US1846346A - Shoe stiffener - Google Patents

Description

Patented Feb. 23, 1932 UNITED STATES PATENT OFFICE.

LUcIEN PAUL MELLERIO Ann WILLIAM Jackson LUND, or LEICESTER, ENGLAND, AS- 'srenoas To UNITED SHOE MACHINERY CORPORATION, OF PATEBSON, N W JERSEY,

' a A CORPORATION OF NEW JERSEY SHOE STIFFENER No Drawing. Application filed November 5, 1927, Serial No. 231,389, and in Great Britain November This invention relates to thermoplastic stiffener-s and is herein disclosed as embodied in a toe stiffener for use in the uppers of boots and shoes.

The manufacture of shoes with. thermoplastic toe stifl'encrs atpresent puts certain mutually opposed requirements upon such toe stiffeners which are difficult to. satisfy. Alfhoughit is not necessary that a thermoplastic toe stiffener shall bequite unaffected by heat such as may be met with in tropical climates, or in exposed situations such as shop windows in temperate climates when exceptional summer heat is encountered, nevertheless the stiffener, even if somewhat softened, must remain fairly firm and capable of holding up the toe portion of the upper of the shoe. Many thermoplastic stiffening compounds capable of satisfying this condition and yet capable of being softened by a degree of heat not injurious to leather are available so that there is no difficulty in producing a thermoplastic stiffener which can be rendered workable for pulling over and lasting by a degree of heat such as it is practicable touse and a. time of heating such as can be devoted economically torendering the stiffener workable and which will give eventually an ade quately stiffened box toe. On the other hand, however, economical shoe manufacture, especially in rather lower grades of work, and the desire of workmen for an easy task create demands for a stiffener that can be rendered workable. by a, minimum of heating and will remainworkable when once softened for a illaxinnun time. This again isa condition that can be easily satisfied by suitable known thermoplastic stiffening agents; and thermoplastic stiffener-s can be produced which will satisfy these requirements and be adequately resistant to the softening influencesof heat which the shoe may ordinarily be exposed to in storage or wear. In such a case, however, assurance thatthe shoe toe will resist adequately allthe conditions of heat it will have to meet should it be exported to the tropics or be ill-advisedly exposed in a sunny shop window on an exceptionally hot day will have been sacrificed. l

At the present time, therefore, thermoplastic toe stiffener-s may be graded roughly into two categoriesthose very easy to work but lacking somewhat in resistance to heat to which the shoe may possibly be exposed and those which, while still quite readily workable, are markedly less easily workable but also much more reliably resistant to the effects of heat which the finished shoe may have to encounter. The difference in the thermoplasticity of the two grades of stiffeners need not be very great to be effective. For example, the range of temperaturein which objectionable softening of the stiffener in the. finished shoe isliable to take place lies between 100 and 130 F.; and the difference between a satisfactory stiffenerand an unsatisfactory one would be that the satisfactory stiffener would resist objectionable softening somewhere in this range at a temperature say 10 higher than would the unsatisfactory one. 1 y

The general object of the invention is to do away with the necessity for this differentiation of grades and to provide stiffeners which are workable as easily as is the one grade above-mentioned and at the same time behave in the shoe as reliably as does the other grade.

According to the present invention the thermoplastic stiffener contains, in addition to the usual thermoplastic substance, a substance which, when the stiffener has been heated at a given temperature to render it plastic to a given degree, effects a change in the thermoplastic quality of the stiffener such that, after the stiffener has become cool,

a higher heat is necessary to bring it to the same degree of plasticity a second time. Thermoplastic stiffeners are commonly heated before the p11lling ove1' operation and again before the lasting operation; and prefi erably the substance used will be such that one or both of these heating operations will efiect the desired change. Although thetemperatures to which toe stiffeners are subjected during the manufacture of shoes vary somewhat, it may be stated that it is common to subject a thermoplastic stiffener to a temperature of from 160 to 190 F. for from one to three minutes prior to the pulling-over operation and then-to subject it to a higher temperature, which may reach 230 F. for from two to three minutes prior to the lasting operation.

Synthetic resins of the phenolic condensation product type, known to the trade as Bakelite, for example, are adapted to produce the desired result which has been described'above'. Such resins may be had in a progressive series, regarded from the point of view of their fusibility or thermoplasticity; and the more fusible or more thermoplastic ones may be changed progressively into the less fusible and less thermoplastic ones by the action of heat, the degree of heat and the time it is applied determining the qualities of the final product. It is this instability under heat-this property of becoming more resistant to heat, the more they are heatedwhich is made use of inthe present invention, it being understood that the particular resin chosen will depend largely upon the amount of heat treatment which can conveniently be given it in the manufacture of any particular type of shoe. Although the two heat treatments commonly given to a thermoplastic stiffener in the manufacture of certain types of shoes as hitherto carried out has been indicated above, it should be understood that an extra heating operation may be performed, if desirable, such operation being entirely independent of the two heating operations referred to above and being prolonged, for example, over a much longer period, the only limits to time and temperature being such as are imposed by the liability of the leather of the shoe to be injured by exposure to too much heat.

Resins of this kind may be incorporated in stiffeners in various ways. For example, a suitable resin of the type known as Bakelite A or thetype known as Bakelite B may be incorporated in a thermoplastic stiffener of the old type, in which the thermoplastic material consists of a mixture of rosin and Montan wax, by dissolving rosin, Montan wax and Bakelite A in a suitable solvent such as a mixture of alcohol and benzol, passing a sheet of felt or other fibrous material through the solution, causing the solvent to evaporate, and cutting stiffeners from the impregnated material; or, the Bakelite A, in the form of a varnish may be used to coat an ordinary stiifener blank consisting of felt impregnated with any usual thermoplastic material such as the mixture of rosin and Montan wax referred to above. Again, a synthetic resin may be incorporated in the thermoplastic stiffener during the manufacture of the stiffener by the commonly used process which consists in immersing a sheet of felt in molten thermoplastic material, permitting the material to cool and then cutting stiffeners from the sheet. In such case the synthetic resin for example Bakelite B in solid, powdered form may be dusted upon-the sheet of felt after it emerges from its molten bath and before it has cooled so that the resin will adhereto the other thermoplastic material. The amountof synthetic resin which is used may, of course, be varied but ordinarily will comprise from ten to fifteen per cent of the weight of the stiffener blank.

In the description as thus far given it has been assumed that the substance, which, upon heating of the stiffener decreases the susceptibility of the stiffener to a second heating, is distributed uniformly throughout or over the surface of the stiffener. It should be understood, however, that such substance may be localized in selected portions if desired. When, for example, a thermoplastic stiffener is to be used in a plain vamp shoe it may be desirable to apply the substance only to the middle and forward portions of the stiffener leaving the rear margin of the stiffener free from any such substance; or, again, the forward curved margin which is bent over the insole in the lasting operation may be left untreated.

lthough the invention has been set forth in connection with certain substances it should be' understood that the invention is not limited in the scope of its application to the substances which have been described.

Having thus' described our invention, what we claim as new and desire to secure by Letters Patent of the United States is 1. A shoe stiffener comprising a thermoplastic substance the thermoplasticity of which substantially. stable under repeated heating and a thermoplastic phenolic condensation product the thermoplasticity of which is unstable under heat.

2. A box toe stiffener comprising a thermoplastic substance the thermoplasticity of which remains substantially unchanged under repeated heating, and a thermoplastic phenolic condensation product the thermoplasticity of which decreases under repeated heating.

3. A box toe stiffener comprising a thermoplastic substance the thermoplasticity of which remains substantially unchanged under repeated. heating and a thermoplastic phenolic condensationproduct in solid form the thermoplasticity of which decreases under repeated heating.

4. Abox toe stiffener comprising a thermoplastic substance the "thermoplasticity of which remains substantially unchanged under repeated heating and a fusible phenolic condensation product.

5. A box toe stiifener comprising a thermoplastic substance the thermoplasticity of which remains substantially unchanged when subjected to a temperature of substantially 230 Fahrenheit for substantially three minutes, and a thermoplastic phenolic condensation product the thermoplasticity of which is decreased when subjected to the same temperature for the same time.

In testimony whereof we have signed our names to this specification.

LUOIEN PAUL MELLERIO. WILLIAM JACKSON LUND.