Preparation method of urea-formaldehyde resin adhesive for ENF-grade artificial board

Abstract

The invention relates to the technical field of adhesive preparation, in particular to a preparation method of a urea-formaldehyde resin adhesive for ENF-grade artificial boards, used raw materials at least comprise formaldehyde, urea, an acid solution, an alkaline solution and epichlorohydrin, and the addition amount of epichlorohydrin accounts for 1-2 wt% of the weight of the urea-formaldehyde resin adhesive; meanwhile, the molar ratio of the formaldehyde to the urea is (0.85-0.95): 1. The adhesive has relatively low free formaldehyde content, higher waterproof performance, longer curing time and higher dry glue bonding strength and wet glue bonding strength, so that the adhesive is more suitable for processing.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesive preparation, and in particular to an E-adhesive having a low free formaldehyde content and meeting green production requirements. NF The invention discloses a preparation method of urea-formaldehyde resin adhesive for high-grade artificial board. Background Art

[0002] The description in this section merely provides background information related to the disclosure of the present application and does not constitute prior art.

[0003] The production of artificial boards consumes a large amount of adhesives, among which urea-formaldehyde resin adhesive is the most widely used and consumed adhesive. Urea-formaldehyde resin adhesive is made by condensation of urea and formaldehyde, and has the advantages of high reactivity, fast curing, low cost, and high adhesive strength. However, it also has the problems of relatively poor waterproofness and relatively high formaldehyde emission.

[0004] To this end, the prior art improves the waterproofness of urea-formaldehyde resin adhesives by adding melamine, polyvinyl alcohol (PVA), etc., and reduces the addition ratio of formaldehyde to urea to reduce the formaldehyde release. For example, the Chinese invention patent application with publication number CN107118722A and titled "A urea-formaldehyde resin adhesive for artificial boards and its preparation process" provides a urea-formaldehyde resin adhesive, which includes the following components by weight: formaldehyde 1000~1350kg, urea 1000~1600kg, melamine 45~130kg, high-efficiency compounding agent 1kg, PVA 5~10kg, sodium hydroxide 12~28kg and formic acid 1~3kg. In the above scheme, the addition amount of melamine accounts for 2~6wt% of the weight ratio of urea-formaldehyde resin, and the addition ratio of formaldehyde to urea is (0.84~1):1. At the same time, the applicant pointed out in the Chinese invention patent application with publication number CN107746696A, entitled "A urea-formaldehyde resin adhesive for artificial boards and its preparation process", that by increasing the amount of melamine, specifically increasing the added amount to 5~10wt%, the waterproofness of the urea-formaldehyde resin adhesive can be improved, but the cost is the need to increase the addition ratio of formaldehyde to urea, specifically to (1.1~1.5):1.

[0005] Obviously, the waterproofness of urea-formaldehyde resin adhesive can only be improved by adding a large amount of melamine. Therefore, firstly, the large amount of melamine added will increase the production cost of the adhesive to a large extent, and cause the brittleness of the adhesive to increase; secondly, during use, a longer curing time is required, which affects the production efficiency of urea-formaldehyde resin adhesive modified by melamine; thirdly, the reaction conditions of melamine-modified urea-formaldehyde resin adhesive are relatively strict, and environmental factors such as temperature and humidity will have a great impact on the reaction process, which leads to the production process of melamine-modified urea-formaldehyde resin adhesive requires stricter control, otherwise the obtained modified adhesive is difficult to meet the requirements. Summary of the invention

[0006] In view of the problems existing in the above method, the present invention is proposed. The purpose of the present invention is to provide an E NF The invention discloses a method for preparing a urea-formaldehyde resin adhesive for a grade artificial board, which can replace melamine to modify the urea-formaldehyde resin adhesive, reduce the free formaldehyde content, realize green production, obtain green building materials products, improve the waterproofness of the adhesive, reduce the production cost of the adhesive, improve the toughness, reduce the brittleness, and its reaction conditions are more relaxed and easy to implement. The invention specifically adopts the following technical solutions: A kind of E NF The invention discloses a method for preparing a urea-formaldehyde resin adhesive for high-grade artificial panels. The raw materials used include at least formaldehyde, urea, an acid solution, and an alkaline solution, and also include epichlorohydrin. The added amount of epichlorohydrin accounts for 1-2wt% of the weight ratio of the urea-formaldehyde resin adhesive. Meanwhile, the molar ratio of formaldehyde to urea is (0.85-0.95):1.

[0007] Preferably, the preparation method comprises an early addition stage, an intermediate acid adjustment stage, a mid-late acid polycondensation stage, and a late alkaline stage after gelation in sequence, and epichlorohydrin is added in any one or more of the early addition stage, the intermediate acid adjustment stage, the mid-late acid polycondensation stage, and the late alkaline stage after gelation.

[0008] Preferably, epichlorohydrin is added in any one or more of the early addition stage, the mid-term acid adjustment stage and the mid-to-late acid polycondensation stage.

[0009] Preferably, epichlorohydrin is added in the early addition stage, the mid-term acid adjustment stage and the mid-to-late acid polycondensation stage, and the ratio of the amount of epichlorohydrin added in each stage is (1.5~2):(1~1.5):1.

[0010] Preferably, epichlorohydrin is added in the early addition stage.

[0011] Preferably, when the preliminary addition stage includes the action of adding epichlorohydrin, the preliminary addition stage is: adding formaldehyde to the reactor, heating to 35-40°C, adjusting the pH value to 8.3-8.5 with an alkaline solution, adding urea and epichlorohydrin, and raising the temperature in the reactor to 70-90°C.

[0012] Preferably, when the mid-term acid adjustment stage includes the action of adding epichlorohydrin, the mid-term acid adjustment stage is: using an acidic solution to adjust the pH value to 4.8-5.0, then adding epichlorohydrin, and maintaining the temperature in the reactor at 88-90°C.

[0013] Preferably, when the mid-to-late acidic polycondensation stage includes the action of adding epichlorohydrin, the mid-to-late acidic polycondensation stage is: maintaining the pH value in the reactor at 4.8-5.0 and the temperature at 88-90° C., and adding epichlorohydrin into the reactor.

[0014] Preferably, when the alkaline stage after the late gelation includes the action of adding epichlorohydrin, the alkaline stage after the late gelation is: maintaining the temperature in the reactor at 88-90°C, adjusting the pH value to 7.0-7.2 with an alkaline solution, adding urea and epichlorohydrin to the reactor, then lowering the temperature in the reactor to 83-85°C and keeping it warm; then, lowering the temperature in the reactor and increasing the pH value in the reactor step by step; finally, when the temperature in the reactor drops below 45°C, continuing stirring for 10-15 minutes.

[0015] Preferably, the acidic solution is formic acid and the alkaline solution is sodium hydroxide solution.

[0016] Compared with the prior art, the present invention provides an E NF The invention discloses a method for preparing a urea-formaldehyde resin adhesive for a grade artificial board, wherein the urea-formaldehyde resin adhesive is modified by using epichlorohydrin, which can not only replace the modification effect of melamine, but also obtain an E-formaldehyde adhesive with low free formaldehyde content. NF The invention discloses a grade environmentally friendly adhesive, and at the same time, the adhesive has good water resistance, high toughness, low brittleness, and higher dry bonding strength and wet bonding strength. In particular, the above effects are particularly evident in the embodiment in which epichlorohydrin is added in stages.

[0017] At the same time, the addition of epichlorohydrin does not affect the curing speed of the urea-formaldehyde resin adhesive, so compared with the prior art, when using the urea-formaldehyde resin adhesive provided by the present application, it has higher production efficiency.

[0018] Additionally, compared to the prior art, the amount of epichlorohydrin required for the technical solution of the present application is lower, and the waterproof performance of the urea-formaldehyde resin adhesive obtained by the technical solution of adding 1~2wt% of the amount can be better than the technical solution of adding 3~5wt% of melamine. Therefore, the technical solution of the present application can reduce the production cost of the modified urea-formaldehyde resin adhesive. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this specification.

[0020] A method for preparing a urea-formaldehyde resin adhesive for ENF-grade artificial panels, the raw materials used include formaldehyde, urea, an acidic solution, an alkaline solution, and epichlorohydrin. The amount of epichlorohydrin added accounts for 1wt% of the weight ratio of the urea-formaldehyde resin adhesive, and the molar ratio of formaldehyde to urea in the final urea-formaldehyde resin adhesive is (0.85-0.95):1. The acidic solution is formic acid, and the alkaline solution is sodium hydroxide solution. In some embodiments, the raw materials used also include polyvinyl alcohol.

[0021] The preparation method sequentially comprises an early addition stage, an intermediate acid adjustment stage, a mid-late acid polycondensation stage, and a late alkaline stage after gelation, and epichlorohydrin is added in any one or more of the early addition stage, the intermediate acid adjustment stage, the mid-late acid polycondensation stage, and the late alkaline stage after gelation.

[0022] When the preliminary addition stage includes the action of adding epichlorohydrin, the preliminary addition stage is: adding formaldehyde to the reactor, raising the temperature to 35-40°C, adjusting the pH value to 8.3-8.5 with an alkaline solution, adding urea and epichlorohydrin, and raising the temperature in the reactor to 70-90°C.

[0023] When the mid-term acid adjustment stage includes the action of adding epichlorohydrin, the mid-term acid adjustment stage is: using an acidic solution to adjust the pH value to 4.8-5.0, then adding epichlorohydrin, and maintaining the temperature in the reactor at 88-90°C.

[0024] When the middle and late acidic polycondensation stage includes the action of adding epichlorohydrin, the middle and late acidic polycondensation stage is: maintaining the pH value in the reactor at 4.8-5.0 and the temperature at 88-90° C., and adding epichlorohydrin into the reactor.

[0025] When the alkaline stage after the late gelation includes the action of adding epichlorohydrin, the alkaline stage after the late gelation is: maintaining the temperature in the reactor at 88-90°C, adjusting the pH value to 7.0-7.2 with an alkaline solution, adding urea and epichlorohydrin to the reactor, then lowering the temperature in the reactor to 83-85°C and keeping it warm; then, lowering the temperature in the reactor and increasing the pH value in the reactor step by step; finally, when the temperature in the reactor drops below 45°C, continuing stirring for 10-15 minutes. Example

[0026] First, prepare the raw materials, which include 40% industrial formaldehyde, urea, 20% formic acid (acidic solution), 30% sodium hydroxide solution (alkaline solution), and epichlorohydrin.

[0027] In the preliminary addition stage, formaldehyde is first added to the reactor, the temperature is raised to 40° C., the pH value is adjusted to 8.3-8.5 using an alkaline solution, urea and epichlorohydrin are added, the temperature is raised to 85° C., and the temperature is kept for 30 minutes.

[0028] In the intermediate acid adjustment stage, an acidic solution is slowly added dropwise to adjust the pH value to 4.8-5.0, and the temperature in the reactor is maintained at 88-90°C.

[0029] In the middle and late acidic polycondensation stage, the pH value in the reactor is maintained at 4.8-5.0 and the temperature is maintained at 88-90°C, and the viscosity test by coating four cups is used to determine whether the stage is completed. For example, when the viscosity of the urea-formaldehyde resin adhesive detected by coating four cups is 85s, the middle and late acidic polycondensation stage can be ended.

[0030] In the alkaline stage after gelling in the later stage, the temperature in the reactor is maintained at 88-90°C, the pH value is adjusted to 7.0-7.2 using an alkaline solution, urea is added to the reactor, and then the temperature in the reactor is reduced to 83-85°C and kept warm for 40 minutes. After that, the temperature in the reactor is reduced step by step and the pH value in the reactor is increased. For example, when the temperature is reduced to 70-75°C, the pH value is controlled to 7.0-7.2 and maintained for 10 minutes; when the temperature is reduced to 60-65°C, the pH value is controlled to 7.5-7.7; finally, when the temperature in the reactor is reduced to 45°C, the pH value is controlled to 8.5-8.7, and stirring is continued for 10-15 minutes. After cooling, the urea-formaldehyde resin adhesive for ENF-grade artificial panels of this embodiment is obtained. Of course, those skilled in the art know that a certain amount of urotropine solution, triethanolamine, etc. can be added in the final stage to avoid the odor of the adhesive.

[0031] During the early stage of material preparation, the amount of epichlorohydrin added should be controlled to be 1wt% of the weight ratio of urea-formaldehyde resin adhesive, and in the final product, the molar ratio of formaldehyde to urea should be (0.85~0.95):1. Example

[0032] The difference between this embodiment and embodiment 1 is that: In the preliminary addition stage, formaldehyde is first added to the reactor, the temperature is raised to 40° C., the pH value is adjusted to 8.3-8.5 using an alkaline solution, and after urea is added, the temperature is raised to 85° C. and kept warm for 30 minutes.

[0033] In the intermediate acid adjustment stage, an acidic solution is slowly added dropwise to adjust the pH value to 4.8-5.0, and epichlorohydrin is added while maintaining the temperature in the reactor at 88-90°C. Example

[0034] The difference between this embodiment and embodiment 1 is that: In the preliminary addition stage, formaldehyde is first added to the reactor, the temperature is raised to 40° C., the pH value is adjusted to 8.3-8.5 using an alkaline solution, and after urea is added, the temperature is raised to 85° C. and kept warm for 30 minutes.

[0035] In the middle and late acidic polycondensation stages, the pH value in the reactor is maintained at 4.8-5.0 and the temperature is maintained at 88-90° C., and epichlorohydrin is added into the reactor. Example

[0036] The difference between this embodiment and embodiment 1 is that: In the preliminary addition stage, formaldehyde is first added to the reactor, the temperature is raised to 40° C., the pH value is adjusted to 8.3-8.5 using an alkaline solution, and after urea is added, the temperature is raised to 85° C. and kept warm for 30 minutes.

[0037] In the alkaline stage after gelation in the later stage, the temperature in the reactor is maintained at 88-90°C, the pH value is adjusted to 7.0-7.2 using an alkaline solution, urea and epichlorohydrin are added to the reactor, and then the temperature in the reactor is lowered to 83-85°C and kept warm for 40 minutes. After that, the temperature in the reactor is lowered and the pH value in the reactor is increased step by step. For example, when the temperature is lowered to 70-75°C, the pH value is controlled to 7.0-7.2 and maintained for 10 minutes; when the temperature is lowered to 60-65°C, the pH value is controlled to 7.5-7.7; finally, when the temperature in the reactor drops to 45°C, the pH value is controlled to 8.5-8.7 and stirring is continued for 10-15 minutes. Example

[0038] First, prepare the raw materials, which include 40% industrial formaldehyde, urea, 20% formic acid (acidic solution), 30% sodium hydroxide solution (alkaline solution), and epichlorohydrin.

[0039] In this embodiment, epichlorohydrin is added in the early addition stage, the mid-term acid adjustment stage, the mid-to-late acid polycondensation stage, and the late alkaline stage after gelation, respectively, and the ratio of the added amount of epichlorohydrin in each stage is 1:1:1.

[0040] In the preliminary addition stage, formaldehyde is first added to the reactor, the temperature is raised to 40° C., the pH value is adjusted to 8.3-8.5 using an alkaline solution, urea and epichlorohydrin are added, the temperature is raised to 85° C., and the temperature is kept for 30 minutes.

[0041] In the intermediate acid adjustment stage, an acidic solution is slowly added dropwise to adjust the pH value to 4.8-5.0, and epichlorohydrin is added while maintaining the temperature in the reactor at 88-90°C.

[0042] In the middle and late acidic polycondensation stages, the pH value in the reactor is maintained at 4.8-5.0 and the temperature is maintained at 88-90° C., and epichlorohydrin is added into the reactor.

[0043] In the alkaline stage after gelation in the later stage, the temperature in the reactor is maintained at 88-90°C, the pH value is adjusted to 7.0-7.2 using an alkaline solution, urea is added to the reactor, and then the temperature in the reactor is lowered to 83-85°C and kept warm for 40 minutes. After that, the temperature in the reactor is lowered and the pH value in the reactor is increased step by step. For example, when the temperature is lowered to 70-75°C, the pH value is controlled to 7.0-7.2 and maintained for 10 minutes; when the temperature is lowered to 60-65°C, the pH value is controlled to 7.5-7.7; finally, when the temperature in the reactor drops to 45°C, the pH value is controlled to 8.5-8.7 and stirring is continued for 10-15 minutes. Example

[0044] The difference between this embodiment and embodiment 5 is that: Epichlorohydrin is added in the early addition stage, the middle acid adjustment stage, the middle and late acid polycondensation stage and the late alkaline stage after gelation respectively, and the ratio of the added amount of epichlorohydrin in each stage is 1.5:1:1. Example

[0045] The difference between this embodiment and embodiment 5 is that: Epichlorohydrin is added in the early addition stage, the mid-term acid adjustment stage, the mid-to-late acid polycondensation stage and the late alkaline stage after gelation respectively, and the ratio of the added amount of epichlorohydrin in each stage is 2:1.5:1. Example

[0046] The difference between this embodiment and embodiment 1 is that: During the early stage of material preparation, the amount of epichlorohydrin added was controlled to be 1.5wt% of the weight ratio of urea-formaldehyde resin adhesive. Example

[0047] The difference between this embodiment and embodiment 1 is that: During the early stage of material preparation, the amount of epichlorohydrin added is controlled to be 2wt% of the weight ratio of urea-formaldehyde resin adhesive. Example

[0048] The difference between this embodiment and embodiment 1 is that: First, prepare the raw materials, which include 40% industrial formaldehyde, urea, 20% formic acid (acidic solution), 30% sodium hydroxide solution (alkaline solution), epichlorohydrin, and polyvinyl alcohol.

[0049] In the preliminary addition stage, formaldehyde is first added to the reactor, the temperature is raised to 40°C, the pH value is adjusted to 8.3-8.5 using an alkaline solution, urea, epichlorohydrin and polyvinyl alcohol are added, the temperature is raised to 85°C, and the temperature is kept for 30 minutes. The amount of polyvinyl alcohol added is 1%.

[0050] Comparative Example 1 The technical solution recorded in the Chinese invention patent application with publication number CN107118722A and titled “A urea-formaldehyde resin adhesive for artificial boards and its preparation process”.

[0051] Comparative Example 2 The technical solution recorded in the Chinese invention patent application with publication number CN107746696A and titled "A urea-formaldehyde resin adhesive for artificial boards and its preparation process".

[0052] The adhesives of Examples 1 to 8 and Comparative Examples 1 and 2 were tested to obtain the test results of water solubility, curing time, boiling resistance, and viscosity. The adhesives of Examples 1 to 8 and Comparative Examples 1 and 2 were used to prepare multilayer plywood with the same amount of glue, raw materials, and production process. Each group of multilayer plywood was tested to obtain the test results of formaldehyde emission, dry bonding strength, and wet bonding strength. Among them, the E0 grade should meet the formaldehyde emission of less than or equal to 0.050 (mg / m 3 ) requirements, E NF The formaldehyde emission level should be less than or equal to 0.025 (mg / m 3 The above test results are shown in Table 1.

[0053] Table 1 Example Water Solubility Curing time(s) Boiling resistance (h) Viscosity (cp) <![CDATA[Formaldehyde emission (mg / m 3 )]]> Dry adhesive strength (MPa) Wet bond strength (MPa) Example 1 0.66 255 14 198 0.015 1.435 1.177 Example 2 0.65 257 14 195 0.015 1.440 1.175 Example 3 0.65 255 14 198 0.015 1.432 1.171 Example 4 0.67 255 14 197 0.015 1.435 1.175 Example 5 0.65 258 14 194 0.015 1.451 1.177 Example 6 0.69 256 16 193 0.015 1.476 1.189 Example 7 0.72 256 17 190 0.015 1.485 1.211 Example 8 0.70 263 18 201 0.015 1.495 1.253 Example 9 0.73 259 19 205 0.015 1.501 1.311 Example 10 0.63 253 15 193 0.015 1.472 1.186 Comparative Example 1 0.51 232 6 210 0.03 1.083 0.865 Comparative Example 2 0.61 281 12 205 0.024 1.307 1.126 It should be understood that the above description is intended to be illustrative and not limiting. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but rather with reference to the foregoing claims and the full scope of equivalents to which such claims are entitled. For the purpose of comprehensiveness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the foregoing claims is not intended to be a waiver of such subject matter, nor should it be considered that the applicant has not considered such subject matter to be part of the disclosed application subject matter.

Claims

1. A kind of E NF The method for preparing a urea-formaldehyde resin adhesive for a grade artificial board comprises raw materials including at least formaldehyde, urea, an acidic solution, and an alkaline solution, and is characterized in that: It also includes epichlorohydrin, and the added amount of epichlorohydrin accounts for 1~2 wt% of the weight ratio of urea-formaldehyde resin adhesive; at the same time, the molar ratio of formaldehyde to urea is (0.85~0.95):

1.

2. E according to claim 1 NF The method for preparing a urea-formaldehyde resin adhesive for a grade artificial board is characterized in that: The preparation method sequentially comprises an early addition stage, an intermediate acid adjustment stage, a mid-late acid polycondensation stage, and a late alkaline stage after gelation, and epichlorohydrin is added in any one or more of the early addition stage, the intermediate acid adjustment stage, the mid-late acid polycondensation stage, and the late alkaline stage after gelation.

3. E according to claim 2 NF The method for preparing a urea-formaldehyde resin adhesive for a grade artificial board is characterized in that: Epichlorohydrin is added in any one or more of the early addition stage, the mid-term acid adjustment stage and the mid-to-late acid polycondensation stage.

4. E according to claim 3 NF The method for preparing a urea-formaldehyde resin adhesive for a grade artificial board is characterized in that: Epichlorohydrin is added in the early addition stage, the mid-term acid adjustment stage and the mid-to-late acid polycondensation stage, and the ratio of the amount of epichlorohydrin added in each stage is (1.5-2):(1-1.5):

1.

5. E according to claim 2 NF The method for preparing a urea-formaldehyde resin adhesive for a grade artificial board is characterized in that: Epichlorohydrin is added in the initial addition stage.

6. E according to claim 2 NF The method for preparing a urea-formaldehyde resin adhesive for a grade artificial board is characterized in that: When the preliminary addition stage includes the action of adding epichlorohydrin, the preliminary addition stage is: adding formaldehyde to the reactor, raising the temperature to 35-40°C, adjusting the pH value to 8.3-8.5 with an alkaline solution, adding urea and epichlorohydrin, and raising the temperature in the reactor to 70-90°C.

7. E according to claim 2 NF The method for preparing a urea-formaldehyde resin adhesive for a grade artificial board is characterized in that: When the mid-term acid adjustment stage includes the action of adding epichlorohydrin, the mid-term acid adjustment stage is: using an acidic solution to adjust the pH value to 4.8-5.0, then adding epichlorohydrin, and maintaining the temperature in the reactor at 88-90°C.

8. E according to claim 2 NF The method for preparing a urea-formaldehyde resin adhesive for a grade artificial board is characterized in that: When the middle and late acidic polycondensation stage includes the action of adding epichlorohydrin, the middle and late acidic polycondensation stage is: maintaining the pH value in the reactor at 4.8-5.0 and the temperature at 88-90° C., and adding epichlorohydrin into the reactor.

9. E according to claim 2 NF The method for preparing a urea-formaldehyde resin adhesive for a grade artificial board is characterized in that: When the alkaline stage after the late gelation includes the action of adding epichlorohydrin, the alkaline stage after the late gelation is: maintaining the temperature in the reactor at 88-90°C, adjusting the pH value to 7.0-7.2 with an alkaline solution, adding urea and epichlorohydrin to the reactor, then lowering the temperature in the reactor to 83-85°C and keeping it warm; then, lowering the temperature in the reactor and increasing the pH value in the reactor step by step; finally, when the temperature in the reactor drops below 45°C, continuing stirring for 10-15 minutes.

10. E according to claim 1 NF The method for preparing a urea-formaldehyde resin adhesive for a grade artificial board is characterized in that: The acidic solution is formic acid and the alkaline solution is sodium hydroxide solution.