toner Adhesion Results

BYK-Gardner Test Results HP Color Laser Jet HP Color Laser Jet Lexmark 5 5 SC1275 Example Leading Edge Trailing Edge (gramForce) # (gramForce) (gramForce) 1 50 20 300 2 20 n/a 300 3 10 n/a 300 4 10 n/a 300 5 50 20 300

6 20 10 300 7 20 n/a 300 8 10 n/a 300 9 20 10 100 10 50 10 140 11 20 10 200 12 50 20 200 13 60 10 40 14 50 20 160 15 50 20 180 16 40 10 120 17 20 10 260 18 10 10 200 19 30 20 240 20 50 10 20 21 50 10 40 22 30 10 20 23 50 10 10 24 30 10 170 25 30 10 170 As is evident from Table 4, Examples #1-25 show an increase in toner anchorage to the substrate. The Lexmark SC-1275 shows the most dramatic improvement owing to the top fusing mechanism. The Hewlett Packard Color LaserJet 5 is a back-side fusing system and shows less, yet very significant, toner anchorage improvement as compared to the uncoated cardstocks listed in Table 3.

One formulation, Example 14, showed a dramatic strengthening in scrape resistance to the BYK-Gardner test. The data is summarized in Table 5.

Table 5: BYK-Gardner Paper Failure Forces Uncoated and Coated (with Example 14) Substrates Coated with Example BYK-Gardner Paper Uncoated Paper Failure Coated Paper Failure Force Force Champion Chambril 60 g 200 g (180g) Wausau Exact Index 140 g 220 g Avery Brand Business 40 g 220 g Card While the invention has been explained in relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification.

Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.