FI71267B - FOERFARANDE FOER TILLVERKNING AV EN ELEKTROMEKANISK FILM - Google Patents

Description

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METHOD FOR MANUFACTURING AN ELECTROMECHANICAL FILM -FÖRFARANDE FÖR TILLVERKNING AV EN ELEKTROMEKANISK FILM

The present invention relates to a method for producing a film for converting the energy of an electric field and a magnetic field into a mechanical energy or a mechanical energy into an electrical energy.

The applicant's Finnish patent application 830547 discloses an electromechanical dielectric film which can be used to implement a wide variety of electromechanical devices and measuring sensors. Previously known multilayer films with bubbles or wrinkles and having a smooth, e.g. electrically conductive layer at the outermost are intended as packaging materials or are too thick for the purposes of this invention. In addition, membrane applications based on piezoelectric phenomena are known. However, the manufacturing technique of this type of film is considerably expensive, requiring large investments, and the film cannot be easily used in electromechanical applications requiring major deformations.

Films prepared by the method of the invention

_ C C

the thickness is e.g. 10x10 m and the voltage resistance 100x10 v / m. The electrostatic force across the membrane is directly proportional to the second power of the voltage across the membrane, and the attraction of the current loops on both sides of the membrane layer is directly proportional to the second power of the current. In films made by the method according to the invention, quantities such as force, pressure, film area and thickness, electric field strength and voltage can be connected together, e.g. by the following equations: F = pA = £ e2a = Eu2a (I) 2 2ha where A = film area and h = film thickness, the other quantities representing, according to their symbols, the known quantities of physics 2 71267. £ is a dielectric constant of quality F / m.

As can be seen from Equation (I), the film of the invention binds together a wide variety of quantities.

It is an object of the present invention to provide a method for manufacturing said film. In order to maximize the electrostatic and electromagnetic forces across the elastic membrane, it is essential that the membrane layers be as thin as possible, as the forces are inversely proportional to the second power of the distances between the electrodes and current conductors. On the other hand, the burst resistance of bubbles in the membrane increases proportionally with decreasing distances (Pashen’s law). In this case, it should be possible to produce small (shallow) air bubbles and orient the foamed film biaxially into the elastic matrix material, whereby the bubbles become flat disc-shaped.

The production method of the film according to the invention is mainly characterized in that the production of a unitary and closed-cell foamed film layer known per se takes place in the following steps: - the heated product is expanded in two directions into a film to provide the desired wall thickness and orientation; - the outer surfaces of the film are at least partially coated with electrically conductive layers.

The production method described above can be a continuous so-called a tubular blown film process commonly used in the manufacture of plastic films. The technique used in the manufacture of capacitors and printed circuits is used to repeat the films and to manufacture the 3 71267 motion elements.

A preferred embodiment of the production method according to the invention is characterized in that, after extrusion, the product is subjected to intercooling, after which it is reheated before being expanded. The heat treatment increases the degree of crystallization of the plastic matrix of the product so that in the expansion the deformation of the film takes place more as a grain boundary slip between the crystal regions, whereby the polymer chains remain better intact and no tears occur.

A preferred embodiment of the manufacturing method according to the invention is also characterized in that the coating of the outer surfaces with electrically conductive layers is carried out selectively in order to obtain a certain pattern, e.g. by pressing. For example, in the case of series-produced electromechanical elements, it is obviously advantageous to provide the desired patterning directly, thus avoiding the need for unnecessary metallization.

Other preferred embodiments of the production method according to the invention are characterized by what is stated in the claims below.

The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which

Fig. 1 shows the basic structure of a film according to the invention,

Figures 2a-2c show a solution according to an embodiment of the invention for placing voltage and current electrodes in a stranded structure, 4 71267

Fig. 3 shows a method of manufacturing a film according to the invention.

In Fig. 1, the plastic matrix A of the dielectric film according to the invention is coated on both sides with metal films B, which may be intact or pre-patterned. The plastic matrix, which may be e.g. polypropylene, is formed of flat blisters C which have been shaped by bi-directional orientation of the plastic matrix. The typical thickness of the finished film product is 10 μπ \.

Figure 2a shows a structure made of a film according to the invention, in which both electrostatic and electromagnetic forces act in the same direction. The film 1 on both sides of the printed conductors 2 on which the points Ul, U2, U3 and U4 via the currents II, 12, Ul and U4 over the voltages constitute the film layers over the electrostatic and the electromagnetic force F of the arrow. The force F is contractile when the current on different sides of the film flows in the same direction (Fig. 2b) and expands the structure when the current flows in a different direction (Fig. 2c) when the element is discharged.

The base material of the film according to the invention, i.e. the plastic layer A in Fig. 1, can also be semi-conductive, a property which is most simply obtainable, e.g. by the addition of soot. In this case, a film whose impedance is temperature-dependent can be produced so that the film can be used in self-adjusting heating elements. Magnetic powder or fibers such as metal fibers can also be added to the base material, whereby known magnetic properties can be exploited, such as induction by a magnetic field. The material used to coat the film may also be a magnetic substance, e.g. nickel.

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In motion elements, it is necessary to get feedback on the magnitude of the motion. This is done, for example, by measuring the capacitance of the structure, the time constant of the LC circuit, the resonant frequency or the phase difference between current and voltage at the measuring frequency supplied with the control voltage, e.g. from the same connections U1-U4.

Such motors are light and sturdy. The specific gravity of the structure is lkg / dm ^ and the force lkN if the body is cubic. The movement is then about 2 cm in the longitudinal direction of the piece. The instantaneous power can be applied to such a body in an almost infinite amount if the inductance of the structure is minimized.

Figure 3 schematically shows a method of manufacturing a film according to the invention, which is biphasic and continuous in nature.

The formation of bubbles in the plastic matrix, i.e. the foaming of the plastic, can be achieved in several different ways. In so-called chemical foaming, a foaming agent is mixed with the plastic, which, when heated, forms a gas, e.g. nitrogen. Variations on this are methods in which the gas is obtained by boiling a liquid, such as water, by adding the liquid as such or e.g. as a solid containing water of crystallization. As the film to be formed cools, the bubbles thus formed withdraw extremely flat, containing essentially only liquid. By heating the film by applying, for example, a high-frequency voltage over it, the liquid is re-evaporated, resulting in a very large expanding movement of the film.

In the so-called "gas injection" technique, freon gas, for example, is pumped into a plastic press, which expands into bubbles as the pressure drops outside the press.

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Figure 3 shows a plastic clamp is denoted by 9 in which gas is pumped into the process Injection of gas into the direction of the arrow 10. In the first stage of production, a pipe 3 with a wall thickness of about 0.4 mm thick is extruded from a plastic press, into which round gas bubbles with a diameter of about 10 μm are formed at ΙΟμιη intervals. There are thus about 20 overlapping bubbles. per pipe wall thickness gauge. The shaping properties of the plastic improve with the degree of crystallization, for which reason the extruded plastic is suitably heat-treated to promote crystallization, in this case by allowing it to cool by means of a cooling member 4. The traction device 5 acts as a conveyor of the pipe, the flattening of the pipe by the traction device shown in the figure is not necessary. In the manufacturing method according to Figure 3, the blowing air from the nozzle 8 passes through the whole process.

The second stage of the process begins with heating the pipe in the heating furnace 6, after which the pipe is oriented biaxially and given the desired wall strength by blowing and pulling the pipe 7 in the transverse direction about 5-fold and in the longitudinal direction about 8-fold compared to the pipe 3. ΙΟμιη. The blowing air or gas is obtained from a nozzle 8, the supply pressure of which is now allowed to expand the heated pipe. Due to the suitable heat treatment, the bubbles do not rupture, but flatten due to the sliding of the crystal regions of the matrix, whereby the matrix material stretches and thins without breaking. The bubbles flattened by the expansion are then about 0.25μιη high, about 80 pm long and about 50 pm wide. The combined theoretical voltage resistance of the bubbles is of the order of 1600 V and the matrix material about 2500 V, respectively, so that a DC / AC resistance of 1000 V is easily achievable with a 10 μm membrane.

It should be noted that not all grades of plastic require intermediate cooling and reheating of pipe 3 7 71 267. After all, this heat treatment aims to increase the degree of crystallization, so that during the transport following the extrusion step, the plastics of sufficient crystallization can be arranged to be expanded directly, as long as their sufficiently high temperature is maintained. Some grades of plastic can also be stretched immediately after the extrusion nozzle.

Finally, the film is wound through a folding wheel 11 onto a roll 12 for post-treatment, i.e. with a conductive layer for coating, which can take place by vacuum evaporation, sputtering or mechanical pressing. It is also possible to form a multilayer film in which the outermost layers are of electrically conductive plastic, which are bonded to the foamable matrix plastic already in the forming step of the pipe 3. In addition to being necessary to effect the film of the invention, coating also plays an important role as an effective gas escape inhibitor.

The film prepared as described above has a very wide range of applications, most of which are mentioned in my FI application 830547. A few more should be mentioned below. Instead of a tubular manufacturing process, the so-called a flat film process in which the film is stretched by pulling the edges of the film, although such a process is somewhat more cumbersome than the blown film method.

The film made according to the invention can be used for measurements based on changes in capacitance, since the capacitance of the film depends on its thickness. Areas of application include pressure sensors, keys and button matrices.

Furthermore, based on the changes in capacitance, the film can be used as a temperature recording member because the gas in the gas bubbles of the film 8 71267 expands according to the temperature. A liquid substance which evaporates at a certain temperature is also possible. The membrane technology can thus be applied, for example, in temperature sensors and devices based on the detection of thermal radiation.

By making a film from a permanently charged and polarizable substance such as polytetrafluoroethylene, devices can be made which provide a voltage corresponding to the change in film thickness, according to the law of capacitor Q = CU. When the charge Q of the film remains constant, the changes in capacitance caused by changes in the thickness of the film are converted directly into a voltage acting over it. Transformers can then be made from the membrane, in which the primary membrane transfers energy to the secondary membrane by means of vibration.

Obsessive changes in the film can be identified by forming a matrix plate in which the local change in the film is effected or recorded from the edges of the film, e.g. by impedance measurements. The matrix plate thus consists of independently addressable elements. One example of this is the previously mentioned button matrix, another important application arises when the gas in the membrane is ionized, whereby the membrane matrix can be used in image matrices for image formation.

It will be clear to a person skilled in the art that the various embodiments of the invention are not limited to the examples given above, but may vary within the scope of the claims set out below. In principle, any material used for the production of films or fibers is suitable as a raw material for the film according to the invention, e.g. viscose. Most gases are also suitable for filling bubbles. Films can also be made as various multilayer films, and particularly thin films are obtained by evaporating the liquid incorporated in the matrix of the matrix away from the film before coating it, thereby producing extremely small gas bubbles.

Claims (11)

10 71 2 67 A method for producing a film (A, 1,7) which converts an electric field and a magnetic field into a mechanical energy or a mechanical energy into an electrical energy, characterized in that the production of a uniform and closed-cell foamed film layer (A) known per se takes place in the following steps: extruding out of the plastic machine tool into a thin-walled product, whereby gas bubbles (C) with the desired density are formed through the product due to foaming; - the heated product (7) is expanded in two directions into a film (A) to obtain the desired wall thickness and orientation; - the outer surfaces of the film are at least partially coated with electrically conductive layers (B). Manufacturing method according to Claim 1, characterized in that the extruded product (3) is formed in the form of a tube and that the biaxial expansion of the product is effected by pressurizing the tube (7). Manufacturing method according to Claim 1 or 2, characterized in that, after extrusion, the product (3) is subjected to intercooling, after which it is reheated before being expanded. Manufacturing method according to Claim 1, 2 or 3, characterized in that the coating of the outer surfaces with an electrically conductive material is carried out selectively in order to obtain a certain pattern, e.g. by pressing. Production method according to one of Claims 1 to 4, characterized in that a water- or crystal-water-containing substance is used as the foaming agent for the film (A). Manufacturing method according to one of Claims 1 to 5, characterized in that the film material (A) is dielectric. Manufacturing method according to claim 6, characterized in that the dielectric film material (A) is polarized to provide a permanent electric field. Manufacturing method according to one of Claims 1 to 5, characterized in that the film material (A) is semi-conductive. Manufacturing method according to one of Claims 1 to 5, characterized in that the film material (A) is a ferromagnetic material. Manufacturing method according to Claim 9, characterized in that the ferromagnetic film material (A) is pre-magnetized. Manufacturing method according to one of Claims 1 to 5, characterized in that the film material (A) is coated with a magnetic, optionally pre-magnetized material (B). 12 71 267