JPH02295710A - Reaction injection molding method - Google Patents

Abstract

PURPOSE:To enhance the foaming rate of the thick wall part of a resin molded product and to prevent a sink mark by mixing a high b.p. foaming agent with a resin molding material and coating the thick wall part molding part of a mold with an amine type foaming accelerator. CONSTITUTION:A high b.p. foaming agent having a b.p. higher than the reaction molding temp. of a resin molding material is preliminarily mixed with the resin molding material while the thick wall part molding part 6 of a mold 5 is coated with an amine type foaming accelerator 7 reacted with the isocyanate component in the above mentioned resin molding material and generating temp. due to the reaction higher than the b.p. of the above mentioned high b.p. foaming agent by spraying after the coating with a release agent. Then, the resin molding material is injected in the mold 5. By this method, in the thick wall part molding part of the mold 5, the temp. of the resin molding material becomes higher than the b.p. of the high b.p. foaming agent by the reaction of the foaming accelerator 7 applied to said part 6 and the isocyanate component in the resin molding material. Therefore, the foaming rate at the thick wall part molding part 6 becomes higher than that at a thin wall part molding part 8 by the contribution of the high b.p. foaming agent to the foaming of the resin molding material.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a reaction injection molding method.

(Prior art) When a resin molded product with thick parts such as ribs is obtained by reaction injection molding, the resin molded product has a surface called a gap on the opposite side from which the thick part protrudes, that is, the back side. It is generally known that defects are likely to occur. In other words, this sink mark occurs because the amount of hardening and shrinkage of the tree is different between the thick part and the surrounding thin part.

As a countermeasure for the sink marks mentioned above, ■ By forming a thin wall part on one side of the thick interior where the wall thickness is smaller than that on the other side, the flow velocity of the resin molding material in the thick part molded part of the mold is approximately equal to that in the surrounding area. (Refer to Japanese Unexamined Patent Publication No. 62-111711), ■ A method to reduce the change in wall thickness around the thick part, ■ A method to pressurize the resin molding material after injection, ■ Low-shrinkage microcapsules A method is known in which the compound is mixed into a resin molding material.

(Problems to be Solved by the Invention) However, the methods ① and ② above impose restrictions on the shape of the resin molded product and require changes in the shape of the mold.
The above method (2) requires a separate pressurizing device, and the above method (2) does not attempt to solve the root cause of the difference in the amount of shrinkage between the thick portion and the thin portion, so no great effect can be expected.

That is, an object of the present invention is to make it possible to efficiently eliminate the sink mark without changing the shape of the mold or adding any special equipment.

(Means for Solving the Problems) In order to solve these problems, the present invention controls the reaction system in reaction injection molding to increase the foaming rate of the resin molding material in the thick-walled parts, thereby preventing the above-mentioned cracks. It is something.

That is, the means for this purpose is a reaction injection molding method for obtaining a resin molded product having a thick wall part using a urethane/urea resin molding material, and the resin molding material contains a high boiling point that is higher than the reaction molding temperature of the resin molding material. While a blowing agent is mixed in, an amine that reacts with the isocyanate component in the resin molding material and whose exothermic temperature due to the reaction is higher than the boiling point of the high boiling point blowing agent is added to the part of the mold that molds the thick interior. The method is characterized in that the resin molding material is injected into a mold after applying a foaming accelerator.

(Function) In the above molding method, in the thick-walled molding part of the mold,
Due to the reaction between the amine foaming accelerator applied thereto and the isocyanate component in the resin molding material, the temperature of the resin molding material becomes higher than the boiling point of the high boiling point foaming agent. Therefore, the high boiling point foaming agent contributes to the foaming of the resin molding material in this thick-walled molded part, so that the foaming rate of the resin molding material becomes higher than that in the surrounding area, and the occurrence of sink marks is prevented. In other words, a high foaming rate means that a resin molded product has many pores and a small amount of resin in the thick part, and the smaller the resin, the lower the shrinkage rate.
This reduces the difference in the amount of shrinkage between the thick portion and the thin portion, which is the cause of sink marks.

(Effects of the Invention) Therefore, according to the present invention, resin molding can be carried out by a simple means of mixing a high boiling point foaming agent into a resin molding material and applying an amine foaming accelerator to the thick-walled molding part of the mold. By increasing the foaming rate in the thick interior of the product, it is possible to prevent sink marks without changing the shape of the mold or adding special equipment.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows a part of a resin molded product 1 obtained by reaction injection molding. The thick portion 2 of the resin molded product 1 is a portion where a rib is provided on one side of the resin molded product 1, and both sides of the thick portion 2 are called thin portions 3.

The formulation of the resin molding material used in the reaction injection molding is as follows.

A. Polyol side polypropylene glycol average molecular weight 4000 84. 8 parts by weight DET
DA (diethyltoluenediamine> 15.0 parts by weight Tin catalyst (dioctyltin dilaurate) 0.12 parts by weight Amine catalyst (triethyldiamine). 0.12 parts by weight Cut glass fiber (diameter lOμ, fiber length 100μ) 24.4 parts by weight Part B. Isocyanate side modified MDI (diphenylmethane diisocyanate) 120 parts by weight High boiling point blowing agent (tetrachloroethane) 5 parts by weight The boiling point of the above high boiling point blowing agent is 146.2°C.

FIG. 2 shows a part of a mold (mold) 5 for obtaining the resin molded product 1. As shown in FIG.

Therefore, in injection molding, a foaming accelerator 7 is applied to the thick-walled part molding part 6 of the mold 5 where the thick-walled part 2 is formed, and the formulation of the foaming accelerator 7 is as follows. It is.

C. Foaming accelerator amine 1; TDA (}luenediamine) 0.5 parts by weight Amine 2, TEDA (}lyethylenediamine) 0.5 parts by weight. On the other hand, after applying a mold release agent, it is applied by spraying.

After applying the foaming accelerator 7, the resin molding material described above is injected into the mold 5. As a result, in the thick-walled molding part 6 of the mold 5, the temperature of the resin molding material rises above the boiling point of the high-boiling point blowing agent due to the reaction between the foaming accelerator 7 applied thereto and the isocyanate component in the resin molding material. It also becomes more expensive.

That is, in the case of this example, the foaming accelerator 7 has T of the amine 1.
Modified M in which DA is an incyanate component of a resin molding material
It reacts with DI to produce a polymeric compound having a urea bond, and the amine 2, TEDA, acts as a catalyst for this reaction. This reaction is fast and generates a large amount of heat, and in the thick internal molding section 6, the temperature of the resin molding material is made higher than the boiling point of the high boiling point blowing agent.

FIG. 3 shows the change over time in the internal temperature of the resin molding material injected into the mold 5, and the characteristic line A in the figure shows the internal temperature change in the thick-walled molded part 6. Line B shows the internal temperature change in the thin-walled portion 8. Note that the thickness of the thin wall portion 3 of the resin molded product 1 is 3.8+a. Further, the curing time of the resin molding material in this case is 20 to 30 seconds.

From Fig. 3, the temperature of the resin molding material exceeds the boiling point (148.2°C) of the high-boiling point foaming agent in 5 to 9 seconds after injection in the thick-walled molded part 6 coated with the foaming accelerator 7, and during this period It can be seen that foaming by the boiling point foaming agent progresses.

On the other hand, the internal temperature of the resin molding material does not rise to the boiling point of the high-boiling point foaming agent in the thin-walled portion molding section 8 to which no foaming accelerator is applied. It can be seen that this does not contribute to foaming of the material.

Therefore, the high boiling point foaming agent contributes to the foaming of the resin molding material in the thick-walled molded section 6, so that the foaming rate of the resin molded material is higher than that in the surrounding area (thin-walled molded section 8). . In other words, a high foaming rate means that the resin molded product 1 has many pores and few resin parts in the thick part 2, and as the resin part decreases, the shrinkage rate decreases. The difference in the amount of shrinkage between the thick portion 2 and the thin portion 3 is reduced. Therefore, sink marks are prevented from occurring on the surface (back surface) 1a of the resin molded product 1 opposite to the thick portion 2.

The injection molding method of the example is as described above, and when 40 resin molded products were obtained by this method, the number of sink mark defects was one. On the other hand, in the case of the conventional method that does not use the above-mentioned high-boiling point foaming agent and foaming accelerator, the number of sink mark defects occurred in 6 out of 40 resin molded products.

In addition to the TDA mentioned above, DETDA (diethyltoluene diamine) can also be used as the amine 1 of the foaming accelerator applied to the thick-walled molded part. Any foaming agent may be used as long as it has the following properties and reacts with the isocyanate component of the resin molding material to locally raise the temperature of the resin molding material to a temperature higher than the boiling point of the high boiling point blowing agent.

Further, when applying the foaming accelerator, it can be mixed into a mold release agent and applied by spraying or the like together with the mold release agent.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, FIG. 1 is a sectional view showing a part of a resin molded product, FIG. 2 is a sectional view showing a part of a mold,
FIG. 3 is a characteristic diagram showing the change in internal temperature of the resin molding material injected into the mold 5 over time. 1...Resin molded product 2...Thick wall part 3...Thin wall part 5...Molding mold 6...Thick wall part molding part 7... Foaming accelerator 8... Thin wall portion molding part

Claims (1)

[Claims] (1) A reaction injection molding method for obtaining a resin molded product having a thick wall part using a urethane or urea resin molding material, wherein a high boiling point blowing agent having a boiling point higher than the reaction molding temperature of the resin molding material is mixed into the resin molding material. On the other hand, an amine-based foaming promoter that reacts with the isocyanate component in the resin molding material and whose exothermic temperature due to the reaction is higher than the boiling point of the high-boiling blowing agent is added to the part of the mold where the thick-walled part is to be molded. A reaction injection molding method comprising: coating a resin molding agent on the resin molding material, and then injecting the resin molding material into a mold.