Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2191431
METHOD FOR TEMPORARY SEALING OR BONDING OF MATERIALS
SPecification
The invention relates to a method for temporary sealing or
bonding of materials, wherein the materials are coated with or
impregnated with a protective material having a sealing and/or
bonding action.
In diverse areas of technology, there are needs for
temporary means of protecting or fastening with respect to
certain parts of a workpiece, e.g.
-- coating or protecting prior to a subsequent process step, or
in general to prevent corrosion for a specific time interval; or
-- protecting the integrity of friable materials or the like.
In the past, the problem has been approached by applying a
covering coating or by using natural or synthetic adhesives.
Known protective agents have the disadvantage that when no longer
needed they must be removed by special solvents or by mechanical
processes. This introduces additional process steps and may
subject the workpiece to deleterious influences.
In Eur. Pat. App. 149,912, microcracks in a catalyst support
are sealed off by means of a melted organic compound which is
allowed to solidify. The organic compound has a low vapor
pressure at room temperature. Therefore, it must be removed from
the catalyst support by burning off. Many materials cannot
tolerate such burning without damage.
The underlying problem of the present invention is to devise
a method of the general type described supra, such that the
materials are less subject to damage in the course of the removal
of the protective agents.
According to the invention, a protective material is used
which is readily volatilized at room temperature or slightly
above. Such materials have appreciable vapor pressure at room
temperature, and thus can be evaporated (sublimated) within a
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reasonably short time, without leaving a residue. This obviates
any further steps to remove the protective material; and damage
to the protected material is essentially avoided.
The protective material, in the molten state or as a
solution or aqueous dispersion, can be applied to the workpiece,
and/or can be used to bind and/or seal the workpiece material, to
achieve its temporary effect. The protective material can than
be removed by evaporation (sublimation) without the need to use
additional solvents.
Because the protective materials are practically insoluble
in water, they can be used, e.g., to render parts of a workpiece
hydrophobic or to seal them, for purposes of protection against
aqueous media employed in a subsequent operation which the
workpiece undergoes. The protective materials may also be used
to bind or render insensitive a workpiece which is friable or
otherwise sensitive; or may be used as temporary support means
for a workpiece undergoing various operations. The volatility of
the protective material used may be varied depending on the
processing to be protected against, and the duration of
protection desired.
Suitable candidates for use as protective materials for the
described purpose are, inter alia, camphene, camphor,
naphthalene, methylnaphthalene, cyclododecane, neopentyl alcohol,
tricyclene (i.e., 1,7,7-trimethycyclo(2.2.1.026)heptane),
menthol, thymol, and diphenyl ether.
The protective material may be dissolved in a solvent before
being applied. Advantageously, the solvent is more volatile than
the protective material. A suitable candidate for use as such a
solvent is, e.g., 2-methylbutane.
For purposes of the invention, the "volatility" of the
applied protective material will be defined as the loss in
thickness (from one side) of a coating comprised of the
protective material in a 24 hr period at temperature 18-20C.
For camphene as the protective material, a coating of a
prescribed thickness lost c. 4.72 mm thickness in 24 hr at the
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stated temperatures. The corresponding figure for cyclodecane
was c. 0.031 mm.
Examples of possible areas of application of the invention
are:
1. Restoration and conservation of art works of various types
Murals can be render-~d temporarily hydrophobic to enable
treatment of the surfaces with aqueous solutions.
Surfaces of art objects can be protected temporarily against
soiling or other agressive influences.
Archeological artifacts may be strengthened for lending or
for shipping to a workshop or laboratory, without risking
complications from the temporary protective materials during the
subsequent restoration ope_ations, and without subjecting the
workpiece to solvents used to remove the protective materials.
The protective material may be employed, e.g., as a mold
release agent in a casting mold, or as a supporting mortar, or as
a protective cover for surfaces.
Example 1: Protecting sensitive articles prior to shipping:
Sensitive articles, e.g. archeological artifacts, paintings,
polychrome wood sculptures, etc., can be bound with a melt or
solution comprising the described protective materials.
1.1:
A painted article comprised of plaster was found at a burial
site. It was desired to preserve the article along with the
surrounding layer of soil. For this purpose, the region in
question was heated to c. 40C with the aid of infrared lamps.
Then a melt comprising tricyclene was quickly applied. The melt,
of low viscosity, readily penetrated. After cooling, it hardened
to a wax-like mass. The solidified tricyclene bound the mass
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which it had penetrated, such that the ensemble could be safely
removed from the dig site. Although it would have been possible
to evaporate the protective material immediately after the
protective operation, in this case it was desired to defer
removal of the protective material to a later time. Accordingly,
the article was packaged in air-tight packaging (polyethylene
film), allowing it to be transported and stored for an
arbitrarily long time. After the package was opened, the
protective material was volatilized without leaving a residue,
thereby leaving the find in unaltered condition. Heat could
optionally be used to accelerate the volatilization.
1.2:
In a situation in which it was desired to avoid heat
exposure of the region to be protected, a solution of the
protective material was used. In particular, a saturated
solution of a mixture of tricyclene and camphene, in pentane
(alternatively, dichloromethane) as the solvent, was prepared, in
particular 90 wt.% tricyclene-camphene mixture and 10 wt.%
solvent, and this was applied and poured onto to the surface of
interest, using a paintbrush and pouring means. Then the solvent
was allowed to evaporate for up to 10 hr. Treatment of the
surface was then repeated. After a subsequent drying of c. 1 hr,
the strength and coherence of the structure had increased
markedly, allowing the article to be safely preserved.
.3:
Sensitive scientific samples, e.g. cylindrical core samples,
can be strengthened against disintegration by prior impregnation,
thereby facilitating sampling.
It was desired to take a core sample of diameter 50 mm from
a mass comprised of a high-salt plaster-like material with low
cohesion. A melt as described above was applied. After cooling,
a core could be taken without risk of crumbling. This was
particularly useful for taking a sample from the painted plaster
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artifact mentioned above. Alternatively, in the manner described
in Example 1.2.
1.4:
Sensitive, heavily damaged painted coatings on art objects
(e.g. paintings or polychrome sculptures) can be covered with
felt or fabric, to provide protection for shipping. Today such
art objects are often protected for shipping with the aid of
Japan paper and an easily removable adhesive.
Similar protective means using cyclodoaecane were effected
as follows:
The melt was sprayed onto the substrate with a hot-spray gun
(supplied by Sata) at c. 65C. For optional additional
protection, a second layer comprising a relatively large mesh
fabric could be affixed with the aid of melt. The method was the
same as described above. The duration of protection was c. 30 da
per millimeter of thickness of cyclodecane ccating.
1.5:
A solution of tricyclene in 2-methylbutane can be used to
provide short term protection, without application of heat. A
saturated solution of tricyclene in 2-methylbutane was prepared
and was applied to a substrate by means of a paintbrush. After
c. 2 min drying time, thin Japan paper was applied, and the same
solution was painted onto the paper. The protective material
volatilizated very quickly (c. 0.2 mm coating thickness per
hour).
xample 2: Temporary binding for purposes of mechnical
operations, such as mechanical cleaning:
Subsequent layers of paint or soils can be removed from
weakly adhering or friable paint layers by mechanical means, with
the use of a melt comprised of temporary protective means, for
penetrating stabilization of the being cleaned.
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It was sought to thin a hard sintered layer of weakly bound
lime mortar with the aid of a powder blasting technique. The
mortar was strengthened temporarily, to prevent breakage of the
mortar surface during the cleaning. The requirement was for a
protective material layer of c. 0.01 mm which would provide
additional strength over several hours. Accordingly,
cyclododecane was chosen as the protective material. The method
used (among various possibly practicable methods) was as follows:
The cyclododecane melt was sprayed on with a hot-spray gun
(supplied by Sata) at c. 65C. A coating of cyclododecane was
formed, which was then melted in a second step, using an infrared
lamp (or optionally a heated spatula). Care was taken to have
the material completely absorbed by the substrate. Where
necessary, residues on the surface were removed with "special
boiling point gasoline". Optionally, ultrasound cleaning means
were applied.
Hard sintered crusts on painted murals present a special
problem. These tend to have deformations and loose segments.
For such situations, the substrate may be heated and a
cyclododecane melt may be applied directly with a paintbrush or
dropwise.
xample 3: Coatings to seal sensitive surfaces --
mold release agents:
In order to protect a porous surface, e.g. when silicone
rubber or latex mold-forming materials are applied, the surface
may be coated with a layer of cyclododecane as a mold release
agent.
A sandstone sculpture with a weathered surface was to have a
mold taken from it with the use of silicone rubber mold-forming
material. A solution of cyclododecane in 2-methylbutane (see
supra) was applied as an intermediate layer. The saturated
solution was applied with a paintbrush. The solvent was
evaporated prior to the mold formation.
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Example 4: Sealing a porous substrate and rendering it
hydrophobic, to protect it when employing
chemical cleaning processes:
Volatile hydrophobizing agents are particularly useful for
temporary sealing of porous substrates, such as natural stone or
mortar. When aqueous cleaning agent solutions are to be used on
surfaces of wall murals, sealing agents can be used to prevent
entry of harmful materials into the pore structure.
The requirement was for a protective material of c. O.01 mm
which would be effective over several hours. Accordingly,
cyclododecane was chosen as the protective material. The method
used (among various possibly practicable methods) was as follows:
A saturated solution of cyclododecane in 2-methylbutane was
prepared and was applied to the substrate with a paintbrush.
After a drying time of c. 1 hr, the excess was removed from the
surface, using the solvent. Then pressure cleaning using aqueous
solutions was carried out; during the cleaning, water could not
penetrate into the pores.
ExamPle 5: Use of a volatile protective material without
fillers or the like, for sealing cracks:
Injected mortars are often used for preservation of murals
and stone sculptures. In order to prevent soiling of the
historical surfaces by these injected materials (and associated
adhesives), cracks and broken edges need to be sealed. Wax-like
protective materials are particularly suited for such sealing.
Tricyclene or cyclododecane may be used in molten form, with
application to the cracks by means of a paintbrush. In some
cases it has proved advantageous to thin cyclododecane with
special boiling point (SBP) gasoline in the amount of 50%. When
patching masonry and the ~ike by pressure injection of mortar,
application of a smooth coating comprising cyclododecane has
proved advantageous. The coating protects the surfaces against
emerging suspension. The cyclododecane is applied as a melt
using an airless heated application device. Soils may be removed
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by direct washing, or are removed automatically when the
protective coating is volatilizated.
Example 6: Binders for supporting-mortars:
Volatile binders can be used in producing a wide variety of
supporting and protective mortars. Fibrous additives may be used
if the melt is suitably thickened with highly disperse silicic
acid (Aerosil). Examples of additive masses are: Nylon fibers,
glass fibers, sand, hollow glass spheres, etc. The method is as
follows:
Dichloromethane as a thinner in the amount of c. 10% is
incorporated in a tricyclene melt. Aerosil is added until a
pasty consistency is attained. Then the additive masses
(fillers) are added until a mortar-like consistency is attained.
The mixture can be used as a supporting mortar for plaster
coatings which need repair or protection. After a suitable
volatilization time (c. 5 mm layer thickness in 24 hr), the
binding character of the binder of the supporting mortar is
eliminated.
2. Use in the construction industry, as a "liquid coating film"
Particularly in the case of refurbishing and repair
operations on existing structures, surfaces which it is desired
to preserve may be coated for protection against water and a wide
variety of soils.
Protective materials may be used to seal surfaces of natural
stone, wood, glass, metal, etc., to protect them during
plastering, painting, and similar operations. The method is
particularly advantageous for surface areas which are not easily
protected with adhesively bonded films according to known
methods.
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ExamPle 1:
Cyclododecane may be applied as a melt at 80c by spraying
The cyclododecane is heated in the heatable reservoir of a Sata
hot-spray gun (or a heatable airless apparatus provided by the
firm Wilhelm Wagner), and at c. 90C is sprayed onto the surface
of the substrate, using compressed air at 2 bar. The distance
between the nozzle and the substrate surface should be c. 10 cm.
ExamPle 2:
Cyclododecane may be applied as an aqueous dispersion. The
dispersion may be applied with a paintbrush, paint roller, or
spray gun. The substrate surface is coated with the dispersion.
After film formation, the surface is protected against waterborne
soils. However, soils which may accumulate should be removed
before the protective material is removed. This may be
accomplished by dry brushing or water washing.
3. Use in the construction industry as a
release agent for concrete forms:
In producing visible (e.g. decorative) architectural
concrete surfaces which are subsequently to be painted, it is
important that any release agent used for the concrete forms not
leave a residue. Cyclododecane satisfies this requirement.
Example 1:
Cyclododecane may be applied as a melt at 80C, by spraying.
The cyclododecane may be heated to c. 90C in a water bath
or other heatable reservoir having a temperature regulator.
The cyclododecane may be charged to the heatable reservoir
of a Sata hot-spray gun (or a heatable airless apparatus provided
by the firm Wilhelm Wagner), and sprayed at c. 90C onto the
surface of the concrete form, using compressed air at 2 bar.
2191431
The distance between the nozzle and the substrate surface
should be c. 10 cm, so that the spray is not excessively cooled.
Example 2:
Cyclododecane is applied to the concrete form as an aqueous
dispersion, using a paintbrush, paint roller, or spray gun.
4. Use in the metals processing sector, to protect
aqainst corrosion and aggressive agents:
A coating comprised of protective materials may be used to
temporarily protect metal surfaces against corrosion. In
particular, when metal articles are being shipped which should
not be painted with anticorrosion paint, it is useful to have a
completely reversible coating methcd which does not require
solvents to remove the coating. If it is desired to remove the
coating at a rate which is accelerated compared with natural
sublimation, this may be accomplished with hot water at 80-90C.
Since cyclododecane has a lower density than water, the
protective material which is washed away can be recovered
mechanically after the wash water is cooled, and can be re-used.
ExamPle 1:
It was desired to protect an unpainted degreased steel plate
temporarily against corrosion. For this purpose, it was coated
with cyclododecane in a hot-spray process.
The cyclododecane was heated to c. 9oC in a water bath. The
cyclododecane was charged to the heatable reservoir of a Sata
hot-spray gun and at c. 90C was sprayed onto the surface of the
steel plate, using compressed air at 2 bar. The distance between
the nozzle and the substrate surface was
c. 10 cm.
2191431
1 . 1 :
To protect an unpainted degreased steel plate temporarily
against corrosion, it was coated with cyclododecane in a dipping
process.
The cyclododecane was heated to c. 80C in an electrically
heated container.
The steel plate was rested on a mesh support and dipped
c. 2 sec in the melt.
After cooling to room temperature, the plate bore a uniform
coating of cyclododecane.
ExamPle 2:
It was desired to temporarily protect an unpainted body part
of an automobile against soiling by bird droppings. For this
purpose, the part was coated with cyclododecane in a hot-spray
process.
The cyclododecane was heated to c. 90C in a water bath. The
cyclododecane was charged to the heatable reservoir of a Sata
hot-spray gun and at c. 90C was sprayed onto the surface of the
metal part, using compressed air at 2 bar. The distance between
the nozzle and the substrate surface was c. 10 cm.
After 14 da, the coating remaining was washed off with water
at c. 80C.
The mixture of wash water and cyclododecane which resulted
was cooled to a temperature below 55C. Cyclododecane floating
on the surface had hardened to form small flakes, enabling it to
be separated from the water using a fine screen of mesh 0.25 mm.
5. Use in theater and film scenery, and in advertisinq, etc.:
A snow-like mass can be created by spraying hot
cyclododecane melt which does not strike a substrate surface.
This mass can be used as imitation snow or the like for several
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days, for decorative or scenic purposes. It undergoes
sublimation without leaving a residue, avoiding costly cleanup.
When hot cyclododecane melt is sprayed onto a plate, board,
wall, or the like, and cooled, a white cyclododecane film is
produced. This allows production of white markings or writing on
a dark background; after a period, the white cyclododecane
volatilizes, automatically erasing the markings or writing. This
affords numerous opportunities for advertising, allowing
temporary texts or images to be applied on top of more lasting
displays. The duration of the overlay (on the order of days)
depends on the thickness of the cyclododecane coating sprayed on.
The sublimation of the cyclododecane leaves no residue.
Spraying-on of a hot menthol melt provides similar results,
except that menthol volatilizes much faster than cyclododecane.
Particularly in sunlight, menthol markings will be very
short-lived.
Example 1:
Solid cyclododecane was heated to c. soC in a water bath.
The resulting cyclododecane melt was charged to the heatable
reservoir of a Sata hot-spray gun and at c. 90C was sprayed onto
a substrate surface, using compressed air at 2 bar. The distance
between the nozzle and the substrate surface was c. 10 cm. A
white coating was produced on the substrate, which coating could
be used for decoration. With the use of suitable spray nozzles,
the coating can be applied in the form of writing or other
graphic. The duration of the overlay depends on the thickness of
the solid cyclododecane coating. The sublimation of the
cyclododecane over a period of days leaves no residue.
Example 2:
An aqueous suspension of solid cyclododecane can be formed
with the use of, e.g., customary wetting agents and dispersants
of the type used in forming dispersions of waxes in water. After
the dispersion is formed, the covering power of the white
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dispersion can be increased by adding solid cyclododecane as
follows:
Solid cyclododecane ground to a powder with particle
sizes S 0.063 mm may be added to the dispersion in a proportion
of 1:1 by volume.
Cyclododecane powder with particle sizes ~ 0.020 mm can
be produced by atomization in a hot-spray process as described
supra and introduced directly to the dispersion in a proportion
of 1:1 by volume.
The ground or atomized cyclododecane component of the
dispersion remains in the dispersion as solid particles which
increase the covering power of the white coating produced when
the dispersion is applied to a substrate with, e.g., a
paintbrush, paint roller, or spray gun.
Instead of adding ground or atomized cyclododecane to the
dispersion, one may add a pigment or other colorant of comparable
fine particle size, wherewith the cyclododecane present in the
dispersion serves as a volatile binder for the added pigment or
colorant, over the selected background.
6. Use in dYeing Processes:
In dyeing textiles, leather, etc, and in the batik method,
the described protective materials may be used.
Thus, one may partially mask textiles with cyclododecane or
camphene, so that no dye is taken up by the masked regions when
the textiles are subjected to dyeing in aqueous media. The
technique may be used to produce artistic images or decorative
effects on textiles or other materials. The known technique of
masking with a wax requires subsequent application of solvents or
heat to remove the masking agent. Not only is this deleterious
to the environment but it may be detrimental to the substrate
material.
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The cyclododecane may be applied as a melt (e.g. to cotton
or linen, etc.) or in dissolved form in the case of a
temperature-sensitive substrate such as silk.
The method may also be used in the case of stain- or spot
removal over part of a surface, wherewith a protective material
such as cyclododecane is used to mask the area surrounding the
stain or spot to protect said area during a removal process
employing, e.g., aqueous removal media.
