阅读说明：本技术 一种脲醛树脂胶粘剂、制备方法及其应用 (Urea-formaldehyde resin adhesive, preparation method and application thereof ) 是由 刘家耀 于 2020-08-04 设计创作，主要内容包括：本发明涉及胶粘剂技术领域,更具体地,本发明涉及一种脲醛树脂胶粘剂、制备方法及其应用,按重量份计,所述脲醛树脂胶粘剂的制备原料包括88～97份甲醛的水溶液、65～75份尿素、0.2～1份聚乙烯醇、8～15份三聚氰胺、1～7份氨水；所述甲醛的水溶液和氨水的重量比为(15～20)：1。本发明提供的脲醛树脂胶粘剂甲醛释放量小,胶合强度好,使用该胶粘剂制备的胶合板,达到环保E0标准,适用于制备环保室内胶合板。(The invention relates to the technical field of adhesives, in particular to a urea-formaldehyde resin adhesive, a preparation method and application thereof, wherein the urea-formaldehyde resin adhesive is prepared from 88-97 parts by weight of aqueous solution of formaldehyde, 65-75 parts by weight of urea, 0.2-1 part by weight of polyvinyl alcohol, 8-15 parts by weight of melamine and 1-7 parts by weight of ammonia water; the weight ratio of the aqueous solution of formaldehyde to the ammonia water is (15-20): 1. the urea-formaldehyde resin adhesive provided by the invention has small formaldehyde release amount and good bonding strength, and the plywood prepared by using the adhesive reaches the environmental protection E0 standard, so that the adhesive is suitable for preparing environmental protection indoor plywood.)

1. The urea-formaldehyde resin adhesive is characterized by comprising, by weight, 88-97 parts of aqueous solution of formaldehyde, 65-75 parts of urea, 0.2-1 part of polyvinyl alcohol, 8-15 parts of melamine and 1-7 parts of ammonia water; the weight ratio of the aqueous solution of formaldehyde to the ammonia water is (15-20): 1; the content of free formaldehyde in the urea-formaldehyde resin adhesive is less than 0.1 wt% according to GB/T14074-2017, and the curing time is 150-250 s.

2. The urea-formaldehyde resin adhesive as claimed in claim 1, wherein the weight ratio of the aqueous solution of formaldehyde to urea is (1.3-1.5): 1.

3. the urea-formaldehyde resin adhesive as claimed in claim 1, wherein the weight ratio of the aqueous solution of formaldehyde to melamine is (8-10): 1.

4. the urea-formaldehyde resin adhesive as claimed in claim 1, wherein the weight ratio of the aqueous solution of formaldehyde to the polyvinyl alcohol is (152-160): 1.

5. the urea-formaldehyde resin adhesive according to any one of claims 1 to 4, wherein the kinetic viscosity of the polyvinyl alcohol at 25 ℃ is 45 to 55mpa.s, and the alcoholysis degree is 99 to 100 mol%.

6. The preparation method of the urea-formaldehyde resin adhesive according to any one of claims 1 to 5, characterized by comprising the following steps:

putting an aqueous solution of formaldehyde, urea accounting for 5-90% of the total weight of the urea, polyvinyl alcohol, melamine accounting for 10-50% of the total weight of the melamine and ammonia water into a reaction kettle, adjusting the pH to 7-8.5, heating to 85-100 ℃, and reacting;

(II) adjusting the pH value to 3.5-4.5;

thirdly, reacting at 85-100 ℃, adjusting the pH to 6-8, and adding the rest urea and melamine in batches at 75-90 ℃ for reaction;

and (IV) adjusting the pH value to 7.5-8.5, cooling and discharging to obtain the catalyst.

7. The preparation method of the urea-formaldehyde resin adhesive according to claim 6, wherein in the step (one), the temperature is raised to 85-100 ℃, and the reaction is carried out until the pH is greater than 6.5.

8. The preparation method of the urea-formaldehyde resin adhesive according to claim 6, wherein in the step (three), the reaction is carried out at 85-100 ℃ until the viscosity: coating the mixture in 4 cups at 35 ℃ for 10-25 s.

9. The preparation method of the urea resin according to claim 8, wherein in the step (three), the reaction is carried out at 85-100 ℃ until the viscosity: coating the mixture at 35 ℃ for 16-17 s in 4 cups.

10. Plywood prepared by using the urea-formaldehyde resin adhesive as defined in any one of claims 1 to 5.

Technical Field

The invention relates to the technical field of adhesives, in particular to a urea-formaldehyde resin adhesive, a preparation method and application thereof.

Background

Urea-formaldehyde resin is the most widely used adhesive in the wood industry, urea-formaldehyde resin produced from urea and formaldehyde by a conventional method has high free formaldehyde content, and a large amount of hydroxymethyl and ether bonds are inevitably present in resin molecules, which is also the reason for poor formaldehyde release and water resistance in the curing process of artificial boards.

Urea-formaldehyde resins are actually free formaldehyde, methylol urea, urea-formaldehyde polymers and methylolated urea-formaldehyde mixtures, and the formaldehyde emissions from man-made boards made with urea-formaldehyde resins are mainly from: free formaldehyde of the urea-formaldehyde resin, formaldehyde released by the decomposition of hydroxymethyl, methylene ether and hemiformal of the urea-formaldehyde resin during hot-pressing curing. Formaldehyde is a recognized potential carcinogen in the world, seriously harms human health, and causes immune dysfunction, liver injury, lung injury and nervous system influence. The volatilization speed of the free formaldehyde in the artificial board for decoration is slower, so that the content of the formaldehyde in the indoor air exceeds the standard for a long time. In order to solve the problem of high free formaldehyde content, the method of reducing the molar ratio of formaldehyde to urea is mainly adopted to produce the urea-formaldehyde resin with low free formaldehyde content in recent years, but the amount of the free formaldehyde of the produced urea-formaldehyde resin still needs to be reduced, and the bonding strength, the storage stability and the water solubility are poor.

Disclosure of Invention

Aiming at some problems in the prior art, the invention provides a urea-formaldehyde resin adhesive in a first aspect, which comprises the following raw materials, by weight, 88-97 parts of aqueous solution of formaldehyde, 65-75 parts of urea, 0.2-1 part of polyvinyl alcohol, 8-15 parts of melamine and 1-7 parts of ammonia water; the weight ratio of the aqueous solution of formaldehyde to the ammonia water is (15-20): 1; the content of free formaldehyde in the urea-formaldehyde resin adhesive is less than 0.1 wt% according to GB/T14074-2017, and the curing time is 150-250 s.

According to a preferable technical scheme of the invention, the weight ratio of the formaldehyde aqueous solution to the urea is (1.3-1.5): 1.

as a preferable technical scheme of the invention, the weight ratio of the aqueous solution of formaldehyde to the melamine is (8-10): 1.

as a preferable technical scheme of the invention, the weight ratio of the formaldehyde aqueous solution to the polyvinyl alcohol is (152-160): 1.

according to a preferable technical scheme of the invention, the kinetic viscosity of the polyvinyl alcohol at 25 ℃ is 45-55 mpa.s, and the alcoholysis degree is 99-100 mol%.

The second aspect of the invention provides a preparation method of the urea-formaldehyde resin adhesive, which comprises the following steps:

putting an aqueous solution of formaldehyde, urea accounting for 5-90% of the total weight of the urea, polyvinyl alcohol, melamine accounting for 10-50% of the total weight of the melamine and ammonia water into a reaction kettle, adjusting the pH to 7-8.5, heating to 85-100 ℃, and reacting;

(II) adjusting the pH value to 3.5-4.5;

thirdly, reacting at 85-100 ℃, adjusting the pH to 6-8, and adding the rest urea and melamine in batches at 75-90 ℃ for reaction;

and (IV) adjusting the pH value to 7.5-8.5, cooling and discharging to obtain the catalyst.

As a preferable technical scheme of the invention, in the step (I), the temperature is raised to 85-100 ℃, and the reaction is carried out until the pH value is more than 6.5.

As a preferable technical scheme of the invention, in the step (three), the reaction is carried out at 85-100 ℃ until the viscosity: coating the mixture in 4 cups at 35 ℃ for 10-25 s.

As a preferable technical scheme of the invention, in the step (three), the reaction is carried out at 85-100 ℃ until the viscosity: coating the mixture at 35 ℃ for 16-17 s in 4 cups.

The invention also provides a plywood prepared by using the urea-formaldehyde resin adhesive.

Compared with the prior art, the invention has the following beneficial effects:

the urea-formaldehyde resin adhesive provided by the invention has small formaldehyde release amount and good bonding strength, and the plywood prepared by using the adhesive reaches the environmental protection E0 standard, so that the adhesive is suitable for preparing environmental protection indoor plywood.

Detailed Description

The present invention is illustrated by the following specific embodiments, but is not limited to the specific examples given below.

In the physical and chemical performance test method for the artificial board and the decorative artificial board with the EO standard GB/T17657-2013, the formaldehyde release amount is measured, namely the dryer is less than 0.5mg/L and the formaldehyde release amount is measured, namely the formaldehyde release amount is measured, and the measured³The climate box is less than 0.05mg/m³The bonding strength meets the requirements of II-type plywood in GB/T9846-2015.

The invention provides a urea-formaldehyde resin adhesive, which is prepared from 88-97 parts of aqueous solution of formaldehyde, 65-75 parts of urea, 0.2-1 part of polyvinyl alcohol, 8-15 parts of melamine and 1-7 parts of ammonia water; the content of free formaldehyde in the urea-formaldehyde resin adhesive is measured to be less than 0.1 wt% according to GB/T14074-2017, and the curing time is 150-250 s.

In one embodiment, the preparation raw materials of the urea-formaldehyde resin comprise, by weight, 93.74 parts of an aqueous solution of formaldehyde, 65-75 parts of urea, 0.2-1 part of polyvinyl alcohol, 8-15 parts of melamine and 1-7 parts of ammonia water.

Aqueous solution of formaldehyde

In one embodiment, the aqueous solution of formaldehyde is a 36 to 38 wt% aqueous solution of formaldehyde.

Preferably, the aqueous formaldehyde solution is a 37 wt% aqueous formaldehyde solution.

Urea

Urea, also known as carbonamide (carbomide), is an organic compound consisting of carbon, nitrogen, oxygen and hydrogen, is a white crystal, one of the simplest organic compounds, is the main nitrogen-containing end product of the metabolic decomposition of proteins in mammals and some fishes, and is also the nitrogen fertilizer with the highest nitrogen content at present.

In one embodiment, the weight ratio of the aqueous formaldehyde solution to the urea is (1.3-1.5): 1.

preferably, the weight ratio of the aqueous formaldehyde solution to the urea is 1.37: 1.

the applicant unexpectedly finds that the bonding strength can be increased due to the excessively high content of formaldehyde, but the release amount of formaldehyde is relatively increased, the content of urea is increased, the bonding strength is reduced, the release amount of formaldehyde is also reduced, and the adhesive is safe and environment-friendly.

Polyvinyl alcohol

In one embodiment, the polyvinyl alcohol has a kinematic viscosity at 25 ℃ of 45 to 55mpa.s and an alcoholysis degree of 99 to 100 mol%.

Preferably, the polyvinyl alcohol has a grade of 20 to 99.

In one embodiment, the weight ratio of the aqueous formaldehyde solution to the polyvinyl alcohol is (152-160): 1.

preferably, the weight ratio of the aqueous formaldehyde solution to the polyvinyl alcohol is 156: 1.

polyvinyl alcohol reacts with formaldehyde to generate polyvinyl formal, which has good toughness and elasticity, improves initial viscosity of resin, reduces brittleness and improves aging resistance of resin, and polyvinyl alcohol and formaldehyde undergo polycondensation reaction while urea and formaldehyde generate Uron rings under acidic conditions.

Melamine

Melamine, commonly known as melamine and protamine, and IUPAC named as 1,3, 5-triazine-2, 4, 6-triamine is a triazine nitrogen-containing heterocyclic organic compound and is used as a chemical raw material. It is a white monoclinic crystal, almost odorless, slightly soluble in water (3.1g/L at room temperature), soluble in methanol, formaldehyde, acetic acid, hot ethylene glycol, glycerol, pyridine, etc., insoluble in acetone, ethers, harmful to the body, and not applicable to food processing or food additives.

In one embodiment, the weight ratio of the aqueous solution of formaldehyde to melamine is (8-10): 1.

preferably, the weight ratio of the aqueous solution of formaldehyde to melamine is 8.9: 1.

in the later period of urea-formaldehyde resin generation, after urea reacts with formaldehyde, under the alkalescent condition, melamine is further condensed with formaldehyde to generate a stable reticular polymer, so that the free formaldehyde of the resin is reduced, the water resistance of the plywood prepared from the resin is obviously improved, and the bonding strength is improved.

Aqueous ammonia

Ammonia water is also called Amonian water, and its main ingredient is NH₃·H₂O, an aqueous solution of ammonia, colorless and transparent and having an offensive odor. The melting point of ammonia is-77.773 deg.C, boiling point is-33.34 deg.C, and density is 0.91g/cm³. The ammonia gas is easily dissolved in water and ethanol, is volatile, has the general property of partial alkali, and is prepared by introducing ammonia gas into water. The ammonia gas is toxic, irritating and corrosive to eyes, nose and skin, and can suffocate people with a maximum allowable concentration of 30mg/m in air³It is mainly used as fertilizer.

In one embodiment, the weight ratio of the aqueous solution of formaldehyde to the ammonia water is (15-20): 1.

preferably, the weight ratio of the aqueous solution of formaldehyde to the aqueous ammonia is 18.7: 1.

the concentration of the ammonia water is 25 wt%.

Ammonia water is added in the early stage to generate hexamethylene tetramine, the polycondensation reaction of the hexamethylene tetramine is promoted in the acid polycondensation stage, and hydrophobic groups are introduced into the resin by a copolycondensation method to improve the water resistance of the resin, so that the wet shear strength of the product is improved, and the flexibility of the resin is improved.

The second aspect of the invention provides a preparation method of the urea-formaldehyde resin adhesive, which comprises the following steps:

putting an aqueous solution of formaldehyde, urea accounting for 5-90% of the total weight of the urea, polyvinyl alcohol, melamine accounting for 10-50% of the total weight of the melamine and ammonia water into a reaction kettle, adjusting the pH to 7-8.5, heating to 85-100 ℃, and reacting;

(II) adjusting the pH value to 3.5-4.5;

thirdly, reacting at 85-100 ℃, adjusting the pH to 6-8, and adding the rest urea and melamine in batches at 75-90 ℃ for reaction;

and (IV) adjusting the pH value to 7.5-8.5, cooling and discharging to obtain the catalyst.

In one embodiment, in the step (one), the temperature is raised to 85-100 ℃ and the reaction is carried out until the pH is more than 6.5.

In one embodiment, in the step (three), the reaction is carried out at 85 to 100 ℃ to obtain a viscosity: coating the mixture in 4 cups at 35 ℃ for 10-25 s.

Preferably, in the step (three), the reaction is carried out at 85-100 ℃ to reach the viscosity: coating the mixture at 35 ℃ for 16-17 s in 4 cups.

In a preferred embodiment, the preparation method of the urea-formaldehyde resin adhesive comprises the following steps:

(1) dividing urea into 4 parts to obtain a first batch of urea, a second batch of urea, a third batch of urea and a fourth batch of urea; dividing melamine into 2 parts to obtain a first batch of melamine and a second batch of melamine;

(2) putting an aqueous solution of formaldehyde into a reaction kettle, adjusting the pH to 8-8.5, adding a first batch of urea, polyvinyl alcohol, a first batch of melamine and ammonia water, stirring, adjusting the pH to 7.8-8, heating to 90-95 ℃, preserving heat for 35-45 min, and finishing heat preservation, wherein the pH is more than 6.5;

(3) adjusting the pH value to 4-4.2;

(4) reacting at 90-94 ℃ until the viscosity: coating the mixture in 4 cups at 35 ℃ for 16-17 s; adjusting the pH value to 6.2-6.5, adding a second batch of urea, and reacting at 85-90 ℃ until the viscosity: coating the mixture in 4 cups at 35 ℃ for 20-22 s; continuously adjusting the pH value to 7-7.5, adding a second batch of melamine, and adjusting the temperature to 84-86 ℃ until the viscosity is as follows: coating the mixture in 4 cups at 35 ℃ for 25-27 s; adding a third batch of urea, keeping the temperature at 78-80 ℃ for 20min, and adjusting the pH to 7.2-7.8;

(5) and cooling to 70 ℃, adding a fourth batch of urea, adjusting the pH to 7.5-8, cooling, and discharging to obtain the urea.

In one embodiment, the weight ratio of the first, second, third and fourth urea batches is (1.8-2.2): (1.6-2): 1: (1.5-2).

Preferably, the weight ratio of the first batch of urea to the second batch of urea to the third batch of urea to the fourth batch of urea is 1.95: 1.86: 1: 1.7.

in one embodiment, the weight ratio of the first melamine batch to the second melamine batch is 1: (4-6.5).

Preferably, the weight ratio of the first melamine batch to the second melamine batch is 1: 6.

step (2)

In one embodiment, the step (2) is: putting an aqueous solution of formaldehyde into a reaction kettle, adding 30 wt% of aqueous alkali to adjust the pH value to 8-8.5, adding a first batch of urea, polyvinyl alcohol, a first batch of melamine and ammonia water, stirring, adjusting the pH value to 7.8-8, heating to 90-95 ℃, preserving heat for 35-45 min, and finishing the heat preservation, wherein the pH value is more than 6.5.

Preferably, the step (2) is: putting the aqueous solution of formaldehyde into a reaction kettle, adding 30 wt% of aqueous alkali to adjust the pH value to 8.2, adding the first batch of urea, polyvinyl alcohol, the first batch of melamine and ammonia water, stirring, adjusting the pH value to 7.9, heating to 92 ℃, preserving the temperature for 40min, and finishing the heat preservation, wherein the pH value is more than 6.5.

The kind of the alkali in the 30 wt% alkali solution of the present invention is not particularly limited and may be conventionally selected by those skilled in the art.

In one embodiment, the 30 wt% alkali solution is a 30 wt% sodium hydroxide alkali solution.

Step (3)

In one embodiment, the step (3) is: adding formic acid, and adjusting the pH value to 4-4.2.

Preferably, the step (3) is: formic acid was added to adjust the pH to 4.1.

Step (4)

In one embodiment, the step (4) is: reacting at 90-94 ℃ until the viscosity: coating the mixture in 4 cups at 35 ℃ for 16-17 s; adding alkali, adjusting the pH value to 6.2-6.5, adding a second batch of urea, and adjusting the temperature to be 85-90 ℃ until the viscosity is as follows: coating the mixture in 4 cups at 35 ℃ for 20-22 s; continuously adjusting the pH value to 7-7.5, adding a second batch of melamine, and adjusting the temperature to 84-86 ℃ until the viscosity is as follows: coating the mixture in 4 cups at 35 ℃ for 25-27 s; adding the third batch of urea, keeping the temperature at 78-80 ℃ for 20min, and adjusting the pH to 7.2-7.8.

Preferably, the step (4) is: reaction at 92 ℃ to viscosity: coating at 35 ℃ for 16s in 4 cups; add base, adjust pH to 6.3, add a second batch of urea, at 88 ℃ to viscosity: coating at 35 ℃ for 21s in 4 cups; the pH was further adjusted to 7.2 and a second melamine batch was added, 85 ℃ to viscosity: coating at 35 ℃ for 26s in 4 cups; adding the third batch of urea, keeping the temperature at 79 ℃ for 20min, and adjusting the pH value to 7.5.

The kind of the base in the step (4) of the present invention is not particularly limited, and those skilled in the art can select it routinely.

In one embodiment, the base in step (4) is sodium hydroxide.

Step (5)

In one embodiment, the step (5) is: cooling to 70 deg.C, adding urea of the fourth batch, adjusting pH to 7.8, cooling, and discharging.

The applicant unexpectedly finds that when the polyvinyl alcohol is used, particularly the polyvinyl alcohol has the dynamic viscosity of 45-55 mpa.s, the alcoholysis degree of 99-100% mol/mol, and particularly the polyvinyl alcohol with the brand number of 20-99 is used for modifying the urea-formaldehyde resin, the bonding strength can be remarkably improved, and the content of free formaldehyde can be reduced.

In addition, the applicant has unexpectedly found that the properties of the urea-formaldehyde resin adhesive are remarkably improved by adding a proper amount of ammonia water in the step (2) and strictly controlling the temperature, viscosity, pH and content of the added substances in each step of the preparation process.

The invention also provides a plywood prepared by using the urea-formaldehyde resin adhesive.

Plywood is a three-layer or multi-layer plate material made up by using wood segments and making them be rotary-cut into single board or sliced into thin wood and using adhesive to make them be glued together, and usually using odd number of layers of single board and making the fibre directions of adjacent layers of single board be mutually perpendicular.