JPH03208610A - Molding method of hollow product - Google Patents

Abstract

PURPOSE:To mold easily the hollow product which has complicated shape and is made of resin or FRP by using a shape storing behavior of a shape-memory resin which constitutes a core and the quickly lowering of modulus of elasticity at high temperature. CONSTITUTION:As a core, the branched tube 2 which is made of shape memory resin in inserted into the mold 1 of the branched tube which is devided into half, and the mold 1 is closed. While the branched tube 2 which is made of the shape-storing resin is warmed in the mold 1, inner pressure is applied to the branched tube 2 with suitable fluid, whereby the branched tube 2 is expanded until the tube 2 is brought in close contact with the mold 1. The core-branched tube 2 is cooled in the state where said expanded state is kept by holding said inner pressure, whereby the expanded shape of the core-branched tube 2 is fixed. Then, the expanded and fixed core 2 is taken out from the mold 1, and is coated with covering resin 3. After the covering resin has been cured with a suitable means, the core is restored to the original shape by heating it again, and the reduced core is drawn out and removed, whereby the molded object 3 with the shape of desired branched tube may be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for shaping hollow products made of resin or fiber-reinforced resin (FRP), which is particularly suitable for manufacturing hollow products with complex shapes.

[Conventional technology] Conventionally, resin hollow products have been manufactured by extrusion molding, injection molding, cast molding, etc., and FRP hollow products have been manufactured by hand lay-up method, filament winding method (hereinafter referred to as FW method), etc. has been done.

Among these methods, all methods except extrusion molding involve coating the core material with resin or FRP and then pulling out the core material, but it is extremely difficult to mold complex-shaped objects, including extrusion molding. there were. For this reason, in the manufacture of complex-shaped products, hollow products may even be used with the core material integrated without removing it.

Using a low-melting point metal for the core material and then melting and removing the core material after shaping has been proposed as a method that can mold complex-shaped objects, but this method is complicated and has low productivity. There is a drawback.

It is also known to mold hollow products using a deformable resin core material. For example, JP-A-61-25
No. 39 and No. 62-19438, a flexible cylindrical material is used as a core material, a fluid is injected into the interior to expand the core material, and resin-impregnated fibers are wrapped around the core material, and then a fluid is injected into the core material to expand the core material. F
A method for manufacturing FRP pipes using the W method has been proposed. JP-A-62-167032 discloses a similar method for manufacturing an FRP cylindrical body using an elastically deformable core material.

However, the above-mentioned conventional molding method using a resin core material has a small expansion force of the core material, so it can only be applied to molding simple shaped objects such as tubular or cylindrical bodies with circular or irregular cross sections. Not suitable for complex-shaped objects. In addition, when winding resin-impregnated fibers using the FW method while the core material is in an expanded state, it is necessary to use a fairly high-strength core material to overcome the tension of the fibers. and is disadvantageous in terms of cost.

JP-A No. 64-63117 discloses that a manifold pipe molding core, which is made by connecting a plurality of members in which a bendable core material with shape retention properties is coated with a heat-resistant elastomer, is deformed into a desired shape, and a mold is formed. A method of manufacturing a resin manifold is disclosed, which comprises inserting the core into a core, coating the surface of the core with resin, and then withdrawing the core. However, with this method, the strength of the core is weak <F
The W method cannot be applied, and the core is made up of multiple members, making the manufacturing process complicated. Furthermore, pulling out the core after coating with resin may be difficult depending on the thickness of the core because the core does not shrink.

[Problems to be Solved by the Invention] The purpose of the present invention is to provide a method for molding hollow products that can be easily used for molding complex-shaped objects, does not require complicated operations, and is advantageous in terms of productivity and economy. It is to provide.

[A Thousand Steps to Solve the Problem] The present inventors focused on the use of shape memory resin as a means to achieve the above object.

Shape memory resin is a thermoplastic resin that retains its deformed shape at room temperature and recovers to its original shape when heated to high temperatures. Among them, polynorbornene, transpolyisobrene, styrene-butadiene copolymer, polyurethane type, polyester type, etc. are known. Such a shape memory resin has the characteristic that it can recover its shape even after a large deformation of 400 to 500%, whereas a shape memory alloy can only recover a deformation of about 7%.

The present inventors found that when a shape memory resin is used as a core material for a precept,
We have discovered that even for hollow products with complex shapes, the core material can be easily removed after molding is completed by utilizing its shape recovery characteristics, and the above objective can be achieved. That is, the core material made of shape memory resin is deformed into a desired shape that is several times larger than the original shape (memorized shape) and then fixed. This core material is coated with resin or FRP, and after the resin hardens, the original shape of the core material is restored by heating, and the core material is removed.

Here, the gist of the present invention is to expand a hollow core material made of a shape memory resin, which has a shape smaller than the hollow part of a hollow product to be molded, by applying internal pressure under heating. The core material that maintains the desired shape is coated with resin or resin-impregnated fibers, and then (a)
Either the resin is cured at a temperature below the shape recovery temperature of the core material, and then the core material is heated above the shape recovery temperature to shrink the core material to its original shape and removed. A resin or fiber-reinforced resin characterized in that the resin is cured at a temperature above the shape recovery temperature while applying liquid internal pressure to the material, and then the internal pressure is removed to allow the core material to recover to its original contracted shape and then removed. A method of forming a hollow product consisting of

[Effect] Hereinafter, the structure and operation of the present invention will be explained in detail.

In the present invention, the shape memory resin used for the core material is not particularly limited, and any shape memory resin can be used as long as it is deformable to the extent that it can be removed from the molded product after shape recovery. For example, existing shape memory resins such as polynorbornene, transpolyisoprene, styrene-putadiene copolymer, polyurethane type, and polyester type, as well as shape memory resins to be developed in the future can be used.

These shape memory resins may be used alone, but in order to improve strength and shapeability, a polymer alloy with a general-purpose resin may be used, although the deformability is somewhat reduced.

Furthermore, when molding by the FW method, it is preferable that the resin has high strength since it is subjected to the tightening tension of the fibers. High strength resins such as polyester and polynorbornene are suitable for this purpose.

Shape memory resin (including polymer alloys) is first molded into a hollow body smaller than the hollow part of the desired molded shape to be easily removed from the desired hollow molded product using an appropriate molding method. , forming a hollow core. This molding can be performed by conventional melt molding methods such as extrusion, injection, and casting.

Next, this hollow core material is expanded while applying internal pressure under heating to form a desired shape that matches the internal shape of the hollow product to be manufactured. This expansion and molding into the desired shape is
It can be carried out in a mold of a desired shape (a combination material of a multi-segmented mold such as a half-split shape). A hollow core material manufactured by melt molding is placed in this mold, and the core material is expanded until it comes into close contact with the mold by applying internal pressure by compressing a fluid inside the core material while heating. By cooling with internal pressure applied, the desired expanded shape is fixed.

The appropriate temperature for heating is 20°C lower than the melting temperature, and since it is easy to deform if it exceeds the shape recovery temperature, the temperature is preferably 10 to 30°C higher than the shape recovery temperature.

As for the method of heating, although the mold can be heated externally, it is convenient to heat the core material by heating the fluid that applies internal pressure. There are no particular restrictions on the fluid that applies internal pressure, and inert gases or liquids such as air, steam, water, and oil can be used as appropriate. The elastic modulus of shape memory resin rapidly decreases at high temperatures, so the weight of shape memory resin is at most 20 to 30 kg.
It can be easily expanded several times with an internal pressure as low as /c1i1.

For cooling, heat radiation to the mold may be used, or the fluid that applies internal pressure may be gradually replaced from a high-temperature fluid to a low-temperature fluid while maintaining the pressure. When cooled, the elastic modulus of the shape memory resin is restored, resulting in a core material fixed in an expanded shape with high strength.

The core material thus formed into the shape of the hollow product to be produced is coated with the resin or resin-impregnated fiber to be shaped. Possible coating methods include, for example, a method in which a mold and a core material are combined and cast, a hand lay-up method, an FW method, and the like. Any coating method can be used as long as it allows resin coating to a desired thickness.

After coating the resin or resin-impregnated fibers, the coating resin is cured by heating at room temperature or at a temperature lower than the shape recovery temperature of the core shape memory resin. This curing can be carried out by natural curing, thermal curing, or irradiation with ultraviolet rays or electron beams, using a method suitable for the resin system. It is not necessary to completely cure the resin at this stage, and it is sufficient that the resin is only partially cured to the extent that the resin can maintain its self-supporting properties even after the core material is removed.

After the coating resin is cured in this manner, the core material is heated above the shape recovery temperature to restore the original shape.

If necessary, this heating can be continued until the resin is fully cured. Since the original shape is very small compared to the molded article, it can be easily removed from the precept. Further, even if the protrusion shape remains, if it is pulled in a heated state, the core material exhibits rubber elasticity in a heated state, so it can be easily deformed and pulled out. Therefore, it is preferable to remove the core material while the core material is in a softened state before being cooled. The removed core material is
It can be reused by applying internal pressure again and performing expansion molding.

If the coating resin is a thermosetting resin and heating above the shape recovery temperature of the core material is required to cure the resin, apply internal pressure inside the core material with a liquid fluid such as water or oil. By heating the resin to a resin curing temperature that is higher than the shape recovery temperature of the core material, the resin can be thermally cured without causing the core material to recover its shape. It is difficult for a gas fluid to sufficiently resist the restoring force of the core resin that occurs during this heating. In this case, after heat curing, if the internal pressure is removed while maintaining the heating above the shape recovery temperature of the core material, the core material will return to its original shape and shrink, so it can be removed in the same way as above. .

The method of the present invention can be used to form various thermosetting, ultraviolet or electron beam curable resins, and the type of resin is not particularly limited. The resin contains a curing agent, a mold release agent, a pigment,
Dyes and other conventional additives can be incorporated. F
In the case of RP molding, in addition to glass fibers, other reinforcing fibers such as carbon fibers and aramid fibers can also be used.

The attached FIGS. 1 to 6 show an overview of the precept method of the present invention.

11 FIGS. 1 to 5 are cross-sectional views showing the manufacturing process in order. FIG. 6 is a perspective view of a desired branch pipe to be molded.

First, as shown in FIG. 1, a branch pipe 2 made of shape memory resin as a core material is inserted into a half-split branch pipe mold 1.
close together. The shape memory resin branch pipe 2 can be produced by fusion-bonding resin pipes formed by extrusion.

This branch pipe 2 made of shape memory resin is heated in the mold 1 and internal pressure is applied to the branch pipe with an appropriate fluid, thereby expanding the branch pipe 2 until it comes into close contact with the mold 1 as shown in FIG. let By maintaining the internal pressure and cooling while maintaining this expanded state, the expanded shape of the core branch pipe 2 shown in FIG. 2 is fixed.

After this, the expanded and fixed core material 2 is taken out from the mold 1,
A coating resin 3 is applied as shown in FIG. After curing the coating resin by an appropriate means, heat it again to return the core material 2 to its original state (Fig. 4), and then pull out and remove the smaller core material to create the desired branch pipe shape. A molded article 3 is obtained (Fig. 125).

Here, the shape-memory resin serving as the core material 2 and the coating resin covering the preform 3 are required to be non-adhesive. If both have adhesive properties, the surface of the core material is coated or coated with a release material before the expanded core material is coated with the coating resin.

As the mold release material, known materials such as silicone oil and fluororesin can be used.

[Examples] The present invention will be explained in more detail with reference to Examples, but it goes without saying that the present invention is not limited to these.

A resin pipe made of shape-memory polyester (manufactured by Nippon Zeon, descendant product name Zeon Shable A-80, shape recovery temperature 80°C) with an outer diameter of 26 m and an inner diameter of 20 mm was formed by extrusion molding using Mitsu Arashi extrusion method. A core branch pipe was produced by fusion bonding so that the branch pipe had the cross-sectional shape shown in 2.

This core branch pipe is molded into a branch pipe-shaped mold (
By closing the half-split shape shown by 1 in Figure 1, insert it into the structure tc) and insert it into the shape memory resin branch pipe.
℃ hot water was injected, and an internal pressure of 20 kg/d was applied and the tube was heated at the same time. The core branch pipe expanded to an outer diameter of 50a and deformed into the same shape as the mold. While maintaining this internal pressure, the core material was cooled by replacing hot water with water, and the expanded shape of the core material was fixed.

Next, the mold is divided and the expanded core branch pipe is taken out.
On the surface of this core material, continuous mat (glass fiber reinforced resin) made of vinyl ester is hand laid up.
It was coated to a thickness of g. After the resin was cured by standing at room temperature for 90 minutes, the coated core material was placed in an oven at 90° C. and heating was started. The core material soon recovered its original shape and shrunk as shown in FIG. Heating was continued in this state for 2 hours to completely cure the covering material, and then the core material was pulled out at 90°C. The branched portion of the core material was easily deformed and could be easily removed.

In the same manner as in Example 1, the core material was expanded and deformed so as to have an expanded shape corresponding to the precept shown in FIG. 7, and the expanded shape was fixed. The core material resin used was a polynorbornene shape memory resin (manufactured by B-Zeon, trade name Nosolex, shape recovery temperature 40°C), and the initial shape of the core material was an outer diameter of 1.
It was a tubular body with a diameter of 10 mm, an inner diameter of 100 am, and a length of 300 mm with one end closed.

The core material in this initial shape was placed in a half-split mold and expanded with hot water at 60°C at an internal pressure of 5 kg/cJ to form a cylindrical container with an outer diameter of 200111J and a length of 300 am as shown in Figure 7. Molded into shape.

After cooling, unsaturated polyester resin-impregnated glass fiber is applied to the surface of the expanded core material to a thickness of 10 mm using a 5-axis FW molding machine.
It was coated so that After drying for 60 minutes at room temperature, it was dried for 8 minutes while applying an internal pressure of 5 kg/d inside the core material using hydraulic pressure.
The resin was completely cured by heating to 0°C for 30 minutes. After removing the oil inside the core material, if it is further heated to 90℃,
The core material quickly recovered to its original shape and could be easily pulled out from the opening of the molded article.

15 [Effects of the Invention] According to the method of the present invention, by utilizing the shape recovery behavior of shape memory resin and the rapid decrease in elastic modulus at high temperatures, it is possible to form complex shapes made of resin or FRP, which was difficult with conventional techniques. Hollow products can be easily formed. Moreover, since the core material can be used repeatedly, productivity is not impaired. Furthermore, the expansion and deformation of the core resin is performed in a low elastic modulus state due to heating, so it can be deformed at low internal pressure, and after cooling and fixing the expanded shape after deformation, it returns to a high elastic modulus,
Since it can exhibit high strength, it is possible to overcome the tension caused by the fibers and obtain a material with sufficient strength as a core material for the FW method at a lower internal pressure than before. Further, after the molded article has hardened, the core material easily returns to its original, very small shape by heating, so it is very easy to pull out the core material from the obtained pre-shaped article.

As described above, although the method of the present invention can be used for molding complex-shaped objects, it is easy to operate and economical, making it extremely useful in industry16.

[Brief explanation of drawings]

1 to 5 are cross-sectional views showing the steps of the method of the present invention, FIG. 6 is a schematic perspective view of a hollow branch pipe formed according to the present invention, and FIG. 7 is a diagram showing another embodiment of the present invention. FIG. 2 is a perspective view of a hollow container molded according to an example. 1. Mold, 2. Shape memory resin core material, 3. Molded article.

Claims (2)

[Claims] (1) A hollow core material made of shape memory resin, which has a shape smaller than the hollow part of the hollow product to be molded, is expanded by applying internal pressure under heating to form it into the desired shape. A core material that retains the desired shape is coated with a resin or resin-impregnated fibers, the resin is cured at a temperature below the shape recovery temperature of the core material, and then the core material is heated to a temperature above the shape recovery temperature to cause the core material to memorize. A method for molding hollow products made of resin or fiber-reinforced resin, characterized by shrinking them to their original shape and removing them. (2) A hollow core material made of shape memory resin, which has a shape smaller than the hollow part of the hollow product to be molded, is expanded by applying internal pressure under heating to form it into the desired shape. A core material that retains the desired shape is coated with resin or resin-impregnated fibers, the resin is cured above the shape recovery temperature while applying liquid internal pressure to the core material, and then the internal pressure is removed to allow the core material to memorize its original shrinkage. A method for molding a hollow product made of resin or fiber-reinforced resin, characterized by recovering the shape and removing it.