golf ball

Abstract

The objective is to provide a golf ball that can be measured using a radar-type ball flight measurement device, and which has a relatively high probability of being able to measure spin regardless of the spin conditions during a driver (W#1) shot or the position of the mark on a marked ball. [Solution] The present invention provides a golf ball comprising a core and a cover layer, wherein a mark detectable by a radar-type ball flight measuring device is placed on the outer surface of the core or the cover layer, and the shape of the mark is a single circle with the center filled in, and the circle has a diameter of less than 20 mm.

Description

[Technical Field]

[0001] The present invention relates to a golf ball in which radar-detectable marks are placed inside the ball so that the spin characteristics of the ball can be detected by radar. [Background technology]

[0002] In recent years, simulation golf for practice or recreational rounds has been conducted in limited indoor spaces. Radar-type ball flight measurement devices are efficient for ball measurement because they can simultaneously measure the flight of an actual ball by tracking its trajectory and the initial conditions with a single machine. Since ball flight measurement devices used outdoors can be brought indoors and set up behind the hitting bay, they are very convenient measurement devices. As an example, Figure 4 shows an indoor golf system 100, in which a golfer hits the ball from the hitting position 102 towards a screen 101 displaying a golf course, with a ball flight measurement device 103 positioned behind it.

[0003] Furthermore, even in a limited indoor space, a single unit can measure the trajectory height, distance, and initial conditions of the ball, including through simulation. However, when using the radar system indoors, there are frequent cases where spin cannot be measured during the initial condition measurement. Therefore, radar-reflective stickers are usually attached to the outside of the golf ball. However, when the ball is repeatedly hit at a target indoors, the reflective stickers peel off, making it impossible to obtain accurate data.

[0004] Prior art has been proposed for golf balls that can measure spin and other properties using radar-based ballistic measurement devices, as described in the following Patent Documents 1 to 5.

[0005] U.S. Patent No. 8,845,442 (Patent Document 1) discloses a method for determining the spin rate of a sports ball by analyzing the modulation of the Doppler radar signal of a rotating ball in flight. However, the modulation signal obtained by this method is relatively weak. That is, in situations where only data of very short ball flight times can be obtained, such as in indoor golf facilities, the modulation signal of an unmarked ball is often too weak to be useful for measuring the spin rate.

[0006] Japanese Patent Publication No. 2022-540479 (Patent Document 2) describes a sports ball that improves the detection of spin characteristics using radar. Specifically, it includes a spherical body having a first reflectivity to radiation generated by the radar used to detect the spin of the ball, and a plurality of markers, each marker having a second reflectivity to radiation generated by the radar used to detect the spin of the ball, and the markers are arranged on the ball such that a great circle extending around the outer surface of the ball is within a distance d from the projection of at least one marker onto the outer surface of the ball. Furthermore, Japanese Patent Application Publication No. 2023-089935 (Patent Document 3) describes a golf ball in which a plurality of radar-detectable marks are arranged in layers, and the plurality of radar-detectable marks include at least 11 non-circular marks arranged at equal intervals. However, because there is more than one mark, under the condition of high spin of 3000 rpm or more during a full shot, the marks may interfere with each other, making it impossible to measure the spin.

[0007] Japanese Patent Publication No. 2022-082449 (Patent Document 4) describes a golf ball having at least one radar-detectable mark placed on a layer, wherein the at least one radar-detectable mark includes three or more intersecting stripes. Furthermore, Japanese Patent Publication No. 2023-089939 (Patent Document 5) proposes a golf ball having a layer on its surface with radar-detectable marks, wherein the marks have a continuous non-circular shape, and the total surface coverage of all existing radar-detectable marks is 0.1-4.0%. However, the marks may be too long, and depending on the orientation of the ball, the marks may interfere with each other, making it impossible to measure spin. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent No. 8845442 [Patent Document 2] Special Publication No. 2022-540479 [Patent Document 3] Japanese Patent Publication No. 2023-089935 [Patent Document 4] Japanese Patent Publication No. 2022-082449 [Patent Document 5] Japanese Patent Publication No. 2023-089939 [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention has been made in view of the above circumstances, and aims to provide a golf ball that can be measured by a radar-type ball flight measuring device and has a relatively high probability of being able to measure spin regardless of the level of spin conditions during a driver (W#1) strike or the set position of the mark on a ball that has a mark. [Means for solving the problem]

[0010] The inventors conducted diligent research to achieve the above objective and found that by placing a reflective mark on the inner or outer surface of a golf ball by drawing a single circular design of a predetermined size using conductive ink, and then hitting the ball with a driver (W#1) at an outdoor and indoor golf driving range, they found that a high probability of spin measurement was obtained under both low-spin and high-spin hitting conditions. Furthermore, they found that the above golf ball achieved a relatively high probability of spin measurement even when the distance from the indoor hitting bay to the wall was short, leading to the present invention. In the following description, the "probability of spin measurement" will be simply referred to as "spin measurement probability."

[0011] Therefore, the present invention provides the following golf ball. 1. A golf ball comprising a core and a cover layer, wherein a mark detectable by a radar-type ballistic measuring instrument is placed on the outer surface of the core or the cover layer, characterized in that the shape of the mark is a single circle with a filled center, and the circle has a diameter of less than 20 mm. 2. The above mark is a circular golf ball as described in item 1 above, with a diameter of 3 to 15 mm. 3. The above mark is a golf ball according to item 1 or 2 above, made of a conductive ink material containing silver in the base polymer. 4. The volume resistivity of the above conductive ink material is 1 × 10⁻⁶ 4 ~50×10 5 The golf ball described in item 3 above has dimensions of Ω·cm. 5. The golf ball according to 1 or 2 above, wherein the cover layer consists of at least one intermediate layer and an outer cover, and the mark is placed on the surface of the intermediate layer. [Effects of the Invention]

[0012] In the golf ball measurable by the radar type trajectory measuring instrument of the present invention, the spin measurement probability can be increased under both low spin hitting conditions and high spin hitting conditions when hitting with a driver (W#1). Further, according to the golf ball of the present invention, a high spin measurement probability can be obtained regardless of the set position of the mark of the ball having a mark, and furthermore, even when the distance from the indoor hitting bay to the wall is short, a high spin measurement probability can be obtained.

Brief Description of Drawings

[0013] [Figure 1] It is a schematic cross-sectional view of a golf ball which is one embodiment of the present invention. [Figure 2] It is a schematic view showing the placement (position of the mark) of the balls of Examples 1 to 4 and Comparative Examples 2 and 4 when hitting the balls. (A) is a plan view seen from above, and (B) is a side view seen from the right side. [Figure 3] It is a schematic view showing the placement (position of the mark) of the ball of Comparative Example 3 when hitting the ball. (A) is a plan view seen from above, and (B) is a side view seen from the right side. [Figure 4] It is a schematic plan view showing an indoor golf system.

Modes for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described in more detail. The golf ball of the present invention has a core and a cover layer composed of one or more layers coated on the core. Usually, a large number of dimples are formed on the outer surface of the cover layer.

[0015] The above core can be formed using a known rubber composition. Examples of the base rubber include polybutadiene, and in particular, it is recommended to use cis-1,4-polybutadiene having at least 40% or more of a cis structure as the main material. In addition, natural rubber, polyisoprene rubber, styrene butadiene rubber, etc. can also be used in combination in this base rubber.

[0016] The above rubber composition may contain metal salts of unsaturated fatty acids such as methacrylic acid and acrylic acid as co-crosslinking agents, and zinc acrylate is particularly suitable from the viewpoint of high resilience. The amount of this co-crosslinking agent can be 10 parts by mass or more, particularly 15 parts by mass or more, with an upper limit of 50 parts by mass or less, particularly 40 parts by mass or less, per 100 parts by mass of the base rubber.

[0017] Organic peroxides can be blended into the above rubber composition, such as 1,1-bis-t-butylperoxy-3,3,5-trimethylcyclohexane, dicumyl peroxide, di(t-butylperoxy)-meth-diisopropylbenzene, and 2,5-dimethyl-2,5-di-t-butylperoxyhexane. Examples of commercially available products include Perkmill D (manufactured by Nippon Oil & Fats Co., Ltd.) and Trigonox 29-40 (manufactured by Kayaku Akzo Co., Ltd.). The amount of these organic peroxides blended is usually 0.1 parts by mass or more, particularly 0.5 parts by mass or more, with an upper limit of 5 parts by mass or less, and particularly 2 parts by mass or less, per 100 parts by mass of the base rubber.

[0018] The above composition may further contain various additives as needed, such as sulfur, water, antioxidants, zinc oxide, barium sulfate, pentachlorothiophenol zinc salt, and zinc stearate. The amounts of these additives are not particularly limited.

[0019] The diameter of the core described above is preferably 32.0 mm or more, more preferably 33.0 mm or more, and as an upper limit, it is preferably 40.5 mm or less, and more preferably 39.5 mm or less.

[0020] Furthermore, the core described above has a deflection hardness [amount of deflection (deformation) when subjected to an initial load of 98N (10kgf) to 1275N (130kgf)] of 2.5 to 5.0 mm, preferably 2.8 to 4.5 mm, and more preferably 3.0 to 3.7 mm. If the deflection hardness is too low, the feel when hitting with a driver may become too hard, and the scratch resistance may be poor. If the deflection hardness is too high, the feel when hitting with a driver may become too soft, and the distance may be significantly reduced.

[0021] The above-mentioned core can be manufactured by known methods. To obtain a core from a core rubber composition, it is preferable to use a conventional kneader (e.g., a Banbury mixer, kneader, and rolls) to knead the mixture, and then use compression molding, in which the resulting compound is molded in a core mold.

[0022] Next, in the present invention, the cover layer covering the core may consist of one or more layers. A thermoplastic or thermosetting resin is used as the base material for each layer of the cover layer, and a thermoplastic resin or thermoplastic elastomer is particularly preferred. An example of a thermoplastic resin is an ionomer resin, and commercially available products such as Hymiran (ionomer resin manufactured by Mitsui Dow Polychemicals) and Surlyn (ionomer resin manufactured by DuPont, USA) can be used. As for thermoplastic elastomers, various thermoplastic elastomers such as polyester-based, polyamide-based, polyurethane-based, olefin-based, and styrene-based can be used, and commercially available products such as Hytrel manufactured by Toray Celanese, Perprene manufactured by Toyobo MC, Pebax manufactured by ARKEMA, Pandex manufactured by DIC Covestropolymer, Santoprene manufactured by Monsanto, ToughTec manufactured by Asahi Kasei, and Dynalon manufactured by ENEOS Material are used. As the above thermoplastic resin or thermoplastic elastomer, it is preferable to use an ionomer resin or a thermoplastic polyurethane elastomer.

[0023] The thickness of each layer of the cover described above should preferably be 0.5 mm or more, especially 0.8 mm or more, with an upper limit of 3.0 mm or less, and especially 2.2 mm or less. If the layers of the cover are too thin, sufficient spin performance may not be obtained, or the resistance to cracking due to repeated impacts may be poor.

[0024] The deflection hardness of a golf ball formed by covering the core with the above-mentioned cover layer, that is, the amount of deflection deformation when subjected to an initial load of 98N (10kgf) to 1275N (130kgf), is usually 2.0mm or more, preferably 2.3mm or more, more preferably 2.5mm or more, with an upper limit of 4.0mm or less, preferably 3.3mm or less, and more preferably 2.8mm or less. If the deflection hardness of the ball is less than the specified amount, the feel of impact becomes too hard, and the amount of spin, especially during iron shots, increases too much, which can significantly reduce the distance. On the other hand, if the deflection hardness of the ball is greater than the specified amount, the actual initial velocity when struck by the club decreases, and the distance, especially when struck with a driver, may decrease.

[0025] To obtain a golf ball by covering the core with the cover layer described above, known methods such as injection molding and compression molding can be employed. For example, when using injection molding, a pre-made solid core can be set in a mold, and the cover material can be introduced into the mold according to conventional methods.

[0026] Furthermore, numerous dimples are formed on the surface of the outermost layer of the cover, and various treatments such as surface preparation, stamping, and painting can be applied to the cover.

[0027] In this invention, marks detectable by a radar-based ballistics measuring device are placed on the outer surface of the core or cover layer. A radar-based ballistics measuring device refers to a device that uses radar, such as "TrackMan," "FlightScope," or "Garmin Approach R10," to measure the movement of the club and the flight of the ball, and can be used both indoors and outdoors. Its features include the ability for the radar to track and measure the actual flight distance and trajectory when used outdoors. Furthermore, even if the measurement distance is short indoors, the height of the trajectory and the total flight distance, including carry and roll, can be confirmed through simulation by estimating from the actually measured data and a vast amount of past data.

[0028] The material marked above is not particularly limited as long as it is made from a radar-detectable material, but conductive ink material is particularly preferred. This conductive ink material can amplify the modulated signal of the reflected radar signal for a rotating ball. Furthermore, even when the ball's flight time is very short, the spin rate and spin axis of the ball can be determined using the spin modulated signal.

[0029] The conductive ink material described above is preferably a material containing silver in its base polymer. Examples of this base polymer include vinyl polymers, urethane polymers, acrylic polymers, epoxy polymers, and resins selected from combinations of two or more of these. An example of a material containing silver in its base polymer is the conductive pen manufactured by Chemtronics (product names "CW2200MTP" and "CW2200STP"). Marks drawn with conductive ink containing silver become easier to detect by radar, and the detection effect is higher than when aluminum or copper is included. Furthermore, drawing with a conductive ink pen eliminates the need to introduce special manufacturing equipment when producing balls.

[0030] The volume resistivity of the above conductive ink material is preferably 1 × 10⁻⁶. 4 Ω·cm or more, more preferably 1 × 10⁻⁶ 5Above Ω·cm, particularly preferably 5×10 5 Above Ω·cm, and as the upper limit value, preferably 50×10 5 Below Ω·cm, more preferably 25×10 5 Below Ω·cm, particularly preferably 12.5×10 5 Below Ω·cm. If this value is too low, the spin measurement probability with the radar may decrease. On the other hand, if this value becomes too large, the conductive ink pen may become too expensive.

[0031] In the present invention, since the above mark is made extremely thin and lightweight compared to the ball, the deterioration of the ball characteristics due to the influence of the mark can be minimized. That is, usually, a mark arranged over a part of the ball may change the characteristics of the ball (for example, the reaction when an impact is applied to the ball with a club) and may change the flight characteristics of the ball in some cases. However, in the present invention, the influence of the mark on the ball characteristics is almost negligible. Also, when putting face marks and side marks on the ball surface, using an ink that is not a conductive ink does not pose an obstacle to spin measurement with the radar, so it is not particularly hindered in the present invention.

[0032] The shape of the above mark is a single circular shape with the inside filled. If the shape of this mark is not circular, the variation in the spin measurement probability with the radar may easily occur depending on the direction in which the ball is hit. Also, if the inside of the circle is not filled, the spin measurement probability may decrease. Also, by using a conductive pen, it becomes easier to draw the mark. For example, by preparing a stencil in advance and using it when drawing, the ease of drawing can be further increased.

[0033] The diameter of the circle of the above mark is preferably 3 mm or more, more preferably 4 mm or more, still more preferably 5 mm or more, and as the upper limit value, preferably less than 20 mm, more preferably 15 mm or less, still more preferably 10 mm or less. Also, the area of the circle of the above mark is preferably 7 mm 2 or more, more preferably 13 mm 2More preferably 20 mm 2 The above is true, and the upper limit is preferably 314 mm. 2 More preferably, 177 mm 2 More preferably 79 mm 2 The following applies. If these values ​​are too small or too large, the probability of spin detection by radar may decrease.

[0034] The area of ​​the above marks on the entire surface of the ball is preferably 0.5% or more, more preferably 0.9% or more, and particularly preferably 1.4% or more, with an upper limit of preferably 22% or less, more preferably 12% or less, and particularly preferably 5% or less. If this value is too small or too large, the probability of spin measurement by radar may decrease.

[0035] The mark is formed on either the surface of the core or the surface of the cover layer, preferably on the surface of the cover layer (resin layer). In particular, it is preferable that the cover layer consists of at least one intermediate layer and an outer cover, and that the mark is placed on the surface of the intermediate layer. If the mark is not formed on the surface of the cover layer, it may be difficult to detect the mark with radar. Also, if the mark is formed on the surface of the outermost layer of the cover layer, a radar-detectable mark will be exposed on the appearance of the golf ball, which may cause discomfort to the user when taking a full shot. On the other hand, if the mark is formed on the surface of the resin of the intermediate layer, the mark will not be visible from the outside, so there will be no discomfort when using the ball.

[0036] Furthermore, if the above marks are formed on the surface of the rubber used as the core material, the marks may crack when repeatedly struck, making them difficult to detect by radar. Therefore, it is preferable to form the marks on the surface of the resin. Also, drawing the above marks on the resin surface allows for clearer depiction.

[0037] In a specific embodiment, the cover layer has a two-layer structure consisting of an intermediate layer and an outer layer. The intermediate layer is made of a resin such as ionomer, and the mark of the present invention is formed on the surface of the intermediate layer. The outer layer uses a urethane resin material as the base polymer, and contains titanium dioxide. By adding titanium dioxide to the urethane material, the cover (outer layer) can cover and conceal the mark, so that the user does not perceive any abnormality in the ball when looking at it from the outside.

[0038] Furthermore, when the above mark is formed on the outer surface of the cover layer, the outer surface is usually painted with a paint composition, and it is desirable to use a material with excellent durability for that paint composition. This is to prevent the mark from peeling off during use of the ball, or to prevent the mark from being exposed on the ball and staining the screen placed in front of the hitting bay of the golf simulator.

[0039] Figure 1 shows a golf ball G, an example of the present invention in which the cover layer is formed in two layers. As shown in Figure 1, this golf ball G comprises a core 1 and two cover layers covering the core. The cover layer consists of an intermediate layer 2 and an outermost layer 3, and numerous dimples D are formed on the outer surface of the outermost layer. A mark M is formed on the surface of the intermediate layer 2.

[0040] The golf ball of the present invention can be formed in accordance with the rules of golf, with a diameter of 42.67 mm or more and a mass of 45.93 g or less. [Examples]

[0041] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0042] [Examples 1-4, Comparative Examples 1-6] As shown in Table 1 below, the following rubber compositions common to each of Examples 1-4 and Comparative Examples 1-5 were used to prepare solid cores for each example by vulcanization at 150°C for 19 minutes.

[0043] [Table 1]

[0044] Further details about the core materials are as follows. • Polybutadiene: Manufactured by ENEOS Material, product name "BR 01" • Zinc acrylate: Product name "ZN-DA85SR" (manufactured by Nippon Shokubai Co., Ltd.) • Zinc stearate: Product name "Zinc Stearate GP" (manufactured by NOF Corporation) • Organic peroxide: Dicumyl peroxide, trade name "Perkmyl D" (manufactured by NOF Corporation) • Sulfur: Product name "Sunmix S-80N" (manufactured by Sanshin Chemical Industry Co., Ltd.), a sulfur masterbatch containing 80% by mass of rubber-grade powdered sulfur. • Water: Purified water (manufactured by Masaki Pharmaceutical Co., Ltd.) • Anti-aging agent: 2,2-methylenebis(4-methyl-6-butylphenol), trade name "Nocrac NS-6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) • Zinc oxide: Product name "Triple Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) • Pentachlorothiophenol zinc salt: Manufactured by Fujifilm & Wako Pure Chemical Industries, Ltd.

[0045] Formation of cover layer (intermediate layer and outermost layer) and conductive mark Next, an intermediate layer with a thickness of 1.20 mm was applied to the core with a diameter of 38.65 mm obtained above by injection molding using the resin material No. 1 compound shown in Table 2 to produce an intermediate layer-coated sphere. For Examples 1-3 and Comparative Example 2, conductive marks were formed on the surface of these intermediate layer-coated spheres in the shape, size, and number shown in Table 3. These conductive marks were formed by drawing marks on the surface of the intermediate layer with a conductive ink pen, product name "CW2200MTP" manufactured by Chemtronics. Subsequently, the outermost layer material (cover material) No. 2 with a thickness of 0.825 mm, as shown in Table 2, was applied to the surface of each intermediate layer-coated sphere by injection molding. At this time, although not specifically shown in the figures, common dimples were formed on the outermost layer surface of each example and comparative example. For Example 4 and Comparative Examples 3-5, conductive marks were formed on the surface of these covers in the shape, size, and number shown in Table 3. The conductive marks were formed by drawing marks on the outermost surface using a conductive ink pen, similar to the method used in Examples 1-3 and Comparative Example 2.

[0046] [Table 2]

[0047] The details of the ingredients listed in Table 2 are as follows. • "Hymilan 1706" and "AM7318" are ionomers manufactured by Mitsui Dow Polychemicals. • "Barium sulfate" - Product name "Precipitated Barium Sulfate 300" manufactured by Sakai Chemical Industry Co., Ltd. • Trimethylolpropane (TMP), manufactured by Tokyo Chemical Industry Co., Ltd. • "Polyethylene wax" - Sanyo Chemical Industries' product name "Sunwax 161P" • "TPU" is a product name "Pandex" manufactured by DIC Covestropolymer, an ether-type thermoplastic polyurethane with a material hardness (Shore D) of 47.

[0048] Table 3 below shows the details of each golf ball example obtained, including the ball structure, the material hardness of each layer, and the core and ball surface hardness.

[0049] [Table 3]

[0050] Comparative Example 6 is a golf ball manufactured by Titleist and sold under the product name "ProV1 RCT," which was purchased from the market. Although the details of the ball's internal structure are unknown, the surface of the intermediate layer has radar-detectable marks as defined in Japanese Patent Publication No. 2022-82449.

[0051] The following impact tests were performed on each of the golf balls obtained.

[0052] [Checking the amount of spin when hitting with a driver (W#1)] We investigated whether spin rate could be measured when a golf hitting robot was fitted with a driver (W#1) club and struck at a head speed of 55 m / s. The club used was a Bridgestone Sports "B Limited-415" driver, 2012 model. The hitting conditions for Comparative Example 1, when the ball was set to spun at approximately 1600 rpm, were defined as low-spin conditions with a driver (W#1) and a head speed (HS) of 55 m / s. Conversely, the hitting conditions for Comparative Example 1, when the ball was set to spun at approximately 3000 rpm, were defined as high-spin conditions with a driver (W#1) and a head speed (HS) of 55 m / s.

[0053] [How to position the ball (position of the mark when batting)] For Examples 1-4 and Comparative Examples 2 and 4, the ball placement during the ball striking test was performed in two ways: as shown in Figure 2(A), the ball was set so that the circular mark M was positioned above the ball surface 1a relative to the launch direction; and as shown in Figure 2(B), the ball was set so that the circular mark M was positioned on the right side of the ball surface 1a relative to the launch direction. Similarly, for Comparative Example 3, the ball placement during the ball striking test was performed in two ways: as shown in Figure 3(A), the ball was set so that the linear mark M was positioned above the ball surface 1a relative to the launch direction; and as shown in Figure 3(B), the ball was set so that the linear mark M was positioned on the right side of the ball surface 1a relative to the launch direction. The arrows in Figures 2 and 3 indicate the launch direction of the ball. In Comparative Example 5, the mark pattern resembled an animal, but the ball was set in the same position as the circular mark in Examples 1-3 and Comparative Examples 2 and 4. For the placement of the unmarked balls in Comparative Example 1 and the commercially available balls in Comparative Example 6, the balls were set randomly.

[0054] [Measurement Environment] (1) Outdoors Under the conditions described above, balls were launched outdoors, and the number of times the spin of each ball could be measured using a radar-based ballistics measuring device was determined. The probability of success was then calculated. The calculated measurement probabilities were evaluated based on the following criteria. ○··· Spin measurement probability is 70% or higher △··· Spin measurement probability is between 60% and 70% ×... Spin measurement probability is less than 60%

[0055] (2) Indoors Under the conditions described above, balls were launched indoors, and the number of times the spin of each ball could be measured using a radar-based ballistics measuring device was determined. The probability of success was then calculated. The calculated measurement probabilities were evaluated based on the following criteria. ○··· Spin measurement probability is 55% or higher △··· Spin measurement probability is between 40% and 55% ×... Spin measurement probability is less than 40% Indoor testing is conducted using an indoor golf system 100, as shown in Figure 4, in which a golfer hits the ball from a hitting position 102 towards a screen 101 displaying a golf course. The distance from the hitting position to the screen is several meters.

[0056] The radar-based ballistic measurement device used in the above outdoor and indoor tests was the "TrackMan NET" model (manufactured by TrackMan).

[0057] The conditions for hitting the golf ball and the results of the judgment for each example are shown in Table 4 below.

[0058] [Table 4]

[0059] As shown in Table 4, the golf balls of Examples 1 to 4 were golf balls in which circular marks with a diameter of 5 to 15 mm were formed on the surface of the intermediate layer or the surface of the ball by marking with conductive ink. As a result, in all examples, a high probability of spin measurement using a radar-type ball flight measurement device was obtained, as well as a high probability of spin measurement indoors. In contrast, the results for the golf balls of Comparative Examples 1 to 6 are as follows. Comparative Example 1 was a ball without radar-detectable marks, and as a result, the probability of spin measurement using a radar-based ballistics measuring device was low. Comparative Example 2 is a golf ball in which a circular mark with a diameter of 20 mm was formed on the surface of the intermediate layer by marking with conductive ink. As a result, the probability of spin measurement using a radar-type ball flight measurement device was low. The probability of spin measurement indoors was also low. Comparative Example 3 is a ball in which a mark was formed by marking the surface of the ball with conductive ink in a line around it. As a result, the probability of spin measurement indoors was low. Comparative Example 4 is a golf ball in which two circular marks with a diameter of 5 mm were formed on the ball surface by marking with conductive ink. As a result, the probability of spin measurement using a radar-type ball flight measurement device was low. The probability of spin measurement indoors was also low. Comparative Example 5 is a golf ball in which an animal (pig) design was marked on the ball surface using aluminum foil to form a mark. As a result, the probability of spin measurement using a radar-type ball flight measurement device was low. The probability of spin measurement indoors was also low. Comparative Example 6 is a golf ball manufactured by Titleist and sold under the product name "ProV1 RCT," purchased from the market. The results showed a low probability of spin measurement using a radar-based ball flight measurement device. Furthermore, the probability of spin measurement indoors was also low.

Claims

1. A golf ball comprising a core and a cover layer, wherein a mark detectable by a radar-type ballistic measuring instrument is placed on the outer surface of the core or the cover layer, characterized in that the shape of the mark is a single circle with a filled center, and the circle has a diameter of less than 20 mm.

2. The golf ball according to claim 1, wherein the above mark is a circle with a diameter of 3 to 15 mm.

3. The above mark is made of a conductive ink material containing silver in the base polymer, as described in claim 1 or 2 of the golf ball.

4. The volume resistivity of the above conductive ink material is 1 × 10⁻⁶ 4 ~50 x 10 5 A golf ball according to claim 3, having dimensions of Ω·cm.

5. The golf ball according to claim 1 or 2, wherein the cover layer comprises at least one intermediate layer and an outer cover, and the mark is placed on the surface of the intermediate layer.

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