WO1998002213A1

WO1998002213A1 - Golfball

Info

Publication number: WO1998002213A1
Application number: PCT/BE1997/000069
Authority: WO
Inventors: Tony Geusens
Original assignee: Astral Intertrade Limited
Priority date: 1996-07-16
Filing date: 1997-06-11
Publication date: 1998-01-22
Also published as: EP0914181A1; AU3085197A

Abstract

A golfball comprising a shell of a plastic material, which shell is seamless and encloses a hollow core. The core preferably contains a gas with a pressure above atmospheric pressure. The invention also relates to a process for manufacturing such a golfball by means of injection moulding, whereby gas is injected in the plastic material in the mould cavity, preferably by means of a moveable gas injection needle that can close off. The invention further relates to a device for manufacturing the above described golfball.

Description

Golfball The present invention refers to a golfball with a shell made of a plastics material and a core

Such golfballs are known from the art The known golfball comprises a solid core out of a plastic material around which core a shell or skin is applied The shell is mostly also made of a plastic material, usually a thermoplastic material The core usually has a diameter of 38 mm The shell usually has a thickness of approximately 2 mm

The known golfball however has a number of disadvantages which affect the game in a negative way, in particular the overall distance a ball can be played (playing distance) and the playability of the golfball With the known golfball the manufacturer always was faced to a trade-off between playing distance and playability The playing distance can be defined as the overall distance a ball can be played The playability can be defined as the "feel" the player experiences while hitting the ball with a golfclub and the spin effect he can thereby give to the ball, which spin effect will enable him to let the ball stop on the green or to force the ball into a hook or a fade

In order tυ obtain a golfball with a good playability its skin should be sufficiently soft Thereto, the golfball should have a low Shore-D hardness The Shore-D hardness of the known gofball has a value of approximately 50. On the other hand, also hard covered balls are known which may have Shore-D values up to 70

It is the aim of the present invention to provide a golfball with an improved playability

This is obtained according to the present invention in that the golfball has a hollow core and a seamiess shell

With the shell being seamless it is to be understood that the shell is essentially formed in one part only The shell is not formed out of different shell parts, for instance hemispheres which are joined together for example by means of gluing, friction welding or mechanical fixation

Because the mass of such a golfball is mainly concentrated in the shell, and virtually all the mass has been removed from the center of the golfball, a golfball with a higher angular moment of inertia can be obtained This will result in a lower spin of the golfball, consequently a reduced occurrence of unwanted slices and hooks and thus an improved playability of the golfball The higher angular moment of inertia will also enhance the roll of the ball on the fairway thus improving the playing distance of the golfball and involve a more stable roll on the green Simultaneously the effect of external forces such as wind and rain can be reduced

The presence of a gas with a pressure above atmospheric pressure in the core allows to obtain a golfball with an increased

COR, and thus a golfball with an improved playing distance In that way, the manufacturer can apply a shell material with a lower Shore-D value, so as to improve the playability of the ball, without thereby having to sacrifice to the playing distance In order to obtain a golfball with a good playing distance, its collision-coefficient or its coefficient of restitution (COR) 'e" should have a value as close to 1 as possible The known golfball has a COR between 0 86 and 0 80

According to a second preferred embodiment of the invention the pressure of the gas inside the core is between

1 ,013 x 10⁵ and 81 ,4 x 10⁵ Pascal, preferably between 1 013 x 10⁵ Pascal and 60 x 10⁵ Pascal, more preferably between 1 013 x 10⁵ Pascal and 40 x 10⁵ Pascal, most preferably between 1 013 x 10⁵ and 20 x 10⁵ Pascal

By varying the pressure of the gas in the core, the COR of the golfball can be varied without thereby necessitating to change the nature of the plastic material of the shell Consequently, the playing distance of the golfball can be influenced, without having to sacrifice to the playability of the ball The known golfball has either a good playing distance and is harder and less playable, or it has a shell or skin with a low Shore-D hardness and therefore has good playability characteristics but it will have a limited flight and roll distance. Several combinations in between are possible by changing the basic raw materials of both the core and the cover, but as mentioned before there will always be a trade-off between distance and playability. The manufacturer wanting to produce golfballs with different playing characteristics, will have to use a vast variety of different materials both for the core and for the cover. Because the core of the golfball according to the present invention comprises an inert gas, a golfball can be obtained of which the playability is less temperature dependent than that of the known golfball. Such a golfball tends far less than the known ball, to become stiff at low temperatures, because a substantial part of the ball consists of gas, and because the physical properties of such gases vary only slightly within the . temperature ranges within which the golfballs are used and the freezing point of inert gases is much lower than the temperatures at which golfballs being used.

Several inert gases can successfully be used according to the invention. Examples of suitable inert gases are nitrogen, helium and argon. The use of inert gases permits to avoid chemical reactions between the gas and the plastic material of the shell. In that way the forming of, for example, holes and sunken areas in the shell or irregularities on the internal surface of the shell, i.e. that surface of the shell that is in contact with the core, which may negatively influence the characteristics of the golfball, can be avoided.

Preferably nitrogen is used as the inert gas, because it is cheap, readily available and can be applied without any danger.

Examples of suitable plastic materials for manufactu ing the shell of the golfball are thermosetting resins, thermoplastic materials and elastomers. Preferably, the shell is made of a thermoplastic material, more preferred an ionomeric thermoplast. lonomeric thermoplastics are mostly ionic copolymers of an olefine, for example ethylene, and an unsaturated carboxylic acid, for example methacrylic acid partially neutralized by metal ions, for example zinc, sodium or lithium (SURLYN, Dupont) or ionic copolymers of acrylic acid partially neutralized with zinc or sodium (IOTEK or ESCORE, Exxon) According to the invention, preferably inorganic fillers are added to the plastics material, so as to impart laminar flow to the plastics material, which improves the processing conditions of the plastics material with the gas injection process described hereafter

According to a fifth preferred embodiment of the invention, the shell has a thickness between 2 and 13 mm, preferably between 4 and 11 mm, more preferably between 7 and 11 mm

The golfball of the present invention can be built up of a shell consisting out of one layer In such case a one-piece golfball is obtained If so desired, one or more additional layers of suitable plastic materials can be applied on top of the shell of the golfball described above In such case a two or multilayer golfball is obtained In that case also, the ball as described above serves as a core ball, whereby the thickness of the shell may be reduced to 2 or 3 mm The shell can for example be coated with a coloured paint layer, for example a polyurethane paint The shell can also be coated with additional layers of plastic materials to change the characteristics of the final golfball and provide golfballs with diverging properties

Also, because the shell of the core ball does not show any welding lines, and because the core ball is made out of one piece, a multilayer ball comprising a core ball of the present invention will have an ideal symmetry Other hollow spheres known from the art are mostly made of two hemispheres glued or welded together

In that way a golfball with a considerably higher angular moment of inertia can be obtained, thanks to the fact that the larger part of the mass of the golfball is located in the shell, i e the outer part of the golfball, and virtually no mass is located in the center of the golfball In that way also, a golfball can be obtained which shows reduced spin rates when hit with a golfclub Consequently less kinetic energy coming from the club head will be transformed into rotational energy of the golfball, thus leaving more kinetic energy for the forward translation of the golfball Lower spin rates will reduce unwanted hooks and slices and a lower backspm will give the ball a longer roll after landing on the fairway The higher angular momentum of inertia will also give the ball a more stable roll on the green when putting Those skilled in the art know that many golfball manufacturers have tried to produce golfballs with a higher moment of inertia by changing the size of the ball and by trying to put the mass of the ball to the outer surface of the ball There is no ball on the market at this time that has as much mass located away from the center of the ball and that has a as high moment of inertia as the ball as claimed in the present invention

Because of the fact that the golfball or core ball of the present invention are made out of only one plastic material, the golfball or core ball can easily be recycled in case of off-spec production, without necessitating preliminary separation steps for removing additional layers that have been applied on top of the shell The known golfball, being made out of different plastic materials, has to be divided into its components before it can be recycled In a further embodiment of the invention the core can further contain one single gas or a mixture of gases, a compressed gas in the liquid state or a mixture of such gases, one single fluid or a mixture of fluids, or mixtures thereof Fluids can for example be added to adapt or enhance the total mass of the golfball The present invention also relates to a device for manufacturing a golfball by means of injection moulding Such a device comprises a mould with a mould cavity for moulding the shell, at least one injection channel with at least one injection nozzle for injecting plastic material into the cavity for moulding the shell and means for injecting gas into said plastic material

Because the gas can be directly injected into the plastic material, with the device of the present invention, a golfball can be made with a shell with a uniform surface, which does not show any unwanted holes or plugs and a shell thickness that is uniform over the entire circumference of the golfball.

The injection channel will preferably be designed in such a way that a uniform divergent stream of the plastic material into the cavity is can be obtained. Thereto, for example a venturi-like channel can for instance be installed around the mould cavity.

If more than one injection channel is used these injection channels can be positioned radially with respect to the mould cavity, but they may also be positioned under a predetermined angle with respect to the radius of the cavity. The angle preferably will be 45°.

The means for injecting gas preferably comprise a gas injection needle, with a gas outlet for injecting the gas. The injection needle is provided to be moveable in and out of the mould cavity, so as to move the gas outlet in and out of said cavity over a distance which is at least one eighth, preferably at least one fourth, of the radius of the cavity. Thereby, the gas injection needle is coupled to a controlled gas injection unit.

Such a needle can be moved throughout the entire thickness of the shell.

The outlet of the gas injection needle is preferably so constructed as to provide a spherical gas pocket around the outlet upon injection of gas. The gas which is injected into the plastic material, will blow or force the plastic material to flow against the inner walls of the cavity. In that way, a shell with the shape of a hollow sphere is formed, in one single step only. The outlet of the needle preferably is constructed in such way that the gas flows randomly in all directions, so as to force the plastic material to flow uniformly in all directions, an to obtain a golfball with a shell with a uniform thickness.

The gas injection needle of the present invention can preferably be closed off, in particular during its movement in and out of the cavity. This will prevent the plastic material being plastic during the process to enter into the needle and obstruct it.

To enable a correct dosage of the gas to be injected, all moving parts of the needle preferably are sealed. Instead of using the above described injection needle, according to the invention, the gas can also be injected through the injection nozzle or through a fixed or retractable modulus

With such a device, a golfball or core ball can be produced by means of only one injection moulding device, in a single production step, without having to remove the golfball out of the machine for the injection of the gas and obtaining the desired gas pressure In other words the process allows the hollow golfball or core ball to be made and the gas to be injected simultaneously, in one and the same device The present invention also relates to a method for producing a golfball, whereby a predetermined amount of plastics material is injected into the mould cavity and gas is injected into said plastic material, whereby the injection of gas is continued until the desired over pressure is obtained According to the invention it is also possible to inject in a first step only part of the required amount of plastic material, and inject thereafter a first amount of gas Subsequently, the rest of the plastic material can be injected, for example immediately thereafter, and the gas pressure can be increased to the desired pressure It is possible to introduce more intermediate steps of dosing plastic material and gas, and the necessity of this largely depends upon the melt characteristics of the used plastic material

Preferably, the gas is injected by means of a gas injection needle, whereby after the predetermined gas pressure is obtained, the gas injection needle is retracted from the plastic material and/or the cavity in one or more steps, until the needle is completely withdrawn from the plastic material and/or the cavity

Because of the fact that the plastic material is still sufficiently fluid and plasticized at the moment the needle is pulled backwards the material will flow into the hole that is left by the withdrawn needle This material will fill up the opening thus closing off the shell, so that the desired over pressure can be maintained in the core of the golfball The retraction of the needle, time and speed, are two parameters of the process that are again highly dependent on the used materials Some materials will require a retraction in different steps

The manufacturing of the known golfball, whether it be a wound ball or a ball with a solid core is well known to those skilled in the art. The prefabrication of a solid core is a complicated, laborious and time consuming activity. The cost of manufacturing these cores is relatively high because of the complex technology and operations involved. It is further known by people skilled in the art that the use of such preformed cores has imposed added quality assurance problems and costs. The manufacturing of a wound core may even be more complicated and is believed to be even more expensive because of the many different production steps involved.

The manufacturing of a golfball or core ball of the present invention is typically a one-step production method which does not require a plurality of manipulations and therefore is a cheaper an quicker way to produce said golfballs or core balls

In general, a golfball should show number of desired mechanical properties such as for example compressibility, Shore-D hardness, total distance performance (carry + roll), moment of inertia, coefficient of restitution, rebound, durability and launch characteristics Furthermore a golfball must comply to the rules set by The Royal and Ancient Golf Club of St Andrews and The United States Golf Association All these data are well known to those skilled in the art and are not further described in this application. The golfball of the present invention can meet all the said requirements.

The present invention is further illustrated by means of the attached figures, the description of the figures and the example

Figure 1 shows the external surface of a golfball Figure 2A shows a cross section of a one-piece golfball.

Figure 2B shows a cross section of a multilayer golfball Figure 3 shows, schematically a preferred embodiment of the device for manufacturing the golfball of the present invention

Figure 4 is an overview of a few steps occurring during the injection of plastic material and gas during the manufacturing of a golfball of the present invention

Figure 5 shows a cross section of a needle for use in the device of figure 3

Figure 6A and 6B show a cross section of a mould cavity with respectively 2 and 8 plastic material injection channels

The external surface of the golfball 1 shown in figure 1 is provided with the so called "dimples" 2

The golfball shown in figure 2 comprises a shell 3 of a plastic material, surrounding a hollow core 4 The core 4 contains a gas under a pressure above atmospheric pressure

The golfball shown in figure 2A is a 'one piece ball', whereby the shell 3 is made out of one single layer The golfball shown in figure 2B is a three-piece ball, whereby the shell 3 of the ball shown in figure 2A is surrounded by a second layer 42 out of a first plastic material, which at its turn is enclosed by a third layer 43 out of a third plastic material In that case the hollow ball shown in figure 2A serves as a core ball, around which additional layers can be applied The second and third plastic material may be the same or different Layer 42 and 43 can for example be applied to the core ball of the present invention, by means of injection moulding or compression moulding or by any other way known in the art It is to be understood that the technique for applying those second and third layers, does preferably not make use of the gas injection described

The device shown in figure 3 is an injection moulding device comprising a raw material storage bunker 5 with an outlet 34 for supplying the plastic material for the shell, for example in granular form, to the extrusion screw 6 for heating and at least partially melting the plastic material The device further comprises a mould 8 with two hemispherical mould cavities 24 and 25 The two hemispheres together form the spherical cavity 9 or plastic material projection area for moulding the shell 3 and/or the one-piece golfball The extruder 6 further comprises at least one injection nozzle 7 for injecting the molten plastic material into the mould cavity 9

If so desired, a plurality of injection nozzles 48 can be provided Figure 6 shows a cross section of a possible configuration of the injection nozzles 48 Thereto, a ventuπ-like injection channel 46, which is connected to the outlet of the extrusion screw 6, is mounted in the mould cavity 9 Either one or a plurality of injection channels 49 can be provided to ensure a uniform flow of the molten plastic mateπal in the mould cavity The channels 49 for leading the molten plastic into the cavity 9 are orientated in such a way that upon ejection via the nozzle 48, the plastic material is projected against the wall of the cavity 38 In that way a homogeneous flow of the plastic material in the mould cavity can be obtained, which results in a shell with a homogeneous thickness Also, the formation of the hollow gas core inside when pressurized gas is injected is facilitated

As can be seen from figure 6, The number of plastic material injection channels 49 can be varied The number of injection channels required can be found through experience and will be determined by several characteristics, such as for example the melt flow index of the selected plastic material

The device also comprises a heating equipement for heating the mould halves 24 and 25 and/or the mould cavity 9, for example electrical resistances (not shown in figure 3) In the same way the device comprises means for cooling the mould cavity 9 and mould halves 24 and 25 down to a desired temperature, for example by means of liquid-cooling (not shown in fig 3)

The device further comprises means for injecting gas in the plastic mateπal (see figure 5) These means preferably comprise a gas injection needle 11, which is provided with means 40, 45 for closing the needle According to a preferred embodiment, the needle 11 can be moved in and out of the cavity 9 over a distance which is at least one fourth, preferably one eighth of the radius of the cavity by means of a hydraulic unit 13 The position of the needle 11 in the cavity 9 preferably is adjustable and so is the course the needle will be allowed to travel within the cavity 9

The gas injection needle 11 comprises a housing 40 which surrounds a tube 44 for supplying gas to an outlet 33, for injecting gas into the mould cavity 9 The tube comprises a gas inlet 35, which is connected to the gas dosing control unit 14 In the tube 44 a piston 36 is mounted, which is moveable in longitudinal direction of the tube 44 for opening and closing the injection needle 11 The piston comprises a broadened extremity 45 that has such a shape as to cooperate with said outlet 33, so as to close off said outlet 33 The outer surface of the 45 extremity can for example have the shape of a dimple, so as to form a dimple on the shell 3 after retraction of the needle 11 The needle 1 further comprises a removable plug 39 to enable the replacement of the seal 37 if necessary The closing and opening of this needle 11 is achieved by the simple up and down movement of the piston 36 and the block 41

A driving mechanism 10 allows to move the mould halves 24 and 25 from and to each other for opening and closing the mould

Because gas is injected into the mould cavity, this internal gas pressure replaces the pressure needed to hold the mould halves together so that the clamping forces for clamping the two mould halves together can be recuded, even in case multicavity moulds are used

The gas supply 14, the gas preferably being nitrogen, comprises a gas bottle 15, a pressure reducing valve 16 for reducing the pressure down to the desired level, and pipes 7 for transporting the gas to the gas injection needle 11 The pipes 17 are equipped with valves 18, 27 and 28 to prevent a back flow of the gas to the gas bottle 15 The gas supply 14 further comprises a compressor 19, for increasing the gas pressure to the desired pressure inside the cavity 9 This compressor 19 can be dπven by an electrical engine 20 A control unit 22 is connected to the driving mechanism

10, the extrusion screw 6, the hydraulic mechanism of the gas injection needle 13 and the compressor 20 The whole process is integrated and once all the parameters of the device are set, a high degree of automation can be reached

For the manufacturing of the golfball or core ball according to the invention, a predetermined amount of plastic material is fed to the extrusion screw 6, where the material will be melted Prior to the injection of the molten material into the cavity 9, the gas injection needle 11 is positioned in the cavity At that time the needle 11 will be closed off In the following step a predetermined amount of molten plastic material is injected into the cavity via the injection nozzle(s) 7 If so desired, the mould cavity can be heated The amount of plastic material injected will a o depend on the desired thickness of the shell to be formed In case the plastic mateπal is injected in several steps, the melt characteristics of the plastic material will also come into account

After a predetermined amount of plastic material has been injected into the mould cavity 9, the gas injection needle 11 is opened Thereto, the piston 36 is pulled downwards in the tube 44 of the needle, gas is supplied to the tube via the needle inlet 35 and furhter injected into the plastic material until a predetermined pressure is obtained Again, the gas pressure required will depend on the characteristics of the plastic material If so desired, the steps of injecting molten plastic material and gas can be repeated one or more times, to obtain a shell with the desired thickness The injection of plastic material and gas can either take place simultaneously or non-simultaneaously

For a given amount of plastics material, the residual thickness of the shell 3 (and hence weight of the golfball or core ball) thus obtained has shown to be a function of the gas injection delay time The shorter the delay between the injection of the plastic material and the injection of the gas, the thinner the shell that can be achieved

The amount of plastic material injected and the gas pressure can be controlled by means of close loop controlling systems, that can be build into the mould and the mould cavities

When the predetermined gas pressure is obtained, the gas needle 11 is closed by pulling the piston 36 backward into the tube 44 until the extremity 45 of the piston engages the opening 33 The needle 11 is retracted from the cavity 9, with a predetermined speed and to a predetermined position The instant at which the gas injection needle is retracted, the speed and position of retraction will be found be experience, because every plastic material will have different flow characteristics which will highly determine whether and with which speed the hole left in the shell by the needle upon its retraction, will be filled up by the molten plastic material

Once the needle 11 is completely retracted, i e to such an extent that the tip of the needle is situated at the level of the wall of the mould cavity 9, the thus formed golfball or core ball will stay in the mould, until the plastic material is sufficiently hardened The time needed to obtain such a hardening will o a depend on the melt- and solidification point of the plastic material To reduce the time the golf ball or core ball has to stay in the mould so as to obtain a sufficient hardening, the mould and mould cavity 9 can be cooled

The amount of heating and cooling, in other words the desired temperatures of the mould and cavities throughout the process, can only be found through experience and will depend on the characteristics of the selected materials According to the invention it is also possible to simultaneously inject molten plastic material and gas into the cavity 9 In the same way, it is possible to introduce the needle 11 into the mould cavity 9, after plastic material has been injected

Figure 4a shows how an amount of plastic material 32 is injected into the mould cavity 9, through the injection nozzle 7

During the injection of the plastic material, the gas injection needle 11 is preferably closed Thereafter, as is shown in figure 4b, the gas injection needle 11 is opened and the gas forces the plastic material to flow randomly, in all directions against the inner wall of the mould cavity 9 The injection of the plastic material can then be continued until the desired, predetermined amount of plastic material is injected (figure 4c and 4d) The gas pressure is adjusted to the desired, predetermined level (gas pressure can be increased after the forming of the ball or decreased or decompressed), after which the needle will be closed Figure 4e finally shows the retracted needle and the completed golfball or core ball, which after the desired level of hardening is reached, can be demoulded

It is to be understood that the figures 4a through 4c show the process steps whereby a one-piece golfball is produced It is obvious that core balls, being only smaller spheres can be produced in exactly the same way In further steps, additional layers can be applied on top of the thus obtained core ball

It is also to be understood that, as mentioned several times above, each plastic material having its own physical characteristics such as melt flow index, melt point, solidification point and so forth, and also each golf ball or core ball with its own dimensions such as diameter and shell thickness, will require its own adapted process parameters These parameters can only be found through experience

EXAMPLE.

In this example or experiment the gas-injection technique was used whereby gas was injected through one needle The thus formed ball was a one-piece hollow golfball with a diameter of 42 7 mm and a weight of +/- 45 grams The cavity in which the golfball was formed had a dimple pattern designed by ASTRAL The plastic material for the manufacturing of the shell was an lonomer of DUPONT, type 83716-126- 1 The density of this lonomer had been increased to 1 2 kg/dm³ by addition of Tι02 The material data which are important for the process are Melt Flow index +/- 1 1 , Average processing temperature 193 ° C, Melting point +/- 85° C, solidification point +/- 45° C

In this case a mould cavity with 4 injection channels was used, whereby the injection channels were symmetrically positioned in cross-section at closing area of the two cavities The described process is one whereby the gas injection took place after the plastic material had been injected In this case we did not have different steps of melt and gas injection simultaneously At the beginning of the process the gas needle was brought into the cavity at a position of 19 mm from the top of the cavity. The needle is closed. The mould was closed and the clamping force is build up to 65 tons. The melt injection cycle was set at 15 seconds although it is to be believed that the melt is injected into the cavity in less then 3 seconds. The gas injection cycle was set at 20 seconds whereby the first 5 seconds and the last 5 seconds the needle is closed to prevent the melt to enter the needle. In this case the gas injection cycle was activated 20 seconds after the melt injection cycle had been terminated. The gas pressure was set at 20 bar and no decompression was done after the gas injection cycle. The needle was than pulled in one step completely out of the cavity area allowing the hot melt to fill the hole left after drawing the needle. After all this the curing (solidification) time was starts. In the present case the total cycle was set to 500 seconds. The temperatures used during this process were: barrel hopper area: 40°C (34, fig 3), injection screw area: 185-190°C, (6,fig 3),nozzle:180°C

(7,fig3), mould: 15° C(24,fig 3)

Claims

CLAIMS.

1 A golfball comprising a shell (3) of a plastic material, which shell (3) encloses a core (4), characterised in that said shell (3) is seamless and said core (4) is hollow 2 A gofball as claimed in claim 1 , characterised in that said core (4) contains a gas with a pressure above atmospheric pressure

3 A golfball as claimed in claim 2, characterised in that the pressure of said gas is between 1 013 x 10^s and 81 04 x 10⁵ Pascal, preferably between 1 013 x 10^s and 20 x 10⁵ Pascal

4 A golfball as claimed in claim 2 or 3, characterised in that said gas is an inert gas, preferably nitrogen

5 A golfball as claimed in any one of the claims 1 to 4, characterised in that said plastic material of which said shell (3) is made, is a thermoplastic material, preferably an lonomeπc thermoplastic material

6 A golfball as claimed in any one of claims 1 to

5, characterised in that in that said shell (3) has a thickness between 2 and 13 mm 7 A golfball as claimed in any one of claims 1 to

6, characterised in that at least one further layer (42, 43) is applied on top of said shell (3)

8 Device for manufacturing a golfball by means of injection moulding, which device comprises an injection mould (8) with a mould cavity (9) for moulding said shell (3), which mould comprises at least one injection channel (44) with at least one injection nozzle (7) for injecting plastic material into said mould cavity (9) for moulding said shell (3), characterised in that said device comprises means (11) for injecting gas into said plastic material 9 Device as claimed in claim 8, characterised in that said means for injecting gas (11) comprise at least one injection needle (11) with an outlet (33), which injection needle (11) is provided to be moveable in and out of said cavity (9) so as to move the outlet (33) in and out of said cavity (9) over a distance which is at least one eighth, preferably at least one fourth, of the radius of said cavity (9).

10. Device as claimed in claim 9, characterised in that said at least one gas injection needle (11) has such a shape as to provide a spherical gas pocket around its outlet (33) upon injection of gas via the needle (11).

11. Device as claimed in claim 9 or 10, characterised in that said needle (11) comprises means (40, 45) for closing off the outlet (33) of said needle (11). 12. Device as claimed in any one of claims 9 to

11 , characterised in that said gas injection needle (11) comprises a housing (40) surrounding a tube (44) for supplying gas to said outlet (33), in which tube (44) a piston (36) is moveably mounted, so that said piston (36) is moveable in longitudinal direction of said tube (44) for opening and closing the injection needle (11) and allowing gas to be injected or not, which piston

(36) comprises an extremity (45) that cooperates with said outlet (33) for closing off said outlet (33).

13. Process for manufacturing a golfball with a shell of a plastics material surrounding a core, via injection moulding in a mould with a mould cavity (9), characterised in that a predetermined amount of plastic material is injected into said mould cavity and gas is injected into said plastic material, and injection of gas is continued until the desired over pressure is obtained.

14. Process as claimed in claim 13, characterised in that a first amount of said thermoplastic material is injected, whereafter a first amount of gas is injected into the thermoplastic material, whereafter the injection of thermoplastic material is continued until a predetermined amount of thermoplastic material has been injected, and the gas injection is continued until a predetermined gas pressure is reached. 15. Process as claimed in claim 13 or 14, characterised in that the plastic material is a thermoplastic material, a gas injection needle (11) is brought into the cavity (9), gas is injected into said thermoplastic material by means of said gas injection needle (11), and after the predetermined gas pressure is obtained, the gas injection needle (11) is retracted from said cavity (9) in one or more steps, until said needle (11) is completely withdrawn from said cavity (9).

16. Process as claimed in any one of claims 13 to 15, characterised in that injection of the gas into the plastic material takes place simultaneously with the injection of the thermoplastic material into the mould cavity (9).