CN113527930A - Photopolymer composition, grating and preparation method thereof - Google Patents
Photopolymer composition, grating and preparation method thereof Download PDFInfo
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- CN113527930A CN113527930A CN202010313839.6A CN202010313839A CN113527930A CN 113527930 A CN113527930 A CN 113527930A CN 202010313839 A CN202010313839 A CN 202010313839A CN 113527930 A CN113527930 A CN 113527930A
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- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D4/00—Coating compositions, e.g. paints, varnishes or lacquers, based on organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond ; Coating compositions, based on monomers of macromolecular compounds of groups C09D183/00 - C09D183/16
- C09D4/06—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 C09D159/00 - C09D187/00
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- G02—OPTICS
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- G02B5/00—Optical elements other than lenses
- G02B5/18—Diffraction gratings
- G02B5/1847—Manufacturing methods
Abstract
The invention relates to a photopolymer composition, a grating and a preparation method thereof. The photopolymer composition of the present invention comprises the following components: a monomer composition having a refractive index of 1.55 or more and containing an acrylate monomer and/or an epoxy compound; a film forming component; a photoinitiator system; and a chain transfer agent and/or a free radical scavenger; wherein the chain transfer agent and/or free radical scavenger is present in an amount of 0.05 to 0.5% by weight based on the total weight of the composition.
Description
Technical Field
The invention belongs to the field of optical materials and equipment, and particularly relates to a photoinduced recording material and a grating formed by the photoinduced recording material, in particular to a photoinduced polymer composition for holographic recording, a grating and a preparation method thereof or a holographic recording system using the photoinduced polymer.
Background
Photosensitive/photopolymer materials use the refractive index change of the material resulting from irreversible photopolymerization for holographic recording. In a typical processing mode, monomers in the photopolymer composition for holographic recording form a (cured) polymer through a polymerization reaction when the element is formed by irradiating the photopolymer composition with a visible light laser. As a result, structural features that can form interference patterns can be created in the elements formed from the photopolymer composition. Meanwhile, by modulating the refractive index, it is made possible to form a phase hologram having high diffraction efficiency. The photosensitive/photopolymer material has the characteristics of high sensitivity, high resolution, high signal-to-noise ratio, low cost, simple processing technology and the like, and is one of the most potential recording materials in the field of volume holographic devices.
For example, optical waveguide devices are a key technology in the AR field. The photopolymer material can be made into an optical waveguide optical element through exposure and fading. The optical waveguide element can be used for manufacturing a display device of augmented reality equipment, and has the advantages of being light and thin, simple in manufacturing process, easy to produce in mass, low in price and the like. To meet the imaging requirements of augmented reality devices, photopolymer materials need to meet the following characteristics: high diffraction efficiency, high refractive index modulation degree, high transparency, no color (less light absorption), low haze and the like.
Although various kinds of photopolymers have been proposed in the market at present, photopolymer materials satisfying the demands of the optical field as described above are also scarce. Currently, the best performing photopolymer on the market is the Bayfol photopolymer from scientific and creative germany, whose product parameters are shown in table 1 below. Although the diffraction efficiency and the refractive index modulation degree of the Bayfol photopolymer reach a higher level, the Bayfol photopolymer is still light yellow after exposure, fading and other steps, the visible light is absorbed to a certain extent, and the light transmittance is less than 90 percent and even less than 80 percent, so that the application of the Bayfol photopolymer in the optical field is limited. For example, the optical waveguide type head display device requires the optical waveguide to have a light transmittance of more than 90%, and if the photo-polymer is colored after being faded, the light is lost after being transmitted, which indirectly affects the imaging effect. Especially, car HUD and aircraft HUD require more to the colour of optical waveguide, if the colour of optical waveguide is too dark, will shelter from the sight, reduce factor of safety.
Table 1: bayfol photopolymer from cottage corporation
Similar to the above, cited document 1 discloses a hologram recording material having improved resolution, heat resistance and sensitivity. However, the diffraction efficiency of the holographic recording material is only 85% at the maximum and the light transmittance is only 85% at the maximum.
Further, the spatial resolution (the number of stripes recorded within 1 mm) of the transmissive diffraction grating is approximately 1000lines/mm, while the spatial resolution of the reflective diffraction grating is more demanding for the photopolymer recording material, which is approximately 4500lines/mm or more. However, the requirements for reflective diffraction gratings are also difficult to achieve with prior art photopolymer recording materials.
Various studies have also been made in the art on photopolymer materials for reflective diffraction gratings.
For example, reference 3 discloses a reflection hologram film whose reflection efficiency can be raised to 99.9% and whose refractive index is adjusted to 0.0763, however, this technique does not pay attention to the light transmittance of the film, and a nanocomposite prepolymer is necessarily used, which increases the manufacturing cost and may deteriorate the haze of the film.
It can be seen that although some degree of improvement has been made in the prior art for photosensitive/photopolymer materials used in holographic recording optical elements, there is room for further research on diffraction gratings (especially reflective diffraction gratings) that simultaneously improve diffraction efficiency, refractive index modulation, light transmittance and reduce haze.
Citations：
Cited document 1: CN 110187603A
Cited document 2: CN 1504828A
Cited document 3: CN 101320208B
Disclosure of Invention
Problems to be solved by the invention
In view of the above-mentioned drawbacks in the art, the present invention provides a photopolymer composition for a diffraction grating, especially for a reflective diffraction grating, which has high diffraction efficiency, high refractive index modulation, and high light transmittance and low haze similar to those of glass, and is simple in manufacturing process and cheap and easily available in raw materials, compared to the existing photopolymer materials for holographic recording.
Further, the present invention is also directed to a grating, especially a reflective diffraction grating, based on the above composition and a method for preparing the same.
Means for solving the problems
According to the intensive research of the inventor of the present invention, it is found that the technical problems can be solved by implementing the following technical scheme:
[1] the present invention first provides a photopolymer composition for a diffraction grating, comprising the following components:
a monomer composition having a refractive index of 1.55 or more;
a film forming component;
a photoinitiator system; and
chain transfer agents and/or radical scavengers;
wherein the chain transfer agent and/or free radical scavenger is present in an amount of 0.05 to less than 0.5% by weight based on the total weight of the composition.
[2] The composition according to [1], which comprises an acrylate monomer and/or an epoxy compound.
[3] The composition according to [2], the epoxy compound has a structure of the following general formula (I):
wherein E represents a group containing an epoxy group, n is an integer of 0 to 4, and each E is the same or different; each Ar is the same or different and independently represents an aryl-containing group; -C (R)1R2) -formation of a carbonyl group, or, R1、R2The same or different, independently represent a hydrogen atom, an aryl group having 6 to 30 carbon atoms, or an alkyl group or alkoxy group having 1 to 10 carbon atoms, and R1、R2The bonding may be by a single bond.
[4] The composition according to [2] or [3], the epoxy compound having a structure of the following general formula (II):
wherein R is1And R2Have the same definition as in formula (I); each R3The same or different, independently selected from hydrogen, halogen and alkyl with 1-5 carbon atoms, and x is an integer of 0-4.
[5] The composition according to [2], wherein the acrylate monomer has a refractive index of 1.55 or more and/or has 3 or more functional groups.
[6] The composition according to any one of [1] to [5], wherein the content of the chain transfer agent and/or the radical scavenger is 0.05 or more and less than 0.5% by weight based on the total weight of the composition.
[7] Further, the present invention also provides a diffraction grating comprising a resin film having a grating structure, the resin film being obtained by curing the composition according to any one of the above [1] to [6].
[8] In addition, the invention also provides a preparation method of the diffraction grating, which comprises the following steps:
a mixing step of mixing the components of the composition according to any one of the above [1] to [6] to obtain a mixture;
a step of forming a grating structure by forming a film of the mixture and forming a grating structure on at least a part of the film,
wherein the step of forming a grating structure includes a step of exposing the film with coherent light.
[9] The method according to [8], wherein the step of forming the grating structure comprises a step of compounding with the mixture using a spacer.
[10] The method according to [8] or [9], wherein the coherent light is derived from visible light.
[11] In addition, the present invention also provides a holographic optical waveguide display element comprising the diffraction grating according to the above [6] or the diffraction grating obtained by the method according to any one of the above [8] to [10].
ADVANTAGEOUS EFFECTS OF INVENTION
Through the implementation of the technical scheme, the invention can obtain the following technical effects:
(1) gratings, especially reflective diffraction gratings, prepared by the photopolymer composition of the present invention have high diffraction efficiency, high refractive index modulation, and high light transmittance and low haze as well as glass, and thus can be widely used for various purposes, such as automobile HUDs, aircraft HUDs, AR glasses, etc.;
(2) the photopolymer composition and the grating have simple manufacturing process, cheap and easily obtained raw materials, and are easy for large-scale industrial production;
(3) the grating prepared by the invention has excellent optical waveguide imaging effect.
Drawings
FIG. 1 is a schematic diagram of a structure of a photopolymer diffraction grating of the present invention;
FIG. 2 is a schematic diagram of a photographing optical path of a diffraction grating;
FIG. 3 is a graph of the diffraction efficiency of the photopolymer diffraction grating obtained in example 2;
FIG. 4 is a photograph of an optical waveguide obtained in example 3;
FIG. 5 is a photograph of the optical waveguide imaging effect obtained in example 3;
fig. 6 is a graph showing the difference in diffraction efficiency between example 1 and comparative example 1 at different positions.
Detailed Description
The present invention will be described in detail below. The technical features described below are explained based on typical embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:
in the present specification, the numerical range represented by "numerical value a to numerical value B" means a range including the end point numerical value A, B.
In the present specification, the numerical ranges indicated by "above" or "below" mean the numerical ranges including the numbers.
In the present specification, the meaning of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.
As used herein, the term "optional" or "optional" is used to indicate that certain substances, components, performance steps, application conditions, and the like are used or not used.
In the present specification, the unit names used are all international standard unit names, and the "%" used means weight or mass% content, if not specifically stated.
In the present specification, the term "particle diameter" as used herein means an "average particle diameter" unless otherwise specified, and can be measured by a commercial particle sizer.
In the present specification, the term "acrylate" includes the meanings of "(meth) acrylate" and "acrylate".
In this specification, the description will be made using "vicinity" to a certain wavelength of light, and it is understood that, for a specific wavelength, some error may occur from a theoretical value in use due to an instrument error or the like, and therefore, the use of "vicinity" indicates that various types of wavelengths defined in the present invention include an instrument error or the like.
In the present specification, reference to "some particular/preferred embodiments," "other particular/preferred embodiments," "embodiments," and the like, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.
< first aspect >
In a first aspect of the present invention, there is provided a photopolymer composition for a diffraction grating comprising the following components: a monomer composition having a refractive index of 1.55 or more; a film forming component; a photoinitiator system; and chain transfer agents and/or free radical scavengers.
The chain transfer agent and/or free radical scavenger is present in an amount of 0.05 to less than 0.5% by weight based on the total weight of the photopolymer composition of the present invention.
Monomer composition
In the present invention, the monomer composition contains a monomer having polymerization reactivity, and the monomer composition suitable for use in the present invention has a refractive index of 1.55 or more, preferably 1.57 or more, more preferably 1.58 or more, further preferably 1.60 or more. In some specific embodiments of the present invention, the total content of the monomer having a refractive index of 1.57 or more in the monomer composition of the present invention is preferably 80% or more, more preferably 90% or more, and further preferably 95% or more, based on the total weight of the monomer composition.
In some specific embodiments of the present invention, the monomer composition of the present invention preferably comprises an acrylate monomer, an epoxy compound, or a mixture thereof, and more preferably, the monomer composition of the present invention comprises both an acrylate monomer and an epoxy compound.
(epoxy compound)
In the present invention, as the epoxy compound which can be used, those having a higher refractive index are preferable. In some preferred embodiments, for example, the epoxy compound preferably has a refractive index of 1.55 or more, or further 1.57 or more, 1.58 or more, 1.60 or more.
In the present invention, the epoxy compound preferably used has a structure of the following general formula (I):
wherein E represents an epoxy group-containing group. In some specific embodiments, each E group may contain 1 or 2 epoxy groups. Further, from the viewpoint of improving the light transmittance and haze of the resulting grating, suppressing the shrinkage of the article, and balancing the processability, in a preferred embodiment, each E group, when present, contains 1 epoxy group.
The structure of the epoxy group is not particularly limited, and the epoxy group is preferably present as an aliphatic epoxy group. In addition, in other embodiments, the epoxy group or epoxy structure of the E group is linked to the Ar group through an ether group. The ether group may be a sulfide group or an oxygen ether group, and is preferably an oxygen ether group from the viewpoint of suppressing dimensional shrinkage after film formation and improving light transmittance and haze of the resulting grating.
In the general formula (I), n representing the number of E groups is an integer of 0 to 4, and each E is the same or different. It goes without saying that the total number of n in the present invention is not 0. In some preferred embodiments, each occurrence of n is 1.
In the general formula (I), Ar is the same or different and independently represents an aryl group-containing group. In some preferred embodiments of the present invention, Ar represents a group having 1 or 2 substituted or unsubstituted benzene rings, and typically, Ar may be selected from the following structures, from the viewpoint of improving light transmittance, haze and refractive index of the resulting grating:
wherein X in the formula (b) is selected from a single bond, O or S atom.
Further, in the above general formula (I), -C (R)1R2) -formation of a carbonyl group, or, R1、R2The same or different, each occurrence independently represents a hydrogen atom, an aryl group having 6 to 30 carbon atoms, or an alkyl or alkoxy group having 1 to 10 carbon atoms, and R1、R2May be bonded via a single bond; r1、R2Independently, an alkyl group or an alkoxy group having 1 to 3 carbon atoms is preferable.
In some preferred embodiments of the present invention, the epoxy compounds suitable for use in the present invention have a structure represented by the following general formula (II):
wherein R is1And R2Have the same definition as in formula (I).
R3Each occurrence is the same or different and is independently selected from hydrogen, halogen and alkyl with 1-5 carbon atoms; preferably 1 to 3 alkyl; x is an integer of 0 to 4, preferably 0 or 1. The halogen may be F, Cl or a Br atom.
In a further preferred embodiment, the epoxy compound suitable for use in the present invention has a structure represented by the following general formulae (II-1) to (II-3):
in the present invention, one kind of the epoxy compound may be used, or a mixture of two or more kinds of the epoxy compounds may be used.
The epoxy compounds suitable for use in the present invention can be obtained by preparation methods usual in the art, and in a typical embodiment, can be carried out using a coupling reaction of epichlorohydrin with a phenolic compound:
further, the epoxy compound of other structure may be contained in addition to the epoxy compound of the above structure necessary for the present invention without affecting the technical effect of the present invention. These epoxy compounds of other structures preferably have a certain refractive index, for example, a refractive index of 1.45 or more, preferably 1.50 or more, and more preferably 1.52 or more.
Further, other epoxy compounds such as:
wherein Y represents a single bond or a heteroatom such as O or S.
In some specific embodiments of the present invention, when the epoxy compound of the present invention is used in combination with an epoxy compound of another structure, the weight and ratio of the epoxy compound of the above structure I or II of the present invention is 80% or more, preferably 90% or more, and more preferably 95% or more, based on the total weight of the epoxy compounds.
Acrylic ester monomer
In the present invention, the acrylate monomer preferably includes an acrylate monomer having a refractive index of 1.55 or more and/or an acrylate monomer having 3 or more functional groups. Further, in some preferred embodiments, the acrylate monomers of the present invention include crosslinkable acrylate monomers, and by these crosslinkable monomers, the crosslinking density of the desired crosslinked structure formed by the photopolymer composition under the action of light and an initiating system is increased, which is beneficial to improving the stability of the grating size, the diffraction efficiency and promoting the achievement of high refractive index modulation degree.
In some embodiments of the present invention, it is believed that an acrylate monomer having a high refractive index is advantageous because the use of a high refractive index can improve the diffraction efficiency and the refractive index modulation of the diffraction grating. Alternatively, in some other specific embodiments of the present invention, the acrylate monomer is selected from acrylate monomers having multiple functional groups. The number of the "plurality" is 3 or more, and more preferably 3 to 8. Such a polyfunctional monomer can be used as a crosslinkable component.
For the acrylate-based monomer having a high refractive index suitable for use in the present invention, it has a refractive index of 1.55 or more, preferably 1.57 or more or 1.58 or more in some specific embodiments.
As the acrylate monomer having a high refractive index that can be used, an acrylate monomer having an aromatic group can be used. The present invention recognizes that the aromatic group selected from one or more of phenyl, biphenyl, naphthyl or fluorenyl in the acrylate monomer contributes to the increase of the refractive index.
In some specific embodiments, among the acrylate monomers, the acrylate monomer having an aromatic group may be selected from: biphenyl-containing acrylates such as [1, 1-biphenyl ] -4, 4-diylbis (2-methacrylate), 4' -biphenyldiacrylate and the like; naphthalene-containing acrylates such as 1-naphthalene methacrylate, 2 '-bis (2-acryloyloxy) -1, 1' -thiobinaphthalene, 2 '-bis [2- (2-acryloyloxyethoxy) -1, 1' -binaphthalene, 2 '-bis [ 2-acryloyloxyethoxy) -1, 1' -thiobinaphthalene and the like.
In addition to the acrylic monomer having an aromatic group, the acrylic monomer having an aromatic group may be optionally substituted with a halogen including fluorine, chlorine or bromine, preferably, bromine. Examples of such acrylate monomers include p-chlorophenyl acrylate, p-bromophenyl acrylate, pentachlorophenyl acrylate, pentabromophenyl acrylate, 2,4, 6-tribromophenyl acrylate, and 2,4, 6-trichlorophenyl acrylate.
In some more preferred embodiments of the present invention, for the acrylate monomer having a refractive index of 1.55 or more, at least one of o-phenylphenoxyethyl acrylate, pentabromophenyl methacrylate, and the like, which are monofunctional, may be used.
Additionally, in some specific embodiments, acrylates having multiple functional groups suitable for use in the present invention may be selected from: at least one of pentaerythritol tetraacrylate, dipentaerythritol penta-/hexa-acrylic acid, an octafunctional degree hyperbranched monomer ETERCURE6361-100 and multifunctional urethane acrylate.
In addition to the above-mentioned acrylate monomers having a high refractive index or having a plurality of functional groups, other types or structures of acrylate monomers may be used without affecting the technical effects of the present invention. These other acrylate monomers may include mono and difunctional acrylates, mono and difunctional urethane acrylates, specifically:
other acrylates that may be used are, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, ethoxyethyl acrylate, ethoxyethyl methacrylate, N-butyl acrylate, N-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, hexyl acrylate, hexyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, butoxyethyl acrylate, butoxyethyl methacrylate, dodecyl acrylate, dodecyl methacrylate, isobornyl acrylate, isobornyl methacrylate, phenyl acrylate, N-carbazole acrylate, and the like.
Other urethane acrylates which may be used are understood to mean compounds having at least one acrylate group which have at least one urethane bond. Such compounds are known to be obtainable by reacting hydroxy-functional acrylates with isocyanate-functional compounds.
For this purpose, isocyanate-functional compounds such as aromatic, araliphatic, aliphatic and cycloaliphatic diisocyanates can be used. Mixtures of such diisocyanates may also be used. Suitable di-, tri-or polyisocyanates are, for example, butylidene isocyanate, Hexamethylene Diisocyanate (HDI), isophorone diisocyanate (IPDI), 2, 4-and/or 2,4, 4-trimethylhexamethylene diisocyanate, bis (4, 4' -isocyanatocyclohexyl) methane isomers and mixtures thereof having any desired isomer content, isocyanatomethyl-1, 8-octane diisocyanate, 1, 4-cyclohexyl diisocyanate, cyclohexanedimethylene diisocyanate isomers, 1, 4-phenylene diisocyanate, 2, 4-and/or 2, 6-toluene diisocyanate, 1, 5-naphthalene diisocyanate, 2,4' -or 4,4' -diphenylmethane diisocyanate, 1, 5-naphthalene diisocyanate, m-methylthiophenyl isocyanate or derivatives thereof having a urethane, urea, carbodiimide, acylurea, isocyanurate, allophanate, biuret, oxadiazinetrione, uretdione or iminooxadiazinedione structure and mixtures thereof. Aromatic or araliphatic diisocyanates are preferred.
Hydroxy-functional acrylates or methacrylates suitable for preparing the above urethane acrylates are listed as follows: 2-hydroxyethyl (meth) acrylate, polyethylene oxide mono (meth) acrylate, polypropylene oxide mono (meth) acrylate, polyalkylene oxide mono (meth) acrylate, poly (. epsilon. -caprolactone) mono (meth) acrylate, e.g. poly (ethylene oxide) mono (meth) acrylate
M100(Dow, Schwalbach, Germany), 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 3-hydroxy-2, 2-dimethylpropyl (meth) acrylate,
Hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl acrylate, hydroxy-functional mono-, di-or tetraacrylates of polyols such as trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol, ethoxylated, propoxylated or alkoxylated trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol or industrial mixtures thereof. Among them, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate and poly (. epsilon. -caprolactone) mono (meth) acrylate are preferable.
In some specific embodiments of the present invention, the sum of the weight of the acrylate monomers having a refractive index of 1.55 or more and/or the acrylate monomers having 3 or more functional groups in the acrylate monomers according to the present invention is 80% or more, preferably 90% or more, and more preferably 95% or more, based on the total weight of the acrylate monomers. In other specific embodiments of the present invention, the sum of the weight of the acrylate monomers having 3 or more functional groups is 5 to 50%, or 10 to 40%, or 15 to 35%, based on the total weight of the acrylate monomers.
Film-forming component
The film-forming component used in the present invention is not particularly limited, but is preferably selected from polymers or resin materials having a certain adhesiveness with a molecular weight of 1000 or more. Preferably, these materials have a relatively low refractive index, and in some specific embodiments, the refractive index of these materials is 1.480 or less.
In the present invention, suitable film-forming components include:
homopolymers of vinyl acetate or copolymers of vinyl acetate with acrylates, ethylene, styrene, etc.;
cellulose esters such as cellulose acetate, cellulose acetate-butyrate;
cellulose ethers such as methyl cellulose, ethyl cellulose, and benzyl cellulose, and the like;
polyvinyl alcohol;
polyvinyl acetals such as polyvinyl butyral, polyvinyl formal and the like;
polyurethanes, generally obtained by reacting polyols such as polytetrahydrofuran, polyethylene glycol, polypropylene glycol, castor oil, and isocyanates such as hexamethylene-1, 6-diisocyanate, 1, 4-cyclohexane diisocyanate, methyl-2, 4-diisocyanate;
styrene/butadiene-based block copolymers;
polyvinylpyrrolidone, and the like.
These may be used alone or in combination of two or more.
From the viewpoint of suppressing dimensional shrinkage of the final grating product and improving diffraction efficiency, the preferable film-forming component of the present invention is selected from at least one of cellulose acetate butyrate, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate.
In addition, for the present invention, it is advantageous to increase the degree of modulation of the refractive index of the final holographic recording material, as the refractive index of the monomer composition including the epoxy compound and/or the acrylate-based monomer described above is higher and the difference in refractive index from the film-forming component is larger. Thus, in some embodiments, the difference in refractive index (n) between the monomer composition comprising the epoxy compound and/or the acrylate monomer and the film-forming componentMonomer composition-nFilm-forming component) The value is above 0.070, preferably above 0.075, further preferably above 0.078.
Photoinitiator system
In the present invention, the photoinitiator system preferably comprises a photoinitiator as well as a co-initiator.
The photoinitiator suitable for the present invention is not particularly limited, but is preferably a dye having photoinitiating activity, and suitable dyes are, for example, Irgacure 784, new methylene blue, thionine, basic red 2, basic yellow, pinacyanol chloride, rhodamine 6G, betacyanine, ethyl violet, victoria blue R, celestine blue, quinaldine red, crystal violet, brilliant green, basic orange G (astrazon orangeg), darura red (darrow red), pyronin Y, rose bengal, potato red Y, mikrolone, 3.3' -carbonylbis (7-diethylaminocoumarin), iodonium (pyrilium I), diiodofluorescein, anthocyanidin and methylene blue, tiana, crystal violet (leuconitrile), malachite green (leuconitrile), and the like. These may be used alone or in combination of two or more.
In some preferred embodiments of the present invention, the photoinitiator suitable for use in the present invention is at least one selected from Irgacure 784, basic red 2, rose bengal, yam red Y, methylene blue, rhodamine 6G, diiodofluorescein, mie ketone, or 3, 3' -carbonylbis (7-diethylaminocoumarin).
The co-initiator suitable for use in the present invention is not particularly limited, but is preferably an N atom-containing, initiating active compound, and examples of the co-initiator include at least one of ethylenediamine, N-phenylglycine, 2- (4-chlorophenyl) -4, 5-diphenylimidazole, and ethyl 4-dimethylaminobenzoate.
Chain transfer agent and radical scavenger
In the present invention, the uniformity and transparency and spatial resolution of the photopolymer diffraction grating can be improved by adding chain transfer agents (chain transfer agents) and/or free radial scavengers (free radial scavengers) to the photopolymer composition.
In the case of the chain transfer agent, it is generally considered that the chain transfer agent terminates the growth of the long-chain radical by reacting with the long-chain radical (Mn. cndot.) and generates a radical (RI. cndot.) which can react only with the monomer.
Therefore, the molecular chain length of the photopolymer is controlled, the chain length distribution is more uniform, and the uniformity of the photopolymer diffraction grating can be improved. At the same time, however, one skilled in the art would also recognize that chain transfer agents may not have a comprehensive effect on the polymerization, migration, etc. of the photopolymer composition, i.e., whether a higher degree of refractive index modulation and diffraction efficiency can be achieved while still improving uniformity. In particular, although the specific mechanism is not clear, it has been unexpectedly discovered that when a chain transfer agent as disclosed below is used in the present invention, not only is the uniformity, transparency and haze of the photopolymer diffraction grating improved, but the original high diffraction efficiency and high refractive index modulation are also maintained.
The chain transfer agent to be used in the present invention is not particularly limited, and examples thereof include mercaptan chain transfer agents such as n-dodecyl mercaptan, 1-mercapto-2-propanol, methyl thioglycolate, thioglycolic acid, methyl 3-mercaptopropionate, and 3-mercaptopropionic acid, sodium formate, citric acid, 4' -azobis (4-homopentanoic acid), and α -methylstyrene dimer. These may be used alone or in combination of two or more.
Additionally, in some preferred embodiments of the present invention, chain transfer agents having less than two chain transfer groups may be used. This is because it is considered that a chain transfer agent having three or more chain transfer groups (e.g., thiol group-containing thiol) may sometimes accidentally participate in the crosslinking reaction, and in extreme cases, may cause an increase in haze and a decrease in diffraction efficiency and refractive index modulation of the photopolymer.
More preferably, the present invention employs a chain transfer agent having a good chain transfer effect, low toxicity and no unpleasant odor, for example, the chain transfer agent of the present invention may be selected from at least one of sodium formate, citric acid and α -methylstyrene dimer.
For the radical scavenger, although the specific mechanism is not clear, it is believed that the radical scavenger can also achieve the same effect as the chain transfer agent.
The radical scavenger which can be used in the present invention is not particularly limited, and may be selected from, for example, 2,6, 6-tetramethyl-1-piperidinyloxy (hereinafter referred to as "TEMPO"), 4-amino-TEMPO, 4-hydroxy-TEMPO, 4-oxo-TEMPO and other TEMPO compounds; 4, 4-dimethyl-3-oxazolidinyloxy or a derivative thereof; 2,2,5, 5-tetramethyl-1-pyrrolidinyloxy or a derivative thereof; a sterically hindered phenolic compound; quinone compounds; phosphites such as tris (2, 4-dibutylphenyl) phosphite and the like; and other stable free radical agents such as phenyl t-butyl nitroxide, 2-bis (4-t-octylphenyl) -1-picrylhydrazyl (DPPH), and the like. These may be used alone or in combination of two or more.
Other ingredients
In the present invention, other components commonly used in the art may be used according to actual production needs as long as the technical effects of the present invention are not affected, and the components include: solvents, levelling agents, wetting agents, defoamers or tackifiers, as well as polyurethanes, thermoplastic polymers, oligomers, compounds having additional functional groups (e.g. acetals, epoxides, oxetanes, oxazolines, dioxolanes) and/or compounds having hydrophilic groups (e.g. salts and/or polyethylene oxides), can be used as additional auxiliaries and additives.
In some embodiments of the invention, the optional solvent is a volatile solvent that has good compatibility with the components of the invention, such as ethyl acetate, butyl acetate, and/or acetone. Although it is generally believed that the use of a solvent may cause a significant dimensional shrinkage effect, even if a solution is used in the photopolymer composition provided by the present invention, the effect of suppressing dimensional shrinkage can be significantly observed compared to the conventional photopolymer composition.
Composition of matter
In the photopolymer composition provided by the present invention, the content of the chain transfer agent and/or the radical scavenger is preferably 0.05 to less than 0.5% by weight based on the total weight of the composition, more preferably 0.05 to less than 0.3%, even more preferably 0.05 to less than 0.1%, and even more preferably 0.06 to 0.09%, from the viewpoint of simultaneously providing the resulting grating with high diffraction efficiency, high refractive index modulation, and high light transmittance and low haze.
Further, in some preferred embodiments, the composition of the photopolymer composition of the present invention may be (based on the total weight of the composition):
the content of the monomer in the composition may be 30 to 60%, preferably 35 to 55%, and more preferably 40 to 50%. Wherein, in some more preferred embodiments of the present invention, when the monomer composition comprises an epoxy compound and an acrylate monomer, the content of the epoxy compound may be 10 to 40%, preferably 15 to 35%, when the content is less than 10%, the shrinkage rate of the grating is high, the grating is easily deformed, and when the content is more than 40%, the diffraction efficiency of the grating is low, and the imaging quality is biased; the content of the acrylate monomer may be 10 to 40%, preferably 15 to 35%, and when the content is less than 10%, the mechanical strength and durability in use of the obtained film are insufficient, and when the content is more than 40%, the processability of the photopolymer composition may be reduced, which may affect the diffraction efficiency of the finally obtained grating.
The content of the film forming component can be 10-40%, 10-30%, preferably 12-25%.
In some more preferred embodiments of the present invention, the photoinitiator may be present in an amount of 0.03 to 0.2%, preferably 0.05 to 0.15%, more preferably 0.06 to 0.1%; the content of the coinitiator may be 0.3 to 1%, preferably 0.4 to 0.8%.
Further, the content of the other components than the above components is not particularly limited, and may be used in accordance with the amount range generally used in the art, provided that the technical effect of the present invention is not affected. For example, in some embodiments, the other components may be present in an amount of 5 to 40%, depending on the type of other components used.
< second aspect >
In a second aspect of the present invention, there is provided a grating based on the photopolymer composition according to the above < first aspect >, and a method for preparing the same.
The grating includes a carrier layer and a polymer film layer. The carrier substrate used may preferably be a layer of a material or a composite of materials that is transparent in the visible spectrum (greater than 85% transmittance in the wavelength range 400-780 nm).
Preferred materials or material composites for the carrier substrate are based on Polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene, polypropylene, cellulose acetate, cellulose hydrate, cellulose nitrate, cycloolefin polymers, polystyrene, polyepoxides, polysulfones, Cellulose Triacetate (CTA), polyamides, polymethyl methacrylate, polyvinyl chloride, polyvinyl butyral or polydicyclopentadiene or mixtures thereof. They are more preferably based on PC, PET and CTA. The material composite may be a foil laminate or a coextrusion. Preferred material composites are double or triple foils constructed according to one of the embodiments A/B, A/B/A or A/B/C. PC/PET, PET/PC/PET and PC/TPU (TPU ═ thermoplastic polyurethane) are particularly preferred.
As an alternative to the aforementioned carrier substrates, it is also possible to use flat glass plates, which are used in particular for the precise imagewise exposure of large areas, for example for holographic lithography (holographic interference lithography for integrated optics, IEEE Transactions on Electron Devices (1978), ED-25(10), 1193-.
Additionally, in some embodiments of the invention, the material or material composite of the carrier substrate may have a release, antistatic, hydrophobic or hydrophilic finish on one or both sides. On the side in contact with the photopolymer composition, the modification mentioned serves the purpose of allowing a non-destructive removal of the photopolymer from the carrier substrate. The modification of the side of the carrier substrate facing away from the photopolymer composition serves to ensure that the media according to the invention meet the specific mechanical requirements, for example in the case of processing in a roll laminator, in particular in the roll-to-roll process. The carrier substrate may have a coating on one side or a coating on both sides.
The thickness of the carrier substrate suitable for use in the present invention may be 1.5mm or less, preferably 20 μm to 1mm, and more preferably 40 μm to 900 μm.
In some specific embodiments of the present invention, the grating may be a laminate of a film formed of a photopolymer composition and the carrier, i.e., the film is formed on the carrier, or the film is sandwiched between two carriers. Therefore, the film formed of the photopolymer in the present invention has a grating structure by exposure, fading, or the like, and it may be present as a hologram recording medium on the support or sandwiched between layers of the support. In other cases, the grating may additionally comprise a cover layer and/or other functional layers, each optionally at least partially associated with the film.
In the present invention, the method for preparing a grating by using the photopolymer composition, the carrier, and the like may include the steps of:
(i) a mixing step of mixing the composition according to the < first aspect > to obtain a mixture;
(ii) a step of forming a grating structure by forming a film of the mixture and forming a grating structure on at least a part of the film,
wherein the step of forming a grating includes a step of exposing the film with coherent light.
(i) Step (ii) of
In some particular embodiments of the invention, the mixture is obtained in the form of a melt or liquid by mixing the photopolymer composition.
The compositions may be mixed in proportion in a suitable container, and mechanical stirring or the like may be employed to render the mixing uniform, if any is desired. The temperature of the mixing is not particularly limited, and in general, mixing under ambient conditions at room temperature or under heating (preheating) can be selected.
In other specific embodiments, the step of mixing may be performed under appropriate heating conditions. The heating temperature may be determined based on the activity of the components of the photopolymer composition and the desired viscosity of the system. Under some conditions it may be desirable to increase the mixing temperature to obtain a lower viscosity to obtain a blend in which the components are mixed uniformly. In addition, it is desirable to control the heating level to be less intense to avoid excessive polymerization within unnecessary processing windows, which can cause difficulties in subsequent processing.
In some preferred embodiments of the invention, the temperature used in the step of mixing is above 60 ℃, more preferably above 70 ℃ and below 110 ℃, preferably below 100 ℃. The resulting mixed melt/liquid can be used immediately or stored briefly at the processing temperature for use.
(ii) Step (ii) of
In this step, a film is formed on a support by using the mixed melt/liquid obtained above, and subjected to exposure treatment to obtain a polymer film having a grating structure. In some specific embodiments of the present invention, the polymer film has a thickness of 15 μm or more, preferably 20 μm or more, and further, the polymer film has a thickness of 50 μm or less, preferably 40 μm or less. The above-mentioned thickness of the polymer film can be coordinated or matched in practice with the use of spacers, for example as described below.
As for the material of the support, the same definition as < first aspect > described above, and in a preferred embodiment, glass may be used as the support. Optionally, the carrier glass sheet is cleaned, dried, etc. prior to use.
In the present invention, the grating structure is formed on at least a portion of the photopolymer film by exposure to light, during which exposure to coherent light can be used to control the microstructure.
In addition, in a preferred embodiment of the present invention, the use of spacers in the polymer film is advantageous for process control from the viewpoint of controlling the thickness of the polymer film, suppressing the dimensional shrinkage of the grating and maintaining high diffraction efficiency, particularly in the case where two carrier layers sandwich one polymer film.
For spacers, in some particular embodiments of the invention, particles that are substantially opaque to visible light may be used. These particles may be inorganic particles, organic particles or metallic particles. The inorganic particles are preferably used in the present invention from the viewpoint of suppressing the dimensional shrinkage of the grating and the production cost.
The kind of the inorganic particles is not particularly limited, and for example, silica, titania, or the like can be used. In some specific embodiments, the inorganic particles have a substantially spherical steric shape; in other specific embodiments, the inorganic particles have an average particle size of 2 to 50 μm, preferably 3 to 40 μm, and the particle size of the spacer may be coordinated, selected or determined with the thickness of the photopolymer film being formed.
As for the method of using the spacer, in the present invention, the spacer may be previously formed on the surface of the support, and this process may be carried out by a method of coating a dispersion system containing the spacer. In some embodiments, the spacer may be dispersed in a hydrocarbon, alcohol, or ketone solvent, for example, to form a dispersion. For these solvents, it is preferable to use a substance having a relatively low boiling point, and examples of the solvent include one or more of benzene, toluene, cyclohexane, pentane, ethanol, isopropanol, acetone, methyl ethyl ketone, and the like. The dried spacer particles (powder) may be directly dispersed in these solvents, or a sol-like substance formed by the spacers may be dispersed in these solvents.
The concentration of the spacer-containing dispersion system may be 0.1 to 3mg/mL, preferably 0.1 to 0.3mg/mL in some specific embodiments of the present invention, and too high a concentration deteriorates the uniformity of dispersion, resulting in a decrease in diffraction efficiency of the grating.
In the present invention, the spacer can be uniformly applied to the surface of the support by a coating method, and the coating method is not particularly limited, and can be performed by a spray coating or spin coating method. After the spacer is formed on the surface of the support by a coating method, the solvent may be removed by heating, blowing, or the like.
Further, the (hot) mixed melt/liquid obtained in the above step (i) is formed into a film on the surface of the side having the spacer on the support. For example, flat, onto a carrier substrate, in which case, for example, devices known to the person skilled in the art, such as knife coating devices (doctor blades, knife rolls, curved bars, etc.) or slit nozzles, etc., can be used. Optionally, if desired, a degassing step is carried out after the coating of the film, in order to eliminate possible bubbles in the film. After coating, a photopolymer film can be obtained by cooling or the like.
In the present invention, the above-described photopolymer film that can be used as a holographic medium can be processed into a hologram by a suitable exposure operation for optical applications in the entire visible (400-760 nm) and near UV range (300-800 nm). Visual holograms include all holograms which can be recorded by methods known to those skilled in the art.
In some preferred embodiments of the present invention, the exposure treatment of the photopolymer film can be performed with two beams of coherent light. The source of the coherent light is not particularly limited, and in some specific embodiments of the present invention, the light may be obtained by splitting a visible laser beam into two coherent light beams of the same or different intensities by an optical element and simultaneously exposing the resulting photopolymer film.
The wavelength of the exposure light source is not particularly limited in the visible light range, and may be selected so as to match the excitation activity of the photoinitiator or co-initiator. In some preferred embodiments of the present invention, a green light source (i.e., having a wavelength of about 532 nm) or a blue light source (i.e., having a wavelength of about 460 nm) may be selected as the exposure light source in view of improving the image quality displayed by the optical waveguide.
By exposure to coherent light, it is possible to present spaced bright and dark regions in the photopolymer film (two beams of coherent light produce alternating bright and dark stripes in the photopolymer composition film). The monomer in the bright area is polymerized under the action of an initiator, and the monomer in the dark area is transferred to the bright area due to the monomer concentration difference, so that the bright area and the dark area are separated due to the monomer concentration difference, and a refractive index difference delta n (refractive index modulation degree) is formed between the bright area and the dark area.
In some embodiments of the invention, two beams of coherent light may be exposed simultaneously from one side of the polymer film (a transmissive grating); in other embodiments, two beams of coherent light are used to expose the polymer from both sides of the polymer film (reflective gratings).
After exposure, refractive index distribution which is distributed in a sine function is formed in the photopolymer film, and the diffraction grating is obtained. The difference between the sinusoidal peaks, i.e., Δ n (degree of refractive index modulation). In some specific embodiments of the invention, Δ n may be 0.022 or more, preferably 0.030 or more, and more preferably 0.032 or more.
Additionally, in some specific embodiments of the present invention, the gratings formed from the photopolymer compositions of the present invention have a diffraction efficiency of 90% or more and preferably 95% or more. In some specific embodiments of the present invention, the gratings formed from the photopolymer composition of the present invention have a haze of 0.6% or less and preferably 0.4% or less, further preferably 0.2% or less, and more preferably 0.1% or less. In some specific embodiments of the present invention, the gratings formed from the photopolymer composition of the present invention have a light transmission of 90% or more, preferably 95%.
In some more preferred embodiments, the holographic diffraction grating of the present invention simultaneously satisfies: the diffraction efficiency is more than 95%, the haze is less than 0.5%, the light transmittance is more than 90%, and the refractive index modulation degree is more than 0.030.
Further, in some preferred embodiments, the shrinkage of the grating formed from the photopolymer composition of the present invention can be controlled to be less than 0.30%, preferably less than 0.25%.
For example, in FIG. 2, a typical exposure light path of the present invention is shown. Visible light laser reaches the beam expanding small hole after passing through the light reducing mirror, the shutter, the half wave plate and the spatial filter for beam expanding, then is changed into parallel light after being aligned with the diameter, and is divided into two beams of laser with the intensity of 6:4 through the polarization spectroscope, wherein one beam is changed from an s state to a p state through the half wave plate, and the two beams of laser are reflected and converged on the photopolymer film through the reflector to generate interference fringes.
After exposure, a holographic diffraction spectrum is formed in the photopolymer film, and then the color of the unexposed areas is removed after irradiation by, for example, an LED lamp or an ultraviolet lamp, to obtain the final reflective diffraction grating comprising the photopolymer film.
In addition, the grating obtained by the invention can be a plane grating or a curved grating with a certain curvature. The method for producing the curved grating is not particularly limited, and in some specific embodiments, a film may be formed on a substrate having a curvature by using the substrate and exposing the substrate. In other embodiments, a planar substrate may be used, and the coating film may be processed into a curved grating with a certain curvature after exposure.
< third aspect >
In a third aspect of the invention, the use of the diffraction grating obtained as described above in the present invention is disclosed. Without limitation, the above-described gratings comprising photopolymer films of the present invention can be used in a variety of holographic display systems in the art, and can be used alone or in combination with other optical elements.
Further, the present invention provides a diffraction grating element for a holographic optical waveguide display system. The element comprises a carrier layer and a photopolymer film layer comprising spacers. The carrier layer, the photopolymer film layer and the spacer are as described or defined in < first aspect > and < second aspect > of the present invention above.
In some preferred embodiments, the grating element is formed by sandwiching a layer of photopolymer film between two carrier layers. The photopolymer film layer is provided with at least two unconnected exposure areas, the exposure areas can be respectively or simultaneously exposed by a group of same coherent light sources, and after post-treatment, two areas with gratings are formed in one grating element.
Typically, the grating elements have a regular shape to facilitate use and installation, and may be in the shape of a strip, a square, or a circular plate.
In some preferred embodiments, the grating element of the present invention has the shape of a long strip, and has exposure regions subjected to exposure or the like at both end regions in the length direction of the long strip, and a grating (holographic recording) structure is formed in each exposure region. And the two exposure areas are physically unconnected. Typically, one exposure area may be used as an incoupling grating area, and the other exposure area may be used as an outcoupling grating area.
The grating element of the present invention can be used in a holographic optical waveguide display device, and is particularly suitable for head-up devices (e.g., AR display glasses devices, etc.) of Augmented Reality (AR) that has strict requirements for diffraction efficiency, refractive index modulation, light transmittance, and the like, and head-up displays (HUDs) of automobiles or aircraft.
Examples
Hereinafter, the present invention will be described by way of specific examples. However, it should be understood that the scope of the present invention is not limited to the following examples.
Example 1
Gratings were prepared and tested by the following steps:
(1) respectively adding 45.8 wt.% of epoxy compound A (the structure of which is shown in II-1) and pentabromophenyl methacrylate mixture, 38.16 wt.% of plasticizer PEG-300, 15.27 wt.% of polyvinylpyrrolidone, 0.08 wt.% of basic orange G, 0.61 wt.% of N-phenylglycine and 0.08 wt.% of alpha-methyl styrene dimer into a lightproof sample bottle, heating to 80 ℃, and uniformly stirring to obtain a mixture, wherein the solution is transparent orange yellow.
(2) A clean 25mm by 25mm glass slide was spin coated with a 0.2mg/mL solution of silica spacer isopropanol having an average particle size of 20 μm at 3000rpm for 15 seconds.
(3) And (3) dropping 20 mu L of the photopolymer composition mixture uniformly mixed in the step (1) on a glass sheet coated with a spacer on a heating table at the temperature of 80 ℃, covering another clean glass sheet with the thickness of 25mm multiplied by 25mm, slightly moving until the photopolymer mixture is completely spread on the glass sheet and no bubbles exist, and cooling to form a film.
(4) Placing the photopolymer film in the step (3) in an exposure light path as shown in figure 2, separating a beam of blue laser with the wavelength of 460nm into two beams of coherent light after polarizing and expanding, converging the two beams of coherent light on the surface of a sample after reflecting, and controlling the exposure light intensity to be 5mW/cm2The exposure time was 10 seconds, and the color of the blue LED was faded for 15 minutes, to obtain a photopolymer reflective diffraction grating having a maximum diffraction efficiency of 93%, a refractive index modulation degree of 0.0246, a transmittance of 90.5%, and a haze of 0.46%.
Example 2
Gratings were prepared and tested by the following steps:
(1) 49.24 wt.% of epoxy compound B (structure shown as II-2) and ETERCURE6361-100, 35 wt.% of plasticizer PEG-200, 15 wt.% of polyvinyl acetate, 0.1 wt.% of rose bengal, 0.58 wt.% of co-initiator N-phenylglycine and 0.08 wt.% of citric acid were added to a sample bottle which was protected from light, heated to 100 ℃ and stirred uniformly to obtain a mixture solution which was transparent pink red.
(2) A clean 25mm by 25mm glass slide was spin coated with a 0.2mg/mL solution of silica spacer isopropanol having an average particle size of 20 μm at 3000rpm for 15 seconds.
(3) And (3) dropping 20 mu L of the photopolymer mixture uniformly mixed in the step (1) on a glass sheet coated with a spacer on a heating table at 100 ℃, covering another clean glass sheet with the thickness of 25mm multiplied by 25mm, slightly moving until the photopolymer mixture is completely spread on the glass sheet and no bubbles exist, and cooling to form a film.
(4) Placing the photopolymer film in the step (3) in an exposure light path as shown in figure 2, separating a laser beam with the wavelength of 532nm into two coherent light beams after polarizing and expanding, converging the two coherent light beams on the surface of a sample after reflecting, and controlling the exposure light intensity to be 10mW/cm2And the exposure time is 15 seconds, and the green LED fades for 15 minutes to obtain the photopolymer reflective diffraction grating. The maximum diffraction efficiency was 95%, the refractive index modulation was 0.0309, the transmittance was 90%, and the haze was 0.032%.
Example 3
Gratings were prepared and tested by the following steps:
(1) 49.24 wt.% of epoxy compound B (the structure is shown as II-2) and pentabromophenyl methacrylate, 35 wt.% of plasticizer PEG-200, 15 wt.% of polyvinyl acetate, 0.1 wt.% of rose bengal, 0.58 wt.% of co-initiator N-phenylglycine and 0.08 wt.% of methyl 3-mercaptopropionate are respectively added into a lightproof sample bottle, the mixture is heated to 100 ℃, and the mixture is uniformly stirred to obtain a transparent pink solution.
(2) A clean 20mm by 70mm glass slide was spin coated with a 0.2mg/mL solution of silica spacer isopropanol having an average particle size of 20 μm at 3000rpm for 15 seconds.
(3) And (3) dropping 20 mu L of the photopolymer mixture uniformly mixed in the step (1) on a glass sheet coated with a spacer on a heating table at 100 ℃, covering another clean glass sheet with the thickness of 20mm multiplied by 70mm, slightly moving until the photopolymer mixture is completely spread on the glass sheet and no bubbles exist, and cooling to form a film.
(4) Placing one end of the photopolymer film in the step (3) in an exposure light path as shown in figure 3, separating a laser beam with the wavelength of 532nm into two coherent light beams after polarization and beam expansion, converging the two coherent light beams on the surface of a sample after reflection, and controlling the exposure light intensity to be 10mW/cm2The exposure time was 15 seconds, resulting in an incoupling grating.
(5) Placing the other end of the photopolymer film in the step (4) in an exposure light path as shown in figure 2, separating a laser beam with the wavelength of 532nm into two coherent light beams after polarizing and expanding, converging the two coherent light beams on the surface of a sample after reflecting, and controlling the exposure light intensity to be 10mW/cm2The exposure time was 15 seconds, resulting in an outcoupled grating.
(6) The coupling-in grating and the coupling-out grating manufactured in the steps (4) and (5) jointly form an optical waveguide, as shown in fig. 4, the optical waveguide is completely colorless and transparent, the diffraction efficiency of the two diffraction gratings is higher than 90%, and the light transmittance is higher than 90%.
(7) The optical waveguide imaging effects obtained in steps (4) to (6) were tested with a micro-projector, as shown in fig. 5.
Comparative example 1
Gratings were prepared and tested by the following steps:
(1) respectively adding 45.88 wt.% of epoxy compound A (the structure of which is shown in II-1) and pentabromophenyl methacrylate mixture, 38.16 wt.% of plasticizer PEG-300, 15.27 wt.% of polyvinylpyrrolidone, 0.08 wt.% of basic orange G and 0.61 wt.% of N-phenylglycine into a lightproof sample bottle, heating to 80 ℃, and uniformly stirring to obtain a mixture, wherein the solution is transparent and orange yellow.
(2) A clean 25mm by 25mm glass slide was spin coated with a 0.2mg/mL solution of silica spacer isopropanol having an average particle size of 20 μm at 3000rpm for 15 seconds.
(3) And (3) dropping 20 mu L of the photopolymer composition mixture uniformly mixed in the step (1) on a glass sheet coated with a spacer on a heating table at the temperature of 80 ℃, covering another clean glass sheet with the thickness of 25mm multiplied by 25mm, slightly moving until the photopolymer mixture is completely spread on the glass sheet and no bubbles exist, and cooling to form a film.
(4) Placing the photopolymer film in the step (3) in an exposure light path as shown in figure 2, dividing a laser beam with the wavelength of 460nm into two coherent light beams after polarizing and expanding, converging the two coherent light beams on the surface of a sample after reflecting, and controlling the exposure light intensity to be 5mW/cm2The exposure time was 10 seconds, and the color of the blue LED was faded for 15 minutes, whereby a photopolymer reflective diffraction grating was obtained, the maximum diffraction efficiency of which was 94%, the refractive index modulation degree of which was 0.0252, the transmittance of which was 85.41%, and the haze of which was 1.25%. As shown in fig. 5, the diffraction efficiency difference between different regions of the grating is large.
Comparative example 2
Gratings were prepared and tested by the following steps:
(1) respectively adding 45.88 wt.% of epoxy compound A (the structure of which is shown in II-1) and pentabromophenyl methacrylate mixture, 38.16 wt.% of plasticizer PEG-300, 15.27 wt.% of polyvinylpyrrolidone, 0.08 wt.% of basic orange G, 0.61 wt.% of N-phenylglycine and 1.0 wt.% of alpha-methylstyrene dimer into a lightproof sample bottle, heating to 80 ℃, and uniformly stirring to obtain a mixture, wherein the solution is transparent and orange yellow.
(2) A clean 25mm by 25mm glass slide was spin coated with a 0.2mg/mL solution of silica spacer isopropanol having an average particle size of 20 μm at 3000rpm for 15 seconds.
(3) And (3) dropping 20 mu L of the photopolymer composition mixture uniformly mixed in the step (1) on a glass sheet coated with a spacer on a heating table at the temperature of 80 ℃, covering another clean glass sheet with the thickness of 25mm multiplied by 25mm, slightly moving until the photopolymer mixture is completely spread on the glass sheet and no bubbles exist, and cooling to form a film.
(4) Placing the photopolymer film in the step (3) in an exposure light path as shown in figure 2, separating a laser beam with the wavelength of 532nm into two coherent light beams after polarizing and expanding, converging the two coherent light beams on the surface of a sample after reflecting, and controlling the exposure light intensity to be 10mW/cm2The exposure time is 10 seconds, and the green LED fades for 15 minutes, so that the maximum diffraction efficiency of the obtained photopolymer reflective diffraction grating is only 28%, the transmittance is 90.5%, and the haze is 0.47%.
It should be noted that, although the technical solutions of the present invention are described by specific examples, those skilled in the art can understand that the present disclosure should not be limited thereto.
Having described embodiments of the present disclosure, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen in order to best explain the principles of the embodiments, the practical application, or improvements made to the technology in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
Industrial applicability
The photopolymer composition of the present invention can be used industrially to produce reflective diffraction gratings.
Claims (11)
1. A photopolymer composition for a diffraction grating, comprising the following components:
a monomer composition having a refractive index of 1.55 or more;
a film forming component;
a photoinitiator system; and
chain transfer agents and/or radical scavengers;
wherein the chain transfer agent and/or free radical scavenger is present in an amount of 0.05 to less than 0.5% by weight based on the total weight of the composition.
2. The composition of claim 1, wherein the monomer composition comprises an acrylate monomer and/or an epoxy compound.
3. The composition of claim 2, wherein the epoxy compound has the structure of formula (I):
wherein E represents a group containing an epoxy group, n is an integer of 0 to 4, and each E is the same or different; each Ar is the same or different and independently represents an aryl-containing group; -C (R)1R2) -formation of a carbonyl group, or, R1、R2The same or different, independently represent a hydrogen atom, an aryl group having 6 to 30 carbon atoms, or an alkyl group or alkoxy group having 1 to 10 carbon atoms, and R1、R2The bonding may be by a single bond.
4. The composition of claim 2 or 3, wherein the epoxy compound has the following general formula (II):
wherein R is1And R2Have the same definition as in formula (I); each R3The same or different, independently selected from hydrogen, halogen and alkyl with 1-5 carbon atoms, and x is an integer of 0-4.
5. The composition of claim 2, wherein the acrylate monomer is an acrylate monomer having a refractive index of 1.55 or more and/or having 3 or more functional groups.
6. The composition according to any one of claims 1 to 5, wherein the chain transfer agent and/or the radical scavenger is contained in an amount of 0.05 or more and less than 0.1% by weight based on the total weight of the composition.
7. A diffraction grating comprising a resin film having a grating structure, wherein the resin film is obtained by curing the composition according to any one of claims 1 to 6.
8. A method for manufacturing a diffraction grating is characterized by comprising the following steps:
a mixing step, mixing the components of the composition according to any one of claims 1 to 6 to obtain a mixture;
a step of forming a grating structure by forming a film of the mixture and forming a grating structure on at least a part of the film,
wherein the step of forming a grating structure includes a step of exposing the film with coherent light.
9. The method of claim 8, wherein the step of forming a grating structure comprises the step of using spacers to compound the hybrid.
10. The method of claim 8 or 9, wherein the coherent light is derived from visible light.
11. A holographic optical waveguide display element comprising a diffraction grating according to claim 7 or a diffraction grating obtained by a method according to any one of claims 8 to 10.
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