Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1998-01-26
2001-08-21
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S220000, C428S480000, C264S148000, C264S160000, C264S210100
Reexamination Certificate
active
06277474
ABSTRACT:
The invention relates to an amorphous, transparently colored sheet of a crystallizable thermoplastic, the thickness of which is in the range from 1 to 20 mm. The sheet comprises at least one dyestuff soluble in the polymer and is distinguished by very good optical and mechanical properties. The invention furthermore relates to a process for the production of this sheet and to its use.
Amorphous, transparently colored sheets having a thickness of between 1 and 20 mm are adequately known. These sheet-like structures are made of amorphous, non-crystallizable thermoplastics. Typical examples of such thermoplastics which are processed to sheets are, for example, polyvinyl chloride (PVC), polycarbonate (PC) and polymethyl methacrylate (PMMA). These semi-finished products are produced on so-called extrusion lines (cf.
Polymer Werkstoffe [polymeric materials], Volume II, Technology 1, Georg Thieme Verlag, Stuttgart 1984). The pulverulent or granular raw material is melted in an extruder. After extrusion, the amorphous thermoplastics can easily be reshaped via polishing stacks or other shaping dies as a result of the constantly increasing viscosity of the amorphous thermoplastic with decreasing temperature. After shaping, amorphous thermoplastics then have an adequate stability, i.e. a high viscosity in order to “stand by themselves” in the sizing die. However, they are still soft enough to be able to be shaped by the die. The melt viscosity and internal rigidity of amorphous thermoplastics in the sizing die is so high that the semi-finished product does not collapse before cooling in the sizing die. In the case of materials which decompose easily, such as, for example, PVC, particular processing aids, such as, for example, processing stabilizers against decomposition and lubricants against too high an internal friction and therefore uncontrollable heating, are needed during extrusion. External lubricants are necessary to prevent the material from sticking to walls and rolls.
In the processing of PMMA, for example, a devolatilizing extruder is employed for the purpose of removal of moisture.
In the production of transparently colored sheets of amorphous thermoplastics, sometimes cost-intensive additives are necessary, which in some cases migrate and can lead to production problems as a result of evaporation and to surface deposits on the semi-finished product. PVC sheets are difficult to recycle or can be recycled only with special neutralization or electrolysis processes. PC and PMMA sheets are likewise difficult to recycle and can be recycled only with a loss of or extreme deterioration in the mechanical properties.
In addition to these disadvantages, PMMA sheets also have an extremely poor impact strength and splinter when fractured or under mechanical stress. In addition, PMMA sheets are readily combustible, so that they may not be employed, for example, for interior applications and in exhibition construction.
PMMA and PC sheets furthermore cannot be shaped in the cold. During cold shaping, PMMA sheets break up into hazardous splinters. During cold shaping of PC sheets, hair cracks and white fracture occur.
EP-A-0 471 528 describes a process for shaping an object from a polyethylene terephthalate (PET) sheet. The intrinsic viscosity of the PET employed is in the range from 0.5 to 1.2. The PET sheet is heat-treated on both sides in a thermoforming mold in a temperature range between the glass transition temperature and the melting temperature. The shaped PET sheet is removed from the old when the extent of crystallization of the shaped PET sheet is in the range from 25 to 50%. The PET sheets disclosed in EP-A-0 471 528 have a thickness of 1 to 10 mm. Since the thermoformed shaped article produced from this PET sheet is partly crystalline and therefore no longer transparent and the surface properties of the shaped article are determined by the thermoforming process and the temperatures and shapes given by this, the optical properties (for example gloss, clouding and light transmission) of the PET sheets employed are unimportant. As a rule, the optical properties of these sheets are poor and in need of optimization.
U.S. Pat. No. 3,496,143 describes vacuum thermoforming of a 3 mm thick PET sheet, the crystallization of which should be in the range from 5 to 25%. However, the crystallinity of the thermoformed shaped article is greater than 25%. On these PET sheets also, no requirements are imposed in respect of optical properties. Since the crystallinity of the sheets employed is already between 5 and 25%, these sheets are cloudy and nontransparent. These sheets comprise neither a dyestuff nor a light stabilizer.
Another disadvantage was that to date it has been possible to obtain amorphous sheets with crystallizable thermoplastics as the main constituent in a thickness of 1 mm or more only with difficulty and in unsatisfactory quality.
The object of the present invention is to provide an amorphous, transparently colored sheet having a thickness of 1 to 20 mm which has both good mechanical and good optical properties.
The good optical properties include, for example, a high light transmission, a high surface gloss, an extremely low clouding and a high image sharpness (clarity). The good mechanical properties include, inter alia, a high impact strength and a high fracture strength.
Furthermore, the sheet according to the invention should be recyclable, in particular without loss of mechanical properties, and poorly combustible, so that, for example, it can also be used for interior applications and in exhibition construction.
The object is achieved by an amorphous, transparently colored sheet having a thickness in the range from 1 to 20 mm, which comprises, as the main constituent, a crystallizable thermoplastic and a soluble dyestuff. The concentration of the soluble dyestuff is preferably in the range from 0.001 to 20% by weight, based on the weight of the crystallizable thermoplastic.
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patent: 4189866 (1980-02-01), Treadaway
patent: 5071993 (1991-12-01), Leppard et al.
patent: 5512620 (1996-04-01), Van Hout et al.
patent: 5800911 (1998-09-01), Sankey et al.
patent: 0359710 (1990-03-01), None
patent: 0680996 (1995-08-01), None
Derwent Abstract No. JP 1242223.
Brunow Rainer
Gawrisch Wolfgang
Murschall Ursula
Frommer & Lawrence & Haug LLP
Hess Bruce H.
Hostaglas, Ltd.
Shewareged B.
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