GB2146282A - Moulding water-proof footwear - Google Patents

Abstract

A water-proof footwear, product and process for making it are described wherein said footwear product is made by forming a foot/leg shell 20 from an elastomeric material in a first injection molding step; and by forming and attaching a sole 40 to said shell 20 in a second injection molding step using said shell 20 as the sealing means along the pinching line 32 of the sole mold (not shown). In the first molding step a sock lining 21 is pulled over a last 11, an elastomeric shell 22 is molded over the lining 21 after which the lined elastomeric shell 20 is removed from the last. The second molding step comprises placing the previously molded shell 20 over a last prior to molding the sole 40. The shell 20 and sole 40 can be of different colours. <IMAGE>

Description

SPECIFICATION Water-proof footwear and method for making same The present invention relates to a process for injection molding of elastomeric compounds to make water-proof footwear and to the water-proof footwear made thereby, and particularly to a process capable of three colour injection molding of such footwear.

Various methods of mechanically molding water-proof footwear presently exist in the art.

These methods include among others, injection molding and slush molding. Slush molding requires a mold whose interior surface is designed to produce the exterior surface of the finished article. The mold is filled with a liquid comprising an elastomeric material and selectively heated to form a gel layer from the liquid against the interior walls of the mold.

The ungelled material is removed and the mold heated to flux the gelled layer, after which the mold is cooled and the fluxed gelled layer stripped from the mold.

Generally, in injection molding, a form is produced by a pattern-making process that resembles the interior space of the finished shoe, e.g. where the foot is placed in the shoe. This foot-form is called a "last" in the trade. Next, the last is surrounded by a mold usuaily composed of two halves. The respective halves of the mold represent left and right sides of the foot and they meet at the approximate vertical mid-line of the long axis of the foot. In injection molding a foot/leg portion (hereinafter "shell") and a sole/foxing portion (hereinafter "sole") is typically molded in one operation. The shell is produced by placing a mold around a last and filling the space in between. The sole is typically made from a mold in a separate operation.The bottom part of the mold forms the tread while the top part of the mold forms the surface where the shell will be joined to the sole. In another operation, the sole and shell are joined by heat and/or with an adhesive by hand. Thus, this method requires at least two different molds, two forming operations and a final assembly operation. However, the use of two different molds permits the use of different colors which is a significant advantage for the manufacturer regarding design and fashion. The use of the tight fitting metal to metal molds results in a "parting line" on the molded product. The parting line is especially prevalent on two color molded articles where the sole and shell are joined.

Normal procedure in two color injection molding of footwear involves either a sole plate which changes position or a dummy sole plate to create a parting line between the two colors of compound used - one color for the shell and the other color for the sole.

From a mechanical standpoint, the necessity of the close fitting metal to metal joint makes the production of a mold for a particular footwear product a labor intensive process.

In addition, the molds tend to wear quickly at these joints and must be replaced frequently or leakage will occur, resulting in rejects or costly repairs (i.e. hand trimming of flashing material caused by leaks).

When attempting to duplicate the irregularities at the line where the sole meets the "upper" (or shell) as exhibited in a hand made autoclave process by producing a mold of the parts of a water-proof rubber shoe, it becomes virtually impossible and certainly impractical to make molds in which the male and female parts will fit properly in an irregular configuration and, moreover, such a mold would have a limited life due to wear.

Footwear having canvas or cloth uppers have been made by forming the upper and then shooting a sole onto the upper. However, water-proof footwear particularly that having a highly irregular joining line have not been made in this manner.

From a fashion standpoint, the presence of the parting line where the sole joins the "upper" is unacceptable to the consumer.

Therefore, hand labor has been used to custom fit the sole to the shell thereby eliminating the parting line, but increasing production cost.

Previously, in the early 1 950's, a slush molded shell was tried in combination with an injection molded sole. However, the inability of the slush molding process to provide uniform and accurate thickness at the sealing or sole joining line resulted in leakage and poor quality products. Thus, this combination of a slush molded shell and injection molded sole was unsatisfactory and the process was abandoned.

Thus, it is desirable to have a process for injection molding water-proof footwear having the irregularities at the sole joining line exhibited by hand made footwear but without a parting line and/or the necessity for high molding costs.

The present invention provides a process for injection molding water-proof footwear that exhibit properties similar to those observed in footwear that are hand made by the autoclave process. The process of this invention comprises forming a foot/leg shell comprising an upper portion and an integral bottom and heel portion in a first injection molding step and forming a sole attached to the shell in a second injection molding step using the shell as a sealing gasket to seal the sole mold when molding the sole.

This invention provides a rapid and reliable process for constructing high quality waterproof footwear from elastomeric substances without the high costs of hand labor. The two step injection molding process readily accommodates two color footwear and using a two color injection molding machine in the second step readily provides a means for making three color footwear.

The articles produced by the process of this invention exhibit the desired effect of having the appearance of a hand made shoe. The process of the invention which utilizes the shell as a sealing gasket when subsequently molding the sole provides the capability for forming a wide variety of irregularities at the joining line, i.e. where the sole joins or ends on the side of the shell. The method of the invention further provides two color molding of footwear without leaving a noticeable pinching line. It further reduces the cost of making molds by eliminating the labor intensive process of making high irregular metal to metal joints.

This invention can be more clearly understood by referring to the accompanying drawings wherein: Figure 1 is a plan view of a water-proof footwear product made in accord with the present invention; Figure 2 is a side elevational view of the footwear product of Fig. 1: Figure 3 is a view of the bottom of the sole illustrated in Fig. 1; Figure 4 is a side elevational view, partiy in cross section, of the footwear illustrated in Figs. 1-3 having a last inserted therein taken along 4-4 of Fig. 1; Figure 5 is a cross sectional view of the footwear product of Figs. 1-3 taken along 5-5 of Fig. 1; Figure 6 is a cross sectional view of the footwear product of Figs. 1-3 taken along 6-6 of Fig. 1; Figure 7 is a cross sectional view of the footwear product of Figs. 1-3 taken along 7-7 of Fig. 1;; Figure 8 is a cross sectional side view of the foot/leg shell used in the footwear product illustrated in Figs. 1-3 taken along 4-4 of Fig. 1; Figure 9 is a side view of the sole portion of the footwear product illustrated in Fig. 2, further illustrating the relationship with the foot/leg shell; Figure 10 is a side view of an alternative embodiment of a footwear product made according to the present invention illustrating a different sole and joining line design; and Figure ii is a side view, partly in cross section, illustrating another embodiment of a footwear product made in accord with the present invention showing yet another sole and joining line design.

In accord with the present invention, one embodiment of a process for injection molding of water-proof footwear comprises molding a shell, placing the shell around a last, and using that last/shell combination as a sealing gasket when molding the sole to the shell. In a preferred embodiment of the invention, the first molding operation involves pulling a sock over a last and injection molding an elastomeric substance over the sock to form a shell that comprises the foot and leg portions (i.e.

foot/leg shell) of the footwear The shell is then used as a sealing gasket for injection molding the sole. Preferably. the shell is constructed to be of substantial thickness at the point of sealing. e.g the shell-sole mold interface, to provide a sealed compartment into which the elastomeric substance for the sole is injected.

The foot/leg shell should be oi sufficient thickness in the sealing area so that the elastomeric material will compress from about 30% to about 70%, preferably from about 35% to about 60%. of its normal thickness (i.e. when not under compression) when the shell is used to seal the mold used for injection molding the sole. Typically the thickness of the shell in the sealing area where the joining or pinching line is formed Wli. be about 1.5 to 8 mm and this thickness will be compressed to about 1 to 4 mm when used to seal the sole mold. In other areas the foot/leg shell is made of a thickness in keeping with the style of the desired product and to effect the desired comfort of the wearer.

Typically. the other areas of the shell will be thinner. However, it is preferable to include approximately one-half of the finished heel thickness in the mold for the shell. This construction, approximately one half the maximum heel thickness, significantly reduces the amount of time required for the shell to cool.

The invention will be further described with reference to the drawings.

Figs. 1-3 illustrate a water-proof footwear product 50 made in accord with one embodiment of the present invention. The waterproof footwear 50 comprises a shell 20 (as shown in Fig. 8) and a sole 40 (shown in Fig.

9). The shell 20 preferably has a lining or sock 21 substantially covering the interior of the elastomeric shell 22. The areas of the shell 20 designated as 23, 26, 27, 28 and 29 in the drawings form the shell upper and numerals 24, 25 and 33 form an intermediate sole and heel of the shell that comprise a rear area 23 that substantially conforms to the vertical portion of the heel placed therein and is formed by the junction of the right and left side areas 28 and 29 respectively, a hee! pad 24 molded from the elastomeric substance, an underfoot area 25, a toe area 26, an overfoot area 27, a right side area 28 and a left side area 29, a sole contact area 33 and an opening 30 for inserting a last or the wearer's foot as shown in Fig. 1. These areas surround an interior space of the shell 20 called the last space 11 where the last is in place before the shell is molded. In addition, the shell 20 has a sealing area around the sealing (or joining) line 32 which is the visible demarcation line between the shell 20 and the sole 40. The sealing line 32 and sealing area thus circumscribe the shell 20 at the height of the lip 41 of the sole 40, which can be very irregular.

The last 10, illustrated in place in the footwear product in Fig. 4, substantially fills the last space 11 and provides a support for molding the shell 20 and sole 40. The last 10 comprises a heel area 12, an arch area 13, a ball-foot area 14, a toe area 1 5 and an ankle area 16.

The sole 40 illustrated in more detail in Figs. 2, 3 and 9 comprises a sole lip 41 formed during the sole molding process and delineating the location of the sealing or pinching line 32. In addition, the sole 40 comprises a rear area 42, a heel portion 43, an arch portion 44, an underfoot or tread portion 45, a toe portion 46 and a shell placement space 47, and a shell interface contact area 48.

In Figs. 1 and 2, the footwear product 50 is illustrated with various designs that can be added to the pattern of the mold for the shell 20. These patterns include a raised external vertical reinforcement rib 51, a heel reinforcement area 52, a toe reinforcement area 53, raised reinforcement ribs 54, an ankle reinforcement area 55, and a logo placement area 56.

The process of the present invention provides a means for injection molding waterproof footwear having a hand made appearance. The process provides reliable means for joining the sole 40 to the shell 20 with wide varieties of joining line variations, that prior to the invention could only be satisfactorily accomplished by the hand autoclave process, while reducing labor and mold manufacturing costs. In addition, the two step process facilitates variability in color usage between the shell 20 and the sole 40.

The sock 21 used for reinforcing the foot/leg shell is typically made of any lightweight fabric or mesh of synthetic and/or natural material, e.g. cotton, wool, etc., that typically used for this purpose in the footwear industry.

The sock must withstand flexing and abrasion, yet avoid significant irritation to the person who wears the product. It may be woven, shaped or fashioned in any conventional manner. It can also be combined with a layer of urethane foam to provide increased comfort and insulation.

The shell 20 which includes the lining 21, the elastomeric shell 22, rear area 23, a heel pad 24, an underfoot area 25, a toe area 26, an over-foot area 27, a right side area 28, a left side area 29, a last insertion space 30, a foot contact area 31, a sole contact area 33 and an interface line 32, is made of any elastomeric substance or thermoplastic elastomeric composition typically used for injection molding of water-proof footwear such as natural rubber, thermoplastic rubber and polyvinyl chloride, etc.

Preferred compositions for the shell are linear or branched polymers having a molecular weight in the range of 150,000 to 250,000 Daltons, and most preferably between 200,000 and 220,000 Daltons. Examples of suitable elastomeric compostions for the practice of this invention are Kraton" 4240 and 4141, which are butadiene-styrene block copolymers available from Shell Chemical. Fillers stabilizers, colorants and plasticizers can be added to the composition before molding.

Blowing agents can also be added to expand the compositions by about 20 to 25%, thereby saving on materials cost.

The shell 20 can be injection molded around a last of any suitable dimension, with or without a sock, by any conventional injection molding means typically used for footwear items, e.g. a controlled shot machine can be used. The shell 20 is molded in a sufficiently accurate manner to provide a dimension of substantially uniform thickness throughout the areas of the shell forming the seal with the sole mole. As aforesaid such thickness at the sealing or pinching line 32 is typically about 1.5 to 8.0 mm, preferably 2 to 6 mm and most preferably about 2 to 4 mm.

However, the particular thickness will depend upon the material being used, its hardness, and the particular sole design. Because the shell 20 is used as a sealing gasket for the sole mold, the sole contact area 31 of the shell 20 must have sufficient pliability, thickness and strength to withstand the pressure exerted by the injected sole elastomer and yet maintain an intimate seal with the sole mold at the sealing line 32 without irreversibly deforming under the pressure or heat condition of injection molding the sole. It is preferred to have a uniform thickness produced around the shell 20 at the sealing or pinching line 32 when the shell 20 is molded, preferably a thickness that is about double the distance between the last 10 and lip 41 or sealing edge of the sole mold when the sold mold and the last are in the normal position for molding the sole.However, some variations in thickness can be tolerated as long as the compression of the shell material is sufficient to prevent leaking without causing irreversible deformation along the sealing line. The optimum thickness depends upon the elasticity of the material used for the shell.

The sole 40 which includes the sole lip 41, rear area 42, a heel portion 43, an arch portion 44, a tread portion 45, a toe porton 46, a shell placement space 47 and a shell interface contact surface 48 which is the interior surface of the sole, is typically made of any elastomeric substance of any suitable color typically used for injection molding footwear as described above, and which, when used under the heat and pressure conditions of injection molding, enables the shell interface contact surface 48 of the sole 40 to become affixed to the sole contact area 33 of the shell 20. Thus, the use of compatible elastomeric substances eliminates the necessity of joining a separate sole and shell in a hand operation by using adhesives, heat, etc., and therefore the manufacturing costs are reduced.

Alternative embodiments of footwear produced by the process of this invention are illustrated in Figs. 10 and 11, wherein the same shell 20 is affixed to a sole 60 of a design substantialy different from that of sole 40. This sole 60 is typically produced to the requirements delineated above and exhibits a more uniform interface line 61. However, uniformity of the surface at the lip 62 is not a prerequisite for successful use of this process, as evidenced by the scalloped lip 41 of sole 40, in Figs. 1 through 9 because the lip 41 is only a part of the sole design from the sole mold. Sealing occurs between the shell 20 and the sole mold at the point of the interface line 32, and also the interface line 61 as illustrated in Fig. 11. Other designs are readily provided by the skilled in the art.

Since the tight fitting metal to metal parting line of a normal mold is eliminated, there is no restriction from a mechanical or fashion standpoint to where the second color of the sole 40 (60) joins with the shell 20. Although it is possible to use this process on one twocolor injection molding machine, the preferred technique is to use two injection molding machines to increase productivity. Preferably, the machines would have a minimum of six stations and more preferably have ten to twelve stations each. The first machine is preferably a one-color injection molding machine to produce the shell 20 and one or two operators run the machine on a 10 to 1 2 second cycle depending upon the shoe height and type of lining.

The first injection molding operation involves pulling a sock lining 21 over a last 10, molding an elastomeric shell 22 over the sock 21, cooling the product as the machine carousel indexes and then removing the fabric lined elastomeric shell 20. Thus, about 1 20 pairs of shells 20 will be produced per hour or about 3,000 pairs of shells on a twenty four hour basis.

The second injection molding machine used to mold the sole is preferably a two color machine so that the finished product can be three colors if desired. The second injection molding step can be done with only one operator who slides the previously molded shell over a last 10, rotates the carousel into the sole molding step and removes the finished two or three color molded article from its last 10. This production method has a comparable cycle to that of the first molding operation and can produce approximately 3,000 pairs of finished shoes in 24 hours.

A further advantage of the method of this invention is that only the sole mold need be changed to produce a different style. Foot shapes change only slightly, if at all, over the years whereas sole designs change rapidly with fashion trends. Thus, various sole designs can be used with the same foot or shell mold and last to achieve several different designs of footwear from one last. Therefore, the sole design can be changed at a considerably lower cost than buying a whole new mold with male and female mating parts instead of only a new sole mold in accord with the present invention. Since the tight fitting metal to metal parting line of a normal mold is eliminated. there is no restriction from a mechanical or fashion standpoint to where the second color of the sole joins with the upper portion of the shoe or boot.

This invention has been described in detail including the preferred embodiment thereof.

However, it will be appreciated that those skilled in the art, upon consideration of this disclosure, may make modifications and improvements within the scope of this invention.

Claims (14)

1. A process for making water-proof footwear comprising: forming a foot/leg shell from an elastomeric material in a first injection molding step; and forming and attaching a sole to said shell in a second injection molding step using said shell as the sealing means along the pinching line of the sole mold.

2. The process of claim 1 wherein the step of forming said shell comprises placing a sock around a last and then forming said shell between the last and a mold.

3. The process of claim 1 wherein said sole mold has an irregular pinching line.

4. The process of claim 1 wherein the elastomeric material used to mold said shell is a different color than the material used to mold said sole.

5. The process of claim 1 wherein said elastomeric material is a thermoplastic compound.

6. The process of claim 5 wherein said elastomeric substance is polyvinyl chloride.

7. The process of claim 5 wherein said elastomeric material is a styrene-butadiene block copolymer.

8. The process of claim 1 wherein said sole is formed using a two color injection molding machine.

9. The process of claim 1 wherein said shell formed in said first forming step has a substantially uniform thickness in the area of the pinching line to seal the sole mold without irreversibly deforming the elastomeric material at the pinching line.

10. The process of claim 2 wherein the elastomeric material of said shell, when placed on a last and positioned in sealing contact with the sole mold for forming and attaching the sole, is compressed from about 30 to about 70% of its normal thickness.

11. A water-proof article of footwear made by forming a foot/leg shell from an elastomeric material in a first injection molding step, and subsequently forming and attaching a sole to said shell in a second injection molding step using said shell as the sealing means along the pinching line of the sole mold.

1 2. The article of footwear as set forth in claim 11 wherein said pinching line is irregular.

1 3. Injection molded water-proof footwear having the appearance of high quality hand made footwear, said water-proof footwear comprising (1) an injection molded foot/leg shell formed with an elastomeric material and having an area of substantially uniform thickness at the sole joining line, and (2) a sole injection molded on said shell to form a sole joining line in said area of substantially uniform thickness, said footwear not having a parting line where the sole joins the shell.

14. The interjection molded water-proof footwear of claim 1 3 wherein the thickness of the elastomeric material in said area of substantially uniform thickness is from about 1.5 to about 8.0.

1 5. A process for making waterproof footwear substantially as hereinbefore described with reference to the accompanying drawings.

1 6. An injection molded footwear substantially as hereinbefore described with reference to the accompanying drawings.