U.S. patent application number 17/491619 was filed with the patent office on 2022-04-28 for golf club shaft.
This patent application is currently assigned to SUMITOMO RUBBER INDUSTRIES, LTD.. The applicant listed for this patent is SUMITOMO RUBBER INDUSTRIES, LTD.. Invention is credited to Takashi NAKANO.
Application Number | 20220126178 17/491619 |
Document ID | / |
Family ID | |
Filed Date | 2022-04-28 |
United States Patent
Application |
20220126178 |
Kind Code |
A1 |
NAKANO; Takashi |
April 28, 2022 |
GOLF CLUB SHAFT
Abstract
A shaft includes a tip end, a butt end, flexural rigidities E1
to E10 at respective points that are located 130 mm, 230 mm, 330
mm, 430 mm, 530 mm, 630 mm, 730 mm, 830 mm, 930 mm, and 1030 mm
apart from the tip end. A ratio (E8/E1) is greater than or equal to
2 and less than or equal to 7. The flexural rigidity E1 is less
than or equal to 2.5 (kgfm.sup.2). The flexural rigidity E8 is
greater than or equal to 5.0 (kgfm.sup.2). When a formula of a
straight line that passes through a point (230, E2) and a point
(630, E6) is represented by y=ax+b, the shaft satisfies the
following relationships R1 and R8:
(130a+b)<E1.ltoreq.(130a+b+0.5) (R1), and
(830a+b)<E8.ltoreq.(830a+b+1.0) (R8).
Inventors: |
NAKANO; Takashi; (Kobe-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO RUBBER INDUSTRIES, LTD. |
Kobe-shi |
|
JP |
|
|
Assignee: |
SUMITOMO RUBBER INDUSTRIES,
LTD.
Kobe-shi
JP
|
Appl. No.: |
17/491619 |
Filed: |
October 1, 2021 |
International
Class: |
A63B 53/10 20060101
A63B053/10; A63B 60/00 20060101 A63B060/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 22, 2020 |
JP |
2020-177560 |
Claims
1. A golf club shaft comprising: a tip end; a butt end; a flexural
rigidity E1 at a point located 130 mm apart from the tip end; a
flexural rigidity E2 at a point located 230 mm apart from the tip
end; a flexural rigidity E3 at a point located 330 mm apart from
the tip end; a flexural rigidity E4 at a point located 430 mm apart
from the tip end; a flexural rigidity E5 at a point located 530 mm
apart from the tip end; a flexural rigidity E6 at a point located
630 mm apart from the tip end; a flexural rigidity E7 at a point
located 730 mm apart from the tip end; a flexural rigidity E8 at a
point located 830 mm apart from the tip end; a flexural rigidity E9
at a point located 930 mm apart from the tip end; and a flexural
rigidity E10 at a point located 1030 mm apart from the tip end,
wherein a ratio (E8/E1) is greater than or equal to 2 and less than
or equal to 7, the flexural rigidity E1 is less than or equal to
2.5 (kgfm.sup.2), the flexural rigidity E8 is greater than or equal
to 5.0 (kgfm.sup.2), when a formula of a straight line that passes
through a point (230, E2) and a point (630, E6) plotted in a graph
on an orthogonal coordinate system having an x-axis that represents
a distance (mm) from the tip end and a y-axis that represents a
flexural rigidity (kgfm.sup.2) is indicated by y=ax+b, the golf
club shaft satisfies the following relationships R1 and R8:
(130a+b)<E1.ltoreq.(130a+b+0.5) (R1), and
(830a+b)<E8.ltoreq.(830a+b+1.0) (R8).
2. The golf club shaft according to claim 1, wherein the golf club
shaft further satisfies the following relationship R81:
(830a+b+0.3).ltoreq.E8.ltoreq.(830a+b+1.0) (R81).
3. The golf club shaft according to claim 1, wherein the flexural
rigidity E9 is less than or equal to (930a+b-0.1).
4. The golf club shaft according to claim 1, wherein the flexural
rigidity E10 is less than or equal to (1030a+b-0.6).
5. The golf club shaft according to claim 1, wherein the golf club
shaft further satisfies the following relationships R3, R4 and R5:
(330a+b-0.2)<E3.ltoreq.(330a+b+0.2) (R3),
(430a+b-0.2)<E4.ltoreq.(430a+b+0.2) (R4), and
(530a+b-0.2)<E5.ltoreq.(530a+b+0.2) (R5).
6. The golf club shaft according to claim 1, wherein the golf club
shaft is formed by a plurality of carbon fiber reinforced resin
layers, the carbon fiber reinforced resin layers include an
intermediate partial bias layer that is disposed apart from the tip
end and apart from the butt end, and an axial directional region in
which the intermediate partial bias layer is disposed includes a
point 830 mm apart from the tip end.
7. The golf club shaft according to claim 6, wherein the
intermediate partial bias layer has a length in an axial direction
of greater than or equal to 250 mm and less than or equal to 550
mm.
8. The golf club shaft according to claim 1, wherein the flexural
rigidity E3 is less than (330a+b), the flexural rigidity E4 is less
than (430a+b), and the flexural rigidity E5 is less than
(530a+b).
9. The golf club shaft according to claim 1, wherein the flexural
rigidity E7 is greater than (730a+b).
10. The golf club shaft according to claim 1, wherein the flexural
rigidity E10 is less than (1030a+b).
11. The golf club shaft according to claim 1, wherein the flexural
rigidity E3 is less than (330a+b), the flexural rigidity E4 is less
than (430a+b), the flexural rigidity E5 is less than (530a+b), the
flexural rigidity E7 is greater than (730a+b), and the flexural
rigidity E10 is less than (1030a+b).
12. The golf club shaft according to claim 1, wherein the flexural
rigidity E10 is less than the flexural rigidity E8.
13. The golf club shaft according to claim 1, wherein the flexural
rigidity E10 is less than the flexural rigidity E9.
14. The golf club shaft according to claim 9, wherein an absolute
value of [E7-(730a+b)] is greater than an absolute value of
[E3-(330a+b)], the absolute value of [E7-(730a+b)] is greater than
an absolute value of [E4-(430a+b)], and the absolute value of
[E7-(730a+b)] is greater than an absolute value of
[E5-(530a+b)].
15. The golf club shaft according to claim 8, wherein an absolute
value of [E8-(830a+b)] is greater than an absolute value of
[E3-(330a+b)], the absolute value of [E8-(830a+b)] is greater than
an absolute value of [E4-(430a+b)], and the absolute value of
[E8-(830a+b)] is greater than an absolute value of [E5-(530a+b)].
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Japanese Patent
Application No. 2020-177560 filed on Oct. 22, 2020. The entire
contents of this Japanese Patent Application are hereby
incorporated by reference.
BACKGROUND
Technical Field
[0002] The present disclosure relates to golf club shafts.
Description of the Related Art
[0003] Physical properties of a golf club shaft, such as flexural
rigidity and torsional rigidity, can be varied depending on
positions of the golf club shaft. The performance of the shaft can
be changed by the distribution of physical properties.
[0004] JP2003-169871A discloses a shaft in which: a position having
a minimum flexural rigidity in the shaft is present in a region
that extends from 15% to 45% of the shaft full length from the
shaft tip end; and a flexural rigidity at a position in a region
that extends from the shaft tip end to less than or equal to 10% of
the shaft full length is 1.2 to 2.5 times the minimum flexural
rigidity.
SUMMARY
[0005] Shafts are required to exhibit excellent performances
regarding flight distance, feeling, and directional stability of
hit balls, for example. The inventor of the present disclosure has
found that a new distribution of flexural rigidity that is
different from conventional distributions can improve performance
of shafts.
[0006] One example of the present disclosure is to provide a golf
club shaft that is excellent in flight distance performance.
[0007] A golf club shaft according to one aspect includes a tip
end, a butt end, a flexural rigidity E1 at a point located 130 mm
apart from the tip end, a flexural rigidity E2 at a point located
230 mm apart from the tip end, a flexural rigidity E3 at a point
located 330 mm apart from the tip end, a flexural rigidity E4 at a
point located 430 mm apart from the tip end, a flexural rigidity E5
at a point located 530 mm apart from the tip end, a flexural
rigidity E6 at a point located 630 mm apart from the tip end, a
flexural rigidity E7 at a point located 730 mm apart from the tip
end, a flexural rigidity E8 at a point located 830 mm apart from
the tip end, a flexural rigidity E9 at a point located 930 mm apart
from the tip end, and a flexural rigidity E10 at a point located
1030 mm apart from the tip end. A ratio (E8/E1) is greater than or
equal to 2 and less than or equal to 7. The flexural rigidity E1 is
less than or equal to 2.5 (kgfm.sup.2). The flexural rigidity E8 is
greater than or equal to 5.0 (kgfm.sup.2). In a graph on an
orthogonal coordinate system having an x-axis that represents a
distance (mm) from the tip end and a y-axis that represents a
flexural rigidity (kgfm.sup.2), when a formula of a straight line
that passes through a point (230, E2) and a point (630, E6) is
indicated by y=ax+b, the golf club shaft satisfies the following
relationships R1 and R8:
(130a+b)<E1.ltoreq.(130a+b+0.5) (R1), and
(830a+b)<E8.ltoreq.(830a+b+1.0) (R8).
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 shows an overall view of a golf club that includes a
golf club shaft according to a first embodiment;
[0009] FIG. 2 is a developed view of the golf club shaft in FIG.
1;
[0010] FIG. 3 is a schematic diagram illustrating a method for
measuring a flexural rigidity EI;
[0011] FIG. 4 shows a graph on an orthogonal coordinate system
having an x-axis that represents a distance (mm) from a tip end and
a y-axis that represents a flexural rigidity (kgfm.sup.2); and
[0012] FIG. 5 is a developed view of a golf club shaft according to
a second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] Embodiments of the present disclosure will be described in
detail below with reference to the drawings as necessary.
[0014] The term "layer" and the term "sheet" are used in the
present disclosure. The "layer" is a term used for after being
wound. In contrast, the "sheet" is a term used for before being
wound. The "layer" is formed by winding the "sheet". That is, the
wound "sheet" forms the "layer".
[0015] In the present disclosure, the same symbol is used in the
layer and the sheet. For example, a layer formed by a sheet s1 is
referred to as a layer s1.
[0016] In the present disclosure, the term "axial direction" means
the axial direction of a shaft. In the present disclosure, the term
"circumferential direction" means the circumferential direction of
a shaft.
[0017] FIG. 1 shows a golf club 2 in which a golf club shaft 6
according to the present disclosure is attached. The golf club 2
includes a head 4, the shaft 6, and a grip 8. The head 4 is
provided at a tip portion of the shaft 6. The grip 8 is provided at
a butt portion of the shaft 6. The shaft 6 is a shaft for a wood
type club. The golf club 2 is a driver (number 1 wood). The shaft 6
is a shaft used for drivers.
[0018] There is no limitation on the head 4 and the grip 8.
Examples of the head 4 include a wood type head, a utility type
head, an iron type head, and a putter head. In the present
embodiment, the head 4 is a wood type head.
[0019] The shaft 6 is formed by a plurality of fiber reinforced
resin layers. In the present embodiment, carbon fiber reinforced
resin layers are used as the fiber reinforced resin layers. The
shaft 6 is in a tubular form. Although not shown in the drawings,
the shaft 6 has a hollow structure. The shaft 6 includes a tip end
Tp and a butt end Bt. In the golf club 2, the tip end Tp is located
inside the head 4. In the golf club 2, the butt end Bt is located
inside the grip 8.
[0020] A double-pointed arrow Ls in FIG. 1 shows the length of the
shaft 6. This length Ls is measured in the axial direction.
[0021] The shaft 6 is formed by winding a plurality of prepreg
sheets. In the prepreg sheets, fibers are oriented substantially in
one direction. Such a prepreg in which fibers are oriented
substantially in one direction is also referred to as a UD prepreg.
The term "UD" stands for unidirectional. The prepreg sheets may be
made of a prepreg other than UD prepreg. For example, fibers
contained in the prepreg sheets may be woven. In the present
disclosure, the prepreg sheet(s) are also simply referred to as a
sheet(s).
[0022] Each prepreg sheet contains fibers and a resin. The resin is
also referred to as a matrix resin. Carbon fibers and glass fibers
are exemplified as the fibers. The matrix resin is typically a
thermosetting resin.
[0023] Examples of the matrix resin in the prepreg sheet include a
thermosetting resin and a thermoplastic resin. From the viewpoint
of shaft strength, the matrix resin is preferably a thermosetting
resin, and more preferably an epoxy resin.
[0024] The shaft 6 is manufactured by a sheet-winding method. In
the prepreg, the matrix resin is in a semi-cured state. In the
shaft 6, the prepreg sheets are wound and cured. This "cured" means
that the semi-cured matrix resin is cured. The curing process is
achieved by heating. The manufacturing processes of the shaft 6
includes a heating process. The heating process cures the matrix
resin in the prepreg sheets.
[0025] FIG. 2 is a developed view of prepreg sheets constituting
the shaft 6. FIG. 2 shows the sheets constituting the shaft 6. The
shaft 6 is constituted by the plurality of sheets. In the
embodiment of FIG. 2, the shaft 6 is constituted by 14 sheets. The
shaft 6 includes a first sheet s1 to a fourteenth sheet s14. The
developed view shows the sheets constituting the shaft in order
from the radial inside of the shaft. The sheets are wound in order
from the sheet located on the uppermost side in the developed view.
In FIG. 2, the horizontal direction of the figure coincides with
the axial direction of the shaft. In FIG. 2, the right side of the
figure is the tip side of the shaft. In FIG. 2, the left side of
the figure is the butt side of the shaft.
[0026] FIG. 2 shows not only the winding order of the sheets but
also the position of each of the sheets in the axial direction. The
same holds true for FIG. 5 described later. For example, in FIG. 2,
an end of the sheet s1 is located at the tip end Tp.
[0027] The shaft 6 includes a straight layer, a bias layer, and a
hoop layer. An orientation angle of the fibers (hereinafter
referred to as fiber orientation angle) is described for each of
the sheets in FIG. 2. A sheet described as "0.degree." is a
straight sheet. The straight sheet forms the straight layer.
[0028] The straight layer is a layer in which the fiber orientation
angle is substantially set to 0.degree. with respect to the axial
direction. Usually, the fiber orientation may not completely be
parallel to the shaft axial direction due to an error in winding,
for example. In the straight layer, an absolute angle of the fiber
orientation angle with respect to the shaft axial direction is less
than or equal to 10.degree.. The absolute angle means an absolute
value of an angle (fiber orientation angle) formed between the
shaft axis line and the orientation of fibers. That is, "the
absolute angle is less than or equal to 10.degree." means that "the
fiber orientation angle is -10 degrees or greater and +10 degrees
or less".
[0029] In the embodiment of FIG. 2, sheets (straight sheets) that
form straight layers are the sheet s1, the sheet s8, the sheet s9,
the sheet s11, the sheet s12, the sheet s13 and the sheet s14. The
straight layers make a great contribution to flexural rigidity and
flexural strength.
[0030] The bias layer is a layer in which the fiber orientation is
substantially inclined with respect to the axial direction. The
bias layer makes a great contribution to torsional rigidity and
torsional strength. Preferably, bias layers are constituted by a
pair of two sheets (herein after referred to as a sheet pair) in
which fiber orientation angles of the respective sheets are
inclined inversely to each other. Preferably, the sheet pair
includes: a layer having a fiber orientation angle of greater than
or equal to -60.degree. and less than or equal to -30.degree.; and
a layer having a fiber orientation angle of greater than or equal
to 30.degree. and less than or equal to 60.degree.. That is, the
absolute angle in the bias layers is preferably greater than or
equal to 30.degree. and less than or equal to 60.degree..
[0031] In the shaft 6, sheets (bias sheets) that form the bias
layers are the sheet s2, the sheet s3, the sheet s4, the sheet s5,
the sheet s6, and the sheet s7. The sheet s2 and the sheet s3
constitute a sheet pair (a first sheet pair). The sheet s4 and the
sheet s5 constitute a sheet pair (a second sheet pair). The sheet
s6 and the sheet s7 constitute a sheet pair (a third sheet pair).
Each sheet pair is wound in a state where the sheets constituting
the sheet pair are stuck together. The shaft 6 includes a plurality
of (three) sheet pairs.
[0032] In FIG. 2, the fiber orientation angle is described for each
sheet. The plus sign (+) and minus sign (-) used with the fiber
orientation angle indicate inclined direction of the fibers. A
sheet having a plus fiber orientation angle and a sheet having a
minus fiber orientation angle are combined in each sheet pair. In
each sheet pair, fibers in respective sheets are inclined inversely
to each other.
[0033] The hoop layer is a layer that is disposed so that the fiber
orientation substantially coincides with the circumferential
direction of the shaft. Preferably, in the hoop layer, the absolute
angle of the fiber orientation angle is substantially set to
90.degree. with respect to the shaft axial direction. However, the
fiber orientation angle to the shaft axial direction may not be
completely set to 90.degree. due to an error in winding, for
example. In the hoop layer, the absolute angle of the fiber
orientation angle is usually 80.degree. or greater and 90.degree.
or less.
[0034] The hoop layer makes a great contribution to crushing
rigidity and crushing strength of a shaft. The crushing rigidity is
a rigidity against crushing deformation. The crushing deformation
is caused by a crushing force that is applied to the shaft inward
in the radial direction of the shaft. In a typical crushing
deformation, the cross section of the shaft is deformed from a
circular shape to an elliptical shape. The crushing strength is a
strength against the crushing deformation. The crushing strength
can relate to the flexural strength. The flexural deformation can
involve the crushing deformation. Particularly when a lightweight
shaft having a thin wall is used, the flexural deformation is more
likely to involve the crushing deformation. Improvement in the
crushing strength can contribute to improvement in the flexural
strength.
[0035] In the embodiment of FIG. 2, a prepreg sheet (hoop sheet)
that constitutes the hoop layer is the sheet s10. The hoop layer
s10 is sandwiched between the straight layer s9 and the straight
layer s11.
[0036] For manufacturing the shaft 6 shown in FIG. 2, a united
sheet is used. The united sheet is formed by sticking a plurality
of sheets together.
[0037] In the embodiment of FIG. 2, four united sheets are used. A
first united sheet is the combination of the sheet s2 and the sheet
s3. A second united sheet is the combination of the sheet s4 and
the sheet s5. A third united sheet is the combination of the sheet
s6 and the sheet s7. A fourth united sheet is the combination of
the sheet s9, the sheet s10 and the sheet s11.
[0038] As described above, in the present disclosure, the sheets
and the layers are classified by the fiber orientation angle.
Furthermore, in the present disclosure, the sheets and the layers
are classified by their length in the axial direction.
[0039] A layer wholly disposed in the axial direction of the shaft
is referred to as a full length layer. A sheet wholly disposed in
the axial direction of the shaft is referred to as a full length
sheet. The wound full length sheet forms the full length layer. A
layer partially disposed in the axial direction of the shaft is
referred to as a partial layer. A sheet partially disposed in the
axial direction of the shaft is referred to as a partial sheet. The
wound partial sheet forms the partial layer.
[0040] A layer that is the bias layer and the full length layer is
referred to as a full length bias layer. A layer that is the
straight layer and the full length layer is referred to as a full
length straight layer. A layer that is the hoop layer and the full
length layer is referred to as a full length hoop layer.
[0041] In the embodiment of FIG. 2, the full length bias layers are
formed by the sheet s2 and the sheet s3. The full length straight
layers are formed by the sheet s9, the sheet s11, the sheet s12,
and the sheet s13. The shaft 6 includes the plurality of full
length straight layers s9, s11, s12 and s13. The full length hoop
layer is formed by the sheet s10. The shaft 6 includes the hoop
layer s10 sandwiched between the full length straight layers s9 and
s11.
[0042] A layer that is the bias layer and the partial layer is
referred to as a partial bias layer. A layer that is the straight
layer and the partial layer is referred to as a partial straight
layer. A layer that is the hoop layer and the partial layer is
referred to as a partial hoop layer.
[0043] In the embodiment of FIG. 2, the partial bias layers are
formed by the sheet s4, the sheet s5, the sheet s6 and the sheet
s7. The partial straight layers are formed by the sheet s1, the
sheet s8 and the sheet s14. A partial hoop layer is not
provided.
[0044] The sheet s4 and the sheet s5 are tip partial bias layers
p1. The tip partial bias layers p1 are disposed on the tip portion
of the shaft 6. One end of each tip partial bias layer p1 is
located at the tip end Tp. The sheet s6 and the sheet s7 are
intermediate partial bias layers p2. The intermediate partial bias
layers p2 are located apart from the tip end Tp and apart from the
butt end Bt. The shaft 6 includes the tip partial bias layers p1
and the intermediate partial bias layers p2. Each tip partial bias
layer p1 does not overlap each intermediate partial bias layer p2
in the axial direction. The center position of each intermediate
partial bias layer p2 in the axial direction is located on the but
end Bt side with respect to the center position of the shaft 6 in
the axial direction. The shaft 6 does not include a butt partial
bias layer.
[0045] A region in the axial direction in which each intermediate
partial bias layer p2 is disposed (hereinafter also referred to as
the axial directional region of each intermediate partial bias
layer p2) includes a point that is located 830 mm apart from the
tip end Tp. The axial directional region of each intermediate
partial bias layer p2 includes a point that is located 730 mm apart
from the tip end Tp.
[0046] Hereinafter, manufacturing processes of the shaft 6 will be
schematically described.
[Outline of Manufacturing Processes of Shaft]
(1) Cutting Process
[0047] The prepreg sheets are cut into respective desired shapes in
the cutting process. Each of the sheets shown in FIG. 2 is cut out
by this process.
[0048] The cutting may be performed by a cutting machine.
Alternatively, the cutting may be manually performed. In the manual
case, a cutter knife is used, for example.
(2) Sticking Process
[0049] In the sticking process, each united sheet described above
is produced by sticking a plurality of sheets together. In the
sticking process, heating and/or pressing step(s) may be carried
out.
(3) Winding Process
[0050] A mandrel is prepared in the winding process. A typical
mandrel is made of a metal. A mold release agent is applied to the
mandrel. Furthermore, a resin having tackiness is applied to the
mandrel. The resin is also referred to as a tacking resin. The cut
sheets are wound around the mandrel. The tacking resin facilitates
the application of the end part of a sheet to the mandrel.
[0051] A wound body is obtained in the winding process. The wound
body is obtained by winding the prepreg sheets around the outside
of the mandrel. For example, the winding is achieved by rolling the
object to be wound on a plane. The winding may be manually
performed or may be performed by a machine. The machine is referred
to as a rolling machine.
(4) Tape Wrapping Process
[0052] A tape is wrapped around the outer peripheral surface of the
wound body in the tape wrapping process. The tape is also referred
to as a wrapping tape. The wrapping tape is helically wrapped while
tension is applied to the tape so that there is no gap between
adjacent windings. The tape applies pressure to the wound body. The
pressure contributes to the reduction of voids.
(5) Curing Process
[0053] In the curing process, the wound body after being subjected
to the tape wrapping is heated. The heating cures the matrix resin.
In the curing process, the matrix resin fluidizes temporarily. The
fluidization of the matrix resin can eliminate air between the
sheets or in each sheet. The fastening force of the wrapping tape
accelerates the discharge of the air. The curing provides a cured
laminate.
(6) Process of Extracting Mandrel and Process of Removing Wrapping
Tape
[0054] The process of extracting the mandrel and the process of
removing the wrapping tape are performed after the curing process.
The process of removing the wrapping tape is preferably performed
after the process of extracting the mandrel.
(7) Process of Cutting Off Both Ends
[0055] Both end portions of the cured laminate are cut off in the
process. The cutting off flattens the end face of the tip end Tp
and the end face of the butt end Bt.
(8) Polishing Process
[0056] The surface of the cured laminate is polished in the
process. Spiral unevenness is present on the surface of the cured
laminate as the trace of the wrapping tape. The polishing removes
the unevenness to smooth the surface of the cured laminate.
(9) Coating Process
[0057] The cured laminate after the polishing process is subjected
to coating.
[0058] The shaft 6 has a flexural rigidity at each position
thereof. The flexural rigidity is also referred to as EI. The value
of the flexural rigidity is also referred to as EI. In the present
disclosure, the unit of EI is "kgfm.sup.2". EI can be measured at
predetermined positions in the axial direction.
[0059] FIG. 3 shows the method for measuring EI. As a measuring
device, a universal testing machine "model 2020 (maximum load: 500
kg)" produced by Intesco Co., Ltd. can be used. The shaft 6 is
supported from below at a first supporting point T1 and at a second
supporting point T2. In the state where the shaft 6 is supported, a
load F1 is applied at a measurement point T3 from above. The load
F1 is applied vertically downward. The distance between the point
T1 and the point T2 is 200 mm. The measurement point T3 is a point
that divides the distance between the point T1 and the point T2
into two equal parts. The amount of bending (flexure) H when the
load F1 is applied is measured. The load F1 is applied by an
indenter D1. The tip end of the indenter D1 is a cylindrical
surface having a radius of curvature of 5 mm. The downwardly moving
speed of the indenter D1 is 5 mm/min. When the load F1 reaches 20
kgf (196 N), the indenter D1 is stopped, and the amount of bending
H in this state is measured. The amount of bending H is a distance
in the vatical direction between the position of the point T3
before the load F1 is applied and the position of the point T3 when
the indenter D1 is stopped. EI is calculated by the following
formula:
EI(kgfm.sup.2)=F1.times.L.sup.3/(48.times.H),
where, F1 denotes a maximum load (kgf), L is a distance (m) between
the support points, and H is the amount of bending (m). The maximum
load F1 is 20 kgf. The distance L between the support points is 0.2
m.
[0060] As the measurement points of EI, the following 10 points are
exemplified. [0061] (Measurement point 1): a point located 130 mm
apart from the tip end Tp [0062] (Measurement point 2): a point
located 230 mm apart from the tip end Tp [0063] (Measurement point
3): a point located 330 mm apart from the tip end Tp [0064]
(Measurement point 4): a point located 430 mm apart from the tip
end Tp [0065] (Measurement point 5): a point located 530 mm apart
from the tip end Tp [0066] (Measurement point 6): a point located
630 mm apart from the tip end Tp [0067] (Measurement point 7): a
point located 730 mm apart from the tip end Tp [0068] (Measurement
point 8): a point located 830 mm apart from the tip end Tp [0069]
(Measurement point 9): a point located 930 mm apart from the tip
end Tp [0070] (Measurement point 10): a point located 1030 mm apart
from the tip end Tp It should be noted that the distances from the
tip end Tp for the measurement points are measured in the axial
direction. These distances are measured from the tip end Tp toward
the butt end Bt.
[0071] In the present disclosure, EI at the measurement point 1 is
denoted by E1. EI at the measurement point 2 is denoted by E2. EI
at the measurement point 3 is denoted by E3. EI at the measurement
point 4 is denoted by E4. EI at the measurement point 5 is denoted
by E5. EI at the measurement point 6 is denoted by E6. EI at the
measurement point 7 is denoted by E7. EI at the measurement point 8
is denoted by E8. EI at the measurement point 9 is denoted by E9.
EI at the measurement point 10 is denoted by E10. The unit of E1 to
E10 is kgfm.sup.2. For specifying the values of E1 to E10, the
values can be rounded off to the first decimal place.
[0072] FIG. 4 shows a graph on an orthogonal coordinate system
having an x-axis that represents a distance (mm) from the tip end
and a y-axis that represents a flexural rigidity (kgfm.sup.2). FIG.
4 is a graph showing Example 1 explained below. In this graph, the
following 10 points having respective coordinates (x, y) are
plotted. [0073] Point (130, E1) [0074] Point (230, E2) [0075] Point
(330, E3) [0076] Point (430, E4) [0077] Point (530, E5) [0078]
Point (630, E6) [0079] Point (730, E7) [0080] Point (830, E8)
[0081] Point (930, E9) [0082] Point (1030, E10)
[0083] For the sake of easy explanation, the point (130, E1) is
also referred to as a point E1. The point (230, E2) is also
referred to as a point E2. The point (330, E3) is also referred to
as a point E3. The point (430, E4) is also referred to as a point
E4. The point (530, E5) is also referred to as a point E5. The
point (630, E6) is also referred to as a point E6. The point (730,
E7) is also referred to as a point E7. The point (830, E8) is also
referred to as a point E8. The point (930, E9) is also referred to
as a point E9. The point (1030, E10) is also referred to as a point
E10.
[0084] In this graph, the formula of a straight line that passes
through the point (230, E2) and the point (630, E6) is represented
by "y=ax+b". This straight line shows a tendency of the overall
rigidity distribution of the shaft. In FIG. 4, the straight line is
shown with a dashed line. This straight line is also referred to as
L1. In the present embodiment, "a" is 0.0052 and "b" is 1.1.
[0085] The straight line L1 can vary from shaft to shaft. The
straight line L1 can be adjusted based on characteristics (e.g.,
head speed) of a golfer, for example. By specifying relative values
of the straight line L1, properties suitable to each shaft can be
specified. The gradient "a" of the straight line L1 can be adjusted
by a taper ratio of the shaft, for example. The y-intercept "b" of
the straight line L1 can be adjusted by the overall wall thickness
of the shaft (e.g., the thickness of the full length straight
layer(s)), for example. When the flexural rigidity on the whole
shaft is changed, the value of "b" can be changed.
[0086] From the viewpoint of not reducing advantageous effects
brought by E1 and E8, the gradient "a" of the straight line L1 is
preferably great. The gradient "a" is preferably greater than or
equal to 0.003, more preferably greater than or equal to 0.004, and
still more preferably greater than or equal to 0.005. An
excessively great gradient "a" can lead to an excessively small E1
and/or excessively great E8. From this viewpoint, the gradient "a"
is preferably less than or equal to 0.008, more preferably less
than or equal to 0.007, and still more preferably less than or
equal to 0.006.
[0087] When the overall flexural rigidity of a shaft is excessively
great, the shaft can become too rigid even for advanced golfers.
Such a shaft having an excessively great overall flexural rigidity
is difficult to swing and gives a bad feeling to the golfer. From
this viewpoint, the y-intercept "b" of the straight line L1 is less
than or equal to 3.0, more preferably less than or equal to 2.0,
and still more preferably less than or equal to 1.5. When the
overall flexural rigidity of a shaft is excessively small, the
shaft can become too flexible even for golfers lacking strength.
Such a shaft having an excessively small overall flexural rigidity
is difficult to swing and gives a bad feeling to the golfer. From
this viewpoint, the y-intercept "b" of the straight line L1 is
preferably greater than or equal to -1.0, more preferably greater
than or equal to 0.0, and still more preferably greater than or
equal to 0.5.
[0088] In the embodiment of FIG. 4, the point E1 is positioned
higher than the straight line L1. That is, E1 is greater than
(130a+b). The point E3 is positioned lower than the straight line
L1. That is, E3 is lower than (330a+b). The point E4 is positioned
lower than the straight line L1. That is, E4 is lower than
(430a+b). The point E5 is positioned lower than the straight line
L1. That is, E5 is lower than (530a+b). The point E7 is positioned
higher than the straight line L1. That is, E7 is greater than
(730a+b). The point E8 is positioned higher than the straight line
L1. That is, E8 is greater than (830a+b). The point E9 is
positioned lower than the straight line L1. That is, E9 is lower
than (930a+b). The point E10 is positioned lower than the straight
line L1. That is, E10 is lower than (1030a+b).
[0089] A portion ranging from the point E3 to the point E5 which
constitutes a large part of the intermediate portion of the shaft
is positioned lower than the straight line L1. Further, a portion
ranging from the point E2 to the point E6 (exclusive) is positioned
lower than the straight line L1. These structures ensure an
appropriate overall bending of the shaft. The head speed can be
improved by the synergistic effect of this overall bending and an
accelerated motion of the tip portion of the shaft.
[0090] The point E7 is positioned farther from the straight line L1
as compared to the positional relationship between the point E1 and
the straight line L1. |E7-(730a+b)| is greater than |E1-(130a+b)|.
The point E7 is positioned farther from the straight line L1 as
compared to the positional relationship between the point E3 and
the straight line L1. |E7-(730a+b)| is greater than |E3-(330a+b)|.
The point E7 is positioned farther from the straight line L1 as
compared to the positional relationship between the point E4 and
the straight line L1. |E7-(730a+b)| is greater than |E4-(430a+b)|.
The point E7 is positioned farther from the straight line L1 as
compared to the positional relationship between the point E5 and
the straight line L1. |E7-(730a+b)| is greater than |E5-(530a+b)|.
The point E7 is positioned farther from the straight line L1 as
compared to the positional relationship between the point E9 and
the straight line L1. |E7-(730a+b)| is greater than |E9-(930a+b)|.
The point E10 is positioned farther from the straight line L1 as
compared to the positional relationship between the point E7 and
the straight line L1. |E10-(1030a+b)| is greater than
|E7-(730a+b)|.
[0091] Such an E7 higher than the straight line L1 can further
improve advantageous effects brought by E8.
[0092] The point E8 is positioned farther from the straight line L1
as compared to the positional relationship between the point E1 and
the straight line L1. |E8-(830a+b)| is greater than |E1-(130a+b)|.
The point E8 is positioned farther from the straight line L1 as
compared to the positional relationship between the point E3 and
the straight line L1. |E8-(830a+b)| is greater than |E3-(330a+b)|.
The point E8 is positioned farther from the straight line L1 as
compared to the positional relationship between the point E4 and
the straight line L1. |E8-(830a+b)| is greater than |E4-(430a+b)|.
The point E8 is positioned farther from the straight line L1 as
compared to the positional relationship between the point E5 and
the straight line L1. |E8-(830a+b)| is greater than |E5-(530a+b)|.
The point E8 is positioned farther from the straight line L1 as
compared to the positional relationship between the point E9 and
the straight line L1. |E8-(830a+b)| is greater than |E9-(930a+b)|.
The point E10 is positioned farther from the straight line L1 as
compared to the positional relationship between the point E8 and
the straight line L1. |E10-(1030a+b)| is greater than
|E8-(830a+b)|.
[0093] It should be noted that the symbol ".parallel." denotes an
absolute value. For example, |E7-(730a+b)| means the absolute value
of [E7-(730a+b)].
[0094] A greater ratio (E8/E1) can improve the golfer's feeling and
enable the tip portion of the shaft to provide an improved kick to
a golf ball (kick means an improved bounce brought by the behavior
of the shaft). The improved kick increases flight distance. From
this viewpoint, the ratio (E8/E1) is preferably greater than or
equal to 2.0, more preferably greater than or equal to 2.4, and
still more preferably greater than or equal to 2.8. An excessively
great ratio (E8/E1) leads to a too flexible E1 and/or too rigid E8,
which reduces the above-described advantageous effects. From this
viewpoint, the ratio (E8/E1) is preferably less than or equal to
7.0, more preferably less than or equal to 6.0, still more
preferably less than or equal to 5.0, and yet still more preferably
less than or equal to 4.0.
[0095] An excessively great E1 causes difficulty in swinging of the
shaft, which also reduces the directional stability of hit balls. A
lower E1 allows a golfer to easily feel the bending of the shaft,
which improves the feeling of the shaft. Such a lower E1 also
accelerates the speed of the tip portion of the shaft, whereby the
tip portion can provide an improved kick to a golf ball. From these
viewpoints, E1 is preferably less than or equal to 2.5
(kgfm.sup.2), more preferably less than or equal to 2.3
(kgfm.sup.2), and still more preferably less than or equal to 2.1
(kgfm.sup.2). An excessively small E1 leads to a flexible tip
portion of the shaft, which reduces the stability of the shaft at
impact and the directional stability of hit balls. Such an
excessively small E1 also causes an insufficient recovery from
bending of the shaft, which hampers the acceleration of the speed
of the tip portion of the shaft ("recovery from bending" is a
phenomenon in which a shaft that is bent during downswing returns
to an unbent state). From these viewpoints, E1 is preferably
greater than or equal to 1.5 (kgfm.sup.2), more preferably greater
than or equal to 1.7 (kgfm.sup.2), and still more preferably
greater than or equal to 1.9 (kgfm.sup.2).
[0096] An excessively small E8 leads to an improper recovery from
bending, which reduces the head speed. A greater E8 increases the
stability of the shaft and leads to an excellent directional
stability of hit balls. Such a greater E8 also provides the golfer
with an improved feeling of load applied by the bending of the
shaft at immediately before the impact. From this viewpoint, E8 is
preferably greater than or equal to 5.0 (kgfm.sup.2), more
preferably greater than or equal to 5.3 (kgfm.sup.2), and still
more preferably greater than or equal to 5.6 (kgfm.sup.2). An
excessively great E8 makes a gripped area of the shaft excessively
rigid, which gives a worse feeling to the golfer and reduces the
head speed. From this viewpoint, E8 is preferably less than or
equal to 6.5 (kgfm.sup.2), more preferably less than or equal to
6.2 (kgfm.sup.2), and still more preferably less than or equal to
5.9 (kgfm.sup.2).
[0097] The shaft 6 satisfies the following relationship R1:
(130a+b)<E1.ltoreq.(130a+b+0.5) (R1)
[0098] Setting E1 to be greater than (130a+b) enhances the
stability of the shaft at impact, which leads to an excellent
directional stability of hit balls. An excessively small E1 causes
an insufficient recovery from bending, which reduces the
acceleration of the speed of the tip portion of the shaft. From
this viewpoint, E1 is preferably greater than (130a+b), more
preferably greater than or equal to (130+b+0.1), and still more
preferably greater than or equal to (130a+b+0.2). An excessively
great E1 makes the shaft difficult to swing, which reduces the
directional stability of hit balls. When E1 is less than or equal
to (130a+b+0.5), the speed of the tip portion of the shaft is
accelerated, whereby the tip portion provides an excellent kick to
a golf ball. From these viewpoints, E1 is preferably less than or
equal to (130a+b+0.5), more preferably less than or equal to
(130a+b+0.4), and still more preferably less than or equal to
(130a+b+0.3).
[0099] As described above, the shaft 6 includes the tip partial
bias layers p1 (see FIG. 2). A region in the axial directional in
which each tip partial bias layer p1 is disposed (hereinafter also
referred to as the axial directional region of each tip partial
bias layer p1) includes the point E1. Since the tip partial bias
layers p1 are included among tip partial layers, E1 is prevented
from becoming excessively great. The above relationship R1 can be
easily achieved by the tip partial bias layers p1. Each tip partial
bias layer p1 contributes to achievement of the relationship R1
regarding the flexural rigidity while increasing the torsional
rigidity of the tip portion of the shaft and enhancing the
directional stability of hit balls. From the viewpoint of obtaining
a proper E1, the length of each tip partial bias layer p1 in the
axial direction is preferably greater than or equal to 130 mm,
still more preferably greater than or equal to 140 mm, and yet
still more preferably greater than or equal to 150 mm. From the
viewpoint of obtaining a proper E1, the length of each tip partial
bias layer p1 in the axial direction is preferably less than or
equal to 300 mm, more preferably less than or equal to 260 mm, and
still more preferably less than or equal to 220 mm.
[0100] The shaft 6 satisfies the following relationship R8. The
shaft 6 satisfies the following relationship R81.
(830a+b)<E8.ltoreq.(830a+b+1.0) (R8)
(830a+b+0.5).ltoreq.E8.ltoreq.(830a+b+1.0) (R81)
[0101] When E8 is excessively small, a proper recovery from bending
cannot be obtained, which reduces the head speed. Setting E8 to be
greater than (830a+b) increases the stability of the shaft during a
swing, which enhances the directional stability of hit balls. Such
a greater E8 also provides the golfer with an improved feeling of
load applied by the bending of the shaft at immediately before the
impact. From these viewpoints, E8 is preferably greater than or
equal to (830a+b+0.1), more preferably greater than or equal to
(830a+b+0.3), and still more preferably greater than or equal to
(830a+b+0.5). An excessively great E8 makes the gripped area of the
shaft excessively rigid, which gives a worse feeling to the golfer.
Such an excessively great E8 also makes the shaft difficult to
swing, which reduces the head speed and the directional stability
of hit balls. From these viewpoints, E8 is preferably less than or
equal to (830a+b+1.0), more preferably less than or equal to
(830a+b+0.9), and still more preferably less than or equal to
(830a+b+0.8).
[0102] As described above, the straight line L1 shows the tendency
of the overall flexural rigidity distribution of the shaft. By
specifying relative values of the straight line L1, properties
suitable to each shaft can be specified. From this viewpoint, the
points E3 to E5 are preferably positioned close to the straight
line L1. Specifically, the points E3 to E5 as explained below are
preferable.
[0103] The point E3 preferably satisfies the following relationship
R3, and more preferably satisfies the following relationship
R31.
(330a+b-0.2)<E3.ltoreq.(330a+b+0.2) (R3)
(330a+b-0.1)<E3.ltoreq.(330a+b+0.1) (R31)
[0104] The point E4 preferably satisfies the following relationship
R4, and more preferably satisfies the following relationship
R41.
(430a+b-0.2)<E4.ltoreq.(430a+b+0.2) (R4)
(430a+b-0.1)<E4.ltoreq.(430a+b+0.1) (R41)
[0105] The point E5 preferably satisfies the following relationship
R5, and more preferably satisfies the following relationship
R51.
(530a+b-0.2)<E5.ltoreq.(530a+b+0.2) (R5)
(530a+b-0.1)<E5.ltoreq.(530a+b+0.1) (R51)
[0106] Thus, in the embodiment of FIG. 4, the flexural rigidity at
the point E8 is higher than the straight line L1. A portion at and
near the point E8 is selectively made rigid relative to the
straight line L1, which accelerates the speed the tip portion of
the shaft to increase the head speed, and enhances the stability of
the shaft during a swing, which can provide the golfer with the
feeling of the load that is kept until the shaft reaches
impact.
[0107] E9 is positioned inside the grip. For this reason, E9 has a
less influence on the stability of swing. However, a lower E9
improves the absorbability of vibration felt by golfer's hands,
which can improve the feeling of the shaft. From these viewpoints,
E9 is preferably less than or equal to (930a+b-0.1), more
preferably less than or equal to (930a+b-0.2), and still more
preferably less than or equal to (930a+b-0.3). A sharp decrease
from E8 to E9 leads to stress concentration, which can reduce the
strength of the shaft. From this viewpoint, E9 is preferably
greater than or equal to (930a+b-1.0), more preferably greater than
or equal to (930a+b-0.8), and still more preferably greater than or
equal to (930a+b-0.6).
[0108] E10 is positioned inside the grip. E10 has a lesser
influence on the stability of swing than E9. However, a lower E10
improves the absorbability of vibration felt by golfer's hands,
which can improve the feeling of the shaft. From these viewpoints,
E10 is preferably less than or equal to (1030a+b-0.6), more
preferably less than or equal to (1030a+b-0.7), and still more
preferably less than or equal to (1030a+b-0.8). A sharp decrease
from E8 to E10 leads to stress concentration, which can reduce the
strength of the shaft. From this viewpoint, E10 is preferably
greater than or equal to (1030a+b-1.8), more preferably greater
than or equal to (1030a+b-1.6), and still more preferably greater
than or equal to (1030a+b-1.4).
[0109] From the viewpoint of enhancing the absorbability of
vibration while obtaining the advantageous effects brought by E8,
E10 is preferably lower than E8, and E10 is preferably lower than
E9.
[0110] As shown in FIG. 2, the shaft 6 includes the sheet s6 and
the sheet s7 as intermediate partial layers. The intermediate
partial layers s6 and s7 are located apart from the tip end Tp and
apart from the butt end Bt. A region in the axial direction in
which the intermediate partial layers s6 and s7 are disposed
(hereinafter also referred to as the axial directional region of
the intermediate partial layers s6 and s7) includes a point that is
located 830 mm apart from the tip end Tp. The axial directional
region of the intermediate partial layers s6 and s7 includes a
point that is located 730 mm apart from the tip end Tp. In the
embodiment of FIG. 2, the number of sheets constituting the
intermediate partial layers is two. The number of sheet(s)
constituting the intermediate partial layer(s) may be one, or may
be three or more, instead of two. The intermediate partial layers
s6 and s7 partially increase the flexural rigidity of the shaft.
The intermediate partial layers s6 and s7 contribute to the
formation of an upwardly protruded portion (hereinafter also
referred to as a "rigidity prominent portion") relative to the
straight line L1 at and near the point E8 in the graph of FIG. 4.
The intermediate partial layer(s) contributes to increase in
[E8-(830a+b)].
[0111] Orientation of carbon fibers in the intermediate partial
layers s6 and s7 are inclined with respect to the axial direction
of the shaft. That is, the intermediate partial layers s6 and s7
are intermediate partial bias layers p2. Since the intermediate
partial layers s6 and s7 are the intermediate partial bias layers
p2, the flexural rigidity of the rigidity prominent portion is
prevented from becoming excessively great. That is, the
intermediate partial bias layers p2 make [E8-(830a+b)] a proper
value. In addition, by using the intermediate partial bias layers
p2, the rigidity of the rigidity prominent portion does not become
excessively great even when the length of the intermediate partial
layers in the axial directional is made longer to a certain extent.
This structure allows the rigidity prominent portion to gradually
change its rigidity, which can alleviate stress concentrations at
the ends of the rigidity prominent portion.
[0112] When the absolute angle of the fiber orientation angle of
the intermediate partial layers (intermediate partial bias layers)
is excessively small, [E8-(830a+b)] tends to become higher than its
proper value. From this viewpoint, the absolute angle of the fiber
orientation angle of the intermediate partial layers (intermediate
partial bias layers) is preferably greater than or equal to
20.degree., more preferably greater than or equal to 30.degree.,
and still more preferably greater than or equal to 40.degree.. When
the absolute angle of the fiber orientation angle of the
intermediate partial layers (intermediate partial bias layers) is
excessively great, [E8-(830a+b)] tends to become lower than its
proper value. From this viewpoint, the absolute angle of the fiber
orientation angle of the intermediate partial layers (intermediate
partial bias layers) is preferably less than or equal to
70.degree., more preferably less than or equal to 60.degree., and
still more preferably less than or equal to 50.degree..
[0113] From the viewpoint of appropriately increasing E8, a length
Lm (see FIG. 2) of the intermediate partial layers in the axial
direction is preferably greater than or equal to 250 mm, more
preferably greater than or equal to 300 mm, and still more
preferably greater than or equal to 350 mm. From the viewpoint of
obtaining proper values of E6 and E9, the length Lm is preferably
less than or equal to 550 mm, more preferably less than or equal to
500 mm, and still more preferably less than or equal to 450 mm.
[0114] FIG. 5 is a developed view of prepreg sheets that constitute
a shaft according to a second embodiment. The embodiment of FIG. 5
is the same as the embodiment of FIG. 2, except that intermediate
partial layers s6 and s7 are intermediate partial straight layers
p3, not intermediate partial bias layers p2. In the embodiment of
FIG. 5, the absolute angle of the fiber orientation angle of the
intermediate partial layers is 0.degree.. In contrast, the absolute
angle of the fiber orientation angle of the intermediate partial
layers is 45.degree. in the embodiment of FIG. 2.
[0115] When the intermediate partial layers are the intermediate
partial straight layers, the flexural rigidity of the rigidity
prominent portion can be excessively great. From the viewpoint of
obtaining a proper value of [E8-(830a+b)], the intermediate partial
layer(s) is/are preferably intermediate partial bias layer(s).
[0116] In a table shown below, the embodiment of FIG. 5 is shown as
Comparative Examples (Comparative Example 2 and Comparative Example
5). The embodiment of FIG. 5, however, can also be an Example.
[0117] For carrying out the measurement of E10, the length Ls of
the shaft needs to be greater than or equal to 1030 mm. As
understood from the measuring method of EI shown in FIG. 3, for
measuring E10, the shaft needs to extends further 100 mm toward the
butt end from a point 1030 mm apart from the tip end Tp. However,
the butt end portion of the shaft can be cut off after the
measurement of E10. From the viewpoint of the measurement of E10,
the length Ls of the shaft is preferably greater than or equal to
1030 mm, more preferably greater than or equal to 1080 mm, still
more preferably greater than or equal to 1130 mm, and yet still
more preferably greater than or equal to 1140 mm. From the
viewpoint of restriction on club length by golf rules, the length
Ls of the shaft is preferably less than or equal to 1210 mm, more
preferably less than or equal to 1200 mm, and still more preferably
less than or equal to 1190 mm.
EXAMPLES
Example 1
[0118] A shaft was produced in accordance with the above explained
manufacturing processes of the shaft. Constitution of sheets in the
shaft was as shown in FIG. 2. The length Ls of the shaft was 1143
mm. A driver head and a grip were attached to the produced shaft to
obtain a golf club.
Examples 2 to 6 and Comparative Examples 1 to 6
[0119] Golf clubs of Examples 2 to 6 and Comparative Examples 1 to
6 were obtained in the same manner as in Example 1 except that
specifications as shown in Table 1 and Table 2 were adopted for
respective clubs. Constitution of sheets and prepreg material were
changed for each shaft to adjust values of E1 to E10.
<Measurement of Flexural Rigidity ET>
[0120] In accordance with the above explained method shown in FIG.
3, EI values at the measurement points E1 to E10 were measured for
each club. The measured values for each club are shown in Table 1
and Table 2.
<Measurement of Flight Distance>
[0121] Five golfers who swing a driver at a head speed of 40 m/s or
greater and have a handicap from 0 to 10 each hit a ball five times
using each of the clubs to measure a flight distance for each shot.
The flight distance is a distance to where a ball hit by the club
finally arrives, and includes a distance by which the ball runs on
the ground. The flight distance shown in Table 1 and Table 2 below
is an average value of measured values per club.
<Directional Stability of Hit Balls>
[0122] The directional stability of the hit ball was also measured
in each of the above performed shots for measuring flight
distances. A distance between the final arrival point of each hit
ball and a line that passes through the initial position of the
ball to be hit and a target position was measured. This distance
was regarded as a plus value, irrespective of whether the hit ball
flied rightward or leftward relative to the target direction. The
average values of the distances of respective clubs were evaluated
(classified) on a scale of 1 to 5, where the score 1 is the highest
average value and the score 5 is the lowest average value. The
higher the score is, the higher the directional stability of hit
balls is. The evaluated scores are shown in below Table 1 and Table
2.
<Head Speed>
[0123] The head speed was also measured in each of the above
performed shots for measuring flight distances. The head speed
shown in Table 1 and Table 2 are average values for respective
clubs.
<Feeling>
[0124] Feeling was also measured in each of the above performed
shots for measuring flight distances. The feeling at impact for
each shot was evaluated on a scale of one to five by each golfer.
The higher the score is, the better the feeling is. The average
values of the evaluated scores for respective clubs are shown in
below Table 1 and Table 2.
TABLE-US-00001 TABLE 1 Specifications and evaluation results for
Examples Unit Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 E8/E1 -- 2.92
2.87 2.54 3.18 3.25 2.87 E1 kgf m.sup.2 1.97 2.01 2.27 1.97 1.97
1.97 E8 kgf m.sup.2 5.76 5.76 5.76 6.26 6.41 5.66 E1 - (130a + b)
kgf m.sup.2 0.19 0.23 0.49 0.19 0.19 0.19 E8 - (830a + b) kgf
m.sup.2 0.34 0.34 0.34 0.84 0.99 0.24 E9 - (930a + b) kgf m.sup.2
-0.14 -0.13 -0.12 -0.14 -0.14 -0.14 E10 - (1030a + b) kgf m.sup.2
-0.83 -0.83 -0.83 -0.73 -0.63 -0.93 Gradient ''a'' of -- 0.0052
0.0052 0.0052 0.0052 0.0052 0.0052 straight line L1 Y-intercept
''b'' of -- 1.1 1.1 1.1 1.1 1.1 1.1 straight line L1 Absolute angle
of degree 45 45 45 45 45 45 fiber orientation angle of intermediate
partial layer(s) Flight distance yard 272 271 270 271 270 269
Directional stability of -- 5.0 4.9 4.8 4.8 4.9 4.5 hit balls (on a
scale of 1 to 5) Head speed m/s 45.5 45.2 45.1 45.1 45.2 44.9
Feeling -- 5.0 4.8 4.7 4.8 4.9 4.6 (on a scale of 1 to 5)
TABLE-US-00002 TABLE 2 Specifications and evaluation results for
Comparative Examples Comp. Comp. Comp. Comp. Comp. Comp. Unit Ex. 1
Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 E8/E1 -- 3.84 2.68 2.38 4.61 3.57
2.15 E1 kgf m.sup.2 1.30 2.78 2.09 1.30 2.09 2.78 E8 kgf m.sup.2
4.97 7.45 4.97 5.97 7.45 5.97 E1 - (130a + b) kgf m.sup.2 -0.48
1.00 0.31 -0.48 0.31 1.00 E8 - (830a + b) kgf m.sup.2 -0.45 2.03
-0.45 0.55 2.03 0.55 E9 - (930a + b) kgf m.sup.2 -0.09 -0.05 -0.07
-0.09 -0.07 -0.05 E10 - (1030a + b) kgf m.sup.2 -1.98 -0.43 -1.98
-0.53 -0.43 -0.53 Gradient ''a'' of -- 0.0052 0.0052 0.0052 0.0052
0.0052 0.0052 straight line L1 Y-intercept ''b'' of -- 1.1 1.1 1.1
1.1 1.1 1.1 straight line L1 Absolute angle of degree 45 0 45 45 0
45 fiber orientation angle of intermediate partial layer(s) Flight
distance yard 261 255 265 266 268 256 Directional stability of --
3.3 4.1 4.4 3.3 4.4 4.1 hit balls (on a scale of 1 to 5) Head speed
m/s 42.6 42.1 43.8 43.2 44.1 42.8 Feeling -- 3.3 3.7 3.4 3.4 4.3
3.8 (on a scale of 1 to 5)
[0125] As shown in Table 1 and Table 2, Examples are highly
evaluated as compared with Comparative Examples.
[0126] The following clauses are a part of invention included in
the present disclosure.
[Clause 1]
[0127] A golf club shaft including:
[0128] a tip end;
[0129] a butt end;
[0130] a flexural rigidity E1 at a point located 130 mm apart from
the tip end;
[0131] a flexural rigidity E2 at a point located 230 mm apart from
the tip end;
[0132] a flexural rigidity E3 at a point located 330 mm apart from
the tip end;
[0133] a flexural rigidity E4 at a point located 430 mm apart from
the tip end;
[0134] a flexural rigidity E5 at a point located 530 mm apart from
the tip end;
[0135] a flexural rigidity E6 at a point located 630 mm apart from
the tip end;
[0136] a flexural rigidity E7 at a point located 730 mm apart from
the tip end;
[0137] a flexural rigidity E8 at a point located 830 mm apart from
the tip end;
[0138] a flexural rigidity E9 at a point located 930 mm apart from
the tip end; and
[0139] a flexural rigidity E10 at a point located 1030 mm apart
from the tip end, wherein
[0140] a ratio (E8/E1) is greater than or equal to 2 and less than
or equal to 7,
[0141] the flexural rigidity E1 is less than or equal to 2.5
(kgfm.sup.2),
[0142] the flexural rigidity E8 is greater than or equal to 5.0
(kgfm.sup.2),
[0143] when a formula of a straight line that passes through a
point (230, E2) and a point (630, E6) plotted in a graph on an
orthogonal coordinate system having an x-axis that represents a
distance (mm) from the tip end and a y-axis that represents a
flexural rigidity (kgfm.sup.2) is indicated by y=ax+b, the golf
club shaft satisfies the following relationships R1 and R8:
(130a+b)<E1.ltoreq.(130a+b+0.5) (R1), and
(830a+b)<E8.ltoreq.(830a+b+1.0) (R8).
[Clause 2]
[0144] The golf club shaft according to clause 1, wherein the golf
club shaft further satisfies the following relationship R81:
(830a+b+0.3).ltoreq.E8.ltoreq.(830a+b+1.0) (R81).
[Clause 3]
[0145] The golf club shaft according to clause 1 or 2, wherein
[0146] the flexural rigidity E9 is less than or equal to
(930a+b-0.1).
[Clause 4]
[0147] The golf club shaft according to any one of clauses 1 to 3,
wherein
[0148] the flexural rigidity E10 is less than or equal to
(1030a+b-0.6).
[Clause 5]
[0149] The golf club shaft according to any one of clauses 1 to 4,
wherein
[0150] the golf club shaft further satisfies the following
relationships R3, R4 and R5:
(330a+b-0.2)<E3.ltoreq.(330a+b+0.2) (R3),
(430a+b-0.2)<E4.ltoreq.(430a+b+0.2) (R4), and
(530a+b-0.2)<E5.ltoreq.(530a+b+0.2) (R5).
[Clause 6]
[0151] The golf club shaft according to any one of clauses 1 to 5,
wherein
[0152] the golf club shaft is formed by a plurality of carbon fiber
reinforced resin layers,
[0153] the carbon fiber reinforced resin layers include an
intermediate partial bias layer that is disposed apart from the tip
end and apart from the butt end, and
[0154] an axial directional region in which the intermediate
partial bias layer is disposed includes a point 830 mm apart from
the tip end.
LIST OF REFERENCE NUMERALS
[0155] 2 Golf club [0156] 4 Head [0157] 6 Shaft [0158] 8 Grip
[0159] s1 to s14 Prepreg sheet (layer) [0160] p2 Intermediate
partial bias layer (Intermediate partial layer) [0161] p3
Intermediate partial straight layer (Intermediate partial layer)
[0162] Bt Butt end [0163] Tp Tip end
[0164] The above descriptions are merely illustrative and various
modifications can be made without departing from the principles of
the present disclosure.
[0165] The terminology used in the description of the various
described embodiments herein is for the purpose of describing
particular embodiments only and is not intended to be limiting. The
use of the terms "a", "an", "the", and similar referents in the
context of throughout this disclosure (especially in the context of
the following claims) are to be construed to cover both the
singular and the plural, unless otherwise indicated herein or
clearly contradicted by context. As used throughout this
disclosure, the word "may" is used in a permissive sense (i.e.,
meaning "having the potential to"), rather than the mandatory sense
(i.e., meaning "must"). Similarly, as used throughout this
disclosure, the terms "comprising", "having", "including", and
"containing" are to be construed as open-ended terms (i.e., meaning
"including, but not limited to,") unless otherwise noted.
* * * * *