JP2020125490A - Surface protective film for prism sheet and prism sheet with surface protective film for prism sheet - Google Patents

Abstract

To provide a surface protective film for prism sheet capable of exhibiting high adhesive force (initial adhesive force) to a prism sheet having repulsive force of 1.0 mN or less when a surface in a prism layer side is displaced with 1 μm at 25°C, hardly adhesion upsetting with time or even under high temperature and capable of being detached without breakage of the prism sheet or adhesive deposition and the prism sheet with the surface protective film for prism sheet, which is protected by adhering the surface protective film for prism sheet.SOLUTION: There is provided a surface protective film for prism sheet for protecting a prism sheet which has a prism layer on a surface and repulsive force of 1.0 mN or less when a surface in a prism layer side is displaced with 1 μm at 25°C, by adhering the same on the prism layer of the prism sheet, having a substrate layer and an adhesive layer, where the adhesive layer has storage elastic modulus at 25°C, E' of 3.0 MPa or less and tanδ at 25°C of 0.2 to 1.1.SELECTED DRAWING: Figure 1

Description

INDUSTRIAL APPLICABILITY The present invention can exert a high adhesive force (initial adhesive force) to a prism sheet having a repulsive force of 1.0 mN or less when the surface on the prism layer side is displaced by 1 μm at 25° C. Alternatively, it is difficult to promote adhesion even under high temperature, and a prism sheet surface protective film that can be peeled without damaging the prism sheet or leaving an adhesive residue, and a prism sheet surface protective film attached to protect The present invention relates to a prism sheet with a surface protection film for a prism sheet.

Conventionally, a surface having a base material layer and a pressure-sensitive adhesive layer laminated on one surface thereof to protect the surface of a member such as an optical device, a metal plate, a coated metal plate, a resin plate, and a glass plate. A protective film (generally referred to as a protect tape or the like) is widely used (for example, Patent Documents 1 to 3).
Among them, the surface protection film is used to protect the surface of an optical member for liquid crystal displays. Optical members include those having an uneven shape on one or both surfaces, such as a prism sheet and a diffusion film.In order to prevent the uneven shape from being damaged, the surface of the optical member should be surfaced prior to use. It is protected by a protective film.

In recent years, liquid crystal displays are required to be thinner and smaller. In such a thin and miniaturized liquid crystal display, it has been proposed to adjust the repulsive force on the side (prism layer) of the prism sheet having the uneven shape so as not to damage the member. In the low repulsion prism sheet, the repulsive force when the surface of the prism layer is displaced by 1 μm at 25° C. is adjusted to be, for example, 1.0 mN or less (hereinafter, such a prism sheet will be referred to as “low repulsion prism sheet”). Also called.).

When a surface protection film is attached to the surface of such a low repulsion prism sheet, the surface shape of the prism sheet is largely deformed by the pressure at the time of attachment, and the deformation is recovered. Peeling is likely to occur at the interface between the prism sheet and the surface protection film, and floating is likely to occur. In order to prevent such floating, it is conceivable to increase the adhesive force of the pressure-sensitive adhesive layer of the surface protective film. However, when a high-adhesive surface protective film is attached on the prism layer of the prism sheet, the adhesive force increases due to an increase in the contact area between the prism sheet and the adhesive layer over time or under high temperature, so-called adhesion. When the surface protection film is peeled off from the prism sheet, the prism sheet may be damaged or adhesive residue may remain when the surface protection film is peeled off. With the conventional surface protection film, while exhibiting high adhesive strength (initial adhesive strength) against the low-repulsion prism sheet, it suppresses the adhesion promotion and peels off without damaging the prism sheet or leaving adhesive residue. It was difficult.

JP-A 1-129085 JP, 6-1958, A JP-A-8-12952

In view of the above situation, the present invention can exhibit a high adhesive force (initial adhesive force) to a prism sheet having a repulsive force of 1.0 mN or less when the surface on the prism layer side is displaced by 1 μm at 25° C. A surface protective film for a prism sheet, which can be formed and which is hard to promote adhesion even with time or under high temperature, and can be peeled without damaging the prism sheet or leaving an adhesive residue, and a surface protective film for the prism sheet. An object of the present invention is to provide a prism sheet with a surface protective film for a prism sheet, which is attached and protected.

The present invention has a prism layer on the surface, and the repulsive force when the surface on the prism layer side is displaced by 1 μm at 25° C. is 1.0 mN or less. A surface protection film for a prism sheet for protection, comprising a base material layer and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer has a storage elastic modulus E′ at 25° C. of 3.0 MPa or less and 25° C. Is a surface protection film for a prism sheet having a tan δ of 0.2 or more and 1.1 or less.
The present invention will be described in detail below.

The present inventors have adjusted the storage elastic modulus E′ at 25° C. and tan δ at 25° C. of a pressure-sensitive adhesive layer for a prism sheet surface protective film having a base material layer and a pressure-sensitive adhesive layer, thereby adjusting the prism. It is possible to exert a high adhesive force (initial adhesive force) on a low repulsive prism sheet having a repulsive force of 1.0 mN or less when the surface on the layer side is displaced by 1 μm at 25° C. However, the present invention has been completed by finding that it is difficult for adhesion to proceed and that the prism sheet can be peeled off without damaging or leaving an adhesive residue.

The surface protective film for a prism sheet of the present invention (hereinafter, also simply referred to as “surface protective film”) is attached to the prism layer of the prism sheet to protect it.
The prism sheet is not particularly limited as long as it has a prism layer on the front surface, but usually has a matte layer or a flat layer on the back surface. The prism layer is a layer having an uneven shape (for example, an uneven shape having a pitch of about 20 to 100 μm).

The prism sheet has a repulsive force of 1.0 mN or less when the surface on the prism layer side is displaced by 1 μm at 25° C. A low-repulsion prism sheet having a prism layer having a repulsion force of 1.0 mN or less is extremely flexible and exhibits excellent performance of not damaging the members of recent thinned and downsized liquid crystal displays. .. On the other hand, since it has such an extremely flexible prism layer, it is difficult for the conventional surface protection film to have both high adhesive strength (initial adhesive strength) and excellent peelability (low adhesion promotion rate). It was
The surface protective film of the present invention solves the problems unique to such a low-repulsion prism sheet, and has high adhesive force (initial adhesive force) and excellent peelability (low adhesion promotion rate) to the low-repulsion prism sheet. It is a balance between The surface protective film of the present invention has, for example, a repulsive force of 0.5 mN or less and 0.05 mN or less when the surface on the prism layer side is displaced by 1 μm at 25° C., and is sufficient even for a low repulsion prism sheet. It is possible to exert a great effect.

The repulsive force when the surface of the prism sheet on the prism layer side is displaced by 1 μm at 25° C. is, for example, a micro indentation hardness tester (for example, an ultra-fine indentation hardness tester manufactured by Elionix, model ENT). -2100), the repulsive force can be measured by a method of measuring a load-displacement curve based on JIS Z2255.

The surface protection film of the present invention has a base material layer and an adhesive layer.
The base material layer is not particularly limited, but preferably contains a polyolefin resin.
The polyolefin resin is not particularly limited, and conventionally known polyolefin resins can be used, and examples thereof include polypropylene (PP) resin and polyethylene (PE) resin.

Examples of the polypropylene resin include homopolypropylene, random polypropylene, block polypropylene and the like. Examples of the polyethylene resin include high-pressure low-density polyethylene, linear low-density polyethylene, and high-density polyethylene. Among them, polypropylene resin is preferable from the viewpoint of transparency, rigidity and heat resistance, and homopolypropylene or a copolymer of propylene and at least one α-olefin is more preferable.

The base material layer is an additive such as an antistatic agent, a release agent, an antioxidant, a weathering agent, a crystal nucleating agent, a resin such as a polyolefin, polyester, polyamide, or an elastomer within a range that does not impair the effects of the present invention. It may contain a modifier.

The thickness of the base material layer is not particularly limited, but the preferred lower limit is 20 μm, and the preferred upper limit is 200 μm. When the thickness of the base material layer is within this range, handleability is excellent. The more preferable lower limit of the thickness of the base material layer is 25 μm, and the more preferable upper limit thereof is 188 μm.

The pressure-sensitive adhesive layer has a storage elastic modulus E′ at 25° C. of 3.0 MPa or less, and a tan δ at 25° C. of 0.2 or more and 1.1 or less. By adjusting the storage elastic modulus E′ and tan δ at 25° C. of the pressure-sensitive adhesive layer in this way, it is possible to obtain a high pressure-sensitive adhesive force (initial pressure-sensitive adhesive force) and excellent releasability with respect to the low-repulsion prism sheet having the above-mentioned specific properties. (Low adhesion progress rate) can be achieved at the same time.

By adjusting the storage elastic modulus E′ at 25° C. of the pressure-sensitive adhesive layer to 3.0 MPa or less, it is possible to improve the adhesiveness when sticking to an adherend and improve the adhesive force (initial adhesive force). On the other hand, it is possible to suppress the progress of adhesion progress over time or under high temperature. The storage elastic modulus E′ at 25° C. of the pressure-sensitive adhesive layer is preferably 2.9 MPa or less, more preferably 2.7 MPa or less, and further preferably 2.5 MPa or less.

By adjusting the tan δ at 25° C. of the pressure-sensitive adhesive layer to be 0.2 or more and 1.1 or less, the adhesiveness at the time of sticking to an adherend is increased and the adhesive strength (initial adhesive strength) is improved. On the other hand, it is possible to suppress the progress of adhesion progress over time or under high temperature.
The tan δ at 25° C. of the pressure-sensitive adhesive layer is preferably 0.25 or more, more preferably 0.3 or more, and further preferably 0.4 or more. Further, in order to prevent the developing force when the surface protective film is unrolled when it is formed into a wound body, tan δ at 25° C. of the pressure-sensitive adhesive layer is preferably 1.0 or less, It is more preferably 0.9 or less, still more preferably 0.8 or less.

The storage elastic modulus E′ and tan δ at 25° C. of the pressure-sensitive adhesive layer are, for example, 10° C./constant temperature constant tensile mode using a viscoelastic spectrometer such as DVA-200 (manufactured by IT Measurement and Control Co.). The dynamic viscoelastic spectrum of the pressure-sensitive adhesive layer can be measured and obtained under the condition of 10 Hz for 10 minutes.

The method for adjusting the storage elastic modulus E′, tan δ at 25° C. of the pressure-sensitive adhesive layer to the above range is not particularly limited, but, for example, a base resin is selected with hardness as an index, and a tackifier is added to the base resin. By adjusting the storage elastic modulus E′ and tan δ within the desired range, a method and the like can be mentioned.

The base resin is not particularly limited, and examples thereof include a styrene-based elastomer, an acrylic-based elastomer, a urethane-based elastomer, and an olephene-based elastomer. Among them, a styrene-based elastomer is preferable because it can exhibit a high adhesive force (initial adhesive force) and the hardness can be easily adjusted by the styrene content.

The styrene elastomer is not particularly limited, and examples thereof include styrene ethylene propylene styrene block copolymer (SEPS), hydrogenated styrene butadiene rubber (HSBR), styrene ethylene butylene styrene block copolymer (SEBS), styrene ethylene propylene block. Copolymer (SEP), styrene-ethylene butylene block copolymer (SEB), styrene-isoprene block copolymer (SI), styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene block copolymer ( SB), styrene-butadiene-styrene block copolymer (SBS) and the like.

In order to adjust the storage elastic modulus E′ and tan δ at 25° C. of the pressure-sensitive adhesive layer within the above range, it is preferable to select the base resin having a hardness of 35 to 50 shore/10 seconds. If a base resin having a hardness within such a range is selected and used, the storage elastic modulus E′ and tan δ at 25° C. of the pressure-sensitive adhesive layer can be relatively easily adjusted to the above range by using the base resin in combination. be able to. A more preferable upper limit of the hardness of the base resin is 47 shore/10 seconds.

When a styrene-based elastomer is used as the base resin, the styrene content in the primary structure is also a guide for selection. Although there are exceptions depending on the secondary structure and the tertiary structure, if a styrene-based elastomer having a styrene content of 5 to 16% by weight is selected, the hardness will be approximately 35 to 50 Shore/10 seconds.
Examples of the styrene elastomer having such a styrene content and hardness include 2063 (styrene ethylene propylene styrene block copolymer (SEPS), styrene content 13% by weight, hardness 36 shore/10 seconds) manufactured by Kuraray Co., Ltd. And JSR's DR1320P (hydrogenated styrene butadiene rubber (HSBR), styrene content 10% by weight, hardness 42 Shore/10 seconds), DR1321P (hydrogenated styrene butadiene rubber (HSBR), styrene content 10% by weight, Hardness 41 shore/10 seconds), DR8300P (styrene ethylene butylene styrene block copolymer (SEBS), styrene content 9% by weight, hardness 47 shore/10 seconds), DR2324P (styrene ethylene butylene styrene block copolymer (SEBS)) , Styrene content 16% by weight, hardness 50 shore/10 seconds), G1645 (styrene ethylene butylene styrene block copolymer (SEBS) manufactured by Kraton, styrene content 13% by weight, hardness 35 shore/10 seconds), etc. Commercially available products of can be used.

The tackifier also serves to adjust the storage elastic modulus E′ and tan δ of the pressure-sensitive adhesive layer at 25° C. within the above range by blending with the base resin.
Examples of the tackifier include petroleum oils such as aliphatic copolymers, aromatic copolymers, aliphatic aromatic copolymers, alicyclic copolymers, alicyclic saturated hydrocarbon resins, and liquid aliphatic resins. Resins, coumarone-indene resins, terpene resins, terpene phenol resins, rosin resins such as polymerized rosins, (alkyl)phenol resins, xylene resins, and hydrogenated products thereof. Above all, when a hydrogenated terpene phenolic resin is used, it is possible to suppress adhesive residue when the protective film is peeled off. Moreover, you may use the tackifier marketed as a mixture with a polyolefin resin. These tackifiers may be used alone or in combination of two or more.
The tackifier preferably has a softening point of 80° C. or higher. By using a tackifier having a softening point of 80° C. or higher, when the surface protective film of the present invention is used as a wound body, it is possible to prevent the developing force at the time of unwinding the surface protective film from rising excessively. .. The softening point of the tackifier is more preferably 90 to 140°C.

The content of the tackifier is not particularly limited as long as the storage elastic modulus E′ and tan δ at 25° C. of the pressure-sensitive adhesive layer can be adjusted within the above range by using the tackifier in combination with the base resin. The preferred lower limit to parts is 10 parts by weight, the preferred upper limit is 80 parts by weight, the more preferred lower limit is 20 parts by weight, and the more preferred upper limit is 60 parts by weight.

The pressure-sensitive adhesive layer may contain additives such as a softening agent, an antioxidant, an anti-adhesive agent, and a release agent, if necessary, for the purpose of controlling the pressure-sensitive adhesive force.

The thickness of the pressure-sensitive adhesive layer is not particularly limited, but the preferred lower limit is 2 μm and the preferred upper limit is 30 μm. When the thickness of the pressure-sensitive adhesive layer is within this range, it is possible to achieve both sufficient adhesion to the adherend and handleability. The more preferable lower limit of the thickness of the pressure-sensitive adhesive layer is 2.5 μm, and the more preferable upper limit thereof is 20 μm.

The method for producing the surface protective film of the present invention is not particularly limited, and for example, another layer may be formed on the layer previously obtained by T-die molding or inflation molding by a known laminating method such as extrusion lamination and extrusion coating. A method of laminating, a method of laminating each layer independently as a film and then laminating each of the obtained films by dry lamination, and the like, but from the viewpoint of productivity, the above base material layer and the above adhesive layer Co-extrusion molding in which each material of (1) is supplied to a multilayer extruder for molding is preferable, and T-die molding is more preferable in terms of thickness accuracy.

FIG. 1 is a schematic view showing an example of a state in which the surface protective film of the present invention is attached to a prism sheet. In FIG. 1, the surface protective film 1 is attached to the prism layer 7 of the transparent film 6 and the prism layer 7 of the low repulsion prism sheet 4 having the mat layer 5 on the back surface. The surface protection film 1 has a base material layer 2 and an adhesive layer 3.

A prism sheet having a prism layer on the surface thereof and having a repulsive force of 1.0 mN or less when the surface on the prism layer side is displaced by 1 μm at 25° C.; and the present invention attached to the prism layer of the prism sheet. The prism sheet with a surface protection film for a prism sheet, which comprises the surface protection film for a prism sheet, is also one aspect of the present invention.

According to the present invention, a high adhesive force (initial adhesive force) can be exerted on a prism sheet having a repulsive force of 1.0 mN or less when the surface on the prism layer side is displaced by 1 μm at 25° C., and The surface protective film for a prism sheet, which does not easily adhere to the surface over time or under high temperature, and can be peeled without damaging the prism sheet or leaving an adhesive residue, and by attaching the surface protective film for the prism sheet. It is possible to provide a protected prism sheet with a surface protection film for a prism sheet.

It is a schematic diagram which shows an example of the state in which the surface protection film of this invention was affixed on the prism sheet.

Hereinafter, the embodiments of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Prism sheet>
The following four types of prism sheets were obtained, and the repulsive force when the surface of the prism sheet on the prism layer side was displaced by 1 μm at 25° C. was measured by the microindentation hardness test method. Specifically, using a micro indentation hardness tester (manufactured by Elionix, ultra-micro indentation hardness tester, model ENT-2100), according to JIS Z2255, a method of measuring curves of load and displacement The repulsive force was measured.

-Prism sheet 1: Pitch spacing of the unevenness of the prism layer is 50 μm, and repulsive force is 0.05 mN when the prism layer side surface is displaced by 1 μm at 25°C
-Prism sheet 2: The pitch spacing of the unevenness of the prism layer is 24 μm, and the repulsive force is 0.2 mN when the surface on the prism layer side is displaced by 1 μm at 25° C.
-Prism sheet 3: Pitch spacing of the irregularities of the prism layer is 50 μm, and the repulsive force is 1 mN when the prism layer side surface is displaced by 1 μm at 25° C.
-Prism sheet 4: The pitch interval of the unevenness of the prism layer is 24 μm, and the repulsive force is 4 mN when the surface of the prism layer side is displaced by 1 μm at 25° C.

<Base resin>
In the examples and comparative examples, the resins shown in Table 1 (resins 1 to 7) were used as the base resin.

<Tackifier>
・Tackifier 1 (trade name "Alcon P125", alicyclic saturated hydrocarbon resin, manufactured by Arakawa Chemical Industry Co., Ltd., softening point 125°C)
-Tackifier 2 (trade name "YS Polystar UH115", hydrogenated terpene phenol resin, Yasuhara Chemical Co., softening point 115°C)
-Tackifier 3 (trade name "Diana Process Oil PW380", (paraffin-based) liquid aliphatic resin, manufactured by Idemitsu Kosan Co., Ltd.)
<Antioxidant>
・Antioxidant (trade name "IRGANOX 1010", manufactured by BASF)

(Example 1)
100 parts by weight of resin 1 as a base resin, 40 parts by weight of tackifier 1 and 1 part by weight of antioxidant were mixed to obtain a pressure-sensitive adhesive composition for forming a pressure-sensitive adhesive layer.
A polyolefin resin (trade name "J715M", polypropylene resin, manufactured by Prime Polymer Co., Ltd.) is used as a raw material for the base material layer, and the pressure-sensitive adhesive composition obtained above is used as a raw material for the pressure-sensitive adhesive layer, and is co-extruded by a T-die method. Then, a surface protection film having a substrate layer of 35 μm and an adhesive layer of 5 μm was obtained.
About the adhesive layer of the obtained surface protection film, using a viscoelasticity spectrometer (DVA-200, manufactured by IT Measurement and Control Co., Ltd.), the dynamic viscosity was measured under the conditions of 10° C./min and 10 Hz in the constant temperature heating tension mode. The elastic spectrum was measured, and the storage elastic modulus E′ and tan δ at 25° C. were measured.

Using the prism sheet 1 as an adherend, a surface protection film having a width of 25 mm was attached so as to cover the prism layer, to prepare a test piece. The application was performed by using a 2 kg pressure-bonding rubber roller in an environment of 23° C. and a relative humidity of 50% RH and pressing at a speed of 300 mm/min.

(Examples 2-17, Comparative Examples 1-7, Reference Example 1)
As shown in Tables 2 to 4, a surface protective film was obtained in the same manner as in Example 1 except that the base resin, tackifier and antioxidant were changed. With respect to the pressure-sensitive adhesive layer of the obtained surface protection film, the storage elastic modulus E′ at 25° C. and tan δ were measured in the same manner as in Example 1.
Further, the prism sheets shown in Tables 2 to 4 were used, and a surface protection film having a width of 25 mm was attached so as to cover the prisms of the prism sheet in the same manner as in Example 1 to prepare a test piece.

<Evaluation>
The following evaluation was performed about the test piece obtained by the Example, the comparative example, and the reference example. The results are shown in Tables 2-4.

(1) Initial adhesive strength The obtained test piece was left for 30 minutes in an environment of 23° C. and relative humidity of 50% RH. After standing, the surface protective film was peeled off from the adherend in a 180° direction at a tension rate of 300 mm/min in accordance with JIS Z0237, and the initial adhesive strength was measured. Further, the initial adhesive strength was judged according to the following criteria.
⊚: 3.5 N/25 mm or more and 6.0 N/25 mm or less ○: 1.0 N/25 mm or more and less than 3.5 N/25 mm, or more than 6.0 N/25 mm and 8.0 N/25 mm or less x:1 Less than 0.0 N/25 mm or more than 8.0 N/25 mm

(2) Adhesion enhancement rate The obtained test piece was left for 168 hours in a temperature environment of 50°C. After standing, the test piece was taken out at room temperature and left for further 60 minutes, and then the surface protective film was peeled from the adherend in a 180° direction at a pulling speed of 300 mm/min according to JIS Z0237, and the adhesive strength with time was measured. did.
Using the obtained initial adhesive strength and adhesive strength over time, the rate of change from initial adhesive strength to adhesive strength over time (adhesion progress rate) was calculated by the following formula, and evaluated according to the following criteria.
In addition, in Comparative Examples 3 and 5, since floating occurred when left for 168 hours in a temperature environment of 50° C., the measurement of the adhesive strength with time was stopped.
Change rate (adhesion progress rate) (%) = (time-dependent adhesion/initial adhesion) x 100
◎: 300% or less ○: Over 300%, 400% or less ×: Over 400%

According to the present invention, a high adhesive force (initial adhesive force) can be exerted on a prism sheet having a repulsive force of 1.0 mN or less when the surface on the prism layer side is displaced by 1 μm at 25° C., and The surface protective film for a prism sheet, which does not easily adhere to the surface over time or under high temperature, and can be peeled without damaging the prism sheet or leaving an adhesive residue, and by attaching the surface protective film for the prism sheet. It is possible to provide a protected prism sheet with a surface protection film for a prism sheet.

1 Surface Protective Film 2 Base Layer 3 Adhesive Layer 4 Low Repulsion Prism Sheet 5 Mat Layer 6 Transparent Film 7 Prism Layer

Claims (2)

A prism sheet having a prism layer on the surface thereof and having a repulsive force of 1.0 mN or less when the surface on the prism layer side is displaced by 1 μm at 25° C. is attached to the prism layer to protect the prism sheet. A surface protection film for a prism sheet,
It has a base material layer and a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer has a storage elastic modulus E′ at 25° C. of 3.0 MPa or less, and a tan δ at 25° C. of 0.2 or more and 1.1 or less. A surface protection film for a prism sheet, which is characterized in that A prism sheet having a prism layer on the surface, wherein the prism sheet has a repulsive force of 1.0 mN or less when the surface on the prism layer side is displaced by 1 μm at 25° C., and is attached on the prism layer of the prism sheet. 1. A prism sheet with a surface protective film for a prism sheet, comprising the surface protective film for a prism sheet according to 1.

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