Compression molding cover body and preparation method and application thereof

Abstract

The invention relates to the technical field of high polymer materials, and particularly discloses a compression molding cover body and a preparation method and application thereof. The invention provides a compression molding cover body. The compression molding cover body is prepared from the following raw materials in parts by weight: 45 to 55 parts of wide molecular weight distribution high-density polyethylene with a molecular weight distribution index of 24 to 27, 45 to 55 parts of narrow molecular weight distribution high-density polyethylene with a molecular weight distribution index of 4 to 6, 0.5 to 0.8 part of fatty acid amide slipping agent and 0.8 to 1.2 parts of layered silicate filler. The compression molding cover body has the advantages of being low in opening torsion, excellent in warping resistance, good in toughness, excellent in coloring performance and the like, the preparation method of the compression molding cover body is convenient to operate, industrial production is easy, and therefore the compression molding cover body can be widely applied to the field of liquid food packaging bottles and has wide application prospects.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and specifically discloses a compression-molded cap, its preparation method, and its application. Background Technology

[0002] Compression-molded caps, with their advantages of ease of use and controllable cost, have become the mainstream packaging component in the packaging of liquid products such as dairy products, beverages, and edible oils. With the widespread adoption of high-speed filling lines in the food and beverage industry, and the continuous upgrading of consumer demands for packaging experience, the market has placed more stringent performance requirements on compression-molded plastic tamper-evident caps. Low opening torque and excellent anti-warping properties have become key factors in evaluating product competitiveness: low opening torque allows for easy opening by consumers of different ages, especially children and the elderly; anti-warping properties directly determine whether the cap can maintain a stable seal with the bottle mouth during high-speed filling, long-distance transportation, and warehousing, effectively preventing leakage of contents, intrusion of external oxygen, or escape of internal carbon dioxide, thereby ensuring product quality and shelf life.

[0003] Currently, most compression-molded caps on the market, especially 38mm compression-molded tamper-evident caps, primarily use high-density polyethylene (HDPE) as the core raw material. While compression molding can achieve efficient cap forming, traditional single-formulation HDPE materials consistently struggle to achieve both low torque and anti-warping properties. Specifically, using HDPE with a narrow molecular weight distribution results in uniform melt flow and good consistency in molding shrinkage, which helps improve the cap's anti-warping ability. However, its melt strength is relatively low, leading to insufficient toughness in the resulting cap. This requires overcoming greater resistance when opening, resulting in higher torque values ​​and failing to meet the need for easy opening. If excessive slip agents are added to reduce opening torque, although this can achieve a low torque effect by reducing the coefficient of friction between the cap and the bottle opening, excessive slip agents tend to precipitate on the inner surface of the cap. This not only adversely affects the adhesion between the sealing gasket and the inner surface of the cap but may also cause the cap to warp and deform under long-term stress, affecting the sealing performance. In addition, the uneven dispersion of pigments is prone to occur in the coloring process of single HDPE materials, resulting in color differences in the finished bottle caps, affecting the consistency of product appearance, and further limiting its application in the high-end packaging field.

[0004] Therefore, how to produce a compression-molded cap that combines low opening torque, excellent anti-warping properties, and stable sealing performance under compression molding process has become an urgent problem to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a compression-molded cap, its preparation method, and its applications. By optimizing the combination and ratio of HDPE with different molecular weight distributions and synergistically using specific additives, this invention designs and manufactures a compression-molded cap that combines low torsion, excellent anti-warping properties, good toughness, and colorability. It is suitable for liquid food packaging bottles and has significant application value and broad market prospects.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a compression-molded cap body comprising the following raw materials in parts by weight: 45-55 parts of high-density polyethylene with a wide molecular weight distribution, 45-55 parts of high-density polyethylene with a narrow molecular weight distribution, 0.5-0.8 parts of fatty acid amide slip agent, and 0.8-1.2 parts of layered silicate filler; The molecular weight distribution index of the wide molecular weight distribution high-density polyethylene is 24-27; the molecular weight distribution index of the narrow molecular weight distribution high-density polyethylene is 4-6.

[0007] This invention, through the optimal selection and weight ratio of high-density polyethylene with specific molecular weight distributions, and the synergistic effect of fatty acid amide-based slip agents and layered silicate fillers, produces a compression-molded cap that combines low torque, excellent anti-warping properties, good toughness, and colorability. Firstly, regarding warping performance, the high-density polyethylene with a specific narrow molecular weight distribution in the matrix material ensures dimensional stability and low shrinkage, fundamentally resisting warping; while the high-density polyethylene with a specific wide molecular weight distribution provides the necessary melt strength and toughness, making the cap less prone to deformation during high-pressure molding and ejection. The layered silicate filler, with its rigidity, further restricts the shrinkage of the polymer chains, and synergistically with the two types of high-density polyethylene, gives the cap excellent anti-warping properties. Secondly, regarding torque, the fatty acid amide-based slip agent effectively migrates to the cap surface, significantly reducing opening torque. The addition of the layered silicate filler not only does not increase torque, but its smooth, layered structure also synergizes with the fatty acid amide, providing a low-friction surface and ensuring stable and low opening torque. Third, regarding toughness, the anchoring effect of the high-density polyethylene with a specific wide molecular weight distribution in the system of this invention ensures that the product has good toughness and does not crack under continuous external stress (such as stacking pressure and transportation vibration), thus improving the product's toughness. Finally, regarding colorability, the combination of high-density polyethylene with wide and narrow molecular weight distribution provides a more compatible matrix, which is more conducive to the dispersion and coloring of dyes, enabling the achievement of a variety of bright and uniform colors to meet the personalized needs of packaging colors.

[0008] Preferably, the melt index of the high-density polyethylene with a wide molecular weight distribution is 1.5 g / 10 min to 3.5 g / 10 min.

[0009] Preferably, the melt index of the narrow molecular weight distribution high-density polyethylene is 5.0 g / 10 min to 8.0 g / 10 min.

[0010] Preferably, the fatty acid amide slip agent includes at least one of erucamide or oleamide.

[0011] By way of example, the present invention is illustrated using erucamide as an example.

[0012] Preferably, the layered silicate filler includes at least one of mica powder, talc powder, wollastonite powder, or kaolin powder.

[0013] For example, the layered silicate filler is ultrafine mica powder that has passed through a 1000-1250 mesh sieve.

[0014] Ultrafine mica powder can be evenly dispersed in the matrix, acting as a nucleating agent and reinforcing agent, effectively inhibiting shrinkage and warping.

[0015] Preferably, the raw materials also include 0.1 to 0.5 parts of dye by weight.

[0016] The high-density polyethylene combination with a specific wide and narrow molecular weight distribution in this invention provides a matrix with better compatibility, allowing the dye to be evenly dispersed and colored uniformly, effectively avoiding the problems of color difference or uneven color that easily occur when dyeing a single material.

[0017] This invention allows for the selection of dyes of appropriate colors to meet the diverse needs of the market, based on the requirements of bottle caps of different colors.

[0018] More preferably, the compression cover is a molded anti-theft cover with a size of 28mm-38mm.

[0019] For example, the molded cap may specifically include a 28mm molded tamper-evident cap, a 30.25mm molded tamper-evident cap, and a 38mm molded tamper-evident cap. The 38mm molded tamper-evident cap is widely used in the packaging of dairy products, beverages, edible oils, etc., but its larger diameter places higher demands on color uniformity, sealing performance, and structural design. The molded cap provided by this invention combines low opening torque, excellent anti-warping properties, good toughness, and excellent coloring performance, better meeting consumer needs and high-end packaging application standards.

[0020] Secondly, the present invention provides a method for preparing the above-mentioned compression-molded cap, comprising the following steps: S1. Weigh the wide molecular weight distribution high-density polyethylene, narrow molecular weight distribution high-density polyethylene, fatty acid amide slip agent and layered silicate filler according to the preset ratio, mix them evenly to obtain a premix; S2. The premixed material is melt-plasticized, homogenized, and sheared using a plasticizing extruder to obtain a molten material mass; S3. Cut the molten material into pellets of a predetermined weight, and then press them under high pressure to obtain a press-molded cap.

[0021] The method for preparing the compression-molded cap provided by this invention can be adapted to existing mainstream compression molding production lines, and is easy to control and achieve large-scale stable production.

[0022] The compression molding cap manufacturing method provided by this invention has excellent process compatibility with existing mainstream compression molding production lines. It can be directly used for production based on existing production equipment without additional investment in equipment upgrades or modifications, significantly improving the economic efficiency of process implementation. In addition, the various steps of the manufacturing process are smoothly connected and easy to operate, making it easy to industrialize and achieve large-scale and stable mass production of compression molded caps, combining production efficiency and cost advantages.

[0023] Preferably, the temperature of the plasticizing extruder is set as follows: 180℃-195℃ for the die head, 160℃-175℃ for zone one, 170℃-185℃ for zone two, and 175℃-190℃ for zone three.

[0024] For example, the plasticizing extruder in this invention is a single-screw plasticizing extruder, purchased from the SACMI Group.

[0025] Preferably, the high-pressure compression molding pressure is 40MPa-60MPa and the holding time is 2s-4s.

[0026] More preferably, the pellets are compression molded using a compression molding die, wherein the core temperature of the compression molding die is 10℃-20℃ and the cavity temperature is 25℃-35℃.

[0027] More preferably, the predetermined weight of the pellet is 1.4g / pill to 3.5g / pill.

[0028] For example, the molten material is cut into pellets of a predetermined weight by a hydraulic shearing device, and then fed into a preheated compression mold by a conveying arm. The mold is quickly closed, and the pellets are subjected to a high pressure of 40MPa-60MPa for compression molding, with the pressure held for 2s-4s. The mold is then opened, and the molded bottle cap is ejected and cooled by air or water mist to solidify, thus obtaining the compressed anti-theft cap.

[0029] For example, when preparing a 28mm compression molded anti-theft cap, the weight of the pellets is 1.7g / pellet to 2.3g / pellet; When preparing a 30.25mm compression molded anti-theft cap, the weight of the pellets is 1.4g / pellet to 1.9g / pellet; When preparing a 38mm compression molded anti-theft cap, the weight of the pellets is 3.0g / -3.5g / pill.

[0030] Thirdly, the present invention provides the application of a compression-molded cap prepared by the method of preparing the compression-molded cap provided in the first aspect or the compression-molded cap provided in the second aspect in liquid food packaging bottles.

[0031] The compression-molded cap provided by this invention not only has advantages such as low opening torque, excellent anti-warping properties, good toughness and excellent coloring performance, but also its preparation method is convenient to operate and easy to industrialize. Therefore, it can be widely used in the field of liquid food packaging bottles and has broad application prospects. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Unless otherwise stated, the experimental methods, detection methods and preparation methods disclosed in this invention all adopt conventional techniques in this technical field.

[0034] To better illustrate the embodiments provided by the present invention, further examples are given below.

[0035] The wide molecular weight distribution (MWD) high-density polyethylene (HDPE) MB6561 used in this invention was purchased from Borouge; narrow MWD HDPE JG910 was purchased from SK Geo Centric; wide MWD HDPE FHP5060 was purchased from PetroChina Fushun Petrochemical Company; narrow MWD HDPE JK910 was purchased from SK Geo Centric; wide MWD HDPE 5731K was purchased from Wanhua Chemical; narrow MWD HDPE CL9500 was purchased from Lotte Chemical; erucamide was purchased from AkzoNobel with a purity of 99.9%; and mica powder was purchased from Bakell and passed through a 1000-mesh sieve.

[0036] Example 1 This invention provides a 38mm compression-molded anti-theft cover, comprising the following parts by weight of raw materials: 45 parts of wide MWD HDPE MB6561, 55 parts of narrow MWD HDPE, 0.6 parts of erucamide, 1.0 part of mica powder (1000 mesh), and 0.2 parts of ultramarine blue; Among them, the wide MWD HDPE MB6561 has a molecular weight distribution index of 26 and a melt index of 1.5 g / 10 min; Narrow MWD HDPE JG910 has a molecular weight distribution index of 5 and a melt index of 5 g / 10 min.

[0037] This invention provides a method for preparing the above-mentioned compression-molded anti-theft cover, which specifically includes the following steps: S1. Weigh out wide MWD HDPE MB6561, narrow MWD HDPE JG910, erucamide, mica powder and ultramarine blue according to the preset ratio, and put them into a high-speed mixer until they are mixed evenly to obtain a premix; S2. The premixed material is added to a plasticizing extruder, which is configured with: 190°C at the die head, 170°C in zone one, 180°C in zone two, and 185°C in zone three. The material is melted, plasticized, homogenized, and sheared by the plasticizing extruder to form a uniform molten material mass. S3. The molten material is cut into 3.2g / balls using a hydraulic shearing device, and then precisely fed into a preheated 38mm compression molding anti-theft cap mold via a conveyor arm. The mold is quickly closed, and the ball is held under pressure at 45MPa for 3 seconds to form the cap. After compression molding, the mold is opened, the formed cap is ejected, and air-cooled for setting. Testing shows that the nominal diameter of the internal thread of the cap is 38mm, thus obtaining the 38mm compression molded anti-theft cap.

[0038] The nominal diameter of the thread forming core of the special mold is 38mm, and the inner diameter of the cavity is 41.2mm; the core temperature of the compression mold is set to 15℃, and the cavity temperature is set to 30℃.

[0039] Example 2 This invention provides a 38mm compression-molded anti-theft cover, comprising the following parts by weight of raw materials: 55 parts wide MWD HDPE MB6561, 45 parts narrow MWD HDPE, 0.7 parts erucamide, 1.2 parts mica powder (1000 mesh), and 0.4 parts titanium dioxide; The molecular weight distribution and melt index of wide MWD HDPE MB6561 and narrow MWD HDPE JG910 are the same as those in Example 1; the preparation method of the 38mm compression molded anti-theft cap is the same as that in Example 1.

[0040] Example 3 This invention provides a 30.25mm compression molded anti-theft cover, comprising the following parts by weight of raw materials: 55 parts of wide MWD HDPE MB6561, 45 parts of narrow MWD HDPE JG910, 0.7 parts of erucamide, 1.2 parts of mica powder (1000 mesh), and 0.4 parts of titanium dioxide; The molecular weight distribution and melt index of wide MWD HDPE MB6561 and narrow MWD HDPE JG910 are the same as those in Example 1.

[0041] This invention provides a method for preparing the above-mentioned compression-molded anti-theft cover, which specifically includes the following steps: S1. Weigh out wide MWD HDPE MB6561, narrow MWD HDPE JG910, erucamide, mica powder and titanium dioxide according to the preset ratio, and put them into a high-speed mixer until they are mixed evenly to obtain a premix. S2. The premixed material is added to a plasticizing extruder, which is configured with: 190°C at the die head, 170°C in zone one, 180°C in zone two, and 185°C in zone three. The material is melted, plasticized, homogenized, and sheared by the plasticizing extruder to form a uniform molten material mass. S3. The molten material is cut into 1.65g / balls using a hydraulic shearing device, and precisely fed into a preheated 3025 specification compression molding anti-theft cap mold via a conveyor arm. The mold is quickly closed, and the ball is held under pressure at 45MPa for 3 seconds for compression molding. After compression molding, the mold is opened, the formed bottle cap is ejected, and air-cooled for shaping. Testing shows that the nominal diameter of the internal thread of the bottle cap is 30.25mm, thus obtaining the 30.25mm compression molded anti-theft cap.

[0042] The nominal diameter of the thread forming core of the special mold is 30.25 mm, and the inner diameter of the cavity is 31.9 mm; the core temperature of the compression mold is set to 15℃, and the cavity temperature is set to 30℃.

[0043] Example 4 This invention provides a 28mm compression-molded anti-theft cover, comprising the following parts by weight of raw materials: 5 parts wide MWD HDPE, 45 parts narrow MWD HDPE, 0.6 parts oleamide, 0.8 parts mica powder (1000 mesh), and 0.1 parts titanium dioxide; The molecular weight distribution and melt index of wide MWD HDPE MB6561 and narrow MWD HDPE JG910 are the same as those in Example 1.

[0044] This invention provides a method for preparing the above-mentioned compression-molded anti-theft cover, which specifically includes the following steps: S1. Weigh out wide MWD HDPE MB6561, narrow MWD HDPE JG910, erucamide, mica powder and titanium dioxide according to the preset ratio, and put them into a high-speed mixer until they are mixed evenly to obtain a premix. S2. The premixed material is added to a plasticizing extruder, which is configured with: 195°C at the die head, 165°C in zone one, 175°C in zone two, and 180°C in zone three. The material is melted, plasticized, homogenized, and sheared by the plasticizing extruder to form a uniform molten material mass. S3. The molten material is cut into 2.0g pellets using a hydraulic shearing device, and then precisely fed into a preheated 28mm / 1881 specification compression molding anti-theft cap mold via a conveyor arm. The mold is quickly closed, and the pellets are held at 55MPa for 2 seconds to compress and form the cap. After compression molding, the mold is opened, the formed cap is ejected, and air-cooled for shaping. Testing shows that the root diameter of the internal thread of the cap is 28mm, which fits the 28 / 1881 standard bottle neck, thus obtaining the 28mm compression molded anti-theft cap.

[0045] The thread forming core of the special mold has a root diameter of 28mm and an inner cavity diameter of 31.0mm; the core temperature of the compression mold is set to 20℃ and the cavity temperature is set to 35℃.

[0046] Example 5 This invention provides a 38mm compression-molded anti-theft cover, which uses the same types and weight proportions of raw materials as in Example 1, but its preparation method specifically includes the following steps: S1. Weigh out wide MWD HDPE MB6561, narrow MWD HDPE JG910, erucamide, mica powder and ultramarine blue according to the preset ratio, and put them into a high-speed mixer until they are mixed evenly to obtain a premix; S2. The premixed material is added to a plasticizing extruder, which is configured with: 180°C at the die head, 160°C in zone one, 170°C in zone two, and 175°C in zone three. The material is melted, plasticized, homogenized, and sheared by the plasticizing extruder to form a uniform molten material mass. S3. The molten material is cut into 3.2g / balls using a hydraulic shearing device, and precisely fed into a preheated 38mm compression molding anti-theft cap mold via a conveyor arm. The mold is quickly closed, and the ball is held under pressure at 60MPa for 2 seconds to form the cap. After compression molding, the mold is opened, the formed cap is ejected, and air-cooled for setting. Testing shows that the nominal diameter of the internal thread of the cap is 38mm, thus obtaining the 38mm compression molded anti-theft cap.

[0047] The nominal diameter of the thread forming core of the special mold is 38mm, and the inner diameter of the mold cavity is 41.2mm; the core temperature of the compression mold is set to 25℃, and the mold cavity temperature is set to 40℃.

[0048] Comparative Example 1 The present invention provides a 38mm compression-molded anti-theft cover as a comparative example. The raw materials and their weight proportions are basically the same as those in Example 1, except that "45 parts of wide MWD HDPE MB6561 and 55 parts of narrow MWD HDPE JG910" are replaced with "100 parts of narrow MWD HDPE JG910". The other types of raw materials and their weight proportions are the same as those in Example 1. The preparation method is the same as that in Example 1, and a 38mm compression-molded anti-theft cover is obtained.

[0049] Comparative Example 2 The present invention provides a 38mm compression-molded anti-theft cover, the raw materials and their weight proportions of which are basically the same as those in Example 1, the only difference being that: no mica powder is added in this comparative example, and the types and weight proportions of the other raw materials are the same as those in Example 1; the preparation method is the same as that in Example 1, and a 38mm compression-molded anti-theft cover is obtained.

[0050] Comparative Example 3 The present invention provides a 38mm compression-molded anti-theft cover as a comparative example. The raw materials and their weight proportions are basically the same as those in Example 1, except that "45 parts of wide MWD HDPE MB6561 and 55 parts of narrow MWD HDPE JG910" are replaced with "100 parts of wide MWD HDPE MB6561". The other types of raw materials and their weight proportions are the same as those in Example 1. The preparation method is the same as that in Example 1, and a 38mm compression-molded anti-theft cover is obtained.

[0051] Comparative Example 4 This invention provides a 38mm compression-molded anti-theft cap as a comparative example. The raw materials and their weight proportions are basically the same as those in Example 1, except that "Wide MWD HDPE MB6561" is replaced with an equal weight proportion of "Wide MWD HDPE FHP5060". The other types of raw materials and their weight proportions are the same as those in Example 1. Among them, the molecular weight distribution index of Wide MWD HDPE FHP5060 is about 30, and the melt index is 1.5g / 10min. The preparation method is the same as that in Example 1, and a 38mm compression-molded anti-theft cover is obtained.

[0052] Comparative Example 5 The present invention provides a 38mm compression-molded anti-theft cap as a comparative example. The raw materials and their weight proportions are basically the same as those in Example 1, except that "narrow MWD HDPE JG910" is replaced with an equal weight proportion of "narrow MWD HDPE JK910". The other types of raw materials and their weight proportions are the same as those in Example 1. Among them, the molecular weight distribution index of narrow MWD HDPE JK910 is about 2, and the melt index is 20g / 10min. The preparation method is the same as that in Example 1, and a 38mm compression-molded anti-theft cover is obtained.

[0053] Example of effect The performance of the compression-molded anti-theft covers prepared in Examples 1-4 and Comparative Examples 1-7 was tested, and the results are shown in Table 1 below.

[0054] Table 1

[0055] As shown in Table 1, compared to the comparative examples, the compression-molded anti-theft cap prepared using the raw materials, their dosage ratios, and preparation methods provided in this invention has advantages such as low opening torque, excellent anti-warping properties, good toughness, and excellent colorability. Compared to Example 1 of this invention, using only narrow MWD HDPE in Comparative Example 1 results in a significant increase in opening torque, decreased toughness (breakage in drop test), and significantly worse anti-warping properties; Comparative Example 2, which does not add mica powder, not only causes severely excessive warping but also affects sealing performance; Comparative Example 3, which uses only wide MWD HDPE, not only causes a significant increase in warping but also exhibits slight color difference, and the opening torque fluctuates considerably.

[0056] A comparison of the data from Example 1 and Comparative Example 4 shows that if the molecular weight distribution index of the wide MWD HDPE used is too high, it will lead to reduced color uniformity and increased warpage. A comparison of Example 1 and Comparative Example 5 shows that if the molecular weight distribution index of the narrow MWD HDPE used is too low, it will lead to a significant decrease in toughness (drop cracking) and a decrease in sealing performance (seal leakage).

[0057] Data analysis of the examples and comparative studies revealed that the specific molecular weight distribution index (MWD) of wide or narrow MWD HDPE, along with the upper and lower limits of their respective amounts, and appropriate preparation process parameters, are crucial to the torsional force, anti-warping properties, toughness, sealing performance, and colorability of the resulting bottle caps. This invention, through the compounding of wide / narrow MWD HDPE with specific molecular weight distribution indices, synergistically combining fatty acid amide slip agents and layered silicate fillers, and optimizing preparation process parameters, provides a compression-molded cap that not only possesses advantages such as low opening torque, excellent anti-warping properties, good toughness, and superior colorability, but also features a convenient preparation method suitable for industrial production, showing broad application prospects in the field of liquid food packaging bottles.

[0058] 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 or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A molded cap, characterized in that, The raw materials include the following parts by weight: 45-55 parts of high-density polyethylene with a wide molecular weight distribution, 45-55 parts of high-density polyethylene with a narrow molecular weight distribution, 0.5-0.8 parts of fatty acid amide slip agent, and 0.8-1.2 parts of layered silicate filler; The molecular weight distribution index of the wide molecular weight distribution high-density polyethylene is 24-27; the molecular weight distribution index of the narrow molecular weight distribution high-density polyethylene is 4-6.

2. The compression-molded cap as described in claim 1, characterized in that, The melt index of the high-density polyethylene with a wide molecular weight distribution is 1.5 g / 10 min to 3.5 g / 10 min; and / or The melt index of the narrow molecular weight distribution high-density polyethylene is 5.0 g / 10 min to 8.0 g / 10 min.

3. The compression-molded cap as described in claim 1, characterized in that, The fatty acid amide-based slip agent includes at least one of erucamide or oleamide; and / or The layered silicate filler includes at least one of mica powder, talc powder, wollastonite powder, or kaolin powder.

4. The compression-molded cap as described in claim 1, characterized in that, Its raw materials also include 0.1 to 0.5 parts of dye by weight.

5. The compression-molded cap body as described in any one of claims 1-4, characterized in that, The compression cap is a molded anti-theft cap with a size of 28mm-38mm.

6. The method for preparing the compression-molded cap according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Weigh the wide molecular weight distribution high-density polyethylene, narrow molecular weight distribution high-density polyethylene, fatty acid amide slip agent and layered silicate filler according to the preset ratio, mix them evenly to obtain a premix; S2. The premixed material is melt-plasticized, homogenized, and sheared using a plasticizing extruder to obtain a molten material mass; S3. Cut the molten material into pellets of a predetermined weight, and then press them under high pressure to obtain a press-molded cap.

7. The method for preparing the compression-molded cap as described in claim 6, characterized in that, The temperature settings of the plasticizing extruder are as follows: 180℃-195℃ for the die head, 160℃-175℃ for zone 1, 170℃-185℃ for zone 2, and 175℃-190℃ for zone 3.

8. The method for preparing the compression-molded cap as described in claim 6, characterized in that, The pressure for high-pressure compression molding is 40MPa-60MPa, and the holding time is 2s-4s.

9. The method for preparing the compression-molded cap as described in claim 8, characterized in that, The pellets are compression molded using a compression molding die, wherein the core temperature of the compression molding die is 10℃-20℃ and the cavity temperature is 25℃-35℃; and / or The weight of the pellets is 1.4g / pill to 3.5g / pill.

10. The use of the compression-molded cap body according to any one of claims 1-5 or the compression-molded cap body prepared by the method according to any one of claims 6-9 in liquid food packaging bottles.

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