THICK FILM ELEMENT HAVING COVERING LAYER WITH HIGH HEAT CONDUCTIVITY

FIELD OF THE INVENTION

The present invention relates to the field of thick film, and more particularly to a thick film element having a covering layer with high heat conductivity.

BACKGROUND OF THE INVENTION

Thick film technology was developed in the 1960s and is widely used in many industries after several decades of development. However, the development of thick film heating technology is not long. Thick film heating elements refer to heating elements that are made by fabricating exothermic materials on a substrate into thick films and providing electricity thereto to generate heat. The conventional heating methods include electrical heated tube heating and PTC heating. Both methods adopt indirect heating. Both electrical heated tube heating and PTC heating conduct heat indirectly with low thermal efficiency, and are structurally huge and bulky. Besides, in consideration of environmental protection, heaters using these two types of heating methods stain easily after repeatedly heating and cleaning thereof is not easy. Additionally, PTC heaters contain lead and other hazardous substances and are easily oxidized, causing power attenuation and short service life.

Chinese application CN2011800393787 discloses a combination of an electrical heating element and a heat dissipator heated thereby. The heating element comprises a substrate, an insulating layer located on the substrate and a thick film conductor located on the insulating layer; wherein the second side of the metallic substrate is in contact with the heat dissipator, which comprises a layer of metallic material on a surface thereof facing the heater. The substrate is brazed to the heat dissipator, and the surface of the heating element over which the thick film conductor extends is substantially equal to the surface of the heat dissipator.

It could be seen from the above technology that the thick film technology is developing gradually; however, the thick film conductors of the above-mentioned thick film heating element are combined with the substrate through the insulating layer, instead of coated on the substrate directly. Such heating element could not transfer heat to the substrate directly when the thick film is given electricity to generate heat, which would affect the heat generating rate. Besides, the above technical solution overcomes heat dissipation problem of the thick film by utilizing external devices, but does not provide solutions in designing thick film elements of specific materials for various products to solve heat dissipation problem caused by excess heating temperature of the thick films. There are few thick film heating products that could realize direct heating, especially for situations in which heating of only a single side is required. The application of a thick film circuit for single-side heat transferring covering layer in the products to transfer heat only on one side to reduce heat loss has greatly broaden the development of heating products. The existing heating devices could meet the demands of heating; however, heating device that performs unilateral heating transfer is rarely seen, or unilateral heat transfer of such device is too poor, making it difficult to reduce heat loss by keeping high unilateral thermal conduction properties.

SUMMARY OF THE INVENTION

To solve these problems mentioned above, the present invention provides a thick film element having a covering layer with high heat conductivity that has the advantages of small volume, high efficiency, environmental-friendly, high safety performance and long service lifespan.

The concept of thick film in the present invention is a term comparative to thin films. Thick film is a film layer with a thickness ranging from several microns to tens of microns formed by printing and sintering on a carrier; the material used to manufacture the film layer is known as thick film material, and the coating made from the thick film is called thick film coating. The thick film element has the advantages of high power density, fast heating speed, high working temperature, fast heat generating rate, high mechanical strength, small volume, easy installation, uniform heating temperature field, long lifespan, energy saving and environmental friendly, and excellent safety performance.

The thick film element having a covering layer with high heat conductivity of the present invention, comprises a carrier, a thick film coating deposited on the carrier and a covering layer overlaid on the coating. The thick film coating is a heating material, and the mode of heating is electrical heating. The carrier, the thick film coating and the covering layer are selected from a material that fulfills every of the following equations:

$λ_{1} A \frac{T_{1} - T_{0}}{d_{1}} = a \times λ_{3} A \frac{T_{3} - T_{0}}{d_{3}}, λ_{2} A \frac{T_{2} - T_{0}}{d_{2}} = b \times λ_{1} A \frac{T_{1} - T_{0}}{d_{1}}, λ_{2} A \frac{T_{2} - T_{0}}{d_{2}} = c \times λ_{3} A \frac{T_{3} - T_{0}}{d_{3}};$

$200 \leq a \leq 10^{4}, 0 < b \leq 1000, 0 < c \leq 5 \times 10^{5};$

T₂<T_{Minimum melting point of the covering layer};

T₂<T_{Minimum melting point of the carrier};

T₀≤30° C.;

wherein the value of

$λ_{1} A \frac{T_{1} - T_{0}}{d_{1}}$

represents the heat transfer rate of the covering layer; the value of

$λ_{2} A \frac{T_{2} - T_{0}}{d_{2}}$

represents tile heating rate of the thick film coating; the value of

$λ_{3} A \frac{T_{3} - T_{0}}{d_{3}}$

represents the neat transfer rate of the carrier;

λ₁represents the heat conductivity coefficient of the covering layer at the temperature of T₁; λ₂represents the heat conductivity coefficient of the thick film coating at the temperature of T₂;
λ₃represents the heat conductivity coefficient of the carrier at the temperature of T₃;
A represents the contact area of the thick film coating with the covering layer or the carrier;
d₁represents the thickness of the covering layer;
d₂represents the thickness of the thick film coating;
d₃represents the thickness of the carrier;
T₀represents the initial temperature of the thick film element;
T₁represents the surface temperature of the covering layer;
T₂represents the heating temperature of the thick film coating;
T₃represents the surface temperature of the carrier;
d₂≤50 μm;
and 10 μm≤d₁≤10 mm, d₃≥10 μm;
T_{Minimum melting point of the carrier}>25° C.;
λ₁≥λ₃;
the covering layer is a dielectric layer covering on the thick film coating by printing or sintering, and the area of the covering layer is larger than that of the thick film coating.

The carrier is the dielectric layer carrying the thick film coating. The thick film coating covers the carrier by printing or sintering, and is the coated substrate of the thick film element.

The heat conductivity coefficient refers to the heat transferred by a one-meter thick material having a temperature difference between two side surfaces of 1 degree (K, ° C.), through one square meter (1 m²) area within one second (1 S) under a condition of stable heat transfer. Unit of the heat conductivity coefficient is watt/meter·degree (W/(m·K), and K may be replaced by ° C.).

The covering layer, the thick film coating and the carrier stick closely with each other at the electrical heating parts of the thick film elements, and both sides of the thick film coating connect to external electrodes. When given electricity, the thick film coating is heated and becomes hot after electricity energy is transformed to thermal energy. Heat generating rate of the thick film coating could be calculated by

$λ_{2} A \frac{T_{2} - T_{0}}{d_{2}}$

according to the heat conductivity coefficient, the contact area, initial temperature, heating temperature and thickness of the thick film coating, wherein T₂represents the heating temperature of the thick film.

The present invention features in that the thick film element has a covering layer with high heat conductivity, and that the heat generating rate of the covering layer, the carrier and the thick film coating should meet the following requirements:

(1) The heat transfer rate of the thick film coating and the covering layer should satisfy the following formula:

$λ_{1} A \frac{T_{1} - T_{0}}{d_{1}} = a \times λ_{3} A \frac{T_{3} - T_{0}}{d_{3}},$

wherein 200≤a≤10⁴; for those thick film elements satisfied the above equation, the heat transfer capability of their covering layer is superior to that of the carrier, which means that the covering layer is fast while the carrier is slow at temperature rising or that the temperature difference between the covering layer and the carrier is large after stable heat balance. Therefore, the thick film elements generally show the technical effect of covering layer heating.

(2) The heat generating rate of the thick film coating and the heat transfer rate of the covering layer should satisfy the following formula:

$λ_{2} A \frac{T_{2} - T_{0}}{d_{2}} = b \times λ_{1} A \frac{T_{1} - T_{0}}{d_{1}},$

wherein 0<b≤1000; if the heat generating rate of the thick film coating is much larger than that of the covering layer, the continuously accumulated heat of the thick film coating could not be conducted away, such that the temperature of the thick film coating keeps rising, and when the temperature is higher than the minimum melting point of the covering layer, the covering layer would begin to melt or even burn, which would destroy the structure of the covering layer or the carrier, thus destroying the thick film elements.

(3) The heat generating rate of the thick film coating and the heat transfer rate of the carrier should satisfy the following formula:

$λ_{2} A \frac{T_{2} - T_{0}}{d_{2}} = c \times λ_{3} A \frac{T_{3} - T_{0}}{d_{3}}, 0 < c \leq 5 \times 10^{5};$

since both the heat conductivity coefficient and heat transfer rate of the carrier is small, if the heat generating rate of the thick film coating is much larger than that of the carrier, the continuously accumulated heat of the thick film coating could not be conducted away, such that the temperature of the thick film coating keeps rising, and when the temperature is higher than the minimum melting point of the carrier, the carrier would begin to melt or with thermal deformation, or even start to burn, which would destroy the structure of the carrier, thus destroying the thick film elements.

(4) The heating temperature of the thick film coating could not be higher than the minimum melting point of the covering layer or the carrier, and should meet the requirements: T₂<T_{Minimum melting point of the covering layer}and T₂<T_{Minimum melting point of the carrier}. Excessively high heating temperature should be avoided to present destruction of the thick film elements.

When the above-mentioned requirements are met, the heat transfer rate of the covering layer and the carrier is determined by the properties of the material and the thick film element:

The formula for calculating the heat transfer rate of the covering layer is

$λ_{1} A \frac{T_{1} - T_{0}}{d_{1}},$

wherein λ₁represents the heat conductivity coefficient of the covering layer, with the unit being W/m·k, and is determined by properties of the materials for preparing the covering layer; d₁represents the thickness of the covering layer, and is determined by the preparation technique and the requirements of the thick film elements; T₁represents the surface temperature of the covering layer, and is determined by the properties of the thick film elements.

The formula for calculating the heat transfer rate of the carrier is

$λ_{3} A \frac{T_{3} - T_{0}}{d_{3}},$

wherein λ₃represents the heat conductivity coefficient of the carrier, with the unit being W/m·k, and is determined by properties of the materials for preparing the carrier; d₃represents the thickness of the carrier, and is determined by the preparation technique and the requirements of the thick film elements; T₃represents the surface temperature of the carrier, and is determined by properties of the thick film elements.

Preferably, the heat conductivity coefficient of the carrier λ₃is ≤3 W/m·k, the heat conductivity coefficient of the covering layer is λ₁≥3 W/m·k; wherein 200≤a≤10⁴, 10≤b≤1000, 10⁴≤c≤5×10⁵.

Preferably, the carrier and the thick film coating is bound by printing or sintering; the thick film coating and the covering layer is bound by printing, sintering, or vacuum.

Preferably, the region between the carrier and the covering layer without the thick film coating is bound by printing, coating, spraying or sintering, or with gluing.

Preferably, the carrier includes polyimides, organic insulating materials, inorganic insulating materials, ceramics, glass ceramics, quartz, stone materials, fabrics and fiber.

Preferably, the thick film coating is one or more of silver, platinum, palladium, palladium oxide, gold and rare earth materials.

Preferably, the covering layer is made from one or more of polyester, polyimide or polyetherimide (PEI), ceramics, silica gel, asbestos, micarex, fabric and fiber.

Preferably, the area of the thick film coating is smaller than or equal to the area of the covering layer or the carrier.

The present invention also provides a use of the thick film elements for coating products with covering layer heating.

The beneficial effects of the present invention are as follows:

(1) The covering layer of the thick film element of the present invention has high heat conductivity, and is suitable for coating products with covering layer heating to improve heat transfer efficiency and reduce heat losses when double-sided heating is not required. The covering layer of the present invention is suitable for thick film elements having a carrier that could be coated with a thick film but has a small heat conductivity coefficient. The covering layer of the present invention has high heat conductivity and could achieve single-sided heat transferring effects.

(2) The three-layered structure of the thick film element of the present invention could be bound directly by printing or sintering, and the thick film coating would heat the covering layer directly without the need of any medium. Hence, heat could be conducted to the covering layer directly, thus improving heat conduction efficiency. Additionally, the covering layer of the present invention is overlaid on the thick film coating, avoiding electric leakage of the thick film coating after given electricity and improving safety performance.

The thick film element of the present invention generates heat by the thick film coating, the thickness ranges of which is at the micrometer level, and has a uniform heat generating rate and long service lifespan.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.

The present invention discloses a thick film element having a covering layer with high heat conductivity, which comprises a carrier, a thick film coating deposited on the carrier and a covering layer overlaid on the coating; the thick film coating is a heating material, and the mode of heating is electrical heating, wherein the carrier, the thick film coating and the covering layer are selected from a material that fulfills every of the following equations:

T₂<T_{Minimum melting point of the covering layer};

T₂<T_{Minimum melting point of the carrier};

T₀≤30° C.;

d₂represents the thickness of the thick film coating, d₂≤50 μm;

and 10 μm≤d₁≤10 mm, d₃≥10 μm;

T_{Minimum melting point of the carrier}>25° C.;

λ₁represents the heat conductivity coefficient of the covering layer, λ₃represents the heat conductivity coefficient of the carrier, and λ₁≥λ₃.

The following embodiments includes 20 thick film elements prepared by the inventors, and the materials for preparing the covering layer, the thick film coating and the carrier of the 20 listed thick film elements all satisfy the equations above. The detailed preparing method and formula are provided as follows:

Embodiments

Silver paste with a heat conductivity coefficient of λ₂is selected to prepare the thick film coating, polyimides with a heat conductivity coefficient of λ₃is selected to prepare the carrier, and polyimides with a heat conductivity coefficient of λ₁is selected to prepare the covering layer. The three layer are bound by sintering. The area of the prepared thick film coating is A₂, the thickness is d₂; the area of the covering layer is A₁, the thickness is d₁; the area of the carrier is A₃, the thickness is d₃.

Turn on an external DC power supply to charge the thick film coating. The thick film starts to heat up; when the heating is stabled, measure the surface temperature of the covering layer and the carrier, and the heating temperature of the thick film coating under a stable heating state are measured. Heat transfer rate of the covering layer and the carrier, and heat generating rate of the thick film coating are calculated according to the following formula:

$λ_{1} A \frac{T_{1} - T_{0}}{d_{1}}, λ_{2} A \frac{T_{2} - T_{0}}{d_{2}}, λ_{3} A \frac{T_{3} - T_{0}}{d_{3}} .$

Tables 1 to 4 are the 20 thick film elements prepared by the inventors. After provided electricity to heat for 2 minutes, the thick film elements are measured according the national standards to obtain the performance data (heat conductivity coefficient, surface temperature) as shown in the Tables. The thickness, contact area, initial temperature are measured before heating.

The methods to measure the heat conductivity coefficient of the covering layer, the thick film coating and the carrier are as follows:

(1) Switch on the power and adjust the heating voltage to a specified value, turn on the power switch of the device with 6V power and preheat for 20 minutes;

(2) Conduct zero calibration for the light spot galvanometer;

(3) Calibrate the standard operating voltage of UJ31 potentiometer according to the room temperature, set the commutator switch of the potentiometer to a standard position and adjusts the operating current of the potentiometer;

As the voltage of the standard batteries vary with the temperature, room temperature calibration is calculated by the following formula:

E
₄
=E
₀−[39.94(t−20)+0.929(t−20)²]; wherein E₀=1.0186V.

(4) Place a heating plate and lower thermoelectric couples on the bottom part of the thin test specimen; place upper thermoelectric couples on the upper part of the thin test specimen. It should be noted that the thermoelectric couples must be placed at the central position of the test specimen, and cold sections of the thermoelectric couples must be placed in an ice bottle.

(5) Place the commutator switch of the potentiometer at the position 1, measure the initial temperatures at the upper part and the lower part of the test specimen; proceed only when the temperature difference between the upper part and the lower part is smaller than 0.004 mV (0.1° C.).

(6) Pre-add 0.08 mV to the initial thermoelectric potential of the upper thermoelectric couples, turn on the heating switch to start heating; meanwhile, watch the time with a stopwatch; when the light spot of a light spot galvanometer returns to zero position, turn off the heating source to obtain excess temperature and heating time of the upper part.

(7) Measure the thermoelectric potential of the lower thermoelectric couples after 4-5 minutes to obtain excess temperature and heating time of the lower part.

(8) Place the commutator switch of the potentiometer at the position 2, turn on the heating switch to measure the heating current.

(9) End the test, turn off the power and clear up the instrument and equipment.

The temperature is measured by using a thermo-couple thermometer as follows:

(1) Connect the thermo-sensing wires to the surfaces of the thick film coating, the carrier, and the covering layer of the heating elements, and the outdoor air.

(2) Provide electricity to the heating product with rated power, and measure the temperature of all parts.

(3) Record the temperature T₀, T₁, T₂, T₃at all parts of the products at every time interval by a connected computer.

The thickness is measured by using a micrometer and by piling up and averaging the values.

The method to measure the melting point is as follows:

The detection instrument: differential scanning calorimeter, model DSC2920, manufactured by TA Instruments (USA). The instrument is qualified (Level A) as verified by Verification Regulation of Thermal Analyzer 014-1996.

(1) Ambient temperature: 20-25° C.; Relative humidity: <80%;

(2) Standard material for instrument calibration: Thermal analysis standard material—Indium, standard melting point 429.7485 K (156.60).

(3) Measuring procedure: referring to “GB/T19466.3—2004/IS0” for the detection procedure.

Repeat the measurement for three times to ensure normal operation of the instrument before sample testing: weight 1-2 ng of the sample, with an accuracy of 0.01 mg, place the sample in an aluminum sample plate. Testing conditions: heat the sample to 200° C. at a rate of 10° C./min, and repeat the measurement for ten times. Measurement model: collect the information of melting points by the computer and instrument, determine the initial extrapolated temperature of the endothermic melting peak by automatic collection of measured data and program analysis of spectra to directly obtain the measurement model. The measurement results are calculated according to the Bessel formula.

Table 1 is the performance data of the covering layers of thick film elements in Embodiments 1 to 20. The details are as follows:

TABLE 1

Covering Layer

Heat

Conductivity

Surface

Initial

Coefficient
Thickness
Temperature
T_{Minimum melting point of the covering layer}
Temperature
Heat Transfer

λ₁(W/m · k)
d₁(μm)
T₁(° C.)
(° C.)
T₀(° C.)
Rate/10⁶

Embodiment 1
7.22
200
110
350
25
0.036822

Embodiment 2
7.23
100
110
350
25
0.073746

Embodiment 3
7.24
80
108
350
25
0.090138

Embodiment 4
7.24
80
102
350
25
0.083622

Embodiment 5
7.24
60
100
350
25
0.0905

Embodiment 6
7.18
60
98
350
25
0.087356667

Embodiment 7
7.18
50
102
350
25
0.1548008

Embodiment 8
7.17
50
100
350
25
0.15057

Embodiment 9
7.23
40
100
350
25
0.1897875

Embodiment 10
7.23
40
102
350
25
0.167013

Embodiment 11
7.2
40
98
350
25
0.15768

Embodiment 12
7.2
35
108
350
25
0.204891429

Embodiment 13
7.15
35
90
350
25
0.159342857

Embodiment 14
7.15
35
90
350
25
0.212457143

Embodiment 15
7.16
30
101
350
25
0.290218667

Embodiment 16
7.24
30
100
350
25
0.181

Embodiment 17
7.24
30
89
350
25
0.262570667

Embodiment 18
7.17
25
90
350
25
0.223704

Embodiment 19
7.22
25
94
350
25
0.3188352

Embodiment 20
7.22
20
92
350
25
0.314431

Table 2 is the performance data of the thick film coatings of thick film elements in Embodiments 1 to 20. The details are as follows:

TABLE 2

Thick Film Coating

Heat

Conductivity

Heating
Initial

Coefficient λ₂
Thickness
Area A₂
Temperature
Temperature
Heat Generating

(W/m · k)
d₂(μm)
(m²)
T₂(° C.)
T₀(° C.)
Rate/10⁶

Embodiment 1
385
30
0.012
118
25
14.322

Embodiment 2
384
30
0.012
116
25
13.9776

Embodiment 3
380
30
0.012
112
25
13.224

Embodiment 4
382
40
0.012
109
25
9.6264

Embodiment 5
382
50
0.01
102
25
5.8828

Embodiment 6
385
45
0.01
104
25
6.758888889

Embodiment 7
385
55
0.014
108
25
8.134

Embodiment 8
380
35
0.014
112
25
13.224

Embodiment 9
382
45
0.014
111
25
10.22062222

Embodiment 10
382
40
0.012
118
25
10.6578

Embodiment 11
382
35
0.012
106
25
10.60868571

Embodiment 12
380
35
0.012
114
25
11.59542857

Embodiment 13
380
20
0.012
108
25
18.924

Embodiment 14
384
25
0.016
98
25
17.94048

Embodiment 15
384
25
0.016
114
25
21.87264

Embodiment 16
385
20
0.01
110
25
16.3625

Embodiment 17
382
20
0.017
98
25
23.7031

Embodiment 18
383
30
0.012
99
25
11.3368

Embodiment 19
384
20
0.016
105
25
24.576

Embodiment 20
382
20
0.013
106
25
20.1123

Table 3 is the performance data of the carriers of the thick film elements in Embodiments 1 to 20. The details are as follows:

TABLE 3

Carrier

Heat

Conductivity

Surface

Initial

Coefficient λ₃
Thickness
Temperature
T_{Minimum melting point of the carrier}
Temperature
Heat Transfer

(W/m · k)
d₃(μm)
T₃(° C.)
(° C.)
T₀(° C.)
Rate/10⁶

Embodiment 1
2.2
4000
45
350
25
0.000132

Embodiment 2
2.1
5000
46
350
25
0.00010584

Embodiment 3
2.02
5500
45
350
25
8.81455E−05

Embodiment 4
3.4
6000
46
350
25
0.0001428

Embodiment 5
2.5
5800
48
350
25
9.91379E−05

Embodiment 6
1.5
7000
45
350
25
4.28571E−05

Embodiment 7
1.8
10000
46
350
25
0.00005292

Embodiment 8
1.9
9000
48
350
25
6.79778E−05

Embodiment 9
2.1
8800
48
350
25
7.68409E−05

Embodiment 10
1.85
9500
50
350
25
5.84211E−05

Embodiment 11
2
10500
50
350
25
5.71429E−05

Embodiment 12
2.01
6000
52
350
25
0.00010854

Embodiment 13
1.8
7000
49
350
25
7.40571E−05

Embodiment 14
1.89
8000
48
350
25
0.00008694

Embodiment 15
1.78
9500
50
350
25
7.49474E−05

Embodiment 16
2.01
11000
52
350
25
4.93364E−05

Embodiment 17
2.34
7800
51
350
25
0.0001326

Embodiment 18
2.03
8500
48
350
25
6.59153E−05

Embodiment 19
1.95
9500
47
350
25
7.22526E−05

Embodiment 20
1.84
5600
47
350
25
9.39714E−05

Table 4 is the heat transfer rates calculated according to the performance data listed in Tables 1, 2 and 3. The heat transfer rates of the covering layer, the thick film coating and the carrier are calculated by ratio to obtain the limiting conditions of the material of the present invention, namely the following equations:

wherein 200≤a≤10⁴, 0<b≤1000, 0<c≤5×10⁵.

TABLE 4

Covering
Thick Film

Layer
Coating

Heat
Heat
Carrier

Transfer
Generating
Heat Transfer

Satisfy the

Rate
Rate
Rate
a
b
c
equations?

Embodiment 1
36822
14322000
132
278.95455
388.95226
108500
Yes

Embodiment 2
73746
13977600
105.84
696.76871
189.53706
132063.49
Yes

Embodiment 3
90138
13224000
88.14545455
1022.6052
146.70838
150024.75
Yes

Embodiment 4
83622
9626400
142.8
585.58824
115.11803
67411.765
Yes

Embodiment 5
90500
5882800
99.13793103
912.86957
65.003315
59339.548
Yes

Embodiment 6
87356.66667
6758888.889
42.85714286
2038.3222
77.371186
157707.41
Yes

Embodiment 7
154800.8
8134000
52.92
2925.1852
52.544948
153703.7
Yes

Embodiment 8
150570
13224000
67.97777778
2214.9886
87.82626
194534.16
Yes

Embodiment 9
189787.5
10220622.22
76.84090909
2469.8758
53.852979
133010.17
Yes

Embodiment 10
167013
10657800
58.42105263
2858.7811
63.814194
182430.81
Yes

Embodiment 11
157680
10608685.71
57.14285714
2759.4
67.279843
185652
Yes

Embodiment 12
204891.4286
11595428.57
108.54
1887.7043
56.593039
106830.92
Yes

Embodiment 13
159342.8571
18924000
74.05714286
2151.6204
118.76278
255532.41
Yes

Embodiment 14
212457.1429
17940480
86.94
2443.7214
84.442819
206354.73
Yes

Embodiment 15
290218.6667
21872640
74.94736842
3872.2996
75.366069
291840
Yes

Embodiment 16
181000
16362500
49.33636364
3668.6936
90.400552
331651.93
Yes

Embodiment 17
262570.6667
23703100
132.6
1980.1709
90.273222
178756.41
Yes

Embodiment 18
223704
11336800
65.91529412
3393.8102
50.677681
171990.43
Yes

Embodiment 19
318835.2
24576000
72.25263158
4412.7832
77.080573
340139.86
Yes

Embodiment 20
314431
20112300
93.97142857
3346.0277
63.964113
214025.69
Yes

The results listed in Table 4 show that the thick films prepared according to Embodiments 1 to 20 all satisfy the equations; and the carrier, i.e. covering layer, has the function of generating heat and the temperature difference between two sides are more than 40° C., so as to achieve the function of heat generation. When in use, the product could reduce heat loss when the covering layer of the thick film element is heated, and the temperature could rise to more than 100° C. after giving electricity for two minutes, which demonstrates that the thick film element of the present invention has high heat generation efficiency.

Tables 5 to 8 are the performance data of the thick film elements in contrasting examples 1 to 10 of the present invention. All the performance data is measured as those shown in Tables 1 to 4. The details are as follows:

TABLE 5

Covering Layer

Heat

Conductivity

Surface

Initial

Coefficient λ₁
Thickness d₁
Temperature
T_{Minimum melting point of the covering layer}
Temperature
Heat Transfer

(W/m · k)
(μm)
T₁(° C.)
(° C.)
T₀(° C. m
Rate/10⁶

Contrasting
7.21
80
42
350
25
0.02757825

Example 1

Contrasting
7.21
80
43
350
25
0.0292005

Example 2

Contrasting
7.22
100
92
350
25
0.0870732

Example 3

Contrasting
7.22
100
91
350
25
0.0810084

Example 4

Contrasting
7.18
200
46
350
25
0.0128163

Example 5

Contrasting
7.18
200
94
350
25
0.0644046

Example 6

Contrasting
7.15
500
45
350
25
0.007436

Example 7

Contrasting
7.22
500
100
350
25
0.058482

Example 8

Contrasting
7.22
600
42
350
25
0.0110466

Example 9

Contrasting
7.24
600
91
350
25
0.0430056

Example 10

TABLE 6

Thick Film Coating

Heat

Conductivity

Heating
Initial

Coefficient λ₂
Thickness d₂

temperature
temperature
Heat Generating

(W/m · k)
(μm)
Area A₂(m²)
T₂(° C.)
T₀(° C.)
Rate/10⁶

Contrasting
382
22
0.018
48
25
7.188545455

Example 1

Contrasting
382
22
0.018
52
25
8.438727273

Example 2

Contrasting
382
25
0.018
98
25
20.07792

Example 3

Contrasting
382
25
0.017
96
25
18.44296

Example 4

Contrasting
382
30
0.017
48
25
4.978733333

Example 5

Contrasting
382
30
0.026
101
25
25.16106667

Example 6

Contrasting
382
32
0.026
49
25
7.449

Example 7

Contrasting
382
32
0.054
104
25
50.925375

Example 8

Contrasting
382
35
0.054
46
25
12.3768

Example 9

Contrasting
382
35
0.054
98
25
43.02411429

Example 10

TABLE 7

Carrier

Heat

Conductivity

Surface

Initial

Coefficient
Thickness d₃
Temperature
T_{Minimum melting point of the carrier}
temperature
Heat Transfer

λ₃(W/m · k)
(mm)
T₃(° C.)
(° C.)
T₀(° C.)
Rate/10³

Contrasting
7.18
2000
41
350
25
0.00103392

Example 1

Contrasting
7.18
2500
37
350
25
0.000620352

Example 2

Contrasting
7.18
3600
77
350
25
0.0018668

Example 3

Contrasting
7.21
1100
86
350
25
0.006797064

Example 4

Contrasting
7.21
1800
41
350
25
0.001089511

Example 5

Contrasting
7.21
2800
84
350
25
0.00395005

Example 6

Contrasting
7.19
3500
35
350
25
0.000534114

Example 7

Contrasting
7.19
3200
88
350
25
0.007643869

Example 8

Contrasting
7.19
3800
32.5
350
25
0.000766303

Example 9

Contrasting
7.2
100
91.5
350
25
0.258552

Example 10

TABLE 8

Covering
Thick Film

Layer
Coating

Heat
Heat
Carrier

Transfer
Generating
Heat Transfer

Satisfy the

Rate
Rate
Rate
a
b
c
equations?

Contrasting
27578.25
7188545.455
1033.92
26.673485
260.65996
6952.7095
No

Example 1

Contrasting
29200.5
8438727.273
620.352
47.070857
288.99256
13603.127
No

Example 2

Contrasting
87073.2
20077920
1866.8
46.643025
230.58668
10755.26
No

Example 3

Contrasting
81008.4
18442960
6797.063636
11.918146
227.66725
2713.3717
No

Example 4

Contrasting
12816.3
4978733.333
1089.511111
11.76335
388.46885
4569.6949
No

Example 5

Contrasting
64404.6
25161066.67
3950.05
16.304756
390.67189
6369.8097
No

Example 6

Contrasting
7436
7449000
534.1142857
13.922114
1001.7483
13946.453
No

Example 7

Contrasting
58482
50925375
7643.86875
7.6508378
870.78717
6662.2514
No

Example 8

Contrasting
11046.6
12376800
766.3026316
14.415454
1120.4171
16151.321
No

Example 9

Contrasting
43005.6
43024114.29
258552
0.1663325
1000.4305
166.40411
No

Example 10

Material and structure of the thick film elements in the Contrasting Examples 1 to 10 listed in the above tables neither meet the material selection requirement of the present invention, nor satisfy the equations of the present invention. After given electricity and heat generation, the temperatures difference between the two sides of the thick film elements of the Contrasting Examples 1 to 10 are not significantly different, and the heating temperature difference between the covering layer and the carrier is smaller than 15° C. . The thick film elements prepared according to such material selections do not meet the requirement of the thick film element having a covering layer with high heat conductivity of the present invention or meet the product requirement of the present invention, which demonstrates the heat transfer rate and correlation of the present invention.

When the thick film elements of the Embodiments 1 to 20 is applied in winter clothes, the side of the covering layer that transfers heat is set adjacent to the direction of the human body, and the carrier of the thick film element is set away from the human body. When given electricity to generate heat, only the covering layer of the thick film element produces heat. The thick film element having a covering layer with high heat conductivity has the following advantageous effects: (1) only the covering layer transfers heat, and requirement for heat conduction performance of the carrier is not strict, which allows a wide range of materials to be selected as the coated substrate of the thick film; (2) the covering layer of the thick film element is required to be very thin, which makes the thick film element much smaller, more exquisite and more light weighted and allows the wearer to feel more comfortable when the thick film is placed in clothes; (3) when the thick film element is applied in clothes, it is only required that the side facing the human body transfers heat, and there is no need for the opposite side to transfer heat, which could avoid filling of thermal isolation materials at the opposite side and could reduce heat loss. In contrast, heat transferring effect between the two sides of the thick film elements in the contrasting examples is not significantly different; when applied in the clothes with a single-side heat transferring covering layer, the thick film elements would cause heat loss and filling thermal isolation materials at the opposite side would be required, thus increasing the cost and weight of the clothes and reducing comfort of the wearer.

According to the disclosure and teaching of above-mentioned specification, those skilled in the art of the present invention can still make changes and modifications to above-mentioned embodiment, therefore, the scope of the present invention is not limited to the specific embodiments disclosed and described above, and all those modifications and changes to the present invention are within the scope of the present invention as defined in the appended claims. Besides, although some specific terminologies are used in the specification, it is merely as a clarifying example and shall not be constructed as limiting the scope of the present invention in any way.

THICK FILM ELEMENT HAVING COVERING LAYER WITH HIGH HEAT CONDUCTIVITY

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