CN110591232A

CN110591232A - Method for preparing high-strength anti-retraction microporous polypropylene expanded beads (EPP) by utilizing layer-by-layer crystallization assembly control

Info

Publication number: CN110591232A
Application number: CN201910780445.9A
Authority: CN
Inventors: 宫瑞英; 王峰忠; 陈静鹤; 李朝旭; 韩冲; 孙并臻; 鞠学刚
Original assignee: Qingdao Zhongkeribang New Material Technology Co ltd; Qingdao Institute of Bioenergy and Bioprocess Technology of CAS
Current assignee: Qingdao Zhongkeribang New Material Technology Co ltd; Qingdao Institute of Bioenergy and Bioprocess Technology of CAS
Priority date: 2019-08-22
Filing date: 2019-08-22
Publication date: 2019-12-20

Abstract

The invention discloses a method for preparing microporous polypropylene foamed beads by utilizing layer-by-layer crystallization assembly control. The preparation method comprises the steps of selecting 20-95 parts of random polypropylene powder as matrix resin, selecting 0.0001-2 parts of beta crystal nucleating agent, granulating, selecting 0.0001-3 parts of inorganic nucleating agent with alpha crystal nucleating agent function, aromatic carboxylate, sorbitol and other series alpha crystal nucleating agents, and granulating again for later use, wherein the total alpha crystal nucleating agent is 0.0001-3 parts of auxiliary agent. In the production process, a batch kettle method is adopted, crystallization nucleating aids with different functions are combined, different crystallization nucleating agents are utilized to coordinate layer-by-layer assembly crystallization, the crystallization speed and the crystal particle size are flexibly combined with the growth and solidification process of foam material cells, the cell sizes of the prepared materials are all between 5 and 20 mu m, and the microporous polypropylene foaming beads in absolute significance are prepared. Can be widely used in the fields of war industry, automobiles, buildings, children toys, food packaging materials, household appliances and the like.

Description

Method for preparing high-strength anti-retraction microporous polypropylene expanded beads (EPP) by utilizing layer-by-layer crystallization assembly control

Technical Field

A method for preparing high-strength anti-retraction microporous polypropylene foaming beads by utilizing layer-by-layer crystallization assembly control belongs to the field of modification processing of high polymer materials. The preparation method specifically relates to polypropylene expanded beads, wherein crystallization nucleating aids with different functions are selected, different crystallization nucleating agents are utilized to coordinate layer-by-layer assembly crystallization, the crystallization speed and the crystal particle size are flexibly combined with the growth and solidification process of foam material cells, and the high-strength retraction-resistant microporous polypropylene expanded beads with the cell size of 5-20 mu m in absolute sense are prepared.

Background

The preparation method of the high melt strength polypropylene expanded beads has been disclosed by relevant research data. CN 104250400 a and CN 104250401a disclose a method for preparing polypropylene expanded beads by using homo-polypropylene with high melt strength as matrix resin and supercritical fluid as foaming agent. The external electron donors with different hydrogen regulation sensitivities are selectively added in different polymerization stages, and the hydrogen concentration in different reactors is regulated to regulate and control the molecular weight, so that the polypropylene containing both high molecular weight fractions and low molecular weight fractions is realized, wherein the high molecular weight fractions ensure the melt strength of the final polymer, and the broadened molecular weight distribution ensures the strain hardening of the final polymer and broadens the foaming window. CN 103665583a and CN 103665420 a disclose a method for preparing propylene ethylene high melt strength polypropylene expanded beads and propylene ethylene butylene high melt strength polypropylene expanded beads, respectively. The high melt strength polypropylene used in the two inventions has not only wider molecular weight distribution, but also the biggest characteristic that the content of the fraction with extremely high molecular weight (molecular weight is more than 500 ten thousand) is higher, and simultaneously the content of the fraction with lower molecular weight (molecular weight is less than 5 ten thousand) is also better than a certain amount, thus the melt strength of the obtained propylene polymer is obviously improved, and the processability of the polymer is also ensured. CN 1676541 a and CN 1474849 a disclose a method for preparing non-crosslinked polypropylene expanded beads at relatively low temperature. The surface-modified polypropylene resin is obtained by dispersing an organic peroxide in non-crosslinked polypropylene resin fine particles and decomposing the peroxide by heating. The DSC curve of this modified polypropylene resin shows a high-temperature absorption peak and a characteristic absorption peak located on the low-temperature side of the high-temperature absorption peak. In recent years, studies on the improvement of the properties of the foamed polypropylene have been focused compared with the conventional EPP. CN 104479165A and CN 106750944A respectively improve the mechanical property and weather resistance of polypropylene materials by quenching polypropylene at-50-10 ℃ and performing low-temperature solid phase foaming and by adding polyolefin elastomer into polypropylene resin, mixing, extruding and granulating through an extruder and then performing kettle type foaming. CN 106633360A adopts high-pressure fluid kettle pressure foaming technology, utilizes the principle of synergistic toughening of a beta nucleating agent and a polyolefin elastomer to prepare a polypropylene foaming bead containing beta crystals and a polyolefin elastomer disperse phase, utilizes the beta crystals to modify the interface bonding behavior of the polypropylene foaming bead, and utilizes the beta crystals and the polyolefin elastomer to improve the low-temperature toughness of polypropylene, thereby preparing the polypropylene foaming bead molding material with high interface bonding strength and excellent low-temperature impact toughness. CN 103509203A utilizes the combination mode of crystalline polypropylene and high-melting point polypropylene, and increases the crystallinity of EPP particles by adding a crystallization nucleating agent, so that the formed spherulites are finer, and the expanded polypropylene beads with high strength, excellent buffering performance and impact absorption performance are prepared. In recent years, not only the improvement of the performance of expanded polypropylene has been a focus, but also the research on the polypropylene expansion process has been receiving attention. At present, the preparation process of polypropylene expanded beads mainly comprises two processes: extrusion and kettle processes. The kettle type foaming method has easily controlled technological conditions, can prepare foaming beads with adjustable multiplying power and closed pore rate, but requires high pressure, large equipment introduction and high cost. CN 106674583A takes a first polypropylene resin with 25-40% of crystallinity and a second polypropylene resin with a melting point of 126-148 ℃ as raw materials, and carries out primary foaming treatment, pre-pressing treatment and secondary foaming treatment on the prepared polypropylene particles, thereby effectively reducing the requirements on foaming temperature and pressure, and reducing the production energy consumption and the input cost of equipment.

One of the major trends in the general basic material industry program in China manufacturing 2025 for advanced petrochemical materials is expanded polypropylene. However, ordinary PP is a semicrystalline polymer, and has a melting point very close to a softening point, so that when a processing temperature exceeds the melting point, the melt strength of PP is rapidly reduced (which makes it difficult to contain the growth of bubbles during foaming, resulting in bubble escape or collapse), and a temperature range suitable for thermoforming is narrow, resulting in defects of products during thermoforming processing. In order to improve the current situation of low melt strength and poor foaming performance in the PP foaming process, researchers have tried many methods to modify linear PP to improve its melt strength, and generally started from increasing the molecular weight of PP, broadening its molecular weight distribution, and introducing long-chain branched structures. The main methods for preparing high melt strength polypropylene (HSMPP) currently include: blending modification, grafting, crosslinking modification and polymerization modification. In general, the molecular weight of PP is increased, the molecular weight distribution is broadened, and a long-chain branched structure is introduced.

EPP is one of polypropylene foaming methods, and other methods include extrusion, molding, and the like. Also, the foaming of polypropylene necessarily involves the melt strength of the polypropylene. However, the foaming of EPP has its particularity, and the foaming process is first understood. The batch kettle method comprises mixing PP and corresponding adjuvants, granulating into fine particles, mixing with dispersing medium, dispersant and foaming agent (common CO)₂) And (3) putting the mixture into a reaction kettle, raising the temperature to be near the melting point of the PP particles (at the moment, the PP particles are softened but not completely melted), keeping the temperature for a period of time to allow the foaming agent to fully permeate into the PP particles, and then opening a valve of the reaction kettle (simultaneously introducing inert gas into the kettle to maintain the pressure of the kettle to be basically constant) to quickly release the pressure to obtain the polypropylene foamed beads. The kettle-type method can be divided into a water-containing method and an anhydrous method according to different dispersion media of a dispersion system in the foaming process: in the former method, water is used as a dispersing medium, small PP particles are uniformly dispersed in the water under the action of a dispersing agent and stirring, on the premise of ensuring that PP particles are not bonded, the PP is softer due to a slightly higher kettle pressure foaming temperature, a foaming agent is more easily dissolved in the PP, and water vapor permeating into the PP also contributes to the function of the foaming agent, so that the foaming pressure of a kettle-type method is only 2-6 MPa, and the existing industrial preparation of EPP basically adopts the kettle-type method.

Polypropylene foaming necessarily involves the melt strength of polypropylene, but EPP foaming is peculiar. It is clear from the preparation of EPP that although EPP is also polypropylene foam, the foaming process does not reach the foaming in its melt flow state, and although the foaming process involves the growth of shot holes, which is related to the melt strength of polypropylene, the PP itself does not reach its melting point in its molten state, and a certain melt strength is maintained. Whether the EPP kettle type foaming method can be combined with the characteristics of the EPP kettle type foaming method or not, the main methods (blending modification, grafting, crosslinking modification and polymerization modification) of the high melt strength polypropylene (HSMPP) on the premise of the aim are broken through, and the idea that the crystallization process is regulated and controlled by utilizing different response degrees of different comonomer sequences distributed in a main matrix to different nucleating agent assembly behaviors so as to realize proper matching of the crystallization speed and the crystallization temperature with the nucleation growth process and realize the crystallization control development of the EPP material of the non-high melt polyolefin material is provided.

1. The invention relates to a method for preparing high-strength anti-retraction microporous polypropylene foam beads by utilizing layer-by-layer crystallization assembly control, which comprises the following specific formula: taking the atactic polypropylene powder as matrix resin, wherein the using amount is 20-95 parts, and preferably 50-90 parts; 0.0001-2 parts of beta crystal nucleating agent; the alpha crystal nucleating agent comprises 0.0001-3 parts of total alpha crystal nucleating agent and 2-20 parts of auxiliary agent. Further preferably, the amount of the beta crystal nucleating agent is 0.0002 to 0.5 part, and the amount of the total alpha crystal nucleating agent is 0.01 to 2 parts.

2. The random polypropylene powder of the invention is used as matrix resin, and specifically comprises the following components: the random polypropylene powder is a blend of one or more of copolymers of propylene (the molar content of propylene in the copolymer is 50-99%) and ethylene (the molar content of ethylene in the copolymer is 0-15%), 1-butene (the molar content of 1-butene in the copolymer is 0-45%), 1-pentene (the molar content of 1-pentene in the copolymer is 0-20%), 1-hexene (the molar content of 1-hexene in the copolymer is 0-20%), 1-heptene (the molar content of 1-heptene in the copolymer is 0-20%), 1-octene (the molar content of 1-octene in the copolymer is 0-20%), 1-nonene (the molar content of 1-nonene in the copolymer is 0-20%), 1-decene (the molar content of 1-decene in the copolymer is 0-20%), and the preferred copolymer is a propylene-butadiene copolymer, One or more blends of propylene-ethylene copolymer or propylene-butylethylene terpolymer. The molecular weight distribution Mw/Mn of the copolymer is 2-20, and the melt flow index (190 ℃ and 2.16Kg) is 1-15 g/10 min.

3. The beta crystal nucleating agent is one or a mixture of two or more of organic carboxylic acid and salts thereof (salts of dicarboxylic acid and IIA metal elements, particularly binary compounds of pimelic acid and calcium stearate), aromatic amide TMB series and rare earth complex WBG series, and further preferably aromatic amide and rare earth. The beta crystal nucleating agent is selected to convert the alpha crystal structure part in the random polypropylene powder resin into a beta crystal structure, so that the polypropylene resin with wider melting range corresponding to the original polypropylene resin powder resin is prepared.

4. The alpha crystal nucleating agent comprises three or more than three of inorganic nucleating agents with alpha crystal nucleating function, alpha crystal nucleating agent aromatic carboxylate, alpha crystal nucleating agent sorbitol and other series alpha crystal nucleating agents, and the using amount of the total alpha crystal nucleating agent is 0.0001-3 parts. Further preferably 0.01 to 2 parts by weight of a total alpha crystal nucleating agent. Different alpha crystal nucleating agents have different influences on the crystallization speed, the crystallization temperature and the crystal form refining degree, and some crystal nucleating agents can be assembled into a network structure in resin, so that the crystallization speed and the crystallization temperature can be properly matched with the bubble nucleus growth process by completely utilizing the layer-by-layer crystallization assembly control of the crystal nucleating agents, and the non-high melt strength EPP material suitable for foaming is developed.

5. The auxiliary agent is one or more of a foaming nucleating agent, an antioxidant, an antistatic agent, a flame retardant, color master batches and a coupling agent. The dosage of the auxiliary agent is 2-20 parts. Further preferably 5 to 15 parts.

6. The foaming nucleating agent in the auxiliary agent is at least one of talcum powder, mica, glass beads, silicon dioxide, calcium carbonate, montmorillonite, kaolin, aluminum oxide, barium sulfate, zinc oxide, zinc stearate and calcium stearate; the antioxidant is at least one of antioxidants 168, 1010, 1076 and 626; the antistatic agent is alkyl imidazoline, quaternary phosphonium salt, quaternary sulfur salt, quaternary ammonium salt, alkyl sulfonate or phosphate; the flame retardant is one or more of magnesium hydroxide, aluminum hydroxide, zinc borate and intumescent flame retardant DTPB; the coupling agent is one or more of silane coupling agent, titanate coupling agent and aluminate coupling agent.

7. The invention relates to a method for preparing high-strength anti-retraction microporous polypropylene expanded beads (EPP) by utilizing layer-by-layer crystallization assembly control, which specifically comprises the following steps:

(1) fully mixing the beta nucleating agent and the random polypropylene resin powder by a high-speed mixer, and granulating by a double screw to prepare polypropylene master batch resin with a wider melting range corresponding to the original polypropylene resin powder resin;

(2) fully compounding polypropylene master batch resin, an inorganic nucleating agent with an alpha crystallization nucleating agent function, alpha crystallization nucleating agent aromatic carboxylate, and an alpha crystallization nucleating agent sorbitol series alpha crystallization nucleating agent with the total alpha crystallization nucleating agent usage amount of 0.0001-3 parts and the auxiliary agent usage amount of 2-15 parts by a high mixing machine, extruding by a double screw rod, water cooling, bracing and cutting into granules to obtain modified polypropylene small particles with the length of 1-2 mm and the diameter of 0.5-2 mm; ,

(3) putting polypropylene particles, a dispersing agent and water into an autoclave, injecting a physical foaming agent into the autoclave under a stirring condition, simultaneously raising the temperature of the autoclave to 120-160 ℃, raising the pressure to 2.0-8.0 MPa, and keeping for 20-60 min after the set temperature and pressure are reached so that the foaming agent permeates into the polypropylene particles;

(4) the pressure of the high-pressure kettle is released controllably, and the polypropylene particle-high pressure water dispersion mixed material is sprayed into a cold water cooling system to obtain polypropylene foaming beads with the foaming ratio of 2-30 times; in order to obtain polypropylene expanded beads with higher expansion ratio, the primarily obtained polypropylene expanded beads need to be subjected to pressure release in a secondary foaming device under the condition of controlling the pressure of 0.1-1.5 MPa for 10-60 s in a steam atmosphere, so as to further obtain polypropylene expanded beads with higher expansion ratio, wherein the expansion ratio is 15-60 times.

(5) And drying the prepared polypropylene foamed beads for 10-48 hours in an environment of 30-60 ℃, injecting the dried polypropylene foamed beads into steam compression molding equipment, and heating and cooling by steam to obtain the polypropylene foamed bead molded body.

8. The dispersant is one or more than two of kaolin, sodium dodecyl sulfonate, aluminum sulfate, calcium carbonate, barium sulfate and aluminosilicate.

9. The physical foaming agent is one or two of carbon dioxide and nitrogen. Carbon dioxide is further preferred.

10. The pressure release rate of the autoclave is 0.3-2.0 MPa/s, and the cooling rate of the polypropylene particle-water dispersion system mixture is 20-40 ℃/s.

11. Compared with the prior art, the invention has the following advantages:

from the development conditions and patent authorization conditions at home and abroad, the method combines the characteristics of an EPP kettle type foaming method, breaks through the main methods (blending modification, grafting, crosslinking modification and polymerization modification) of high melt strength polypropylene (HSMPP) on the premise of the aim, proposes the angle of realizing the regulation and control of crystallization process by utilizing different nucleating agent assemblies from the distribution of sequence structures, thereby realizing the proper matching of crystallization speed and crystallization temperature with the growth process of a bubble nucleus, develops the assumed research of a foaming non-high melt strength EPP material, and further promotes the synthesis of a special structure polyolefin foaming material (EPP) for realizing the regulation and control of melt strength by crystallization by designing the distribution of a comonomer sequence structure. These studies have not been attempted before, either in terms of design or in terms of specific experimental design. The patent is researched and started from crystallization regulation, foaming process and performance research, a series of researches such as a catalytic system, process design, material structure design and the like in chemical production are further combined to obtain a preliminary assumption target result, and the new assumptions are also shown to be completely feasible, follow-up work follows, so that a new idea is provided for developing a new special polyolefin material structure design, and a new method for developing a polyolefin material based on the structure into a non-high melt strength EPP material by utilizing crystallization regulation is also provided. Compared with mature application products at home and abroad, the size of the foam hole is more than 200 microns, the size of the blast hole can be controlled within dozens of microns very little, and the microporous material in a strict meaning is achieved, so that the EPP material can be flexibly regulated and controlled according to the patent, the size of the microporous structure of the EPP material is less than 50 microns, the foaming temperature can be controlled below 130 ℃, the foaming pressure is lower than 2.5MPa, and the microporous foamed polypropylene beads with the structure can still be obtained, the steam pressure required by the molding products of the microporous foamed polypropylene beads is small, the molding pressure is only 1.2-2.5kPa, and meanwhile, the microporous material can show the special high-strength, high-resilience, conductivity and other excellent performances of the microporous material.

Detailed Description

Example 1

(1) Fully mixing 0.05g of beta nucleating agent calcium terephthalate and 600g of random polypropylene resin powder with the melting point of 145 ℃ by a high-speed mixer, and granulating by a double screw to prepare polypropylene master batch resin with a wider melting range corresponding to the original polypropylene resin powder resin;

(2) fully compounding 300g of polypropylene master batch resin, 0.1g of alpha crystallization nucleating agent aromatic aryl phosphonate (NA-21), 0.6g of alpha crystallization nucleating agent sorbitol (3988) and 8g of auxiliary agent by using a high-speed mixer, extruding by using a double screw rod, water cooling, bracing and granulating to obtain modified polypropylene small particles with the length of 1.2mm and the diameter of 1 mm; ,

(3) putting polypropylene particles, a dispersing agent and water into an autoclave, injecting a physical foaming agent into the autoclave under the stirring condition, simultaneously raising the temperature of the autoclave to 131 ℃, raising the pressure to 3.0MPa, and keeping for 20min after the set temperature and pressure are reached to enable the foaming agent to permeate into the polypropylene particles;

(4) and injecting the polypropylene particle-high pressure water dispersion mixed material into a cold water cooling system at a controllable pressure release speed of 1.1MPa/s in the high-pressure kettle, wherein the foaming ratio of the polypropylene foaming beads is 11 times. The cell density was 0.08 g/cc. The cell structure of the expanded beads is illustrated in FIG. 1.

Example 2

(1) Fully mixing beta nucleating agent TMB-50.03 g and random polypropylene resin powder with the melting point of 145 ℃ 600g by a high-speed mixer, and granulating by a double screw to prepare polypropylene master batch resin with a wider melting range corresponding to the original polypropylene resin powder resin;

(2) fully compounding 300g of polypropylene master batch resin, 1g of inorganic nucleating agent talcum powder with the function of alpha crystallization nucleating agent, 100.3 g of alpha crystallization nucleating agent NA, 0.4g of alpha crystallization nucleating agent sorbitol (3904) and 5g of auxiliary agent by a high-speed mixer, extruding by a double screw rod, water cooling, drawing strips, and cutting granules to obtain modified polypropylene small particles with the length of 1.5mm and the diameter of 1.2 mm; ,

(3) putting polypropylene particles, a dispersing agent and water into a high-pressure kettle, injecting a physical foaming agent into the high-pressure kettle under the stirring condition, simultaneously raising the temperature of the high-pressure kettle to 135 ℃ and the pressure to 3.5MPa, and keeping for 30min after the set temperature and pressure are reached to enable the foaming agent to permeate into the polypropylene particles;

(4) and injecting the polypropylene particle-high pressure water dispersion mixed material into a cold water cooling system at a controllable pressure release speed of 1.0MPa/s in the high-pressure kettle, controlling the pressure of 0.3MPa in a secondary foaming device in a steam atmosphere, maintaining the pressure for 30s, and releasing the pressure to further obtain the polypropylene foaming beads with higher foaming ratio, wherein the foaming ratio is 30 times. The cell density was 0.035 g/cc. (5) And drying the prepared polypropylene expanded beads for 12 hours in an environment at 60 ℃, injecting the dried polypropylene expanded beads into a steam compression molding device, heating by steam, and cooling to obtain a polypropylene expanded bead molding body.

Example 3

(1) Fully mixing 0.09g of beta nucleating agent light calcium carbonate and 600g of random polypropylene resin powder with the melting point of 137 ℃ by a high-speed mixer, and granulating by a double screw to prepare polypropylene master batch resin with a wider melting range corresponding to the original polypropylene resin powder resin;

(2) fully compounding 300g of polypropylene master batch resin, 1.2g of inorganic nucleating agent mica with the function of alpha crystallization nucleating agent, NA-110.3 g of alpha crystallization nucleating agent, 0.4g of alpha crystallization nucleating agent sorbitol (3940) and 7g of auxiliary agent by a high-speed mixer, extruding by a double screw rod, water cooling, drawing strips and cutting into granules to obtain modified polypropylene small particles with the length of 1.5mm and the diameter of 1.2 mm; ,

(3) putting the polypropylene particles, the dispersing agent and water into an autoclave, injecting a physical foaming agent into the autoclave under the stirring condition, simultaneously raising the temperature of the autoclave to 132 ℃ and the pressure to 3.5MPa, and keeping for 30min after the set temperature and pressure are reached to enable the foaming agent to permeate into the polypropylene particles;

(4) and injecting the polypropylene particle-high pressure water dispersion mixed material into a cold water cooling system at a controllable pressure release speed of 1.0MPa/s in the high-pressure kettle, controlling the pressure of 0.3MPa in a secondary foaming device in a steam atmosphere, maintaining the pressure for 30s, and releasing the pressure to further obtain the polypropylene foaming beads with higher foaming ratio, wherein the foaming ratio is 35 times. The cell density was 0.029 g/cc. (5) And drying the prepared polypropylene expanded beads for 12 hours in an environment at 60 ℃, injecting the dried polypropylene expanded beads into a steam compression molding device, heating by steam, and cooling to obtain a polypropylene expanded bead molding body.

Example 4

(1) 0.009g of beta nucleating agent WBG and 600g of random polypropylene resin powder with the melting point of 135 ℃ are fully mixed by a high-speed mixer and granulated by a double screw to prepare polypropylene master batch resin with wider melting range corresponding to the original polypropylene resin powder resin;

(2) fully compounding 300g of polypropylene master batch resin, 1.2g of inorganic nucleating agent mica with the function of alpha crystallization nucleating agent, NA-110.3 g of alpha crystallization nucleating agent, 0.4g of alpha crystallization nucleating agent sorbitol (3988) and 7g of auxiliary agent by a high-speed mixer, extruding by a double screw rod, water cooling, drawing strips and cutting into granules to obtain modified polypropylene small particles with the length of 1.5mm and the diameter of 1.2 mm; ,

(3) putting the polypropylene particles, the dispersing agent and water into an autoclave, injecting a physical foaming agent into the autoclave under the stirring condition, simultaneously raising the temperature of the autoclave to 129 ℃ and the pressure to 3.5MPa, and keeping for 30min after the set temperature and pressure are reached to enable the foaming agent to permeate into the polypropylene particles;

(4) and injecting the polypropylene particle-high pressure water dispersion mixed material into a cold water cooling system at a controllable pressure release speed of 1.5MPa/s in the high-pressure kettle, controlling the pressure of 0.3MPa in a secondary foaming device in a steam atmosphere, maintaining the pressure for 30s, and releasing the pressure to further obtain the polypropylene foaming beads with higher foaming ratio, wherein the foaming ratio is 45 times. The density of the foam is 0.019 g/cc. (5) And drying the prepared polypropylene expanded beads for 12 hours in an environment at 60 ℃, injecting the dried polypropylene expanded beads into a steam compression molding device, heating by steam, and cooling to obtain a polypropylene expanded bead molding body.

The above examples illustrate the present invention in detail. It is to be understood that the above description is not intended to limit the present invention, and the present invention is not limited to the above examples, and that various changes, modifications, additions, deletions, and substitutions which may be made by those skilled in the art within the spirit of the present invention are also within the scope of the present invention.

Claims

1. A method for preparing high-strength anti-retraction microporous polypropylene foam beads by utilizing layer-by-layer crystallization assembly control is characterized by comprising the following steps: the formula is as follows: taking 20-95 parts of atactic polypropylene powder as matrix resin; 0.0001-2 parts of beta crystal nucleating agent; the alpha crystal nucleating agent comprises 0.0001-3 parts of total alpha crystal nucleating agent and 2-15 parts of auxiliary agent.

2. The random polypropylene powder as a matrix resin according to claim 1, wherein: the random polypropylene powder is a blend of one or more of copolymers of propylene (the molar content of propylene in the copolymer is 50-99%) and ethylene (the molar content of ethylene in the copolymer is 0-15%), 1-butene (the molar content of 1-butene in the copolymer is 0-45%), 1-pentene (the molar content of 1-pentene in the copolymer is 0-20%), 1-hexene (the molar content of 1-hexene in the copolymer is 0-20%), 1-heptene (the molar content of 1-heptene in the copolymer is 0-20%), 1-octene (the molar content of 1-octene in the copolymer is 0-20%), 1-nonene (the molar content of 1-nonene in the copolymer is 0-20%), 1-decene (the molar content of 1-decene in the copolymer is 0-20%), wherein the molecular weight distribution Mw/Mn of the copolymer is 2-20, the melt flow index (190 ℃, 2.16Kg) is 1-15 g/10 min.

3. The method for preparing high-strength anti-retraction cellular polypropylene expanded beads by layer-by-layer crystallization assembly control as claimed in claim 1, wherein the beta crystallization nucleating agent is one or a mixture of two or more of organic carboxylic acid and its salts (referring to salts of dicarboxylic acid and group IIA metal elements, especially binary compound of pimelic acid and calcium stearate), aromatic amide TMB series and rare earth complex WBG series, and the amount is 0.0001-2 parts.

4. The method for preparing high-strength shrinkage-resistant cellular polypropylene expanded beads by using layer-by-layer crystallization assembly control as claimed in claim 1, wherein the alpha crystal nucleating agent comprises three or more than three of series of alpha crystal nucleating agents such as inorganic nucleating agents with alpha crystal nucleating function, alpha crystal nucleating agent aromatic carboxylates, alpha crystal nucleating agent sorbitols and the like, and the total alpha crystal nucleating agent is 0.0001-3 parts by weight.

5. The method for preparing the high-strength retraction-resistant cellular polypropylene expanded beads by utilizing layer-by-layer crystallization assembly control as claimed in claim 1, wherein the auxiliary agent is one or more of a foaming nucleating agent, an antioxidant, an antistatic agent, a flame retardant, a color master batch and a coupling agent. The dosage of the auxiliary agent is 2-15 parts.

6. The method for preparing high-strength shrinkage-resistant cellular polypropylene expanded beads by using layer-by-layer crystallization assembly control as claimed in claim 1, wherein the foam nucleating agent in the auxiliary agent of claim 5 is at least one of talc powder, mica, glass beads, silica, calcium carbonate, montmorillonite, kaolin, alumina, barium sulfate, zinc oxide, zinc stearate, and calcium stearate; the antioxidant is at least one of antioxidants 168, 1010, 1076 and 626; the antistatic agent is alkyl imidazoline, quaternary phosphonium salt, quaternary sulfur salt, quaternary ammonium salt, alkyl sulfonate or phosphate; the flame retardant is one or more of magnesium hydroxide, aluminum hydroxide, zinc borate and intumescent flame retardant DTPB; the coupling agent is one or more of silane coupling agent, titanate coupling agent and aluminate coupling agent.

7. The method for preparing high-strength shrinkage-resistant microporous polypropylene expanded beads (EPP) by using layer-by-layer crystallization assembly control according to any one of claims 1 to 6, comprising the following steps:

8. The method of claim 7, wherein the dispersant is one or more of kaolin, sodium dodecylbenzenesulfonate, aluminum sulfate, calcium carbonate, barium sulfate, and aluminosilicate.

9. The method of claim 7, wherein the physical blowing agent is one or both of carbon dioxide and nitrogen.

10. The method according to claim 7, wherein in the step (4), the pressure release rate of the autoclave is 0.3 to 2.0MPa/s, and the cooling rate of the polypropylene particle-water dispersion mixture is 20 to 40 ℃/s.