KR20170108557A

KR20170108557A - Protection Film for FPCB Process

Info

Publication number: KR20170108557A
Application number: KR1020160032653A
Authority: KR
Inventors: 조영호; 최규하; 이정우
Original assignee: 도레이첨단소재 주식회사
Priority date: 2016-03-18
Filing date: 2016-03-18
Publication date: 2017-09-27

Abstract

In the present invention, provided is a heat-resistant protective film for a flexible printed circuit board (FPCB) process, in which an adhesive layer is formed on a white polyester base film having total transmittance of 30% or less. According to the present invention, by using the adhesive applied to the heat-resistant protective film for the FPCB process and the white polyester film, it is possible to maintain heat resistance of the adhesive used in the heat-resistant protective film for the FPCB process, to improve productivity and reduce defects in the FPCB process by reducing inhibition of adhesion increase, adhesive transference, and film tearing which can occur during an FPCB hot press process by securing high visibility, and to apply the heat-resistant protective film to all CL and CCL including black CL, which has been difficult to be applied before.

Description

Heat Protection Film for FPCB Process {Protection Film for FPCB Process}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant protective film for an FPCB process, and more particularly, to a heat-resistant protective film for a FPCB process, which uses a white polyester film as a base film to maintain heat resistance of a pressure- A heat-resistant protective film for an FPCB process capable of improving the productivity of a FPCB process and reducing defects by improving adhesion of a pressure-sensitive adhesive, transfer of a pressure-sensitive adhesive, and film tear.

As the technology has been developed recently, the tendency of miniaturization, thinning, densification and high bending of electronic products is accelerating. As a result, printed circuit board (PCB), which is easy to be embedded even in a narrow space, A flexible printed circuit board (FPCB) has been developed which can be miniaturized and densified and has bending flexibility repeatedly.

Such flexible printed circuit boards have been rapidly increasing in demand due to the development of electronic devices such as portable terminals, LCDs, cameras, and printer heads. At present, the use of a flexible printed circuit board also tends to increase rapidly in order to achieve high density of circuit patterns.

In order to produce such a flexible printed board, a dry film is laminated on a copper clad laminate having a copper foil layer formed on one side of an insulating film such as a polyimide resin, and then a circuit pattern is formed by exposure, development and etching, A coverlay film is applied to the outside of the copper-clad laminate, and the laminate is subjected to a surface treatment and a post-treatment.

Through these processes, it is necessary to protect the Cu surface on one side in exposure, development, etching both sides, and multi CCL. A protective film such as the one described above is used thereon, and a protective film is attached to the CCL and the CL bonding process called a hot press. Therefore, a protective film having high heat resistance is required. In addition, since the CCL and CL are formed as a thin film for the miniaturization, thinning and densification, the workability is lowered and the protective film is attached to the thinned CL and CCL to improve the workability by compensating the thickness. In the case of the transparent protective film used therein, the defective ratio is increased due to the inability to distinguish the protection film after the hot press, and the defective ratio is reduced by using the opaque Matt film. However, the productivity is deteriorated due to the tearing of the film after hot pressing , There is a demand for a heat-resistant protective film having heat resistance, while improving visibility as opaque matte (Matt) protective film.

An object of the present invention is to provide a heat-resistant protective film for an FPCB process in which the heat resistance of a pressure-sensitive adhesive used in a heat-resistant protective film is maintained and visibility is secured, thereby suppressing an increase in adhesive force caused by the FPCB hot press process, .

In order to achieve the above object, the present invention provides a heat-resistant protective film for FPCB process, wherein a pressure-sensitive adhesive layer is formed on a white polyester base film having a total light transmittance of 30% or less.

The thickness of the pressure-sensitive adhesive layer is preferably 5 to 20 占 퐉 and the adhesive strength is preferably 10 to 100 gf / 25 mm.

Wherein the pressure-sensitive adhesive layer comprises 50 to 90% by weight of a soft acrylic monomer having a glass transition temperature of the homopolymer of less than 0 占 폚; 1 to 48% by weight of a hard monomer having a glass transition temperature of 0 占 폚 or higher of the homopolymer; And 1 to 10% by weight of a crosslinking monomer.

The total light transmittance of the protective film is preferably 25% or less.

According to the present invention, by using the pressure-sensitive adhesive applied to the heat-resistant protective film for the FPCB process and the white polyester film, the heat resistance of the pressure-sensitive adhesive used in the heat-resistant protective film for the FPCB process is maintained and visibility is ensured, It is possible to improve the productivity of FPCB process and reduce defects by improving the adhesive strength increase, adhesive transfer and film tear, and it has become possible to apply to all CL and CCL including black CL which was difficult to apply.

1 is a schematic cross-sectional view of a heat-resistant protective film for FPCB process according to an embodiment of the present invention.

1, in the heat-resistant protective film for FPCB process according to the present invention, a pressure-sensitive adhesive layer (2) is formed on a white polyester base film (1). On the pressure-sensitive adhesive layer, a known release film 3 may be laminated and stored.

[White polyester base film]

The use of the white polyester film as the base film in the present invention is for imparting visibility to the protective film without changing the adhesive property. The white polyester film is a polyester film having fine bubbles and has a total light transmittance of 30% or less in the range of 400 to 700 nm. The white polyester film in which fine bubbles are formed in the film can be obtained by finely dispersing an inorganic polymer such as a high-melting-point emulsion polymer or barium sulfate in polyester as a film base material and stretching it. At the time of stretching, voids (bubbles) are formed around the nonconductive polymer particles, and since they exhibit a scattering action in the light, they are whitened and the total light transmittance is lowered.

The polyester used as a base material of the white polyester film is preferably a polyester such as ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol and the like, and terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, A dicarboxylic acid represented by an acid, a sebacic acid, or the like; and a polymer obtained by condensation polymerization. Specific examples thereof include polymethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate . In the case of the present invention, polyethylene terephthalate and polyethylene naphthalate are particularly preferable. Most preferably, polyethylene terephthalate is used. The polyethylene terephthalate film is excellent in heat resistance, water resistance, durability, and chemical resistance.

The fine bubbles are formed by finely dispersing a thermoplastic resin or an inorganic particle having a high melting point and an average particle diameter of 1 占 퐉 or less in a film base material such as polyester, and then stretching it (for example, biaxial orientation) . At the time of stretching, voids (bubbles) are formed around the thermoplastic resin or inorganic particles for emergency, and since they exhibit a scattering action in light, it becomes whitened and a low total light transmittance can be obtained.

Polyesters and non-commercial thermoplastic resins used for this purpose include, for example, poly-3-methylbutene-1, poly-4-methylpentene-1, polyvinyl- But are not limited to, polyethylene terephthalate, 2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, polymethylstyrene, polydimethylstyrene, polyfluorostyrene, , Cellulose triopropionate, polyvinyl fluoride, polychlorotrifluoroethylene, and the like, and the like. Among them, polyolefin, particularly polymethylpentene, is preferable for the polyester base material. The addition amount of the thermoplastic resin for emergency is preferably 5 wt% or more and 25 wt% or less based on 100 wt% of the total weight of the entire polyester film.

In order to obtain high optical properties and stable film formability when inorganic particles are used to form fine bubbles, titanium dioxide, barium sulfate, magnesium sulfate, magnesium sulfate, aluminum oxide, zinc oxide, magnesium oxide, calcium carbonate, Barium carbonate, silica and the like are preferable. They can be used singly or in a mixture of two or more kinds. Among them, barium sulfate particles and titanium dioxide particles are particularly preferable because high optical properties and film forming stability are obtained. On the other hand, the content of the inorganic particles used for this purpose is usually in the range of 5 wt% or more and 70 wt% or less based on the total weight of the polyester film.

The thickness of the above-described base film may be variously applied, but it is preferable to use a film having a thickness of 10 to 200 mu m.

On the other hand, a white polyester film having a total light transmittance of 30% or less is preferable in order to impart visibility to the protective film without changing the adhesive property. When the light transmittance exceeds 30%, whether or not the protective film and the PI film are adhered to each other after hot pressing is not visually recognized, which may cause defects in the subsequent protective film removing step and the like.

[Pressure sensitive adhesive layer]

The heat-resistant protective film for FPCB process of the present invention is obtained by forming an acrylic pressure-sensitive adhesive layer on the base film described above. The acrylic pressure-sensitive adhesive is used in an amount of from 50 to 90% by weight of the soft acrylic monomer having a glass transition temperature of the homopolymer of 0 占 폚 or less; 1 to 48% by weight of a hard monomer having a glass transition temperature of 0 占 폚 or higher of the homopolymer; And 1 to 10% by weight of a crosslinking monomer.

The soft acrylic monomers impart flexibility and adhesion to the pressure sensitive adhesive of the present invention. For this purpose it is possible to choose from the group consisting of butyl (meth) acrylate, hexyl acrylate, hexyl methacrylate, n-propyl (meth) acrylate, n-tetradecyl (meth) acrylate and 2-ethylhexyl acrylate More than one is used.

The hard acrylic monomer serves to impart cohesive force to the pressure sensitive adhesive of the present invention. For this purpose, at least one selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl methacrylate, vinyl acetate, styrene and acrylonitrile may be used.

The crosslinking monomers are used for copolymerizing soft monomers with soft monomers. For this purpose, at least one selected from the group consisting of a monomer containing a hydroxy group, a monomer containing a carboxyl group and a monomer containing nitrogen is used. Here, the monomer containing a hydroxy group may be at least one selected from the group consisting of 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl Acrylate, 2-hydroxyethylene glycol (meth) acrylate or 2-hydroxypropylene glycol (meth) acrylate, and the monomer containing a carboxyl group is (meth) acrylic acid, maleic acid or fumaric acid, The nitrogen-containing monomer may be acrylamide, N-vinylpyrrolidone or N-vinylcaprolactam. The above crosslinking monomers may be used alone or in combination of two or more.

Further, according to the present invention, the glass transition temperature of the acrylic copolymer resin is -50 ° C to 0 ° C, preferably -45 ° C to -10 ° C. When the glass transition temperature is less than -50 ° C, even if the pressure-sensitive adhesive composition is cured to have a three-dimensional network structure, the glass transition temperature of the polymer itself is low, , The cured adhesive composition has a three-dimensional network structure more densely in molecular structure than a composition having a low glass transition temperature. The adhesive itself is viscoelastic, which in this case is more biased toward elasticity. In this case, the protective film has to protect against the foreign object or external impact, but the elasticity is high, and when the viscosity is low, the product can not absorb the external impact and damage the product.

As described above, the acrylic polymer resin used in the adhesive layer of the heat-resistant protective film for FPCB process is characterized in that two kinds of acrylic polymer resins having different glass transition temperatures (Tg) are used as the hard and soft acrylic resins, This is because it is possible to solve this problem by mixing a polymer resin having a glass transition temperature different from that of the polymer resin having no adhesive residue in a high temperature process and easily controlling the adhesive force.

The acrylic polymer resin used in the present invention preferably has a weight average molecular weight of 300,000 or more and 2,000,000 or less. When the weight average molecular weight is less than 300,000, the adhesive residual phenomenon occurs due to a decrease in cohesive strength. When the weight average molecular weight is more than 2,000,000, The workability is deteriorated, the molecular weight is increased, and the elasticity and adhesion of the pressure-sensitive adhesive are increased.

The wettability of the pressure-sensitive adhesive to the adherend depends on the cohesive strength of the pressure-sensitive adhesive or the thickness of the pressure-sensitive adhesive. If the cohesive force of the pressure-sensitive adhesive is increased, the wettability against the bending of the surface of the substrate becomes low. Such wettability with respect to the adherend can achieve properties required for the control of the glass transition temperature of the copolymer and the thickness of the adhesive film.

In order to set the Tg of the copolymer to -50 캜 or higher, the type and polymerization ratio of each monomer should be appropriately selected.

First, the tackiness (degree of stickiness of the pressure-sensitive adhesive) in the film-type pressure-sensitive adhesive of the present invention is determined depending on the combination of the soft monomer and the hard monomer among the monomer components constituting the pressure-sensitive adhesive. If the content of soft monomer is increased, the glass transition temperature of the pressure sensitive adhesive is lowered and the tack properties are increased. If the content of the hard monomer is increased, the glass transition temperature of the pressure sensitive adhesive increases and the tack characteristics are lowered.

The thickness of the heat-resistant protective film adhesive layer for the FPCB process according to the present invention is 5 to 20 탆 in dry film thickness and 10 to 100 g / 25 mm in adhesive strength. If the thickness of the pressure-sensitive adhesive layer is thinner than 5 占 퐉, the adhesiveness to CCL and CL is inferior and the pressing of CCL and CL is caused by R-chip roughness of the film. If the thickness is thicker than 20 占 퐉, And the pressure-sensitive adhesive transfer may occur after hot pressing. If the adhesive strength is less than 10 g / 25 mm, peeling and etching solution penetration may occur in the process. If it exceeds 100 g / 25 mm, the FPCB surface may be damaged or curled when removed.

The curing agent used in the heat-resistant protective film adhesive layer for the FPCB process according to the present invention may be variously used depending on the concentration of the epoxy curing agent and the use range of the curing agent to improve the curing rate, heat resistance and visibility. The content of the curing agent is suitably in the range of 1 to 10 parts by weight based on 100 parts by weight of the acrylic polymer resin. If the amount of the curing agent is less than 1 part by weight, crosslinking may not be sufficiently carried out and surface transfer may occur. If the amount is more than 10 parts by weight, excessive curing agent may enter the side reaction.

Hereinafter, the present invention will be described in detail with reference to examples. These embodiments are merely illustrative examples for the purpose of more specifically describing the present invention, and the scope of the present invention is not limited by these embodiments.

1. Manufacture of pressure-sensitive adhesive copolymer (acrylic copolymer)

The soft monomer, the hard monomer and the crosslinking monomer were introduced in the amounts shown in the following Table 1 in a 1,000 ml chemical reactor equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen injecting apparatus, and 100 g of ethyl acetate as a solvent was added thereto. 0.02 g of azo azobisdimethylvaleronitrile (ADMVN) was added and polymerization reaction was carried out at 50 캜 for 15 hours in a nitrogen stream to obtain an acrylic copolymer resin.

division Polymer resin manufacturing Soft monomer n-BA 50g
2-HEA 10g
2-EHA 10 g Hard monomer MA 15g
MMA 10g Crosslinking monomer HBA 5g n-BA: n-butyl acrylate
2-HEA: 2-hydroxyethyl acrylate
2-EHA: 2-ethylhexyl acrylate
MMA: methyl methacrylate
MA: methyl acrylate
AA: Acrylic acid
HBA: Hydroxybutyl acrylate

2. Manufacture of pressure sensitive adhesive

A pressure-sensitive adhesive (PSA) was prepared in the composition shown in Table 1 below.

division Production Example 1 Production Example 2 Production Example 3 Production Example 4 Production Example 5 Production Example 6 Production Example 7 Polymer resin 100 100 100 100 100 100 100 Hardener content One 5 10 5 5 5 5 Nano particle content
(500 nm or less)
-
-
-
0.005
-
-
0.01 * Nanoparticles: carbon black

[Example 1]

In Example 1, 5.0 g of an epoxy curing agent was homogeneously mixed with 100 g of the acrylic polymer resin polymerized under the conditions of Production Example 2 of Table 1, and then white PET (total light transmittance of the base film itself was 23% Mu] m and dried at 160 DEG C for 1 minute to prepare a protective film sample.

[Comparative Example 1]

In Comparative Example 1, 5.0 g of an epoxy curing agent was uniformly mixed with 100 g of the acrylic polymer resin polymerized under the conditions of Production Example 2 of Table 1, followed by coating with 5 탆 of white PET after PSA and drying at 160 캜 for 1 minute, Respectively.

[Comparative Example 2]

In Comparative Example 2, 5.0 g of the epoxy curing agent was uniformly mixed with 100 g of the acrylic polymer resin polymerized under the conditions of Production Example 2 of Table 1, followed by 20 占 퐉 coating of white PET after PSA and drying at 160 占 폚 for 1 minute to obtain a sample Was prepared

[Comparative Example 3]

In Comparative Example 3, 1.0 g of the epoxy curing agent was uniformly mixed with 100 g of the acrylic polymer resin polymerized under the conditions of Production Example 1 of Table 1, and then coated with white PET to 10 탆 after PSA and dried at 160 캜 for 1 minute, Respectively.

[Comparative Example 4]

In Comparative Example 4, 10.0 g of an epoxy curing agent was uniformly mixed with 100 g of the acrylic polymer resin polymerized under the conditions of Production Example 3 of Table 1, and then coated with 10 탆 of transparent PET after PSA and dried at 160 캜 for 1 minute, Respectively.

[Comparative Example 5]

In Comparative Example 5, 5.0 g of an epoxy curing agent and 0.001 g of nanoparticles (500 nm or less) were uniformly mixed with 100 g of the acrylic polymer resin polymerized under the conditions of Production Example 4 of Table 1, And dried at 160 DEG C for 1 minute to prepare a sample.

[Comparative Example 6]

In Comparative Example 6, 5.0 g of the epoxy curing agent was uniformly mixed with 100 g of the acrylic polymer resin polymerized under the conditions of Production Example 5 of Table 1, followed by coating with 10 탆 of Matte PET after PSA and drying at 160 캜 for 1 minute, Respectively.

[Comparative Example 7]

In Comparative Example 7, 5.0 g of an epoxy curing agent was uniformly mixed with 100 g of the acrylic polymer resin polymerized under the conditions of Production Example 6 of Table 1, 10 탆 of the PET was coated on transparent PET, and the resultant was dried at 160 캜 for 1 minute, Respectively.

[Comparative Example 8]

In Comparative Example 8, 5.0 g of an epoxy curing agent and 0.01 g of nanoparticles (500 nm or less) were uniformly mixed with 100 g of the acrylic polymer resin polymerized under the conditions of Production Example 7 of Table 1, And dried at 160 DEG C for 1 minute to prepare a sample.

[Experimental Example]

1. Adhesive thickness

The thickness of the adhesive layer was measured using a micrometer.

2. Adhesion measurement

The prepared samples were peeled off at a rate of 10 m / min and a 180 ° angle using an AR-1000 measuring device after normal lamination with PI and copper foil at room temperature and hot press at 160 ° C and 7.7 Mpa for 30 minutes.

3. Identification of PSA residues

The fabricated sample was laminated with general PI and copper foil, and after hot pressing at 160 ° C and 7.7 MPa for 30 minutes, it was confirmed whether the pressure-sensitive adhesive was transferred.

4. Confirm visibility

Whether visually distinguishable between transparent products and visually improved products was visually confirmed.

5. Total light transmittance measurement

A sample was vertically placed on an automatic digital haze meter of Nippon Denshoku Co., Ltd., and light having a wavelength of 400 to 700 nm was transmitted in a direction perpendicular to the sample placed vertically.

6. Film tear after hot press

The samples were subjected to hot pressing at 160 ° C and 7.7 MPa for 30 minutes after laminating with general PI and copper foil. The degree of tearing was judged when the film was torn.

As can be seen from the examples of Table 2 above, when the content of the curing agent is 0.1 to 10 parts by weight based on 100 parts by weight of the polymer resin and the thickness of the pressure sensitive adhesive is 5 to 20 占 퐉 and the white film is used, Can be confirmed.

On the other hand, in Comparative Examples 1 and 2, all the contents were the same as in Examples, but the thickness of the pressure-sensitive adhesive was changed to 5 and 20. However, when the thickness was 5, no CCL and CL were laminated at room temperature, The cohesive force of the adhesive agent was weakened, and the adhesive strength was increased and residues were formed. In the protective films of Comparative Examples 3 and 4, PSA residues were generated due to the curing agent content. Comparative Examples 5 and 8 incorporated nanoparticles to improve the visibility compared to transparent PET. However, for the purpose of high transmittance and low transmittance, When the content was increased, the CCL and CL were not lyophilized at room temperature and the adhesive property was lost. In Comparative Example 6, the opaque matte PET film was applied, and basic sticking property and visibility were secured. However, there was a problem that the visibility was deteriorated when the film was completely sealed after hot pressing due to film tear phenomenon and high transmittance after hot pressing. In Comparative Example 7, it was confirmed that the visibility was lowered by using transparent PET.

1. Base film 2. Adhesive layer
3 .. Release Film 10 .. Heat Protection Film for FPCB Process

Claims

A heat-resistant protective film for FPCB process, wherein a pressure-sensitive adhesive layer is formed on a white polyester base film having a total light transmittance of 30% or less.

The heat-resistant protective film for an FPCB process according to claim 1, wherein the thickness of the pressure-sensitive adhesive layer is 5 to 20 占 퐉 and the pressure-sensitive adhesive force is 10 to 100 gf / 25 mm.

The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-
Relative to 50 to 90% by weight of a soft acrylic monomer having a glass transition temperature of the homopolymer of less than 0 占 폚; 1 to 48% by weight of a hard monomer having a glass transition temperature of 0 占 폚 or higher of the homopolymer; And
1 to 10% by weight of a cross-linking monomer; and an acrylic copolymer containing 1 to 10% by weight of a crosslinking monomer.

The heat-resistant protective film for FPCB process according to claim 1, wherein the total light transmittance is 25% or less.