U.S. patent application number 13/084306 was filed with the patent office on 2011-07-28 for process and apparatus for forming thermosetting material.
This patent application is currently assigned to DSM IP ASSETS B.V.. Invention is credited to Jan NUSSELDER, Hubertus STIJNEN, Rudolfus VAN BENTHEM.
Application Number | 20110180207 13/084306 |
Document ID | / |
Family ID | 33487992 |
Filed Date | 2011-07-28 |
United States Patent
Application |
20110180207 |
Kind Code |
A1 |
VAN BENTHEM; Rudolfus ; et
al. |
July 28, 2011 |
PROCESS AND APPARATUS FOR FORMING THERMOSETTING MATERIAL
Abstract
The invention relates to a process for forming a cured,
partially cured or uncured thermosetting material, comprising: an
irradiation step wherein the thermosetting material is exposed to
electromagnetic radiation which to a significant extent is within
the near-infrared range in such a way that the temperature of the
irradiated thermosetting material is brought to between 40.degree.
C. and 400.degree. C., and a forming step wherein the irradiated
thermosetting material is brought into a desired shape, whereby the
forming step is executed during and/or subsequent to the
irradiation step. The invention also relates to an apparatus for
carrying out the said process and to a thermosetting material.
Inventors: |
VAN BENTHEM; Rudolfus;
(Limbircht, NL) ; NUSSELDER; Jan; (Sweikhuizen,
NL) ; STIJNEN; Hubertus; (Dilsen-Stokkem,
BE) |
Assignee: |
DSM IP ASSETS B.V.
Heerlen
NL
|
Family ID: |
33487992 |
Appl. No.: |
13/084306 |
Filed: |
April 11, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10558407 |
Nov 28, 2005 |
7951323 |
|
|
PCT/NL2004/000384 |
May 27, 2004 |
|
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13084306 |
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Current U.S.
Class: |
156/275.5 ;
156/380.9 |
Current CPC
Class: |
B29B 13/08 20130101;
B29C 35/0805 20130101; B29B 13/023 20130101; B29C 2035/0822
20130101; B29C 65/1416 20130101; B29C 35/08 20130101 |
Class at
Publication: |
156/275.5 ;
156/380.9 |
International
Class: |
B29C 65/14 20060101
B29C065/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2003 |
NL |
1023563 |
Claims
1. Apparatus for shaping a multilayer laminate preform having at
least on layer comprised of a partially cured thermosetting phenol
and/or aminoplast resin, comprising: a) means of irradiating the
multilayer laminate preform with electromagnetic radiation, whereby
near infrared range with a wavelength of between 0.8 .mu.m and 1.5
.mu.m is at least 10% of the electromagnetic radiation, expressed
in energy per surface area, that is directed at the multilayer
laminate preform; and b) means of exerting deformation force on the
irradiated multilayer laminate preform.
2. Apparatus according to claim 1, comprising means to irradiate
the multilayer laminate perform with said electromagnetic radiation
during the shaping of the multilayer laminate preform.
3. Apparatus according to claim 1, wherein the intensity of the
electromagnetic radiation aimed at the multilayer laminate preform
can be set between 100 and 8000 kW/m.sup.2.
4. Apparatus according to claim 1, comprising means to expose the
multilayer laminate preform with said electromagnetic radiation
from several sides.
5. Apparatus according to claim 1, wherein means are present to
terminate the irradiation step when the temperature of the
multilayer laminate preform has reached the desired temperature,
such termination being automated with the aid of temperature
measurement on the multilayer laminate preform and a feedback
circuit.
6. Apparatus according to claim 1, wherein means are present to
shape the multilayer laminate preform in 2D or 3D during the
deformation step.
7. Apparatus according to claim 1, wherein the means of exerting
deformation force are means for shaping the multilayer laminate
preform into the arc of a circle with a radius of at most 3 cm.
8. Apparatus according to anyone of claims 1, comprising means to
measure the deformation force as executed on the multilayer
laminate perform during shaping.
9. Apparatus according to claim 8, comprising means to adjust the
amount of radiation as a function of the deformation force.
10. Process for optimizing an existing apparatus for heating and/or
forming a multilayer laminate preform having at least on layer
comprised of a partially cured thermosetting phenol and/or
aminoplast resin, characterized in that a radiation source is added
which emits electromagnetic radiation which to a significant extent
is within the near-infrared range.
Description
[0001] This application is a divisional of commonly owned copending
U.S. Ser. No. 10/558,407, filed on Nov. 28, 2005 (U.S. Pat. No.
______), which is the national phase application under 35 USC
.sctn.371 of PCT/NL2004/000384, filed May 27, 2004 which designated
the U.S. and claims priority to The Netherlands Patent Application
No. 1023563, filed May 28, 2003, the entire contents of each of
which are hereby incorporated by reference.
[0002] The invention relates to a process for forming an uncured,
partially cured or cured thermosetting material. The invention also
relates to an apparatus for forming a cured or uncured
thermosetting material. The invention further relates to a
thermosetting material.
[0003] A process for forming a cured or uncured thermosetting
material is known, and is described in for example U.S. Pat. No.
3,730,828. The thermosetting material, a laminate containing a
melamine-formaldehyde (MF) resin, is heated by infrared lamps to a
temperature of approximately 325.degree. F. (163.degree. C.) and
then formed. In known processes the reported temperature generally
is determined on the basis of surface measurements for instance
with the aid of melting chalk crayons or other techniques known to
those skilled in the art.
[0004] The known process has the disadvantage that the heating
technique requires much time. A heating time--to a temperature
which, as is known, often lies between 160.degree. C. and
190.degree. C.--varying from tens of seconds for a thermosetting
material of a few tenths of a millimeter thickness to many minutes
for a thermosetting material of a few millimeters thickness is not
unusual. As a result a number of unwanted side effects such as
blistering, undesired curing, and degradation can occur. Due to the
required time and due to the occurring side effects it is not often
possible to achieve the ideal forming temperature and it is
necessary to make do with forming at a lower than ideal
temperature, which in its turn entails a strongly increased risk of
crack formation and/or fracture during or after forming.
Furthermore, in the known process it is often necessary to use
thermosetting materials which have cured to a lesser degree than
desirable, as viewed from the requirements specified for the end
products, because the forming step cannot otherwise be completed
without crack formation or even fracture. Also, in the known
process it is often necessary to add plasticisers to the
thermosetting material, because the forming step cannot otherwise
be completed without crack formation or even fracture; however,
adding a plasticiser to the thermosetting material often leads to
deterioration of various properties in the end product such as
reduced scratch resistance and/or reduced chemical resistance.
[0005] It is the object of the invention to largely avoid the said
disadvantages.
[0006] The said object is achieved in that the process comprises:
[0007] an irradiation step wherein the thermosetting material is
exposed in such a way to electromagnetic radiation which to a
significant extent is within the near-infrared range that the
temperature of the irradiated thermosetting material is brought to
between 40.degree. C. and 400.degree. C.; and [0008] a forming step
wherein the irradiated thermosetting material is brought into a
desired shape, whereby the forming step is executed during and/or
subsequent to the irradiation step.
[0009] The advantage of the process according to the invention is
that radiation within the near-infrared range ensures much faster,
through-and-through heating of the thermosetting material than in
the known case of heating by for example regular infrared
radiation. Due to this faster heating the most optimal temperature
for the forming step can be reached, while the risk of unwanted
side effects such as blistering is minimised by the short time
required for the irradiation step and forming step. It is a further
advantage of the process according to the invention that the amount
of reject material of the thermosetting material-containing end
products due to the occurrence of unwanted side effects can be
reduced in comparison with the known process.
[0010] The process according to the invention is applied to a
thermosetting material. Thermosetting materials are known per se. A
known characteristic of a thermosetting material is that it is
cured so as to obtain it in the form in which it is ultimately
used. As is known, a thermosetting material, once completely cured,
can no longer be turned into molten form without degrading it on a
molecular scale. When a thermosetting material has been cured
partially, almost completely or completely, some forming, such as
forming in the forming step according to the invention, is still
possible, usually with the aid of a heating step. As is known, to
this end it is generally recommended to heat the thermosetting
material beyond the glass transition temperature (T.sub.g). The
thermosetting materials which can be used in the process according
to the invention preferably contain --OH, --NH, and/or
--SH-comprising compounds; more preferably the thermosetting
material comprises a phenol resin and/or an aminoplast resin. A
thermosetting material may in practice contain several compounds,
such as a combination of a phenol resin and an aminoplast resin,
for example in separate layers. The thermosetting material contains
with particular preference an aminoplast resin. Examples of
aminoplast resins are a melamine-formaldehyde resin (MF), a
urea-formaldehyde resin (UF) and a melamine-urea-formaldehyde resin
(MUF). The thermosetting material used in the process according to
the invention may contain a filler; this is a substance which does
not significantly contribute to the curing process, but is usually
intended to impart other specific properties such as strength or
surface texture. Such fillers are known per se and include paper as
a filler in a laminate; wood chips as a filler in a chipboard. The
thermosetting material according to the invention can also be a
layer on a substrate; an example of such an application known per
se is a coating on a metal or plastic substrate. The substrate can
be a cured or uncured thermosetting material, but the substrate
can, as indicated, also be another material such as a metal or a
thermoplastic.
[0011] The thermosetting material which is used in the process
according to the invention has or has not been cured; it is not
necessary that the curing has already taken place, it may be,
however, that this has already taken place partly or even entirely
or almost entirely. Preferably the thermosetting material has
already been cured at least partially. The advantage of this is
that the material to some extent already possesses the mechanical
properties of the end product, such as rigidity, so that the
material is easier to handle. More preferably the thermosetting
material has already been completely or almost completely cured.
The degree of curing of the thermosetting material may be derived
from DSC or, preferably, TMDSC measurements. (TM)DSC stands for the
known technique of (Thermally Modulated) Differential Scanning
calorimetry. For known thermosetting materials, the skilled person
knows the peak in the TMDSC curve that is attributable to curing.
For the said thermosetting material, the temperature at which the
forming step takes place is also known. As reference, the TMDSC
curve of the thermosetting material in non-cured state is
determined. From this curve, the peak attributable to curing is
determined; from this peak, the curing enthalpy (.DELTA.H) up to
the temperature at which forming takes place is then calculated.
The thus determined .DELTA.H value is defined as a 0% degree of
curing. A fully cured thermosetting material will show--up to the
forming temperature--no peak attributable to curing, thus a
.DELTA.H value of 0; this is defined as a 100% degree of curing.
Intermediate .DELTA.H values are easily re-calculated into--and are
hereby defined as--intermediate percentages of curing. Preferably,
the thermosetting material has--as it enters the process according
to the invention been cured at least 40% or 50%; more preferably,
the thermosetting material has been cured at least 60% or 70%; most
preferably, the thermosetting material has been cured at least 80%
or 90%. It may be beneficial to ensure that the thermosetting
material has not been cured 100%, but rather only 98%, or
preferably only 95%; this has the advantage that the thermosetting
material can be formed into more extreme shapes during the forming
step according to the invention.
[0012] The thermosetting material is exposed in the irradiation
step of the process according to the invention to radiation that
lies to a significant extent within the near-infrared range. "To a
significant extent" in the framework of this invention means that
near-infrared radiation is the largest, largest but one or the
largest but two part of the electromagnetic radiation expressed in
energy per surface area, that is directed at the thermosetting
material. Radiation within the near-infrared range refers to
radiation with a wavelength of between 0.8 .mu.m and 1.5 .mu.m.
This type of radiation typically causes heating but not
photo-curing (i.e. curing as a result of the direct breaking of
atomic bonds through photons). Preferably at least 10% of the
electromagnetic radiation, expressed in energy per surface area,
aimed at the thermosetting material is within the near-infrared
range. More preferably at least 15% or 20% of the electromagnetic
radiation aimed at the thermosetting material is within the
near-infrared range. The advantage of this is that the unwanted
side effects such as blistering have little opportunity to develop
due to the speed with which the process according to the invention
can be carried out. Still more preferably at least 30% or 40%, with
special preference at least 45% or 50% and most preferably at least
55%, 60% or even at least 70% or 75% of the electromagnetic
radiation aimed at the thermosetting material is within the
near-infrared range. In order to ensure fast heating to the desired
temperature it is preferable to direct at least 1 or 5 kW/m.sup.2,
or even 10 kW/m.sup.2 of electromagnetic radiation at the
thermosetting material. This also has the advantage that, as a
consequence of rapid heating, a wider operating window is formed:
the thermosetting material can be heated up within a larger
temperature range than with the known process, without too many
unwanted side effects ocurring. More preferably at least 30 or 50
kW/m.sup.2, with special preference at least 100 or 200 kW/m.sup.2,
and most preferably at least 400 or 800 kW/m.sup.2 of
electromagnetic radiation is aimed at the thermosetting material.
On account of the high effectiveness of near-infrared radiation in
the process according to the invention it is preferable to aim at
most 10000 or 9000, more preferably at most 8000 or 6000, and most
preferably at most 5000 kW/m.sup.2 of electromagnetic radiation at
the thermosetting material.
[0013] The thermosetting material will heat up as a result of
exposure to near-infrared radiation. In the process according to
the invention the thermosetting material is brought to a
temperature of between 40.degree. C. and 400.degree. C. It has been
found that the heating of the thermosetting material by
near-infrared radiation is very effective because near-infrared
radiation penetrates very deep into the thermosetting material. As
a consequence, the temperatures mentioned herein can be determined
in the same way as in the known process referred to, that is, with
the aid of surface measurements, but the average temperature in the
thermosetting material in the process according to the invention
will be higher at the same surface temperature than when known
heating techniques are employed. It is an advantage of the process
according to the invention that the thermosetting material heats up
more homogeneously than with the application of known heating
techniques such as standard infrared irradiation. A temperature of
at least 40.degree. C. is generally necessary to be able to apply
the forming step according to the invention to the thermosetting
material. With increasing temperature it is becomes increasingly
easy to apply the forming step according to the invention. An
additional advantage of heating the thermosetting material with
near-infrared radiation to a higher temperature than 40.degree. C.
can also be that any further or residual curing can also be
initiated. The optimal temperature to which the thermosetting
material is heated depends in part on the specific composition of
the material; these temperatures are usually known or can be
determined by means of simple experiments. If the thermosetting
material is heated to a very high temperature, undesired effects
such as degradation can occur. In particular a temperature above
400.degree. C. is not recommendable because very fast degradation
of the thermosetting material then occurs. Preferably the
thermosetting material is heated to at least 100.degree. C. or
140.degree. C., more preferably to at least 150.degree. C. or
170.degree. C., most preferably to at least 180.degree. C. or even
190.degree. C. Preferably the thermosetting material is heated to
at most 350.degree. C. or 300.degree. C., more preferably to at
most 250.degree. C., most preferably to at most 220.degree. C. If
the T.sub.g of the thermosetting material is known, it is
recommended to heat the thermosetting material to at least
10.degree. C. or 20.degree. C. above T.sub.g, preferably at least
30.degree. C. or even 50.degree. C. above T.sub.g, more preferably
at least 75.degree. C. or 100.degree. C. above T.sub.g, while
remaining at or below 400.degree. C. If the thermosetting material
comprises an aminoplast resin, it will usually be necessary to heat
to a temperature of between 100.degree. C. and 220.degree. C.,
preferably between 160.degree. C. and 190.degree. C.
[0014] As a consequence of the large penetration depth of
near-infrared radiation as used in the process according to the
invention, the thermosetting material can have a large thickness
with heating yet taking place much more uniformly across the
thickness than with known heating techniques such as standard
infrared radiation. Preferably the thermosetting material has a
thickness of at most 30 or 25 mm, more preferably at most 20 mm or
10 mm, still more preferably at most 8 mm, with special preference
at most 6 mm and most preferably at most 5 mm. For relatively thick
thermosetting materials, for example with a thickness of 6 mm to 25
or 30 mm, it can be advantageous to irradiate the thermosetting
material in the irradiation step from several sides; for example,
if the thermosetting material is flat or almost flat, from the top
and the underside. It can also be advantageous to irradiate from
one side and at the same time to position a material that reflects
near infrared radiation, such as a metal, in such a way that that
non-absorbed radiation is reflected so that the reflected radiation
once again penetrates the thermosetting material. In a special
preferred embodiment the thermosetting material consists of at
least 2 layers and is characterised in that at least one layer is a
reflective layer; this means that the reflective layer comprises a
material that reflects near-infrared radiation. The invention
therefore relates also to a thermosetting material that contains a
reflective material. Examples of such reflective materials are
metals such as aluminium. The reflective material can be present as
a continuous phase in the reflective layer; the reflective material
can also be present in the form of dispersed reflective particles.
The reflective layer can be the surface layer on one side of the
thermosetting material, with the electromagnetic radiation being
directed at the thermosetting material from for example another
side. Preferably the thermosetting material comprises at least 3
layers and the reflective layer is not on the surface of the
thermosetting material; more preferably the thermosetting material
comprises at least 4 layers with the reflective layer substantially
or entirely in the middle of the thermosetting material. The
advantage of this is that if the thermosetting material is
irradiated from several sides, the heating takes place evenly; also
it is possible to effectively treat in the irradiation step
relatively thick thermosetting materials with a total thickness of
for example 15 mm or 20 mm or more.
[0015] The thermosetting material will usually have a thickness of
at least 25 .mu.m, preferably at least 0.1 mm, more preferably at
least 0.5 mm. If the thermosetting material is used in the process
according to the invention in the form of a laminate, the thickness
will usually be between 0.6 and 1.2 mm, since such thicknesses
commonly occur in practice.
[0016] As a consequence of the effective, deeply penetrating
heating effect of the near-infrared radiation, the irradiation step
can usually be carried out faster than known irradiation steps.
Preferably the thermosetting material is irradiated for 0.01 to 60
seconds; more preferably for 0.1 to 30 seconds; still more
preferably for 0.5 to 20 seconds, most preferably for 1 to 10
seconds.
[0017] In a preferred embodiment of the process according to the
invention the temperature of the thermosetting material is measured
at a high frequency, for example a few tens of times or even a few
hundreds to thousands of times per second. The duration of the
irradiation step can be determined in this embodiment by means of a
feedback circuit: in this way it is possible to terminate the
irradiation step the moment a predetermined temperature, being an
aforementioned temperature to which the thermosetting material must
be heated, is reached. Preferably this embodiment is automated with
the aid of the said temperature measurement and feedback
circuit.
[0018] During or upon completion of the irradiation step in the
process according to the invention a forming step is applied
wherein the irradiated thermosetting material is brought into a
desired shape. Such a forming step is known per se to those skilled
in the art. Forming can take place along one axis, also known as 2D
forming. Forming can also take place along two intersecting axes,
also known as 3D forming. The degree of forming is dependent on the
desired shape of the end product and on the maximum possible amount
of forming allowed by the thermosetting material. In the forming
process it is in general important to prevent the thermosetting
material from cracking or fracturing. This can happen if the
thermosetting material is excessively deformed, that is, into the
arc of a circle with too small a diameter. In this connection it
holds that 3D forming is more difficult to accomplish, which means
it sooner leads to crack formation or fracture than 2D forming. It
holds in general that a higher temperature of the thermosetting
material, in particular a temperature higher than the T.sub.g,
makes a higher degree of forming possible during the forming step.
The process according to the invention has the advantage that, due
to rapid heating of the thermosetting material which makes it
possible to heat to a higher temperature than when use is made of
known heating processes such as standard infrared radiation so that
unwanted side effects such as blistering are partially or entirely
avoided, a higher degree of forming is possible than with the known
process. The thermosetting material can, in the process according
to the invention and at the temperature optimal for the material,
usually be formed into the arc of a circle having a radius of at
most 3 cm, preferably at most 2, more preferably at most 1 or 0.8
and most preferably 0.6 cm or even 0.4 cm without the thermosetting
material crack formation or breaking. It holds here also that the
maximum degree of forming to be achieved must be seen as a function
of the thickness of the thermosetting material, where it generally
holds that the thicker the material, the more limited the forming
possibilities. By way of indication, the forming step according to
the invention can be practised to form the arc of a circle with a
radius that is 10 times or a higher multiple of the thickness of
the thermosetting material, preferably 8 times or a higher
multiple, more preferably 6 times or a higher multiple and most
preferably 5 times or a higher multiple.
[0019] The forming step according to the invention can be executed
upon completion of the irradiation step. In a preferred embodiment
of the process according to the invention, the forming step is done
at least partly during the irradiation step: the thermosetting
material is thus heated or further heated while it is being brought
into the desired shape. This method of operation is enabled by the
quick and through-and through heating effect of the near-infrared
radiation. The advantage of this embodiment is that the process
according to the invention can be executed much quicker than when
the irradiation step and the deformation step are executed
subsequently; another advantage of this embodiment according to the
invention is that a much more precise amount of irradiation can be
administered, namely only so much as is needed--at the moment when
it is needed, thereby ensuring an even further reduction of
undesired side effects occurring in the thermosetting material can
be achieved; a yet further advantage of this embodiment is that any
curing or further curing of the thermosetting material is postponed
as much as possible to after the forming step has been executed,
since the forming is done as the heating takes place.
[0020] As is known to the skilled person, a certain amount of force
(deformation force) is exerted during the forming step in order to
achieve the end result, i.e. bring the thermosetting material into
its predetermined desired shape. For thermosetting materials, the
said deformation force will typically decrease with increasing
temperature of the thermosetting material. The said deformation
force should remain within certain limits: a very high deformation
force indicates a shift towards an unfavourable deformation
mechanism, leading to cracks in, or breakage of the thermosetting
material. A very low deformation force, on the other hand,
indicates that the temperature of the thermosetting material is
higher than necessary, thus leading to waste of energy and
promotion of unwanted side effects. The precise limits beyond which
a deformation force should be considered as being too high or too
low will, as the skilled person will appreciate, depend on
parameters such as the thickness and properties of the
thermosetting material itself; as an approximation, these limits
can be considered to be the same as in case of a deformation step
which is done with a pre-heated thermosetting material, whether or
not said pre-heating was done according to the invention. In any
case, a deformation force accompanied by crack formation in the
thermosetting material is typically considered to be too high; on
the other hand, a deformation force accompanied by unwanted side
effects such as degradation is typically considered to be too
low.
[0021] Preferably, the apparatus in which the forming step is being
done at least partly during the irradiation step is equipped in
such a fashion that an indication or a measurement of the said
deformation force is provided. If the indication or measurement
shows that the deformation force as needed in order to achieve the
predetermined desired deformation is too high, then the amount of
near-infrared irradiation to which the thermosetting material is
exposed should be increased. On the other hand, if the indication
or measurement shows that the deformation force as needed is too
low, then, by the same principle, the amount of near-infrared
irradiation to which the thermosetting material is exposed should
be decreased. Preferably, the deformation force measurement and
subsequent adjustment of the amount of irradiation is
automated.
[0022] If the thermosetting material is to be a layer on a
substrate, it can be advantageous or necessary to carry out the
forming step only for the thermosetting material to ensure that the
thermosetting material conforms to the shape of the substrate.
[0023] It is possible to carry out the irradiation step for the
thermosetting material as a whole. This is advantageous because it
is much more difficult with the known processes to heat a large
surface area, for example 0.5 to 2 m.sup.2without unwanted side
effects occurring. The process according to the invention thus
enables 3D forming of large moulded articles of thermosetting
materials, such as chairs or other pieces of furniture.
[0024] In another preferred embodiment of the process according to
the invention the irradiation step is only applied to a part of the
thermosetting material, namely only the part to be formed in the
forming step. The advantage of this is that there is no way of
unwanted side heating effects, such as blistering or degradation,
occurring in unirradiated parts. A further advantage of the
preferred embodiment is that the irradiated part of the
thermosetting material will cool down faster after the forming
step, since heat can then be dissipated to the non-heated parts,
which reduces still further the probability of unwanted side
heating effects in the irradiated part. Irradiating only a part of
the thermosetting material can be accomplished by means of a
technique known per se; it is possible, for example, to place a
mask, fashioned from a material that screens or reflects
electromagnetic radiation, such as a metal, between the
near-infrared source and the thermosetting material.
[0025] If the process according to the invention is done on an
uncured or partially cured thermosetting material, then the heating
of the thermosetting material to a temperature lying between
40.degree. C. and 400.degree. C. may, as a beneficial side effect,
lead to a partial or even complete curing of the thermosetting
material. If however there was no curing or partial curing, it may
be advantageous to execute, subsequent to the forming step, a
post-curing step wherein the thermosetting material is exposed to
electromagnetic radiation which to a significant extent is within
the near-infrared range in such a way that the temperature of the
irradiated thermosetting material is brought to or maintained at a
temperature lying between 40.degree. C. and 400.degree. C. The
advantage of post-curing the thermosetting material is that a
higher degree of curing usually leads to improved properties of the
thermosetting material, such as thermal- and chemical resistance
and mechanical properties.
[0026] During and/or after completion of the forming step or the
post-curing step according to the invention, a cooling step can be
carried out. The aim of the cooling step is to cool the
thermosetting material rapidly; this has the advantage that the
aforementioned unwanted side effects are limited still further. The
cooling step can be carried out by means of processes known per se
to those skilled in the art, such as through forced air cooling or
through direct contact between a cooling element and the
thermosetting material.
[0027] The invention also relates to an apparatus for forming a
thermosetting material. The apparatus according to the invention is
suitable for practising the above-mentioned process. The apparatus
comprises means known per se for forming the thermosetting
material. The apparatus also comprises means of irradiating the
thermosetting material with electromagnetic radiation which to a
significant extent is within the near-infrared range. Such means
are, albeit for a different application, known per se to those
skilled in the art.
[0028] An apparatus according to the invention can be based on an
apparatus which is known from European standard EN 438-2 (1991) and
described in chapter 21 `Formability (Process B)` and FIG. 22 of
this standard, whereby the radiation source described in the
above-mentioned standard must be replaced by a radiation source
which emits radiation which to a significant extent is within the
near-infrared range; such radiation sources are known per se and
are produced by for example AdPhos.RTM.. Preferably, the apparatus
according to the invention comprises means to irradiate the
thermosetting material during the forming thereof, said irradiation
being done with electromagnetic radiation which to a significant
extent is within the near-infrared range. With this apparatus,
embodiments of the process according to the invention where the
forming step is executed partly or wholly simultaneously with the
irradiation step can be implemented. Preferably, the said apparatus
comprises means to measure the deformation force as executed on the
thermosetting material in order to obtain the desired degree of
forming, and means to adjust the amount of irradiation to which the
thermosetting material is exposed during forming as function of the
deformation force.
[0029] In addition to an apparatus which is suitable for carrying
out the said radiation step and forming step, the invention also
relates to optimising an existing apparatus for heating and/or
forming a thermosetting material wherein the optimisation comprises
adding a radiation source which emits electromagnetic radiation
which to a significant extent is within the near-infrared range.
Addition of the near-infrared radiation source allows the
advantages of the invention, such as accelerated and/or localized
heating and the achievement of higher temperatures in the
thermosetting material, to be achieved without a completely new
apparatus needing to be made.
[0030] The present invention will be illustrated by means of
Examples and comparative Experiments.
EXAMPLE 1
[0031] A flat piece of HPL (high-pressure laminate) consisting of
core layers and surface layers was heated by means of irradiation.
The HPL as chosen is suitable for so-called post-forming, i.e. a
forming step subsequent to the preparation of the HPL; this
indicates that the laminate was not fully cured. The core layers
consisted of natron kraft paper, impregnated with commercially
available phenol-formaldehyde resin. The surface layers consisted
of white paper, impregnated with a commercially available
melamine-formaldehyde resin. As is known, both phenol-formaldehyde
resins and melamine-formaldehyde resins as used in practice
comprise additives. The total thickness of the laminate was 0.8 mm.
The irradiation source was a near-infrared (NIR) lamp (supplier:
Adphos); about 50% of its radiation falls within the NIR range. The
laminate was heated with an intensity of 250 kW/m.sup.2 (total),
from room temperature to a temperature between 160.degree. C. and
190.degree. C.--this being the operating window of the post-forming
step for this type of laminate--within 4 seconds. After heating,
the laminate could be successfully 2D-formed. Forming was done to
the arc of a circle having an 8 mm radius. No cracking or
degradation was observed.
Comparative Experiment A
[0032] The same HPL laminate as in Example 1 was heated from room
temperature to a temperature between 160.degree. C. and 190.degree.
C.; however, use was made of a lamp emitting regular infrared
radiation. The irradiation step took 30 seconds; only then could
the laminate be formed.
Example 2
[0033] An HPL laminate having the same structure as in Example 1
but having a total thickness of 4 mm was subjected to the same
irradiation step as in Example 1. The temperature at the surface
was measured, as usual. Additionally, the temperature in the core
of the laminate was also measured; this could be achieved through
the incorporation of a thermocouple inside the laminate during the
process of preparing the HPL. After 18 seconds, the core had
reached the post-forming temperature of 160.degree. C.; at that
moment, the surface temperature was 180.degree. C. After heating,
the laminate could be successfully 2D-formed. Forming was done to
the arc of a circle having a 40 mm radius. No cracking or
degradation was observed.
Comparative Experiment B
[0034] The same 4 mm HPL laminate as in Example 2 was heated;
however, use was made of a lamp emitting regular infrared
radiation. The irradiation step took 3 minutes; only then had the
core reached 160.degree. C. At that moment, however, serious
degradation of the surface had occurred. This rendered the laminate
unsuitable for further use. The experiment was stopped.
Example 3
[0035] Example 2 was repeated with an HPL laminate of 8 mm
thickness. In this experiment, the near-infrared radiation was not
continuous but pulsating in order to avoid overheating of the
surface. After 2 minutes, the core had reached 160.degree. C.,
starting from room temperature; the surface temperature was between
190 - 200.degree. C.
Comparative Experiment C
[0036] The same 8 mm HPL laminate as in Example 3 was heated, with
the objective of increasing the temperature from room temperature
to a temperature between 160.degree. C. and 190.degree. C.;
however, use was made of a lamp emitting regular infrared
radiation. After 4.5 minute, the core had reached 150.degree. C.;
prolonged irradiation, however, did not result in an increase of
core temperature to 160.degree. C. or above. The experiment was
therefore stopped.
[0037] From the Examples 1-3 and Comparative Experiments A-C, it
clearly follows that the use of near-infrared radiation allows
faster and more in-depth heating of a laminate than regular
infrared radiation, thereby enabling a quicker and better forming
process, even when regular heating sources are not able to
successfully heat the laminate (e.g. at higher thicknesses).
Example 4-7
Comparative Experiment D
[0038] The HPL laminate of Example 1 was subjected to a post-curing
step by irradiation with NIR lamps (supplier: Adphos); about 50% of
its radiation falls within the NIR range. The laminate was heated
with an intensity of 250 kW/m.sup.2 (total). The degree of
additional curing in the core and in the surface layer was
determined as function of irradiation time, by means of a TMDSC
measurement. TMDSC stands for the known technique of Thermally
Modulated Differential Scanning calorimetry; this technique enables
the skilled person to distinguish reversible processes (such as
attributable to a T.sub.g transition) from non-reversible processes
such as the curing of a thermosetting material. The peak
attributable to curing could be identified with additional
certainty since it is known from this type of laminates that curing
takes place at temperatures lying between about 120.degree. C. and
about 180.degree. C. In the measurements of this Example, the
samples were placed in a closed high-pressure re-usable stainless
steel sample holder so as to prevent the loss of any water vapour
as generated during the curing. Heating rate was 2.5 .degree. C.
per minute; the temperature modulation had an amplitude of
0.5.degree. C. and a period of 90 seconds. The degree of additional
curing was defined as 0% for the sample that had not been exposed
to any post-curing step (Comparative Experiment D). A 100%
additional curing score was awarded if the TMDSC curve showed no
peak at all that could be attributed to curing. Intermediate scores
are arrived at by first measuring the curing enthalpy (.DELTA.H) in
the Example, expressing this curing enthalpy as a percentage of the
curing enthalpy of Comparative Experiment D, and subtracting the
said percentage from 100%.
[0039] The results are summarized in the table:
TABLE-US-00001 Example/ Irradiation time Degree of additional
Degree of additional Experiment (seconds) cure (%)-core cure
(%)-surface D 0 0 0 4 0.5 20 77 5 1 27 85 6 2.5 82 100 7 4 100
100
[0040] Examples 4-7 clearly show that a post-curing step can be
done successfully by means of the use of near-infrared radiation.
The difference in percentages between core and surface are
primarily attributed to the known fact that phenolic resins--i.e.
the resins in the core - cure at a slower pace than the
melamine-formaldehyde resins as present in the surface.
* * * * *