Production process sequence of piezoelectric thin film, stretch film process is the second process.
Prolonging the thin diaphragm is drawn, it is the state of PVDF melt crystallization get a phase morphology, into Lu Xiangjing type.
The crystal shape, its molecular axis is like spring spiral structure, the arrangement of the dipole as the molecular axis rotation and change direction, at this point, the dipole orientation is no rules, then it's polarity offset each other, and make the spontaneous polarization quantity is very small.
If the PVDF wafer after stretching in a certain direction, diaphragm of a crystal phase into crystal, the dipole orientation arrangement of basic trend, also enhance the piezoelectric.
Crystal type of identification method, can use ir absorption and X ray diffraction image method to confirm.
With equipment of PVDF membrane tensile stretch film work, in a specially designed diaphragm on the tensile equipment.
Stretching equipment is simple: one end is fixed splint, on the other side is driven by the screw moving plywood.
Stretch of diaphragm, the ends of diaphragm are respectively fixed on the mobile splint and fixed splint, start the motor, the deceleration driven screw rotation, then splint slow movement, the membrane stretched thin.
This drawing multiples of thinning, determined by process conditions, generally within 3 ~ 5 times.
Diaphragm tensile speed is slow, steady operation of the chuck, driven by ordinary motor, through the planet cycloidal pinwheel reducer reducer after using the wheel connection that drives the moving clamp screw rotation, to complete the operation of the lead screw drive mobile chuck drive.
Diaphragm is drawn at the same time, to be on the width of the diaphragm (
Perpendicular to the tensile direction)
Local heating heater for heating medium copper heat source 甴 resistance heater.
Editor using membrane tensile equipment, May 30 - tensile membrane thickness
2000 mu m, width 100 -
350 mm, the tension drive motor power 500 w, 200 - resistance heating power
Process conditions and work requirements PVDF membrane tensile stretch film temperature at local heating: 60
PVDF membrane tensile extension ratio: 4 times the left and right sides.
Stretching chuck speed: 1 -
50mm / min。
The film stretching equipment requirements are as follows.
1) stretch run chuck should be smooth movement speed, in 15 - in her work
Within the scope of 50 mm/min is adjustable.
Thinner diaphragm stretching with a high speed, thick film with low speed.
(2) by the local heating temperature of the stretch film to be adjustable within 60 ℃ (
Thick film with high temperature, the film with the work of low temperature heating temperature is constant, temperature fluctuate should not more than plus or minus 2 ℃.
(3) copper heating carrier contact with the membrane heating surface should be smooth level off, job runtime remain parallel to the membrane surface, running direction and membrane stretch in the opposite direction.
(4) by drawing PVDF film should level off, thickness and width size should agree: thickness tolerance within + / - 5, the width tolerance is plus or minus 0.
Membrane is not allowed to have impurities, buckling and bubble phenomenon.
5. Stretch film work environment should be clean, no dust, the dry air, humidity is not more than 60%.
6. The thickness of the diaphragm is drawn after the tolerance to + / - 3 microns.
When less than 120 microns thick to transparent film, more than 250 microns for milk white flakes.
Before 7) stretch of diaphragm after annealing treatment, keep stretch state.
So, every piece of film should be equipped with special support rod bolt after stretch, supported by pull the film after stretching.