JP7485000B2 - Adhesive resin composition and laminated film made of same - Google Patents

Description

The present invention relates to an adhesive composition and a laminated film having an adhesive layer made of the same. In particular, the present invention relates to an adhesive composition having excellent adhesion to an adherend and excellent peelability, and a laminated film having an adhesive layer made of the same.
Background Art

Conventionally, protective films have been used to protect components such as prism sheets used in optical applications, and synthetic resin sheets, stainless steel sheets, aluminum sheets, decorative plywood, steel sheets, and glass sheets used in construction materials from scratches when they are stacked for storage, transported, or subjected to secondary processing such as bending and pressing. Protective films have also been used to protect home appliances, precision machinery, and automobile bodies from scratches when they are transported in the manufacturing process.
Such a protective film must have good adhesive properties and, after use, must be easily peelable without contaminating the surface of the adherend with the adhesive.

In recent years, the variety of adherends has increased, and many types of adherends are seen, ranging from those with smooth coated surfaces to those with surface irregularities.
The back surface of the prism sheet is smooth compared to the prism surface, which has large surface irregularities, but the back surface has fine irregularities, which not only diffuses the light from the backlight evenly, but also prevents interference due to close contact with other components and makes scratches and other appearance defects less noticeable.

Therefore, the back surface of the prism sheet is protected by a protective film when the prism sheets are stored in a stack or when they are transported.
However, as time passes after the protective film is attached to the adherend, the adhesive strength of the protective film increases (so-called adhesion increase), making it difficult to peel off. It is known that this problem becomes more pronounced when the product to which the surface protective film is attached is exposed to high temperatures during transportation, storage, etc. This problem is particularly likely to occur when the surface of the product (adherend) has an uneven shape.

Protective films used on adherends with fine surface irregularities are known that use an adhesive layer made of a polymer block mainly composed of aromatic alkenyl compound units, in which aromatic alkenyl compound units are continuous, and an aromatic alkenyl-conjugated diene copolymer block containing conjugated diene (butadiene) units and aromatic alkenyl compound units randomly, with a copolymer content of aromatic alkenyl compound units of 35 to 55 mass% (e.g., Patent Document 1). However, these films do not provide both adhesive strength and ease of peeling over time.

JP 2014-169347 A

The object of the present invention is to provide a film that has sufficient adhesive strength when applied to an adherend having fine surface irregularities, such as the back surface of a prism sheet, and that is not likely to increase in adhesive strength even when exposed to high temperatures during transportation and storage, and is easily peeled off from the adherend, so that no adhesive residue remains on the adherend even after the protective film is peeled off.

The present invention is an adhesive resin composition comprising a block copolymer and satisfying the following conditions (1), (2), (3), (4), and (5).
(1) The block copolymer is
It is a block copolymer containing the following polymer block A and the following polymer block B.
Polymer block A: A polymer block in which aromatic alkenyl compound units are continuous and mainly composed of aromatic alkenyl compound units. Polymer block B: An aromatic alkenyl-conjugated diene copolymer block containing conjugated diene units and aromatic alkenyl compound units randomly. (2) The content of aromatic alkenyl compound units in the block copolymer is 50 mass% or more.
(3) The content of polymer block A in the block copolymer is 15% by mass or more.
(4) The hydrogenation rate of the double bonds derived from the conjugated diene units in the polymer block B is 90 mol % or more.
(5) The mass average molecular weight (Mw) of the block copolymer is 180,000 or less.

In this case, it is preferable that the block copolymer comprises the following copolymer (I) and/or copolymer (II).
Copolymer (I): Containing the following polymer block A and polymer block B, and consisting of a hydrogenated product of a copolymer having a structure represented by the general formula [AB]n (wherein A represents polymer block A, B represents polymer block B, and n represents an integer of 1 to 3).
Copolymer (II): This comprises a hydrogenated copolymer containing the following polymer block A and the following polymer block B and having a structure represented by the general formula A-B-A (the symbols in the formula are as defined above).
Polymer block A: A polymer block in which aromatic alkenyl compound units are continuous and mainly composed of aromatic alkenyl compound units. Polymer block B: An aromatic alkenyl-conjugated diene copolymer block containing conjugated diene units and aromatic alkenyl compound units randomly.

In this case, the adhesive resin composition according to claim 1 or 2 has a content of the adhesive assistant in the adhesive resin composition of 1 to 50 mass %.

In this case, it is preferable that the adhesive aid is a hydrogenated terpene phenol resin. The adhesive resin composition according to claim 3.

Furthermore, in this case, it is preferable that the content of the organic lubricant in the adhesive resin composition is 0.1 to 2 mass %.

Furthermore, in this case, it is preferable that the organic lubricant is ethylene bisstearamide and/or calcium stearate.

Furthermore, in this case, a laminated film having a base layer mainly composed of a polypropylene resin and an adhesive layer made of the adhesive resin composition on one side of the base layer is preferable.

Furthermore, in this case, a laminated film having a base layer mainly composed of a polypropylene resin, an adhesive layer made of the adhesive resin composition on one side of the base layer, and a release layer on the opposite side of the adhesive layer is preferable.

Furthermore, in this case, the laminated film is suitable for use in protecting the back surface of the prism sheet.

When the adhesive resin composition of the present invention is applied to an adherend having fine surface irregularities, such as the back surface of a prism sheet, it has sufficient adhesive strength, and even when exposed to high temperatures during transportation and storage, the adhesive strength is not likely to increase, and it is easy to peel off from the adherend, so that no adhesive residue is left on the adherend even after the protective film is peeled off, and the composition can maintain its functionality.

(Block Copolymer)
The block copolymer in the present invention is a block copolymer containing the following polymer block A and the following polymer block B.
Polymer block A: A polymer block in which aromatic alkenyl compound units are continuous and mainly composed of aromatic alkenyl compound units. Polymer block B: An aromatic alkenyl-conjugated diene copolymer block containing conjugated diene units and aromatic alkenyl compound units randomly. Here, the term "randomly" is interpreted in a broad sense and means that the sequence distribution of the conjugated diene units and aromatic Group 4 alkenyl compound units follows a certain statistical law obtained by simultaneously polymerizing a mixture of a conjugated diene and an aromatic alkenyl compound.

The content of aromatic alkenyl compound units in the block copolymer (St(A+B)) must be 50% by mass or more. If the content of aromatic alkenyl compound units is less than 50% by mass, the initial adhesive strength may be too strong or the adhesive strength may be easily increased. On the other hand, the content of aromatic alkenyl compound units is preferably 80% by mass or less. If it exceeds 80% by mass, the initial adhesive strength may not be observed. More preferably, it is 55% by mass or more, and even more preferably, it is 60% by mass or more.

The content of the aromatic alkenyl compound unit in the block copolymer (St(A+B)) is a numerical value defined by the following formula.
The aromatic alkenyl compound unit content is determined by 1H-NMR. The aromatic alkenyl compound unit content can also be determined by infrared spectroscopy, which gives values almost equivalent to those obtained by 1H-NMR.

St(A+B)=
[(mass of units derived from aromatic alkenyl compound monomer units in the block copolymer)/(mass of all units derived from monomers in the block copolymer)]×100 (% by weight)

The content of polymer block A in the block copolymer must be 15% by mass or more. If the content of polymer block A is less than 25% by mass, the initial adhesive strength may be too strong, causing adhesive residue or the adhesive strength may be easily increased. It is more preferably 30% by mass or more.
On the other hand, the content of the polymer block A is preferably 50% by mass or less. If it exceeds 50% by mass, the initial adhesive strength may not be observed. It is more preferably 45% by mass or less, and even more preferably 40% by mass or less.

The hydrogenated product of block copolymer B in the present invention has excellent heat resistance and weather resistance, so it is preferable that 90% or more, preferably 95% or more, and more preferably 98% or more of the double bonds derived from the conjugated diene monomer units are hydrogenated to convert unsaturated bonds into saturated bonds. If it is less than 90%, not only will adhesion to an adherend having fine irregularities not be obtained, but heat resistance and weather resistance will be of concern.

The weight-average molecular weight of the block copolymer is preferably 30,000 to 180,000. If the weight-average molecular weight is less than 30,000, the polymer may adhere to manufacturing equipment during the process of desolvating and drying the polymer, making industrial production difficult. On the other hand, if the weight-average molecular weight exceeds 180,000, not only will adhesion to adherends having fine surface irregularities not be obtained, but solubility in solvents and heat melting properties will be poor, and industrial processing into pellets or film production by melt coextrusion may also be difficult. More preferably, it is 60,000 to 180,000, even more preferably 100,000 to 180,000, and particularly preferably 150,000 to 180,000.

The melt flow rate (MFR) value of the block copolymer is preferably in the range of 0.1 to 20 g/min, more preferably 1 to 15 g/min. By setting the melt flow rate value in the range of 0.1 to 20 g/min, not only can the industrial production of the aromatic vinyl block copolymer be facilitated, but also excellent processability can be provided during film formation. If the melt flow rate value is less than 0.1 g/min, the solubility in the solvent during polymerization is poor, the thermal melting property is reduced, and it may be difficult to remove the polymer from the production equipment. This difficulty is a problem that may reoccur during film formation.
On the other hand, if the melt flow rate is more than 20 g/min, the polymer adheres to and remains inside the production equipment during the process of removing the solvent from the polymer and drying it, making it difficult to remove the polymer. This difficulty can also reoccur during film production.

The block copolymer of the present invention preferably comprises the following copolymer (I) and/or copolymer (II).
Copolymer (I): Contains the following polymer block A and the following polymer block B, and has the general formula [AB]
n (wherein A represents polymer block A, B represents polymer block B, and n represents an integer of 1 to 3).
The copolymer is a hydrogenated product having a structure represented by the formula:
Copolymer (II): This comprises a hydrogenated copolymer containing the following polymer block A and the following polymer block B and having a structure represented by the general formula A-B-A (the symbols in the formula are as defined above).
Polymer block A: A polymer block in which aromatic alkenyl compound units are continuous and mainly composed of aromatic alkenyl compound units. Polymer block B: An aromatic alkenyl-conjugated diene copolymer block containing conjugated diene units and aromatic alkenyl compound units randomly.

(Polymer Block A)
The polymer block A in the present invention is a polymer block in which aromatic alkenyl compound units are continuous and mainly composed of aromatic alkenyl compound units. The aromatic alkenyl compound units are not particularly limited, but examples thereof include aromatic vinyl monomer units such as styrene, tert-butylstyrene, α-methylstyrene, p-methylstyrene, p-ethylstyrene, divinylbenzene, 1,1-diphenylethylene, vinylnaphthalene, vinylanthracene, N,N-dimethyl-p-aminoethylstyrene, N,N-diethyl-p-aminoethylstyrene, and vinylpyridine. Among these, the "aromatic vinyl monomer unit" is preferably a styrene unit.
Examples of the repeating units other than the aromatic alkenyl monomer units include repeating units derived from compounds copolymerizable with the aromatic alkenyl monomer units, such as repeating units derived from conjugated diene compounds and (meth)acrylic acid ester compounds. Among these, 1,3-butadiene and isoprene are preferred because of their high copolymerizability with the aromatic alkenyl monomer units.
The polymer block A must be composed of aromatic alkenyl monomer units as the main repeating units. Specifically, the content of the aromatic alkenyl monomer units is preferably 80% by mass or more, more preferably 90% by mass or more. By setting the content of the aromatic alkenyl monomer units within this range, the adhesive strength, the ability to follow the unevenness of the adherend surface, and the ability to be unwound from a roll can be further improved.

(Polymer Block B)
The polymer block B in the present invention is an aromatic alkenyl-conjugated diene copolymer block containing conjugated diene units and aromatic alkenyl compound units randomly. By containing units derived from conjugated diene units and units derived from aromatic alkenyl compound units randomly, even if a protective film using the pressure-sensitive adhesive resin composition of the present invention is attached to an adherend having fine surface irregularities and then exposed to high temperatures during transportation and storage, adhesion is unlikely to increase.
The conjugated diene monomer unit constituting the polymer block B in the present invention is a repeating unit derived from a conjugated diene monomer. The conjugated diene monomer unit is not particularly limited, but examples thereof include 1,3-butadiene, 1,2-butadiene, isoprene, 2,3-dimethyl-butadiene, 1,3-pentadiene, 2-methyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 1,3-cyclohexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, myrcene, and chloroprene. Among them, at least one repeating unit selected from 1,3-butadiene unit or isoprene unit, which has high polymerization reactivity and excellent adhesion and weather resistance, is preferable. Furthermore, in order to obtain high mechanical strength, it is more preferable to select 1,3-butadiene unit.
In addition, the polymer block B is preferably an aromatic vinyl-conjugated diene copolymer block containing conjugated diene monomer units and aromatic vinyl monomer units randomly.

The hydrogenated product of block copolymer B in the present invention has excellent heat resistance and weather resistance, so it is preferable that 90% or more, preferably 95% or more, and more preferably 98% or more of the double bonds derived from the conjugated diene monomer units are hydrogenated to convert unsaturated bonds into saturated bonds. If it is less than 90%, not only will adhesion to an adherend having fine irregularities not be obtained, but heat resistance and weather resistance will be of concern.

(Adhesive resin composition)
The adhesive resin composition of the present invention is characterized by containing a block copolymer that satisfies the following conditions (1), (2), (3), (4), and (5).
(1) The block copolymer is a block copolymer containing the following polymer block A and the following polymer block B.
Polymer block A: A polymer block in which aromatic alkenyl compound units are continuous and mainly composed of aromatic alkenyl compound units. Polymer block B: An aromatic alkenyl-conjugated diene copolymer block containing conjugated diene (butadiene) units and aromatic alkenyl compound units randomly. (2) The content of aromatic alkenyl compound units in the block copolymer is 50 mass% or more.
(3) The content of polymer block A in the block copolymer is 25% by mass or more.
(4) The hydrogenation rate of the double bonds derived from the conjugated diene units in the polymer block B is 90 mol % or more.
(5) The mass average molecular weight (Mw) of the block copolymer is 180,000 or less.

In addition to the block copolymer, the adhesive resin composition of the present invention may contain, as necessary, known additives such as adhesive assistants, organic lubricants, antioxidants, light stabilizers, UV absorbers, fillers, pigments, styrene-based block phase reinforcing agents, softeners, adhesion promoter inhibitors, olefin-based resins, silicone-based resins, liquid acrylic copolymers, and phosphate ester-based compounds.

(Adhesive aid)
In the present invention, an adhesive aid can be added for the purpose of increasing the adhesive strength of the adhesive resin composition. Examples of the adhesive aid include petroleum-based resins such as aliphatic copolymers, aromatic copolymers, aliphatic-aromatic copolymers, and alicyclic copolymers; coumarone-indene resins; terpene resins; terpene phenol resins; rosin-based resins such as polymerized rosin; phenolic resins; xylene resins, and the like. Hydrogenated versions of these resins and other materials generally used in adhesives can be used without particular limitation.
The adhesive aid preferably has a glass transition temperature of 30°C or higher. If the adhesive has a glass transition temperature of less than 30°C, it may bleed out at room temperature and may be difficult to handle. The adhesive aid preferably has a glass transition temperature of 65°C or higher, taking into account the high temperature acceleration. Among the adhesive aids, terpene phenol resins are preferred, and hydrogenated terpene phenols are particularly preferred. If the adhesive aid has a phenol group, it is expected that the electrical affinity with the adherend will act, and the adhesive strength will be more independent of temperature. In addition, hydrogenation can reduce the concern of discoloration due to high temperatures or over time.
The adhesive aid may be used alone or in combination of two or more kinds. When the adhesive aid is a hydrogenated resin, the peelability and weather resistance are further improved. The adhesive aid in the adhesive layer is preferably a hydrogenated resin.

The content of the adhesive aid in the adhesive resin composition is preferably 1 to 50% by mass. The adhesive aid is expected to improve the adhesive strength and acceleration due to the effect of plasticizing the adhesive resin composition and the effect of inhibiting the molecular movement of the adhesive. If the content of the adhesive aid exceeds 50% by mass, the compatibility with the adhesive resin composition becomes poor, and a decrease in the initial adhesive strength may be observed. More preferably, it is 40% by mass or less, and even more preferably, it is 30% by mass or less.

(Organic Lubricant)
Considering excessive bleeding at room temperature or high temperature, the organic lubricant used in the present invention is preferably a saturated fatty acid bisamide or a fatty acid metal salt.Specific examples include ethylene bisstearic acid bisamide and a metal salt of stearate.These may be used alone or in combination of two or more.

The content of the organic lubricant in the adhesive resin composition is preferably 0.1 to 2 mass %. The organic lubricant is expected to have the effect of suppressing the increase in adhesive strength. However, if the organic lubricant exceeds 2 mass % relative to the adhesive resin composition, there is a concern that the organic lubricant will bleed out significantly at high temperatures or over time, contaminating the adherend. In view of the bleed-out at high temperatures or over time, the organic lubricant used in the present invention is preferably one with a high melting point, and specific examples include ethylene bis stearamide and calcium stearate.

(Antioxidant)
The antioxidant used in the present invention is not particularly limited, and examples thereof include commonly used antioxidants such as phenol-based (monophenol-based, bisphenol-based, polymeric phenol-based), sulfur-based, and phosphorus-based.

(Light stabilizer)
The light stabilizer used in the present invention includes a hindered amine compound.

(Ultraviolet absorber)
The ultraviolet absorbing agent used in the present invention is not particularly limited, and examples thereof include salicylic acid-based, benzophenone-based, benzotriazole-based, and cyanoacrylate-based agents.

(Softener)
In the present invention, a softener can be added to reduce the hardness of the adhesive resin composition. The softener is also effective in improving the adhesive strength. As the softener, for example, low molecular weight diene polymer, polyisobutylene, hydrogenated polyisobutylene, hydrogenated polybutadiene, paraffinic process oil, naphthenic process oil, aromatic process oil, castor oil, tall oil, natural oil, liquid polyisobutylene resin, polybutene, or hydrogenated products thereof, which are generally used in adhesives, can be used without any particular limitation. These softeners may be used alone or in combination of two or more kinds.

(filler)
Examples of the filler include calcium carbonate, magnesium carbonate, silica, zinc oxide, and titanium oxide.

(Laminated film)
The laminated film according to the present invention can be obtained by laminating an adhesive layer made of the adhesive resin composition on a substrate layer. The substrate layer may further have a release layer on the side opposite to the adhesive layer.
This will be explained in detail below.

(Adhesive Layer)
The pressure-sensitive adhesive layer in the present invention is made of the above-mentioned pressure-sensitive adhesive composition and has a thickness of usually about 1 to 30 μm, preferably 2 to 10 μm.

The initial adhesive strength of the laminated film of the present invention is preferably 2 cN/25 mm or more and 20 cN/25 mm or less. If it is 2 cN/25 mm or more, it will not peel off or float during handling or transportation, and if it is 20 cN/25 mm or less, excessive force is not required when peeling it off. More preferably, it is 3 cN/25 mm or more and 15 cN/25 mm or less. Even more preferably, it is 3 cN/25 mm or more and 10 cN/25 mm or less. Particularly preferably, it is 3 cN/25 mm or more and 8 cN/25 mm or less.
The initial adhesion was measured as follows.
A linear pressure of 15 kN/m was applied from the side opposite to the adhesive layer of the laminated film at a speed of 2 m/min in an environment of 23±2° C. and 50±5% R.H. so that the surface of the adhesive layer of the laminated film was in contact with the back surface of the prism sheet.
The obtained test piece was left for 30 minutes in a room at 23±2° C. and a relative humidity of 50±5% R.H., and then the 180° peel strength (unit: cN) at a width of 25 mm was measured at a peel speed of 300 mm/min in accordance with JIS Z0237, and this was taken as the initial adhesive strength.

The adhesive strength over time of the laminated film of the present invention is preferably 2cN/25mm or more and 80cN/25mm or less. If it is 2cN/25mm or more, it will not peel off or float during handling or transportation, and if it is 80cN/25mm or less, excessive force is not required when peeling it off. More preferably, it is 3cN/25mm or more and 70cN/25mm or less. Even more preferably, it is 3cN/25mm or more and 60cN/25mm or less. Particularly preferably, it is 3cN/25mm or more and 45cN/25mm or less.
The adhesion over time was measured as follows.
Test pieces were prepared under the same conditions as the prism sheets used to measure the adhesive strength over time. After leaving them for one week in an atmosphere of 65°C ± 2°C and a load of 6 kg/400 cm2, the 180° peel strength at a width of 25 mm was measured at a peel speed of 300 mm/min in accordance with JIS Z0237, and this was taken as the adhesive strength over time.

The adhesion enhancement rate of the laminated film of the present invention is preferably 1000% or less. When the adhesion enhancement rate is 1000% or less, the working conditions when peeling the film from the adherend become more constant, and the working efficiency is improved. More preferably, it is 800% or less, even more preferably 600% or less, and particularly preferably 500% or less.
The adhesion increase rate was calculated using the initial adhesion and the adhesion over time using the following formula.
Adhesion increase rate = (adhesion strength over time / initial adhesion strength) x 100 (%)

In the present invention, the peel strength between the surface of the adhesive layer and the surface of the opposite side of the adhesive layer is preferably in the range of 200 cN/25 mm or less at 23° C. from the viewpoint of the unwinding property of the film when the laminated film is in a roll form. If the peel strength exceeds 200 cN/25 mm, problems such as partial stretching and deformation of the film will occur when the laminated film is unwound in a roll form. The lower limit of the peel strength between the surface of the adhesive layer and the surface of the opposite side of the adhesive layer of the laminated film is a practical value of about 1 cN/25 mm, or even about 5 cN/25 mm. More preferably, it is 2 to 100 cN/25 mm, and even more preferably, it is 3 to 50 cN/25 mm.

(Base layer)
The substrate layer in the present invention can be formed of a polyolefin resin. The polyolefin resin is a polymer using an olefin monomer such as ethylene, propylene, or α-olefin, and refers to a polyolefin resin in which the proportion of the olefin monomer in the total monomers constituting the polyolefin resin is 70 mol % or more. Examples of the polyolefin resin contained in the substrate include polyethylene resins such as ethylene homopolymer, ethylene-α-olefin copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid ester copolymer, and ethylene-vinyl acetate copolymer; polypropylene resins such as propylene homopolymer, propylene-α-olefin copolymer, and propylene-ethylene copolymer; butene homopolymer; homopolymers or copolymers of conjugated dienes such as butadiene and isoprene, and the like. Examples of the polyethylene resin include high density polyethylene, medium density polyethylene, and low density polyethylene. The form of copolymerization may be random, block, or ternary copolymer.
The polyolefin resins may be used alone or in combination of two or more kinds.

The polyethylene resin is obtained by using ethylene as a main component. Of the total structural units of the polyethylene resin (100% by mass), the proportion of structural units derived from ethylene is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more.

The polypropylene resin is obtained by using propylene as the main component. The proportion of structural units derived from propylene in 100% by mass of all structural units of the polypropylene resin is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. It is preferable that the base layer of the present invention is mainly made of a polypropylene resin in terms of heat resistance, weather resistance, and adhesion to the adhesive layer.

The thickness of the substrate layer in the present invention is preferably 10 μm or more, and more preferably 100 μm or less. When the thickness of the substrate is 10 μm or more and 100 μm or less, the handleability of the laminated film is further improved.

When the laminated film of the present invention consists only of a base layer and an adhesive layer made of the adhesive composition, it is preferable to impart surface irregularities in order to reduce the peel force between the surface of the base layer and the surface of the adhesive layer, thereby reducing the contact area with the adhesive layer.
In this case, in consideration of the resin composition of the adhesive layer of the present invention, the average surface roughness SRa of the surface of the release layer is preferably 0.40 μm or more, more preferably 0.850 μm or less in terms of average surface roughness SRa, and particularly preferably 0.500 μm or more and 0.700 μm or less.
By setting the average surface roughness SRa of the surface of the adhesive layer of the base layer and the surface of the opposite side of the adhesive layer to 0.40 μm or more, the protective performance and peeling force of the adherend can be improved. If the surface roughness of the release layer is lower than 0.40 μm, the film will not be easily unwound when rolled. If the surface roughness of the base layer is higher than 0.850 μm, the surface irregularities of the base layer may be transferred to the surface of the adhesive layer, resulting in a significant decrease in adhesive force.

In order to make the average surface roughness SRa 0.40 μm or more, it is possible to add a resin incompatible with homopropylene or random polypropylene, or to suitably use a propylene-ethylene block copolymer as the resin used for the base layer. When a propylene-ethylene block copolymer is used, the unevenness is less likely to change due to changes in the production machine or the melt-kneading conditions during film formation, enabling stable production.
The average surface roughness SRa can be increased by increasing the molecular weight of the ethylene-propylene rubber in the propylene-ethylene block copolymer or by increasing the amount of ethylene. Also, the average surface roughness SRa can be increased by mixing an incompatible resin into the propylene-ethylene block copolymer.
In addition, in the extrusion step described below, the average surface roughness SRa can also be increased by lowering the shear rate applied to the resin or lengthening the residence time.
On the other hand, in order to reduce the average surface roughness SRa, it is effective to mix a homopolypropylene resin with the propylene-ethylene block copolymer.

As the resin incompatible with the propylene-ethylene block copolymer, a 4-methylpentene-1 polymer or a 4-methyl-1-pentene/α-olefin copolymer can be suitably used. The α-olefin is not particularly limited as long as it is copolymerizable with ethylene, propylene, and 4-methyl-1-pentene, and examples thereof include ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-pentene, and 1-heptene.
Other examples include low-density polyethylene, high-density polyethylene, copolymers of ethylene and a small amount of α-olefin, copolymers of ethylene and vinyl acetate, polystyrene, alicyclic olefin resins, polyester resins, polyamide resins, etc. In particular, 4-methylpentene-1 polymers or 4-methyl-1-pentene/α-olefin copolymers are preferred because they not only roughen the surface to a matte state, but also reduce the surface free energy of the film surface, which is expected to further reduce the peel force.

The amount of 4-methylpentene-1 polymer or 4-methyl-1-pentene/α-olefin copolymer having 4 or more carbon atoms in the base layer (resin component constituting the base layer) is in the range of 0% to 35% by mass. If the amount of α-olefin (co)polymer having 4 or more carbon atoms exceeds 35% by mass, the film formability of the base layer will be poor when attempting to laminate the raw materials of the base layer and the adhesive layer by co-extruding using a T-die or the like.

(Release Layer)
The release layer in the present invention is provided on the substrate layer on the opposite side to the adhesive layer, whereby the functions are distributed between the substrate layer and the release layer, making it possible to accommodate a wider range of uses.

In this case, it is preferable to impart surface irregularities to reduce the peeling force between the surface of the release layer and the surface of the adhesive layer, thereby reducing the contact area with the adhesive layer.
In consideration of the resin composition of the adhesive layer of the present invention, the average surface roughness SRa of the surface of the release layer is preferably 0.40 μm or more. It is more preferable that the average surface roughness of the surface is 0.850 μm or less in terms of SRa, and particularly preferably 0.500 μm or more and 0.700 μm or less.

By making the average surface roughness SRa of the release layer 0.40 μm or more, the protective performance and peeling force of the adherend can be improved. If the surface roughness of the release layer is less than 0.40 μm, the film will not be easily unwound when rolled. If the surface roughness of the release layer is more than 0.850 μm, the surface irregularities of the release layer may be transferred to the surface of the adhesive layer, resulting in a significant decrease in adhesive force.

In order to make the average surface roughness SRa 0.40 μm or more, a resin incompatible with homopropylene or random polypropylene can be added as the resin used for the release layer, or a propylene-ethylene block copolymer can be suitably used. When a propylene-ethylene block copolymer is used, the uneven state is unlikely to change due to changes in the production machine or the melt-kneading conditions during film formation, and stable production is possible.
The average surface roughness SRa can be increased by increasing the molecular weight of the ethylene-propylene rubber in the propylene-ethylene block copolymer or by increasing the amount of ethylene. Also, the average surface roughness SRa can be increased by mixing an incompatible resin into the propylene-ethylene block copolymer.
In addition, in the extrusion step described below, the average surface roughness SRa can also be increased by lowering the shear rate applied to the resin or lengthening the residence time.
On the other hand, in order to reduce the average surface roughness SRa, it is effective to mix a homopolypropylene resin with the propylene-ethylene block copolymer.

As resins that are incompatible with propylene-ethylene block copolymers, α-olefin (co)polymers with 4 or more carbon atoms, such as 4-methylpentene-1 (co)polymers, can be suitably used. Other examples include low-density polyethylene, high-density polyethylene, copolymers of ethylene and a small amount of α-olefin, copolymers of ethylene and vinyl acetate, polystyrene, polyester resins, and polyamide resins. 4-methylpentene-1 (co)polymers are particularly preferred, as they not only roughen the surface to a matte shape, but also reduce the surface free energy of the film surface, which is expected to further reduce the peel force.

The blending amount of the α-olefin (co)polymer having 4 or more carbon atoms in the release layer (resin component constituting the release layer) is in the range of 0% by mass to 35% by mass. If the blending amount of the α-olefin (co)polymer having 4 or more carbon atoms exceeds 35% by mass, the film formability of the base layer is deteriorated when the base layer and the adhesive layer are laminated by coextrusion.
The thickness of the release layer is not particularly limited. The thickness of the release layer is preferably 2 μm or more and preferably 10 μm or less. When the thickness of the release layer is 2 μm or more and 10 μm or less, the handleability of the laminated film is further improved.

Methods for producing the laminated film of the present invention include, for example, a method in which the adhesive composition and the polyolefin resin for the base layer, and, if necessary, the polyolefin resin for the release layer are charged into separate extruders, melted, and co-extruded from a T-die to laminate, a method in which other layers are laminated onto a layer obtained by inflation molding by a lamination method such as extrusion lamination or extrusion coating, and a method in which each layer is made into an independent film and then each obtained film is laminated by dry lamination. From the viewpoint of productivity, however, co-extrusion molding in which the materials for the release layer, the base layer, and the adhesive layer are each fed into a multi-layer extruder and molded is preferred, and T-die molding is more preferred from the viewpoint of thickness accuracy.

The surface protection film of the present invention is used to protect the surface of an adherend that has a smooth surface or fine irregularities, and is particularly effective when the surface roughness is about 0.1 to 0.3 μm.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.
The measurement method is shown below.

(1) Initial adhesive strength The surface protection film obtained above was attached so that the adhesive layer surface was in contact with the back surface of the prism sheet to prepare a test piece. The surface protection film was attached at a speed of 2 m/min under an environment of 23±2°C and 50±5% RH, with a linear pressure of 15 kN/m applied from the outside of the surface protection film (i.e., the side opposite to the adhesive layer surface). The following laminator was used for the attachment.
Laminator manufacturer: Tester Sangyo Co., Ltd.
Model: SA-1010-S
Roll: Heat-resistant silicon rubber roll Roll diameter: Φ200
The obtained test piece was left for 30 minutes in a room at 23±2° C. and a relative humidity of 50±5% R.H., and then the 180° peel strength (unit: cN) at a width of 25 mm was measured at a peel speed of 300 mm/min in accordance with JIS Z0237, and this was taken as the initial adhesive strength.

(2) Adhesion strength over time The obtained surface protection film was attached under the same conditions as the prism sheet used in the evaluation of the initial adhesion strength in (1), and left for one week in an atmosphere of 65°C ± 2°C and a load of 6 kg/ ⁴⁰⁰ cm2. After that, the 180 degree peel strength at a width of 25 mm was measured at a peel speed of 300 mm/min in accordance with JIS Z0237, and this was taken as the adhesion strength over time.

(3) Adhesion Increase Rate Using the initial adhesive strength and the adhesive strength over time obtained in (1) and (2) above, the rate of change from the initial adhesive strength to the adhesive strength over time (adhesion increase rate) was calculated using the following formula.
Rate of change (rate of adhesive increase) = (adhesive strength over time/initial adhesive strength) x 100

(4) Peeling Force The obtained surface protection film was stacked on top of the other film so that the adhesive layer of one film faces the release layer of the other film, and a test piece was cut out to a size of 110 mm (the winding direction when the film was manufactured) x 40 mm (the direction perpendicular to the winding direction when the film was manufactured), which was sandwiched between copy paper from above and below, a weight of 60 kg was placed on top of it, and the test piece was left standing for 72 hours in a room at a temperature of 40°C. Thereafter, the test piece was left standing for 1 hour in a room at 23±2°C and a relative humidity of 50±5% R.H., and (
The resistance value when peeling at 180 degrees at a speed of 300 mm/min using an Autograph (registered trademark) (AGS-J) manufactured by Shimadzu Corporation was recorded as the peel force [cN/25 mm].
A polyester sheet with a thickness of 190 μm and a size of 40 mm×170 mm was prepared as a gripping margin for the measurement sample, and attached to the edge of a 110 mm×40 mm test piece with cellophane tape with a width of 15 mm to serve as a gripping margin for the measurement. Measurements were performed three times for each sample, and the average value was regarded as the peel strength of the sample.

(5) Surface Roughness The surface roughness of the opposite side of the adhesive layer of the obtained laminated film was evaluated using a three-dimensional roughness meter (manufactured by Kosaka Laboratory, model number ET-30HK) with a stylus pressure of 20 mg, a measurement length in the X direction of 1 mm, a feed speed of 100 μm/sec, a feed pitch in the Y direction of 2 μm, 99 recorded lines, a height direction magnification of 20,000 times, and a cutoff of 80 μm. The surface roughness was calculated in accordance with the definition of arithmetic average roughness described in JIS B 0601 (1994).
The arithmetic mean roughness (SRa) was evaluated by carrying out three trials each and averaging the results.

(6) Content of Aromatic Alkenyl Compound Unit in Block Copolymer Each raw material resin and mixed resin sample was dissolved in CDCl3, and 1H-NMR was measured under the following conditions.
Equipment: Fourier transform nuclear magnetic resonance equipment (AVANCE 500 manufactured by Bruker Biospin)
Measurement solution: 10 to 30 mg of sample was dissolved in 0.6 ml of deuterated chloroform, to which 5 to 10 vol % of trifluoroacetic acid was added.
1H resonance frequency: 500.13 MHz
Detection pulse flip angle: 45°
Data acquisition time: 4.0 seconds Delay time: 1.0 seconds Number of integrations: 20 to 100 Measurement temperature: 25 to 40°C

(7) Content of Polymer Block A in Block Copolymer The spectrum of homopolystyrene was compared with the infrared spectrum of each raw resin and mixed resin sample to calculate the content of polymer block A.

(8) Weight average molecular weight Each raw material resin and mixed resin sample was dissolved in tetrahydrofuran (sample concentration: 0.05% by mass). The solution was filtered through a 0.20 μm membrane filter, and the obtained sample solution was subjected to GPC analysis under the following conditions. The molecular weight was calculated in terms of standard polystyrene.
GPC device conditions: Device: High-performance liquid chromatograph HLC-8220 (TOSOH)
Column: TSKgel SuperHZM-H + SuperHZM-H + SuperHZ2000 (TOSOH)
Solvent: THF (tetrahydrofuran)
Flow rate: 0.35 mL / min
Injection volume: 10 μL
Temperature: 40°C
Detector: RI
Data processing: GPC data processing system (TOSOH)

The raw material resins used in the following examples and comparative examples are shown below.

1) S1605: Product name "S1605", hydrogenated styrene-butadiene copolymer, manufactured by Asahi Kasei Corporation, MFR = 3.5 g/10 min, hydrogenation rate of double bonds derived from conjugated diene units of polymer block B = 100%, weight average molecular weight = 180,700, density = 1.00 g/cc, content of aromatic alkenyl compound units = 66 mass%, content of polymer block A = 31 mass%, mixture of copolymers of structural formula A-B-A and structural formula A-B.

2) L613: Product name "L613", hydrogenated styrene-butadiene copolymer, manufactured by Asahi Kasei Corporation, MFR = 5.0 g/10 min, hydrogenation rate of double bonds derived from conjugated diene units of polymer block B = 100%, weight average molecular weight = 138,200, density = 1.00 g/cc, content of aromatic alkenyl compound units = 32 mass%, content of polymer block A = 35 mass%, mixture of copolymers of structural formula A-B-A and structural formula A-B.

3) S1606: Product name "S1606", hydrogenated styrene-butadiene copolymer, manufactured by Asahi Kasei Corporation, MFR = 4.0, hydrogenation rate of double bonds derived from conjugated diene units of polymer block B = 100%, weight average molecular weight = 169,900, density = 0.96 g/cc, content of aromatic alkenyl compound units = 50 mass%, content of polymer block A = 25 mass%, copolymer of structural formula A-B-A.

4) H1221: Product name "H1221", hydrogenated styrene-butadiene copolymer, manufactured by Asahi Kasei Corporation, MFR = 4.5/10 min, hydrogenation rate of double bonds derived from conjugated diene units in polymer block B = 100%, weight average molecular weight = 147,600, density = 0.89 g/cc, content of aromatic alkenyl compound units = 12 mass%, content of polymer block A = 12 mass%, copolymer without polymer block B.

5) UH115: Product name "UH115", hydrogenated terpene phenol resin, manufactured by Yasuhara Chemical Co., Ltd., glass transition temperature = 65°C

6) TH130: Product name "TH130", terpene phenol resin, manufactured by Yasuhara Chemical Co., Ltd., glass transition temperature = 80℃

7) EB-P (Product name "EB-P", ethylene bisstearic acid amide, manufactured by Kao Corporation)

(Comparative Example 4)
The adhesive composition was composed of 100 parts by weight of S1606, a polyolefin resin (product name "WF836DG3", propylene-ethylene random copolymer, manufactured by Prime Polymer Co., Ltd., MFR = 4.5/10 min, melting point = 164 ° C, ethylene copolymerization amount = 0.3 mass%) as a raw material for the base layer, and a polyolefin resin (product name "BC3HF", polypropylene-ethylene block copolymer, manufactured by Prime Polymer Co., Ltd., melting point = 171 ° C, ethylene content = 9 mass%) as a raw material for the release layer. The adhesive layer resin was extruded at a discharge rate of 6 kg/h using a 40 mmφ single screw extruder, the base material layer resin was extruded at a discharge rate of 30 kg/h using a 90 mmφ single screw extruder, and the release layer resin was extruded at a discharge rate of 4 kg/h using a 60 mmφ single screw extruder, using a three-layer T die (lip width 850 mm, lip gap 1 mm), and cooled with a cooling roll to obtain a laminated film with a thickness of 6 μm, 30 μm, and 4 μm for the adhesive layer, base material layer, and release layer, and a width direction length of 650 mm. The results are shown in Table 1.

(Comparative Examples 5 to 7, Examples 5 to 7, Comparative Example 8, Comparative Examples 1 to 3)
A laminated film was obtained in the same manner as in Comparative Example 4 , except that the raw material resin and additive contents of the adhesive layer, and further the thickness and contents of the adhesive layer were changed as shown in Table 1. The results are shown in Table 1.

When the laminated films of Examples 5 to 7 were attached to the back surface of a prism sheet, they had sufficient adhesive strength to the back surface, and the adhesive strength did not increase even after one week under high humidity, and there was also little blocking with the release layer.
In contrast, the laminated films of Comparative Examples 1 and 2 had too strong adhesion to the back surface and were difficult to peel off from the back surface.

The laminated film of Comparative Example 3 had a high adhesion to the back surface after one week in high humidity conditions, and was difficult to peel off from the back surface.

The pressure-sensitive adhesive composition of the present invention and the surface protection film of the present invention are suitable for use in protecting the surfaces of prism sheets and the like, particularly their back surfaces, and are therefore industrially useful.

Claims (7)

A laminated film having a base layer mainly composed of a polypropylene-based resin, and an adhesive layer on one side of the base layer, the adhesive layer being made of an adhesive resin composition containing 90 % by mass or more of a block copolymer and satisfying the following conditions (1), (2), (3), (4), (5), and (6):
(1) The block copolymer comprises the following copolymer (I) and copolymer (II):
Copolymer (I): Containing the following polymer block A and polymer block B, and consisting of a hydrogenated product of a copolymer having a structure represented by the general formula [AB]n (wherein A represents polymer block A, B represents polymer block B, and n represents an integer of 1 to 3).
Copolymer (II): This comprises a hydrogenated copolymer containing the following polymer block A and the following polymer block B and having a structure represented by the general formula A-B-A (the symbols in the formula are as defined above).
Polymer block A: a polymer block in which aromatic alkenyl compound units are continuous and the content of the aromatic alkenyl compound units is 80 mass% or more. Polymer block B: an aromatic alkenyl-conjugated diene copolymer block containing conjugated diene units and aromatic alkenyl compound units randomly. (2) The content of the aromatic alkenyl compound units in the block copolymer is 55 mass% or more and 61 mass% or less.
(3) The content of polymer block A in the block copolymer is 25% by mass or more.
(4) The hydrogenation rate of the double bonds derived from the conjugated diene units in the polymer block B is 90 mol % or more.
(5) The mass average molecular weight (Mw) of the block copolymer mixture is 180,000 or less.
(6) Contains terpene phenolic resin and/or organic lubricant. The laminated film according to claim 1, wherein the content of the terpene phenol resin in the adhesive resin composition is 1 to 50 mass %. The laminated film according to claim 2, wherein the terpene phenol resin is a hydrogenated terpene phenol resin. The laminated film according to any one of claims 1 to 3, wherein the content ratio of the organic lubricant in the adhesive resin composition is 0.1 to 2 mass%. The laminated film according to any one of claims 4, wherein the organic lubricant is ethylene bisstearic acid amide and/or calcium stearate. The laminated film according to any one of claims 1 to 5, which has a release layer on the opposite side of the base layer to the adhesive layer. The laminate film according to claim 6 , which is used to protect the back surface of a prism sheet.