JPH07134108A - Thermal conductivity coefficient measuring method for low thermally conductive sheet - Google Patents

Abstract

PURPOSE:To provide a method to measure easily and precisely the thermal conductivity coefficient of a low thermally conductive sheet such as a sheet of paper, a film made of resin, etc., by using only one sheet. CONSTITUTION:Regarding a thermal conductivity measuring method for a low thermally conductive sheet to measure the thermal conductivity of the low thermally conductive sheet 2 by measuring the temporary temperature change of a heat radiating source and near the source when heat is transmitted by the thermal conductivity to the low thermally conductive sheet 2, which is an object to be measured, from the heat radiating source; the heat radiating source is a strip-like metal thin wire 11 heated by electricity application and the strip-like metal thin wire 11 is formed on the surface of a standard substance 3 whose thermal conductivity is already known. The low thermally conductive sheet 2 is brought into contact with the surface of the standard substance 3 including the strip-like metal thin wire 11 and the temporary temperature change in the heat radiating source and near the heat radiating source is measured by measuring the change of the electric resistance of the strip-like metal thin wire 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the thermal conductivity of a low thermal conductive sheet having a thermal conductivity of less than 10 W / (mK) such as a paper or a resin film, and particularly to the low thermal conductivity. The present invention relates to a method for measuring the thermal conductivity of only one sheet without stacking a large number of sheets.

[0002]

2. Description of the Related Art Conventionally, a pulse heating method, a periodic heating method, a heat ray probe method and the like have been known as methods for measuring the thermal conductivity of a sheet-like substance.

In the pulse heating method, a heating source and a temperature sensor are formed at a certain distance on a strip-shaped sample,
This is a method of measuring the thermal conductivity of a sample by the temperature response at a temperature observation point on the sample surface when the sample is heated in a pulsed manner by laser light or the like. On the other hand, the periodic heating method irradiates a part of the sample of the strip-shaped sheet with light, periodically heats it, and obtains the temperature conductivity of the sample by observing the temperature response at a point apart from the heated part. It is a method of measuring the thermal conductivity.

In the hot wire probe method (also called box probe method), a thin heating wire is pressed against stacked sheet-like samples to heat them, and the temperature change at the center of the heating wire at that time is measured by using a thermocouple. This is a method of measuring the thermal conductivity of the sample by measuring.

[0005]

The above-mentioned prior art has the following problems, and it is extremely difficult to measure the thermal conductivity of a sheet-like substance.

First, problems of the pulse heating method and the periodic heating method will be described.

In these methods, the sheet material is transparent,
Alternatively, when the reflectance is high and light is not absorbed, the light is not converted into heat, so the temperature rise is small and sufficient measurement cannot be performed. Therefore, conventionally, a thin carbon film has been spray-coated on the surface of such a sheet-like substance to cause light absorption. At that time, it is necessary to form this carbon coating thinly and uniformly. If the carbon coating film is thick, heat mainly flows to this carbon coating film, and the thermal conductivity of the sheet material cannot be accurately determined. Particularly, in the case of a sheet-like substance having a small thermal conductivity, this tendency becomes large, and therefore the thickness of the carbon coating film must be about 1 μm or less. However, it is very difficult to form such a thin coating film with good adhesion and without warping of the sheet.

Further, in the case of a sheet which easily absorbs a liquid such as paper, the carbon component permeates into the inside of the paper by spray coating, so that the thermal conductivity of the paper itself cannot be obtained. Even if the light absorption layer can be formed only on the surface of the paper by another method, it is difficult to form a thin layer uniformly because of the surface roughness of the paper.

As described above, in the pulse heating method and the periodic heating method, it is necessary to preliminarily precisely process the surface of the sheet to be measured. This is difficult and time consuming. In addition, the thickness of the sheet is thin, or the surface of the sheet is in a porous state or a state where the surface roughness is large, so that appropriate surface treatment may not be possible, and the sheet whose thermal conductivity can be measured is limited. There's a problem.

Next, problems of the hot wire probe method will be described. Usually, the diameter of the heating wire used in this method is 0.
It is 1 to 1 mm. On the other hand, the thickness of the paper to be measured is usually 40 to 80 μm, and the thickness of the resin film is 3
˜50 μm. In order to obtain the thermal conductivity accurately by this method, the thickness of the sheet to be measured needs to be larger than the diameter of the heating wire. However, as described above, since the thickness of the measured sheet is often smaller than the diameter of the heating wire, it is difficult to measure the accurate thermal conductivity of the measured sheet by this method.

Therefore, conventionally, when measuring the thermal conductivity of a sheet to be measured such as paper using this method, 20 sheets of the sheet have been used.
The thermal conductivity of a stack of up to 50 sheets is measured, and the thermal conductivity of the sheet is determined based on the measured thermal conductivity. However, in this case, a slight gap is formed between the sheets, and the air layer there functions as a heat insulating layer, so that the thermal conductivity is measured to be small. Further, since the degree of the voids is not uniform, the accurate thermal conductivity of the measured sheet has not been obtained.

Further, in the hot wire probe method, the temperature of the heating wire is measured by using a thermocouple. However, in the case of the measured sheet having a small thermal conductivity, the thermocouple is more than the heat transmitted to the measured sheet. Since more heat is conducted and escapes, the accuracy of the thermal conductivity measurement deteriorates.

In view of the above problems, it is an object of the present invention to provide a method for accurately and simply measuring the thermal conductivity of a low thermal conductivity sheet such as paper or resin film with one sheet. To do.

[0014]

The method for measuring the thermal conductivity of a low thermal conductive sheet according to the present invention is such that when heat is applied from a heat source to a low thermal conductive sheet which is an object to be measured, the heat source and the In the method for measuring the thermal conductivity of a low thermal conductivity sheet for determining the thermal conductivity of the low thermal conductivity sheet by measuring a transient temperature change in the vicinity, the heat source is a strip-shaped metal thin wire that is electrically heated, The strip-shaped thin metal wire is formed on the surface of a reference material having a known thermal conductivity, and the low-thermal-conductivity sheet is in contact with the surface of the reference material including the strip-shaped thin metal wire, and the heat source and its source. The measurement of the transient temperature change in the vicinity is performed by measuring the change of the electric resistance value of the strip-shaped metal thin wire.

The method for measuring the thermal conductivity of the low thermal conductivity sheet according to claim 2 is the same as the method for measuring the thermal conductivity of the low thermal conductivity sheet according to claim 1, wherein the strip-shaped metal thin wire is heated to a constant temperature. The power supply that supplies power is a power supply that can supply constant power regardless of changes in the electrical resistance value of the strip-shaped metal thin wire, and the power supply exceeds the set value of power at the rise of power immediately after starting power supply. It is characterized in that it almost reaches the set power value in a time of 0.1 microsecond or more and 1 millisecond or less.

According to a third aspect of the present invention, there is provided a method for measuring thermal conductivity of a low thermal conductivity sheet according to the first aspect of the present invention, wherein the strip-shaped thin metal wire has a line width of 1 to 20.
It is characterized by comprising a metal thin film having a thickness of 1 to 20 mm and a thickness of 0.05 to 1 μm.

A method for measuring the thermal conductivity of the low thermal conductivity sheet according to claim 4 is the method for measuring the thermal conductivity of the low thermal conductivity sheet according to claim 1, wherein the surface of the reference material containing the strip-shaped metal thin wire is included. Is characterized in that a thin film of a low thermal conductive insulator having a thickness of 0.1 to 1 μm is formed.

[0018]

According to the present invention, a reference substance having a known thermal conductivity is brought into close contact with the surface of the low thermal conductivity sheet, and a strip-shaped metal thin wire which is a heat source is interposed therebetween, whereby the strip-shaped metal thin wire can be accurately formed. By measuring the electric resistance value,
The thermal conductivity of one low thermal conductivity sheet can be accurately and uniquely measured.

Furthermore, by supplying electric power which does not exceed the set power value to the strip-shaped metal thin wire by a constant power source to generate heat, or by setting the width, length and thickness of the strip-shaped metal thin wire within a predetermined range. The thermal conductivity of the low thermal conductivity sheet can be measured extremely accurately.

Further, even if a thin film of a low thermal conductive insulator is interposed between the reference material including the strip-shaped metal fine wire and the low thermal conductive sheet, the thermal conductivity of one low thermal conductive sheet is similarly obtained. Can be measured accurately.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a heat conduction model showing the measurement principle of the present invention. This figure shows a cross-sectional view of a configuration in which a heating wire 1 is sandwiched between a measured sheet 2 made of a low thermal conductivity sheet and a reference substance 3 having a known thermal conductivity. Here, it is assumed that the plane sizes of the measurement target sheet 2 and the reference substance 3 are sufficiently larger than the diameter of the heating wire 1.

At this time, the thermal conductivity λ of the measured sheet 2 is expressed by the following equation (1).

[0024] Here, q is the unit length of the heating wire 1, the amount of heat generated per unit time, t is the time from the start of heating, lnt is the natural logarithm of t, T is the temperature of the heating wire 1, and λ _R Is reference substance 3
Is the thermal conductivity of.

The differential term of the equation (1) is a slope of temperature rise with respect to logarithmic time, and if this slope can be measured, the thermal conductivity λ of the measured sheet 2 can be obtained.

FIG. 2 is a plan view showing an example of a fine wire pattern serving as the heating line in order to explain the method of measuring the thermal conductivity of the measured sheet 2 in the embodiment of the present invention. A metal film of aluminum, nickel, tantalum, or the like is formed to a thickness of 0.1 to 1 μm on the surface of a reference material 3 such as glass or silicone rubber having a known thermal conductivity.
Next, the metal film is patterned by a lithography method or the like to form the strip-shaped metal thin wire 11, the current supply pad 15, and the voltage measurement pad 16. The fine wire 11 has a width w of 1 to 20 μm, a length L of 1 to 20 mm, and an aspect ratio L / w of 50 to 20,000.

After that, the measured sheet 2 is placed on the surface of the reference substance 3 including the fine wire 11 and brought into close contact therewith. Aa ′ in FIG.
FIG. 3 shows a sectional view taken along the line. The change in the electric resistance value of the thin wire 11 with temperature is measured in advance.

Using the sample thus prepared, as shown in FIG.
The thermal conductivity of the measured sheet 2 is measured by the measuring system shown in FIG. The constant power source 17 in this figure is the probe 2 for current supply.
A current is supplied to the thin wire 11 through 5 to heat the thin wire 11, and the voltage applied to the thin wire 11 is sequentially detected through the voltage measuring probe 26 so that the power supplied to the thin wire 11 is supplied at a set value. It is a power supply that can control the current. The current flowing in the thin wire 11 and the applied voltage are measured by the current / voltage measuring device 18, and the electric resistance value of the thin wire 11 and the temperature of the thin wire 11 at that time are calculated by a computer. In addition to this, the computer 19 calculates the electric power supplied to the thin wire 11 and the heat generation amount of the thin wire 11 per unit length / unit time.

Here, the internal function of the constant power source 17 will be described with reference to the block diagram shown in FIG.
First, the input voltage value is detected by the voltage detector 31 and sent to the integrator 33. On the other hand, the current value output by the current output device 36 is detected using the current detector 32, and this is also sent to the integrator 33. The integrator 33 integrates the voltage value and the current value, converts them into power values, and sends them to the comparator 34. The comparator 34 compares the power value with the power setting value 35 to determine an output current value so as to match the power setting value 35, and sends the output current value to the current output device 36. Thus
The sequentially controlled current is output from the current output device 36 to the outside.

In this way, it is possible to measure the transient change in the temperature of the thin wire in a minute time immediately after heating the thin wire. FIG. 6 is an example of a graph showing the temperature rise of the thin wire 11 with respect to the elapsed time thus obtained. The gradient dT / dlnt of the straight line portion is obtained from the graph, and the calorific value q (q becomes a constant value by the use of the constant power source 17) and the thermal conductivity λ _R of the reference substance 3 are calculated by the above equation (1). By assigning to
The thermal conductivity of can be calculated.

Now, here, the constant power source 17 according to the present invention
Will be added. As described above, the constant power source 17 can control the output power to a constant value, but has a thickness of 1
In the measurement of the thermal conductivity of a thin sheet having a thickness of not more than mm, the following matters have been further clarified by the inventors' earnest research.

A description will be given below with reference to the drawings.

FIG. 7 is a graph showing the rise of the output power immediately after the power supply by the constant power source 17 is started. In this figure, curve a is for the constant power source 17 according to the present invention, and curve b is for the conventional constant power source. Further, P _s is a set value of electric power, and t _o is a rise time until the output power reaches 90% of the set value P _s . First, the rise in the output power by the conventional constant power supply, overshoot far exceeds the setting value P _s immediately after the output as shown by the curve b is generated, then the set value P to reach a set value P _s There was ringing before and after _s . When the thin wire 11 was heated using such a constant power source, abnormal heating due to initial overshoot, fluctuation of the thin wire temperature due to ringing, and the like occurred. Therefore, a graph having a linear temperature rising portion as shown in FIG. 6 could not be obtained, and it was difficult to obtain the thermal conductivity of the measured sheet 2. This seems to be because the conventional constant-power power supply does not consider the stability of rising on the order of milliseconds or less.

Therefore, the constant power source 17 having the characteristic of the curve a in FIG. 7 is newly made to realize the present invention. The rise time t _o of the constant power source 17 is 0.1 μm.
It is s or more and 1 ms or less. The lower limit of t _{o is} the limit of the performance that can be realized by the constant power source, and the upper limit of t _o is the thickness of the sheet whose thermal conductivity can be measured, and is 10 μm in the case of the PET (polyethylene terephthalate) film described below. This is the value required to do the above.

Further, the fluctuation of the output power of the constant power source 17 according to the present invention is kept within ± 1%. If the fluctuation value exceeds this value, a smooth curve as shown in FIG. 6 cannot be obtained, and it becomes difficult to identify the straight line section, and thus it becomes difficult to obtain the thermal conductivity. As described above, the constant power source 17 is an important element that characterizes the present invention.

Example 1 Using this method for measuring thermal conductivity, PET having a thickness of 10 μm was used.
An example will be described for the case where the film is measured.

As shown in FIG. 2 (plan view) and FIG. 8 (cross-sectional view), a fine wire 11 made of a nickel film having a width w of 5 μm, a length L of 10 mm and a film thickness of 0.3 μm is formed on a quartz glass substrate ( It is formed on the surface of the reference substance 3 having a plate thickness of 1.0 mm).

Next, after measuring the change in the electric resistance value of the thin wire 11 due to the temperature, the PET film which is the sheet 2 to be measured is placed on the surface of the reference substance 3 including the thin wire 11. Furthermore,
In order to spread this PET film uniformly, the cover material 4 is placed on it. The cover material 4 is a flat plate material having a smooth surface and its thermal conductivity is clearly different from that of the film to be measured. In this example, the same quartz glass substrate as the reference material 3 was used. Finally, attach the weight 5 weighing about 40 g to the cover material 4
I put it on top.

The thin wire 11 of the sample system thus prepared was heated, and the temperature rise (T) of the thin wire 11 and the elapsed time (lnt) expressed in logarithm were obtained. The result is shown in FIG. The thermal conductivity of the PET film can be obtained from the slope of the straight line AB in this figure. The portion before the point A in the figure shows the minute voids generated between the reference substance and the PET film, and the portion after the point B shows the minute voids generated between the PET film and the cover material.

In order to make the straight line portion of FIG. 9 easy to understand,
A graph in which the vertical axis has a temperature gradient is shown in FIG. From this graph, about 25-40 immediately after the heating of the thin wire 11 is started.
It can be seen that the temperature gradient is constant in the ms time range (see the straight line AB portion in the figure). By substituting the constant value of this temperature gradient for dT / dlnt in the above-mentioned formula (1), the thermal conductivity λ of the PET film λ = 0.12 W
/ (M · K) was calculated.

As described above, according to the present invention, the thickness of the resin film is 10 μm without being coated with a carbon film or the like.
That is, the thermal conductivity of one thin resin film can be accurately and easily measured.

Example 2 An example will be described in which the thermal conductivity of a thermal transfer paper having a thickness of about 70 μm, which is commercially available as a word processor printing paper, is measured by using this thermal conductivity measuring method.

As shown in FIG. 2 (plan view) and FIG. 11 (cross-sectional view), a thin wire 11 made of an aluminum film having a width w of 10 μm, a length L of 10 mm and a film thickness of 0.5 μm is 7059.
It is formed on the surface of the reference substance 3 made of a glass substrate (made by Corning, barium borosilicate glass plate, plate thickness 0.7 mm). Next, a protective layer 6 made of a silicon dioxide film having a thickness of 1 μm is formed on the surface of the reference material 3 including the thin wires 11 so as not to cover the current supply pad 15 and the voltage measurement pad 16.
Was formed.

A thermal transfer sheet, which is the sheet to be measured 2, is placed on this, and a cover material 4 is placed to spread the thermal transfer sheet evenly. Same as reference material for cover material 4
A 7059 glass substrate was used. Finally, a weight of about 40g 5
Was placed on the cover material 4. The protective layer 6 is provided to prevent the fine wire 11 from being damaged or broken by the sheet 2 to be measured. The thin wire 11
The change of the electric resistance value due to temperature is measured in advance after forming the protective layer 6.

The thin wire 11 of the sample system thus prepared was heated, and the temperature rise (T) of the thin wire 11 with respect to the elapsed time (t) was measured. This result is represented by the temperature gradient dT / dlnt with respect to the elapsed time (lnt) represented by logarithm and is shown in the graph of FIG. From this graph, in the time range of about 25 to 80 ms immediately after the heating of the thin wire 11 is started,
It can be seen that the temperature gradient is constant (see the straight line CD portion in the figure). From the value of this temperature gradient, the thermal conductivity λ = 0.31 W / (m
・ K) was calculated. Since the thickness of the protective layer is as thin as 1 μm or less and the heat capacity is small, it has almost no influence on the measurement of temperature change on the order of milliseconds or more.

As described above, according to the present invention, since it is not necessary to coat the surface of the paper with a carbon film or the like, the thermal conductivity of only the paper can be measured accurately and easily. In addition, since it is not necessary to measure ten or more sheets of paper in piles, the gap between the sheets of paper does not affect the measurement, and the thermal conductivity of one sheet of paper can be accurately measured. Furthermore, the length L with respect to the width w of the thin wire
Is sufficiently long, the heat loss from both ends of the thin wire can be neglected sufficiently, and therefore the thermal conductivity can be measured with high accuracy.

The present invention is not limited to the above embodiment, but can be modified as necessary.

[0048]

INDUSTRIAL APPLICABILITY As described above, the present invention is a measuring method capable of uniquely obtaining the thermal conductivity of a low thermal conductive sheet such as paper or resin film by using a simple analytic formula. There is no need to pretreat the sheet or to superimpose a large number of sheets to be measured, and it is possible to measure the thermal conductivity of only one sheet to be measured accurately and easily.

[Brief description of drawings]

FIG. 1 is a sectional view of a heat conduction model showing the measurement principle of the present invention.

FIG. 2 is a plan view showing an example of a fine line pattern for explaining the method for measuring the thermal conductivity of the measurement target sheet in the example of the present invention.

FIG. 3 is a cross-sectional view taken along line aa ′ of FIG.

FIG. 4 is a diagram showing a configuration of a measurement system for explaining a thermal conductivity measurement method in an example of the present invention.

FIG. 5 is a block diagram for explaining internal functions of a constant power source.

FIG. 6 is a graph showing an example of temperature rise of a thin wire with time.

FIG. 7 is a graph showing the rise of electric power immediately after starting the electric power supply from the constant electric power source.

FIG. 8 is a sectional view of a thin line portion showing the first embodiment of the present invention.

FIG. 9 is a graph showing the temperature rise of the thin line with the passage of time in the first embodiment of the present invention.

FIG. 10 is a graph showing changes in temperature gradient of a thin line with time in the first embodiment of the present invention.

FIG. 11 is a sectional view of a thin line portion showing a second embodiment of the present invention.

FIG. 12 is a graph showing changes in the temperature gradient of the thin line with the passage of time in the second embodiment of the present invention.

[Explanation of symbols]

 1 Heating Line 2 Measured Sheet 3 Reference Material 4 Cover Material 5 Weight 6 Protective Layer 11 Fine Wire 15 Current Supply Pad 16 Voltage Measurement Pad 17 Constant Power Supply 18 Current / Voltage Measuring Device 19 Calculator 25 Current Supply Probe 26 Voltage Measurement Probe 27 Current-voltage converter 31 Voltage detector 32 Current detector 33 Accumulator 34 Comparator 35 Power setting value 36 Current output device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ikuyo Hashi Hiro 40-40 Matsugaoka, Taishiro-ku, Sendai City, Miyagi Prefecture

Claims (4)

[Claims] 1. When heat is applied from a heat source to a low thermal conductive sheet as an object to be measured by heat conduction, a transient temperature change of the heat source and its vicinity is measured to measure the low thermal conductive sheet. In the method for measuring the thermal conductivity of a low thermal conductivity sheet for obtaining the thermal conductivity, the heat source is an electrically heated strip-shaped metal thin wire, and the strip-shaped metal thin wire is formed on the surface of a reference material whose thermal conductivity is known. The low thermal conductivity sheet is in contact with the surface of the reference material containing the strip-shaped metal fine wire, and the transient temperature change of the heat source and the vicinity thereof is measured by measuring the electrical resistance value of the strip-shaped metal thin wire. The method for measuring thermal conductivity of a low thermal conductive sheet, comprising: 2. A power source for supplying a constant power to electrically heat the strip-shaped metal thin wire, which is a power supply capable of supplying a constant power regardless of a change in an electric resistance value of the strip-shaped metal thin wire,
Moreover, the power source does not exceed the set value of the power at the rise of the power immediately after starting the power supply, and reaches almost the set power value in a time of 0.1 microsecond or more and 1 millisecond or less. The method for measuring thermal conductivity of a low thermal conductive sheet according to claim 1. 3. The strip metal thin wire has a line width of 1 to 20 μm,
The method for measuring thermal conductivity of a low thermal conductivity sheet according to claim 1, wherein the method comprises a metal thin film having a length of 1 to 20 mm and a thickness of 0.05 to 1 μm. 4. The low thermal conductive sheet according to claim 1, wherein a thin film of a low thermal conductive insulator having a thickness of 0.1 to 1 μm is formed on the surface of the reference material including the strip-shaped metal thin wires. Method for measuring thermal conductivity of.