Patent Grant
7173805
Electrophotographic (“EP”) devices, such as laser printers, photocopiers, fax machines, all in one devices, and multi-function devices, are used to form images. The conductive components of EP and electrostatic-dissipative devices may include polymers, such as polyurethane elastomers.
However, most polymers, such as polyurethane, have relatively low conductivity and, therefore, static charges build up on the components and may adversely affect operations of the equipment.
The disclosed embodiments can be more readily ascertained from the following detailed description when read in conjunction with the accompanying drawings in which:
A polymer material, such as a polyurethane material, having increased conductivity is disclosed. The polyurethane material includes at least one alkaline salt that provides conductivity to the polyurethane material. The polyurethane material also includes a polyol having at least one moiety that increases the conductivity of the polyurethane material. The polyol may be a polyester polyol or a polyether polyol. The combination of the moiety and the alkaline salt may provide increased conductivity to the polyurethane material. The alkaline salt may be a lithium salt including, but not limited to, LiClO4, lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium trifluoromethane sulfonate (LiCF3SO3), lithium bis (trifluoromethanesulfonyl) imide (LiN(CF3SO2)2), lithium bis (perfluoroethylsulfonyl) imide (LiN(SO2CF2CF3)2), lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl) imide (LiN(CF3SO2)(C4F9SO2)), lithium tris (trifluoromethanesulfonyl) methane (LiC(CF3SO2)3), and mixtures thereof.
The moiety present in the polyol may be capable of interacting with an ion of the alkaline salt. For instance, if the alkaline salt is a lithium salt, the lithium ion may chelate the moiety of the polyol. The moiety in the polymer may include a polyether functional group having at least two carbon atoms between oxygen atoms. The moiety may include ethylene glycol (“EG”) (—CH2CH2O—), di(ethylene glycol) (“DEG”) ((—CH2CH2O—)2), tri(ethylene glycol) (“TEG”), tetra(ethylene glycol), poly(diethylene glycol), poly(ethylene oxide), and mixtures thereof. As shown in
The DEG or EG may provide sufficient spacing between the oxygen atoms to form an energetically favored 5-membered ring, which provides relatively high solvation of the cation of the alkaline salt.
Without being tied to a particular theory, it is believed that that if the polyol includes the EG moiety and adipic acid, the EG moiety is not as effective of a chelator as DEG due to sharing of the resonance structure with the carboxyl group.
The polyol may also have a low glass transition temperature (“Tg”). Since it is believed that transport of the alkaline ion depends on its interaction with the EG or DEG moiety on the polyol, the mobility of the polyol may play a role. A low Tg of the polyol may be desired because the lower the Tg, the higher the ion transport efficiency. The Tg of the polyol may be less than approximately −38° C. The Tg of the polyol may depend on the chemical structures of the polyol and isocyanate used in the polyol. By utilizing a polyol having a low Tg, the polyol may have a higher mobility, which provides fast lithium ion transport to the polyurethane material. The fast lithium ion transport corresponds to a short electrical response time or relaxation time for the polyurethane material, which may reduce electrical memory and ghosting in the electrophotographic printing process.
The polyol may be a polyester polyol or a polyether polyol. The polyol may be synthesized by techniques including a condensation reaction of a diol with a dicarboxylic acid. The diol may include, but is not limited to, a glycol. For instance, a polyalkylene glycol, such as DEG, TEG, tetraethylene glycol, or mixtures thereof may be used. The dicarboxylic acid may include, but is not limited to, adipic acid (“AA”), malonic acid, glutaric acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, brassylic acid, succinic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, phthalic acid, terephthalic acid, isophthalic acid, and mixtures thereof. In one embodiment, the polyester polyol includes AA and DEG and has the following structure:
In another embodiment, the polyester polyol includes AA and TEG. It is understood that other dicarboxylic acids, besides AA, may be used in the polyester polyol. Examples of polyether polyols include, but are not limited to, poly(ethylene glycol), poly(propylene glycol), and poly(tetramethylene glycol).
Isocyanate compounds may be used in the polyaddition reaction to cure or crosslink the polyol. Isocyanate compounds may include, but are not limited to, a diisocyanate, such as tolylenediisocyanate, 4,4-diphenylmethanediisocyanate, xylylenediisocyanate, naphthylenediisocyanate, paraphenylenediisocyanate, tetramethylxylenediisocyanate, hexamethylenediisocyanate, dicyclohexylmethanediisocyanate, isophoronediisocyanate, or tolidinediisocyanate.
Polyols having the moieties described above are commercially available. Examples of polyester polyols include Desmophen® 1700 and Desmophen® 1800, which are available from Bayer Polymers (Pittsburgh, Pa.), and 3500DEA, which is available from Specialty Resins Corp. (Auburn, Me.). Examples of polyether polyols include Multranol® from Bayer Polymers (Pittsburgh, Pa.) and Voranol® from Dow Chemicals (Midland, Mich.).
The alkaline salt may be present at a concentration ranging from approximately 0.01 wt % of a total weight of the polyurethane material to approximately 10 wt % of the total weight of the polyurethane material. In one embodiment, the alkaline salt is present from approximately 0.01 wt % of the total weight of the polyurethane material to approximately 5 wt % of the total weight of the polyurethane material.
The polyurethane material may optionally include additional ingredients, depending on the desired properties of the polyurethane material. These ingredients may include, but are not limited to, cure accelerators, flame retardants, thickeners, anti-foaming agents, light stabilizers, antioxidizers, leveling agents, or wetting agents.
The polyurethane material may be formed by adding the alkaline salt to the polyol or a precursor of the polyol. The alkaline salt may be added to the polyol at a temperature ranging from approximately 25° C. to approximately 100° C. When the alkaline salt is dissolved, the polyol may be combined with the isocyanate composition to form the polyurethane material. If the polyurethane material utilizes any of the optional ingredients, these optional ingredients may also be combined with the alkaline salt and the polyol. For instance, the alkaline salt may be added to a solution of the polyol or a precursor of the polyol. The solution may then be cured to produce the polyurethane material. The alkaline salt may be blended with the polyol before the polyol is crosslinked so that the alkaline salt is evenly and homogeneously blended and dispersed in the polyurethane material.
The polyurethane material may have a low resistivity or a high conductivity. As would be understood by one of ordinary skill in the art, resistivity is the inverse of conductivity. In contrast, a polyurethane material lacking the moiety in the polyol may have a significantly higher resistivity. The polyurethane material also may have a long shelf-life or long life span.
Since the moiety or moieties in the polyol increases the conductivity of the polyurethane material, the alkaline salt may be present in the polyurethane material at a lower concentration. In other words, a lower concentration of the alkaline salt may be used to achieve a desired conductivity. Therefore, the problems previously associated with large amounts of lithium salts may be ameliorated.
The polyurethane material may be formed into a desired shape, such as by placing the polyurethane material into an appropriately shaped mold. Alternatively, the polyurethane material may be coated, sprayed, or otherwise applied onto a substrate. For the sake of example only, the polyurethane material may be formed into a roller, plate, square block, sphere, or brush. The roller 1 may include a shaft 2 and a layer of the polyurethane material 3 surrounding the shaft 2, as illustrated in
The shaft 2 of the roller 1 may be a solid metal mandrel or a hollow metal cylinder formed from a conductive metal including, but not limited to, iron, copper, or stainless steel. Alternatively, the shaft 2 may be formed from a conductive plastic. The polyurethane material 3 may be applied to the outer periphery of the shaft 2 by coating the shaft 2 with the polyurethane material 3 or by dipping the shaft 2 into a solution of the polyurethane material 3. The polyurethane material 3 may then be dried. For the sake of example only, the roller 1 may be a developer roller. However, the polyurethane material may also be used in other types of rollers 1 that dissipate electrical charge or perform charge management functions, such as transfer rollers or charge rollers. The polyurethane material may also be used in image transfer blankets, electrostatic dissipative devices, electromagnetic (“EM”) shielding, or paper handling devices.
The roller 1 may be used in a developer system 10, as shown in
As previously mentioned, the roller 1 may be a developer roller 1′ in an EP device 12, as illustrated in
The following examples describe polyurethane materials that may be used in various embodiments. The examples are merely illustrative and are not meant to limit the scope of the claimed subject matter in any way.
Polyurethane coupons were prepared that included LiClO4 and the polyester polyols indicated in Table 1. Each of formulations A–G included a DEG polyester polyol(s) and LiClO4. Formulation I included non-DEG polyester polyol(s) and LiClO4. The polyurethane coupons were prepared by combining the indicated parts by weight of the polyester polyol(s) with the indicated percentage of LiClO4. The materials were then cured with isocyanates, such as Mondur 501® from Bayer Polymers.
1 DEG = diethylene glycol, AA = adipic acid, BDO = butanediol, EG = ethylene glycol, TMP = trimethylopropane
2 1700 = Desmophen ® 1700, 3500DEA = 3500DEA, 1800 = Desmophen ® 1800, 207 = Rucoflex ® 207, Baytec 120P = Baytec ® ENC 120P, 2505 = Desmophen ® 2505, 1037 = Desmophen ® 1037-55
3 % LiClO4 = g of LiClO4 per (100 g polyol resins + g isocyanate + g other additives)
Resistance of the polyurethane coupons was measured with an Agilent 4339B high resistance meter (Agilent Technologies (Palo Alto, Calif.)) at 250V having a one second charge. The dimensions of the tested polyurethane coupons were 10 cm×1 cm×0.2 cm. The resistivity of each of Formulations A–G and I is shown in Table 1.
The resistivity data of each of Formulations A–G and I was plotted against the percent of LiClO4, as shown in
Formulations C and F included similar concentrations of LiClO4 (0.40%–0.43%). Formulations C and F included DEG. Formulations C and F had resistivities of 2.30 Mega ohm-cm and 3.00 Mega ohm-cm, respectively. Since resistivity and conductivity have an inverse relationship, higher conductivities are observed with the DEG-containing polyurethane materials.
Each of Formulations B, C, E, and F included the same DEG-containing polyester polyol with differing LiClO4 concentrations (0.83%, 0.42%, 0.21%, and 0.40%, respectively). A comparison of these Formulations indicates that all had a resistivity of less than approximately 7 Mega ohm-cm, which shows that the decreased resistivities were achieved even when lower LiClO4 concentrations were used. The resistivity reached a plateau at about 0.45% LiClO4. At higher concentrations of LiClO4, smaller decreases in resistivity were observed.
In addition, the dynamic resistance of the DEG-containing polyols (Formulations A–F) was measured. After about 30 minutes of subjecting the Formulations to the measuring conditions, those Formulations having a LiClO4 concentration higher than 0.83% or 1.0 phr oozed gel after resting. It is believed that these Formulations included non-chelated LiClO4 (i.e., LiClO3 that was not participating in ion transport), which caused gel formation.
In summary, as shown by the resistivity data, the DEG-containing polyols provided the most efficient use of the lithium ion for conductivity. In contrast, for the non-DEG polyurethane materials, additional LiClO4 was added to achieve the same resistivity or amount of “mobile lithium.” However, as previously discussed, using additional LiClO4 negatively affects the polyurethane material, such as decreasing long term stability and life span.
Polyurethane coupons are prepared as described in Example 1, except that the DEG-containing polyester polyols are replaced with TEG-containing polyester polyols.
Resistance of the polyurethane coupons is measured, as described in Example 1. The resistivity of the polyurethane coupons is lower than the resistivity of polyurethane coupons that do not include TEG.
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