An antibacterial composition comprising: (a) a first component including at least one gram positive bacteristatic or bactericidal compound selected from the group consisting of lantibiotics, pediocin, and lacticin class bacteriocins, and lytic enzymes; and (b) a second component including at least one compound selected from the group consisting of hops acids and hops acid derivatives, and the method of applying said composition to the surfaces of solid food.

1. Field of the Invention
The present invention discloses a process for inhibiting or retarding the outgrowth of bacteria on food products by treatment with a composition which includes one or more hops acid extracts or modified hops acid extracts plus one or more safe and suitable gram positive bacteristatic or bactericidal preparations from the lantibiotics, pediocin, lacticin class bacteriocin and/or lytic enzyme categories. More specifically, the process comprises using as an ingredient or applying to a food surface a composition including nisin, and/or lysozyme and beta hops acids in order to reduce or eliminate gram positive spoilage or pathogenic bacteria, and, most especially, all strains of the harmful pathogen Listeria monocytogenes. An important public health concern is the ability of pathogenic listerial species, especially Listeria monocytogenes, to grow at commercial refrigeration temperatures at which processed foods are normally stored for long periods of time. This ability to grow under standard conditions of distribution makes Listeria monocytogenes one of the top public health risks associated with raw and processed foods today. Any new antimicrobial system must be effective in commercial food systems, with formulation and temperature conditions reflecting actual practices. The new compositions of this patent are effective in a variety of foods, especially at the refrigerated storage and handling temperatures typical of foods at risk for listerial contamination.
2. Technology Description
The extent of food borne infections and intoxications in the United States was quantitatively documented in the CAST report of 1994 (Foodborne Pathogens: Risks and Consequences. Task Force Report No. 122, Council for Agricultural Science and Technology, Washington D.C.), as well as being extensively characterized in the past few years due to better reporting systems and programs (CDC. 1988c. 1997 Final FoodNet Surveillance report. U.S. Department of Health and Human Services, October, 1998). In order to reduce the prevalence of listeriosis and other food borne infections, a wide variety of research has been conducted to develop compositions which function as food grade anti-bacterial ingredients. Individual compounds have been disclosed in this research, with little if any commercial benefit or use, primarily because single compounds typically lack the efficacy or are too costly to use in food processing and formulations. At this time, there is still a need for better control of gram positive pathogens such as Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, Clostridium botulinum, C. perfringens, and the like, which pose significant health risks to consumers. In addition, other gram positive spoilage bacteria such as lactobacilli, streptococci, bacilli, enterococci, and micrococci species are known to cause spoilage, though not normally illness, and are often the principal agents in reducing the shelf life and freshness of selected foods.
Both pathogenic and spoilage bacteria can occur in raw food materials, but heat processing tends to reduce bacterial loads dramatically. After processing, most foods are at risk for recontamination prior to packaging, distribution, and final consumption, when they may be exposed to pathogens in the food handling environment. Even in the cleanest processing facilities, selected pathogens may contaminate the already processed foods, usually at very low levels. In the case of cold tolerant pathogens, primarily various listerial species, they may then grow unchecked on the food during distribution and storage until final consumption. The more such pathogens grow in a food product, the higher the risk of infection among consumers of that food product. This is a special concern for ready to eat meats and dairy products, as such foods are not heated or processed again by the user prior to consumption. In such cases, the most likely risk is from Listeria species that grow well under refrigeration. Consumption of elevated levels of any pathogen is recognized to increase the risk of infection, especially among infants, the elderly, pregnant women, and any immune compromised individuals. In 1998, it is estimated that there were approximately 500 deaths in the U.S. caused by listeriosis presumably contracted from foods. Among major food pathogens, listeriosis has the highest mortality, exceeding 20% according to Meade, et al. (Food-related illness and death in the United States, CDC 5:5, September-October 1999). In light of the risk and the large social cost, an urgent need for systems to prevent listerial growth in foods is recognized by U.S public health agencies, the Food and Drug Administration (FDA), and the United States Department of Agriculture (USDA). The subject of this invention is a novel, food grade (Generally Recognized as Safe), flavor neutral composition that targets Listeria in actual food systems, especially in processed, ready to eat meat products. The desired effect of such a composition is to kill or reduce the levels of Listeria bacteria in foods that are at risk for post processing survival or contamination by such species. In addition, risks associated with other gram positive bacteria, including the above mentioned spoilage types, as well as less common strains of the Corynebacteria, Diplococci, Mycobacteria, Streptococci, and Streptomyces genuses have also been noted as problems in food products and may benefit from such a process or composition.
In 1992 and 1993, U.S. Pat. Nos. 5,096,718 and 5,260,061 disclosed the use of metabolites of propionic acid bacteria in certain foods to increase the shelf life of treated food products. These metabolites demonstrate enhanced efficacy against gram negative bacteria but, unfortunately, are not effective against gram positive bacteria.
U.S. Pat. No. 5,217,950 suggested the use of nisin compositions as bactericides. Nisin is a lantibiotic, more specifically, a polypeptide with antimicrobial properties which is produced in nature by various strains of the bacterium Lactococcus lactis. Nisin is indeed primarily effective against gram positive bacteria; however, the common gram positive pathogen Listeria monocytogenes is more resistant to nisin than most other species of gram positive bacteria. The need to enhance the activity of nisin against Listeria monocytogenes is well recognized and accounts for the fact that nisin by itself is not used as an antilisterial agent commercially. The U.S. Pat. No. 5,217,950 patent therefore suggests the combination of a chelating agent, such as disodium ethylenediaminetetraacetic acid (EDTA) or other acetate salts or citrate salts with nisin to effect a broader range of activity against both Listeria species as well as selected gram negative bacteria.
U.S. Pat. Nos. 5,573,797; 5,593,800 and 5,573,801 disclose antibacterial compositions which include a combination of a Streptococcus or Pediococcus derived bacteriocin or synthetic equivalent antibacterial agent in combination with a chelating agent. The composition is applied to the surface of the food to be treated either by direct application or by incorporating the composition onto a flexible film casing which is placed into intimate contact with the food surface. The chelating agent binds free divalent cations in the outer membrane of gram negative cells, improving permeability to the antibacterial agents. In the case of the U.S. Pat. No. 5,573,801, the application of nisin alone to the surface of cooked meats is disclosed, but the efficacy of this single ingredient is so limited that it has not been employed commercially.
U.S. Pat. No. 5,458,876 suggests the combination of a antibiotic (such as nisin) with lysozyme as an antibacterial. In this case, lysozyme breaks down the cell wall and weakens the structural integrity of the target cell so that the antibacterial agent becomes more effective in damaging or killing the bacterial cell. In particular, this combination proves to be effective in improving the antibacterial efficacy of nisin against Listeria monocytogenes, yielding a significant reduction, though not a complete elimination, of listeria at safe and suitable levels of use.
EP 0 466 244 discloses a composition having improved antibacterial properties comprising a mixture of at least one of each of the following groups of compounds: (I) a cell wall lysing substance or a salt thereof, (II) an antibacterial compound and (III) an adjuvant selected from organic acids acceptable for use in food products or preparations for cosmetic use or personal hygiene or salts of these acids, phosphates and condensed phosphates or the corresponding acids, and other sequestering agents. Preferably (I) is lysozyme, (II) may be a bacteriocin (e.g. nisin or pediocin), and (III) may be acetic acid, sodium diacetate, lactic acid, citric acid, propionic acid, tartaric acid, orthophosphates, hexametaphosphates, tripolyphosphates, other polyphosphates or sequestering agents containing substituted or non-substituted amino groups, for example EDTA.
EP 0 453 860 suggests the combination of nisin with a phosphate buffer effective at a pH of between 5.5 and 6.5 to eradicate gram negative bacteria from surfaces.
WO 97/23136 suggests a bacterial decontamination method which involves treatment with a solution of low concentration alkali metal orthophosphate combined with either osmotic shock and/or lysozyme in solution and/or nisin in solution. This reference tested the combination of low concentrations of trisodium orthophosphate with lysozyme against certain bacteria on lettuce leaves or chicken skin, and the combination of low concentrations of trisodium orthophosphate with nisin against certain bacteria on chicken skin.
The published Australian patent application AU-A-186041/88 discloses the use of bacteria lysing enzyme products with N-acetylmuramidase, e.g. lysozyme, together with non-enzymatic preservatives for preserving foodstuffs. Non-enzymatic preservatives mentioned in this publication are complexing agents such as citric acid and EDTA, amino acids, particularly amino acids, such as cysteine, alanine, tyrosine and glycine and nucleosides and nucleotides such as inosine 5xe2x80x2-inosine monophosphate or phosphates such as tetrasodiumpyrophosphate (diphosphate), sodium tripolyphosphate (triphosphate) and polyphosphate or reddening agents such as alkali metal nitrates.
U.S. Pat. No. 5,286,506 discloses the use of the fat soluble beta acids extract of hops for their bacteriostatic effects against Listeria monocytogenes in foods at 6 to 50 ppm by weight of the food. In addition, U.S. Pat. Nos. 5,370,863 and 5,455,038 suggest that certain hops acid derivatives that are chemically hydrogenated may have antibacterial activity against listeria species. However, these extracts are not food grade (GRAS) and are not allowed for use in foods outside of brewing.
Finally, Johnson et al disclose in the International Journal of Food Microbiology 33 (1996) 195-207 that hops acids and hops acid derivatives have limited efficacy against listerial species in fat containing foods such as cheeses, meats, sauces, and dressings, presumably due to the migration or entrapment of the beta acids into the fat emulsion and their subsequent unavailability for inhibition of bacterial growth in the aqueous portion of the food emulsion. The problem of the lack of activity of hop beta acids in fat containing foods has prevented them from being used commercially as natural antimicrobial agents for control of listeria or other gram positive pathogens.
To the extent necessary for completion of this patent application, all of the above cited references are expressly incorporated by reference.
In light of the above teachings, there still exists a need in the art for a method for treating foods with bactericidal compositions that are active at reasonable usage levels in common food applications that are at risk for gram positive pathogens. More specifically, there exists a need for effective treatments that can be conveniently integrated into existing processing protocols for these products. Finally, there exists a need for more complete and effective reduction, or even elimination, of harmful gram positive pathogens by use of safe, suitable, and cost effective levels of food grade antimicrobial ingredients such as nisin, lysozyme, and hops acids.
It is now discovered, quite surprisingly, that a composition which has a first component that includes one or more gram positive bacteristatic or bactericidal compounds from one or more of the following classes of materials: lantibiotics, pediocin, and/or lacticin class bacteriocins, or lytic enzymes, and a second component which includes one or more natural hops acids or hops resins or derivatives thereof provides excellent antibacterial properties, especially against potentially harmful bacteria of the listeria genus, by dramatically surpassing the antibacterial efficacy of any of the individual components or of previously published compositions.
One embodiment of the present invention comprises an antibacterial composition containing as a first component: (a) one or more gram positive bacteristatic or bactericidal compounds from one or more of the following classes of materials: lantibiotic, pediocin, and lacticin class bacteriocins, and/or lysozyme, a natural enzyme from egg white; and as a second component (b) one or more hops acids or hops acid derivatives or hops resin or hops resin derivatives. Particularly preferred is a composition containing a lantibiotic bacteriocin, lysozyme, and beta hops acid extract.
In another embodiment, the present invention provides a method for retarding growth, reducing viable numbers, or totally eliminating gram positive bacteria, and especially Listeria monocytogenes, in food products comprising the step of treating the surfaces of said food product with an effective amount of a composition comprising as a first component: (a) one or more gram positive bacteristatic or bactericidal compounds from one or more of the following classes of materials: lantibiotics, pediocin and lacticin class bacteriocins, or lytic enzymes; and as a second component (b) one or more hops acid or hops acid derivatives or hops resin or hops resin derivatives.
It is an object of the present invention to provide a process for treating food products in order to protect again st harmful bacteria and in order to maintain the antibacterial activity of the composition even on or in a fat containing food.
An additional object of the present invention is to provide a novel composition having substantially greater antibacterial properties than previously observed for the individual components of the composition.
These, and other objects, will readily be apparent to those skilled in the art as reference is made to the detailed description of the preferred embodiment.
In describing the preferred embodiment, certain terminology will be utilized for the sake of clarity. Such terminology is intended to encompass the recited embodiment, as well as all technical equivalents which operate in a similar manner for a similar purpose to achieve a similar result.
The present invention provides a novel antibacterial composition and its use in a process for reducing, retarding, or totally eliminating harmful bacteria from food surfaces, even in fat containing foods.
The novel antibacterial composition comprises: (a) one or more gram positive bacteristatic or bactericidal compounds from one or more of the following classes of materials: lantibiotics, pediocin and lacticin class bacteriocins, or lytic enzymes; and (b) one or more hops acid extracts or hops acid derivatives or hops resin or hops resin derivatives.
The first component of the inventive composition is one or more compounds having bacteristatic or bactericidal activity against gram positive bacteria. Such compounds preferably include, but are not limited to lantibiotic, pediocin, and lacticin class bacteriocins and/or lysozyme from egg white, shellfish, or other natural sources. Combinations of more than one compound having bacteristatic or bactericidal activity against gram positive bacteria (e.g., nisin and lysozyme) are specifically contemplated as failing within the more preferred scope of the first component of the present invention.
A first class of gram positive bacteristatic compounds comprises a lantibiotic. The term xe2x80x9clantibioticsxe2x80x9d was coined by Schnell et al. (1988. Nature 333:276-278) to describe a group of bacteriocins including nisin which contain the amino acid lanthionine and other xe2x80x9cnon-proteinxe2x80x9d amino acids. The common properties of these bacteriocins are reviewed by Kellner et al. (1988. Eur. J. Biochem 177:53-59) wherein they note that xe2x80x9c . . . polycyclic polypeptide antibiotics possess a high content of unsaturated amino acids (dehydroalanine, dehydrobutrine) and thioether amino acids (meso-lanthionine, (2S, 3S, 6R)-3-methyllanthionine). Furthermore, lysinoalanine, 3-hydroxyaspartic acid and S-(2-aminovinyl)-D-cystine are found in some members.xe2x80x9d Members of this group include nisin, subtilin, pep 5, epidermin, gallidermin, cinnamycin, Ro09-0198, duramycin and ancovenin. These ribosomally synthesized peptide antibiotics contain from 19 to 34 amino acids and are produced by various microbes including Staphylococcus species, lactic acid bacteria, Bacillus species and Streptomyces species. In addition to their unique composition of non-protein amino acids, they can be distinguished from other polypeptide antibiotics on the basis of their specificity. Bacteriocins in general, and the lantibiotics in particular, are characterized by a very narrow spectrum of action. Thus, only a few species of bacteria are sensitive to a particular bacteriocin at practical, safe and suitable concentrations. At normal, legally permitted levels of use in foods (eg., up to 12.5 ppm of pure nisin in a food system), such bacteriocins tend to have only bacteristatic (ie, growth inhibiting) properties at best. This is in contrast with other broad spectrum polypeptide antibiotics, such as polymyxin B1 which are actively bactericidal against a wide range of bacteria, even at very low levels of use, as well as the xe2x80x9clytic peptidesxe2x80x9d discussed by Jaynes et al., in published international application WO 89/00194, which are active against most bacteria, yeasts and even mammalian cells.
Nisin is a ribosomally coded peptide which occasionally occurs as a dimer with a molecular weight of about 7000. It contains several unusual amino acids including beta-methyllanthionine, dehydroalanine, and lanthionine among its total of 34 amino acids. There are five unusual thio-ether linkages in the peptide which contribute to its stability in acid solutions. Nisin is one of the most thoroughly characterized bacteriocins, and shares remarkable homology of structure and action with other lantibiotics, for example Subtilin and epidermin [Buchman et al 1988. J. Bio. Chem. 263 (31):16260-16266]. Recent reviews of nisin, its physical properties and uses include xe2x80x9cBacteriocins of Lactic Acid Bacteriaxe2x80x9d, T. R. Klaenhammer, 1988. Biochimie 70:337-349, xe2x80x9cNisinxe2x80x9d, A. Hurst, 1981. Avd. Appl. Microbiol. 27:85-121, and U.S. Pat. No. 4,740,593. Nisin is the collective name describing several closely related substances which exhibit similar amino acid compositions, and some limited range of antibiotic activity. This phenomenon is discussed by E. Lipinska in xe2x80x9cAntibiotics and Antibiosis in Agriculturexe2x80x9d (M. Woodbine, Ed.) 1988, pp. 103-130.
The use of nisin to combat L. monocytogenes has been reported by M. Doyle; xe2x80x9cEffect of Environmental and Processing Conditions on Listeria Monocytogenesxe2x80x9d, Food Technology, 1988.42(4):169-171. This reference describes the initial inhibition of the organism""s growth (for about 12 hours) and reports that L. monocytogenes may grow at a pH level as low as 5.0 and is resistant to alkaline pH with the ability to grow at pH 9.6.
Nisin is commercially available from Rhodia Inc. in a standardized 2.5 weight percent preparation under the trademark Novasin(trademark). Lantibiotic containing protein may also be present as a low level fermentation by-product in certain varieties of cheddar or American cheese and in the fermented skim milk product known as MICROGARD(copyright) MG300 . In practice the lantibiotic is added to the food product in amounts between about 1 to about 100 ppm (by weight of solution used for treatment) of active ingredient (nisin), with preferred levels of 1 to 12.5 ppm, based on safety and suitability of use in foods.
As alternatives to use of lantibiotics in the preferred combination, it is also known that use of a Pediococcus bacterial metabolite, specifically pediocin, as a substitute can yield efficacious results. Though the pediocins are not yet approved for use in foods, they may yet be accepted for commercial application in the future. In addition, the new class of streptococcal bacteriocins called lacticins, especially Lacticin 3147 as described in Irish Patent Application No. 980500, should produce similar activity against gram positive bacteria. Like the lantibiotics, both pediocins and lacticins are known to have bacteristatic activity primarily against a limited range of gram positive bacteria.
A second class of gram positive bactericidal proteins comprises the lytic enzymes especially lysozyme, most commonly derived from egg albumin in a food grade extraction process, but also available from arctic scallops, human milk, tears, and other natural sources. When lysozyme is used as an antimicrobial, it is added to the food product in amounts between about 20 to about 500 ppm (by weight of solution used for treatment), more preferably between about 50 to about 200 ppm, primarily to inhibit Clostridium tyrobutyricum in ripened cheeses. Lysozyme is not bactericidal at these levels against other gram positive bacteria, but it has been used at higher levels (greater than 1000 ppm, typically 2000 ppm or more) to remove the cell wall from a wide range of gram positive bacteria.
Lysozymes (Muramidase; mucopeptide N-acetylmucamoylhydrolase; 1,4-.beta-N acetylhexosaminodase, E.C. 18.104.22.168) are mucolytic enzymes which have been isolated from various sources and are well characterized enzymes. First discovered in 1922 by W. Fleming, egg white lysozyme was among the first proteins sequenced, the first for which a three dimensional structure was suggested using x-ray crystallography and the first for which a detailed mechanism of action was proposed. Its antimicrobial activity against gram positive bacteria is well documented, for example by V. N. Procter et al in CRC Crit. Reviews in Food Science and Nutrition, 1988, 26(4):359-395. The molecular weight of egg white lysozyme is approximately 14,300 to 14,600, the isoelectric point is pH 10.5-10.7. It is composed of 129 amino acids which are interconnected by four disulfide bridges. Similar enzymes have been isolated and characterized from other sources including such diver se producers as Escherichia coli bacteriophage T4 and human tears. Despite slight differences (for example, the human lysozyme has 130 amino acids) the capacity for hydrolysis of acetylhexosamine polymers remains essentially the same. Accordingly, for purposes of this invention, the term lysozyme is intended to include those cell wall or peptidoglycan degrading enzymes which have the ability to hydrolyze acetylhexosamine and related polymers.
Lysozyme is known to kill or inhibit the growth of bacteria and fungi, and is used in Europe to control the growth of the spoilage organism Clostridium tyrobutyricum in a wide variety of cheeses. It has also been proposed for use in a variety of other food preservation applications and has been reported to inhibit the growth of (and in some cases kill) Listeria monocytogenes (Hughey et al, 1987, Appl. Environ. Microbiol 53:2165-2170). Lysozyme derived from egg albumin with an activity of about 20,000 Shugar units/mg is commercially available from Rhodia under the trademark NovaGARD(trademark).
In summary, the first component of the novel composition is preferably the previously disclosed combination of lantibiotics and lytic enzymes, especially the more preferred combination of nisin and egg-white lysozyme.
The second component of the novel composition is one or more hops acid extracts or hops acid derivatives or hops resins or hops resin derivatives or combinations of some or all of these. The bitter components of the hops used in beer making, particularly the beta-acids, have now been found to be useful as bactericidal agents in food products, particularly in combination with the above mentioned bacteristatic and/or bactericidal components. The most prevalent groups of bitter acids contained in hops are the alpha-acids and the beta-acids, also referred to as humulones and lupulones, respectively. Both contribute bitterness to beer, but the alpha-acids are much more bitter than the beta-acids and not desirable for use in most food products. Producers of hops extracts isolate the alpha and beta acids commercially by various chromatographic methods and have recently developed a technique to separate the two acid fractions using liquid carbon dioxide under supercritical conditions. A by-product of the operation is a product which contains approximately 61 weight percent beta-acids, the remainder consisting essentially of hops resins. This by-product can be standardized with malto dextrin or other food grade carrier, spray dried, and used as an antibacterial food ingredient. A preferred beta hops acids composition is commercially available as a natural flavor extract containing 1 weight percent beta hops acids.
The alpha-acids contained in hops are commonly known as humulone, cohumulone and adhumulone, while the beta-acids contained in hops are commonly known as lupulone, colupulone and adlupulone. Chemically modified derivatives of hops acids or hops resins which have demonstrated antibacterial properties such as hexahydrocolupulone and tetrahydroisohumulone, as disclosed in U.S. Pat. No. 5,455,038, are specifically contemplated for use in association with the present invention. Also considered as specifically contemplated for use in association with the present invention is the use of the acid salt forms of the hops acids or hops resins.
In practice, the hops acid or resin or derivatives thereof is added to the food product in amounts between about 0.1 to about 50 ppm of active ingredient (by weight of solution used for treatment), more preferably between about 0.40 to about 20 ppm.
Other additives which can be present in the inventive composition include, but are not limited to the following materials: other antibacterial, such as chitosan or its derivatives, and/or chelating agents, natural or synthetic seasonings, essential oils, and/or flavors, dyes and/or colorants, vitamins, minerals, nutrients, enzymes, binding agents such as guar gum and xanthan gum and the like. In particularly preferred embodiments, guar gum is present in the inventive composition to aid in the binding of the antimicrobial components to the food surface being treated. The addition of these materials is not considered critical to the success of the present invention and would be considered within the skill of the artisan.
The antimicrobial composition of the present invention may be used in connection with any food product which is susceptible to microbial degradation. These include, but are not limited to fruits and vegetables including derived products, grain and grain derived products, dairy foods, meat, poultry, and seafood. In particularly preferred embodiments, the composition is used in connection with meat, poultry and/or seafood, more particularly with fat containing cooked meats such as hotdogs, sausages, roast beef, turkey, corned beef and deli meats.
To reduce the amount of bacteria on a food surface, the novel composition is simply applied to the food surface either before or after cooking. In practice the application of the composition of matter to the food surface may either be a direct application or an indirect application. The use of the term xe2x80x9cfood surfacexe2x80x9d is defined to include any and all internal or external surfaces of the food product being treated.
The composition according to the present invention is most readily used by applying it on the exterior surface of a blended food product, such as a hot dog or bologna, or of a solid food, such as a piece of roasted beef, so as to minimize loss of activity in the fat phase of the food. The composition may alternatively be included in the emulsion or raw ingredients of a food such as sauces or salsas, before or after cooking, or to the interior of solid products, such as hams, by injection or tumbling. In still other embodiments, the composition may be applied as a marinade, breading, seasoning rub, glaze, colorant mixture, and the like, the key criteria being that the antimicrobial composition be available to the surface subject to bacterial degradation. In a preferred embodiment, the composition may be indirectly placed into contact with the food surface by applying the composition to food packaging materials or casings and thereafter applying the packaging to the food surface. The use of surface treatment strategies, whether direct or indirect, benefits from the minimization of loss into the fat phase of the fat containing food product. The bacteristatically or bactericidally optimum effective amount to be used will depend on the composition of the particular food product to be treated and the method used for applying the composition to the food surface, but can be determined by simple experimentation.
In a preferred embodiment of this invention, the antibacterial composition comprises from about 38.5 to 99.8 parts by weight of the first component, which includes at least one bacteristatic or bactericidal compound selected from the group consisting of lantibiotics, pediocin, lacticin class bacteriocins, and lytic enzymes; to about 61.5 to 0.2 parts by weight of the second component, which includes at least one compound selected from the group consisting of hops acids, hops acid derivatives, hops resins, and hops resin derivatives; all parts by weight being based on the total weight of the first and second components of the composition.
In a more specifically preferred composition embodiment of this invention wherein the first component comprises two compounds, it is preferred that the composition comprises, as a first component, from about 1.0 to 2.5 parts by weight lantibiotic, and from about 37.5 to 97.3 parts by weight lytic enzyme; and as a second component, from about 61.5 to 0.2 parts by weight of at least one compound selected from the group consisting of hops acids, hops acid derivatives, hops resins, and hops resin derivatives; all parts by weight being based on the total weight of the first and second components of the composition.

Antibacterial composition for control of gram positive bacteria in food applications


A page pack for a printing press wherein the housing for the ink pump and motor assemblies also serves as a heat sink for the heat generated by the motor drive units. The housing comprises a body for receiving a plurality of positive displacement ink pumps each comprising a pump cylinder and at least one pump piston, with all such bores being arranged substantially parallel to each other and lying in a given plane. The housing includes openings for accommodating pump drive motors with their output shafts arranged so as to lie parallel to each other and in a plane slightly offset from an intersecting plane in which the pumps are positioned. The pump housing further includes means for positioning a motor control circuitboard in the housing such that a plurality of individual high current driver units each has its own metal heat sink, and such that these individual heat sinks are secured in use to a master metal heat sink either positioned adjacent or forming a part of the housing, whereby there is an intimate heat exchange relation between the motor driver units and the housing.

The present invention relates generally to components of large printing presses, and in particular, to an advantageous construction and arrangement of controls for the "page pack" portion of the system used to deliver ink to the inking rolls of such large printing presses.
By way of background, the mechanism used to ink the rollers in large scale, high speed printing presses, such as those used to print daily newspapers, has several important components, namely, an orifice plate, an ink rail and several ink pump assemblies. The orifice plate receives a supply of ink from a pumping system and forms and positions a film or bath of ink adjacent the inking roller of the press, which in turn picks up the ink and transfers it to an impression roller.
The ink rail component usually supports four pump assemblies by positioning the pump housings in a desired relation to the other components. Each pump housing customarily positions six or eight ink pumps, one for each column of the page being printed. Cumulatively, the housing and one set of ink pumps, their associated drive mechanism, the drive controls, and the associated fittings and manifolding are sometimes called a "page pack." Here, a page pack is contained within the width of one page of a newspaper, i.e., approximately 13-14 inches.
In presses dating back several years, the ink pumps themselves were of a valveless, positive displacement type pump utilizing rod-like piston with a chordwise relief on one end, movably received in a ported cylinder. The piston rotated and reciprocated within the cylinder, drawing in and expelling ink through inlet and outlet ports. These pumps are constructed and arranged in a known manner such that with one portion of the working cycle, the piston is withdrawn at the time the relief is indexed with an inlet passage. This withdrawal motion pulls ink by suction through the inlet port and into a closed end working chamber. In a second portion of the operating cycle, the piston strokes back towards the closed end of the cylinder at the same time its rotary motion indexes the relief with an outlet port in the opposite side of the cylinder. This movement causes the ink that has just filled the working chamber of its cylinder to be displaced outwardly through the exhaust port. As the rotation and reciprocation of the piston continue, this cycle is repeated.
In the recent past, approximately 10 or more years ago, the drive mechanism for some of these pumps was changed significantly. In the older style pumps, a mechanical master drive system operated through a power train of gears and shafts to rotate and stroke the ink pump pistons. Volume control was achieved by varying the angle between the driving and the driven elements. Because pump output per cycle is dependent on the effective angle between the rotational axes of the piston and cylinder on the one hand and the driving member on the other hand, some sort of angle-changing mechanism was required.
The prior art used complex mechanical arrangements for varying this effective angle (minimizing the angle down to and including zero when pump output was to approach and reach zero), and such arrangements created significant maintenance and quality control problems as well as being expensive initially.
Because the industry recognized its many shortcomings in the approach of changing ink pump output rate by varying the driving member/driven member angle as explained above, a different kind of drive system was developed some years ago. This system provided individual electric drive motors for each pump assembly instead of using a common drive source. Now, volume control is achieved on a continuous basis by utilizing a stepping motor for each pump, and an electronic digital control arrangement. Such an arrangement is sometimes termed a "digital" page pack.
In this arrangement, one output pulse from a driver circuit causes the stepping motor to move one step, and this in turn causes the pump to rotate a very small fraction of one complete rotation. Typically, one complete 360.degree. revolution requires 300 to 400 individual steps, and hence, in the case of a 400 step motor, 400 individual pulses would be required to achieve one rotation.
The time interval between pulses determines the rate; the longer the interval, the slower the rate. The advantage of such a control system is that both true zero movements as well as very minute pump movements may be achieved.
With a system wherein the page pack includes six or eight stepping motors and six or eight pumps, each motor can be driven at its own rate, entirely independently of the rate of any other motor. This rate is established by the operator, and control of each pump rate is achieved by inputting signals at a control keyboard. Accordingly, a microprocessor keyboard can be used to set the output rate of each of the individual pumps, thereby varying the amount of ink fed to a counterpart portion of the orifice plate with each pump revolution. Thus, if the impression cylinder printing a newspaper page had a large ink requirement near the center of the page and a great deal of "white space" near the margins, then the individual pumps near the center of each page pack will be made to operate at a relatively higher rate to furnish more ink in keeping with the requirements of the inking roller, whereas the peripheral pumps would operate at a lower or zero settings because the ink demand for a white space area of the paper is much less.
Referring now to the aspect of overall press speed, the amount of ink consumption for a given ink density is also directly proportional to press speed, which itself is variable. In this connection, a second advantageous feature of the above stepping motor control arrangement is that the overall, real-time frequency of these stepper motor drive pulses may be increased or decreased by an overall rate controller which is in turn slaved to or governed by a tachometer system. Accordingly, once the relative control rate for the individual pumps is set, ink delivery at a certain rate is assumed. However, if the press speed as a whole decreases, then it is necessary to decrease the rate at which all of the individual ink pumps operate in order to compensate for the reduced ink demand. The converse is true; in the event the press begins running at a comparatively higher speed, the rates of all the pumps must increase in direct proportion to press speed.
Accordingly, known control systems am able to establish a series of settings which establish the relative rate flow of the individual ink pumps within all of the page packs, and these relative settings are kept proportional to press speed by a tachometer system that takes actual press speed into account.
Even with the improved page packs of the type just referred to, there has been a need for further improvement, inasmuch as the reliability and maintainability of such systems has not been as great as might be desired. In this connection, it must be realized that considering the enormous number of impressions made by newspaper printing presses, and the requirement that daily papers be printed on an almost continuous basis, the need for high reliability cannot be over emphasized.
In prior arrangements, over a particular period of time, a few of the output driver units typically operated almost continuously, while other driver units operated only intermittently or sometimes not at all. Thus, each of the driver chips developed a different temperature rise. Although the heat sinks associated with these chips were adequate under some conditions, it is accepted that lower temperature operation is more favorable to durability and reliability than is operation at or near the peak permissible operating temperature of the output driver chips.
In these past arrangements, particularly where the array of chips was located adjacent a keyboard or other control remote from the pumps and motors, favorable heat dissipation arrangements were not able to be achieved. It would be desirable if a heat sink arrangement could be made such that the temperature rise in certain chips would still be relatively modest even if such chips were operating continuously. By providing the combination of a greater heat sink capacity, as well as the ability to spread or dissipate the heat, particularly to those areas which am inherently cooler-running, better reliability is possible.
According to the invention, the arrangement of the driver chips on the board can enable the mass and the inherent heat capacity of the pump housing to be utilized in such a way as to improve reliability and serviceability of the electronic components in the page pack.
According to the present invention, it has been found possible to do away with remote positioning of certain parts or components of the control system, whereby only the keyboard and a few other elements need be positioned near the operator or pressman, while the others can be positioned adjacent the page pack, i.e., near the individual pumps and motors. In this arrangement, better packaging, and especially better control of generated heat, can be achieved, resulting in increased longevity and decreased service requirements. Thus, certain elements of the ink control system, particularly the motor and pump housings and the printed circuitboard comprising most of the motor control and drive circuits can be effectively arrayed to achieve optimum temperature rise control. In this way, their reliability can be significantly increased. According to the invention, an improved arrangement of packaging for these components has been provided with such arrangement being economical, effective and achievable at modest cost.
In view of the failure of the prior art to provide printing ink pump packages of optimum reliability and economy, it is an object of the present invention to provide an improved digital page pack, or pump-motor-and control system for printing press ink pumps.
A further object of the invention is to provide a component mounting arrangement with improved control of electrically generated heat.
Another object of the invention is to provide an improved page pack wherein a single housing for the pumps positions the motors and also includes a flanged body and a master heat sink rail that is in intimate heat exchange relation with the heat sinks on the output drivers for the stepping motors used to control the ink pumps.
A still further object of the invention is to provide an arrangement whereby, on a printed circuitboard type control assembly, plural high current output driver units, each having its own small heat sink, are arrayed in a common plane and arranged to be fastened to a metal element serving as a master heat sink.
Yet another object of the invention is to provide an arrangement of heat sink materials, including a portion which is integrally cast with the page pack pump and motor housing and another master heat sink portion which may be fixed to the integrated heat sink elements on the output drivers and thereafter placed in intimate heat exchange relation with the remainder of the housing.
A still further object of the invention is to provide a control system for an array of printing press ink pumps which includes housing having openings for receiving ink pump and the output shafts of individual drive motors, a mounting surface for the drive motors, and end and sidewall housing flanges, with each flange including a slot for receiving a circuitboard, and with one flange including a master heat sink mounting surface, so that with the margins of a circuitboard disposed within and positioned by the slots, the master heat sink can be fastened both to the individual heat sinks forming a part of the circuitboard and to flange on the housing.
Another object of the invention is to provide an improved arrangement for component mounting in an ink pump system, wherein the control system includes a remote keyboard, pump drive circuitry on a circuitboard, with the drive components of the circuitboard being positioned adjacent the pump motors and in intimate heat exchange relation with the housing for the motors.
The manner in which the foregoing and other objects of the invention are achieved in practice will become more fully apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.

Page pack having novel heat sink arrangement for pump motor drive units


A unilaterally self-adhesively coated adhesive tape, comprising

The invention relates to an adhesive tape comprising a polyolefin-based backing unilaterally coated with a solvent-free adhesive composition based on natural rubber latex and to the use of said adhesive tape as packaging tape.
Adhesive tapes with films based on polyolefins, such as biaxially oriented polypropylene, for example, and adhesive compositions based on solvent-containing natural rubber or aqueous acrylate dispersions are known and are supplied by known manufacturers.
A description is given, for example, in xe2x80x9cPackaging Tapesxe2x80x9d by Stefan Rxc3x6ber in Handbook of Pressure Sensitive Adhesive Technology, Third Edition, edited by Donatas Satas, Satas and Associates, Warwick, Rhode Island pp. 787-814. Further descriptions can be found in European Adhesives and Sealants 10(4), 1993, 29, by G. Pedala, and European Adhesives and Sealants 2(2), 1985, 18, by R. W. Andrew.
Owing to the known disadvantages associated with the production of solvent-containing adhesive tapes, such as, for example, the difficulty of recycling solvents, the emission of solvent to the environment, the workplace hazard due to highly flammable solvents, and the restriction on coating speed imposed by the drying of the adhesive composition, solvent-free technologies for producing adhesive tapes are advancing in importance.
A disadvantage to add to the above-described problems of the solvent technology is the need to break down the natural rubber during the production of the adhesive composition, in a process known as mastication. This results in the adhesive composition having a cohesiveness which decreases markedly in accordance with the extent of breakdown under mechanical load.
The deliberate industrial process of breaking down rubber under the combined action of shear stress, temperature, and atmospheric oxygen is referred to in the technical literature as mastication and is generally carried out in the presence of chemical auxiliaries, which are known from the technical literature as masticating agents or peptizers, or, more rarely, as xe2x80x9cchemical plasticizing aidsxe2x80x9d. In rubber technology, the mastication step is needed in order to make it easier to integrate the additives.
According to Rxc3x6mpp (Rxc3x6mpp Lexikon Chemiexe2x80x94Version 1.5, Stuttgart/New York: Georg Thieme Verlag 1998) mastication is a term used in rubber technology for the breaking down of long-chain rubber molecules in order to increase the plasticity and/or reduce the (Mooney) viscosity of rubbers. Mastication is accomplished by treating, in particular, natural rubber in compounders or between rolls at very low temperatures in the presence of masticating agents. The high mechanical forces which this entails lead to the rubber molecules being xe2x80x9ctorn apartxe2x80x9d, with the formation of macro radicals, whose recombination is prevented by reaction with atmospheric oxygen. Masticating agents such as aromatic or heterocyclic mercaptans and/or their zinc salts or disulfides promote the formation of primary radicals and so accelerate the mastication process. Activators such as metal (iron, copper, cobalt) salts of tetraazaporphyrins or phthalocyanines permit a reduction in the mastication temperature. In the mastication of natural rubber, masticating agents are used in amounts from about 0.1 to 0.5% by weight in the form of masterbatches, which facilitate uniform distribution of this small amount of chemicals in the rubber mass.
Mastication must be clearly distinguished from the breakdown known as degradation which occurs in all of the standard solvent-free polymer technologies such as compounding, conveying, and coating in the melt.
Degradation is a collective term for different processes which alter the appearance and properties of plastics. Degradation may be caused, for example, by chemical, thermal, oxidative, mechanical or biological influences or else by exposure to radiation (such as (UV) light). Consequences are, for example, oxidation, chain cleavage, depolymerization, crosslinking, and/or elimination of side groups of the polymers. The stability of polymers toward degradation may be increased by means of additives: for example, by adding stabilizers such as antioxidants or light stabilizers.
The use of adhesive compositions of this kind based on natural rubber hotmelt pressure-sensitive adhesives for adhesive tapes, especially packaging tapes, for sealing cartons made from recycled paper, or cardboard packaging, results in premature opening of the cartons. If there is sufficiently great tension across the lid of the carton, caused by the pressure of the packaged material in the carton or by the tension of the packaging material, which opposes sealing, the adhesive tape becomes detached from the surface of the carton and the carton opens as result of slippage of the packaging tape.
The cohesion and, with it, the packaging security afforded by adhesive tapes with an adhesive composition based on natural rubber may be improved either by crosslinking the rubber adhesive composition and/or by means of a variant preparation of the adhesive composition in the course of which the natural rubber used is broken down to a much-reduced extent and therefore has a higher molecular weight. This makes it possible to counter slippage of the adhesive tapes on the carton surface, as described above.
Solvent-free technologies for producing adhesive tapes, especially packaging tapes, have to date been restricted to the use of adhesive composition based on acrylate dispersions and to the use of melting, thermoplastic elastomers.
An advantage of these thermoplastic elastomers, predominantly block copolymers containing polystyrene blocks, is the relatively low softening point and the corresponding simplification of the application or coating process, and also the avoidance of the above-described disadvantages of the solvent-based technologies.
The unfavorable aging behavior and the profile of properties of such packaging tapes at elevated temperatures, the poor thermal stability, lead to premature opening of the cartons packaged with these tapes and/or a packaging tape performance profile which generally has some adverse features. Moreover, the process temperatures, which are very high in some cases, are detrimental to certain types of adhesive composition.
Further solvent-free systems based on aqueous adhesives, such as adhesive systems based on polyvinyl acetate, polyvinyl acetate-ethylene copolymers, neoprene, styrene-butadiene, polyurethane and polyvinyl alcohol, for example, are used little if at all owing to a price and/or performance structure which is unfavorable for adhesive tapes, particularly packaging tapes.
An overview of the most important aqueous adhesive systems and also their use is given in xe2x80x9cSolvent free adhesivesxe2x80x9d, T. E. Rolando (H. B. Fuller) in Rapra Rev. Rep. 1997, 9(5), 3-30 Rapra Technology Ltd.
Various routes to the solvent-free preparation and processing of pressure-sensitive rubber adhesives are known.
An overview of such adhesive compositions and their use in the field of pressure sensitive adhesives (PSAs) is given in xe2x80x9cNatural Rubber Adhesivesxe2x80x9d (G. L. Butler in Handbook of Pressure Sensitive Adhesive Technology, Third Edition, edited by Donatas Satas, Van Nostrand Reinhold New York, pp. 261-287).
All of the known processes are characterized by very extensive rubber breakdown. For the further processing of the compositions for self-adhesive tapes, this necessitates extreme crosslinking conditions and also has the consequence of an application profile which is to some extent restricted, especially as regards the use of resultant self-adhesive tapes at relatively high temperatures.
Solvent-free hotmelt PSAs based on nonthermoplastic elastomers, such as natural rubber or other high molecular weight rubbers, for example, lack sufficient cohesion for the majority of applications, in the absence of a step of crosslinking the adhesive composition, and are therefore unsuited to use in the context of an adhesive packaging tape. The reason for this failure of noncrosslinked adhesive compositions based on natural rubber is the relatively large reduction in molecular weight as a result of processing, and/or as a result of the preparation process of the adhesive compositions based on natural rubber, and the resultant reduced or inadequate cohesion of the adhesive compositions.
CA 698 518 describes a process for achieving production of a composition by adding high proportions of plasticizer and/or by simultaneously strong mastication of the rubber. Although this process can be used to obtain PSAs having an extremely high tack, the achievement of a user-compatible shear strength is possible only to a limited extent, even with a relatively high level of subsequent crosslinking, owing to the relatively high plasticizer content or else to the severe breakdown in molecular structure of the elastomer to a molecular weight average of Mwxe2x89xa61 million.
The use of polymer blends, where besides nonthermoplastic natural rubber use is also made of block copolymers, in a ratio of approximately 1:1, represents essentially an unsatisfactory, compromise solution, since it results neither in high shear strengths when the self-adhesive tapes are used at relatively high temperatures nor in significant improvements on the properties described in CA 698 518.
Raw natural rubber latex is supplied from the plantations and is purified, preserved, and concentrated by means of appropriate methods. A general description of the types of latex and methods of processing is given in xe2x80x9cNaturkautschukxe2x80x94Technisches Informationsblattxe2x80x9d [Natural rubberxe2x80x94technical information sheet], Malaysian Rubber Producers Research Association, L1, 1977, and in xe2x80x9cKautschuktechnologiexe2x80x9d [Rubber technology], Werner Hofmann, Gentner Verlag, Stuttgart p. 51 ff.
Natural rubber latex is harvested as a natural product from trees known as latex trees. After various processing steps for separation and purification, four basic types of natural rubber latices are distinguished:
1. Standard natural rubber latex with a high ammonia content of 0.7% by weight
2. Natural rubber latex with a low ammonia content of 0.2% by weight in combination with zinc oxide and tetramethylthiuram disulfide  less than 0.035% by weight
3. Natural rubber latex doubly centrifuged, of particularly high purity
4. Natural rubber latex partly vulcanized, for specialty applications
Mastication and the associated breakdown of the natural rubber is not necessary when preparing adhesive compositions based on natural rubber latex, since in the case of the solvent-free aqueous adhesive composition the simple mixing of the components is not accompanied by mastication and thus by a breakdown of the molecule under mechanical load. This results in a close interlooping of the natural rubber latex/isoprene molecules, a high molecular weight owing to absence of mastication, a broad molecular weight distribution, and a low softening point Tg.
These factors result in a very good balance between cohesion and adhesion in the adhesive composition resulting from resin blends, and also in a profile of properties which is of very high performance for adhesive tapes, over a very wide temperature range.
These positive characteristics over a wide temperature range are exploited for the adhesive tape described in JP 56 030 481, comprising an adhesive composition based on natural rubber latex. Through the use of the natural rubber latex, a robustness to impact at low temperatures is described.
A further point is that natural rubber latex features a particularly wide spectrum of applications. Thus natural rubber latex is suitable on the one hand for use as an adhesive composition for packaging materials and on the other hand for applications outside of adhesive technology.
A disadvantage of adhesive composition systems based on natural rubber latex is the poor stability of the natural rubber latex raw material to mechanical load and the associated coagulation of the natural rubber latex in the adhesive composition. This sensitivity to shearing restricts the ease of handling and the usefulness of the natural rubber latex for adhesive composition technology and the adhesive tape industry. The production of adhesive tapes wherein the adhesive composition comprising natural rubber latex can be coated at high speed onto a film is not known.
Through the use of stabilizing resin dispersions and/or surface-active substances, such as emulsifiers, for example, it is possible to increase significantly the stability of the natural rubber latex. However, increasing the stability of natural rubber latex using surface-active substances at high concentrations goes hand in hand with a drastic loss of cohesion of the adhesive composition, with the consequence that adhesive compositions modified in this way cannot be used for packaging tapes.
The general use of natural rubber latex for adhesive compositions and also latex-stabilizing resin dispersions is described in xe2x80x9cTackified waterborne adhesive for PSA tapesxe2x80x9d, J. G. de Hullu, European Adhesives and Sealants, 12 (1998), p. 11-12. Through the use of such natural rubber latex-stabilizing resin dispersions, it becomes possible to process or coat adhesive compositions based on natural rubber latex. The trouble-free application of the dispersion adhesive compositions to a polymeric backing enables an industrially practicable and economically rational adhesive tape production process. The use of this technology is made possible by employing a suitable adhesive composition and by technically setting and optimizing the coating lines.
The application and development of an adhesive tape which unwinds quietly and is suitable for packaging applications has not been described in this context. The use of adhesive tapes with quiet unwind, particularly for carton sealing, however, is of great importance within the packaging industry in order to reduce the noise load in the packing houses and hence to increase work performance. The capacity for quiet unwinding is of fundamental importance in order to position an adhesive packaging tape within the middle to top price/performance segment.
Resin dispersions based on rosins and/or their derivatives are used for a large number of water borne polymers. In particular, rosin esters find application here. In general, there is an increase in the adhesion properties on the surfaces. The softening point of the corresponding rosin or derivative may be selected accordingly. In the adhesive tape segment, these resin dispersions serve as tackifiers for the respective adhesive compositions, in order to optimize the adhesion properties on different surfaces, and are therefore used in combination with corresponding hydrocarbon resin dispersions (principal resin component).
In general terms, natural rubber latex is a known component of adhesive compositions and is described, inter alia, in patents. The fields of use of such adhesive compositions based on natural rubber latex are applications in the sector of labels and plaster technology.
The preparation of aqueous adhesive compositions based on natural rubber latex is known. These adhesive compositions are used as described above for producing self-adhesive labels. This is done using the customary methods of preparing dispersion adhesives.
The preparation of adhesive composition systems which comprise natural rubber latex is likewise described in EP 0 960 923 A1. This discloses not only the preparation of dispersion adhesive compositions but also the incorporation of natural rubber latex into other natural rubber adhesive systems using compounders, mixers or extruders. The adhesive compositions prepared in this way may be coated onto film or nonwoven. An improvement in the packaging properties of such adhesive tapes by means of a controlled, enduring crosslinking of the adhesive composition, which also may be used as part of a rational production process, has not been described.
When using adhesive composition variants based on natural rubber latex it is the casexe2x80x94as already set out abovexe2x80x94that enduring crosslinking is unnecessary for achieving good packaging qualities that are superior to the majority of other adhesive composition systems.
Through the use of the above-described stabilizing resin dispersions and also by using natural rubber latex, and accordingly in the absence of any mechanical breakdown of the rubber whatsoever, it is possible to prepare, process, and apply adhesive compositions based on natural rubber latex and thus to produce adhesive tapes, since the adhesive composition possesses very high cohesion and hence optimum packaging security.
Not only for adhesive packaging tapes for sealing cartons but also for other adhesive packaging tapes, such as strapping tapes, therefore, the natural rubber-based adhesive composition must have sufficient cohesion.
In the case of the natural rubber adhesive compositions, the adhesive tapes are provided with a reverse-face coating in order to reduce the unwind force. This coating of the reverse face is necessary in order to prevent overstretching of the backing during application. Without a reduction in unwind force by reverse-face coating, the backing becomes overstretched during rapid unwind, owing to excessive unwind forces, and this significantly impairs the packaging security. Moreover, reverse-face-coated adhesive tapes of this kind exhibit loud and clattering unwind. Because of such unwind characteristics, adhesive tapes of this kind are suitable only for sale and use at the lower price and performance levels.
In the case of the adhesive tapes with a backing based on polyolefins, preferably polypropylene, in combination with an adhesive composition based on acrylate dispersions, quiet and clatterless unwind of adhesive tapes is achieved by surface treatment of the side of the backing that faces away from the adhesive composition. This is generally accomplished by means of corona treatment. It is described in EP 0 096 841. This corona treatment of the backing reverse face, carried out for example after coating during the cutting process, increases the unwind force of the adhesive tapes and thus prevents flaking of the adhesive composition from the backing. This flaking of the adhesive composition from the backing on the basis of the unwind process leads to loud, clattering unwind. As a result of the corona treatment of the reverse face to an appropriate extent, the adhesive tape acquires quiet unwind. The unwind force, and with it the unwind characteristics as well, are set and adjusted by appropriate corona treatment of the reverse face. At the present state of development, all adhesive tapes without reverse-face corona treatment exhibit loud unwind.
The corona treatment of the adhesive tapes is accompanied substantially by disadvantages. First, it entails an additional workstep requiring additional machinery. In the case of corona treatment during the cutting process, only cutting machines with a cutting corona can be used. In some cases this necessitates additional acquisition of machinery. Secondly, the precise extent of the corona treatment is decisive in achieving the desired effect. This brings with it a high degree of process uncertainty, necessitating increased quality control.
In the case of an inadequate corona output, the desired effect of quiet unwind is not fully achieved, and, since the resultant finished adhesive tapes cannot be aftertreated, production of reject product is the consequence. In the case of too strong a corona output, the unwind force is increased excessively, leading to backing overstretch, backing tear, or a transfer of the adhesive composition during the unwinding of the adhesive tape.
Monoaxially and biaxially oriented films based on polypropylene are used in large quantities for adhesive packaging tapes. Whereas biaxially oriented films based on polypropylene are preferred for the use of adhesive packaging tape for carton sealing, monoaxially oriented polypropylene films find application in the strapping tapes segment. These films are notable for very high tensile strength and low extension in the longitudinal direction and are highly suited to bundling and palletization. When using adhesive compositions which exhibit inadequate cohesion or inadequate anchoring of the adhesive composition to the film, the slippage of the strapping tapes results in slipping of the pallets and thus in inadequate securement of the pallets. Insufficient anchoring of the adhesive composition on the film leads, when using carton sealing tapes, to premature opening of the packed cartons.
Thermoplastic films based on polyvinyl chloride (PVC) are used to produce adhesive tapes by a variety of manufacturers. Particularly films based on PET are distinguished by high elongation at break and thermal stability of from 130xc2x0 C. to 175xc2x0 C., and resistance toward dilute alkalis and acids. Moreover, films based on polyesters possess a very high abrasion resistance and penetration resistance, but are less widespread in the field of adhesive packaging tapes owing to their relatively high price in relation to polyolefin-based films.
In the production of adhesive tapes with adhesive compositions based on natural rubber, both water-based and solventborne primers are used as adhesive promoters between adhesive composition and backing film. These adhesive promoters that are used possess in part a crosslinking effect on the natural-rubber-based adhesive composition which is applied from solution.
It is an object of the present invention to provide adhesive tapes comprising films based on oriented polyolefins and solventlessly prepared adhesive compositions based on natural rubber latex, said tapes exhibiting quiet unwind even at very high unwind speeds and without the need to activate by corona treatment that side of the backing of the adhesive tape that is opposite to the adhesive composition. This quiet unwind should be retained even at very high unwind speeds.
Furthermore, the adhesive tapes ought to unwind easily. Additionally, the novel adhesive tapes ought to possess outstanding suitability for use as packaging tapes for commercial cardboard packaging.
This object is achieved by means of an adhesive tape as specified in the main claim. The subclaims relate to advantageous developments of the subject matter of the invention.
Furthermore, the invention provides proposals for using the adhesive tape of the invention.
The invention accordingly provides a unilaterally self-adhesively coated adhesive tape comprising a film based on oriented polyolefins in which that side of the film remote from the adhesive layer exhibits no surface treatment.
The film is provided on one side with an adhesive layer prepared from a mixture comprising
Hydrocarbon resin is a collective term for thermoplastic polymers which are colorless to intense brown in color and have a molar mass of generally  less than 2000.
They may be divided into three main groups according to their provenance: petroleum resins, coal tar resins, and terpene resins. The most important coal tar resins are the coumarone-indene resins. The hydrocarbon resins are obtained by polymerizing the unsaturated compounds that can be isolated from the raw materials.
Included among the hydrocarbon resins are also polymers obtainable by polymerizing monomers such as styrene and/or by means of polycondensation (certain formaldehyde resins), with a correspondingly low molar mass. Hydrocarbon resins are products with a softening range that varies within wide limits from  less than 0xc2x0 C. (hydrocarbon resins liquid at 20xc2x0 C.) to  greater than 200xc2x0 C. and with a density of from about 0.9 to 1.2 g/cm3.
They are soluble in inorganic solvents such as ethers, esters, ketones, and chlorinated hydrocarbons, and insoluble in alcohols and water.
By rosin is meant a natural resin which is recovered from the crude resin from conifers. Three types of rosin are differentiated: balsam resin, as a distillation residue of turpentine oil; root resin, as the extract from conifer rootstocks; and tall resin, the distillation residue of tall oil. The most significant in terms of quantity is balsam resin.
Rosin is a brittle, transparent product with a color ranging from red to brown. It is insoluble in water but soluble in many organic solvents such as (chlorinated) aliphatic and aromatic hydrocarbons, esters, ethers, and ketones, and also in plant oils and mineral oils. The softening point of rosin is situated in the range from approximately 70 to 80xc2x0 C.
Rosin is a mixture of about 90% resin acids and 10% neutral substances (fatty acid esters, terpene alcohols, and hydrocarbons). The principal rosin acids are unsaturated carboxylic acids of empirical formula C20H30O2, abietic acid, neoabietic acid, levopimaric acid, pimaric acid, isopimaric acid, and palustric acid, as well as hydrogenated and dehydrogenated abietic acid. The proportions of these acids vary depending on the provenance of the rosin.
Films which may be used in accordance with the invention include monoaxially and biaxially oriented films based on polyolefins, then films based on oriented polyethylene or oriented copolymers containing ethylene and/or polypropylene units.
Monoaxially oriented polypropylene is notable for its very high tensile strength and low elongation in the longitudinal direction and is used, for example, to produce strapping tapes. Monoaxially oriented films based on polypropylene are particularly preferred for producing the adhesive tapes of the invention, especially for bundling and palletizing cardboard packaging and other goods.
The thicknesses of the monoaxially oriented films based on polypropylene are preferably between 25 and 200 xcexcm, in particular between 40 and 130 xcexcm.
Monoaxially oriented films are predominantly single-layered, although multilayer monoaxially oriented films may also be produced in principle. The known films are predominantly one-, two- and three-layer films, although the number of layers chosen may also be greater.
For the production of the adhesive tapes of the invention, used among other things for secure carton sealing, particular preference is further given to biaxially oriented films based on polypropylene with a draw ratio in the longitudinal (machine) direction of between 1:4 and 1:9, preferably between 1:4.8 and 1:6, and a draw ratio in the transverse (cross) direction of between 1:4 and 1:9, preferably between 1:4.8 and 1:8.5.
The moduli of elasticity achieved in the machine direction, measured at 10% elongation in accordance with ASTM D882, are usually between 1000 and 4000 N/mm2, preferably between 1500 and 3000 N/mm2.
The thicknesses of the biaxially oriented films based on polypropylene are in particular between 15 and 100 xcexcm, preferably between 20 and 50 xcexcm.
Biaxially oriented films based on polypropylene may be produced by means of blown film extrusion or by means of customary flat film units. Biaxially oriented films are produced both with one layer and with a plurality of layers. In the case of the multilayer films, the thickness and composition of the different layers may also be the same, although different thicknesses and compositions are also known.
Particularly preferred for the adhesive tapes of the invention are single-layer, biaxially or monoaxially oriented films and multilayer biaxial or monoaxial films based on polypropylene which have a sufficiently firm bond between the layers, since delamination of the layers in the course of the application is disadvantageous.
The adhesion of the adhesion promoter on the thermoplastic film based on polyolefins may be improved by means of corona treatment or flame pretreatment, since, especially, the surfaces of the films based on oriented polyolefins may be treated by means of these widely known processes, such as corona treatment or flame treatment. Preference is given to surface treatments by corona treatment.
An overview of the processes for surface treatment is contained, for example, in the article xe2x80x9cSurface pretreatment of plastics for adhesive bondingxe2x80x9d, A. Kruse; G. Krxc3xcger, A. Baalmann and O. D. Hennemann; J. Adhesion Sci. Technol., Vol. 9, No. 12, pp. 1611-1621 (1995).
The biaxially oriented films for the adhesive tapes of the invention are heavily corona- or flame-pretreated on the side facing the adhesive composition or, where present, the adhesion promoter, but are not surface-treated and/or corona- or flame-pretreated on the side remote from the composition.
In an further preferred embodiment of the invention, an adhesion promoter is present between the optionally flame- or corona-treated film and the adhesive layer, and guarantees the effective bonding of the adhesive composition to the film and the crosslinking of the adhesive composition.
The adhesion promoter used optionally between adhesive composition and backing film optimizes the bond between the specified layers.
The application rate of the adhesive layer is in particular from 10 to 45 g/m2. In one preferred embodiment, the application rate set is from 13 to 28 g/m2.
In one particularly preferred variant, the adhesive compositions of the adhesive tapes of the invention include from 45 to 60% by weight of natural rubber latex. Also in accordance with the invention are other natural rubber latices and also mixtures of different types of natural rubber latices.
Depending on application, the following componentsxe2x80x94independently of one anotherxe2x80x94may be added to the adhesive composition;
With further preference, the adhesive layer contains up to 20% by weight of at least one resin dispersion based on hydrocarbon resins having a softening point of from 20xc2x0 C. to 85xc2x0 C.
The adhesive composition may in particular include from 0.05 to 20% by weight and, preferably, from 2 to 15% by weight of the additional resin dispersion.
The raw material used for the adhesive tapes of the invention is preferably standard natural rubber latex with an ammonia content of 0.7% by weight, firstly because the natural rubber latex mentioned offers price advantages and secondly because its relatively high ammonia content provides the natural rubber latex with effective stabilization. Substantially, natural rubber latex is very highly suitable for the use of adhesive compositions for adhesive tapes. Owing to the latex""s very high molecular weight, the interlooping of the molecule chains, low glass transition temperature, and absence of mastication during the preparation of the adhesive compositions, adhesive compositions based on natural rubber latex display an excellent balance between adhesion and cohesion.
These properties ensure a very high level of packaging security when adhesive tapes comprising a natural rubber latex-based adhesive composition are used, especially in connection with the use of critical carton types and low temperatures. The mechanical stability of the natural rubber latex may be critical with regard to mechanical shearing loads. Strong mechanical shearing loads lead to coagulation of the natural rubber latex, meaning that it cannot be processed. Possibilities for stabilizing the adhesive compositions based on natural rubber latex toward mechanical loads include firstly the use of appropriate stabilizing resin dispersions and secondly the use of emulsifiers.
The adhesive tapes of the invention preferably comprise natural rubber latex at between 35% to 70% by weight of the standard natural rubber latex with a high ammonia content.
Aqueous resin dispersions, i.e., dispersions of resin in water, are known. Their preparation and properties are described, for example, in xe2x80x9cResin Dispersionsxe2x80x9d, Anne Z. Casey in Handbook of Pressure Sensitive Adhesive Technology, Second Edition, edited by Donatas Satas, Van Nostrand Reinhold New York, pp. 545-566.
Dispersions of hydrocarbon resins are likewise known and are offered, for example, by Hercules BV under the trade name Tacolyn.
For the adhesive tapes of the invention, resin dispersions based on hydrocarbon resins or modified hydrocarbon resins as principal resin component are used. The adhesive composition comprises between 20 to 65% by weight of the resin dispersion. The solids content of the resin dispersion is in particular between 40 and 70% by weight, preferably between 45 and 60% by weight.
The use of rosin dispersions and/or of derivatives of rosin dispersions is employed in the adhesive tape sector to optimize the adhesion properties for adhesive compositions. Through an appropriate choice of the softening point in combination with an optimized resin/natural rubber ratio it is possible to exert a positive influence on the unwind characteristics of the adhesive tapes of the invention. Accordingly, through the use of suitable rosin dispersions, the transition speeds (from quiet unwind to loud unwind) of the adhesive tapes of the invention are shifted significantly toward higher unwind speeds.
For the adhesive tapes of the invention, resin dispersions based on rosins or modified rosins are used as a secondary resin component. The adhesive composition contains between 0.5 to 20% by weight of the resin dispersion and preferably between 1.5 and 15% by weight of the resin dispersion. The solids content of the resin dispersion is in particular between 40 and 70% by weight, preferably between 45 and 60% by weight. The softening point of the rosin or of the modified rosin is between 5xc2x0 C. and 60xc2x0 C., preferably between 12xc2x0 C. and 50xc2x0 C.
Also in accordance with the invention is the use of resin dispersions based on mixtures of different hydrocarbon resins and rosins and/or on modified rosins and also on mixtures of inventive hydrocarbon resins and rosins with other resins.
Also in accordance with the invention is the use of resin dispersions based on mixtures of different hydrocarbon resins and also on mixtures of inventive hydrocarbon resins with other resins.
Likewise known are resin dispersions based on modified hydrocarbons, and of particular interest in this context are C5/C9 hydrocarbon resin dispersions which have been modified with aromatics. The polarity of the resin dispersion and thus of the adhesive composition may be adjusted by way of the proportion of aromatics. As well as the polarity of the adhesive composition, the hardness of the resin is influenced. The lower the aromatics content, the lower the polarity of the modified hydrocarbon resin dispersion.
Aging inhibitors for adhesive compositions based on natural rubber are known. Three different kinds of aging inhibitor are used in particular as antioxidants for adhesive compositions: aging inhibitors based on amines, on dithiocarbamates, and on phenols. Phenol-based aging inhibitors are very effective under the influence of UV radiation and sunlight.
For the adhesive tapes of the invention, phenol-based aging inhibitors are used. The adhesive composition comprises in particular from 0.1 to 5% by weight of an aging inhibitor based on phenols. Also in accordance with the invention is the use of other types of aging inhibitor, such as aging inhibitors based on amines and dithiocarbamates, for example.
Organic and inorganic pigments for adhesive compositions based on natural rubber are known. For the coloring of adhesive compositions based on natural rubber, use is made in particular of titanium dioxide or of titanium dioxide in combination with different-colored color pigments.
For the adhesive tapes of the invention, suitable organic and/or inorganic color pigments are used in dispersion form. The adhesive composition preferably comprises from 0.05 to 20% by weight of an organic and/or inorganic color pigment. Also in accordance with the invention is the use of pigments based on mixtures of different organic and inorganic pigments.
The use of alkoxylated alkyl phenols as plasticizers is proposed, inter alia, in xe2x80x9cModification of Acrylic Dispersionsxe2x80x9d, Alexander Zettl in Handbook of Pressure Sensitive Adhesive Technology, Second Edition, edited by Donatas Satas, Van Nostrand Reinhold New York, p. 471. The properties of the alkoxylated alkyl phenols are determined by the alkyl radical and predominantly by the structure of the polyglycol ether chain. In one preferred embodiment, propoxylated alkyl phenol is used. Water-soluble alkoxylated alkyl phenols are preferred.
The use of alkylphenol polyglycol ethers as emulsifiers for stabilizing the natural rubber latex dispersion adhesive composition is proposed, inter alia, in xe2x80x9cCompounding Natural Latex in water-based PSAsxe2x80x9d, Richard C. Oldack and Robert E. Bloss in Adhesive Age, April 1979, pp. 38-43.
The properties and the stabilizing effect of the alkoxylated alkyl phenols or, generally, of the polyethyleneoxyethanolate condensates are determined predominantly by the polyglycol ether chain. A correlation has been found in this context between the length of the polyglycol ether chain and the stabilizing effect on natural rubber latex.
The adhesive compositions of the invention may comprise from 0.05 to 5% by weight of alkoxylated alkyl phenol, in one preferred embodiment from 1 to 3% by weight.
The adhesive tapes of the invention may be produced by the known methods. An overview of customary production methods can be found, for example, in xe2x80x9cCoating Equipmentxe2x80x9d, Donatas Satas in Handbook of Pressure Sensitive Adhesive Technology, Second Edition edited by Donatas Satas, Van Nostrand New York, pp. 708-808. The known methods of drying and cutting the adhesive tapes are likewise to be found in the Handbook.
The adhesive tapes of the invention are suitable for a large number of adhesive tape applications. One important field of application is that of packaging applications. The adhesive tapes are suitable for use as carton sealing tapes, general adhesive packaging tapes, strapping tapes, and adhesive tapes for sealing plastic packaging and plastic bags. The adhesive tapes are suitable for pallet securement. Further applications are the bundling of loose goods and goods for transit, such as pipes, planks, etc. The adhesive tapes of the invention may be used to secure, for example, refrigerators and other electrical and electronic appliances when in transit. Further applications include label protection, surface protection, in the construction sector, for example, and tear-open strips for packaging. Applications within the office sector are also possible.
The adhesive packaging tapes have running lengths in particular of 66, 100 and 1000 m. Common roll widths chosen are 18, 24, 36, 48, 50 and 72 mm.
The preferred colors are brown, white, and transparent. Printing is carried out on rolls 144 or 150 mm in width, which are then again cut to the abovementioned widths.

Adhesive tape particularly for packaging use

Abstract: a. a film based on oriented polyolefins, in which that side of the film remote from the adhesive layer exhibits no surface treatment,

Abstract: b. an adhesive layer applied to one side of the film, prepared from a mixture comprising

Abstract: from 35 to 70% by weight of a natural rubber latex,

Abstract: from 20 to 65% by weight of a resin dispersion based on a hydrocarbon resin, and

Abstract: from 0.5 to 20% by weight of a resin dispersion based on a rosin or on a derivative of a rosin.