JPH0422465B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a membrane-coated sensor, particularly a method for manufacturing a membrane-coated sensor used in the medical field. [Prior Art] Conventionally, most of the sensors used in the medical field are not inserted into the body or used for extracorporeal circulation, but are incorporated into external measuring devices and measured using the batch method, so there is no need to sterilize them. I stopped talking. For example, in the case of PH sensors, glass membrane electrodes are sometimes sterilized by autoclaving, but this has the drawback of shortening the life of the electrodes. Also, a polymer film-coated electrode that is excellent as a small medical sensor (Japanese Patent Application Laid-open No. 155049/1983)
In this case, autoclave sterilization will cause the inner electrode membrane to elute and deteriorate the electrode properties. On the contrary,
As a method to prevent the internal electrode film from eluting, a method of coating it with a polyvinyl alcohol film (patent application 1986-
No. 101724, Japanese Patent Application No. 120564/1983), but these methods have the disadvantages that it takes time for the electrode characteristics to become stable and that there are large variations from electrode to electrode. [Problems to be Solved by the Invention] The present invention has an electrode configuration that prevents electrode deterioration due to heat treatment, speeds up the stabilization time until stable electrode characteristics are reached, and eliminates variations in characteristics between electrodes. A method of manufacturing a membrane-coated sensor is provided. [Means for Solving the Problem] In order to solve this problem, the method for manufacturing a membrane-coated sensor of the present invention includes the steps of: coating the surface of a conductive substrate with a redox functional layer that exhibits a redox function;
A step of coating the surface of the redox functional layer with a partition layer that prevents outflow of the redox functional layer, a step of coating the surface of the partition layer with an ion-selective layer exhibiting ion selectivity, and heat treatment. It consists of a process. [Function] Through this step, in order to prevent the redox functional layer from eluting into the ion-selective layer due to heat treatment, a partition layer is first coated between the two membranes, and the redox functional layer and the ion-selective layer are coated. Heat treatment is performed in order to quickly form a hydration layer in the layer to speed up the time it takes for the electrode properties to stabilize, and to eliminate variations in the electrode properties. [Examples] Examples will be specifically described below with reference to the drawings. FIG. 1 is a block diagram of the ion sensor of this embodiment. First, conductive substrate 1 (diameter 1.1 mm, length 3.0
A lead wire 2 made of Teflon (registered trademark) coated copper wire (diameter 0.2 mm) is fixed to the bottom surface 1a of the conductive substrate 1 with a conductive adhesive 3, and the outer periphery is fixed so that the tip of the conductive base 1 is exposed by about 1.5 mm. It was covered with a heat shrink tube 4 and insulated with epoxy adhesive 5. As the conductive substrate 1 used in the ion sensor of the present invention, for example, basal plane pyrolytic graphite (basal plane pyrolytic graphite) is used.
graphite (hereinafter referred to as BPG), conductive carbon materials such as glassy carbon; metals such as gold, platinum, copper, silver, palladium, nickel, iron, etc., especially noble metals, or those containing indium oxide, tin oxide, etc. on the surface of these metals. Examples include those coated with a semiconductor. In particular,
Conductive carbon materials are preferred, with BPG being particularly preferred. In order to make the ion sensor compact, the conductive substrate 1 is in the form of a stick, and a redox functional layer 6 is adhered to an area of 1 to 20 mm ² on the outer circumferential surface or the outer circumferential surface and the tip surface. If the area is smaller than this, the electrode membrane resistance of the ion carrier membrane will exceed 50 MΩ at 10° C., which is undesirable, and if it is larger, the ion sensor will not be compact. The stake may be either cylindrical or prismatic, but a cylindrical one with a rounded tip is particularly preferred in terms of moldability and film adhesion. Conventionally, the basal surface of BPG has been mainly used as the electrode surface. However, the inventor
We have discovered that the edge surface of BPG can also be used effectively, and that it is also possible to fabricate a stitch-like electrode using BPG. BPG is particularly superior in terms of stability of sensor operation. For example, if the BPG stake is cylindrical, the diameter should be
It is preferable to set it as 0.1-2 mm. An electrolytic reaction is carried out in a three-electrode cell in which the conductive substrate 1 is a working electrode, a saturated sodium chloride calomel electrode is a reference electrode, and platinum is a counter electrode, to form a redox functional layer 6. The redox functional layer 6 has the property that an electrode formed by adhering it to the surface of the conductive substrate 1 can generate a constant potential on the conductive substrate 1 through a redox reaction. In particular, it is preferable that the potential does not vary depending on the oxygen gas partial pressure. As such a redox functional layer 6, for example, quinone-
Organic compound film or polymer film that can perform hydroquinone type redox reaction, amine-
Preferred examples include organic compound films or polymer films capable of performing quinoid-type redox reactions, and conductive substances such as poly(pyrrole) and poly(thienylene). Here, the quinone-hydroquinone type redox reaction refers to, for example, one expressed by the following reaction formula, taking the case of a polymer as an example. (In the formula, R ₁ and R ₂ represent, for example, a compound with an aromatic-containing structure.) In addition, the amine-quinoid type redox reaction is the same as the above-mentioned polymer, for example, as shown in the following reaction formula. refers to something expressed as (−N=R ₃ ) _o1 −−N−+H ⁺ , +e ⁻ −−−−−−→ ←−−−−−− (−NH−R ₄ ) _o1 −−NH− (in the formula, R ₃ , R ₄ represents, for example, a compound having an aromatic-containing structure.) Examples of compounds that can form such a redox functional layer 6 include the following compounds (a) to (d). (In the formula, Ar ₁ is an aromatic nucleus, each R ₅ is a substituent, m ₂ is 1 to the effective valence number of Ar ₁ , and n ₂ is 0 to
A hydroxy aromatic compound represented by (representing the effective valence number of Ar ₁ -1). The aromatic nucleus of Ar ₁ may be a monocyclic one such as a benzene nucleus, or a polycyclic one such as an anthracene nucleus, a pyrene nucleus, a chrysene nucleus, a perylene nucleus, a coronene nucleus, etc. Moreover, not only a benzene bone nucleus but also a heterocyclic bone nucleus may be used. Examples of the substituent R ₅ include an alkyl group such as a methyl group, an aryl group such as a phenyl group,
and halogen atoms. Specifically, for example, dimethylphenol, phenol,
Hydroxypyridine, o- or m-benzyl alcohol, o-, m- or p-hydroxybenzaldehyde, o- or m-hydroxyacetophenone, o-, m- or p-hydroxypropiophenone, o-, m- or p-
Hydroxybenzophenone, o-, m- or p-carboxyphenol, diphenylphenol, 2-methyl-8-hydroxyquinoline,
5-hydroxy-1,4-naphthoquinone, 4-
(p-hydroxyphenyl)2-butanone, 1,
5-dihydroxy-1,2,3,4-tetrahydronaphthalene, bisphenol A, salicylanilide, 5-hydroxyquinoline, 8-hydroxyquinoline, 1,8-dihydroxyanthraquinone, 5-hydroxy-1,4-naphthoquinone, etc. Can be mentioned. (b) The following formula (In the formula, Ar ₂ is an aromatic nucleus, each R ₆ is a substituent, m ₃ is 1 to the effective valence number of Ar ₂ , and n ₃ is 0 to
An amino aromatic compound represented by (representing the effective valence number of Ar ₂ -1). As the aromatic nucleus of Ar ₂ and the substituent R ₆ , the same ones as Ar ₁ and the substituent R ₅ in compound (a) are used. Specific examples of amino aromatic compounds include aniline, 1,2-diaminobenzene, aminopyrene, diaminopyrene, aminochrysene, diaminochrysene, 1-aminophenanthrene, 9-aminophenanthrene, 9,10-diamino Phenanthrene, 1-aminoanthraquinone, p-phenoxyaniline, o-phenylenediamine, p-chloroaniline, 3,5-dichloroaniline, 2,4,6-trichloroaniline, N-methylaniline, N- phenyl-p
-phenylenediamine, etc. (c) Quinones such as 1,6-pyrenequinone, 1,2,5,8-tetrahydroxynarizalin, phenanthrenequinone, 1-aminoanthraquinone, purpurin, 1-amino-4-hydroxyanthraquinone, anthralfin, etc. kind. Among these compounds, 2,6-xylenol and 1-aminopyrene are particularly preferred. (d) Pyrrole and its derivatives (eg, N-methylpyrrole), thiophene and its derivatives (eg, methylthiophene), and the like. Furthermore, as a compound capable of forming a redox function according to the present invention, poly(N-methylaniline)
[Onuki, Matsuda, Koyama, Journal of the Chemical Society of Japan, 1801-1809
(1984)], poly(2,6-dimethyl-1,4-phenylene ether), poly(o-phenylenediamine), poly(phenol), polyxylenol;
(a) to (d) such as quinone-based vinyl polymer condensation compounds such as pyrazoquinone-based vinyl monomer polymers and isoalloxazine-based vinyl monomer polymers;
An organic compound containing the compound of (a) to (d), a low polymerization degree polymer compound (oligomer) of the compound (a) to (d), or (a) to (d) fixed to a polymer compound such as a polyvinyl compound or a polyamide compound. Examples include those having the redox reactivity such as. In this specification, the term polymer includes both homopolymers and interpolymers such as copolymers. In the present invention, in order to deposit a compound capable of forming the above-mentioned redox functional layer 6 on the conductive substrate 1, an amino aromatic compound, a hydroxy aromatic compound, etc. can be deposited by electrolytic oxidation polymerization method or electrolytic deposition method. A polymer synthesized on a conductive substrate 1 of conductive carbon, noble metal, etc. by a method or a polymer synthesized by application of electron beam irradiation, light, heat, etc., dissolved in a solvent, is used as a conductive substrate. 1 by coating or dipping, a method of reacting in a gas phase under vacuum and depositing directly on the conductive substrate 1, and a method of directly depositing it on the conductive substrate 1 by irradiating it with light, heat, radiation, etc. It is possible to use a method such as attaching the material to the surface of the material. Among these methods, electrolytic oxidative polymerization is particularly preferred. The electrolytic oxidative polymerization method is carried out by electrolytically oxidizing and polymerizing an amino aromatic compound, a hydroxy aromatic compound, etc. in a solvent in the presence of an appropriate supporting electrolyte, and coating the surface of the conductive substrate 1 with a polymer layer. be done. Examples of the solvent include acetonitrile, water, dimethylformamide, dimethyl sulfoxide, propylene carbonate, methanol, etc., and examples of the supporting electrolyte include sodium perchlorate, sulfuric acid, disodium sulfate, phosphoric acid, boric acid, and tetrafluorophosphoric acid. Preferred examples include potassium and quaternary ammonium salts. The thickness of the redox functional layer 6 is preferably 0.01 μm to 1.0 mm, particularly 0.1 to 100 μm.
If it is thinner than 0.01 μm, the effect of the present invention will not be sufficiently achieved, and if it is thicker than 1.0 mm, it is not preferable for downsizing the sensor. Moreover, the redox functional layer 6 used in the present invention
can be used by impregnating it with an electrolyte. Examples of the electrolyte include phosphoric acid, dipotassium hydrogen phosphate, sodium perchlorate, sulfuric acid, tetrafluoroborate, and tetraphenylborate. A convenient method for impregnating the redox functional layer 6 with an electrolyte is to cover the conductive substrate 1 with the redox functional layer 6 and then immerse it in an electrolyte solution. The partition layer 7, which is coated further on the surface of the electrode in which the conductive substrate 1 is coated with the redox functional layer 6 as described above, is formed between the redox functional layer 6 and the ion-selective layer 8. It has the function of preventing the movement of substances constituting each layer and transmitting the potential difference generated in the ion-selective layer 7 due to contact with ions and ions to the redox functional layer 6. Examples of the layer having such a function include a polymer layer containing an electrolyte solution or an aqueous solution, a cellulose derivative, and a water-soluble polymer layer, among which a polyvinyl alcohol (hereinafter abbreviated as PVA) layer is particularly suitable. It is mentioned as a thing. To cover the redox functional layer 6 with the partition layer 7, for example, prepare a 10% aqueous solution of PVA or a 10% aqueous PVA solution containing an electrolyte solution, and thoroughly immerse the redox electrode in this solution → pull it up → air dry → 150°C. Repeat the drying process with
The desired thickness can be adjusted. A PH buffer is preferable as the electrolyte solution, and for hydrogen ions,
Citrate and phosphate solutions are preferred. The pH range is preferably 2 to 8. The thickness of the PVA layer is preferably 0.2 μm to 10 mm, preferably 1 μm to
800 μm, particularly preferably 100 μm to 500 μm. As the ion-selective layer 8 coated on the surface of the partition layer 7, a membrane (neutral carrier membrane) in which a polymer compound supports an ion carrier material for the analyte ions and, if necessary, an electrolyte salt, is used. . For example, the following ion carrier substances are used depending on the ion to be detected. () Hydrogen ions The following materials were used as hydrogen ion carrier materials. For example, the following formula (In the formula, R ⁷ , R ⁸ and R ⁹ are the same or different alkyl groups, and at least two of them are
1 represents an alkyl group having 8 to 18 carbon atoms) and amines represented by the following formula: (In the formula, R ¹⁰ represents an alkyl group having 8 to 18 carbon atoms.) Compounds represented by the following can be mentioned, and a preferable example is tri-n-dodecylamine. Among these, tridodecylamine is particularly preferred. () Potassium ion valinomycin; nonactin, monactin;
dicyclohexyl-18-crown-6, naphtho-15-crown-5, bis(15-crown-
Examples include crown ether compounds such as 5), among which valinomycin and bis(15-crown-5) are preferred. () Sodium ion Aromatic amides or diamides, aliphatic amides or diamides, crown compounds such as bis[(12-crown-4)methyl]
Dodecylmalonate, N,N,N,N-tetrapropyl-3,6-dioxanate diamide, N,N,N',N'-tetrabenzyl-1,
2-ethylenedioxydiacetamide, N,
N'-dibenzyl-N, N'-diphenyl-1,
2-phenylene diacetamide, N, N',
N″-triheptyl-N,N′,N″-trimethyl-4,4′,4″-propyridine tris(3-oxbutylamide), 3-methoxy-N,N,N,
N-tetrapropyl-1,2-phenylenedioxydiacetamide, (-)-(R,R)-4,5
-dimethyl-N,N,N,N-tetrapropyl-3,6-dioxaoctane diamide, 4-
Methyl-N,N,N,N-tetrapropyl-
3,6-dioxaoctane diamide, N,
N,N,N-tetrapropyl-1,2-phenylenedioxydiacetamide, N,N,N,N
-tetrapropyl-2,3-naphthalenedioxydiacetamide, 4-t-butyl-N,N,
N,N-tetrapropyl-1,2-cyclohexanedioxy-diacetamide, cis-N,
N,N,N-tetrapropyl-1,2-cyclohexanedioxydiacetamide, trans-
Examples include N,N,N,N-tetrapropyl-1,2-cyclohexanedioxydiacetamide, among which bis[(12-crown-4)methyl]dodecylmalonate is preferably used. () Chlorine ion (In the formula, R ₇ , R ₈ , R ₉ are the same or different alkyl groups having 8 to 18 carbon atoms, and R ₁₀ is hydrogen or an alkyl group having 1 to 8 carbon atoms.) salt and the following formula Examples include triphenyltin chloride represented by: () Calcium ion calcium bis[di-(n-octylphenyl)phosphate], (-)-(R,R)-N,
N'-bis[(11-ethoxycarbonyl)undecyl]-N,N',4,5-tetramethyl-3,
Preferred examples include 6-dioxaoctane-diamide and calcium bis[di(n-decyl)phosphate]. () Hydrogen carbonate ion (In the formula, R ₁₁ , R ₁₂ and R ₁₃ are each the same or different and represent an alkyl group having 8 to 18 carbon atoms, R ₁₄ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X ^- is
Cl ^- , Br ^- or OH ^- ) Quaternary ammonium salt represented by the following formula: (In the formula, R ₁₆ represents a phenyl group or an alkyl group (C _{1 to 18} ), and R ₁₇ represents a hydrogen atom, a methyl group, or an octadecyl group.) A tertiary amine compound represented by the following formula; Examples include compounds represented by: Examples of electrolyte salts include sodium tetrakis(p-chlorophenyl)borate, potassium tetrakis(p-chlorophenyl)borate, and the following formula (R ₁₈ ) ₄ NBF ₄ (wherein R ₁₈ is an alkyl group, preferably a carbon number of 2 to 2). (6) shows the alkyl group. Examples of polymer compounds include organic polymer compounds such as vinyl chloride resin, vinyl chloride-ethylene copolymer, polyester, polyacrylamide, and polyurethane, and inorganic polymer compounds such as silicone resin. A material that is difficult to dissolve is used. Examples of such plasticizers include dioctyl sebacate, dioctyl adipate, dioctyl maleate, di-n-octylphenylphosphonate, and the like. In order to further coat the surface of the partition wall 7 on the conductive substrate 1 with the ion-selective layer 8 having such a composition, for example, 50 to 500 parts by weight of the plasticizer is added to 100 parts by weight of the polymer compound that is the carrier. , ion carrier material 0.1
or 50 parts by weight and an electrolyte salt etc. dissolved in a solvent (e.g. tetrahydrofuran) is placed on the partition wall 7 of the conductive substrate 1 to a thickness of 1 μm to 10 mm, and dried at room temperature or under heating, or A method can be used in which the conductive substrate 1 covered with the redox functional layer 6 and the partition walls 7 is immersed in a solution and then dried in the same manner. The thickness of the ion-selective layer 8 thus coated is preferably 1 μm to 10 mm. In this example, an ion sensor is produced in which a redox functional layer is coated on BPG by an electrolytic oxidation polymerization method, and a polyvinyl alcohol layer containing an electrolyte and an ion carrier layer are further coated thereon. Here, the BPG, the redox functional layer, and the ion carrier layer are constituent elements of the electrode that exhibit a potential according to the target ion concentration in the measurement solution, and the polyvinyl alcohol layer prevents the redox functional layer from eluting into the ion carrier layer. play a role. By subjecting the ion sensor to heat treatment, particularly autoclave sterilization, not only is the ion sensor sterilized, but the electrode characteristics are quickly stabilized and variations between the electrodes are eliminated. Autoclave sterilization conditions are sterilization temperature
The temperature is preferably 100 to 130°C, particularly preferably 115 to 125°C. The time is preferably 10 minutes or more, especially 10 minutes.
~40 minutes is preferred. Pressure is gauge pressure 1.0Kgf/
cm ² to 2.5 Kgf/cm ² is preferred. As for the atmosphere,
A water vapor atmosphere may be used, but in order to improve the preservation condition after sterilization, it is preferable to use a solution vapor atmosphere close to the pH of living organisms (7.4). , a vapor atmosphere of an aqueous citrate solution is preferred, and a vapor atmosphere of an aqueous phosphate solution is particularly preferred. As this phosphate, sodium hydrogen phosphate is preferred.
When the test ion is a potassium ion, sodium ion, calcium ion, chloride ion, or hydrogen carbonate ion, a dilute aqueous solution (0.1mM to 10mM,
Particularly preferred is a vapor atmosphere (1mM to 5mM). (Example of electrode creation) Basal plain pyrolithic graphite (hereinafter abbreviated as BPG) with a rounded tip (diameter 1
mm) using conductive adhesive, and then insulating the surrounding area with an insulating tube and epoxy resin to create a BPG electrode. this
Poly(2,6-dimethylphenol) (hereinafter referred to as PXY) was prepared using a BPG electrode as a working electrode, a saturated sodium chloride Calomero electrode (hereinafter referred to as SSCE) as a reference electrode, and a platinum winding as a counter electrode under the following electrolytic conditions. The electrolytically oxidized polymer film of BPG is coated on top of the BPG. <Electrolyte composition> 2,6-dimethylphenol 0.5M Sodium perchlorate 0.2M Solvent: Acetanitle <Electrolytic conditions> After three potential sweeps of 0 to 1.5 volts (vs. Ag/AgCl), +1.5 volts (vs. Ag/AgCl) Next, the above PXY-coated BPG electrode was immersed in a 10% by weight aqueous polyvinyl alcohol solution (polymerization degree of polyvinyl alcohol 2000) containing 50mM phosphate and 0.154M sodium chloride and pulled up. ,
The drying process is repeated three times and a polyvinyl alcohol film is coated (film thickness 100 μm to 300 μm). next,
The above electrode is immersed in a dipping solution having the following composition, pulled up and dried, and coated with a proton carrier membrane (film thickness: 0.8 mm). <Dipping liquid composition> Tridodecylamine Potassium tetrakis(p-chlorophenyl)borate Bis(2-ethylhexyl)sebacic acid Polyvinyl chloride Solution: Tetrahydrofuran The PH sensor prepared above was sterilized in an autoclave under the conditions shown in Table 1.

[Table] (Experimental Example) Figures 2 and 3 show changes over time in electrode characteristics (standard electrode potential: E ⁰ , electrode membrane resistance: R) before and after sterilization. There was no effect of sterilization conditions on the properties after sterilization (equilibrium potential, electrode membrane resistance), and the variation in properties between electrodes that was observed before sterilization was resolved by sterilization. Furthermore, no elution of PXY was observed due to sterilization. Comparative Example 1 A PH sensor prepared in the same manner as in Example was not sterilized, and its characteristics (standard electrode potential: E ⁰ ) were measured over time, and the results are shown in FIG. For electrodes that are not sterilized, it takes more than 10 days for E ⁰ to stabilize, and there are variations between electrodes. Comparative Example 2 A PH sensor not covered with the polyvinyl alcohol layer in the example was prepared, sterilized under the same conditions as in the example, and the change over time of the electrode membrane resistance R before and after sterilization was measured, and the results are shown in FIG. It is clear that the electrode membrane resistance changes significantly after sterilization. As described above, when the PH sensor of the present invention is sterilized in an autoclave, the electrode characteristics do not deteriorate, and on the contrary, variations in characteristics between electrodes are eliminated, and the characteristics are quickly stabilized. In this embodiment, a PH sensor has been described, but the same applies to other membrane-coated sensors such as ion sensors and enzyme sensors. [Effects of the Invention] According to the present invention, a membrane-coated sensor can be manufactured that has an electrode configuration that prevents electrode deterioration due to heat treatment, speeds up the stabilization time until stable electrode characteristics are reached, and eliminates variations in characteristics between electrodes. I can provide a method.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of the ion sensor of this embodiment, Fig. 2 is a diagram showing the change in standard electrode potential of the PH sensor of this embodiment over time, and Fig. 3 is a diagram of the electrode membrane resistance of the PH sensor of this embodiment. Figure 4 is a diagram showing changes over time in the standard electrode potential of a PH sensor that is not sterilized. Figure 5 is a diagram showing changes over time in the electrode membrane resistance of a PH sensor that is not coated with a polyvinyl alcohol layer. . In the figure, 1... conductive substrate, 1a... bottom surface, 2...
... Lead wire, 3 ... Conductive adhesive, 4 ... Heat shrinkable tube, 5 ... Epoxy adhesive, 6 ... Redox functional layer, 7 ... Partition layer, 8 ... Ion selective layer.

Claims (1)

[Scope of Claims] 1. A step of coating the surface of a conductive substrate with a redox functional layer that exhibits a redox function, and coating the surface of the redox functional layer with a partition layer that prevents the redox functional layer from flowing out. A method for manufacturing a membrane-coated sensor, comprising the steps of: coating the surface of the partition layer with an ion-selective layer exhibiting ion selectivity; and heat-treating. 2. In the step of coating the redox functional layer, the conductive substrate is used as a working electrode, a saturated sodium chloride calomel electrode is used as a reference electrode, and a platinum winding is used as a counter electrode, and the coating is carried out by electrolysis.
A method for manufacturing a membrane-coated sensor as described in . 3. The partition layer is made of polymeric polyvinyl alcohol containing an electrolyte, and in the coating process, the conductive substrate coated with the redox functional layer is coated by repeating dipping, pulling up, and drying into an aqueous polyvinyl alcohol solution. A method for manufacturing a membrane-coated sensor according to claim 1, characterized in that: 4. In the step of coating the ion-selective layer, the conductive substrate coated with the redox functional layer and the partition layer is repeatedly dipped in a dipping liquid, pulled up, and dried. 2. A method for manufacturing a membrane-coated sensor according to item 1. 5 The conditions for the heat treatment in the heating step are temperature
2. The method for manufacturing a membrane-coated sensor according to claim 1, wherein the temperature is 100 to 130°C for 10 minutes or more. 6 The atmospheric pressure during the heat treatment is 1.0 in gauge pressure.
6. The method for manufacturing a membrane-coated sensor according to claim 5, characterized in that the film-coated sensor is 2.0 Kgf/cm ² .