氣體反壓技術Gas Counter Pressure Technology,簡稱GCP),在1970年代開始有研究人員,在應用於射出成型的模內形成一個預定的壓力來改善發泡成型的成品表面品質。並在1980年後開始應用在工業上的用途。是用惰性氣體在射出成型機在射出動作前,在模穴內預先充滿一恆定的壓力的惰性氣體。 塑膠材料因受潮材料內會含有一定的比率的水分,在射出動作時,塑膠材料必須Tm點(融點軟化點)溫度以上,在高溫的狀況下,水分會形成氣泡,氣泡會浮於融溶塑料的表面上。氣泡在表面上,會因流動的方向被拉成長條銀色的絲條狀,這是所謂的銀紋;本研究在塑膠材料在作射出動作原料流入模腔時,利用模腔內有一定的恆定惰性氣體壓力,此時的惰性氣體壓力一開始就能抑制融膠進入時的發泡,使塑膠材料成品表面因而不會有銀紋現象。 研究結果顯示,原料的含水率高低與射出樣品表面銀紋的多寡有正面的關係;受潮原料在射出時,使用氣體反壓(Gas Counter Pressure, GCP)是可以有效改善產品表面銀紋的現象。利用不同的氣體反壓壓力與不同含水率進行射出取其樣品分析比對,氣體反壓壓力越大,銀紋表面現象會因此而減少;當反壓壓力到50Bar時,不管含水率的多寡,表面已不見銀紋的現象,因此,證明氣體反壓製程是可以有效改善受潮原料在射出時的銀紋現象。當使用真空膏將排氣道封住,讓模腔形成密閉狀態,受潮原料射出樣品顯示產品的射出末端,銀紋現象會少於產品的射出前端,此一微觀的特徵對射出產品表面問題的解析有其幫助。
Gas counter pressure technology was developed in 1970 and was used in industry since 1980. This technology is to maintain a constant pressure in the mold before injection starts. Plastic pellets contain a certain percentage of vapor. During injection molding the melt was heated to melting temperature, the vapors grow into bubbles and will be flipped to the surface due to fountain flow effect and cause the silver streaks. This study focuses on using GCP to restrict the growth of vapors and avoid the silver streaks under different polymer moisture content. The results show that the silver streaks were affected mainly by the polymer moisture content. Further more GCP can eliminate the silver streaks under highly moisture material. When the GCP raised to 50 bar, the silvery streaks can be eliminated under different moisture content polymer. On the other hand, using vacuum glue to seal the mold is also helpful in reduce the silver streaks.