CN108976425A - A kind of preparation method of polyurethane-epoxy resin block copolymerization water-base resin - Google Patents

Abstract

A kind of preparation method of polyurethane-epoxy resin block copolymerization water-base resin, comprising the following steps: (1) oligomer dihydric alcohol and di-isocyanate reaction are obtained into base polyurethane prepolymer for use as；(2) epoxy resin, piperazine and water-soluble solvent is added, reaction to epoxide number is 0, obtains mixture；(3) deionized water with quality such as added water-soluble solvents is added, stirs evenly, then staticly settle out polymer, washes polymer, obtains precursor resin；(4) gained precursor resin is heated up, be added organic acid, stirring, be added deionized water, stir 20-35min to get.The present invention realizes the block copolymerization of polyurethane resin and epoxy resin, overcomes limitation of the synthetic method of common polyurethane epoxy material to epoxy resin introduction volume；And the present invention can adjust the performance of products obtained therefrom by adjusting formulation parameter.

Description

A kind of preparation method of polyurethane-epoxy resin block copolymerization waterborne resin

technical field

The invention relates to the field of polyurethane-epoxy resin materials, in particular to a method for preparing a polyurethane-epoxy resin block copolymerized water-based resin, which is particularly suitable for cathodic electrophoretic coatings.

Background technique

There are many kinds of epoxy resins and their application fields are wide. However, the unmodified epoxy resin has high crosslinking density after curing, resulting in excessive internal stress, and the product has defects such as brittleness, easy cracking, and poor impact resistance, which limit its application field. Polyurethane has good flexibility, and its copolymerization modification with epoxy resin can achieve complementary advantages and obtain polyurethane epoxy materials with better performance. There are usually three methods for preparing polyurethane epoxy materials: mechanical blending method, direct graft copolymerization method and epoxy ring-opening method.

The mechanical blending method is to wrap the epoxy resin with a hydrophilic polyurethane prepolymer, and then hydrate it to obtain an epoxy-modified polyurethane resin emulsion. The advantage of this method is that it is easy to prepare a stable resin emulsion, but there are two disadvantages. First, the method is simply a physical blend, and the two resins do not have chemical bonds. The advantages of the two resins complement each other, so it is difficult to obtain a paint film with excellent performance; secondly, the epoxy resin can be stably dispersed into the emulsion by being wrapped, so the increase in the epoxy resin increases the particle size of the obtained resin emulsion. become larger, and even part of the epoxy resin cannot be coated, which affects the stability of the resin emulsion, resulting in the use of less epoxy resin to modify polyurethane, thus affecting the application range of the product.

The direct graft copolymerization method is to synthesize a polyurethane prepolymer first, and then the prepolymer reacts with the secondary hydroxyl groups in the epoxy resin to introduce polyurethane into the epoxy resin. The advantage of this method is that the properties of the obtained paint film are better than those obtained by the mechanical blending method. The disadvantage is that it is difficult to prepare a stable resin emulsion, because in the polymerization reaction, epoxy resin will produce branches after participating in the reaction. Therefore, when the amount exceeds a certain range, the molecular weight of the reactant will increase sharply, making it difficult for the resin to be hydrated or to obtain a stable emulsion.

The epoxy ring-opening method is to use a small molecular acid, amine or alcohol to perform a ring-opening reaction with an epoxy resin to generate a hydroxyl-terminated epoxy resin, and then react it as a polyol with a diisocyanate. The method increases the amount of epoxy resin used, and the prepared paint film has excellent performance. However, the disadvantage is that the ring-opening reaction process of epoxy resin is difficult to control and cannot be completely opened. Therefore, the obtained modified resin emulsion contains epoxy groups and small molecule ring-opening agents (such as acids, amines, etc.), affect the storage stability of the emulsion.

Contents of the invention

The technical problem to be solved in the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a polyurethane-epoxy resin block copolymerized water-based resin with a relatively simple process, and the obtained polyurethane-epoxy resin block copolymerized water-based resin is stable in storage sex is better.

The technical scheme that the present invention solves its technical problem adopts is, a kind of preparation method of polyurethane-epoxy resin block copolymerization waterborne resin, comprises the following steps:

(1) Put the oligomer diol and diisocyanate into the reaction bottle, the reaction temperature is 50°C~80°C, and react for 1~3h to prepare the polyurethane prepolymer;

The ratio of the oligomer dibasic alcohol and diisocyanate should make the ratio of the amount of substance of the isocyanate group in the diisocyanate to the ratio of the amount of substance of [OH] in the oligomer dibasic alcohol be 1.5-2:1;

(2) Add epoxy resin, piperazine and water-soluble solvent to the polyurethane prepolymer obtained in step (1), stir evenly, raise the temperature to 30°C~70°C, and react for 3~8 hours until the epoxy value is 0 , to get a mixture;

The addition of the water-soluble solvent is 60-100% of the total mass of polyurethane prepolymer, epoxy resin, and piperazine;

The ratio of epoxy resin and piperazine is controlled by chain extension parameter Rt and hard segment content H%;

Control the chain extension parameter Rt=1.2~1.6, Rt={n(amino group)/[n(epoxy group)+n(isocyanate group)]}, n represents the amount of substance (number of moles). Controlling Rt within this range can control the molecular weight of the synthetic resin. Generally, Rt>1.0 ensures that the block copolymer is terminated with an amine group; the amino group is the secondary amine in piperazine, and the epoxy group is the epoxy group in the epoxy resin. , The isocyanate group is the isocyanate group in the polyurethane prepolymer.

Control the hard segment content H% to be 10~60% (preferably 20-50%); H%={[m(epoxy resin)+m(piperazine)]/ [m(epoxy resin)+m(piperazine) )+ m (polyurethane prepolymer)] }, m represents the quality of the substance. The hard segment content H% is the hard segment content, which can adjust the flexibility of the synthetic resin.

(3) Add deionized water of the same quality as the added water-soluble solvent to the mixture obtained in step (2), stir evenly, then let stand to precipitate the polymer, wash the polymer with water, and obtain the precursor resin;

(4) Raise the temperature of the precursor resin obtained in step (3) to 40-55°C, add an organic acid equivalent to 1.2-16.0% (preferably 2.8-10.0%) of the mass of the precursor resin, stir for 3-10 minutes, and add an organic acid equivalent to the mass of the precursor resin 1-3 times the amount of deionized water, stirred for 20-35min (emulsification), and the polyurethane-epoxy resin block copolymerized water-based resin was obtained.

Further, in step (1), the oligomer diol is at least one of polycaprolactone diol, polyethylene adipate, and polytetrahydrofuran diol, among which preferably Polycaprolactone diol.

Further, in step (1), the molecular weight of the oligomer diol is 400-4000, wherein the preferred molecular weight is 1000-2000.

Further, in step (1), the diisocyanate is toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI) At least one of, among which at least one of toluene diisocyanate (TDI) and isophorone diisocyanate (IPDI) is preferred.

Further, in step (2), the epoxy resin is at least one of epoxy E-51, epoxy E-44, epoxy E-20, epoxy E-12, preferably epoxy E-44, E-20. The lower the epoxy value, the smaller the amine value in the water-based resin.

Further, in step (2), the water-soluble solvent is one or both of N,N-dimethylformamide, tetrahydrofuran, acetone, and N-methylpyrrolidone, among which N,N-dimethyl At least one of formamide and tetrahydrofuran.

There are three reasons for adding a water-soluble solvent to the reaction: first, it dissolves the reactant, and makes the reactant molecules fully contact, so that the reaction is more complete; second, it can reduce the viscosity of the reaction system, which is beneficial to the heat transfer and Heat dissipation; third, it is a water-soluble solvent, so after the reaction is stopped, only need to add deionized water to precipitate the precursor resin, and the mixture of solvent and water can be recycled after simple distillation and dehydration, so , eliminating the step of solvent removal in the general water-based resin preparation process.

Further, in step (2), the reaction is controlled at a temperature of 45-60°C.

Further, in step (2), the reaction time is controlled to be 4-6h.

Further, in step (4), the organic acid is at least one of glacial acetic acid, lactic acid, formic acid, propionic acid, oxalic acid and the like.

The design principle of the present invention: Synthesize polyurethane prepolymer with oligomer diol and diisocyanate, carry out chain extension polymerization reaction with piperazine and epoxy resin, adjust the molecular weight of synthetic resin by controlling the material ratio of copolymer and flexibility to prepare a series of linear multi-block macromolecular resins.

The present invention adopts the purpose of piperazine chain extension to have the following two points: 1. piperazine is a cyclic structure material, which can be modified by chain extension to improve the strength of synthetic resin film; 2. piperazine two ends are secondary amino groups, and its Chain extension has the following two advantages. First, while introducing ionizable amine groups into the synthetic resin, the amine value of the resin is kept in a lower range. Second, it can react with isocyanate groups and epoxy groups at a lower temperature, and its speed is much faster than the reaction speed of secondary hydroxyl groups on epoxy and isocyanate groups. Therefore, the reaction process is simple and economical.

The purpose of chain extension of polyurethane prepolymer used in the present invention has the following three points: 1. the two ends of polyurethane prepolymer are isocyanate groups, which can react with the secondary amino group in piperazine at a lower temperature; 2. the introduction of polyurethane prepolymer It can make the synthesized resin have certain flexibility; ③The polyurethane prepolymer contains a hydrophobic segment, which can cover the blocked isocyanate curing agent, so that the curing agent and the resin can be electrophoresed to the surface of the electrode synchronously and proportionally.

In the present invention, epoxy resin is used as the hard segment, polyurethane prepolymer is used as the soft segment, piperazine is used as the chain extender, and the molecular weight of the synthetic resin is controlled by adjusting the chain extension parameter (Rt). By adjusting the hard segment content (H%) To adjust the flexibility of the synthetic resin, a series of polyurethane-epoxy resin linear block copolymers are precisely prepared, and after neutralization and hydration, a series of polyurethane-epoxy resin block copolymerization water-based resins can be obtained. The synthetic precursor resin can also be combined with Compounded with blocked isocyanate to make cathodic electrophoretic coating.

The reaction formula of the preparation process of the polyurethane-epoxy resin block copolymerized water-based resin of the present invention is as follows:

Compared with the prior art, the present invention has the following advantages:

(1) In the present invention, epoxy resin is used as the hard segment, polyurethane prepolymer is used as the soft segment, piperazine is used as the chain extender, the molecular weight of the synthetic resin is controlled by adjusting the chain extension parameters, and the synthetic resin is adjusted by adjusting the content of the hard segment. The flexibility of the resin. This synthetic method has realized the block copolymerization of polyurethane resin and epoxy resin, has overcome the synthetic method of common polyurethane epoxy resin material to the limitation of epoxy resin introduction amount; The properties of the resulting product are adjusted.

(2) The present invention uses polyurethane prepolymer, epoxy resin and piperazine to carry out chain extension polymerization reaction, wherein both ends of piperazine are secondary amino groups, which can react with isocyanate groups and epoxy groups at lower temperatures, Therefore, the reaction process is simple and economical, and its two amino groups are secondary amines, so that the amine value of the synthesized polyurethane-epoxy resin block copolymerized water-based resin is low.

(3) The present invention adopts a water-soluble solvent, which can be miscible with water in any proportion. Therefore, water can be used as a precipitating agent in the present invention, and the precursor resin is precipitated from the reaction solution, and the resulting solvent is mixed with water. The mixed solution can be recycled after simple distillation and dehydration. This method eliminates the solvent removal step in the traditional water-based resin preparation process, and at the same time neutralizes the hydrated water-based resin to achieve the goal of zero VOC.

Detailed ways

The present invention will be described in further detail below in conjunction with specific examples.

Embodiment 1 (comparative example)

Taking formula parameters Rt=1.10, H%=30w% as an example, the preparation method of polyurethane-epoxy resin block copolymerized waterborne resin is as follows:

(1) Put 25.39 g of polycaprolactone diol (molecular weight Mn=2000) and 5.64 g of isophorone diisocyanate (IPDI) into the reaction bottle, the reaction temperature is 80 ℃, and react for 2 hours to prepare Obtain polyurethane prepolymer 31.03g;

The ratio of the oligomer dibasic alcohol and diisocyanate makes the ratio of the amount of substance of the isocyanate group in the diisocyanate to the ratio of the amount of substance of [OH] in the oligomer dibasic alcohol be 2:1;

(2) Add 10.00 g of epoxy E-44, 3.30 g of piperazine and 40.21 g of N,N-dimethylformamide to the polyurethane prepolymer obtained in step (1), stir evenly, heat up to 55°C, and react for 5 h ; Reaction until the epoxy value is 0, the mixture is obtained;

(3) Add deionized water of the same quality as the added water-soluble solvent to the mixture obtained in step (2), stir evenly, then let stand to precipitate the polymer, wash the polymer with water, and obtain the precursor resin;

(4) Heat the precursor resin obtained in step (3) to 45°C, add glacial acetic acid equivalent to 2.9% of the mass of the precursor resin, stir for 5 minutes, add deionized water equivalent to twice the mass of the precursor resin, and stir for 30 minutes to emulsify, and you can get Polyurethane-epoxy resin block copolymerization water-based resin.

Example 2

Taking formula parameters Rt=1.20, H%=30w% as an example, the preparation method of polyurethane-epoxy resin block copolymerized waterborne resin is as follows:

(1) Put 30.05 g of polycaprolactone diol (molecular weight Mn=2000) and 6.69 g of isophorone diisocyanate (IPDI) into the reaction bottle, the reaction temperature is 80 ℃, and react for 2 hours to prepare Obtain polyurethane prepolymer 36.74g;

The ratio of the oligomer dibasic alcohol and diisocyanate makes the ratio of the amount of substance of the isocyanate group in the diisocyanate to the ratio of the amount of substance of [OH] in the oligomer dibasic alcohol be 2:1;

(2) Add 11.59 g of epoxy E-44, 4.16 g of piperazine and 41.98 g of N,N-dimethylformamide to the polyurethane prepolymer obtained in step (1), stir evenly, heat up to 55°C, and react for 5 h ; Reaction until the epoxy value is 0, the mixture is obtained;

(3) Add deionized water of the same quality as the added water-soluble solvent to the mixture obtained in step (2), stir evenly, then let stand to precipitate the polymer, wash the polymer with water, and obtain the precursor resin;

(4) Heat the precursor resin obtained in step (3) to 45°C, add glacial acetic acid equivalent to 3.6% of the mass of the precursor resin, stir for 5 minutes, add deionized water equivalent to 2 times the mass of the precursor resin, and stir for 30 minutes to emulsify to obtain Polyurethane-epoxy resin block copolymerization water-based resin.

Example 3

Taking formula parameters Rt=1.25, H%=30w% as an example, the preparation method of polyurethane-epoxy resin block copolymerized waterborne resin is as follows:

(1) Put 27.90 g of polycaprolactone diol (molecular weight Mn=2000) and 6.21 g of isophorone diisocyanate (IPDI) into the reaction bottle, the reaction temperature is 80 ℃, and react for 2 hours to prepare Obtain polyurethane prepolymer 34.11g;

The ratio of the oligomer dibasic alcohol and diisocyanate makes the ratio of the amount of substance of the isocyanate group in the diisocyanate to the ratio of the amount of substance of [OH] in the oligomer dibasic alcohol be 2:1;

(2) Add 10.63 g of epoxy E-44, 3.99 g of piperazine and 38.98 g of N,N-dimethylformamide to the polyurethane prepolymer obtained in step (1), stir evenly, heat up to 55°C, and react for 5 h ; Reaction until the epoxy value is 0, the mixture is obtained;

(3) Add deionized water of the same quality as the added water-soluble solvent to the mixture obtained in step (2), stir evenly, then let stand to precipitate the polymer, wash the polymer with water, and obtain the precursor resin;

(4) Heat the precursor resin obtained in step (3) to 45°C, add glacial acetic acid equivalent to 3.7% of the mass of the precursor resin, stir for 5 minutes, add deionized water equivalent to 2 times the mass of the precursor resin, and stir for 30 minutes to emulsify to obtain Polyurethane-epoxy resin block copolymerization water-based resin.

Example 4

Taking formula parameters Rt=1.30, H%=30w% as an example, the preparation method of polyurethane-epoxy resin block copolymerized waterborne resin is as follows:

(1) Put 28.86 g of polycaprolactone diol (molecular weight Mn=2000) and 6.42 g of isophorone diisocyanate (IPDI) into the reaction bottle, the reaction temperature is 80 ℃, and react for 2 hours to prepare Obtain polyurethane prepolymer 35.28g;

The ratio of the oligomer dibasic alcohol and diisocyanate makes the ratio of the amount of substance of the isocyanate group in the diisocyanate to the ratio of the amount of substance of [OH] in the oligomer dibasic alcohol be 2:1;

(2) Add 10.86 g of epoxy E-44, 4.26 g of piperazine and 40.32 g of N,N-dimethylformamide to the polyurethane prepolymer obtained in step (1), stir evenly, heat up to 55°C, and react 5 h; react to epoxy value 0, get mixture;

(3) Add deionized water of the same quality as the added water-soluble solvent to the mixture obtained in step (2), stir evenly, then let stand to precipitate the polymer, wash the polymer with water, and obtain the precursor resin;

(4) Heat the precursor resin obtained in step (3) to 45°C, add glacial acetic acid equivalent to 3.9% of the mass of the precursor resin, stir for 5 minutes, add deionized water equivalent to twice the mass of the precursor resin, and stir for 30 minutes to emulsify, and you can get Polyurethane-epoxy resin block copolymerization water-based resin.

Example 5

Taking formula parameters Rt=1.30, H%=40w% as an example, the preparation method of polyurethane-epoxy resin block copolymerized waterborne resin is as follows:

(1) Put 30.44 g of polycaprolactone diol (molecular weight Mn=2000) and 6.55 g of isophorone diisocyanate (IPDI) into the reaction bottle, the reaction temperature is 80 ℃, and react for 2 hours to prepare Obtain polyurethane prepolymer 36.99g;

The ratio of the oligomer dibasic alcohol and diisocyanate makes the ratio of the amount of substance of the isocyanate group in the diisocyanate to the ratio of the amount of substance of [OH] in the oligomer dibasic alcohol be 2:1;

(2) Add 18.51 g of epoxy E-44, 6.25 g of piperazine and 49.41 g of N,N-dimethylformamide to the polyurethane prepolymer obtained in step (1), stir evenly, heat up to 55°C, and react for 5 h ; Reaction until the epoxy value is 0, the mixture is obtained;

(3) Add deionized water of the same quality as the added water-soluble solvent to the mixture obtained in step (2), stir evenly, then let stand to precipitate the polymer, wash the polymer with water, and obtain the precursor resin;

(4) Heat the precursor resin obtained in step (3) to 45°C, add glacial acetic acid equivalent to 5.0% of the mass of the precursor resin, stir for 5 minutes, add deionized water equivalent to 2 times the mass of the precursor resin, and stir for 30 minutes to emulsify to obtain Polyurethane-epoxy resin block copolymerization water-based resin.

Example 6

Taking formula parameters Rt=1.30, H%=50w% as an example, the preparation method of polyurethane-epoxy resin block copolymerized waterborne resin is as follows:

(1) Put 25.00 g of polycaprolactone diol (molecular weight Mn=2000) and 5.41 g of isophorone diisocyanate (IPDI) into the reaction bottle, the reaction temperature is 80 ℃, and react for 2 hours to prepare Obtain polyurethane prepolymer 30.41g;

The ratio of the oligomer dibasic alcohol and diisocyanate makes the ratio of the amount of substance of the isocyanate group in the diisocyanate to the ratio of the amount of substance of [OH] in the oligomer dibasic alcohol be 2:1;

(2) Add 23.30 g of epoxy E-44, 7.16 g of piperazine and 48.70 g of N,N-dimethylformamide to the polyurethane prepolymer obtained in step (1), stir evenly, heat up to 55°C, and react for 5 h ; Reaction until the epoxy value is 0, the mixture is obtained;

(3) Add deionized water of the same quality as the added water-soluble solvent to the mixture obtained in step (2), stir evenly, then let stand to precipitate the polymer, wash the polymer with water, and obtain the precursor resin;

(4) Heat the precursor resin obtained in step (3) to 45°C, add glacial acetic acid equivalent to 6.4% of the mass of the precursor resin, stir for 5 minutes, add deionized water equivalent to 2 times the mass of the precursor resin, and stir for 30 minutes to emulsify to obtain Polyurethane-epoxy resin block copolymerization water-based resin.

Example 7

Taking formula parameters Rt=1.25, H%=50w% as an example, the preparation method of polyurethane-epoxy resin block copolymerized waterborne resin is as follows:

(1) Put 13.40 g of dehydrated polycaprolactone diol (molecular weight Mn=1000) and 3.50 g of toluene diisocyanate (TDI) into the reaction bottle, the reaction temperature is 60 ℃, and react for 2 hours to prepare the polyurethane pre- Polymer 16.9g;

The ratio of the oligomer dibasic alcohol and diisocyanate makes the ratio of the amount of substance of the isocyanate group in the diisocyanate to the ratio of the amount of substance of [OH] in the oligomer dibasic alcohol be 1.5: 1;

(2) Add 12.48 g of epoxy E-51, 4.42 g of piperazine and 27.04 g of tetrahydrofuran to the polyurethane prepolymer obtained in step (1) into the reaction flask, stir evenly, raise the temperature to 50°C, and react for 6 h; The epoxy value is 0, and the mixture is obtained;

(3) Add deionized water of the same quality as the added water-soluble solvent to the mixture obtained in step (2), stir evenly, then let stand to precipitate the polymer, wash the polymer with water, and obtain the precursor resin;

(4) Heat the precursor resin obtained in step (3) to 45°C, add lactic acid equivalent to 10.0% of the mass of the precursor resin, stir for 5 minutes, add deionized water equivalent to 3 times the mass of the precursor resin, and stir for 30 minutes to emulsify to obtain polyurethane -Epoxy resin block copolymerized water-based resin.

Example 8

Taking formula parameters Rt=1.25, H%=50w% as an example, the preparation method of polyurethane-epoxy resin block copolymerized waterborne resin is as follows:

(1) Put 17.18g of polyethylene adipate (molecular weight Mn=2000) and 2.60g of hexamethylene diisocyanate (HDI) into the reaction flask, the reaction temperature is 50℃, After 2 hours of reaction, 11.61 g of polyurethane prepolymer was prepared;

The ratio of the oligomer dibasic alcohol and diisocyanate makes the ratio of the amount of substance of the isocyanate group in the diisocyanate to the ratio of the amount of substance of [OH] in the oligomer dibasic alcohol be 1.8:1;

(2) Add 17.02g of epoxy E-20, 2.76g of piperazine and 31.65g of N-methylpyrrolidone to the polyurethane prepolymer obtained in step (1), stir evenly, raise the temperature to 45°C, and react for 7 hours; A value of 0 results in a mixture;

(3) Add deionized water of the same quality as the added water-soluble solvent to the mixture obtained in step (2), stir evenly, then let stand to precipitate the polymer, wash the polymer with water, and obtain the precursor resin;

(4) Heat the precursor resin obtained in step (3) to 45°C, add propionic acid equivalent to 4.4% of the mass of the precursor resin, stir for 5 minutes, add deionized water equivalent to 1.5 times the mass of the precursor resin, stir for 30 minutes to emulsify, and then get Polyurethane-epoxy resin block copolymerization water-based resin.

The performance detection embodiment of each embodiment gained polyurethane-epoxy resin block copolymerization waterborne resin:

Before testing, the polyurethane-epoxy resin block copolymerization water-based resin to be tested is prepared into a cured product: the obtained polyurethane-epoxy resin block copolymerization water-based resin and BL3370 MPA are pressed according to n (active hydrogen): n (isocyanate group) = 2 Compounding, then pour into a polytetrafluoroethylene mold, wait for the water to evaporate and dry, put it in a 120°C oven and bake for 20 minutes, and then obtain a cured product sample.

The application of each embodiment gained polyurethane-epoxy resin block copolymer resin in cathodic electrophoresis can adopt the following methods:

First take the prepared polyurethane-epoxy resin block copolymer resin, add it and blocked isocyanate into the container in a certain proportion, stir until homogeneous with a disperser, the stirring speed is 600r/min, and then add an appropriate amount of organic acid, Continue to stir for 5 minutes, then add deionized water into the container, after stirring for 30 minutes, adjust the solid content of the emulsion to 20w%, and then obtain a uniformly dispersed electrophoretic emulsion; use tinplate or other metal plates as cathodes, and use electrophoresis voltage 40-120V Electrophoresis for 30-150s; after the end, take out the metal plate, rinse the surface of the deposited layer with deionized water, bake at 120°C for 30min, and finally obtain a sample with a flat and smooth coating film.

Experimental Results and Characterization

Through the research of Examples 1 to 8 above, the effects of formula parameters on resin structure parameters, water-based resin performance, water-based resin cured product performance, resin cathodic electrophoretic fluid and paint film performance were explored. The characterization results are as follows.

(1) Influence of formula parameters on resin structure parameters

The effect of Rt on the molecular weight of the synthetic resin was explored. The experimental results are shown in Table 1.

It can be seen from Table 1 that as Rt increases, the molecular weight of the synthetic resin decreases, and the molecular weight distribution (D) increases overall. Because the larger the Rt, the more excess amino substances, the more the number of amino-terminated macromolecules formed, the smaller the molecular weight of the resin; The relative gap becomes larger, so the molecular weight distribution becomes wider.

(2) The influence of formula parameters on the performance of water-based resin

The influence of formulation parameters on the properties of waterborne resins was explored. The experimental results are shown in Table 2.

It can be seen from Table 2 that when H% is constant and Rt is 1.10, the synthetic resin cannot be hydrated; when Rt≥1.20, the particle size of the emulsion decreases with the increase of Rt, which is mainly because the molecular weight of the synthetic resin Decrease, while the amine value increases, so under the same degree of neutralization, the number of ionized amine groups increases, and the hydrophilicity of the resin increases.

When Rt is constant, the particle size of the emulsion decreases with the increase of H%, which is mainly because the amine value of the synthetic resin increases with the increase of H%, and under the same degree of neutralization, the ionized amine groups of the resin increase , the hydrophilicity of the resin increases.

(3) The influence of formula parameters on the properties of cured products

The influence of formulation parameters on the mechanical properties of synthetic resin cured products was explored. The experimental results are shown in Table 3.

It can be seen from Table 3 that when H% remains constant and Rt increases, the tensile strength decreases and the elongation at break increases, mainly because on the one hand the Rt is large and the molecular weight of the synthetic resin is small, that is, the molecular chain is short and the molecular chain There are few physical entanglement points between them; on the other hand, the Rt is large, and the active hydrogen content of the resin is small, resulting in few chemical crosslinking points of the resin.

When Rt remains unchanged and H% increases, the tensile strength increases and the elongation at break decreases, mainly because on the one hand, H% increases, the rigid structure of the modified resin increases, and the cohesion of the cured product increases; on the other hand H% increases, the active hydrogen content of the resin increases, and the chemical crosslinking points of the resin increase.

(4) Influence of formulation parameters on the performance of resin cathodic electrophoretic fluid

The influence of formulation parameters on the performance of resin cathodic electrophoretic fluid was explored. The experimental results are shown in Table 4.

It can be seen from Table 4 that when H% is constant and Rt is 1.20, the cathodic electrophoresis liquid prepared by synthetic resin is a milky white turbid liquid, and the mechanical stability and storage stability are not up to standard. This is mainly because the synthetic resin has a large molecular weight. And there are fewer amine groups that can be ionized, so its hydrophilicity is poor. After wrapping the closed curing agent, the dispersion stability of the emulsion is poor (the resin in this case can only be used as a water-based coating); when Rt When ≥1.25, the conductivity and pH value of the electrophoretic solution increase with the increase of Rt, which is mainly because the molecular weight of the synthetic resin decreases and the amine value increases, so under the same degree of neutralization, the ionized The amine group increases, and the amine group is both a salt-forming group and a basic group. Therefore, the Rt increases, and the conductivity and pH of the electrophoretic solution increase.

When the Rt is constant and the H% content increases, the conductivity and pH of the electrophoretic solution increase with the increase of H%, which is mainly because the increase of H% increases the number of amine groups introduced by the synthetic resin, that is, the amine value Therefore, under the same degree of neutralization, the ionized amine group increases, and the amine group is both an ionizable group and a basic group, so H% increases, and the conductivity of the electrophoretic solution and pH increase.

(5) The influence of formula parameters on the performance of electrophoretic paint film

The influence of formula parameters on the performance of electrophoretic paint film was explored. The experimental results are shown in Table 5.

It is known from Table 5 that under the same electrophoresis conditions, when H% is constant and Rt increases, the hardness of the paint film decreases, the thickness and gloss increase, and the water resistance and acid and alkali resistance decrease, and when Rt = 1.25, The paint film is much more resistant to alkali than to acid. This is mainly because, on the one hand, the Rt increases, the molecular weight of the modified resin is small, that is, the molecular chain is short, the physical entanglement points between the molecular chains are few, and the active hydrogen content of the resin is small, resulting in few chemical crosslinking points of the resin. , so the paint film hardness, water resistance, and acid and alkali resistance decrease; on the one hand, the increase in Rt increases the amine value of the synthetic resin, and the amine group is both a salt-forming group and a hydrophilic group. Therefore, the increase in the amine value makes While the conductivity of the synthetic resin cathodic electrophoretic fluid increases, the water resistance of the synthetic resin decreases, so the thickness of the paint film increases under the same electrophoresis conditions, and the water resistance of the paint film decreases. On the other hand, the positively charged colloidal particles are neutralized and precipitated by OH- near the cathode, and the obtained coating is cured into a paint film after baking. Therefore, under acidic conditions, the amine groups in the paint film are ionized, which is easy to make the paint However, this phenomenon does not occur in alkaline conditions, so when Rt = 1.25, the alkali resistance of the paint film is much stronger than the acid resistance.

It is known from the table that under the same electrophoresis conditions, Rt remains unchanged and H% increases, the thickness, hardness and alkali resistance of the paint film increase, the gloss and water resistance decrease, and the alkali resistance is generally stronger than the acid resistance. The main reason is that on the one hand, the increase of H% increases the rigid structure of the synthetic resin, increases the cohesion of the cured product, and the active hydrogen content of the resin increases, and the chemical crosslinking points of the resin increase. Therefore, the increase of H% increases the hardness of the paint film and Alkali resistance increases; on the one hand, as H% increases, the amine value of the synthetic resin increases, and the amine group is both a salt-forming group and a hydrophilic group. Therefore, while the conductivity of the cathodic electrophoretic solution increases, the synthetic The water resistance of the resin, and under the same electrophoresis conditions, the migration speed of charged colloidal particles increases, that is, the speed of electrodeposition increases, but when the speed of electrodeposition exceeds a certain speed, it is easy to make the paint film rough and even pile up. Therefore, H % increases, the thickness of the paint film becomes larger, and the gloss and water resistance decrease. On the other hand, the positively charged colloidal particles are neutralized and precipitated by ^OH- near the cathode, and the obtained coating is cured into a paint film after baking. Therefore, under acidic conditions, the amine groups in the paint film are ionized, which is easy to make the paint The anti-dissolution phenomenon of the film appears, but this phenomenon does not appear in alkaline conditions, so the alkali resistance of the paint film is stronger than the acid resistance in general.

Attached detection method:

1. Performance test of water-based resin and its prepared electrophoretic fluid

(1) Determination of epoxy value

Weigh 0.5000-1.5000 g of resin, place it in a 150 ml Erlenmeyer flask, add 20.0 ml of hydrochloric acid-acetone solution (1 ml of concentrated hydrochloric acid, dissolved in 40 ml of acetone, ready-to-use), stopper the bottle tightly, shake Mix well to dissolve the sample completely. Put it in a cool place for 1 hour, add 2-3 drops of methyl red indicator dropwise, and then titrate with 0.2 mol/L NaOH standard solution. When the color of the solution changes from red to yellow, it is the end point. Do the same blank experiment, and the calculation method is as follows:

In the formula: E ---- epoxy value (mol/100g);

V ₀ ---- the volume of NaOH solution consumed by the blank (ml);

V ₁ ---- the volume of NaOH solution consumed by the sample (ml);

W ---- the quality of the sample (g);

N _NaOH - the concentration of NaOH solution (mol/L);

(1) Emulsion Appearance: Visually observe the state of the prepared emulsion. Example: color, transparency, presence or absence of condensation, etc.;

(2) Emulsion solid content: refer to "GB/T 1725-2007 Determination of non-volatile content of paints, varnishes and plastics";

(3) Mechanical stability of the emulsion: There is no relevant test standard for the mechanical stability of the emulsion, and it is tentatively shown in the table with reference to the existing experimental methods.

Mechanical stability level and classification method level Grading method Level 1 No phase separation at 1500 r/min×20 min level 2 No phase separation at 2000 r/min×20 min Level 3 No phase separation at 2500 r/min×20 min level 4 No phase separation at 3000 r/min×20 min Level 5 No phase separation at 3500 r/min×20 min Level 6 No phase separation at 4000 r/min×20 min

Among them, the higher the level, the better the stability of the electrophoretic coating emulsion. Generally, if there is no phase separation after centrifugation at 3000 r/min for 20 minutes, it can be considered that the emulsion has no phase separation after standing at room temperature for 6 months.

(4) pH measurement of electrophoresis solution: use PHS-3C pH meter to measure;

(5) Determination of the conductivity of the electrophoretic solution: refer to HG/T3335-1997 (1985) "Methods for the determination of the conductivity of electrophoretic paint";

(6) Determination of particle size of the emulsion: The particle size and distribution of the emulsion were measured with a Zetasizer Nano ZS particle size distribution analyzer from Malvern, UK.

, Cured product performance test

Referring to ASTM D2707-1985, the cured product was cut into a standard sample, and a tensile test was performed at room temperature with a tensile tester at a tensile speed of 90 mm/min to test the tensile strength and elongation at break of the cured product.

, coating performance test

(1) Pencil hardness: refer to "GB/T 6739-2006/ISO 15184:1998 Paint and Varnish Pencil Method for Determination of Paint Film Hardness";

(2) Adhesion: refer to "GB/T 9286-1998/ISO 2409:1992 Cross-cut test of paint and varnish film";

(3) Flexibility: Refer to "GB/T 1731-1993 Determination of Paint Film Flexibility";

(4) Determination of paint film thickness: measured by DR-330 coating thickness gauge;

(5) Determination of paint film gloss: refer to "Determination of 20°, 60° and 85° specular gloss of paint films of paints and varnishes and paint films without metallic pigments" GB/T9754-2007.

Claims (10)

1. a kind of preparation method of polyurethane-epoxy resin block copolymerization water-base resin, which comprises the following steps:

(1) by oligomer dihydric alcohol and diisocyanate investment reaction flask, reaction temperature is 50 DEG C ~ 80 DEG C, reacts 1 ~ 3h, system It is standby to obtain base polyurethane prepolymer for use as；

(2) epoxy resin, piperazine and water-soluble solvent is added into step (1) gained base polyurethane prepolymer for use as, stirs evenly, heats up To 30 DEG C ~ 70 DEG C, 3 ~ 8 h are reacted, reaction to epoxide number is 0, obtains mixture；

(3) deionized water with quality such as added water-soluble solvents is added into step (2) gained mixture, stirs evenly, then Polymer is staticly settled out, polymer is washed, obtains precursor resin；

(4) precursor resin obtained by step (3) is warming up to 40-55 DEG C, addition is equivalent to having for precursor resin quality 1.2 ~ 16.0% Machine acid, stirs 3-10min, and the deionized water for being equivalent to 1-3 times of precursor resin quality is added, and it is poly- to get arriving to stir 20-35min Urethane-epoxy resin block copolymerization water-base resin.

2. the preparation method of polyurethane-epoxy resin block copolymerization water-base resin according to claim 1, feature exist In, in step (1), the ratio of the oligomer dihydric alcohol and diisocyanate, so that the isocyanate group in diisocyanate Substance amount and the ratio between the amount of substance of [OH] in oligomer dihydric alcohol be 1.5-2 ︰ 1.

3. the preparation method of polyurethane-epoxy resin block copolymerization water-base resin according to claim 1 or 2, feature Be, in step (2), the additional amount of the water-soluble solvent, be base polyurethane prepolymer for use as, epoxy resin, piperazine gross mass 60- 100%；

The proportion of epoxy resin and piperazine is controlled with chain extension parameter Rt and hard segment content H%；

Control chain extension parameter Rt=1.2 ~ 1.6, Rt={ n (amino)/[n (epoxy group)+n (isocyanate group)] }, n expression thing The amount of matter；Amino is the secondary amine in piperazine, and epoxy group is the epoxy group in epoxy resin, and isocyanate group is base polyurethane prepolymer for use as In isocyanate group；

Controlling hard segment content H% is 10 ~ 60%；H%={ [m (epoxy resin)+m (piperazine)]/[m (epoxy resin)+m (piperazine) + m (base polyurethane prepolymer for use as)] }, m indicates the quality of substance；Hard segment content H% is hard segment content, adjustable synthetic resin Flexibility.

4. the preparation method of polyurethane-epoxy resin block copolymerization water-base resin according to claim 1 or 2, feature It is, in step (1), the oligomer dihydric alcohol is polycaprolactone diols, polyadipate diglycol ester, poly- tetrahydro At least one of furans dihydric alcohol.

5. the preparation method of polyurethane-epoxy resin block copolymerization water-base resin according to claim 1 or 2, feature It is, in step (1), the oligomer dihydric alcohol molecular weight is 400-4000.

6. the preparation method of polyurethane-epoxy resin block copolymerization water-base resin according to claim 1 or 2, feature It is, in step (1), the diisocyanate is toluene di-isocyanate(TDI), isophorone diisocyanate, diphenyl methane two At least one of isocyanates, hexamethylene diisocyanate.

7. the preparation method of polyurethane-epoxy resin block copolymerization water-base resin according to claim 1 or 2, feature It is, in step (2), the epoxy resin is at least one of epoxy E-51, epoxy E-44, epoxy E-20, epoxy E-12.

8. the preparation method of polyurethane-epoxy resin block copolymerization water-base resin according to claim 1 or 2, feature It is, in step (2), the water-soluble solvent is n,N-Dimethylformamide, tetrahydrofuran, acetone, N-Methyl pyrrolidone One or both of.

9. the preparation method of polyurethane-epoxy resin block copolymerization water-base resin according to claim 1 or 2, feature It is, in step (2), control reaction is 45-60 DEG C of temperature；The control reaction time is 4-6h.

10. the preparation method of polyurethane-epoxy resin block copolymerization water-base resin according to claim 1 or 2, feature It is, in step (4), the organic acid is at least one of glacial acetic acid, lactic acid, formic acid, propionic acid, oxalic acid.