Image forming apparatus including filter for removing particulates

1. An image forming apparatus comprising:

an image forming unit configured to form a toner image on a recording material by using toner containing a parting agent;

a fixing unit provided with a first rotatable member and a second rotatable member contacting said first rotatable member, configured to form a fixing nip portion for fixing the toner image on the recording material by applying heat and pressure while feeding and nipping the recording material;

a heating portion configured to heat said first rotatable member; and

a removal unit provided in a neighborhood of said fixing unit and configured to remove particulate dust generated due to vaporization of the parting agent by heat in said fixing unit,

wherein said removal unit includes:

a sheet-like filter provided with a base layer and a collecting layer laminated on said base layer for collecting dust,

a holding unit configured to hold said filter in a cylindrical shape, a longitudinal direction of said filter held in the cylindrical shape being along a rotational axis direction of said first rotatable member and the collecting layer being disposed inside of the base layer with respect to a radial direction of said filter held in the cylindrical shape, and

a fan generating an air flow inside of said cylindrical shape which causes air passing from outside of said filter to inside of said filter to flow with respect to the radial direction of said filter.

2. An image forming apparatus according to claim 1 , wherein said image forming unit includes an image bearing member configured to bear the toner image and rotate, and a transfer portion configured to transfer the toner imager from said image bearing member to the recording material, and

wherein said filter held in the cylindrical shape by said holding unit is provided between said transfer portion and said fixing unit with respect to a feeding direction of the recording material.

3. An image forming apparatus according to claim 2 , wherein said filter held in the cylindrical shape by said holding unit is disposed at a side of said first rotatable member relative to said fixing nip portion in a direction perpendicular to the feeding direction of the recording material.

4. An image forming apparatus according to claim 1 , wherein said holding unit includes a beam portion, and

wherein said beam portion holds an end of said filter and an opposing end of said filter so as to hold said filter in the cylindrical shape.

5. An image forming apparatus according to claim 4 , wherein said filter held in the cylindrical shape is formed with openings at both ends thereof in the rotational axis direction of first rotatable member, and

wherein said holding unit is provided with shielding portions disposed at openings of both ends and configured to maintain said filter in the cylindrical shape and to shield said openings to prevent air from intruding.

6. An image forming apparatus according to claim 4 , wherein said removal unit is provided with a cage shielding portion disposed so as to surround outside of said filter in a circumferential direction of said filter held in the cylindrical shape and configured to maintain said filter in the cylindrical shape.

7. An image forming apparatus according to claim 1 , wherein said holding unit is provided so as to enclose said filter formed beforehand in the cylindrical shape, and maintains said filter in the cylindrical shape by fixing an outer periphery of said filter.

8. An image forming apparatus according to claim 7 , wherein said holding unit is a first holding unit, and

wherein said removal unit includes a second holding unit provided inside of said filter held by said first holding unit in the cylindrical shape and configured to hold said filter by nipping said filter from inside between said second holding unit and said first holding unit.

9. An image forming apparatus according to claim 1 , wherein said holding unit is provided inside of said filter formed beforehand in the cylindrical shape, and holds said filter in the cylindrical shape by fixing said filter from inside.

10. An image forming apparatus according to claim 1 , wherein a surface density of said filter is 50 (g/m 2 ) or more and 300 (g/m 2 ) or less.

11. An image forming apparatus according to claim 10 , wherein said collecting layer is formed of a nonwoven fabric of a polypropylene fiber and said base layer is formed of a nonwoven fabric of a polyethylene terephthalate fiber.

12. An image forming apparatus according to claim 1 , wherein said collecting layer is adhered to said base layer, and

wherein an area of said collecting layer and an adhering area of said collecting layer and said base layer satisfy the following formula:

1/120<the adhering area/the area of said collecting layer<⅓.

13. An image forming apparatus according to claim 1 , wherein said collecting layer is composed of a glass fiber filter.

14. An image forming apparatus according to claim 1 , wherein said filter is composed of a PTFE filler made by laminating said collecting layer as a PTFE membrane filter and said base layer as a reinforcing filter.