KR20120045937A - Polystyrene adhesive film, and manufacturing method for the film - Google Patents

Abstract

PURPOSE: A polystyrene-based adhesive film is provided to fill the gap between an electrode assembly and a case by dissolved into an electrolyte during charging/discharging, thereby protecting an electrode assembly from external impact and dispersing heat generated during charging/discharging. CONSTITUTION: A polystyrene-based adhesive film comprises: a substrate film manufactured by mixing 50-200 parts by weight of a styrene-butadiene-styrene block copolymer to 100.0 parts by weight of commercial polystyrene; and an adhesive layer formed by spreading acrylic adhesive on one side of the substrate film by a transfer method. The styrene-butadiene-styrene block copolymer comprises 50-60 weight% of styrene, and 40-50 weight% of butadiene. The thickness of the substrate film is 35-45 micron. The thickness of the adhesive layer is 5-10 micron.

Description

Polystyrene adhesive film and manufacturing method thereof {polystyrene adhesive film, and manufacturing method for the film}

The present invention relates to a polystyrene pressure-sensitive adhesive film and a method for producing the pressure-sensitive adhesive film is coated with an acrylic pressure-sensitive adhesive on one side of the polystyrene-based film and easily dissolved in the electrolyte of the secondary battery.

One of the important parts of the portable device, the secondary battery is essentially installed in devices such as mobile phones, laptops, video cameras, electric vehicles, etc. As the device device becomes smaller and lighter, the secondary battery is used to increase the charging capacity while reducing the size. High energy and high density are becoming increasingly important.

The secondary battery has a structure in which a cathode and an anode formed by applying, drying, roll pressing, and cutting an active material on a substrate, and an electrode jelly roll manufactured by inserting and winding a separator between the cathode and the anode are embedded in a case. Efforts have been made to achieve high capacity batteries, such as winding a thin and long electrode more tightly in a secondary battery having a structure to accommodate a large amount of active material.

Cylindrical secondary batteries are in the form of accommodating the electrode jelly roll in a cylindrical case and injecting the electrolyte solution and sealing, and the rectangular secondary battery is a form of pressing the electrode jelly roll to flatten it and then stored in the rectangular case.

Safety issues should be considered along with the pursuit of high capacity of batteries, which are largely classified into mechanical stability and thermal stability problems. Mechanical stability problems are caused by scratches on the electrodes due to external conditions such as impact on the battery. Say safety.

The thermal stability problem is caused by the failure of heat dissipation due to the exothermic reaction inside the battery to the outside, so when the electrode of the battery is tightly wound, it dissipates heat generated internally during charging and discharging at high current to the outside. It is not known, and thus the temperature continues to rise, causing thermal runaway, which reduces battery safety.

Secondary batteries may cause high temperature and high pressure inside the battery due to abnormal operating conditions such as internal short circuits, overcharge conditions exceeding the allowable current and voltage, exposure to high temperature, dropping or deformation due to external shocks, resulting in battery explosion. In particular, a secondary battery including a jelly roll-type electrode assembly wound by placing a separator between a positive electrode, a negative electrode, and a separator therebetween is more susceptible to internal short circuits due to structural weakness, dropping or external impact. Is holding.

In order to maintain a wound shape, a secondary battery including a jelly roll-type electrode assembly is wrapped in a wound electrode assembly with a finishing tape, which is an adhesive film, and then stored in a case, and an electrical cap assembly is formed between the negative electrode tab and the positive electrode tab connected to the electrode assembly. After connecting with the cap assembly to seal the case, the electrolyte is injected through the electrolyte injection hole formed in the cap assembly or case, and then the electrolyte injection hole is sealed to complete the secondary battery.

The finishing tape material surrounding the outer surface of the conventional jelly roll type electrode assembly is mainly polypropylene (PP) resin. Since the polypropylene resin is not dissolved in the electrolyte, the jelly roll type electrode assembly is pressed in the case and is hard. When the electrolyte is injected, the electrolyte impregnation level is lowered and the life characteristics of the electrode assembly are deteriorated.

In addition, heat is generated by the charging and discharging of the secondary battery, and the electrode assembly expands and contracts due to the heat. In addition, the electrode assembly receives a force in one direction in the case due to external shocks, and thus a gap is formed between the electrode assembly and the case. As a result, the electrode assembly flows inside the case, which shortens the life of the secondary battery and causes a failure.

The problem to be solved by the present invention is to provide a pressure-sensitive adhesive film for finishing tape surrounding the electrode assembly of the secondary battery is dissolved in the electrolyte of the secondary battery and at the same time does not lower the electrolytic capacity of the electrolyte.

In order to achieve the above object, the present invention, a base film prepared by mixing 50 to 200 parts by weight of styrene-butadiene-styrene block copolymer to 100 parts by weight of general-purpose polystyrene; And a pressure-sensitive adhesive layer formed by applying an acrylic pressure-sensitive adhesive to one surface of the base film by a transfer method.

In this case, the styrene-butadiene-styrene block copolymer is preferably 50 to 60% by weight of styrene and 40 to 50% by weight of butadiene.

In addition, the thickness of the base film is 35 ~ 45㎛, it is preferable that the thickness of the adhesive layer is 5 ~ 10㎛.

In addition, the base film is preferably produced by a bubble blowing molding method.

Moreover, it is preferable that the said acrylic adhesive is an oligomer which has 2-ethylhexyl acrylate or n-butyl acrylate as a main component, and the short-chain alkylacrylate or alkyl methacrylate was added here.

In addition, the present invention is to prepare a mixture by mixing 50 to 200 parts by weight of styrene-butadiene-styrene block copolymer having a styrene content of 50 to 60% by weight and 40 to 50% by weight of butadiene content in 100 parts by weight of general-purpose polystyrene ; Melting the mixture to a temperature of 150 ~ 170 ℃ and molding to a thickness of 35 ~ 45㎛ to prepare a base film; Preparing an acrylic pressure-sensitive adhesive by adding 2-ethylhexyl acrylate or n-butyl acrylate as a main component and adding a short chain alkyl acrylate or alkyl methacrylate and a small amount of copolymerization; Preparing a transfer film having a release layer and a pressure-sensitive adhesive layer having a thickness of 5 to 10 μm formed on the base film layer sequentially; It provides a method for producing a polystyrene adhesive film comprising a; and the adhesive layer of the transfer film is in contact with the base film and then heated and pressurized at a temperature of 80 ~ 150 ℃ to transfer the adhesive layer to the base film. .

At this time, the molding of the base film is preferably made of a bubble blowing method.

The polystyrene adhesive film according to the present invention is attached to the electrode assembly of the secondary battery and dissolved in the electrolyte during charging and discharging to fill the gap between the electrode assembly and the case accommodating the electrode assembly, thereby protecting the electrode assembly from external shock and filling ㆍ Disperses heat generated in the discharge process, thereby preventing the performance of the secondary battery.

In addition, since the melted adhesive film minimizes the influence on the discharge capacity of the electrolyte, the initial discharge capacity is maintained for a long time has the effect of increasing the life of the secondary battery.

1 is an assembly view of a secondary battery manufactured by using the adhesive film according to the present invention for the finishing tape of the electrode assembly.

Polystyrene (polystyrene) pressure-sensitive adhesive film of the present invention is a finishing tape surrounding the jelly roll-type electrode assembly in the secondary battery manufacturing process, a polystyrene film as a base film is to be produced by applying an acrylic adhesive to the transfer method.

The base film is manufactured by mixing styrene-butadiene-styrene (SBS) block copolymer in general purpose polystyrene (GPPS) to melt and extrude.

The general purpose polystyrene is a thermoplastic resin, which is easy to be molded and excellent in thermal stability, and has excellent affinity with various colorants to impart various colors, and has good dimensional stability and strength of molded articles.

Although the physical properties of such general-purpose polystyrene are determined by the average molecular weight, molecular weight distribution, etc., the molecular weight range is preferably 20,000 to 30,000, and the molecular weight distribution is preferably 2.5 to 3.0.

If the molecular weight is out of the range, there is a problem such as a decrease in the fluidity index, etc. If the molecular weight distribution is wide, the mechanical strength of the product is not good, it is not preferable.

Styrene-butadiene-styrene copolymer used in the production of the base film is a thermoplastic resin composition having a styrene content of 50 to 60% by weight and a butadiene content of 40 to 50% by weight, and is added to modify physical properties of the base film and is plastic. It is used to improve impact resistance and impact strength at low temperatures.

The content of the styrene-butadiene-styrene copolymer is preferably 50 to 200 parts by weight, preferably 80 to 150 parts by weight, with respect to 100 parts by weight of the general-purpose polystyrene. The improvement of impact or impact strength is insufficient.

The base film may further contain various additives, if necessary, such as anti-blocking agents, antistatic agents, lubricants, antioxidants, slip agents, fillers and the like.

The amount of such additives may be appropriately used depending on the use, and it will be appreciated by those skilled in the art that it is not difficult to determine an appropriate range of contents. For example, 5 to 20 parts by weight of the additives based on 100 parts by weight of the general-purpose polystyrene Can be added.

As described above, the mixture of the general-purpose polystyrene and the styrene-butadiene-styrene copolymer is melted and molded into a film. The melting temperature is preferably 150 to 170 ° C., and the thickness of the film is suitable for use in finishing tapes of secondary batteries. It is preferable that it is made to ˜45 μm.

If the thickness is less than 35㎛, the adhesive film may be damaged when the electrode assembly wrapped with the finishing tape is inserted into the case as well as the manufacturing process difficulties.If the thickness exceeds 45㎛, the relative amount of the adhesive film dissolved in the electrolyte increases. Therefore, the ratio of the electrolyte is lowered, which hinders the performance of the secondary battery.

The method of forming the film may be all methods such as solution casting, melt compression, melt extrusion, bubble blowing, calendering, etc., but the bubble blowing molding method is most preferred.

The bubble blowing molding method is advantageous in manufacturing the base film having a thickness of 35 to 45 μm required by the present invention during the stretching operation at low installation cost, and the base film in the present invention is important for thermal stability. In this case, the cooling rate can be uniformly adjusted by air, thereby obtaining stable and uniform film properties.

In the polystyrene pressure-sensitive adhesive film according to the present invention, an adhesive layer is formed on one surface of the base film in order to provide adhesiveness, so that the base film is fixed to the electrode assembly while maintaining the wound form of the jelly roll-type electrode assembly to be attached. .

The component of the adhesive layer is preferably an acrylic adhesive, which is a kind of vinyl polymer such as a base film, and since the base film and the adhesive layer have a similar structure, when the adhesive film is dissolved in an electrolyte, physical property changes due to different components are suppressed. It works.

The acrylic pressure-sensitive adhesive is, for example, 2-ethylhexyl acrylate, n-butyl acrylate having a low glass transition temperature as a main component and a short chain alkyl acrylate or alkyl methacrylate is added as a component to give cohesion thereto. It may be a small copolymer copolymerized oligomer to act as a crosslinking point, the alkyl acrylate having flexibility and elasticity than the alkyl methacrylate is preferable for the finishing tape of the jelly roll type electrode assembly.

As a method of forming the adhesive layer on the base film, a known method such as gravure, offset, kissbar, knife, mayer bar, or coma method may be used, but in the present invention, the adhesive layer is formed using a transfer method. .

In order to form a pressure-sensitive adhesive layer on the base film by first preparing a transfer film having a base film layer, a release agent layer and a pressure-sensitive adhesive layer in sequence, and then the adhesive layer of the transfer film is in contact with the base film and then heated and pressurized The adhesive layer is transferred to the base film, and the temperature at the time of transfer is preferably 80 to 150 ° C.

The base film layer may be a synthetic resin such as polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene (polyethylene), polypropylene, nylon, or polycarbonate, The release agent layer may be a paraffin wax or a silicone release agent, a polyurethane, a nitro cellulose, or an acrylic resin release agent, and the adhesive layer may be an acrylic adhesive described above.

The thickness of the pressure-sensitive adhesive layer of the transfer film is preferably 5 ~ 10㎛, which is the same or similar to the thickness of the pressure-sensitive adhesive layer formed by transferring the transfer film to the base film, if the thickness of the pressure-sensitive adhesive layer is less than 5㎛ This insufficient adhesion force to fix the jelly roll-type electrode assembly may cause the adhesive film to detach when the electrode assembly is inserted into the case of the secondary battery, and if the thickness exceeds 10 μm, the amount of the adhesive film dissolved in the electrolyte increases. As the ratio of the electrolyte is lowered, which hinders the performance of the secondary battery, it is not preferable.

The thickness of the release agent layer which facilitates peeling off of the base film layer and the adhesive layer when the base film layer is removed after transfer is not particularly limited within a range that does not interfere with the transfer process. The thickness of the layer is 15 ~ 40㎛, the thickness of the release agent layer may be formed of 3 ~ 7㎛.

As described above, the adhesive layer of the transfer film is transferred to the base film, and then the base film layer is peeled off to manufacture the polystyrene adhesive film according to the present invention.

Hereinafter, the present invention will be described in more detail based on the following examples, comparative examples and test examples.

It is to be understood, however, that the invention is not to be construed as limited to the embodiments set forth herein, but is capable of modifications and equivalents within the spirit and scope of the invention. Will be apparent to those skilled in the art to which the present invention pertains.

≪ Example 1 >

General polystyrene (G144, Dongbu Hannong Co., Ltd.) and styrene-butadiene-styrene copolymer (602P, Kumho Petrochemical Co., Ltd., Korea) are sufficiently mixed in the same weight ratio, and then blown to form a film by a bubble blowing method. To a new film extruder.

The injected mixture was melted at 160 ° C. in the blown film extruder, and the initial cooling rate was decreased to allow the formed film to cool slowly. A base film having a thickness of 40 μm was prepared by pulling and winding.

Next, paraffin wax was applied to a 30 μm-thick base film layer made of polyethylene terephthalate with a thickness of 5 μm to form a release agent layer, and an oligomer obtained by copolymerizing n-butyl acrylate and methyl acrylate on the surface of the release agent layer was 8. It was applied to a thickness of μm to prepare a transfer film having an acrylic pressure-sensitive adhesive layer.

The coating was carried out by applying a release agent layer or an acrylic pressure-sensitive adhesive layer material to a copper plate depth of 150 mesh and applying a rubber roller to the upper surface of the base film layer or the release agent layer at a speed of 65 m / min.

After putting the pressure-sensitive adhesive layer of the transfer film on the base film to be in contact with the thermal transfer at 120 ℃ to transfer the pressure-sensitive adhesive layer on the base film and peeled off the base film layer to prepare a polystyrene adhesive film according to the present invention.

<Example 2>

In Example 1, except that methyl methacrylate was used instead of methyl acrylate as the material of the acrylic pressure-sensitive adhesive layer, that is, the oligomer copolymerized with n-butyl acrylate and methyl methacrylate was used. Polystyrene pressure-sensitive adhesive film was prepared in the same manner as.

Comparative Example 1

In Example 1, an adhesive film was prepared in the same manner as in Example 1, except that polypropylene was used as a material of the base film instead of a mixture of general purpose polystyrene and styrene-butadiene-styrene copolymer.

Comparative Example 2

In Example 1, an adhesive film was prepared in the same manner as in Example 1 except that the base film was manufactured by extrusion molding in a T-die instead of a blown film extruder.

Comparative Example 3

In Example 1, after coating the oligomer copolymerized n-butyl acrylate and methyl acrylate to 8㎛ thickness using a gravure printing method on one side of the prepared base film, it was dried for 10 minutes at 80 ℃ An adhesive film was prepared.

Test Example 1 Mechanical Property Comparison

Tensile strength, tear strength, elongation rate, shrinkage rate and adhesive force of the adhesive films obtained in Examples and Comparative Examples were measured and the results are shown in Table 1 below.

unit Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 How to measure The tensile strength N / ㎠ 3120 3110 3130 2980 3120 KS M 3503 Phosphorus strength N / cm 960 950 1050 960 960 KS M 3503 Elongation % 5 4 3 5 5 KS M 3503 Shrinkage % 9 9 7 12 11 100 ℃ 30 seconds adhesiveness G _f / 25 mm 420 400 420 420 380 KS A 1107

As can be seen in Table 1, the tensile strength, tear strength, elongation and shrinkage of Comparative Example 1 using polypropylene as the material of the base film Examples 1, 2 and Significant difference with Comparative Examples 1 and 3 was shown, and Comparative Example 3 in which the adhesive layer was formed by gravure printing rather than transfer method was the lowest in adhesive strength, and methyl methacrylate instead of methyl acrylate as the material of the adhesive layer. Example 2 using the slightly lower pressure-sensitive adhesive layer than methyl methacrylate it can be seen that it is more advantageous to form a pressure-sensitive adhesive containing methyl acrylate by the transfer method.

<Test Example 2> Charge and discharge test

First, in a solution in which polyvinylidene fluoride (PVDF) was dissolved in N-methyl-2-pyrrolidinone (NMP), a lithium-containing composite oxide powder as a positive electrode active material, and a conductive agent Acetylene black and artificial graphite were added and stirred and mixed to prepare a positive electrode mixture composed of 92.2% by weight of the positive electrode active material, 1.8% by weight of acetylene black, 2.2% by weight of artificial graphite, and 3.8% by weight of polyvinylidene fluoride solution.

The positive electrode mixture was coated on both sides of an aluminum foil having a thickness of 20 μm, dried, and pressed to form a positive electrode using a roller compressor.

Next, mesocarbon microbeads (MCMB) powder as a negative electrode active material and artificial graphite as a conductive agent were added to the solution of polyvinylidene fluoride dissolved in N-methyl-2-pyrrolidone, and stirred and mixed. A negative electrode mixture comprising 86.5 wt% of negative electrode active material, 9.5 wt% of artificial graphite, and 4.0 wt% of polyvinylidene fluoride was prepared.

The negative electrode mixture was coated on both sides of a copper foil having a thickness of 15 μm, dried, and pressed under a roller compactor to prepare a negative electrode.

At this time, the filling density and the electrode length were adjusted so that the design capacity ratio of the cathode to the design capacity of the anode after molding was 1.03 to 1.10.

Next, a non-aqueous solvent was prepared in which the volume ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC) was 1: 2, and 1.1 M was used as an electrolyte salt. After adding lithium hexafluorophosphate (LiPF ₆ ), 3% by weight of triphenyl phosphate, 1% by weight of vinyl ethylene carbonate and 0.1% by weight of biphenyl were added to form a liquid non-aqueous electrolyte solution. Prepared.

After welding the aluminum positive lead and the nickel negative lead to the positive electrode and the negative electrode, respectively, the positive electrode, the porous separator and the negative electrode made of polyethylene are laminated in this order, and the spirally wound so that the negative electrode is located outside to form a jelly roll type electrode assembly ( 1) was produced (see FIG. 1).

The adhesive films of Examples 1 and 2 and Comparative Examples 1 to 3 are attached to the electrode assembly as a finishing tape, and as shown in FIG. The upper end tape (2) was attached, and the lower end tape (3) was attached to the outer peripheral surface of the lower.

The electrode assembly 1 with the pressure-sensitive adhesive film attached thereto is housed in a case 4 having an upper opening, and the negative electrode lead is disposed on the bottom surface of the case 4, and the positive electrode lead is placed on a sealing plate of the opening of the case 4. And welded.

Next, 4 ml of the electrolyte is injected into the case 4 so that the electrode assembly 1 is sufficiently impregnated, and then the sealing plate is sealed and fixed to the case 4 to design a lithium ion secondary battery having a design rating of 1600 mAh. Was prepared.

First, the adhesive films prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were impregnated and stirred in the electrolyte solution, and it was confirmed that all of the remaining adhesive films except for Comparative Example 1 using polypropylene as the base film were dissolved.

Next, a charge and discharge cycle test was performed at room temperature on the secondary battery using the adhesive films of Examples and Comparative Examples, and the discharge capacity (initial discharge capacity) was measured at one cycle, and the shaker (KS-500, Korea Instruments) was used. Manufacture, Korea) and after 1 hour shaking at 100rpm to obtain the discharge capacity after 50 cycles are shown in Table 2 below.

The charge / discharge cycle test was conducted for 1 hour after charging to 4.2V with a current value equivalent to 0.5C of the design rated capacity, and then discharged to 2.7V with the same current value.

unit Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Initial discharge capacity ㎃h 1630 1630 1640 1630 1620 After 50 cycles
Discharge capacity ㎃h 1490 1470 1380 1430 1420 Capacity reduction rate % 8.6 9.8 15.9 12.3 12.3

As shown in Table 2, the discharge capacity after 50 cycles showed a capacity reduction rate of less than 10% in Examples 1 and 2 according to the present invention, while the comparative example showed a capacity reduction rate of 12 to 16%. It can be seen that the capacity reduction rate in Comparative Example 1 using polypropylene as the base film is high.

From the above results, the polystyrene adhesive film according to the present invention dissolves in the electrolyte during the charging and discharging process and fills the gap between the electrode assembly and the case accommodating the electrode assembly, thereby protecting the embedded electrode assembly from external impact. It is judged that there is an effect of preventing the performance degradation of the secondary battery by dispersing the heat generated in the discharge process, the polypropylene pressure-sensitive adhesive film of Comparative Example 1 is not dissolved in the electrolyte, the electrode assembly is exposed to external impact and heat, so It is judged that the life is shortened by that much.

1: Jelly roll type electrode assembly, 2: Upper end tape, 3: Lower end tape, 4: Case

Claims (7)

A base film prepared by mixing 50 to 200 parts by weight of styrene-butadiene-styrene block copolymer with 100 parts by weight of general-purpose polystyrene; And
And a pressure-sensitive adhesive layer formed by coating an acrylic pressure-sensitive adhesive on one surface of the base film by a transfer method. The method according to claim 1,
The styrene-butadiene-styrene block copolymer is a polystyrene adhesive film, characterized in that the styrene content of 50 to 60% by weight and the butadiene content of 40 to 50% by weight. The method according to claim 1,
The thickness of the base film is 35 ~ 45㎛, the thickness of the adhesive layer is a polystyrene adhesive film, characterized in that 5 ~ 10㎛. The method according to claim 1,
The base film is a polystyrene adhesive film, characterized in that produced by the bubble blowing molding method. The method according to claim 1,
The acrylic pressure-sensitive adhesive is a polystyrene pressure-sensitive adhesive film, characterized in that the oligomer to which 2-ethylhexyl acrylate or n-butyl acrylate is the main component, and short-chain alkyl acrylate or alkyl methacrylate is added. Preparing a mixture by mixing 50 to 200 parts by weight of styrene-butadiene-styrene block copolymer having a styrene content of 50 to 60% by weight and a butadiene content of 40 to 50% by weight to 100 parts of general-purpose polystyrene;
Melting the mixture to a temperature of 150 ~ 170 ℃ and molding to a thickness of 35 ~ 45㎛ to prepare a base film;
Preparing an acrylic pressure-sensitive adhesive by adding 2-ethylhexyl acrylate or n-butyl acrylate as a main component and adding a short chain alkyl acrylate or alkyl methacrylate and a small amount of copolymerization;
Preparing a transfer film having a release layer and a pressure-sensitive adhesive layer having a thickness of 5 to 10 μm formed on the base film layer sequentially; And
After the pressure-sensitive adhesive layer of the transfer film in contact with the base film to heat and pressurized at a temperature of 80 ~ 150 ℃ to transfer the pressure-sensitive adhesive layer to the base film; manufacturing method of a polystyrene adhesive film comprising a. The method of claim 6,
The molding of the base film is a method for producing a polystyrene adhesive film, characterized in that the bubble blowing method.

Images