Extrusion blow molding foamed polyethylene product and preparation method thereof

Abstract

The invention discloses an extrusion blow molding foamed polyethylene product and a preparation method thereof, and relates to the technical field of packaging materials. The extrusion blow molding foamed polyethylene product comprises the following components in percentage by weight: 1-3% of foaming agent master batch, 93-96% of matrix resin and 3-4% of color master batch. The foaming agent master batch comprises the following components in percentage by weight: 45-60% of ethylene-vinyl acetate copolymer and 40-55% of core-shell thermal expansion foaming agent. According to the extrusion blow molding foamed polyethylene product and the preparation method thereof, in the blow molding process, the shell of a core-shell type thermal expansion foaming agent is softened, alkane in the inner core is gasified and expanded, the expanded shell is cooled and shaped, and bubbles with the diameter smaller than 100 microns are formed in the product, so that the foaming effect is achieved; therefore, the purpose of reducing the use of plastic materials is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of packaging materials, in particular to an extrusion blow-molded foamed polyethylene product and a preparation method thereof. Background Art

[0002] After waste plastics enter the environment, they are difficult to degrade and are likely to cause long-term and deep-seated ecological and environmental problems. Packaging is the main area of ​​plastic consumption, accounting for about 40% of the total plastic consumption. Therefore, it is a general trend to design lightweight plastic hard packaging materials, which account for the largest proportion of packaging materials, and extrusion blow molding products account for the largest proportion of hard packaging. The simplest way to lightweight extrusion blow molding products is to reduce the use of plastic materials by changing the structural design, but this method is limited to reducing the use of plastic materials. When the thinning reaches a certain level, the performance of the blow molding products will not meet the use requirements. Compared with pure plastics, foam plastics have the advantages of low density and high specific strength. Therefore, it is a good choice to introduce air or other gases into the product by foaming to achieve the purpose of reducing the amount of plastic materials.

[0003] For the foaming of injection molding, extrusion and compression molding products, there are relatively mature solutions on the market. For extrusion blow molding products, there is currently no mature foaming solution in the industry. The foam cells of products prepared by the traditional chemical foaming method are too large, usually several hundred microns, or even more than 1000 microns, which has a great impact on the appearance quality and mechanical properties of blow molding products, and the residual chemical reagents may have an adverse effect on the product contents, and cannot meet the use requirements of daily chemical and food industries. It is currently commonly used in the preparation of automobile air intake ducts or air ducts (for example, Chinese patent CN113896973A, Chinese patent CN114379061A, Chinese patent CN114425895A). Another method is supercritical gas foaming, which requires a substantial modification of traditional extrusion blow molding processing equipment (for example, Chinese patent CN109955493A), and the equipment cost is high. Therefore, the field of extrusion blow molding needs a simple and easy foaming solution. Summary of the invention

[0004] To solve the above technical problems, the present invention provides an extrusion blow molded foamed polyethylene product and a preparation method thereof, wherein a core-shell type thermal expansion foaming agent is introduced, which foams when heated during the extrusion blow molding process, thereby obtaining an extrusion blow molded foamed polyethylene product.

[0005] The specific technical solutions include the following:

[0006] In a first aspect, an extrusion blow-molded polyethylene foam product is provided, comprising the following components in weight percentage: 1-3% foaming agent masterbatch, 93-96% base resin, and 3-4% color masterbatch.

[0007] Furthermore, the foaming agent masterbatch comprises the following components in weight percentage: 45-60% of ethylene-vinyl acetate copolymer and 40-55% of core-shell type thermal expansion foaming agent.

[0008] Furthermore, the shell of the core-shell type thermal expansion foaming agent is composed of polyacrylonitrile copolymer, and the comonomer of the polyacrylonitrile copolymer is one or more of acrylonitrile, methacrylonitrile, methyl acrylate, methyl methacrylate, methacrylic acid, and butyl acrylate.

[0009] Furthermore, the core of the core-shell type thermal expansion foaming agent is a low-boiling alkane, and the low-boiling alkane is one or more of isopentane, isohexane, n-hexane, n-heptane, isooctane, and n-octane.

[0010] Furthermore, the average particle size of the core-shell type thermal expansion foaming agent is 10-30 μm.

[0011] Furthermore, the core-shell type thermal expansion foaming agent has an initial foaming temperature of 120-150°C and a maximum foaming temperature of 170-200°C.

[0012] Furthermore, the melting point of the ethylene-vinyl acetate copolymer is 60-80°C.

[0013] In a second aspect, a method for preparing the extrusion blow molded foamed polyethylene product according to the first aspect is provided, comprising the following steps:

[0014] (1) Preparation of foaming agent masterbatch: a core-shell type thermal expansion foaming agent and an ethylene-vinyl acetate copolymer are plasticized and mixed in an internal mixer, and the uniformly mixed melt is fed to a single screw extruder by a conical forced feeder, and extruded and granulated by the single screw extruder to obtain a foaming agent masterbatch;

[0015] (2) Mixing: Add base resin, color masterbatch and foaming agent masterbatch into a high-speed mixer and mix them evenly;

[0016] (3) Blow molding: The uniformly mixed material is blow molded by a single-screw extrusion blow molding machine to obtain an extrusion blow molded foamed polyethylene product.

[0017] Furthermore, in step (1), the mixing temperature of the internal mixer is 60-120°C, and the extrusion temperature of the single screw extruder is 80-120°C.

[0018] Furthermore, in step (3), the extrusion temperature of the blow molding is 170-180° C., and the blowing pressure is 0.2-0.4 MPa.

[0019] The present invention introduces a core-shell type thermal expansion foaming agent into the blow molding process, wherein the shell is a thermoplastic polymer and the core is a low-boiling hydrocarbon. During the blow molding process, the shell of the core-shell type thermal expansion foaming agent softens, the alkane in the core gasifies and expands, and the swollen shell is cooled and shaped to form bubbles with a diameter of less than 100 μm in the product, thereby achieving a foaming effect, thereby achieving the purpose of reducing the use of plastic materials. Compared with the prior art, the extrusion blow molding foamed polyethylene product and the preparation method thereof provided by the present invention have the following beneficial effects:

[0020] 1. No equipment modification is required, and the foaming of extrusion blow molded polyethylene products can be achieved by simply adjusting the formula and process.

[0021] 2. Through the optimization of formulation and blow molding process conditions, the pore diameter of the extrusion blow molded polyethylene foam product is less than 100μm. When the apparent density of the product is reduced by 5-15%, the strength of the product remains above 90%, and the performance meets most application requirements.

[0022] 3. This method is universal and can be used to blow-mold hollow products such as polyethylene barrels, bottles, and boxes. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0024] Figure 1 This is a SEM image of the cross section of Example 1 of the present invention;

[0025] Figure 2 This is a SEM image of the cross section of Example 2 of the present invention;

[0026] Figure 3 This is a SEM image of the cross section of Example 3 of the present invention;

[0027] Figure 4 This is a SEM image of a cross section of Example 4 of the present invention;

[0028] Figure 5 This is a SEM image of the cross section of Example 5 of the present invention;

[0029] Figure 6 This is a SEM image of the cross section of Comparative Example 1 of the present invention;

[0030] Figure 7 This is a SEM image of the cross section of Comparative Example 2 of the present invention;

[0031] Figure 8 This is a SEM image of the cross section of Comparative Example 3 of the present invention;

[0032] Fig. 9 This is a SEM image of the cross section of Comparative Example 7 of the present invention. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0035] It should also be understood that the terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0036] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0037] In order to more fully understand the technical content of the present invention, the technical solution of the present invention is further introduced and illustrated in conjunction with specific embodiments below.

[0038] Unless otherwise specified, the "%" described in the present invention refers to weight percentage.

[0039] Preparation method of extrusion blow molding foamed polyethylene products:

[0040] (1) Preparation of foaming agent masterbatch: a core-shell type thermal expansion foaming agent and ethylene-vinyl acetate copolymer are plasticized and mixed in an internal mixer at a mixing temperature of 60-120° C., and the uniformly mixed melt is fed to a single screw extruder by a conical forced feeder, and extruded and granulated by the single screw extruder to obtain a foaming agent masterbatch, and the extrusion temperature of the single screw extruder is 80-120° C.;

[0041] (2) Mixing: Add base resin, color masterbatch and foaming agent masterbatch into a high-speed mixer and mix them evenly;

[0042] (3) Blow molding: The uniformly mixed material is blow molded by a single screw extrusion blow molding machine. The extrusion temperature of the blow molding is 170-180°C and the blowing pressure is 0.2-0.4 MPa to obtain an extrusion blow molded foamed polyethylene product.

[0043] In the following examples, the products prepared are all laundry detergent bottles (blow-molded bottles) with a capacity of 1 kg and a handle, and the weight of the blow-molded bottles without foaming is 65±0.3g. For all examples, the thickness of the bottle body is 1±0.1mm by adjusting the die gap during the blow molding process.

[0044] The raw materials used in the embodiments and comparative examples are:

[0045] Base resin (high-density polyethylene): brand number is 5502s, melt index is 0.18g / 10min.

[0046] Ethylene-vinyl acetate copolymer (EVA): EVA1 has a melting point of 60°C and a VA (vinyl acetate) content of 33%; EVA2 has a melting point of 80°C and a VA content of 28%.

[0047] Core-shell thermal expansion foaming agent:

[0048] EBA1: The shell is composed of polyacrylonitrile copolymer, the comonomers of which are acrylonitrile, methyl methacrylate and methacrylic acid copolymer, and the core is a blend of isohexane and isooctane. The average particle size (D50) of EBA1 is 10-16μm, the initial foaming temperature is 121-131℃, and the maximum foaming temperature is 177-192℃.

[0049] EBA2: The shell is composed of polyacrylonitrile copolymer, the comonomers of which are acrylonitrile, methyl methacrylate and methacrylic acid copolymer, and the core is a blend of isohexane and isooctane. The average particle size (D50) of EBA2 is 20-30μm, the initial foaming temperature is 136-146℃, and the maximum foaming temperature is 188-200℃.

[0050] EBA3: The shell is composed of polyacrylonitrile copolymer, the comonomers of which are acrylonitrile, methyl methacrylate and methacrylic acid copolymer, and the core is a blend of isooctane and n-octane. The average particle size (D50) of EBA3 is 20-30μm, the initial foaming temperature is 169-189℃, and the maximum foaming temperature is 209-229℃.

[0051] EBA4: The shell is composed of polyacrylonitrile copolymer, the comonomer of which is acrylonitrile, methyl methacrylate and butyl acrylate copolymer, and the core is a blend of isopentane and isohexane. The average particle size (D50) of EBA4 is 9-15μm, the initial foaming temperature is 80-95℃, and the maximum foaming temperature is 118-133℃.

[0052] Masterbatch: Commercially available PE carrier green masterbatch.

[0053] Performance Testing

[0054] 1. Apparent density and weight test of blow molded products

[0055] In order to characterize the effect of adding core-shell thermal expansion foaming agent on the foaming rate of the product, the apparent density of the extrusion blow molded foamed polyethylene products and the weight of the blow molded bottles of the examples and comparative examples were tested. The sample strips were cut from the blow molded bottles, and the apparent density of each sample was tested with a densitometer (AR-120-4S, Guangdong Qiya Testing Equipment Co., Ltd.), and 5 different positions were taken on the bottle body to calculate the average value. The weight test of the blow molded bottle was carried out on an electronic balance (PL3002-1C Mettler-Toledo Instruments (Shanghai) Co., Ltd.), and 10 samples of each sample were taken and the average value was taken.

[0056] 2. Strength test of blow molded products

[0057] In order to test the effect of adding core-shell thermal expansion foaming agent on the strength of the product, we tested the compressive strength and drop performance of the blow-molded bottle. The compressive strength test was carried out by placing the empty bottle with a cap vertically on a universal testing machine (AGS-J, Shimadzu Instruments (Suzhou) Co., Ltd.), with a compression speed of 100mm / min. The maximum pressure was taken as its compressive strength. Ten bottles of each type were tested and the average value was taken. The drop test was to add a nominal weight (1kg) of water to the bottle, and then drop it at a height of 1.2m for a total of 3 times, namely vertical drop, plane drop and side drop. Ten samples of each type were made, and the number of broken or leaking bottles was recorded and the breakage rate was calculated. The drop breakage rate was required to be 0%. If damage or leakage was found in the drop test, the test was judged to be unsuccessful. Generally, when the compressive strength can be maintained at 90% of that of pure resin products, the drop strength of the product can meet the requirements.

[0058] The drop performance of the product is closely related to the tensile strength of the material. In order to further characterize the effect of foaming on the strength of the material, we tested the tensile properties of the material. The specific test method is as follows: Use a punching machine to cut the blow-molded bottle into dumbbell-shaped strips with a thickness of about 1.0 mm, a length of 10 cm, and a width of 10 mm. Use an AGS-J universal testing machine (Shimadzu Instruments (Suzhou) Co., Ltd.) to test the tensile strength of the strips at a tensile rate of 50 mm / min.

[0059] 3. Microscopic morphology observation of blow molded products

[0060] For the extrusion blow molded foamed polyethylene products (blow molded bottles) prepared in the examples and comparative examples, we carried out liquid sectioning in liquid nitrogen. After gold spraying, the section was observed using a Phenom ProX scanning electron microscope (Themo Scientific).

[0061] Example 1

[0062] An extrusion blow-molded foamed polyethylene product comprises the following components in weight percentage: 1.25% of foaming agent masterbatch, 94.75% of base resin (5502s), and 4% of color masterbatch.

[0063] The foaming agent masterbatch comprises the following components in weight percentage: 60% of ethylene-vinyl acetate copolymer (EVA1) and 40% of core-shell type thermal expansion foaming agent (EBA1).

[0064] The method for preparing the extrusion blow-molded foamed polyethylene product comprises the following steps:

[0065] (1) Preparation of foaming agent masterbatch: a core-shell type thermal expansion foaming agent and ethylene-vinyl acetate copolymer are plasticized and mixed in an internal mixer at a mixing temperature of 60° C., and the uniformly mixed melt is fed to a single screw extruder by a conical forced feeder, and extruded into granules by the single screw extruder at an extrusion temperature of 100° C. to obtain a foaming agent masterbatch;

[0066] (2) Mixing: Add base resin, color masterbatch and foaming agent masterbatch into a high-speed mixer and mix them evenly;

[0067] (3) Blow molding: The uniformly mixed material is blow molded by a single screw extrusion blow molding machine. The extrusion temperature of the blow molding is 170° C., the screw speed is 80 rpm, and the blowing pressure is 0.3 MPa to obtain an extrusion blow molded foamed polyethylene product.

[0068] Example 2

[0069] The difference between Example 2 and Example 1 is that in the preparation method of the extrusion blow-molded foamed polyethylene product in Example 2, the extrusion temperature of the blow molding in step (3) is 175°C, the blowing pressure is 0.2 MPa, and the other conditions are the same as in Example 1.

[0070] Example 3

[0071] The difference between Example 3 and Example 1 is that the weight percentage of the foaming agent masterbatch in the extrusion blow molded foamed polyethylene product of Example 3 is 1%, the weight percentage of the matrix resin is 95%, and in the preparation method of the extrusion blow molded foamed polyethylene product of Example 3, the extrusion temperature of the blow molding in step (3) is 175°C, the blowing pressure is 0.3MPa, and the other conditions are the same as those in Example 1.

[0072] Example 4

[0073] An extrusion blow-molded foamed polyethylene product comprises the following components in weight percentage: 1.8% of foaming agent masterbatch, 95.2% of base resin (5502s), and 3% of color masterbatch.

[0074] The foaming agent masterbatch comprises the following components in weight percentage: 45% of ethylene-vinyl acetate copolymer (EVA2) and 55% of core-shell type thermal expansion foaming agent (EBA2).

[0075] The method for preparing the extrusion blow-molded foamed polyethylene product comprises the following steps:

[0076] (1) Preparation of foaming agent masterbatch: a core-shell type thermal expansion foaming agent and ethylene-vinyl acetate copolymer are plasticized and mixed in an internal mixer at a mixing temperature of 80° C., and the uniformly mixed melt is fed to a single screw extruder by a conical forced feeder, and extruded into granules by the single screw extruder at an extrusion temperature of 100° C., thereby obtaining a foaming agent masterbatch;

[0077] (2) Mixing: Add base resin, color masterbatch and foaming agent masterbatch into a high-speed mixer and mix them evenly;

[0078] (3) Blow molding: The uniformly mixed material is blow molded by a single screw extrusion blow molding machine. The extrusion temperature of the blow molding is 175° C., the screw speed is 30 rpm, and the blowing pressure is 0.4 MPa to obtain an extrusion blow molded foamed polyethylene product.

[0079] Example 5

[0080] The difference between Example 5 and Example 4 is that the weight percentage of the foaming agent masterbatch in the extrusion blow molded foamed polyethylene product of Example 5 is 1.5%, the weight percentage of the base resin is 95.5%, and the other conditions are the same as those of Example 4.

[0081] Comparative Example 1

[0082] The difference between Comparative Example 1 and Example 1 is that the core-shell thermal expansion foaming agent used is EBA3, and the other conditions are the same as those of Example 1.

[0083] Comparative Example 2

[0084] The difference between Comparative Example 2 and Example 1 is that the core-shell thermal expansion foaming agent used is EBA4, and the other conditions are the same as those of Example 1.

[0085] Comparative Example 3

[0086] The difference between Comparative Example 3 and Example 1 is that the product contains only 96% of PE raw material 5502s and 4% of masterbatch, and no foaming masterbatch is added. In addition, in the preparation method, the extrusion temperature of the blow molding in step (3) is 175°C, the screw speed is 100rpm, and the blowing pressure is 0.6MPa. The other conditions are the same as those in Example 1.

[0087] Comparative Example 4

[0088] The difference between Comparative Example 4 and Example 1 is that the weight percentage of the foaming agent masterbatch in the extrusion blow molded foamed polyethylene product is 5%, the weight percentage of the matrix resin is 91%, and in the preparation method of the extrusion blow molded foamed polyethylene product in Comparative Example 4, the blowing pressure of the blow molding in step (3) is 0.2 MPa, and the other conditions are the same as those in Example 1.

[0089] Comparative Example 5

[0090] The difference between Comparative Example 5 and Example 1 is that, in the method for preparing the extrusion blow-molded foamed polyethylene product in Comparative Example 5, the extrusion temperature of the blow molding in step (3) is 165°C, and the blowing pressure is 0.6 MPa, and the other conditions are the same as those in Example 1.

[0091] Comparative Example 6

[0092] The difference between Comparative Example 6 and Example 1 is that, in the method for preparing the extrusion blow-molded foamed polyethylene product in Comparative Example 6, the extrusion temperature of the blow molding in step (3) is 185°C, and the blowing pressure is 0.2 MPa, and the other conditions are the same as those in Example 1.

[0093] Comparative Example 7

[0094] The difference between Comparative Example 7 and Example 1 is that, in the method for preparing the extrusion blow-molded foamed polyethylene product in Comparative Example 7, the blowing pressure of the blow molding in step (3) is 0.6 MPa, and the other conditions are the same as those in Example 1.

[0095] Comparative Example 8

[0096] The difference between Comparative Example 8 and Example 1 is that, in the method for preparing the extrusion blow-molded foamed polyethylene product in Comparative Example 8, the blowing pressure of the blow molding in step (3) is 0.1 MPa, and the other conditions are the same as those in Example 1.

[0097] The performance tests were conducted on the extrusion blow molded foamed polyethylene products of Examples 1-5 and the products of Comparative Examples 1-8. The test results are shown in Table 1 below:

[0098] Table 1 Performance test results of Examples 1-5 and Comparative Examples 1-8

[0099]

[0100]

[0101] Note: “-” means the product failed to form.

[0102] From the test results in Table 1, it can be seen that the extrusion blow molding foamed polyethylene products of Examples 1-5 are made using conventional extrusion blow molding equipment, and only the formula and process need to be adjusted to achieve foaming of the products. Compared with the unfoamed PE product of Comparative Example 3, its density is increased from 0.945 g / cm 3 Reduced to 0.803-0.898g / cm 3 , the reduction is 5-15%. Because the thickness of the products is close, the weight of the blow-molded bottles is reduced by 5-15%. Figure 1 This is a SEM image of the cross section of Example 1 of the present invention. Figure 2 This is a SEM image of the cross section of Example 2 of the present invention. Figure 3 This is a SEM image of the cross section of Example 3 of the present invention. Figure 4 This is a SEM image of the cross section of Example 4 of the present invention. Figure 5 This is a SEM image of the cross section of Example 5 of the present invention. Figure 1-5 It can be seen that the cells of the extrusion blow molded foamed polyethylene products prepared in Examples 1-5 are all closed cells, the cell size is uniform, and the diameter is within the range of 10-100 μm. These closed and relatively uniform cells maintain the strength of the material to a great extent. After foaming, the tensile strength is reduced from 30.2 MPa (Comparative Example 3) when it is not foamed to 27.6 MPa (Example 5) at most, that is, the strength retention rate is more than 90%. This maintains good compression and drop strength of the packaging bottle. The packaging bottles produced by the extrusion blow molded foamed polyethylene products of Examples 1-5 did not fall and break during the test, meeting the use requirements.

[0103] The following factors have a great influence on the foaming of extrusion blow molded polyethylene foam products, including the starting foaming temperature and maximum foaming temperature of the core-shell type thermal expansion foaming agent, the content of the core-shell type thermal expansion foaming agent, the extrusion temperature in blow molding, and the blowing pressure.

[0104] Figure 6 This is the SEM image of the cross section of Comparative Example 1 of the present invention, Figure 7 This is the SEM image of the cross section of Comparative Example 2 of the present invention, Figure 8 It is the SEM image of the cross section of comparative example 3 of the present invention. Figure 6-Figure 8 Combined with the test results in Table 1, it can be seen that the initial foaming temperature of EBA3 used in Comparative Example 1 is 169-189°C, and the maximum foaming temperature is 209-229°C. Its foaming temperature is above the extrusion blow molding temperature (170°C), so almost no foaming occurs, and only a small amount of small-sized microspheres ( Figure 6 ), and its density is similar to that of Comparative Example 3 without adding a foaming agent. However, the foaming temperature of EBA4 used in Comparative Example 2 is too low, and it has already foamed during the mixing, extrusion and granulation process of the first step of preparing the foaming agent masterbatch. When the foamed material is extruded and blow-molded at a higher temperature, its polymer shell breaks at high temperature ( Figure 7 ), so it is almost not foamed, and its density is similar to that of Comparative Example 3 without added foaming agent.

[0105] It can be seen from the test results of Examples 1-5 that as the foaming agent content increases, the pore content increases and the density decreases. However, when the foaming agent masterbatch content is too high, the bubble content in the extruded embryo is large and the melt strength is low. It is easy to blow even at a blowing pressure of 0.2 MPa, so no sample is collected (Comparative Example 4).

[0106] Extrusion blow molding temperature also has an important influence on blow molding foaming. As shown in Comparative Example 5, when the extrusion temperature is too low, even with a blow molding pressure of 0.6MPa, the extruded parison cannot be blown up. On the contrary, as shown in Comparative Example 6, when the extrusion temperature is too high, even with a blow molding pressure of 0.2MPa, the foamed parison is easily blown apart. Therefore, when the extrusion blow molding temperature is too high or too low (Comparative Example 5, Comparative Example 6), molding cannot be performed and no samples are collected.

[0107] It can be seen from the extrusion blow molded foamed polyethylene products of Examples 2-4 that, under the same conditions, as the blowing pressure increases, the bubbles change from spherical to ellipsoidal, and the number decreases. This is because excessive blowing pressure will squeeze the already foamed microspheres. When the blowing pressure is too high, the bubbles will become a thin slit, or even rupture in large numbers ( Fig. 9 ),in, Fig. 9 The SEM image of the cross section of comparative example 7 of the present invention is shown in FIG. Therefore, the density of comparative example 7 is only 2% lower than that of the unfoamed product. Of course, the test results of comparative example 8 show that when the blowing pressure is too low, the extruded parison cannot be inflated and the product cannot be obtained.

[0108] In short, the method of the present invention does not require any equipment modification, and can be directly used on an existing extrusion blow molding machine to achieve foaming of extrusion blow molded polyethylene products by adjusting the formula and process. The foam cells formed by microsphere foaming are closed cells with a diameter of 10-100 μm. When the apparent density of the product is reduced by 5-15%, the strength of the product can still be maintained at more than 90%, and the performance of the product meets the use requirements. The present invention can achieve lightweight extrusion blow molded polyethylene products and can be used to reduce the use of plastic materials. This method is versatile and can be used for foaming hollow products such as blow molded polyethylene barrels, bottles, and boxes.

[0109] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. An extrusion blow molded foamed polyethylene product, characterized in that: The invention comprises the following components in weight percentage: 1-3% of foaming agent master batch, 93-96% of base resin and 3-4% of color master batch.

2. The extrusion blow molded foamed polyethylene product according to claim 1, characterized in that: The foaming agent masterbatch comprises the following components in weight percentage: 45-60% of ethylene-vinyl acetate copolymer and 40-55% of core-shell type thermal expansion foaming agent.

3. The extrusion blow molded foamed polyethylene product according to claim 2, characterized in that: The shell of the core-shell type thermal expansion foaming agent is composed of polyacrylonitrile copolymer, and the comonomer of the polyacrylonitrile copolymer is one or more of acrylonitrile, methacrylonitrile, methyl acrylate, methyl methacrylate, methacrylic acid, and butyl acrylate.

4. The extrusion blow molded foamed polyethylene product according to claim 2, characterized in that: The core of the core-shell type thermal expansion foaming agent is a low-boiling alkane, and the low-boiling alkane is one or more of isopentane, isohexane, normal hexane, normal heptane, isooctane and normal octane.

5. The extrusion blow molded foamed polyethylene product according to claim 2, characterized in that: The average particle size of the core-shell type thermal expansion foaming agent is 10-30 μm.

6. The extrusion blow molded foamed polyethylene product according to claim 2, characterized in that: The core-shell type thermal expansion foaming agent has an initial foaming temperature of 120-150°C and a maximum foaming temperature of 170-200°C.

7. The extrusion blow molded foamed polyethylene product according to claim 2, characterized in that: The melting point of the ethylene-vinyl acetate copolymer is 60-80°C.

8. The method for preparing an extrusion blow molded foamed polyethylene product according to any one of claims 2 to 7, characterized in that: The following steps are involved: (1) Preparation of foaming agent masterbatch: a core-shell type thermal expansion foaming agent and an ethylene-vinyl acetate copolymer are plasticized and mixed in an internal mixer, and the uniformly mixed melt is fed to a single screw extruder by a conical forced feeder, and extruded and granulated by the single screw extruder to obtain a foaming agent masterbatch; (2) Mixing: Add base resin, color masterbatch and foaming agent masterbatch into a high-speed mixer and mix them evenly; (3) Blow molding: The uniformly mixed material is blow molded by a single-screw extrusion blow molding machine to obtain an extrusion blow molded foamed polyethylene product.

9. The method for preparing an extrusion blow molded foamed polyethylene product according to claim 8, characterized in that: In step (1), the mixing temperature of the internal mixer is 60-120°C, and the extrusion temperature of the single screw extruder is 80-120°C.

10. The method for preparing the extrusion blow molded foamed polyethylene product according to claim 8, characterized in that: In step (3), the extrusion temperature of the blow molding is 170-180°C, and the blowing pressure is 0.2-0.4MPa.

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