Abstract: There is provided a golf ball bearing highly fashionable marks representing a brand name and a play number, both of which are excellent in visibility. The golf ball has two sorts of marks printed on its ball body surface. The two marks have similar colors and a CIE L*a*b* color difference (&Dgr;E) between the colors of theses marks is in the range of 5 to 50.

Abstract: An apparatus for making a golf ball is disclosed. The apparatus is a molding assembly for making a golf ball which includes a mold body that defines a molding cavity. The molding cavity is adapted to accommodate and preferably retain a golf ball core during a molding operation of one or more layers about the core. The molding assembly includes at least one material flow inlet, at least one material flow channel extending between and providing fluid communication with a material flow inlet and the molding cavity. At least one portion of the material flow channel has a plurality of bends and at least one branching intersection adapted to promote turbulence in a liquid flowing therethrough. A method of making a golf ball is also disclosed. A golf ball made from the disclosed molding apparatus and/or process is also disclosed.

Abstract: The present invention is a golf ball having a core, a cover and a lattice structure aerodynamic pattern. The core has a diameter of 1.53 inches to 1.55 inches, and a PGA compression of 60 to 75 points. The cover has a thickness of 0.060 inch to 0.090 inch. The cover has a Shore D hardness less than 58 as measured on the golf ball. The golf ball has a COR that is greater than 0.782 points at 143 feet per second.

Abstract: A method of casting a portion of a golf ball comprising the steps of providing a single component that is blocked and stable at a first predetermined temperature and becomes unblocked at a second predetermined temperature, wherein said second predetermined temperature is higher than the first predetermined temperature; and reacting said single component at the second predetermined temperature to form the surrounding layer.

Abstract: The present invention is directed to improved regulation multi-layer golf balls. A smaller and lighter core is produced and metal particles, or other heavy weight filler materials, are included in the cover compositions. The resulting molded golf ball exhibits enhanced interior perimeter weighting. Preferably, the particles are included in a relatively thick inner cover layer (or mantle) of a solid, three-piece multi-layered golf ball. The size and weight of the core is reduced in order to produce an overall golf ball which meets, or is less than, the 1.62 ounce maximum weight limitation specified by the United States Golf Association. The combination of the present invention produces a golf ball with an increased moment of inertia and/or a greater radius of gyration and thus generates lower spin. This results in a golf ball exhibiting enhanced distance without substantially effecting the feel and durability characteristics of the ball.

Abstract: In a golf ball including a core and a cover of at least one layer, the cover layer is formed of a heated mixture of an ionomer resin and a metal salt such as magnesium stearate. The heated mixture exhibits such a crystal melting behavior that when measured by DSC, the difference between first and second peak temperature is up to 30° C. The ball is improved in resilience.

Abstract: The present invention is directed towards a multilayer golf ball which comprises a core having a treated surface and a cover layer having a plurality of dimples, wherein the cover layer is disposed concentrically about the core and bonded to the core preferably without an adhesive. The multilayer golf balls may alternatively or additionally be formed such that at least one layer of the core has a treated surface and is bonded, preferably without an adhesive, to an adjacent layer. The golf balls may be prepared by forming a first portion of a golf ball, wherein the first portion has a surface, treating the surface of the first portion to increase the adhesion thereof, and bonding at least a portion of a second portion concentrically about the surface of the portion.

Abstract: Molding equipment and related techniques for forming a golf ball are disclosed. The molding equipment includes the use of a mandrel with a spherical portion sized to fit within a molding chamber. The molding equipment and related processes are particularly useful when forming the various layers by reaction injection molding.

Abstract: Molding equipment and related techniques for forming a golf ball are disclosed. The golf ball comprises a core and a cover layer, wherein the cover layer provides one or more deep dimples that extend through the cover layer to and/or into a layer or component underneath are disclosed. The cover may be a single layer or include multiple layers. If the cover is a multi-layer cover, the dimples extend to or into at least the first inner cover layer, and may extend into two or more inner cover layers. If the cover is a single layer, the dimples extend to or into the core. The cover layer(s) may be formed from any material suitable for use as a cover, including, but not limited to, ionomers, non-ionomers and blends of ionomers and non-ionomers. The dimples may be spherical or non-spherical, and the portion of the dimple that extends to or into the next inner layer may be the same or different shape as the outer portion of the dimple.

Abstract: Molding equipment and related techniques for forming a golf ball with one or more deep dimples are disclosed. The golf ball comprises a core and a cover layer, wherein the cover layer provides one or more deep dimples that extend through the cover layer to and/or into a layer or component underneath are disclosed. Preferably, the deep dimples are at least twice the depth of conventional dimples, more preferably, three or four times the depth of the conventional dimples. The deep dimples may be spherical or non-spherical, and the portion of the dimple that extends to or into the next inner layer may be the same or different shape as the outer portion of the dimple.

Abstract: Molding equipment and related techniques for forming a golf ball are disclosed. The golf ball comprises a core and a cover layer, wherein the cover layer provides one or more deep dimples that extend through the cover layer to and/or into a layer or component underneath are disclosed. The cover may be a single layer or include multiple layers. The cover layer(s) may be formed from any material suitable for use as a cover, including, but not limited to, ionomers, non-ionomers and blends of ionomers and non-ionomers. The molding equipment and related processes are particularly useful when forming the various layers by reaction injection molding.

Abstract: Molding equipment and related techniques for forming a golf ball are disclosed. The golf ball comprises a core and a cover layer, wherein the cover layer provides one or more deep dimples that extend through the cover layer to and/or into a layer or component underneath are disclosed. The molding equipment provides one or more selectively positionable knock-out pins along the surface of the molding chamber. These pins are specially tailored such that after their retraction subsequent to molding, the resulting voids are deep dimples. The molding equipment and related processes are particularly useful when forming the various layers by reaction injection molding.

Abstract: A golf ball is provided having a controlled variable moment of inertia. The golf ball includes a core defining at least one hollow channel. At least one movable weight is located within each hollow channel. The end of the hollow channel at the outer edge of the core is enclosed with a plug. The movable weight and plug may each further include a magnet or the hollow channel may include a placement member such as a spring to control the movement of the weight. When the present golf ball is struck, the spin rate forces the weights to move from the interior of the core outwardly towards the outer edge of the core, thereby varying the moment of inertia of the golf ball. A method of manufacturing the present golf ball is also provided. The golf ball also significantly reduces hooks and slices due to the gyroscopic effect of the moving weight(s) to the outer edge of the core.

Abstract: A golf ball is made by a process comprising:

Abstract: A high CoR golf ball having predetermined moment of inertia is provided. A portion of the golf ball preferably contains substantially no filler, which contributes to the increased resilience of the ball. In accordance to one aspect of the invention, the portion with substantially no filler is an outer core of the ball. The innermost core should have a high specific gravity. Additionally, the outermost layers of the ball may have a low specific gravity. Preferably, the portion with substantially no filler is relatively larger than other portions of the ball.

Abstract: The present invention is a golf ball that has a coefficient of restitution at 143 feet per second that is greater than 0.8015, and an USGA initial velocity less than 255.0 feet per second. The golf ball is preferably a solid three-piece golf ball with a thermosetting polyurethane cover, an ionomer blend intermediate layer and a polybutadiene core.

Abstract: In a golf ball comprising a solid core, a mantle, and a cover, the mantle is formed of a thermoplastic elastomer having a Shore D hardness of 30-52, the cover is formed of a thermoplastic resin loaded with a particulate inorganic filler, the solid core has a surface JIS C hardness 10-22 units greater than a center JIS C hardness, and the golf ball has an inertia moment of 82.5-85.5 kg·cm2. The ball is improved in durability and feel when hit with clubs of different types.

Abstract: A multi-piece golf ball includes a core having a diameter of 30 to 40 mm, at least one intermediate layer including the outermost layer having a thickness of 0.5 to 2.0 mm, and a cover having a thickness of 1.0 to 3.0 mm. The core is made from a rubber composition mainly containing polybutadiene. The outermost layer is made from a non-ionomer based thermoplastic resin. The cover is made from a material obtained by dispersedly blending at least one kind of silicone powder selected from a silicone rubber powder, a silicon resin powder, and a composite powder thereof, in a main resin component containing an ionomer resin in an amount of 50% by weight or more. The core has a hardness corresponding to a deflection in a range of 3.5 to 6.5 mm under an applied load of 100 kg.

Abstract: A process for making a golf ball with one or more deep dimples is disclosed. The process utilizes a molding assembly for making a golf ball which includes a mold body that defines a molding cavity. The molding cavity is adapted to accommodate and preferably retain a golf ball core during a molding operation of one or more layers about the core. The molding assembly includes at least one material flow inlet, at least one material flow channel extending between and providing fluid communication with the material flow inlet and the molding cavity. At least one portion of the material flow channel has a plurality of bends and at least one branching intersection adapted to promote turbulence in a liquid flowing therethrough. The molding cavity includes at least one outwardly extending protrusion that forms a deep dimple that extends through the cover of the golf ball to and/or into the underlying component of the golf ball upon molding.

Abstract: Disclosed is a process to increase adhesion between two adjacent layers. The process comprises roughening the surface of one layer followed by chlorination of the roughened surface and joining of the layers, or treating the surface of one layer with a silicone-based adhesion promoter and joining the layers. In one preferred embodiment the process comprises roughening the surface of one layer, followed by chlorination of the roughened surface, joining of the layers and post-treatment of the molded layers at an elevated temperature for a predetermined time.

Abstract: A solid golf ball has a solid core and a cover formed of a resin composition comprising the reaction product of a thermoplastic polyurethane elastomer with dicyclohexylmethane-4, 4″-diisocyanate. The ball is efficiently moldable and meets such requirements as a pleasant feel, ease of control, high resilience, and minimized scuffs by iron shots.

Abstract: The invention provides a golf ball having a cover, intermediate layers and/or a core comprising in whole or in part of water resistant polyurethane elastomers. The polyurethane elastomers may be blended with conventional materials employed to form golf balls, covers and intermediate layers.

Abstract: A solid golf ball with a polyurethane cover is provided which is satisfactory in the moldability of the cover and in ball characteristics such as a shot feeling and a flight distance. The solid golf ball of the invention includes a solid center, an intermediate layer, and a polyurethane cover. A material having a flexural modulus of from 150 to 420 MPa is used for the intermediate layer in order for the golf ball to offer satisfactory shot feeling and flight distance. By the use of a vulcanizate of a rubber composition containing a diphenyl disulfide for the solid center, the golf ball can exhibit an increased flight distance. In order to enhance the moldability of the cover a urethane prepolymer having a residual isocyanate monomer content of not more than 0.5% by mass is used.

Abstract: A golf ball having an integral means for sensing temperature whereby a golfer can readily determine if a golf ball is at the optimum temperature for play. For purposes of indicating temperature, the ball incorporates a thermochromic section that will change color or become transparent or translucent at a predetermined temperature. The thermochromic section may be printed in such a manner to indicate the condition of the ball.

Abstract: A golf ball which produces high spin rate and accordingly readily stops even when being shot from a rough or in the rain is provided. Such a golf ball is constituted of a core and a cover and the cover has a loss tangent of 0.15 to 0.70 at −10° C. in a temperature distribution curve for dynamic viscoelasticity measured in a tensile mode under conditions of temperature increasing rate of 4° C./min, frequency of 10 Hz and initial strain of 1.0 mm.

Abstract: A golf ball includes at least a core, an inner cover, and an outer cover. The inner and outer covers are of different colors. A portion of the inner cover penetrates the outer cover and is exposed to the outside on the surface of the golf ball. The exposed portion constitutes a mark portion on the surface of the golf ball. Further, an auxiliary layer is provided in contact with the inner cover. The auxiliary layer has a color different from those of the inner and outer covers and has an end surface which is exposed to the outside on the surface of the golf ball within the mark portion. Either the inner cover or the auxiliary layer completely covers the core.

Abstract: Golf balls having a core including a material formed from a controlled-isomer polybutadiene, a crosslinking agent, and a free-radical initiator, or a reaction product thereof, and a cover having a plurality of dimples disposed about the core, wherein the controlled-isomer polybutadiene includes at least about 10 percent to 80 percent trans-isomer and no more than about 5 percent vinyl-configuration polybutadiene and wherein the controlled-isomer polybutadiene has both an absolute molecular weight of at least about 250,000 and a polydispersity of no more than about 3 prior to crosslinking. In particular, golf balls having a compression below about 80 without significant loss of resilience can be advantageously prepared with such materials. Methods of preparing such golf balls are also recited.

Abstract: The golf ball comprises all known cores provided with a cover produced by a polymer blend that combines the durability of a conventional cover with the feel of a traditional balata cover having a plurality of dimples in a modified dodecahedron pattern. The dodecahedron consists of twelve pentagons, which are subdivided into a total of sixty triangles. The triangles are then further subdivided into rows into which various diameter dimples are placed. The dimple pattern can be arranged to produce a pattern of ten great circles, which are free of dimples. The cover formulation is a blend of various ethylene/methacrylic acid copolymers wherein at least one copolymer has a high modulus and at least one copolymer has a moderate modulus forming a miscible blend having a PDI index that maximizes durability while still maintaining feel and playability.

Abstract: A sound-producing golf ball includes an outer shell with a shock-absorbent inner housing having a rechargeable micro-battery positioned therein. A micro-generator coupled to a rotatably mounted shaft is positioned in the housing. A pendulum depending from the shaft is urged downwardly by gravity for rotating the shaft as the golf ball rolls while in play, thus generating electricity for recharging the micro-battery. A sound chip having a memory for storing audible messages is positioned in the housing along with a sound generator for audibilizing the messages when energized. The housing may include a receiver for receiving a signal from a transmitter for selectively energizing operation of the sound chip and sound generator. The housing presents a geodesic configuration and includes a plurality of interconnected tetrahedral structures for absorbing impact forces.

Abstract: A multi-layer golf ball and methods for preparing a portion thereof including a core having at least one core layer, a mantle having at least one layer including an amount of reinforcing polymer component and a resilient polymer component disposed concentrically adjacent the core, and at least one cover layer disposed concentrically adjacent the mantle, wherein the layer of the mantle is sufficiently rigid to inhibit the resilient polymer component from substantially altering shape prior to crosslinking. The invention also includes an elastomeric composition including a polybutadiene having a high molecular weight average and a predominantly 1,4-cis content, a free-radical initiator, and a reinforcing polymer component having a sufficiently low viscosity at a mixing temperature to permit substantially uniform dispersion of the polymer component with the polybutadiene and having a crystalline melting point sufficiently low to permit mixing while avoiding substantial crosslinking.

Abstract: In a golf ball comprising a core and a cover, the cover is formed of a cover stock based on a mixture of an ionomer resin and a thermoplastic polyurethane elastomer and having a hardness of at least 55 as measured by a ASTM D2240 type D durometer. The cover stock avoids any discoloration upon long-term UV exposure and is easy to mold. The ball has advantages including moderate backspin upon driver shots, good travel distance performance, and durability against repetitive hits.

Abstract: A golf ball having a thermosetting polyurethane cover composed of a blend of polyurethane prepolymers is disclosed herein. The blend may be a dual blend with a TDI-based polyurethane prepolymer blended with a second diisocyanate polyurethane prepolymer, typically a PPDI-based polyurethane prepolymer. The blend may also be a tri-blend with a TDI-based polyurethane prepolymer blended with two other diisocyanate polyurethane prepolymers, typically two different PPDI-based polyurethane prepolymers. The golf ball has a durability of at least 3.5 on a shear test rating of the cover.

Abstract: The invention is intended to provide a solid golf ball with a polyurethane cover having satisfactory formability and ball properties. The solid golf ball of the invention comprises a solid core, and a polyurethane cover for covering the solid core, wherein the difference in Shore D hardness between a center portion and a surface portion of the solid core is at least 15; the polyurethane cover has a thickness (t) of not more than 1.0 mm, and is formed from a cured urethane composition having Shore D hardness (D) of from 35 to 60; a product of the thickness(t) and the Shore D Hardness (D) of the cured urethane composition is ranging from 10 to 45(10≦D×t≦45); and the urethane composition comprises an isocyanate group-terminated urethane prepolymer having the residual polyisocyanate monomer content of not more than 0.1 mass %, and an aromatic polyamine compound.

Abstract: Molds made from a porous metal material allow for superior injection and compression molding of golf ball portions, such as cores, intermediate layers and covers. Use of the porous material in the sections contacting molding material, such as mold sections forming cavities, pins, or runners, allows for production of superior ball portions, with reduced formation of pin marks, knit lines, and other imperfections leading to degradation of the properties of the resulting portions. All or part of the mold can be made from the porous metal. Particular mold apparatus incorporate vacuum and/or compression devices to improve venting and release of the ball portions from the mold. Also, methods for preparing a layer for a golf ball incorporates using a mold made from a porous material and incorporating use of vacuum or pressurizing devices.

Abstract: A thread rubber exhibiting good impact resilience and reduced in breakage during a winding step, and a golf ball employing such thread rubber are provided. The thread rubber composition for a golf ball has 0.5-7.0 parts by weight of sulfur and 0.5-5.0 parts by weight of vulcanization accelerator blended with respect to 100 parts by weight of a rubber component including either one of polyisoprene rubber, natural rubber and polybutadiene rubber, or a mixture thereof. The rubber component has a cis-1,4 bond content of from 90.0% to 93.8%. The blended amount of the sulfur is made greater than the blended amount of the vulcanization accelerator.

Abstract: The present invention is directed to an improved golf ball and a method of winding that includes measuring and controlling thread stress directly, rather than maintaining and controlling the level of tension on the threads. The golf ball includes a center, a wound layer that surrounds the center to form a wound core, and a cover that surrounds the wound core. The wound layer is formed of at least one thread, and the wound layer includes a plurality of radially extending sections, each section has a thread stress. The stress within each section is substantially constant, but at least two radially extending sections have different stresses. The method for winding thread onto a golf ball center to form a wound core comprises the steps of measuring a stress within a portion of the thread; winding the thread about the golf ball center while applying a force on the thread to form a plurality of portions with predetermined thicknesses and varying the stress between the portions.

Abstract: In a multi-piece golf ball comprising a solid core, an intermediate layer, and a cover, the intermediate layer and/or the cover is formed of a heated mixture having a melt index of at least 1.0 dg/min and comprising (a) an olefin-carboxylic acid random copolymer and/or (d) a metal ion-neutralized olefin-carboxylic acid random copolymer and/or a metal ion-neutralized olefin-carboxylic acid-carboxylate random copolymer; (b) a fatty acid or derivative having a molecular weight of at least 280; and (c) a neutralizing basic inorganic metal compound. All expressed in Shore D hardness, the intermediate layer has a hardness of 40-63, the cover has a hardness of 45-68, and they satisfy the relationship: the hardness of solid core at its center≦the hardness of intermediate layer≦the hardness of cover.

Abstract: A multi-piece solid golf ball includes a solid core, at least one intermediate layer, and a cover having at least one cover layer. The solid core has a compression deflection of 3.0 mm or more, the intermediate layer is mainly made from a thermoplastic resin and has a Shore D hardness of 45 to 55 and a specific gravity of 1.2 or less, and the cover has a Shore D hardness of 60 or more and a thickness of 1.6 to 2.3 mm. The golf ball further comprises a ratio of the compression deflection of a sphere composed of the solid core covered with the intermediate layer to the compression deflection of the solid core is more than 0.900 and less than 0.970; and a difference in JIS-C hardness between the surface and the center of the solid core is equal to or less than 5.

Abstract: A solid golf ball having a plurality of dimples formed in its surface is characterized in that at least 70% of the entire dimples have a point of inflection at a position of 75 to 90% of their depth, and the overall dimple volume proportion is 0.7 to 0.9%.

Abstract: The present invention provides a three-piece solid golf ball having good shot feel and excellent flight performance. The present invention relates to a three-piece solid golf ball comprising a core, an intermediate layer formed on the core, and a cover covering the intermediate layer, wherein the golf ball is obtained by adjusting a correlation between the amounts of organic sulfide compound, organic peroxide and co-crosslinking agent in a rubber composition for a core, and a correlation between surface hardness of the core, intermediate layer hardness, cover hardness, thickness of the intermediate layer and thickness of the cover, to a specified range.

Abstract: A golf ball having a high rotational moment of inertial core assembly is disclosed. The core assembly may comprise a low specific gravity core and non-uniform thickness, high specific gravity intermediate layer. This sub-assembly is preferably encased within a soft cover. The low specific gravity core is preferably made from a foamed polymer or from a polymer with its specific gravity reduced, and the non-uniform thickness, high specific gravity core preferably has outer projections, inner projections or both disposed thereon. The projections increase the durability of the intermediate layer, thereby allowing polymers with high flexural modulus to be used as the intermediate layer. Alternatively, the inner and outer projections may extend circumferentially to form webs or ribs on the intermediate layer to increase its stiffness. The ball may comprise a second non-uniform thickness layer, wherein one or both of the intermediate layers comprise high specific gravity materials.

Abstract: A golf ball 1 has a core 2 and a cover 3. For molding a core 2, a rubber composition is extruded from a kneading machine, and cut at a predetermined length to obtain a preforming material. The preforming material is placed in a mold and the mold is clamped. An upper portion and lower portion of the mold mate for more than or equal to 15 seconds, and thereafter they are unclamped until a clearance between the upper and lower portions becomes from 3 mm to 8 mm, then, the mold is shut. The shutting time is determined to be from 0.5 second to 5.0 seconds. By this unclamping of the mold, a residual air in a spherical cavity is released, which results in elimination of defective products.

Abstract: A golf ball having a surface with an alignment indicia which includes a longitudinal segment and a latitudinal segment is disclosed herein. Preferably, the longitudinal segment extends along a pole of the golf ball and has a length ranging from 1.00 inch to 1.5 inches.

Abstract: A thread rubber exhibiting good impact resilience in an elongated state, and a golf ball using such thread rubber are provided. The vulcanized thread rubber composition is obtained by vulcanizing a thread rubber composition including at least 50 wt % of polyisoprene rubber having a cis 1,4 bond content of 80-95% and a trans 1,4 bond content of 2-4% within a rubber component. In the vulcanizate, a ratio of a crosslinked density of polysulfide bonds with respect to a total crosslinked density is more than 70%. The golf ball is made using this vulcanized thread rubber composition.

Abstract: This application discloses a golf ball printing ink enabling printing a clear mark which is free of any void or pinhole and has superior impact resistance and scuffing resistance without the need for a primer coat, a golf ball printing method utilizing the ink, and a golf ball bearing thereon a mark printed with the ink. The ink includes an epoxy resin and a coloring agent, and preferably further includes an isocyanate compound as a curing agent.

Abstract: Golf balls and compositions for use in ball cores, covers and intermediate layers incorporate syndiotactic 1,2-polybutadiene having crystallinity and other specified physical properties. Golf balls incorporating the compositions of the present invention provide flexibility in golf ball design to improve ball performance, such as hit feel and spin rate, without adversely affecting shear-cut resistance of the ball. Also, methods for making golf balls include preparing a composition comprising syndiotactic 1,2-polybutadiene having crystallinity, and then incorporating the composition into a golf ball. The methods can include injection molding only, or injection and compression molding. When the composition being molded incorporates crosslinking agents, co-crosslinking agents, or crosslinking accelerators, preferred methods include inducing partial or total crosslinking of the composition at preferred steps of making the golf balls.

Abstract: The present invention is directed towards a multi-layered core golf ball that comprises a center, a cover and a thin laminate comprising of at least one core layer formed around the center to create an inner ball, wherein the laminate includes at least one outer core layer that is relatively stiff and hard relative to the center, at least one outermost core layer that is heavily filled with a density increasing material and at least one core layer that functions as a moisture vapor barrier. One core layer may serve to provide all the functions in a single layer.

Abstract: A practice golf ball and its associated method of manufacture is claimed. The practice golf ball includes a hollow inner shell made of inexpensive molded plastic. The inner shell is molded so that the outer surface of the inner shell contains a dimple pattern. A first coating covers the inner shell. The first coating is applied as a liquid, wherein the first coating conforms to the dimple pattern on the inner shell. The first coating has a degree of elasticity greater than that of the plastic inner shell. A second coating covers the first coating. The second coating is also applied as a liquid, wherein the second coating conforms to the dimple pattern of the inner shell and the intervening first coating. The second coating has a degree of tear resistance greater than that of the plastic inner shell.

Abstract: The present invention provides ink for golf ball that can be used in printing a mark directly on a cover made from ionomer resin, without the need for a primer coat, while ensuring high durability. The printing ink comprises an acrylic resin and a coloring agent. A golf ball having a durable mark printed thereon and a method of printing a mark efficiently on a surface of a ball body by using the ink are also provided.

Abstract: In connection with a golf ball comprising a core, an intermediate resin layer, and a cover, the invention provides a mold defining therein a spherical cavity for molding the resin layer. The mold is divided into a pair of mold halves each of which has at least three segments which are removably assembled to define the spherical cavity, each of the segments being provided on its cavity-defining surface with at least one projection. When the core is placed in the mold cavity, the projections support the core in place. The resin layer having perforations can be effectively molded and readily removed from the mold.