WO2019120897A1

WO2019120897A1 - Ultra-thin light-shielding double-sided pressure-sensitive adhesive tape and roll product thereof

Info

Publication number: WO2019120897A1
Application number: PCT/EP2018/082647
Authority: WO
Inventors: Gero Maatz; Yanjie REN; Wenwen ZHU; Xiaofei Li
Original assignee: Tesa Se
Priority date: 2017-12-19
Filing date: 2018-11-27
Publication date: 2019-06-27
Also published as: CN207862251U

Abstract

The present utility model relates to an ultra-thin light-shielding double-sided pressure-sensitive adhesive tape and a roll product thereof, and in particular, said adhesive tape has a black PET material layer and a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer which are arranged on the front and back main surfaces of the black PET material layer. Said black PET material layer has a thickness of 3-5 microns, and said adhesive tape has a total thickness of ≤15 microns, with the standard deviation of the total thickness of said adhesive tape being ≤1 micron. The adhesive tape of the present utility model is particularly suitable for use as a light-shielding double-sided pressure-sensitive adhesive tape, and is used for producing various different products, in particular electronic products.

Description

Ultra-thin light-shielding double-sided pressure-sensitive adhesive tape and roll product thereof

Technical Field

The present utility model pertains to the field of adhesive materials, and more particularly relates to an ultra-thin light-shielding double-sided pressure-sensitive adhesive tape and a roll product thereof.

Background Art

In the industrial age, pressure-sensitive adhesive (PSA) tapes (i.e., pressure-sensitive tapes) are widely used processing auxiliaries.

For use in the electronics industry, very stringent requirements are placed on PSA tapes. They are required to exhibit minor outgassing properties and can be used within a wide temperature range, exhibiting a low manufacturing tolerance and ensuring a very high bonding strength for a very low total thickness.

In particular, with the miniaturization and thinning of electronic products, higher requirements have been placed on light-shielding double-sided pressure-sensitive adhesive tapes. For example, the fixing of a backlight unit to a housing often requires the use of a double-sided adhesive tape.

Currently, common black double-sided pressure-sensitive adhesive tape structures often have various disadvantages. For example, in almost all existing light-shielding double-sided pressure-sensitive adhesive tapes, PSA layers containing a black dye are used, or a carrier film layer is printed with a black dye and the printed layer is then further provided with a PSA layer. However, these printed layers often have unevenness. In addition, black dyes are often unstable (the stability is often 1 year or less), and often migrate or transfer to the adhesive material during use, thereby affecting performance.

In order to satisfy performance indexes such as light-shielding performance, adhesion and flatness, the total thicknesses of the existing light-shielding double-sided pressure-sensitive adhesive tapes are at least 30 microns or more. In addition, the existing light-shielding double-sided pressure-sensitive adhesive tapes have a higher thickness tolerance, and an uneven light-shielding effect. For example, for a class of black PSA tapes in the prior art, Cr⁺ azo dyes are used, and consequently, the dyes may not only be aggregated, but may also be transferred to substrates. Therefore, there is an urgent need in the art to develop a novel light-shielding double-sided pressure-sensitive adhesive tape having excellent light-shielding properties, a lower total thickness, excellent mechanical properties and excellent stability.

Summary of the Utility Model

An object of the present utility model is to provide a light-shielding double-sided pressure-sensitive adhesive tape having excellent light-shielding properties, a lower total thickness, excellent mechanical properties and excellent stability.

In a first aspect, the present utility model provides an ultra-thin light-shielding double-sided pressure-sensitive adhesive tape comprising a structural layer laminated from top to bottom, said structural layer comprising:

(a) a first pressure-sensitive adhesive layer having a thickness of a1 ;

(b) a black PET material layer having a thickness of b; and

(c) a second pressure-sensitive adhesive layer having a thickness of a2,

wherein a main surface of said black PET material layer is bonded to said first pressure-sensitive adhesive layer, and the other main surface of said black PET material layer is bonded to said second pressure-sensitive adhesive layer;

and said black PET material layer has a thickness of 3-5 microns, and the sum of a1 +b+a2 is < 15 microns, with the standard deviation of the total thickness of said adhesive tape being < 1 micron.

In another preferred embodiment, the standard deviation of the total thickness of said adhesive tape is < 0.5 microns.

In another preferred embodiment, said adhesive tape has a total thickness of 10-15 microns, preferably 12-15 microns.

In another preferred embodiment, said black PET material layer has a thickness of 3.5-4.5 microns.

In another preferred embodiment, said black PET material layer has a thickness of 4.0-4.5 microns.

In another preferred embodiment, said first pressure-sensitive adhesive layer and/or second pressure-sensitive adhesive layer are colourless, transparent PSA material layers. In another preferred embodiment, said first pressure-sensitive adhesive layer is a transparent PSA material layer having a thickness of 1 -6 microns.

In another preferred embodiment, said first pressure-sensitive adhesive layer is a transparent PSA material layer having a thickness of 2-4 microns. In another preferred embodiment, said second pressure-sensitive adhesive layer is a transparent PSA material layer having a thickness of 1-6 microns.

In another preferred embodiment, said second pressure-sensitive adhesive layer is a transparent PSA material layer having a thickness of 2-4 microns.

In another preferred embodiment, said first pressure-sensitive adhesive layer and said second pressure-sensitive adhesive layer have the same thickness.

In another preferred embodiment, said first pressure-sensitive adhesive layer and said second pressure-sensitive adhesive layer have different thicknesses.

In another preferred embodiment, said first pressure-sensitive adhesive layer and said second pressure-sensitive adhesive layer are transparent.

In another preferred embodiment, said adhesive tape has an ultraviolet light and/or visible light transmittance of < 5%.

In another preferred embodiment, the outer surface of said first pressure-sensitive adhesive layer is provided with a first peelable layer; and/or the outer surface of said second pressure-sensitive adhesive layer is provided with a second peelable layer.

In another preferred embodiment, said adhesive tape further comprises a first peelable layer and/or a second peelable layer, said first peelable layer is compounded on or covers the outer surface of the first pressure-sensitive adhesive layer, and said second peelable layer is compounded on or covers the outer surface of the second pressure-sensitive adhesive layer.

In another preferred embodiment, said first peelable layer and/or second peelable layer are the same peelable layer.

In another preferred embodiment, said peelable layers are directly bonded to the first pressure-sensitive adhesive layer and/or the second pressure-sensitive adhesive layer.

In another preferred embodiment, said adhesive tape is a roll product or a sheet product. In another preferred embodiment, said black PET material layer is a PET film layer with carbon black as a filler.

In another preferred embodiment, said adhesive tape is provided with a roll core, and said adhesive tape surrounds said roll core to form a roll product.

In a second aspect of the present utility model, there is provided a roll product comprising: a roll core,

and the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape as described in the first aspect of the present utility model surrounding said roll core.

In another preferred embodiment, said roll has a width of 0.5-2.5 metres. In another preferred embodiment, said roll has a length of 2-2000 metres, preferably 5-500 metres.

It should be understood that within the scope of the present utility model, combinations can be made between the above-mentioned technical features of the present utility model and various technical features described in detail below (e.g., in embodiments) to form new or preferred technical solutions. Due to space limitations, no more details will be given here.

Brief Description of the Drawings

Figure 1 shows the structure of an ultra-thin light-shielding double-sided pressure-sensitive adhesive tape in one embodiment of the present utility model, in which peelable layers are omitted.

Figure 2 shows the structure of an ultra-thin light-shielding double-sided pressure-sensitive adhesive tape in another embodiment of the present utility model, in which a peelable layer located on the first pressure-sensitive adhesive layer A1 is shown. Figure 3 shows the structure of an ultra-thin light-shielding double-sided pressure-sensitive adhesive tape in another embodiment of the present utility model, in which a first peelable layer on the first pressure-sensitive adhesive layer A1 and a second peelable layer on the second pressure-sensitive adhesive layer A2 are shown.

In each figure, the signs are as follows:

1 1 : first pressure-sensitive adhesive layer;

12: black PET material layer;

13: second pressure-sensitive adhesive layer;

14: first peelable layer; and

15: second peelable layer.

Detailed Description of Embodiments

After extensive and in-depth research, the present inventors have developed a structurally novel ultra-thin light-shielding double-sided pressure-sensitive adhesive tape for the first time. It is unexpectedly discovered in the present utility model that by adding an inorganic filler such as carbon black, a carrier film with a very high light-shielding rate even at an ultra-thin thickness can be prepared. After said ultra-thin carrier film is compounded with pressure-sensitive adhesive layers having a specific thickness, a light-shielding double-sided pressure-sensitive adhesive tape having excellent light-shielding properties, a very low total thickness, an excellent total thickness standard deviation, excellent mechanical properties and excellent stability can be prepared. On this basis, the present utility model is completed.

Terminology

As used herein, the terms “adhesive tape of the present utility model”, “ultra-thin light-shielding double-sided pressure-sensitive adhesive tape of the present utility model”, “pressure-sensitive adhesive tape of the present utility model”, etc., are interchangeable, and refer to the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape in the first aspect of the present utility model.

In the present utility model, the term“above”,“below”,“left”, or“right” is used for the convenience of description. It should be understood that these positional relationships are relative and do not impose additional limitations to the scope of protection of the present utility model.

As used herein, the term“PSA” refers to pressure-sensitive adhesives, and in Chinese meaning is Yaminjiao or Yaminnianheji.

As used herein, the term“PET” refers to polyethylene terephthalate in English.

Ultra-thin light-shielding double-sided pressure-sensitive adhesive tape

The present utility model provides an ultra-thin light-shielding double-sided pressure-sensitive adhesive tape comprising a carrier film layer, and pressure-sensitive adhesive layers laminated on the two main surfaces of said carrier film layer.

Typically, the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape of the present utility model comprises the following layers laminated together from top to bottom:

(a) a first pressure-sensitive adhesive layer A1 having a thickness of a1 ;

(b) a black PET material layer B having a thickness of b; and

(c) a second pressure-sensitive adhesive layer A2 having a thickness of a2,

wherein a main surface of said black PET material layer is bonded to said first pressure-sensitive adhesive layer, and the other main surface of said black PET material layer is bonded to said second pressure-sensitive adhesive layer.

One characteristic of the present utility model is that said black PET material layer has a thickness b, which not only has excellent light-shielding properties, but is also very thin, and the b thereof being generally 3-5 microns.

Another characteristic of the present utility model is that the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape of the present utility model has a very low total thickness, generally 20 microns or less. In the present utility model, the thickness of the adhesive tape is the sum of the thickness of the carrier layer (i.e., the black PET material layer), the thickness of the two PSA layers, and the thickness of other layers which are optionally present where appropriate. Preferably, in the present utility model, the sum of a1 +b+a2 is < 15 microns.

In one preferred embodiment, in particular in the case of a three-layer adhesive tape, the difference between the thickness b of the carrier layer and the sum of the thicknesses (a1 and a2) of the PSA layers is not greater than 15 microns, and is very preferably less than 13 microns, most preferably less than 12 microns.

Another characteristic of the present utility model is that the standard deviation of the total thickness of the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape of the present utility model is very small, generally < 1 micron, preferably < 0.5 microns, more preferably < 0.2 microns.

Black PET material layer

With regard to the film carrier layer in the present utility model, all film-like polymer carriers can be used in principle, wherein an inorganic filler such as carbon black is incorporated into said film polymer carrier.

Typically, in the present utility model, for suitable carrier film layers, polyethylenes, polypropylenes, polyethersulfones, polyamides, polyimides, polyetherimides, polyesters, polyphenylene sulfides, polyamideimides, polyetherimides, polymethacrylates, styrene-based films, polycarbonates, polyether ketones, polyaryls, polyurethanes, polyacrylates, polybutyrals, polyethylene-vinyl acetate, polyethylene naphthalate and fluorinated polymers may be used. These types of polymers can be used alone or in combination with each other. In a particularly preferred method, a polyester film is used, and a PET film (polyethylene terephthalate film) is particularly preferred.

From advantageous applications of the present utility model, the PET film has a high tensile strength and a very good thickness tolerance. At this point, the absolute thickness tolerance is more and more improved by using increasingly thinner films.

Preferably, the film carrier layer of the present utility model contains no or barely contains any dye or other pigment, especially contains no organic dye.

In the present utility model, a very preferred solution is to fill only with a black inorganic pigment. In the present utility model, graphite, carbon black or similar carbon compounds are particularly suitable. By using different filling amounts, the transparency (transmittance) and the degree of blackness of the film can be adjusted.

Taking the black PET material layer of the present utility model as an example, it has the following characteristics: 1 . no volatile organic compounds compared with the printed film; 2. better colour distribution, and high uniformity; 3. no uneven pattern caused by printing; 4. higher light resistance (blackness); 5. carbon black, etc., do not have the problems of migration, aggregation, etc., and therefore the stability is high; and 6. being more environmentally friendly.

Pressure-sensitive adhesive layer

Another main structure in the novel ultra-thin light-shielding double-sided pressure-sensitive adhesive tape of the present utility model is a pressure-sensitive adhesive layer (PSA material layer).

In the present utility model, pressure-sensitive adhesives (PSA) as the main component of the pressure-sensitive adhesive layer include (but are not limited to): acrylates, natural rubbers, synthetic rubbers, silicone and/or EVA adhesives.

In the present utility model, transparent PSAs are particularly advantageous because they do not contain any pigments or dyes, thus avoiding the risk of transferring a pigment or dye to another material.

Preferably, in order to improve the adhesion of PSA, the black PET material layer may also be pretreated by means of, for example, an etching, corona or plasma pretreatment. In the present utility model, the thickness of the adhesive layer is not particularly limited as long as it satisfies the requirements for bonding properties and the requirements for the total thickness of the novel adhesive tape of the present utility model.

Generally, the thickness of the adhesive layer affects the bonding strength of the double-sided adhesive tape. Advantageously, the solution is employed such that the bonding strength of the adhesive tape is sufficient for a particular end use, and more specifically for use in an electronic assembly in the manner as described in the description. To this end, it is very advantageous that the adhesive layers, in each case, are each at least 0.5 microns thick, preferably 1 micron thick.

The PSA layers located on both sides may advantageously be the same. Alternatively, depending on applications, the first and second PSA layers may also advantageously be different from each other. More specifically, they are different in terms of the layer thicknesses thereof and/or the chemical compositions thereof. In this way, for example, different adhesions may be provided. Particularly preferred PSA systems for the double-sided pressure-sensitive adhesive tape of the present utility model are acrylate adhesives, natural rubber adhesives, synthetic rubber adhesives, silicone adhesives or EVA adhesives. However, in principle, all other PSAs known to a person skilled in the art may also be used [for the prior art, see for example Bonatas Satas’s “Handbook of Pressure Sensitive Adhesive Technology” (van Nostranb, New York 1989)].

For natural rubber adhesives, natural rubber is ground to a molecular weight (weight average) of not less than about 100,000 Daltons, preferably not less than 500,000 Daltons, and additised.

In the case of a rubber/synthetic rubber acting as an adhesive raw material, there is a possibility of a wide range of variations. A natural rubber or synthetic rubber may be used, or any desired blend of natural rubbers and/or synthetic rubbers may be used; according to the required grade of purity and of viscosity, in principle, one or more natural rubbers, for example, of RSS, ADS, TSR or CV type, may be selected from those of all existing grades, and one or more synthetic rubbers may be selected from randomly copolymerised styrene-butadiene rubber (SBR), butadiene rubber (BR), synthetic polyisoprene rubber (IR), isobutylene-isoprene rubber (HR), halogenated isobutylene-isoprene rubbers (XIIR), acrylate rubber (ACM), as ethylene-vinyl acetate copolymer (EVA), and polyurethane and/or blends thereof.

Further preferably, in order to improve the processability of the rubber, a thermoplastic elastomer may be added thereto in a weight content of 10-50 wt% based on the total amount of elastomer. As representatives, mention may be particularly made of particularly compatible styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS) types in this respect.

In a preferred embodiment of the present utility model, it is preferable to use a (meth)acrylate PSA (for the purpose of the present description, this term includes polyacrylate- and/or polymethacrylate-based PSAs).

A monomer is preferably selected such that the resulting polymer can serve as a PSA at room temperature or higher. More specifically, for the use of the PSA, the fraction of a corresponding monomer is selected such that the glass transition temperature (Tg) of the polymerised product is < 15°C. The monomer is preferably selected such that the resulting polymer can serve as a PSA at room temperature, more specifically such that the resulting polymer has pressure-sensitive adhesive properties in accordance with Bonatas Satas’s Handbook of Pressure Sensitive Adhesive Technology (van Nostranb, New York 1989, pp. 444-541 ). In the sense of the dynamic glass transition temperature of an amorphous system and the melting temperature of a semicrystalline system, the glass transition temperature of the polymer forming the base of the PSA is advantageously lower than 15°C, which can be determined by means of dynamic mechanical analysis (DMA) at a low frequency. In another embodiment of the present utility model, the composition of said comonomer is selected such that said PSA can be used as a thermally activable PSA. More specifically, for the use of the thermally activable PSA (or hot melt adhesive), in other words, for a substance that becomes tacky only upon heating, the fraction of the monomer is selected such that the glass transition temperature of the copolymer (Tg) is from 15°C to 100°C, preferably from 30°C to 80°C, more preferably from 40°C to 60°C (in the sense of the dynamic glass transition temperature of the amorphous system and the melting temperature of the semicrystalline system), which can be determined by means of dynamic mechanical analysis (DMA) at a low frequency.

A polymer may preferably be obtained by polymerizing a monomer mixture consisting of an acrylate and/or a methacrylate and/or free acids thereof, with the formula of CH2=CH(RI)(COOR2), in which Ri is H or CH3 and R2 is an alkyl chain with 1 -20 carbon atoms or H.

The molar mass Mw of the polyacrylate used is preferably > 200000 g/mol (as determined by means of gel permeation chromatography).

In a very preferred embodiment, acrylic or methacrylic monomers are used, including acrylates and methacrylates having an alkyl group containing 4-14 carbon atoms, preferably 4-9 carbon atoms. Without wishing to be limited by this list, examples are methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonyl acrylate, lauryl acrylate, stearyl acrylate, docosyl acrylate, and branched isomers thereof, such as isobutyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isooctyl acrylate and isooctyl methacrylate.

Other classes of compounds which may be used are monofunctional acrylates and/or methacrylates of bridged cycloalkyl alcohols composed of at least 6 carbon atoms. The cycloalkyl alcohols may also be substituted with, for example, C1 -C6 alkyl, halogen atoms, or cyano.

In one solution, a monomer with a polar group is used, and examples of said polar group are carboxyl, sulfonic acid and phosphonic acid groups, hydroxyl, lactams and lactones, N-substituted amides, N-substituted amines, carbamates, epoxy, mercaptans, alkoxyl or cyano, and ethers.

Moderately alkaline monomers are, for example, N,N-dialkyl-substituted amides such as N,N-dimethylacrylamide, N,N-dimethylacrylamide, N-tert-butylacrylamide,

N-vinylpyrrolidone, N-vinyl lactam, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, diethylaminoethyl acrylate, N-hydroxymethylacrylamide, N-(butoxymethyl)methylacrylamide, N-hydroxymethylacrylamide, N-(ethoxymethyl)acrylamide, N-isopropylacrylamide, this list being not exhaustive.

For further improvement, a resin may be mixed into the PSA. As a tackifying resin to be added, all tackifier resins previously known and described in documents may be used. Representatives which may be mentioned include pinene resins, indene resins and rosins, disproportionation, hydrogenation, polymerization and esterification derivatives thereof and salts thereof, aliphatic and aromatic hydrocarbon resins, terpene resins and terpene-phenolic resins, and further includes C5, C9 and other hydrocarbon resins. In order to adjust the properties of the resulting adhesive according to requirements, any desired combination of these and other resins may be used. Generally, any resin that is compatible (soluble) with said polyacrylate may be used: specifically, mention may be made of all aliphatic, aromatic and alkyl aromatic hydrocarbon resins, hydrocarbon resins based on pure monomers, hydrogenated hydrocarbon resins, functionalised hydrocarbon resins and natural resins. Reference can be particularly made to the introduction of the state of knowledge in Donatas Satas’s “Handbook of Pressure Sensitive Adhesive Technology” (van Nostrand, 1989).

In the present utility model, similarly, it is preferable to use a transparent resin that is highly compatible with the polymer to improve transparency. Hydrogenated or partially hydrogenated resins often have these properties.

In addition, plasticisers, other fillers (such as fibres, carbon black, zinc oxide, chalk, solid or hollow glass beads, microspheres made of other materials, silicon dioxide, and silicates), nucleating agents, electrically conductive materials (such as conjugated polymers, doped conjugated polymers, metallic pigments, metallic particles, metal salts, and graphite), expanding agents, compounding agents and/or anti-ageing agents may be optionally added, wherein the anti-ageing agents are added, for example, in the form of a primary antioxidant and an auxiliary antioxidant or in the form of a light stabiliser.

Preferably, the average molecular weight Mw of the PSA formed during radical polymerization is selected such that it is in the range of 200000-4000000 g/mol; in particular, for the further use of the present utility model, a PSA having an average molecular weight Mw of from 400000-1400000 g/mol is prepared. The mass distribution may also be bimodal or multimodal. The average molecular weight is determined by means of size exclusion chromatography (GPC).

Release liner

The adhesive tape of the present utility model may further contain a peelable layer (i.e., a release liner). In the present utility model, a release liner may be provided on said double-sided PSA layer on one or both sides. The release liner prevents the PSA layer from sticking to each other when the adhesive tape is wound. With regard to the use of the double-sided PSA tape of the present utility model, the release liner should be as flat as possible. Therefore, release liners based on polymer films, papers, fabric materials and/or metal foils may be used. Examples of usable papers include cellophanes or“clay-coated” (kaolin-coated) papers. The thickness of the substrate material is preferably 10-500 microns, depending on a processing technique that follows.

In a very preferred embodiment, the substrate material used for the release liner is a polymer film. There may be, for example, based on polyethylenes, polypropylenes, polyethersulfones, polyamides, polyimides, polyetherimides, polyesters, polyphenylene sulfides, polyamideimides, polyetherimides, polymethacrylates, styrene-based films, polycarbonates, polyether ketones, polyaryls, polyurethanes, polyacrylates, polybutyrals, polyethylene-vinyl acetate, or polyethylene naphthalate. The polymer film may be relaxed, or either uniaxially or biaxially oriented.

From the manufacture of the double-sided PSA tape, a polyester film based on polyethylene terephthalate (PET) is particularly preferred.

For the release function, the substrate may be further provided with at least one release coating. The release coating is preferably based on silicone, a fluorinated silicone or a fluorinated polymer. A compound based on a long aliphatic chain may be used as the release coating.

Preparation method

The present utility model further provides a method for preparing the adhesive tape of the present utility model.

In order to prepare an ultra-thin light-shielding double-sided pressure-sensitive adhesive tape, in a preferred solution, PSA is applied from a solution onto a specific PET carrier material of the present utility model. In principle, the adhesive may also be applied from a melt; however, this may cause the adhesive tape to have a higher thickness tolerance.

For application from the melt, the preparation method may relate to necessarily removing the solvent from the PSA. In this case, any technique known to a person skilled in the art may in principle be used. A very preferred technique involves concentration using a single-screw or twin-screw extruder. The twin-screw extruder may be operated either in the same direction or in the opposite direction. It is preferable to distil off a solvent or water in two or more vacuum sections. Counter-heating is also carried out according to the distillation temperature of the solvent. The total content of the residual solvent is preferably < 1 %, more preferably < 0.5%, and very preferably < 0.2%. Further processing of the hot melt is carried out from the melt.

For application as a hot melt, different coating methods may be used. In one solution, the PSA is applied by means of a roll coating method. In another solution, the application is carried out by means of a melt die. In a further preferred solution, the application is carried out by means of extrusion. The extrusion application is preferably carried out by using an extrusion die.

The extrusion die used may be advantageously derived from one of the following three types: a T-die, a fishtail die and a coat hanger die. The difference between these types is that the runner designs thereof are different.

By means of application, the PSA may also be oriented.

In addition, the PSA may be necessarily cross-linked. In a preferred solution, thermal cross-linking is carried out by using an electron beam and/or UV radiation.

Depending on a UV photoinitiator used, the UV cross-linking irradiation is carried out by means of short-wave ultraviolet irradiation in the wavelength range of 200-400 nm; specifically, the irradiation is carried out by using a high-voltage or medium-voltage mercury lamp having an output power of 80-240 W/cm. The intensity of the irradiation adapts to the corresponding quantum yield of the UV photoinitiator and the set degree of cross-linking.

Moreover, in an advantageous embodiment, the PSA may be cross-linked by using an electron beam. Typical irradiation devices that can be advantageously used include a linear cathode system, a scanner system, and a segmented cathode system, wherein an electron beam accelerator is used. A detailed description of the technical field and the most important process parameters are provided in Skelhorne, Electron Beam Processing, in Chemistry and Technology of UV and EB formulation for Coatings, Inks and Paints, Vol.1 , 1991 , SITA, London. A typical accelerating voltage is set between 50 kV and 500 kV, preferably between 80 kV and 300 kV. The scatter dose used is in the ranges of between 5 kGy to 150 kGy, specifically between 20 kGy and 100 kGy. In page 1413/19 of the description of CN 101679814 B, both of the two cross-linking methods or other methods capable of high energy irradiation may also be used.

In a very preferred solution, the adhesive is applied from a solution. In this case, very different coating methods may be used. The coating here may also be carried out from a die, or may be carried out either by means of a knife coater or by means of spray coating or by means of a roll applicator, or by means of printing. For very thin coatings, the spray coating method or the roll coating method is particularly suitable. The thickness tolerance of the coating is improved by means of higher dilution with a solvent, as the solvent is subsequently evaporated. In this way, the thickness tolerance of a particular coating assembly is determined by this mechanism. In the case of application from a solution, these mechanisms produce a limited tolerance for the PSA film coated from the solution, the tolerance is further reduced by means of evaporation that leads to a loss of the solvent.

After the PSA containing the solvent is applied, the solvent is removed. This is particularly preferably done in a drying channel with a very long residence time. Generally, at different temperature sections, heating proceeds to a high level to prevent the formation of bubbles. In addition, the final drying temperature should be higher than the boiling point of the solvent so as to minimise the subsequent outgassing of the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape.

In the first step, the PSA is applied onto the release liner. This is preferably done from a very dilute solution. In one preferred embodiment, the solid content of the solution is less than 25%, very preferably less than 15%. The use of a very low solid content (a solid content of less than 15%) makes it possible to reduce the layer thickness tolerance of the coating of the PSA tape film.

For example, for the weight of the coating, by using a roll applicator, a layer thickness tolerance of 1 g/m²±30% (dried solids) may be obtained, wherein the ±30% corresponds to a fluctuation of 0.3 g/m² in absolute terms.

After the first step of the application of the PSA, the adhesive is dried in a drying tunnel and the solvent is removed. Introduced heat may also be utilised for initiating a thermal cross-linking reaction. It may also be required to use UV and/or an electron beam for the cross-linking of the composition. To this end, the techniques which have already mentioned in the melt process may be used.

After the application and drying of the pressure-sensitive adhesive, a carrier film is laminated to the adhesive. For this purpose, it may be necessary to pretreat the carrier film by means of, for example, corona. The lamination should be carried out without bubbles. It should also be ensured that a tensile stress, especially in the case of a solution in which the carrier film is very thin, is selected to be much lower than the breaking tension of the carrier film. In a preferred embodiment, said tensile stress is at least 50% lower than the breaking tension of the carrier film.

In addition, in order to produce an ultra-thin light-shielding double-sided pressure-sensitive adhesive tape, a second PSA layer also needs to be applied. This can be done by using the method mentioned above. In principle, the PSA in the second coating may be directly applied to the carrier film (an assembly formed from the release liner, the PSA layer, and the carrier film). However, this is not a preferred embodiment, because in this case stress may be generated in the downstream drying channel due to the introduction of heat. A very preferred solution comprises the steps of first applying the second PSA onto the release liner, then drying same in a drying channel, and then, laminating same on the carrier film side together with the assembly formed from the release liner, the PSA, and the carrier film. This enables the carrier film to avoid thermal loading, which is advantageous for a carrier film with a layer thickness of less than 4 microns, more preferably a layer thickness of less than 2 microns.

Also in this operation step, it may also be necessary to cross-link the PSA layer with UV and/or an electron beam in accordance with the method determined hereinabove.

In a very preferred solution, an ultra-thin light-shielding double-sided pressure-sensitive adhesive tape is used in said assembly as a double-liner product. Said double-liner solution makes it possible to avoid air inclusions and bubbles; otherwise, the air inclusions and bubbles may adversely affect the thickness tolerance of the product and lead to non-uniformity of the properties of the present utility model during use.

Application

The adhesive tape of the present utility model is particularly suitable for use as a light-shielding double-sided pressure-sensitive adhesive tape, and is used for producing various different products, in particular electronic products. Representative electronic products include (but are not limited to): liquid crystal data display systems (liquid crystal displays, LC displays, and LCD) required for computers, televisions, notebook computers, PDA, mobile phones, digital cameras, etc.

Typically, the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape of the present utility model is used for bonding a reflective film in a housing of a backlight unit. For this use, one or two release films or release papers may be used for lining the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape. In the first step, a perforated product (die cut part) is produced, for which a typical flat-bed, rotary or laser die cutting method may be used here. In a very preferred embodiment, the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape is first laminated to the reflective film over the entire area.

For this purpose, it is necessary to remove the release liner and then carry out a lamination step. The lamination of the reflective film must be carried out in a manner of not containing bubbles or impurities, thereby avoiding unevenness.

For example, the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape has been completely or partially bonded to the reflective film, prior to the formation of a desired shape therein in a die cutting process. Subsequently, said release liner is removed from the assembly comprising the reflective film and the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape, and the assembly is then placed in the housing of the backlight unit. The housing may be made of a plastic or a metal. It is very preferable to use a plastic such as polycarbonate.

Compared with the prior art, the main advantages of the adhesive tape of the present utility model comprise:

(1 ) being very thin on the premise of meeting mechanical strength;

(2) excellent light-shielding performance. The light transmittance is very low, wherein the ultraviolet light and/or visible light transmittance of the adhesive tape is < 5%;

(3) the raw materials used are environmentally friendly and safe;

(4) the inorganic filler such as carbon black does not migrate and aggregate, and therefore the stability is high;

(5) uniform colour distribution;

(6) no need for printing, and no uneven pattern caused by printing; and

(7) Compared with printed films, the adhesive tape of the present utility model has no volatile organic compounds and is more environmentally friendly.

The present utility model is further illustrated below in conjunction with specific examples. It should be understood that these examples are only used for describing the present utility model, rather than limiting the scope of the present utility model. In the following examples, conventional conditions or conditions suggested by manufacturers are generally used for experimental methods in which the specific conditions are not specified. Unless otherwise stated, percentages and parts are by weight and in parts by weight.

1. Measurement of total thickness of adhesive tape and measurement of thickness of PET layer

The measurement is carried out in accordance with a standard method of DIN 53370.

In addition, the measurement may also be carried out in accordance with ASTM D 1000-04 (01 September 2004) (No. 21 to 27) using the following parameters: a disk diametre of 10 mm (No.23.1 .2.); and an applied pressure of 4 N (No.23.1 .3.); with the test conditions being: a temperature of 23°C and an atmospheric humidity of 50%; the evaluation being conducted within one hour; and the measurement being carried out at a distance of 10 cm in the crosswise direction of the moving adhesive tape.

Furthermore, as an alternative to the measurement, AFERA 4000/PSTC 33 may be used accordingly, wherein the parameters used are the same as above. The standard deviation s is calculated by means of the following formula:

wherein n is the number of data values, x, represents a single measurement, and x represents the average of all measurements.

2. Determination of light transmittance (%)

The measurement is carried out in accordance with a standard method of DIN 5033-4.

Example 1

Ultra-thin light-shielding double-sided pressure-sensitive adhesive tape No. 1

As shown in figure 1 , the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape of this example comprises the following layers laminated from top to bottom:

(a) a first pressure-sensitive adhesive layer 1 1 having a thickness of 4 microns;

(b) a black PET material layer 12 having a thickness of 4.5 microns; and

(c) a second pressure-sensitive adhesive layer 13 having a thickness of 4 microns, wherein a main surface of said black PET layer is bonded to said first pressure-sensitive adhesive layer, and the other main surface of said black PET layer is bonded to said second pressure-sensitive adhesive layer;

and said adhesive tape has a total thickness (a1 +b+a2) of 12.5 microns.

After measurement, said adhesive tape has a total thickness standard deviation of < 0.3 microns, and a light transmittance of < 5%.

Example 2

Ultra-thin light-shielding double-sided pressure-sensitive adhesive tape No. 2

As shown in figure 2, the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape of this example comprises the following layers laminated from top to bottom:

(a0)a first peelable layer 14;

(a) a first pressure-sensitive adhesive layer 11 having a thickness of 3.5 microns;

(b) a black PET material layer 12 having a thickness of 5 microns; and

(c) a second pressure-sensitive adhesive layer 13 having a thickness of 3.5 microns, wherein a main surface of said black PET layer is bonded to said first pressure-sensitive adhesive layer, and the other main surface of said black PET layer is bonded to said second pressure-sensitive adhesive layer;

and said adhesive tape has a total thickness (a1 +b+a2) of 12 microns.

After measurement, said adhesive tape has a total thickness standard deviation of < 0.5 microns, and a light transmittance of < 3%.

Example 3

Ultra-thin light-shielding double-sided pressure-sensitive adhesive tape No. 3

As shown in figure 3, the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape of this example comprises the following layers laminated from top to bottom:

(a0)a first peelable layer 14;

(a) a first pressure-sensitive adhesive layer 1 1 having a thickness of 5 microns;

(b) a black PET material layer 12 having a thickness of 5 microns;

(c) a second pressure-sensitive adhesive layer 13 having a thickness of 5 microns; and

(d ) a second peelable layer 15,

wherein a main surface of said black PET layer is bonded to said first pressure-sensitive adhesive layer, and the other main surface of said black PET layer is bonded to said second pressure-sensitive adhesive layer;

and said adhesive tape has a total thickness (a1 +b+a2) of 15 microns.

After measurement, said adhesive tape has a total thickness standard deviation of < 0.5 microns, and a light transmittance of < 4%. All the documents mentioned in the present utility model are cited in the present application by reference, as if each document is cited alone as a reference. In addition, it should be understood that after reading the above-mentioned contents taught by the present utility model, a person skilled in the art could make various changes or modifications to the present utility model, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims

Patent claims

1 . An ultra-thin light-shielding double-sided pressure-sensitive adhesive tape, characterised in that said adhesive tape comprises a structural layer laminated from top to bottom, said structural layer comprising:

(a) a first pressure-sensitive adhesive layer A1 having a thickness of a1 ;

(b) a black PET material layer B having a thickness of b; and

(c) a second pressure-sensitive adhesive layer A2 having a thickness of a2, wherein a main surface of said black PET material layer is bonded to said first pressure-sensitive adhesive layer, and the other main surface of said black PET material layer is bonded to said second pressure-sensitive adhesive layer;

2. The adhesive tape of claim 1 , characterised in that said adhesive tape has a total thickness of 10-15 microns.

3. The adhesive tape of claim 1 , characterised in that said adhesive tape has a total thickness of 12-15 microns.

4. The adhesive tape of claim 1 , characterised in that said black PET material layer has a thickness of 3.5-4.5 microns.

5. The adhesive tape of claim 1 , characterised in that said black PET material layer has a thickness of 4.0-4.5 microns.

6. The adhesive tape of claim 1 , characterised in that said first pressure-sensitive adhesive layer is a transparent PSA material layer having a thickness of 1 -6 microns.

7. The adhesive tape of claim 1 , characterised in that said first pressure-sensitive adhesive layer is a transparent PSA material layer having a thickness of 2-4 microns.

8. The adhesive tape of claim 1 , characterised in that said second pressure-sensitive adhesive layer is a transparent PSA material layer having a thickness of 1 -6 microns.

9. The adhesive tape of claim 1 , characterised in that said second pressure-sensitive adhesive layer is a transparent PSA material layer having a thickness of 2-4 microns.

10. The adhesive tape of claim 1 , characterised in that the outer surface of said first pressure-sensitive adhesive layer is provided with a first peelable layer; and/or the outer surface of said second pressure-sensitive adhesive layer is provided with a second peelable layer.

1 1. The adhesive tape of claim 1 , characterised in that said adhesive tape is a roll product or a sheet product.

12. A roll product, characterised in that said roll product comprises

a roll core,

and the ultra-thin light-shielding double-sided pressure-sensitive adhesive tape of claim 1 surrounding said roll core.

13. The roll product of claim 12, characterised in that said roll has a width of 0.5-2.5 metres.

14. The roll product of claim 12, characterised in that said roll has a length of 2-2000 metres.