Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CURING OF RESINS
The present invention relates to a method of controlling the curing of
a resin and to a resin modified to provide such control. The invention also
includes the application of the method and the use of the resin in the
production of articles.
In the production of plywood, for example, individual layers of wood
are coated with resin, pressed together and subjected to heat in order to
cure the resin. The time for which the heat is supplied to obtain a cure can
be considerable slowing down the production process. Curing times can be
reduced by mixing a catalyst with the resin, but this may interfere with the
production process itself as curing may start either before or during the
application of the resin.
According to one aspect of the present invention, there is provided
a method of curing a resin including the steps of trapping a catalyst which
when released into the resin initiates curing, mixing the trapped catalyst
with the resin and releasing the catalyst into the resin to initiate curing at
the desired time.
According to another aspect of the present invention, there is
provided a method of manufacturing a product comprising at least two parts
including the steps of coating one of the parts at least partially with a
resin
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having a trapped catalyst distributed therein, placing the parts together with
the resin therebetween and releasing the catalyst into the resin to initiate
curing at the desired time.
The invent'ron also includes products made by the above method and
resins with distributed catalysts for use in the above methods.
The catalyst may be trapped either by encapsulation or by
adsorption/absorption into the structure of a suitable substrate such as
almond shell.
The resin may be any of the following Polyester resin, Vinyl
esterresin, Phenol formaldehyde resin, Epoxy resin, Acrylic resin,
melaminelurea formaldehyde resin, Phenolic resin.
The catalyst may be any appropriate catalyst such as:-
Organic peroxides for example Di benzoyl peroxide, Methyl ethyl keto-
peroxide, Cumene hydroperoxide, Acetylacetone peroxide Isold under trade
name Triganox 44B), tert-Butyl peroxybenzoate (sold under trade name
Triganox C), tert-Butyl-2-ethyl hexanoate (sold under trade name Triganox
21 ), tert-Butylperoxy-3,5,5, trimethyl hexanoate (sold under trade name
Triganox 42s), Cumene hydroperoxide Isoid under trade name Triganox
K-80), Biz (4-tert-butylcyclohexyl-peroxdicarbonate) (sold under trade name
Perkadox 16). Amine Catalysts for example: Diethyltetra amine,
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Triethylamine Isocyanates, Boron tri fluoride, UV Curing Catalysts, Alkyl
Carbonates for example: Propylene and Ethylene carbonate, and mineral and
organic acids such as Formic acid, toluene sulphonic acid, or sulphuric acid.
The encapsulating material may be any one of the following; gelatine,
thermoset resins, fats, waxes, thermoplastics, polymeric compounds, or
silane compounds or any of the encapsulation materials disclosed in the
applicants copending international application published under publication
No. WO 98/26865.
Accelerators may also be used such as Colbalt octoate (sold under
trade name NL-49-P), Diethylaniline fsold under trade name NL-64-10P).
Ammonium Sulphate or Ammonium Chloride.
The size of the encapsulated or coated particles may lie in the range
0.5 to 1000 microns.
Embodiments of the invention will now be described, by way of
16 example.
In a first embodiment, which relates to the manufacture of plywood,
layers of plies of wood are coated with resin, placed together with the resin
sandwiched between adjacent plies and subject to pressure urging them
together and/or heat to cure the resin so that the plies adhere strongly
together. In the conventional methods of production pressure and heat may
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have to be applied for a considerable period of time, for example, several
minutes, adding to the production time and to the expense of production.
In accordance with the invention, a catalyst is distributed through the resin.
The catalyst is distributed through the resin. The catalyst which may be
propylene carbonate, ethylene carbonate or any other suitable catalyst
initiates curing of the resin to produce a bond between adjacent plies of
wood. However, if curing is initiated too early or progresses too quickly,
it may be difficult or impossible to carry out the manufacturing process
satisfactorily and/or efficiently. For example, if curing is already
proceeding
when the pees are coated with res~ 'rt may not be possible to coat the plies
readily and, even if it is, the strength of the bond between plies may be
adversely affected.
In order to overcome this possible disadvantage, the release of the
catalyst into the resin to initiate curing is controlled by encapsulating the
catalyst. Encapsulation is achieved by irradiating the catalyst with
ultrasound in the presence of an encapsulating material to produce
microcapsules of catalyst coated with encapsulating material. The coating
isolates the catalyst from the resin even though the encapsulated resin
capsules are distributed through the resin. In this state, the resin may be
applied to the plies of wood as described previously, but curing will not
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begin and will therefore not affect this process until the granules are
ruptured to release the catalyst into the resin. Rupturing may be effected
by irradiating the capsules with ultrasound or by heat or any other suitable
method.
In an alternative method of encapsulation, catalyst is adsorbed into
the surface of granules of an inert substance which are coated with an
encapsulating material again by irradiating with ultrasound. In both cases
the size of the coated particles would generally lie in the range 0.5 to 1000
microns.
The catalyst may be any of the following materials, or any mixture
thereof:-
Organic peroxides for example Di benzoyl peroxide, Methyl ethyl keto-
peroxide, Cumene hydroperoxide, Acetylacetone peroxide (sole under trade
name Triganox 44B), tert-Butyl peroxybenzoate (sold under trade name
Triganox C, tart-Butyl-2-ethyl hexanoate (sold under trade name Triganox
211, tert-Butylperoxy-3,5,5, trimethyl hexanoate (sold under trade name
Triganox 42s), Cumene hydroperoxide (sold under trade name Triganox
K-80), Biz (4-tert-butylcyclohexyl-peroxdicarbonate) (sold under trade name
Perkadox 16). Amine Catalysts for example: Diethyltetra amine,
Triethylamine Isocyanates, Boron tri fluoride, UV Curing Catalysts, A
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Carbonates for example: Propylene and Ethylene carbonate and mineral and
organic acids such as Formic acid, toluene sulphonic acid, or sulphuric acid.
Accelerators may also be used such as Colbalt octoate 4sold under
trade name , NL-49-P1, Diethyianiline (sold under trade name NL-64-10P).
The encapsulating material may be any one of the following or any
mixture thereof:- gelatine, thermoset resins, fats, waxes, thermoplastics,
polymeric compounds, or silane compounds or any of the encapsulation
materials disclosed in the applicants copending international application
published under publication No. WO 98/26865.
The resin may be any one of the following or any mixture thereof:-
Polyester resin, Vinyl esterresin, Phenol formaldehyde resin, Epoxy resin,
Acrylic resin, melamine/urea formaldehyde resin, Phenolic resin.
In a second embodiment, a catalyst is trapped by absorption into a
suitable substrate rather than by adsorption as previously described. A
suitable substrate is almond shell which has a surface which facilitates
absorption/adsorption of catalyst into 'rts porous structure. The catalyst is
formic acid and the resin is a melamine/urea formaldehyde resin although
other catalysts and resins, for example, as detailed above may be used.
The process for making the almond shell formic acidltoluene
sulphonic acid catalyst material is as follows.
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i) The formic acid/toluene sulphonic acid is first
dissoived/dispersed inrnto acetone. Acetone acts as a carrier solvent
for the acid catalyst into the porous structure of the almond shell.
ii) almond shell is then added to the acid/acetone mixture.
iii) The acid/acetone/almond shell mixture is sonicated using a
20kHz, 400 Watt ultrasonic probe for 3-5 minutes until the
acetonelacid has absorbed/adsorbed into the almond shell structure.
This process can be easily observed by a significant thickening
appearance of the mixture. One of the reasons a solvent is used is
in order for ultrasound to work effectively with a high solid almond
shell content present. Excess liquid is required li.e. acetone) in
which cavitation can develop. When the cavitation bubbles collapse,
a large energy source/shock wave is created and 'rt is this energy
which drives the liquid mixture into the almond shell structure.
iv) The acetone solvent is removed from the slurry mixture using
drying methods leaving just the acid catalyst embedded in the almond
shell. The acetone may be removed and re-cycled using condensers.
The almond shell/acid catalyst product is a fairly free flowing powder
which can be easily dispersed in resin.
Acetone is used as a solvent because;
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a) It has very good dissolving properties. For example, para
toluene sulphonic acid catalyst (PTSA) which is a solid powder,
needs to be dissolved in the acetone before 'rt can be driven into the
almond shell.
b) It has a very low boiling point which facilitates its removal
during the drying process at low temperature. This is a very
important characteristic when formic acid is used because this
catalyst has a relatively low boiling point and therefore if high drying
temperatures were used, the formic acid would be removed as well.
c) The presence of acetone in the svnication process keeps the
temperature very low (specific heat capacity characteristic) reducing
or eliminating vaporisation problems.
When the almond shell/acid catalyst is dispersed with the resin, the
molecules of the resin are so large that they cannot access the almond shell
structure very easily or quickly and therefore cannot come into contact with
the acid catalyst which is embedded in the structure. Curing of the resin
will therefore not begin. The acid catalyst can be activated by heat. This
will cause the structure to expand and open up allowing the resin to get at
the catalyst. It needs to be noted that this is not an encapsulation
technology and no coating has been used. However a coating could be
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applied if the end user/application required much greater pot-life stability.
It will be appreciated that the above embodiments have been
described by way of example only and that many variations are possible
without departing from the scope of the invention. For example, the
method of the invention may be applied to any product manufacture where
one or more parts are coated and/or impregnated with a curable resin either
to enable the parts to be secured together or as part of the production
process.
Felts or glass fibre may be impregnated with a curable resin of the
invention formed into a desired shape and the resin then cured. Material
may be supplied pre-impregnated with resin for use in a downstream
production process. These material composites could be employed in the
following general areas:-
il Bvat construction,
ii) Automotive industry - for example interior/exterior components
and body panels,
iii) Train/Aeorplane construction - for example interior/exter'ror
components and body panels,
iv) Off shore marine/oil drilling applications,
v) Building construction - wall panels (interior/exterior), roofing
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vi) House-hold goods,
vii) Surface coatings
viii) Fire retardent foams/coatings/compos'rtes,
ix) Binders for the paint and paper
industry,
x) Binders for use in the foundry
industry,
xi) Filament windings,
xii) Plastic extrusions,
xiii) Adhesives,
xiv) MDF/Particle Board,
xvl Dough Moulding compounds,
xvi) Pre-impregnated products,
xvii) Binders for concrete applications used in the
building/construction industry.
