Elastomer modified PVC (polyvinyl chloride) sealant and preparation process of low-torsion claw type unscrewing cover

Abstract

The invention belongs to the technical field of food packaging and sealants, and particularly relates to an elastomer modified PVC sealant and a preparation process of a low-torsion claw type unscrewing cover. The elastomer modified PVC sealant comprises the following components in percentage by mass: 50-75% of polyvinyl chloride paste resin; 15-25% of a plasticizer; 5-10% of a vinyl chloride-acrylate copolymer; 2 to 10% of a polybutadiene-polysiloxane-acrylate elastomer; and 0.5-5% of calcium stearate. The preparation technology comprises the following steps that common PVC sealant and elastomer modified PVC sealant are sequentially sprayed to the inner surface of the rotating claw type unscrewing cover through a fixed glue spraying procedure, then baking forming is conducted, and the low-torsion claw type unscrewing cover is obtained. According to the invention, a special double-layer glue injection process and a special elastomer modified PVC sealant are adopted, so that the sealing stability is ensured, and meanwhile, the uncovering torsion is reduced.

Description

Technical Field

[0001] This invention belongs to the field of food packaging and sealant technology, specifically relating to the preparation process of an elastomer-modified PVC sealant and a low-torque claw-type screw cap. Background Technology

[0002] In food packaging, glass bottles are widely used for condiments, canned fruits, canned fish and meat, wine, and beverages due to their safety, environmental friendliness, transparency, aesthetic appeal, non-toxicity, odorlessness, good barrier properties, low cost, and recyclability. Among the bottle caps used in conjunction with glass bottles, claw-type screw caps are widely used due to their rigidity, excellent sealing performance, and attractive printing.

[0003] The manufacturing process of claw-type screw caps generally involves placing a sealing gasket inside a pre-molded empty cap and then hot-pressing it together, or injecting liquid sealant into the cap. The sealant is then distributed within the injection molding area by the centrifugal force of the cap's high-speed rotation, and finally cured by high-temperature baking. Existing claw-type screw cap sealants primarily use PVC sealant. However, PVC has poor flexibility, often requiring the addition of large amounts (over 30%) of plasticizers to improve its processing and sealing performance. Excessive plasticizer content can lead to migration and health risks. Furthermore, PVC has poor low-temperature resistance, easily becoming brittle at low temperatures, affecting sealing stability. Finally, to ensure the adhesion strength and stability between the PVC sealant and the cap, it needs strong adhesion. However, this strong adhesion also results in a greater torque required during opening, making opening the cap inconvenient. Summary of the Invention

[0004] In view of the shortcomings and deficiencies of the existing technology, the primary objective of this invention is to provide an elastomer-modified PVC sealant.

[0005] Another objective of this invention is to provide a manufacturing process for a low-torque claw-type screw cap.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] An elastomer-modified PVC sealant comprising the following components in weight percentage:

[0008] Polyvinyl chloride paste resin 50~75%;

[0009] Plasticizer 15~25%;

[0010] 5-10% vinyl chloride-acrylate copolymer;

[0011] 2-10% polybutadiene-polysiloxane-acrylate elastomer;

[0012] Calcium stearate 0.5-5%;

[0013] The polybutadiene-polysiloxane-acrylate elastomer was prepared by the following method:

[0014] Liquid polybutadiene, divinyl-terminated polysiloxane, and acrylate monomers were dissolved in an organic solvent, and then an initiator was added and heated for copolymerization. After the reaction was completed, the mixture was dried and granulated to obtain polybutadiene-polysiloxane-acrylate elastomer.

[0015] The role of the polybutadiene-polysiloxane-acrylate elastomer in this application is as follows:

[0016] 1. Plasticizing and toughening polyvinyl chloride with elastomers can reduce the amount of easily migratable plasticizers added, reducing the plasticizer content to below 25%, while improving the flexibility and low-temperature resistance of the sealant.

[0017] 2. By introducing polysiloxane chains with low surface tension, the surface lubricity of the sealant is improved, which can reduce the frictional resistance when unscrewing the cap, thus reducing the opening torque while ensuring the seal.

[0018] Preferably, the number-average molecular weight (Mn) of the liquid polybutadiene is 2000-10000; and the number-average molecular weight of the divinyl-terminated polysiloxane is 2000-10000.

[0019] Preferably, the acrylate monomer is at least one selected from butyl acrylate, ethyl acrylate, hydroxyethyl acrylate, and methyl methacrylate.

[0020] Preferably, the mass ratio of the liquid polybutadiene, the divinyl-terminated polysiloxane, and the acrylate monomer is (5~10):(5~20):100.

[0021] Preferably, the organic solvent is at least one selected from benzene, toluene, xylene, cyclohexane, and n-hexane. The organic solvent is removed by subsequent drying until no residue remains, to meet the requirements of food packaging materials.

[0022] Preferably, the initiator is benzoyl peroxide (BPO) or azobisisobutyronitrile (AIBN).

[0023] Preferably, the plasticizer is at least one of diisononyl cyclohexane-1,2-dicarboxylic acid (DINCH), tributyl acetylacetonate (ATBC), dioctyl terephthalate (DOTP), and polyester adipic acid.

[0024] Preferably, the acrylate segment content in the vinyl chloride-acrylate copolymer is 5-10% by mass. The vinyl chloride-acrylate copolymer is a commercially available raw material in the art. Its role in this application is as follows:

[0025] 1. As a co-plasticizer for polyvinyl chloride, it can reduce the amount of easily migrating plasticizers required;

[0026] 2. As a compatibilizer for polybutadiene-polysiloxane-acrylate elastomer, it improves the compatibility between polybutadiene-polysiloxane-acrylate elastomer and polyvinyl chloride.

[0027] A manufacturing process for a low-torque claw-type screw cap includes the following steps:

[0028] (1) Pour ordinary PVC sealant and elastomer modified PVC sealant into different dispensing buckets, and then connect them to the molding machine through pipelines;

[0029] (2) Ordinary PVC sealant and elastomer modified PVC sealant are sprayed onto the inner surface of the rotating claw screw cap through a fixed spraying process, and then baked to form a low-torque claw screw cap.

[0030] Preferably, the ordinary PVC sealant comprises the following components in weight percentage:

[0031] Polyvinyl chloride paste resin 40~65%;

[0032] Plasticizer 25-40%;

[0033] 0-10% vinyl chloride-acrylate copolymer;

[0034] Calcium stearate 0.5-5%;

[0035] Filler content: 1-10%.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] (1) The low-torque claw screw cap of the present invention innovatively adopts a double-layer PVC sealant spraying process. The bottom layer uses ordinary PVC sealant to improve the adhesion to the claw screw cap; the outer layer uses elastomer-modified PVC sealant, which has significantly improved flexibility and low-temperature resistance, thus improving the sealing effect. At the same time, the introduction of low surface tension polysiloxane improves the surface lubricity of the sealant, which can reduce the frictional resistance of the screw cap, thereby reducing the opening torque while ensuring sealing stability.

[0038] (2) The elastomer modified PVC sealant of the present invention can achieve plasticizing and toughening effects by adding polybutadiene-polysiloxane-acrylate elastomer, and can reduce the amount of easily migratable plasticizers to below 25%, thereby reducing the risk of plasticizer migration. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0040] Example 1

[0041] 1. Formulation of elastomer-modified PVC sealant:

[0042] Weigh out 61% polyvinyl chloride paste resin, 20% DINCH plasticizer, 8% vinyl chloride-acrylate copolymer resin, 7% polybutadiene-polysiloxane-acrylate elastomer resin and 4% calcium stearate by weight percentage, add them to a high-speed mixer and mix evenly to obtain elastomer-modified PVC sealant.

[0043] The preparation method of the polybutadiene-polysiloxane-acrylate elastomer resin is as follows:

[0044] Liquid polybutadiene (Mn≈6000), divinyl-terminated polysiloxane (Mn≈8000), and butyl acrylate monomer were dissolved in a mixed solvent of toluene and n-hexane at a mass ratio of 8:12:100. Then, AIBN initiator was added and the mixture was heated to 70°C for 4 hours to copolymerize. Then, n-butyl mercaptan chain transfer agent was added and the reaction was continued at this temperature for 1 hour. After the reaction was completed, the mixture was spray-dried and granulated to obtain polybutadiene-polysiloxane-acrylate elastomer resin.

[0045] 2. Preparation of ordinary PVC sealant:

[0046] Weigh out 55% polyvinyl chloride paste resin, 30% DINCH plasticizer, 5% vinyl chloride-acrylate copolymer resin, 4% calcium stearate and 6% calcium carbonate filler by mass percentage, add them to a high-speed mixer and mix evenly to obtain ordinary PVC sealant.

[0047] 3. Preparation of low-torque claw-type screw cap:

[0048] (1) Pour ordinary PVC sealant and elastomer modified PVC sealant into different injection barrels, and then connect them to the molding machine through pipelines.

[0049] (2) Ordinary PVC sealant and elastomer modified PVC sealant are sprayed onto the inner surface of the rotating claw screw cap through a fixed spraying process, and then baked at about 180°C for 60 seconds to form a low-torque claw screw cap.

[0050] The elastomer-modified PVC sealant obtained in this embodiment has a tensile strength of 1.62 MPa and an elongation at break of 176% after molding. After being treated at -40℃ for 168 hours, the tensile strength retention rate is 95.7% and the elongation at break retention rate is 94.5%.

[0051] Tests showed that 20 samples of the same model of food and beverage claw-type screw-on glass bottle sealing packaging had an opening torque of 0.9-1.2 N·m and no leakage when held at 0.2 MPa for 1 minute, indicating good sealing performance and ease of opening.

[0052] Example 2

[0053] 1. Formulation of elastomer-modified PVC sealant:

[0054] Weigh out 64.5% polyvinyl chloride paste resin, 15% DINCH plasticizer, 10% vinyl chloride-acrylate copolymer resin, 10% polybutadiene-polysiloxane-acrylate elastomer resin and 0.5% calcium stearate by mass percentage, add them to a high-speed mixer and mix evenly to obtain elastomer-modified PVC sealant.

[0055] The preparation method of the polybutadiene-polysiloxane-acrylate elastomer resin is as follows:

[0056] Liquid polybutadiene (Mn≈3000), divinyl-terminated polysiloxane (Mn≈10000), and butyl acrylate monomer were dissolved in a mixed solvent of toluene and n-hexane at a mass ratio of 5:20:100. Then, AIBN initiator was added and the mixture was heated to 70°C for 4 hours to copolymerize. Then, n-butyl mercaptan chain transfer agent was added and the reaction was continued at this temperature for 1 hour. After the reaction was completed, the mixture was spray-dried and granulated to obtain polybutadiene-polysiloxane-acrylate elastomer resin.

[0057] 2. Preparation of ordinary PVC sealant:

[0058] Weigh out 50% polyvinyl chloride paste resin, 40% DINCH plasticizer, 5% calcium stearate and 5% calcium carbonate filler by mass percentage, add them to a high-speed mixer and mix evenly to obtain ordinary PVC sealant.

[0059] 3. The preparation of the low-torque claw-type screw cap is the same as in Example 1.

[0060] The elastomer-modified PVC sealant obtained in this embodiment has a tensile strength of 1.55 MPa and an elongation at break of 182% after molding. After being treated at -40℃ for 168 hours, the tensile strength retention rate is 96.4% and the elongation at break retention rate is 95.0%.

[0061] Tests showed that 20 samples of the same model of food and beverage claw-type screw-on glass bottle sealed packaging had an opening torque of 0.8-1.0 N·m and no leakage when held at 0.2 MPa for 1 minute, indicating good sealing performance and ease of opening.

[0062] Example 3

[0063] 1. Formulation of elastomer-modified PVC sealant:

[0064] Weigh out 65% polyvinyl chloride paste resin, 25% DINCH plasticizer, 5% vinyl chloride-acrylate copolymer resin, 2% polybutadiene-polysiloxane-acrylate elastomer resin and 3% calcium stearate by weight percentage, add them to a high-speed mixer and mix evenly to obtain elastomer modified PVC sealant.

[0065] The preparation method of the polybutadiene-polysiloxane-acrylate elastomer resin is as follows:

[0066] Liquid polybutadiene (Mn≈8000), divinyl-terminated polysiloxane (Mn≈5000), and butyl acrylate monomer were dissolved in a mixed solvent of toluene and n-hexane at a mass ratio of 10:5:100. Then, AIBN initiator was added and the mixture was heated to 70°C for 4 hours to copolymerize. Then, n-butyl mercaptan chain transfer agent was added and the reaction was continued at this temperature for 1 hour. After the reaction was completed, the mixture was spray-dried and granulated to obtain polybutadiene-polysiloxane-acrylate elastomer resin.

[0067] 2. Preparation of ordinary PVC sealant:

[0068] Weigh out 62% polyvinyl chloride paste resin, 25% DINCH plasticizer, 10% vinyl chloride-acrylate copolymer resin, 2% calcium stearate and 1% calcium carbonate filler by mass percentage, add them to a high-speed mixer and mix evenly to obtain ordinary PVC sealant.

[0069] 3. The preparation of the low-torque claw-type screw cap is the same as in Example 1.

[0070] The elastomer-modified PVC sealant obtained in this embodiment has a tensile strength of 1.83 MPa and an elongation at break of 148% after molding. After being treated at -40℃ for 168 hours, the tensile strength retention rate is 95.2% and the elongation at break retention rate is 93.6%.

[0071] Tests showed that 20 samples of the same model of claw-type screw-on glass bottles for food and beverages had an opening torque of 1.1-1.4 N·m and no leakage was observed when the bottles were held at 0.2 MPa for 1 minute, indicating good sealing performance and ease of opening.

[0072] Comparative Example 1

[0073] A formulation of an elastomer-modified PVC sealant:

[0074] Weigh out 61% polyvinyl chloride paste resin, 20% DINCH plasticizer, 15% polybutadiene-polysiloxane-acrylate elastomer resin (same as in Example 1) and 4% calcium stearate by weight and add them to a high-speed mixer and mix evenly to obtain elastomer-modified PVC sealant.

[0075] The elastomer-modified PVC sealant obtained in this comparative example had a tensile strength of 1.38 MPa and an elongation at break of 150% after molding. After being treated at -40℃ for 168 hours, the tensile strength retention rate was 93.0% and the elongation at break retention rate was 91.6%.

[0076] Tests showed that the opening torque of 20 samples of the same model of food and beverage claw-type screw cap glass bottles ranged from 1.4 to 1.7 N·m, and the leakage rate was 10% after holding the pressure at 0.2 MPa for 1 minute.

[0077] The results above, along with those of Example 1, show that without using vinyl chloride-acrylate copolymer as a compatibilizer for polybutadiene-polysiloxane-acrylate elastomer resin, the mechanical properties, low-temperature resistance, lubricity, and sealing performance of the resulting PVC sealant are significantly reduced.

[0078] Comparative Example 2

[0079] A PVC sealant formulation:

[0080] Weigh out 61% polyvinyl chloride paste resin, 20% DINCH plasticizer, 15% vinyl chloride-acrylate copolymer resin and 4% calcium stearate by weight percentage, add them to a high-speed mixer and mix evenly to obtain PVC sealant.

[0081] The PVC sealant obtained in this comparative example had a tensile strength of 1.54 MPa and an elongation at break of 130% after molding. After being treated at -40℃ for 168 hours, the tensile strength retention rate was 86.1% and the elongation at break retention rate was 83.6%.

[0082] Tests showed that 20 samples of the same model of food and beverage claw-type screw-on glass bottle sealing packaging had an opening torque of 1.8-2.2 N·m and no leakage was observed when the pressure was maintained at 0.2 MPa for 1 minute.

[0083] The results above, along with those of Example 1, show that without the addition of polybutadiene-polysiloxane-acrylate elastomer resin for modification, the mechanical properties, low-temperature resistance, and lubricity of the resulting PVC sealant are significantly reduced, the torque required for opening the cap is significantly increased, and opening the cap is inconvenient.

[0084] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An elastomer-modified PVC sealant, characterized in that: It contains the following components in percentage by mass: Polyvinyl chloride paste resin 50~75%; Plasticizer 15~25%; 5-10% vinyl chloride-acrylate copolymer; 2-10% polybutadiene-polysiloxane-acrylate elastomer; Calcium stearate 0.5-5%; The polybutadiene-polysiloxane-acrylate elastomer was prepared by the following method: Liquid polybutadiene, divinyl-terminated polysiloxane, and acrylate monomers were dissolved in an organic solvent, and then an initiator was added and heated for copolymerization. After the reaction was completed, the mixture was dried and granulated to obtain polybutadiene-polysiloxane-acrylate elastomer.

2. The elastomeric modified PVC sealant according to claim 1, characterized in that: The number-average molecular weight of the liquid polybutadiene is 2000-10000; the number-average molecular weight of the divinyl-terminated polysiloxane is 2000-10000.

3. The elastomeric modified PVC sealant according to claim 1, characterized in that: The acrylate monomer is at least one of butyl acrylate, ethyl acrylate, hydroxyethyl acrylate, and methyl methacrylate.

4. The elastomeric modified PVC sealant according to claim 1, characterized in that: The mass ratio of the liquid polybutadiene, the divinyl-terminated polysiloxane, and the acrylate monomer is (5~10):(5~20):

100.

5. The elastomeric modified PVC sealant according to claim 1, characterized in that: The organic solvent is at least one of benzene, toluene, xylene, cyclohexane, and n-hexane.

6. The elastomeric modified PVC sealant according to claim 1, characterized in that: The initiator is benzoyl peroxide or azobisisobutyronitrile.

7. The elastomeric modified PVC sealant according to claim 1, characterized in that: The plasticizer is at least one of cyclohexane-1,2-dicarboxylic acid diisononyl ester, acetylsicitrin tributyl ester, dioctyl terephthalate, and adipic acid polyester.

8. The elastomeric modified PVC sealant according to claim 1, characterized in that: The acrylate segment in the vinyl chloride-acrylate copolymer has a mass percentage content of 5-10%.

9. A manufacturing process for a low-torque claw-type screw cap, characterized in that: Includes the following steps: (1) Pour ordinary PVC sealant and elastomer modified PVC sealant into different dispensing buckets, and then connect them to the molding machine through pipelines; (2) Ordinary PVC sealant and elastomer modified PVC sealant are sprayed onto the inner surface of the rotating claw screw cap through a fixed spraying process, and then baked to form a low-torque claw screw cap.

10. The manufacturing process of a low-torque claw-type screw cap according to claim 9, characterized in that: The ordinary PVC sealant contains the following components in weight percentage: Polyvinyl chloride paste resin 40~65%; Plasticizer 25-40%; 0-10% vinyl chloride-acrylate copolymer; Calcium stearate 0.5-5%; Filler content: 1-10%.