An adhesive for artificial stone and its preparation method

Abstract

The present invention belongs to the technical field of waste plastic recycling and reuse, and specifically relates to an adhesive for artificial stone and a preparation method thereof. The adhesive is prepared by depolymerizing waste PET through alcoholysis catalyzed by a catalyst, re-polycondensing the mother liquor containing impurities such as oligomers and monomers generated by the depolymerization of PET after alcoholysis and a solvent, and then diluting with a diluent. The performance of the adhesive can be regulated by controlling the process conditions of depolymerization and polycondensation. By mass percentage, the composition of the adhesive for artificial stone is as follows: unsaturated polyester resin 70-90%; residual organic solution 5-30%; organic insoluble matter 0.5-5%; the balance is inorganic insoluble matter. The adhesive prepared by the present invention has excellent performance, and its preparation method is simple and the production cost is low. It can be used for large-scale industrial production, thus realizing the recycling and high-value reuse of waste plastics.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste plastic recycling and reuse, and particularly relates to an adhesive for artificial stone and a preparation method thereof. Background Art

[0002] Artificial stone is a new type of environmentally friendly composite material, which is made by mixing unsaturated polyester resin with fillers and pigments, adding a small amount of initiator, and through a certain processing procedure. Compared with traditional building materials such as stainless steel, ceramics, and natural stones, artificial stone has more diverse functions, richer colors, and a wider application range in the fields of indoor and outdoor decoration, kitchen countertops, washbasins, etc. As the core raw material of artificial stone, resin adhesives are usually made of polyester resin, epoxy resin, or acrylic resin. However, due to the high prices of epoxy resin and acrylic resin, they are mainly used in the manufacture of high-end materials. Therefore, the vast majority of artificial stone production uses polyester resin, especially unsaturated polyester resin (UPR). Unsaturated polyester resin is favored because of its low viscosity, easy molding, good gloss, light color, easy production of various bright colors and patterns, rapid curing, and operability at room temperature.

[0003] Currently, the industrial production of UPR adopts the vacuum distillation method, that is, unsaturated polyester (UP) is obtained by polycondensation of unsaturated dibasic acid and dibasic alcohol or saturated dibasic acid and unsaturated dibasic alcohol, and then diluted with vinyl monomers containing double bonds (such as styrene) to obtain unsaturated polyester resin. According to the position of the carboxyl group in the saturated dibasic acid in the raw materials, the production of unsaturated polyester resin can be divided into isophthalic, orthophthalic, and terephthalic unsaturated polyester resins. Since various types of unsaturated polyester resins have different performance emphases, the actual artificial stone adhesive will mix different types of resins according to requirements to prepare products with superior comprehensive performance. However, the main raw material of terephthalic unsaturated polyester resin, terephthalic acid, is relatively expensive, so it cannot be widely used in the mid- to low-end artificial stone field. Currently, an effective method to reduce the cost of terephthalic monomer raw materials is to convert waste polyethylene terephthalate (PET) into terephthalic oligomers or monomers, and then process them through the vacuum distillation method to prepare unsaturated polyester resin. This method not only effectively reduces the raw material cost of terephthalic oligomers or monomers, helps to improve the sustainability of artificial stone, but also realizes the recycling of waste plastics and environmental protection.

[0004] As one of the earliest developed, largest in production, and most widely used polyester products, PET accounts for approximately 18% of the global plastic market. However, the current recycling rate of PET only accounts for 28.4% of the total production. Therefore, it is urgent to effectively recycle PET. Currently, the conventional PET recycling methods at home and abroad mainly include physical and chemical methods. The physical method involves heating and melting PET and then extruding it into pellets. Although the process flow is relatively simple, it requires high-quality raw materials and multiple pretreatment processes, resulting in relatively high industrial production costs. Chemical degradation (and / or depolymerization) is the most common method, which mainly includes hydrolysis, alcoholysis, and aminolysis, etc. Alcoholysis is the most effective. In alcoholysis, the methanol alcoholysis process is relatively traditional and simple, but the product purification process is relatively complex. In addition, since the boiling point of methanol is low and the alcoholysis temperature is usually much higher than the boiling point of methanol, the methanolysis process inevitably involves high temperature and pressurization, which increases the safety issues of the process. The conditions required for glycol alcoholysis are milder (no high pressure) compared to methanolysis. It degrades (and / or depolymerizes) the polyester PET into diethylene glycol terephthalate or long-chain oligomers through a catalyst, thereby achieving the purpose of alcoholysis.

[0005] At present, in the process of repolymerizing PET into unsaturated resin after alcoholysis, the selection of catalysts in the alcoholysis step has always been the focus and difficulty of research. Commonly used catalysts include metal acetates (such as Zn, Co, Mn, etc.), titanium phosphate, stannous octoate, and superacids, etc. However, since the above catalysts can all dissolve in the solvent, the color and quality of the unsaturated resin after depolymerization are greatly affected, and it is difficult to separate the catalyst from the product, and it cannot be reused. In order to facilitate the separation of the catalyst from the depolymerization product, many heterogeneous catalysts have been developed by researchers. These catalysts are usually metal oxides that have been specially compounded and modified. They have good thermal stability and can be used for the alcoholysis of PET at higher temperatures. Moreover, such catalysts are insoluble in the solvent and are more easily separated from the PET degradation (and / or depolymerization) products, which helps to improve the quality of the repolymerized products. However, due to the large particle size of the existing metal oxide catalysts, their catalytic activity and catalytic effect are far less than those of homogeneous catalysts such as metal salts. Therefore, in the field of using waste PET for degradation (and / or depolymerization) and then preparing unsaturated resin binders, it is necessary to combine the advantages and disadvantages of soluble catalysts (homogeneous catalysts) and heterogeneous catalysts, and develop a quasi-homogeneous catalyst that combines the advantages of both and overcomes the disadvantages of both. Among them, quasi-homogeneous catalysis means that the catalyst is uniformly dispersed in the medium in the form of nanoparticles to form a quasi-homogeneous system for catalytic reactions. The term quasi-homogeneous catalysis comes from colloid chemistry and can be classified into the category of homogeneousization of heterogeneous catalysts, that is, the mechanism is still heterogeneous catalysis, but it can achieve nanoscale uniform dispersion in the solvent. This approximately homogeneous system is conducive to the full contact between the reactants and the catalyst, reduces the problem of mass transfer and diffusion, and thus improves the catalytic activity. In addition, the quasi-homogeneous catalyst can also be left in the product mother liquor containing the depolymerized monomers or oligomers as a functional additive without separation, and is used for the subsequent synthesis of high-value-added functional unsaturated polyester resins, so that the process of preparing unsaturated resin binders by alcoholysis of waste PET can save the process of filtering and separating the catalyst, impurities and alcoholysis products after alcoholysis.

[0006] In addition, since commercial PET on the market needs to meet the requirements of specific fields, PET plastics need to be modified and colored. The modification of PET plastics can be divided into the following methods: ① Filling modification: The properties of PET plastics are changed by adding fillers. Commonly used fillers include glass fiber, carbon fiber, graphite, silicate, etc. Filling modification can improve the strength, stiffness and heat resistance of PET. ② Initiator modification: The characteristics of PET plastics are changed by adding initiators. Initiators can initiate cross-linking reactions, thereby improving the thermal stability and chemical resistance of PET. ③ Additive modification: The properties of PET plastics are changed by adding various additives. Commonly used additives include plasticizers, flame retardants, antioxidants, stabilizers, etc. Additive modification can improve the processing performance, weather resistance and flame retardant performance of PET. ④ Blending modification: PET plastics are blended with other polymers, and the properties of PET are changed by changing the compatibility. Commonly used blends include PET / polycarbonate, PET / polyamide, etc. Blending modification can improve the toughness, impact resistance and heat resistance of PET. ⑤ Chemical modification: The structure and properties of PET plastics are changed through chemical reactions. Commonly used chemical modification methods include transesterification reaction, acid-catalyzed reaction, acid anhydride method, etc. The above chemical modification can change the molecular structure of PET, making it more complex and dense, while improving its properties, it will also increase the difficulty of alcoholysis reaction. Therefore, commercial PET plastics may contain enhanced PET, fillers and other polymers, which are usually not easily alcoholyzed, and then need to be removed by filtering the mother liquor after alcoholysis. Otherwise, the PET containing impurities can usually only be recycled at a lower grade, and the recycled materials are reduced in quality and function compared with the raw materials. At the same time, no matter how it is recycled, it will eventually become waste. In addition, the equivalent recycling of PET containing impurities also faces economic problems. For example, during 2021 in Europe, the cost of the most common recycled plastic type (post-consumer PET) doubled and became more expensive than its virgin plastic equivalent. Through comprehensive analysis, the current research focus of the technology for depolymerizing and recycling waste PET to manufacture artificial stone binders is concentrated in the following aspects: (1) New technologies for economic and efficient degradation (and / or depolymerization) of waste PET; (2) New technologies for polymerizing the products after degradation (and / or depolymerization) of waste PET and the mother liquor containing impurities; (3) Reducing the cost of the binder and improving the performance of the binder.

[0007] Chinese invention CN107840947A discloses a method for synthesizing unsaturated polyester using PET composite film waste, in which zinc acetate and stannous chloride are used as alcoholysis catalysts. Although the alcoholysis effect is good, both of these homogeneous catalysts are soluble in the solvent, and the catalysts cannot be separated, which will affect the quality of the subsequent products.

[0008] Chinese invention CN110156932A discloses a method for preparing unsaturated polyester resin from waste polyester textiles. Solid zinc oxide is used as an alcoholysis catalyst. This heterogeneous catalyst overcomes the drawback that homogeneous catalysts cannot be separated. However, due to the large particle size and poor dispersion performance of this solid catalyst, it still takes 4.5 - 5.5 h to complete alcoholysis even when the dosage is relatively large. At the same time, filtration and separation are still required after alcoholysis, and the steps are too complex.

[0009] Chinese invention CN111647147A discloses a method for preparing fiber - source unsaturated polyester resin from waste polyester textiles. After the polyester fiber is alcoholyzed, the un - alcoholyzed fibers separated out are used as fiber - reinforced materials for other purposes, and the liquid part after separation is subjected to a polycondensation reaction to obtain fiber - source unsaturated polyester resin with high bonding strength. Although this method prepares fiber - source unsaturated polyester resin with high bonding strength, it is necessary to filter the fiber - reinforced materials that cannot be alcoholyzed, and the preparation process is complex.

[0010] I. Duque - Ingunza et al. published an article "Synthesis of unsaturated polyester resin from glycolysed postconsumer PET wastes" in Journal of Material Cycles and Waste Management (Volume 15, 2013). They used sodium carbonate as a homogeneous catalyst, and after reacting the purified precipitated BHET with other raw materials, it was converted into unsaturated polyester resin, and its comprehensive performance was excellent. However, this preparation method requires the mother liquor after alcoholysis to be placed at low temperature with water injection. By using the difference in solubility, the monomer BHET is precipitated in water, filtered, dried, and then converted. This preparation method will cause partial monomer loss, and the steps are too complex.

[0011] Therefore, there is an urgent need to develop a technology for manufacturing artificial stone binders with high efficiency and low cost. Specifically, it is to provide an economical and efficient new method for depolymerizing waste PET, a new technology for polycondensing the products after depolymerization to synthesize unsaturated resins, and then applying the unsaturated resins to artificial stone binders. Summary of the Invention

[0012] Aiming at the problems of high raw material cost and complex preparation process of resin - type binders in the existing market, the present invention provides a binder for medium - and low - end artificial stone. When this binder is mixed and pressed with inorganic artificial stone aggregates of different sizes and shapes for artificial stone, it has the characteristic of self - adapting molecular weight (viscosity) distribution. The present invention also provides a preparation method for the binder for artificial stone. For plastic products with a PET content ≥ 80%, there is no need for complex sorting and purification processes. At the same time, the quasi - homogeneous catalyst can be left in the mother liquor containing impurities without separation after alcoholysis and directly used for the polymerization reaction, saving the filtration step. The binder containing impurities also contains organic insolubles and inorganic insolubles, both of which can be used as fillers for artificial stone.

[0013] The binder for artificial stone described in the present invention is obtained by treating through three processes: depolymerization of waste PET by catalytic alcoholysis, re - polycondensation, and dilution.

[0014] By mass percentage, the composition of the binder for artificial stone is as follows:

[0015]

[0016] Among them, the unsaturated polyester resin is divided into oligomers with an average molecular weight divided into oligomers, mid - polymers with and high - polymers with

[0017] The PET content in the waste PET ≥ 80%. The waste PET includes, but is not limited to, waste bottle - grade, packaging protective films, electrical and electronic products, polyester, plastic processing leftovers collected by factories, and various waste plastic products including used materials and textile fibers.

[0018] The unsaturated polyester resin is p - type unsaturated polyester resin.

[0019] The remaining organic solvents are one or more of alcohols, antioxidants, acid anhydrides, polycondensation catalysts, diluents, or polymerization inhibitors.

[0020] The organic insolubles are polymers that are difficult to alcoholyze, and are one or more of polyethylene, polypropylene, polyvinyl chloride, polystyrene, acrylonitrile - butadiene - styrene copolymer, or modified PET.

[0021] The inorganic insolubles are nano - metal - oxide - based crystal particles in the quasi - homogeneous catalyst and inorganic modifiers contained in the waste PET.

[0022] The alcohols include, but are not limited to, polyols; the polyols include one or more of ethylene glycol, diethylene glycol, propylene glycol, glycerol, or neopentyl glycol, preferably one or more of ethylene glycol or diethylene glycol.

[0023] The antioxidant is one or more of triphenyl phosphate or phenothiazine; preferably triphenyl phosphate.

[0024] The acid anhydride includes but is not limited to maleic anhydride or tetrahydrophthalic anhydride.

[0025] The polycondensation catalyst includes but is not limited to one or more of benzoic acid, sulfuric acid or phosphoric acid.

[0026] The diluent includes but is not limited to one or more of styrene, vinyltoluene, divinylbenzene, methyl methacrylate, diallyl phthalate or triallyl cyanurate.

[0027] The polymerization inhibitor includes but is not limited to one or more of hydroquinone, p-methoxyphenol, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, 2-tert-butylhydroquinone, p-benzoquinone or methylhydroquinone.

[0028] The modified PET is one or more of crystalline modified PET, glass fiber reinforced modified PET, chemically modified PET or blended modified PET.

[0029] The crystalline modified PET is one or more after being modified by a nucleating agent or a crystallization accelerator.

[0030] The nucleating agent includes monomer types (carbon black, graphite, zinc powder, aluminum powder); metal oxide types (ZnO, MgO, Al 2 O 3 , Fe 3 O 4 ); clay types (talc, clay, pyrophyllite); inorganic salts such as carbonates (Na 2 CO 3 , MgCO 3 ), silicates (CaSiO 3 , MgSiO 3 ), sulfates (CaSO 4 , RaSO 4 ), phosphates (Ca 3 (PO 4 ) 2 , Mg 3 (PO 4 ) 2 ; organic salts such as Na, Li, Ba, Mg, Ca salts of monocarboxylic acids, Na, K, Ca salts of benzoic acid, Na, K salts of aromatic hydroxy sulfonic acids, Mg, Zn salts of organic phosphorus compounds; high molecular substances such as polytetrafluoroethylene powder and high melting point PET; nano-inorganic composite modification types (nano-SiO 2 , nano-TiO2 , one or more of nano-montmorillonite).

[0031] The crystallization promoter includes one or more of low molecular weight compounds (benzophenone, tetrachloroethane, polyethylene glycol dibenzoate, triphenyl phosphate, phthalate, amide ester, imide ester), high molecular weight compounds such as polycaprolactone and its end-capped compounds, polyglycols (polyethylene glycol, polypropylene glycol and their end-capped compounds), polyolefins (alicyclic carboxylic acid modified polyolefins), and polyamides.

[0032] The glass fiber reinforced modified PET is PET modified by one or more of glass fiber, carbon fiber, γ-aminopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and polyvinylpyrrolidone.

[0033] The chemically modified PET is PET copolymer modified by one or more of neopentyl glycol, polyethylene naphthalate, and polybutylene glycol.

[0034] The blend modified PET is PET blend modified by one or more of nylon 6, polyhexamethylene adipamide, methyl methacrylate, glycidyl methacrylate grafted polyethylene, polypropylene, ethylene-propylene copolymer, acrylonitrile-butadiene-styrene terpolymer, styrene-butadiene-styrene triblock copolymer, hydrogenated styrene-butadiene-styrene triblock copolymer, ethylene-propylene rubber, and nitrile rubber.

[0035] The quasi-homogeneous catalyst described is a monodisperse nano-metal oxide-based dispersion, and the monodisperse nano-metal oxide-based dispersion is one or more of a monodisperse nano-zinc oxide-based dispersion, a monodisperse nano-ceria-based dispersion, a monodisperse nano-cobalt oxide-based dispersion, a monodisperse nano-tin oxide-based dispersion, a monodisperse nano-ferroferric oxide-based dispersion, or a monodisperse nano-manganic manganic oxide-based dispersion; preferably a monodisperse nano-zinc oxide-based dispersion; the average particle size of the metal oxide-based particles in the nano-metal oxide-based dispersion is 1-100 nm, preferably 1-30 nm.

[0036] The monodisperse nano-zinc oxide-based dispersion is a dispersion in which one or more of the secondary phase metal elements cerium, cobalt, tin, iron, manganese, titanium, and antimony are doped into the nano-zinc oxide crystal particles with the primary phase metal element being zinc;

[0037] The monodisperse nano-ceria-based dispersion is a dispersion in which one or more of the secondary phase metal elements zinc, cobalt, tin, iron, manganese, titanium, and antimony are doped into the nano-ceria crystal particles with the primary phase metal element being cerium;

[0038] The monodisperse nano cobalt oxide-based dispersion is a dispersion in which one or more of the secondary phase metal elements zinc, cerium, tin, iron, manganese, titanium, and antimony are doped into nano cobalt oxide crystal particles with cobalt as the primary phase metal element;

[0039] The monodisperse nano tin oxide-based dispersion is a dispersion in which one or more of the secondary phase metal elements zinc, cerium, cobalt, iron, manganese, titanium, and antimony are doped into nano tin oxide crystal particles with tin as the primary phase metal element;

[0040] The monodisperse nano iron oxide-based dispersion is a dispersion in which one or more of the secondary phase metal elements zinc, cerium, cobalt, tin, manganese, titanium, and antimony are doped into nano iron oxide crystal particles with iron as the primary phase metal element;

[0041] The monodisperse nano manganese oxide-based dispersion is a dispersion in which one or more of the secondary phase metal elements zinc, cerium, cobalt, tin, iron, titanium, and antimony are doped into nano manganese oxide crystal particles with manganese as the primary phase metal element;

[0042] The molar fraction of the secondary phase metal element in the primary phase metal element is 1-40%.

[0043] The quasi-homogeneous catalyst described above is a monodisperse nano metal oxide-based dispersion, and the monodisperse nano metal oxide-based dispersion is a composition of nano metal oxide crystal particles, a surfactant, and a liquid solvent.

[0044] The mass of the nano metal oxide crystal particles is 10-50% of the total mass of the quasi-homogeneous catalyst, preferably 20-40% of the total mass of the quasi-homogeneous catalyst, and more preferably 25-35% of the total mass of the quasi-homogeneous catalyst.

[0045] The surfactant is one or more of a silane coupling agent, a non-silane surface modifier, or a titanate coupling agent.

[0046] The mass of the surfactant is 0.1-5% of the total mass of the quasi-homogeneous catalyst, preferably 0.5-3% of the total mass of the quasi-homogeneous catalyst.

[0047] The liquid solvent is a mixture of alcohol and water, and in the liquid solvent, the alcohol and water are mixed in any ratio.

[0048] The alcohol in the liquid solvent is one or more of a monohydric alcohol or a polyhydric alcohol.

[0049] The monohydric alcohol in the liquid solvent includes one or more of ethanol, isopropanol, cyclohexanol, or isooctanol, preferably isooctanol.

[0050] The polyols in the liquid solvent include one or more of glycerol, ethylene glycol, diethylene glycol, propylene glycol, or neopentyl glycol, preferably one or more of diethylene glycol or ethylene glycol.

[0051] The mass of the liquid solvent is 45 - 85% of the total mass of the catalyst.

[0052] The inorganic modifiers contained in the waste PET include one or more of inorganic reinforcing fibers or mineral fillers.

[0053] The inorganic reinforcing fibers are one or more of ceramic fibers, metal fibers, carbon fibers, or glass fibers.

[0054] The mineral fillers are one or more of calcium carbonate (heavy calcium, light calcium, nano - calcium), talc powder, wollastonite, barite powder, barium sulfate, kaolin, bentonite, silica powder, quartz powder, mica powder, graphite, titanium dioxide, white carbon black, or dolomite powder.

[0055] The properties of the binder for artificial stone are as follows:

[0056] Appearance: colorless or light yellow transparent viscous liquid;

[0057] Thermal stability at 80°C: ≥24 h;

[0058] Viscosity: 0.5 - 2.5 Pa·s, at 25°C;

[0059] Gel time: 10 - 20 min, at 25°C.

[0060] The preparation method of the binder for artificial stone includes the following steps:

[0061] (1) Catalytic alcoholysis reaction: Add waste PET, alcohol, quasi - homogeneous catalyst, and antioxidant into the reaction kettle and stir. Carry out the catalytic alcoholysis reaction under nitrogen protection. After PET is depolymerized into monomers or oligomers, cool down to obtain a mother liquor containing impurities.

[0062] (2) Polycondensation reaction of the depolymerization product containing impurities: Add a polycondensation catalyst and acid anhydride into the mother liquor containing impurities, heat up and carry out the polycondensation reaction. When the solution reaches the initial acid value, turn on the external vacuum pump to evacuate the water by force. When the target acid value is reached, stop evacuating the vacuum, cool down, add a polymerization inhibitor and stir to obtain an unsaturated resin.

[0063] (3) Dilution: Continuously cool down the unsaturated resin, add a diluent, and mix evenly to obtain an unsaturated polyester resin binder, that is, the binder for artificial stone.

[0064] Among them:

[0065] The mass ratio of the waste PET: alcohol: quasi-homogeneous catalyst: antioxidant: anhydride: polycondensation catalyst: polymerization inhibitor: diluent is (3-4):(2-3):(0.005-0.05):(0.01-0.05):(1-2):(0.1-0.3):(0.005-0.01):(1-2).

[0066] In step (1), the temperature of the catalytic alcoholysis reaction is 150-250 °C, and the time of the catalytic alcoholysis reaction is 0.5-2 h.

[0067] In step (2), the temperature of the polycondensation reaction is 170-230 °C, the total time of the polycondensation reaction is 2-4 h, the heating rate is controlled to be lower than 15 °C / h, the initial acid value is 30-40 mgKOH / g, the target acid value is 5-25 mgKOH / g, the temperature is decreased to 180-190 °C, and a polymerization inhibitor is added and stirred for 0.5-1 h.

[0068] In step (2), the method used for acid value detection is potassium hydroxide reagent detection.

[0069] In step (2), when evacuating, the vacuum degree is maintained not to exceed -0.086 MPa.

[0070] In step (3), the unsaturated resin is further cooled to 80-100 °C, and the temperature of the diluent is maintained at 70-90 °C.

[0071] In step (1), the PET catalytic alcoholysis catalyst preferably uses a quasi-homogeneous catalyst, which is a liquid-phase dispersion with monodisperse nano-metal oxide-based nanoparticles as the catalyst. The metal oxide-based particles in the dispersion are in a highly dispersed state, such as a monodisperse state or a state with only slight soft agglomeration. In the reaction of alcoholyzing PET, the catalyst particles exist in the form of monodisperse or nearly monodisperse particles, and can be in full contact with PET, and almost no diffusion (including external diffusion and internal diffusion resistance) in the heterogeneous catalytic process needs to be overcome, thus approximately achieving the homogeneous catalytic effect, which is the quasi-homogeneous catalytic effect. When using this quasi-homogeneous catalyst to catalyze the alcoholysis of PET, we unexpectedly found that when the quasi-homogeneous catalyst alcoholyzes PET, it depolymerizes PET into oligomers and monomers, rather than degrading PET.

[0072] In steps (1) and (2), the mother liquor containing impurities includes monomers and their oligomers, organic insoluble substances, inorganic insoluble substances, nano-metal oxide-based crystal particles, and alcohol, etc.

[0073] The monomers and their oligomers include, but are not limited to, one or more of bis(2-hydroxyethyl) terephthalate and its oligomers, dimethyl terephthalate and its oligomers, and diethylene glycol terephthalate and its oligomers.

[0074] In the present invention, the preparation of the nano-zinc oxide crystal particles used in the quasi-homogeneous catalyst can adopt the methods of US Invention US2010028236A1 and US2010298123A1, and then through formulation modulation, further phase transfer dispersion and other process methods to obtain a quasi-homogeneous catalyst characterized by a nano-zinc oxide-based dispersion that can depolymerize polyester. Its advantages are that the metal oxide crystal particles in the quasi-homogeneous catalyst have small particle size, uniform particle size, are easy to disperse, and at the same time the preparation method is economical, efficient and can be mass-produced.

[0075] The waste PET feeding equipment used in the present invention is composed of a sorting equipment, a cleaning equipment, a PE jaw crusher, a first bucket elevator, a pulse dust collector, a pulverizer, a second bucket elevator and a storage bin. The initial materials are screened and separated by the sorting equipment, the excess sand and other impurities are washed away by the cleaning equipment, and are transported by a vibrating conveyor belt, initially crushed by the PE jaw crusher, then secondary processed by the pulverizer, and separated and refluxed by a grinding head sieve. The refluxed materials need to be pulse dusted. The material conveying devices are all bucket elevators for conveying, and a dust collector needs to be installed on the top of the storage bin. After the initial materials are sorted, cleaned and pulverized, the diameter of the waste PET particles remains between 0.1 mm and 20 mm.

[0076] The reaction equipment in the present invention is successively connected by a storage tank, a gas pressure control room, a reflux device and a heating and stirring reaction kettle. The storage tank is also used as a safety tank at the same time. At the start of the reaction, raw material alcohol solution, waste PET, catalyst, etc. are added, the nitrogen valve is opened. After the reaction is complete, a small amount of product is collected at the discharge port for inspection. After passing the inspection, the next step is carried out. The storage tank is a storage tank for temporarily storing the raw material alcohol solution and also a safety tank. Negative pressure is involved in this reaction. To avoid safety accidents, the gas pressure control room is not directly connected to the reaction kettle. Equipment inspection and daily maintenance should be done well for chemical unit operations.

[0077] "Inorganic artificial stone aggregate" refers to the main component used to manufacture artificial stone materials, usually natural stone or quartz sand. The aggregate plays a role in filling and strengthening the material during the manufacture of artificial stone. Common artificial stone aggregates include: ① Natural stone: such as marble, granite, limestone, etc.; ② Quartz sand.

[0078] "PET containing impurities" means that pure PET needs to be modified to a certain extent to meet the usage requirements of a certain application. Therefore, in the PET materials circulating in the market, in addition to pure PET, there are also certain functional additives, organic and inorganic reinforcing materials, etc. At the same time, a very small amount of other plastic insoluble substances will be doped in the actually recycled PET.

[0079] For polymers, "depolymerization" refers to the reaction of decomposing covalently bonded polymers (such as polyesters, polysaccharides, etc.) into oligomers and / or monomers by chemical methods (such as acidolysis or alkalinolysis) or enzymatic methods. "Degradation" means the decomposition of macromolecules of high molecular compounds into smaller molecules. Plastic degradation is the decrease in the molecular weight of polymers and the deterioration of the physical properties of polymer materials (plastics). Typical manifestations are: plastics becoming brittle, cracked, softened, hardened, losing mechanical strength, etc. The aging and deterioration of plastics are a kind of degradation phenomenon. When "monodisperse" is associated with metal oxide particles, its general definition refers to the dispersion index of metal oxide particles in a liquid medium.

[0080] Generally, the "dispersion index" is defined as the second average particle size of the particles (obtained by analyzing with a dynamic light scattering instrument (DLS) (d DLS )) divided by the initial average particle size of the particles (generally measured by TEM or SEM (d TEM , D SEM ))). The smaller the dispersion index, the closer the dispersion liquid is to monodisperse. The typical dispersion index of monodisperse is less than 10 and greater than 1. Generally speaking, "monodisperse" means that the particles in the liquid medium basically do not agglomerate or form lumps, and are dispersed in the liquid medium at the same time. When a quasi-homogeneous catalyst characterized by a monodisperse nano-metal oxide-based dispersion is used for the catalytic depolymerization of plastics, its essence is still heterogeneous catalysis. However, due to the small particle size and uniform dispersion in the solvent at the nano level, this quasi-homogeneous system breaks through the theoretical boundaries between homogeneous and heterogeneous systems, is conducive to the full contact between reactants and catalysts in the waste PET alcoholysis system, reduces the mass transfer resistance, and thus improves the catalytic activity.

[0081] The beneficial effects of the present invention are as follows:

[0082] 1. In the process of depolymerizing waste PET for producing the binder for artificial stone, the advantages of using a quasi-homogeneous catalyst to depolymerize waste PET are as follows:

[0083] (1) The quasi-homogeneous catalyst is a non-heavy metal oxide-based nano-dispersion, which is non-toxic and more environmentally friendly;

[0084] (2) Due to the nano-effect and good dispersion of the quasi-homogeneous catalyst particles, the amount of catalyst used is small, the catalytic efficiency is high, the time is short, and the reaction temperature is low;

[0085] (3) The quasi-homogeneous catalyst particles can be separated from the alcoholysis products and can be recycled;

[0086] (4) The quasi-homogeneous catalyst can also remain in the monomers after depolymerization as an auxiliary agent without separation, and be used for the subsequent synthesis of high-value-added functional unsaturated polyester resins, such as artificial stones and process resins with excellent antibacterial and mildew-proof properties.

[0087] 2. The beneficial aspects of the binder for artificial stone prepared by the present invention in terms of process are as follows:

[0088] (1) The separation step of mother liquor impurities from PET monomers and oligomers is reduced in the process.

[0089] (2) The present invention can control the molecular weight (viscosity) distribution of the binder by controlling the process conditions of depolymerization and polycondensation, and the binder consumption can be saved in the preparation of artificial stone.

[0090] 3. The beneficial aspects of the binder for artificial stone prepared by the present invention are as follows:

[0091] (1) The binder for artificial stone prepared by the present invention can be precisely self-adapted to aggregates of different sizes, enabling the prepared artificial stone to have a more compact structure, thereby improving its strength, sealing performance, stain resistance and color stability, and greatly increasing the practicality and durability of the artificial stone.

[0092] (2) For the binder for artificial stone prepared by the present invention, the organic insoluble matters can be used as flexible fillers for artificial stone, increasing the flexibility, wear resistance or chemical resistance of the artificial stone; the inorganic insoluble matters can be used as rigid fillers for artificial stone, helping to fill the gaps between aggregates in the artificial stone and playing the functions of increasing strength, improving stability, enhancing texture and controlling costs during the manufacture of artificial stone, with high economic and environmental benefits.

[0093] (3) The binder for artificial stone prepared by the present invention is compounded with orthophthalic unsaturated resin and isophthalic unsaturated resin in proportion, and the fluidity, curing time, color, transparency, surface gloss of the resin itself, as well as the strength, hardness and heat resistance after curing can be regulated. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] Figure 1 Graph of the change of the molecular weight distribution of the binder with time in Example 1;

[0095] Figure 2 Schematic structural diagram of the waste PET feeding device;

[0096] Figure 3 Process flow chart of unsaturated polyester resin;

[0097] Figure 4 TEM electron micrograph of the monodisperse cobalt-doped zinc oxide dispersion in Example 1.

[0098] In the figure: 1. Sorting equipment; 2. Cleaning equipment; 3. PE jaw crusher; 4. First bucket elevator; 5. Pulse dust collector; 6. Pulverizer; 7. Second bucket elevator; 8. Storage bin; 9. Storage tank; 10. Pneumatic control room; 11. Return device; 12. Heating and stirring reaction kettle. Detailed implementation mode

[0099] The present invention will be specifically described and illustrated below in conjunction with embodiments.

[0100] Embodiment 1

[0101] The quasi-homogeneous catalyst in this embodiment is a monodisperse nano-zinc oxide-based dispersion, which contains cobalt-doped nano-zinc oxide crystal particles, silane coupling agent KH-550, and ethylene glycol.

[0102] Among them, the molar ratio of cobalt to zinc in the cobalt-doped nano-zinc oxide crystal particles is 1:10, the mass of the cobalt-doped nano-zinc oxide crystal particles is 30% of the total mass of the quasi-homogeneous catalyst, the silane coupling agent KH-550 is 2% of the total mass of the quasi-homogeneous catalyst, and the rest is ethylene glycol. The particle size of the cobalt-doped nano-zinc oxide crystal particles is about 10 nm, and the dispersion index is about 2.

[0103] The binder for artificial stone is prepared according to the following steps:

[0104] (1) Catalytic alcoholysis reaction: Put 3.7 kg of waste PET, 2.5 kg of ethylene glycol, 0.0123 kg of monodisperse nano-zinc oxide-based dispersion, and 0.02 kg of antioxidant triphenyl phosphate into the reaction kettle, introduce nitrogen, gradually heat up to 210 °C, keep warm for 1 h, then remove the heating, and cool down to 160 °C to obtain a mother liquor containing impurities.

[0105] (2) Polycondensation reaction of the depolymerization product containing impurities: Directly add 1.7 kg of maleic anhydride and 0.19 kg of benzoic acid to the mother liquor containing impurities, control the heating rate, keep the temperature constant at 200 °C and react for 1.5 h. When the acid value is measured to be 32 mg KOH / g, turn on the external vacuum pump to evacuate the water, and the vacuum degree does not exceed -0.086 MPa. Continue to keep the temperature constant at 200 °C and react for 0.5 h until the acid value reaches 24 mg KOH / g. Stop evacuating, cool down to 185 °C, add 0.008 kg of hydroquinone, stir for 0.5 h, and continue to cool down.

[0106] (3) Dilution: When the temperature is cooled down to 90 °C, add 1.4 kg of styrene for dilution, keep the styrene at 90 °C, and mix evenly to obtain a resin product, that is, the binder for artificial stone.

[0107] The viscosity, average molecular weight of the binder for artificial stone and the content of each component in the resin were detected. As can be seen from Table 1, it is a finished product of oligomer binder, and the content of unsaturated polyester resin in the product is 70.39%.

[0108] Example 2

[0109] The binder for artificial stone was prepared according to the following steps:

[0110] (1) Catalytic alcoholysis reaction: Put 3.7 kg of waste PET, 2.5 kg of ethylene glycol, 0.0123 kg of the same quasi-homogeneous catalyst as in Example 1 and 0.02 kg of antioxidant triphenyl phosphate into the reaction kettle, introduce nitrogen, gradually heat up to 210 °C, keep warm for 1 h, then remove the heating, and cool down to 160 °C to obtain a mother liquor containing impurities.

[0111] (2) Polycondensation reaction of the depolymerization product containing impurities: Directly add 1.7 kg of maleic anhydride and 0.19 kg of benzoic acid to the mother liquor containing impurities. Control the heating rate, keep the temperature at 200 °C and react for 1.5 h. Then, when the acid value is measured to be 35 mg KOH / g, turn on the external vacuum pump to evacuate the water. The vacuum degree does not exceed -0.086 MPa, and continue to keep the temperature at 200 °C and react for 1.5 h until the acid value reaches 15 mg KOH / g. Stop evacuating the vacuum, cool down to 185 °C, add 0.008 kg of hydroquinone, stir for 0.5 h, and continue to cool down.

[0112] (3) Dilution: When the temperature is cooled down to 90 °C, add 1.4 kg of styrene for dilution, and mix evenly to obtain the resin product, that is, the binder for artificial stone.

[0113] The viscosity, average molecular weight of the binder for artificial stone and the content of each component in the resin were detected. As can be seen from Table 1, it is a finished product of medium polymer binder, and the content of unsaturated polyester resin in the product is 78.51%.

[0114] Example 3

[0115] The binder for artificial stone was prepared according to the following steps:

[0116] (1) Catalytic alcoholysis reaction: Put 3.7 kg of waste PET, 2.5 kg of ethylene glycol, 0.0123 kg of the same quasi-homogeneous catalyst as in Example 1 and 0.02 kg of triphenyl phosphate into the reaction kettle, introduce nitrogen, gradually heat up to 210 °C, keep warm for 1 h, then remove the heating, and cool down to 160 °C to obtain a mother liquor containing impurities.

[0117] (2) Polycondensation reaction of the depolymerized product with impurities: Directly add 1.7 kg of maleic anhydride and 0.19 kg of benzoic acid to the mother liquor containing impurities. Control the heating rate, keep the reaction at 200 °C for 1.5 h, and when the acid value is measured to be 38 mg KOH / g, turn on the external vacuum pump to evacuate the water, with the vacuum degree not exceeding -0.086 MPa. Continue to keep the reaction at 200 °C for 2.5 h until the acid value reaches 8 mg KOH / g. Stop evacuating the vacuum, cool down to 185 °C, add 0.008 kg of hydroquinone, stir for 0.5 h, and continue to cool down;

[0118] (3) Dilution: When the temperature is cooled down to 90 °C, add 1.4 kg of styrene for dilution, and mix evenly to obtain the resin product, that is, the binder for artificial stone.

[0119] The viscosity, average molecular weight and the content of each component in the resin of the binder for artificial stone are detected. As can be seen from Table 1, it is a finished product of a high-polymer binder, and the content of unsaturated polyester resin in the product is 87.96%.

[0120] Comparative Example 1

[0121] The binder for artificial stone is prepared according to the following steps:

[0122] (1) Catalytic alcoholysis reaction: Put 3.7 kg of waste PET, 2.5 kg of ethylene glycol, 0.0123 kg of commercially available nano-zinc oxide (the initial average particle size d TEM is about 30 nm and there is serious agglomeration) and 0.02 kg of triphenyl phosphate into the reaction kettle, introduce nitrogen, gradually heat up to 210 °C, keep warm for 1 h, then remove the heating and cool down to 160 °C to obtain the mother liquor containing impurities;

[0123] (2) Polycondensation reaction of the depolymerized product with impurities: Directly add 1.7 kg of maleic anhydride and 0.19 kg of benzoic acid to the mother liquor containing impurities. Control the heating rate, keep the reaction at 200 °C for 1.5 h, and when the acid value is measured to be 30 mg KOH / g, turn on the external vacuum pump to evacuate the water, with the vacuum degree not exceeding -0.086 MPa. Continue to keep the reaction at 200 °C for 2.5 h until the acid value reaches 26 mg KOH / g. Stop evacuating the vacuum, cool down to 185 °C, add 0.008 kg of hydroquinone, stir for 0.5 h, and continue to cool down;

[0124] (3) Dilution: When the temperature is cooled down to 90 °C, add 1.4 kg of styrene for dilution, and mix evenly to obtain the resin product, that is, the binder for artificial stone.

[0125] The viscosity, average molecular weight and the content of each component in the resin of the binder for artificial stone are detected. As can be seen from Table 1, it is a finished product of a high-polymer binder, and the content of unsaturated polyester resin in the product is 83.29%.

[0126] Example 4

[0127] Mix fine quartz sand with a particle diameter of 0 - 0.25 mm: medium quartz sand with a particle diameter of 0.25 - 0.5 mm: coarse quartz sand with a particle diameter of 0.5 - 1 mm: large quartz sand with a particle diameter of 1 - 30 mm: fine glass sand with a particle diameter of 0 - 0.25 mm: medium glass sand with a particle diameter of 0.25 - 0.5 mm evenly according to the mass ratio of 30:20:20:10:10:10 to obtain inorganic composite aggregate. Add 5 parts of the oligomer binder finished product of Example 1, 5 parts of the polymer binder finished product of Example 3, 1.0 part of KH-550 silane coupling agent, 1.4 parts of benzoyl peroxide (BPO), and 0.02 part of tetramethylthiuram disulfide (TMTD) accelerator to 100 parts of the inorganic composite aggregate. After mixing them evenly, inject them into a mold, and carry out medium-temperature curing at 30°C for 6.0 h after vacuum vibration compaction molding. After it is molded, an artificial stone plate is obtained, and the product can be obtained after cutting and polishing.

[0128] Example 5

[0129] Mix fine quartz sand with a particle diameter of 0 - 0.25 mm: medium quartz sand with a particle diameter of 0.25 - 0.5 mm: coarse quartz sand with a particle diameter of 0.5 - 1 mm: large quartz sand with a particle diameter of 1 - 30 mm: fine glass sand with a particle diameter of 0 - 0.25 mm: medium glass sand with a particle diameter of 0.25 - 0.5 mm evenly according to the mass ratio of 30:20:20:10:10:10 to obtain inorganic composite aggregate. Add 5 parts of the middle polymer binder finished product of Example 2, 5 parts of the polymer binder finished product of Example 3, 1.0 part of KH-550 silane coupling agent, 1.4 parts of benzoyl peroxide (BPO), and 0.02 part of tetramethylthiuram disulfide (TMTD) accelerator to 100 parts of the inorganic composite aggregate. After mixing them evenly, inject them into a mold, and carry out medium-temperature curing at 30°C for 6.0 h after vacuum vibration compaction molding. After it is molded, an artificial stone plate is obtained, and the product can be obtained after cutting and polishing.

[0130] Example 6

[0131] Mix fine quartz sand with a particle diameter of 0 - 0.25 mm: medium quartz sand with a particle diameter of 0.25 - 0.5 mm: coarse quartz sand with a particle diameter of 0.5 - 1 mm: large quartz sand with a particle diameter of 1 - 30 mm: fine glass sand with a particle diameter of 0 - 0.25 mm: medium glass sand with a particle diameter of 0.25 - 0.5 mm in a mass ratio of 30:20:20:10:10:10 to obtain an inorganic composite aggregate. Add 5 parts of the oligomer binder finished product of Example 1, 5 parts of the middle polymer binder finished product of Example 2, 1.0 part of KH-550 silane coupling agent, 1.4 parts of benzoyl peroxide (BPO), and 0.02 part of tetramethylthiuram disulfide (TMTD) accelerator to 100 parts of the inorganic composite aggregate. After mixing them evenly, inject them into a mold, perform vacuum vibration compaction molding, and then cure at medium temperature at 30 °C for 6.0 h. After it is molded, an artificial stone plate is obtained, and the product can be obtained after cutting and polishing.

[0132] Example 7

[0133] Mix fine quartz sand with a particle diameter of 0 - 0.25 mm: medium quartz sand with a particle diameter of 0.25 - 0.5 mm: coarse quartz sand with a particle diameter of 0.5 - 1 mm: large quartz sand with a particle diameter of 1 - 30 mm: fine glass sand with a particle diameter of 0 - 0.25 mm: medium glass sand with a particle diameter of 0.25 - 0.5 mm in a mass ratio of 30:20:20:10:10:10 to obtain an inorganic composite aggregate. Add 3.3 parts of the oligomer binder finished product of Example 1, 3.3 parts of the middle polymer binder finished product of Example 2, 3.3 parts of the high polymer binder finished product of Example 3, 1.0 part of KH-550 silane coupling agent, 1.4 parts of benzoyl peroxide (BPO), and 0.02 part of tetramethylthiuram disulfide (TMTD) accelerator to 100 parts of the inorganic composite aggregate. After mixing them evenly, inject them into a mold, perform vacuum vibration compaction molding, and then cure at medium temperature at 30 °C for 6.0 h. After it is molded, an artificial stone plate is obtained, and the product can be obtained after cutting and polishing.

[0134] Example 8

[0135] Mix fine quartz sand with a particle diameter of 0 - 0.25 mm: medium quartz sand with a particle diameter of 0.25 - 0.5 mm: coarse quartz sand with a particle diameter of 0.5 - 1 mm: large quartz sand with a particle diameter of 1 - 30 mm: fine glass sand with a particle diameter of 0 - 0.25 mm: medium glass sand with a particle diameter of 0.25 - 0.5 mm in a mass ratio of 30:20:20:10:10:10 to obtain an inorganic composite aggregate. Add 4 parts of the finished oligomer binder of Example 1, 3 parts of the finished medium polymer binder of Example 2, 3 parts of the finished high polymer binder of Example 3, 1.0 part of KH-550 silane coupling agent, 1.4 parts of benzoyl peroxide (BPO), and 0.02 part of tetramethylthiuram disulfide (TMTD) accelerator to 100 parts of the inorganic composite aggregate. After mixing them evenly, inject them into a mold, and after vacuum vibration pressing and forming, cure at medium temperature at 30 °C for 6.0 h. After it is formed, an artificial stone plate is obtained, and the product can be obtained after cutting and polishing.

[0136] Example 9

[0137] Mix fine quartz sand with a particle diameter of 0 - 0.25 mm: medium quartz sand with a particle diameter of 0.25 - 0.5 mm: coarse quartz sand with a particle diameter of 0.5 - 1 mm: large quartz sand with a particle diameter of 1 - 30 mm: fine glass sand with a particle diameter of 0 - 0.25 mm: medium glass sand with a particle diameter of 0.25 - 0.5 mm in a mass ratio of 30:20:20:10:10:10 to obtain an inorganic composite aggregate. Add 4 parts of the finished oligomer binder of Example 1, 3 parts of the finished medium polymer binder of Example 2, 3 parts of the finished high polymer binder of Comparative Example 1, 1.0 part of KH-550 silane coupling agent, 1.4 parts of benzoyl peroxide (BPO), and 0.02 part of tetramethylthiuram disulfide (TMTD) accelerator to 100 parts of the inorganic composite aggregate. After mixing them evenly, inject them into a mold, and after vacuum vibration pressing and forming, cure at medium temperature at 30 °C for 6.0 h. After it is formed, an artificial stone plate is obtained, and the product can be obtained after cutting and polishing.

[0138] Example 10

[0139] Mix fine quartz sand with a particle diameter of 0 - 0.25 mm: medium quartz sand with a particle diameter of 0.25 - 0.5 mm: coarse quartz sand with a particle diameter of 0.5 - 1 mm: large quartz sand with a particle diameter of 1 - 30 mm: fine glass sand with a particle diameter of 0 - 0.25 mm: medium glass sand with a particle diameter of 0.25 - 0.5 mm in a mass ratio of 30:20:20:10:10:10 to obtain an inorganic composite aggregate. Add 4 parts of the oligomer binder finished product of Example 1, 2 parts of the medium polymer binder finished product of Example 2, 2 parts of the high polymer binder finished product of Example 3, 1 part of commercially available ortho-phthalic unsaturated polyester, 1 part of commercially available meta-phthalic unsaturated polyester, 1.0 part of KH-550 silane coupling agent, 1.4 parts of benzoyl peroxide (BPO), and 0.02 part of tetramethylthiuram disulfide (TMTD) accelerator to 100 parts of the inorganic composite aggregate. After mixing them evenly, inject them into a mold, and after vacuum vibration pressing and forming, cure at medium temperature at 30°C for 6.0 h. After it is formed, an artificial stone board is obtained, and the product can be obtained after cutting and polishing.

[0140] Example 11

[0141] The binder for artificial stone is prepared according to the following steps:

[0142] (1) Catalytic alcoholysis reaction: Put 3 kg of waste PET, 2 kg of diethylene glycol, 0.035 kg of the same quasi-homogeneous catalyst as in Example 1, and 0.03 kg of triphenyl phosphate into a reaction kettle, introduce nitrogen, gradually heat up to 150°C, keep warm for 2 h, then remove the heating, and cool down to 160°C to obtain a mother liquor containing impurities.

[0143] (2) Polycondensation reaction of the depolymerization product containing impurities: Directly add 1.2 kg of maleic anhydride and 0.1 kg of phosphoric acid to the mother liquor containing impurities. Control the heating rate, keep the reaction at a constant temperature of 170°C for 3 h, then measure the acid value. When the acid value is 40 mg KOH / g, turn on the external vacuum pump to evacuate the water, with the vacuum degree not exceeding -0.086 MPa, continue to keep the reaction at a constant temperature of 200°C for 1 h, until the acid value reaches 23 mg KOH / g, stop evacuating the vacuum, cool down to 180°C, add 0.005 kg of hydroquinone, stir for 0.5 h, and continue to cool down.

[0144] (3) Dilution: When the temperature drops to 80°C, add 2 kg of diallyl phthalate for dilution, and mix evenly to obtain a resin product, that is, the binder for artificial stone.

[0145] Detect the viscosity, average molecular weight of the binder for artificial stone, and the content of each component in the resin. As can be seen from Table 1, it is a high polymer binder finished product, and the content of unsaturated polyester resin in the product is 71.3%.

[0146] Example 12

[0147] The binder for artificial stone is prepared according to the following steps:

[0148] (1) Catalytic alcoholysis reaction: Put 4 kg of waste PET, 3 kg of ethylene glycol, 0.045 kg of the same quasi-homogeneous catalyst as in Example 1, and 0.05 kg of triphenyl phosphate into the reaction kettle, introduce nitrogen, gradually heat up to 250 °C, keep warm for 0.5 h, then remove the heating, and cool down to 160 °C to obtain a mother liquor containing impurities.

[0149] (2) Polycondensation reaction of the depolymerization product containing impurities: Directly add 1.9 kg of tetrahydrophthalic anhydride and 0.3 kg of benzoic acid to the mother liquor containing impurities, control the heating rate, keep the temperature constant at 230 °C and react for 1 h. When the acid value is measured to be 35 mg KOH / g, turn on the external vacuum pump to evacuate the water, with the vacuum degree not exceeding -0.086 MPa, continue to keep the temperature constant at 200 °C and react for 1 h. When the acid value reaches 20 mg KOH / g, stop evacuating the vacuum, cool down to 190 °C, add 0.01 kg of hydroquinone, stir for 0.5 h, and continue to cool down.

[0150] (3) Dilution: When the temperature is cooled down to 100 °C, add 1 kg of divinylbenzene for dilution, and mix evenly to obtain a resin product, namely the binder for artificial stone.

[0151] The viscosity, average molecular weight of the binder for artificial stone and the content of each component in the resin are detected. As can be seen from Table 1, it is a finished product of a high-polymer binder, and the content of unsaturated polyester resin in the product is 80.21%.

[0152] According to the national standard (GB / T 2567-2021), relevant tests are carried out on the binders for artificial stone prepared in Examples 1-3 and Comparative Example 1, and the test results are shown in Table 1 below.

[0153] According to the national standard (GB / T 41919-2022) "Artificial Stone Building Plates", the hardness (Mohs hardness), water absorption rate (%), bending property (MPa), compressive strength (MPa), and abrasion resistance (abrasion pit chord length mm) of the artificial stone building plates prepared in Examples 4-10 are tested, and the results are shown in Tables 2-4 below.

[0154] Table 1 Test Results of Binder for Artificial Stone

[0155]

[0156] Table 2 Size Indexes of Artificial Stone Plates in Examples 4-10

[0157] Size (mm) Allowable deviation of size (mm) Flatness (mm) Example 4 Type I: (2440×760)×1200 ±0.7 ≤0.70 Example 5 Type I: (2440×760)×1200 ±0.7 ≤0.70 Example 6 Type I: (2440×760)×1200 ±0.7 ≤0.70 Example 7 Type I: (2440×760)×1200 ±0.7 ≤0.70 Example 8 Type I: (2440×760)×1200 ±0.7 ≤0.70 Example 9 Type I: (2440×760)×1200 ±0.7 ≤0.70 Example 10 Type I: (2440×760)×1200 ±0.7 ≤0.70

[0158] Table 3 Appearance Conditions of Artificial Stone Plates in Examples 4-10

[0159]

[0160]

[0161] Table 4 Technical indicators of artificial stone plates in Examples 4 - 10

[0162] Mohs hardness Water absorption rate (%) Flexural property (MPa) Compressive strength (MPa) Wear resistance (chord length of wear scar mm) Example 4 6.0 ≤0.04 48.0 155 29.0 Example 5 6.3 ≤0.03 48.1 154 28.5 Example 6 6.5 ≤0.03 47.8 157 28.5 Example 7 6.6 ≤0.03 48.9 158 29.5 Example 8 6.7 ≤0.03 50.1 160 31.5 Example 9 5.6 ≤0.03 47.3 151 28.6 Example 10 7.0 ≤0.03 50.3 163 32

[0163] As can be seen from Examples 1 - 3, under the catalytic alcoholysis of waste PET by the quasi - homogeneous catalyst, as the total time of the subsequent polycondensation reaction increases, the acid value of the product unsaturated polyester resin gradually decreases, which indicates that the degree of polycondensation and the average molecular weight of the unsaturated polyester resin gradually increase; as is well known, since the molecular weight has a great influence on viscosity, the increase in the average molecular weight will lead to an increase in the viscosity of the unsaturated polyester resin (Table 1); and from the acid value changes of Example 3 and Comparative Example 1 (Table 1), it can be seen that under the same conditions, there is still some unreacted maleic anhydride in Comparative Example 1, thus proving that the catalytic alcoholysis effect of the heterogeneous catalyst (commercially available nano - zinc oxide powder) on PET is far inferior to that of the quasi - homogeneous catalyst, which in turn leads to a large amount of polymers in the mother liquor after the alcoholysis is completed. Re - polymerization will result in a relatively large average molecular weight, but the viscosity will not increase. At the same time, as the total time of the polycondensation reaction increases, the raw materials such as maleic anhydride in the reaction system decrease, and the yield of the corresponding unsaturated polyester resin increases, while the contents of organic and inorganic insoluble substances in the product do not change much when the PET alcoholysis is complete. As can be seen from Examples 11 - 12, when preparing the binder, the properties and yield of the binder can be regulated by controlling the process conditions of depolymerization and polycondensation.

[0164] Examples 4-10 are artificial stone plates prepared from the above different binder combinations. The performance of the artificial stone plates is judged from the dimensional indexes, appearance conditions and technical indexes of the artificial stone plates. As can be seen from Tables 2, 3 and 4, the dimensional indexes, appearance conditions and technical indexes of the artificial stone plates in Examples 4-10 all meet the national standard (GB / T 41919-2022). However, Table 3 shows that there is 1 and 2 pores respectively in the artificial stones prepared in Examples 5 and 9. It is inferred that when preparing the artificial stone in Example 5, the oligomer binder was not added, resulting in pores formed by the tiny gaps unfilled during the polymerization of coarse quartz sand; for the 2 pores on the artificial stone prepared in Example 9, it is speculated that the hydrophilicity of the heterogeneous catalyst (commercially available zinc oxide) may increase the interfacial tension in the resin system, thereby affecting the dispersion performance of the unsaturated resin solution, and thus bubbles are likely to be generated during the curing process. The comprehensive performance of the artificial stone prepared in Example 10 is better than that in Example 8. The reason is that in Example 10, through formula modulation, 1 part of the medium-polymer binder product in Example 2 and 1 part of the high-polymer binder product in Example 3 required for preparing the artificial stone in Example 8 are replaced with 1 part of commercially available ortho-phthalic unsaturated polyester and 1 part of commercially available m-phthalic unsaturated polyester, indicating that the binder for artificial stone prepared by the present invention can be compounded with ortho-phthalic unsaturated resin and m-phthalic unsaturated resin in a certain proportion to enhance the strength, hardness and other indexes of the cured artificial stone.

[0165] Analysis of Examples 4-10 in Table 4 shows that during the preparation of artificial stone, when other conditions are the same, the performance indexes of the artificial stone prepared by the synergistic use of oligomer binder, medium-polymer binder and high-polymer binder are higher than those of the artificial stone prepared by only using two of them. It is speculated that the reason is that the large, medium and small base materials cannot fit well with two of the low, medium and high polymer binders; in Example 8, the corresponding amounts of low, medium and high polymer binders are added according to the amounts of the large, medium and small base materials, and the obtained artificial stone has the best comprehensive performance. Thus, it can be obtained that when the molecular weight (viscosity) distribution is adapted to the graded aggregate required for the artificial stone, the mixing and bonding requirements of aggregates with different sizes and shapes can be better met. At the same time, when a specific aggregate artificial stone formula needs to be generated, the oligomer, medium-polymer and high-polymer can be mixed in proportion to achieve precise adaptation, and further ensure that the resin binder has good comprehensive performance in the artificial stone prepared by mixing and pressing with the filler. When comparing Example 8 and Example 9, it is found that when the high-polymer binder prepared in Comparative Example 1 is used to replace the high-polymer binder prepared in Example 3, the comprehensive performance of the artificial stone decreases. Therefore, it can be concluded that the quasi-homogeneous catalyst plays a significant role in the field of binders for artificial stone made from PET.

[0166] Although the present invention has been described in detail by means of the accompanying drawings and in conjunction with the embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and all such modifications or substitutions should fall within the scope of the present invention.

Claims

1. An adhesive for artificial stone, characterized in that, it is obtained by three processes of depolymerization by alcoholysis catalyzed by a quasi-homogeneous catalyst from waste PET, followed by polycondensation and dilution; By mass percentage, the composition of the adhesive for artificial stone is as follows: Unsaturated polyester resin 70-90%; Residual organic solution 5-30%; Organic insolubles 0.5-5%; Inorganic insolubles the balance; Among them, the unsaturated polyester resin has an average molecular weight of 500 < ≤ 2000 oligomer, 2000 < ≤ 3500 medium polymer and 3500 < ≤ 5000 high polymer combination; The inorganic insolubles are nano-metal oxide-based crystal particles in the quasi-homogeneous catalyst and inorganic modifiers contained in waste PET; The quasi-homogeneous catalyst is a monodisperse nano-zinc oxide-based dispersion; The monodisperse nano-zinc oxide-based dispersion is a dispersion in which one or more of the secondary phase metal elements cerium, cobalt, tin, iron, manganese, titanium, and antimony are doped into nano-zinc oxide crystal particles with the primary phase metal element being zinc.

2. The adhesive for artificial stone according to claim 1, characterized in that, the PET content in the waste PET ≥ 80%; the unsaturated polyester resin is a terephthalic type unsaturated polyester resin; the residual organic solution contains alcohol, antioxidant, acid anhydride, polycondensation catalyst, diluent, and inhibitor; the organic insolubles are polymers that are difficult to alcoholyze, and are one or more of polyethylene, polypropylene, polyvinyl chloride, polystyrene, acrylonitrile-butadiene-styrene copolymer, or modified PET.

3. The adhesive for artificial stone according to claim 2, characterized in that, the alcohol is a polyol, and the polyol is one or more of ethylene glycol, diethylene glycol, propylene glycol, glycerol, or neopentyl glycol; the antioxidant is one or more of triphenyl phosphate or phenothiazine; the acid anhydride is maleic anhydride or tetrahydrophthalic anhydride; the polycondensation catalyst is one or more of benzoic acid, sulfuric acid, or phosphoric acid; the diluent is one or more of styrene, vinyltoluene, divinylbenzene, methyl methacrylate, diallyl phthalate, or triallyl cyanurate; the inhibitor is one or more of hydroquinone, p-methoxyphenol, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, 2-tert-butylhydroquinone, p-benzoquinone, or methylhydroquinone.

4. The adhesive for artificial stone according to claim 1, characterized in that, the average particle size of the zinc oxide-based particles in the nano-zinc oxide-based dispersion is 1-100 nm.

5. The adhesive for artificial stone according to claim 1, characterized in that, the molar fraction of the secondary phase metal element in the primary phase metal element is 1-40%.

6. The adhesive for artificial stone according to claim 2, characterized in that, the inorganic modifier contained in the waste PET is one or more of inorganic reinforcing fibers or mineral fillers; the inorganic reinforcing fibers are one or more of ceramic fibers, metal fibers, carbon fibers, or glass fibers; the mineral fillers are one or two or more of calcium carbonate, talcum powder, wollastonite, barium sulfate, kaolin, bentonite, quartz powder, mica powder, graphite, titanium dioxide, white carbon black, or dolomite powder.

7. The adhesive for artificial stone according to claim 1, characterized in that, The properties of the binder for artificial stone are as follows: Appearance: colorless or light yellow transparent viscous liquid; Thermal stability at 80°C: ≥24 h; Viscosity: 0.5 - 2.5 Pa·s at 25°C; Gelling time: 10 - 20 min at 25°C.

8. A method for preparing the binder for artificial stone according to any one of claims 1 - 7, characterized in that it comprises the following steps: (1) Catalytic alcoholysis reaction: Add waste PET, alcohol, quasi - homogeneous catalyst and antioxidant into a reaction kettle and stir. Conduct the catalytic alcoholysis reaction under nitrogen protection. After PET is depolymerized into monomers or oligomers, cool down to obtain a mother liquor containing impurities; (2) Polycondensation reaction of the depolymerization product containing impurities: Add a polycondensation catalyst and acid anhydride into the mother liquor containing impurities, heat up and conduct the polycondensation reaction. When the solution reaches the initial acid value, turn on the external vacuum pump to evacuate the water by force. When the target acid value is reached, stop evacuating, cool down, add a polymerization inhibitor and stir to obtain an unsaturated resin; (3) Dilution: Continuously cool down the unsaturated resin, add a diluent, and mix evenly to obtain an unsaturated polyester resin binder, that is, the binder for artificial stone.

9. The method for preparing the binder for artificial stone according to claim 8, characterized in that the mass ratio of the waste PET: alcohol: quasi - homogeneous catalyst: antioxidant: acid anhydride: polycondensation catalyst: polymerization inhibitor: diluent is (3 - 4):(2 - 3):(0.005 - 0.05):(0.01 - 0.05):(1 - 2):(0.1 - 0.3):(0.005 - 0.01):(1 - 2).

10. The method for preparing the binder for artificial stone according to claim 8, characterized in that in step (1), the temperature of the catalytic alcoholysis reaction is 150 - 250°C, and the time of the catalytic alcoholysis reaction is 0.5 - 2 h; in step (2), the temperature of the polycondensation reaction is 170 - 230°C, the total time of the polycondensation reaction is 2 - 4 h, the initial acid value is 30 - 40 mgKOH / g, the target acid value is 5 - 25 mgKOH / g, cool down to 180 - 190°C, and add a polymerization inhibitor and stir for 0.5 - 1 h; in step (3), continuously cool down the unsaturated resin to 80 - 100°C.

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