Synthetic process of waterborne polyurethane

Abstract

The invention belongs to the field of high polymer materials, and provides a synthetic process of waterborne polyurethane, which comprises the following steps: mixing isocyanate and polyol, and reacting at 80-90 DEG C for 2-5 hours; at 70-90 DEG C, adding a chain extender into the reaction system in a continuous supplementing manner, completing feeding within 1-3 hours, and continuing to react for 1-3 hours after feeding is completed, so as to obtain the product. According to the polyurethane emulsion synthesis process disclosed by the invention, a more uniform and stable waterborne polyurethane product can be produced, and the production efficiency and the stability of emulsion performance among batches are obviously improved.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and particularly relates to a synthesis process of waterborne polyurethane. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] The synthesis of waterborne polyurethane adopts a kettle reaction. First, the raw materials (isocyanate, chain extender, polyol, etc.) are added to the reactor for prepolymerization, then acetone is added to adjust the viscosity and perform pre-chain extension treatment, and finally water is added for phase inversion to achieve the transformation of the emulsion from the "W / O (oil-in-water)" state to the "O / W (water-in-oil)" state, and acetone is removed to obtain a polyurethane emulsion. In the emulsion synthesis process, the prepolymerization reaction is the key. The commonly used process is the one-time feeding reaction of the three-component raw materials or the preferential reaction of polyols and isocyanates, and then the chain extender is added for reaction. The advantage of the two reaction modes is that the reaction efficiency can be guaranteed, but the disadvantage is that the prepolymerization reaction cannot be stably controlled. Slight changes in the process operation may lead to significant differences in the molecular chain structure of the polyurethane. At the least, the emulsions synthesized with the same formula have obvious performance differences, and the emulsion performance is not controllable enough. At the worst, it leads to demulsification, sedimentation, stratification, and even coagulation of the kettle, which seriously affects the qualified rate of finished products and production progress.

[0004] The paper "The Effect of Chain Extension Method on the Structure and Properties of Waterborne Polyurethane" discloses the use of a step-by-step chain extension method to prepare waterborne polyurethane. However, it is a small-scale laboratory experiment and cannot meet the requirements of industrial production at the tonnage level. At the same time, in industrial production, this method has a high probability of a condensation risk when adding acetone to adjust the viscosity.

[0005] On the other hand, the purpose of the traditional step-by-step addition method is to prevent the reaction from being too rapid and the exothermic heat from leading to reaction failure or side reactions. However, in the industrial production process of water-based polyurethane, step-by-step addition still has the risk of overheating and excessive viscosity. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a process for synthesizing waterborne polyurethane. The present invention uses a continuous addition method, prolongs the time for adding the chain extender, makes the reaction heat release slower, and controls the temperature in the reactor in combination with a cooling method to ensure the smooth progress of the main reaction, thereby improving the yield, production efficiency and stability of the emulsion performance between batches.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides a process for synthesizing waterborne polyurethane, comprising:

[0009] Mix isocyanate and polyol and react at 80-90°C for 2-5h;

[0010] At 70-90°C, add the chain extender to the reaction system by continuous addition, complete the feeding within 1-3 hours, and continue the reaction for 1-3 hours after the feeding is completed;

[0011] Acetone is added to adjust the viscosity, a pre-chain extender is added to extend the chain, acetone is removed after dispersion with water, and the emulsion solid content and viscosity are adjusted to a suitable level to obtain the product.

[0012] At present, there is a deviation in the emulsion stability of domestic water-based polyurethane emulsions. The present invention adjusts the synthesis process at a low cost to improve the reaction success rate of the water-based polyurethane emulsion.

[0013] Different from the traditional method of adding chain extenders within 5 minutes, the present invention has found that by continuously adding chain extenders, that is, extending the time for adding chain extenders (addition is completed within 1-3 hours), the reaction exotherm can be effectively controlled, the normal progress of the main reaction is ensured, and the performance stability and film-forming strength of the emulsion between batches are improved.

[0014] In some embodiments, the isocyanate is selected from at least one of hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), dicyclohexylmethane 4,4-diisocyanate (HMDI), and 1,4-cyclohexane diisocyanate (CHDI).

[0015] In some embodiments, the polyol is a polyether polyol, a polyester polyol, or a polycarbonate polyol.

[0016] In some embodiments, the chain extender is a polyol chain extender.

[0017] Preferably, the chain extender is at least one of BDO, EDO, PDO, CDO and DMPA.

[0018] In some embodiments, the pre-chain extender is an amine chain extender.

[0019] It should be noted that the present invention has no requirements for the specific amounts of isocyanate, polyol and chain extender, and any formula that can synthesize an aqueous polyurethane emulsion is applicable.

[0020] In some embodiments, the temperature is controlled by combining at least two of water cooling, liquid nitrogen cooling, and chilled water cooling.

[0021] In some embodiments, double coils or triple coils are used to control the temperature, and different coolants circulate separately to form a closed loop;

[0022] In some embodiments, the double coils are cooled by ordinary water and frozen water, and ordinary water and liquid nitrogen;

[0023] In some embodiments, the three coils are ordinary water cooling, chilled water, and liquid nitrogen three coils.

[0024] The second aspect of the present invention provides waterborne polyurethane prepared by the above method.

[0025] The third aspect of the present invention provides the use of continuously adding a chain extender to improve the finished product qualification rate and performance stability of waterborne polyurethane.

[0026] Beneficial Effects of the Invention

[0027] (1) The synthesis process of the present invention achieves more effective control over the polyurethane molecular chain, improves the yield rate in the waterborne polyurethane synthesis process, and improves the quality of waterborne polyurethane synthesis at a low cost.

[0028] (2) The preparation method of the present invention is simple, practical and easy to promote. DETAILED DESCRIPTION

[0029] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0030] As described in the background technology, isocyanate, polyol, and chain extender are put into the reactor at one time for prepolymerization, which can easily lead to local violent reactions. The more violent the local reaction, the more heat is released. The temperature difference in different areas of the reactor leads to obvious differences in the distribution of the reaction molecular chains, resulting in unstable performance between emulsion batches and even gelation.

[0031] Isocyanate and polyol are preferentially put into the reactor for prepolymerization. Although the irregular distribution of the molecular chain is suppressed to a certain extent, after the chain extender is added, the free isocyanate reacts with the chain extender very quickly. If the chain extender cannot be quickly dispersed, it is easy to cause violent local reactions, and the heat of the reaction will aggravate the occurrence of side reactions.

[0032] In order to solve the above problems, the present invention provides a synthesis process of waterborne polyurethane, comprising:

[0033] (1) Isocyanate and polyol react preferentially for a period of time (2-5 hours), and the temperature in the kettle is controlled at 80-90°C;

[0034] (2) adding chain extender to the kettle in a continuous manner, controlling the addition flow rate according to the specific addition amount, completing the feeding within 1-3 hours, and continuing the reaction for 1-3 hours after the feeding is completed, and controlling the temperature in the kettle at 70-90° C.;

[0035] (3) The reactor cooling method adopts a combination of water cooling and liquid nitrogen cooling (and / or chilled water cooling) to control the temperature, and double coils or three coils are used for temperature control (double coils refer to ordinary water cooling and chilled water cooling, ordinary water cooling and liquid nitrogen cooling, and different coolants circulate separately to form a closed loop; three coils refer to ordinary water cooling, chilled water, and liquid nitrogen three coils, and different coolants circulate separately to form a closed loop.)

[0036] The principle is explained as follows:

[0037] The purpose of process (1) is to ensure that the polyol reacts with the isocyanate first and completely. If the temperature is too low, the degree of reaction will be affected, or the reaction time will be delayed, affecting the production efficiency. If the temperature is too high, it is easy to cause side reactions, which is not worth the cost. Therefore, the reaction temperature of process (1) needs to be strictly controlled. Conventional water heating or heat dissipation methods can achieve heating and heat preservation, but the heat dissipation and cooling are slow, which is easy to cause the occurrence of local overheating and abnormal reaction problems.

[0038] Process (2) is the key point of the present invention, that is, the feeding amount and feeding cycle of the chain extender are controlled by flow metering and time setting, thereby avoiding the over-reaction problem (local overheating and side reactions) caused by one-time feeding. Although the feeding cycle of the chain extender is extended, the heat dissipation efficiency in the kettle is improved, the local overheating problem is avoided, and the smooth progress of the main reaction is guaranteed to the greatest extent.

[0039] Process (3) is an optimization and transformation of the reactor equipment. By connecting chilled water and / or liquid nitrogen, the heat exchange and cooling efficiency of the reactor is improved to ensure that the temperature in the reactor is effectively controlled.

[0040] The invention prolongs the time of emulsion synthesis to a certain extent, but greatly improves the finished product qualification rate and performance stability of the emulsion.

[0041] The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0042] In the following examples, the amounts of HDI, polyester polyol, chain extender, acetone, and pre-chain extender are determined according to the formula of commercially available waterborne polyurethane.

[0043] Example 1

[0044] (1) The reactor cooling method adopts a combination of water cooling and frozen water cooling to control the temperature, and double-disc temperature control is performed. HDI and polyester polyol with a molecular weight of 2000 are added according to the formula ratio requirements, and the reaction is preferentially performed for 2 hours. The temperature in the reactor is controlled at 85°C. During the production process, the reactor temperature is 85±2°C, and the temperature stability is good;

[0045] (2) Add chain extender (BDO) to the kettle in a continuous manner, control the addition flow rate according to the specific addition amount, complete the feeding within 1 hour, continue the reaction for 2 hours after the feeding is completed, and control the temperature in the kettle at 80°C, and the actual temperature is about 80±2°C;

[0046] (3) After the reaction is completed, acetone is added to reduce viscosity, a pre-chain extender (ethylenediamine) is added to extend the chain, water is added to disperse, and desolventization is performed to obtain a finished emulsion;

[0047] (4) Produce two batches of products (4 tons each, the same below) in accordance with the above process, and take samples from each batch for performance testing.

[0048] Example 2

[0049] The reactor was cooled by normal water cooling and temperature control. The materials were added in the manner of Example 1. During the reaction of HDI and polyol, the temperature rose to 95°C at the highest and cooled slowly. The same formula was added with an equal amount of chain extender. The feeding was completed within 1 hour by continuous addition. After the feeding was completed, the reaction was continued for 2 hours. The temperature in the reactor was controlled at 80°C, and the actual temperature reached 100°C at the highest. The other processes were the same as in Example 1, and 2 batches of products were produced normally. Samples were taken from each batch to test the performance.

[0050] Comparative Example 1

[0051] Referring to the cooling method of Example 1, in step (1), isocyanate, chain extender and polyol are added to the reactor at one time, the reaction temperature is controlled at 80°C, the actual maximum temperature is 100°C, the reaction is highly exothermic, the finished emulsion has obvious residue, and the emulsion stability is poor.

[0052] Comparative Example 2

[0053] Refer to the process of Example 1, but in step (2), the chain extender is added to the reactor in a one-time manner (the chain extender is added within 5 minutes), the reaction temperature is controlled at 80°C, the actual maximum temperature is 90°C, the finished emulsion has residue, and 2 batches of products are produced, and samples are taken from each batch for performance testing.

[0054] Comparative Example 3

[0055] Refer to the process of Example 1, but in step (2), the chain extender is added to the reactor in 3 times, 1 / 3 is added each time, and the addition is completed within 5 minutes, with an interval of 20 minutes each time. The reaction temperature is controlled at 80°C, the actual maximum temperature is 86°C, and 2 batches of products are produced. The finished emulsions have slight residues, and the filling ratio is slightly better than that of Comparative Example 2. Samples are taken from each batch to test the performance.

[0056] Table 1 Waterborne polyurethane performance test results

[0057]

[0058] As shown in Table 1, Example 1 has the best performance and the best stability between batches. According to the process records, the temperature control is the most stable. The effects of the other examples and comparative examples are all biased, especially Comparative Example 1, in which the emulsion stability is poor, there is obvious sedimentation, and the emulsion cannot be used.

[0059] From the comparison between Example 1 and Comparative Example 3, it can be seen that, compared with the "step-by-step feeding method", the continuous feeding method of the present invention can better improve the performance stability and film-forming strength of the waterborne polyurethane.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for synthesizing waterborne polyurethane, characterized in that: include: Mix isocyanate and polyol and react at 80-90°C for 2-5h; At 70-90°C, add the chain extender to the reaction system by continuous addition, complete the feeding within 1-3 hours, and continue the reaction for 1-3 hours after the feeding is completed; Acetone is added to adjust the viscosity, a pre-chain extender is added to extend the chain, acetone is removed after dispersion with water, and the emulsion solid content and viscosity are adjusted to a suitable level to obtain the product.

2. The process for synthesizing waterborne polyurethane according to claim 1, characterized in that: The isocyanate is selected from at least one of hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4-diisocyanate and 1,4-cyclohexane diisocyanate.

3. The synthesis process of waterborne polyurethane according to claim 1, characterized in that: The polyol is polyether polyol, polyester polyol or polycarbonate polyol.

4. The process for synthesizing waterborne polyurethane according to claim 1, characterized in that: The chain extender is a polyol chain extender, such as at least one of BDO, EDO, PDO, CDO, and DMPA.

5. The process for synthesizing waterborne polyurethane according to claim 1, characterized in that: The front chain extender is an amine chain extender.

6. The process for synthesizing waterborne polyurethane according to claim 1, characterized in that: The temperature is controlled by combining at least two of water cooling, liquid nitrogen cooling and chilled water cooling.

7. The process for synthesizing waterborne polyurethane according to claim 1, characterized in that: Double or triple coils are used to control the temperature, and different coolants circulate separately to form a closed loop.

8. The process for synthesizing waterborne polyurethane according to claim 7, characterized in that: The double coils adopt two coiling modes: ordinary water cooling and frozen water cooling, ordinary water cooling and liquid nitrogen cooling; Alternatively, the three coils are in the form of ordinary water cooling, chilled water, and liquid nitrogen three coils.

9. The waterborne polyurethane prepared by the method described in any one of claims 1 to 8.

10. The application of continuous addition of chain extender in improving the finished product qualification rate and performance stability of waterborne polyurethane.

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