FIELD OF THE INVENTION This application is related to the field of toners and in particular relates to liquid toner comprising toner particles and carrier liquid.

BACKGROUND OF THE INVENTION The adhesion of toner particles to a final substrate such as coated paper is an important factor in its usability in copying and printing processes. As is well-known, the liquid developer comprises toner particles dispersed in an electrically insulating organic liquid. The toner particle comprises a pigment, a resin and other additives because of the necessity for coloring property, chargeability, fixing property and dispersion stability. In the liquid development process, the toner particles are charged and, during development of latent electrostatic images, they are attracted to image portions of the latent images.

While adhesion is less problematic for porous paper substrates, adhesion to less liquid permeable coated paper, plastic film and, further, metal plate may cause more of a problem of adhesion.

In a case of using the liquid toner for electrostatic charge development, different from the case of using the powder developer, images are often fixed on the material to be printed without using a heat roller upon fixing. This is accomplished by utilizing a heated intermediate transfer member which receives the developed image from the latent image bearing surface and transfers it to the final substrate. The image is heated on the intermediate transfer member; transfer therefrom to the final substrate is accomplished by heat and pressure. Generally, this method fixes the image on the final substrate and no further fixing is required.

However, there still may be a problem in meeting a cellophane tape peeling test. Particularly, this may result in a significant problem in a case where the material to be printed is made of such a material as not permitting permeation of the

SUBSTTTUTV SHUT (RULE 2β)

liquid toner for electrostatic charge development, for example, the coated paper or plastic film.

To improve the adhesion between the liquid toner for electrostatic charge development and the material to be printed as the foregoing problem and, particularly, to obtain satisfactory adhesion also to a material to be printed such as a plastic film or metal for which no improvement for the adhesion due to the permeation of the liquid toner for electrostatic charge development can be expected. Various methods have been used to improve image adhesion and abrasion resistance.

In PCT publication WO/92/17823, liquid toners utilizing a blend of polymers as the major component of toner particles contained in the liquid toner are described. The toner materials which are disclosed are acid modified ethylene vinyl acetate terpolymers (ELVAX) and ionomer materials (Surlyns), which are metal salts of an olefinic resin containing carboxyl groups. These blends are described as having a desirable viscosity at a low fusing temperature, which is related to the blend, and a relatively high abrasion resistance caused by the presence of the metal salts of an olefinic resin containing carboxyl groups. Images formed from these materials also have a high peel resistance.

U.S. Patent 5,308,729 describes a liquid toner including particles made up of about 60% of an olefinic resin containing carboxyl groups ( Nucrel ) and 40% ionomer having a similar structure. While there is no mention of any special abrasion or peel resistant properties of the toner, the need for a sufficient "fuse grade" defined as resistance to abrasion, etc. , is mentioned in the patent.

Other methods for improving adhesion, such as coating of the substrate are also known.

The use of Surlyns as base materials is known in the art. However, use of such materials by themselves is limited since the Surlyns are hard and difficult to grind, even in the presence of carrier liquid.

Nucrel materials are routinely used as the polymer for toner particles. However, such materials have abrasion resistance which may not be sufficient for certain applications.

SUMMARY OF THE INVENTION The present invention is directed to a blend of toner polymers including a blend of an olefinic resin containing carboxyl groups and a metal salt of an olefinic resin containing carboxyl groups. In particular, it has been found that images produced from liquid toners having toner particles based on such blends have an abrasion resistance which is greater than that of toners based on the olefinic resin itself. Furthermore, substantial improvement in abrasion resistance is still achieved for relatively low percentages of metal salts of olefinic resins containing carboxyl groups, such as between about 15 and about 30 percent. Toners with lower percentages of the metal salts grind more easily than those with higher percentages.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns an improvement for adhesion with a material to be printed by using a liquid toner for electrostatic charge development applied to visualization of electrostatic latent images.

Adhesion of the toner to the material to be printed, particularly, coated paper, plastic film, metal film or the like having a low permeability for the toner material of the liquid toner for electrostatic charge development can be improved remarkably, by using a liquid toner for electrostatic charge development comprising, as the main component of the liquid toner for electrostatic charge development, a blend of an olefinic resin containing carboxyl groups and a metal salt of an olefinic resin containing carboxylic groups.

The olefinic resin containing carboxyl groups used in the present invention, can be one of the many resins used in the toner art, for example, ethylene methacrylic acid copolymer, ethylene ethylacrylate copolymer, ethylene maleic acid copolymer, and the like.

The metal salt of the olefinic resin containing carboxyl

groups used in the invention includes the group of resins generally referred to as ionomer resins. Typical examples include, for example, Na salt, Zn salt and Ca salt of ethylene methacrylic acid copolymer. Further, those having VICAT softening point of the resin within a range from 50 to 100 ^β C are especially useful in liquid toners for electrostatic charge development.

Although the olefinic resin containing the carboxyl groups provides adhesion to some extent when used alone, adhesion improvement is obtained when it is used in admixture with about 15% by weight to about 30% by weight of the metal salt of the olefinic resin containing the carboxyl groups based on the entire content of the constituent resin. Lower percentages of the salt, as for example between 5% and 15%, also give improved adhesion. There are no particular restrictions on the other components of the toner particles and colorants, such as pigments or dyes, and other materials as known in the art can be used.

The liquid toner used in the present invention can be manufactured by any of the methods known in the art such as, for example, dispersing the toner material and carrier liquid at an elevated temperature at which the resins are solvated by the carrier liquid, cooling the resultant material while stirring is continued, adding a further amount of carrier liquid and grinding the resultant mixture in an atritter until particles having an average size of 1 to 3 microns is achieved. Applicable methods are described, for example in US Patent 5,192,638, the disclosure of which is incorporated herein by reference.

A charge director is generally added to the liquid developer used in the present invention to promote charging of the toner particles.

As the charge director, all of the known charge directors can be used, for example: metal salts of fatty acid, such as naphthenic acid, octenic acid, oleic acid, stearic acid and lauric acid, metal salts of sulfosuccin c acid ester, oil-soluble metal sulfonate as described in Japanese Patent Publication JP-B- 45000556, metal salts of abietinic acid, or hydrogenated

abietinic acid as described in Japanese patent Publication JP-B- 48025666, Ca salt of alkyl benzene sulfonic acid as described in Japanese Patent JP-B-55002620, nonionic surface active agent such as metal aromatic carboxylate or sulfonate, and polyxyethylated alkyl amine as described in Japanese Patent Laid-Open JP-A- 52107837, oils and fats such as lecithin and linseed oil, polyvinyl pyrrolidone and organic acid ester of polyhydric alcohols and other charge directors as are known in the art.

Methods for producing toner and charge directors which are useful for the invention are described in PCT published applications WO/90/14617; WO/91/2297; WO/92/14191; WO/93/11471; and PCT applications PCT/NL94/00157 and PCT/NL95/00188, the disclosures of which are incorporated herein by reference.

The materials to be printed used in the present invention have no particular restriction and they include, for example, common paper, coated paper and art paper in the case of paper, and film or sheet such as of polyethylene terephthalate (PET), polypropylene, polystyrene and nylon in a case of plastic film as the object thereof. Further, the material to be printed also includes metal plate or metal sheet such as of aluminum or iron.

Now, the present invention will be explained more in detail by referring to examples. In the examples, "Parts" represent "parts by weight" and "%" represents "% by weight", respectively.

Example 1 The following mixture is dispersed by heating and stirring as described above:

9% Polyethylene methacrylic acid copolymer ( "Nucrel 925", manufactured by Dupont Co.);

4% Na salt of Ethylene methacrylic acid copolymer ( "Himiran 1707", manufactured by Mitsui Dupont Polychemical Co.); 4% Carbon black; and

80% Isopar H (manufactured by Exxon Co.). The mixture is ground for 20 hours in an atritter to obtain a concentrated liquid developer. Isopar H is added to dilute the

concentrate to a liquid developer (printer) having 1.5% solid content. A liquid developer for evaluation of images is prepared by adding 0.2 parts of zirconium octylate (a charge director) to 1000 parts of this liquid developer. When this is used as the

5 developer for printing in a Savin 870 copier manufactured by Savin Co. , the reflection density in a solid area of the resultant images on common paper when measured by a reflection densitometer ("Macbeth RZ-918, manufactured by Macbeth Co. ) is about 1.25 without background staining. When the same liquid

10 developer is used to print on PET film, the image quality was also satisfactory.

To check adhesion, a cellophane tape manufactured by Nichiban was placed onto a solid portion of the image, rubbed five times with a finger and removed (peeled off) from the paper.

15 The amount of image left on the substrate is viewed and the quality of the image is determined on a scale of 1-5, where transferring about half of the image area on the peeled cellophane tape is level 3 of the 5 levels of evaluation. No transfer of the image to the peeled cellophane tape gives a

20 rating of 5. When all the material transfers to the tape, the rating is 1. Intermediate levels, i.e., between levels 3 and 5 represent intermediate quality.

The result of the cellophane tape peeling test on common paper with the toner of Example 1, is 4.

25 EXAMPLE 2

The following mixture is dispersed by heating and stirring as described above, except that the following materials were used:

11% Polyethylene methacrylic acid copolymer ( Nucrel 925",

— manufactured by Dupont Co. );

2% Zn salt of ethylene methacrylic acid copolymer ( "Himiran 1706", manufactured by Mitsui Dupont Polychemical Co. ); 4% Carbon black; and 80% Isopar H (manufactured by Exxon Co. ).

-^ The ground mixture is diluted and charged as described above with respect to Example 1.

The reflection density is about 1.36. When the images are printed on PET, the cellophane peeling test gives a quality of 4.

Example 3

The following mixture is dispersed by heating and stirring as described above, except that the following materials were used:

9% Polyethylene methacrylic acid copolymer ( "Nucrel 101", manufactured by Dupont Co.);

4% Zn salt of ethylene methacrylic acid copolymer ( "Himiran 1706", manufactured by Mitsui Dupont Polychemical Co. ); 4% Carbon black; and

80% Isopar H (manufactured by Exxon Co.).

The ground mixture is diluted and charged as described above with respect to Example 1. The reflection density is about 1.30. When the images are printed on a nylon film, the cellophane peeling test gives a quality of 4.

Example 4 The following mixture is dispersed by heating and stirring as described above, except that the following materials were used:

9% Polyethylene methacrylic acid copolymer ("Nucrel 101", manufactured by Dupont Co.);

4% Zn state of ethylene methacrylic acid copolymer ( "Himiran 1706", manufactured by Mitsui Dupont Polychemical Co. ) 4% Carbon black; and

80% Isopar H (manufactured by Exxon Co.).

The ground mixture is diluted and charged as described above with respect to Example 1. The reflection density is about 1.35. When the images are printed on aluminum sheet, the cellophane peeling test gives a quality of 4.

Comparative Example 1 The following mixture is dispersed by heating and stirring and heating as described above, except that the following materials were used:

Ethylene methacrylic acid copolymer

13% ("Nucrel 101", manufactured by Dupont Co. );

4% Carbon black; and

83% Isopar H (manufactured by Exxon Co.). The ground mixture is diluted and charged as described above with respect to Example 1.

The reflection density is about 1.38. When the images are printed on PET, the cellophane peeling test gives a quality of 2.