Hi to all,
First and foremost i would like to really express my gratitude and appreciation for this site/forum. The information that can be found here with regards to chemical science, mechanical know how, and especially hard won battles resulting in experience are a real treasure chest. During the last few days i have read many posts and replys, and the assistance given is truly unselfish and exceptional. A couple of the real stand out guys - please forgive me if i dont mention your name - Skip, Len, Louis, DwightDixon, you guys are awesome! I can only hope that one day I can know a fraction of what you guys have forgotten, and am modest enough to pass it on.
Ok now to the problem at hand... Let me first give you guys some background info - We are a smallish compounder based in South Africa, with the vast majority of our products being utilized in the cable and moulding industries. To date our products have done well in the market and fulfill our customers requirements (putting it this way cos i have come to realize we could improve here and there
Recently we have had enquiries to compound amongst others a clear flex grade for curtain material, and a clear flex grade for cling wrap. Sounds easy enough but we just dont seem to be able to manufacture either of them to be able to meet the required standards. Problems with the flex curtain grades are mostly around clarity and sometimes with the material sticking or streaking on the customers die. Problems with the cling also include clarity, but are mostly to do with what appears to be undispersed polymer gels that degrade on the customers machine and result in black spots on the cling wrap or a popped bubble.
Please excuse me for going on and on, but i hope to try and give you guys as much info to work with as possible. Also as previously stated i have read many posts regarding similiar problems and have tried to eliminate as many potential problems as possible before handing my work on to someone else to do......
i have tried these products on two of our lines which are:
1) Buss KD neader 1410, with segmented screws, take-off extruder into die-face with pellitizing head.
2) Buss Kneader 160mm solid screw, with right-angled take-off extruder into die face with pellitizing head. Take-off extruder bolts onto kneader to form compression zone>
The formulation for the cling is as follows:
Polymer (K71) Film grade 100phr
Stabiliser CaZn CZ116 2phr
Loxiol G10V 2phr
Stearic Acid 0,2phr
Lubex AF50 1phr
As for the cling material, I have :
1)Ensured the hi-speed mixer dump valve is not leaking dry resin into the hopper,
2)Tweaked the mixer sequence as recommended, ie polymer first to 65C, then plasticisor and stabilisor until dry point etc etc.
3)Increased the mixer dump tempereture to between 115 and 120C to try ensure volatiles are released.
4) Played with differnt temp settings on the compounder, as with feed vs screw ratios to try ensure better melt/fusion within the compounder, resulting in various melt plug lengths.
The material exiting the die face looks good, no discolouration(natural clear colour - slightly offwhite/yellow). We blow test samples in our lab and the "balloon" looks good, but on closer inspection has stretchmarks on the surface(for lack of a better description), also small polymer nibs are noticed. I think it is these nibs that are conglomerating in the customers machine and then being extruded out onto the film. Some stay a while longer and are then seen as black particles on the bubble. These look to be almost crystilline in appearance and are smooth and glossy.
Our sister company manufactures the same grade (formulation) with great success, but they do use a twin screw with a significantly higher LD ratio. So I ask the following questions:
1) Do you think the polymer gels are a result of the mixing process, or an insufficient state of fusion within the compounder, or a combination of both? If so, how do i determine this and what are possible solutions?
2) How can one determine if the state of fusion within the compounder is good enough?
3) How can one tweak the formulation to promote better fusion in the compounding stage and overall heat stabilty at the customers stage?
4) Am i correct is saying that one shouldnt use a formulation as a generic to cover all machine types, but basically adjust it to suit different machine types if not individual machines? If so what do you recommend one should bear in mind for the Busses?
As far as the flex for the curtains:
Polymer (K71) Film grade 100phr
Stabiliser - Reagens 398 2phr
Stearic Acid 0.4phr
Ultramarine Blue 0.012phr
The main concern here is clarity with sometimes a complaint that the material sticks on the die. Again it must be said that our sister company produces this material quite better than we can.( I might add at this point that we have tried to resolve this with our sister companies aid but as they have not really had these problems, they also are at a loss)
From the insights gained through this forum, I think our problem concerning the clarity is insufficient fusion in the Buss compounder? I have swopped out feed segments for additional mixing segments, resulting in the melt plug length increasing, and overall higher temperetures in the compounder and on the die face, but with the same poor clarity. Put too much heat and the pellets become a smear on the die-face....
External lubs might aid the sticking problem on the customers die, but this will again negatively impact on clarity?
How could i tweak or alter this formulation to better suit the Buss for fusion, whilst gaining clarity and improving the release on the die?
OY!! Looking at this, I realize I have asked for quite a lot of help, please believe me when I say it wasnt easy to come forth and stand in your shadows with the begging bowl in my hands.
Any and all advice or assistance would be greatly appreciatted.
Thanks and regards