JPS6055965B2 - Manufacturing method of temperature sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a temperature sensor using a conductive organic material, and in particular, by heat-treating an aromatic polyimide resin, a linear, band-like or planar shape with excellent thermal stability can be produced. It provides a temperature sensor.

Conventionally, a temperature sensor using an inorganic oxide, generally called a thermistor, has been widely used as a temperature sensor for detecting the temperature at a certain point.

This inorganic oxide temperature sensor has excellent reliability, so there is little room for other temperature sensors to be used. Today, there is an increasing demand for not only detecting point temperature but also accurately detecting the temperature of objects with planar, linear, or more complex shapes. Linear and planar temperature sensors are required to detect the temperature of such objects. However, the above-mentioned inorganic oxides are difficult to process into linear or planar shapes, and are therefore unsuitable for such purposes. Generally, temperature sensors are required to have the following characteristics.

(1) The temperature dependence of the resistance value, that is, the B constant is large. (2) The resistance value to be detected is appropriate.

(3) It must have excellent heat resistance. If there is an organic material that satisfies these conditions, it must be promising as a temperature sensor because orange materials generally have good moldability.

The present invention relates to a method for manufacturing an organic temperature sensor that satisfies the above conditions. The remarkable development of polymer chemistry in recent years has led to wonderful developments in the field of thermal stability, which has traditionally been considered the biggest drawback of organic materials. These materials are called heat-resistant polymers, and typical examples include fluorinated oxygen resin, poly(phenylene) oxide, polyvaraxylylene, aromatic polysulfone, polyamide, aromatic polyamideimide, polyesterimide, and aromatic polyimide. , polybenzimidazole, etc. are known. These materials not only have excellent heat resistance but also a large coefficient of resistance, so if an appropriate resistance value can be imparted to them, they could be excellent materials for temperature sensors. However, the specific resistance values of the above polymers are all 1016 to 1 Cf! Since it is an insulator of about OΩG, it cannot be used as a temperature sensor as it is. 196fF. IBM's S. D. Bruck is DuPont's Kapton H film (polyimide film)
is thermally decomposed in a vacuum at a high temperature of 800'C or higher.
It was discovered that it changes into a conductor of ×10-2Ωα.

This type of thermal decomposition method is thought to be an effective method for imparting electrical conductivity to heat-resistant polymers, but it is not necessarily applicable to all heat-resistant polymers, and it is not always applicable to all heat-resistant polymers. Several conditions are necessary, such as being high and allowing recombination to occur after decomposition. This type of thermal decomposition method has not been able to find any suitable use for the resulting conductor, and further research has not progressed. However, for the purpose of a temperature sensor, the electrical conductivity does not necessarily need to be large, and it is sufficient to have a range of about 1010 to 1σΩCm, so if such electrical conductivity can be imparted, it will be possible to create new and large applications. There is no doubt that it will open up. From this point of view, the present invention attempts to obtain a novel temperature sensor using a thermal decomposition reaction of polyimide resin. First, it is necessary to keep the resistance value of pyrolytic polyimide (abbreviated as PPI) within the range of 1010 to 1σΩCm.

Therefore, using Kapton H film, a predetermined. 4 in temperature
Heat treatment was performed in a Hr vacuum, and the resistance value was measured. The results are shown in FIG. The resistance value decreases rapidly with the heat treatment temperature, and under the heat treatment condition of 4 hours, it was 1010Ω at 550℃.
It has become clear that the resistance becomes 1σΩ or less at temperatures above 700°C. Next, we learned the B constant of the resistor and determined whether it could be used as a temperature sensor.

Figure 2 shows the processing temperature when heat-treated under the above conditions and the B constant of the obtained resistor (calculated between 20°C and 200'C).
Indicates the relationship between It goes without saying that a larger B constant is better as a temperature sensor, but with recent advances in detection circuits, a B constant value of 100 degrees is considered to be sufficient for use as a temperature sensor. According to Figure 2, the B constant when heat treated at 550°C is 38001.
1000 at 700°C, indicating that resistors in these ranges can be used satisfactorily as temperature sensors. FIG. 3 shows the temperature-resistance characteristics of the resistor after being treated at 600° C. for 4 hours. The temperature-temperature-resistance characteristic shows typical semiconductor characteristics in which the IOgρ (ρ is specific resistance)-temperature characteristic is a straight line up to at least 300°C, indicating that it has excellent properties as a temperature sensor. . Such excellent thermal stability was unimaginable for conventional organic temperature sensors. FIG. 4 shows the relationship between the treatment time and the specific resistance value ρ in the case of heat treatment at 600 degrees Celsius.

At 600° C., the resistance value was not constant even after 8 hours of heat treatment, indicating that thermal decomposition was in progress.

Figure 5 shows the relationship between treatment time and weight loss % based on TGA measurements conducted to predict the progress rate of the thermal decomposition reaction.In thermal decomposition at 650°C, the weight loss is a constant value of 47% in about 3 hours. reach %.

Therefore, it can be seen that the reaction can be completed in a treatment time of 3 hours or less at a temperature higher than this. In order to control the specific resistance value and the B constant, there is a method of controlling the characteristics by processing temperature,
One possible method is to control the characteristics using processing time, but in terms of reproducibility, the method of controlling processing temperature is clearly superior.

For example, in order to obtain a resistance value of 1107 Ωo at 650°C, the processing time must be reduced to about 5 to 2 times, but this is the point where the weight loss curve decreases rapidly, so accurate control is virtually impossible. It's possible. On the other hand, it is not impossible to obtain a resistance value of 1010 Ωα or less even at a temperature of 550° C. or less if heat treatment is performed for a very long time of 10 hours or more. However, such a long time is not realistic in actual manufacturing sites, considering ease of operation, productivity, etc. Considering the above, the specific resistance value is 1010Ωd~1σ, which is the preferable condition for a temperature sensor.
It can be seen that in order to obtain a P-circle film that satisfies the ΩDlB constant of 1000 or more, it is sufficient to perform heat treatment at a heat treatment temperature of 550 to 700° C. for 1 hour to several hours or more. Note that similar results can be obtained by increasing the heat treatment time in an inert gas atmosphere other than vacuum. As described above, it has been found that by appropriately selecting the processing method, it is possible to reduce the variation in resistivity value to within ±300% and the variation in B constant to within ±10%.

Since the actual resistance value can be controlled by the electrode width, there is no need to worry much in this case, and a variation in the B constant of within ±10% is sufficient for a temperature sensor. As described above, the PPI film has excellent properties as a temperature sensor, but several additional features can be improved.

The first is that it is easy to form, and by cutting out a film-like polyimide into an arbitrary shape and heat-treating it, a planar sensor of any shape can be made. Second, PPL itself is relatively fragile;
Although it is not suitable for use as a flexible temperature sensor, it can be easily pulverized into fine powder, so it is possible to make a printing type temperature sensor by dispersing the powder in a polymer binder. The biggest problem with these types of temperature sensors is agglomeration of conductors. The third characteristic of PPI powder is that, unlike PPI graphite, it is an organic material containing many hydrogen atoms, so it is compatible with most polymeric binders and solvents, and shows almost no formation of secondary particles due to agglomeration. That's the point. For example, binders include polyurethane, epoxy, phenoxy, silicone, polyimide, polyamide, imide, chlorocarbon, polyxylene, polyester, polyvinyl, acrylic, phenol, melamine, guanamine, polyamide, polysulfide, etc., which have mechanical properties such as adhesiveness and film properties. are selected taking into consideration. Examples of PPI temperature sensors having such characteristics are shown below.
<Example 1>, 8 In Examples 1 and 2, electrodes were printed directly on the PPI film and used as a temperature sensor as is.

FIG. 6 shows a configuration diagram of a parallel electrode quip sensor which is generally used when the resistivity value is less than 1 Cf'ΩCm. 1 is an insulating substrate made of ceramic or the like, on the surface of which a sensor film 2 is adhered.

The reason why such an insulating substrate is used is to supplement the mechanical strength of the sensor film. The electrode 3 is selected from carbon paste, graphite paste, silver paste, etc., and is printed on the sensor film. It has been confirmed that the sensor constructed in this manner exhibits excellent responsiveness to temperature. Embodiment 2> FIGS. 7A and 7B are block diagrams of a sandwich type sensor that is generally used when the resistivity value is 101 Ωα or more.

2 is a sensor film, 3 is an electrode coated on the sensor film, and 4 is a metal foil for taking out a lead wire.

With such a configuration, the resistance value of the sensor that is actually measured can be set to a value of 100 MΩ or less. <Example 3> Here, an example of a combination obtained by dispersing PPI in a polymer binder is shown.

A 5% by weight acetamide/pyrrolidone solution of polyimide was cast onto a glass substrate to form a film with a thickness of 0.1 to 0.5μ, cured at 300°C for about 30 minutes, and then the glass substrate was immersed in water. A polyimide film was dispersed. This film was pyrolyzed in vacuum at various temperatures from 500°C to 900°C for about 4 hours, and then crushed in an attritor for 2 hours.
A powder of 00 mesh or less was obtained. Data is shown when an epoxy resin is used as the binder and the PPI to binder ratio is 80:20. A paste consisting of PPI-epoxy was thoroughly kneaded using three rolls, and was formed into a film by coating and printing on a ceramic substrate using a J3OO mesh screen. The table shows the electrical properties of the film. I can do that.

A constant binder/filler ratio means that only the electrical properties can be controlled while the mechanical properties of the composition change little, which is an important advantage of the present invention. Long-term stability of resistance value is 10% between 85℃ and 500C@
It can be said that it is extremely excellent.

Further, the maximum operating temperature was about 250°C. The above PPl
It was also possible to form a film using polyester resin as a binder, making it ideal for use in flexible circuits using a polyester base.

In addition, when silicone is used as a binder, 350
A conductive composition with heat resistance up to ℃ was obtained, which is suitable for use as a heater. As described above, the present invention is a PPI film made by heat-treating polyimide in a temperature range of 5500C to 700C for 1 hour or more in a vacuum or inert gas, or a film made by powdering this PPI and mixing it with a binder. to form a desired shape such as dots, lines, or planes,
This is a method for manufacturing an organic temperature sensor in which electrodes are formed on this film or membrane, and it is possible to obtain temperature sensors in complex shapes such as dots, lines, and planes.

[Brief explanation of the drawing]

Figure 1 shows the relationship between resistivity and processing temperature when Kapton H film is thermally decomposed in vacuum at a predetermined temperature for 4 hours. Figure 3 shows the relationship between the B constant and processing temperature when thermal decomposition is carried out at 600°C.
Figure 4 is a diagram showing the temperature-resistance characteristics when thermally decomposed in vacuum for time. Figure 4 is a diagram showing the relationship between specific resistance value and processing time when Kapton H film is thermally decomposed at 600°C in vacuum.
The figure shows a weight loss curve when Kapton H film is heat-treated in vacuum. Figure 6 is a plan view showing the configuration of a sensor consisting of parallel electrodes. Figure 7 A and b are a plan view and cross section of a sensor consisting of sandwich electrodes. There is a diagram. DESCRIPTION OF SYMBOLS 1... Insulating substrate, 2... PPI film, 3... Electrode, 4... Metal foil for taking out the electrode.

Claims (1)

[Claims] 1 Polyimide in vacuum or inert gas,
A method for manufacturing a temperature sensor, characterized in that electrodes are formed on a film that essentially contains a material obtained by thermal decomposition in a temperature range of 700°C. 2. The method for manufacturing a temperature sensor according to claim 1, wherein the thermal decomposition time is from one hour to several hours or more. 3 Using film-like polyimide as the polyimide,
A method for manufacturing a temperature sensor according to claim 1, wherein an electrode is formed on the film after thermal decomposition. 4. The method for manufacturing a temperature sensor according to claim 1, wherein the polyimide after thermal decomposition is powdered and mixed into a binder, and the powder is coated on a substrate and formed on a film by printing or the like. 5 As a binder, polyurethane, epoxy, phenoxy, silicone, polyimide, polyamide-imide,
Fluorocarbon, polyxylene, polyester, polyvinyl, acrylic, phenol, melamine, guanamine,
The method for manufacturing a temperature sensor according to claim 4, using either polyamide or polysulfide.