Method of image reproduction and materials therefor

A method of making a screen stencil that is capable of reproducing lines of the order of 0.1 mm, has undercutting of less than 0.01 mm, excellent bridging characteristics, and a durability in excess of 50,000 copies comprising the steps of:

• covering the screen filaments with a photopolymer that is essentially free of uncombined acrylates and has narrow band ultraviolet sensitivity and a spreadable but self supporting viscosity characteristic, and an attenuated ultraviolet transmissivity, the cured photopolymer having an elastomeric characteristic and negligible shrinkage, the screen filaments being covered by spreading a first photopolymer layer through the screen into contact with an underlying film master;
• exposing the first layer until dry through the film master affixed directly thereto;
• spreading a second photopolymer layer on the side opposite the film master while the film master is retained in position by the contacting layer;
• exposing the photopolymer layers to ultraviolet radiadiation through the film master for a time sufficient to cure the photopolymer to a depth encapsulating the filaments, the time interval being selected relative to screen thickness to cure at least a portion of the second layer while bonding it to the first;
• removing the film master image from the cured photopolymer;
• removing uncured portions of the photopolymer;
• and
• postcuring by exposing the photopolymer to ultraviolet radiation from the direction opposite to the prior exposure for a time approximating the total time of the prior exposures.

A method of making a screen stencil that is capable of reproducing lines of the order of 0.1 mm, has undercutting of less than 0.01 mm, excellent bridging characteristics, and a durability in excess of 50,000 copies comprising the steps of:

• overlying the screen on a film master;
• covering the screen filaments with a wet photopolymer that contains an acidic constituent and that is essentially free of uncombined acrylates and has a narrow band ultraviolet sensitivity and a spreadable but self supporting viscosity characteristic, and an attenuated ultraviolet transmissivity, the cured photopolymer having an elastomeric characteristic and negligible shrinkage and being spread through the screen into contact with the underlying film master;
• lowering the ultraviolet transmissivity of the photopolymer by the incorporation of a selected percentage, less than 1% by weight, of a black radiation absorbing particulate of approximately 56 nanometers average particle size;
• exposing the photopolymer to ultraviolet radiation through the film master affixed directly thereto for a time sufficient to cure the photopolymer to a depth less than the thickness of photopolymer but encapsulating the filaments, the film master being retained in position relative to the screen solely by the wet photopolymer during irradiation;
• removing uncured photopolymer and the film master from the cured stencil for the making of reproductions;
• and
• removing the stencil after use by contacting the stencil with an alkaline solution.

The method of making a screen stencil from a film master comprising the steps of:

• overlaying the screen on the film master;
• spreading a thick layer of a wet photopolymer having a high sensitivity to radiation in the 360-380 nanometer band and an elastomeric property when cured across the screen and into contact with the underlying film master, the photopolymer including a light transmission limiting component and having a viscosity such that the wet photopolymer and film master remain in place despite handling of the screen;
• irradiating the wet photopolymer layer through the image layer for a selected time related to the intensity of the irradiating source to cure photopolymer in the pattern of the film master to a depth less than the total thickness of photopolymer but encompassing both sides of the screen such that all filaments of the screen in exposed areas are encapsulated, the film master being retained in position relative to the screen solely by the wet photopolymer layer during irradiation;
• and
• removing uncured photopolymer and the film master from the cured stencil.

The method of making a screen stencil from a film master comprising the steps of:

• overlaying the screen on the film master;
• spreading a thick layer of a photopolymer having a high sensitivity to radiation in the 360-380 nanometer band and an elastomeric property when cured across the screen and into contact with the underlying film master, the photopolymer including a light transmission limiting component and having a viscosity such that the photopolymer and film master remain in place despite handling of the screen;
• irradiating the photopolymer layer through the image layer for a selected time related to the intensity of the irradiating souce to cure photopolymer in the pattern of the film master to a depth less than the total thickness of photopolymer but encompassing both sides of the screen such that all filaments of the screen in exposed areas are encapsulated;
• wherein the photopolymer is spread on one side of the screen in a first layer which is irradiated through the film master on the same side in a first exposure, and then a second layer of excess thickness is spread on the second side of the screen to penetrate into contact with the layer on the first side throughout the image region and wherein the irradiation of the second layer through the film master provides progressive curing to a predetermined limited depth that is uniform throughout the screen;
• removing uncured photopolymer and the film master from the cured stencil;
• and
• irradiating the photopolymer layer from the side opposite the film master position after removal of uncured photopolymer.

The method of preparing a screen stencil comprising the steps of:

• progressively layering photopolymerizable material containing radiation attenuating particulate through and onto the screen to surround the filaments thereof;
• adhering a film master to the photopolymerizable material on one side of the screen at the initiation of the layering;
• successively exposing the photopolymerizable material to activating radiation through the master during the progressive layering, to cure the material to a depth encapsulating the filaments of the screen in exposed regions;
• removing excess uncured material from the side opposite the master;
• removing the master from the cured layer and screen;
• and
• removing uncured material to leave the stencil image on the screen.

A process for making a screen stencil with minimum undercutting, excellent bridging, high resolution and high durability comprising the steps of:

• disposing a first layer of photopolymeric material on one side of the screen, the material having a viscosity sufficient to be retained by the screen despite handling in different orientations and being polymerizable in response to ultraviolet radiation, the material including less than 2% of a light absorbing additive;
• affixing a photographic transparency bearing an image to the first layer of material in a position in which the image is to be reproduced as a stencil;
• exposing the first layer of material to ultraviolet light through the transparency to at least partially cure the first layer in a pattern corresponding to the image of the transparency;
• disposing a second layer of the photopolymeric material on the opposite side of the screen from the first layer, the second layer having an excess thickness of material;
• exposing the material to ultraviolet light through the transparency for a time sufficient to cure the second layer to a selected depth and adhere and join to the first layer such that each filament of the screen in an exposed area is encapsulated in cured material;
• removing excess uncured material from the second layer;
• separating the photographic transparency from the first layer;
• and
• removing uncured photopolymeric material from the screen, whereby an image is embedded firmly on the screen and firmly united thereto.

The method of making a screen stencil comprising the steps of:

• at least partially curing a coating of photopolymer material on a first side of the screen while the film master is adhered thereto and held in position thereby;
• layering an excess thickness of photopolymer material on the second side of the screen, the material being wet and nonself flowing under normal handling;
• and
• polymerizing the photopolymer material to a desired depth by exposure to radiation through the at least partially cured coating and the adhered master for a selected interval to completely encapsulate the screen.