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1 Training Courses on Polyurethane Adhesives Part I: Formulation How to Formulate Polyurethane Based Adhesives: A Complete Overview of Key Ingredients and Latest Formulation Techniques Edward M. Petrie (SpecialChem Expert Team)

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Training Courses on Polyurethane Adhesives Part I: FormulationHow to Formulate Polyurethane Based Adhesives: A Complete Overview of Key Ingredients and Latest Formulation Techniques Edward M. Petrie(SpecialChem Expert Team)

1

Seminar Objectives Learn capability of polyurethane adhesives Learn about their versatility and breadth Learn the formulation possibilities

Chapter 1 - Introduction

2

Seminar Contents - Part I1) Slide Show PresentationChapter 1. Introduction 2. Types of PU adhesives 3. PU chemistry Morphology and physical properties

4. 5. 6. 7. 8.

PU adhesive composition Isocyanates and Polyols Additives and other raw materials Common formulations Current and future development

60 minutes

2) Questions and AnswersOn-line interaction

30 minutesChapter 1 - Introduction3

Chapter 1 Introduction

4

DefinitionPU adhesives contain a number of urethane groups in the molecular backbone or are formed during use Urethane groupO NCO H

Many complex reactions can occur simultaneously or sequentially

Diversity Diversity Versatility VersatilityChapter 1 - Introduction5

Why the Attraction to PU Adhesives?Good adhesion achieved through: Chemical bonding with water, hydroxyls on substrate surface Physical bonding through van der Waals forces and low surface energy Mechanical through low viscosity and diffusion into porous substrates

Specific mechanical properties achieved through molecular composition Toughness and other viscoelastic properties Elasticity and modulus Crosslinking density

Many types, methods of application, and cure speeds are possible

Chapter 1 - Introduction

6

Advantages and Disadvantages of PU AdhesivesAdvantages Highly versatile chemistry Flexible, tough, or rigid Bonds a variety of plastics Can be formulated as 1 or 2 component system Slow to fast curing time Good low temperature properties Good environmental resistance Good chemical, oil resistance below 50C

Disadvantages Moisture sensitivity during storage and application Only average bond strength to metal without a primer Precise mix ratio required for certain products Requires good mixing Maximum temperature of 100-150C for specially formulated PUs Hydrolytic stability is a problem for certain types

Chapter 1 - Introduction

7

Chapter 2 Types of Polyurethane Adhesives

8

Classification of PU Adhesives and SealantsPolyurethane adhesives vary widely in composition and are used in many different applications and in various market segments

Chapter 2 Types of PU Adhesives

9

Chapter 3 Polyurethane Chemistry

10

Polyurethane ChemistryUrethanes are generally produced from isocyanates, represented as:RN=C=O

Properties revolve around the universal and rapid reaction between the NCO group and any organic compound containing an extractable hydrogen atom Reaction with a hydroxyl terminated polymer (e.g., alcohol, polyester or polyether polyol, derivatives of castor oil or hydrocarbons)R N = C = O + HO - R (Isocyanate) (Alcohol) H O | || R N C O R (Urethane)

Chapter 3 PU Chemistry

11

Isocyanate Polyol ReactionPolyether or Polyester Polyol Diisocyanate

HO~~~~~~~ OH

+

OCN R NCO

O

OPolyurethane

~~~~O C NH R NH C O~~~~~Urethane GroupChapter 3 PU Chemistry

12

Chapter 4 Polyurethane Adhesive Composition

13

Polyurethane Adhesive CompositionIsocyanate Active Hydrogen Compound Catalyst Chain Extender Additives Drying agents Antioxidant UV Inhibitor Antimicrobial Leveling agent Colorant Adhesion Promoters Fillers and Extenders Other Polymers14

Chapter 4 PU Adhesive Composition

Manufacture of Polyurethane AdhesivesUrethane adhesive and sealants are generally made in a batch process Prepolymer is made in a standard mix tank Adhesive or sealant is made in a high torque mixer Mixer control is important for consistent viscosity

It is necessary to avoid moisture contamination Reactions run under a nitrogen blanket or in a vacuum

Reactors are always jacketed for temperature control

Chapter 4 PU Adhesive Composition

15

Chapter 5 Isocyanates and Polyols

16

IsocyanatesMDI (methylene diphenyl diisocyanate) TDI (toluene diisocyanate) Polymeric isocyanates used for crosslinking (e.g., polymethylene polyphenylene isocyanate) Prepolymers Isocyanate prereacted with some or all of the polyol (not all of the polyol is used) very low viscosity

Chapter 5 Isocyanates and Polyols

17

IsocyanatesTriphenylmethane triisocyanate (Desmodur R) Polymethylene polyphenyl isocyanate (PAPI) Aliphatic isocyanates - Less reactive, non-yellowing, more resistant to UV, slightly higher thermal resistance, lower resistance to oxidation, more expensive HDI (hexamethylene diisocyanate) IPDI (isophorone diisocyanate)

O=C=N-

- CH2 -

-N=C=O

MDI (methylene diphenyl diisocyanate)

Chapter 5 Isocyanates and Polyols

18

PolyolsPolyether Polyol Low temperature properties Hydrolysis resistance Lower cost Easier processing Low viscosity Not as reactive as polyesterR R R R HO (CH2-CH-O)n R (O-CH-CH2)m OH R (O-CH-CH2) OH HO (CH2-CH-O)n m

Polyether polyol Polyether polyol

Polyester Polyol Good adhesion High strength, modulus, and hardness Better resistance to oxidation, elev. temp. Linear to highly branchedChapter 5 Isocyanates and Polyols

OH R O (CO-R-CO-O-R-O)n H OH R O (CO-R-CO-O-R-O)n H Polyester polyol Polyester polyol

19

PolyolsPolytetramethylene ether glycol (PTMG) Polycaprolactone glycol Polybutadiene (PolyBD) glycol Improved hydrolytic stability Lower moisture vapor transmission Lower tensile strength and modulus Polycarbonates Fatty alcohols Castor oil Polyester amide

Others

Chapter 5 Isocyanates and Polyols

20

PolyolsImportant factors in selection of a polyol: Chemical type Chemical type MW MW Functionality Functionality Chain structure Chain structureFlexible Molecular Weight 1000-6500 Functionality 2 to 3 Hydroxyl value (mg KOH/g) 28-160 Glass Transition Temperature -40 to 60C NCO / OH Ratio LowerChapter 5 Isocyanates and Polyols

Rigid 150-1600 3 to 8 250-1000 +60 to 40C Higher21

Comparison of PU Polyols

Chapter 5 Isocyanates and Polyols

22

PrepolymersA prepolymer is a low molecular weight urethane polymer that retains the ability to react further Prepolymers are formed by partially reacting the available isocyanate groups with a curative Partial reaction is possible by controlling the ratios of the reactants Called xmers

Important parameters in prepolymer design: Mc: average MW between crosslinks % NCO: if value is too high in one-part systems gassing can occur NCO/OH ratio control mole % of xmer formed

Chapter 5 Isocyanates and Polyols

23

Chapter 6 Additives and Other Raw Materials

24

Catalysts, Chain Extenders, CrosslinkersCatalysts Tertiary amines (e.g., triethanol amine) Transition metals (e.g., dibutyl tin dilaurate, DBTDL)

Chain Extenders (diamines or diols) Reacts with isocyanate then phase separates into domains (hard segments) Each extender molecule more than doubles the length of the rigid segment Used to produce stiffer hard segments Used to crosslink

Crosslinkers Low molecular weight compounds containing active hydrogen with a minimum functionality of 325

Chapter 6 Additives and Other Raw Materials

Other CurativesPolythioethers React with isocyanate Provides some of the properties of polysulfide sealants

Amines Aromatic amines provide rigid, hard adhesives Aliphatic amines (e.g., polyetheramine) are extremely reactive with isocyanatesNecessary to slow down the rate of reaction for practical use; therefore, blocking agents are used

Blocking Agents Reversibly react with isocyanates (phenols, methylethylketoxime, caprolactam, malonates, etc.)

Chapter 6 Additives and Other Raw Materials

26

AdditivesUsually added to the polyol component Generally does not take part in the reaction All additives must be free of water (or foaming and poor adhesion); solvents must have a H20 and alcohol content of less than 0.02% StabilizersAntioxidant (e.g., phenolic) at a 2% level UV stabilizer Antimicrobial at a 0.3% level Hydrolysis stabilizer

Adhesion promoters (e.g., organosilane) Fillers Drying agents at a 2-5% levelTriethyl ortho formate Calcium sulfate Molecular sieves Zeolite

OthersChapter 6 Additives and Other Raw Materials27

Plasticizers, Extenders, and SolventsNot usually required urethane is typically flexible enough Plasticizers are used to improve elongation, reduce prepolymer viscosity, and lower hardness Phthalate type plasticizer commonly used

Extenders are used to primarily lower cost Aromatic oils Asphalts Coal tars

Solvent containing adhesives are formulated with dry organic solvents Ketones, lower alkyl esters (e.g., acetates), methylene chloride and trichloroethylene Certain flow agents (cellulose acetate butyrate, vinyl acetate copolymers, etc.) can be added

Chapter 6 Additives and Other Raw Materials

28

Chapter 7 Common Formulations

29

PU Adhesive FormulationReactive Polyurethane Adhesives One-component adhesives (solvent, water, and 100% solids) Two-component adhesives (solvent, water, and 100% solids) Reactive hot melts Wood binders

Non-Reactive Polyurethane Adhesives Solvent borne adhesives Hot melt adhesives Water based adhesives

Chapter 7 Common Formulations

30

Two Component Reactive AdhesivesGenerally composed of a diisocyanate terminated prepolymer as one component, and a polyol and polyamine crosslinking agent and catalyst as a second component Solventless and low solvent content adhesives Function as an adhesive or sealant

Chapter 7 Common Formulations

31

Typical Two Component PU Formulation

Chapter 7 Common Formulations

32

Moisture Cured One Component AdhesivesMoisture cure Ambient conditions, shelf life, and foaming can be a problem Can be applied either with or without solvent

Chapter 7 Common Formulations

33

Blocked One Component AdhesivesReaction is reversible, and generally temperatures of 120-160C are required for deblockingOCN R NCO + 2BH O O || || B C HN R NH C B

Blocking agents include phenols, branched alcohols, methylethyl ketoxime and e-caprolactam

Chapter 7 Common Formulations

34

Other One Component PU Adhesive TypesAnaerobic Prepared by reacting hydroxyethyl methacrylate with TDI or an NCO terminated prepolymer; a hydroperoxide is added, and the mixture stored in an oxygen permeable container with air Polymerization takes place when access to oxygen is eliminated in the joint

Solid Polyol A solid polyol, such as pentaerythritol, is simply mixed into the adhesive/sealant. When heated, the polyol melts and reacts with the isocyanate

Chapter 7 Common Formulations

35

Reactive Hot Melt (HMPUR) AdhesivesSolid polyether or polyester polyol mixtures are reacted with an excess of diisocyanate to produce a prepolymer The prepolymer is cooled into a hot melt product that can flow at relatively low temperatures 85-140C Molten prepolymer has a high degree of green strength Once applied the residual non-reacted isocyanate groups react with moisture to form a thermosetting structure Prepolymer contributions: Higher NCO/OH ratio: lower melt viscosity, lower elongation, higher tensile modulus and extended open times Lower NCO/OH ratio: thermoplastic characteristics with improved flexibility and toughness36

Chapter 7 Common Formulations

Isocyanate Wood Binders, Primers, SolutionsAromatic isocyanates (predominantly MDI) used for manufacture of: Oriented strand board (OSB), Medium density fiberboard (MDF), and Particleboard

Isocyanates solutions can be used as primers for coatings and adhesives Isocyanates solutions can be blended with various types ofelastomers (solvent blends) as rubber cements SBR Natural Rubber Neoprene Nitrile37

Chapter 7 Common Formulations

Solvent Based and Hot Melt Non-Reactive AdhesivesThermoplastic polyurethanes such as Estane (Goodrich) and Desmocoll (Bayer) Solvent systems can either be applied directly (permeable substrate), as a contact adhesive, or as a coating and then hot pressed Hot melt adhesives are most commonly applied as an extruded film for laminating applications Properties depend on formulation and selection of diisocyanates, polyols, chain extenders, and plasticizers

Chapter 7 Common Formulations

38

Water Based AdhesivesPU lattices can be prepared in various ways: Special monomers are polymerized in an aqueous medium to produce a thermoplastic PU Thermoplastic PU is dissolved in solvent and emulsified in water, then the solvent is removed Isocyanate terminated PU prepolymer is blocked and emulsified in water together with a crosslinking agent.

Chapter 7 Common Formulations

39

Water Based AdhesivesAqueous polyurethane dispersion usually contain: 40% thermoplastic resin (for aqueous inertness) Aliphatic diisocyanate polymer (for light stability), and An anionic surfactant

Can be cured at room temperature; however strength, adhesion, and water resistance are greater when dried for several minutes at 120-175C

Chapter 7 Common Formulations

40

Chapter 8 Current and Future Development

41

Recent Development ActivitiesExamples of development:Hybrid PU adhesives Ethylene / vinyl acetate copolymers Epoxy Acrylics Blocked isocyanates Pressure sensitive acrylic prepolymers Urethane toughened acrylate adhesives Reactive hot melts Pressure sensitive Anaerobic and radiation curing mechanisms Non-sagging without fillersChapter 8 Current and Future Development42

Reactive Epoxy UrethanesMixture of epoxy and polyurethane oligomers with pendant epoxy groups Curing of epoxy groups unites the urethane and non-urethane components Tough, durable adhesive films Good adhesion to oily surfaces and plastics

Chapter 8 Current and Future Development

43

End of Presentation for Session I

44

Seminar Contents - Part IISelecting and Applying Polyurethane Adhesives:Overview of major applications and key performances to match your end-use requirements1. IntroductionMarkets and applications Comparison to other adhesive systems Range of types and properties

2. Application variablesHealth and Safety

3. Reaction rates 4. Types of polyurethane adhesives and their use 5. Stability in various environments Part II: Wed May 26, 200445

Backup Slides and Additional Material

47

Common PU Adhesive Reactions

Chapter 3 PU Chemistry

48

Common PU Adhesive Reactions

Chapter 3 PU Chemistry

49

Reaction VersatilityIsocyanates react with active hydrogen compounds in the order:R2NH > R-NH2 > Ar-NH2 > R-OH > R2OH ~ H20 > Ar-OH > R-SH

Isocyanate coreactants of commercial significance are: Polyester Polyols Polyether Polyols Amines Polycaprolactones Polyglycols Natural and Hydroxyl Containing Oils

Polymerization and/or crosslinking will occur depending on the amount and nature of the diisocyanates, stoichiometric amount and type of comonomer, and conditions of curing As with other polymers, additives are used to further modify the systems for specific end-use properties

Chapter 3 PU Chemistry

50

Crosslinking CapabilityLinear, thermoplastic PUs are obtained by using compounds with two reactive groups such as diisocyanates and diols Crosslinking occurs when: Polyols with three or more hydroxyl groups (i.e., a functionality of 3 or more) are reacted with an isocyanate, or when Isocyanates with three or more Isocyanate groups are reacted with a polyol. There is an excess of isocyanates (linkages of allophanate and biuret).

The amount of crosslinking determines the stiffness of the polymer, strength, and resistance to environmental factors

Chapter 3 PU Chemistry

51

CrosslinkingPolyurethanes exhibit both chemical crosslinking and physical crosslinking Physical and chemical crosslinking sometimes overlap Crosslinking does not always produce the expected effect because of disruption of the domain structure (especially at low levels of crosslinking)

Chapter 3 PU Chemistry

52

Polyurethane MorphologyPU molecule consists of two separate phases or microdomains (pseudocrosslinking) Hard segmentpolyisocyanate and low molecular weight hydroxy compound (a short chain polyol or a diamine chain extender) Crosslinks the soft segment

Soft segmentsHydroxy terminated diols Greater flexibility and elongation, resistance to low temperature Lower hardness, modulus, abrasion resistance

At elevated temperatures two phases become one amorphous, soft phaseChapter 3 PU Chemistry53

Polyurethane Morphology

1 Flexible PUR 2- 40% rigid segments 3- 60% rigid segments 4- Rigid PUR

Chapter 3 PU Chemistry

54

Polyisocyanates Provide Varied Adhesion PropertiesIsocyanates react readily with a variety of other functional groups Di- and polyisocyanates can undergo self-polymerization to form three dimension resins in situ Isocyanates are quite soluble in many organic substances, and due to their small molecular size readily permeate insoluble porous structures The reaction of di- and polyisocyanates with hydroxyl bearing polyesters and polyethers produce the strong, polar, hydrogen bonded flexible PUs which wet substrates very well Isocyanates provide elastomer- metal bonds with flexible to rigid gradation in physical properties between the elastomer and metal which provides superior fatigue life

55

Polyols and Hydrolytic Stability

Hydrolysis Resistance as a Function of Change in Stress at BreakAll polyurethane elastomers: 80 shore A, immersed in water at 80CChapter 5 Isocyanates and Polyols56

PolyolsProperties of Adhesive Films Based on Mixtures of PolyolsPolyol PO1 = 5% hydroxyl content Polyol PO2 = 1.3% hydroxyl content A = modulus at 100% elongation B = tensile strength C = elongation at break

Chapter 5 Isocyanates and Polyols

57

FillersFillers that reduce shrinkage, improve strength, reduce costs, adjust viscosityBarytes Hydrated Alumina Clays Quartz Flour Slate Flour Fumed Silica

Particulate fillers increase density and hardnessCaCO3 has a catalytic effect on isocyanate reaction Aluminum hydroxide reduces flammability Carbon black reinforces and provides UV protection Colloidal and microexpanded silica are thixotropic agents

Flaky fillers are used for surface properties, appearance, etc. Fibrous fillers (organic and inorganic) reinforce PU; generally increase rigidity and elastic modulus

Chapter 6 Additives and Other Raw Materials

58

ThixotropyThixotropic agents are used to provide non-sag properties or to reduce penetration in absorbent substrates Usually fumed silica or bentonite is used as an additive to provide thixotropy However, carbon black, fibers, and treated clays can also increase thixotropy Bayer has developed amine terminated prepolymers (ATEP) that provide fast B-stage reaction for thixotropy Generally need automated meter, mix, and dispense equipment for fast Bstage development

Chapter 6 Additives and Other Raw Materials

59

Silane Primer / Additive Improves Moisture ResistanceAdhesion promoters can be applied as a primer or as a component in the adhesive formulation Generally silanes are used to provide:A chemical bridge between the surface and organic polymer or between organic polymers A barrier to prevent moisture penetration into the interface Effective dispersion of fillers and reduction in the apparent viscosity of the system

Isocyanate Terminated PU, Adhesion to Al(1. Urethane is Adiprene L-100, 2. Substrates degreased and etched, 3. Most commonly recommended for pot life)

Chapter 6 Additives and Other Raw Materials

60

UV Stabilizers and AntioxidantsRequired with aromatic isocyanates and polyether polyols UV absorbers and stabilizers are commonly employed when PU is exposed to light Carbon black Titanium dioxide Tinuvin P (Ciba-Giegy) Zinc oxide Certain molybdates

Antioxidants neutralize free radicals that are formed by the reaction of various chemical bonds with oxygen Iganox 1010 (Ciba-Giegy) Hindered phenols and amines

UV stabilizers and antioxidants work synergistically, so they are often used together

Chapter 6 Additives and Other Raw Materials

61

Stabilizers Hydrolytic StabilityImproved hydrolytic stability (most often required for polyester urethanes) Carbodiimide (e.g., Staboxal P from Bayer) Satrastab developed by SATRA (Shoe and Allied Trades Assoc., Kettering, England) Elimination or reduction of ester groups in the polyol Hydrolysis resistance increases in the order of ether > polycaprolactone > polyester

Chapter 6 Additives and Other Raw Materials

62

Other StabilizersFungicides (most often required for polyester urethane) Copper-8-quinolinolate N-(trichloromethylthio) phthalimide (e.g., Fungitrol 11 from Nuodex)

Improved heat resistance Non-stabilized PU are not recommended for service temperatures greater than 100C Heat resistance can be improved through exclusion of catalyst residues from the polymer and by tailoring the polyurethane structure Antioxidants and hybrid with epoxy and other resins

Chapter 6 Additives and Other Raw Materials

63

Polymers Sometimes Used with PU Adhesives

64

Polyurethane Metal Adhesive

65

Solvent-Free General Purpose Reactive Adhesive

66

Solvent Based Reactive Adhesive

67

Thermoplastic PU Contact Adhesive

68