JPH03229704A - Material for optical card recording medium - Google Patents

Abstract

PURPOSE:To prepare the tittle material showing little birefringence, warpage of the plate by moisture absorption, and heat distortion and having an excellent resistance to impact and solvent by conducting the cast molding polymerization of a compsn. comprising a specific acrylate mixture, a specific rubberlike polymer, and a crosslinker in the presence of a radical polymn. initiator. CONSTITUTION:The title material is prepd. by the cast molding polymerization in the presence of a radical polymn. initiator of a compsn. comprising: 100 pts.wt. monomer mixture comprising 90-40wt.% alkyl acrylate of formula I (wherein R<1> and R<2> are each 1-2C alkyl) and 10-60wt.% acrylate of formula II (wherein R<3> is H or CH3; and R<4> is phenyl, benzyl, 4-20C alkyl, or 4-20C cycloalkyl); 0.5-10 pts.wt. rubberlike polymer having 0.5-5 carboxyl groups based on 100 monomer units constituting the polymer, a Tg of 0 deg.C or lower, a refractive index at the wavelength of D-line of 1.489-1.499, and a surface free energy gammac higher than that of a copolymer obtd. by copolymerizing the monomer mixture; and 0.1-10 pts.wt. crosslinker.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has low birefringence, little warping of the plate due to moisture absorption, thermal deformation, etc., excellent impact resistance, improved punching workability, and solvent resistance. The present invention relates to a material for optical recording media, particularly for optical card recording media, which has excellent properties.

[Conventional technology and its problems]

Transparent materials for optical recording media include polycarbonate,
Polymethyl methacrylate (PMMA), polystyrene, amorphous polyolefin, alloys of these polymers, and copolymers with acrylic monomers are known.

However, when these transparent materials are used as substrate materials for optical card recording media, polycarbonate has a drawback of high birefringence.

Further, in the case of PMMA, there is a drawback that warping of the plate occurs due to moisture absorption. In particular, materials used for optical disks and optical cards are prone to warpage due to moisture absorption and T
There are problems such as low g and easy thermal deformation.

There have been various proposals for improving acrylic resins such as PMMA. For example, in JP-A-58-11515, benzyl methacrylate and methyl methacrylate (M
Copolymer of methacrylic acid ester having an alkoxyl group having 10 or more carbon atoms and MMA in No. 59-122509, copolymer of MMA and No. 58-5318, No. 5
No. 8-5354 is a copolymer of cyclohexyl methacrylate and other vinyl monomers, No. 61-159408
In No. 61-141716, phenylcyclohexylhensyl methacrylate and M
Copolymer with MA, No. 61-183307, copolymer of ethylenically unsaturated monomer and MMA, No. 61-15
No. 2708 is a copolymer of MMA and MMA, and No. 63-17909 is a copolymer of cyclopentyl acrylate or methacrylate and MMA.
Attempts have been made to improve the drawbacks of PMMA by using copolymers with PMMA and the like.

However, although it is possible to obtain a substrate with low hygroscopicity through the various improvements described above, as is generally recognized with acrylic resins, it has the disadvantages of being easily broken due to low impact resistance, and poor punching processability of optical card substrates. However, it still has the drawback of poor solvent resistance, which is required when coating dye-based recording materials containing solvents.

The present inventors have already proposed a material for optical storage media that solves the above-mentioned drawbacks (Japanese Patent Application Nos. 1-180372).

A composition obtained by mixing a rubber-like polymer having a specific functional group and refractive index, and a crosslinking agent having a specific reactivity in a (meth)acrylate monomer mixture that yields a hydrophobic polymer, By polymerizing by cast molding in the presence of a radical polymerization initiator, a molded article with improved impact resistance and solvent resistance can be produced. This molded article has a sea-island structure, and it is thought that the rubber component forming the islands absorbs impact force, thereby satisfying the desired performance.

On the other hand, when applying a dye-based recording material to the surface of a molded object, the dispersion form of the resin phase and rubber phase on the surface of the molded object differs depending on the type of rubbery polymer used, making it difficult to apply the dye sufficiently uniformly. There are problems and they need to be resolved.

[Technical means to solve problems]

The present invention maintains the good transparency, light resistance, and low birefringence of PMMA, while improving its disadvantages of hygroscopicity, breakability, and solvent resistance.
Provided is a material for an optical card recording medium that has improved dye coating properties in a rubber-reinforced PMMA resin.

The present invention comprises: (a) 100 parts by weight of a mixture consisting of an alkyl acrylate represented by formula (1) and an acrylate represented by formula (2) in a weight ratio of 971 to 4/6; Contains 0.5 to 5 000H groups (carboxyl groups) per 100 monomer units in combination, has a glass transition temperature (Tg) of 0°C or less, and has a refractive index of 1.489 to 1 at the wavelength of the D line. .499 of the copolymer obtained by copolymerizing acrylate-+1 having a surface free energy (γC) shown in (a) above. A composition consisting of 0.5 to 10 parts by weight of a larger rubbery polymer and (c) 0.1 to 10 parts by weight of a crosslinking agent is polymerized by cast molding in the presence of a radical polymerization initiator. The present invention relates to the obtained optical card recording medium material.

The invention will be explained in more detail below.

In the present invention, specific examples of alkyl acrylates represented by formula (1) include methyl methacrylate (MM
A), ethyl methacrylate, etc. may be mentioned, but ethyl methacrylate is particularly preferred.

Specific examples of acrylates represented by formula (2) include:
Examples include isobutyl methacrylate, 2-ethylhexyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, cyclododecyl methacrylate, isobornyl methacrylate, and benzyl methacrylate.

These compounds can be used alone or in combination of two or more.

The rubbery polymer used in the present invention has 0 carboxyl groups per 100 monomer units of the polymer.
．． 1 to 5, the Tg is 0°C or less, the refractive index at the wavelength of the D line is in the range of 1.489 to 1.499, and the surface free energy (γC) is expressed by the above formulas (1) and (2).
γ of a copolymer obtained by copolymerizing acrylates shown in ). It is preferably larger and soluble in the acrylates represented by formulas (1) and (2).

Specific examples of rubber-like polymers include: (1) polymerization of ethyl acrylate, styrene, and acrylic acid or methacrylic acid in a specific monomer composition ratio; (2) polymerization of ethyl acrylate, benzyl acrylate, and acrylic acid or methacrylic acid in a specific monomer composition ratio; Examples include those obtained by polymerizing propyl acrylate, benzyl acrylate, and acrylic acid or methacrylic acid at a specific monomer composition ratio.

As a method for producing the rubbery polymer, known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be employed, but it is particularly preferable to produce the polymer by an emulsion polymerization method. .

The monomer composition ratio during polymerization varies depending on the monomers used, but the refractive index of the produced polymer is between 1°489 and 1.489°.
It is adjusted to fall within the range of 499. The weight average molecular weight of the polymer is preferably 50,000 or more, particularly preferably 200,000 or more in terms of polystyrene.

The above-mentioned rubbery polymer is used for the purpose of imparting impact resistance to a cast molded plate. During cast molding, the rubbery polymer undergoes phase separation and the molded plate forms a sea-island structure. If the refractive index of the rubbery polymer is within the range of 1.489 to 1.499, the long-lasting transparency of the acrylic resin will not be impaired.

The amount of the rubbery polymer added is 0.00 parts by weight per 100 parts by weight of the mixture of acrylates represented by formulas (1) and (2).
5 to 10 parts by weight is preferred. If it is less than 0.5 parts by weight, the effect of improving impact resistance will be small, and if it exceeds 10 parts by weight, impact resistance will be improved but surface hardness will decrease.

The crosslinking agent used in the present invention is not particularly limited, and commonly known crosslinking agents can be used.

Preferred crosslinking agents are intramolecular compounds, specific examples of which include glycidyl acrylate, glycidyl methacrylate, and the like.

During cast molding, these crosslinking agents react with carboxyl groups in the rubbery polymer to form a crosslinked structure within the rubber and strengthen the adhesion between the rubber interface and the bulk layer.

Still another preferred crosslinking agent has at least two radically polymerizable functional groups in its molecule, and
A small number of its functional groups are C-C=C groups (allyl groups).

Specific examples include allyl acrylate, allyl methacrylate, diallyl-〇-phthalate, diallyl-m
-Phthalate (diallyl isophthalate), diallyl-
Examples include phthalic acid esters such as p-phthalate, aliphatic diallyl ester compounds such as aromatic diallyl ether, glycerin diallyl ester, and aliphatic diallyl ether compounds. These allyl compounds are crosslinking agents with double bonds that have specific reactivity, and can prevent sink marks due to volume changes (shrinkage) during cast molding.

For the above-mentioned reasons, it is particularly preferable to use a combination of a vinyl compound having a glycidyl group in the molecule and a vinyl compound having an allyl group in the molecule as the crosslinking agent.

The amount of crosslinking agent added is 0.1 to 10 parts by weight per 100 parts by weight of the mixture of acrylates i represented by formulas (1) and (2).
Parts by weight are preferred. If the amount added is less than 0.1 parts by weight, the adhesion between the rubber interface and the bulk layer will be weak, resulting in a decrease in the impact resistance and solvent resistance of the molded plate, and if it exceeds 10 parts by weight, the solvent resistance will not be sufficient. However, the adhesion of the surface hardening agent decreases.

Examples of the radical initiator used in the present invention include organic peroxides such as Perbutyl-pv, Perbutyl-0, and Perbutyl-11 Perhexa-0 manufactured by NOF Corporation. These can be used alone or in a mixture of two or more.

During cast molding, weathering agents, mold release agents, and polymerization rate regulators (
Various additives such as chain transfer agents, polymerization inhibitors, etc.) and epoxidation reaction catalysts can be mixed. The polymerization temperature in cast molding is preferably 50 to 150°C, and the polymerization can be carried out while changing the polymerization temperature in multiple stages.

In the transparent plate obtained by the above cast molding, the formula (1
The copolymers of acrylates shown in ) and (2) form the bulk phase, and the rubbery polymer forms the dispersed phase. The surface free energy (Tc) of this copolymer and polymer was measured by the following method.

A copolymer of acrylates represented by formulas (1) and (2) or a rubbery polymer, which was separately synthesized by bulk polymerization, was dissolved in cyclohexanone at 5% by weight, and this solution was poured onto a glass plate by a tilting method. After application, dry at 110°C for 1 hour. Next, a wetting index standard solution (water-ethyl cellosolve system) was dropped onto this dry test piece, and the wetting angle θ was measured using a contact angle measuring device.
Measure. cos θ and surface tension T of wettability index standard solution
From the plot, T at COSθ=1 was determined by extrapolation, and the value of T was taken as the surface free energy (re) of the copolymer or polymer.

Various physical properties of the transparent plate obtained by cast molding were evaluated as follows.

Physical properties Measuring method Light transmittance: Measure the transmittance at 830 nm.

Hardness: Pencil scratch method for coating film with pencil hardness JIS K5401.

Impact strength, measured according to ASTM D256 (kg, c
m/cm).

Birefringence: 2P method (nm).

Water absorption rate; 100mm x 100mm Xo, 4mm
The plate was immersed in water at 23°C for 124 hours, and the rate of weight change (χ) before and after immersion was measured.

Solvent resistance: immerse the test piece in acetone at room temperature for 2 minutes,
Visually observe whitening on the surface of the test piece after drying.

Tg: DSC bending resistance, JIS [5400] Using a bending tester, attach a 2 mm diameter mandrel, insert a 50 mm wide, 0.4 mm thick test piece, and measure the angle at which the test piece breaks when bent. measurement.

Surface hardening: Spin code a commercially available ultraviolet curable hard coating agent to a thickness of 6 μm on a test piece, harden with a high pressure mercury lamp, and obtain JISKO202-8-
Base grain peeling test according to No. 12.

Spin code a 5% cyclohexanone solution of Subiron Blue (manufactured by Odugaya Kagaku ■) onto a test piece, and observe the application state with a microscope.

pigment Spreadability 〔Example〕 Examples of the present invention are shown below.

■ Synthesis example 1 of rubbery polymer used in the examples of the present invention 1i! equipped with a stirrer, reflux device, and dropping funnel! In a polymerization kettle, 510 g of deionized water and 2.6 g of sodium lauryl sulfate were added.
An aqueous solution consisting of 15.3 g of polyethylene glycol mono-P-octylphenyl ether and 0.35 g of potassium persulfate was charged, and the temperature was raised to 60° C. while nitrogen gas was blown into the kettle. When the internal temperature reached 60°C, a monomer mixture of 132.6 g of ethyl acrylate, 37.4 g of hensyl acrylate, and 1.7 g of acrylic acid was started to be added dropwise from the dropping funnel. Internal temperature 60°C
The dropwise addition was completed over a period of 5 hours while maintaining the temperature.

During this time, potassium persulfate was added in 5 portions of 0.1 g every hour after the start of polymerization. After completing the dripping, reduce the internal temperature to 6
Stirring was continued for an additional hour while maintaining the temperature at 0''C to complete the polymerization.

After diluting the polymer emulsion obtained above twice with deionized water, 100 g of common salt was added with stirring. The precipitated rubbery polymer was thoroughly washed with water and dried, and the dried polymer was dissolved in 800 cc of tetrahydrofuran. This solution was added dropwise to 3 Il of a mixed solution of 371 methanol/deionized water, and a rubbery polymer was purified by reprecipitation. The yield of the polymer after drying under reduced pressure was 149 g, and the refractive index was 1.
4914, weight average molecular weight in terms of polystyrene is 350
000, surface free energy (rc) is 34.9dy
n/cm.

■Synthesis example 2 of a rubbery polymer with a low Tc used in a comparative example of the present invention As a monomer mixture, 140 g of butyl acrylate, 30.7 g of styrene, 1.7 g of acrylic acid, and n-
A polymer was produced in the same manner as in Synthesis Example 1 except that 0.035 g of octyl mercaptan was used in the monomer mixture. The yield of polymer was 159 g and the refractive index was 1.49.
10. Weight average molecular weight in terms of polystyrene is 58,500
0, surface free energy Crt) is 29.5 dyn/
It was cm.

Example 1 120 g of methyl methacrylate, 80 g of cyclohexyl methacrylate, 1 g of glycidyl methacrylate, and 1 g of allyl methacrylate were mixed and thoroughly stirred. 8 g of the polymer produced in Synthesis Example 1 was added to this and stirred until completely dissolved. Next, 0.6 g each of Perbutyl Pv and Perbutyl I manufactured by NOF ■ were added as polymerization initiators. To the resulting solution, 20 mg of BG-170 (trade name) manufactured by Ippo Sha Yushi Kogyo (trade name) was added as a release agent, stirred thoroughly until uniform, and the solution was pressure-filtered through a filter with an average pore size of 1 uII+.

The filtered solution 41d was transferred to a glass cell (300 mm x 300 m) assembled with a gasket in advance.
m) After injecting the inside and completely removing the air inside, 6
A transparent plate having a thickness of 0.4o+m was produced by heating at 0°C for 4 hours and then at 125°C for 3 hours. The evaluation results of the obtained plates are shown in Table 1.

The Tc of the methacrylate copolymer forming the bulk phase of the transparent plate of Example 1 is 32.5 dyn/cm, which is smaller than the Tc of the rubbery polymer.

Example 2 Example 1 was repeated, except that instead of 80 g of cyclohexyl methacrylate, a mixture of 20 g of cyclohexyl methacrylate and 60 g of isobutyl methacrylate was used. The evaluation results are shown in Table 1.

The Tc of the methacrylate copolymer forming the bulk phase of the transparent plate of Example 2 is 32.0 dyn/cm, which is smaller than the Tc of the rubbery polymer.

Example 3 Example 2 was repeated except that 80 mg of Nofumer MSD (trade name) manufactured by NOF ■ was added to 100 g of solution as a chain transfer agent. The evaluation results are shown in Table 1.

Example 4 Instead of 80 g of cyclohexyl methacrylate, t-
Example 1 was repeated except that 80 g of butyl methacrylate was used. The evaluation results are shown in Table 1.

The Tc of the methacrylate copolymer forming the bulk phase of the transparent plate of Example 4 is 32.2 dyn/cm, which is smaller than the TC of the rubbery polymer.

Examples 5 and 6 Example 2 was repeated, except that instead of 1 g of allyl methacrylate, 2.0 g of allyl methacrylate was used in Example 5, and 4 g of diallyl 1-phthalate was used in Example 6. The evaluation results are shown in Table 1.

Comparative Example 1 To 200 g of methyl methacrylate, 0.6 g each of Perbutyl Pv and Perbutyl ■ were added as polymerization initiators, and 20+w of BG-170 (trade name) was added as a release agent.
Using the added solution, a transparent plate with a thickness of 0.4 mm was produced by injecting it into a glass cell in the same manner as in Example 1, heating it at 60 °C for 4 hours, and then heating it at 125 °C for 3 hours. .

The evaluation results of the obtained plates are shown in Table 2.

Comparative Example 2 Example 1 was repeated, except that instead of 8 g of the polymer obtained in Synthesis Example 1, 8 g of the polymer obtained in Synthesis Example 2 was used. The evaluation results are shown in Table 2.

In this case, Tc of the methacrylate copolymer forming the bulk phase is γ of the rubbery polymer. bigger.

Comparative Example 3 Comparative Example 2 was repeated except that 80 mg of Nofumer MSD (trade name) was added to 100 g of solution as a chain transfer agent. The evaluation results are shown in Table 2.

〔Effect of the invention〕

According to the present invention, it is possible to obtain a transparent material for optical card recording media that has little birefringence, plate warping due to moisture absorption, thermal deformation, etc., has excellent impact resistance and solvent resistance, and has good dye coating properties. .

Claims (1)

[Scope of Claims] (a) Consisting of an alkyl acrylate represented by formula (1) and an acrylate represented by formula (2), ▲Numerical formula,
There are chemical formulas, tables, etc.▼...(1) (In the formula, R^1 and R^2 each represent an alkyl group with 1 to 2 carbon atoms.) ▲There are mathematical formulas, chemical formulas, tables, etc.▼... -(2) (In the formula, R^3 represents a hydrogen atom or a methyl group, and R^4 represents a phenyl group, a benzyl group, an alkyl group having 4 to 20 carbon atoms, or a cycloalkyl group having 4 to 20 carbon atoms. ) 100 parts by weight of a mixture with a weight ratio of 9/1 to 4/6; (b) CO per 100 monomer units of the polymer;
Contains 0.5 to 5 OH groups (carboxyl groups), has a glass transition temperature (Tg) of 0°C or less, has a refractive index in the range of 1.489 to 1.499 at the wavelength of the D line, and has a free surface. 0.5 to 10 parts by weight of a rubbery polymer whose energy (γc) is larger than the γc of the copolymer obtained by copolymerizing the acrylates shown in (a) above, and (c) 0.1 part by weight of a crosslinking agent. -10 parts by weight of a composition, in the presence of a radical polymerization initiator, by cast molding to polymerize the composition for an optical card recording medium.