CA2023567A1

CA2023567A1 - 2-part urethane composition for improved adhesion on cold rolled steel

Info

Publication number: CA2023567A1
Application number: CA 2023567
Authority: CA
Inventors: Asok Sengupta
Original assignee: Individual
Current assignee: 3M Co
Priority date: 1989-10-16
Filing date: 1990-08-17
Publication date: 1991-04-17
Also published as: JPH03157452A

Abstract

ABSTRACT

A polyurethane composition comprising (A) the reaction product of a polyisocyanate and a mixture of (i) a polycaprolactone polyol and (ii) a hydrophobic polyol, (B) a silane coupling agent, and (C) a thermoplastic resin is provided. The molar equivalent ratio of the isocyanate groups of polyisocyanate to the hydroxyl groups of the mixture is in the range of from 1.1:1 to 10:1.

Description

2 ~ 7 PAl!EN~
FN 4 4 3 3 3 LlSA 7A

2-PART tlRETHANE COMPOSITION FOR IMPROVED ADHE5ION ON COLD
ROLLED STEEL

This invention relates to polyurethane compositions.
1~

Polyurethane compositions are provided either as one-part or two-part compositions. The one-part composi-tions are usually moisture-curable. Thus, while they are very useful, their moisture sensitivity creates some prob-lems in storage and handling. Moisture sensitivity is particularly troublesome when less than an entire container of the materi~ls is needed to complete a ~ob. Although it is possible to reseal a partially used container, the effor~
~ required is time consuming and expensive~ Additionally, when a small container of such a one-part composition is opened, it is often virtualIy impossible to satisfactorily reseal it.
Moisture sensitivity presents yet another problem.
~ecause of the dependence o .~uch one-part compositions upon ambient molsture to cure, their cure rate cannot be accu~
rately predicted. For example, in high humidity environ-ments, the composition will ge~erally cure satis~actorlly in a short period of time. However, in low humidity : 30 enYironments i.t is usually necessary to add moisture to achiave a satisfactory rate of cureO
Such one-part compositions also often contain organic solvents in order to render them ~as~ to handle.
This of course presents pollution problems and limits their usefulness to those substrates not susceptible to degradation by such solvents. While the organic solvénts can usually be eliminated from these compositions, this , .-- .
, :

2023~S7 gener~lly raises the viscosity and limits the methods by whlch they can be applied.
Examples of one-part, moisture-curable polyurethane compositions include those shown in U.S.

3,776,869 to Sirota and U.S. 4,539,345 to Hansen. The Sirota patent discloses a polyurethane resin/terpene-phenolic resin/solvent composition. The Hansen patent discloses an isocyanate prepolymer/terpene-phenol~c resin/silane adduct/solvent composition.
Two-part urethane compositions provide a method of avoiding at least some of the above problems. Such compositions exhibit ini~ial good adhesion to a substrate.
They also exhibit good strengths as exemplified by their overlap shear strength.
However, upon aging, these compositions exhibit a substantial reduction in adhesion and strength due to the effects of various environmental factors such as humidity.
Examples of two-part polyurethane compositions include those disclosed in U.S. 4,507,44~; U.S. 4,503,1897 U.S. 4,206,299; U.S. 4,076,89~; U.S. 4,305,863; U.~.
3,766,131; U.S. 3,900,686; U.5. 4,193,909, U.S. 3,886,206;
U.S. 3,886,216; U.S. 4,582,889 and Canadian Patent 1,195,337. None of these patents disclose the two part compositions of this invention.

The present invention provides, in one aspect, a two-part composition which ~orms a polyurethane material upon curing and which has initial high bond strength and which retains a substantial level of its initial bond strength upon aging under rigorous environmental conditions.
This composition comprises (I) an organic polyisocyanate as a first component, and ~II) a mixture of active hydrogen containg components made up of (i) a polycapzolactone polyol, and (ii) a hydrophobic polyol a~ a second componentO
A silane coupling agent, and a thermoplastic resin selected from terpene resins and resins having an actlve hydrogen group thereon are also included as a part of the two part . . .

' ' ' ., ' , .

- ~023~

composltion. Preferably the polyisocyanate is provided as the only ingredient of the first component while the remaining ingredients are mixed toge~her and provided as the second component.
As used herein "hydrophobic polyol" means a polyol whose moisture content will increase by no more than 0.1%
(preferably no more than 0.05% most preferably no more than 0.03%) when exposed to 66% relative humidity at 21C for 7 hours. Thus, for example, if a polyol has an initial moisture content of 0.1%, it will have a final moisture content of no more than 0.2~ after exposure to the above conditions. Moisture content is measured by the Karl Fisher method using a Metrohm 652-RF-Coulometer from Sybron/Brinkmann Instruments Co., a division of sybron Corp.
of Westbury, New Yor~. "Acid number", as used herein, refers to the number of milligrams of KO~ needed to neutralize one gram of polyol. "Hydroxyl number", as used herein, refers to the number of miligrams of KOH having the same hydroxyl content as one gram of polyol. "NCO
equivalent weight", as used herein, refers to the quotient obtained by dividin~ the number average molecular weight of an isocyanate by the number o~ reactive isocyanate groups therein~
The cured polymer resulting from the reaction oX
the above-ingredients constitutes another embodlment of the invention. The cured polymer has excellent adhe ion to unprimed metal, glass and concrete. And, when exposed to conditions of high humidity, the cured polymer retains a substantlal level (e.g., at least 75~) of its initiAl bond strength. The composition of the invention can also contain 3~ fillers, including glass bubbles without suf~ering a loss in adhesive strength.

In the practice of the present invention, the polyisocyanate is an organic polyisocyanate which contains at least two isocyanate groups. Useful polyisocyanates include both aliphatic and aromatic polyisocyanates.
.

. ,. .,,,, .,, .. . .. . , ., . - .. .
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- 2023~7 Preferably they contain at least two isocyanate g~oups per molecule. Additionally, it is preferred that the polyisocyanate not crystallize when stored a~ 0C for several hours. Moreover, the polyisocyanate may be a monomeri~ polyisocyanate, a polymeric polyisocyanate, or an isocyanate-terminated prepolymer.
Examples of useful aromatic polyisocyanates include 2,4-toluene diisocyanate (TDI), mixtures thereof with 2,6-toluene diisocyanate (usually about 80/20 by weight, respectively), 4,4-diphenylmethane diisocyanate (MDI), m-phenylene diisocyanate, - 3,3'-dimethyl-4,4'-diphenylene diisocyanate, 3,3'-dimethoxy-4,4'-bisphenylene diisocyanate, 3,3'-diphenyl-4,4' biphenylene diisocyanate, 4,4'-biphenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 3,3'-dichloro-4,4'-biphenylene diisocyanate, and 1,5-naphthalene diisocyanate. The diisocyanates may contain other substitutents, although those which are free from reactive groups other than the two isocyanate groups are ordinarily preferred. In the case of the aromatic compounds, the isocyanate groups may be attached either to the same or to differen~ rings.
Useful aliphatic polyisocyanates include ethylene diisocyanate, ethylidene diisocyanate, isophorone diisocyanate (IPDI), propylene-1,2-diisocyanate, butylene-1,3-diisocyanate, tetramethylene dlisocyanate, hexamethylene diisocyanate and decamethylene diisocyanate are suitable as ~re alicyclic compounds such as 1,2- and 1,4-cyclohexylerle diisocyanates, and 4,4'-methylene-bis-~cyclohexylisocyanate).
Examples of isocyanate-terminated prepolymers useful in the invention contain sufficie~t isocyanate groups to be ~ured or polymerized upon exposure to appropriate conditions. Suitable prepolymers of this type are described in a number of p~blications including ~irk-Othmer "Encyclopedia of Chemical Technolog~," 3rd ~dition~ 23, 576-608 (1983), and include polyisocyante prepolymers based on MDI such as Mondur~MXP-744 from Mobay Chemical Company.

.

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202~

Also, isocyanate--functional derivative(s) of TDI
and MDI may be used, such as liquid mixtures o~ the isocyanate-functional derivative with melt;ng point modifiers (e.g., mixtures of MDI with polycarbodiimide adducts such as "Isonate 143L", commercially available from Dow Chemical Co., and "Mondur CD", commercially available from Mobay Chemical Corp.~; polymeric diphenylmethane diisocyanates (e.g., "PAPI", and the series "PAPI 20"
through "PAPI 901", commercially available from Dow Chemical Co., "Mondur MR", "Mondur MRS", and Mondur MRS-10", commercially available from Mobay Chemical Corp~, and "Rubinate M", commercially available from ICI Chemicals, Inc.); and blocked isocyanate compounds formed by reacting aromatic isocyanates or the above-described isooyanate functional derivatives with blockins agents such as ketoximes and like. Such blocked isocyanate compounds will, for convenience, be regarded herein as isocyanate-functional derivatives of MDI or TDI.
The prepolymers are made using conventional methods. Typically, they are prepared by reac~ing an excess of one or more polyisocyanates with one or more polyols to produce a substantially linear prepolymer having residual isocyanate functionality.
The polyisocyanate of the invention is present in a quanti~y such that the isocyanate to hydroxyl molar equivalent ratio (NCO/OH) is from 1:1 to about 10~ re-~erably, th~ polyisocyanate i5 present in an amount su~-ficient to provide an NCO/OH ratio in the range o~ 1 to 1.4:1 and more preferably a ratio of 1.1:1. When the amount of polyisocyanate present is such that the NCO/OH ratio is 30 above 1.4:1, the initial overlap shear strength of the cured composition is much improved hut the complete cure takes lonyer and requires heat to achieve. At levels of isocy-anate such that the NCO/OH ratio is below 1:1, the initial overlap shear strength of the cured composition is lower.
3 The active hydrogen-containin~ component contains polyols having low acid numbers. These polyols comprlse two or more hydroxyl groups and have a backbone containing for example, aliphatic, olefinic, ether, ester, thioether, urethane, or urea linkages. The polyol~ ~re monomers, oligomers or polymers, but preferably are oli~omers or polymers.
At least one of the polyols is hydrophobic~ having S a low a~finity for moisture, an acid number less than 0.8, and a number average molecular weight preferably between about 900 and 2400. The hydrophobic polyols preferably have 2 to 3 hydroxyl groups per molecule. Expressed in terms of hydroxyl number, the hydrophobic polyols preferably have a hydroxyl number between about 45 and 1~8.
Suitable hydrophobic polyols for use in this invention include polytetramethylene oxide glycols, propylene oxide-terminated polypropylene glycols, propylene glycols, hydroxyl-terminated polybutadienes,~aliphatic glycols, fatty alcohols, and functionalized triglycerides ~e.g., castor oil). Mixtures of hydrophobic polyols can be used if desired.
Examples of useful hydrophobic polyols are "QO
Polymeg" 650, 1000, ~r 2000 polytetramethylene oxide glycol (commercially available from Quaker Oats Co.), "Teracol 650, 1000 and 2000" polytetramethylene oxide glycol (commercially available from E. I. duPont de Nemours and Co.~ Inc.~, "Niax" series "PCP", and "Capped Polyols", as well as "Polymer Polyols", and "Poly bd" hydroxyl-terminated ~5 polybutadienes (com~ercially available from ~tocheYn Inc.).
Preferably these materials are ~ree from ethylene oxide units.
~ preferred subclass of hydrophobic polyols for use in this invention are the unctionalized triglyceride oils, partioularly those containing hydroxyl group functionality. Examples of the~e materials are castor oil~
Lesquerella, Palmeri and other wild plant oils.
The hydrophobic polyol comprises from about 80 to 60 parts by weight of the active hydrogen~containi~g component, preferably from about 75 to about 65 parts and most preferably 70 to 65 parts by weight. A particularly preerred composition employs 68 parts by weight of the ~6-. , . . -' : , ~. : ' .'' '''' ' ': -: , ~: : ' 202~7 hydrophobic polyol.
The active hydrogen containing component mixture also contains a polyester polyol, preferably a polycaprolactone polyol, having a number average molecular weight of about 200 to about 900, preferably from about 300 to about 600, and an acid number of less than 0.3. For compositions wherein the molecular wei~ht of the polycaprolactone is greater than 900, the initial adhesion and strength is reduced. At molecular weights below 300, the initial adhesion of the resultant cured composition improves, but the composition is less flexible. The polycaprolactone polyol preferably has at least 2 hydroxyl groups per molecule, most preferably at least 3.
Suitable commercially available polycaprolastone polyols include "Tone" series polyols (commeroially available from Union Carbide Corporation).
The polyes~er polyol is present in the active hydrogen containing component mixture from about 20 to about 40 parts by weight, preferably from about 25 to about 35 parts, and most preferably from about 30 to about 35 parts by weight. A particularly preferred composition employs 32 parts by weight o the polyester polyol.
The silane coupling agent useul in the composition of the invention includes mercaptosilanes, primary and secondary aminosilanes, epoxy silanes and acrylic silanes. Epoxy silanes are preerred. Suitable commercially available silane compounds include "A-151'i vinyltriethoxysilane, 'IA-153" phenyltriethoxysilane, "A-162"
methyltriethoxysilane, "A-174" acrylato tris methoxy silane, "A-186" Beta-3,4-(epoxycyclohexyl)ethylt r imethoxysilane~
"A-187" gamma-glycidoxypropyltrimethoxysilane, "A-l~9"
gamma~mercaptopropyltrimethoxysilane, "A-llO0"
gamma-aminopropyl-triethoxy~ilane (all commercially available from Union Carbide Corporation), and "Z-6070"
methyltrimethoxysilane, "Z-6071" phenyltrimethoxysilane, "Z-6072" dimethyldimethoxysilane, "Z-6073"
methylphenyldimethoxysilane, "Z-6074"
diphenyldimethoxysilane, "Z-6020" N-2 0 2 3 ~ 6 7 (trimethoxysilylpropyl)ethylenediamine, "XZ-2-2023" N-(dimethoxymethylsilylisobutyl)ethylenediamine, "Z-6030"
~amma-methacryloxypropyltrimethoxysilane, "Z-6040"
gamma-glycidoxypropyltrimethoxysilane, and "XZ-8-0999"
gamma- chloropropyltrimethoxysilane (all commercially available from Dow Corning Corporation).
The silane compounds typically are obtained as clear liquids. They can be used neat or in a suitable solvent. Suitable solvents are non-reactive organic materials such as toluene, naphtha, methyl ethyl ketone, and the like. Preferably they are used neat in the compositions of the invention.
The amount of silane compound is adjusted to provide desired handling characteristics before cure and a desired level of adhesion (measured initially~and aft2r exposure to environmental conditions) after cure. ThiS
amount will vary depending upon the particular ingredients present in the composition, and the substrate and environmental conditions with which the composition will be used. In general, the amount of silane compound present is from about 0.005 to about 10 parts by weight of silane compound per 100 parts active hydrogen containing component mixture, preferably about 0.5 to 4 parts o silane compound per 100 parts active hydrogen containing component mixture, and most preferably, about 1 to 2 parts by weight.
The thermoplastic resin o~ the instant inv~ntion can be a terpene resin or a resin having an active hydrogen functional group thereon, or mixtures thereo~. Suitable commercially available terpene resins include "Piccolyte A"
series, e.g. "A-85", A-100", "A-125", and "A-135" resins;
nPiccolyte S" series, e.g~ "5-100", "S-115", "S-125", and "5-135" resins; and "Piccolyte C" series, e.g. "C-100l', "C-125", and "C-135" resins (~11 commercially available from ~ercules Incorporated). Examples of resins having an active hydrogen functional group thereon that are useful in the compositions of the invention include terpene-phenolic resins such as 'IPiccofyn'' series "A-100", "A-115", T-125", and "A-135" resins (commercially available from Hercules _~_ . ' , , . ~023~67 Incorporated); hydrogenated rosin esters such as "Foral"
series "85" and "105" rosins (commercially available from Hercules Incorporated); phenolic-modified rosin esters, and polymerized rosi~ esters.
The thermoplastic resins typically are in the form of a flaked or lumpy solid. To combine them with the ingredients of the invention, it is frequently convenient to crush the solid into powder form. In the two part composition of the invention, the thermoplastic resin in powder form is typically added to the active hydrogen containing component mixture and then heated with mixing until the resin completely dissolves and/or a homogeneous mixture is achieved. This ~ypically occurs at from about 70C to about 115C.
The amount of thermoplastic resin preferably is adjusted to provide desired handling characteristics before cure and a desired level of adhesion tmeasured initially and after exposure to humidity conditions) after cure. This amount will vary depending upon certain properties of the particular resin employed, e.g. solubility of the resin in the active hydrogen containing component mixture and the amount of active hydrogen funct;onality of the resin having an active functional group thereon. The amount of thermoplastic resin employed in the invention is from about 1 to about 20 parts by weight resin per 100 parts by weight active hydrogen containing component mixture, preferably about 1 to about 10 parts by wei~ht, and most preerably about 5 to 6 parts by weight per 100 parts by weight o~ the active hydrogen containing component mixture. Compositions containing amounts of thermoplastic resin above 20 parts result in cured compositions having lower initial shear strengths.
The composition of the invention can also contain a urethane-forming catalyst such as those well known to persons skilled in the art. Suitable catalysts include organometallic compounds such as dibutyltin dilaurate, tertiary amines such as "Dabco HB", and mixtures thereof.
Typically, the amount of catalyst present in the invention 2~2~7 is small, usually less than 0.5 parts by welghk catalyst per 100 parts of active hydrogen containing camponent m1xture.
In addition, the compositions of the invent~on can contain other adjuvents to provide desired handling and curing characteristics. Suitable adjuvants include reinforcing fillers, extending fillers, drying agents, inhibitors, thixotropic agents, UV absorbers, UV
stablilizers, antioxidants, colorants, surfactants, wetting aids and dispersants. The amounts and types of adjuvants will vary depending upon the particular ingredients present in the composition, th~? substrate, and the environmental conditions under which t.~e composition will be used. Such adjuvants are typically selected and their amounts adjusted emperically based on techniques and tests well known to those skilIed in the art.
The compositions of the invention can be put up in packages in accordance with techni~ues known to those skilled in the art. Suitable packages include, for example, cans, drums, double barrel syringes, tubes, and the like.
The composition of the invention may be applied by any suitable technique such as spray, dip, brush, roll coat, trowel, and the like. Preferably, the composition is spray applied using two-component spray equipment with the , isocyanate component, Part A, at ambient temperature and the remaining ingredi~nts, Part B, at a temperature o~ up to 66C.
The compositions of the invention can be employed in any application where a high performance adhe~ive, ~ coating, or sealant is desired~ ~t is especially useful where the bonded, coated, or sealed part will experience a high humidity enviromnent. The compositions of the invention can be applied to a variety o~ articles and substrates, such as articles or substrates of metal, plastic, wood, leather, masonry, textiles, glass, and the like.
The following examples will illustrate the practice of this invention, but are not intended to limit , ~2~67 its scope. All parts are parts by we~ght unless otherw~se specified.

_ . _ _ _ Two part compositions according to the invention were prepared in which Part A comprised a polyisocyanate and Part ~ comprised ~i) a mixture of a polycaprolactone polyol and a hydrophobic polyol, (ii) a silane coupling agent, and (iii) a thermoplastic resin. Part A was stored in a sealed container under nitrogen until needed. Part B was prepared by mixing the following ingredients at a suitable temperature in a lined can until a uniform mixture was obtained.
Table A lists the nature of the ingredients employed in the compositions. Table B lists the compositions of each Example and the mix ratios employed in the subsequent testing. All quantities are in parts by weight unless otherwise noted.

~5 ~` ~023~7 TABLE~; A

~ondurTMXP-744 (Mobay Chemical Co. polyisocyanate, equivalent weight of 187, NCO content of 22.5 - 23.5) 5 Desmodur MW ( Mobay Chemical Co.
dicyclohexylmethane-4,4'-diisocyanate) Isonate 143L (Dow Chemical Co. polyisocyanate, NCO
equivalent weight about 144.5) ToneTM0305 (Polycaprolactone polyol from Union Carbide, max acid no .-0 . 25, OH no.=310, avg. molec. wgt.~540) Castor Oil DB ~ (Triglyceride of Ricinoleic acid ~rom Cas Chem, acid no.=0.6, OH no.-164, avg.
molec. wgt.=928, % moisture increase 0.008) Poly bdTMR-45 HT (Rydroxyl terminated polybùtadiene from Atochem Inc ., OH no.=47, avg. molec.
wgt.=2800, ~ moistura increase = 0.022) TeracolTM2000 (Polytetramethylene ether glycol from Dupont, max. acid no.=0.05, o~ no.~53-S9~
molec. wgt. about 2000) -20 TeraColTM650 (Polytetramethylene ether glycol from Dupont, max. acid no.=0.05, OH
no.=160-187, molec. wgt. about 650, moisture increase - 0.07~
U~-28 (Dimethyl Tin Dilaurate ~rom Witco Chemical Co.) 2~
Dabco HB (Catalyst from Air Products) A-187 (Gamma-glycidoxy propyltrimethoxysilane from Union Carbide) PiccofynS~A 135 (Terpene phenolic resin from Hercules Inc.l Piccolyte~MA 135 (Terpene resin from Hercules Inc.~
Foral M85 (Hydrogenated rosin ester from Hercules Inc.) 3 ~ ~ 7 o~,` 0 O ~ . o c~
C ~ . . . . I
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. Rh: ~ h ,q O OP~ rlO 41 O ~~ UE.I O O t) Ur-l 0 0 r~ O O
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a~ o o ~ O ~ ~ S~ 1 o - . .

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- ' 2~23~67 For all examples other than Examples 3 and 4, a predetermined quantity of Part A and Part B was mixed together in a plastic cup at ambient room temperature (i.e., 22C) using a spatulaO The mixture was then applied to a 1.25 x 1.25 cm area of each of several 2.5 cm x 10 cm cold rolled steel test coupons. A bond was then made to each by separate second cold rolled steel test coupons by joining a 1.25 x 1.25 cm area of the second coupons to the first coupons. A bond thickness of from 0.~13 to ~.18 cm was obtained by sprinkling a minute amount of glass beads ~Class-4A, from Ferro, Cataphone Division) into the mixture beore bonding. The test coupons were held toge~her by means of paper clamps overnight. The bond~d samples were cured at 22C for 7 days followed by 50VC for 7 days.
A portion of the test specimens were then tested for overlap shear strength, within about 30 minutes after removal from the environment, using Instron tensile tester and following the procedure of ASTM D1002-72 (Reapproved 1983). The test method was modified to employ a 2mm/minute cross-head speed.
After initial curing, others of the test specimens were subjected to high humidity at 70C and 100% R.H. for 4 days. These samples were then tested for ~verlap shear strength as described above.
For examples 3 and 4, Part A and Part B were applied using conventional spray applicator equipment and techniques to cold rolled steel. Part A was kept at 22~C
while Part ~ was kep~ at 66C during deliv~ry to the spray equipment. The mixture was sprayed onto a ~.25 x 1.25 cm area of each of the substrates. A wet film thickness of 0.013 to 0.018 cm was obtained. A bond was then made by joining a 1.25 x 1.2~ cm area of separate substrate of like material to the sprayed substrates. The bonds were held together by means of paper clamps for a period of 2-~3 hours and then tested as described above.
The results of all testing is shown in Table C.
S rength values are reported in megaPascals ~MPa~. These values represent an av~rage of from 5 to 7 separate test --lq--..

023~7 coupons. Ret~ntion is reported in % o~ original overlap shear strength after being conditioned.

T~B~E C
HUMIDITY
INITIA~ CONDIT~ON
~X~lPLE STRENGTHSTRENGTH RETENTION
~MPa) (MPA) ~96) 10.4 g.5 92 2 9.. 1 8.5 93 3 14 . 65 5 . 85 96 4 6 . 81 5 . 85 86 5 . 96 6 . 94 116 8 . 03 9 . 96 1~5 7 4.3 6.67 155 8 3 . 49 4 . 08 117 This data demonstrates that in all cases, the compositions of the invention retain at least 75%, and preferably over 90%, of their initial overlap shear strength after rigorous conditioning.

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-15- ~:

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Claims

1. A polyurethane composition comprising (A) the reaction product of a polyisocyanate and a mixture of active hydrogen-containing components made up of (i) from 20 to 40 parts by weight of a polycaprolactone polyol having an acid number of less than 0 r 3 and r correspondingly, (ii) from 80 to 60 parts by weight of a hydrophobic polyol having an acid number of less than 0.8, wherein the molar equivalent ratio of the isocyanate groups of said polyisocyanate to the hydroxyl groups of said mixture is in the range of from 1:1 to 10:1, and (B) a silane coupling agent present at a level of from 0.005 to 10 parts by weight per 100 parts by weight of said mixture, and (C) a thermoplastic resin selected from the group consisting of terpene resins and resins having an active hydrogen functional group thereon, said resin being present at a level of from 1 to 20 parts by weight per 100 parts by weight of said mixture.

2. A polyurethane composition according to claim 1 wherein said mixture comprises from 25 to 35 parts by weight of said polycaprolactone polyol and, correspondingly, from 75 to 65 parts by weight of said hydrophobic polyol.

3. A polyurethane composition according to claim 1 wherein said ratio is in the range of from 1.1:1 to 1.4:1.

4. A polyurethane composition according to claim 1 wherein said coupling agent is present at a level of from 1 to 2 parts by weight per 100 parts by weight of said mixture.

5. A polyurethane composition according to claim 1 wherein said thermoplastic resin is present at a level of from 1 to 10 parts by weight per 100 parts by weight of said mixture.

6. A polyurethane composition according to claim 1 wherein said polycaprolactone polyol has at least two hydroxyl groups per molecule.

7. A polyurethane composition according to claim 6 wherein said polycaprolactone polyol has a molecular weight of at least 300 and at most 600.

8. A polyurethane composition according to claim 1 wherein said hydrophobic polyol is selected from the group consisting of functional triglycerides, polytetramethylene ether glycol, and hydroxyl-terminated polybutadiene.

9. A polyurethane composition according to claim 1 wherein said thermoplastic resin is one having an active hydrogen functional group and is selected from the group consisting of terpene phenolic resin and rosin ester resin.

10. A two-part composition comprising:
I. as a first component, a polyisocyanate, and II. as a second component and admixture of A) a mixture of active hydrogen-containing components of (a) from 20 to 40 parts by weight of a polycaprolactone polyol having an acid number of less than 0.3 and, correspondingly, (b) from 80 to 60 parts by weight of a hydrophobic polyol having an acid content of less than 0.8, B) a silane coupling agent, and C) a thermoplastic resin selected from the group consisting of terpene resins and resins having an active hydrogen functional group thereon, said resin being present at a level of from l to 20 parts by weight per 100 parts by weight of said mixture of active hydrogen-containing components;
wherein the molar equivalent ratio of the isocyanate groups of said polyisocyanate to the hydroxyl groups of said mixture of active hydrogen-containing components is in the range of from 1:1 to 10:1 when said first and second components are mixed together.

JVLAP3.8