The present invention relates to photo initiator compositions for curing photo curable resins.

BACKGROUND ART

Resin-compositions, which are polymerizable and/or crosslinkable by electromagnetic radiation, such as electromagnetic radiation comprising UV, visible and IR light, are suitable for use in many applications. In the resin-compositions the electromagnetic radiation affects photo initiator systems in the resins.

Photo initiator systems are widely used in industrial applications and serve to facilitate the curing of curable resins, such as epoxy resins, by means of light, such as UV light or IR light.

Polymerized resins are used in several industrial applications, e.g., fiber reinforced products like wings for windmills and hulls for boats, but also fiber reinforced linings for pipe rehabilitations, tanks and sewers is a well known technology. Also known are such durable coatings for metal, constructions or buildings.

Several photo initiator systems have been developed, and different photo initiator systems may cure resins at different wavelengths or resins with a specific composition.

However, there has been a long-felt need in the field of (photo) curing of curable resincompositions to find improved and reliable photo initiator systems for curing resins and methods for providing cured structural parts, i.e., parts and resin objects having a thickness of at least 0.5 to 8 mm and having appropriate mechanical properties such as tensile strength and modulus, hardness, adhesion and chemical resistance as well as low shrinkage.

Safety considerations also play a major role when curing a polymerizable or crosslinkable resin mixed with (co)polymerizable free monomer, i.e., in a reactive or non- reactive diluent. Reactive or non-reactive diluents are generally relatively volatile compounds that may be dangerous because of explosion risks at incidentally occurring high temperatures, and because of toxicity aspects during preparation of the cured materials. The process of curing is also time consuming. Moreover, the photo initiator systems used today have a rather short period in which they can be stored. This is due to the fact that the ingredients in the photo initiator compositions have very short storage stability. Thus, the photo initiator compositions have to be mixed with the photo curable resins and used within few weeks.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide photo initiator compositions for curing photo curable resins which provide an efficient curing and have good storing properties, good mechanical properties, easy handling, and are an economical alternative to traditional resin systems.

The photo initiated resins according to the invention apply for the same general purpose as described for traditional resins. The photo initiated resin composition can be used together with photo curable resins and reinforcing materials for providing cured products. The photo curable resins can for example be styrene based resins or epoxybased resins. The reinforcing materials could be any fibers or particles normally applied in cured objects such as nano-particles, glass fibers, polyolefin fibers, flax, linen, carbon fibers, steel and Kevlar fibers or basalt, and any combinations thereof. The resin composition is also used with fillers, and extenders to achieve the desired properties.

The invention aims at improving photo initiator compositions in respect of the storage stability, easy handling with improved properties. The invention is characterized by having two, three or more independent photo initiators with a storage life of at least 1 month to 2 years for sealed packages under normal conditions. The compositions are mainly used with unsaturated polyester resin, vinyl ester resin, epoxy acrylates, polyester acrylates, photo cured acrylates resins, and most styrene, methyl styrene containing resins. The resin systems containing the invented composition are exposed to UV-LED or UV light, which cured within few seconds.

The invention provides a composition with two or more photo initiators containing resin compositions which can be used with unsaturated polyester resin, vinyl ester resin, bisphenol-based epoxy resins, cycloaliphatic epoxy resins, epoxy acrylates, polyester acrylates, photo cured acrylates resins, and most styrene, methyl styrene containing resins with 1 % to 10 %, typically 4 % to 8 %. After mixing, the composition is used together with reinforcing material and the resin composition is exposed to UV LED light at 360 nm to 520 nm wavelength, typically 380 nm to 480 nm wavelength, at 0.001 W/cm2 to 10 W/cm2 intensity for curing. The composition is used with reinforcing material such as nano-particles, glass fibers, polyolyfine fibers, flax, linen, carbon fiber, basalt or similar reinforcing materials in a thickness of 0.2 to 8 mm, typically 2 to 5 mm. The reinforcing material is wetted with the photo initiator composition to provide a resin filled fiber composition that is being cured when exposed to the UV LED light. The photo initiator composition of the invention can, when mixed with resins and reinforcing materials, also be used to reinforcement of CIPP (cured-in-place pipe) and load carrying constructions.

The compositions according to the invention have proven to cure fast, even in thick reinforced materials from 2-8 mm, and are an economical alternative to conventional cured systems having similar mechanical properties.

The present invention relates to a photo initiator composition for curing photo curable resins comprising at least two photo initiators, camphorquinone as photosensitizer, and an epoxy-based resin, wherein at least one of the photo initiators is a cationic photo initiator, and wherein the composition after being added to reinforcing material is curable with UV light having wavelengths in the range 360 nm to 520 nm.

In an embodiment, the present invention provides a photo initiator composition for curing photo curable resins comprising at least two photo initiators selected from 4- isopropyl-4’-me-thyldiphenyliodonium tetrakis(pentafluorophenyl)borate) and phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide, and at least one photosensitizer selected from camphorquinone, and wherein diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide and phenyl bis (2,4,6-trimethyl- benzoyl)phosphine oxide each constitutes at least 10 % of the composition, and camphorquinone constitutes at least 0.2% of the composition.

It has been realised that the unique compositions with the selected photo initiators combined with camphorquinone provide excellent curing of resins and moreover have good properties in respect of curing. In an embodiment, the photo initiator compositions comprise the ingredients:

Bisphenol A/F resin 10 - 45 % diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide 10 - 30 % phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide 10 - 30 % camphorquinone 1 - 30 %

The compositions including Bisphenol A/F resin serve to improve the properties of the compositions.

All percentages are weight-% (percent % (w/w)).

The photo initiator composition according to the invention can be used in amounts of about 1 % to about 10 %, such as about 4 % to about 8%, for curing of unsaturated polyester resin, vinyl ester resin, epoxy acrylates, polyester acrylates, photo cured acrylates resins, and also styrene and methyl styrene containing resins. When the photo initiator composition is mixed with a resin and applied with reinforcing material, the mixture can be cured with a short reaction time. Furthermore, the photo initiator composition has excellent properties in respect of storage and can be stored for a long time.

The compositions provide a resin product (cured resin) with good mechanical properties, e.g., in respect of strength.

The photo initiator composition is applied together with reinforcing materials, preferably selected from nano-particles, glass fibers, polyolyfine fibers, flax, linen, carbon fiber, basalt or similar reinforcing materials. The compositions can be applied together with reinforcing materials with a thickness of about 0.1 to 10 mm, such as about 2 to 5 mm. Thus, the compositions can be applied in rather thick layers and still be cured.

For the purpose of curing the photo initiator compositions, in an embodiment the compositions are exposed to UV LED light wavelengths ranging from about 360 nm to about 520 nm, such as from 380 nm to 480 nm, with an intensity from about 0.001 W/cm2 to 10 W/cm ² . LED light is convenient and cost effective in use compared with traditional light sources. During the curing process the compositions are exposed to UV LED light for up to 1 to 200 seconds, such as up to 10 to 60 seconds. Thus, it is possible to obtain a cured resin in less than three and a half minutes.

When the composition is exposed to an UV LED light source, the UV LED light source is in an embodiment moved over the surface of the resin filled fibre at the speed of about 5 m/hr to about 80 m/hr.

The invention provides a photo initiator and epoxy composition comprising: Epoxy resins 75 - 95 %

Benzopinacole 0.5 - 5 %

A solution of Bis[4-(diphenylsulfonio)phenyl]sulfide bis(hexafluoroantimonate) and Antimonate(l-), hexafluoro, diphenyl[(phenylthio)phenyl]sulfonium 1 - 7 %

Camphorquinone 0.1 - 5 %

(4-(1-methylethyl)phenyl)-(4-thylphenyl)iodonium tetra-kis(pentafluorophenyl)borate(1-) 0.001 -5 %.

In a preferred embodiment, the photo initiator and epoxy composition comprises:

Epoxy resins 75 - 95 %

Benzopinacole 0.2 - 5 %

A solution of Bis[4-(diphenylsulfonio)phenyl]sulfide bis(hexafluoroantimonate) and Antimonate(l-), hexafluoro, diphenyl[(phenylthio)phenyl]sulfonium 1 - 7 %

Camphorquinone 0.3 - 4 %

(4-(1-methylethyl)phenyl)-(4-thylphenyl)iodonium tetra-kis(pentafluorophenyl)borate(1-) 0.001 - 5 %

In another preferred embodiment, the photo initiator and epoxy composition comprises:

Epoxy resins 75- 95 %

Benzopinacole 0.5 - 5%

A solution of Bis[4-(diphenylsulfonio)phenyl bis(hexafluoroantimonate) and Antimonate(l-), hexafluoro, diphenyl[(phenylthio)phenyl]sulfonium 0.4 - 3 % Camphorquinone 0.2 - 2.0 %

(4-(1-methylethyl)phenyl)-(4-thylphenyl)iodonium tetra-kis(pentafluorophenyl)borate(1-) 0.001 - 5 %.

In the above-mentioned photo initiator and epoxy compositions, the Bis[4- (diphenylsulfonio)phenyl]sulfide bis(hexafluoroantimonate) and antimonate(l-), hexafluoro, diphenyl[(phenylthio)phenyl]sulfonium may be provided in a dry form.

Alternatively, the Bis[4-(diphenylsulfonio)phenyl]sulfide bis(hexafluoroantimonate) and antimonate(l-), hexafluoro, diphenyl[(phenylthio)phenyl]sulfonium may be provided in a solution such as a propylene carbonate solution.

The cationic photointiator mix (sulfanediyldibenzene-4,1-diyl)bis(diphenylsulfonium) bis(hexafluoroantimonate) in propylene carbonate is available from Lambsom Group Ltd. under the name Speed cure 976.

The cationic photointiator (Tolycumyl) iodonium tetrakis (pentafluorophenyl) borate is available as Bluesil PI 2074 from Elkem Silicones.

The photo initiator and epoxy compositions are used together with reinforcing materials as liquid epoxy resins, solid epoxy resins, semi liquid epoxy resins, cycloaliphatic epoxy resins, cycloaromatic epoxy resins as well as epoxy resins diluents for hybrid photo polymerisation.

The photo initiator and epoxy compositions have very good adhesion to various substrates and exhibit low shrinkage, typically below 2% volumetric, and are moreover curable in thick reinforced materials having a thickness from about 2 mm to about 8 mm.

In an embodiment, the photo curable epoxy based resin is filled in reinforcing materials selected from nano-particles, glass fibers, polyolyfine fibers, flax, linen, carbon fiber, basalt or mixtures thereof, in a thickness of about 0.1 mm to about 10 mm, typically from about 2 mm to about 5 mm, and exposed to the UV LED light source having a wavelength in the range 360 - 520 nm, preferably in the range 380 - 480 nm, at the intensity of 0.001 W/cm ² to 10 W/cm ² up to 1 to 200 seconds, typically from 10 to 60 seconds. In an embodiment, the photo initiator composition comprising:

Epoxy resins 75 - 95 %

Benzopinacole 0.2 - 5 %

A solution of Bis[4-(diphenylsulfonio)phenyl]sulfide bis(hexafluoroantimonate) and Antimonate(l-), hexafluoro, diphenyl[(phenylthio)phenyl]sulfonium 0.4 - 7 %

Camphorquinone 0.1 - 5 %

(4-(1-methylethyl)phenyl)-(4-thylphenyl)iodonium tetra-kis(pentafluorophenyl)borate(1-) 0.001 - 5 % is exposed to the UV LED light source, which is moved over the surface of the resin- filled fibre at the speed of 5 to 80 m/hr.

The photo curable epoxy based resin adds good properties to the reinforcing materials.

In another aspect, the invention provides a method for curing the composition according to any of claims 1 - 12, wherein the composition is exposed to UV LED light for up to 1 to 200 seconds and moved over the surface of the resin-filled fibre at the speed of 5 to 80 m/hr.

In another aspect, the invention thus provides for the use of the photo initiator composition together with reinforcing materials such as nano-particles, glass fibers, polyolefin fibers, carbon fibers, steel, Kevlar fibers and basalt.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in further details with reference to some examples.

EXAMPLE

1 . UV LED curing of unsaturated polyester resin with photo initiator com- position according to the invention.

1.1. Light Cure

The photo initiators phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide (BAPO) and diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) have an absorption band in the long wave UV around 350 - 420 nm, and are combined with long wave absorber camphorquinone at 450-470 nm, which leads to a very good through cure in the unsaturated polyester resin or other resins containing styrene.

The photo initiators absorb the light to form an excited triplet state that goes on to have two active free radicals via alpha-cleavage of the CO-alkyl bond called phosphinoyl and benzoyl radicals.

The free radicals are reacted with double bonds of vinyl monomer and polyester resin. Towards the end of the polymerization process the low molecular weight vinyl monomer, especially styrene, copolymerizes with the ethylenic unsaturated cross- linked matrix.

Preparation

1.2.1 Preparation of the Photo initiators composition.

The bisphenol A/F based epoxy is heated up to 50°C, and TPO is added while con- tin- uously stirring. When the TPO is dissolved completely, BAPO and camphorquinone are added. The mixture is stirred continuously at 50°C until the photo initiators have mixed/dissolved completely.

The % of the ingredients as below:

Bisphenol A/F resin 60 %

TPO 12 %

BAPO 24 %

Camphorquinone 4 %

1.2.2 Preparation of the unsaturated polyester resin system.

The photoinitiator mixture is added to the unsaturated polyester resin while continuously stirring till the mixture becomes homogenous.

The % of the ingredients below:

Unsaturated polyester resin 96 %

Photo initiator composition 4 % 1 .3 Application of the resin composition.

1.3.1 Clear cast resin.

A mould was prepared with the above prepared composition mixture with unsaturated polyester resin. A source of UV LED light, which has a wavelength of 440 to 460 at the intensity from 0.1 to 10 W/cm2, was applied up to 1 to 200 seconds, typically 10 to 60 seconds. The reaction generates heat up to 100 to 200°C. The cured items were cooled down to room temperature and tested for the physical as well as mechanical properties.

Clear cast resin physical and mechanical properties:

Tensile strength 50-70 MPa (ASTM D 638 - 2a)

Tensile modulus 30-4000 MPa (ASTM D 638 - 2a)

Flexural strength 100-110 MPa (ASTM D 790)

Flexural modulus 30-4000 MPa (ASTM D 790)

Shore D hardness 85-90 (ASTM D 2240)

Glass transition temperature (Tg) 100 -120°C (ASTM E1356-08)

1.3.2 Glass fiber application.

The above prepared composition mixture with unsaturated polyester resin was also applied on 3 to 6 mm thick polyolefin-based fibre under dark conditions. The source of UV LED light, which has a wavelength of 440 to 460 at the intensity from 0.1 to 10 W/cm ² , was ignited. The light moved over the surface of the resin-filled fibre at the speed of 10 to 80 m/hr. The fiber-reinforced structure was allowed to cool down to room temperature and the ultimate mechanical properties were measured.

Pull-off Adhesion on cast iron 5 - 7 MPa (ASTM D4541)

Pull-off Adhesion on Cured polyester resin surface 6 - 8 MPa (ASTM D4541) Reaction scheme:

Camphorqiunone

BAPO phosphinoyl radical benzoyl radical

Alpha cleavage of BAPO and TPO

Cured polymer matrix EXAMPLE 2

2. Photo initiator mixture used for hybridisation with vinyl monomers and epoxy resin.

The above-described photo initiator mixture was used for the hybridisation of vinyl monomers and epoxy resin with photo initiator bluesil PI 2074 (4-isopropyl-4’-me- thyldiphenyliodonium tetrakis(pentafluorophenyl)borate) along with onium salts, such as triphenyl sulfonium salts, diaryl iodonium salts, ferrocenium salts and various other metallocene compounds, and as photosensitizer camphorquinone. The epoxy resins are mainly solid epoxy resins, liquid epoxy resins, semi liquid epoxy resins and various type of epoxy resin diluents. The vinyl monomers are various types of acrylates, styrenes and Diallyl phthalates for improvement of the mechanical, physical as well as the thermal properties of the resin system.

The cationic photointiator composition Speed cure 976 ((sulfanediyldibenzene-4,1- diyl)bis(diphenylsulfonium) bis(hexafluoroantimonate) in IPA) available from Lamb- som Group Ltd. was used. Absorption maxima of the composition appear at 230 and 295 nm.

Moreover, the cationic photointiator (Tolycumyl) iodonium tetrakis (pentafluorophenyl) borate was used. The cationic photointiator is available as Bluesil PI 2074 from Elkem Silicones.

The reaction is a hybrid reaction of the free radical polymerisation and cationic polymerisation, which contributes to good mechanical properties of the end polymer matrix.

The % of the ingredients are as below:

Expoxy resins 98.8 %

Benzopinacole 0.4 %

Speedcure 976 0.3 %

Camphorquinone 0.2 %

Bluesil PI 2074 0.3 % The mixture was applied on 1 to 6 mm thick fibre under dark conditions. The source of UV LED light having a wavelength of 440 to 460 at the intensity from 0.1 to 10 W/cm2 was ignited, and the fibres with the mixture were exposed to light for 7-15 seconds. The fiber-reinforced structure was allowed to cool down to room temperature, and the ultimate mechanical properties were measured.

Clear cast resin physical and mechanical properties:

Tensile strength 60-70 MPa (ASTM D 638 - 2a)

Tensile modulus 30-4500 MPa (ASTM D 638 - 2a)

Flexural strength 90-120 MPa (ASTM D 790)

Flexural modulus 30-4500 MPa (ASTM D 790)

Shore D hardness 90 - 95 (ASTM D 2240)

Glass transition temperature (Tg) 120-140°C (ASTM E1356-08)

Reaction scheme:

Crosslinked polymer EXAMPLE 3

Storage stability

The storage stability of the photo initiator composition provided in example 2 was tested.

5 kg of the composition was stored in a PE container at room temperature avoiding direct sunlight, i.e. at common storage conditions. Three samples (triplicate) were taken in 16 mm test tubes at day 0, 14 and 29, respectively. The samples were subjected to 450 nm LED at an intensity of 673 W/km ² . The temperature and the duration of time for the composition to reach the maximum temperature were measured.

The results are shown in the below Table 1 :

Reactivity:

Table 1

It was found that the peak temperatures and the duration of time required for the composition to reach the peak temperature was stable during the period from day 0 to day 14 and at day 29. Thus, the composition has a storage stability of at least 1 month.

EXAMPLE 4

Shrinkage I chemical resistance

Shrinkage as an indication of the chemical resistance of the photo initiator composition provided in example 2 was tested. The solution was poured into molds of 4 mm x 10 mm x 100 mm and cured at 450 nm LED at an intensity of 673 W/km ² . Shrinkage I chemical resistance was measured by identifying the difference in weight of the cured product after immersion in different immersion solutions at 60°C for 30 days. For each solution three samples were tested (triplicate). The immersion solutions, initial weight of the cured composition and the weight of the cured composition after immersion and the calculated difference in weight (average for the three samples tested per solution) are shown in the below Table 2.

The immersion solutions applied were water at different pH (3, 7, and 11 , respectively) adjusted by adding 5% NaOH, 30% NaOH, 5% HCI, 15% H2SO4, 10% or HNO3, respectively, and xylene, alcohol ethanol and styrene.

As shown in Table 2, the shrinkage for the product tested is very limited - in the majority of the tests, the shrinkage was below 1%. Also, when immersed in water of pH 3 and 15% H2SO4, the shrinkage was below 2%. In 5% HCI, the shrinkage observed was slightly above 2%. Thus, in conclusion, the chemical resistance of the cured product is very high.

Table 2