WO2000060024A1

WO2000060024A1 - Topcoats for improved laser printing and methods of using the same

Info

Publication number: WO2000060024A1
Application number: PCT/US2000/009335
Authority: WO
Inventors: Michael T. Waterman; Christopher D. Meader; Paul Lender
Original assignee: Avery Dennison Corp
Current assignee: Avery Dennison Corp
Priority date: 1999-04-07
Filing date: 2000-04-07
Publication date: 2000-10-12
Anticipated expiration: 2001-10-07
Also published as: AU4333700A

Abstract

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 15 g in the BYK-Gardner test. The invention also relates to printable substrates having a topcoat which improves adhesion of 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.

Description

Title: TOPCOATS FOR IMPROVED LASER PRINTING AND METHODS OF

USING THE SAME

Cross Reference to Related Applciations

This applications claims priority from provisional application 60/1 28, 1 30, filed April 7, 1 999, the entire disclosure of which is hereby incorporated by reference.

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 1 7, 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 1 1 which are "written" onto an electrostatically charged photo-conductor 1 2 by a laser 1 3. The photo-conductor 1 2 carries the charged the toner where it is deposited to the base sheet 1 4. The substrate plus toner is passed through at least one fuser roller 1 5 to impregnate the image onto the sheet. Fig. 2A, is a schematic of a backside fuser assembly, where toner components 1 1 on substrate 1 4 are passed by fuser roller 1 5 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 1 1 on substrate 1 4 are passed by fuser roller 1 5 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

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, alcohols (such as lower alcohols, 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 1 0% to about 35 %, or from 1 2% 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, 2,4-dimethyl-2-ethyl-hexane-1 ,3-diol, 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, 2,2,4-trimethyl-1 ,6-hexanediol, thiodiethanol, 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 additionally carry an ~S0₃ M group. The aromatic monomers include benzene, naphthalene, anthracene, diphenyl, oxydiphenyl, suiphonyldiphenyl and methylenediphenyl nuclei. Examples of difunctional aromatic monomers additionally carrying an ~SO₃ M group which may be mentioned are sulphoisophthalic acid, sulphoterephthalic acid, sulphophthalic acid and 4- sulphonaphthalene-2N-dicarboxylic acid. In one embodiment, the compositions that are the subject-matter of the invention employ copolymers based on isophthalate/suiphoisophthalate. 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)isophthaiic 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, 4,543,31 5; 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 XX21 0, 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 1 5%, or up to about 8% by weight. The lower limit 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 1 4% 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 additional additives include waxes which include micronized hydrocarbon wax of Micro Powders, Inc. and Jonwax 26, Jonwax 1 20 (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 Carbowax^® 400 and Surfynol 1 04 or Surfynol 440 (available from Air

Products and Chemicals, Allentown, Penna. 1 81 05), 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 1 1 1 (Henkel Corporation); thermal regulators such as Silojet P-405 (an amorphous precipitated silica of Grace Davison); cobinders, such as

Flexthane 620 (aqueous polyurethane emulsion 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. 1 91 05); 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

The topcoats formulations of Table 2 are prepared as follows:

( 1 ) Example #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 1 5-60 minutes allowing for complete dispersion of Component A. The mixture is passed through a 1 50// 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 additional 1 5 minutes. Component C (Table 2), if present, is then added in one pass to the stirring formulation and agitated for 1 5 minutes. Once all components have been thoroughly mixed, the final formulation is filtered through a 200 y 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 additional 1 5 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 1 60 grams per minute to the stirring solvent. The system is stirred for an additional 1 0 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 1 0 minutes.

Table 2

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-1 275 by Lexmark

Toner Adhesion Testing:

BYK-Gardner Balanced Beam Scrape Adhesion and Mar Tester SG-81 01 as specified according to ASTM D-21 97

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-1 275.

Toner Anchorage Testing Procedure: ( 1 ) All samples are tested using the BYK Gardner SG-81 01 with a steel rod stylus, part #SG-81 04, available from BYK Gardner. (2) All samples are printed from the HP Color LaserJetδ 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-1 275.

Table 3:BYK-Gardner Toner Adhesion Results on Non-topcoated Substrates

Table 4: BYK-Gardner Toner Adhesion Results

As is evident from Table 4, Examples #1 -25 show an increase in toner anchorage to the substrate. The Lexmark SC-1 275 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 1 4, 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 1 4) Substrates Coated with Example BYK-Gardner

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.

Claims

1 . 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 in the BYK-Gardner test.

2. The topcoat of claim 1 wherein the polymeric binder is a polyester, a polyvinyl acetate, a polyvinyl pyrrolidinone, or mixture or two or more thereof.

2. The topcoat of claim 1 wherein the polymeric binder is a sulfonated polyester.

3. The topcoat of claim 1 wherein the polymeric binder is a polyester or sulfonated polyester derived from a phthalic acid or anhydride and diol.

4. The topcoat of claim 1 wherein the polymeric binder is a sulfonated polyester having degree of sulfonation from about 0. 1 to about 30% by mole.

5. The topcoat of claim 1 further comprising a functional additive.

6. The topcoat of claim 6 wherein the functional additive is a wax, surfactant, thermal regulator, or thickener.

7. The topcoat of claim 6 wherein the functional additive is a micronized wax. 8. The topcoat of claim 6 wherein the functional additive is a polyethylene glycol surfactant.

8. The topcoat of claim 6 wherein the functional additive is a polyethylene glycol surfactant.

9. The topcoat of claim 6 wherein the functional additive is a silica thermal regulator.

1 0. An aqueous topcoat composition comprising a major amount of a water and a minor amount of a polyester binder and a functional additive.

1 1 . The topcoat of claim 1 1 wherein the polyester is a sulfonated polyester.

1 2. The topcoat of claim 1 1 wherein functional additive is silica.

1 3. A printable substrate comprising a substrate having a topcoat derived from the composition of claim 1 .

1 4. The printable substrate of claim 1 3 wherein the substrate is paper stock, a color transparency, a laminated structure and a metallized paper.

1 5. The printable substrate of claimn 1 3 wherein the substrate is a paper card stock.

1 6. The printable substrate of claim 1 3 wherein the substrate has a thickness of at least about 5 mils.

1 7. A method of improving the adhesion of toner to a paper substrate comprising the steps of treating a paper substrate with the composition of claim 1 , removing the solvent and printing the paper substrate.