A polyvinyl chloride (PVC) sealing strip for refrigerators, its preparation method and application

Abstract

This invention discloses a polyvinyl chloride (PVC) sealing strip for refrigerators, its preparation method, and its application, belonging to the field of sealing material technology. The PVC sealing strip for refrigerators is mainly prepared from the following raw materials in parts by weight: 140-160 parts PVC, 4.2-4.8 parts stabilizer, 70-140 parts dioctyl terephthalate, 10-20 parts tributyl acetylacetonate, 20-40 parts epoxidized soybean oil, and 80-90 parts conductive filler. This sealing strip meets the requirements for flexible sealing in low-temperature environments and also possesses good electromagnetic shielding performance.

Description

Technical Field

[0001] This invention relates to the field of sealing materials technology, and in particular to a polyvinyl chloride sealing strip for refrigerators, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In the large-scale home appliance manufacturing sector, refrigerators, as common household appliances, are of paramount importance in terms of performance and quality. Among these, the refrigerator's sealing strip plays a crucial role in its sealing effect, insulation performance, and internal environmental stability. Traditional refrigerator sealing strips mostly use ordinary PVC material; however, with the development of new refrigerators such as smart freezers, higher requirements have been placed on sealing strips.

[0004] On the one hand, smart freezers need to detect goods with RFID tags inside, requiring excellent shielding to prevent the internal antenna from detecting goods outside and causing damage. However, traditional PVC sealing strips are significantly inadequate in terms of electromagnetic shielding performance, making it difficult to meet this requirement. On the other hand, in low-temperature environments, especially under harsh conditions below -30°C, traditional PVC sealing strips are prone to becoming brittle, resulting in poor sealing and ineffective sealing, affecting the overall performance of the freezer. Moreover, existing PVC sealing strips cannot simultaneously achieve the flexibility required below -30°C to ensure sealing performance and adequate RFID frequency electromagnetic shielding effectiveness. There is a contradiction between the two: excessive plasticizers can improve low-temperature flexibility but may damage the conductive network formed by conductive fillers, reducing the shielding effect; excessive conductive fillers can improve shielding effectiveness but will increase material rigidity, making it prone to brittleness at low temperatures.

[0005] In existing technologies, various methods have been attempted to solve the problems of PVC sealing strips. One method is to add conductive fillers, such as metal powder, to PVC. However, the performance of such fillers is unstable at low temperatures, making it difficult to guarantee the effectiveness of the sealing strip in low-temperature environments. Another method is to use a multi-layer structure, such as coating a conductive layer on the outer layer of PVC. However, this processing method is complex and costly, which is not conducive to large-scale production applications. Yet another method is to use nanomaterials, such as carbon nanotubes or graphene. Although these materials are used in small quantities and have significant effects, it is difficult to guarantee uniform dispersion, and their high cost limits their widespread application in actual production. Therefore, developing a PVC sealing strip for refrigerators that can meet the requirements of flexible sealing in low-temperature environments and also has good electromagnetic shielding performance has become an urgent technical challenge. Summary of the Invention

[0006] In view of this, the present invention provides a polyvinyl chloride sealing strip for refrigerators, its preparation method and application.

[0007] In a first aspect, the present invention provides a polyvinyl chloride sealing strip for refrigerators, which is mainly prepared from the following raw materials in parts by weight: 140-160 parts of polyvinyl chloride, 4.2-4.8 parts of stabilizer, 70-140 parts of dioctyl terephthalate, 10-20 parts of tributyl acetylacetonate, 20-40 parts of epoxidized soybean oil, and 80-90 parts of conductive filler.

[0008] Preferably, the mass ratio of dioctyl terephthalate, tributyl acetylacetonate, and epoxidized soybean oil is 7:1:2. Under these conditions, the glass transition temperature of the material can be effectively reduced, and its low-temperature flexibility can be improved.

[0009] Preferably, the conductive filler is nano-carbon black and carbon fiber, with a mass ratio of nano-carbon black to carbon fiber of 7-13:1. Nano-carbon black can fill the insulating crystalline regions of PVC, disrupting the insulation of PVC and forming a basic conductive network. Carbon fiber can act as a conductive bridge, connecting the dispersed nano-carbon black particles and improving the continuity and integrity of the conductive network. Under these conditions, excellent electromagnetic shielding performance can be achieved.

[0010] Preferably, the polyvinyl chloride (PVC) is SG-5 PVC. Different types of PVC have different molecular structures and performance characteristics. When combined with a specific plasticizer system, SG-5 PVC can better achieve low-temperature flexibility and, in synergy with other raw materials, enable the sealing strip to maintain good performance even below -30°C, which is a significant advantage over other types of PVC.

[0011] Preferably, the stabilizer is a zinc-calcium stabilizer. Zinc-calcium stabilizers have good thermal stability and weather resistance, effectively preventing PVC degradation during processing and use, ensuring the stability of the sealing strip's performance, and extending its service life.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned polyvinyl chloride sealing strip for refrigerators, comprising the following steps: (1) Mix polyvinyl chloride with a stabilizer to obtain mixture A, and mix dioctyl terephthalate, tributyl acetyl citrate and part of epoxidized soybean oil to obtain a composite plasticizer; (2) Add the composite plasticizer to mixture A and mix to obtain modified polyvinyl chloride; (3) The modified polyvinyl chloride is mixed. First, some conductive filler is added and mixed. Then, the remaining epoxidized soybean oil is added. Finally, the remaining conductive filler is added to obtain conductive polyvinyl chloride. (4) The conductive polyvinyl chloride is preheated, pressure-set, and cooled to obtain the product.

[0013] The remaining epoxidized soybean oil is added in the later stage of mixing to disperse the filler and improve conductivity. Preferably, the mass ratio of epoxidized soybean oil in step (1) to epoxidized soybean oil in step (3) is 3:1.

[0014] Preferably, in step (2), the composite plasticizer is added to mixture A in 3-4 batches for mixing at a temperature of 40-50°C for 2-3 minutes, followed by heat preservation for 10-15 minutes. Adding the composite plasticizer in 3-4 batches avoids local aggregation of the composite plasticizer, ensuring that the plasticizer can fully contact the PVC and exert a synergistic plasticizing effect.

[0015] Preferably, in step (3), the mixing temperature is 150-180℃, the mixing speed is 60-70 r / min, a portion of the conductive filler is added first and mixed for 2-3 minutes, then the remaining epoxidized soybean oil is added and mixed for 1-2 minutes, and finally the remaining conductive filler is added and mixed for 2-3 minutes. The conductive filler is added in two stages to optimize dispersion by reducing processing difficulty and improving conductivity. The mass ratio of the portion of conductive filler to the remaining conductive material is 3:1. If added all at once, it often leads to uneven dispersion.

[0016] Preferably, in step (4), the preheating temperature is 150~180℃, the preheating time is 2~3 minutes, the pressure setting time is 3~4 minutes, and the temperature after cooling is 80~100℃.

[0017] Thirdly, the present invention provides the application of the above-mentioned PVC sealing strip for refrigerators or the PVC sealing strip for refrigerators prepared by the above-mentioned preparation method in refrigerators and freezers.

[0018] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) This invention addresses the dual technical challenges of low-temperature flexibility and electromagnetic shielding through specific raw material composition and proportions. A composite plasticizing system composed of dioctyl terephthalate, tributyl acetylacetonate, and epoxidized soybean oil creates a synergistic plasticizing effect. Tributyl acetylacetonate rapidly lowers the glass transition temperature of PVC, initially improving low-temperature flexibility; dioctyl terephthalate enhances the compatibility between the plasticizer and PVC, preventing precipitation; while epoxidized soybean oil has low plasticizing efficiency on its own, it provides stable spatial isolation and, in synergy with the first two plasticizers, can lower the glass transition temperature of PVC to below -30°C under specific dosages of the three plasticizers, ensuring low-temperature flexibility. Simultaneously, the combination of nano-carbon black and carbon fiber forms a stable conductive network within the PVC matrix, meeting the electromagnetic shielding requirements within the RFID frequency range. These two components synergistically resolve the core contradiction between low-temperature flexibility and shielding.

[0019] (2) The PVC sealing strip for refrigerators of the present invention conforms to the ISO 177:2016 standard. When heated at 70℃±2℃ for 7 days, the mass loss is only about 2%, which avoids contamination of goods in the freezer and meets the hygiene requirements. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0021] Figure 1 These are DMA curves of Embodiment 1 and Comparative Example 1 of the present invention; Figure 2 These are DMA curves of Embodiment 1 and Comparative Example 2 of the present invention; Figure 3 These are conductivity statistics for Examples 1-6 and Comparative Example 4 of the present invention; Figure 4 These are conductivity statistics for Embodiments 1, 4, Comparative Example 3, and Comparative Example 4 of the present invention. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] The technical solution of the present invention will be further described below with reference to specific embodiments. Unless otherwise specified, the raw materials, reagents or devices used in the following embodiments can be obtained from conventional commercial channels or by existing known methods.

[0024] The component dosages of the PVC sealing strips for refrigerators in Examples 1-4 are shown in Table 1: Table 1. Component dosage of PVC sealing strips for refrigerators in Examples 1-4

[0025] The preparation method of the PVC sealing strip for refrigerators in Examples 1-3 includes the following steps: (1) Add polyvinyl chloride and stabilizer to a pulverizer, stir and mix evenly to obtain mixture A. Mix dioctyl terephthalate, tributyl acetyl citrate and part of epoxidized soybean oil to obtain composite plasticizer.

[0026] (2) Place the mixture A in a pulverizer and add the composite plasticizer into the pulverizer in 3 batches. The mixing temperature is 40°C and the mixing time is 3 minutes. Keep warm for 15 minutes. After each addition, start the pulverizer and stir to obtain the modified polyvinyl chloride material.

[0027] (3) The modified polyvinyl chloride was placed in a torque rheometer for mixing to become a fluid state. The mixing temperature was 180℃ and the mixing speed was 60r / min. First, some nano carbon black and carbon fiber were added and mixed for 3 minutes. Then, the remaining epoxidized soybean oil was added and mixed for 2 minutes. Finally, the remaining nano carbon black and carbon fiber were added and mixed for 2 minutes to obtain conductive polyvinyl chloride.

[0028] (4) The obtained conductive polyvinyl chloride is placed into the sealing strip mold for molding. The preheating temperature is 170℃, the preheating time is 2 minutes, the pressure setting time is 3 minutes, and the temperature after cooling is 100℃.

[0029] The component amounts of the PVC sealing strips for refrigerators in Comparative Examples 1-6 are shown in Table 2: Table 2 shows the component dosages of PVC sealing strips for refrigerators in Comparative Examples 1-6.

[0030] Produced and processed according to the preparation method of Example 1.

[0031] Effect verification 1. The relevant performance of the sealing strips obtained in Examples 1-6 and Comparative Examples 1-6 were evaluated respectively, and the results are shown in Table 3: Test methods: The glass transition temperature (Tg) of the sealing strip was determined using a dynamic mechanical analyzer under tensile conditions at a heating and cooling rate of 3℃ / min. Tensile strength and elongation at break were tested according to the method provided in GB / T 1040.3-2006 / ISO 527-3:1995. Electrical conductivity was measured using an ST2263 dual-electrical-value four-probe tester. Mobility was tested according to the method provided in ISO 177:2016.

[0032] Table 3 Test results of Examples 1-6 and Comparative Examples 1-6

[0033] Low-temperature flexibility (glass transition temperature Tg) analysis: The Tg values ​​of Examples 1-6 all reached or were below -30°C, meeting the stringent operating conditions required for refrigerators.

[0034] Comparative Example 1 and Comparative Example 1: With the same total plasticizer parts (140 parts), Comparative Example 1 replaced ESO with a higher part of the high-efficiency plasticizer ATBC (42 parts), but its Tg was only -21°C. This unexpectedly proves that a single component with higher plasticizing efficiency is not necessarily more effective. ATBC, DOTP, and ESO must form a specific composite system to produce a synergistic effect and significantly reduce Tg. Adding a high-efficiency plasticizer alone is actually detrimental to low-temperature flexibility.

[0035] Comparing Example 1 and Comparative Example 2: With the exact same formulation, Comparative Example 2, using SG-3 type PVC, had a Tg of -21°C, significantly higher than -30°C in Example 1 (SG-5 type). This indicates that the regular molecular chain structure of SG-5 type PVC is more conducive to the uniform embedding of composite plasticizers, which is key to achieving ultra-low Tg.

[0036] Comparative Example 6 further confirms the above conclusions. Even with the use of more total plasticizer (150 parts), the Tg of SG-3 type PVC can only reach -25°C.

[0037] Electromagnetic shielding performance (conductivity) analysis: All embodiments meet the requirements for shielding RFID signals. Regarding the shielding effect test, in our actual tests, a PVC sealing strip with a conductivity of 30 (S / m) was sufficient to shield RFID signals. We placed an RFID tag at the door of the shielded cabinet, and with the PVC sealing strip in place, the smart freezer could not detect the tag, thus achieving the shielding effect.

[0038] Comparing Example 1 with Comparative Examples 3-5 demonstrates the necessity of the composite conductive filler. When the mass ratio of nano-carbon black to carbon fiber deviates from the preferred range (7-13:1): the conductivity of Comparative Example 3 (ratio 4:1) drops to 21.8 S / m; the conductivity of Comparative Example 4 (carbon black only) is 30.11 S / m; and the conductivity of Comparative Example 5 (carbon fiber only) is only 12.7 S / m. This confirms that carbon black forms the basic conductive network, and carbon fiber acts as a "conductive bridge" connecting the network nodes; high conductivity can only be achieved through synergy between the two at a specific weight ratio.

[0039] It is noteworthy that the conductivity of Comparative Example 6 (45.88 S / m) is higher than that of all other examples. Combined with its poor Tg (-25°C) and high migration (4.6%), we infer that while the system of SG-3 PVC with a high ATBC content unexpectedly promotes a certain directional arrangement of the conductive filler, its overall flexibility and resistance to exudation are extremely poor, making it unsuitable as a practical sealing strip. This counterexample underscores the necessity for this invention to balance the formation of the conductive network through a specific PVC type and plasticizer system, while ensuring acceptable Tg and migration.

[0040] Durability and hygiene (migration rate) analysis: The migration rates of Examples 1-6 were all below 2.91%, far lower than the 3.9%-4.6% of Comparative Examples 1-3 and 6, meeting the stringent hygiene requirements of ISO 177:2016 for food contact materials (refrigerator seals may come into contact with food). The low migration rate means that the plasticizer is less likely to leach out during long-term use, preventing contamination of the refrigerator's internal environment and ensuring the long-term stability of the seal's performance.

[0041] Mechanical property (tensile strength and elongation at break) analysis: Examples 1-6 all exhibited good overall mechanical properties. The elongation at break of the examples was higher than that of the comparative examples, indicating that the sealing strips had good ductility and flexibility, resulting in better sealing performance. Among them, Example 1 had the highest tensile strength (15.84 MPa), and Example 2 had the highest elongation at break (135.2%), demonstrating that the sealing strip of the present invention possesses both strength and toughness, and can withstand the deformation caused by repeated opening and closing of doors without breaking. In contrast, the elongation at break of all comparative examples was less than 112%, indicating insufficient flexibility and a tendency to fail due to brittleness after long-term use.

[0042] Based on the data in Table 3, this invention successfully achieved a balance between low-temperature flexibility (Tg≤-30℃), qualified electromagnetic shielding performance (conductivity≥31.5 S / m), low plasticizer migration rate (≤2.91%), and good mechanical properties by limiting the PVC type, specific composite plasticizer system, and specific composite conductive filler, thus resolving the long-standing contradictions in the prior art.

[0043] The DMA test method was as follows: Example 1, Comparative Example 1, and Comparative Example 2 were tested using a dynamic thermomechanical analyzer (TA Instruments Q800) according to the method provided in GB / T40396-2021. The test results are shown in [Figure number missing]. Figure 1 and Figure 2 .

[0044] Figure 1 This is a DMA curve graph of Example 1 and Comparative Example 1 of the present invention. Under the condition that the total proportion of plasticizer is the same, the glass transition temperature (Tg) depends on the plasticizing efficiency of each plasticizer. Dioctyl terephthalate is a medium-efficiency plasticizer, tributyl acetylacetonate is a high-efficiency plasticizer, and epoxidized soybean oil has low efficiency. From the single dimension of plasticizing efficiency, tributyl acetylacetonate is more efficient than epoxidized soybean oil. Since the formulation contains a higher content of tributyl acetylacetonate, a lower Tg should be obtained. Figure 1 As can be seen, the glass transition temperature of Example 1 is lower, while that of Comparative Example 1 is higher, indicating that epoxidized soybean oil provides structural stability, long-lasting spatial isolation, and synergistic compatibility.

[0045] Figure 2 This is a DMA curve diagram of Embodiment 1 and Comparative Example 2 of the present invention. From... Figure 2 As can be seen, the glass transition temperature of Example 1 is lower, while that of Comparative Example 2 is higher. The core reason is that the molecular chain structure of SG-5 PVC is more regular, with fewer branches, and has better compatibility with the three plasticizers. The plasticizer molecules can insert into the molecular chains of SG-5 more efficiently and uniformly, weakening the intermolecular forces more effectively, thus significantly reducing the Tg. On the other hand, the molecular chain regularity of SG-3 PVC is lower, with more branches, which hinders the insertion of plasticizer molecules and results in uneven plasticizer dispersion, leading to a higher Tg and failing to meet the low-temperature flexibility requirements below -30°C.

[0046] Figure 3 These are conductivity statistics for Examples 1-6 and Comparative Example 4 of the present invention. Figure 4 This is a statistical chart of the conductivity of Embodiments 1, 4, Comparative Example 3, and Comparative Example 4 of the present invention. From... Figure 3 and Figure 4 It can be seen that the mass ratio of nano-carbon black to carbon fiber affects the electrical conductivity.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A polyvinyl chloride sealing strip for refrigerators, characterized in that, It is mainly prepared from the following raw materials in parts by weight: 140-160 parts of polyvinyl chloride, 4.2-4.8 parts of stabilizer, 70-140 parts of dioctyl terephthalate, 10-20 parts of tributyl acetylacetonate, 20-40 parts of epoxidized soybean oil, and 80-90 parts of conductive filler.

2. The PVC sealing strip for refrigerators as described in claim 1, characterized in that, The mass ratio of dioctyl terephthalate, tributyl acetyl citrate and epoxidized soybean oil is 7:1:2; The conductive filler is nano-carbon black and carbon fiber, and the mass ratio of nano-carbon black to carbon fiber is 7-13:

1.

3. The PVC sealing strip for refrigerators as described in claim 1, characterized in that, The polyvinyl chloride is SG-5 polyvinyl chloride.

4. The PVC sealing strip for refrigerators as described in claim 1, characterized in that, The stabilizer is a zinc-calcium stabilizer.

5. The method for preparing a PVC sealing strip for refrigerators as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Mix polyvinyl chloride with a stabilizer to obtain mixture A, and mix dioctyl terephthalate, tributyl acetyl citrate and part of epoxidized soybean oil to obtain a composite plasticizer; (2) Add the composite plasticizer to mixture A and mix to obtain modified polyvinyl chloride; (3) The modified polyvinyl chloride is mixed. First, some conductive filler is added and mixed. Then, the remaining epoxidized soybean oil is added. Finally, the remaining conductive filler is added to obtain conductive polyvinyl chloride. (4) The conductive polyvinyl chloride is preheated, pressure-set, and cooled to obtain the product.

6. The preparation method according to claim 5, characterized in that, The mass ratio of the epoxidized soybean oil in step (1) to the epoxidized soybean oil in step (3) is 3:

1.

7. The preparation method according to claim 5, characterized in that, In step (2), the composite plasticizer is added to mixture A in 3 to 4 batches for mixing. The mixing temperature is 40 to 50°C, the mixing time is 2 to 3 minutes, and the mixture is kept warm for 10 to 15 minutes.

8. The preparation method according to claim 5, characterized in that, In step (3), the mixing temperature is 150-180℃, the mixing speed is 60-70r / min, first add some conductive filler and mix for 2-3 minutes, then add the remaining epoxidized soybean oil and mix for 1-2 minutes, and finally add the remaining conductive filler and mix for 2-3 minutes.

9. The preparation method according to claim 5, characterized in that, In step (4), the preheating temperature is 150~180℃ and the preheating time is 2~3 minutes; the pressure setting time is 3~4 minutes; and the temperature after cooling is 80~100℃.

10. The application of the PVC sealing strip for refrigerators as described in any one of claims 1 to 4, or the PVC sealing strip for refrigerators prepared by the preparation method described in any one of claims 5 to 9, in refrigerators and freezers.

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