Biocidal plastic material

Details Biocidal plastic material Biocidal plastic material

2000-01-03

2003-10-14

Szekely, Peter (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C523S201000, C523S351000, C525S902000, C428S521000

Reexamination Certificate

active

06632855

ABSTRACT:

The present invention relates to plastics materials, in particular to plastics which are resistant to the growth of certain microbiological species, such as fungi or bacteria.
Plastics materials are very commonly used in the manufacture of a wide variety of articles such as refrigerators, worktops, shelves etc. These articles may be likely to come into contact with biological species which are harmful to health and which may spread and grow upon the surface of the article. The control of harmful microbes is also desirable in certain medical applications when the growth of bacteria etc. on benchtops, trays etc. is to be prevented. The incorporation of a biocidal compound into the plastics used in such applications may therefore provide beneficial effects in that the growth of bacteria or fungi on the lining of a fridge, for example, may be inhibited.
Certain polymeric materials, e.g. polyvinylchloride, are susceptible to biological attack, especially from fungi. In order to reduce or prevent the degradation of plastics resulting from such biological attack, biocidal products have been developed for incorporation into plastics materials or paints to kill the fungi or bacteria responsible or prevent their proliferation. It is also known to incorporate biocidal compounds into plastics to prevent the growth of bacteria or fungi found in food products. Examples of the latter type of product are described in U.S. Pat. No. 5,433,424, JP-A-06287403 and JP-A-07071 869 amongst others, and articles such as food-praparation surfaces and household food containers etc are already widely available to consumers.
WO-96/29361 describes a biocidal polymeric matrix comprising a support matrix, an antimicrobial agent and a carrying agent, wherein the carrying agent and the antimicrobial agent are adapted to form at least one hydrogen bond or salt bridge therebetween.
WO 96135205 describes a white cover for piano keys formed by injection moulding a homogeneous dispersion of a methyl methacrylate resin and 0.5-2% of an antibacterial agent comprising a ceramic body prepared by sintering and mixing calcium phosphate and metallic silver.
WO 98/21253 describes polymers which have antimicrobial properties consisting of copolymers of non-functional vinyl monomers with vinyl comonomers of specified composition having ionic functionality.
WO 96/22023 describes the use of 2-alkyl or 2-aralkyl benzisothiazolin-3-one derivatives as fungicides for plastics materials.
JP-A-08257493 describes the use of a steel plate which has a paint coating incorporating inorganic aggregates containing anti-bacterial compound, as a lining for refrigerators, freezers or heating cabinets.
JP-A-08145394 and JP-A08145392 describe the use of plastics incorporating anti-microbial compounds for use in ventilator apparatus.
EP-A-606762 describes a composition of a styrene polymer, an antibacterial agent and a compound having a specific functional group to produce an antibacterial resin composition.
U.S. Pat. No. 4,533,435 describes an antimicrobial paper for packaging surgical supplies which incorporates antibacterial compounds in a vinylic polymer binding agent.
The incorporation of antimicrobial agents is reviewed by D. Smock in Plastics Formulating and Compounding, March/April 1997 page 16 and Plastics World March 1992 page 58.
The present invention provides a plastics material which has biocidal activity which is useful in the manufacture of articles having biocidal properties e.g. for use in food storage and preparation areas or medical applications. By “biocidal” we include biostatic activity, i.e. where the proliferation of microbiological species is reduced or eliminated in addition to true biocidal activity where microbiological species are killed. We also include activity against fungi, bacteria and other microbiological species in the meaning of “biocidal”.
According to the invention, we provide a plastics material having biocidal activity comprising an acrylic polymeric material and a biocidal compound wherein said acrylic material incorporates from 5% to 50% by weight of the total polymer present of a rubbery copolymer.
Preferred biocidal compounds include triclosan, compounds based on heavy metals, especially silver, on inorganic carriers such as zeolites, hydroxyapatite, zinc oxide, titanium dioxide, zirconium phosphate, isothiazolones, benzisothiazolin-3-one derivatives, 10, 10′ oxybisphenoxyarsine, isothiazolines, zinc pyrithione, folpet (trichloromethyl thio-phthalimide). Examples of biocidal compounds which are effective in the invention include those sold under the trademarks DENSIL™ S (2,3,5,6 tetrachloro-4(methyl sulphonyl)pyridine available from Zeneca Ltd), SK-NOB-Z™ (a silver-containing zirconium phosphate available from Sanai of Japan) and VANQUISH™ (n-butyl 1,2-benzisothiazoline available from Zeneca Ltd). The present invention is directed towards improving the biocidal activity of acrylic materials containing known biocidal compounds and not to the biocidal compounds themselves and so it is envisaged that biocidal compounds other than those listed above may also be effectively used in the acrylic materials of the invention. The selection of any particular biocide for articles of the invention must be made with due regard to the end-use of the article and to the particular properties of the biocide, i.e. its activity against certain types of micro-organisms, toxicity, processability etc. It is not within the teaching of this document to provide guidance on the suitability of any one biocidal compound for any particular end-use.
The biocide is preferably present at a concentration of at least 0.25% by weight, more preferably at least 1% by weight of the polymer, e.g. 0.5-3% by weight.
The acrylic polymeric material comprises a homopolymer or copolymer of at least one C
1-6
alkyl (C
0-8
alk)acrylate. Preferred acrylic materials are homopolymers or copolymers of the methyl, ethyl, butyl, 2-ethylhexyl, cyclohexyl or phenyl esters of acrylic acid or methacrylic acid. One example of a preferred acrylic material comprises a homopolymer or copolymer of methyl methacrylate a copolymer comprising 80-100% of methyl methacrylate residues and 0-20% of a comonomer of a further acrylate or methacrylate selected from those materials listed above.
The composition of the acrylic material is selected according to the application in which the material is to be used. For example, if the plastics material is intended to be extruded into a sheet for subsequent thermoforming, e.g. to form a lining for a refrigerated cabinet, then an acrylic material formulated for thermal moulding should be selected. Such acrylic materials may advantageously be copolymers of methyl methacrylate with a minor amount (e.g. 1-20 % wt) of an alkyl acrylate, e.g. methyl, ethyl or butyl acrylate and having a molecular weight of less than 500,000. For example a suitable copolymer is derived from about 90% methyl methacrylate and about 10% of ethyl acrylate having a weight average molecular weight of about 80,000-120,000. The acrylic plastics material may be used as a coating over a base material which may be another polymer, such as another acrylic layer, PVC or a styrene based polymer for example. Acrylic materials have good weathering and chemical resistance as well as providing a high gloss finish and therefore a coating of acrylic having these properties may be provided to impart a suitable surface finish to another article. The acrylic polymer may contain additives such as fillers, colorants, impact modifiers, matting agents etc.
The acrylic material incorporates from 5% to 50% by weight of the total polymer present of a rubbery copolymer. By a rubbery copolymer, we mean materials which have a glass transition temperature which is less than room temperature, preferably less than 0° C., e.g. less than −20° C. We also incide block copolymers which include a rubbery, low T
g
block, often with harder, higher T
g
blocks. Such materials are well known for use as toughening agents for improving the impact resistance of acrylic materials. Suitab

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