JPH1158476A - Thin plate-shaped molded item and method for molding the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a molded item, in which the double refraction thereof is made small, such as a thin sheet-shaped injection molded item which is useful in an optical service requiring optical characteristics or in the field of display or such as a decorated injection molded item such as a Fresnel lens, and a method for molding it. SOLUTION: In the thin sheet-shaped molded item comprising a thermoplastic resin containing a norbornane skeleton represented by formula (where A, B, C and D each show a hydrogen atom or monovalent organic group), the thermoplastic resin is filled into a die whose surface temperature is equal to or higher than the glass transition point (Tg) of resin and the temperature of the die is maintained at a temperature equal to or higher than Tg to relax the shear strain at the time of filling the resin and then the die is cooled, and the optical strain is 50 nm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin sheet-like injection molded article useful for optical applications requiring optical characteristics and a display field, and a decorative injection molded article such as a Fresnel lens. The present invention relates to a molded article that needs to be controlled to a small size and a molding method thereof.

[0002]

2. Description of the Related Art Heretofore, a thin injection molded product of an optical resin has been molded at a mold temperature equal to or lower than a glass transition temperature (hereinafter, referred to as Tg) of the resin in order to facilitate cooling and solidification. However, in such a conventional method, since the flow path solidifies and flows during molding, a large shear stress is applied,
Since the molecular orientation in the flow direction is large, the optical anisotropy is large, and the birefringence of the thin injection-molded product is usually as large as 100 nm or more, and the range where the transparent resin is used for optical applications is limited.

[0003]

Injection molding is an excellent molding method to obtain molded articles of various shapes, but the molecular orientation is not sufficiently relaxed and the shear stress is frozen as residual stress. It was not possible to mold a molded article having excellent optical properties with small birefringence. In order to meet such a demand, the present invention fills (injects) a molten resin into a mold heated to a temperature of Tg or higher when performing injection molding, and maintains the state for a certain period of time to form a molding having a small birefringence. It has been found that a product can be obtained, and the present invention has been completed.

[0004]

That is, the present invention relates to a thin plate-shaped molded article made of a thermoplastic resin, wherein the thermoplastic resin is heated to a temperature equal to or higher than the glass transition temperature (Tg) of the resin. Filling in a mold, cooling the mold after holding the mold temperature at a temperature of Tg or more to alleviate the shear strain at the time of filling, and cooling the sheet, characterized by an optical distortion of 50 nm or less. The present invention provides an article and a molding method thereof.

[0005] The thermoplastic resin in the present invention includes P
A transparent thermoplastic resin such as an MMA resin, a polycarbonate, and a thermoplastic norbornene resin can be used. The thermoplastic norbornene-based resin that can be used in the present invention has a norbornane skeleton in its repeating unit. For example, as this thermoplastic resin,
It contains a norbornane skeleton represented by the general formulas (1) to (4).

[0006]

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[0007]

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[0008]

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[0009]

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(In the formula, A, B, C and D represent a hydrogen atom or a monovalent organic group.) Examples of the thermoplastic resin having a norbornane skeleton which can be used in the present invention include those described in 60-1
68708, JP-A-62-252406,
JP-A-62-252407, JP-A-2-1334
No. 13, JP-A-63-145324, JP-A-63-264626, JP-A-1-240517, JP-B-57-8815, and the like. .

Preferred examples of the thermoplastic resin include at least one tetracyclododecene derivative represented by the following general formula (5) or an unsaturated cyclic compound copolymerizable with the tetracyclododecene. Examples include hydrogenated polymers obtained by hydrogenating a polymer obtained by metathesis polymerization.

[0012]

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(Wherein A to D are the same as above.) In the tetracyclododecene derivative represented by the general formula (5), a polar group may be contained in A, B, C and D. Heat resistance and good affinity with the mold surface are preferable in that high surface accuracy can be obtained. Further, the polar group ^{_{- (CH 2) n COOR 3}} ( wherein, R ³ is a hydrocarbon group having 1 to 20 carbon atoms, n represents an integer of 0) is a group represented by It is preferable because the resulting hydrogenated polymer has a high glass transition temperature. Especially,
It is preferable that one group represented by — (CH ₂ ) _n COOR ³ is contained per molecule of the tetracyclododecene derivative of the general formula (5). In the general formula,
R ³ is a hydrocarbon group having 1 to 20 carbon atoms, which is preferable in terms of decreasing the hygroscopicity of the obtained hydrogenated polymer as the number of carbon atoms increases, but is preferably lower than the glass transition temperature of the obtained hydrogenated polymer. From the viewpoint of balance, a chain alkyl group having 1 to 4 carbon atoms or a (poly) cyclic alkyl group having 5 or more carbon atoms is preferable, and a methyl group, an ethyl group, and a cyclohexyl group are particularly preferable. Further,-(CH ₂ ) _n C
The tetracyclododecene derivative of the general formula (5) in which a hydrocarbon group having 1 to 10 carbon atoms is simultaneously bonded as a substituent to the carbon atom to which the group represented by OOR ³ is bonded, reduces the hygroscopicity. It is preferred. In particular, the tetracyclododecene derivative of the general formula (5) in which the substituent is a methyl group or an ethyl group is preferable in that the synthesis is easy. Specifically, 8-methyl-8-methoxycarbonyltetracyclo [4.4.0.1 ^2,5 . [ ^1,7,10 ] dodec-8-ene is preferred.

These tetracyclododecene derivatives or a mixture of an unsaturated cyclic compound copolymerizable therewith can be used, for example, in JP-A-4-77520, page 4, upper right column, line 12 to page 6, lower right column. The thermoplastic resin used in the present invention can be obtained by metathesis polymerization and hydrogenation by the method described in line 6. In the present invention,
The hydrogenated polymer desirably has an intrinsic viscosity ([η] inh) measured at 30 ° C. in chloroform of 0.3 to 1.5 dl / g. When [η] inh is in the above range, the resulting resin has a good balance of moldability, heat resistance, and mechanical properties. Further, the glass transition temperature (Tg) of the hydrogenated polymer is preferably in the range of 100 ° C to 250 ° C, particularly preferably in the range of 120 to 200 ° C. If the temperature is lower than 100 ° C., the heat resistance of a molded article made of the resin is inferior. On the other hand, when the Tg exceeds 250 ° C., the molding temperature becomes high, and it becomes difficult to obtain a high-quality molded product such that the resin is burnt and colored. The hydrogenation rate of the hydrogenated polymer is at least 50%, preferably at least 90%, more preferably at least 98%, as measured by 60 MHz, ¹ H-NMR. The higher the hydrogenation rate, the better the stability to heat and light. In the present invention,
The hydrogenated polymer used as the thermoplastic resin having a norbornane skeleton preferably has a gel content of 5% by weight or less, more preferably 1% by weight, in the hydrogenated polymer.
It is preferred that

As the polycarbonate resin used in the present invention, those containing an aromatic bisphenol such as bisphenol A as a main component, for example, Panlite (manufactured by Teijin Chemicals Ltd.), Lexan (manufactured by General Electric), Iupilon (Mitsubishi) Gas Chemical Co., Ltd.) and Toughlon (Idemitsu Petrochemical Co., Ltd.). The acrylic resin used in the present invention preferably has a heat deformation temperature of 100 ° C. or higher.
Kuraray) and Chemax (manufactured by Sumika Haas Co., Ltd.). These acrylic resins may be modified with a cyclohexyl group or a norbornene-based resin, or may be imidized.

The thermoplastic resin used in the present invention may contain, if necessary, a known antioxidant such as 2,6-di-t-butyl-4-methylphenol, 2,2'-dioxy-3,
3'-di-t-butyl-5,5'-dimethylphenylmethane, tetrakis [methylene-3- (3,5-di-t-
Butyl-4-hydroxyphenyl) propionate] methane, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl-benzene, stearyl-
β- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2′-dioxy-3,3′-
Di-t-butyl-5,5′-diethylphenylmethane,
3,9-bis [1,1-dimethyl-2- [β- (3-t
-Butyl-4-hydroxy-5-methylphenyl) propionyloxy] ethyl], 2,4,8,10-tetraoxyspiro [5,5] undecane, tris (2,4-di-t-butylphenyl) phospho Phyte, cyclic neopentanetetraylbis (2,4-di-t-butylphenyl) phosphite, cyclic neopentanetetraylbis (2,6-di-t-butyl-4-methylphenyl) phosphite, 2,2-methylenebis (4,6-
Di-t-butylphenyl) octyl phosphite can be added.

Further, in addition to the above-mentioned antioxidant, if necessary, an ultraviolet absorber such as pt-butylphenyl salicylate, 2, 2
2'-dihydroxy-4-methoxybenzophenone,
2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2- (2′-dihydroxy-4′-m-octoxyphenyl) benzotriazole; stabilizer, antistatic agent, flame retardant, for improving impact resistance An elastomer or the like can be added. Further, additives such as a plasticizer and a softener can be added for the purpose of improving moldability and workability.

The thin plate-shaped molded article of the present invention is prepared by filling the above-mentioned thermoplastic resin into a mold heated to a temperature higher than Tg of the resin by injection or the like, and setting the mold temperature to Tg or higher. After alleviating the shear strain at the time of filling by holding at, cooling and taking out can be carried out.

As a result of our intensive studies, the reason why birefringence is greatly developed in injection molded products is that the molecules near the surface of the mold during injection molding are oriented by the shear stress in the flow direction.
It has been found that, due to the mold temperature set lower than the Tg of the thermoplastic resin, the solidified resin is cooled and solidified from the mold surface and is frozen as it is. Further, since the generated shear stress is cooled and solidified before being alleviated, the stress is frozen, which causes an increase in residual strain. According to the present invention, it is possible to prevent the resin from being cooled and solidified during filling of the molten resin by injecting the resin while the mold is heated to a temperature equal to or higher than the Tg of the thermoplastic resin. In this case as well, when the mold temperature is lower than Tg, the molecules are once oriented in the flow direction during the flow, but since the mold temperature is equal to or higher than Tg, the molecular chains still rotate even after the mold is filled. ,
It is in a state in which it can move, such as expansion and contraction, and the molecules that have been oriented by being kept at a temperature equal to or higher than Tg gradually relax, and the anisotropy gradually decreases, so that a molded article with small birefringence can be obtained.

If the mold temperature is equal to or higher than Tg, it is possible to obtain a molded article having good optical properties, but the molecular orientation is relaxed in a shorter time as the mold temperature is higher. Therefore, in order to shorten the molding cycle, it is desirable to increase the temperature of the mold as much as possible. Preferably, the temperature is maintained at (Tg + 20) ° C. or higher, more preferably (Tg + 30) ° C. or higher. If it is difficult, a sufficient holding time is required for relaxing the molecular orientation.

In the present invention, the method of heating the mold may be any method. For example, a commonly used method is to arrange a flow path of water and oil in a mold, control a medium such as water and oil to a temperature equal to or higher than the Tg of the thermoplastic resin, and control a mold temperature. A method of heating a mold by embedding a heater in the mold, a method of providing an electrically conductive layer capable of conducting electricity on the surface of the mold, and heating and heating by applying electricity
There is no particular limitation on the method of heating from outside or inside the mold by an induction heating device, or the method of heating from outside the mold by irradiation with far-infrared rays using a halogen lamp or a ceramics heater. It is preferable that the heating of the mold is performed rapidly. The heating rate is usually 5 ° C.
/ Min or more, preferably 1 ° C / sec or more, more preferably 5 ° C / sec or more.

The temperature of the thermoplastic resin when injected into the mold is (Tg + 50) ° C. to (Tg +
200 ° C., more preferably (Tg + 70) ° C. to (Tg + 180) ° C., particularly preferably (Tg + 90) ° C. to (Tg + 150) ° C. When the resin temperature is lower than Tg + 50 ° C., distortion occurs in the molded optical molded product, the birefringence is increased, the optical characteristics are deteriorated, and the transfer accuracy of the mold surface is deteriorated. On the other hand, when the resin temperature is higher than Tg + 200 ° C.,
The resin may be colored yellow, or may be decomposed or burnt, and in any case, it is difficult to obtain a thin plate-shaped molded product aimed at by the present invention.

In the sheet-like molded product molded by the method of the present invention, when the mold temperature is lower than Tg, the cooling proceeds rapidly. The molecular orientation of the flow is greatest near the mold surface where the shear stress is maximum, and is the part that receives cooling first, so within a few seconds from the start of filling, this orientation layer becomes Tg or less, The molecular orientation is frozen without being relaxed, and causes optical distortion to remain. On the other hand, when the mold temperature is set to Tg or higher, the orientation layer near the mold surface is also maintained at Tg or higher, so that the molecular orientation is relaxed with time, and then cooled to Tg or lower to take out the molded product. No distortion remains. Even if the thickness distribution is in the molded product, the effect is exhibited.

The relaxation of the shear strain at the time of filling is preferably 50 nm or less, more preferably 10 nm or less, particularly preferably 5 nm or less, as represented by the retardation of the molded article. The relaxation time of the shear strain at the time of filling varies depending on the resin temperature and the molecular weight of the resin, but when the mold temperature is Tm (° C.) and the holding time (relaxation time) is t (second), logt + (Tm− Tg) /
The value of 20 is preferably 3.5 or more, more preferably 4 to 6, and particularly preferably 4.5 to 5.5. That is, the difference (° C.) between the mold temperatures Tm and Tg is 50 ° C.
In this case, the holding time t is preferably at least 10 seconds, particularly preferably at least 100 seconds. Also, the mold temperature Tm
When the difference (° C.) between Tg and Tg is 70 ° C., the holding time t is preferably at least 1 second, particularly preferably at least 10 seconds.

In the present invention, the mold filled with the resin is cooled rapidly after holding the mold filled with the resin for a predetermined time Tg or more. The cooling rate is not particularly limited, but is preferably 4 ° C./min or more. It is more preferably at least 20 ° C./min, particularly preferably 1 to 10 ° C./sec. As a cooling method,
A method using natural cooling or a method using a cooling device is used. However, a cooling method using a cooling device is more preferable in the method using natural cooling since the cooling rate may greatly change depending on environmental conditions.

The birefringence of the sheet-like molded article of the present invention obtained by the above method has a birefringence of 50 nm or less, preferably 30 nm or less.
Hereinafter, it is more preferably 10 nm or less, particularly preferably 5 nm or less. The thickness of the molded product is preferably 10 mm or less, more preferably 0.1 to 7 mm.
mm, more preferably 0.2 to 5 mm, particularly preferably 0.3 to 3 mm.

In the present invention, the shape of the thin plate-shaped molded product surface may be various shapes such as a flat plate, a tapered or stepped surface, a surface having irregularities, a flat surface, a curved surface, a free-form surface, a rectangle, and a disk. . The same effects as described above can be obtained with these thin plate-shaped molded products having various shapes, and the surface properties are also improved because the transfer of the mold surface is improved. In addition, the formation of a Fresnel lens shape having fine irregularities on the surface thereof, and a disk having fine irregularities formed by a stamper are particularly effective in improving the shape transfer. The thin plate-shaped molded product of the present invention can be used for a wide range of applications such as thin lenses such as Fresnel lenses, optical disks, and optical thin plates.

[0028]

The present invention will be described more specifically with reference to examples, reference examples and comparative examples, but the present invention is not limited to these examples.

Examples 1 to 5, Comparative Examples 1 and 2 As thermoplastic resins, intrinsic viscosity 0.55, Tg 171 ° C.
Norbornene resin (ARTON manufactured by Nippon Synthetic Rubber Co., Ltd.)
Was used. This resin was injected and maintained at a mold temperature while changing the mold temperature and the holding time at a resin temperature of 310 ° C. using a flat mold having a size of 200 × 150 × 1.5 mm. Thereafter, the molded product was taken out when the mold temperature reached 150 ° C. after cooling. In order to prevent sink marks on the surface of the molded product, the molten resin was kept for a fixed time after filling. In the mold, a sheathed heater was installed on each of the fixed side and the movable side, so that the mold could be heated. For cooling, the temperature-controlled oil was circulated inside the mold on both the fixed side and the moving side. After the molded article was taken out, the retardation at the center of the molded article was measured using an ellipsometer (manufactured by Mizojiri Optical). In molding, the heating rate of the mold surface was 10 ° C./min, and the mold cooling rate after molding was 7 ° C./min.
Minutes. Table 1 shows the evaluation results.

[0030]

[Table 1]

As can be seen from Table 1, the mold temperature is Tg +
Even if the temperature is sufficiently higher than 20 ° C. or the mold temperature is maintained with a sufficient holding time even at around Tg + 20 ° C. (Examples 1 to 5), a molded product having a small retardation and excellent optical properties can be obtained. . On the other hand, Comparative Example 1 is an example in which the mold temperature is lower than Tg, and good retardation cannot be obtained even if the holding time is sufficient. Comparative Example 2 is an example in which the holding time is short when the mold temperature is around Tg + 30 ° C., and the reduction of the retardation is insufficient.

Examples 6 to 8 and Comparative Examples 3 and 4 As a thermoplastic resin, a polycarbonate resin having a Tg of 148 ° C. (PANLIGHT AD5503 manufactured by Teijin Chemicals Ltd.) was used. This resin was prepared in the same manner as in Example 1 by 200 × 150
× 1.5 mm plate-shaped mold, resin temperature 260
Injection was performed while changing the mold temperature and the holding time under the condition of ° C. to maintain the mold temperature. After that, it is cooled and the mold temperature is
When the temperature reached ° C, the molded product was taken out. In order to prevent sink marks on the surface of the molded product, the molten resin was kept for a fixed time after filling.

[0033]

[Table 2]

Examples 9 to 11 and Comparative Examples 5 to 6 A heat-resistant polymethyl methacrylate resin having a Tg of 120 ° C. was used as a thermoplastic resin. This resin was injected in the same manner as in Example 1 using a 200 × 150 × 1.5 mm plate-shaped mold as described above, while changing the mold temperature and holding time at a resin temperature of 300 ° C. The mold temperature was maintained. Thereafter, the molded product was cooled and when the mold temperature reached 95 ° C., the molded product was taken out. In order to prevent sink marks on the surface of the molded product, the molten resin was kept for a fixed time after filling.

[0035]

[Table 3]

[0036]

According to the present invention, the birefringence of the obtained molded article can be reduced by setting the mold temperature and the holding time to specific conditions during the injection molding of the resin, and the conventional resin cannot be used. It can also be used for applications requiring high optical characteristics.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 69:00 B29L 7:00 11:00

Claims (4)

[Claims] 1. A thin plate-shaped molded article made of a thermoplastic resin, wherein the thermoplastic resin is filled in a mold heated to a temperature higher than a glass transition temperature (Tg) of the resin. A thin plate-like molded product characterized by having an optical distortion of 50 nm or less, which is obtained by cooling at a temperature maintained at a temperature of Tg or higher to alleviate the shear distortion at the time of filling and then cooling. 2. Injecting a thermoplastic resin into a mold heated to a mold surface temperature equal to or higher than Tg of the resin, and setting the mold temperature to Tg.
2. The method for forming a thin plate-shaped molded product according to claim 1, wherein cooling is performed after the above-described holding and relaxation of the shear strain at the time of filling are performed. 3. The thin plate-shaped molded article according to claim 1, wherein the thermoplastic resin is a thermoplastic norbornene-based resin. 4. The thin plate-shaped molded article according to claim 1, wherein the thermoplastic resin is at least one selected from an acrylic resin and a polycarbonate resin.