KR20030038143A - Manufacturing method of E0 grade Melamine-Urea-Formaldehyde Resin(MUF) and adhesive for medium density fiber board by use of MDF Resin - Google Patents

Abstract

PURPOSE: A method for preparing a melamine-urea-formaldehyde resin and an adhesive for medium density fiberboard(MDF) using the resin are provided, to reduce the amount of the unreacted formaldehyde contained in the resin and the discharging amount of formaldehyde of MDF remarkably, and to improve the physical properties of MDF. CONSTITUTION: The method comprises the steps of polycondensing 0-10 wt% of melamine and formaldehyde(wherein the molar ratio of formaldehyde to an amino group is 1.3-2.2) at a pH 7.3-9.0 at a temperature of 80-95 deg.C; adding urea to the obtained one in the molar ratio of formaldehyde to an amino acid of 0.75-0.9 and polycondensing the mixture at a pH of 6.8-7.8 and at a temperature of 80-95 deg.C; adding an acidic catalyst to the product to make the pH be 4.0-6.8; adding an alkali catalyst to the product to neutralize the solution by making the pH be 6.0-8.0; adding urea to the obtained product in the molar ratio of formaldehyde to an amino acid of 0.53-0.62 and polycondensing the mixture; and adding urea to the obtained product in the molar ratio of formaldehyde to an amino acid of 0.38-0.46 and polycondensing the mixture, and aging it for 1-6 hours.

Description

Manufacturing method of E0 grade Melamine-Urea-Formaldehyde Resin (MUF) and adhesive for medium density fiber board by use of MDF Resin}

The present invention relates to a method for preparing melamine-urea-formaldehyde resin, and an adhesive for medium-density fiberboard using the same, and more particularly, to formaldehyde / urea in each polymerization step when condensation of formaldehyde and urea by a multi-step polymerization step. By limiting the molar ratio of (amino group) to a specific range and producing a melamine-urea-formaldehyde resin through a aging process, the amount of unreacted formaldehyde in the resin is drastically reduced, and during the manufacture of medium density fiberboard (MDF) The present invention relates to an adhesive for medium-density fiberboard which significantly reduces the formaldehyde emission of the MDF prepared by using an appropriate amount of the resin, EMDI (Emulsifiable methylen diphenyl diisocyanate) and a release agent as an adhesive, and also improves the physical properties of the MDF.

Medium density fiberboard is a wood plate product with a density of 0.4 ~ 0.8 g / cm ³ made by combining and molding the wood fiber obtained by dissolving at high temperature with wood as the main raw material with a synthetic resin adhesive. Production from mm to 30 mm thick is possible. Uniform fiber distribution and dense texture over the entire thickness allows complex machining operations to be performed without rupture of the face or sides. MDF is therefore used for table tops, doors, and drawer fronts with side moldings or surface finishes. It is also smooth and firm on the surface and is ideal for overlaying or painting decorative films or veneers. Its excellent stability, machinability and high strength make it an alternative to ordinary wood for drawers, cabinet rails, mirror frames and moldings.

As the adhesive for use in manufacturing MDF, urea-formaldehyde resin or melamine-urea-formaldehyde resin is widely used. However, formaldehyde is generated when the resin is cured in the thermocompression process when producing the MDF with the adhesive, and the formaldehyde gas is harmful to the environment and the human body, and in particular, severely irritates the eyes and mucous membranes of the human body.

Thus, much effort has been made in the wood panel industry to date to reduce such formaldehyde emissions, and US Pat. No. 4,997,905 is a known technique for reducing such formaldehyde emissions. The U.S. Patent No. 4,997,905 describes the production of melamine-urea-formaldehyde resin by producing melamine in an amount of about 2 to 6% to produce a low formaldehyde board, but the amount of urea post-condensation after condensation reaction is excessive. There is a problem that the physical properties are remarkably inferior and in the case of a thin plate causes blistering and productivity decrease, so it is difficult to use economically in the manufacturing process.

In addition, E1 grade (formaldehyde emission amount: less than 1.5 mg / l) MDF was produced using the above adhesive, but there is still a problem that formaldehyde occurs, using the adhesive E0 (formaldehyde emission amount: 0.5 mg / Less than l) When used in the production of MDF has been a problem that the board properties are degraded and process abnormalities occur.

Thus, the present inventors condensed formaldehyde and urea in a multistage polymerization process in order to solve the above problems, by limiting the molar ratio of formaldehyde / (amino group) to a specific range in each polymerization process and through the aging process melamine Significantly lowered the amount of unreacted formaldehyde in the resin by preparing urea-formaldehyde resin, and an appropriate amount of the resin, emulsifiable methylen diphenyl diisocyanate (EMDI), and a release agent as an adhesive when preparing a medium density fiberboard (MDF). By using the mixture, the present invention has been completed.

Accordingly, an object of the present invention is to provide a method for preparing melamine-urea-formaldehyde resin which significantly reduces the formaldehyde emission of MDF and excellently improves the physical properties of MDF, and an adhesive for medium density fiberboard using the same.

The present invention provides a method for producing a melamine-urea-formaldehyde resin by polycondensing melamine, urea and formaldehyde monomers,

1) a step in which a molar ratio of formaldehyde / (amino group) of 1.3 to 2.2 and melamine 0 to 10 wt% are added at pH 7.3 to 9.0, followed by condensation polymerization at 80 to 95 ° C;

2) condensation polymerization of the reaction product at a molar ratio of formaldehyde / (amino group) at 0.75 to 0.9 with urea at a pH of 6.6 to 7.8 and a polymerization temperature of 80 to 95 ° C;

3) adding an acid catalyst to the reactants to acid reaction at pH 4.0 to 6.8;

4) adding an alkali catalyst to the reaction to neutralize to pH 6.0 ~ 8.0;

5) condensation-polymerizing by adding urea at a molar ratio of formaldehyde / (amino group) of 0.53 to 0.62 to the reactant;

6) a step of condensation polymerization of urea at a molar ratio of 0.38 to 0.46 of formaldehyde / (amino group) to the reaction product followed by aging for 1 to 6 hours;

It characterized by a method for producing a melamine-urea-formaldehyde resin consisting of.

The present invention is further characterized by an adhesive for medium density fiberboard comprising 70 to 99% by weight of melamine-urea-formaldehyde resin, 1 to 20% by weight of EMDI and 0 to 10% by weight of release agent.

Referring to the present invention in more detail as follows.

In order to minimize the amount of unreacted formaldehyde in the melamine-urea-formaldehyde resin used as an adhesive in the manufacture of MDF, the present invention reduces the molar ratio of F / (NH ₂ ) from 1: 0.38 to 0.46 to produce an E0 grade MDF resin. When using this, a medium density fiberboard (MDF) is produced by using an appropriate amount of the resin, EMDI (Emulsifiable methylen diphenyl diisocyanate) and a release agent mixed with an appropriate amount of adhesive to significantly reduce the formaldehyde emission of the prepared MDF, MDF It also relates to an adhesive for medium density fiber boards with excellent physical properties.

The preparation method of the E0 melamine-urea-formaldehyde resin according to the present invention will be described in more detail for each process as follows.

First, the first step is a step of adding a formaldehyde / (amino group) molar ratio of 1.3 to 2.2 and melamine 0 to 10% by weight at pH 7.3 to 9.0 and then polycondensation at 80 to 95 ℃, for 50 to 70 minutes The reaction is carried out using NaOH, KOH, Na ₂ CO₃ and the like as the pH adjuster. When the molar ratio of formaldehyde / (amino group) is less than 1.3, monomethylol urea (monomethylol urea, hereinafter referred to as MMU) which is less reactive in the methylol reaction of melamine, urea and formaldehyde is mainly produced, resulting in a molar ratio of 1.3 or higher. Due to the small amount of dimethylol urea (hereinafter referred to as DMU), the productivity of the product decreases due to the delay in curing time, which is a characteristic of low formaldehyde resin, due to the low reactivity of the resin. When the concentration of the amino group capable of reacting with the formaldehyde group is small, there is a problem that formaldehyde participating in the reaction does not react sufficiently. In addition, if the pH is less than 7.3, the pH value is reduced by the hydrogen ions generated during the reaction, the methylol reaction and the methylene reaction proceeds at the same time, it is difficult to control the reaction, if the pH exceeds 9.0 condensation polymerization reaction There is a problem that the resin is difficult to produce properly.

The second step is the step of condensation polymerization at pH 6.8 to 7.8 and polymerization temperature of 80 to 95 ° C by adding urea with a molar ratio of 0.75-0.9 to formaldehyde / (amino group) to the reactant, and reducing the residual amount of formaldehyde in the resin. Additional components of urea are added to continue the reaction following the polycondensation reaction of the first process. If the molar ratio of formaldehyde / (amino group) is less than 0.75, low molecular polymers are formed in the polycondensation reaction of the second step, so that the physical properties of the board are significantly decreased. As the remaining amount increases, formaldehyde emission from board increases, making it difficult to produce E0 products. In addition, when the pH is less than 6.8, there is a problem in that the pH value is reduced by the hydrogen ions generated during the reaction, making it difficult to control the reaction process, and when the pH exceeds 7.8, the polycondensation reaction becomes difficult, so that the resin is not properly produced. There is.

The third step is to add acidic catalyst to the reactant to acid reaction at pH 4.0 to 6.8, and to improve adhesion performance by condensation of MMU and DMU produced up to the second step, formic acid and phosphoric acid as acidic catalyst. , Glacial acetic acid, and the like.

The fourth step is to add an alkali catalyst to the reactant to neutralize the pH to 6.0 to 8.0. The fourth step is to stop the continuous reaction of the polymer produced in the condensation reaction and to maintain an appropriate molecular weight. The alkali catalyst is NaOH, KOH, Na ₂ CO₃ or the like is used.

The fifth step is a step of condensation polymerization of urea by adding formaldehyde / (amino group) at a molar ratio of 0.53 to 0.62 in the reaction product, and further adding urea to reduce the residual amount of formaldehyde in the resin and continuing the condensation polymerization reaction. Perform. If the molar ratio of formaldehyde / (amino group) is less than 0.53, urea is present in excess, which causes a problem that the remaining amount of urea is not reacted with formaldehyde remaining after acid reaction and the curability is inferior. Exceeding the excessive amount of unreacted formaldehyde, there is a problem that tends to increase the amount of formaldehyde emission in the manufacture of the board. In order to shorten the hardening time of resin in the said process, a hardening accelerator may be added.

The sixth step is a step of condensation polymerization of urea at a molar ratio of 0.38 to 0.46 of formaldehyde / (amino group) to the reactant, followed by aging for 1 to 6 hours, and additionally urea is added to reduce the amount of formaldehyde in the resin. Continue to carry out the polycondensation reaction. If the molar ratio of formaldehyde / (amino group) is less than 0.38, there is a problem in that the curability of the resin is reduced due to the increase of residual urea and the properties of the board are lowered and blistering occurs. I'm having trouble producing a class board. In addition, after the reaction is completed through the aging process, the residual amount of formaldehyde in the final resin can be lowered to less than 0.05% to prepare an E0 melamine-urea-formaldehyde resin. In the above process, a stabilizer may be added to increase the storage stability of the resin and to reduce the amount of formaldehyde released.

The monomer used in the melamine-urea-formaldehyde resin manufacturing process according to the present invention described above is made up of melamine 0-10% by weight, urea 38-46% by weight, formaldehyde 52-56% by weight at 37% concentration, and these Each monomer component is appropriately divided into the entire condensation polymerization step.

On the other hand, the melamine-urea-formaldehyde resin according to the present invention has a problem that the physical properties and durability of the board when used as an adhesive in the MDF as the amount of formaldehyde remaining in the resin is less than 0.05% compared to the general E2, E1 board have. Therefore, when the melamine-urea-formaldehyde resin according to the present invention is used as an adhesive in the manufacture of medium density fiberboard, an appropriate amount of EMDI and a releasing agent is added and used to solve the problem of the physical properties of the board and the process problems.

Accordingly, the present invention comprises an adhesive for medium density fiberboard comprising 70 to 99% by weight of melamine-urea-formaldehyde resin, 1 to 20% by weight of EMDI, and 0 to 10% by weight of release agent.

EMDI, which acts as a crosslinking agent and a hardening agent in the adhesive for medium density fiberboard, lowers the MDF thickness and improves the water resistance and the physical properties of the board, is preferably contained in an amount of 1 to 20% by weight. There is a problem that the physical properties of the deterioration, and if it exceeds 20% by weight, sticking occurs in the board spots and process piping due to the coating efficiency decreases, there is a serious problem in productivity.

When the EMDI is added to the adhesive for the medium density fiberboard, the physical properties of the board are increased, but sticking occurs between the steel belt and the board. It is preferable to contain-10 weight%, and it is good to use a mold release agent content on the basis of 50% in EMDI injection amount. If the content of the releasing agent exceeds 10% by weight, there is a problem in that the economy is inferior and the thickness expansion coefficient of the board is worsened. The release agent includes an internal mold release agent and an external mold release agent, and an internal mold release agent may use a mixture of zinc stearate (Zn-Stearate) and paraffin wax in an amount of 0 to 10% by weight, and an external mold release agent may be polyethylene nonylphenol. The solution can be used by the spray method on the surface of the steel belt at a speed of 0.5 to 1.0 kg / min.

As such, the melamine-urea-formaldehyde resin according to the method of the present invention lowers the amount of formaldehyde emission in the resin to E0 grade, and shortens the curing time during the thermopressing process by adding an appropriate amount of EMDI and a release agent when preparing MDF using the resin. In addition, by securing the storage stability to improve the physical properties of the board (sticking) in the manufacturing process, problems such as blisters were also solved.

Although this invention is demonstrated in detail based on an Example, this invention is not limited to an Example.

Example 1 Preparation of Melamine-Urea-Formaldehyde Resin

6000 parts by weight of 37% formalin, 250 parts by weight of melamine, 1000 parts by weight of urea and 4.5 parts by weight of caustic soda were added to the reactor, and the temperature was raised to 80 ± 5 ° C while stirring. When enough reaction, 1400 parts by weight of the secondary urea was added and reacted while maintaining the reaction temperature of 85 ± 5 ℃ at pH 7.2 ± 0.3. After the methylol reaction in alkali was sufficient, formic acid was added to adjust the pH to 5.5 ± 0.5, followed by acid reaction, and after confirming the cloudy point, a third element was added. The third step was adjusted to pH 7.0 ± 0.5 by adding 750 parts by weight of urea, 300 parts by weight of curing accelerator and 7.5 parts by weight of caustic soda to neutralize. When the reaction was sufficient, 1100 parts by weight of the fourth urea was added to mature for about 2 ± 0.5 hours. Finally, 700 parts by weight of urea and 33 parts by weight of stabilizer were added to cool the solution. The completed resin was transferred to a storage tank and aged for 2 ± 1 days.

Example 2. Preparation of Melamine-Urea-Formaldehyde Resin

37% formalin 6000 parts by weight, melamine 500 parts by weight, urea 1200 parts by weight, caustic soda 6 parts by weight was added to the reactor and heated to 85 ± 5 ℃ while stirring. 1200 parts by weight of the secondary urea was adjusted to pH 7.5 ± 0.5 to react with maintaining the reaction temperature of 85 ± 5 ℃. When sufficient reaction is performed, formic acid is added to adjust pH to 5.0 ± 0.5. When acid reaction is sufficient while the reaction is sufficient, neutralize with caustic soda, add 1200 parts by weight of tertiary urea and 100 parts by weight of curing accelerator to add 20 ± 10 After reacting for 1 minute, 1100 parts by weight of the fourth urea was reacted, cooled, and aged for about 1.5 ± 0.5 hours, 33 parts by weight of the stabilizer was added to terminate the reaction. The completed resin was transferred to a storage tank and aged for 2 ± 1 days.

Example 3 Preparation of Melamine-Urea-Formaldehyde Resin

37% formalin 6000 parts by weight, melamine 650 parts by weight, 1200 parts by weight of urea, 100 parts by weight of starch, 7 parts by weight of caustic soda was added to the reactor and heated to 85 ± 5 ℃ while stirring. 1100 parts by weight of the secondary urea was adjusted to pH 7.5 ± 0.5 to maintain the reaction temperature of 85 ± 5 ° C. When sufficient reaction is performed, formic acid is added to adjust pH to 5.5 ± 0.5. When the reaction is sufficient, neutralize with caustic soda and add 1300 parts by weight of tertiary urea and 150 parts by weight of curing accelerator for 20 ± 10 minutes. After the reaction, the reaction was carried out by adding 1100 parts by weight of the quaternary urea, followed by cooling. After aging for about 2 ± 1 hour, 60 parts by weight of the stabilizer was added to terminate the reaction. The completed resin was transferred to a storage tank and aged for 2 ± 1 days.

Example 4.

MDF was prepared using 96% by weight of the melamine-urea-formaldehyde resin obtained in Example 1, 4% by weight of EMDI, 0% by weight of an internal release agent, and 0% by weight of an external release agent as an adhesive. MDF production conditions were hot pressed at 190 ℃ for 30 seconds at a pressure of 30 kg _f / cm ² , the physical properties of the MDF thus prepared are shown in Table 1 below.

Example 5.

MDF was prepared by using 70% by weight of the melamine-urea-formaldehyde resin obtained in Example 2, 20% by weight of EMDI, 9% by weight of an internal release agent, and 1% by weight of an external release agent as an adhesive. MDF production conditions were hot pressed at 190 ℃ for 30 seconds at a pressure of 30 kg _f / cm ² , the physical properties of the MDF thus prepared are shown in Table 1 below.

Example 6.

MDF was prepared using 96% by weight of the melamine-urea-formaldehyde resin obtained in Example 3, 4% by weight of EMDI, 0% by weight of an internal release agent, and 0% by weight of an external release agent as an adhesive. MDF production conditions were hot pressed at 190 ℃ for 30 seconds at a pressure of 30 kg _f / cm ² , the physical properties of the MDF thus prepared are shown in Table 1 below.

Comparative Example 1.

MDF was prepared by a conventional method using a conventional melamine-urea-formaldehyde resin for MDF, and the physical properties of the prepared MDF are shown in Table 1 below.

As shown in Table 1, the MDF of Examples 4 to 6 according to the present invention can produce an E0 MDF board having a formaldehyde emission amount of less than 0.5 mg / l, and at the same time lowering the thickness expansion rate of the prepared MDF to improve water resistance and It was confirmed that the physical properties of the board was improved. On the other hand, MDF prepared using the conventional melamine-urea-formaldehyde resin as an adhesive was confirmed that the release of formaldehyde as high as 2.2 mg / l.

As described above, since the melamine-urea-formaldehyde resin according to the method of the present invention significantly lowers the amount of residual formaldehyde in the resin, an appropriate amount of the resin, EMDI (Emulsifiable methylen diphenyl diisocyanate) and a release agent is mixed and used. When used as an adhesive for manufacturing a medium density fiberboard (MDF), the amount of formaldehyde emission of the prepared MDF is significantly reduced, and the physical properties of the MDF are also improved, so that it can be usefully used as an adhesive for manufacturing MDF.

Claims (2)

In the method of producing a melamine-urea-formaldehyde resin by condensation of melamine, urea and formaldehyde monomer, 1) a step in which a molar ratio of formaldehyde / (amino group) of 1.3 to 2.2 and melamine 0 to 10 wt% are added at pH 7.3 to 9.0, followed by condensation polymerization at 80 to 95 ° C; 2) condensation polymerization of the reaction product at a pH of 6.8 to 7.8 and a polymerization temperature of 80 to 95 ° C. by adding urea with a molar ratio of formaldehyde / (amino group) of 0.75 to 0.9; 3) adding an acid catalyst to the reactants to acid reaction at pH 4.0 to 6.8; 4) adding an alkali catalyst to the reaction to neutralize to pH 6.0 ~ 8.0; 5) condensation-polymerizing by adding urea at a molar ratio of formaldehyde / (amino group) of 0.53 to 0.62 to the reactant; 6) a step of condensation polymerization of urea at a molar ratio of 0.38 to 0.46 of formaldehyde / (amino group) to the reaction product followed by aging for 1 to 6 hours; Method for producing a melamine-urea-formaldehyde resin, characterized in that consisting of. 70-99% by weight of the melamine-urea-formaldehyde resin according to the method of claim 1, 1 to 20% by weight of emulsifiable methylen diphenyl diisocyanate (EMDI) and 0 to 10% by weight of a release agent for medium-density fiberboard glue.