|Title of Invention||
"A PROCESS FOR PRODUCING THERMOSET-BONDED FIBRE MOULDINGS"
|Abstract||The present invention relates to a process for producing thermoset-bonded fibre mouldings characterized in that at least two fibre layers produced in a manner as herein described, with different thermoset binders are combined with one another and are hardened at temperatures above the hardening temperatures of the thermoset binders.|
|Full Text||The present invention relates to a process for producing thermoset-bonded fibre mouldings.
Shaped parts produced of fibres, such as are used for example in automobile manufacturing as climate-regulating sound-absorbing parts and shaped parts with high surface and shatter strength are conventionally produced by compression molding and simultaneous curing of phenolic resin-bonded fiber layers (formed fabrics). These products have the disadvantage that they occasionally, especially when they are exposed to the effects of increased temperatures and humidity, produce a disturbing odor which is largely due to the curing agent (hexamethylene tetramine) and its amine decomposition products.
According to EP-A 0 254, 807, this problem is solved by using a powder-form mixture as the bonding agent comprising a phenolic resin which is nonthermo-reactive and one or more condensation product from the group of phenoli-resins, amino resins or epoxide resins. Although the odor formation due to hexamethylene tetramine can thereby be avoided, a residual odor from the phenolic resin remains.
OBJECTS OF THE INVENTION
It is an object of the invention to provide shaped fibrous
elements with a thermosetting resin as the bonding agent which maintain good mechanical, sound-absorption and incombustible properties of phenolic resin bonded fibrous shaped elements free of any odor development of the phenolic resins.
It is another object of the invention to provide a method to produce shaped fibrous elements having increased strength with a weight reduction of the motor vehicle components without any quality loss.These and other objects and advantages of the invention will become obvious from the following detailed description.
Accordingly, there is provided a process for producing thermoset-bonded fibre mouldings characterized in that at least two fibre layers with different thermoset binders are combined with one another and are hardened at temperatures above the hardening termperatures of the thermoset binders.
The thermosetting resin bonding agents may be self-curing resins or may be provided with a curing agent or curing catalyst which are cured to form a high polymer product at an elevated specific temperature. Examples of suitable thermosetting resins
are diallylphthalate resins, epoxide resins, urea resins, melamine resins, melamine-urea resins, melamine-phenolic resins, phenolic resins and mixtures thereof. TheYresins are based on phenolic resins and epoxide resins.
It is surprising that the fibrous shaped elements produced by the invention do not develop an odor of phenolic resin or amine degradation products of hexamethylene tetramine although the individual thermosetting resin bonded fiber layers, and thus also the entire fibrous shaped elements are permeable to air and gas. It is a further unexpected advantage of these fibrous shaped elements that they exhibit increased strength so that it becomes possible to achieve the same strength with thinner fibrous shaped elements of the invention as can be attained with conventional, heavy fibrous shaped elements only bonded with phenolic resin. In particular, a further increase in strength and a decrease of the odor emissions is attained if the fiber layers provided with the thermosetting resin bonding agents are produced according to a carding process.
Examples of phenolic bonding agents are all condensation products of phenols and aldehydes, especially phenol, cresol or xylenol with formaldehyde, more preferably resols and conventional novolac most preferably mixtures of novolac and hexamethylene tetramine. Usually, the phenolic resins are used in the form of powders.
The bonding agents based on epoxide resins are usually a powder mixture of epoxide compounds with at least two epoxy groups per molecule and a curing agent. Latent curing agents are preferred to obtain sufficient processing time between the time of mixing and of curing. Examples of latent curincg agents are acid anhydrides or imidazole derivatives but preferred are novolacs or metal complex compounds such as described in EP-B 0,518,908.
Examples of fibers are inorganic fibers such as glass fibers and organic fiber-like materials or any fiber mixtures. Preferred are organic fibers such as wool, cotton, staple fibers, jute, flax, hemp, polyester or acrylic fibers. A large portion of the fiber material used may be obtained from discarded textile materials by way of a reclamation process which fibers are mixed by methods known per se with the particular bonding agents and placed into discrete fiber layers (formed fabrics, in particular carded formed fabrics ) .According to the invention, several fiber layers (formed fabric webs) with at least two different thermosetting resin bonding agents are placed one on top of the other. Preferably tnere are used one or several fiber layers together with phenolic resin as the bonding agent as the inner layer and its upper side and bottom side each are provided with a covering layer comprising one or several fiber layers comprising epoxide resin as the bonding The individual fiber layers or the stacked structure (intermediate products) are cut to size in a marner known per se and can be either precured and cured at a later time while being shaped, or the stacked structures are immediately cured as sheets at temperatures above the curing temperatures of the thermosetting resin bonding agents. In the simplest case, fibrous formed fabrics are combined with, in each instance, different bonding agents as semifinished products and are molded and cured at a temperature above the curing temperature of the thermo Setting resin bonding agents potentially while being shaped. For example, a hat rack with a weight per unit area of 2500 g/m2 may be fabricated from two semifinished products each weighing 500 g/m2 with an epoxide resin-curing agent mixtures as the bonding agent and an interspaced semifinished product weighing 1500 g/m2 with novolac-hexamethylene tetramine as the bonding agent.
The preferred method of the invention for the production of the thermosetting resin bonded fiber layers is the carding process in which the fibers are combed out to extremely fine piles which then are provided with bonding agents and are stacked in longitudinal and transverse position until the desired weight per unit area is obtained with the upper covering laysr, middle layer and lower layer comprising different bonding agents, if desired. The middle layers preferably comprise also phenolic resins and the upper and lower outer layers epoxide resins as the bonding agent.
In a particularly preferred method, fibrous formed fabrics (fiber layers) are produced by the carding process such that over the continuously produced fiber felt are sprinkled in the longitudinal direction over three equally or differently wide zones different bonding agents whereby the inner zone contains the bonding agent for the inner layer of the fibrous shaped element and the two outer zones contain the bonding agent (s) for the upper and lower outer layer of the fibrous shaped element. The formed fabric web produced in this way is arranged in a cross-folding technique such that the newly formed Fiber felt comprises fiber layers with different bonding agents,
This formed fiber felt is briefly heated such that the thermosetting resin bonding agents melt and are fixed on the fiber, but are not cured. The formed fiber felt is then cooled and fitted. Lastly, the intermediate products produced in this way, potentially while being shaped, are molded and cured in a manner known per se and for this purpose several of these semifinished products can also be placed one above the other and molded together and cured.
In the following example, there is described a preferred embodiment to illustrate the invention. However, it is to be understood that the invention is not intended to be limited to the specific embodiment.
The phenolic resin bonding agent used was a phenol novolac with a softening point of 98°C mixed with 6 wt% of hexamethylene tetramine and, the epoxide resin bonding agent used was a mixture of an epoxide resin based on bisphenol A (epoxide equivalent: 183; softening point: 75°c) and 5 wt% of a latent curing agent comprising a pulverized "solid solution" of 30% 2-methyl-imidazole in 70% of a phenol novolac having a high melting point.
Using the carding process, a fibrous formed fabric comprising a textile fiber mixture and powder resin bonding agents was produced continuously. Over the fibrous formed fiber feet , the different bonding agents were sprinkled in the longitudinal direction over three zones of equal widths. The: two out.p.r zones received the epoxide resin bonding agent and the inner zone received the phenolic resin bonding agent. The formed fiber felt produced in this way was arranged in a cross-folding iecnnigue known per se so that a new formed fiber felt was formed in which the inner layer comprised the phenolic resin and the upper and the lower outer layer comprised the epoxide resin as the bonding agent.
The said formed fiber felt was conducted through a circulating air oven kept at 150°C at such a rate that this bonding agents melted and became fixed on the fibers but were not cured. The web was then cooled, fitted and then, while being shapad, molded for 60
seconds at 18C-190°C and 170 bars and cured. the thermosetting resin bonded tibrous shaped element was self-extinguishing and, when exposed to external flames, had a low smoke density. The fibrous shaped element was free of odors, even under the effect of increased temperatures (40-70°C) and humidity (90% relative ambient humidity). Compared to a fibrous shaped element bonded only with phenolic resins of the same weight per unit ares , it possessed a strength which was increased by 27% and no separation phenomena of individual layers, the so-called splitting, were observed.
Various modifications of the elements and method of the invention may .be made without departing from the spirit or scope thereof and it is to be understood that the invention ie intended to be limited only as defined in the appended
1. A process for producing thermoset-bonded fibre mouldings
characterized in that at least two fibre layers produced in a
manner as herein described, with different thermoset binders are
combined with one another and are hardened at temperatures
above the hardening temperatures of the thermoset binders.
2. A process as claimed in claim 1, wherein the fibre layers
are combined with one another in such a way that one or more
fibre layers with binder based on phenolic resin form the inner
ply, and the inner ply is provided at its upper and lower side in
each case with an outer ply composed of one or more fibre
layers which contain binder based on epoxy resin.
3. A process as claimed in claims 1 and 2, wherein the fibre
layers provided with thermoset binder are produced by the
4. A process as claimed in claims 1 to 3, wherein said
process comprises sprinkling of the fibre web with different
binders in the longitudinal direction, in three zones of equal or
different width, such that the inner zone contains phenolic-resin
binder and the two outer zone contains epoxy-resin binder, the
fleece web thus produces is laid using the cross-laying technique
such that the newly formed fleece web contains an inner ply
with phenolic resin and an upper and a lower outer ply with
epoxy resin, this fleece web is heated for a short time such that
the binders melt and fix on the fibre but do not harden, the
fleece web is then cooled, prepared, and compressed and
hardened with optional shaping.
5. A process for producing thermoset-bonded fibre mouldings substantially herein described with reference to the foregoing examples.
|Indian Patent Application Number||769/DEL/1998|
|PG Journal Number||11/2008|
|Date of Filing||24-Mar-1998|
|Name of Patentee||BAKELITE AG,|
|Applicant Address||GENNER STR. 2-4, D-58642 ISERLOHN LETMATHE, GERMANY|
|PCT International Classification Number||D04H 1/08|
|PCT International Application Number||N/A|
|PCT International Filing date|