US3442207A - Electrical printing apparatus using screen with thick coating to define image - Google Patents

Description

I May 6, 1969 Filed June 5. 1965 W. E. JOHNSON ELECT AL PRINTING APPARATUS USING SCREEN WI THICK COATING TODEFINE IMAGE M Sh eefg,

lnuezzlor. MLLIQM E. JOHNSON wN/Z P461104 HrTOE/VfV-S May 6, 1969 w. E. JOHNSON INTING APPARATUS US WITH THICK COATING TO DEFINE 1m SCREEN IMAGE ELECTRICAL PR Sheet Filed June 5, 1965 United States Patent ELECTRICAL PRINTING APPARATUS USING SCREEN WITH THICK COATING T0 DEFINE IMAGE William E. Johnson, Temperance, Mich., assignor to Owens-Illinois, Incorporated, a corporation of Ohio Filed June 3, 1965, Ser. No. 461,126 Int. Cl. B41f 15/00 US. Cl. 101114 4 Claims ABSTRACT OF THE DISCLOSURE Processes of the general type with which the present invention is concerned are disclosed in my co-pending applications Ser. Nos. 393,817, now abandoned, and 439,799 now Patent No. 3,301,179 issued Jan. 31, 1967, filed Aug. 31, 1964, and Mar. 15, 1965, respectively, and assigned to the assignee of the present application.

The present invention is, in general, directed to improvements in stencil screens employed in such processes.

One object of the present invention is to provide a stencil screen for use in electrical decorating processes of the type referred to above which achieves an extremely high degree of resolution and sharpness in the powder image applied to the article.

It is another object of the invention to provide stencil screens capable of applying a sharply defined multicolor image of uniform density and thickness.

It is another object of the present invention to provide methods and apparatus for electrically applying an imageshaped layer of printing powder particles to a non-conductive article surface.

It is another object of the invention to provide improved stencil screens and methods for preparing such screens.

It is another object of the invention to provide an improved method for preparing stencil screens adapted to apply image-shaped layers of printing powder particles of different colors in adjacent or abutting relationship to each other on an article surface with a high degree of image resolution.

Other objects and features of the invention will become apparent by reference to the following specification and to the drawings.

In the drawings:

FIGURE 1, is a schematic diagram, partially in cross section, of a presently known electrical printing process;

FIGURE 2, is a schematic diagram, similar to FIG- URE 1, showing one form of the present invention;

FIGURE 3, is a schematic diagram, partially in section, of a second form of the invention;

FIGURE 4, is an elevational view of one of two stencil screens employed in a two color decorating process;

FIGURE 5, is a schematic cross sectional diagram showing a portion of the screen of FIGURE 5 and a sectional view of the image applied thereby to an article 3,442,207 Patented May 6, 1969 surface, the section being taken approximately on the line 5-5 of FIGURE 4;

FIGURE 6 is an elevtional view of the mating stencil screen employed in connection with the screen of FIG- URE 4 in the two color decorating process;

FIGURE 7, is a sectional view similar to FIGURE 5, showing the stencil of FIGURE 6 and a cross section of the resultant image;

FIGURE 8, is an elevational View of one of two stencils employed in a second two color decorating operation;

FIGURE 9, is a sectional view, similar to FIGURE 5, of the stencil of FIGURE 8 and its resultant image;

FIGURE 10, is an elevational view of the second stencil employed in conjunction with the stencil of FIG- URE 8; and

FIGURE 11, is a cross sectional view of the stencil of FIGURE 10 and its corresponding image.

In FIGURE 1 of the drawings, there is schematically illustrated an arrangement for applying an image-shaped layer of printing powder particles to the surface of an article A in accordance with the teachings of my copending application Ser. No. 439,799, filed Mar. 15, 1965, and assigned to the assignee of the present application. The apparatus disclosed in FIGURE 1 includes a platelike support 20 of electrically conductive material upon which is supported a loosely packed bed of printing powder particles 22. A stencil screen designated generally 24 is supported at a pre-selected distance above the surface of bed 22, while the article A is in turn supported above screen 24 at a selected distance as by electrically nonconductive spacers 26.

Stencil screen 24 is preferably constructed with a metallic frame 28 which supports an open mesh wire screen 30 having mesh openings larger than the maximum size of powder particles in bed 22. A coating 32 is applied to a portion of screen 30 to fill and mask the mesh openings and an uncoated portion 34 of the screen is provided to define an image-shaped aperture through which powder particles can pass from bed 22 to the surface of article A.

Screen 24 may be prepared in accordance with the teachings of United States Patents Nos. 3,100,150, 3,170,- 791 or 3,170,792. In general, the process of preparing a screen 24 includes the steps of applying a coating of a material such as those specified in the above-mentioned patents to the entire area of screen 30. The various coatings include a light sensitizing agent which, when exposed to light, transforms the coating material from a water soluble state to a water insoluble state. The coated screen is then covered with an opaque positive film of the desired design and exposed to light. After exposure, the exposed screen is Washed with water, and the coating on the nonexposed portions of the screen is dissolved, thereby forming the image-defining aperture 34.

As described in detail in my above-mentioned application Ser. No. 439,799, suitable voltage sources V1 and V2 are electrically connected to powder bed support plate 20, the wire mesh 30 and to article A as illustrated in FIG- URE 1. A pulse time control circuit schematically indicated at 36 is employed to control the time period of energization of voltage sources V1 and V2. Voltage sources V1 and V2 when energized electrically charge powder particles in bed 22 and establish an electric field extending from the upper surface of the powder bed support 20 to to the registered surface of article A. The charged particles are impelled by the electric field to pass upwardly 3 from powder bed '22 toward-the surfaceof article A. The masked portion of stencil 24 defined by coating 32 restricts the passage of particles to the surface of article A to those particles which pass through image aperture 34.

Because the opposed surfaces of article A and powder bed support plate 20 are parallel to each other, the lines of force of the electric field extend vertically in straight lines and hence those particles which reach the surface of article A are deposited on the article surface over an area corresponding in size and shape to that of image aperture 34.

Pulse time control circuit 36 functions in a manner described in detail in my co-pending application Ser. No. 439,799 to automatically de-energized voltage sources V1 and V2 when a predetermined quantity of particles, representing an image-shaped layer of preselected thickness, is deposited upon the surface of article A.

While the electric field configuration is such that particles transferred from bed 22 to the surface of article A tend to travel in straight vertical paths, several effects are present which tend to divert the particles from truly vertical paths. Among these effects are air currents, electric field gradients, interparticle repulsion, retransfer and mechanical collisions.

Air currents are generated due to the fact that a large number of particles are impelled substantially simultaneously through a relatively confined space, while electric field gradients exist because of the presence of the wire mesh in aperture 34 which causes the electric lines of force to be deflected toward the individual wires. Particleto-particle repulsion exists because of the like nature of the charges on the individual particles, while mechanical collisions between particles are unavoidable. Retransfer occurs when a particle reaching the surface of article A loses its original charge and becomes charged in the reverse sense by virtue of its contact with the article surface and is thereby repelled, further increasing the probability of mechanical collision. All of these effects tend to decrease image resolution by scattering particles in transit in a manner such that some of the particles strike the article surface at locations out of a vertical registry with image aperture 34, thereby producing a lack of sharpness around the edges of the applied image.

The degree of resolution attainable in the arrangement shown in FIGURE 1 is a function of the gap or spacing between screen 30 and the surface of article A. The larger the gap, the less resolution can be achieved.

In FIGURE 2, one embodiment of the present invention is disclosed in which a stencil 24 is constructed with a coating 32' on the upper side of screen 34' which is of a thickness sufficient to perform the function of spaces 26 in the FIGURE 1 embodiment. With the exception of the thickened coating 32' on the upper side of screen 34', the arrangement is the same as that of FIGURE 1.

As described in United States Patents 3,100,150, 3,170,- 791 and 3,170,792, the various coatings may be applied to the screen by a squeegee, a normal application of the coating in this manner usually resulting in a coating having a thickness of approximately one mil. The thickened coating 32' of the FIGURE 2 embodiment is achieved by applying the coating several layers, drying the coating between the application of successive layers. In this manner, a coating of the desired thickness may be built up on one side of the screen mesh 34. The coating materials are sufficiently transparent that the formation of the image aperture may be accomplished by the photographic exposure and washing technique described in the three patents referred to above.

The thickness of coating 32' is chosen in accordance with the desired image density or thickness of the layer of particles deposited upon the Surface of article A. In normal glass decorating processes, the usually desired thickness of the image-shaped layer of particles applied to the article surface is approximately to 6 mils, and the thickness of coating 32 in such case would be approximately 8 mils, as measured from the upper side of screen 30. As explained above, the thickness of the imag shaped layer of particles applied to the surface of article A is accurately regulated by the pulse time control circuit 36 as described in detail in my co-pending application Ser. No. 439,799.

In FIGURE '3, there is disclosed a further embodiment of the invention especially adapted to decorate the surface of an article A of electrically non-conductive material. In the previously described embodiments of FIG- URES 1 and 2, the article A must, in order to perform its function as an equipotential surface of the electric field, possess a reasonable degree of electrical conductivity. In many instances, it is desired to decorate an article, such as a plastic bottle for example, which is constructed of a material which for all practical purposes is electrically non-conductive.

In FIGURE 3, a stencil designated generally 124 is supported, as in the FIGURE 1 embodiment, between an electrically conductive powder bed support 20 upon which is supported a loosely packed bed 22 of printing powder particles. In the embodiment of FIGURE 3, the frame 126 of stencil 124 is constructed of an electrically nonconductive material and a wire mesh 130 is fixedly secured within frame 126. The screen coating 132 is applied in several successive layers, as in the FIGURE 2 embodiment, to provide a coating of selected thickness above the upper surface of screen 130 and the image aperture 134 is formed as described above. On the upper surface of the thickened screen coating 132, a layer of electrically conductive material 136 is applied, the conductive material 136 being applied only to the upper surface of coating 132 and not extending downwardly along the side edges of image aperture 134. The conductive layer 136 may take the form of a relatively thin metallic foil or may be applied by coating the upper surface of the stencil coating 132 with an electrically conductive paint.

In this embodiment, the combined thickness of stencil coating 132 and conductive layer 136 constitutes the predetermined thickness of spacing between the surface of article A and screen 130. In the FIGURE 3 embodiment, voltage source V2 is electrically connected to the conductive layer 136 instead of to the article as in the previous embodiment. Because the screen frame 126 in the FIGURE 3 embodiment is electrically non-conductive, the electrical connection is made directly to the wire mesh.

In operation, voltage sources V1 and V2 are energized as in the FIGURE 1 embodiment, thereby establishing an electric field having a hole in the uppermost electrode of the field constituted by conductive layer 136. In the FIGURE 3 embodiment, the field strength of the lower field-the field between powder bed support 20 and screen 130is strong enough so that particles are accelerated through the screen in image aperture 134 with sufficient velocity to reach the surface of article A. As a layer of particles begins to be formed on the surface of article A within image aperture 134, the particles effectively bridge the gap or opening and thus, in effect, electrically fill the hole in upper electrode 136. Electrode 136 dissipates the charge on those particles with which it is in direct or indirect electrical contact and the particles adhere to the surface of article A by the mechanical compaction of the layer. As in the previous embodiment, pulse time control circuit 36 acts to de-energize voltage sources V1 and V2 when a predetermined quantity or thickness of particles has been accumulated on the surface of article A. 4

All of the embodiments described above have been disclosed in connection with the formation of a single color image on the article surface. The manner in which the thickened stencil coating is formed in the FIGURES 2 and 3 embodiments enables a convenient method for forming multicolor images having a high degree of reso lution. In FIGURES 4 through 7, the application of the FIGURE 2 embodiment to a multicolor image is shown in one exemplary form, while FIGURES 8 through 11 inclusive show a similar application of the FIGURE 3 embodiment to a multicolor image. In both instances, the ultimate image is assumed to be a circular image crossed by a diametrically extending diagonal stripe, with the stripe being of one color and the remainder of the circular background of a second color.

Referring first to FIGURES 4 through 7, two stencils are employed to form a smooth surfaced layer of particles in the form of a two color image on the surface of a conductive article A. In FIGURE 4, the first stencil 150 is shown in elevation having a two part image aperture 152 in the shape of the background portion of the ultimate image to be of a first color. The coated or masked portion of the stencil includes the diagonal strip 154 extending between the two parts of image aperture 152, strip 154 corresponding to the diagonal stripe of the image which will be of the second color. The stencil 150 is prepared in the manner described above in connection with the FIGURE 2 embodiment and, as best seen in the cross sectional view of FIGURE 5, the stencil coating is thickened on the article surface side of the stencil to provide the desired spacing between the stencil screen wire 156 and the surface of article A.

The first color portions of the image, corresponding in shape to image aperture 152 are then applied to the article surface by placing the article surface in contact with the stencil and establishing the electric field as described above. In FIGURE 5, a sectional view of the article A with the first color image portions 158 applied is shown separated from the stencil.

The second stencil 160 is shown in elevation in FIG- URE 6. Stencil 160 is formed with an image aperture 162 formed in accordance with the dimensions of the diagonal stripe in the ultimate image. As best seen in the sectional view of FIGURE 7, the stencil coating is formed with a circular recess 164 which extends inwardly from the article facing surface of the stencil coating to a depth equal to or slightly greater than the thickness of the previously applied image portions 158.

Stencil 160 is so formed in the following manner. Assuming that an eight mil spacing is desired between the wire mesh of the stencil and the article surface, and that the desired image layer thickness is five mils, the wire mesh of stencil screen 160 is first coated with two layers of a coating of the type described in United States Patents Nos. 3,100,150, 3,170,791 or 3,170,792 and is then exposed through a positive film having a diagonal opaque stripe corresponding to image aperture 162. The exposed stencil is then washed in water to form a stencil having a coating approximately two mils in thickness with an image aperture in the shape of aperture 162 through the coating.

Additional layers of coating are then applied until the desired coating thickness of eight mils is achieved. A positive film having an opaque circular portion is then placed on the coated stencil in registry with the diagonal stripe portion 162 and again the stencil is exposed to light. A second washing operation results in recess 164. The bottom of recess 164 is formed by the surface of the second layer of coating which was rendered water insoluble by the original exposure.

The stencil 160 is then carefully placed in registry with the previously applied image layer 158, aperture 162 registering with the space between the two previously applied image layers 158. A powder transfer operation as described above is then performed with the second color of powder to achieve the desired image. The resulting image is smooth surfaced in that both color portions of the image are layers of the same thickness The electrical transfer conditions are the same in each case because the mesh to surface spacing is the same.

In FIGURES 8 through 11, a generally similar process for applying the same two color image to a non-conductive article A is illustrated. In this case, it is somewhat more convenient to apply the diagonal stripe first and the background color second. This is because in applying the diagonal stripe first, the electrically conductive layer 186 is in contact with the powder of the diagonal stripe entirely around the periphery of the stripe during its application. Similar electrical contact is achieved on the circular portions of the periphery of the background in the second powder application. While electrical contact will exist between the first and second applied powder layers, the electrical conductivity of the powder is no where near as great as that of the electrically conductive layer. By proceeding in the manner shown in FIGURES 8 through 11, the maximum amount of direct contact between the electrically conductive layer or coating on the stencil and the powder actually being: applied is achieved.

As indicated in FIGURES 8 and 9, a stencil having the diagonal stripe portion of the image defined by an image aperture 172 is made in the manner described in connection with FIGURE 3 above and the diagonal stripe portion 174 of the image is applied. The second stencil is made according to the technique described above in connection with stencil 160, the difference being only in that the masked and unmasked portions of the image aperture 182 are reversed as compared to the FIGURE 6 embodiment. In the completed stencil 180, the masked portion 184 representing the diagonal stripe has a thickness of two mils while the combined thickness of the coating and conductive layer 186 will be the eight mils of the example. In order to prevent undue distortion of the electric field, it is preferable not to apply a conductive layer to the diagonal masked portion 184 because of the close proximity of this surface to the wire mesh of the stencil.

While I have described certain embodiments of the invention in detail, it will be apparent to those skilled in the art that the disclosed embodiments may be modified. Therefore, the foregoing description .is to be considered exemplary, rather than limiting, and the true scope of the invention is that defined in the following claims.

I claim:

1. For use in an apparatus for applying a second imageshaped layer of predetermined thickness composed of printing powder particles of a first color and a known size range to an article surface in adjacent registry with a previously applied first image shaped layer of the same thickness of particles of a different color; a stencil having an image-defining aperture therethrough comprising an open mesh screen having mesh openings larger than the maximum size of powder particles in said known size range, a coating filling and masking the mesh openings of said screen over a first portion only of said screen, the remaining portion of said screen constituting said image-defining aperture corresponding in shape to said second image-shaped layer, said coating on one side of said screen being of a thickness greater than the predetermined thickness of the layer of particles to be applied to an article surface whereby the screen mesh is positioned at a preselected spacing from the article surface when the coating at said one side of said screen is engaged with the article surface, and means defining a recess in said coating corresponding in shape to said first image shaped layer and having a depth at least equal to the thickness of said first layer.

2. A stencil as defined in claim 1 further comprising a layer of electrically conductive material on the surface of said coating.

3. Apparatus for electrically applying an image-shaped layer of predetermined thickness composed of printing powder particles capable of being electrically charged and having sizes falling within a given size range, said apparatus comprising a bed of printing powder particles of said given size range, an electrically conductvie open mesh screen having mesh openings of a uniform size larger than the maximum size of said particles, an electrically non-conductive coating on one side of said screen filling the screen openings over a first portion of said screen to define a masked portion surounding an unmasked portion of said screen constituting an image-defining aperture through said coating, said coating being of a thickness greater than the predetermined thickness of the layer of printing powder particles, means supporting said screen in a preselected spaced relationship to said bed of printing powder particles with said coating on the side of said screen remote from said bed, means for supporting an article in contact with said coating with the article surface extending across said image-defining aperture, electric power supply means electrically connected to said screen and operable, when energized, to establish an electric field between said bed and said article surface operable to electrically charge powder particles in said bed and to impel charged particles from said bed through said image defining aperture in said coating to said article surface, said coating confining the particles to that portion of said article surface exposed to said bed by the aperture in said coating, and means operable upon energization of said electric power means for de-energizing said power :means when a layer of particles of said predetermined thickness has been applied to said article surface.

4. Apparatus as defined in claim 3 for applying said image-shaped layer to said article surface in adjacent 25 relationship to a previously applied layer of particles, said stencil coating having a recess therein extending inwardly from the side of said coating remote from said screen to a depth equal to or greater than the thickness of said previously applied layer of particles and less than the thickness of said coating, said recess being in the shape of the first applied layer of particles.

References Cited UNITED STATES PATENTS 839,187 12/1906 Norton 117-23 2,787,556 4/1957 Haas 11717.5 2,940,864 6/ 1960 Watson 117-17.5 3,228,326 1/ 1966 C-hildrcss 1011 14 3,241,483 3/1966 D-ulf l0 1-129 3,245,341 4/1966 Childress et al 101-122 3,253,540 5/1966 Lusher 101- 170 3,294,017 12/1966 St. John 101114 3,301,179 1/1967 Johnson 101-114 EDGAR S. BURR, Primary Examiner.

US. Cl. X.R. 101-127, 129

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