JP5063399B2 - Plastic rod lens, rod lens array, rod lens plate, image sensor and printer - Google Patents

Description

  The present invention relates to a plastic rod lens and rod lens array, a rod lens plate, an image sensor, and a printer that can be used as an optical transmission path for a light converging rod lens, an optical sensor, and the like.

The plastic rod lens is a plastic lens element having a cylindrical shape and a refractive index decreasing toward the outside from the central axis, and forms an erecting equal-magnification image. Usually, both end faces of the plastic rod lens are mirror-polished so as to be a plane perpendicular to the central axis in order to form an accurate image.
Further, two or more plastic rod lenses may be arranged in parallel and integrated by bonding to form a rod lens array. The rod lens array is widely used as a part for an image sensor in various scanners such as a hand scanner, a copying machine, and a facsimile, and as a writing device for a light emitting diode (LED) printer.
Such a plastic rod lens and a lens array using the plastic rod lens are expanding its application field because of its low cost and a compact optical system.

In recent years, plastic rod lenses have been developed that have as little chromatic aberration as glass and have excellent color characteristics, which has been difficult with conventional plastics. For example, Patent Document 1 discloses that when an alicyclic and / or heterocyclic ring-containing methacrylate and an aromatic ring-containing methacrylate, a fluorinated alkyl methacrylate, or methyl methacrylate is used as a raw material for a lens, the refractive index and the Abbe number at the center are as follows. It is disclosed that a plastic rod lens having a high refractive index and an Abbe number lowering toward the outside and having almost no chromatic aberration can be obtained.
The plastic lens having such optical performance can be expected to be applied to a printer complex machine having a high-resolution color scanner function of 600 dots / inch (dpi) or more. However, since the plastic rod lens has a lower heat-resistant temperature of the material than the glass rod lens, it has a problem that the optical performance is likely to deteriorate when used for a long time.
International Publication WO2007 / 011013

  It is an object of the present invention to provide a plastic rod lens and rod lens array, a rod lens plate, a rod lens plate, an image sensor, and a printer using the same that have a small deterioration in optical performance even after long-term use and have good color characteristics. .

  The present inventors have found that a plastic rod lens or a lens array changes its refractive index distribution when it is exposed to a high temperature for a long period of time, causing a decrease in optical performance. It has also been found that heat resistance is improved by adjusting the refractive index distribution, specifically by reducing the outer refractive index. Based on this knowledge, the following plastic rod lens, lens array, rod lens plate, image sensor, and printer were invented.

That is, the present invention includes the following aspects.
[1] A plastic rod lens having a cylindrical shape with a radius R and having a refractive index distribution in which the refractive index decreases from the central axis toward the outside.
In a cross section perpendicular to the central axis, when the refractive index distribution is approximated to a quadratic curve distribution represented by the following formula (1), the approximate refractive index n (L) in the range of 0.95R to R is 0. higher than the measured refractive index _{n n} ranging .95R～R, the measured refractive index of the central portion 100, the measured refractive index of the outermost portion upon a 0, the measured refractive index in the range of 0R~0.15R Is a ratio in which the measured refractive index in the range of 100, 0.25R to 0.90R is 90 to 50, and the measured refractive index in the range of 0.95R to R is 25 to 0,
A central portion where the measured refractive index is 100, a first portion located radially outside the central portion, and a measured refractive index of 90 to 80, and a radially outer side continuously to the first peripheral portion A second portion having an actually measured refractive index of 80 to 40, a third portion having a measured refractive index of 40 to 1 and being located radially outward from the second peripheral portion. An outer peripheral portion that is located radially outward from the third portion and has an actually measured refractive index of 0, the central portion, the first portion, the second portion, and the third portion And the ratio of the thickness of the radial direction with the said outer peripheral part is 5-30: 15-50: 15-40: 2-10: 0.5-10, The plastic rod lens characterized by the above-mentioned.
^{_{n (L) = n 0 {}} 1- (g 2/2) L 2} (1)
(Where n ₀ is the refractive index at the central axis of the plastic rod lens (central refractive index), L is the distance from the central axis of the plastic rod lens (0 ≦ L ≦ R), and g is the refractive index distribution of the plastic rod lens. (The constant n (L) is an approximate refractive index at a position of distance L from the central axis of the plastic rod lens.)
[ 2 ] A rod lens array in which two or more plastic rod lenses according to [1 ] are arranged in parallel,
The moderation transfer function (MTF) after heat treatment for 1000 hours in an environment of a temperature of 60 ° C. and a relative humidity of 90% is 40% at wavelengths of 470 nm, 525 nm, and 630 nm at a spatial frequency of 12 line pairs / mm. This is the rod lens array.
[ 3 ] A rod lens plate in which many plastic rod lenses according to [1 ] are arranged in parallel in two dimensions.
[ 4 ] An image sensor comprising the rod lens array according to [ 2 ] or the rod lens plate according to [ 3 ].
[ 5 ] A printer comprising the rod lens array according to [ 2 ] or the rod lens plate according to [ 3 ].

The plastic rod lens, rod lens array, and rod lens plate of the present invention have small optical performance degradation and excellent color characteristics.
In addition, the image sensor and printer of the present invention can maintain high resolution without deterioration in optical performance even when used for a long period of time.

(Plastic rod lens)
The plastic rod lens of the present invention has a cylindrical shape with a radius R, and has a refractive index distribution in which the refractive index decreases toward the outside from the central axis.
The plastic rod lens of the present invention has a refractive index distribution in a cross section perpendicular to the central axis, in the range of 0.95R to R when the refractive index distribution is approximated to a quadratic curve distribution represented by the following formula (1). approximate refractive index n (L) is higher than the measured refractive index _{n n} ranging 0.95R～R. In the detailed description of the present invention, the uncured material constituting each layer is cured, the refractive index of the cured product is expressed as an actually measured refractive index, and a measured value obtained by measuring the refractive index at the radial position of the rod lens. Is expressed as an approximate refractive index.
^{_{n (L) = n 0 {}} 1- (g 2/2) L 2} (1)
In formula (1), n ₀ is the refractive index (central refractive index) at the central axis of the plastic rod lens, L is the distance from the central axis of the plastic rod lens (0 ≦ L ≦ R), and g is the refractive index of the plastic rod lens. A rate distribution constant, n (L), is an approximate refractive index at a position of a distance L from the central axis of the plastic rod lens.
The conjugate length of the plastic rod lens of the present invention is approximated by the following formula (2). According to this equation, the conjugate length is determined by the refractive index distribution constant g and the lens length Z. For this reason, the refractive index distribution constant g and the lens length Z are arbitrarily set according to the conjugate length design of the optical apparatus to be used.
Tc = Z + 2 {− (1 / n ₀ / g) tan (Z · g / 2)} (2)
In formula (2), Tc is the conjugate length of the plastic rod lens, and Z is the length of the plastic rod lens.
In the plastic rod lens having such a refractive index distribution, even if the refractive index distribution in the radial direction changes due to exposure to a high temperature, the change in optical performance is small (that is, the heat resistance is high). Further, the chromatic aberration is small and the color characteristics are excellent.

Further, since the optical performance changes when exposed to high temperature becomes smaller, the approximation refractive index n in the range of 0.9R~R (L) is, from the measured refractive index _{n N} ranging 0.9R～R Is preferably high.

In the plastic rod lens of the present invention, when the refractive index of the central portion is 100 and the refractive index of the outermost portion is 0, the measured refractive indexes in the range of 0R to 0.15R are 100, 0.25R to It is preferable that the measured refractive index in the range of 0.90R is 90 to 50, and the measured refractive index in the range of 0.95R to R is 25 to 0. If the refractive index distribution has such a ratio, a plastic rod lens with higher heat resistance can be obtained.
Furthermore, the measured refractive index in the range of 0.25R to 0.9R is more preferably 85 to 50, and the measured refractive index in the range of 0.95R to R is more preferably 23 to 0.

The central refractive index n ₀ in the plastic rod lens of the present invention is 1.4 ≦ n ₀ ≦ 1.6, and the difference between the central refractive index n ₀ and the refractive index n ₁ of the outermost part is n ₀ −n ₁ ≧ It is preferable that it is 0.01.
In the plastic rod lens of the present invention, the radius R is preferably 0.08 mm or more and 0.4 mm or less. When the radius R is 0.4 mm or less, the conjugate length can be shortened and the optical system can be made compact. Further, by shortening the conjugate length, the difference in conjugate length between 470 nm and 630 nm is further reduced, so that the color characteristics are further improved.
On the other hand, it is preferable that the radius R is 0.08 mm or more in order to facilitate processing and handling when manufacturing the rod lens array or the image sensor.

In the plastic rod lens of the present invention, the refractive index distribution constant g is preferably 0.4 mm ⁻¹ ≦ g ≦ 2.0 mm ⁻¹ at a wavelength of 525 nm. When the refractive index distribution constant g is 2.0 mm ⁻¹ or less, one period length of the plastic rod lens can be increased, and processing and handling are facilitated when a rod lens array is manufactured.
If the refractive index distribution constant g is 0.4 mm ⁻¹ or more, the one-cycle length of the plastic rod lens is shortened, so that the conjugate length Tc is reduced and the optical system can be made compact.
Therefore, if the refractive index distribution constant g is in the above range, it is possible to achieve both compactness of the optical system and handleability of the plastic rod lens.

  In the plastic rod lens of the present invention, the product (g · R) of the refractive index distribution constant g and the radius R preferably satisfies 0.1 ≦ g · R ≦ 0.3. When the product of the refractive index distribution constant g and the radius R is within the above range, a plastic rod lens having a large depth of focus, a short conjugate length, and a large amount of emitted light can be obtained.

The plastic rod lens of the present invention contains a light absorber containing a light absorber in a range perpendicular to the central axis within 80 μm from the outer peripheral surface of the plastic rod lens to the central axis and 0.6 R or more from the central axis. It is preferable that a layer is formed.
If the light absorber is contained in the plastic rod lens as described above, the flare light or rod caused by the irregular portion of the refractive index distribution formed on the outer periphery of the plastic rod lens without significantly reducing the amount of emitted light Crosstalk when a lens array is formed can be prevented. As a result, the lens performance can be improved.
Note that if the light absorber is included in a region closer to the central axis than 0.6R, or the light absorber is included in a region exceeding 80 μm on the central axis side from the outer peripheral surface of the plastic rod lens, the amount of emitted light is reduced. There is a tendency.

The light absorber absorbs light in at least a part of the wavelength region of the visible light and near infrared light regions.
As the light absorber, various dyes, pigments, and pigments that can absorb light in at least a part of the wavelength range of visible light and near infrared light can be used. These light absorbers are light absorbers that absorb only a specific wavelength range, and two or more kinds of light absorbers that absorb different wavelengths may be used in combination. For example, when a plastic rod lens is used in a color scanner, dyes that absorb light of each wavelength of RGB can be used in combination.
Moreover, as a light absorber, what absorbs only a specific wavelength range among visible light (about 400 nm-about 700 nm) and near infrared (about 700 nm-about 1000 nm) as mentioned above may be used. Those that absorb water may be used. When forming a layer that absorbs all light in the visible light region, it is necessary to use a black light absorber such as carbon black or graphite carbon mixed with a plurality of types of light absorbers. it can.

  The light absorber is preferably present uniformly in the light absorber-containing layer. In that case, it is preferable that the light absorber molecules are uniformly dispersed or bonded in the polymer constituting the light absorber-containing layer.

  Moreover, 0.001-10 mass% is preferable and, as for content in the light absorber content layer of a light absorber, 0.001-1 mass% is more preferable.

The method for producing the plastic rod lens of the present invention may be any method such as an addition reaction method, a copolymerization method, a gel polymerization method, a monomer volatilization method, an interdiffusion method, The interdiffusion method is preferable in terms of accuracy and productivity.
Hereinafter, the mutual diffusion method will be described.

First, the refractive index n and the Abbe number ν after curing are such that n ₁ > n ₂ >...> _{N N} and ν ₁ > ν ₂ >...> Ν _N (N ≧ 3). An uncured laminate (hereinafter, referred to as a concentric laminate) in which the refractive index and the Abbe number are sequentially decreased from the central axis toward the outside using a composite spinning nozzle or the like using a composite spinning nozzle or the like. It is shaped into a “filament”.
Next, an interdiffusion treatment for interdiffusing substances between adjacent layers is performed so that the refractive index distribution between each layer of the filamentous body is preferably continuous, and thereafter or simultaneously, the filamentous body is cured. A plastic rod lens raw yarn is obtained (spinning process).
Here, the interdiffusion treatment is a treatment for giving a thermal history for several seconds to several minutes at 10 to 60 ° C., more preferably 20 to 50 ° C. in a nitrogen atmosphere.
Next, the plastic rod lens raw yarn obtained by the spinning step is subjected to a heat stretching treatment as necessary, and then subjected to a relaxation treatment, and appropriately cut into a predetermined size, whereby the plastic rod lens of the present invention is obtained. obtain.

Uncured material that is used in the production of plastic rod lenses of the present invention, the refractive index n _c after curing of the uncured material to be laminated to the center, the after curing of the uncured material to be laminated to the outermost layer It is preferable to select such that the difference in the refractive index n _p is n _c −n _p ≧ 0.02. Thus selecting the uncured material, the difference in refractive index n ₁ of the central refractive index n ₀ and outermost portions of the plastic rod lens after interdiffusion, easily and n ₀ -n ₁ ≧ 0.01 be able to.

In order to make the refractive index distribution of the obtained plastic rod lens close to an ideal distribution and to increase the heat resistance, the number N of uncured materials to be used is set to 4 or more, more preferably in the range of 4 to 6. Is preferred.
In the case of N = 5, the refractive index of each layer is 100/90 to 80/80 to 40 / in the order of the first layer to the fifth layer when the first layer is 100 and the fifth layer is 0. 40 to 1/0, and the ratio of the thickness of each layer may be 5 to 30/15 to 50/15 to 40/2 to 10 / 0.5 to 10 in order from the first layer to the fifth layer. preferable. In the preferred embodiment of the present invention, the refractive indexes of the first layer to the fifth layer are described for convenience. However, since the mutual diffusion is performed in each layer, the manufactured rod lens is strictly laminated. It does n’t mean that. That is, when the measured refractive index of the central portion is 100, the plastic rod lens is located radially outside the central portion, and the first portion having the measured refractive index of 90 to 80 and the radius continuous to the first portion. A second part having an actually measured refractive index of 80 to 40, a third part having an actually measured refractive index of 40 to 1 and a third part that is located radially outside the second part. In other words, it has an outer peripheral portion that is located outside in the radial direction and whose measured refractive index is zero.

The viscosity of the uncured product at 50 ° C. is preferably 10 ² to 10 ⁷ Pa · s. If the viscosity is less than 10 ² Pa · s, thread breakage may easily occur during shaping, and it may be difficult to form a filament. On the other hand, if it exceeds 10 ⁷ Pa · s, the operability at the time of shaping may be poor, and the concentricity of each layer may be impaired, or the filament may have a large thickness.

As the uncured product, a radical polymerizable vinyl monomer or a composition comprising a radical polymerizable vinyl monomer and a polymer soluble in the monomer (soluble polymer) can be used. . Among them, the viscosity of the uncured product when forming the filament from the uncured product can be easily adjusted, and a continuous refractive index distribution can be easily formed from the central axis of the filament to the outside. A composition comprising a radical polymerizable vinyl monomer and a soluble polymer is preferred.
As the soluble polymer, polymethyl methacrylate (refractive index: 1.49) and polymethyl methacrylate copolymer (refractive index: 1.47 to 1.50) are preferable. Among these, polymethyl methacrylate is more preferable because it is excellent in transparency and has a high refractive index.

  Each layer preferably contains a soluble polymer having the same refractive index. If each layer contains a soluble polymer having the same refractive index, a plastic rod lens having a continuous refractive index distribution from the central axis toward the outside can be easily obtained.

In order to cure the filament formed from the uncured material, it is preferable to add a polymerization initiator in an amount of 0.01 to 2% by mass in the uncured material. As the polymerization initiator, there are a thermosetting initiator and a photocuring initiator, both of which can be used.
As the thermosetting initiator, a peroxide-based or azo-based initiator is usually used.
Examples of photocuring initiators include benzophenone, benzoin alkyl ether, 4′-isopropyl-2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexyl phenyl ketone, benzyl methyl ketal, 2,2-diethoxyacetophenone, chlorothioxanthone. Thioxanthone compounds, benzophenone compounds, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, N-methyldiethanolamine, and triethylamine.

When the uncured product is cured, the filament containing the thermosetting initiator and / or the photocuring initiator is subjected to heat treatment or photocuring treatment. When the uncured product contains both a thermosetting initiator and a photocuring initiator, both heat treatment and photocuring treatment can be performed.
The thermosetting treatment can be performed by heat-treating an uncured product containing a thermosetting initiator for a predetermined time in a curing processing section such as a heating furnace controlled at a constant temperature.
The photocuring treatment can be performed by irradiating an uncured product containing a photocuring initiator with ultraviolet rays from the surroundings. Examples of the light source used for the photocuring treatment include a carbon arc lamp that generates light having a wavelength of 150 to 600 nm, a high-pressure mercury lamp, a medium-pressure mercury lamp, a low-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a chemical lamp, a xenon lamp, and a laser beam.

  In order to stably produce the filamentous material, it is preferable to add a polymerization inhibitor in order to prevent polymerization until the curing treatment. Examples of the polymerization inhibitor include quinone compounds such as hydroquinone and hydroquinone monomethyl ether, amine compounds such as phenothiazine, and N-oxyl compounds such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl. Compounds and the like.

The spinning step can be performed using, for example, a plastic rod lens raw yarn manufacturing apparatus as shown in FIG.
The plastic rod lens yarn manufacturing apparatus 10 includes a concentric composite spinning nozzle 11, a containing body 12 for containing the filament A discharged from the concentric circular spinning nozzle 11, and a concentric composite spinning nozzle for the containing body 12. 11, the inert gas introduction pipe 13 connected to the side 11, the inert gas discharge pipe 14 connected to the outlet 12 a side of the container 12, and the first light provided outside the center in the longitudinal direction of the container 12. An irradiator 15, a second light irradiator 16 provided outside the container 12 on the inert gas discharge pipe 14 side, and a take-up roller 17 disposed on the downstream side of the container 12 are provided.
In the container 12, the part from the concentric circular composite spinning nozzle 11 to the point immediately before the light from the first light irradiator 15 hits the mutual diffusion processing part 12 b, and the part to which the light from the first light irradiator 15 hits is the first curing processing part. The part which the light of 12c and the 2nd light irradiation machine 16 hits is called the 2nd hardening process part 12d.

In the production of the plastic rod lens raw yarn using the production apparatus 10, an inert gas (for example, nitrogen gas) is introduced into the container 12 from the inert gas introduction pipe 13 and the container 12 is introduced from the inert gas discharge pipe 14. The inert gas inside is discharged.
With the inert gas flowing in this manner, the uncured filament A is discharged from the concentric composite spinning nozzle 11, and the filament A is passed through the container 12. At this time, mutual diffusion is caused in each layer constituting the filament A by the interdiffusion processing unit 12b, and the first curing unit 12c irradiates the filament A with light by the first light irradiator 15, In the 2 hardening process part 12d, the 2nd light irradiation machine 16 irradiates light to the filament A, and it hardens | cures it.
Then, the plastic rod raw yarn B is obtained from the container 12 by being taken up by the take-up roller 17.

The plastic rod lens raw yarn obtained by the spinning process may be continuously sent to the heat stretching process as it is, if necessary, or once wound on a bobbin or the like and sent to the heat stretching process, You may cut | disconnect to desired length.
The heat stretching treatment may be performed in a batch manner or continuously. The heat stretching treatment and the relaxation treatment may be performed continuously or discontinuously.

The heat stretching treatment and the relaxation treatment can be performed using, for example, a stretching / relaxation treatment apparatus as shown in FIG.
The stretching / relaxation processing device 20 includes a first nip roller 21, a second nip roller 22, a third nip roller 23, a first heating furnace 24 disposed between the first nip roller 21 and the second nip roller 22, and a second nip roller 22. A second heating furnace 25 is provided between the nip roller 22 and the third nip roller 23.

The heat stretching process can be performed using, for example, the stretching / relaxation processing apparatus 20 described above. That is, the plastic rod lens raw yarn B obtained by curing is supplied to the first heating furnace 24 by the first nip roller 21, and the plastic rod lens raw yarn B that has passed through the first heating furnace 24 is supplied to the first heating furnace 24 by the second nip roller 22. For example, a method of drawing and stretching at a speed higher than that of the 1-nip roller 21 may be used.
The temperature of the atmosphere in the first heating furnace 24 in the heat stretching treatment is appropriately set according to the material of the plastic rod lens, etc., but is preferably set to a glass transition temperature (Tg) of the plastic rod lens + 20 ° C. or higher. The draw ratio is appropriately determined depending on the desired plastic rod lens diameter, and can be adjusted by the peripheral speed ratio between the first nip roller 21 and the second nip roller 22.

The relaxation treatment can be performed using, for example, the stretching / relaxation treatment apparatus 20 described above. That is, the stretched plastic rod lens raw yarn C is supplied to the second heating furnace 25 by the second nip roller 22, and the plastic rod lens raw yarn C that has passed through the second heating furnace 25 is supplied by the third nip roller 23 to the second nip roller 22. And a method of taking out and relaxing at a slower rate.
The temperature of the atmosphere in the second heating furnace 25 for relaxation treatment is appropriately set according to the material of the plastic rod lens and the like, but is preferably equal to or higher than the Tg of the plastic rod lens. The relaxation rate (length after relaxation treatment / length before relaxation treatment) is appropriately determined depending on the desired plastic rod lens diameter, but is preferably about 99/100 to 1/2. . If relaxation processing is performed at such a relaxation rate, shrinkage of the plastic rod lens can be suppressed. If the relaxation rate is too small, the unevenness of the lens diameter increases, which is not preferable. The relaxation rate can be adjusted by the peripheral speed ratio between the second nip roller 22 and the third nip roller 23.

  In the finally obtained plastic rod lens, the polymer constituting the plastic rod lens preferably has a mass average molecular weight of 10,000 to 100,000.

(Rod lens array)
Next, the rod lens array of the present invention will be described.
The rod lens array of the present invention has two or more of the plastic rod lenses arranged in parallel.
As an example of a rod lens array, as shown in FIG. 3, two or more plastic rod lenses 31, 31,... Are arranged in a row in parallel between two substrates 32, 32 and fixed. Is mentioned.
When the plastic rod lens 31 is fixed to the substrate 32, a known adhesive 33 is used. The adhesive 33 may include a light shielding agent such as carbon black.
Adjacent plastic rod lenses 31, 31 may be in close contact with each other, or may be arranged at a certain interval. In the case where a single interval is provided, it is preferable that the interval between the plastic rod lenses 31, 31 is constant.

  The rod lens array satisfies Tc (630) −Tc (470) ≦ 0.3 mm and Tc (525) ≦ 12 mm when the conjugate length of the rod lens array with respect to light of wavelength λnm is Tc (λ). MTF after heat treatment for 1000 hours in an environment of temperature 60 ° C. and relative humidity 90% has a wavelength of 470 nm (B), 525 nm (G), and 630 nm (R) at a spatial frequency of 12 line pairs / mm. Each is preferably 40% or more. With such a rod lens array, it is possible to capture an image clearly.

Here, the conjugate length Tc and MTF are measured as follows.
That is, using a grating pattern having a spatial frequency of 12 line pairs / mm (that is, 600 dpi), light from a light source is incident through a grating pattern on a rod lens array whose both end surfaces perpendicular to the optical axis are polished. Next, the lattice image is read by a CCD line sensor installed on the imaging plane, and the maximum value (i _max ) and minimum value (i _min ) of the measured light quantity are measured. Then, MTF (Moderation Transfer Function) is obtained by the following equation (2).
MTF (%) = {(i _max −i _min ) / (i _max + i _min )} × 100 (2)
At this time, the distance between the grating pattern and the incident end of the rod lens array and the distance between the exit end of the rod lens array and the CCD line sensor are made equal. Then, the MTF is measured by moving the grating pattern and the CCD line sensor symmetrically with respect to the rod lens array, and the distance between the grating pattern and the CCD line sensor when the MTF is the best is the conjugate length Tc.

The rod lens array of the present invention is manufactured by a known method. For example, first, plastic rod lenses 31, 31... Cut to a certain length are arranged in parallel between two substrates 32, 32 so that the adjacent plastic rod lenses 31, 31 are in close contact with each other. Fix it. In this state, an adhesive 33 containing a light shielding agent such as carbon black is injected between the plastic rod lenses 31 and 31 and between the plastic rod lens 31 and the substrate 32 to be cured.
Then, if necessary, it is cut into a desired length, and the end surface of the plastic rod lens 31 is mirror-finished by cutting with a diamond blade or the like to obtain the rod lens array 30a.

  The rod lens array is not limited to that shown in FIG. 3, and for example, plastic rod lenses may be stacked in two or more stages. In that case, it is preferable that the plastic rod lenses are arranged closest to each other so that the gap between the plastic rod lenses is minimized.

Since the rod lens array of the present invention uses the above plastic rod lens, it has high heat resistance, and even when exposed to high temperatures for a long period of time, the optical performance is hardly lowered.
In addition, since the rod lens array of the present invention has small chromatic aberration, the difference in conjugate length with respect to light of different wavelengths is small, and it is excellent in color characteristics and can form a high-resolution color image sensor.

(Rod lens plate)
Next, the rod lens plate of the present invention will be described.
As shown in FIG. 4, the rod lens plate of the present invention has a large number of the plastic rod lenses 31, 31.
A known adhesive 33 is used for fixing the plastic rod lenses 31, 31 to each other. The adhesive 33 may include a light shielding agent such as carbon black.
Adjacent plastic rod lenses 31, 31 may be arranged in close contact with each other, or may be arranged at a certain interval. When arrange | positioning at a fixed space | interval, it is preferable to make the space | interval of adjacent plastic rod lenses 31 and 31 constant.

The rod lens plate of the present invention is manufactured by a known method. For example, first, a large number of plastic rod lenses 31, 31... Cut to a certain length are arranged closest so that the plastic rod lenses 31 and 31 are in close contact with each other.
Next, in this state, an adhesive 33 containing a light-shielding agent such as carbon black is injected into the gap between the plastic rod lenses 31 and 31 and cured.
After that, if necessary, it is cut into a desired length, and the end surface of the plastic rod lens 31 is mirror-finished by cutting with a diamond blade or optical polishing to obtain the rod lens plate 30b.
Further, if necessary, an antireflection coating may be applied to reduce the loss of light quantity due to reflection on the end surface of the rod lens plate.

The rod lens plate of the present invention can be used for an image sensor or the like that reads information over a wide area because plastic rod lenses are two-dimensionally arranged in parallel.
In addition, since the rod lens plate of the present invention uses the above plastic rod lens, it has high heat resistance, and even when exposed to high temperatures for a long period of time, its optical performance is hardly lowered.
Furthermore, since the rod lens plate of the present invention has small chromatic aberration, it has excellent color characteristics and can be used for a high-resolution color image sensor.

(Image sensor)
Next, the image sensor of the present invention will be described.
The image sensor of the present invention comprises the rod lens array or the rod lens plate.
As an example of the image sensor of the present invention, a photoelectric conversion element that receives light and converts it into an electrical signal, a light source for illuminating a read original, and a rod that forms an image of reflected light from the read original on the photoelectric conversion element A lens array or a rod lens plate is provided as a basic configuration, and a cover glass for stably fixing a read original is included as necessary.

  The light source used in the image sensor of the present invention is for illuminating the original surface, and incandescent light bulbs, cold cathode fluorescent lamps, LEDs, etc. are used. It is done. These light sources may be used in combination with a filter element for the purpose of cutting a specific wavelength.

In the image sensor of the present invention, a color image sensor can be formed using a plurality of types of LEDs having different emission wavelengths. When used as a color image sensor, the peak of the emission wavelength of the LED is 450 to 480 nm (blue), 510 to 560 nm (green), and 600 to 660 nm (red), respectively, for the purpose of improving color reproducibility. Is preferred.
When the emission wavelength peaks are three colors of red (R), green (G), and blue (B), light sources of three colors of red (R), green (G), and blue (B) are provided. A lighting device can be used. The illuminating device includes a light guide made of a member having excellent light transmittance such as acrylic resin, and a light source is disposed at one end of the light guide. The light emitted from the light source enters the light guide, and the incident light repeats total reflection at the interface between the light guide and air, and propagates through the light guide.

  The operation of the image sensor of the present invention will be described using a color image sensor as an example. The original that is pressed against and supported by the cover glass is sequentially illuminated by switching light of three colors R, G, and B from an oblique direction by an illumination device. Light having color information of three colors R, G, and B reflected from the original is imaged on the photoelectric conversion element by the rod lens array or the rod lens plate. The photoelectric conversion element converts light having color information of three colors R, G, and B into an electric signal. The image information converted into the electrical signal is transmitted to a system unit including a computer or the like, and the system unit processes electrical signals of three colors R, G, and B to reproduce a color image.

  Since the image sensor of the present invention includes the rod lens array or the rod lens plate, the deterioration in optical performance is small even when used for a long period of time, and the color characteristics are excellent. It can be read and used for a high-resolution color scanner or the like.

(Printer)
Next, the printer of the present invention will be described.
The printer of the present invention comprises the rod lens array or the rod lens plate. As a specific example, the rod lens array or the rod lens plate, an LED chip arranged on one end side of the rod lens array or the rod lens plate, and arranged as an array of LEDs as a light source, and the rod lens array or the rod lens plate And a photosensitive film or photographic film (photographic printing paper) disposed on one end of the image forming apparatus, and writing image information on the photosensitive body or photosensitive film using a light source of three primary colors.
Further, the light source of the printer is not limited to the LED chip, and a light source such as a liquid crystal shutter and an EL array can also be used.
The operation of the printer of the present invention will be described using an LED printer as an example.
Light from a light source composed of an LED chip is imaged on a charged photosensitive drum by a rod lens array or a rod lens plate to form an electrostatic latent image. Toner is attached here, and the sheet is pressed against the photosensitive drum to transfer the toner. This toner is fixed on the paper by heat and pressure and used as the output of the LED printer. At this time, if the image is monochrome, this process is performed once with only black toner, and if it is color, this process is performed 3 times with RGB toner.

  Since the printer according to the present invention includes the rod lens array or the rod lens plate, the optical performance is not deteriorated even when used for a long time, and the chromatic aberration is small. Since the condition is small, it can be used as a high-resolution color printer or photo printing apparatus.

Hereinafter, the present invention will be described specifically by way of examples.
In the following examples, physical properties of a plastic rod lens or a rod lens array were measured as follows.
<Refractive index distribution>
The measurement was performed using an Interfaco interference microscope manufactured by Carl Zeiss.
<Conjugate length (Tc) and resolution (MTF)>
Measurements were made using a grating pattern having a spatial frequency of 12 line pairs / mm (ie 600 dpi). Specifically, light from a light source is incident on a rod lens array whose both end surfaces perpendicular to the optical axis are polished through a lattice pattern, a lattice image is read by a CCD line sensor installed on the imaging surface, and the measurement light quantity is measured. The maximum value (i _max ) and the minimum value (i _min ) were measured, and MTF (moderation transfer function) was determined by the following equation (2).
MTF (%) = {(i _max −i _min ) / (i _max + i _min )} × 100 (2)
At that time, the distance between the grating pattern and the entrance end of the rod lens array and the distance between the exit end of the rod lens array and the CCD line sensor were made equal. Then, the MTF was measured by moving the grating pattern and the CCD line sensor symmetrically with respect to the rod lens array, and the distance between the grating pattern and the CCD line sensor when the MTF was the best was defined as the conjugate length.

Example 1
Components shown in Table 1 below were blended to prepare stock solutions for forming the first to fifth layers.
In Table 1, PMMA is polymethyl methacrylate, MMA is methyl methacrylate, TDMA is tricyclo [5.2.1.0 ^2,6 ] decanyl-8-methacrylate, BzMA is benzyl methacrylate, and 8FM is 2,2,3,3. It is 4,4,5,5-octafluoropentyl methacrylate.

In Example 1, the following Example 2, and Comparative Examples 1 and 2, PMMA having a viscosity [η] = 0.40 [P] (measured in methyl ethyl ketone at 25 ° C.) was used. Further, 1-hydroxycyclohexyl phenyl ketone was added as a photocuring initiator and hydroquinone (HQ) was added as a polymerization inhibitor to each stock solution.
In addition, for the purpose of suppressing crosstalk light and flare light, the dye Blue ACR (manufactured by Nippon Kayaku Co., Ltd.) is used for the whole stock solution in each stock solution for the fourth layer and the fifth layer before heating and kneading. , Dye MS Yellow HD-180 (manufactured by Mitsui Chemicals), dye MS Magenta HM-1450H (manufactured by Mitsui Chemicals), dye KAYASORB CY-10 (manufactured by Nippon Kayaku Co., Ltd.) as follows Added.
Fourth layer: Blue ACR 280 ppm
MS Yellow HD-180 60ppm
MS Magenta HM-1450H 30ppm
KAYASORB CY-10 60ppm
5th layer: Blue ACR 6000 ppm
MS Yellow HD-180 60ppm
MS Magenta HM-1450H 1400ppm
KAYASORB CY-10 110ppm

  Next, the stock solution of each layer was heated and kneaded at 70 ° C., and then extruded from a concentric five-layer composite spinning nozzle at the same time while being arranged so that the refractive index after curing gradually decreased from the center toward the outside. The temperature of the composite spinning nozzle was 50 ° C. The ejection ratio of each layer is converted into the ratio of the thickness of each layer in the radial direction of the plastic rod lens (the radius in the first layer), and the first layer / second layer / third layer / fourth layer / fifth layer. Layer = 24/31 / 39.2 / 2.8 / 3. Here, the first layer is the innermost side and the fifth layer is the outermost side.

Next, a plastic rod lens raw yarn was manufactured from the obtained raw solution using a plastic rod lens raw yarn manufacturing apparatus 10 shown in FIG.
Specifically, nitrogen gas was introduced into the container 12 from the inert gas introduction pipe 13 and the inert gas in the container 12 was discharged from the inert gas discharge pipe 14.
Further, while the filament A extruded from the concentric composite spinning nozzle 11 is taken up by the take-up roller 17 (200 cm / min), it passes through the interdiffusion treatment part 12b having a length of 30 cm, thereby causing mutual diffusion between the layers. I let you.
Subsequently, in the center of the first curing treatment unit 12c (first light irradiation unit) in which 18 chemical lamps having a length of 60 cm and 20 W around the central axis are arranged at equal intervals continuously in two upper and lower stages, The filament A was passed through and cured. Further, the filament A was passed through the center of the second curing processing section (second light irradiation section) in which three 2.0 KW high-pressure mercury lamps were arranged at equal intervals around the central axis, and completely cured. . The nitrogen flow rate in the interdiffusion treatment unit 12b was 80 L / min.
The radius of the plastic rod lens yarn thus obtained was 0.291 mm.
Next, the obtained plastic rod lens yarn was stretched 4.62 times in an atmosphere of 145 ° C., and subjected to relaxation treatment so that the relaxation rate was 600/923 in an atmosphere of 119 ° C. Thus, a plastic rod lens having the first layer 41, the second layer 42, the third layer 43, the fourth layer 44, and the fifth layer 45 was obtained from the inside as shown in FIG.
In the obtained plastic rod lens, a layer having a thickness of about 10 μm from the outer peripheral surface toward the center and a substantially uniform mixture of dyes was formed.

The radius R of the obtained plastic rod lens was 0.168 mm, and the measured refractive index of each layer was as shown in Table 2. The refractive index distribution constant g at a wavelength of 525 nm was 0.84 mm ⁻¹ .
A quadratic curve approximating the refractive index distribution of this plastic rod lens and the refractive index of each layer are shown in FIG. The approximate refractive index in the range of about 0.94R to R was higher than the actually measured refractive index in the range of 0.94R to R.

A number of the obtained plastic rod lenses were juxtaposed in parallel in a row between two phenolic resin substrates while adhering adjacent ones (0.36 mm intervals). Next, an adhesive (“Sdyne 9607K” manufactured by Sekisui Fuller) was filled in a gap between the substrate and the plastic rod lens and between the plastic rod lenses, and cured and fixed. Thereafter, both end surfaces perpendicular to the central axis of the plastic rod lens were mirror-cut with a diamond blade to obtain a rod lens array having a plastic rod lens length of 4.4 mm. The conjugate length Tc at 525 nm of this rod lens array was 10.0 mm, and the MTF at that time was 67%.
Tc at each wavelength of 470 nm, 525 nm, and 630 nm of this rod lens array was measured. The results are shown in Table 3. Moreover, MTF of each wavelength was measured at Tc 10.0 mm. The results are shown in Table 4.

Further, the obtained rod lens array was subjected to wet heat treatment for 1000 hours in an environment of a temperature of 60 ° C. and a relative humidity of 90%, and then MTF of each wavelength was measured at Tc 10.0 mm. The results are shown in Table 5.
The MTF of each wavelength after the wet heat treatment was 40% or more, and a high resolution was maintained. The image read by the image scanner incorporating the rod lens array after the wet heat treatment was clear.

(Example 2)
Stock solutions of each layer were prepared with the compositions shown in Table 1. Next, in the same manner as in Example 1, a plastic rod raw yarn (radius 0.291 mm) was produced. However, the ejection ratio of each layer is converted into the ratio of the thickness (radius in the first layer) of each layer in the radial direction of the plastic rod lens, and the first layer / second layer / third layer / fourth layer / The fifth layer was 21/34/37/6/2.
Next, the obtained plastic rod lens yarn was stretched 3.38 times in an atmosphere of 135 ° C., and subjected to relaxation treatment so that the relaxation rate was 540/675 in an atmosphere of 114 ° C. Thus, a plastic rod lens having the first layer 41, the second layer 42, the third layer 43, the fourth layer 44, and the fifth layer 45 was obtained from the inside as shown in FIG.
In the obtained plastic rod lens, a layer having a thickness of about 14 μm from the outer peripheral surface toward the center and a substantially uniform mixture of dyes was formed.

The radius R of the obtained plastic rod lens was 0.174 mm, and the measured refractive index of each layer was as shown in Table 2. The refractive index distribution constant g at a wavelength of 525 nm was 0.84 mm ⁻¹ .
FIG. 7 shows a quadratic curve approximating the refractive index distribution of this plastic rod lens and the refractive index of each layer. The approximate refractive index in the range of about 0.92R to R was higher than the actually measured refractive index in the range of 0.92R to R.

Using the obtained plastic rod lens, a rod lens array having a plastic rod lens length of 4.4 mm was obtained in the same manner as in Example 1 except that the interval between the plastic rod lenses was changed from 0.36 mm to 0.37 mm. The conjugate length Tc at 525 nm of this rod lens array was 10.0 mm, and the MTF at that time was 72%.
Tc at each wavelength of 470 nm, 525 nm, and 630 nm of this rod lens array was measured. The results are shown in Table 3. Moreover, MTF of each wavelength was measured at Tc 10.0 mm. The results are shown in Table 4.
Further, this rod lens array was subjected to a wet heat treatment for 1000 hours in an environment of a temperature of 60 ° C. and a relative humidity of 90%, and then MTF of each wavelength was measured at Tc 10.0 mm. The results are shown in Table 5.
The MTF of each wavelength after the wet heat treatment was 40% or more, and a high resolution was maintained. The image read by the image scanner incorporating the rod lens array after the wet heat treatment was clear.

(Comparative Example 1)
Stock solutions of each layer were prepared with the compositions shown in Table 1. Next, in the same manner as in Example 1, a plastic rod raw yarn (radius 0.291 mm) was produced. However, the ejection ratio of each layer is converted into the ratio of the thickness (radius in the first layer) of each layer in the radial direction of the plastic rod lens, and the first layer / second layer / third layer / fourth layer / The fifth layer was 21/25/33/19/2.
Next, the obtained plastic rod lens yarn was stretched 3.5 times in an atmosphere of 134 ° C., and subjected to relaxation treatment so that the relaxation rate was 500/700 in an atmosphere of 115 ° C. Thus, a plastic rod lens having the first layer 41, the second layer 42, the third layer 43, the fourth layer 44, and the fifth layer 45 was obtained from the inside as shown in FIG.
In the plastic rod lens, a layer having a thickness of about 39 μm from the outer peripheral surface toward the central portion and a substantially uniform mixture of dyes was formed.

The radius R of the obtained plastic rod lens was 0.185 mm, and the actually measured refractive index of each layer was as shown in Table 2. The refractive index distribution constant g at a wavelength of 525 nm was 0.84 mm ⁻¹ .
A quadratic curve approximating the refractive index distribution of this plastic rod lens and the refractive index of each layer are shown in FIG. The approximate refractive index in the range of about 0.89R to 0.98R was lower than the actually measured refractive index in the range of 0.89R to 0.98R.

Using the obtained plastic rod lens, a rod lens array having a plastic rod lens length of 4.4 mm was obtained in the same manner as in Example 1 except that the interval between the plastic rod lenses was changed from 0.36 mm to 0.39 mm. The conjugate length Tc at 525 nm of this rod lens array was 10.0 mm, and the MTF at that time was 62%.
Tc at each wavelength of 470 nm, 525 nm, and 630 nm of this rod lens array was measured. The results are shown in Table 3. Moreover, MTF of each wavelength was measured at Tc 10.0 mm. The results are shown in Table 4.
Further, this rod lens array was subjected to a wet heat treatment for 1000 hours in an environment of a temperature of 60 ° C. and a relative humidity of 90%, and then MTF of each wavelength was measured at Tc 10.0 mm. The results are shown in Table 5.
The MTF of each wavelength after the wet heat treatment was less than 40%, and the resolution was lowered. Further, the image read by the image scanner incorporating the rod lens array after the wet heat treatment was unclear.

(Comparative Example 2)
Stock solutions of each layer were prepared with the compositions shown in Table 1. Next, in the same manner as in Example 1, a plastic rod raw yarn (radius 0.291 mm) was produced. However, the ejection ratio of each layer is converted into the ratio of the thickness (radius in the first layer) of each layer in the radial direction of the plastic rod lens, and the first layer / second layer / third layer / fourth layer / The fifth layer was 23.5 / 31.5 / 39/3/3.
Next, the obtained plastic rod lens raw yarn was stretched 4.62 times in an atmosphere of 145 ° C. and subjected to relaxation treatment so that the relaxation rate was 600/924 in an atmosphere of 119 ° C. As a result, a plastic rod lens 40 having a first layer 41, a second layer 42, a third layer 43, a fourth layer 44, and a fifth layer 45 was obtained from the inside as shown in FIG.
In the plastic rod lens, a layer having a thickness of about 10 μm from the outer peripheral surface toward the central portion and a substantially uniform mixture of dyes was formed.

The radius R of the obtained plastic rod lens was 0.168 mm, and the measured refractive index of each layer was as shown in Table 2. The refractive index distribution constant g at a wavelength of 525 nm was 0.84 mm ⁻¹ .
A quadratic curve approximating the refractive index distribution of this plastic rod lens and the refractive index of each layer are shown in FIG. The approximate refractive index in the range of approximately 0.94R to 0.97R was lower than the measured refractive index in the range of 0.94R to 0.97R.

Using the obtained plastic rod lens, a rod lens array having a plastic rod lens length of 4.4 mm was obtained in the same manner as in Example 1. The conjugate length Tc at 525 nm of this rod lens array was 10.0 mm, and the MTF at that time was 80%.
Tc at each wavelength of 470 nm, 525 nm, and 630 nm of this rod lens array was measured. The results are shown in Table 3. Moreover, MTF of each wavelength was measured at Tc 10.0 mm. The results are shown in Table 4.
Further, this rod lens array was subjected to a wet heat treatment for 1000 hours in an environment of a temperature of 60 ° C. and a relative humidity of 90%, and then MTF of each wavelength was measured at Tc 10.0 mm. The results are shown in Table 5.
The MTF of each wavelength after the wet heat treatment was less than 40%, and the resolution was lowered. Further, the image read by the image scanner incorporating the rod lens array after the wet heat treatment was unclear.

In the rod lens arrays of Examples 1 and 2, the chromatic aberration ΔTc (difference between Tc (470) and Tc (630)) was as small as 0.1 mm, and the variation in MTF at each wavelength was small. In the rod lens arrays of Examples 1 and 2, the MTF after the wet heat test was high, and the heat resistance was high.
In contrast, the rod lens arrays of Comparative Examples 1 and 2 also had small chromatic aberration ΔTc and small variations in MTF at each wavelength, but the MTF after the wet heat test was low and the heat resistance was low.

  The plastic rod lens, the rod lens array, and the rod lens plate of the present invention have a small deterioration in optical performance and excellent color characteristics. By using such a rod lens array or rod lens plate, it is possible to obtain a high-resolution color image sensor or a high-resolution color printer with little deterioration in optical performance even when used for a long period of time.

It is a schematic block diagram which shows the apparatus for manufacturing the raw yarn of a plastic rod lens. It is a schematic block diagram which shows the apparatus which performs a heating extending | stretching and relaxation process to the raw yarn of a plastic rod lens. It is sectional drawing which shows an example of the rod lens array of this invention. It is sectional drawing which shows an example of the rod lens plate of this invention. It is a figure which shows a cross section perpendicular | vertical to the central axis of the plastic rod lens in an Example and a comparative example. FIG. 3 is a diagram showing the refractive index distribution of each layer in the plastic rod lens of Example 1. FIG. 6 is a diagram showing the refractive index distribution of each layer in the plastic rod lens of Example 2. It is a figure which shows the refractive index distribution of each layer in the plastic rod lens of the comparative example 1. It is a figure which shows the refractive index distribution of each layer in the plastic rod lens of the comparative example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Manufacturing apparatus of plastic rod lens raw yarn 11 Concentric circular composite spinning nozzle 12 Container 13 Inert gas introduction pipe 14 Inert gas discharge pipe 15 1st light irradiation machine 16 2nd light irradiation machine 17 Take-up roller 20 Stretching / relaxation Processing device 21 First nip roller 22 Second nip roller 23 Third nip roller 24 First heating furnace 25 Second heating furnace 30a Rod lens array 30b Rod lens plate 31 Plastic rod lens 32 Substrate 33 Adhesive 40 Plastic rod lens 41 First layer 42 2nd layer 43 3rd layer 44 4th layer 45 5th layer

Claims (5)

A plastic rod lens having a cylindrical shape with a radius R and having a refractive index distribution in which the refractive index decreases toward the outside from the central axis,
In a cross section perpendicular to the central axis, when the refractive index distribution is approximated to a quadratic curve distribution represented by the following formula (1), the approximate refractive index n (L) in the range of 0.95R to R is 0. higher than the measured refractive index _{n n} ranging .95R～R, the measured refractive index of the central portion 100, the measured refractive index of the outermost portion upon a 0, the measured refractive index in the range of 0R~0.15R Is a ratio in which the measured refractive index in the range of 100, 0.25R to 0.90R is 90 to 50, and the measured refractive index in the range of 0.95R to R is 25 to 0,
A central portion where the measured refractive index is 100, a first portion located radially outside the central portion, and a measured refractive index of 90 to 80, and a radially outer side continuously to the first peripheral portion A second portion having an actually measured refractive index of 80 to 40, a third portion having a measured refractive index of 40 to 1 and being located radially outward from the second peripheral portion. An outer peripheral portion that is located radially outward from the third portion and has an actually measured refractive index of 0, the central portion, the first portion, the second portion, and the third portion And the ratio of the thickness of the radial direction with the said outer peripheral part is 5-30: 15-50: 15-40: 2-10: 0.5-10, The plastic rod lens characterized by the above-mentioned.
^{_{n (L) = n 0 {}} 1- (g 2/2) L 2} (1)
(Where n ₀ is the refractive index at the central axis of the plastic rod lens (central refractive index), L is the distance from the central axis of the plastic rod lens (0 ≦ L ≦ R), and g is the refractive index distribution of the plastic rod lens. (The constant n (L) is an approximate refractive index at a position of distance L from the central axis of the plastic rod lens.) A rod lens array in which two or more of the plastic rod lenses according to claim 1 are arranged in parallel,
The moderation transfer function (MTF) after heat treatment for 1000 hours in an environment of a temperature of 60 ° C. and a relative humidity of 90% is 40% at wavelengths of 470 nm, 525 nm, and 630 nm at a spatial frequency of 12 line pairs / mm. This is the rod lens array. A rod lens plate in which a plurality of plastic rod lenses according to claim 1 are arranged in parallel two-dimensionally. An image sensor comprising the rod lens array according to claim 2 or the rod lens plate according to claim 3 . A printer comprising the rod lens array according to claim 2 or the rod lens plate according to claim 3 .

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