Electrostatic latent image developing agent and image forming method

1. An electrostatic latent image developing agent comprising a toner and a carrier, wherein:

the surface of the toner is covered with a plurality of particles that comprises:

at least first particles having a volume resistivity of 1×10 14 Ωcm or greater and an average primary particle diameter in a range of 40 nm to 50 nm, and

second particles having a volume resistivity of 1×10 14 Ωcm or greater and an average primary particle diameter of less than 50 nm,

wherein a total covering ratio on the surface of the toner of the second particles is higher than a total covering ratio of said at least first particles, and a sum of the total covering ratios of said at least first particles and said second particles is higher than a total covering ratio of other particles present on the toner surface;

a shape factor SF 1 of the toner is in the range of from 100 to 140;

the carrier is a resin coated carrier; and

at least a coating resin layer of the resin coated carrier comprises a positively charging resin and a quaternary ammonium salt compound.

2. An electrostatic latent image developing agent according to claim 1 , wherein a volume resistivity of the carrier is in the range of from 1×10 9 Ωcm to 1×10 13 Ωcm.

3. An electrostatic latent image developing agent according to claim 1 , wherein a core material component exposure ratio of the carrier is 20% or less.

4. An electrostatic latent image developing agent according to claim 1 , wherein the toner is manufactured by a wet method.

5. An electrostatic latent image developing agent according to claim 1 , wherein the particles comprise silicone-treated silica.

6. An electrostatic latent image developing agent according to claim 1 , wherein a content of the quaternary ammonium salt compound is in the range of from 1 to 60 parts by mass per 100 parts by mass of the positively charging resin.

7. An electrostatic latent image developing agent according to claim 1 , wherein an amount of the positively charging resin is in the range of from 0.05 to 5.0% by mass with respect to a total mass of the carrier.

8. An electrostatic latent image developing agent according to claim 1 , wherein an average film thickness of the positively charging resin is in the range of from 0.1 to 10 μm.

9. An electrostatic latent image developing agent according to claim 1 , wherein a volume resistivity of the carrier is in the range of from 10 9 to 10 13 Ωcm at a development contrast potential in the range of from 10 3 to 10 4 V/cm.

10. An electrostatic latent image developing agent according to claim 1 , wherein an amount of the particles is in the range of from 0.3 to 5 parts by mass per 100 parts by mass of the toner.

11. An electrostatic latent image developing agent according to claim 1 , wherein a volume average particle diameter of the toner is in the range of from 2 to 12 μm.

12. An electrostatic latent image developing agent according to claim 1 , wherein a ratio of a volume average particle diameter of the carrier to a volume average particle diameter of the toner is in the range of from 2:1 to 15:1.

13. An image forming method comprising at least:

a charging step of charging a surface of an electrostatic latent image bearing member;

an electrostatic latent image forming step of forming an electrostatic latent image on the surface of the electrostatic latent image bearing member;

a developing step of transforming the electrostatic latent image into a toner image by using an electrostatic latent image developing agent;

a transfer step of transferring the toner image formed on the surface of the electrostatic latent image bearing member onto a surface of a receiving substrate;

a fixing step of thermally fixing the toner image transferred onto the surface of the receiving substrate; and

a cleaning step of removing the toner remaining on the surface of the electrostatic latent image bearing member,

wherein:

the electrostatic latent image developing agent comprises a toner and a carrier;

the surface of the toner is covered with a plurality of particles that comprises:

at least first particles having a volume resistivity of 1×10 14 Ωcm or greater and an average primary particle diameter in a range of 40 nm to 50 nm, and

second particles having a volume resistivity of 1×10 14 Ωcm or greater and an average primary particle diameter of less than 50 nm,

wherein a total covering ratio on the surface of the toner of the second particles is higher than a total covering ratio of said at least first particles, and a sum of the total covering ratios of said at least first particles and said second particles is higher than a total covering ratio of other particles present on the toner surface;

a shape factor SF 1 of the toner is in the range of from 100 to 140;

the carrier is a resin coated carrier; and

at least a coating resin layer of the resin coated carrier comprises a positively charging resin and a quaternary ammonium salt compound.

14. An image forming method according to claim 13 , wherein a volume resistivity of the carrier is in the range of from 1×10 9 Ωcm to 1×10 13 Ωcm.

15. An image forming method according to claim 13 , wherein a core material component exposure ratio of the carrier is 20% or less.

16. An image forming method according to claim 13 , wherein the toner is manufactured by a wet method.

17. An image forming method according to claim 13 , wherein the particles comprise silicone-treated silica.

18. An image forming method according to claim 13 , wherein a content of the quaternary ammonium salt compound is in the range of from 1 to 60 parts by mass per 100 parts by mass of the positively charging resin.