A soft PVC composition for injection molding and preparation method thereof

Abstract

The present application relates to the field of modified plastic technology, and specifically to a soft PVC composition for injection molding and a preparation method thereof. The soft PVC composition for injection molding comprises the following components in parts by weight: 50 parts of PVC resin, 24-60 parts of plasticizer, 120-160 parts of polyester elastomer, 0-30 parts of filler, 3-4 parts of heat stabilizer, 2-3 parts of acrylate processing aid, 0.3-0.9 parts of lubricant, and 0.5-1 parts of phosphite; the plasticizer comprises at least one of orthophthalic plasticizer, paraphthalic plasticizer, paraphenylene plasticizer, polyester plasticizer, and epoxy soybean oil. The present application adopts polyester elastomer to reduce thermal deformation and cracks caused by high temperature, thereby improving the strength and durability of the product, and adopts plasticizer to improve the compatibility between PVC resin and other components such as polyester elastomer, which helps to improve the bonding strength of the soft PVC composition for injection molding, making it more durable and reliable during use.

Description

Technical Field

[0001] The present application relates to the technical field of modified plastics, and in particular to a soft PVC composition for injection molding and a preparation method thereof. Background Art

[0002] PVC (polyvinyl chloride) is a popular and widely used synthetic material in the world today. Its global usage ranks second among various synthetic materials. PVC is produced and used worldwide at a growth rate of 4% per year. Soft PVC can also be used for the edging of front and rear windshields of cars due to its advantages of easy molding, easy coloring, low cost and strong plasticity.

[0003] When wrapping the windshield with PVC material, the two ends need to be connected together at the corners through injection molding, and finally assembled around the glass to act as a seal. The injection molding method refers to the process of bringing the molten PVC material into contact with the two ends of the PVC edging strip fixed in the mold cavity to achieve fusion of the two. The entire process requires a very high melt temperature. Since PVC materials are sensitive to temperature, the melt temperature cannot be too high during injection molding of corners, otherwise it is easy to produce problems such as charring and bulging during continuous production. The current solution is to apply a layer of primer to the end face of the PVC edging strip before injection molding the corners to increase the bonding strength of the PVC material at normal injection molding temperature. Since the PVC material needs to be primed for each operation, the production process is increased and it is not very convenient. Summary of the invention

[0004] In order to solve the problem that a primer needs to be applied to the end surface of a PVC material used as an edge strip of a car windshield, the present application provides a soft PVC composition for injection molding. The composition has excellent bonding strength through the combination of a plasticizer and a polyester elastomer, and can be operated without applying a primer, thereby reducing the production process.

[0005] In a first aspect, the present application provides a soft PVC composition for injection molding, which adopts the following technical solution:

[0006] A soft PVC composition for injection molding, comprising the following components in parts by weight: 50 parts of PVC resin, 24-60 parts of plasticizer, 120-160 parts of polyester elastomer, 0-30 parts of filler, 3-4 parts of heat stabilizer, 2-3 parts of acrylic acid ester processing aid, 0.3-0.9 parts of lubricant, and 0.5-1 parts of phosphite;

[0007] The plasticizer includes at least one of orthophthalic plasticizers, paraphthalic plasticizers, paraphenylene plasticizers, polyester plasticizers, and epoxidized soybean oil.

[0008] By adopting the above technical solution, the plasticizer can penetrate between the molecular chains of the PVC resin, increase the distance between the molecular chains, and thus reduce the melting temperature and melt viscosity of the PVC resin. This helps to make the PVC resin flow and fill the mold more easily during the injection molding process, reduce thermal decomposition and degradation caused by high temperature, and thus maintain the performance of the PVC material. The plasticizer can improve the compatibility between the PVC resin and other components such as polyester elastomers, so that they are better combined. This helps to improve the bonding strength of the soft PVC composition for injection molding, making it more durable and reliable during use.

[0009] Polyester elastomer is a material with high toughness and elasticity. Adding it to PVC resin can significantly improve the toughness of soft PVC compositions for injection molding. This helps to reduce thermal deformation and cracks caused by high temperatures, thereby improving the strength and durability of the product.

[0010] Preferably, the plasticizer is an orthophthalic plasticizer, and the weight portion of the orthophthalic plasticizer is 50-70 parts.

[0011] By adopting the above technical solution, phthalic plasticizers, such as diisononyl phthalate (DINP) and di(2-propylheptyl)phthalate (DPHP), have excellent compatibility with PVC resin. This compatibility originates from the interaction between the ester group in the plasticizer molecular structure and the chlorine atom in the PVC molecular chain, which enables the plasticizer to effectively penetrate between the PVC molecular chains, reduce the melting temperature and melt viscosity of PVC, and thus improve the processing performance and flexibility of PVC. Phthalic plasticizers not only have good compatibility with PVC, but also have certain compatibility with polyester elastomers. This compatibility helps to promote the close bonding between PVC and polyester elastomers during the injection molding process, so that the two can form a uniform melt, thereby improving the overall performance and bonding strength of the soft PVC composition for injection molding.

[0012] Although phthalates are compatible with PVC and polyester elastomers, they are not chemically bonded to each other, but rather rely on weak physical interactions (such as van der Waals forces and hydrogen bonds) to hold them together. Therefore, phthalates are prone to migration during processing and use, especially under high temperature, pressure or external media.

[0013] Considering the migration of phthalates, in order to ensure that the content of plasticizers in the soft PVC composition for injection molding is stable and sufficient, more phthalates need to be added. However, too much plasticizer may aggravate the migration phenomenon, leading to product performance degradation and environmental pollution. Therefore, it is a relatively reasonable choice to control the content of phthalates within the range of 50-70 parts. This range can not only ensure the effective distribution and combination of plasticizers in PVC and polyester elastomers, but also better control the risk of migration.

[0014] Preferably, the plasticizer is a para-phthalene plasticizer, and the weight portion of the para-phthalene plasticizer is 35-60 parts.

[0015] By adopting the above technical scheme, p-phenylene plasticizers have better migration resistance than ortho-phthalate plasticizers. This is mainly because the molecular structure of p-phenylene plasticizers contains larger benzene rings, which makes its molecular volume larger and not easy to migrate out of PVC products. Therefore, adding an appropriate amount of p-phenylene plasticizer to the soft PVC composition for injection molding can effectively improve the migration resistance of the product and extend the service life of the product. P-phenylene plasticizers perform relatively poorly in terms of compatibility with PVC and polyester elastomers. This is mainly because the molecular structure of p-phenylene plasticizers is quite different from that of PVC and polyester elastomers, resulting in weak interaction between them.

[0016] The content of terephthalate plasticizers in soft PVC compositions for injection molding needs to be controlled within a reasonable range. If the content is too high, although the migration resistance of the product can be further improved, it may aggravate the compatibility problem with PVC and polyester elastomers, resulting in a decrease in product performance. If the content is too low, the migration resistance advantage of terephthalate plasticizers may not be fully utilized.

[0017] Preferably, the plasticizer is a benzene plasticizer, and the weight portion of the benzene plasticizer is 25-40 parts.

[0018] By adopting the above technical solution, benzene plasticizers, such as trioctyl trimellitate (TOTM), have better heat resistance than other types of plasticizers. This is mainly because benzene rings are introduced into the molecular structure of benzene plasticizers, making their molecules more stable and more effectively resisting the effects of high melting temperatures on PVC resins. During the injection molding process, high melting temperatures may cause thermal decomposition and degradation of PVC resins, thereby affecting the performance of the products. The addition of benzene plasticizers can effectively improve the thermal stability of PVC resins, reduce the occurrence of thermal decomposition and degradation, and thus ensure that the soft PVC composition for injection molding has good processing performance and physical properties.

[0019] The compatibility of benzene plasticizers with PVC and polyester elastomers is relatively poor. This is mainly because the molecular structure of benzene plasticizers is quite different from that of PVC and polyester elastomers, resulting in weak interaction between them. Therefore, during the injection molding process, benzene plasticizers may not be able to evenly penetrate between the molecular chains of PVC and polyester elastomers, thereby affecting the overall performance and bonding strength of the soft PVC composition for injection molding. This poor compatibility problem may cause quality problems such as delamination and cracking of the product during use.

[0020] The content of benzene plasticizers in soft PVC compositions for injection molding needs to be controlled within a relatively low range. If the content is too high, although the heat resistance of the product can be further improved, it may aggravate the compatibility problem with PVC and polyester elastomers, resulting in a serious decline in product performance. If the content is too low, the heat resistance advantage of benzene plasticizers may not be fully utilized.

[0021] Preferably, the plasticizer is a mixture of orthophthalic plasticizer, paraphthalic plasticizer and paraphenylene plasticizer.

[0022] Preferably, the mass ratio of the orthophthalic plasticizer, the paraphthalic plasticizer and the paraphenylene plasticizer is 15:(6-10):(4-8).

[0023] By adopting the above technical solution, orthophthalic plasticizers have good compatibility with PVC and polyester elastomers. Compared with orthophthalic plasticizers, paraphthalic plasticizers have better migration resistance and heat resistance. Parthenol plasticizers have excellent heat resistance. The three plasticizers can be mixed to take advantage of each other and cooperate with each other to achieve a balanced effect. Orthophthalic plasticizers provide good compatibility and processing performance; paraphthalic plasticizers enhance migration resistance and heat resistance; and parthenol plasticizers further improve heat resistance and flame retardancy.

[0024] Orthophthalic plasticizers have the best compatibility with PVC, so they are used as the main plasticizer. Paraphenylene plasticizers have good migration resistance and heat resistance, but slightly poor compatibility, so they are used as auxiliary plasticizers and their content should be lower than that of orthophthalic plasticizers. Although paraphenylene plasticizers have excellent heat resistance and flame retardancy, they have the worst compatibility, so their content should be the lowest.

[0025] Preferably, the hardness of the polyester elastomer is 25-35D.

[0026] By adopting the above technical solution, if the hardness of the polyester elastomer is too low, its strength and wear resistance may be reduced, and too low hardness may also cause the polyester elastomer to be easily deformed or damaged during use, thereby affecting its service life. If the hardness of the polyester elastomer is too high, its elasticity may be reduced, and too high hardness may also lead to insufficient fluidity and difficulty in filling the mold.

[0027] Preferably, the average degree of polymerization of the PVC resin is 1500-3000.

[0028] By adopting the above technical solution, PVC resin with low polymerization degree is more likely to break when subjected to external force, thereby reducing the durability and service life of the product. Although PVC resin with low polymerization degree may have a lower melt viscosity during processing, which is conducive to plasticization and flow, too low polymerization degree may result in insufficient melt strength of the resin, making it difficult to maintain shape stability. When the average polymerization degree of PVC resin increases, the length of the molecular chain will be extended accordingly, resulting in a higher melt viscosity of the resin during processing. This will increase the difficulty and cost of processing because higher temperature and pressure are required to plasticize and flow the resin. At the same time, PVC resin with high polymerization degree may be more prone to degradation in a molten state, thereby affecting its processing performance and product quality.

[0029] In a second aspect, the present application provides a method for preparing a soft PVC composition for injection molding, using the following technical solution:

[0030] A method for preparing a soft PVC composition for injection molding, which is used to prepare the soft PVC composition for injection molding, comprises the following steps:

[0031] High-speed mixing: mixing the formulated amount of PVC resin, plasticizer, polyester elastomer, filler, heat stabilizer, acrylate processing aid, lubricant and phosphite with high-speed stirring to obtain a preliminary mixture, wherein the stirring speed of the high-speed stirring is 500-600 rpm;

[0032] Cooling and mixing: the initial mixture is further subjected to low-speed stirring and cooling and mixing to obtain a final mixture, wherein the stirring speed of the low-speed stirring is 20-30 rpm;

[0033] Extrusion granulation: The final mixture is subjected to extrusion granulation to obtain a soft PVC composition for injection molding.

[0034] By adopting the above technical solution, raw materials such as PVC resin, plasticizer, polyester elastomer, filler, heat stabilizer, acrylate processing aid, lubricant and phosphite can be quickly mixed by high-speed stirring at 500-600rpm. High-speed stirring helps the interaction and dispersion between the raw materials, ensuring that the components are evenly distributed in the mixture.

[0035] After high-speed mixing, the initial mixture is then stirred and cooled at a low speed of 20-30rpm to further consolidate the mixing effect and avoid excessive heat and mechanical stress caused by excessive stirring. Low-speed stirring helps the mixture maintain uniformity during the cooling process and prevents stratification or agglomeration of components.

[0036] The preparation method ensures the full mixing and uniform distribution of the raw materials by combining high-speed and low-speed stirring, thereby improving the quality stability and consistency of the soft PVC composition for injection molding. During the mixing and cooling process, proper temperature control can prevent the mixture from being degraded due to overheating or solidified due to overcooling, thereby ensuring the performance of the final product.

[0037] Preferably, in the high-speed mixing step, the termination temperature of the high-speed mixing is 110-125°C; and in the cooling mixing step, the cooling temperature of the cooling mixing is ≤55°C.

[0038] By adopting the above technical solution, during the high-speed mixing stage, as the high-speed rotation causes friction between the materials to generate heat, the temperature continues to increase. When the temperature is raised to the range of 110-125°C, the PVC resin, plasticizer and other additives can begin to soften and undergo a certain degree of plasticization. Plasticization helps the interaction and dispersion between the components and improves the uniformity of the mixture. Appropriate heating temperature can accelerate certain chemical reactions, such as the interaction between plasticizers and PVC resins. These reactions help to enhance the compatibility and stability of the mixture.

[0039] Cooling helps to further stabilize the components in the mixture and prevent unwanted chemical reactions during subsequent processing. Appropriate cooling temperature can reduce the viscosity of the mixture, making it easier to process and handle. Reducing viscosity helps reduce energy consumption and wear during extrusion granulation. During the cooling process, the components in the mixture are easier to maintain a dispersed state due to the lower temperature. This helps prevent agglomeration and ensures the uniformity of the final product.

[0040] In summary, this application has the following beneficial effects:

[0041] Since the present application adopts polyester elastomer to reduce thermal deformation and cracks caused by high temperature, thereby improving the strength and durability of the product, and adopts plasticizer to improve the compatibility between PVC resin and other components such as polyester elastomer, it helps to improve the bonding strength of the soft PVC composition for injection molding, making it more durable and reliable during use. DETAILED DESCRIPTION

[0042] The raw materials in this application include the following parts:

[0043] PVC resin: polyvinyl chloride resin, a commercial product with CAS number 9002-86-2;

[0044] Phthalate plasticizer: di(2-propylheptyl)phthalate (DPHP), diisononyl phthalate (DINP), etc. may be used. This application uses DPHP as an example and uses a commercial product with a CAS number of 53306-54-0;

[0045] Benzene plasticizer: dioctyl terephthalate (DOTP), dioctyl oxalate (DOA), etc. can be used. This application uses DOTP as an example and uses a commercial product with a CAS number of 6422-86-2;

[0046] Triphenylene plasticizer: Trioctyl trimellitate (TOTM), triisooctyl trimellitate (TIOTM), etc. may be used. This application uses TOTM as an example and uses a commercial product with a CAS number of 3319-31-1;

[0047] Polyester plasticizer: commercially available product from Senya New Materials Co., Ltd.;

[0048] Epoxidized soybean oil: a commercial product with CAS number 8013-07-8;

[0049] Hardness 25D polyester elastomer: a commercially available product of foamed hot melt grade Haicui material 25D produced by Dongguan Jinfu New Materials Co., Ltd.;

[0050] Hardness 30D polyester elastomer: a commercially available product of DuPont brand 3046 from the United States;

[0051] Hardness 35D polyester elastomer: a commercially available product of foamed hot melt grade Haicui material 35D produced by Dongguan Jinfu New Materials Co., Ltd.;

[0052] Hardness 40D polyester elastomer: a commercially available product of DuPont brand 4056 from the United States;

[0053] Filler: Calcium carbonate, talcum powder, etc. can be used. This application takes calcium carbonate as an example and uses a commercially available product with CAS number 471-34-1;

[0054] Calcium zinc stabilizer: a commercially available product with the brand number 91660 produced by Baerlocher of Germany;

[0055] Acrylate processing aid: a commercially available product with CAS No. 302911-96-2;

[0056] Oxidized polyethylene wax: a commercially available product with CAS number 110119-84-1;

[0057] Phosphite: There are many types of phosphites, including triphenyl phosphite, triethyl phosphite, dimethyl phosphite, etc. This application uses dimethyl phosphite as an example, and uses a commercial product with a CAS number of 822-39-9;

[0058] The present application is further described in detail below with reference to examples and comparative examples.

[0059] Example 1

[0060] A method for preparing a soft PVC composition for injection molding comprises the following steps:

[0061] High-speed mixing: 50kg PVC resin (average degree of polymerization is 2500), 60kg DPHP, 140kg polyester elastomer (hardness 30D), 25kg calcium carbonate, 3.5kg calcium zinc stabilizer, 2.5kg acrylic acid ester processing aid, 0.6kg oxidized polyethylene wax and 0.8kg phosphite are mixed at high speed, the stirring speed of high-speed mixing is 550rpm (500-600rpm is possible), the end temperature is 120℃ (that is, when the temperature reaches 120℃, the high-speed mixing is stopped), and the initial mixture is obtained;

[0062] Cooling and mixing: the initial mixture is stirred and cooled and mixed for 1 hour at a low speed, the stirring speed of the low speed stirring is 30 rpm, and the cooling temperature of the cooling and mixing is 25° C. to obtain a final mixture; the cooling temperature in Example 1 is room temperature 25° C., and the cooling temperature can be further reduced to speed up the cooling speed;

[0063] Extrusion granulation: The final mixture is extruded and granulated to obtain a soft PVC composition for injection molding.

[0064] Example 2-3

[0065] Example 2-3 Based on the preparation method of Example 1, the content of each component of the soft PVC composition for injection molding is adjusted, and the specific adjustment is shown in Table 1.

[0066] Comparative Example 1-2

[0067] Comparative Example 1-2 Based on the preparation method of Example 1, the content of each component of the soft PVC composition for injection molding was adjusted, and the specific adjustment is shown in Table 1.

[0068] Table 1 Contents of components and performance test of soft PVC compositions for injection molding of Examples 1-3 and Comparative Examples 1-2

[0069]

[0070] Performance testing

[0071] The soft PVC compositions for injection molding of Examples 1-3 and Comparative Examples 1-2 were subjected to the following performance tests. The test results are shown in Table 1.

[0072] Bond strength and bond strength after aging

[0073] The soft PVC composition for injection molding is made into a 10cm*10cm*2mm thin sheet, fixed in the mold cavity, and the soft PVC composition for injection molding in the molten state is injection-molded with the soft PVC composition for injection molding in the mold cavity to form a dumbbell bar, and the injection temperature is 210°C. The dumbbell bar is cut perpendicular to the weld mark so that the weld mark is located in the middle of the cut dumbbell bar. The bonding strength of the cut dumbbell bar is measured according to ISO 37 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber", and the bonding strength after aging is measured after the cut dumbbell bar is boiled in 80°C water for 24 hours.

[0074] As shown in Table 1, by comparing Examples 1-3 with Comparative Example 1-2, it can be seen that the bonding strength and bonding strength after aging of Examples 1-3 are much higher than those of Comparative Example 1-2, indicating that the addition of DPHP and polyester elastomer can effectively improve the bonding strength of PVC and also ensure the bonding strength after aging.

[0075] In addition, by comparing Examples 1-3, it is found that Example 1 has the best comprehensive performance, so Example 1 is preferred.

[0076] Embodiment 4-6

[0077] In Example 4-6, based on the preparation method of Example 1, the amount of DPHP added was adjusted. The specific adjustments are shown in Table 2.

[0078] The soft PVC compositions for injection molding of Examples 4-6 were subjected to the above performance tests. The test results are shown in Table 2.

[0079] Table 2: Addition amount of DPHP and performance test table of Example 1 and Examples 4-6

[0080]

[0081] Referring to Table 2, it can be seen from the comparison between Example 1 and Examples 4-6 that as the amount of DPHP added increases, the bonding strength and the bonding strength after aging show a trend of first increasing and then decreasing, which may be due to the excellent compatibility between di(2-propylheptyl)phthalate (DPHP) and PVC resin, and also has a certain compatibility with polyester elastomer. This compatibility helps to promote the close combination between PVC and polyester elastomer during the injection molding process, so that the two can form a uniform melt, thereby improving the bonding strength and bonding strength after aging of the soft PVC composition for injection molding. When the amount of DPHP added exceeds a certain range, it may be due to the excessive content of DPHP that it is easy to migrate during processing and use, resulting in degradation of product performance, thereby reducing the bonding strength and bonding strength after aging of the soft PVC composition for injection molding.

[0082] Examples 7-10

[0083] Example 7 Based on the preparation method of Example 1, 60 kg of DPHP was replaced with 50 kg of DOTP, and the other conditions remained unchanged.

[0084] In Examples 8-10, based on the preparation method of Example 7, the amount of DOTP added was adjusted. The specific adjustments are shown in Table 3.

[0085] The soft PVC compositions for injection molding of Examples 7-10 were subjected to the above performance tests. The test results are shown in Table 3.

[0086] Table 3: Addition amount and performance test table of DOTP in Example 1 and Examples 7-10

[0087]

[0088] Referring to Table 3, it can be seen from the comparison between Example 1 and Examples 7-10 that as the amount of DOTP added increases, the bonding strength and the bonding strength after aging show a trend of first increasing and then decreasing. This may be because the molecular structure of dioctyl terephthalate (DOTP) contains a large benzene ring, which makes its molecular volume large and not easy to migrate out of the PVC product. This migration resistance helps to improve the bonding strength and bonding strength after aging of the soft PVC composition for injection molding. When the amount of DPHP added exceeds a certain range, the compatibility of the excessively high content of DOTP with PVC and polyester elastomers may be relatively poor, resulting in degradation of product performance, thereby reducing the bonding strength and bonding strength after aging of the soft PVC composition for injection molding.

[0089] Examples 11-14

[0090] Example 11 Based on the preparation method of Example 1, 60 kg of DPHP was replaced with 35 kg of TOTM, and the other conditions remained unchanged.

[0091] Examples 12-14 are based on the preparation method of Example 11, with the addition amount of TOTM adjusted. The specific adjustments are shown in Table 4.

[0092] The soft PVC compositions for injection molding of Examples 11-14 were subjected to the above performance tests, and the test results are shown in Table 4, respectively.

[0093] Table 4: Addition amount and performance test table of TOTM in Example 1 and Examples 11-14

[0094]

[0095] Referring to Table 4, it can be seen from the comparison between Example 1 and Examples 11-14 that as the amount of TOTM added increases, the bonding strength and the bonding strength after aging show a trend of first increasing and then decreasing. This may be because trioctyl trimellitate (TOTM) has better heat resistance than other types of plasticizers, and can effectively improve the thermal stability of PVC resin, reduce the occurrence of thermal decomposition and degradation, thereby improving the bonding strength and bonding strength after aging of the soft PVC composition for injection molding. When the amount of DPHP added exceeds a certain range, the compatibility of the excessively high content of TOTM with PVC and polyester elastomer may be relatively poor, resulting in degradation of product performance, thereby reducing the bonding strength and bonding strength after aging of the soft PVC composition for injection molding.

[0096] Examples 15-19

[0097] Example 15 Based on the preparation method of Example 1, 60 kg of DPHP is replaced with 60 kg of a mixture of DPHP, DOTP and TOTM, wherein the mass ratio of DPHP, DOTP and TOTM in the mixture is 15:8:6, and the other conditions remain unchanged.

[0098] Examples 16-19 are based on the preparation method of Example 15, and the mass ratio of DPHP, DOTP and TOTM is adjusted. The specific adjustments are shown in Table 5.

[0099] The soft PVC compositions for injection molding of Examples 15-19 were subjected to the above performance tests, and the test results are shown in Table 5, respectively.

[0100] Table 5 Plasticizer types and performance test table of Example 1 and Examples 15-19

[0101]

[0102] Referring to Table 5, it can be seen from the comparison between Example 1 and Examples 15-19 that the mixture of DPHP, DOTP and TOTM can further improve the bonding strength and the bonding strength after aging of the soft PVC composition for injection molding. DPHP provides good compatibility and processing performance, DOTP enhances migration resistance and heat resistance, and TOTM further improves heat resistance and flame retardancy. The mass ratio of the three is best at 15:8:6.

[0103] Examples 20-21

[0104] Examples 20-21 are based on the preparation method of Example 1, except that DPHP is replaced with other plasticizers, and the other conditions remain unchanged. The specific adjustments are shown in Table 6.

[0105] The soft PVC compositions of Examples 20-21 were subjected to the above performance tests, and the test results are shown in Table 6.

[0106] Table 6 Plasticizer types and performance test table of Example 1, Example 15 and Examples 20-21

[0107]

[0108] Referring to Table 6, it can be seen from the comparison between Example 1 and Examples 20-21 that polyester plasticizers and epoxidized soybean oil can also be used in the present application.

[0109] Examples 22-24

[0110] In Examples 22-24, based on the preparation method of Example 1, the hardness of the polyester elastomer is adjusted. The specific adjustments are shown in Table 7.

[0111] The soft PVC compositions of Examples 22-24 were subjected to the above performance tests. The test results are shown in Table 7.

[0112] Table 7 Hardness and performance test table of polyester elastomers of Example 1 and Examples 22-24

[0113]

[0114] Referring to Table 7, it can be seen from the comparison between Example 1 and Examples 22-24 that as the hardness of the polyester elastomer increases, the bonding strength and the bonding strength after aging show a trend of first increasing and then decreasing. It is possible that the increasing hardness of the polyester elastomer can improve the structural stability of the soft PVC composition for injection molding, thereby improving the bonding strength and the bonding strength after aging of the soft PVC composition for injection molding. When the hardness of the polyester elastomer exceeds a certain range, the polyester elastomer with too high hardness may cause insufficient fluidity, thereby reducing the bonding strength and the bonding strength after aging of the soft PVC composition for injection molding.

[0115] Examples 25-28

[0116] In Examples 25-28, based on the preparation method of Example 1, the average degree of polymerization of the PVC resin was adjusted. The specific adjustments are shown in Table 8.

[0117] The soft PVC compositions of Examples 25-28 were subjected to the above performance tests, and the test results are shown in Table 8.

[0118] Table 8 Average degree of polymerization and performance test table of PVC resin of Example 1 and Examples 25-28

[0119]

[0120] Referring to Table 8, it can be seen from the comparison between Example 1 and Examples 25-28 that as the average degree of polymerization of the PVC resin increases, the bonding strength and the bonding strength after aging show a trend of first increasing and then decreasing. It is possible that when the average degree of polymerization of the PVC resin increases, the length of the molecular chain will be correspondingly extended, resulting in a higher melt viscosity of the resin during processing, thereby improving the bonding strength and the bonding strength after aging of the soft PVC composition for injection molding. When the hardness of the polyester elastomer exceeds a certain range, the PVC resin with a high degree of polymerization may be more easily degraded in a molten state, thereby reducing the bonding strength and the bonding strength after aging of the soft PVC composition for injection molding.

[0121] Examples 29-34

[0122] In Examples 29-34, based on the preparation method of Example 1, the termination temperature of high-speed mixing and the cooling temperature of cooling mixing are adjusted. The specific adjustments are shown in Table 9.

[0123] The soft PVC compositions for injection molding of Examples 29-34 were subjected to the above performance tests, and the test results are shown in Table 9 respectively.

[0124] Table 9 Termination temperature, cooling temperature and performance test table of Example 1 and Examples 29-34

[0125]

[0126] Referring to Table 9, it can be seen from the comparison between Example 1 and Examples 29-34 that as the termination temperature increases, the bonding strength and the bonding strength after aging show a trend of first increasing and then decreasing. It is possible that heating allows the PVC resin, plasticizer and other additives to begin to soften and undergo a certain degree of plasticization, which helps the interaction and dispersion between the components and improves the uniformity of the mixture, thereby improving the bonding strength and the bonding strength after aging of the soft PVC composition for injection molding. When the termination temperature exceeds a certain range, the bonding strength and the bonding strength after aging of the soft PVC composition for injection molding may be reduced due to overheating and decomposition of the PVC resin.

[0127] As the cooling temperature continues to decrease, the bonding strength and the bonding strength after aging show a trend of continuous increase. Cooling helps to further stabilize the components in the mixture. During the cooling process, the components in the mixture are easier to maintain a dispersed state due to the decrease in temperature, thereby improving the bonding strength and the bonding strength after aging of the soft PVC composition for injection molding.

[0128] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A soft PVC composition for injection molding, characterized in that: The invention comprises the following components in parts by weight: 50 parts of PVC resin, 24-60 parts of plasticizer, 120-160 parts of polyester elastomer, 0-30 parts of filler, 3-4 parts of heat stabilizer, 2-3 parts of acrylic acid ester processing aid, 0.3-0.9 parts of lubricant, and 0.5-1 parts of phosphite; The plasticizer is a mixture of orthophthalic plasticizer, paraphthalic plasticizer and paraphenylene plasticizer; The mass ratio of the orthophthalic plasticizer, the paraphenylene plasticizer and the paraphenylene plasticizer is 15: (6-10): (4-8); The hardness of the polyester elastomer is 25-35D.

2. The soft PVC composition for injection molding according to claim 1, characterized in that: The average polymerization degree of the PVC resin is 1500-3000.

3. The method for preparing the soft PVC composition for injection molding according to any one of claims 1 to 2, characterized in that: The following steps are involved: High-speed mixing: mixing the formulated amount of PVC resin, plasticizer, polyester elastomer, filler, heat stabilizer, acrylate processing aid, lubricant and phosphite with high-speed stirring to obtain a preliminary mixture, wherein the stirring speed of the high-speed stirring is 500-600 rpm; Cooling and mixing: the initial mixture is further subjected to low-speed stirring and cooling and mixing to obtain a final mixture, wherein the stirring speed of the low-speed stirring is 20-30 rpm; Extrusion granulation: The final mixture is subjected to extrusion granulation to obtain a soft PVC composition for injection molding.

4. The method for preparing the soft PVC composition for injection molding according to claim 3, characterized in that: In the high-speed mixing step, the termination temperature of the high-speed mixing is 110-125°C; in the cooling mixing step, the cooling temperature of the cooling mixing is ≤55°C.

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