JPH047363B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing solid urea resin. Solid urea resin is sometimes used when making urea resin molding materials. Conventionally, solid urea resins have been obtained by reducing the water content in the initial condensation syrup of urea resins and solidifying them by cooling. At that time, an expensive vacuum dryer was required to dehydrate the material to prevent the reaction from proceeding, leading to an increase in the cost of the final material. Since the reaction was stopped at a young stage of resin reactivity, it was necessary to increase the subsequent degree of condensation, which resulted in large post-shrinkage. This invention aims to solve these problems. This is accomplished by using a relatively water-poor syrup and absorbing the water with an acrylic polymer absorbent. Therefore, this invention aims at obtaining a solid urea resin by reducing the water content in the initial condensation syrup of urea resin and solidifying it by cooling. The gist of this invention is a method for producing a solid urea resin, which is characterized by absorbing moisture by dispersing an acrylic polymer absorbent into the solid urea resin. This will be explained in detail below. In this invention, the initial condensation syrup of urea resin used is one obtained by carrying out the reaction at a water content of 13 to 25% by weight. When the amount of water added is less than 13% by weight, it becomes difficult to control the reaction, and when it exceeds 25% by weight, dehydration becomes difficult. The blending conditions, reaction conditions, etc. other than the amount of water to be added are the same as usual. When an acrylic polymer absorbent is added to the syrup and stirred well at room temperature to uniformly disperse the syrup, the water in the syrup is absorbed by the acrylic polymer absorbent, completing the dehydration of the syrup. The acrylic polymer absorbent is usually in the form of powder, and "Aqua Keep" commercially available from Seitetsu Kagaku Kogyo Co., Ltd. is known. This material is preferably added in an amount of 0.5 to 5% by weight based on the solid urea resin.
If it is less than 0.5% by weight, the dehydration effect will be weak, and 5% by weight.
This is because when the amount exceeds 1, gas release properties tend to deteriorate. The acrylic polymer absorbent is a thermoplastic polymer that remains in the molding material, so as its relative amount increases, the stress that causes it to expand and deform under heating temperatures of 140 to 150 degrees Celsius increases. The crosslinking of the thermosetting urea resin makes it impossible to contain the gas, and gas blisters tend to persist forever. After the moisture in the syrup has been absorbed, it is cooled and solidified. Cooling and solidification are performed in the same manner as before. The polymeric absorbent may be added after cooling the syrup. The solid urea resin thus obtained is made into a molding material by an appropriate method, such as by blending it with a normal dried urea resin product together with a mold release agent and a coloring agent, and pulverizing and mixing. As mentioned above, this invention dehydrates the charged water and condensed water in the syrup at room temperature using an acrylic polymer absorbent. To easily avoid sagging, and to maintain a component state with a large plasticizing effect on solid urea resin. The use of a vacuum dryer can be omitted, making it possible to simplify the process, improve productivity, and reduce energy costs. In other words, the dehydration step, which conventionally required 5 to 8 hours, is omitted, resulting in the above effects. Furthermore, since heating and dehydration are not performed, the degree of reactivity of the resin in the syrup can be advanced, and the subsequent degree of condensation can be reduced. Therefore, a molded article made of a molding material obtained using this solid urea resin has a small aftershrinkage. Since the thermoplastic resin (acrylic polymer absorbent) contained in the molding material expands under processing conditions that cause post-shrinkage, this also makes it possible to suppress the effects of post-shrinkage of the urea resin. Next, an example will be described together with a conventional example. Examples 1-5 350g of paraformaldehyde, 80g of water and 10%
10 ml of caustic soda aqueous solution was added and heated. When the temperature of the system reached 75℃, stir for 15 minutes and add 352g of urea.
and the reaction proceeded at 60°C with thorough stirring.
After 10 minutes, an acrylic polymer absorbent (trade name: Aqua Keep 10SH) was added in the amount shown in Table 1, stirred well to uniformly disperse, and then cooled to solidify. Crush the obtained solid urea resin into appropriate sizes,
15 parts by weight was added to 100 parts by weight of a normal dry urea resin product, and 0.6 parts by weight of zinc stearate and the required amount of pigment were added, and the mixture was pulverized and mixed in a ball mill to obtain a molding material. [Conventional example] Dehydration was carried out in the same manner as in the past, without using an acrylic polymer absorbent. A molding material was obtained in the same manner as in the example. The performance of the molding materials of the example and the conventional example is as follows:
It was as shown in the table. 【table】

Claims (1)

[Scope of Claims] 1. In obtaining a solid urea resin by reducing the water content in the initial condensation syrup of urea resin and solidifying it by cooling, the water content of 13~
A method for producing solid urea resin, which is characterized by absorbing water by dispersing an acrylic polymer absorbent into the solid urea resin at a concentration of 25% by weight. 2. The method for producing a solid urea resin according to claim 1, wherein the amount of the acrylic polymer absorbent added to the syrup is 0.5 to 5% by weight based on the solid urea resin.