TITLE ELECTROSTATIC DRY TONERS CONTAINING DEGRADABLE RESINS

DESCRIPTION TECHNICAL FIELD

This invention relates to dry electrostatic toners having improved properties. More particularly, this invention relates to toners containing a degradable polymeric resin.

BACKGROUND A T It is known that a latent electrostatic image can be developed with toner particles. A latent electrostatic image may be produced by providing a photo-conductive layer with a uniform electrostatic charge and subsequently discharging the electrostatic charge by exposing it to a modulated beam of radiant energy. Other methods are known for forming latent electrostatic images. For example, one method is providing a carrier with a dielectric surface and transferring a preformed electrostatic charge to the surface.

Useful toners comprise a thermoplastic resin and a suitable colorant such as a dye or pigment. The colored toner particles are normally less than 10 Um average size as measured by a Malvern 3600E laser diffraction light scattering particle analyzer. It has also been found desirable to add to toners a charge director compound. U. S. Patent Nos. 4, 925, 764 and 765 Madeleine (1990) are directed to excellent charge director compounds and their manufacture. Other prior art charge director compounds are also disclosed in columns l and 2 of these patents. These Madeleine patents and the prior art patents recited in columns l and 2 thereof are hereby incorporated herein by reference. They provide relevant background for the present invention.

Because of environmental concerns, recycling of used paper is becoming ever more important. However, paper printed with toners has been found to be greatly unacceptable for making quality recycled paper because the toner printing contaminates the recycled paper product. Toners are particularly difficult to remove from paper because the conventional resin is melt-fused and so very tightly bonded. Even after de-inking, the residual toner imparts to recycled paper a gray cast and also a black spotted appearance.

SUMMARY OF THE INVENTION In accordance with this invention there is provided an electrostatic toner for printing having improved degradability compatible with the recycling of printed paper, comprising particles of a degradable resin.

DETAILED DESCRIPTION OF THE INVENTION

The toners of this invention comprise particles of a polymeric resin containing at least one unit selected from the group consisting of: (1) (0(CRlR2) _n CO) _p (2) (0CRlR ² C00CRlR2C0) _q

(3) (OCRl 2CRlR2θCR*lR2cθ) _r

(4 ) (OCR ¹ R ² CR ¹ R ² 0CR ¹ R2CR ¹ R2CO) _S and

(5) (NH (CRlR2) _n CO) t wherein n is a whole number 2, 4 & 5, the total of p, q, r, s and t being 50 to about 5,000, and Rl and R2, which can be the same or different, are hydrogen, hydrocarbyl containing 1 to 12 carbon atoms, or substituted hydrocarbyl containing 1 to 12 carbon atoms, the resin particles having an average by area particle size of less than 10 Um.

The preferred toners of this invention comprise degradable polymeric resins selected from the

- 3 - group consisting of homopolymer of any of units (1) to (5) , block or random copolymers of at least two units of (1) to (5) , blends of homopolymers of any of units (1) to (5) , block or random copolymers of at least two units of (1) to (5) , and combinations thereof.

Preferable polymeric resins are those wherein Rl and R2 are independently hydrogen or methyl. The most preferable resins are those that contain polylactic acid units. Desirably, at least 50% of the polymeric content of the resin is polylactic acid units. Also, especially preferred units are epsilon-caprolactone, delta-valerolactone, lactide(3,6-dimethyl-l,4-dioxan- 2,5-dione), glycolid(l,4-dioxan-2,5-dione) , l,5-dioxepan-2-one, l,4-dioxan-2-one, beta-butyrolac- tone and beta-propylactone.

The polymers may be synthesized by polymeri¬ zation directly from the acid precursors, or by poly¬ merization of cyclic monomeriσ or dimeriσ (depending on the acid type) lactone. Polymerization from the cyclic lactone is preferred for producing high molecular weight polymers because equilibrium reactions with the intermediate, cyclic dimer and low molecular weight species place practical limits on the molecular weight of polymers produced directly from the hydroxy acid.

The polymeric resins of this invention have weight average molecular weights from about 400 to about 600,000, preferably 100,000 to 450,000.

Throughout the specification the term degradable means that the polymeric resin component of the developer is biodegradable, for example in landfills, but more importantly is hydrolysable by exposure to aqueous conditions. The degradation rate is consistent with its intended usage, i.e., the product does not degrade significantly in normal storage and use, but will degrade in a reasonable time after discarding. As is known in the art, hydrolysis

degradation is dependent on the degree of crystallinity; higher crystallinity polymers degrade more slowly. For hydrolysis preferably slightly basic or acidic, whereupon the polymeric resin is hydrolyzed to monomeric or low molecular weight units that are suitable for recycle reuse to prepare polymer.

In addition to degradability, the polymeric resins have the ability to disperse a colorant, e.g., pigment, etc.; and the ability to be ground to form particles between 0.1 Um and 10 Um, average by area size.

As indicated above, additional components that can be present in the electrostatic toner are colorants, such as pigments or dyes and combinations thereof. The colorant, e.g., a pigment, may be present in the amount of up to about 60 percent by weight based on the total weight of solid toner, preferably 0.01 to 30% by weight based on the total weight of toner. The amount of colorant may vary depending on the use of the developer.

Other ingredients may be added to the electrostatic toner, such as fine particle size oxides, e.g., silica, alumina, titania, etc.; preferably in the order of 0.5 Um or less can be dispersed into the liquified resin. These oxides can be used instead of the colorant or in combination with the colorant. Metal particles may also be added. Also, one or more charge enhancing substances, such as those disclosed in the aforementioned Madeleine patents, may be added. Plasticizers in small amounts, such as lactides or lactic oligomers, may sometimes be desirable.

Numerous methods may be employed to produce the toner of the present invention. One method is to melt blend the resin, the pigment and the charge control agent, followed by mechanical attrition.

Other methods include those well known in the art such

as spray drying and dispersion polymerization. For example, a solvent dispersion of a resin, pigment and charge control agent are spray dried under controlled conditions, thereby resulting in the desired product. Such a toner prepared in this manner results in a positively charged toner in relationship to the carrier materials used.

The electrostatic toners of this invention demonstrate good image quality, and are useful in copying, e.g., making office copies of black and white s well as various colors; or color proofing, e.g., a reproduction of an image using the standard colors: yellow, cyan, magenta together with black as desired. In copying and proofing, the toner particles are applied to a latent electrostatic image. A major advance in the art is that the developers of this invention are biodegradable and more importantly degradable by hydrolysis, which removes the ink and breaks down the resin to units that can be isolated easily and reconverted to polymeric resin. Paper printed with these developers can be processed by standard paper recycle treatment without leaving a gray or spotted discoloration to the recycled paper made therefrom.

For determining the recyclability and the nature of recyclable paper made from paper printed with the toner of the present invention, the following test procedure, which is consistent with TAPPI Standards, may be used:

1. Cut 100 grams printed paper into 1/4" squares

Repulp in lab repulper, in the presence of bleach liquor for 30 minutes at 50oC Bleach liquor

* 95% liquor * 5% paper by weight

* 1 gram NaOH by weight on paper

* 3 grams sodium silicate by weight on paper

* 1 gram calcium carbonate

* trace fatty acid soaps * 2 liters Dl water

2. Digest for 1 hour at 40°C, without agitation

3. Isolate paper via course screening, flotation and washing 4. Prepare 3 grams handsheets - for TAPPI

Diano S-4 or TB1C 5. Measure brightness and dirt count. Obtain ISO and GE brightness measurements, as well as *L*a*b color readings.

EXAMPLE Polymerization of S-Lactide with Dysprosium Tris(2-N,N-dimethylaminoethoxide) .

In a dry box, S-lactide (7.60 g) is weighed in a 100 ml. RB flask equipped with a stirring bar. Methylene chloride (40 ml.) is added. To the stirred solution, under argon, dysprosium tris(2-N,N-dimethyl- a inoethoxide) (1.0 ml. of a 0.1 M solution in toluene) is added. After approximately twenty-one hours, the polymerization is terminated with 50 ml. of 5% HCl. Additional methylene chloride is added and the organic phase separated and washed again with 5% HCl (1 x 50 ml.), then with 50 ml. of 5% sodium bicarbonate and finally with water (3 x 50 ml.). After drying over anhydrous sodium sulfate and filtration, the organic phase is concentrated via rotoevaporation. The polymer is precipitated in hexanes and dried under vacuum. Yield: 5.15 g (67.7%). GPC analysis: Mn - 70700, Mw = 82,900, PD - 1.17 (PET STD.) .

The above polymer (1.02 g) and dichloromethane (10 ml.) are added to an oven dried

100 ml. RB flask. To this stirred solution, 0.5 g anhydrous sodium sulfate and 0.5 ml. of dimethyl sulfate are added. After one and a half hours the sodium sulfate is filtered off and the resulting solution added to hexanes. The precipitated polymer is filtered and dried in vacuo. Yield: 0.7 g (70%); 1H NMR (CDCI ₃ ) 3.4 (s, Mβ3N+) .

Preparing the toner. A toner composition is prepared by melt blending followed by mechanical attrition 10 parts of Black Pearl carbon black with 90 parts of this polylaσtide. Three parts of the above toner and 97 parts of an uncoated ferrite carrier are blended into a developer composition. The developer composition is then roll milled. After rill milling the triboelectriσ charge on the tone is measured using a vertex model T-lOO Triboelectric Tester. Tribotester measurements are made by loading the developer composition into a Faraday cage and using a stream of air to remove charged particles that are finer than the cage screen. The opposite net charge remaining on the developer composition is neutralized and measured. The polymer is found to charge the toner negatively.