RAMAN BOARDS
Sigma Diamond Dotted Paper
Raman Boards offers Sigma diamond dotted paper in a range of thicknesses with a coating of epoxy resin
formulation. We have developed this product with capability to coat the resin on one or on both sides of
high grade Sigma Press paper. The base paper has been proven for usage as insulation in transformers
and coated paper is completely compatible with transformer oil when thermally aged.
The epoxy resin is coated in squares of dimension 9.5mm and is spaced at a distance of 6.7mm between
squares. The squares are arranged in a manner that their diagonals lie parallel and perpendicular to
machine direction of the paper. The epoxy dots are arranged in such a pattern that ensures an offset
relationship exists between the dots on concentric paper layers, thus creating the maximum bonding
surface. The thickness of the epoxy resin coating is 0.01mm on each side, ± 0.002mm tolerance and is
independent of the base paper thickness. The size, shape thickness and placement of the dots ensure
effective vacuum drying and oil impregnation
.
The epoxy resin is maintained in reactive “B stage” dry and tack free, will melt upon increasing the curing
0
temperature to 120 to 140 C this facilitates firm and permanent bonding with the conductor.
The non-
reactive “C stage” is reached after a curing time of 6-8 hours. The insulation is then in the stable duroplastic
condition, unaffected by further heating which will occur during service.
The advantage in use of partially coated insulation press paper lies in the internal strengthening of the coil
due to adhesion to conductor, provides passage for quick evacuation of air and moisture during drying
process thereby minimizing risks of
partial discharge, quick impregnation and flow of oil through the
channels.
One-stop shop for transformer insulation
RAMAN BOARDS
Sigma Diamond Dotted Paper
The Sigma Diamond dotted paper is available in roll form in base paper thickness of 0.075mm (3 mil),
0.125mm (5 mil), 0.175mm (7 mil) and 0.25mm (10 mil). The standard width of rolls is 500, 750 and 1500mm
and standard roll diameter of 350mm. Rolls are supplied on 76mm ID core. Other thickness are available on
request, minimum quantity of 1.0 MT.
The Sigma Diamond dotted paper rolls must be stored with packing in dry condition and away from direct
0
sunlight at a maximum ambient temperature of 30 C. The rolls are to be stored upright condition to prevent
0
bonding between layers. The shelf life is maximum 180 days when stored below 30 C
Procedure for Determination of Bond strength
The Sigma diamond dotted paper should bond firmly and evenly to the conductor. The bonding strength or
tensile shear strength can be checked as follows

Prepare four layers of specimens of sigma diamond dotted paper of size 50 x 50 mm.

Take two flattened Aluminum or copper plates with dimension of 150mm x 50mm and thickness of 0.5 mm,

clean using solvent followed by an hot air oven drying for one hour at 100 Deg C

Place the paper specimen in between aluminum or copper plates for 6 hours at 1400 C and 2 psi pressure.

The bonded samples are then tested for tensile shear strength with a pull rate of 110mm per minute at this
stage separation must take place in the paper layer and not on the adhesion surface.
Tolerance on
Thickness, (%) range
± 10.0
On Roll Width, ( mm)
 5.0
One-stop shop for transformer insulation
RAMAN BOARDS
Sigma Diamond Dotted Paper
Reference Grade & Standard
Tests conducted as per IEC 60641-2, Methods of Test
Color & Appearance: Natural Brown & Matte with mesh mark on both sides
Physical Properties
3.0 mil
5.0 mil
7.0 mil
10 mil
0.075
0.125
0.175
0.250
0.068 - 0.083
0.112 - 0.138
0.158 – 0.192
0.225 – 0.275
0.90 – 1.0
0.90 – 1.0
0.90 – 1.0
0.90 – 1.0
Moisture content, (%), max
8.0
8.0
8.0
8.0
Shrinkage MD, (%), max
1. 0
1. 0
1. 0
1. 0
Shrinkage CD, (%), max
1.50
1.50
1.50
1.50
Shrinkage PD, (%), max
9.0
9.0
9.0
9.0
8
8
8
8
6.0 - 9.0
6.0 - 9.0
6.0 - 9.0
6.0 - 9.0
10.0
10.0
10.0
10.0
1. 0
1. 0
1. 0
1. 0
60/35
50/30
50/30
50/30
1.0/5.0
1.0/5.0
1.5/5.0
1.5/5.0
9/60
9/60
8/50
7/50
120 - 140
120 - 140
120 - 140
120 - 140
Curing Time (hours), Range
4-6
4-6
4 -6
4-6
Bonding Shear Strength (psi), min @ 140 Deg C for
6 hours & load 2 psi.
> 40
> 40
> 40
> 40
Thickness (mm)
t
Thickness Tolerance (mm), range
Density, (g/cc), min
Chemical Properties
Conductivity of Aqueous extract, (mS/m), max
≤1.60 mm
pH of. Aqueous extract, range
Oil Absorption, (%), min
≤1.60 mm
Ash Content, (%), max
Mechanical Properties
Tensile Strength (Mpa), min MD/CD
≤1.60 mm
Elongation, (%), min, MD/CD
Electric Strength Properties
Dielectric Strength Air/Oil (kV/mm), min
≤1.60 mm
Recommended Parameters for Curing
Curing Temperature (Deg C), Range
These values do not constitute specification of our products and also provided are values in accordance with the IEC specification. Since test conditions cannot always duplicate actual field
installations or end use, Raman Boards make no warranties with respect to such data and assume no responsibility for performance characteristics resulting from conditions which may differ
from those used in laboratory tests.
One-stop shop for transformer insulation