GB2567222A

GB2567222A - Method of manufacture

Info

Publication number: GB2567222A
Application number: GB1716416.1A
Authority: GB
Inventors: Morrish John; Morrish Mark
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-10-06
Filing date: 2017-10-06
Publication date: 2019-04-10
Anticipated expiration: 2037-10-06
Also published as: GB2567222B; GB201716416D0

Abstract

A method of securing a magnet 30 to a plastic moulding 40 comprising the steps of a) providing a magnet comprising a body composed of a ferrite material and a thermoplastic binder; b) providing a mold body (54, fig. 5) comprising first and second portions operable to be engaged with each to define a cavity (56, fig. 6), at least the first portion being formed of metal; c) locating a magnetised surface of the magnet within the cavity adjacent to an inner surface of the first portion; d) injecting hot plastic at a temperature sufficient to melt the thermoplastic binder into the mould cavity around the magnet, fusing the hot plastic to the binder; and e) allowing the hot plastic to cool to form a moulded product comprising a plastic moulding bonded to the magnet body. The overmoulding method saves the need to manually adhere a magnet to a moulding. Also claimed is a moulded plastic product 10, such as a fridge magnet, comprising a plastic moulding 40 fused to an at least partially embedded magnet 30.

Description

METHOD OF MANUFACTURE

The present invention relates to a method of securing a magnet within a plastic moulding. In particular, the present invention relates to a method of securing a magnet within a plastic fridge magnet item.

BACKGROUND TO THE INVENTION

A conventional fridge magnet typically comprises an item such as a plastic plaque, badge, or other plastic or metal item with an attractive, funny or thought-provoking image provided thereon. A magnet is adhered to the rear surface of the item such that the fridge magnet may be held on a magnetic surface, such as fridge or radiator, by virtue of magnetic attraction between the magnet of the fridge magnet and the metal surface to which is attracted.

The typical magnetic material used as a magnet in conventional fridge magnets is a ferrite material mixed with a thermoplastic binder and magnetised on one side to facilitate magnetic attraction between the magnet and the magnetic surface on which the fridge magnet is to be held.

Conventional fridge magnets are manufactured by adhering the magnet to the rear surface of the item to be displayed. Normally pre-cut rectangular ferrite type magnets covered on one side with double sided adhesive tape are used. The release paper on one surface of the double sided adhesive tape is striped off and the adhesive tape adhered to the ferrite magnet during the course of manufacture. The remaining piece of release paper (on the opposing surface of the double sided adhesive tape) is removed from the ferrite magnet manually to adhere the ferrite magnet to the plastic moulding. The adhesive that is normally used is acrylic or rubber based.

However, there are several disadvantages of such a design. For example, the adhesive can fail with the resultant detachment of the display item from the magnet. This can result in damage to the display item if it falls from a significant height. This is a very common problem when the fridge magnet is displayed in an environment which is warm and/or humid. Heat and moisture will often facilitate the failure of the adhesive and the detachment of the display item from the magnet.

Further, the fridge magnet is often of significant thickness due to the combined depth of the display item and the adhered magnet. Although this may not be a concern in many circumstances, it can prevent the slim-line look that may be desired for some fridge magnet designs.

Even more importantly, the adhering of the magnet to the display item is typically a manual operation, as discussed above, using magnetic material covered with double sided adhesive The accurate manual placing of this magnet with respect to both the double sided adhesive tape and, subsequently, the display item is slow and involves wasting the release paper on both sides. This adds to the manufacture time and costs and is clearly not efficient when producing many such fridge magnets. There is therefore a need for an improved method of manufacture of such items.

SUMMARY OF THE INVENTION

The present invention seeks to address the problems of the prior art.

Accordingly, the present invention provides a method of securing a magnet to a plastic moulding, the method comprising the steps of providing a magnet comprising a body composed of a ferrite material and a thermoplastic binder, wherein the magnet body has an outer surface and wherein the magnet body has a first magnetised surface; providing a mould body, the mould body comprising first and second portions, wherein each portion has a first outer surface and a second inner surface, each portion being operable to be engaged with the other such that the respective inner surfaces define a mould cavity, and wherein the first portion comprises a metal material; locating the first magnetised surface of the magnet within the cavity adjacent the inner surface of the first portion; injecting hot plastic at a temperature sufficient to melt the thermoplastic into the mould cavity around the magnet; and allowing the hot plastic to cool to form a moulded product comprising a plastic moulding bonded to the magnet body.

In one embodiment, the second portion of the mould body comprises a metal material.

A method according to the invention may further comprise the step of removing the plastic moulding from the mould body in order to release the plastic device with the embedded magnet.

Preferably, the thermoplastic material comprises clear or coloured Polystyrene, ABS, StyreneAcrylic-Nitrile (SAN), or other suitable Thermoplastic material, Polypropylene or similar thermoplastic material. However, it is to be appreciated that any suitable thermoplastic material known to the skilled person may be used instead of, or in addition to, the materials listed herein.

It is preferred that the temperature of the hot plastic is in the range of from 120 to 300 °C and more preferably, in the range of from 150 to 250 °C.

Preferably, the magnet is fused to the plastic of the moulded plastic product. This is achieved through melting of the carrier i.e. thermoplastic binder of the magnet at the surface of the magnet body. The melted thermoplastic binder may then fuse with the injected hot plastic, thus fusing the magnet body to the plastic moulding once cooled.

The magnet or magnets may be accurately located within the mould cavity or cavities manually. However, it is preferred that the magnet or magnets are preferably accurately placed by robot into the mould cavity or cavities, where they are held in place relative to the metal mould surface by magnetic attraction.

Preferably, the moulded plastic product comprises a fridge magnet. However, it is to be appreciated that the moulded plastic product with embedded magnet may comprise other desirable plastic objects, such as, but not limited to picture frames, keyrings, plastic signage, magnetic car number plates and sales signage, plastic mountable utensils, and the like.

In one embodiment, the moulded plastic product comprises a magnetic fixing such as, but not limited to, magnetic fixings for notice boards, games score boards, board game pieces and the like.

A further aspect of the present invention provides a moulded plastic product comprising a plastic moulding fused to an at least partially embedded magnetised magnet. Such a moulded plastic product may be manufactured using a method according to a first aspect of the present invention.

Preferable, the moulded plastic product comprises a fridge magnet. However, it is to be appreciated that the moulded plastic product with embedded magnet could comprise any other desired product, as previously described.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a prior art fridge magnet in accordance with a first embodiment of the present invention;

Figure 2 is a cross-sectional view of the prior art fridge magnet of figure 1;

Figure 3 is a plan view of an embodiment of a plastic moulding produced by a method according to a first aspect of the present invention;

Figure 4 is a cross-sectional view of the embodiment of figure 3;

Figure 5 is a cross-sectional view of a mould arrangement for producing the plastic moulding of figure 3, with the mould in an open configuration; and

Figure 6 is a cross-sectional view of the mould arrangement of figure 5 in a closed configuration.

DETAILED DESCRIPTION OF THE INVENTION

Figures 1 and 2 illustrate a prior art fridge magnet 10 having a plastic body 20 with a front surface 22 and a rear surface 24. Magnet 30 is attached to the rear surface 24 of plastic body 20 by means of adhesive layer 40.

During manufacture, the plastic body 20 is created by any suitable means. In this example, plastic body 20 is prepared by injection moulding. However, any other suitable manufacturing means may be employed including, but not limited to die-cut plastic, card, wood or metal sheet material. Adhesive layer 40 is then applied to the rear surface 24 of plastic body 20 post moulding, and the front surface 32 of magnet 30 placed in contact with adhesive layer 40 such that adhesive layer 40 is located between the front surface 32 of magnet 30 and the rear surface 24 of plastic body 20. Once the adhesive layer 40 has cured, the magnet 30 is securely held in adhesive contact with plastic body 20.

Adhesive layer 40 can be provided using any suitable adhesive. However, adhesive layer 40 is typically provided by adhering a first surface of conventional double sided self-adhesive material or sticky pad 40 of suitable dimensions to the rear surface 24 32 of the magnet 30. Magnet 30 is then adhered to the plastic body 20 by adhering an opposing surface of self-adhesive material or sticky pad 40 to the rear surface 24 of plastic body 20 such that double sided sticky pad 40 is located between the rear surface 24 of plastic body 20 and the rear surface 32 of magnet 30.

However, there are several drawbacks to this method of manufacture and the resultant fridge magnet quality. The method of manufacture requires significant manual input to locate a first surface 42 of the double sided sticky pad 40 on the rear surface 24 of plastic body 20 and then subsequently expose the opposing sticky second surface 44 of double sided sticky pad 40 and locating magnet 30 in place on the second surface 44 such that the double sided sticky pad 40 is located between the plastic body 20 and the magnet 30, thereby adhering the magnet 30 to plastic body 20. This level of manual input limits productivity and increases manufacturing costs. In addition it is difficult and time consuming to accurately place the magnets on the moulding.

Further, although the magnet 30 may initially be securely adhered to the rear surface 24 of plastic body 20, over time or subsequent immediate environmental conditions, the adhesive can fail and the magnet 30 ultimately become detached from the plastic body 20. For example, the heat and humidity of the kitchen environment may cause the adhesive of the sticky pad 40 to fail, and the plastic body 20 to detach from magnet 30 with resultant potential damage to the plastic body as it detaches from the magnet 30 and falls from the fridge to the floor.

A further disadvantage of such an arrangement is that the magnet 30 and adhesive layer (or sticky pad) 40 inherently add to the thickness of an object 10, such as a fridge magnet or the like. This can result in a product 10 that is thicker than desired and projects and undesirable amount from the surface to which it is attached in a non-aesthetically pleasing manner.

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An alternative method of construction of a conventional prior art fridge magnet comprises an adhesive layer laminated directly to the magnet. To assemble the fridge magnet, a protective strip has to be removed from the surface of the magnet and the magnet carefully located in place on the plastic body and pressure applied to push the magnet and plastic body into firm adhesive contact with one another. Although such a construction can result in a fridge magnet of lesser width than that constructed using double sided sticky pads, the same problems occur with respect to manual requirement during production and failure of the adhesive layer in humid or hot conditions.

Figures 3 and 4 show a first embodiment of an object, in this case a fridge magnet 10, produced using a method according to a first aspect of the present invention.

Although figures 1 and 3 look similar, it is clear from the cross-sectional views of figures 2 and 4 clearly show the differences between the present invention and the conventional prior art. The same reference numerals have been used to indicate similar features for the purposes of comparison.

Plastic body 20 comprises a first front surface 22 and a second opposing rear surface 24 having a recessed portion 50. Recessed portion 50 has a surface 52 in contact with rear surface 32 of magnet 30. A magnet 30 is located within and fused to the surface of recessed portion 50. Thus, magnet 30 is permanently attached to plastic body 20, does not add to the thickness of the final fridge magnet and cannot therefore detach from plastic body 20, even in hot or humid environments.

The present invention provides a method of production of a product such as a fridge magnet 10 as shown in figures 3 and 4. Such a method involves injection moulding of the plastic body 20 of the fridge magnet 10 around a magnet 30.

A mould 54 is provided comprising multiple portions defining a cavity 56 into which hot plastic may be injected during an injection moulding process. At least one portion of the mould 54 comprises a metal material. A magnet 30 comprising a ferrite material and thermoplastic binder and having appropriate dimensions to attach to an inner surface 58 of at least one portion of the mould 54 is introduced into the cavity 56 and located adjacent to an inner surface 58 of at least one metal portion of the mould 54. It will be appreciated that the magnet 30 is held in place under magnetic attraction to the metal mould portion 54. In addition, locking studs 60 may be present on the mould cavity surface 58, located so as to press on the magnet 30 ensuring the magnet 30 does not move when the semi molten plastic is injected around the magnet 30 under high pressure.

Hot plastic is injected into the mould 54 via one or multiple injection holes (not shown) to fill the space defined by the cavity 56 and magnet 30. This plastic would normally consist of typically clear or coloured thermoplastic material such as, but not limited to, one or more of Polystyrene, ABS, Styrene-Acrylic-Nitrile (SAN), Polypropylene. However, it is to be appreciated that any suitable similar thermoplastic material injected under pressure and temperature conditions experienced in the injection moulding process may be used. The temperature conditions used in the injection moulding process are typically 120 to 300 °C. After injection of the thermoplastic material, the mould 54 (and contents) are allowed to cool before the resultant moulded product 10 is removed from the mould 54.

During the injection moulding process, the high temperature of the injected hot plastic is sufficient to melt the thermoplastic binder at the surface of the magnet 30 while in contact with the hot injected plastic. This mixing of the two melted plastics at the surface of the magnet 30 results in fusion of the plastics to one another on cooling, thereby permanently fixing the magnet 30 in place within the moulded plastic product 10.

The resultant fridge magnet 10 comprises a plastic body 20 having a permanently embedded magnet 30 which will not become detached under environmental conditions such as high temperature or humidity and will not detach over time due to adhesive failure as is the case with conventional prior art fridge magnets.

It is to be understood that the example provided is a fridge magnet. However, as previously described, the moulded product may comprise any suitable plastic product containing an embedded magnet, provided it can be made as described in the above example.

Although aspects of the invention have been described with reference to the embodiment shown in the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiment shown and that various changes and modifications may be effected without further inventive skill and effort.

Claims

1. A method of securing a magnet to a plastic moulding, the method comprising the steps of:

a. Providing a magnet comprising a body composed of a ferrite material and a thermoplastic binder, wherein the magnet body has an outer surface and wherein the magnet body has a first magnetised surface;

b. Providing a mould body, the mould body comprising first and second portions, wherein each portion has a first outer surface and a second inner surface, each portion being operable to be engaged with the other such that the respective inner surfaces define a mould cavity, and wherein the first portion comprises a metal material;

c. Locating the first magnetised surface of the magnet within the cavity adjacent the inner surface of the first portion;

d. Injecting hot plastic at a temperature sufficient to melt the thermoplastic into the mould cavity around the magnet; and

e. allowing the hot plastic to cool to form a moulded product comprising a plastic moulding bonded to the magnet body.

2. A method according to claim 1, wherein the second portion of the mould body comprises a metal material.

3. A method according to claim 1, further comprising the step of removing the plastic moulding from the mould body.

4. A method according to any preceding claim, wherein the thermoplastic material comprises one or more of Polystyrene, Styrene-Acrylic-Nitrile (SAN), and Polypropylene.

5. A method according to any preceding claim, wherein the temperature of the hot plastic is in the range of from 100 to 300 °C.

6. A method according to any preceding claim, wherein the magnet is fused to the plastic of the moulded plastic product.

7. A method according to any preceding claim, wherein the moulded plastic product comprises a fridge magnet.

8. A method according to any preceding claim, wherein the moulded plastic product comprises a magnetic fixing.

9. A moulded plastic product comprising a plastic moulding fused to an at least partially embedded magnetised magnet.

10. A moulded plastic product according to claim 9, wherein the moulded plastic product comprises a fridge magnet.