Copper plate etching technology

Copper plate making plays a decisive role in letterpress printing, packaging printing, and electro-aluminum hot stamping. The plate making process is more complex than the inside. To make a printing plate that meets the printing requirements, one must be familiar with its lack of workmanship and strict control over each link. Otherwise, it is easy to produce quality accidents. The process operations are briefly described as follows:

First, mesh copper etching plate

1. Plate selection

The plate used for copper plate making requires a thickness of 0.8 to 2.0 mm, and a common copper plate of 1.0 to 1.6 mm. Copper plates for plate making are special plates. They contain metals such as cadmium, tellurium and silver. When corroded, they are easier than pure copper. Generally, they are required to be free from impurities, streaks, and have a smooth surface and moderate hardness.

2. Preparation of etching solution (ferric chloride solution)

The main component of the etching solution is ferric chloride, which is a compound of iron oxide and hydrochloric acid. It is a yellow solid or black-brown crystal that is easily deliquescent.

In the etching process, the water dissolves into a golden yellow liquid and copper produces a displacement redox effect.

Corrosion solution preparation: Dissolve ferric chloride with water to the required concentration. One concentration is 35 to 40 degrees, and filtered and clarified.

The prepared ferric chloride solution has a sweet taste. If odoriferous hydrochloric acid is smelled, it indicates that the acidity in the ferric chloride solution is too large, and the old corrosive solution or the slightly acidic trichlorm solution is required. Iron solution reconciliation.

3. Cleaning liquid preparation

The role of the cleaning liquid is to clean the impurities of the copper plate, so that the copper and the ferric chloride contact well to get a better corrosion effect. The copper plate is treated with a cleaning solution to treat the plate before and after etching. Cleaning liquid preparation:

Acetic acid 50cc

Salt 150g

25cc hydrochloric acid

Water 500cc

The various drugs mentioned above may be appropriately increased or decreased, but it should be noted that hydrochloric acid should not be too much, so as not to affect the film.

4. Printing

Stencil printing is the exposure treatment of a copper plate surface coated photosensitive film, which is a mixture of animal glue or resin and other polymer compounds and dichromate. After being exposed to light, the photosensitive plastics do not dissolve in water, and the unexposed areas are soluble in water, so that the copperplate layout will show the lines and dots of the original, and then it will be turned into a corrosion-resistant enamel by heating and baking, and it will reach the letterpress plate. Claim.

Shaiban is an important process of copperplate plate making process. It requires very strict requirements for the photographs of the meshes. Generally, it requires the high-profile parts of the image (highlights) to be transparent, and it is appropriate to photograph 3.5 to 4.5. More than 30% of the outlets, the low-key parts of the image (shade) black spots to shoot 0.5 ~ 1 is appropriate, the idea is to black to be round, must follow a small solid reflective spot, so that the layout can be displayed after the corrosion layer.

(1) Abrasive plate: Choose good quality, moderate hardness, no scarring, rough grain hardwood charcoal milling, grinding plate should be careful, the milled plate has no carbon scratch lines, smooth and clean, no grease, Can make the photosensitive liquid coating evenly attached firmly.

(2) Coating Bakeplate: Set the temperature and rotation speed of the baking plate in advance, clamp the plated plate on the plate, and turn it on. After flushing the plate with clean water, the plate surface is coated with a photo-sensitive liquid under weak light. The photo-sensitive liquid must flow uniformly, without streaks, without bubbles, and without dust inclusions. The rotation speed during drying should be determined by the concentration of the photosensitive liquid, and the film should not be too thin or too thick. The drying platen temperature should not exceed 70°C to avoid dark reaction of the photosensitive film and accelerate hardening, resulting in failure after the printing. Coating baking temperature is generally 50 °C, speed 60 ~ 80 rotation, time 5 to 10 minutes.

Photographic solution preparation

A liquid

PVA (degree of polymerization 500, water soluble 85°C～90°C) 100g

Water 1000 cc

After cooking for one and a half hours, it is filtered (about 4 degrees).

Liquor

Water 100 cc

Ammonium dichromate 10~14g

When the liquid is cooled to 45°C, the two liquids are mixed.

If the PVA polymerization degree is too high, it is easy to paste the plates during printing, and a small amount of sodium sulfonate, ethanol, glacial acetic acid, etc. can be added during cooking.

(3) Exposure: After the film is dried, the film is relatively densely packed with the film of the film on the vacuum stencil and compacted for exposure. The exposure time should be determined according to the temperature, the temperature, and the intensity of the light source. The light source uses a xenon lamp or other lamps as the light source. Under normal circumstances, the lamp distance is 0.5 to 1 meters and the exposure time is 3 to 5 minutes.

(4) Development: After exposure, rinse the unprinted film on the plate surface with clean water. Use a 1% methyl violet dye for easy observation to make the plate show a clear image. Rinse the plate with water. After rinsing, if there is still a small amount of residue on the plate, it can be wiped off with cotton, and then rinsed with water.

(5) Hard film: immersed in 10% chromic acid solution for 20 to 30 seconds. Immediately flush with water. Rinse and place it on the plate holder to allow it to dry naturally.

The chromic acid in the hardener is a strong oxidizer that can make the film astringent and dehydrated to become more sturdy.

(6) Bakeware

The copper plate after the chromic acid hardening is baked on an electric furnace or a constant temperature oven. The copper-plate adhesive film is baked to change from yellow to strong brown-red enamel corrosion-resistant film. Baking temperature 180 °C ~ 190 °C, baking time about 10 minutes.

5. Network repair

Prior to the repair of the outlets, first use a thin ferric chloride solution to clean the plated residue and use a cleaning solution to treat the layout. The general method of network repair is to use lacquer or transfer ink (anti-acid ink) to fill incomplete mesh points in the direction of the mesh angle, and the light at the mesh point can be traced to the same width as the mesh line width, and the size is etched and etched. The dots, the dark place can be connected to the network from the angle of the cross-shaped grid, leaving a hole with the same size of the layout of the screen, and in the corrosion of the mesh copper plate copper coated back.

When gravitational dots should be well-grounded, the cutting blade is the same as the ordinary zinc plate scraper, except that the tip of the blade is tilted upwards by about 10° to facilitate the advancement and sculpt the groove.

6. Corrosion

Corrosion of the mesh copper plate is divided into mechanical, hydrostatic corrosion and hydrostatic corrosion. However, the hydro-chemical corrosion has many techniques, such as upward or downward corrosion, layered corrosion, and brush and ash corrosion, which are separately described as follows:

(1) Hydrostatic plate facing down corrosion

Brush the plate, clamp the copper plate on both sides with a plate, face down, obliquely insert into the etching solution, and then gently move the corroded plate to eliminate the bubbles attached to the plate, avoiding the bubbles It is isolated from the ferric chloride etching solution and forms a site that cannot be corroded to cause discarded printing.

After etching for a period of time, the sidewalls of the outlets are eroded away and the perimeter of the outlets is suspended into a mushroom top shape. The observation of large outlets can be judged by the reflective condition of the adhesive film. The adhesive film is surrounded by copper and does not reflect light. Due to the non-corrosive copper support, the parts are reflective and the bright spot size is the size of the etched dots.

(2) slewing plate facing up corrosion

The hydrostatic surface of the hydrostatic plate tends to cause the impurities produced by the action of ferric chloride and copper to sink to the bottom of the network. As a result, the corrosion of the ferric chloride solution is hindered, and only the edges of the network can be etched. The level is loose and the depth of the dot is not enough, so this method of erosion is only applicable to the image that makes the dark part less light.

(3) coating layered corrosion

The use of a corrosion in the mesh copper plate tends to result in the loss of a low-key layout and a dull tone, and the screen is not sharp enough. Therefore, most of them adopt layered repair and corrosion to make each level prominent. The order of layered coating corrosion is dark tone - sub-dark tone - middle tone - sub-light tone - bright tone. The first corrosion allowed the dark spot to reach the required point. After the first etching, the first coating was performed. Covering the darkest part of the layer will not allow the corrosion to continue, followed by a second corrosion, so that the dark level and the sub-shadow level open, the corrosion time is not much, after the second corrosion is completed, the second coating, coated with dark Levels and sub-shadow levels. For the third time, the middle tone level and the dark tone level were pulled apart. After the third erosion, the third time the painting was done, except for the glorified part. Finally, it eroded and the bright spots eroded to below 10%, showing a bright sensation. In the layered coating corrosion, it is necessary to have a good grasp of the corrosion time, and the time between them is generally 5:1:2:2. Corrosion through layered coating can basically achieve distinct layout and rich color tone. However, manuscripts are ever-changing and should be applied flexibly according to the situation when applying corrosion.

Several problems that should be paid attention to in repairing corrosion

1 According to the original color and the length of corrosion time, decide to use a soft or hard tone. Soft pen calls less ink and lighter, lighter and softer with the pen, the ink layer can be painted on the top of the dot, it applies to the face of people, distant mountains and distant waters and the sky and other bright layers. The hard pens are rich in ink and strong in ink. The pen is straight and powerful. The ink must be completely blinded. It is suitable for sharp and neat outlines of black and white, and the neat edges of buildings.

2 Before printing, the plate should be handled cleanly and rubbed with magnesium carbonate powder. After the coating is applied, it should be roasted with fire so that the transferred ink will be firmly attached to the dots.

3 Before and after the corrosion, both the ferric chloride solution and the cleaning solution should be used to clean the layout, and after the corrosion, brushes, felts, etc. should be used to wipe the residual film around the dot to facilitate corrosion.

(4) Brushing corrosion

When the corrosion of halftone dots is between 20% and 25%, remove the plate and rinse the net with ferric chloride. Do not use the cleaning solution first, and do not use a brush to keep the edge of the film around the dots. Dry the plate.

The appropriate size of the pen (head cut 3/4) as a small brush, water brush to the need to mention the brightness of the site. Generally, the high-definition layer is wiped to remove the film edge on the top of the mesh, and then the surface is washed with a cleaning liquid (not to be brushed) and then etched. In this way, the level of the partial light part can be improved.

(5) Mechanical, hydrostatic combined corrosion

The mesh copper plate is first placed on the corrosive machine to impact corrosion for a period of time. When the halftone spot is about 20%, hydrostatic corrosion is performed. If mechanical impact corrosion is used completely, a bright part network spot will be formed due to the large impact of the space and multiple corrosion. However, due to the small gaps, the dark outlets are subject to less impact and corrosion, which will make the layout harder and fail to meet quality requirements.

7. Problems that should be noticed in the corrosion of mesh copper plate

(1) Ferric chloride etching solution With the increase of the amount of corrosive copper, the color of the corrosive solution changes from golden yellow to yellow brown to yellowish green to dark green, and the corrosion performance also decreases. Therefore, frequent attention should be paid to the adjustment. . The surface of the old ferric chloride etching solution is prone to generate an oxide film. If it is stained on the copper plate surface, it will interfere with corrosion, cause spots, streaks, and the oxide film covering the surface of the solution should be removed at any time before use.

(2) The ferric chloride corrosion solution is heavily corrosive to copper. At the bottom of the etching solution, yellow copper chloride and other yellow impurities are deposited. Such impurities, if adhered to the copper plate, can also cause accidents. The tank should be frequently removed. Precipitated impurities ensure the corrosive solution is clean.

(3) The concentration of the ferric chloride corrosion concentration has a great influence on the corrosion of copper, and the concentration is preferably about 38 to 40 degrees.