Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1997-07-02
2001-04-03
Kuhns, Allan R. (Department: 1732)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C156S078000, C264S045300, C264S045900, C264S156000, C264SDIG006
Reexamination Certificate
active
06210788
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing a thermoplastic material for immobilization and/or protection of a part of the body, wherein a thermoplastic base material is chosen which is admixed with at least one filler.
BACKGROUND OF THE INVENTION
Various applications are possible in this context, in particular for immobilization purposes in medical and paramedical applications, for protective purposes in sport and for use in the production of shoes.
In the fields of application of orthopaedics, physical rehabilitation and sports medicine large amounts of plaster are still being used. Furthermore, in this context as in radiotherapy and radiology, a whole series of immobilization and fixation materials are employed such as thermoplastic plate materials and thermosetting bandaging materials.
PRIOR ART
In the light of the abovementioned applications, the existing materials have the drawback of having a relatively high density. This high density results in two significant troublesome problems with respect to the abovementioned applications: the materials have a relatively high weight which limits user comfort and which may even trouble the user, and the therapeutic use of the materials used is diminished.
This may even lead to a medical problem, owing to the user being forced to greater exertion as a result of the greater weight.
This high density makes it impossible, in radiotherapy applications, in particular those employing low-energy sources, to transmit radiation through such dense materials without this having an adverse effect on the skin of the patient. The materials in moulded form are placed on the skin of the patient and fixed to a baseplate in order to put the patient in an immobile and reproducible position. These materials do not sufficiently transmit the radiation of, in particular, low-energy sources, as a result of which the radiation builds up immediately below the plastic material and can thus damage the skin.
In radiology, the relatively high density of most existing materials or intermediate constitutes a problem in that they do not sufficiently transmit the types of radiation and thus produce interferences on the image which may diminish the visibility of details on the image or may even cause distortion.
Additionally, there is disclosed by EP-A-0575012 the addition in said method, as the filler, a specific percentage of microspheres, said percentage being such that a foamed thermoplastic material is obtained which exhibits a specific mechanical strength and flexibility, said microspheres forming a foaming agent, and wherein the obtained mixture of thermoplastic material as the base material and foaming agent is subjected to at least one further processing step, and wherein the mixing of said base material and said foaming agent is effected by subjecting said mixture to an extrusion step with a set temperature and a set residence time of the mixture in the extrusion means.
OBJECT OF THE INVENTION
It is an object of the invention to provide a solution to the abovementioned problems.
SUMMARY OF THE INVENTION
To this end, according to the invention, there is provided a method for producing a thermoplastic material for immobilization and/or protection of a part of the body wherein there is specifically provided that the microspheres contain a lightweight gas which, when exposed to a specific temperature, causes the microspheres to expand within the mixture, the latter being likewise subjected to an expansion process which makes it possible to effect a significant reduction in weight of the intermediate. Thanks to the invention, a foamed intermediate is obtained which is sufficiently strong and more user-friendly than existing intermediates, owing to which the invention primarily has a lower density and consequently a lower weight and better transmissivity for radiation sources which are used in radiotherapy and in radiodiagnostics and thus makes the invention further suitable for immobilization and/or protection of a part of the body, wherein it is possible to achieve a substantial reduction in density of the material. Thus, in the course of the plastic being processed into an intermediate, the density of the plastic is lowered by a corresponding percentage. Furthermore, the lighter an immobilization, fixation or protection material, the more pleasant it is for the user. It results from the foregoing that the present invention differs from the teachings of “Database WPI, Section Ch, Week 8604, Derwent Publications Ltd., London, GB; Class A 32, AN 86-023788” in that the mixing of the base material and the foaming agent is effected by subjecting said mixture to an extrusion step with a set temperature and a set residence time of the mixture in the extrusion means.
In particular, said foaming agent is added in accordance with a percentage which is within the range from 0.1% to 10%, it thus being possible to achieve a reduction in density of the material of between 1 and 60%. Thus, in the course of the plastic being processed into an intermediate, the density of the plastic is lowered by a percentage of between 1% and 60%. Furthermore, the lighter an immobilization, fixation or protection material, the more pleasant it is for the user.
According to a generally advantageous embodiment of the invention. During the extrusion step, the temperature is, in particular, set to such a value that an expansion process of the mixture is started under the influence thereof.
More in particular, said residence time of said mixture is set, during the extrusion step, within a time interval between a minimum value t
min
, which is defined by a low time threshold, below which no expansion of said foaming agent takes place, and a maximum value t
max
which is defined by a high time threshold, beyond which combustion of said mixture may take place.
According to a preferred embodiment of the invention, the expansion process of said mixture is tailored to the extrusion step and takes place completely within the latter, the expansion process being stopped, at the latest, when the extrusion step is stopped. If not, the process continues during the processing of the intermediate, which leads to undesirable effects.
According to a further advantageous embodiment, said mixture is subjected to a multiple extrusion step, a multiple, in particular double, extrusion being carried out in the same step on said mixture. Thus better dispersion is obtained of the two components of the mixture, base material and foaming agent. Moreover, very accurate control of the processing temperature is thus accomplished.
This ensures, not least thanks to accurate control of the further extrusion parameters, in particular residence time, that the expansion process can be adequately controlled in order to arrive at a serviceable end product; owing to the foaming agent being well dispersed in the matrix base material. In particular, in this case the base material chosen is a low-temperature thermoplastic which exhibits a processing temperature which is less than 100° C., preferably between 40° C. and 90° C., more preferably between 50° C. and 80° C. Alternatively it is also possible, in this context, for the base material chosen to be a high-temperature thermoplastic which exhibits a processing temperature which is greater than 100° C., preferably between 120° C. and 180° C.
This is further assisted by the foaming agent being added in the form of a powder, in particular in a percentage within a range between 0.5 and 5%, preferably between 1 and 4%.
According to a yet further advantageous embodiment of the invention, said mixture is subjected to a two-dimensional extrusion, said foaming agent in particular being blended into resin granules or a so-called masterbatch, and said foaming agent is added in the form of the said resin granules. Thanks to this it was found that the foaming agent in the form of a masterbatch can be readily dispersed in the matrix base material. It was consequently possible to make the various base materials into a plate having a relatively smaller thickness, f
Baker & Botts L.L.P.
Kuhns Allan R.
LandOfFree
Method for producing a thermoplastic synthetic material and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing a thermoplastic synthetic material and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing a thermoplastic synthetic material and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2456811