Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F222/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a carboxyl radical and containing at least one other carboxyl radical in the molecule; Salts, anhydrides, esters, amides, imides, or nitriles thereof
  • C08F222/10—Esters
  • C08F222/1006—Esters of polyhydric alcohols or polyhydric phenols
  • C08F222/106—Esters of polycondensation macromers
  • C08F222/1065—Esters of polycondensation macromers of alcohol terminated (poly)urethanes, e.g. urethane(meth)acrylates
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J109/00—Adhesives based on homopolymers or copolymers of conjugated diene hydrocarbons
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J133/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Adhesives based on derivatives of such polymers
  • C09J133/04—Homopolymers or copolymers of esters
  • C09J133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J133/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Adhesives based on derivatives of such polymers
  • C09J133/04—Homopolymers or copolymers of esters
  • C09J133/14—Homopolymers or copolymers of esters of esters containing halogen, nitrogen, sulfur or oxygen atoms in addition to the carboxy oxygen
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J175/00—Adhesives based on polyureas or polyurethanes; Adhesives based on derivatives of such polymers
  • C09J175/04—Polyurethanes
  • C09J175/14—Polyurethanes having carbon-to-carbon unsaturated bonds
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J175/00—Adhesives based on polyureas or polyurethanes; Adhesives based on derivatives of such polymers
  • C09J175/04—Polyurethanes
  • C09J175/14—Polyurethanes having carbon-to-carbon unsaturated bonds
  • C09J175/16—Polyurethanes having carbon-to-carbon unsaturated bonds having terminal carbon-to-carbon unsaturated bonds
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J4/00—Adhesives based on organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond ; adhesives, based on monomers of macromolecular compounds of groups C09J183/00 - C09J183/16
  • C09J4/06—Organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond in combination with a macromolecular compound other than an unsaturated polymer of groups C09J159/00 - C09J187/00

Definitions

• the present invention relates to an optical transparent dual cure adhesive composition, and process for preparing the dual cure adhesive composition, and uses thereof. More particularly, the present invention relates to optical transparent adhesive composition, which is both UV curable and thermal curable. For example, it can be used for the bonding of touch screen and substrate of an electronic device.
• UV curable (abbreviated as UV cure) adhesives were reported in the 1960s, since then considerable achievements were achieved through an extensive research. UV cure adhesives refer to adhesives that may cure rapidly under UV radiation. Today, UV cure adhesives have been successfully applied in many fields of industrial assembly, especially high-tech industries where fast assembly is required, such as liquid crystal display (LCD) manufacturing, cameras and other optical products manufacturing, CD manufacturing, watch-making industry, mobile phone keypad assembly, electronic circuit board manufacturing, electronic components manufacturing in optoelectronic information industry such as manufacturing of the polarized components. UV cure adhesives are also widely used in the commodity sector, such as the manufacturing of glass furniture, assembly of glass crafts, assembly of toys, jewelry and other decorations, since a high and efficient productivity can thus be achieved.
• LCD liquid crystal display
• WO 2010/111316 A2 is directed to an optical assembly having a display panel, wherein an adhesive layer or adhesive composition is used as the display panel, so that the display panel is bonded to the substantially transparent substrate.
• the adhesive layer comprises the reaction product of a multifunctional (meth)acrylate oligomer, a reactive diluent comprising a monofunctional (meth)acrylate monomer; and a plasticizer, wherein the reaction product in the adhesive layer can be obtained by initiating polymerization using UV-photoinitiators.
• shadow areas may exist between the liquid crystal panel and the substrate, that is, areas that light cannot transmit or penetrate, UV/visible light cannot transmit through these areas, thus the adhesives cannot be cured completely, and may cause problems such as corrosion, aging fatigue or peeling of unbonded edges.
• the shadow areas are for example the edge areas where ink coatings exist, and etc.
• One solution to above problems is to combine adhesives having different cure mechanisms, such as dual cure mechanism adhesive.
• Alexander P. Mgaya et al propose a dual cure mechanism adhesive, wherein one cure mechanism is based on the drying of the adhesive, which is mainly due to the evaporation of water or other volatile substances in emulsion of adhesive components; the other cure mechanism is UV or visible light irradiation.
• This adhesive has the following components: a water-based emulsion; (meth)acrylate functionalized monomer capable of polymerizing or crosslinking; and at least one UV-photoinitiator; wherein said water based emulsion is cured or crosslinked by water evaporation/coagulation.
• Daniel L. Gooman et al propose a phase-separated dual-cure elastomeric adhesive formulation, characterized in that the dual cure elastomeric adhesive is E-beam cured and heat cured at relatively low temperature; this adhesive can be used for bonding structure which is thick or has irregular shapes, for example, the structural parts in automobile or aeroplane having irregular shapes.
• This adhesive mainly comprises: urethane acrylate oligomer sensitive to irradiation; reactive dilute sensitive to irradiation; hydroxy group containing compounds, such as saturated polyol; compounds containing isocyanate functional group, such as polyisocyanate, or urethane prepolymer.
• This patent proposes to rotate the structure to be bonded, and e-beam irradiation is conducted for two or more times and heat cure is conducted at relatively low temperature for a certain period of long time, so as to cure the adhesive completely.
• thermoplastics for example, vinyl resin, such as PVC, PVDC, and PS; un-polymerizable plasticizer are used; and the thermoplastics is in the form of dispersion in the plasticizer, wherein the use of thermoplastics and plasticizer cause the unsaturated monomer, prepolymer or polymer having acrylate group would not lead to a sticky surface upon UV irradiation.
• Optional component includes reactive dilute, such as monofundional acrylate, and the heating step requires a condition of at least 80° C., preferably 80-200° C., so as to obtain a full cure product.
• a first subject matter of the present invention is an optical transparent dual cure adhesive composition, based on the total weight of the adhesive composition, the composition comprises:
• UV-photoinitiator 0.5-5 wt % of UV-photoinitiator
• thermal initiator 0.5-5 wt % of thermal initiator.
• an optical transparent dual cure adhesive composition based on the total weight of the adhesive composition, the composition comprises:
• UV-photoinitiator 0.5-5 wt % of UV-photoinitiator
• thermal initiator 0.5-5 wt % of thermal initiator.
• an optical transparent dual cure adhesive composition based on the total weight of the adhesive composition, the composition comprises:
• UV-photoinitiator 0.5-5 wt % of UV-photoinitiator
• thermal initiator 0.5-5 wt % of thermal initiator.
• Another aspect of the invention also relates to the uses of the adhesive composition for bonding a touch screen and substrate of an electronic device.
• cur refers to a change in state, condition, and/or structure in a material that is usually, but not necessarily, induced by at least one variable, such as time, temperature, moisture, radiation, presence and quantity in such material of a cure catalyst or accelerator, or the like.
• the terms cover partial as well as complete cure.
• the terms mean at least partially crosslinked, and in more preferred embodiments substantially or fully crosslinked.
• the term “dual cure” used herein refer to UV cure induced by using UV-photoinitiator as well as thermal cure induced by using thermal initiator, the UV light cure refers to a cure under the irradiation of UV light for a certain period of time, and the thermal cure refers to a cure under certain temperature for a certain period of time.
• Photo curable oligomer or polymer having (meth)acryloxy group or vinyl group is a functionalized oligomer or polymer, on the molecular chain thereof, there exists (meth)acryloxy group or vinyl group reactive to UV light irradiation.
• These oligomer or polymer is a polymer preferably having low to medium molecular weight, for example, usually said functionalized oligomer or polymer can have number average molecular weight of about 300 to about 50000 Daltons, preferably 800-40000 Daltons, more preferably 1000-35000 Daltons, more preferably 3000-25000 Daltons, more preferably 5000-20000 Daltons.
• Said (meth)acryloxy and/or vinyl functional group could be located at the end(s) of the polymer chain, or may be distributed along the polymer chain thereof.
• the functional group(s) on said functionalized oligomer or polymer chain curable by irradiation preferably have average degree of functionality of more than 0 to less than or equal to 3, especially from 0.5 to 2.5.
• average degree of functionality refers to the average number of (meth)acryloxy group or vinyl functional group per macromolecular chain.
• oligomer or polymer examples include (meth)acryloxy group functionalized urethane oligomer, such as (meth)acryloxy group functionalized polyether urethane, and (meth)acryloxy group functionalized polyester urethane, polyisoprene having (meth)acryloxy group or vinyl group and the like.
• oligomer or polymer and preparation thereof are known in art, for example, please refer to the disclosures in U.S. Pat. Nos. 4,574,138, 4,439,600, 4,380,613, 4,309,526, their entire contents are incorporated here by reference.
• the adhesive composition Based on the total weight of the adhesive composition, the adhesive composition contains 10-90 wt % of said functionalized photo curable oligomer or polymer, preferably 20-85 wt %, more preferably 30-70 wt %.
• (meth)acryloxy group is CH 2 ⁇ CRC(O)O—, wherein R is H or CH 3 .
• the term “(meth)acryloxy group” represents acryloxy, methacryloxy group or their combination;
• the term “(meth)acrylic acid” represents acrylic acid, methacrylic acid or their combination;
• the term “(meth)acryl” represents acryl, methacryl or their combination, and so on.
• “Urethane oligomer having (meth)acryloxy group” is a specific and non-limited but preferred example of the photo curable oligomer or polymer having (meth)acryloxy group or vinyl group, which is an urethane oligomer having (meth)acryloxy group, and sometimes it is also referred to as urethane(meth)acrylate oligomer.
• the urethane oligomer having (meth)acryloxy group preferably has an average degree of functionality of more than 0 and equal to or less than 3; more preferably 0.5-2.5.
• the urethane oligomer having (meth)acryloxy group preferably has a number average molecular weight of 1000-25000 Daltons, more preferably 1500-10000 Daltons, even more preferably 2000-8000 Daltons.
• the urethane oligomer having (meth)acryloxy group in accordance with the present invention preferably has a T g of from ⁇ 80 to 0° C., more preferably from ⁇ 60 to 0° C.
• Said urethane oligomer having (meth)acryloxy group preferably has a Brookfield viscosity of 1000 centipoise (cps) to 190000 cps, more preferably from 2000 cps to 150000 cps; even more preferably from 5000 to 100000 cps at a temperature of 25° C. at a shear rate of 2.55s ⁇ 1 , measurable by HAAKE Rotational Rheometer with a cone plate (35 mm diameter).
• Useful and preferred urethane oligomer having (meth)acryloxy group includes commercially available products, for example, said urethane oligomer may preferably include: urethane diacrylate CN9018, CN9021, CN3108, CN3211, CN8004 commercially available from Sartomer, Co., Exton, Pa.; GENOMER 4188/EHA (mixture consisting of 80 wt.
• the amount of said urethane oligomer having (meth)acryloxy group used in the adhesive composition of the present invention depends from the amounts of the other components used for forming the adhesive composition, and the desired properties of the adhesive composition.
• the adhesive composition may include about 40-90 wt % of the urethane oligomer having (meth)acryloxy group, preferably from about 45-85 wt %, more preferably 50-80 wt %, more preferably 60-70 wt %.
• examples of the urethane acrylate oligomer used in the present invention include, for example CN9018, CN9021, CN3108, CN3211, CN8004 from Sartomer Company, Inc.
• the urethane oligomer having (meth)acryloxy group may be used alone or in any desired combination of several urethane oligomers having (meth)acryloxy group; the specific types and combination thereof depend from the desired properties of the products.
• Polyisoprene having (meth)acryloxy group or vinyl group Another non-limited example of photo curable oligomer or polymer having (meth)acryloxy group or vinyl group is polyisoprene having (meth)acryloxy group or vinyl group.
• this is an isoprene polymer modified by reactive functional groups, for example, polyisoprene grafted with acrylate group, or polyisoprene grafted with vinyl groups.
• the backbone or main chain of the macromolecule polyisoprene may have a number average molecular weight of 10000-50000 Daltons, preferably 12000-40000 Daltons; more preferably 15000-35000 Daltons.
• this exemplified acrylate functional group or vinyl functional group may be located at the end(s) of the isoprene oligomer, or may be pendant to branches of isoprene oligomer.
• the polyisoprene having acryloxy or vinyl functional group used in accordance with the present invention may have a Brookfield viscosity, at a temperature of 25° C. at a shear rate of 2.55 s ⁇ 1 , several thousands to tens of thousands cps, for example 10000-100000 cps, or 15000-80000 cps, or 25000-60000 cps, measurable by HAAKE Rotational Rheometer with a cone plate (35 mm diameter).
• polyisoprene having acryloxy or vinyl functional group are as follows: polyisoprene UC203, UC102, commercially available from KURARAY CO., LTD, and the like.
• polyisoprene having acryloxy or vinyl functional group can be used in at an amount of 10-80 wt %, preferably 20-70 wt %, more preferably 30-60 wt %.
• polyisoprene having acryloxy or vinyl group may be used alone or in any combination of several polyisoprenes having acryloxy or vinyl group.
• the specific types and combination thereof depend from the desired properties of the adhesive products.
• (Meth)acrylate The adhesive composition in accordance with the present invention also makes use of (meth)acrylate.
• Said (meth)acrylate is, for example, aliphatic alkyl(meth)acrylate, and (meth)acrylate having epoxy function, and the like. It could be a monofunctional (meth)acrylate, i.e., there is only one (meth)acrylate group within its molecule, it could also be a multifunctional (meth)acrylate, i.e., it is a (meth)acrylate having two or more than two (meth)acrylate group within its molecule.
• the (meth)acrylate monomer preferably is monofunctional- and multifunctional alkyl(meth)acrylates, monofunctional- and multifunctional alkenyl(meth)acrylates, and monofunctional- and multifunctional heterocyclo(meth)acrylates.
• Said alkyl moiety preferably is an alkyl group having from 1 to 20 carbon atoms, which may further have one or more substituents selected from an alkyl group having from 1 to 20 carbon atoms, an alkoxy group having from 1 to 20 carbon atoms, an aryloxy group having from 6 to 20 carbon atoms, an epoxy group having from 2 to 20 carbon atoms, hydroxyl and the like.
• the alkenyl moiety preferably is an alkenyl group having from 2 to 20 carbon atoms, which may further have one or more substituents selected from an alkyl group having from 1 to 20 carbon atoms, an alkoxy group having from 1 to 20 carbon atoms, an acryloxy group having from 6 to 20 carbon atoms, an epoxy group having from 2 to 20 carbon atoms, hydroxyl and the like.
• the heterocyclic group preferably is a heterocyclic group having from 2 to 20 carbon atoms, and having a hetero atom selected from nitrogen and oxygen.
• the heterocyclic group may have one or more substituents selected from an alkyl group having from 1 to 20 carbon atoms, an alkoxy group having from 1 to 20 carbon atoms, an aryloxy group having from 6 to 20 carbon atoms, an epoxy group having from 2 to 20 carbon atoms, hydroxyl and the like.
• Preferred examples of monofunctional acrylate component are isobornyl(meth)acrylate, tetrahydrofurfuryl(meth)acrylate, alkoxylated tetrahydrofurfuryl(meth)acrylate, and mixtures thereof.
• Preferred examples of multifunctional acrylate component are: ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, pentaerythritol tri(meth)acrylate. pentaerythritol tetra(meth)acrylate, trimethylolpropane(meth)acrylate, tetraethylene glycol di(meth)acrylate and the like, and mixture thereof.
• said (meth)acrylate is selected from the group consisting of: methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, tetrahydrofurfuryl(meth)acrylate, lauryl acrylate, isooctyl acrylate, isodecyl acrylate, 2-phenoxy ethyl acrylate, 2-ethylhexyl(meth)acrylate, isobornyl(meth)acrylate, dicyclopentenyloxyethyl(meth)acrylate, dicyclopentadienyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, caprolactone acrylate, morpholine(meth)acrylate, hexanediol di(me)acryl
• (meth)acrylate monomers are selected from the group consisting of: isobornyl acrylate, hydroxypropyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate. ethylene glycol dicyclopentenyl ether methacrylate, and combination thereof.
• the amount of (meth)acrylate component would depend from the amounts of other components used for forming the adhesive composition, and the desired properties of the adhesive composition.
• the contents of (meth)acrylate in the adhesive composition is 5-55 wt %; preferably 10-55 wt %, more preferably 10-50 wt %, more preferably 20-45 wt %; more preferably 25-40 wt %, and most preferably 20-40 wt %.
• the adhesive composition comprises photoinitiator.
• Said photoinitiator may include UV-photoinitiator and visible light photoinitiator.
• said photoinitiator preferably refers to UV-photoinitiator.
• UV-photoinitiator is well known in the art, and can be used to initiate the photo polymerization of all the above functionalized photo curable oligomer, polymer having (meth)acryloxy group or vinyl group.
• UV photoinitiators are generally effective in the wavelength range of 200 to 400 nm, and particularly in the portion of the spectrum that borders on the invisible light and the visible portion just beyond this spectrum, e.g. from >200 nm up to about 390 nm. Examples thereof may be benzyl ketal, hydroxy ketone, amino ketone, acyl phosphine oxide, and the like.
• Photoinitiators that will respond to UV radiation to initiate and induce cure of the (meth)acrylate functionalized curable component which are useful in the present invention include preferably benzophenone and substituted benzophenones, acetophenone and substituted acetophenones, benzoin and its alkyl esters, diethoxy acetophenone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, N-methyldiethanolamine benzophenone, 2-hydroxy-methyl-1-phenylpropan-1-one, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide, and combination thereof.
• the UV-photoinitiator may be used alone, or in any desired combination thereof.
• Above UV-photoinitiators are just for purpose of illustration, rather than limiting the UV-photoinitiator useful in the present invention.
• the amount of LJV-photoinitiator used, based on the total weight of the adhesive composition, may be 0.5-5 wt %, preferably 1-4 wt %, more preferably 2-3 wt %.
• thermal initiator In the adhesive composition according to present invention, thermal initiator is to be used to initiate the polymerization and cure of the composition.
• Thermal initiator usually includes azo compounds, peroxides, and other thermal initiator(s) well known to those skilled in the art, which is capable of releasing radicals under heating conditions, and combination thereof.
• peroxides are used in the present invention.
• the peroxide useful in the present invention preferably includes organic peroxide and inorganic peroxide.
• Non-limited examples of organic peroxide may be peroxy-dicarbonate, for example di(2-ethylhexyl)peroxydicarbonate; acyl peroxide, for example, dilauroyl peroxide; alkyl peroxide, for example 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane; peroxyesters, for example tert-butyl peroxybenzoate, and the like.
• organic peroxide is also well known in the art, and non-limited examples of organic peroxide may be persulfate, for example, potassium persulfate, sodium persulfate and ammonium persulfate, and the like.
• peroxide thermal initiator may be used alone, or two or even more peroxides may be used together.
• the thermal initiator preferably used is organic peroxide, particularly peroxy esters, and the preferred example thereof is tert-butyl peroxybenzoate, as well as alkyl peroxide, the non-limited example thereof is 1,1-di(tert-butyl peroxy)-3,3,5-trimethyl cyclohexane.
• the amount of the ester peroxide and alkyl peroxide used, based on the total weight of the adhesive composition, is 0.5-5 wt %, preferably 1-4 wt %, more preferably 2-3 wt %.
• the adhesive composition may optionally include liquid polybutadiene component.
• the liquid polybutadiene here is an oligomer of butadiene, i.e., it is a product obtainable by anion polymerization or coordination polymerization, and the degree of polymerization, or the molecular weight thereof or viscosity thereof may be controllable by adjusting the initiator, the amount thereof, the chain transfer agent, the amount thereof, and etc.
• the liquid polybutadiene may have a number average molecular weight of 1000-30000 Daltons, preferably 1500-25000 Daltons, more preferably 2000-20000 Daltons, more preferably 3000-10000 Daltons; and the Brookfield viscosity thereof at 25° C. at a shear rate of 2.55 s ⁇ 1 may be hundred cps to tens of thousands cps, for example 500 cps-50000 cps, preferably 1000 cps-30000 cps, more preferably 3000 cps-20000 cps, still more preferably 5000 cps-15000 cps, measurable by HAAKE Rotational Rheometer with a cone plate (35 mm diameter).
• the liquid polybutadiene useful in the present invention may be those commercially available products, and the non-limiting examples thereof may be: Polybutadiene Ricon 130, Ricon156, LBR307, LBR305 and etc commercially available from Sartomer Company, Inc.; wherein Polybutadiene Ricon 130 has a number average molecular weight of about 2500; and Polybutadiene Jamaican 156 has a number average molecular weight of 1400; or Polybutadiene LBR307, LBR305 commercially available from KURARAY CO., LTD; the number average molecular weight thereof are about 8000 and 26000, respectively.
• the liquid polybutadiene is selected from the group consisting of: PB-3600 from Daicel Chemical co., and Ricon130 polybutadiene from Sartomer Company, Inc.
• the amount of liquid polybutadiene used may be 0-50 wt %, preferably 10-40 wt %, more preferably 20-35 wt %.
• the adhesive composition according to the present invention may optionally contain other additives well known to those skilled in the art, for example, non limiting to: light stabilizer, thermal stabilizer, promoter to photo initiation, promoter to thermal initiation, level agent, toughening agent, thickening agent, and etc.
• said additives may account for 0.01-1 wt %, or 1%-2 wt %, or 0-2 wt %.
• “Substrate to be bonded” The present inventive adhesive composition is particularly suitable for bonding touch screen and substrate of electronic devices.
• the electronic devices include mobile phone, television, palm PDA, notebook, table PC, and other devices having a touch screen.
• the touch screen may be any type of panel in the art, for example, liquid crystal display panel, plasma display panel, and organic electroluminescent panel, and the like.
• the substrate may be any type in the art as well, generally it includes glass or polymeric material.
• Useful glass comprises, but not limiting to, borosilicate glass, soda-lime glass, and any other glasses suitable for display screen.
• Useful polymeric material includes polyester film, for example polyethylene terephthalate PET, polycarbonate film or polyacrylate film, for example, polymethyl methacrylate film, and cycloolefin polymeric film, for example, ZEONOX and ZEONOR from Zeon Chemicals L. P.
• Said substrate preferably has a reflective index comparable with those of display screen, for example, from about 1.4 to about 1.7. Typical thickness of substrate may be about 0.5 to about 5 mm.
• the adhesive composition in accordance with the present invention may be prepared as follows: into a mixing container with conventional stirring means, under the condition of substantially complete darkness, in a predetermined ratio, each components of the adhesive composition are fed into and mixed. Mixing is usually conducted at ambient temperature, or a temperature slightly higher or lower than ambient temperature. Mixing should last for a sufficient time to ensure a uniformly dispersed components, thus obtaining the adhesive composition. Store the thus obtained adhesive composition in dark environment, for subsequent bonding between touch screen and substrate.
• the volume of the mixing container is not specifically defined, per specific requirements, it could be, for example, about 1-100 L, or 5-50 L, or 10-30 L, and etc.
• the mixing container could be such as those commercially available; with a conventional stirring means, such as, paddle stirrer, anchor stirrer, propeller stirrer and the like, the speed of rotation generally depends from the type of the stirrer and the viscosity of adhesive components, and etc. For example. It could be 10 rpm-500 rpm, or 50 rpm-300 rpm, or rotor-stator stirrer may also be adopted, with a speed of rotation of, for example, 300-4000 rpm, preferably 1500-3000 rpm.
• the mixing time could be about 1-10 minutes, or 2 to 8 minutes, or 4-6 minutes and etc; thus obtaining the adhesive composition.
• UV Cure After the touch screen and substrate is bonded with the adhesive composition in accordance with the present invention, the bonded assembly should be cured.
• UV cure of the bonded assembly UV source covering the range of 200 nm-400 nm wavelength could be adopted, for example, with an irradiation power of 100 mW/cm 2 .
• irradiation could be conducted for seconds to tens of seconds, for example 5-30 seconds, or even longer. The irradiation power and time could be easily determined by those skilled in the art per the requirements of products.
• the present invention may take use of commercially available lamp assembly, including an arc lamp, for example, please refer to those disclosed in U.S. Pat. No. 6,520,663 and 6881964, the contents thereof are incorporated here by reference.
• UV cure oven may also be adopted, for example, Loctite UVALOC 1000 from Henkel AG.
• Thermal cure After UV cure, the bonded sample will be further thermal cured.
• Thermal cure may be conducted by any conventional means in the art without any limitation. For example, it may be performed by using an oven with a hot air circulating oven with adjustable temperature controller.
• the specific thermal cure temperature may be, for example 50-150° C., or 60-140° C., 70-120° C., most preferably 80-90° C.
• the time of thermal cure depends on the specific adhesive composition, for example, in case of high content of thermal initiator, cure time could be relatively short, such as 30 minutes to 1.5 hours, and in case of low content of thermal initiator, cure time could be relatively long, such as 1-3 hours.
• Testing Methods involved in the present invention In accordance with the present invention, specifically, testing methods involved are described as follows:
• Viscosity is used to describe the flowing resistance of a liquid, and in principle, it reflects the inner molecular friction.
• the testing instrument used to measure the viscosity of uncured adhesive composition may be commercially available Brookfield rotating viscosity meters, and testing temperature is ambient temperature (about 25° C.), or room temperature, or 60° C. and etc., and the testing may preferably be performed per the specification in ASTM D1086-1997.
• the unit of viscosity is poise or centipoise.
• viscosity is measured at 25° C. at a shear rate of 2.55 s ⁇ 1 by HAAKE Rotational Rheometer with a cone plate (35 mm diameter).
• Light transmittance is an index to describe the transmission of light through a material, typically, it is expressed as a ratio of intensity of transmissive light I t to intensity of incident light I 0 .
• the testing of light transmittance of the adhesive composition may typically measured by conventional commercially available UV light spectrophotometer.
• the thickness of the two pieces of testing samples adopted in the adhesive composition may be controlled in a certain range, for example, about 100 ⁇ m.
• Testing of light transmittance may preferably be conducted according to the specification in ASTM D1005-2007.
• an adhesive is regarded as optically transparent, if it exhibits an optical transmission of at least 85%.
• Bonding Strength is used to characterize the joining strength between two pieces of bonded materials, after the bonding between the samples are sufficiently cured.
• the thickness of the adhesive coating generally is controlled per specific requirements, such as at about 100 ⁇ m.
• Substrate may be selected, per requirements, as glass sheet, acrylate resin sheet, or polyester sheet. In the present testing, the size of glass substrate sample is typically of 100 mm long, 10 mm wide and 2 mm thick.
• Testing equipment for bonding strength may preferably be an universal tensile machine, the mode thereof may be, for example, Instron 5569 from Instron Inc.
• the procedure for measuring the bonding strength is, for example, as follows: dropping the adhesive to be tested in one of the center of a piece of glass sheet, copper wire having 100 um in diameter is disposed at two sides of the adhesive for the purpose of controlling the thickness thereof. Then another piece of glass is lapped vertically above the adhesive, forming a lapping sample in cross form. The lapped sample is further put into a UV cure oven (for example, Loctite UVALOC 1000, Henkel AG) to carry out UV cure. Predetermined condition is: irradiation for 30 seconds, the power thereof is 100 mW/cm 2 .
• a UV cure oven for example, Loctite UVALOC 1000, Henkel AG
• the cured sample is further placed at room temperature for 24 hours, then universal tensile machine is used to tensile the bonded sample vertically in opposed direction.
• the tensile speed may be set as 2 inches/min.
• the bonding strength (unit: MPa) could be obtainable via dividing the value of force recorded in the machine by the lapping area.
• Molecular weight of the starting materials of the adhesive composition includes number average molecular weight, weight average molecular weight, and the like. Unless indicated otherwise, measurement of said molecular weight is conducted by using gel permeation chromatography (GPC) well known and widely adopted in the relevant art. In the measurement, polystyrene having a narrow molecular weight distribution may be used as standard, for example, and tetrahydrofuran may be used as the mobile phase, and the flowing speed, for example, may be 0.8 mL/min, and the column temperature for example, may be 35° C.
• GPC gel permeation chromatography
• a UV light source covering the emitting wavelength of 200 nm-400 nm, having an irradiation power of 100 mW/cm 2 was used to irradiate the boding of adhesive composition between glass and polycarbonate (PC) sheets for 30 seconds.
• the adhesive composition between glass and PC sheets was thermal cured.
• the cure time depended on specific components of the adhesive composition.
• the adhesive composition between glass sheet and glass sheet was cured for 30 seconds, and according to the above mentioned testing method, the bonding strength of the adhesive composition was measured.
• UV light-visible light spectrophotometer was adopted to measure the light transmittance of the adhesive material after curing.
• the thickness of the cured adhesive material was controlled at about 100 ⁇ m. Testing method was per the specification of ASTM D1005-2007. After the irradiation of 100 mW/cm 2 UVA for the adhesive composition between glass and glass sheets for 30 seconds, the light transmittance of the adhesive composition was measured accordingly.
• polyisoprene having UC-203 Kuraray Company
• average degree of methacryloxy group 2-2 functionality 3, number average molecular weight: about 35,000, Tg: ⁇ 60° C. liquid polybutadiene 3-1 Ricon130 (Sartomer Company, Inc.), number average molecular weight: about 2500
• (meth)acrylate monomer 4-1 commercially available isobornyl acrylate (meth)acrylate monomer 4-2 commercially available hydroxypropyl methacrylate (meth)acrylate monomer 4-3 commercially available 2-(2-ethoxyethoxy)ethyl acrylate (meth)acrylate monomer 4-4 commercially available ethylene glycol dicyclopentenyl ether methacrylate
• UV-photoinitiator 5-1 2-hydroxy-2-methyl-1-phenyl-1-propanone (BASF company, Inc.)
• Adhesive composition 1 was formulated according to the composition in Table 1 and formulating method as stated below:
• the formulating procedure of the adhesive composition was as follows: Under a condition of darkness, feeding all above components (total: 100 g) into a plastic barrel having a volume of 150 g in the order listed above, mounting a SpeedMixerTM mixer produced by FlackTech Inc. in the barrel, and all the components were mixed and dispersed at a rotation of 2000-2400 rpm for 10 minutes, thus obtaining a transparent adhesive composition 1.
• Adhesive composition 2 was formulated according to the composition in Table 2 and method as stated in example 1.
• Adhesive composition 3 was formulated according to the composition in Table 3 and method as stated in example 1.
• Adhesive composition 4 was formulated according to the composition in Table 4 and method as stated in example 1.
• Adhesive composition 5 was formulated according to the composition in Table 5 and method as stated in example 1.
• Adhesive composition 6 was formulated according to the composition in Table 6 and method as stated in example 1.
• Adhesive composition 7 was formulated according to the composition in Table 7 and method as stated in example 1.
• Adhesive composition 8 was formulated according to the composition in Table 8 and method as stated in example 1
• Adhesive composition 9 was formulated according to the composition in Table 9 and method as stated in example 1.
• Adhesive composition 10 was formulated according to the composition in Table 10 and method as stated in example 1.
• Example 1 Example 2
• Example 3 Example 4
• Example 5 test 1 cured within cured within cured within cured within 30 seconds 30 seconds 30 seconds 30 seconds 30 seconds test 2 cured within 1 cured within 2
• cured within 2 could not cured within 1 cured within 2 hour at 80° C. hours at 90° C. cured hour at 80° C. hours at 90° C. test 3 >0.6 MPa >0.6 MPa >0.6.

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