Printing with PP/PE requires bed adhesion methods exclusive to polyolefins.
Polyolefins, are general-use thermoplastics with high surface energy and high polarity. In injection molding or screw extrusion, they are regarded as commodity plastics, meaning they are very common in our lives. Most of plastics we find on earth is PP or PE in some form.
They are easy to melt, process, and remelt although with decreasing Molecular Weight every cycle.
In 3D Printing, this is not the case. FDM 3D Printing today favors low-warp, low polarity, and low shrinkage polymers such as PLA and PET. And to an extent, ABS and PS. Polyolefins are basically the opposite of those.
To successfully 3D Print Polyolefins, standard methods of build plate adhesions like PEI coating and Glue coating fails right out of the first extruded line. Bare glass, Sitall glass, Borosilicate glass is of no exception to this case. This is caused by opposing polarities these materials have. Think water and oil, that’s what it is for Polyolefins and standard adhesion methods today.
However, it is not completely impossible. Methods such as packing tape, specialized PP glues, and using pure PP sheets as build surface have been successfully used in printing them.
The Packing Tape Method
Clear packing tapes are made of PP. One side is bare and the other side is lined with an adhesive that was corona-treated to laminate onto PP. This is the best way to start low-cost and works well for small prints. As printing PP requires high bed temperatures to increase the heat inside the build envelope, the adhesives starts weakening and the tape softens. This usually results in the printed object sticking well to the tape, but the tape peels off the build plate. This is also caused by bubbles during application that expands due to heating, effectively removing adhesion of the tape to the build plate. Warping of the printed PP itself contributes greatly to the failure as such :
Specialized PP Glue
Reports indicate that specialized glues for printing PP results in a positive experience. If it makes economical sense to the user, using them is much justified.
PP Sheets as Build Plates
Polyolefins such as PP and PE sticks only to themselves and nothing less. This method of using 1-3mm PP sheets as printing surface has existed since RepRap. Without heating, the print will stick. Unfortunately in most cases, it fuses completely, hence requiring labor and mechanical methods to release which would easily damage the sheets since they are thin and PP is easy to cut. Some use cases are okay with this, some are not. These sheets are usually quite cheap and easily replaceable. However, PP is very sensitive to heat and the sheets will bow and warp during printing, even without bed heat. The heat from the first layer alone will do this.
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PP Composites as Build Plates
MP-30, short for Materium Plate 30, is a PP copolymer and fiber composite. Its matrix is made from PP copolymer which fuses partially with PP. This adhesion method is similar to using pure PP sheets however, MP-30 is much stiffer and, formulated for 3D Printing with Recycled Plastics. The reinforcing fibers acts as stiffeners and a phase separator, preventing both warp and complete fusing at the same time. During use, the nozzle need not be squishing during first layer. It is even advised to give it more distance to ease separation after printing. Any extrudates that are deposited on MP-30 will stick due to like-to-like adhesion but still separable due to material difference. It is to be understood that with this type of adhesion, unlike Van der Waals commonly exploited by PEI beds, MP-30 is inherently a consumable to be replaced. With good care and use, it will last very long.
The first print on an MP-30 WILL leave marks and it is considered normal. Luckily, this only changes the surface roughness and esthetics. Sanding it may mask the marks. Sometimes, a chip off MP-30 may have fused too well with the print and taken apart during removal. This is also considered normal. With use, the surface will gradually become uneven and needs re-leveling.
Leveling or Tramming an MP-30 requires it to be heated to flattening temperatures. Since only mechanical means are used to clamp it (clips), heating will flatten a bowing/curving MP-30. Since it is a polymer, magnetic/inductive sensors used for Z-probe will NOT work. Only touch-based and mechanical-based probes are possible, unless the user chose to make modifications to the build plate, such as applying aluminium stickers on probing points.