Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Stratified or layered articles
Reexamination Certificate
1999-12-03
2002-06-11
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Stratified or layered articles
C156S284000, C156S305000, C264S122000, C264S123000, C264S308000
Reexamination Certificate
active
06403002
ABSTRACT:
The present invention relates to a method for producing a shaped body, which method comprises the following steps:
(1) applying a layer of pulverulent material to a surface,
(2) patternwise applying at least one liquid to the layer of pulverulent material, forming a layer of patternwise bound-together pulverulent material,
(3) repeating steps (1) and (2) a predefined number of times, so that a number of successive layers of patternwise bound-together powder, is formed, the successive layers of bound-together pulverulent material together forming the shaped body, and
(4) removing the unbound powder.
A method of this kind is known from EP-A-0,431,924. According to this European patent application, a binder is applied as the liquid to the layer of powder applied on the surface, also that a layer of patternwise bound-together powder is produced. Generally, this takes place using one or more inkjet cartridges. However, a drawback of this method is that the risk of the inkjet cartridges becoming blocked by the binder is high, certainly if a conventional inkjet printer is used. Furthermore, the use of a liquid binder has the disadvantage that it is generally slightly sticky and is therefore more difficult to handle.
The object of the present invention is to provide a solution to these problems and to this end is characterized in that the liquid comprises water and the pulverulent material comprises at least one component which forms a binder after contact with water in step (2).
The advantage of this method is that a liquid is used which is not in itself sticky, so that this liquid is easy to handle and that the risk of blockage when inkjet cartridges are used is minimal.
Of course the use of water is very environmentally friendly. In the method according to the invention all the respective components are easy to handle.
This latter factor is a major advantage in particular when using the so-called “drop-on-demand” inkjet cartridges. A drop-on-demand inkjet cartridge of this nature is known and generally comprises two rows of openings which deliver drops of the liquid to be sprayed out when an electrical signal is received.
It is known per se from EP-A-0,431,924 to use a solvent as a liquid for binding the pulverulent material. The use of water containing liquids, which with a component from the pulverulent material in step (2) form a binder is however not disclosed.
It is also known from EP-A-0,431,924 to heat the bound-together layers of powder, optionally during the application of the liquid binder, in order to promote hardening of the bound-together powder and to stimulate any chemical curing reactions which take place at elevated temperature.
In the method according to the invention, it is preferred to dry the bound-together layers of powder, by heating them, after each execution of step (1) and/or (2) or after every two or more executions of step (1) and/or (2). Particularly preferably, drying is carried out after every two to six executions of step (1) or (2). This heating can take place in numerous ways, for example by means of hot air, infrared irradiation and exposure to microwaves. However, in the context of the present invention it has been found that very good results are obtained if the drying is carried out immediately after step (1) and before step (2) by placing a heated plate on or just above the layer of pulverulent material which was applied last. The advantage of carrying out drying after step (1) is that the layer of powder which was applied last is still dry, with the result that there will be less tendency for powder to adhere to the plate when the plate is placed on the layer of powder which was applied last. The temperature to which heating is carried out is dependent on the type of powder which is employed. However, the temperature preferably lies below the melting temperature of that component of the powder composition which has the lowest melting point. The temperature will generally lie between 50 and 120° C. If desired, the heated plate can also be used to apply pressure to the applied layer of powder.
The water containing liquid which is applied to each layer of pulverulent material is preferably applied in the form of one or more fine jets of droplets. Particularly preferably, the liquid is applied in the form of a plurality of fine jets of droplets, the liquids in the different jets being of different colours. This can be achieved very effectively by making use of an inkjet printer, which are known per se.
It is also possible to produce coloured objects by making use of different colours. The locations where each specific colour is to be applied to the shaped body to be produced can be set accurately by means of correctly programming a connected computer. Techniques of this kind are known per se for inkjet printers.
In addition to water the liquid used preferably also comprises 1-50% by weight, preferably 5-25% by weight, of one or more flow promoters. Flow promoters of this nature are surface-active agents and are intended to reduce the surface tension, so that the liquid can be sprayed out of the very small openings in the inkjet cartridges in drops. Examples of suitable flow promoters are glycols, such as diethylene glycol and monoethylene glycol, and lower alkanols, such as ethanol, 1-propanol and 2-propanol. It is also possible to use combinations of two or more flow promoters of this nature. A very suitable combination is, for example, a mixture of diethylene glycol and 2-propanol.
The liquid may contain one or more colorants. If a plurality of inkjet cartridges are used, it is possible to use a plurality of liquids, the colours of which differ from one another, so that a shaped body comprising different colours can be produced.
As has been mentioned, the pulverulent material comprises a component which, as a result of coming into contact with the liquid sprayed on, forms a binder (the “adhesive component”). In addition, the powder may comprise a filler. If fillers are applied the shaped body obtained by the method according to the invention can for instance be sintered, fired or annealed, to remove the binder component and to obtain a shaped body from the material of the filler. Examples of fillers are metal powder, glass beads, glass fibres, ceramic materials, plastics, silica, sand etc. Thus it is for example possible to produce a shaped body completely consisting of glass, steel, iron etc.
Preferably the pulverulent material comprises apart from the component, which as a result of coming into contact with the water sprayed, forms a binder, a secondary binder. Such a secondary binder comprises in particular a thermosetting material or thermoplastic material. Thermosetting materials are materials which cure under the influence of heat, such as polyester powder coatings. An example of this is the polyester powder coating type LT produced by Lakfabriek Korthals B. V. Thermoplastic materials are materials which soften or melt by heating and which solidify again upon cooling.
The above thermosetting and thermoplastic materials are called secondary binders in the present context. The presence of secondary binders provides the possibility to manufacture quickly and simple a shaped body by means of the method according to the invention, which can be additionally reinforced after completion by a heat treatment.
Suitable adhesive components are in particular powders which form a binder after coming into contact with the water containing liquid. Examples are dextrin powder, (carboxy)methylcellulose, wallpaper adhesive powder, gelatin, inulin, gum arabic, polyvinyl alcohol, cement, plaster, a water soluble salt and finely ground granulated sugar. A powder in which the adhesive component is polyvinyl alcohol, (carboxy)methylcellulose, gelating and/or dextrin is preferred. Examples of suitable polyvinyl alcohol powders are completely or partially hydrolysed polyvinyl alcohols, such as those which are sold under the trade name Mowiol. Suitable grades are, for example, Mowiol 3-83, Mowiol 18-88 and Mowiol 10-98. A polyvinyl alcohol powder can be prepared b
Buss Muller Technology GmbH
Vargot Mathieu D.
Young & Thompson
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