Patent Publication Number: US-2004053792-A1

Title: Conveyor lubricant

Description:
[0001] This invention relates to lubricants, particularly but not exclusively to conveyor lubricants and to their use in a method of lubrication.  
       [0002] Conveyor lubricants are used widely, particularly in the food and beverage industries, in order to lubricate and clean a variety of belt-type and other conveyors. Conveyors are used, for example, to move bottles, jars, cans and the like around the factory and the lubricant allows the articles to slip relative to the surface of the conveyor, so preventing them from falling over or from falling off the conveyor. In addition, in marshalling areas where the articles congregate before a subsequent process, the lubricant enables the conveyor to slip under the articles in a continuous fashion.  
       [0003] Hitherto, the most widely used conveyor lubricants have been those based on soap solutions. These solutions typically also contain agents to control water hardness and may also contain surfactants and organic solvents. Other lubricants include those based on synthetic detergents and these compositions typically also contain organic solvents. More recently, dry conveyor lubricants based on, for example, fluorinated plastics such as PTFE (polytetrafluoroethylene) have been introduced by the lubricant industry. These lubricants typically have the consistency of a creamy liquid suspension and contain a small quantity of water and some organic solvents.  
       [0004] Conventional lubricants of the soap-based or synthetic detergent-based type are, for example, disclosed in DE 4419926, WO 92/13050, WO 94/03562 and U.S. Pat. No. 3,404,090.  
       [0005] DE 4419926 discloses a detergent composition based on special surfactants. The composition comprises an amphoteric/zwitterionic surfactant, a mixed ether and an alkyl and/or alkenyloligoglycoside. The emphasis in this publication is on the properties of the surfactant.  
       [0006] WO 92/13050 discloses a conventional lubricant based upon diamine acetate salts and is said to have good anitmicrobial properties. The diamine acetate salts serve as the main lubricating component and, if desired, an alcohol can be added to the composition as a solvent Up to 20% by weight of the composition of a non-ionic surfactant can also be included in order to enhance the lubricity. Typically, the lubricant compositions to be used are prepared by diluting a concentrate in water by a factor of about 200.  
       [0007] WO 94/03562 (or equivalent publication U.S. Pat No. 5,474,692) describes a conventional synthetic-type lubricant based on fatty amines. Up to 20% of an auxiliary component, which can be an alcohol, can be used as a solubiliser. The lubricant compositions are diluted with water by a factor of preferably between 300 and 500 before use.  
       [0008] U.S. Pat. No. 3,404,090 describes a conventional water-based lubricant composition based upon the combination of two surfactants. These are an N-secondary -aliphatic-hexahydropyrimidine-2-thione and a bis(2-hydroxyethyl) aliphatic amine oxide. The surfactants are said to work synergistically and thus give increased lubrication. The concentration of each surfactant in the formulation can be as low as twenty parts per million.  
       [0009] There are a number of disadvantages associated with each of these existing lubricants. Typically, with soap-based lubricants very large volumes of water are required to provide a sufficiently dilute product, which can make formulation undesirably cumbersome. Further, most of the soap solution (up to 90%) applied to the conveyor is lost through run-off from the conveyor, thus necessitating regular re-application which is both time-consuming and wasteful. Soap-solutions are susceptible to bacterial attack, which can lead to slime formation and odour problems, and may eventually cause blockages within the conveyor system. Similarly, owing to the large volumes of water involved, water-hardness can be a problem, leading to scum formation and potential blockages. Soap-based lubricants also often lead to undesirable foaming. The foam can work its way up the sides of the articles on the conveyor, which may necessitate further cleaning, and may potentially have an adverse effect upon any labelling on the article. Synthetic detergent-based lubricants share many of the disadvantages of the traditional soap-based lubricants, although they tend to be less susceptible to bacterial attack and suffer less from problems associated with water-hardness. Nevertheless, in terms of lubricity, detergent-based lubricants generally perform less well than soap-based lubricants. Dry lubricants have the advantage of requiring much lower volumes of product than either soap- or detergent-based lubricants, but have generally not been well-received by industry. Dry lubricants generally do not have any cleaning properties: in fact, they pick up dirt easily and so the conveyors quickly become dirty and soiled with used lubricant. Conveyors treated with dry lubricants are difficult to clean, and proper cleaning will normally necessitate the use of solvent-based cleaning fluids, which from a health and safety point of view is less than ideal. Owing to their consistency, the application of dry lubricants to the conveyor can be difficult to regulate and control. In addition, dry lubricants tend to be very persistent, adhering strongly not only to the conveyor but also to the bottom and sides of the articles thereon, which at best is undesirable and may require further cleaning, and at worst may have a deleterious effect on either the articles themselves or on any associated labelling. Also dry lubricants do not distribute easily throughout the conveyor system, meaning that many concealed components (eg wear strips) do not actually become lubricated at all.  
       [0010] Another class of lubricants are those based on gels. U.S. Pat. No. 4,781,847 describes one such gel lubricant composition. The gel comprises water, 0.5 to 25 wt % polyalkylene glycol having a molecular weight of about 1000 to 15000, and an effective gelling amount of a viscosity modifier consisting of a mixture of at least two components. The gels are described as being particularly useful in the installation of electrical and telephone cable in conduit This sort of gel composition is intended to dry out gradually, but is said to leave little residue upon evaporation of the liquid phase. Even after evaporation, the gel is said to maintain substantial lubricating properties and this appears to be because of the high level of polyalkylene glycol. Being a gel, and particularly a gel which dries out leaving at least some residue, the composition described in U.S. Pat. No. 4,781,847 (and similar gel compositions) is generally unsuitable for use on conveyors. One reason is that these gel compositions do not “flow” and this is an important requirement for conveyor lubricants.  
       [0011] We have now found a way of overcoming the aforementioned problems. In particular, we have found a water-based lubricant which, surprisingly, either substantially reduces or completely overcomes the disadvantages of both water-based and dry prior art lubricants.  
       [0012] According to the present invention, there is provided water-based conveyor lubricant composition comprising water, a viscosity modifier at a concentration of from 0.01% to 5% by weight of the composition, and a humectant.  
       [0013] The invention also provides a method of lubricating a conveyor, which method comprises applying to the conveyor a composition according to the invention. We prefer to apply the composition directly, that is, without any need for dilution, although dilution of a concentrated solution of the composition prior to application can be employed if desired.  
       [0014] The use of a viscosity modifier provides a lubricant composition with the consistency of a viscous liquid, and thus leads to a dramatic reduction in the quantity of water needed when compared to prior art water-based conveyor lubricants. This reduction is both in terms of the quantity of water needed for dilution of the product (which dilution is preferably not needed at all for the present composition), and in terms of the wastage which occurs through run-off of the lubricant from the conveyor. By providing a viscosified water-based lubricant, the water is effectively kept in place on the conveyor system, thus minimising loss of product through unwanted run-off. Water itself has a viscosity of 1 mPa s at 20° C., and traditional soap solutions have similar viscosities—typically ranging from about 1 mPa s to about 5 mPa s. The viscosity of the present lubricant is much higher, being at least about 25 mPa s, and preferably greater than this. Owing to the reduced quantity of water needed, bacterial growth is kept to a minimum, which reduces build up of slime. Formulating to provide an appropriate viscosity enables good distribution of the lubricant throughout the conveyor system, and thus, in particular, provides good lubrication of concealed parts of the conveyor (such as wear strips). Unlike dry lubricants, the present lubricant composition provides good cleaning properties, and is itself easy to clean from the conveyor system. Unlike previous soap-based lubricants, the lubricant of the invention can be applied directly to the conveyor system without the need for dilution (although dilution can be used if desired), and displays substantially no foaming. Essentially, the present conveyor lubricant combines the advantages of known lubricants, whilst minimising the attendant disadvantages: thus excellent lubricity is achieved without significant water loss or soiling problems.  
       [0015] The viscosity modifier can be chosen from a wide variety of materials, so long as a suitably viscosified composition is provided. Examples of suitable viscosity modifiers include cellulose derivatives, natural gums and gels, synthetic resins and polymers and surfactants. By cellulose derivatives we mean particularly to include non-ionic ethers of cellulose with methyl chloride, propylene oxide and/or ethylene oxide. Examples include methyl cellulose (available under the trade names Benecel or Blanose from Hercules Limited of Salford, Lancashire), hydroxyethylcellulose or hydroxypropylcellulose (available under the trade names Natrosol and Klucel respectively from Hercules Limited), and a mixture of methyl cellulose, methyl hydroxyethylcellulose and methyl hydroxypropylcellulose (available under the trade name Culminal from Hercules Limited). Other examples include products marketed by Twinstar under the names Akucell, Gabrose, Tylose H, and Tylose MH (which are, respectively, carboxymethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, and methyl hydroxyethylcellulose). Suitable natural gums and gels include gum arabic, pectin, alginates (eg agar and carageenans), tragacanth, guar gum, xanthan gum, and starch or modified starch. Suitable synthetic resins include Carbopol resins (which are cross-linked acrylic polymers) available from Goodrich. Various surfactants can, if desired, be used to provide an increase in viscosity, although high concentrations of surfactant are usually necessary, and so use of a surfactant as the viscosity modifier, though possible, is generally not preferred. We prefer to use cellulose derivatives, such as, for example, hydroxyethyl cellulose or hydroxymethyl cellulose as the viscosity modifier. Cellulose derivatives have the advantage of conferring good caustic resistance upon the lubricant thus enabling good toleration of alkali, where present.  
       [0016] The choice of viscosity will be at least in part determined by the rheology required by the particular application. Cellulose derivatives, for example, have the advantage of being generally pseudo-plastic, which means that the viscosity is reduced when the rate of shear is high. For a conveyor, this means that the lubricant will stay in place on the conveyor surface (i.e. not run off or flow), but that it will thin and flow easily when a force is applied (such as, for example, from a container or article on the conveyor).  
       [0017] It is possible for the viscosity of the present lubricant to vary over a large range—from as low as about 25 mPa s up to about 100,000 mPa s. Such a range can be achieved using, for example, cellulose derivatives at a concentration (% by wt of composition) of from about 0.1% to about 2%. Typically, however, for many applications, a viscosity of from about 50 mPa s to a few thousand mPa s will normally be sufficient. Our preferred range is from about 100 to about 5000 mPa s. A preferred concentration of viscosity modifier is from 0.25 to 1.0% by weight of the composition. The viscosity modifier is not used in a quantity which would cause gelling of the composition. The exact viscosity can be varied according to the particular characteristics (such as, for example, the speed) of the conveyor to which the lubricant is applied. Thus, in a complete system involving several conveyors, for optimum performance, it may be advantageous to use several different lubricants, each with its own particular viscosity.  
       [0018] An important feature of the present composition is the presence of a humectant, it being understood that two or more compatible humectants can be used of desired. The humectant is needed to keep the lubricant moist and in a flowable condition, and to prevent it from drying out. Generally, quite a high level of humectant is required. Broadly speaking, quantities of between 5 and 80% by weight of the composition can be used, but we prefer to use between about 10 and 40% by weight, and most preferably between about 20 and 30% by weight of the composition. Suitable humectants include, but are not limited to, for example, glycerin, triethanolamine, triacetin and diacetin, with glycerin being particularly preferred. With glycerin, an amount of from 20 to 30% by weight is particularly preferred, with around 25% by weight being a typical concentration. If an insufficient quantity of humectant is used, the lubricant slowly dries out and becomes sticky, owing to a build up of residue from the viscosity modifier. Under these circumstances, the composition will not properly lubricate a conveyor and the articles moving thereon, and will lead to unwanted soiling of the equipment. Effectively, therefore, when a suitable quantity of humectant is used, it enables, together with the viscosity modifier, a sufficient quantity of water to be held in place, or “contained”, within the composition so as to achieve good lubrication. Essentially, it is the water which is being used to lubricate, and the combination of viscosity modifier and humectant enables the water to he held stably in place. The result is to achieve good lubrication without loss of water, which is the main disadvantage of prior art water-based lubricants. The use of a humectant in the above quantities in a water-based lubricant composition has not hitherto been disclosed, nor have the possible benefits of so doing been appreciated.  
       [0019] By the term humectant, we mean to include all those compounds which can retain or preserve moisture but are not in solid form in the lubricant composition. We prefer to use hygroscopic compounds, that is, those which absorb water. Particularly preferred are those humectants which can absorb or “hold” in place a significant quantity of water relative to the weight of the humectant. Compounds which can, for example, absorb at least one quarter of their own weight of water are preferred. In this respect, glycerin (which absorbs at least 50% of its own weight of water) and compounds with similar properties to glycerin are particularly advantageous.  
       [0020] The present compositions can most accurately be described as “viscous liquids”—they are not gels.  
       [0021] Whilst a conveyor lubricant consisting only of water, 0.01 to 5% by weight viscosity modifier and humectant can be used with good results, we prefer to include additional components, each of which contributes to improving the overall performance of the lubricant.  
       [0022] Thus, in a preferred aspect of the invention, the conveyor lubricant also comprises one or more surfactant and/or one or more biocide. A generalised conveyor lubricant composition, with preferred ranges indicated, is as follows:  
                                       Component   Range (% by wt)   Preferred range (% by wt)                  Water   q.s. 100   q.s. 100       Viscosity modifier   0.01-5   0.25-1.0       Humectant     5-80     10-40       Surfactant     0-1    0.1-0.5       Biocide     0-1    0.1-0.5                  
 
       [0023] We prefer to include a surfactant in the conveyor lubricant in order to assist in wetting the surface of the conveyor when the lubricant is applied. Any suitable surfactant can be used which provides good wetting properties without adversely affecting the properties of the conveyor lubricant. For example, polyethylene glycol 400 monolaurate is a particularly preferred surfactant, although many other similar compounds, as will be clear to the skilled man, may be used. Depending upon the type of humectant and/or biocide used, we have found that it is not always necessary to include a specific surfactant to improve wetting, since some suitable humectants and biocides (such as, for example, glycerin and tertiary alkyl amines) will in themselves provide sufficient surfactant properties to enable good wetting of the conveyor surface.  
       [0024] A biocidal agent is preferably included in the lubricant composition in order to kill bacteria and thus ensure little or no build-up of mould or slime. It is possible to use any suitable biocide, provided the agent exhibits no adverse effects upon the properties of the lubricant composition. Suitable biocides include, for example, tertiary alkyl amines, such as bis(3-aminopropyl) dodecylamine, and triclosan with tertiary alkyl amines being particularly preferred.  
       [0025] Suitably, the conveyor lubricant composition is provided with a pH of about 7, although this is not critical. If, for example, an amine-based biocide (such as a tertiary alkyl amine) is employed the consequent increase in alkalinity of the lubricant is preferably neutralised by including, for example, a corresponding amount of citric acid (or similar compound) in order to restore the pH balance.  
       [0026] The conveyor lubricant composition is preferably formulated by first mixing the viscosity modifier with the water. Suitably, warm water is employed and the solution containing viscosity modifier only is preferably stirred for about half-an-hour, or until the full required viscosity (and stability) is achieved. Thereafter, humectant and any further ingredients are added to the composition as desired, by simple mixing and stirring.  
       [0027] The present conveyor lubricant has the advantage of being able to be directly applied to the conveyor at a desired point (or at several different points) in the conveyor system, without requiring any prior dilution of the lubricant, as is necessary with soap-based lubricants. Dilution of a concentrate can, however, be used if desired. This can help promote overall efficiency and economy within the factory. It is possible to apply the lubricant to the conveyor at the desired point by a variety of methods, although we prefer to apply the lubricant using a brush system. Alternatively, the lubricant can be sprayed on to the conveyor if desired, although this is not generally preferred, and may, in fact prove difficult if not impossible with lubricants of high viscosity. Generally, dosing intervals of at least one hour or more are typical for the present lubricants. There is substantially no drying out of the lubricant during these periods.  
       [0028] Typically, the conveyors we have in mind for which the present lubricant is particularly suitable are chain and slat type conveyors (either plastic or metal, for example) of the kind usually found in the bottling and canning industries. However, there will be many other sorts of conveyors to which the lubricant composition of the present invention can be applied with very satisfactory results. The present lubricant is also of utility in conveyor systems moving a wide range of articles other than simply bottles and cans including, for example, crates. It is essential that the components of the present lubricant are compatible with the articles to be moved along the conveyor. In this respect, soap solutions (particularly at high concentrations) have the disadvantage of being detrimental to bottles made from PET. We expect the present lubricant composition to have the advantage of being compatible with a very wide range of article materials, including PET.  
       [0029] The following Examples illustrate compositions according to the invention. 
     
    
    
     EXAMPLE 1 
     [0030]                                               % wt/wt                                                    Water   74           Hydroxyethylcellulose 1     0.5           Glycerin 2     25           PEG 400 monolaurate 3     0.25           Bis(3-aminopropyl)dodecylamine 4     0.25                                                                        
     [0031] Hydroxyethylcellulose (5 g) was mixed with constant stirring to 740 g of warm water (at approximately 40° C.) for 30 minutes. Glycerin (250 g), PEG 400 monolaurate (2.5 g) and biocide (2.5 g) were then added and the mixture stirred to provide a homogenous solution. The viscosity was 1000 mPa s.  
     [0032] Examples 2-5 were made in the same way as Example 1.  
     EXAMPLE 2  
     [0033] This shows the simplest kind of formulation.  
                                                       % wt/wt                                                    Water   89.5           Hydroxyethylcellulose 1     0.5           Glycerin 2     10.0                                  
 
     EXAMPLE 3  
     [0034] This shows a general purpose conveyor lubricant.  
                                                       % wt/wt                                                    Water   74.55           Hydroxyethylcellulose 1     0.25           Glycerin 2     25.0           Bis(3-aminopropyl)dodecylamine 5     0.10           PEG 400 monolaurate 3     0.10                                              
 
     EXAMPLE 4  
     [0035] This illustrates a ‘dry-line’ formulation for use in areas where dripping etc. of lubricant from the conveyor needs to be minimal or completely eliminated.  
                                                       % wt/wt                                                    Water   59.79           Hydroxyethylcellulose 6     0.20           Glycerin 2     40.00           Trichlosan   0.01                                              
 
     EXAMPLE 5  
     [0036] This illustrates a lubricant suitable for use with a heavily loaded conveyor.  
                                                       % wt/wt                                                    Water   59.3           Hydroxyethylcellulose 1     0.5           Glycerin 2     40.0           Bis(3-aminopropyl)dodecylamine 5     0.2                                  
 
     [0037] The above formulations were found to provide excellent lubrication when applied to either a slat or chain type conveyor. Good distribution of the lubricant throughout the conveyor was observed, and no significant run-off of lubricant from the conveyor surfaces was seen.