Pressure-sensitive adhesive composition

Abstract

Provided are a seal tape and a secondary battery. The seal tape for adhering an electrode assembly includes a pressure-sensitive adhesive layer including a cured product of a pressure-sensitive adhesive composition including a polymer including a polar functional group-containing monomer as a polymerization unit, and is expanded in contact with an electrolyte solution to be detached from the electrode assembly, and therefore, isotropic volume expansion and contraction of the electrode assembly may be induced by repeated charging and discharging of a secondary battery and a disconnection phenomenon in which an electrode is disconnected may be prevented.

Claims

1. A pressure-sensitive adhesive composition, comprising: a polymer having a polymerization unit derived from a (meth)acrylic acid ester monomer, a monomer represented by Formula 1 and a crosslinkable monomer containing a crosslinkable functional group: ##STR00004## where R.sub.1 represents hydrogen or an alkyl group having 1 carbon atom to 12 carbon atoms, R.sub.2 represents an alkylene group having 1 carbon atom to 6 carbon atoms, R.sub.3 represents hydrogen, an alkyl group having 1 carbon atom to 12 carbon atoms, an aryl group having 6 carbon atoms to 24 carbon atoms or an arylalkyl group having 6 carbon atoms to 48 carbon atoms, and n is 0 or more, wherein the polymer includes 158 parts by weight to 300 parts by weight of the monomer represented by Formula 1 with respect to 100 parts by weight of the (meth)acrylic acid ester monomer in a polymerized form.

2. A pressure-sensitive adhesive composition comprising: a polymer having a polymerization unit derived from a (meth)acrylic acid ester monomer, a monomer represented by Formula 2 and a crosslinkable monomer containing a crosslinkable functional group: ##STR00005## where R.sub.1 represents hydrogen or an alkyl group having 1 carbon atom to 12 carbon atoms, and R.sub.3 represents hydrogen, an alkyl group having 1 carbon atom to 12 carbon atoms, and aryl group having 6 carbon atoms to 24 carbon atoms or an aryl alkyl group having 6 carbon atoms to 48 carbon atoms, p+q is 1 or more, p is 0 to 100, and q is 0 to 100, wherein the polymer includes 158 parts by weight to 300 parts by weight of the monomer represented by Formula 2 with respect to 100 parts by weight of the (meth)acrylic acid ester monomer in a polymerized form.

3. The composition according to claim 1, wherein the monomer represented by Formula 1 is at least one selected from methoxyethyl (meth)acrylate, methoxyethoxyethyl (meth)acrylate, ethoxyethoxyethyl (meth)acrylate, ethoxytriethyleneglycol (meth)acrylate, polyethyleneglycol (meth)acrylate, polyethyleneglycolmethylether (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, propoxylated nonylphenol (meth)acrylate, ethoxylated phenol (meth)acrylate, or polypropyleneglycol (meth)acrylate.

4. The composition according to claim 1, wherein the crosslinkable monomer includes at least one crosslinkable functional group selected from a hydroxyl group, a carboxyl group, an epoxy group, a glycidyl group, an isocyanate group, an amide group, an amino group or an alkoxysilyl group.

5. The composition according to claim 1, wherein the polymer includes 0.1 parts by weight to 10 parts by weight of the crosslinkable monomer with respect to 100 parts by weight of a (meth)acrylic acid ester monomer in a polymerized form.

6. The composition according to claim 1, wherein the pressure-sensitive adhesive composition further includes a crosslinking agent.

7. The composition according to claim 6, wherein the crosslinking agent is included in an amount of 0.001 parts by weight to 10 parts by weight with respect to 100 parts by weight of the total composition.

8. The composition according to claim 6, wherein the crosslinking agent includes at least one selected from an isocyanate-based compound, an epoxy-based compound, an aziridine-based compound or a metal chelate-based compound.

9. A seal tape, comprising: a base layer; and a pressure-sensitive adhesive layer including a cured material of the pressure-sensitive adhesive composition of claim 1, which is formed on one surface of the base layer.

10. The seal tape according to claim 9, wherein the base layer is at least one selected from an acryl film, a polyolefin film, a polyamide film, a polycarbonate film, a polyurethane film, a cellulose acetate film or a polyester film.

11. The seal tape according to claim 10, wherein the polyester film is at least one selected from a polyethyleneterephthalate film, a polyethylenenaphthalate film or a polybutyleneterephthalate film.

12. The seal tape according to claim 9, wherein the base layer has a thickness of 10 m to 200 m.

13. The seal tape according to claim 9, wherein the pressure-sensitive adhesive layer has a thickness of 2 m to 100 m.

14. The seal tape according to claim 9, wherein the pressure-sensitive adhesive layer has a peeling strength at room temperature of 370 gf/25 mm or less with respect to glass, which is measured at a peeling rate of 5 mm/sec and a peeling angle of 180 degrees.

15. A secondary battery, comprising: an electrode assembly including a positive electrode plate, a negative electrode plate and a separation film interposed between the positive electrode plate and the negative electrode plate; and the seal tape of claim 9 adhered to a circumferential surface of the electrode assembly by means of the pressure-sensitive adhesive layer.

16. The secondary battery according to claim 15, wherein the seal tape is adhered to surround the circumferential surface including a closing part in which the outermost end of the separation film of the circumferential surface of the electrode assembly is located.

17. The secondary battery according to claim 15, wherein the pressure-sensitive adhesive layer has a peeling strength at room temperature of 1200 gf/25 mm or less with respect to the separation film, which is measured at a peeling rate of 5 mm/sec and a peeling angle of 180 degrees.

18. The secondary battery according to claim 15, which has a cylindrical shape.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic cross-sectional view of an exemplary seal tape of the present application;

(2) FIG. 2 is a schematic diagram of an exemplary secondary battery of the present application;

(3) FIG. 3 is an image of a stereoscopic structure formed after the seal tape of Example 1 of the present application is in contact with an electrolyte;

(4) FIG. 4 is an image of a surface after the seal tape of Comparative Example 1 of the present application is in contact with an electrolyte;

(5) FIG. 5 is an image of a cross-section of a stereoscopic structure formed after a seal tape of Example 4 of the present application is in contact with an electrolyte;

(6) FIG. 6 is an image of a cross-section of the seal tape of Comparative Example 1 of the present application after a contact with an electrolyte;

(7) FIG. 7 is a surface roughness graph obtained by mathematically modeling the cross-section of the stereoscopic structure formed after the seal tape of Example 4 of the present application is in contact with an electrolyte; and

(8) FIG. 8 is a surface roughness graph obtained by mathematically modeling the cross-section of the seal tape of Comparative Example 1 of the present application after a contact with an electrolyte.

MODE FOR INVENTION

(9) Hereinafter, the present application will be described in detail with reference to examples and comparative examples, but the scope of the present application is not limited to the following examples.

(10) Physical properties presented in the examples and comparative examples were evaluated by the following methods.

(11) 1. Measurement of Weight Average Molecular Weight

(12) A weight average molecular weight of a pressure-sensitive adhesive composition was measured using GPC under the following conditions. Standard polystyrene produced by Agilent Technologies was used to provide a calibration curve, and measurement results were converted.

(13) <Conditions for Measuring Weight Average Molecular Weight>

(14) Measuring Tool: Agilent GPC (Agilent 1200 series, U.S.)

(15) Column: Two connected PL mixed B

(16) Column Temperature: 40 C.

(17) Eluent: Tetrahydrofuran

(18) Flow Rate: 1.0 mL/min

(19) Concentration: 2 mg/mL (100 L injection)

(20) 2. Measurement of Peeling Strength to Glass

(21) A specimen was prepared by cutting a seal tape to have a size of 25 mm200 mm (widthlength). Afterward, the specimen was adhered to a glass plate by means of a pressure-sensitive adhesive layer using a 2 kg rubber roller, stored at room temperature for approximately 2 hours, and a peeling strength was measured while the seal tape was peeled at a peeling rate of 5 mm/sec and a peeling angle of 180 degrees using a tension tester.

(22) 3. Measurement of Peeling Strength to Separation Film

(23) A specimen was prepared by cutting a seal tape to have a size of 25 mm200 mm (widthlength). Afterward, the specimen was adhered to a separation film (SRS olefin-based separation film) of an electrode assembly by means of a pressure-sensitive adhesive layer using a 2 kg rubber roller, stored at room temperature for approximately 2 hours, and a peeling strength was measured while the seal tape was peeled at a peeling rate of 5 mm/sec and a peeling angle of 180 degrees using a tension tester. When the peeling strength exceeded 400 gf/25 mm, the separation film was separated and broken, and therefore it was impossible to measure the peeling strength.

(24) 4. Observation of Surface Shape

(25) Specimens prepared by the methods of the Examples or Comparative Examples were dipped in a carbonate-based electrolyte, maintained in a sealed state at room temperature for 1 day, and removed from the electrolyte to take a photograph of a surface shape using a digital camera. The images are shown in FIGS. 3 and 4.

(26) In addition, the surface shape of the seal tape was observed, and whether a stereoscopic structure was or was not observed was evaluated according to the following criteria:

(27) <Criteria for Evaluating Whether Stereoscopic Structure was or was not Formed>

(28) : A stereoscopic structure was apparently observed with the naked eye.

(29) : A stereoscopic structure was not observed with the naked eye.

(30) x: There was no stereoscopic structure.

(31) 5. Measurement of Center Line Average Roughness (Ra)

(32) Specimens prepared by the methods of Example 4 and Comparative Example 1 were dipped in a carbonate-based electrolyte, maintained in a sealed state at room temperature for 1 day, and removed from the electrolyte to take a photograph of a cross-section of the specimen using an optical microscope, and then the images are shown as FIGS. 5 and 6. In Example 4, as a pressure-sensitive adhesive layer absorbed an electrolyte solution to form a stereoscopic structure, the pressure-sensitive adhesive layer had a certain haze, and thereby an interface with a transparent PET base was clearly observed. However, in Comparative Example 1, the pressure-sensitive adhesive layer did not absorb the electrolyte solution, did not have a haze, and thus it was difficult to observe an interface between a transparent pressure-sensitive adhesive layer and a PET base with the naked eye.

(33) A pixel value of a photograph of a cross-section of the specimen of Example 4 or Comparative Example 1 was calculated, the number of the pixels were converted into a length using a dimension of a ruler and mathematically remodeled to obtain surface roughness curves shown in FIGS. 7 and 8, respectively, and a center line average roughness value was calculated by a method that will be described below. Specifically, in the roughness curve, a standard length (L) was extracted by approximately 2.3 mm in a direction of an average line, an average line direction was represented as an x axis, a longitudinal direction was represented as a y axis, a roughness curve was represented by y=f(x), and a center line average roughness value was obtained from Equation 1:

(34) $\begin{array}{cc}{R}_a=\frac{1}{L}{}_0^L.Math.f\left(x\right).Math.\mathrm{dx}& \left[\mathrm{Equation}1\right]\end{array}$

(35) 6. Observation of Detachment

(36) Seal tape specimens (widthlength=50 mm57 mm) prepared by the methods of the examples or comparative examples were adhered to an electrode assembly (length 60 mmdiameter 17 mm), the electrode assembly was dipped in a carbonate-based electrolyte, a phenomenon of detaching the seal tape from a surface of the electrode assembly was observed, a detached area was calculated by measuring a width and a length, and then a ratio of the detached area with respect to an area adhered to the electrode assembly (625 mm.sup.2) was calculated.

(37) 7. Evaluation of Battery Performance

(38) A cylindrical battery was configured by adhering seal tape specimens prepared by the method of the examples or comparative examples to an electrode assembly, inserting the electrode assembly into an exterior can, injecting an electrolyte solution into the exterior can, and sealing the exterior can. Four cylindrical battery samples prepared as described above were prepared, charging and discharging were repeated 10 times for each sample, the battery was disassembled to take the electrode assembly apart, and formation of cracks were observed while a positive electrode/a separation film/a negative electrode/a separation film were disassembled.

Preparation Example 1. Preparation of Polymer (A1)

(39) A monomer mixture composed of 58 parts by weight of n-butyl acrylate (n-BA), 40 parts by weight of methoxy ethyl acrylate (MEA) and 2 parts by weight of hydroxybutyl acrylate (HBA), and 0.02 parts by weight of n-dodecanethiol as a chain transferring agent were put into a 1000 cc reaction vessel in which a nitrogen gas is refluxed and a cooling system is equipped to easily control a temperature, and 150 parts by weight of ethyl acetate (EAc) was added as a solvent. Afterward, to remove oxygen, a nitrogen gas was purged at 60 C. for 60 minutes, and then the resulting mixture was maintained at 60 C. The mixture was homogenized, and 0.04 parts by weight of azobisisobutyronitrile (AIBN) was added as a reaction initiator. The mixture was reacted for 8 hours, thereby preparing a polymer (A1) having a weight average molecular weight of 800,000. Here, the parts by weight are represented by wt %.

Preparation Example 2. Preparation of Polymer (A2)

(40) A polymer (A2) having a weight average molecular weight of 700,000 was prepared by the same method as described in Preparation Example 1, except that 40 parts by weight of methoxy ethoxy ethyl acrylate (MOEOEA) was added instead of 40 parts by weight of methoxy ethyl acrylate used in Preparation Example 1. Here, the parts by weight are represented by wt %.

Preparation Example 3. Preparation of Polymer (A3)

(41) A polymer (A3) having a weight average molecular weight of 600,000 was prepared by the same method as described in Preparation Example 1, except that 40 parts by weight of ethoxy ethoxy ethyl acrylate (EOEOEA) was added instead of 40 parts by weight of methoxy ethyl acrylate used in Preparation Example 1. Here, the parts by weight are represented by wt %.

Preparation Example 4. Preparation of Polymer (A4)

(42) A polymer (A4) having a weight average molecular weight of 780,000 was prepared by the same method as described in Preparation Example 1, except that 68 parts by weight of n-BA, 30 parts by weight of MEA, and 2 parts by weight of HBA were added instead of 58 parts by weight of n-BA, 40 parts by weight of MEA and 2 parts by weight of HBA used in Preparation Example 1. Here, the parts by weight are represented by wt %.

Preparation Example 5. Preparation of Polymer (A5)

(43) A polymer (A5) having a weight average molecular weight of 790,000 was prepared by the same method as described in Preparation Example 1, except that 48 parts by weight of n-BA, 50 parts by weight of MEA, and 2 parts by weight of HBA were added instead of 58 parts by weight of n-BA, 40 parts by weight of MEA and 2 parts by weight of HBA used in Preparation Example 1. Here, the parts by weight are represented by wt %.

Preparation Example 6. Preparation of Polymer (A6)

(44) A polymer (A6) having a weight average molecular weight of 750,000 was prepared by the same method as described in Preparation Example 1, except that 38 parts by weight of n-BA, 60 parts by weight of MEA, and 2 parts by weight of HBA were added instead of 58 parts by weight of n-BA, 40 parts by weight of MEA and 2 parts by weight of HBA used in Preparation Example 1. Here, the parts by weight are represented by wt %.

Preparation Example 7. Preparation of Polymer (A7)

(45) A polymer (A7) having a weight average molecular weight of 730,000 was prepared by the same method as described in Preparation Example 1, except that 28 parts by weight of n-BA, 70 parts by weight of MEA, and 2 parts by weight of HBA were added instead of 58 parts by weight of n-BA, 40 parts by weight of MEA and 2 parts by weight of HBA used in Preparation Example 1. Here, the parts by weight are represented by wt %.

Preparation Example 8. Preparation of Polymer (B1)

(46) A polymer (B1) having a weight average molecular weight of 800,000 was prepared by the same method as described in Preparation Example 1, except that a monomer mixture composed of 98 parts by weight of n-butyl acrylate and 2 parts by weight of hydroxybutyl acrylate was added and the methoxy ethyl acrylate used in Preparation Example 1 was not added. Here, the parts by weight are represented by wt %.

Preparation Example 9. Preparation of Polymer (B2)

(47) A polymer (B2) having a weight average molecular weight of 800,000 was prepared by the same method as described in Preparation Example 1, except that a monomer mixture composed of 93 parts by weight of n-butyl acrylate and 7 parts by weight of acrylic acid was added and the methoxy ethyl acrylate used in Preparation Example 1 was not added. Here, the parts by weight are represented by wt %.

Preparation Example 10. Preparation of Polymer (B3)

(48) A polymer (B3) having a weight average molecular weight of 790,000 was prepared by the same method as described in Preparation Example 1, except that 88 parts by weight of n-BA, 10 parts by weight of MEA, and 2 parts by weight of HBA were added instead of 58 parts by weight of n-BA, 40 parts by weight of MEA and 2 parts by weight of HBA used in Preparation Example 1. Here, the parts by weight are represented by wt %.

Preparation Example 11. Preparation of Polymer (B4)

(49) A polymer (B4) having a weight average molecular weight of 800,000 was prepared by the same method as described in Preparation Example 1, except that 78 parts by weight of n-BA, 20 parts by weight of MEA, and 2 parts by weight of HBA were added instead of 58 parts by weight of n-BA, 40 parts by weight of MEA and 2 parts by weight of HBA used in Preparation Example 1. Here, the parts by weight are represented by wt %.

Example 1

(50) Preparation of Pressure-Sensitive Adhesive Composition

(51) 0.3 parts by weight of a tolylene diisocyanate adduct of trimethylol propane as a multifunctional isocyanate-based crosslinking agent was put into an ethyl acetate solution with respect to 100 parts by weight of the prepared polymer (A1), diluted to a suitable concentration in consideration of coatability, and uniformly mixed.

(52) Preparation of Seal Tape

(53) The pressure-sensitive adhesive composition prepared in Example 1 was coated and dried on one surface of a poly(ethylene terephthalate) (PET) film (thickness: 19 m), thereby forming a uniform coating layer having a thickness of 6 m. Subsequently, a releasing film was laminated on the coating layer, and aged for 3 days under conditions of a constant temperature (25 C.) and a constant humidity, thereby preparing a seal tape.

(54) Formation of Electrode Assembly and Battery

(55) A seal tape was adhered to cover approximately 50% of an area of a circumference of an electrode assembly (diameter of cross-section: 17.2 mm) formed in a jelly roll shape including a negative electrode, a positive electrode and a separation film, and the assembly was inserted into a cylindrical can (diameter of cross-section: 17.5 mm). Subsequently, a carbonate-based electrolyte was injected into the can and sealed, and therefore a battery was completed.

Examples 2 to 11 and Comparative Examples 1 to 4

(56) In the preparation of the seal tape, a composition ratio of the pressure-sensitive adhesive layer was changed as shown in Tables 1 and 2, and a seal tape and a battery were formed by the same method as described in Example 1.

(57) TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 7 Base Type PET PET PET PET PET PET PET layer Thickness 19 m 19 m 19 m 19 m 19 m 19 m 19 m Pressure- Acrylic Acrylic Preparation Preparation Preparation Preparation Preparation Preparation Preparation sensitive copolymer copolymer Example Example Example Example Example Example Example adhesive 1 (A1) 1 (A1) 1 (A1) 1 (A1) 1 (A1) 2 (A2) 3 (A3) layer Composition BA/MEA/ BA/MEA/ BA/MEA/ BA/MEA/ BA/MEA/ BA/MOEOEA/ BA/EOEOEA/ ratio HBA = HBA = HBA = HBA = HBA = HBA = HBA = 58/40/2 58/40/2 58/40/2 58/40/2 58/40/2 58/40/2 58/40/2 Molecular 800,000 800,000 800,000 800,000 800,000 700,000 600,000 weight Isocyanate curing agent 0.5 1 1.5 2 4 2 2 (parts by weight) Thickness 6 m 6 m 6 m 6 m 6 m 6 m 6 m

(58) TABLE-US-00002 TABLE 2 Example Comparative Example 8 9 10 11 1 2 3 4 Base Type PET PET PET PET PET PET PET PET layer Thickness 19 m 19 m 19 m 19 m 19 m 19 m 19 m 19 m Pressure- Acrylic Acrylic Preparation Preparation Preparation Preparation Preparation Preparation Preparation Prepartion sensitive copolymer copolymer Example Example Example Example Example Example Example Example adhesive 4 (A4) 5 (A5) 6 (A6) 7 (A7) 8 (B1) 9 (B2) 10 (B3) 11 (B4) layer Composition BA/MEA/ BA/MEA/ BA/MEA/ BA/MEA/ BA/ BA/ BA/MEA/ BA/MEA/ ratio HBA = HBA = HBA = HBA = HBA = AA = HBA = HBA = 68/30/2 48/50/2 38/60/2 28/70/2 98/2 93/7 88/10/2 78/20/2 Molecular 780,000 790,000 750,000 730,000 800,000 800,000 790,000 800,000 weight Isocyanate curing agent 2 2 2 2 2 1 2 2 (parts by weight) Thickness 6 m 6 m 6 m 6 m 6 m 6 m 6 m 6 m

(59) Physical properties measured for Examples and Comparative Examples are summarized and listed in Tables 3 and 4.

(60) TABLE-US-00003 TABLE 3 Example 1 2 3 4 5 6 7 Peeling strength 312 274 236 182 172 221 197 to glass (gf/25 mm) Peeling strength 400 or more 400 or more 400 or more 93 29 102 96 to separation film (separation (separation (separation (gf/25 mm) film was film was film was separated) separated) separated) Detachment after electrolyte (50%) (70%) (100%) (100%) (100%) (100%) (100%) solution injection (Detached area/Adhered area 100) Formation of stereoscopic structure after being dipped in electrolyte solution Center line 193 186 177 195 198 201 213 average roughness of stereoscopic structure Ra(m) Evaluation One of the One of the No No No No No of battery four batteries four batteries crack crack crack crack crack performance had a crack had a crack

(61) TABLE-US-00004 TABLE 4 Example Comparative Example 8 9 10 11 1 2 3 4 Peeling strength 88 183 195 205 58 374 44 67 to glass (gf/25 mm) Peeling strength 99 150 179 188 52 400 or more 47 61 to separation film (separation (gf/25 mm) film was separated) Detachment after x x x x electrolyte (100%) (100%) (100%) (100%) solution injection (Detached area/Adhered area 100) Formation of x x x stereoscopic structure after being dipped in electrolyte solution Center line 156 196 227 230 1.4 1.3 3.7 68 average roughness of stereoscopic structure Ra(m) Evaluation No No No No All of the All of the All of the Two of the of battery crack crack crack crack four batteries four batteries four batteries four batteries performance had cracks had cracks had cracks had cracks