WO1991017872A1

WO1991017872A1 - Etching method, etching stencil and apparatus for manufacture of stencil

Info

Publication number: WO1991017872A1
Application number: PCT/GB1991/000737
Authority: WO
Inventors: Christopher John Boxall
Original assignee: Finch, William, Edward
Priority date: 1990-05-11
Filing date: 1991-05-09
Publication date: 1991-11-28
Also published as: AU7799791A

Abstract

A perforating unit for making a stencil comprises a pin holding plate (1) and a support plate (2), the pin holding plate (1) being movable up and down on guide pegs (6) secured to the support plate (2). The plates (1, 2) are provided with matching matrices of through holes (3). Springs (9) disposed around the pegs (6) urge the two plates (1, 2) apart. An intermediate plate (10) is located between the pin holding plate (1) and the support plate (2). A channel (11) for receiving a plastics strip to be perforated is defined between the intermediate plate (10) and the support plate (2). In use, pins (5) are held in the holes (3) in the pin holding plate (1). The pins (5) are arranged in a pattern in which the plastics stencil strip is desired to be perforated. A plastics strip is placed in the channel (11), and a platten is placed over the pin holding plate (1) and depressed so that the pins perforate the plastics strip to form a stencil. The invention includes the use of the stencil in the sandblasting of security indicia into vehicle windows.

Description

ETCHING METHOD, ETCHING STENCIL AND APPARATUS FOR MANUFACTURE OF STENCIL

The present invention relates to a method of etching indicia on to a substrate. The invention also relates to apparatus for making a stencil useful in the etching process. More particularly, the invention is concerned with etching vehicle registration numbers on to vehicle windows for security purposes.

The theft of cars is a serious and growing problem. One measure which has been adopted to combat car theft is to etch the car registration number into one or more, and preferably all, of the windows of a car. This makes it very inconvenient for criminal^'s to remove all identifying features from a stolen car, and helps the police to return stolen cars to their rightful owners.

Conventionally, such etching has been carried out chemically or by sandblasting. Chemical etching is largely the preserve of motorists who wish to do their own etching, using kits which can be purchased at any motorists' shop.

Chemical etching tends to produce a result which is not very neat and is somewhat unsightly. More seriously, the etching is very superficial and can be polished out. Chemical etching has thus not found favour with the owners of the more expensive models of car.

Car window etching is now also performed professionally by many garages and etching businesses. Professional etchers generally prefer to use sandblasting to etch car windows, because this technique permits deep etching which cannot be polished out. Such sandblasting etching is normally carried out in the United Kingdom to comply with the relevant British Standard, BS AU209, which specifies a minimum depth.

Whatever etching technique is used, it is necessary to employ a stencil bearing the car registration number. One known stencil employed with chemical etching consists of a self-adhesive plastics strip perforated by a computer-controlled perforating press; orders for strips bearing designated registration numbers are placed with the company operating the machine by customers, to whom the completed stencils are sent. The perforated plastics strips are adhered to car windows and have etching paste applied to them. The suppliers of these self-adhesive stencils recommend against their use with sandblasting.

A computer-controlled perforating press is very expensive and, of course, liable to break down.

Customarily, sandblasting etching has been performed using stencils comprising reusable plastics or brass stencils in which individual letters or numbers are punched out. Individual stencil plates are put in a carrier to form a whole registration number, the carrier is placed against a car window and a sandblaster is swept across the stencil.

Although economic, reusable stencils quickly become worn and etching performed using such stencils is frankly a mess. Such etching has thus not proved popular, especially when applied to more expensive cars.

Many car manufacturers etch registration numbers on to the windows of new vechicles or have the numbers etched on by their retail agents. It is reported that, despite trying a number of different etching techniques such manufacturers receive tens of complaints per week each in the UK regarding the quality of the etching.

Perforating presses are well known and, excluding computer-controlled or electronic machines, the present inventor is not aware of any perforating apparatus which can perforate a sequence of any combination of letters and numbers. One reason for this is the difficulty of accommodating numbers and letters of different widths. In particular, simple mechanical perforating units have hitherto allowed a fixed space for each digit irrespective of the width thereof; obviously, the letters "W" and "I" are normally substantially different in width and a very unattractive appearance results if the space allocated to each digit is not adjusted accordingly.

There therefore exists a need for a system for etching registration numbers on car windows which is neat and does not require the use of expensive apparatus. It would also be desirable to provide means for etching security or other indicia on to other substrates than car windows cheaply, effectively irremovably and neatly; any such means should desirably be sufficiently flexible to etch any desired sequence of letters and numbers on to a substrate.

In one aspect therefore, the invention lies in the use of a perforated stencil for the sandblasting of vehicle registration numbers on to vehicle windows for security purposes. The stencil is preferably a perforated plastics strip. More generally, the invention includes a method of sandblasting indicia into a substrate in which a perforated stencil bearing the indicia is used. The present invention also provides a perforating unit for making a perforated stencil. The unit preferably comprises a first plate through the thickness of which passes a matrix of holes to guide perforating pins. The unit also has a second plate containing a matrix of holes matching the matrix in the first plate. The plates lie spaced apart, superposed one above the other, such that the holes in one plate are aligned with the holes in the other. The plates are movable towards and away from each other, between positions of lesser and greater spacing and are urged apart.

More generally stated, the perforating unit comprises a pin holder in which is defined a matrix of through holes for holding perforating pins, and a support for supporting material to be perforated, the support having defined therein a matrix of through holes matching the matrix in the pin holder, the pin holder and the support being arranged for movement relative to one another such that pins in the pin holder can be inserted into the holes in the support and then withdrawn, any material disposed over the holes being perforated by the pins as they move to enter the holes. The pin holder and the support are normally in the form of plates.

In normal use of the preferred unit, one of the plates, which can conveniently be designated the second plate or support plate, forms the bottom of the apparatus and is oriented more or less horizontally. The guide holes in the plates are thus oriented in a direction which is generally upward and the first plate is located above the support plate. Perforating pins are disposed in the guide holes in the first or pin holding plate, where they are held by stop means against downward movement through the guide holes; normally, the pins are held by means of enlarged pinheads which cannot enter the guide holes. The pins are arranged in some desired pattern, e.g. in the form of a vehicle registration number. A strip or sheet of material, e.g. plastics material, is supported on the upper face of the bottom support plate. The pin holding plate and the perforating pins are depressed so that the pins perforate the strip or sheet and their ends pass into the guide holes in the support plate, as does the waste material. The pin holding plate is then allowed to move back to its starting position and retract the perforating pins. The perforated strip or sheet is then removed.

The plates may conveniently be held relative to one another by guide means provided on one plate and engaged with the other for sliding movement therewith. Preferably, the guide means comprises a plurality of pegs, normally three or especially four pegs being used. At one end, the pegs are firmly secured to one of the plates, usually the second plate, for example by screw fitting. The other plate is provided with through holes which snugly receive the pegs for sliding of the plate along the pegs towards and away from the plate to which the pegs are secured. The free ends of the pegs may be enlarged, as for example by the use of a cap, to act as a stop to prevent the free plate escaping the pegs.

The perforating unit desirably comprises means to prevent the strip or sheet from moving with the pins when they are retracted after perforating the strip or sheet. The means normally comprises stop means between the pin holding and support plates and dedirably forms, with the support plate, a channel between the stop means and the support plate in which the sheet or strip may be slidingly received and its movement controlled. Preferably, the stop means is in the form of an intermediate plate superposed over the support plate. The intermediate plate and the support plate define therebetween a channel to receive the strip or sheet and desirably to control its movement. In one embodidment, the channel is formed by spacing the plates from one another by the use of spacer means between them. In another embodiment, a shallow groove extends from an edge of the intermediate plate in its face which faces the support plate, raised shoulders being defined on either side of the groove. The shoulders abut the support plate. The channel to receive the strip or sheet is defined by the side and bottom walls of the groove and by the area of the support plate opposed to the groove. The intermediate plate must, of course, allow passage of the perforating pins therethrough; to this end, it may be provided with a matrix of holes matched and aligned with those in the first and second plates or, more simply, it may have the region through which the pins must pass completely removed. Provision of a matrix of holes in the intermediate plate helps guide the perforating pins. The intermediate plate may be secured to the support plate, e.g. by screws.

The first and second (pin holding and support) plates are suitably urged apart by resilient means arranged between the two. For example, a sheet of resilient foam rubber or plastics material may be arranged between the two; if the apparatus includes an intermediate plate, the resilient sheet or other resilient means may act through the intermediate plate and not bear directly on the second plate. As an alternative to a resilient sheet, one or more springs may be used; for example, in one embodiment the first and second plates are urged apart by coil springs arranged around pegs which guide the movement of the first plate as described above. The plates of the perforating unit are desirably made of metal, e.g. steel, brass or aluminium.

Strips or sheets perforated using the apparatus of the invention may be used as stencils for sandblasting etching, for example in etching vehicle registration numbers or other markings on to vehicle windows. Other suitable substrates may also be etched or marked with security markings by sandblasting or chemically, including house and office contents, such as furniture or electronic equipment. For example, plastics substrates may be marked using a paste containing a solvent for the plastics material and a colouring material. The paste is placed over a stencil (preferably made using the perforating unit of the invention) and, after an elapse of time, the colouring material becomes incorporated in the substrate in the pattern carried by the stencil; this method of marking is included in the invention.

The first or pin holding plate and the perforating pins may be depressed by use of a platten, for example of a mechanical press.

The perforating unit may be sold in a kit comprising the unit and perforating pins, and optionally plastics strip or sheet for use therewith. The kit may further include sandblasting apparatus.

The invention includes the use of a perforating unit of the invention in the preparation of an etching stencil and also the etching or marking of a substrate using a stencil prepared using a perforating unit of the invention. The method of marking a substrate comprises placing material to be perforated on the support therefor; before or after so placing the material, locating pins in the pin holder; moving the pin holder and the support together such that the pins perforate the material; moving the pin holder and support apart or allowing them to move apart; removing the perforated material; placing the perforated strip or sheet on the substrate as a stencil; and applying etching or marking material to the stencil such that the substrate is etched or marked in a pattern corresponding to the pattern of the perforations.

The present invention is further described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a side view of a perforating unit according to the invention; and

Figure 2 is an exploded view of the perforating unit of Figure 1.

Referring now to the Figures there is shown a perforating unit comprising a first (pin holding) plate 1 and a second (support) plate 2. The first plate 1 lies above the second plate 2 in superposed relationship thereto, but spaced apart therefrom. In the illustrated embodiment, both plates are made of a metal such as brass or anodized aluminium, for example. In the first plate 1 there is formed a matrix of holes 3 passing through the thickness of the plate 1. In the illustrated embodiment the holes 3 are arranged regularly in parallel rows, with each hole equidistant from its nearest neighbours, but the invention is not restricted to such an arrangement. Each hole is suitably 0.5 to 1.5 mm from its nearest neighbours. The matrix of holes is suitably located in a central area of the plate 1. In the illustrated embodiment the matrix comprises an array of 5 x 40 holes. The holes 3 act as guide holes for perforating pins 4 whose function is to perforate material put in the press. For clarity, the pins 4 are not shown in Figure 2. Stop means is provided to prevent the pins 4 falling through the holes 3; the stop means may conveniently be provided by enlarged * heads 5 on the pins, which heads are too big to pass through the holes 3. It can be seen in the Figures that the guide holes 3 and, when present, pins 4 are oriented perpendicularly to the plate of the first plate 1.

A matching matrix of through holes is provided in the second plate 2; the holes in the second plate 2 are aligned with those in the first plate 1.

The unit is constructed to permit relative movement of the first 1 and second 2 plates toward and away from each other, between positions of lesser and greater separation. This construction may conveniently be achieved by arranging for one plate e.g. the first plate 1, to be in sliding engagement with guide means, for example two or more pegs, extending from the other plate; stop means is preferably provided to prevent the slidable plate disengaging from the guide means.

In the illustrated embodiment, the guide means is constituted by four pegs 6, extending perpendicularly from the major face of the second plate 2 which faces the first plate 1. Whilst it is not essential for there to be four guide pegs 6, it is preferred for three or four pegs 6 to be used. The pegs 6 need to be fixed firmly to the second plate 2, and we have found it convenient to screw the pegs 6 into threaded holes (not shown) in the second plate 2. The pegs 6 are slidingly received in guide channels or holes 7 in the first plate 1. The free ends 8 of the pegs 6 may be provided with a screw cap or otherwise provided with an enlarged cross-sectional area to form stop means to prevent the first plate 1 becoming disengaged from the pegs 6.

Resilient means is provided to urge the first 1 and second 2 plates apart. The resilient means may be one or more springs, for example coil springs 9, which in the illustrated embodiment are to be seen arranged around the pegs 6. It is also possible to use a pad of resilient foam plastics or rubber material between the two plates 1 and 2 as the resilient means, so long as it does not interfere with the functioning of the perforating pins 4.

An intermediate plate 10 is disposed between first plate 1 and the second plate 2. A channel 11 for receiving material to be perforated is defined between the intermediate plate 10 and the second plate 2. In one embodiment, the channel 11 is formed by spacing the intermediate plate 10 from the second plate 2 by spacer means between the two; for example washers may be provided at the bases of the pegs 6.

In the illustrated embodiment, the channel 11 is defined between the second plate 2 and a groove 12 formed in the bottom surface of the intermediate plate 10. The groove 12 extends between opposed edges of the intermediate plate 10, whereby it and hence the channel 11 are open at each end. Raised shoulders 13, 13a are defined on either side of the groove 12 and are seated on the second plate 2. In effect, therefore, the shoulders 13, 13a act as spacers to separate the bottom face of the intermediate plate 10, represented by the floor 14 of the groove, from the second plate 2. In use, perforating pins 4 are placed in the guide holes 3 of the first, pin holding plate 1 in some desired pattern, for example to form a vehicle registration number. The present inventor has found pins with a diameter of 3/64 inch (1.19 mm) to be satisfactory, but the pin size is not critical so long as the lower ends are spaced above the second or support plate 2 by a distance greater than the thickness of the material to be perforated when the press is in the rest position. A strip or sheet of material to be perforated, e.g. plastics strip, is laid on the top surface of the support plate 2.

In the illustrated embodiment, the material to be perforated is inserted into the channel 11 between the intermediate plate 10 and second plate 2. The shoulders 13, 13a guide the material into the correct position over the matrix of holes, but guides are not essential. However, the channel 11 between the intermediate plate 10 and the second plate 2 is preferably provided with guide means to help locate the material to be perforated and to help restrain it against movement.

The perforating pins 4 are then depressed, by downwardly applying a suitable platten means on to the pinheads 5. The pins pass through the material laid on the support plate 2 and into the guide holes in the plate, whereby the material is perforated with a pattern of holes corresponding to the pattern of the pins 4.

The platten means is finally raised to allow the first plate 1 to be urged upwards to its rest position. The pins 4 follow the first plate 1 and are retracted, so that the perforated material can be removed from the unit. The intermediate plate 10 holds down the perforated material and prevents it being taken up by the retracting pins. In perforating units without an intermediate plate, it is preferred to provide stop means to prevent perforated material being retracted with the pins, so that the pins can be freed from the material.

The pins 4 are desirably blunt-ended punch pins, manufactured to withstand repeated punching. The platten means is normally part of a mechanical press e.g. a screw press.

It takes an operator with modest experience no more than two and a half minutes to manually place the perforating pins 4 in the guide holes 3 in the pattern of a vehicle registration number. Car sales outlets in the UK are provided with a 'block' of sequential registration numbers to allocate to the cars they sell; thus in such an organisation it would normally be necessary to change only one or two digits of an existing registration number when preparing to make a stencil to etch the windows of a car before it is delivered to a customer. In these circumstances, it takes only a few moments to arrange the pins into a new registration number.

The perforating unit can therefore be operated quickly by persons who do not have to undergo special training; moreover purchase of a perforating unit of the invention does not involve substantial capital expenditure, and any garage or vehicle sales organisation or professional vehicle window etcher can readily afford to buy one. Never before has stencil preparation apparatus been available in practice to such people. One advantage of the perforating unit is that the space between adjacent digits can be the same in all cases, i.e. the width allotted to each digit can be adjusted in accordance with the width actually occupied by the digit. The result is aesthetically pleasing compared with arrangements in which the space allotted to each digit is fixed, irrespective of the width of the digit itself. To put it another way, in the present invention the positions of the digits can be shifted to the left or right at will within the matrix.

The plastics strip used as the stencil may be made of nylon, for example. It is preferably self-adhesive, to facilitate holding the stencil on a substrate.

The perforated strip is placed over the substrate to be etched or marked and the indicia perforated in the strip are etched or marked in the substrate by suitable means. Normally, the etching will be performed using an etchant paste or a sandblaster. The use of such a perforated strip as a stencil in the sandblasting etching of vehicle windows or other substrates is believed to be novel.

In the case of vehicle windows, sandblasting is much preferred to chemical etching, since it results in deep etching which cannot be polished out and in an appearance which is attractively neat. Indeed, the etching can be used to enhance the appearance of a vehicle by colouring the individual holes of the etching with paint. The paint may be placed in the holes by spraying it over the stencil in position over the etching; alternatively, the etched area can be painted after removal of the stencil and the surface paint immediately removed by wiping with a blade or cloth, for example. Any suitable abrasive material or 'sand' may be used to perform the sandblasting, but aluminium oxide sand has been found preferable.

When vehicle windows are to be etched, it is convenient to perforate simultaneously a number of plastics strips in a stack. In this way, a fresh stencil can be used for each etching while only one perforating operation is required. The number of strips in the stack may be equal to the number of windows in the car concerned. A stack of eight strips is sufficient to etch all the windows of most cars, but more strips can be used for cars with a greater number of windows or if it is desired to etch the mirrors or glass light covers. A stack of self-adhesive strips may be used, each strip being adhered to the one below. Of course, simultaneous perforation of a plurality of strips or sheets can be used in any circumstances where the same indicia are to be etched or marked a plurality of times.

Claims

1. A perforating unit comprising a pin holder in which is defined a matrix of through holes for holding perforating pins, and a support for supporting material to be perforated, the support having defined therein a matrix of through holes matching the matrix in the pin holder, the pin holder and the support being arranged for movement relative to one another such that pins in the pin holder can be inserted into the holes in the support and then withdrawn, any material disposed over the holes being perforated by the pins as they move to enter the holes.

2. A perforating unit as claimed in claim 1, wherein the pin holder and the support are in the form of plates, the plates being arranged for movement into and out of a position in which they are superposed and in which any pins in the pin holder plate extend into the holes in the support plate.

3. A perforating unit as claimed in claim 2, wherein the plates are in superposed relationship and are arranged for relative movement towards each other into the position in which any pins in the pin holder plate extend into the holes in the support plate or away from each other, and the unit further comprises resilient means to urge the plates apart.

4. A perforating unit, comprising two plates in superposed relationship and arranged for relative movement towards and away from each other, and resilient means to urge the plates apart, each plate having a matrix of through holes which extend between its opposed major faces, the matrices in the two plates being matched and the holes in each plate being aligned with those in the other, in use the holes in one of the plates being perforating pin guides to hold pins to perforate material supported on the face, facing the one plate, of the other plate.

5. A perforating unit as claimed in claim 3 or claim 4 wherein one of the two plates is provided with guide means with which the other is slidingly engaged, to guide the movement of the engaged plate towards and away from the other plate.

6. A perforating unit as claimed in claim 5, wherein the guide means comprises two or more pegs secured to the plate provided with the guide means and extending perpendicularly from the face of this plate which faces the other plate, the pegs being slidingly received in holes in the other plate.

7. A perforating unit as claimed in claim 5 or claim 6, wherein the guide means is provided with a stop to prevent disengagement of the slidable plate from the guide means .

8. A perforating unit as claimed in any one of claims 3 to

7, wherein the resilient means comprises a spring or a pad of resilient material arranged between the two plates so as to bear directly or indirectly on them.

9. A perforating unit as claimed in any one of claims 3 to

8, wherein means are provided to hold down supported material with respect to the supporting plate face on which it is supported, so that in use, when the perforating pins retract after perforating the supported material, the material is not retracted with the pins.

10. A perforating unit as claimed in claim 9, wherein the holding means comprises an intermediate plate between the first and second plates and in superposed relationship to the supporting plate face, the intermediate plate and the supporting plate face defining a channel to receive material to be perforated and the intermediate plate being so formed that it does not interfere with the perforating pins in use.

11. A perforating unit comprising:

a support plate having a supporting face to support material to be perforated, two or more guide rods or pegs extending perpendicularly from the supporting face;

an intermediate plate engaged with the guide rods or pegs and in superposed relationship to the supporting face of the support plate, the intermediate plate and the supporting face of the support plate defining a channel to receive material to be perforated and the intermediate plate bearing directly or indirectly on the support plate;

a pin holding plate for holding perforating pins and slidingly engaged with the guide rods or pegs in superposed relationship to the intermediate plate on the other side thereof to the support plate; and

resilient means arranged between the pin holding plate and intermediate plate to urge the pin holding plate away from the intermediate and support plates;

the support plate and the pin holding plate each having a matrix of through holes extending across the thickness of the plate, the holes in the pin holding plate being guide holes to hold perforating pins, the matrices in the two plates being matched and the holes in each face being aligned with the holes in the other, and the intermediate plate and the resilient means being so formed and arranged that they do not interfere with the perforating pins in use.

12. A perforating unit as claimed in any one of claims 3 to 11, in which the pin guide holes are in generally upright orientation and at least some of the pin guide holes contain perforating pins, the pins having an enlarged head to stop them falling through the holes and their other ends being spaced from the volume which would in use be occupied by the material to be perforated.

13. A method of etching or marking a substrate using a stencil prepared using a perforating unit as claimed in any one of claims 3 to 12, comprising:

orienting the unit so that the matrix holes are in a more or less upright position with the pin guide holes generally above the aligned holes in the lower (support) plate;

inserting pins into at least some of the pin guide holes, stop means being provided to prevent the pins falling out of the guide holes;

before or after the pins are inserted, placing on the upper face of the support plate, above the hole matrix, a strip or sheet of material to form the stencil;

depressing the perforating pins so that they perforate the strip or sheet;

allowing the pins to retract under the action the resilient means urging the pin holding plate upwards;

removing the perforated strip or sheet from the unit;

placing the perforated strip or sheet on the substrate as a stencil; and applying etching or marking material to the stencil such that the substrate is etched or marked in a pattern corresponding to the pattern of the perforations.

14. A method as claimed in claim 13, wherein the material applied to the stencil is a chemical etching paste or abrasive material blasted against the stencil in a sandblasting process.

15. A method as claimed in claim 14 wherein the material applied to the stencil is abrasive material blasted against it in a sandblasting process and etched holes in the substrate are filled with paint or other colouring material, the surrounding substrate surface being cleaned of any colouring material which contacts it.

16. A method as claimed in any one of claims 13 to 15, wherein the substrate is a vehicle window or other glass article.

17. A kit comprising a perforating unit as claimed in any one of claims 1 to 12 and perforating pins and optionally plastics strip or sheet for use therewith and/or sandblasting apparatus.

18. The sandblasting etching of vehicle windows with security indicia, in which the stencil has been prepared using a perforating unit as claimed in any one of claims 1 to 12 or a method as claimed in any one of claims 13 to 16.

19. The use of a perforated stencil for the sandblasting of vehicle registration numbers into vehicle windows for security purposes.

20. A method of sandblasting a vehicle registration number or other indicia into a vehicle window or other substrate, wherein a perforated stencil bearing the indicia is used.

21. A method as claimed in claim 20, wherein the stencil is a strip of plastics material.

22. The use of a perforating unit to prepare a perforated stencil in a sandblasting etching process.