JPH0753951Y2 - Reaction injection mold - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for obtaining a non-foamed resin product such as a fast-curing polyurethane rubber by reaction injection molding.

[0002]

2. Description of the Related Art In the reaction injection molding method, in which two or more kinds of liquids are mixed, poured into a mold, and then reacted and cured (solidified) to obtain a molded product, bubbles ( In addition to air holes, it also includes vacuum holes. When two or more liquids are rapidly mixed for the purpose of improving productivity or homogenizing the mixing by increasing the curing speed (for example, when so-called collision mixing is performed by the mixing head of the injection device). Bubbles are particularly apt to enter.

The reaction injection molding method has hitherto been adopted to obtain a foamed product, and it is rarely applied to a non-foamed (solid) resin product. Therefore, the conditions for non-foaming molding by the same method have not been established yet, but in general, the method of injecting the resin liquid (mixed liquid) after depressurizing the mold close to vacuum is taken. There is.

[0004]

[Problems to be Solved by the Invention] If the inside of the mold is kept in a state close to a vacuum, air will be less likely to be mixed into the resin in the mold, but the pin will not be included in the product actually molded. There are many hole-shaped bubbles. According to the investigation by the inventors, the cause is (a) air is already entrained in the liquid at the stage of mixing the liquids or injecting the mixed liquid (that is, before the liquid reaches the mold). It is believed that, due to shrinkage during curing, vacuum holes and the like are generated along with sink marks, and air holes due to the above also expand.

In view of these points, the present invention provides a reaction injection molding die capable of obtaining a bubble-free non-foamed resin product.

[0006]

[MEANS FOR SOLVING THE PROBLEMS] The reaction injection molding die of the present invention comprises a) a closed space into which an overflow resin solution flows together with the air extruded from the molding cavity when the resin solution (mixed solution) is injected. And a b) a mating surface of each of the combined molds or a contact surface between them and the insert part is provided with a very small gap communicating with the molding cavity.

[0007]

In the mold of the present invention, when the amount of the resin liquid that exceeds the inner volume of the molding cavity is injected, the air in the cavity is first pushed out by the resin liquid into the closed space of a) above. At the same time, the resin liquid overflowing from the cavity flows into the lower part of the space. The air pushed into the space has a pressure equal to or higher than the atmospheric pressure, but the pressure is transmitted to the resin liquid in the entire cavity via the resin liquid flowing into the lower portion. The resin liquid cures under pressure, and the shrinkage that accompanies curing is compensated by the effect of the feeder, so sink marks do not occur during curing and vacuum holes are created in the molded product. Nothing. It should be noted that no special equipment or device such as a compressed air source or a fluid pressure cylinder for exclusively performing this pressurizing action is required.

Most of the air contained in the resin liquid at the time of mixing a plurality of liquids or at the moment of injection into the mold flows into the above-mentioned closed space, but a small amount of air that cannot flow there. The air component flows into the gap in b) above. Therefore, air bubbles containing air (thus, those that do not completely disappear even when pressure is applied) do not occur in the cavity that is the main body of the molded product.

Although the resin liquid flows into the gap having a small thickness together with the air, the resin liquid that slightly flows in serves as a sealing material and blocks the remaining resin liquid, so that even if there are no packings, etc. The pressure based on the closed space effectively acts on the resin liquid in the cavity.

[0010]

1 (a) and 1 (b) are sectional views of a mold according to an embodiment of the present invention (FIG. 1 (b) is same as FIG. 1 (a)).
Is a BB cross section).

The illustrated mold 1 is for obtaining a drum cleaning blade used in a copying machine or the like by injection molding of fast-curing polyurethane. Injection device 4
In the mixing head 5, the two kinds of liquids are impinged and mixed to form a fast-curing polyurethane resin liquid, which is subsequently injected at high speed into the molding cavity 2 of the mold 1 and cured to obtain a product. (Unfinished molded product). The size of the blade body (polyurethane part), that is, the size of the cavity 2 is approximately 1.5 mm × 30 mm
× 300 mm. The advantages of this molding method are that it is possible to obtain a homogeneous product because the mixing is sufficiently performed while the viscosity is low, and the productivity is high because the curing time is short. Reference numeral 5a in the mixing head 5 is a discharge port of the urethane prepolymer which is the main component, and reference sign 5b is a curing agent discharge port located at a position facing the discharge port 5a.

In the figure, reference numeral 11 is an upper mold, and reference numeral 12 is a lower mold. Both of them are assembled by inserting an insert part 3 serving as a blade mounting bracket as shown in FIG. Reference numeral 14 is a positioning pin for the component 3, and reference numeral 13 in FIG. 3A is a positioning pin for the upper die 11 with respect to the lower die 12. Further, reference numeral 15 is a packing interposed on the mold matching surface at a position slightly (about 5 mm) away from the cavity 2. The upper mold 11 and the lower mold 12
The mold clamping mechanism is not shown in the figure.

Cavity 2 obtained at high speed by collision mixing
If bubbles (air holes / vacuum holes) are generated in the mixed resin liquid injected into the mold, a blade having an excellent cleaning function cannot be molded. Therefore, the mold 1 should be modified as follows. is there. That is,

1) As shown in FIG. 1A, a residual pressure pot 20 communicating with the upper part of the cavity 2 is attached to the upper mold 11. The pot 20 includes a pipe portion 21 that penetrates the upper portion of the upper mold 11.
And a sealed space 22 connected to the end, a piston 23 densely inserted through an O-ring into the inner circumference of the space 22,
And a set screw 24 that determines the position (height) of the piston 23 for adjusting the volume of the space 22. When the resin liquid is injected into the cavity 2 as shown in FIG.
(Including), and apply a positive pressure to the resin liquid.
In the embodiment, the inner volume of the space 22 is set to be 20 to 30% of the inner volume of the cavity 2.

2) Of the mating surfaces of the upper mold 11 and the lower mold 12, a portion inside the packing 15 as shown in FIG.
Further, as shown in FIG. 7B, gaps 30a and 30b having a small thickness (20 to 30 μm) are provided between the upper mold 11 and the lower mold 12 and the insert part 3 into which they are sandwiched. The thickness of the gaps 30a and 30b is so thin that the resin liquid flowing into the gap loses fluidity and functions as a sealing material (thus preventing continuous outflow of the resin liquid).
Moreover, the dimensions are thick enough to allow the air content in the resin liquid to enter with a slight amount of the resin liquid. The gap 30b between the insert part 3 and the insert part 3 also has a function of absorbing variation in the thickness of the part 3. That is, even if the same component 3 is made slightly thicker, the upper mold 11 and the lower mold 12 that sandwich it are not opened unnecessarily and the thickness of the cavity 2 is not increased. The accuracy is high.

In this example, a polyurethane blade was molded using the mold 1 as described below.

Preparation of Urethane Prepolymer (Main Component): Polyol (eg Polyethylene Adipate)
50.4 parts and polyisocyanate (for example, 4 '
41.0 parts of diphenylmethane diisocyanate) to obtain a polyurethane prepolymer having an isocyanate group content of 15.0%, and this is heated to 60 ° C. The viscosity at this temperature is 100 to 500 cP.

Preparation of curing agent: polyol or 1.4
A curing agent obtained by mixing butanediol and the like is heated to about 50 ° C. The viscosity at this temperature is still 100-500.
It is cP.

Collision mixing and injection: 1 beforehand
With respect to the mold 1 heated to 45 ° C., the tip nozzle of the injection device 4 is brought into contact with the recess 16 of the mold 1, and the main agent and the curing agent are discharged into the mixing head 5 through the discharge ports 5a and 5b.
After mixing by colliding them, the mixed resin liquid is runner 1
It is injected so as to fill the cavity 2 via 7. The mixing ratio at the time of collision mixing is as follows: main agent / hardening agent = 100/97
(Weight ratio), and the discharge pressure from the discharge ports 5a and 5b is 15
0 kg / cm ² , injection amount per unit time is 45 g / s
At ec, an amount of resin liquid that overflows from the cavity 2 and enters the residual pressure pot 20 is injected in about 0.5 seconds (with a viscosity of 100 to 500 cP).

After the above, when the mold 1 is opened and the molded product is taken out after the curing time has elapsed, it enters into the gaps 30a and 30b and becomes a small burr (a part to be cut off in the finishing step). Although some bubbles were observed,
There were no air bubbles, which are practically problematic, in the portion molded in the cavity 2 as the body of the blade.

Incidentally, three comparative examples tried before this example will be introduced below.

COMPARATIVE EXAMPLE 1: The residual pressure pot 20 of the mold 1 has its upper portion (piston 23, etc.) opened, and has a gap 30a.3.
0b is not provided. Into such a mold, the resin liquid is injected under the same conditions as the above while maintaining the inside of the cavity 2 at atmospheric pressure (normal pressure). The obtained molded product has innumerable bubbles throughout.

Comparative Example 2: Using the same mold as in Comparative Example 1, a vacuum pump is connected to the residual pressure pot 20. The tip nozzle of the injection device 4 is applied to the mold (recess 16 thereof),
The inside of the cavity 2 is depressurized to 3 mmHg by a vacuum pump, and then the resin liquid is injected in the same manner as above. In the molded product thus obtained, larger air bubbles were present in the whole than in Comparative Example 1, although the number was small.

Comparative Example 3: The same mold as that of Comparative Example 1 is used, but a compressed air source connectable to the residual pressure pot 20 is prepared. Cavity 2 at atmospheric pressure as in Comparative Example 1
Immediately after that, the air source is connected to the residual pressure pot 20 and 0.3 k is added to the resin solution in the cavity 2.
A pressure of g / cm ² is applied and the pressurized state is maintained until the resin liquid is cured. Bubbles are observed in the molded product, but the number is smaller and the size is much smaller than in Comparative Examples 1 and 2.

[0025]

[Effect of the Invention] According to the reaction injection mold of the present invention,
It is possible to obtain a non-foamed resin molded product having no bubbles (air holes / vacuum holes). At that time, it is preferable from the viewpoint of productivity because the material (blending) that has been apt to contain bubbles in the past due to its high curing rate is preferable in terms of productivity. In addition, collision mixing or the like, which is usually easy to involve bubbles, is taken as a mixing means. Therefore, it is also advantageous in improving mixing efficiency and uniformity of mixed materials. In addition, there is also an advantage that no special pressurizing means such as a compressed air source or a fluid pressure cylinder is required, the structure is simple and low cost, and suitable for continuous production.

[Brief description of drawings]

FIG. 1 is a sectional view of a mold according to a first embodiment of the present invention. Of these, FIG. 7B shows a BB cross section of FIG.

[Explanation of symbols]

 1 Mold 2 Mold Cavity 3 Insert Part 22 Sealed Space 30a / 30b Gap

Claims (1)

[Scope of utility model registration request] 1. At the time of injecting a resin liquid, a closed space into which an overflow resin liquid flows together with air extruded from a molding cavity is provided, and is provided on a mating surface of each combined mold or a contact surface between them and an insert part. , A mold for reaction injection molding, which has a very small gap communicating with the molding cavity.