In-situ fiberized reinforced polyolefin heat shrink tubing and preparation method thereof

Abstract

The invention relates to the technical field of heat shrinkable tubes, and in particular to an in-situ fiberized reinforced polyolefin heat shrinkable tube and a preparation method thereof. The in-situ fiberized reinforced polyolefin heat shrinkable tube comprises the following components in parts by weight: 100 parts of a main masterbatch, 15 parts of a filling and reinforcing agent, 1-2 parts of a dispersant, 1 part of a lubricant, 0.2 parts of an antioxidant, and 5 parts of a coloring and reinforcing agent; wherein the main masterbatch comprises 70-90 parts of ethylene vinyl acetate and 10-30 parts of high-density polyethylene; the filling and reinforcing agent is activated calcium carbonate; a first-level in-situ fiberized main masterbatch is prepared by mixing ethylene vinyl acetate and high-density polyethylene; activated heavy calcium carbonate is prepared and mixed with the dispersant and the main masterbatch to obtain a second-level main masterbatch, and then a lubricant, an antioxidant, and a coloring and reinforcing agent are added to prepare an overall raw material; the overall raw material is granulated to prepare an in-situ fiberized heat shrinkable tube, and the tube is extruded for injection molding, electron accelerator irradiation cross-linking, and expansion molding to obtain the in-situ fiberized reinforced polyolefin heat shrinkable tube.

Description

Technical Field

[0001] The present invention relates to the technical field of heat shrinkable tubes, and in particular to an in-situ fiberized reinforced polyolefin heat shrinkable tube and a preparation method thereof. Background Art

[0002] Currently, common heat shrink tubing and molded products on the market are a common way to protect cables. However, ordinary polyolefin heat shrink products use polyethylene or ethylene vinyl acetate copolymer as raw materials. The problem with this material is that its physical properties such as tensile strength and wear resistance are poor, and it cannot be used in harsh application environments that require high friction, high tensile strength, and crack resistance. This product may suffer from defects such as tearing and breakage due to mechanical deficiencies in the event of instantaneous and sudden damage, and cannot protect electronic components.

[0003] Chinese patent application publication number CN101987892A discloses a heat shrink tubing and its materials, which are prepared from the following materials in the indicated weight parts: 70-85 parts polyethylene and 12-25 parts modified material; wherein the modified material is selected from two of the following materials: EPDM rubber, medium-density polyethylene, and linear low-density polyethylene. The heat shrink tubing manufactured using these materials has high physical strength and is suitable for use in fields with special strength requirements such as high-speed railways, communication sheaths, and cable accessories.

[0004] Chinese Patent Application Publication No. CN110272580A discloses a superconducting, fast-shrinking heat shrink tubing composed, by weight, of the following components: 40 parts linear low-density polyethylene (LLDPE), 60 parts ethylene-vinyl acetate copolymer (EVA), 15 parts aluminum oxide (Al2O3), 20 parts magnesium oxide (MgO), 1.2 parts antioxidant 300 (A300), 1.5 parts thermally conductive carbon black masterbatch (CMB), 0.3 parts lubricant erucamide (Er2O3), and 0.3 parts dispersing lubricant silicone masterbatch (SMB). The superconducting, fast-shrinking heat shrink tubing of the present invention utilizes high-thermal-conductivity, low-cost LLDPE, high-thermal-conductivity aluminum oxide and magnesium oxide fillers, and thermally conductive carbon black masterbatch to increase the overall thermal conductivity of the product. This allows for more uniform and rapid heating at the same heating temperature, improving heat shrinkage efficiency. Furthermore, the heat shrink tubing achieves more uniform internal heat dissipation at high temperatures, resulting in superior physical properties compared to conventional products with lower thermal conductivity.

[0005] It can be seen that the above-mentioned heat shrink tubing and its materials have the following problems: the use of EPDM rubber in the modified material can significantly improve the physical properties of the heat shrink tubing, but EPDM rubber is very expensive and is not suitable for mass production and cost control of heat shrink products. Heat shrink tubing without EPDM rubber has poor physical properties and cannot be used in harsh application environments with high friction, high tensile strength, and crack resistance requirements. Summary of the Invention

[0006] To this end, the present invention provides an in-situ fiberized reinforced polyolefin heat shrink tubing and a preparation method thereof, so as to overcome the problem of poor physical properties of heat shrink products not containing EPDM rubber in the prior art.

[0007] To achieve the above object, the present invention provides an in-situ fiberized reinforced polyolefin heat shrinkable tubing, wherein the raw materials of the heat shrinkable tubing are composed of the following components by weight: 100 parts of main masterbatch, 15 parts of filler and reinforcing agent, 1-2 parts of dispersant, 1 part of lubricant, 0.2 parts of antioxidant, and 5 parts of coloring and reinforcing agent;

[0008] The main masterbatch is composed of 70-90 parts of ethylene vinyl acetate and 10-30 parts of high-density polyethylene, in parts by weight. The VA content of the ethylene vinyl acetate is 14%, and the melt index is 3g / 10min-5g / 10min; the melt index of the high-density polyethylene is 0.5g / 10min-2g / 10min.

[0009] The filling and reinforcing agent is activated calcium carbonate, and the activation method is: using a phosphate coupling agent to modify the surface of calcium carbonate powder, wherein the mesh size of the heavy calcium carbonate is 500 mesh;

[0010] The dispersant is erucamide; the lubricant is zinc stearate; the antioxidant is composed of a complex of hindered phenol antioxidant and phosphite antioxidant, wherein the composite ratio of the hindered phenol antioxidant and the phosphite antioxidant is 1:2; and the coloring reinforcing agent is carbon black masterbatch.

[0011] On the other hand, the present invention also provides a method for preparing an in-situ fiberized reinforced polyolefin heat shrinkable tubing, comprising:

[0012] Step S1, preparing a primary in-situ fiberizing masterbatch by mixing ethylene vinyl acetate and high-density polyethylene;

[0013] Step S2, preparing activated heavy calcium carbonate, and mixing the activated heavy calcium carbonate with a dispersant and a main masterbatch to obtain a secondary main masterbatch;

[0014] Step S3, adding lubricant, antioxidant and coloring reinforcing agent to the secondary main masterbatch to prepare the overall raw material;

[0015] Step S4, granulating the overall raw materials to prepare an in-situ fiberized heat shrinkable masterbatch;

[0016] Step S5: Extruding and injection molding the heat shrink masterbatch, performing electron accelerator irradiation cross-linking and expansion molding to obtain an in-situ fiberized reinforced polyolefin heat shrink tubing.

[0017] Furthermore, in the step S1, it includes:

[0018] Step S11, adding ethylene vinyl acetate and high-density polyethylene into a blender according to a ratio to obtain a mixed masterbatch;

[0019] Step S12, adding the mixed masterbatch to a screw granulator with a water-cooled strand-type die head, wherein the granulation temperature is 180°C to 220°C, the die head temperature is 220°C, and the water temperature of the water tank cooling system is 20°C to 30°C; wherein the speed ratio of the rear end tractor of the water-cooled strand-type die head to the main engine of the screw granulator is 30:1, and the stretching ratio is 8:1, so that the strand masterbatch is longitudinally stretched significantly, and the high-density polyethylene islands in the sea-island effect are longitudinally stretched into fibers, thereby obtaining an in-situ fiberized primary main masterbatch;

[0020] Step S13 , detecting whether the in-situ fiberized primary masterbatch has any fractures, and adjusting the blending time in step S11 based on the fracture detection result.

[0021] Furthermore, in step S13, the fracture percentage is calculated based on the fracture point characteristics of the in-situ fibrillated primary masterbatch, the material form of the in-situ fibrillated primary masterbatch after stretching, and the speed ratio of the rear end tractor of the water-cooled strand-type die and the main body of the screw granulator, and the blending time in step S11 is adjusted according to the fracture percentage;

[0022] The fracture point characteristics include radial fracture and axial fracture, and the material form includes the length and diameter of the in-situ fiberized primary main masterbatch after stretching.

[0023] Furthermore, in step S2, it includes:

[0024] Step S21, using a carrier fluidized bed to dry the ground calcium carbonate, using glass beads with a particle size of 6 mm as the carrier material, and setting the drying temperature to 120° C.;

[0025] Step S22: The dried heavy fine calcium carbonate powder is recovered through a cyclone separator (primary collection) and a bag filter (secondary collection), wherein the tail gas temperature is controlled at 90°C to 105°C to ensure that the water content of the finished product is ≤0.5%;

[0026] Step S23, adding dehydrated heavy calcium carbonate powder into a high-speed mixer, then adding 2.4% by mass of an atomized phosphate coupling agent, stirring at high speed for 20 to 25 minutes, and activating the surface of the heavy calcium carbonate at an activation temperature of 110° C. to 130° C.;

[0027] Step S24, performing a hydrophobicity test on the activated heavy calcium carbonate to determine its activation degree;

[0028] Step S25, adding the activated ground calcium carbonate and the primary main masterbatch into a high-speed mixer, and determining the high-speed stirring time based on the degree of activation determined by the hydrophobicity test results in step S24, and performing high-speed stirring to allow the unfiberized ethylene vinyl acetate sea in the sea-island effect in step S12 to perform secondary modification on the activated ground calcium carbonate, thereby further activating it;

[0029] Step S26: adding the dispersant into a high-speed stirrer, stirring the activated heavy calcium carbonate and the primary masterbatch at high speed for 5 minutes to obtain a secondary masterbatch.

[0030] Furthermore, in step S25, the high-speed stirring time is inversely proportional to the activation degree of the test result of the hydrophobicity test in step S24.

[0031] Furthermore, in step S3, the lubricant, antioxidant and coloring reinforcing agent are added to the secondary main masterbatch and then stirred at high speed for 5 to 10 minutes to complete the mixing of the overall raw materials.

[0032] Furthermore, in the step S4, the overall raw materials are added to a screw granulator at a granulation temperature of 105° C. to 110° C. to prepare an in-situ fiberizing heat shrinkable masterbatch.

[0033] Compared with the prior art, the beneficial effect of the present invention is that the present invention produces a high-density polyethylene fiberizing masterbatch through a two-step method of heating blending and low-temperature stretching, so that the heat shrinkable product produced can cope with stretching, bending and wear in harsh environments, and has higher toughness than ordinary heat shrinkable tubes without changing the rigidity.

[0034] Furthermore, the present invention adopts ethylene vinyl acetate as the main material, so that the product has a certain flexibility and bendability, while the fiberized high-density polyethylene can increase the overall tensile strength of the product, making the product less likely to crack or break during use; at the same time, high-density polyethylene has higher temperature resistance, which can ensure that the heat shrinkable product has higher temperature resistance and maintains stiffness and strength at high temperatures than conventional heat shrinkable products.

[0035] Furthermore, the present invention can significantly improve the dispersibility and affinity of large-particle heavy calcium carbonate in ethylene vinyl acetate and high-density polyethylene by performing two-step activation of heavy calcium carbonate using a phosphate coupling agent and ethylene vinyl acetate, and the use of ethylene vinyl acetate does not incur additional costs.

[0036] Furthermore, the present invention uses activated heavy calcium carbonate as a filling and reinforcing agent, which produces an interfacial effect with ethylene vinyl acetate and high-density polyethylene, so that the heat shrinkable product has excellent impact strength, acid resistance and flame retardancy without using expensive high-strength materials, allowing it to withstand extreme environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a flow chart of the method for preparing the in-situ fiberized reinforced polyolefin heat shrink tubing of the present invention;

[0038] Figure 2 This is a flow chart of step S1 in the method for preparing the in-situ fiberized reinforced polyolefin heat shrink tubing of the present invention;

[0039] Figure 3 The flowchart of step S2 in the method for preparing the in-situ fiberized reinforced polyolefin heat shrink tubing of the present invention is shown. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0041] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside", and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0042] Furthermore, it should be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0043] See also Figure 1 As shown, it is a flow chart of the method for preparing an in-situ fiberized reinforced polyolefin heat shrinkable tubing of the present invention; the present invention provides a method for preparing an in-situ fiberized reinforced polyolefin heat shrinkable tubing, comprising:

[0044] Step S1, preparing a primary in-situ fiberizing masterbatch by mixing ethylene vinyl acetate and high-density polyethylene;

[0045] Among them, the VA content in ethylene vinyl acetate is 14%, and the melting index is 3g / 10min~5g / 10min;

[0046] The melt index of high-density polyethylene is 0.5g / 10min~2g / 10min;

[0047] See also Figure 2 As shown, it is a flow chart of step S1 in the method for preparing the in-situ fiberized reinforced polyolefin heat shrink tubing of the present invention; specifically, in the step S1, it includes:

[0048] Step S11, adding ethylene vinyl acetate and high-density polyethylene into a blender according to a ratio to obtain a mixed masterbatch;

[0049] Step S12, adding the mixed masterbatch to a screw granulator with a water-cooled strand-type die head, wherein the granulation temperature is 180°C to 220°C, the die head temperature is 220°C, and the water temperature of the water tank cooling system is 20°C to 30°C; wherein the speed ratio of the rear end tractor of the water-cooled strand-type die head to the main engine of the screw granulator is 30:1, and the stretching ratio is 8:1, so that the strand masterbatch is longitudinally stretched significantly, and the high-density polyethylene islands in the sea-island effect are longitudinally stretched into fibers, thereby obtaining an in-situ fiberized primary main masterbatch;

[0050] Step S13, detecting whether the in-situ fibrillated primary masterbatch has any fractures, and adjusting the blending time in step S11 based on the fracture detection result;

[0051] Specifically, in step S13, the fracture percentage is calculated based on the fracture point characteristics of the in-situ fibrillated primary masterbatch, the material form of the in-situ fibrillated primary masterbatch after stretching, and the speed ratio of the rear end tractor of the water-cooled strand-type die and the main body of the screw granulator, and the blending time in step S11 is adjusted according to the fracture percentage;

[0052] The fracture point characteristics include radial fracture and axial fracture, and the material form includes the length and diameter of the in-situ fiberized primary main masterbatch after stretching.

[0053] In a specific embodiment, the surface morphology of the in-situ fibrillated primary masterbatch is photographed by a machine vision detection device, and the fracture areas of the radial fracture and the axial fracture are obtained based on the surface image obtained by the photographing;

[0054] Specifically, the fracture percentage is determined by the following formula:

[0055]

[0056] Where:

[0057] b is the fracture percentage (%); S h is the total radial fracture area, in square meters (m²); S kis the total axial fracture area, in square meters (m²); q is the ratio of the speed of the strand die head to the speed of the screw pelletizer; d is the diameter of the primary masterbatch, in meters (m); L is the length of the primary masterbatch, in meters (m); f is an empirical constant;

[0058] Preferably, in the preparation method provided by the present invention, q=30, L=8d, and f=200.

[0059] Then we can get,

[0060]

[0061] If the calculated breakage percentage b is less than or equal to 2%, it is determined that there is no need to adjust the blending time; if the calculated breakage percentage b is greater than 2%, it is determined that the blending time needs to be adjusted.

[0062] It can be understood that when the fracture area of ​​the in-situ fibrillated primary masterbatch is greater than the threshold value, it means that in its island structure, the particle size of the dispersed phase (i.e., high-density polyethylene island) is uneven and its toughening effect is poor. At this time, by increasing the blending time, the high-density polyethylene can form an island structure earlier, and during the second blending in the screw granulator, the particle size of the dispersed phase can gradually decrease and tend to be stable. However, too long blending time may cause the dispersed phase particles to re-aggregate. The actual implementer can set the blending time according to the actual situation or a comparison table formed by the historical blending time that has passed the fracture qualification test and the corresponding fracture percentage data.

[0063] Preferably, the blending time is set according to the following empirical formula:

[0064] ;

[0065] Wherein, T is the blending time, in minutes (min); and it is stipulated that the blending time T≤15min; g is the blending time compensation coefficient, in min / %, preferably, 2.5min / %.

[0066] It can be understood that the smaller the breakage percentage, the shorter the blending time can be set. When the breakage percentage b is less than or equal to 2%, the blending time T reaches a minimum value of 5. When the breakage percentage b is 6%, the blending time T reaches a maximum value of 15.

[0067] The present invention adopts a two-stage blending method of transitioning from a "sea-sea" structure to a "sea-island" structure, first premixing the vinyl acetate and the high-density polyethylene to form a dual-continuous phase mixed masterbatch, and then adding the mixture into a screw granulator for secondary blending, thereby refining the dispersed phase and improving the dispersion uniformity.

[0068] Step S2, preparing activated heavy calcium carbonate, and mixing the activated heavy calcium carbonate with a dispersant and a main masterbatch to obtain a secondary main masterbatch;

[0069] See also Figure 3 As shown, it is a flow chart of step S2 in the method for preparing the in-situ fiberized reinforced polyolefin heat shrink tubing of the present invention; specifically, in the step S2, it includes:

[0070] Step S21, using a carrier fluidized bed to dry the ground calcium carbonate, using glass beads with a particle size of 6 mm as the carrier material, and setting the drying temperature to 120° C.;

[0071] In step S22, the dried heavy fine calcium carbonate powder is recovered through a cyclone separator (primary collection) and a bag filter (secondary collection), and 500-mesh dehydrated heavy calcium carbonate is taken. The tail gas temperature is controlled at 90-105°C to ensure that the water content of the finished product is ≤0.5%;

[0072] Step S23, adding dehydrated heavy calcium carbonate powder into a high-speed mixer, then adding 2.4% by mass of an atomized phosphate coupling agent, stirring at high speed for 20 to 25 minutes at an activation temperature of 110 to 130° C., so that the surface of the heavy calcium carbonate is activated;

[0073] Step S24, performing a hydrophobicity test on the activated heavy calcium carbonate to determine its activation degree;

[0074] In step S25, the activated heavy calcium carbonate and the primary main masterbatch are added into a high-speed mixer, and the high-speed stirring time is determined based on the degree of activation of the hydrophobicity test result in step S24, and high-speed stirring is performed to allow the unfiberized ethylene vinyl acetate sea in the island effect in step S12 to perform secondary modification on the activated heavy calcium carbonate to further activate it.

[0075] Specifically, in step S25, the high-speed stirring time is inversely proportional to the activation degree of the test result of the hydrophobicity test in step S24.

[0076] In a specific embodiment, the hydrophobicity detection is specifically:

[0077] Weigh 5g of the activated ground calcium carbonate sample to an accuracy of 0.01g. Use a beaker to take 200ml of distilled water into a 250ml separatory funnel, add 40ml to 50ml of water in advance, then add the sample to the separatory funnel at one time, add water to 200ml, and shake back and forth at a speed of 120 times / min for 1min (lay the separatory funnel flat, and then shake it in a way that it is tilted up and down at 45°. The force should not be too strong to avoid damaging the original coating of the calcium carbonate); gently place it on the funnel stand and let it stand for 30min. After obvious stratification, place the sunken calcium carbonate in a glass sand crucible that has been pre-weighed at (105±5)℃ (accurate to 0.01g), filter to remove water, place it in a constant temperature drying oven at (105±5)℃ and dry it to a constant weight, accurate to 0.01g.

[0078] The degree of activation is expressed as mass fraction w and the value is expressed as %, and is calculated according to the following formula:

[0079] w=[1-(m2-m1) / m]x100%, where:

[0080] m2 is the mass of the crucible and the uncoated calcium carbonate after drying, in grams (g); m1 is the mass of the crucible, in grams (g); m is the mass of the sample, in grams (g);

[0081] It can be understood that when the activation degree w is small, it means that the heavy calcium carbonate has not been fully activated, and the high-speed stirring time should be increased to allow polyvinyl acetate to perform secondary modification on the heavy calcium carbonate and fully activate it. The actual implementer can set the high-speed stirring time according to the actual situation or based on the high-speed stirring time of the activated heavy calcium carbonate and the primary main masterbatch of the heat shrink tubing that has passed the qualification inspection in historical data.

[0082] Preferably, the high-speed stirring time is set according to the following empirical formula:

[0083] ;

[0084] Wherein, t is the high-speed stirring time, in minutes (min); and it is stipulated that the high-speed stirring time t≤15min; s is the stirring compensation coefficient, in min / %, preferably, -1min / %; n is the reference time, in minutes (min), preferably, 105min.

[0085] It can be understood that the higher the activation degree, the shorter the high-speed stirring time can be set. When the activation degree w is 100%, the high-speed stirring time t reaches a minimum value of 5. When the activation degree w is 90%, the high-speed stirring time t reaches a maximum value of 15.

[0086] The present invention adopts polyvinyl acetate to perform secondary modification on heavy calcium carbonate, thereby reducing the friction between the heavy calcium carbonate and the high-density polyethylene and lowering the melt viscosity, thereby obtaining better mechanical properties and reducing the usage of dispersants and lubricants without increasing costs.

[0087] Step S26, adding the dispersant into a high-speed stirrer, and stirring at high speed for 5 minutes with the activated heavy calcium carbonate and the primary masterbatch to obtain the secondary masterbatch;

[0088] Wherein, the dispersant is erucamide.

[0089] Step S3, adding lubricant, antioxidant and coloring reinforcing agent to the secondary main masterbatch to prepare the overall raw material;

[0090] Specifically, in step S3, the lubricant, antioxidant and coloring reinforcing agent are added to the secondary main masterbatch and then stirred at high speed for 5 to 10 minutes to complete the mixing of the overall raw materials.

[0091] The lubricant is zinc stearate; the antioxidant is composed of a complex of a hindered phenol antioxidant and a phosphite antioxidant, wherein the composite ratio of the hindered phenol antioxidant to the phosphite antioxidant is 1:2; and the coloring reinforcing agent is carbon black masterbatch.

[0092] It will be understood by those skilled in the art that the erucamide dispersant, the zinc stearate lubricant, the hindered phenol antioxidant, the phosphite antioxidant and the carbon black masterbatch coloring reinforcing agent are prior art, and their specific brands and models can be selected according to actual conditions during implementation, which will not be described in detail here.

[0093] Step S4, granulating the overall raw materials to prepare an in-situ fiberized heat shrinkable masterbatch;

[0094] Specifically, in step S4, the overall raw materials are added to a screw granulator at a granulation temperature of 105° C. to 110° C. to prepare an in-situ fiberizing heat shrinkable masterbatch.

[0095] It can be understood that the technology of using a screw granulator to granulate the raw materials is not limited to the above-mentioned implementation. Those skilled in the art can select the granulation process according to the specific actual scenario. Among them, using a granulation temperature of 105°C to 110°C can prevent the fiberized high-density polyethylene from melting and keep it in a crystalline state, and cause the ethylene vinyl acetate sea in the island effect to melt to prepare the in-situ fiberized heat shrinkable masterbatch of the present invention.

[0096] Step S5: Extruding and injection molding the heat shrink masterbatch, performing electron accelerator irradiation cross-linking and expansion molding to obtain an in-situ fiberized reinforced polyolefin heat shrink tubing.

[0097] Those skilled in the art will understand that the injection molding, the electron accelerator irradiation cross-linking and the expansion molding are existing technologies, and these existing technologies can be adjusted or replaced based on actual conditions while achieving the same effect, and will not be elaborated here.

[0098] Example 1:

[0099] Step S11, adding 90 kg of ethylene vinyl acetate and 10 kg of high-density polyethylene according to a ratio into a blender and blending for 5 to 10 minutes to obtain a mixed masterbatch;

[0100] Step S12, adding the mixed masterbatch to a screw granulator with a water-cooled strand-type die head, wherein the granulation temperature is 180°C to 220°C, the die head temperature is 220°C, and the water temperature of the water tank cooling system is 20°C to 30°C; wherein the speed ratio of the rear end tractor of the water-cooled strand-type die head to the main engine of the screw granulator is 30:1, and the stretching ratio is 8:1, so that the strand masterbatch is longitudinally stretched significantly, and the high-density polyethylene islands in the sea-island effect are longitudinally stretched into fibers, thereby obtaining an in-situ fiberized primary main masterbatch;

[0101] Step S13, detecting whether the in-situ fibrillated primary masterbatch has any breakage, and adjusting the blending time in step S11 based on the breakage detection result; in the step, it was detected that the masterbatch had breakage (the breakage percentage was 4.2%), and the blending time in step S11 was adjusted to 10.5 minutes, and the primary masterbatch was newly prepared, and the breakage percentage of the new primary masterbatch was detected to be 1.022%;

[0102] Step S21, using a carrier fluidized bed to dry 15 kg of heavy calcium carbonate, using glass beads with a particle size of 6 mm as the carrier material, and setting the drying temperature to 120° C.;

[0103] Step S22: The dried heavy fine calcium carbonate powder is recovered through a cyclone separator (primary collection) and a bag filter (secondary collection), and 500-mesh dehydrated heavy calcium carbonate is used. The tail gas temperature is controlled at 90°C to 105°C to ensure that the water content of the finished product is ≤0.5%.

[0104] Step S23, adding dehydrated heavy calcium carbonate powder into a high-speed mixer, then adding 0.6 kg of atomized phosphate coupling agent, stirring at high speed for 20 to 25 minutes, and activating the surface of the heavy calcium carbonate at an activation temperature of 110° C. to 130° C.;

[0105] Step S24, performing a hydrophobicity test on the activated heavy calcium carbonate to determine its activation degree; the activation degree is measured to be 92%;

[0106] In step S25, the activated heavy calcium carbonate and the primary main masterbatch are added to a high-speed mixer, and based on the test result of the hydrophobicity test in step S24, that is, the activation degree is 92%, high-speed stirring is performed for 13 minutes, so that the unfiberized ethylene vinyl acetate sea in the island effect in step S12 performs secondary modification on the activated heavy calcium carbonate to further activate it.

[0107] Step S26: add 1 kg of erucamide dispersant into a high-speed stirrer, and stir it with the activated heavy calcium carbonate and the first-level main masterbatch at high speed for 5 minutes to obtain the second-level main masterbatch.

[0108] Step S3: add 1 kg of zinc stearate lubricant, 0.2 kg of composite antioxidant and 5 kg of carbon black masterbatch to the secondary main masterbatch and stir at high speed for 5 to 10 minutes to complete the mixing of the overall raw materials.

[0109] Step S4: adding the overall raw materials into a screw granulator at a granulation temperature of 105° C. to 110° C. to prepare an in-situ fiberizing heat shrinkable masterbatch.

[0110] Step S5: Extruding and injection molding the heat shrink masterbatch, performing electron accelerator irradiation cross-linking and expansion molding to obtain an in-situ fiberized reinforced polyolefin heat shrink tubing.

[0111] Example 2:

[0112] The difference between this embodiment and Example 1 is that this embodiment only changes step S11 in Example 1, and adds 80 kg of ethylene vinyl acetate and 20 kg of high-density polyethylene according to the ratio into a mixer and blends for 5 to 10 minutes to obtain a mixed masterbatch; the rest is the same as Example 1.

[0113] Example 3:

[0114] The difference between this embodiment and Example 2 is that this embodiment only changes step S26 in Example 2, adding 2 kg of erucamide dispersant into a high-speed stirrer, and stirring it with activated heavy calcium carbonate and the first-level main masterbatch at high speed for 5 minutes to obtain a second-level main masterbatch; the rest is the same as Example 2.

[0115] Example 4:

[0116] The difference between this embodiment and Example 3 is that this embodiment only changes step S11 in Example 3, adding 70 kg of ethylene vinyl acetate and 30 kg of high-density polyethylene according to the ratio into a mixer and blending for 5 to 10 minutes to obtain a mixed masterbatch; the rest is the same as Example 3.

[0117] Example 5:

[0118] The difference between this embodiment and Example 3 is that this embodiment only changes step S22 in Example 3, and the dried heavy fine calcium carbonate powder is recovered through a cyclone separator (primary capture) and a bag filter (secondary capture), and only 500-mesh dehydrated heavy calcium carbonate is used, wherein the tail gas temperature is controlled at 90°C to 105°C to ensure that the water content of the finished product is ≤0.5%; the rest is the same as Example 3.

[0119] Example 6:

[0120] The difference between this embodiment and Example 3 is that this embodiment only changes step S22 in Example 3, and the dried heavy fine calcium carbonate powder is recovered through a cyclone separator (primary capture) and a bag filter (secondary capture), and only 700-mesh dehydrated heavy calcium carbonate is used, wherein the tail gas temperature is controlled at 90°C to 105°C to ensure that the water content of the finished product is ≤0.5%; the rest is the same as Example 3.

[0121] Example 7:

[0122] The difference between this embodiment and Example 3 is that this embodiment only changes step S22 in Example 3, and the dried heavy fine calcium carbonate powder is recovered through a cyclone separator (primary capture) and a bag filter (secondary capture), and only 900-mesh dehydrated heavy calcium carbonate is used, wherein the tail gas temperature is controlled at 90°C to 105°C to ensure that the water content of the finished product is ≤0.5%; the rest is the same as Example 3.

[0123] Example 8:

[0124] The difference between this embodiment and Example 1 is that when using activated heavy calcium carbonate with an activation degree of 92%, the high-speed stirring in step S25 is not performed, and the activated heavy calcium carbonate and the dispersant are directly added to the primary main masterbatch and stirred to obtain the secondary main masterbatch.

[0125] Please see the table below for specific data:

[0126] Table 1 Component formula of the in-situ fiberized reinforced polyolefin heat shrink tubing prepared in Examples 1 to 4

[0127]

[0128] Table 2 Component formula of the in-situ fiberized reinforced polyolefin heat shrink tubing prepared in Examples 5 to 7

[0129]

[0130] Table 3 Test results of in-situ fiberized reinforced polyolefin heat shrink tubing prepared in Examples 1 to 4

[0131]

[0132] Table 4 Test results of in-situ fiberized reinforced polyolefin heat shrink tubing prepared in Examples 5 to 7

[0133]

[0134] Table 5 Test results of in-situ fiberized reinforced polyolefin heat shrink tubing prepared in Examples 1 and 8

[0135]

[0136] From Tables 1 and 3 above, we can see that:

[0137] When the dispersant component is 1 part, the product with high vinyl acetate component (Example 1) has a higher elongation at break and lower tensile strength, indicating good toughness. The product with 80 parts of vinyl acetate component (Example 2) has good wear resistance and high strength retention, indicating good hardness.

[0138] When the dispersant component is 2 parts, the product with a high vinyl acetate component (Example 3) has a higher elongation at break and a lower tensile strength, indicating good toughness. At the same time, its strength retention rate is also high. Only the wear resistance is poor, indicating that its hardness is not significantly different from that of the product with a low vinyl acetate component (Example 4).

[0139] When the vinyl acetate component is 80 parts and the high-density polyethylene component is 20 parts, the product with a low dispersant component (Example 2) has a lower elongation at break, lower tensile strength, lower strength retention, and lower wear resistance, indicating that its performance is overall weaker than that of the product with a high dispersant component (Example 3).

[0140] In summary, among Examples 1 to 4, Example 3 has the best component ratio, and the use of a high dispersant component and a relatively low vinyl acetate component results in the best overall product performance.

[0141] It can be seen from Tables 2 and 4 above that after activation, the low-mesh dehydrated heavy calcium carbonate has a better filling and reinforcing effect on the main masterbatch, and the overall performance of the product is better.

[0142] It can be seen from Table 5 above that when the activation of the activated heavy calcium carbonate in step S23 is not sufficient, if the activated heavy calcium carbonate is not secondary modified by the unfiberized ethylene vinyl acetate sea in the sea island effect in step S12 to further activate it, its filling and reinforcement of the main masterbatch will be greatly reduced, affecting the mechanical properties of the manufactured product.

[0143] In summary, among Examples 1 to 8, the product prepared in Example 5 has the best overall performance.

[0144] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A method for preparing an in-situ fiberized reinforced polyolefin heat shrink tubing, characterized in that: The raw materials of the heat shrinkable tube are composed of the following components by weight: 100 parts of main masterbatch, 15 parts of filling and reinforcing agent, 1-2 parts of dispersant, 1 part of lubricant, 0.2 parts of antioxidant, and 5 parts of coloring and reinforcing agent; The main masterbatch is composed of 70-90 parts of ethylene vinyl acetate and 10-30 parts of high-density polyethylene, in parts by weight. The VA content of the ethylene vinyl acetate is 14%, and the melt index is 3g / 10min-5g / 10min; the melt index of the high-density polyethylene is 0.5g / 10min-2g / 10min. The filling and reinforcing agent is activated calcium carbonate, and the activation method is: using a phosphate coupling agent to modify the surface of heavy calcium carbonate powder, wherein the mesh size of the heavy calcium carbonate is 500 mesh; The dispersant is erucamide; the lubricant is zinc stearate; the antioxidant is composed of a complex of a hindered phenol antioxidant and a phosphite antioxidant, wherein the composite ratio of the hindered phenol antioxidant to the phosphite antioxidant is 1:2; the coloring reinforcing agent is a carbon black masterbatch; The preparation method comprises: Step S1, preparing a primary in-situ fiberizing masterbatch by mixing ethylene vinyl acetate and high-density polyethylene, wherein said step S1 includes: Step S11, adding ethylene vinyl acetate and high-density polyethylene into a blender according to a ratio to obtain a mixed masterbatch; Step S12, adding the mixed masterbatch to a screw granulator with a water-cooled strand-type die head, wherein the granulation temperature is 180°C to 220°C, the die head temperature is 220°C, and the water temperature of the water tank cooling system is 20°C to 30°C; wherein the speed ratio of the rear end tractor of the water-cooled strand-type die head to the main engine of the screw granulator is 30:1, and the stretching ratio is 8:1, so that the strand masterbatch is longitudinally stretched significantly, and the high-density polyethylene islands in the sea-island effect are longitudinally stretched into fibers, thereby obtaining an in-situ fiberized primary main masterbatch; Step S13, detecting whether the in-situ fibrillated primary masterbatch has any fractures, and adjusting the blending time in step S11 based on the fracture detection result; In step S13, the fracture percentage is calculated based on the fracture point characteristics of the in-situ fibrillated primary masterbatch, the material form of the in-situ fibrillated primary masterbatch after stretching, and the speed ratio of the rear end tractor of the water-cooled strand-type die head to the main body of the screw pelletizer, and the blending time in step S11 is adjusted according to the fracture percentage; wherein the fracture point characteristics include radial fracture and axial fracture, and the material form includes the length and diameter of the in-situ fibrillated primary masterbatch after stretching; Step S2, preparing activated heavy calcium carbonate, and mixing the activated heavy calcium carbonate with a dispersant and a main masterbatch to obtain a secondary main masterbatch; Step S3, adding lubricant, antioxidant and coloring reinforcing agent to the secondary main masterbatch to prepare the overall raw material; Step S4, granulating the overall raw materials to prepare an in-situ fiberized heat shrinkable masterbatch; Step S5: Extruding and injection molding the heat shrink masterbatch, performing electron accelerator irradiation cross-linking and expansion molding to obtain an in-situ fiberized reinforced polyolefin heat shrink tubing.

2. The method for preparing the in-situ fiberized reinforced polyolefin heat shrink tubing according to claim 1, characterized in that: In the step S2, it includes: Step S21, using a carrier fluidized bed to dry the ground calcium carbonate, using glass beads with a particle size of 6 mm as the carrier material, and setting the drying temperature to 120° C.; Step S22: The dried heavy fine calcium carbonate powder is recovered through a cyclone separator and a bag filter, wherein the tail gas temperature is controlled at 90°C to 105°C to ensure that the water content of the finished product is ≤0.5%; Step S23, adding dehydrated heavy calcium carbonate powder into a high-speed mixer, then adding 2.4% by mass of an atomized phosphate coupling agent, stirring at high speed for 20 to 25 minutes, and activating the surface of the heavy calcium carbonate at an activation temperature of 110° C. to 130° C.; Step S24, performing a hydrophobicity test on the activated heavy calcium carbonate to determine its activation degree; Step S25, adding the activated ground calcium carbonate and the primary main masterbatch into a high-speed mixer, and determining the high-speed stirring time based on the degree of activation determined by the hydrophobicity test results in step S24, and performing high-speed stirring to allow the unfiberized ethylene vinyl acetate sea in the sea-island effect in step S12 to perform secondary modification on the activated ground calcium carbonate, thereby further activating it; Step S26: adding the dispersant into a high-speed stirrer, stirring the activated heavy calcium carbonate and the primary masterbatch at high speed for 5 minutes to obtain a secondary masterbatch.

3. The method for preparing the in-situ fiberized reinforced polyolefin heat shrink tubing according to claim 2, characterized in that: In the step S25, the high-speed stirring time is inversely proportional to the activation degree of the test result of the hydrophobicity test in the step S24.

4. The method for preparing the in-situ fiberized reinforced polyolefin heat shrink tubing according to claim 1, characterized in that: In step S3, the lubricant, antioxidant and coloring reinforcing agent are added to the secondary main masterbatch and then stirred at high speed for 5 to 10 minutes to complete the mixing of the overall raw materials.

5. The method for preparing the in-situ fiberized reinforced polyolefin heat shrink tubing according to claim 1, characterized in that: In the step S4, the overall raw materials are added to a screw granulator at a granulation temperature of 105° C. to 110° C. to prepare an in-situ fiberizing heat shrinkable masterbatch.

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