1. A preparation method of a blocked isocyanate latent curing agent is characterized by comprising the following steps:

s1, uniformly mixing the first end-capping reagent, the organic tin catalyst and the organic solvent to prepare a mixed solution; the first end-capping reagent is selected from indole compounds;

and S2, under the protection of inert gas, mixing the diphenylmethane diisocyanate trimer with the mixed solution to carry out the first end-capping reaction.

2. The method for preparing a blocked latent isocyanate curing agent according to claim 1, wherein in step S1, the indole compound is at least one selected from indole and trimethylindole.

3. The method of claim 1, wherein in step S1, the organotin catalyst is dibutyltin dilaurate.

4. The method for preparing a blocked latent isocyanate curing agent according to claim 1, wherein in step S1, the mass ratio of the diphenylmethane diisocyanate trimer to the first blocking agent is (1-1.5): 1.

5. the method for preparing a blocked latent isocyanate curing agent according to claim 1, wherein in step S1, the first blocking agent, the organotin catalyst and the organic solvent are uniformly mixed and then dehydrated to prepare a mixed solution; preferably, the dehydration treatment is dehydration by heating; further preferably, the heating temperature for heating dehydration is 70-75 ℃.

6. The method for preparing a blocked latent isocyanate curing agent according to claim 5, further comprising the step of S3: heating the material obtained by the step S2 to 80-90 ℃, and adding a second end-capping reagent for a second end-capping reaction; the second end-capping reagent is selected from alcohols and/or phenols.

7. A blocked isocyanate latent curing agent obtained by the method for producing a blocked isocyanate latent curing agent according to any one of claims 1 to 6.

8. Use of the blocked latent isocyanate curing agents according to claim 7 for the production of adhesives and coatings.

9. A binder, characterized in that raw materials thereof comprise a base binder, a deblocking catalyst and the blocked isocyanate latent curing agent according to claim 7; the deblocking catalyst is selected from a chelated tin catalyst; preferably, the base binder is selected from at least one of universal glue, polyurethane resin, polyester resin, epoxy resin and SBS rubber resin.

10. A coating material which is characterized in that raw materials thereof comprise a base resin, a deblocking catalyst and the blocked isocyanate latent curing agent according to claim 7; the deblocking catalyst is selected from a chelated tin catalyst; preferably, the base resin is at least one selected from the group consisting of a hydroxyl resin, a vinyl resin, a polyurethane resin, a polyester resin, an epoxy resin, and an SBS rubber resin.

Background

As one of the important raw materials for the polyurethane industry, isocyanates have been put into practical use in industry in many different types of products, and new products are continuously being launched. The isocyanate monomer has the defects of high monomer toxicity, high reaction activity, easiness in nucleophilic reagent (such as water) reaction and the like, so that the isocyanate monomer has high requirements on environmental equipment in the storage and use processes. At present, blocked isocyanates are one of the effective solutions to the above problems. The blocked isocyanate curing agent is an important chemical product, is widely applied to the field of coatings and adhesives, has the advantages of low toxicity, good stability and the like compared with isocyanate monomers such as MDI, TDI and the like, but is limited by the technical level, the problem that the deblocking temperature of the blocked isocyanate curing agent on the market is overhigh generally exists at present, and the use of the series of materials is limited by the minimum deblocking curing temperature of 110 ℃.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a blocked isocyanate latent curing agent, and a preparation method and application thereof.

The invention provides a preparation method of a blocked isocyanate latent curing agent, which comprises the following steps:

s1, uniformly mixing the first end-capping reagent, the organic tin catalyst and the organic solvent to prepare a mixed solution; the first end-capping reagent is selected from indole compounds;

and S2, under the protection of inert gas, mixing the diphenylmethane diisocyanate trimer with the mixed solution to carry out the first end-capping reaction.

The preparation method of the blocked isocyanate latent curing agent provided by the embodiment of the invention has at least the following beneficial effects: the preparation method adopts the end capping agent indole compound to seal the isocyanate group (-NCO) in the diphenylmethane diisocyanate tripolymer (MDI tripolymer), and the prepared closed isocyanate latent curing agent has strong stability at room temperature and good storage stability; the curing agent can realize deblocking at low temperature of 60 ℃ in the presence of a chelated tin catalyst, and has high reaction activity.

In some embodiments of the present invention, in step S1, the indole compound is at least one selected from indole and trimethylindole.

In some embodiments of the present invention, in step S1, the organotin catalyst is selected from dibutyltin dilaurate.

In some embodiments of the present invention, in step S1, the mass ratio of the diphenylmethane diisocyanate trimer to the first blocking agent is (1-1.5): 1.

in some embodiments of the present invention, in step S1, after the first capping agent, the organotin catalyst, and the organic solvent are uniformly mixed, a dehydration treatment is performed to prepare a mixed solution; preferably, the dehydration treatment is dehydration by heating; further preferably, the heating temperature for heating dehydration is 70-75 ℃. Through the dehydration treatment, residual moisture in the system is eliminated, and the influence of moisture on the subsequent end-capping reaction is avoided.

Step S2 specifically includes slowly dropping diphenylmethane diisocyanate trimer into the mixed solution under the protection of an inert gas to perform a first end-capping reaction. The inert gas can be nitrogen, helium, neon, argon, etc.; preferably, nitrogen is used.

In some embodiments of the present invention, the method further comprises step S3: heating the material obtained by the step S2 to 80-90 ℃, and adding a second end-capping reagent for a second end-capping reaction; the second end-capping reagent is selected from alcohols and/or phenols, wherein the phenols are preferably phenol.

In a second aspect of the present invention, a blocked isocyanate latent curing agent is provided, which is prepared by any one of the methods for preparing the blocked isocyanate latent curing agent provided in the first aspect of the present invention. The deblocking temperature of the blocked isocyanate latent curing agent under the action of a chelated tin catalyst can be as low as 60 ℃.

The blocked isocyanate latent curing agent according to a preferred embodiment of the present invention has at least the following advantageous effects: the blocked isocyanate latent curing agent has good storage stability and low-temperature deblocking activity, and particularly has strong stability at room temperature and good storage stability; and the deblocking can be realized at the low temperature of 60 ℃ in the presence of a chelated tin catalyst, and the reaction activity is higher.

In a third aspect of the present invention, there is provided a use of any one of the blocked isocyanate latent curing agents set forth in the second aspect of the present invention in the preparation of adhesives and coatings.

In the fourth aspect of the invention, the binder is provided, and the raw materials of the binder comprise a base binder, a deblocking catalyst and any one of the blocked isocyanate latent curing agents provided by the second aspect of the invention; the deblocking catalyst is selected from chelated tin catalysts. Preferably, the base binder is selected from at least one of universal glue, polyurethane resin, epoxy resin and SBS rubber resin.

In the fifth aspect of the invention, a coating is provided, the raw materials of which comprise a base resin, a deblocking catalyst and any one of the blocked isocyanate latent curing agents provided by the second aspect of the invention; the deblocking catalyst is selected from chelated tin catalysts. Preferably, the base resin is at least one selected from the group consisting of a hydroxyl resin, a vinyl resin, a polyurethane resin, a polyester resin, an epoxy resin, and an SBS rubber resin. If the base resin is hydroxyl resin, the dosage proportion of the raw material closed isocyanate latent curing agent and the hydroxyl resin in the coating can be 1:1 in combination.

Detailed Description

The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.

Example 1

The embodiment prepares the blocked isocyanate latent curing agent, and the specific process comprises the following steps:

1000mL of organic solvent butanone, 200g of first end-capping agent indole and 1g of organic tin are catalyzedThe reagent dibutyltin dilaurate was placed in a reaction kettle (three-hole flask), the stirring paddle was turned on, the rotation speed was controlled at 300rpm, and the solution was heated to 73 ℃ to dehydrate for 30 min. Under the protection of dry nitrogen, 170g of polymeric MDI (specifically adopting Wanhua chemical PM-200, and the product brand isPM-200) is slowly dripped into the reaction kettle, and dripping is finished within 4 hours; and then heating the materials to 85 ℃, adding 10g of second end-capping reagent phenol for reaction for 1 hour, and discharging to obtain the closed isocyanate latent curing agent.

The content of-NCO groups in the blocked isocyanate latent curing agent prepared by the method is 17 percent by adopting a di-n-butylamine method, namely, every 100g of curing agent contains 17g of-NCO groups.

The prepared blocked isocyanate latent curing agent is placed in a thermostat with the humidity of 70% and the temperature of 25 ℃ and can be stored for more than 180 days. In addition, the blocked isocyanate latent curing agent prepared above was mixed with a chelate tin catalyst (specifically, Asahua 301 in Japan), and after deblocking at 60 ℃ for 1 hour, the NCO content thereof was measured to be 63% or more of the theoretical calculated value (i.e., the NCO content in polymeric MDI).

When in use, the blocked isocyanate latent curing agent and the hydroxyl resin to be cured are mixed according to the molar ratio of-NCO group to-OH group of 1:1, and then a chelated tin catalyst (specifically, Japan Asahua 301) is added to react for 10min at 60 ℃ to be completely cured.

Example 2

The embodiment prepares the blocked isocyanate latent curing agent, and the specific process comprises the following steps:

1000mL of organic solvent butanone, 150g of first end-capping agent trimethylindole, and 1g of organotin catalyst dibutyltin dilaurate were placed in a reaction kettle (three-hole flask), a stirring paddle was started, the rotation speed was controlled at 400rpm, and the solution was heated to 74 ℃ and dehydrated for 30 min. Under the protection of dry nitrogen, 150g of polymeric MDI (specifically adopting Wanhua chemical PM-200, and the product brand isPM-200) is slowly dripped into the reaction kettle, and dripping is finished within 4 hours; and then heating the materials to 85 ℃, adding 10g of second end-capping reagent glycerol, reacting for 1h, and discharging to obtain the closed isocyanate latent curing agent.

Example 3

The embodiment prepares the blocked isocyanate latent curing agent, and the specific process comprises the following steps:

1000mL of organic solvent butanone, 100g of first end-capping agent indole and 1g of organic tin catalyst dibutyltin laurate were placed in a reaction kettle (three-hole flask), a stirring paddle was started, the rotation speed was controlled at 350rpm, and the solution was heated to 74 ℃ and dehydrated for 30 min. Under the protection of dry nitrogen, 150g of polymeric MDI (specifically adopting Wanhua chemical PM-200, and the product brand isPM-200) is slowly dripped into the reaction kettle, dripping is finished for 4 hours, and discharging is carried out, thus obtaining the closed isocyanate latent curing agent.

Comparative example 1

This comparative example, which was prepared as a blocked latent isocyanate curing agent, differs from example 1 mainly in the choice of the first blocking agent. The specific process comprises the following steps:

100mL of butanone serving as an organic solvent, 200g of phenol serving as a first end-capping agent and 1g of dibutyltin laurate serving as an organic tin catalyst are placed in a reaction kettle (three-hole flask), a stirring paddle is started, the rotating speed is controlled to be 350rpm, and simultaneously the solution is heated to 74 ℃ for dehydration for 30 min. Under the protection of dry nitrogen, 170g of polymeric MDI (specifically adopting Wanhua chemical PM-200, and the product brand isPM-200) is slowly dripped into the reaction kettle, and dripping is finished within 4 hours; and then heating the materials to 85 ℃, adding 10g of second end-capping reagent phenol for reaction for 1 hour, and discharging to obtain the closed isocyanate latent curing agent.

Comparative example 2

This comparative example, which was prepared as a blocked latent isocyanate curing agent, differs from example 1 mainly in the choice of the first blocking agent. The specific process comprises the following steps:

100mL of butanone serving as an organic solvent, 200g of methylimidazole serving as a first end-capping agent and 1g of dibutyltin laurate serving as an organic tin catalyst are placed in a reaction kettle (three-hole flask), a stirring paddle is started, the rotating speed is controlled to be 350rpm, and simultaneously the solution is heated to 74 ℃ for dehydration for 30 min. Under the protection of dry nitrogen, 170g of polymeric MDI (specifically adopting Wanhua chemical PM-200, and the product brand isPM-200) is slowly dripped into the reaction kettle, and dripping is finished within 4 hours; and then heating the materials to 85 ℃, adding 10g of second end-capping reagent phenol for reaction for 1 hour, and discharging to obtain the closed isocyanate latent curing agent.

Application example 1

The blocked isocyanate latent curing agent obtained in example 1 was used for the preparation of coatings. Specifically, 100g of Disemann chemical SN-805 polyester resin and 35g of the blocked isocyanate latent curing agent obtained in example 1 were mixed, and then 0.3g of a chelate tin catalyst (Japanese Asahi chemical 301) was added to prepare a coating material; after 90 days of storage at room temperature, the viscosity of the paint increased from 12000PCS to 170000PCS, and no gel was observed.

The coating is coated on a stainless steel sheet and solidified in an oven at 60 ℃ for 10min, the stainless steel sheet is taken out and cooled to room temperature, the surface hardness of a paint film is 3H, the stainless steel sheet is heated for 10min by reflow soldering at 288 ℃, and the Bayer number test of the paint film is more than B1.

Application example 2

The blocked isocyanate latent curing agent obtained in example 1 was used for the preparation of an adhesive. Specifically, 20g of the blocked isocyanate latent curing agent obtained in example 1 and 0.3g of a chelate tin catalyst (Japanese Asahi chemical 301) were added to 100g of an SBS universal glue having a general heat resistant temperature of 50 ℃ to prepare a binder; the adhesive is stored for 90 days at normal temperature, and the viscosity of the adhesive is unchanged. The adhesive bonding substrate product is placed in a 60 ℃ oven to be heated for 10min, then the temperature is raised to 80 ℃, the bonded object is continuously baked for 48h without adhesive failure, and the peel strength is more than 1.5 Newton/square centimeter.

Application example 3

The blocked isocyanate latent curing agent prepared in comparative example 1, comparative example 2 and example 3 was mixed with the chelate tin catalyst at a mass ratio of 1000:3, respectively, the temperature of the mixed materials was raised to different temperatures, the NCO content of the mixed materials was measured by the di-n-butylamine method after 1min, and the percentage of the actually measured NCO content to the theoretical NCO content, that is, the percentage of the measured NCO content to the NCO content in polymeric MDI, was calculated, and the results are shown in table 1.

In addition, the blocked isocyanate latent curing agent prepared in comparative example 1, comparative example 2 and example 3 was mixed with dibutyltin dilaurate catalyst in a mass ratio of 1000:3, the temperature of the mixed material was raised to different temperatures, the NCO content of the mixed material was measured by the di-n-butylamine method after 1min, the percentage of the actually measured NCO content to the theoretical NCO content was calculated, and the results are shown in table 2.

TABLE 1

Temperature/. degree.C	60	70	80	90	100	110	120	130	140	150	160	170	180	190
															Comparative example 1	0	0	0	0	0	0	0	7	14	43	77	95	92	77
Comparative example 2	0	0	0	0	0	0	0	0	0	0	0	32	77	94.2
															Example 3	10	37	95.4	95.7	94.2	95	93.8	90	90.8	90	87.6	95.5	-	-

TABLE 2

As can be seen from the above tables 1 and 2, when indole is used as the blocking agent in example 3 of the present application, the blocked isocyanate latent curing agent prepared in example 3 has a lower deblocking temperature than the blocked isocyanate latent curing agent prepared in comparative example 1 and comparative example 2, which use phenol and methylimidazole as the blocking agent, respectively, and the chelated tin catalyst can provide more NCO release under the same temperature conditions.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.