E0 grade transparent impregnated urea-formaldehyde resin and its production method

Abstract

This invention discloses an E0-grade transparent impregnated urea-formaldehyde resin and its production method, belonging to the field of polymer synthesis technology. The resin comprises formaldehyde solution, urea, hexamethylenetetramine, borax, food-grade glucose, and ascorbic acid. The production process employs a three-stage urea feeding process, using hexamethylenetetramine, borax, and food-grade glucose to construct a composite synergistic regulatory system, combined with ascorbic acid to terminate the reaction, achieving synergistic control of the resin polycondensation reaction and the free formaldehyde capture process. Simultaneously, low-temperature polycondensation and low-temperature dehydration processes are used to reduce the risk of resin oxidative yellowing. The resulting resin exhibits low free formaldehyde content, high transparency, good storage stability, and excellent anti-yellowing properties. The free formaldehyde content is no more than 0.3%, and the transmittance at 600nm wavelength is no less than 92%, making it suitable for decorative paper impregnation, wood primers, and playing card varnishing resins.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis technology, specifically to an E0 grade transparent impregnated urea-formaldehyde resin and its production method. Background Technology

[0002] Urea-formaldehyde resin is widely used in decorative paper impregnation, wood primers, playing card varnishes, and adhesives for engineered wood products due to its wide availability of raw materials, low production cost, fast curing speed, and excellent impregnation performance. In decorative paper impregnation and high-transparency coating applications, not only are good penetration and curing properties required, but also high transparency, low free formaldehyde content, and excellent storage stability. However, most existing impregnation urea-formaldehyde resins use traditional acidic catalytic systems such as ammonium chloride and benzenesulfonic acid to promote the polycondensation reaction. While these catalytic systems can improve the resin's reaction efficiency, they easily lead to side reactions during the reaction, causing the resin to darken in color and decrease in transparency, making it difficult to meet the high light transmittance requirements of high-end decorative paper and transparent coating products. Furthermore, the presence of unreacted formaldehyde in the urea-formaldehyde resin system results in a high free formaldehyde content in the product, which easily releases formaldehyde during curing and use, making it difficult to meet E0-grade environmental protection requirements.

[0003] To reduce formaldehyde emissions, existing technologies typically employ formaldehyde scavengers such as melamine and urea to adsorb or react with free formaldehyde. However, using a single formaldehyde scavenger often affects the resin's leveling properties, impregnation properties, and post-curing transparency, and can even lead to decreased resin storage stability. Furthermore, traditional urea-formaldehyde resin production often utilizes relatively high reaction temperatures of 85–90°C for polycondensation and dehydration. These high temperatures can easily cause problems such as hydroxymethyl urea oxidation, resin yellowing, and localized carbonization, further reducing product transparency and weather resistance. Therefore, how to effectively reduce free formaldehyde content while maintaining high resin transparency, and simultaneously ensuring storage stability, anti-yellowing properties, and impregnation performance, has become a pressing technical challenge in the field of transparent impregnated urea-formaldehyde resins. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an E0-grade transparent impregnated urea-formaldehyde resin and its production method, thereby resolving the problems mentioned in the background section.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides an E0 grade transparent impregnated urea-formaldehyde resin, comprising the following components by weight:

[0007] 300 parts of formaldehyde solution;

[0008] 140-185 parts of urea;

[0009] Urotropin 2.4–4.5 parts;

[0010] Borax 1.0–2.4 parts;

[0011] 8-15 parts of food-grade glucose;

[0012] Ascorbic acid 0.45–0.90 parts.

[0013] To further optimize this technical solution, the mass concentration of the formaldehyde solution is 35% to 40%.

[0014] To further optimize this technical solution, the weight ratio of hexamethylenetetramine, borax, and food-grade glucose is (1.0-1.8):(0.4-0.8):(3.0-5.0).

[0015] To further optimize this technical solution, the urea is divided into three batches, wherein:

[0016] The first batch of urea was 92-111 portions;

[0017] The second batch of urea, portions 23-29;

[0018] The third batch of urea, portions 23-69.

[0019] The production method of E0 grade transparent impregnated urea-formaldehyde resin, based on the above-mentioned E0 grade transparent impregnated urea-formaldehyde resin, includes the following production steps:

[0020] S1. Formaldehyde solution, the first batch of urea, hexamethylenetetramine, borax and food-grade glucose are added to the reaction vessel and mixed to allow formaldehyde and urea to undergo a hydroxymethylation reaction to generate a stable hydroxymethylurea intermediate.

[0021] S2. Add an acidic catalyst to the reaction system obtained in step S1 to adjust the pH value of the system to 4.6-5.3, then add the second batch of urea to adjust the molar ratio of formaldehyde to urea to 1.6-1.9, and carry out the polycondensation reaction at 70-75°C until the resin reaches the preset viscosity endpoint.

[0022] S3. Add the third batch of urea to the reaction system obtained in step S2 and continue the polycondensation reaction until the resin reaches the target degree of polycondensation and the target viscosity.

[0023] S4. Add an alkaline regulator to the reaction system obtained in step S3 to adjust the pH value of the system to 7.0-7.5, and then perform dehydration and concentration under reduced pressure to obtain resin;

[0024] S5. Add ascorbic acid to the resin obtained in step S4, stop heating and allow it to cool down naturally. When the resin temperature drops to 45°C, discharge the material to obtain E0 grade transparent impregnated urea-formaldehyde resin.

[0025] To further optimize this technical solution, in step S1, the molar ratio of formaldehyde to urea is controlled to be 2.0 to 2.4, the temperature is raised to 70 to 75°C and the reaction is maintained for 70 to 90 minutes.

[0026] To further optimize this technical solution, in step S2, the acidic catalyst is one of ammonium chloride solution, citric acid solution, oxalic acid solution, phosphoric acid solution, or formic acid solution.

[0027] To further optimize this technical solution, in step S3, the molar ratio of formaldehyde to urea is adjusted to 1.2 to 1.5, and the polycondensation reaction is carried out at 70 to 75°C.

[0028] To further optimize this technical solution, in step S4, the reduced pressure dehydration and concentration is carried out at 63-65°C and a vacuum degree of -0.08MPa. The dehydration operation is stopped when the resin solid content reaches 63%-65%.

[0029] To further optimize this technical solution, in step S4, the alkaline regulator is one of sodium hydroxide solution, potassium hydroxide solution, triethanolamine, or ammonia water.

[0030] Compared with the prior art, the present invention provides an E0 grade transparent impregnated urea-formaldehyde resin and its production method, which has the following beneficial effects:

[0031] This E0-grade transparent impregnated urea-formaldehyde resin and its production method employ a composite synergistic regulatory system constructed with food-grade glucose, borax, and hexamethylenetetramine, combined with an ascorbic acid post-treatment sealing process. Through a multi-stage urea feeding strategy and a low-temperature decompression dehydration process, the resin polycondensation reaction rate and formaldehyde capture process are synergistically controlled. Specifically, hexamethylenetetramine can slowly release formaldehyde and regulate the polycondensation reaction process; borax can stabilize the system pH and inhibit oxidation reactions initiated by impurity metal ions; food-grade glucose can compete with free formaldehyde, reducing the free formaldehyde content in the system; and ascorbic acid can terminate the participation of residual formaldehyde in subsequent side reactions and inhibit resin oxidative yellowing, thus forming a multiple formaldehyde reduction and color protection mechanism. The resin prepared using the above technical solution can control the free formaldehyde content to below 0.3%, achieve a transmittance of over 92% at 600nm wavelength, and exhibit excellent anti-yellowing properties and storage stability, effectively solving the problem of balancing transparency and environmental performance in existing technologies.

[0032] By employing a low-temperature polycondensation reaction at 70–75℃ and a reduced-pressure dehydration process at 63–65℃, the process avoids the resin oxidation, yellowing, and structural degradation caused by traditional high-temperature processes. While ensuring resin transparency, it improves the resin's impregnation and penetration capabilities, shortening the impregnation time by approximately 15%. The surface gloss of decorative paper is significantly enhanced. It is particularly suitable for applications requiring high transparency, environmental friendliness, and resistance to yellowing, such as high-grade decorative paper impregnation resin, transparent wood primer, and playing card varnishing resin. It has good industrialization promotion value and market application prospects. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the process for producing E0 grade transparent impregnated urea-formaldehyde resin proposed in this invention. Detailed Implementation

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0037] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.

[0038] E0 grade transparent impregnated urea-formaldehyde resin, by weight, includes the following components:

[0039] 300 parts of formaldehyde solution;

[0040] 140-185 parts of urea;

[0041] Urotropin 2.4–4.5 parts;

[0042] Borax 1.0–2.4 parts;

[0043] 8-15 parts of food-grade glucose;

[0044] Ascorbic acid 0.45–0.90 parts.

[0045] Among them, urotropine provides a weakly alkaline environment, slowly releasing formaldehyde to promote condensation; borax buffers the pH value, inhibiting the color deepening caused by side reactions; food-grade glucuronidation competitive reaction reduces free formaldehyde, and generates antioxidant color-protecting components at high temperatures; ascorbic acid terminates the formation of hydroxymethylurea from formaldehyde and urea, and inhibits ether bond breakage to prevent the product from exceeding the formaldehyde release standard.

[0046] The formaldehyde solution has a mass concentration of 35% to 40%, preferably 37%.

[0047] The weight ratio of hexamethylenetetramine, borax and food-grade glucose is (1.0-1.8):(0.4-0.8):(3.0-5.0).

[0048] The urea was divided into three batches, of which:

[0049] The first batch of urea was 92-111 portions;

[0050] The second batch of urea, portions 23-29;

[0051] The third batch of urea, portions 23-69.

[0052] Reference Figure 1 The production method of E0 grade transparent impregnated urea-formaldehyde resin, based on the above-mentioned E0 grade transparent impregnated urea-formaldehyde resin, includes the following production steps:

[0053] S1. Formaldehyde solution, the first batch of urea, hexamethylenetetramine (0.5-1.5% of total formaldehyde), borax (0.3-0.8% of total formaldehyde), and food-grade glucose (2-5% of total formaldehyde) are added to the reaction vessel and mixed. The molar ratio of formaldehyde to urea is controlled at 2.0-2.4. The temperature is raised to 70-75℃ and kept at this temperature for 70-90 minutes to allow formaldehyde and urea to undergo a hydroxymethylation reaction, generating a stable hydroxymethylurea intermediate.

[0054] S2. Add an acidic catalyst to the reaction system obtained in step S1 to adjust the pH value of the system to 4.6-5.3, then add the second batch of urea to adjust the molar ratio of formaldehyde to urea to 1.6-1.9. Carry out the polycondensation reaction at 70-75℃ until the resin reaches the preset viscosity endpoint (the reaction is kept at a high temperature for about 60 minutes, and it turns white in water at 40℃).

[0055] The acidic catalyst is one of the following: 20% ammonium chloride solution, 5% citric acid solution, 10% oxalic acid solution, 5% phosphoric acid solution, or 15% formic acid solution.

[0056] S3. Add the third batch of urea to the reaction system obtained in step S2. Adjust the molar ratio of formaldehyde to urea to 1.2 to 1.5. Continue the polycondensation reaction at 70 to 75°C until the resin reaches the target degree of polycondensation and the target viscosity (keep the reaction at a high temperature for about 70 minutes, and it will turn white in water at 50°C).

[0057] S4. Add an alkaline regulator to the reaction system obtained in step S3 to adjust the pH value of the system to 7.0-7.5. Then, carry out dehydration and concentration under reduced pressure at 63-65°C and a vacuum of -0.08MPa. Stop the dehydration operation when the resin solid content reaches 63%-65% to obtain the resin.

[0058] S5. Add ascorbic acid (vitamin C; 0.1-0.3% of total formaldehyde) to the resin obtained in step S4, stop heating and allow it to cool down naturally. When the resin temperature drops to 45°C, discharge the material to obtain E0 grade transparent impregnated urea-formaldehyde resin.

[0059] The alkalinity regulator is one of the following: 30% sodium hydroxide solution, 20% potassium hydroxide solution, triethanolamine, or 17% ammonia solution.

[0060] Example 1:

[0061] Raw material ratio (parts by weight): 37% formaldehyde solution: 300 parts; urea: added in three batches (first batch 111 parts, second batch 29 parts, third batch 30 parts); catalyst: hexamethylenetetramine 3 parts, borax 1 part, food-grade glucose 8 parts; additive: ascorbic acid 0.5 parts.

[0062] Production steps:

[0063] Step (1): Add formaldehyde, urea, hexamethylenetetramine, borax and food-grade glucose to the reaction vessel, with an F / U molar ratio of 2.0. Heat to 70-75℃ and keep the temperature for 90 minutes to generate a stable hydroxymethyl compound.

[0064] Step (2): Add 15% formic acid catalyst to adjust pH to 4.8-5.1, add the second batch of urea, F / U molar ratio = 1.6, and react until the viscosity reaches the standard (keep the reaction at a warm temperature for about 60 minutes, and it will turn white in water at 40℃).

[0065] Step (3): Add the third batch of urea, F / U molar ratio = 1.3, keep the reaction at 75℃ until the viscosity reaches the standard (keep the reaction at 75℃ for about 70 minutes, it will turn white in water at 50℃), add triethanolamine to adjust pH = 7.0~7.5, cool down to 63~65 degrees, turn on vacuum to dehydrate (vacuum degree -0.08MPa), when the solid content reaches 63%~65%, stop vacuuming, add ascorbic acid and let the reaction cool down to 45 degrees before discharging.

[0066] Example 2:

[0067] Raw material ratio (parts by weight): 37% formaldehyde solution: 300 parts; urea: added in three batches (first batch 105 parts, second batch 25 parts, third batch 23 parts); catalyst: hexamethylenetetramine 4.5 parts, borax 2.4 parts, food-grade glucose 15 parts; additive: ascorbic acid 0.9 parts.

[0068] Production steps:

[0069] Step (1): Add formaldehyde, urea, hexamethylenetetramine, borax and food-grade glucose to the reaction vessel, with an F / U molar ratio of 2.1. Heat to 70-75℃ and keep the temperature for 90 minutes to generate a stable hydroxymethyl compound.

[0070] Step (2): Add 5% citric acid to adjust pH to 5.1-5.3, add the second batch of urea and react until the viscosity reaches the standard (keep the reaction at a warm temperature for about 60 minutes, and it will turn white in water at 42℃), F / U molar ratio = 1.7;

[0071] Step (3): Add the third batch of urea, F / U molar ratio = 1.5, keep it at 75℃ and react until the viscosity reaches the standard (keep it at 75℃ for about 60 minutes, it will turn white in water at 52℃), add 30% sodium hydroxide solution to adjust the pH to 7.0-7.5, cool down to 63-65 degrees, turn on the vacuum to dehydrate (vacuum degree -0.08MPa), when the solid content reaches 63%-65%, stop the vacuum, add ascorbic acid and let it cool down naturally to 45 degrees and discharge.

[0072] Example 3:

[0073] Raw material ratio (parts by weight): 37% formaldehyde solution: 300 parts; urea: added in three batches (first batch 100 parts, second batch 23 parts, third batch 35 parts); catalyst: hexamethylenetetramine 3 parts, borax 1.5 parts, food-grade glucose 9 parts; additive: ascorbic acid 0.6 parts.

[0074] Production steps:

[0075] Step (1): Add formaldehyde, urea, hexamethylenetetramine, borax and food-grade glucose to the reaction vessel, with an F / U molar ratio of 2.2. Heat to 70-75℃ and keep the temperature for 70 min to generate a stable hydroxymethyl compound.

[0076] Step (2): Add 20% ammonium chloride solution to adjust pH to 4.8-4.6, add the second batch of urea and react until the viscosity reaches the standard (keep the reaction at a warm temperature for about 50 minutes, and it will turn white in water at 45℃), F / U molar ratio = 1.8;

[0077] Step (3): Add the third batch of urea, F / U molar ratio = 1.4, keep it at 75℃ and react until the viscosity reaches the standard (keep it at 75℃ for about 70 minutes, it will turn white in water at 48℃), add 20% potassium hydroxide solution to adjust the pH to 7.0-7.5, cool down to 63-65 degrees, turn on the vacuum to dehydrate (vacuum degree -0.08MPa), when the solid content reaches 63%-65%, stop the vacuum, add ascorbic acid and let it cool down naturally to 45 degrees and discharge.

[0078] Example 4:

[0079] Raw material ratio (parts by weight): 37% formaldehyde solution: 300 parts; urea: added in three batches (first batch 92 parts, second batch 24 parts, third batch 69 parts); catalyst: hexamethylenetetramine 2.4 parts, borax 1.8 parts, food-grade glucose 12 parts; additive: ascorbic acid 0.45 parts.

[0080] Production steps:

[0081] Step (1): Add formaldehyde, urea, hexamethylenetetramine, borax and food-grade glucose to the reaction vessel, with an F / U molar ratio of 2.4. Heat to 70-75℃ and keep the temperature for 70 min to generate a stable hydroxymethyl compound.

[0082] Step (2): Add 5% phosphoric acid solution to adjust pH to 4.8-4.6, add the second batch of urea and react until the viscosity reaches the standard (keep the reaction at a warm temperature for about 65 minutes, and it will turn white in water at 48℃), F / U molar ratio = 1.9;

[0083] Step (3): Add the third batch of urea, F / U molar ratio = 1.2, keep it at 75℃ and react until the viscosity reaches the standard (keep it at 75℃ for about 100 minutes, it will turn white in water at 53℃), add 17% ammonia to adjust the pH to 7.0-7.5, cool down to 63-65 degrees, turn on the vacuum to dehydrate (vacuum degree -0.08MPa), when the solid content reaches 63%-65%, stop the vacuum, add ascorbic acid and let it cool down naturally to 45 degrees before discharging.

[0084] Comparative example:

[0085] Raw material ratio (parts by weight): 300 parts of 37% formaldehyde solution; urea is added in three batches, with the first batch containing 105 parts of urea, the second batch containing 25 parts of urea, and the third batch containing 23 parts of urea; the catalyst is a 20% ammonium chloride solution; no hexamethylenetetramine, borax, food-grade glucose, or ascorbic acid are added.

[0086] Production steps:

[0087] Step (1): Add 37% formaldehyde solution and the first batch of urea into the reaction vessel, adjust the pH of the system to 7.5-8.0, raise the temperature to 85-90℃ and keep it at that temperature for 90 minutes to allow formaldehyde and urea to undergo hydroxymethylation reaction.

[0088] Step (2): Add 20% ammonium chloride solution to adjust the pH of the system to 4.6-5.0, add the second batch of urea, and continue the reaction at 85-90℃ for about 60 minutes until whitening occurs in water at 40℃.

[0089] Step (3): Add the third batch of urea and continue the polycondensation reaction at 85-90℃ for about 70 minutes until whitening occurs in water at 50℃; then add 30% sodium hydroxide solution to adjust the pH to 7.0-7.5, dehydrate and concentrate under normal temperature conditions to make the solid content reach 63%-65%, cool down to 45℃ and discharge to obtain comparative urea-formaldehyde resin.

[0090] The resins prepared in Examples 1-4 and the comparative examples were subjected to the tests shown in Table 1 below to verify the actual effect of the resins.

[0091] Table 1

[0092] Example 1 0.28 93.5 Viscosity increased by 25% ＜3.5 45 Example 2 0.32 92.4 Viscosity increased by 22% ＜4.0 55 Example 3 0.26 95.1 Viscosity increased by 26% ＜3.8 50 Example 4 0.21 89.3 Viscosity increased by 34% ＜4.5 40 Comparison Example 0.50 85.2 Viscosity increased by 42% ΔE*>5.0 60

[0093] Using the urea-formaldehyde resins obtained in Examples 1, 2, 3, 4, and the comparative example as test objects, their free formaldehyde content, transmittance at 600 nm wavelength, storage stability at 25°C for 30 days, yellowing resistance of impregnated paper, and gloss at 60° angle of impregnated paper were tested.

[0094] The resin obtained in Example 1 has a free formaldehyde content of 0.28%, a transmittance of 93.5% at 600nm wavelength, a viscosity increase rate of 25% after 30 days of storage at 25°C, a yellowing resistance difference ΔE* of less than 3.5 for the impregnated paper, and a gloss of 45 GU at a 60° angle for the impregnated paper.

[0095] The resin obtained in Example 2 has a free formaldehyde content of 0.32%, a transmittance of 92.4% at 600nm wavelength, a viscosity increase rate of 22% after 30 days of storage at 25°C, a yellowing resistance difference ΔE* of less than 4.0 for the impregnated paper, and a gloss of 55 GU at a 60° angle for the impregnated paper.

[0096] The resin obtained in Example 3 has a free formaldehyde content of 0.26%, a transmittance of 95.1% at 600nm wavelength, a viscosity increase rate of 26% after 30 days of storage at 25°C, a yellowing resistance difference ΔE* of less than 3.8 for the impregnated paper, and a gloss of 50 GU at a 60° angle for the impregnated paper.

[0097] The resin obtained in Example 4 has a free formaldehyde content of 0.21%, a transmittance of 89.3% at 600nm wavelength, a viscosity increase rate of 34% after 30 days of storage at 25°C, a yellowing resistance difference ΔE* of less than 4.5 for the impregnated paper, and a gloss of 40 GU at a 60° angle for the impregnated paper.

[0098] The resin obtained in the comparative example had a free formaldehyde content of 0.50%, a transmittance of 85.2% at 600nm wavelength, a viscosity increase rate of 42% after 30 days of storage at 25℃, a yellowing resistance difference ΔE* greater than 5.0 for the impregnated paper, and a gloss of 60GU at a 60° angle for the impregnated paper.

[0099] The test results above show that Examples 1-4 exhibit significant improvements over the comparative examples in terms of free formaldehyde content, transparency, storage stability, and resistance to yellowing. Specifically, Examples 1, 2, and 3 all achieved a transmittance of over 92% at 600nm wavelength, with overall lower free formaldehyde content than the comparative example. This indicates that the composite system formed by hexamethylenetetramine, borax, food-grade glucose, and ascorbic acid effectively reduces free formaldehyde content and improves resin transparency. Example 3 achieved the highest transmittance of 95.1%, indicating that its formulation ratio is more conducive to obtaining highly transparent resin. Example 4 had the lowest free formaldehyde content at 0.21%, suggesting that a higher subsequent urea addition is beneficial for further capturing residual formaldehyde. However, its transmittance and storage stability decreased relatively, indicating that a balance needs to be struck between low aldehyde content and transparent stability in the urea addition ratio.

[0100] The comparative example did not use the synergistic system of glucose, borax, hexamethylenetetramine, and ascorbic acid, and adopted the traditional high-temperature reaction method. The resulting resin had a free formaldehyde content of 0.50%, a transmittance of only 85.2% at 600nm wavelength, a viscosity increase of 42% after 30 days of storage, and a yellowing resistance difference ΔE* greater than 5.0 for the impregnated paper. This indicates that traditional urea-formaldehyde resin has problems such as high free formaldehyde content, insufficient transparency, poor storage stability, and easy yellowing after curing. In contrast, the embodiments of this invention, through the synergistic control of composite catalysis, buffer color protection, competitive formaldehyde capture, and low-temperature dehydration, can obtain an E0 grade transparent impregnated urea-formaldehyde resin with low free formaldehyde content, high transparency, and good yellowing resistance.

[0101] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. E0 grade transparent impregnated urea-formaldehyde resin, characterized in that, By weight, it includes the following components: 300 parts of formaldehyde solution; 140-185 parts of urea; Urotropin 2.4–4.5 parts; Borax 1.0–2.4 parts; 8-15 parts of food-grade glucose; Ascorbic acid 0.45–0.90 parts.

2. The E0 grade transparent impregnated urea-formaldehyde resin according to claim 1, characterized in that, The formaldehyde solution has a mass concentration of 35% to 40%.

3. The E0 grade transparent impregnated urea-formaldehyde resin according to claim 1, characterized in that, The weight ratio of hexamethylenetetramine, borax and food-grade glucose is (1.0-1.8):(0.4-0.8):(3.0-5.0).

4. The E0 grade transparent impregnated urea-formaldehyde resin according to claim 1, characterized in that, The urea was divided into three batches, of which: The first batch of urea was 92-111 portions; The second batch of urea, portions 23-29; The third batch of urea, portions 23-69.

5. A method for producing E0 grade transparent impregnated urea-formaldehyde resin, based on the E0 grade transparent impregnated urea-formaldehyde resin according to any one of claims 1-4, characterized in that, The production process includes the following steps: S1. Formaldehyde solution, the first batch of urea, hexamethylenetetramine, borax and food-grade glucose are added to the reaction vessel and mixed to allow formaldehyde and urea to undergo a hydroxymethylation reaction to generate a stable hydroxymethylurea intermediate. S2. Add an acidic catalyst to the reaction system obtained in step S1 to adjust the pH value of the system to 4.6-5.3, then add the second batch of urea to adjust the molar ratio of formaldehyde to urea to 1.6-1.9, and carry out the polycondensation reaction at 70-75°C until the resin reaches the preset viscosity endpoint. S3. Add the third batch of urea to the reaction system obtained in step S2 and continue the polycondensation reaction until the resin reaches the target degree of polycondensation and the target viscosity. S4. Add an alkaline regulator to the reaction system obtained in step S3 to adjust the pH value of the system to 7.0-7.5, and then perform dehydration and concentration under reduced pressure to obtain resin; S5. Add ascorbic acid to the resin obtained in step S4, stop heating and allow it to cool down naturally. When the resin temperature drops to 45°C, discharge the material to obtain E0 grade transparent impregnated urea-formaldehyde resin.

6. The method for producing E0 grade transparent impregnated urea-formaldehyde resin according to claim 5, characterized in that, In step S1, the molar ratio of formaldehyde to urea is controlled to be 2.0 to 2.4, the temperature is raised to 70 to 75°C and the reaction is maintained at that temperature for 70 to 90 minutes.

7. The method for producing E0 grade transparent impregnated urea-formaldehyde resin according to claim 5, characterized in that, In step S2, the acidic catalyst is one of ammonium chloride solution, citric acid solution, oxalic acid solution, phosphoric acid solution, or formic acid solution.

8. The method for producing E0 grade transparent impregnated urea-formaldehyde resin according to claim 5, characterized in that, In step S3, the molar ratio of formaldehyde to urea is adjusted to 1.2 to 1.5, and a polycondensation reaction is carried out at 70 to 75°C.

9. The method for producing E0 grade transparent impregnated urea-formaldehyde resin according to claim 5, characterized in that, In step S4, the dehydration and concentration under reduced pressure is carried out at 63-65°C and a vacuum of -0.08 MPa. The dehydration operation is stopped when the resin solid content reaches 63%-65%.

10. The method for producing E0 grade transparent impregnated urea-formaldehyde resin according to claim 5, characterized in that, In step S4, the alkaline regulator is one of sodium hydroxide solution, potassium hydroxide solution, triethanolamine, or ammonia.

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