Polymer for enhancing toughness of polyurethane coating as well as preparation method and application of polymer

Abstract

The invention discloses a polymer for enhancing the toughness of a polyurethane coating as well as a preparation method and application of the polymer. The polymer is prepared by carrying out polymerization reaction on polyisocyanate and at least one active hydrogen compound which serve as raw materials. Wherein the polyisocyanate is diisocyanate which has a benzene ring structure and has a molecular weight in a range of 180-245, and the active hydrogen compound is an alcohol compound which has 2-4 hydroxyl groups and a flash point in a range of 120-205 DEG C; meanwhile, the ratio of a carbamate group (-NH-CO-) in the polymer is controlled to be 18-30wt% based on the total mass of the polymer. When the prepared polymer is used for a polyurethane coating, the coating of a product shows excellent flexibility on the basis of maintaining the original mechanical properties.

Description

Technical Field

[0001] The present invention relates to a method for preparing a polymer, and particularly to a polymer for enhancing the toughness of a polyurethane coating, a preparation method thereof, and an application thereof. Background Art

[0002] In the field of two-component polyurethane coatings, aromatic and araliphatic polyisocyanates are widely used due to the excellent mechanical properties and good gloss of their products. However, the coatings usually exhibit the characteristics of "hard and brittle", resulting in poor impact resistance. Even under relatively small stress, defects are easily generated in the paint film, which cannot meet the application scenarios with relatively high requirements for the flexibility of the paint film.

[0003] In Patent CN105940030A, a preparation method of an XDI-type curing agent is disclosed, and a TMP-modified XDI adduct is synthesized. Compared with TDI, the TMP-modified derivative of XDI has slightly improved flexibility, but the performance is still not excellent enough. Moreover, this product requires the additional addition of an organic solvent to reduce the viscosity of the system, and the presence of VOC is also not conducive to environmental protection. Summary of the Invention

[0004] In view of the above problems existing in the prior art, the present invention provides a polymer for enhancing the toughness of a polyurethane coating and a preparation method thereof.

[0005] The inventors of the present application have found that by using a specific active hydrogen compound to react with an isocyanate and limiting the content of the carbamate formed by the reaction within a certain range, when the polymer thus prepared is used in a polyurethane coating, the coating of the product can exhibit excellent flexibility while maintaining the original mechanical properties.

[0006] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0007] The present invention provides a polymer for enhancing the toughness of a polyurethane coating, and the polymer is prepared by a polymerization reaction using a polyisocyanate and at least one active hydrogen compound as raw materials;

[0008] Wherein, the polyisocyanate refers to a diisocyanate having a benzene ring structure and a molecular weight in the range of 180-245, such as 180, 190, 200, 210, 220, 230, 240, and the active hydrogen compound refers to an alcohol compound having 2-4, such as 2, 3, 4 hydroxyl groups and a flash point in the range of 120-205 °C, such as 120 °C, 140 °C, 160 °C, 180 °C, 200 °C, 205 °C;

[0009] Meanwhile, control the proportion of urethane groups (-NH-CO-) in the polymer to be 18-30 wt%, such as 18 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, preferably 18.6-29.1 wt%, based on the total mass of the polymer.

[0010] In the present invention, the polyisocyanate is selected from at least one of toluene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, and tetramethylxylylene diisocyanate, and preferably xylylene diisocyanate.

[0011] In the present invention, the active hydrogen compound is selected from at least one of diethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, glycerol, butanetriol, pentanetriol, pentaerythritol, and preferably diethylene glycol.

[0012] In the present invention, a polymer is prepared from a polyisocyanate and an active hydrogen compound, and this process is a method already disclosed in the art. Those skilled in the art can screen the specific operating conditions with reference to the prior art, and there are no special requirements in the present invention. In some specific examples, for the polymerization reaction, the reaction temperature is 70-100 °C, such as 70 °C, 80 °C, 90 °C, 100 °C, preferably 75-100 °C, and the reaction time is 1.5-5.0 h, such as 1.5 h, 2.0 h, 3.0 h, 4.0 h, 5.0 h, preferably 2.0-5.0 h.

[0013] In the polymer of the present invention, the reaction of the isocyanate with the active hydrogen compound can generate urethane groups (-NH-CO-). When the proportion of the generated urethane groups is controlled to be 18.6-29.1 wt%, the coating of its product exhibits excellent flexibility while maintaining the original mechanical properties. When the proportion of the urethane component groups is higher than the upper limit of this ratio, the functionality will decrease significantly, thereby resulting in a decrease in the hardness of the coating; while when it is lower than the lower limit of this ratio, due to the too low proportion of the bifunctional component, the impact resistance cannot be improved.

[0014] The present invention provides a method for preparing the above polymer for enhancing the toughness of polyurethane coatings. Those skilled in the art should understand that the following preparation method is only an exemplary illustration of the source method of the polymer product with the above characteristics in the present invention, but does not constitute any limitation.

[0015] In a preferred embodiment, the present invention provides a method for preparing a polymer for enhancing the toughness of polyurethane coatings, and the steps include:

[0016] (1) Mix an excessive amount of polyisocyanate and the active hydrogen compound evenly, and then raise the temperature for polymerization reaction;

[0017] (2) After the polymerization reaction for a period of time, the reaction solution is subjected to thin-film evaporation to remove part of the free isocyanate monomer, and a polymer for enhancing the toughness of the polyurethane coating is obtained.

[0018] In step (1) of the present invention, based on the isocyanate group, the molar ratio of the polyisocyanate to the active hydroxyl compound based on the hydroxyl group is 5-12, such as 5, 6, 7, 8, 9, 10, 11, 12, and preferably 5-9.

[0019] In step (1) of the present invention, for the polymerization reaction, the reaction temperature is 70-100 °C, such as 70 °C, 80 °C, 90 °C, 100 °C, and preferably 75-100 °C.

[0020] In step (2) of the present invention, for the polymerization reaction, the reaction time is 1.5-5.0 h, such as 1.5 h, 2.0 h, 3.0 h, 4.0 h, 5.0 h, and preferably 2.0-5.0 h.

[0021] In step (2) of the present invention, for the thin-film evaporation, the temperature is 140-200 °C, such as 140 °C, 160 °C, 180 °C, 200 °C, and preferably 140-190 °C; the pressure is 10-90 Pa, such as 10 Pa, 30 Pa, 50 Pa, 70 Pa, 90 Pa, and preferably 10-85 Pa; the residence time is 8-40 min, such as 8 min, 10 min, 20 min, 30 min, 40 min, and preferably 10-40 min.

[0022] In step (2) of the present invention, part of the free isocyanate monomer is removed to ensure that the monomer content in the final polymer product is less than 0.5 wt%, such as 0.49 wt%, 0.4 wt%, 0.3 wt%, 0.2 wt%, 0.1 wt%.

[0023] In the present invention, steps (1) and (2) of the preparation method are both carried out in a nitrogen environment.

[0024] In the present invention, the prepared polymer may not contain an organic solvent, or an organic solvent may be added for dilution according to needs, which does not affect the performance of its products either. However, when calculating the proportion of the urethane component, the mass of the solvent needs to be deducted.

[0025] Preferably, the organic solvent is selected from polar solvents, preferably one or more of toluene, xylene, acetone, tetrahydrofuran, chlorobenzene, dichlorobenzene, dichloromethane, dichloroethane, 1,3-dioxane, methyl acetate, ethyl acetate, butyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, ethyl propionate, propyl propionate, butyl propionate;

[0026] Preferably, the concentration of the polymer after dilution with the organic solvent is 65-85 wt%, such as 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%.

[0027] Preferably, the operation of diluting the polymer with an organic solvent is carried out in a nitrogen environment.

[0028] The polymer for enhancing the toughness of the polyurethane coating of the present invention can be applied to fields such as exterior wall decoration, automotive exterior decoration, photovoltaic and wind power coatings, etc., and is particularly suitable for the photovoltaic field.

[0029] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0030] The toughened polymer described in the present invention has products with the characteristics of high hardness, high toughness, and impact resistance, overcoming the disadvantages of the products of traditional aromatic polyisocyanates being "hard and brittle", making the coatings that need to be exposed outdoors for a long time more durable. In addition, this product has room temperature fluidity, can be diluted without adding external solvents, and is safe and environmentally friendly. Detailed implementation mode

[0031] The following examples will deeply illustrate the method provided by the present invention. However, the present invention is not limited to the listed examples, and should also include any other well-known changes within the scope of the claims of the present invention. The specific application of the present invention is not limited to the applications mentioned in the examples. Those familiar with the field can make extended changes to the present invention through the concept of the present invention, and these simple changes are within the protection scope of the present invention.

[0032] The following test methods are adopted in the embodiments of the present invention:

[0033] (1) NCO content: Tested in accordance with standard GB / T 12009.4;

[0034] (2) Test method for viscosity: The dynamic mechanical viscosity is measured using a BrookField DV-IPrime viscometer with an S21 rotor at 25 °C;

[0035] (3) Test method for the content of free unreacted isocyanate monomers: Adopt national standard GB / T18446-2009 and test by Agilent GC-7890B gas chromatography of Agilent;

[0036] (4) Determination method for urethane content: The urethane content is denoted as p (wt%), and can be calculated by the following formula,

[0037]

[0038] In the formula, X Ais the conversion rate (%) of the polyisocyanate monomer, m 1 is the total mass (g) of the polyisocyanate monomer charged in the reaction stage, m 2 is the mass (g) of the polymer, N 2 is the NCO content (wt%) of the polymer, L 3 is the content (wt%) of the free monomer in the polymer, and A is the theoretical NCO ratio (wt%) of the isocyanate monomer.

[0039] (5) Mechanical property test: The prepared polymer was pretreated according to the following "coating preparation method", and the pencil hardness and impact strength (direct impact) of the coating were measured according to the corresponding test standards.

[0040] Impact strength: Tested by the QCJ-100 film impact tester of Riven according to GB / T 1732-93;

[0041] Pencil hardness: Tested by the BGD 506 pencil hardness tester of Biuged according to GB / T 6739-2006;

[0042] Coating preparation method: The prepared polymer was mixed with a polyol (ACR7502, Tongde Chemical Industry) at a ratio of 1.02 of the equivalent ratio (NCO / OH) of the isocyanate group in the polymer to the hydroxyl group in the polyol ACR7502, and then adjusted to a mixed solution with a solid content of 50 wt% with a mixed solvent (composition: ethyl acetate / butyl acetate = 1 / 1 / (mass ratio)) to prepare a polyurethane coating.

[0043] In the following examples, the raw material information used is as follows:

[0044] Xylylene diisocyanate (XDI): molecular weight 188.18, Wanhua Chemical, purity > 99%;

[0045] Tetramethylxylylene diisocyanate: molecular weight 244, Wanhua Chemical, purity > 99%;

[0046] Polyol: ACR7502, Tongde Chemical Industry, purity > 99%;

[0047] Ethyl acetate: Aladdin reagent, purity > 99%;

[0048] Butyl acetate: Aladdin reagent, purity > 99%;

[0049] Diethylene glycol: flash point 143 °C, Aladdin reagent, purity > 99%;

[0050] Glycerol: flash point 177 °C, Aladdin reagent, purity > 99%;

[0051] Pentaerythritol: flash point 200 °C, Aladdin reagent, purity > 99%;

[0052] Polypropylene glycol 400: flash point 230 °C, Aladdin reagent, purity > 99%;

[0053] Unless otherwise specified, other raw materials and reagents can be obtained through commercial channels.

[0054] The reactions, separations, and dilution processes in the following examples and comparative examples were all carried out in an environment with sufficient dry nitrogen.

[0055]

Example 1

[0056] To prepare a polymer for enhancing the toughness of polyurethane coatings, the steps are as follows:

[0057] Add 3000 g (31.88 mol - NCO) of xylylene diisocyanate into the flask, heat it to 80 °C in a water bath heating pot, then add 199.03 g (3.75 mol - OH) of diethylene glycol into the flask. During this period, keep stirring and control the polymerization reaction at 80 °C for 2.5 h to obtain a reaction solution. The reaction solution is subjected to thin-film evaporation to remove some unreacted monomers. The separation temperature is 145 °C, the separation pressure is 35 Pa, and the separation time is 12 min. Finally, collect the heavy fraction to obtain the polymer product;

[0058] The basic indexes and performance test results of the polymer are shown in Table 1, where the molar ratio of the isocyanate group of the polyisocyanate to the hydroxyl group of the active hydroxyl compound is denoted as R, and the urethane content is denoted as p (wt%).

[0059]

Example 2

[0060] To prepare a polymer for enhancing the toughness of polyurethane coatings, the steps are as follows:

[0061] Add 3000 g (24.56 mol - NCO) of tetramethylxylylene diisocyanate into the flask, heat it to 70 °C in a water bath heating pot, then add 166.96 g (4.9 mol - OH) of pentaerythritol into the flask. During this period, keep stirring and control the polymerization reaction at 70 °C for 3.0 h to obtain a reaction solution. The reaction solution is subjected to thin-film evaporation to remove some unreacted monomers. The separation temperature is 160 °C, the separation pressure is 20 Pa, and the separation time is 16 min. Finally, collect the heavy fraction to obtain the polymer product. The basic indexes and performance test results of the polymer are shown in Table 1.

[0062]

Example 3

[0063] To prepare a polymer for enhancing the toughness of polyurethane coatings, the steps are as follows:

[0064] Add 3000 g (31.88 mol - NCO) of xylylene diisocyanate into a flask, heat it up to 80 °C in a water bath heating pot, then add 115.15 g (3.75 mol - OH) of glycerol into the flask. Keep stirring during this process and control the polymerization reaction at 80 °C for 4.0 h to obtain a reaction solution. Remove some unreacted monomers from the reaction solution through a thin - film evaporator. The separation temperature is 140 °C, the separation pressure is 70 Pa, and the separation time is 8 min. Finally, collect the heavy components to obtain a polymer product. The basic indexes and performance test results of the polymer are shown in Table 1.

[0065]

Example 4

[0066] Steps for preparing a polymer for enhancing the toughness of a polyurethane coating are as follows:

[0067] Add 3000 g (31.88 mol - NCO) of xylylene diisocyanate into a flask, heat it up to 90 °C in a water bath heating pot, then add 52.87 g (1 mol - OH) of diethylene glycol and 91.76 g (2.99 mol - OH) of glycerol into the flask. Keep stirring during this process and control the polymerization reaction at 90 °C for 5.0 h to obtain a reaction solution. Remove some unreacted monomers from the reaction solution through a thin - film evaporator. The separation temperature is 170 °C, the separation pressure is 80 Pa, and the separation time is 20 min. Finally, collect the heavy components to obtain a polymer product. The basic indexes and performance test results of the polymer are shown in Table 1.

[0068]

Example 5

[0069] Steps for preparing a polymer for enhancing the toughness of a polyurethane coating are as follows:

[0070] Add 3000 g (31.88 mol - NCO) of xylylene diisocyanate into a flask, heat it up to 100 °C in a water bath heating pot, then add 142.17 g (2.68 mol - OH) of diethylene glycol and 36.48 g (1.07 mol - OH) of pentaerythritol into the flask. Keep stirring during this process and control the polymerization reaction at 100 °C for 4.5 h to obtain a reaction solution. Remove some unreacted monomers from the reaction solution through a thin - film evaporator. The separation temperature is 150 °C, the separation pressure is 50 Pa, and the separation time is 24 min. Finally, collect the heavy components to obtain a polymer product. The basic indexes and performance test results of the polymer are shown in Table 1.

[0071]

Example 6

[0072] Steps for preparing a polymer for enhancing the toughness of a polyurethane coating are as follows:

[0073] Add 3000 g (31.88 mol - NCO) of xylylene diisocyanate into a flask, heat it up to 95 °C in a water bath heating pot, then add 37.60 g (0.71 mol - OH) of diethylene glycol, 65.25 g (2.13 mol - OH) of glycerol, and 12.06 g (0.35 mol - OH) of pentaerythritol into the flask. Keep stirring during this period and control the polymerization reaction at 95 °C for 4.0 h to obtain a reaction solution. Remove some unreacted monomers from the reaction solution through a thin - film evaporator. The separation temperature is 145 °C, the separation pressure is 10 Pa, and the separation time is 40 min. Finally, collect the heavy fraction to obtain a polymer product. The basic indexes and performance test results of the polymer are shown in Table 1.

[0074]

Example 7

[0075] Prepare a polymer for enhancing the toughness of polyurethane coatings. The steps are as follows:

[0076] Add 3000 g (31.88 mol - NCO) of xylylene diisocyanate into a flask, heat it up to 75 °C in a water bath heating pot, then add 192.25 g (3.62 mol - OH) of diethylene glycol into the flask. Keep stirring during this period and control the polymerization reaction at 75 °C for 3.5 h to obtain a reaction solution. Remove some unreacted monomers from the reaction solution through a thin - film evaporator. The separation temperature is 190 °C, the separation pressure is 90 Pa, and the separation time is 28 min. Finally, collect the heavy fraction to obtain a polymer product. The basic indexes and performance test results of the polymer are shown in Table 1.

[0077]

Comparative Example 1

[0078] Add 3000 g (31.88 mol - NCO) of xylylene diisocyanate into a flask, heat it up to 80 °C in a water bath heating pot, then add 130.14 g (2.45 mol - OH) of diethylene glycol into the flask. Keep stirring during this period and control the reaction at 80 °C for 2.5 h to obtain a reaction solution. Remove some unreacted monomers from the reaction solution through a thin - film evaporator. The separation temperature is 145 °C, the separation pressure is 35 Pa, and finally collect the heavy fraction to obtain a polymer product. The basic indexes and performance test results of the polymer are shown in Table 1.

[0079]

Comparative Example 2

[0080] Add 3000 g (31.88 mol - NCO) of xylylene diisocyanate into a flask, heat it up to 80 °C in a water bath heating pot, then add 199.03 g (3.75 mol - OH) of diethylene glycol into the flask. Keep stirring during this process and control the reaction at 80 °C for 2.5 h to obtain a reaction solution. Remove part of the unreacted monomers from the reaction solution through a thin - film evaporator. The separation temperature is 185 °C and the separation pressure is 35 Pa. Finally, collect the heavy components to obtain a polymer product. The basic indexes and performance test results of the polymer are shown in Table 1.

[0081]

Comparative Example 3

[0082] Add 3000 g (31.88 mol - NCO) of xylylene diisocyanate into a flask, heat it up to 80 °C in a water bath heating pot, then add 750.22 g (3.75 mol - OH) of polypropylene glycol 400 (flash point 230 °C) into the flask. Keep stirring during this process and control the reaction at 80 °C for 2.5 h to obtain a reaction solution. Remove part of the unreacted monomers from the reaction solution through a thin - film evaporator. The separation temperature is 145 °C and the separation pressure is 35 Pa. Finally, collect the heavy components to obtain a polymer product. The basic indexes and performance test results of the polymer are shown in Table 1.

[0083]

Comparative Example 4

[0084] Refer to the method of Example 1, the difference is only that: xylylene diisocyanate is replaced by an equal amount of hydrogenated xylylene diisocyanate, and other operations and conditions remain unchanged. A polymer is prepared, and the basic indexes and performance test results of the polymer are shown in Table 1.

[0085]

Comparative Example 5

[0086] Refer to the method of Example 1, the difference is only that: xylylene diisocyanate is replaced by an equal amount of toluene diisocyanate (molecular weight 174.16), and other operations and conditions remain unchanged. A polymer is prepared, and the basic indexes and performance test results of the polymer are shown in Table 1.

[0087]

Comparative Example 6

[0088] Refer to the method of Example 1, the difference is only that: diethylene glycol is replaced by an equal amount of ethylene glycol (flash point 111 °C), and other operations and conditions remain unchanged. A polymer is prepared, and the basic indexes and performance test results of the polymer are shown in Table 1.

[0089]

Comparative Example 7

[0090] Refer to the method of Example 1, the difference is only that: diethylene glycol is replaced by an equal amount of isobutanol, and other operations and conditions remain unchanged. A polymer is prepared, and the basic indexes and performance test results of the polymer are shown in Table 1.

[0091] Table 1 Basic indicators and performance test results of examples and comparative examples

[0092]

Claims

1. A polymer for enhancing the toughness of polyurethane coatings, characterized in that, the polymer is prepared by a polymerization reaction using polyisocyanate and at least one active hydrogen compound as raw materials; wherein, the polyisocyanate refers to a diisocyanate having a benzene ring structure and a molecular weight in the range of 180 - 245, and the active hydrogen compound refers to an alcohol compound having 2 - 4 hydroxyl groups and a flash point in the range of 120 - 205 °C; Meanwhile, control the proportion of urethane groups in the polymer to be 18 - 30 wt%, preferably 18.6 - 29.1 wt%, based on the total mass of the polymer.

2. The polymer according to claim 1, characterized in that, the polyisocyanate is selected from at least one of toluene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, and tetramethylxylylene diisocyanate, preferably xylylene diisocyanate.

3. The polymer according to claim 1, characterized in that, the active hydrogen compound is selected from at least one of diethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, glycerol, butanetriol, pentanetriol, pentaerythritol, and preferably diethylene glycol.

4. A preparation method of the polymer for enhancing the toughness of polyurethane coatings according to any one of claims 1 - 3, characterized in that the steps include: (1) Mix an excessive amount of polyisocyanate and the active hydrogen compound evenly, and then raise the temperature for a polymerization reaction; (2) After the polymerization reaction for a period of time, subject the reaction solution to thin - film evaporation to remove part of the free isocyanate monomer, thereby obtaining the polymer for enhancing the toughness of polyurethane coatings.

5. The preparation method according to claim 4, characterized in that, in step (1), based on the isocyanate group of the polyisocyanate and the hydroxyl group of the active hydroxyl compound, the molar ratio of the two is 5 - 12, preferably 5 - 9; and / or in step (1), for the polymerization reaction, the reaction temperature is 70 - 100 °C, preferably 75 - 100 °C.

6. The preparation method according to claim 4, characterized in that, in step (2), for the polymerization reaction, the reaction time is 1.5 - 5.0 h, preferably 2.0 - 5.0 h; and / or in step (2), for the thin - film evaporation, the temperature is 140 - 200 °C, preferably 140 - 190 °C, the pressure is 10 - 90 Pa, preferably 10 - 85 Pa, and the residence time is 8 - 40 min, preferably 10 - 40 min; and / or in step (2), remove part of the free isocyanate monomer to ensure that the monomer content in the final polymer product is less than 0.5 wt%.

7. The preparation method according to claim 4, characterized in that, both steps (1) and (2) are carried out in a nitrogen environment.

8. The preparation method according to claim 4, characterized in that, the prepared polymer can be diluted by adding an organic solvent; Preferably, the organic solvent is selected from polar solvents, preferably one or more of toluene, xylene, acetone, tetrahydrofuran, chlorobenzene, dichlorobenzene, dichloromethane, dichloroethane, 1,3-dioxane, methyl acetate, ethyl acetate, butyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, ethyl propionate, propyl propionate, and butyl propionate.

9. The preparation method according to claim 8, wherein, the concentration of the polymer after dilution with the organic solvent is 65-85 wt%; and / or the operation of diluting the polymer by adding the organic solvent is carried out under a nitrogen atmosphere.

10. Application of the polymer for enhancing the toughness of the polyurethane coating according to any one of claims 1-3 or the polymer for enhancing the toughness of the polyurethane coating prepared by the method according to any one of claims 4-9 in the fields of exterior wall decoration, automotive exterior decoration, and photovoltaic and wind power coatings, especially suitable for the photovoltaic field.

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