US2743931A - Practice or play ball and method of making same - Google Patents

Description

y 1, 1956 R. w. POOLEY ET AL 2,743,931

PRACTICE 0R PLAY BALL AND METHOD OF MAKING SAME Filed Feb. 26, 1953 INVENTORS R. M P0015) A. C. KOf/lP/V BY .A T T ORNEY United States Patent PRACTICE oR PLAY BALL AND METHOD or MAKING SAME Application February 26, 1953, Serial No. 339,072

6 Claims. emu-199 v This invention relates to la practice or play ball and method'of making the same. 'More particularly it relates to apractice or play ball which represents an improvement in the type of ball shown in Barton U. S. Patent 2,484,397. In particular, the ball of our invention exhibits greatly improved'dime'nsional stability, sharper defi nition and retention. of a molded surface pattern such as a dimple design, and closer simulation of regulation balls, e. g., golf balls or baseballs, than is possible by prior art practice.

The practice golf ball which is the subject matter of the Barton patent is a spherical mass of closed-cell expanded plasticized polyvinyl chloride closely simulating a regulation golf ballin size and appearance but characterized by its lightweight, its deadness, its short flight when struck with a golf club and its ability to substantially duplicate the flight characteristics ofa regular golf ball except on a muchsmaller scale. The specific exemplifications of practice golf b'a'lls given in the Barton patent utilize a high-boiling organicliquid plasticizer which is capable of dissolving powdered polyvinyl chloride upon heating to form a gel"which upon cooling retain the closed-cell structure which is an essential characteristic of the Barton ball.

In the accompanying drawings:

Fig. l.portrays a pre form .ofraw stock used for making the core of the ball;

Fig. 2'shows the beginning of the miniature molding operation; v

Fig. 3 shows the end of th'elminiature 'molding operation;

Fig. 4 portrays the end ofthe 'expanding step applied to the miniature core;

Fig. 5 shows the expanded .core with the fpaint which is to form the shell applied thereto;

Fig. 6 shows the end of the idirn'pling operation used in making a practice glolfba'll, and

Fig. 7 shows, on a reduced scale, a practice or play baseball made in accordance with our invention.

The present invention'is based upon our discovery that a practice or play ball which has exceptionally improved size dimensional stability and which is far superior, from the standpoints of appearance and simulation of a regulation ball such as a regulation golf ball or a regulation baseball, to an expanded closed-cell ball consisting of polyvinyl chloride plas'ticized with an organic liquid plasticizer and containing no vulcanizablefelastomer is obtained by forming the ball with aninner core of closedcell expanded polyvinyl chloride or equivalent vinyl resin plasticized with both a high-boiling organic liquid plasticizer and a vulcanizable rubberymateria1 which before vulcanization is compatible withand capable of plasticizing the vinyl resin, this rubbery copo'lymer being vulcanized at an appropriate'tim'e during the formation of the ball, and a thin continuoussurrounding outer shell formed of unexpanded plastic, this shell 'being-sufliciently tough to impart an exceedingly long service life, being sufiiciently flexible so that the-ball has substantially the playing behavior of the 'expalnd'ed"core by itself, that is, the

playing characteristics which it would have if the shell were omitted, and being capable of taking and retaining over the life of the ball any sharply defined outer pattern imparted thereto in a final molding operation.

The playing ball of our invention exhibitsseveral important advantages over prior art balls of this'general type. A major advantage is that the rubbery material used in the core not only functions as a plasticizer-for the vinyl resin during the processing and formation of the ball but is fixed or mechanically locked by vulcanization so that in the finished ball it forms a sort of molecular network all through the core, this network being elastic, i. e., self-retractible upon deformation, and-serving to me.- chanically lock the closed-cell structure of the core against dimensional change because the vulcanized rubber component, although flexible, tends always to resume the size which it had at the end of the vulcanization, which in this process it completed at the end of the expansion cycle. Thus it will be seen that the rubbery component behaves very difierently in a closed-cell resinous structure from the high-boiling organic liquid plasticizers commonly used for vinyl resins like polyvinyl chloride. In any event, regardless of theory, the ball of our invention has far greater resistance to change in size, shape, or dimension than a ball wherein the plasticizer for the vinyl resin consists of high-boiling organic liquid material. A second major advantage-of the ball 'of our invention is that the tough outer plastic shell contributes far greater durability and resistance to surface failure upon prolonged use, for example in the case of apractice golf ball through successive hard hits made by a golf, club, than would be possessed'by the core alone and at the same tiine gives greatly improved definition of a pattern impressed injthe surface of the finished ball so that, in the case of -a practice golf ball, it more strikingly resembles a'regulation golf ball than a ball in which dimple definition is imparted directly to the surface of the closed-cell .plas-. ticized polyvinyl chloride. Likewise, in the case of. :a practice baseball, the shell gives sharp definition of simulated stitching and retention of this pattern indefinitely. Another advantage is that the use of our shell enables the production of a perfectly whiteball even though th'e core may be formulated from a colored composition. Thus, it allows the use of a blowing agent which causes discoloration of'the core, one such blowing agentfbeing dinitrosopentamethylenetetramine (Unicel NDi") which causes the core material of our invention to be light't an in color and, therefore, unattractive on the surface of the finished ball. The shell is tenaciously adhered to the core by integral bonding thereto during themanufacture of the ball and does not-separatetherefrom during the life of the ball. The dimpling or other final molding used to impress a desired pattern to the-shell compresses the core material very slightly at the points beneath the dimples or other surface indentations but the shell is sufficiently rigid to retain the dimpled or other impressed pattern sharply throughout the life of the ball despite any outward pressure that may be exerted by the core and at the same time the shell is so thin and flexible that our ball presents all of the advantages presented by the 'Barton ball.

The preferred rubbery material is a sulfur-vulcaniza- -ble copolymer of butadiene and acrylonitrile, typically containing from 15 to 45% by weight of'bo'und acrylonitrile, the balance being butadiene. Other rubbery materials which are compatible with and plasticizers for the vinyl resin can be used. We almost invariably use a rubbery eopolymer of an aliphatic conjugated diolefin hydrocarbon, especially butadiene, and another copolymerizable monomer, especially acrylonitrile or a. homolog thereof.

The core of our ball is preferably formed from a mixture of polyvinyl chloride, butadiene-acrylonitrile rubbery copolymer and high-boiling organic liquid plasticizer in relative proportions of from 30 to 125 parts of the rubbery copolymer and from 60 to 80 parts of the liquid plasticizer per 100 parts of polyvinyl chloride. The total plasticizer, i. e., the sum of the rubbery copolymer and the organic liquid plasticizer, will generally range from 100 to 175 parts per 100 parts of polyvinylchloride.

Any suitable chemical blowing agent which will decompose upon heating at temperatures of 250 F. or thereabove to form a harmless gas, especially nitrogen, and will form closed cells can be employed in making the core, examples being alpha, alpha'-azobisisobutyronitrile, diazoaminobenzene, p,p'-oxy bis (benzene sulfonyl hydrazide), dinitrosopentamethylenetetramine, etc. Selection of the blowing agent and the amount thereof are well within the skill of the art. The amount of blowing agent used is adjusted to yield the proper size of final ball at room temperature after the necessary expansion cycle. Core compositions which yield balls which are too small require the use of more blowing agent while compositions which yield balls which are too large require less blowing agent. Generally the amount of active blowing agent will be from to 100 parts per 100 parts of polyvinyl chloride.

Curatives for the rubbery component are incorporated in the mixture used in forming the core. These curatives comprise a vulcanizing agent, usually sulfur, an activator, usually zinc oxide in admixture with stearic acid, and, if desired, vulcanization accelerators of known type. Other conventional rubber compounding ingredients can be included.

In addition, it is desirable to include stabilizers of known type to protect the rubber against deterioration. It may also be desirable to include a pigment such as titanium oxide. The compounding of the core material will be obvious from this disclosure.

The ingredients of the core stock are mixed together to a uniform mixture in any suitable manner after which the core stock is preferably shaped into pro-forms having the correct volume and weight, the volume of each preferably being substantially less than that of the miniature mold cavity. By using a pre-form of lesser volume than the miniature mold cavity we enable the miniature mold to be held completely closed under moderate moldclosing pressure. All operations up to this point are conducted in the cold, using care not to heat the stock to such an extent as to decompose the blowing agent or pre-cure the rubber component to an appreciable extent.

We prefer that the original stock be sufficiently deformable and putty-like in nature and sufficiently condensed (i. e., deusified to remove entrapped air) that pro-forms of exact weight and volume can be dinkedout from regularly or irregularly shaped pieces of the condensed compound.

The preferred deformable and putty-like consistency of the original compound facilitates the loading of the small mold cavitie used in the miniature molding step by enabling the preparation of solid, easily handled, preforms of exact weight and volume for charging the individual miniature mold cavities, so that an expanded core of exactly the right weight and volume is obtained. These solid pre-forms are not tacky or sticky and can be easily loaded into the miniature mold cavities. In the light of this disclosure those skilled in the art can easily prepare a stock of the desired putty-like consistency.

One way of making the preferred stock of putty-like consistency which can be accurately dinked-out into non-sticky pre-forms of exact weight and volume for use in the miniature molding step is to disperse a mixture of powdered vinyl resin and the liquid plasticizer as the disperse phase in a continuous phase of the rubber component. This can be done by adding a, mixture of the resin and plasticizer to the banded rubber on an open rubber mill, mixing being continued until a continuous sheet of well mixed compound is obtained. The other ingredients (blowing agent, vulcanizing agents, etc.) are incorporated in any suitable way; typically all of them but the rubber stabilizer are included in the disperse phase by previously mixing them with the powdered resin and liquid plasticizer. Mixing temperatures are kept throughout as near room temperature as possible to prevent decomposition of the blowing agent. Incorporation of the ingredients in the foregoing way gives a non-sticky deformable stock of putty-like consistency which usually has appreciable resilience or nerve but which is ideally suited for the dinking-out operation. The preforming (or dinking-out) of the stock is preferably done by extruding or tubing to densify the compound and remove entrapped air, cutting off into pellets, and putting these pellets in spherical mold cavities which have the exact volume desired for the pre-forms and which upon closing squeeze out the excess stock between the lands. It is often desiralbe to pre-heat the pellets in an air oven at 200-300 F. for l0-20 minutes to render the stock softer and more yielding so that it does not spring back objectionably in this preforming step. Such pre-heating is so conducted as not to decompose the blowing agent, fuse the mixture, or vulcanize the rubber.

When this deformable putty-like stock is used, the volume of the pre-forms should equal 78-96% of the volume of the miniature mold cavity. A figure of is preferred.

Instead of a deformable putty-like stock such as is described above, we can less preferably employ a paste-like mixture of powdered rubber, powdered resin, liquid plasticizer and other components described here in. Thus we can take the commercially available materials known as Geon Polyblends which are colloidal" blends of polyvinyl chloride and butadiencacrylonitrile rubber made by coagulation of mixed latices thereof and blend them with suitable amounts of liquid plasticizer and with blowing agent, curatives, etc., to give a paste-like mix which is then passed several times through an extruder (e. g., a meat grinder equipped with a screen). We can then extrude a solid rod of the mixed stock and form it into pellets or biscuits which should be somewhat smaller in volume than the miniature mold cavity, preferably of a volume equal to -97% of the volume of the miniature cavity. This type of stock is objectionable because of its sticky nature and because it is not adapted to be accurately formed into pre-forms of exact weight and volume.

Typically we then proceed as follows: We place the preforms in smooth, spherical mold cavities of a size much smaller than that of the finished core, typically /4 inch in diameter in the case where a practice golf ball is to be made or 1.22 inches in case a practice baseball is desired. We then subject these pre-forms to molding heat and pressure (using a temperature of at least 250 F. and a pressure sufiicient to hold the mold closed) to fuse the resin, rubber and plasticizer into a single homogeneous phase, decompose the blowing agent to form gas which is retained under pressure, either as small bubbles or in solution or both, and at the same time partially vulcanize the rubber component sutficiently to retain the gas as closed cells during the subsequent expansion, vulcanization being completed in a later stage. In this step we use a temperature of at least 250 F. and more commonly at least 300 F. We then cool the mold under pressure to approximately room temperature, remove the miniature cores from the mold and heat them unconfined at an elevated temperature, preferably at least 300 F., e. g., at 325-375 F. for 20-90 minutes, to complete vulcanization of the rubber component and effect expansion to the greatest possible extent which is to a size much greater than that of the core of the finished ball. The expanded c'ores'iare next cooled toapprdximatelyj room temperature,

appearance. The expanded cores are now ready for the application of the shell.

It is essential that the core'be expanded in the unconfined expansion step to a maximum size much greater than the sizeof the core in'the finished'ball (typically to a. volume at least 25% greater than 'the core of the final 'ball) and 'that'upon' cooling toroom temperature it have the aforementioned wrinkled shrunken surface. Otherwise, thefinaI result would not be a dimensionally stable ball. The highly unattractive wrinkled surface of the core issubsequently-concealed andat the same'time' given durability by application of the shell.

The volume of the miniature mold is usually equal to from M; to that of the core of the finished ball.

Presence and vulcanization of the rubber component are essential from the standpoint of achieving-dimensional stability in the balls of our invention. The rubber permits expansion of the core composition at temperatures suflicientlyhigh 300 F. or'above) to relieve all internal strains and stresses in a mannerwhich can be likened to the annealing of metals. Such relief of internal stresses and strains in this step is in large measure responsible f forthe're markable dimensional stability of the final core. Such'dimension'alstability is not possible if the rubber is "omitted or is not vulcanized.

We prefer to'form the shell of a'white pigmented solid mixture of polyvinyl chloride and a high-boiling organic liquidplasticizer'therefor in amount ranging from 30 to 80 parts of the plasticizer per 100 parts of polyvinyl chloride. As the high-boiling organic liquid plasticizer, we can use any plasticizer known to be capable of plasticizing polyvinyl chloride. Generally these liquid plasticizers are ethers or esters. Examples are dioctyl -phthalate, dibutyl sebacate, dioctyl sebacate, tricresyl phosphate, dibutyl phthalate, linear polyesters, etc. We prefer to employ in the shell compound suitable proportions of stabilizers for the polyvinyl chloride, and suitable proportions of white pigment, especially titanium dioxide.

We prefer to form the shell by dipping the expanded cores in a white pigmented organic solvent'solution of the shell compound, typically applying two or three coats. of

this paint as required to give the proper shell thickness, the thickness of each coat typically ranging from 0.5 to 4 mils, with proper drying times between coats and after the final coat. We then give the dried, painted balls a light dusting with a mold parting agent such as zinc stearate and then subject them to a refrigeratingo'r freezing operation 'to cool them to a low temperature, preferably below 40 F., to contract them 'to a size substantially less than the 'fin'al size 'o'fth'e balls, in preparation for final molding 'to impress the desired surface pattern on the shell and give a perfectly spherical ball. We then place Z-the cold balls in a cold finalsurface-forming mold typically having the desired final diameter, e. g., 1.72" inthe case of a golf ball or 2.93" in case of a baseball. The balls should be so contracted by the cooling step as not to extend over 'the'lands of the mold which would have the undesirable result of cutting oif of a portion of the balls by the closing mold halves and giving a defective ball. The molds are then closed and subjected to suitable heat and pressure to eflectsurface shaping of the shell. In the case of a golf ball we usually use 600-1200 lbs. per cavity :pressure and heat 415 minutes at 300 F. We'then cool the surface shaping molds down to room temperature while keeping the molds under pressure and remove the balls which are now finished except for application of colored paint to fill branding or stitching indentations, this being an incidental operation.

In the drawings, a Ipre-form 1 (Fig. 1) of raw puttylike core stock (which was pre-formed by the above-de- F scribed dinking-out operation which caused the forma "non ofig'r'oove Ia around tlre extmded'p'ellet ofstpck) is placed between miniature mold halves 2 and 3, which together form a-smoothmold cavity in'diameter, and the mold halves 'are closed together. The pre-form 1 is then molded under 'heat and pressure in the miniature 'mold, yielding a miniature spherical core 4 (Fig. 3)

which contains minute bubbles of gas under pressure and/or gas in solution. After thoroughly cooling the mold, the mold halves 2 and 3 are separated and core 4 is removed,'exp'andin'g slightly as it-is released from the mold cavity, expansionbeing greater from a mold which is less cooled. The core4' is then heated upon open'tray '5 in circulating air to a suitably elevated temperature (preferably 32'5-3 7 5" F.) and expanded to form thecore fi'which has a roughly spherical "shape and at this point is much larger than the core of the finished'ball. After the expansion step the core 6 iscooled to room tempera- 'agentand subjected to freezing "(i. e. refrigeration) to shrink it so that it will fit into a 1.72" dimpled mold cavity formed by dimpling moldhalves 8. and 9 of Fig. 6 without extending over the lands of the mold which would cause the core to be cut by the closing mold halves 8 and 9 and result ina defective ball. The mold halves 8 and 9 are then closed under pressure and the mold is then 'heated under pressure to effect-the dimpling after which it is cooled to atemperature'approaching room temperature.

This operation yields the finished practice golf ball 10 having the dimples 11 over itsentire outer surface, these dimples being formed by deformation of the shell 7 and core 6 so as to closely simulate an ordinary .golf ball. If desired, a name brand can be engraved on the interior of the dimpling mold formed by halves Sand 9 so that the name brand is transferred to the shell 7 during the dimpling operation The branding indentations are subsequently filled with a colored paint to make the brand name legible.

Instead of using a vinyl resin as the basis of the shell composition, we can use "other thermoplastic resins which aretough and flexible, or becomeso upon plasticization, which are soluble in organicsolvents so as to permit application to the core, which give a tack-free, water-resistaut, abrasion-resistant and wear-resistant surface, which allow the core of the finished ball to be deformed indefinitely in play, e. :g., under the blows of the golf club,

which allow the ball to assumeitsoriginal shape immediately after removal'of the deforming force, which are capable of'tightly adhering to the core, and which are capable of being given sharp definition in the final shellm'oldi'ng operation and of retaining this sharp definition indefinitely. Examples of other thermoplastic resins are polymethyl acr'ylate, polyethyl 'ac'rylate, polymethyl methacrylat'e, polyethyl'methacrylate, etc., and copolymers of various alkylacrylates and 'alkyl methacrylates. If the resin is not sufficiently flexible, 'a plasticizer should be vr sion of the core. The coating should dry at a temperature of not 0ver'140 F. Mild heat (-not over F.) to accelerate drying of room temperature coatings is permissible. There should be at least 30 minutes of drying at room temperature between coats to insure adequate drying.

Although the relative proportions of core and shell in the finished ball can vary widely without departing from the spirit of our invention, typically the shell makes up from to 40% by weight of the finished ball and from 1 to 4% by volume thereof, the core correspondingly making up from 80 to 60% by weight and from 99 to 96% by volume of the ball.

A practice golf ball made by our invention has substan tially the same diameter as a regulation golf ball which at present is 1.68 in diameter. However, the diameter can vary somewhat from this figure, for example from 1.65 to 1.80". A practice baseball will usually have a diameter of approximately 2.9 inches, where a hard baseball is simulated. If a softball is simulated it will of course be larger.

The core of our ball is characterized by its extremely light weight, its density generally not exceeding 8 lbs. per

cubic foot and more commonly not exceeding 5 lbs. per

cubic foot.

The total weight of our practice golf ball will generally be from 60 to 100 grains. Our practice baseball will usually weigh from 300 to 350 grains.

The following examples illustrate our invention more fully.

EXAMPLE 1 Core compound Ingredients: Parts by weight Polyvinyl chloride 100 Butadiene-acrylonitrile rubbery copolymer containing about combined acrylonitrile 100 Ester-type liquid plasticizer 65 Unicel ND dinitrosopentamethylene- All of the foregoing ingredients except the rubbery copolymer and rubber antioxidant were mixed together in a powder mixing blender. The rubbery copolymer and rubber antioxidant were milled on a conventional two roll rubber mill until banded. The blend of powders and liquid prepared in the powder mixing blender was then added to the banded rubber, mixing being continued until a continuous sheet of well-mixed compound was obtained. Mixing temperatures were maintained throughout as near to room temperature as possible to prevent premature decomposition of the blowing agent. The resulting sheet was then extruded while cold into a rod of stock, this operation serving to densify the compound by removing entrapped air so that shaped pre-forms of stock having precise volume and weight could be prepared by a conventional procedure. These pre-forms were then made by a dinking-out step in which a length of extruded stock representing an excess was placed between two hemispherical mold cavities so that the cavity was entirely filled with compound and the excess stock was squeezed beyond the mold cavity lands by the closing pressure of the mold halves. This dinking-out was done in the cold and yielded pre-forrns which due to the resilience of the stock sprang into the irregular shape shown in Fig. 1 upon opening the preforming mold, groove 1a being formed along the line of removal of the flash in the dinking-out operation. These preforms had a volume equal to approximately 88% of the miniature mold cavity volume. These pre-forms were then molded in miniature in a 4 diameter smooth surfaced miniature mold under a closing pressure of 4,000 lbs. per cavity and at a temperature of 335 F. for 20 minutes whereupon the molds were cooled while 8 under pressure to bring the miniature molded balls to below 120 F. The molds were then opened and the smooth-surfaced partially cured miniature balls were then removed. There was some slight expansion of the balls as they were released from the mold cavity. The partly cured balls were then heated on an open tray in circulating air at 365 F. for about 60 minutes. During this expansion and heat treatment certain volatiles were removed from the balls inasmuch as they lost about 15% of their original weight during this treatment. Vulcanization of the rubber component was now complete. The expanded balls were not perfect spheres but were slightly irregular. This irregularity was completely removed in the subsequent dimpling operation applied to the shell.

The expanded balls were then cooled to room temperature and dipped into a solvent solution of paint having the following formulation.

Shell compound or paint Ingredients: Parts by weight Polyvinyl chloride 100 Ester-type liquid plasticizer 53 Stabilizers for polyvinyl chloride 6 Titanium oxide 20 Methyl ethyl ketone (solvent) 537 Three coats of the foregoing paint were applied with drying between coats. The dried painted balls were then contracted by cooling to a diameter such that they would not be cut by the dimpling mold and then dimpled in exactly the manner described above using dimpling molds having a diameter of 1.720". The finished balls had the following composition:

By By Component Weight, Volume,

grains percent Closed-cell Core (compound given above) 52 97 Non-porous Shell formed of 3 coats of above vinyl paint 28 3 EXAMPLE 2 Example 1 is duplicated exactly except that the stock used for making the core has the following formulation and expansion is accomplished with less heat.

Core compound Ingredients: Parts by weight Geon Polyblend 50OX479; (polyvinyl chloride, butadiene-acrylonitrile copoly- This formulation was prepared by blending all of the powders together, separately mixing both liquids together and adding the mixed liquids to the powders with stirring until all three liquids had been absorbed. The mixture was then tumbled for 15 minutes to give complete mixing. The resulting blend was passed through a meat grinder equipped with a 20 mesh screen for nine passes. The tubing attachment was then placed on the meat grinder and on the tenth pass a solid rod of mixed compound Was extruded. This rod was cut off into pellets which were formed into preforms which were processed into final balls in the same manner as in Example 1, except that the partly cured balls were heated on an open tray in circulating air for about 20 minutes at 325 F.

in some cases, when using a paste-like core compound like that used in Example 2, it is helpful in getting a 9 good dispersion of stabilizers, etc., to withhold about of the plasticizer until the mixture has been given several passes through the moat grinder whereupon the withheld plasticizer is, added and the mixture is .given the remaining passes through the grinder.

EXAMPLE 3 EXAMPLE 4 Example 1 was duplicated essentially except that a practice baseball was made. The .pre-form waslarger, having a weight of 290 grainsand the pro-form die had a cavity diameter of 1.22". The stock biscuits had a volume of approximately 88% of the miniature mold cavity which was formed by two smooth surface hemispherical mold halves having a diameter of 1.27. The

miniature mold was closed under a pressure of 9,750

pounds per cavity minimum clamping force and the miniature was cured for minutes to 335 F. in this mold.

The miniature cured core was expanded for 60 minutes at 365 F. Again about 15% loss of weight occurred during the expansion. Three coats of the vinyl paint were applied, giving a shell weight of 90 grains. After cooling by freezing the ball was molded in an engraved finishing mold having a diameter of 2.93" to simulate the surface of a baseball. The mold was closed and the ball was molded for 15 minutes at 300 F. and cooled under pressure for 15 minutes to room temperature. This formed simulated seams, stitching and branding. The seam, stitching and branding indentations were then filled with a colored .paint. The final ball had a diameter of 2.9:.1 inch, and had the following composition:

By By Component Weight, 7 Volume, Grains Percent Gore .i 2 46 98 Shell 90 2 The resulting ball (which is portrayed in Fig. 7) was very suitable as a play ball which would not injure people or objects struck by it.

Although we have described our invention with specific reference to practice golf balls and baseballs, our invention can be used to make any type of practice or play ball exhibiting lightness, close simulation in appearance of conventional balls, and complete freedom from danger to personnel or property. A. beach ball is an example. The halls of our invention are completely water-impervious and will float indefinitely on water and do not readily pick up dirt. Should they become dirty they can easily be cleaned.

As the resinous component in our core and shellwe generally use polyvinyl chloride or a copolymer of a major proportion, say 85-99%, of vinyl chloride and a minor proportion, say 151%, of vinyl acetate. Instead of using a vinyl chloride-vinyl acetate copolymer, we can use any other similar thermoplastic copolymer of a major proportion of vinyl chloride and a minor proportion of another copolymerizable monomer such as methyl acrylate, diethyl maleate, vinylidine chloride, etc. These vinyl resins all possess the necessary property of being fully compatible with the rubbery copolymer used in the core. The copolymers referred to are considered to be equivalent to polyvinyl chloride.

From the foregoing description it will be seen that our invention provides a practice ball having all of the of a regular ball.

appearance of a regular ball.

' 10 iadvantages-of'the ball shown by Barton. Thus,=ourball, not only initially but throughout its long life, has the dimensions, shape and appearance of a regulation -ball and is characterized by its light weight, deadness, short flight, freedom from hazard in use, and ability tosubstantially duplicate on a small scale the flight behavior In addition it has far greater dimensional stability and simulates much more closely the The introduction of the vulcanized rubber component in theclosed-cell structure is responsible for markedly improved dimensionalstabil- 'ity but it materially decreases the durability of the closed- -cell structure so that it will not withstand'normal playing usage, e. g., successive hard golf club drives. Also, the

maximum expansion followed by shrinkage gives an {unattractive wrinkled surface which would not be saleable.

However, the novel shell completely overcomes these defects, contributing the required durability and wearresistance, and adds greatly to the appearanceandflclose simulation of a regulation ball, by virtue of its ability to take and retain sharp surface definition for-an indefinite period of time. The shell protects'the core against failure by reason of its tough flexible nature and the tenaciousness with which it is adhered to the core.

Having thus described our invention, what we claim and desire to protect by Letters Patent is:

1. As a new article of manufacture, a practice or play ball comprising an inner spherical core formed of a flexible compressible resilient closed-cell expanded uniform mixture of a thermoplastic resin selected from the .group consisting of polyvinyl chloride and copolymersof a major proportion of vinyl chloride and a minor proportion of another copolymerizable monomer, a vulcanized rubbery copolymer of an aliphatic conjugated diolefin hydrocarbon and another copolymerizable monomer, said rubbery copolymer before vulcanization being compatible with said resin, and high-boiling organic liquid plasticizer for said resin, said core having a density of not over 8 pounds per cubic foot, and a thin continuous unexpanded plastic shell surrounding said core, said shell comprising a layer of ,plasticized thermoplastic resin selected from the group consisting of polyvinyl chloride and copolymers of a major proportion of vinylchloride and a minor prointegrally bonded to said core, said shell constituting from 20 to' 40% by weight and from 1 to 4% by volume of the ball, being capable of taking and maintaining sharp surface pattern definition over a long period of time, being tough and highly wear-resistant, protecting said core against failure in service, being flexible and tenaciously adherent to said core, being so flexible that the ball has substantially the playing behavior of the core alone, and permitting deformation of said core indefinitely in play without separation or cracking of said shell.

2. As a new article of manufacture, a practice or play ball comprising an inner spherical core formed of a flexible compressible resilient closed-cell expanded uniform mixture of a thermoplastic resin selected from the group consisting of polyvinyl chloride and copolymers of a major proportion of vinyl chloride and a minor proportion of another copolymerizable monomer, a vulcanized butadiene-acrylonitrile rubbery copolymer which before vulcanization is compatible with said vinyl resin, and high-boiling organic liquid plasticizer for said vinyl resin, said core having a density of not over 8 pounds per cubic foot, and a thin continuous unexpanded plastic shell surrounding said core, said shell comprising a layer of a mixture of a thermoplastic resin selected from the group consisting of polyvinyl chloride and copolymers of a major proportion of vinyl chloride and a minor proportion of another copolymerizable monomer and highboiling organic liquid plasticizer for said vinyl resindeposited directly on said core by drying from a solution of said resin and a high-boiling organic liquid plasticizer therefor in a volatile organic solvent, said layer being directly and integrally bonded to said core, said shell constituting from to 40% by weight and from 1 to 4% by volume of the ball, being capable of taking and maintaining sharp surface pattern definition over a long period of time, being tough and highly wear-resistant, protecting said core against failure in service, being flexible and tenaciously adherent to said core, being so flexible that the ball has substantially the playing behavior of the core alone, and permitting deformation of said core indefinitely in play without separation or cracking of said shell.

3. As a new article of manufacture, a practice or play ball comprising an inner spherical core formed of a flexible compressible resilient closed-cell expanded uniform mixture of a thermoplastic resin selected from the group consisting of polyvinyl chloride and copolymers of a major proportion of vinyl chloride and a minor proportion of another copolymcrizable monomer, a vulcanized butadiene-acrylonitrile rubbery copolymer which before vulcanization is compatible with said vinyl resin, and highboiling organic liquid plasticizer for said vinyl resin, the foregoing components being employed in relative proportions of from to 125 parts of said rubbery copolymer and from 60 to 80 parts of said plasticizer per 100 parts of said vinyl resin, said core having a density of not over 8 pounds per cubic foot, and a thin continuous unexpanded plastic shell surrounding said core, said shell comprising a layer of a mixture of a thermoplastic resin selected from the group consisting of polyvinyl chloride and copolymers of a major proportion of vinyl chloride and a minor proportion of another copolymerizable monomer and high-boiling organic liquid plasticizer therefor in relative proportions of from 30 to 80 parts of said plasticizer per 100 parts of said vinyl resin deposited by drying from a solution of said resin and said plasticizer in a volatile organic solvent, said layer being directly and integrally bonded to said core, said shell constituting from 20 to by weight and from 1 to 4% by volume of the ball, being capable of taking and maintaining sharp surface pattern definition over a long period of time, being tough and highly wear-resistant, protecting said core against failure in service, being flexible and tenaciously adherent to said core, being so flexible that the ball has substantially the playing behavior of the core alone, and permitting deformation of said core indefinitely in play Without separation or cracking of said shell.

4. The method of making a practice or play ball which comprises molding a miniature spherical core containing gas under pressure from a mixture of a thermoplastic resin selected from the group consisting of polyvinyl chloride and copolymers of a major proportion of vinyl chloride and a minor proportion of another copolymerizable monomer, a vulcanizable rubbery copolymer of an aliphatic conjugated diolefin hydrocarbon and another copolymerizable monomer, said rubbery copolymer before vulcanization being compatible with said vinyl resin, a high-boiling organic liquid plasticizer for said vinyl resin, a chemical blowing agent, and a vulcanizing agent for said rubbery copolymer, under such conditions as to decompose said blowing agent, partially vulcanize said rubbery copolymer so that it will retain the gas evolved by the blowing agent, and yield a miniature core in which said vinyl resin, rubbery copolymer and plasticizer constitute a single homogeneous phase and in which the generated gas is retained under pressure, expanding said miniature core to closed-cell form. in which it has a volume at least 25% greater than the core of the finished ball and completing vulcanization of said rubbery copolymer by applying heat to the core while it is free to expand, cooling the expanded core to approximately room temperature to shrink it to a size approximating the core of the finished ball and impart a wrinkled shrunken surface thereto, applying directly to the resulting core a thin continuous shell of a tough flexible unexpanded and unexpandable plastic material capable of receiving and maintaining sharp surface pattern definition, said shell constituting from 20 to 40% by weight and from 1 to 4% by volume of the finished ball and comprising a layer of a mixture of a thermoplastic resin selected from the group consisting of a polyvinyl chloride and copolymers of a major proportion of vinyl chloride and a minor proportion of another copolymerizablc monomer and a hi gh-boiling organic liquid plasticizer and being deposited directly upon said core by drying from a solution of said resin and said plasticizer in a volatile organic solvent, said shell being so flexible that the finished ball has substantially the playing behavior of the core alone and allowing the core of the finished ball to be deformed indefinitely in play without separation of said shell from said core, contracting the coated core to a size substantially smaller than the final ball by cooling below room temperature, and imparting a surface pattern to the coating of the contracted coated core by molding the same under heat and pressure to form the finished ball the core of which has a density not exceeding 8 pounds per cubic foot.

5. The method of claim 4 wherein said core-forming mixture contains polyvinyl chloride, a butadieneacrylonitrile rubbery copolymer, and high-boiling organic liquid plasticizer in relative proportions of from 30 to 125 parts of said copolymer and from 60 to parts of said plasticizer per parts of said polyvinyl chloride, and wherein said shell is formed from a mixture of polyvinyl chloride and a high-boiling organic liquid plasticizer therefor in relative proportions of from 30 to 80 parts of said plasticizer per 100 parts of said polyvinyl chloride.

6. The method of making a practice or play ball which comprises forming a pre-form of a deformable mixture of putty-like consistency comprising a thermoplastic resin selected from the group consisting of polyvinyl chloride and copolymers of a major proportion of vinyl chloride and a minor proportion of another copolymerizable monomer, a butadiene-acrylonitrile rubbery copolymer which before vulcanization is compatible with said vinyl resin, high-boiling organic liquid plasticized for said vinyl resin, a chemical blowing agent, and a vulcanizing agent for said rubbery copolymer, said rubbery copolymer being in the continuous phase and said vinyl resin and liquid plasticizer being in the disperse phase, said pre-form having a volume of from 78 to 96% of that of the hereinaftermentioned spherical mold activity, molding this pre-form under heat and pressure in a smooth-surfaced spherical mold cavity having a volume of from A, to that of the core of the finished ball and thereby decomposing said blowing agent, partially vulcanizing the rubbery material so that it will retain the gas evolved by the blowing agent, and thereby forming a miniature spherical core in which said vinyl resin, rubbery copolymer and plasticizer constitute a single homogeneous phase and in which the generated gas is retained under pressure, heating said core while it is free to expand to complete vulcanization of said rubbery copolymer and cause maximum expansion to closedcell form having a volume at least 25% greater than the core of the finished ball, cooling the expanded core to approximately room temperature to shrink it to a size approximating the core of the finished ball and impart a wrinkled shrunken surface thereto, applying to the resulting core a thin continuous unexpandable plastic shell comprising a layer of a thermoplastic resin selected from the group consisting of polyvinyl chloride and copolymers of a major proportion of vinyl chloride and a minor proportion of another copolymerizable monomer, said last-named vinyl resin being plasticized with high-boiling organic liquid plasticizer, said layer being deposited on said core by drying from a solution of said resin and said plasticizer in a volatile organic solvent, said shell constituting from 20 to 40% by weight and from 1 to 4% by volume of the finished ball, being capable of receiving and maintaining sharp surface definition, being so flexible that the finished ball has substantially the playing behavior of the core alone and allowing the core of the finished. ball to be deformed indefinitely in play without separation of said shell from said core, cooling the coated core below room temperature to contract it to a size substantially smaller than the final ball, and imparting a surface pattern to the coating of the contracted coated core by molding under heat and pressure to form the finished ball the core of which has a density not exceeding 8 pounds per cubic foot.

14 UNITED STATES PATENTS Voit Apr. 25, Eden Dec. 27, Daly et a1. Nov. 2, Barton Oct. 11, Smith Oct. 17, Daly et a1. Oct. 9,

FOREIGN PATENTS Great Britain Nov. 29,

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