JPH10300901A - Lens for laser beam printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lens for laser beam printers which is excellent in heat resistance, low water absorptivity and balance of a double refractive index value by forming the lens of a polymer contg. specific structural units. SOLUTION: The lens for laser beam printers formed of the polymer contg. the structural units expressed by the formula is used. In the formula, R<1> denotes a hydrogen atom or to 25C hydrocarbon group, alicyclic hydrocarbon group or substd. hydrocarbon group, (n) denotes a positive integer. The polymer consisting of the repeating units expressed by the formula has the double refraction exhibiting the positive value. The methyl methacrylate polymer has the double refraction exhibiting the negative value. The lens for laser beam printers having the zero or nearly zero double refraction is thus obtd. The repeating components expressed by the formula of the polymer are preferably the components in which R<1> is a methyl group or of >=6C in terms of the heat resistance. Such components are more particularly preferably methyl, cyclohexyl, tricyclodecanyl and adamantyl groups.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens used for a laser beam printer.

[0002]

2. Description of the Related Art In recent years, high-performance transparent thermoplastic resins have been demanded in various fields including optical and automotive applications. In particular, the requirements for various characteristics of lens materials for obtaining clear images are increasing for lenses for laser beam printers. In particular, three items of low hygroscopicity, low birefringence, and high heat resistance are important characteristics.

At present, glass and plastic materials are mainly used as lens materials. However, glass materials cannot be said to be excellent in mechanical strength, mass productivity and cost.

In such a situation, as a lens material, polymethyl methacrylate (PMMA), which is a transparent thermoplastic resin, is mainly used in terms of strength and productivity. Although this polymethyl methacrylate has a low birefringence, it has problems in that it has high water absorption and low heat resistance. That is, since a dimensional change is caused by water absorption, distortion occurs when the laser beam is projected onto the drum, and the image quality is likely to deteriorate. Also, dimensional changes occur due to heat. Polycarbonate is known as a resin having excellent heat resistance and water absorption.

[0005]

However, since polycarbonate has a large birefringence, there is a problem in that when used as a lens material for a laser beam printer, projection light is dispersed. In general, as the performance of lenses increases, the birefringence must be reduced, and a method of improving heat resistance and water absorption at the expense of birefringence is not practical.

SUMMARY OF THE INVENTION An object of the present invention is to provide a lens for a laser beam printer having a good balance of heat resistance, low water absorption and birefringence.

[0007]

The gist of the present invention resides in a lens for a laser beam printer molded from a polymer containing a structural unit represented by the following general formula (1).

[0008]

Embedded image

Wherein R ¹ represents a hydrogen atom, a hydrocarbon group having 1 to 25 carbon atoms, an alicyclic hydrocarbon group or a substituted hydrocarbon group, and n represents a positive integer.

A polymer comprising a repeating unit represented by the general formula (1) has a positive value of birefringence. The methyl methacrylate polymer has a negative value of birefringence. That is, the present invention provides a lens for a laser beam printer whose birefringence is zero or nearly zero.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The content of the repeating unit of the general formula (1) in the polymer used in the present invention is not particularly limited. However, considering the balance among heat resistance, water absorption and birefringence, it is 20% by weight. It is preferably at least 30% by weight, more preferably at least 30% by weight. If the content is too small, the heat resistance tends to be insufficient.

As the repeating unit component of the general formula (1) of the polymer, R ¹ is preferably a methyl group or a compound having 6 or more carbon atoms from the viewpoint of heat resistance, and methyl, cyclohexyl, tri Particularly preferred are cyclodecanyl and adamantyl groups.

The components other than the repeating unit of the general formula (1) of the polymer include (meth) acrylates such as methyl methacrylate and methyl acrylate, styrene, α-methylstyrene, acrylonitrile, and fluorinated methacrylate. Although exemplified, methyl methacrylate is most preferable in terms of transparency and birefringence.

The lens for a laser beam printer of the present invention has two surfaces, a light incident surface and a light exit surface, as lens surfaces. In order to project the laser light diffused on the YZ plane in FIG. 1 onto the drum surface without distortion, the light incident surface and the light emission surface are curved.

The birefringence of this lens is preferably 60 × 10 ^-6 or less, more preferably 40 × 10 ^-6 or less. If the birefringence is too high, its use in high performance laser beam printers is limited. The lens for a laser beam printer of the present invention can be formed by an injection molding method or an injection compression molding method.

[0016]

The present invention will be described below in detail with reference to examples. The "%" used in the examples is all% by weight.
It is.

The molecular weight of the polymer was determined by the GPC method (solvent: chloroform) using PMMA as a standard. The polymer composition was quantified by 1H NMR (solvent: chloroform-d, measurement temperature: 60 ° C.).

Saturated water absorption The injection molded product was dried at 90 ° C, weighed, and then immersed in warm water at 25 ° C until the weight reached equilibrium. The weight after the equilibrium was measured and determined by the following equation. Saturated water absorption (%) = [(water absorption-dry weight) / dry weight] × 100 Birefringence The value of a light having a wavelength of 546 nm was measured using a polarizing microscope. The value obtained by dividing the measured value by the thickness is the birefringence. VICAT softening temperature Measured according to ASTM D1525.

Example 1 In a flask having a capacity of 2 liters, 824 g (4 mol) of tricyclodecanyl acrylate, 160 g (4 mol) of paraformaldehyde having a purity of 75%, and 60 g of 1,4-diazabicyclo [2,2,2] octane (0.53 g) mol), p-methoxyphenol 616mg, t-
120 g of butyl alcohol while air bubbling
The reaction was performed at 80 ° C. for 5 days. After the completion of the reaction, the reaction solution was poured into 3 L of methanol and stirred for 30 minutes. Then, the mixed solution was allowed to stand at −20 ° C. overnight to obtain 712 g (yield: 79.2%) of bis (α-hydroxymethylacrylic acid tricyclodecanyl) ether as white crystals.

In a 5 L flask containing 2500 ml of toluene as a solvent, 200 g of bis (α-hydroxymethyl acrylate tricyclodecanyl) ether and 300 g of methyl methacrylate (MMA) were put and dissolved. To this solution was added 3 g of pertetra A (manufactured by NOF Corporation, purity: 20 wt.%) As an initiator, and the mixture was stirred for 40 minutes while purging with nitrogen. Thereafter, the mixture was heated to 95 ° C. to start the polymerization, and the polymerization was performed for 7 hours.

This reaction solution was put into a large amount of methanol to precipitate a polymer, which was filtered and washed with methanol. This is vacuum dried to obtain 455 g of a powdery polymer (yield:
91%).

This polymer was injected into an injection molding machine (Toshiba Machine Co., Ltd.)
Supplied by the company IS-100), cylinder temperature 270 ° C, mold temperature 100 ° C, injection pressure 1400kg / cm2, total length 80mm, width 3mm (central part 15mm), thickness 12m
m toric lens, total length 30 mm, width 3 mm
(Central part 7 mm) A spherical lens having a thickness of 12 mm was molded.

When a part of the obtained lens was cut and its physical properties were measured, the following favorable results were obtained.

Molecular weight of polymer: Mn = 98,000 Polymer composition: tricyclodecanyl ester / methyl methacrylate = 40/60 Saturated water absorption: 1.1% Birefringence: 10 × 10 ^-6 VICAT Softening temperature: 140 ° C. Yellowness Index (YI value): 1.4.

Comparative Example 1 Using a polycarbonate resin (AD9000TG manufactured by Teijin Chemicals Limited), a lens for a laser beam printer was molded under the molding conditions of a cylinder temperature of 300 ° C., a mold temperature of 110 ° C., and an injection pressure of 1600 kg / cm 2. When a part of the obtained lens was cut and its physical properties were measured, the saturated water absorption was 0.5%, and the VIC
AT softening temperature was excellent at 155 ° C, but birefringence was 100 × 10
^It was as big as ^-6 .

Comparative Example 2 Using polymethyl methacrylate (Acrypet VH manufactured by Mitsubishi Rayon Co., Ltd.), cylinder temperature 260 ° C., mold temperature 8
A lens for a laser beam printer was molded under molding conditions of 0 ° C. and an injection pressure of 1400 kg / cm 2. When a part of the obtained lens was cut and its physical properties were measured, the birefringence was
Although it was excellent at 20 × 10 ⁻⁶ , the VICAT softening temperature was as low as 115 ° C. and the saturated water absorption was as high as 2.1%.

[0027]

The lens for a laser beam printer of the present invention has an excellent balance among heat resistance, water absorption and birefringence, and can be used as a lens for a next-generation laser beam printer.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an optical system of a laser beam printer.

[Explanation of symbols]

 1 Toric lens 2 Spherical lens

Claims (1)

[Claims] 1. A lens for a laser beam printer molded from a polymer containing a structural unit represented by the following general formula (1). Embedded image (Wherein, R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 25 carbon atoms or an alicyclic hydrocarbon group, a substituted hydrocarbon group,
n represents a positive integer. )