GB2416732A

GB2416732A - Moulded tape measure housing part

Info

Publication number: GB2416732A
Application number: GB0416509A
Authority: GB
Inventors: Barry Lee
Original assignee: Fisco Tools Ltd
Current assignee: Fisco Tools Ltd
Priority date: 2004-07-23
Filing date: 2004-07-23
Publication date: 2006-02-08
Also published as: GB0416509D0

Abstract

The invention provides tape measure housing (12) comprising a first part (14) and a second part (16). The first and second parts (14, 16) are coated with a coating material (10). The coating material (10) covers at least part of a join (18) between the first and second parts (14, 16) and is intimately contacted with and physically and/or chemically bonded to said first and second parts (14, 16) to connect them together. The parts of the tape measure are loaded into parts 14, 16 which latter are brought together to form joint 18 through a tongue and groove joint. After joining with screws at points 22, the assembled parts are placed into a mould and elastomeric coating 10 is injected. The parts 14, 16 are injection moulded.

Description

Housing This invention relates to a housing for a tape measure and to a

tape measure including such a housing.

It is well known to provide a flexible short tape measure wound onto a spool such that the tape measure can be unwound from the spool for use and then retracted after use for convenient storage.

A spindle is usually formed on or connected to the housing that contains the wound tape measure spool and return spring. The housing is usually formed in two parts, one part bearing the spindle on which the spool, onto which the tape measure is wound, is mounted, and the second part coordinating with the first part to either wholly or partially enclose the tape measure. In either case, the complete housing having an opening through which the tape measure can be extended or retracted.

In addition, it is known to provide a flexible long tape measure which is connected by a leader to a winding drum within a housing.

The drum is usually formed integrally with or connected to a winding handle used to wind the long tape measure onto the drum.

The drum is usually at least partially enclosed by the housing.

The housing is usually formed in at least two parts and has an opening through which the long tape measure can be extended and retracted.

There are various methods known for connecting together the first and second parts of the housing of a long or a short tape measure.

The most common method of connecting the two parts is to use screws. This method is however time consuming, as each screw must be individually inserted, and increases the manufacturing costs of the housing due to an increased number of components i.e. screws.

In addition, the mould tools for forming the housing for use with this method of connection are costly due to the inclusion of integral screw posts for joining the two parts of the housing together which complicates the tooling required for forming the housing.

A further method of connecting the two parts is to provide a "click-fit" connection, for example, as described in GB 2369103.

In this method, one part has a number of lipped lugs extending from it and the other part has a number of recesses or overhangs that cooperate with the lugs, the lip of the lug on one part being engaged in the recess or under the overhang on the other part. In order to achieve connection, the two parts are simply pushed together, each lug being slightly resiliently deformable.

The problem with click-fit connections is that in order to provide a positive connection between the two parts of the housing, both the lugs and the portions incorporating the overhang or recess must be made from a material that is only very slightly resiliently deformable, to allow connection of the lugs with the recess or overhang. To achieve low cost and simple manufacturing processes, such materials are generally reasonably brittle plastics. Unfortunately, these may be susceptible to shock fractures if, for example, the tape measure is dropped onto a hard surface. This may result in the separation of the two parts of the housing rendering the tape measure damaged or unusable. Also, the tooling required to produce the lips and lugs necessary for a click-fit connection is intricate so raising the cost of the mould tools required to form the housing.

The two parts of the tape measure housing are generally made from rigid plastic material, typically ABS polymer. This material is relatively low cost and can be easily injection moulded to form the two parts of the housing. One disadvantage of the rigid plastic materials used to form the housing its that they are generally reasonably brittle and may crack or shatter if subjected to mechanical shock, for example if the tape measure is dropped.

This problem is compounded in the case of short tapes by the relatively dense coiled metal measuring tape mounted on the spindle which exerts a reasonably large force on the housing if the tape measure is dropped.

It is therefore known to provide an elastomeric coating on at least part of the outside surface of the housing. This coating performs two functions. First, elastic deformation of the coating absorbs mechanical shocks to the housing so protecting the rigid plastic material from which the two parts of the housing are made.

Secondly, the elastomeric coating provides a surface with increased coefficient of friction compared to the generally smooth rigid plastic of the two parts of the housing. This provides a gripping surface that reduces the chances of the tape measure slipping from the user's hand during use.

Elastomeric coatings on tape measures in the prior art are generally applied to the tape measure housing by one of a number of methods. In a first method, the elastomeric coating is thermally moulded onto each of the two parts of the housing before they are joined together, as described in US patent No. 6,226,886.

In a second method, a jacket of elastomeric material is fitted over the tape measure housing after the two parts of the housing have been joined together. A third method may comprise trapping the elastomeric coating between the two parts of the housing as they are assembled, so holding the elastomeric material in place.

In a fourth method, protrusions are provided on the elastomeric component which are forced through corresponding holes in the rigid housing parts and cooperating with the corresponding holes to attach the elastomeric component to the rigid housing parts, as described in US patent No. 6,272, 765.

The problem with the first method of applying the elastomeric coating is that all of the problems previously outlined with joining the two parts of the housing (increased number of components, connecting lugs susceptible to shock fracture etc.) still remain. Also, the overmoulding of the elastomeric coating may distort the housing parts, due to elevated temperatures used in the overmoulding process, resulting in an uneven join when the housing parts are assembled.

With the second method of applying the elastomeric coating, as the coating is applied as a jacket after the housing is assembled, the coating must have sufficient elasticity to stretch over at least part of the housing. In this case, the elasticity of the coating and the fact that it is not attached to the housing, means that during use the coating can stretch and deform thus allowing movement of the housing inside the coating.

Where the elastomeric component is trapped between the two parts of the housing as they are assembled, mechanical wear on the trapped part of the elastomeric coating may result in breakage of the trapped elastomer and therefore detachment of the coating from the rigid housing.

Where the elastomeric component is provided with protrusions that are forced through corresponding holes in the rigid housing parts, mechanical wear on the protrusions may result in them breaking and so detaching the elastomeric coating from the rigid housing.

To overcome these problems, it is common to screw the elastomeric coating to the rigid housing. It would also be possible to bond the elastomeric coating to the rigid plastic housing using an adhesive. However, this would further increase manufacturing costs and would introduce a further step into the manufacturing process, that of inserting an additional screw or applying the adhesive to the rigid plastic housing.

In addition, none of these methods of applying an elastomeric coating to the housing reduce the need for additional components, such as screws, to join the two parts of the housing together.

The present invention provides a tape measure housing comprising two or more parts wherein the two or more parts are, at least partially, connected by an external coating material thus reducing or eliminating the need for additional connecting components. If the coating material is elastomeric, it may form a reduced-slip gripping surface and may also perform a shock absorbing function to protect the tape measure housing.

In a first aspect, the present invention comprises a tape measure housing comprising a first and a second part wherein said first and second parts are coated at least partially with a coating material, which coating material covers at least part of the join between said first and second parts and wherein said coating material is intimately contacted with and physically and/or chemically bonded to said first and second parts.

In some embodiments, the said coating material may be an elastomeric material.

If the coating material is elastomeric, it is preferably selected from the group comprising TPE, TPU, melt processable rubber and elastomeric alloy.

In alternative embodiments, the said coating material may be a rigid plastics material.

If the coating material is a rigid plastics material, it is preferably selected from the group comprising ABS, polyearbonate, polystyrene polyester, nylon and acetal.

In some embodiments the first and second parts of the housing are made from a rigid plastics material.

In preferred embodiments, the first and second parts of the housing are made from a material selected from the group comprising ABS, polyearbonate, polystyrene polyester, nylon and acetal or mixtures or alloys of any of these.

The coating material is preferably applied to the first and second parts of the housing by injection overmoulding.

Furthermore, in some embodiments, no additional components hold together the first and second parts.

The present invention also comprises a tape measure having a housing according to the present invention.

The present invention further comprises a method of making a tape measure housing according to the present invention comprising the steps of: forming said first and second parts by an injection moulding process; assembling the first and second parts with a tape measure mechanism; overmoulding a coating material around the assembled first and second parts so that the coating material covers at least a part of the join between the first and second parts.

Defini ti one By short tape measure is meant a tape measure comprising a spooled concave metal tape mounted on a spindle and biased into a spooled condition.

By long tape measure is meant a tape measure comprising a spooled flat tape which may be made from metal or fibreglass. A long tape measure may further comprise a winding handle operably connected to the tape spool allowing re-spooling and optionally also unspooling of the tape.

Physical bonding is defined herein as involving direct contac between the coating material and the rigid plastic housing with no intermediate compound, such as adhesive, between the coating material and the housing and with no mechanical interaction or additional components attaching the coating material to the rigid plastic housing. The physical bonding referred to herein may comprise intimate mixing of the coating material with the rigid plastic material of the housing at the coating material/rigid plastic interface.

Chemical bonding is defined herein as the formation of new chemical bonds directly between molecules of the coating material and molecules of the rigid polymer housing material.

At least some of the problems listed above with the prior art elastomeric coatings may be overcome by the present invention.

In the present invention, the housing of the tape measure is formed in two or more parts. A first part may bear the structure onto which the tape measure is wound (a spindle for short tapes or a drum and winding apparatus for long tapes) and a second part coordinates with the first part to at least partially enclose the tape measure.

The parts of the housing are made from a rigid plastic material.

This material may be any one of acrylonitrile-butadiene-styrene terpolymer (ABS), polystyrene or polycarbonate, and is preferably ABS.

In the present invention, at least two parts of the rigid plastic housing are confronted and then coated, at least in part, with a coating material such that the coating material covers at least part of the joint region between the at least two parts of the housing so connecting the at least two parts together.

When assembled, the housing may generally be considered to have two opposed faces with one or more edges joining said opposed faces. The join between the two or more parts of the housing may generally occur along the one or more edges of the housing.

It is preferable that the coating material covers at least part of the join along the one or more edges of the housing, and extends to cover at least part of at least one of the said two opposed faces of the housing. Even more preferably, the coating material covers a first part of the join along the one or more edges of the housing, at least part of at least one of the said two opposed faces of the housing and a second separate part of the join along the one or more edges of the housing. In a preferred embodiment said first and second separate parts of the join along one or more edges of the housing are spatially separated.

It is also envisaged that the coating material may cover a plurality of separate parts of the join between the two or more parts of the housing.

The two or more parts of the housing may be held together prior to the coating material being applied.

As such, one part of the two or more part housing may have one or more lipped lugs extending from it with another part of the two or more part housing having recesses or overhangs formed in it which cooperate with the lugs, the lip of the lug being engaged in the recess or under the overhang.

The two or more parts of the housing may alternatively be connected by screws or other additional components.

It is also envisaged that the two or more parts of the housing may be conically welded together prior to application of the coating material.

Alternatively, the two or more parts of the housing may remain disconnected prior to the coating material being applied, the two parts simply being confronted and then being coated at least in part with the coating material. In this case, in the assembled housing, at least two of the two or more parts of the housing are only connected together by the coating material. This reduces the number of components required to assemble the housing.

Where the coating material is an elastomeric material, this provides an increased resistance to mechanical shock over the prior art rigidly assembled housing. Where two or more parts of the housing are joined by an elastomeric material, in the event of mechanical shock, the two or more parts may move relative to each other, due to the elasticity in the elastomeric coating, without damage to the housing. In this case, the elastomeric coating gives, i.e. stretches, to allow the two or more parts to move relative to each other and exerts a force to hold the two or more parts together and return them to their original relative positions.

The housing may further comprise one or more rigid plastic posts inside the housing and projecting between two parts of the housing. These one or more posts may be formed integrally with and project entirely from one part of the two or more part housing to meet another part of the two or more part housing when the two or more parts of the housing are confronted. Alternatively, these one or more posts may be partially formed integrally with each of two parts of the two or more part housing, (i.e. each of the one or more posts is split with two parts of the two or more parts of the housing each holding a part of the one or more posts) such that when the two or more parts of the housing are confronted, the two parts of the one or more posts meet.

In either case, there may exist a mating assembly at the joint between either the two parts of the one or more posts, or the one or more posts and the opposite part of the housing.

These one or more posts may be hollow so that when the two or more parts of the housing are confronted, the hollow post forms a passage passing through the housing of the tape measure. Said passage may be open at one or both ends.

When the coating material is applied to the rigid plastic housing, it is preferably applied over the ends of any passages so formed through the housing thereby filling the passages with coating material and linking the two or more parts of the housing (fig. 6).

Where the coating material is an elastomer, this type of elastomeric link through passages in the housing, has a small amount of flexibility from the elasticity of the elastomeric material. This results in a joint between the two or more parts of the housing that is more tolerant of mechanical shocks than rigid joints, such as screwed joints.

It is also preferable that any seeping of the molten coating material into the join between the two or more parts of the housing, known as flooding, is minimised during the application of the coating material.

In order to minimise flooding of the joint, one part of the housing may have one or more protruding rims that fit into one or more grooves in another part of the housing when the housing parts are confronted so providing a "tongue and groove" type joint. In addition to or as an alternative to the tongue and groove joint, a crushable rib may be provided on one part of the housing with a groove in another part of the housing. When the crushable rib is inserted into the groove of the other part of the housing and a joining pressure is applied, the crushable rib is deformed so as to obstruct the groove and restrict flooding of the joint thereby formed when the coating material is applied. Furthermore, other arrangements known in the art to minimise flooding of joint with overmould material may be used to join the two or more parts of the housing together prior to application of the coating material.

The coating material is preferably applied by placing at least part of the rigid plastic housing into a mould and injection moulding molten coating material around the rigid plastic housing.

After the coating material has cooled and solidified, at least two of the two or more parts of the rigid plastic housing are held together by the coating material which is intimately contacted with the at least two of the two or more parts of the housing. In this case, intimate contact includes physical and/or chemical bonding.

Physical bonding between the coating material and the housing may be enhanced by the inclusion on all or part of the housing of protrusions, undercuts, holes, grooves or roughened surfaces.

These features add physical attachment points for the coating material to bond to as well as increasing the bonding surface area. Protrusions such as rib details on at least part of the housing are particularly preferred as these provide an improved bonding surface compared with a flat surface as the ribs provide a larger bonding surface area and melt more readily than a flat surface so increasing the mixing of the coating material with the rigid housing material. Chemical bonding between the coating material and the rigid plastic housing is also enhanced by the above features due to the increased intimate contact area.

The coating material is chosen such that after it solidifies following molten injection moulding around at least part of the rigid plastic housing, it is physically and/or chemically bonded to the rigid plastic housing. A number of physical properties of the coating material and the rigid plastic material influence the physical and/or chemical bonding between the two materials.

First, the molten coating material preferably wets the rigid plastic of the two part housing. This allows the two materials to come into intimate contact so increasing the ease with which the coating material molecules and the rigid plastic molecules can mix.

It is also preferable that the coating material has a similar polarity to the rigid plastic material. This reduces electrostatic repulsions between the two materials, again allowing them to come into intimate contact and so increasing the ease with which the molecules of the two materials can mix.

Furthermore, the coating material preferably has a similar melting temperature to the rigid plastic material. More preferably the melting temperature of the coating material is the same as or higher than, even more preferably higher than, that of the rigid plastic material. This allows the molten coating material to soften or melt the surface of the rigid plastic material when it is contacted with it hence allowing a greater mobility of the molecules forming the rigid plastic material. This in turn results in an increased mixing of the molecules of the coating material and the rigid plastic material, due to the higher rate of diffusion of the molecules of molten plastic material as compared to the plastic material in its solid state, so forming a stronger bond between the two materials.

The specific coating material used will depend on the rigid plastic material from which the tape measure housing is made and will be chosen to form a physical and/or chemical bond with the rigid plastic housing. Matching of coating materials to plastic materials in order to maximise the strength of the bond between them is known in the art.

The coating material may be chosen from any elastomeric material known in the art such as styrene based block copolymer (SBS or SEBS), ester based block copolymer, urethane based block copolymer (TPU), amide based block copolymer, cross-linked thermoplastic olefins, not cross-linked thermoplastic olefins, melt processable rubber or elastomeric alloy, or may be a rigid plastic material such as ABS polymer, polyearbonate, polystyrene, polyester, nylon or acetal. Preferably the coating material is an elastomeric material.

If the preferred ABS rigid plastic housing is used, the preferred elastomeric coating material may be any one of styrene based block copolymer (SBS or SEBS), ester based block copolymer, urethane based block copolymer (TPU), amide based block copolymer, cross- linked thermoplastic olefins, not cross-linked thermoplastic olefins, melt processable rubber or elastomeric alloy and is preferably TPE or TPU.

Preferably the injection moulding is performed with the mould at an elevated temperature when the coating material is introduced in order to reduce the cooling rate of the coating material relative to that obtained by using a mould at room temperature. The mould temperature may fall in the range 20 C to 60 C.

It is also preferred that the holding pressure of the mould during injection moulding is minimized to avoid pressure deformation of the rigid plastic housing. Preferably no holding pressure is applied to the mould during injection moulding. Furthermore, it is preferred that the hold time, i.e. the time for which the mould remains closed following injection, is minimised and preferably there is substantially no hold time.

It is envisaged that the present invention may be used on all or part of the housing of either "long tape" measures (figs. 2 to 5) or "short tape" measures (fig. 1).

Preferred, non-limiting embodiments of the present invention will now be described with reference to accompanying figures in which: Fig. 1 shows a perspective view of a short tape measure with an overmould coating applied to a part of the housing; Fig. 2 shows a perspective view of a long tape measure with an overmould coating applied to a part of the housing; Fig. 3 shows a front view of a long tape measure as shown in Fig. 2; Fig. 4 shows a perspective view of a long tape measure with no overmould coating; Fig. 5 shows a front view of a long tape measure as shown in Fig. 4; and Fig. 6 shows a cross section through line X-X and line Y-Y in Fig. 1 and Fig. 2 respectively.

Fig. 1 shows a short tape measure housing 2, formed from two housing parts 4 and 6. The two parts 4 and 6 are joined together at a joint 8. A overmould coating 10 is applied that covers at least part of the joint 8 and connects the two parts, 4 and 6, of the housing 2 together.

The two housing parts 4 and 6 are independently made from ABS rigid plastic material by injection moulding processes that are well known in the art. The metal tape, spindle, spring loaded spooling mechanism, tape brake and any other internal parts of the short tape measure are then loaded into the two housing parts 4 and 6 and the two housing parts 4 and 6 are brought together along the join line 8. The joint 8 is a tongue and groove type joint.

The assembled housing parts 4 and 6 are then placed into a mould assembly and an elastomeric overmould coating 10 is applied which covers at least a portion of the joint 8. The mould assembly is warmed to 60 C prior to injection of molten overmould coating material. The mould is closed with a minimum effective holding pressure. Molten elastomeric overmould coating is then injected into the warmed mould and allowed to solidify on cooling. As soon as possible after injection, the mould is opened and the joined housing parts are ejected. The tongue and groove type joint 8 minimises flooding by the molten elastomeric coating material of the joint region between the two housing parts 4 and 6. When the elastomeric overmould coating has solidified, the mould assembly is released and the tape measure is removed. The two housing parts 4 and 6 of the short tape measure 2 are now held together, at least in part, by the elastomeric overmould material 10.

Figs. 2 and 3 show a long tape measure 12, formed from two housing parts 14 and 16. The two housing parts 14 and 16 are joined together at a joint 18. An overmould coating 10 is then applied that covers at least part of the joint 18 and connects the two housing parts, 14 and 16, together.

The two housing parts 14 and 16 are independently made from ABS rigid plastic material by injection moulding processes that are well known in the art. The drum, fabric tape and leader, winding mechanism and any other internal parts of the long tape measure are loaded into the two housing parts 14 and 16 and the parts 14 and 16 are brought together to form a joint along line 18. The joint along line 18 is a tongue and groove type joint. The two housing parts 14 and 16 are then joined together by screws at points 22 which will not be covered by the elastomeric overmould coating 10 in the finished product. The assembled housing parts 14 and 16 are then placed into a mould assembly and an elastomeric coating 10 is applied which covers at least a part of the joint line 18. The Would assembly is warmed to 60 C prior to injection of molten elastomeric coating material. The mould is closed with lo a minimum effective holding pressure. Molten elastomeric overmould coating is then injected into the warmed mould and allowed to solidify on cooling. As soon as possible after injection, the mould is opened and the joined housing parts are ejected. The tongue and groove type joint 18 minimises flooding by the molten elastomeric coating material of the joint region between the two housing parts 14 and 16. When the elastomeric overmould coating has solidified, the mould assembly is released and the tape measure is removed. The two housing parts 14 and 16 of the long tape measure 12 are now held together, at least in part, by the elastomeric coating overmould material 10. In this embodiment, the two housing parts are also connected together by screws 22 in order to hold together the two housing parts, 14 and 16, in places where they are not connected by the overmould coating 10.

Figs. 4 and 5 show a long tape measure 12 as in figs. 2 and 3, before the elastomeric overmould coating 10 has been applied. In addition to the screws 22 connecting the two housing parts, 14 and 16, there are also passages 24 formed through the housing 12 in the area which is to be covered by the elastomeric overmould coating 10 in fig. 3. When the elastomeric coating 10 is applied, the coating material forms a connection through the passages 24 and connects the two housing parts, 14 and 16, together.

Fig. 6 shows a partial cross section along line X-X in fig. 1 or line Y-Yin fig. 2. Fig. 6 will be described with reference to the line Y-Y in fig. 2. However this description also applies to the line X-X in fig. 1 with substitution of the reference numerals 2, 4, 6 and 8 for the numerals 12, 14, 16 and 18 respectively.

In Fig. 6, the two housing parts, 4 and 6, are connected at the joint 8 by a tongue and groove joint. The tongue 34 is formed on one of the housing parts 4, and the groove 36 is formed in the other housing part 6. A hollow post 25 joins the two housing parts, 4 and 6 forming a passage through the tape measure. The post 25 is formed in two parts 26 and 28 projecting from the two housing parts 4 and 6 respectively. Where the two parts 26 and 28 of the post 25 meet, a recess 32 in one of the parts of the post, 28, accepts a projection 30 formed on the other part of the post, 26, to join the two parts of the post, 26 and 28 together. The overmould coating 10 fills the hole in the hollow post 25 formed between the two housing parts, 4 and 6. The overmould coating therefore forms a link 38 between the two housing parts without the use of additional components such as screws.

If the overmould coating is elastomeric, the link 38 through the hollow post which joins the two housing parts 4 and 6 together, is an elastic link. Such an elastic link allows the two housing parts 4 and 6 to separate by a small amount whilst remaining connected by the elastic link 38. This allows for separation of the housing parts if, for example, the tape measure is dropped onto a hard surface. This separation of the two parts 4 and 6 absorbs some of the energy of the impact and results in the housing parts 4 and 6 being less likely to break on impact. The elastic link 38 also provides a restoring force if the two parts of the housing 4 and 6 separate. C m

Claims

1. A tape measure housing comprising a first part and a second part

wherein said first and second parts are coated at least partially with a coating material, which coating material covers at least part of a join between said first and second parts and wherein said coating material is intimately contacted with and physically and/or chemically bonded to said first and second parts.

2. A tape measure housing according to claim 1 wherein said coating material is an elastomeric material.

3. A tape measure according to claim 2 wherein said elastomeric material is selected from the group comprising TPE, TPU, melt processable rubber and elastomeric alloy.

4. A tape measure housing according to claim 1 wherein said coating material is a rigid plastics material.

5. A tape measure housing according to any one of the preceding claims wherein the first and second parts of the housing are made from a rigid plastics material.

6. A tape measure housing according to claim 4 or 5 wherein said rigid plastics material is selected from the group comprising ABS, polycarbonate, polystyrene, nylon, polyester, acetal and alloys of these materials.

7. A tape measure housing according to any one of the preceding claims wherein the coating material is applied by injection overmoulding.

8. A tape measure housing according to any one of the preceding claims wherein no additional components hold together the first and second parts.

9. A tape measure having a housing according to any one of the preceding claims.

10. A method of making a tape measure housing according to any one of claims 1 to 8 comprising the steps of: forming said first and second parts by an injection moulding process; assembling the first and second parts with a tape measure mechanism; overmoulding a coating material around the assembled first and second parts so that the coating material covers at least a part of the join between the first and second parts.