JP2002131519A - Projection lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a large-sized projection lens having high shape accuracy in spite of the light-weight and inexpensive one, assembled especially in a projection device projecting an image not from a perpendicular direction to a screen but from an oblique direction, especially, from an obliquely lower side, and projecting the high definition image free from distortion and deformation. SOLUTION: This projection lens is provided with a reflection layer on the surface of resin base material formed to be a specified curved surface, and the mean value of the phase difference of in-plane double refraction per unit thickness with respect to incident light from the perpendicular direction to the optical functional surface of the resin base material at the curved surface part of the lens is set to <=30 nm/mm in an area being at least 60% of the area of the optical functional surface, and a metallic reflection film and a transparent protective coat are successively formed at the curved surface part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a projection lens. It can be expected to be applied to projection devices such as overhead projectors, window displays, front data projectors, etc. In detail, mirror (reflection mirror) type used for high-precision, high-definition projection devices, especially rear projection TVs The present invention relates to a resin curved surface projection lens.

[0002]

2. Description of the Related Art Conventionally, the materials used for such large-sized optical components requiring high precision have been overwhelmingly made of inorganic glass or metallic materials such as aluminum and steel. This is due to the excellent optical precision of the inorganic glass or metal material, particularly the ability to obtain images with little distortion even if there is a temperature change, and the high suitability for precision cutting and polishing.

[0003]

However, in the case of using glass or a material such as aluminum or steel, in the case of glass, a method of hot-pressing the glass is generally used. It is necessary to heat evenly to over ℃, the equipment with such a heating device itself becomes expensive, the cycle time becomes long considering the heating and cooling time, and a high shape that can withstand high temperature compression Since a mold having accuracy and durability is also required, there is a disadvantage that the glass part becomes very expensive.

For this reason, when used as a component for a projection device, it can be used only for very special applications where high cost is acceptable, and has not been widely used as a device for general office use or for home use. Also, when using metal materials such as aluminum and steel materials, it is basically necessary to manufacture each one by precision cutting and polishing, so the parts themselves are extremely expensive and are not suitable for mass production. There was a problem.

For example, Japanese Patent Laid-Open No. 9-96775
Describes the invention of an image projection device having a function of correcting trapezoidal distortion when an image is projected obliquely, but `` except for the case where the projection objective lens of the projection device has a very large aperture, The movable range is relatively narrow, but a large-diameter projection objective lens increases the size of the entire apparatus and increases the manufacturing cost. "

One of the means for solving the problems of the manufacturing process and the manufacturing apparatus as described above is to manufacture with a resin material which is relatively easy to mold. In the case of injection molded products and compression molded products, warpage, sink marks, or poor transfer of the shape (curved surface) from the mold occurs due to the inherent property of thermoplastic resin that molding shrinkage is extremely large. In particular, it cannot be used as a projection lens that also has a function of correcting trapezoidal distortion during oblique projection, and it is not possible to obtain a large (large area and thick) molded product with high shape precision that can obtain high-definition image quality. Was.

In the case where a heat or light curable resin such as an epoxy or diacrylate resin is used as a material, curing shrinkage occurs in an amount of 5 to 20 vol%. It cannot be used as a projection lens having a large size (large area and thick wall) and high shape accuracy capable of obtaining high-definition image quality.

Further, it takes several hours to several tens of hours for the curing time of the curable resin or the annealing treatment after the initial curing (acceleration of curing, improvement of crosslink density, relaxation of residual stress), which is not suitable for mass production. There was a problem.

[0009]

Means for Solving the Problems In view of the above problems, the present inventor has made intensive studies and found that when manufacturing a projection lens using a thermoplastic resin, a specific physical property value is controlled within a specific range. As a result, it was found that a highly accurate and low-distortion reflective surface could be obtained, and the present invention was completed.

That is, the gist of the present invention is: (1) A projection lens in which a reflection layer is provided on a surface of a resin substrate formed on a predetermined curved surface, wherein the optical function of the resin substrate in the curved surface portion of the lens is The average value of the in-plane birefringence retardation per unit thickness with respect to the incident light from the direction perpendicular to the surface is set to 30 nm / mm or less in a region of at least 60% of the area of the optically functional surface. The present invention relates to a projection lens in which a metal reflection film and a transparent protective film are sequentially formed.

[0011] The following contents are also aspects of the present invention. (2) The projection lens according to (1), wherein the thickness of the resin substrate at the reflection surface portion of the projection lens is within ± 50% of the average thickness of the resin substrate. (3) The plane area is 150 cm ² or more, and the minimum width of the plane is 1
The projection lens according to (1) or (2), wherein the projection lens has a thickness of 0 cm or more and a molded product thickness of 3 mm or more. (4) The resin according to any one of (1) to (3), wherein the resin base material is mainly composed of an amorphous thermoplastic resin having a Tg ≧ 70 ° C. and a saturated water absorption of less than 1% at 60 ° C. and 90 RH%. The projection lens according to any one of the above. (5) The projection lens according to any one of (1) to (4), wherein the reflection layer is an aluminum vapor-deposited film having a thickness of 1000 to 3000 °. (6) The projection lens according to any one of (1) to (5), wherein the transparent protective layer is a metal oxide film having a thickness of 100 to 1000 °.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below.
As the resin constituting the base material of the projection lens of the present invention, a normal thermoplastic resin is used. Specifically, acrylic resins such as polymethyl methacrylate, polycarbonate resins, polyester carbonate resins, aromatic polyester resins, polysulfone resins, polyethersulfone resins, styrene-based resins such as polystyrene and acrylic-styrene copolymers, and cyclic polyolefin resins And the like. In particular, an amorphous thermoplastic resin is preferable because of its low molding shrinkage.

Regarding the evaluation of the amorphousness, the density of the amorphous portion and the density of the crystalline portion were estimated from the infrared absorption peak value on page 171 of the first edition of “Polycarbonate Handbook” published by Nikkan Kogyo Shimbun, for example. A method for obtaining the degree of crystallinity from the density of a molded article is introduced. This “density method”
It is preferable that the amorphous molded article has a crystallinity of 20% or less, more preferably 15% or less, and most preferably 10% or less.

More specifically, it is preferable to use a polycarbonate resin because it has moldability, strength, economy (material cost) and the like. The case of using polycarbonate will be described more specifically. The preferred molecular weight of the polycarbonate used in the present invention is 18 in terms of viscosity average molecular weight.
About 2,000 to 25,000, more preferably 20,000 to
23000.

When the molecular weight is less than 18,000, the molded plate may be broken when subjected to heat shock (a state in which heating and cooling are repeated or rapidly performed during use). Further, when the molecular weight is less than 18,000, the projection lens of the present invention is, as described later, for one of its purposes, to create a thick large molded product, because of its use, and therefore mainly after removing the mold during molding. At the time of cooling, volume distortion may occur due to a temperature difference between the inside and the surface, and cracking may occur.

If the molecular weight of the polycarbonate exceeds 24000, the viscosity is too high, and at a low molding temperature that does not cause thermal deterioration, the mirror surface is precisely transferred, or the warpage and deformation of the molded article are suppressed. The relaxation of the orientation of the molecular chains becomes insufficient, and the molding time becomes long, which is industrially disadvantageous. The method for measuring the viscosity average molecular weight is as follows. Using an Ubbelohde capillary viscometer, the intrinsic viscosity [η] at 20 ° C. in methylene chloride was measured,
The viscosity average molecular weight (Mv) is determined by the following equation. [Η] = 1.23 × 10 ⁻⁴ × (Mv) E0.83 The polycarbonate used in the present invention has a terminal OH (hydroxyl group).
Is preferably less than 700 ppm, more preferably less than 500 ppm, particularly preferably less than 350 ppm.

When the terminal OH content exceeds 700 ppm, the adhesion between the polycarbonate resin and the mirror surface of the mold becomes strong after the hot press treatment, and there is a problem that it becomes difficult to release the molded product from the mold. There is. The method for determining the amount of terminal OH is as follows. Titanium tetrachloride / acetic acid method (Makromol Chem, 88, 215 (196
According to 5), colorimetry is performed.

It is preferable to use a release agent and a heat stabilizer as additives when the projection lens of the present invention is formed by using polycarbonate. Examples of the release agent include fatty acid ester (total esterified product, partially esterified product) such as glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, and higher alcohol fatty acid ester, and silicon-based one.
The amount used is preferably from 30 to 500 ppm, more preferably from 80 to 300 ppm, based on the raw material resin, and from 100 to 2 ppm.
Most preferably, it is 00 ppm.

At the time of molding, the release agent segregates at the interface with the mold and facilitates peeling of the molded article from the mold. Release agent is 30
If the amount is less than ppm, problems such as breakage, deformation, and surface damage due to poor mold release may occur when the molded product is separated from the mold. If it exceeds 500 ppm, problems may occur in the adhesion and durability of the reflective layer formed when the reflective layer is formed on the substrate surface by sputtering or the like.

More specifically, the release agent may bleed out to the interface between the molded article and the reflective film at an initial stage or over time, causing problems such as peeling of the reflective film. As the release agent, among the above, it is preferable to use a glycerin ester-based release agent.
About 200 ppm, preferably 100 to 200 ppm
It is about.

Specific examples of the heat stabilizer include, for example,
2,6-di-tert-butyl-p-cresol, 2,6-di-tert-butyl-4-hydroxymethylphenol, 2,
6-di-t-butyl-4-ethylphenol, 2,4
6-tri-t-butylphenol, butylated hydroxyanisole, cyclohexylphenol, styrenated phenol, 2,5-di-t-butylhydroquinone, n
-Octadecyl-3- (3 ', 5'-di-t-butyl-
4'-hydroxyphenyl) propionate, 2,2 '
-Methylenebis (4-methyl-6-t-butylphenol), 4,4'-isopropylidenebisphenol,
4,4'-methylenebis (2,6-di-t-butylphenol), 1,1-bis (4'-hydroxyphenyl)
Cyclohexane, 2,2′-thiobis (4-methyl-6
-T-butylphenol), 1,1,3-tris (2 ′
Phenolic compounds such as -methyl-4'-hydroxy-5'-t-butylphenyl) butane; aldol-α-
Naphthylamine, phenyl-α-naphthylamine, phenyl-β-naphthylamine, N, N′-diphenyl-p
-Phenylenediamine, 1,2-dihydro-2,2,4
Amine-based dilauryl thiodipropionates such as trimethylquinoline, sulfur-based compounds such as dimyristyl thiodipropionate and distearyl thiodipropionate triphenyl phosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite, tris ( Nonylphenyl) phosphite, tris (mono- and di-nonylphenyl) phosphite, 4,4′-butylidenebis (3-methyl-6-tert-butylphenyl) -ditridecylphosphite, distearylpentaerythritol diphosphite, Trilauryl trithiophosphite,
And trioctadecyl phosphite, o-cyclohexyl phenyl phosphite, diisodecyl pentaerythritol diphosphite, dinonyl phenyl pentaerythritol diphosphite, tetraphenyl dipropylene glycol diphosphite, tris (2,4-di-t-
Butylphenyl) phosphite, 4,4′-isopropylidenediphenyltetraalkyl phosphite, 4,
4'-isopropylidenebis (3-methyl-6-t-butylphenyl) -ditridecyl phosphite, 1,1,
3-tris (2'-methyl-4'-ditridecylphosphite, 1,1,3-tris (2'-methyl-4'-ditridecylphosphite-5'-t-butylphenyl)
Phosphorus compounds such as butane and poly (dipropylene glycol) phenyl phosphite, 9,10-dihydro-9-
Oxa-10-phosphenanthrene-10-oxide,
10-decyloxy-9,10-dihydro-9-oxa-
10-phosphaphenanthrene, 10- (3 ′, 5′-
Di-tert-butyl-4-hydroxybenzyl) -9,10
And phosphaphenanthrene-based compounds such as -dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

The amount of the heat stabilizer used is 100
-1000 ppm is preferable, and 300-800 ppm is more preferable. The heat stabilizer prevents decomposition of the polycarbonate resin, and as a result, facilitates release from the mold. If the amount of the heat stabilizer is less than 100 ppm, the effect of preventing the resin from being oxidized at the time of molding is low, and the oxidized resin and the like increase the adhesion to the mold, and there is a problem in releasing the molded product from the mold. May occur.

When the amount is more than 1000 ppm, not only the antioxidant effect is saturated and the improvement effect cannot be expected, but also when the antioxidant is present at a high concentration, it acts as a hydrolysis catalyst for polycarbonate. Decomposes and phenolic OH is generated at the molecular chain end of the polycarbonate resin. The phenolic OH has high adhesion to the mirror surface of the mold, and as described above, the mold releasability between the molded product and the mold deteriorates, and as a result, the molded product surface is damaged or the cycle time becomes longer. There is.

Polycarbonate resin is presently the most preferred resin, but materials usable for the projection lens of the present invention are not limited to this. Resins considered as usable materials are amorphous, thermoplastic and high Tg.
(Glass transition temperature). The reason that amorphous is desirable is that, in the case of a crystalline resin, the density greatly changes during crystallization, and the size of the molded product cannot be ignored optically due to the density difference from the amorphous phase (for example, an area of 1 mm square). (Having a height difference of 1/4 wavelength or more) in the inner surface of the substrate, which causes a decrease in shape accuracy.

The reason why thermoplasticity is desirable is that, in the case of a curable resin such as an epoxy-based resin, a diacrylate, or a dimethacrylate-based resin, a problem of curing shrinkage occurs during curing by ultraviolet light or heat. The curing shrinkage of the curable resin is usually 10 to 20 vol%, and the shape change and transfer accuracy become insufficient due to the volume change.

The reason why a high Tg is desirable is that it is necessary to guarantee an image of up to 60 ° C. as a part for home or office devices. Tg ≧ 80 ° C. (meaning 80 ° C. or more) is desirable in the case of an amorphous thermoplastic resin material in view of safety in order to prevent deformation of the optical component at 60 ° C. However, this is only a guideline from room temperature fluctuations during normal use and the degree of heat build-up in the device. Considering that the device is installed near a heat source such as a stove, it does not deform further at 80 ° C and splashes of boiling water. Considering that it flies, more preferably 100 ° C
It is a desirable range not to deform.

Therefore, Tg is preferably Tg ≧ 80 ° C., preferably Tg ≧ 100 ° C., and more preferably Tg ≧ 120 ° C. Further, a preferable physical property required as a resin material to be used is low hygroscopicity. Low hygroscopicity is less than 1 wt% in resin as saturated water absorption (ASTM D570),
Preferably, the resin material is less than 0.5 wt%.

The reason is that the projection lens of the present invention forms a reflection layer made of metal such as aluminum on the surface by vapor deposition or the like and uses it as a reflection (projection) type mirror optical component, as will be described later. In consideration of the fact that the molded product to be obtained is large and thick as an optical component and that moisture is hardly absorbed (absent) from the reflective layer side which is a metal layer, one side (reflection Moisture absorption starts from the side without the layer), and when it expands (swells) due to the moisture absorption, deformation occurs, the shape changes, and the light control accuracy as an optical component decreases. Thereby, for example, defocusing, deformation of an image, and the like occur.

The transparent material which satisfies the above-mentioned low hygroscopicity includes, in addition to polycarbonate resin, polyester-carbonate resin, polysulfone resin such as polyether sulfone, polysulfone, amorphous polyolefin resin, polyarylate resin, non-polar functional group. A special acrylic resin which is introduced and suppresses the hygroscopicity may be used. The projection lens obtained by the present invention is a relatively large product as an optical product. Needless to say, a large (large area and large wall thickness) optical product is more difficult to prevent optical distortion than a small optical component, resulting in more difficult molding.

The specific size of the projection lens to be obtained in the present invention is, for example, a projection lens having a plane area of 150 cm ² or more, a minimum plane width of 10 cm or more, and a molded product thickness of 3 mm or more. Further, in a large projection type image device having a screen area exceeding 30 inches, the above-mentioned projection lens is required to have strict shape accuracy, and in order to obtain a projection image without unnatural feeling, one pixel area on the lens is required. It is desirable that the shape error in the vertical direction with respect to the surface inside is within ± submicron or less. If there is a shape error exceeding this, the pixels on the screen will be distorted from the original shape, and in severe cases, they will be split into several parts to form an image on the screen. In a large lens of the type which is usually enlarged about 20 times and projected on a large screen of 30 inches or more, the size of one pixel on the lens has a width of about several mm to 1 cm.

Further, the shape error on the entire optical function surface is ± 8.
0 μ, more preferably ± 50 μ, even more preferably ± 3
Desirably, it is 0 μm or less. If the entire optical functional surface deviates from the above range due to warpage, sink mark, or the like, the image looks unnatural due to sagging or distortion. By molding the above-mentioned resin so as to satisfy specific conditions, a base material for such a large projection lens can be obtained.

The specific conditions are as follows: the above-mentioned raw material resin is heated and melted, introduced into a mold having a cavity having a predetermined shape formed on a predetermined curved surface, and cooled and solidified to obtain a molded product (base material). At this time, the average value of the in-plane birefringence phase difference per unit thickness with respect to the incident light from the direction perpendicular to the optical functional surface of the resin substrate in the curved surface portion (optical functional surface) of the lens is calculated as At least 60 including the central part of the area
%, Preferably 70%, more preferably 80% in the region of 30 nm / mm or less, preferably 20 nm / m
m, more preferably 10 nm / mm or less, most preferably 5 nm / mm or less.

The optical function surface is a portion (surface) that does not need to be optically distorted and plays a role of an optical component. In manufacturing, a portion that does not need to perform an optical function may be formed around the optical function surface, but such an edge portion is not included. In addition, the central portion of the optical function surface refers to a central portion viewed in plan. By forming the in-plane birefringence retardation of at least 60% including the central portion of the optical function surface so as to be within the above range, a desired projection lens can be obtained.

A specific method for obtaining such a base material will be described by taking a case of polycarbonate as a main example. 1 and 2 are longitudinal sectional views of an example of a mold used to mold the projection lens of the present invention. In the figure, 1 is a mirror mold, 2 is a heater, 3 is a peripheral frame, 4 is a back mold, 5 is a heater,
6 and 7 are cooling devices, 8 is a load, 9 is a reduced pressure heating tank, and 10 is a resin substrate.

The raw material resin for the base material such as a polycarbonate resin is preferably dried with a vacuum dryer or the like. This is because moisture remaining in the raw material resin may cause foaming and deformation of the base material. As drying conditions, 80 to 120
The drying under reduced pressure may be carried out at a temperature of about 3 to 6 hours, and in terms of the amount of moisture, the moisture in the resin may be about 200 ppm or less.

As the raw material resin, any shape such as powder, pellet, and plate (prepreg) can be used, but it is preferable to use a prepreg having a shape similar to that of the final molded product. It is preferable for heating uniformly and quickly. When using a prepreg, it is preferable in terms of molding to use a prepreg that is about 5 to 20% thicker than the thickness of the final molded product.

At the same time, considering the simplicity of setting in a mold, the dimension in the plane direction is preferably smaller by about 3 to 20% in the front direction than the dimension in the plane direction of the final molded product. Also, the weight of the prepreg is desirably the same as that of the final molded product or about 10% heavier. If the prepreg is heavier than the final molded product, the excess resin amount is removed after molding as burrs or protrusions.

An example of a process for manufacturing the projection lens of the present invention will be described. The heater 2 and the mirror mold 1 are arranged on the cooling device 6, and the peripheral frame 3 is arranged around the mirror mold 1.
These molding devices are placed in the reduced pressure heating tank 9 and the heater 2
Temperature was set to 170 ° C and the apparatus was operated for about 30 minutes (typically 10 minutes).
(Approximately 60 minutes) Preheat the entire apparatus until the temperature becomes substantially uniform.

The surface of the mold 1 is formed of a resin material of Tg to Tg-3.
Around 0 ° C, for example, 12 in case of polycarbonate resin
What is necessary is just to preheat to about 0-150 degreeC. After completion of preheating,
A prepreg of a resin (polycarbonate or the like) forming the base material 10 is placed thereon, or a pellet or the like is spread so as to have a substantially uniform thickness as a whole. It is preferable to use a prepreg, and the prepreg is preferably about 3 to 20% thicker than the thickness of the lens to be obtained.

The projection lens is to prevent warping and deformation.
The whole thickness is almost the same, that is, the thickness of the resin base material at the reflection surface portion of the projection lens is ± the average thickness of the resin base material.
It is desirable that the thickness be within 50%. When the thickness in the product is largely different, the contraction stress at the time of cooling is biased, so that warping or deformation often occurs. It is also conceivable to provide a rib around the lens for reinforcement, but in this case, the thickness of the portion provided with the rib is not included in the calculation of the average thickness.

It is desirable that the amount of the pellets to be spread on a mold is approximately the same as the weight of the target molded product. Decompression is started in the above state. The degree of pressure reduction is about −60 kPa to −102 kPa with respect to the atmospheric pressure. This degree of pressure reduction is preferably -60 kPa or less, and more preferably -93 kPa or less. If the pressure is higher than -60 kPa, bubbles are trapped inside the molded article, and the shape and warpage of the entire molded article change depending on the ambient temperature, and the precision as an optical component may be reduced.

Further, the resin is not sufficiently filled into the end of the molded product, specifically, for example, the tip of a tongue-shaped mounting portion for attaching to an external device provided around the molded product. In some cases, the molded product lacks a part. The above-mentioned degree of pressure reduction and Tg of the resin material + 10 to 40 at a temperature of about 30 to 100 ° C.
For about a minute, with the inside being sufficiently melted, the pressure is once returned to the atmospheric pressure, and then the back mold 4, the heater 5, and the cooling device 7 are arranged.

In this state, a load 8 of 10 to 50 kg is applied. The total weight including the back mold 4 is about 20 to 60 kg. The pressing pressure on the molding is about 4 kPa. The rear surface shape is formed by placing the load 8 on the rear surface mold 4. When unevenness is generated in the back surface shape or when bubbles are caught, the thickness of each portion varies, and as a result, the shape accuracy is not obtained as described above.

An appropriate pressure range is 1 to 10000 kPa
, Preferably 2 to 2000 kPa. More preferably, 4 to 1000 kPa is desirable. When the pressure is lower than this pressure, the formation of the back surface shape is insufficient, and when the pressure exceeds this pressure, the orientation of the molecular chains is insufficiently relaxed, so that the molded product may be warped or deformed.

Since the decompression and heating tank 9 is used, the lid is covered so that the pressure can be restored once and the hand can be accessed. It is better to cover the surface with a press. The back mold 4, the heater 5, the cooling device 7 and the load 8 are applied, the pressure is reduced again, and the temperature is controlled. At this time, the degree of pressure reduction is controlled to −60 kPa (preferably below).

The degree of pressure reduction is also -60 kP
a, more preferably −93 kPa or less, but since the inside is at a higher temperature than in the above-described steps, it is more preferable to further increase (decrease) the degree of pressure reduction. The heating temperature depends on the T of the raw resin constituting the resin substrate 10.
It is preferable that the temperature is higher by 50 to 120 ° C. than that of g. More preferably, the temperature is 70 to 100 ° C. higher than the Tg of the raw resin,
Most preferably, the temperature is 80 to 90 ° C. higher than Tg.

If the temperature is higher than this temperature, even under an inert gas atmosphere, the resin undergoes thermal degradation, the decomposition of the molecular chains of the raw material resin proceeds, the number of terminal OH groups increases, and the mold is released from the mold. It is considered that the molded article becomes defective and damage to the surface of the molded article occurs. The heating and holding time is 1 to 60 minutes, preferably 5 to 40 minutes, and more preferably 10 to 30 minutes. If the time is exceeded, the cycle time becomes longer and the suitability for industrialization is reduced.

It is preferable to control the lower heater 2 of the heaters 2 and 5 to a temperature higher by about 20 to 120 ° C. than the upper heater 5 for about 10 to 60 minutes after the start of heating. By doing so,
The effect of preventing air bubbles from staying inside the resin substrate 10, particularly on the mirror side of the mirror mold 1, is expected. Ultimately 5
The heaters 2 and 5 are controlled to a temperature that is approximately 0 to 120 ° C. higher and substantially the same, and is maintained for approximately 5 to 30 minutes.

Next, an inert gas is introduced into the reduced pressure heating tank 9 while maintaining the heated state from the reduced pressure state, and the pressure is restored to about the atmospheric pressure. After the pressure recovery step, at the stage where cooling is started, the in-plane birefringence phase difference per unit thickness with respect to incident light from a direction perpendicular to the optically functional surface of the resin base material in the curved surface portion of the desired lens. Molding is performed so that the average value is 30 nm / mm or less in a region that is at least 60% or more of the area of the optical function surface.

In molding the base material, a colorant is added to the base resin,
It is conceivable that a filler or the like is mixed in, and the base material becomes colored or opaque, making it difficult to measure birefringence. in this case,
For example, when the base material is colored with a dye or the like, the measurement wavelength is changed within the visible light range, and the measurement is performed at a wavelength at which the transparency of the base material increases. It is simple to change the wavelength using a wavelength filter such as a band filter. In the case of coloring by mixing pigments, carbon black, fillers, etc., the raw resin in a state in which additives that cause opacity such as coloring agents and fillers are not added is molded under the same conditions. The value of birefringence will be used.

It is desirable that the gas to be restored is an inert gas such as nitrogen. However, even if it contains a little oxygen, there is no problem in the effect of suppressing the generation of bubbles or defoaming the generated bubbles. However, since the aerobic gas oxidizes and degrades the resin surface, it may cause mold release failure or damage to the molded product surface, which is not preferable. From this viewpoint, the oxygen concentration in the inert gas used to recover the pressure is 10 vol.
% (Volume%), more preferably less than 5 vol%, most preferably less than 2 vol%.

After the pressure recovery, the inside of the resin reaches a peak temperature (a temperature higher by about 30 to 120 ° C. than Tg, preferably 50 ° C.
After maintaining the temperature for about 10 to 40 minutes after the temperature reaches (100 ° C. higher temperature), the cooling operation is started. Here, the orientation is relaxed to obtain low birefringence. Flow a cooling medium such as cooling water through the cooling devices 6 and 7, and set the heaters 2 and 5 to Tg to Tg.
The temperature is lowered to about + 30 ° C., and this temperature is maintained for about 10 to 40 minutes.

After maintaining this state for 10 to 40 minutes, the settings of the heaters 2 and 5 are lowered by 10 to 50 ° C. from the previous set temperature and maintained for about 10 to 40 minutes, and the heater is further heated to 120 ° C. over 10 to 40 minutes. Reduce the temperature of the hot plate. Thus, the temperature drops very slowly. As described above, the molded article is gradually cooled at a cooling rate of about 0.5 to 5 ° C./min.

Regarding the cooling rate, the surface of the molded product is (30 (° C./min)) at the point of passing Tg, preferably 10 ° C. above and below Tg, more preferably 15 ° C. above and below Tg.
The cooling rate is desirably equal to or less than / (average thickness of molded article (mm)), and is preferably (20 (° C./min))/
(Average thickness of molded article (mm)) or less, more preferably (10
(° C / min)) / (Average molded article thickness (mm)), most preferably (5 (° C / min)) / (average molded article thickness (mm))
It is desirable that:

When the cooling rate is higher than the cooling rate, a temperature distribution, an internal stress and a reorientation are generated in the inside, and warpage, deformation and sink are generated, thereby lowering the shape accuracy. This is more pronounced for thicker, larger molded products. The reason why cooling in the vicinity of Tg is particularly important is that the volume change of the resin when passing through Tg is extremely large, and when the temperature falls below Tg, the movement of the molecular chain is fixed.
This is because the influence on the shape accuracy such as warpage, deformation and sink is particularly large.

If the pressure at the time of cooling is too high, the orientation is difficult to be relaxed.
The range of kPa is desirable, preferably 2 to 2000 kPa, more preferably 4 to 1000 kPa. If the pressure is too low, the mirror transfer may be insufficient. On the other hand, if the cooling rate and the pressure during cooling are properly controlled, molding using an injection molding machine is also possible. Of course, in the mold,
It will be necessary to install a heating device, a cooling device, a pressure control device, etc. that can be precisely controlled.

The substrate thus slowly cooled under a predetermined pressure is taken out of the mold. On the surface of the base material taken out of the mold, a reflection layer made of a metal deposition film or the like is provided. Aluminum (A
L), silver (Ag) and the like are conceivable, but aluminum and its alloys are preferably used in view of reflectance in the visible region, durability and cost.

Usually, the substrate is washed before performing the vapor deposition. The reason for washing is to remove oils and fats adhering to the surface and bleed additives, to obtain an appearance free from defects such as spots and fogging after the formation of the reflective vapor deposition film, and to improve the adhesion of the reflective film. An example of the cleaning method is as follows.

After being immersed in a CFC solution at room temperature for about 10 to 120 seconds, it is immediately taken out and put into a vapor deposition apparatus. If the immersion time is too long or the temperature is too high, in the case of a polycarbonate resin, damage such as cracks and crazes is likely to occur on the molded product surface. Examples of other cleaning methods include, for example, immersion in ethanol at room temperature for about 1 to 30 minutes, and ultrasonic cleaning with warm water of about 30 to 60 ° C. containing about 0.1 ppm of a surfactant for 3 to 30 minutes. A method of addition is given.

After taking out of the washing tank, rinse well with pure water,
Dry in a vacuum drying oven at a temperature of about 50 to 120 ° C. for about 1 to 6 hours. An example of a vapor deposition process will be described. After the cleaning treatment of the base material, the molded product is put into a vacuum evaporation tank, kept under reduced pressure for about 10 to 60 minutes, and the molded product is sufficiently dried, and then the degree of vacuum is increased.

The degree of vacuum is 1 × 10−4 to 1 × 10−6 kP
a, chrome (Cr) is sequentially applied to the mirror surface side of the molded product in an amount of 30 to 1000 ° and AL is set to 800 to 4000.
を, silicon oxide (SiO2 or SiOx) 200 to 10
Deposition is performed so as to be 00 °. The preheating of the substrate need not be particularly performed. In order to improve the adhesion of the deposited film, the underlying layer should be made of aluminum oxide (AL) rather than SiOx.
It is preferable to use 2O3), Cr, or the like, and it is particularly preferable to use Cr as the underlayer. Further, the thickness of the underlayer is preferably 30 to 1000, and 100 to 5
00 ° is more preferable.

If the thickness is larger than this range, cracks and peeling are likely to occur in the deposited film due to the difference in linear expansion coefficient from the resin substrate. On the other hand, when the thickness is smaller than this range, the effect of blocking moisture from the vapor deposition film side to the inside is insufficient, and the film is likely to peel off after the high temperature and high humidity test. A reflective film is formed on the aspherical surface side of the molded product. However, in order to suppress warpage due to a residual stress of the reflective film or a difference in linear expansion coefficient from the resin material, the reflective film is made of an aluminum vapor-deposited film of 1000 mm or more. Desirably, the thickness is 3000 mm.

When the thickness is less than 800 °, the reflectance is 70
%, The efficiency of light source usage is reduced, and 4000Å
Exceeding the range is not preferable because the reflective film is cracked or peeled off due to residual stress in the aluminum vapor-deposited film and / or a difference in linear expansion coefficient from the resin base material, or deformation such as warping occurs in the entire mirror. . From the above viewpoint, the thickness of the aluminum vapor-deposited film is more preferably 1,000 to 300.
0 °, more preferably 1500 ° to 2500 °.

It is preferable to form a protective layer such as a SIOx film on the AL reflective layer in order to prevent the AL film from being oxidized and deteriorated. S
The thickness of the IOx film is 100-1000Å, preferably 20
It is preferably about 0 to 800 °, more preferably about 400 to 600 °. If the protective layer is too thick, the deposited film is likely to be cracked or peeled off due to the difference in linear expansion coefficient from the base material. On the other hand, if the protective layer is too thin, the effect of blocking oxygen and the like from the protective layer side to the inside is insufficient, and corrosion of AL is likely to occur.

It is desirable that the reflectance in the visible light region be as high as possible, but from the viewpoint of effective use of the light amount of the light source, it is desirable that the average value in the visible region is 70% or more.
It is more preferably at least 80%, most preferably at least 90%. The theoretical reflectance of aluminum is about 93% as an average value in the visible region. The resin aspherical mirror of the present invention is a mirror-type transparent thermoplastic resin-based aspherical projection lens used for a projection device such as a liquid crystal projector or a DLP projector, and has a plane area of 150 cm ² or more and a flat surface. In a molded article mirror having a minimum width of 10 cm or more and an average thickness of the molded article of 3 mm or more, in a curved surface portion of a lens, incident light from a direction perpendicular to an optical functional surface of a resin base material. The average value of the in-plane birefringence retardation per unit thickness is set to 30 nm / at least in a region including at least 60% of the area of the optical function surface.
mm or less, and a metal reflective film and a transparent protective film are sequentially formed on the curved surface portion.

In measuring the birefringence phase difference,
If there are scratches or fine irregularities on the surface, the light is scattered and may affect the measurement result, so it is adjusted to the same refractive index as the base material, and the base resin is not violated in a short time at room temperature It is effective to apply a refractive index liquid to the surface or immerse the liquid in a refractive index adjusting liquid for measurement. When the resin base is colored with a dye or the like, it is effective to shift the measurement wavelength of the birefringence phase difference to a region having a high transmittance in the visible region, for example.

The substrate to be measured was placed in a parallel Nicol state.
A birefringence measurement device of the type that measures the birefringence phase difference from the change in light transmittance when the substrate to be measured is rotated when the substrate to be measured is rotated, the transmittance of the substrate to be measured is If it is about 10% or more, there is a possibility of measurement. When the light transmittance of the substrate to be measured is less than 10%, a dye, a pigment,
Evaluation is made on a base material formed with the same materials and conditions without adding a coloring agent such as carbon black.

When a metal vapor deposition film, a dielectric vapor deposition film, or the like is formed on the surface of the molded product, evaluation is performed after removing the film by etching with an acid or alkali solution. Plane area is 1
In high-precision optical parts with a minimum width of 50 cm ² or more and a minimum width of 10 cm or more, when made of a resin material, self-support is insufficient if the thickness is at least 2 mm or more. It is difficult to achieve.

It is preferable that the thickness be 3 mm or more, more preferably 4 mm or more, and most preferably 5 mm or more. Note that the resin mirror of the present invention is widely applied to devices requiring a large aspherical mirror that requires a highly accurate surface shape, regardless of a rear projector device such as a liquid crystal rear projector and a DLP rear projector. Can be.

The projection lens of the present invention has high shape accuracy despite being lightweight and inexpensive, and is incorporated in a projection device which projects not diagonally to the screen but diagonally, particularly diagonally downward, and has a trapezoidal shape. The present invention relates to a projection lens capable of correcting distortion and the like and projecting a high-definition image without distortion and deformation. The purpose of arranging the projectors in the oblique direction, particularly in the obliquely downward direction, is mainly to save space and secure the degree of freedom in arranging the projectors and the screen.

For example, a rear projection television is made thinner, and a projector in a front projector is arranged on a presenter's hand (conventionally, it was necessary to project vertically on a screen. It is necessary to install the projector on a stepladder at a high altitude), and it is effective when the projector is arranged in a place where it is inconspicuous in a window display or a 3D display.

[0072]

EXAMPLE 1 A projection lens was manufactured using a mold having the structure shown in FIGS. As a resin material, a viscosity average molecular weight of 15
000, Tg = 148 ° C. (DSC method) polycarbonate resin was used. The saturated water absorption of this resin is 0.3wt%
(ASTM D570). This was used after drying.

First, a plane projection dimension 2 having a curved surface represented by the following equation (1) and having a base at a position 40 mm from the center of the aspheric surface is shown below.
A mirror mold 1 (stamper) of a 5 cm square aspherical mold was manufactured. A back mold 4 (top cover mold) is sandwiched between the stamper and the resin mold so that the average thickness of the resin molded article becomes 10 mm, and the mirror mold 1 and the back mold 4 can be disassembled. It was made to be surrounded by a metal (aluminum) peripheral frame 3.

This is filled with 650 g of resin pellets, assembled together with a frame (hereinafter, sometimes referred to as a mold assembly), and sandwiched between heaters 2 and 5 and cooling devices 6 and 7. Put the whole in vacuum heating tank 9 and
The pressure was reduced to 0 kPa. After that, electricity was supplied to the heaters 2 and 5, and the temperature was raised to 240 ° C. Next, while maintaining the heating state, nitrogen gas was introduced into the reduced pressure heating tank 9 and the pressure was returned to the atmospheric pressure (returned pressure) over 10 minutes.

After the pressure recovery, 4.5 kPa per resin molded product area
Was applied. Thirty minutes after the energization, the lower heater 2 was set at 240 ° C. and the upper heater 5 was set at 240 ° C. for 30 minutes. In this state, the heaters 2 and 5 are maintained at 160 ° C. for 50 minutes, and then the heaters 2 and 5 are maintained at 140 ° C. for 30 minutes while cooling the water by flowing water into the cooling devices 6 and 7 while adjusting the flow rate. Heaters 2, 5
Was kept at 110 ° C. for 30 minutes and slowly cooled. Calculations showed that the cooling rate at the time of passing Tg was 0.7 ° C./min.

The temperature was lowered to 100 ° C. at a rate of 3 ° C./min, the vacuum heating tank 9 was opened, and the assembled mold was taken out.
The molds 1 and 4 were disassembled and released, and the internal resin substrate 10 was taken out.

[0077]

(Equation 1)

(C = 1 / r, c: curvature, r
: Radius, k: conical ratio, A, B, C, and D are coefficients) r = −160 k = −8.0 A = 7.0E−9 B = −9.0E−14 C = 6.5E−19 D = −2.0E−24 The coordinates were set as shown in FIG.

The average thickness of the resin substrate at the reflection surface of the projection lens is 10 mm, and the maximum thickness is 12 m.
m, and the minimum thickness was 8 mm. Further, with respect to this molded product, the birefringence phase difference at a wavelength of 590 nm was measured on the entire optical function surface (for each divided cell of about 300 μ square). For the measurement of the birefringence phase difference, KOBRA-CCD / X manufactured by Oji Scientific Instruments was used, and the measurement was carried out for each divided cell of about 300 μ square, and the measured value was evaluated by processing.

In the measurement, in order to cancel the influence of light scattering due to minute irregularities and scratches on the surface of the substrate, a refractive index adjusting liquid adjusted to the same refractive index as that of the substrate is applied to the surface so as to prevent bubbles from entering. And measured. With respect to the measured value of each divided cell, the average value of the measured values of 75% from the lower one was found to be 50 nm. Therefore, the birefringence phase difference per unit thickness was 5 nm / mm.

The surface of this molded product was thoroughly washed with ethanol and further warm water containing a surfactant, dried, and then, Cr / AL / SiOx was coated on the surface with 100 ° / 1500 ° / 4.
It was deposited to a thickness of 00 °. The reflectance of visible light is measured with a reflection spectrophotometer, but cannot be measured accurately on curved surfaces.
An evaporation layer was formed on a flat plate having the same thickness and manufactured by the same process as above, and the reflection film was measured. As a result, the average was 80%.

An image having 1 million pixels was projected on this mirror, and further projected onto a 100 cm × 76 cm screen from diagonally below. As a result, a good image was obtained without being conscious of distortion and deformation. The projection magnification was about 20 times in area magnification. The present optical system can be suitably used, for example, as a rear projection television or a window display of a system that projects diagonally from below.

[0083]

Example 2 The pellets used in Example 1 were replaced with a thickness of 1
Molding was performed in the same manner as in Example 1 using a prepreg having a width of 2 mm and a length of 240 mm and a length of 240 mm (referred to as a preformed body previously formed into a plate). In this case, the heating time after the double pressure was shortened by 10 minutes. The cooling time to 160 ° C is 10
Although it was shortened by a minute, a lens equivalent to that of Example 1 was obtained.

[0084]

Example 3 Tg = 143 ° C. (DSC method)
Amorphous polyolefin resin (ARTON-
D) was used. The saturated water absorption of this resin is 0.2% by weight
(ASTM D570). Hot press molding was performed in the same manner as in Example 1 to obtain a molded product. The birefringence retardation per unit thickness was 5 nm / mm.

The thickness of the resin base material at the reflection surface portion of the projection lens is such that the average thickness is 10 mm and the maximum thickness is 12 m
m, and the minimum thickness was 8 mm. After thoroughly cleaning the surface of this molded article with ethanol and warm water containing a surfactant,
After drying, the surface is coated with Cr / AL / SiOx at 100Å.
/ 1500 ° / 400 °.

The reflectance of visible light is measured by a reflection spectrophotometer, but cannot be measured accurately on a curved surface. Therefore, an evaporation layer on a flat plate having the same thickness and manufactured by the same process as above is formed.
It was 80% on average when the reflection film was measured. An image of 1 million pixels was projected on this mirror, and further projected onto a 100 cm x 76 cm square screen from obliquely below. As a result, a good image without distortion and deformation was obtained.

The projection magnification was about 20 times in area magnification. That is, a lens almost equivalent to that of Example 1 was obtained.

[0088]

Comparative Example 1 As a material, a PMMA resin (Acrippet MD, manufactured by Mitsubishi Rayon Co., Ltd.) having a Tg of 93 ° C. (DSC method) was used. The resin has a saturated water absorption of 1.4 wt% (ASTM D
570). The injection mold having the aspherical profile of Example 1 and the heating / cooling piping was manufactured.
FANUC 300t injection compression molding machine FANUC R
It was set on an OBOSHOTi series α-300iA injection molding machine. The resin was injected into the mold at a mold temperature of 80 ° C., an injection temperature of 330 ° C., and an injection pressure of 300 MPa. After maintaining the state for 20 minutes, the mold was opened and the molded product was taken out.

With respect to this molded product, the birefringence phase difference at a wavelength of 650 nm was measured over the entire effective reflection surface. For the measurement of the birefringence phase difference, KOBRA-CCD / X manufactured by Oji Scientific Instruments was used, and the measurement was carried out for each divided cell of about 300 μ square, and the measured value was evaluated by processing.

In the measurement, in order to cancel the influence of light scattering due to minute irregularities and scratches on the surface of the substrate, a refractive index adjusting liquid adjusted to the same refractive index as that of the substrate is applied to the surface so as to prevent bubbles from entering. And measured. With respect to the measured value of each divided cell, the average of the measured values of the lower 60% was 400 nm. Therefore, the birefringence phase difference per unit thickness was 40 nm / mm.

The aspherical surface of this molded product was thoroughly washed with ethanol and warm water containing a surfactant, dried, and then the surface was coated with Cr / AL / SiOx at 100 ° / 1500 ° / 4.
It was deposited to a thickness of 00 °. The visible light reflectance is 80 on average
%Met. After holding this mirror at 25 ° C. and 80 RH% for 48 hours, an image having 1 million pixels was projected in the same manner as in Example 1, and further projected onto a 100 cm × 76 cm square screen from diagonally below. Deformation of the image due to sink marks, deformation of the shape of the pixels, and deformation of the image in which both the left and right shoulders hang down due to the warpage of the substrate were observed.

[0092]

Comparative Example 2 As a material, a PMMA resin (Acrypet MD manufactured by Mitsubishi Rayon Co., Ltd.) having a Tg of 93 ° C. (DSC method) was used. The resin has a saturated water absorption of 1.4 wt% (ASTM D
570). The injection mold having the aspherical profile of Example 1 and the heating / cooling piping was manufactured.
It was set on a 350-ton injection molding machine made by Nissei Plastic Co., Ltd. Mold temperature 200 ° C, injection temperature 330
The above resin is injected into this mold at 30 ° C. and an injection pressure of 30 MPa, then cooled at a rate of 1 ° C./min until the mold temperature reaches 75 ° C., held at that temperature for 10 minutes, and then the mold is opened and the molded product is opened. Was taken out.

With respect to this molded product, the birefringence phase difference at a wavelength of 590 nm was measured over the entire effective reflection surface. For the measurement of the birefringence phase difference, KOBRA-CCD / X manufactured by Oji Scientific Instruments was used, and the measurement was performed for each divided cell of about 200 μ square, and the measured value was evaluated by processing.

In the measurement, in order to cancel the influence of light scattering due to minute irregularities or scratches on the surface of the base material, a refractive index adjusting liquid adjusted to the same refractive index as that of the base material is applied to the surface so as to prevent bubbles from entering. And measured. With respect to the measured value of each divided cell, the average value of the measured values of the lower 60% was 600 nm. Therefore, the birefringence phase difference per unit thickness was 60 nm / mm.

The average thickness of the thickness of the resin substrate at the reflection surface of the projection lens measured at 529 points at lattice points at 1 cm intervals was 8 mm, the maximum thickness was 13 mm, and the minimum thickness was 5 mm. The aspheric surface of this molded product is ethanol,
After washing well with warm water containing surfactant and drying,
On the surface, Cr / AL / SiOx was coated at 200/150.
Deposition was performed at a thickness of 0 ° / 400 °. The visible light reflectance was 80% on average.

After holding this mirror at 25 ° C. and 40 RH% for 48 hours, and then at 50 ° C. and 98 RH% atmosphere for 6 hours, an image having 1 million pixels was projected as in Example 1 and further 100 cm × 76 cm. When projected onto the corner screen from obliquely below, the side opposite to the vapor-deposited film of the mirror molded product expanded due to moisture absorption and warped, and deformation of the image in which both left and right shoulders were sagging was observed.

[0097]

EFFECT OF THE INVENTION The projection lens of the present invention has high shape accuracy despite being lightweight and inexpensive, and is particularly incorporated in a projection device that projects not diagonally to the screen but diagonally, particularly diagonally downward. ,
This is a large projection lens that can project high-definition images without distortion and deformation.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an example of a mold used to mold a projection lens according to the method of the present invention.

FIG. 2 is a longitudinal sectional view of an example of a mold used for molding a projection lens according to the method of the present invention.

FIG. 3 is a coordinate setting diagram according to the first embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Mirror surface mold 2 Heater 3 Perimeter frame 4 Backside mold 5 Heater 6 Cooling device 7 Cooling device 8 Load 9 Decompression heating tank 10 Resin substrate Z Coordinate on the rotationally symmetric axis of the aspherical surface with the aspherical center as the origin h Aspherical surface Rotational symmetry axis of the aspherical surface with the origin at the center and distance coordinates in the vertical direction

Claims (6)

[Claims] 1. A projection lens in which a reflection layer is provided on a surface of a resin substrate formed on a predetermined curved surface, wherein the light is incident on the curved surface portion of the lens in a direction perpendicular to the optical functional surface of the resin substrate. The average value of the in-plane birefringence phase difference per unit thickness with respect to light is set to 30 nm / mm or less in a region of at least 60% of the area of the optical function surface, and a metal reflective film and a transparent protective film are sequentially formed on the curved surface portion. A projection lens characterized by being formed. 2. The projection lens according to claim 1, wherein the thickness of the resin substrate on the optical function surface of the projection lens is within ± 50% of the average thickness of the resin substrate. . 3. The projection lens according to claim 1, wherein a plane area is 150 cm ² or more, a minimum width of the plane is 10 cm or more, and a molded product thickness is 3 mm or more. 4. A resin base material having a Tg ≧ 70 ° C. and a 60 ° C. 90 R
The projection lens according to any one of claims 1 to 3, wherein an amorphous thermoplastic resin having a saturated water absorption at H% of less than 1% is a main component. 5. The projection lens according to claim 1, wherein the reflection layer is an aluminum deposited film having a thickness of 1000 to 3000 °. 6. The projection lens according to claim 1, wherein the transparent protective layer is a metal oxide film having a thickness of 100 to 1000 °.