[ Question ] Will the plastic bags coated enterprises should be how to choose the material ? What are the areas that need attention ?
[ Q ] Reference material for extrusion coating material more stringent requirements Bila Si , bad choice of raw materials , will produce illiquidity peel strength is insufficient. Thus, the selection of raw materials to the attention of the performance of the following points:
1, has good flow properties
Good flowability to film uniformity , coating uniformity of film thickness . As long coated die , especially foldback long coated on both sides at once die head, double head , wide tarpaulin with die material melt flow inside the die long distance , through a relatively long time , die within the resistance is large, do not choose a good resin flow will cause uneven thickness of the membrane , the flow rate range, the temperature of the die lip not wait , there will be a partial loss of the first cooling viscoelastic , and weaving cloth adhesive is not strong . Indicators to measure melt index of liquidity M1, in general, polyethylene is 4 ~ 15g/10min, polypropylene 7 ~ 30g/10min more appropriate.
2 , has a melt strength
The melt outflow from the die to have a certain viscoelasticity , that is higher melt strength . As the melt cast into the distance is a woven traction stretching process , there is a certain draw ratio , it requires a certain degree of intensity to melt not pulled broken or pulled off . The distance from the die mouth woven , as pulling speed die weight and inertia caused by other reasons , the melt flow properties can not be good to avoid uneven membrane reactor or vertical thickness , the resin melt index and can not too high. Stretching the melt index of the polypropylene material 2 ~ 6g/10min to appropriate values , it is inappropriate for the coating , the flow is too slow , easy to produce the phenomenon of uneven thickness .
3, has a good thermal stability
As coating conditions at a high temperature , the extrusion temperature is generally about 290 ℃ , Bila Si material higher. Resin melt coating film during contact with air , the surface oxidation reaction of a carbonyl group, increased binding capacity . However, the high temperature causes the polyolefin resins, particularly polypropylene, thermal aging . Thus to choose a good thermal stability resin .
4, other performance options
Select a narrow molecular weight distribution polyolefin resin . Wide molecular weight distribution will be uneven cast film flow stress , causing membrane split , size fluctuation margins , perforation and other phenomena . If the molecular weight is too high , there will be too fast crystallization rate , decrease the bond strength phenomenon . Resin not containing excess lubricant , to affect adhesion. Isotactic index of the resin should be greater than 95% , wherein the random content increased, the influence degree of crystallinity , the melt strength effect .
Currently on the market more types of coating materials . According to type of material is divided into two categories, namely, PP and PE ( polypropylene and polyethylene ) . In principle, the substrate is a woven polypropylene PP coating material should be selected , the substrate is woven polyethylene PE coating material should be selected . By the production process can be divided into homopolymers and copolymers . Domestic coating material to homopolymers based. Currently, the coating material and the second substrate is different coating materials for functional requirements are also different, so we had to blend modified based special coating material . Special coating material , although the scope is small, but highly targeted , can be applied to specific substrates coated and get the features it needs . Such as low temperature coating materials, coating materials such as anti-aging .