Screen Printing Photographic Plate Making Equipment (5)

4. Shaiban light source and printing equipment.

In the screen-making process, photographic sensitization has gradually replaced the traditional hand-carving method. Photolithography is a very important process in photolithography process. How to correctly choose and use the printing plate light source is of great significance for improving the quality of screen printing plate, effectively saving energy, simplifying the operation and maintenance operator's health, and reducing the production cost. Since the type of photosensitive resin is different, it is necessary to choose to use a light source that meets the needs of various photosensitive materials.

In addition, when printing, it is necessary to fully study the size of the plate, the output power of the light source, the distance between the plate and the light source, and pay special attention to the function of the light reflecting plate.

The type of light source for the printing plate is basically the same as the type of camera light source, such as a carbon lamp, a xenon lamp, a fluorescent lamp (a low-pressure mercury lamp), a high pressure mercury lamp, an ultra-high pressure mercury lamp, a metal halide lamp, and the like.

At present, the color sensitivity of various screen-sensitive materials we use is mostly distributed between 250 and 510 nm. Therefore, theoretically speaking, any light source with a peak wavelength between 250 and 510 nm on the luminescence spectral energy distribution curve can be used for screen printing. Figures 2-96 and 2-97 are the color-sensing curves of the screen-sensitive material and the spectral-energy distribution curves of the copying light source, respectively, for the reader's reference.

1 selection of print light source.

a. The emission spectrum of the light source should match that of the light-sensitive material. The energy of light varies with wavelength and frequency. The shorter the wavelength, the higher the frequency, and the greater the photon energy. When the light is absorbed by the material in the process of radiation, since the photon has a certain energy, the material undergoes physical and chemical changes, and the chemical reaction caused by the light energy is called a photochemical reaction.

The so-called photochemical matching means that the spectral output distribution of the selected light source should match that of the photosensitive material. That is, the wavelength range in which the light-sensitive material absorbs light and the photochemical reaction occurs is exactly the output range of the light source light emission spectrum, and the maximum absorption peak of the light-sensitive material happens to be at the output peak of the light source. In this way, the light energy of the light source is absorbed by the photosensitive material as much as possible and a photochemical reaction takes place. For this reason, it is best to understand the colorimetric range and absorption peaks of the silkscreen photoresists we have chosen. The colorimetry can be approximated by UV or phosphorescence spectroscopy, but it must be pointed out that in some cases UV absorption spectra Chromaticity is consistent both in the range and in the intensity distribution, and is not completely consistent in most cases. Because absorbing light does not mean that a photochemical reaction completely occurs. There are also dielectric materials that are limited to the plate making process. Short wave regions (below 320 nm) that can react chemically cannot be represented.

b. High luminous efficiency and high intensity. The luminous efficiency of the light source, in particular the conversion rate of the ultraviolet light, is high and the luminous intensity or brightness is large.

Under other conditions unchanged, the greater the power and luminous efficiency of the light source, the greater the luminous intensity or brightness, the higher the illumination of the exposed surface, and the shorter the time required for the photosensitive material to obtain the same exposure. .

Saving electricity, shortening plate-making time, and increasing production efficiency have always been the pursuit of screen printing plate-making workers. Some units have used ammonium dichromate-PVA-based emulsions in the past, dodged with xenon lamps and general fluorescent lamps, and after using diazo-based and acrylic-based photosensitive resins (photosensitive adhesives), they also used fluorescent lamps to print, resulting in 60 minutes. There is no printing in the sun. After switching to black light, it takes only 5 minutes to complete. As a result, energy consumption dropped to less than one tenth, and the plate making speed increased by more than ten times. Some units were exposed using charcoal lamps and xenon lamps. A 3 kW light source was exposed for 10 minutes while a 200 watt black light was used for 5 minutes. The energy consumption ratio is 30:1. This fully demonstrates the significance of rational choice of light sources in saving energy and increasing production efficiency.

Acrylic photosensitive materials for screen printing sensitive adhesive, its photopolymerization is caused by the non-initiated system, its color sensitivity mainly depends on the sensitization - initiating system. In the case of benzoin ethers, class II ketals, acetophenones, and benzoin dimethyl ether, the colorimetric range is between 250 and 390 nm, and the peak is between 300 and 360 nm. High pressure mercury lamps, black light lamps, and metal halide lamps, monochrome fluorescent lamps, blue light lamps and other effects are all poor. When the sensitization system consisting of thioxanthone derivatives and tertiary wrists initiates the system, the color property is 250 to 430 nm and the peak shifts to around 390 nm. Therefore, the monochromatic fluorescent lamp is an ideal light source, and the high-pressure and ultra-high pressure mercury lamps and Metal halide lamps can better match. When coumarin ketones and amines are used as sensitization-initiating systems, the color sensing range can be extended to around 600 nm with a peak between 450 and 500 nm, so various light sources are very effective, even argon laser sources, Deuterium lamps, charcoal lamps, xenon lamps, sunlight, fluorescent lamps and other light sources have become practical. Only such photosensitive materials need to operate in the darkroom.

Recently, attempts to produce silk-sensitive emulsions using water-soluble polymers such as water-soluble nylon and polyvinyl-pyrrolidone and bis-azide compounds have been primarily successful. The range is mostly between 250 and 450 nm, and the light source used is also black light and light. Fluorescent lamps, metal halide lamps, and high-pressure, ultra-high-pressure mercury lamps.

c. Safety and hygiene. Since the copying light source requires a particularly large voltage, it is necessary to provide safety measures in terms of electrical failures. When the external light source is used, it must be heated. Therefore, special attention must be paid to heat dissipation. Ultraviolet rays from the light source can cause eye and skin injuries, so the environmental management of the operation site is very important.

As we all know, the spectrum of carbon lamp and xenon lamp has a wide range of distribution, and the UV light emitted from it has a strong injury to the human body. During the use of such light sources, ozone is generated, and a small amount of ozone is good for people, and a large amount is serious health.

The intense infrared light emitted by the light source has a burning effect on the human eye. In the hot summer, a high-powered xenon lamp or dichroic lamp is installed in the house, which can make the temperature in the house unbearably high, plus the discharge of the carbon lamp. It also produces nitrogen oxides and volatile helium dust that can affect human health and cause environmental pollution.

d. Workability and economy. In the platemaking process, due to the cumbersome daily operations such as the replacement of light sources and the cleaning of the site, a certain amount of technology is required. Therefore, it can be said that the use of light sources is an annoying problem. The operating cost is also a very important issue, so comprehensive cost accounting is required for lamp life (effective time), exposure time, labor costs, and depreciation of lamps and lanterns.

Therefore, the light source that can be started instantaneously, withstands a high number of switches, has a long life, and can reach a rated brightness within a short time after being turned on, is generally welcomed by the plate-making manufacturers.

e. The image has good reproducibility. Image reproducibility refers to whether the film faithfully reproduces the image on the original plate, and the other is determined by factors such as light source, printing plate, and development. Image reproducibility is also affected by the degree of adhesion between the master and the photosensitive film, direct light, and the like.

f. The spectral energy is stable. The stability of the energy distribution of the radiation spectrum of the light source is better. Within the effective period of use, there should be no significant change in the distribution of spectral energy.

g. Light source heat radiation is small. To ensure that the light source has sufficient luminous intensity or brightness, the thermal radiation of the light source should be as small as possible. When using high-power and strong light sources, forced cooling (air-cooled, water-cooled) and other measures shall be taken to the lamp and other measures shall be taken to keep the exposed surface temperature of the photosensitive material below 32°C.

h. Uniform luminous intensity. The luminous intensity of the illuminated surface of the light source should be as uniform as possible. The design of the exposure device shall ensure that the illumination difference of the exposed areas of the photosensitive material does not exceed 15%.

i. Light source environment adaptability. The light source should have strong environmental adaptability, and it can work normally under various temperature, air flow and voltage variations.

Of course, in actual production, it is unrealistic to choose a light source that can fully meet the above requirements. The purpose of the above-mentioned selection principle is only to hope that the plate-making operator should consider the influence of the light source on the exposure quality of the photosensitive material when choosing to use the plate-making light source.

2 printing equipment. The plate-making machine is the main printing equipment and is an exposure device for photosensitive materials. Mainly by the glass frame, chassis, vacuum pumps, lamps and other components. It differs from the ordinary printers in that the large glass frame is at the bottom and the rubber frame is at the top. Lights can be placed below or on the side.

a. Simple drying rack. If you do not have a vacuum plate, you can also make a simple printing equipment. For example: to make a triangular iron frame, coupled with a thick (5mm or more) white glass, surrounded by a rubber band, the protective glass is not squeezed on the four sides of the triangular iron frame. When printing silk screen version, first place the photographic soft bottom plate on the white glass, and then reconnect the screen frame with the photosensitive layer. The frame is filled with foam plastic blocks, and a flat plate is placed in the frame. The plate is pressed again. Below the weight is a strong light. Now many self-made simple printing plate racks, some with a wooden box, four weeks inside the box posted aluminum skin, fitted with fluorescent tubes. Place a piece of thick glass on the top of the box. Place the bottom plate on the glass during the printing, put on the coated silk steel plate, and then compact the seal on it to print.

The above-mentioned drying racks can only be used for making simpler pictures and texts. The fine picture and text still require a vacuum printing machine.

b. Vacuum printing machine. When printing plates made of fine lines or dots, special screen plate stencils with vacuum tensioners and selected light sources must be used.

Screen printing machine has two forms: one is a horizontal printing machine, and the other is a vertical printing machine. These two kinds of printing machine, compact structure, glass drying frame, vacuum pump, light source are in the same box body, easy to operate, suitable for small and medium-sized screen printing.

Cold light source screen printing machine adopts vacuum suction pressure setting device to ensure that screen and positive pictures are solid, and use cold light lamp with radiation source and photosensitive material sensitive light area as light source, so that the exposure speed is greatly improved (exposure time 1 ~ 2.5 minutes). Light radiation is reduced, and operating conditions are greatly improved. Saving 85% or more, is the ideal light source for printing.

The vacuum plate making machine used for silk screen making is a frame with a glass plate on one side, and a frame with a blanket on the other side. The two are connected with a special hinge, and at one end, there are handles for fixing the two frames. A rubber band with a height of 10 to 15 mm and a width of 20 to 30 mm is embedded around the blanket. When the two frames are fixed by a handle assembly, the apex of the band is tightly adhered to the glass plate to block the incoming air, and the internal air is vacuum-pumped. After extraction, the plate can be completely sealed with the positive plate. The silver emulsion film surface of the positive plate at the time of printing should be in close contact with the screen emulsion surface, and the emulsion film surface of the positive plate must be carefully determined.

In the printing, the screen plate coated with the emulsion is first placed on the glass plate together with the positive plate, covered with a blanket, and the two frames are fastened. The vacuum is used to pump the air out of the plate to make it close. 2-98). When the glass surface is horizontally eliminated horizontally during exposure, exposure at a certain distance is the most used method. There is also a chandelier type in which the glass faces upward and the light source is irradiated from above. The light source is irradiated from the lower side with the glass facing downwards; the light source moves along the glass surface in various types of scanning.

The vertical layout of the layout, there must be a certain distance between the version and the light source, in the installation requires a considerable site, from the perspective of reducing the site, the use of chandeliers and light source type.

In order to miniaturize the printing frame itself, it is no longer necessary to use the conventional vacuum drying frame wrapped by the blanket cover, but only to vacuum suction the pattern inside the plate frame, generally known as the suction type printing plate Machine (Figure 2-99). This type can reduce the volume of the vacuum drying frame, and the light emitted from it can enter the interior of the printing frame, so light does not spread to the outside. However, if the size of the printing frame and the printing frame do not match, vacuum suction cannot be performed. The advantage of the suction type printing machine is that: the area is small; the blanket can be used permanently; the vacuuming time is short; the printing plate has a high efficiency for a long time; the light is not leaked because the light source is set inside the printing frame. . The disadvantage is that when the size of the printing plate changes, the blanket needs to be replaced accordingly; multiple small frames are difficult to print at the same time.

In order to get a good edition, only the printing plate in the printing