Kanglibang CL-26AB-5 Silicone Primer for Bonding PP

I.What is CL‑26AB‑5? Can it bond PP?
Yes, but with a prerequisite.
CL‑26AB‑5 is a two‑component, single‑coat heat‑curing silicone adhesive/primer developed by Kanglibang for thermal‑vulcanisation bonding of difficult‑to‑bond plastics (PP, nylon, etc.) to silicone rubber.
It is applied during injection moulding or compression moulding at elevated temperatures, allowing uncured silicone to cure and bond to the PP part directly in the mould. However, the PP surface must be pretreated by corona, plasma, or flame treatment for CL‑26AB‑5 to deliver its full bonding strength.
Typical applications: silicone‑PP baby bottles, PP protective tapes/films, PP seals, etc.
 

II.Why is PP difficult to bond, and how does CL‑26AB‑5 overcome this?
PP (polypropylene) is a non‑polar material with a very low surface energy (approx. 29–32 mN/m) and high chemical inertness. Most adhesives cannot wet it properly or form chemical bonds, which is why PP is considered “hard‑to‑bond”.
CL‑26AB‑5 solves the problem in two stages:
1. Surface pretreatment (the critical step): Corona, plasma, or flame treatment introduces polar groups (e.g. hydroxyl, carbonyl) onto the PP surface, raising its surface energy and chemical reactivity.
2. Chemical bonding: CL‑26AB‑5 contains special adhesion promoters and coupling agents. During hot vulcanisation, these react with the activated polar groups on the pretreated PP surface and simultaneously crosslink with the silicone rubber network. This creates a strong chemical anchorage – when tested, the silicone tears while the adhesive layer remains intact.

III. Is there a quantitative standard for the corona/plasma treatment?
Yes. After corona, plasma, or flame treatment, the PP surface energy should reach 38 mN/m or higher (dyne level). A dyne pen is a quick and practical tool to verify this: if the treated surface shows a dyne value ≥38, it is considered ready for adhesive application.
Flame treatment is also effective, but careful control of flame distance and exposure time is required to avoid surface degradation or distortion of the PP part.

IV. What bonding performance can be expected?
• Adhesion strength: Strong enough that the silicone substrate tears before the bond fails – the adhesive layer remains intact.
• Temperature resistance: ‑60 °C to 200 °C (long‑term); short‑term up to 230 °C.
• Environmental resistance: Good waterproof and shock‑absorbing properties.
• Food‑contact approval: The CL‑26 series has passed FDA, SGS, and LFGB food‑grade certifications, making it suitable for food‑contact applications.

V. Is CL‑26AB‑5 one‑component or two‑component? What are the storage requirements?
• Type: Two‑component – Part A (base adhesive) and Part B (platinum catalyst).
• Mixing ratio: A : B = 1 : 1 by weight.
• Shelf life: 3 months when stored unopened at ≤25 °C in a cool, dry place.
• Precautions: Contains organic solvents which evaporate easily; keep containers tightly sealedafter each use. Operate in a well‑ventilated area, away from heat and open flames.