GB2328950A - Nailable compounds - Google Patents

Abstract

A synthetic gap filling composition capable of bonding to a wide variety of adherends, which can be nailed without cracking and which retains a firm grip on the adhered surface in use, is used especially as an adhesive for repair, restoration or reshaping of animal hoof keratin, or for adhering a horseshoe to the hoof before nailing. The composition comprises an acrylic functional composition containing eg acrylic monomers such as methyl methacrylate and methacrylic acid, and includes 20-65 % by weight of of an acrylic or methacrylic functional acrylonitrile butadiene oligomer.

Description

NAILABLE COMPOUNDS This invention is concerned with adhesives, repair compounds and fillers hereinafter called repair adhesives, which have good adhesion to animal keratin as well as a wide variety of other adherends. These repair adhesives are capable of filling large gaps, permit the driving of mechanical fasteners through them without cracking and maintain a tight grip on the mechanical fasteners even under a repeated impact or fatigue environment.

Applications for materials with this unusual and difficult combination of properties to satisfy are varied but this invention is concerned solely with the repair, restoration or reshaping of animal hoof keratin and the bonding of the keratin to other adherends, especially steel, aluminium, nylon, polyurethane and the like.

Many horses are shod every six to eight weeks to allow them to carry out their allotted function without excessive wear to their hooves. This is usually done with metal shoes which are mechanically fixed by nailing through the keratin based hoof wall. Depending on the condition ofthe hoof and the level of care taken this can result in physical damage to the hoof. When this happens it results in loss of use and frequently pain and lameness.

The remedies are to let the damage grow out naturally which may take weeks to months; to reshoe and risk further damage, pain and ingress of disease; or to repair it.

Likewise there are many other animals, including cattle, where repair and protection is necessary for their comfort and utility after their hooves have suffered damage for whatever reason.

Animals do not care to stand still for long, and so a repair adhesive compound meeting the criteria above and which is easy to use under a wide range of ambient conditions and enables simple and effective repair of the damage and/or attachment of protective materials, once applied, in around 1 - 15 minutes, preferably 3 - 8 minutes is required.

The product must gel and become firm enough and sufficiently bonded for the animal to support its weight on the repaired hoof without damage to the repair and to be nailed as if undamaged hoof without cracking or disbonding, and to be cut, shaped and rasped to obtain required contours, all within a few minutes after application. Not only must the hardened repair be capable of being nailed without cracking or splitting, but it must also retain the grip on any nails which have been hammered through it.

The functions ofthe repair adhesive ofthis invention are to make good cracked, holed and missing keratin in an animal's hoof, to bond repair and protective material to hoof keratin and to bond wearing surfaces under the general description of shoes to animal keratin regardless of whether mechanical fasteners are used as well or not. The repair adhesives may also be used for altering and improving the shape of an animal's foot where deformed or deficient in any way.

It is the purpose of this invention to provide such repair adhesives for use with keratin which are superior to any that have been provided hitherto and as such represent a major improvement over the state of the art.

There are many types ofchemical resin capable of filing and setting well in large gaps and adhering to a wide range of adherends. These include principally the well known and highly developed epoxy, polyurethane, unsaturated polyester and acrylic based materials.

However, until now none of them fully meet the requirements specified above.

The epoxy resins cure by addition reaction and adhere well to many surfaces, but do not readily lend themselves to the rapid cure rates required in these applications unless they contain large amounts of polythiol accelerators and curing agents. When formulated in this way they possess a very unpleasant smell, get very hot when curing even in small bulk and most importantly are hard and not impact resistant. It is almost impossible to drive a horseshoe nail through such compositions and they usually crack when attempts are made to do so, making them quite unsuitable for the intended use. Such compositions have been suggested as hoof repair fillers in such a way that the fixing nails are applied first and the filler then moulded around them. Clearly a very difficult and uneconomic approach and one that would not allow renailing when required. In addition to these disadvantages the products have only moderate adhesion to keratin.

Polyurethanes may be compounded to polymerise quickly and can be designed to be suitable for nailing. But they suffer from only moderate adhesion to keratin and rather low resistance to aqueous exposure which tends to be a feature of the animal foot environment. In addition they also suffer from a storage problem in which the isocyanate containing component is very susceptible to reaction with water and water vapour and may seal itself into the container either before use or between repeat uses by reaction with water from any source. As a result of these deficiencies polyurethanes are little used for this type of application.

Unsaturated polyester resins are widely formulated as gap and dent fillers for automotive repair but are quite unsuitable for current requirements. Whilst they can certainly solidify rapidly their adhesion to metals and keratin is limited and their resistance to impact loading and nailing very poor.

Acrylic adhesives are well known and used in many chemical versions and forms. These range from the one part anaerobic thread locking adhesives and ionically curing 'superglues' to the toughened two part radical curing products used either as premixed adhesives or by the separate application of one component to one adherend and the second to the other.

The anaerobic acrylics by definition cure only in the absence of oxygen and so polymerise in between adherends where oxygen can be excluded. It is for this reason that they are so useful as thread locking products. Whereas for applications requiring the filling of larger gaps or porous materials such adhesives are of no value unless oxygen can be excluded or they will not polymerise. In most such applications filling large or irregular gaps oxygen cannot be excluded and anaerobic adhesives cannot be used for them.

In much the same way the acrylic superglues, which have their curing reaction initiated by weak ionic materials, such as water, on the adherend surfaces and in which reaction soon terminates in the absence of more ionic initiation species, cannot bond porous materials well or be used to fill substantial gaps between adherends.

However, acrylic radical cured two pack adhesives form the best prospective class for this type of application. They adhere well to keratin, they are good in resistance to water, they cure quickly and they can be made to be very tough without being too hard to nail or cracking. Products ofthis type have been used for the repair of holes in horse hoof keratin and have been practically very superior to those employing epoxy, polyurethane or polyester resins. Such materials consist essentially oftwo parts. The major volume component consists usually of acrylic monomers, cure accelerators and functional tougheners. They do not normally contain polymeric materials as these cause both skinning during the actual application of the product, and increase the viscosity greatly making them difficult to mix and apply in a simple manner. The second part of such compositions is essentially the free radical supplying catalyst and a carrier for it. The carrier largely acts as a plasticiser to the final cured product although a limited amount of reaction with other species present can occur depending on the chemical nature of the carrier. Other fillers and plasticisers may be used to obtain desired end properties.

Typical of compositions ofthe type used up till now are: ACRYLIC COMPONENTS Single acrylic ester monomers or blends of several such monomers either mono or polyinctional, styrene or substituted styrene and the like.

An unsaturated acid either purely organic or partially inorganic or both.

Acrylic fUnctional toughening entities based on reactive polybutadiene oligomers.

Fillers.

Other flow control agents.

Curing accelerators - usually ofthe nndialkyl aromatic amine type.

* Stabilisers CATALYST COMPONENT Liquid epoxy functional or other plasticisers.

Fillers.

Other flow control agents One or more peroxides.

Either component may contain other solids, compounds, waxes and additional plasticisers, elastomers or liquids which are not in themselves substantially reactive with that component on storage.

The unsaturated acrylic component can contain various combinations of the many methacrylic, acrylic and styrenic functional monomers or polyfunctional materials, for example, but not limited to furfilryl methacrylate, 2 hydroxy propyl methacrylate, trimethylene glycol dimethacrylate, ethylene glycol dimethacrylate, cyclohexyl methacrylate, 2-ethyl hexyl methacrylate, methacrylic functional phosphate esters, bisphenol A diepoxy dimethacrylate and styrene.

The toughening oligomers are made by the reaction of an acrylic or methacrylic epoxy containing compound such as glycidyl methacrylate with a carboxy terminated butadiene compound with a carboxyl content of between 0.3 and 0.6 gm mols per kg and a functionality of around 2.0. These compounds may also have the hydroxyl group generated by this reaction removed by reaction with an isocyanate if required.

These compositions have been the state of the art and have fulfilled some of the requirement for hoof repair applications as well as some of those for other end uses where mechanical fasteners are driven through them. However, when a nail is removed from these cured filler adhesives the hole generated stays open and does not contract indicating permanent deformation and less than desired resilience. Nail removal can be very easy because one small blow from the point reduces the friction load and the nail falls out (Figure 1). It can be easily seen that during the harsh environment experienced by a nailed repaired hoof the nails may easily become loose and lose their load carrying capacity and effectiveness. At best this should result in nail replacement but can also result in damage to the hoof, damage to or loss ofthe repair, the shoes becoming detached and serious injury.

We have now surprisingly found that the replacement of the carboxylated butadiene oligomer intermediate with one based on a carboxylated acrylonitrile butadiene intermediate results in a product with excellent resilience as well as adhesion and toughness. As such when nailed and the nail is removed, which is with difficulty, the nail hole largely closes within a few seconds to minutes indicating that the cured composition has not lost elastic memory and is capable of keeping a tight grip on the nail or other mechanical fastener as the case may be.

A further indication of the advantage obtained by this invention is apparent upon visual examination of a wide range of compositions containing either the polybutadiene oligomer or the polybutadiene acrylonitrile oligomer. In every case the penetration of a sharp implement such as a nail or the point of a Shore D scale hardness tester gives a clean sided clear hole with the polybutadiene compositions whereas with the polybutadiene acrylonitrile compositions an irregular smaller hole is seen surrounded by the characteristic 'stress whitening' oftough materials, the whitening being caused by multiple small scale cavitation and cracking demonstrating the absorption of large amounts of energy as demanded by the applications for this invention.

The invention is demonstrated by the following examples: A two part acrylic composition (A) was prepared with a methacrylic functional butadiene oligomer with an initial carboxyl content of 0.45 gm mols carboxyl per kilogram. The methacrylic flinctionality was introduced by reaction ofthe carboxyl groups with glycidyl methacrylate. (BGMA) A two part acrylic composition of this invention (B) was made by using a glycidyl methacrylate reacted carboxyl acrylonitrile butadiene oligomer with an initial carboxy content of 0.50 gm mols per kilogram and a bound acrylonitrile content of 21%.

(ABGMA) A two part acrylic composition of this invention (C) was made identically to example (B) but using other monomer ingredients and accelerator.

EXAMPLE 1 (A) (B) (C) ACRYLIC COMPONENTS (all parts by weight) Methyl methacrylate 55.0 55.0 Methacrylic acid 5.0 5.0 5.0 BOMA 40.0 - - ABGMA - 40.0 40.0 Tetrahydroflirturyl methacrylate - - 55.0 mineral filler 25.0 25.0 25.0 fumed silica 7.0 7.0 7.0 nndimethylptoluidine 1.5 1.5 n-phenyl diethanolamine - - 1.0 The catalyst part of the composition was the same for all three examples: CATALYST COMPONENT Liquid epoxy fUnctional plasticiser 23 Chalk 19 Fumed silica 1 50% dibenzoyl peroxide in phthalate plasticiser 4 (all parts by weight) (A), (B) and (C) were all mixed with the catalyst in the ratio of three parts acrylic composition to one part by weight catalyst.

All three gave a soft buttery texture that was extremely easy to place into large gaps and to smooth over readily. All had set solid within six minutes at 210C. After 10 minutes a lcm thick casting of each was nailed with a typical horseshoe nail. All nailed easily.

After 24 hours the protruding tips of the nails were tapped gently with the casting supported on a frame. In the case of Example A the nail was easily removed and the hole produced scarcely closed at all (Fig. 1). With Examples B and C the nails were difficult to remove eventually with pliers and the remaining holes quickly closed within a few minutes almost to the point of being unable to see through them (Fig 2).

It was found that in order to obtain these excellent nailing properties the level of ABGMA in the liquid contents of the acrylic component should be between 20 and 65% by weight and preferably between 30 and 55% by weight.

EXAMPLE 2 A composition of Example B was used to bond an aluminium horseshoe to the cleaned but uneven keratin bottom layer of a horse hoof. The shoe was nailed through the cured adhesive to act as a 'peel stopper' and no cracking or disbonding occurred. After 3 weeks of normal active use the shoe remained bonded, the nail was tight and no cracking appeared to occur. Shoes made of other materials such as steel or polyurethane have been found to behave similarly.

EXAMPLE 3 A composition of Example B was used to bond a steel horseshoe and an aluminium horseshoe together with an overlap at one end of each shoe. The glue line thickness was controlled at 3mm and the combined bonded joint suspended from the unbonded end of the aluminium shoe thus placing it under load. The assembly was allowed to age exposed to a normal equable climate with a temperature range of from -7 C to +3 10C and an average annual rainfall of 40 mm per year. After 32 months the joint remained unbroken despite the steel surface having extensively corroded outside the bonded area.

This experiment shows the excellent water resistance of the composition to debonding even on unstable surfaces.

EXAMPLE 4 Two horses each having an approximately 2cm square 1cm deep hole in a front hoof were selected for a practical repair test. The surfaces of the holes were treated by removing damaged keratin with a hoof knife and the exposed healthy keratin wiped with a clean swab soaked in acetone. One hole was repaired with composition (A) and the other with composition (B). Five minutes after the fillers had set they were rasped with a ffle to give conformation to the hoof contour and then nailed through as part of the process of fitting new steel shoes. Neither filler composition cracked or was particularly difficult to nail.

After one day the horses were returned to their normal routine in a riding school and the repairs were examined weekly. After 3 weeks composition (A) was showing signs of hole enlargement. After 6 weeks these holes had grown. At this point the hoof was ready for trimming and the fitting of new shoes. The nail clenches were removed and the shoes detached easily showing significantly enlarged holes. One day later the holes appeared unaltered. Attempts to renail through the original composition (A) at a different point to the original nail holes proved difficult and resulted in bending of the nails.

By contrast in the case of composition (B) the old shoe was more difficult to remove after the clenches had gone because the nail through the repair was still tightly held. 24 hours after removal the hole had closed up showing the resilience of this repair. In the same way nailing through composition (B) was relatively easy without damaging the nails.

It can be seen from this comparison that composition (B) is generally more suitable for equine hoof repair than composition (A). Furthermore it can be readily imagined that where more extensive repair is concerned and several nails are passed through composition (A) there is a real risk of the shoe becoming loose on use and ultimately of shoe detachment. Composition (B) is clearly superior in this respect and is the material most likely to meet all the needs of extensive equine hoof repair.

It will be obvious to those versed in the art that the levels of fillers, ratio and type of accelerators and catalysts may be changed as required to alter the gel and cure speed and physical texture of the uncured and cured systems. The key inventive step in this type of product is the use of the acrylic functional acrylonitrile butadiene oligomer.

Claims (11)

What we claim is:

1) Adhesives, repair compounds and fillers for animal hoof keratin based on an acrylic functional composition in which the acrylic functional species present includes 20% to 65% by weight of an acrylic or methacrylic functional acrylonitrile butadiene oligomer.

2) As claim (1) where the acrylic or methacrylic functional acrylonitrile butadiene oligomer represents from 30 - 55% ofthe acrylic functional species present by weight.

3) A composition according to claims (1) and (2) which is cured and bonded to at least one adherend of animal keratin.

4) A product according to claims (1) to (3) which is used for the repair of damaged animal keratin hoof.

5) A product according to claims (1) - (3) which is bonded to animal keratin and used for the purpose of remedial hoof modification.

6) A product according to claims (1) - (3) which is used for bonding attachments to animal keratin.

7) A product according to claims (1) - (3) which is used for bonding horseshoes and the like to hoof keratin.

8) A cured and bonded composition according to claims (1) - (3) which does not crack or disbond when a horseshoe nail or other veterinary mechanical fastener is driven through it.

9) A cured composition according to claims (1) to (3) which maintains a strong grip on horseshoe nails or other veterinary mechanical fasteners as seen by the closure of the holes formed by the initial application of such fasteners after they have been removed.

10) The cured product according to any of the preceding claims.

11) A process for repairing, reshaping or protecting animal keratin with products according to any of the preceding claims.