JP2655541B2 - Volume phase hologram film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a volume phase hologram film, and more particularly, to a poly (N-vinylcarbazole) (hereinafter abbreviated as PVCz) volume phase type hologram film having excellent tensile strength. Related to hologram films.

(Prior Art) Conventionally, a volume phase hologram has long been called a new optical element. In recent years, for example, its usefulness as a coupling element of a head-up display has attracted attention, and its position has been established.

The volume phase hologram as described above was generally considered as an optical element recorded on a photosensitive recording layer fixed on an optically transparent substrate such as a glass substrate.

In addition, the volume phase hologram is for recording an interference wave of laser light on a thin film of about 20 μm, and when a visible light laser is used, a lattice having a spacing of about 0.1 to 0.2 μm is recorded inside the film. During exposure, the position of the photosensitive recording layer must be fixed with an accuracy of about 0.01 to 0.02 μm.

In the post-processing after exposure, the photosensitive recording layer is swelled and contracted, and the modulation of the refractive index of the portion recorded by the laser beam is further increased. At this time, this recording layer must cause swelling and shrinkage change only in the direction perpendicular to the film surface. Therefore, both of the exposure and development constraints inevitably lead to a fixed view that the volume phase hologram is supported and fixed on a rigid substrate, and there is no inconvenience as a conventional simple form optical component. .

Conventionally, the material for forming the recording layer of the volume phase hologram is:
At present, two types, a dichromated gelatin type and a PVCz type, are known, both of which are polymers. However, the first property required of the recording layer made of these polymers is that a volume phase hologram can be recorded, and it is sufficient that the recording layer has sufficient strength to exhibit the function as a volume phase hologram on a substrate.

However, in recent years, a hologram film that can be processed into various forms without such a protective member such as glass, a substrate, or the like has been required.

(Problems to be Solved by the Invention) On the other hand, the dichromated gelatin system is a water-soluble polymer as its basic property, and therefore has a water absorbing property. However, the use of a substrate such as glass is essential for this protection.

On the other hand, PVCz recording media have water resistance as a property completely opposite to gelatin dichromate,
There is no need for a protective film from moisture as in the dichromated gelatin system.

In addition, naturally, a film form is expected from the properties as a polymer.

In general polymer films, when the mechanical strength is insufficient, the strength can be compensated by increasing the thickness, but in the volume phase hologram,
As the hologram principle suggests, changing the thickness changes the characteristics of the hologram itself (for example, the half width of the diffraction peak is inversely related to the thickness), so increasing the thickness increases the strength of the hologram film. Is inconvenient.

The principle of volume phase holograms is that light cross-links are generated inside the film as described above, and the difference in the degree of these cross-links is swelled and shrinks internally through a development process called shrinkage, resulting in refractive index modulation. I have. Therefore, the resulting distortion must be stored frozen in the film so as to produce a difference in refractive index, ie, density.

Conventionally, commercially available PVCz has a weight average molecular weight of 70 to
The molecular weight distribution was 950,000, and the molecular weight distribution was 4.5 to 5.5. The hologram obtained by using this had a very low strength when formed into a film, and could not be handled without a support plate at all.

Accordingly, an object of the present invention is to provide a PVCz-based volume phase hologram film having sufficient strength even as a single film.

(Means for Solving the Problems) The above object is achieved by the present invention described below.

That is, the present invention is a volume phase hologram film in which a volume phase hologram is recorded on a polymer film mainly composed of PVCz, and the tensile strength of the film is 5 N / mm ² or more. .

(Function) By using PVCz having a weight average molecular weight of 1,000,000 or more and a molecular weight distribution of 3 or less as a material for forming a hologram recording medium, a volume phase type hologram film having sufficient strength as a film alone can be obtained. Obtained, and this hologram film has excellent high diffraction efficiency,
It has high transparency, low haze, and suppression of shift of the diffraction peak wavelength.

In contrast, PVCz, which has been conventionally used as a hologram recording medium, has a weight-average molecular weight in terms of polystyrene of 700 to 950,000 even at a high molecular weight, and its molecular weight distribution is 4.5 to 5.5.
A hologram film having a sufficient strength was not obtained because of having such a weight average molecular weight and molecular weight distribution.

(Preferred Embodiment) Next, the present invention will be described in more detail with reference to preferred embodiments.

PVCz in the present invention is obtained by polymerization of N-vinylcarbazole, and PVCz obtained by a usual method or commercially available PVCz has a weight average molecular weight and a molecular weight distribution as described above. Conventional PVCz can be purified, for example, purified by molecular weight fractionation with a solvent, and the low molecular weight component can be removed to obtain PVCz having a specific weight average molecular weight and a specific molecular weight distribution used in the present invention.

The weight-average molecular weight referred to in the present invention is a molecular weight in terms of polystyrene, and is a value determined by gel permeation chromatography at a column temperature of 27 ° C. using tetrahydrofuran as a solvent. Columns were Shodex KF-807, KF8
0M, exclusion limit 2 × 10 ⁸ , 3 × 10 ⁷ connected, 2 × 10 ^{7 to}
Up to 1.2 × 10 ³ polystyrene as standard).

For the separation of the molecular weight, any conventionally known separation method such as a method using various solvents having different solubility in PVCz or a method of changing the concentration may be used. As an example, fractionation was performed by changing the mixing ratio of a good solvent and a poor or non-solvent to PVCz, and changing the solubility of the mixed solvent to PVCz to remove low molecular weight.

In molecular weight fractionation, as a good solvent for PVCz,
For example, pyridine, quinoline and derivatives thereof, cyclic ethers such as dioxane and tetrahydrofuran, benzene, toluene, xylene (ortho, meta, para and mixtures thereof), ethylbenzene, n-propylbenzene, cumene, phenol, cresol , Chlorobenzene, dichlorobenzene, nitrobenzene, benzyl alcohol, benzyl chloride, benzyl bromide,
Benzene and naphthalene derivatives such as α-methylnaphthalene and α-chloronaphthalene, halogen-substituted saturated or unsaturated hydrocarbons such as pyran, dichloromethane, chloroform, trichloroethylene, trichloroethane, dichloroethane and bromoform, acetone, methyl ethyl ketone, methyl Ketones such as isobutyl ketone and cyclohexanone; esters such as ethyl acetate and ethyl formate;
Other amines, amides and the like can be mentioned, and an appropriate one is selected or used in combination from these.

The non- or poor solvent used for molecular weight fractionation includes, for example, n-pentane, n-hexane, n-heptane, n-heptane,
Alkanes such as octane, isooctane and cyclohexane, cycloalkanes, alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, tert-butyl alcohol, n-amyl alcohol and isoamyl alcohol; Ethers such as diethyl ether, methyl ethyl ether, diisopropyl ether and the like can be mentioned, and appropriate ones are selected or used in combination.

A good solvent and a poor solvent as described above, when the mixture is heated, PVCz is sufficiently dissolved, and when cooled, it is mixed with a ratio at which PVCz of a high molecular weight range is precipitated to obtain a purified solvent,
The PVCz is dissolved therein by heating and then cooled. At this time, the high molecular weight PVCz is precipitated, and the low molecular weight component is in a dissolved state.
The ones with abundance of 10,000 or more PVCz are obtained, and these operations are performed by changing the type of the solvent, the mixing ratio, and the like as necessary, so that the content of the low-molecular-weight PVCz is small and the molecular weight distribution is narrow. PVCz is obtained.

According to a detailed study of the present inventors, when the weight average molecular weight of purified PVCz is 1,000,000 or more, and its molecular weight distribution is 3 or less, by using this as a volume phase hologram recording medium, It has been found that various problems as described above are advantageously solved and a hologram film having excellent strength can be obtained. In particular, those having a molecular weight distribution of 2 or less, those having a weight-average molecular weight of 200,000 or less, those having a PVCz content of 1% by weight or less, and those having a weight-average molecular weight of 1,000,000 or more.
Those in which VCz accounts for 50% by weight or more of the whole polymer can further advantageously achieve the object of the present invention.

As described above, one of the separation methods for obtaining PVCz used in the present invention.
Although an example has been described, it is obvious that PVCz used in the present invention can be easily obtained by any purification method other than the above-mentioned fractionation method.

Since the above PVCz has no light absorption band on the longer wavelength side than 400 nm, when used as a hologram recording medium, a halogen compound, preferably an iodine compound and / or
Alternatively, it must be activated against the broad radiation by a bromine compound.

Such a halogen compound coexists in PVCz and constitutes a recording layer having a sufficient sensitivity even in a visible wavelength range.Specific examples of preferred are carbon tetraiodide, iodoform and ethylene tetraiodide. And iodine compounds and bromine compounds such as triiodoethane, tetraiodoethane, pentaiodoethane, hexaiodoethane, carbon tetrabromide and ethylene tetrabromide. These halogen compounds are described above.
For example, 100 to 1 part by weight is added to 100 parts by weight of PVCz.

If the addition amount of the halogen compound as described above is too small, the sensitivity of the obtained recording medium is low, and it is not preferable because the exposure takes a long time, and if it is too large, the undecomposed halogen compound remains in the recording medium and later. Since it is necessary to remove all of them, it is not preferable because it causes voids in the recording medium.

Furthermore, in the present invention, it is better not to use a plasticizer when preparing a recording medium.For example, when a plasticizer is mixed, the plasticizer remaining without being eluted in the swelling / shrinking step during development swells like PVCz. -It is necessary to undergo a contraction action, and after the contraction, a refractive index distribution other than the modulation of the refractive index satisfying the Bragg condition may occur in the recording medium. Of course, this does not necessarily mean that it cannot be used within a range that does not cause inconvenience as described above.

The volume phase hologram film of the present invention has the above-mentioned PVCz
And a sensitizer is dissolved in a suitable solvent, for example, a good solvent as described above to obtain a photosensitive solution, the viscosity of which is appropriately adjusted, and the viscosity is adjusted to form a coating film on a suitable substrate such as a glass plate or a plastic film. It is obtained by forming, exposing, developing and peeling.

The recording medium formed as described above is exposed by an optical system as shown in FIG. 1 using a coherent laser of two light beams of object light and reference light, which are coherent visible light up to 560 nm.

Subsequent to the exposure step, not only the PVCz forming the recording layer, but also a crosslinked product of PVCz generated by the photoreaction is immersed in a solvent that hardly elutes, and the unreacted halogen is removed from the recording layer. The compound alone is almost completely eluted and removed to remove coloring. This step can also serve as the following swelling step.

The subsequent developing step includes two steps, a swelling step and a shrinking step.

That is, the hologram latent image is formed by the exposure step, and the recording layer from which the halogen compound has been removed is treated with a swelling liquid as a first solvent to cause swelling according to the formed hologram pattern. In the subsequent treatment with the second solvent, the swollen recording layer is contracted, and the hologram is amplified and fixed according to the swollen state.

The swelling solution, which is the first solvent in the hologram development step, is a solvent that hardly elutes in a short time with respect to the crosslinked and uncrosslinked products of PVCz generated as a result of the photoreaction between PVCz and the halogen compound. is there. As such a solvent, a solvent having an appropriate swelling power is selected or used in combination from the good solvents listed as the purification solvent in the present invention.

Further, the shrinking liquid as the second solvent does not have a swelling or dissolving effect on the recording layer, and any solvent compatible with the swelling liquid can be used. An appropriate one is selected from the solvents or used in combination.

Further, the processing conditions such as the temperature and time of each step vary depending on the type of the recording layer and the type of the solvent to be used, and cannot be unconditionally specified, but generally, each step is about 10 ° C. to 70 ° C. A sufficient effect can be obtained by treating for several seconds to several minutes at the above temperature.

The hologram film can be peeled from the substrate by any method. For example, the hologram film is preferably peeled off in a non-solvent or water that does not dissolve or swell the hologram film. Further, at the time of peeling, the hologram film has a sufficient strength, so that it is not necessary to break, melt or swell the substrate.

The hologram film of the present invention obtained as described above has a tensile strength of 5 N / mm ² or more in a tensile test at a speed of 500 mm / min., And is sufficiently processed and used as a film alone in various applications. Has handling strength. If the tensile strength is less than 5 N / mm ² , the film breaks or breaks when processing the film, and the object of the present invention cannot be achieved.

(Effects) By using PVCz having the specific weight average molecular weight and molecular weight distribution as described above, a volume phase hologram that can be sufficiently handled and variously processed even in a state of being separated from the substrate can be obtained.

Also, the above-mentioned volume phase type hologram film is a conventional type.
Maximum diffraction efficiency of volume phase hologram using PVCz is 98
% To 99.9%, and the transmittance was 80% at 600 nm, 92%, and the haze was 1%.
What was 12% at a thickness of 0 μm is improved to 2% or less.

(Examples) Next, the present invention will be described more specifically with reference to examples and comparative examples.

Example 1 20 g of PVCz (Rubican M-170, manufactured by BASF) was added to 600 ml of a mixed solution of dioxane / isopropyl alcohol (weight ratio: 3/1), and the mixture was heated to 80 ° C. to be dissolved. Cooled to ° C.

The precipitated PVCz was separated by decantation and separated
PVCz was added to 200 ml of a mixed solution of dioxane / isopropyl alcohol (weight ratio: 3/1) and stirred, and the polymer was washed several times to obtain purified PVCz.

Dissolve part of the above sample in tetrahydrofuran,
A gel permeation chromatograph was used at a column temperature of 27 ° C. The column was connected to Shodex (Showa Denko KK) KF-807 and KF80M, and the weight average was based on polystyrene (Showa Denko KK). The molecular weight and molecular weight distribution were determined as follows.

Weight average molecular weight 1.52M Molecular weight distribution 1.48 Content of PVCz with a molecular weight of 200,000 or less 0.8% by weight Content of PVCz with a molecular weight of 1,000,000 or more 62% by weight Add 2.5g of this sample and 0.25g of carbon tetraiodide to 40ml of chlorobenzene, The mixture was completely dissolved by stirring in a dark place to obtain a photosensitive solution.

The above photosensitive solution was coated on a washed glass plate using a spinner (manufactured by Kyowa Semiconductor) and dried to a thickness of 7.2 μm.
Was formed.

The recording layer was exposed to an optical system shown in FIG. 1 using an Ar laser (488 nm) to record a hologram.

After exposure, the film was immersed in toluene at 35 ° C. for 2 minutes and xylene at 35 ° C. for 2 minutes, immersed in heptane at 20 ° C. for 2 minutes, and dried to obtain a volume phase hologram.

When the reflection diffraction efficiency of the hologram was measured, 51
The maximum reflection / diffraction efficiency is 99% at the light of 8 nm, the transmittance at the light of 600 nm is 87%, and the haze (total haze value) is
Haze meter based on JISK7105 (manufactured by Nippon Denshoku Co., Ltd.)
Was 1.7%.

Next, the hologram was immersed in water, peeled off and dried to obtain a hologram film of the present invention. When various performances of this hologram film were measured in the same manner as described above,
No performance change was observed.

The hologram film was cut into a strip-shaped length 75mm and width 10 mm, was 14N / mm ² was determined with a breaking strength 500 mm / min. Speed by a tensile tester, sufficient strength to handle by hand Had.

Example 2 A hologram film of the present invention having a thickness of 7.4 μm was obtained in the same manner as in Example 1 except that purified PVCz having a molecular weight of 1.2 million and a molecular weight distribution of 2.8 was used.

The maximum diffraction efficiency of this hologram film is 98% (518nm)
And a transmittance of 87% (600 nm). The breaking strength was determined in the same manner as in Example 1 to be 11 N / mm ² .

Comparative Example 1 PVCz (Rubican M-170) before purification in Example 1
Was used to obtain a volume phase hologram film of a comparative example in which the recording layer was formed, exposed and developed in the same manner as in Example 1 except that the thickness of the recording layer was changed to 16 μm.
When this hologram was measured in the same manner as in Example 1, the diffraction efficiency was only 4%, the transmittance was poor at 68%, and it was clearly cloudy, and the haze value did not need to be measured.

The hologram film was subjected to a tensile test and found to have a breaking strength of 4.8 N / mm ² , which was brittle.

The PVCz before purification was measured under the same conditions as in Example 1. As a result, the weight average molecular weight was 920,000, and the molecular weight distribution was 5.4.

Comparative Example 2 Except that the purified PVCz in Example 1 was replaced by 2.5 g of unpurified PVCz (Tubicol 210SP, manufactured by Anan Kosyu Co., Ltd.), and the thickness of the recording layer was changed to 19 μm, the other operations were carried out. Example 1
The formation, exposure and development of the recording layer were performed in the same manner as in the above to obtain a volume phase hologram film of Comparative Example. This hologram also has a maximum diffraction efficiency of 23% (520 nm), a transmittance of 73%, and a haze of 21%. When subjected to a tensile test, it has a strength of 4.0 N / mm ² , and is very brittle and fragile. Met.

When the PVCz before purification was measured under the same conditions as in Example 1, the weight average molecular weight was 780,000, and the molecular weight distribution was 4.
It was 6.

[Brief description of the drawings]

 FIG. 1 shows a hologram recording optical system used in the embodiment.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takasato Taniguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-2-18592 (JP, A)

Claims (2)

(57) [Claims] 1. A volume phase hologram, wherein a volume phase hologram is recorded on a polymer film mainly composed of poly (N-vinylcarbazole), and the film has a tensile strength of 5 N / mm ² or more. Type hologram film. 2. The poly (N-vinylcarbazole) has a weight average molecular weight of 1,000,000 or more and a molecular weight distribution of 3
2. The volume phase hologram film according to claim 1, wherein: