Surface and Coatings Technology 169–170(2003) 592–594

0257-8972/03/$ - see front matter� 2003 Elsevier Science B.V. All rights reserved.PII: S0257-8972Ž03.00122-1

Improvement on the qualities of photosensitive members with coldsealing

Jin Young Kim*, Yong Sun Won, Chang Hyun Kim, Ji Chul Yoo, Hee Taek Yum

R&D Center, Samsung Electro-Mechanics, Suwon, Kyounggi-do 442-743, South Korea

Abstract

Organic photo-conductor(OPC) drum used in a laser printer comprises photosensitive substrates including an anodized layerformed on the surface of an aluminum or aluminum alloy base. Hot sealing method has been dominantly used to seal the poresof anodized aluminum of OPC drum. Cold sealing procedure has been applied to enhance the sealing quality of OPC drum andthe result showed that cold sealing method is more effective than hot sealing when the pore size is extremely small. As a result,defects such as spots on the printed images, smudges and cracks on the surface of OPC drum have been removed. Adhesionstrength between photosensitive layers and the surface of anodized aluminum has greatly increased with improvement of sealingquality.� 2003 Elsevier Science B.V. All rights reserved.

Keywords: Hot sealing; Cold sealing; Organic photo-conductor drum; Anodized aluminum

1. Introduction

Organic photo-conductor(OPC) drum is one of themain components of a laser printer. The image isgenerated by the laser beam which reaches on the light-sensitive drum as the pattern of an electric charge. Thetoner particles adhere to this pattern after the drum hasbrushed against the developing rollerw1x (Fig. 1).

OPC drum is comprised of several photosensitivelayers including a charge generating layer and a chargetransporting layer which coat the surface of anodizedaluminum substrate. The anodized aluminum layer hasporous structure containing columnar hexagonal cellsconsisting of central pores 30 nm in diameter.

Sealing of the pores formed in the surface of OPCdrum has been dominantly accomplished by immersionin boiling water, procedure known as ‘hydrothermalsealing or hot sealing’w2–5x.

While hot sealing method with nickel acetate bathwas adopted, defects such as dots on the printed images,smudges and cracks on the surface of anodized alumi-num were reported from both the sides of manufacturersand users of OPC drum. Since poor quality of sealingcan be an origin of these defects, cold sealing using a

*Corresponding author. Tel.:q82-31-210-6397; fax:q82-31-210-3324.

E-mail address: jy1974@samsung.co.kr(J.Y. Kim).

nickel fluoride bath has been newly adopted to improvethe quality of sealing. In spite of its economical advan-tages cold sealing has not been commonly used in OPCdrum with several difficulties related to the characteris-tics of printed images.

Improvement on the sealing quality after using coldsealing method and investigation on the sealing mecha-nism has been discussed.

2. Experiments

Sealing conditions are described as follows:● Hot sealing: 0.5 gyl of nickel acetate, 858C and 7

min.● Cold sealing: 0.5 gyl of nickel fluoride, additives less

than 0.5 gyl, room temperature and 7 min.

Sealing conditions were analyzed by FE-SEM(Hita-chi S-4700) equipped with EDS(Noran Vantage). FT-IR (Bio-Rad, FTS 65A) and IC (Dionex DX-500) areused to analyze the composition of sealants.

3. Results and discussion

In hot sealing using nickel acetate bath, aluminumoxide on the wall of pores is transformed into bohemite

593J.Y. Kim et al. / Surface and Coatings Technology 169 –170 (2003) 592–594

Fig. 1. A schematic of a laser printer.

Fig. 3. Defects found in OPC drum.

Fig. 2. The surface of imperfectly sealed anodized aluminum layer. Fig. 4. Proposed schematic of plugged pores after cold sealing.

which is formed at the temperature of above 808C. Thebasic reaction in a hot sealing process can be expressedby w3x

Al O qH O™2AlO(OH); bohemite2 3 2

This conversion results in the volume expansion andclosing of porosity. The bohemite can be formed attemperature above 808C and it exhibits the corrosionpreventing effect for aluminumw5x.

The supply of water by diffusion process has to becontinued for this transformation to occur in the lowerarea of the pores. However, diffusion process of H O2

towards the anodic oxide is not easy, especially, whenthe pore size is small, resulting in poor sealing. Fig. 2shows the surface of imperfectly sealed anodized alu-minum layer after hot sealing.

As the sealing has not been thoroughly done, variouskinds of defects such as black spots(or white ones, ina reversed development system), smudges and crackson the surface of anodized layer have occurred. Directcharge injection from the aluminum substrate passed

through the unsealed pores originates the undesirablespots on the printed images. Cracks can be generatedon the surface of aluminum oxide during the storagedue to the expansion of air filled in pores as thetemperature rises(Fig. 3).

Cold sealing procedure based on nickel fluoride solu-tions has fostered since the 1980sw6–8x.

The mechanism of cold sealing has not become wellunderstood so far. A possible scheme of the cold nickelfluoride sealing is suggestedw6x.

y yAl O q6F q3H O™2AlF q6OH2 3 2 3

q2 yNi q2OH ™Ni(OH)2

Al O q3H O™2Al(OH)2 3 2 3

These reactions are synergistic, leading to coprecipi-tates within the micropores and eventually blocking thepores. EDS analysis of the cross-section of the poresconfirms that nickel hydroxide seals the pore(Fig. 4).

The problem of continuous growing of hydroxide hasbeen solved by the use of endcapping agent. Addition-ally, an amine type of organic additive is used tofacilitate penetrating of sealant into the pores. As a

594 J.Y. Kim et al. / Surface and Coatings Technology 169 –170 (2003) 592–594

Fig. 5. The surface of anodized aluminum after(a) hot sealing and(b) cold sealing.

result, spots and smudges have not generated anymore.High quality of cold sealing has come to be provedgood in the prevention of cracks. Moreover, a remarka-ble improvement of the adhesion strength between thephotosensitive layer and the anodized layer, an unex-pected outcome, was achieved. Evaluation of adhesionshowed that adhesion strength increased more than fivetimes after the new sealing method was adopted(Fig.5).

4. Conclusion

Cold sealing method using a nickel fluoride has beenadopted to seal the anodized aluminum of OPC drum.The pores were thoroughly impregnated with nickelhydroxide in the cold sealing method. Special additiveshave been used to stop further formation of hydroxidesand to facilitate the sealing process. As a result, previ-ously reported defects such as spots on the printedimages, cracks and smudges on the surface of aluminumoxide have been terminated.

In addition, adhesion strength has increased more thanfive times with the improvement on the sealing quality.

References

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845–854.w8x C. Liden, Contact Dermatitis 31(1994) 22–24.