Magnetic Printing Technology and Mechanical Discussion--Gravure Printing (III)

(4) Making carbon photo paper to make photogravure, we must first use the image of the positive photo that is lined up to dry on a special carbon paper. The image on the carbon paper is transferred to the surface of the plate cylinder. It is called carbon. The drying process of paper is divided into the following steps.

1 Sensitization of carbon paper Carbon paper itself does not have sensitization properties, so it must be sensitized before the carbon paper is dried.

2 Before the drying of carbon paper, check the original and construction sheets against the draft. The contents of the checkup include: graphic content, specifications, page numbering, cutting or die cutting, bite size, etc.
Check the technical parameters of the layout, if meet the construction requirements, you can dust the version, flatly into the drying rack exposure drying.

(3) The carbon version of the paper is transferred to the surface of the gravure cylinder after the adhesive layer of the carbon paper after the sunscreen and the solarization. There are two wet methods and dry methods.

a. Wet method The carbon paper with sunrays and sunrays is put into the sink and soaked. Then it is attached to the surface of the plate cylinder to separate the paper base from the film. When the paper base is peeled off, the film stays on Roller surface, as shown in Figure 2-31.

Due to the action of water, the film needs to expand and the image is easily deformed, which is obviously very unfavorable for the overprint product. Therefore, it is not adopted when transferring the color to the printing plate carbon paper.

b. Dry method First prepare the plate cylinder and clean the surface of the cylinder with magnesium carbonate (MgCO3) and dilute hydrochloric acid solution. The carbon paper is aligned with the rule line on the plate press, and the film is sprayed onto the surface of the drum, between the carbon paper and the roller, and the carbon paper is tightly adhered to the preliminarily pressed under the pressure of the rubber roller. Coated gravure cylinder. As shown in Figure 2-32.

After the carbon paper was overprinted, after development, a different thickness of resist film was formed on the surface of the gravure cylinder. The thin part of the resist film is a dark part on the positive graph, while the thick part of the resist film is a bright part on the positive graph. In addition, the surface of the entire gravure cylinder is covered with a "10" shaped screen line resist film.

After development, after rinsing and drying, the graphic image on the surface of the plate cylinder is revealed.

(5) The anti-corrosion paint is coated with an acid-resistant asphalt or varnish on the blank part of the plate cylinder, and it will not be corroded during the corrosion process. Paint anti-corrosion paint, also known as the paint lacquer.

(6) Corrosion The plate cylinder is placed in a solution of ferric chloride and etched so that the part of the picture is corroded and then dented.

Copper reacts with ferric chloride to form copper chloride:

2FeCl3+Cu→2FeCl2+CuCl2

During the etching process, the ferric chloride solution passes through the resist film and the copper. Since the developed film corresponds to the darker portion of the document, the thinner the portion that is brighter, the darker portion of the adhesive layer. Thin, corrosion solution is relatively easy to infiltrate, and the corrosion is deeper; while in the bright tone part, the adhesive layer is thin, the corrosion solution is relatively easy to infiltrate, and the corrosion is deeper; while in the bright tone part, the adhesive layer is thicker, and the infiltrating layer of the etching solution is less The depth of corrosion is relatively shallow.

(7) Chrome Plating The gravure cylinder is hand-etched or mechanically corroded, cleaned, wiped with gasoline, blown dry, rubbed with magnesium carbonate, and then inspected, trimmed, proofed, and chrome plated.

The purpose of chrome plating is to increase the hardness of the surface and increase the printability.

Chromium plating can be used as a stationary plating bath. Horizontal plating baths can also be used. The main components of the plating bath are: CrO3 and H2O4.

3. Photo dot gravure

The method of making a gravure plate with carbon paper is only used as a basis for teaching and teaching in foreign countries, and China is currently still in use. Although the operating experience has provided a lot of help for today's photogravure workers, there are indeed many factors that affect the variability of platemaking, and it brings a lot of difficulties to practical operation. For example, the quality and processing of carbon paper, temperature and humidity changes in the plate making shop, preparation and mastering of the etching solution, exposure control, etc. will all directly affect the stability of the plate quality. Even if the operation is strictly in accordance with the technical regulations and the various processes of the production process are controlled, it is still impossible to achieve dataization and standardization, and the quality of the platemaking is difficult to be stabilized.

In recent years, there have been photogravure ingraters that do not use carbon paper for making plates. The dot-gravure platemaking process mainly includes the following aspects.

(1) How to select a manuscript for the preparation of a manuscript. It can be roughly weighed according to many factors such as manuscript forgery, magnification, and model. The general rule is: the original color can be directly to the net; the original color cast is more, the magnification is large, the need for revision and trimming should adopt continuous tuning. The single picture plane can be directly screened;

In addition to gravure photography and electronic color separation methods, there are also two processes, direct screening and continuous color separation screening. That is, the original document is turned into a negative image, and then the negative image is contacted and screened to make a positive image.

(2) Production process of dot gravure dot dot gravure printing is to apply a layer of uniform photosensitive adhesive directly on the surface of the gravure cylinder to replace the traditional carbon paper transfer graphic method.

The production process of dot gravure is:

Plate cylinder processing - coating photosensitive solution - exposure plate - development - ink - corrosion - trim - chrome - check to complete the plate making operation. Here are the main steps:

1 Coating the photosensitive liquid Coating the photosensitive liquid in two ways: spray gun coating method and ring coating method.

Dot gravure plate roller coating of the photographic solution: polyvinyl phthalate ester photosensitive solution (Kodak's KR, Tokyo, Japan should be TPR), photoresist composition of the photosensitive liquid and polyvinyl alcohol as the main Photosensitive liquid. In order to obtain a certain thickness of the photoreceptor solution, it must be dried quickly. Generally, it can be forced to dry using an infrared heating device.

a. Gun coating method uses compressed air to spray the photosensitive liquid onto the surface of the plate cylinder through the gun mouth (see Figure 2-33).

b. The ring coating method utilizes the principle of slip ring box casting, and the photosensitive liquid is applied to the surface of the plate cylinder to form a photosensitive layer (see Figure 2-34).

2 After the printing plate coated with photosensitive liquid is dried and formed, the plate cylinder is driven by the DC motor to rotate, the positive film is tightened and exposed on the surface, and the water-cooled xenon lamp is used for light band exposure, as shown in Fig. 3 -35 shows.

In order to make the picture smooth and closely fit on the surface of the plate cylinder, the transfer of images and images is substantial, and a small amount of paraffin can be rubbed between the positive plate and the plate cylinder.

3 After developing the printing plate, you can develop it.

4 Etching The etching method of the photo dot gravure is the same as the gravure corrosion.

Photo dot gravure, the use of dot area size and the depth of the image of the dual factors of corrosion to express the level of the original screen, the quality of the printed matter is far more than the convex India. Its print quality features ink thick, eye-catching patterns, colorful, rich layers, high definition and fascinating features.

The use of photo dot gravure printing plates for packaging and decorating products can produce satisfactory results.

In addition to gravure plates, three methods of gravure gravure, gravure and photo gravure gravure plates, there are also gravure gravure plates. The automaticity of the "Bumeland" automatic platemaking system is relatively high. It is a new method of direct plate making that directly forms a digital system from an analog system.