JP5969761B2 - Method for producing pressure-sensitive adhesive composition, method for producing pressure-sensitive adhesive layer, and method for producing protective film - Google Patents

Description

  The present invention relates to a method for producing a pressure-sensitive adhesive composition, a pressure-sensitive adhesive comprising the pressure-sensitive adhesive composition obtained by this method, and a protective film having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition. More specifically, a method for efficiently producing a pressure-sensitive adhesive composition containing a (meth) acrylic acid ester copolymer having very little residual monomer and low molecular weight polymer, high molecular weight, and a molecular weight distribution of 3.5 or less, It has a pressure-sensitive adhesive composed of the pressure-sensitive adhesive composition obtained by this method, and a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition, and exhibits sufficient adhesive strength when applied to various adherends. Further, the present invention relates to a protective film in which, when peeled off, residue adhesion due to the pressure-sensitive adhesive layer is extremely small.

Conventionally, protective films have been used for surface protection in various image display devices such as LCD (liquid crystal display), touch panel, CRT (CRT), PDP (plasma display panel), EL (electroluminescence), and optical recording media. It is used for the purpose of antiglare and antireflection. Moreover, in LCD, it is used in order to protect a polarizer. This protective film generally has a pressure-sensitive adhesive layer on one side of the base film, and a functional coating layer such as antistatic performance and antifouling performance on the other side, or a hard coat layer if necessary. Is provided. And since it is excellent in an optical characteristic and the design of an adhesive is comparatively easy, the acrylic adhesive which has a (meth) acrylic acid ester copolymer as a main ingredient is used for the said adhesive layer.
When such a protective film is applied to the adherend via an adhesive layer, it is known that a slight residue adheres at an invisible level, and this uses an acrylic adhesive. In this case, it is known that it is caused by residual monomers and low molecular weight components present in the (meth) acrylic acid ester copolymer as the main agent.

  Patent Document 1 includes a pressure-sensitive adhesive composition containing a (meth) acrylate copolymer (A) having a weight average molecular weight of 200,000 to 2,000,000 and a molecular weight distribution of less than 2.5 obtained by living radical polymerization. A protective film having a pressure-sensitive adhesive layer, wherein the proportion of the low molecular weight component having a weight average molecular weight of 50,000 or less in the (meth) acrylic acid ester copolymer (A) is less than 5% by mass. A featured protective film is disclosed.

JP 2011-74380 A

Living radical polymerization in the technique described in Patent Document 1 has a long polymerization time and high cost, and a metal derived from a polymerization initiator is contained in the pressure-sensitive adhesive layer. Heavy peeling between the sheets has been a problem.
The present invention has been made under such circumstances, using a (meth) acrylic acid ester copolymer as a main component in the pressure-sensitive adhesive composition, and having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition. In addition, when affixed to various adherends, in addition to exhibiting sufficient adhesive strength, when peeled from the adherend, it provides a protective film with very little residue due to the adhesive layer, It aims at providing the method of manufacturing the said adhesive composition efficiently.

As a result of intensive studies to achieve the above object, the present inventors have obtained the following knowledge.
A (meth) acrylic acid ester copolymer having a high molecular weight with a weight average molecular weight within a predetermined range and a molecular weight distribution of 3.5 or less is obtained by suspension polymerization in an aqueous medium, and then an organic solvent. It discovered that the adhesive composition which consists of an organic solvent solution used for adhesive layer formation of a protective film was obtained efficiently by substituting.
The present invention has been completed based on such findings.

That is, the present invention
[1] After obtaining a (meth) acrylic acid ester copolymer (A) by suspension polymerization in an aqueous medium,
The liquid containing the component (A) is subjected to a solid-liquid separation treatment, and the obtained solid content is subjected to organic solvent substitution to dissolve in an organic solvent,
The component (A) has a weight average molecular weight of 800,000 to 2,500,000 and a molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn ratio) of 3.5 or less, and the molecular weight of the component (A) is 100,000 or less. A method for producing a pressure-sensitive adhesive composition, comprising obtaining a pressure-sensitive adhesive composition having a low molecular weight polymer content of less than 2.0 area%,
[2] The method for producing a pressure-sensitive adhesive composition according to the above [1], wherein the pressure-sensitive adhesive composition contains a crosslinking agent,
[3] A method for producing a pressure-sensitive adhesive layer, which is formed by the pressure-sensitive adhesive composition obtained by the method described in [1] or [2] above , and [4] the method described in [ 3 ] above. method for producing a protective film to a viscosity Chakuzaiso obtained by the method, characterized in that provided on one side of the substrate,
Is to provide.

  According to the present invention, a (meth) acrylic acid ester copolymer is used as a main component in the pressure-sensitive adhesive composition, and has a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition, and is applied to various adherends. In addition to exhibiting sufficient adhesive strength, when peeled, it provides a protective film with very little residue resulting from the adhesive layer and a method for efficiently producing the adhesive composition can do.

First, the manufacturing method of the adhesive composition of this invention is demonstrated.
[Method for producing pressure-sensitive adhesive composition]
The production method of the pressure-sensitive adhesive composition of the present invention is a (meth) acrylic acid ester having a weight average molecular weight of 800,000 to 2,500,000 and a molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn ratio) of 3.5 or less. A method for producing a pressure-sensitive adhesive composition comprising an organic solvent solution containing a copolymer (A), wherein the component (A) is obtained by suspension polymerization in an aqueous medium, and the organic solvent is substituted. Features.

((Meth) acrylic acid ester copolymer (A))
In the method for producing the pressure-sensitive adhesive composition of the present invention, first, a (meth) acrylic acid ester copolymer (A) having the following properties (hereinafter simply referred to as “copolymer (A)”) may be used. ) By suspension polymerization in an aqueous medium.
In the method for producing a pressure-sensitive adhesive composition of the present invention, the (meth) acrylic acid ester copolymer (A) obtained by suspension polymerization in an aqueous medium is a component contained as a main component in the pressure-sensitive adhesive composition. And has the following properties. The “(meth) acrylic acid ester” refers to both an acrylic acid ester and a methacrylic acid ester. The same applies to other similar terms.

<Properties of copolymer (A)>
The (meth) acrylic acid ester copolymer (A) has a weight average molecular weight Mw in the range of 800,000 to 2.5 million, and a molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn ratio) of 3.5 or less. It is necessary to be. When the weight average molecular weight is less than 800,000, the ratio of low molecular weight polymer components having a molecular weight of 100,000 or less inevitably increases, and adhesion of residues to the adherend cannot be prevented. On the other hand, when it exceeds 2.5 million, the smoothness of the coated surface is deteriorated due to an increase in the viscosity of the pressure-sensitive adhesive composition, and optical properties such as transparency are deteriorated. Moreover, in order to suppress such an increase in viscosity, a large amount of solvent is required in the organic solvent substitution described later, which is not preferable from the viewpoint of cost or environmental measures. In consideration of a small amount of residue, adhesion durability, coating suitability, and the like, the weight average molecular weight is preferably from 1,000,000 to 2,400,000, more preferably from 1,200,000 to 2,300,000.
On the other hand, when the molecular weight distribution (Mw / Mn ratio) exceeds 3.5, an increase in the low molecular weight polymer component in the (meth) acrylic acid ester copolymer (A) is caused. May not be achieved. A preferred molecular weight distribution (Mw / Mn ratio) is 3.4 or less, particularly preferably 2.0 to 3.0. In addition, the said weight average molecular weight Mw and number average molecular weight Mn are the values of standard polystyrene conversion measured by the gel permeation chromatography (GPC) method.

Furthermore, in the said (meth) acrylic acid ester copolymer (A), the ratio of the low molecular weight polymer component of the molecular weight 100,000 or less contained in it measured by GPC method is less than 5 area% Is preferred. When the ratio of the low molecular weight polymer component is 5% by area or more, a protective film having a pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive composition containing such a copolymer is applied to the adherend. When affixed via an adhesive layer, adhesion of residue to the adherend may not be suppressed to a sufficiently low level.
Therefore, the ratio of the low molecular weight polymer component having a molecular weight of 100,000 or less is more preferably 4.6 area% or less, further preferably 3.6 area% or less, and 2.0 area% or less. Is particularly preferred.

<Composition of copolymer (A)>
The (meth) acrylic acid ester copolymer (A) is a (meth) acrylic acid ester monomer unit (a) having an alkyl group having 1 to 20 carbon atoms (hereinafter referred to as a non-functional monomer unit (a And a (meth) acrylic acid ester monomer unit (b) having a reactive functional group (hereinafter sometimes referred to as a functional monomer unit (b)). And a mass ratio of 80:20 to 99.9: 0.1 is preferable. The reactive functional group in the functional monomer unit (b) is a functional group that becomes a cross-linking point cross-linked by a cross-linking agent described later, and the content of the functional monomer unit (b) is Based on the total amount with the non-functional monomer unit (a), if it is less than 0.1% by mass, the (meth) acrylic acid ester copolymer (A) is insufficiently crosslinked, and the resulting pressure-sensitive adhesive is It may be inferior in adhesive strength or durable adhesiveness. On the other hand, if it exceeds 20% by mass, gelation tends to occur during the production of the pressure-sensitive adhesive, and the pot life after addition of the crosslinking agent becomes too short, which may cause workability problems. In addition, the cohesive force becomes too high, and the adhesive force may be lowered to deteriorate the adhesion to the adherend.
The more preferable content of the functional monomer unit (b) is 0.5 to 10% by mass based on the total amount with the non-functional monomer unit (a), and more preferably 1 to 8% by mass. %.

  The (meth) acrylic acid ester copolymer (A) is a (meth) acrylic acid ester having a C 1-20 alkyl group that forms the non-functional monomer unit (a), It can be produced by copolymerizing a (meth) acrylic acid ester having a reactive functional group that forms the functional monomer unit (b) and another monomer used as desired.

  Examples of the (meth) acrylic acid ester having an alkyl group having 1 to 20 carbon atoms include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and pentyl (meth) acrylate. , Hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, myristyl (meth) acrylate, palmityl (meth) acrylate And stearyl (meth) acrylate. These may be used alone or in combination of two or more.

  On the other hand, examples of (meth) acrylic acid ester having a reactive functional group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 2-hydroxybutyl. Hydroxyalkyl (meth) acrylate such as (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, monomethylaminoethyl (meth) acrylate, monoethylaminoethyl (meth) acrylate, monomethylamino And monoalkylaminoalkyl (meth) acrylates such as propyl (meth) acrylate and monoethylaminopropyl (meth) acrylate. These may be used singly or in combination of two or more. In the present invention, hydroxyalkyl (meth) acrylate is preferably used from the viewpoint of crosslinkability and the like.

  Examples of other monomers used as desired include vinyl esters such as vinyl acetate and vinyl propionate; olefins such as ethylene, propylene and isobutylene; halogenated olefins such as vinyl chloride and vinylidene chloride; styrene Styrene monomers such as α-methylstyrene; diene monomers such as butadiene, isoprene and chloroprene; nitrile monomers such as acrylonitrile and methacrylonitrile; acrylamide, N-methylacrylamide, N, N- Examples include acrylamides such as dimethylacrylamide. These may be used alone or in combination of two or more.

From the viewpoint of performance as an adhesive, the (meth) acrylic acid ester copolymer (A) is a copolymer of butyl acrylate and 4-hydroxybutyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, A copolymer of 4-hydroxybutyl acrylate, a copolymer of butyl acrylate and 2-hydroxyethyl acrylate, a copolymer of butyl acrylate, cyclohexyl acrylate and 4-hydroxybutyl acrylate, or butyl acrylate, A copolymer of methyl acrylate and 4-hydroxybutyl acrylate is preferred.
In this case, the content of 4-hydroxybutyl acrylate units or 2-hydroxyethyl acrylate units serving as crosslinking points in the copolymer is preferably about 0.5 to 10% by mass.

<Polymerization of copolymer (A)>
In the method for producing the pressure-sensitive adhesive composition of the present invention, the (meth) acrylic acid ester copolymer (A), which is a component contained as a main component in the pressure-sensitive adhesive composition, has a high molecular weight (Mw: In order to obtain a (meth) acrylic acid ester copolymer having such a property, the molecular weight distribution is small (3.5 or less). A suspension polymerization method in a medium is employed.

<Suspension polymerization method>
There is no restriction | limiting in particular about the suspension polymerization method in an aqueous medium, A conventionally well-known method can be used.
Specifically, first, in the aqueous medium, each monomer component constituting the (meth) acrylic acid ester copolymer described above, an oil-soluble radical initiator, a chain transfer agent such as dodecyl mercaptan, a surfactant and If necessary, a dispersion stabilizer such as polyvinyl alcohol and other additives are added and premixed, and homogenized by a homogenizer to adjust the particle size of the oil droplets. Examples of the homogenizer include a colloid mill, a vibration stirrer, a two-stage high-pressure pump, a high-pressure jet from a nozzle and an orifice, and ultrasonic stirring. Furthermore, the adjustment of the oil droplet size is affected by the control of shear force during homogenization, the stirring conditions during polymerization, the type of reactor, the amount of surfactants and additives, etc. Appropriate conditions can be selected by simple preliminary experiments.
Next, the liquid homogenized in this way is sent to a polymerization vessel, heated while slowly stirring, and polymerization is usually carried out at a temperature in the range of 30 to 80 ° C. for about 6 to 24 hours. .

  Examples of the oil-soluble radical initiator (polymerization catalyst) include diacyl peroxides such as dibenzoyl peroxide, di-3,5,5-trimethylhexanoyl peroxide, and dilauroyl peroxide, diisopropyl peroxydicarbonate, and di-sec-butyl. Peroxydicarbonates such as peroxydicarbonate, di-2-ethylhexylperoxydicarbonate, peroxyesters such as t-butylperoxypivalate and t-butylperoxyneodecanoate, or acetylcyclohexylsulfonyl peroxide, disuccinic acid peroxide Organic peroxides such as 2,2′-azobisisobutyronitrile, 2,2′-azobis-2-methylbutyronitrile, 2,2′-azobisdimethylvalero Or the like can be used azo compounds such as tolyl. These catalysts can be used singly or in combination of two or more, and the amount used is appropriately selected according to the type and amount of the monomer and the charging method, but usually per 100 parts by weight of the monomer used. , 0.001 to 5.0 parts by mass.

  On the other hand, examples of the surfactant include alkyl sulfate salts such as sodium lauryl sulfate and sodium myristyl sulfate, alkyl aryl sulfonates such as sodium dodecylbenzenesulfonate and potassium dodecylbenzenesulfonate, sodium dioctylsulfosuccinate, Sulfosuccinic acid ester salts such as sodium dihexyl sulfosuccinate, fatty acid salts such as ammonium laurate and potassium stearate, polyoxyethylene alkylsulfuric acid ester salts, polyoxyethylene alkylarylsulfuric acid ester salts, and sodium dodecyl diphenyl ether disulfonate Anionic surfactants, sorbitan monooleate, polyoxyethylene sorbitan monostearate, etc. Nonionic surfactants such as rubitan esters, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, and cationic surfactants such as cetyl pyridinium chloride and cetyl trimethyl ammonium bromide These may be used singly or in combination of two or more, and the amount used is generally 0.05 to 5 parts by mass, preferably 100 parts by mass of the monomer used. Can be appropriately selected within the range of 0.2 to 4.0 parts by mass.

The aqueous medium used in the suspension polymerization refers to water or an organic solvent miscible with water, for example, a mixed solvent of a lower alcohol and water.
By suspension polymerization in such an aqueous medium, the weight average molecular weight is 800,000 to 2,500,000, the molecular weight distribution is 3.5 or less, and the average particle diameter is about 10 to 200 μm, preferably 10 to 150 μm ( A suspension containing the (meth) acrylic acid ester copolymer (A) particles is obtained.
In addition, the molecular weight (weight average polymerization degree) of the (meth) acrylic acid ester copolymer (A) can be prepared depending on the reaction temperature, the amount of a radical initiator or a chain transfer agent (molecular weight adjusting agent), and the like. The average particle diameter of the copolymer (A) particles can be measured by a light scattering method.

<Organic solvent substitution>
In the method for producing the pressure-sensitive adhesive composition of the present invention, the copolymer (A) particles obtained by suspension polymerization of the (meth) acrylic acid ester copolymer (A) in an aqueous medium as described above. The pressure-sensitive adhesive composition comprising an organic solvent solution is prepared by substituting the suspension containing the organic solvent with an organic solvent and, if desired, blending additional components described later.
The organic solvent substitution can be performed, for example, by the method shown below.
First, the suspension containing the copolymer (A) particles is subjected to solid-liquid separation treatment such as filtration or centrifugation to obtain a wet cake of the copolymer (A). Is added and dissolved to obtain an organic solvent solution containing the copolymer (A). At this time, when the aqueous layer is separated from the organic layer, the aqueous layer is preferably removed. It is also preferable to add a hydrophobic organic solvent to the suspension containing the copolymer (A) particles, and dissolve and extract the copolymer (A) particles to the organic solvent side by a liquid separation operation.

Examples of the organic solvent used for this organic solvent substitution include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane, aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methylene chloride and ethylene chloride, methanol, ethanol, Examples thereof include alcohols such as propanol and butanol, ketones such as acetone, methyl ethyl ketone, 2-pentanone and isophorone, esters such as ethyl acetate and butyl acetate, and cellosolve solvents such as ethyl cellosolve.
These organic solvents may be used individually by 1 type, and may be used in combination of 2 or more type. Moreover, as the usage-amount, what is necessary is just the quantity used as the density | concentration and viscosity which can be coated as an adhesive composition, and there is no restriction | limiting in particular.

The pressure-sensitive adhesive composition is prepared by blending an additive component as desired in an organic solvent solution in which the (meth) acrylic acid ester copolymer (A) thus obtained is dissolved. .
<Additive components>
In the organic solvent solution obtained by replacing the organic solvent in this manner, various additive components such as a crosslinking agent, a tackifier, an antioxidant, an ultraviolet absorber, a light stabilizer, and a silane coupling agent are optionally added. Inorganic / organic fillers, colorants and the like can be added in appropriate amounts.

<Crosslinking agent>
In the organic solvent solution obtained by the method of the present invention, the crosslinking agent to be blended as necessary is not particularly limited, and any one of those conventionally used as a crosslinking agent in acrylic resins can be appropriately selected. It can be selected and used. Examples of such crosslinking agents include polyisocyanate compounds, epoxy resins, melamine resins, urea resins, dialdehydes, methylol polymers, aziridine compounds, metal chelate compounds, metal alkoxides, and metal salts. A compound is preferably used.
Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, and hydrogenated diphenylmethane diisocyanate. Polyisocyanates and the like, and biurets, isocyanurates, and adducts that are a reaction product of low molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, castor oil (for example, , Trimethylolpropane-modified tolylene diisocyanate) and the like.
In this invention, this crosslinking agent may be used individually by 1 type, and may be used in combination of 2 or more type. Moreover, although the usage-amount is based also on the kind of crosslinking agent, it is 0.01-20 mass parts normally with respect to 100 mass parts of said (meth) acrylic acid ester copolymers (A), Preferably, it is 0.1. -10 parts by mass, particularly preferably in the range of 0.5-5 parts by mass. In addition, the compounding of the crosslinking agent suitably improves the cohesive force of the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition, and when the pressure-sensitive adhesive layer is peeled off from the adherend, adhesion of the residue on the adherend It is preferable from a viewpoint of reducing.

<Tackifier>
In the organic solvent solution obtained by the method of the present invention, there are no particular limitations on the tackifier contained as necessary, such as rosin derivatives, polyterpene resins, aromatic modified terpene resins and their hydrides, terpene phenol resins. , Coumarone-indene resin, aliphatic petroleum resin, aromatic petroleum resin and its hydride, styrene or low molecular weight polymer of substituted styrene, and the like. This tackifier may be used individually by 1 type, and may be used in combination of 2 or more type. What is necessary is just to select suitably content of the said tackifier according to the desired performance of the said adhesive composition.
The tackifier is used by dissolving in the monomer mixture at the time of suspension polymerization of the (meth) acrylic acid ester copolymer (A) in the aqueous medium. You may make it contain.

As described above, the organic solvent solution of the copolymer (A) is blended with various additive components as desired, and further, by adjusting the viscosity by adding an organic solvent so that the viscosity becomes optimum for coating. It becomes an adhesive composition. The organic solvent whose viscosity is adjusted may be the same as or different from that used for preparing the organic solvent solution of the copolymer (A). It can be used by appropriately selecting from organic solvents used for organic solvent substitution.
The pressure-sensitive adhesive composition comprising the organic solvent solution thus obtained can be used for forming a pressure-sensitive adhesive layer of a protective film. The protective film having the pressure-sensitive adhesive layer can be adhered to the adherend with sufficient adhesive strength when attached to the adherend, and when peeled off, there is very little adhesion of the residue to the adherend. It has the characteristics.

This invention also provides the protective film which has the adhesive which consists of an adhesive composition obtained with the manufacturing method mentioned above, and the adhesive layer formed with this adhesive composition.
Next, the protective film of the present invention will be described.
[Protective film]
The protective film of this invention has an adhesive layer formed with the adhesive composition obtained by the manufacturing method mentioned above. That is, the protective film of the present invention preferably has the pressure-sensitive adhesive layer on one surface of the substrate, and further has a release film laminated on the exposed surface side of the pressure-sensitive adhesive layer. The laminated film is particularly preferable.

(Base material)
In the protective film of the present invention, preferred examples of the substrate include paper substrates and plastic films. There is no restriction | limiting in particular as a paper base material, For example, a Japanese paper, a western paper, a quality paper, a glassine paper, a craft paper, a full pack paper, a crepe paper, a clay coat paper, a top coat paper, a synthetic paper etc. can be mentioned. On the other hand, the plastic film is not particularly limited. For example, polyester film such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene film, polypropylene film, cellophane, diacetyl cellulose film, triacetyl cellulose film, acetyl cellulose butyrate film. , Polyvinyl chloride film, polyvinylidene chloride film, polyvinyl alcohol film, ethylene-vinyl acetate copolymer film, polystyrene film, polycarbonate film, polymethylpentene film, polysulfone film, polyether ether ketone film, polyether sulfone film, poly Etherimide film, polyimide film, fluororesin Irumu, polyamide film, acrylic resin film, norbornene resin film, a cycloolefin resin film. In addition, when using a protective film for optical purposes, the inspection work should be performed with the protective film attached to the adherend, or the protective film may be visually recognized from above while the protective film is attached to the consumer's preference. In some cases, the substrate is preferably a transparent plastic film.
This plastic film can be subjected to surface treatment on one side or both sides by an oxidation method or a concavo-convex method, if desired, for the purpose of improving adhesion to a layer provided on the surface. Examples of the oxidation method include corona discharge treatment, plasma treatment, chromic acid treatment (wet), flame treatment, hot air treatment, ozone / ultraviolet irradiation treatment, and examples of the unevenness method include a sand blast method, a solvent, and the like. Treatment methods and the like. These surface treatment methods are appropriately selected according to the type of the base film, but generally, the corona discharge treatment method is preferably used from the viewpoints of effects and operability. Moreover, what gave the primer process to the single side | surface or both surfaces can also be used.
There is no restriction | limiting in particular in the thickness of a base material, Although it selects suitably, Usually, it is 10-250 micrometers, Preferably it is the range of 25-200 micrometers.

(Adhesive layer)
In the protective film of the present invention, the pressure-sensitive adhesive layer provided on one surface of the base material is formed by directly applying and drying the pressure-sensitive adhesive composition obtained by the production method of the present invention on the base material. can do. In addition, it is also preferable to laminate | stack a release film on the adhesive layer from a viewpoint of adhesion prevention of dust etc. to an adhesive layer. Moreover, it is also preferable to apply | coat and dry the said adhesive composition on the mold release process surface of a release film, and to form an adhesive layer. In this case, a protective film can be manufactured by sticking this pressure-sensitive adhesive layer with a release film on one surface of the substrate.
As a method for applying the pressure-sensitive adhesive composition, a known method such as knife coating, roll coating, bar coating, blade coating, die coating, gravure coating or the like can be applied to a predetermined thickness. A drying method can be used.
The thickness of the pressure-sensitive adhesive layer is usually about 2 to 30 μm, preferably 5 to 25 μm.
Here, the surface roughness of the pressure-sensitive adhesive layer on the side not in contact with the base material (adherent adhesion side) is preferably less than 1 μm, more preferably less than 0.5 μm, and less than 0.3 μm. It is particularly preferred that The surface roughness (Ra) of the pressure-sensitive adhesive layer is preferably in the above range from the viewpoint of preventing adhesive residue on the adherend during peeling while sufficiently maintaining the adhesive strength to the adherend. The surface roughness can be obtained according to JIS B 0601-1994.
The haze value of the pressure-sensitive adhesive layer is preferably 0 to 10%, more preferably 0.01 to 2%, and particularly preferably 0.1 to 1%. From the viewpoint of preventing adhesive residue and ensuring adhesive strength, the haze value is preferably within the above range. The haze value can be obtained according to JIS K 7136.

(Coating layer)
In the protective film of this invention, the coating layer which has antistatic performance and / or antifouling performance can be provided in the surface on the opposite side to the adhesive layer of a base material.
The coating layer having antistatic performance can be formed, for example, by applying and drying a coating liquid in which a conductive material is dispersed in a thermoplastic resin matrix.
On the other hand, a coating layer having antifouling performance can be formed by applying and drying a coating liquid generally containing a fluororesin.
As a coating method of the various coating liquids, for example, a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method, or the like can be used.
The thickness of the coating layer having the conductive performance thus formed is usually about 0.05 to 1 μm, preferably 0.3 to 0.7 μm. The thickness of the coating layer having antifouling performance is Usually, it is about 1 to 10 nm, preferably 3 to 8 nm. In addition, it is preferable to provide such a coating layer because a protective film can be stored as a wound body (roll) until use without using a release film.

(Release film)
Examples of the release film that is optionally provided on the pressure-sensitive adhesive layer include paper such as glassine paper, coated paper, and laminated paper, and various plastic films coated with a release agent such as silicone resin. . As a plastic film, what was mentioned by the said plastic film can be used suitably. Although there is no restriction | limiting in particular about the thickness of this release film, Usually, it is about 10-100 micrometers.
(Properties of the adhesive layer)
<Adhesive strength>
The protective film is required to be sufficiently adhered without being peeled off while being attached to the adherend, and to be easily peeled off when unnecessary. In consideration of being used in optical applications, in the present invention, a polymethyl methacrylate plate (hereinafter sometimes referred to as “PMMA plate”) is measured as an adherend.
The measurement is performed by pressing a pressure-sensitive adhesive layer of a protective film having a width of 25 mm × 100 mm on a PMMA plate and leaving it in an environment of 23 ° C. and a relative humidity of 50% for 24 hours. The peeling is performed at a peeling angle of 180 °.
The adhesive strength is preferably 30 to 1000 mN / 25 mm, and more preferably 60 to 500 mN / 25 mm. If it is less than 30 mN / 25 mm, it may peel off unintentionally, and if it exceeds 1000 mN / 25 mm, adhesion of residue may increase.
<Gel fraction>
The gel fraction of the pressure-sensitive adhesive layer in the protective film of the present invention is preferably in the range of 90 to 100%. Setting the gel fraction within such a range is effective in reducing the amount of residue adhering to the adherend after the pressure-sensitive adhesive layer obtained has been applied to the adherend and removed. It is. From such a viewpoint, the gel fraction is particularly preferably 95 to 100%.
The method for measuring the gel fraction will be described in detail later.
<Residual particle number test>
When the protective film of the present invention is applied to an adherend via an adhesive layer, the amount of residue attached is selected using a silicon wafer as the adherend and using a laser surface inspection apparatus (details will be described later). This can be determined by confirming the amount of residue adhering to the surface. The reason why the silicon wafer is selected as the adherend is that it is easy to numerically measure the amount of residue attached. If the number of residual particles is 200 (pieces / 4 inch wafer) or less, it can be said that the adhesive layer has very little residue on various adherends.
<Heavy peelability>
The rate of increase in peel strength after leaving the protective film of the present invention (configuration: PET / adhesive layer / release film) under conditions of 70 ° C. and dry for 500 hours is less than 100%, and peel strength with time of coating It can be said that it is a pressure-sensitive adhesive layer with little rise.

  By using the protective film of the present invention having such properties, each function can be obtained by adhesion of residues even in application to functional optical members that require a high level of surface cleanliness among adherends. It is expected that the damage can be suppressed.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
In addition, about the acrylic acid ester copolymer obtained in each case, it is low by the gel permeation chromatography (GPC) method, the weight average molecular weight Mw of the standard polystyrene conversion, the number average molecular weight Mn, and the weight average molecular weight 100,000 or less. The content of the molecular weight polymer was determined by the following method.
<GPC method>
Measuring device: Tosoh's high-speed GPC device "HLC-8120GPC", high-speed columns "TSK gold column H _XL- H", "TSK Gel GMH _XL ", "TSK Gel G2000 H _XL " ) In this order and measured.
Column temperature: 40 ° C., liquid feed rate: 1.0 mL / min, detector: differential refractometer

Moreover, about the protective film obtained in each case, the adhesive force with respect to polymethylmethacrylate (PMMA), the gel fraction of an adhesive layer, the number of residual particles (residual particle number test), and heavy peelability are calculated | required by the following method. It was.
(1) Adhesive strength to PMMA A 25 mm wide, 100 mm long sample was cut out from the protective film, the release film was peeled off, and affixed to a PMMA board [manufactured by Mitsubishi Rayon Co., Ltd., “Acrylite L001”], then Kurihara Seisakusho Pressurize in an autoclave under the conditions of 0.5 MPa, 50 ° C., and 20 minutes. Then, after being left for 24 hours in an environment of 23 ° C. and a relative humidity of 50%, using the tensile tester [Orientec, “Tensilon”] in the same environment, a peeling speed of 300 mm / min, a peeling angle of 180 Measure the adhesive strength under the condition of °.
(2) Gel fraction An adhesive thickness of 20 μm was sampled to a size of 80 mm × 80 mm, wrapped in a polyester mesh (mesh size 200), and the weight of the adhesive alone was weighed with a precision balance. The weight at this time is M1. The pressure-sensitive adhesive was immersed in an ethyl acetate solvent using a Soxhlet (extractor), refluxed and treated for 16 hours. Thereafter, the pressure-sensitive adhesive was taken out, air-dried in an environment of a temperature of 23 ° C. and a relative humidity of 50% for 24 hours, and further dried in an oven at 80 ° C. for 12 hours. The weight of only the pressure-sensitive adhesive after drying was weighed with a precision balance. The weight at this time is M2. The gel fraction is expressed as (M2 / M1) × 100 (%).
(3) Residual particle number test The protective film obtained in the example or the comparative example was attached in a clean room by reciprocating a 5 kg (49N) rubber roller on a mirror surface of a 4-inch silicon wafer at room temperature, After leaving for 60 minutes, peeling was performed. At this time, the number of residual foreign matters having a particle size of 0.27 μm or more on the wafer was measured by a laser surface inspection apparatus (manufactured by Hitachi Electronics Engineering).
(4) Heavy peelability The peel strength of the protective film obtained in Examples or Comparative Examples after leaving for 500 hours at 70 ° C. and dry conditions (hereinafter sometimes referred to as “after 70 ° C. accelerated charging”) The rate of increase was determined by the following formula, and the heavy peelability was evaluated according to the following criteria.
<Method of measuring peel force>
Sampling was performed to 25 mm width × 150 mm length, and the release force of the release film was measured using Tensilon manufactured by Orientec Corporation. Peeling speed: 300 mm / min, peeling angle: 180 °
<Calculation formula of peel force increase rate>
[(Peeling force after accelerated introduction at 70 ° C.) / (Peeling force before accelerated introduction at 70 ° C.)] × 100
<Evaluation of heavy peelability>
○: Increase rate of peel force is less than 150% ×: Increase rate of peel force is 150% or more (5) Surface roughness of adhesive layer JIS B using a laser microscope [Keyence Corporation “VK-9700”] Measured according to 0601-1994.
(6) Haze value of pressure-sensitive adhesive layer A single pressure-sensitive adhesive was bonded to soda lime glass, and measured according to JIS K 7136 using [Nippon Denshoku Industries Co., Ltd. haze meter "NDH-2000"]. .

Example 1 (Reference Example 1)
(1) Manufacture of acrylic ester copolymer comprising random copolymer by suspension polymerization Mass ratio of butyl acrylate (BA), cyclohexyl acrylate (CHA) and 4-hydroxybutyl acrylate (4HBA) as monomers An acrylic acid ester copolymer composed of a random copolymer of BA / CHA / 4HBA was produced by suspension polymerization in the following aqueous medium using a ratio of 78: 20: 2. The properties of this copolymer are shown in Table 1.
<Suspension polymerization>
Into a glass round bottom flask equipped with a stirrer, 300 parts by mass of water was added, and 0.7 parts by mass of polyvinyl alcohol as a dispersion stabilizer and 2 parts by mass of sodium dodecylbenzenesulfonate as a surfactant were dissolved and stirred. While stirring at 300 rpm with a blade, the monomer mixture (mass ratio 78: 20: 2) composed of BA, CHA and 4HBA described above and 2,2′-azobisisobutyronitrile 0 as a polymerization initiator were used. After adding 9.9 parts by mass and premixing, the mixture was homogenized by a homogenizer to prepare an aqueous suspension in which the particle size of the oil droplets was adjusted. Next, the temperature of the reaction system is raised to about 70 ° C. while stirring this aqueous suspension, and the reaction is carried out by maintaining the temperature at a constant temperature for 4 hours, so that the average particle diameter of particulate BA / CHA / 4HBA is about 50 μm. An acrylic ester copolymer comprising a random copolymer was produced.
(2) Preparation of pressure-sensitive adhesive composition After the suspension containing the acrylate copolymer particles obtained in (1) above was filtered to obtain a wet cake of the copolymer, acetic acid was added to the wet cake. Ethyl was added and dissolved to obtain an ethyl acetate solution having a solid concentration of 15% by mass.
In this solution, an isocyanurate type HDI [trade name “Coronate HX” manufactured by Nippon Polyurethane Industry Co., Ltd., NCO content: 21.3 mass%, solid content: 100%] 3 mass as a crosslinking agent per 100 mass parts of the copolymer. A pressure-sensitive adhesive composition was prepared by adding 0.005 parts by weight of dibutyltin dilaurate as a crosslinking accelerator and 2 parts by weight of acetylacetone as a crosslinking retarder.
(3) Production of Protective Film As the base film, the antistatic antifouling polyethylene terephthalate film with a thickness of 38 μm [manufactured by Toray Industries, Inc., trade name “PET38SLD52”] is obtained by the above (2). The adhesive composition was applied with a knife-type coating machine so that the dry thickness was 5 μm, and then heated and dried at 90 ° C. for 1 minute to form an adhesive layer.
Subsequently, the adhesive layer with a PET base material obtained above was bonded to the release treatment surface of a release film of 38 μm thickness [manufactured by LINTEC, trade name “SP-PET381031”], and a protective film was attached. It produced and various characteristics were calculated | required about this protective film. The results are shown in Table 2.

Examples 2-3 (Reference Examples 2-3), Example 4
Example 1 is the same as Example 1 except that the monomer mixture of the mass ratio shown in Table 1 was used instead of the monomer mixture of BA, CHA, and 4HBA (mass ratio 78: 20: 2) in Example 1. In the same manner, suspension polymerization in an aqueous medium was performed to produce an acrylate copolymer comprising three types of random copolymers. The properties of each copolymer are shown in Table 1.
In Example 4, 7.2 parts by mass of the copolymer obtained by suspension polymerization was added to 100 parts by mass of methanol and stirred at room temperature to form a precipitate. Next, this precipitate was separated by decantation and then washed with 50 parts by mass of methanol. Thereafter, methanol was removed by decantation, and the properties of this precipitate are shown in Table 1. By such a purification treatment, the weight average molecular weight is considerably increased as compared with Examples 1 to 3, the content ratio of the low molecular weight polymer having a molecular weight of 100,000 or less is reduced, and the molecular weight distribution is reduced. I understand.

  Next, each pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, and each protective film was prepared to obtain various properties. The results are shown in Table 2.

Comparative Example 1
(1) Production of acrylic acid ester copolymer by solution polymerization (free radical polymerization) BA, 2-ethylhexyl acrylate (2EHA) and 4HBA were used as monomers in a mass ratio of 75: 20: 5, and The acrylic acid ester copolymer of BA / 2EHA / 4HBA was produced by the free radical polymerization shown. The properties of this copolymer are shown in Table 1.
<Solution polymerization (free radical polymerization)>
After nitrogen gas is sealed in a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen introduction tube, 90 parts by mass of ethyl acetate, 20 parts by mass of 2EHA, 75 parts by mass of BA, 5 parts by mass of HBA, polymerization initiator 2,2 Then, 0.2 part by mass of '-azobisisobutyronitrile (AIBN) was charged and reacted at the reflux temperature of ethyl acetate for 7 hours with stirring. After completion of the reaction, 95 parts by mass of toluene was added and cooled to room temperature to obtain an acrylate copolymer solution having a solid content of 30% by mass.
Thereafter, a pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, and a protective film was further produced. The various properties of this protective film are shown in Table 2.

Comparative Example 2
(1) Production of acrylic ester copolymer by solution polymerization (living radical polymerization) Using BA, CHA and 4HBA as monomers in a mass ratio of 78: 20: 2, An acrylate copolymer comprising a random copolymer of BA / CHA / 4HBA was produced. The properties of this copolymer are shown in Table 1.
<Solution polymerization (living radical polymerization)>
In an argon-substituted glove box, 68.5 μL of ethyl-2-methyl-2-n-butylterranyl-propionate, 107 g of BA, 27.4 g of CHA, 2.7 g of 4HBA, and 4.6 mg of 2,2′-azobisisobutyronitrile were added. The reaction was carried out at 60 ° C. for 20 hours.
After completion of the reaction, the reactor is removed from the glove box, and the reactant in the reactor is dissolved in 500 mL of ethyl acetate, and then the polymer solution is passed through a column made of activated alumina [manufactured by Wako Pure Chemical Industries, Ltd.] Toluene was added so that the solid content of the polymer solution was 30% by mass.
Hereinafter, a pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, and a protective film was further produced. The various properties of this protective film are shown in Table 2.

[note]
Mw: weight average molecular weight Mn: number average molecular weight BA: butyl acrylate CHA: cyclohexyl acrylate 4HBA: 4-hydroxybutyl acrylate MA: methyl acrylate 2EHA: 2-ethylhexyl acrylate

As can be seen from Table 1, the acrylic acid ester copolymers of Examples 1 to 4 obtained by suspension polymerization in an aqueous medium are acrylic acid obtained by solution polymerization by the free radical method of Comparative Example 1. The weight average molecular weight is larger than that of the ester copolymer, the content ratio of the low molecular weight polymer having a molecular weight of 100,000 or less is small, and the molecular weight distribution is small.
Moreover, as can be seen from Table 2, the protective films of the present invention of Examples 1 to 4 have higher adhesiveness to PMMA and a smaller number of residual particles than the protective film of Comparative Example 1.
On the other hand, the protective film of Comparative Example 2 using the pressure-sensitive adhesive composition for solution polymerization by the living radical method has a problem that the heavy peelability increases with time.

The method for producing the pressure-sensitive adhesive composition of the present invention includes a pressure-sensitive adhesive containing a (meth) acrylic acid ester copolymer having very little residual monomer and low molecular weight polymer, high molecular weight, and a molecular weight distribution of 3.5 or less. The composition can be produced efficiently.
In addition, it has an adhesive layer formed of the adhesive composition, and when it is attached to various adherends, it exhibits sufficient adhesive force, and when peeled, it results from the adhesive layer It is possible to provide a protective film with very little residue adhesion.

Claims (4)

After obtaining the (meth) acrylic acid ester copolymer (A) by suspension polymerization in an aqueous medium,
The liquid containing the component (A) is subjected to a solid-liquid separation treatment, and the obtained solid content is subjected to organic solvent substitution to dissolve in an organic solvent,
The component (A) has a weight average molecular weight of 800,000 to 2,500,000 and a molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn ratio) of 3.5 or less, and the molecular weight of the component (A) is 100,000 or less. A method for producing a pressure-sensitive adhesive composition, comprising obtaining a pressure-sensitive adhesive composition having a low molecular weight polymer content of less than 2.0 area%.   The manufacturing method of the adhesive composition of Claim 1 in which an adhesive composition contains a crosslinking agent. It forms with the adhesive composition obtained by the method of Claim 1 or 2, The manufacturing method of the adhesive layer characterized by the above-mentioned. Method for producing a protective film and providing a Chakuzaiso viscosity obtained by the method of claim 3 on one surface of a substrate.