US 2484397 A
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Oct. 11, 1949. B. (LEARTON 2,484,397
PRACTICE-GOLF BALL Filed Jan. 30, 1948 A TTIORNEY Patented'oct. 11, 1949 PRACTICE GOLF BALL Bernard C. Barton, Clifton, N. J., assignor to United States Rubber Company, New
N. Y., a corporation of New Jersey Application January 30, 1948, Serial No. 5,439
4 Claims. (Cl. 273-62) Still another requirement is that they have along life and be capable of being struck without showing signs of wear or disintegrating. In the past practice golf balls have almost invariably been made of textile fibers such as yarn. However, such practice golf balls have not been entirely satisfactory for a variety of reasons among which the following may be mentioned. They soon lose their shape. Their flight is erratic. They are highly absorbent and pick up dirt and moisture very rapidlv. particularly when they are used out-of-doors. They do not simulate a standard golf ball either in a pearance or in flight.
I have now found that a practice golf ball which is free of the above disadvantages of prior art practice golf balls and which has certain exceptional advanta es may be made from closed cell expanded plasticized polyvinyl chloride. By making a spherical closed cell ball of expanded plasticized polyvinyl chloride having the dimensions of a standard golf ball, there is obtained a practice golf ball which has many advantages over prior art practice golf balls, particularly over the usual yarn practice golf ball. If such a closed cell expanded plasticized polyvinyl chloride ball be made in such a way that its surface is dimpled or is given any uniform pattern of projections or indentations or both such as is conventionally applied to standard golf balls to give them trueness of flight. the resulting practice golf ball strikingly resembles the standard golf ball and this adds markedly to its appeal.
In the accompanying drawing Fig. l is a front elevation, partially in section, of a dimpled practice golf ball made in accordance with my invention and Fig. 2 is an enlarged vertical central sectional view of a portion of the practice golf ball illustrated in Fig. 1 and shows in exaggerated detail the closed cell construction of the ball.
The practice golf ball of my invention is characterized by its light weight, its density generally not exceeding 8 lbs. per cubic ft. and more commonly being not over lbs. per cubic ft. The density may range downwardly from these limits to as low as 3 lbs, per cubic ft. The practice golf ball of my invention is particularly characterized by' its low resilience and its deadness compared with either a closed cell cellular rubber ball or a sponge rubber ball of similar size. Thus in rebound tests carried out under uniform conditions closed cell cellular rubber balls bounced above five to seven times higher than the closed cell polyvinyl chloride ball of my invention. The cellular rubber balls rebounded from nine to twelve times before coming to rest, whereas my cellular polyvinyl chloride ball rebounded only twice. In the same test the sponge rubber ball bounced four to five times higher than the ball of my invention, and rebounded nine to thirteen times before coming to rest. Low rebound, indicative of deadness, is a highly desirable property in a practice golf ball. A swing which would drive a standard golf ball 250 yards will drive the closed cell polyvinyl chloride practice ball of the present invention a maximum distance of only about 25 yards so that its flight may be readily observed at close range, whereas the same swing will drive the cellular rubber balls from to yards. My improved ball responds in the same manner as a regular golf ball to faulty swinging of the club, giving on a smaller scale excellent reproductions of the hook and the slice, whereas a sponge rubber ball does not show this behavior at all, and cellular rubber balls are too lively to show this behavior at close range. Thus the use of the practice golf ball of the present invention facilitates practice, making possible careful observation of vagaries in the flight of the ball resulting from faulty swinging of the club. It also greatly reduces the amount of walking required to recover the ball, thereby making practice less tiring and enabling a much greater number of practice strokes within a given period of time. The deadness of the ball also permits practice simulating actual play in areas of restricted size, 0. g., in gymnasiums or in small yards. I
The closed cell expanded polyvinyl chloride practice golf balls of my invention may be made in a number of ways. One method of producing such a ball consists of the steps of (1) forming a plastisol, i. e., a paste of finely divided polyvinyl chloride and a plasticizer therefor which is capable upon the application of heat of dissolving the polyvinyl chloride to form a gel which upon cooling to room temperature will be a solid material capable of retaining its shape, (2) admixing with such a plastisol a chemical blowing agent capable of generating an expanding gas upon the application of heat to the plastisol to gel it, (3) heating the plastisol under high presuct wherein the cells do intercommunicate. closed cells of the chemically blown ball of my invention range in diameter from 0.001 to 0.10 inch,
sure in an under-sized mold which conveniently is 7 inch in diameter and thereby effecting simultaneous gelation of the plastisol and generation of the inflating gas by decomposition of ithfl blowing agent, (4) cooling and removing the "miniature molded ball, (5) expanding it in hot water or in an air oven to approximately regulation golf ball size, 1. e., 1.68 inch, and (6) dimpling the expanded ball by heating it in a regular golf 'ball mold. Alternatively, the dimpling may be accomplished in the minature mold during step (3) above.
For example, a mixture of powdered polyvinyl chloride, a plasticizer and a blowing agent, in suitable proportions, is formed. A mold having a spherical mold cavity having either smooth walls or walls provided with a suitable design to give a dimpled or similar pattern in miniature to the pre-molded ball is filled with the resulting mixture. This mold has a spherical mold cavity which is considerably smaller than the size of a standard golf ball and which conveniently is H inch to inch in diameter. The mold is tightly closed by the application of high pressure, and
;' heat is applied to the mold to cause the blowing agent to decompose or gasify and to cause the plastisol to gel. A high external pressure is maintained on the mold in an efiort to hold it closed against the internal pressure of the generated gas. After the blowing agent has gasified and the polyvinyl chloride has gelled the mold is cooled, the pressure is released and the miniature ball is removed from the mold. At this stage the ball has been only partially expanded and the gas is contained under pressure in very small pores within the plasticized resin. The thus prepared ball is then caused to expandfurther to several times its original size to give a very light cellular ball while still retaining its spherical shape, by
';- heating it, as by placing the ball in warm water or in heated air or in any other heated fluid medium in which it is free to expand so that the thermoplastic resin softens and the pressure of the gas causes the pores to become greatly enlarged. Upon cooling the ball retains its expanded shape.
It should be noted that the present invention I relates to closed-cell gas-expanded balls, the cells of which do not communicate with one another, in contrast to a sponge or open cell type of prod- The the exact diameter depending upon the fineness of comminution of the blowing agent which, it will be understood, is substantially insoluble in the plastisol and is uniformly dispersed in finely -.divided form therethrough.
The polyvinyl chloride resin used in practicing my invention is a well-known material. I prefer to use polymerized polyvinyl chloride having a molecular weight of at least 12,000 as measured by known methods and a K value of more than 40 and preferably about 60. (For K value see Fikentscher, Cellulose-chemie 1932, page 58.) Al- 1 most invariably the polyvinyl chloride employed bis(p-xenyl)triazene may be used. The proportion of the blowing agent employed may vary depending upon the density and degree of cellularity desired in the ball and upon the particular blowing agent used. When the preferred blowing agent, alpha,alpha'-azobisisobutyronitrile, is employed, I generally use from 12 to 40 parts thereof per parts by weight of polyvinyl chloride.
Any plasticizer which is capable of dissolving the particles of the polyvinyl chloride upon heating to form a gel may be employed. Examples are dioctyl phthalate, tricresyl phosphate, dibutyl phthalate, dicapryl phthalate and other high boiling esters and ethers known to be plasticizers for polyvinyl chloride. Usually from V2 to 2 parts by weight of the plasticizer per one part of the polyvinyl chloride is employed. More commonly the plasticizer is used in an amount ranging from 65 to parts per 100 parts of polyvinyl chloride, but these ranges are not critical for the purposes of my invention.
It is also advantageous to employ in the formulation a small quantity of a heat or light stabilizer for the polyvinyl chloride, an example being from 2 to 5 parts of calcium stearate per 100 parts of polyvinyl chloride.
The time and temperature of the preliminary heating operation will vary with the blowing agent employed. The temperature should be sufficiently elevated to both decompose the blowing agent and cause the plasticizer to dissolve the resin. When using the preferred blowing agent, alpha,alpha'-azobisisobutyronitrile, the preliminary heating is carried out at a temperature of from 250 to 350 F. for from 6 to 15 minutes.
While the ball of the present invention usually consists of the plasticized polyvinyl chloride in.
closed cell expanded form, with or without a stabilizer for preventing decomposition of polyvinyl chloride by heat or light, under some circumstances it may be desirable to include in the formulation a small amount of a filler or a pigment provided the type and amount of -such filler and pigment is not such as to unduly increase the weight of the ball. For example, the density of the ball generally should not be over 8 lbs. per cubic ft. for satisfactory results. If any filler or pigment is used it preferably is white in color in order that the resulting practice golf ball may still have the white color of a standard golf ball.
The ball of my invention has a perfectly spherical shape and does not become distorted from blows of the golf club, in marked contrast to practice golf balls made of yarn which never are perfectly round and become quite distorted after a few practice drives.
The ball of my invention has a smooth imperforate skin covering its entire exterior surface. This is the result of the molding operation which prevents the formation of ruptured cells at the surface. As a conseduencathe surface of the ball does not readily pick up moisture, dirt or other foreign matter.
The practice golf ball of my invention has substantially the same diameter as a regulation golf ball. At present a regulation golf ball is 1.68 inches in diameter. The diameter of the practice golf ball of my invention may vary some! what from this figure without departing from the inventive concept. For example, the diameter of the practice golf ball of the present invention may range from 1.6 to 1.75 inches although it is preferred that it be as near 1.68 inches as possible in order that practice conditions may simulate ac- 75 tual playing conditions as nearly as possible.
In the drawing the golf ball I is shown as a solid mass of closed cell expanded plasticized polyvinyl chloride. The dimples formed in the surface of the golf ball are designated by reference numeral 2. The showing of Fig. 2 is exaggerated. It will be understood that some of the individual cells in the ball are so small that they cannot be seen with the naked eye but only with amagnifying glass. v
Example 1 The following formulation is prepared:
. Parts by weight Polyvinyl chloride 100 Calcium stearate 3 Tricresyl phosphate 90 Alpha,alpha'-azobisisobutyronitrile 18 The polyvinyl chloride, calcium stearate and alpha, alpha azobisisobutyronitrile are dry mixed whereupon the plasticizer is stirred in.
The mix at this point is still a relatively dry powder. It is transformed into a homogeneous paste or plastisol by passing it three to five times through a meat chopper. Both halves of a smooth spherical mold having a cavity inch in diameter are filled with the resulting mixture, a slight excess being added to one mold half to insure a coherent ball being formed when the mold is closed. The filled and closed mold is then heated eight minutes at a platen temperature of 330 F. (90 lbs. steam) at a mold-closing pressure of 3600 p. s. 1.; it is then cooled seven minutes whereupon it is opened and the ball is removed. The
ball is noticeably larger than the mold cavity when removed, being about inch in diameter. If the ball were removed when warm it would expand so rapidly as to be torn by the edge of the mold cavity. Next the ball is heated in water at 85 C. for 15 minutes which expands it to standard golf ball size, 1. e., to a diameter of approximately 1.68 inches. The ball is held under the water by a close-mesh wire screen. The expanded ball is then dimpled in a pair of golf ball mold cups 1.68 inches in diameter by heating it for 12 minutes at a platen temperature of 230 F., the hydraulic pressure exerted on the mold cups not exceeding 100 lbs. per ball. High pressure in this dimpling operation can cause defective dimpling, the ball expanding enough to seal the mold at the joint before the air is expelled. The mold is cooled to room temperature before releasing the hydraulic pressure.
Example 2 Example 1 is duplicated except that the following formulation is used, and that amold H inch in diameter is employed in the molding operation.
Par-ts by weight Polyvinyl chloride 100 Calcium stearate 3 Dioctyl phthalate 65 Alpha,alpha'-azobisisobutyronitrlle From the foregoing, it will be seen that the present invention provides a practice golf ball having many advantages. The ball is white and has the appearance of a standard golf ball. Its surface is smooth and non-absorbent. The texture of the surface is deceptively similar to that of a standard golf 'ball. It has a very short flight due to its light weight and its deadness and low resilience and can be used indoors, if desired, with-out injury to the ball or to the surroundings. In its flight characteristics it duplicates very closely the behavior of a regular golf ball, ex apt ly. It retains its perfectly round shape indefinitely. Watercannot penetrate the ball so that it retains its lightness even though it is used in wet grass. In fact, because of the closed cell nature of the ball it floats indefinitely on the surface of water. Because of the non-absorbent nature of the ball it does not readily pick up dirt and if it should happen to become dirty it can be washed with water without possibility of penetration into the interior. The ball is economical to manufacture and because of its close simulation of the appearance of a standard golf ball it has a strong appeal to golf players.
The term plastisol is used herein with the meaning which has become well-established in the art. See for example the article A New Technique in Coatings," by G. M. Howell and R. W. Quarles appearing in Official Digest, published by the Federation of Paint and Varnish Production Clubs, issue #263, December 1946, which contains a thorough exposition of the nature and properties of plastisols. Reference may also be made to Modern Plastics Encyclopedia, 1947, vol. 1, pages 140 and 484, published by Plastics Catalogue Corporation, New York, and to British Patent No. 500,298 which however effects the gelatinization of the plastisol without the application of pressure.
Having thus described my invention, what I claim and desire to protect by Letters Patent is:
1. As a new article of manufacture, a practice golf ball having a uniform structure throughout and comprising a spherical mass composed throughout of closed-cell expanded plasticized polyvinyl chloride, said ball having substantially the dimensions, shape and appearance of a standard golf ball but being characterized by its light weight, its deadness, its short flight, and its ability to substantially duplicate on a small scale the flight characteristics of a regular golf ball.
2. As a new article of manufacture, a practice golf ,ball having a uniform structure throughout and comprising a spherical mass composed throughout of closed-cell expanded plasticized polyvinyl chloride, said mass comprising a gelatinized mixture of polyvinyl chloride and plasticizer in proportions corresponding to from to 2 parts of plasticizer per one part of polyvinyl chloride, said ball having substantially the dimensions, shape and appearance of a standard golf ball but being characterized by its light weight, its density being not over 8 lbs. per cubic ft., its deadness, its short flight, and its ability to substantially duplicate on a small scale the flight characteristics of a regular golf ball.
3. As a new article of manufacture, a practice golf ball having a uniform structure throughout and comprising a spherical mass composed throughout of closed-cell expanded plasticized polyvinyl chloride, said mass comprising a gelatinized mixture of polyvinyl chloride and plasticizer in proportions corresponding to from 65 to 125 parts of plasticizer per parts of poly vinyl chloride, said ball having substantially the dimensions, shape and appearance of a standard golf ball but being characterized by/ its light weight, its density being not over 8 lbs. per cubic ft., its deadness, its short flight, and its ability to substantially duplicate on a small scale the flight characteristics of a regular golf ball.
4. As a new article of manufacture, a practice golf ball having a uniform structure throughout 8 flight, and its ability to substantially duplicate on a small scale the flight characteristics of a regular golf ball.
BERNARD C. BARTON.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Name Date Landreth Nov. 27, 1934 Number