Method of making an insole

Abstract

Method of making insole of non-woven bonded fiber sheet material including a shank portion of greater stiffness and density than the forward portion in which a through layer of non-woven fiber sheet including a heat-softenable binder is associated with one or more layers of non-woven fiber sheet including binder in the heel and shank or waist portion of the insole and the layers in the heel and shank or waist portion are consolidated by heat and pressure to a unitary board-like state in the heel and shank region. The insole including the heel and shank region may be given a contour approximating the contour of a bottom of a foot in a pressing operation and may also incorporate a layer of stiff plastic sheet material.

Parent Case Text

This is a division of application Ser. No. 342,999, filed Mar. 20, 1973, now U.S. Pat. No. 3,835,558 dated Sept. 17, 1974.

Description

FIELD OF THE INVENTION

This invention relates to improvements in methods of making materials for use in the manufacture for shoes.

BACKGROUND OF THE INVENTION

Known insoles for incorporation in a shoe include those having a forepart which is flexible to permit the shoe to bend as a wearer walks and a more rigid heel seat and waist portion which gives strength to the shoe in the heel seat and waist region thereof and to which the heel of a shoe is commonly attached using suitable fastening members, for example nails or staples. The forepart portion of such insoles comprises a suitable flexible insoling material, for example water laid fibrous sheet material bonded with natural or synthetic rubber. The heel seat and waist portion of such an insole comprises a more rigid fiberboard, commonly known as shankboard. Insoles of this type may be cut from a composite board made by sticking together a rectangular piece of flexible forepart maaterial and shankboard; an edge portion of each piece of board is skived, thus giving a tapered edge portion, and suitable adhesive is applied to the skived edge portion of each material, the skived edge portions are then brought into contact and the adhesive thereon bonds the two pieces together. When the adhesive has set, insoles are cut from the so-formed composite board. The insoles cut from the board have a lap joint in the region of the ball of the foot. After the insoles have been cut out it is a known practice to impart a shape corresponding approximately to the contour of the bottom of a foot to the insoles by subjecting them to pressure applied by dies having a suitable shape in a suitable machine.

SUMMARY OF THE INVENTION

One of the various objects of the present invention is to provide an improved method of manufacturing a unitary shoe insole having a stiff rear portion and a flexible forepart.

To this end and in accordance with a feature of the preseent invention a unitary shoe insole is formed by assembling through and partial layers of non-woven bonded fiber and combining them with a unitary insole by heat and pressure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a showing of the completed insole.

FIG. 2 is an exploded view of the insole and pressing means.

FIG. 3 is a cross-section of the insole taken on line III--III of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An insole 10 according to the present invention is a non-woven bonded fiber sheet having an outline shape for incorporation in footwear and is constructed to have a rear portion 12 of greater density and rigidity than the fore part 14. The insole may be formed from one or more through layers 16 having an outline shape corresponding to that of the insole and one or more short layers 18 bonded to a rear portion 20 of the through layer. Each of the through layers is a non-woven bonded fiber batt which may be made by first forming an intermediate batt by garnetting, cross-laying and needling fibers and then introducing a binder into this intermediate batt. Any of the usual fibers employed in making non-woven fabrics may be used including nylon, rayon, polyester and cotton and mixtures of these. Suitable binders include heat softenable resinous materials such as the vinyl polymer and copolymer resins, polystyrene, polyacrylates and methacrylates, polymers and copolymers of isobutylic and butadiene, natural resins and mixtures of these. The melting point of these resinous materials must be high enough not to soften in use but low enough to be softened for bonding together of layers in the press. The binder may be applied as an aqueous emulsion or as a volatile organic solvent solution or in powder form. The amount of binder is not particularly critical and an amount of the order of about equal parts by weight of fibers and binder in the non-woven layer has been found useful. At least one short layer of each illustrative insole also consists of a similar non-woven bonded fiber batt. The rear, heel seat and waist portion of the illustrative insoles, comprising both the through layer or layers and the short layer or layers, has greater density and rigidity and is at least as thick as and preferably is thicker than the forepart of the insole.

In a preferred method of making the insoles of the present invention, the non-woven bonded fiber layers which are to form the insole are assembled in face-to-face relation. The assembly may comprise at least one through layer consisting of a non-woven bonded fiber batt having an outline shape corresponding to that of the insole and one or more short layers at least one of which consists of a non-woven bonded fiber batt and each of which has an outline shape corresponding with the outline shape of a rear portion of the through layer. The assembly may be prepared by arranging a number of layers of non-woven bonded fiber batt in face-to-face relation and cutting the insole assembly from the assembled layers, so that the outline shape of the short layers correspond with the rear portions of the through layer. It will be understood that the assembly may be made by cutting the through layer or layers, cutting the short layers separately and assembling the pre-cut layers to provide the insole assembly. If desired, a short layer portion may be made of a non-woven bonded fiber material having a thickness double or three times the thickness of the through layer rather than by use of a plurality of short layers.

The insole assembly is subjected to heat and pressure in either a high-frequency welding press or a press having electrically heated platens. The heat and pressure causes the layers to bond together through the action of the bonding agent in the fiber layers in the rear portion of the insole assembly, and the rear portion is consolidated or densified so that it has a greater density and rigidity than the forepart portion. It is preferred that the density of the rear portion be at least 50 percent greater than in the forepart portion.

In a modified form of the invention, in addition to the one or more short layers of non-wover fiber batt, there is used one or two short layers (of the same outline shape as the bonded fiber batt short layer) of a stiff, heat softenable sheet material suitably a sheet of resin plastic such as polyvinyl chloride, vinyl chloride copolymers, polypropylene, polystyrene, polyamides or other thermoplastic or stiff sheet material. The sheet material other than non-woven bonded fiber batt is preferably selected to be resistant to nails being pulled therethrough. Also, it is desirable that the plastic sheet material is of a type of plastic material which is heated when subjected to a high-frequency electric field. Where thermoplastic resin sheet, e.g. polyvinyl chloride, short layers are used, the heat and pressure is preferably supplied by a high-frequency welding press because the resin such as polyvinyl chloride is heated rapidly by the high-frequency fields and would be difficult to heat at a sufficiently fast rate to achieve adequate bonding in a reasonable length of time if a press of the heated platen type were to be used.

In carrying out the methods of the invention, it is preferred that the presser members 24, 26 by which the insoles are heated and pressed are shaped to impart to the insoles a shape corresponding approximately to the bottom of a foot.

One of the presser members may conveniently be a suitably shaped metal member and the other of the presser members may be a partially shaped resilient member having a flexible electrode embedded therein, the resilient presser member being such that as the two presser members are pressed toward each other so that the resilient member forces the insole assembly against the rigid metal member and molds it to the shape of the metal member. Where the insole assembly is to be shaped at the same time as the layers thereof are bonded together a shank member 28 of metal or other strong stiff material be bonded to the insole assembly in the heating and pressing step. Where the press is a high-frequency welding press, the shank member may be coated with polyvinyl chloride powder or the like as a bonding agent. Where a metal shank is to be incorporated in this way it may be unnecessary to provide a recess for the shank as, provided there is a sufficient thickness of compressible material, for example non-woven bonded fiber batt present, the pressure exerted by the press will force the shank into the layers of the insole assembly and embed it therein.

In the method using a high-frequency welding press, it is necessary that parts, at least, of the insole assembly comprise material which is heated by application of a high-frequency electric field. Preferably where the insole assembly comprises a non-woven fiber batt the fibers of which are bonded by a binder, the binder will comprise a material which is heated by application of a high-frequency electric field.

Conveniently, insoles in accordance with the invention may have a suitable finish, for example a material comprising 50 parts by weight of an aqueous dispersion of carboxylated high nitrile content synthetic rubber having a solids content of about 42 percent by weight and containing zinc oxide as a curing agent, 50 percent by weight of an aqueous dispersion of a vinyl chloride copolymer having a solids content of from about 55 to about 59 percent by weight, 10 parts by weight of 10 percent sodium carboxymethyl cellulose as a thickening agent and 5 parts by weight of a suitable color dispersion, for example a water based dispersion, instead of a stuck-in sock such as is used in many shoes at present.

The above and other of the various objects and several features of the present invention will become more clear from the following description of illustrative shoe insoles and methods of manufacture thereof aforementioned, hereinafter set out as Examples 1 to 5. It will be realized that these illustrative insoles and methods have been selected for description to illustrate the invention by way of example and not of limitation of the invention.

EXAMPLE 1

A non-woven fiber batt was formed by garnetting a mixture of fibers in the ratio of about one third by weight of 4 denier nylon staple fibers from 1 to 4 inches in average length with no staple exceeding 71/2inches and about two thirds by weight of viscous rayon fibers of mixed denier up to 11 (most fibers having a denier of about 3) and having a mixed staple length between 11/2 inches and 3 inches. The resulting light-weight, non-woven fiber web was cross-laid to form a thicker web and this thicker web was passed through a needle loom to consolidate the web and form an intermediate non-woven batt. The intermediate batt had a weight of about 480 grams per square meter, and was between 2.5 and 3.0 millimeters in thickness. This intermediate batt was then passed through an impregnating bath composed of an aqueous dispersion of vinyl chloride copolymer having a solids content of from 55 to 59%. From the bath the impregnated material was passed between stripper rolls to remove excess impregnant and was dried by passing it through a drying oven and round heated drying drums (the drums being heated by steam at 40 p.s.i.). The non-woven bonded fiber batt so formed consisted of 1 part by weight fiber to 1 part by weight of binder. The impregnated and dried material was about 2.5 millimeters in thickness.

Next, a piece of non-woven bonded fiber batt, prepared as described above, measuring 12 inches by 8 inches, was laid on a cutting block of a cutting press. A second piece of the non-woven bonded fiber batt measuring 71/4 inches by 8 inches was placed on top of the first piece with one of its 8 inch long edges in alignment with an 8 inch edge of the first piece and with the 71/4 inch long edges in alignment with the 12 inch edges of the first piece. Finally, a third piece of the non-woven bonded fiber batt measuring 71/4 inches by 8 inches was laid on top of the second piece, in alignment therewith. A cutting die, having the outline shape of an insole to be made, was placed on the materials, positioned so that the region of the die which was to cut out a forepart portion of an insole overlay only the first piece of the non-woven bonded fiber batt, the line marking the front edges of the second and third pieces of material lay in a ball region of an insole cut by the die and a rear region of the die (which was to cut out a heel seat and waist portion of the insole) overlay the first, second and third pieces of the material. The press was then operated to cause the die to cut the material to form an assembly comprising a through layer (cut from the first piece) having an outline shape corresponding to that of the insole and two short layers (each having an outline shape corresponding to that of a rear, heel seat and waist portion of the insole), the assembly being such that the outline shape of the short layers corresponded to the outline shape of the rear portion of the through layer.

The resulting assembly was placed between the platens of a high-frequency welding press, resting on a silicone rubber sheet three-sixteenths of an inch thick having a flexible electrode embedded in it, the sheet being secured to the lower platen and the assembly was covered by a foam silicone rubber sheet one-half inch thick. The silicone rubber was provided to prevent loss of heat from the assembly to the metal platens of the press, silicone rubber being a thermally insulating material of low dielectric loss. The air line pressure applied was 80 p.s.i. and the ram diameter was 41/2 inches. The input power applied was 1.9 amps and the frequency of the high-frequency field was 39 MHz. The assembly was allowed to remain in the press under pressure for 15 seconds and was subject to the high-frequency electric field for the first 9 seconds of this time.

The assembly was next removed from the high-frequency press and the three layers were found to be firmly bonded together. The forepart portion of the insole thus formed was about 2 millimeters in thickness and had a density of about 0.45 grams per cc. (the initial density of the forepart was about 0.40 grams per cc.). The heel seat and waist portion of the insole was about 3.10 millimeters in thickness and its density was about 0.78 grams per cc. The flexural rigidity of the material of the heel seat and waist portion of the insole was found to be of the same order as the flexural rigidity of Grade 1 shankboard 3 millimeters thick and was found to be considerably greater than the flexural rigidity of the forepart portion of the insole. Heel-attaching pins were driven through the heel seat and waist portion of the first illustrative insole and through Grade 1 shankboard 3 millimeters thick: slightly greater loads were needed to pull the heel pin out of the insole made according to the Example than were required to pull the pin from the Grade 1 shankboard.

The insole of the Example was subjected to heating and was then subjected to an insole molding operation, using a commercial twin sole molding machine. The molded insole so formed was found to be suitable for use as an insole in the manufacture of shoes. Insoles made as described above were suitable for use in the manufacture of men's shoes without any additional treatement: for use in the manufacture of women's shoes the heel seat and waist portion was reinforced in known manner by attaching a metal shank member, using eyelets.

EXAMPLE 2

The general procedure of Example 1 was repeated, except that three short layers of the non-woven bonded fiber batt were used in the heel seat and waist portion. The forepart portion of the insole (which consisted of only one layer, the through layer, of the non-woven bonded fiber batt) was slightly over 2 millimeters in thickness and slightly over 0.4 grams per cc. in density. The rear, heel seat and waist portion of the insole was 3.6 millimeters thick and had a density of 0.86 grams per cc. The forepart portion of this insole had a flexural rigidity similar to that of the forepart portion of the insole of Example 1. However, the flexural rigidity of the heel seat and waist portion of the insole made in this Example was noticeably greater than that of the insole of the first Example and was of the same order as Grade 1 shankboard 3.5 millimeters thick. The flexural rigidity of the heel seat and waist portion of the insole was considerably better then that of a Grade 1 shankboard 3.5 millimeters thick after both had been subjected to soaking in water for 6 hours. The load per millimeter thickness of the material required to remove heel attaching nails from the heel seat and waist portion of the insole was significantly greater than that required to remove nails from Grade 1 shankboard 3.5 millimeters thick, especially after both had been subjected to soaking in water for 6 hours.

EXAMPLE 3

The methods of Examples 1 and 2 were repeated except that instead of a high-frequency press, a press with heated platens was used to supply heat to the assembly. In each case, the thickness, density, flexural rigidity and the load required to remove the heel pin from the material were found to be about the same as for the first and second products. It was found, however, that there was some tendency for the layers of the product corresponding to Example 2 to delaminate.

EXAMPLE 4

Insoles were made by methods corresponding to Examples 1 to 3 with the exception that the different impregant composition was used; namely, a plasticized polystyrene dispersion having a solids content of about 50 percent. The insoles were similar in properties to the corresponding one of the Examples 1 through 4, except that those made using highfrequency heating corresponding to Examples 1 and 2 were slightly less dense than the insoles according to Examples 1 and 2.

EXAMPLE 5

Further insoles were prepared using a non-woven bonded fiber batt such as in Example 1 but using an impregant composition comprising 80 parts by weight of an aqueous dispersion of a vinyl chloride copolymer having a solids content of about 55 to about 59 percent by weight and 20 parts by weight of an aqueous dispersion of carboxylated high nitrile-content synthetic rubber having a solids content of about 42 percent by weight and containing zinc oxide as a curing agent. The impregnated batt was dried as described in Example 1 and the impregnating conditions were so chosen that the ratio of fiber to binder in the dried non-woven bonded fiber batt was 1:1 by weight.

In making one of these insoles, a piece 12 inches by 8 inches of the non-woven fiber batt was placed on the cutting block of a cutting press and a sheet of stiff polyvinyl chloride resin 71/4 inches by 8 inches was laid on top of the non-woven fiber batt with an 8 inch side in alignment with one of the 8 inch sides of the non-woven fiber piece and with the 71/4 sides in alignment with the 12 inch sides of the bonded fiber sheet. A further piece of non-woven bonded fiber batt 71/4 inch by 8 inches was laid on top of the polyvinyl chloride sheet. An insole assembly was cut from this and the assembly treated in the high frequency press in the manner described in Example 1. In this case the polyvinyl chloride sheet was slightly over one half mm. thick and had a weight of 900 grams of square meter.

The resulting insole had a forepart portion, which was 21/2 mm. thick and had a density of about 0.4 grams per cc. and had a rear, heel seat and waist portion which was about 3 mm. thick and had a density of about 1 gram per cc. The heel seat and waist portion of this insole had a slightly greater flexural rigidity than the heel seat and waist portion of the product of the first example. The load per millimeter thickness required to pull a heel-attaching nail through the heel seat and waist portion of this insole were considerably greater than that required for the product of Example 1.

A further insole was made in a manner similar to that just described except that two layers of the polyvinyl chloride sheet material were used. The forepart portion of this insole was 21/2 mm. thick and had a density of about 0.4 grams per cc. The rear, heel seat and waist portion of the insole was 31/2 mm. and had a density of slightly over 1 gram per cc. This insole had a slightly greater flexural rigidity than did the product of Example 2 and a considerably greater load was required to pull the heel-attaching nails through the heel seat and waist portion.

Both insoles of this example were suitable for use in the manufacture of shoes.

EXAMPLE 6

Insoles were made by procedures corresponding to Examples 1 and 2 with the exception that a small piece of polyvinyl chloride sheet material, one-half mm. thick and having a weight of 900 grams per square meter was placed in the heel seat region prior to assembly under heat and pressure in the high-frequency press so that the polyvinyl chloride sheet becomes an integral part of the insole in the heel seat region into which the heel attaching nails are to be driven.

Claims

Having thus described our invention what we claim as new and desire to secure as Letters Patent of the United States is:

1. The method of making an insole comprising forming an assembly in face to face relation of a through layer of non-woven bonded fiber comprising a thermoplastic bonding agent having a softening point below the melting point of the fiber of said layers and above the temperatures to which said insole will be subjected in use and having an outline shape corresponding to that of the insole and at least one short layer or a non-woven bonded fiber having an outline shape corresponding with or lying within the outline shape of a rear portion of a through layer and subjecting the assembly to heat and pressure to bond said through and short layers together through the action of said bonding agent and to densify portions of said assembly comprising both through and short layers so that said portions have greater density and rigidity than portions not comprising both through and short layers.

2. The method of making an insole as defined in claim 1 in which said assembly is subjected to heat and pressure between heated platens.

3. The method of making an insole as defined in claim 2 in which said platens are shaped to impart to the insole a contour corresponding approximately to a bottom of a foot.

4. The method of making an insole as defined in claim 1 in which said assembly is subjected to heat and pressure between platens at least one of the platens including a resilient surface having an electrode embedded therein and in which heat to bond said layers together and to densify portions of the assembly are generated by establishing a high frequency field from said electrode to heat the bonded fiber.

5. The method of making an insole as defined in claim 3 in which said platens are shaped to impart to the insole a contour corresponding approximately to a bottom of a foot.

6. The method of making an insole as defined in claim 1 in which a layer of stiff resin material is disposed in the region of the heel seat of the insole portion of the non-woven bonded fiber material in said assembly and is joined to a bonded fiber layer by said heat and pressure to provide a region in which heel attaching nails may be driven.

7. The method of making an insole as defined in claim 1 in which a shank stiffener member is disposed in the waist portion of said assembly and is embedded in and bonded to a non-woven bonded fiber layer by said heat and pressure.

8. The method of making an insole as defined in claim 7 in which said shank stiffener is coated with a thermoplastic resin prior to assembly with said layers of non-woven bonded fiber.