Flame-retardant adhesive composition, coverlay film using same, and flexible copper-clad laminate

Abstract

The flame-retardant adhesive composition contains a styrene-based elastomer containing a carboxyl group, an epoxy resin, and a phosphorus-containing oligomer including a structural unit represented by general formula (1), and the epoxy resin content is 1-20 parts by mass and the phosphorus-containing oligomer content is 10-50 parts by mass with respect to 100 parts by mass of the styrene-based elastomer containing carboxyl groups. ##STR00001##
(wherein, R.sup.1 and R.sup.2 are each independently a hydrogen atom or a methyl group, n is an integer of 1-20.)

Claims

1. A flame-retardant adhesive composition comprising: (A) a carboxyl group-containing styrene-based elastomer, (B) an epoxy resin, and (C) a phosphorus-containing oligomer comprising a structural unit represented by the following formula (1): ##STR00005## wherein R.sup.1 and R.sup.2 are each independently a hydrogen atom or a methyl group, and n is an integer of 1 to 20, wherein a content of the epoxy resin (B) is from 3 to 17 parts by mass, and a content of the phosphorus-containing oligomer (C) is from 10 to 50 parts by mass, based on 100 parts by mass of a content of the carboxyl group-containing styrene-based elastomer (A).

2. The flame-retardant adhesive composition according to claim 1, wherein an acid value of the carboxyl group-containing styrene-based elastomer (A) is from 0.1 to 20 mgKOH/g.

3. The flame-retardant adhesive composition according to claim 1, wherein a main chain chemical structure of the carboxyl group-containing styrene-based elastomer (A) is derived from at least one styrene-based elastomer selected from the group consisting of a styrene-butadiene block copolymer, a styrene-ethylene propylene block copolymer, a styrene-butadiene-styrene block copolymer, a styrene-isoprene-styrene block copolymer, a styrene-ethylene butylene-styrene block copolymer, and a styrene-ethylene propylene-styrene block copolymer.

4. The flame-retardant adhesive composition according to claim 1, wherein a weight-average molecular weight of the phosphorus-containing oligomer (C) is from 1000 to 10000.

5. The flame-retardant adhesive composition according to claim 1, wherein a phosphorus concentration in the flame-retardant adhesive composition is from 0.7% to 3% by mass, based on 100% by mass of a solid content of the flame-retardant adhesive composition.

6. The flame-retardant adhesive composition according to claim 5, wherein the phosphorus concentration in the flame-retardant adhesive composition is from 1% to 2% by mass, based on 100% by mass of the solid content of the flame-retardant adhesive composition.

7. A coverlay film comprising an adhesive layer comprising the flame-retardant adhesive composition according to claim 1, wherein the adhesive layer is formed on one surface of a polyimide film or an aramid film.

8. A flexible copper-clad laminated board, wherein a copper foil is laminated on one surface of a polyimide film or an aramid film with the flame-retardant adhesive composition according to claim 1.

9. A bonding sheet comprising an adhesive layer comprising the flame-retardant adhesive composition according to claim 1, wherein the adhesive layer is formed on one surface of a releasable film.

10. The flame-retardant adhesive composition according to claim 1, wherein the content of the phosphorus-containing oligomer (C) is from 10 to 40 parts by mass, based on 100 parts by mass of the content of the carboxyl group-containing styrene-based elastomer (A).

11. The flame-retardant adhesive composition according to claim 1, wherein the content of the phosphorus-containing oligomer (C) is from 12 to 32 parts by mass, based on 100 parts by mass of the content of the carboxyl group-containing styrene-based elastomer (A).

12. The flame-retardant adhesive composition according to claim 1, wherein the content of the phosphorus-containing oligomer (C) is from 14 to 32 parts by mass, based on 100 parts by mass of the content of the carboxyl group-containing styrene-based elastomer (A).

13. The flame-retardant adhesive composition according to claim 1, wherein an acid value of the carboxyl group-containing styrene-based elastomer (A) is from 0.5 to 18 mg KOH/g.

14. The flame-retardant adhesive composition according to claim 1, wherein an acid value of the carboxyl group-containing styrene-based elastomer (A) is from 1.0 to 15 mg KOH/g.

15. The flame-retardant adhesive composition according to claim 1, wherein a weight-average molecular weight of the phosphorus-containing oligomer (C) is from 1,200 to 8,000.

16. The flame-retardant adhesive composition according to claim 1, wherein a weight-average molecular weight of the phosphorus-containing oligomer (C) is from 1,500 to 5,000.

17. The flame-retardant adhesive composition according to claim 1 further comprising a curing agent, wherein a content of the curing agent is set so that a functional group equivalent of the curing agent is from 0.2 to 2.5, based on 1 epoxy equivalent of the epoxy resin (B).

18. The flame-retardant adhesive composition according to claim 1, further comprising a curing agent, wherein a content of the curing agent is set so that a functional group equivalent of the curing agent is from 0.4 to 2.0, based on 1 epoxy equivalent of the epoxy resin (B).

19. The flame-retardant adhesive composition of claim 1, wherein the content of the epoxy resin (B) is from 3 to 12 parts by mass, based on 100 parts by mass of the content of the carboxyl group-containing styrene-based elastomer (A).

Description

EXAMPLES

(1) Hereinafter, the present invention is specifically described using Examples. The present invention is not limited to the Examples. In the following description, part(s) and % are based on mass.

(2) 1. Measurement Method and Evaluation Method

(3) (1) Weight Average Molecular Weight

(4) GPC measurement was carried out under the following conditions to obtain Mw of elastomers and phosphorus-containing oligomers. The Mw was calculated by converting the retention time measured by GPC based on the retention times of the standard polystyrenes.

(5) Device: Allians 2695 (manufactured by Waters Corporation)

(6) Column: Two TSK gel Super Multipore HZ-H and two TSK gel Super HZ2500

(7) (manufactured by TOSOH CORPORATION)

(8) Column temperature: 40 C.

(9) Eluent: Tetrahydrofuran 0.35 ml/min

(10) Detector: RI

(11) (2) Adhesive Peel Strength

(12) A polyimide film (Kapton 100EN, tradename, available from DU PONT-TORAY CO., LTD.) having a thickness of 25 m was prepared, and a liquid state adhesive composition was roll coated onto the surface thereof. Subsequently, the film attached with the coated film was stood still in an oven, and dried at a temperature of 100 C. for 3 minutes. A film (an adhesive layer) having a thickness of 25 m was formed to obtain a coverlay film. Thereafter, a rolled copper foil with a thickness of 35 m was superposed onto the surface of the adhesive layer of the coverlay film so that they were surface contacted, and laminated under conditions of a temperature of 120 C., a pressure of 0.2 MPa and a speed of 0.5 m/min. The laminated material (polyimide film/adhesive layer/copper foil) was then subjected to heating and pressing under conditions of a temperature of 180 C. and a pressure of 3 MPa for 1 minute, thereafter, subjected to heating for curing at 180 C. for 1 hour to obtain a flexible copper-clad laminated board. The flexible copper-clad laminated board was cut to prepare adhesion test pieces with a predetermined size.

(13) For evaluating adhesiveness, 180 degree adhesive peel strength (N/mm) when the polyimide film is peeled off from the adhesion test piece was measured under conditions of a temperature of 23 C. and a tensile speed of 50 mm/min according to JIS C 6481. A width of the adhesion test piece at the time of the measurement was made 10 mm.

(14) (3) Resin Flowing-out Property

(15) Punching was applied to the coverlay film and a hole with 6 mm was formed. A rolled copper foil having a thickness of 35 m was superposed onto a surface of the adhesive layer of the coverlay film so that they were surface contacted, and laminated under conditions of a temperature of 120 C., a pressure of 0.2 MPa and a speed of 0.5 m/min. Subsequently, the laminated material (polyimide film/adhesive layer/copper foil) was subjected to heating and pressing under conditions of a temperature of 180 C. and a pressure of 3 MPa for 1 minute. At this time, flowing-out of a resin component was occurred at a hole end of the polyimide hole portion of the integrally laminated material. A maximum flowing-out length from the hole end was measured. It was judged that smaller maximum flowing-out length is good, and larger is poor resin flowing-out property. This resin flowing-out property is to evaluate embedding property at the wiring portion of the FPC related products.

(16) (4) Solder Heat Resistance

(17) The following test was carried out by the conditions conforming to JIS C 6481. The adhesion test piece was cut to 20 mm square, and left under conditions at 23 C. and 55% RH for 24 hours. Thereafter, the test piece was floated on a solder bath while making the surface of the polyimide film upside at a predetermined temperature for 60 seconds, and a foamed state at the surface of the adhesion test piece was observed. At this time, an upper limit temperature at which no foam is observed to the adhesion test piece was made the temperature of the solder heat resistance.

(18) (5) Insulation Reliability

(19) To the coverlay film was laminated a copper-clad laminated board onto which a pattern of L/S=50/50 (a thickness of wiring; 50 m, a distance between wirings; 50 m) had been formed under conditions of a temperature of 120 C., a pressure of 0.2 MPa and a speed of 0.5 m/min. The laminated material of the polyimide film/adhesive layer/copper-clad laminated board was then subjected to heating and pressing under conditions of a temperature 180 C. and a pressure of 3 MPa for 1 minute, thereafter, subjected to heating for curing at 180 C. for 1 hour to obtain a test piece.

(20) A dedicated wire was connected to a terminal of the test piece, an insulation reliability test between wires was carried out under conditions of an applied voltage of 60V DC, a temperature of 120 C., a humidity of 90% and a testing time of 4 hours. After the test, appearance was observed. A case where no remarkable color change of the wiring or small degree of the same was judged as , and not a case was judged as x. A case where the insulation resistance value is higher than 110.sup.8 was judged as , and a case where it is lower than the same was judged as x.

(21) (6) Flame Retardancy

(22) A polyimide film (Kapton 50EN, tradename, available from DU PONT-TORAY CO., LTD.) having a thickness of 12.5 m was prepared, and a liquid state adhesive composition was roll coated onto the surface thereof. Subsequently, the film attached with the coated film was stood still in an oven, and dried at a temperature of 100 C. for 3 minutes. A film (an adhesive layer) having a thickness of 25 m was formed to obtain a coverlay film. Thereafter, an aramid film (MICTRON, tradename, available from TORAY INDUSTRIES, INC.) with a thickness of 4.4 m was superposed onto the surface of the adhesive layer of the coverlay film so that they were surface contacted, and laminated under conditions of a temperature of 120 C., a pressure of 0.2 MPa and a speed of 0.5 m/min. The laminated material (polyimide film/adhesive layer/aramid film) was then subjected to heating and pressing under conditions of a temperature of 180 C. and a pressure of 3 MPa for 1 minute, thereafter, subjected to heating for curing at 180 C. for 1 hour to obtain a test piece for evaluating flame retardancy.

(23) The test piece for evaluating flame retardancy was subjected to a thin material vertical burning test confirming to the UL94 standard, and the flame retardancy test passed (VTM-0) was judged as , and not passed was judged as x.

(24) 2. Raw Materials of Flame-retardant Adhesive Composition

(25) 2-1. Elastomer

(26) (1) Carboxyl Group-containing Styrene-based Elastomer a1

(27) A maleic acid modified styrene-ethylene butylene-styrene block copolymer Tuftec M1913 (tradename) available from Asahi Kasei Chemicals Corporation was used. A styrene/ethylene butylene ratio in this copolymer is 30/70. Mw is 150,000. An acid value is 10 mgKOH/g.

(28) (2) Carboxyl Group-containing Styrene-based Elastomer a2

(29) A maleic acid modified styrene-ethylene butylene-styrene block copolymer Tuftec M1911 (tradename) available from Asahi Kasei Chemicals Corporation was used. A styrene/ethylene butylene ratio in this copolymer is 30/70. Mw is 150,000. An acid value is 2 mgKOH/g.

(30) (3) Styrene-based Elastomer a3

(31) A styrene-ethylene butylene-styrene block copolymer Tuftec H1041 (tradename) available from Asahi Kasei Chemicals Corporation was used. A styrene/ethylene butylene ratio in this copolymer is 30/70. Mw is 150,000. An acid value is 0 mgKOH/g.

(32) (4) Urethane-based Elastomer

(33) PANDEX T-5102 (tradename) available from DIC Corporation was used. There is no melting point of this elastomer, and an acid value thereof is 0.5 mg KOH/g.

(34) (5) Acid Modified NBR-Based Elastomer

(35) A carboxyl group-containing nitrile rubber Nipol 1072J (tradename) available from ZEON CORPORATION was used. A bonded acrylonitrile amount of this elastomer is 27% (a center value).

(36) 2-2. Epoxy Resin

(37) (1) Epoxy Resin b1

(38) A dicyclopentadiene type polyfunctional epoxy resin EPICLON HP-7200 (tradename) available from DIC Corporation was used. An epoxy equivalent of the epoxy resin b1 is 259 g/eq.

(39) (2) Epoxy Resin b2

(40) A naphthalene type polyfunctional epoxy resin EPICLON HP-4700 (tradename) available from DIC Corporation was used. An epoxy equivalent of the epoxy resin b2 is 165 g/eq.

(41) (3) Epoxy Resin b3

(42) A bisphenol A type epoxy resin Epikote jER828 (tradename) available from Mitsubishi Chemical Corporation was used. An epoxy equivalent of the epoxy resin b3 is 189 g/eq.

(43) 2-3. Flame Retardant

(44) (1) Flame Retardant c1

(45) A phosphorus-containing oligomer Nofia OL-1001 (tradename) available from FRX POLYMERS INC., was used. This phosphorus-containing oligomer is a compound represented by the general formula (2). Mw is 2,000 to 3,000. A phosphor content is 8.5%, and a glass transition temperature (Tg) is 83 C.

(46) (2) Flame Retardant c2

(47) A phosphorus-containing oligomer Nofia OL-3001 (tradename) available from FRX POLYMERS INC., was used. This phosphorus-containing oligomer is a compound represented by the general formula (2). Mw is 3,500 to 4,500. A phosphor content is 10.0%, and a glass transition temperature (Tg) is 85 C.

(48) (3) Flame Retardant x

(49) A trisdiethyl phosphinate aluminum EXOLIT OP-935 (tradename) available from CLARIANT K.K. was used. A phosphor content in the flame retardant x is 24%.

(50) (4) Flame Retardant y

(51) Aluminum hydroxide HIGILITE 42M (tradename) available from SHOWA DENKO K.K. was used.

(52) 2-4. Others

(53) (1) Curing Agent

(54) A phenol novolac resin PHENOLITE TD-2090 (tradename) available from DIC Corporation was used.

(55) (2) Curing Accelerator

(56) An imidazole-based curing accelerator CUREZOL C11-Z (tradename) available from SHIKOKU CHEMICALS CORPORATION was used.

(57) (3) Solvent

(58) A mixed solvent comprising toluene and methyl ethyl ketone (a mass ratio=90:10) was used.

(59) 3. Production of Flame-Retardant Adhesive Composition and Evaluation Thereof

Examples 1 to 6 and Comparative Examples 1 to 8

(60) Into a 1,000 ml flask equipped with a stirring device were added the starting materials with a ratio as shown in Table 1 and Table 2. The mixture was stirred at room temperature for 6 hours to dissolve in the solvent to produce liquid state flame-retardant adhesive compositions. The obtained liquid state adhesive compositions were subjected to various kinds of evaluations. The results are shown in Tables 1 and 2.

(61) TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 Composition Carboxyl group-containing styrene-based 100 100 100 100 100 (parts by elastomer a1 mass) Carboxyl group-containing styrene-based 100 elastomer a2 Epoxy resin b1 6 6 12 6 Epoxy resin b2 6 Epoxy resin b3 6 Flame retardant c1 14 32 14 14 15 Flame retardant c2 12 Curing accelerator 0.2 0.2 0.2 0.2 0.4 0.2 Toluene 360 360 360 360 360 360 Methyl ethyl ketone 40 40 40 40 40 40 Phosphor concentration (% by mass) 1.0 2.0 1.0 1.0 1.0 1.0 Evaluation Resin flowing-out property (mm) 0.15 0.12 0.14 0.19 0.18 0.11 Adhesive peel strength (N/mm) 0.70 0.50 0.71 0.75 0.65 0.60 Solder heat resistance ( C.) 280 280 300 280 300 280 Insulation reliability Appearance Insulation resistance value Flame retardancy

(62) TABLE-US-00002 TABLE 2 Comparative Example 1 2 3 4 5 6 7 8 Composition Carboxyl group-containing styrene-based 100 100 100 100 100 (parts by elastomer a1 mass) Carboxyl group-containing styrene-based elastomer a2 Styrene-based elastomer a3 100 Urethane-based elastomer 100 Acid modified NBR-based elastomer 100 Epoxy resin b1 6 6 30 6 6 Epoxy resin b2 Epoxy resin b3 6 6 Flame retardant c1 14 7 17 13 14 14 Flame retardant c2 Flame retardant x 5 Flame retardant y 100 Curing agent 8.6 Curing accelerator 0.2 0.2 1.0 0.2 0.2 0.2 0.2 0.2 Toluene 360 360 360 360 360 360 360 360 Methyl ethyl ketone 40 40 40 40 40 40 40 40 Phosphor concentration (% by mass) 1.0 0.5 1.0 1.0 1.0 0.0 1.0 1.0 Evaluation Resin flowing-out property (mm) 0.55 0.19 0.62 0.02 0.12 0.01 0.09 0.08 Adhesive peel strength (N/mm) 0.41 0.97 0.15 0.55 0.66 0.12 0.88 0.79 Solder heat resistance ( C.) 220 300 280 220 260 240 220 260 Insulation reliability Appearance x x x x x Insulation resistance value x x x Flame retardancy x x x

(63) From the results in Table 1, it can be understood that the flame-retardant adhesive compositions of Examples 1 to 6 are materials excellent in all the characteristics. On the other hand, Comparative example 1 uses the styrene-based elastomer having no carboxyl group, so that adhesiveness, heat resistance and insulation reliability are insufficient. Comparative example 2 is an example in which the content of the phosphorus-containing oligomer (C) is out of the range of the present invention, so that flame retardancy is not sufficient. Further, Comparative examples 3 and 4 are examples in which the content of the epoxy resin (B) are out of the range of the present invention, so that the effects of the present invention cannot be obtained. Comparative examples 5 and 6 which use flame retardants other than the phosphorus-containing oligomer (C) of the present invention are insufficient in insulation reliability, adhesiveness and heat resistance. Moreover, Comparative examples 7 and 8 which use elastomers other than the carboxyl group-containing styrene-based elastomer (A) of the present invention cannot obtain flame retardance even when the phosphorus-containing oligomer (C) of the present invention is used with predetermined amounts, and insulation reliability is also insufficient.

INDUSTRIAL APPLICABILITY

(64) The flame-retardant adhesive composition of the present invention is excellent in adhesiveness to a polyimide film, or the like. When two parts are bonded, the adhered portion therebetween is excellent in heat resistance and insulation reliability, so that it is suitable for manufacturing related products of a flexible printed wiring circuit board such as a coverlay film, a flexible copper-clad laminated board, and a bonding sheet.