JPS613340A - Adhering method of optical disk - Google Patents

Abstract

PURPOSE:To eliminate uneven recording sensitivity and to improve the reliability of a combined disk by pressurizing the recording surface of an optical disk by means of a heating roll from the release paper side of a planar hot melt so that the adhesive agent is thermally transferred to said surface. CONSTITUTION:The planar hot melt adhesive agent is heated to melt by the heating transfer roll 3 from the release paper side and is transferred onto the reflective surface of the disk. A pair of such disks are laminated in a manner that the adhesive agent coated sides face each other; thereafter the disks are press-bonded to each other within the open time. Since the adhesive agent coated surfaces have a good release property from the release paper, said surfaces are smooth and therefore no foam enters the adhered surfaces of the disk and the deterioration such as warpage and waving of the disk with time is obviated. The uneven sensitivity is eliminated as well. Melting of only the required quantity of the adhesive agent suffices and therefore the double-faced disk is obtd. with good workability.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an adhesive method for bonding together a pair of optical discs such as playback-only video discs and compact discs that reproduce information using laser light, and disc memories that can record and playback (erase). Regarding the method.

[Technical background of the invention and its problems]

In general, video discs and compact discs 2
Optical disk substrates such as memories are made by full injection molding of thermoplastic resin, especially acrylic resin or polycarbonate.

The substrate produced in this manner has excellent transferability of information patterns, substrate transparency, and heat resistance, and has low aqueous properties and birefringence, making it excellent as a substrate for optical disks.

An optical disc that can only be played on one side has a structure in which a metal reflective film is provided on the recording surface of the substrate by vapor deposition or sputtering, and an organic protective film is further applied thereon. (See Figure 2) Double-sided playable optical discs have a structure in which two optical discs each have a recording surface with a metal reflective film on only one side, the recording surfaces of which are rotated relative to each other, and then glued together using hot melt adhesive. By adopting such a structure, the recording capacity of the optical disk is doubled, and economic deformation due to changes in environmental temperature and humidity is reduced. (See Figure 3) As a hot melt adhesive suitable for this purpose, JP-A-58-1
For 08044, l) Softening point: 140'C or less 2) Normal state tensile adhesive strength 20°C I Kg/cnt or more 3) Melt viscosity I
A material having a characteristic of 1 ooop or less at Z160°C has been proposed.

Moreover, as a method of applying this adhesive, Japanese Patent Application Laid-Open No. 58-6
As seen in 536, a roll coater is generally used.

However, when applied with a roll coater, there is a drawback that the surface of the applied film is not smooth. This is because, as shown in Figure 4, when the hot melt film is transferred from the roll surface to the recording surface of the disk that is the adherend, the transferred film moves back toward the roll due to the adhesiveness of the hot melt itself. If the hot melt adhesive cannot be applied smoothly on the recording surface of the disc, when a pair of discs are pasted together, air bubbles will be trapped in the adhesive layer, causing the resulting stretched disc (double-sided playback i: An economical variant of iT ship disks is available. Moreover, since it does not look good, it is a problem in terms of product value.

In the case of a disc memory type in which optical discs can be recorded, the presence or absence of air bubbles in the adhesive layer provided on the recording film causes differences in the heat diffusion of the laser beam from the recording film, so it depends on the location on the recording surface. [Objective of the Invention] The present invention provides a method for smoothly applying a hot melt adhesive onto the recording surface of a disk.
(The purpose is to improve the reliability of double-sided discs (discs that can be played on both sides) and to eliminate uneven recording sensitivity.

[Summary of the invention]

The present invention is a method of bonding a pair of optical discs each having a recording surface on one side with the recording surfaces (tl:l facing each other) so that double-sided playback is possible.
Regarding the adhesion method for making an optical discla, a planar hot melt with release paper was used as the adhesive.kA17J14
This hot melt adhesive layer is heated and transferred from the release paper side to the recording surface of the optical disc using a transfer roll, and then the optical disc with the hot melt adhesive layer provided thereon is pressed and bonded with the hot melt adhesive layers facing each other. It is characterized by

The planar hot melt adhesive 1 with release paper can be made by applying the hot melt adhesive onto release paper (also called a separator) using a roll coater or spray, and is generally rolled and then removed. It's good to handle it.

The ingredients of this hot melt adhesive are the same as those sold in normal pellet or block form. In other words, as a constituent component, thermoplastic resin (pace polymer)
, tackifiers, waxes, etc., and if necessary, antioxidants and fillers are added. Typical base polymers include ethylene-vinyl acetate copolymer (EVA),
Examples of the tackifier include polyethylene ethylene, acidic polypropylene, ethylene-ethyl acrylate copolymer, polyamide, polyester, etc., and tackifiers include rosin and rosin derivatives, pinene-based resins, and the like.

In addition, waxes (7) include paraffin wax, microcrystalline wax, low-molecular pre-PE wax, modified wax, etc. stability, etc.) and performance (adhesive, heat resistance, cold resistance, etc.)
will be taken into consideration and decided.

Currently available sheet hot melt adhesives with release paper include Nitto Denko M-5200, M-521o, M
-521,3 etc. release paper is not limited to paper, but is also made of high density polyethylene,
Plastic films with good release properties from hot melt adhesives, such as polyester and polyimide, may also be used.

[Embodiments of the invention]

As shown in Figure 1, the planar hot melt adhesive is heated and melted from the release paper (separator) side using a heated transfer roll (a roll with an infrared lamp sunk in the shaft hole) and transferred to the reflective surface of the disk. If the melting point of the hot melt adhesive is high and heating the roll from the release paper side is insufficient for heat transfer, use far infrared rays or a hot air oven before passing the hot melt adhesive through the heated transfer roll. Direct preheating is preferable.The surface of the hot-melt adhesive coated on the reflective surface side of the disk in this way has good releasability from the release paper and is therefore very smooth. When a pair of these were pressed together during open time with the hot-melt adhesive coated surfaces facing each other, the coated surfaces were smooth, so it was possible to bond them together neatly without introducing air bubbles.

〔effect〕

By manufacturing double-sided discs using the adhesive method of the present invention, it is possible to prevent air from being sucked into the adhesive layer, so there is no change in the shape of the disc over time such as warping or ridges, and it is also easy to use with laser light. In the case of a disk memory that can write kW of information into the recording layer, sensitivity unevenness is also eliminated. Also 1
In the method of the present invention, only the amount of hot melt adhesive required for bonding is used after being thermally melted, so the hot melt adhesive does not deteriorate due to heat oxidation in a heating tank, unlike conventional methods, and the equipment is also designed. Since it does not get dirty, maintenance and workability are also very good.

Furthermore, since the hot melt adhesive transferred to the disk has good releasability from the release paper (separator), there is no peeling of the recording film or reflective film.

[Brief explanation of drawings]

FIG. 1Ii is a schematic diagram showing the hot melt coating method (thermal transfer method) of the present invention, FIG. 2 is a sectional view of a single-sided reproduction disc, and FIG. 3 is a sectional diagram of a double-sided reproduction disc. The π4 diagram is a schematic diagram showing a conventional hot melt coating method. 1. Planar hot melt feeding roll, 2.. Senokurator winding roll, 3.. heating transfer roll, 4. Pressure roll, 5.. Pre-warming ζ-16.. Preservation film, 7.. Reflective film, 8.Substrate, 9.Adhesive layer Representative, patent attorney, aide) J. Yu (and 1 other person) Figure 1 Figure 3 Figure 4

Claims (1)

[Claims] A pair of optical discs with a recording surface on one side are pasted together with the recording sides facing each other, and a sheet hot melt with release paper is used as the adhesive to create an optical disc that can be played on both sides, and the adhesive is heated. A method for adhering an optical disc, which comprises applying pressure to the recording surface of the optical disc from the release paper side with a rolled roll to cause thermal transfer to the recording surface, and then pressing the recording surfaces while facing each other.