JPH028889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a molded structure by reaction injection molding and a method for molding the same.

Insulating structures such as cages for storing frozen meat, vegetables and fruits, refrigerator housings, housings for external air vents, cutting-type precision machinery, and electronic equipment require rigidity and lightness in addition to insulation and cooling functions. Conventionally, the inner layer is made of polystyrene foam and the outer layer is made of polypropylene or ABS resin (acrylonitrile).
It utilizes a three-layer laminate, that is, a sandwich structure made of a molded body of butadiene/styrene terpolymer (butadiene/styrene terpolymer). However, in order to manufacture such a sandwich structure, it is necessary to mold the inner layer and the outer layer separately, so two types of molds must be prepared, and the molding and assembly are labor-intensive, which ultimately increases the product price. It gets expensive.

Therefore, lightweight molded products using the RIM (reaction injection molding) method, which can integrally mold a heat-insulating structure consisting of a high-density, dense and robust outer layer and a low-density foamed inner layer, are beginning to be put into practical use. Although the deficiencies of the conventional Sanderch structure are being solved by this, a problem has arisen in that such a RIM structure does not have sufficient strength, which limits its use.

An object of the present invention is to provide a RIM structure that eliminates the drawbacks of the prior art described above, maintains heat insulation properties, and provides high strength without sacrificing light weight, and a method for molding the same. Furthermore, the present invention is characterized in that by appropriately selecting the overall density of the structure and the ratio of the density of the outer layer and the inner layer, it is possible to provide a structure that has excellent surface robustness and satisfactory bending strength. do.

This structure is characterized in that a reinforcing body is inserted inside the structure mainly to improve bending strength. Any type of lightweight material that does not chemically react with the RIM molded material and has the necessary mechanical strength can be used as the reinforcing material, but preferred materials include a spongy metal material, gold or There are laminates, fibers entwined with glass wool or steel wool, and felt fibers, which can be selected in consideration of the shape of the structure to be inserted, the required strength and lightness, etc. Also,
If there is a risk that the structure will heat up or have poor insulation properties due to the inclusion of metals, this can be prevented by coating these metals with plastic.
The RIM method of this invention is characterized by a means for attaching it to the reinforcing body and holding it in the RIM mold;
Alternatively, by using a device that can lock the holding means to the upper mold or lower mold of the mold, the reinforcing body can be set at an appropriate position in the mold carry assembly and then a predetermined mixing can be carried out. The purpose is to inject a liquid into a cavity to produce the desired structure.

Hereinafter, this invention will be explained in detail using the drawings. A schematic process diagram of the RIM method according to the present invention is shown in FIG. 1, and a schematic cross-sectional view of an embodiment of a reaction injection molding machine using this method is shown in FIG. Referring to both figures, liquid A containing a polyhydroxy compound, low boiling point solvent, catalyst, water, etc. and liquid B consisting of polyisocyanates are first introduced into head mixer 1 and mixed, and then transferred to a reaction injection molding machine. A gate 5 is provided in a cavity 4 formed by an upper mold 2 and a lower mold 3 configured as 10.
It is then injected under a predetermined pressure. Then, the foaming and curing reaction progresses under temperature control by the fluid circulating through the temperature control tube 9, and after a predetermined demolding time has elapsed, the molds 2 and 3 are opened and the molded product is demolded using the ejector pins 6. be exposed. At this time, the reinforcing body 7 is set in advance at a predetermined location within the cavity 4 prior to molding.

Lid 11 as a structure obtained in this way
A package consisting of a case 12 and a case 12 is shown in FIG. The overall view is shown in figure a, and from the longitudinal sectional view in figure b, it can be seen that the reinforcing body 7 has been inserted to strengthen the structure. Because of this reinforcement set,
In FIG. 2, one end of the suspended thin thread-like holders 8 _a and 8 _a attached to the reinforcing body 7 is held between the upper die 2 and the lower die 3 on the parting surface thereof, and the other end is held between the upper die 2 and the lower die 3. is fixed on the lower die 3. After the reinforcing body 7 is set in the mold in this way, if the mixed liquid is injected, the mixed liquid is foamed and hardened with the reinforcing body inserted, and the subsequent steps proceed. Then, a part of the suspended type holder _8a exposed from the molded structure is cut with an appropriate cutter, and after this is removed, the mold is removed. Further, in some cases, it is possible to adopt a method in which the holder is removed after demolding. In addition, if this holder cut mark is noticeable on the surface of the molded product, it is desirable to cover the spot by painting or applying a pattern in order to maintain the appearance.

Next, the holder for reinforcing body set will be further explained, although some of it will be duplicated. There are two types of this holder, a suspension type and a locking type, and it is of course possible to use both types together. In addition to the type shown in Fig. 2 described above, the suspension type holder _8a may be made of at least two thin steel wires or nylon threads, with a reinforcing body placed on top of these, and each Both ends may be locked by the upper die 2 or the lower die 3, or the parting surfaces thereof may be held between the two dies. At this time, in order to stably lock the slightly thick steel wire that holds the heavy reinforcing body to the parting surface of the mold, each end of the steel wire can be attached to the parting surface of the lower mold using, for example, a groove-shaped lock. Handling is convenient if a stopper (not shown) is appropriately provided.

FIG. 4 shows a state in which the reinforcing body 7 is supported and set on the inner surface of the lower mold 3 by several locking type holders _8b . As shown, a T- or Y-shaped holder 8 _b made of thin steel wire or having a curved tip is shown, and it can be seen that the tip is attached to the reinforcing body 7 in a suitable manner. FIGS. 5a and 5b show various locking type holders 8 _b1 , 8 _b2 ,
8 _b3 , 8 _b4 , 8 _b5 and the state in which the reinforcing body 7 is locked therewith are schematically shown. The holder 8 _b1 shown in a is
For example, it has a cylindrical shape and is molded or processed using the same type of material as the structure to be molded into a similar configuration. Then, by appropriately selecting the thickness, it can be attached to the upper surface inside the lower mold 3 and the side surface (not shown) using adhesive if necessary, as shown in FIG. Once attached, the reinforcing body 7 will be set at a predetermined location within the cavity 4 formed between the upper mold 2 and the lower mold 3. This setting method may be performed by attaching the holder 8 _b1 to the reinforcing body 7. In addition, the Y-shaped holder 8 _b
2. Inverted L-shaped holder 8 _b3 and V-shaped holder 8 _b5
As shown in b, the leading end of the reinforcing body 7 is attached to hold it on the inner surface of the lower mold 3. Further, 8 _b4 indicates a part of the reinforcing body 7, such as a tip of a steel wire, which is processed and used as a holder. Note that the end portion of the holder may be exposed on the outer surface of the molded product, and in that case, it is desirable to apply a suitable coating to cover the spot. In the case of a locking type holder, unlike when using a suspension type holder, the holder is difficult to be exposed from the molded product, so there is an advantage that the step of cutting and removing the exposed portion can be omitted.

As mentioned above, when liquid A and liquid B are mixed and injected into the cavity in which the reinforcing body is set under a predetermined pressure of about 10 kg/cm ² or less to cause foaming and curing, the reinforcing body 7 is inserted. A sandwich-like structure is obtained consisting of a low-density inner layer 13 and two high-density outer layers 14 forming side skins. A partial sectional view of one embodiment is shown in FIG. 6, and a reinforcing body 7 made of sponge-like aluminum used therein is shown in FIG. Such reinforcements are convenient because their porosity and strength can be easily adjusted using known techniques.
When carrying out this RIM method, the low boiling point solvent in liquid A vaporizes and generates foam cells, but if this is used to adjust the amount of mixed liquid injected into the cavity, the outer layer and inner layer of the molded product can be separated. It has been found that the overall density can be set arbitrarily within a range of about 10 to 1000 Kg/m ³ . However, for such a structure, the lower the overall density, the higher the insulation, but the lower the strength. Conversely, the higher the overall density, the higher the strength, but the product price will be higher due to the influence of material costs. Become. Generally, an overall density of at ^least 50Kg/m3 is required due to practical strength requirements, and a total density of 800Kg/m3 is generally required from the standpoint of insulation performance and product price.
It has been found that it is undesirable to exceed too much Kg/m ³ .

Liquid A and B used as molding materials for these structures
The liquid can be of any type available to those skilled in the art. For example, the polyhydroxy compounds contained in liquid A include sorbitol, sucrose,
Alkylene oxide adducts of polyhydric alcohols such as 1,4-polybutadiene glycol, bisphenol A, glycerin, and pentaerythritol, alkylene oxide adducts of amine compounds (ethylenediamine, tolylene amine, diaminodiphenylmethane, etc.), dicarboxylic acids or their anhydrides It has been found that there are polyester polyols obtained from polyols and polyhydric alcohols, and these can be used alone or in combination.

In addition, trichloromonofluoromethane, dichlorodifluoromethane, trichlorotrifluoroethane, methylene chloride, heptane, hexane, acetone, etc., which are commonly used as blowing agents for urethane foam, can be used as low boiling point solvents. confirmed. Additives include catalysts that promote the foaming reaction between polyisocyanate and polyhydroxy compounds (e.g., triethylenediamine, dimethylamine, dibutistin dilaurate).
In addition to foam stabilizers (e.g. alkylene oxide-modified polydimethylsiloxane, fluorine compounds), water that acts as a foaming agent, organic or inorganic fillers, pigments, paints, flame retardants, antioxidants, etc. are mixed. Can be used.

Next, for the polyisocyanate as liquid B,
4.4'-Diphenylmethane diisocyanate (MDI
), crude MDI, hexamethylene diisocyanate, tolylene diisocyanate,
Examples include polyphenylene polymethylene isocyanate, which can be used alone or in combination. The composition of each component when using such A liquids and B liquids is shown in FIG. 8 in terms of weight ratios for representative examples A, B, and C.

Furthermore, as mentioned above, the outer layer forming the skin layer of the structure obtained as described above is dense, robust, and exhibits high density, while the inner layer forming the inner core layer is foamed and exhibits low density. It is. It has also been found that the ratio of the two densities can be varied over a wide range by adjusting the injection speed, injection pressure, mold temperature, etc. of the mixed liquid. When this density ratio is small, the surface of the structure lacks hardness, causing the problem that the surface will be damaged by a slight external force.On the other hand, when it is too large, the mechanical strength of the inner layer will be weak, resulting in a somewhat rough surface. It was confirmed that the disadvantage of easy deformation of the external shape becomes noticeable due to rough handling. Therefore, as a result of various tests and studies, this density ratio is practically 2:1 to 25:1.
It was confirmed that the level was suitable.

Finally, typical practical test results for the structure shown in FIG. 6 using the reinforcing body 7 shown in FIG. 7 are listed as Examples 1 to 7 in FIG. has been added for comparison. These structures were all foamed and cured for 8 minutes using the mixed solution shown in Figure 8A, and the temperature of the mixed solution was 25-30°C.
℃, and the mold temperature was selected to be in the range of 40 to 60℃. Note that similar results were obtained even when B or C in FIG. 8 was used as the mixed liquid and other types of reinforcing bodies were used. From the practical requirements of the structure, bending strength (JIS Z2248
It has been empirically determined that the surface hardness shown in the figure requires a pencil hardness of H ^or higher, so the density ratio of the outer layer and inner layer should be 2:1 or higher.
This confirms that the ratio should be 25:1. The present invention
Of course, the present invention is not limited to these examples.

As is clear from the above description, the RIM structure obtained by the present invention has the practical effect of not losing its light weight and having excellent strength by selecting an appropriate reinforcing body. In addition, it has the advantage of having good heat insulation properties and sound properties, high productivity, and low product price.

[Brief explanation of drawings]

Fig. 1 is a schematic process diagram of the molding method of the present invention, Fig. 2 is a sectional view of a reaction injection molding machine using this, Fig. 3 is a schematic diagram showing a package made of the structure according to the invention, and Fig. 4 is a Fig. 5 is a diagram showing how the reinforcing body is set using a locking type holder;
Figure 6 is a partial sectional view of the structure, Figure 7 is an external view of one embodiment of the reinforcing body, Figure 8 is a chart showing examples of liquids A and B, and Figure 9 is about each example. It is a chart showing the results of performance tests conducted. 2: Upper mold, 3: Lower mold, 4: Cavity, 7: Reinforcement body, 8 _a : Suspension type holder, 8 _b , 8 _b1 to 8 _b5 : Locking type holder, 10: Reaction injection molding machine, 13 : inner layer, 14: outer layer.

Claims (1)

[Scope of Claims] 1. A reaction injection molded structure consisting of a high-density outer layer and a low-density inner layer and having an overall density of 50 to 800 Kg/m ³ , comprising a polyhydroxy compound, a low-boiling solvent, a catalyst and Reinforced reaction injection molding is performed by reaction injection molding using a mixture of liquid A containing water and liquid B consisting of polyisocyanates, and a reinforcing body for improving bending strength is inserted into the inner layer. Molded structure. 2. In the reinforced reaction injection molded structure according to claim 1, the density ratio of the outer layer and the inner layer is 2:
A reinforced reaction injection molded structure characterized by a ratio of 1 to 25:1. 3. The reinforced reaction injection molded structure according to claim 1 or 2, characterized in that the reinforcing body is a spongy metal body, a metal net, or a piece in which glass wool or steel wool is entangled with the reinforcing body. Reinforced reaction injection molded structure. 4. A reinforced reaction injection molded structure according to claim 3, characterized in that the reinforcing body is coated with a plastic coating. 5. The reinforced reaction injection molded structure according to claim 1 or 2, characterized in that the reinforcing body is a felt-like filament of ceramic, glass, metal, plastic, or cotton. Reaction injection molded structure. 6. A method for molding a reinforced reaction injection molded structure, characterized by comprising the following steps. (b) A step of setting the reinforcing body at a predetermined location in the cavity between the upper mold or the lower mold by locking it to the upper mold or the lower mold in a reaction injection molding machine using a suspended type holder; (b) A step of mixing a liquid A containing a polyhydroxy compound, a low boiling point solvent, a catalyst and water, and a liquid B consisting of a polyisocyanate, and injecting the mixture into the cavity to foam and harden the mixture, and (c) After a predetermined demolding time has elapsed, the exposed portion of the holder is removed from the obtained molded product, and then the molded product is demolded. 7. A method for molding a reinforced reaction injection molded structure, characterized by comprising the following steps. (b) A process of setting the reinforcing body at a predetermined location in the cavity of the reaction injection molding machine by locking the reinforcing body to the inner surface of the lower mold using a locking type holder; (b) Polyhydroxy compound , a step of mixing liquid A containing a low boiling point solvent, catalyst and water, and liquid B consisting of polyisocyanates, and injecting this into the cavity to foam and harden; The process of demolding the obtained molded product after the molding time has passed.