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Converters in the sealant, tape and damping business buy a polymer but sell a promise: that a facade joint will not leak for twenty years, that a roll of tape will still stick after a summer in a warehouse, that a floor pan will not boom at highway speed. Each of those promises is decided by how the compound is built around the butyl, not by the grade name on the bag. This guide sets out what a converter should specify, and what to test, when choosing among the butyl and halobutyl grades used for sealants, tapes and damping compounds.
Three Product Forms, Three Different Compound Logics
The same polymer family ends up in products that behave nothing alike, because the compounder is asked to deliver a different balance of flow and cohesion in each. Before comparing grades, fix which of these you are actually making, since the answer changes every later decision.
| Product Form | Cure State | What It Must Do | How It Usually Fails |
|---|---|---|---|
| Mastic, caulk and solvent-borne sealant | Uncured, permanently tacky | Wet the substrate, stay flexible, resist slump in a vertical joint | Skinning in the cartridge, sag, loss of adhesion after weathering |
| Butyl tape and preformed sealant strip | Uncured or lightly cured | Hold permanent tack, resist flow at warehouse temperature, peel cleanly from release liner | Cold flow off the roll, liner transfer, cohesive split when unwound |
| Damping sheet and sound deadener | Cured, heavily filled | Convert vibration to heat across a temperature band, bond to panel through paint bake | Inconsistent damping after a filler change, blistering, poor panel adhesion |
| Waterproofing membrane and flashing | Cured or semi-cured | Hold a continuous barrier at low gauge, survive site handling and overlap | Pinholes from poor dispersion, seam failure, cracking at cold bend |
Notice how little of that is about air permeability, which is the property butyl is usually sold on. In sealants and tapes, the permeability of the polymer sets a ceiling on performance, but what the customer experiences is tack, cohesion and ageing. In damping, the polymer is a matrix for filler, and the filler does most of the acoustic work.
Four Grades, and Why Two of Them Share the Same Mooney
Chambroad Sinopoly's butyl and halobutyl range includes four grades that converters most often evaluate for these products. The values below are the ones published on the company's grade pages and in its submitted material documentation:
| Grade | Architecture | Mooney ML(1+8) 125°C | Volatile Matter | Where It Fits |
|---|---|---|---|---|
| IIR1953 | Linear general-purpose butyl | 51.0 ± 5.0 | ≤ 0.3 wt% | Mastic and tape bases where green strength and cost matter |
| BIIR2828 | Brominated butyl | 32.0 ± 4.0 | ≤ 0.50 wt% | Highly filled or highly plasticised compounds; adhesion-critical bonds |
| CIIR1338 | Chlorinated butyl | 38.0 ± 4.0 | ≤ 0.50 wt% | Industrial and chemical-exposed seals; heat-ageing service |
| SIIR | Star-branched halogenated butyl | 38.0 ± 5.0 | ≤ 0.50 wt% | Damping and high-strength sealing where filler loading is high |
CIIR1338 and SIIR sit at the same Mooney centre, which is exactly why they make a useful comparison. Mooney measures resistance to flow, not the shape of the molecule, and a star-branched polymer with the same viscosity as a linear one behaves differently in every step after mixing. The branches raise tensile and tear strength and improve filler dispersion, which is why the branched grade is positioned in the sealing and shock absorption range for high-frequency vibration work. Chambroad publishes a comparison of 4.7 percent better filler dispersion and 8 to 12 percent better air tightness against conventional butyl for the branched grade, together with a shorter mixing time and a wider cure window. Those are the supplier's own figures, and the sensible way to treat them is as a hypothesis to test on your mixer, not as a specification.
The remaining three grades separate cleanly by job. IIR1953 is the high-viscosity general-purpose base: it develops green strength early, which is what a mastic or a preformed strip needs to hold shape, and it carries the tightest volatile limit in the group at 0.3 wt%. BIIR2828 at 32 Mooney is the grade that lets you push filler and oil loading without losing processability, and its brominated cure site is what makes a cured bond to a substrate achievable. CIIR1338 cures on zinc oxide alone and is the choice where the seal sees heat or chemical exposure rather than permanent tack.
The Tack and Cohesion Trade-Off Nobody Warns You About
In an uncured tape or mastic, tack is the product. In the warehouse and in the customer's process, tack is also the problem. A compound formulated for high immediate tack usually gives some of that back as cold flow: the roll deforms under its own weight, the liner transfers, and the tape that felt perfect on the bench is unusable after a month in a container.
Specify the balance explicitly, in numbers, and do it with two tests rather than one. Probe tack tells you what happens in the first second of contact. A shear or creep test at elevated temperature tells you what happens over a summer. A compound can pass the first and fail the second, which is why converters who qualify on tack alone end up reformulating after the first hot shipment.
Three levers control the balance, and they interact. Tackifier resins raise immediate adhesion while lowering cohesion if overdone. Plasticiser and process oil improve wetting and low-temperature flexibility but migrate, and migration is what causes staining on porous substrates. Polymer architecture sets the floor: a branched grade holds more cohesion at the same viscosity, which buys formulation room you would otherwise have to find in the resin system.
Filler Loading Decides Damping, and Dispersion Decides Repeatability
A damping sheet is mostly filler by weight. The polymer's job is to hold that filler in a continuous matrix that stays bonded to the panel and converts strain into heat over the temperature range where the vehicle or machine actually vibrates. That makes two things critical: how much filler the compound accepts, and how evenly it is distributed.
Loading capacity is a viscosity question, which is why a low-Mooney grade such as BIIR2828 is often the practical starting point for heavily filled sheets and a branched grade earns its place where strength cannot be sacrificed for loading. Distribution is a mixing question: undispersed filler creates local stiff and soft regions, and the acoustic result stops matching the design intent even though every ingredient is on the batch card.
Damping performance is also temperature-dependent by nature. Every viscoelastic compound has a transition band where loss factor peaks, and the formulation shifts that band. Ask for the loss factor curve, not a single number, and check it at the frequency and temperature your application actually sees. A supplier who can only quote one loss factor at room temperature is giving you a marketing figure.
Process Decisions to Settle Before You Buy Polymer
- Solution or hot melt. Solvent-borne mastics are built by dissolving the polymer, and solution viscosity does not track Mooney in a straight line. Ask the supplier for the grade's behaviour in your solvent at your solids level before you commit to a viscosity target.
- Uncured or cured. An uncured tape lives on permanent tack and has no crosslink to rely on for cohesion. Once you decide to cure, the ZnO addition point for a chlorinated grade becomes a process constraint, not a detail: zinc oxide starts the cure on contact at temperature and must go in late with the mixer running cool.
- Mixing temperature. Butyl masticates and warms quickly, and a compound that reaches scorch temperature in the mixer will show up as a rough extrudate rather than as a failed batch. Record the dump temperature every batch and treat a drift as a signal.
- Volatiles and porosity. A dense damping sheet or a thin membrane has nowhere for gas to escape during cure. This is where the 0.3 wt% volatile limit of the general-purpose grade and the 0.50 wt% limits of the halobutyl grades stop being paperwork, and where asking for the actual batch value rather than the limit pays for itself.
A Converter's Test Plan
Run these on your own compound, cured or aged on your own cycle, before you write a purchase order:
- Probe tack and peel adhesion on the actual substrate, not on a standard test panel. Aluminium, galvanised steel, PVC and painted panel each behave differently.
- Shear or creep at elevated temperature to fix the cold-flow limit of an uncured product.
- Cold bend or low-temperature flexibility for membranes and tapes that will be installed in winter.
- Gas or water-vapour permeability on a sheet at production gauge, using the method your laboratory is accredited for.
- Loss factor by dynamic mechanical analysis across the service temperature band, for any damping product.
- Heat ageing and weathering, including adhesion retention after water immersion and UV exposure.
- Bleed, staining and odour, especially for interior automotive and building products where a migrated plasticiser becomes a warranty claim.
Keep a retained sample of every polymer lot alongside the finished-product test results. When a damping sheet drifts or a tape starts to flow, the retained sample is what tells you whether the polymer moved or your process did.
Supplier Verification for a Converter
Automotive NVH and sealing supply chains push IATF 16949 expectations back onto the polymer producer, and building products push consistency and documentation expectations instead. Either way, the questions are the same. Chambroad Sinopoly's submitted documentation lists IATF 16949 and ISO 9001 quality certification for the butyl and halobutyl plants, together with ISO 14001 environmental certification numbered 00225E33461R2M, ISO 45001 occupational health and safety certification numbered CQM25S23270R2M, and ISO 50001 energy management certification numbered 00225EN0790R1M. Check the scope line and the validity dates on each before you file them.
- Batch trend, not batch certificate. Ask for the last twenty Mooney and volatile results and look at the spread inside the window. A converter running a tight extrusion or calender cares about the spread far more than about the midpoint.
- Delivery form. Bale size, wrapping and anti-tack agent all affect your handling and your contamination risk; confirm them against your mixer's feed arrangement.
- Contamination control. Metal detection and grade segregation through the line, because a fragment in a membrane becomes a leak and a fragment in a damping sheet becomes a rejected part.
- Change notification. A written clause covering process and formulation changes, so a reformulated polymer does not silently invalidate your customer's approval.
What to Put in the Enquiry
- Product form and cure state: mastic, tape, damping sheet or membrane, cured or uncured.
- Target viscosity in your process, whether that is Mooney, solution viscosity or melt index equivalent.
- Filler and oil loading you intend to run, as parts per hundred rubber.
- Service temperature band and the substrate you must bond to.
- Documents wanted: current grade sheet with test methods, batch trend data, management-system certificates with scope.
- Sample quantity and delivery form, plus the packaging you will run in production.
Related material sits in the weather-resistant sealing, sound insulation and waterproof membrane sections, and the full grade list is under rubber products.
Reformulating a Sealant, Tape or Damping Compound?
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