The reaction process inside the adhesive layer is shown as follows. In aqueous solution, potassium dichromate is in ionic state: K2Cr2O7 → 2K + + Cr2O7 –, in which: Cr2O7 — + h2o-2cro4 — + 2H +. In other words, the ionic forms of potassium dichromate in acid and alkaline solutions are different: when the solution is alkaline, dichromate ions react in the direction of generating chromate ions. The oxidation effect of dichromate ion on colloid is stronger than that of chromite ion. Therefore, in order to weaken the oxidation of dichromate ions and slow down the dark reaction, an appropriate amount of ammonia can be added to the potassium dichromate solution to enhance the alkalinity of the solution. Solution to the problem of matte hardening of carbon paper.

It has three functions:

     1. The reaction is carried out in the direction of generating chromate ions. At this time, the orange potassium dichromate shows a light yellow color, and the dark reaction inside the carbon paper adhesive layer is weakened.

    2. Improve the adhesion of colloidal substances so that the adhesive film can adhere closely to the layout.

    3. Inhibit the activity of microorganisms to prevent the deterioration of photosensitive solution.

    After ammonia is added to the photosensitive solution, the pH value is usually between 7.5 and 8.8, which is slightly alkaline. In the drying process, ammonia gradually decreases and becomes slightly acidic. Therefore, the photosensitivity of the film gradually increases, which does not affect the use effect. Because higher room temperature will also lead to the separation of pure chromic acid from chromic acid, it is necessary to set a refrigerator. It must be noted that the humidity inside the refrigerator should be consistent with the relative humidity of the studio.Solution to the problem of matte hardening of carbon paper.

      1、 Carbon paper continues to harden after exposure

     If the exposed carbon paper is stored for 20h in a certain humid environment and then printed, it will not be developed. Practice has proved that if carbon paper is stored for one day after drying the mesh in the wet season, and then go to the sun map, this kind of carbon paper is often not easy to adhere to the plate cylinder, even if it has been attached to the cylinder. 

    Therefore, it is required that the carbon paper that has been exposed to the mesh and positive map should be published immediately, so as not to delay the interval between printing and printing for a long time. If the delay time is too long, it will bring some difficulties to the development and corrosion work. Plate makers must cooperate with each other, strengthen work planning, timely clean the drum and do a good job of degreasing; Prepare for plate development by pouring the developing hot water in advance.

     Another way to prevent dark hardening of adhesive layer is to add 0.3% potassium citrate to 4% sensitization solution

(K3C6H5O7. H2O) as a cleaning agent can prevent the latent image of the adhesive layer. The photosensitivity of the adhesive layer can be improved by increasing the acidity of potassium dichromate (K2Cr2O7) solution, but it will also accelerate the dark hardening of the adhesive layer.Solution to the problem of matte hardening of carbon paper.

     2、 A new substitute for carbon paper — presentiment light gravure anti-corrosion diaphragm

     Several pre photosensitive gravure resist films have been tried in the past. At present, there is a new kind of carbon paper with preview light; There is also a carbon paper substitute, with a film rotofilm on the back, which is a patented film for printing. German premonitory light carbon paper has been tried in China, but there is not enough data on its effective performance.

      On the other hand, rotofilm has been used in many printing houses for several years. It can replace the screen positive picture with continuous positive adjustment picture and magenta or gray contact screen (two positive picture printing method in dulchen dultgen mesh method).Solution to the problem of matte hardening of carbon paper.It is a positive color film, so it must be washed under the dark red safety light. The magenta screen used with roto film is exposed through K2 or #3385 ground glass yellow filter, while the continuous positive adjustment picture is exposed through ground glass #5840 UV filter.