阅读说明：本技术 一种无甲醛强耐水性聚醋酸乙烯酯木材胶黏剂的制备方法 (Preparation method of formaldehyde-free high-water-resistance polyvinyl acetate wood adhesive ) 是由 程增会 张代晖 金立维 王春鹏 储富祥 李守海 于 2020-06-17 设计创作，主要内容包括：本发明属于胶黏剂技术领域,具体涉及一种无甲醛强耐水性聚醋酸乙烯酯木材胶黏剂的制备方法。该方法首先通过半连续乳液聚合法,采用引入丙烯酸酯单体与醋酸乙烯酯共聚合的方法制得聚醋酸乙烯酯乳液；然后将制得的乳液胶黏剂经pH调节至中性,后与水性交联剂、阳离子改性剂、增稠剂混合均匀,得到不含甲醛强耐水的聚醋酸乙烯酯胶黏剂产品。本发明制得的聚醋酸乙烯酯胶黏剂耐水性能良好,无甲醛,属于高固含量产品,黏度大小可按要求进行调节。(The invention belongs to the technical field of adhesives, and particularly relates to a preparation method of a formaldehyde-free high-water-resistance polyvinyl acetate wood adhesive. Firstly, preparing polyvinyl acetate emulsion by introducing an acrylate monomer and vinyl acetate for copolymerization through a semi-continuous emulsion polymerization method; and then adjusting the pH value of the prepared emulsion adhesive to be neutral, and uniformly mixing the emulsion adhesive with a water-based cross-linking agent, a cation modifier and a thickening agent to obtain a formaldehyde-free and strong-water-resistant polyvinyl acetate adhesive product. The polyvinyl acetate adhesive prepared by the invention has good water resistance and no formaldehyde, belongs to a product with high solid content, and the viscosity can be adjusted according to requirements.)

1. A preparation method of a formaldehyde-free high-water-resistance polyvinyl acetate wood adhesive is characterized by comprising the following specific preparation steps:

firstly, synthesizing polyvinyl acetate emulsion, wherein the components in parts by weight are as follows: 2-5 parts of polyvinyl alcohol, 42-47 parts of vinyl acetate, 0.1-0.15 part of buffering agent, 0.1-0.2 part of oxidant in a redox initiation system, 0.11-0.22 part of reducing agent and 0.3-1.2 parts of acrylate monomer, firstly, dissolving the polyvinyl alcohol completely in a 90-95 ℃ aqueous solution, when the temperature is reduced to 50-60 ℃, sequentially adding part of vinyl acetate monomer, all buffering agent and reducing agent in the redox initiation system, raising the reaction temperature to 70-80 ℃, then adding the oxidant in a first redox initiation system, carrying out polymerization reaction, after reacting for 20min, dropwise adding the mixture of the rest vinyl acetate and the acrylate monomer with carboxyl and the oxidant in the rest of redox initiation agent by using an injector, reacting for 3-5 h, and cooling to obtain a polyvinyl acetate emulsion;

and step two, adjusting the pH value of the polyvinyl acetate emulsion prepared in the step one to be neutral by 8% potassium hydroxide aqueous solution, then uniformly mixing 100 parts of the prepared polyvinyl acetate emulsion with 0.1-1.0 part of aqueous cross-linking agent, 2-10 parts of cationic modifier and 1-3 parts of active calcium carbonate according to the proportion, and selecting a thickening agent to adjust the viscosity of the adhesive according to the viscosity requirement.

2. The method for preparing a formaldehyde-free strong water-resistant polyvinyl acetate wood adhesive according to claim 1, wherein the polyvinyl alcohol used in the first step is RS-2117 of jequiry corporation of japan.

3. The method for preparing the formaldehyde-free high-water-resistance polyvinyl acetate wood adhesive as claimed in claim 1, wherein the redox initiator used in the step one is tartaric acid/hydrogen peroxide.

4. The method for preparing the formaldehyde-free high-water-resistance polyvinyl acetate wood adhesive as claimed in claim 1, wherein the buffering agent used in the step one is sodium acetate.

5. The method for preparing the formaldehyde-free high-water-resistance polyvinyl acetate wood adhesive according to claim 1, wherein the acrylic ester monomer with carboxyl used in the step one is any one of acrylic acid and methacrylic acid.

6. The method for preparing the formaldehyde-free strong water-resistant polyvinyl acetate wood adhesive according to claim 1, wherein the redox initiator used in the step one is added in a mass ratio of 3:7 between the first batch and the second batch.

7. The method for preparing the formaldehyde-free high-water-resistance polyvinyl acetate wood adhesive as claimed in claim 1, wherein the aqueous cross-linking agent used in the second step is any one of UN-178 and WIN-28.

8. The method for preparing the formaldehyde-free high-water-resistance polyvinyl acetate wood adhesive according to claim 1, wherein the cationic modifier used in the second step is any one of cationic rosin emulsion, polyamide epichlorohydrin (PAE) and cationic acrylate emulsion.

9. The method for preparing the formaldehyde-free strong water-resistant polyvinyl acetate wood adhesive according to claim 1, wherein the thickener used in the second step is any one of ASE-60, Addenosol 1016, TH5020 and TH 5202.

Technical Field

The invention belongs to the technical field of wood adhesives, and particularly relates to a preparation method of a formaldehyde-free high-water-resistance polyvinyl acetate wood adhesive.

Background

The polyvinyl acetate emulsion is single-component emulsion, has the characteristics of low price, convenient production, high bonding strength, no toxicity and the like, has wide application range due to the advantages of wide compatibility with other resins, good bonding property, small pressure required during bonding, colorless and transparent adhesive film, no pollution to material surfaces, flexibility and the like, is applied to various fields of wood processing, fabric bonding, furniture assembly, manufacturing industry, packaging industry, home decoration and the like, becomes a large product in the industry, and the dosage of the polyvinyl acetate emulsion is greatly increased along with the rapid development of national economy. However, PVAc also has a number of disadvantages: is a linear long chain polymer, and has weak polar attraction between molecular chains and glass transition temperature: (T _g) Low (about 27 ℃), when the temperature is higher thanT _gThe molecular chain mobility becomes large and the elastic modulus rapidly decreases. Under the damp and hot condition, the adhesive strength is greatly reduced, so that the cold resistance, the moisture resistance and the mechanical stability are lacked, and the creep resistance is poor. When the polyvinyl acetate is in contact with water or in a high-humidity environment, partial acetyl groups on a molecular chain are easily hydrolyzed into hydroxyl groups, the hydrophilic hydroxyl groups easily adsorb water molecules to the cementing layer, and the water molecules penetrate through the wood and the cementing layer to permeate into the interface between the wood and the PVAc, so that the cementing layer is softened, the bonding strength is reduced, and the defects limit the application of the PVAc polymer.

In order to improve its properties such as glass transition temperature, water resistance, tensile strength, etc., it has been also taught that by blending or copolymerizing with other monomers, a PVAc emulsion having excellent properties can be obtained by using a protective colloid having excellent water resistance. For example, in the US patent US 20040082706, isocyanate is mentioned as a cross-linking agent to improve the water resistance and the bonding strength of the emulsion adhesive, but the isocyanate cross-linking agent is generally expensive, which results in the increase of the cost of the emulsion adhesive. In the chinese patent publication No. CN 107974219a, an adhesive with good water resistance is prepared by copolymerizing vinyl acetate and lauryl methacrylate, and the water resistance can reach the european D3 standard, but the glass transition temperature of lauryl methacrylate is relatively low, so the adhesive has poor heat resistance, and the adhesive layer is easily deformed and slides at higher environmental temperature. In the patent of publication No. CN 108624261a, toughened phenolic resin is blended with polyvinyl acetate to obtain an emulsion adhesive with excellent comprehensive properties, but the introduction of phenolic resin can cause the emulsion adhesive to contain a small amount of formaldehyde, which is harmful to human body and environment, so the application of the emulsion adhesive is limited to a certain extent. Therefore, the development of the environment-friendly high-performance polyvinyl acetate emulsion adhesive has very important practical significance.

Disclosure of Invention

The technical problem to be solved is as follows: in order to solve the problems of low bonding strength, poor water resistance, formaldehyde-containing toxic substances and the like of the conventional polyvinyl acetate adhesive in the market in the wood bonding process, the invention leads the emulsion adhesive to generate certain crosslinking in the use process by introducing the cationic modifier and the acrylate carboxyl functional group and using the modified polyvinyl alcohol as a protective colloid and the like, and the introduction of the cationic group can enhance the acting force of the adhesive and the adhesive surface, thereby obtaining the polyvinyl acetate emulsion adhesive which has good water resistance, adjustable viscosity, high solid content and no formaldehyde.

The technical scheme is as follows: a preparation method of a formaldehyde-free high-water-resistance polyvinyl acetate wood adhesive comprises the following preparation steps:

step one, synthesizing polyvinyl acetate emulsion, wherein the components in parts by weight are as follows: 2-5 parts of polyvinyl alcohol, 42-47 parts of vinyl acetate, 0.1-0.15 part of buffering agent, 0.1-0.2 part of oxidant, 0.11-0.22 part of reducing agent and 0.3-1.2 parts of acrylate monomer in a redox initiation system. Firstly, completely dissolving polyvinyl alcohol in an aqueous solution at the temperature of 90-95 ℃, sequentially adding part of vinyl acetate monomer, all buffering agents and reducing agents in a redox initiation system when the temperature is reduced to 50-60 ℃, increasing the reaction temperature to 70-80 ℃, then adding oxidizing agents in a first batch of redox initiation system, carrying out polymerization reaction, dropwise adding the rest of vinyl acetate and acrylic ester monomer mixture with carboxyl groups and the rest of oxidizing agents in a second batch of redox initiation system by using an injector after reacting for 20min, reacting for 3-5 h, and cooling to obtain polyvinyl acetate emulsion.

And step two, adjusting the pH value of the polyvinyl acetate emulsion prepared in the step one to be neutral by 8% potassium hydroxide aqueous solution, then uniformly mixing 100 parts of the prepared polyvinyl acetate emulsion with 0.1-1.0 part of aqueous cross-linking agent, 2-10 parts of cationic modifier and 1-3 parts of active calcium carbonate according to the proportion, and selecting a thickening agent to adjust the viscosity of the adhesive according to the viscosity requirement.

Preferably, the polyvinyl alcohol used in step one is RS-2117 from Coly, Japan.

Preferably, the redox initiator used in step one is tartaric acid/hydrogen peroxide.

Preferably, the buffer used in step one is sodium acetate.

Preferably, the acrylate monomer having a carboxyl group used in the first step is any one of acrylic acid and methacrylic acid.

Preferably, the mass ratio of the oxidant in the redox initiator used in step one, the first batch to the second batch, is 3: 7.

Preferably, the water-based cross-linking agent used in the second step is any one of UN-178 or WIN-28.

Preferably, the cationic modifier used in the second step is any one of cationic rosin emulsion, PAE and cationic acrylate emulsion.

Preferably, the thickener used in step two is any one of Rohm and Haas ASE-60, Addenosol 1016, TH5020 and TH 5202.

The invention has the beneficial effects that: the polyvinyl acetate emulsion adhesive provided by the invention is modified by the cationic modifier, has a certain cross-linking structure, is excellent in water resistance after film formation, does not contain formaldehyde in the used raw materials, solves the problem of formaldehyde from the source, and is an environment-friendly water-based emulsion adhesive.

The water-resistant polyvinyl acetate emulsion adhesive prepared by the invention has the advantages of simple preparation process, simple and convenient operation, no peculiar smell in the whole reaction process, and no harm to human bodies.

Detailed Description

Parts not mentioned in the text are the same as or can be realized by the prior art. The following are preferred embodiments of the present invention, but the present invention is not limited to the following embodiments, and some modifications to the embodiments will be considered as the protection scope of the present invention.

Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.