The important raw material of epoxy insulation board is glass fabric. What special properties does glass fabric have to meet the performance requirements of epoxy insulation board? We summarize the following points.
(1) Mechanical property
Glass fibric has a high tensile strength,
and its strength is related to the fiber diameter, fiber length, and alkali
content. The finer the fiber, the higher the strength, and the shorter the
fiber, the higher the strength. The strength of the fiber increases with the
decrease of the alkali content, and the strength of the fiber increases with
the temperature of the glass melt when drawing the fiber, and increases with
the speed of drawing and winding. The strength of glass fibric is greatly
reduced after friction damage. The glass fibric is woven into a cloth. Although
it is protected by a lubricant, the loss of glass strength is still large. The
order of strength is: one weave and one pattern → twill → plain
(2)
Permeability
Glass fibric is a cylinder without
capillary structure, and the fiber itself cannot be penetrated by water and
resin. In order to improve the penetrating ability, the surface area of the adsorption resin is increased. There are three measures. ① Pull the fiber very thin:
increase the surface area of the same mass; ② reduce the twist of the
yarn: the twist of the glass yarn has high twist, medium twist, low twist, and
no twist. The filling resin increases. Laminated yarn twist is generally 40 ~
110 twists / m, and non-twisted glass cloth is used; ③Density reduction:
Density reduction is also to increase the void and increase the amount of resin
filled. As the twist and density decrease, the strength of the glass fibric
also decreases, but due to the increase in the resin penetration ability, the
strength of the laminate increases instead.
(3)
Dielectric property
The dielectric properties of glass fabric
are related to the alkali content. Increasing the alkali content decreases the
surface resistance and increases the dielectric loss. The effect of alkali is
more significant under the condition of high temperature and humidity, but the
dielectric strength of glass fibric is good.
(4)
Thermal performance of glass fabric
The alkali-free glass fabric has high heat
resistance, and its mechanical and electrical properties are stable below 200 °
C. Due to the lubricant on the surface of the glass fiber, the tensile strength
of the glass cloth rises at 100 ~ 150 ° C. Because the lubricant is heated, the
viscosity increases, which strengthens the friction protection effect on the
fiber; at 150 ~ 200 ° C, the lubricant is further cured, and The tensile
strength is the highest; after 200 ℃, the strength decreases due to thermal
decomposition; 300 ℃ decreases to 80% of the original strength; 400 ℃ decreases
to 55%; the 600 ℃ strength almost disappears. This loss of strength, which is
much lower than the glass transition temperature, is related to the shrinkage
caused by the ultra-rapidly formed fibers after heating. Thermal shrinkage is
one of the characteristics of glass fibers. The heat shrinkage phenomenon of
glass fiber (cloth) is very instructive for the production of laminated
products. The combination of temperature and pressure during hot pressing
should be noted. Practice has proved that the hot pressing temperature is
higher than 170 ℃, and the internal temperature of thick products is nearly 200
℃. If the pressure is not matched well, the strength will be greatly reduced.
Attention should be paid to the change of steam pressure (high temperature to
low temperature) during the hot pressing process and the pressure maintenance
during cooling. Glass fiber performance is relatively stable below 200 ° C.
(5)
Chemical resistance
Glass fibric is insoluble in organic
solvents, has strong resistance to mildew, tapeworms, bacteria and decay, and
is not affected by oils, most acids and corrosive vapors (except hydrofluoric
acid and hot phosphoric acid).