GB2115823A - Sealant composition having improved slump resistance - Google Patents

Abstract

A sealant composition having excellent UV and oxidative stability along with improved slump resistance comprises a selectively hydrogenated monoalkenyl arene-diene multiblock copolymer, a selectively hydrogenated monoalkenyl arene-diene two block copolymer, a tackifying resin compatible with the hydrogenated diene blocks and a high softening point monoalkenyl polymer block compatible resin.

Description

SPECIFICATION Sealant composition having improved slump resistance The invention relates to a sealant-composition. More particularly, the invention relates to a sealant composition based on two different block copolymers, a midblock tackifying resin and a high softening point resin.

Various sealant compositions have been disclosed in the prior art. The basic patent in this field is Harlan, U.S. Patent No. 3,239,478, which shows combinations of styrene-diene block copolymers with tackifying resins and the like to produce a wide spectrum of sealants and adhesives. However, in the past it has not been possible to prepare transparent sealant compositions which meet all the desired characteristics of a good sealant. At present, the market for weatherable, transparent sealants is dominated by 100% solids, chemically curing silicone sealants. While silicone sealants give excellent performance in a wide range of applications, transparent silicone sealants are actually quite turbid and are very expensive. Sealants made with non-hydrogenated styrenediene block copolymers, such as those disclosed in U.S.Patents Nos. 4,101,482, 4,101,483 and 4,101,484 lack the necessary oxidative and UV stability. Sealants based on commercially available hydrogenated styrene-diene block copolymers, such as those disclosed in U.S. Patent No. 4,113,914, also have a shortcoming in that they contain inorganic filler and therefore cannot be made transparent.

An improved sealant composition was disclosed in U.S. Patent No. 4,296,008. That sealant was based on a specific block copolymer component having low molecular weight polystyrene end blocks, a midblock compatible resin and a silane coupling agent. One of the distinctive features of such sealants was the good UV and oxidative stability along with a cohesive failure mechanism. However, such sealants do not possess sufficient resistance to slump at higher ( < 500 C) temperatures which is necessary for applications such as architectural glazing.

A new sealant composition has now been found that possesses a significantly improved balance of properties.

The present invention broadly comprises a sealant possessing excellent UV and oxidative stability along with much improved slump resistance. Specifically, the present invention comprises: a) about 50 to about 90 parts by weight of a multiblock copolymer having at least two end blocks A and at least one midblock B wherein the A blocks are monoalkenyl arene polymer blocks and the B blocks are substantially completely hydrogenated conjugated diene polymer blocks, the number average molecular weight of the A blocks being between about 7,100 and about 15,000, and the monoalkenyl arene content of the multiblock copolymer being between about 20% and 40% by weight;; b) about 50 to about 10 parts by weight of a CD two block copolymer where the C block is a polymonoalkenyl areneblock having a number average molecular weight of between about 15,000 and 55,000 and the D block is a substantially completely hydrogenated conjugated diene polymer block having a molecular weight between about 30,000 and about 120,000, wherein the total of the parts by weight of said multiblock copolymer plus the parts by weight of said two block copolymer employed in said sealant composition equals 100 parts by weight; -c) about 10 to about 100 parts by weight of a high softening point resin compatible with block A of said multiblock copolymer and having a softening point above about 11 00C; and d) about 75 to about 250 parts by weight of a tackifying resin compatible with block B of said multiblock copolymer.

The approach taken in the sealant of this invention is to base the sealant on a blend of a multiblock copolymer, which has high cohesive strength and high elasticity, and a two block copolymer, which has low cohesive strength and little elasticity. This allows control of the cohesive strength ofthe sealant relatively independently of the resin components in the sealant. Because of the relatively high percentage of monoalkenyl arene polymer in the block copolymers, relatively high concentrations of high softening point A block compatible resin can be included in the sealant without sacrificing clarity. This allows preparation of transparent sealants which have good slump resistance at higher (700 C) temperatures.The resulting excellent balance of properties was not expected since the addition of the two block copolymer would not be predicted to improve slump resistance. In fact, the addition of the two block copolymer would normally be predicted to result in poorer slump resistance.

The advantage of clarity in the sealant is that one does not need to match the colour of the sealant to the colour of the substrate since the colour of the substrate will show through the sealant.

In a preferred embodiment, the B block is a hydrogenated polybutadiene block and the D block is a hydrogenated polyisoprene block.

The multiblock copolymers employed in the present invention may have a variety of geometrical structures, since the invention does not depend on any specific geometrical structure, but rather upon the chemical constitution of each of the polymer blocks. Thus, the structures may be linear, radial or branched so long as each multiblock copolymer has at least two polymer end blocks A and at least one polymer mid block B as defined above. Methods for the preparation of such polymers are known in the art. Particular reference will be made to the use of lithium based catalysts and especially lithium-alkyls for the preparation of the precursor polymers (polymers before hydrogenation). U.S. Patent No.

3,595,942 not only describes some of the polymers of the instant invention but also describes suitable methods for their hydrogenation. The structure of the polymers is determined by their method of polymerization. For example, linear polymers result by sequential introduction of the desired monomers into the reaction vessel when using such initiators as lithium-alkyls or dilithiostilbene and the like, or coupling a two segment block copolymer with a difunctional coupling agent. Branched structures, on the other hand, may be obtained by the use of suitable coupling agents having a functionality with respect to the precursor polymers of three or more. Coupling may be effected with coupling agents such as mono or dihaloalkanes or -alkanes and divinyl benzenes as well as certain polar compounds such as silicon halides, siloxanes or esters of monohydric alcohols with carboxylic acids.The presence of any coupling residues in the polymer may be ignored for an adequate description of the polymers forming a part of the compositions of this invention. Likewise, in the generic sense, the specific structures also may be ignored. The invention applies especially to the use of selectively hydrogenated polymers having the configuration before hydrogenation of the following typical species: polystyrene-polybutadiene-polystyrene (SBS) poly(alpha-methylstyrene)-polybutadiene-poly(alpha-methylstyrene).

It will be understood tnat both blocks A and B may be either homopolyrner or random copolymer blocks as long as each block predominates in at least one class of the monomers characterizing the blocks and as long as the A blocks individually predominate in monoalkenyl arenes and the B blocks individuaily predominate in conjugated diene units. The term monoalkenyl arene will be taken to include especially styrene and its analogs and homologs including alphamethylstyrene and ringsubstituted styrenes, particularly ring-methylated styrenes. The preferred monoalkenyl arenes are styrene and alpha-methylstyrene, and styrene is particularly preferred. Conjugated dienes include specifically butadiene and isoprene, with butadiene being preferred.When the monomer employed is butadiene, it is preferred that between about 35 and about 65 mol percent of the condensed butadiene units in the butadiene polymer block have 1,2 configuration, as measured by a standard NMR technique. Thus, when such a block is hydrogenated, the resulting product is, or resembles, a regular copolymer block of ethylene and butene-1 (EB). Most preferably, the 1 ,2content is about 45%. If the conjugated diene employed is isoprene, the resulting hydrogenated product is or resembles a regular copolymer block of ethylene and propylene (EP).

The average molecular weights of the individual blocks are very important aspects of the present invention and may vary only with certain limits. In most instances, the monoalkenyl arene A blocks will have number average molecular weights in the order of 7,100 to 15,000, preferably about 7,500 to about 10,000, while the conjugated diene blocks either before or after hydrogenation will have average molecular weights in the order of about 21,000 to about 120,000, preferably 28,000 to 78,000. The total average molecular weight of the multiblock copolymer is typically in the order of 35,000 to about 150,000, preferably from about 42,000 to about 100,000, and depends upon geometry of the polymer. These molecular weights are most accurately determined by tritium counting methods or osmotic pressure measurements.The diene block molecular weight is effectively set by the limitations on monoalkenyl arene block molecular weight and the weight percentage of monoalkenyl arene along with the geometry of the copolymer.

The proportion of the monoalkenyl arene blocks should be between about 20 and 40% by weight of the multiblock copolymer, preferably between about 25% and 35% by weight.

The C-D two block copolymer is also prepared via organolithium catalysis. Prior to hydrogenation the C block is a monoalkenyl arene polymer block and the D block is a conjugated diene polymer block.

Conjugated dienes include specifically butadiene and isoprene, with isoprene being preferred. When the diene employed is butadiene it is preferred that between about 35 and about 65 mol percent of the condensed butadiene units in the butadiene polymer block have 1,2 configuration, as measured by a standard NMR technique. Preferably the C block is a polystyrene block. The average molecular weight of the C block is between about 15,000 and 55,000, preferably between about 25,000 and 45,000.

The average molecular weight of the D block is between about 30,000 and 120,000, preferably between about 60,000 and 110,000. The weight ratio of C block to D block is between about 1:8 and about 1 :1, preferably about 1 :3 and about 1:1.5.

Hydrogenation of the precursor block copolymers is preferably effected by use of a catalyst comprising the reaction products of an aluminium alkyl compound with nickel or cobalt carboxylates or alkoxides under such conditions as to substantially completely hydrogenate at least 80% of the aliphatic double bonds while hydrogenating no more than about 25% of the alkenyl arene aromatic double bonds. Preferred block copolymers are those where at least 99% of the aliphatic double bonds are hydrogenated while less than 5% of the aromatic double bonds are hydrogenated.

The block copolymer component by itself lacks the required adhesion. Therefore, it is necessary to add an adhesion promoting or tackifying resin that is compatible with the elastomeric B block. A common tackifying resin is a diene-olefin copolymer of piperylene and 2-methyl-2-butene having a softening point of about 950C. This resin is available commercially under the tradename Wingtack 95, and is prepared by the cationic polymerization of 60% piperylene, 10% isoprene, 5% cyclopentadiene, 1 5% 2-methyl-2-butene and about 10% dimer. See U.S. Patent No. 3,577,398. Other tackifying resins of the same general type may be employed in which the resinous copolymer comprises 20--80 weight percent of piperylene and 80-20 weight percent of 2-methyl-2-butene.The resins normally have softening points (ring and ball) between about 800C and about 11 50C. Other adhesion promoting resins which are also useful in the compositions of this invention include hydrogenated resins, esters of rosins, polyterpenes, terpenephenol resins, and polymerized mixed olefins. For best UV resistance, it is preferred that the tackifying resin be a saturated resin, e.g., a hydrogenated dicyclopentadiene resin such as Excorez 5380 resin made EXXON or a hydrogenated polystyrene or hydrogenated polyalphamethylstyrene resin such as XPS 657 resin made by Hercules. Part or all of this resin may be replaced by a low molecular weight polyisobutene oligomer such as Indopol H-1 500 or an extender oii substantially free of aromatic or other unsaturated ring structures, such as TUFFLO 6056 (both ex.

ARCO).

The amount of adhesion promoting resin employed varies from about 75 to about 250 parts by weight, preferably between about 125 to about 200 parts by weight.

Another component of the present invention is a high softening point, A block-compatible resin.

Compatibility is judged by the method disclosed in U.S. Patent No. 3,91 7,607. The resin must have a softening point above about 11 OOC, as determined by ASTM method E 28, using a ring and ball apparatus. Useful resins include coumarone-indene resins, polystyrene resins, vinyl toluene-alphamethylstyrene copolymers, and polyindene resins. Much preferred is a poly(alpha methylstyrene)-resin.

The amount of arene-block-compatible resin varies from about 10 to about 100 parts by weight.

An optional component of the present invention is a silane coupling agent. These silanes are important in improving the water resistance of the bond between the sealant composition and glass or other substrates. In general, these silane coupling agents are ambifunctional molecules with the unique ability to improve the bond between organic polymers and many mineral surfaces; and to retain composite properties after prolonged exposure to moisture.

Chemically, silane coupling agents are hybrid materials that possess the dual functionality of an organic reactive group at one end of the molecule and the inorganic silanol functionality on the opposite end. Generically, all silane coupling agents can be represented by the formula (RO)3Si X. In this formula, X represents a functional organic group such as chlorine, mercaptan, amines or diamines, epoxy, vinyl, or methacrylate. These reactive organic groups are attached through a stable carbon linkage, usually a (CH2)a group, to the silicon. At the silicon or inorganic end of the molecule are hydrolyzable alkoxy or acetoxy groups (RO). These methoxy or acetoxy groups on silicon undergo rapid hydrolysis in aqueous solutions, or upon exposure to moist air to form the reaction 2SiOH (silanol) functionality.Thus, two quite different chemically reactive groups are at opposite ends of the same silane coupling agent molecule.

When employed, the amount ot silane coupling agent varies from 0.1 parts by weight to about 10 parts by weight, preferably about 0.5 to about 2.5 parts by weight. When the amount of silane coupling agent is between about 0.25 and about 2.5 parts by weight, the sealant retains its translucency and clarity.

The compositions of this invention may be modified with supplementary materials including pigments, fillers and the like as well as stabilizers and oxidation/UV stabilizers.

For some applications it may be desirable to apply the sealant as a hot melt. In that situation, no additional solvents or carriers are required. However, in other situations it is desirable to employ the sealants at ambient temperatures. In that case additional solvents or carriers are added. Suitable carrier materials include organic solvents such as hexanes, naphthas, and toluene, ester solvents such as ethyl acetate and propyl acetate and ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone. The amount of carrier added varies from 0 to about 400 parts by weight, preferably about 0 to about 200 parts by weight.

The invention is further illustrated by means of the following illustrative embodiment, which is given for the purpose of illustration only and is not meant to limit the invention to the particular components and amounts disclosed.

Illustrative embodiment I In Illustrative Embodiment I, various sealants are prepared. Sealants numbered 1-7 and 11 are outside the invention, while sealants numbered 8-10 are according to the invention. The various components are defined below.

Tradename Composition KRATON(!) GX-1 657 A selectively hydrogenated SBS block copolymer according to U.S.

4,296,008.

KRATON G-1 652 A selectively hydrogenated SBS (ABA) block copolymer according to the present invention.

KRATON GX-1701 A selectively hydrogenated Si (CD) two block copolymer according to the invention.

ARKON P-85 A fully saturated hydrocarbon resin substantially free of aromatic or other unsaturated ring structures and with a softening point of about 850C.

KRlSTALEX 3085 An aromatic resin, mostly compdsed of polymerized alpha methyl styrene and with a softening point of about 850C.

KRISTALEX 3100 An aromatic resin, mostly composed of polymerized alpha methyl styrene and with a softening point of about 100 C.

KRISTALEX 1120 An aromatic resin, mostly composed of polymerized alpha methyl styrene and with a softening point of about 1 200C.

XPS 532 An aromatic resin, mostly composed of polymerized alpha methyl styrene and with a softening point of about 1400 C.

Silane A-1 89 Gamma-mercaptopropyltrimethoxysilane Cabosil Fumed colloidal silica The various formulations all contained about 2.5 to about 3.1 parts by weight of a standard antioxidant plus U.V. stabilizer package. The formulations and results are presented below in Table I:: Table I Compositions and properties of sealant formulations Composition 1 2 3 4 5 6 7 8 9 10 11 KRATON GX-1657 100 100 100 100 100 67 - - - - KRATON G-1652 - - - - - - 67 67 67 67 67 KRATON GX-1701 - - - - - 33 33 33 33 33 33 ARKON P-85 167 167 167 167 167 167 167 167 167 167 167 KRISTALEX 308511 67 - - - 67 - - - - - KRISTALEX 310021 - 67 - - - 67 67 - - - KRISTALEX 112031 - - 67 - - - - 67 - 33 XPS 53241 - - - 67 - - - - 67 - Silane A-189 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.1 1.2 Toluene 120 120 120 120 120 120 120 120 120 107.5 95.5 Cabosil - - - - 6 - - - - - Table I (cont'd) Compositions and properties of sealant formulations Properties5) Clarity Clear Clear Opaque Opaque Clear Clear Clear Clear Clear Clear Clear Slump after 1 wk. at 50 6) 3 - - 3 1 1 0 0 0 0 Slump after 1 wk. at 70 6) 3 - - 3 2 2 0 0 0 0 Peel Strength Orig. (pli) 49 53 - - 41 33 48 44 30 43 27 Peel Strength, After 1 wk. 50 54 - - 53 39 48 44 37 44 30 water soak (pli) Hardness, Shore A 20 21 - - 22 18 25 26 31 15 13 1) Softening point (manufacturers data) 85 C.

2) Softening point (manufacturers data) 100 C.

3) Softening point (manufacturers data) 120 C.

4) Softening point (manufacturers data) 140 C.

5) Measured on dry samples, except for viscosity. Clarity was judged on samples cost from 50 solids solutions in toluene.

6) Measured on "x"x2" sample with two of the 2"x" faces adhered to vertical aluminium plates and the other two horizontal. 0=no slump, 1=some slump, 2=severe slump, 3=completely melted.

Clear sealants for applications as architectural glazes have the following requirements: 1) High solids content ( > 70%).

2) Clarity.

3) Elasticity, with a hardness of about 25 Shore A.

4) Resistance to slump of the dried sealant at higher ( > 500C) temperatures.

Formulations which meet the first three requirements using blends of KRATON GX-1657, a midblock compatible resin (ARKON P-85, ex. Arakawa) and an end block compatible resin (KRISTALEXt) 3085, ex. Hercules) were made. However, these formulations slumped at higher temperatures and so could not meet the last requirement. KRISTALEX 3085 has a softening point of 850C and when it was replaced by a higher softening point analog, KRISTALEX 3100, clarity was retained but the slump resistance was not improved (compositions &num;1 and &num;2 in Table I). When still higher softening point resins were used (compositions &num;3 and &num;4) the products were no longer clear.

Cabosil gave no improvement in slump resistance (composition &num;5), but when one third of the KRATON GX-1657 was replaced by an S-EP polymer with a very high molecular weight polystyrene segment (composition &num;6), slump resistance, although still unsatisfactory, was improved. This product was too soft for the application, probably because about half the total block polymer content was nonload bearing two block, either S-EP, or S-EB from the KRATON GX-1657. When this KRATON GX1657 was replaced by a stronger, harder material containing no S-EB (KRATON G-1 652), hardness was increased (composition &num;7), but slump resistance was unchanged. However, it was now possible to add very high softening point resins while maintaining clarity (compositions &num;8 and &num;9) and these gave the desired combination of slump resistance and clarity.

In further work it was shown that the high softening point resin could be reduced in amount (&num;10) or omitted (&num;11) while still retaining slump resistance, but the products were soft and hard to process.

Claims (8)

Claims

1. A sealant composition possessing excellent oxidative and UV stability along with improved slump resistance comprises: a) about 50 to about 90 parts by weight of a multiblock copolymer having at least two end blocks A and at least one midblock B wherein the A blocks are monoalkenyl arene polymer blocks and the B blocks are substantially completely hydrogenated conjugated diene polymer blocks, the number average molecular weight of the A blocks being between about 7,100 and about 15,000, and the monoalkenyl arene content of the multiblock copolymer being between about 20% and about 40% by weight;; b) about 50 to about 10 parts by weight of a CD two block copolymer where the C block is a polymonoalkenyl arene block having a number average molecular weight of between about 1 5,000 and about 55,000 and the D block is a substantially completely hydrogenated conjugated diene polymer block having a molecular weight between about 30,000 and about 120,000; wherein the total of the parts by weight of said multiblock copolymer plus the parts weight of said two block copolymer employed in said sealant composition equals 100 parts by weight; c) about 10 to about 100 parts by weight of a high softening point resin compatible with block A of said multiblock copolymer and having a softening point above about 11 00C; and d) about 75 to about 250 parts by weight of a tackifying resin compatible with block B of said multiblock copolymer.

2. The composition of claim 1 also containing about 0.1 to about 10 parts by weight of a silane coupling agent.

3. The composition of claim 1 wherein said A blocks and said C blocks are polystyrene blocks.

4. The composition of claim 1 wherein said B blocks are substantially completely hydrogenated polybutadiene blocks.

5. The composition of claim 1 or claim 4 wherein said D block is a substantially completely hydrogenated polyisoprene block.

6. The composition of claim 1 wherein said tackifying resin is a mixture of two or more resins.

7. A hot melt, transparent sealant composition according to claim 1.

8. A solvent-containing transparent sealant composition according to claim 1.