CA2116399C - Golf ball and method for making same - Google Patents

Abstract

The present invention relates to a golf ball having an increased shelf life, and a method for making the same. The golf ball has a moisture barrier layer surrounding the core. The moisture barrier layer has a low water vapor transmission rate in order to prevent the permeation of moisture into the core. The invention is particularly useful for two and multi-piece solid golf balls, but also can be applied to one-piece and wound golf balls.

Description

GOLF BALL AND METHOD FOR MAKING SAME
Field of the Invention The present invention relates to golf balls, and more particularly relates. to golf balls having an increased shelf life.
Background of the Invention The distance a golf ball will travel when hit by a golf club is a function of many factors, including angle of trajectory, clubhead speed and coefficient of restitution. The coefficient of restitution ("COR") is a measurement familiar to those skilled in the golf ball art.
One way to measure the COR is to propel a ball at a given speed against a hard massive surface, and measure its incoming and outgoing velocity. The COR is the ratio of the outgoing velocity t.o the incoming velocity and is expressed as a decimal bfaween zero and one.
There is no United States Golf Association limit on the COR of a golf ball, but the initial velocity of the golf ball cannot exceed :250+-5 feet/second. As a result, the industry goal for initial velocity is 255 feet/second, and the industry strives to maximize the COR without violating this limit.
In a one-piece: solid golf ball, the COR will depend on a variety of characteristics of the ball, including its composition and hardness. For a given composition, COR will generally increase as hardness is increased. In a two-piece solid golf ball, which includes a core and a cover, one of the purposes of the cover is to produce a gain in COR over that of the core. When the contribution of the core to high COR is substantial, a lesser contribution is required from the cover. Similarly, when the cover contributes substantially to high COR of the ball, a lesser contribution is needed from the core.
Conventional one-piece golf balls and cores for two-piece golf balls camprise an elastomer, such as a high cis content polybutadiene, which is combined with a zinc or other metal salt of an a,8, ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, crotonic acid, or cinnam:ic acid, etc. To achieve higher 21 ~~39g COR, small amounts of a metal oxide such as zinc oxide can be added. In addition, larger amounts of zinc oxide than are needed to achieve the desired coefficient can be included in order to increase the core weight so that the finished ball more closely approaches the U.S.G.A. upper weight limit of 1.620 ounces. Other materials also can be used in the core compos:itj.on including compatible rubbers or ionomers, and low molecular weight fatty acids such as stearic acid. Free radical initiator catalysts such as peroxides are added to the core composition so that on application of heat and pressure, a complex curing or cross-linking reaction takes place. Golf ball core compositions are discussed in further detail in U.S. Patent No. 5,018,740.
The covers of aolid two-piece golf balls are typically made from a material which will contribute to the durability of the ball. hurthermore, as mentioned above, the use of a cover enables a tcigher COR to be achieved for golf balls having a specific hardness. In addition, inclusion of a cover will i:acilitate processing of the golf balls.
The covers o1: two-piece s~y~u ~V11 l.ic.~ii.r u'-"
generally formed from durable ionomeric resins such as those manufactured by E. I. DuPont de Nemours & Company under the trademark "Sur=Lynn" , and by Exxon Corporation under the trademarks "Esc:orR" and "IotekR" . Ionomeric resins are generally ionic copolymers of an olefin such as ethylene and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, or malefic acid. Metal ions, such as sodium or zinc, are used to neutralize some portion of the acidic groups in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e.,, durability, etc. for golf ball cover construction.

21~.639~
~ . 3 Ionomeric golf balls covers frequently captain a fluorescent material and/or. a dye or pigment which imparts to the outer surface of the ball the desired color characteristics. Trademarks or other indicia are stamped on the outer surface of the ball cover, which is then coated with one or more thin layers of a clear coat material. The clear coat gives the ball a glossy finish and protects the indicia stamped on the cover. Clear coat materials which are well known in the art, typically include epoxies and urethanes.
Summary of the Invention It has now been :Found that when solid and wound golf balls are subjected to prolonged storage under ambient conditions, the CORs of the golf balls tend to decrease over time. As the CORs of i:he balls decrease, their weight increases. The reduction in COR and the weight gain is believed to be due to the absorption of moisture within the balls. It has been found that moisture is not only absorbed and retained by golf balls soaked in water, but also by golf balls which are stored under conditions in which moisture is in the air, including indoor and outdoor conditions of "average" humidity, i.e. 25-35% relative humidity (RIi), as well as conditions of high humidity, i.e.
65-75% RH, or more. The degree of COR loss within a specified period of time has been found to be higher for golf balls which are stored in a highly humid environment than for golf balls which are stored in an environment of lower humidity. COR loss :is greater for golf balls which are soaked in warm water than for golf balls which are soaked in cooler water. The present invention overcomes the COR loss problem described above by surrounding the core of a golf ball with a moisture barrier which has a lower water vapor transmission rate that the cover of the ball. The moisture barrier most preferably is positioned between the cover and the core, but also can be positioned between the cover and clear coat. Although the barrier theoretically can be positioned outside the clear coat in ~~10~~9 ~ . 4 certain cases, this is less desirable since it may subject the layer to damage during use. Preferably, the moisture barrier is a layer having a thickness on the order of between molecular thickness and 20 mils and is used in conjunction with a cover which has a thickness of at least about 25-30 mils, and preferably is on the order of 50-100 mils.
Another prefer:rec3 form of the invention is a golf ball core for use in making a solid or wound golf ball having a cover. The core includes an outer moisture barrier which has an average thickness of no more than about 20 mils and exhibits a lower water vapor transmission rate than the cover.
In another preferred form, the invention is a golf ball comprising a. ventral core, a cover, and a moisture barrier surrounding the core, the moisture barrier being effective to reduce the loss in coefficient of restitution of the golf ball after storage for six weeks at about 100°F and about 70% relative humidity by at least 5%, preferably by at least 10-:15%.
In yet another preferred form, the invention is directed to a golf ball core for use in making a one, two or multi-piece golf ball. The core has an interior core portion having an outer surface and a moisture barrier in intimate engagement with the outer surface having an average thickness of no more than about 20 mils and a water vapor transmission rate of about 0 . 2 g ~ mi 1 / 100 inl ~ day at 90% RH, 100°F, ASTM D-96 or Less. More preferably, the moisture barrier has an average thickness of about 10 mils or less and a water vapor transmission rate of about 0.05 g~mil/100 inz~day at 90% ~tH,, 100°F, ASTM D-96 or less. Most preferably, the water vapor transmission rate of the barrier is 0.03 g~mil/100 i.n2~day at 90% RH, 100°F, ASTM D-96 or less.
The moisture barrier layer according to the invention preferably is a continuous layer surrounding the entire core. The layer can be formed of any moisture 211fi3~~
barrier material which, at: the thickness used, does not significantly affect the favorable playability characteristics of the golf ball, and provides for a reduction in the rate of entry of water and/or water vapor 5 into the golf ball core, preferably to a degree sufficient to reduce COR loss of the :ball by at least about 5% for a golf ball stored at 100°F and about 70% RH. In one preferred form of the invention, the moisture barrier layer is formed from a different material than the core, and comprises or consists of at least one member of the group consisting of vinylidene chloride, which preferably is in the form of polyvinylidene: chloride, vermiculite, i.e. a mica-like material which is a hydrated-magnesium-aluminum silicate formed by the geochemical alteration of biotite.
Other types of barrier materials which form separate layers also can be used. In anotraer preferred form, the moisture barrier layer is formed in situ as the reaction product of a barrier-forming material and the outer surface of the core. For example, fluorination of the outer surface of the core has been found to form a useful barrier layer on the outer surface to reduce c.OR loss over time. It is expected that other gaseous barrier-forming substances known to those skilled in t:he art also can be reacted with the outer surface of the core material to act as a barrier layer or film.
When applied between the core and cover of a two-piece golf ball, the barrier layer has a lower water vapor transmission rate than the cover. Preferably, this rate is very low, i.e. less than about 0.2 g~mil/100 in2~day at 90%
RH, 100°F, ASTM D-96, and :more preferably less than about 0.05 g~mil/100 in2~day at 90% RH, 100°F, ASTM D-96. The moisture barrier layer is particularly well suited for use with a two-piece solid golf ball having a polybutadiene composition core and an :ionomer cover.
Yet another prefE:rred form of the invention is a method for reducing the loss in coefficient of restitution of a golf ball upon exposure to moisture. The method ~~~.~J~~

includes the provision for a moisture barrier layer_ around the golf ball core. In a two-piece or multi-piece golf ball, the moisture barrier layer has a lower permeability of water than the cover. In a one-piece golf ball or another preferred two-;piece or multi-piece ball, the moisture barrier layer has a thickness of no more than about 20 mils and preferably has a water vapor transmission rate of no more than about 0.2-0.3 g~mil/100 in2~day at 90%
RH, 100°F, ASTM D-96. Along these same lines, the invention includes a method for making a galf ball having a core, the method comprising the step of forming a moisture barrier around t:he core, the moisture barrier being effective to reduce the loss in coefficient of restitution of the golf ball after storage for six weeks at about 100°F and about 70% relative humidity by at least 5%.
An object of the present invention is to provide a golf ball having a longa_r shelf life than conventional golf balls.
Another object of ttxe invention is to provide a one, two, or multi-piece golf ball in which the loss in COR
due to moisture is substantially reduced.
Yet another ob:jeca of the invention is to provide a golf ball which substani~ially retains its original COR
upon exposure to a wide range of temperatures and humidity levels.
Yet another object of the invention is to provide a method of making a golf ball having the advantages described above.
Other objects would be in part obvious arid in part pointed out more in detail hereinafter.
The invention accordingly comprises the article possessing the features, properties arid the relation of elements exemplified in the following detailed disclosure, and the several steps and the relation of one or more of such steps with respect to each of the others as described below. _. .

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Detailed Description of the Invention The present invention recognizes the problem that conventional golf balls which are stored for an extended period of time can undergn a reduction in COR duE: to the gradual permeation of liquid water and/or water vapor into the core. The invention overcomes this newly-recognized problem by providing a moisture barrier around the golf ball core for substantially preventing, or at least reducing, the entry of water vapor and liquid water into the core.
The invention is particularly applicable to a two-piece solid golf ball sucr~ as a ball having an overall diameter of 1.680 inchea or more which includes a cover which is about 30-110 mils thick. In two-piece solid golf balls, the moisture barrier preferably i.s a moisture-impermeable membrane which is positioned between the central core and the cover. 4ahen placed at this location, it is likely that minimal design and manufacturing changes will be required for manufacturing the golf ball, because the moisture barrier is protected by a durable ionomeric or balata cover. Furthermo:re,, because the moisture barrier is sandwiched tightly between the core and the cover, the strength of the physical or chemical bonds holding the moisture barrier in place: need not be as strong as the bonding which would be rs:quired if the moisture barrier were positioned on the outer surface of the golf ball. It is noted, however, that it is also possible to :Locate a non-brittle moisture ba:rr:ier of a two-piece ball between the cover and primer or betweE:n the primer and clear coat, as long as the moisture :barnier is sufficiently durable that the ball has acceptable playability and wear characteristics. In a one--piece ball, the moisture barrier generally is located on the outer surface of the core.
The moisture b~ar~cier should be sufficiently thick to result in a reduction in the permeability oi' liquid water and water vapor into the core of a golf ball, while being thin enough to avoid having an adverse impact on the 2.16339 playability of the ball.. As a practical matter, it is desirable to select a ba:rr:Ler material which has very low water permeability in order that only a thin layer of the barrier is required. As used herein, the term "water permeability" refers to t:he: ab~.lity of liquid water and/or water vapor to permeate through a layer such as a coating on a golf ball into the c~ol.f ball core.
Generally, a po:lyvinylidene chloride moisture barrier positioned between thE: core and cover of a two piece ball and which hays a thickness of L/2 - :?0 mils (depending on the effectiveness of the barrier) will reduce COR loss. Preferably, the polyvinylidene chloride moisture barrier is less than half tlhe thickness of the coven. Some non-limiting examples of commercially available polyvinylidene chloride moisture barriers (Dow Chemical Co.) which can be used in accordance with the invention include:
Barrier ~»~ater vapor transmission gate (g~mil/100 in2~day at 2 0 - _.._ -.- . 9 0 % RH , _ 10 0 ~ F~ A S T:M D-9 61 Saran R Resin f-279 0.02 Saran R Resin f-239 0.03 SaranR MA 119 0.05 SaranR 525 0.13 Saran Wraps Films 0.20 It is expected that Saran x~arr~.ers with a thickness of 1/2 - 20 mils placed directly over the core will not otherwise substantially affect i~he: playability of the ball.
Typically the barrier laye~c has a thickness of 5-15 mils.
Also, it has been found that the polyvinylidene chloride layer can be covered by a film of metallized polyester, such as aluminized polyester, to form a moisture barrier.
If the barrier is to be placed outside the ccover, it. should be sufficiently thin to av°oid interfering with the effectiveness of the dimplea.
Vermiculite barriers, preferably of about 1-15 mils, more preferably f>-1.0 rails, also will reduce the initial rate of COR loss when placed between the core and cover.

e~ e~

While the thic~:neas <~f a moisture barrier farmed in situ, such as by fluorinating a golf ball core, cannot be conveniently measured, it is expected that. such harriers may be of molecular layer thickness and certainly are thinner than most, if not: a.11, of the film-forming barrier layers applied as coatings, such as polyvinylidene chloride and vermiculite. It is expected that fluorination of the outer surface of a golf ball cover alsa will form a moisture barrier layer.
The moisture barrier of the invent i:on also can be adapted for use with conventional one-piece golf balls, such as those having an overall diameter of 1.680 inches or more. As mentioned above, 'this type of moisture barrier is located between the core and the primer c~r between the primer and clear-coat.
The moisture barrier layer of thc~ invention is useful to protect cores c:or~tairving polybutadiene and metal salts of unsaturated ca:rboxy~s_ic acids such as acrylic, methacrylic, crotonic and cimamic acids, etc. It is expected that the moisture barrier also c:an be used in conjunction with cores made of other materials, including two-piece cores such as those described in U.S. Patient No.
5,072,944, and in conjunction °,aith wound cores.
The cover material of a two-piece golf ball generally has a lower water vapor transmis:~ion rate than the core material. Ionomers which are copolymers of ethylene and a metal salt. of an unsaturated carboxylic acid have been preferred for u.se as golf ball cover material due to their high durability, contribution to good ~~OR and compressibility. These ionomers have been found by the inventors to be better barriers to water vapor transmission than many other thermoplastics. Such covers have, in the past, been about 40-100 mils thick. While for two piece balls, ionomeric covers are preferred for use in conjunction with the moisture barriers of the invention, the invention also encomp~~sses golf balls having covers.
made of other materials, several non-limiting examples of ~116~~9 which include nylons,. thermoplastic: urethanes, polyurethane, acrylic acid, methacrylic acid, thermoplastic rubber polymers consisting of k~lock copolymers in which the elastomeric midblock of t'.he molecular is an unsaturated rubber or a saturated ol_ef in rubber, a . g . KratonR rubbers (Shell Chemical Co.), polyethylene, and synthE~tic or natural wlcanized rubber such as balata.
In order- to be affective, the moisture barrier should have a lower water vapor transmission rate than the other layers which are betwE=.en the core and the outer .surface of the ba~_1, i.e.. the cover, primer' (if included) and clear coat. As used herein, "water vapor transmission rate" refers to the rate as expressed in units of g~mil/100 in2~day at 90% RH, 100"F, A~bTM D-96. The water vapor transmission rate of th.e moiFsture barrier preferably is significantly les:~ than 1. 5 c~ ~ mi 1 / 100 in2 ~ clay at 90% RH, 100°F, ASTM D-96.
The effectiveness c~f a moisturN barrier will depend upon the composition of the barrier ,and its thickness. From a practi~~al standpoint, it is preferred that the moisture barriE:r is ~:ffective to reduce the loss in coefficient of the golf bal L after storage for six weeks at about 100°F and about '70% RH by at least 5%, <3nd more preferably by at least 10%-15%, as compared to the loss in coefficient of restitution of a golf ball which does not include the moisture barrier, has the same type of core and cover (if included), a:nd is stored under substantially identical conditions. It: i~. noted that barriers which produce a reduction in CnR doss of 0.5 t:o 5% are also within the scope of this invE;ntion. If a thick :moisture barrier is placed over i~hs: core or cover, it is necessary to reduce the cower th~.ck:nes:~ by an amount equal. to the thickness of the barrier in order that the golf ball which has improved moisture resistance is identical in size to a corresponding ba~_1 which does not include a moisture barrier. Although the moisture barrier prE~ferably is not an ionomer, it is within the scope of the invention to form spALn~ioa~os ~1 ~~~19 a cover having several layc;rs of diffe~~ent ionomeric materials, one of which has a considerably lower water vapor transmission rated thaxd the others and therefore serves as a moisture barrier.
It has been found .hat a variety of different types of materials will sere as moisture barriers to reduce COR loss when usE:d to form a layer surrounding the core of a two-piece ball. These matE:rials include polyvinylidene chloride, vermiculite and the reaction product of the thermoplastic core material, e.g.
polybutadiene andjor other core components, with i=luorine gas. It is expected that any film-forming materia7l having a water vapor transmis:cion rate which is less than the water vapor transmission rate of the cover material can be used as a moisture barrier for two-piece solid balls.
Materials which impregnate thfr outer layer of the core to form a barrier layer which has a Lowers water_ vapor transmission rate than the cover also may be used according to the present invention. Tde impregnating agent would fill in the pores in the core :surface. As mE~ntioned above, barrier materials having waiter vapor trunsm~.ssion hates as low as 0.02 g~m11,~100 in2~~3ay at 90~ RH, 100°F, A~cTM D-96 are available, such as S~~ran Resin F-278 (Dow Chemical Co.).
The effect upon the COR and weight of finished golf balls due to prolonged storage under ambient (indoor) conditions (70-80°F) and due tc~ prolonged storage in a high humidity oven (100°F, about: 70'~ RH) has been determined for solid two-piece and wound three-piece golf balls sold by various suppliers. The golf balls which were tested had ionomeric or balat.a covers. P~Ieasurements of COR relative to initial COR and weight gain relative to initial weight were made monthly for five months, except that during one month no measurements of we:ight~ gain and COR were taken for the balls in the high humidity oven. Each sample contained about six golf balls, ar,~d the results were averaged. The results are provided on Table; 1A and l.B. The values of 1"
weight gain arnd Cc~-R loss shown on Table. 1A and 1B, as well as on the remaining tables, arE~ cumulative. In this application, oven humidity o~= "about 70~" constitutes a humidity which is predomin ~tely at 69--71% beat many experience temparary fl.uctuat:ions between about 67% and 72%.
As show: on T<~bl.es LA and 1B~ thf~ golf :balls in the high humidity oven lzad a greater weighty gain .and more loss in COR than the same type of golf bal_1 stored under ambient condition:. A1.1 of the golf bal.l.s dept in the high humidity oven exhibited at lc ast some COR loss. Most of the balls in the high humidi~.y oven experienced ,~ weight gain of at lceast O.lg after 5 months. Mc;st of 'the golf balls stored under ambient conditions for 5 months 1.5 experienced a mea:~urable: COR loss. While ttse weight change for most of the balls stored under ambient conditions was too small tcp be detectE:d, it is belie~~ed that minor increases in we ic~~t probably occurred .
Changes in the COR and weight; of golf balls due to prolonged expeisure too various climatic conditions was determined far two-piece solid golf ball:: and uncovered cores for two-piece solid g~~lf balls. Measurements of weight were taker, in m~_ll.igrs~ms :in orc:~er ro detect small weight changes which werE: not detectable in the 2~ experimental work shown on Tale 1A and 1B. The two-piece balls which were used in the tests were unfinished, i.e., did not have a pr:~mer or clear coat an t:he cuter surface of the cover. Ball types X and Y had the: same type of polybutadiene core and different cover m~~terial;~. Ball type Z constituted an uncovered core having the same size and compositi on a s the cores of ball t:ypec X and Y . The cover materials compris~ad blends of commercially available ionomers. The changes i.n COR and weight: were measured every two weeks during 2~ 16-wEeek period of exposure to each climatic condition. Ths: resuyts showing chzrnges in COR and weight are pi-ovicted on Table 2. Each sample contai.ned_ 6 golf balls, and the results were averacled.
spAZ.n/ io2 /Us ~~1~3~~
l..' As shown on TahlE:2, the golf balls which had the greatest reduction in C:OR were in l:he high are those that humidity oven at LUOF and and those soaked ~~t least 70%
RH, in water at ?5F and iC~Ol?.'Phe balls suojected to the latter types of conditions also had the greatest. weight gain. It is believed that t?'~.e weight gain resulted from moisture absorption. A;s weight gain increased, COR

decreased.

A comparison of ~covEr~ed golf ball: stored in the high humidity oven and those maintained at room temperature conditions shows that the ~20R loss of coverf~d balls in the high humidity oven after 2 we~;ks was generally comparable to the COR loss c~f bal7.s stored at room temperat.urE~ for about 16 weeks. The COR loss of uncovered cores stored in the high humidity coven for 2 wf~eks was generally comparable to the COR loss caf uncovered cores stored under ambient conditions for 12-14 weeks.
The results an Tablc: 2 also show that uncovered cores Z had a higher loss in ':OR and a larder weight gain over time than covered gol:E balls X and Y s~.ibjected to the same conditions. Thud,~ t:he cover material has a lower permeability of ~~aater and grater vapor than the core material. Table 2 also show: that one-piece golf' balls, i.e. galf balls wt-~ich dc. not leave an ionomer coven, would experience an even greate~c CC~R loss over rime than two-piece balls due to moisture ab~:orption and rE~tention within the core.
The effect on ~COIZ loss over time clue to t:he type of cover material which is used for a two-piece so7.id golf ball was determinE~d for unfinished golf balls which each had the same type of polybutadiene core composition and were covered with a variety of different commE:rcially available cover comp~~s:itions and blE~nds thereof .
Additional cover types wlnic:h were used i_nclu.de methacrylic acid, acrylic acid and po7Lyet~ylene~ Each of the covers had a thickness o3' S5 m:il:~. Measurements of weight gain 14 ~ ~ ~ ~ 3 and COR loss were determined after 2, 5, 9, 23 and 42 days.
The results are shown on Table 3.
As shown on Table 3, the overall COR loss after 42 days for the ionomer covers hanged from a loss of 0.004 for ionomer 9 to a loss of 0.024 for ionomer 10. With the exception of the polyethylene covered balls, the golf balls balls had a generally consistent correlation between COR
loss and weight gain in that a larger weight gain corresponded to a larger COR loss, while a smaller weight gain corresponded to a smaller COR loss.
Having generally described the invention, the following examples are included for purposes of illustration so that the invention may be more readily understood, and are in no way intended to limit the scope of the invention unless otherwise specifically indicated.
The cores primarily consist of polybutadiene compositions used in commercially available golf balls. Examples of suitable compositions are discussed in U.S. Patent No.
4,726,590 and U.S. Patent No. 5,018,740. The covers are formed from commercially available ionomers. Examples of suitable cover compositions are discussed in U.S. Patent Nos.
5,120,791 and 4,884,814.
EXAMPLE 1 - Golf balls having cares coated with polyvinyliaene chloride A first group of polybutadiene golf ball cores, designated as sample 4A, were dipped for about 5 seconds in a solution containing 20 parts polyvinylidene chloride (Saran Resin F-239, Dow Chemical Company), 65 parts tetrahydrofuran (THF) and 35 parts toluene. A second 3~J sample of cores designated as s<~mple 4B were dipped for 5 seconds in a solution containing 20 parts polyvinylidene chloride (Saran Resin F-279, Dow Chemical Co.), 65 parts THF and 35 parts toluene. A third group of golf ball cores, designated as sample 4C, were dipped in the same 3.5 solution as sample 4B, and subsequently, after drying, were 211fi33~
wrapped with an aluminized mylar film. The film was stretched to be relatively wrinkle-free and was applied in a thickness such that the total thickness of the polyvinylidene chloride and mylar was about 10 mils. The 5 balls were finished with an epoxy-polyurethane clear coat.
The initial average COR and averall film thickness was determined for each of samples 4A-4C, and the average COR
was determined for a control sample 4X of 3 uncoated golf ball cores. The cores of samples 4A, 4B, 4C and 4X all had 10 the same composition. The cores of samples 4A-C and 4X
were each covered with the same blend of commercially available ionomeric cover materials such that all of the balls had the same outer diameter. All the golf balls and cores were placed in a high humidity oven at 100°F and 70%
15 RH. Measurements of COR were taken after 2 weeks, 6 weeks, and 10 weeks. The COR values, cumulative COR loss after 2, 6 and 10 weeks, and initial film thicknesses are shown on Table 4.
As shown on Table 4, each of the samples of balls having a moisture barrier experienced a smaller overall COR
loss than the balls in control sample 4X. After 6 weeks, the balls in sample 4X, made from uncoated cores, experienced a COR loss of (19/807)~100 = 2.35%. The balls of samples 4A-4C experienced a COR loss of (14/800)~100 =
1.75% after six weeks. Thus, the inclusion of a moisture barrier resulted in a (2.35 - 1.75)~100/2.35 - 25.5%
smaller COR loss after six weeks than the COR loss of golf balls which did not include a moisture barrier. After 10 weeks, the balls of samples 4A, 4B and 4C had undergone 22.0%, 17.6% and 8.1% smaller COR losses, respectively, than the balls of sample 4X.
Film thicknesses ranging from 7 mils to 10 mils all were suitable thicknesses for reducing the amount of COR loss. It is expected, based upon these results, that thinner and thicker layers of polyvinylidene chloride also can be used as moisture barriers.

An additional sample of cores similar to those of sample 4C were further coated with a second coating of polyvinylidene chloride (Saran Resin F-279, Dow Chemical Company) over the layer of metallized polyester. COR
measurements, as well as initial film thicknesses were determined. This sample did not result in an improvement in COR loss as compared to the control, and it is believed that the results may have been due to procedural difficulties in applying the barrier layers.
EXAMPLE 2 - Golt balls having fluorinated cores Golf ball cores made of a polybutadiene composition were fluorinated in a 8-10% fluorine-nitrogen atmosphere for 30 minutes at 25°C. Fluorination was conducted by FluoroTec GmbH (Germany) using a proprietary process. Eleven of the fluorinated cores were covered with a cover stock formed from commercially available ionomers containing zinc and sodium and were designated as sample 5A. Twelve cores were covered with the same cover stock at the same thickness for use as a control, and were designated as sample 5X (cove:r control). Three cores remained uncovered and were designated sample 5Y (core control). The balls remained unfinished.
The initial COR of each golf ball and uncovered core was determined. The initial weight of the balls in each sample was determined by weighing three balls in each sample and determining an average for each sample.
Measurements of weight gain were taken after 2, 5, 9, 23 and 53 days. COR measurements were made after 5, 9, 23 and 53 days. Average values for weight gain and COR loss for each sample are shown on Table 5.
As indicated on Table 5, the golf balls having fluorinated cores had a smaller weight gain and a smaller COR loss after 23 days than the golf balls having untreated cores. After 7 1/2 weeks, the balls of sample 5A had a (20/804)~100 = 2.49% COR loss. The balls of sample 5X
experienced a COR loss of 3.07%. The cores of sample 5Y

211fi339 had a 4.06% COR loss. Thus, the inclusion of the moisture barrier reduced COR loss of covered golf balls after 7 1/2 weeks by (3.07 - 2.49)~100/3.07 = 18.9%.
As was expected, the uncovered golf ball cores of sample 5Y had a higher weight gain and greater COR loss than the covered golf balls of sample 5X. Although the control cores of sample 5Y were from a different lot than the cores of the covered golf balls, this is not believed to have substantially affected the experimental results.
EBAMPLE 3 - Golf balls having cores coated with vermiculite Nine polybutadiene golf ball cores were designated as sample 6A and were dipped in a solution of epoxy, which was used as an adhesive for the vermiculite.
Nine cores of the same composition, designated as sample 6B, were dipped in the same epoxy solution as those of sample 6A and were subsequently dipped three times in a 100% inorganic dispersion of vermiculite in water sold as MicroliteR 903 (W. R. Grace & Co., Cambridge, MA). This solution contained 7.5% solids and <28% oversized particles, and had a Ph of 7-9 and a viscosity of 200-1000 centipoise. Eleven golf ball cores of the same composition, designated as sample 6C, were dipped three times in the vermiculite solution described above, and, after drying, were dipped once in the epoxy solution described above.
Seven golf ball cores. were designated as sample 6D and were dipped three times in the above-described vermiculite solution. Twelve golf ball cores were designated as sample 6X (control.) and were not coated. All of the golf balls were covered with the same ionomer cover stock, had the same outer diameter, and were finished with an epoxy-polyurethane clear coat.
The initial COR of each of the golf balls samples 6A-6D as well as the golf balls designated as control sample 6X was determined.
spAr.n/ io2 /os 1 f3 .
The golf balls were placed in the high humidity' oven at 100°F, 70% RH for 12 weeks. Measurements of COR
loss were taken after 2 weeks, 8 weeks and 12 weeks.
Results are shown in Table 6.
As shown in Table 6, the COR loss for the golf balls having a vermiculite-coated core initially was slower than the loss for the control sample. After 10 weeks, the COR of control sample 6X had decreased by 3.45%, while the COR of sample 6H, 6C and 6D had decreased by 2.90%, 3.39%
and 3.14%.
It is noted that while the golf ball cores of samples 6A and 6X were from a different lot than those of samples 6B-6D, this difference is not believed to have affected the experimental results.
As shown by the above examples, a variety of different types of materials can be used as a moisture barrier to reduce the COR loss of a golf ball over time resulting from exposure to moisture.
As will be apparent to persons skilled in the art, various modifications and adaptations of_the product and method above described will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.

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Claims (20)

1. A non-wound golf ball, comprising a central core, a cover having a thickness of at least about 30 mils and comprising a member selected from the group consisting of ionomers, acrylic acid, methacrylic acid and polyethylene surrounding the core, and a moisture barrier surrounding the core and located between the cover and the core, the moisture barrier having a lower water vapor transmission rate than the cover and an average thickness substantially less than the cover thickness, the moisture barrier having a water vapor transmission rate which is sufficiently low to reduce the loss of coefficient of restitution of the golf ball by at least 5% if the ball is stored at 100° F. and 70% relative humidity for six weeks as compared to the loss in coefficient of restitution of a golf ball which does not include the moisture barrier, has the same type of core and cover, and is stored under substantially identical conditions.

2. A golf ball according to claim 1, wherein the moisture barrier comprises a continuous layer.

3. A golf ball according to claim 2, wherein the continuous layer has an average thickness of 20 mils or less.

4. A golf ball according to claim 3, wherein the continuous layer has an average thickness of 10 mils or less.

5. A golf ball according to claim 1, wherein the moisture barrier comprises the reaction product of a barrier-forming material and the core.

6. A golf ball according to claim 5, wherein the barrier-forming material comprises fluorine.

7. A golf ball according to claim 1, wherein the moisture barrier has a water vapor transmission rate of less than about 0.2 g .cndot. mil/100 in2 .cndot. day at 90% RH, 100° F., ASTM D-96.

8. A golf ball according to claim 1, wherein the moisture barrier comprises vinylidene chloride.

9. A golf ball according to claim 1, wherein the moisture barrier comprises vermiculite.

10. A golf ball according to claim 1, wherein the cover comprises ionomer.

11. A golf ball according to claim 1, wherein the core is a solid core.

12. A non-wound golf ball comprising a central core, a cover comprising a member selected from the group consisting of ionomers, acrylic acid, methacrylic acid and polyethylene, and a moisture barrier surrounding the core and located between the cover and the core, the moisture barrier having a thickness of less than 20 mils and a water vapor transmission rate of less than 1.5 g .cndot. mil/l00 ins day at 90% RH, 100° F., ASTM D-96.

13. A golf ball according to claim 12, wherein the moisture barrier comprises the reaction product of a barrier-forming material and the core.

14. A golf ball according to claim 13, wherein the barrier forming material comprises fluorine.

15. A golf ball according to claim 12, wherein the moisture barrier comprises vermiculite.

16. A golf ball according to claim 12, wherein the cover comprises ionomer.

17. A golf ball according to claim 12, wherein the core is a solid core.

18. A method for reducing the loss in coefficient of restitution of a two-piece, non-wound golf ball upon exposure to moisture, the golf ball having a core and a cover with a thickness of at least 30 mils which comprises a member of the group consisting of ionomers, acrylic acid, methacrylic acid and polyethylene, the method comprising the steps of providing a golf ball core and forming a moisture barrier around the core for reducing the rate of entry of water into the core, the moisture barrier being located between the cover and the core having a water vapor transmission rate of less than 1.5 g .cndot. mil/100 in2 .cndot. day at 90%
RH, 100° F. ASTM D-96.

19. A method according to claim 18, wherein the cover comprises ionomer.

20. A method according to claim 18, wherein the core is a solid core.