CA1128383A - Copolymers of dimethyldiallylammonium chloride and n-methylolacrylamide as water-insensitive electroconductive polymers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Copolymers containing from 40 PERCENT to 85 percent by weight dimethyldiallylammonium chloride and at least 15 perccnt but less than 60 percent by weight N-mcthylolacrylamide. These polymers are electroconductive and become water-insensitive after being applied to a substrate.

Description

~~P~3~3 BACKGROUND OF THE INVENTION
This invention relates to electroconductive polymers, electro-conductive materials and processes for preparing electroconductive ] 0 paper.

Electroconductive paper may be used for a variety of purposes.
Nonimpact printing processes such as electrostatographic, electro-photographic, electrographic, "Electrofax(~' and other processes call for the placement of an electric charge on the paper. In electro-photography, the paper contains a photo-responsive or photo-conductive layer of material, such as a specially treated zinc oxide, which causes the charge to be dissipated in an area where light strikes it, thus leaving a pattern of the charged areas which is a reproduction of the image aesired. The charged area attracts a powdered or other usually particulated image-forming material which may be fused or otherwise treated to make the image permanent. In electrography, electrostatics are used without radiation. The electrical charge is deposited only in the imaged areas. The cornmon characteristic of all of these processes is the use of an electrically conductive base

2 5 paper .

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3~3 C-1184 Similarly, dielectric paper has a substrate which may be paper or plastic, an electroconductive coating and a top dielectric coating which will accept and hold an electrical charge until the paper is contacted with toner.

ln the present methods of preparing dielectric and other forms of electroconductive paper, the substrates are coated with an aqueous conductive coating formulation and topcoated with solvent based di-electric or photoconductive, i. e. zinc oxide, formulations. This method has many disadvantages such as the high cost of energy related materials associated with solvent coatings, the increased fire hazards of organic solvents, the high cost of solvent recovery systems and slower coating speeds which are characteristic of solvent based coating systems .

The use of an aqueous topcoat in conjunction with an aqueous lS conductive coating is impractical when the topcoat is applied directly on the conductive layer. Migration of the conductive species occurs during the topcoating causing a breakdown of the aqueous dielectric emulsi~n and/or poisoning of the dielectric topcoat.

SUMMARY OF THE INVENTION
This invention is directed to an electroconductive coating formulation which overcomes the aforementioned disadvantages of solvent based coating systems. This formulation comprises an electroconductive polymer which, although applied from an aqueous slurry, becomes water-insensitive upon drying thereby permitting the use of an aqueous based dielectric topcoat without migration of the - conductive species into the dielectric layer.

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3~33 c 1184 The electroconductive polymer useful in the formulati~n of this invention is a copolymer containing from 40 percent to about 85 percent by weight dimethyldiallylammonium chloride and at least about 15 but less than 60 weight percent N-methylolacrylamide, preferably 15 to 30 percent by weight N-methylolacrylamide. The polymers of this invention have a molecular weight of at least 100, 000 and preferably at least 500, 000.

The copolymers of dimethyldiallylammonium chloride and N-methylolacrylamide may be prepared by conventional solution polymeri~ation techniques, as for example those described in U. S.
Patent No. 2,923, 701 or U. S, Patent No. 3,288, 770 Although the copolymers described in these patents may be sufficiently crosslinked under a:ny pH conditions, basic pH's are preferred. Acidic pH curing leads to a breakdown of the aqueous dielectric emulsi~n when applied.

The crosslinking agent used in the preparation of these co-polymers is preferably ammonia, but other amines and acid-containing compounds may be used. A number of catalysts for crosslinking for N-methylolacrylamide have been described in the literature.

The copolymers of dimethyldiallylammonium chloride and N-methylolacrylamide are formulated in an aqueous system which contains the polymer, a crosslinking agent, water and, if desired, a binder and a pigment. The polymers of this invention will generally be employed in amounts ranging from about 0.1 to 4. 0 pounds per .
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3~3 3000 square feet of material to be coated. Substrates such as paper and synthetic substrates, as for example MYLAR (polyethylene glycol terephthalate), nyl~n and polyethylene, may be coated by the polymers of this invention. Conventional coating techniques may be used.

Dielectric resins may be used alone but they usually are mixed with pigments such as barium sulfate, zinc sulfide, calcined clay, 7inc oxide and other additives to insure good runability. Suitable aqueous-based dielectric resins include styrene/methyl methacrylate, vinyl acetate/methyl methacrylate, vinyl acetate/crotonic acid and styrene/butadiene copolymers.

The following examples illustrate the preparation and utility of the polymers of this invention.

Dimethyldiallylammonium chloride (320. 5 grams of a 67. 4%
aqueous solution), ethylenediaminetetraacetic acid (0. 3 grams), isopropanol (4. 0 grams) and deionized water (159. 8 grams) are charged to a kettle with agitatic~. The pH is adjusted to 7. 0 - 7. 5 with dilute hydrochloric acid and the system purged with nitrogen for one hour while heating to 100C. A solution of ammoniu~n per-sulfate (21, 3~o, 12. 7 grams, 11. 7 ml) and a solution of sodium car-bonate (19. 3%, 12. 7 grams, 10. 6 ml) are added to the mixture at rates of 0. 0647 ml/min. and 0. 0588 ~nl/min., respectively, for three hours while N-methylolacrylamide (60. 0%, 90 grams, 81. 8 rnl) is metered at the rate of 1. 49 ml/min. for the first 30 minutes, 2S 0. 68 ml/min. for the next 30 minutes, 0. 40 ml/min. for the following

- 4 -~ ~ z~3~33 C-1184 30 minutes and 0. 07 ml/min, for the last 60 minutes. During the additions, reflux is maintained and a slow stream of nitrogen is bubbled over the surface. Refluæ is maintained for one hour after the additi~ns are complete and additional deioni7ed water (75. 0 grams) is added and the reaction mixture cooled to ambient temperature. The pH is then adjusted to 7 0 - 7. 5 with dilute sodium hydroxide and the reaction mixture discharged.

A typical conductive polymer formulation would contain 25%
conductive polymer, 20% binder, 50% pigment and 5% of a suitable crosslinking agent. The pigment is generally prepared in a 65% ac~ive solids slurry. The required amount of crosslinking agent is solubilized in a portion of the dilution water. The final coating preparation is prepared by adding, in the following order: clay (134. 6 grams), electroconductive polymer (109. 3 grams of 40% solution), dilution water (120 grams), binder (67. 3 grams of 52% active terpolymer of ethylene, vinyl acetate and N-methylolacrylamide) and crosslinking agent (8. 8 grams of NH4Cl in 60 grams of water). The pign~ented formulation is adjusted to pH 8 with NH40H. The coating should be smooth and free of grit formation.

Barrier-coated paper is manually coated with the formulation described above. The coated sheets are dried for 15 seconds on a Print Dryer and ~or 15 minutes in a 135C. forced air oven. The 2S coated sheets are conditioned overnight at 50% RH and 7ZF, after which they are weighed to obtain coatweight, then evaluated for con-ductivity.

_ 5 ~2~3383 C- 1 184 Circles of 3. 375 inches diameter are cut from the conditioned coated sheets. Surface resistivity (con~uctivity) is measured by g a Keithley Resistivity Adapter and Keithley Electrometer. The test specimens are placed in the adapter, coated side down. A direct current of lO0 volts is applied across the surface and the resistivity (measured in amperes) is read directly from the electrometer. The surface resistivity in ohms/unit of area is calculated using the following equation:

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Surface Resistivity (ohms/square) (S. R. ) = 53. 4 x applied voltage electrometer reading in amperes Test specimens are then subjected to a water soak test in which the test specimens are i~mersed for 15 seconds in a 1000 ml beaker which contains 900 ml of mildly agitated water. The test specimens are then dried for 10 minutes at 110C. in an oven and reconditioned at 50% RH
and 72F. overnight. The test specimens are then lightly calendered at about 500 psi and the surface resistivity again measured. The difference in the two readings, before and after the water soak test, indicates the level of water resistance. In this regard, smaller differences are indicative of greater degrees of water resistance.
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Table l sets forth comparisons between a number of sheets coated with 90/lO copolymers of dimethyldiallylammonium chloride/
N-methylolacryla~nide and an 80/20 copolymer of dimethyldiallyl-ammonium chloride/N-methylolacrylamide.

3~3 C-1184 Table 1 Appr ox.
Polymer SR (Ohms, Square)Loss in SheetComp. %Coatweight 50% RH __Conductivity No.by Weight$~/3000 ft. 2Before After(I:n Decades) 90/10 . 27 7. 6 x 1071. 9 x 10113, 4 2 90/10 . 19 8. 5 x 1072. 0 x 10113. 4 3 90/10 .25 1. 1 x 1088.0 x 109 1. 7 4 90/10 .31 1. 1 x 1081.6 x 1011 3,0 90/10 .18 8.6x 107 3.8x 109 1.5 6 90/10 .19 7.0~ 107 1.4x 1011 3,4 7 90/10 .23 6.3 x 1071.~ x 109 1.6 8 80/20 ,21 1. 8 x 1088. 0 x 108 0.6 9 90/10 , 18 9.5 x 1074.5 x 1ol0 2.5 90/10 . 16 1. 1 x 1083. 1 x 109 1.2 Several copolymers of 80 weight percent di~nethyldiallyl-ammonium chloride and 20 weight percent N-methylolacrylamide having a range in viscosity were prepared in accordance with the procedure of Example 1 and evaluated by the procedure of ~ample 3.
~' The results of these tests are set forth below in Table 2.

Table Z
Appr ox.
Brookfield SR (Ohms, Square) Loss in Sample Viscosity Coatweight 50% RH Conductivity No. (cps) 7~/3000 ft.2 Before After(In Decades) 4110 .79 1.4x 108 9.~x 10g 0.8 1.30 4.1x107 1.5x10 0.8 2 1358 . 7Z 2. 1 x 108 1 4 x 1090 7 1.2 5. 8 x 107 1 8 x 1080 7 3 682 . 60 3. 6 x 108 4. 9 x 1~9 1. 1 1.0 4,5x107 1.6x108 0.7 4 2920 . 47 3. 1 x 108 1. 3 æ 1090. 6 .98 5.7x 107 1.3x 108 0.6 2088 . 43 2.2 x 108 1. 3 x 109 0. 9 .90 1.0x 108 2,5x 108 0.2 Several copolymers of dirnethyldiallylammonium chloride and N.methylolacrylamide having varying amounts of the two monomers were prepared i:n accordance with the procedures of Example 1 and evaluated in accordance with procedures of Example 3. Table 3 shows that while substantial losses in conductivity occur in the 90/10 dimethyl-diallylammonium chloride/N-methylolacrylamide (DMDA.AC/N-MAM) coated shcet, those sheets coated with the copolymers of this invention exhibited much less conductivity loss.

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. - 8 -~ ~ zf 33~33 c 1 1 84 Table 3 ~ = . _ Appr c~x.
DMDAAC/ SR (Ohm99 Square) Loss in SheetNMAMCoatweight 50% RH Conductivity No.Composition #/3000 ft.2 Before Aftex (I:n Decades) ... . .
A - 1 90/10 . 34 4. 5 x 107 6. 3 x 101 3. 2 2 .49 2.5 x 107 4.5 x 101 3.2 B - 1 85115 . 44 3. 8 x 107 6. 1 x 108 1. 2 2 . 62 2, 7 x 107 ~. 5 x 107 0. 6 t, 10C - 1 80/20 . 30 6. 9 x 107 1. 2 x 109 1. 4 2 .46 4.~x 107 1.8x 108 0.7 D - 1 75/25 . 35 7.1 x 107 2. 3 x 108 0. 5 2 .54 4.9x 107 1.7x 108 0.7 E - 1 70/30 . 33 1. 5 x 108 7. 9 x 108 0. 6 .46 8.8x 107 2.4x 1o8 0.4 ~; , ,, :
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Claims (7)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. An electroconductive paper which contains a layer of a coating composition which contains a copolymer containing at least 15 to less than 60 percent by weight N-methylolacrylamide and from 40 to about 85 percent by weight dimethyldiallylammonium chloride.

2. An electroconductive paper as in Claim 1, wherein the copolymer is present in a concentration of at least 0.1 pound per 3000 square feet of paper.

3. An electroconductive paper as in Claim 1, wherein the polymer containing layer also contains a binder,

4. An electroconductive paper as in Claim 3, wherein the polymer containing layer also contains a pigment,

5. An electroconductive paper as in Claim 1, wherein the paper also contains a dielectric layer.

6. An electroconductive paper as in Claim 1, wherein the paper also contains a photoconductive layer.

7. A method of making electroconductive paper which comprises coating said paper with at least 0.1 pound per 3000 square feet of a copolymer which contains at least 15 to less than 60 percent by weight N-methylolacrylamide and from 40 to about 85 percent by weight dimethyldiallyl-ammonium chloride.