CA2113961A1 - One part cross-linkable hot melt adhesives - Google Patents

Abstract

ABSTRACT

A one-part hot melt adhesive composition comprising (i) a silane cross-linkable copolymer of the general formula:
~(CH2CH2)x(COM)y(TER)w~

wherein TER is an ethylenically unsaturated monomer other than ethylene; COM is:

wherein Z is -CO-O-CH2CH2~; m is 0 or 1; n is 0 or 1;
R1=R2 is H or CH3; R3 is CH3 or C2H5; x, y, and w are numerals, x is greater than 50, and ;
and ;
wherein MWcom is the molecular weight of the comonomer and MWter, is the molecular weight of the termonomer;
(ii) an encapsulated silane condensation catalyst;
and (iii) optionally a tackifier and/or wax; wherein said composition has a melt index greater than 100.

Description

396~- ~

O~7E PART eRO8E~LINRABL~E HO~ NEI,T ;;

ADHEE;IVES

FIELD Oli' T~{E INVl~NTION
: The present invention relates to one part moisture ~ :
crosslinkable compositions based on polyolefinic silane copolymers containing encapsulated siliane crosslinking catalyst, methods for manufacturing to said compositions ~ :
and to said encapsulated crosslinking catalysts. ~ ~
.~:
, ~
BACXGROU~D OF T~E I~VEN~IO~

The polyolefin hot melt adhesive industry in the United States alone has grown steadily from l00 million pounds in 1970 to over 600 million pounds in l99l. Low density polyethylene (LDP~) makes up approximately 25% of the polyolefins used in hot melt formulations, while ethylene-vinyl acetate (EVA) copolymer makes up most of the rest. A typical polyole~in-based hot melt adhesive is composed mainly of two or three components, namely, polyole~in polymer (40-70 wt%), a modifying or tacki~ying resin (30-40 wt%) and a petroleum wax (0-20wt%), wherein the quantity and relative amount o~ each material is 2~396~.

governed by the desired performance of the adhesive. The polyolefin polymer forms the backbone of the adhesive and provides strength and toughness. The Melt Index (MI) of a thermoplastic polymer is a measure of melt viscosity, wherein a high MI corresponds to a low viscosity.
Typically, for adhesive purposes, polyolefin polymers with high melt index (MI) values of 100-2000 are required to achieve desired adhesive properties. The modifying or tackifying resin contributes surface wetting and tack, while petroleum wax is used to lower melt viscosity, reduce cost and control setting speed. Other additives such as antioxidants, fillers, and the like known in the hot melt adhesive art are also present to enhance certain properties.
It is known that the thermoplastic nature of existing uncrosslinked polrolefin-based hot melt adhesives limits their heat resistance. Typically, the polymers melt at <110C, which results in the destruction of the strength and integrity of the adhesive. Shear Adhesion Failure Temperatures (SAFT's) of existing polyolefinic-based hot melt adhesive systems occur _ <100C.
It is also known that polyamide and polyester-based hot melt adhesives offer some, but limited, improvements in temperature resistance due to their higher melting points, although these materials are still thermoplastic, not crosslinked, and have maximum SAFT's in the range of 180C. Further, these polymers, which are produced in batch processes, are more expensive than polyolefins such as LDPE and ethylene vinyl silane (EVS) copolymers which are produced on reactors by continuous bulk polymerization. It is known, therefore, that only crosslinked hot melt adhesives offer real high temperature and solvent resistance.
Reactive epoxy resins, acrylic resins, and 211396~ :

polyurethanes, most commonly available in two-part systems, have been developed to achieve this. However, these materials tend to have cost and performance trade-offs when compared to polyolefin based hot melt adhesive compositions. For example, fast setting products tend to sacrifice flexibility. Also, there are unfavourable industrial hygiene issues associated with these aforementioned reactive systems. For example, the isocyanate groups in the polyurethane systems are sensitizing agents.
At the present time, the major way to produce crosslinked polyolefin-based hot melts is to subject the finished article to ionizing radiation such as ~-rays or electron beams. This irradiation offers a commercially unfeasible proposition in most instances. Polyolefinic silane copolymers such as ethylene-vinyl silane (EVS) copolymers offer another means of crosslinking.
Polyolefinic silane copolymers harden or crosslink in the pr~sence of water in a manner analogous to the curing of silicone rubbers. Generally a silane condensation catalyst is required although there are reports where application of heat alone in air can induce crosslinking (U.S. Pat. 3,225,018 - Zutty, issued Dec. 21 1965, U.S. Pat. 3,392,156 - Donaldson, issued July 9, 1968, and D.J. Bullen, G. Capaccio, C.J. Frye, T. Brock, Brit. Polym. J., 21, 117-123, (1989).
There are five known factors which in~luence the crosslinking of polyolefinic silane copolymers, namely, 1) catalyst concentration in the copolymer, 2) water concentration in the copolymer and external to it, 3) temperature, 4) sample geometry, and -.

5) silane content EVS crosslinking is reported to be first order with .'~ . ' ': ' ' -' ~ ,, i"i . ..

211396~

respect to catalyst concentration and first order with respect to water concentration in the polymer (A. K. Sen et al, J. Appl. Polym. Sci., 44, 1153-1164, (1992).
Typical levels of residual water in EVS are 100 ppm or less.
The effect of temperature on crosslinking in the presence of catalyst can be approximated by the Arrhenius relationship, the rate of crosslinking approximately doubles with every 10C increase in temperature ( A. X.
Sen et al, J. Appl. Polym. Sci., 44, 1153-1164, (1992).
Sample geometry also plays a role by affecting the time of diffusion of external environmental water into the EVS copolymer. This environmental water in addition to the residual water absorbed in the EVS at the point of fabrication of the finished sample. The diffusion of - environmental water into the sample is governed by ~ick's Law of Diffusion which is:
Conc. of Water a (l/Thickness)2 ~ Conc. Gradient.
Therefore cure can be increased by increasing the concentration of water outside the sample and by reducing the sample cross-section.
The copolymerization of ethylene and vinyl silane in a continuous bulk reactor to produce ethylene vinyl silane copolymer is described in aforesaid USP's 3,~25,018, and 3,392,156, and U.S. Patent 4,297,310 - S.
Akutsu, et al, issued Oct. 27, 1981. Such EVS copolymers contain the vinyl silane comonomer grouping in the range of about 0.5 - 6 wt% based on the weight of the copolymer. U.S. Patent No. 4,689,369 - Ishino et al, issued August 25, 1987, describes cross-linkable copolymers produced by the reactor polymerization of silanes having an unsaturated and hydrolysable groups for use in various molding fields, such as electric power cables, pipes, tubes, films, and hollow and foamed mouldings. Japan Kokai Tokkyo Koho JP 01,301,740 -2113~

Tachibana et al, filed May 31, 1988 describes heat resistant hot melt adhesive compositions comprising silane modified polyolefins, organotin silane condensation catalysts, polyols, and, optionally, tackifiers andtor waxes. One practical drawback acknowledged in this application is that even at low temperatures the crosslinking reaction starts once the silane copolymer and catalyst are mixed. This has the effect of seriously limiting the shelf life of the composition. In order to achieve shelf-life the catalyst must be packaged separately from the polyolefin silane copolymer until near the time of application resulting in a two-part adhesive.
There still remains a significant need in the hot melt adhesive industry for shelf stable one-part adhesive formulations which have improved solvent and higher temperature resistance, wherein one-part compositions can be placed in a single package and remain non-crosslinked until used.
Encapsulation of various products has been documented extensively. Gutcho has compiled a large volume of patents which describe the encapsulation processes for a wide variety of biologically active ingredients. (M. Gutcho, Capsule Technology Microencapsulation, Noyes Data Corp., 1972.) A literature review of encapsulation techniques is also set forth by Kondo (A. Kondo, Microcapsule Processing and Technology, Ed. J.W. Van Valkenberg 1979.). In it he descrihes many examples of encapsulation. One example of interest is the encapsulation of an amine epoxy resin (tJ.S. Patent 3,167,602). In this example an amine epoxy resin curing agent is encapsulated with a wax. These capsules are then used in the preparation o~ one-liquid-type epoxy adhesives. The encapsulation was accomplished by ~?

21~3~6~

dropping the amine compound through a film of molten wax which was floated on water at 70C. The amine drops are encapsulated to a thickness of 70 to 100 microns and fall through the water to cooler water at the bottom of the tank where the wax solidifies. The recovered capsules are stable for weeks at room temperature but release the amine component when heated. This allows the amine to then function as an epoxy curing agent.
Methods of encapsulation of active ingredients in a polymer shell have been described for a variety of applications, for example, for drug delivery (V.
Lenaerts, et al, Biomaterials, 5, 65-68, (1984).
Generally, the active ingredient is dissolved in a vinyl monomer which is emulsified and then polymerized to ~orm small polymeric particles containing the active ingredient.
Encapsulation of chemical catalysts for use in EVS
crosslinking reactions by emulsion polymerization could reasonably be anticipated to result in unacc~ptable experimental results. Problems that could be anticipated include reaction of the catalysts with the water used in the emulsion, reaction of the catalysts with the vinyl monomers, and reaction of the vinyl polymerization catalysts with the silane condensation catalysts.
Another parameter critical to this invention relates to the degree of damage to the catalyst containing particles during their dispersion in the polyolefinic sila~e copolymer. This factor, and the relative compatibility of the silane condensation catalyst to the encapsulating material vs the polyolefinic silane copolymer, determines how well the catalyst is localized in the encapsulent. The more complete the localization of the catalyst the more shelf-stable the adhesive.
Ano~her anticipated factor is the m.p. and viscosity of the silane condensation catalyst which would affect its 21~39~

diffusion mobility.
As a result of extensive investigations, we have discovered novel, hot melt adhesive formulations which are shelf-stable, yet, when momentarily melted during application above defined temperatures described ;~
hereinbelow start crosslinking upon exposure to water. -,:

BUMNARY OF THE :I:NVENTION
:
It is thus an object of the present invention to provide novel one-part, shelf-stable adhesive compositions comprising polyolefinic silane copolymers mixed with silane condensation catalysts that are encapsulated in such a manner that the catalysts are not able to initiate crosslinking until the adhesive is momentarily melted during application above the m.p. or softening point of the material encapsulating the catalyst.
It is a further object of the present invention to provide methods of adhering a first substrate to a second substrate by use of said hot-melt adhesive compositions.
It is yet a further object to provide novel encapsulated silane condensation catalysts.
These and other advantages and objects of the present invention will become apparent upon a reading of the specification as a whole.
Benefits of encapsulating the silane condensation catalysts can be realized if the material encapsulating the catalyst melts above ~ 120C. The high MI
polyolefinic silane copolymers have crystalline melting points <110C and we have found it possible to produce an encapsulated catalyst that can be dispersed into the polyolefinic silane copolymers below the m.p. of the material encapsulating the catalyst. The catalyst therefore remains localized within the encapsulent.

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2 ~ L 3 ~ 6 ~

Hot melt adhesives, for example glue sticks, are generally melted above 150C when applied to the substrate. Therefore if the m.p. or softening point of the encapsulating material is below this adhesive application temperature the catalyst will be dispersed in the adhesive and be able to initiate crosslinking.
Surprisingly, we have found that silane condensation catalyst can be dissolved in vinyl monomer, emulsi~ied, polymerized, recovered as a powder and be mixed into polyolefinic silane copolymers below ~ 120C
to produce one part shelf-stable adhesive formulations which, when momentarily melted during application above the m.p. or softening point of the material encapsulating the catalyst, crosslink upon exposure to moisture.
It is also generally practiced in the plastics industry to introduce additives into polymer via the masterbatch route. In this technique a concentrated mixture of the additive is prepared in an inert polymer carrier resin which is then letdown in the final product to the desired concentration. It is generally desired to use a masterbatch with similar melting and viscosity characteristics as the final product to ensure proper mixing of the additive.
Surprisingly, we have found that by compounding silane condensation catalyst into materials which melt above ~ 130C and grinding these materials into powders, that these powders can be dispersed in polyolefinic silane copolymers below ~ 120C to produce one component shelf-stable adhesive formulation that, when momentarily melted above the m.p. or softening point of the catalyst containing powder, cro~slink upon exposure to moisture.
Accordingly, in one aspect the invention provides a hot melt adhesive composition comprising an encap~ulated silanol condensation catalyst, optionally a tackifier and or wax, and a silane cross-linkable copolymer o~ the ~.: .,: : : . -2~3~1 - 9 - SL370 ~ ~;
general formula~
~(CH2CH2)~(COM)y(~ER)w~
wherein TER is an ethylenically unsaturated monomer other than ethylene; and wherein COM is:
(CH2 CR
( CH2 (CHR2) n Zm . :
Si(oR3) and Z is -CO-O-CH2CH2-; m is 0 or 1; n is 0 or 1;
Rl=R2 is H or CH3; R3 is CH3 or C2Hs; x,y and w are numerals,and x is greater than 50, - ~
and 0.5 < (MMC~) y ~ 100 < 10.0; ~ ;~
2 0 [ 2 8--X + (MWO,~ Y ~ ( MWT~R ) W ]

and o< (MW~BR? W X 100 < 50;
[28-X + (MW""",)-Y + (MW1,ER)OW]
wherein MWC~ is the molecular weight of the comonomer, MM~r is the molecular weight of the termonomer; ::
having a melt index greater than 100.
Preferably, the EVS copolymer has.a melt index (MI) of greater than 200, and more preferably, greater than 400.
In one preferred aspec~t the invention provides a composition as hereinabove defined wherein ~aid copolymer is a graPt copolvmer of the general formula selected from the group consisting of:

~ ., .. . .:

21~ 3~

CH2 CH2 ) X ( CH2 I H ) y ( TER) w jCH2 (R3 0) 3 Si wherein R3 is CH3 or C2H5; TER is an ethylenically 10unsaturated monomer other than ethylene;
and ~CH2 C~2)x (CH2 fH)y (TER)W~
fH2 f-CH3 f=0 OCH2CH2CH2 Si (0 CH3) 3 ~ I :

and x, y and w are as hereinabove defined.
In a more preferred aspect the invention provides a composition as hereinabove defined wherein said copolymer has the general formula selected ~rom the group consisting of~
~CH2 CH2)X(CH2 C Rl)y (TER)w ; :
Si (oR2) 3 . ; ~ ~ :

and ~:

~CH2 CH2)X (CH2 C Rl)y (TER)w~
1 . :~::
C0-O(CH2)3 Si(o C~I3)3 where Rl is H or CH3 and R2 is CH3 or C2H5; and TER, x, y, and w are hereinabove defined; and wherein said copolymer is prepared by radically polymerizing a polymerizable:~
monomeric mixture consisting essentially o~ ethylene and at least one ethylenically unsaturated silane compound selected ~rom the group consisting o~
vinyltrimethoxysilane, vinyltriethoxysilane and methacryloxypropyltrimethoxysilane under a pressure 2~3~61 ~ SL370 ranging from 1000 to 4000 kg/cm2, and containing said silane compound in an amount of from 0.5 to 10 wt.%.
Most preferably, the ethylenically unsaturated silane compound is vinyl trimethoxysilane.
Generally these copolymers are known as ethylene-vinyl silane (EVS) copolymers.
The present invention in one aspect is based on the surprising discovery that silane condensation catalysts can be temporarily deactivated or localized by encapsulation so that when the catalysts are compounded into EVS copolymer at temperatures less than ~120C they do not promote EVS crosslinking upon storage under ambient conditions of temperature and humidity, but, when these mixtures are heated momentarily above the m.p. or softening point of the material encapsulating the catalyst during application of the adhesive, ~he catalyst ~-is released and starts promoting EVS crosslinking.
Yet a further aspect of the invention provides an encapsulated silane condensation catalyst comprising silanol condensation catalysts preferably selected from the general classes of acidic compounds such as carboxylic acids and basic compounds such as organic titanates, and organic complexes or carboxylates of lead, tin, cobalt, iron, nickel and zinc such as lead naphenate, tetramethyl titanate, and dibutyltin dilaurate encapsulated in a material softening or melting close to or above, the so~tening or melting point of the E~S
copolymer in which it is mixed.
Encapsulating materials include any inert high melting material compatible with EVS copolymers and silane condensation catalysts and which can be prepared as a fine powder preferably less than 48 mesh.
Methods of producing fine powder particles are well known in the art and include grinding of solids or spray drying of solutions or emulsions. Thus, the encapsulated .;: ' ' .. ' . i . . ' ! : , 2 1 ~ 3 9 6 1 catalysts of use in the practice of the invention may be obtained in fine powder form by such methods.
In one preferred aspect of the invention the encapsulating material is prepared by the polymerization of an emulsion of vinyl monomers containing silane condensation catalyst to produce a powder of spherical particles Ca. 1/3 ~m in diameter.
Such methods include a method of encapsulating the silane condensation catalyst by dissolving or dispersing the catalyst in monoethenically unsaturated monomer(s~, emulsifying the monome~(s) containing catalyst in water usually with the aid of surfactants or colloid stabilizers, and polymerizing the monomer(s) by free radical means at room temperature or above to produce an emulsion of solid capsules. The emulsion is then dried to yield free flowing powder of encapsulated silane condensation catalyst.
An encapsulated silane condensation catalyst may be further encapsulated with a second polymer to produce a so-called core/shell capsule. This is accomplished by adding another charge of monoethenically unsaturated monomer(s) and optionally surfactants, coloidal stablizers, and free radical catalyst, to the emulsion of silane condensation catalyst capsules. This second charge of monomer(s) coats the capsules and is polymerized by free radical means at room temperature and above to produce core/shell capsules.
The encapsulated catalyst is preferably encapsulated with a material in alternative embodiments where the T8 or softening point of the polymer encapsulaking the silane condensation catalyst is above the temperature at which the capsules can be compounded into ~VS, generally 120C.
The monoethenically unsakurated monomers preferably comprise mixkures of methacrylic acid (MA~) and methyl - . -21~ 3~1 methacrylate (MMA), the silane condensation catalyst is dibutyltin dilaurate (DBTDL), the surfactant is sodium dodecyl sulphate, and the free radical initiator is ammonium persulphate, wherein the polymerization reactions are effected under nitxogen at 65-85C.
More preferably, the catalyst is encapsulated in a so-called core/shell capsule. The monoethenically unsaturated monomer used to make the capsule core polymer is preferably styrene, the silane condensation catalyst is an oligomer of dioctyl tin maleate (DOTM), the urfactant is an ethoxylate of nonylphenol, and the free radical initiator is a redox mixture of sodium metabisulphite, ferric sulphate, and ammonium persulphate. The reaction being carried out at 20C
under nitrogen.
The monoethenically unsaturated monomer used to make the capsule shell polymer is acrylonitrile, and wherein additional sodium metabisuphite and ammonium persulphate is optionally added and reacted at 20-40C under nitrogen.
In another preferred aspect of the invention, the encapsulating material is a polymer compatible with EVS
which melts above the temperature at which the encapsulated catalyst is compounded into the EVS-based adhesive but which melts or softens below the application temperature of the adhesive.
In yet another preferred aspect of the invention, the encapsulating material is a solid compatible with ~VS
and the silane condensation catalyst which melts above the temperature at which the encapsulated catalyst is compounded into the EVS-based adhesive but which melts or softens below the application temperature of the adhesive.
Tackifiers of use in the practice of this aspect of the invention are preferably selected from the general ~ 21 13961 classes of resins, based on their chemical nature, consisting of rosin, modified rosin, rosin derivatives, hydrocarbon resins and terpene resins.
However, the person skilled in the art will know or could readily determine without the need for undue experimentation which tackifiers would be of value. By way of guidance, wood resins, gum resins, tall oil resins, hydrocarbon resin, and modified terpene resins as described in "Handbook of Adhesives, page 562, are of use -in the present invention. Examples of such tackifiers are set forth in Table 1.
~A~E 1 _ _ _ _ : .
Ring and Ball Softeniny Point Trademark Tackifier Class (C) Acid Number l _ I
Zonester 65 Rosin ester type 65C 78 ¦
i . _ I .
Sylvatac 140 Rosin ester type _ 139C 140 Nirez 1135 Terpene type i35C __ _ I : -., Nirez 2019 Terpene type 123C __ ~
_ 20 STA-TAC B Hydrocarbon type100C __ _ Betaprene 255 Hydrocarbon type 132C __ I .
Zonatac 115 Hydrocarbon 115C __ Modified Terpene I -The relative amounts of ethylene vinyl silane (EVS) and tackifying resin may be readily determined by the skilled person in the adhesion art. Typically, the EVS
copolymer constitutes 30-95% w/w and the tacki~ier 5-70~
wlw .

21~396 ~i Th~ adhesive compositions may be made by compounding the adhesive components above the softening temperature of the material encapsulating the silane condensation catalyst and then cooling the mixture to temperatures below the softening temperature of the material encapsulating the catalyst, generally <120C, before compounding the catalyst capsules into the mixture.
The compositions of the invention as hereinbefore defined may further comprise a diluent, carrier, adjuvant and the like. Such a carrier is a petroleum wax present in a concentration of 0-20% w/w. Petroleum waxes of use in the compositions of the present invention have been used in prior art hot melt adhesive compositions comprising polyolefin polymer and tackifying resins to reduce viscosity and cost.
The adhesive compositions according to the invention are of use as hot melt adhesives with substrates within, for example, the fields of paper laminates, cases, cartons, book binding, labels, bags, textiles, carpet seams, furniture, cans, tubes, drums and the like.
Accordingly, in a further aspect, the invention provides a method of adhering a first substrate to a second substrate, which method comprises applying a hot melt adhesive composition according to the invention as hereinbefore defined to either or both of said first substrate and said second substrate and adhering said substrates one to the other.
T~e various techniques of applying the composition of the invention as hot melt adhesives fall within the skill of the art.

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21~396~ :

DETAILED DE5C~IPTIO~ OF THE INVBNTION

The ethylene silane-crosslinkable copolymers o~ use in the compositions of the present invention are copolymers consisting essentially of ethylene and an ethylenically unsaturated silane compound having a hydrolyzable organic group.
The term "consisting essentially of" used herein means that the ethylene copolymer can contain up to 50 wt% of copolymerizable monomers other than ethylene and the ethenically unsaturated silane compound having a hydrolyzable organic group. Examples o~ such optional ~ -~
monomers include ~-ole~ins such as propylene, hexane~
and 4-methylpentene-1; vinyl esters such as vinyl acetate and vinyl butyrate; unsaturated organic acid derivatives such as methyl acrylate, ethyl acrylatP and methyl methacrylate; unsaturated aromatic monomers such as styrene and ~-methylstyrene; and vinyl ethers such as vinylmethyl ether and vinylphenyl ether. These optional monomers can be present in the ethylene copolymer in any forms, e.g. a graft form, a random form or a block form.
Ethylene and the unsaturated silane compound are copolymerized under any conditions such that copolymerization of the two monomers occur. More specifically, those monomers are copolymerized under a pressure of 500 to 10,000 kg/cm2, preferably 1,000 to 4,000 kg/cm~, and at a temperature of 100 to 400C, preferably 150 to 350C, in the presence of a radical polymerization initiator, optionally together with up to about 50 wt% of a comonomer and a chain transfer agent.
The two monomers are brought into contact with each other simultaneously or stepwise in a vessel or tube type reactor.
In the copolymerization o~ ethylene and the unsaturated silane compound, any radical polymerization ~ ':
~1~3~61 . - 17 - SL370 initiators, comonomers and chain transfer agents, which are conventionally used in homopolymerization of ethylene or copolymerization of ethylene with other monomers can be used.
Examples of radical polymerization initiators include (a) organic peroxides such as lauroyl peroxide, dipropionyl peroxide, benzoyl peroxide, di-t-butyl peroxide, t-butyl hydroperoxide, and t-butyl peroxyisobutyrate; (b) molecular oxygen; (c) azo lo compounds such as azobisisobutyronitrile and azoisobutylvaleronitrile; and (d) peroxydicarbonates such as n-butyl peroxydicarbonate, n-propyl peroxydicarbonate, isopropyl peroxydicarbonate, and sec-butyl peroxydicarbonate.
Examples of the chain transfer agent include (a) paraf~inic hydrocarbons such as methane, ethane, propane, butane and pentane; (b) ~-olefins such as propylene, butene-1 and hexene-1; (c) aldehydes such as formaldehyde, acetaldehyde and n-butylaldehyde; (d) ketones such as acetone, methyl ethyl ketone and cyclohexanone; (e) aromatic hydrocarbons; (f) chlorinated hydrocarbons; and (g) hydrogen.
While the copolymer of use in the present invention can be in the form of a normal copolymer of ethylene and unsaturated organosilane copolymerized under high pressure using a stirred autoclave reactor with free radical initiators as hereinabove described, the copolymer can also be of the form of a graft copolymer prepared by graft polymerization of an unsaturated organo silane onto polyethylene or copolymers of ethylene and other monomers. While methods of making such copolymers are known in the art, the copolymers of use in the present invention are novel in having MI > 100.
Examples of silane condensation catalysts include:
(a) organometallic basic compounds particularly solids ` 2~L13~6~ ~

such as oligomeric dialkyltin maleates and liquids such as dibutyltin dilaurate; (b) organic titanates; (c) acidic compounds such as carboxylic acids.
The catalyst encapsulating materials prepared by emulsion polymerization of vinyl monomers consist essentially of vinyl monomers emulsified using surfactants and initiated using free radical or redox initiators.
The catalyst may be encapsulated with any type of polymer produced from any type of monoethenically unsaturated monomer. Preferably the polymer may be produced from any monomer or mixture of monomers such that ideally the Tg of the resulting polymer is approximately 125C. If the encapsulation is performed below this temperature the particles may be further coated with a higher Tg polymer. Typical monomers used include vinyl aromatic compounds such as styrene, ring substituted styrenes, which include vinyl toluene, 3,4-dimethyl styrene, and p-isopropylstyrene. Acrylic acid and methacrylic acid are also used. Alkyl methacrylic or acrylic esters may also be used which commonly include methyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, ethyl hexyl acrylates, lauryl methacrylate, and many others. Other monomers include methacrylonitrile, acrylonitrile, vinyl chloride, vinylidine chloride, vinyl acetate, etc.
As mentioned above the encapsulated catalyst may be further encapsulated with a second polymer. This is advantageous when the catalyst is encapsulated in a polymer which possesses a Tg which is too low, when the polymer does not effectively encapsulate the catalyst, the polymer is not compatible with the EVS, or for other reasons. The second polymer may be produced from any `~
monomer or mixture of monomers as listed in the paragraph above such that ideally the T~ of the resulting polymer ~ ~:,~, . . . . . .
,1, "' ' , 21139~ ~

is approximately 125C. The requirements of monomers and other conditions to produce such so called heterogeneous core/shell polymers are well known and are aptly reviewed by Lee and Rudin (S. Lee, A. Rudin, in "Polymer Latexes", E.S. Daniels, E.D. Sudol, M.S. El-Aasser, Eds., ACS
Symposium Series 492, Washington, DC., 1992, P.234-254).
Chain transfer agents or bi- or polyfunctional crosslinking monomers may also be used to enhance or retard catalyst release. The chain transfer agents decrease the molecular weight of the polymer increasing the rate of catalyst diffusion from the particles while crosslinking agents increase the molecular weight of the polymer retarding the catalyst diffusion from the particle. Typical examples of chain transfer agents includemercaptoethanol, iso-octylmercaptopropanoate, or carbon tetrachlorideO Typical crosslinking monomers are ethylene dimethacrylate, allyl methacrylate, divinyl benzene, 1,3-butanediol dimethacrylate, and the like.
Examples of ionic initiators commonly used for free radical latex polymerizations are ammonium or potassium persulphate. Hydrophobic nonionic initiators include 2,2-azobis (isobutyronitrile) and benzoyl peroxide.
Further diversity in initiators may be obtained by the use of water soluble nonionic initiators such as tertiary butyl hydroperoxide and hydrogen peroxide. The initiator 4,4-azo-bis-(4-cyanovaleric acid) in its acid state is oil soluble but may be neutralized to become an ionic water soluble initiator.
The above initiators are thermal initiators which require heat to produce radicals. Redox systems offer further ~reedom in that they allow for generation of free radicals at lower temperatures. Tertiary butyl hydroperoxide/sodium metabisulphite or potassium persulphate/sodium bisulphite/iron II redox couples are examples of this. Reactions in the presence of these 5t i,,i, . . .

:
21139~ ~
- 20 - SL370 ~
initiators allow polymerizations to proceed at room temperature. The concentrations of initiators typically used are from 0.01 to 2% based on the weight of monomer.
Many types of surfactants commonly used in the art of emulsion polymerization may be used. Typical, although not exclusive, surfactants include alkylbenzenesulphonates, such as sodium dodecylbenzenesulphonate, and alkylsulphonates such as sodiumdodecylsulphonate. Nonionic surfactants and lo polymer stabilizers such as ethoxylated alkyl phenols, poly(vinyl alcohol), and poly(acrylic acid) may also be used.
Typical concentrations of surfactants used in the encapsulation procedure are 0 to 10% based on the weight of the monomer. When it is desirable to coat the encapsulated catalyst with a second polymer to produce a shell, less or no surfactant is added so that during shell formation the new polymer formed resides on the surface of existing particles instead of forming new particles.
The catalyst encapsulating materials consisting of powdered high melting polymers compatible with EVS
include, for example: (a) polypropylene; (b) ethylene-propylene copolymer~; and (c~ any other polymer which melts above the temperature at which the encapsulated catalyst would be compounded into the EVS but melts below the adhesive application temperature7 The catalyst encapsulating materials consisting of powdered high melting solids compatible with EVS include, for example: (a) glucose; (b) methylhydroquinone; and (c) any other compatible solid which melts above the temperature at which the encapsulated catalyst would be compounded into the EVS, but which melts below the adhesive application temperature.
The crosslinkable compositions of the present ~ ...

21~39~

invention are sufficient if they have the above-described compositions prior to kneading. For example, the ingredients of the invention as hereinabove defined may be prepared into the desired composition in a kneader.
Kneading can be conducted by conventional methods. Use of an extruder is preferred. The kneaded product containing an encapsulated silanol condensation catalyst is applied in molten form above the softening or m.p. of the encapsulent to adhere two substrates. The adhesive then crosslinks upon exposure to water or water vapour.
The following description and examples are provided to further illustrate the compositions of the present invention, but are by no means intended as limiting.

DETAI~ED D~8CRIP~ION OF PREFERRED EMBODIMENT~

EVS copolymers of ethylene and vinyltrimethoxysilane in pellet form maintained dry in water impermeable packaging produced either by graft copolymerization or by high pressure free radical polymerization were used in the following experiments. The material produced ky high pressure free radical polymerization is a new version of AQUA-LINK~ (AT PLASTICS INC., Ontario Canada) produced having MI of >100.
Hot melt adhesive formulations are mixed by heating and stirring the components in closed or open vessels. ;; ;
Generally, this method would not work with crosslinkable hot melt adhesive compositions, because once a crosslinking catalyst was added, the adhesive would start to cure and set-up in the pot. Even with encapsulated catalysts described in this document it is inadvisable to leave the encapsulated catalyst in the molten EVS
adhe~ive formulation for extended periods of time. Given time, the catalyst could diffuse out of the encapsulent, ~, .
;",.. . . .

:~... , ~ , . .. ..

- 22 - 2113 9 6 ~ SL370 a phenomenon accelerated at higher temperatures.
The adhesive components are preferentially compounded in a manner that minimizes the exposure of the encapsulated catalyst to extended heat history above -120C. The adhesive formulation containing encapsulated catalyst can then be stored as a solid at ambient conditions, or preferentially in packaging to minimize moisture ingress into the adhesive, until the adhesive is ready for use. As stated previously~ the rate of crosslinking is dependent on the water content of the adhesive. Minimizing water content will help prevent premature crosslinking, especially once the adhesive is melted.
Therefore, in order to minimize the heat exposure of the encapsulated catalyst and also because some of the tackifiers only melt above 120C, the EVS copolymer and the other adhesive components were homogenized first either on a roll mill, in a heated stirred pot, or in an extruder. After this the adhesive formulation was cooled below 120C and the encapsulated catalyst dispersed in the adhesive formulation prior to fabricating the adhesive into its final commercial shape and cooling the adhesive to ambient temperature for storage prior to use.
Formulations containing regular non-encapsulated catalyst and formulation containing no catalyst were used as controls. The encapsulent softened at 129C as measured by DSC.
% Gel values of the adhesive compounds were measured one week and one month after compounding.
After compounding, the adhesives were collected and immediately pressed into a 1.8mm thick 150mm x 180mm plaque at 120C and 15000 kg pressure. These plaques were then stored in a cabinet over saturated calcium nitrate solution at 50% R.H. and ambient temperature. %
Gel values were measured over time to follow the cure of ~:!:: : ... . . .

2 ~ 6 ~

the adhesive according to ASTM D2756 on powdered adhesive packaged in stainless steel "teabags" and suspended in boiling xylenes. These results are summarized in TABL~
2, using dibutyltin dilaurate silane conden~ation catalystO

- Cure of ~iah ~I EVS after ~illinc ~ 115C
Reg~lar Encal~sulat~d 10 AJubieDt Catalvst Catalvst CurQ Ti~ 2 5 0 UI E VS with EVS with EV6 1 week 096 16% 0 . 796 1 month - 3696 18%
:.
After 1 week a portion of the plaque made with the 20 encapsulated catalyst and a portion of the plaque without -catalyst were re-introduced on a roll mill at 180C, above the softening point of the encapsulating material, and milled for 2 minutes. After milling the compounds were immediately pressed into plaques at 150C and 5000 25 kg. The plaques were stored for 1 week in a cabinet over saturated calcium nitrate at 55% R.H. and ambient temperature. The results are given in TABLE 3.
: ~ .

Cure of ~iah ~I EV~ after ~illing @~800C
Enaa~ulated nt Catal~t Cur~ Ti~ 250 MI ~VB with EVS
1 week 0.6% 23.7%

The results shown in the Tables illustrate that encapæulation of the catalyst in an appropriate material and compounding the encapsulated catalyst into EVS at low (~120C) temperatures below the melting or softening point of the material encapsulating the catalyst produces ,,",, ~, , 2~139~.

shelf stable compounds that do not crosslink upon storage for at least 1 week at ambient conditions, unlike EVS
compounds containing un-encapsulated catalyst. However, when the compound containing the encapsulated catalyst is melted at high temperatures above the softening or melting point of the material encapsulating the catalyst, then the catalyst is released and causes the EVS to crosslink upon storage at ambient conditions.
The following examples are provided to illustrate the embodiments of the invention.

EXAMP~ 1 Dibutyltin dilaurate (DBTDL) silane condensation was encapsulated in a polymer via emulsion polymerization as follows.
The polymer encapsulating the DBTDL ideally should possess a softening point, or glass transition temperature Tg of at approximately 125C so that the encapsulated product can be blended into EVS at approximately 120C without release of DBTDL. -~
Monomers were selected for encapsulatibn such that the Tg of the resulting polymer would be 125C using the Fox equation: ~ -ltTg = wl/Tgl ~ w2/Tg2 ~ ~
where wl and w2 are the weight fraction6 of the polymer ~ -and Tgl and Tg2 are the glass transition temperatures of the respective polymers in degrees Kelvin.
0.75g sodium dodecyl sulphate surfactant was dissolved in 375g deionized water. 25g DBTDL was added to the mixture of monomers, 80 g methyl methacrylate (MMA) Tg=105C and 20g methacrylic acid (MAA) Tg=228C.
This mixture was then added to the surfactant solution and homogenized for 5 minutes using a high speed disperser (~2000 rpm).

: :: ... ~ -, : , .

211396~

The emulsion was transferred to a glass reactor fitted with a mechanical stirrer and an overhead condenser. The reactor was heated in an 85C water bath.
While heating the emulsion was stirred at ~400 rpm and the initiator solution consisting of l.Og ammonium persulphate in lng deionized water was added. The head space in the reaction vessel was initially rapidly purged with N2 for 1 minute and subsequently slow purged for the remainder of the reaction.
When the reactor contents reached 70C (in about 7 minutes) the bath temperature was reduced to 65C to control the reactor temperature. A maximum temperature of 87C was reached in the reactor after 13 minutes from the start of the reaction. The reactor contents were allowed to react a further 5 minutes, then cooled to room temperature.
The latex was poured onto a glass dish and allowed to evaporate to dryness overnight. A fine white powder resembling talcum powder was obtained. Another way of isolating the product on a commercial saale would be to pass the emulsion through a spray dryer.

EXAMP~E 2 .
The fine white powder from example 1 was analyzed for tin content by neutron activation analysis and found to contain 4.5~ tin. This corresponds to 25~ DBTDL, the expected value.
The Tg of the encapsulated catalyst sample was measured using differential scanning calorimetry (DSC) using a Perkin Elmer DSC-4 System-~. The polymer had a broad transition around 76C, another sharper transition at 129C, and a broad transition from 167-179C.
Heterogeneous particles are composed of different polymer types and thus are expected to produce more than ,.,j, ,~" ~ ir,, , ~ . , ," " , ~ , ~ "" ,,, ,, ";" " ., , ~ ", ~,,, - 26 - 2~1396~ SL370 one measurable Tg. The lowest transition at 76C is likely the Tg of the polymer plasticized with DBTDL. The second transition at 129C is likely the T8 of unplasticized polymer as confirmed by the Fox equation calculation. The third transition is likely due to two phenomena, the T~ of a MAA rich outer shell and an exotherm due to loss of' surface due to coalescence.
(S.L. Bertha, R.M. Ikeda, J. Appl. Polym. Sci., 15 105 (1971)). Such structural heterogeneity is common.
This was confirmed using a melting point apparatus.
A small amount of material was placed in a capillary tube and slowly heated using a Meltemp apparatus. The powder ~-~
became translucent at 160+5C. This was designated the upper softening point.
~ -EX~MPLE 3 The catalyst activity was tested by compounding the following 3 samples on a laboratory two roll mill at 200C for 5 minutes:
: .
Sample #1) 250 MI EVS copolymer Sample #2) 250 MI EVS copolymer Regular DBTDL Catalyst masterbatch Sample #3) 250 MI EVS copolymer Encapsulated DBTDL Catalyst (Example 1) Both samples #2 and #3 above were formulated to contain 100 ppm Sn.
The samples were pressed into l.8mm x 150mm x 180mm plaques in a press at 150C at 5000 kg pressure. The plaques were cured by submerging in 90C water overnight.
%Gel values for the plaques were measured according to ASTM D2756 on powdered sample packaged in stainless steel "teabags" and suspended in boiling xylenes.

,.- : ' . ~ ', ., ~ :

-i:
- 27 21~3961 SL370 ~AMPLE %Gel 1 9-~i%
2 56.5%
3 52.2%

This proved the encapsulated catalyst was still active.

E~AMPLE 4 : , :., In order to test if the encapsulated catalyst is 15: unable to promote EVS crosslinking if it is compounded into EVS at low temperatures the following 3 samples were compounded on a laboratory 2 roll mill at 115C for 2 minutes:

Sample #1) 250 MI EVS
Sample #2~ 250 MI EVS
Regular DB~DL catalyst masterbatch Sample #3) 250 MI EVS
Encapsulated DBTDL catalyst (Example 1) Both samples #2 and #3 were formulated to contain 100 ppm Sn.
The three samples were pressed into 1.8mm x 150mm x 180mm plaques at 120C and 15000 kg pressure. The plaques were stored in a cabinet over saturated calcium nitrate solution at 50i~ R.H. and ambient temperature for one month. The ~Gel values were measured as described in Example 3 and shown in TABLE 2.
Encapsulating the catalyst and compounding it into EVS at low temperatures prevented the catalyst from promoting EVS cure for at least 1 week.
After one week, portions o~ the uncured plaques from Sample #1 and Sample #3 were then milled on a two roll - 28 - 2113~6~ SL370 laboratory mill at 180C for 2 minutes. The milled samples were pressed into plaques at 150C and 5000 kg pressure and stored again in a cabinet over saturated calcium nitrate at 50% R.H. and ambient temperature for one week. The %Gel values were measured as described in Example 3 and the results shown in TABLE 3.
Heating the EVS containing the encapsulated catalyst above the upper softening temperature of the encapsulent released the DBTDL catalyst into the EVS and allowed it to promote crosslinking.

EXA~PLE S ~;

A solid silane condensation catalyst, an oligomer of -dioctyltin maleate (DOTM), was compounded into polypropylene of two different MI values on a laboratory two roll mill under the conditions shown below~
8ANPLE FORMULA Condition~
5-1 90g 2 MI PP 190C mill 10g catalyst 5-2 90g 20 MI PP 185C mill 10g catalyst :
The catalyst m.p. is -90C. These samples were grbund in a Wiley mill to <48 mesh.

DOTM silane condensation catalyst was encapsulated in a polymer via emulsion polymerization as follows.
1.5g of a 70~ solution of a 40 mole ethoxylate of nonylphenol in water was dissolved in 345g of water. 20g of DOTM was dissolved in 80g styrene monomer. This was then added to the surfactant water solution under .,, ,, . , . , ~ . . , . . . . . ,, ,. , , ~ , - 29 - 211396~ S~370 agitation.
The resulting emulsion was transferred to a glass reactor fitted with a mechanical stirrer, an overhead condenser and a thermometer. The temperature of the reactor contents were maintained at 20~C using a thermostated water bath. The emulsion was stirred at -400 rpm. The head space was initially rapidly purged with N2 for 1 minute and subsequently purged slowly for the remainder of the reaction.
The initiator was a redox system consisting of sodium metabisulphite, ferric sulphate, and ammonium persulphate. A sodium metabisulphite solution, 1.0g in 10g water, was added to the reactor. A ferric sulphate solution, .05g in 10g of water, wae then added. Finally 1.0g of ammonium persulphate dissolved in 10g of water was added. After reacting for 1 hour, 1.0g of sodium metabisulphite and 1.0g of ammonium persulphate were again added and reacted for another hour. After reacting for 2 hours 50% of the styrene had reacted as was indicated by gravimetric analysis. At that time a further 1.0g of sodium metabisulphite and 1.0g of ammonium persulphate were again added along with 350g of water and 100g of acrylonitrile monomer~ Within 10 minutes the reactor contents reached a maximum of 40C
indicating the reaction of the acrylonitrile. The product was allowed to react of a further 30 minutes and filtered to remove any coagulum.
The latex was poured into a glass dish and allowed to dry overnight. A fine white powder was obtained.

A graft copolymer of low density polyethylene (LDPE) and vinyltrimethoxysilane (VT~OS), designated EVS graft zopolymer was prepared using a Berstorff ZE40 40mm co-21~3~6~

rotating twin screw extruder. The Berstorff extruder had temperature zones set at 140-150-175-185-185-180-160-115C (feed ~ die) and extruder speed at 150 rpm. A 400 MI LDPE (AT 193) was starve fed into the extruder to give 25 kg/hr output. A solution of ~7 wt% VulCup-R peroxide in VTMOS was injected into the second zone of the extruder at a rate of 10 g/min. This was monitored through loss in weight of the VTMOS solution container.
The EVS graft copolymer was stranded through a water bath and pelletized. The pellets were dried 1 hr in a forced air oven at 50C and then sealed in a moisture barrier foil pouch. The MI of the EVS graft copolymer was measured by ASTM D1238 as 240 g/10 min. The ~ silane content of the EVS graft copolymer was measured at ~2 wt%
by Fourier Transform Infrared (FTIR) Spectroscopy using a calibration curve prepared from known standards of EVS
reactor copolymers.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims (15)

1. A one-part hot melt adhesive composition comprising (i) a silane cross-linkable copolymer of the general formula:
-(CH2CH2)X(COM)y(TER)w-wherein TER is an ethylenically unsaturated monomer other than ethylene; COM is:

wherein Z is -CO-O-CH2CH2-; m is 0 or 1; n is 0 or 1;
R1=R2 is H or OH3; R3 is CH3 or C2H5; x, y, and w are numerals, x is greater than 50, and ;
and ;
wherein MMcom is the molecular weight of the comonomer and MWter, is the molecular weight of the termonomer;
(ii) an encapsulated silane condensation catalyst;
and (iii) optionally a tackifier and/or wax; wherein said composition has a melt index greater than 100 .

2. A composition as claimed in Claim 1 wherein said copolymer has the general formula selected from the group consisting of:

and where R1 is H or CH3 and R2 is CH3 or C2H5; and TER is an ethenically unsaturated monomer other than ethylene;
and wherein said copolymer is prepar d by radically polymerizing a polymerizable monomeric mixture consisting essentially of ethylene and at least one ethylenically unsaturated silane compound selected from the group consisting of vinyltrimethoxysilane, v i n y l t r i e t h o x y s i l a n e a n d methacryloxypropyltrimethoxysilane under a pressure ranging from 1000 to 4000 kg/cm2, and containing said silane compound in an amount of from 0.5 to 10 wt.%. and wherein x, y and w are as defined in Claim 1.

3. A composition as claimed in Claim 1 wherein said copolymer is a graft copolymer of the general formula selected from the group consisting of:

wherein R3 is CH3 or C2H5; TER is an ethylenically unsaturated monomer other than ethylene;

and wherein x, y and w are as defined in Claim 1.

4. A composition as claimed in Claim 2 wherein said ethylenically unsaturated silane compound is vinyl trimethoxysilane.

5. A composition as claimed in Claim 1 wherein said silane compound is present in an amount selected from the range 0.5% to 12% W/W.

6. A composition as claimed in Claim 5 wherein said silane compound is present in an amount selected from the range 1.5 to 4.5%W/W.

7. A composition as claimed in Claim 1 wherein said tackifier is selected from the general classes of resins, based on their chemical nature, consisting of rosin, modified rosin, rosin derivatives, hydrocarbon resins and terpene resins.

8. A composition as claimed in Claim 1 comprising 30-95% W/W of said ethylene vinyl silane copolymer and 5-70% W/W of said tackifier resins.

9. A method of adhering a first substrate to a second substrate, which method comprises applying a hot melt adhesive composition as claimed in Claim 1 to either or both of said first substrate and said second substrate and adhering said substrates one to the other.

10. A method of preparing a composition as claimed in claim 1 comprising compounding said encapsulated silane condensation catalyst encapsulated with an encapsulating material, in admixture with said silane cross-linkable copolymer.

11. A method as claimed in claim 10 comprising compounding said encapsulated silane condensation catalyst and said copolymer at a temperature below the softening temperature of said material encapsulating said catalyst.

12. An encapsulated silane condensation catalyst comprising a silane condensation catalyst encapsulated with an encapsulating material.

13. An encapsulated silane condensation catalyst as claimed in claim 12 in the form of a core-shell capsule produced by emulsion polymerization.

14. An encapsulated silane catalyst as claimed in claim 12 wherein said encapsulating material has a Tg softening point greater than 120°C.

15. A composition as claimed in claim 1 wherein TER is vinyl acetate in an amount selected from the range 2% to 40% w/w.