WO2000057070A1

WO2000057070A1 - Threaded articles having cured deformable coating thereon

Info

Publication number: WO2000057070A1
Application number: PCT/US2000/007494
Authority: WO
Inventors: Frederick F. Newberth, Iii; Dennis T. Callanan
Original assignee: Loctite Corporation
Priority date: 1999-03-22
Filing date: 2000-03-22
Publication date: 2000-09-28
Also published as: TW449648B; AR023110A1; AU3906500A

Abstract

An unassembled threaded article (10) including a thread engaging portion with thread grooves (12) and a fully cured solid deformable material (14) coated thereon. The cured deformable material is sufficiently flexible and deformable to conform to the surface of a corresponding mating threaded part and to sealingly engage the mated parts to provide a seal or locking function therebetween.

Description

THREADED ARTICLES HAVING CURED DEFORMABLE COATING THEREON

FIELD OF THE INVENTION

The present invention generally relates to the area of articles having preapplied sealants thereon. More particularly, the present invention relates to threaded articles having a coating or layer of cured material which is sufficiently deformable to allow mating with a corresponding threaded part.

BRTEF DESCRIPTION OF RELATED TECHNOLOGY

The use of liquid polymerizable or curable substances for the purpose of sealing and locking interfitting parts is well known in the art. Early threadlocking compositions were applied in liquid form shortly before or at the time of assembly of the interfitting parts. The compositions were applied wet and cured only after the interlocking of the mated parts. Such locking compositions, however, were not suitable for many applications in industries with high rates of assembly and mass production, such as the automotive industry.

As a result pre-applied sealant and locking coatings were developed for use in these industries. Indeed, pre-applied sealant coatings are now preferred in such industries due to their many advantages. Pre-applied sealant or locking coatings which were initially developed were deposited on threaded fasteners as dry to the touch coatings in which uncured polymerizable fluids were encapsulated or skinned over within a dry coating on the fastener. Assembly of the fasteners with a corresponding threaded part, e.g. a nut, caused fracture of the microcapsule coating or skin and exposure of the underlying polymerizable fluid to curing conditions, e.g. anaerobic cure. For instance, U.S. Patent No. 4,325,985 describes a method in which a polymerizable fluid material is deposited on a threaded part, and a separate fluid film-forming cover coat is applied thereover immediately after, forming a thin, solid, dry, non-tacky film by brief exposure to radiation, such as ultra-violet radiation. The radiation-curable film-forming cover coat is cured through its depth, leaving the polymerizable locking material still fluid for subsequent cure upon mating of threaded parts. The radiation-curable film is a protective skin designed to be dry and non-tacky.

U.S. Patent No. 4,632,944, discloses a dual curing composition for use on threadlocking articles. The first curing mechanism is initiated by radiation such as ultraviolet radiation light.

An opacifier, such as a powder, is dispersed therein rendering the polymerizable solution opaque to the radiation beyond the surface layer. A dry tack free crust is therefore formed on the surface. The second polymerization mechanism is thereafter initiated on the remaining polymerizable fluid once the two engineering parts are assembled together.

Pre-applied fasteners, i.e. fasteners having a sealant or locking composition on their threads, are normally shipped in bulk. They are often loose in the shipping container and in direct contact with each other. Pre-applied fasteners which rely on a protective skin over a fluid sublayer have a potential for rupture of the skin in the shipping containers or storage, with subsequent leakage of the polymerizable composition is common, resulting in unusable parts.

Fasteners may adhere to each other due to this leakage, or be difficult to handle due to uncured liquid contaminating their exterior. In such cases, the fastener product is rendered unusable. Further, the skin enclosing the polymerizable fluid is usually not an integral part of the final polymerized composition. The adhesive force of the resultant bond may not be as great as if it were the polymerizable fluid alone.

Other alternatives to the skinned over uncured liquid versions of pre-applied threadlocking products have been developed. Fully cured latex coatings are a known alternative for sealing purposes. Cured latex coatings do not suffer from potential rupture of polymerizable liquid, but are expensive to produce because they require oven curing at relatively high temperatures for 45 minutes or longer. The most common method used in the industry today to dry latex coatings is to employ the use of a gas fired oven. Typically the forced hot air is recirculated within the confines of the oven's inner housing. Temperatures are typically maintained at 155°F (68°C) +/- 10°F). This method of drying is costly and its relative inefficiency is increased by heat loss at the entrance and exit of the conveyor belt openings which run through the housings of conventional industrial ovens. Care must also be exercised so that the temperature does not reach the point of creating steam which causes creators on the surface of the coating. When creators are present, the integrity of the adhesion is compromised and the coating will chip and peel off the threaded fastener, as well as creating an undesirable appearance. It becomes necessary to control the ramp-up speed and allow the fastener to uniformly heat through to avoid removing the water too rapidly. Moreover, latex coatings often become brittle and flake or peal during storage, particularly if exposed to uncontrolled environmental conditions. Additionally, dried latex coatings do not possess the capability to be further physically tailored or altered to the particular needs of threaded applications.

It is apparent that a need exists for an unassembled threaded article having a preapplied coating which does not suffer from the aforementioned drawbacks.

SUMMARY OF THE INVENTION

The present invention provides such a threaded article, as well as a method of manufacturing the threaded article. Also provided is a method of sealing using the threaded article of the present invention.

The present invention is directed to unassembled, i.e. uncoupled, threaded articles such as nuts, bolts, screws, pipes and the like, having a cured deformable sealant or locking material adheringly coating at least a portion of the threads. The sealant composition is applied in the uncured form to the threads and desirably in the thread grooves of the article and subjected to curing conditions, i.e. desirably photoirradiation, such as ultraviolet (UN) radiation, for the purpose of fully curing the composition into a solid deformable thread-adherent coating on an unassembled threaded unit. The deformability of the cured sealant allows for sealing engagement of the coated threads with a corresponding coated or uncoated threaded article for example, a nut and bolt assembly. During assembly of the mating threads of the parts, the sealant deforms and compresses to allow for engagement of the threads of the mating part without substantial loss of the physical unity of the sealant, such that it remains in place and performs its sealing function. The sealant remains in the grooves of the male and female coupled assembly and provides a fluid tight seal due to the deformability, flexibility and adherent characteristics of the cured layer. Mating of the corresponding threaded parts is thus possible while retaining sealant properties. Of course, coating of the thread grooves of each corresponding mating part, e.g. both a nut and bolt, is also contemplated.

The present invention also relates to a method of manufacturing an unassembled threaded article having a cured deformable solid sealant composition coating at least a portion of the thread groove of said article.

The sealants of the present invention may be fully cured on the threaded article prior to mating with another threaded part. This is a major departure from the prior art, where compositions were only fully cured after two threaded parts were assembled together. The deformability of the sealant permits mating with a corresponding threaded part. Because the sealant is cured, the articles can be stored next to each other, for example, in a large bin and shipped for use without fear of rupture of uncured sealant, or sticking of adjacent parts together. Moreover, due to the use of curing conditions such as photoirradiation, the parts can be quickly and efficiently cured without expensive heat curing ovens, thereby substantially lowering the energy consumed, the time required to make the article and the overall cost of production.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a unassembled threaded male part in the form of a fastener including the cured deformable sealant composition in the thread grooves. Figure 2 is a cross section of the fastener in Figure 1 showing the cured sealant composition in the thread grooves.

Figure 3 is a perspective view of a unassembled threaded female part in the form of a nut.

Figure 4 is a cross section of Figure 4 showing a cured deformable sealant in the thread grooves.

DETAILED DESCRIPTION OF THE INVENTION Numerous sealants may be used and tailored to the means of the particular threaded part or application. The deformability and elastomeric flexibility of the cured sealants as measured by specific hardness ranges allows for tailoring of a threaded article to meet specific needs.

The cured deformable solid sealant compositions useful in the present invention include elastomeric deformable materials such as silicone, urethane, silicone-acrylate, urethane-acrylate, co-polymers and combinations thereof. The cured composition should cover a sufficient portion of the thread grooves of the threaded article to permit a seal to be formed when the article is mated. Generally, a bead of the composition is applied around the thread grooves and cured through exposure to photoirradiation. While any suitable curing mechanism may be employed, UN radiation is preferred for practical considerations and to obtain the manufacturing efficiencies and cost effectiveness this curing mechanism affords.

One example of a UN curable silicone composition useful in the present invention is described in U.S. Patent No. 5,300,608 (Chu), the disclosure of which is expressly incorporated herein by reference. The photocurable silicone composition is described therein include to alkoxy-terminated organopolysiloxanes represented by the formula: ( ³)a R1 (R³)a (R5O)₃-(a₊b)— Si— O- -Si-O- -S i (OR5)₃._(a+b)

(R4)b R2 (R⁴)t

wherein R¹, R², R³ and R⁴ may be identical or different and are monovalent hydrocarbon radicals having up to 10 carbon atoms (C ₀), or halo or cyano substituted hydrocarbon radicals; R³ may also be a monovalent heterohydrocarbon radical having up to 10 carbon atoms (C,_.10), wherein the heteroatoms are selected from the group consisting of haloatoms, O, N; R⁵ is alkyl (C_rC₁₀), preferably methyl, ethyl or isopropyl; R⁵ may also be a CH₂CH₂OCH₃; N is an integer; a is 0, 1 or 2; b is 0, 1 or 2; and a+b is 0, 1 or 2. In a particularly desirable embodiment, R³ is a methacryloxypropyl group, R⁴ and R⁵ are methyl groups, and R¹ and R² are methyl groups. The alkoxy-terminated organopolysiloxanes can be prepared as described in the '608 patent.

In general, the polymerized coating or layer on the threaded article is the reaction product of a composition which includes about 35% to about 99.5% and desirably about 40% to about 80% of a curable polymer which is flexible and deformable when cured; and about 0.5 to about 10% of a suitable catalyst or free-radical initiator. Optionally up to about 65% of one or more fillers and other additives may be included.

In one desirable embodiment, the deformable cured material is a sealant which includes one or more polymerized polyorganosiloxane polymers and a photoinitiator. For example useful polymerizable polyorganosiloxanes include, without limitation, (meth)acryloxyalkyl dimethoxysiloxy-terminated poly(dimethylsiloxane) polymers, such as acryloxymethyl dimethoxysiloxy-terminated poly (dimethylsiloxane), and methacryloxypropyl dimethoxysiloxy- terminated poly (dimethylsiloxane) and combinations thereof. Others made in accordance with the aforementioned formula of the '605 patent are contemplated. The above-mentioned dual cuing polymers may be fully cured using irradiation, moisture cure, or a combination of both. For purposes of efficiency irradiation such as by uv and/or visible light may be most desirable.

Useful photoinitiators include benzophenone and substituted benzophenones, acetophenone and substituted acetophenones, benzoin and its alkyl esters, xanthone and substituted xanthones. Desirable photoinitiators include diethoxy-acetophenones, benzoin methyl ether, diethoxyxanthone, chloro-thio-xanthane, azo-bisisobutyronitrile and combinations thereof. Visible light initiators include comphoroquinone peroxyester initiators and a-fluorene carboxylic acid peroxyesters. Particularly desirable photoinitiators include 2-hydroxy-2-methyl-

1-phenyl-propan-l-one, available as Darocur 1173 (EM Industries, Inc.) and 2-benzyl-2- (dimethylamino)-l-[4-morpholinyl) phenyl]-l-butanone, available as Irgacure 369 (Ciba-Giegy). Photoinitiators are used in amounts sufficient to effectuate cure, which is generally in amounts of about 0.5% to about 10% by weight.

Useful moisture cure catalysts include metal salts typically selected from titanium, tin, zirconium and combinations thereof. For example, tetraisopropoxytitanate and tetrabutoxytitanate are particularly useful, although numerous others, such as those disclosed in U.S. Patent No. 4,111,890, may also be employed and are herein incorporated by reference. Moisture catalysts are used in amounts sufficient to effectuate cure, which is generally in the amounts of about 0.1% to about 10% by weight.

In instances where peroxy free radical initiators are used, such compounds may include hydroperoxides, such as cumene hydroperoxide, paramenthane hydroperoxide, tertiary butyl hydroperoxide; and peresters which hydrolyze to peroxides, such as tertiary butyl perbenzoate, and the like. Peroxy compounds are typically present in amounts of about 0.5% to about 10% by weight.

In another desirable embodiment, the deformable cured material includes a polyurethane polymer. Polyurethane polymers useful include urethane-acrylates such as aliphatic oligomers which are sufficiently deformable when cured to achieve the purposes of the invention. These polymers may be used in amounts of about 35% to about 95% by weight, and desirably about 40%) to about 60% by weight. They may be formulated to cure by more than one mechanism, if desired, such as by photoirradiation and room temperature cure.

Other polymers useful include olefinic elastomer compounds which when cured meet the requisite deformability and sealing requirements. For example, styrene-butadiene copolymers, butyl rubber, polyisoprene rubber and polysulfide rubber may be used. Thermoplastic polymers which are or can be rendered sufficiently deformable to be used on threaded parts are also contemplated. Polymerizable components which are extremely hard and/or brittle are generally not useful in the present invention, because they would tend to crumble when assembled and would be less able to create an effective seal. Additionally, assembly of the parts would be very difficult and impractical, since their inability to deform and conform as the mating threads are coupled would necessitate breaking apart the cured resin and destroying the layer on the threads.

The cured polymers useful in the present invention may be partially sliced or cut when the threaded parts carrying them are mated due to the frictional forces exerted. However, the polymers are intended to be sufficiently tough and flexible to prevent crumbling and to retain sufficient cohesive structure and adherence to the threaded part to provide a sealing function between mating threads, and in some instances a concomittant locking function. The sealing function is desirably one which resists the flow of a gas or fluid such that the inventive articles having the cured materials applied thereon may be used in applications such as pipe fittings and other mechanical applications involving the coupling of threaded parts where liquid or gas may otherwise escape.

The polymerizable polymer compositions used to form the cured material on the threaded articles of this invention may include a wide variety of additional agents such as cure accelerators, i.e. secondary and tertiary organic amines, organometallic complexes, as well as sulfimides which are well known in the art. These are typically used in amounts of about 0.1 to about 5% by weight.

Other additives include thickeners, plasticizers, dyes, lubricating agents, diluents, odor masking agents, chelators, inhibitors, adhesion promoters, elastomers and the like.

Active diluents which are particularly desirable include such compounds as isobornyl acrylate, ethoxyethyl acrylate, N,N-dimethyl-acrylamide, tetrahydrofurfuryl acrylate and the like.

Silane adhesion promoters are also useful and include such compounds as hexamethyl disilizane, glycidoxypropyltrimethoxysilane, aminopropyl-trimethoxysilane, methacryloxyproplytrimethoxyslane and others known to those skilled in the art.

Application of the polymerizable compositions to the threaded parts may be accomplished in a variety of ways. Most desirably, application is by automated production methods. Dipping, spraying, beading or other applicating methods are useful. A sufficient portion of the threads of the threaded article is generally coated such that sealing is accomplished when the part is mated. The amount applied to the threads will depend on the geometry, size and intended application of the threaded article.

In one desirable embodiment of the invention, a uv curable silicone-acrylate compositions is employed which when fully cured on the threaded part is sufficiently deformable to sealingly engage a corresponding mating threaded part. The parts are mated without destroying the overall cohesiveness and structural integrity of the polymer in a manner such that it is able to perform its sealing function. For example, pipe fittings joined in this manner showed effective sealing against air pressure at 100-120 psi. This composition provides the capability of high speed production of threaded nuts and bolts and other threaded members, which can be lined up on an assembly line or conveyor belt and rapidly exposed to UN light. In the case of silicone-acrylate polymerizable compounds, any portions which inadvertently fail to cure during UN exposure will later cure at room temperature by atmospheric moisture. Full cure is desirably intended prior to assembly of the threaded parts.

In some embodiments, the cured deformable materials of the present invention have a Shore A hardness range of about 25 to about 35 and an elongation of about 50% to about 300%.

In other embodiments, Shore D-2 hardness in the range of 25 to 35 are also useful. The hardness range will be a function of the polymerizable material chosen.

The threaded articles of the present invention may have a variety of metal and/or plastic surfaces. For example, stainless steel, chromium, bronze, nickel, titanium, aluminum, zinc and the like are all contemplated. Phosphate and oil finishes, as well as various anodized surfaces are also contemplated. It is generally unnecessary to degrease or clean the fasteners before coating and curing the deformable sealant thereon, although it is common to do so for many applications.

Turning to the drawings, Figure 1 shows a perspective view of a male threaded article 10 in the form of as fastener having external threads 12 on its surface. A portion of the threads and thread groove are coated or filled with photocured deformable sealant composition 14. Figure 2 shows a cross section of the fastener along its longitudinal axis, again showing the sealant 14 in the groove 12.

Figure 3 shows a female threaded article 11 which also includes sealant 14 in the thread grooves. Figure 4 is a cross section of Figure 3.

The male threaded fastener 10 of Figure 1 is coupled with the corresponding female threaded part 11 to form a fastener assembly. The sealant composition is shown on both of the coupled parts, but in practice is likely to be on only one of the parts. Generally, for ease of application, the sealant is applied to the male member.

Threaded pipe joints is another particularly desirable application. Regardless of the type of threaded article, sufficient coverage of the threads ensures adequate sealing, and desirably obtains a fluid-tight seal.

The coating process of the present invention is very rapid and lends itself to high rates of production and commercial practice. In instances where photocuring is the method of choice, one application of the curable composition followed by irradiation is desirably all that is required to achieve a fully photocured deformable composition on the threaded article. The cured deformable sealant must adhere well to the surface of the thread grooves in order to withstand mating of the parts and provide its sealing function. The articles of the present invention do not suffer from flaking or pealing of the cured sealant as is typically of latex coatings and remain substantially in place as an integral part of the threaded article to which they are applied.

The invention may be further understood with reference to the following non-limiting examples. Percent weights are per the total sealant composition, unless otherwise specified.

EXAMPLE 1 Composition A

Acryloxymethyl dimethylsilyl-terminated poly(dimethylsiloxane) 51 Precipitated silica filler 18

Adhesion promotor 3

Methacryloxypropyl dimethoxysilyl-terminated poly(dimethylsiloxane) 25

Photoinitiator _3

100 Composition B

Reactive diluent 49.8

Aliphatic urethane acrylate oligomer 45.0

Fluorescent dye 0.1 Wetting agent 0.5

Photoinitiator 3.5

Photoinitiator 1.5

Odor Mask 100

Composition B had a Shore D-2 hardness of 27 and an elongation of 200-240%. Composition C

(meth)acryloxyalkyl dimethoxysiloxy-terminated poly(dimethoxysiloxane) 94.0

Photoinitiator 3.5

Fluorescent dye 1

Adhesion promotor 1

Tetraisopropyl titanate Q.5

100 Composition D

Reactive acrylic diluent 42.5

Aerosil silica thickener 2

Ethylene acrylic elastomer 2.5 Dye 0.1

Photoinitiator 2

Urethane acrylate oligomer 49.4 Adhesion promoters 1.5

100

Composition E

Acryloxymethyl dimethylsilyl-terminated poly(dimethylsiloxane) 54

Precipitated silica filler 19 Adhesion promotor 3

Methacryloxypropyl dimethoxysilyl-terminated poly(dimethylsiloxane) 20

Photoinitiator _4

100 Composition F

(commercially available latex³)

Deionized water 27.71 Surfactant 0.4 Acrylic emulsion¹ 34.03

Anti-foam agent 0.01

Corrosion inhibitor 0.9

Fungicide 0.3

Filler/lubricant 9.0 Color 6.05

Ammonium Hydroxide (thickener) 0.68

Acrylic emulsion² 12 .0

100 ¹ Rhioplex MV-17K, Rohm & Haas

² Acrysol ASE-60, Rohm & Haas

³ Nibraseal™, Loctite Corporation

Composition G

Reactive acrylic diluent 39

Odor Mask 0.5

Chelator 0.1

Photoinitiator 0.75

Urethane acrylate oligomer 59.55

Slip agent 0.1 100

EXAMPLE 2

The thread grooves of one-half inch threaded steel plugs were coated with compositions A-F respectively.

Compositions A-E were photocured using UN radiation at 50 mw for 1 minute. Composition F, the commercially available latex composition sold under the tradename

Nibraseal #516, was dried in an oven at 158°F for 30 minutes. The plugs were assembled into a corresponding pipe tee and pressure tested for sealing characteristics at pressure. The results are shown below in Tables 1 &2 below.

TABLE 1 SEAL TEST RESULTS

TABLE 2 SEAL TEST RESULTS

EXAMPLE 3

This method of the present invention provides an improved production rate due to the cure speed of the UN curing sealants. The following Table compares oven drying speed of a latex acrylic emulsion to UN curing rates of a photocurable silicone composition for the same amount of material on a weight basis.

The cure data was generated using a Loctite UN Curing Wand System, 983675. A 12mm cure spot was created by mounting the wand tip ³/ of an inch above the coated surface. The relative effective irradiance was measured at 365nm wavelength with an output of 50mw/cm². The same amount of thread groove coverage was used for each fastener. These results highlight the overall efficiency and convenience of the present invention. Cure speed and overall efficiency can be further in increased through the use of multiple radiation sources.

TABLE 3

CURE RATES

COMPOSITION F

The invention described herein may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention and are intended to be included in the following claims.

Claims

WHAT IS CLAIMED IS:

1. An unassembled article of manufacture comprising a threaded surface for engaging a corresponding threaded mating part, said threaded surface having a polymerized solid material thereon, said polymerized solid material being sufficiently deformable to conform to and allow assembly with said corresponding threaded mating part when assembled therewith and to provide sealing and/or locking engagement therebetween.

2. The article of claim 1 wherein said polymerized solid material includes polymers selected from the group consisting of silicone, urethane, silicone-acrylate, urethane-acrylate, polyolefins, and copolymers and combinations thereof.

3. The article of claim 1 in the form of an exteriorly threaded member.

4. The article of claim 1 in the form of an interiorly threaded member.

5. The article of claim 1 in the form of a bolt, screw, nut, pipe or tube.

6. The article of claim 1 wherein said polymerized solid material is the reaction product of a composition comprising: a) about 50% to about 98% by weight of one or more polyorganosiloxane polymers; and b) about 0.1 to about 5.0% by weight moisture curing catalyst.

7. The article of claim 1 wherein component a) is one or more (meth)acryloxyalkyl dimethoxysiloxy-terminated poly(dimethyoxyslanes).

8. The article of claim 1 wherein the fully solid deformable composition has an elongation of about 10% to about 300%.

9. The article of claim 1 wherein said polymerized solid material is the reaction product of a composition comprising: a) about 35% to about 95% by weight of a polymerizable polyurethane polymer; and b) about 0.05% to about 10% by weight of a photoinitiator.

10. The article of claim 9 further including a (meth)acrylic reactive diluent.

11. The article of claim 10 wherein component a) is one or more aliphatic urethane acrylate oligomers.

12. The article of claim 10 wherein component c) is selected from the group consisting of ethoxyethyl acrylate, hydroxyethyl acrylate, isobornyl acrylate, N,N-dimethylacrylamide, tetrahydrofurfuryl acrylate and combinations thereof.

13. The article of claim 1 wherein said polymerized solid material is the reaction product of a composition comprising: a) about 50% to about 98% by weight of one or more (meth)acryloxyalkyl dimethoxysiloxy-terminated poly(dimethylsiloxane) polymers; b) about 0.5% to about 10% by weight of a photoinitiator; and c) about 0.1% to about 5.0% by weight of a moisture curing catalyst.

14. The article of claim 13 wherein the photoinitiator is selected from the group consisting of benzophenone, dialkoxybenzophenones, dialkoxyacetophenones, benzoin, Michler's ketone and combinations thereof.

15. The article of claim 13 wherein the moisture curing catalyst is a metal salt of tin, titanium or zirconium.

16. The article of claim 15 wherein said metal salt is tetraisopropoxytitanate or tetrabutoxytitanate .

17. The article of claim 1 wherein said threaded article is made from stainless steel, zinc, aluminum, chromium, bronze, titanium, nickel, plastic and combinations thereof.

18. A method of manufacturing a threaded article which is capable of sealingly coupling with a coπesponding threaded part to form a sealed assembly comprising: a) providing a threaded article; b) applying a polymerizable sealant composition to the threads of said threaded article; and c) polymerizable said sealant composition to provide a fully cured deformable layer which allows mating with another threaded part to provide a seal therebetween.

19. The article of claim 1, wherein said polymerized solid material has a Shore A hardness of about 25 to 35.

20. The article of claim 1 wherein said polymerized solid material has a Shore D-2 hardness of about 25-32.