LAMINATING FILM OF PLASTIC/TEFLON-SILICON AND METHOD FOR PREPARING THE SAME

[Technical Field] The present invention relates to a laminating film of plastic/Teflon-silicon and a method for preparing the same, more precisely a laminating film of plastic/Teflon-silicon with improved bond strength between plastic or Teflon and silicon rubber resulted from the processes of activating the reactive functional group by treating the surface of the plastic or Teflon substrate with plasma and adding silane coupling agent forming chemical bond with the above reactive functional group to the silicon rubber, and a method for preparing the same.

[Background Art]

Silicon rubber has excellent heat resistance and electric insulating property in addition to elasticity peculiar to rubber, so that it has been used as a gasket for various electronic products.

However, the silicon rubber shows problems that it is not only difficult to laminate to other substrate for its intrinsic release properties but also has poor dimensional stability during rework for its elastic hysteresis. To solve the above problems of silicon rubber, it has been attempted to attach silicon rubber to a plastic substrate such as polyester film using a bonding agent or a tape coated with an adhesive. But, in that case, silicon rubber is bonded physically with the adhesive coated tape, suggesting that it can be easily separated from each other by a certain impact (given from outside) such as heat. Owing to its excellent heat resistance, electric insulating property, and

elasticity peculiar to rubber, silicon rubber has widely been used for producing LCD and PDP panels and as a bonding sheet for the attachment of those panels to flexible printed circuit (FPC).

However, even though as a bonding sheet, the silicon rubber has intrinsic release property and (it) also shows weak surface adhesion properties, so that anisotropic conducting film (ACF) coupling panels and FPC is tend to adhere on the rubber surface, which might be a reason for a poor product.

To solve the above problem, Teflon film having excellent release property can be used. However, this film is easily deformed by heat and as a result showing a short life-time. Therefore, the bonding sheet is separately feeded by installing the Teflon film having excellent release property in the (bottom) lower part and the silicon rubber having excellent heat resistance and elasticity in the upper part.

The present inventors tried to overcome the above problems and finally completed this invention by confirming that the binding force between the plastic or Teflon substrate and silicon rubber can be significantly increased by the processes of generating the reactive functional group by treating the surface of the plastic or Teflon substrate with plasma; coating liquid silicone rubber (LSR) containing silane coupling agent forming chemical bond with the reactive functional group onto the plastic or Teflon substrate; and curing thereof.

[Disclosure]

[Technical Problem]

To solve the above problems of conventional arts, inventors have been studied and found that the bond strength is increased significantly by generating

reactive functional group on the plastic or Teflon substrate surface by plasma treatment, and by coating Liquid Silicon Rubber(LSR) containing silane coupling agent forming chemical bond with the reactive functional group to the plastic or Teflon substrate and then by curing thereof. An (The) object of the present invention is to provide a laminating film of plastic/Teflon-silicon contributing to the significant increase of bonding strength between the plastic or Teflon substrate and silicon rubber.

Another object of the present invention is to provide a method for preparing the laminating film of plastic/Teflon-silicon.

[Technical Solution]

To achieve the above objects, the present invention provides a laminating film of plastic/Teflon-silicon which contains the plastic or Teflon substrate having the reactive functional group generated on its surface by plasma treatment; silane coupling agent forming chemical bond with the reactive functional group; and silicon rubber containing the silane coupling agent and being coated on the plastic or Teflon substrate.

The present invention also provides a method for preparing the laminating film of plastic-silicon, comprising the following steps: i ) generating the reactive functional group on the surface of the plastic or Teflon substrate by plasma treatment; and i i ) coating the surface of the plastic or Teflon substrate with liquid silicon rubber containing silane coupling agent for the chemical bonding with the above reactive functional group and curing thereof. The present invention is described in detail hereinafter.

i ) Generating reactive functional group on the surface of the plastic or Teflon substrate by plasma treatment

In this step, plasma treatment is performed on the surface of the plastic or Teflon substrate in order to increase the bond strength between the plastic or Teflon substrate and the liquid silicon rubber coated on the substrate. By the plasma treatment, the reactive functional group is generated on the surface of the plastic or Teflon substrate, which is probably containing oxygen in the reactive functional group such as -OH, -OOH, -COOH, -C-O-, -C=O, -O-C-O-, etc. The plasma treatment is performed under the general condition but it is preferably carried out under the pressure of up to 1 x 10 ^'3 torr for the effective generation of the reactive functional group on the surface of the plastic or Teflon substrate. If the plasma treatment is performed under the higher pressure, arc discharge resulted by impurities will be a problem or generation density of the reactive functional group might be reduced because of scattering.

The amounts of oxygen and argon injected into ion gun for the plasma treatment are not limited, but the weight ratio of oxygen to argon is preferably 1 :1 - 4:1.

As the induced voltage increases during the plasma formation, discharging density of the plasma increases, resulting in the increase of the generation of the reactive functional group on the surface of the plastic substrate.

So, the induced voltage is preferably 10 - 4000 W, more preferably, 100 - 3000 W.

It is generally expected that surface etching will be observed after the plasma treatment. However, as shown in Figure 1 - Figure 3, contact angles of PET before the plasma treatment (Figure 1), right after the plasma treatment

(Figure 2) and 24 hours after the plasma treatment (Figure 3), were respectively 67.27°, 3.27° and 39.86°. And contact angles of Teflon before the plasma treatment (Figure 4), right after the plasma treatment (Figure 5) and 24 hours after the plasma treatment (Figure 6), were respectively 109.46°, 24.25° and 47.37°. Theses results indicate that the reactive functional groups are generated on the surface of the plastic or Teflon substrate by the plasma treatment but as time went by those reactive functional groups are reduced by the reaction with substances in the air. So, it was confirmed that the plastic or Teflon substrate of the present invention can have reactive functional groups on its surface after plasma treatment.

As the plastic substrate, not only a film with a polar group on its surface but also an olefin based film with a nonpolar group can be used. In particular, films used for electronic material such as polyethylene film, polypropylene film, polystyrene film, polyester film, polyamide film, polyimide film, polycarbonate film, and tetraacetylcellulose film are preferred.

The Teflon film of the present invention includes not only the Teflon film itself but also a fabric sheet containing glass fiber to increase dimensional stability and tensile strength of the laminating film. ii ) Coating liquid silicon rubber containing silane coupling agent on the surface of the plastic or Teflon substrate and curing thereof

In this step, the surface of the plastic or Teflon substrate is coated with liquid silicon rubber containing silane coupling agent that is chemically bonded to the reactive functional group formed on the surface of the plastic or Teflon substrate, followed by curing. The silane coupling agent herein increases bonding strength by inducing polymerization reaction between the plastic or

Teflon substrate and the silicon rubber.

The silane coupling agent can be one or more compounds selected from the compounds represented by the following formula 1. [Formula 1 ]

I ^ό

O

I

R ₁ -O-Sj-O-R ₂

I

O

(Wherein, R ₁ is hydrogen or vinyl group, and R ₂ - R4 are Ci - Ci ₈ alkyl group or C ₃ - C-iβ alkyl group having epoxy group at terminal.)

The preferable content of the silane coupling agent is 0.1 - 30 weight part for 100 weight part of silicon rubber and 0.5 - 15 weight part is more preferred. If the content of the silane coupling agent is less than 0.1 weight part, bonding strength will be decreased. If the content is more than 30 weight part, air bubbles will be formed because of by-products, which results in poor bonding strength as well.

In the present invention, a tin compound can be used as a catalyst to induce satisfactory reaction of the silane coupling agent with the reactive functional group formed on the surface of the plastic or Teflon film and this tin compound is represented by the following formula 2. [Formula 2]

I

R.

(Wherein, R ₅ - Rs are Ci - Ci ₈ alkyl group.)

The content of the catalyst is 0.05 - 5 weight part for 100 weight part of silicon rubber and 0.1 - 2 weight part is more preferred. The silicon rubber can be produced from the materials comprising dimethyl siloxane, siloxane with vinyl group and siloxane based cross-linking agent, but not (always) limited thereto.

The liquid silicon rubber can additionally contain inorganic fillers, liquid silicon curing catalysts, and physical property modifiers, in addition to curing agents.

[Description of Drawings]

The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:

Figure 1 is a photograph showing the contact angle of the surface of the plastic substrate before the plasma treatment.

Figure 2 is a photograph showing the contact angle of the surface of the plastic substrate right after the plasma treatment.

Figure 3 is a photograph showing the contact angle of the surface of the plastic substrate 24 hours after the plasma treatment.

Figure 4 is a photograph showing the contact angle of the surface of the Teflon substrate before the plasma treatment.

Figure 5 is a photograph showing the contact angle of the surface of the Teflon substrate right after the plasma treatment. Figure 6 is a photograph showing the contact angle of the surface of the

Teflon substrate 24 hours after the plasma treatment.

[Best Mode]

Hereinafter, the embodiments of the present invention will be described in detail with reference to accompanying drawings.

[Examples] Example 1

The reactive functional group was generated on the surface of the polyethylene terephthalate (PET) film by using plasma processing apparatus (weight ratio of oxygen to argon: 4:1 , induced voltage: 1 ,000V / 0.2-1. OA (200-1000W)).

The surface of the plastic film treated with plasma was coated with the liquid silicon rubber composition comprising 55 weight part of liquid silicon [Poly(dimethyl siloxane) fluid] finished with vinyl group, 3 weight part of a curing agent [Poly(methylhydro siloxane-co-dimethyl siloxane) fluid], 40 weight part of an inorganic filler (alumina), 0.5 weight part of a silane coupling agent, 0.1 weight part of a tin compound catalyst, 0.5 weight part of a platinum based liquid silicon curing catalyst, and 0.9 weight part of a physical property modifier (silica nano-particles), followed by curing at 100 ⁰ C for 5 minutes, resulting in the laminating film of plastic-

silicon.

Example 2

An experiment was performed by the same manner as described in example 1 except that 25.5 weight part of liquid silicon finished with vinyl group and 30 weight part of a silane coupling agent were used.

Example 3

An experiment was performed by the same manner as described in example 1 except that 40.5 weight part of liquid silicon finished with vinyl group and 15 weight part of a silane coupling agent were used. Example 4

An experiment was performed by the same manner as described in example 1 except that 48.6 weight part of liquid silicon finished with vinyl group, 5 weight part of a silane coupling agent and 2 weight part of a tin compound catalyst were used. Comparative Example 1

The surface of the plastic film non-treated with plasma was coated with the liquid silicon rubber composition comprising 40.5 weight part of liquid silicon finished with vinyl group, 3 weight part of a curing agent, 40 weight part of an inorganic filler, 15 weight part of a silane coupling agent, 0.1 weight part of a tin compound catalyst, 0.5 weight part of a liquid silicon curing catalyst, and 0.9 weight part of a physical property modifier, followed by curing at 100 ⁰ C for 5 minutes, resulting in the laminating film of plastic-silicon.

Comparative Example 2

An experiment was performed by the same manner as described in example 1 except that the content of the liquid silicon finished with vinyl group was adjusted to 55.6 weight part and the silane coupling agent was not used.

Example 5 The reactive functional group was generated on the surface of the Teflon film by using plasma processing apparatus (weight ratio of oxygen to argon: 4:1 , induced voltage: 1 ,500V / 0.2-1.0A (300-1 ,500W)).

The surface of the Teflon film treated with plasma was coated with the liquid silicon rubber composition comprising 55 weight part of liquid silicon [Poly(dimethyl siloxane) fluid] finished with vinyl group, 3 weight part of a curing agent [Poly(methylhydro siloxane-co-dimethyl siloxane) fluid], 40 weight part of an inorganic filler (alumina), 0.5 weight part of a silane coupling agent, 0.1 weight part of a tin compound catalyst, 0.5 weight part of a platinum based liquid silicon curing catalyst, and 0.9 weight part of a physical property modifier (silica nano- particles), followed by curing at 100 ^° C for 5 minutes, resulting in the laminating film of Teflon-silicon.

Example 6

An experiment was performed by the same manner as described in example 5 except that 25.5 weight part of liquid silicon finished with vinyl group and 30 weight part of a silane coupling agent were used.

Example 7

An experiment was performed by the same manner as described in example 5 except that 40.5 weight part of liquid silicon finished with vinyl group and 15 weight part of a silane coupling agent were used. Example 8

An experiment was performed by the same manner as described in example 5 except that 48.6 weight part of liquid silicon finished with vinyl group, 5 weight part of a silane coupling agent and 2 weight part of a tin compound catalyst were used. Comparative Example 3

The surface of the Teflon film non-treated with plasma was coated with the liquid silicon rubber composition comprising 40.5 weight part of liquid silicon finished with vinyl group, 3 weight part of a curing agent, 40 weight part of an inorganic filler, 15 weight part of a silane coupling agent, 0.1 weight part of a tin compound catalyst, 0.5 weight part of a liquid silicon curing catalyst, and 0.9 weight part of a physical property modifier, followed by curing at 100 ⁰ C for 5 minutes, resulting in the laminating film of Teflon-silicon. Comparative Example 4

An experiment was performed by the same manner as described in example 5 except that the content of the liquid silicon finished with vinyl group was adjusted to 55.6 weight part and the silane coupling agent was not used. [Experimental Example]

The plastic-silicon films prepared in examples 1 - 4 and comparative examples 1 - 2, and the Teflon-silicon films prepared in examples 5 - 8 and comparative examples 3 - 4 proceeded to peel test and the results are shown in Table 1 and Table 2. [Table 1 ]

As shown in Table 1 , peeling was observed after 24 hours from the production in the plastic film non-treated with plasma of comparative example 1 and the film treated with plasma but not containing the silane coupling agent of comparative example 2. On the contrary, the films of examples 1 - 4, treated with plasma and coated with liquid silicon rubber containing the silane coupling agent, were not peeled after 24 hours from the production and even after 500 hours at 120 ^° C . [Table 2]

As shown in Table 2, peeling was observed after 24 hours from the production in the Teflon film non-treated with plasma of comparative example 3 and the film treated with plasma but not containing the silane coupling agent of comparative example 4. On the contrary, the Teflon films of examples 5 - 8,

treated with plasma and coated with liquid silicon rubber containing the silane coupling agent, were not peeled after 24 hours from the production and even after 500 hours at 120 ^° C .

[Industrial Applicability]

The laminating film of plastic/Teflon-silicon of the present invention has significantly improved bond strength (force) between the plastic or Teflon substrate and silicon rubber by chemical bond between the reactive functional group formed on the surface of the plastic or Teflon substrate by plasma treatment and the silane coupling agent included in the silicon rubber.