JPH01218809A - Manufacture of hollow plastic product - Google Patents

Abstract

PURPOSE:To eliminate defects such as unevenness, deformation generated by pressure and enhance accuracy of wall thickness by effecting resin curing preliminarily in an internal pressure retaining material or its outside. CONSTITUTION:Heat curing or ordinary temperature curing resin is applied to an internal pressure retaining material. In case of a prepreg, said resin is wound on the internal pressure retaining material or the prepreg itself is made the internal pressure retaining material. If necessary, reinforced fibers and further non-woven cloth are wound around the internal pressure retaining material thus prepared, and said material is placed in a mold. High temperature air is introduced into the internal pressure retaining material, which is fit to the mold, and at the same time, ordinary temperature air is introduced therein. In case ordinary temperature curing resin is used, said procedure is carried out quickly and the room temperature air is introduced therein. A rim molding monomer is introduced between the internal pressure retaining material and the mold by the conventional method and molding is carried out after curing. Heat resistance and resistance to chemicals are not required for a tube. Said process is particularly suitable for sports items which need the wall thickness accuracy very much such as a tennis racket, a shaft for a golf club and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing lightweight plastic products useful for pipe-like structures such as tennis racket and golf club shafts.

(Prior Art and its Problems) Plastic products such as tennis rackets and golf club shafts are usually made hollow to reduce their weight.

There is a method of drilling holes in plastic products to make them hollow, but this process is time-consuming and difficult to make into complex shapes. Another method is to wrap reinforcing fibers impregnated with thermosetting resin around a mandrel, set it in a mold, heat harden it, and then pull out the mandrel, but this method cannot be applied to products with complex shapes, so limited to those in the form of

Furthermore, a method has been proposed in which a tube is set in a mold, air pressure is applied inside the tube, and then a rim molding composition is injected. In this method, it is very difficult to balance the internal pressure of the duplex and the injection pressure of the rim molding composition, and uneven thickness, collapse or splitting of the duplex is likely to occur.

(Means for Solving the Problems) The present inventors have overcome the above-mentioned drawbacks and have discovered a method for producing plastic products with high wall thickness accuracy even in complex shapes.

That is, the present invention provides a method for manufacturing a hollow plastic product in which a tube-shaped or bag-shaped internal pressure retaining body is arranged in a mold, and a rim molding composition is injected and hardened between the internal pressure retaining body and the mold. Provided is a method for producing a hollow plastic product, characterized in that a holder is coated in advance with a thermosetting or room temperature curable resin and cured.

According to the present invention, the shape of the internal pressure holding body is fixed by coating the internal pressure holding body with a thermosetting or room temperature curing resin and then curing the resin. The internal pressure holding body may be any material having flexibility to conform to the shape of the mold by injecting air or the like, and may be a tube-shaped or bag-shaped material made of nylon, cellophane, rubber, polyester, polyether ketone, or the like.

Various types of thermosetting or room temperature curable resins are known, and for example, epoxy-based, urethane-based, polyester-based, and vinyl ester-based resins are common. These are usually available as compositions by combining curing agents and resins. In the case of this type of composition, it may be coated onto the internal pressure retaining body by a method such as coating. Moreover, this resin may be a prepreg. prepreg
is made by impregnating continuous fibers such as glass or carbon, woven fabric, or mat with thermosetting plastic mixed with a hardening agent as a reinforcing agent, and then leaving it in a semi-dry state to lose its stickiness. say.

The internal pressure holding body may be cured after coating the prepreg or by introducing hot air into the holding body. Further, as a heating method, the mold may be directly heated while applying internal pressure.

Rim molding refers to reaction injection molding, and in the case of the present invention, an internal pressure retaining body is placed in a mold, high temperature air is introduced into the internal pressure retaining body to harden the thermosetting or room temperature hardening coating, and then the metal is molded. This is a method in which a reactive monomer is introduced into a mold and reacted at room temperature or at an elevated temperature to perform molding. The resin obtained by rim molding may be any conventional resin such as polyurethane, poly, amide, etc. The rim molding composition suitable for the present invention is UBE nylon (UX-21
).

In the present invention, reinforcing fibers may be arranged between the internal pressure holding body and the mold. Any reinforcing fibers that are normally used in fiber-reinforced plus decks may be used. Typical examples of reinforcing fibers include aramid fibers, carbon fibers, glass fibers, and the like. The most preferred reinforcing fiber is carbon fiber. The fibers can be in any form, braided or unbraided.

According to the present invention, a nonwoven fabric layer may be further provided between the mold and the reinforcing fibers to improve the appearance of the product. Examples of nonwoven fabrics that can be used include glass fiber paper, carbon fiber paper, polyester nonwoven fabric, and nylon nonwoven fabric. This nonwoven fabric preferably has a fiber density of 2 to 3.5 Vo1%, preferably 5 to 20 Vo1%, so that the flow of the rim fluid is appropriate. If the fiber density is greater than 35Vo1%, the resin will be difficult to penetrate and the appearance will be poor. In addition, if it is less than 2Vo1%, the nonwoven fabric itself becomes too sparse, and even if a nonwoven fabric layer is provided as the outermost layer of the carbon fiber plaid layer, there may be places where the lower plaid layer directly adheres to the mold wall surface, or the nonwoven fabric layer The resistance when the rim liquid flows becomes extremely small, and the rim liquid preferentially penetrates into the nonwoven fabric layer rather than the carbon fiber plaid layer, which has higher flow resistance, and becomes difficult to penetrate into the carbon fiber plaid layer. Also, woven cloth may be used as long as the fiber density is within this range.

According to the manufacturing method of the present invention, a thermosetting or room temperature curing resin is applied to the internal pressure holding body. In the case of prepreg, it is wound around an internal pressure holding body or the prepreg itself is used as the internal pressure holding body. The obtained internal pressure retaining body is reinforced with reinforcing fibers, if necessary.
Wrap the nonwoven fabric around it and place it inside the mold. High-temperature air is introduced into the internal pressure holding body, and the thermosetting resin is cured at the same time as it is forced along the mold. In the case of a room-temperature curing resin, the above procedure is quickly carried out and room-temperature air is introduced. After curing, a rim-forming monomer is introduced between the internal pressure holding body and the mold by a conventional method to perform molding.

(Effects of the Invention) According to the present invention, since the internal pressure holding body or the outside thereof is cured with resin in advance, deformation due to pressure does not occur unlike when the tube is filled with air, and defects such as uneven thickness hardly occur. do not have. In addition, curing of thermosetting or room temperature curing resin,
If this is carried out by introducing high temperature air into the internal pressure holding body, it will fit better into the shape of the mold and the accuracy of the wall thickness will be improved.

Also, the tube does not require heat resistance or chemical resistance.

The method of the present invention is particularly suitable for sports products such as tennis rackets and golf club shafts, which require high accuracy in wall thickness.

(Example) The present invention will be explained in more detail with reference to Examples. However, the present invention is not limited to these examples.

Example Mitsubishi Kasei (
CF fiber UD prepreg manufactured by Co., Ltd. was wrapped around it. A glass fiber mat was wound thereon, and a CF fiber braid manufactured by Toho Rayon Co., Ltd. was further set in the winding mold. Next, an air pressure of 1.5 kg/cab was applied to the tube and the mold was held at 130°C for 60 minutes to react and harden the UD prepreg.The mold was further heated to 150°C and the mold was heated to 150°C.
Unreacted monomer of MC Nylon UX-21 manufactured by Co., Ltd. was injected at a resin pressure of 1.5 kg/am''.

A hollow frame with good wall thickness accuracy could be molded without tearing the tube.

Patent applicant Sumitomo Rubber Industries, Ltd.

Claims (1)

[Claims] 1. A method for producing a hollow plastic product, in which a tube-shaped or bag-shaped internal pressure retaining body is arranged in a mold, and a rim molding composition is injected and hardened between the internal pressure retaining body and the mold. . A method for manufacturing a hollow plastic product, characterized in that the internal pressure retaining body is coated in advance with a thermosetting or room-temperature curable resin and then cured. 2. The manufacturing method according to claim 1, wherein the material coated with a thermosetting or room temperature curable resin is a prepreg. 3. The manufacturing method according to claim 1, wherein reinforcing fibers are placed on the cured resin layer of the internal pressure holding body, and then the rim molding composition is injected. 4. The manufacturing method according to claim 3, further comprising disposing a nonwoven fabric on the reinforcing fibers. 5. A hollow plastic product obtained by the manufacturing method according to any one of claims 1 to 4.