Chalkless writing board

Sept 17, 1963

W. J. MCDONALD

CHALKLESS WRITING BOARD

Filed May 5, 1961

3,103,751

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United States Patent Office 3,103,751

Patented Sept. 17, 1963

3,103,751

CHALKLESS WRITING BOARD Wilfred J. McDonald, Trans Canada Hotel, Mattawa, Ontario, Canada

Filed May 5, 1961, Ser. No. 107,947

Claims. (Cl. 35—61)

This invention relates to writing boards and more particularly to a magnetic type writing board.

Slate or paper boards in black, green or other various suitable colours, commonly referred to as black boards, are the most common of the writing boards presently utilized. Markings are made thereon by sliding a stylus of chalk upon the surface whereupon a portion of the chalk lightly adheres to the surface of the board. This type of board is extremely dusty and dirty as will be apparent to those who have used the same.

A chalkless type of writing board is also known consisting of a backing sheet covered with a thin film of pressure-sensitive adhesive material, normally common sealing wax and a thin sheet of opaque material placed thereover. The opaque material is a colour contrasting to the backing material, and normally is attached at one marginal edge to the backing material. Marking on the board is made by pressing a rigid stylus against the opaque sheet and thereby adhering the opposite surface to the pressure-sensitive adhesive. This type of writing board normally wears out very rapidly, thus requiring frequent replacement.

Magnetic type writing boards have previously been proposed, for example, the type disclosed in U.S.P. 2,589,601, March 18, 1952; the present invention being directed to an improvement thereover.

. It is the principal object of the present invention to provide a relatively permanent type of writing board.

It is a further object of the present invention to provide a writing board whereby the writing may be neatly and easily erased therefrom.

A still further object of the present invention is to provide a reusable relatively permanent type of writing board which is easily and cheaply manufactured.

A still further object is to provide a writing board of the magnetic type wherein the markings are substantially uniform and of even intensity throughout.

The above objects and advantages are attained in a writing board consisting of a substantially rigid opaque sheet of material spaced from a backing sheet to define therebetween a chamber confining a plurality of metallic pins slidably mounted in apertures in the backing sheet and which pins are of a colour contrasting to the opaque she^t. Markings appear on the opaque sheet by drawing a magnetic stylus over the outer surface of the opaque plate and thereby attracting the pins to the inside surface of the plate. Adhesive forces between the pins and the plate will maintain the pins on the surface of the plate. In the preferred embodiment of the invention a gelatinous type of material is applied to the inside surface of the opaque plate thereby increasing the adhesive forces between the pins and the plate.

A further understanding of the invention may be had from, reading the following detailed description in conjunction with the accompanying drawing, illustrative of the preferred embodiment of the invention and in which: . FIGURE 1 is a vertical elevation view in partial section of a writing board constructed in accordance with the present invention and illustrating handwriting on the surface thereof,

FIGURE 2 is a vertical cross-sectional elevation taken along section 2—2 of FIGURE 1 and

FIGURE 3 is a cross-sectional view of a modified writing board.

Referring now to the drawings, shown therein is a writing board 10 consisting of a backing plate 11, a back peripheral spacer 12, a central plate 14, a front peripheral spacer 12α and a front plate 15 held in an assembled position as illustrated in FIGURE 2 as by a U-shaped molding 16 or other suitable means.

The plates 11 and 14 are made from a nonmagnetic material, preferably Lucite. The front plate 15 is a transparent, nonmagnetic plate, preferably ordinary plate glass, however any other transparent or translucent nonmagnetic material may also be used.

The spacer 12 is secured to one face of the backing plate 11 and also to one face of the central plate 14, by any suitable adhesive, adjacent their peripheral edges to hold the plates 11 and 14 in spaced relationship to define therebetween a fluid-confining chamber 17. It is to be understood that the plates may also be held in spaced relationship by other means, for example, walls integrally formed with the plate .11 adjacent to the peripheral edges thereof and projecting outwardly therefrom. The edges _2Q of these walls may be secured to the plate 14 by any suitable means, for example pressure sensitive adhesive.

The front plate 15 is similarly spaced from and secured to the opposite face of the plate 14 to define therebetween a fluid-confining chamber 18.

_2g A plurality of spaced apertures 19 extend through the central wall 14 to provide communication between the chambers 17 and 18, and preferably consist of a bore 19α extending partially through the centre plate 14, and a bore 19b (of smaller diameter than that of a bore 19α) 3θ extending through the remaining portion of the plate.

The junction of the bores 19α and b present a shoulder 19c, the purpose of which will become apparent later.

As illustrated in FIGURE 2, the centre plate 14 preferably consists of two sheets, 14α and b, laminated to 35 form a single plate. The bore 19α extends through the sheet 14α while the bore 19 b (preferably concentric with bore 19α) extends through the sheet 146.

Pins 20 of permanent magnetic material, having a north and south magnetic pole, are slidably mounted in 4θ the bores 19α. The pins 20 are of greater length than the distance between the plates 14 and 15 and shorter than the distance from the shoulder 19c to the nearest surface of the plate 15. This allows sliding movement of the pins on an axis transverse to the plane surfaces of 4₅ the plates.

The inside surface (that is the surface forming one wall of the chamber 18) of the plate 15 is covered with a thin coating of transparent gelatinous material thereby assisting in adhering to the tiny magnetic pins to the 50 inside surface of the plates.

The chambers 17 and 18 and the bores 195 and the portion 19α not occupied by the pins 20, are filled with a very opaque white, black or other suitably coloured liquid of low specific gravity.

'Markings appear upon the surface of the board as a magnetic stylus 28 is drawn over the outer surface of the plate 15, when the end of the stylus and the nearest end of the pins 20 are of opposite magnetic polarity. To erase the markings, the opposite polarity of the stylus is ₆₀ brought in near proximity to the glass and thus the magnetic repulsion force drives the pin away from the surface and into the bore 19 until it abuts against the shoulder 19c.

As the pins 20 slide in the bores 19α, the fluid flows 65 through the bore 19b and it will thus be readily apparent that the diameter of the bores 19b will affect the rate of movement of the pin. Effectively the bore 195 is an orifice and the laws governing fluid flow in orifices are applicable.

Erasure of the markings from the board may be accomplished by passing a mechanical vibrator over the outer surface of the transparent plate. The vibration

3,103,751 ³would mechanically dislodge the pins from the inside surface of the plate and slide, by gravity, into the apertures. Such vibrator may consist of a standard dimension eraser brush operated electrically or by any other convenient means.

While the preferred embodiment has been disclosed, many modifications will occur to those skilled in the art. While shown herein the device contains two fluid chambers 17 and 18, it will be apparent to those skilled in the art that the writing board may also consist of spaced plates 21 and 22 (see FIGURE 3) defining therebetween a chamber 23 filled with a suitable gas, for example air, or a low specific gravity fluid. In such construction, bores 24 (adapted to receive the magnetic pins 20) would not extend through the entire thickness of the plate when using a fluid, however, they may do so when using air as the dampening medium. In the latter instance, the diameter of the aperture opening to atmosphere would affect the dampening motion of the pin. It would be obvious that the amount of tolerance between the pin 20 and the bores 24 will also affect the dampening motion of the pins as they are slid inwardly into the bores 24 or outwardly therefrom. As previously explained, the bores 24 may project through the plate 22 when utilizing air as the dampening medium and in this instance, the diameter of the bore adjacent to the outer surface of the plate will be less than the portion of the bore in which the pins slide. Again the pins will be of some length greater than the distance between the plates and the tolerance of such amount that the pins when in their outermost position will be guided by the bores 24.

A writing board of the latter type may only be effectively used in a horizontal position while the type referred to with reference to FIGURES 1 and 2 will operate in either a horizontal or vertical position but preferably in a substantially vertical position. It must, however, be realized that to operate in a horizontal position, the adhesive force between the pin and the plate must be greater than the force of gravity acting upon the pin.

Many further modifications will occur to those skilled in the art but that to which protection is desired as secured by Letters Patent is as defined in the appended claims.