JPH0365804B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for producing crosslinked urea formaldehyde polymer particles useful as paper fillers. <Prior Art> It is known that fine cross-linked urea-formaldehyde polymer particles are added to paper as a so-called filler for the purpose of improving paper properties such as opacity. Methods for producing such particles are also known. For example, in Japanese Patent Publication No. 57-26686, a specific urea formaldehyde initial condensate and an acidic aqueous solution are mixed under specific conditions, the mixed solution is continuously fed onto a rotating endless belt, and reaction solidification is performed on the belt.
A method for producing crosslinked urea formaldehyde polymer particles is disclosed, which is characterized in that the produced polymer is then taken out, and the particles produced in this way are, for example, made into a slurry, neutralized, and further agglomerated in a pulverizer. It is stated that it can be unraveled and used as a filler for paper. <Problems to be Solved by the Invention> The crosslinked urea formaldehyde polymer particles thus obtained are an aqueous dispersion. However, aqueous dispersions are inconvenient to transport and store, and require a large amount of cost. This is particularly disadvantageous when the manufacturing plant for such filler and the paper mill that uses it are located far apart. For this reason, the dispersion liquid is filtered to form a cake, which is convenient for transportation and storage, and then redispersed and used during papermaking. By the way, the cross-linked urea formaldehyde polymer particles used as paper filler have an average particle diameter of 0.1~
Individual particles (hereinafter referred to as primary particles) of 1.0μ are aggregated to an average size of 1 to 30μ (hereinafter referred to as secondary particles). Regarding the average primary particle diameter being 0.1 to 1.0μ, the
-26686, but at the same time the average secondary particle size must be in the range 1-30μ, preferably 1-10μ. That is, the average secondary particle diameter is
If it is less than 1μ, the paper retention rate during paper making will decrease, making it impossible to obtain the desired paper performance. On the other hand, if the average secondary particle diameter exceeds 30μ, although the yield rate is high, the dispersion in the paper is insufficient, and as a result, the desired paper performance cannot be obtained. This is extremely important; even if the average primary particle size is in the range of 0.1 to 1.0μ, if the average secondary particle size is outside the range of 1 to 30μ, the paper filler of crosslinked urea formaldehyde polymer particles The performance as When the crosslinked urea formaldehyde polymer particles are cake-like, the diameter of the dispersed particles when redispersed in a pulp slurry or the like becomes the secondary particle diameter. Therefore, the average primary particle diameter of cake-like crosslinked urea formaldehyde polymer particles is determined by the reaction conditions of the urea formaldehyde initial condensate and the acidic aqueous solution, but the average secondary particle diameter is determined by the process of pulverizing the dispersion and the pulverizing process. The present inventors have newly discovered that this is determined by the conditions of the process in which the material is passed.
In other words, the inventors have found that under stirring conditions such as those used to prepare pulp slurry, the average secondary particle diameter is hardly affected by such stirring conditions, and is almost uniquely determined by the conditions of the pulverization and passing steps. This became clear. The object of the present invention is to provide a method for producing a cake of cross-linked urea-formaldehyde polymer particles having an appropriate average secondary particle size as a paper filler by selecting appropriate grinding and pulverization conditions in the production of cross-linked urea-formaldehyde polymer particles. It is about providing. <Means for Solving the Problems> That is, the present invention reacts an initial condensate of urea and formaldehyde with an acidic aqueous solution, and then forms a slurry of the dispersion, which has an average particle diameter of 0.1 to 1.
In a method for producing a cake consisting of fine cross-linked formaldehyde polymer particles in which individual particles of 1.0μ have aggregated to an average size of 1 to 30μ, the slurry-formed dispersion is pulverized by an impact pulverizer, and then continuously This is a method for producing a urea resin filler, which is characterized by forming a cake in a type vacuum filtration device. Generally, industrially used crushers include ball mills, vibrating ball mills, special ball mills, impact crushers, roller mills, jet crushers, and colloid mills. Even if only a type pulverizer is used and other pulverizers are used, a filler having an average secondary particle size suitable for paper filler cannot be obtained. The impact crusher may be of a screen type, an axial flow type, a rotating disk type, etc., and any of them may be used, and a pin type mill, which is a type of rotating disk type, is particularly desirable. In addition, there are generally pressurized devices and vacuum devices, but in order to achieve the object of the present invention, a vacuum device is required. When a pressurizer is used, the average secondary particle size not only exceeds 30μ, but sometimes when used as a filler in paper, it becomes lumpy and significantly reduces the commercial value of the paper. Furthermore, the vacuum filtration device must be of a continuous type, and a batch type would complicate the work of forming a cake, making it unsuitable for industrial-scale production. The continuous vacuum strainer may be a cylindrical type, a disk type, or a horizontal strainer such as a table, pan, or belt type, and an Oliver type strainer, which is a type of cylindrical type, is particularly preferred. Both the crusher and the strainer must be as described above; if only one is as described above, the object of the present invention will not be achieved. The cross-linked urea-formaldehyde polymer dispersion in the present invention is prepared by reacting an initial condensate of urea-formaldehyde with an acidic aqueous solution to form a slurry. The initial condensate is usually prepared in a ratio of 1 to 2.5 moles of formaldehyde to 1 mole of urea.
The reaction was carried out at a pH of 4 to 9 and a temperature of 40 to 100°C. Examples of the acidic aqueous solution used include mineral acids such as sulfuric acid, hydrochloric acid, and nitric acid, organic acids such as oxalic acid, chloroacetic acid, and maleic acid, sulfamic acid, and ammonium hydrogen sulfate. The initial condensate reacts by mixing with an acidic aqueous solution to obtain an aggregate of cross-linked urea-formaldehyde polymer particles, which is coarsely ground and, if necessary, water is added to obtain a dispersion of cross-linked urea-formaldehyde polymer particles. . This is usually neutralized with an alkali such as caustic soda. <Function> In the present invention, the pulverization is carried out using an impact pulverizer, and the step of filtration into a cake is carried out using a continuous vacuum filtration machine, so that when the cake is redispersed, the average secondary particle size is 1 to 30μ. Therefore, a urea resin filler desirable as a filler for paper can be obtained. <Example> Examples will be described below. Production example: Mix 38.4 parts of a 37% formaldehyde aqueous solution (all percentages hereinafter refer to weight percent), 18.9 parts of urea, 0.7 parts of carboxymethyl cellulose, and 42.0 parts of water, and make 20% caustic soda water. The pH was adjusted to 7 and the reaction was carried out at 70°C for 2 hours to obtain a urea formaldehyde initial condensate. 180 parts of a 2.7% sulfuric acid aqueous solution was added to 100 parts of this initial condensate, mixed, and left for 1 hour. The resulting gel was coarsely ground and stirred to obtain a crosslinked urea formaldehyde polymer particle dispersion. When this dispersion was observed under a scanning electron microscope after drying, it was found to be aggregates with an average particle size of 0.2 μm. This dispersion liquid was used in all subsequent Examples and Comparative Examples. Example 1 The dispersion of the production example was ground with a pin mill and then passed through an Oliver filter to obtain a solids content of 21.5%.
A cake-like urea resin filler was obtained. After dispersing this filler in water using a stirrer, the average secondary particle size was measured using a Coulter counter and found to be 4.1 μm. This filler is hereinafter referred to as Example 1 filler. Example 2 The solid content was determined in the same manner as in Example 1 except that a belt filter was used as the filter and a micro pulverizer was used as the rotary disk type impact crusher.
A cake-like urea resin filler having a content of 20.8% was obtained. The average secondary particle diameter of this filler was measured in the same manner as in Example 1 and was found to be 8.5μ. This filler is hereinafter referred to as Example 2 filler. Comparative Example 1 A cake-like urea resin filler having a solid content of 21.2% was obtained in the same manner as in Example 1, except that a ball mill was used as the crusher. The average secondary particle diameter of this filler was measured in the same manner as in Example 1 and was found to be 36μ. This filler is hereinafter referred to as Comparative Example 1 filler. Comparative Example 2 A cake-like urea resin filler having a solids content of 21.3% was obtained in the same manner as in Example 1 except that a colloid mill was used as a pulverizer. The average secondary particle diameter of this filler was measured in the same manner as in Example 1 and was found to be 0.8μ. This filler is hereinafter referred to as Comparative Example 2 filler. Comparative Example 3 A cake-like urea resin filler having a solids content of 21.3% was obtained in the same manner as in Example 1 except that a filter press was used as the filter. The average secondary particle diameter of this filler was measured in the same manner as in Example 1 and was found to be 42μ. This filler is hereinafter referred to as Comparative Example 3 filler. Application Example Table 1 shows the results of paper making using the filler of Example 1 and the fillers of Comparative Examples 1 to 3. The paper was made as follows. Namely N.
1% pulp slurry with freeness (CSF) 330ml containing 30 parts BKP, 30 parts TMP and 40 parts RGP
Add 2 parts of a 20.0% aluminum sulfate aqueous solution in terms of Al ₂ (SO ₄ ) _{3.18H 2} O to 2000 parts and stir for 2 minutes. Subsequently, 1 part of each urea resin filler was added on a dry weight basis and stirred for 5 minutes to obtain a prepared slurry. Next, paper is made using a TAPPI square sheet machine.
After drying the wet paper obtained by press dehydration using a drum dryer with a surface temperature of 110℃, a linear pressure of 40Kg/cm was applied.
Passed through the calendar twice at 65% humidity and 20% temperature.
Seasoned for 24 hours in a constant humidity and constant temperature room at ℃.
I got processed paper. The physical properties of these pressurized papers were measured and shown in Table 1.
Note that the physical properties were measured by the following method. The basis weight was measured and calculated according to JIS (P-8111). The stiffness was calculated by measuring the thickness of the paper according to JIS (P-8118) and using the formula (basis weight/thickness) x 1000. The white paper opacity is based on the literature (Paper Technology Times, Showa
It was measured according to the method described in September 1952 issue, pages 1 to 13).

[Table] <Effects> As is clear from Table 1, in Example 1 according to the method of the present invention, a urea resin filler having an average secondary particle size suitable as a paper filler was obtained, and this was used to make paper. The pressurized paper produced by this method has excellent white paper opacity, but in Comparative Examples 1 to 3, which are not based on the present invention, the average secondary particle diameter of the obtained filler was in an inappropriate range as a filler for paper, and it was difficult to use it. The white paper opacity of the paper made using this method is inferior.

Claims (1)

[Claims] 1 The initial condensate of urea and formaldehyde is
After reacting with an acidic aqueous solution, a cake consisting of fine cross-linked formaldehyde polymer particles in which individual particles with an average particle size of 0.1 to 1.0μ aggregated to an average size of 1 to 30μ is obtained from the slurry-formed dispersion after reacting with an acidic aqueous solution. 1. A method for producing a urea resin filler, which comprises pulverizing the slurry-formed dispersion using an impact pulverizer and turning it into a cake using a continuous vacuum filter.