PRESSURE-SENSITIVE ADHESIVE ON THE BASIS OF ACRYLONITRILE BUTADIENE RUBBERS

Abstract

The invention relates to pressure-sensitive adhesive material which contains as a base polymer at least one or more solid acrylonitrile butadiene rubbers and adhesive resins, wherein the proportion of adhesive resins is in the range from 30 to 130 phr, characterized in that the acrylonitrile content in the solid acrylonitrile butadiene rubber(s) is between 10 and 30 percent by weight.

Claims

1. A pressure-sensitive adhesive comprising, as base polymer, at least one or a plurality of solid acrylonitrile-butadiene rubber(s) and tackifier resins, the fraction of the tackifier resins being 30 to 130 phr, wherein the acrylonitrile content in the solid acrylonitrile-butadiene rubber(s) is between 10 and 30 wt %.

2. The pressure-sensitive adhesive as claimed in claim 1, wherein the base polymer consists only of acrylonitrile-butadiene rubber.

3. The pressure-sensitive adhesive as claimed in claim 1, wherein the acrylonitrile content in the acrylonitrile-butadiene rubber is between 10 and 25 wt %.

4. The pressure-sensitive adhesive as claimed in claim 1, wherein the fraction of the tackifier resins is 50 to 120 phr.

5. The pressure-sensitive adhesive as claimed in claim 1, wherein the tackifier resins comprise terpene-phenolic resins and/or polyterpenes.

6. The pressure-sensitive adhesive as claimed in claim 1, further comprising at least one liquid acrylonitrile-butadiene rubber, the acrylonitrile content in the liquid acrylonitrile-butadiene rubber(s) being between 10 and 30 wt %.

7. The pressure-sensitive adhesive as claimed in claim 6, wherein the fraction of the liquid acrylonitrile-butadiene rubbers is up to 20 wt %.

8. The pressure-sensitive adhesive as claimed in claim 1, which consists of a composition only of solid or only of solid and liquid acrylonitrile-butadiene rubber and tackifier resin, and optionally, aging agents and release assistants.

9. The pressure-sensitive adhesive as claimed in claim 1, wherein apart from the acrylonitrile butadiene rubber and tackifier resin, the fractions of all added substances selected from the group consisting of synthetic rubbers, thermoplastic elastomers, fillers, dyes, aging inhibitors, plasticizers and, release assistants, do not in total exceed 5 wt %.

10. An adhesive tape which is single-sided or double-sided comprising the pressure-sensitive adhesive as claimed in claim 1.

11. The adhesive tape of claim 10, where the coat weight (coating thickness) of the pressure-sensitive adhesive is between 10 and 150 g/m.sup.2.

12. A method for bonding parts in electronic devices, comprising a step of applying a pressure-sensitive adhesive as claimed in claim 1 to a substrate.

13. A method for bonding decals or labels, comprising a step of applying a pressure-sensitive adhesive as claimed in claim 1 to a substrate.

14. The pressure-sensitive adhesive as claimed in claim 2, wherein, aside from acrylonitrile-butadiene rubber, there is no further polymer in the pressure-sensitive adhesive.

15. The pressure-sensitive adhesive as claimed in claim 3, wherein the acrylonitrile content in the acrylonitrile-butadiene rubber is between 15 and 20 wt %.

16. The pressure-sensitive adhesive as claimed in claim 4, wherein the fraction of the tackifier resins is 60 to 110 phr.

17. The pressure-sensitive adhesive as claimed in claim 7, wherein the fraction of the liquid acrylonitrile-butadiene rubbers is between 1 and 15 wt %.

18. The pressure-sensitive adhesive as claimed in claim 17, wherein the fraction of the liquid acrylonitrile-butadiene rubbers is between 2 and 10 wt %.

19. The pressure-sensitive adhesive as claimed in claim 9, wherein apart from the acrylonitrile butadiene rubber and tackifier resin, the fractions of all added substances, do not in total exceed 5 wt %.

20. The pressure-sensitive adhesive as claimed in claim 19, wherein apart from the acrylonitrile butadiene rubber and tackifier resin, the fractions of all added substances, do not in total exceed 2 wt %.

Description

[0119] Further details, objectives, features, and advantages of the present invention will be elucidated in more detail below by reference to a number of figures which represent preferred working examples. In these figures

[0120] FIG. 1 shows a single-sided pressure-sensitive adhesive tape,

[0121] FIG. 2 shows a double-sided pressure-sensitive adhesive tape,

[0122] FIG. 3 shows a carrier-free pressure-sensitive adhesive tape (adhesive transfer tape).

[0123] FIG. 1 shows a single-sidedly adhering pressure-sensitive adhesive tape 1. The pressure-sensitive adhesive tape 1 has an adhesive layer 2 produced by coating one of the above-described PSAs onto a carrier 3. The PSA coat weight is preferably between 10 and 50 g/m.sup.2.

[0124] Provided additionally (not shown) may be a release film, which covers and protects the adhesive layer 2 before the pressure-sensitive adhesive tape 1 is used. The release film is then removed before use from the adhesive layer 2.

[0125] The product construction shown in FIG. 2 shows a pressure-sensitive adhesive tape 1 with a carrier 3, coated on both sides with a PSA and therefore having two adhesive layers 2. The PSA coat weight per side is in turn preferably between 10 and 200 g/m.sup.2.

[0126] With this embodiment as well, at least one adhesive layer 2 is preferably lined with a release film. In the case of a rolled-up adhesive tape, this one release film may optionally also line the second adhesive layer 2. However, it is also possible for a plurality of release films to be provided.

[0127] It is possible, furthermore, for the carrier film to be provided with one or more coatings. Moreover, only one side of the pressure-sensitive adhesive tape may be furnished with the inventive PSA, and a different PSA may be used on the other side.

[0128] The product construction shown in FIG. 3 shows a pressure-sensitive adhesive tape 1 in the form of an adhesive transfer tape, in other words a carrier-free pressure-sensitive adhesive tape 1. For this construction, the PSA is coated single-sidedly onto a release film 4, to form a pressure-sensitive adhesive layer 2. The PSA coat weight here is customarily between 10 and 100 g/m.sup.2. This pressure-sensitive adhesive layer 2 is optionally also lined on its second side with a further release film. For the use of the pressure-sensitive tape, then, the release films are removed.

[0129] As an alternative to release films it is also possible for example to use release papers or the like. In that case, however, the surface roughness of the release paper ought to be reduced, in order to realize a PSA side that is as smooth as possible.

[0130] In order to enhance the cohesive properties of the PSA, it may also be crosslinked with the methods described above and, in particular, through the addition of peroxides, or with irradiation with high-energy radiation. This has positive effects on properties, in particular, such as the push-out or the behavior in a falling-ball test, whereas properties such as the peel adhesions tend to fall. The PSAs are therefore preferably not crosslinked.

Test Methods

[0131] Unless otherwise indicated, the measurements are carried out under test conditions of 231 C. and 505% relative humidity.

Softening Point

[0132] The figures for the softening point T.sub.S of oligomeric and polymeric compounds, such as of the resins, for example, are based on the ring & ball method according to DIN EN 1427:2007 with corresponding application of the provisions (investigation of the oligomer sample or polymer sample instead of bitumen, with the procedure otherwise retained); the measurements are made in a glycerol bath.

Peel Adhesion

[0133] The peel strength (peel adhesion) was tested in a method based on PSTC-1.

[0134] A strip of the pressure-sensitive adhesive tape, 0.5 cm wide, consisting of a PET film 23 m thick and etched with trichloroacetic acid and of an adhesive coating applied thereto and 50 m thick is adhered to the test substrate in the form of an ASTM steel plate by being rolled on back and forth five times using a 4 kg roller.

[0135] The surface of the steel plate is cleaned with acetone beforehand. The plate is clamped in, and the self-adhesive strip is peeled from its free end on a tensile testing machine at a peel angle of 180 and a speed of 300 mm/min, and a determination is made of the force needed to achieve this. The results are reported in N/cm and are averaged over three measurements and reported with standardization to the width of the strip in N/cm.

[0136] The initial peel adhesion (peel adhesion to steel) was measured immediately after bonding and not more than 10 minutes after bonding.

[0137] For the determination of the chemical resistance, the bonded specimens, after rolling, were subjected to different storage regimes.

[0138] First of all, all of the specimens after bonding were stored for 24 hours at 23 C. and 50% relative humidity.

[0139] As a blank value, specimens were stored in each case for 72 hours at 65 C. and 90% relative humidity. Following the storage, the samples were stored for a further 24 hours at 23 C. and 50% relative humidity and then subjected to measurement.

[0140] For the determination of the chemical resistance, the specimens were stored at 65 C. and 90% relative humidity in oleic acid (CAS No. 112-80-1, grade with a purity of at least >90%) or in a 75:25 (vol%) mixture of ethanol and water. For the ethanol/water storage a closeable vessel was used in order to prevent loss of ethanol by evaporation. Following storage, the specimens are first rinsed off with distilled water and then stored for 24 hours at 23 C. and 50% relative humidity. Only then was the peel adhesion measured as described above. The retention of the peel adhesion is calculated through the ratio of the measurement after storage in oleic acid or ethanol/water (in a ratio of 75/25) to the blank value.

Rolling Ball Tack

[0141] The rolling ball tack was measured by the PSTC-6 method (Test Methods for Pressure Sensitive Adhesive Tapes, 15.sup.th edition; publisher: Pressure Sensitive Tape Council, Northbrook (Ill.), USA), with the following modifications being made: [0142] use of stainless steel ball bearing balls (stainless steel 1.4401), diameter 7/16 inch, mass 5.7 g [0143] preparation of balls: thorough cleaning with cotton wool and acetone; the clean balls prior to the measurement series are stored in an acetone bath (balls are completely surrounded by the acetone) for 15 minutes; at least 30 minutes before the start of measurement, the balls are removed from the acetone bath and stored open under standard conditions (231 C., 505% relative humidity) for drying and conditioning [0144] each ball is used only for one measurement.

[0145] The tack was determined as follows: as a measure of the tack with a very short contact time, a measurement was made of what is called the rolling ball tack. A strip of the adhesive tape about 25 cm long was fastened under tension horizontally on the test plane with the adhesive side upward. For the measurement, the steel ball was accelerated under the Earth's gravity by rolling down a ramp with a height of 65 mm (angle of inclination: 21). From the ramp, the steel ball was directed immediately onto the adhesive surface of the sample. A measurement was made of the distance travelled on the adhesive until the ball reached standstill. The rolling path length thus determined serves here as an inverse measure of the tack of the self-adhesive composition (in other words, the shorter the rolling distance, the greater the tack, and vice versa). The respective measurement was obtained (as a length report in mm) from the average value of five individual measurements on five different strips of each adhesive tape.

Falling Ball Test (Impact Toughness, Ball Drop)

[0146] A square, frame-shaped sample was cut out of the adhesive tape under test (outside dimensions 33 mm33 mm; border width 3.0 mm; inside dimensions (window opening) 27 mm27 mm). This sample was adhered to an ABS frame (outside dimensions 50 mm50 mm; border width 12.5 mm; inside dimensions (window opening) 25 mm25 mm; thickness 3 mm). Adhered on the other side of the double-sided adhesive tape was a PMMA window of 35 mm35 mm. ABS frame, adhesive tape frame and PMMA window were bonded such that the geometric centers and the diagonals each lay on top of one another (corner on corner). The bond area was 360 mm.sup.2. The bond was pressed at 10 bar and 23 C. for 5 s and stored for 24 hours with conditioning at 23 C./50% relative humidity.

[0147] Immediately after storage, the adhesive assembly composed of ABS frame, adhesive tape and PMMA sheet was placed with the protruding edges of the ABS frame onto a frame structure (sample holder) in such a way that the assembly was oriented horizontally and the PMMA sheet pointed downward, hanging freely. A steel ball with the weight indicated in each case was dropped perpendicularly, centered on the PMMA sheet, from a height of 250 cm (through the window of the ABS frame) onto the sample arranged in this way (measuring conditions 23 C., 50% relative humidity). Three tests were carried out with each sample, unless the PMMA sheet had become detached beforehand.

[0148] The ball drop test is deemed to be passed if the adhesive bond has not detached in any of the three tests.

[0149] The maximum height at which the test is still passed is reported as the measurement value.

Push-Out Strength (Z-Plane)

[0150] The push-out test provides information on the extent to which the bond of a component in a frame-shaped body, such as of a window or display in a housing, is resistant.

[0151] A rectangular, frame-shaped sample was cut out of the adhesive tape under test (outside dimensions 43 mm33 mm; border width 2.0 mm in each case; inside dimensions (window opening) 39 mm29 mm, bond area 288 mm.sup.2 on each of the top and bottom sides). This sample was adhered to a rectangular ABS plastic frame (ABS=acrylonitrile-butadiene-styrene copolymers) (outside dimensions 50 mm40 mm; border width of the long borders 8 mm in each case; border width of the short borders 10 mm in each case; inside dimensions (window opening) 30 mm24 mm; thickness 3 mm). Adhered on the other side of the double-sided adhesive tape sample was a rectangular PMMA sheet (PMMA=polymethyl methacrylate) with dimensions of 45 mm35 mm. The full bond area of the adhesive tape available was utilized. The ABS frame, adhesive tape sample and PMMA window were bonded such that the geometric centers, the bisecting lines of the acute diagonal angles and the bisecting lines of the obtuse diagonal angles of the rectangles each lay on top of one another (corner on corner, long sides on long sides, short sides on short sides). The bond area was 288 mm.sup.2. The bond was pressed at 10 bar and 23 C. for 5 s and stored for 24 hours with conditioning at 23 C./50% relative humidity.

[0152] Immediately after storage, the adhesive assembly composed of ABS frame, adhesive tape and PMMA sheet was placed with the protruding edges of the ABS frame onto a frame structure (sample holder) in such a way that the assembly was oriented horizontally and the PMMA sheet pointed downward, hanging freely.

[0153] A plunger is then moved through the window of the ABS frame, perpendicularly from above, at a constant speed of 10 mm/s, so that it presses centrally onto the PMMA plate, and a record is made of the respective force (determined from respective pressure and contact area between plunger and plate) as a function of the time from the first contact of the plunger with the PMMA plate until shortly after the plate has fallen (measuring conditions 23 C., 50% relative humidity). The force acting immediately prior to the failure of the adhesive bond between PMMA plate and ABS frame (maximum force F.sub.max in the force-time diagram in N) is recorded as the answer of the push-out test.

Static Glass Transition Temperature Tg

[0154] Glass transition pointsreferred to synonymously as glass transition temperaturesare reported as the result of measurements by dynamic scanning calorimetry (DSC) in accordance with DIN 53 765, especially sections 7.1 and 8.1, but with uniform heating and cooling rates of 10 K/min in all heating and cooling steps (compare DIN 53 765; section 7.1; note 1). The initial sample mass is 20 mg.

[0155] The intention of the text below is to illustrate the invention using a number of examples, without thereby wishing to subject the invention to unnecessary restriction.

Preparation of the PSAs

[0156] The pressure-sensitive adhesives (PSAs) set out in the examples were homogenized as solvent-based compositions in a kneading apparatus with a double-sigma kneading hook. The solvent used was butanone (methyl ethyl ketone, 2-butanone). The kneading apparatus was cooled by means of water cooling.

[0157] First of all, in a first step, the solid acrylonitrile-butadiene rubber was pre-swollen with the same amount of butanone at 23 C. for 12 hours. This preliminary batch, as it is called, was then kneaded for 2 hours. Subsequently, again, the amount of butanone selected above and, optionally, the liquid NBR rubber were added in two steps with kneading in each case for 10 minutes. Thereafter the tackifier resin was added as a solution in butanone with a solids content of 50%, and homogeneous kneading was continued for 20 minutes more. The final solids content is adjusted to 30 wt % by addition of butanone.

Production of the Test Specimens

[0158] The PSA was coated onto a PET film, 23 m thick and etched with trichloroacetic acid, by means of a coating knife on a commercial laboratory coating bench (for example from the company SMO (Sondermaschinen Oschersleben GmbH)). The butanone was evaporated in a forced air drying cabinet at 105 C. for 10 minutes. The slot width during coating was adjusted so as to achieve a coat weight of 50 g/m.sup.2 following evaporation of the solvent. The films freed from the solvent were subsequently lined with siliconized PET film and stored pending further testing at 23 C. and 50% relative humidity.

EXAMPLES

[0159]

TABLE-US-00001 Example 1 Example 2 Example 3 Example 4 Example 5 Initial Initial Initial Initial Initial mass of mass of mass of mass of mass of Raw material solids [%] solids [%] solids [%] solids [%] solids [%] Nipol 0% 0% 0% 0% 0% N41H80 Nipol 401 67% 67% 67% 50% 57% Nipol DN 0% 0% 0% 0% 0% 2850 Nipol 1042 S 0% 0% 0% 0% 0% Dertophene 33% 0% 0% 0% 0% T 110 Dertophene 0% 0% 0% 33% 33% T Rosin 0% 0% 0% 0% 0% Novares 0% 33% 0% 0% 0% TK 90 Cumar 130 0% 0% 33% 0% 0% Novares 0% 0% 0% 0% 0% C120VL Picco AR85 0% 0% 0% 0% 0% Nipol 1312 0% 0% 0% 17% 10% LV Example 6 Example 7 Example 8 Example 9 Initial mass Initial mass Initial mass Initial mass Raw material of solids [%] of solids [%] of solids [%] of solids [%] Nipol N41H80 0% 0% 0% 0% Nipol 401 62% 0% 0% 50% Nipol DN 2850 0% 67% 57% 0% Nipol 1042 S 0% 0% 0% 0% Dertophene 0% 0% 0% 0% T 110 Dertophene T 33% 0% 0% 50% Rosin 0% 0% 0% 0% Novares TK 90 0% 0% 0% 0% Cumar 130 0% 0% 0% 0% Novares 0% 0% 0% 0% C120VL Picco AR85 0% 33% 29% 0% Nipol 1312 LV 5% 0% 14% 0% Initial mass of solids [%] denotes in each case [wt %].

TABLE-US-00002 Comparative Comparative Comparative Comparative example 1 example 2 example 3 example 4 Initial mass Initial mass Initial mass Initial mass Raw material of solids [%] of solids [%] of solids [%] of solids [%] Nipol N41H80 50% 0% 0% 57% Nipol 401 0% 0% 0% 0% Nipol DN 2850 0% 0% 0% 0% Nipol 1042 S 0% 67% 57% 0% Dertophene 50% 0% 0% 0% T 110 Dertophene T 0% 0% 0% 0% Rosin 0% 0% 29% 29% Novares TK 90 0% 0% 0% 0% Cumar 130 0% 0% 0% 0% Novares 0% 0% 0% 0% C120VL Picco AR85 0% 33% 0% 0% Nipol 1312 LV 0% 0% 14% 14%

TABLE-US-00003 Mooney viscosity ACN content ML 1 + 4, 100 C. T.sub.g Name [wt %] [MU] [ C.] Nipol 401 18.5 73 to 83 37 Nipol 1312 LV 26.5 9000 to 16000* 23 Nipol DN 2850 28.0 45 to 55 22 Nipol 1042 S 33.5 73 to 83 17 Nipol N41H80 41.0 72 to 88 9 *For Nipol 1312LV the Brookfield viscosity is stated in [mPa * s], measured with spindle 4, 12 rpm, 50 C.

TABLE-US-00004 Name Chemical basis Manufacturer Softening point Dertophene Terpene-phenolic resin DRT 112 C. T 110 Dertophene Terpene-phenolic resin DRT 95 C. T Rosin Abietic acid 85 C. Novares Aliphatically modified Rtgers 85 to 95 C. TK 90 hydrocarbon resin Cumar 130 Coumarone.Indene Neville 125 to 135 C. resin Novares Coumarone.Indene Rtgers 115 to 125 C. C120-VL resin Picco AR85 Aromatically modified Eastman 87 C. hydrocarbon resin Eastman

TABLE-US-00005 Example Example Example Example Example Test 1 2 3 4 5 Peel adhesion [N/cm] 5.9 6.3 3.8 12.4 8.4 ASTM steel Blank value [N/cm] 16.5 26.0 11.0 23.4 27.5 (3 d, 65 C.) 3 d, 65 C., [N/cm] 4.9 7.9 6.4 4.9 6.1 oleic acid 3 d, 65 C., [N/cm] 4.46 5.9 9.9 5.35 8.4 EtOH/H.sub.2O Push-out [N] 46 41 47 Ball-drop [cm] 230 250 250 Rolling ball [mm] 46 54 49 17 28 tack Example Example Example Example Test 6 7 8 9 Peel adhesion [N/cm] 12.8 5.2 12.6 7.8 ASTM steel Blank value [N/cm] 28.7 10.6 28.3 8.0 (3 d, 65 C.) 3 d, 65 C., [N/cm] 5.5 3.6 4.6 4.3 oleic acid 3 d, 65 C., [N/cm] 9.5 5.7 4.9 10.4 EtOH/H.sub.2O Push-out [N] 57 94 Ball-drop [cm] 250 250 Rolling ball [mm] 52 48 23 30 tack

TABLE-US-00006 Com- Com- Com- Com- parative parative parative parative Test example 1 example 2 example 3 example 4 Peel adhesion [N/cm] dead dead dead 2.8 ASTM steel Blank value [N/cm] 4.1 (3 d, 65 C.) 3 d, 65 C., [N/cm] 0.5 oleic acid 3 d, 65 C., [N/cm] 0 EtOH/H.sub.2O Push-out [N] Ball-drop [cm] Rolling ball [mm] >250 >250 >250 60 tack

[0160] To produce the specimens for the falling-ball and push-out tests, the PSA was coated using the laboratory coating bench onto a siliconized PET film. The coatings were subsequently dried at 105 C. for 10 minutes. The adhesive films with a layer thickness of 50 m were laminated onto either side of a corona-pretreated PET film 12 m thick, to give a double-sided adhesive tape specimen.

[0161] As is apparent from the examples, the inventive adhesive exhibits significant peel adhesion even after 72 hours' storage in ethanol/water or in hot oleic acid at 65 C.

[0162] Surprisingly, and unforeseeably for the skilled person, this improved quality is attributable to the acrylonitrile content in the acrylonitrile-butadiene rubber. Although the chemical resistance of acrylonitrile-butadiene rubber is known and is utilized for many applications in the automotive sector, high resistance toward apolar media (in this case oleic acid) is customarily achieved with a high ACN content. Typically, therefore, acrylonitrile-butadiene rubbers with an ACN content of 41 wt % or more are used. The admixing of rubbers with low ACN contents is generally practiced only for the purpose of adjusting the mechanical properties, but often at the expense of the chemical resistance. Entirely surprisingly it has emerged that exclusively PSAs based on acrylonitrile-butadiene rubbers with an ACN content of less than 30 wt % exhibit sufficient chemical resistance toward apolar media.

[0163] Particularly high resistances toward polar and apolar media are achieved with PSAs which contain acrylonitrile-butadiene rubbers with an ACN content of less than 25 wt % and, even more preferably, less than 20 wt %.

[0164] It is surprising, moreover, that the PSAs of the invention maintain the good peel adhesion forces not only after exposure to very apolar chemicals (oleic acid, for example) but also to very polar chemicals ethanol/water.

[0165] In assessing the resistance, it is not just the absolute level of the peel adhesion that is of interest here, but also the percentage change after exposure to the chemicals, in comparison to the blank value.

[0166] The stated chemicals (oleic acid and ethanol/water) are used only as representatives. The PSAs of the invention are also resistant to chemicals such as sebum, perfumes, dilute sulfuric acid, oil/water emulsions and water/oil emulsions of the kind used in cosmetic products, and brake fluid. This list as well is not conclusive, but instead is exemplary in its nature.

[0167] The values measured for the falling-ball test (ball-drop) and for the push-out test demonstrate the excellent suitability of the pressure-sensitive adhesives of the invention for the adhesive bonding of windows or displays in housings. A particular surprise here is the shock resistance determined in the falling-ball test.