Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-01-15
2002-03-19
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S105000, C524S310000, C524S311000, C524S317000, C524S318000, C428S412000, C264S173160
Reexamination Certificate
active
06359042
ABSTRACT:
The present invention provides moulding compositions
a) containing thermoplastic, aromatic polycarbonates with a weight average molecular weight {overscore (M)}
w
(measured in a known manner) of 27,000 to 40,000, preferably 30,000 to 36,000 and in particular 32,000 to 36,000,
b) a concentration of UV absorber, which has a molecular weight of 370, preferably 500 or greater, in particular 500 to 3000, in amounts of 3.5 to 20 wt. %, preferably 5 wt. % to 15 wt. %, with respect to the weight of polycarbonate, and
c) two types of mould release agents comprising
c.1) monoesters formed from glycerine and a fatty acid in amounts of 0.01 to 0.1 wt. %, with respect to the weight of polycarbonate and
c.2) (partial)esters of tetra- to hexahydric alcohols in amounts of 0.05 to 0.25 wt. %, with respect to the weight of polycarbonate,
which are characterised in that the ratio by weight of c.1) to c.2) is between 1:25 and 1:2 and preferably between 4:25 and 10:25.
Polycarbonate moulding compositions according to the invention are particularly suitable as coatings for polycarbonate sheets which are preferably prepared by the coextrusion process.
Thus the invention also provides the use of polycarbonate moulding compositions according to the invention as UV absorber-containing coverings, preferably as an external layer, on coextruded polycarbonate sheets.
The invention also provides a process for preparing laminated materials comprising thermoplastic polycarbonates by the known coextrusion method, which is characterised in that polycarbonate moulding compositions according to the invention are used as the external layer of the laminated material.
In addition, the invention provides laminated materials consisting of thermoplastic aromatic polycarbonates obtained by the process according to the invention.
EP-A-0 320 632 (Le A 25 600) describes coextruded sheets made from UV absorber-containing polycarbonates with a relative solution viscosity of 1.31 (measured at 25° C. in 0.5% strength solution in dichloromethane), which corresponds to a {overscore (M)}
w
(weight average molecular weight) of about 31,000 (page 10, example). The UV absorbers have a {overscore (M)}
n
>500 and are particularly preferably used in amounts of 5 wt. %. to 10 wt. % (page 2, line 38). Lubricants and/or mould release agents may be added (page 9, line 43).
These types of sheet may now be optimised with regard to the transverse unevenness of the surface of the sheets, the evaporation of the UV absorber from the polycarbonate melt, in particular during coextrusion while applying a vacuum, which is required in order to produce sheets with hollow cavities, and with regard to polycarbonate abrasion which can be caused by the sizing unit in the extruder during cooling of the coextruded polycarbonate sheets.
Increased evaporation of the UV absorber from the polycarbonate melt leads to fouling of the sizing unit and then to the production of white spots on the surface of the sheets. Polycarbonate abrasion leads to powdery deposits on the coextruded polycarbonate sheets.
The object of the present invention was to make the coextrusion process in accordance with EP 0 320 632 more reliable, that is to retain the good quality of the surfaces of the coextruded polycarbonate sheets or even to improve them during long term operation, in particular with a continuous mode of operation. This is achieved in accordance with the invention by adding a specific combination of esters.
Although EP-B-0 213 413 describes the use of combinations of esters (page 6, lines 25 to 37) in polycarbonates, the amount of UV absorber is only 0.1 to 0.7 wt. % (page 6, line 42). In addition the UV absorber mentioned there has an M
n
<500 (page 6, lines 43 to 45). The molecular weight of the polycarbonate is between 13,000 and 18,000 (page 2, lines 11 and 12). The sheets made from these polycarbonates are not produced by extrusion or coextrusion (page 6, line 64 to page 7, line 2). Thus the disclosure in EP 0 213 413 gives no indication of the solution to the problem mentioned here.
Japanese document Hei-2-225 558 describes the production of polycarbonate sheets by extrusion and has the objective of preparing sheets with extremely good surfaces (see the introduction of Hei). The polycarbonate used has an {overscore (M)}
w
of, for example, 27,700 (examples from Hei). In order to obtain sheets with good surfaces, partial esters of polyhydric alcohols are added, according to Hei (see Claim from Hei). Glycerine monostearate and pentaerythrityl monopalmitate are mentioned as partial esters for examples. Ester mixtures may also be used. Glycerine monostearate and mixtures with glycerine monostearate as the major component are preferred. UV absorbers in amounts of 0.1 to 0.7 wt. % may be added to the polycarbonates according to Hei, wherein UV absorbers with M
n
>500 are not mentioned. However, Hei-2-225 558 does not disclose UV protection provided by coatings and does not mention coextrusion.
Our comparison tests, however, show that the ester behaves quite differently (comparison D) and in addition that 0.7 wt. % of UV absorber is not sufficient to protect the coating against weathering (comparison E).
Although a mixture of 0.01 parts of glycerine monostearate and 0.03 parts of pentaerythrityl tetrastearate are added to the polycarbonate for extrusion in accordance with EP-A-0 300 485, example 1, page 8, as a mould release agent, the EP-A does not give any indication about the addition of UV absorbers.
Our EP-A-0 649 724 (Le A 29 892) disclosed a process for preparing multi-layered plastic sheets from branched polycarbonates with molecular weights {overscore (M)}
w
of 27,000 to 29,000 by coextrusion of a core layer and at least one outer layer with 1 wt. % to 15 wt. % of UV absorber. The plastic sheets obtained have excellent surfaces.
It is mentioned on page 5, line 9 of the EP-A, that conventional mould release agents may be added to the branched polycarbonates in addition to the UV absorber.
Now, if conventional mould release agents are added to the branched polycarbonates in EP-A-0 649 724 in the hope of being able to prepare polycarbonate sheets with good surface properties, even above the molecular weight of 29,500 which is critical for processing purposes, then it is found, surprisingly, that both pentaerythrityl tetrastearate and glycerine monostearate and mixtures of these two with glycerine monostearate as the major component, produce poor surfaces on the coextruded sheets with regard to both the deposition of UV absorber and polycarbonate abrasion.
Simply reversing the ratio of pentaerythritol tetrastearate and glycerine monostearate, surprisingly, leads to the production of coextruded sheets with excellent surfaces, even above the critical molecular weight of 29,500 claimed in EP-A-0 649 724.
According to EP-A-0 732 360, polycarbonates with a concentration of two types of esters (Claim 1) are disclosed. UV stabilisers may be added (page 3, line 11). The type and amount of UV stabiliser is not described.
Thermoplastic, aromatic polycarbonates for UV absorber-containing outer layers in the context of the present invention are either homopolycarbonates or copolycarbonates. The polycarbonates may be linear or branched in a known manner.
Some, up to 80 mol. %, preferably 20 mol. % to 50 mol. %, of the carbonate groups in the polycarbonates according to the invention may be replaced with aromatic dicarbonate groups. These types of polycarbonates which have both acid groups from carbonic acid and acid groups from aromatic, dicarboxylic acids incorporated in the molecular chain are more accurately called aromatic polyester carbonates. For simplicity they will be included, in the context of the present application, within the general term thermoplastic, aromatic polycarbonates.
Preparation of polycarbonates to be used according to the invention is performed in a known manner from diphenols, carbonic acid derivatives, optional chain terminators and optional branching agents, wherein some of the carbonic acid derivatives are replaced by aromatic, dicarbox
Anders Siegfried
Haese Wilfried
Löwer Hartmut
Nising Wolfgang
Bayer Aktiengesellschaft
Buttner David J.
Preis Aron
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