2,2,6,6-Tetramethyl-4-piperidine derivatives as antimicrobial additives for polymer resins

Abstract: Antimicrobial agents comprise 2,2,6,6-tetramethyl-4-piperidine derivatives. When added to resins, these antimicrobial agents provide antimicrobial resin compositions, which in turn provide antimicrobial articles. These antimicrobial agents provide resins, synthetic fibers or the like with not only outstanding antimicrobial activity but also excellent heat resistance, weatherability and deterioration resistance without impairing the transparency and safety of these materials.

Description: BACKGROUND OF THE INVENTION a) Field of the Invention This invention relates to the use of antimicrobial agents in transparent resin articles, especially to the use of antimicrobial agents capable of imparting excellent weatherability to resins, synthetic fibers or the like without impairing the safety and transparency of these materials. b) Description of the Related Art Traditionally, antimicrobial agents have been classified roughly into an inorganic type and an organic type. A problem associated with inorganic antimicrobial agents is that, when incorporated as additives in resins, synthetic resins, paints or the like, resulting products are deteriorated in physical properties such as transparency and mechanical strength although these products are good in heat resistance and weatherability. With respect to the safety of inorganic antimicrobial agents, on the other hand, their effects on the ecosystem due to accumulation of metals such as silver as a result of future mass consumption are of concern because these antimicrobial agents contain metal ions such as silver ions. A problem associated with organic antimicrobial agents, on the other hand, is that when incorporated as additives in resins, synthetic fibers, paints or the like, resulting products are accompanied by drawbacks in heat resistance and weatherability although these products are good in mechanical strength. Depending on the kinds of organic antimicrobial agents employed, a problem with respect to the transparency of resulting products may also arise. DATABASE WPI Section Ch, Week 9008 Derwent Publications Ltd., London, GB; Class D22, AN 90-057645 XP002107442 and SU-A-1 500 667 disclose the use of 4-acetylamino-2,2,6,6-tetramethylpiperidine as bactericide. DATABASE WPI Section Ch, Week 9818 Derwent Publications Ltd., London, GB; Class A82, AN 98-201602 XP002107443 and JP-A-10-053509 disclose an antibacterial composition containing zinc oxide and an organic compound having an optionally mono-substituted 2,2,6,6-tetramethyl-4-piperidyl group. This composition is useful in an antibacterial resin coating composition. CHEMICAL ABSTRACTS, vol. 125, no. 1, 1 July 1996 Columbus, Ohio, US; abstract no. 6015, XP002107437 and JP-A-08-059972 disclose polycarbonate-polyester compositions containing hindered amines for moisture-heat-resistant moldings. CHEMICAL ABSTRACTS, vol. 122, no. 14, 3 April 1995 Columbus, Ohio, US; abstract no. 163378, XP002107438 and JP-A-06-313210 disclose photochromic acrylic fibers containing bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate. CHEMICAL ABSTRACTS, vol. 108, no. 10, 7 March 1988 Columbus, Ohio, US; abstract no. 76459, XP002107439 and JP-A-62-185723 disclose a discoloration resistant composition containing bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate. EP-A-0 387 489 discloses the use of substituted 2,2,6,6-tetramethyl-4-amino-piperidine amides as fungicides. DE-A-42 28 792 discloses the use of pyridylaminopiperidine derivatives as fungicides. CHEMICAL ABSTRACTS, vol. 113, no. 21, 19 November 1990 Columbus, Ohio, D8: US; abstract no. 191181, XP002107440 and JP-A-02-167261 disclose the use of 4-(N-acyl-N-alkylamino)-2,2,6,6-tetraalkylpiperidines as bactericides and fungicides. CHEMICAL ABSTRACTS, vol. 110, no. 3, January 16, 1989 Columbus, Ohio, US; abstract no. 20986, S.G.FRANZBLAU ET AL.: "Structure-activity relationships of selected phenazines against Mycobacterium leprae in vitro", XP002107441 discloses antimicrobial phenazine derivatives containing a 2,2,6,6-tetramethylpiperidine as substituent at the imino nitrogen atom. SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-described problems and hence to provide the use of an antimicrobial agent which, when incorporated as additives in resins, synthetic fibers or the like, can impart excellent weatherability and deterioration resistance to resulting products without impairing the transparency and safety of these materials. As a result of extensive research, the present inventors have found that a 2,2,6,6-tetramethyl-4-piperidine derivative, when added to resins, synthetic fibers or the like, can impart stable antimicrobial activity and excellent weatherability and deterioration resistance to these materials without impairing their transparency and safety, leading to the completion of the present invention. To achieve the above object, the present invention provides the use of an antimicrobial agent comprising a 2,2,6,6-tetramethyl-4-piperidine derivative according to claim 1. The antimicrobial agent used according to the present invention can impart not only excellent antimicrobial activity but also superb heat resistance, weatherability and deterioration resistance to resins, synthetic fibers or the like without imparting the safety and transparency of these materials. Further, the resin composition making use of the antimicrobial agent and the article made of the resin composition have the above-described outstanding properties. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS The present invention will next be described in further detail on the basis of preferred embodiments. 2,2,6,6-Tetramethyl-4-piperidine derivatives useful in the practice of the present invention are compounds having the following structure in their molecules. wherein R represents a hydrogen atom or an alkyl group. As 2,2,6,6-tetramethyl-4-piperidine derivatives for use in the present invention, known compounds can be employed. Particularly, at least one of the following compounds (a)-(e): (a) Bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (b) Poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazin-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}] (d) Tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate (e) Tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate is used according to the present invention. Among the above compounds, the compounds (a) and (b) are especially good in safety because they are described in the Positive List of Japan Hygienic Olefin and Styrene Plastics Association (JHOSPA) and their use in food containers and packages is permitted. These compounds can be used either singly or in combination. The 2,2,6,6-tetramethyl-4-piperidine derivatives useful in the practice of the present invention have melting points or softening points in a range of from 80 to 135°C and have excellent dispersibility in resins, so that they can provide antimicrobial resin compositions having high transparency. The 2,2,6,6-tetramethyl-4-piperidine derivatives useful in the practice of the present invention are known to impart weatherability and deterioration resistance especially to resins, and can hence provide superior antimicrobial resin compositions to conventional organic antimicrobial agents. The antimicrobial activity of each antimicrobial agent according to the use of the present invention appears to be developed through a mechanism to be described next. Namely, the 2,2,6,6-tetramethyl-4-piperidine structure is believed to form a quaternary ammonium salt, which is considered to induce injuries of cell membranes and walls of microorganisms and denaturation and/or respiratory inhibition of zymoproteins, thereby presumably exhibiting antimicrobial activity. No particular limitation is imposed on the resin to be used in the antimicrobial resin composition according to the use of the present invention. Illustrative usable resins can include polyethylene resins, polypropylene resins, polyester resins, polystyrene resins, polyvinyl chloride resins, polyurethane resins, polyacrylic resins, polyamide resins, polyvinyl alcohol resins, and cellulose resins. The amount of the 2,2,6,6-tetramethyl-4-piperidine derivative used in the present invention is from 0.05 to 5 parts by weight per 100 parts by weight of the resin. An amount of the 2,2,6,6-tetramethyl-4-piperidine derivative smaller than 0.05 part by weight leads to low antimicrobial effect, so that in the case of bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, antimicrobial effect can hardly be observed against Gram-negative bacteria. On the other hand, an amount of the 2,2,6,6-tetramethyl-4-piperidine derivative greater than 5 parts by weight involves a potential problem that physical properties of the resulting resin composition may be adversely affected. Pigments, resin additives, other antimicrobial agents and/or the like can be added in the antimicrobial resin composition according to the present invention to such extents as not impairing the advantageous effects of the present invention. No particular limitation is imposed on the article having antimicrobial activity according to the use of the present invention insofar as use is made of the antimicrobial agent incorporated in a resin composition according to the present invention. As illustrative examples, however, the following articles may be mentioned. (1) Molded or otherwise formed, antimicrobial articles: Articles obtained by molding or otherwise forming antimicrobial resin compositions of the invention by injection molding, extrusion, blow molding or the like. More specific examples can include food containers, waste or rubbish receptacles, stationery, housings of electric or electronic appliances, cosmetic containers, vehicle interior parts, kitchen utensils, bathroom utensils, and clothing storage containers. (2) Antimicrobial fibers: Articles obtained by forming the antimicrobial resin compositions used in the present invention into fibers by spinning or the like, and those obtained by forming such fibers into woven fabrics or nonwoven fabrics. More specific examples can include clothing and carpets. (3) Antimicrobial paints: The antimicrobial resin compositions used according to the present invention can be formulated into paints by using solvents or the like. The present invention will hereinafter be described in detail on the basis of Examples and Comparative Examples, in which all designations of "part" or "parts" are by weight basis unless otherwise specifically indicated. The following antimicrobial agents were employed in the Examples: Antimicrobial agent a: Bis(2,2,6,6-tetramethyl-4-piperidyl)sepacate (CAS No. 52829-07-9). Antimicrobial agent b: Poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazin-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}] (CAS No. 71878-19-8). Antimicrobial agent c: A mixed ester of 1,2,3,4-butanetetracarboxylic acid with 2,2,6,6-tetramethyl-4-piperidinol and 3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane (CAS No. 119524-47-9). Antimicrobial agent d: Tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate (CAS No. 91274-89-4). Antimicrobial agent e: Tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate (CAS No. 64022-61-3). Example 1 A cell suspension, which had been subjected to preculture at 37°C for 16 hours on a nutrient broth medium, were diluted 200-fold to obtain an inoculating cell suspension. The antimicrobial agent a was added at 500 ppm to the inoculating cell suspension. 5-mℓ Aliquots of the inoculating cell suspension were then placed in sterilized L-tubes, followed by incubation at 37°C for 24 hours. The viable cell count of the cultured liquid medium was determined by the agar plate dilution method (shaker flask method). Antimicrobial activity tests were conducted using Escherichia coli and Staphylococcus aureus. The results are presented in Table 1. Examples 2-5 Antimicrobial tests were conducted in a similar manner as in Example 1 except that the antimicrobial agents b to e were used in place of the antimicrobial agent a. The results are presented in Table 1. Comparative Example 1 Antimicrobial activity tests were conducted in a similar manner as in Example 1 except for the omission of the antimicrobial agent. The results are presented in Table 1. Example 6 A low-density polyethylene resin (100 parts) and the antimicrobial agent a (0.3 part) were kneaded under heat and then formed into a transparent sample film. Antimicrobial activity was tested in a similar manner as in Example 1 except that 1.0 g of the sample film was added instead of the addition of 500 ppm of the antimicrobial agent a. Further, weatherability was also tested in accordance with JIS K7113. Described specifically, the sample film was punched in the No. 2 dumbbell size and then exposed for 500 hours under a sunshine weatherometer. The elongation at break of the test piece after the exposure was measured by a tensile tester. The results are presented in Table 2. Examples 7-10 Antimicrobial activity tests were conducted in a similar manner as in Example 6 except that the antimicrobial agents b to e were used in place of the antimicrobial agent a. The results are presented in Table 2. Comparative Example 2 Antimicrobial activity tests were conducted in a similar manner as in Example 6 except for the omission of the antimicrobial agent. The results are presented in Table 2. Example 11 A polypropylene resin (100 parts) and the antimicrobial agent a (0.5 part) were kneaded under heat and then formed into a transparent sample plate of 5 cm x 5 cm. A cell suspension, which had been subjected to preculture at 37°C for 16 hours on the nutrient broth medium, were diluted with a phosphate buffer to obtain an inoculating cell suspension. The inoculating cell suspension was dropped onto a surface of the sterilized sample plate at four corners and a diagonal center thereof in an amount of 0.1 mℓ per location. After the sample plate was incubated at 37°C and 90% or higher relative humidity for 24 hours in a sterilized Petri dish, cells were washed off with the phosphate buffer, and the viable cell count was then determined by the agar plate dilution method (dropping method). Antimicrobial activity tests were conducted using Escherichia coli and Staphylococcus aureus. The results are presented in Table 3. Examples 12-15 Antimicrobial activity tests were conducted in a similar manner as in Example 11 except that the antimicrobial agents b to e were used in place of the antimicrobial agent a. The results are presented in Table 3. Comparative Example 3 Antimicrobial activity tests were conducted in a similar manner as in Example 11 except for the omission of the antimicrobial agent. The results are presented in Table 3. Example 16 A saturated polyester (100 parts) and the antimicrobial agent a (0.3 part) were kneaded under heat and then spun into transparent sample fibers. In a sterilized vial, 0.4 g of the sample fibers was inoculated with 0.2 mℓ of a cell suspension which had been subjected to preculture at 37°C for 16 hours on the nutrient broth medium and then to dilution. After the sample fibers were incubated at 37°C for 18 hours, cells were washed off with a physiological saline, and the viable cell count was then determined by the agar plate dilution method. Antimicrobial activity tests were conducted using Staphylococcus aureus and Klebsiella pneumoniae . The results are presented in Table 4. Examples 17-20 Antimicrobial activity tests were conducted in a similar manner as in Example 16 except that the antimicrobial agents b to e were used in place of the antimicrobial agent a. The results are presented in Table 4. Comparative Example 4 The saturated polyester was kneaded under heat and then spun into transparent sample fibers. In a sterilized vial, 0.4 g of the sample fibers was inoculated with 0.2 mℓ of a cell suspension which had been subjected to preculture at 37°C for 16 hours on the nutrient broth medium and then to dilution. Immediately after the inoculation, the sample fibers were washed with the physiological saline to separate cells from the sample fibers, and the viable cell count was then determined as an initial value by the agar plate dilution method. Another 0.4 g portion of the sample fibers, which had been inoculated likewise, was incubated at 37°C for 18 hours, from which cells were washed off with the physiological saline. The viable cell count was then determined by the agar plate dilution method. Antimicrobial activity tests were conducted using Staphylococcus aureus and Klebsiella pneumoniae. The results are presented in Table 4. Example 21 The resin composition of Example 6 was kneaded under heat and then extruded into a plastic food tray. It was confirmed to have excellent antimicrobial activity.

Claims: Use of 0.05 to 5 parts by weight of at least one compound selected from the group consisting of: (a) bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, (b) poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazin-2,4,diyl}{2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}], (c) a mixed ester of 1,2,3,4-butanetetracarboxylic acid with 2,2,6,6-tetramethyl-4-piperidinol and 3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane, (d) tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, and (e) tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, per 100 parts by weight of a resin as an antimicrobial agent in a transparent resin article consisting essentially of a resin and said antimicrobial agent, wherein the antimicrobial agent does not impair the transparency of said resin article. Use according to claim 1, whereby the antimicrobial agent is incorporated in an antimicrobial resin composition. Use according to claim 2, whereby the antimicrobial resin composition is molded. Use according to claim 2, whereby the antimicrobial resin composition is formed into a fiber. Use according to claim 2, whereby the antimicrobial resin composition is formulated into a paint.

Inventors: HAYASHI KOZABURO, HOSHINO AKIRA, SIBATA MASAYUKI, HAYASHI, KOZABURO, HOSHINO, AKIRA, SIBATA, MASAYUKI
Applicants: DAINICHISEIKA COLOR CHEM, DAINICHISEIKA COLOR & CHEMICALS MFG. CO. LTD.
Application year: 1999
Main classification: A01N43
IPC codes: A01N43, A01N25