Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – With liberating or forming of particles
Reexamination Certificate
1997-09-19
2001-05-01
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
With liberating or forming of particles
C264S118000, C264S122000, C264S134000
Reexamination Certificate
active
06224799
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
This invention relates to the manufacture of additive concentrates, especially coloured additive concentrates, for use in the manufacture of thermoplastic articles.
Known colour concentrates consist of a polymer resin composition containing high concentrations of pigments or dyes which is usually in the form of pellets or in diced form. (See, for example, Modern Plastics, Mid-October 1991, pages 155, 156 and 158.) The concentrates can comprise relatively large particles, for example fibre in flock form or flake material such as mica. A fabricator can make products of desired colour and appearance in a simple and reproducible manner by blending a polymer resin, also known as a let-down resin, with a small proportion, for example up to about 4% by weight, of an additive concentrate, also known as a masterbatch. Processing is easier and less messy when masterbatch pellets are used rather than colourants or other additives in liquid or dry form. The use of masterbatches also facilitates handling during storage, transport and weighing. Such known concentrates are typically made by melt-compounding the colourant or other additive into the polymer resin carrier using an intensive mix such as a screw extruder, Banbury-type mixer or compounding mill. Colour concentrates typically comprise 50 to 80% by weight pigment or dye. Concentrates which comprise large particles generally contain lower concentrations because of compounding difficulties.
Thomas B Reeve, in an article entitled “Studies in Pigment Dispersion for Plastics” published in Plastics—Meeting Challenges of the Future, ANTEC '82, 40th Annual Technical Conference & Exhibition, San Francisco, Calif., May 10-13, 1982, pages 389-392 (RAPRA Abstract 229169), describes a process in which pigments, titanium dioxide and resin were dry-blended to produce a tint concentrate which was subsequently extrusion compounded to produce a colour concentrate. If the extrusion compounding step was omitted, colour strength development was considerably reduced and a much greater degree of specking was also observed.
U.S. Pat. No. 5,187,202 discloses a pelletised colour concentrate which comprises up to about 80% by weight of a thermoplastic polymer, at least about 5% and up to about 30% by weight of a cellulosic short fibre or flock, and up to about 10% by weight of at least one dispersant aid. The concentrate may be made by intimate mixing of the components in known types of high-shear mixer or extrusion equipment.
It is an object of the present invention to provide a method of producing additive concentrates which can comprise high levels of large particles, particularly in the form of fibres or flakes.
BRIEF SUMMARY OF THE INVENTION
According to the invention is provided a process for the manufacture of an additive colour concentrate which comprises shaped coloured particles of the additive, being fibres and/or flakes of size from 5 &mgr;m to 10 mm and a binder of a thermoplastic polymer or prepolymer or a wax including the steps of:
(a) mixing the particles of the additive and the binder in the dry state at ambient temperature;
(b) compacting the resulting mixture, optionally with heat sufficient to soften the binder, but insufficient to form significant melting of the particles so as to form a coherent body; and
(c) optionally comminuting the resulting body.
The shaped particles in the additive concentrate produced by the present invention take the form of fibres, for example fibre flock, or flake, for example an organic flake material such as chopped or ground polymer based film such as viscose or other polymer or cross-linked polymer based film material or an inorganic material such as mica. The particles may all have substantially the same shape and size, or can be of different shapes and sizes. If flake particles are used, being a substantial proportion of the concentrate, it has been found desirable to incorporate a small proportion, for example 0.25 to 15, preferably 1 to 10, percent by weight, of particles in the form of fibres. They may all be of one colour and material or may be of different colours and/or materials or may be colourless or uncoloured i.e. natural. In one embodiment the concentrate comprises particles of at least 2 different colours. The additive concentrates are colour concentrates containing coloured, for example dyed or pigmented fibre, flock or flake.
It is preferred that substantially all the binder particles have a maximum dimension in the range 10 to 100 &mgr;m.
Preferred fibres may have a diameter in the range 5 &mgr;m to 60 &mgr;m, often 7 to 30 &mgr;m, and a length in the range 500 &mgr;m to 10 mm or 100 &mgr;m or 250 &mgr;m to 10 mm. Such fibres are commonly referred to as staple fibres, and may also be referred to as flock, particularly when they have a length below about 5 mm. Fibre flock may be prepared by cutting longer fibres to lengths of about 250 &mgr;m or above. Shorter flock may be prepared by grinding, for example cryogenic grinding. Preferred flakes may have a basis weight in the range 10 to 50 grams per square meter in the plane of the flake and maximum dimensions in the range 50 &mgr;m to 5 mm or 10 &mgr;m or 25 &mgr;m to 5 mm. Suitable flakes may be prepared for example by chopping, or grinding or shredding (including cryogenically grinding) a polymer film. It will be appreciated that the particles should desirably be of a shape and composition such that they do not damage the processing equipment, for example by abrasion. Accordingly, the use of glass flake may generally be less favoured as compared with glass fibre.
The shaped particles may consist essentially of a natural organic polymer, a synthetic organic polymer or glass. They may consist essentially of a natural polymer which has been processed, for example they may consist essentially of natural cellulose or cellulose in the form of regenerated viscose. Use of synthetic organic polymers or processed natural organic polymers may be preferred. Use of glass particles may alternatively be preferred in some applications. Examples of suitable types of glass include A-, C-, E- and S-glass. Each polymer particle usually contains a single type of polymer but may contain a mixture of more than one type of polymer. The particles within the blend may consist of the same or different types of polymer or polymer mixture. The material of the polymer particles should be chosen having regard to compatibility between this material and the binder in which the particles are to be incorporated. A specific type of polymer particle is unplasticised cellulose film, optionally pigmented, for example regenerated cellulose film such as that made by the viscose process, which has been reduced to the specified size and optionally dyed or pigmented.
The polymer particles are preferably both mechanically and thermally stable under the temperatures encountered during processing, in particular thermoplastic processing, so that they substantially retain their original shape and do not degrade during such processing. Deformation of the particles during processing may give rise to a streaky appearance in a plastics article made thereby. The polymer particles should remain individual and discrete during the production of the additive concentrate. The polymer may be a thermoplastic polymer provided that the particles do not undergo significant deformation during the pressing operation. It has been found that certain thermoplastic polymers, particularly semi-crystalline polymers, may be processed at above their glass transition temperatures without the occurrence of such deformation. Other thermoplastic polymers, particularly amorphous polymers, are preferably processed below their glass transition temperatures. The polymer may be crosslinked, and may be thermoset. The polymer may be a polymer which has inherent mechanical stability at temperatures up to the decomposition temperature of the polymer, this d
Ortiz Angela
Quarles & Brady LLP
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