Adhesive Contact Electrification Imaging

Abstract

A method of imaging wherein an imaging member including an adhesive coating is placed in contact with an image bearing original and, when stripped therefrom, retains a latent electrostatic charge pattern corresponding to image and background areas of said image bearing original. The latent image is then developed to produce a visible image.

Description

BACKGROUND OF THE INVENTION

Many methods are known for forming an image in response to a pattern of light and shadow. The most common of these is a chemical method wherein the color of a light sensitive chemical is changed by the action of light. Ordinary photographing and blueprinting are examples of this. Other chemical methods are known in which light is used to alter the hardness, tackiness, solvent resistance or ink receptivity of a suitable material. Such methods are widely used in the graphic arts and electronic industries. Other methods have come into use in recent years which rely on electrical properties of photoconductive materials rather than on chemical properties. A layer of such material is exposed to a pattern of light and shadow and the resulting electrical pattern is used to control the selective attraction or repulsion of some form of marking material to the photoconductive layer. Methods are also known in which the conductivity pattern is used to control electrochemical reactions which create geometric changes at an interface.

The above methods all require an exposure step to produce the image while the method utilizing the photoconductive material also includes a charging step, such as that utilized in xerographic process.

SUMMARY OF THE INVENTION

This invention relates to a novel method for image formation and, in particular, offers a method for producing images whereby the steps of light exposure and charging may be eliminated in image reproduction.

In accordance with the present invention, an imaging member including an adhesive coating is placed in contact with an image bearing original having background and image areas thereupon and, when stripped therefrom, the imaging member retains a latent electrostatic pattern which is different in areas corresponding to the background and image areas of the original. The electrostatic pattern is positively developed by applying developer powder thereto having a charge opposite to the latent electrostatic image pattern on the imaging member. A negative may be developed using powder having a charge opposite to the latent electrostatic background pattern on the imaging member.

The adhesive layer may be employed to charge a photoconductive material, utilized in an imaging process, by placing the photoconductive material in contact therewith and by stripping the layer from the photoconductive surface, the surface then being selectively discharged in accordance with an imagewise pattern of light.

It is, accordingly, an object of the present invention to provide a novel imaging method.

It is a further object of the invention to provide a novel imaging method whereby the steps of light exposure and charging may be eliminated in image reproduction.

It is another object of the invention to provide a simple procedure for charging a photoconductive material utilized in an imaging process.

It is a further object of the present invention to provide a novel imaging method wherein an imaging member including an adhesive layer is placed in contact with an image bearing original and then stripped therefrom, the imaging member retaining a latent electrostatic pattern which is subsequently developed on either side of the adhesive layer bearing imaging member.

It is still a further object of the invention to provide a simple, inexpensive method of image reproduction.

DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description which is to be read in conjunction with the accompanying drawings wherein:

FIG. 1 is a flow chart depicting the process for reproducing an image in accordance with the invention, and

FIGS. 2, 3, and 4 are schematic representations of the apparatus used in the method in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, there is illustrated a flow chart depicting the sequences utilized in the present invention. The steps of the process may be stated as follows:

1. An image bearing original is placed in contact with the adhesive coating of an imaging member.

2. The imaging member is stripped from the original, a latent electrostatic pattern corresponding to the image and background areas of the original remaining on both sides of the imaging member.

3. The adhesive coating is contacted by developer powder which is electrically charged. This results in the production of a visible powder image of the latent electrostatic charge pattern formed in Step 2. In this step, the powder should have a polarity opposite to that of the charged pattern corresponding to the image areas of the original to develop a positive image or of a polarity opposite to that corresponding to background areas of the original to develop a negative image. Development may be carried out on either side of the imaging member.

4. The image is fixed to the imaging member. This may conveniently be accomplished by heating, or by chemical fixing, or other similar processes.

5. As shown by the dashed lines, an alternate procedure may be followed wherein the developed powder image can be transferred to a receiving material, such as ordinary paper, by a suitable electrical, mechanical, or chemical process and the transferred image is fixed to the receiving material by any of the techniques set forth in Step 4.

Referring now to FIGS. 2, 3, and 4, the various steps utilized in the present invention are illustrated schematically. FIG. 2 illustrated the initial step in the process wherein an imaging member 18, comprising a substrate 20, coated with a adesive layer 22, is placed in contact with an image bearing original 24 containing the image 26 to be reproduced. An example of an imaging member which can be utilized in the present invention is Scotch tape, manufactured by the Minnesota Mining and Manufacturing Company, Minneapolis, Minn.

Referring now to FIG. 3, when the imaging member 18 is stripped from the image bearing original 24, surface areas 21, and 23 of the substrate 20 and adhesive layer 22, respectively, corresponding to the area of image 26, are positively charged in the example illustrated. The remaining surface areas of substrate 20 and layer 22 are charged negatively, corresponding to the background areas of the image bearing original 24.

The production of charge on the imaging member is caused by a process called contact electrification. The electrochemical potential in the interior of any neutral object depends on the structure of the material and on the dipole layer on the faces of the object. When two initially neutral areas are in contact with one another, electric charge will tend to move from one body to another so as to equalize the electrochemical potential (or the Fermi energy). A triboelectric series can be established in which materials above a given listed one will donate electrons to it, and materials below this given one will accept electrons from it. It is believed that the image areas of an image bearing original adhere differently than the background areas. These adhesion differences are translated during the stripping operation into electrostatic charge differences, produced by electrification as described above, capable of direct development. Whenever background and image areas have different adhesive properties, such as prints in journals, books, and raised or depressed letters in plastic material or metal, copies can be successfully produced. Depending on the electrical properties of the original, the electrostatic charge pattern transferred to the imaging member 18 is either positively or negatively charged in the image areas, the background areas having charge of the opposite polarity. In the example illustrated, the imaging member 18 is positively charged in the image areas and negatively charged in the background areas. The physical arrangement of the original also determines whether the image transferred to the imaging member 18 is a negative or positive. For example, when the image bearing original contains raised letters, only the image, or raised areas, are charged and retain the developer powder since the adhesive coating did not contact the background and a positive copy is produced. In the case of a depressed letter, when the paper only contacts the background, the image is negative. Printed letters develop generally as positives although it is possible, depending upon the triboelectric properties of the image bearing original and the adhesive coated substrate, and the charge on the developer powder, to obtain the reverse effect, thereby developing a negative. Also illustrated in FIG. 3 is receptacle 30 containing development powder 32 therein. The powder is preferably poured upon the surface of substrate 20 to develop the latent electrostatic image 21. The powder may alternately be applied to adhesive layer 22 to similarly develop the latent electrostatic image. In this latter case, the adhesive layer and developer powder combination should be chosen such that the powder will adhere to the layer due to the oppositely charged areas of the layer, and not because of the adhesive property of the layer. In the case illustrated, developer powder is negatively charged so that it can adhere to the positively charged image area of substrate 20 and not the negatively charged background. If the charge transferred to the image areas of the adhesive coating and substrate is negative, the charge on the developer powder should be positive to produce a positive image.

Referring now to FIG. 4, the developed image 37 may be fixed into imaging member 18 by heat fusion such as that produced by a fixing unit 38 positioned adjacent adhesive layer 22. The fixing unit 38 alternately may be located adjacent the image 37 formed on the surface of substrate 20. In this case, a resistance heating type fixture is illustrated. HOwever, other techniques known in the art may also be utilized, including the subjection of the image to a solvent vapor, or the like. The fixing techniques described hereinabove should fix the image 37 without seriously affecting the characteristics of the imaging member 18. The developed powder image 37 may be transferred to a receiving material 36, such as ordinary paper, by charging the receiving material with charge of a polarity opposite to the powder image polarity and bringing material 36 adjacent to or in contact with substrate 20. Other transfer methods may be used. For example, various chemical transfer methods or methods involving hydroscopic action are available.

The transferred image can be fixed to the receiving material 36 by the same procedure described hereinabove for fixing image 37 to imaging member 18.

The type of development process used in FIG. 3 is secondary. For example, magnetic brush development, cascade development, and other known techniques are all feasible. In the step of developing the electrostatic image it has been found that various resinous powders are very satisfactory. These powders should be caused to assume an electric charge of the opposite polarity of the charge on image areas of the adhesive layer 22 or substrate 20 to obtain a positive image. This may be done by means of devices which spray electric charges or may be effected by triboelectric action in a mixture of the developer powder and a carrier material, the particular materials chosen being determined and selected in accordance with a triboelectric series, wherein it may be ascertained that the developer component will assume the proper polarity charge upon triboelectric reaction with the carrier material. A primary function of the carrier material is to insure that the developer powder assumes the proper electrostatic charge polarity by contact with the carrier.

The invention may be carried out successfully when the adhesive coating is a good electrical insulator and when a large portion of the surface area of the insulator is brought into contact with the surface of the other. The adhesive coating should preferably not tear or otherwise mutilate the image bearing original when it is stripped therefrom.

The imaging member 18 can be utilized as a charging device. For example, a photoconductive material utilized in an imaging process requires charging as the first step. The conventional technique in the xerographic process, for example, utilizes a corotron which adds free gaseous ionic charges to the surface of a photoconductive plate by the utilization of a very high voltage supply. The corotron is eliminated in the present invention by contacting the plate with the adhesive layer and subsequently stripping the imaging member 18 from the plate. A uniform electric charge remains on the plate surface. Selective discharge of the plate is then carried out by imagewise illumination thereof. The image is developed and transferred to a receiving material by the techniques described previously.

The invention described above provides a simplified imaging process for use in a home copying system wherein the emphasis lies on material sophistication and not on machine requirements. For example, the charging, development, and illumination units utilized in the electrostatic copying machines presently available can be replaced by the adhesive material utilized in the present invention and a material, such as paper, which in composite form comprises a donor sheet containing charged developer powder. The imaging member containing the adhesive layer is brought into contact with an image bearing original and then stripped therefrom, as described previously. The paper containing the charged developer powder is then placed in contact with, or adjacent to, the imaging member. The charged powder, if charged to the proper polarity, will adhere to the latent electrostatic charge pattern, corresponding to the image area, on the imaging member, thereby producing a visible image. The developer powder preferably should adhere tightly to the surface of the imaging member, reducing the possibility of smudging, erasure, etc., and thereby eliminating the necessity of providing a fixing unit for the home copying system.

While the invention has been described with reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the invention without departing from its essential teachings.

Claims

What is claimed is:

1. A method of forming an image comprising the steps of:

placing an insulating member which comprises an adhesive layer overlying a substrate in contact with an original having image and nonimage areas thereon, said image and nonimage areas differing in adhesion characteristics, said adhesive layer contacting said original and having a different triboelectric property than said original,

stripping said insulating member from said image bearing original, an electrostatic charge pattern of a first polarity being formed on said insulating member, and

applying a developer powder having a charge of a polarity opposite to that of said electrostatic charge pattern to said insulating member, thereby forming an image on said insulating member.

2. The method as defined in claim 1 including the step of fixing the image on said insulating member.

3. The method as defined in claim 1 wherein the developer powder is applied to said adhesive layer.

4. The method as defined in claim 1 wherein the developer powder is applied to said substrate.

5. The method as defined in claim 1 wherein a positive image is formed on said insulating member.

6. The method as defined in claim 1 wherein a negative image is formed on said insulating member.

7. The method as defined in claim 1 including the step of placing a receiving material charged to a polarity opposite to that of said developer powder adjacent to said insulating member, thereby transferring the image to said receiving material.

8. The method as defined in claim 7 further including the step of fixing the image transferred to said receiving material.