WO1998008220A1

WO1998008220A1 - Process for bonding optical media

Info

Publication number: WO1998008220A1
Application number: PCT/US1996/018913
Authority: WO
Inventors: Chau T. Ha; Wayne M. Hector; Karl F. Rist
Original assignee: Imation Corp.
Priority date: 1996-08-21
Filing date: 1996-11-18
Publication date: 1998-02-26
Also published as: AU1083397A

Abstract

The present invention describes a process for assembling optical elements, including two sided optical disks comprising the steps of: a) providing a first element and a second single-side optical element; b) applying a curable adhesive composition to one surface of at least the second single-side element; c) initiating a cure of said adhesive composition; and d) placing said adhesive composition in which cure has been initiated into contact with a surface of the first element. The present invention also includes the adhesive composition used in the method above. That adhesive composition is preferably a high tack latex/rubber curable composition.

Description

PROCESS FOR BONDING OPTICAL MEDIA Background of the Invention

Field of the Invention The present invention relates to laminated optically readable elements including cards and especially disks, particularly one or two-side readable (and optionally recordable or writable) elements disks, a method for assembling such disks, and the final disk product produced by that method.

Background of the Art

With rapid growth in data storage and home entertainment applications, much more capacity than is available on today's optical (i.e., optically readable) elements and especially optical compact discs (CD) is needed. The next generation CD or DVD format provides one side and possibly two sides of readable information on the disk. This type of disk requires a bonding step to assemble two approximately 0.6 mm discs (at least one of which disks is readable and/or writable) to make up DVD media with final thickness of 1.2 mm. There are many technical complications which must be overcome in the provision of a DVD format disk to satisfy the needs of the industry with respect to performance. In addition to such obvious requirements as information storage ability, abrasion resistance, stable optical clarity, stable physical dimensions, and other features which are fundamental to the ability of the DVD disk to perform, the disk must be easily manufactured and provide uniform physical dimensions when initially constructed, so that it can be readily addressed by the reading system. The presently envisioned manufacturing method for DVD disks involves the securement of two separate single-face disk elements of approximately 0.6 mm in a single or dual readable layer configuration to form a two-sided DVD format disk with a final thickness of .2 mm. Amongst other complications, an immediate problem in this type of manufacturing process has been encountered. Any adhesive applied to the interior faces of the two single- face disks is spread by the pressure of the bonding process. This spreading is not easily controlled, and is not uniform across the diameter or along a radius of the disk. The adhesive becomes spread thinner or thicker in various areas. This causes two distinct types of problems, waves and tilt. Waves are, as the name implies, undulating variations in the thickness of the composite disk, usually progressing in a circular variation around the disk. Tilt is an effect resulting from variations in thickness anywhere from the central portion of the disk to the outer edges of the disk. Tilt is generally regarded as the angular variation from a line normal to the surface of the disk from the entrance surface. The entrance surface is the surface of the disk which is addressed by the laser during reading of the disk. The tilt on a two-sided disk may be read from one or both of the entrance surfaces, that is, read from both readable surfaces of the disk. Tilt is measured as a standard in the industry, for example, on an OMP ODS130 Optical Disk Scanner, as exemplified in OMP BV (Copyright), 1994 Operating Manual 3.1. Tilt can be brought about by adhesive thickness variations and stress induced in the disks during manufacture or processing. This tilt tends to be a radial variation in dimension. The allowable tilt on the DVD media is significantly less than on the standard CD media, thus, any process that might have potential of introducing stress or variations in adhesive thickness to the disc must be monitored very closely.

There are presently two commercial bonding methods which have been proposed for DVD media: hot melt and UV-bonding. However, there are several disadvantages associated with each of these methods. For the hot melt bonding method, the equipment and raw material costs are high. The use of high melt temperatures may also place adverse stress on the disks which is undesirable. In addition, unique masking or printing at the inner diameter (ID) is needed for hiding the cosmetically undesirable hot melt glue. In the UV-bonding process, a semi- transparent side B (this requirement requires very tight control on the thickness of Al or any other metal) is needed for allowing at least 1% of UV transmission for the curing process. Also, the shrinkage of the photopolymer adhesive can greatly affect the tilt of the bonded media. Therefore, tight process controls are required for this UV bonding process. It would be desirable if a simple, cost-efficient bonding method and materials for securing the two faces of disks could be provided which enables the two-sided disks to have good physical alignment, controlled flexibility, and acceptable levels of tilt.

U.S. Patent No. 4,990,208 describes a disc and process for its manufacture comprising two substrates glued together by an adhesive which is hardened by ultraviolet radiation. The substrates may be polycarbonate, with each base 1.2 mm thick, and after one of the substrates has been coated with adhesive, the two substrates are pressed together under partial pressure.

U.S. Patent No. 4,892,606 describes a process for forming an optically readable disc by laminating two substrates together using a curable adhesive between the two substrates. Curable adhesives, including acrylic or epoxy adhesives are described as UV curable compositions with granular or filler-type spacers. Control of the viscosity of the adhesive during coating is emphasized.

U.S. Patent No. 4,503,531 describes a video disc with a pair of separate substrate discs bonded together with a temperature active (hot-melt adhesive) adhesive comprising a mixture of thermoplastic elastomers. A tackifier (e.g., rosin esters, terpene, and phenolic resins) is added to the composition to render the adhesive pressure-sensitive. The hot-melt adhesive has a Tg of not more than 140 °C. The adhesive has a specific range of adhesive strength to effect the desired level of performance.

U.S. Patent No. 5,085,925 describes an optical recording medium with a protective layer. The medium is adhered to the optical recording medium by an adhesive layer comprising a thermoplastic adhesive composition comprising a tackifier, and at least one acrylic polymer selected from a) ethylene-acrylic acid copolymer; b) ethylene-acrylate ester copoly er; and c) ethylene-maleic anhydride- acrylic acid terpolymer.

U.S. Patent No. 5,194,928 describes a composition and method used for adhering optical recording substrates together to form two-side optical discs, the composition comprising an unsaturated polyester oligomer, pressure sensitive acrylic polymer, polymerization initiator, and polyisocyanate compound. The process comprises coating or impregnating the pressure sensitive composition onto one or two optical disc substrates and heating or irradiating the composition to cure the adhesive into place.

U.S. Patent No. 5,458,940 describes the application of a vibration dampening layer to an optical disk. An adhesive is applied to a sheet (e.g., polyester, polyimide, and other film forming polymers), the sheet is cut-out in the form of a disk (preferably with a liner over the adhesive), and the adhesively coated /08220 sheet is adhered to the disk (column 7). Amongst the adhesives described is a crosslinked, pressure-sensitive acrylate adhesive.

Summary of the Invention One-side or two-side readable (and/or writable) disks are provided by providing two one side readable disk components or a blank component and a one- side readable component. A non-readable face of at least one disk (and preferably both disks) is coated with an adhesive. At least one, and preferably both, of said adhesives comprises a latex (which may be pressure-sensitive) thermoplastic adhesive which is curable, crosslinkable, or polymerizable to a three-dimensional state. The tacky adhesive is formed in the UV irradiation step prior to placing the adhesively coated faces together, the faces are then placed together. The adhesive composition comprises a solvent-free or low volatile solvent (less than 1%) content composition. The preferred adhesive composition comprises low Tg crosslinkable monomers, tackifiers, low Tg polymers, initiators, and optional coupling agents.

The "in-line processing radiation curable tacky or pressure-sensitive adhesive" bonding method described in this Invention provides a very fast, low cost and low stress bonding process which produces bonded one-side or two-side readable (and/or writable) media such as DVD-ROM, DVD-RAM or DVD-R media with good tilt performance. No special inner diameter (ID) masking or printing is required and there is no special transparency requirement on either side.

Detailed Description of the Invention

The present invention describes processes for assembling a laminated optical element comprising the steps of: a) providing a first optically readable element and a second element having a shape similar to the shape of said first element; b) applying a curable adhesive composition to one surface of said either element (and preferably to one surface of both elements); c) curing said adhesive composition to form a tacky adhesive; and d) placing said tacky adhesive into contact with a surface of said second optically-readable element to bond said first element and said second element. More broadly, the process of the present invention may be described as a process for assembling a laminated optical element comprising the steps of: a) providing a first optically readable element and a second element; b) screen printing a curable adhesive composition to one surface of said either element; c) curing said adhesive composition to form a tacky adhesive; and d) placing said tacky adhesive into contact with a surface of said second element to bond said first element and said second element.

The present invention relates to readable and/or writable elements and especially disk format media which has one or two readable exterior faces. The most preferred media (hereinafter referred to as two-side or two-bonded disks, "2SD") may be optically readable or writable and thereafter optically readable on both faces of the disk or on only one face of the laminated disk. Any readable disk material on a polymeric substrate may be used in the practice of the present invention. As the format proposed for DVD disks is 1.2 mm thickness, each disk element preferably should be approximately 0.6 mm thick so the 2SD is 1.2 mm thick. If the format changes, the individual disk components will likewise change. The process will work with any dimension disk, e.g., from 0.2 mm to 3.0 mm (per component thickness). Preferred thickness would be from 0.58 to 0.62 mm per disk component, more preferably from 0.59 to 0.61 mm, and most preferably from 0.598 to 0.602 mm or even closer to exactly 0.600 mm. Preferred polymeric substrates include polycarbonate, polyacrylates (e.g ., polymethylmethacrylate) and polyester, but any optically clear polymeric film forming polymer can be used as the carrier layer for the information bearing layer of the optical disk. The information bearing layer of the 2SD disk may be any optically readable (and/or writable) system known. For example, vesicular systems, absorbing dye systems, metallic reflective, metallic radiation absorbent systems, inorganic optical absorbence/reflectance systems and the like may be used. The appropriate information recording or recorded layer is applied on one surface of the polymeric carrier layer and two of the carrier layers with the readable/recordable optical layers thereon are adhered together (with the readable layers inward or outward, depending upon the nature of the system). The optical elements to be laminated include at least one optically readable element and a second element, which does not have to be optically readable. As is known in the art, a "single side" optical disk may contain an information layer at two or more different depths, which may be read by adjusting the focus position of the laser system. For example, when the optically readable element is secured to a fixed or non-machine insertable object, the process and materials of the present invention can be used to adhere the readable element to the second substrate. The second substrate may have the same shape as the first element (e.g., disk shaped), or may be different in size and shape. The present invention particularly describes a process for assembling a laminated one or two sided optical disk comprising the steps of: a) providing a first and a second single-side optical disk or a first blank element and a one-side readable/writable disk element; b) applying a curable adhesive composition to one surface of at least the first single-side disk (and preferably to each internal face of both first and second optical disks); c) initiating a cure of said adhesive composition (on one disk element or component if only one disk element is coated, and on both disks if both internal faces are coated); and d) placing said adhesive composition(s) in which cure has been initiated into contact with a surface of the second single-side disk component (a coated surface of the other disk being included within the concept of a surface of the other disk).

The adhesive composition is preferably a pressure-sensitive or merely tacky curable composition, and becomes a crosslinked (thermoplastic, tacky, or pressure- sensitive) adhesive layer.

The preferred adhesive composition of the present invention has a critical minimum number and type of components which enable the best performance of the practice of the present invention, particularly if the composition is to be applied by screen printing processes. Screen printing of the adhesive offers a unique benefit of the present invention. Disk elements, or other shaped components to be laminated into an optically readable element, may be precoated with the preferred adhesives by a screen printing technique, and then laminated. Release/cover layers may be applied over the screen printed layers, and the cover sheets removed immediately before the lamination process. Screen printing is an accurate, low waste coating method, especially for shaped elements, and is easily achieved. Coating of large sheets with subsequent cutting out of shaped components, which process was necessitated by the limitations on the ability of the adhesives to be coated except by large area coating techniques such as bar coating, roll coating, web coating, gravure coating, etc., is inefficient and wasteful. The most preferred adhesive composition of the present invention is shown in the examples and comprises a combination of rubber adhesive and crosslinked latex adhesive, and this is termed a thermoset latex/rubber adhesive.

Most traditional adhesive formulations are designed for web coating, roller coating, or hot melt method of application. In general, these traditional adhesives used in web and roller coatings contain large amounts of solvent that require conventional or infrared (LR) heating in the drying process. In liquid form, the adhesive is stringy, the polymeric networks and agglomerated materials forming string-like adhesions within the composition. This prevents the compositions from being applied by screen printing or spin coating methods, because the coherency provided by the strings is an adverse physical property for the coating methods and renders proper flow and material distribution difficult. Many screen printable or spin coatable photopolymers are thermoset materials. Upon radiation, the photopolymers crosslink and form films having no tack or very low tack. The purpose of this invention is to create a novel composition with novel properties which couple the necessary adhesive characteristics for optical disk lamination with the screen printable and spin coatable properties of the photopolymers necessary for processing. This produces unique radiation curable adhesives that can be processed via screen printing, spin coating, roller coating, web coating, or curtain coating. Some of the benefits for this type of adhesives are the absence of solvents, fast cycle time at milder processing conditions (radiation processing is faster and milder than conventional and infrared (TR) heating processes or hot melt process), ideal flexibility/stiffness properties, and durability.

The preferred adhesive composition contains three main components, 1) low Tg thermoset monomers (or an appropriate mixture of monomers which provide low Tg thermoset properties, e.g., non-crosslinking monomers plus crosslinking monomers and/or crosslinking agents), 2) tackifiers, and 3) thermoplastic resins. Crosslinkable resins with low softening temperatures or Tg's, e.g., softening or adherent temperatures of less than 150° C, preferably less than 125° C, more preferably less than 100° C, and most preferably above 30° C and below 80° C, are also useful in the practice of the present invention. The important point being that the adhesives have low stick temperatures (low temperatures at which they are sufficiently tacky as to enable adhesion with other surfaces) and are curable to a three dimensional state. The most preferred compositions are the pressure-sensitive or tacky crosslinkable adhesives described herein.

Thermoset monomers.

The mixture low Tg thermoset monomers used in the formulation serve as a backbone of the cured polymer film. By low Tg in the practice of the present invention it is meant that the cured product of the mixture of monomers has a Tg of less than 140° C. Preferably the monomers have a Tg between -150 and 140° C, more preferably between -150 and 50° C. The low Tg and low degree of unsaturation of selected monomers allow the crosslinked backbone to behave as a low tack adhesive rather than as a typical abrasion resistant, highly crosslinked radiation curable coating. Preferred low Tg monomers are alkyl acrylates (including substituted alkyl such as alkoxy-alkyl, cyclic alkyl such as cyclohexyl and substituted cycloalkyl, and aryl such as phenyl and 5 or 6 membered rings comprised of C, N, S, and O ring atoms). Such acrylates include, but are not limited to isooctyl acrylate, 2-ethoxyethyl acrylate, cyclohexyl acrylate, 2- methoxyethyl acrylate, tetrahydrofurfuryl acrylate, lauryl methacrylate, stearyl methacrylate, octyl acrylate, lauryl acrylate, 2(2-ethoxyethoxy) ethylacrylate, 1,6- hexanediol diacrylate or a mixture of these compounds. Crosslinking materials are known crosslinking agents for acrylic systems, including, for example, polyacrylic functional materials, such as di-(meth)acrylate crosslinkers, di-, tri-, tetra-, and penta-acrylates, bis-phenol-A-diacrylates, polyurethane-, polyester-, and polyepoxy- diacrylates, alkyl diol diacrylates (e.g., 1,6-hexanediol diacrylate), etc. Tackifiers:

To ensure that the adhesive formulation forms a high tack and high shear adhesive upon UV radiation, selected tackifier(s) are added to the formulation. The degree of tack and shear is designed via proper selection of tackifier. For providing the necessary rigidity to the adhesive for maintaining the dimensional stability of the bonded disk 2SD element, high Tg tackifiers are preferably used. The Tg of the tackifier is preferably in the range of 50-170° C, and more preferably from 70-120° C. Examples of tackifiers are rosin based tackifiers (e.g., Unirez 6008), terpene based tackifiers and hydrocarbon based tackifiers (e.g., Pinacolyte A-135). Tackifiers can be purchased from Union Camp, Exxon, BASF, Arizona Chemical,

Hercules, etc.

.Thermoplastic resins:

The thermoplastic resins provide the necessary morphology for both the screen printing and the spin coating processes. The thermoplastic acrylic resins particularly provide means for controlling the viscosity and shrinkage of the formulations. The low Tg type of thermoplastic resin (low Tg in the practice of the invention with respect to the thermoplastic polymer meaning a Tg between 10 and 50° C, most preferably between 15 to 50° C ) such as polybutyl methacrylate or polyisobutylmethacrylate is most preferred, because it would improve the adhesive characteristics of the cured films.

Photoinitiators:

Any commercial photoinitiator or a mixture of photoinitiators that activate in the 400-250 n wavelength region is sufficient. Photoinitiators which are spectrally sensitized to this region of the electromagnetic spectrum as by the use of spectral sensitizing dyes, may also be used. Such initiators may include, but are not limited to, free radical initiators such as benzophenones, and the like. Specific examples include 2-hydroxy-2-methyl-l-phenyl-propane-l-one, 1- hydroxycyclohexylphenyl ketone, 2-methyl-l-[4-(methylthio)phenyl]-2- morpholinopropanone-1 and 2,4,6-[trimethylbenzoyldiphenylphosphine]oxide, and the like. Coupling Reagents:

Organofunctional silane coupling reagents can be used optionally in the adhesive formulation at an additive level for obtaining the desirable moφhology of the cured adhesive. Silane additives migrate to the surface of the adhesive after processing and undergo hydrolysis and self-condensation to form crosslinks to the polymer network. Thus, desirable properties can be contributed by these compounds. Organofunctional silanes are well known in the art and include epoxy- silanes, amino-silanes, acrylic-silanes and the like, as shown in such references as U.S. Patent Nos. 4,520,142; 4,497,861; and 5,204,219.

Disks are traditionally described in the art as having an information side and a read side. The read side is the side of the disk or disk element from which information is read, whether this be by optical (reflected light) or magnetic sensing. The information side of the disk or element is the underside of the layer (the internal face of a laminated disk and the back side of a single-side disk) or the distal side from which the information is read.

The process of the present invention comprises the steps of applying the adhesive of the invention to a first disk surface (the information surface) of an optically readable/writable disk (preferably applying the adhesive to each information surface of both of the two disks), exposing the adhesive to UV radiation, and contacting the adhesive after it has been cured to a second disk surface. The process allows for the manufacture of a laminated disk having a tilt of less than 10 mRad (milliradians, as measured on the industry standard of an OMP tester), more preferably less than 6.5 mRad still more preferably less than 6.3 mRad., and most preferably less than 6.0 mRad immediately after assembly. The process of the present invention can provide disks with less then 5 mRad, less than 4.0 mRad, less then 3.0 mRad, and even less then 2.0 mRad on a consistent basis. The process of the present invention is also capable of providing disks with a tilt less than 6.5 mRad, and most preferably less than 6.0 mRad after environmental stress at 70°C/85% Rel. Hum. for 96 hours. A unique feature of the present invention is that the adhesive is tacky after fully curing from the irradiation step, remains tacky for the life of the product, yet provides the stiffness, flexibility, and high shear resistance necessary for bonding the disk elements together. The final product therefore has the two disk elements bonded by a pressure-sensitive or tacky crosslinked adhesive. The adhesive will also provide the necessary flexibility/stiffness to the standard optical disk units bound together.

The compositions of the present invention will usually comprise 10-70% (preferably 30-50%) by weight of the mixture of thermoset monomers, and 5-30% by weight thermoplastic polymer, 1-70% (preferably 20-50%) by weight of tackifier, and 0.1 to 15% (preferably 0.5 to 12%) by weight of photoinitiator.

A schematic representation of the preferred practice of the present invention is shown as follows, where each information surface of the two disks used in the assembly are coated with the adhesive, preferably by screen printing procedures.

&τrxn|^*nrt, spin COT<, CT ITJIICT cert rraterial onto side Λ Scran prii , spn ccβt , or i lσ cat material orto a^'de B Step l

UVcucSdeA Sfcp2

Larrirβtmg

Sfcp3

Examples Examples 1-3

Three formulations of adhesive compositions of the present invention were prepared as shown below:

Component Composition 1 Composition 2

(Wt %) (Wt%) Isooctyl acrylate 35 34

2(2-Ethoxyethoxy) ethylacrylate 19 19 1,6-hexanediol diacrylate 05 05

Poly n-butyl methacrylate 19 19 Unirez™ 6008 20 20

N- [3 -(Trimethoxysilyl)propyl]- 00 01 ethylene diamine

Darocure™ 4265 02 02

Component Composition 3

(Wt %)

Isooctyl acrylate 29 2(2-Ethoxyethoxy) ethylacrylate 10

1,6-hexanediol diacrylate 4.9

Poly n-butyl methacrylate 9

Unirez™ 6008 24

Pinacolyte A-135 15 N.N-dimethyl acrylamide 4

Darocure™ 4265 4

FC 431 (fluorinated coating aid from 3M) 0.1

The above compositions were individually screen printed onto one face each of two 0.6 mm thick disks in less than two seconds. Ultraviolet radiation drying of the layer was performed in about 2.0 seconds. The adhesive layers were irradiated with UV radiation from an H-bulb of Fusion System, Inc. lamp to cure and tackify the composition. The adhesively coated faces of the two 0.6 mm disks were brought together in a lamination step to produce a 1.2 mm disc. The resulting disk was compared with a disk manufactured with a commercially manufactured DVD-5 readable disk made with a hot melt adhesive (Warner Advanced Media Operations). The resulting tilt data are show vnn bbeellooww:: Disc Radius (mm) Tilt (Invention) Tilt (Hot-Melt)

(Composition 3) mRad mRad

24 -0.5 -6.3 35 -0.3 -4.3 46 -2.0 -4.6 57 -1.0 -4.5

Another important consideration in the manufacture of DVD media is the need for sufficient stiffness and rigidity so that the media are able to maintain dimensional stability over time, without unacceptable progressive change in warp and tilt. In the present invention it is preferred to use high Tg tackifiers to improve these characteristics. The preferred range of Tg for the tackifier is between 70 and 120° C. The value of the selection of high Tg tackifiers is demonstrated in data shown in Tables 1 and 2 recording shear and peel strength. As shown in these data, the crosslinked adhesive composition containing tackifier with a Tg of 85° C has both higher shear strength and higher peel strength than the same composition with a tackifier having a Tg of only 25° C.

Table 1

Sample Shear Strength in kg (lb) Peel Strength (g) (measured with an Instron (measured at a speed of 90 4201 with 5.1 cm (2-inch) in min. at an angle of 160° wide samples moving at 30.5 using a polyester release test c min (12 in min.) on a 3M Adhesion Sled)

Sample 1 - Composition 1 with Unirez 6008 as the 18 kg (40 lbs) 35 tackifier, Tg=85° C Sample 2 - Composition 1 with Alpha-25 as the 5.5 kg (12 lbs) tackifier, Tg = 25° C The amount of tackifier present in the formulation also has important effects upon the physical stability of the bonded disks. It has been found that the preferred percent of tackifier or combinations of tackifiers in the formulation is between 20 to 70% by weight of the total weight of the composition. This point is demonstrated in the data shown in Table 2 regarding shear strength and peel strength as a function of the percent preferred tackifier (Unirez 6008).

Table 2

Samples (Composition 2) Shear Strength Peel Strength

(%/wt. Tackifier) in kg (lb) (g)

0 0 5

10 6 kg (14 lbs) 20

20 10 kg (22 lbs) 35

39 41 kg (90 lbs) >50

Shear strength and peel strength in Table 2 were measured in the same manner as that data in Table 1.

Claims

WHAT IS CLAIMED:

1. A process for assembling a laminated optical element, comprising the steps of: a) providing a first optically readable element and a second other element similar in shape to said first element; b) applying a curable adhesive composition to one surface of at least one of said elements; c) curing said adhesive composition to form a tacky adhesive; and d) placing said tacky adhesive into contact with a surface of the other element to bond said first element and said second element.

2. A process for assembling an optical storage disk, comprising the steps of: a) providing a first and a second single-side optical storage disk element; b) applying a curable adhesive composition to one surface of each of said first and second optical storage disk elements; c) curing said adhesive composition on said one surface on both said first and second optical storage disk elements to form a tacky adhesive on both said first and second optical storage disk elements; and d) placing said tacky adhesive on said first optical storage disk element into contact with the tacky adhesive on said second optical storage disk element to bond said first and second optical storage disk elements together.

3. A process for assembling an optical disk comprising the steps of: a) providing a first and a second single-side optical disk element; b) applying a curable adhesive composition to one surface of said first optical disk element; c) curing said adhesive composition on said one surface to form a tacky adhesive; and d) placing said tacky adhesive into contact with a surface of said second optical disk element to bond said first and second optical disk elements.

4. The process of any of claims 1-3, wherein said adhesive composition comprises:

10-70% by weight of thermoset monomers, 5-30% by weight thermoplastic polymer, 1-70% by weight of tackifier, and 0.1 to 15% by weight of photoinitiator.

5. The process of claim 4, wherein said thermoset monomers form a polymer with a Tg of less than 140° C, said thermoplastic polymer has a Tg of between 10 and 80° C, and said tackifier has a Tg of from 70 to 120° C.

6. The process of any of claims 1-5, wherein average tilt provided in said optical element is less than 6.3 mRad.

7. The process of any of claims 1-6, wherein step b) is performed by spin coating.

8. The process of any of claims 1-6, wherein step b) is performed by screen printing.

9. The process of any of claims 1-6, wherein said optically readable disks have thicknesses of 0.58 to 0.62 mm.

10. A crosslinkable adhesive composition comprising:

10-70% by weight of thermoset monomers having a Tg of less than 140° C, 5-30% by weight thermoplastic polymer having a Tg of between 10 and 80° C, 1-

70% by weight of tackifier, and 0.1 to 15% by weight of photoinitiator, and said tackifier has a Tg of from 50 to 170° C.

11. A laminated optical disk comprising a first optical storage disk element, a second optical disk element, and an adhesive layer bonding said first and second optical storage disk elements, wherein said adhesive layer comprises a thermoset latex/rubber adhesive.

12. The article of claims 10 or 11, wherein said adhesive comprises a crosslinked polymer derived from 2-10% of 1,6-hexanediol diacrylate, 15-40% isooctylacrylate, 5-15% 2(2-ethoxyethoxy)ethylacrylate, 5-25% polymethacrylate, 10-55% by weight tackifier selected from the group consisting of rosin tackifier and hydrocarbon tackifier, 0-10% amoφhous fused silica, 0-5% N,N- dimethylacrylamide, and 2-12% free radical photoinitiator.

13. The laminated optical storage disk of claim 11, wherein said adhesive comprises a crosslinked acrylate adhesive and tackifier.