JPS60217227A - Preparation of urea-formaldehyde precondensate - Google Patents

Abstract

PURPOSE:To obtain the titled condensate useful for increasing non-transparency of paper, useful as an additional matter for improving high polymer material such as natural rubber, etc., having improved shelf stability and a high solid content, obtained by reacting urea with formaldehyde in a specific ratio under specified conditions, regulating a solid content. CONSTITUTION:1.0mol urea is condensed with 1.7-4.0mol formaldehyde at 3- 6pH at 20-100 deg.C for preferably 2-4hr, and solid content in the reaction product is adjusted to 30-70wt%, give the desired condensate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a urea-formaldehyde precondensate which serves as an intermediate raw material for crosslinked urea-formaldehyde polymers that can be used as additives for modifying natural and synthetic polymeric materials.

Conventional cross-linked urea-formaldehyde polymers are used as reinforcing agents for natural and synthetic rubber, thixo-i and lobbying agents for paints,
It is known to be used as a paper quality improver.

Regarding the manufacturing method of cross-linked urea formaldehyde polymer, for example, Japanese Patent Publication No. 51'-23801 describes a one-step method and a two-step method.
A process method is disclosed. In the 1-step method, all reaction components and process additives are added first and the reaction is allowed to proceed until a directly cross-linked, insoluble, infusible urea-formaldehyde polymer gel is formed. In this case, it is difficult to control the reaction and it is difficult to obtain a steady reaction product, so it is hardly used industrially.

The two-step process consists of a first step in which urea is reacted with formaldehyde in aqueous solution to form an aqueous precondensate, and a first step in which urea is reacted with formaldehyde in an aqueous solution to form an aqueous precondensate in the presence of a suitable curing catalyst and at an elevated temperature. There is also a method comprising a second step of producing an insoluble and infusible product in the form of a gel or precipitate by curing the condensate. In addition, in Japanese Patent Publication No. 46-28087, sulfamic acid or various water-soluble ammonium hydrogen sulfates were added to an aqueous solution of a precondensate (initial condensate) of urea and formaldehyde, and crosslinked urea was used as a reinforcing filler for elastomers. A method for producing a formaldehyde polycondensation product is disclosed in JP-A-57-53518.
Also, after mixing formaldehyde aqueous solution, urea, carboxymethyl cellulose, and water, P)l was adjusted with caustic soda water and reacted to obtain an initial condensate, and several percent of 1i & acid aqueous solution was added to this to form a cross-linked urea-formaldehyde polymer. A method of obtaining a dispersion of particles is disclosed.

Performing the reaction in two steps in this way is an extremely advantageous method from a reaction engineering and industrial perspective in order to impart target chemical and physical properties to the final product, and is commonly used. This is how it is done.

Furthermore, as an embodiment, the first step can be carried out in a fully equipped factory capable of mass production, and the second step can be carried out by each user, in which case cross-linked urea formaldehyde polymer is used as an additive. This is because, since the polymer is usually used in the form of a dispersion in water, precipitation and drying steps are not required, and the product can be managed according to each purpose.

In such cases, the sulfate produced in the first step has good storage stability, has a high solids content, and is suitable for initial condensation without interfering with the reaction in the second step, that is, the reaction after catalyst addition. It is required that it be a thing.

Considering the reaction conditions of the first step from these points of view, in the aforementioned Japanese Patent Publication No. 4B-28087, urea 1.0
Formaldehyde 1.0-2.0 mol per mol, PH6
~θ, temperature 40-100°C, JP 13?157-535
In No. 19, 1 formaldehyde per 1.0 mole of urea
．． 4-1.9 mol, P)l 8-lO1 temperature 10°-9
Initial condensates are produced at 5°C, and these initial condensates (hereinafter the condensates of the first step are referred to as initial condensates) are substantially still at the stage of urea adducts (methylolated products). Because of this, storage stability is problematic. In other words, at 30'O, a white poorly soluble precipitate is observed within 2 days, and at temperatures below 10°C, a large amount of soluble precipitate is generated, which is not only inconvenient to handle, but also requires the second step if one reaction has proceeded. It also interferes with the reaction. The solid content of the initial condensate is usually about 28%, and if the reaction is carried out under conditions that increase the solid content, the storage stability will further deteriorate.

In view of these circumstances, we investigated various reaction conditions and found favorable conditions for the purpose of obtaining an initial condensate with excellent storage stability and a high solid content.

It was recognized that the filling obtained using this initial condensate also exhibited unexpected effects, and this led to the completion of the present invention.

That is, the composition of the present invention has a charging ratio of 1.7 to 4.0 mol of formaldehyde per 1.0 mol of urea, and a pH of 3.
~6. A method for producing a urea formaldehyde initial condensate, which is characterized by carrying out a condensation reaction under reaction conditions such that the temperature is 20 to 100°C and the solid content in the reaction product is 30 to 70% by weight. .

It is already known that factors involved in the formation of a urea-formaldehyde initial condensate are the molar ratio of urea and formaldehyde and the PI3 temperature. As a result of various studies regarding these factors, the following was clarified.

That is, by reacting on the acidic side, the adduct (
methylene compound) to a condensate (methylene compound), reducing the number of methylol groups that are reactive groups, increasing stability during storage, and having a low molar ratio (mole ratio of formaldehyde to urea). and an insoluble precipitate is formed, which deteriorates the performance of the final target additive, and if the molar ratio is too high, the intramolecular dehydration condensation reaction proceeds and by-products that do not react with urea are generated. It turned out to be a disadvantage.

These will be explained in more detail.

(1) Number of moles of formaldehyde per mole of urea (
When F/U (hereinafter referred to as F/U) is less than 1.7, insoluble precipitable precipitates are generated during the reaction to obtain the initial condensate, which deteriorates the performance of the final target additive. Furthermore, when F/U exceeds 4.0, intermolecular methylenation reaction becomes difficult to occur, and at the same time, a reaction inert substance, that is, a uron ring, is generated due to intramolecular dehydration condensation, and the yield of the desired initial condensate product decreases. This is disadvantageous. In addition, the urea and formaldehyde can be added all at once or in two or more portions.

(2) When the pH exceeds 6, methylenation is difficult to occur;
Storage stability is poor because a large amount of methylol is produced. Furthermore, if the pH is less than 3, poorly soluble sedimentary precipitates are produced as by-products, which deteriorates the performance of the final target additive.

In addition, it is also possible to proceed with methylolization by setting the pH to the alkaline side at the beginning of the reaction, and then to carry out the reaction by setting the pH to 3 to 6.

(3) Regarding the temperature, the upper limit for the reaction at normal pressure is 1
If the temperature is lower than 20°C, the methylol compound will precipitate during the reaction, and the reaction time will become significantly longer, which is not practical.

(4) The reaction time is determined by the pH and temperature during the reaction, and is usually 2 to 3 minutes at a pH of 4 to 5.80°C.
It's time.

(5) Concerning the concentration of solid content at the end of the reaction, if the solid content exceeds 70% by weight, storage stability will deteriorate, and if it is less than 30% by weight, there will be disadvantages in terms of storage and transportation. To adjust the concentration of solid content, conventional concentration methods and water addition methods can be used.

The solid content is the weight of the remaining liquid after taking approximately 0.5 g of the product after the reaction and drying it at 105°C for 3 hours, expressed as a percentage of the weight before drying. .

Note that melamine, benzoguanamine, acetoguanamine, spiroguanamine, phenylacetoguanamine, dicyandiamide, or cyanamide may be used in place of one part of urea, and acetaldehyde, acrolein, crotonaldehyde, glyoxal, or furfural may be used in place of one part of formaldehyde. It is possible.

The present invention will be further explained below with reference to Examples.

Examples 1 to 7 In Example 1, 1.2 parts of sodium salt of carboxymethyl cellulose (all parts by weight hereinafter) were added to 37%
Dissolve in 78.1 parts of formalin, add 20.7 parts of urea, add dilute sulfuric acid, keep the pH at 4.5 using an ordinary glass electrode PH meter, and react at a temperature of 7°C for 2 hours. Then, the concentration was adjusted by concentration and dilution to obtain a reaction product, that is, an initial synthesized product. In this case, F/U of the initial condensate is 2.8. The solid content was measured using the method described above, and the temperature was maintained at 40'C and 10C to determine the number of days until precipitates were visually observed.

In parallel with this, 108 parts of a 12.5% urea aqueous solution and 280 parts of 2.3% dilute sulfuric acid were added to 100 parts of the initial condensate aqueous solution (solid content 55% by weight) before any precipitates were observed, and after mixing, approximately It was left at 70°C for 20 minutes. Obtained gel material 46
After roughly crushing 8 parts with a stainless steel rod, 400 parts of water was added and stirred with a propeller type stirring blade for about 2 hours to form a slurry. Add to this 28% ammonia water 12
After reacting for 60 minutes, the pH of the system was adjusted to 7 to 8, and the mixture was further pulverized in a mill under Colloid to obtain a dispersion of crosslinked urea formaldehyde polymer particles. This dispersion was filtered and vortexed, and after drying, the particle size was measured using an electron microscope. In addition, the obtained dispersion of crosslinked urea formaldehyde particles was prepared so that the weight of the polymer particles contained therein was 1 part per 100 parts of dry pulp weight of bleached hardwood pulp (LBKP).
It is added to the pulp slurry so that it is 0 parts, and paper is made using a square sheet machine under normal paper making conditions, for example, using 1 part of 0 gin-based sizing agent and 3 parts of sulfuric acid per 100 parts of dry pulp. The opacity of the paper was measured. The basis weight of the paper was adjusted to 75 gr/m2. Opacity can be measured using Hunter method, for example, JIS P
813B.

The above measured values are listed in Table 1 together with the reaction conditions for preparing the initial condensate.

In Examples 2 to 7, the reaction conditions F/U, PI3 temperature, and reaction time were as shown in Table 1, and the solid content, storage stability, and packing content of the obtained initial condensate were The performance was measured in the same manner as in Example 1, and the measurement results are shown in Table 1.

Comparative Example An example of the conventional method was carried out in comparison with the above example and is shown in Table 1.

As is clear from the above Examples and Comparative Examples, the initial condensate obtained by the present invention has excellent storage stability, and the filler prepared from the initial condensate obtained by the present invention has a low paper opacity. We also obtained the unexpected result of increasing 0 , and the method of the present invention
"Industry" - something of extremely great value.

Claims (1)

[Claims] In proceeding with the condensation reaction of urea and formaldehyde in an aqueous solution, the charging ratio is 1.7 to 4.0 mol of formaldehyde per 1.0 mol of urea, the pH is 3 to 6, and the temperature is 2.
0~100'C! 1. A method for producing a urea formaldehyde initial condensate, which comprises reacting the product with a solid content of 30 to 70% by weight.