Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles
Reexamination Certificate
2000-09-15
2003-05-13
Staicovici, Stefan (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
C264S123000, C264S128000, C047S057700, C047S05900R, C047S064000
Reexamination Certificate
active
06562267
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the manufacture of a mineral wool plant growth substrate, and the obtainable mineral wool plant growth substrate.
2. Description of the Prior Art
Plant growth substrates may have the form of plugs accommodatable in a tray hole, of cubes having a foil around the standing side surfaces, of plastic rapped slabs, or of grannulate.
Conventional mineral wool plant growth substrates are based on a coherent matrix of mineral wool of which the mineral wool fibres are mutually connected by cured binder which is generally a phenol-formaldehyde resin. Due to the use of this type of binders the matrix of mineral wool has to be provided with a so called wetting agent in order to impart the hydrophobic mineral wool matrix with hydrophilic properties. That is, the matrix can absorb in a relatively short time period up to saturation amounts of water. This type of conventional plant growth substrates imparted with hydrophilic properties by the use of a wetting agent are for instance disclosed in GB-A-1 336 426. The use of wetting agents, in particular of Triton trade name has several disadvantages. One disadvantage is that Triton may have toxic,effects, and is leached out of the plant growth substrates after a period of flushing nutrient solution through the plant growth substrate. This means that over a time period the wetting agent is removed out of the matrix of mineral wool such that after water depletion it is difficult if not impossible to rewet the hydrophilic plant growth substrate because it lost its hydrophilic properties.
WO 97/07664 discloses a hydrophilic plant growth substrate that obtained its hydrophilic properties from the use of a furan resin as a binder. The use of a furan resin allows the abandonment of the use of a wetting agent. Accordingly, this known hydrophilic plant growth substrate does not suffer from the disadvantages relating to the use of a wetting agent, in particular of Triton. A disadvantage of the use of a furan resin as a binder for a coherent matrix of mineral wool fibres for a plant growth substrate, is that the furan resin is relatively expensive. Accordingly, the use of these hydrophilic plant growth substrates having a cured furan resin binder is less economical.
It is disclosed in WO 97/07664 that the furan resin may consist in a copolymer of the furan molecule monomer and other monomers, such as formaldehyde and phenol. Formaldehyde and phenol may be used in amounts up to 50% and examplefied is an amount of 5-10%. Although it is reported that using these monomers the hydrophilic character may be adjusted in the desired sense, it is found that there is insufficient control of the polymerization of the furan monomers on the one hand and formaldehyde and phenol on the other, so that expensive installations or difficult formulation recepies are required for obtaining an hydrophilic plant growth substrate. The complex manufacturing process results in relatively expensive hydrophilic plant growth substrates.
SUMMARY OF THE INVENTION
The invention has for its object to provide a hydrophilic plant growth substrate that does not suffer from the disadvantages in relation to the use of a wetting agent or the disadvantage of using a furan resin or a copolymer of furan and phenol formaldehyde.
The present invention is based on the finding that when mineral wool fibres are provided with a phenol formaldehyde resin and provided with a furan resin, that is with two separate resin polymers and not with one resin copolymer, hydrophilic properties are obtainable without the use of a wetting agent and while using a relatively small amount of furan resin in relation to the phenol formaldehyde resin.
Accordingly, the present invention provides a process for the manufacture of a mineral wool plant growth substrate having a coherent hydrophilic matrix of mineral wool fibres connected by cured binder, comprising the steps of:
i. providing mineral wool fibres;
ii. applying to the mineral wool fibres as a binder a phenol-formaldehyde resin and a furan resin;
iii. forming a matrix of the mineral wool fibres; and
iv. curing the binder.
The plant growth substrates according to the invention comprise a coherent matrix of mineral wool. As mineral wool may be used stone wool, glass wool and/or slag wool. These matrices are produced using conventional production methods which only depend on the starting
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
For the plant substrates according to the invention, use may be made of a coherent matrix of mineral wool. Coherency is obtained by curing the applied furan resin such that the mutual fibres are mechanically connected. However, it is noted that the plant growth substrate may consist of a so-called granulate having the form of mineral wool flakes comprising a number of fibres and having a particle size of 0.2-5 cm.
Hydrophilic character means in the context of the present invention that water is absorbed to a substantial extent/amount which may be measured in the so-called sinking test in water to which is not added any surfactant or mechanical force is applied to the substrate. It is noted that without the inclusion of a wetting agent the plant growth substrate of the invention has good plant growth (hydrophilic) properties. In the sinking test the sinking time of the hydrophilic plant growth substrate according to the present invention is generally less than 1 minute, in particular less than 30 seconds, and preferably and most times in the range of 5-25 seconds.
The density of the hydrophilic plant growth substrate according to the present invention is adjustable and depends on the density of the plant growth substrate just before the binder mixture of phenol formaldehyde resin and furan resin is cured. The density is generally in the range of 10 kg/m
3
to 150 kg/m
3
and practically in the range 30-100 kg/M
3
, such as 40-70 kg/m
3
.
By phenolic resins are meant the group of phenole based resins, e.g. phenol-formaldehyde resin and phenol-urea-formaldehyde resin, as they are described in for instance Knop and Pilato: “Phenolic resins”, Springer Verlag 1985”. The phenol-formaldehyde resins are well known in the art as thermocurable binders. The resin preparation can be used in a non-polymerized or partly polymerized form. The resin preparation is atomized into a gas flow and after contact with mineral fibres is deposited thereon and cured by a temperature treatment, whereby the mineral wool-containing fibres are mutually joined by the cured resin.
The phenol-formaldehyde resin contains both phenol and formaldehyde in a molar ratio of 1:2.8 and more, such as up to 1:6. In general the quantity of formaldehyde is over the stoichiometric amount, such as in the ratio 1:3.1 to 1:5, for instance 1:3.6. The excess of formaldehyde avoids the possibility of phenol remaining present in gaseous form in the gas flow and being emitted to the environment after atomizing of the resin preparation and evaporation of the water present therein. Urea is present as an additive for optimal polymerization.
The resin preparation generally also contains ammonia for the purpose of binding the excess amount of formaldehyde relative to phenol. If required the ammonia emission can be significantly repressed by neutralizing ammonia in the resin preparation by making use of a sugar compound. The sugar compound may added before the binder is ready for use even before the ammonia is added. According to one preparation procedure the addition of this sugar compound takes place before atomizing of the resin preparation, thereby avoiding due to the reaction of ammonia with the sugar compound ammonia eventual neutralization and thereby reduction of function as resin stabilizer. Addition of the sugar compound during resin preparation is possible. The resin preparation eventually becomes unstable and unsuitable for use as binder for mineral wool. It is proposed that the sugar compound and/or the ammonia is added to the resin preparation timely before applying of the resin prep
De Groot Jacob Frank
Hansen Erling Lennart
Rockwool International A/S
Staicovici Stefan
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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