DE10146805B4 - Method for producing a film for lining casings - Google Patents

Abstract

A process for producing a doctor blade cast film using a foundry slurry containing 3.6% by weight of butyl benzyl phthalate as a plasticizer, 5.4% by weight of PV-butyral PV-alcohol PV acetate as a binder, and 91% by weight of a Ferrite powder, the composition ZnO: 25 mol% NiO: 25 mol% Fe2O3: 50 mol% and an organic solvent mixture in order to achieve the appropriate viscosity of the slurry.

Description

The invention relates to a method for producing a film for the passive electromagnetic protection of electrical or electronic systems. This passive protection concerns both the functioning of the systems by avoiding reflections or field elevations in their interior and the penetration of electromagnetic radiation from the outside (immunity to interference) and the protection of the environment from possibly emerging from the system so-called electric smog.

With the development of higher and higher frequency ranges, constant reduction of power requirements and the continuing trend towards miniaturization of electronic components, new standards are set to ensure the reliability and functional safety of electronic systems. The industry is committed to meeting these needs with dedicated package designs, shields, and appropriate circuit design, and is increasing its efforts.

In the housing industry so far only metal shields, metal foils and metallized plastic parts are used. Although the principle of shielding is suitable for reducing the leakage / entry of electromagnetic fields, it has the considerable disadvantage that reflection and field elevations are present inside the housing which impair the function of electronic components, which as a rule results in additional shielding requirements inside the housing.

As the trend in the electronics sector is clearly towards even higher frequencies, reflections and field concentrations are all the more disadvantageous and reduce the reliability of electronic systems. This results in the need to introduce new solutions. Previous protective mechanisms in housings are only active nature. Passive protection mechanisms have so far been used only in the cable industry through the use of shielding surfaces and ferrite rubber compounds.

The application and dimensioning of novel absorbent layers as a layer system in housings or subracks has not previously been reported. Also, the application in terms of increasing the screen attenuation and the prevention of internal field elevation has nowhere been set out as a patent or professional publication. US Patent Publications only relate to the internal protection of electronic components in PC cases and do not consider the shield attenuation of the entirety of all the components housed in the case.

Arrangements or materials for protection against electromagnetic waves per se are widely known from the patent literature, but always represent only solutions to partial aspects of the above-outlined object of "protection to both sides" by, for example, at least partially reflective or have other serious disadvantages :
DE 196 00 230 A1 describes the so-called Herzsche grid of two mutually perpendicular grids. Here is an expected from the geometric dimensions, here undesirable high selectivity in terms of absorbed frequency range and also such an arrangement is limited to simple bodies, such as cubes and cylinders.

The technical solution after DE 195 25 636 A1 consists of a ferrite plate, which is provided with a resistive layer. Here, only a reflection attenuation is expressly sought and with respect to the ferrite plate is also the oe restriction to simple body.

To DE 43 24 916 A1 It is known to process ferrite powder with cement or synthetic resin as a binder to form elements for lining of measuring chambers. The flexibility in terms of shape here analogous to building stone on stone only in large, but not given in smaller devices and systems.

DE 42 05 803 A1 refers to absorbers in the Hz or kHz range with electrically conductive phases, such as Ni, Cr, Fe, C. The frequency range in which this absorber is effective, is no longer sufficient today.

DE 38 11 571 A1 refers to foam absorbers with graphite and ferrite, which is supposed to absorb light and sound at the same time, ie represents a typical mass product with application focus in building construction.

The US patent US 5,443,900 describes an absorber arrangement of a variety of extremely thin metal-coated plastic layers. Ferrites are not used here and the figures show extremely narrow-band absorption in the vicinity of 10 GHz.

The US patent US 5 583 318 A refers to multilayer absorbers having a plurality of thick layers, each with textured surfaces. Such an arrangement is very expensive to manufacture and has considerable thickness dimensions.

The publication DE 35 39 509 A1 describes a shielding composite film with dispersed conductive fibers and a conductive or semiconducting particulate filler. Ferrite-based fillers are not used here.

A large group of composite materials made of a polymer with powdered soft ferrite filler relates to the rational production even of intricately shaped cores for inductive components (for example EP 0 542 200 A1 ; EP 0 764 955 A1 ; EP 0 921 534 A1 ; EP 0 986 074 A1 ). In this context EP 0 558 178 A2 the high permeability values of an injection moldable composition of certain polymers with copper-containing nickel-zinc ferrite powder, without reference to the application for electromagnetic protection.

Composite materials for the suppression of electromagnetic interference are also known in which, in a preferably organic binder phase, semi-hard magnetic alloy particles ( EP 0 884 739 A1 ) or two groups of soft magnetic particles of different resonance frequency, which may consist of both alloys and of ferrites ( EP 0 785 557 A1 ) are dispersed. In the latter case, the suppression effect to reach about 2 Ghz, which is not satisfied in view of the high cost of the combined application of two different soft magnetic materials with different resonance characteristics.

Finally, a ferrite compound material with high electromagnetic absorption is known (US Pat. DE 100 00 523 A1 ), which consists of an ethylene-vinyl acetate copolymer, the 85 to 90% by weight of ferrites are added. Another condition for effectiveness is a restriction to a sheet resistance of 370 to 390 ohms.

The DE 28 51 388 C3 relates to a waveguide with a coating for absorbing radio frequency interference. Granules Ni-Zn ferrites can be used for absorption because of their magnetic properties. Their use, however, cause high costs, so that with the DE 28 51 388 C3 is based on the use of other materials.

The DE 199 11 394 A1 relates to composites in the form of a paint or foil to be used for the broadband shielding of electromagnetic waves. The composites consist of at least one magnetic and one conductive component and a binder. The binder should consist of organic polymers, preferably a PE-PVAC copolymer. Information on the production of a film can not be found in the document.

Of the DE 40 03 908 A1 are mixtures of high temperature resistant polymers and fillers removable, which have a very high filler content and particularly suitable for shielding electromagnetic radiation and as a microwave absorber in the form of hollow bodies, moldings, profiles, fibers, films or coatings. Again, no indication of the production of a film is included.

The invention has for its object to provide a product for highly effective passive electromagnetic protection of electrical or electronic systems to improve their reliability and environmental compatibility, the method for producing corresponding housing parts or linings easily feasible, even with complicated housing shapes adaptable and safe compliance with the shielding characteristics.

This object is achieved by the invention described in the claims.

The films produced in this way have excellent screen damping properties and serve as a film for lining housings the effective passive electromagnetic protection or the absorption of electromagnetic radiation.

The invention with its manufacturing method will be explained in the following general and then in detail with reference to Example 2. The attached figures show:

1 an illustration of the shear roller assembly used,

2 a schematic representation of the film casting,

3 Particle size distribution of the ferrite powder after dry grinding,

4 SEM micrograph of ferrite powder at about 2000x magnification

5 X-ray diffractogram of the ferrite powder,

6 Hysteresis curve of the injected compound material,

7 Reflection damping of the injection-molded compound material,

8th Shield attenuation of the injection-molded compound,

9 Stripline measuring arrangement for determining the reflection attenuation,

10 Measuring cell for shielding attenuation measurement,

11 Probe antenna geometry,

12 Reflection damping of the cast film,

13 Reflection damping of the rolled foil.

Ferrite powder production (prior art)

For the production of soft ferrites of the types:
A _1-x B _x Fe ₂ O ₄ or A1 _{-xy / 2} B _{xy / 2} Fe _{2 + y} O ₄ or C _z A _{1 -xy / 2-z} B _{xy / 2-z / 2} Fe _{2 + y} O ₄
With
A ... Ni, Mn;
B ... Zn;
C ... Co, Ti, Cu
0. ≤ x ≤ 1
0≤y≤0.3
0 ≤ z ≤ 0.3
the oxides of the above elements are used. These are first wet-mixed and then dried. The calcination of the mixed oxides takes place at 1050 ° C. After calcination, a fine grinding takes place in the planetary ball mill. The finely ground, calcined powder is then sintered and finely ground. The particle size distribution of the ferrite powders is in the range 1-300 μm, the mean particle size (d50) assuming values in the range from 2 μm to 100 μm.

Compound production and processing (prior art)

The soft ferrites produced in this way are sheared ( 1 ) or extruder or kneader to a compound granules, with 50% by mass to 90% by mass of ferrite powder, processed on the basis of a thermoplastic. As thermoplastics, polyethylenes, polypropylenes, ethyl-vinyl acetate copolymers and polyamides are used. The resulting ferrite polymer compound granules are then further processed by rolling, extrusion or injection molding into films or housing components.

Film casting technical processing

The produced soft ferrite powders are processed into a casting slip. This is composed of 10% by mass to 30% by mass of an organic solvent mixture, 1% by mass to 5% by mass of plasticizer, 1% by mass to 10% by mass of binder and a percentage of residual ferrite powder. The homogenization of the slurry is carried out by homogenizing for several hours in a ceramic drum. The homogeneous slurry is placed in a pouring box and poured over a stationary docter blade onto a moving casting pad ( 2 ). In a downstream drying section, the solvents are removed. The cast film is assembled in the next step and serves the housing lining.

Embodiment 1 (Prior Art)

Injection-molded housing component made of ferrite polymer compound

Ferritpulverherstellung

• Batch size 250 g

Composition:

• ZnO: 25 mol%
• NiO: 25 mol%
• Fe ₂ O ₃ : 50 mol%

Test sample:

• ZnO: 42.879 g
• NiO: 39.278 g
• Fe ₂ O ₃ : 168.238 g00

wet mixing:

• Duration: 2 h
• Powder: 250 g
• Balls: 1 kg
• Water: 250 ml
• Container: plastic drum
• Speed: 44 rpm

calcination:

• Duration: 4 hours
• Temperature: 1050 ° C
• Heating up: 10 K / min
• Cooling: 10 K / min

Fine grinding (wet):

• Mill: planetary ball mill
• Grinding time: 30 '
• Speed: 100

Filling the grinding bowls:

• Number: 2
• Powder: 125 ml each
• Steel balls: 500 g
• Water: 80 ml

Sintering powder:

• Duration: 4 hours
• Temperature: 1300 ° C
• Heating up: 10 K / min
• Cooling: 10 K / min

drying:

• Duration: 30 '

grinding:

• Balls: steel balls, 750g
• Container: plastic drum
• Speed: 44 rpm

In 3 the grain size distribution of the ferrite powder after dry grinding is shown. 4 shows a SEM micrograph of the ferrite powder with the composition Ni0.5Zn0.5Fe2O4 and 5 the X-ray diffractogram of this ferrite powder.

Production of the ferrite polymer compound and injection molding

250 g of the ferrite powder are mixed with 34 g of ethylene vinyl acetate copolymer and dried at 80 ° C in a drying oven for 2 h. Subsequently, the compounding via the shear roller. The compound skin removed from the roller is comminuted in the granulator and homogenized again over the shear roller. After re-crushing the injection molding processing takes place.

6 shows the hysteresis curve of the injected compound material. 7 shows the reflection loss of the injection-molded ferrite compound material; it is on average 10 dB to 15 dB. The measurement takes place in a stripline in combination with a network analyzer. 8th shows the shield attenuation of an injection-molded ferrite compound housing, measured in the far field according to ASTM standard. Here, the measuring arrangement consists of two round chambers. Each chamber has two radius-opposed BNC beech, the inner conductor of which is connected to the wire which acts as a transmitting and receiving antenna. To measure the screen attenuation, the blank sample was first placed between the chambers, tightly screwed and the network analyzer normalized to the resulting transmission characteristic. Then the blank sample was replaced by the measurement sample, so that the network analyzer now displays the screen attenuation as a measurement result. The measured shielding attenuations are in the range of up to 12 dB. 9 shows the stripline measuring arrangement, for determining the reflection attenuation, 10 shows the arrangement of the measuring cell for the screen attenuation measurement. Additional measurements on injection-molded housing components in a probe antenna geometry ( 11 ) in an absorber space gave a mean attenuation of 15 dB in the frequency range from 60 MHz to 1 GHz.

Embodiment 2

Ferrite polymer compound film for housing lining, produced by film casting

The Ferrritpulverherstellung takes place analogously to Example 1 with a batch size of 5000 g.

The ferrite powder is processed into a casting slurry. This consists of:
3.6 mass% of plasticizer, Santicizer ^® 160 butyl benzyl phthalate
5.4% by weight binder, PV butyral PV alcohol PV acetate
91% by weight ferrite powder

Furthermore, an organic solvent mixture is added to achieve the appropriate viscosity of the slurry.

The homogenization of the slip takes place by 24-hour processing in a ceramic drum with steel balls. The homogeneous slip is poured in a docter blade into a film of length 7000 × 300 mm 2. After drying the film, the average film height is 1050 microns.

12 shows the reflection loss of the film, measured in a stripline arrangement. In the measured frequency range an average attenuation of 2 dB is achieved.

Embodiment 3 (Prior Art)

Ferrite polymer compound film for housing lining, produced by film rolling

The Ferrritpulverherstellung takes place analogously to Example 1 with a batch size of 5000 g.

5000 g of the ferrite powder are mixed with 1250 g of polyethylene and dried at 80 ° C in a drying oven for 2 h. Subsequently, the compounding via the shear roller. The compound skin removed from the roller is comminuted in the cutting mill. The ferrite polymer compound granules are rolled into a foil in a heatable rolling mill. The film thickness is 1 mm. 13 shows the reflection loss of the film, measured in a stripline arrangement. In the measured frequency range an average attenuation of 1 dB is achieved.

Claims (2)

A process for producing a doctor blade cast film using a foundry slurry containing 3.6% by weight of butyl benzyl phthalate as a plasticizer, 5.4% by weight of PV-butyral PV-alcohol PV acetate as a binder, and 91% by weight of a Ferrite powder, the composition ZnO: 25 mol% NiO: 25 mol% Fe ₂ O ₃ : 50 mol% and an organic solvent mixture in order to achieve the appropriate viscosity of the slurry. Use of the film produced according to claim 1 for lining casings for the purpose of passive electromagnetic protection and / or absorption of electromagnetic radiation.

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