GB2133326A

GB2133326A - Blasting mask and method of making and using the same

Info

Publication number: GB2133326A
Application number: GB08334400A
Authority: GB
Inventors: Larry L Cooper; Philip G Saunders
Original assignee: Container Graphics Corp
Current assignee: Container Graphics Corp
Priority date: 1983-01-18
Filing date: 1983-12-23
Publication date: 1984-07-25
Also published as: GB2133326B; GB8334400D0

Abstract

The blasting mask can comprise a thin backing sheet (38) of polyester, and a layer (40) of polymerizable material affixed to the backing sheet and being of a predetermined size and shape. The blasting mask is preferably made by photographing a shape to be reproduced to form a negative. A blasting mask blank is then provided which comprises the backing sheet and a uniform layer of polymerizable material thereon. Ultraviolet light is shone through the negative onto the blank which polymerizes the material from a monomer to a polymer in the areas where it receives the ultraviolet light to harden it. The remaining material is washed away to leave bare spaces on the backing sheet. The resulting mask is adhered to grit- erodible material in which the shape is to be reproduced, and blasting grit is directed toward the grit-erodible material for a sufficient time to erode the erodible material to a desired depth. The blasting mask can be placed on the grit-erodible material with the backing sheet contiguous with the material or with the hardened material contiguous with the grit-erodible material. In the latter instance, the hardened material can be adhered to the grit-erodible material and the backing sheet peeled away from the hardened material. <IMAGE>

Description

SPECIFICATION Blasting mask and a method of making and using the same This invention relates to a blasting mask and to a method of making and using same.

A blasting mask in accordance with the invention comprises a thin backing sheet which can be of plastic, such as a polyester material, preferably Mylar, a registered trademark of DuPont, in the order of a few thousandths inch thick. A hardened layer of photosensitized material of predetermined size and shape is adhered to the backing sheet with the backing sheet being totally exposed or bare in those portions where the hardened material does not exist. The edges of the hardened material are substantially perpendicular to the backing sheet to provide clean lines for the blasting grit. The photosensitive material is converted from a monomer to a polymer by being exposed to triggering energy waves, preferably in the form of ultraviolet light.

In the method of making and using the grit blasting mask in accordance with the invention, a shape which is to be reproduced in grit-erodible material such as stone, wood, glass or plastic, is first produced on or placed against a suitable background and a photograph taken thereof to produce a suitable light-control sheet or negative.

A blasting mask blank is provided which includes a thin backing sheet preferably of polyester material such as Mylar in the order of a few thousandths inch thick. This backing sheet has a layer of photosensitive material thereon which is in a soft or even liquid state but portions of which become harder when subjected to ultraviolet light or other suitable triggering energy waves. The light is then directed through the negative to the blasting mask blank to cause the light to strike the photosensitive layer either within the area defined by the shape on the negative, if the shape is originally darker than the background, or in the background around the shape, if the original shape is lighter than the background.

The portion of the photosensitive layer which is not subjected to the light remains in its original relatively soft or liquid condition while the material struck by the light polymerizes and becomes harder. The unsensitized material can then be removed simply by washing it away with a solvent or liquid detergent. This material is removed completely to provide a bare surface on the backing sheet. The edges of the shape of the sensitized material are substantially perpendicular to the plane of the backing sheet, forming an abrupt offset therebetween to achieve a sharp, well-defined shape on the grit-blasted surface of the grit erodible material in which the shape is to be formed.

The now-completed blasting mask is placed on the surface of the grit-erodible material in the desired position. The backing sheet can be placed contiguous to t'- e surface but the harder sensitized material forming the shape can also be placed in contact with the surface. In either event, the blasting mask can be adhered to the surface with -a suitable adhesive to prevent shifting. Blasting grit, which can be in the form of silica sand, steel shot, or aluminum oxide, by way of example, is then directed toward the blasting mask which destroys the bare plastic backing sheet, while not having any significant effect on the polymerized photosensitive material. The blasting grit is then applied until the backing sheet is destroyed and the grit-erodible material is eroded to a desired depth.Particularly where the grit-erodible material is easily eroded by the blasting grit, the blasting mask can be placed with the harder sensitized material in contact with the surface and adhered thereto by a suitable adhesive. The backing sheet can then be peeled away and the blasting grit is then directed toward the surface as before.

However, with no backing sheet to be destroyed, the blasting grit can be directed with somewhat greater control toward the grit-erodible material.

This technique is particularly suitable for producing shapes in glass or mirrors including where select portions of the silver coating of the mirror are to be removed by blasting.

The new blasting mask and method enable more intricate designs or shapes, including even pictures, including photographs, to be reproduced in grit-erodible materiels, and smaller letters can also be formed than with the masks and the methods heretofore employed. The blasting mask can also be made much more quickly than heretofore when masks were usually hand cut or sometimes die-cut and then stripped by hand.

Particularly for more simple shapes, the masks can be used over again by placing the harder sensitized material forming the shapes on a new backing sheet to form a new blasting mask or directly on the surface of the grit-erodible material. In any event, the negative can be reused to form new blasting masks with a relatively small amount of time and labor involved.

It is, therefore, a principle object of the invention to provide an improved blasting mask and method for forming a desired shape in a grit erodible material.

Another object of the invention is to provide a blasting mask and shape-reproducing method having the advantages discussed above.

Many other objects and advantages of the invention will be apparent from the following detailed description of preferred embodiments thereof, reference being made to the accompanying drawings, in which: Fig. 1 is a somewhat schematic view in perspective of artwork in the form of a shape and background being photographed by a camera; Fig. 2 is an enlarged, schematic view in perspective of a negative, a blasting mask blank, and a light source for producing an image on the blank corresponding to the shape on the negative; Fig. 3 is a greatly enlarged view in trai7syerse cross section of the blasting mask blank, curter exposure, taken generally along the line 3-3 of Fig. 2;; Fig. 4 is a schematic view in section showing a grit blasting nozzle for directing grit toward the blasting mask located on the surface of a griterodible material; and Fig. 5 is a schematic view similar to Fig. 4 but showing the blasting mask on the surface of griterodible material in a different position.

Referring to Fig. 1, artwork, in the form of a shape or design 10, shown for purposes of illustration in the form of a cross, is drawn on or positioned against a plain background sheet 12. A thin border line 14 and a wider border line 16, with a space 1 8 therebetween, are located near the edges of the sheet. The cross preferably is drawn on the background sheet or can be a separate piece adhered to the background sheet or can be a separate piece spaced from the background sheet. A camera 20 is used to photograph the shape to produce a light-control sheet or negative 22 (Fig. 2) of the same size as the shape to be reproduced on the grit-erodible surface. A positive instead of a negative can also be made by using positive film.Negative, as used here, is intended in the broad sense to be film with an image thereon corresponding to the shape to be reproduced. The negative 22 can be produced by other techniques, too, such as by drawing the shape or design with an opaque substance on a light-transmitting sheet, by way of example, or using a silk-screen process. A negative produced by photography, however, provides a relatively easy way of producing a light-transmitting sheet with a shape thereon, wherein either the shape or the background area around the shape is lighttransmitting, depending upon which is to be eroded in the grit-erodible material in which the shape is to be reproduced.

A source 24 of triggering energy waves, such as an ultraviolet light, is then positioned on one side of the control sheet or negative 22 and a blasting mask blank 26 is positioned on the other side of the negative 22. The blank 26 is positioned in contact with the negative 22 to produce a shape of the same size as the negative 22, being spaced apart here for purposes of illustration.

In this instance, the negative 22 has a transparent or more light-transmitting area 28 corresponding in shape to the dark cross 10 of Fig. 1, and has an opaque or less light-transmitting area 30 around the area 28 corresponding to the light background sheet 1 2 of Fig. 1. The negative also has wider and narrower border lines 32 and 34 which are more light-transmitting, corresponding to the dark border lines 14 and 1 6 of Fig. 1 , with a space 36 therebetween, which is less light-transmitting or opaque.

The grit-blasting mask 26 comprises a thin backing sheet 38 (Fig. 3) of plastic material or even paper and a layer 40 of photo-sensitive material, preferably commercially-available photopolymer material. The backing sheet 38 can be of a polyester material such as Mylar and can have a thickness preferably from 0.0005 inch to 0.015 inch. The layer 40 of material is initially in a soft or liquid state on the backing sheet and is polymerized or more fully polymerized when subjected to triggering energy waves, commonly ultraviolet light. This layer preferably is from 0.003 inch to about 0.25 inch in thickness. The areas of the layer which are subjected to the ultraviolet light for a predetermined period of time become harder as polymers and remain on the backing sheet.The portions of the layer which do not receive the ultraviolet light remain soft or liquid as monomers and can be subsequently washed away by a suitable solvent or detergent.

The soft material in this instance is completely washed away to leave a bare surface on the backing sheet 38 so that it can be fully contacted and quickly worn away by blasting grit.

As shown in Fig. 3, a light-struck, harder area 42 of the photosensitive material converted to a polymer, shown cross-hatched, corresponds in shape to the area 28 of the negative 22. Outer thick and thin areas 44 and 46 correspond to the areas or lines 32 and 34 of the negative 22. A light-shielded, soft or liquid area 48 surrounding the harder area 42 corresponds to the opaque area 30 of the negative, the soft area remaining so as a monomer since it does not receive the ultraviolet light which is blocked out by the opaque area 30. Similarly, a thin outer area 50 between the areas 46 and 48 corresponds to the spacing 36 of the negative 22 and remains soft or liquid since it likewise does not receive ultraviolet light which is blocked out by the opaque area 36.

When the unpolymerized areas 48 and 50 are removed, the edges of the polymerized areas 42, 44, and 46 are substantially perpendicular to the plane of the backing sheet 38 to provide clean lines for producing the shape on the grit-erodible material.

The now-completed grit-blasting mask 52 can then be positioned on a body 54 of grit-erodible material such as stone, with the backing sheet 38 placed in contact or contiguous relationship with the surface of the body 54. The mask 52 is preferably adhered to the body 54 by suitable adhesive to prevent shifting under the force of the blasting grit. Blasting grit is then directed over the mask 52 such as by a suitable blasting nozzle 56.

The blasting grit erodes the bare backing sheet 38 while having substantially no effect on the polymerized areas 42, 44 and 46. The blasting grit is applied until the surface of the body 54 is eroded to a desired depth to complete the shape or design in the body. It will be seen in this instance that the dark cross 10 of Fig. 1 will remain as the flat surface on the body 54, under the hardened area 42, while the light background 12 and the space 1 8 will be eroded into the surface, leaving border lines flush with the surface of the body 54 corresponding to the hardened areas 44 and 46. A light cross 10 on a dark background 1 2 will produce the opposite result.

The completed grit-blasting mask 52 can also be positioned on the body 54 of grit-erodible material with the polymerized areas 42, 44, and 46 placed in contact or contiguous relationship with the surface of the body 54 with the backing sheet 38 spaced from the surface of the body. The mask 52 is preferably adhered to the body 54 by a suitable adhesive to prevent shifting by the grit.

The blasting grit is then directed over the mask, as before, to erode the bare backing sheet 38 while having substantially no effect on the polymerized areas 42, 44 and 46. The blasting grit is applied until the desired depth in the body 54 is reached.

Particularly with some sensitive material such as glass or mirrors, as where the silver layer on the back of the mirror is to be removed, it is preferable to remove the backing sheet 38 before blasting.

Otherwise, as the blasting grit is applied, it may erode some portions of the backing sheet faster than others and cause undesirable excessive erosion in portions of the grit-erodible material. In such instances, with the mask in the position of Fig. 5, the hardened areas 42, 44 and 46 are adhered more strongly to the surface than the adherance between the hardened areas and the backing sheet. The backing sheet then can simply be peeled away from the hardened areas after they have been adhered to the grit-erodible surface and the blasting grit applied in the same manner as before.

The mask can be reused by repositioning the light-struck areas 42, 44 and 46 on another griterodible body or on another backing sheet, if desirable and practical. Otherwise, new blasting masks can be readily made by simply reusing the existing control sheet or negative 22 in combination with the ultraviolet light 24 and a new blasting mask blank 26.

Claims

1. A method of making and using a grit-blasting mask for reproducing a shape in grit-erodible material, said method comprising producing a light-control sheet having a substantially translucent area and a substantially opaque area, one of which is of the desired shape, providing a blasting mask blank comprising a substrate backing sheet and a layer of photosensitive material thereon, directing light through the lightcontrol sheet onto the blasting mask blank to harden areas of the photosensitive material, removing other areas of photosensitive material from the backing sheet to leave bare portions of said backing sheet therebelow, placing the resulting blasting mask on grit-erodible material in which the shape is to be reproduced, and subsequently directing blasting grit toward the grit-erodible material for a sufficient time to erode the grit-erodible material.

2. A method of making and using a grit-blasting mask according to claim 1 characterized by producing the light-control sheet by photographing the shape on a background to produce the control sheet in the form of a negative.

3. A method according to claim 1 characterized by placing said blasting mask on the grit-erodible material with the backing sheet contiguous with the grit-erodible material.

4. A method according to claim 1 characterized by placing the blasting mask on the grit-erodible material with the hardened material contiguous with the grit-erodible material.

5. A method according to claim 4 characterized by adhering the hardened material to the griterodible material and removing the backing sheet from the hardened material before directing the blasting grit toward the grit-erodible material.

6. A method according to claim 1 characterized by said photosensitive material being a polymerizable material and directing the triggering energy waves through said control sheet in the form of ultraviolet light.

7. A grit-blasting mask comprising a thin backing sheet of grit-erodible material, a layer of sensitized material on said backing sheet and being of predetermined size and shape, the edges of said layer being substantially perpendicular to the plane of said backing sheet, with said backing sheet being bare in all portions where no layer is present.

8. A grit-blasting mask according to claim 7 characterized by said backing sheet being made of polyester material.

9. A blasting mask according to claim 8 wherein said polyester material is Mylar.

10. A blasting mask according to claim 7 characterized by said layer of sensitized material being a polymerized material.

11. A blasting sheet according to claim 7 characterized by said sensitized material being sensitized by ultraviolet light, causing it to polymerize.

12. A blasting mask according to claim 7 characterized by said backing sheet having a thickness from 0.0005 inch to 0.015 inch.

13. A blasting mask according to claim 12 wherein said hardened sensitized material has a thickness from about 0.003 inch to about 0.25 inch.

14. A method of making and using a gritblasting mask for reproducing a shape in griterodible material, said method comprising producing a control sheet having a substantiallytranslucent area and a substantially opaque area, one of which is of the desired shape, providing a blasting mask blank comprising a substrate backing sheet and a layer of polymerizable material thereon, directing triggering energy waves through the control sheet and onto the blasting mask blank to cause polymerization of areas of the polymerizable material, removing other areas of the polymerizable material from the backing sheet to leave bare portions of said backing sheet therebelow, placing the resulting blasting mask on grit-erodible material in which the shape is to be reproduced and subsequently directing blasting grit toward the grit-erodible material for a sufficient time to erode the griterodible material.

15. A method of making and using a gritblasting mask according to claim 1 4 characterized by producing the control sheet by photographing the shape on a background to produce the control sheet in the form of a negative.

16. A method according to claim 14 characterized by directing the triggering energy waves through said control sheet in the form of ultraviolet light.

1 7. A method of making and using a gritblasting mask according to claim 14 characterized by placing the blasting mask on the grit-erodible material with the polymerized material in contact with the grit-erodible material.

18. A method according to claim 1 7 characterized by adhering the polymerized material to the grit-erodible material and removing the backing sheet from the polymerized material before directing the blasting grit toward the griterodible material.