Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-04-24
2001-11-27
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S447000, C524S449000, C524S451000, C523S210000, C523S211000, C521S079000, C521S090000, C521S092000, C521S098000
Reexamination Certificate
active
06323269
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to mineral containing thermoplastic granules and their production and use especially in the production of thermoplastic end products.
2. Brief Description of the Prior Art
It is well known in the production of thermoplastic materials and articles produced from such materials, eg by mixing or compounding followed by a shaping process such as molding, extrusion or blowing, to incorporate in the material an additive known as a blowing agent which when the material is heated and/or compressed during processing causes release of a gas into the material. Foamed lightweight materials may be produced thereby. In the prior art, the blowing agent is incorporated as a separate ingredient in the composition to be mixed or compounded together with the other ingredients to be included in the composition. Extensive mixing of the blowing agent with the other ingredients and the base thermoplastic, ie the thermoplastic material which will provide the matrix in the end product, is required in the compounding stage to ensure that these ingredients are fully and homogeneously mixed throughout the material to be formed.
It is an object of the present invention to provide an improved, more convenient way of introducing a blowing agent into a thermoplastic material.
It is also an object of the present invention to provide an improved method of nucleating gas release from a blowing agent in a thermoplastic material.
It is also an object of the present invention to provide a new granule form suitable for providing a carrier medium for introducing a blowing agent into a thermoplastic material.
These and other objects which will become apparent are met by the present invention.
SUMMARY OF THE INVENTION
According to the present invention in a first aspect there is provided a mineral-containing thermoplastic granule for incorporation in a thermoplastic material to produce a thermoplastic end product, the granule comprising at least 50% by weight of an inorganic particulate material, at least 0.1% by weight of an additive comprising a blowing agent, and the balance comprising a thermoplastic binder.
According to the present invention in a second aspect there is provided a method of producing a foamed thermoplastic material which includes the steps of (a) adding to a base thermoplastic material a plurality of granules each comprising at least 50% by weight of an inorganic particulate material, at least 0.1% by weight of an additive comprising a blowing agent the balance being a thermoplastic binder; (b) mixing or compounding the granules with the base thermoplastic material to form a modified thermoplastic material; and (c) shaping the modified thermoplastic material to produce an end product, wherein in either step (b) or step (c) or heat is applied which causes gas from the blowing agent to be released to produce foaming in the modified thermoplastic material.
Preferably the inorganic particulate material forms at least 50% by weight, eg from 50% to 91%, by weight of the granules on a dry weight basis. Preferably, the blowing agent forms at least 1% by weight, eg from 1.0% to 42% by weight of the granules. The thermoplastic binder may form from 8% to 20%, especially from 8% to 15% by weight of the granules.
The non-binder ingredients of the granules may form from 85% to 95%, eg from 85% to 92% by weight of the granules, the thermoplastic binder forming the balance. The non-binder ingredients of the granules, namely inorganic particulate material and blowing agent, may be present in the granules in a weight ratio in the range of from about 1:99 to about 99:1.
By incorporating the blowing agent in the granule according to the first aspect of the invention and by incorporation of a multiplicity of such granules in a thermoplastic composition to produce an end product by compounding and shaping, the procurement and delivery of ingredients to be employed in the thermoplastic composition is simplified and the mixing and compounding of ingredients may be carried out more easily with reduced energy and at lower cost.
In addition, the use of granules in accordance with the first aspect of the invention beneficially acts as a nucleating agent for the release of gas from the blowing agent and thereby provides a network of particles which nucleate the foaming process producing a larger number of fine pores compared with the smaller number of large pores obtained when no mineral is added. Pores have been determined to be typically 0.2 mm to 0.4 mm in size where the inorganic particulate material is added together with the blowing agent compared with typically 0.6 mm to 1.5 mm where the blowing agent is used alone.
DESCRIPTION OF THE INVENTION
In the granule according to the first aspect of the present invention the blowing agent may comprise one of the known blowing or gas generating agents employed in the prior art to produce foaming during heating in a thermoplastic material being processed. The gas produced may for example comprise nitrogen, carbon dioxide or one or more optionally halogenated hydrocarbons. The blowing agent may be selected to produce gas at a given temperature and/or pressure. Examples of blowing agents include triazoles, tetrazoles, dialkyldicarbonates, carbonamides, eg azodicarbonamide, dicyclohexamine, cyclic aminoethers, sulfur hexafluoride, halocarbons, morpholines, cyclopentadiene, polycarboxylates, sodium aluminum hydroxy carbonate and citric acid derivatives, eg hydrocerol. Other blowing agents may also be used. These may be used alone, in blends, or in combination with injection of an inert gas such as nitrogen, carbon dioxide or other gas or gas generating material. Other additives, eg stabilizers, molecular traps, catalysts, etc. may be included as part of the blowing agent composition to facilitate gas generation from the blowing agent chemical.
Other optional additives normally incorporated in a thermoplastic composition, eg as additives to the inorganic material or other components employed therein may be included in the granule according to the first aspect of the invention, eg up to 10% by weight based on the weight of the inorganic particulate material.
Use of granules which comprise an inorganic particulate material, eg calcium carbonate, together with a polymeric thermoplastic binder, for incorporation in a base thermoplastic composition to produce a filled, thermoplastic end product is known, eg from CA-A-2,016,447, and improvements to such granules are described in WO95/17441 which corresponds to the parent U.S. Application from which the present U.S. Application is derived. The present invention takes advantage of such granules as a convenient carrier medium for uniformly adding the blowing agent to the base thermoplastic composition and acting as a nucleation agent for bubble formation in the base composition in a controlled, uniform manner.
In the thermoplastic granule according to the first aspect of the present invention the inorganic particulate material may comprise any one or more of the materials well known for use as fillers or extenders in plastics material. For example, it may comprise a white inorganic particulate pigment or filler selected from alkaline earth metal carbonates, especially calcium carbonate, kaolin, calcined kaolin, wollastonite, bauxite, talc and mica. The inorganic particulate material may contain a minor amount, eg up to 10% by weight (based on the weight of the inorganic particulate material), of a coating material or additive, which is known to facilitate intimate mixing and contacting of the inorganic material with plastics materials, in this case the binder of the granule, eg a latex or a surface treatment coating such as a fatty acid or derivative thereof. Desirably, although not essentially, the inorganic particulate material comprises an alkaline earth metal carbonate, eg calcium carbonate, magnesium carbonate, calcium magnesium carbonate or barium carbonate. Such a carbonate may be obtained from a natural source, eg marble, chalk, limestone or dolomite, or may
Calhoun Allison R
Skelhorn David A.
Acquah Samuel A.
Finnegan, Henderson Farabow, Garrett and Dunner L.L.P.
Imerys Pigments, Inc.
Rajguru U. K.
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