The Blog recently received the following question(s) about migratory slip development COF in a lamination:
one of our customer require a very thin laminated which is 37 PET/PE (12 micron polyester film & 25 micron PE film. Due to thin film structures, we have added 2% slip additive in sealing layer but after lamination with solvent less two component, we got higher C.O.F above the customers specification limit as defined by the customer. We have then further added some percentage of high slip film grades but after lamination the film to film C.O.F is still high on the polyester to polyester side and the PE to PE Side. We have increased the time of testing & re-checked the C.O.F. The C.O.F drops to some extent but not very much.
Now we need a solution in which we get stable C.O.F after lamination and under the range of specification limit. Kindly suggest how long to wait after lamination before we should test the samples & slitting the product. Also, how do we reduce this time and what will we do to get lower C.O.F values after lamination.
Answer(s): This is the classic problem with migratory slip technologies which I discussed in the original post which generated the question, and this question is very common for the use of migratory slip technologies. It is also common for slip films COF to drop after lamination and to then slowly recover if given enough time and sufficient slip in the film. The answer is multifaceted so will require a complex set of answers. Therefore, I will give a series of replies over the next several days to the various parts of the question(s) which relate to the problem of inconsistent slip bloom in films and in laminations so keep tuned in.
While we don’t know the type or concentrations of the migratory slip being used in this problem lamination, we can see form the question that the use of a “high” slip films shows some improvement but is not solving the problem. We also don’t know the COF target but for most slip films it would be a film to film COF of 0.2 so we will assume this level for the PE side. For the PET surface the COF should be controlled by the PET film formulation which would contain an anti block particle to set the PET COF. PET surface COF should also be affected to some degree by slip levels on the PET surface. The PET film to film COF should be checked before lamination to make sure the PET film is within specification for the customers target.
As I would not expect a great deal of slip migration into or through the PET film, slip on the PET surface would be controlled by transfer in the roll. In addition the lamination adhesive is likely scalping some additive from the PE lowering the slip concentration in the PE film and therefore on the PE surface. Lower PE slip concentrations will lower slip transfer to the PET surface and increase the COF on all film surfaces, unless we can boost the slip bloom to the PE surface. What I would also do for the PET surface is check the PET film for its antiblock formulation to insure it is in specification.
A first approach to improve the slip bloom would be to hot room age the lamination. What is hot room aging? As the question notes, the COF decreases if they wait longer to check the COF and they want to know how long to wait. This of course is a terrible situation for a production product. In general the rate of slip bloom will depend on the storage temperature, and the time of storage. For OPP slip films it was common to heat the film rolls to 49C for 72 hours to force the slip to bloom to the surface and lower the COF. While this generally worked, sometimes it did not (remember the question, is it winter yet?). So a first approach to see if the lamination COF will ever recover would be to take a stack of film samples and heat over night in an oven at 49C and measure the COF to see if it is dropping. This will determine if there is sufficient slip in the formulation for the COF to recover. I would plot COF vs. time at 49C and see if the COF drops and if it reaches a lower limit (hopefully below the customer specification). If necessary I would titrate the product slip level. What do I mean? If I am to use the migratory slip technology, I would prepare a series of laminations with different slip levels in the PE film. then I would age the samples at room temperature and in the oven as described and check the COF off line and every 24 hours after that and see how low the COF drops as a function of slip concentration and storage time and temperature. Then I would choose the PE slip formulation to meet the customer requirements for COF.
In the long run I would change the COF technology to get a more robust product design and I will outline this after I break down this question further.