Note: Descriptions are shown in the official language in which they were submitted.
2~ 7~ pcr ~s92/~293~
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PROCESS FOR PREPARING ELECTROMAGNETIC
RADIATION IMAGED MATERIAL
This invention relates to a process for preparing
electromagnetic radiation imaged material and to an
article of manufacture comprising an adherent sheet-like
photoresist laminate which can be transferred to a
surface to introduce a pattern into the surface using a
particulate etchant such as a sandblast.
! More particularly, the invention relates to a photoresist
laminate which can be adherently applied to the surface
of an object or material, for the purpose of revealing or
exposing in the surface of the object or material, a
pattern. The resist laminate contains a layer of
photoresist composition which when exposed to light a
specific desired pattern can be developed when the resist
is applied to the surface of the object or material, the
pattern can be selectively revealed by the action of an
etchant.
Over the years a great deal of interest has been focused
on the art of etchin~ patterns into surfaces of objects.
Such patterns can be decorative, informative, can be for
the purpose of providing nonskid surface properties, can
be useful in forming copper printed wiring board pat-
terns, and can be useful in many other application where
a specific pattern is desired.
Grit blasting has been effected in the past by employing
a pattern mask prepared manually from rubber, paper, or
various plastics and attaching the pattern mask -to the
article to be etched employing an adhesive. This method
is time consuming and cannot be used to etch fine image
details on a repetitive basis.
In the past, expensive metal templates have been held or
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attached to the surfaces and grit blasted at the
templates to produce the etch. This method, since the
templates must have small metal parts holding the
template together, cannot produce fine detail. Ad-
ditionally the metal template loses its shape withrepeated use, and distorts the design.
The surface of the article can also be etched by silk
screen printing an image in relief onto a very fine
sticky backing paper. This me~hod re~uires a very strong
ink image. The sticky backing paper is dampened and
adhered to ~he surface. The ink imaye is then grit
blasted. The grit material must, however, penetrate
through the paper and its adhesive before affecting the
surface. During this time, the ink image must withstand
the grit blasting. The resultant image is more of a
frost than an etch, and is best suited for producing
large num~ers of etched items since the method is too
costly for etching small numbers of items.
Die cut vinyl stencils are also produced as an etchant
mask, and the time, effort and cost factors make the use
of such stencils undesirable.
Several companies produce photoresist masks commercially
in the United States. Each such mask has a commonalty in
that an emulsion containing a photosensitizer and a
reactive monomeric and/or polymeric substance is applied
to a substrate which is then exposed, either dry or wet,
to sufficient quantities of electromagnetic radiation of
an appropriate wave leng~h to activate polymerization or
crosslinking catalys~s, agents, initiators or mixtures
thereof. The unexposed areas remain soluble to the
action of solven~s such as water, alcohols, hexane,
benzene and when exposed to such solvents by the use of
a washout device reveal the desired pattern or design.
The exposed areas are rendered insoluble and form the
mask. ~hile the commercial productions can produce
reasonable detail, some detail is destroyed during the
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washout. The method by which these marks are, by simple
adhesive, transferred to the object to be etched,
requires the masks to be burnished while applying. The
failure rate for loss of pieces and fine detail which
does not make the transfer, or is blown off the glass in
the blasting is substantial.
One American company produces a laminated resist,
produced much the same as the previous commercial mask,
which has as an additional production step a thin film
laminated to the polymerized resist. The transfer of
this mask is better, but the production costs of this
additional step make the mask very expensive. The loss
of fine detail during washout is a problem.
Liquid photoresists are also commercially available which
are painted or sprayed onto the surface of the object to
be etched, and then exposed when dry to achieve a desired
image. While the process does work, there are serious
problems when working with any but a planer surface, and
presents problems on water sensitive surfaces. The
process is time consuming, expensive, and must be cleaned
using special expensive removers.
Accordingly, a substantial need exists for a photoresist
that is extremely easy to use, can readily develop an
image or pattern, can be used on both water sensitive
surfaces and surfaces having curves and ~ontours. Such
a photoresist, which can be produced quickly and inexpen-
sively while providing extremely fine detail which
transfers intact and adheres so fine detail is not blown
off during the blasting is in demand.
We have found that by exposing a previously imaged
photoresist sheet to a proper-amount of electromagnetic
radiation for a specific time period, prior to exposure
to solvents by the use of a washout device, we can
produce a controllable integral membrane layer in the
imaged photoresist sheet. Surprisingly, we have found
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that when e~posed to solvent by use of a washout device,
- the integral membrane remains intact, and greatly
enhances the amount of detail that is available for
transfer. By being integral, this membrane actually
increases the amount of fine detail that can be easily
transferred to the object to be etched. Using this
invention line widths of .0039 inches can be imaged,
washed out, transferred and successfully etched.
Additionally we have found that any or Tll of the
following advantages may be achievable:
(a3 The method is very simple.
(b) No appreciable additional costs are incurred.
(c) Compound and inward curves can be masked without
distortion.
(d) Water sensitive matPrials can be masked and etched
without damage~
(e) Substrate.material can be quickly and easily
stripped off.
(f) Application time of the mask on the object to be
etched is greatly reduced.
(~) Clean up or mask removal is fast; no special agents
needed.
(h) Etching time is reduced per ob~ect since all detail
stays in place, resulting in increased
production.
(i) Better resolution, finer detail, and higher quality
are produced which increases product
sales.
Brief Description of the Drawings
Fig. 1 is a view of a generally rectangle portion
diagram of a preferred resist laminate which is made of
a substrate which has ~een coated with a photosensitive
resist.
Fig. 2 is an enlarged sida view diagram of a method
of forming an unrevealed pattern in the surface of the
~T/US 92~02 93 9
photosensitive resist by exposure to a film image and a
electromagnetic radiation source.
Fig. 3 is an enlarged side view diagram of a method
of forming an integral membrane in the previously imaged
photo resist sheet, Fig. 2.
Fig. 4 is an enlarged side view diagram of the wash
out device, and water or chemical solvent spray, reveal-
ing the imaged pattern, leaving the integral membrane
i intact on the substrate.
10Fig. 5 is an enlarged side view diagram of the
imaged photoresist, applied to the object to be etched,
by means of an adhesive coating. The integral membrane
! holds all pattern pieces in place while the substrate is
stripped away.
15Fig. 6 is an enlarged side view diagram of the
applied photoresist, on the ob;ect to be etched, being
blasted with abrasive, propelled from an abrasion etching
device, producing an etched pattern in the object.
Fig. 7 is an enlarged side diagram of a method of
forming an integral membrane in photosensitive laminates
for later use.
R~ference Numerals In Drawings
20 photo sensitive resist 33 revealed image
22 substrate 34 adhesive layer
24 electromagn~tic source 36 surface to be etched
25 timing device 38 etched area
26 unrevealed image 40 abrasion etching device
27 image transfer means 42 abrasive
28 integral membrane 44 repelled abrasive
30 wash out device 46 etched image
32 water or chemical solvent spray
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Detailed Discussion of the Invention
Resist Layer
The resist laminate of the invention generally is made of
a resist layer, a substrate layer, and an adhesive layer.
The resist layer of the laminate generally comprises
compositions that are photosensitive. The ph!otosensitive
compositions typically interact wi~h light to transform
the composition from a soluble state into an insoluble
film. Typically, resist compositions contain reactive
mono/or polymeric substances along with photo activated
initiators. Such polymer suspensions are well known in
the art and are available from a number of suppliers.
One of the preferred resists is sold by The Chromaline
Corporation under the name SBX.
Substrate
The support layer of this invention commonly comprises a
web, film, or other such substrate which can be coated
with the resist composition of the invention. The
substrate ~ be mechanically stron~ to permit rapid
manufacture of the resist laminate and ~ be flexible
to allow for the easy removal after transfer of the
resist mask to the object to be etched.
Such substrate materials are readily available from a
number of suppliers.
The preferred substrate of this invention is a transpar-
ent or translucent sheet-like material which is less than
4 mil mylar polyester, produced by DuPont.
Adhesive layer
The photoresist laminate of the invention comprises an
8~7~ ~)C~ 92~0293 9
adhesive layer that is used to adherently apply the
laminate to the object for etching. The adhesive layer
can be water activated, pressure sensitive, heat ac-
tivated, or other adhesive form. The adhesive layer is
preferably a pressure sensitive adhesive which is
typically an adhesive composition having a high degree of
tack and cohesive strength. Such adhesives may be
applied by a large variety of means; spray, brush, roll
! coating, or in the photoresist polymer suspension.
Pressure sensitive adhesives tend to bond almost instan-
taneously to a surface with slight contact pressure at
the interface between the adhesive and the contacted
surface. In practice pressure sensitive adhesives
commonly are used in conjunction with a pressure sen-
sitive release liner comprising a backing material suchas paper, textile, plastic film, or metal foil which has
a generally silicone release coating to ensure that a
release liner can be removed from the pressure sensitive
adhesive without reducing the adhesive properties of the
adhesive mass and without any removal of the pressure
sensiti~e adhesive. The removable release liner makes it
practical to store imaged sheets wi~h the adhesive
applied for later use, or for shipment.
The preferred pressure sensitive adhesives are well known
to the art, and are commonly available through a variety
of sources including 3-M.
Methods of use
The photoresist laminate articles of manufacture of the
invention are typically used by adhering the exposed, re-
exposed, washed out laminate to the object to be etched.The substrate is stripped off and the resist is sxposed
to the action of a particulate etchant. Many variations
of this basic etching process can be formed without
departing from the spirit and scope of the invention
since the steps can be rearranged to suit a particular
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resist laminate construction, and the desired end use of
the resultant sheets.
Fig. l is a diagram of a generally rectangle portion of
a preferred resist laminate which is made of a substrate
22 which has been coated with a photosensitive resist 20.
The coating may be produced by various well known coating
methods, and can be applied in a variety of thicknesses
directly related to the intended use of the resist. The
preferred thickness of the photosensitive resist 20 is
between 3 mil and 5 mil.
Fig. 2 is an enlarged side view diagram of a method of
forming an unrevealed image 26 in the surface of the
photosensitive resist 20, by exposure to a image transfer
means 27 and a electromagnetic radiation source 24. This
known art generally requires sufficient electromagnetic
radiation 24 to be applied to photosensitive resist 20 to
cause the crosslinking or polymerization of the resist
into an insoluble state. The image transfer means 27
repels the electromagnetic radiation 24 and the un-
revealed image 26 remains soluble.
Fig. 3 is an enlarged side view diagram of a method offorming an integral membrane 28 in the previously imaged
photosensitive resist sheet Fig. 2. The previously
imaged photosensitive resist sheet is re introduced, or
exposed a second time to the electromagnetic radiation
24. The image transfer means 27 is not present. The
preferred method exposes the laminate with the photosen-
sitive resist 20 in the reverse of Fig. 2, with the
substrate 22 in the direct path of the electromagnetic
radiation 24. The areas of unrevealed image 26 are now
brie~ly exposed for a specific time period, using a
timing device 25, through the substrate 22, forming a
integral membrane 28. The specific time to produce the
membrane varies in direct relation to the time of
electromagnetic radiation from a specific source, aæ is
well kno~n. The steps can be rearranged to suit a
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particular manufacturing or use method with substantially
the same results.
Fig. 4 is an enlarged side view diagram of the wash out
device 30, and water or chemical solvent spray 32,
revealing the revealed image 33 and the integral membrane
28 left intact on the substrate 22. The integral
membrane 28 spans all the revealed image areas 33 and has
held them in place during the wash out process. The
stabilizing effect of the integral membrane greatly
improves the resolution capability of the photosensitive
resist since all fine detail is held in place, and is not
eroded at the roots.
Fig. 5 is an enlarged side view diagram of the imaged
photoresist 20, applied to the object to be etched 36, by
the means of an adhesive coa~ing 34. The integral
membrane 28 now holds all pattern pieces in place without
loss or distortion while substrate 22 is stripped away
manually. The transfer method allows previously dif-
ficul~ surfaces including compound and inward curves to
be successfully masked, as well as application to other
surfaces which are sensitive to the presence of water.
F~g. 6 is an enlarged side view diagram of the applied
photoresist 20, applied to the object to be etched 36, by
means of an adhesive coating 34. The integral membrane
28 holds the various small parts in place while expssed
; to the abrasive 42. The membrane rapidly erodes when
exposed to the action of the abrasive, and after suf-
ficient exposure to the etchant, the etched image 46 is
developed in the object surface. The holding in place of
the small pieces by the membrane allows deeper etching of
the image since the small pieces do not blow off.
Fig. 7 is an enlarged side view diagram of the photores-
ist 20 on substrate 22 exposed to electromagnetic
radiation 24. The preferred method for producing
photoresist laminates for storage or shipment for use at
PCT~JS 9 2 / ~ 2 9 3 9
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a later time is to expose the laminate briefly for a
specific time to produce a membrane 28' by means of a
timing device 25 and deposit the exposed laminate in
expo~ure proof means for later re-exposure, Fig. 2,
washout Fig. 4, application with adhesive coating Fig. 5,
stripping of substrate Fig. 5, and etching Fig. 6.
Although the description above contains many specificati-
ons these should not be construed as limiting the scope
of the invention but as merely providing illustrations of
some of the presently preferred ~mbodiments of this
invention. For example, the invention can be utilised on
sheets which are produced and exposed while liquid or
semi-liquid as well as dry.
Thus the æcope of the invention should be determined by
the appended claims and their legal equivalen~s, rather
than by the examples given.
