EP0000571B1 - Process for the production of an original - Google Patents

Description

The invention relates to a method for producing an original, in which a recording layer located on a carrier is exposed in terms of information and lattice to form a relief image, the recording layer being exposed through separate color separation templates which are transparent in the area of the respective projection color and whose partial image areas overlap-free adjoin each other, and in which the recording layer is developed after exposure.

Such a method is known from GB-A-6 825 AD 1906, according to which the colored projection image is generated by imaging the diffracted light, for which purpose the color separation images are modulated with gratings of different grating constants in accordance with the color separations. An attempt is made to store the different grid images in one layer by superimposing two grids of very different grid constants. For this purpose, a relatively coarse grating is superimposed on the actual color-determining grids with different grating constants in the color separation exposure, which is also shifted into new positions with each exposure, the distance between the individual positions being smaller than the grating constant of the coarse grating. Such a double grating technique with partial displacement of the grating is very difficult to handle. Relief gratings with uniform grating constants and a rectangular grid profile are not used, and the undiffracted light is not used for the projection. Such an imaging technique does not lead to an exact color-accurate projection of the relief grid images.

With the from the magazine Laser u. Opto-Electronics No. 3/1976, pages 16/17 known ZOD (Zero Order Diffraction) technology, grid-like images are generated. Three nickel matrices are produced from the relief images, which correspond, for example, to three primary color grid patterns in yellow, magenta and cyan in a photoresist, with which colorless thermoplastic foils made of, for example, polyvinyl chloride are embossed. These foils are mechanically superimposed and when projected with conventional projectors, colored projection images are obtained from the colorless relief images. The grid-like screening is carried out with relief grids of rectangular cross-section, the grid period being approximately 1.5 .mu.m. For each color separation in magenta, yellow and cyan, a nickel matrix with different relief depth is created separately, with which one of the separate embossed images is created. The relief depths are different, with the relief depth being greatest for the cyan extract and smallest for the yellow extract. These embossed images are rasterized. The embossed images are overlaid on a three-layer relief image from which colored images can be projected. The technique described produces very bright, high resolution color images. The relief images can be reproduced relatively cheaply and quickly by embossing.

A disadvantage that complicates the introduction of this technique is the complex manufacturing process with three completely separate work steps for producing the individual embossed relief images corresponding to the color separations. Another disadvantage is that the three separate relief images are put together to fit the duplicate image required for the color projection. In the German patent 26 57 246, which does not belong to the state of the art, a solution is already specified which avoids these disadvantages. The relief image is then composed of the relief partial images corresponding to the individual color separations in such a way that differently colored areas, which can also be halftone dots in rasterized images, are arranged in one plane, but the differently colored areas do not overlap, but at most touch . Relief images of this type are very well suited for the representation of areal multicolored templates, such as graphic representations, in the form of relief grid structures in one plane.

In the method disclosed in the German patent specification 26 57 246, the lattice-like exposure and the imagewise color separation exposures are carried out at different times, the lattice-like exposure taking place through the photoresist layer up to the carrier material. This process works with three primary colors.

A further development of the grid image recording uses four basic colors, for which corresponding color separation templates for the color separation exposures by simple contact exposure are used.

The object of the invention is to improve the method described in the introduction in such a way that, with at least the same quality of the projection images in terms of brightness and sharpness, time is saved in the exposures of the recording layer.

This object is achieved according to the invention in that the exposure is lattice-like and then information-wise, that the lattice-like exposure takes place over the entire image area and to a uniform relief depth which is smaller than the thickness of the recording layer, that the information-wise exposure is provided by each color separation template different energy density is carried out and that the energy density used in each imagewise exposure is smaller than that required for the exposure of a similar recording layer by the same color separation template without prior grid exposure to achieve the desired separation color.

The procedure is such that up to a uniform relief depth, that of a certain one Projection color corresponds, is exposed lattice. The grating depth for the respective color separation image is thus adjusted in the case of the grating-free image-wise exposure. The explanation for this seems to be that the relief depth initially increases in a lattice construction phase, since the exposed parts of the layer expose faster than the layer parts previously covered by webs of the structural lattice, and then there is a lattice removal phase in which the relief depth decreases again, especially when approaching to the wearer in the final stage of the exposure. Apart from the final phase, the lattice structure and lattice degradation is largely independent of the layer thickness of the recording material, for example a photoresist. The reproducibility and the luminosity of the projection colors are in any case the same or even better than if the recording material is exposed immediately in a grid-like manner until the support is reached.

In an embodiment of the invention, exposure is lattice-like to a uniform relief depth which corresponds to the projection color green or yellow. The number of imagewise color separation exposures can thereby be reduced by one, which saves time.

It is obvious that all recording parameters must be kept constant with great accuracy for the reproducible generation of predetermined relief depths and thus certain projection colors. In order to take fluctuations in the projection colors due to influences that are difficult to detect into account, a calibration curve is recorded, from which the effective exposure times of the recording material can then be found for some time.

To produce an original, approximately 2.5 μm thick layers of a photoresist are exposed imagewise and lattice-wise on a support. The imagewise exposure is preferably carried out in contact with the respective color separation template or a black separation template, the lattice-like exposure in contact with a lattice template, for example a glass plate with translucent areas and areas opaque covered by metal bars. In the preferred positive photoresists with o-quinonediazides, in which the exposed layer parts are detached during development, actinic light is radiated in, for example parallel light from a 200 watt high-pressure mercury lamp through a quartz lens with a focal length of f = 15 cm and through a blue glass filter with a maximum Transmission of 75% of the light intensity at 400 nm wavelength. To produce a metal die for embossing the information carrier, the original is coated with a thin, electrically conductive layer on which a metal coating is deposited. Then the original and the metal coating, whose contact surface with the original represents the negative relief image of the original, are separated from one another. A deformable material from which the information carrier is produced, for example polyvinyl chloride, is embossed with the metal die thus produced in a manner known per se under pressure and under mostly temperature-related viscosity reduction.

The following examples show the projection colors that occur at specific radiated energy densities.

example 1

First, a calibration curve for an approximately 2.5 µm thick layer of a positive working photoresist is known, for example, by Shipley Comp. Inc., Newton, Mass., USA. For this purpose, the photoresist is applied to a bare transparent polyester film by spinning and drying. This layer is then irradiated with actinic light in a contact arrangement with a grid of 600 lines / mm made of metal webs on a glass plate, developed in an aqueous alkaline manner and irradiated with white light. Depending on the energy density supplied, the projection colors of the calibration curve listed in column 2 of Table 1 occur.

If, for example, the projection color green is to be obtained in the later image-wise exposure, without having to carry out a homogeneous subsequent exposure using a color separation template for green, a new, similar recording layer is exposed with a grid of 240 mJ / cm ² and then post-exposed. Depending on the energy density supplied for the post-exposure, the projection colors listed in table 1 in column 4 occur.

As a comparison shows, the projection color deviates magenta, which is a red with a tint in blue, which corresponds to an irradiated energy density of 360 mJ / cm ² in the grid exposure, from the projection color blue-violet, which corresponds to an irradiated energy density of 120 mJ / cm ² corresponds to the homogeneous post-exposure, although an energy density of 240 mJ / cm ² + 120 mJ / cm ² = 360 mJ / cm ^{2 as} a whole was applied by the post-exposure to the recording layer, ie the same amount as in the lattice exposure alone . This color difference is due to the fact that, during lattice exposure, the layer parts of the photoresist lying below the lattice webs are not directly exposed, but are only slightly degraded by scattered light, while in homogeneous post-exposure the lattice is removed and the layer parts which are no longer covered are degraded by exposure .

The image is produced in such a way that a new layer of photoresist is exposed with a grid of 240 mJ / cm ² . Subsequently, exposure is carried out under suitably placed color separation templates, which are only transparent at the image areas of the respective color separation color and at the white image areas, namely to achieve the projection colors red / yellow / blue, the color separation templates with energy densities of 70/90/120 mJ / m ² shines through. A black separation template is crossed over to the grating and a grid of 138 lines / mm is placed on the pre-exposure and an energy density of 140 mJ / cm ^{2 is} irradiated.

After the aqueous alkaline development, the original obtained is irradiated with white light and a colorful image is projected according to the original by means of an optical system with a light intensity of 1: 2.8. The black parts of the image can be described as dark brown rather than black. The spectral transmissions, which are shown in the figure, were measured at the colored image points. Above a scattered light component of approximately 3%, transmissions with maximum values of around 50% build up, curve A for blue-violet a maximum at approximately 460 nm, curve B for green a maximum at approximately 510 nm, curve C for yellow Maximum of approximately 620 nm and curve D for red, with an orientation towards magenta, have a maximum at approximately 650 nm.

If the original is further processed into an embossing die by producing a metal mold with which PVC foils can be embossed, the exposure times must be multiplied by a factor of 1.06 for the corresponding color rendering of the embossed PVC foils to take into account different refractive indices between PVC film and the photoresist layer.

Example 2

An approximately 3.5 .mu.m thick layer of the same photoresist as in Example 1 is irradiated with actinic light in a contact arrangement with a grid of 138 lines / mm of metal webs on a glass plate, developed in aqueous solution and irradiated with white light. The projection light is guided through a long focal length, dimmed optics. Depending on the size of the supplied energy densities, the projection colors listed in Table 2, Column 2 occur.

As long as the projection color yellow is obtained in the later image-wise exposure without post-exposure, a similar recording layer with an energy density of 120 mJ / cm ² is exposed in a lattice and then post-exposed in an image. Depending on the supplied energy densities, the projection colors given in table 2, column 4 occur.

The imagewise exposure is carried out analogously to the method described using Example 1.

Example 3

An approximately 2.5 .mu.m thick layer of a sensitometrically harder photoresist than in Examples 1 and 2 is irradiated in a contact arrangement with a grid of 600 lines / mm made of metal bars on a glass plate with actin-safe light, developed in aqueous alkaline solution and irradiated with white light. The projection light is imaged by optics with a light intensity of 1: 2.8. Depending on the energy densities supplied, the following projection colors appear in table 3, column 2.

From the small gradation of the energy densities compared to the photoresist used in Example 1, it can be seen that the photoresist used works sensitometrically hard. For color gradation by homogeneous post-exposure, 90 mJ / cm ² is first irradiated through a grid of 600 lines / mm in order to obtain the projection color blue-violet. Subsequent exposure is carried out homogeneously. Depending on the energy densities supplied, the projection colors listed in Table 3, Column 4 occur.

Claims (6)

1. A process for the preparation of an original, wherein the recording layer which has been applied to a carrier material is information-wise and grid-wise exposed and developed to give a relief image, the recording layer being exposed through individual color separation originals which are transparent in the areas of the appropriate projection colors and whose part-image areas adjoin one another without overlapping, and wherein the recording layer is developed after the exposure, characterized in that after the grid-wise exposure the information-wise exposure is carried out, in that the grid-wise exposure is carried out over the entire image area and up to a uniform relief depth which is smaller than the thickness of the recording layer, in that the information-wise exposure is carried out with a different energy density for each color separation original, and in that said energy density used for each image-wise exposure through an individual color separation original is lower than the energy density required for an exposure of a similar recording layer through the same color separation original without a preceding grid-wise exposure, to obtain the required projection color.

2. A process according to claim 1, characterized in that the grid-wise exposure is carried out up to a uniform relief depth which corresponds to the projection color green.

3. A process according to claim 1, characterized in that the grid-wise exposure is carried out up to a uniform relief depth which corresponds to the projection color yellow.

4. A process according to claims 1 through 3, characterized in that after the grid-wise exposure (n-1) part-imagewise exposures are carried out through color separation originals without a grid and at graded energy densities, n being the number of projection colors used in the color system.

5. A process according to claims 1 through 4, characterized in that the exposure is carried out through an original for a black separation.

6. A process according to claims 1 through 5, characterized in that the color separation originals are transparent in the image areas of the particular color separation colors and in the white image areas only.

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