# US 5,348,761 A · Use of a swellable plastic and process for making a resistive moisture sensor

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- Number: US 5,348,761 A
- Document ID: US5348761A
- Status: Granted
- Kind: A
- Application number: 07/835,471
- Filed: 1992-02-28
- Granted: 1994-09-20
- Earliest claimed: 1989-08-29
- Assignees: E + E Elektronik Gesellschaft m.b.H.; Lenzing Aktiengesellschaft
- Inventors: Helmut Mitter; Walter Scharizer; Herbert Sollradl; Norbert Rossak
- Web page: https://patentgrep.com/patent/US5348761A

## CPC

- G01M 3/045: {with electrical detection means}
- G01N 27/121: {for determining moisture content, e.g. humidity, of the fluid (moisture content of the tested material G01N27/048)}
- Y10S 252/963: Humidity or moisture indicators
- G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

A process is disclosed for producing a swellable plastic resistive moisture sensor comprising dispersing an additive selected from the group consisting of carbon in powder, dust or soot form, carbon black, graphite, a metal in powder or dust form, and mixtures thereof, into a plastic comprising a polyimide or a copolyimide or both formed from diisocyanate and dianhydride reactants.

## Claims

### Claim 1

A process for producing a swellable plastic resistive moisture sensor comprising dispersing an additive selected from the group consisting of carbon in a powder, dust or soot physical state, carbon black, graphite, a metal in a powder or dust physical state, and mixtures thereof, into a plastic comprising a polyimide or a copolyimide or both formed from diisocyanate and dianhydride reactants.

### Claim 2 (depends on 1)

The process according to claim 1, wherein said additive is selected from the group consisting of graphite in a weight percent concentration of up to 50% and carbon black in a weight percent concentration of 3-15%, wherein said additive has a specific surface area of 100 m/g to 1000 m/g.

### Claim 3 (depends on 1)

The process according to claim 1, wherein dispersing agents are used for said additive and said additive has an average particle size of 25 micrometers or smaller.

### Claim 4 (depends on 1)

The process according to claim 1, further comprising dissolving a polyimide or a copolyimide, having been completely imidized, in a polar solvent, dispersing said additive using a dispersing agent until the additive is homogeneously distributed in the polyimide or copolyimide, and applying said polyimide or copolyimide with said additive to an inert support, and drying.

### Claim 5 (depends on 4)

The process according to claim 4, wherein drying is conducted in at least two to seven stages, with the first stage at a temperature ranging between 80.degree. and 140.degree. C., and each succeeding stage at a temperature increased by 50.degree. to 80.degree. C.

### Claim 6 (depends on 5)

The process according to claim 5, wherein the maximum drying temperature for any stage is 280.degree. C.

### Claim 7 (depends on 5)

The process according to claim 5, wherein the maximum drying temperature for any stage is 260.degree. C.

### Claim 8 (depends on 4, 5)

The process according to claims 4 or 5, wherein the specific resistance of said plastic is 0.5 to 50 kiloOhm-cm.

### Claim 9 (depends on 4, 5)

The process according to claims 4 or 5, wherein the specific resistance of said plastic is 5 to 30 kiloOhm-cm.

### Claim 10 (depends on 4)

The process according to claim 4, wherein said copolyimide comprises, 3,3'4,4'-benzophenone tetracarboxylic acid dianhydride and at least one compound selected from the group consisting of toluylene diamine and toluylene diisocyante and at least one compound selected from the group consisting of 4'4-methylene-bis-(phenylamine) and 4,4'-methylene-bis-(phenylisocyanate), in a polar solvent.