Toner, developer, and image forming apparatus

1. A toner, comprising:

a copolymerization resin,

wherein the copolymerization resin comprises: a unit derived from a polyester resin including a polycarboxylic acid having a valence of 2 or more and a polyol having a valence of 2 or more; and a unit derived from a resin having a polyhydroxycarboxylic acid skeleton, where the unit derived from the resin having a polyhydroxycarboxylic acid skeleton is bonded to the unit derived from the polyester resin via at least one of a urethane group and a urea group, and

wherein the toner has a relative degree of crystallization of 10% or more and less than 50%.

2. The toner according to claim 1 , wherein an endothermic peak temperature of the toner measured by differential scanning calorimetry is 50° C. or more and less than 80° C.

3. The toner according to claim 1 , wherein a glass transition temperature of the toner measured by differential scanning calorimetry is 20° C. or more and less than 50° C.

4. The toner according to claim 1 , wherein an amount of compression deformation at 50° C. of the toner measured by a thermomechanical analysis method is 5% or less.

5. The toner according to claim 1 , further comprising a crystalline resin other than the copolymerization resin.

6. The toner according to claim 1 , wherein a mass ratio A/B of the unit derived from the polyester resin indicated by A to the unit derived from the resin having a polyhydroxycarboxylic acid skeleton indicated by B in the copolymerization resin is 20/80 to 50/50.

7. The toner according to claim 1 , wherein the copolymerization resin has a weight average molecular weight of 20,000 to 100,000.

8. The toner according to claim 1 , wherein a ratio Q2/Q1 satisfies expression (1) below and Q1 satisfies expression (2) below where Q1 is an amount of heat absorbed in a first raising of a temperature of the toner in DSC and Q2 is an amount of heat absorbed in a second raising of a temperature of the toner in DSC:

0≦ Q 2/ Q 1<0.30  (1);

and

Q 1>10 J/g  (2).

9. A developer, comprising:

a toner, wherein the toner comprises:

a copolymerization resin,

wherein the copolymerization resin comprises: a unit derived from a polyester resin including a polycarboxylic acid having a valence of 2 or more and a polyol having a valence of 2 or more; and a unit derived from a resin having a polyhydroxycarboxylic acid skeleton, where the unit derived from the resin having a polyhydroxycarboxylic acid skeleton is bonded to the unit derived from the polyester resin via at least one of a urethane group and a urea group, and

wherein the toner has a relative degree of crystallization of 10% or more and less than 50%.

10. An image forming apparatus, comprising:

an electrostatic latent image bearing member;

an electrostatic latent image forming unit configured to form an electrostatic latent image on the electrostatic latent image bearing member;

a developing unit configured to develop the electrostatic latent image with a toner to form a visible image;

a transferring unit configured to transfer the visible image onto a recording medium; and

a fixing unit configured to fix the visible image transferred onto the recording medium,

wherein the toner comprises:

a copolymerization resin,

wherein the copolymerization resin comprises: a unit derived from a polyester resin including a polycarboxylic acid having a valence of 2 or more and a polyol having a valence of 2 or more; and a unit derived from a resin having a polyhydroxycarboxylic acid skeleton, where the unit derived from the resin having a polyhydroxycarboxylic acid skeleton is bonded to the unit derived from the polyester resin via at least one of a urethane group and a urea group, and

wherein the toner has a relative degree of crystallization of 10% or more and less than 50%.