DE19814018A1 - Ceramic-polymer, ceramic-ceramic or ceramic-metal composite, e.g. a piezoceramic-polymer composite for an ultrasonic transducer - Google Patents

Abstract

Composite materials are produced by positioning structured and sintered ceramic foils in a mold and then casting a different material in the mold. Composite materials are produced by (a) structuring, optionally laminating and sintering green dip or foil cast ceramic foils; (b) placing the vertical parallel spaced foils or the laminate in a mold; (c) casting another material (e.g. a binder/polymer/plastic, molten metal, molten glass or a ceramic slip) in the mold; and (d) fettling the hardened composite structure.

Description

field of use

General: Composites with ceramic components are becoming increasingly popular Interest. A new process is registered here, which is used to manufacture ver composite materials made of ceramic / polymer, ceramic / ceramic and ceramic / metal is suitable. The process for the production of a composite material was developed Made of piezoceramic and polymer, but it is also for other material combinations suitable (see solution of the task). The invention is first based on the example of Piezoceramic / polymer composites explained.

Piezoceramic / polymer composites: Piezoelectric ceramics / polymer composites, such as B. the 1-3 composite are used as ultrasonic transmitters and / or receivers. Especially because of their good coupling behavior to water, they are used in the following three areas of application:

• - As nautical converters in ships, they serve as navigation aids for recognition of shallows, schools of fish, other ships, submarines and underwater bodies.
• - In medicine, they are used both for diagnosis and for therapy sets, e.g. B. to carry out prenatal examinations or to crush the kidney stones.
• - They enable non-destructive work in materials technology and in test laboratories fabric testing.

State of the art

According to the current state of the art, there are three main manufacturing processes for piezoelectric ceramics / polymer composites: The sawing technology (Dice & Fill) [89 Smi], [81 Sav], [95 Jan], the ceramic injection molding [95 Gen], [92 Bow] and the lithography-electroforming-impression technique (LIGA) method [95 Bac], [92 Rog], [92 Nök].

The sawing technique is based on a mostly dry pressed, already sintered, piezo  electrical ceramic block, which crosses according to the desired structure is sawn in so that rods made of piezoceramic remain. After filling the structure with a polymer and remove the bottom plate that the resulting If structural elements (e.g. rods) are held together beforehand, the component is obtained.

With the help of the ceramic injection molding with an appropriate tool the desired structural body is first produced in the green state. After this Sintering is also filled with a polymer and the base plate (if necessary) removed to maintain the component.

The LIGA process is a complicated, multi-stage process based on the principle the "lost form" works. First of all, by means of an exposure process desired structural pattern by X-ray onto a masked polymer transfer resist layer. The irradiated areas are then in one Developer selectively extracted. The cavities created are by electroplating Impression transferred to a metal impression tool. With this tool now z. B. plastic molds that are used as a "lost form" can. I.e. they are filled with a ceramic slip, then ge dries. When sintering, the plastic mold burns without residue and you get the ceramic molded body, which is analogous to the previous method Filling with polymer can be transferred to the piezoelectric composite component can.

Disadvantages of the prior art

Each of the foregoing manufacturing processes has typical disadvantages that with low quantities, changing geometries / dimensions and with the Production of very fine structures. In detail they are Disadvantages of the different methods:

Dice & Fill technique

• - high expenditure of time per piece when sawing → low throughput
• - high rejection rate due to breakage, especially with fine structures
• - restrictions regarding the geometries (e.g. curvatures, radii)

Injection molding process

• - high tool costs
• - inflexible regarding changed geometries
• - maximum fineness of the structures ∼ 100 µm [92 Bow]
• - Tool wear due to abrasive ceramics

LIGA technology

• - Elaborate, costly mold production by lithography and Electroforming
• - inflexible regarding changed geometries
• - Defined furnace guidance necessary to structure the organic burnout not to damage

bibliography

[89 Smi] WA Smith, "The Role of Piezo Composites in Ultrasonic Transducers", Proc. IEEE Ultrasonic Symposium 1989 pp. 755-766
[81 Sav] HP Savakus, KA Klicker, RE Newnham, "PZT-Epoxy Piezoelectric Transducers: A Simplified Fabrication Procedure", Mat.Res.Bull. vol.16 p. 677-680
[92 Bow] LJ Bowen, KW French, "Fabrication of piezoelectric Ceramic / Polymer Composites by Injection Molding", Proc. 8 ^th

IEEE Meeting, ISAF, 1992 pp. 160-163
[92 Nök] F. Nöker, E. Beyer, "Production of microstructure bodies from ceramics", Keramische Zeitschrift 44 [10], 1992 pp. 677-681
[92 Rog] A. Rogner, J. Eicher, D. Münchmeyer, R.-P. Peters, J. Mohr, "Review The LIGA technique - what are the new opportunities," J. Micromech. Microeng. 2.1992 pp. 133-140
[95 Jan] VF Janas, TF McNulty, FR Walker, RP Schaeffer, A. Safari, "Processing of 1-3 Piezoelectric Ceramic / Polymer Composites", J.Am. Ceram.Soc. 78 [9] 1995 pp. 2425-2430
[95 Bac] W. Bacher, W. Menz, J. Mohr, "The LIGA Technique and Ist Potential for Microsystems - A Survey", IEEE Transactions on Industrial Electronics vol. 42 [5] 1995 pp. 431-441
[95 gene] R. Gentilman, D. Fiore, H. Pham, W. Serwatka, L. Bowen, "Manufacturing of 1-3 piezocomposite SonoPanel ™ transducers", Smart Structures and Materials 1995, SPIE proceedings vol. 2447 pp. 274-281

Technical task

Because of the disadvantages mentioned, there is a need for a flexible manufacturer drive, the manufacturing of differently designed at low manufacturing costs Piezoceramic polymer composite components in terms of geometry and fineness of Structure allowed.

Solution of the task

According to the invention, the solution is possible by using the inexpensive, easy-to-handle film casting process, via which planar ceramic green films are produced, which can be easily processed in the unsintered state. To manufacture the green foils, a ceramic slip is used that contains organic binder components. Various processes such as sawing, punching and laser processing are suitable as structuring processes for these foils. Structuring with lasers has proven to be particularly suitable, especially with the copper vapor laser, since this results in particularly clean cut edges of the green film and any geometrical structuring of the films can be carried out. When structuring, it is important that the structures are held together via a remaining web or frame (see Fig. 1), so that the later rods can initially be handled as a composite for further processing.

Fig. 1

Structured film piece

The structured foils are sintered with these frames / web to the actual ceramic. During sintering, there was a geometrical warping of the rod structure of the green sheet ( Fig. 2), which must be prevented.

Fig. 2

Sintering distortion of fine structures due to shrinkage due to the firing process

Unstructured green foils of the same size are used to solve the problem Underlay used, which then a regular, distortion-free shrinkage of the entire enable placed film stacks.

By using suitable spacers ( Fig. 3) or a slide box system, the sintered, structured foils are stacked in a mold at a defined distance and poured in under vacuum with a suitable castable polymer.

Fig. 3

U-shaped spacer

After the polymer has hardened, it is sawed into the actual 1-3 bond, whereby the piezoceramic rods are separated from the frame ( Fig. 4).

Fig. 4

Design principle for foil-derived piezo transducers using the example of a 1-3 composite

Through final post-treatments such as surface treatment, metal Finally, the finished composite component is obtained in polarization and polarization.

This method can also be used to produce other composite structures in which a component is ceramic. Various composite structures such as e.g. B. 1-3 (see Fig. 4) or 3-3 composite (see Fig. 10). In the case of the 3-3 composite, the structured ceramic green foils have to be laminated into a three-dimensionally connected framework before the sintering. This sintered composite is then filled with polymer (see Fig. 10).

In principle, ceramics can be combined with polymers, metals and other ceramics. Eg:

• a) Ceramic / polymer: Instead of piezoceramic, other oxidic ones cannot oxidic or carbon-containing ceramics are used. Even the poly mer can be of different types, with the sintered ceramic in each case Plastic is embedded.
• b) Ceramic / metal: Instead of plastic, the sintered ceramic structure can also be cast with liquid metals. This requires the mold material be inorganic in nature.
• c) Ceramic / Ceramic: The unsintered or sintered ceramic structure can also filled with ceramic slips from other materials. In this case there is another sintering process to produce the final composite material.

The invention thus provides a versatile way of manufacturing various composite materials that have at least one ceramic Contain component that is introduced as pre-structured ceramic.

Advantages of the invention

This problem solution results in the following advantages for the manufacturing process of composite materials, in particular piezoelectric composites, and for the components themselves:

• - low investment and costs for a production line
• - High flexibility regarding component dimensions, structural geometries and Material combinations
• - continuous film production
• - Continuous structuring possible, e.g. B. band punches, lasers
• - Recyclability of green film residues
• - Fast material removal by processing in the green state
• - Controllable processing
• - Creation of complicated, three-dimensional structures with undercuts, Cavities and baglocks possible
• - High flexibility through any structure in the green sheet, by Ver Use of green foils between 5 µm and 2 mm thick (production of larger Thickening by lamination of green foils before structuring) and in batches the sintered foils into larger composites
• - Training and handling of very fine structures down to approx. 50 µm
• - No handling of fiber bundles or other fine structure particles
• - The formation of bars / frames in the structuring of the foils enables Implementation of this method in a manageable technology
• - Placing green foils enables the implementation of this method with delay free sintered intermediates
• - Use of spacers or slide box systems for adjustment defined distances of the sintered foils from each other.

example

The new manufacturing process for piezoelectric composite components based on Structured, ceramic films are based on the following exemplary embodiments described in more detail and shown with the help of drawings and tables:

Fig. 5: Flow chart of the manufacturing process

Fig. 6: Flow chart of slip treatment

Fig. 7: Structured film piece and U-shaped spacer

Fig. 8: Shrinkage-related sintering of fine structures due to the firing process

Fig. 9: Construction principle for foil-derived piezo transducers using the example of a 1-3 composite

Fig. 10: Construction principle of a 3-3 composite
Table 1: Casting slip composition for PZT
Table 2: Piezoelectric properties

Fig. 5

Flow chart of the manufacturing process

The manufacturing process for piezoelectric ceramic / polymer composites is shown in the adjacent flow diagram. Based on a ceramic Pouring slurry, here using the example of an offset from lead zirconium titanate PZT (Table 1) is used with a film casting machine according to Dr. Blade process a ceramic Film produced. Because the dry shrinkage of the green sheet in the thickness direction is between 50 and 70%, the gap distance of the doctor blade as required between 100 and 2000 microns set to a dried green sheet desired Obtain thickness (e.g. 700 µm).

The slip preparation is carried out according to the flow diagram in Fig. 6.

Table 1

Slip composition

Fig. 6

Flow chart for slip production

In a ball mill, first the solvent and a suitable disper greed presented. Then, after adding ceramic powder, there is a forty-eight hourly dispersion process. In the second step, Binder and Plasti are processed in batches added and homogenized for a further 48 hours. Finally, the finished Casting slurry vented for 1 hour at a vacuum of 300 hPa to ensure no bubbles.

After the cast film has dried, it can be structured using suitable means - mechanically using punching tools or thermally using a laser. Above all, fine rod structures are desired ( Fig. 7a). A fine rod geometry with rod cross-sections ≦ 0.7 × 0.7 mm ² and a rod spacing ≦ 0.4 mm is necessary for 1-3 composites.

The copper vapor laser is e.g. B. for the processing of ceramic green foils very much well suited. Due to its high pulse frequency and low power to achieve a very good stock removal behavior without the material having to be wide To affect heat affected zones along the cut edges and so z. B. the Deteriorate cutting edge quality.

The structured green foils obtained in this way can now optionally to dic keren foils, such as or three-dimensional structures, for. B. the 3-3 composite ( Fig. 10).

After the lamination, the sintering takes place, the green film being transferred to the actual ceramic. This is one of the main problems with the further processing of structured foils or bodies. The structures introduced generally change the sintering behavior of the foils, ie sintering may occur ( Fig. 8). Such problems occur especially with the fine rod structures of 1-3 Composites, since the unstructured areas ( Fig. 8a and b) show a different shrinkage behavior than the structured areas (8c). In the center (see Fig. 8c) will be no delay because the Schwindungskräfte are symmetrical. The sintering draft in area a) is larger than in the interrupted areas, the webs ( Fig. 8b to c), so that the distortion shown occurs. There are no different shrinkage forces in the direction of the strips. To solve this problem, it has surprisingly been found that placing an unstructured green sheet of the same size as a firing aid prevents this delay. There is a regular shrinkage behavior which is transferred by adhesive forces to structured foils or foil stacks lying above it, so that the problem is solved in the entire stack.

Fig. 7

a) Structured film piece

b) U-shaped spacer

Fig. 8

Sintering of fine structures due to shrinkage due to the firing process

Since the organic components of the green film (see slip offset) are decomposed during sintering and emerge from the ceramic green body, the decomposition of the organic components between 100 and 600 ° C must be heated slowly (∼ 50 ° C / h) in the temperature range. The sintering temperature is around 1200 ° C. Following the sintering process, the structured and sintered foils are stacked in a mold using U-shaped spacers ( Fig. 7b) made of ceramic, plastic or the like, or a slide box system with defined distances ( Fig. 9). Then a polymer, e.g. B. Epoxy resin poured into the mold. This is done under vacuum to prevent the inclusion of bubbles.

Fig. 9

Design principle for foil-derived piezo transducers using the example of a 1-3 composite

Fig. 10

Principle of a 3-3 Compo site

After the polymer has hardened, the auxiliary edges of the ceramic foils are removed using suitable tools (e.g. saws) that have held the rods in position ( Fig. 9). By grinding the surfaces, metallizing the end faces and polarizing the ceramics, you finally get to the finished component.

The following table shows the measured piezoelectric properties of the Components produced by this method are shown. The first column shows the properties of the starting powder, the second column a composite of was constructed from foils structured with YAG laser. The third column shows Properties of a copper vapor laser-structured component and the fourth column represents a mechanically structured component.

Table 2

Properties of the 1-3 composites produced by this film technique

Claims (10)

1. Manufacturing process for composite materials, characterized in that

• a) it is based on ceramic films, the z. B. can be produced via the film casting process or immersion process.
• b) the ceramic foils are structured in the green state.
• c) the structured ceramic foils are optionally laminated.
• d) the structured and possibly laminated foils are sintered.
• e) the sintered, structured foils are placed at a defined distance parallel to one another, perpendicularly in a mold or, in the case of the laminated structure, represent a self-supporting body which is placed in a mold.
• f) the shape with the ceramic contained therein with another material such. B. binder / polymer / plastic, molten metal, molten glass or ceramic slip is cast into a composite material
• g) the hardened composite material structure is separated from any existing webs by a separating cut.

2. The method according to claim 1, characterized in that in the case of the manufacture of a ceramic / ceramic Composite the ceramic contained in the mold also as unsintered, so-called called green ceramics. In this case, after Pour a drying step with the ceramic slip onto which then the sintering step follows. 3. The method according to claim 1b, characterized in that the green sheets by laser, e.g. B. the copper steam laser (CVL) or other methods, e.g. B. Mechanical processes be structured. 4. The method according to claim 1b, characterized in that the green foils are structured so that a Web at the ends or an outer frame remains, which is the finer structure gives a hold. This web is removed at the end of the procedure (see claim 1e). 5. The method according to claim 1d, characterized in that the structured green foils for sintering be stacked using an unstructured film of the same size as a base is used, the sintering of the introduced structures throughout Prevents stack. 6. The method according to claim 1e, characterized in that the sintered substrates by means of spacing Holders of a defined thickness can be stacked in a form so as to achieve the desired  Set the distance between the substrates. 7. The method according to claim 1e, characterized in that the sintered substrates in a box be inserted according to the slide box principle to the desired distance between the substrates. 8. The method according to claim 1f, characterized in that the shape is bubble-free with the vacuum liquid component is poured. 9. The method according to claim 1f, characterized in that the shape depending on the temperature stress consists of a temperature-resistant material. 10. The method according to claim 1, characterized in that a piezoceramic, with a polymer such as. B. an epoxy resin to a so-called 1-3 polymer / piezo composite is shed.