WO2016146349A1

WO2016146349A1 - Pressure sensitive adhesive composition and infrared transparent black tape, the process of preparing thereof and use thereof

Info

Publication number: WO2016146349A1
Application number: PCT/EP2016/053755
Authority: WO
Inventors: Daniel Klier
Original assignee: Tesa Se
Priority date: 2015-03-13
Filing date: 2016-02-23
Publication date: 2016-09-22
Also published as: CN106032458A

Abstract

The present application is related to pressure sensitive adhesive composition and infrared transparent black tape, the process of preparing thereof and use thereof. Specifically, the application in the field of bonding technology is related to infrared transparent black pressure sensitive adhesive, especially infrared transparent tape. The pressure sensitive adhesive and tape have transparency in the visual light region between 400 and 780 nm significantly lower than that in the near infrared region between 780 and 1000 nm. Furthermore, the present application is related to the process of preparing the pressure sensitive adhesive and tape, and use thereof, such as use in many fields of optoelectronics.

Description

Pressure sensitive adhesive composition and infrared transparent black tape, the process of preparing thereof and use thereof

Technical Field

The present invention is in the field of bonding technology, specifically the present invention is related to a pressure sensitive adhesive composition, which can be used to prepare infrared transparent black adhesive. The present invention is also related to a tape comprising the above pressure sensitive adhesive, especially infrared transparent black tape. Furthermore, the present invention is related to the process of preparing the pressure sensitive adhesive and the tape, and use thereof, especially use in the field of optoelectronics.

Background

Optical sensors either work in specific noncontiguous wavelength ranges, or the functional range thereof extends in much wider electromagnetic radiation wavelength ranges. In order to integrate this type of optical sensors into a structure designed for it, special materials and production techniques which are compatible with the functional ranges of the optical sensors are required. The optical sensors are mostly consisting of transmitters and receivers, which respectively transmit or receive at defined wavelength ranges. In video surveillance techniques, CCTV or web camera are normally used, they should provide observer or surveillance software with reliable high-quality images in the daytime and in the nighttime. Furthermore, these video surveillance equipments should not be seen by the public, or at least should be unremarkable, and should be protected from destruction. These three requirements are realized by corresponding sensors cleverly integrated in a camera. Night vision function in the dark is achieved by emitting near infrared light such as at 850 nm or 940 nm. All the objects reflect near infrared radiation, which can be detected by receiving sensors. In order to hide the surveillance device, the housing must have a black layer, which allows sufficient visible light to pass and allows as much as possible of ("the more the better") near infrared light to pass the black layer.

In order to detect the destruction behavior, rangefinders, also called proximity sensors or proximity detection devices, consisting of infrared emitting diode and infrared receiving diode can be used, and the infrared emitting diode and the infrared receiving diode are placed in distinct angles. As soon as an unwanted object gets into a region very near the sensor, the object reflects the near infrared light emitted by the infrared emitting diode back to the infrared receiving diode and triggers a quiet tampering alarm. Such object can be a bag that is pulled over the device or color that is sprayed on the device. Because this anti tampering mechanism should be invisible to the aggressor, these sensors must be invisibly integrated into the device. The position of this anti destruction sensor should be invisible to the aggressor, so that the aggressor cannot take some target-oriented actions to tamper this safety mechanism, or is not warned to have to take these mentioned actions to tamper the device. Since these devices normally have black appearance, a suitable filter is required that is nearly transparent in near infrared light range and nearly opaque in visible light range. Furthermore, this filter should have a structure that can be easily integrated into a device, such as a surveillance device. Sometimes a visual transparency of 5 to 20 % is required for the function of these devices. Up to now, the following type of optical filter is well known, i.e., optical filters produced by coating infrared transparent black paint on plates or films which are transparent to visible light and infrared light. As this type of colored pigment used to provide optical functions is mostly coarse particle, the known paint must be coated in thick layer through screen printing. This printing technique is complicated and expensive, and results in coatings with poor quality. In particular, the thickness tolerance of the optical filter is very poor, and thus the homogeneity of the optical filter is also poor, and this possibly results in functional failure of the instrument produced therefrom. Another possibility is provided by preparing inherently black colored, infrared transparent film, wherein pigment is uniformly distributed in the film resin per se. However, this method has the following disadvantage: the minimum thickness of the film is very large. By increasing the melt flow index, high shear force can be obtained when mixing, which facilitates pigment to uniformly distribute in resin, so as to obtain very uniform film. However, once high content of pigment or dye is mixed into the film resin, small defects occur during orientation of the film due to fracture of the film nearby caused by the pigment. Furthermore, the stability of the films is unsatisfactory because the tensile strength at break is very low. In order to obtain sufficient blackness even with thin film, resins filled with very high amount of pigment must be used, leading to fragile and unstable film. This type of film lacks cohesion, and leads to fracture in subsequent use. Due to the above-mentioned reasons, this type of film is currently not commercially available. The high thickness makes the film very stiff, what leads to loss of flexibility of the tape, and thus the tape cannot adapt to curved surfaces and will slowly detach because of the permanent strain of the stiff film. Such stiff films also cannot adapt to rough surfaces or even flat surfaces that are partly coated or printed with some ink.

It is well known in the prior art that, high content of any particulate additives such as pigment can greatly reduce the peel adhesion or completes deteriorate the peel adhesion, and normally pigment is incompatible with many cross linking agents of adhesive, thus one skilled in the art normally would not consider blending normal transparent substrates with functional, infrared-transparent black adhesive. Furthermore, this type of adhesive has long development cycle and high costs. In particular, the most challenging issue is how to obtain the desired homogeneity, and the reasons are that pigments have higher density compared with adhesives, and heavier pigments would settle to the bottom of a container. In particular, low viscosity necessary for the adhesive is not suitable for dispersing suitable pigment into adhesives, such as melt of PET or PMMA resin. Summary of the Invention

The aim of the invention is shown to provide infrared transparent black pressure sensitive adhesive composition and infrared transparent black tape.

Further aim of the invention is to provide pressure sensitive adhesive composition and tape, which have transparency in the infrared region 850-950 nm twice or above, three times or above, or four times or above of the transparency in the visible light region 400-700 nm.

Yet further aim of the invention is to provide pressure sensitive adhesive composition and tape, which can conquer the defects existing in the prior art as mentioned above, such as low tensile strength at break, low peel adhesion, too big thickness, poor homogeneity, high production cost, as well as unsuitableness for rough and curved surfaces. The aim of the invention is achieved through the following embodiments:

The present invention discloses a pressure sensitive adhesive composition, which comprises base polymer, pigment and optionally tackifier resin, wherein the content of the pigment is 0.1 -20 wt%, and the content of the tackifier resin is 0-33 wt%, and the pressure sensitive adhesive composition can be used to prepare infrared transparent black pressure sensitive adhesive.

In one aspect of the invention, the content of the pigment is 0.1 - 10 wt%, preferably 0.1-5 wt%, more preferably 0.5-3.5 wt%, most preferably 1 -3.5 wt%, and the content of the tackifier resin is 1 -33 wt%, preferably 5-30 wt%, more preferably 10-25 wt%, most preferably 15-23 wt%. In another aspect of the invention, the pressure sensitive adhesive has a transparency in the infrared region 850-950 nm, which is twice or above, three times or above, or four times or above of the transparency in the visible light region 400-700 nm.

In yet another aspect of the invention, the tackifier resin has a softening point between 50 and 150 °C, preferably between 80 and 145 °C, and a molar mass between 400 and 20000 g/mol, preferably between 500 and 2000 g/mol.

In still another aspect of the invention, the tackifier resin is selected from terpene phenolic resins, rosin esters, hydrogenated terpene phenolic resins, polyterpene resins, hydrocarbon resins and acrylic resins, preferably selected from terpene phenolic resins and acrylic resins.

In another aspect of the invention, the pigment is black pigment, red pigment, yellow pigment, blue pigment, brown pigment or the combination thereof, preferably black pigment, red pigment or the combination thereof. In yet another aspect of the invention, the pigment comprises HPP Black 8230,

Paliogen Black L0086, Lumogen Black F 4280, HPP Black 823, Solvent Black 32, Neozapon Black X55, Lumogen Black F 4281 , Neptune Red NR543, Sicopal Yellow l 160FG, Sicopal Blue 6310, Sicopal Brown 2595, or the combination thereof. In still another aspect of the invention, the base polymer is selected from acrylic polymer, silicone, polyurethane, styrene-isoprene-styrene block copolymer, styrene-butadiene blockcopolymer and polyester.

The present invention further discloses a process to prepare said pressure sensitive adhesive composition, comprising the following steps: 1) the pigment is mixed with the tackifier resin to obtain a homogenous master batch;

2) the master batch is mixed with base polymer and optionally additional tackifier resin.

In one embodiment of the invention, the first mixing step is carried out using the following instrument: extruders, kneaders, ball mills, dispersers, blade stirrers or vessel mixers. In another embodiment of the invention, the first mixing step is carried out at room temperature by adding solvents.

In yet another embodiment of the invention, the first mixing step is carried out at higher temperature with the molten resin.

The present invention discloses an infrared transparent black tape, which comprises at least one adhesive layer and optionally a substrate, wherein the adhesive layer is produced from said pressure sensitive adhesive composition. In one embodiment of the invention, the tape has a transparency in the visible light region between 400 and 700 nm of below 40%, preferably below 20%, more preferably below 15%, most preferably below 12%, and a transparency in the infrared region between 850 and 950 nm of above 60%, preferably above 70%, more preferably above 75%.

In another embodiment of the invention, the substrate comprises infrared transparent polymer(s) that can be processed into film.

In yet another embodiment of the invention, the substrate comprises polyester, such as polyethylene terephthalate, polycarbonate, polymethylmethacrylate, polyethylenenapthalate; polyacrylate; polyolefin, such as polypropylene, polyethylene, polystyrene; polyimide; cellulose triacetate; polysulfone, ethylene propylene copolymer; especially polyethylene terephthalate and polymethylmethacrylate. In one embodiment of the invention, the tape has a tensile strength at break of above 80 N/mm², preferably above 100 N/mm², more preferably above 150N/mm², most preferably above 160N/mm².

In another embodiment of the invention, the tape has a peel adhesion of above 5 N/cm, preferably above 7 N/cm, more preferably above 7.5 N/cm, most preferably above 8 N/cm.

In yet another embodiment of the invention, the tape has a haze in the 400 to 950 nm wavelength range, especially at 850nm, of below 5, preferably below 4, more preferably below 3, most preferably below 2.

In one embodiment of the invention, the tape is a single sided adhesive tape consisting of a substrate and an adhesive layer coated thereon. The substrate has a thickness between 1 and 500 μπι, preferably between 1 and 100 μηι, more preferably between 2 and 50 μηι and most preferably between 2 and 12 μηι, and the adhesive layer coated on the substrate has a thickness between 1 and 2000 μιη, preferably between 5 and 50 μηι and more preferably between 10 and 30 μηι. The tape has a total thickness between 12 and 80 μηι, preferably between 12 and 42 μιη. In another embodiment of the invention, the tape is a double sided adhesive tape consisting of a substrate and two infrared transparent black adhesive layer coated on both sides of the substrate. Each adhesive layer has a thickness between 1 and 2000 μηι, preferably between 5 and 125 μηι, more preferably between 5 and 50 μηι and most preferably between 10 and 30 μηι, and the substrate has a thickness between 1 and 500 μηι, preferably between 2 and 50 μηι and most preferably between 2 and 12 μηι. The tape has a total thickness between 5 and 4500 μηι, preferably between 12 and 150 μηι and most preferably between 22 and 72 μηι.

In yet another embodiment of the invention, the tape is a transfer tape consisting of the adhesive itself. The tape has a thickness between 1 and 2000 μηι, preferably between 5 and 150 μηι, more preferably between 5 and 100 μηι and most preferably between 10 and 50 μηι.

The invention is also related to a process to prepare an infrared transparent black tape, wherein said pressure sensitive adhesive composition is coated onto a substrate or liner.

According to one aspect of the invention, the process further comprises a drying step after the coating step.

The invention is also related to use of said pressure sensitive adhesive composition or said tape in the field of optoelectronics.

According to one aspect of the invention, the fields of use of said pressure sensitive adhesive composition or said tape are as follows: surveillance technique; consumer electronics, especially in remote control units, handhelds, phones; automotive industry, such as dashboards that contain displays and sensors, and building and construction, such as door access systems. The pressure sensitive adhesive composition and tape of the invention possess the desired optical properties, i.e., they are infrared transparent, visually black.

The pressure sensitive adhesive composition and tape of the invention also have low haze. Furthermore, by using the pressure sensitive adhesive composition and tape of the invention, the following technical effects can be achieved: high tensile strength at break, high homogeneity, sufficient and stable peel adhesion, simple production process with low cost as well as low total thickness of the tape.

Detailed Description of the Invention

Surprisingly, suitable infrared transparent black pressure sensitive adhesive can be prepared, wherein pressure sensitive adhesive is incorporated with pigment with a sufficiently high content, and meanwhile retains sufficiently high peel adhesion.

The pressure sensitive adhesive composition comprises base polymer, pigment and optionally tackifier resin, wherein the content of the pigment is 0.1-20 wt%, and the content of the tackifier resin is 0-33 wt%, and the pressure sensitive adhesive composition can be used to prepare infrared transparent black pressure sensitive adhesive.

Preferably, the content of the pigment is 0.1 - 10 wt%, preferably 0.1 -5 wt%, more preferably 0.5-3.5 wt%, most preferably 1 -3.5 wt%, and the content of the tackifier resin is 1 -33 wt%, preferably 5-30 wt%, more preferably 10-25 wt%, most preferably 15-23 wt%.

In principle, any kind of tackifier resin can be used to mix with the pigment before adding the mixture to the base polymer. In particular, the tackifier resin has a softening point between 50 and 150 °C, preferably between 80 and 145 °C, and a molar mass between 400 and 20000 g/mol, preferably between 500 and 2000 g/mol. Terpene phenolic resin, rosin esters, hydrogenated terpene phenolic resins, polyterpene resins, hydrocarbon resins and acrylic resins can be used as tackifier resin. Most preferred are water white resins with low haze and color like terpene phenolic and acrylic resins. In principle any kind of base polymers can be used, for example acrylic polymer, silicone, polyurethane, SIS (styrene-isoprene-styrene block copolymers), SBC (styrene-butadiene blockcopolymers) and polyester adhesives. Especially suitable adhesives are based on acrylic polymer, due to their advantageous properties, especially optical transparency.

The pigment is black pigment, red pigment, yellow pigment, blue pigment, brown pigment or the combination thereof, preferably black pigment, red pigment or the combination thereof. As pigment, the pigment based on polycyclic aromatic hydrocarbon compound perylene has been proved to be especially advantageous, wherein desired optical properties can be obtained through substitution with different functional groups on the perylene. 2,9-bis[(4-methoxyphenyl)methyl]- anthracene [2, 1 ,9-D,E,F:6,5, 10-D',E',F'] diisoquinolin - l ,3,8, 10(2H,9H)-tetrone (HPP Black 8230, K-lmaxs) is a suitable example. Commercially available pigments Paliogen Black L0086 (BASF), Lumogen Black FK4280 (BASF) or Lumogen FK4281 (BASF) can also be used. Further pigments that can be used alone or in combination comprise Sicopal Yellow Kl 160 FG (BASF), Sicopal Blue K63 10 (BASF) and Sicopal Brown K2595 (BASF). The particle size of the pigments is preferably below 50 μηι, especially preferred below 10 μηι.

HPP Black 8230; Paliogen Black L0086, CAS 83524-75-8

However, other pigments or dyes with the corresponding optical properties can also be used, such as HPP Black 823 (K-lmaxs), pigment black 32 (Liangang) or Neozapon Black X55 (BASF). A metal complex dye comprising chromium is shown below, wherein different organic substitutes can be introduced on the aromatic base structure. Also colored pigments such as Neptune Red NR543 (BASF) can be used to obtain infrared transparent red tape, as pure Neptune Red NR543 pigment results in visually red adhesive layer. Pigments with other colors can also be used to obtain other visual color. Furthermore, Neptune Red NR543 (BASF) can be used to adjust the color of infrared transparent black tapes. If colored adhesive layer does not have a deep gray or black appearance, for example, if it comprises blue or red components, adequate amount of other single color pigments can be used to compensate the colored component to get a deep black appearance.

Neozapon Black X55, Solvent Black 29 (CAS 61901-87-9)

Base structure of Neozapon Black X55 coordinated with Chrome

Neptune Red NR543 (BASF, CAS-509-34-2) Pigments with excellent stability and low interaction with the matrix pigment based colors are preferred. The pigments normally have better transparency in the near infrared region than in the visible light region. The pigment content must be exactly adjusted so that the transparency in the visible light region is sufficient low but not too low and the transparency in the near infrared region is still sufficiently high, so that they can be used to prepare some sensors hat require a certain visibility in the visible light region (such as ambient light sensor, which is used to switch color to black/white mode). The transparency in the near infrared region is twice or above of that in the visible light region, more preferably, the transparency in the infrared region is above 40% and the transparency in the visible light region is below 20%, even more preferably, the transparency in the infrared region is above 70% and the transparency in the visible light region is below 15%. Additionally, it is preferred that the transparency in the visible light region is kept on the same level with a flat curve, especially between 2% and 20%, more preferably between 5% and 15%, and most preferably between 6% and 1 1 %. In the near infrared region it is also preferred that the curve is very flat, and once it reaches a constant level at the wavelengths above 800 nm, it does not deviate to more than 10% absolute higher than the constant level or more than 10% absolute lower than the constant level (For example, when the constant level is 80%, the curve does not comprise any point indicating a transparency of above 90% or below 70%).

Furthermore, especially preferred are combinations of pigments that bear a very flat curve in the visible light region in the wavelength of between 400 and 780 nm. For example, the aim can be obtained by using a combination of Paliogen Black L0086 (0.8 wt%) and Neozapon Black X55 (BASF, 0.8 wt%) in a 50 μη thick infrared transparent black adhesive layer. Any other combinations that have a visible light transparency of between 5 and 15 % and have a very good black appearance can be used. In particular, the pressure sensitive adhesive of the present invention has a transparency in the infrared region 850-950 nm, which is twice or above, three times or above, or four times or above of the transparency in the visible light region 400-700 nm.

Especially advantageous ways to produce such pressure sensitive adhesive are shown as follows: firstly the pigment is mixed with the tackifier resin to obtain homogenous takifier resin/pigment master batch, and then the master batch and optionally additional tackifier resin are added into base polymer, in order to prepare homogenous, functional pressure sensitive adhesive composition. Regarding the first mixing step, different mixing devices can be used to disperse the pigment into the tackifier resin such as extruders, kneaders, ball mills, dispersers, blade stirrers and vessel mixers; the mixing can be conducted at room temperature by adding suitable solvents, or at higher temperature with the molten resin.

It is especially advantageous to add terpene phenolic resin/pigment master batch as powder into a pure base polymer solution or a base polymer solution comprising tackifier resin, in order to obtain a very homogeneous infrared transparent black coating.

The infrared transparent tape of the present invention comprises the pressure sensitive adhesive of the present invention, and the tape can be produced with multiple embodiments, so as to allow users to realize the diversified designing solutions of the products. In one embodiment, single sided adhesive tape is consisting of a substrate and an adhesive layer coated thereon. The substrate has a thickness between 1 and 500 μηι, preferably between 1 and 100 μηι, more preferably between 2 and 50 μηι and most preferably between 2 and 12 μηι. The adhesive layer coated on the substrate normally has a thickness between 1 and 2000 μηι, preferably between 5 and 50 μηι and more preferably between 10 and 30 μιη. In an advantageous embodiment, the infrared transparent black tape has a total thickness between 12 and 80 μηι, preferably between 12 and 42 μη .

In another embodiment, a double sided adhesive tape is consisting of a substrate and two infrared transparent black adhesive layer coated on both sides of the substrate. Each adhesive layer has a thickness between 1 and 2000 μιη, preferably between 5 and 125 μιη, more preferably between 5 and 50 μηι and most preferably between 10 and 30 μηι. The two adhesive layers can have different thickness in the above-mentioned ranges. The substrate has a thickness between 1 and 500 μη , preferably between 2 and 50 μπι and most preferably between 2 and 12 μιη. In an advantageous embodiment, the double sided adhesive tape consisting of three layers has a total thickness between 5 and 4500 μιη, preferably between 12 and 150 μιη and most preferably between 22 and 72 μηι.

In another embodiment, the tape is consisting of the adhesive itself, and it is also called transfer tape. Such transfer tape has a thickness between 1 and 2000 μιη, preferably between 5 and 150 μηι, more preferably between 5 and 100 μηι and most preferably between 10 and 50 μη .

To ensure that the tape can be unwind and processed easily, the tape can comprise at least one liner. For transfer tape only comprising an adhesive layer, the at least one liner is located at either side or both sides of the adhesive layer. For tape comprising substrate and adhesive layer, the at least one liner is located at the side of the adhesive layer opposite to the substrate. Alternatively, the substrate of a single sided adhesive tape can be coated with a release agent. Liners and release agents are commonly known to the expert in the art.

In principle, all infrared transparent polymers that can be processed into film through extrusion or other film forming processes can be used as the substrate. The following can be used: polyester, such as PET (polyethylene terephthalate), PC (polycarbonate), PMMA (polymethylmethacrylate), PEN (polyethylenenapthalate); polyacrylate; polyolefin, such as PP (polypropylene), PE (polyethylene), PS (polystyrene); PI (polyimide); cellulose triacetate; polysulfone, ethylene propylene copolymer. PMMA and PET are especially preferred, as they can produce substrate with excellent mechanical properties and very low haze value. Optically transparent substrates with a haze of below 20%, preferably below 10%, most preferably below 5% at the whole wavelength of 400-lOOOnm are preferably used. Because any kind of unfilled standard substrate can be combined with infrared transparent black adhesive coating to obtain infrared transparent black tape, tapes with very good mechanical stability can be produces with low cost. Due to the good mechanical stability, these tapes can be easily integrated into any existing production lines suitable for normal tapes. The substrates have a tensile strength of above 30 N/mm², preferably above 80 N/mm², more preferably above 100 N/mm² and most preferably above 150 N/mm². In another embodiment, partly or highly filled filmic infrared transparent black substrates can be combined with infrared transparent black adhesives, wherein the type and content of pigments in the substrates and adhesives can be the same or different.

When pigment Paliogen Black L0086 is used in a transfer tape with a thickness of 50μηι, a pigment concentration of 0.1 to 5 wt%, especially 0.5 to 3 wt% and most preferably 1 to 1.5 wt% leads to feasible results. If the adhesive layer thickness is reduced, the pigment concentration has to be enhanced accordingly to keep the same optical properties.

The infrared transparent black tape of the invention have a transparency in the visible light region between 400 and 700 nm of below 40%, preferably below 20%, more preferably below 15%, most preferably below 12%, and a transparency in the infrared region between 850 and 950 nm of above 60%, preferably above 70%, more preferably above 75%.

The infrared transparent black tape of the invention have a tensile strength at break of above 80 N/mm², preferably above 100 N/mm², more preferably above 150N/mm², most preferably above 160N/mm².

The infrared transparent black tape of the invention have a peel adhesion of above 5 N/cm, preferably above 7 N/cm, more preferably above 7.5 N/cm, most preferably above 8 N/cm.

The infrared transparent black tape of the invention have a haze in the 400 to 950 nm wavelength range, especially at 850nm, of below 5, preferably below 4, more preferably below 3, most preferably below 2.

Examples

A) Synthesis of base polymer AC-1

A standard 200 1 tank reactor suitable for radical polymerization is filled with 3.14 kg acrylic acid, 58.4 kg 2-ethylhexylacrylate, 1 1 kg methylacrylate and 53.3 kg acetone/benzine/isopropanole (49:49:2). After 45 minutes of stirring and degassing with nitrogen the reactor is heated to 58°C. After the temperature was reached 40 g 2,2^,-azoisobutyronitrile (AIBN) is added. After adding the AIBN the jacked of the reactor is heated to constant 75°C and left at this temperature. After one hour reaction additional 40 g AIBN is added. After 5 h and lOh the reaction mixture was diluted with each 15 kg acetone/isopropanole (90: 10). After further 6 and 8 h each 100 g dicyclohexylperoxydicarbonate (Perkadox 16 company Akzo Nobel) diluted in each 800 g acetone was added. The reaction was terminated after 24 h reaction time and the reaction mixture cooled to room temperature. B) Method for preparing the adhesive coating solution

27 wt% of the pigment or pigment mixture and 73 wt% of the tackifier resin are mixed in a twin screw extruder (Coperion ZSK 18 MEGAlab, 18 mm Da (outer screw diameter), 1 1.7 kW electric engine power) at 105°C and 1000 rpm and an output of 3 kg/h to obtain pigment/tackifier resin master batch. The master batch was granulated to small pallets. The obtained granulate and additional tackifier resin was mixed with the base polymer (for example base polymer AC-1) for 30 minutes. The ratio of the additional tackifier resin and pigment/tackifier resin master batch is adjusted in a way that the ratio of base polymer and total amount of tackifier resin meets the target and can be kept constant independent of the pigment concentration. Lastly, 0.3 mass parts of tris(2,4-pentandionato)aluminium (cross linker) based on 100 mass parts base polymer are added to the obtained mixture and mixed.

C) Method for making the adhesive layer

The above obtained adhesive coating solution was coated onto a substrate or liner (depending if it is a single sided tape or a transfer tape) with a dry thickness of 50 or 25 μηι (according to the sample table). The solvent was dried at 120 °C in a drying oven for 15 minutes. The open adhesive side was covered with a 50 μηι thick siliconized polyester liner after drying.

D) Method of making the substrate T3 (screenprinted PET)

A 23 μηι thick polyester film (Mitsubishi Hostaphan RNK 23) is coated with 8 g/m² (dry coating weight) of Teikoku IPX-HF 30821 paste using screen printing process and dried for 15 minutes at 120°C in a drying oven.

E) Method of making the substrate T4 (colored PET)

97.8 kg dried polyester granulate (Invista 6020) and 2.2 kg BASF Paliogen Black L0086 are molten in an extruder at 180 °C and mixed. At 265 °C the melt is casted onto a cooling roller and is stretched at 90°C three times in machine direction and afterwards three times in cross direction. Thermofixation is finally done for 8 seconds at 230°C.

F) List of raw material used

T 1 : Mitsubishi Hostaphan RNK 23

· T2: Evonik Plexiglas 9F001 ^• 0066J: Pigment on basis carbon black BASF Microlith Black 0066 J

^• X55 : BASF Neozapon Black X55

GA-90: Arakawa Pensel GA-90 rosin ester based tackifier

543: BASF Neptun Red Base 543 (based on Xanthene, Rodamin B)

· UP-1010: Toagosei UP-1010 acrylic resin

^• TF-95 : Xinyi Songyuan TF-95 terpene phenolic resin

^• 2-Ethylhexylacrylate: TCI fine chemicals product AO 144 (2-ethylhexylacrylate monomer, CAS 103- 1 1-7)

Methylacrylate: TCI fine chemicals product AO 145 (Methyl Acrylate, CAS 96-33-3)

Acrylic Acid: TCI fine chemicals product AO 141 (Acrylic Acid, CAS 79- 10-7)

^• Acetone: Sigma-Alddrich product V0800022 VETEC (Acetone >99%, CAS 67-64- 1)

^• Benzine: Shell Chemicals product Q2266 (SBP 60/95 LNH or Shellsol 60/95 LNH))

Isopropanole: Shell Chemicals product S l l l l (Isopropylalkohol, CAS 67-63-0)

^• Perkadox: Akzo Nobel product Perkadox 16 (Di(4-tert-butylcyclohexyl) peroxydicarbonate, powder), CAS 15520- 1 1 -3

· AIBN: Sigma- Aldrich product 441090 2,2 '-Azobis(2-methylpropionitrile),

CAS 78-67- 13140

G) Measuring methods

Transparency (total transmittance)

The transparency is measured according to method ASTM D 1003 except that the values for different wavelengths are not computed to match CIE standard illuminant C or A using a UVVIS spectrometer with integrating sphere. The transparency is observed at distinct wavelengths of 550 and 850 nm. The transparency is related to the total light transmittance of all angles. Uniformity The transmission of 10 points randomly chosen on the surface of one A4 sheet of sample is measured with a UVVIS spectrometer Analytik Jena Specord 250 Plus BU in transmission mode at 550 nm. The smallest value is subtracted from the biggest value and divided by the transmission to get the Uniformity in percent of the transmission. Values below 2 are related to a good quality of highly uniform samples.

Haze 850 nm (diffuse transmission)

The transparency is measured according to method ASTM D 1003 except that the values for different wavelengths are not computed to match CIE standard illuminant C or A using a UVVIS spectrometer with integrating sphere. The haze is observed at a wavelength of 850 nm. The haze is related to the light transmittance with an angel of bigger 2.5°.

Visual Blackness

The visual blackness is judged by human eye by placing the sample onto a white opaque surface and judging the blackness. If a solid black appearance can be observed the sample is judged with "+". If any color shades appear like yellowish or bluish components appear or if the sample is rather grey than black the sample is judged with

Peel Adhesion (Steel)

The peel adhesion (bond strength) is tested in accordance with PSTC-1. A PSA layer is applied to a PET film 23 μηι thickness. A strip of this specimen 2 cm wide is adhered to a sanded steel plate by rolling over the specimen back and forth five times using a 5 kg roller. The plate is clamped in and the self-adhesive strip is pulled off from its free end on a tensile testing machine at a peel angle of 180° and a speed of 300 mm/min. The results are reported with the unit N/cm. Table 1: List of raw materials needed for preparation of the samples SI - S5 according to methods A - F

Table 2: Measurement results for samples SI - S5

Above table shows that an inherent near infrared transparent black backing like the PMMA film from Evonik used for sample S2 has a too low tensile strength at break (57 N/mm²) all though the thickness of 75 μηι is very big. After coating of the adhesive layer of 50 μηι thickness to total tape thickness is 125 μιη what is too thick to fit in most design gaps. Additionally such thick tape will not be flexible enough to easily adhere to rough or curved surfaces. For these two reasons sample S2 is not a suitable solution. A thin PET backing like the 23 μιη PET film used for sample S3 that was printed with an infrared transparent black ink is thin and has good tensile strength but the uniformity is poor and the process requires an additional expensive processing step. Additionally inks are mostly incompatible with the adhesive, especially it interacts with the cross linking mechanism of the adhesive and destroys the peel adhesion in mid to long term. Due to the poor uniformity also sample S3 is not suitable. An inherent near infrared transparent black PET backing as used for sample S4 has a better tensile strength at break compared to S2 but still the tensile strength is not sufficient.

Only the sample S I according to the invention fulfills the requirements of high tensile strength at break, high uniformity, sufficient and stable peel adhesion, easy manufacturing process and low total tape thickness. If no substrate is required the transfer tape according to sample S5 can be used. In principle S5 can be laminated on any suitable substrates of PET, PMMA or other filmic materials.

The following examples are based on different pigments, adhesive layer thicknesses and pigment concentrations according to the invention.

Table 3: Adhesive layer based on Paliogen Black L0086 (25 μπι thickness)

Table 4: Adhesive layer based on Paliogen Black L0086 (50 μπι thickness)

Visual Blackness - + + + +

Uniformity [%] 2 2 1 2 2

Haze 850 nm 2 1 2 2 2

PA [N/cm] 8.1 8.2 8.3 8.2 8.1

The above table 4 shows that, at the 5.0% pigment/tackifier resin master batch content (corresponding to 1.41wt% of pigment content), the infrared transparency is sufficient (above 75%). Meanwhile, the adhesive is sufficiently black. At the 3% mater batch content, the visually transparency is so large (20.6%) that there is not enough black color. Therefore, a master batch content of 5% is especially suitable. Additionally, the products obtained have excellent uniformity, haze and peel adhesion.

Table 6: Comparative example, adhesive layer based on Carbon Black (50 μηι thickness)

Pigment [g] 0.81 1.35 1.89 2.43 3.24

Solids Total [g] 95.35 95.89 96.43 96.97 97.78

Pigment/Ink [wt%] 0.85 1.41 1.96 2.51 3.31

Cross Linker [g] 0.218 0.218 0.218 0.218 0.218

Transp. 550 nm [%] 13.8 4.5 0.6 0.2 0.1

Transp. 850 nm [%] 1 1 3.5 1.1 0.3 0.1

Visual Blackness - + + + +

Uniformity [%] 5 5 5 4 6

Haze 850 nm NA NA NA NA NA

PA [N/cm] 5.8 6.5 6 6.1 5.9

The above tables 5 and 6 show the adhesives produced by using the pigment 0066J. Through matched selection of the concentrations, visual blackness can be obtained, but the transparency in the infrared range (see Transp. 850 nm) is not sufficient in all the cases. Furthermore, the uniformity and peel adhesion are poor.

The following Tables 7 and 8 show experimental results based on red pigment Neptune Red NR543. Table 7: Adhesive layer based on Neptune red NR543 (25 μπι thickness)

Table 8: Adhesive layer based on Neptune red R543 (50 μιη thickness)

Acetone [g] 27 27 27 27 27

Isopropanole [g] 3 3 3 3 3

Perkadox 16 [g] 0.2 0.2 0.2 0.2 0.2

Acetone [g] 1.6 1.6 1.6 1.6 1.6

Tackifier Resin [g] 2.19 3.65 5.11 6.57 8.77

Additional Takifier

Resinfg] 19.43 17.97 16.51 15.05 12.85

Takifier Resin Total [g] 21.62 21.62 21.62 21.62 21.62

Pigment [g] 0.81 1.35 1.89 2.43 3.24

Solids Total [g] 95.35 95.89 96.43 96.97 97.78

Pigment/Ink [wt%] 0.85 1.41 1.96 2.51 3.31

Cross Linker [g] 0.218 0.218 0.218 0.218 0.218

Transp. 550 nm [%] 36.7 25.6 11.3 6.7 1.4

Transp. 850 nm [%] 83.1 75.9 66.8 62.1 59.1

Visual Blackness - - - - +

Uniformity [%] 3 2 3 3 3

Haze 850 nm 3 4 4 5 3

PA [N/cm] 7.3 7.8 7.8 7.6 7.5

The above tables 7 and 8 show the adhesives produced by using the red pigment Neptune Red NR543. The transparency in the infrared region (Transp. 850 nm) is much higher than the transparency in the visible light region (Transp. 550 nm). However, only when the adhesive layer has a thickness of 50μηι, and the pigment/takifier resin master batch has a content of 12% (corresponding to a pigment content of 3.31wf%), visual blackness is obtained. Furthermore, excellent peel adhesion is obtained.

The following Tables 9 and 10 show experimental results based on black pigment BASF X55. Table 9: Adhesive layer based on BASF X55 (25 μπι thickness)

Table 10: Adhesive layer based on BASF X55 (50 μηι thickness)

The above tables 9 and 10 show that, the black pigment BASF X55 results in excellent effects similar to those of black pigment L0086. At the 7.0% pigment/tackifier resin master batch content (corresponding to 1.96 wt% of pigment content), 25 μιη thick adhesive layer, the infrared transparency is sufficient (91 %), and meanwhile, the adhesive is sufficiently black. At the 5.0% pigment/tackifier resin master batch content (corresponding to 1.41wt% of pigment content), 50 μηι thick adhesive layer, the infrared transparency is sufficient (86%), and meanwhile, the adhesive is sufficiently black. Additionally, the products obtained have excellent uniformity, haze and peel adhesion. The following Tables 1 1 and 12 show experimental results based on black pigment L0086 and tackifier resin GA-90.

Table 11: Adhesive layer based on BASF Paliogen Black L0086 and Tackifier resin GA-90 (25 μιη thickness)

Adhesive Layer G-L86-25-03% G-L86-25-05% G-L86-25-07% G-L86-25-09% G-L86-25-12%

Pigment L00K6 L00S6 L00X6 L0086 L0086

Tackifier Resin GA-90 GA-90 GA-90 GA-90 GA-90

Adhesive Base Polymer AC- 1 AC- 1 AC- 1 AC- 1 AC- 1

Adhesive Thickness [μιη] 25 25 25 25 25

Acrylic Acid [g] 3.14 3.14 3.14 3.14 3.14

2-Ethylhexylacrylate [g] 58.5 58.5 58.5 58.5 58.5

Methylacrylate [g] 11 11 11 1 1 1 1

Acetone [g] 26.12 26.12 26.12 26.12 26.12

Benzine [g] 26.12 26.12 26.12 26.12 26.12

Isopropanole [g] 1.07 1.07 1.07 1.07 1.07

AIBN [g] 0.08 0.08 0.08 0.08 0.08

Acetone [g] 27 27 27 27 27

Isopropanole [g] 3 3 3 3 3

Perkadox 16 [g] 0.2 0.2 0.2 0.2 0.2

Acetone [g] 1.6 1.6 1.6 1.6 1.6

Tackifier Resin [g] 2.19 3.65 5.11 6.57 8.77

Additional Takifier

Resinfg] 19.43 17.97 16.51 15.05 12.85

Takifier Resin Total [g] 21.62 21.62 21.62 21.62 21.62

Table 12: Adhesive layer based on BASF Paliogen Black L0086 and Tackifier resin GA-90 (50 μιτι thickness)

Adhesive Layer G-L86-50-03% G-L86-50-05% G-L86-50-07% G-L86-50-09% G-L86-50- 12%

Pigment L0086 L0086 L0086 L0086 L0086

Tackifier Resin GA-90 GA-90 GA-90 GA-90 GA-90

Adhesive Base Polymer AC- 1 AC- 1 AC- 1 AC- 1 AC- 1

Adhesive Thickness [μηι] 50 50 50 50 50

Acrylic Acid [g] 3.14 3.14 3.14 3.14 3.14

2-Ethylhexylacrylate [g] 58.5 58.5 58.5 58.5 58.5

Methylacrylate [g] 11 11 11 1 1 1 1

Acetone [g] 26.12 26.12 26.12 26.12 26.12

Benzine [g] 26.12 26.12 26.12 26.12 26.12

Isopropanole [g] 1.07 1.07 1.07 1.07 1.07

AIBN [g] 0.08 0.08 0.08 0.08 0.08

Acetone [g] 27 27 27 27 27

Isopropanole [g] 3 3 3 3 3

Perkadox 16 [g] 0.2 0.2 0.2 0.2 0.2

Acetone [g] 1.6 1.6 1.6 1.6 1.6

Tackifier Resin [g] 2.19 3.65 5.11 6.57 8.77

Additional Takifier

Resinfg] 19.43 17.97 16.51 15.05 12.85

Takifier Resin Total [g] 21.62 21.62 21.62 21.62 21.62 Pigment [g] 0.81 1.35 1.89 2.43 3.24

Solids Total [g] 95.35 95.89 96.43 96.97 97.78

Pigment/Ink [wt%] 0.85 1.41 1.96 2.51 3.31

Cross Linker [g] 0.218 0.218 0.218 0.218 0.218

Transp. 550 nm [%] 20.6 10.2 3.8 0.03 0.01

Transp. 850 nm [%] 82.2 75.4 62.2 55.9 48.7

Visual Blackness - + + + +

Uniformity [%] 1 2 2 2 3

Haze 850 nm 3 2 2 3 2

PA [N/cm] 6.9 7.2 7.3 7.2 6.5

The following Tables 13 and 14 show experimental results based on black pigment L0086 and tackifier resin UP-1010.

Table 13: Adhesive layer based on BASF Paliogen Black L0086 and Tackifier resin UP-1010 (25 μπι thickness)

Adhesive Layer U-L86-25-03% U-L86-25-05% U-L86-25-07% U-L86-25-09% U-L86-25- 12%

Pigment L0086 L0086 L0086 L0086 L0086

Tackifier Resin UP-1010 UP- 1 010 U P- 10 UP- 1010 UP- 1010

Adhesive Base Polymer AC- 1 AC- 1 AC- 1 AC- 1 AC-1

Adhesive Thickness [μηι] 25 25 25 25 25

Acrylic Acid [g] 3.14 3.14 3.14 3.14 3.14

2-Ethylhexylacrylate [g] 58.5 58.5 58.5 58 · 5

Methylacrylate [g] 11 11 11 1 1 11

Acetone [g] 26.12 26.12 26.12 26.12 26.12

Benzine [g] 26.12 26.12 26.12 26.12 26.12

Isopropanole [g] 1.07 1.07 1.07 1.07 1.07

AIBN [g] 0.08 0.08 0.08 0.08 0.08

Acetone [g] 27 27 27 27 27

Isopropanole [g] 3 3 3 3 3

Perkadox 16 [g] 0.2 0.2 0.2 0.2 .7

Acetone [g] 1.6 1.6 1.6 1.6 1.6

Tackifier Resin [g] 2.19 3.65 5.11 6.57 8.77

Table 14: Adhesive layer based on BASF Paliogen Black L0086 and Tackifier resin UP- 1010 (50 μπι thickness)

Additional Takifier

Resin[g] 19.43 17.97 16.51 15.05 12.85

Takifier Resin Total [g] 21.62 21.62 21.62 21.62 21.62

Pigment [g] 0.81 1.35 1.89 2.43 3.24

Solids Total [g] 95.35 95.89 96.43 96.97 97.78

Pigment/Ink [wt%] 0.85 1.41 1.96 2.51 3.31

Cross Linker [g] 0.218 0.218 0.218 0.218 0.218

Transp. 550 nm [%] 20 9.9 4.5 0.08 0.02

Transp. 850 nm [%] 81.2 74.9 64.1 51.3 42.6

Visual Blackness - + + + +

Uniformity [%] 1 1 1 1 2

Haze 850 nm 1 1 1 2 1

PA [N/cm] 6.2 5.4 5.6 5.8 5.5

The above tables 1 1 to 14 show that, by using tackifier resins GA-90 and UP- 1010, excellent effects are obtained which are similar to those of tackifier resin TF-95.

Claims

Claims:

1. A pressure sensitive adhesive composition, which comprises base polymer, pigment and optionally tackifier resin, wherein the content of the pigment is 0.1 -20 wt%, and the content of the tackifier resin is 0-33 wt%, and the pressure sensitive adhesive composition can be used to prepare infrared transparent black pressure sensitive adhesive.

2. The pressure sensitive adhesive composition according to claim 1 , wherein the content of the pigment is 0.1 -10 wt%, preferably 0.1 -5 wt%, more preferably 0.5-3.5 wt%, most preferably 1 -3.5 wt%, and the content of the tackifier resin is 1-33 wt%, preferably 5-30 wt%, more preferably 10-25 wt%, most preferably 15-23 wt%.

3. The pressure sensitive adhesive composition according to claim 1 or 2, wherein the pressure sensitive adhesive has a transparency in the infrared region 850-950 nm, which is twice or above, three times or above, or four times or above of the transparency in the visible light region 400-700 nm.

4. The pressure sensitive adhesive composition according to any of claims 1 to 3, wherein the tackifier resin has a softening point between 50 and 150 °C, preferably between 80 and 145 °C, and a molar mass between 400 and 20000 g/mol, preferably between 500 and 2000 g/mol.

5. The pressure sensitive adhesive composition according to any of claims 1 to 4, wherein the tackifier resin is selected from terpene phenolic resins, rosin esters, hydrogenated terpene phenolic resins, polyterpene resins, hydrocarbon resins and acrylic resins, preferably selected from terpene phenolic resins and acrylic resins.

6. The pressure sensitive adhesive composition according to any of claims 1 to 5, wherein the pigment is black pigment, red pigment, yellow pigment, blue pigment, brown pigment or the combination thereof, preferably black pigment, red pigment or the combination thereof.

7. The pressure sensitive adhesive composition according to any of claims 1 to 6, wherein the pigment comprises HPP Black 8230, Paliogen Black L0086, Lumogen Black FK4280, HPP Black 823, Solvent Black 32, Neozapon Black X55, Lumogen Black FK4281 , Neptune Red NR543, Sicopal Yellow K1 160FG, Sicopal Blue K6310, Sicopal Brown K2595, or the combination thereof.

8. The pressure sensitive adhesive composition according to any of claims 1 to 7, wherein the base polymer is selected from acrylic polymer, silicone, polyurethane, styrene-isoprene-styrene block copolymer, styrene-butadiene blockcopolymer and polyester.

9. A process to prepare the pressure sensitive adhesive composition according to one of the preceding claims, comprising the following steps:

1) the pigment is mixed with the tackifier resin to obtain a homogenous master batch;

10. The process according to claim 9, wherein the first mixing step is carried out using the following instrument: extruders, kneaders, ball mills, dispersers, blade stirrers or vessel mixers.

1 1. The process according to claim 9 or 10, wherein the first mixing step is carried out at room temperature by adding solvents.

12. The process according to claim 9 or 10, wherein the first mixing step is carried out at higher temperature with the molten resin.

13. An infrared transparent black tape, which comprises at least one adhesive layer and optionally a substrate, wherein the adhesive layer is produced from the pressure sensitive adhesive composition according to any of claims 1 to 8.

14. The tape according to claim 13, which has a transparency in the visible light region between 400 and 700 nm of below 40%, preferably below 20%, more preferably below 15%, most preferably below 12%, and a transparency in the infrared region between 850 and 950 nm of above 60%, preferably above 70%, more preferably above 75%.

15. The tape according to claim 13 or 14, wherein the substrate comprises infrared transparent polymer(s) that can be processed into film.

16. The tape according to any of claims 13 to 15, wherein the substrate comprises polyester, such as polyethylene terephthalate, polycarbonate, polymethylmethacrylate, polyethylenenapthalate; polyacrylate; polyolefin, such as polypropylene, polyethylene, polystyrene; polyimide; cellulose triacetate; polysulfone, ethylene propylene copolymer; especially polyethylene terephthalate and polymethylmethacrylate.

17. The tape according to any of claims 13 to 16, which has a tensile strength at break of above 80 N/mm², preferably above 100 N/mm², more preferably above 150N/mm², most preferably above 160N/mm².

18. The tape according to any of claims 13 to 17, which has a peel adhesion of above 5 N/cm, preferably above 7 N/cm, more preferably above 7.5 N/cm, most preferably above 8 N/cm.

19. The tape according to any of claims 13 to 18, which has a haze in the 400 to 950 nm wavelength range, especially at 850nm, of below 5, preferably below 4, more preferably below 3, most preferably below 2.

20. The tape according to any of claims 13 to 19, which is a single sided adhesive tape consisting of a substrate and an adhesive layer coated thereon.

21. The tape according to claim 20, wherein the substrate has a thickness between 1 and 500 μηι, preferably between 1 and 100 μηι, more preferably between 2 and 50 μηι and most preferably between 2 and 12 μηι, and the adhesive layer coated on the substrate has a thickness between 1 and 2000 μπι, preferably between 5 and 50 μπι and more preferably between 10 and 30 μηι.

22. The tape according to claim 20, wherein the tape has a total thickness between 12 and 80 μηι, preferably between 12 and 42 μηι.

23. The tape according to any of claims 13 to 19, which is a double sided adhesive tape consisting of a substrate and two infrared transparent black adhesive layer coated on both sides of the substrate.

24. The tape according to claim 23, wherein each adhesive layer has a thickness between 1 and 2000 μιη, preferably between 5 and 125 μηι, more preferably between 5 and 50 μηι and most preferably between 10 and 30 μηι, and the substrate has a thickness between 1 and 500 μη , preferably between 2 and 50 μιη and most preferably between 2 and 12 μηι.

25. The tape according to claim 23, wherein the tape has a total thickness between 5 and 4500 μηι, preferably between 12 and 150 μιη and most preferably between 22 and 72 μιη.

26. The tape according to any of claims 13 to 19, which is a transfer tape consisting of the adhesive itself.

27. The tape according to claim 26, wherein the tape has a thickness between 1 and 2000 μιη, preferably between 5 and 150 μιη, more preferably between 5 and 100 μηι and most preferably between 10 and 50 μηι.

28. A process to prepare an infrared transparent black tape, wherein the pressure sensitive adhesive composition according to any of claims 1-8 is coated onto a substrate or liner.

29. The process according to claim 28, wherein the process further comprises a drying step after the coating step.

30. Use of the pressure sensitive adhesive composition according to any of claims 1 to 8 or the tape according to any of claims 13 to 27 in the field of optoelectronics.

31. Use according to claim 20, wherein the fields of use are as follows: surveillance technique; consumer electronics, especially in remote control units, handhelds, phones; automotive industry, such as dashboards that contain displays and sensors, and building and construction, such as door access systems.