JPH10110146A - Surface-protecting film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject film producing no fish eye, which may cause entrainment while it is stuck to an adherend, and not excessively increasing in tackiness under heating by compounding a plasticizer of given vinyl acetate content in its adhesive layer. SOLUTION: This film is obtained by laminating one side of a base layer of polyolefinbased resin film with an adhesive layer which contains 0.1 to 5wt.% of a plasticizer containing, as the major ingredient an, hylene-vinyl acetate copolymer with 10 to 47wt.% of vinyl acetate, and melting at 30 deg.C or lower. It is preferable that the copolymer has a melt flow rate of approximately 2 to 20 g/10min, and is used as a composition incorporated with an ethylene-ethyl acrylate copolymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface protective film which is used for protecting a surface of a synthetic resin plate or the like, and particularly suitable for protecting components of a liquid crystal display such as a polarizing plate or a retardation plate.

[0002]

2. Description of the Related Art In order to prevent the surface of a liquid crystal display member such as a synthetic resin plate, especially a polarizing plate or a retardation plate from being damaged or adhered during processing or transportation, various surface protective films have been used. I have. These surface protective films are peeled off and removed after processing or after use such as after transportation.

[0003] Such a surface protective film generally has a pressure-sensitive adhesive layer formed on one surface of a substrate layer made of a thermoplastic resin film such as polyethylene, polypropylene, polyethylene terephthalate or the like.

As one of the methods for producing the surface protective film, there is a method in which a pressure-sensitive adhesive composition dissolved in a solvent is applied on a substrate film, and then the solvent is removed in a drying step to obtain a surface protective film. However, in this method, it is necessary to remove a large amount of solvent in the drying step, and not only the equipment scale is increased, but also the obtained surface protective film cannot completely remove the solvent in the drying step, There is also a disadvantage that when the solvent remaining in the pressure-sensitive adhesive layer is adhered to the object to be protected, the solvent will attack the surface of the object to be protected.

As a method for producing a surface protective film which solves the above-mentioned problem of the solvent, there is a method of applying a heat-melted adhesive composition to a base film. However, according to this method, a pressure-sensitive adhesive composition having a high cohesive force has a high melt viscosity, and thus has a drawback that application becomes difficult. Furthermore, in this method, the adhesive strength between the substrate and the pressure-sensitive adhesive is weak as it is with respect to the polyolefin resin film substrate,
When the surface protective film is peeled from the object to be protected after use, a phenomenon in which the adhesive remains on the surface of the object to be protected, that is, a so-called adhesive residue occurs.

As a method for producing a surface protective film that solves this adhesive residue, there is a method in which a substrate layer is hot-melted together with a pressure-sensitive adhesive composition and co-extruded (hereinafter abbreviated as co-extrusion method). In this method, since no solvent is used, there is no contamination to the protected object, and further, the base material composition and the pressure-sensitive adhesive composition are melted and adhered in the mold, so that the adhesive force between the base material and the pressure-sensitive adhesive is strong, Will not remain.

In recent years, a surface protection film formed by a co-extrusion method has been used as a surface protection film used for a synthetic resin plate for the reasons described above. As such a surface protective film, for example, JP-A-54-13357
No. 8 discloses 50 to 90 parts by weight of a low-density polyethylene having a density of 0.91 to 0.93 g / cm @ 3, and a ratio (Mw / M) between a weight average molecular weight (Mw) and a number average molecular weight (Mn).
n) is 9-15 and the density is 0.955-0.
High-density polyethylene having a density of 962 g / cm @ 3
A surface protective film in which an adhesive resin layer made of an ethylene-unsaturated ester copolymer is laminated on one surface of a polyethylene resin layer made of parts by weight.

[0008] The surface protective film used for the synthetic resin plate is preferably one produced by a co-extrusion method because the adhesive is hardly left on the surface and the object to be protected is easily attacked by a solvent. As the resin constituting the base material, polyethylene resin is preferably used because it is inexpensive and easy to mold.

However, in the surface protective film disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 54-133578, the polyethylene resin constituting the substrate has a wide molecular weight distribution, and a relatively high ratio of a small molecule to a large molecule. Are mixed. In particular, the above-mentioned molecules having a large molecular weight are hardly melted at the time of forming a film and cause fisheye. This fish eye generated on the surface protection film,
While being affixed to an object to be protected such as a synthetic resin plate, and a large number of sheets are stacked and stored or transported, indentations are generated on the surface of the object to be protected, thereby deteriorating the commercial value of the object to be protected such as a synthetic resin plate. .

In recent years, demand for these synthetic resin plates for optical applications such as a polarizing plate used in a liquid crystal display device has been increasing, and the indentation due to the fish eyes causes distortion of an image of the liquid crystal display device. For example, there is a problem of causing optical defects. In addition, the fish eye is not only an indent, but air bubbles are entrapped between the synthetic resin plate and the pressure-sensitive adhesive layer of the surface protection film with the fish eye as a nucleus,
There is a possibility that the synthetic resin plate itself may be erroneously recognized as a surface abnormality, and it is a major problem to reduce fish eyes in the surface protective film.

[0011]

SUMMARY OF THE INVENTION The inventor of the present invention has intensively studied measures for suppressing fish eyes which cause the above-mentioned entrainment of air bubbles and measures for preventing an increase in the adhesive strength of an adhesive layer during heating. The inventors have found that the above-mentioned problems can be solved at once by adopting a specific blending system of ethylene-vinyl acetate copolymer / plasticizer having a specific vinyl acetate content, and have completed the present invention. It is.

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and has as its object to substantially produce fish eyes which cause air bubbles to be trapped when affixed to an adherend. An object of the present invention is to provide a surface protective film which is free from heat and has little increase in adhesive strength due to heating.

[0013]

According to the present invention, a base layer made of a polyolefin-based resin film is provided on one surface with an ethylene-vinyl acetate copolymer having a vinyl acetate content of 10 to 47% by weight as a main component and having a melting point. 0.1 to less than 30 ° C plasticizer
The gist of the present invention is a surface protective film characterized by being laminated with an adhesive layer containing 5% by weight.

The polyolefin resin used as the base material layer in the present invention is not particularly limited.
For example, a polymer obtained by a high-pressure method or a polymer obtained by using a Ziegler-Natta catalyst or a metallocene catalyst alone or in combination under low-pressure conditions (especially a polymer polymerized using a metallocene catalyst has a narrow molecular weight distribution, and a The bleed out of low molecular weight components is small), that is, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ethylene-
α-olefin copolymer, polypropylene and the like. These thermoplastic resins can be used alone or in combination of two or more.

The above-mentioned polyolefin resin used as the base material layer may contain an ultraviolet absorber, an antioxidant,
A coloring agent or the like may be added.

In the present invention, an ethylene-vinyl acetate copolymer used in the pressure-sensitive adhesive layer (hereinafter abbreviated as EVA)
Means that the vinyl acetate content (hereinafter abbreviated as VAC) is 1
It is 0 to 47% by weight, preferably 12 to 28% by weight.
When the VAC is less than 10% by weight, the adhesion of the surface protective film to the adherend is too small, and the surface protective film is easily peeled off from the adherend at the time of transportation after application.
Does not sufficiently fulfill the function of surface protection. EVA exceeding 47% by weight is difficult to handle because the adhesiveness is too high.
Also, it is difficult to obtain because it is not commercially available.

The melt flow rate (MF) of the above EVA
R) is preferably from 2 to 20 g / 10 min, more preferably from 2 to 9 g / 10 min. MFR of the above EVA is 2g
If it is less than / 10 minutes, the flowability during extrusion molding is small, so that the load is large and extrusion molding becomes difficult. Also, 20g /
If it exceeds 10 minutes, the fluidity at the time of extrusion molding is too large, so that the adhesive layer using the EVA flows before being cooled and solidified, and the extrusion molding becomes difficult.

The above EVA may be used alone, but ethylene-ethyl acrylate copolymer, polybutadiene, ethylene-α-olefin copolymer, styrene-
It may be used as a composition to which a resin such as a butadiene copolymer or a rubber is added.

The melting point of the plasticizer used in the pressure-sensitive adhesive layer in the present invention is 30 ° C. or lower, preferably 20 ° C. or lower, and it is almost liquid at room temperature. As the above plasticizer,
Although not particularly limited, for example, phosphoric acid-based, phthalic acid-based, fatty acid-based, polyester-based, epoxy-based plasticizers such as octyl epoxy stearate, and epoxy-based processing aids such as α-olefin oxide A phenol-phosphite antioxidant can also be used in the same manner as the above-mentioned plasticizer since it can plasticize the above-mentioned EVA or the above-mentioned EVA composition containing EVA as a main component.

The amount of the plasticizer added is 0.1 to 5% by weight.
Is limited to If the amount is less than 0.1% by weight, it is difficult to prevent an increase in adhesive strength during heating or at a high temperature. If the amount exceeds 5% by weight, the adhesive strength decreases,
At room temperature, it becomes difficult to adhere to the adherend.

If necessary, an ultraviolet absorber, an antioxidant, a tackifier, a coloring agent, and the like may be added to the EVA or the EVA composition containing EVA as a main component used as the pressure-sensitive adhesive layer.

The thickness of each of the base layer and the pressure-sensitive adhesive layer constituting the surface protection film is appropriately determined depending on the use of the surface protection film. The thickness of the base layer is generally 10 to 80 μm.
m, the thickness of the pressure-sensitive adhesive layer is generally set to about 5 to 30 μm.

The method for producing the surface protective film of the present invention is not particularly limited. For example, an EVA containing the above-mentioned polyolefin resin and the above-mentioned EVA as main components can be used.
The composition was melt-kneaded using a single-screw extruder or a twin-screw extruder, respectively, using a T-die or a circular die,
Polyolefin resin to be a base material layer and E to be an adhesive layer
A method in which an EVA composition containing VA as a main component is formed into a film by a co-extrusion method of two or more layers, and the pressure-sensitive adhesive composition is extruded on one surface of a polyolefin resin film as a base material by an extrusion lamination method. A method of laminating the pressure-sensitive adhesive layer, a method of applying an organic solvent solution of the pressure-sensitive adhesive composition on one surface of a polyolefin-based resin film to be a base material layer, and drying to form a pressure-sensitive adhesive layer are exemplified.

The surface protective film of the present invention has a high adhesion at room temperature by using EVA containing a high ratio of vinyl acetate for the pressure-sensitive adhesive layer, thereby reducing the repulsion of the generated fish-eye projections. Since it has superior adhesive strength, entrapment of air bubbles is suppressed. Therefore, at the time of sticking to the adherend, the entrapment ratio of the bubbles created by the fish eyes in the surface protective film, that is, the bubble ratio [bubble ratio (%) = ｛total number of bubbles involved (number / m ² ) / total fish eyes (Pcs / m
² ) Δ × 100] can be suppressed to 30% or less, usually 10% or less. If the bubble ratio exceeds 30%, the synthetic resin plate to which the surface protection film is attached is erroneously recognized as a surface abnormality of the synthetic resin plate itself due to the inclusion of bubbles.

Further, when processing is performed by applying heat while the surface protective film is adhered to the adherend, the plasticizer uniformly dispersed in the adhesive layer at room temperature bleeds from the adhesive layer by heating. Since an oil film is formed at the interface with the adherend to prevent the adhesive strength of the pressure-sensitive adhesive layer from increasing, the surface protective film after use can be peeled off from the adherend very easily, and the adhesive remains. Is substantially free of contamination.

Therefore, it can be suitably used for protecting the surface of a liquid crystal display component such as a synthetic resin plate, particularly a polarizing plate or a retardation plate.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

(Examples 1 to 6) As a base material layer, low-density polyethylene (trade name "Milason 12" manufactured by Mitsui Petrochemical Industries, Ltd.) was extruded into a film having a thickness of 40 μm by an inflation method. VAC1 on one side
An EVA composition comprising 4% EVA (manufactured by Mitsui DuPont Polychemicals Co., Ltd., trade name “Evaflex 560”) and a plasticizer having the type and the amount (% by weight) shown in Table 1 was used as an adhesive layer. The layers were laminated by an extrusion lamination method so as to have a thickness of 20 μm to prepare a surface protective film.

Comparative Examples 1 and 2 Example 1 was used as a substrate layer.
The low-density polyethylene film used in Example 1 was used, and the adhesive layer was composed of 6% VAC EVA (manufactured by Mitsubishi Chemical Corporation, trade name "LV260") and a plasticizer of the type and addition amount (% by weight) shown in Table 2. EVA composition as an adhesive layer,
The layers were laminated by an extrusion lamination method so as to have a thickness of 20 μm to prepare a surface protective film.

Comparative Examples 3 and 4 Example 1 was used as a base material layer.
The low-density polyethylene film used in the above was used, and as the pressure-sensitive adhesive layer, VAC 28% EVA (trade name “Evaflex 260” manufactured by DuPont-Mitsui Polychemicals Co., Ltd.) and the type and addition amount (% by weight) shown in Table 2 E consisting of a plasticizer
The VA composition was laminated as an adhesive layer by an extrusion lamination method so as to have a thickness of 20 μm to prepare a surface protective film.

(Comparative Examples 5 to 13) The low-density polyethylene film used in Example 1 was used as the base material layer, and the EVA used in Example 1 and the type and amount shown in Table 3 were used as the adhesive layer. An EVA composition comprising a plasticizer (wt%) was laminated as an adhesive layer by an extrusion lamination method so as to have a thickness of 20 μm to produce a surface protective film.

In order to evaluate the performance of the surface protective films obtained in Examples and Comparative Examples, each surface protective film was applied to an adherend using a pressure roll at normal temperature (20 ° C.) and a pressure of 2 kg / cm ^2. With air bubbles, adhesive strength (g / 25m
m) The adhesive strength to the adherend after application at room temperature and the adhesive strength to the adherend after heating were measured by the following methods. The measurement results are shown in Tables 1 to 3, respectively.

1. Bubble ratio: The obtained surface protective film is attached to a polarizing plate of 100 cm in length and 100 cm in width with a laminator, and the number of fish eyes having a diameter of 0.05 mm or more in the polarizing plate is counted. Similarly, the number of bubbles having a diameter of 0.1 mm or more generated by using the fish eyes as nuclei is counted. The bubble ratio was calculated from the total number of fish eyes and the total number of bubbles involved according to the following equation.

Bubble rate (%) = [total number of bubbles involved (pieces /
m ² ) / total number of fish eyes (pieces / m ² )] × 100

2. Adhesive force (g / 25 mm): (Adherend:
(Polycarbonate resin plate) Adhesive force to adherend at room temperature: JIS Z 0237
The adhesive strength was measured by a 180-degree peeling method according to the above. Adhesive force to adherend after heating: heated at 180 ° C. × 5 minutes, allowed to cool naturally, and then similarly to JIS Z 0237
The adhesive strength was measured by a 180-degree peeling method according to the above.

[0036]

[Table 1]

As is clear from Table 1, all of the surface protective films of Examples 1 to 6 had an adhesive force at ordinary temperature at a level at which there was no problem in practical use, reduced the entrapment of air bubbles, and showed that Adhesive strength (peeling force) is 100
g / 25 mm or less, and there is substantially no increase in adhesion due to heating, indicating that the used surface protective film is easily peeled off from the adherend attaching surface.

[0038]

[Table 2]

As is clear from Table 2, all of the surface protective films of Comparative Examples 1 to 4 have practical problems in adhesive strength at room temperature, and those using EVA having a low VAC are as described above. However, even if the film cannot be stuck or can be stuck and the peeling force after heating is appropriate, the entrapment of air bubbles is increased. Conversely, those using EVA with a high VAC are difficult to peel off from the adherend surface in order to suppress the entrapment of air bubbles, and when a large amount of a plasticizer is added to the EVA with a high VAC, the initial As a result, the expression of adhesive force was inhibited, and the result was that application was impossible.

[0040]

[Table 3]

As is clear from Table 3, all of the surface protective films of Comparative Examples 5 to 12 to which a plasticizer solid at room temperature was added had an adhesive force (peeling force) of 200 after heating.
g / 25 mm or more, and it was difficult to peel off from the surface of the adherend.

[0042]

Since the surface protective film of the present invention is constituted as described above, it does not substantially generate fish eyes which cause entrainment of air bubbles in an adherend, and is not affected by heating. Little increase in adhesion. Therefore, it can be suitably used for protecting the surface of a synthetic resin plate, particularly a component of a liquid crystal display such as a polarizing plate or a retardation plate.

Claims (1)

[Claims] 1. One side of a base layer made of a polyolefin resin film is mainly composed of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 10 to 47% by weight and a melting point of 3%.
A surface protective film comprising a pressure-sensitive adhesive layer containing 0.1 to 5% by weight of a plasticizer having a temperature of 0 ° C. or lower.