JPH0773858B2 - Reaction injection molding method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reaction injection molding method, and more particularly to a reaction injection molding method using a mold structure for producing a molded product having a good surface condition.

2. Description of the Related Art It is known that the reaction injection molding (hereinafter referred to as RIM) method is applied to molding various polymers such as polyurethane, nylon, epoxy resin, phenol resin, and polydicyclopentadiene. However, with this RIM method, sink marks (depression phenomenon that occurs on the surface of the molded product) and minute bubbles frequently occur on the surface of the resulting molded product, and it is difficult to obtain a molded product with a good surface condition. is there. In the RIM method, a chemical reaction is carried out in a mold to polymerize a monomer into a polymer, and at that time, shrinkage of the mold contents occurs. However, the speed of the chemical reaction is non-uniform due to the temperature gradient of the mold and the difference in heat conduction between the thick and thin parts of the molded product, and the reaction speed is high, and therefore the reaction components are found in the part where the curing shrinkage is fast. As a result, a dent is generated on the surface of the molded product, and at the same time, the pressure between the dent and the mold is reduced.
It is presumed that extremely fine bubbles such as entrained bubbles existing on the surface of the molded product expand and expand, which significantly deteriorates the surface appearance of the molded product. Therefore, the sink prevention method is required. In the usual thermoplastic resin injection molding method, in order to prevent sink marks, the injection speed of the thick part is reduced to stabilize the skin layer,
Moreover, although program control is performed such as increasing the holding pressure, such control is extremely difficult because the RIM method targets reactive liquid mixtures.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to provide a RIM method capable of obtaining a molded product having a good surface condition without sink marks.

Means for Solving the Problems As a result of earnest research on a sink preventing method suitable for the RIM method, the present inventors have found that a polyfluorinated ethylene resin (for example, a product referred to as a registered trade name Teflon) on one surface of a mold. When a sheet (plate) such as a cellophane, a metal plate, etc. is inserted and molded, the sheet contracts and slides in close contact with the surface of the molded product to obtain a molded product with a good surface condition. The present invention has been achieved and the present invention has been achieved.

Thus, according to the present invention, in a reaction injection molding method of injecting a molding material into a mold and polymerizing and curing it in a solid state to produce a molded article, a polyfluorinated ethylene resin sheet is provided on one surface of the mold. A reaction injection molding method is provided, which comprises producing a molded article in which sink marks due to curing shrinkage are prevented by injecting a molding material after holding a cellophane sheet or a metal plate.

Hereinafter, the components of the present invention will be described in detail.

(Sheet) The sheet that is inserted into the RIM mold and held on one side is
There is no particular limitation as long as it does not melt depending on the molding material and does not deform due to heat generated during the polymerization / curing reaction. Examples of such a sheet include a Teflon (registered trademark) sheet, a cellophane sheet, a metal plate (which may be plated if necessary), and particularly, the Teflon (registered trademark) sheet is molded. It is preferable because it gives good results regardless of the type of material.

By the way, in order to obtain a molded product having a smooth surface condition, it is preferable that the surface condition of the sheet is also smooth, and particularly a sheet having a transfer-plated surface gives the molded product a good surface condition. However, the sheet used in the present invention is not limited to one having a smooth surface state, and a sheet having various uneven patterns can also be used. For example, when an embossed sheet is used, a molded product having no sink mark and having an uneven pattern on one surface can be obtained.

The thickness of the sheet can be freely selected from a plate-shaped one to a film-shaped one according to the purpose. The preferred thickness of the sheet is 0.1 mm to 3 mm.

(Holding of Sheet) As a method of holding the sheet on one surface of the mold, for example, the following method is available.

(1) The sheet is lightly fixed (temporarily fixed) to one surface of the mold by using the double-sided adhesive tape at several places.

(2) One end of the sheet is sandwiched between the upper and lower molds.
(Refer to FIG. 2) (3) The mold set with the sheet is turned down. (See FIG. 1) (RIM) The reaction injection molding (RIM) method of the present invention can be applied to any ordinary RIM device, and is not limited to the collision mixing type device.

Also, as for the molding material, it can be applied to all resins to which RIM can be applied. As the resin, polyurethane,
Polymers of norbornene-type monomers such as nylon, epoxy resin, phenol resin, unsaturated polyester, and polydicyclopentadiene are available.

In the RIM method, when the molding material is injected into the hot mold,
The material quickly polymerizes and hardens into a solid state and shrinks. When the sheet is held on one side of the mold, the sheet slides in close contact with the surface of the molded product as the material cures and shrinks, and sink marks due to shrinkage are prevented. The reason why the sheet slides due to shrinkage of the molded product is presumed to be that the sheet follows the stress generated during shrinkage due to polymerization and curing of the material.

When the sheet is used, a molded product having no sink mark is obtained even if there is a slight temperature gradient in the mold. Further, if the temperature of the mold surface not holding the sheet is increased, a better result can be obtained. As described above, the Teflon (registered trademark) sheet smoothly slides due to the shrinkage of the molded product regardless of the type of molding material (from polar to non-polar) and gives good results.

When the mold is opened, the sheet can be easily removed from the surface of the molded product that has been cured.

Examples Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Dicyclopentadiene monomer was placed in two containers,
(A) On the other hand, add diethylaluminum chloride to a concentration of 0.0033 mol per mol of the monomer,
Further, n-propanol was added so that the concentration would be 0.0033 molar. (B) On the other hand, tri (tridecylammonium) molybdate was added as a catalyst to a concentration of 0.0004 mol per mol of the monomer.

Next, the two reaction solutions were mixed with a static mixer at a volume ratio of 1: 1 and had a space volume of 200 cc and a temperature of 90 ° C.
It was poured into a mold heated at 30 seconds for 30 seconds and reacted for 3 minutes. These series of operations were performed under a nitrogen atmosphere.

As shown in Fig. 2, the cellophane sheet (thickness
0.1 mm) was held on one side by sandwiching it with the lower mold.

When the mold was opened after the reaction was completed, the cellophane sheet was immediately dislocated from the surface of the molded product, and a molded product having a good surface condition without sink marks or fine bubbles was obtained on both sides.

For comparison, when reaction molding was performed in exactly the same manner as in Example 1 except that the sheet was not set in the mold,
Only molded products with sink marks on both sides were obtained. In addition, minute bubbles were found in some areas with sink marks.

Example 2 (Polyurethane RIM) Polyoxypropylene triol (Niax31-28 manufactured by Union Carbide, hydroxyl equivalent 200 as a polyol component in liquid A)
35.3 parts of 3), a chain extender (Niax50- manufactured by Union Carbide)
1180, hydroxyl equivalent 47.6) and 15.1 parts of dibutyl tin laurate at a ratio of 0.012 parts, and mixed with one of the B liquids as crude M
49.5 parts of DI (Isonate 191, NCO equivalent 138.9, manufactured by Upjohn) is taken, and collision mixing pressure is 15 at a ratio of 70 parts of A solution to 30 parts of B solution.
The mixture was mixed at 0 kg / cm ² and had a space volume of 200 cc, and was poured into a mold heated to 100 ° C. in 1 second and reacted for 5 minutes.

In the mold, a Teflon (registered trademark) sheet (thickness 1 mm) was lightly fixed on one surface of the mold shown in FIG. 1 with a double-sided adhesive tape.

After completion of the reaction, when the mold was opened, the Teflon (registered trademark) sheet was immediately dislocated from the surface of the molded product, and a molded product having a good surface condition without sink marks or fine bubbles was obtained on both surfaces.

For comparison, when reaction molding was performed in exactly the same manner as in Example 2 except that the sheet was not set in the mold,
Only molded products with sink marks on both sides were obtained. In addition, minute bubbles were found in some areas with sink marks.

Example 3 (Nylon RIM) 50 parts of ε-caprolactam in one container and 3.6 ml of 3 molar phenylmagnesium bromide catalyst, 5 in the other container.
0 part of ε-caprolactam and 4.3 parts of terephthaloylbiscaprolactam were taken, and both reaction solutions were heated to 80 ° C. Collision mixing pressure 40K at a ratio of 1: 1 of the above two reaction liquids
The mixture was mixed at g / cm ² and was injected into a mold having a space of 200 cc and heated to 140 ° C. in 1 second, and reacted for 2 minutes.

As shown in Fig. 1, a plate (1.5 mm thick) made by plating a stainless steel plate with hard chrome was set in the lower mold in the mold.

After completion of the reaction, when the mold was opened, the stainless steel plate was immediately displaced from the surface of the molded product, and a molded product having a good surface condition without sink marks or fine bubbles was obtained on both surfaces.

For comparison, when reaction molding was performed in exactly the same manner as in Example 3 except that the sheet was not set in the mold,
Only molded products with sink marks on both sides were obtained. In addition, minute bubbles were found in some areas with sink marks.

Example 4 9 of dicyclopentadiene and tricyclopentadiene:
1 (weight ratio) of 100 parts by weight of mixed monomers, 6.5 parts by weight of styrene-isoprene-styrene block copolymer (SIS: manufactured by Nippon Zeon Co., Ltd., trade name Quintac 3421) and polybutadiene (manufactured by Nippon Zeon Co., BR-1220). ) 1 part by weight was added and mixed into two containers, one containing 40 mmol of diethylaluminum chloride, 42 mmol of n-propanol and 20 mmol of silicon tetrachloride with respect to the mixed monomer. (A)
liquid).

On the other hand, for mixed monomers, tri (tridecyl)
Ammonium molybdate was added so as to have a concentration of 10 mmol, and further 3 parts by weight of a phenolic antioxidant (Ethanox 702, trade name, manufactured by Ethyl Corporation) was added per 100 parts by weight of the mixed monomer (solution B).

Except that the reaction stock solution prepared by mixing the above-mentioned solution A and solution B in a volume ratio of 1: 1 was used and the mold temperature was heated to 70 ° C.
Reaction injection molding was carried out in the same manner as in Example 1. When the mold was opened after the polymerization reaction for about 3 minutes, the cellophane sheet was immediately dislocated from the surface of the molded product, and a molded product having a good surface condition without sink marks or fine bubbles was obtained on both surfaces.

For comparison, when reaction injection molding was performed in the same manner as in Example 4 except that the sheet was not set in the mold, sink marks were formed on both sides, and minute bubbles were scattered on the sink marks. Was done.

EFFECTS OF THE INVENTION The present invention is suitable for the RIM method by adopting a simple structure in which a sheet (plate) such as a Teflon (registered trademark) sheet, cellophane sheet, and stainless plate is held on one surface in a mold. It is possible to prevent sink marks and to obtain an excellent effect of obtaining a molded product having a good surface condition.

[Brief description of drawings]

1 and 2 are schematic cross-sectional views of RIM molds suitable for carrying out embodiments of the present invention. 1 ... Mold, 2 ... Sheet, 3 ... Filling port,

Claims (1)

[Claims] 1. A reaction injection molding method for producing a molded product by injecting a molding material into a mold and polymerizing and curing it into a solid state, wherein a polyfluorinated ethylene resin sheet or cellophane sheet is provided on one surface of the mold. Alternatively, a reaction injection molding method characterized in that a molded product in which sink marks due to curing shrinkage are prevented is produced by holding a metal plate and then injecting a molding material.