Micanite is a composite of mica and a binder: mica paper or mica splittings are impregnated with shellac, epoxy or silicone resin and pressed in several layers under pressure and heat into sheets, foils and moulded parts. Commercial rigid mica sheets consist of at least 90 % mica and at most 10 % binder, withstand 500 °C continuously with muscovite and 700 °C with phlogopite, and hold more than 20 kV/mm at 20 °C (Hesselmann, datasheet Mikanit FEST HM, to IEC 60243). This article explains the mineral and its two types, the binders, the grades to IEC 60371, the properties of the rigid sheet, processing and applications, and it shows how we punch micanite into insulation and molded parts to drawing.
Micanite from GOBA: supply forms, thicknesses and enquiry
GOBA supplies Micanite from a single piece, as material or as a finished part to your drawing.
- Supply forms
- Sheet and board, Roll and slit roll, Cut-to-size, Die-cut part to drawing
- Thicknesses
- To your specification. GOBA processes materials from 7 µm to 3 mm.
- Versions
- As sheet or as roll, based on muscovite or phlogopite.
- Slit rolls
- Widths from 5 to 1,600 mm, tolerance ±0.1 mm, cores of 25, 55, 76 or 152 mm
- Die-cut and formed parts
- Material thickness 0.023 to 3.0 mm, dimensions up to 1,000 × 2,000 mm
- Quantity
- From 1 piece, from sample to series
- Lead time
- Two weeks at most when the material is in stock
What we need for your quotation
- Drawing or dimensions
- Quantity
- Material and thickness
For rolls also width, length, core diameter, core material (for example plastic) and tolerances.
Mica: the mineral that sets the first temperature limit of micanite
Mica is a sheet silicate. Its crystals split parallel to the layers into thin, tough flakes, and the Mohs hardness is 2 parallel to the layer and 4 across it (Wikipedia, mica group). For electrical insulation the point is that the mineral is inorganic: it contains no carbon chain that heat, ozone or partial discharge could decompose. Pure muscovite holds 25 to 200 kV/mm depending on the flake, has a relative permittivity of 7 and a dissipation factor of 1.5 to 5 x 10-4 at 1 MHz (Amidon, mica and glass capacitors). Why these values are so low is explained in the article on dielectric losses. More than half of the world’s natural mica comes from India (Wikipedia).
Muscovite, the potassium mica
Muscovite (KAl2[(OH,F)2AlSi3O10]) is colourless to silver grey, has a density of 2.77 to 2.88 g/cm³ (Wikipedia, muscovite) and is the most common and electrically best natural mica. It carries the higher dielectric strength and the higher tensile strength, but it starts to calcine at around 600 °C, meaning it gives off its water of crystallisation and becomes brittle (IDT Dichtungstechnik). That is why every manufacturer rates muscovite micanite at 500 °C continuous and 800 °C short-term.
Phlogopite, the magnesium mica
Phlogopite (KMg3[(F,OH)2AlSi3O10]) is amber to brown, not transparent, with a density of 2.78 to 2.85 g/cm³ (Wikipedia, phlogopite). It loses less than 5 % of its mass up to 1,000 °C (IDT Dichtungstechnik) and therefore carries 700 °C continuously and 1,000 °C short-term. In return, tensile and flexural strength are lower, and its thermal expansion coefficient of 27 x 10-6 /K is almost four times that of muscovite at 7 x 10-6 /K (HPF Minerals).
| Property | Muscovite micanite | Phlogopite micanite | Source |
|---|---|---|---|
| Continuous temperature | 500 °C | 700 °C | Hesselmann, Diel, Monoco |
| Short-term temperature | 800 °C | 1,000 °C | Hesselmann, Diel, Monoco |
| Tensile strength (ISO 527) | 140 to 150 N/mm² | 100 to 110 N/mm² | Hesselmann |
| Flexural strength (ISO 178) | 200 to 230 N/mm² | 170 N/mm² | Hesselmann, Diel |
| Dielectric strength, rigid (IEC 60243, 20 °C) | over 25 kV/mm | over 20 kV/mm | Dexlu |
| Expansion of the mineral | 7 x 10-6 /K | 27 x 10-6 /K | HPF Minerals |
Our recommendation: muscovite as long as the continuous temperature at the part stays below 500 °C. It is cheaper, electrically stronger and mechanically tougher. Phlogopite pays off only when the heating element really runs above 500 °C or when the sheet is exposed to arcs and metal splashes. Where mica sits on the temperature ladder above aramid paper and polyimide is set out in the article on high-temperature insulation.
Shellac, epoxy, silicone: the binder sets the second temperature limit
Mica flakes do not hold together without a binder. The first micanite around 1900 glued mica splittings with shellac (wissen.de, lexicon), and in 1923 a patent replaced shellac with a glycerol phthalate resin so that the sheet would survive a tin bath at 300 °C (DE 401485 C). Today the standard IEC 60371-3-9 permits shellac, alkyd, epoxy and silicone. The binder decides which of the two temperature limits applies:
- Shellac at 4 to 7 % binds commutator micanite for 130 °C, alkyd vinyl and epoxy at the same content for 155 °C (Asheville Mica, segment mica). Here the binder limits, and the part follows thermal classes B and F.
- Moulding micanite carries 15 to 40 % shellac, alkyd, epoxy or silicone (IEC 60371-3-9, table 1) and softens between 100 and 140 °C so that it can be hot-formed into sleeves and caps (Micaworld).
- Heater micanite and flexible micanite carry at most 10 % and 8 % silicone resin respectively (Hesselmann). The silicone partly burns off in service, the loss on ignition stays below 1 % at 500 °C, and the sheet remains load-bearing. Here the mineral limits.
The purchasing rule is therefore: on a heater micanite datasheet the temperature refers to the mica, on a commutator or moulding micanite datasheet it refers to the resin. Anyone who transfers a 500 °C datasheet to a shellac-bonded moulded part is off by 370 kelvin.
Manufacturing: from mica block to rigid sheet
IEC 60371-1 distinguishes two raw materials: mica splittings, meaning laminae split from blocks, and mica paper, a web of very small mica flakes without binder. Almost all sheets today are made from paper:
- Mica is ground or opened up by calcining and laid on a paper machine into a web of 80 to 200 g/m² (SIDA, mica insulation guide).
- The paper is impregnated with silicone, epoxy or shellac resin. Resin-rich layers go into the hot press, resin-poor tapes are vacuum impregnated later (Wikipedia, Kunstglimmer).
- Several layers are stacked to the target thickness and pressed at 5 to 15 MPa and 150 to 250 °C (SIDA). Commutator micanite is then ground on one or both faces, heater micanite stays unground (IEC 60371-1, clause 4.1).
Micanite grades to IEC 60371: commutator, heater, moulding, flexible
IEC 60371 describes mica products in nine sheets, from commutator separators (sheet 1) via rigid materials for heating equipment (sheet 3) to moulding micanite (sheet 9). The trade’s German grade names map onto these sheets.
| Grade | Construction and binder | Thickness | Continuous temperature | Use |
|---|---|---|---|---|
| Commutator micanite | splittings or paper, 4 to 7 % shellac, alkyd or epoxy, ground | 0.2 to 2 mm, tolerance ±0.02 to ±0.05 mm (Pamica, Asheville Mica) | 130 to 155 °C | segment insulation in DC and traction motors |
| Heater micanite | at least 90 % mica paper, max. 10 % silicone, unground | 0.1 to 100 mm (Diel) | 500 °C (M), 700 °C (P) | heating wire carriers, cover plates, sleeves in household and industrial heaters |
| Moulding micanite | 15 to 40 % shellac, alkyd, epoxy or silicone (IEC 60371-3-9) | 0.10 to 7.00 mm | by binder, temperature index to IEC 216-1 | hot-formed sleeves, caps, tubes, commutator cones |
| Flexible micanite | at least 92 % mica paper, max. 8 % silicone, density 1.8 to 1.9 g/cm³ | 0.1 to 6.0 mm (Hesselmann) | 500 °C (M), 700 °C (P) | cold-wrapped sleeves, separators, covers in hair dryers and fan heaters |
| Mica foil, micanite foil | phlogopite paper on glass fabric with silicone, 205 to 750 g/m² | 0.14 to 0.49 mm (Hesselmann SI) | limit temperature 1,200 °C | coil insulation and slip layer in coreless induction furnaces |
| Mica tape | mica paper on glass or PET, 5 to 25 % epoxy, partly for VPI | 0.08 to 0.2 mm per layer | thermal class 155 to 220 | main insulation of high-voltage windings, fire-resistant cables |
The last row marks the boundary of this article. Micanite is the material in sheet form, mica tape is the flexible product that is wrapped around coils and conductors and then impregnated with resin. Both are made from the same mica paper, but the tape receives its binder only after wrapping, the sheet already at the factory.
Rigid mica sheets: properties, thicknesses and tolerances
The values below come from the datasheets of Hesselmann, Diel and Monoco for silicone-bonded heater micanite and apply to muscovite and phlogopite alike unless stated otherwise.
| Property | Value | Test standard |
|---|---|---|
| Mica content | at least 90 % up to 2 mm, 85 to 90 % above | IEC 60371-2 |
| Density | 2.15 g/cm³, smoothed 2.25 g/cm³ | IEC 60371-2 |
| Dielectric strength at 20 °C | over 20 kV/mm up to 2 mm, over 25 kV/mm from 2 mm | IEC 60243 |
| Dielectric strength at 400 °C | 13 kV/mm | IEC 60243 (Monoco) |
| Dielectric strength at 600 °C | 10 kV/mm | IEC 60243 (Monoco) |
| Insulation resistance | over 1017 Ω·cm at 23 °C, over 1012 Ω·cm at 550 °C | IEC 60093 |
| Water absorption | under 1 % after 24 h | ISO 62 |
| Thermal conductivity | 0.3 W/(m·K) perpendicular, 3.0 W/(m·K) in the plane of the sheet | Monoco |
Two rows of this table are regularly overlooked. First, dielectric strength falls with temperature: at 600 °C, 10 kV/mm remain of 25, so a sheet is sized for the voltage at operating temperature. Second, the sheet is ten times below the mineral, because binder layers, air inclusions and flake boundaries open the path for breakdown. The property in kV/mm and its measurement are explained in the article on electrical dielectric strength, and which voltage a finished part must hold in routine testing in the article on voltage withstand.
The breakdown voltage of the whole sheet grows more slowly than linearly with thickness: a 0.1 mm sheet holds around 20 to 25 kV, a 0.5 mm sheet 10 to 15 kV and a 3 mm sheet 5 to 8 kV per millimetre (SIDA). Thick sheets are therefore bought for mechanics and heat, thin ones for voltage. Available are 0.1 to 100 mm (Diel, Dumico) in formats from 1,000 x 1,200 mm to 1,000 x 2,400 mm (ISO-tech, Hesselmann). The thickness tolerances per Diel belong on every drawing:
- 0.1 mm: ±0.03 mm, 0.2 to 0.4 mm: ±0.04 mm, 0.5 to 0.7 mm: ±0.05 mm, 1.0 mm: ±0.07 mm
- 1.5 mm: ±0.10 mm, 2 to 5 mm: ±7 %, 5 to 30 mm: ±5 %, 30 to 100 mm: ±3 %
Commutator micanite is held much tighter because the segment pitch of the commutator depends on it: Pamica specifies -0.00/+0.02 mm with at most 0.03 mm spread within one sheet.
Processing micanite: punching with a hold-down, bending, dust
Micanite can be punched, sheared, sawn, drilled and milled, but it behaves differently in the tool from film or pressboard. The sheet is a stack of layers. Any force across the layers can separate them, and delamination at the cut edge later becomes the electrical weak point (Top-Heater, machining mica). The datasheets of Hesselmann and Diel therefore call for a hold-down system in the punching tool: the sheet is clamped around the cut before the punch enters, otherwise the edge chips off.
- Tooling: mica is abrasive. For series production the punching tool needs carbide or coated cutting edges, otherwise the edge turns rough after a few thousand strokes (SIDA).
- Bending: only flexible micanite can be cold-formed, with a radius of at least ten times the thickness (SIDA). For sleeves Hesselmann recommends 150 °C for at most one minute. Rigid sheets break when bent, and a laser leaves a heat-affected zone that can separate the layers (Top-Heater).
- Dust: mica dust is silicate. Sawing, drilling and milling need extraction and respiratory protection (SIDA). Punched sheets hardly produce dust.
- Storage: dry, silicone-bonded material keeps for 24 months, epoxy-bonded for 12 months, because the resin continues to cure (SIDA).
In stamping and forming we process rigid mica sheets from 0.1 to 3.0 mm up to a part size of 1,000 x 2,000 mm. For samples and small series we use steel rule dies, for tight tolerances and high volumes solid steel tools on the automatic press, and for mica always with a hold-down. Micanite foil and flexible micanite from the roll we slit by shear cutting to widths of 5 to 1,600 mm with ±0.1 mm.
Where micanite is used: from the toaster to the traction machine
Micanite sits wherever current and heat act on the same part and no organic insulating material lasts any longer. The applications follow the temperature:
- Heating wire carriers in hair dryers, toasters, fan heaters and tumble dryers: sheets of 0.3 to 1.0 mm around which a NiCr or FeCrAl wire is wound (SIDA, Heater Technology). Which other insulating parts sit in ovens and dryers is shown in the article on white goods, and our production for them is described under household appliances.
- Flat heating elements for tools and packaging machines: a NiCr 80/20 heating conductor between two micanite cover plates, 1.5 to 2 mm thick, up to 400 °C and 4 W/cm² (IHP Heating), with phlogopite up to 450 °C and 5 W/cm² (Freek).
- Commutators in DC and traction motors: ground separators with 91.5 to 92 % mica content (Cogebi, traction).
- High-voltage machines and inverter drives: mica is the only common insulating material that partial discharges do not erode. What corona does to film and paper is covered in the article on corona discharge.
- Coreless induction furnaces: mica foil up to 1,200 °C as coil insulation (Hesselmann SI).
- Battery systems: mica sheets as barriers between cells and modules that must survive a thermal runaway above 800 °C for a short time, described in the article on thermal insulation in battery systems.
Micanite or Nomex, micanite or mica tape: which material when
The most common objection to micanite is that it is too brittle and too expensive for series parts. That is true below 250 °C. There Nomex up to 220 °C and Kapton up to 240 °C do the same job, can be folded and cost less per part. Above 250 °C the calculation flips: of the organic materials only PTFE and polyimide remain, with limited service life, and from 300 °C only the mineral. The brittleness is handled by a tool with a hold-down, and at 0.3 to 1.0 mm thickness the part is not loaded in bending inside the appliance.
The second confusion concerns mica tape: anyone who needs a part to drawing ends up with micanite. Anyone insulating a winding ends up with the tape.
How GOBA processes micanite into insulating parts
We stock mica as sheet and as master roll and make punched parts, strips and blanks from it to your drawing: heating wire carriers and cover plates for heating elements, separators for white goods, barriers on cell contour for battery modules and sleeves of flexible micanite. The choice between muscovite and phlogopite, between rigid and flexible, we make with you on the basis of continuous temperature, voltage at operating temperature and geometry. Our range of mica materials, aramid papers, polyimide films and laminates is listed under insulation materials.
For an enquiry we need three things: the continuous temperature at the part, the test voltage and the drawing with thickness and tolerance. Send us the drawing, we check tool and grade and quote you the price per part for samples and series.
