數位印版在紙張上之網點複製特性

Abstract

電腦直接製版技術（CTP）在國外經多年的研發與市場變動的迫切需求後漸趨成熟，在國內卻最近三年才逐漸引進。電腦直接製版為將電腦編排完成的數據資料，以雷射光束掃描在 CTP 印刷版材上直接製版，因省略輸出底片過程，節省印刷成本和大幅縮短印刷前製作業時間。由於看好 CTP 的潛力無窮，技術的導入及應用成為投資業界關注的焦點，除了投資成本、高速網路傳輸作業、系統整合、教育訓練等為業界所評估外，各種 CTP 版材之網點複製能力與製程穩定性更是考量評估的重點之一。因此，本研究以實驗研究法為本質，針對目前印刷業界較常採用之三種主流 CTP 版材作為實驗對象，另外，並採用平版業界普遍使用之傳統 PS 鋁版作為比較對象，旨在探討三種主流 CTP 版材和傳統 PS 版彼此間在印版及其印刷品之網點複製能力差異性和穩定性之比較。每種版材利用其專屬印版輸出設備各輸出 20 套，採用 GretagMacbeth D118C 量測每一塊版的特定區域之網點面積，並將其個別觀察值並輸入電腦記錄及匯整，利用管制圖來檢測其網點複製特性及穩定性，從四種版材中分別選取各自版材中網點複製穩定性最佳之 5 套印版以實際進行印刷，每套印版各印製 100 張印刷品並以系統隨機抽樣方式從中各抽取 50 張樣本，因此實驗共得 1000 張樣本（20套印版 x50張紙），本研究以 GretagMacbeth SpectroEye 量測儀器來測量每一張樣張特定區域之網點面積、滿版濃度以及印刷反差，並將其數據記錄、匯整，藉以分析各種版材彼此間在印版及其印刷品之網點複製特性（Dot Reproduction）的差異，結果顯示，在印版之網點複製部分，四種版材以銀鹽 CTP 版複製之印版網點面積最接近原稿階調；感光樹脂 CTP 版和熱感式 CTP 版複製之印版各階調網點面積均有網點擴大／減少的現象；在印刷品之網點複製部分，感光樹脂 CTP 版在10%、25%、50%、75%、90%等階調之網點面積百分比均為最大，而傳統 PS 版的網點面積百分比則較小；印版到印刷品網點複製部分，銀鹽 CTP 版印製之印刷品在網點擴大百分比為最小，感光樹脂 CTP 版從印版到紙張上之網點擴大百分比則較其他三種版材高。

Computer-to-plate (CTP) is a completely electronic system that produces print- ing plates for direct mounting on the printing press without the use of film. With CTP technology, text and graphics are digitally transferred directly from the computer to the printing plate, making the image on the plate a potentially more accurate repro- duction than one done from film. Computer-to-plate reduces the plate-making process to minutes instead of hours. Compared with the conventional printing method, the CTP technology can save manpower and production time for printers, as well as reduce pollution. The adaptation of, and investment in, CTP techno- logies has been a major issue in Taiwan’s printing industry since 1998. The main considerations regarding CTP investment include CTP's production time, cost and dot-reproduction stability and quality. Therefore, the stability of the CTP plates and their quality of tone reproduction are the two major concerns of potential CTP investors. This experimental study investigated the differences between three major CTP plates and one conventional Pre-sensitized (PS) plate in Taiwan, with regard to dot- reproduction quality, stability, and relative capability on paper. The CTP plate materials used in this experiment included Silver Halide, Photopolymer, Thermal and PS plates. A digital test form and color con- trol bars were designed for the three CTP plates, and a film generalized from the test form and color bars was also developed for exposing the PS plates. Twenty sets of plates were used for each of the four plate types, and their dot images were measured by GretagMacbeth D 118C. The plate readings were then entered onto statistics soft- ware for analysis and the best 5 sets of plates were selected for the final press runs. One hundred sheets were printed for each set of plates and 50 of them were randomly selected for the final analysis. Therefore, a total of 1000 printed sheets were sampled and read by a Gretag SpectroEye. The dot r