Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Utility Patent
1998-06-22
2001-01-02
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S100000, C525S443000, C528S301000, C428S480000
Utility Patent
active
06169131
ABSTRACT:
The invention relates to a plastic sheeting for use in the construction industry. Examples of such a sheeting are a sheeting based on a polyolefin, for example polyethylene, which is used, in particular, as a temporary provision against rain and wind for buildings still under construction, and sheeting based on poly(vinylchloride), which is used, in particular, as a damp-proof course above, for example, window and door frames and adjacent brickwork and, often reinforced by a woven, as a roofing material. These known sheetings have the drawback, however, that their permeability to water vapour is very poor, as a result of which it is virtually impossible to control humidity, and condensation and rot may occur. To counter this drawback, the sheeting is perforated in some cases. This additional treatment, however, adversely affects the tear strength of the sheeting and may locally result in small leaks.
EP-A-167714 and JP-A-0490337 disclose plastic sheeting for the construction industry which is permeable to water vapour. The plastics selected in these publications are polyetheramide and polyesterester block copolymers, the polyetheramide block copolymer being able to retain more than its own weight in water. The use of these known water vapour-permeable plastic sheetings encounters a number of drawbacks, however. Thus the polyether-amide block copolymer sheeting has virtually no mechanical strength once it has absorbed water, and its rate of production is limited by the limited crystallinity and crystallization rate of the polyetheramide block copolymer. Because of this and also because of the higher price of the starting material, the sheeting is relatively expensive. Sheets of polyesterester block copolymers have the major drawback that they are not suitable for long-term use in a humid environment, owing to the polyesterester block copolymer being highly sensitive to hydrolysis which, inter alia, causes a rapid fall-off in strength.
An object of the invention is therefore a water-impermeable, yet water vapour-permeable plastic sheeting, which does not have the above-mentioned drawbacks and is suitable for use in the construction industry.
This object has been achieved by means of a plastic sheeting made of a polyetherester block copolymer.
Polyetherester block copolymers are thermoplastic copolymers having elastomeric characteristics, the copolymer being composed of hard, readily crystallizable segments and of soft or elastomeric segments, of which the currently most common can be described by the following general formulae:
The hard segments preferably comprise alkylene terephthalate units, but it is also possible for units derived from other aromatic dicarboxylic acids, for example naphthalenedicarboxylic acid, p-diphenyldicarboxylic acid and isophthalic acid to be present in the hard segments. Examples of alkylenediols are ethylene glycol, propylene glycol, butylene glycol or hexylene glycol, but it is also possible for the glycol of butene to be used for the preparation of the esters for the hard segment.
The soft segments are generally poly(alkylene oxides) esterified with terephthalic acid. Here, too, it is possible for other aromatic acids to be used. Preference is given to the use of poly(propylene oxide) or poly(tetramethylene oxide). It is possible for ethylene oxide units to be incorporated in minor amounts, i.e. less than 50 mol %, preferably less than 30 mol %, in the poly(alkylene oxide) segments, for example by employing polypropylene oxide chains terminated with ethylene oxide.
A comprehensive description of polyetherester block copolymers and their preparation can be found in Encyclopedia of Polymer Science and Technology, Volume 12, pages 76-177 (1985) and the references reported therein.
Various polyetherester block copolymers are commercially available from a number of companies under various tradenames, for example ARNITEL E and P of DSM, the Netherlands, HYTREL of E.I. Du Pont De Nemours, USA, and LOMOD of General Electric Plastics, USA.
Varying the ratio hard/soft segment and using different alkylene oxides and molar weights of the soft segments makes it possible to obtain block copolyesters having different hardnesses, for example between Shore D 30 and 80. Preferably, polyetherester block copolymers having a Shore D hardness between about 35 and 60 are employed for the sheeting according to the invention. Block copolymers whose hardness is too low often have less good processing characteristics into sheeting, owing to the relatively low crystallinity and crystallization rate. At higher hardnesses, the bending strength and the water vapour permeability decrease unduly.
Depending on the desired pattern of characteristics, those skilled in the art will be able to select the correct polyetherester block copolymer for the sheeting according to the invention.
The polyetherester block copolymer of the sheeting may contain the usual additives, for example stabilizers, dyes or pigments, fillers, processing aids, for example release agents, etc.
For most applications it is necessary for the sheeting according to the invention to satisfy the nonflammability requirements imposed by the authorities. A requirement often applicable to construction sheeting is the DIN 4102 B2 classification. This involves a sheet being suspended vertically and a specified Bunsen burner having a flame length of 20 mm being directed, at an angle of 45 degrees, against the edge or the surface of the sheet. The flame is held against the sheet for 15 seconds, after which the burn time until the flame tip reaches a mark (150 mm above the flame application point) is measured. If this burn time is 20 seconds or longer (measured on 5 samples), the B2 classification is complied with.
Known flame retardants for use in construction sheeting are combinations of a halogenated organic compound with antimony oxide, as reported, for example, in EP-A-0109928. Quite apart from the drawbacks, corrosivity and potential toxicity, this combination proves unable, according to the invention, even at a high concentration in the sheeting, to conform with DIN 4102 B2. Other known flame retardants for sheeting are metal hydroxides, for example alumina trihydrate and magnesium hydroxide in high concentrations, 60-80 wt %, see U.S. Pat. No. 4,851,463. Owing to the high concentration required of these inorganic materials in the sheeting, the mechanical characteristics are significantly impaired, which means that the use thereof must be avoided.
Most surprisingly, the inventors have found that the use of melamine, melamine compounds, for example melamine cyanurate, and melamine condensation products, for example melam, in the sheeting results in a flame retardancy which meets the B2 classification. The use of melamine cyanurate in flame-retarding compositions for polyetherester copolymers is known. JP-A-2-88668 discloses that melamine cyanurate, if added in very low concentration to the commonly used halogenated organic flame retardant, enhances its effectiveness. In a comparative experiment it is shown that the effect of the use of melamine cyanurate as the only flame retardant is negligable.
The content of melamine, melamine compound or melamine condensation product in the sheet is between 7 and 30 wt %, based on the polyetherester copolymer. Preferably, the content is between 9 and 25 wt %. The content is primarily determined by the desired level of flame retardancy and depends, inter alia, on the thickness of the sheet.
In the case of very thin films for instance <50 &mgr;m, a content of 5 wt. % may already suffice to fulfill the DIN 4102 B2 requirement. However the reinforcing backing and/or additives adversely influence the flame retarding so that higher contents, >7 wt. %, are preferred.
The particle size of the flame-retarding compound is preferably chosen to be as small as possible, preferably <50 &mgr;m, more preferably <20 &mgr;m. The best results are achieved with a particle size of <10 &mgr;m.
If required, it is additionally possible to use, in the composition of the flame-resistant she
Borggreve Reinoldus J. M.
Goertz Henricus J. J.
Hulskotte Richerdes J. M.
DSM N.V.
Pillsbury Madison & Sutro LLP Intellectual Property Group
Short Patricia A.
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