US 3652269 A
Photoconductive elements containing a photoconductor and a binder comprising polymers of halogenated polyethylenes are described. These elements can be sensitized and charged either negatively or positively.
Claims available in
Description (OCR text may contain errors)
United States Patent Contois et al.
[451 Mar. 28, 1972  PHOTOCONDUCTIVE ELEMENTS CONTAINING HALOGENATED POLYETHYLENE BINDERS Lawrence E. Contois; Stewart H. Merri both of liochester, "w
Eastman Kodak Company, Rochester, NY.
Filed: Aug. 27, 1968 Appl. No.: 755,716
U.S. Cl ..96/1-5, 96/1.6 Int. Cl. ..G03g 5/00, C08f 3/22 Field of Search ..260/92.8 AC, 94.9 H; 96/1 References Cited UNITED STATES PATENTS Rusignuoloet al. 96/87 3,250,615 5/1966 Van Allan et al ..96/1 3,265,497 8/1966 Kosche ..96/1.1
Assistant Examiner-M. B. Wittenberg Attorney-William H. .I. Kline, James R. Frederick and Fred L. Denson  ABSTRACT Photoconductive elements containing a photoconductor and a binder comprising polymers of halogenated polyethylenes are described. These elements can be sensitized and charged either negatively or positively.
20 Claims, No Drawings PHOTOCONDUCTIVE ELEMENTS CONTAINING HALOGENATED POLYETHYLENE BINDERS This invention relates to novel electrophotographic elements having coatings of binder-containing photoconductive compositions and also to processes for producing images using these elements.
Binder-containing photoconductive compositions have been widely used in the preparation of electrophotographic elements. In electrophotographic reproduction processes, these elements are utilized in the formation of latent electrostatic images. ln some applications the photoconductive compositions contain an organic photoconductor and a sensitizer uniformly admixed in an inert resinous binder. Many binders are currently used in connection with a wide variety of available organic photoconductor compounds and compositions. Typical binders are ordinary polymeric materials, e.g., phenolic resins, ketone resins, acrylic ester resins, polystyrene, etc. However, these binders usually do not impart any particular improvement in light sensitivity to the system. The light sensitivity as indicated by the electrical speed of these particular systems is ordinarily due wholly to the organic photoconductor and sensitizer.
Chlorinated polyethylenes having a low chlorine content, i.e., less than about 33 percent chlorine, have been used as binders for organic photoconductors. These polymers generally shift the spectral sensitivity of the photoconductive composition but are insoluble in most solvents and must be heated with the photoconductor to temperatures generally ranging above 80 C. for 15 hours or more. This required heating step makes the binder more soluble eliminating coating and compatibility problems and also causes a reaction to occur between the binder and photoconductor so that the spectral sensitivity of the reaction product is shifted. These materials are more fully described in British Pat. No. 964,878.
It is therefore, an object of this invention to provide improved novel binder-containing photoconductive compositions which exhibit high light sensitivities.
it is another object to provide transparent electrophotographic elements having the high speed characteristic of the novel photoconductive compositions of this invention.
It is a further object of this invention to provide a process for producing images using these novel electrophotographic elements.
These and other objects of this invention are accomplished by a photoconductive composition which contains a nonpolymeric organic photoconductor admixed with a binder which is a halogenated polyethylene having at least 50 weight percent halogen in the polymer composition. It has been discovered that such compositions exhibit increased light sensitivities as evidenced by greater electrical speeds. In particular, substantial increases in electrical speeds (i.e., toe and shoulder speeds) are obtained with reference to the standard H and D curve as compared to electrical speeds attainable with many other polymeric binder compositions. These increases in electrical speed are observed when the coating accepts a suitable potential (e.g., 500-600 volts) and the relative speed of the coating is determined on the basis of the reciprocal of the exposure required to reduce the potential of the surface charge by 100 volts (shoulder speed) or to 100 volts (toe speed). The reduction of the surface potential to 100 volts or below is significant in that it represents a requirement for suitable broad area development of a latent image. The relative speed at 100 volts is a measure of the ability to produce and henceforth to develop or otherwise utilize the latent image. When the photoconductor is absent from the coating and only a conventional binder is used, the surface potential does not drop to or below 100 volts and therefore no speed can be assigned to such a composition. When an organic photoconductor is part of the coating in many conventional polymeric binders, the surface potential of the resultant composition usually drops below l volts, and thus, a definite speed can be ascertained. However, these speeds are improved when the binders of this invention are employed.
In preparing the photoconductive compositions of this invention, a halogenated polyethylene containing at least 50 percent by weight of halogen and preferably 50 to weight percent halogen is mixed with a non-polymeric organic photoconductor in a suitable solvent at room temperature. No heating is required in that there are no solubility or coating problems. Also, there is no waiting period for a reaction to occur. The composition is thoroughly mixed and then coated on an electrically conducting support in a well-known manner, such as swirling, spraying, doctor-blade coating, and the like.
The novel halogenated binders of this invention are effective for enhancing the electrophotosensitivity of a wide variety of photoconductors. The preferred photoconductors are those organic compounds which exhibit an electrophotosensitivity to light and are capable of forming substantially transparent elements when coated on transparent film bases. An especially useful class of organic photoconductors is referred to herein as organic amine photoconductors. Such organic photoconductors have as a common structural feature at least one amino group. Useful organic photoconductors which can be spectrally sensitized in accordance with this invention include, therefore, arylamine compounds comprising (1) diarylamines such as diphenylamine, dinaphthylamine, N,N'-diphenyl- N-phenyll -naphthylamine; N-phenyl-Z- naphthylamine; N,N-diphenyl-p-phenylenediamine; 2-carboxy-5-chloro-4'-methoxydiphenylamine; p-anilinophenol; N,N-di-2-naphthyl-p-phenylenediamine; those described in Fox US. Pat. No. 3,240,597 issued Mar. I5, 1966, and the like, and (2) triarylamines including nonpolymeric triarylamines, such as triphenylamine, N,N,N',N'-tetraphenylm-phenylenediamine; 4-acetyltriphenylamine, 4-hexanoyltriphenyl-amine; 4-lauroyltriphenylamine; 4-hexyltriphenylamine, 4-dodecyl-triphenylamine, 4,4-bis(diphenylamino)benzil, 4,4-bis(diphenyl-amino)-benzophenone, and the like. Other useful amine-type photoconductors are disclosed in US. Pat. No. 3,180,730 issued Apr. 27, l965. In addition, photoconductive substances capable of being spectrally sensitized in accordance with this invention are disclosed in Fox US. Pat. No. 3,265,496 issued Aug. 9, 1966, and include those nonpolymeric photoconductors represented by the following general formula:
GN-AQ wherein A represents a mononuclear or polynuclear divalent aromatic radical, either fused or linear, (e.g., phenyl, naphthyl, biphenyl, binaphthyl, etc.), or a substituted divalent aromatic radical of these types wherein said substituent can comprise a member such as an acyl group having from one to about six carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from one to about six carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from one to about six carbon atoms (e.g., methoxy, ethoxy, propoxy, pentoxy, etc.), or a nitro group; A represents a mononuclear or polynuclear monovalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), or a substituted monovalent aromatic radical wherein said substituent can comprise a member, such as an acyl group having from one to about six carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from one to about six carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from one to about six carbon atoms (e.g., methoxy, propoxy, pentoxy, etc.), or a nitro comprises an alkyl group, an alkoxy group, an acyl group or a nitro group.
Polyarylalkane photoconductors are particularly useful in producing the present invention. Such photoconductors are Preferred polyarylalkane photoconductors can be represented by the formula:
D J+E M wherein each of D, E and M is an aryl group and J is a hydrogen atom, an alkyl group, or an aryl group, at least one of D, E and M containing an amino substituent. The aryl group attached to the central carbon atom are preferably phenyl groups, although naphthyl groups can also be used. Such aryl groups can contain such substituents as alkyl and alkoxy typically having one to eight carbon atoms, hydroxy, halogen, etc. in the ortho, meta or para positions, ortho-substituted phenyl being preferred. The aryl groups can also be joined together or cyclized to form a fluorene moiety, for example. The amino substituent can be represented by the formula wherein each L can be an alkyl group typically having one to eight carbon atoms, a hydrogen atom, an aryl group, or together the necessary atoms to form a heterocyclic amino group typically having five to six atoms in the ring such as morpholino, pyridyl, pyrryl, etc. At least one of D, E, and M is preferably p-dialkylaminophenyl group. When J is an alkyl group, such an alkyl group more generally has one to seve carbon atoms.
Representative useful polyarylalkane photoconductors include the compounds listed below:
TABLE A Compound No. Photoconductor Compound Name 4-dimethylaminotetrlphenylmethane 4-diethylaminotetraphenylmethane Australian Pat. No. 248,402. Other organic photoconductors that can be sensitized in accordance with the invention include organometallic compounds which are the organic derivatives of Group [Va and Va metals such as those having at least one aminoaryl group attached to the metal atom as described in Ser. No. 650,664 filed July 3, 1967. Exemplary organometallic compounds are the triphenyl-p-dialkylaminophenyl derivatives of silicon, germanium, tin and lead and the tri-p-dialkylaminophenyl derivatives of arsenic, antimony, phosphorous and bismuth.
Another class of photoconductors useful in this invention are the 4-diary1amino-substituted chalcones. Typical compounds of this type are low molecular weight non-polymeric ketones having the general formula:
wherein R and R are each phenyl radicals including substituted phenyl radicals and particularly when R is a phenyl radical having the formula:
where R; and R are each aryl radicals, aliphatic residues of one to twelve carbon atoms such as alkyl radicals preferably having one to four carbon atoms or hydrogen. Particularly advantageous results are obtained when R is a phenyl radical including substituted phenyl radicals and where R, is diphenylaminophenyl, dimethylaminophenyl, or phenyl.
The photoconductive layers of the invention can also be sensitized by the addition of effective amounts of sensitizing compounds to exhibit improved electrophotosensitivity. Sensitizing compounds useful with the photoconductive compounds of the present invention can be selected from a wide variety of materials, including such materials as pyrylium, thiapyrylium, and selenapyrylium dye salts disclosed in VanAllan et al. U.S. Patent 3,250,615; fluorenes, such as 7,12-dioxo-13-dibenzo(a,h)fluorene, 5,10-diox0-4a,l l-diazabenzo(b)fluorene,3,13 dioxo 7 oxadibenzo(b,g)fluorene, and the like; aromatic nitro compounds of the kinds described in U.S. Pat. No. 2,610,120; anthrones like those tTsclosed in U.SYPaiT'NbQ 2,675,287} quinbnes, USTPHENE.
Where a sensitizing compound is employed with the binder and organic photoconductor to form a sensitized electrophotographic element, it is the normal practice to mix a suitable amount of the sensitizing compound with the coating composition so that, after thorough mixing, the sensitizing compound is uniformly distributed in the coated element. Other methods of incorporating the sensitizer or the effect of the sensitizer may, however, be employed consistent with the practice of this invention. in preparing the photoconductive layers, no sensitizing compound is required to give photoconductivity in the layers which contain the photoconducting substances of this invention, therefore, no sensitizer is required in a particular photoconductive layer. However, since relatively minor amounts of sensitizing compound give substantial improvement in speed in such layers, the sensitizer is preferred; The amount of sensitizer that can be added to a photoconductor-incorporating layer to give effective increases in speed can vary widely. The optimum concentration in any given case will vary with the specific photoconductor and sensitizing compound used. In general, substantial speed gains can be obtained where an appropriate sensitizer is added in a concentration range from about 0.000] to about 30 percent by weight based on the weight of the film-forming coating composition. Normally, a sensitizer is added to the coating composition in an amount by weight from about 0.005 to about 5.0 percent by weight of the total coating composition.
Solvents useful for preparing coating compositions with the binders of the present invention can include a wide variety of organic solvents for the components of the coating composition. For example, benzene; toluene; acetone; 2-butanone; chlorinated hydrocarbons such as methylene chloride; ethylene chloride, and the like; ethers, such as tetrahydrofuran and the like, or mixtures of such solvents can advantageously be employed in the practice of this invention.
In preparing the coating compositions utilizing the binders disclosed herein useful results are obtained where the photoconductive substance is present in an amount equal to at least about 1 weight percent of the coating composition. The upper limit in the amount of photoconductive material present can be widely varied in accordance with usual practice. It is normally required that the photoconductive material be present in an amount ranging from about 1 weight percent of the coating composition to about 99 weight percent of the coating composition. A preferred weight range for the photoconductive material in the coating composition is from about weight percent to about 60 weight percent.
Coating thicknesses of the photoconductive composition on a support can vary widely. Normally, a wet coating thickness in the range of about 0.001 inch to about 0.01 inch is useful in practice of the invention. A preferred range of coating thickness is from about 0.002 inch to about 0.006 inch before drying although such thicknesses can vary widely depending on the particular application desired for the electrophotographic element.
Suitable supporting materials for coating the photoconductive layers of the present invention can include any of the electrically conducting supports, for example, paper (at a relative humidity above percent); aluminum-paper laminates; metal foils, such as aluminum foil, zinc foil, etc.; metal plates, such as aluminum, copper, zinc, brass, and galvanized plates; vapor deposited metal layers such as nickel or aluminum and the like.
An especially useful conducting support can be prepared by coating a support material such as poly(ethylene terephthalate) with a layer containing a semiconductor dispersed in a resin. Likewise, a suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of maleic anhydride and a vinyl acetate polymer. Such conducting layers and methods for their optimum preparation and use are disclosed in U.S. Pat. Nos. 3,007,901 and 3,267,807.
The compositions of the present invention can be employed in photoconductive elements useful in any of the well known electrophotographic processes which require photoconductive layers. One such process is the xerographic process. In a process of this type, an electrophotographic element held in the dark, is given a blanket electrostatic charge by placing it under a corona discharge to give a uniform charge to the surface of the photoconductive layer. This charge is retained by the layer owing to the substantial dark insulating property of the layer, i.e., the low conductivity ofthe layer in the dark. The electrostatic charge formed on the surface of the photoconductive layer is then selectively dissipated from the surface of the layer by imagewise exposure to light by means of a conventional exposure operation such as for example, by a contact-printing technique, or by lens projection of an image, or reflex or bireflex techniques and the like, to thereby form a latent electrostatic image in the photoconductive layer. Exposing the surface in this manner forms a pattern of electrostatic charge by virtue of the fact that light energy striking the photoconductor causes the electrostatic charge in the light struck areas to be conducted away from the surface in proportion to the intensity of the illumination in a particular area.
The charge pattern produced by exposure is then developed or transferred to another surface and developed there, i.e., either the charge or uncharged areas rendered visible, by treatment with a medium comprising electrostatically responsive particles having optical density. The developing electrostatically responsive particles can be in the form of a dust, or powder and generally comprise a pigment in a resinous carrier called a toner. A preferred method of applying such a toner to a latent electrostatic image for solid area development is by the use of a magnetic brush. Methods of forming and using a magnetic brush toner applicator are described in the following U.S. Pats. Nos. 2,786,439; 2,786,440; 2,786,441; 2,811,465; 2,874,063; 2,984,163; 3,040,704; 3,117,884; and reissue Re 25,779. Liquid development of the latent electrostatic image may also be used. In liquid development the developing particles are carried to the image-bearing surface in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature, for example, U.S. Pat. No. 2,297,691 and in Australian Pat. No. 212,315. ln dry developing processes the most widely used method of obtaining a permanent record is achieved by selecting a developing particle which has as one of its components a low-melting resin. Heating the powder image then causes the resin to melt or fuse into or on the element. The powder is, therefore, caused to adhere permanently to the surface of the photoconductive layer. In other cases, a transfer of the charge image or powder image formed on the photoconductive layer can be made to a second support such as paper which would then become the final print after developing and fusing or fusing respectively. Techniques of the type indicated are well known in the art and have been described in a number of U.S. and foreign patents, such as U.S. Pats. Nos. 2,297,691 and 2,551,582, and in RCA Review," vol. 15 (1954) pages 469-484.
The compositions of the present invention can be used in electrophotographic elements having many structural variations. For example, the photoconductive composition can be coated in the form of single layers or multiple layers on a suitable opaque or transparent conducting support. Likewise, the layers can be contiguous or spaced having layers of insulating material or other photoconductive material between layers or overcoated or interposed between the photoconductive layer or sensitizing layer and the conducting layer. It is also possible to adjust the position of the support and the conducting layer placing a photoconductor layer over a support and coating the exposed face of the support or the exposed or overcoated face of the photoconductor with a conducting layer. Configurations differing from those contained in the examples can be useful or even preferred for the same or different application for the electrophotographic element.
The invention is further illustrated by the following examples which include preferred embodiments thereof.
EXAMPLE 1 1.5 Grams of a chlorinated polyethylene binder containing 53.6 weight percent chlorine, 0.5 grams of 4,4-benzylidinebis(N,N-diethyl-m-toluidine) photoconductor and 0.02 grams of 2,4-(4-ethoxyphenyl)-6-(4-n-amyloxystyryl)pyrylium fluoroborate sensitizer are dissolved in 15.6 grams of methylene chloride by stirring the solids in the solvent for one hour at room temperature. The resulting solution is hand coated at a wet coating thickness of 0.004 inch on a conducting layer comprising the sodium salt of a carboxyester lactone, such as described in U.S. Pat. No. 3,260,706, which in turn is coated on a cellulose acetate film base. The coating block is maintained at a temperature of 32 C. This electrophotographic element is charged under positive corona source until the surface potential, as measured by an electrometer probe, reaches about 600 volts. It is then subjected to exposure from behind a stepped density gray scale to a 3,000 K. tungsten source. The exposure causes reduction of the surface potential of the element under each step of the gray scale from its initial potential, V,,, to some lower potential, V, whose exact value depends on the actual amount of exposure in meter-candleseconds received by the area. The results of the measurements are plotted on a graph of surface potential V vs. log exposure for each step. The shoulder speed is the numerical expression of multiplied by the reciprocal of the exposure in metercandle-seconds required to reduce the 600 volt charged surface potential by 100 volts. The toe speed is the numerical expression of 10 multiplied by the reciprocal of the exposure in meter-candle-seconds required to reduce the 600 volt charged surface potential to 100 volts. This coating is found to have a positive 100 V. toe speed of 105. Similar results are obtained when 0.5 gram of bis(4-diethylamino)-l,l,l-triphenylethane or 0.5 gram of bis(4-diethylamino)-tetraphenylmethane are used as photoconductors in place of the 4,4-benzylidinebis(N,N-di-ethyl-m-toluidine).
EXAMPLE 2 Example I is repeated using chlorinated polyethylenes having varying weight percentages of chlorine. These percentages and positive 100 volt toe speed are set forth in the following Table B.
' Binder was insoluble in coating composition and thus could not be coated.
EXAMPLE 3 Example I is repeated except that the photoconductor used is 4,4'-bis(diphenylaminochalcone) and the binder used is a chlorinated polyethylene containing 62.4 percent chlorine. A positive 100 volt toe speed of 280 is obtained. When the same element is negatively charged, good negative toe speeds are obtained.
EXAMPLE 4 Example 3 is repeated except that the sensitizer used is 6- chloro- 1 '-methyl- 1 ,2,3 '-triphenylimidazo[4,5-b]-quinoxalino-3'-indolocarbocyanine p-toluene sulfonate. A positive 100 volt toe speed of 400 is obtained.
EXAMPLE 5 In order to demonstrate the improvement in speeds obtainable with the novel binders of this invention, a photo conductive composition similar to Example 1 is prepared using a conventional polystyrene binder. The positive 100 volt toe speed of this composition is 4. When a poly(vinylbutyral) binder is used, the positive 100 volt toe speed is 32.
EXAMPLE 6 The coating compositions of Example l-4 are again coated in the manner described in Example 1. In a darkened room, the surface of each of the photoconductive layers so prepared is charged to a potential of about +600 volts under a corona I charger. The layer is then covered with a transparent sheet bearing a pattern of opaque and light transmitting areas and exposed to the radiation from an incandescent lamp with an illumination intensity of about meter-candles for 12 seconds. The resulting electrostatic latent image is developed in the usual manner by cascading over the surface of the layer a mixture of negatively charged black thermoplastic toner particles and glass beads. A good reproduction of the pattern results in each instance.
The halogenated polymers used as binders in accordance with the invention in the above examples can be made by treating a solution in solvent of a low density polyethylene with halogen until the desired halogen content is reached. The polymer is recovered by conventional techniques.
The invention has been described in detail with particular reference to preferred embodiments thereof but is will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.
1. An electrophotographic element comprising a support having coated thereon a photoconductive compositioncomprising a non-polymeric organic photoconductor and a halogenated polyethylene binder containing at least 50 percent by weight halogen.
2. The element of claim 1 wherein the binder is chlorinated polyethylene.
3. The electrophotographic element of claim 1 wherein the photoconductive composition contains a sensitizer selected from the group consisting of carbocyanine, pyrylium, thiapyrylium and selenapyrylium dye salts.
4. An electrophotographic element comprising a support having coated thereon a photoconductive composition comprising a non-polymeric organic photoconductor and a halogenated polyethylene binder containing 50 to 70 percent by weight halogen.
5. The element of claim 4 wherein the binder is chlorinated polyethylene.
6. An electrophotographic element comprising a support having coated thereon a photoconductive composition comprising a non-polymeric organic photoconductor, a sensitizer and a halogenated polyethylene binder containing 50 to 70 percent by weight halogen.
7. The electrophotographic element of claim 6 wherein the photoconductor is selected from the group consisting of polyaryl alkanes having at least one amino aryl group and 4-diarylamino-substituted chalcones.
8. The electrophotographic element of claim 6 wherein the sensitizer is selected from the group consisting of carbocyanine, pyrylium, thiapyrylium and selenapyrylium dye salts.
9. The electrophotographic element of claim 6 wherein the binder is chlorinated polyethylene.
10. An electrophotographic element comprising a support having coated thereon a phctoconductive composition comprising ID to about 60 weight percent of 4,4'-benzylidinebis(N,N-diethyl-m-toluidine) as an organic photoconductor,
0.005 to about 5.0 weight percent 2,4-(4-ethoxyphenyl)-6-(4- n-amyloxystyryl)pyryiium fluoroborate as a sensitizer and chlorinated polyethylene containing 50 to 70 percent by weight of chlorine.
11. An electrophotographic element comprising a support having coated thereon a photoconductive composition comprising 10 to about 60 weight percent of 4,4'-bis(diphenylamino) chalcone as an organic photoconductor, 0.005 to about 5.0 weight percent 2,4-(4-ethoxyphenyl)-6-(4)namyloxystyryl) pyrylium fluoroborate as a sensitizer and chlorinated polyethylene containing 50 to 70 percent by weight of chlorine.
12. An electrophotographic element comprising a support having coated thereon a photoconductive composition comprising 10 to about 60 weight percent of 4,4-bis(di-phenylamino)chalcone as an organic photoconductor, 0.005 to about 5.0 weight percent 6-chloro-l'-methyl-l,2,3'-triphenylimidazo [4,5-b] quinoxalino-3-indolocarbocyanine ptoluene sulfonate as a sensitizer and chlorinated polyethylene containing 50 to 70 percent by weight of chlorine as a binder.
13. A process for producing a visible image comprising the steps of preparing an electrophotographic element by coating a photoconductive composition containing a non-polymeric polymeric organic photoconductor and a halogenated polyethylene binder having at least 50 percent by weight of halogen on a support, exposing the element in an imagewise manner to produce a latent image and developing the element to produce a visible image.
14. The process of claim 13 wherein the binder contains 50 to 70 percent by weight of halogen.
15. The process of claim 13 wherein the binder is chlorinated polyethylene.
16. A process for producing a visible image comprising the steps of a. mixing at room temperature a non-polymeric organic photoconductor, a solvent, a sensitizer for said photoconductor and a halogenated polyethylene binder, having at least 50 percent by weight of halogen,
b. coating said mixture on a support to form an electrophotographic element,
c. drying said element at a temperature of less than 35 C,
d. charging said element to at least 550 volts,
e. exposing said element in an imagewise manner to a pattern of actinic radiation to form a latent image and f. developing said latent image to form a visible image.
17. The process of claim 16 wherein the binder is chlorinated polyethylene.
18. The process of claim 16 wherein the binder is a halogenated polyethylene containing 50 to 70 percent by weight of halogen.
19. The process of claim 16 wherein the binder is chlorinated polyethylene containing 50 to 70 percent by weight of chlorine.
20. The process of claim 16 wherein the solvent is methylene chloride.