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透明聚碳酸酯PC加玻纖塑料件加工注意問題
透明塑膠PC+gf產品由于透光率要高,所以PC+gf塑料制品表面質量的要求必須嚴格,不能有任何斑紋、氣孔、泛白、霧暈、黑點、變色、光澤不佳等缺陷,因而在整個注塑過程對原料、設備、模具、甚至產品的設計,都要十分注意和提出嚴格甚至特殊的要求。
另外,由于透明PC+gf塑料多為熔點高、流動性差,因此為保證產品的表面質量,往往需要較高的溫度,注射壓力、注射速度等工藝參數也要作細微調整,使注塑料時既能充滿模,又不會產生內應力而引起產品變形和開裂。
因此從原料準備,對設備和模具要求、注塑工藝和產品的原料處理幾方面都要進行嚴格的操作。
1.原料的準備與干燥
由于在PC+gf塑料中含有任何一點雜質,都可能影響產品的透明度,所以在儲存、運輸、加料過程中都必須注意密封,保證原料的干凈。
特別是原料中含有水分,加熱后會引起原料的變質,所以一定要做干燥處理。在注塑的時候,加料必須使用干燥的料斗。還要注意一點的是干燥的過程中,輸入的空氣最好應經過濾、除濕,以便保證不會污染原料。
2.機筒、螺桿及其附件的清潔
為防止PC+gf原料污染和在螺桿及附件凹陷處存有舊料或雜質,特別在熱穩定性差的樹脂存在,因此在使用前、停機后都應用螺桿清洗劑清洗干凈各件,使其不得粘有雜質,當沒有螺桿清洗劑時,可用PE、PS等樹脂清洗螺桿。
當臨時停機時,為防止原料在高溫下停留的時間過長,引起解降,應將干燥機和機筒溫度降低,如PC+gf、PMMA等機筒溫度都要降至160℃以下(料斗溫度對于PC應降至100℃以下)。
3.在模具設計上應注意的問題
為了防止出現原料回流動不暢,或冷卻不均造成塑料成型不良,產生表面的缺陷和變質,一般在模具設計時候,應該注意以下幾點:
壁厚應盡量均勻一致,脫模斜度要有足夠大;
過渡部分應圓滑,并逐步過渡,防止有尖角、銳邊產生,特別是PC+gf產品一定不要有缺口;
澆口、流道盡可能寬大、粗短,且應根據收縮冷凝過程設置澆口位置,必要時應加冷料井;
模具的表面應光潔,粗糙度低(最好低于0.8);
排氣孔。槽必須要足夠,以及時排出空氣和熔體中的氣體;
除PET外,壁厚不要太薄,一般不得小于lmm。
4.注塑工藝方面應該注意的問題
為了減少內應力和表面質量缺陷,在注塑工藝方面應注意以下幾方面的問題:
注射壓力:一般較高,以克服熔料粘度大的缺陷,但壓力太高會產生內應力造成脫模因難和變形;
注射速度:在滿足充模的情況下,一般宜低,最好能采用慢一快一慢多級注射;
保壓時間和成型周期:在滿足產品的充模,不產生凹陷、氣泡的情況下;宜盡量短,以盡量減低熔料在機筒停留的時間;
螺桿轉速和背壓:在滿足塑化質量的前提下,應該盡量低,為防止產生解降的可能;
模具溫度:制品的冷卻好壞,對質量影響極大,所以模溫一定要能精確控制其過程,有可能的話,模溫宜高一些好。
5.其他方面的問題
由于為了要防上表面質量惡化,一般注塑的時候應盡量少用脫模劑;當用回用料時不得大于20%。
對于除PET外,制品都應進行后處理,以消除內應力,PMMA應在70-80t熱風循環干燥4小時;PC應在清潔空氣、甘油、液體石臘等加熱110-135℃,時間按產品而定,最高需要10多小時。而PET必須經過雙向拉伸的工序,才能得到良好機械性能。
部分型號部分物性表
EVA (ethylene vinyl acetate copolymer #) /1375/ America flintcomb ash
Use: other
Feature notes: food packaging, general use
Important parameters: melt flow rate: 2 g/10min density: 0.924 g/cm3 tensile strength: 12 MPa breaking elongation: 700% hardness: 48 VEKA softening point: 90 C
Manufacturer: American flint Hill resources
EVA (ethylene vinyl acetate copolymer # /625/ TOSOH)
Use: other
Important parameters: melt flow rate: 14 g/10min density: 0.935 g/cm3, tensile strength: 12 MPa elongation at break: 640% bending modulus: 50 MPa hardness: 94 VEKA softening point: 57 C embrittlement temperature: -70 C
Manufacturer: Tung Cao Co., Ltd., Japan
EVA (ethylene vinyl acetate copolymer #) /UE-1825/ Brazil Quattor
Use: foaming
Important parameters: melt flow rate: 2.5 g/10min density: 0.94 g/cm3 tensile strength: 13 MPa breaking elongation: 855% hardness: 41 thermal deformation temperature: 63 C
Manufacturer: Quattor Petrochemical Industries Co, Brazil
EVA (ethylene vinyl acetate copolymer #) /3150/ DuPont dow
Use: Film
Characteristic notes: heat stabilizers, BHT antioxidants
Important parameters: melt flow rate: 2.5 g/10min density: 0.94 g/cm3 VEKA softening point: 69 centigrade filler content: 15%
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /3180/ DuPont dow
Use: hot-melt
Characteristic notes: heat stabilizers, BHT antioxidants
Important parameters: melt flow rate: 25 g/10min density: 0.95 g/cm3 VEKA softening point: 43 centigrade filler content: 28%
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /150/ DuPont dow
Use: hot-melt
Characteristic notes: heat stabilizers: Antioxidants of BHT
Important parameters: melt flow rate: 43 g/10min density: 0.957 g/cm3 VEKA softening point: 36 centigrade filler content: 32%
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /240/ DuPont dow
Use: hot-melt
Characteristic notes: heat stabilizers: Antioxidants of BHT
Important parameters: melt flow rate: 43 g/10min density: 0.951 g/cm3 VEKA softening point: 40 centigrade filler content: 28%
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /560/ DuPont dow
Use: Film
Characteristic notes: heat stabilizers: BHT antioxidants
Important parameters: melt flow rate: 2.5 g/10min density: 0.935 g/cm3 VEKA softening point: 71 centigrade filler content: 15%
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /FL 00226CC/ Mobil Exxon
Use: other
Important parameters: hardness: 83 VEKA softening point: 46.9 C
Manufacturer: Exxon Mobil Corp
EVA (ethylene vinyl acetate copolymer #) Yanshan petrochemical /155/
Use: film, foaming, pipe
Characteristic notes: foaming, film, tube extrusion
Important parameters: melt flow rate: 2 g/10min
Manufacturer: Sinopec Beijing Yanhua Petrochemical Limited by Share Ltd
EVA (ethylene vinyl acetate copolymer # Lotte chemical /VE700/)
Use: other
Characteristic notes: antioxidants, automatic flow auxiliaries
Important parameters: density: 28 g/cm3 hardness: 69 VEKA softening point: 40 C
Manufacturer: Korean Music Corporation
EVA (ethylene vinyl acetate copolymer #) Yanshan petrochemical /4F2/
Use: other
Important parameters: melt flow rate: 2.2 g/10min
Manufacturer: Sinopec Beijing Yanhua Petrochemical Limited by Share Ltd
EVA (ethylene vinyl acetate copolymer #) Yanshan petrochemical /9J1/
Use: other
Important parameters: melt flow rate: 0.9 g/10min
Manufacturer: Sinopec Beijing Yanhua Petrochemical Limited by Share Ltd
EVA (ethylene vinyl acetate copolymer #) /11D569/ DuPont dow
Use: other
Important parameters: melt flow rate: 13 g/10min density: 0.938 g/cm3 VEKA softening point: 63.9 C
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) /11D625/ DuPont dow
Use: other
Important parameters: melt flow rate: 7.3 g/10min density: 0.94 g/cm3 VEKA softening point: 68 C
Manufacturer: Dow DuPont Co
EVA (ethylene vinyl acetate copolymer #) Yanshan petrochemical /9J2/
Use: foaming
Important parameters: melt flow rate: 2.1 g/10min
Manufacturer: Sinopec Beijing Yanhua Petrochemical Limited by Share Ltd
EVA (ethylene vinyl acetate copolymer #) /28150/ MPI
Use: other
Characteristic notes: high fluidity
Important parameters: melt flow rate: 150 g/10min density: 0.946 g/cm3 tensile strength: 43.4 MPa breaking elongation: 641% flexural modulus: 13.1 MPa hardness: 72
Manufacturer: MPI company, USA
EVA (ethylene vinyl acetate copolymer #) /1626/ Korea China
Use: other
Characteristic notes: copolymer, good processability
Important parameters: melt flow rate: 3 g/10min density: 0.949 g/cm3 fracture elongation: 900% VEKA softening point: 48 C embrittlement temperature: -76 C
Manufacturer: Korea Hwa comprehensive chemical company
EVA (ethylene vinyl acetate copolymer #) /1628/ Korea China
Use: other
Characteristic notes: copolymer, good processability
Important parameters: melt flow rate: 18 g/10min density: 0.949 g/cm3 fracture elongation: 920% VEKA softening point: 46 C embrittlement temperature: -76 C
Manufacturer: Korea Hwa comprehensive chemical company
EVA (ethylene vinyl acetate copolymer #) /NUC-3223/ Japan Younika
Use: other
Important parameters: melt flow rate: 1.4 g/10min density: 0.93 g/cm3 tensile strength: 20 MPa breaking elongation: 700%
Manufacturer: onica Corporation, Japan