WO2007105924A1

WO2007105924A1 - Releasing film and method for preparing the same

Info

Publication number: WO2007105924A1
Application number: PCT/KR2007/001288
Authority: WO
Inventors: Young-Hee Kim; Seong-Hwan Kim; Chang-Keun Choi
Original assignee: Youl Chon Chemical Co., Ltd.
Priority date: 2006-03-15
Filing date: 2007-03-15
Publication date: 2007-09-20
Also published as: KR100721655B1

Abstract

Provided is a releasing film comprising a paper, an adhesive layer formed on either one or both faces of the paper, and a polypropylene-based film provided on either one or both faces of the paper with the adhesive layer interposed therebetween, wherein the polypropylene-based film is composed of a single or multi-layer of polypropylene -based resin having methyl group, and the single layer or the outermost layer of the multi-layer directly contacts the adhesive layer on a region where the releasing film is to be attached.

Description

RELEASING FILM AND METHOD FOR PREPARING THE

SAME

Technical Field

[1] The present invention relates to a releasing film for use in a bonding sheet or a coverlay of a flexible printed circuit board (FPCB), and a method for preparing the same. Background Art

[2] A flexible printed circuit board (FPCB) is provided with a coverlay for protecting a conductive surface having a circuit pattern thereon. The coverlay is generally formed so that for example, semi-cured epoxy of an adhesive layer is provided on a polyimide film and a releasing film (releasing liner) is attached thereto.

[3] Meanwhile, a bonding sheet is used for bonding the respective FPCBs in a multi- layered FPCB structure. The bonding sheet is provided with adhesive layers on both faces thereof, and releasing films are respectively formed on the adhesive layers.

[4] Such a releasing film used in the bonding sheet or the coverlay of the FPCB is required to have an enough peel-off force against the adhesive layer existing on the bonding sheet or the coverlay where the releasing film is to be attached to, and is also reuqired to have resistance to heat and pressure in the manufacturing process to be carried out later.

[5] The releasing film has been made so that a silicone coating solution for increasing releasing force is applied onto a polymer film such as polyethyleneterephtalate film or polyethylene film, or otherwise, a silicone compound such as polydimethylsiloxane is contained in a composition itself for manufacturing the polymer film.

[6] FIG. 1 is a schematic view of an exemplary releasing film structure for a coverlay of the FPCB or a bonding sheet according to the prior art.

[7] As shwon in FIG. 1, the polymer films 2 such as polyethylene film are extrusion- coated onto the both faces of the paper 1, and a silicone coating layer 3 is formed on the upper face of one of the films 2.

[8] The silicone is organopolysiloxane having a main chain of -Si-O-Si- bonding in general and a side chain of organic group such as methyl group (-CH ). Since the silicone has the methyl group as the organic side chain, it has lower surface energy due to low molecular force between methyl groups, which lowers surface tension of molecules. Thus, forming a silicone coating layer having the above surficial property on the releasing film can make the releasability increased.

[9] However, the releasing film in which the silicone coating layer is formed on the polymer film or the releasing film in which the silicone compound is contained inside the polymer film has following problems.

[10] First, the silicone compound applied onto the polymer film or the silicone compound contained inside the polymer film is transferred into the epoxy adhesive layer, thereby causing a big problem of deteriorating adhesion force of the coverlay or the bonding sheet.

[11] Moreover, in case where the silicone compound is applied to the polymer film, a primer is additionally applied onto the polymer film in order to improve adhesion force between the polymer film and the silicone compound. However, in the case, the efficiency and economy of the process can be deteriorated due to the additional process. As well, it is apprehended that the primer itself is transferred into the adhesive layer and also the releasing film is rendered lightly peeled-off due to an aging process in case of adding crosslink agent for improving the adhesion force.

[12] Meanwhile, impurities are inevitably introduced or contaminants occur between the base film and the polymer film in manufacturing a releasing film in the prior art, thereby causing defects of the releasing film.

[13] Furthermore, in case where the releasing film containing the impurities is attached to the coverlay, it is difficult to distinguish them from those contained in the coverlay or the bonding sheet, so that quality control is difficult. Disclosure of Invention

Technical Problem

[14] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a releasing film for use in a bonding sheet or a coverlay of a flexible printed circuit board (FPCB) and a method for preparing the same, wherein a silicone compound and other additives are not transferred into an adhesive layer on the bonding sheet or the coverlay where the releasing film is attached to while the releasing film has high releasability, the processing property for making the releasing film is excellent so that upon punching, breakage does not occur, there is aslo no contraction at high temperature and breakage occurrence during low temperature storage, and the manufacturing costs are lower than those of conventional releasing films.

[15] Another object of the present invention is to provide a releasing film for use in a bonding sheet or a coverlay of a flexible printed circuit board (FPCB) and a method for preparing the same, capable of preventing defects of the releasing film due to impurities or contaminants occurring in the process of manufacturing the releasing film, thereby facilitating the quality control. Technical Solution [16] In order to accomplish the above objects, there is provided a releasing film for use in a bonding sheet or a coverlay of a flexible printed circuit board (FPCB) and a method for preparing the same, the releasing film comprising: a paper; an adhesive layer formed on either one or both faces of the paper; and a polypropylene-based film being on either one or both faces of the paper with the adhesive layer interposed therebetween, wherein the polypropylene-based film is composed of a single layer or multi-layer of polypropylene-based resin having methyl group, and the single layer or the outermost layer of the multi-layer directly contacts the adhesive on a region where the releasing film is to be attached to.

[17] In an exemplary embodiment according to the invention, the polypropylene-based film contains 1 to 2wt% of anti-blocking agent, which is an additive, to total weight of the polypropylene-based film.

[18] In an exemplary embodiment according to the invention, both faces of the paper is provided with the polypropylene-based films having the same thicknesses.

[19] In an exemplary embodiment according to the invention, the paper is glassine.

[20] In an exemplary embodiment according to the invention, the thickness of the paper is preferably 20 to 200D, more preferably 50 to 10OD.

[21] In an exemplary embodiment according to the invention, the density of the paper is preferably 0.5 to 1.5g/cm , more preferably 1.0 to 1.2g/cm .

[22] In an exemplary embodiment according to the invention, the polypropylene-based film is an OPP (oriented polypropylene) film.

[23] In an exemplary embodiment according to the invention, the thickness of the polypropylene-based film is preferably 5 to 50D, more preferably 10 to 25D.

[24] In an exemplary embodiment according to the invention, the adhesive is preferably acrylic resin or urethane-based resin.

[25] In an exemplary embodiment according to the invention, the polypropylene-based film is a milk-white polypropylene-based film.

[26] In an exemplary embodiment according to the invention, the polypropylene-based film is composed of three layers of a skin layer, an intermediate layer and a skin layer, wherein both skin layers are polypropylene-based resinous layers and the intermediate layer is a milk-white polypropylene-based resinous layer which is composed of 10 to 25wt% of titanium dioxide and 75 to 90wt% of polypropylene-based resin.

[27] In an exemplary embodiment according to the invention, the thickness ratio of the skin layer, the intermediate layer and the skin layer is 1 to 2: 6 to 8: 1 to 2.

[28] In an exemplary embodiment according to the invention, when the anti-blocking agent is inevitably added to the outermost skin layer, the anti-blocking agent is added within a range of more than 0wt% and not more than 0.2wt% to 100 weight percentage of the total resinous composition of the skin layer. [29] In an exemplary embodiment according to the invention, the thickness of the skin layer is 3D or more.

[30] In an exemplary embodiment according to the invention, the milk-white polypropylene-based film has 98% or more haze.

[31] In an exemplary embodiment according to the invention, an ink layer is further provided between the paper and the polypropylene-based film in addition to the adhesive layer.

[32] In an exemplary embodiment according to the invention, a layer made of the mixture of adhesive and ink is provided between the paper and the polypropylene- based film.

[33] In an exemplary embodiment according to the invention, the content of the ink is 10 to 30wt% to 100 weight percentage of the total adhesive and ink.

[34] In an exemplary embodiment according to the invention, in case that the both faces of the paper is provided with the polypropylene-based films interposing the adhesive layer therebetween, one polypropylene-based film contacting the adhesive on a region where the releasing film is to be attached to is an OPP film, and the other polypropylene-based film not contacting the adhesive on a region where the releasing film is to be attached to is a CPP film.

[35] In an exemplary embodiment according to the invention, in case that only one face of the paper is provided with the polypropylene-based film interposing the adhesive layer therebetween, a PET film or a nylon film is provided on the other face of the paper not contacting the adhesive on a region where the releasing film is to be attached to, with interposing an adhesive layer therebetween.

Advantageous Effects

[36] According to the present invention, the silicone compound and other additives of the releasing film are not transferred into an adhesive layer while the releasing film has high releasability, the processing property for making the releasing film is excellent so that upon punching breakage does not occur, there is no contraction at high temperature and breakage occurrence during low temperature storage, and the manufacturing costs are lower than those of the conventional releasing films.

[37] Moreover, the concealing property of the releasing film is excellent, thereby preventing occurrence of the inferior releasing film products due to impurities or contaminants occurring in the process of manufacturing the releasing film. Further, it is possible to distinguish impurities in the releasing film from those introduced into the coverlay, and as well it is easy to control the quality. Brief Description of the Drawings

[38] FIG. 1 is a schematic view of an exemplary releasing film structure according to the prior art.

[39] FIG. 2 is a schematic view of an exemplary releasing film structure according to a first embodiment of the present invention.

[40] FIG. 3 is a schematic view of an exemplary releasing film structure according to a second embodiment of the present invention.

[41] FIG. 4 is a schematic view of an exemplary polypropylene-based film structure used in the embodiment of the present invention.

[42] FIG. 5 is a schematic view of an exemplary releasing film structure according to a third embodiment of the present invention.

[43] FIG. 6 is a schematic view of an exemplary releasing film structure according to a fourth embodiment of the present invention.

[44] FIG. 7 is a schematic view of an exemplary releasing film structure according to a fifth embodiment of the present invention. Mode for the Invention

[45] A releasing film according to the present invention is a film in which a polypropylene-based film is adhered to one side or both sides of paper by means of an adhesive.

[46] As for the polypropylene-based film, in order to prevent that an additive that may exist on an outermost portion of the film or exist inside the film is transferred into the adhesive existing in a region where the releasing film is to be attached to, the amount of the additive or the position to which the additive is added is controlled. Alternatively, the additive is made not to be added originally. In addition, in order to prevent such transference originally, the outermost layer of the polypropylene-based film directly contacts the adhesive existing in a region where the releasing film is to be attached to without forming any coating layer on the outermost layer.

[47] According to the present invention, a film is formed on one side or both sides of the paper not by extrusion-coating but by adhesion, thereby forming a releasing film. In this case, as for the film, a polyethylene or polyethyleneterephthalate film is not used, but a polypropylene-based film having the methyl group is used.

[48] That is, in case that a film composed of polypropylene-based resin having the methyl group is used, the surface tension is lowered due to the methyl group so that the bonding force with other molecules such as an adhesive may be reduced. Thus, sufficient releasability can be obtained without using a silicone compound (which may be added inside the film or coated on the film).

[49] Moreover, in case that an additive should be inevitably added to the polypropylene- based film, the additive may be transferred into the epoxy adhesive such as a coverlay or a bonding sheet. Therefore, according to the present invention, the transference of the additive can be made to be prevented originally.

[50] In case that the polypropylene-based film is composed of a multi-layer of polypropylene-based resin, an additive is added to the inner layers other than the outermost layer contacting the adhesive where the releasing film is attached to (control of adding position).

[51] There is often the case that the adding effect is increased only when the additive is added to the polypropylene-based resinous layer contacting the adhesive where the releasing film is attached to depending on the additive. In this case, the additive is added to the polypropylene-based resinous layer so that the upper limit of the adding amount should be restricted (the control of adding amount).

[52] FIG. 2 is a schematic view of an exemplary releasing film structure according to a first embodiment of the present invention.

[53] As shown in FIG. 2, the releasing film for use in a bonding sheet or a coverlay of a flexible printed circuit board (FPCB) according to the present invention has a structure in which a polypropylene -based film 20 having the methyl group is bonded to the paper 10 by means of an adhesive 30.

[54] The paper 10 may be clean paper, particularly glassine, which is excellent in processing property and dimensional stability.

[55] In the present invention, as compared to the case that the polypropylene-based film is solely used, in case that the paper 10 is used together with the polypropylene-based film, the dimensional stability is much higher, and upon punching, a crack does not occur on the film.

[56] The thickness of the paper 10 is preferably 20 to 200D, and more preferably 50 to

10OD. Below 2OD, the thickness of the paper is so thinner that upon processing, tearing of the paper occurs, and the stiffness of the paper is weakened so as to deteriorate the workablity. Above 200D, cost increase and workablility degradation occur. In case that the thickness of the paper 10 is particularly between 50 and 10OD, the stiffness is excellent and the workability is good.

[57] The density of the paper 10 is preferably 0.5 to 1.5g/cm in view of the workability etc. That is, below 0.5g/cm , paper powders are blown off, which is not preferable upon die cutting. Above 1.5 g/cm , there is a problem in that tensile strength, bursting strength, and folding endurance of the paper 10 are degraded.

[58] Meanwhile, the density of the paper 10 is more preferably 1.0 to 1.2 g/cm . In the present invention, especially in case that the paper 10 particularly having the density of lg/cm or more is laminated with the polypropylene-based film, bursting upon punching can be considerably reduced, and as well cuttability and breakage occurrence in low temperature storage can be further reduced.

[59] The polypropylene-based film is nonpolar and has excellent water repellency in addition to high releas ability due to having the methyl group. As for the polypropylene-based film, particularly uniaxially or biaxially oriented polypropylene film (OPP) is used.

[60] The thickness of the polypropylene-based film 20 is preferably 5 to 5OD, and more preferably 10 to 25D. Below 5D, working of solvent dry lamination (SDL) is difficult. Above 50D, the manufacturing costs and the stiffness increase so that workability degradation occur.

[61] According to the present invention, in order to prevent the transference into for example, the epoxy adhesive of the coverlay or the bonding sheet, an additive is not added in the polypropylene-based film as much as possible. Further, such material which is possibly transferred (e.g., silicone compound) is not coated onto the outermost surface of the film. Thus, the transference of the additive into the adhesive can be originally blocked so that adhesion degradation does not occur.

[62] Meanwhile, there is often the case that an anti-blocking agent (AB agent) has to be inevitably added (e.g., lwt% or more to the total weight of the polypropylene-based film) to the polypropylene-based film 20 so as to prevent defects such as blocking or folding occurrence upon winding after extension of the film. Silica of 2 to 4D is preferably used as the AB agent.

[63] However, even in such inevitable addition of AB agent, the amount of the AB agent, which is an additive, should be controlled within the range where the diffusion into the adhesive does not occur.

[64] The upper limit of the adding amount of the AB agent for preventing the transference into the adhesive is 2wt% or less to the total weight of the polypropylene- based film.

[65] Thus, the adding amount of the AB agent should be controlled to be 1 to 2wt% to the total weight of the polypropylene-based film.

[66] In this regard, as described later, the adding position of the AB agent can be controlled, and especially if the adding position is the outermost layer contacting the adhesive, the upper limit should be restricted to a much lower level (0.2wt% or less to the total weight of the outermost layer).

[67] The polypropylene-based films 20 laminated on both sides of the paper 10 may or may not be identical to each other, but when the thicknesses are different from each other, a curling phenomenon possibly occurs in the direction of thick thickness part. Furter, in order to prevent such a curling phenomenon, tension control should be conducted upon manufacturing. Therefore, the thicknesses of the films laminated on both sides of the paper are preferably identical to each other.

[68] According to the present invention, the paper and the polypropylene-based film are laminated not by extrusion coating but by an adhesive, so that the peeling-off between the paper and the film can be prevented. The adhesive may be acrylic resin or urethane-based resin. However, it is preferable to adopt the acrylic resin as the adhesive because of its excellent heat resistance.

[69] Although FIG. 2 illustrates that the polypropylene-based films are provided on both sides of the paper, the film can be provided on only one side of the paper. However, in order to prevent the curling phenomenon of the film at the side contacting the epoxy adhesive, the polypropylene-based film is preferably formed on both sides of the paper, and as described above, the thicknesses of the films are preferably identical to each other.

[70] FIG. 3 is a schematic view of an exemplary releasing film structure according to a second embodiment of the present invention.

[71] As shown in FIG. 3, the releasing film for use in the bonding sheet or the coverlay of the FPCB is particularly a milk-white polypropylene-based film 21.

[72] That is, in case of adopting the milk-white polypropylene-based film, even when impurities are introduced or contaminants occur upon lamination between the paper and the film, concealment is increased so as to precisely check the defect state after the lamination of the coverlay or the bonding sheet and the existence of impurities of the coverlay or the bonding sheet, thereby facilitating the quality control. In order to provide sufficient concealment, the milk-white polypropylene-based film preferably has the haze of 98% or more.

[73] FIG. 4 is a schematic view of an exemplary polypropylene-based film structure used in the embodiment of the present invention.

[74] The milk-white color of the polypropylene-based film is obtained by containing particularly titanium dioxide. Since titanium dioxide however is also an additive, as set forth above, when it is added to the polypropylene-based film, the transference into the adhesive may occur.

[75] Thus, according to the present invention, as shown in FIG. 4, the polypropylene- based film is composed of a three-layered polypropylene-based resin including an main intermediate layer M and skin layers S on both sides, wherein the main intermediate layer comprises 10 to 25wt% of titanium dioxide and 75 to 90wt% of polypropylene-based resin (preferably, homo polypropylene).

[76] Below 10wt% of titanium dioxide, the film can have no concealment, and above

25wt% of titanium dioxide, cost increase and peeling-off between the main intermediate layer and the skin layer occur, thereby possibly causing the transference of titanium dioxide into the adhesive.

[77] It is possible to add titanium dioxide to the skin layer (inner skin layer) near the side of paper in order to merely prevent the transference of titanium dioxide into the adhesive. However, in such a case of adding titanium dioxide to the inner skin layer, the concealment is slightly lowered than that in the case of the adding titanium dioxide to the main intermediate layer. Thus, titanium dioxide is preferably added to the main intermediate layer instead of the inner skin layer. Although titanium dioxide may be once added to the main intermediate layer and then the inner skin layer, this is not preferable because the concealment does not greatly increase while the manufacturing costs increase unnecessarily.

[78] The thickness of the both skin layers of the polypropylene-based film is preferably

3D or more. Below 3D, the skin layer is so thinner that upon extrusion, some parts thereof may not be extruded. Meanwhile, the skin layer is required for the lamination with the intermediate layer, and merely needs a minimum thickness. Thus, The thickness of the both skin layers is preferably 3D.

[79] Moreover, the thickness ratio of the skin layer, the main intermediate layer, and the skin layer of the polypropylene -based film is preferably 1 to 2: 6 to 8: 1 to 2. The main intermediate layer contains titanium dioxide to obtain milk-white color. For that the haze of the main intermediate layer is made to be 98% or more, the thickness ratio of the skin layer, the intermediate layer, and the skin layer is preferably 1 to 2: 6 to 8: 1 to 2.

[80] Meanwhile, as set forth above, the polypropylene-based film may contain the AB agent in order to prevent the defects such as blocking and folding occurrence upon winding after extension of the film.

[81] The AB agent is preferably added to the polypropylene-based resinous layer (the paper-side skin layer in FIG. 4) contacting the adhesive in view of the prevention of defects of blocking and folding occurrence. However, the AB agent may be also added to the inner skin layer in addition to the main intermediate layer.

[82] In the case that the AB agent is added to the polypropylene-based resinous layer

(the paper-side skin layer in FIG. 4) contacting the adhesive, the upper adding limit has to be restricted to prevent the transference of the AB agent into the adhesive. Thus, the adding amount of the AB agent to the skin layer is 0.2wt% or less to the total 100 weight of the resin composition of the skin layer.

[83] FIG. 5 is a schematic view of an exemplary releasing film structure according to a third embodiment of the present invention.

[84] As shown in FIG. 5, other than the adhesive layer, an ink layer 40 is further provided between the paper 10 and the polypropylene-based film 20 or 21.

[85] The ink layer 40 is for concealing impurities or other contaminants interposed between the paper and the polypropylene-based film during process.

[86] When the ink layer 40 is adopted together with the milk-white polypropylene-based film 21, the concealment of the releasing film is further improved. Alternatively, it is possible to use not a milk-white but common polypropylene-based film together with the ink layer 40 so as to provide the concealment.

[87] Regarding the concealment, while it is possible to provide the ink layer 40 to the surface of the polypropylene-based film in the side of the adhesive where the releasing film is to be attached, considering the problem of the transference into the adhesive and the fact that the releasability can be increased by directly contacting the polypropylene-based film having the methyl group to the adhesive, the ink layer 40 should exist between the paper and the polypropylene-based film as shown in FIG. 5.

[88] The color of the ink layer is provided as white color or bright color so as to check the existence of impurities of the coverlay and the bonding sheet upon the lamination of the coverlay or the bonding sheet.

[89] FIG. 6 is a schematic view of an exemplary releasing film structure according to a fourth embodiment of the present invention.

[90] As shown in FIG. 6, a layer 35 made of a mixture of the adhesive and ink may be provided between the paper 10 and the polypropylene-based film 20 or 21.

[91] As set forth above, the ink layer 40 is preferably provided between the paper 10 and the polypropylene -based film 20 or 21, and the adhesive layer 30 is provided between the paper 10 and the polypropylene -based film 20 or 21. In this case, to form the ink layer 40 as well as the adhesive layer 30 is not preferable in view of the process efficiency and the manufacturing costs because for example, an extrusion process should be additionally added in that case and the thickness of a product itself becomes increased.

[92] Therefore, when ink and the adhesive are mixed to form a single layer 35 made of the mixture, the concealment can be further improved without reduction in process efficiency, increase in manufacturing costs and product thickness.

[93] In the layer 35 made of mixture of the ink and the adhesive, 10 to 30wt% of pigment is containe. If below 10wt%, the concealment deteriorates, and if above 30wt%, compatibility with the adhesive is not good. The pigment may be either inorganic pigment such as titanium dioxide or organic pigment.

[94] FIG. 7 is a schematic view of an exemplary releasing film structure according to a fifth embodiment of the present invention.

[95] As shown in FIG. 7, in the releasing film according to the fifth embodiment, particularly a CPP (cast polypropylene) film 22 as a polypropylene-based film is provided on the side not contacting the adhesive where the releasing film is to be attachted to. That is, the releasing film is configured so that for example, the OPP film 20 is provided to the side contacting the paper, and the CPP film 22 that is transformed less than the OPP film 20 is provided to the other side, thereby providing the effect of preventing the contraction of the releasing film during hot pressing. Meanwhile, according to another embodiment, it may be configured so that the polypropylene- based film is provided on only one side of the paper, and a film other than the polypropylene-based film is provided on the other side of the paper. Herein, the film other than the polypropylene-based film may be a PET film or a nylon film, which is less-transformable than the OPP film.

[96] <Experiment 1 : detachability, remaining adhesion, processing property, thermal shrinkage, and dimensional stability tests>

[97] To prepare a releasing film of an example, an OPP film (Product name: ycc-ppOOl from Youl Chon Chemicals Co., Ltd,) having the methyl group was laminated on both sides of glassine using acrylic resin (Product name: TM215 from TOYO Co., Ltd.) as an adhesive. The compound for manufacturing the OPP film had no additive, and the OPP film manufactured has no coating layer of the additive. The bonding using the acrylic resin was performed by direct gravure coating method.

[98] To prepare a releasing film of a comparative example 1, polypropylene (Product name: SL270 from Honam Petrochemicals Corp.) films were only extrusion-laminated on both sides of glassine without using an adhesive. The composition for the polypropylene film contained therein neutralizer and antioxidant as an additive.

[99] To prepare a releasing film of a comparative example 2, polypropylene (Product name: LB5000 from LG chemicals Co., Ltd.) films were extrusion-coated on both sides of glassine, and silicone [Product name: SD7234 from Dow Corning Corp.; heavy stripping control agent (Product name: SO7210 from Dow Corning Corp.) is used together with the SD7234] was coated on the upper side polypropylene film.

[100] As a releasing film of a comparative example 3, a polypropylene (Product name:

HFI l HPTl from Samsungtotal Petrochemicals Co., Ltd.) film was solely used. Unlike the polypropylene film of the comparative example 1, the polypropylene film of the comparative example 3 does not contain therein any additive.

[101] To prepare a releasing film of a comparative example 4, films composed of

99.5wt% of low-density polyethylene (Product name: petrosen213 from TOSOH SMD Co.) and 0.5wt% of polydimethylsiloxane having epoxy group (Product name: KF- 1001 from Shin-Etsu Chemical Co., Ltd.) were extrusion-laminated on both sides of glassine.

[102] To compare the releasing film of the example with those of the comparative examples, detachability, remaining adhesion, processing property, thermal shrinkage, and dimensional stability tests were performed. A test temperature was 23+3 ⁰C and the relative humidity was 65+5%.

[103] Detachabilitv (test method: FINAT No. 10^s)

[104] The releasing films of the example and the comparative examples and a polyimide base film were laminated with a common semi-curable epoxy adhesive for a coverlay at a rate of lOm/min using a 2kgf press roll, and the laminated product was aged at 60 ⁰C for 72 hours. The strength (unit: gf/50mm) required for stripping the polyimide film from the releasing film at an angle of 180 degrees and a rate of 3m/min was measured.

[105] Remaining adhesion (test method: FINAT No. 11^s)

[106] Upon contact of the releasing films of the example and the comparative examples with the adhesive, whether or not a portion of the releasing film was transferred into the adhesive and the adhesion force deteriorated was measured.

[107] After standard tapes with an adhesive (Nitto 31B) were bonded to the releasing films of the example and the comparative examples and a fluoric film respectively, the resulting films were held under a pressure of 70g/cm in 70 ⁰C oven for 20 hours, and then held at room temperature for 4 hours. The remaining adhesion was estimated by measuring the ratio (%) of the adhesion force B of the standard tapes bonded to the releasing films of the example and the comparative examples to the adhesion force A of the standard tape bonded to the fluoric film. The remaining adhesion rate (%) can be expressed as a following equation 1.

[108] [Equation 1]

[109] Remaining adhesion rate (%) = (Adhesion force B of the standard tape bonded to the releasing films/ Adhesion force A of the standard tape bonded to the fluoric film) D 100

[110] processing property

[111] In case of the releasing film for the coverlay of FPCB, the processing property is regarded as excellent when foreign matters are not produced upon die-cutting. The surface state upon die-cutting was determined with the naked eye for measuring the processing property. The determination results were classified into the following.

[113] Δ: Good surface state upon cutting

[114] D : Poor surface state upon cutting

[115] Thermal shrinkage

[116] In case that the releasing film and the coverlay of the FPCB or the bonding film are laminated with each other, the dimensional stability at high temperature in the releasing film is an important factor because the epoxy adhesive of the coverlay or the bonding sheet is in a high temperature pre-preg state. Thus, the dimension variation was measured for the releasing film held for 15 minutes at 50, 120, and 140 ⁰C, respectively.

[117] First, the releasing films of the example and the comparative examples were cut to

20mm width x 220mm length, and reference points were punctured at the center position in a width direction with 200mm intervals (α). The releasing films were put in an oven set to a temperature and held for 15 minutes, and then the distance (β) between the reference points was measured so as to determine the thermal shrinkage. The thermal shrinkage rate is expressed as the following equation 2.

[118] [Equation 2] [119] Thermal shrinkage rate (%) = [(α-β)/α] x 100 [120] Dimensional stability [121] The releasing films of the example and the comparative examples were cut to 100mm width x 100mm length, and were held at -20 ⁰C for 24 hours in a constant temperature and humidity chamber. Then, the resulting releasing films were processed with breaking to thus check the occurrence of a crack with the naked eye for measuring the dimensional stability. The test was carried out ten times for each releasing film of the example and the comparative examples. The test results are estimated as follows.

[122] ©: No crack in 10 [123] Δ: 1 to 2 cracks in 10 [124] D: more than 3 cracks in 10 [125] The measuring results for each test item are shown in Table 1. [126] Table 1

[127] As can be seen in Table 1, the comparative examples 1, 2, and 4 have poor remaining adhesion rate. This is because in case of the releasing film of the comparative example 1, the additive is transferred into the side contacting the adhesive, and in case of the releasing films of the comparative examples 2 and 4, silicone compounds are transferred into the standard tapes, thereby deteriorating the adhesion force.

[128] Further, the releasing film of the comparative example 1 has poor detachability as well as poor remaining adhesion rate due to severe tranference phenomenon. Like this, the additive is transferred into the epoxy adhesive, so that upon later process, the coverlay of the FPCB or the bonding sheet is peeled-off from a copper thin film and the like. [129] Meanwhile, in case of the comparative example 3, it can be seen that the high temperature dimensional stability is degraded because of high shrinkage rate particularly at 120 and 140 ⁰C.

[130] On the contrary, the releasing film of the example has proper releasability, and shows no reduction in adhesion force (low remaining adhesion force). Further, the releasing film of the example shows good surface state upon die-cutting, so the processing property is confirmed to be excellent. In addition, the releasing film of the example has no problem in dimensional stability.

[131] As like above, it can be seen that the releasing film of the present invention simultaneously satisfies low thermal shrinkage rate, good processing property upon die- cutting, good breakage feature upon punching, high detachability, and high remaining adhesion rate, which are required to the releasing film.

[132] <Experiment 2: test of concealment and detachability between the layers>

[133] To prepare a releasing film of a first example, a polypropylene-based film composed of a main intermediate milk-white homo polypropylene layer comprising 10wt% of titanium dioxide and 90wt% of homo polypropylene and both skin home polypropylene layers was laminated on the glassine using acrylic resin (Product name: TM215 from TOYO Co., Ltd.) as an adhesive.

[134] The polypropylene-based film had no additive and no coating layer. The bonding using the acrylic resin was carried out by direct gravure coating method.

[135] A releasing film of a second example was prepared identical to the releasing film of the first example excluding that the amount of titanium dioxide of the intermediate layer comes to 20wt% (the remaining amount is 80wt% of homo polypropylene).

[136] A releasing film of a third example was prepared identical to the releasing film of the first example excluding that the amount of titanium dioxide of the intermediate layer comes to 25wt% (the remaining amount is 75wt% of homo polypropylene).

[137] A releasing film of a first comparative example was prepared identical to the releasing film of the first example excluding that the amount of titanium dioxide of the main intermediate layer comes to 9wt%.

[138] A releasing film of a second comparative example was prepared identical to the releasing film of the first example excluding that the amount of titanium dioxide of the main intermediate layer comes to 26wt%.

[139] A releasing film of a third comparative example was prepared identical to the releasing film of the first example excluding that 15wt% of calcium carbonate was added to the main intermediate layer instead of adding 10wt% of titanium dioxide (the remaining amount is 85wt% of homo polypropylene).

[140] A releasing film of a fourth comparative example was prepared identical to the releasing film of the first example excluding that 5wt% of calcium carbonate was further added to the main intermediate layer in addition to 10wt% of titanium dioxide (the remaining amount is 85wt% of homo polypropylene).

[141] (The word "comparative" in the comparative examples 1 to 4 are merely intended to compare them with particularly the examples 1 to 3 in view of the amounts of titanium dioxide and calcium carbonate. Thus, it is apparent that the comparative examples 1 to 4 pertain to the technical scope of the present invention.)

[142] Unlike the releasing film of the first example, a releasing film of a fourth example was prepared so that a polypropylene film was provided without adding titanium dioxide. However, a white ink layer was printed in a thickness of 2D between the polypropylene-based film and the paper, and was laminated on the glassine using an adhesive. The others were identical to the example 1.

[143] Unlike the releasing film of the first example, a releasing film of a fifth example was prepared such that a polypropylene film without titanium dioxide was laminated on the glassine using an adhesive. White pigment was mixed to the adhesive. The white pigment was added by 10wt% relative to the total mixture compound of the adhesive and the white pigment.

[144] A releasing film of a sixth example was prepared identical to the releasing film of the fifth example excluding that the content of the white pigment comes to 30wt% relative to the total mixture compound of the adhesive and the white pigment.

[145] A releasing film of a fifth comparative example was prepared identical to the releasing film of the fifth example excluding that the content of the white pigment comes to 9wt% relative to the total mixture compound of the adhesive and the white pigment.

[146] A releasing film of a sixth comparative example was prepared identical to the releasing film of the fifth example excluding that the content of the white pigment comes to 35wt% relative to the total mixture compound of the adhesive and the white pigment.

[147] (The word "comparative" in the comparative examples 5 and 6 are intended to compare them with particularly the examples 5 and 6 in view of the content of the white pigment. Thus, it is apparent that the comparative examples 5 and 6 pertain to the technical scope of the present invention.)

[148] The concealment measurement was conducted as follows. That is, a color density tester and a pattern-less black film were prepared. The pattern-less black films were brought into close contact with the release liners of the films of the examples and the comparative examples, and pouch density values were measured more than five times using the tester and then the average value was obtained.

[149] The interlayer detachability was measured as follows. That is, a common tape

(adhesive tape available from 3M) was adhered to the skin layer, and upon detaching, the occurrence of interlayer detachment was checked with the naked eye. The case of no interlayer detachment was expressed as "X", and the case of occurrence of interlayer detachment was expressed as "O".

[150] Table 2 shows the test results. As a reference for comparison with the test results in Table 2, the color density of pure white A4 paper was 0.11, and that of the pattern-less black film was 2.10. Therefore, as the density value approaches 0.11, the concealment feature is excellent, whereas as the density value approaches 2.10, the concealment feature is poor.

[151] Table 2

[152] As can be seen from Table 2, the examples 1 to 3 show excellent concealment features and interlayer detachability. However, the comparative example 1 has poor concealment feature when the amount of titanium dioxide reduces to 9wt%, and the comparative example 2 shows occurrence of interlayer detachment when the amount of titanium dioxide increases to 26wt%.

[153] Meanwhile, the comparative examples 3 and 4 used CaCO instead of TiO for whitening effect. The comparative examples 3 and 4 added with CaCO however shown reduction in mechanical strength and the occurrence of interlayer detachment due to foaming due to CaCO , so they are not preferable.

[154] In case of the examples 4 to 6, the concealment feature was comparatively good, and shown no interlayer detachment. [155] In the comparative example 5, when the amount of the pigment came to 9wt%, the color density was considerably reduced so that the concealment feature became poor. In the comparative example 6, when the amount of the pigment came to 35wt%, the adhesion force between the glassine itself and the polypropylene was weakened so that interlayer detachment occurred. This may be because the compatibility with the adhesive deteriorated. Industrial Applicability The releasing film of the present invention is used in the coverlay of of the flexible printed circuit board or the bonding sheet.

Claims

Claims[ 1 ] A releasing film comprising: a paper; an adhesive layer formed on either one or both faces of the paper; and a polypropylene-based film being on either one or both faces of the paper with the adhesive layer interposed therebetween, the polypropylene -based film being composed of a single layer or multi-layer of polypropylene-based resin having methyl group, and the single layer or the outermost layer of the multi-layer directly contacting the adhesive on a region where the releasing film is to be attached to. [2] The releasing film according to claim 1, wherein in addition to the polypropylene-based resin, the polypropylene-based film further contains 1 to2wt% of anti-blocking agent, which is an additive, to total weight of the polypropylene-based film. [3] The releasing film according to claim 2, wherein both faces of the paper is provided with the polypropylene-based films having the same thicknesses. [4] The releasing film according to one of claims 1 to 3, wherein the paper is glassine. [5] The releasing film according to one of claims 1 to 3, wherein the thickness of the paper is 20 to 200D. [6] The releasing film according to claim 5, wherein the thickness of the paper is 50 to 10OD. [7] The releasing film according to one of claims 1 to 3, wherein the density of the paper is 0.5 to 1.5g/cm . [8] The releasing film according to claim 7, wherein the density of the paper is 1.0 to

1.2g/cm .

[9] The releasing film according to one of claims 1 to 3, wherein the polypropylene- based film is an OPP (oriented polypropylene) film. [10] The releasing film according to one of claims 1 to 3, wherein the thickness of the polypropylene-based film is 5 to 50D. [11] The releasing film according to claim 10, wherein the thickness of the polypropylene-based film is 10 to 25D. [12] The releasing film according to one of claims 1 to 3, wherein the adhesive is acrylic resin or urethane-based resin. [13] The releasing film according to claim 1, wherein the polypropylene-based film is a milk-white polypropylene-based film. [14] The releasing film according to claim 13, wherein the polypropylene-based film is composed of three layers of a skin layer, an intermediate layer and a skin layer, wherein both skin layers are polypropylene -based resinous layers and the intermediate layer is a milk-white polypropylene-based resinous layer which is composed of 10 to 25wt% of titanium dioxide and 75 to 90wt% of polypropylene-based resin.

[15] The releasing film according to claim 14, wherein the thickness ratio of the skin layer, the intermediate layer, and the skin layer is 1 to 2: 6 to 8: 1 to 2.

[16] The releasing film according to claim 14, wherein an anti-blocking agent as an additive is added to the skin layer within a range of more than 0wt% and not more than 0.2wt% to the total weight of the skin layer.

[17] The releasing film according to claim 14, wherein the thickness of the skin layer is 3D or more.

[18] The releasing film according to claim 13, wherein the milk-white polypropylene- based film has 98% or more haze.

[19] The releasing film according to claim 1, wherein an ink layer is further provided between the paper and the polypropylene-based film in addition to the adhesive layer.

[20] The releasing film according to claim 1, wherein a layer made of a mixture of adhesive and ink is provided between the paper and the polypropylene-based film.

[21] The releasing film according to claim 20, wherein the amount of the ink is 10 to

30wt% to 100 weight percentage of the total amount of the adhesive and the ink.

[22] The releasing film according to claim 1, wherein in case that the both faces of the paper is provided with the polypropylene-based films interposing the adhesive layer therebetween, one polypropylene-based film contacting the adhesive on a region where the releasing film is to be attached to is an OPP (oriented polypropylene) film, and the other polypropylene-based film not contacting the adhesive on a region where the releasing film is to be attached to is a CPP (cast polypropylene) film.

[23] The releasing film according to claim 1, wherein in case that only one face of the paper is provided with the polypropylene-based film interposing the adhesive layer therebetween, a PET (polyethyleneterephtalate) film or a nylon film is provided on the other face of the paper not contacting the adhesive on a region where the releasing film is to be attached to, with interposing an adhesive layer therebetween.

[24] A method for preparing a releasing film comprising the step of: bonding a polypropylene-based film on either one or both faces of a paper with an adhesive, the polypropylene -based film being made to be composed of a single or multilayer of polypropylene-based resin having methyl group, and the single layer or the outermost layer of the multi-layer being made to directly contact the adhesive on a region where the releasing film is to be attached to.