KR101434565B1 - Thick membrane type PTC heating element with Conductive paste composition - Google Patents

Abstract

The present invention relates to a polymer PTC conductive paste composition comprising a composite conductive powder in which carbon nanotubes, conductive carbon black and graphite are mixed, a crystalline polymer, and an elastic curable resin, wherein the base resin It is possible to reduce the resistance increase phenomenon due to the thermal deformation of the semiconductor device.

Description

[0001] The present invention relates to a thick film type PTC heating element including a conductive paste composition,

The present invention relates to a thick film PTC heating element including a conductive paste composition, and more particularly to a thick film type PTC heating element including a conductive paste composition for reducing a rise in resistance due to thermal deformation of a base resin contained in a binder PTC heating element.

With the rapid development of the electronic industry, the importance of conductive polymers is increasing. Electrically conductive polymer is one of the functional polymers, which imparts conductivity to the polymer material. This makes it possible to obtain economical materials capable of not only obtaining excellent physical and chemical properties and functional properties useful for polymeric materials but also reducing production costs. The application fields are diversified and specialized for anti-static, self-heating or electromagnetic wave absorption, and many conductive composite materials are being manufactured for such applications.

In general, the polymer plays an excellent role as an electrical insulator due to its low electrical conductivity. However, if a conductive filler (carbon nanotube (MWNT or SWNT), carbon black, carbon fiber, metal, etc.) is put in the polymer, It forms a path and acts as a path of electrons, and therefore, it also serves as an electrical conductor.

PTC (Positive Temperature Coefficient) is a characteristic that the resistance is low due to low resistance at a room temperature, but the electrical resistance is rapidly increased in a relatively narrow temperature range as the temperature rises. As the temperature increases, the semi-crystalline polymer containing the conductive filler increases the layer between the filler particles in the polymer due to the thermal expansion in the melting region of the polymer, so that the flow of the electrons is disturbed. As the temperature increases, Suddenly, a phenomenon that is greatly increased is called "magnetoresistance control function" and it is called PTC phenomenon.

Therefore, a material having such characteristics is used in an electric circuit such as a circuit protection device that changes in accordance with ambient temperature and current conditions to prevent damage to a product or electric furnace.

FIG. 1 is a graphical illustration showing that conductive particles are added in a polymer binder, and a phenomenon in which a flow is shut off due to a distance between conductive particles due to thermal expansion of the binder when the temperature is raised is blocked.

In the case of a surface heating film which is currently being commercialized, if a substance capable of accumulating heat is placed on the surface of the film, the temperature is increased due to the heat trapping phenomenon, and there is a risk to the product or a risk of fire. To avoid these hazards, most products use temperature sensors that shut off the current at the right temperature.

However, since the temperature sensor only detects the temperature of the attached part, it is not possible to control the temperature of the other part even if the other part is overheated, so that the risk of damage to the product and fire can not be completely blocked.

In order to solve such a problem, a coating with a heat generating coating layer having a PTC function is applied. In this case, when the thermal overheating is caused by overheating due to the self-control phenomenon caused by the temperature rise without the temperature sensor, the crystalline portion of the crystalline polymer contained in the binder is converted into an amorphous state. When the crystalline part of the polymer becomes amorphous, the distance between the conductive materials is distant and the electric current is blocked, so that the risk of fire can be blocked.

However, most of the products using the conventional polymer PTC heating element maintain a constant temperature, and the thermal expansion of the crystalline polymer contained in the binder accelerates and thermal deformation of the base resin, which serves to hold the crystalline polymer, occurs. As a result, the distance between the conductive materials is excessively distanced, and the initial resistance resistance value of the PTC heating element rises sharply and the heat is not generated. Thus, the reliability of the PTC heating element deteriorates in the long term.

The present invention has been proposed in order to solve the problems described above, and it is an object of the present invention to provide a conductive paste composition with reduced resistance increase due to thermal deformation of a base resin upon heat generation in a thick film PTC heating element, The object of the present invention is to provide a PTC heating element.

Disclosure of the Invention In order to solve the above-mentioned technical problems, the conductive paste composition of the present invention comprises a composite conductive powder comprising carbon nanotubes, conductive carbon black and graphite; Crystalline polymer; And an elastic curable resin.

In one embodiment of the present invention, it is preferable that the crystalline polymer has a crystallinity of 20 to 80 and is a resin having a melting point in a range of 20 to 250 ° C.

In one embodiment of the present invention, the crystalline polymer is one selected from the group consisting of polybutylene terephthalate (PBT), polypropylene-based, low-density polyethylene-based, high-density polyethylene-based and polyethylene wax Or more.

In one embodiment of the present invention, the elastic curable resin preferably includes at least one member selected from the group consisting of an acrylic urethane copolymer, a modified acrylic urethane copolymer, a urethane copolymer and a modified urethane copolymer Do.

In one embodiment of the present invention, the conductive paste composition includes a conductive powder obtained by mixing 0.1 to 10 parts by weight of carbon nanotubes, 1 to 50 parts by weight of conductive carbon black, and 1 to 50 parts by weight of graphite .

In one embodiment of the present invention, the conductive paste composition preferably comprises 1 to 50 parts by weight of a crystalline polymer having a crystallinity of 20 to 80 and a melting point of 20 to 250 캜.

In one embodiment of the present invention, the conductive paste composition preferably comprises 1 to 50 parts by weight of an elastic curable resin.

In one embodiment of the present invention, the carbon nanotube is one selected from the group consisting of Single-Wall Nanotubes (SWNT), Double-Wall Nanotubes (DWNT), Multi-Wall Nanotubes (MWNT), and Fullerene Or more.

In order to solve the above technical problems, the thick film PTC heating element includes a polymer PTC conductive paste composition.

The present invention has the effect of reducing resistance increase due to thermal deformation of the base resin included in the binder at the time of heat generation of the thick film PTC heating element.

FIG. 1 shows a phenomenon in which an electrical current flows through a conductive particle due to thermal expansion of a polymer binder.
FIG. 2 is a graph showing the rate of change of resistance with time in units of 8 hours with respect to the embodiment and the comparative example.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and will be described in detail in the detailed description. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The exotherm is a conductive paste composition comprising a carbon nanotube, conductive carbon black, a composite conductive powder of graphite, a crystalline polymer, and a curable resin.

Carbon nanotubes are a new material with six carbon hexagons connected together to form a tube. Carbon nanotubes are materials that are more conductive than conventional conductive carbon, but because of the strong van der Waals force between the carbon nanotubes, the carbon nanotubes are in the form of bundles that are intertwined with each other The dispersibility in the binder is limited. Therefore, by applying a composite conductive powder composition in which carbon black having excellent dispersibility and hexagonal plate-like structure are mixed with graphite having excellent structural stability and dispersibility, a polymer PTC conductive paste having a stable resistance value Composition can be provided.

The kind of the carbon nanotubes contained in the composition of the present invention is determined by the number of bonds forming the wall. The carbon nanotubes included in the composition according to an exemplary embodiment of the present invention may be single wall carbon nanotubes (SWNTs), double wall carbon nanotubes (DWNTs), multiwall carbon nanotubes MWNTs Multi-Wall Carbon Nanotubes) may be used.

Preferably, the carbon nanotubes are selected from among multi-wall nanotubes (MWNTs) and single-wall nanotubes (SWNTs), which are relatively highly utilizable because of their excellent thermal conductivity and electrical conductivity and relatively high oxidation temperatures. One or more carbon nanotubes may be used, but are not limited thereto.

The kind of the conductive carbon black is not particularly limited, but a conductive carbon black having a DBP absorption rate of 50 to 700 (cc / 100 g) can be used. Preferably, conductive carbon black having a DBP absorption of 100 to 500 (cc / 100 g), which is excellent in dispersibility and paste viscosity control, can be used. In order for carbon black to be used as a conductive material, the secondary structure must be highly developed and the number of particles per unit volume must be high. Therefore, the carbon black has a small particle diameter and a large surface area, the DBP absorption rate is high and the conductivity is excellent.

Conductive carbon black having a DBP absorption rate of 50 cc / 100 g or less is not suitable for a PTC conductive paste composition because of its large particle diameter and small surface area, resulting in poor conductivity. In the case of conductive carbon black having a cc / Because of its small size and high surface area, it has good conductivity, but it is inadequate because of its small particle size and poor dispersibility and flow properties and printability, which are required properties of PTC conductive paste.

The conductive graphite has an electrical resistance of 0.013 to 0.025? Cm, a Natural Crystalline Graphite of a friction coefficient of 0.090 to 0.094, an electrical resistance of 0.04 to 0.08? Cm, a synthetic graphite of a friction coefficient of 0.1 to 0.2, At least one conductive graphite selected from the group consisting of amorphous graphite having a coefficient of friction of 0.06? Cm and a friction coefficient of 0.2 to 0.3 can be used.

Natural Crystalline Graphite, which is preferably low in battery resistance and coefficient of friction, may be used, but is not limited thereto.

The crystalline polymer is preferably a polymer having a crystallinity of 20 to 80 and a melting point in a range of 20 to 200 캜, and the curable resin preferably has elasticity.

In order for the conductive paste composition to exhibit its performance as a PTC heating element, the crystalline polymer contained in the composition must remain in a crystalline form below the melting point. When the temperature rises to the melting temperature, the crystal structure of the crystalline polymer undergoes deformation and expansion of the volume, which causes the distance between the conductive particles to expand and the resistance value to rise. When the temperature again falls below the melting point, the crystalline polymer again forms a recrystallization, so that the distance between the conductive particles approaches and the resistance value should be lowered.

Therefore, the crystalline polymer that realizes the PTC performance is preferably a polymer having a crystallinity of 20 to 80 and a melting point in the range of 20 to 250 ° C. This is because when the crystallinity is too high, deformation occurs excessively at the melting point and the temperature becomes lower than the melting point, and when the recrystallization is carried out, a re-crystallization is formed in a state where the distance between the conductive particles is distant, Is too low, PTC performance is not implemented.

In addition, the crystalline polymer having a melting point of 20 캜 or lower is not suitable as a paste composition because it is deformed even at room temperature or lower and hardly has a constant resistance value. Further, in the case of a crystalline polymer having a melting point of 200 ° C or higher, the temperature at which a PTC phenomenon occurs (a volume window occurs due to heat) is too high to cause repeated durability and a change in resistance, which is unsuitable as a paste composition. Therefore, the crystalline polymer which realizes the PTC performance is preferably a polymer having a crystallinity of 20 to 80 and a melting point in the range of 20 to 250 ° C. The crystalline polymer for realizing the PTC performance may be a polypropylene resin, a low-density polyethylene resin, a high-density polyethylene resin, a polybutylene terephthalate (PBT) resin, a polyethylene wax (PE WAX) Polyethylene wax (PE-WAX) having a crystallinity of 40 to 50 and a melting point of 40 to 100 DEG C is preferable, but not limited thereto. The polyethylene wax (PE WAX) has a crystallinity of 40 to 50 than other crystalline polymers, and since the recrystallization is stably formed after the volume expansion due to thermal deformation at the melting point, the PTC performance can be stably realized and the melting point is 40 to 100 ° C. Conductive paste can be easily worked at room temperature and the optimum PTC performance can be realized in a range of 40 to 100 ° C. in which polymer PTC characteristics are generally required.

 PTC Heat Resistant Base resin that can stably maintain physical properties during thermal expansion and contraction expansion due to thermal deformation of polymer is an elastic curable resin such as acrylic / urethane copolymer, modified acrylic / urethane copolymer, urethane copolymer, Modified urethane copolymers, and the like, preferably acrylic / urethane copolymers and modified acrylic / urethane copolymers, but are not limited thereto.

The thick film PTC heating element including the conductive paste composition of the present invention should have printability, dispersibility, and flowability, and the basic physical properties of the coating film such as strength and adhesion after coating should be maintained. In addition, as described above, the crystalline polymer must have elasticity so as to stably maintain the physical properties upon thermal expansion and contraction expansion.

 In order to achieve the above properties, the thick film PTC heating element including the conductive paste composition of the present invention is required to have an acrylic / urethane copolymer copolymerized with acryl and urethane having excellent dispersibility, printability, It is preferable to select a modified acrylic / urethane copolymer as the base resin.

The elastic curable resin fixes the composite conductive powder composition of carbon nanotube, conductive carbon black, and graphite and the crystalline polymer, thereby stably maintaining the flow of the conductive powder when the PTC heating element is used for a long time, And serves to prevent a phenomenon in which resistance due to deformation increases.

Hereinafter, the present invention will be described in more detail with reference to examples. However, it is to be understood that the present invention is not limited thereto, and that various changes and modifications may be made by those skilled in the art to which the present invention pertains.

[ Example  One]

5 parts by weight of multi-wall carbon nanotubes (MWNT), 5 parts by weight of natural graphite, 5 parts by weight of conductive carbon black, 10 parts by weight of polyethylene wax (PE-WAX), 100 parts by weight of an acrylic / urethane copolymer resin 100 50 parts by weight of butylacrylate acetate as a solvent as a diluent was added to the mixture to adjust the viscosity. The mixture was stirred with a stirrer and dispersed and mixed in a three-stage roll to prepare a polymer PTC conductive paste composition.

A polymer PTC conductive paste composition was printed on a PET film by a screen printing method to form a coating film, which was then dried at 140 DEG C for 20 minutes. At this time, the thickness of the coating film was about 8 mu m. A PTC heating element was prepared by forming an electrode layer on the resistive film with a silver paste (solid content: 72%) and laminating a laminated film thereon.

A current of 220 V was applied to both terminals of the PTC heating element to generate heat up to the maximum temperature at which the PTC development temperature appeared, and the current was measured using a digital multimeter to calculate the initial resistance value and the maximum temperature resistance value, And the PTC characteristics were analyzed. The results are shown in Table 1 below.

[ Example  2]

 10 parts by weight of multi-walled carbon nanotubes (MWNT), 10 parts by weight of natural graphite, 10 parts by weight of conductive carbon black, 10 parts by weight of polyethylene wax (PE-WAX), 100 parts by weight of an acrylic / urethane copolymer resin 100 50 parts by weight of butylacrylate acetate as a solvent as a diluent was added to the mixture to adjust the viscosity. The mixture was stirred with a stirrer and dispersed and mixed in a three-stage roll to prepare a polymer PTC conductive paste composition.

A polymer PTC conductive paste composition was printed on a PET film by a screen printing method to form a coating film, which was then dried at 140 DEG C for 20 minutes. At this time, the thickness of the coating film was about 8 mu m. A PTC heating element was prepared by forming an electrode layer on the resistive film with a silver paste (solid content: 72%) and laminating a laminated film thereon.

A current of 220 V was applied to both terminals of the PTC heating element to generate heat up to the maximum temperature at which the PTC development temperature appeared, and the current was measured using a digital multimeter to calculate the initial resistance value and the maximum temperature resistance value, And the PTC characteristics were analyzed. The results are shown in Table 1 below.

[ Comparative Example 1 ]

20 weight parts of multi-walled carbon nanotubes (MWNT), 10 weight parts of polyethylene wax (PE-WAX), 100 weight parts of an acrylic / urethane copolymer resin as an elastic curable resin, 50 weight parts of butylglycol acetate as a diluent And the mixture was stirred and mixed by a three-stage roll to prepare a polymer PTC conductive paste composition.

A polymer PTC conductive paste composition was printed on a PET film by a screen printing method to form a coating film, which was then dried at 140 DEG C for 20 minutes. At this time, the thickness of the coating film was about 8 mu m. A PTC heating element was prepared by forming an electrode layer on the resistive film with a silver paste (solid content: 72%) and laminating a laminated film thereon.

A current of 220 V was applied to both terminals of the PTC heating element to generate heat up to the maximum temperature at which the PTC development temperature appeared, and the current was measured using a digital multimeter to calculate the initial resistance value and the maximum temperature resistance value, And the PTC characteristics were analyzed. The results are shown in Table 1 below.

[ Comparative Example  2]

5 parts by weight of multi-walled carbon nanotubes (MWNT), 5 parts by weight of natural graphite, 5 parts by weight of conductive carbon black, 10 parts by weight of polyethylene wax (PE-WAX), 100 parts by weight of heat- And 50 parts by weight of butylglycol acetate were added to adjust the viscosity. The mixture was stirred with a stirrer and dispersed and mixed in a three-stage roll to prepare a polymer PTC conductive paste composition.

A polymer PTC conductive paste composition was printed on a PET film by a screen printing method to form a coating film, which was then dried at 140 DEG C for 20 minutes. At this time, the thickness of the coating film was about 8 mu m. A PTC heating element was prepared by forming an electrode layer on the resistive film with a silver paste (solid content: 72%) and laminating a laminated film thereon.

A current of 220 V was applied to both terminals of the PTC heating element to generate heat up to the maximum temperature at which the PTC development temperature appeared, and the current was measured using a digital multimeter to calculate the initial resistance value and the maximum temperature resistance value, And the PTC characteristics were analyzed. The results are shown in Table 1 below.

[ Comparative Example  3]

5 parts by weight of multi-walled carbon nanotubes (MWNT), 5 parts by weight of natural graphite, 5 parts by weight of conductive carbon black, 10 parts by weight of polyethylene wax (PE-WAX), 100 parts by weight of heat- And 50 parts by weight of in-butyl glycolacetate were added to adjust the viscosity. The mixture was stirred with a stirrer and dispersed and mixed in a three-stage roll to prepare a polymer PTC conductive paste composition.

A polymer PTC conductive paste composition was printed on a PET film by a screen printing method to form a coating film, which was then dried at 140 DEG C for 20 minutes. At this time, the thickness of the coating film was about 8 mu m. A PTC heating element was prepared by forming an electrode layer on the resistive film with a silver paste (solid content: 72%) and laminating a laminated film thereon.

A current of 220 V was applied to both terminals of the PTC heating element to generate heat up to the maximum temperature at which the PTC development temperature appeared, and the current was measured using a digital multimeter to calculate the initial resistance value and the maximum temperature resistance value, And the PTC characteristics were analyzed. The results are shown in Table 1 below.

Example 1
Example 2
Comparative Example 1
Comparative Example 2
Comparative Example 3
Initial resistance value (Ω)

1150
875
1215
1089
1578
Maximum temperature resistance (Ω)
7520
4725
5224

7405
8679
PTC development temperature
(° C)
60
60
60
60
60
PTC Properties
6.5
5.4
4.3
6.8
5.5

As can be seen from Table 1, when comparing Example 1 with Comparative Example 1, the resistance values are similar to those obtained by using carbon nanotubes alone, a mixture of carbon nanotubes, conductive carbon black, and graphite, As a result, it can be confirmed that Example 1 in which carbon nanotubes, conductive conductive carbon black, and graphite are mixed shows excellent performance.

Also, when comparing Example 1 and Comparative Example 2, it can be confirmed that PTC characteristics are similar. The PTC development temperature was the same as that of the polyethylene wax (PE-WAX) having a crystallinity of 40 to 50, because the PTC development temperature was 60 ° C in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 The performance is determined.

In the case of Comparative Example 3, when the thermally drying type polyester resin was used, it was confirmed that the PTC characteristic was 5.5, which is significantly lower than that of Example 1 and Comparative Example 2. It can be confirmed that the PTC characteristics are reduced due to the high molecular weight of the polyester.

The PTC development temperature was the same as that of the polyethylene wax (PE-WAX) having a crystallinity of 40 to 50, because the PTC development temperature was 60 ° C in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 The performance is determined.

FIG. 2 is a graph showing the rate of change of resistance with time in units of 8 hours with respect to the embodiment and the comparative example.

The PTC heating elements of Examples 1, 2, and Comparative Example 1 and Comparative Example 2 were maintained at a PTC developing temperature of 60 ° C for 8 hours by applying an alternating voltage of 220 V and then completely turned off, The resistance change amount was measured to evaluate the repeated durability when used for a long time. The resistance change was measured for 7 days with a cycle time of 8 hours per day. The results are shown in Table 2 below.

test
cycle

Example 1

Example 2
Comparative Example 1
Comparative Example 2

Comparative Example 3
resistance
(Ω)
Rate of change
(%)
resistance
(Ω)
Rate of change
(%)
resistance
(Ω)
Rate of change
(%)
resistance
(Ω)
Rate of change
(%)
resistance
(Ω)
Rate of change
(%)
0 times
1150
0.00
875
0.00
1215
0.00
1089
0.00
1578
0.00
1 time
1161
1.00
878
0.30
1240
2.10
1143
5.00
1734
9.89
Episode 2
1172
1.90
889
1.60
1275
4.90
1194
9.60
1812
14.83
3rd time
1178
2.40
891
1.80
1287
5.90
1224
12.40
1924
21.93
4 times
1184
3.00
895
2.30
1299
6.90
1294
18.80
2104
33.33
5 times
1187
3.20
896
2.40
1288
6.00
1375
26.30
2543
61.15
6 times
1189
3.40
895
2.30
1287
5.90
1576
44.70
2748
74.14
7 times
1188
3.30
898
2.60
1295
6.60
2100
92.80
3378
144.07

As can be seen from Table 2, when comparing Example 1 and Comparative Example 1, it was confirmed that the use of carbon nanotubes alone has a higher rate of change in resistance than a case where carbon nanotubes, conductive carbon black, and graphite are mixed. Comparing Example 1 and Comparative Example 2, it was found that when the thermal drying type acrylic was used, the stability of the thermal expansion caused by shrinkage expansion was lowered and the resistance value was increased to a large extent. In the case of using an elastic thermosetting resin, And it has been confirmed that it has excellent durability.

While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be apparent to those skilled in the art that changes may be made.

Claims (9)

Composite conductive powder obtained by mixing carbon nanotubes, conductive carbon black, and graphite;
A crystalline polymer having a crystallinity of 20 to 80 and a melting point of 20 to 250 캜; And
A conductive paste composition comprising an elastic curable resin.
delete The method according to claim 1,
Wherein the crystalline polymer comprises at least one member selected from the group consisting of polybutylene terephthalate (PBT), polypropylene-based, low-density polyethylene-based, high-density polyethylene-based and polyethylene wax (PE-WAX) Conductive paste composition.
The method according to claim 1,
Wherein the elastic curable resin comprises at least one member selected from the group consisting of an acrylic urethane copolymer, a modified acrylic urethane copolymer, a urethane copolymer and a modified urethane copolymer.
The method according to claim 1,
Wherein the conductive powder comprises:
0.1 to 10 parts by weight of the carbon nanotubes, 1 to 50 parts by weight of the conductive carbon black, and 1 to 50 parts by weight of the graphite.
The method according to claim 1,
And 1 to 50 parts by weight based on 100 parts by weight of the total composition.
The method according to claim 1,
Wherein the elastic curable resin is contained in an amount of 1 to 50 parts by weight based on 100 parts by weight of the total composition.
6. The method of claim 5,
The carbon nanotube may include at least one selected from the group consisting of SWNTs (Single-Wall Nanotubes), DWNTs (Double-Wall Nanotubes), MWNTs (Multi-Wall Nanotubes), and fullerenes Conductive paste composition.
9. A thick film PTC heating element comprising the conductive paste composition according to any one of claims 1 to 8.

Images