US 3779750 A
Novel polymeric photoconductors are described which have as a repeating unit thereof a moiety having formula I or II shown below:
Claims available in
Description (OCR text may contain errors)
United States Patent [191 Merrill et al.
[451 Dec. 18, 1973 ELECTROPHOTOGRAPHIC ELEMENT WITH A PHOTOCONDUCTIVE COPOLYMER  Inventors: Stewart H. Merrill; Thomas B.
Brantly, both of Rochester, NY.
 Assignee: Eastman Kodak Company,
[22' Filed: Sept. 25, 1972 ] Appl. N0.: 292,037
3,533,787 10/1970 Merrill et al 96/1.5
Primary Examiner-Norman G. Torchin Assistant Examiner-John L. Goodrow Attorney-Robert W. Hampton et a1.
[5 7] ABSTRACT Novel polymeric photoconductors are described which have as a repeating unit thereof a moiety having formula I or 11 shown below:
wherein R is an aromatic radical and R is an alkylene group having 0 or more carbon atoms. Photoconductive homopolymers and copolymers are described.
14 Claims, No Drawings ELECTROPHOTOGRAPHIC ELEMENT WITH A PHOTOCONDUCTIVE COPOLYMER This invention relates to electrophotography and to novel photoconductive substances for use in photoconductive elements.
Electrophotographic processes employ an electrophotographic or photoconductive element comprising a coating of a photoconductive insulating material on a conductive support. The element is given a uniform surface charge in the dark and is then exposed to am image pattern of activating electromagnetic radiation such as light or X-rays. The charge on the photoconductive element is dissipated in the illuminated area to form an electrostatic charge pattern which is then developed by contact with an electroscopic marking material. A marking material or toner, as it is called, whether carried in an insulating liquid or in the form of a dry powder, deposits on the exposed surface in accordance with either the charge pattern or the discharge pattern, as desired. Then, if the photoconductive element is of a non-reuseable type, the developed image is fixed by fusion or other means to the surface of the photoconductive element. If the element is of the reuseable type, e.g., a selenium-coated drum, the image is transferred to another surface such as paper and then fixed to provide a copy of the original.
All of this is well-known and has been described in many patents and other literature, for example, in a patent of Carlson, US. Pat. No. 2,297,691, issued Oct. 6, 1942, and in more recent work such as Electrophotography by R. M. Schaffert, published by Focal Press Limited, 1965.
The photoconductive compounds that have been used in electrophotographic processes have included both organic and inorganic compounds. More recently, various polymeric organic compounds have been proposed for use as organic photoconductors in electrophotographic elements. The polymeric organic photoconductive materials have been found desirable for a number of reasons. For instance, the polymeric organic photoconductive materials are not leached out of a photoconductive composition when treated by various processing solvents as readily as various non-polymeric organic photoconductive materials. In addition, the polymeric organic photoconductive materials are not subject to crystallization when incorporated as a photoconductive insulating layer in an electrophotoconductive element as are many non-polymeric organic photoconductive materials. Also, in many instances, polymeric photoconductive materials may be utilized to form a photoconductive insulating layer in an electrophotographic element without the addition thereto of various resinous binder materials which are generally utilized when non-polymeric organic and inorganic photoconductive materials are employed in an electrophotographic element.
Among the various polymeric organic photoconductive materials which have been found useful in electrophotographic processes are various poly(vinylcarbazole) and halogenated poly(vinylcarbazole) com pounds. In addition, polymers and copolymers containing repeating units of a vinyltriarylamine moiety such as described in US. Pat. No. 3,265,496, issued Aug. 6, 1966, have been found useful in electrophotographic processes.
In accordance with this invention, there is provided a novel class of polymeric photoconductors comprising a triarylamine moiety linked to the backbone chain of a vinyl polymer. In a preferred embodiment of the in vention, novel copolymeric photoconductors are described.
In addition to the fact that the present invention provides the art of electrophotography with a novel polymeric photoconductor for use in electrophotographic imaging elements and processes, other advantages may also be obtained. For example, many known polymeric photoconductors are relatively brittle and do not adhere well to a substrate. Such disadvantages are typical of homopolymers of vinylcarbazole and homopolymers of vinyltriarylamine such as described, in part, in US. Pat. No. 3,265,496. However, in accord with the present invention, it has been discovered that polymeric photoconductors exhibiting improved flexibility and adhesive properties are obtained. These improved physical properties are especially apparent in accord with a preferred embodiment of the invention wherein novel photoconductive copolymers are provided as described hereinafter.
Typical photoconductive compositions of the invention can be represented as follows:
Homopolymers having repeating units of Copolymers wherein at least one of the repeating units thereof is l or ll above and wherein at least one other repeating unit thereof is selected from the group consisting of ill and
R, R, X and Y set forth in the above-noted formulas I-lV are defined as follows:
X represents an aromatic radical including a substituted aromatic or an alkyl radical including a substituted alkyl. Representative aromatic radicals include a mononuclear or polynuclear monovalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.); or a substituted divalent aromatic radical wherein said substituent can comprise a member, such as an acyl group having 1 to about 6 carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having I to about 6 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.), a halogen substituent such as a chlorine or bromine atom, or a nitro group. Representative alkyl radicals include alkyl groups having one to about eight carbon atoms including a substituted alkyl radical wherein said substituent can comprise an aromatic radical including a mononuclear or polynuclear monovalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), an acyl group as described hereinabove, an alkoxy group as described above, a halogen atom as described above, or a nitro group;
Y represents a hydrogen atom, an alkyl radical having one to about six carbon atoms, or a hydroxy radical;
R represents a mononuclear or polynuclear monovalent aromatic radical either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.) or a substituted divalent aromatic radical wherein said substituent represents a member selected from the group consisting of an alkyl group having one to about six carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), or an alkoxy group as described hereinabove, the R radicals in formulas I and II being the same or different;
R represents an alkylene group having zero to about six carbon atoms. Where R has zero carbon atoms, R becomes merely a univalent chemical bond.
ln those embodiments of the invention where copolymers are provided as described above, the resultant copolymers typically contain at least about 10 weight percent of repeating units having formula l or II above. Although copolymers having smaller amounts of repeating units l or ll may be used, the photoconductive properties of such copolymers are substantially reduced.
Typical preparative procedures for making the polymeric photoconductor of the invention are set forth in Examples 1 and 2 which follow hereinafter. Typically, these polymers may be made by reacting existing vinyl polymers containing free hydroxyl groups with (a) appropriate acid chloride derivatives of a triarylamine such as triphenylamine, e.g., p-diphenyl-amino-benzoyl chloride and, if desired, (b) other reactants which preferably can contribute desirable sensitometric and/or physical properties, for example, acid halides of a halogenated benzoic acid.
The polymeric photoconductive materials of the invention can be employed in a photoconductive layer with or without a binder and with or without sensitizing addenda. Generally, because of the film-forming properties of a polymeric material, a binder is not required. In such case, a photoconductor formed is dissolved in a suitable solvent and generally can be coated on a support to form a self-supporting hydrophobic layer. Normally, a chain length of at least three units is desirable to obtain sufficient polymeric characteristics to form a self supporting layer. As indicated hereinabove, one advantage of the polymeric photoconductive materials of the invention, especially the copolymeric photoconductive materials, is that the materials exhibit a high degree of flexibility when coated as a film on a support layer. In certain cases, however, a resinous binder may usefully be added to a photoconductive substance of the invention, for example, to the various homopolymeric photoconductive materials of the invention, to provide a resultant layer exhibiting improved flexibility and film-forming properties.
Preferred binders, if a binder is utilized in preparing photoconductive compositions of the invention, are polymers or mixtures thereof having fairly high dielectric strength and which are good electrically insulating film-forming vehicles. Materials of this type comprise styrene-butadiene copolymers; silicone resins; styrenealkyd resins; silicone-alkyd resins; soya-alkyd resins; poly(vinyl chloride); poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers; poly(vinyl acetate); vinyl acetate-vinyl chloride copolymers; polyvinyl acetals, such as poly(vinyl butyral); polyacrylic and methacrylic esters, such as poly(methyl methacrylate), poly(n-butyl methacrylate poly(isobutyl methacrylate), etc.; polystyrene; nitrated polystyrene; poly(- methyl-styrene); isobutylene polymers; polyesters, such as poly(ethylenealkaryloxyalkylene terephthalate); phenolformaldehyde resins; ketone resins; polyamide; polycarbonates; etc. Methods of making resins of this type have been described in the prior art, for example, styrene-alkyd resins can be prepared according to the method described in US. Pat. Nos. 2,361,019 and 2,258,423. Suitable resins of the type contemplated for use in the photoconductive layers of the invention are sold under such trademarks as Vitel PE- lOl, Cymac, Piccopale 100, and Saran F-220. Other types of binders which can be used in the photoconductive layers of the invention include such materials as paraffin, mineral waxes, etc.
Solvents of choice for preparing coating compositions of the present invention can include a number of solvents such as benzene, toluene, acetone, 2- butanone, chlorinated hydrocarbons, e.g., methylene chloride, ethylene chloride, etc., ethers, e.g., tetrahydrofuran or mixtures of these solvents, etc.
In preparing the coating composition useful results are obtained where the photoconductor 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 photoconductor substance present is not critical. As indicated previously, the polymeric materials of the present invention in many cases do not require a binder in order to obtain a self-supporting coating on the support. In those cases where a binder is employed, it is normally required that the photoconductor substance be present in an amount from about 1 weight percent of the coating composition to about 99 weight percent of the coating composition. A preferred weight range for the photoconductor substance in the coating composition is from about 10 weight percent to about 60 weight percent.
Coating thicknesses of the photoconductive composition on a support can vary widely. Normally a coating in the range from about 0.0001 inch to about 0.004 inch is useful for the invention. The preferred range of coating thickness is found to be in the range from about 0.0002 inch to about 0.001 inch.
Suitable supporting materials for electrophotographic elements of the invention include electrically conducting supports, such as paper or conventional film supports, for example, cellulose acetate, cellulose nitrate, polystyrene, poly(ethylene terephthalate),
poly(vinyl acetal), polycarbonate and related films having a conductive substrate thereon. An especially useful conducting support can be prepared by coating a transparent film support material with a layer containing a semiconductor such as cuprous iodide dispersed in a resin. Suitable conducting coatings also can be prepared from the sodium salt of a carboxyester lactone of maleic anhydride-vinyl acetate copolymer. Such conducting layers and methods for their optimum preparation and use are disclosed in Minsk U.S. Pat. No. 3,007,901, issued Nov. 7, 1961; Trevoy U.S. Pat. No. 3,245,833, issued Apr. 12, 1966; Sterman et al. U.S. Pat. No. 3,262,807, issued July 26, 1966; etc. Additional useful conductive layers include carboncontaining layers such as conductive carbon particles dispersed in a resin binder. Metal coated papers; metalpaper laminates; metal foils such as aluminum foil, etc; metal plates such as aluminum, copper, zinc, brass and galvanized plates, etc; as well as vapor deposited metal layers such as silver, nickel, or aluminum or. conventional film supports are also useful as are conductive or conductor-coated glasses.
The electrophotographic elements of the invention can utilize an inner layer between the conducting support and the photoconductive layer. Materials useful for this layer can include substances such as poly(vinyl acetate) as described, for example, in U.S. Pat. No. 3,438,773, by Hayashi et al., issued Aug. 15, 1969. Other inner layers can be used which may function as adhesive inner layers such as a terpolymer of vinylidene chloride-acrylonitrile-acrylic acid.
Sensitizing compounds, if desired for use with the photoconductive elements of the present invention, can be selected from a wide variety of materials, including such materials as pyrylium dye salts including thiapyrylium dye salts and selenapyrylium dye salts disclosed in VanAllan et al. U.S. Pat. No. 3,250,615; fluorenes, such as 7,12-dioxo-13'dibenzo(a,h)fluorene, 5,- -dioxo-4a,l 1-diazabenzo(b)fluorene, 3,1 3-dioxo-7- oxadibenzo(b,g)fluorene, and the like; co-crystalline complexes of a poly(carbonate) resin and a pyrylium dye as described in U.S. Pat. No. 3,615,414, issued Oct. 26, 1971 and U.S. Pat. No. 3,679,407 issued July 25, 1972; aromatic nitro compounds of the kind described in U.S. Pat. No. 2,610,120; anthrones like those disclosed in U.S. Pat. No. 2,670,284; quinones, U.S. Pat. No. 2,670,286; benzophenones U.S. Pat. No. 2,670,287; thiazoles U.S. Pat. No. 2,732,301; mineral acids; carboxylic acids, such as maleic acid, diand trichloroacetic acids, and salicylic acid; sulfonic and phosphoric acids; and other electron acceptor compounds as disclosed by H. Hoegl, J. Phys. Chem., 69,
No. 3, 755-766 (March 1965), and U.S. Pat. No. 3,232,755. The amount of sensitizer that can be added to a photoconductive composition of the invention to give effective increases in speed can vary widely. The optimum concentration 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 0.0001 to about 10 weight percent or more based on the weight of the coating composition. Normally, sensitizers are added to the coating composition in an amount of about 0.005 to about 5.0 percent by weight of the total coating composition.
The following examples describe the preparation of various photoconductive materials and photoconductive elements of the present invention.
Example 1 Preparation of Intermediates A. 4-Formyltriphenylamine Fifty grams (0.2 mole) of triphenylamine is suspended in a mixture of 50g (0.68 mole) of dimethylformamide and 50 ml of odichlorobenzene and stirred. The resulting mixture is cooled in an ice-water bath and 56g (0.36 mole) of phosphoryl chloride is added slowly. The resulting reaction is exothermic. The temperature is maintained at about 40C. by controlling the rate of addition of phosphoryl chloride. After the addition is completed, the resulting mixture is warmed on a steam bath for 3 hours during which time it turns dark. The mixture is cooled and neutralized with a solution of sodium acetate in water. Crude 4-formyltriphenyl-amine, 38g, 0.14 mole, percent yield, separates as an orange solid. After three recrystallizations from isopropyl alcohol the melting point of the light yellow product is 131.5-132.SC.
Calcd. for C, H, NO: C, 83.5; H, 5.5; N, 5.1.
Found: C, 82.9; H, 5.5; N, 5.1.
B. p-Diphenylaminobenzoyl chloride To a solution of 4-acetyltriphenylamine in tetrahydrofuran is added three moles of aqueous potassium hypochlorite with stirring. After two hours the solution is acidified. The 4-carboxy-triphenylamine is collected and recrystallized from ethanol. 1t melts at 202204C.
Calcd. for C H NO C, 78.9; H, 5.2; N, 4.8.
Found: C, 78.9; H, 5.2; N, 4.9.
To 20g of this acid in 250ml of dry benzene is slowly added a slight excess of thionyl chloride. The mixture is refluxed for an hour, then evaporated to dryness under vacuum. The residue is recrystallized from 300 ml of ligroin which gave 18g of product, m.p. 1 l4-1 15C.
C. 3-(p-Diphenylaminophenyl)propionyl chloride In 50ml dry pyridine is dissolved 68.3g (0.25 mole) 4-formyltriphenylamine and 26.0g (0.25 mole) malonic acid. The solution is heated on a steam bath for 5 hours. The product is isolated'by pouring the solution into water and acidifying with hydrochloric acid to remove the pyridine. The solid material is filtered off and extracted with ethyl ether to remove residual starting material. A 33 percent yield (10.5g) of p-N,N- diphenylaminocinnamic acid, m.p. 176178C., is recovered.
p-Diphenylaminocinnamic acid (100.0g; 0.318 mole) is dissolved in tetrahydrofuran and hydrogenated at 60 psi at room temperature over palladium on charcoal. The solution is filtered and the tetrahydrofuran evaporated. The residual oil is crystallized from aceto nitrile. Eighty grams of product, melting at 126-128C, are obtained.
Calcd. for C,,H, NO C, 79.21; H, 6.03; N, 4.40.
Found: C, 78.8; H, 6.4; N, 4.6.
To a rapidly stirring solution of 63.4g (0.20 mole) 3- (p-diphenylaminophenyl)propionic acid in 250ml dry benzene is added, in small portions, 41 .6g (0.20 mole) phosphorous pentachloride. The resulting solution is stirred for one and one half hours and then the volatile components are removed by vacuum evaporation. The residue is taken up in ethyl ether and the mixture is filtered. After evaporation of the ether, distillation at 157C., 2p. mercury, yields 30g of the acid chloride.
Example 2 Preparation of Polymers I. Poly(vinyl p-diphenylaminobenzaldehyde acetalco-vinyl m-bromobenzoate) To a suspension of 4.4g of poly(vinyl alcohol) (Dupont Elvanol 71-30) in I ml of acetic acid and 0.5g of phosphoric acid is added 18g of 4-formyltriphenylamine. The mixture is stirred on a steam bath for one hour then poured into isopropyl alcohol to precipitate the polymer. When dry, this polymer is dissolved in I00 ml of pyridine, and to it is added 15g of mbromobenzoyl chloride over I minutes. The mixture is stirred at 50C. for two hours, then poured into isopropyl alcohol to precipitate the product. Analysis shows a nitrogen content of 1.4 percent which corresponds to 34 weight percent of vinyl diphenylaminobenzaldehyde acetal units.
ll. Poly(vinyl m-bromobenzoate-co-pdiphenylaminobenzoate) A suspension of swollen poly(vinyl alcohol) is prepared by heating 5.6g of Dupont Elvanol 52-22 in 100 ml of pyridine for an hour at 90C. To this, at 50C. is added dropwise 1 lg of bromobenzoyl chloride followed by ISg of p-diphenylaminobenzoyl chloride in 30 ml of methylene chloride. Following stirring at 5060C. for 2 hours the mixture is diluted with 200 ml of methylene chloride and poured into isopropyl alcohol to precipitate the product. Analysis for bromine shows it to contain 63 percent by weight of vinyl bromobenzoate.
lll. Poly(vinyl p-diphenylaminophenylpropionate) This polymer is made from 1.7g of poly(vinyl alcohol) and g of diphenylaminophenylpropionyl chloride in a procedure similar to that used to prepare polymer ll.
IV. Poly(vinyl m-bromobenzoate-co-pdiphenylaminophenyl propionate) This polymer is made from 3.9g of poly(vinyl alcohol), 7.7g of m-bromobenzoyl chloride, and ll.7g of diphenylaminophenylpropionyl chloride in the same manner as is polymer II. Bromine analysis shows it to contain 42 weight percent vinyl bromobenzoate units.
Example 3 Examination of Electrophotographic Properties Solutions of 2.0g of polymers 1 through IV of Exam ple 2 and 0.0l6g of 2,6-bis-(ethoxyphenyl)-4-(4- pentyloxy-phenyl) thiapyrylium perchlorate in l 1.7 ml of methylene chloride are coated at a 0.004 inch wet thickness on a transparent support having a conducting layer of the sodium salt of a polymeric carboxyester lactone described in US. Pat. No. 3,260,706. The dried coatings are flexible and adhered well to the support.
To determine the speed of the electrophotographic elements described above, each is electrostatically charged under, for example, a corona source until the surface potential, as measured by an electrometer probe, reaches some suitable initial value V typically about 600 volts. The charged element is then exposed to a 3,000K tungsten light source through a stepped density gray scale. 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 the exact value of which depends upon the amount of exposure in meter-candle-seconds received by the area. The results of these measurements are then plotted on a graph of surface potential V vs. log exposure for each step, thereby forming an electrical characteristic curve. The electrical or electrophotographic speed of the photoconductive composition can then be expressed in terms of the reciprocal of the exposure required to reduce the surface potential to any fixed selected value. The actual positive or negative shoulder speed is the numerical expression of IO divided by the exposure in meter-candle-seconds required to reduce the initial surface potential V,, to some value equal to V minus I00. This is referred to as the I00 volt shoulder speed. Similarly, the actual positive or negative toe speed is the numerical expression of I0 divided by the exposure in meter-candle-seconds required to reduce the initial potential V to an absolute value of I00 volts. An apparatus useful for determining the electrophotographic speeds of photoconductive compositions is described in Robinson et al U. S. Pat. No. 3,449,658, issued .Iune I0, 1969. The results of these tests are set forth in Table I.
TABLE I Electrical Speed of Sensitized Polymeric Photoconductors Speed Positive Negative Polymer Shoulder Toe Shoulder Toe l I400 90 570 II 800 57 630 32 Ill I200 I60 950 IV I800 250 I200 I00 The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
1. An electrophotographic element comprising an electrically conductive support and a photoconductive insulating layer comprising a polymer having as a repeating unit thereof a moiety selected from the group consisting of wherein R represents an alkylene group having zero to about six carbon atoms and R represents an aromatic radical selected from the group consisting of unsubstituted aromatic radicals, aromatic radicals having an alkyl substituent, and aromatic radicals having an alkoxy substituent.
2. The invention as described in claim 1 wherein said polymer is a homopolymer.
3. The invention as described in claim 1 wherein said polymer is a copolymer comprising at least two different repeating units, one of said repeating units selected from the group consisting of wherein R represents an alkylene group having zero to six carbon atoms and R represents an aromatic radical selected from the group consisting of unsubstituted aromatic radicals, aromatic radicals having an alkyl substituent, and aromatic radicals having an alkoxy substituent; and one of said repeating units selected from the group consisting of wherein R is an alkylene groups having zero to six carbon atoms and R represents an aromatic radical selected from the group consisting of unsubstituted aromatic radicals, aromatic radicals having an alkyl substituent, and aromatic radicals having an alkoxy substituent.
7. The invention as described in claim 6 wherein said polymer is a homopolymer.
8. The invention as described in claim 6 wherein R is an aromatic radical selected from the group consisting of unsubstituted phenyl radicals, phenyl adicals radicals an alkyl substituent containing one to about six carbon atoms in the alkyl moiety, and phenyl radicals having an alkoxy substituent containing one to about six carbon atoms in the alkoxy moiety.
9. The invention as described in claim 6 wherein R is a phenyl radical.
10. The invention as described in claim 6 wherein said polymer is poly(vinyl p-diphenylaminophenylpropionate).
11. A photoconductive insulating composition comprising a copolymer having at least 2 different repeating units, one of said repeating units selected from the group consisting of wherein R represents an alkylene group having zero to about six carbon atoms and R represents an aromatic radical selected from the group consisting of unsubstituted aromatic radicals, aromatic radicals having an alkyl substituent, and aromatic radicals having an alkoxy substituent; and one of said repeating units selected from the group consisting of lll and
OB-Ow wherein Y is a member selected from the group consisting ofa hydrogen atom, an alkyl radical, and a hydroxy radical, and X is an aromatic radical or an alkyl radical.
12. The invention as described in claim 11 wherein said copolymer contains a repeating unit having formula I and a repeating unit having formula III and wherein R is an aromatic radical selected from the group consisting of unsubstituted phenyl radicals, phenyl radicals having an alkyl substituent containing one to about six carbon atoms in the alkyl moiety, and phenyl radicals having an alkoxy substituent containing one to about six carbon atoms in the alkoxy moiety; X is selected from the group consisting of halogensubstituted alkyl radicals containing one to about eight carbon atoms in the alkyl moiety and halogenated aromatic radicals.
13. The invention as described in claim 11 wherein said copolymer contains a repeating unit having formula II and a repeating unit having formula III and wherein R is an aromatic radical selected from the group consisting of unsubstituted phenyl radicals, phenyl radicals having an alkyl substituent containing one to about six carbon atoms in the alkyl moiety, and phenyl radicals having an alkoxy substituent containing one to about six carbon atoms in the alkoxy moiety;
is selected from the group consisting of halogensubstituted alkyl radicals containing one to about eight carbon atoms in the alkyl moiety and halogenated aromatic radicals.
14. The invention as described in claim 11 wherein said copolymer is selected from the group consisting of 39 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,779,750 mud December 18, 1973 Stewart H Merrill and Thomas B. Brantly Patent No.
Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby 'corrected as shown below:
Column 9, line 68, "adieale" should be deleted.
Column 10, line 1, after "icals" insert "having".
Signed andsealed this Lpth day of June 1971+ (SEAL) Attest:
EDWARD M.FLETCHER,JR. c. MARSHALL 1mm Attesting Officer Commissioner of Patents