Method for preparing urea-formaldehyde precursor and urea-formaldehyde precursor obtained thereby

Abstract

The present invention provides a method for preparing a urea-formaldehyde precursor used in the preparation of a urea-formaldehyde resin, and a urea-formaldehyde precursor prepared by the method.

Description

Method for manufacturing a urea-formaldehyde precursor and a urea-formaldehyde precursor obtained by the method thereof

[0001] The present invention relates to a method for manufacturing a urea-formaldehyde precursor and a urea-formaldehyde precursor obtained by the method thereof.

[0002] In general, wax is added to increase water resistance during the manufacture of wood-based building materials such as medium-density fiberboard (MDF), plywood, flooring, and particle board. Due to the water resistance of wax itself, a small amount of wax added during the manufacture of wood-based building materials improves dimensional stability, such as water absorption rate and thickness expansion rate of the manufactured wood-based building materials, but the effect is temporary and limited.

[0003] Adhesives used in wood-based construction materials are essential for a strong bond between wood veneers, and one such adhesive is urea-formaldehyde resin (UF resin).

[0004] Urea-formaldehyde resin is a thermosetting resin produced through the reaction of urea and formaldehyde, and is widely used primarily as an adhesive for wood products. Urea-formaldehyde resin possesses advantages such as low cost, excellent adhesion, and a fast curing time. The manufacturing process of urea-formaldehyde resin generally consists of two steps: the first step involves reacting urea and formaldehyde under alkaline conditions to form methylolated urea, and the second step involves condensing the methylolated urea under acidic conditions to form an insoluble cross-linked resin. During this process, conditions such as reaction temperature, pH, and molar ratio significantly influence the properties of the final resin.

[0005] In conventional manufacturing methods for urea-formaldehyde resins, additives such as melamine, resorcinol, and phenol have been used to enhance resin performance and improve water resistance. However, the use of these additives increases resin costs and can compromise the inherent advantages of urea-formaldehyde resins, such as their low cost and excellent workability. Furthermore, concerns regarding the environment and health regarding urea-formaldehyde resins have been raised due to formaldehyde emissions. To address this, the development of low-emission resins that minimize formaldehyde release is required. For example, methods to reduce emissions by controlling the molar ratio (FMR) of formaldehyde to urea are being studied. Generally, while higher FMR values ​​increase formaldehyde emissions, they also improve adhesion and water resistance. Therefore, manufacturing methods for urea-formaldehyde resins must balance resin performance with environmental impact, and to achieve this, the optimization of various manufacturing conditions is necessary.

[0006] [Prior Art Literature]

[0007] [Patent Literature]

[0008] Patent No. 10-0552548

[0009] The problem that the present invention aims to solve is to provide a urea-formaldehyde precursor and a method for manufacturing the same, which can ensure high storage stability and excellent physical properties in the final manufactured wood-based building material while having a low unreacted formaldehyde content during the production of a urea-formaldehyde resin.

[0010] To solve the above problem, the present invention provides a method for manufacturing a urea-formaldehyde precursor comprising: a reaction preparation step of introducing formaldehyde into a reactor and controlling the pH and temperature; a first reaction step of introducing urea in a molar ratio of 0.20 to 0.35 based on 1 mole of formaldehyde and carrying out the reaction; a second reaction step after the first reaction step, introducing urea in an amount of 0.005 mol / min to 0.015 mol / min based on 1 mole of formaldehyde introduced in the reaction preparation step and carrying out the reaction for 15 to 25 minutes; a reaction control step after the second reaction step of introducing the reaction by controlling the temperature to 90 to 100℃ and the pH to 4.4 to 4.8; and a reaction termination step after the reaction control step of introducing an amine-based neutralizing agent and NaOH.

[0011] In addition, the present invention provides a urea-formaldehyde precursor having a Formaldehyde to Urea Molar Ratio (FMR) value of 2 or higher.

[0012] Furthermore, the present invention provides a method for manufacturing a urea-formaldehyde resin by additionally mixing urea into a urea-formaldehyde precursor to adjust the FMR to 0.80 to 1.3.

[0013] The urea-formaldehyde resin produced according to the manufacturing method of the present invention has a low content of unreacted formaldehyde and can be applied to eco-friendly wood-based building materials. Since a urea-formaldehyde precursor with a high content of unreacted formaldehyde is produced first, storage stability can be ensured.

[0014] Hereinafter, various embodiments of the present invention are described with reference to the accompanying drawings. The present invention is not limited to specific embodiments and should be understood to include various modifications, equivalents, and / or alternatives of the embodiments of the present invention. In relation to the description of the drawings, similar reference numerals may be used for similar components.

[0015] In this document, expressions such as "have," "can have," "include," or "can include" refer to the existence of the relevant feature (e.g., numerical values, functions, actions, or components, etc.) and do not exclude the existence of additional features.

[0016] In this document, expressions such as “A or B,” “at least one of A or / and B,” or “one or more of A or / and B” may include all possible combinations of items listed together. For example, “A or B,” “at least one of A and B,” or “at least one of A or B” may refer to cases including (1) at least one A, (2) at least one B, or (3) both at least one A and at least one B.

[0017] As used in this document, the expression "configured to" may be replaced, depending on the context, with, for example, "suitable for," "having the capacity to," "designed to," "adapted to," "made to," or "capable of." The term "configured to" does not necessarily mean "specifically designed to."

[0018] The terms used in this document are used merely to describe specific embodiments and are not intended to limit the scope of other embodiments. Singular expressions may include plural expressions unless the context clearly indicates otherwise. Terms used herein, including technical or scientific terms, may have the same meaning as generally understood by those skilled in the art described in this document. Terms used in this document that are defined in general dictionaries may be interpreted as having the same or similar meaning as they have in the context of the relevant technology, and are not to be interpreted in an ideal or overly formal sense unless explicitly defined in this document. In some cases, even terms defined in this document may not be interpreted to exclude the embodiments of this document.

[0019] The embodiments disclosed in this document are presented for the purpose of explaining and understanding the disclosed technical content and are not intended to limit the scope of the invention. Accordingly, the scope of this document should be interpreted to include all modifications or various other embodiments based on the technical concept of the invention.

[0020] Hereinafter, preferred embodiments of the present invention will be described in detail. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, and should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0021] Therefore, it should be understood that the configurations of the embodiments described in this specification are merely some of the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention, and that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0022] Throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0023] The present invention will be described in detail below.

[0024] Method for manufacturing a urea-formaldehyde precursor

[0025] A method for preparing a urea-formaldehyde precursor according to one embodiment of the present invention comprises: a reaction preparation step of introducing formaldehyde into a reactor and controlling the pH and temperature; a first reaction step of introducing urea in a molar ratio of 0.20 to 0.35 based on 1 mole of formaldehyde and carrying out the reaction; a second reaction step of introducing urea in an amount of 0.005 mol / min to 0.015 mol / min based on 1 mole of formaldehyde introduced in the reaction preparation step for 15 to 25 minutes and carrying out the reaction after the first reaction step; a reaction control step of introducing the reaction by controlling the temperature to 90 to 100℃ and the pH to 4.4 to 4.8 after the second reaction step; and a reaction termination step of introducing an amine-based neutralizing agent and NaOH after the reaction control step.

[0026] In this specification, "urea-formaldehyde precursor" refers to a material in a partially polymerized state that is a material prior to the final material when making a final material through a chemical reaction, and is a material prior to the final resin production stage in which urea is additionally added during the production of the urea-formaldehyde resin by increasing the proportion of formaldehyde significantly before the synthesis of the final urea-formaldehyde resin.

[0027] In this specification, the term FMR is generally an abbreviation for "Formaldehyde to Urea Molar Ratio," representing the molar ratio of formaldehyde to urea, and an FMR value greater than 1 means that formaldehyde has a higher molar ratio than urea. The FMR value is calculated through the molar ratio of formaldehyde to urea input in the overall process.

[0028] The urea-formaldehyde resin used in the manufacture of conventional wood-based building materials is manufactured by synthesizing and controlling the molar ratio of urea to formaldehyde to an FMR value between 0.70 and 1.30. The manufactured urea-formaldehyde resin is mixed with wood materials and used as an adhesive in the manufacture of wood-based building materials such as PB and MDF.

[0029] As a result of the inventors' research, it was confirmed that when a urea-formaldehyde precursor is prepared before manufacturing the urea-formaldehyde resin, and then urea is additionally added in the next step to adjust the FMR value to 0.70 to 1.30 to manufacture the urea-formaldehyde resin, the amount of unreacted formaldehyde contained in the urea-formaldehyde resin can be reduced while having an FMR value equivalent to that of commercially available urea-formaldehyde resins. Furthermore, it was discovered that by shortening the curing time of the urea-formaldehyde resin, the manufacturing yield can be increased when manufacturing wood-based building materials, and excellent physical properties can be secured, with a low amount of formaldehyde emission due to the low unreacted formaldehyde content in the urea-formaldehyde resin.

[0030] In other words, the present invention is characterized by first preparing a urea-formaldehyde precursor with a very high unreacted formaldehyde content, distributing it with enhanced storage stability, and then immediately producing a urea-formaldehyde resin by mixing urea with the said urea-formaldehyde precursor on the process line during the production of wood-based building materials.

[0031] According to one embodiment of the present invention, the urea-formaldehyde precursor may have an unreacted formaldehyde content of 5 to 20 weight% based on 100 weight% of the urea-formaldehyde precursor. Preferably, it may be 6 to 18 weight%, and more preferably, 6 to 15 weight%. By including unreacted formaldehyde within the above-described range, the curability of the urea-formaldehyde resin produced finally can be increased, and the amount of formaldehyde emitted from wood-based building materials using said resin can be reduced. In addition, since it is in the state of a precursor before being completed as a resin, the viscosity does not increase during long-term storage, thereby ensuring storage stability.

[0032] Below, each step of the method for manufacturing the above-described urea-formaldehyde precursor is explained in detail.

[0033] The above reaction preparation step may involve adjusting the temperature to 50 to 70°C and the pH to 8.1 to 8.9 after the introduction of formaldehyde. By heating the formaldehyde so that the subsequent reaction can continue under conditions higher than room temperature, the methylolation reaction of the subsequently introduced urea can be facilitated.

[0034] The above first reaction step may be a methylolation reaction in which urea is added to heated formaldehyde in a molar ratio of 0.20 to 0.35 based on a molar amount of formaldehyde of 1, and then the temperature is adjusted to 85 to 95°C and the pH to 5.90 to 6.20. NaOH may be added to adjust the pH.

[0035] The above second reaction step may involve adjusting the temperature to 85 to 95°C and the pH to 4.4 to 4.8. Similar to the first reaction step described above, NaOH may be additionally added to adjust the pH.

[0036] In the above second reaction step, urea is additionally added, and the reaction is carried out by adding urea at an amount of 0.005 mol / min to 0.015 mol / min for 15 to 25 minutes, based on 1 mol of formaldehyde added in the reaction preparation step. The above addition rate may preferably be 0.006 mol / min to 0.013 mol / min, and more preferably 0.007 mol / min to 0.010 mol / min. By controlling the addition rate within the above-described range, the binding of urea reacting with formaldehyde can be controlled, and the content of unreacted formaldehyde contained in the manufactured urea-formaldehyde precursor can be secured within the range according to one embodiment of the present invention.

[0037] The above reaction control step may involve controlling the temperature to 90 to 105°C and the pH to 4.4 to 4.8. Similar to the first reaction step described above, NaOH may be additionally added to control the pH. The reaction is terminated by entering the reaction termination step after the urea-formaldehyde precursor satisfies 330 to 480 cPS according to the Brookfield viscometer.

[0038] The above reaction termination step involves introducing an amine-based neutralizing agent and NaOH to terminate the final reaction and produce a urea-formaldehyde precursor, wherein the temperature in the above reaction control step is lowered to 30 to 65 ℃ and the pH at the time of final production is set to 8.0 to 8.5. NaOH may be introduced to adjust the pH.

[0039] The above amine-based neutralizing agent may include one or more selected from the group consisting of triethanolamine (TEA), hexamethylenediamine (HMDA), bis-hexamethylenetriamine (BHMTA), ammonia, and tetraethylenepentamine (TEPA).

[0040] Urea-formaldehyde precursor

[0041] According to one embodiment of the present invention, a urea-formaldehyde precursor is manufactured by the manufacturing method described above, and may have an FMR value of 2 or higher. Preferably, it may be 2.1 or higher and 3 or lower, and more preferably, 2.2 or higher and 2.6 or lower. As described above, the urea-formaldehyde precursor of the present invention is manufactured with residual formaldehyde present at a high concentration, and can subsequently be synthesized into a urea-formaldehyde resin by additionally adding urea. Conventionally manufactured urea-formaldehyde resins may undergo a long distribution process during which some of the polymerization of the manufactured urea-formaldehyde resin may decompose (e.g., hydrolysis due to moisture), and formaldehyde is released and present within the resin. By dividing this process into two stages and immediately manufacturing the product on-site by adding urea, the reaction between urea and formaldehyde is enhanced, thereby reducing the content of unreacted formaldehyde.

[0042] The above urea-formaldehyde precursor may have an unreacted formaldehyde content of 5 to 20 weight% based on 100 weight% of the precursor. Preferably, it may be 6 to 15 weight%, and more preferably, 6 to 10 weight%. By including unreacted formaldehyde within the above-described range, the curability of the finally manufactured urea-formaldehyde resin can be increased, and the amount of formaldehyde emitted from wood-based building materials using said resin can be reduced. In addition, storage stability can be ensured as the viscosity does not increase during long-term storage. Furthermore, by controlling the speed as described above, the urea-formaldehyde precursor can have a viscosity of 250 to 350 cPS, and the urea-formaldehyde precursor can secure physical properties with a gel time of 15 to 30 sec.

[0043] Generally, the refractive index (RI) of commercially available urea-formaldehyde resins is typically between 1.54 and 1.55, which plays an important role in the transparency and gloss of the resin. The refractive index is closely related to the molecular structure of the resin. In the case of UF resins, the refractive index tends to increase as the molecular weight increases. This is because the density of the resin and intermolecular interactions increase. A urea-formaldehyde precursor according to one embodiment of the present invention may have a refractive index of 1.2 to 1.50, which is lower than the refractive index of commercially available urea-formaldehyde resins, allowing confirmation that it is in a precursor state.

[0044] Method for manufacturing urea-formaldehyde resin

[0045] According to one embodiment of the present invention, by additionally mixing urea into the urea-formaldehyde precursor described above, a urea-formaldehyde resin having an FMR value of 0.70 to 1.30 can be produced.

[0046] Generally, the FMR value of urea-formaldehyde resins ranges from 0.7 to 2.0, but recently, due to environmental and health concerns, there is a trend toward using lower FMR values ​​(1.0 or less). While higher FMR values ​​offer faster curing speeds and higher adhesive strength, they can be problematic due to the release of higher levels of formaldehyde. Conversely, lower FMR values ​​result in lower formaldehyde emissions but lower adhesive strength and water resistance.

[0047] Typically, FMR can be controlled by adjusting the number and amount of urea added during the synthesis process, and the FMR value is not measured directly but is generally calculated based on the ratio of the initial reactants. Currently, one of the main goals of current research is to maintain the performance of the resin while using low FMR values ​​(e.g., 0.7 or 1.0).

[0048] Presumably, when urea-formaldehyde resin is manufactured by mixing urea at a wood-based building material manufacturing site after distributing it in the form of a urea-formaldehyde precursor according to one embodiment of the present invention, even if the formaldehyde content in the mixture is somewhat high, as the reaction proceeds, urea itself acts as a formaldehyde capture agent to synthesize the urea-formaldehyde resin, and since the reaction proceeds with a relatively high content of unreacted formaldehyde, it is believed that excellent curing properties and water resistance can be secured for the finally manufactured resin.

[0049] In particular, when a urea-formaldehyde resin is manufactured in two steps using a urea-formaldehyde precursor according to one embodiment of the present invention, the unreacted formaldehyde content of the final manufactured urea-formaldehyde resin can be reduced to 0.50% or less.

[0050] The above-described urea-formaldehyde resin can be used in the manufacture of wood-based building materials. The wood-based building material is formed using wood as a raw material and urea-formaldehyde resin as an adhesive to produce molded products such as PB and MDF.

[0051] The above wood materials may include raw logs, and the raw logs may include one or more species selected from the group consisting of natural materials such as tropical hardwoods including Merbau, Burckella, Bangkirai, Malas, and Kwila; fast-growing species including Radiata pine, Eucalyptus, and Acasia; and temperate softwoods and hardwoods including Korean red pine, Korean pine, Ulleungdo white pine, Black pine, Japanese yew, Temple juniper, Southern Japanese hemlock, Korean fir, Needle fir, and Dahurian larch.

[0052] In addition, recycled wood may be used depending on the material. Recycled wood consists of industrial waste wood or general waste wood; industrial waste wood is mainly from construction sites, while general waste wood mainly consists of waste wood from everyday household items such as furniture.

[0053] In addition, it may include agricultural residues such as sugarcane (Bagasse), rice husks, and rice straw.

[0054] According to another embodiment of the present invention, various additional constituent materials for manufacturing wood-based building materials from urea-formaldehyde resin may be included. For example, as other types of adhesive functional resins, phenol-formaldehyde (PF) resin and melamine-formaldehyde (MF) resin may be included, and preservatives, flame retardants, colorants, moisture-proof agents and curing agents may be additionally included.

[0055] The present invention will be described in more detail below through examples. These examples are intended solely to explain the present invention more specifically, and it will be obvious to those skilled in the art that the scope of the present invention is not limited by these examples according to the gist of the present invention.

[0056] Examples and Comparative Examples

[0057] Example 1

[0058] As a reaction preparation step, 1,351 g (23.84 mol of formaldehyde) with a 53% concentration of formaldehyde is prepared and added to the reactor, and NaOH with a 30% concentration is added to make the pH 8.5 and the temperature is adjusted to 60°C.

[0059] As a first reaction step, 410 g (6.82 mol) of urea is added, and 30% concentration NaOH is added to raise the pH to 6.0. The temperature is set to 90°C when adding NaOH, and then, when the pH reaches 6.0 with the addition of NaOH, the temperature is cooled to 85°C.

[0060] As a second reaction step, urea is added to the reactor at an input rate of 0.19 mol / min for 20 minutes. The total amount of urea added is 3.8 mol (228.23 g). As the reaction proceeds, if the pH drops below 6.0, additional NaOH is added to maintain it.

[0061] As a reaction control step, 30% concentration NaOH is added to raise the temperature to 95°C and the pH to 6.0. After the reaction proceeds, if 360 cPS is satisfied according to the Brookfield viscometer, the reaction is entered into the reaction termination step.

[0062] As a reaction termination step, 5g of tetraethylenepentaamine was added as an amine-based neutralizing agent, and 30% NaOH was added to terminate the reaction so that the final pH was 8.58, and a compound (urea-formaldehyde precursor) was obtained.

[0063] Examples 2 to 6 and Comparative Examples 1 to 3

[0064] A compound was obtained in the same manner as in Example 1, except that the input rate of the urea in the second reaction step was controlled as shown in the table below.

[0065] Remarks Secondary Reaction Step Element Injection Rate (mol / min) Injection Time (min) Reaction Preparation Step Based on 1 mol of formaldehyde Secondary Reaction Step Element Injection Rate (mol / min) Secondary Reaction Step Total Amount of Injected Element (g) Secondary Reaction Step Total Moles of Injected Element (mol) Example 1 0.19 0 200.00 79 72 28.23 3.80 Example 20.15 5 200.00 65 0 18 6.14 3.01 Example 30.16 7 200.00 70 200.46 3.34 Example 40.21 200.00 88 0 25 2.00 4.20 Example 50.23 1 200.00 97 0 27 7.78 4.62 Example 60.31 0 15 0.01 300 37 2.28 4.64 Comparative Example 10.107200.00450128.862.15Comparative Example 20.381200.01600458.197.63Comparative Example 33.8010.160228.233.80

[0066] Comparative Example 4

[0067] Without proceeding with the second reaction step, 638.23g of urea was entirely added to the first reaction step, and the remaining reaction was carried out in the same manner as in Example 1 to obtain a urea-formaldehyde resin composition.

[0068]

[0069] Preparation of urea-formaldehyde resin

[0070] Urea was additionally added to the compounds of Examples 1 to 6 and Comparative Examples 1 to 4, which are the urea-formaldehyde precursors, and the reaction was carried out to adjust the final FMR to 0.92 to prepare urea-formaldehyde resins. These were designated as Preparation Examples 1 to 10, respectively. For example, Preparation Example 1 is the urea-formaldehyde resin obtained from Example 1, and Preparation Example 10 is the urea-formaldehyde resin obtained from Comparative Example 4. Comparative Preparation Example 1 is a commercially available urea-formaldehyde resin from S. Kleber with an FMR of 0.92. Comparative Preparation Example 1 does not undergo the two-step process of adding urea to the urea-formaldehyde precursor to obtain the urea-formaldehyde resin.

[0071] Measurement of compound properties in examples and comparative examples

[0072] The physical properties of the urea-formaldehyde precursors of Examples 1 to 6 and Comparative Examples 1 to 4 were measured and are shown in Table 2 below.

[0073] Appearance: After visual inspection, O if transparency is high, X if cloudiness or foreign substances are present.

[0074] Viscosity: Brookfield viscometer standard, room temperature 25℃.

[0075] Unreacted formaldehyde: Detected formaldehyde content % relative to 100 wt% of the final compound.

[0076] Gel time: Using Sunshine Instruments, the materials of the examples and comparative examples were diluted to 50% solid content, and ammonium chloride was added as a catalyst. After taking 2g of the sample, it was stirred at a constant speed at 100°C, and the time at which further stirring was impossible was measured.

[0077] Refractive index: Measured using an Abbe refractometer at 20°C using sodium D rays.

[0078] Remarks Appearance Solid Content (%) Viscosity (cPS) Gel Time (s) Unreacted Formaldehyde (%) Refractive Index FMR Example 1 059.09 293 20.5 17.5 11.4 22.22 Example 2 058.65 320 23.67.2 11.4 32.43 Example 3 059.05 320 21.37.03 1.4 42.35 Example 4 058.87 350 19.79 6.5 31.4 12.16 Example 5 059.21 310 20.5 16.45 1.4 12.08 Example 6 059.34 299 21.66.10 1.4 22.08 Comparative Example 1060.1232317.81.352.66 Comparative Example 2X60.236057.52.801.511.65 Comparative Example 3X60.538331.77.321.522.24 Comparative Example 4x61.237030.57.451.512.24

[0079] Measurement of physical properties of the compound in the preparation example

[0080] The physical properties of the compounds of Preparation Examples 1 to 10 and Comparative Preparation Example 1 were measured. The results are shown in Table 3.

[0081] Remarks Appearance Solid Content (%) Viscosity (cPS) Gel Time (s) Unreacted Formaldehyde (%) Refractive Index FMR Preparation Example 1 O6 3.63 166.8 55.45 0.34 1.46 10.92 Preparation Example 2 O6 2.05 18 0.25 8.1 10.30 1.46 30.92 Preparation Example 3 O6 3.02 166.45 5.03 0.33 1.45 90.92 Preparation Example 4 O6 2.5 167.35 6.5 0.36 1.44 20.92 Preparation Example 5 O6 2.08 15 0.45 3.1 10.3 81.4530.92 Manufacturing Example 6062.5515552.050.401.4670.92 Manufacturing Example 7063.02146.855.880.611.4890.92 Manufacturing Example 8062.8815555.310.751.4600.92 Manufacturing Example 9X61.55150.858.990.981.4240.92 Manufacturing Example 10X63.41170.552.781.051.4650.92 Comparative Manufacturing Example 1065.00130.057.000.921.510.92

[0082] Measurement of storage stability of compounds in examples and comparative examples

[0083] After storing the compounds of Examples 1 to 6 and Comparative Examples 1 to 4 at 25°C, the viscosity on the first day, after 10 days, after 25 days, and after 40 days was measured using a Brookfield viscometer. The results are shown in Table 4.

[0084] Remarks First 10 days later 25 days later 40 days later Example 1 293320375412 Example 2 320330363421 Example 3 320345372414 Example 4 350375412453 Example 5 310335363402 Example 6 299332374406 Comparative Example 1 232378436518 Comparative Example 2 360415467502 Comparative Example 3 383452494526 Comparative Example 4 370425487514

[0085] As can be seen above, it was confirmed that Examples 1 to 6 of the present invention have higher storage stability, as the increase in viscosity after 40 days is lower than that of Comparative Examples 1 to 4. In the case of Comparative Example 1, although the initial viscosity is low because the amount of formaldehyde is greater than the total amount of urea added, it was confirmed that the increase in viscosity of the resin is relatively higher because the excess formaldehyde in the composition causes an additional reaction in the urea resin that has already reacted within the composition, thereby transforming the chain-like urea resin into a branched-chain structure.

[0086] Measurement of storage stability of the compound in the preparation example

[0087] After storing the compounds of Preparation Examples 1 to 10 and Comparative Preparation Example 1 at 25°C, the viscosity on the first day, after 10 days, after 25 days, and after 40 days was measured using a Brookfield viscometer. The results are shown in Table 5.

[0088] Remarks First 10 days later 25 days later 40 days later Manufacturing Example 1 166.8 200 310 630 Manufacturing Example 2 180.2 20 290 670 Manufacturing Example 3 166.4 180 287 585 Manufacturing Example 4 167.3 210 298 623 Manufacturing Example 5 150.4 230 310 610 Manufacturing Example 6 155 240 312 636 Manufacturing Example 7 146.8 190 330 722 Manufacturing Example 8 155 210 331 755 Manufacturing Example 9 150.8 200 345 780 Manufacturing Example 10 170.5 198 354 763 Comparative Manufacturing Example 1 130.0 268 532 Gel

[0089] manufacturing of particle board

[0090] The manufacturing of the particle board was carried out under the following conditions, and the compounds prepared in Manufacturing Examples 1 to 10 and Comparative Manufacturing Example 1 were mixed and used.

[0091] Board thickness: 9mm

[0092] Adhesive content (Resin content): 80 kg / m² 3 (Based on urea-formaldehyde resin solid content, solid)

[0093] Press temperature: 190℃

[0094] Press time: 180 seconds

[0095] Subsequently, measurements were performed under the following conditions. The results are shown in Table 6.

[0096] KS F 3104 Particle Board Quality Standard (Type 180, Type U), EN321-V313 Peel Strength* (MPa) > 0.3 Flexural Strength* (MPa) > 18 Formaldehyde Emission* (mg / L) Thickness Expansion Rate* (24h, %) < 12 Manufacturing Example 1 10.4 120 1.2 11 120.3 42 21.2 310 30.3 82 11.2 611 Manufacturing Example 2 10.3 42 21.2 110 20.3 623 1.2 79.8 30.3 32 11.2 510 Manufacturing Example 3 10.4 02 1.2 31 120.4 11 91.2 510 30.3 92 11.3 011 Manufacturing Example 410.33221.301020.36211.359.530.35191.3411 Manufacturing Example 510.34191.301020.35201.299.930.39211.2811 Manufacturing Example 610.35191.301020.38211.231130.34201.2510 Manufacturing Example 710.33211.519.320.34231.491130.36201.5110 Manufacturing Example 810.32191.421020.31201.439.830.30211.4210 Manufacturing Example 910.35201.491020.33191.459.830.34211.4710 Manufacturing Example 1010.33201.481120.32201.511030.30191.5110.4 Comparative Manufacturing Example 110.32191.471020.33211.4710.230.30201.4911* Peel strength: Internal Bond, Flexural strength: Modulus of rupture* Formaldehyde emission: Desiccator method* Thickness expansion rate: Thickness swelling

Claims

1. A reaction preparation step of introducing formaldehyde into a reactor and controlling the pH and temperature; A first reaction step in which urea is added at a molar ratio of 0.20 to 0.35 based on 1 mole of formaldehyde to proceed with the reaction; After the first reaction step above, a second reaction step in which urea is added in an amount of 0.005 mol / min to 0.015 mol / min for 15 to 25 minutes, based on 1 molar of formaldehyde added in the reaction preparation step above, to carry out the reaction; After the above second reaction step, a reaction control step in which the reaction is carried out by adjusting the temperature to 90 to 100℃ and the pH to 4.4 to 4.8, and A method for preparing a urea-formaldehyde precursor, comprising a reaction termination step of adding an amine-based neutralizing agent and NaOH after the above reaction control step.

2. In Claim 1, A method for preparing a urea-formaldehyde precursor, wherein the reaction preparation step involves adjusting the temperature to 50 to 70°C and the pH to 8.1 to 8.9 after introducing formaldehyde.

3. In Claim 1, A method for preparing a urea-formaldehyde precursor, wherein the first reaction step above involves adjusting the temperature to 85 to 95℃ and the pH to 5.90 to 6.20 after adding urea.

4. In Claim 1, A method for preparing a urea-formaldehyde precursor, wherein the above secondary reaction step involves controlling the temperature to 85 to 95℃ and the pH to 4.4 to 4.

8.

5. In Claim 1, A method for manufacturing a urea-formaldehyde precursor, wherein the urea-formaldehyde precursor manufactured in the above reaction control step enters the reaction termination step after satisfying a Brookfield viscometer standard of 330 to 480 cPS.

6. In Claim 1, A method for manufacturing a precursor in which the final urea-formaldehyde precursor manufactured above has an unreacted formaldehyde content of 5 to 20 weight% based on 100 weight% of the precursor.

7. A urea-formaldehyde precursor having an FMR (Formaldehyde to Urea Molar Ratio) value of 2 or higher.

8. In Claim 7, The above urea-formaldehyde precursor is a urea-formaldehyde precursor having a viscosity of 250 to 350 cPS.

9. In Claim 7, The above urea-formaldehyde precursor is a urea-formaldehyde precursor having a gel time of 15 to 30 sec.

10. In Claim 7, The above urea-formaldehyde precursor is a urea-formaldehyde precursor having a refractive index (RI) of 1.2 to 1.

50.

11. A method for manufacturing a urea-formaldehyde resin, wherein urea is additionally mixed into the urea-formaldehyde precursor of Claim 7 to adjust the FMR to 0.80 to 1.3.