PRESSURE-SENSITIVE ADHESIVE COMPOUND WITH HIGH FILLER CONTENT

Abstract

Pressure-sensitive adhesives (PSAs) and tapes comprising said PSAs are provided. The PSAs comprise at least one poly(meth)acrylate and at least 40% by volume, based on a total volume of the pressure-sensitive adhesive, of a mixture of at least two fillers. The mixture of at least two fillers comprises at least one filler Fi.sub.sph comprising or consisting of essentially spherical particles and the PSAs may conduct heat and/or provide electrical resistivity for electronic device or component applications.

Claims

1. A pressure-sensitive adhesive comprising a. at least one poly(meth)acrylate; b. at least 40% by volume, based on a total volume of the pressure-sensitive adhesive, of a mixture of at least two fillers, wherein the mixture of at least two fillers comprises at least one filler Fi.sub.sph consisting of essentially spherical particles.

2. The pressure-sensitive adhesive of claim 1, wherein the at least one filler Fi.sub.sph has a particle size distribution, determined by laser diffraction (red laser, 830 nm) on a sample of 0.40 g in 1 l of deionized water (dispersant: 1 g Na.sub.4P.sub.2O.sub.7×10 H.sub.2O ultrapure) and reported with reference to the numerically assessed distribution of diameters D(n), of d50=1.5-23*d10 and d90=36-75*d10.

3. The pressure-sensitive adhesive of claim 1, wherein only the at least one filler Fi.sub.sph consists of essentially spherical particles and is present in a weight excess with respect to the further filler or the entirety of the further fillers.

4. The pressure-sensitive adhesive of claim 3, wherein the weight excess is 2:1 to 15:1.

5. The pressure-sensitive adhesive of claim 1, wherein the at least one filler Fi.sub.sph consists of aluminum oxide or aluminum hydroxide.

6. The pressure-sensitive adhesive of claim 5, wherein the at least one filler Fi.sub.sph consists of aluminum hydroxide.

7. The pressure-sensitive adhesive of claim 1, wherein the pressure-sensitive adhesive comprises boron nitride as a further filler in addition to the at least one filler Fi.sub.sph.

8. The pressure-sensitive adhesive of claim 1, wherein the pressure-sensitive adhesive contains the mixture of at least two fillers to an extent of at least 60% by volume.

9. The pressure-sensitive adhesive of claim 1, wherein the pressure-sensitive adhesive contains poly(meth)acrylates in a total amount of 10% to 30% by weight, based on a total weight of the pressure-sensitive adhesive.

10. An electronic device comprising the pressure-sensitive adhesive of claim 1.

11. A method comprising: connecting a cooling plate and single cells of at least one multiple interconnected electrochemical assembly such that an adhesive tape comprising the pressure-sensitive adhesive of claim 1 provides connection between the cooling plate and the single cells.

Description

EXAMPLES

Test Methods

Method 1: Bond Strength on Aluminum

[0122] The bond force was determined under test conditions of temperature 23° C.+/−1° C. and rel. air humidity 50%+/−5%. The specimens were cut to a width of 20 mm and stuck to an aluminum plate. The aluminum plate was cleaned and conditioned prior to the measurement. For this purpose, the plate was first wiped with solvent and then left exposed for 5 minutes for the solvent to be able to evaporate off. The side of the adhesive tape remote from the test substrate was then covered with 75 μm-thick etched PET film, which prevented the specimen from expanding during the measurement. Thereafter, the test specimen was rolled onto the substrate. For this purpose, the tape was rolled five times back and forth with a 4 kg roll at a rolling speed of 10 m/min. Three days after the rolling, the plate was inserted into a special holder that enables the specimen to be pulled off at an angle of 90°. The bond force was measured with a Zwick tensile tester. The measurement results are reported in N/cm and are the average of five individual measurements.

Method 2: Thermal Conductivity in z Direction

[0123] Thermal conductivity was measured to ASTM D5470 (through-plane) with the LW-9389 model from the manufacturer LonGwin.

Method 3: Particle Size Distribution

[0124] Particle size distribution was determined by laser diffraction, using a “Cilas 1064” laser granulometer. The device has a measurement range of 0.04-500 μm, divided into 100 classes. 0.40 g of the filler to be examined was weighed into the cuvette provided and dispersed using the device's ultrasound function in 1000 ml of deionized water containing 1 g of Na.sub.4P.sub.2O.sub.7×10 H.sub.2O ultrapure for 60 s.

[0125] The sample was then irradiated with a red laser of wavelength 830 nm. The grain distribution was derived from the intensity of diffraction of the laser light (evaluation according to Fraunhofer).

Method 4: Electrical Resistivity

[0126] Measurements of surface resistivity and volume resistivity were made on the pressure-sensitive adhesives. Measurement was effected with a Milli-TO 3 from Fischer Elektronik (S/N 1005651) with guard ring electrode according to DIN IEC 60093 and DIEN IEC 60167.

Preparation of the Polymers

Copolymer 1:

[0127] A conventional reactor for free-radical polymerizations was charged with 67.0 kg of n-butyl acrylate, 30.0 kg of 2-ethylhexyl acrylate, 3.0 kg of acrylic acid and 66.6 kg of acetone/isopropanol (94:6). After passing nitrogen gas through for 45 minutes while stirring, the reactor was heated up to 58° C., and 50 g of AIBN dissolved in 500 g of acetone was added. Subsequently, the external heating bath was heated to 75° C. and the reaction was conducted constantly at this exterior temperature. After 1 h another 50 g of AIBN dissolved in 500 g of acetone was added, and after 4 h the mixture was diluted with 10 kg of acetone/isopropanol mixture (94:6).

[0128] After 5 h and after 7 h, further initiator was respectively supplied in the form of 150 g of bis(4-tert-butylcyclohexyl) peroxydicarbonate, each time dissolved in 500 g of acetone. After a reaction time of 22 h, the polymerization was stopped and cooled down to room temperature. The product had a solids content of 55.8% and was dried. The resulting polyacrylate had an average molecular weight M.sub.w of 605000 g/mol, a polydispersity D (Mw/Mn) of 4.27 and a static glass transition temperature T.sub.g of −45° C.

Copolymer 2:

[0129] A reactor was initially charged with a monomer mixture consisting of 67 kg of n-butyl acrylate, 30 kg of ethylhexyl acrylate and 3 kg of acrylic acid, and also 0.15 kg of Irgacure 651 (manufacturer: Ciba), and the mixture was stirred under inert atmosphere and irradiated with a mercury vapor lamp at a UV dose of 12 mW/cm.sup.2 for 10 min, such that a viscous mass formed therefrom. The syrupy copolymer-monomer mixture obtained in this way was then used in the subsequent production experiments.

[0130] Further components of the pressure-sensitive adhesives: [0131] Plasticizer: diisononyl cyclohexane-1,2-dicarboxylate, commercially available under the Hexamoll Dinch name (BASF) [0132] Filler 1: aluminum hydroxide, commercially available under the Apyral 20× name (Nabaltec AG); d10=0.8-1.1 μm; d50=2-18 μm; d90=40-60 μm [0133] Filler 2: boron nitride platelets, commercially available under the Polartherm PT 131 name (Momentive USA) [0134] Filler 3: hexagonal aluminum hydroxide, commercially available under the Martinal OL 104-LEO name (Huber Martinswerk) [0135] Crosslinker 1: pentaerythritol tetraglycidyl ether, commercially available under the 749 Epoxy Dullent name (DOW) [0136] Crosslinker 2: [3-(2,3-epoxypropoxy)propyl]triethoxysilane, commercially available under the Dynasilan GLYEO name (Evonik) [0137] Crosslinker 3: tris(2,4-pentanedione)aluminum(III), commercially available, TCI-Chemicals product number A0241, 8.7% in acetone [0138] Crosslinker 4: hexane-1,6-diol acrylate, commercially available under the Ebecryl 7100 name (Cytec Surface Specialties) [0139] Accelerator 1: isophoronediamine, commercially available under the Vestamin IPD name (Evonik) [0140] Accelerator 2: 3-aminopropyltriethoxysilane, commercially available under the Dynasilan AMEO name (Evonik).

Production of the Pressure-Sensitive Adhesives

[0141] Pressure-sensitive adhesives 1 to 6 were compounded using a Z kneader having a nameplate volume of 1500 cm.sup.3. The resultant compositions were shaped to a layer with a Lauter hot press; the roll nip was set to 1000 μm by means of spacer screws.

[0142] UV curing of the pressure-sensitive adhesives produced with copolymer 2

[0143] The UV curing was conducted in a black box with black light lamps from Sylvania. The UV dose set was 6 mW/cm.sup.2.

[0144] Irradiation was as follows: 3×30 s with a gap of 30 s between the respective irradiations; then 3×60 s with a gap of 30 s between the respective irradiations; followed by irradiation from each side for 300 s.

Pressure-Sensitive Adhesive 1

[0145] The kneader was initially charged with 198 g of copolymer 1 and heated to 160° C. While mixing constantly, 46.2 g of filler 2 was added in portions and incorporated homogeneously, followed by 416 g of filler 1, likewise in portions. A total of 9.9 g of plasticizer 1 was incorporated homogeneously into the adhesive in two steps. After a further 15 minutes, 2.5 g of crosslinker 3 was added dropwise and incorporated homogeneously within 5 min. The adhesive was removed from the kneader while still hot and shaped to a 1000 μm-thick layer.

Pressure-Sensitive Adhesive 2

[0146] The kneader was initially charged with 120 g of copolymer 1 and heated to 160° C. While mixing constantly, 48 g of filler 2 was added in portions and incorporated homogeneously, followed by 432 g of filler 1, likewise in portions. A total of 6 g of plasticizer 1 was incorporated homogeneously into the adhesive in two steps. After a further 15 minutes, 1.5 g of crosslinker 3 was added dropwise and incorporated homogeneously within 5 min. The adhesive was removed from the kneader while still hot and shaped to a 1000 μm-thick layer.

Pressure-Sensitive Adhesive 3

[0147] The kneader was initially charged with 98 g of copolymer 1 and heated to 160° C. While mixing constantly, 88 g of filler 2 was added in portions and incorporated homogeneously, followed by 250 g of filler 1, likewise in portions. A total of 32 g of plasticizer 1 was incorporated homogeneously into the adhesive in two steps. After a further 15 minutes, 1.25 g of crosslinker 3 was added dropwise and incorporated homogeneously within 5 min. The adhesive was removed from the kneader while still hot and shaped to a 1000 μm-thick layer.

Pressure-Sensitive Adhesive 4

[0148] Under yellow light, the kneader was initially charged with 198 g of the syrupy copolymer 2 and heated to 60° C. While mixing constantly, 46.2 g of filler 2 was added in portions and incorporated homogeneously, followed by 416 g of filler 1, likewise in portions. A total of 9.9 g of plasticizer 1 was incorporated homogeneously into the adhesive in two steps. The adhesive was removed from the kneader while still hot, shaped to a 1000 μm-thick layer and then cured as described above.

Pressure-Sensitive Adhesive 5

[0149] Under yellow light, the kneader was initially charged with 120 g of the syrupy copolymer 2 and heated to 60° C. While mixing constantly, 48 g of filler 2 was added in portions and incorporated homogeneously, followed by 432 g of filler 1, likewise in portions. 6 g of plasticizer 1 was incorporated homogeneously into the adhesive. The adhesive was removed from the kneader while still hot, shaped to a 1000 μm-thick layer and then cured as described above.

Pressure-Sensitive Adhesive 6

[0150] Under yellow light, the kneader was initially charged with 98 g of the syrupy copolymer 2 and heated to 60° C. While mixing constantly, 88 g of filler 2 was added in portions and incorporated homogeneously, followed by 250 g of filler 1, likewise in portions. 32 g of plasticizer 1 was incorporated homogeneously into the adhesive in portions. The adhesive was removed from the kneader while still hot, shaped to a 1000 μm-thick layer and then cured as described above.

Pressure-Sensitive Adhesives 7 to 12 were Produced by the Following Method:

Step 1: Concentration

[0151] The base polymer P (copolymer 1 or 2) was very substantially freed of solvent (residual solvent content 0.3% by weight) by means of a single-screw extruder (concentrating extruder, Berstorff GmbH, Germany). The parameters for the concentration of the base polymer were as follows: screw speed 150 rpm, motor current 15 A; a throughput of 58.0 kg/h of liquid was achieved. For the concentration, a vacuum was applied to three different domes. The reduced pressures were each between 20 mbar and 300 mbar. The exit temperature of the concentrated hotmelt P was about 115° C. The solids content after this concentration step was 99.8%.

Step 2: Production of the Pressure-Sensitive Adhesive—Blending with the Further Components

[0152] This step was conducted in a pilot plant corresponding to the diagram in FIG. 2.

[0153] The base polymer P was melted in the concentrating extruder 10 as per step 1 and conveyed thereby as polymer melt through a heatable hose 11 into a planetary roll extruder 20 (PRE) from ENTEX (Bochum) (more particularly, a PRE having four independently heatable modules T1, T2, T3, T4 was used). The plasticizer was fed in at the metering orifice 22, and the filler 1 at metering orifices 23 and 24. All components were mixed to give a homogeneous polymer melt.

[0154] By means of a melt pump 25a and a heatable hose 25b, the polymer melt was transferred into a twin-screw extruder 30 (from BERSTORFF) (introduction position 33). At position 34, crosslinker and accelerator were added. Subsequently, the entire mixture was freed of all trapped gas in a vacuum dome V at a pressure of 175 mbar. Thereafter, at position 35, the filler 2 was added and subsequently incorporated homogeneously. The resultant melt mixture was transferred to the outlet 36.

[0155] The adhesive was shaped while still hot as described above to give a 1000 μm-thick layer.

[0156] Constituents and amounts for the production of the pressure-sensitive adhesives can be found in table 1 below. The amounts supplied are reported in the relevant units per hour owing to the continuous procedure.

Table 1: Pressure-Sensitive Adhesives 7-12—Constituents and Amounts

[0157]

TABLE-US-00001 TABLE 1 Pressure-sensitive adhesives 7-12-constituents and amounts PSA No. 7 8 9 10 11 12 13 (comp.) Copolymer 1 (kg/h) 20.95 20.95 19.8 19.8 20.94 20.94 20.95 Filler 1 (kg/h) 62.1 62.1 71.29 71.29 53.42 53.42 Filler 2 (kg/h) 6.9 6.9 7.92 7.92 18.8 18.8 Filler 3 (kg/h) 14.95 Crosslinker 1 (ml/h) 25.34 23.95 25.33 25.34 Crosslinker 2 (ml/h) 27.0 25.49 26.95 Accelerator 1 (ml/h) 227.72 215.22 227.61 227.72 Accelerator 2 (ml/h) 66.16 62.53 66.13 Plasticizer 1 (kg/h) 1.48 1.48 0.99 0.99 6.84 6.84 1.48 PSA = pressure-sensitive adhesive comp. = Comparative example
PSA=pressure-sensitive adhesive
comp.=Comparative example

[0158] The test results achieved with the pressure-sensitive adhesives produced are given in table 2.

Table 2: Test Results

[0159]

TABLE-US-00002 TABLE 2 Test results Thermal Pressure- conductivity Bond sensitive in z strength on adhesive direction aluminum No. (W/(m*K) (N/cm)  1  0.72 15    2 1.2 7.8  3 2.5 3    4 0.6 11    5 0.9 5.5  6 2.1 0.5  7  0.75 14    8  0.72 15    9  1.21 8.2 10  1.19 8.5 11  2.48 3   12  2.53 3.5 13 (comp.) 0.4 15.8 

[0160] For all pressure-sensitive adhesive compositions, electrical volume resistances of 4.94*10.sup.13 to 5.21*10.sup.14 Ω*cm were measured.