US1770794A - Tennis string - Google Patents

Description

'No Drawing.

Patented July 15, 1 930 UNITED STATES PATENT, oFFicE GUSTAVE s. marnnmor ELIZABETH, NEW JERSEY, ASSIGNOR T0 JOHNSON & :ronnson, or NEW BRUNSWICK, NEW JERSEY, A conronnrrou on NEW JERSEY TENNIS STRING and disadvantages of steel strings'are similar to those of silk. Vhether covered or not,

steel strings are less lively than gut and steel strung rackets have a difierent feel.

There are on the market at present only a few synthetic strings. Braided strings are rapidly disappearing. A few special strings, combining gut and silk, have been offered, but their disadvantages over-shadow any apparent advantages.

The silk string offers the best solution provided it can be improved as to resiliency and as to waterproof properties.

After extended experimentation with many raw materials and divers methods of fabrication and treatment, I have devised a comparatively low cost strand which practically equals the resiliency of gut and for durability and over all efficiency is far superior to gut. It possesses the further merit that in appearance it is almost identical with gut in that it is substantially transparent, a

cross-section of the string revealing nofibrous structure. And the new strand may he untwisted with even more difiiculty than is the case with gut strings.

In-the practice of m invention, '1 start with silk in the boiled-o condition, i. e. free from the silk gum, ceresin. of ceresin is highly important for I have found that the presence of this substance is 'a deterrent to successful impregnation and accounts for past failures. A size of silk which has proven satisfactory is 22 thread 13/15 Japan tram.

Having, as stated, completely removed all traces of ceresin, the strands of silk are twisted and drawn under desirable tension through an appropriate glue mixture which is held at a carefully regulated temperature.

The elimination Application filed July 9, 1927. Serial No. 204,667.

In general, the higher the temperature, the better the impregnation. However, it is not desirable to raise the temperature of the glue appreciably beyond 7 0 (1., otherwise hydrolysis of the glue takes place and the finishedstring is likely to be decidedly brittle. The temperature is regulatedaccording to the fluidity of the glue and the appearance of the twisted string.

As a result of testing a number of types of cementing agents such as glass, resins, varnishes, lacquers, etc., I have found that a true colloid in solid form to the jelly form results in a true colloid jelly which shrinks uniformly and dries without any. separation from the strands. I

Inthose tests in which varnishes or lacquers were used, it was found that the resulting strings were quite large, poorly impregnated, slow in drying, and not at all satisfactoryas tennis strings.

F lexibilityinthe finished string is essential, otherwise the string will almost certainly break at the frame in the stringing process. The desired flexibility may be obtained by the use of a satisfactory softening agent in the glue mixture. However, the use of such agent in the required amount tends to confer uponthe string a resin-like surface so that when the string is pulled through a racket form it. slips at intervals as though it were treated with pine resin. Obviously, this condition is altogether undesirable inasmuch as it makes for non-uniformity of tension. To overcome this action of the softening agent, I add a good lubricant such as castor oil, lard or other vegetable or animal product; Good results have also been had with petroleum oils. The oil is stirred into the glue mixture until a uniform emulsion is formed "in which no trace of oil may be observed. Such an emulsion may be kept almost indefinitely with no separation into its components and glycol, triethylene glycol, the various p satisfactory products are given in the accompanying table,

It will be noted. that the compositionpf the glue mixture or emulsion may bevaried over rather wide limits according to the characteristics desired in the product. Other softening agents such ,as glycol, diethyleine glycerins, etc'., may be substituted for the glycerin used in the present process, and various oils of almost any stituted for the lard.

The properties of the finished pendlargely upon its structure. string having from two to four twists to the inch, and referably a twist of three turns to the inch, as proven eminently satisfactbry. A string containing glue as: such is not waterproof. By vproper treatment, however, the glue may be rendered very resistant to the action of moisture. The common tanning agents for leather are in general capable of rendering glue moisture-proof. Amon these are formaldehyde, other aldehydes, hexamethylene tetramine, tannic acid, potassium dichromate, and chromium and aluminum salts. .From the standpoint of ease of handling, low price and results obtained, formaldehyde has been most satisfactory. As carried out at present, curing is obtained orlgin may be substring de- A twisted by exposing the twisted string to the vapor of formaldehyde in a closed environment.

e use of solutions of formaldehyde containing the softening agent used in the glue mixture has also proved satisfactory.

After removal from the curing vessel the strings are stretched tightly and allowed to remain until dry. The quality of the strings is improved somewhat if the drying is conducted under considerable tension.

After the strings are thoroughly dried, any small surface irregularities may be removed by polishing with lard or other oil.

A satisfactory string must possess a breakuse of between fifty or sixty strands of 22 thread 13/15 Japan tram.

sand paper or equivalent, whereupon the strings are wiped off with well qualified or may readily be qualified for other purposes by modifying the glue bath, by proper choice of caplllary bore or other trim, and/or by varying the number of strands. For example it maysreplace raw hide in hookless belt lacing.

Having described my invention, I clann:

synthetic gut, comprising tw sted strands of degummed silk, and an emulsified colloidal bond having lubricating and water-proofing properties.

In testimony whereof I afiix my signature.

GUSTAVE S.MATHEY.

Strings ofa solid color may be providedby simply adding the emulsion or glue mixture. Where more than one color is required, the use .of two or more kinds of colored silk will insure the desired combination of colors.

While the present tended for use as a desired color to the product is mainly in substitute for gut itis