THERMALLY CONDUCTIVE ACRYLIC ADHESIVE TAPE AND THE MANUFACTURING THEREOF

Abstract

A thermally conductive acrylic adhesive tape, which includes 600-800 parts by weight of a metal hydroxide, and 100 parts by weight of an acrylic copolymer that is based on least one alkyl(meth)acrylate and 1-30 parts by weight of a polar group containing monomer, wherein that thermally conductive acrylic adhesive tape also includes 10-50 parts by weight of a phosphate ester and 10-50 parts by weight of a plasticizer. Further, a method for manufacturing the thermally conductive acrylic adhesive tape is disclosed.

Claims

1. A thermally conductive acrylic adhesive tape, which comprises 600-800 parts by weight of a metal hydroxide, 100 parts by weight of an acrylic copolymer that is based on least one alkyl(meth)acrylate and 1-30 parts by weight of a polar group containing monomer, wherein the thermally conductive acrylic adhesive tape also comprises 10-50 parts by weight of a phosphate ester and 10-50 parts by weight of a plasticizer.

2. The thermally conductive acrylic adhesive tape according to claim 1, wherein the polar group comprises a carboxyl group.

3. The thermally conductive acrylic adhesive tape claim 1, wherein it exhibits a thermal conductivity of at least 2 W/m K as determined by use of the modified transient plane method.

4. The thermally conductive acrylic adhesive tape of claim 1, wherein it has a thickness of 10 to 5000 micron.

5. The thermally conductive acrylic adhesive tape of claim 1, wherein the metal hydroxide is aluminiumhydroxide.

6. The thermally conductive acrylic adhesive tape of claim 1, wherein it comprises a 10-50 parts by weight of a phosphate ester to 100 parts by weight of acrylic copolymer.

7. The thermally conductive acrylic adhesive tape of claim 1, wherein it comprises 10-50 parts by weight of a plasticizer to 100 parts by weight of acrylic copolymer.

8. The thermally conductive acrylic adhesive tape of claim 1, wherein it comprises acrylic copolymer that is based on at least one alkyl(meth)acrylate and 1-30 parts by weight of a polar group containing monomer.

9. The thermally conductive acrylic adhesive tape of claim 1, wherein it comprises a crosslinking monomer, such as 1,6-hexanedioldiacrylate and/or 1,4-butanedioldiacrylate.

10. A process for making a thermally conductive acrylic adhesive tape comprising the steps of partially polymerizing a mixture of alkyl (meth)acrylate(s) and polar group containing monomer(s) to obtain a syrup, then adding further components, as thermally conductive fillers, crosslinking monomers, initiators, and the like to said syrup to form a coatable syrup, and coating said coatable syrup onto a carrier film, followed by polymerizing said coatable syrup by UV light and under inert conditions.

11. The process of claim 10, wherein a chain control agent is added to the mixture of alkyl (meth)acrylate(s) and polar group containing monomer(s).

12. The process of claim 11, wherein the chain control agent is n-dodecyl mercaptan.

Description

EXAMPLES

Comparative Example 1

[0034] A mixture is formed by mixing 9000parts 2-ethylhexyl acrylate, 1000 parts n-vinyl caprolactam and 4 parts.-% 2,2-dimethoxy-2-phenyl acetophenone. In total 600 grams of said mixture is placed in a glass container and said mixture is degassed for 5 minutes by flushing nitrogen at a rate of 3 liter/minute. After 5 minutes, said mixture is exposed to UV light. The UV light consists for >80% of UVA light (300-400 nm) and has an intensity of 10 mJ/cm2. The exposure to UV light is stopped when a syrup is obtained which as a viscosity of approx. 1

[0035] A coatable mixture was formed by mixing 50 parts of syrup with 50 parts of aluminium hydroxide (Onyx Elite-Huber).

Example 1

[0036] A syrup was prepared according comparative example 1.

[0037] A coatable syrup was prepared by mixing 443 parts of syrup with 500 parts of aluminium hydroxide (Onyx Elite-Huber), 23 parts of a phosphoric acid ester and 34 parts of a plasticizer.

[0038] The viscosity of comparative example 1 and example 1 was determined with a Brookfield rheometer and the results are given in the table below. The results clearly show that example 1 has a much lower viscosity (with the same content of aluminium hydroxide) than comparative example 1. Alternatively, when not aiming for a lower viscosity, it is possible to increase the amount metal hydroxide in example 1 before reaches the same viscosity as found in comparative example 1. The results show that a lower viscosity and/or higher content of metal hydroxide can be achieved by using a specific amount of phosphoric acid ester and plasticizer in the coatable syrup.

TABLE-US-00001 Comparative example 1 Example 1 25 rpm 11,096 mPas 2,540 mPas

Example 2

[0039] A mixture of is formed by mixing 9000 parts 2-ethylhexyl acrylate, 1000 parts acrylic acid, 4 parts 2,2-dimethoxy-2-phenyl acetophenone and 2.5 parts of n-dodecyl mercaptan. In total 600 grams of said mixture is placed in a glass container and said mixture is degassed for 5 minutes by flushing nitrogen at a rate of 3 liter/minute. After 5 minutes, said mixture is exposed to UV light. The UV light consists for >80% of UVA light (300-400 nm) and has an intensity of 10 mJ/cm2. The exposure to UV light is stopped when a monomer conversion of approx. 10% is achieved and a syrup is formed which has a viscosity of approx. 500 mPas. Next, a coatable syrup is formed by mixing 10.94 parts of syrup with 0.012 parts of 1,6-hexanedioldiacrylate, 0.048 parts of 2,2-dimethoxy-2-phenyl acetophenone, 2.3 parts of a phosphoric acid polyester, 3.4 parts of dibutyl terephthalate and 83.3 parts of aluminium hydroxide (Apyral 20-Nabaltec). The coatable syrup has a viscosity of 20 Pas (250 rpm; Brookfield) at 25 C. Air bubbles are removed from the coatable syrup by degassing the coatable syrup for 10 minutes under a vacuum (<10 mbar).

[0040] A 1.5 mm thick layer of coatable syrup is coated onto a siliconized BOPET film, cover with a second siliconized BOPET film and exposed to UV light for 2.5 minutes. The UV light consists for >80% of UVA light and has an intensity of 10 mJ/cm2. During the exposure to UV light, the heat generated by the UV initiated polymerization of the coatable syrup is removed by blowing air over the outer surfaces of the siliconized BOPET films. After removal of the siliconized BOPET films a thermally conductive acrylic adhesive tape is obtained.

[0041] The thermal conductivity of said thermally conductive acrylic adhesive tape is determined by using the modified transient plane source technique and found to be 3.0 W/m K. Example 2 shows that a highly thermally conductive acrylic tape can be manufactured by using the composition according to the invention.

Example 3

[0042] The thermally conductive acrylic adhesive tape is made according to example 2, except that 1000 parts of n-vinyl caprolactam is used instead of 1000 parts acrylic acid.

[0043] The mechanical properties of the thermally conductive acrylic adhesive tape of example 2 and example 3 have been determined by measuring the stress-strain curve, displayed as Figure. The results are given in the figure below. The results clearly show that the mechanical properties of the thermally conductive acrylic adhesive tape which comprises an acrylic copolymer based on 1000 parts acrylic acid has better mechanical properties. The tensile strength and maximum elongation are significantly higher.

[0044] The bonding properties of the thermally conductive acrylic adhesive tape of example 2 and example 3 have been determined by measuring the 90 degrees peel strength on stainless steel substrates, an aluminium backing foil, and a dwell time of 8 hours at room temperature. The results are given in the table below. The results clearly show that the thermally conductive adhesive tape according to example 2 has much better peel strengths (bonding properties).

TABLE-US-00002 1000 parts n-vinyl 1000 parts acrylic acid caprolactam 90 degree peel strength 13.5 N/inch 3.9 N/inch