JPH04308852A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obtain the electrophotographic sensitive body which has the sensitivity in positive electrification, is stable to temp. and humidity, eliminates the image flow by the degradation in surface resistance at and under a high temp. and high humidity by the surface deposits of paper dust, etc., after the repetitive use, can prevent the image abnormality corresponding to the parts existing near a main electrifier part 1 and transfer electrifier during the interruption of use on a photosensitive drum even when used particularly after the interruption of the use for a specified period of time and has further high hardness and film strength and excellent wear resistance and durability in spite of the thin protective layer. CONSTITUTION:The electrophotographic sensitive body is formed by laminating a charge transfer layer, a charge generating layer and a protective layer in this order on a conductive base. In addition, a thermosetting silicone resin, urethane elastomer, vapor synthesized silica formed by substituting the hydroxyl group on the surface with a trimethyl siloxyl group, or vapor synthesized silica formed by substituting the hydroxyl group on the surface with a polydimethyl siloxane to impart a hydrophobic property thereto, and further an antioxidant as a protective layer into this photosensitive body.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photoreceptor containing an organic photoconductive substance, and more particularly to an electrophotographic photoreceptor that is positively charged.

0002

[Prior Art] In the past, photoreceptors made of inorganic photoconductive materials such as selenium, selenium-tellurium alloy, cadmium sulfide, and zinc oxide have been widely used as electrophotographic photoreceptors. Research is progressing on organic photoconductive materials, which have characteristics such as the ability to select compounds that exhibit photoconductivity in an appropriate wavelength range.

Electrophotographic photoreceptors using organic photoconductive substances in their photosensitive layers have advantages such as easy film formation, high flexibility and a large degree of freedom in design, low cost, and non-polluting properties. However, the sensitivity and photoreceptor life were inferior compared to inorganic photoconductive materials. Therefore, in order to improve these problems, electrophotographic photoreceptors such as laminated electrophotographic photoreceptors, in which the photosensitive layer is formed by separating the functions of a charge generation layer and a charge transport layer, have been proposed, and have been put into practical use. It's arrived. Since the charge transport agent generally used in this laminated electrophotographic photoreceptor is an electron-donating substance such as pyrazoline, hydrazone, or oxazole, the charge transport layer is of a hole transport type, and therefore a charge transport layer is formed on the charge generation layer. When laminated, it is used with a negative charge.

On the other hand, these electrophotographic photoreceptors are usually repeatedly subjected to the processes of charging, exposure, development, transfer, cleaning, and static elimination, but in this series of processes, positive charging is faster than negative charging. Corona discharge is stable, and the amount of ozone generated is small, so there is little property deterioration due to ozone oxidation. In addition, conventionally used inorganic photoreceptors such as selenium and selenium-tellurium alloys are used with a positive charge, so there is a strong demand for an organic photoreceptor that can be used with a positive charge because these electrophotographic processes can be shared.

[0005] In order to obtain a positive charge with a structure in which a charge generation layer is laminated on a normal charge transport layer, an electron accepting substance such as trinitrofluorenone may be used as a charge transport agent. Receptive substances are not generally used because they are rarely available with high mobility, are chemically unstable, and have harmful effects such as carcinogenicity. Therefore, in order to enable positive charging using an electron donating substance, a structure has been proposed in which a charge transport layer and a charge generation layer are laminated in this order on a conductive support. They have drawbacks such as large carrier injection into the charge transport layer, which reduces chargeability, and generally because the charge generation layer is a thin layer, mechanical strength is low and durability is poor.

Therefore, we have proposed a three-layer structure in which a protective layer of a thin resin film is further provided on the charge transport layer and charge generation layer, or a four-layer structure consisting of a charge transport layer, a charge generation layer, a charge injection blocking layer, and a surface protection layer. Proposal of the structure, as well as the charge transport layer and charge generation layer.
In the layer structure, increase the resin ratio of the charge generation layer to 5μm.
Proposals have been made to improve mechanical strength by increasing the thickness of the charge generation layer, and to maintain sensitivity by adding a charge transport agent to the charge generation layer. (For example, The Third International Congress on Advance Inn
Non-impact printing technology:
The 3rd International C
ongress on Advances in No.
n-Impact Printing Technology
ogies proceedings p115, Electrophotography Society No.5
Proceedings of the 9th Research Symposium, p. 184, etc.) In the case of resin thin films, polyester resins, polyvinyl butyral resins, phenolic resins, cellulose acetate, styrene-maleic anhydride copolymers, polyamide resins, polyimide resins, and melamine are generally used as protective layers for photoreceptors. Resins, etc. (e.g., Japanese Patent Publication No. 38-15446, Japanese Patent Publication No. 51-15748, Japanese Patent Publication No. 52-24414, Japanese Patent Publication No. 56-34
860, Japanese Patent Publication No. 56-53756, Japanese Patent Publication No. 60-55357, Japanese Patent Publication No. 61-22345, etc.); It cannot be said to be sufficient in terms of stability, and there is a problem of image blurring or image blurring due to a decrease in surface resistance under high temperature and high humidity conditions, especially due to surface deposits such as paper dust after repeated use.

[0007] In addition, these protective layers made of thin resin films do not have sufficient durability when they are thin, and on the other hand, when the film thickness is increased, the residual potential increases and the repeatability characteristics deteriorate.

[0008] Therefore, a method of using a protective layer in which a metal oxide is dispersed in a binder resin (for example,
Special Publication No. 57-39846, Special Publication No. 58-1210
44, Japanese Patent Publication No. 59-223445, etc.), however, metal oxides in the binder resin are insoluble in the binder resin and solvent, and their shape is lumpy, so they may not be present in the protective layer. Even if the content is constant, the resistance value will fluctuate depending on the dispersion state, making the characteristics unstable. Also, unless the blending ratio, particle size, etc. are carefully controlled, environmental fluctuations in chargeability and residual potential, It has the disadvantage of causing repeated fluctuations.

[0009]

[Problem to be solved by the invention] Therefore, in any case, there have not been many satisfactory characteristics in terms of sensitivity, durability, etc., and only high durability against scratches and abrasion during repeated use has been obtained. In addition, it has less surface resistance reduction due to surface deposits such as paper dust, is stable in use environments such as temperature and humidity, can be used with positive charge, and satisfies the characteristics required as an electrophotographic photoreceptor. It is desired to develop an electrophotographic photoreceptor with a long life.

[0010] Especially when used continuously in a high temperature and high humidity environment,
Even if a normal image is obtained during continuous use, if it is used again after a certain period of interruption, blurring may occur due to the areas on the photoconductor drum that were near the main charger and transfer charger during the interruption of use. There was a problem with image abnormalities such as flow.

[0011]

[Means for Solving the Problems] In view of the above-mentioned problems, the present invention provides a structure in which a charge transport layer, a charge generation layer, and a protective layer are laminated in this order on a conductive support, and the protective layer is thermosetting. Contains silicone resin, urethane elastomer, vapor-phase synthetic silica whose surface hydroxyl groups have been replaced with trimethylsiloxyl groups, or vapor-phase synthetic silica whose surface hydroxyl groups have been made hydrophobic by replacing them with polydimethylsiloxane, and an antioxidant. Due to the electrophotographic photoreceptor, it is positively charged and sensitive, stable against temperature and humidity, and there is no image blurring due to a decrease in surface resistance under high temperature and high humidity conditions due to surface deposits such as paper dust after repeated use. In particular, even when the drum is used again after a certain period of interruption, there are no image abnormalities corresponding to the areas on the photoreceptor drum that were near the main charger and transfer charger during the interruption of use, and even if the protective layer is thin, The present invention provides an electrophotographic photoreceptor that has high hardness, high film strength, and excellent wear resistance and durability.

0012

[Function] The electrophotographic photoreceptor of the present invention is positively charged and sensitive by laminating a charge transport layer, a charge generation layer and a protective layer in this order on a conductive support.

Further, in the electrophotographic photoreceptor of the present invention, by using a thermosetting silicone resin as a protective layer, a coating film with high hardness and excellent light transmittance and weather resistance can be obtained. At the same time, by containing urethane elastomer, wear resistance is improved and
It prevents the inherent moisture permeability of silicone resin, stabilizes the resistance of the protective layer under high temperature and high humidity conditions, and improves image fading.

Furthermore, by containing the urethane elastomer, it is possible to prevent cracks caused by curing shrinkage of the silicone resin during film formation and to improve adhesion to the lower layer.

[0015] The electrophotographic photoreceptor of the present invention includes the following in the protective layer:
In addition to the thermosetting silicone resin and urethane elastomer, it also contains gas-phase synthetic silica in which the hydroxyl groups on the surface are replaced with trimethylsiloxyl groups, or vapor-phase synthetic silica in which the hydroxyl groups on the surface are replaced with polydimethylsiloxane to make it hydrophobic. , improves the hardness of the photoconductor surface, reduces the surface friction coefficient, improves the water repellency, stain resistance, and cleaning properties of the surface, increases the durability and toner filming resistance of the photoconductor, and makes it suitable for practical use. This can significantly improve the lifespan.

The silica contained at the same time must be hydrophobic, and by being hydrophobically treated, it prevents the adsorption of ions such as moisture and ozone products, and improves the water repellency of the surface of the photoreceptor. , reduce the coefficient of friction of the surface, reduce the adhesion of surface deposits to the protective layer,
It improves the function of cleaning devices such as blades for surface deposits, prevents image blur due to a decrease in surface resistance due to deposits such as paper dust during repeated use, and significantly extends the actual usage life. .

The electrophotographic photoreceptor of the present invention also includes a thermosetting silicone resin, a urethane elastomer,
By containing an antioxidant in addition to gas-phase synthetic silica in which the surface hydroxyl group is replaced with a trimethylsiloxyl group or gas-phase synthetic silica in which the surface hydroxyl group is replaced with polydimethylsiloxane to make it hydrophobic,
In particular, even when the photosensitive drum is used again after being suspended for a certain period of time, it is possible to prevent image abnormalities corresponding to the portions of the photosensitive drum that were located near the main charger and transfer charger during the suspension of use.

[0018]

EXAMPLES The electrophotographic photoreceptor of the present invention will be explained in detail below.

The thermosetting silicone resin used in the protective layer of the electrophotographic photoreceptor of the present invention is a thermosetting silicone resin of an alkoxysilane hydrolyzate, and the hydrolyzate is trifunctional or tetrafunctional. Any type of alkyl group may be used as long as it has a functional silanol group, and examples of the alkyl group include a methyl group.

These thermosetting silicone resins are preferably those that are soluble in alcoholic solvents as a hydrolyzate of alkoxysilane, can be applied without corroding the lower layer, and can be condensed by heat treatment after forming the coating. It hardens to produce a highly hard and durable film.

Similarly, the urethane elastomer contained in the protective layer is preferably one that is soluble in alcoholic solvents because it does not corrode the underlying layer.

[0022] The alcohol-soluble urethane elastomer is
After condensation of isocyanate and an equivalent excess of polyol in a low-boiling solvent such as acetone, n-hexane, or ethyl acetate, 1-propanol, 2-propanol, 1-butanol, or It can be obtained by replacing it with an alcoholic solvent containing at least one selected from 2-butanol, 2-methylpropanol, 1-pentanol, 2-pentanol, diacetone alcohol, and the like.

At the same time, vapor-phase synthetic silica in which the surface hydroxyl groups contained in the protective layer are substituted with trimethylsiloxyl groups is obtained by mixing high-purity silica with an average primary particle size of 5 to 50 nm by hexamethylene dicarbonate. Examples include those treated with hydrophobic treatment such as silazane. At the same time, vapor-phase synthetic silica, which is made hydrophobic by replacing the hydroxyl groups on the surface contained in the protective layer with polydimethylsiloxane, is made of highly pure silica with an average primary particle size of 5 to 50 nm, which is made of organic silicone compound. Examples include those that have been subjected to hydrophobic treatment.

The protective layer of the electrophotographic photoreceptor of the present invention is prepared by dissolving the hydrolyzate of these alkoxysilanes and the urethane elastomer in a solvent that dissolves both, and applying a coating solution in which hydrophobic silica is dispersed to the photosensitive layer. It is coated on top by a conventional coating method such as dip coating, spin coating, or spray coating, dried, and then hardened by heat treatment. The heat treatment temperature is 80°C to 200°C,
Considering the heat resistance of the photosensitive layer, the temperature is preferably about 80°C to 120°C. The thickness of the protective layer is 0.1 to 5 .mu.m, and preferably 0.2 to 2 .mu.m in consideration of electrophotographic properties, adhesion, and abrasion resistance.

The ratio of the thermosetting silicone resin to the urethane elastomer in the protective layer is preferably from 2:8 to 8:2 in solid weight ratio after drying, and as the ratio of the silicone resin decreases, the surface hardness increases. Moreover, if the ratio of silicone resin is too large, cracks may occur due to curing shrinkage of the silicone resin during film formation, and the adhesion with the lower layer may deteriorate.

Furthermore, the hydrophobic silica dispersed in the protective layer has the following advantages in terms of stability of the coating liquid, coating strength, film formability, etc.
The amount added is in the range of 1 to 150 parts by weight, preferably 5 to 100 parts by weight, based on 100 parts by weight of the total solid content of the protective layer.

Examples of the electron-donating substance used in the charge transport layer of the electrophotographic photoreceptor of the present invention include compounds having an electron-donating group such as an alkyl group, an alkoxy group, an amino group, and an imide group, anthracene, pyrene, and phenanthrene. Polycyclic aromatic compounds or derivatives containing them, heterocyclic compounds such as indole, oxazole, oxadiazole, carbazole, thiazole, pyrazoline, imidazole, triazole, etc. or derivatives containing them. These electron-donating substances and binder resin are dissolved in a suitable solvent and applied by a normal coating method such as dip coating, spin coating, or spray coating.
It is dried to form a charge transport layer, but if the electron donating substance is a polymer compound, the charge transport layer may be formed alone without mixing with a binder resin. The thickness of the charge transport layer is several μm to several tens of μm, preferably 5 to 25 μm.
The thickness is m.

[0028] Further, as the charge generating substance used in the charge generating layer of the electrophotographic photoreceptor of the present invention, phthalocyanine type,
Azo series, squarerium series, cyanine series, quinone series,
Examples include various pigments or dyes such as perylene-based pigments. The charge-generating layer is prepared by adding and dispersing these pigments or dyes and a suitable binder resin, and then applying and heating a coating solution prepared using a conventional coating method such as dip coating, spin coating, or spray coating. It is dried and formed to a film thickness of several μm, preferably 0.2 to 2 μm.

The binder resin used in the charge generation layer and the charge transport layer is used as necessary for the purpose of improving adhesion with other layers, improving the uniformity of the coating film, and adjusting fluidity during coating. , specifically polyester, polyvinyl chloride,
Examples include polyvinyl butyral, polyvinyl acetate, polycarbonate, acrylic resin, methacrylic resin, silicone resin, and copolymers of these resins. The solvent may be one that dissolves the charge generating agent, charge transporting agent, or binder resin, and specifically, halogenated hydrocarbons, halogenated aromatics, aromatics, ketones, and esters. , ethers, etc. can be used.

The conductive support used in the electrophotographic photoreceptor of the present invention may be any conventionally known conductive support, including metal plates and drums made of aluminum, aluminum alloy, tin oxide, Plates made of metal oxides such as indium oxide, or those metals and metal oxides, etc., are vacuum evaporated, sputtered, laminated,
These include various plastic films, papers, etc. that have been applied by coating and treated to be conductive.

Furthermore, the electrophotographic photoreceptor of the present invention has an adhesive layer of casein, polyvinyl alcohol, polyvinyl butyral, polyamide, etc. or A barrier layer can be provided.

In this way, the electrophotographic photoreceptor of the present invention is formed by laminating a photosensitive layer consisting of a charge transport layer and a charge generation layer and a protective layer on a conductive support. A charge transport layer, a charge generation layer, and a protective layer are laminated in this order, and are positively charged and sensitive.

Examples of the present invention will be described in detail below, but the present invention is not limited to the combinations shown in the following examples.

An electrophotographic photoreceptor according to an embodiment of the present invention will be described below. 1,1-bis(P-diethylaminophenyl)-4,4-diphenyl-1,3-butadiene
1 part by weight and 1 part by weight of polycarbonate (manufactured by Bayer AG, trade name: Macrohole N) were dissolved in 9 parts by weight of methylene chloride, and this coating liquid was dip coated on an aluminum drum with an outer diameter of 25 mm, and 1 part by weight was heated at 80°C. After drying for a while, a charge transport layer having a thickness of 20 μm was formed.

Next, 5 parts by weight of τ-type metal-free phthalocyanine (manufactured by Toyo Ink Mfg. Co., Ltd.) and acrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., trade name: Dianal HR664) were added.
4 parts by weight and 1 part by weight of melamine resin (trade name: Super Beckamine L145-60, manufactured by Dainippon Ink Co., Ltd.) were dispersed in 115 parts by weight of s-butyl alcohol. This coating liquid was dip-coated onto the charge transport layer and dried at 130° C. for 1 hour to form a charge generation layer having a thickness of 0.2 μm.

In addition, 70 parts by weight of thermosetting silicone resin (manufactured by Toshiba Silicone Corporation) and urethane elastomer (trade name: OLESTAR NL2, manufactured by Mitsui Toatsu Chemical Co., Ltd.)
249E) and 2 parts by weight of the phenylenediamine antioxidant DPPD (N,N' diphenyl-P-phenylenediamine) in 1000 parts by weight of n-butyl alcohol.
30 parts by weight of vapor-phase synthetic silica (manufactured by Cabot Corporation, trade name: CABOSIL TS-530) in which the hydroxyl group on the surface has been replaced with a trimethylsiloxyl group is added to the coating liquid dissolved in 1 part by weight, and dispersed by ultrasonic dispersion. A coating liquid was prepared. This coating liquid was dip-coated onto the charge generation layer, heat-treated at 110° C. for 1 hour, and cured to form a protective layer with a thickness of 1 μm.

The electrophotographic photoreceptor thus obtained was installed in a self-made image testing machine and exposed to high temperature and high humidity (35°C, 85R).
After printing 8,000 sheets at 100% H%), the images were evaluated after being left as they were for 8 hours. FIG. 1 is a block diagram of an image testing machine for an electrophotographic photoreceptor in an embodiment of the present invention.

In FIG. 1, 1 is a main charging section, 2 is a laser exposure section for writing an electrostatic latent image, 3 is a non-magnetic one-component DC flying developing section, 4 is a paper and paper transport section, 5 is a transfer section, and 6 is a transfer section. The fixing section 7 is a toner cleaning section using a urethane blade.

The evaluation results are shown in (Table 1).

[0040]

[Table 1]

As described above, according to this embodiment, an electrophotographic photoreceptor is formed by laminating a charge transport layer, a charge generation layer, and a protective layer in this order on a conductive support, and a thermosetting layer is used as the protective layer. By containing silicone resin, urethane elastomer, and vapor-phase synthetic silica in which the hydroxyl groups on the surface are replaced with trimethylsiloxyl groups, the paper is positively charged and sensitive, stable against temperature and humidity, and can be used repeatedly. There is no image blurring due to a decrease in surface resistance under high temperature and high humidity conditions due to surface deposits such as powder, and even when the main charger and the The present invention provides an electrophotographic photoreceptor that can prevent image abnormalities caused by areas near the transfer charger, has high hardness and film strength even with a thin protective layer, and has excellent abrasion resistance and durability. .

A second embodiment of the present invention will be described below. In the protective layer of the first example, vapor-phase synthetic silica in which the hydroxyl groups on the surface were substituted with trimethylsiloxyl groups (manufactured by Cabot Corporation, trade name: CABOSIL TS-530) was used.
), except that the coating liquid was prepared by adding gas-phase synthetic silica (manufactured by Cabot Corporation, trade name: CABOSIL TS-720), which had been made hydrophobic by replacing the hydroxyl groups on the surface with polydimethylsiloxane. A charge transport layer, a charge generation layer, and a protective layer were formed in the same manner as in the example, and image evaluation was performed in the same manner as in the first example.

The evaluation results are shown in (Table 1). A third embodiment of the present invention will be described below.

In the protective layer of the first embodiment, instead of 2 parts by weight of the phenylenediamine antioxidant DPPD (N,N'diphenyl-P-phenylenediamine),
A charge transport layer, a charge generation layer, and a protective layer were prepared in the same manner as in the first example except that the bisphenol-based antioxidant 2,2'-methylenebis(4-methyl-6-t-butylphenol) was used in an amount of 2 parts by weight. was formed, and image evaluation was performed in the same manner as in the first example.

[0045] The evaluation results are shown in (Table 1). A fourth embodiment of the present invention will be described below.

In the protective layer of the first embodiment, instead of 2 parts by weight of the phenylenediamine-based antioxidant DPPD (N,N' diphenyl-P-phenylenediamine),
Thiobisphenyl antioxidant 4,4'-thiobis(
A charge transport layer, a charge generation layer, and a protective layer were formed in the same manner as in the first example except that the amount was 2 parts by weight (3-methyl-6-t-butylphenol); Image evaluation was performed.

[0047] The evaluation results are shown in (Table 1). A comparative example of the present invention will be described below.

In the protective layer of the first example, 70 parts by weight of thermosetting silicone resin (manufactured by Toshiba Silicone Corporation) and urethane elastomer (manufactured by Mitsui Toatsu Chemical Co., Ltd.) were used.
Product name Orester NL2249E) 30 parts by weight
- In a coating liquid dissolved in 1000 parts by weight of butyl alcohol,
Add 30 parts by weight of vapor-phase synthetic silica (trade name CABOSIL TS-530, manufactured by Cabot Corporation) in which the surface hydroxyl groups are substituted with trimethylsiloxyl groups, and disperse by ultrasonic dispersion to prepare a coating liquid. Except for the created
A charge transport layer, a charge generation layer, and a protective layer were formed in the same manner as in the first example, and image evaluation was performed in the same manner as in the first example.

The evaluation results are shown in (Table 1).

[0050]

As described above, in the present invention, an electrophotographic photoreceptor is formed by laminating a charge transport layer, a charge generation layer, and a protective layer in this order on a conductive support, and the protective layer is thermosetting. A silicone resin, a urethane elastomer, a vapor-phase synthetic silica whose surface hydroxyl groups have been replaced with trimethylsiloxyl groups, or a vapor-phase synthetic silica whose surface hydroxyl groups have been made hydrophobic by replacing them with polydimethylsiloxane, and an antioxidant. By containing this material, it is positively charged and sensitive, stable against temperature and humidity, and there is no image blurring due to a decrease in surface resistance under high temperature and high humidity conditions due to surface deposits such as paper dust after repeated use. In particular, even when the photosensitive drum is used again after a certain period of interruption, image abnormalities corresponding to the areas near the main charger and transfer charger can be prevented during the interruption of use, and the protective layer is thin. However, it is possible to make an electrophotographic photoreceptor with high hardness and film strength, and excellent wear resistance and durability.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an image testing machine for an electrophotographic photoreceptor in a first embodiment of the present invention.

[Explanation of symbols]

1 Main charging section 2 Laser exposure section for electrostatic latent image writing 3 Non-magnetic one-component DC flying development section 4 Paper and paper transport section 5 Transfer section 6 Fixing section

Claims (6)

[Claims] 1. An electrophotographic photoreceptor formed by laminating a photosensitive layer and a protective layer for the photosensitive layer on a conductive support, wherein the protective layer comprises a thermosetting silicone resin, a urethane elastomer, and a surface layer. An electrophotographic photoreceptor comprising gas-phase synthetic silica in which hydroxyl groups are substituted with trimethylsiloxyl groups and an antioxidant. 2. The electrophotographic photoreceptor according to claim 1, wherein the photosensitive layer is formed by laminating a charge transport layer and a charge generation layer in this order on a conductive support. 3. The electrophotographic photoreceptor according to claim 1, wherein the antioxidant is at least selected from bisphenols, thiobisphenyls, and phenylenediamines. 4. An electrophotographic photoreceptor formed by laminating a photosensitive layer and a protective layer for the photosensitive layer on a conductive support, wherein the protective layer comprises a thermosetting silicone resin, a urethane elastomer, and a surface layer. An electrophotographic photoreceptor characterized by containing gas-phase synthetic silica made hydrophobic by replacing hydroxyl groups with polydimethylsiloxane, and an antioxidant. 5. The electrophotographic photoreceptor according to claim 4, wherein the photosensitive layer is formed by laminating a charge transport layer and a charge generation layer in this order on a conductive support. 6. The electrophotographic photoreceptor according to claim 4, wherein the antioxidant is at least selected from bisphenols, thiobisphenyls, and phenylenediamines.