Polyurethane modified acrylate aqueous emulsion and preparation method thereof

Abstract

The invention relates to the technical field of chemical adhesives, and discloses a polyurethane modified acrylate aqueous emulsion and a preparation method thereof. The polyurethane modified acrylate aqueous emulsion is prepared from a polyurethane dispersion and polyacrylate; the polyurethane dispersoid is formed by polymerizing isophorone diisocyanate, polycaprolactone polyol, 2, 2-bis (hydroxymethyl) propionic acid and trimethylolpropane; the polyacrylate is formed by polymerizing methyl methacrylate, butyl acrylate and N-methylacryloyl glycine. According to the polyurethane modified acrylate aqueous emulsion and the preparation method thereof disclosed by the invention, the prepared aqueous emulsion is nanoscale, and after the aqueous emulsion is prepared into a film, the tensile strength of the film is increased along with the increase of the addition amount of N-methylacryloylglycine, and the elongation at break of the film is reduced along with the increase of the addition amount of N-methylacryloylglycine; when the addition amount of the N-methylacryloyl glycine is 1.96% and 3.85% of the total amount of the monomer, the optimal tensile strength and elongation at break are achieved, and the N-methylacryloyl glycine copolymer can be used for preparing chemical adhesives.

Description

Technical Field

[0001] The invention relates to the technical field of chemical adhesives, in particular to polyurethane modified acrylate aqueous emulsion and a preparation method thereof. Background Art

[0002] Polyacrylate (PA) is a high molecular polymer formed by emulsion polymerization of acrylic ester monomers. As a widely used polymer material, polyacrylate has many excellent properties, such as good mechanical properties, light resistance, weather resistance, acid and alkali corrosion resistance, and its raw materials are abundant, low price, and simple synthesis process. At the same time, the polymer coating has good toughness and strong aging resistance. Therefore, it is widely used in leather finishing, architectural coatings, wood, adhesives and other fields.

[0003] However, polyacrylates also have some shortcomings, such as poor water resistance and stain resistance, easy to lose viscosity at high temperature, and easy to be brittle at low temperature, which affect the application value of the product and further limit the development of polyacrylates. With the development of society, single polyacrylate materials have been difficult to meet people's needs. Modifying polyacrylates to give them better performance has become a hot topic in current research.

[0004] Among the many modification methods, polyurethane modification is undoubtedly a very common polyacrylate (PA) modification method.

[0005] Polyurethane (PU) refers to a macromolecular polymer with a carbamate group (-NHCOO-) in the main chain. It is generally formed by the polymerization of isocyanate and compounds containing active hydrogen, and can be divided into polyester polyurethane and polyether polyurethane. Polyurethane molecules contain ether bonds, ester bonds, and urethane bonds, which can form hydrogen bonds to enhance the intermolecular forces, so that the coating has good chemical and mechanical properties, such as good low temperature resistance, chemical corrosion resistance, good flexibility, and strong adhesion.

[0006] However, a single polyurethane also has the disadvantages of poor water resistance, insufficient weather resistance, poor high temperature resistance, insufficient stability, and low solid content. By applying it to the modification of polyacrylate, a polyurethane acrylate (PUA) composite emulsion with both properties can be obtained. The composite emulsion cured coating has excellent high temperature resistance and mechanical processing performance, and has been widely used in inks, coatings, adhesives and other fields.

[0007] At present, there are the following methods for polyurethane modified acrylate: Physical blending refers to first preparing stable PU and PA emulsions, and then mechanically blending the prepared PU and PA emulsions to obtain a composite emulsion that has some excellent properties of both emulsions. This method mainly uses the hydrogen bonds formed by hydrogen atoms on polyurethane and oxygen atoms on acrylate to improve the compatibility of the two macromolecules. The crystal regions of acrylate can be evenly distributed in the material, thereby improving the overall performance of the material. However, due to the weak hydrogen bonding effect and significant thermodynamic differences between the two components, simple mechanical blending makes the compatibility of the two components unsatisfactory, and the gloss and light transmittance of the resulting coating are poor. In addition, the blending method requires the preparation of two emulsions, which is complex and energy-intensive.

[0008] The cross-linking blending method is to add a cross-linking agent to the polyurethane and acrylate emulsion blending system and use mechanical stirring to evenly mix the two and produce cross-linking. Since the cross-linking mixing combines the two macromolecules through chemical bonds, a better blended emulsion can be obtained compared with simple mechanical mixing. However, this method also requires the preparation of two emulsions in advance, and the introduction of the cross-linking agent will increase the amount of volatile organic compounds (VOCs), affecting the film-forming process.

[0009] Composite copolymerization and composite emulsion copolymerization are to form different structural systems of polyurethane and acrylate through different polymerization methods. Compared with physical blending, composite copolymerization is conducive to the formation of a complex phase structure. PU and PA phases are entangled at the molecular or atomic level. The synergistic effect between the two makes the coating have better properties, such as solvent resistance, water resistance, good stability and tensile strength, but the activity of unsaturated bonds will be affected by the monomer chain length, thereby affecting the degree of polymerization and phase separation of the system, and then affecting the performance of the coating. Wang et al. used isophorone diisocyanate (IPDI) to modify hydroxyethyl acrylate (PCLA2) through addition reaction with polyethylene glycol monoacrylate (PEA6) and polycaprolactone, and synthesized two UV-curable polyurethane acrylate polymers. The results show that the UV-cured polymer film has a uniform phase structure and has a high glass transition temperature and storage modulus.

[0010] Core-shell copolymerization, using the seed method to synthesize an emulsion with acrylate as the core and polyurethane as the shell, is currently the most studied method for acrylate modification. First, prepare a polyurethane emulsion, then swell the acrylate monomer into the polyurethane emulsion, and allow the acrylate monomer to undergo free radical polymerization. Due to the hydrophilic / hydrophobic effect, the acrylate enters the interior of the particle to form a core, and the polyurethane molecular chain has a high hydrophilicity, forming the shell of the colloid particle, and finally generating a stable PUA emulsion. This composite emulsion combines the weather resistance of acrylate and the adhesion of polyurethane, which can significantly improve the weather resistance, water resistance, film forming and mechanical properties of the emulsion. However, the emulsion is limited by the morphological structure of the two resins, and the characteristics of the two cannot be fully reflected after film formation. Therefore, a cross-linking structure is often introduced into this core-shell composite structure to improve the compatibility of the two polymers, thereby improving the hardness, strength, stability and durability of the material. The cross-linking structure includes shell-shell cross-linking and core-shell cross-linking. Shell-shell cross-linking is the self-cross-linking of the shell polyurethane, and core-shell cross-linking is the cross-linking formed by introducing monomers that can react with the core and shell. Wang et al. prepared waterborne polyurethane dispersions and successfully prepared a series of polyurethane / polyacrylate composite emulsions through free radical copolymerization with acrylate monomers. As the mass fraction of glycidyl methacrylate (N-methacryloyl glycine) increased from 0 to 3%, the water absorption of the composite emulsion decreased from 18% to 7.8%, and the tensile strength increased from 2.51 MPa to 5.82 MPa.

[0011] Interpenetrating polymer network (IPN) is a special composite structure with "forced miscibility" and "molecular synergy" effects at the molecular or atomic level. At least one of its components is a cross-linked structure. The phase organization is refined by the entanglement of the chains of different components, thereby improving the compatibility and bonding between the phases. The synthesized IPN makes the composite material have excellent static and dynamic mechanical properties and a wide operating temperature range. There are three preparation methods for PUA interpenetrating networks: (1) First, a PU prepolymer containing a carboxyl group is prepared by a solution method, then it is neutralized with a tertiary amine and self-emulsified to obtain a PU seed emulsion, and finally an acrylate monomer containing propyl acrylate or diene is added to carry out a composite emulsion polymerization to obtain an IPN type emulsion.

[0012] (2) First, the acrylate monomer mixture is used as solvent, and then the PU solution is prepared by traditional solution polymerization. Finally, the acrylate monomer containing PU is emulsion polymerized in the aqueous solution under the action of initiators, emulsifiers and other auxiliary agents to obtain an IPN type emulsion. Since this method does not require organic solvents, has a simple process and is easy to operate, it is a feasible method for preparing PUA emulsions.

[0013] (3) PU and PA emulsions with functional groups are prepared separately and mixed, polycondensed and cross-linked to prepare the IPN elastomer PUA.

[0014] N-methacryloylglycine is a compound with a special structure and potential for wide application. In terms of chemical structure, it combines the characteristics of olefin groups and amino acid groups. The methacryloyl group contains a carbon-carbon double bond, has high reactivity, and can participate in a variety of polymerization reactions. The glycine part gives it certain biocompatibility and potential biological activity.

[0015] .

[0016] In the field of materials, N-methylacryloylglycine can be used to prepare polymer materials. It can participate in polymerization as a monomer to synthesize polymers with specific properties, such as for coatings, adhesives, etc. These polymers may have good adhesion, chemical resistance and certain cross-linking properties, thereby improving the overall quality of the material.

[0017] In the biomedical field, it also shows certain potential. It can participate in the synthesis of biomedical materials, such as hydrogels for tissue repair. Its special structure can interact with other biomolecules or materials, providing specific functions for biomaterials, and helping to promote the development of the biomedical field. Summary of the invention

[0018] The invention aims to provide a polyurethane modified acrylate aqueous emulsion and a preparation method thereof. The prepared aqueous emulsion is nano-scale. After the aqueous emulsion is prepared into a film, the tensile strength thereof increases with the increase of the amount of N-methacryloyl glycine added, while the elongation at break decreases. When the amount of N-methacryloyl glycine added is 1.96% and 3.85% of the total amount of monomers, the film has the best tensile strength and elongation at break, and can be used for preparing chemical adhesives.

[0019] To achieve the above object, the present invention provides a polyurethane-modified acrylate aqueous emulsion, comprising a polyurethane dispersion and polyacrylate; The polyurethane dispersion is polymerized from isophorone diisocyanate, polycaprolactone polyol, 2,2-bis(hydroxymethyl)propionic acid and trimethylolpropane; Polyacrylate is prepared by polymerization of methyl methacrylate, butyl acrylate, and N-methacryloyl glycine.

[0020] The present invention also provides a method for preparing the above-mentioned polyurethane modified acrylate aqueous emulsion, comprising the following steps: Step 1, preparation of polyurethane dispersion: Isophorone diisocyanate, polycaprolactone polyol, 2,2-bis(hydroxymethyl)propionic acid and trimethylolpropane are dissolved in N-methylpyrrolidone, stirred, dissolved, a catalyst is added, heated in a water bath, reacted under a nitrogen atmosphere, and then 2-hydroxyethyl acrylate is added and reacted to obtain a double-bond terminated polyurethane prepolymer, after the prepolymer temperature is reduced to room temperature, it is neutralized with triethylamine, the neutralization degree is 100%, and a polyurethane dispersion is obtained by adding an appropriate amount of distilled water; Step 2: Preparation of core-shell polyurethane modified acrylate aqueous emulsion: The mixture of acrylic monomers is added to the polyurethane dispersion obtained in step 1, and a polymerization reaction is carried out using potassium persulfate as an initiator. After copolymerization is completed, a polyurethane-modified acrylic ester aqueous emulsion with a core-shell structure is obtained.

[0021] Furthermore, in step 1, the catalyst is dibutyltin dilaurate.

[0022] Furthermore, in step 2, the mixture of acrylic monomers is methyl methacrylate, butyl acrylate and N-methacryloylglycine.

[0023] Furthermore, the mass percentage of the N-methylacryloylglycine in the acrylate monomer mixture is 0.66%-6.25%.

[0024] Furthermore, the mass percentage of the N-methylacryloylglycine in the acrylate monomer mixture is 1.96%.

[0025] Furthermore, the mass percentage of the N-methylacryloylglycine in the acrylate monomer mixture is 3.85%.

[0026] The present invention also provides the use of the polyurethane modified acrylate aqueous emulsion in the preparation of an adhesive.

[0027] The advantages and positive effects of the polyurethane modified acrylate aqueous emulsion and the preparation method thereof of the present invention are: 1. This application is the first to study the addition of N-methacryloyl glycine to an acrylic monomer mixture in a polyurethane-modified acrylate aqueous emulsion to form a polyurethane-modified acrylate aqueous emulsion. The particle size of the obtained aqueous emulsion is nanometer-scale. As the amount of N-methacryloyl glycine added increases, the particle size increases, and the polydispersity index increases.

[0028] 2. The aqueous emulsion prepared by the present invention is nano-scale. After the aqueous emulsion is prepared into a film, its tensile strength increases with the increase of the amount of N-methacryloyl glycine added, and its elongation at break decreases. When the amount of N-methacryloyl glycine added is 1.96% and 3.85% of the total monomer amount, it has the best tensile strength and elongation at break, and can be used to prepare chemical adhesives.

[0029] The technical solution of the present invention is further described in detail below through embodiments. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further illustrated by the following examples.

[0031] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0032] Unless otherwise defined, the instruments, equipment and reagents used in the present invention are all commercially available.

[0033] Abbreviations table: IPDI: Isophorone diisocyanate PCL: Polycaprolactone polyol DMPA: 2,2-bis(hydroxymethyl)propionic acid DBTDL: Dibutyltin dilaurate NMP: N-methyl-2-pyrrolidone TMP: Trimethylolpropane TEA: triethylamine MMA: Methyl Methacrylate HEA: 2-Hydroxyethyl acrylate THF: Tetrahydrofuran KPS: Potassium Persulfate BA: Butyl acrylate PUA: Polyurethane / Polyacrylic Acid PU: Polyurethane Example 1 Preparation of PUA composite emulsion: Step 1: Preparation of polyurethane dispersion: PCL was dried under vacuum at 100 °C before use in a humidified oven equipped with a mechanical stirrer, a thermometer, a nitrogen inlet, and a CaCl 2Add IPDI (3.0 g), PCL (4.0 g), DMPA (1.5 g) and TMP (0.2 g) to a four-mouth glass reactor with a drying tube condenser, add an appropriate amount of NMP, stir, dissolve, add DBTDL (0.02 g), heat to 80 ° C in a water bath, react for 2 hours under a nitrogen atmosphere, then add HEA (0.28 g) and react for 1.5 hours. Obtain a double-bond terminated polyurethane prepolymer. After the prepolymer temperature drops to room temperature, neutralize it with TEA (1.0 g) for 15 minutes, and the neutralization degree is 100%. A polyurethane dispersion with a solid content of 30 wt% is obtained by adding an appropriate amount of distilled water.

[0034] Step 2: Preparation of core-shell polyurethane modified acrylate aqueous emulsion: Polyurethane dispersions are used not only as macromonomers but also as macroemulsifiers.

[0035] The core-shell PUA composite emulsion was prepared by soap-free emulsion polymerization. The anionic aqueous polyurethane dispersion synthesized above was used as the seed emulsion.

[0036] A mixture of MMA (0.4 g), BA (0.2 g) and N-methacryloylglycine was added to the polyurethane dispersion obtained in step 1. An aqueous solution of KPS (0.02 g) was dripped into the reactor at 80°C over 2 hours.

[0037] When KPS is added to the dispersion, the acrylate monomer swelled in the polyurethane dispersion is initiated. After the addition, the polymerization reaction is carried out at 80°C for 3 hours. After the copolymerization is completed, a core-shell structured polyurethane modified acrylate emulsion is obtained.

[0038] In step 2, the amounts of N-methylacryloylglycine used were 0 g, 0.004 g, 0.008 g, 0.012 g, 0.024 g, 0.032 g, and 0.04 g, respectively, to obtain samples 1-7.

[0039] Example 2 Preparation of membrane samples for detection: The polyurethane modified acrylate emulsion sample obtained in Example 1 was poured onto a flat polytetrafluoroethylene disc, preliminarily dried naturally at room temperature, and then dried at 60° C. for 24 hours to prepare a uniform film. After demolding, the film was stored in a desiccator to avoid moisture for later use.

[0040] Example 3 Determination of particle size of the obtained polyurethane-modified acrylate aqueous emulsion: The particle size of the emulsion samples 1-7 obtained in Example 1 was determined by the dynamic light scattering (DLS) method using a Malvern instrument. The samples were diluted with water to the appropriate concentration according to the instrument instructions. The particle size was characterized by the mean diameter (Dz) and the particle size distribution was characterized by the polydispersity index (PDI). They were automatically calculated by a computer connected to the machine.

[0041] Table 1 Particle size and polydispersity index of polyurethane modified acrylate aqueous emulsion samples 1-7

[0042] Table 1 shows the Dz and PDI of PUA emulsions with different N-methacryloylglycine contents. The average particle size increases with increasing N-methacryloylglycine content.

[0043] The more N-methacryloylglycine is added, the greater the Dz and PDI of the composite emulsion.

[0044] When partially neutralized PU prepolymer is dispersed in water, the prepolymer chains begin to rearrange themselves by placing their ionic groups on the particle surface as much as possible; this rearrangement leads to the formation of relatively stable PU particles. As the amount of N-methacryloylglycine increases, more larger micelle particles with more ionic groups may be integrated to stabilize the system. Therefore, as the amount of N-methacryloylglycine increases, the Dz and PDI of the resulting emulsion increase.

[0045] Example 4 Determination of mechanical properties of the film sample formed by the obtained polyurethane-modified acrylate aqueous emulsion: The mechanical properties of the films were measured at room temperature using a fully automatic universal material testing machine (Tinius Olsen Series 1000) according to GB / T528-2009. The ultimate tensile strength and elongation at break of all samples were investigated. The dumbbell specimens were tested at room temperature using this machine with a crosshead speed of 100 mm / min. The quoted values ​​are the average of three measurements, and the average is calculated.

[0046] Table 2 Mechanical properties of polyurethane modified acrylate aqueous emulsion films

[0047] The data in Table 2 show the effect of adding different amounts of N-methacryloylglycine on the mechanical properties of the film. With the increase of N-methacryloylglycine, the density of cross-linking sites increases, resulting in an increase in tensile strength and a decrease in elongation at break.

[0048] The tensile strength of the polyurethane modified acrylate emulsion film without N-methacryloyl glycine was 2.26 MPa and the elongation was 568%. After adding N-methacryloyl glycine, its tensile strength changed from 2.26 MPa to 9.98 MPa. At the same time, the elongation at break decreased from 568% to 319%.

[0049] The present invention uses N-methacryloyl glycine for the preparation of polyurethane modified acrylate aqueous emulsions for the first time, obtains a series of polyurethane modified acrylate aqueous emulsions containing N-methacryloyl glycine, and detects the relevant properties thereof, and finds that the mechanical properties of the polyurethane modified acrylate aqueous emulsions after adding N-methacryloyl glycine are significantly improved. It is also determined that when the addition amount of N-methacryloyl glycine is 1.96% and 3.85% of the total monomer amount, the tensile strength and elongation at break are optimal.

[0050] Therefore, the present invention adopts the above-mentioned polyurethane modified acrylate aqueous emulsion and the preparation method thereof. The prepared aqueous emulsion is nanometer-level. After the aqueous emulsion is prepared into a film, the tensile strength thereof increases with the increase of the amount of N-methacryloyl glycine added, and the elongation at break decreases. When the amount of N-methacryloyl glycine added is 1.96% and 3.85% of the total monomer amount, the film has the best tensile strength and elongation at break, and can be used to prepare chemical adhesives.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. Polyurethane modified acrylate aqueous emulsion, Features: Includes polyurethane dispersions and polyacrylates; The polyurethane dispersion is polymerized from isophorone diisocyanate, polycaprolactone polyol, 2,2-bis(hydroxymethyl)propionic acid and trimethylolpropane; Polyacrylate is prepared by polymerization of methyl methacrylate, butyl acrylate, and N-methacryloyl glycine.

2. The method for preparing the polyurethane modified acrylate aqueous emulsion according to claim 1, It is characterized in that The following steps are involved: Step 1, preparation of polyurethane dispersion: Isophorone diisocyanate, polycaprolactone polyol, 2,2-bis(hydroxymethyl)propionic acid and trimethylolpropane are dissolved in N-methylpyrrolidone, stirred, dissolved, a catalyst is added, heated in a water bath, reacted under a nitrogen atmosphere, and then 2-hydroxyethyl acrylate is added and reacted to obtain a double-bond terminated polyurethane prepolymer, after the prepolymer temperature is reduced to room temperature, it is neutralized with triethylamine, the neutralization degree is 100%, and a polyurethane dispersion is obtained by adding an appropriate amount of distilled water; Step 2: Preparation of core-shell polyurethane modified acrylate aqueous emulsion: The mixture of acrylic monomers is added to the polyurethane dispersion obtained in step 1, and a polymerization reaction is carried out using potassium persulfate as an initiator. After copolymerization is completed, a polyurethane-modified acrylic ester aqueous emulsion with a core-shell structure is obtained.

3. The preparation method according to claim 2, Features: In step 1, the catalyst is dibutyltin dilaurate.

4. The preparation method according to claim 2, Features: In step 2, the mixture of acrylic monomers is methyl methacrylate, butyl acrylate and N-methacryloylglycine.

5. The preparation method according to claim 4, Features: The mass percentage of the N-methylacryloylglycine in the acrylate monomer mixture is 0.66%-6.25%.

6. The preparation method according to claim 5, Features: The mass percentage of the N-methylacryloylglycine in the acrylate monomer mixture is 1.96%.

7. The preparation method according to claim 5, Features: The mass percentage of the N-methacryloylglycine in the acrylate monomer mixture is 3.85%.

8. Use of the polyurethane modified acrylate aqueous emulsion as claimed in claim 1 in the preparation of an adhesive.

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