WO2010080679A1

WO2010080679A1 - An antistatic high temperature resistant polyimide adhesive tape

Info

Publication number: WO2010080679A1
Application number: PCT/US2009/069789
Authority: WO
Inventors: Hongbin Geng; Qing Wu; Songwen Ling; Haikun Xiong
Original assignee: 3M Innovative Properties Company
Priority date: 2009-01-09
Filing date: 2009-12-30
Publication date: 2010-07-15
Also published as: CN101775259A

Abstract

An antistatic high temperature resistant polyimide adhesive tape is provided which comprises a polyimide substrate including two major surfaces; a conductive layer including at least a conductive polymer coated on at least one major surface of said substrate; a silicone primer disposed upon said conductive layer; and a silicone adhesive layer disposed upon the silicone primer.

Description

AN ANTISTATIC HIGH TEMPERATURE RESISTANT POLYIMIDE

ADHESIVE TAPE

Field Of The Invention

The present invention relates to an adhesive tape, and particularly, to an antistatic high temperature resistant polyimide adhesive tape.

Background

With the rapid development of electronic technology, the gradual reduction of the physical sizes of integrated circuits, the gradual increment of integrated degree, and the wide application of more new macromolecule materials, static discharge has become increasingly important and the problem of static protection has further drawn wider attention increasingly. When a printed circuit board (PCB) is subjected to wave welding or a reflow welding, a high temperature shielding adhesive tape is needed to protect its gold fingers and some elements. For example, in recent years, the temperature of a lead-free reflow welding has reached to 280°C-300°C. If parts of the elements are relatively sensitive, they can be prone to be affected by the produced static (the static produced during the process of peeling the adhesive tape from the PCB board), and therefore, on the one hand, the high temperature adhesive tape is required to have a relatively good high temperature resistance, that is, there is no residual adhesive left at peeling after the high temperature; on the other hand, the high temperature resistant shielding adhesive tape is further required to have an antistatic function.

At present, some high temperature resistant antistatic adhesive tapes in the market still have the following problems: (1) Ionic additives are introduced into adhesive layers or the interlayer of an adhesive layer and a substrate. The static conducting performance of the obtained adhesive tape mainly depends on the humidity in the environment; under a high temperature environment, antistatic effect can not be exerted normally. (2) Conductive metal particles or macromolecular microparticles are introduced into the adhesive. Though the obtained adhesive tape can sustain a static conducting function by itself without depending on the humidity in the environment, because the surface or the slightly raised micron grade conductive particles thereof contact some tiny elements, on the one hand, it is possible to result in a short circuit; on the other hand, little conductive particles can be left on the device surface after peeling the adhesive tape; and the introduction of the conductive particles will affect some performances of the adhesive itself, for example, reducing bonding strength, coherence strength and the like.

(3) Because conductive substances have been added solely or simultaneously into a substrate, primer or adhesive layer, the light transmittance of the adhesive tape can be caused to decrease which makes it disadvantageous to check whether there are bubbles or residual adhesive and the like existing in the adhesive layer after a PCB was subjected to a high temperature.

Some inventors have proposed the following solutions for these problems. For example, US Patent Publication 2006/0251892Al discloses an antistatic single-side or double side adhesive tape. This adhesive tape is characterized in that, a conductive primer is presented between a substrate and an adhesive layer which includes conductive metal particles or a conductive polymer, a resin of polypropylene or phenolic aldehyde or rubber, and a cross-linking agent, and can be obtained by a conventional coating method; the primer has a coating thickness in a range of 0.5-25 microns; the single-side adhesive tape has a structure of adhesive layer/conductive primer/substrate; the double side adhesive has a structure of adhesive layer/conductive primer/substrate/conductive primer/adhesive layer, adhesive layer/conductive primer/substrate/adhesive layer; an adhesive system of the adhesive tape is an acrylic acid pressure sensitive adhesive; however, this adhesive tape does not have high temperature resistant performance. US Patent 5,631,079 discloses a high temperature resistant antistatic adhesive tape; the adhesive tape has an adhesive layer of an acrylic acid pressure sensitive adhesive containing surface-conducting encapsulated particles with a particle diameter below 1 micron. The adhesive tape can retain performance in which there is no residual adhesive left at peeling after being immersed into a melting metal tin liquid (235°C-265°C) for at least 5 seconds.

Europe Patent EP422919 also discloses an antistatic high temperature resistant adhesive tape. The adhesive tape includes a substrate, an intermediate conductive layer (between the substrate and an adhesive layer) and a conductive adhesive layer. The substrate includes a high temperature resistant polyimide thin film. The intermediate conductive layer is a macromolecular coating containing conductive particles, or a vacuum plating metal layer, or a composite aluminum foil, and a surface resistance thereof is not less than IxIO⁷ ohms. The conductive adhesive layer contains conductive particles with relatively large particles, and the conductive particles can even protrude out of the surface of the adhesive layer to connect a contacting surface with the intermediate conductive layer. When the intermediate conductive layer utilizes an aluminum foil and the adhesive system is an organosilicon pressure sensitive adhesive, an silicon primer is needed to be coated with a silica gel after being coated on the aluminum foil. At this time, after bending the aluminum foil to pierce the silicon primer and the silica gel, parts of the pierced points directly contact the object being stuck, and thus a connection is formed, that is, an antistatic function takes effect. Therefore, it is need not to add any conductive particles into the adhesive layer. However, in a case of a relatively large tension, the above described bend is inclined to recover and the pierced points will be out of service, and therefore the antistatic function will be lost. Additionally, US Patent 5,637,368 discloses a high temperature resistant antistatic adhesive tape. The adhesive tape has a structure as follows (in sequence): polyimide film/vanadium pentoxide coating/silicon primer/ silica gel. The vanadium pentoxide coating is accomplished using an aqueous vanadium pentoxide dispersed liquid (containing a polymer with sulphonic acid groups) in a specific coating manner. Vanadium pentoxide is an opaque substance.

In summary, through the high temperature resistant antistatic adhesive tapes disclosed in the above described patents have satisfied a high temperature resistant and antistatic function to a certain extent, none of them can overcome the problems described above simultaneously.

Therefore, it is necessary to develop a high temperature resistant antistatic adhesive tape which can eliminate the problems described above simultaneously.

Summary

An object of the invention is to provide a high temperature resistant antistatic polyimide adhesive tape which not only finds a good balance between the antistatic performance and the high temperature resistant performance, but also avoids the problems induced by ionic additives and conductive particles, and has a good light transmittance.

Thus, the invention provides an adhesive tape which comprises: a polyimide substrate including two major surfaces; a conductive layer including at least one conductive polymer coated on at least one major surface of said substrate; a silicone primer disposed upon said conductive layer; and a silicone adhesive layer disposed upon the silicone primer.

The adhesive tape according to certain embodiments of the invention is characterized in that it has good static resistance (for example, a static voltage produced when the adhesive tape is peeled is below 100 volts (v)), there are no conductive particles on the contacting surface with the substrate, a high temperature resistance (for example, being suffered at 280⁰C for 10 min or more), good light transmittance, and can be easily prepared (for example, being prepared using conventional coating methods), and therefore, it has a excellent compositive performance. The adhesive tape of the invention is particularly applicable to the shielding for the PCB sensitive elements being subjected to a wave welding or a reflow welding.

Brief Description of the Drawings

Figure 1 illustrates a structural schematic view of one embodiment according to the invention.

Detailed Description

In the invention, unless specially stated otherwise, the term "adhesive tape" is not limited to a tape shape, but also includes such as a piece shape, as well as any other shapes corresponding to the application situations.

The invention provides an adhesive tape which comprises: a polyimide substrate including two major surfaces; a conductive layer including at least one conductive polymer coated on at least one major surface of said substrate; a silicone primer disposed upon said conductive layer; and a silicone adhesive layer disposed upon the silicone primer. In the invention, the polyimide substrate is not subjected to any limitation and the conventional polyimide substrates applicable to the adhesive tape field can be used in the invention.

According to certain preferable embodiments, the conductive polymer in the adhesive tape of the invention is selected from polythiophene, complexes of polythiophene and polyvinyl benzene sulfonic acid (EPDT/PSS), polyaniline, polyfuran, polyphenylsulfonic acid, or various mixtures thereof.

According to certain preferable embodiments, the conductive polymer in the adhesive tape of the invention comprises from 20 wt% to 50 wt% of the total weight of the conductive layer. According to certain preferable embodiments, the conductive layer in the adhesive tape of the invention further comprises at least one selected from aqueous resins, cross- linking agents, dispersants, coupling agents, doping agents, deionized water/solvent mixing liquids, and pH adjusters. The aqueous resins include, but are not limited to, acrylic resins, polyurethane resins, epoxy resins, phenolic resins, organosilicon dispersoids, or modified resins of the above described resins. The aqueous resin preferably comprises from 40 wt% to 70 wt% of the total weight of the conductive layer. The cross- linking agents include, but are not limited to, melamines, aziridines of two or more functionalities, isocyanates or the prepolymers thereof. The cross-linking agent is, for example, a silane type coupling agent such as KH560, KH550 which preferably comprises from 0.1 wt% to 5 wt% of the total weight of the conductive layer. The doping agents include, but are not limited to, metal salts, Lewis acids, non-protonic polar solvents (such as, dimethylformamide (DMF), dimethylacetamide (DMAC), N-methyl pyrrolidone (NMP) and the like), and mixtures thereof. The doping agent preferably comprises from 0.1 wt% to 5 wt% of the total weight of the conductive layer. The said pH adjusters include, but not limited to, aqueous ammonia, dimethyl ethanolamine, and the mixtures thereof. The pH adjustor preferably comprises from 0.1 wt% to 0.2 wt% of the total weight of the conductive layer.

According to certain preferable embodiments, the conductive layer in the adhesive tape of the invention has a coating thickness of 0.1-0.5 microns and therefore the cost thereof is relatively low, and this is another prominent advantage of the adhesive tape of the invention.

According to certain preferable embodiments, the conductive layer in the adhesive tape of the invention has a surface resistance of 1x10 -1x10 Ω. According to certain preferable embodiments, the primer used in the adhesive tape of the invention is a silicone primer, such as, SS4191 obtained from Momentive Performance Materials Group (Shanghai, China), 7499(organo tin) obtained from DowCorning (Shanghai, China) and KR-3006A obtained from Shin-Etsu (Taipei, China). According to certain preferable embodiments, the silicone adhesive in the adhesive layer in the adhesive tape of the invention is a condensation type (organo-tin catalytic type) silicone adhesive, such as, PSA610/518 obtained from Momentive Performance Materials

Group (Shanghai, China) and 7406/7355/7566/280A obtained from DowCorning (Shanghai, China).

The structure of the above described adhesive tape can be extended to a double side adhesive tape and the structure of both sides can be the same or different. For example, both sides of the substrate can be coated with a conductive layer including at least a conductive polymer, a silicone primer disposed upon said conductive layer, and a silicone adhesive layer disposed upon the silicone primer, respectively. Additionally, one side of the substrate can be coated with a conductive layer including at least a conductive polymer, a silicone primer disposed upon said conductive layer, and a silicone adhesive layer disposed upon the silicone primer, while another side of the substrate can be further coated with a silicone primer and a silicone adhesive layer, respectively. The adhesive tape of the invention can have a release film (liner) disposed on the adhesive layer.

The invention is described in detail below by combining drawings and examples. These detailed descriptions do not limit the protective range of the invention. In the invention, unless stated otherwise, all of the contents of the percents, parts, proportions and the like are on a basis of weight.

Figure 1 illustrates a structural schematic view of one embodiment according to the invention. In Figure 1, a substrate 1, a conductive coating 2, a primer 3 and an adhesive layer 4 are shown from the top down. Examples:

Comparative scheme for abbreviations and matters:

Testing methods:

1. Static dissipation time a. A tester put on a pair of static protection gloves and placed a pre-cut 150 mm x 150 mm sample into a testing chamber of a static dissipation apparatus (Model 406C, ElectroTech Systems, Inc. (ETS)); b. A testing value of surface charge for the sample is reset and a high voltage of 5000 V is applied to the sample instantly; c. A TEST button is pressed and the applied voltage is stopped immediately, then a static dissipation time is recorded; generally, if the time exceeds 30s, it is considered that the insulating property is good and the testing will be stopped manually; if the time is shorter than 0.01s, it is considered that the sample has a static conducting function.

2. A Test for static voltage at unwinding a. An adhesive tape (with a width of 25 mm, a length of 33 m, and an internal diameter for roll core of 76.2 mm) is placed on a IMASS testing apparatus (with a model of SP-2000) and unwound at a speed of 2286 mm/min; b. A tester put on a pair of static protection gloves, grasped a 3M 718 static testing apparatus and aimed an infrared detector at a part of the unwound adhesive tape to measure the static voltage produced during the unwinding.

3. A Test for high temperature resistance a. An adhesive tape with a width of 25 mm is stuck on a 50 mmx50 mm steel plate with a thickness of 2 mm, then placed into a heating oven having been raised to a high temperature of 280⁰C; b. After 10 min, the steel plate is taken out immediately. There are no bubbles or fish eyes between the adhesive tape and the steel plate. There is no residual adhesive left on the adhesive tape at peeling under the high temperature; there is also no residual adhesive left at peeling after the steel plate has been cooled to the room temperature. 4. Evaluating standard for transparency

An adhesive tape is stuck on a printed circuit board (PCB) and the transparency of the adhesive tape is evaluated optically. The standard is as follows:

0: The elements under the adhesive tape are invisible completely. 1 : The elements under the adhesive tape can be seen gleamingly.

2: The elements under the adhesive tape can be seen clearly.

Example 1 1. Raw materials Substrate: 6051, a polyimide film with a thickness of 25 microns, provided by Tianjin

Tianyuan Electronic Material Co., Ltd.; Silicone primer: SS4191 (SS4191A, SS4191B, SS4192C and SS4259C), provided by

Momentive Performance Materials Group (Shanghai); Silicone adhesive: 7406, provided by DowCorning (Shanghai); A-75, a 75% BPO, provided by AKZO NOBEL (Changshu);

Conductive coating: Baytron P, provided by H. C. Stark (Germany);

Sancure 825, aqueous polyurethane, provided by Shanghai Younger Chemical

Co., Ltd.;

D604, a non-ionic fluorine type surfactant, provided by Air Products & Chemical (China) Investment Co., Ltd. (Shanghai);

A- 187, a silane type coupling agent, provided by Momentive Performance

Materials Group (Shanghai); NMP, reagent grade; dimethyl ethanolamine, reagent grade; water, deionized water; ώo-propanol, reagent grade. 2. Preparation method 2.1 formulations a. A formulation for conductive coating:

Table 1 A formulation for conductive coating (unit: gram)

Note: Each raw material was added slowly in sequence under stirring.

b. A formulation for primer:

Table 2 A formulation for silicone primer (unit: gram)

C. A formulation for adhesive

Table 3 A formulation for 7406 silicone adhesive (unit: gram)

2.2 Preparation process

The above described conductive coating mixing liquid was coated on one side of a polyimide face with a thickness of 25 microns with a 25 OLPI screen printing roller and dried in a heating oven with a highest setting temperature of 180⁰C. The coating thickness was controlled to be 0.1-0.5 microns. Subsequently, a silicone primer with a thickness of 0.1-0.5 microns was coated on the conductive coating and was dried at a highest setting temperature of 140⁰C. At last, a silicone adhesive was further coated the silicone primer and dried to be solidified. The thickness of the coated adhesive was 25-30 microns.

2.3 Performances

Table 4 The testing performances of example 1

Example 2 1. Raw materials Substrate: 6051, a polyimide film with a thickness of 25 microns, provided by Tianjin

Tianyuan Electronic Material Co., Ltd.;

Silicone primer: SS4191(SS4191A, SS4191B, SS4192C and SS4259C), provided by Momentive Performance Materials Group; Silicone adhesive: 7355, provided by DowCorning; A-75, provided by AKZO NOBEL; DCBPO, Provided by Degussa; Conductive coating: Baytron P, provided by H. C. Stark;

HD-MBO 19, provided by Beijing Jinhweili Applied Chemical Products Co., Ltd.;

Cymel 325, provided by Cytec/Conap Company;

D604, provided by Air Products & Chemical (China) Investment Co., Ltd. (Shanghai);

A-187, provided by Momentive Performance Materials Group (Shanghai); NMP, reagent grade; dimethylacetamide, reagent grade; water, deionized water; ώo-propanol, reagent grade.

2. Preparation method 2.1 formulations a. A formulation for conductive coating:

Table 5 A formulation for conductive coating (unit: gram)

Note: Each raw material was added slowly in sequence under stirring. b. A formulation for primer:

Table 6 A formulation for silicone primer (unit: gram)

C. A formulation for adhesive

Table 7 A formulation for silicone adhesive (unit: gram)

2.2 Preparation process

The preparation process in example 2 was the same as that in example 1.

2.3 Performances

Table 8 The testing performances of example 2

Example 3 1. Raw materials

Substrate: 6051, a polyimide film with a thickness of 25 microns, provided by Tianjin

Tianyuan Electronic Material Co., Ltd.;

Silicone primer: SS4191(SS4191A, SS4191B, SS4192C and SS4259C), provided by Momentive Performance Materials Group (Shanghai); Silicone adhesive: 7355, provided by DowCorning (Shanghai);

7406, provided by DowCorning (Shanghai); A-75, provided by ARKEMA (Changshu); Conductive coating: Baytron P, provided by H.C.Stark(Germany);

HD-MBO 19, provided by Beijing Jinhweili Applied Chemical Products Co., Ltd.;

Cymel 325, provided by Cytec/Conap Company (Shanghai); D604, provided by Air Products & Chemical (China) Investment Co., Ltd.;

A-187, provided by Momentive Performance Materials Group (Shanghai); NMP, reagent grade; dimethylacetamide, reagent grade; water, deionized water; iso-propanol, reagent grade;

Release films: SILFLU 50MD07, provided by Siliconenature; SILFLU 75MD07W, provided by Siliconenature.

2. Preparation method 2.1 formulations

A. A formulation for conductive coating:

Table 9 A formulation for conductive coating (unit: gram)

Table 10 A formulation for silicone primer (unit: gram)

C. A formulation for adhesive

Table 11 A formulation for 7355 silicone adhesive (unit: gram)

2.2 Preparation process Firstly, a conductive coating, a silicone primer and a 7406 silicone adhesive were coated respectively on a side of PI film, and the process and coating thickness is the same as those in example 1; then, a white fluorine release film (SILFLU 50MD07W) was online recombined. Subsequently, a silicone primer and a 7355 silicone adhesive were coated respectively on another side of PI (the other side thereof is recombined with a release film) wherein the silicone adhesive had a thickness of 0.05 mm. Finally, SILFLU 75MD07 was on-line recombined. 2.3 Performances

Table 13 The testing performances of example 3

Example 4 1. Raw materials

Momentive Performance Materials Group (Shanghai); Silicone adhesive: 7355, provided by DowCorning (Shanghai);

HD-MBO 19, aqueous polyacrylic acid, provided by Beijing Jinhweili Applied Chemical Products Co., Ltd.;

2. Preparation method 2.1 formulations

A. A formulation for conductive coating:

Table 14 A formulation for conductive coating (unit: gram)

Table 15 A formulation for silicone primer (unit: gram)

C. A formulation for adhesive

Table 16 A formulation for 7355 silicone adhesive (unit: gram)

2.2 Preparation process Firstly, a conductive coating, a silicone primer and a 7406 silicone adhesive were coated respectively on a side of PI film, and the process and coating thickness is the same as those in example 1; then, a white fluorine release film (SILFLU 50MD07W) was online recombined. Subsequently, a silicone primer and a 7355 silicone adhesive were coated respectively on another side of PI wherein the silicone adhesive had a thickness of 0.05 mm. Finally, SILFLU 75MD07 was on-line recombined. 2.3 Performances

Table 18 The testing performances of example 4

Comparative example 1

1. Raw materials

Tianyuan Electronic Material Co., Ltd.;

Silicone primer: SS4191(SS4191A, SS4191B, SS4192C and SS4259C), provided by Momentive Performance Materials Group (Shanghai); Silicone adhesive: 7355, provided by DowCorning (Shanghai); A-75, provided by ARKEMA (Changshu).

2. Preparation method 2.1 formulations

A. A formulation for primer:

Table 19 A formulation for silicone primer (unit: gram)

C. A formulation for adhesive

Table 20 A formulation for silicone adhesive (unit: gram)

2.2 Preparation process

The preparation process in comparative example 1 was the same as that in example 1 except that only a silicone primer and a silicone adhesive were coated without coating the conductive layer.

2.3 Performances

Table 18 The testing performances of comparative example 1

Comparative example 2

An adhesive tape was prepared according to a method disclosed in example 1 of EP422919 and was subjected to a performance testing according to the testing method in example 2. The transparency thereof was 0 or 1. The static dissipation time thereof was less than 0.01 s. The temperature resistant condition was that: it could only persist for 5 seconds at 250⁰C at best.

Claims

What is claimed is:

1.An adhesive tape comprising: a polyimide substrate including two major surfaces; a conductive layer including at least one conductive polymer coated on at least one major surface of said substrate; a silicone primer disposed upon said conductive layer; and a silicone adhesive layer disposed upon the silicone primer.

2. The adhesive tape according to claim 1, wherein said conductive polymer is selected from polythiophene, complexes of polythiophene and polyvinyl benzene sulfonic acid, polyaniline, polyfuran, polyphenylsulfonic acid, and combinations thereof.

3. The adhesive tape according to claim 1, wherein said conductive polymer comprises from 20 wt% to 50 wt% of the total weight of the conductive layer.

4. The adhesive tape according to claim 1, wherein said conductive layer further comprises at least one selected from aqueous resins, dispersants, coupling agents, doping agents, deionized water/solvent mixing liquids, and pH adjustors.

5. The adhesive tape according to claim 1, wherein said conductive layer further comprises a cross-linking agent.

6. The adhesive tape according to claim 4, wherein said aqueous resin is selected from acrylic resins, polyurethane resins, epoxy resins, phenolic resins, organosilicon dispersoids, and combinations thereof.

7. The adhesive tape according to claim 4, wherein said aqueous resin comprises from 40 wt% to 70 wt% of the total weight of the conductive layer.

8. The adhesive tape according to claim 5, wherein said cross-linking agent is selected from melamines, aziridines of 2 functionalities or more, isocyanates or the prepolymers thereof, and combinations thereof.

9. The adhesive tape according to claim 5, wherein said cross-linking agent comprises from 1 wt% to 25 wt% of the total weight of the conductive layer.

10. The adhesive tape according to claim 4, wherein said coupling agent is a silane type coupling agent.

11. The adhesive tape according to claim 4, wherein said coupling agent comprises from 0.1 wt% to 5 wt% of the total weight of the conductive layer.

12. The adhesive tape according to claim 4, wherein said doping agent is selected from metal salts, Lewis acids, non-protonic polar solvents, and mixtures thereof.

13. The adhesive tape according to claim 4, wherein said doping agent comprises from 0.1 wt% to 5 wt% of the total weight of the conductive layer.

14. The adhesive tape according to claim 4, wherein said pH adjuster is selected from aqueous ammonia, dimethyl ethanolamine, and the mixtures thereof.

15. The adhesive tape according to claim 4, wherein said pH adjuster comprises from 0.1 wt% to 0.2 wt% of the total weight of the conductive layer.

16. The adhesive tape according to claim 1, wherein said conductive layer has a coating thickness of from 0.1 microns to 0.5 microns.

17. The adhesive tape according to claim 1, wherein said silicone adhesive layer is a condensation type silicone pressure sensitive adhesive layer.

18. The adhesive tape according to claim 1, wherein said adhesive tape is a double side adhesive tape.

19. The adhesive tape according to claim 1, wherein both sides of said adhesive tape have the same structure.

20. The adhesive tape according to claim 1, further comprising a releasing film disposed upon said silicone adhesive layer.