CN106543326B

CN106543326B - Method for preparing low-viscosity EVA emulsion

Info

Publication number: CN106543326B
Application number: CN201510590672.7A
Authority: CN
Inventors: 陈博; 于鲁强; 刘小萌; 刘金伟
Original assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petrochemical Corp
Current assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petrochemical Corp
Priority date: 2015-09-16
Filing date: 2015-09-16
Publication date: 2019-12-24
Anticipated expiration: 2035-09-16
Also published as: CN106543326A

Abstract

The invention relates to a method for preparing low-viscosity EVA emulsion, which comprises the steps of adding vinyl acetate (VAc) monomer and acetalized PVA into an emulsifier aqueous solution, then adding initiator to initiate emulsion polymerization, and carrying out copolymerization reaction on ethylene and VAc monomer. The invention adopts acetalized PVA as a colloid protective agent, can obviously reduce the viscosity of the system, obtains an EVA emulsion product with excellent particle shape and good stability, greatly widens the application range of the EVA emulsion, and meets different requirements. And the single-kettle intermittent process avoids the problems of high difficulty in multi-kettle operation, high cost and energy consumption of the device and the like, and has higher industrial application value.

Description

Method for preparing low-viscosity EVA emulsion

Technical Field

The invention relates to a method for preparing low-viscosity EVA emulsion.

Background

The EVA emulsion produced by the emulsion polymerization method has moderate content of vinyl acetate (VAc), and the product has excellent flexibility, transparency, low-temperature flexibility, weather resistance, chemical corrosion resistance and compatibility with fillers and color masterbatch. The EVA emulsion product has high strength, no toxicity, environmental protection and excellent adhesive property, can be used in the fields of textile, light industry, coating, plastic toughening, building preparation, polymer blend coating, rubber modification and the like, has wide application, continuously increases the domestic and foreign demand and is rapidly developed in recent years. In the prior art, the method for preparing the EVA emulsion comprises adding the VAc monomer and the colloid protective agent into an emulsifier aqueous solution, and then adding an initiator to carry out copolymerization reaction between ethylene and the VAc monomer.

Patent EP0373313a2 describes the preparation of a high-solids ethylene-vinyl acetate latex. The pressure of polymerization ethylene is 47.0MPa, and the polymerization is respectively initiated at 40 ℃ and 65-82 ℃, and the reaction time is 15min and 3.0 h. The VAc content of the product is 65.0-80.0 wt.%, and the product viscosity is 200-38000 mpa.s. The patent CN1302027C initiates polymerization at 40-60 ℃ to prepare high-solid EVA latex, the weight of reaction ethylene is not counted by pressure, the reaction time is 10.0h, the VAc content of a product is 75.0-99.0 wt%, and the viscosity is 5000 mpa.s. The patent CN101200518A adopts a hydrogen peroxide-ferrous sulfate system, and the polymerization is initiated by step temperature control at two stages of 70-75 ℃ and 75-80 ℃ respectively, the ethylene reaction pressure is 9.0-10.0MPa, the product viscosity is 3843mpa.s.

In addition, patent CN102030858B initiates polymerization reaction at 60-65 and 75-80 ℃ under ethylene reaction pressure of 4.0-5.0 and 5.4-5.7MPa respectively, and the reaction time is 10-15mim and 1.5-3.0 h. The VAc content of the product was 54.50 wt%, viscosity 1162 mpa.s. The patent CN103665241A describes a production process of a cationic ethylene-vinyl acetate copolymer emulsion, which selects a compound system of a cationic emulsifier and a nonionic emulsifier, and the product VAc content is 50.0 wt%, and the viscosity is 200-. The EVA emulsion prepared by the prior art has high product viscosity, easy particle agglomeration, general product stability and narrow application range.

Therefore, the product prepared by the existing EVA emulsion polymerization process has high viscosity, poor particle shape and emulsion stability, difficult storage and limited application range.

Disclosure of Invention

The invention provides a method for preparing low-viscosity EVA emulsion, which adopts modified polyvinyl alcohol (PVA) to replace the traditional PVA, can obviously reduce the viscosity of a product, and maintains the particle shape and the toughness strength. The obtained EVA emulsion product has good stability, moderate VAc content and excellent performance, and can meet different requirements.

The method for preparing the low-viscosity EVA emulsion comprises the following steps: adding vinyl acetate (VAc) monomer and acetalized PVA into an emulsifier aqueous solution, and then adding an initiator to initiate emulsion polymerization so as to carry out copolymerization reaction of ethylene and VAc monomer.

In the examples of the present invention, the acetalized polyvinyl alcohol (PVA) was used as a colloid protecting agent in an amount of 1.5 to 9.0 wt% based on the amount of the VAc monomer, and the acetalization degree of PVA was 8.0 to 13.5%. Such methods for acetalizing PVA are well known in the industry: under acidic conditions, PVA and formaldehyde undergo a condensation reaction through a high molecular functional group, and two vinyl alcohol units consume one formaldehyde molecule to generate a molecular lactol compound. In the concrete operation, the pH value of the emulsion can be adjusted to 1.5-3.5, preferably 2.0-2.5 by using hydrochloric acid, then formaldehyde is dropped into the emulsion, and the emulsion is reacted for 0.5-2 hours at the temperature of about 85-95 ℃, preferably for 1 hour at the temperature of about 90 ℃. Specifically, reference is made to "modification of polyvinyl acetate emulsion acetalization, Sun Risheng, bonding, Vol.15, No. 3, pp.18-21, 1994". In the invention, the acetalization degree is mainly controlled by pH value, the pH value is increased, the reaction speed is reduced, the reaction is more sufficient, and the acetalization degree of polyvinyl alcohol is high; the pH value is too low, the reaction speed is too fast, the acetalation reaction is incomplete, and the acetalation degree is low. The PVA is usually added when no initiator is added to form monomer micelles, and is added in the middle stage of micelle growth in the polymerization reaction, so that the aim of stabilizing the polymerization system and maintaining the particle morphology is fulfilled. However, the application of acetalized PVA in EVA preparation has not been reported in relevant documents.

In the embodiment of the invention, the emulsifier is a nonionic surfactant, preferably alkylphenol ethoxylates OP-10, and the amount of the emulsifier is 5.0-25.0 wt% of the amount of the VAc monomer.

In the embodiment of the invention, the initiator is a water-soluble free radical initiator, and is selected from one of inorganic salt initiators, azo initiators, inorganic peroxide initiators and inorganic redox initiators, and one or more of the initiators are selected from the same initiator for use in combination. The inorganic salt initiator is selected from at least one of ammonium persulfate, sodium persulfate and potassium persulfate; the azo initiator is selected from at least one of azobisisobutyrimidazoline hydrochloride, azobiscyanovaleric acid and azobisisobutylamidine hydrochloride; the inorganic peroxide initiator is at least one selected from hydrogen peroxide, sodium peroxide and potassium peroxide. The amount of the initiator is 0.01-4.0 wt% of the amount of the VAc monomer.

In the embodiment of the present invention, a basic substance is used as a pH adjuster selected from at least one of sodium hydroxide, sodium bicarbonate, sodium carbonate, potassium hydroxide, potassium bicarbonate and potassium carbonate during the copolymerization reaction, and more preferably sodium bicarbonate. The amount of the pH value regulator is 0.05-5.0 wt% of the amount of the VAc monomer.

The invention can adopt single kettle intermittent process to prepare EVA emulsion, and the raw material is directly pumped into the copolymerization reaction kettle from the kettle top through a high-pressure metering pump. The copolymerization reaction conditions are as follows: the reaction temperature is 40-125 ℃, the ethylene pressure is 3.0-25.0MPa, and the reaction time is 2.0-8.0 hours. The pH value during the reaction is controlled to be 1.5-9.0, preferably 6.5-7.5.

According to the invention, the content of VAc in the copolymer in the EVA emulsion is 35.0-95.0 wt%; the viscosity of the emulsion is 85-150 mpa.s. The expression "content of VAc in the copolymer" means the content of polymerized units corresponding to vinyl acetate in the EVA copolymer.

In an embodiment of the invention, the method comprises continuously introducing VAc monomer, initiator, emulsifier, colloid protective agent, pH regulator and ethylene into a copolymerization reaction kettle, continuously leading out a copolymerization product from the kettle, and carrying out subsequent separation and treatment of the product. The demulsification of the product and the extraction of the polymer can be carried out to characterize the performance of the related polymer.

In a specific embodiment of the invention, the single reactor is a copolymerization reactor, a stirring mechanism is arranged in the single reactor, a liquid-phase feeding hole for feeding the emulsifier/colloid protective agent, the initiator, the pH value regulator and the vinyl acetate and a nitrogen and ethylene feeding hole are arranged at the upper part of the single reactor, a discharging hole is arranged at the lower part of the single reactor and is communicated with a material defoaming tank and a degassing tank, and a pH value regulator groove and an antifoaming agent groove are arranged at the upper part of the material defoaming tank. The raw materials and the products are added and led out in the whole polymerization process by adopting a high-pressure metering pump.

In one embodiment of the invention, the stirring mechanism is located at the central axis position in the copolymerization reaction kettle and consists of a driving device, a transmission device, a stirring shaft and a stirring paddle which are connected in sequence. The stirring paddle can use an anchor paddle, a turbine paddle, a ribbon paddle or a composite paddle combination of the anchor paddle and the turbine paddle.

In one embodiment of the invention, a stirring shaft is longitudinally arranged in the center of the copolymerization reaction kettle, blades are arranged on the stirring shaft, and a motor positioned on the upper side of the kettle body drives the stirring shaft to rotate through a transmission mechanism. The lower end of the kettle body is provided with an end enclosure, and a discharge hole is reserved at the bottom of the end enclosure. Injecting raw materials and an initiator into a kettle from a liquid phase feed inlet, introducing nitrogen and discharging oxygen, adding ethylene for polymerization reaction, and adopting a single kettle intermittent process.

It will be appreciated that commercially available monomers such as VAc monomers typically contain polymerization inhibitors and purification, such as distillation, must be carried out to remove the polymerization inhibitor prior to copolymerization.

The invention can also add other polymerization monomers for copolymerization while EVA is polymerized. The polymerization monomer used in the copolymerization may be an olefin such as propylene, n-butene, isobutylene, 1-hexene or 1-octene. The addition amount ratio of these polymerization monomers is selected within a range not to hinder the achievement of the object of the present invention.

On the basis of the existing EVA emulsion polymerization process, the modified PVA is added into a reaction system to serve as a colloid protective agent, so that the emulsion stability is improved. The specific method is to acetalize PVA to condense hydroxyl in the macromolecular chain of PVA into acetal group. The acetal group is a hydrophobic group, has certain steric hindrance, can destroy the symmetry of PVA molecules, weaken the interaction between PVA molecular hydroxyl groups and between the hydroxyl groups and water molecules, prevent PVA molecular chain convergence, weaken the hydrogen bond effect of a copolymerization system, and reduce the gelation effect. The PVA subjected to acetalation treatment can obviously stabilize latex particles, reduce the viscosity of a system, prevent adhesion, effectively avoid emulsion breaking and gel effect generation and greatly improve the stability of the emulsion. Along with the increase of the acetalization degree of the PVA, the water solubility of the PVA is reduced, and the effect of the protective colloid is gradually lost, so that the stability of the emulsion can be obviously improved and the viscosity of the emulsion can be reduced by controlling the acetalization degree of the PVA within a certain range. The invention has the advantages of low cost of raw materials, simple and convenient operation and good stability of the target emulsion. And a single kettle intermittent process is adopted, so that the problems of high difficulty in multi-kettle operation, high device cost and energy consumption and the like are solved, and the method has high industrial application value.

Drawings

FIG. 1 is a schematic diagram of an ethylene-vinyl acetate emulsion single-kettle copolymerization batch process device of the invention.

In the figure: 1 is a copolymerization reaction kettle; 2 is an emulsifier/colloid protective agent groove; 3 is an initiator tank; 4-1 and 4-2 are pH value regulator grooves; 5 is VAc monomer tank; 6-2, 6-3, 6-4, 6-5, 6-7 and 6-9 are high-pressure metering pumps; 7 is a material defoaming tank; 8 is a defoaming agent groove; and 9 is a defoaming machine.

Detailed Description

The invention is further illustrated by the following examples.

A copolymerization reaction device for preparing the low-viscosity EVA emulsion as shown in figure 1. Adopts single-kettle intermittent operation, and comprises a copolymerization reaction kettle 1, a feeding mechanism and a product post-treatment part. The upper part of the copolymerization reaction kettle 1 is provided with an emulsifier/colloid protective agent feed inlet, an initiator feed inlet, a pH value regulator feed inlet, a vinyl acetate liquid phase feed inlet, and N₂And an ethylene feed port. The emulsifier/colloid protective agent tank 2 is communicated with the copolymerization reaction kettle 1 through a high-pressure metering pump 6-2, the initiator tank 3 is communicated with the copolymerization reaction kettle 1 through a high-pressure metering pump 6-3, the pH value regulator tank 4-1 is communicated with the copolymerization reaction kettle 1 through a high-pressure metering pump 6-4, and the VAc monomer tank 5 is communicated with the copolymerization reaction kettle 1 through a high-pressure metering pump 6-5. The copolymerization reaction kettle 1 is internally provided with a stirring mechanism comprising a motor, a stirring paddle and a stirring shaft. The stirring mechanism comprises a stirring motor, a transmission device (not shown in the figures), a stirring shaft and a stirring paddle fixed on the stirring shaft. When the reaction kettle works, the stirring paddle and part of the stirring shaft are positioned below the reaction liquid level.

The lower part of the copolymerization reaction kettle 1 is provided with a discharge hole which is communicated with a feed inlet of the material defoaming tank 7. The pH value regulator tank 4-2 and the defoamer tank 8 are respectively communicated with the material defoaming tank 7 through a high-pressure metering pump 6-7. The discharge hole of the material defoaming tank 7 is communicated with the feed inlet of the defoaming machine 9 through a high-pressure metering pump 6-9.

Before the reaction, the emulsifier aqueous solution is added into a copolymerization reaction kettle 1 through an emulsifier/colloid protective agent tank 2, and copolymerization is carried out through a VAc monomer tank 5VAc monomer is added into the reactor 1, and acetalized PVA is added into the copolymerization reactor 1 through the emulsifier/colloid protective agent tank 2. Then adding initiator and pH value regulator, and introducing N₂And (3) discharging oxygen, pressing ethylene into the copolymerization reaction kettle 1, and carrying out ethylene-vinyl acetate emulsion copolymerization reaction after the pressure is constant. After the reaction is finished, the material discharged from the copolymerization reaction kettle 1 enters a material defoaming tank 7, and a pH value regulator and a defoaming agent are added for product post-treatment. The material discharged from the material defoaming tank 7 is finally pumped into a defoaming machine 9 to remove unreacted ethylene gas. In the polymerization and post-treatment processes, the raw materials and the products are added and led out by adopting high-pressure metering pumps 6-2, 6-3, 6-4, 6-5, 6-7 and 6-9 for pumping.

In the examples, four methods of nuclear magnetism, elemental analysis, thermogravimetry and infrared are adopted to determine the content of VAc in the EVA product. The emulsion viscosity was measured using a model NDJ-4 rotational viscometer.

Example 1

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 3.0 wt% of the amount of the VAc monomer, and the acetalization degree of the PVA is 8.0%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 65.9 wt%, the viscosity of the emulsion is 91mpa.s, the stability of the emulsion is good, and the emulsion can be stably stored for 15 months.

Example 2

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 3.0 wt% of the amount of the VAc monomer, and the acetalization degree of the PVA is 8.5%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 65.9 wt%, the viscosity of the emulsion is 98mpa.s, the stability of the emulsion is good, and the emulsion can be stably stored for 14 months.

Example 3

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 3.0 wt% of the amount of the VAc monomer, and the acetalization degree of the PVA is 9.0%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 65.8 wt%, the viscosity of the emulsion is 108mpa.s, the stability of the emulsion is good, and the emulsion can be stably stored for 14 months.

Example 4

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 3.0 wt% of the amount of the VAc monomer, and the acetalization degree of the PVA is 9.5%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 66.0 wt%, the viscosity of the emulsion is 113mpa.s, the stability of the emulsion is good, and the emulsion can be stably stored for 13 months.

Example 5

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 3.0 wt% of the amount of the VAc monomer, and the acetalization degree of the PVA is 10.0%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 66.1 wt%, the viscosity of the emulsion is 117mpa.s, the stability of the emulsion is good, and the emulsion can be stably stored for 13 months.

Example 6

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 3.0 wt% of the amount of the VAc monomer, and the acetalization degree of the PVA is 10.5%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 66.1 wt%, the viscosity of the emulsion is 122mpa.s, the stability of the emulsion is good, and the emulsion can be stably stored for 13 months.

Example 7

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 3.0 wt% of the amount of the VAc monomer, and the acetalization degree of the PVA is 11.0%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 66.1 wt%, the viscosity of the emulsion is 125mpa.s, the stability of the emulsion is good, and the emulsion can be stably stored for 12 months.

Example 8

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the usage of the colloid protective agent PVA after acetalization treatment is 3.0 wt% of the usage of the VAc monomer, the usage of the PVA acetalization degree is 11.5%, and the usage of the pH value regulator sodium bicarbonate is 0.5 wt% of the usage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 66.0 wt%, the viscosity of the emulsion is 130mpa.s, the stability of the emulsion is good, and the emulsion can be stably stored for 12 months.

Example 9

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 3.0 wt% of the amount of the VAc monomer, and the degree of acetalization of the PVA is 12.0%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 65.9 wt%, the viscosity of the emulsion is 136mpa.s, the stability of the emulsion is good, and the emulsion can be stably stored for 11 months.

Example 10

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 3.0 wt% of the amount of the VAc monomer, and the degree of acetalization of the PVA is 12.5%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 65.9 wt%, the viscosity of the emulsion is 139mpa.s, the stability of the emulsion is good, and the emulsion can be stably stored for 10 months.

Example 11

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 3.0 wt% of the amount of the VAc monomer, and the acetalization degree of the PVA is 13.0%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the monomer VAc; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 66.0 wt%, the viscosity of the emulsion is 144mpa.s, the stability of the emulsion is better, and the emulsion can be stably stored for 9 months.

Example 12

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 3.0 wt% of the amount of the VAc monomer, and the acetalization degree of the PVA is 13.5%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 66.1 wt%, the viscosity of the emulsion is 148mpa.s, the stability of the emulsion is better, and the emulsion can be stably stored for 8 months.

Example 13

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 1.5 wt% of the amount of the VAc monomer, and the acetalization degree of the PVA is 13.5%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under these conditions, the VAc content of the polymerization product was 66.0% by weight and the viscosity of the emulsion was 150 mPa.s. The emulsion has good stability, and can be stably stored for 7 months.

Example 14

Ammonium persulfate is used as an initiator, and the total dosage is 0.3 wt% of vinyl acetate; in an O/W system, the dosage of the surfactant op-10 is 10.0 wt% of the dosage of the VAc monomer; the amount of the colloid protective agent PVA subjected to acetalization treatment is 9.0 wt% of the amount of the VAc monomer, and the degree of acetalization of the PVA is 13.5%; the dosage of the pH value regulator sodium bicarbonate is 0.5 wt% of the dosage of the VAc monomer; the polymerization temperature is 75 ℃, the ethylene reaction pressure is 75.0MPa, the polymerization time is 5h, and the pH value in the reaction process is controlled to be 6.5. Under the condition, the VAc content of the polymerization product is 65.9 wt%, the viscosity of the emulsion is 165mpa.s, the stability of the emulsion is better, and the emulsion can be stably stored for 7 months.

Comparative example 1

The addition and reaction conditions were the same as in example 1, except that unmodified conventional PVA was used as the colloid protection agent and no acetalized modified PVA was used. Under these conditions, the VAc content of the polymerization product was 70.7% by weight and the viscosity of the emulsion was 221 mpa.s. The emulsion particles of the product are partially adhered, and the emulsion is placed for 5 months to generate emulsion breaking precipitation.

Comparative example 2

The charging and reaction conditions were the same as in example 1 except that the acetalized modified PVA was used as a colloid-protecting agent and the acetalization degree was 7.5%. Under these conditions, the VAc content of the polymerization product was 69.0% by weight and the viscosity of the emulsion was 183 mPa.s. And a small part of latex particles of the product is adhered, and emulsion breaking precipitation appears when the latex is placed for 4.5 months, which indicates that the acetalization degree of the modified PVA is lower.

Comparative example 3

The charging and reaction conditions were the same as in example 1 except that the acetalized modified PVA was used as a colloid-protecting agent and the acetalization degree was 14.0%. Under the conditions, the VAc content of the polymerization product is 69.9 wt%, and the viscosity of the emulsion is 383 mpa.s. The viscosity of the product is sharply increased, latex particles are seriously adhered, insoluble substances can be seen after the emulsion is discharged, and the significance of continuously improving the degree of acetal of the modified PVA is small.

In examples 1-12, the viscosity of the emulsion gradually increased. In comparison, the emulsions of examples 1-4 have a better overall performance. It is stated that within the scope of the present invention, the lower the acetalization degree of PVA, the better, since increasing the acetalization degree of PVA reduces its water solubility, precipitates during the copolymerization and loses the protective colloid's effect.

Comparing examples 1-12 with comparative example 1, it is demonstrated that the emulsion product has moderate VAc content and viscosity and stable system by using acetalized modified PVA as colloid protective agent; comparing the examples with comparative examples 2 and 3, it is shown that the acetalization degree of the modified PVA does not exceed the range defined by the present invention.

In summary, in the single-kettle intermittent production process of ethylene-vinyl acetate copolymerization, the acetalization modified PVA is used as the colloid protective agent, so that the system viscosity can be obviously reduced, the EVA emulsion product with excellent particle shape and good stability can be obtained, the application range of the EVA emulsion is greatly expanded, and different requirements are met. And the single-kettle intermittent process avoids the problems of high difficulty in multi-kettle operation, high cost and energy consumption of the device and the like, and has higher industrial application value.

It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.

Claims

1. A method for preparing low-viscosity EVA emulsion comprises adding VAc monomer and acetalized PVA into emulsifier aqueous solution, adding initiator to initiate emulsion polymerization, and allowing ethylene and VAc monomer to perform copolymerization reaction; the degree of acetalization of the PVA is 8.0-9.5%.

2. The method of claim 1, wherein the acetalized PVA is present in an amount of 1.5 to 9.0 wt.% based on the amount of VAc monomer.

3. The method according to claim 1 or 2, characterized in that the emulsifier is a non-ionic surfactant.

4. The method of claim 3, wherein the emulsifier is alkylphenol ethoxylates OP-10.

5. The method according to claim 3, wherein the amount of emulsifier is 5.0-25.0 wt% of the amount of VAc monomer.

6. The method according to claim 1 or 2, wherein the initiator is a water-soluble radical initiator selected from one of inorganic salt type initiators, azo type initiators, inorganic peroxide type initiators and inorganic redox type initiators.

7. The method of claim 6, wherein the amount of initiator is 0.01 to 4.0 wt% of the amount of VAc monomer.

8. The method according to claim 1 or 2, wherein a basic substance selected from at least one of sodium hydroxide, sodium bicarbonate, sodium carbonate, potassium hydroxide, potassium bicarbonate and potassium carbonate is used as a pH regulator during the copolymerization reaction.

9. The method according to claim 8, wherein the amount of the pH regulator is 0.05 to 5.0 wt% based on the amount of the VAc monomer.

10. The process according to claim 1 or 2, characterized in that the copolymerization reaction conditions are: the reaction temperature is 40-125 ℃, the ethylene pressure is 3.0-25.0MPa, the reaction time is 2.0-8.0 hours, and the pH value in the reaction process is controlled to be 1.5-9.0.

11. The method of claim 10, wherein the copolymerization reaction conditions are: the pH value in the reaction process is controlled to be 6.5-7.5.

12. The method according to claim 1 or 2, wherein the EVA emulsion is obtained with a VAc content of 35.0-95.0 wt.% in the copolymer; the viscosity of the emulsion is 85-150 mpa.s.

13. The process according to claim 1 or 2, wherein the copolymerization is carried out by adding other polymerization monomers simultaneously with the copolymerization.

14. The method of claim 13, wherein the polymerized monomer is at least one of propylene, n-butene, isobutylene, 1-hexene, and 1-octene.