CN115894831A - Preparation method and application of urea-formaldehyde resin capable of being infinitely water-soluble - Google Patents
Preparation method and application of urea-formaldehyde resin capable of being infinitely water-soluble Download PDFInfo
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Abstract
The invention discloses a preparation method of infinite water-soluble urea-formaldehyde resin, which comprises the following steps: s1: feeding materials into the reaction kettle for the first time; s2: heating for reaction; s3: after cooling, adjusting the pH value, and carrying out heat preservation reaction; s4: carrying out secondary feeding reaction; s5: and (5) cooling and discharging. The urea-formaldehyde resin disclosed by the invention is applied to the impregnation process, the water solubility of the urea-formaldehyde resin is enhanced, the urea-formaldehyde resin can be mutually dissolved with water in any proportion, the stability of the resin is increased, the storage period of the resin is prolonged, meanwhile, the fluidity of the resin is improved, the penetration of the resin on paper is improved in the impregnation process, a less penetrating agent can be added, and the cost is saved.
Description
Technical Field
The invention relates to the field of C08G12/12, in particular to a preparation method and application of urea-formaldehyde resin capable of being infinitely dissolved in water.
Background
The urea-formaldehyde resin is semitransparent, resists weak acid and weak base, has good insulating property, and can be widely applied to the adhesive due to strong caking property, high curing speed and low cost. However, the urea-formaldehyde resin has certain toxicity and short storage period due to the existence of free formaldehyde, and can yellow in only 2-3 months, thus influencing the use.
CN114656608A discloses a urea-formaldehyde resin for artificial board veneering and a preparation method thereof, wherein a strong acid weak base weak acid process route is used, three times of polycondensation reaction are carried out, and a tackifier and a nano active additive are added to improve the adhesive. CN114507328A discloses a preparation method of urea-formaldehyde resin for an environment-friendly plate, urea is added in three batches, and polyvinyl alcohol, ammonia water, nano chitosan and melamine are added, and the urea-formaldehyde resin for the environment-friendly plate is obtained by ultrasonic oscillation.
The urea-formaldehyde resin obtained by the patent has high degree of gluing and low formaldehyde emission, but all the processes need to add various auxiliary agents, the cost is high, the storage performance of the obtained urea-formaldehyde resin is improved, but the urea-formaldehyde resin still becomes yellow and goes bad after being stored for a long time, the storage life needs to be improved, the fluidity of the resin is poor, and a large amount of penetrating agents needs to be added when the urea-formaldehyde resin is used in the process of an impregnation process.
Disclosure of Invention
Aiming at the problems, the invention discloses a preparation method of infinite water-soluble urea-formaldehyde resin, which comprises the following steps:
s1: feeding materials into the reaction kettle for the first time;
s2: heating for reaction;
s3: after cooling, adjusting the pH value, and carrying out heat preservation reaction;
s4: carrying out secondary feeding reaction;
s5: and (5) cooling and discharging.
In one embodiment, the S1 includes: formaldehyde was added to the reactor, pH adjusted with sodium hydroxide, and the first batch of urea was added.
Preferably, the molar ratio F/U1 of the added amount F of formaldehyde to the added amount U1 of the first urea batch = (2.8-3.2): 1.
further preferably, the molar ratio of the added amount F of formaldehyde to the added amount U1 of the first urea batch is F/U1=3.09:1.
in one embodiment, the pH is adjusted to 8.5 to 9.5 using sodium hydroxide.
Preferably, the pH is adjusted to 8.5-9 using sodium hydroxide.
Further preferably, the pH is adjusted to 9 using sodium hydroxide.
Urea and formaldehyde can obtain methylol urea under acidic condition or alkaline condition, but under acidic condition, the produced methylol urea is unstable, side reaction is easy to occur, and polycondensation is carried out to produce methylene urea or hydroxymethyl methylene diurea, and these components affect the performance of adhesive, so domestic industrial production is mostly carried out under alkaline medium, and pH is controlled to be 7.5-8.5, in addition, the mole ratio of formaldehyde and urea also has great influence on the synthesis of urea-formaldehyde resin, when the mole ratio of formaldehyde and urea is F/U <1, a large amount of monomethyl urea is produced, which can only be further subjected to polycondensation reaction to form linear polymer, and can not be used as adhesive, when F/U = (1-2): 1, stable monomethylol ureas and dimethylol ureas are formed, and if F/U >2, trimethylol ureas and tetramethylol ureas are formed in addition to the monomethylol ureas and dimethylol ureas. The applicant divides urea into two batches, and controls the molar ratio F: U1= (2.8-3.2) of formaldehyde to the first batch of urea: 1, the alkalinity of the solution is improved, sodium hydroxide is used for adjusting the pH value to be 8.5-9.5, more dimethylolurea and trihydroxymethylurea can be generated while the monohydroxymethylurea is stably generated, more crosslinking main bodies are provided for the subsequent process, the crosslinking degree of the resin is improved, the mechanical property of the resin is improved, and if the pH value is higher than 9.5, methylene sediment is generated, and the reaction liquid is turbid.
In one embodiment, the S2 includes: heating to 85-95 deg.C, timing and maintaining for 20-35 min.
Preferably, the S2 includes: heating to 90-92 deg.C, timing and keeping the temperature for 25-30 min.
Further preferably, the S2 includes: the temperature is increased to 90 ℃, and the temperature is kept for 30 minutes by timing.
In order to produce more dimethylol and trimethylol urea, it is not sufficient to adjust the molar ratio of formaldehyde to the first urea and the pH of the solution, and the Applicant found that more dimethylol and trimethylol urea can be produced by controlling the reaction temperature at 85-95 ℃ for 20-35 minutes of timed incubation, and the Applicant considered that the possible reason is: under alkaline conditions, formaldehyde is easy to generate side reaction and is oxidized into formic acid, or sodium formate and methanol are generated through disproportionation reaction, and the two reactions consume the raw material formaldehyde. More importantly, the viscosity and the waterproof property of the glue are influenced, and in order to reduce the influence of the side reaction, the reaction time is strictly controlled to be 20-35 minutes, and the reaction temperature is controlled to be 85-95 ℃.
In one embodiment, the S3 includes: cooling to 65-70 deg.c, adding acid to regulate pH value and maintaining the temperature for reaction.
Preferably, the S3 includes: cooling to 66-69 deg.C, adding acid to regulate pH value, and reacting while maintaining the temperature.
Further preferably, the S3 includes: cooling to 67 ℃, adding acid to adjust the pH value, and carrying out heat preservation reaction.
In one embodiment, the acid is added to adjust the pH to 2.8 to 3.0 using an inorganic salt.
Preferably, the pH is adjusted to 2.9 by adding an acid.
Further preferably, the inorganic salt is selected from any one of ammonium sulfate, ammonium chloride, and ammonium nitrate.
In one embodiment, the holding time in the step S3 is 50 to 70min.
Preferably, the heat preservation time in the step S3 is 60min.
In the process of synthesizing resin, reaction time and reaction temperature are two important factors, the reaction temperature is too high, the reaction speed is accelerated, the obtained resin has small average molecular weight, low solid content and small viscosity, the reaction temperature is too low, the reaction rate is slow, the reaction time is prolonged, the obtained resin has large average molecular weight and large viscosity, but the water solubility is poor, and the storage period is short. In the prior art, formaldehyde and urea with low molar ratio are usually reacted under the condition of strong acid (pH 1.5-2.0) to ensure that the addition reaction of the urea and the formaldehyde is smoothly carried out, and the reaction time is delayed by adding a proper buffering agent, but the prepared urea-formaldehyde resin adhesive still turns yellow after being placed for a long time, and the stability needs to be improved.
However, through a great deal of experiments, the inventor creatively discovers that the resin obtained by adding acid to adjust the pH value to 2.8-3.0 at 65-70 ℃ and keeping the temperature for 50-70min at regular time has high viscosity and excellent water solubility, can be dissolved in water at any ratio, is still transparent and does not turn yellow after being stored for 2 years, and the inventor thinks that the possible reason is that: under the acidic condition, hydroxymethyl in the urea formaldehyde, the dimethylol urea and the trihydroxy methyl urea can react to generate Uron rings, so that the water resistance and the stability of the urea formaldehyde resin can be improved, and the content of free formaldehyde can be reduced.
In one embodiment, the S4 includes: and (4) adjusting the pH value to 7.5-8.0 by using sodium hydroxide, adding a second batch of urea, timing and preserving heat for reaction.
Preferably, sodium hydroxide is used to adjust the pH to 7.7-7.9 in the S4 step.
Further preferably, sodium hydroxide is used in the step S4 to adjust the pH to 7.8.
In one embodiment, the sum of the amount of urea added in the second portion U2 and the amount of urea added in the first portion U1 is related to the amount of formaldehyde added F, and the molar ratio is: F/(U1 + U2) = (1.6-1.8): 1.
preferably, the sum of the urea adding amount U2 of the second batch and the urea adding amount U1 of the first batch has a relationship with the formaldehyde adding amount F, and the molar ratio is as follows: F/(U1 + U2) = (1.7-1.75): 1.
further preferably, the sum of the added amount U2 of the second urea and the added amount U1 of the first urea is in relation to the added amount F of formaldehyde, and the molar ratio is as follows: F/(U1 + U2) =1.72:1.
in one embodiment, the holding time in the step S4 is 20-40min.
Preferably, the heat preservation time in the step S4 is 25-35min.
Further preferably, the heat preservation time in the step S4 is 30min.
In the synthesis process of the urea-formaldehyde resin, urea can be added in multiple batches, and the inventor finds that aiming at the system of the invention, the urea is added in two batches, and the proportion of adding the urea for two times is controlled, so that the content of free formaldehyde can be reduced, the mechanical property of the resin is improved, and the effect of infinite water solubility is realized, and the inventor considers that the possible reason is that: controlling the molar ratio F/U1 of the addition amount F of the formaldehyde to the addition amount U1 of the first batch of urea when the urea is added for the first time, wherein the molar ratio F/U1 is (2.8-3.2): 1, under the condition that the molar ratio of formaldehyde to urea is high, dimethylol urea and trihydroxy methyl urea can be generated as much as possible, the crosslinking degree of a system is improved, and after urea is added in the second batch, the molar ratio of the adding amount of formaldehyde to the total feeding amount of urea is ensured to be (1.6-1.8): 1, the content of free formaldehyde can be reduced, and more hydrophilic group hydroxymethyl can be generated under a lower alkaline condition, so that the technical effect of the invention is realized.
In one embodiment, the S5 includes: cooling to below 35 deg.C, and discharging.
The invention also discloses application of the unlimited water-soluble urea-formaldehyde resin prepared by the preparation method. Especially in the process of the impregnation process, the water solubility of the urea-formaldehyde resin is enhanced, the urea-formaldehyde resin can be mutually dissolved with water in any proportion, the stability of the resin is improved, the storage period of the resin is prolonged, meanwhile, the fluidity of the resin is improved, the penetration of the resin to paper in the process of the impregnation process is improved, a less penetrating agent can be added, and the cost is saved.
Has the advantages that:
1. the invention controls the molar ratio F of formaldehyde to the first urea to be U1= (2.8-3.2): 1, the pH is adjusted to 8.5-9.5 by using sodium hydroxide, so that more dimethylol urea and trihydroxy methyl urea can be generated at the same time of stably generating the monohydroxy methyl urea.
2. The invention controls the reaction temperature at 85-95 ℃, keeps the temperature for 20-35 minutes by timing, can generate more dimethylol urea and trihydroxy methyl urea, lightens side reactions and improves the viscosity.
3. The invention adjusts the pH value to 2.8-3.0 by adding acid at 65-70 ℃, keeps the temperature for 50-70min by timing, and the obtained resin has high viscosity and excellent water solubility, can be mutually dissolved with water at any ratio, is still transparent and does not turn yellow after being stored for 2 years.
4. According to the invention, the urea is added in two batches, and the proportion of the urea added twice is controlled, so that the content of free formaldehyde can be reduced, the mechanical property of the resin is improved, and the effect of infinite water solubility is realized.
5. The urea-formaldehyde resin disclosed by the invention is applied to the impregnation process, the water solubility of the urea-formaldehyde resin is enhanced, the urea-formaldehyde resin can be mutually dissolved with water in any proportion, the stability of the resin is increased, the storage period of the resin is prolonged, meanwhile, the fluidity of the resin is improved, the penetration of the resin on paper is improved in the impregnation process, a less penetrating agent can be added, and the cost is saved.
Detailed Description
Example 1
The embodiment 1 discloses a preparation method of infinite water-soluble urea resin, which comprises the following steps:
s1: 37% formaldehyde was charged to the reactor, the pH was adjusted to 8.5 using sodium hydroxide, and the first batch of urea was added. The molar ratio F/U1 of said formaldehyde F to the first urea U1=2.8:1.
s2: the temperature is raised to 85 ℃, and the temperature is kept for 35 minutes by timing.
S3: cooling to 65 ℃, adding ammonium sulfate to adjust the pH value to 2.8, and keeping the temperature for reaction for 70min.
S4: and (4) adjusting the pH value to 7.5 by using sodium hydroxide, adding a second batch of urea, timing, keeping the temperature and reacting for 40min.
The sum of the second urea adding amount U2 and the first urea adding amount U1 has a relationship with the formaldehyde adding amount F, and the molar ratio is as follows: F/(U1 + U2) =1.6:1.
s5: cooling and discharging: cooling to 35 deg.C, and discharging.
Example 2
The embodiment 2 discloses a preparation method of infinite water-soluble urea-formaldehyde resin, which comprises the following steps:
s1: 37% formaldehyde was charged to the kettle, the pH was adjusted to 9.5 using sodium hydroxide, and the first batch of urea was added. The molar ratio F/U1 of the formaldehyde F to the first urea U1=3.2:1.
s2: the temperature is raised to 95 ℃, and the temperature is kept for 20 minutes.
S3: cooling to 70 deg.C, adding ammonium sulfate to adjust pH to 3.0, and reacting for 50min.
S4: and (4) adjusting the pH value to 8.0 by using sodium hydroxide, adding a second batch of urea, timing, keeping the temperature and reacting for 20min.
The sum of the second urea adding amount U2 and the first urea adding amount U1 has a relationship with the formaldehyde adding amount F, and the molar ratio is as follows: F/(U1 + U2) =1.8:1.
s5: cooling and discharging: cooling to 35 deg.C, and discharging.
Example 3
The embodiment 3 discloses a preparation method of infinite water-soluble urea-formaldehyde resin, which comprises the following steps:
s1: 37% formaldehyde was charged to the reactor, the pH was adjusted to 9 using sodium hydroxide, and the first batch of urea was added. The molar ratio F/U1 of said formaldehyde F to the first urea U1=2.9:1.
s2: the temperature is raised to 92 ℃, and the temperature is kept for 30 minutes by timing.
S3: cooling to 66 ℃, adding ammonium sulfate to adjust the pH value to 2.9, and keeping the temperature for reaction for 55min.
S4: and (4) adjusting the pH value to 7.7 by using sodium hydroxide, adding a second batch of urea, timing, keeping the temperature and reacting for 35min.
The sum of the second urea adding amount U2 and the first urea adding amount U1 has a relationship with the formaldehyde adding amount F, and the molar ratio is as follows: F/(U1 + U2) =1.7:1.
s5: cooling and discharging: cooling to 35 deg.C, and discharging.
Example 4
The embodiment 4 discloses a preparation method of unlimited water-soluble urea-formaldehyde resin, which comprises the following steps:
s1: 37% formaldehyde was charged to the kettle, the pH was adjusted to 8.7 using sodium hydroxide, and the first batch of urea was added. The molar ratio F/U1 of the formaldehyde F to the first urea U1=3.1:1.
s2: the temperature is raised to 90 ℃, and the temperature is kept for 25 minutes in a timing way.
S3: cooling to 69 deg.C, adding ammonium sulfate to adjust pH to 2.9, and reacting for 65min.
S4: and (4) adjusting the pH value to 7.9 by using sodium hydroxide, adding a second batch of urea, timing, keeping the temperature and reacting for 25min.
The sum of the second urea adding amount U2 and the first urea adding amount U1 has a relationship with the formaldehyde adding amount F, and the molar ratio is as follows: F/(U1 + U2) =1.75:1.
s5: cooling and discharging: cooling to 35 deg.C, and discharging.
Example 5
This embodiment 5 discloses a method for preparing an infinitely water-soluble urea-formaldehyde resin, which includes the following steps:
s1: 37% formaldehyde was charged to the reactor, the pH was adjusted to 9 using sodium hydroxide, and the first batch of urea was added. The molar ratio F/U1 of formaldehyde F to urea U1 of the first batch =3.09:1.
s2: the temperature is raised to 90 ℃, and the temperature is kept for 30 minutes in a timing way.
S3: cooling to 67 deg.C, adding ammonium sulfate to adjust pH to 2.9, and reacting for 60min.
S4: and (4) adjusting the pH value to 7.8 by using sodium hydroxide, adding a second batch of urea, timing, keeping the temperature and reacting for 30min.
The sum of the second urea addition U2 and the first urea addition U1 has a relationship with the formaldehyde addition F, and the molar ratio is as follows: F/(U1 + U2) =1.72:1.
s5: cooling and discharging: cooling to 35 deg.C, and discharging.
Comparative example 1
The comparative example 1 discloses a preparation method of infinite water-soluble urea-formaldehyde resin, which comprises the following steps:
s1: 37% formaldehyde was charged to the reactor, the pH was adjusted to 8 using sodium hydroxide, and the first batch of urea was added. The molar ratio F/U1 of said formaldehyde F to the first urea U1=3.5:1.
s2: the temperature is raised to 90 ℃, and the temperature is kept for 30 minutes in a timing way.
S3: cooling to 67 deg.C, adding ammonium sulfate to adjust pH to 2.9, and reacting for 60min.
S4: and (4) adjusting the pH value to 7.8 by using sodium hydroxide, adding a second batch of urea, and performing heat preservation reaction for 30min.
The sum of the second urea adding amount U2 and the first urea adding amount U1 has a relationship with the formaldehyde adding amount F, and the molar ratio is as follows: F/(U1 + U2) =1.72:1.
s5: cooling and discharging: cooling to 35 deg.C, and discharging.
Comparative example 2
The comparative example 2 discloses a preparation method of unlimited water-soluble urea-formaldehyde resin, which comprises the following steps:
s1: 37% formaldehyde was charged to the reactor, the pH was adjusted to 9 using sodium hydroxide, and the first batch of urea was added. The molar ratio F/U1 of said formaldehyde F to the first urea U1=3.09:1.
s2: the temperature is increased to 80 ℃, and the temperature is kept for 30 minutes.
S3: cooling to 67 deg.C, adding ammonium sulfate to adjust pH to 2.9, and reacting for 60min.
S4: and (4) adjusting the pH value to 7.8 by using sodium hydroxide, adding a second batch of urea, timing, keeping the temperature and reacting for 30min.
The sum of the second urea addition U2 and the first urea addition U1 has a relationship with the formaldehyde addition F, and the molar ratio is as follows: F/(U1 + U2) =1.72:1.
s5: cooling and discharging: cooling to 35 deg.C, and discharging.
Comparative example 3
The comparative example 3 discloses a preparation method of infinite water-soluble urea-formaldehyde resin, which comprises the following steps:
s1: 37% formaldehyde was charged to the reactor, the pH was adjusted to 9 using sodium hydroxide, and the first batch of urea was added. The molar ratio F/U1 of said formaldehyde F to the first urea U1=3.09:1.
s2: the temperature is raised to 90 ℃, and the temperature is kept for 30 minutes in a timing way.
S3: cooling to 55 deg.C, adding ammonium sulfate to adjust pH to 2, and reacting for 60min under heat preservation.
S4: and (4) adjusting the pH value to 7.8 by using sodium hydroxide, adding a second batch of urea, timing, keeping the temperature and reacting for 30min.
The sum of the second urea adding amount U2 and the first urea adding amount U1 has a relationship with the formaldehyde adding amount F, and the molar ratio is as follows: F/(U1 + U2) =1.72:1.
s5: cooling and discharging: cooling to 35 deg.C, and discharging.
Comparative example 4
The comparative example 4 discloses a preparation method of infinite water-soluble urea-formaldehyde resin, which comprises the following steps:
s1: 37% formaldehyde was charged to the reactor, the pH was adjusted to 9 using sodium hydroxide, and the first batch of urea was added. The molar ratio F/U1 of said formaldehyde F to the first urea U1=3.09:1.
s2: the temperature is raised to 90 ℃, and the temperature is kept for 30 minutes in a timing way.
S3: cooling to 67 deg.C, adding ammonium sulfate to adjust pH to 2.9, and reacting for 60min.
S4: and (4) adjusting the pH value to 7 by using sodium hydroxide, adding a second batch of urea, and timing and preserving heat for reaction for 50min.
The sum of the second urea adding amount U2 and the first urea adding amount U1 has a relationship with the formaldehyde adding amount F, and the molar ratio is as follows: F/(U1 + U2) =1.5:1.
s5: cooling and discharging: cooling to 35 deg.C, and discharging.
Comparative example 5
The comparative example 5 discloses a preparation method of unlimited water-soluble urea-formaldehyde resin, which comprises the following steps:
s1: 37% formaldehyde was charged to the kettle, the pH was adjusted to 9 using sodium hydroxide, and the first batch of urea was added. The molar ratio F/U1 of said formaldehyde F to the first urea U1=3.09:1.
s2: the temperature is increased to 80 ℃, and the temperature is kept for 30 minutes.
S3: cooling to 55 deg.C, adding ammonium sulfate to adjust pH to 1.5, and reacting for 60min under heat preservation.
S4: and (4) adjusting the pH value to 7.8 by using sodium hydroxide, adding a second batch of urea, and performing heat preservation reaction for 30min.
The sum of the second urea adding amount U2 and the first urea adding amount U1 has a relationship with the formaldehyde adding amount F, and the molar ratio is as follows: F/(U1 + U2) =1.72:1.
s5: cooling and discharging: cooling to 35 deg.C, and discharging.
And (3) performance testing:
the urea-formaldehyde resin obtained in the examples 1-5 and the comparative examples 1-5 is mixed with glue, specifically, according to the mass parts, 100 parts of urea-formaldehyde resin is added into a glue mixer, 10 parts of flour and 0.5 part of ammonium chloride are added, and the mixture is stirred for 20 minutes to obtain the urea-formaldehyde resin glue.
1. And (3) testing the stability: the urea-formaldehyde resin adhesives obtained in examples 1 to 5 and comparative examples 1 to 5 were left at 40 ℃ and observed for deterioration time, which was recorded as A for more than 1 month and B for one month.
2. And (3) white drop test: the urea resin glue obtained in examples 1 to 5 and comparative examples 1 to 5 was dropped into 20mL of water with a suction tube, and was changed to A without turning white and to B without turning white.
| Stability of | White drop | |
| Example 1 | A | A |
| Example 2 | A | A |
| Example 3 | A | A |
| Example 4 | A | A |
| Example 5 | A | A |
| Comparative example 1 | B | B |
| Comparative example 2 | B | B |
| Comparative example 3 | B | B |
| Comparative example 4 | B | B |
| Comparative example 5 | B | B |
Claims (10)
1. The preparation method of the urea-formaldehyde resin capable of being infinitely dissolved in water is characterized by comprising the following steps:
s1: feeding materials into the reaction kettle for the first time;
s2: heating for reaction;
s3: after cooling, adjusting the pH value, and carrying out heat preservation reaction;
s4: carrying out secondary feeding reaction;
s5: and (5) cooling and discharging.
2. The method according to claim 1, wherein S1 comprises: formaldehyde was added to the reactor, pH adjusted with sodium hydroxide, and the first batch of urea was added.
3. The process according to claim 2, wherein the molar ratio of the formaldehyde addition F to the urea addition U1 of the first batch F/U1= (2.8-3.2): 1.
4. the method according to claim 3, wherein the pH is adjusted to 8.5 to 9.5 using sodium hydroxide.
5. The method according to claim 1, wherein the S2 includes: heating to 85-95 deg.C, timing and maintaining for 20-35 min.
6. The method according to claim 1, wherein the S3 includes: cooling to 65-70 deg.c, adding acid to regulate pH value and maintaining the temperature for reaction.
7. The method according to claim 6, wherein the pH is adjusted by adding an acid to 2.8-3.0 by using an inorganic salt, and the holding time is 50-70min.
8. The method according to claim 1, wherein the S4 includes: and (4) adjusting the pH value to 7.5-8.0 by using sodium hydroxide, adding a second batch of urea, timing and preserving heat for reaction.
9. The preparation method according to claim 8, characterized in that the sum of the added amount U2 of the second urea and the added amount U1 of the first urea is related to the added amount F of formaldehyde, and the molar ratio is as follows: F/(U1 + U2) = (1.6-1.8): 1.
10. use of an infinitely water-soluble urea-formaldehyde resin prepared according to the preparation method of any one of claims 1 to 9 in a paper impregnation process.
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