Method of making a composite racket

A composite racket having at least one portion made of a thermoplastic resin and having the remaining portion made of a thermosetting resin is disclosed. The thermoplastic and thermosetting resins provide different dynamic stiffness, flexibility and toughness so that the racket possesses desired characteristics in the zones where they are necessary. The racket is fabricated by preforming a fiber reinforced thermoplastic resin in a first mold to form one of the frame portions and placing this preformed portion in a second mold. A fiber reinforced thermosetting resin is then formed into the other frame portion in the second mold and joined to the frame portion formed using thermoplastic resin at the throat section of the racket.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a composite racket, and particularly to a 
composite racket which is made of a thermoplastic resin with a continuous 
fibrous matrix in at least one portion thereof and made of a thermosetting 
resin with a continuous fibrous matrix at the other portion. 
2. Brief Description of the Prior art 
It has been known that racket frames made of epoxy resins provide the 
advantages of high rigidity, good striking characteristics and easy 
fabrication. However, such racket frames produce substantial initial shock 
which will cause injury to the users and, in addition, cannot provide a 
sufficient impact strength Attempts were made to improve the impact 
strength and reduce initial shock or vibrational forces by altering the 
fibrous materials used in combination with the epoxy resins or by 
modifying the orientations of fibers. Nevertheless, the improved effects 
obtained thereby are not satisfactory owing to the limitation of using a 
single type of matrix resin. Use of a thermoplastic resin such as Nylon in 
the fabrication of the racket frame has been recently suggested for the 
purposes of reducing initial shock and vibrational forces and improving 
the impact strength. However, the high flexibility of the thermoplastic 
resin lowers the striking characteristics and the fabrication of a racket 
with a composite thermoplastic material is difficult. 
U.S. Pat. No. 5,071,125 which is owned by the applicant of this invention 
discloses a racket which is made of two or more than two materials. It 
also discloses a preferred embodiment comprised of a head made of a 
material of high rigidity and a shaft made of a less rigid or stiff 
material so as to reduce shock transmitted to the hand of the user. 
There are other patents such as U.S. Pat. Nos. 4,367,871, 4,052,060, 
4,725,059, 4,746,119, 4,906,002 and 4,007,929 which concern the connection 
of two or more than two component parts of a racket frame. A composite 
racket disclosed in U.S. Pat. No. 4,725,059 comprises a shaft portion, two 
branches of a throat portion and a frame portion all of which are made of 
composite materials Each portion has a foam core and a sheath comprised of 
fiber webs or braids impregnated with a synthetic resin. The foam cores 
and the sheaths of the portions are made of different materials. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a racket frame which has at least 
one portion made of a thermoplastic resin and the other portion made of a 
thermosetting resin. 
Another object of this invention is to provide a racket frame which is made 
of a thermosetting resin of high rigidity in at least one portion and made 
of a thermoplastic resin of less rigidity in the other portion thereby 
acquiring the advantages of both the thermosetting and the thermoplastic 
resin while compensating for the disadvantages thereof. 
According to the present invention, a racket frame comprises at least one 
portion made of a thermoplastic resin and the other portion made of a 
thermosetting resin. In one aspect of the invention, a racket frame is 
fabricated by: preforming a shaft portion by using a first composite 
material containing a thermoplastic resin; placing said preformed shaft 
portion in a mold having a cavity to shape the head and the shaft 
simultaneously; and forming a head portion by using a second composite 
material containing a thermosetting resin in said mold, said head portion 
being formed integrally with said shaft portion; wherein said 
thermoplastic resin has a melting point higher than the curing temperature 
of said thermosetting resin. Preferably, the thermoplastic resin a low 
rigidity and the thermosetting resin has a high rigidity. 
In another aspect of the invention, the thermoplastic resin is Nylon or 
polycarbonate or a thermoplastic alloy and the thermosetting resin is 
epoxy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIG. 7, a preferred embodiment of the racket of this invention 
includes a head portion 30 which is made of a composite material 
containing an epoxy resin and a shaft portion 20 including a throat 22 and 
made of a composite material containing nylon. 
An example of the process for fabricating the racket of this invention 
comprises the first step of forming the shaft portion and the second step 
of forming the head portion together with the shaft portion. 
As shown in FIG. 1, a fabric material saturated with a Nylon resin 
composition is tailored and wrapped around a tube to form a roll member 
The resin-saturated fabric roll is placed in a first mold (FIG. 3) which 
has a mold cavity to form the shaft of the racket and is heated to 240 deg 
C. During heating, compressed air is introduced into the tube to create a 
pressure sufficient to pressurize the roll against the wall of the cavity 
of the mold. Afterward, the mold is cooled to harden the content thereof 
thereby resulting in a rough shaft. The rough shaft is placed in a second 
mold (FIG. 2) which has a cavity to impart the shape of a racket so as to 
combine with the head portion which will be formed later therein. 
In forming the head portion, another fabric material saturated with an 
epoxy resin composition is tailored and wrapped around a tube to form a 
roll. The resin-impregnated fabric roll is placed in the second mold, and 
the tube thereof is inserted through the rough shaft and connected to a 
compressed air supply. After heating the mold to 150 deg C. to cure the 
epoxy resin and providing an appropriate interior air pressure via the 
tube, the mold is cooled and a racket frame is thereby obtained 
Referring to FIG. 2, a second mold 10 for forming the racket of this 
invention comprises a lower mold which has a cavity 11 to impart the shape 
of a racket. The cavity 11 has a portion to shape the head of the racket 
and another portion to shape the shaft of the racket. The lower mold can 
be closed by an upper mold and can be fastened thereto by means of locking 
means 13. 
In FIG. 3, a first mold 10' for shaping the shaft of a racket is shown, 
having a cavity 11' to shape the racket shaft including a throat section. 
The cavity 11' has a substantially Y section which includes two arms 11a 
each of which has inward projecting wall surfaces 14 along the length L 
(preferably 1-15 cm) thereof thereby reducing the width of each arm 11a to 
D. Due to the portion of each arm 11a with a reduced width, the resultant 
preformed shaft has restricted joint portions in the throat section 
thereof which joint portions can overlappingly connected to the joint ends 
of the head which is formed later. 
In FIG. 4, another example of the first mold 10" is shown, having a cavity 
11 to shape a shaft without a throat section. The mold cavity 11 has 
inward projecting wall surfaces 15 along the length L to provide a 
restricted joint end of the shaft. 
As shown in FIGS. 5 and 6, a shaft 20 preformed in the first mold 10' of 
FIG. 3 is placed in a second mold 10 of FIG. 2 and the joint ends 22 of 
the throat section 24 thereof are joined with the joint ends 32 of the 
fabric roll to form a head 30. In joining, the fabric of the head 30 
overlaps the restricted joint ends of the shaft 20. These joints are 
strong and do not bulge. During the molding operation, air is supplied 
through the air tube 40 and the mold is heated. The crude product obtained 
from the mold 10 is further subjected to a conventional finishing process. 
When comparing the racket of this invention with a conventional racket, 
this invention provides the following advantages: 
1. This invention provides a composite racket construction achieved by 
using two different composite materials thereby obtaining the advantageous 
characteristics of both materials and compensating for the disadvantages 
thereof. 
2. This invention provides a composite racket construction which has a high 
rigidity at its head while having a degree of flexibility to reduce shock 
at its shaft. 
3. The racket of this invention may have a joint or more than one joint 
according to the number of the materials used to fabricate the racket. 
While Nylon and epoxy are used in combination in the above-mentioned 
preferred embodiment, this invention is not limited thereto. Polycarbonate 
can be used instead of nylon in accordance with this invention. In 
addition, any combination of thermoplastic and thermosetting resins which 
can provide different dynamic stiffness and flexibility may be used 
according to this invention. Furthermore, although the above-mentioned 
embodiment shows that the head portion is made of a matrix thermoplastic 
resin and that the shaft including the throat is made of a matrix 
thermosetting resin, in another embodiment of this invention, a racket may 
have its throat made of a matrix thermoplastic resin and have its shaft 
and head made of a matrix thermosetting resin. According to still another 
aspect of this invention, the racket which is made of the same materials 
as the first embodiment can be fabricated by separately forming the head 
and the shaft thereof and then joining them using a tenon joint and 
fasteners. 
With the invention thus explained, it is apparent that various 
modifications and variations can be made without departing from the scope 
of this invention. It is therefore intended that the scope of this 
invention be limited only as in the appended claims.