JPH0466248B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] 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 cross-linked urea-formaldehyde polymer particles used as paper filler have an average particle size of 1 to 1.
These particles are aggregated to a size of ~30μ (hereinafter referred to as secondary particles). Average primary particle size is 0.1~1.0μ
This is disclosed in the above-mentioned Japanese Patent Publication No. 57-26686, but at the same time, the average secondary particle diameter must be in the range of 1 to 30 microns, preferably 1 to 10 microns. That is, if the average secondary particle diameter is less than 1 μm, the retention rate in paper 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 On the other hand, 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 separated liquid is filtered to form a cake, which is convenient for transportation and storage, and then redispersed and used during papermaking. It goes without saying that such a cake preferably has as low a moisture content as possible, ie, a high solids content. Especially when it is used as a filler for mass-produced paper such as newspaper rolls, the amount of filler used is enormous, and an increase in the solids content of the cake, even by about 1% by weight, is extremely significant. be. The solids content of the cake obtained by passing through a conventional cross-linked urea formaldehyde polymer particle dispersion is approximately 25% by weight, but due to the above-mentioned circumstances, it has been desired to further increase this content. . As a result of various studies, the present inventor found that the cake obtained by slurrying the polymer produced by reaction solidification and filtering it before pulverization has a higher solid content than the cake obtained by filtering it after pulverization. I found out. In other words, it is stored and transported in the form of a cake, and then redispersed and crushed just before use.
It turns out that there are huge benefits. However, such a cake is very hard and difficult to make into a slurry, and the average secondary particle size of the pulverized product is
It was larger than 30μ, making it unsuitable for use as a filler for paper. The inventor conducted further studies and found that the solid content of the cake is high, that it is easy to form a slurry, and that the average secondary particle size of the product obtained after pulverization is 1 to 1.
The present invention was achieved by finding the conditions under which the thickness becomes 30μ. [Means for Solving the Problems] The present invention involves reacting a desired condensate of urea and formaldehyde with an acidic aqueous solution, slurrying it to form a dispersion, and then grinding it to form fine cross-linked urea-formaldehyde. A method for producing a urea resin filler made of polymer particles, characterized in that a crosslinked urea formaldehyde polymer dispersion is filtered through a continuous vacuum filtration machine to form a cake, then slurried again, and then pulverized using an impact pulverizer. This is a method for producing a urea resin filler. There are generally pressurization vessels and vacuum sieves, but in order to achieve the purpose of the present invention, a vacuum sieve is required. When using a pressurizer, the resulting cake is extremely hard and difficult to slurry, and even if it is forcibly slurried and pulverized, the average secondary particle size of the resulting crosslinked urea formaldehyde polymer particles is 30 μm. Not only that, 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. In addition, as a crusher, ball mills, vibrating ball mills, special ball mills, impact type crushers, roller mills, jet crushers, colloid mills, etc. are generally used industrially. Even if only the impact type crusher is used and other crushers are used, it is not possible to obtain a filler having an average secondary particle size suitable for paper filler. The impact crusher may be of a screen type, an axial flow type, a rotary disk type, etc., and any of them may be used, and a free crusher, which is a type of rotary disk type, is particularly desirable. Both the strainer and the crusher 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 a desired condensate of urea and formaldehyde with an acidic aqueous solution to form a slurry. The initial condensate is usually urea 1
The reaction is carried out at a ratio of 1 to 2.5 moles of formaldehyde per mole, at a pH of 4 to 9, and at 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 is reacted by mixing with an acidic aqueous solution to obtain an aggregate of cross-linked urea-formaldehyde polymer particles, which is crushed and, if necessary, water is added.
A dispersion of crosslinked urea formaldehyde polymer particles is obtained. This is usually neutralized with an alkali such as caustic soda. [Operation] Such a dispersion is dehydrated using a continuous vacuum filter to form a cake. The solids content of the cake obtained is approximately 27% by weight. The slurry is then made into a slurry again and pulverized using an impact pulverizer, but if storage or transportation is required, it is preferable to do this in the form of a cake with a solids content of 27% by weight. Of course, if the material does not require storage or transportation and is used immediately as a paper filler, it is immediately subjected to the slurry process after dehydration. Slurrying can usually be easily carried out by adding water and stirring. This is because dehydration is performed in a continuous vacuum strainer in the previous step, and if other strainers are used, it is difficult to form a slurry. The resulting slurry is crushed in an impact crusher,
It serves as a filler for crosslinked urea formaldehyde polymer particles having an average secondary particle diameter of 1 to 30 microns, preferably 1 to 10 microns. [Example] Examples will be described below. Production example: Mix 38.4 parts of a 37% formaldehyde aqueous solution (hereinafter all percentages are by weight), 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, and the mixture was allowed to stand for 1 hour. The resulting gel was coarsely ground, water was added, stirred, and then neutralized with a caustic soda solution to obtain a crosslinked urea formaldehyde polymer particle dispersion. This dispersion liquid was used in all subsequent Examples and Comparative Examples. Example 1 The dispersion of the production example was passed through an Oliver filter to obtain a cake. Approximately 3 g of this cake was placed in a watch glass and treated in a hot air dryer at 105°C for 60 minutes, and the ratio of the weight after treatment to the weight before treatment (hereinafter referred to as solid content) was 27.3%. Ta. Water was added to this cake again and stirred to form a slurry. It was extremely easy to form a slurry. This slurry was pulverized using a free pulverizer to obtain a dispersion of crosslinked urea formaldehyde polymer particle filler.
When the average secondary particle diameter was measured using a Coulter counter, it was 4.9μ. This filler is hereinafter referred to as Example-1 filler. Comparative Example 1 A cake-like urea resin filler 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 39μ. This filler is hereinafter referred to as Comparative Example-1 filler. Comparative Example 2 A urea resin filler was obtained in the same manner as in Example 1 except that a colloid mill was used as the pulverizer. The average secondary particle diameter of this filler was measured in the same manner as in Example 1, and was found to be 0.85μ. This filler is hereinafter referred to as Comparative Example-2 filler. Comparative Example 3 A cake was obtained by filtering the dispersion of the production example using a filter press as a filter. The solid content of this cake was measured and found to be 27.8%. An attempt was made to form a slurry by adding water to the cake and stirring it again, but it was extremely difficult to form a slurry and took a long time, and the resulting slurry contained many large lumps. This slurry was pulverized using a free pulverizer to obtain a dispersion of crosslinked urea formaldehyde particle filler. The average secondary particle size of this filler was 45μ. Comparative Example 4 The dispersion of the production example was ground using a free grinder and then passed through an Oliver filter to obtain a cake. The solid content of this cake was 24.5%, which was 2.8% lower than in Example 1. Example 2 Example 1 was repeated, except that a table-type horizontal filter was used in place of the Oliver-type filter used in Example 1, and a shaft-grain impact crusher was used in place of the free crusher.
A cake having a solids content of 26.3% and crosslinked formaldehyde polymer particles having an average secondary particle size of 8.5μ were obtained. Application Example Table 1 shows the results of paper making using the Example 1 filler and the Comparative Examples 1 to 3 fillers. 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 processed 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】

〔effect〕

As is clear from Table 1, in Example 1 according to the method of the present invention, an average of 2
A urea resin filler having a particle size of The secondary particle size is in an inappropriate range as a paper filler, and the white paper opacity of paper made using this is poor, and in processed paper using Comparative Example 3 filler, spots appear on the paper surface. did. From the above, the effects of the filler produced by the method of the present invention are clear, and the present invention has great significance.

Claims (1)

[Claims] 1 The initial condensate of urea and formaldehyde is
A urea resin consisting of fine crosslinked formaldehyde polymer particles in which individual particles with an average particle diameter of 0.1 to 1.0μ aggregate to an average size of 1 to 30μ is obtained from a slurry-formed dispersion after reacting with an acidic aqueous solution. A method for manufacturing a urea resin filler, characterized in that the slurry dispersion is filtered through a continuous vacuum filter to form a cake, then slurried again, and then pulverized using an impact pulverizer. Production method.