Method for manufacturing a plastic board

Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making

Reexamination Certificate

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Details

C264S046400, C264S046800, C264S259000, C264S267000, C264S275000, C264S511000

Reexamination Certificate

active

06193916

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for manufacturing a monolithic plastic board with a thickness of at least 6 mm, preferably (20±10) mm, which board is constructed as structural foam and comprises a sandwich-like structure with a foam core and closed skin plates.
2. Description of the Prior Art
Such a method and board obtained therewith is known for instance from U.S. Pat. No. 4,096,218.
Known from this American patent specification is a method according to which a few seconds after completion of injection of the plastic the mould cavity is enlarged in a predetermined time and in controlled manner. By making use of a foaming agent and application of gas counter pressure can thus be achieved that the foam structure is of good quality, while the skin of the obtained board has a closed and smooth structure.
According to the said American patent the mould is held for a predetermined time in its closed starting position, whereafter the mould undergoes a determined expansion in a subsequent specified period. After reaching maximum expansion cooling takes place for a time, whereafter the formed board can be removed.
Attention is also drawn to U.S. Pat. No. 4,133,858, which deals with a related technique and wherein mention is also made of a number of possible plastics for use in the context of this technique and substances such as foaming agents for adding thereto.
Since it has been found that with the known method boards of a sufficiently high quality cannot be obtained, it is an object of the invention to provide a method with which a board of improved quality can be manufactured.
A further object of the invention is to perform the known method such that it lends itself to prior placing in the mould of a decorative foil such that this foil is positioned on an outer surface of the obtained board.
Yet another object of the invention is to perform the method such that the obtained board has an optimum flatness within very narrow tolerances or, more generally, has a form which within very narrow tolerances is the same as the desired nominal form.
Yet a further object of the invention is to perform the method such that less expensive plastics, for instance plastics of recycled quality, are also usable to obtain a board with the desired superior properties.
SUMMARY OF THE INVENTION
In order to realize the above stated objectives the invention provides a method for manufacturing a monolithic plastic board with a thickness of at least 6 mm, preferably (20±10) mm, which board comprises a sandwich-like structure with a foam core and closed skin plates, which method comprises the following steps to be performed in suitable sequence of:
(1) providing an injection moulding device with a plastic-plasticizing and injection device and a mould which comprises at least two mould parts displaceable relative to each other by displacing means, which mould parts in a closed first extreme position bound a mould cavity connecting onto the plasticizing and injection unit and in an open second extreme position release a formed board for removal, which displacing means are adapted to move the mould parts at a chosen speed;
(2) providing foaming means for causing foaming in the mould cavity of plastic injected into the mould cavity;
(3) providing blocking means for temporarily rendering the foaming means inactive, for instance gas feed means for feeding gas under pressure to the mould cavity;
(4) energizing the blocking means;
(5) energizing the plasticizing and injection unit in the first extreme position of the mould in order to inject heated plastic into the mould cavity;
(6) ending the energizing of the blocking means;
(7) ending the energizing of the plasticizing and injection unit;
(8) energizing the displacing means such that the mould parts displace relative to each other in accordance with the graph below, wherein the hatched area shows the limits of the progress of the ratio of the displacement (d) to the starting thickness (a) in time (t):
wherein the slope h is in principle not limited; and
(9) causing the formed board to cool to a chosen temperature, fully opening the mould cavity and removing the cooled board.
Attention is drawn to the fact that, in contrast to the stated prior art, the invention is not limited to the use of the so-called gas counter pressure with which foaming of the injected plastic in the mould cavity can be temporarily discontinued.
The accompanying claims
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relate to specific embodiments of the method according to the invention. It is noted that the mentioned materials and substances are only summarized by way of example without any limitative significance.
The slope h corresponds with the greatest possible speed which can be realized by the associated injection moulding device. It must therefore be understood that the relevant upper limit is determined only by the injection moulding device used and is not essentially related to the choices made within the scope of the invention.
The invention also relates to a monolithic plastic board manufactured with application of the method according to any of the claims
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. Such a board can in particular have a form such that the board has a non-round shape and a bent peripheral edge.
The invention further relates to a method for manufacturing a plastic board on which is arranged a cover foil.
The object of the invention is to provide a method for manufacturing such a board, in addition to the board itself, such that the cover foil is not only situated on the surface thereof but also extends round the peripheral edge of the board such that during normal use, for example as a table top, the peripheral edge of the foil is invisible.
For this purpose the invention provides a method for manufacturing a plastic board provided with a cover foil, which method comprises the following steps to be performed in suitable sequence of:
(1) providing an injection moulding device with a plastic-plasticizing and injection device and a mould which comprises at least two mould parts displaceable relative to each other, which mould parts in a closed first extreme position bound a mould cavity which connects onto the plasticizing and injection unit and which has a shape adapted to the shape of the board for manufacturing, and which mould parts in an open second extreme position release a formed board for removal;
(2) manufacturing a cover foil preform with an undercut peripheral edge shape which is adapted to the shape of the board for manufacturing such that the cover foil can extend round the peripheral edge of the board for manufacturing;
(3) placing the preform against the wall of the opened mould cavity remote from the plastic feed opening connected to the plastic-plasticizing and injection device and holding said preform in position therein by means of holding means;
(4) closing the mould cavity and energizing the plasticizing and injection unit to inject into the mould cavity plasticized plastic which can adhere with the preform;
(5) ending the energizing of the plasticizing and injection unit;
(6) moving the mould parts in the direction of the second extreme position; and
(7) causing the formed board with cover foil adhered thereto to cool to a chosen temperature, fully opening the mould cavity and removing the manufactured board.
In preference a method is applied which comprises performing step (4) with polypropylene (PP) as the plastic for injecting. A superior board can be obtained with such a method, while polyvinylchloride (PVC) is avoided as plastic.
In a further embodiment of the latter specified method, the method comprises the steps of
(9) performing step (8) and
(10) performing step (4) such that the manufactured board has a thickness of at least 6 mm, preferably (20±10) mm, which board comprises a sandwich-like structure with a foam core and closed skin plates.
This latter method can preferably be performed by making use of the step of
(11) performing step (10) by making use of the specifications according to the non-prepublished Netherlands patent a

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