IL278475A - Photo -crosslinkable composition - Google Patents

Description

Technical Field The invention concerns mainly a novel family of photo-initiators and polymeric itions for induced cross-linking.

Background Photo-curing, and light induced rization of monomers and ers is well known and d mainly to systems containing double bond of Acrylic and Methacrylic groups in rs and oligomers.

Photo-initiators developed for curing and polymerization of monomers and oligomers containing Acrylic and Methacrylic double bonds possess good miscibility with above systems to provide high efficacy of free radical formation (high yield of free radicals formation out from monomer under UV-light).

In case polymers with low compatibility of the state of the art photo- initiator efficacy of radical formation becomes very low. Photo-initiator of low compatibility forms clusters, where self-quenching of excited les of photo-initiators is responsible for very low radical yield and thus rates of radical reactions in polymer matrix. Thus application of the state of the art photo-initiators for photo-crosslinking of polyolefins is of low efficiency, moreover photo-initiators start to bloom out of polyolefins very fast because of very low limit of their solubility in efins.

A few known photo-initiators for polyolefins and copolymers /1-4/ have limited application because work in UV-C region of UV-spectrum (256nm or 278nm) and give rise to photo-degradation of polyolefin polymers chain together with photo-cross—linking. /1/ US 10,519,286 BZ /2/ EP 0490854 /3/ Q. Wu, B. Qu, Polymer Engineering and Science, July 2001, Vol. 41, Number 7, pp. 1220-1226 /4/ WO 2019/159169 A1 l Description The inventors of this invention have developed a family of thio-alkyl benzophenones that may be used as photo-initiators for cross-linking of different polymers including polyolefms and copolymers of olefins and different co-monomers as Acrylates and Methacrylates, Vinyl acetate, etc. All developed photo-initiators are benzophenone derivatives with Norrish II ism of radical ons initiation in polymer matrix.

Developed photo-initiators possess high compatibility with non-polar polymers (in particular, efins and olefins mers) to enhance the rate of radical formation by hydrogen atom abstraction from polymer chain.

Developed photo-initiators have in their structure sulfur conjugated with benzene ring of benzophenone. The latter is responsible for strong absorption of this type of photo-initiators in UV-A region (wave length > 280nm) with much less destructive effect on polymer chain compared to known benzophenone derivatives (absorption in UV-C at 256nm as in /2/).

The invention further provides a photo-initiator formulation or composition sing, at least, one thio-alkyl benzophenone with general formula (1) as: a (1) R4 R3 R2 R1 Where: R1 is -S-R5, -R5 = -(CI-12)n —CH3, n= 4 -30 R2 is H or -S-R6, or —-R9, R6 = -(CH2)m-CH3, m = 4-30 R9 = -O-(CH2)|-CH3, 1:41-30 R3 is H or —S-R7, or Rm, R7 = -(CH2)k —CH3, k= 4 -30 R10 = -O-(CH2)j-CH3, j=4-30 R4 is H or —S-R3, or R. 1, R3 = -(CH2)i-CH3, i = 4-30 Rn = -O-(CH2)p-CH3, p=4-30 All above derivatives have high extinction coefficient in UV-A region (higher than 100001/mole x cm)) providing high efficiency of radicals formation in efin containing photo-initiators with l chemical formula (I). The main mechanism of ls formation is Norrish II mechanism. Compounds having structure according to formula (I) of the invention can be used as photo-initiators of cross-linking of different polymers such as ABS copolymers, Styrene Butadiene copolymers, LDPE, LLDPE, MDPE, HDPE, PP, copolymers of ethylene and propylene, copolymers of ethylene with acrylic and Methacrylic rs, copolymers of ethylene and vinyl acetate, copolymers of ne and vinyl alcohol, etc.

Photo—initiators according to formula (I) of the invention can be used for cross-linking of solution of ible polymers and polymers blends of immiscible polymers as well by exposure of polymers, polymer solutions and polymer blends containing photo-initiators according to formula (I) to UV-A light of appropriate wave length.

Depending on chemical structure of polymer to be cross-linked, photo- induced cross-linking crosslinking initiated by initiator of general formula (I) can occur via hydrogen abstraction reaction between excited molecule of photo-initiator and polymer molecule to be crosslinked or via electron transfer process between photo-initiator molecule and synergist (e.g. amine derivative) to give a charge transfer complex (CTC), followed by proton transfer leading to formation of amino-alkyl radical and radical of photo-initiator. Formed radicals abstract hydrogen from polymer molecule to start crosslinking reaction.

Excitation of photo-initiator molecule can be performed either by Mercury lamp with on spectrum ranging from 200nm to 700nm or by LED UV—A source with emitting wave lengths distribution substantially pping with absorption spectrum of initiator with l formula (1) of the invention.

Depending on required total gel fraction in polymer (crosslinking density) formed in polymer after irradiation, concentration of initiator can be ranging from 0.05 up to 15%.

In order to enhance photo-crosslinking process synergists (e.g. amines derivatives) or ers (different acrylic and Methacrylic multi- onal monomers and oligomers) can be used er with photo- initiator of general formula (I) of the invention. ‘ 4 Detailed Description of Embodiments High efficiency of photo-crosslinking can be provided only in case photo- initiator possesses appropriate compatibility with polymeric matrix. It means polymer and photo-initiator have similar Hansen solubility parameters. More specially, the vector differences of polar, dispersion and hydrogen bonds ents of Hansen solubility parameters ( 5p, 5d, on) are to be less than 6.0 (J/cm3)“2.

High solubility of photo-initiators of the invention accounts for close interaction of exited state of photo-irradiated benzophenone tive (Norrish II mechanism of radicals initiation) and polymer molecule on the molecular level, to increase substantially transfer of energy from exited photo-initiator to polymer molecule or molecule of synergist, followed by formation of alkyl radical by ction of hydrogen from backbone of irradiated polymer.

In the Table 1 below Hansen solubility parameters for pure benzophenone photo-initiator, 1,2 polybutadiene and hylene are presented.

Vector difference of Hansen lity parameters for pair pure Benzophenone — Polyethylene proved to be 9.0 (J/cm3)”2. Thus, higher than maximal value of vector of difference of Hansen ter presented above (6.0 “2. The latter means there is no compatibility between polyethylene and benzophenone.

Table l Solubility Parameters of Benzophenone, Polyethylene and 1,2 tadiene Solubility Parameter J/cm3 ”2 Pol eth lene —__ 1 2 17.3 2.2 2.5 P01 butadiene 19.5 In case of 1,2 Polybutadiene vector difference of solubility parameters was ed as 6.05 (J/cm3)”2 meaning limited solubility of henone in this polymer.

Incompatibility ofphoto-initiator and polymer matrix results in ng of photo-initiator on polymer surface shortly after its introduction in polymer together with very low efficiency of photo-initiator as source of formation alkyl radicals in polymer under exposure to UV-light. Photo- crosslinking efficacy of photo-initiator immiscible with polymer will be very low if any.

As it was mentioned above for the pair Benzophenone-1,2 Polybutadiene vector difference of Hansen parameters ,6.05 )“2’ is close that for miscibility limit ,6.0 (J/cm3)“2. Practically this means relatively low miscibility and cross-linking capacity, in ular in case of used high concentrations of photo-initiator in the polymer (>0.5%).

Photo-initiators of the invention possess satisfactory compatibility with polyethylene of different densities, linear low y polyethylene, polypropylene and other polyolefins such as copolymers of ethylene with methacrylates, tes, vinyl acetate, propylene, etc.

In the Table 2 data presented on the solubility parameters of the benzophenone derivatives according to general a (I) of the invention.

Below we present method of synthesis of two initiators with general Formula (1) 1. Synthesis of 4-(1-Dodecythio)«benzothenone, Photo-initiator (1) according Formula (1) where R, = -S-(CH2). l-CH3, R2=H, R3=H, R4 :H: 261 g of benzophenone, 6.3g of Cooper powder, 10g of KI and 414g ofK2C03 are placed in 101iters reactor supplied with stirrer and reflux condenser. In the reactive mixture 200g of Dodecanethiol and 2.0 liters of dry Dimethylformamide (DMF) are added. The e of reagents to be boiled during 15 hours in the nitrogen atmosphere.

The t (DMF) is removed in vacuum (100-120mm Hg). Obtained residue is treated by 3.0 liters of toluene followed by filtration through paper filter. The t left on the filter is rinsed by 2 liters of water.

Residual water is removed from filter by drying at 90C. Left product to be subjected to crystallization fiom methanol. The final yield of the photo-initiator is 280g (some 75%) 2. Synthesis of 4,4i-(1-Dodecythio)-Benzothenone, Photo-initiator (2) according Formula (1) where R1 = -S-(CH2)1 i-CH3, R2=-S-(CH2)11- CH3, R3=H, R4=Hz The method of synthesis of the Photo-Initiator (2) is very similar to that for the Photo-Initiator (1). Using main reagents are 4,4,- Dibromobenzothenone (340g), cooper powder (12.6g), KI (20g), K2C03 (828g) and Dodecanethiol (400g) The yield of reaction is 495g of Photo-initiator (2), 85%.

The vector of the difference of solubility parameters of low density polyethylene and photo-initiator number 1 in the Table 2 was calculated as 1.36 (J/cm3)“2, for photo-initiator number 2 in the Table 2 vector of solubility parameters difference was ated as 0.65 (J/cm3)“2. In both cases basing on assessments done photo-initiator number 1 and number 2 in the Table 2 should possess high compatibility with polyethylene and other polyolefins as well. Above photo-initiators will not bloom out of polyethylene and other polyoleflns up to high concentrations in polymers (at least 5%).

Table 2 Solubility Parameters of Benzophenone Derivatives of the Invention Number of Photo- Photo— Initiator Initiator Structure According to Formula R1 = -S- (CH2): l-CH3 (CH2); l-CH3 R3 = H R4 = H In below Examples, the efficiency of photo-induced cross-linking of LDPE in the presence of photo-initiators of l formula (I) is ed to induced cross-linking of photo-initiator 4- hydroxybenzophenone laurate (Cas 142857-24—7) and photo-initiator according to W0 2019/ 1 591 69 /4/, with R1: -O-CH2-COO-CH2-CH3, R2: -O-(CH2)7-CH3, R3=H, mentioned as initiator 4 It is well known that direct introduction of additives in polymers, as powders or liquids, leads to inhomogeneous distribution followed by non- even cross-linking in r bulk. Thus, before final mixing with polyolefins, master batches of particular photo-initiators were ed.

Concentration of the photo-initiators in master batches was 10% w/w.

Master batches were produced by twin screw extruder with construction of screws providing very homogeneous distribution of photo-initiators in the master batch. Adding of photo-initiators into polyolefins via master batches leads in ucible s in terms of changes of properties after photo-induced cross-linking process.

Two types of experiments utilizing photo-initiators of the invention are presented in the examples below: -Cross-linking films of LDPE in a single bubble extrusion process in order to improve tensile properties of films (e.g. for packaging), while keeping UV-treated r in form e for melt welding; -Cross-linking of LLDPE primary tube of oriented film made by a double bubble technology, in order to increase tensile properties of the polymer melt during orientation of the first bubble by inflation (stretching). The final t is shrink film used for packaging of ent goods or g of flesh food (e.g. poultry).

In the case of regular film cross-linking, LDPE made film was UV- irradiated off line. Irradiation of films was conducted from both sides.

In the case of oriented films production, UV-sources was placed on line to irradiate both sides of primary film to be oriented.

Photo-initiators were introduced in polymers via -batches containing 10% of initiators by dosing systems mounted on the hopper of extruder.

Thickness of regular films was some 90microns. Degree of cross-linking of films of that type was tested by measuring creep time of film (1.0inch width) at 137C with load of 57g Thickness of oriented films was some 20microns. Degree of cross-linking of these films was tested by fixing creep time of film (1.0inch width) at 137C with load of 19g. 1.0mm, 2.0mm and 3mm thick slabs of polyolefins (LDPE, I—IDPE) were prepared by the method of melt pressing to simulate cable insulating coatings or pipes. Cross-linking promoters [e.g. trimethylol propane trimethacrylate (TMPTMA), Tri-allyl-iso-cyan-urate (TAIC) were added as master s containing between 5% and 30% of cross-linking promoter. Efficacy of used photo-initiators was tested by measurement of gel fraction in irradiated polymer by well-known method of extraction of sol fraction in boiling xylene.

Slabs were irradiated by UV-light of Mercury lamp of medium pressure equipped with conveyor. Power of lamp used was 1.0kW. Appropriate nce was used to measure exposure dose a specimen ed in J/cmz.

The Table 3 presents data on re dose needed to cross-link of samples to get creep time of ISSec to acquire desired tensile properties.

As it well seen from the Table 3, photo-initiators according to the Formula I in Samples 1. And 2 proved to be substantially more effective than comparative photo-initiator as regards cross-linking of LDPE.

In the Table 4, data are presented on the exposure dose needed to obtain 153ec creep time for ed films made of LLDPE of 20microns thick in case of on line irradiation of primary tube of 0.4 mm thick by UV- lamp.

Table 3 Creep Times of Irradiated Films Number of Photo-Initiator Used Concentration Exposure Sample of Photo- Dose*, J/cm2 Initiator, % According Formula (I), R] = -S-(CH2)] l' CH3 R2 = H R3 = H R4 = H According to Formula i (I), R] = -S-(CH2)[|- CH3 R2 = -S-(CH2)1|-CH3 R3 = H R4 = H 4- 0.35 Hydroxybenzophenone Laurate, Cas 142857- 24-7” Photo-Initiator -4 0.25 5.0 W02019/159169 A1 ure Dose in .l/cm2 to obtain creep time for irradiated LDPE made films of 90microns thick ning photo—initiators according Formula I and comparative photo-initiator. Exposure Dose to get ISSec creep tome at 135C and 57g loading. Irradiation from both sides of film ** Comparative photo-initiator Table 4 Creep Times of Photo-Irradiated Oriented Films Number of Initiator Used Concentration Exposure Sample of Photo- Dose*, J/cm2 Initiator, % According Formula I, 0.30 R] = -S-(CH2)11-CH3 R2 = H R3 = H R4 = H According to Formula 0.35 ( I),R| = -S-(CH2)| 1‘ CH3 R2 = -S-(CH2)1 1-CH3 R3 = H R4 = H 3. 4-Hydroxybenzophenone0 Laurate, Cas 142857- 24-7” ure Dose in J/cm2 to obtain creep time for ated LDPE made films of 20microns thick containing photo-initiators according Formula I and comparative photo-initiator. Exposure Dose to get ISSec creep tome at 137C and 19g loading. Thickness of irradiated primary tube was 0.4mm ** Comparative photo-initiator As it is clear from the Table 4, that photo-crosslinking with usage of photo-initiators based on Formula 1 proved to be more effective than cross-linking with application of ative photo-initiator.

In the Table 5 data are presented on exposure dose needed to achieve 65% gel fi'action in samples of different polyethylenes and of different thicknesses. Gel fraction is measured as e left after extraction in boiled xylene during 48h in the presence of 0.1% of antioxidant Irganox 1 01 O.

Table 5 Exposure Doses ) Needed to Obtain 65% Gel Fraction in ent Samples of LDPE Made Slabs of Various Thicknesses Nu Sample Thick Concen Concent Expo mbe Name —Bness, tration ration of of photo- promote initiator (TMPT According e O to Formula (1), RI: “'8" -(CH2)I 1-- CH3, R2 = H, R3=H, R4=H According . o to Formula (1), RI: '8' -(CH2)I 1-- CH3, R2 = H, R3=H, R4=H According E"O H {)1 y—n o -O u—i O -N to Formula (1), RI: '8' -(CH2)11-- According . . to Formula (1), RI: -S- -(CH2)n-- 4- Hydroxyben zophenone Laurate, Cas 1 42857-24- 7, Comparative sam . le 4- Hydroxyben one Laurate, Cas 1 4285 7-24- 79 Comparative sam u le Photo- Initiator -4 Data in the Table 5 show that compositions based on photo-initiators according to Formula (I) are substantially more effective than photo- initiator used as comparative sample.

Bearing in mind photo-initiators according to Formula (1) absorb light in UV-A region and photo-initiator used as comparative sample absorb light in UV-C region, an application of both types of above initiators in multilayer films can substantially accelerate cross-linking process. In the Table 6 data are presented on irradiation of 5 layers’ film where 15‘, 2'“, 4th and 5th layers of ayer film contain photo-initiators. In the comparative sample all layers excepting the layer number 3 contain only initiator 4-hydroxybenzophenone e (absorption maximum at 256nm, UV-C). In the example according to this invention lSt and 5th layers contain 4-hydroxybemzophenone laurate, but 2nd and 4th layers of ayer film contain photo-initiator of this invention with structure according Formula (I). Photo-Initiator absorbs at 325nm (UV-A region). 11 Table 6 Application of the Photo-Initiator of the ion in Multi-Layer Film Type of Photo— l"t 2"d 3d 4th 5‘“ Initiator Iaye laye lay laye r* r er r Accordin According to 0 0.35 0 0.35 0 g to Formula (1), % % Inventio RI: -S- - n (CH2)1 r-CH3, R2 = H, R3=H, R4=H 4- Hydroxybenzop henone Laurate, Cas -24- 7 4- 0.35 0.35 0.35 0.35 Hydroxybenzop % % % % henone Laurate, Cas -24- 7 *Multi-layer oriented film of 5 layers in total. Film is produced by double bubble technology, irradiation of the first bubble of total thickness of 500microns. Thickness of each layer is 100microns.

Thickness of each layer is 100microns.

Irradiation was performed on both sides of primary tube.

The thickness of each layer was rons, it was primary tube irradiated before orientation to produce final oriented multi-layer film of total thickness of 20microns.

The Table 6 contains results on exposure doses under UV-Lamp to get creep time of ISSecunds for 20micron oriented film at 135C and 37g loading.

As it well seen from the Table 6, the ation of photo-initiator active in UV-C range and photo-initiator of the ion active in UV-A range in different layers results in substantial decrease of exposure dose needed to attain required creep time of the final oriented film made of LDPE meaning the same level of cross-linking can be achieved with lower dosage applied.

Claims (17)

Claims

1. Photo-Crosslinkable composition ting of polyolefins or copolymers of olefins either with other olefins of different nature (e.g. ethylene and propylene, ethylene and butylene, etc.) or with co-monomers of different nature (e.g. ne and methyl- methacrylate or vinyl e, etc.) and photo-initiator of general chemical structure as below: Formula (1) Where: R! is -S-R־, -R5 = -(CH2)״ -CH3, n= 4 -30 R2 is H or -S-R6, or -R9, R» = -(CH2)m-CH3, m = 4-30 R9= -O-(CH2)1-CH3,1=4-30 R3 is H or -S-R7, or R!o, R7 = -(CH2)k -CHj, k= 4 -30 R,0 = -O-(CH2)j-CH3,j=4-30 R4 is H or-S-Rg, or R״, R8 = -(CH2)؛-CH3, i = 4-30 R11 = -O-(CH2)p-CH3, p=4-30

2. Photo-Crosslinkable composition as in the Claim 1, where concentration of initiator ranges from 0.01% up to 15%, better from 0.1% to 10%.

3. Photo-Crosslinkable composition as in the Claim 1 and containing synergist

4. Photo-Crosslinkable composition as in the Claim 1 and 3 where synergist is proton donor

5. Photo-Crosslinkable ition as in the Claim 4 where proton donor is alcohol or amine

6. Photo-Crosslinkable composition as in Claims 1 and 3 where concentration of photo-initiator ranges from 0.01% up to 15%, better from 0.1% to 10% and concentration of synergist ranges from 0.01% to 15% better from 0.1% to 10%

7. Photo-Crosslinkable composition as in the Claim 1 and containing cross-linking promoter 13

8. Photo-Crosslinkable ition as in the Claim 7, where er comprises substances containing double bonds (Vinyl, Acrylic, Methacrylic, etc.). Double bond can be end groups (e.g. Acrylic double bond) or internal double bonds (e.g. double bonds in oleates, linseed oil or poly-dienes)

9. Photo-Crosslinkable composition as in the Claim 7, where crosslinking promoter containing double bonds can be mono- functional or multi-functional

10. Photo-Crosslinkable ition containing photo-initiator according to the claim 1 and crosslinking promoter, where concentration of photo-initiator and promoter ranges from 0.01% up to 15%, better from 0.1% to 10% each.

11. .Photo-Crosslinkable composition containing photo-initiator as in the Claim 1, ist as in the Claim 3 and promoter as in the Claim 1.

12. Crosslinkable composition as in the Claim 11 containing 0.01% to 15% each of photo-initiator, synergist and promoter, better 0.1% to 10% of each.

13. Photo-Crosslinkable composition according to Claim 1 can contain antioxidants (e.g. like hindered phenols), Hindered Amine Light Stabilizers (HALS), UV-absorbers of henone, hydroxy- riazole or ne types.

14. Photo-Crosslinkable composition composed of photo-initiator ing to Formula (1), synergist, cross-linking promoter, anti- oxidant, Hindered Amine Light Stabilizer (HALS) and UV- absorber.

15. Photo-Crosslinkable composition according to the Claim 14 where concentration of photo-initiator ranges from 0.01% to 10%, concentration of synergist ranges from 0.01% to 10%, concentration of promoter ranges from 0.01% to 10% each, concentration of antioxidant ranges from 0.01% to 2.0%, concentration of HALS ranges from 0.01 to 5%, concentration of UV-absorber ranges from 0.01% to 5.0%

16. Method of synthesis of photo-initiators according to Formula (1). Representative syntheses of photo-initiators with general structure according to the Formula (I), is presenting below: Synthesis of 4-(l-Dodecythio)-benzothenone, Photo-initiator (1) according Formula (1) where R! = -S-(CH2)11-CH3, R2=H, R3=H, R4 =H: 261g of benzophenone, 6.3g of Cooper powder, 10g of KI and 414g of K2CO3 are placed in lOliters reactor supplied with stirrer and reflux condenser. In the reactive mixture 200g of Dodecanethiol and 2.0 14 [Link] mailto:olegb@mobichem-sci.com [Link] http://www.mobichem-sci.com liters of dry Dimethylformamide (DMF) are added. The mixture of reagents to be boiled during 15 hours in the nitrogen atmosphere. The solvent (DMF) is removed in vacuum (100-120mm Hg). Obtained residue is treated by 3.0 liters of toluene followed by filtration through paper filter. The product left on the filter is rinsed by 2 liters of water. Residual water is removed from filter by drying at 90C. Left product to be subjected to crystallization from methanol. The final yield of the photo-initiator is 280g (some 75%) Synthesis of 4,4 -(1-Dodecythioj-Benzothenone, Photo-initiator (2) according Formula (1) where R! = 2)n-CH3, R2=-S-(CH2)11- CH3, R3”H, R4 H: The method of synthesis of the Photo-Initiator (2) is very similar to that for the Initiator (1). Using main reagents are 4,4 - Dibromobenzothenone , cooper powder (12.6g), KI (20g), K2CO3 (828g) and Dodecanethiol (400g) The yield of reaction is 495g of Photo-initiator (2), 85%.

17. Method of photo-cross-linking of polyolefins by Light Emitting Diodes (LED) light sources 1 8. Method of photo-cross-linking of efins by LED light sources in UV-C, UV-B and UV-A regions of light spectrum M OB I Ch em ScientifkEngineeringLtd. /f ----- Dr. Oleg Berezin ___ ** Director P.O.B. 45390. !9 Hartum St.. Bar m.91451. Jerusalem, Israel lei: 972-2-5860324 Fax: 972-2-5902602, :054-4948370 e-mail: olegb@mobichem-sci.com. www.mobichem-sci.com