### Common Types of Original Manuscripts in Screen Printing
The commonly used original manuscripts for screen printing generally fall into three categories: black-and-white line pattern manuscripts, color continuous tone manuscripts, and color printed manuscripts (secondary manuscripts).
#### Q: How many types of line manuscripts are there? Can hand-drawn manuscripts be replaced by computer-drawn ones?
#### A: Black-and-white line pattern manuscripts typically come in two forms: hand-drawn and computer-generated. Hand-drawn manuscripts can further be divided into reflective manuscripts and transmissive manuscripts. Reflective manuscripts are hand-drawn on white paper, while transmissive manuscripts consist of text, graphics, and tables drawn with carbon black ink on tracing paper. With a density D=3 or higher, these can be directly used to expose silk screens.
Computer-generated manuscripts involve creating documents, patterns, and tables using various software programs. These are then output via laser printers onto transparent film or tracing paper and used as screen printing originals. Currently, some factories use high-precision computer-generated manuscripts to improve print quality.
#### Q: Why are color reversal films often chosen as screen printing originals?
#### A: Continuous tone color originals include:
1. **Color reversal film**, which is the most ideal transmissive original for screen printing reproduction. It has high image clarity, vibrant colors, rich gradations, and strong three-dimensional effects, making it suitable for high-magnification enlargement. The density range is D=0.1~3.8, sometimes reaching above 4. High-end scanners or electronic color separators are required to ensure image quality. The magnification ratio can reach up to ten times, making it suitable for large-format screen printing and ideal for large advertisements.
2. **Color photographs**, which are produced by enlarging from color negatives and can serve as reflective originals. However, during the enlargement process, some details may be lost, or improper operation may lead to color imbalance, discoloration, and uneven tones. The density range is D=0.1~2.6, with coarse dye particles. Scanned with flatbed scanners, the images tend to appear dirty when enlarged beyond 4~7 times, leading to distortion at higher magnifications.
3. **Color positive film**, which is also copied from color negatives. Its image quality is similar to that of color photographs, serving as a transmissive original. The density range is D=0.1~2.8, and it is scanned with flatbed scanners at a magnification ratio of 4~7 times.
#### Q: Why are color negatives unsuitable as separation originals?
#### A: Color negatives have an amber-colored layer on their surface, making it difficult to find the black and white fields during scanning. This makes calibration challenging, and the image effect cannot be clearly seen. The colors in the image are complementary to those of the original scene, resulting in a reversed image. Generally, they are not used as originals but can be flipped to produce positives or photographs for use as screen printing originals.
#### Q: Why do printed originals need to be descreened? Why can't they be enlarged for reproduction?
#### A: Printed originals, also known as secondary originals, are mostly halftone reflective originals. They are Y, M, C, K four-color prints that have undergone compression processing. Their density range is low, between 0.1~1.6, sometimes reaching 1.8. The gradations are not rich. When reproducing from secondary originals, the density must remain consistent, allowing only for reproduction at the original size without enlargement, as enlargement would cause severe distortion. The density of printed originals is lower than the density recognition capability of scanners. To prevent moiré patterns during electronic separation reproduction, the screen pattern must first be removed and blurred. If no descreening function is available, the screen angles must be adjusted.
#### Q: Why is it necessary to use a laser imagesetter to output halftone positive films?
#### A: Inkjet printers, laser printers, and laser imagesetters can all output transparent films for use as screen printing originals, but their densities and image precision (resolution) vary.
1. **Inkjet printers** can output transparent films and tracing paper. They print exceptionally vivid color documents and black-and-white files using colored ink. However, the density of the output film is low, and the quality is poor. These are only suitable for text and pattern screen printing.
2. **Laser printers** can also output transparent films and tracing paper. Using electrostatic imaging principles, toner adheres to the corresponding graphic areas on the photoconductor's surface to form an image. After heating, the toner melts and fixes onto the transparent base. The image consists of coarse toner particles, resulting in uneven gradations, low image density, loss of small dots, deformation of large dots, sand eyes, and dirt on the plate. These are suitable for pattern and text block screen printing but not for color halftone originals.
3. **Laser imagesetters** use lasers as the light source, modulated by crystal modulators or galvanometer systems, controlled by computers to expose silver halide film. After development, high-precision halftone silver halide negatives are obtained. The output from laser imagesetters has high resolution, high density, clean dots and lines, clear images, and rich gradations, making them the best negatives for halftone screen printing.
#### Q: Are small laser imagesetters available for purchase? Which models are recommended?
#### A: High-end printing jobs are usually sent to platemaking centers to output halftone silver halide negatives. Small laser imagesetters on the market, such as Hangguang GP9002 and Yingzhou Linden390, can output A3 silver halide films. Based on technical specifications, they meet the precision requirements for general screen printing tasks. Priced around 20,000~30,000 RMB, they are suitable for medium and small screen printing factories.