WO2024246087A1

WO2024246087A1 - Tool material for producing lenses; method for its preparation and its use

Info

Publication number: WO2024246087A1
Application number: PCT/EP2024/064695
Authority: WO
Inventors: Luca Lucera; Agnes VERES-NAGY; Yee Song KO
Original assignee: Ams-Osram International Gmbh
Priority date: 2023-05-30
Filing date: 2024-05-29
Publication date: 2024-12-05

Abstract

The invention concerns a tool material for preparing lenses obtainable by crosslinking a first perfluoropolyether having at least one first crosslinking group and a second perfluoropolyether having at least one second crosslinking group in the presence of a photoinitiator. Furthermore, the invention concerns a method for preparing the tool material and the use of the tool material for preparing lenses.

Description

TOOL MATERIAL FOR PRODUCING LENSES ; METHOD FOR ITS PREPARATION AND

ITS USE

The present application claim priority from patent application DE 10 2023 114 174 . 0 dated May 30^th , 2023 , the disclosure of which is incorporated herein by reference in its entirety .

The present invention concerns tool materials for preparing optical lenses , a method for the preparation of the tool material and its use .

BACKGROUND

The trend towards miniaturization and the associated increase in demand for micro-optical components made of glass have greatly changed glass optics production in recent years : Grinding and polishing, i . e . , direct manufacturing processes , cannot produce the glass optics in the required quantities . For this reason, precision moulding is now establishing itself as a new, alternative manufacturing technology . In this process , a preformed and polished glass blank is heated and formed using two , usually ceramic , mould halves . In this way, a large number of high-precision optical components can be efficiently manufactured from glass .

In the manufacture of plastic optics , wafer-based production is already an established process that can be used to produce a wide variety of micro-optics on wafers up to 200 mm in size . In the production of glass optics , the technologies are significantly more complex, since glass and tool material interact chemically more strongly due to the higher temperatures during the manufacturing process and the tools wear out more quickly .

To minimize the effort required to handle and assemble the ever-smaller optics , manufacturers are increasingly turning to developments in the semiconductor industry . Here , thousands of computer chips have been manufactured from silicon wafers for years . The fact that a large number of chips can be accommodated on a single wafer means that the chips can not only be manufactured cost-effectively, but can also be easily processed and assembled . Wafer-based manufacturing has already proven suitable for plastic optics . For example , hundreds of small plastic optics can already be manufactured on wafers up to 300 mm in size .

That is , as pointed out above , in order to achieve a high-volume production of optical lenses or lens assemblies , they are fabricated simultaneously on a wafer-scale using photopolymer replication .

Optical plastic lenses are usually made of epoxy materials and the material is chosen depending on the desired use , for example depending on the desired refractive index .

This has several advantages . First . The manufacturing and also the investment costs are low . Second, it is possible that a high throughput is achieved so that a high-volume production of optical lenses is possible . Furthermore , reflowable materials are available . Finally, there are no limitations to the metal masters hitherto used so that as a result various metal masters can be used, such as LW, e-beam lithography, 2PP etc . ) .

However , the simultaneous fabrication on a wafer-scale using photopolymer replication has also some drawbacks . This production method requires several process steps to obtain the final optical lens or the final optical lens assembly, wherein the several steps include the lens design and also the tool selection . Furthermore , a long lead time is required . Thirdly, alignment tolerances are sometimes not sufficient and have to be improved .

In the following , an overview of available lens types and some of their properties are given :

There are refractive lenses ( aspherical , convex , concave ) having a lens sag /depth of structure ) of 40 to 400 pm and a diameter in the range of 0 . 2 to 4 mm. The single element mastering technology is SPDT ( single point diamond turn ) or micromachining . The wafer scale mastering technology is the recombination with Robocop (with ± 5 pm (XYZ ) ) . The typical replicated lens quality is : R_a about 5 nm, form error is ± 1 pm, the slope max is 60 ° . Further, there are known so called refractive Fresnel (also with partially reflective structures such as microprisms) with a lens sag of 10 to 50 pm and a diameter in the range of 0.2 to 10 mm. The typical replicated lens qualities are as follows: R_a about 20 nm; ridges R < 1 pm, bottom grooves R about 0.25*depth. Moreover, there are also known refractive micro lens arrays with a lens sag of 2 to 50 pm and a diameter of 0.005 to 0.8 mm (which means that the lenses of this type are very small) . The typical replicated lens qualities are: R_a about 20 nm; RoC ± 4 %. The single element mastering technology and the wafer scale mastering technology of the refractive Fresnes and the refractive micro lens arrays are laser-writer (SPDT/Recombination) . A further lens type are the diffractive microoptics with a lens sag of 1 to 10 pm and a diameter range of 0.2 to 20 mm having the following replicated lens qualities : smallest feature size about 1 pm and structure depth ± 4 %. The single element mastering technology and the wafer scale mastering technology are laser writer

(E-beam/recombination) .

The challenge for the production of lenses is that a good repetition quality with a high shape reproducibility is required.

The tool material (also designated as "master" in the production of lenses) can be characterized regarding the deviation from nominal lens shape and swelling. These issues increase, when the tool material is used multiple times, but this is the usual use of the tool material, i.e., it is used several times for producing lenses.

The swelling is induced by contact of the tool material with the lens material. An ideal tool material has zero swelling induced by the contact with the master and the lens material .

The form error, i.e. , the deviation of the lens from the nominal lens shape, occurs as a shape variation of number of recombined/replicated lenses. That is, the form error is the measured lens shape minus the nominal lens shape. A possible cause is an aging plastic deformation of the tool material or lens material for example caused by adhesion. An ideal tool material has zero form error over the largest possible number of recombined/replicated lenses .

It is an obj ect of the present invention to provide tool materials having a lower swelling compared to commonly used lens materials , a higher Tg and a higher E' which allow for better shape reproduction compared to the softer material reported in literature and prior art , and a high number of imprintable lenses with small form variation is possible . Furthermore , it is an obj ect of the present invention to provide a method for producing said tool material and the use of it for producing lenses .

SUMMARY OF THE INVENTION

This and other obj ects are addressed by the subj ect matter of the independent claims . Features and further aspects of the proposed principles are outlined in the dependent claims .

According to the present invention, there is provided a tool material for preparing lenses in particular for wafer level optics and nanoimprint technology obtainable by crosslinking a first perfluoropolyether ( hereinafter designated also as "PEPE" ) having at least one first crosslinking group and a second perfluoropolyether having at least one second crosslinking group in the presence of a pho to initiator .

The first perfluoropolyether can have one to four crosslinking groups , in particular two crosslinking groups .

The second perfluoropolyether can have one to four crosslinking groups , in particular four crosslinking groups .

The first crosslinking group and the second linking group can be selected independently from acrylate groups and methacrylate groups .

The molecular weight of the first perfluoropolyether can be 1000 to The molecular weight of the second perfluoropolyether can be 1000 to 4000.

The first perfluoropolyether can have the following formula:

Short linear aliphatic Urethane block

(PFPE: bifunctional perf luoropolyether-urethane methacrylate also referred to as or

Ethene, 1,1,2, 2-tetraf luoro-oxidized, polymd . , reduced, Et esters, reduced, N- [2- [ (2-methyl-l-oxo-2-propen-l-yl) oxy] ethyl] carbamates, CAS-No. : 1385773-87-4 (taken From the MSDS) )

The second perfluoropolyether can have the following formula: 2

• Tetrafunctional derivative Long cycloaliphatic

Urethane block perfluoropolyether -tetraurethane acrylate also referred to as XCF2O- ( CF2CF2O ) m ( CF2O ) n-CF2X where X is CH2OCOCH=CH2 which in IUPAC terms could be written like 2-methyl-2- (prop-l-en-2-yl) -1, 3-dioxolane-4- carboxylic acid-perf luoropolyether-2-methyl-2- (prop-l-en-2-yl ) -1, 3- dioxolane-4-carboxylic acid.

An amount of the first perfluoropolyether can be higher than an amount of the second perfluoropolyether. The photoinitiator can be selected from a benzophenone compound, a phosphinate compound, and a mixture of these two , wherein the benzophenone can be methylpropiophenone , and wherein the phosphinate can be the phosphinate TPO-L ( i . e . , ethylphenyl ( 2 , 4 , 6- trimethylbenzoyl ) phosphinate .

An amount of the benzophenone compound can be higher than an amount of the phosphinate compound .

The amount of the photoinitiator can be 0 . 5 wt . % to 7 . 5 wt . % , referred to the tool material .

Furthermore , the present invention provides a method for preparing a tool material , in particular the tool material as outlined above , wherein a first perfluoropolyether having at least one first crosslinking group and a second perfluoropolyether having at least one second crosslinking group and at least on photoinitiator are mixed and cured/ crosslinked .

The present invention relates as well to the use of the tool material as described herein for preparing lenses .

SHORT DESCRIPTION OF THE DRAWINGS

Further aspects and embodiments in accordance with the proposed principle will become apparent in relation to the various embodiments and examples described in detail in connection with the accompanying drawings in which

Figure 1 illustrates the measurement of the swelling;

Figure 2 illustrates the form error of lenses ;

Figures 3A and 3B illustrate the difference between two tool formulations : one showing liquid material ( not fully curable ) due to oxygen inhibition, the other showing no liquid residuals . ; and Figure 4 is a graph showing the shape variation from the nominal design vs . number of recombined lenses .

DETAILED DESCRIPTION

The following embodiments and examples disclose various aspects and their combinations according to the proposed principle . The embodiments and examples are not always to scale . Likewise , different elements can be displayed enlarged or reduced in size to emphasize individual aspects . It goes without saying that the individual aspects of the embodiments and examples shown in the figures can be combined with each other without further ado , without this contradicting the principle according to the invention . Some aspects show a regular structure or form. It should be noted that in practice slight differences and deviations from the ideal form may occur without , however, contradicting the inventive idea .

In addition, the individual figures and aspects are not necessarily shown in the correct size , nor do the proportions between individual elements have to be essentially correct . Some aspects are highlighted by showing them enlarged . However , terms such as "above" , "over" , "below" , "under" "larger" , "smaller" and the like are correctly represented with regard to the elements in the figures . So , it is possible to deduce such relations between the elements based on the figures .

As outlined above , according to the present invention there is provided a tool material for preparing lenses , like optical lenses or lens assemblies , for example as wafer level optics and for nanoimprint technology obtainable by reacting a first perfluoropolyether having at least one first crosslinking group and a second perfluoropolyether having at least a second crosslinking group in the presence of a pho to initiator .

The term "tool material" used according to the present invention means the polymer immediately obtainable after the reaction of the two PFPE in the presence of the photoinitiator as well as the material in the form suitable for preparing the lenses , also designated as "master" in this technical field, i . e . , a material having a specific design for producing the lenses .

According to the present invention, there is provided a tool material by reacting a first PFPE with a second PFPE . The two employed PFPE materials are different from each other in at least one aspect , for the example the chemical nature , like the type and/or number of crosslinkable groups and/or the molecular weight .

The reaction carried out between the first PFPE and the second PFPE in the presence of a photoinitiator can be considered as a crosslinking reaction or curing reaction .

In some aspects curing can be achieved with a dose of 15000 mJ/cm² ( 250 mW/cm2 for 60s or 500 mW/cm² for 30s or 40 mW/cm² for 375 s ) for thicknesses below 1 mm. Lower doses can as well lead to full cure depending to the lamp used (broadband, LED) , thickness of the sample and other parameters . The reaction can be carried out in such a way to ensure a complete crosslinking/curing, which can be checked for example by Fourier transformed infrared spectroscopy ( FTIR) .

Mixture of different functionalizations of commercially available PFPE grades allow for fine tuning of thermo-mechanical properties of the material .

A mixture of two different PFPE functionalizations ( for example tetraacrylate for the second PFPE and bi-methacrylate for the first PFPE ) allows for a wide range of hardnesses , glass transition temperatures and other properties that help overcome some of the limitations induced by the features of pure bi-methacrylate PFPEs .

The low swelling, mechanically tuneability, and low surface energy of the mould material allows for more repeatable , stable reproduction of micro and nanostructures lenses .

The materials according to the present invention show low swelling compared with commonly used lens materials , a high number of imprintable lenses with small form variation . The tool material according to the present invention has a higher Tg , higher E ' which allow for better shape reproduction compared to the softer material reported in literature and prior art .

Low swelling allows for small shape variation by subsequent contact with uncured lens material ; harder formulations result in higher resolution in reproducing the shape .

The two PFPE materials employed in the tool material according to the present invention are different from each other . One problem when the first PFPE material is used as sole material ( that is , without the second PFPE material ) for the tool material can be that an oxygen induced curing inhibition is observed . The presence of the second PFPE material in addition to the first PFPE material reduces this problem. It is beneficial that the second polymer has some acrylic groups compared to the first polymer that has methacrylic ones . Acrylic groups are more reactive , thus leading to faster cure and minimization of the oxygen induced inhibition .

For example , when the tool material is prepared of 100 wt% bi- methacrylated PFPE compared with a tool material prepared of 70 wt . % of a bi-methacrylated PFPE and also 30 wt . % of a tetra-acrylated PFPE , and the two tool materials were cured between glass wafers with 350 micron spaces , there was observed a different oxygen curing inhibition effect at the edges of the sample ( exposed to oxygen) . That is , by adding tetra-acrylated PFPE to the bi-methacrylated PFPE , the inhibition of curing induced by oxygen can be inhibited .

PFPE are a group of plastics , usually liquid to pasty at room temperature , that are fluoropolymers composed of fluorine , carbon and oxygen .

PFPEs have the following general formula :

Wherein n and m are chosen depending on the desired molecular weight of the final PFPE . The molecular weight of the PFPE is usually measured by GPC (Gel Permeation Chromatography) .

Perfluoropolyethers can be obtained by reacting a metal halide with a perfluoric acid halide , a C2 - to C4 -substituted ethyl epoxide , a C3+ fluoroketone , or combinations of two or more thereof , then reacting the intermediate with hexafluoropropylene oxide or tetraf luoroxetane , then esterifying, reducing the ester to its corresponding alcohol and converting it with a base to a salt , reacting it with a C3+ olefin, and fluorinating the fluoropolyether .

On the other hand, PFPE are commercially available as well .

The chemical bond of PFPE is very stable and the plastic very inert . The covalent carbon-f luorine bond in PFPE has a high binding energy of 448 kJ/mol .

The first PFPE employed in the tool material according to the present invention can have one to four crosslinking groups , for example two crosslinking groups .

The second PFPE employed in the tool material according to the present invention can have one to four crosslinking groups , for example four crosslinking groups .

According to the present invention, the first crosslinking group and the second linking group can be independently from each other selected from the group consisting of acrylate and methacrylate groups . For example , the first PFPE can have two methacrylate groups and/or the second PFPE can have four acrylate groups . The crosslinking groups can be bound to the PFPE by employing linker , for example linker groups with urethane moieties , like linear aliphatic urethan groups and/or cyclo-aliphatic urethane groups .

With the type of end group , for example the acrylate group and the methacrylate group , it is possible to influence the properties regarding the reactivity and the radiant energy for the full cure . The reactivity is increased from the methacrylate group to the acrylate group . On the other and, the radiant energy for the full cure is increased from the acrylate group to the methacrylate group .

This gives the possibility to tune the properties of the obtained tool material according to the present invention to fulfil suitably the requirements for the intended end use .

The first PFPE can have a molecular weight (MWn) from about 1000 to about 4000 , for example about 1500 to about 2000 , such as about 1800 .

The second PFPE can have a molecular weight (MWn) from about 1000 to about 4000 , for example about 1500 to about 2000 , such as about 1500 .

In the tool material according to the present invention, there are present two different PFPE materials , which differ in their chemical structure . The Molecular weight of these materials can be different from each other or they can be the same . For example , the first PFPE material can have a molecular weight of 1800 , whereas the second PFPE can have a molecular weight of 1500 .

With the molecular weight , it is possible to influence the properties of the tool material and, therefore to tailor it to the desired use . With the increase of the molecular weight , the release can be improved so that for example the lens material can be easier released from the tool material . Furthermore , with the increase of the molecular weight the optical transparency is increased . On the other hand, the shrinkage and the compatibility of the tool material are increased by lowering the molecular weight of the PFPE material used for the tool material according to the present invention . Therefore , by selecting appropriately the molecular weight of the PFPE material used for the tool material according to the present invention, it is possible to influence among others the properties of the release , the optical transparency, the shrinkage and the compatibility . This gives the possibility to tune the final tool material to be particularly suitable for the intended end use .

The first PFPE employed in the tool material according to the present invention can have the following formula :

o PFPE backbone \ O

MW_n = 1800 AMU \

- Sho -rt linear aliphatic

Urethane block

An example of this PFPE is the commercially available product Fluorolink® MD700 , which is a bifunctional PFPE-urethane methacrylate . When used as the main component of a photocurable formulation, Fluorolink® MD700 is suitable as an oligomer for producing low optical loss polymeric waveguides and cladding of optical fibres . Fluorolink® MD700 can also be used as a surface modifying additive in acrylic UV- curable systems : in fact , thanks to its tendency to migrate to the aircoating interface , Fluorolink® MD700 imparts outstanding water/oil repellency, antigraffiti and antifingerprint properties .

Furthermore , the second perfluoropolyether employed in the tool material according to the present invention can have the following formula : ₂

■ Tetrafunctional derivative Long cycloaliphatic

Urethane block

One example of this PFPE is the commercially available Fluorolink® AD1700, which is a solution of a PFPE-tetraurethane acrylate in a mixture of ethyl acetate and butyl acetate (1:1 by weight) . Fluorolink® AD1700 is particularly suitable to be used as a surface modifying additive in acrylic UV-curable coatings and paints: in fact, thanks to its tendency to migrate to the air-coating interface, it lowers the surface tension of the cured coating imparting outstanding water/oil repellency, antigraffiti and antifingerprint properties.

The amount of the first PFPE in the tool material according to the present invention can be higher than the amount of the second PFPE.

The first PFPE material can be used in the tool material according to the present invention in an amount of about 90 wt . % to more than about 50 wt.%, such as about 90 wt.%, about 80 wt.%, about 75 wt.%, about 70 wt.%, about 60 wt.%, referred to the tool material according to the present invention.

The second PFPE material can be used in the tool material according to the present invention in an amount of about 10 wt.% to less than about 50 wt.%, such as about 10 wt.%, about 20 wt.%, about 25 wt.%, about 30 wt.%, about 40 wt.% and less than about 50 wt.%, referred to the tool material according to the present invention.

Varying the amounts of the first PFPE material and the second PFPE material makes it possible to tune the properties of the final tool material according to the present invention to the desired end use.

Furthermore, it has been found a higher content of the second PFPE, for example the tetra-acrylated PFPE, leads to higher Tg, higher E' , higher viscosity and lower shrinkage of the final tool material according to the present invention . When the amount of the second PFPE is increased from about 10 wt . % to 40 wt . % of the tool material according to the present invention, it was observed that Tg , and E ' are increased with the increasing amount of the second PFPE . Furthermore , the viscosity is increased and the shrinkage is reduced by increasing the amount of the second PFPE .

However , the amount of the second PFPE should not exceed 50 wt . % of the total composition of the tool material due to the high viscosity which in certain cases depending on the end use may not be desired .

The tool material according to the present invention is obtainable by use of a photoinitiator . Photoinitiators are chemical compounds that decompose in a photolysis reaction after absorption of (UV) light , thus forming reactive species that can start ( initiate ) a reaction ( usually a polymerization) . The reactive species are radicals or cations .

Photoinitiators are usually classified by type of reactive species ( cationic , radical ) , sometimes by molar mass ( low molecular or polymer ) .

Photoinitiators for the radical chain reaction are divided into two types . Type 1 photoinitiators generate radicals directly in a photofragmentation, usually by alpha-cleavage . The radical formed then initiates chain polymerization . Type 2 photoinitiators , on the other hand, abstract a hydrogen atom from a neighbouring molecule . This then triggers the chain polymerization . Tertiary amines are usually added, since they form particularly effective starting radicals and thus increase reactivity .

Frequently used industrial photoinitiators are derived from o-hydroxy- , o-alkoxy- or o-amino-aryl ketones or also from acyl phosphine oxides . Occasionally, there are also applications for photolabile aliphatic azo compounds , which can decompose both thermally and photochemically .

As photoinitiator employed for preparing the tool material according to the present invention, all types of radical photoinitiator can be used. The photoinitiator based on phosphinates react very fast, but on the other hand they are more hindered by oxygen. Therefore, it is advantageous to use a combination of a phosphinate type photoinitiator, for example TPO-L (ethylphenyl (2 , 4, 6-trimethylbenzoyl ) phosphinate ) , with another radical photoinitiator, for example of the phenone type, like methylpropinophenone .

According to the present invention, when a combination of the initiator of the benzophenone type is used together with the initiator of the phosphinate type, the amount of the benzophenone can be higher than the amount of the phosphinate type radical initiator.

Furthermore, the amount of the photoinitiator can be about 0.5 wt.% to about 7.5 wt.%, such as about 1.0 wt.% to 5 wt.%, such as about 2 wt.%, referred to the tool material.

It has been found that varying the photoinitiator content does not impact significantly the properties of the cured material in respect of the glass transition temperature (Tg) . When the amount of the photoinitiator is 5 wt . % and 1 wt.%, the Tg for both tool materials is nearly the same .

Furthermore, it has been found that by increasing the photoinitiator amount the value for the storage modulus (E' ) is decreased. That is, the amount of photoinitiator can be used to reduce the E' value to get a softer tool material if this should be commercially desired.

The present invention furthermore relates to a method for preparing a tool material, in particular the tool material according as described above, wherein a first perfluoropolyether having at least one first crosslinking group and a second perfluoropolyether having at least a second crosslinking group and at least on photoinitiator are mixed and cured .

To put it into other words, according to the present invention, there is provided a tool material by reacting a first perfluoropolyether (PFPE) with a second PFPE in the presence of a photoinitiator. The three components first PFPE , second PFPE and photoinitiator are described in detail above so that it is referred to the above detailed description .

To allow this reaction, the three components are first mixed with each other . Such a mixing can be achieved by usual means , for example by giving the three components into a vessel and to ensure mechanically the mixing .

The curing/crosslinking can be achieved at 365 nm with a dose of 250 mJ/cm² . The reaction can be carried out in such a way to ensure a complete crosslinking/curing, which can be checked for example by Fourier transformed infrared spectroscopy ( FTIR) .

In a further aspect , the present invention relates to the use of the tool material according to the present invention for preparing lenses , for example the simultaneous production on wafer-scale using photopolymer replication . According to the present invention, there can be produced optical lenses or lens assemblies .

As materials for the lenses , the usually employed materials can be used known to the s killed person hitherto used for preparing lenses , for example the lens material are epoxy materials chosen depending on the intended use , for example chosen depending on required refractive index .

With the use according to the present invention, it is possible to produce lenses for cameras , such as p-cameras . The lenses are not necessarily for emitting LED although the principle can be used for it .

As pointed out above , the present invention enables to prepare lenses by using the tool material according to the present invention wherein the swelling is reduced compared to lenses of the prior art as well as the form stability is increased compared as well with lenses of the prior art . These effects achieved according to the present invention are further illustrated in the following figures 1 and 2 .

Figure 1 illustrates the measurement of the swelling . The tool material can be characterized regarding the deviation from nominal lens shape ( see below ) and swelling . These issues increase , when the tool material is used multiple times , but this is the usual use of the tool material , i . e . , it is used several times for producing lenses .

The swelling is induced by contact of the tool material with the lens material . An ideal tool material has zero swelling induced by the contact with the tool material and the lens material . PFPE used as components of the tool material show little swelling with the usual lens material , such as epoxy materials , siloxane materials and acrylic materials .

As can be taken from Fig . 1 , in order to evaluate the swelling, a swelling test is applied in with the profile is measured with a profilometer and the profile z [pm] is shown vs . the x in mm, wherein the swelling is indicated by the two arrows in the graph showing x vs . y -

Figure 2 illustrates the form error of lenses . The form error, i . e . , the deviation of the lens from the nominal lens shape , occurs as a shape variation of number of recombined/replicated lenses . That is , the form error is the measured lens shape minus the nominal lens shape . A possible cause is an aging plastic deformation of the tool material or lens material for example caused by adhesion . An ideal tool material has zero form error over the largest possible number of recombined/replicated lenses .

In Fig . 2 , the black line represents the center and fit nominal shape compared to the measured shape in grey . The form error is the measured lens shape minus the nominal lens shape . Examples :

In the following examples represented in the following table the components as indicated, i . e . , the photoinitiator as well as the main components ( first PFPE and second PFPE ) were mixed and then cured . The curing was carried out to achieve full curing of the materials , which was confirmed by FTIR analysis . Curing was carried out with a dose of 15000 mJ/cm² ( 250 mW/cm2 for 60s or 500 mW/cm² for 30s or 40 mW/cm² for 375 s ) for thicknesses below 1 mm. .

As photoinitiator a mixture of methylpropiophenone and the phosphinate TPO-L ( ethylphenyl ( 2 , 4 , 6-trimethylbenzoyl ) phosphinate ) has been used . The amount of the mixtures of the two photoinitiators was from 1 wt . % to 5 wt . % , referred to the mixture of the components .

The used PFPE were a dimethacrylated PFPE which was commercially available under the trademark Fluorolink® MD700 from the company Solvay . This dimethacrylated PFPE contains a PFPE backbone and two methacrylate groups bound to this backbone , wherein to each end of the backbone one methacrylate group is bound via a linear aliphatic urethane block . This first PFPE has a molecular weight of 1800 as informed by the vendor . This PFPE is designated in the following table as "MD700" .

The second PFPE employed was an acrylated tetrafunctional PFPE sold by Solvay under the trade mark Fluorolink® AD1700 . It contains a PFPE backbone , wherein to each end of the backbone two methacrylate groups are bound via a cyclo-aliphatic urethane block were bound . The molecular weight was 1500 as informed by the vendor . This second PFEP is designated in the following table as AD1700 .

From the mixtures of the components tools (masters ) for forming lenses have been made , and lenses are produced using these tools by conventional methods . The s killed person does know materials and the method steps for preparing lenses so that it is referred thereto . In the following table , the properties evaluated are indicated . These properties are measured by usual methods known in this field which are known to the skilled person .

Type IT: methylpropiophenone; Type I: phosphinate (TPO-L)

Usually, conventional tool materials, like silicone PDMS, have a swelling of 4 to 5 pm. As can be taken from the results shown in the table the swelling is reduced by employing the materials according to the present invention.

Furthermore, it seems from the results shown in the table that the increase of the glass transition temperature (Tg) and the storage modulus E' is better when the tool material according to the present invention is used. A higher Tg indicates that the material is more stable at room temperature and leads to harder structure so that the tool material keeps the shape over a longer time. The shrinkage volume is lower in combinations. Furthermore, a higher viscosity indicates also that the material is harder so that material changes over time are reduced.

As can be taken from a comparison of Tool 3 with Tool 5 of the table, varying the photoinitiator content does not impact significantly the properties of the cured material in respect of the Tg . In Tool 3 the amount of the photoinitiator is 5 wt.%, whereas the amount of the photoinitiator in Tool 5 is 1 wt.%. The Tg for both tool materials are nearly the same (25.10 °C for Tool 3 vs . 25.60 °C for Tool 5) .

From a comparison of Tool 3 and Tool 5 it can be taken further that by increasing the photoinitiator amount the value for E' is decreased. The amount of the photoinitiator for Tool 3 is 5 wt.% and E' has the value of 30.5 MPa. In contrast thereto, in Tool 5 the amount of the photoinitiator is 1 wt.% and the value for E' is 61.5 MPa. That is, the amount of photoinitiator can be used to reduce the E' value to get a softer tool material if this should be commercially desired.

Furthermore, it can be taken from the table that a higher AD1700 content leads to higher Tg, higher E' , higher viscosity and lower shrinkage. This is evidenced in table 4 by a comparison of Tools 2, 4, 6, and 7. The amount of the second PFPE AD1700 is increased from Tool 2 to Tool 7 from about 10 wt.% to 40 wt.%. It can be observed that Tg, and E' are increased when the amount of AD1700 is increased. Furthermore, the viscosity is increased and the shrinkage is reduced by increasing the amount of AD1700 .

However , the amount of AD1700 should not exceed 50 wt . % of the total composition of the tool material due to the high viscosity which in certain cases depending on the end use may not be desired .

Furthermore , the results as sown in the table evidence that the swelling is sufficiently low . Furthermore , good initial results for recombination with alternative materials are shown .

As can be taken from the above experimental results , with the tool material according to the present invention, it is possible to tune the mechanical properties of the final tool for preparing lenses .

Another relevant property of the tool materials according to the present invention are described in the following .

One problem when MD700 is used as sole material ( that is , without AD1700 ) for the tool material is that an oxygen induced curing inhibition is observed . The presence of AD1700 in addition to MD700 reduces this problem.

Tool 1 ( see above table ) contains 100 wt . % MD700 , whereas Tool 6 contains 70 wt . % MD700 and also 30 wt . % AD1700 . The tool materials of Tool 1 and Tool 6 were cured between glass wafers with 350 micron spaces . Observed was a different oxygen curing inhibition effect ( see Fig . 3a and 3b ) . For Tool 1 (without added AD1700 ) the curing inhibition region extends up to 125 microns from the edge . In contrast thereto , it was not visible for Tool 6 . Thus , by adding AD1700 the inhibition of curing induced by oxygen can be inhibited b the presence of AD1700 , in particular in the amounts as indicated in the above table .

Furthermore , the tool material according to the present invention provides a good lens shape fidelity . When the tools for the fabrication of lenses are used over time in various cycles for producing lenses . The shape of the lenses may vary in an undesired way . The shape variation from the nominal design should be as low as possible. This lens shape fidelity is very good for the tool material according to the present invention. As can be taken from Fig. 4, the lens shape fidelity after about 200 recombined lenses is very good, i.e., an almost flat curve has been found in a graph showing the shape variation from the nominal design vs. about 200 recombined lenses. The shape variation from the nominal design is less than 0.5 pm; the curve is almost flat showing that only very small variations between the different lenses occur.

Claims

1 . Tool material for preparing lenses obtainable by crosslinking a first perfluoropolyether having at least one first crosslinking group and a second perfluoropolyether having at least one second crosslinking group in the presence of a photoinitiator .

2 . Tool material according to claim 1 , wherein the first perfluoropolyether has one to four crosslinking groups .

3 . Tool material according to any of the preceding claims , wherein the second perfluoropolyether has one to four crosslinking groups .

4 . Tool material according to any of the preceding claims , wherein the first crosslinking group and the second linking group are independently selected from acrylate and methacrylate groups .

5 . Tool material according to any of the preceding claims , wherein the molecular weight of the first perfluoropolyether is 1000 to 4000 .

6 . Tool material according to any of the preceding claims , wherein the molecular weight of the second perfluoropolyether is 1000 to 4000

7 . Tool material according to any of the preceding claims , wherein the first perfluoropolyether has the following formula :

o PFPE backbone \ ⁰

MW_n = 1800 AMU \

Short linear aliphatic

Urethane block

Tool material according to any of the preceding claims , wherein the second perfluoropolyether has the following formula : ₂

■ Tetrafunctional derivative Long cycloaliphatic

Urethane block

9. Tool material according to any of the preceding claims, wherein an amount of the first perfluoropolyether is higher than an amount of the second perfluoropolyether.

10. Tool material according to any of the preceding claims, wherein the photoinitiator is selected from a benzophenone compound, a phosphinate compound and a mixture of these two.

11. Tool material according to claim 10, wherein the benzophenone is methylpropiophenone.

12. Tool material according to claim 10 or 11, wherein the phosphinate is ethylphenyl ( 2 , 4, 6-trimethylbenzoyl ) phosphinate .

13. Tool material according to any of claims 10 to 12, wherein an amount of the benzophenone compound is higher than an amount of the phosphinate compound.

14. Tool material according to any of the preceding claims, wherein the amount of the photoinitiator is 0.5 wt . % to 7.5 wt.%, referred to the tool material.

15. Method for preparing a tool material, in particular the tool material according to any of the preceding claims, wherein a first perfluoropolyether having at least one first crosslinking group and a second perfluoropolyether having at least one second crosslinking group and at least on photoinitiator are mixed and cured.

16. Use of the tool material according to any of claims 1 to 14 for preparing lenses.