JP3948725B2 - Thermal history estimation sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a sensor for easily estimating a thermal history, that is, a history temperature and its history time, installed on a subject whose lifetime is determined mainly by deterioration of organic materials due to deterioration of organic materials. It relates to the history estimation method.
[0002]
[Prior art]
Various materials used in the industry and industrial products manufactured using them are often subjected to thermal stress during their production or use, and the physical properties of the materials and product functions are affected by the thermal stress. In many cases, it will eventually endure its use and end its life.
In general, in a product in which an organic substance is used for a part or all of a material, it is known that thermal stress is a factor that greatly affects the product life.
[0003]
This heat stress is a main factor that causes deterioration of the organic material constituting the product due to chemical change, and the degree of the deterioration of the various physical properties and the speed of progress are functions of temperature and time. Therefore, when trying to know the life and degree of deterioration of materials and products, it is not enough to simply measure temperature or time. It is important to know the temperature and time of exposure at the same time. The heat history after the elapsed time of use must be estimated.
[0004]
Conventionally, various methods are known for measuring temperature. Typically, there are materials (temperature indicating materials) that are accompanied by a phenomenon such as discoloration or melting depending on the temperature of a thermolabel or the like. In addition, measurement using a thermocouple or a radiation thermometer is also widely performed.
However, the temperature measurement alone cannot grasp the time of exposure to temperature, which is important when knowing the life and the degree of deterioration of materials and products, and it is impossible to grasp the heat history.
[0005]
On the other hand, as a means of measuring temperature and time, that is, thermal history, it can be achieved by constantly monitoring a thermocouple or a radiation thermometer and recording the temperature and time. In addition to being complicated, the apparatus is complicated and cannot be used in the absence of a power source.
[0006]
In addition, a method has been proposed in which the thermal history is estimated by measuring the change in physical properties of the material by utilizing the fact that the physical properties of the material gradually change due to the thermal history. For example, a method of estimating a thermal history from a spectrum by capturing a change in chemical structure using an infrared spectrum (see, for example, Patent Document 1). A method of estimating the thermal history from two different measurement methods (for example, differential scanning calorimetry (DSC) and dynamic viscoelasticity measurement (DMA)) for measuring a substance to be measured collected from a working device. Patent Document 2), a method of measuring the amount of change in the low-temperature crystallization characteristics of the heat of fusion curve (see, for example, Patent Document 3), and a method using the difference in reflection absorbance between two wavelengths of light (see, for example, Patent Document 4). .) Etc. are known. Although these methods can estimate the thermal history with a certain degree of accuracy, they require special analyzers and the like, and are not easy methods on site.
In view of the above problems, an object of the present invention is to provide a thermal history estimation sensor that can easily estimate the thermal history of materials and products using organic substances, and an estimation method thereof, which is impossible with conventional means. To do.
[0007]
[Patent Document 1]
JP 60-42643 A [Patent Document 2]
JP-A-3-37557 [Patent Document 3]
Japanese Patent Laid-Open No. 9-170989 [Patent Document 4]
JP 2001-22805 A [Means for Solving the Problems]
As a means for estimating the heat history of the present invention, two metal plates, which are bonded by pressing with an adhesive containing metal powder spherical particles, are used as a heat history sensor and exposed to a thermal environment. When it is desired to know the thermal history of a material or product that is attached to or incorporated in the material or product that is being used, the thermal history is estimated by measuring the electrical variables of the sensor.
[0009]
Here, two metal plates are bonded by pressurizing with an adhesive containing metal particles. A thermal history sensor is such that electrical variables such as resistance and capacitance change gradually with temperature and time. In the sensor manufactured in (1), a means for measuring the temperature, time, and electrical change in advance, creating a master curve and comparing it is prepared.
[0010]
Next, a new sensor prepared in the same manner as described above is incorporated in the product in advance, and when it is desired to know its thermal history, such means are used to measure the electrical resistance of the sensor, for example. The objective is achieved by estimating the thermal history by comparing the value with the master curve.
[0011]
The metal plate used in the sensor is not particularly limited as long as it is relatively rigid and does not easily deform, and does not melt or significantly deteriorate (oxidize, etc.) in the operating temperature range. A suitable material is selected from Al, Ti, Fe, Ni, Cu, Zn, Ag, Pt, Au, Mo, W or alloys thereof. The thickness of the plate is not particularly limited as long as it is not thick enough to cause deformation at the time of production, but generally it is preferably about 1 mm to 5 mm.
[0012]
When the two metal plates are bonded together, an adhesive containing metal powder is used. Although there are various types of metal powder, the metal particles used here are preferably spherical particles having a size of about 50 μm to 2 mm and having a relatively uniform particle diameter.
[0013]
The metal particles can be used without particular limitation as long as the conductivity, chemical and physical properties are stable at the operating temperature, and are generally Al, Cu, Ag, Ni, Au, Pt or Powder particles such as alloys thereof are preferred.
[0014]
Furthermore, the compounding quantity to an adhesive agent can be freely mix | blended so that it may match the target characteristic in the wide range of 1-80 wt%.
[0015]
The adhesive to be used is not particularly limited, but an adhesive having a certain degree of rigidity and relatively strong adhesion to the metal plate or metal powder particles to be used is desirable. Of these, epoxy-based, acrylic-based, urethane-based, imide-based and the like are preferably used in view of physical properties.
[0016]
Further, the glass transition temperature of the adhesive to be used is appropriately selected depending on the temperature range in which the sensor is used, but is determined in consideration of the use temperature of the product to be incorporated.
[0017]
In addition, when the metal particle-containing adhesive is applied, sandwiched between metal plates, and cured, the adhesive needs to be cured in a pre-pressurized state so that the metal particles contained in the adhesive layer are deformed. The degree of pre-pressurization at this time is appropriately selected depending on the type, size, content, and the like of the metal particles, and is generally cured under a pressure of about 0.1 to 10 MPa.
The curing temperature at this time also varies depending on the adhesive to be used, but is generally between room temperature and 250 ° C.
[0018]
After the adhesive is hardened, cool it to room temperature with pre-pressurization, release the pre-pressurization, shape the end face, and seal or cover the electrical variable value so that it does not change due to external contamination or moisture. Appropriate end face processing is performed, and the heat history sensor is provided.
[0019]
FIG. 1 is a schematic external view of a thermal history estimation sensor according to the present invention, and FIG. 2 shows an enlarged schematic view of its cross-sectional structure.
[0020]
Such a heat history sensor can be selected depending on the type of metal plate, the glass transition temperature of the adhesive, the elastic modulus after curing, the type and content of metal particles, the pressing conditions during the manufacturing process, the curing temperature, the curing time, etc. It is easy to create one with the characteristics
The thermal history sensor obtained in this way is prepared in advance as described above, and the thermal history sensor is installed at an appropriate location of the product whose thermal history is to be estimated. Measure electrical variables and estimate the thermal history of the product by comparing it with a master curve created in advance.
[0021]
[Action]
The sandwiched metal particles are constrained between the metal plates as the adhesive is cured while being elastically deformed and plastically deformed by pressurization.
Therefore, the repulsive force acts as an internal stress inside the adhesive layer, but at a temperature much lower than the glass transition temperature of the adhesive, the adhesive is hardly deformed by the internal stress resulting from the repulsive force of the metal particles. For example, when the change in resistance is captured as an electrical variable, the initial electrical resistance hardly changes, but when the temperature rises and near the glass transition temperature, the elastic modulus of the adhesive decreases and the internal stress is relieved. A so-called creep phenomenon that gradually deforms occurs. At this time, the contact state between the metal particles and the metal plate changes, the contact resistance changes, and the electrical resistance gradually increases. This increase in electrical resistance is a function of the exposed temperature and time and is determined by the thermal history.
DETAILED DESCRIPTION OF THE INVENTION
[0022]
Hereinafter, although one form of the Example of this invention is described, it is not limited to embodiment shown below.
Two aluminum plates of length 50 × width 50 × thickness 3 mm were prepared as electrodes, and the adhesive surface was degreased with acetone and dried. On the other hand, about 30mm% of copper particles mixed into an epoxy adhesive (glass transition temperature 120 ° C) as spherical particles with a diameter of about 0.1mm and a uniform particle size are mixed on one aluminum plate with a thickness of about 0.2mm. Then, it was laminated with the other aluminum plate and cured by heating at 100 ° C. for 4 hours under a pre-pressurization of 1 MPa. The test piece was cut to a size of 10 mm × 10 mm and the end face was polished, and then sealed with an epoxy resin so that the electrical variable did not change due to contamination or moisture absorption of the end face, to obtain a thermal history sensor. Needless to say, the electrical variable includes a change in AC impedance such as a resistance change and a capacitance change.
[0023]
Some of these sensors were left in a thermostatic chamber at different temperatures, and changes in electrical variables were measured. Here, the resistance change was traced as an electrical variable. A curve as shown in FIG. 3 was obtained with time, and this was used as a master curve.
Moreover, when the same heat history sensor was created by the same method as the above embodiment except that epoxy adhesives (160 ° C. and 180 ° C.) having different glass transition temperatures were used, as shown in FIG. 4 and FIG. A curve was obtained.
[0024]
Also, in the temperature range higher than the glass transition temperature of the adhesive used for the thermal history sensor, the elastic modulus of the adhesive is greatly reduced, so the rate of change of resistance is extremely large, and practically around the maximum allowable temperature allowed for the product. It is desirable to use a thermal history sensor using an adhesive having a glass transition temperature of
[0025]
Generally, in the thermal history sensor of the present invention, the usable temperature range is from a temperature about 50 ° C. lower than the glass transition temperature of the adhesive used to a temperature about 10 ° C. higher than the vicinity of the glass transition temperature. By incorporating several thermal history sensors made using adhesives having different glass transition temperatures, the estimation accuracy of the thermal history is further improved.
[0026]
【The invention's effect】
As is apparent from the above description, by using the thermal history sensor of the present invention, estimation of thermal history, which has been difficult in the past, can be performed extremely simply.
Obtaining a thermal master curve, incorporating a sensor with the same characteristics as the master curve into the product, and grasping the thermal history easily by means of comparing the master curve with the means to measure the electrical variables of the sensor when necessary, Can be estimated.
[Brief description of the drawings]
FIG. 1 is a schematic external view of a thermal history sensor according to the present invention. FIG. 2 is a schematic enlarged sectional view of a thermal history sensor according to the present invention. FIG. 3 is a thermal history of a thermal history sensor prepared using an adhesive having a glass transition temperature of 120.degree. Master curve showing the relationship between the electrical resistance and the master curve [Fig. 4] Master curve showing the relationship between the thermal history and the electrical resistance of the thermal history sensor made using an adhesive having a glass transition temperature of 160 ° C [Fig. 5] Glass transition temperature of 180 ° C Master curve showing the relationship between thermal history and electrical resistance of thermal history sensors made with adhesives
1 Metal plate
2 Adhesive layer
3 Metal particles

Claims (3)

When a metal plate (1) is bonded with a mixture of metal particles (3) and an adhesive to form a sandwich structure having an adhesive layer (2), the metal particles (3 ) are bonded and cured when the metal plate (1) is bonded and cured. The thermal history estimation sensor using the metal plate (1) as an electrode. The thermal history estimation sensor according to claim 1, wherein the adhesive has a glass transition temperature of 0 to 250 ° C. Thermal history estimating sensor according to claim 1 or 2, wherein in that a means for comparing the master curve prepared in advance with means for measuring the electrical changes between the electrodes.

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