JP2000090495A - Optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical disk having excellent tilt characteristics. SOLUTION: This optical disk is produced by laminating optical disk substrates on both faces of an adhesive layer. The adhesive layer consists of an acrylic adhesive compsn. The acrylic adhesive compsn. is prepared from an acrylic copolymer comprised of a monomer mixture containing, as main components, (A) acrylate monomers, (B) monomers having carboxyl groups, and at least either (C) hydrophobic acrylate monomers or (D) vinyl acetate monomers. In the acrylic adhesive compsn., the amt. of the component (A) is 50 to 95 wt.% of the whole monomer mixture, the amt. of the component (B) is 1 to 18 wt.% of the whole monomer mixture. When the component (C) is used, its amt. is 3 to 40 wt.%, and when the component (D) is used, its amt. is 3 to 40 wt.% of the whole monomer mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc having two optical disc substrates bonded to both sides of a pressure-sensitive adhesive layer (double-sided pressure-sensitive adhesive sheet).

[0002]

2. Description of the Related Art Generally, an optical disk is composed of two optical disk substrates bonded to each other.
At least one of the optical disk substrates has a recording layer. Such an optical disk substrate bonding method is disclosed, for example, in Japanese Patent Application Laid-Open No. 61-8 / 1986.
As disclosed in Japanese Patent No. 0534, a method in which an adhesive is sandwiched between two optical disk substrates and both optical disk substrates are pressed together and bonded together, an ultraviolet curable adhesive is inserted between the two optical disk substrates, There is a method of curing and bonding the ultraviolet curable adhesive, a method of sandwiching a thermoplastic sheet between two optical disk substrates, and bonding the two optical disk substrates by heating.

However, the above-described bonding method using an adhesive requires a troublesome work of applying the adhesive to the optical disk substrate, and thus has a disadvantage in that the workability is poor. Moreover, it is difficult to apply the adhesive evenly to the optical disk substrate, and the parallelism of the bonded optical disk substrates may be deteriorated, or air may be mixed into the adhesive and air bubbles may be generated at the joints. There is also a problem. Further, when the two optical disk substrates are bonded and pressed, the adhesive protrudes from the peripheral portion of the optical disk substrate to generate burrs, which necessitates a deburring operation, and is inferior in productivity and workability. There are also disadvantages. In particular, when the above-mentioned ultraviolet curable adhesive is used, when the adhesive is cured, there is a disadvantage that the adhesive shrinks and adversely affects the recording layer of the optical disk substrate. On the other hand, the laminating method using the above-mentioned thermoplastic sheet has a drawback that heat resistance is inferior, and causes a problem when used in a vehicle such as a car navigation system and a CD autochanger, which have been growing in demand in recent years.

Therefore, in recent years, a double-sided pressure-sensitive adhesive sheet such as a pressure-sensitive pressure-sensitive adhesive tape has been used instead of the adhesive or the thermoplastic sheet. The use of the double-sided pressure-sensitive adhesive sheet has the advantage that the thickness of the optical disk can be determined in advance, the smoothness is improved, and the recording layer of the optical disk substrate is not adversely affected.

[0005]

However, the optical disk must also have excellent tilt characteristics, and an optical disk bonded using the double-sided pressure-sensitive adhesive sheet has a disadvantage that the tilt characteristics are inferior. here,
The tilt characteristic is a characteristic representing a shake angle during rotation of the optical disk. If the tilt characteristic is poor, a laser beam hitting the optical disk does not correctly return to the detector, causing a reading error.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an optical disk having excellent tilt characteristics.

[0007]

In order to achieve the above object, an optical disk of the present invention is an optical disk in which an optical disk substrate is bonded to both sides of an adhesive layer, wherein the adhesive layer has the following acrylic-based property. It is configured to be formed of the pressure-sensitive adhesive composition (X). (X) Acrylic copolymer mainly containing a monomer mixture containing at least one of the following components (C) and (D) as an essential component together with the following components (A) and (B): Wherein the content of the component (A) is 50 to 95% by weight of the whole monomer mixture, and the content of the component (B) is 1% of the whole monomer mixture.
１８18% by weight, the content when the component (C) is used is 3-40% by weight of the whole monomer mixture, and the content when the component (D) is used is 3） 40% by weight of the whole monomer mixture. An acrylic pressure-sensitive adhesive composition set to ４０40% by weight. (A) An acrylate monomer represented by the following general formula (1). CH ₂ = CR ¹ COOR ² (1) (wherein, R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkyl group having 4 to 14 carbon atoms.) (B) Carboxyl group-containing monomer . (C) A hydrophobic acrylate monomer represented by the following general formula (2). CH ₂ ＣＲCR ³ COOR ⁴ (2) (wherein, R ³ represents a hydrogen atom or a methyl group, and R ⁴ represents a hydrophobic organic group having an alicyclic structure.) (D) Vinyl acetate monomer body.

In the present invention, the content when the component (C) is used refers to the content when the component (C) is contained in the monomer mixture. The purpose is to exclude cases where no component (C) is contained. Similarly, (D)
The content when the component is used refers to the content when the component (D) is contained in the monomer mixture, and is intended to exclude the case where the component (D) is not contained in the monomer mixture. .

That is, the inventor has conducted intensive studies to obtain an optical disc having excellent tilt characteristics. In the course of this research, we focused on the pressure-sensitive adhesive layer that bonds two optical disk substrates, and repeated research focusing on the material for forming the pressure-sensitive adhesive layer. As a result, together with the specific acrylate monomer (A component) and the carboxyl group-containing monomer (B component), the specific hydrophobic acrylate monomer (C component) and the vinyl acetate monomer (D component) An acrylic pressure-sensitive adhesive composition using an acrylic copolymer containing a monomer mixture containing at least one of the essential components as a main component, wherein the content of each component in the monomer mixture is specified. The special acrylic pressure-sensitive adhesive composition (X) set in the range was determined. The inventors have found that an optical disc in which an optical disc substrate is bonded to both sides of a pressure-sensitive adhesive layer formed of this special acrylic pressure-sensitive adhesive composition (X) has excellent tilt characteristics, and arrived at the present invention.

[0010]

Next, embodiments of the present invention will be described in detail.

[0011] The optical disk of the present invention is formed by bonding two optical disk substrates to both surfaces of an adhesive layer. The optical disc of the present invention is most characterized in that the pressure-sensitive adhesive layer is formed of a special acrylic pressure-sensitive adhesive composition (X).

The optical disk substrate is not particularly limited as long as it is used for an ordinary optical disk, but it is preferable to use an optical disk substrate having a protective layer formed on a recording layer. The recording layer may be formed only on one of the two optical disc substrates, and the protective layer formed on the recording layer may be omitted.

The shape of the pressure-sensitive adhesive layer is not particularly limited as long as it is formed of a special acrylic pressure-sensitive adhesive composition (X). it can. Examples of the double-sided PSA sheet include a double-sided PSA sheet without a support (a double-sided PSA sheet without a support) and a double-sided PSA sheet with a support (a double-sided PSA sheet with a support). The support-less double-sided pressure-sensitive adhesive sheet is prepared by, for example, directly applying the acrylic pressure-sensitive adhesive composition (X) on a polyethylene terephthalate (PET) separator, drying, and then drying the PET.
It can be manufactured by peeling off the separator made of the resin. On the other hand, the support-containing double-sided pressure-sensitive adhesive sheet, for example,
It can be produced by directly photographing the acrylic pressure-sensitive adhesive composition (X) on both surfaces of the support. Alternatively, it can be prepared by transferring the acrylic pressure-sensitive adhesive composition (X) applied on the separator to both surfaces of the support. The support is not particularly limited, but a plastic film having an appropriate tensile strength is preferable, and examples thereof include a polyethylene film and a PET film.

The above-mentioned pressure-sensitive adhesive layer (double-sided pressure-sensitive adhesive sheet)
Is preferably not more than 0.12 mm, particularly preferably not more than 0.08 mm, in the holding force test under wet heat. In addition, the deviation | distance of the said holding | maintenance force test under moist heat can be measured as follows. That is, first, the above-mentioned pressure-sensitive adhesive layer (double-sided pressure-sensitive adhesive sheet) was heated at 80 ° C. ×
Store for 4 days in an environment of 80% RH. Then, a bake plate is adhered to one surface of the pressure-sensitive adhesive layer (double-sided pressure-sensitive adhesive sheet) as an adherend (adhesive area: 20 mm long × 10 m wide)
m), a load of 500 g and a temperature of 80 ° C. × 80% RH.
After holding for a time, the displacement distance between the pressure-sensitive adhesive layer (double-sided pressure-sensitive adhesive sheet) and the bake plate is measured with a microscope. The other surface of the pressure-sensitive adhesive layer (double-sided pressure-sensitive adhesive sheet) is provided with PET for reinforcement.
It is preferable to attach a substrate such as a film.

The special acrylic pressure-sensitive adhesive composition (X), which is used as a material for forming the pressure-sensitive adhesive layer, is used together with a specific acrylate monomer (component A) and a carboxyl group-containing monomer (component B). Of a hydrophobic acrylate monomer (C
Component) and a vinyl acetate monomer (component (D)) as an essential component. The acrylic pressure-sensitive adhesive composition (X) is characterized in that the content of each component in the monomer mixture is set in a specific range. In the present invention, "acrylic copolymer containing a monomer mixture as a main component"
This is intended to include the case where the acrylic copolymer comprises only a monomer mixture.

The specific acrylate monomer as the component A is represented by the following general formula (1). These may be used alone or in combination of two or more. CH ₂ = CR ¹ COOR ² (1) (wherein, R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkyl group having 4 to 14 carbon atoms.)

In the general formula (1), examples of the alkyl group having 4 to 14 carbon atoms represented by R ² include a butyl group, an isobutyl group, an isoamyl group, a hexamyl group, a hexyl group, a heptyl group, a 2-heptyl group. Examples include an ethylhexyl group, an isooctyl group, an isononyl group, and an isodecyl group.

Preferred specific examples of the acrylate-based monomer (component A) represented by the above general formula (1) are those wherein R ¹ is a hydrogen atom and R ² is a 2-ethylhexyl group.
-Ethylhexyl acrylate.

The content of the specific acrylate monomer (component A) is 50 to 95% by weight of the whole monomer mixture.
(Hereinafter abbreviated as “%”), and is preferably 60 to 90%. That is, if the content of the component A is less than 50%, it is difficult to obtain an appropriate initial adhesive strength, and if it exceeds 95%, the adhesive property becomes poor, and the composition is not suitable for punching.

The carboxyl group-containing monomer as component B includes acrylic acid, methacrylic acid, itaconic acid,
Maleic acid, crotonic acid and the like can be mentioned. These may be used alone or in combination of two or more.

The carboxyl group-containing monomer (component B)
Must be set in the range of 1 to 18% of the entire monomer mixture, and is preferably 3 to 12%. That is, if the content of the B component is less than 1%, the adhesive strength is reduced, and if it exceeds 18%, the composition becomes too hard and has poor pressure sensitivity, and the adhesive strength is reduced.

The specific hydrophobic acrylate monomer as the component C is represented by the following general formula (2). CH ₂ ＣＲCR ³ COOR ⁴ (2) (wherein, R ³ represents a hydrogen atom or a methyl group, and R ⁴ represents a hydrophobic organic group having an alicyclic structure.)

In the general formula (2), the hydrophobic organic group having an alicyclic structure represented by R ⁴ may be two or more if the alicyclic structure is hydrophobic. And may have a substituent in the alicyclic structure portion. Examples of such a hydrophobic acrylate monomer (component C) include cyclohexyl acrylate, cyclopentyl acrylate, isobornyl acrylate, t-butyl cyclohexyl acrylate, cyclohexyl methacrylate, cyclopentyl methacrylate, isobornyl methacrylate, and t-butyl. And cyclohexyl methacrylate. These may be used alone or in combination of two or more.

When the above-mentioned specific hydrophobic acrylate monomer (component C) is used, the content of the component C must be set in the range of 3 to 40% of the whole monomer mixture, and is preferably used. 5 to 30%. That is, when the content of the C component is less than 3%, it becomes difficult to obtain a holding power under moist heat,
If it exceeds 40%, it is difficult to obtain a proper initial adhesive strength. By setting the content of the C component in the above-mentioned predetermined range, the hydrophobicity of the polymer (acrylic copolymer) is improved, and the deformation of the pressure-sensitive adhesive composition is small under a wet heat environment in a tilt test. Thus, good tilt characteristics can be obtained. The above-mentioned specific hydrophobic acrylate monomer (component C) can be omitted when the following vinyl acetate monomer (component D) is used.

When the above-mentioned vinyl acetate monomer (D component) is used, the content of the D component is 3 to 40% of the whole monomer mixture.
%, Preferably in the range of 5 to 30%
It is. That is, if the content of the D component is less than 3%, it is difficult to obtain a holding force under moist heat, and if it exceeds 40%, it is difficult to obtain a proper initial adhesive strength. By setting the content of the component D in the above-mentioned predetermined range, the low molecular weight component of the polymer (acrylic copolymer) is reinforced by vinyl acetate, and the deformation of the pressure-sensitive adhesive composition under moist heat is reduced. Less likely to occur. The vinyl acetate monomer as the component D can be omitted when the above-mentioned specific hydrophobic acrylate monomer (component C) is used.

In addition, in addition to the above-mentioned components, additives such as tackifier may be appropriately added to the above-mentioned monomer mixture in order to improve adhesiveness.

The above-mentioned special acrylic pressure-sensitive adhesive composition (X)
Can be manufactured, for example, as follows.
That is, first, together with a specific acrylate monomer (A component) and a carboxyl group-containing monomer (B component), a specific hydrophobic acrylate monomer (C component) and a vinyl acetate monomer (D component) ) Is prepared, and these are mixed at a specific ratio to obtain a monomer mixture. Next, the monomer mixture is copolymerized by solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, or the like to obtain an acrylic copolymer. In this case, if necessary, a polymerization initiator such as azobisisobutyronitrile can be used. Then, a cross-linking agent is added to the acrylic copolymer as needed, and the holding power under moist heat is adjusted, whereby the intended acrylic pressure-sensitive adhesive composition (X) can be obtained. The crosslinking agent is not particularly limited as long as it causes a crosslinking reaction with the acrylic copolymer.

The optical disk of the present invention uses the acrylic pressure-sensitive adhesive composition (X) thus obtained,
After forming a pressure-sensitive adhesive layer (double-sided pressure-sensitive adhesive sheet) according to the above-described method, it can be manufactured by bonding optical disk substrates to both surfaces thereof.

The thickness of the pressure-sensitive adhesive layer (double-sided pressure-sensitive adhesive sheet) is limited by the total thickness of the optical disk including the optical disk substrate, the recording layer and the protective layer, and is usually about 35 to 60 μm. It can be changed as appropriate by changing the thickness of the layer, the protective layer, or the standard of the total thickness of the optical disk.

Next, examples will be described together with comparative examples.

[0031]

Example 1 A flask was charged with 75 parts of 2-ethylhexyl acrylate (component A), 5 parts of acrylic acid (component B), and 20 parts of isobornyl acrylate (component C) in a 50% base using ethyl acetate as a solvent. Further, 0.2 parts of azobisisobutyronitrile was added as a polymerization initiator,
Polymerization was carried out at 0 ° C. for about 3 hours. Ethyl acetate was dropped on the way to give a final base of 30%. Thereafter, aging was performed at 76 ° C. for about 2 hours to obtain an acrylic polymer. Next, 1,3 was added to the obtained acrylic polymer as a crosslinking agent.
1.0 part of -bis (N, N-diglycidylaminomethyl) cyclohexane (Tetrad C, manufactured by Mitsubishi Gas Chemical Company) was blended to prepare an acrylic pressure-sensitive adhesive composition. And
The acrylic pressure-sensitive adhesive composition was applied on a PET separator prepared in advance so that the film thickness after drying was 50 μm, and then dried at 120 ° C. for 3 minutes using a dryer.
Further, another PET separator was bonded to the other surface of the pressure-sensitive adhesive layer to prepare a double-sided pressure-sensitive adhesive sheet (a support-less double-sided pressure-sensitive adhesive sheet) provided with PET separators on both surfaces.
In producing the optical disk, the PET separator is peeled off from both sides of the double-sided pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet without a support), and then the optical disk substrate is bonded to the peeled surface.

[0032]

Examples 2 to 7 and Comparative Examples 1 to 4 The mixing ratio of each component was changed as shown in Table 1 below. Otherwise, Example 1
A double-sided PSA sheet (support-less double-sided PSA sheet) was obtained in the same manner as in Example 1.

[0033]

[Table 1]

Using the thus obtained double-sided PSA sheets of Examples and Comparative Examples, the gel fraction, the displacement distance in the holding power test under moist heat, the adhesive strength, the punching property, and the amount of change in tilt were as follows. Was measured according to the standard of The results are shown in Table 2 below. The measurement was made using PET.
The test was performed in a state where the separator made of the resin was peeled off.

[Gel Fraction] The pressure-sensitive adhesive composition was dissolved in ethyl acetate, and the ratio of the unelutable component to the whole was determined.

[Deviation Distance of Holding Force Test under Moist Heat] The double-sided pressure-sensitive adhesive sheet was stored for 4 days in an environment of 80 ° C. × 80% RH. Then, a bake plate is adhered to one surface of the double-sided pressure-sensitive adhesive sheet as an adherend (adhesive area: 20 mm in length × 10 mm in width), and is held for 1 hour under the conditions of a load of 500 g and 80 ° C. × 80% RH. The displacement distance between the adhesive sheet and the bake plate was measured with a microscope. A PET film was bonded to the other surface of the double-sided pressure-sensitive adhesive sheet for reinforcement. Then, those with a displacement distance of 0.08 mm or less were marked with ◎, those with a displacement exceeding 0.08 mm and 0.12 mm or less were marked with ○, and those with a displacement distance exceeding 0.12 mm were marked with x.

[Adhesive Strength] On one side of the double-sided pressure-sensitive adhesive sheet,
An SUS304BA plate was adhered as an adherend, and the 180 ° peeling adhesive force was measured using a universal tensile test at a sample width of 20 mm and a tensile speed of 50 mm / min. And the adhesive strength is 3
Those with 50 g / 20 mm or more are ○, 350 g / 20 mm
Those less than were indicated as x.

[Punching Property] A double-sided pressure-sensitive adhesive sheet was punched out into a donut shape having an outer diameter of 119 mm and an inner diameter of 23 mm using a Thomson mold by half-cutting, scraping was performed, and the adhesive-cutting property was observed. Then, those with good adhesive breakage were indicated by ○, and those with some glue re-adhering and being dragged out and showing the glue running out were indicated by x.

[Amount of Tilt Change] After the PET separator was peeled off from both sides of the double-sided pressure-sensitive adhesive sheet, an optical disk substrate was bonded to the peeled surface to produce an optical disk. This optical disk was stored in a horizontal state under a moist heat environment of 80 ° C. × 80% RH for 3 days. Then, using a tilt tester,
The amount of change in the radial tilt value before and after storage was measured.
The tilt test was performed at a rotation speed of 120 rpm while the center of the disk was pressed with a load of 200 g, with a diameter of 33 mm, and the tilt angles at a radius of 23 mm and a radius of 58 mm were measured, and the average value was defined as the tilt value. When the amount of tilt change is 0.35 deg or less, ○, 0.35 deg
Those exceeding g were indicated as x.

[0040]

[Table 2]

From the results shown in Table 2, all the products of Examples are excellent in all the properties such as the gel fraction, the deviation distance in the holding power test under moist heat, the adhesive strength, the punching property, and the change in tilt. Understand.

On the other hand, it can be seen that all of the comparative examples are inferior in any of the above-mentioned characteristics, and none of them are excellent in all the characteristics. In particular, since the content of 2-ethylhexyl acrylate (component A) exceeds the predetermined range, the product of Comparative Example 1 has poor paste-cutting properties and poor punching properties. Since the content of acrylic acid (component B) exceeds the predetermined range, the product of Comparative Example 2 becomes too hard and the adhesive strength is reduced. It can be seen that the product of Comparative Example 3 is inferior in adhesive strength because the content of 2-ethylhexyl acrylate (component A) is lower than the predetermined range and the content of vinyl acetate (component D) exceeds the predetermined range. It can be seen that the product of Comparative Example 4 had a large deviation distance in the holding power test under wet heat because the content of vinyl acetate (D component) was below the predetermined range.

[0043]

As described above, the optical disk of the present invention
An optical disk substrate is bonded to both surfaces of the adhesive layer. Then, the pressure-sensitive adhesive layer is formed along with a specific hydrophobic acrylate monomer (C) together with a specific acrylate monomer (component A) and a carboxyl group-containing monomer (component B).
Component) and a vinyl acetate monomer (Component D) as an essential component. Since it is formed of the special acrylic pressure-sensitive adhesive composition (X) in which the content of each component in the monomer mixture is set in a specific range, it has excellent tilt characteristics.

Claims (2)

[Claims] An optical disk comprising an adhesive layer and optical disk substrates bonded to both surfaces of the adhesive layer, wherein the adhesive layer is formed of the following acrylic adhesive composition (X). . (X) Acrylic copolymer mainly containing a monomer mixture containing at least one of the following components (C) and (D) as an essential component together with the following components (A) and (B): Wherein the content of the component (A) is 50 to 95% by weight of the whole monomer mixture, and the content of the component (B) is 1% of the whole monomer mixture.
１８18% by weight, the content when the component (C) is used is 3-40% by weight of the whole monomer mixture, and the content when the component (D) is used is 3） 40% by weight of the whole monomer mixture. An acrylic pressure-sensitive adhesive composition set to ４０40% by weight. (A) An acrylate monomer represented by the following general formula (1). CH ₂ = CR ¹ COOR ² (1) (wherein, R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkyl group having 4 to 14 carbon atoms.) (B) Carboxyl group-containing monomer . (C) A hydrophobic acrylate monomer represented by the following general formula (2). CH ₂ ＣＲCR ³ COOR ⁴ (2) (wherein, R ³ represents a hydrogen atom or a methyl group, and R ⁴ represents a hydrophobic organic group having an alicyclic structure.) (D) Vinyl acetate monomer body. 2. The optical disc according to claim 1, wherein the pressure-sensitive adhesive layer formed of the acrylic pressure-sensitive adhesive composition (X) has the following property (α). (Α) The deviation distance of the holding force test under wet heat is 0.12 mm or less.