BACKGROUND ART Generally, a silicon rubber having superior elasticity is widely used in such fields as defense industry, air industry, car, and application fields thereof requiring high degree of reliability and stability. Also, the silicon rubber is also used in a high degree electric and electronic industry due to a superior electric property of the silicon rubber.

In detail, the silicon rubbers can be divided into rubbers for general plasticizing, heat resistant rubbers used in high temperature condition, flame retardant rubbers or extrusion rubbers used in electric appliances, and heat releasing rubbers used in heat releasing sheet using superior heat conductivity.

The heat releasing silicon rubber is used in electric appliances, in which heat of high temperature is generated, to prevent the temperature in the appliance from being risen by releasing the heat to outer side. Generally, the silicon rubber used for releasing heat is adhered to the products using an adhesive or the other means, and it is not easy to separate the silicon rubber from the adhered material once the silicon rubber is adhered to the adhered

material. Especially, if the silicon rubber is adhered on a product of high price such as plasma display panel (PDP) and the life span of the product is reached, the silicon rubber should be separated from the product for recycling. However, in above case, the adhesive force between the silicon rubber and the product is so strong that the silicon is hard to be separated.

In addition, the component of high price may be damaged during separating process, and thereby, it becomes impossible to recycle the components.

Therefore, there is required an efficient method for separating the silicon rubber from the adhered material.

Conventionally, a release agent is added in the adhesive to reduce the adhesive force of the adhesive.

The release agent is an agent for weakening adhesive force between two materials, such as, between metal and plastic or between the metal and rubber, and for making the separation of two materials easy. And the release agent is divided into a physical release agent and a chemical release agent according to the operation. The physical release agent is dried powder or a material having a foaming property at low temperature, and the chemical release agent is a material having a foaming property at high temperature and dissolved chemically. In actual use, the physical release agent and the chemical release agent may be used together as mixed.

Korean Laid-open Patent No. 96-36243 discloses an art granting adhesiveness and separating property to a polymer film simultaneously using an adhesive including a release agent.

In above publication, a foaming agent is used as the release agent and

an organic adhesive and other additives are added into the agent, and these are applied on the polymer film to grant the separating property to the polymer film. Also, an oily acryl-based adhesive is used as the organic adhesive.

However, there is a limitation in using the adhesive including the foaming agent in order to make the silicon rubber have adhesive force and releasing property. The silicon rubber has low adhesiveness with the adhesive, moreover, when the release agent is added to the adhesive, it becomes difficult to adhere the silicon rubber to an adhered material since the adhesiveness is reduced more and more.

Also, the organic adhesive causes environmental pollution, and if is used in the product of high price such as the PDP, it may changes the characteristics of the product.

Therefore, there rise necessaries for developing an adhesive which is able to maintain the adhesiveness of the silicon rubber more than a predetermined level and to make the separation easy at any time, and for improving the separating property of the adhesive.

TECHNICAL GIST OF THE PRESENT INVENTION Therefore, an object of the present invention is to provide a silicon rubber having a separating property, as well as an adhesive force.

Another object of the present invention is to provide a method for releasing in a heat releasing system used in a plasma display panel.

To achieve the objects of the present invention, there is provided an adhesive silicon rubber having a releasing property comprising: a first

adhesive layer, including an aqueous acryl-based adhesive, formed on a surface of the silicon rubber; and a second adhesive layer, including a foaming agent, formed on the first adhesive layer.

Also, there is provided a releasing method of an adhesive silicon rubber which reduces the adhesive force of the second adhesive layer by heat processing the silicon rubber in a state that the silicon rubber is charged in a chamber at a temperature range of 50°C~200°C for 5 minutes-2 hours.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 A is a cross-sectional view showing a silicon rubber according to the present invention; Figure 1 B is a schematic view showing a heat releasing system in a plasma display panel according to an embodiment of the present invention; Figure 1C is a schematic view showing a silicon rubber which is released after heat processing; Figure 2A is a photograph showing charging of glass substrate on which the silicon rubber is adhered and an aluminum frame into a chamber for heat processing; Figure 2B is a photograph showing the glass substrate on which an adhesive is released ; and Figure 2C is a photograph showing the glass substrate and the aluminum frame on which the adhesive is released.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with reference to accompanying drawings.

A silicon rubber according to the present invention is made by forming a first adhesive layer including an aqueous acryl-based adhesive on a surface of the silicon rubber and a second adhesive layer including a foaming agent on the first adhesive layer. Figure 1A is a cross-sectional view showing the silicon rubber according to the present invention, as shown therein, the first adhesive layers 12 and the second adhesive layers 14 are formed on both surfaces of the silicon rubber 10.

The first adhesive layer grants a basic adhesive force so that the silicon rubber can be adhered to another material. On the other hand, the second adhesive layer reduces the adhesive force between the silicon rubber and adhered material.

The second adhesive material may be constructed only by the foaming agent, and may be constructed by the foaming agent and the aqueous acryl- based adhesive, that is, the matrix element. In detail, a non-solvent type aqueous acryl-based adhesive harmless to human body and environment including acrylic acid ester-based copolymer mainly and a physical foaming agent made of heat expansive fine particles which are micro capsulated are attenuated in distilled water.

The aqueous acryl-based adhesive used in the present invention does not contaminate the surface of the adhered material since harmful remaining is not remained when the humidity is evaporated after the silicon rubber is adhered to the adhered material.

To control the adhesive force of the adhesive, the viscosity of the adhesive should be controlled first. Therefore, most releasing agents used for reducing the adhesive force of the adhesive functions as reducing the viscosity of the adhesive. For example, the foaming-releasing agent is added into the adhesive, and makes very tiny air pores to reduce the viscosity of the adhesive, and the chemical releasing agent decomposes the elements of the adhesive to reduce the viscosity.

In the present invention, the second adhesive layer including the physical foaming agent made of heat expansive fine particles which are micro capsulated is formed on the silicon rubber, and after that, the silicon rubber is heat processed at an appropriate temperature. Then the fine particles in the foaming agent are expanded to reduce the adhesive force of the second adhesive layer, and the second adhesive layer is attached to the first adhesive layer, and thereby the silicon rubber can be separated from the adhered material without any remaining.

The conventional foaming-separating adhesive used the chemical foaming agent. However, the chemical foaming agent should be dissolved in an organic solvent, and emits gas when foaming. However, the present invention uses the physical foaming agent made of heat expansive fine particles which are micro capsulated by attenuating the agent in the distilled water. The size of the fine particle in the physical foaming agent is 10-40um before foaming, and is expanded to 40~1 00pm after foaming. The foaming temperature and condition can be variable according to usage object. Also, the kinds and added amount of the foaming agent is decided after considering

the expansion degree of the fine particles and the degree of reducing the adhesive force.

In the heat processing for releasing of the adhesive silicon rubber, it is desirable that the heat processing time is increased as the heat processing temperature is low. In detail, it is desirable that the heat processing temperature is in a range of 50°C~200°C, preferably 100°C-150°C. in addition, it is desirable that the heat processing time is 5 minutes ~ 2hours, preferably, 20 minutes-1 hour.

If the heat processing temperature is too high, the adhesive and the material on which the adhesive is applied may be distorted. In addition, if the heat processing temperature is too low, it is difficult to improve the releasing property.

It is desirable that the heat processing time is maintained long as the heat processing temperature is low, however, if the heat processing is continued for a long time, the productivity is reduced. Therefore, it is important that the appropriate heat processing time.

The silicon rubber of the present invention adhered to a material is heat processed at temperature of 50°C-200°C for 5 minutes ~2 hours in a state that the silicon rubber is charged into a chamber. Thereby, the adhesive force of the second adhesive layer can be reduced, and the releasing between the silicon rubber and the material can be made.

The silicon rubber of the present invention has the first adhesive layer which maintains the adhesive force thereof, and therefore, the strong adhesive force can be maintained until the releasing. In addition, when the

silicon rubber and the adhered material are separated from each other by heat processing for reducing the adhesive force of the second adhesive layer, the adhering material is not remained on the adhered material, and thereby the surface of the adhered material can be maintained to be clean.

On the other hand, the silicon rubber does not have good adhesive force with the adhesive, and therefore, it is desirable that the adhesive is reinforced by treating the surface of the silicon rubber.

In the present invention, ion particles which is accelerated by being added energy as maintaining the vacuum state are injected to one or both surfaces of the silicon rubber under reactive gas atmosphere, and thereby a new chemical bond is formed on the surface of the silicon rubber to reinforce hydrophilicity and adhesive force.

Generally, when the silicon rubber having a hydrophobicity is surface modified using an ion auxiliary reaction method, a hydrophilic functional group is formed on the surface of the silicon rubber and a wet property of the silicon rubber. That is, a surface contact angle with the water is reduced. In addition, the hydrophilic functional group formed on the surface makes the adhesion of adhesive, metal thin film deposition, and paint adhesion possible.

The ion beam energy in the present invention is in a range of hundreds - thousands of eV. And the reactive gas is injected to control the surface property by forming the functional group on the surface without change in a physical structure of the silicon rubber. That is, the hydrophilicity can be improved without any change of the characteristics of the silicon rubber which is surface modified. In detail, the ion having 0. 5 ~ 5. 0keV energy make some

parts of the carbon bond in the silicon polymer react with the reactive gas, and thereby the hydrophilic functional group such as a double bond of the carbon and the gas to modify the surface of the silicon rubber into the hydrophilicity The amount of ion irradiation in the present invention is in a range of 10'3~1 or8 according to the characteristics required to the products, and the ion particles used are selected one or more in a group of oxygen, nitrogen, hydrogen, hydrocarbon, and argon. Also, one or more gases are selected from the group of oxygen, hydrogen, and nitrogen, and used as the reactive gas.

Hereinafter, an embodiment of the present invention will be described in more detail. However, the scope of the present invention is not limited by the following descriptions, and all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.

As an embodiment of the present invention, the silicon rubber having superior heat releasing property is adhered between a glass substrate used in the plasma display panel and a metal substrate for releasing the heat generated from the glass substrate using an adhesive.

The aqueous acryl-based adhesive is used as the adhesive. The first adhesive layer is formed by applying the adhesive on the silicon rubber, and the second adhesive layer including the foaming agent is formed on the first adhesive layer. Also, the silicon rubber is reinforced the adhesive force with the adhesive by a surface treatment in advance.

Figure 1 B is a schematic view showing a heat releasing system of the

plasma display panel according to the present invention.

The glass substrate 20 and the metal substrate 30 are attached on both surfaces of the silicon rubber 10 on which the first adhesive layer 12 and the second adhesive layer 14 are formed. An aluminum having superior heat conductivity is used as the metal substrate.

The heat releasing system was charged into a chamber and heated by the temperature more than 100°C. Figure 2A is a photograph showing the system charged into the chamber. The heat processing temperature was started from 100°C, and the temperature was risen by 10°C until the temperature is reached 150°C. In addition, the heat processing time was 5 minutes initially, and increased by 5 minutes to 1 hour for respective heat processing temperatures. The releasing property of the adhesive was improved. Therefore, the glass substrate and the metal substrate were separated from the silicon rubber easily.

Figure 1 C is a schematic view showing the silicon rubber 10 released from the glass substrate 20 and from the metal substrate 30 after heat processing. The first adhesive layer 12 is remained on the surface of the silicon rubber due to the adhesive force with the silicon rubber, and the second adhesive layer is not remained on the glass substrate and the metal substrate since the adhesive force of the second layer is reduced by expanding of the physical foaming agent 14'which is micro capsulated.

Figures 2B and 2C are photographs showing the glass substrate and the aluminum frame on which the adhesives are released respectively. The glass and the aluminum frame maintain very clean surfaces without the

adhesive, as shown therein.

The heat processing temperature and time showing optimal releasing property are 140°C and 45 minutes, respectively.

INDUSTRIAL APPLICABILITY As so far described, according to the present invention, the releasing property can be granted to the silicon rubber with the adhesiveness.

Especially, in case that the silicon rubber for heat releasing is used in a product of high price, the various components can be recycled by separating the silicon rubber from the product. Also, the silicon rubber does not contaminate the environment, and does not changes the properties of the product even if the silicon rubber is contacted to the product.