PTC heat trace cable and preparation method therefor

Abstract

Disclosed in the present invention are a PTC heat trace cable and a preparation method therefor. The PTC heat trace cable is obtained by mixing a molten polymer with tetrapod-like zinc oxide whiskers which are subjected to surface coating modification, milling same, then co-extruding same and two parallel core wires to make a conductive plastic layer both be coated onto the outer layers of the two core wires and fill in space between the two core wires, and carrying out cooling, curing and molding. The mass ratio of the polymer to the tetrapod-like zinc oxide whiskers which are subjected to surface coating modification is 100:(5-15). A method for preparing the tetrapod-like zinc oxide whiskers which are subjected to surface coating modification comprises: depositing a metal film layer on a surface of a tetrapod-like zinc oxide whisker by means of a physical vapor deposition method. By preparing tetrapod-like zinc oxide whiskers having metal film layers on the surfaces thereof as a conductor filler, the repeatability and the stability of the obtained PTC heat trace cable are effectively improved. The PTC heat trace cable has good application prospects.

Description

A PTC heating cable and its preparation method Technical Field

[0001] The present invention relates to the technical field of polymer composite materials, and in particular to a PTC heating tape and a preparation method thereof. Background Art

[0002] Conductive polymer composite materials with a positive temperature coefficient (PTC) effect can be obtained by blending conductive fillers with polymer matrix materials. Such materials are widely used in technical fields such as heaters, sensors, and heating cables.

[0003] Self-limiting PTC heating cables are a relatively common application product using this material. The polymer PTC material contains a conductive network that is connected and conductive at room temperature. At room temperature, due to the low resistivity of the conductive network, the PTC heating cable will heat up rapidly under high-flux current. This heating causes the polymer matrix material in the polymer PTC material to expand. Under this expansion, the conductive network will gradually disconnect, thereby reducing the current flux and inhibiting heating. In the prior art, carbon black or metal particles are usually used as conductive fillers. Such conductive fillers have a fast reaction speed under temperature effects, but the fillers themselves are small in size and have poor dispersion during the dispersion process with the polymer material. As the polymer expands and crystallizes repeatedly, poorly dispersed conductive particles will shift within the matrix, ultimately causing the conductive network to differ significantly from the initial state. This results in poor material performance repeatability and low product stability.

[0004] Currently, the stability improvement of polymer PTC heating cables is mainly based on the improvement of the dispersion of conductive fillers. How to provide a PTC heating cable with better stability and high performance repeatability has become one of the technical problems that need to be solved urgently.

[0005] Summary of the Invention

[0006] In view of this, the present invention proposes a PTC heating tape and a preparation method thereof, aiming to improve the stability and repeatability of the PTC heating tape.

[0007] The technical solution of the present invention is achieved as follows: The present invention provides a method for preparing a PTC heating tape, comprising the following steps:

[0008] A molten polymer is mixed with surface-coated modified tetrapod-shaped zinc oxide whiskers and then kneaded, and then co-extruded with two parallel core wires so that the outer layers of the two core wires and the space between the two core wires are coated with a conductive plastic layer. The PTC heating tape is obtained by cooling and solidifying. The mass ratio of the polymer to the surface-coated modified tetrapod-shaped zinc oxide whiskers is 100:(5-15). The preparation method of the surface-coated modified tetrapod-shaped zinc oxide whiskers includes depositing a metal film layer on the surface of the tetrapod-shaped zinc oxide whiskers by physical vapor deposition.

[0009] In some embodiments, additives such as stabilizers, flame retardants, antioxidants, pigments, etc. may be added to the conductive plastic layer.

[0010] In some embodiments, the metal film layer deposited on the surface of the surface-coated modified tetrapod-shaped zinc oxide whiskers is a copper film.

[0011] In some embodiments, in the surface-coated modified tetrapod-shaped zinc oxide whiskers, the mass ratio of zinc oxide whiskers to metallic copper is 1:(0.001-0.01).

[0012] In some embodiments, the tetrapod-shaped zinc oxide whiskers have a diameter of 0.5-5 μm and a length of 10-50 μm.

[0013] In some embodiments, the polymer is one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0014] In some embodiments, before depositing the metal film layer on the surface of the tetrapod-shaped zinc oxide whiskers, the process further includes cleaning the tetrapod-shaped zinc oxide whiskers with hydrochloric acid.

[0015] In some embodiments, after cleaning the zinc oxide whiskers with hydrochloric acid and before depositing the metal film layer on the surface of the tetrapod-shaped zinc oxide whiskers, the method further includes cleaning the tetrapod-shaped zinc oxide whiskers in a plasma atmosphere.

[0016] In some embodiments, when the molten polymer is mixed with the surface-coated modified tetrapod-shaped zinc oxide whiskers and then kneaded, carbon black is further added, and the mass ratio of the polymer to the carbon black is 100:(2-5).

[0017] On the other hand, the present invention also provides a PTC heating tape prepared by the above method.

[0018] In some embodiments, the PTC heating tape is further coated with an insulating layer on the outside of the conductive plastic layer.

[0019] In some embodiments, the PTC heating tape is further coated with a sheath layer on the outside of the insulation layer.

[0020] In some embodiments, a shielding layer may be further provided between the insulating layer and the sheath layer of the PTC heating tape.

[0021] The PTC heating tape and its preparation method of the present invention have the following beneficial effects compared with the prior art:

[0022] The present invention adopts four-needle zinc oxide whiskers as the base material of the filled conductor, and deposits a metal layer on the surface of the four-needle zinc oxide whiskers to make the four-needle zinc oxide whiskers conductive. Compared with conventional dispersed conductor particles, the four-needle zinc oxide whiskers have stronger dispersion stability in the polymer matrix. Even in the process of high-cycle use, the relative position stability of the four-needle zinc oxide whiskers is good, which can avoid the stability degradation problem caused by the slippage of the conductor filler. Secondly, after dispersion, the four-needle zinc oxide whiskers have good overlap properties in the polymer matrix. At room temperature, the initial current value of the heating tape is large and the heating response speed is fast. Secondly, during the heating process, the surface-deposited metal film will also cause expansion cracks between the four-needle zinc oxide whiskers and the four-needle zinc oxide whiskers. The cracks will also reduce the conductive effect of the conductor network, so that the temperature feedback effect of the PTC heating tape is good. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] Preparation Example 1

[0025] Four-needle zinc oxide whiskers with a diameter of 0.5-5 μm and a length of 10-50 μm are added to a vacuum coating machine. The vacuum degree in the vacuum coating machine is maintained at 500 Pa. Argon is used as the working gas and copper is used as the evaporation source. The copper is heated to 1200° C. and the copper source is started to be evaporated. The temperature of the four-needle zinc oxide whiskers is maintained at 40° C. During the evaporation process, the four-needle zinc oxide whiskers are stirred at a stirring speed of 5-30 rpm. When the mass ratio of the four-needle zinc oxide whiskers to the copper coating film on the surface reaches 1:0.001, the evaporation is stopped to obtain surface-coated modified four-needle zinc oxide whiskers.

[0026] Preparation Example 2

[0027] On the basis of Preparation Example 1, other conditions were kept unchanged, and the mass ratio of the tetrapod-shaped zinc oxide whiskers to the copper plating film on the surface was set to 1:0.005.

[0028] Preparation Example 3

[0029] On the basis of Preparation Example 1, other conditions were kept unchanged, and the mass ratio of the tetrapod-shaped zinc oxide whiskers to the copper plating film on the surface was set to 1:0.01.

[0030] Comparative Preparation Example 1

[0031] On the basis of Preparation Example 1, other conditions were kept unchanged, and the mass ratio of the tetrapod-shaped zinc oxide whiskers to the copper plating film on the surface was set to 1:0.0005.

[0032] Comparative Preparation Example 2

[0033] On the basis of Preparation Example 1, other conditions were kept unchanged, and the mass ratio of the four-needle zinc oxide whiskers to the copper plating film on the surface was set to 1:0.02.

[0034] Preparation Example 3

[0035] On the basis of Preparation Example 1, keeping other conditions unchanged, the tetrapod-shaped zinc oxide whiskers were cleaned with hydrochloric acid in advance, dried to constant weight after cleaning, and then subjected to vapor deposition.

[0036] Preparation Example 4

[0037] On the basis of Preparation Example 1, keeping other conditions unchanged, the four-needle zinc oxide whiskers were cleaned with hydrochloric acid in advance, dried to constant weight after cleaning, and then cleaned in an oxygen plasma atmosphere for 5 minutes, and then evaporated.

[0038] Comparative Preparation Example 3

[0039] On the basis of Preparation Example 1, other conditions were kept unchanged, aluminum was used as the evaporation source, and the heating temperature of aluminum during the evaporation process was 400°C.

[0040] Comparative Preparation Example 4

[0041] On the basis of Preparation Example 1, other conditions were kept unchanged, iron was used as the evaporation source, and the heating temperature of iron during the evaporation process was 1100°C.

[0042] Comparative Preparation Example 5

[0043] On the basis of Preparation Example 1, other conditions were kept unchanged, zinc was used as the evaporation source, and the heating temperature of zinc during the evaporation process was 600°C.

[0044] Comparative Preparation Example 6

[0045] On the basis of Preparation Example 1, while keeping other conditions unchanged, nanorod-shaped zinc oxide whiskers with a diameter of 0.5-5 μm and a length of 10-50 μm were used to replace the four-needle zinc oxide whiskers.

[0046] Example 1

[0047] 100 parts of high-density polyethylene and 5 parts of the surface-coated modified four-needle zinc oxide whiskers prepared in Preparation Example 1 were weighed separately, mixed and added to a plastic purifier. The heating temperature of the feed zone of the plastic purifier was 150°C, the heating temperature of the middle section was 170°C, the temperature of the extrusion zone was 190°C, and the die head temperature was 60°C. After melt mixing in the plastic purifier, they were co-extruded with two parallel copper strands in the die head part of the extruder to obtain a PTC heating tape with a conductive plastic layer coated on the surface.

[0048] Example 2

[0049] On the basis of Example 1, keeping other conditions unchanged, the amount of the surface-coated modified four-needle zinc oxide whiskers prepared in Preparation Example 1 was 10 parts.

[0050] Example 3

[0051] On the basis of Example 1, keeping other conditions unchanged, the amount of the surface-coated modified four-needle zinc oxide whiskers prepared in Preparation Example 1 was 15 parts.

[0052] Comparative Example 1

[0053] On the basis of Example 1, keeping other conditions unchanged, the amount of the surface-coated modified four-needle zinc oxide whisker prepared in Preparation Example 1 was 1 part.

[0054] Comparative Example 2

[0055] On the basis of Example 1, keeping other conditions unchanged, the amount of the surface-coated modified four-needle zinc oxide whiskers prepared in Preparation Example 1 was 20 parts.

[0056] Example 4

[0057] On the basis of Example 1, keeping other conditions unchanged, the surface-coated modified four-needle zinc oxide whiskers prepared in Preparation Example 2 were used.

[0058] Example 5

[0059] On the basis of Example 1, keeping other conditions unchanged, the surface-coated modified four-needle zinc oxide whiskers prepared in Preparation Example 3 were used.

[0060] Comparative Example 3

[0061] On the basis of Example 1, keeping other conditions unchanged, the surface-coated modified four-needle zinc oxide whiskers obtained in Comparative Preparation Example 1 were prepared.

[0062] Comparative Example 4

[0063] On the basis of Example 1, keeping other conditions unchanged, the surface-coated modified four-needle zinc oxide whiskers obtained in Comparative Preparation Example 2 were prepared.

[0064] Example 6

[0065] On the basis of Example 1, keeping other conditions unchanged, the surface-coated modified four-needle zinc oxide whiskers prepared in Preparation Example 3 were used.

[0066] Example 7

[0067] On the basis of Example 1, keeping other conditions unchanged, the surface-coated modified four-needle zinc oxide whiskers prepared in Preparation Example 4 were used.

[0068] Example 8

[0069] On the basis of Example 1, keeping other conditions unchanged, the surface-coated modified four-needle zinc oxide whiskers obtained in Comparative Preparation Example 3 were prepared.

[0070] Example 9

[0071] On the basis of Example 1, keeping other conditions unchanged, the surface-coated modified four-needle zinc oxide whiskers obtained in Comparative Preparation Example 4 were prepared.

[0072] Example 10

[0073] On the basis of Example 1, keeping other conditions unchanged, the surface-coated modified four-needle zinc oxide whiskers prepared in Comparative Preparation Example 5 were used.

[0074] Comparative Example 5

[0075] On the basis of Example 1, keeping other conditions unchanged, an equal amount of carbon black was used to replace the surface-coated modified four-needle zinc oxide whiskers prepared in Preparation Example 1.

[0076] Example 11

[0077] On the basis of Example 1, keeping other conditions unchanged, 2 parts of carbon black were added.

[0078] Example 12

[0079] On the basis of Example 1, keeping other conditions unchanged, 3 parts of carbon black were added.

[0080] Example 13

[0081] On the basis of Example 1, keeping other conditions unchanged, 5 parts of carbon black were added.

[0082] Comparative Example 6

[0083] On the basis of Example 1, keeping other conditions unchanged, the surface-coated modified four-needle zinc oxide whisker prepared in Comparative Preparation Example 6 was used.

[0084] Performance testing

[0085] 1. Stability test:

[0086] The PTC heating cables prepared in Examples 1-10 and Comparative Examples 1-8 were placed in an oven and subjected to a heating and cooling cycle. The maximum temperature was 140°C at a heating rate of 10°C / min. After reaching 140°C, the temperature was maintained for 10 minutes, and then the temperature was cooled to 30°C at a cooling rate of 10°C / min. The cycles were repeated 10 times, 50 times, and 100 times, respectively. The resistivity at 30°C was measured before and after each cycle. The results are shown in the following table:

[0087] The post-cycle resistivity data of the above-mentioned examples and comparative examples show that the PTC heating tape prepared using the preparation method of the present invention has good repeatability. Compared with conventional conductor fillers such as carbon black, the use of four-needle zinc oxide whiskers with a surface-coated metal film layer as a conductor filler has good performance reproducibility. Compared with conventional carbon black conductor fillers, after 100 heating cycles, it can still maintain a room-temperature conductivity close to that of the initial state. Through experimental comparison, it can be found that when copper is used as the plating metal material, it has better stability and repeatability than other metals. It is believed that this may be related to the conductivity and self-repair ability of copper. Secondly, copper has higher stability than aluminum and iron and is not easily oxidized.

[0088] The PTC heating cables before and after the stability test were heated to test their upper limit of self-limiting temperature. The following data were obtained:

[0089] The comparative data are as follows:

[0090] Heating performance tests show that when the whisker type and amount are within the preferred ranges of the present invention, and when the whisker preparation conditions are also within the preferred range, the resulting PTC heating tape exhibits good heating stability. However, when the whisker amount is too small, the surface coating is too low, or when the metal film-coated tetrapod-shaped zinc oxide whiskers are not used, the heating performance of the corresponding PTC heating tape decreases sharply, and reproducibility is also poor. In Comparative Example 2, the heating tape overheated and burned after power was applied, failing to achieve self-limiting temperature. Therefore, no data was recorded.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a PTC heating tape, characterized in that: The steps include: The molten polymer and the surface-coated modified four-needle zinc oxide whisker are mixed and kneaded, and then co-extruded with two parallel core wires so that the outer layer of the two core wires and the space between the two core wires are coated with a conductive plastic layer, and cooled and solidified to obtain a PTC heating tape; the mass ratio of the polymer to the surface-coated modified four-needle zinc oxide whisker is 100:(5-15), and the preparation method of the surface-coated modified four-needle zinc oxide whisker includes depositing a metal film layer on the surface of the four-needle zinc oxide whisker by physical vapor deposition.

2. The method for preparing the PTC heating tape according to claim 1, characterized in that: The metal film layer deposited on the surface of the surface-coated modified four-needle zinc oxide whisker is a copper film.

3. The method for preparing the PTC heating tape according to claim 2, characterized in that: In the surface-coated modified four-needle zinc oxide whiskers, the mass ratio of the zinc oxide whiskers to the metal copper is 1:(0.001-0.01).

4. The method for preparing the PTC heating tape according to claim 1, characterized in that: The diameter of the tetrapod-shaped zinc oxide whiskers is 0.5-5 μm and the length is 10-50 μm.

5. The method for preparing the PTC heating tape according to claim 1, characterized in that: The polymer is one of polyethylene, polypropylene and polyvinylidene fluoride.

6. The method for preparing the PTC heating tape according to claim 1, characterized in that: Before depositing the metal film layer on the surface of the four-needle zinc oxide whisker, the process also includes cleaning the four-needle zinc oxide whisker with hydrochloric acid.

7. The method for preparing a PTC heating tape according to claim 6, characterized in that: After the zinc oxide whiskers are cleaned with hydrochloric acid and before the metal film layer is deposited on the surface of the four-needle zinc oxide whiskers, the method further includes cleaning the four-needle zinc oxide whiskers in a plasma atmosphere.

8. The method for preparing a PTC heating tape according to claim 1, characterized in that: When the molten polymer is mixed with the surface-coated modified four-needle zinc oxide whisker and then kneaded, carbon black is also added, and the mass ratio of the polymer to the carbon black is 100:(2-5).

9. A PTC heating tape prepared by the method for preparing a PTC heating tape according to any one of claims 1 to 8.

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