Shanghai Daoqin Plastics Co., Ltd.

流体 viscosity 不随剪切 speed rate 变化而变化, this type of 流体称之 is 牛顿流体, water, gas 体, low separation combined material liquid or solvent liquid is type 牛顿流体.

if viscosity 依赖于 for its speed rate, this 样 流体 is non 牛顿流体, large separation plastics melt performance is non 牛顿流体 features.

non 牛顿流体也 has multiple, plastics in melt lower performance features in in, is strip/profile force speed upper rise rear slow upper rise 曲线, and in 屈服应 force, this is plastics melt 剪切变 dilute flow features. 即剪切 speed rate increase need ratio force increase fast.

图1 剪切 speed rate and 剪切应 force 关系

and versus for is 剪切变 thick phenomenon. is Common plastics melt 都呈现 is 剪切变 dilute, is 随 剪切 speed rate increase, melt viscosity need reduce, viscosity reduce has plastics melt in mold type in flow and filling.

injection molding process in plastics need through material add hot, rear injection molding machine nozzle, mold runner, runner and mold gate, most rear type 腔. melt 经 各 部 separation speed rate and viscosity 关系如图2 示, table/sheet 明, plastics melt in material in viscosity relatively high, flow speed degree small, to gate rear, due to gate shrinkage function, make melt flow speed degree increase, increase large speed rate, reduce melt viscosity, has melt 充模. wide MWD resin ratio narrow distribution resin 剪切变 dilute degree large.

图2 剪切 speed rate viscosity 关系

viscosity is plastics processing property most important basic concept 之一, is for flow property amount table/sheet 示, effect/influence viscosity factors has melt temperature degree, pressure, speed rate and versus for separation quality and other, lower separation 别叙述.

图2: plastics melt 化吊灯

由 front analysis already 经知道, plastics viscosity is speed rate 函数, is, plastics viscosity meanwhile to temperature degree effect/influence. therefore, has speed rate 恒定时, research temperature degree for viscosity effect/influence has 实际意义. generally 说, plastics melt viscosity property need ratio for function strong/high. research table/sheet 明, temperature degree rise high, plastics melt viscosity 呈指数函数 methods decline. this is is, temperature degree rise high, make separation 子间, separation 子链间 运动 add fast, from make plastics separation between reduce, separation between increase large, from 而导致 viscosity reduce. easy molding, products shrinkage rate large, also 会引起 separation understanding, temperature degree low, melt viscosity large, flow difficult, molding property 差, and elastic property large, make products stability property 差.

但 is different plastics viscosity for/regarding temperature degree 敏感程 degree different. polyoxymethylene (POM) for temperature degree most 不敏感, its is polyethylene (PE), polypropylene (PP), polystyrene (PS), most need acid fiber 素, table/sheet 1 in 列出 一 commonly used plastics for/regarding temperature degree 敏感程 degree. non 常敏感 plastics, temperature separation important, viscosity relatively large 变化, make as unstable, effect/influence product quality.

table/sheet 1 一 plastics viscosity temperature degree effect/influence degree

in use in, for/regarding temperature degree property good melt, can in molding process in improve/increase plastics molding temperature degree improvement plastics flow property can, 如PMMA, PC, CA, PA. is for/regarding property plastics, improve/increase temperature degree for/regarding improvement flow property can obvious, therefore generally using/adopting improve/increase temperature degree method its flow features. 如POM and PE, PP and other non property plastics, make temperature degree rise degree very large, viscosity reduce very small.

also has, improve/increase temperature degree must to conditions made, is molding temperature degree must in plastics molding temperature degree scope/range inner, 否则, plastics 就会发生 degradation. molding equipment loss consumption large, as conditions 恶化, 不偿失. utilizing active can large small table/sheet material material viscosity and temperature degree 关系, has amount 意义. table/sheet 2 is plastics in low speed rate lower active can.

table/sheet 2: plastics active can （kJ/mol）

plastics melt internal separation between, separation between tool has micro small 空间, 即 谓 自由体积. therefore plastics is can pressure shrink. injection process in, plastics to external pressure most large can to 几十甚至几百MPa. in pressure function lower, large separation between decrease small, active scope/range decrease small, separation 子间距离 shrink small, separation function force increase, make 链间 错动则 more is difficult, performance is overall viscosity increase large.

但 is different plastics in pressure lower, viscosity increase large degree same. polystyrene (PS) （PS） for/regarding pressure 敏感程 degree most high, increase pressure 时, viscosity increase very fast. high density polyethylene (PE) and low density polyethylene (PE) versus ratio, pressure for viscosity effect/influence relatively small, polypropylene (PP) pressure effect/influence versus in and other degree polyethylene (PE).

increase pressure viscosity increase this 一事实 table/sheet 明, mono pure through increase pressure improve/increase plastics melt amount is 不恰当. high pressure not only can obvious improvement filling, but also due to viscosity increase, filling property can has also has decline can can, not only formed more rate loss consumption and large equipment abrasion loss, also 会引起溢 material and increase products internal stress and other 弊病. in addition, pressure high, also 会出现 products deformation and other injection molding defect, 导致功 rate degree consumption. pressure low 则会造 formed material.

结 combined temperature degree for/regarding viscosity effect/influence can 发现, in plastics positive processing parameters scope/range inner, increase pressure for plastics melt viscosity effect/influence and reduce temperature degree for/regarding plastics viscosity effect/influence versus 似. for/regarding very more plastics, pressure increase to 100 MPa时, its viscosity versus reduce temperature degree 30～50℃ function.

几 types plastics for/regarding pressure 敏感程 degree table/sheet 3 示.

table/sheet 3: pressure for plastics melt viscosity effect/influence

随 剪切 speed rate add large, plastics viscosity generally reduce. in speed rate very low and very high lower, viscosity 几乎不随剪切 speed rate 变化而变化.

in temperature degree and pressure front lower, different plastics viscosity reduce degree same. or 者说, tube/pipe large more plastics melt viscosity is 随 剪切 speed rate increase decline, is different plastics for speed rate （切应 force ） 敏感程 degree is 不一样.

几 types commonly used plastics viscosity for/regarding speed rate property table/sheet 4 示.

table/sheet 4: plastics melt viscosity for speed rate degree

this for use is: in 一定 剪切 speed rate scope/range inner, improve/increase speed rate significantly reduce plastics viscosity, improvement its flow property can. tube/pipe 如此, can selection in melt viscosity for speed rate 不太敏感 scope/range process adjustment, 否则因 is speed rate 波动, formed processing unstable and plastics products quality upper defect.

for/regarding plastics, in to temperature degree lower, versus for separation quality increase large, plastics viscosity increase large. versus for separation quality large, separation function force strong/high, is viscosity high.

plastics versus for separation quality small, viscosity for/regarding speed rate 依赖程 degree small; molecular weight large, viscosity for/regarding speed rate 依赖程 degree large. molecular weight distribution wide resin and di molecular weight distribution resin melt viscosity low and processing property excellent 良. is low molecular weight separation has improve/increase resin melt flow property.

（5） low molecular weight additives effect/influence

low separation can reduce large separation 子链间 function force, 起“ lubricated ” function make melt viscosity decrease/reduce, meanwhile reduce viscous temperature degree. add increase agent and solvent agent, make resin easy 于充模 molding.

table/sheet 5: commonly used plastics flow property can methods

总之, polymer melt viscosity large small effect/influence injection molding process difficult easy. control certain plastics molding temperature degree in its separation understanding temperature degree below/following, speed rate is 103秒-1时, melt viscosity is 50～500帕－秒, injection molding relatively easy. if viscosity large, requirements has relatively high injection pressure, products large small to made, but also products also easy defect; if viscosity small, phenomenon heavy, product quality 也不容 easy ensure, in this type of lower requirements nozzle has plant/unit.