CS202990B1 - Process for preparing urea formaldehyde resins - Google Patents

Description

The invention relates to a process for the production of urea-formaldehyde resins.

Urea-formaldehyde resins are widely used as binders in the woodworking industry for the production of particle board, fibreboard and other boards, veneer, wood glue and wood-based materials. They are also used in the production of sand-casting molds and for soil consolidation, for example in road construction.

The known process for producing urea-formaldehyde resins consists of the following basic steps. First, the reaction of urea with formaldehyde takes place in an alkaline medium to form methyl urea derivatives - addition step. This is followed by condensation of methyl urea derivatives in acidic medium, neutralization of the condensation solution, partial drying of the resin obtained until a dry matter content of 60 to 65% by weight is reached. This is followed by further condensation of the resin with urea, the resin is cooled, stabilized and standardized. See, for example, R. Z. Tjomkina Sintetičeskije klei in hole-brabotke, publishing house Lesnaya premyslenost, M., 1971.

The reaction of urea with formaldehyde in an alkaline medium is normally carried out at a molar ratio of urea to formaldehyde of 1: 2, at a pH of 7.5 to 8.5 and at a temperature of 96 to 98 ° C for 45 minutes,

The condensation of methyl urea derivatives in an acidic medium, for example in the presence of sulfuric acid or benzenesulfonic acid, is carried out at the same temperature, but at a pH of 5.0-5.4. It is important that as a prerequisite for the production of stable water-miscible of the products is a higher reaction rate in the reaction stage of urea with formaldehyde in the presence of lye than the rate in the degree of condensation in an acid medium. The condensation solution obtained is neutralized with an aqueous alkaline solution at a temperature of 60 to 95 DEG C. until a pH of 7.5 to 8.0 is reached. The neutralized condensation solution is dried to the necessary dry substance content, and the subsequent condensation of the resin with urea takes place within 30 minutes, at a temperature of 50 to 65 ° C and at a pH of 6.8 to 7.2, until the final urea / formaldehyde ratio reaches setpoints. The resulting resin was cooled to 35 ° C, ammonia water was added thereto to stabilize to achieve a pH of 7.5-9 and subjected to standardization.

In the plastics industry, two problems need to be addressed in the field of urea-formaldehyde resins, namely the improvement of the resin production process in order to intensify it and the development of a range of urea-formaldehyde resins to meet the current needs of consumers. One of the latest requirements is to produce resins with a high curing rate and an increased shelf life of the glue - 1 part by weight of ammonium chloride per 100 parts by weight. resin parts - with improved hygienic properties.

The known process does not provide for the production of urea-formaldehyde resins having both a high curing rate - the curing time of the above glue for 40 seconds at 100 ° C - and an increased shelf life of the solution, i.e. at least 10 hours at 20 ± 1 Deň: 32 ° C. Moreover, the synthesis time is quite long - 90 minutes.

The main direction from the intensification of the urea-formaldehyde resin production process which has recently been the focus of interest is the increase in synthesis temperature. Indeed, such a measure leads to a shortening of the reaction time of the urea with formaldehyde, but on the other hand it is necessary that the process be carried out under pressure. This significantly complicates the equipment requirements required for the reaction and thus makes it more expensive. What is particularly important is that such a process does not ensure the production of resins that would. they combined high cure speed with increased glue shelf life at low free formaldehyde content.

It is also known to produce urea-formaldehyde resins by reacting urea with formaldehyde at 70 to 98 ° C in the presence of zinc chloride / L. Scheiber Khimija and Synthetic pitch technology - Goschimizdát M. L. 1949 /. The process involves a number of such steps as neutralization, urea treatment and others. In this way an impregnating solution for the molding compositions is obtained. However, the requirements imposed on such substances differ from those required for adhesive resins. In addition, in order to improve the physico-mechanical properties of the synthetic materials, zinc chloride is added in considerable amounts.

It is an object of the invention to overcome these disadvantages. SUMMARY OF THE INVENTION It is an object of the present invention to change the process conditions of the process for producing urea-formaldehyde resins based on the reaction of urea with formaldehyde so as to obtain both fast-curing urea-formaldehyde resins with extended shelf life and shelf life of the glue.

... »with a content of free formaldehyde in the resin of not more than 0,8 2 and of only slightly toxic resins with a content of free formaldehyde of not more than 0,3 2 and a curing time of not more than 55 seconds at 100 ° C with higher process productivity.

The problem has been solved and the disadvantages of the prior art have been eliminated in a process for producing urea-formaldehyde resins consisting of reacting urea with formaldehyde at 70-98 ° C in the presence of zinc chloride in a condensation solution, neutralizing, evaporating and further reacting the intermediate with urea at 50 to 65 ° C, the reaction with urea after neutralization being carried out before or after evaporation of the condensation solution according to the invention, characterized in that zinc chloride is used in an amount of from 0.05 to 0.15 parts by weight per 100 parts wt. urea.

The advantages of the process according to the invention are particularly evident in comparison with the known processes also using zinc chloride.

It is known to produce co-condensation products of zinc chloride, urea and formaldehyde, for example as disclosed in U.S. Pat. No. 1,992,180, with a zinc chloride content of from 6 to 57 parts by weight. per 100 parts by weight. urea. Stable products suitable for further curing are thereby obtained. It is stated in the patent that stable liquid products are obtained in the process according to the invention when the zinc chloride content is greater than 62% by weight. urea. At 62 contents, turbid condensation solutions are formed and the stability of the finished product decreases strongly.

When the zinc chloride content is 2 2, calculated on the weight of urea, slurries and non-liquid products are formed. In this patent it is emphasized that in the case of a zinc chloride content of less than 62, calculated on the weight of urea, stable liquid products cannot be obtained.

Zinc chloride is used in this patent as well as in other patents, for example in U.S. Pat. No. 2,098,022, relating to pulps impregnated with such urea-ZnCl-formaldehyde resins, in amounts that are rather an additional component substances and not the additive. This is already emphasized in the name of the resin, urea-ZnCl ₂ -formaldehyde resin.

The function of zinc chloride when added to urea and formaldehyde is explained as an analogy to the function of sulfur when added to rubber.

The process according to the invention yields liquid stable products which are characterized by a high cure rate, low toxicity and a prolonged shelf life of the solution.

In the classical two-stage synthesis of urea-formaldehyde resins by known methods, the condensation is carried out in 90 minutes to give a product having a free formaldehyde content of 2X and a methylol group content of 18 to 20 Z.

Condensation by the process of the invention in the presence of catalytic amounts of zinc chloride makes it possible to substantially reduce the duration of the process. Table 1 below shows data showing the effect of individual amounts of zinc chloride on the duration of the condensation.

Table 1

Reaction time of urea with formaldehyde in min

The amount of ZnCl ₂ in parts by weight. per 100 parts by weight. urea.

0.05 0.15 0.25 0.3

Content in Z wt.

methylo- lové groups free formal- dehyd methylo- lové groups free formal- dehyd methylol groups free formal- dehyd methylo- lové groups free formal- dehyd 5 6.79 15.33 8.90 11.31 12.48 9.03 ’ 13.27 8.26 10 15.10 8.04 17.54 4.08 18.61 3.81 19.44 . 3.47 15 Dec 19.06 3.73 22.34 2.36 20.71 1, 81 20.05 1, 72 20 May 22,00 2.41 20.12 2, 03 16.27 1, 42 15.42 1, 35 30 19.81 1.97 14.90 1, 30 5.91 1,28 8.20 1.31 45 9.65 1.26 8.97 1, 29 8.84 1,28 8.90 1, 34 60 9.00 1.30 8.7 1, 32 8.83 1, 28 8.82 1.29 From these data is obviously is possible get for presence chloride zinc already

after 30 to 15 minutes of condensation, a condensation solution having parameters analogous to those of conventional processes and which represents the final degree of reaction - the content of methylol groups and free formaldehyde. This means that the reaction rate of the reaction of formaldehyde with urea increases with increasing catalyst.

Since the addition of urea to formaldehyde in the presence of zinc chloride proceeds at a high rate and in a weakly acidic medium, there has been the possibility of developing a one-step highly productive process for producing urea-formaldehyde resins based on simultaneous addition and condensation processes.

However, it was essential not only to develop an intensive technological process for the production of these urea-formaldehyde resins, but also to ensure the production of resins of such properties as to meet current consumer requirements. The use of zinc chloride as a catalyst in the reaction, while maintaining other parameters, makes it possible to produce such resins. Table 2 below provides data demonstrating the effect of different doses of zinc chloride on the properties of synthetic resins.

202990 4

Table 2

Properties Quantity of ZnCl in parts by mass per 100 parts by mass of urea

formaldehyde resins 0.05 0.10 0.15 0.20 0.25 <5.30 0.35 0.40 relative viscosity, sec. 25 43 60 72 81 '89 99 123 concentration of hydrogen ions / pH value / 6.8 6.8 7.1 7.0 7.0 7.0 6.85 6.9 free formaldehyde content in 0.93 0.72 0.60 0.56 0.51 0.45 0.38 0.35 content of methylol groups in 22.4 16.7 13.3 13.1 10.2 9.6 9.07 8.82 content of auché substance in 64.8 66.0 65.2 65.5 65, 0 65.3 65.2 65.9 cure time of solution at 100 C, sec. 24 31 40 43 49 61 74 86 solution shelf life at 20 ± 1 ° C, hr. 9 13 18 20 May 24 25 27 Mar: 33 The relative viscosity was measured to viskoi zímetru s diameter nozzles 4 mm.

From these values, it is clear that zinc chloride promotes an increase in the shelf life of the urea-formaldehyde resin glue at room temperature by increasing the stability of the system, but its curing time at 100 ° C is reduced.

At the same time, it can be seen that the intensification of the urea-formaldehyde resin production process, which, inter alia, has a high curing rate along with an increased service life at a low content of free formaldehyde, is ensured by using well-defined doses of zinc chloride.

The use of zinc chloride as a catalyst makes it possible to carry out the condensation in one step instead of the classical two-step process and further to reduce the condensation time from conventional

1.5 hours for 15 to 30 minutes. In addition, the use of zinc chloride as a catalyst in the condensation process results in stable products even at such a small condensation time. By using zinc chloride in said catalytic amounts, it was possible to obtain both a rapidly curing carbamide resin having a high solution cure speed of 40 sec at 100 ° C, an increased solution pot life of at least 10 hours at 20 ± 1 ° C, and low content of free formaldehyde - below 0.8% and on the other hand slightly poisonous resins with a content of free formaldehyde not more than 0.3 2 at curing time not more than 55 sec.

The zinc chloride is easy to process, well soluble in water, allowing it to be used in a continuous process for producing urea-formaldehyde resins without any difficulty. Another technological advantage of using the catalyst according to the invention is that the pH of its solution is higher than the pH of the acid solutions that are used as the catalyst in the acid degree of condensation in current large-scale production. This prevents the formation of coagulate during the phase of catalyst introduction into the condensation solution. The formation of such coagulates leads to regular blockage of the pipeline and shutdown of the apparatus to remove the coagulate.

Thus, an intensified process for the production of urea-formaldehyde resins having a high curing speed, a long solution life and a low content of free formaldehyde has been developed.

The process according to the invention for the production of urea-formaldehyde resins has been elaborated in two variants - continuous and non-continuous and represents a one-step process of reacting urea with formaldehyde in an aqueous solution while heating. The use of zinc chloride makes it possible to intensify the process by about twice, and allows the production of rapidly curable and slightly poisonous resins with an increased pot life.

By using rapidly curable and slightly poisonous urea-formaldehyde resins in the manufacture of particle board, the pressing time is reduced and thus the amount of product is increased by 15-20%. The use of only slightly toxic urea-formaldehyde resins also improves the hygienic conditions in the manufacture and use of the fiber boards. Boards made on the basis of these weakly toxic urea-formaldehyde resins are widely used in private construction and construction.

The use of fast-curable urea-formaldehyde adhesive resins, for example when fastening furniture parts in presses, enables to increase press performance by reducing the dwell time of the press parts by two to three times and ensures smooth operation throughout the work shift due to long shelf life. The resin prepared according to the invention can be used not only for rapid veneering, but also for gluing furniture and other parts made of wood materials under contact or high-frequency heating. In addition, this resin can be used in the manufacture of veneer wood, joinery and building components and other parts.

The process for producing the urea-formaldehyde resins according to the invention is technologically simple and can be carried out advantageously in the following manner.

As the starting material for the production of urea-formaldehyde resins according to the invention, solid urea or, at elevated temperature, a liquid urea intermediate product having a base content of at least 70 Z - a urea melt is used. The best technical-economic parameters are usually exhibited by a continuous process with high individual outputs, in which a liquid intermediate of urea production is used.

A urea solution in neutralized formalin or a mixture of urea melt and formalin is continuously fed to a reactor equipped with a stirrer, a thermometer and a reflux condenser. The zinc chloride solution is continuously fed into the same reactor. The temperature of the reaction mixture is 70 to 98 ° C, the pH is 4.5 to 5.5, the residence time of the reaction mixture in the reactor is 20 to 45 minutes. The resulting condensation solution is neutralized and introduced into an evaporation apparatus, where it is evaporated under vacuum or at atmospheric pressure until the desired dry matter content. Urea and, if necessary, stabilizing additives are added to the resulting solution.

'' O

That is, the post-condensation step, which is carried out at a temperature of 50 DEG to 65 DEG C. The process according to the invention does not preclude the post-condensation after neutralization even before the solution evaporates, i.e. before drying. This makes it possible to reduce the loss of formaldehyde and also to reduce its content in the distillate by about 10 times. The resin obtained is cooled and transferred to a finished product warehouse where it is filled into tanks, drums and containers for shipment to consumers.

In the discontinuous process according to the invention, formalin is introduced into a reactor equipped with a stirrer, a thermometer and a reflux condenser, neutralized with an alkaline solution and the reaction mixture is heated to the boiling point of the mixture after addition of urea and zinc chloride. 5. The resulting condensation solution was neutralized to pH 7.0-8.5 and then evaporated to the desired dry matter content. The post-condensation step can be carried out both before _? after evaporation. The resulting resin is cooled and filled into containers for shipping to the consumer.

In order to further understand the process of the invention, examples of a process for producing urea-formaldehyde resins are given below.

He did

A 3-neck flask equipped with a stirrer, reflux condenser and thermometer was charged with 405 g of 37% formalin neutralized with 1 N sodium hydroxide solution. Then 166.8 urea was added to the flask. The resulting mixture was stirred for 30 minutes at 20 ° C and the resulting solution had a pH of 7.75. Then, 0.33 ml of a 50% aqueous zinc chloride solution was added to the flask, dropping the pH of the solution to 6.74. The contents of the flask were heated in a water bath to 96 ° C, pH 5.2. Condensation was performed under these conditions within 30 minutes. The pH of the condensation solution was 5.1. The resulting condensation solution was cooled to 60-70 ° C, neutralized with 1 N sodium hydroxide solution to pH 6.8, and a second portion of urea - 32.7 g as a solution was added. The additional condensation was carried out at 50-65 ° C for 30 minutes, after which water was removed at 65-70 ° C and diluted to a refractive index of 1.462,

The resin obtained had the following properties:

concentration of hydrogen ions - pH value 7.25 relative viscosity at 20 ° C, sec. 31.4 content of free formaldehyde in 2 wt. 0.63 content of methylol groups in 2 wt. 14.2 dry matter content in 2 wt. 65,6 solution cure time at 100 ° C, in sec. 31, solution storage time at 20 ° C, in 15 hours

Example 2

A three-necked flask equipped with a stirrer, reflux condenser and thermometer was charged with 405 g of 372 formalin, neutralized with 1 N sodium hydroxide solution. 166.8 g of urea were then added. The resulting mixture was stirred for 30 minutes at room temperature, then the pH of the solution was adjusted to 7.7. Then, 0.33 mL of 502 zinc chloride solution was added, dropping the pH to 5.9, and the contents of the flask were heated in a water bath to 96 ° C. The pH was 4.85. The condensation solution was cooled to 65-70 ° C and neutralized with 1N sodium hydroxide solution to pH 7.4. Water was removed at 65-70 ° C and diluted to refractive index 1.458. After drying, additional condensation was performed at 65 ° C for 20 minutes; to this end, 32.7 g of urea as a 702 solution were added.

The resin obtained had the following properties;

concentration of hydrogen ions - pH value 7.35 relative viscosity at 20 ° C, sec. 33.5 content of free formaldehyde in 2 wt. 0.48 content of methylol groups in X wt. 14.0 dry matter content in 2 wt. 64,5 o

solution cure time at 100 ° C in sec, 32 solution storage time at 20 ° C in hr 17.

Example 3

A three-necked flask equipped with a stirrer, reflux condenser and thermometer was charged with 607 g of 372 formalin and 279 ml of 722 urea melt. After the addition of 0.5 ml of 502 zinc chloride solution, the resulting reaction mixture was heated to a water temperature at 70-80 ° C and a pH of 5.01 and then neutralized with 1N sodium hydroxide solution to a pH of 6.96. On post-condensation, a second portion of urea melt was added in an amount of 54.6 ml at 50-65 ° C over 30 minutes, after which the water was removed at dilution to a refractive index of 1.462.

The resin obtained had the following properties:

concentration of hydrogen ions - pH value 7,08 relative viscosity at 20 ° C, sec. 28,9 content of free formaldehyde in Z wt. 0,6 content of methylol groups in Z wt. 11.15 dry matter content in Z wt. 65.0. 'cure time of solution at 100 ° C per sec.' 28 shelf life of the solution at 20 ° C in hours 13

He attaches

A three-necked flask equipped with a stirrer, reflux condenser and thermometer was charged

607.5 g 372 formalin and 279 ml 722 urea melt were added 0.5 ml 502 zinc chloride solution. The resulting reaction mixture was heated in a water bath at 96-98 ° C and at pH 5.02 for 30 minutes. It was then neutralized with 1 N sodium hydroxide solution to pH 7.18. Water was removed by heating and diluting to a refractive index of 1.464. A second portion of the urea melt was then added in an additional condensation amount of 54.6 ml. This additional condensation was carried out at a temperature of 50 to 65 ° C.

The resin obtained had the following properties:

concentration of hydrogen ions - pH value 6.64 relative viscosity at 20 ° C, sec. 23.5 content of free formaldehyde in Z wt. 0.64 content of methylol groups in Z wt. 12.74 dry matter content in Z wt. 64.7 cure time of the solution at 100 ° C in sec. 36 storage time of the solution at 20 ° C in hours 12

Example 5

A three-necked flask equipped with a stirrer, reflux condenser and thermometer was charged

607.5 g of 37Z formalin and 279 ml of 72Z urea melt. Then, 0.7 ml of a 50Z zinc chloride solution was added and the reaction mixture was heated for 30 minutes at 96-98 ° C and a pH of 4.96, then neutralized with 1N sodium hydroxide solution to a pH of 6.75. The water was removed at dilution to a refractive index of 1.462 and postcondensation was carried out at a temperature of 50-65 ° C when 54.6 ml of urea melt were added.

The melt obtained had the following properties:

concentration of hydrogen ions - pH value 6.51 relative viscosity at 20 ° C, sec. 57, free formaldehyde content in Z wt. 0.37 content of methylol groups in Z wt. 13.1 dry substance content in Z wt. 67.2 cure time of solution at 100 ° C in sec. 39 storage time of solution at 20 ° C in hr. 21

Example

A three-necked flask equipped with a stirrer, reflux condenser and thermometer was charged with 270 g of 37 Z formalin, neutralized with 1N sodium hydroxide solution. Then 111.2 g of urea were added. The pH of the mixture after dissolution was 8.05. To the reaction mixture was added 0.1 g of a 50Z zinc chloride solution and the mixture was heated on a water bath for 30 minutes at 96-98 ° C and pH 4.95. The condensation solution was neutralized with 1N sodium hydroxide solution, cooled to 65 ° C, then a second portion of urea (21.8 g) was added in the form of a 70Z solution, followed by condensation at this temperature. Water was removed at 65 ° C and diluted to refractive index of 1,460. ·

The resin obtained had the following properties:

concentration of hydrogen ions - pH value 7.35 relative viscosity at 20 ° C, sec. 18 content of free formaldehyde in Z wt. 0,8 content of methylol groups in Z wt. 18.1 dry matter content in Z wt. 63.0 cure time of the solution at 100 ° C in sec 28 storage time of the solution at 20 ° C in hr 10.

Example7

To a three-necked flask equipped with a stirrer, reflux condenser and thermometer was charged 6.95 g of 37% sodium hydroxide-neutralized formalin and 340 g of urea was added. 0.47 g of solid zinc chloride was then added and the contents of the flask were heated in a water bath at 96-98 ° C and at a pH of 4.7-5.1. The resulting condensation solution was neutralized, water was removed to a refractive index of 1.469, and 97.8 g of urea melt were added for additional condensation. The additional condensation was carried out at a temperature of 50 to 65 ° C.

The resin obtained had the following properties:

concentration of hydrogen ions - pH value 6.7 relative viscosity at 20 ° C, sec. 121 free formaldehyde content in% by weight 0,6 content of methylol groups in% by weight 18.3 dry matter content in X wt. 67 cure time of the solution at 100 ° C in sec. 36 storage time of the solution at 20 ° C in hr 11

Example

81.4 kg of 36.5% formalin neutralized to pH 7.65 were charged to the stirrer-reflux reactor and 27 kg of urea were added. 50 g of a 50% zinc chloride solution were added to the reaction mixture and the condensation was carried out at boiling point. When the desired water number was reached, the condensation solution was neutralized, water was removed to a refractive index of 1.470 and an additional 7.3 kg of urea was added for further condensation. This subsequent condensation took place at a temperature of 50 to 65 ° C,

The resin obtained had the following properties:

concentration of hydrogen ions relative viscosity at 20 free formaldehyde content methylol group content dry matter content% by weight solution curing time p shelf life th

pH value 6.8 C _of sec. 1 10 % wt. 0.72 % wt. 20.4. 65 ^l at 100 ° C sec. 34 at 20 ° C in hr. 10.5

Example 9

A three-necked flask equipped with a stirrer, stirrer, reflux condenser and thermometer was charged with 270 g of 37% formalin neutralized with 1N sodium hydroxide solution. Then 100 g of urea and 0.285 g of a 50% zinc chloride solution were added, the mixture was heated to 96-98 ° C and condensed for 30 minutes at pH 4.7-5.2. The condensation solution was neutralized to pH 7.2 and water was removed at 65-70 ° C and diluted to refractive index 1.462. 43 g of urea were then added to the condensation. This second condensation was run for 30 minutes at 50-65 ° C.

The resin obtained had the following properties:

concentration of hydrogen ions - pH value 7.5 relative viscosity at 20 ° C, sec. 36 content of free formaldehyde in% wt. 0,21 content of methylol groups in% by weight 18,0 dry matter content in% wt. 64 cure time of the solution at 100 ° C in sec. 48 storage time of the solution at 20 ° C in hours 18

Example 10

A three-necked flask equipped with a stirrer, reflux condenser and thermometer was charged with 270 g of 37% formalin neutralized with alkaline solution, 0.285 g of 50% zinc chloride solution and 140 g of 72% urea melt. The mixture was heated and condensation was carried out at 96-98 ° C, at a pH of 4.8-5.1. Then the condensation solution was neutralized, water was removed at 65 ° C and diluted to refractive index of 1.463, then 65 g of urea melt were added for subsequent condensation. This second condensation was carried out at a temperature of 50 to 65 ° C.

The resin obtained had the following properties:

concentration of hydrogen ions - pH value 7.4 relative viscosity at 20 ° C, sec. 34 content of free formaldehyde in Z wt. 0.26 content of methylol _x groups in Z wt. 14.1 dry matter content in Z wt. 65.4 cure time of solution at 100 ° C in sec. 47 storage time of solution at 20 ° C in hr 22

Claims (1)

SUBJECT OF THE INVENTION A process for producing urea-formaldehyde resins by reacting urea with formaldehyde at 70-98 ° C in the presence of zinc chloride in a condensation solution, neutralizing, evaporating and further reacting the intermediate with urea at 50-65 ° C, wherein the reaction with urea after neutralization is carried out before or after evaporation of the condensation solution, characterized in that zinc chloride is used in an amount of from 0.05 to 0.15 parts by weight per 100 parts by weight. urea.