GB2236071A

GB2236071A - Toothbrush with liquid-crystal timer

Info

Publication number: GB2236071A
Application number: GB9020076A
Authority: GB
Inventors: Mark Fairhurst
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-09-15
Filing date: 1990-09-14
Publication date: 1991-03-27
Also published as: GB8920988D0; GB9020076D0

Abstract

A toothbrush (1) has a handle (5) incorporating liquid crystal material (7) which undergoes a reversible visible colour change when passing from one to the other of first and second temperatures, the lower of which is at least 25 DEG C, and is so located that the change is induced by heat from the user's hand and gives an indication of the duration of brushing. <IMAGE>

Description

A TOOTHBRUSH This invention relates to toothbrushes and in particular, but not exclusively, to toothbrushes for children.

In order to encourage children to use toothbrushes for dental hygiene, manufacturers have devised methods of making toothbrushes more appealing for children to use.

This has led to the development of toothbrush handles bearing designs of, or being configured to the shape of, animals, cartocn characters or the like.

An aim of the present invention is to provide a novel type of toothbrush having a handle incorporating a display means which changes its display when heated, e.g. by being he'd in the hand for a period of time.

According to the present invention a toothbrush comprisins â handle incorporating a display means, is charac terised in that the display means comprises liquid crystal material which undergoes a reversible visible colour change when passing from one to the other of first and second temperatures, the second temperature lying within a given temperature range having a minimum temperature which is greater than said first temperature and which is at least 2500.

The said minimum temperature is deliberately selected to be above the normal room temperature of the room in which the toothbrush is intended to be used and the said given temperature range is intended to include all normal temperatures that the liquid crystal material would be expected to be heated to on a user manually holding the handle of the brush for a period of time. Thus the display provided by the display means is intended to change when the user either heat the handle by picking it up and holding it for a period of time or allows the handle to cool by releasing the manual grip so that the handle is then able to cool from the hand-heated temperature to room temperature over a short period of time.

Preferably the handle of the toothbrush is made of transparent plastics material, e.g. thermoplastics material, in which the liquid crystal material is completely surrounded or embedded, any change in the display being visible through the plastics material. The rate at which heat is transferred between the handle surface and the embedded liquid crystal material depends on the depth that the liquid crystal material is positioned or embedded in the plastics material cf the handle, the difference In temperature between the handle surface and the liquid crystal material and the thermal conductIvIty of the handle material (and of any other material between the handle surface and the liquid crystal material).Conveniently, the toothbrush is deliberately designed so that there is a specific time delay, typically of from 10 te 40 seconds, for example about SO seconds, before the display changes after a user picks up and tightly holds the handle of the toothbrush (assuming that the liquid crystal material is initially at a typical room temperature of 20.= C and the user's hand skin temperature is 34.DC - j,2. an initia' temperature difference of about 13or). Typically such a time delay is achieved by embedding liquid crystal material approximately lmm below the surface of a polypropylene handle.Other typical handle materials are polyester, polyamide or polystyrene materials and the depth of posi- tioning the liquid crystal material within the handle can be adjusted to match the thermal conductivity of the handle material so as to achieve a desired time delay for any given initial temperature difference between the liquid crystal material and the user's hand skin temperature. The advantage of having a time delay between the time that the handle of a toothbrush is gripped and the time that the display changes is that the display twill only change if the toothbrush handle is held for a certain length of time.

Thus children are encouraged to hold or use a toothbrush for a specific length of time - i.e. at least until the display changes - thereby encouraging dental hygiene.

Children can also provide proof in a simple manner to an overseeing parent or other person that he or she has held the brush for at least a specific period of time.

Various types of temperature responsive licuid crystal material well known to persons skilled in the art may be used for the display means. Preferably, however, the temperature responsive liquid crystal material is ther- mochromic, displaying so-called "colour play' (,.e. a reversible change of colour through a range of cclcurs) over a predeterminêd colour play temperature range and appearing opaque, e.g. black, at temperatures above and below the colour play temperature range. In this case the predetermined colour play temperature range ccnver.iently is the same as the said given temperature range, the said minimum temperature preferably being at least 2s00, e.g.

290C, and the colour play temperature range typically being from 290C to 400. Alternatively, but less preferably, the liquid crystal material may be of the type which is normal ly opaque, e.g. green when backed with a black backing layer, at temperatures immediately below the said minimum temperature but which clears at the said minimum temperature (i.e. the clearing point) and remains transparent at temperatures immediately above the clearing point.

Typically the liquid crystal material is in the form cf an "ink" of microencapsulated droplets of liquid crystal material which is conveniently printed, e.s. silk screen printed, on a carrier layer, e.g. of plastics material.

The liquid crystal material may be provided on a single carrier layer or sandwiched between two carrier latters. In the case where the, or one of the, carrier layer(s) is positioned between the liquid crystal material and the side of the handle from which the display is to be viewed, the carrier layer in question will be transparent. A contrasting backing layer, e.g. of printing "ink", will normally be arranged behind the liquid crystal material.

Conveniently the handle is moulded around the liquid crystal material, the latter suitably being carried cn a carrier layer. Alternatively, however, a recess may be formed In the handle in which a closure member is fixed, e;g. adhesively or by a snap-fit. In this case, the closure member may carry the liquid crystal material or the closure member ma; clamp the liquid crystal material, carried on a carrier layer, against the bcttom of the recess.Another less preferred alternative is for the liquid crystal material and carrier member merely te be adhered to the handle, e.g. within a handle recess, but to have ne handle material covering the liquid crystal material and carrier member. In all designs the liquid crystal material is protected from being contacted by water by the surrounding handle material and/or by cther means, e.g. a water-impermeable carrier means.

The liquid crystal material, on colour change, may be arranged to display any convenient design, e.g. a pictorial design, such as a cartoon character or the like, andíor writing.

An embodiment ef the invention will now be described, by way of example, with particular reference to the accompanying drawing, in which Figure 1 is a schematic perspective view of a toothbrush according to the invention in a partly assembled condition, and Figure 2 is a sectional view, cn an enlarged scale, of the end of the handle of the toothbrush showr in Figure 1.

Figure 1 shows a partly assembled toothbrush, generally designated by the reference numeral 1, comprising a head 2 having bristles 3 extending from a head part 4 and a handle 5. The head part 4 is integrally formed with the handle 5 and 15 made of any suitable non-toxic, clear, plastics material, e.g. an easily washable, high temperature resis tant thermoplastic material. Preferably the toothbrush should have smooth surfaces with no ridges for trapping food particles.

The end cf the handle 5 has a closed slot 6 formed therein in which a strip 7 of material incorporatIng ther- mochromic liquid crystal material is inserted :Figure 1 shows the strip 7 only partially inserted in the slot 6).

When the strip 7 is fully inserted in the sot 6. the end cf the handle is closed by a plastics closure member 8 adhered to the end of the handle 5 to provide â waterproof seal for protecting the strip 7. The strip 7 is typically embedded approximately 1mm beneath one of the surfaces of the handle 5 and forms a close fit with the surrounding slot 6.

The strip 7 typically comprises a backing layer of plastics material on which is coated an opaque backing ink and a layer of printed thermochromic liquid crystal material. The liquid crystal material is intended to undergo a reversible change of colour when heated by a user holding the handle so that the hand skin temperature heats the liquid crystal material, after a suitable time delay of typically about 30 seconds, past a critical temperature.

This critical temperature is chosen to be above normal room temperature and below a person's hand skin temperature. In practice the critical temperature should be at least 250 C, e.g. 2900. The liquid crystal material may exhibit colour play in excess of the critical temperature, e.s. from 29 OOC and is conveniently printed in the form of a cartoon character or the like.

Claims

1. A toothbrush comprising a handle incorporating a display means, characterised in that the display means comprises liquid crystal material which undergoes a rever- sible visible colour change when passing from one te the other of first and second temperatures, the second temperature lying within a given temperature range having a minimum temperature which is greater than said first temperature and which is at least 250 C.

2. A toothbrush according to claim 1, in which the said mizen temperature range is intended to include all normal temperatures that the liquid crystal material. is expected to be heated to on a user manually holding the handle of the brush for a period of time.

3. A toothbrush according to claim 1 or 2, in which sad handle is made of transparent plastics material and the liquid crystal material is completely surrounded or embedded therein, any change in the display being visible through the plastics materIal.

4. A toothbrush according te claim 3, desIgned so that there is a specific time delay of from 10 to 40 seconds before the display changes after a user picks up and tightly holds the handle of the toothbrush.

5. A toothbrush according to claim 3 or 4, in which the said liquid crystal material is embedded approximately lmm below the surface of the handle which is made of poly- propylene.

6. A toothbrush according to any of the preceding claims, in which the said handle is made of polypropylene, polyester, pclyamide or polystyrene materials.

7. A toothbrush according to any of the preceding claims, in which the temperature responsive liquid crystal material is thermochromic, displaying "colour play" over a predetermined colour play temperature range and appearing opaque at temperatures above and below the colour play temperature range.

8. A toothbrush according te claim 7, in which the said predetermIned colour play temperature range is the same as the said given temperature range.

9. A toothbrush according to claim 8, in which the said minimum temperature is at least 280C and the colour play temperature range is from at least 2800 to 4".

10. A toothbrush according t any of claims 1 to 6. In which the liquid crystal material is of the type which is normally opaque at temperatures Immediately below the said minimum temperature but which clears at the said minimum temperature and remains transparent at temperatures immediately above the clearing point.

11. A toothbrush according to any of the preceding claims, in which the liquid crystal material is in the form of an "ink" of microencapsulated droplets of liquid crystal material which IS printed on a carrier layer.

12. A toothbrush according to claim 11, in which the liquid crystal material is provided on a single carrier layer.

13. A toothbrush according to claim 11, in which the liquid crystal material is sandwiched between two carrier layers.

14. A toothbrush according to any of the preceding claims, in which the handle is moulded around the liquid crystal material.

15. A toothbrush according to any of claims 1 to 13, in which a recess is formed in the handle in which a closure member is fixed.

16. A toothbrush according to any of claims 1 to 13, in which the liquid crystal material is on a carrier member adhered to the handle.

17. A toothbrush according to any of the preceding claims, in which the liquid crystal material, on colour change, is arranged to display any convenient design.

18. A toothbrush constructed and arranged substantially as herein described with reference to, and as illustrated in, Figures 1 and 2 of the accompanying drawing.