CA1140797A - Method of producing embossed designs on surfaces - Google Patents

Abstract

A B S T R A C T
A method for producing embossed designs on work surfaces such as on molds, rolls or dies. A photomechanically imageable transfer material is exposed to the design to be embossed. The material is developed and the acid resistant design material remaining on a backing sheet is mechanically transferred to the work surface by burnishing the back of the backing sheet. The surface is then etched and the acid resistant design elements removed so that the embossed work surface is ready for use.

Description

-~4[7797 FIELD OF THE INVENTION
This invention relates generally to the formation of designs on work surfaces and more particularly concerns a novel simplified process for forming the desired designs on surfaces of molds, rolls and dies used in the formation of articles generally made of de~ormable materials.

DISCUSSION OF THE PRIOR ART
The prior art is well represented by United States patent 3,052,581. The normal practice is to reproduce the desired design on a flat metal plate, usually made of zinc, by photo engraving. An adherent waxy bituminous acid resistant substance is then spread over th~ surface of the plate to fill the design areas which have been etched out of the surface.
The design is removed frQm that surface by means of tissue paper which has been brought in firm surface contact with the adherent waxy material. This tissue paper is then used as a means of transferring the design from the flat plate to the

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~ 1 5 ~0 79 l ~I mold surfaces. The tissue paper is moistened with a solution 2 ¦l of alcohol and water acting as a release agent t:o facilitate its

3 II,removal leaving the waxy material in place in the mold. ~fter

4 Ithe mold is etched, the waxy material is removed by means o~ a ¦solvent and the mold is then available to be employed for ma~ing 6 ¦I plastic articles. -I A particular disadvantage of this process is that the8 waxy acid resistant substance tends to be ~lowable i.f the pressure 9 of application to the mold surface appreciably exceeds the neces-sary pressure. This presents a real limltation on the fineness 11 I;of pattern elements which can be transferred accurately.
12 ~¦ Processes for etching gravure printing cylinders and 13 li plates involve etching designs in metal surfaces. Ho~ever, the 14 jiconsiderations for such etching are substantially dif-Eerent from !¦mold engraving. The former relates to what may be termed two-16 l~dimensional uses, depth of etch being necessary only to the 17 j'extent of design delineation for printing purposes. Mold -~ j 18 ¦,engraving, on the other hand, the subject of the present inve~Icn, 19 ¦Irelates to three-dimensional uses, that is, an actual surface Itexture in an article made with the engraved mold~ Steps to 21 ¦provide a surface etch are in many instances unsatisfactory for 22 Imaking a deeper etch for surface texturing. ~ ~

I , , ' .1 ,1 ,, 1 _UMM~RY OF THE I-~V~ITION
It is an object of this invention to provide a simpliEied method for producing embossed designs on work surfaces such as on molds, rolls and dies. For purposes o~ simplification the term "mold" will generally be used herein. This novel process requires fewer steps and fewer materials than the prior art method and thereby reduces both the time and cost necessary to emboss the sur~aces of mold cavities. Not only is the present process simpler and quicker, it allows finer designs to be produced in a more positive manner than the prior art processes.
A master negative of the pattern to be reproduced is prepared and this pattern is exposed to a photomechanically imageable transfer material. Upon development, the hardened image areas are acid resistant and are then transferred by means of the backing sheet on which the image is formed, to the mold surfaces. This backing sheet is rubbed or burnished with a blunt stylus to transfer the image areas to the mold surface which has normally been appropriately prepared prior to appli-cation of the elements of the acid resistant image. The mold 2Q surface is then etched, the image elements removed and the mold is then ready to be employed for makin~ plastic articles. The term "plastic" is to be broadly interpreted herein to include any deformable materials including rubber, metals which are surface textured by dies, and metals, fabric or paper which are textured or embossed by means of rolls.
In keeping with the foregoing there is provided in accordance with the present invention a method for engraving designs on complex curved work 30 ~

1 surfaces such as on molds, dies or the like tha-t can be etched with a suitable etchant, said work surfaces being employed Eor producing embossed designs on the corresponding complex curved surfaces of products formed from deformable materials, said method comprising the steps of:
preparing a master transparency from art work comprising the desired design;
exposing transfer material to said design on said master transparency, said transfer material comprising an emulsion, the exposed portion of which is resistant upon exposure to the etchant, said emulsion being on a backing sheet;
removing unexposed areas of said emulsion to define discrete etchant resistant image elements on said backing sheet;
transferring said image elements from said backing sheet to said work surfaces;
etching said work surfaces with a suitable etchant; and removing said image elements from said work surfaces.

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40-~9 7 Il BRII,F DESCRIPTION OF THE D~WI~G
1 ¦I The objects, advantages and features of this invention 2 ¦I will become readily apparent from the following detailed 3 ~i description ~hen read in conjunction w;th the accompanying 4 ¦I drawing in which:
li Fig. 1 is a perspective view of a mold cavity ~aving a 6 ¦~ pattern formed on its surfaces by means o~ the present invent;on;
7 I Fig. 2 is the original.copy of the design to be embossed 8 I, onto the mold sur~aces;
9 I Fig. 3 shows the negative made from ~.he oxig-Lnal copy o~
i Fig. 2;
11 il Fig. 4 is a fragmentary view with partial sep~ration 12 Ij showing the transfer material used or the invention;
13 1I Fig. 5 is a perspective view of the arrangement for 14 ll exposing the transfer material to the design;
, Fig. 6 shows the clear protective film being removed 16 I from exposed emulsion;
17 ! Fig. 7 is a perspective view of the developing step;
18 , Fig. 8 is an enlarged ~ragmentary perspective view of 19 the polyester backing sheet with the acid resistant design elements thereon;
21 Fig. 9 is a fragmentary sectional view of a portion of 22 a mold showing the minutely roughened surface thereof;
23 Fig. 10 is a fragmentary sectional view of a mold surface¦
24 j on an enlarged scale showingthebacking sheet and design,elemen-ts;
~ against the mold surface together with the burnishing step ior 26 ¦ transferring the design elements from the backing sheet to the 27 j mold surface;

~ _5_ Ii ' 1 1 1 4~ 7 9~i 1 iI ~ig. 11 shows the backing sheet being removed from the 2 , transferred design elements;
3 ll Fig. 12 is an enlarged fragmentary sectional view showing 4 1l the mold surface at the end o~ the etching step; and I Fig. 13 shows the mold surface of Fig. 12 a~ter removal 6 I of the acid resistant design elemen~s.
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j DESC~IPTION OF THE PREFERRED EMBODIMENT

7 ! With reference now to the drawîng and more particularly 8 ¦I to Fig. 1 thereo~, there is shown a mold cavity 21 having 9 ¦l internal wall surfaces 22 with decorative patterns 23 embossed ~I therein. For purposes of this description, a relatively simple 11 ,I pattern having the letter "E" flanked by decorative areas is 12 ¦' sho~. Of course, very intricate sur~ace textures,-p,atterns or 13 ¦~ designs may be used. It will be understood by those skiiled in 14 ¦¦ the art that any design capable of being photographically or 15 ! otherwise reproduced may be formed as a design in relief on the 16 inner surface of the cavity of a mold so that articles ~ormed in 17 the cavity will have the design embossed therein as an in-tegral 18 part of their outer surface.
lg li The original copy 24 (Fig. 2) from which the master film ~j negative 25 (Fig. 3) is to be made is nor~ally black and white 21 I art work. The copy may be of any desired size and will often 22 i be larger than the actual embossed design so that it can be 23 1~ reduced photographically and stlll reta~n desired iine lino Il 'i !.1. . . .
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~ U'~9'7 l ~ quality. The master film negative is made rom the original 1 art work by conventional photographic procedures. The film is 3 ! sho~n herein as a negativebut a positive transparency may be used 4 ~l if desired. Photomechanîcally imageable transfer material 26 1~ sho~n in Fig. 4 is then exposed as shown in Fig. 5~ An opaque 6 ¦I masking paper28 provides the support for the transfer material 26-7 I which is comprised of a clear protecti~e liner 27, emulsion 8 ! layer 31 and polyester backing 32, with the clear liner in ~ conronting relationship with the masking paper. On top o:E
transfer material 26 is master negative 25 and on top of that 11 is glass plate 33. A conventional light source 34 provides the 12 radiation for exposing the emulsion in the transfer material to 13 ~, the pattern of negative 25. Examples of light sources will be 14 1l, set forth hereinbelow. When exposure is complete, the clear ¦, liner 27 is peeled away from the exposed emulsion as shown in 16 I~, Fig. 6, leaving the exposed emulsion 31 on polyester backing 17 ll sheet 32. Liquid developer 35 is then poured onto the ex`posed 18 11 transfer material and an appropriate tool such as a pad or a 19 ¦ brush 36 is used to spread the developer evenly over the exposed 20 - ¦ surface to facilitate development of the emulsion as -indicated 21 ¦ in Fig. 7. ~hen the image is fully visible, the transfer 22 , material is rinsed with water and dried. At this point (see 23 ~I Fig. 8), the transfer material 26 comprises polyester backlng 24 ¦¦ sheet 32 and acid resistant transferable material 37 in discrete ¦1 areas in the form of the pattern desired. The material ~7 thus 26 ¦I formed has the proper de~ree of tackiness to enable it to adhere 27 ¦! to the mold surface without being so soft as to flow when sub3ect 28 I to pressure during ap-lication to the mold.

1 ¦~ A fragmentary sectional view of a portion of a mold 2 1' cavity is shown in Fig. 9. Inner surface 22 of mold 21 has an 3 ~ overall "tooth" or minutely roughened surface which may be formed 4 ,¦ by subjecting the surface to a mold acid bath so as to etch the ¦I surface and condition it for reception of the acid ~esistant 6 l1 transfer material. Other suitable means for roughening the 7 ~, surface may be used, including both mechanical and chemical 8 jj means. However, it ~las been found that this process will work 9 ¦I well on roughened or Oll polished surfaces and all intermediate ¦ surface textures. The backing sheet and transfer material ll j elements are applied to the surface of the mold as shown in 12 i Fig. lO so that the transfer material 37 makes intimate contact 13 ~i with surface 22. The transfer material is actually transferred 14 ~, from the backing sheet to the mold surface by burnishing as l, shown. Stylus 41 has a smooth, blunt end 42 which enables the 16 ,~ operator to provide a relatively large pressure to a relatively 17 ¦ small area to thereby transfer the acid resistant material, 18 'i which is hard to the touch but adherent to the mold surface l9 ~, ~Jhen burnished, from the backing sheet. Other stylus shapes j may be used, but it will generally be a blunt ended instrument.
21 I As the burnishing step progresses, the image ~ill take on a gray 22 I appearance through sheet 32 indicating that the transfer material 23 elements are being separated from the skeet and transferred onto 24 li the surface of the mold. When transfer of the design elements ~ has been accomplished, the backing sheet is simply remov,ea, since 2~ ¦¦ it does not adhere to anything after transfer, as shown in 27 !I Fig~ ll, leaving the acid resistant transfer material 37 in the 28 il desired pattern on surface 22 of the mold. It has been found Il . ' .

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~ l~or~s~7 1 ! that when sufficient pressure has been applied to cause the 2 ll acid resistant material 37 to adhere to the mold surface, it has 3 ¦~ separated from the backing sheet. The acid resistant material 4 I will adhere to one surface or the other.
¦ An etching solution 43, normally acid based and having 6 I properties appropriate for the material o~ the mold, is applied 7 I to the mold surface or sufficient time to etch away the mold in 8 1l areas not protected by ~he acid resistant transfer material 37, 9 ¦¦ leaving raised areas ~4 as shown in ~'ig. 12. I~hen this has been accomplished the acid resistant materi.al may be removed 11 mechanically by an abrasive or by an abrasive in combination 12 with a solution such as alcohol to weaken the bond with the mold , 13 !I surface, leaving the mold with the design embossed thereon as 14 !i raised areas 4~ in Fig. 13. A typical e~ample of a completed 15 ¦I mold is shown in Fig. 1.
16 ll It will be appreciated that the present inventîon elimi- !
17 il nates several intermediate steps of the prior art, specifically 18 etching oE the zinc trans-Eer plates, pulling of the wax tissue 19 transfers therefrom, and application of a release agent to separate the tissue from the wax pattern applied to the mold 21 surface. This invention proceeds directly from photographic 22 exposure of the transfer material to the application of the 23 ¦ design onto the surface of the mold.- Not only is processing time;
24 ¦ significantly reduced but, more lmportantly, quality can be I improved by elimina-ting some oE the steps in the prior ar-t 26 ¦i processes, each of which may lead to loss of pattern definition.
27 Ij Further, by proceeding directly from the photographic step to 28 applic-tion of tbe patte n to the mold surfacc, exceplionally l~ _9_ l 11~0797 I

1 ll fine detail can be included in the design which will faithfully 2 ¦l be reproduced on the item made and surface textured within the 3 ¦I mold cavity.
4 ! Ano~her factor in being able to maintain the fine detail

5 ! of the original art work in the finished mold is the exposure

6 I parameters. For example, over exposure, either in time or in

7 I light intensity, can result in the transfer material being too

8 ¦ hard to properly adhere to -the mold sur~ace, that is, it will be

9 ~ lacking the necessary characteristic of tac~iness. On the other I hand, too little exposure, while sufficient to create pattern 11 ¦ definition on the transfer material, may resuLt i.n soft acid 12 j resistant pattern material 37 which does not readily separate 13 li from the backing sheet as a consequence of the burnishing step, 14 ¦~ and at the same time is flowable under burnishing pressure.
¦' This could effectively destroy fine pattern definition. Further- i 16 ¦ more, under exposure may prevent proper development o the 17 ~'~ pattern material so that its acid resistant characteristic is lS !¦ inadequate, that is, even if it could be transerred to the mold 19 ¦ surface, it would not function properly in masking the desired I areas of that surface against acid etching. Thus, if the correc~
21 degree o~ tackiness is not achieved, the resist may fail during 22 the etching step resulting in a damaged mold. Optimum tackiness 23 for a làrge majority of applications, using an 11 inch by 14 inch 24 film (27.94 by 35.56 mm) may be achieved by means o- a light ¦ source consisting of four &0 watt, 120 volt, ultraviolet 26 ! fluorescent tubes spaced from the transfer material by 1.5 inches 27 I (3.81 mm) for about 45 seconds. The exposure time may vary 2~ 1l between 30 and 90 seconds in actual practice. A typical, 1, . -10-, ~1 .
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1 l ~U 79 7 1 '; suitable, commercially available exposure unit is 3M ~odel 2 ll, EU-~000, which may be employed to achieve the desired exposure 3 ll, characteristics specified abovè. It should be recognized that 4 ~I the above exposure parameters are examples only and many combi-1i nations of light sources, distances and exposure times may 6 i! produce useful results.
7 ~! An example of the material suitable for use as the 8 ~I trans~er material is a product sold under the name I.N.T. by 9 ¦¦ 3~1 Company. A suitable developing solution for the material is ¦¦ the 32~ Brand In~age'N Transfer Developer. Tests have shown that ~ the trans~er material 37 is cibout 0.5 mil (0.0127 mm) thick and 12 ¦I can withstand various etching formulations which are known for 13 1i, particular mold surface materials which etch to a depth appro-14 I priate for the particular pattern requirements and type o~ metal 15 li being etched. It will be readily appreciated by ~hose skilled 16 ! in the art that the depths of etch required for embossed or 17 , molded-in textured patterns are signi~icantly greater -than the ~8 i! depths required for gravure or lithographic printing suraces l9 ¦~, so that the processing considerations are significantly dif-ferent~
~¦ when preparing a mold for textured patterns. The typical dep-~h 21 1l of etch ranges between 0.003 inch (0.00762 mm) to 0,015 inch-22 I (0.038l mm), depending upon type of pattern, product application, 23 ! and aesthetic considerations, among others. However, heavier, ~4 ! coarser patterns may be etched to depths at least as great , as 0.05 inch (0.127 mm). It may be said that etching in~olved 26 I in graphic techniques relates to two dimensional considerations 27 I while the textured molds of this invention are concerned with 28 1l three dimens}ons.

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l l' The process of this invention may be used on all co~on 2 ¦ mold-making materials, such as pre-hardened steel (an example 3 ~ being P20), hardened tool steels (such as S-7), aluminum (6061 4 I for example)t and beryllium copper, among others.
5 I It should be recognized that the above materials and 6 ! specifications are examples only and are not definitive of the 7 ¦ present invention. In light of the above disclosure, it is 8 ¦ likely that modifications and i~provements will occur to those 9 1 skilled in the art which are within the scope o~ this in~ention.

Claims (15)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for engraving designs on complex curved work surfaces such as on molds, dies or the like that can be etched with a suitable etchant, said work surfaces being employed for producing embossed designs on the corresponding complex curved surfaces of products formed from deformable materials, said method comprising the steps of:
preparing a master transparency from art work comprising the desired design;
exposing transfer material to said design on said master transparency, said transfer material comprising an emulsion, the exposed portion of which is resistant upon exposure to the etchant, said emulsion being on a backing sheet;
removing unexposed areas of said emulsion to define discrete etchant resistant image elements on said backing sheet;
transferring said image elements from said backing sheet to said work surfaces;
etching said work surfaces with a suitable etchant; and removing said image elements from said work surfaces.
2. The method recited in claim 1 wherein said transferring step comprises the intermediate steps of:
placing said backing sheet on the work surfaces with said elements in intimate contact therewith;

Claim 2 continued burnishing the surface of said backing sheet with a blunt instrument to thereby firmly engage the image elements with the work surface and remove said image elements from said backing sheet; and removing said backing sheet from said transferred image elements.

3. The method recited in claim 1 wherein:
said transfer material comprises said emulsion sandwiched between a clear protective film and said backing sheet, said method comprising the further step of:
removing said protective film from said exposed emulsion after said exposing step.

4. The method recited in claim 1 wherein said developing step comprises the further step of spreading developing solution evenly over said exposed emulsion.

5. The method recited in claim 1 wherein said etching step is accomplished with a solution appropriate for the material of the work surface.

6. The method recited in claim 1 wherein said removing step is accomplished mechanically by an abrasive.

7. The method recited in claim 6 wherein said removing step further employs a solution to soften said image elements.

8. The method recited in claim 1 wherein said method-comprises the further step of preparing the work surfaces by roughening prior to said transferring step.

9. A method for engraving designs on complex curved work surfaces such as on molds, dies or the like that can be etched with a suitable etchant, said work surfaces being employed for producing embossed designs on the corresponding complex curved surfaces of products formed from deformable materials, said method comprising the steps of:
preparing a master transparency from art work comprising the desired design;
exposing transfer material to said design on said master transparency, said transfer material comprising an emulsion, the exposed portion of which is tacky and resistant upon exposure to an acid etchant, said emulsion being on a backing sheet;
removing unexposed areas of said emulsion to define discrete tacky and etchant resistant image elements on said backing sheet;
mechanically directly transferring said image elements from said backing sheet to said work surfaces;
etching said work surfaces; and removing said image elements from said work surfaces.

10. The method recited in claim 9 wherein said transferring step comprises the intermediate steps of:
placing said backing sheet on the work surfaces with said elements in intimate contact therewith;
burnishing the surface of said backing sheet with a blunt instrument to thereby firmly engage the image elements with the work surface and remove said image elements from said backing sheet; and removing said backing sheet from said transferred image elements.

11. The method recited in either claims 9 or 10 wherein said exposing step exposes said transfer material so as to enable said developed etchant resistant material to have sufficient tackiness to adhere to the work surfaces and having sufficient hardness to prevent flowing during said transferring step.

12. The method recited in either claims 9 or 10 wherein said exposing step exposes said transfer material so as to enable said developed etchant resistant material to have sufficient tackiness to adhere to the work surfaces and being sufficiently hard so it separates from said backing sheet during said transferring step.

13. The method recited in claims 1 or 2 wherein said exposing step comprises:
placing a plurality of ultraviolet fluorescent tubes approximately 3.8 mm from said transfer material;
energizing said tubes; and maintaining said energized tubes at said position with respect to said transfer material for between 30 and 90 seconds.

14. The method recited in either claims 1 or 9 wherein said etching step continues until the depth of etch in the work surfaces reaches between 0.00762 mm and 0.127 mm.

15. The method recited in claims 9 or 10 wherein said exposing step comprises:
placing a plurality of ultraviolet fluorescent tubes approximately 3.8 mm from said transfer material;
energizing said tubes; and maintaining said energized tubes at said position with respect to said transfer material for between 30 and 90 seconds.