Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-04-26
2001-02-06
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C264S045400, C521S051000, C521S145000
Reexamination Certificate
active
06184259
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a synthetic material obtained from a thermoplastic polymer, said material being advantageously used for the production of articles which are provided with good physical and mechanical properties as well as a remarkable lightness.
Besides, the present invention relates to a process for the production of said material and to the use of the above cited material to produce shoe components, advantageously soles.
The present invention is particularly applied to the production of light articles, e.g. articles manufactured by shoe industries, more particularly to the production of shoe soles.
BACKGROUND ART
The use of foamed polyvinylchloride (in the following PVC) for the production of many different articles which are obtained, for example, by means of the screw injection molding technique or by means of a transfer or intrusion device or by means of an extrusion process is well known in the art.
Generally, to carry out said techniques a material is used which is based on foamed PVC, said foamed PVC being combined with suitable additives which provide the final product with suitable physical and mechanical properties and which improve its production process.
Among said additives, we can mention, for instance, the plasticizers which have the specific function to soften the starting polymer; the stabilizers which prevent occuring of undesired thermal and/or light degradations; the internal and/or external lubricants which allow the material to be easily worked.
However, it is also known that the products obtained from a material which is based on foamed PVC suitably combined with the above cited additives involve some inconveniences and drawbacks which remarkably limit the use of said products.
First of all, the articles obtained by a material which is based on a traditional foamed plasticized PVC as described above are characterized by a density value which is generally higher than 0.7 g/cm
3
, thus said articles are inevitably rather heavy.
Instead, lightness is a very important feature in the production of many different articles, e.g. shoe soles as mentioned above.
A further drawback of the articles belonging to the state of the art and obtained from the above cited material consists in that their external surface generally shows clearly evident streakings caused by the generation of consistent amounts of gazeous products produced by the decomposition of the foaming agent of the starting composition.
It appears to be clear that said streakings are not desirable since they provide the finished product with a poor aesthetical aspect which is absolutely unacceptable for particular kinds of products.
In addition to the above cited streakings, which lower the quality of the article, gazeous bubbles can be formed inside of it. Said Bubbles are uncontrollably generated during the production process and can also have remarkable dimensions.
It is evident that said gazeous bubbles are absolutely undesirable since they can cause swellings and, generally, a decrease of the mechanical properties of the article as well the lowering of the quality thereof.
A further aspect which is very important in specific applications consists in that foamed PVC does not provide the finished product with excellent physical and mechanical properties, e.g. with a satisfactory abrasion resistance.
Owing to the above cited disadvantages and drawbacks caused by the use of a material which is based on foamed PVC, it is often preferable to replace said PVC with other kinds of polymers, e.g. foamed bicomponent polyurethane.
In fact, although foamed bicomponent polyurethane is more expensive as well as more difficult to be molded and treated during the production process than foamed PVC, it allows to produce very light articles having very high superficial quality.
DESCRIPTION OF THE INVENTION
The present invention aims to obviate the disadvantages and drawbacks which are typical of the background art, and to provide, thus, for a material comprising a thermoplastic polymer as main component, said material being advantageously light and characterized by good physical and mechanical properties.
This is achieved by means of a material having the features disclosed in claim
1
.
The dependent claims outline particularly advantageous forms of embodiment of the material according to the invention.
Besides, the present invention concerns a process for the production of a granular material which is based on a thermoplastic polymer suitable for being successively molded or extruded to obtain a plurality of articles, e.g. shoe components.
Said process is carried out by means of the features disclosed in claim
13
.
The claims dependent on claim
13
outline particularly advantageous forms of embodiment of the process according to the invention.
Finally, the present invention concerns the use of a material as disclosed above for the production of shoe components, particularly soles.
Said use is disclosed in claim
16
.
According to an important feature of the present invention, the chemical formulation of the material which is used to produce light articles comprises at least a thermoplastic polymer to which polymeric microspheres containing isopentane are added.
More preferably, the term “thermoplastic polymer” indicates a foamed PVC resin, but it is evident that any cured rubber can be advantageously used, e.g. a styrene-butadiene rubber (SBR) or any other thermoplastic polymer.
As cited above, in addition to the thermoplastic polymer of the starting composition, the material according to the present invention comprises polymeric microspheres containing isopentane.
Said microspheres act as foaming agent and are added in amounts of some parts per 100 parts of thermoplastic polymer according to the kind of thermoplastic polymer which is used and according to the article to be produced, i.e. according to the features as well as to the physical and mechanical properties to be provided to said article.
According to a particularly preferred form of embodiment of the invention, the polymeric coating which is used to obtain said microspheres is methacrylonitrile-polymethylmethacrylate, said microspheres being for instance marketed under the trade name EXPANCEL®.
Said polymeric microspheres containing isopentane are added during the preparation of the material and, more particularly, at the end of the mixing stage of the components since it is very important that said microspheres do not break and do not expand before a predetermined instant of time.
Successively, when said microspheres expand, i.e. during the molding or the extrusion stage of the article or during the calendering stage, said microspheres undergo a structural collapse due to the temperature effect; however, said structural collapse does not cause the breaking of the microspheres.
Thus, a changement of the microspheres surface occurs, said surface becoming sufficiently flexible to allow the expansion of the isopentane which is contained inside of said microspheres avoiding the gas escaping from the latter as well as their consequent breaking.
Therefore it is also necessary that the extruder is operated in order not to break said microspheres, the extruder being placed downstream of a turbomixer and having the specific function to turn the previously obtained material into granules.
In the same way, also the successive molding stage, e.g. the injection molding, to obtain any kind of article has to be operated by taking care that any adjustment of the principal parameters, e.g. rate, pressure, temperature, is carried out in order to avoid the breaking of the polymeric microspheres containing isopentane and to assure their expansion at a predetermined instant of time.
In the case where a given article is not produced by injection molding, but it is obtained by extrusion or calendering, it is evident that similar expedients have to be adopted so as to maintain the integrity and the expansion of said microspheres.
Since the microspheres are added to the mixture after the mixing of the other components and, advantageously, imme
Pasetto Renzo
Peretti Giorgio
Foelak Morton
Interplastica, S.r.l.
Oppenheimer Wolff & Donnelly LLP
LandOfFree
Material containing expandable microspheres and process for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Material containing expandable microspheres and process for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Material containing expandable microspheres and process for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2580162