JP2002308940A - Method for polymerizing polymer for self-adhesive and self-adhesive composition, and self-adhesive product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a self-adhesive product excellent in the balance between self-adhesive power and cohesive power by selecting a polymerization method permitting reduction in the amount of a smelly and irritative residual vinyl acetate monomer and that of a low-molecular weight matter adversely affecting self-adhesive properties in manufacturing a polymer for a self-adhesive using the vinyl acetate monomer. SOLUTION: The method for manufacturing the polymer for the self-adhesive comprises radically polymerizing a monomer component essentially comprising at least one alkyl (meth)acrylate and vinyl acetate, where 70-100 mass% of vinyl acetate employed and a part of a monomer other than vinyl acetate are charged into a reactor in advance to initiate the polymerization and subsequently the rest of the monomer component is charged into the reactor to continue the polymerization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polymerizing a polymer for an adhesive comprising an alkyl (meth) acrylate and vinyl acetate as essential constituent monomers at a high polymerization rate so as to reduce residual vinyl acetate. The present invention also relates to a pressure-sensitive adhesive composition containing the pressure-sensitive adhesive polymer, and a pressure-sensitive adhesive product having a pressure-sensitive adhesive layer obtained from the pressure-sensitive adhesive composition.

[0002]

2. Description of the Related Art Acrylic pressure-sensitive adhesives containing alkyl (meth) acrylate as a main constituent are heat-resistant, weather-resistant, water-resistant, oil-resistant, etc. in addition to basic physical properties such as tack, adhesion and cohesion. It is widely used for adhesive products such as adhesive labels, sheets, and tapes.

[0003] Among the above three basic physical properties of the pressure-sensitive adhesive, the adhesive strength and the cohesive strength are known as contradictory physical properties. That is,
When the adhesive strength is improved, the cohesive strength is reduced, and when the cohesive strength is increased, the adhesive strength is reduced. Therefore, it is quite difficult to improve the physical properties of both while maintaining the balance between them.

In order to improve the cohesive force while maintaining a high adhesive force, the polymer constituting the adhesive is not easily cross-linked three-dimensionally, but the polymer itself is increased in molecular weight to secure a high adhesive force. It has been found useful to increase the entanglement of the polymer chains.

[0005] Kano and Akiyama et al. In a terpolymer (terpolymer) comprising 2-ethylhexyl acrylate, vinyl acetate and acrylic acid, a vinyl acetate unit reduces the self-cohesive force (hydrogen bond) of acrylic acid. Reports that it promotes intermolecular interactions (entanglement of molecular chains) with different polymers (Journal of the Adhesion Society of Japan; Vol. 29, P560, 19)
93).

[0006] From the above report, a copolymer consisting of 2-ethylhexyl acrylate and acrylic acid and a copolymer of acrylic acid 2-ethylhexyl.
When a terpolymer consisting of ethylhexyl, vinyl acetate and acrylic acid is designed to have the same glass transition temperature (Tg), the copolymer containing no vinyl acetate has less entanglement between polymer chains, Thus, it is considered that a terpolymer using vinyl acetate as a constituent monomer has a large entanglement between polymer chains. If the entanglement between polymer chains increases and the cohesive force increases due to the difficulty in loosening the molecular chains, it is possible to avoid a decrease in adhesive strength, as compared to the case where the crosslink density is increased and the cohesive force is increased. It is considered that a polymer for an adhesive having an excellent balance between the pressure-sensitive adhesive strength and the adhesive strength is obtained. In addition, since it is not necessary to increase the crosslink density, it is considered to be excellent in stress relaxation property, and it is considered that, for example, a curved surface sticking property (an edge lift property) is also excellent.

Accordingly, the present inventors have studied a polymer for an adhesive containing (meth) acrylic acid alkyl ester and vinyl acetate as essential constituent monomers. It has been found that when a polymerization method in which a monomer mixture having a uniform composition is hardly polymerized and a monomer mixture having a uniform composition is dropped by solution polymerization is employed, the conversion is not so high, and the residual monomer is almost vinyl acetate.

[0008] Residual monomers cause an unpleasant odor of the adhesive product. In particular, it is not preferable to mix odorous or irritating compounds such as vinyl acetate in the polymer. Is difficult to separate from the polymer in terms of energy and cost, and is almost impossible.

From such a viewpoint, a method is usually employed in which a post-addition polymerization initiator called a booster is added to the system immediately before the end of the polymerization, and the residual monomer is forcibly polymerized to reduce the amount. . In this case, the amount of the booster for the residual monomer is considerably larger than the amount of the initiator for the monomer in the early stage of the polymerization reaction, in consideration of the probability that the residual monomer and the initiator meet, and the necessity of reliably polymerizing the residual monomer. It is currently being added. However, since a large amount of the initiator is present for the small amount of the monomer remaining in the system just before the end of the polymerization, the polymer formed after the addition of the booster is,
Most are of very low molecular weight. And this low molecular weight substance becomes a cause which reduces the cohesive force of an adhesive.

Further, in the case of a polymerization reaction in which vinyl acetate is an essential constituent monomer, when the same monomer composition is polymerized by a usual method of dropping, most of the remaining monomer becomes vinyl acetate. Even if the reduction method is adopted, the low molecular weight product produced after the addition of the booster becomes polyvinyl acetate having low tackiness, which adversely affects the tackiness characteristics.

[0011]

Therefore, in the present invention, when polymerizing an adhesive polymer using vinyl acetate, the amount of odor and irritating residual vinyl acetate monomer is reduced, and the adhesive property is improved. An object of the present invention was to find a polymerization method capable of reducing a low molecular weight substance having an adverse effect, and to provide an adhesive product having an excellent balance between adhesive force and cohesive force.

[0012]

According to the polymerization method of the present invention, which solves the above-mentioned problems, a monomer component containing essentially one or more alkyl (meth) acrylates and vinyl acetate is subjected to radical polymerization to form a pressure-sensitive adhesive. A method for producing a polymer, in which 70 to 100% by mass of vinyl acetate used and a part of monomers other than vinyl acetate are charged into a reactor first to start polymerization, and the remaining Is characterized in that the monomer component is charged into a reactor and polymerized.
By initially charging 70 to 100% by mass of the total amount of vinyl acetate, the polymerization rate can be increased, and the amount of residual vinyl acetate or low molecular weight substances, especially vinyl acetate which adversely affects the adhesive properties, is mainly used. Was able to be reduced.

It is preferable that the monomer component further contains a functional group-containing monomer having a functional group capable of reacting with the functional group of the crosslinking agent. By introducing a functional group into the pressure-sensitive adhesive polymer, crosslinking can be performed with a cross-linking agent, so that pressure-sensitive adhesive properties such as cohesive strength can be improved.

The present invention also includes a pressure-sensitive adhesive composition containing the pressure-sensitive adhesive polymer obtained by the above polymerization method, and a pressure-sensitive adhesive product having a pressure-sensitive adhesive layer obtained from the pressure-sensitive adhesive composition.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, in the present invention, when polymerizing an adhesive polymer using vinyl acetate, vinyl acetate has a low copolymerizability with an alkyl (meth) acrylate. An ordinary solution polymerization method performed while dropping a monomer mixture having a composition solves the problem that the residual amount of an odorous or irritating vinyl acetate monomer increases. Hereinafter, the present invention will be described in detail. In addition,
The term "polymer", unless otherwise specified as "homopolymer", is intended to represent a multi-component copolymer over a copolymer or terpolymer.

The polymerization method of the present invention is a radical polymerization by solution polymerization, wherein 70% of vinyl acetate used is used.
１００100% by mass and a part of the monomer other than vinyl acetate (referred to as an initially charged monomer component) are first charged into a reactor to start polymerization, and then the remaining monomer component (referred to as a charged monomer component) is added. It has the greatest point where it is charged into the reactor and polymerized. According to this method, vinyl acetate is easily copolymerized with the alkyl (meth) acrylate, and the polymerization rate is improved.

The initially charged monomer component comprises 70 to 100% by mass of vinyl acetate used and a small amount of a monomer other than vinyl acetate. 70% by mass or more of vinyl acetate,
This is because the initial charge is effective in reducing the amount of residual monomers and improving the polymerization rate. The lower limit of the initial charge amount of vinyl acetate is preferably 80% by mass, more preferably 90% by mass, and still more preferably 95% by mass. It is most preferable to initially charge the entire amount of vinyl acetate, that is, 100% by mass. If all of the initially charged monomers are vinyl acetate alone, a homopolymer of polyvinyl acetate may be generated. Therefore, the amount of the monomer other than vinyl acetate is equal to the initial charged amount of vinyl acetate to 3 times (mass). ratio)
It is preferable that the initial preparation is performed to the extent.

The concentration of the initially charged monomer component in the reactor (the concentration of the initially charged monomer component in a mixture with the solvent and the initially charged monomer component before polymerization) is 30 to
80% by mass is preferred. If the amount is less than 30% by mass, the molecular weight of the polymer hardly increases. A more preferred concentration of the initially charged monomer component is 40 to 70% by mass.

The concentration of the initially charged monomer component can be appropriately changed according to the polymerization solvent. For example, when using toluene or the like, which is likely to cause chain transfer, as the polymerization solvent, it is preferable to increase the concentration of the initially charged monomer component in order to increase the molecular weight. However, it is recommended to use ethyl acetate, which causes less chain transfer, as the solvent in the initial stage of the polymerization because the calorific value increases and the temperature control is difficult.

The dosing monomer component is a mixture of monomers not initially charged. The first charge of the monomer component for charge is preferably carried out after the start of the polymerization of the initially charged monomer component charged into the reactor and at a point in time when the conversion does not exceed 50%. If the polymerization rate of the initially charged monomer component exceeds 50%, a considerable amount of vinyl acetate-rich polymer is already formed in the reactor, and a well-balanced pressure-sensitive adhesive polymer cannot be obtained. There is a possibility that the sex cannot be reduced. In this sense, it is recommended that the initial charging of the monomer component for charging be performed at a stage where the polymerization rate of the initially charged monomer component is low.
It is more preferably performed at a stage of 0% or less, further preferably 10% or less, and most preferably immediately after the initiation of polymerization of the initially charged monomer component. The start time of the polymerization can be measured as the time when the heat generation due to the polymerization is started by measuring the internal temperature of the polymerization vessel. Further, when the polymerization is carried out at the reflux temperature, it can be regarded as the point in time when the volatilization of the polymerization solvent becomes intense.

The monomer component for charging is preferably divided into three or more portions, and dripping is most preferable. The polymerization initiator must be used for the initially charged monomer component and for the charging monomer component, and the initially charged monomer component is charged to the reactor, and the charging monomer component is charged when the charging monomer component is added. Add together. A booster (post-addition initiator) may be added at a later stage of the polymerization.
This is because, in the method of the present invention, the residual monomer of vinyl acetate in the late stage of the polymerization is small, and even if a booster is used, there is no inconvenience such as formation of a homopolymer of vinyl acetate.

The method of the present invention employs a solution polymerization method because the heat of polymerization during polymerization is easily removed and the operability is good. Specific examples of the solvent include aromatic hydrocarbons such as toluene and xylene; aliphatic esters such as ethyl acetate and butyl acetate; alicyclic hydrocarbons such as cyclohexane;
Examples thereof include aliphatic hydrocarbons such as hexane and pentane, but are not particularly limited as long as the polymerization reaction is not inhibited. These solvents may be used alone or in a combination of two or more.

Examples of the polymerization initiator include methyl ethyl ketone peroxide, benzoyl peroxide, dicumyl peroxide, t-butyl hydroperoxide,
Cumene hydroperoxide, t-butyl peroxy octoate, t-butyl peroxy benzoate, lauroyl peroxide, trade name "Niiper BMT-K
Organic peroxides such as "40" (manufactured by NOF Corporation; a mixture of m-toluoyl peroxide and benzoyl peroxide); azobisisobutyronitrile (AIBN); trade name "ABN-E" [Nippon Hydrazine Industry 2,2'-azobis (2-methylbutyronitrile)], trade name "AB
A known radical polymerization initiator such as an azo compound such as "NV" [manufactured by Nippon Hydrazine Industry Co., Ltd .; 2,2'-azobis (2,4-dimethylvaleronitrile)] can be used. The amount of the initiator is 0.01 to 1 based on the mass of the monomer.
It is preferable to use it so that it may be mass%. The polymerization conditions such as the polymerization temperature and the polymerization time may be appropriately set according to, for example, the type of the polymerization solvent and the polymerization initiator, and are not particularly limited. Also, the reaction pressure is not particularly limited, and may be any of normal pressure (atmospheric pressure), reduced pressure, and increased pressure. The polymerization reaction is desirably performed in an atmosphere of an inert gas such as a nitrogen gas.

From the viewpoint of adhesive properties, the weight average molecular weight Mw of the whole polymer for an adhesive is preferably 200,000 or more, more preferably 300,000 or more. Although the upper limit is not particularly limited, it is difficult to synthesize a polymer exceeding 2,000,000 in solution polymerization, and therefore it is preferably 2,000,000 or less, more preferably 1,000,000 or less.

Next, monomers that can be used as monomers for the pressure-sensitive adhesive will be described. In the present invention, vinyl acetate is used as an essential component in order to obtain the above-mentioned effect of improving cohesion due to the entanglement of molecular chains and to reduce the temperature sensitivity of the pressure-sensitive adhesive. Temperature sensitivity means that the adhesive becomes hard in a low-temperature atmosphere and cannot wet the adherend and does not exhibit sufficient adhesive strength, or the adhesive becomes hard and peels off from the adherend. And the degree to which the properties of the pressure-sensitive adhesive change depending on the temperature, such as the property that the pressure-sensitive adhesive becomes soft and causes cohesive failure in a high-temperature atmosphere. Since vinyl acetate does not have a very high copolymerizability with an alkyl (meth) acrylate, the resulting pressure-sensitive adhesive polymer is an aggregate of polymers of various compositions having different copolymerization ratios of vinyl acetate. It is thought that the temperature may be reduced. In order to obtain the effect of reducing the temperature sensitivity, it is preferable that vinyl acetate is used in an amount of 2 to 35% by mass of the pressure-sensitive adhesive monomer component (total). 2
If the amount is less than 35% by mass, the effect is not sufficiently exhibited, and if the amount is more than 35% by mass, the adhesive strength and the adhesive properties are undesirably deteriorated. The lower limit of the more preferable vinyl acetate use amount is 4% by mass, and the upper limit is 30% by mass.

The alkyl (meth) acrylate, which is the second essential component, is a main component for exhibiting adhesive strength. Specifically, (meth) acrylates having 1 to 12 carbon atoms in the alkyl group are preferred, for example, methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylate
Butyl acrylate, isobutyl (meth) acrylate,
Examples thereof include cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, dodecyl (meth) acrylate, and stearyl (meth) acrylate. One or more of these can be used.

In the case of forming a polymer for an adhesive using only vinyl acetate and an alkyl (meth) acrylate, 2-35% by mass of vinyl acetate and 98-65% by mass of at least one alkyl (meth) acrylate are used. It is preferred to use.

In consideration of the adhesive properties, it is preferable that the monomer component for the adhesive further contains a functional group-containing monomer. The functional group-containing monomer is not particularly limited as long as it has a functional group capable of reacting with the functional group of the pressure-sensitive adhesive polymer crosslinking agent, but a carboxyl group-containing monomer and a hydroxyl group-containing monomer are preferably used. This is because the crosslinking reaction proceeds promptly.

As the carboxyl group-containing monomer,
(Meth) acrylic acid, itaconic acid, crotonic acid, maleic anhydride, and the like. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate,
3-hydroxypropyl (meth) acrylate, (meth)
“Placcel F” series (manufactured by Daicel Chemical Industries, Ltd.), which is a polycaprolactone-modified product of 2-hydroxypropyl acrylate, 4-hydroxybutyl (meth) acrylate, and 2-hydroxyethyl (meth) acrylate; One or more of these can be used.

The functional group-containing monomer is preferably used in an amount of 0.1 to 15% by mass. If less than 0.1% by mass,
Insufficient crosslinking may result in low crosslinking density and insufficient cohesion. However, use of more than 15% by mass is not preferable because the pressure-sensitive adhesive becomes too hard. The lower limit of the more preferred amount is 0.2% by mass and the upper limit is 10% by mass. When the functional group-containing monomer is contained in the pressure-sensitive adhesive monomer component, the pressure-sensitive adhesive monomer component is 100% by mass.
It is preferable that the content of the alkyl (meth) acrylates therein is 50 to 97.9% by mass. Outside this range, the adhesive strength tends to decrease.

The monomer component for the pressure-sensitive adhesive may contain other monomers. Specifically, 2- (meta)
Acidic phosphoric acid ester monomers such as acryloyloxyethyl acid phosphate; nitrogen-containing monomers such as (meth) acrylamide, N, N'-dimethylaminomethyl (meth) acrylate, imide (meth) acrylate, and N-methylol (meth) acrylamide ; (Meta)
Nitrile group-containing monomers such as acrylonitrile; polyfunctional monomers such as ethylene glycol di (meth) acrylate; halogen-containing monomers such as vinyl chloride; styrene;
Aromatic monomers such as α-methylstyrene; vinyl ether; vinyl propionate; and the like, and one or more of these can be used. When these "other monomers" are used, the amount is preferably 0 to 20% by mass in the monomer component for an adhesive, and the amount of the alkyl (meth) acrylate is preferably 50 to 77.9% by mass. When other monomers exceed 20% by mass,
It is not preferable because the amount of the alkyl (meth) acrylate used is reduced, or the Tg of the pressure-sensitive adhesive is increased, and properties such as adhesive strength are lowered.

The pressure-sensitive adhesive monomer is appropriately combined with the pressure-sensitive adhesive monomer as described above to obtain a pressure-sensitive adhesive polymer. As a guide, it is preferable to combine the polymers so that the Tg of the polymer is −60 ° C. to + 30 ° C. The Tg of the polymer is
It can be determined by DSC (differential scanning calorimeter), DTA (differential thermal analyzer), and TMA (thermomechanical analyzer). Further, since the Tg of the homopolymer is described in various documents, the Tg of the copolymer can also be determined from the Tgn (K) of each homopolymer and the mass fraction (Wn) of the monomer by the following formula. .

[0033]

(Equation 1)

Incidentally, if the Tg of the main homopolymer is shown,
106 ° C for polyacrylic acid, 8 for polymethyl acrylate
° C, polyethyl acrylate 22 ° C, polyacrylic acid n
-Butyl is -54 ° C, 2-ethylhexyl polyacrylate is -70 ° C, 2-hydroxyethyl polyacrylate is -15 ° C, and 2-hydroxyethyl polymethacrylate is 5 ° C.
5 ° C., 105 ° C. for polymethyl methacrylate, 32 ° C. for polyvinyl acetate, 125 ° C. for polyacrylonitrile, 100 ° C. for polystyrene, and 130 ° C. for polymaleic acid.

The pressure-sensitive adhesive polymer obtained by the polymerization method of the present invention preferably forms a pressure-sensitive adhesive layer of a pressure-sensitive adhesive product in a form crosslinked with a predetermined amount of a crosslinking agent. This is because when crosslinked with a crosslinking agent, various physical properties such as cohesive force are improved. As the cross-linking agent, a compound having two or more functional groups in one molecule, which is a functional group of the functional group-containing monomer and has a reactivity with a functional group introduced into the pressure-sensitive adhesive polymer, can be used. . Examples of such a functional group include an isocyanate group, an epoxy group, an amino group, a methylol group, an alkoxymethyl group, an imino group, a metal chelate group, and an aziridinyl group. Specific compounds include a polyfunctional isocyanate compound, a polyfunctional epoxy compound, a polyfunctional melamine compound, a metal crosslinking agent, an aziridine compound, and the like.

Examples of the polyfunctional isocyanate compound having two or more isocyanate groups include tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate, xylylene diisocyanate, meta-xylylene diisocyanate, 5-naphthalenediisocyanate,
Diisocyanate compounds such as hydrogenated diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate; bulletin polyisocyanate compounds such as "Sumidur N" (manufactured by Sumitomo Bayer Urethane Co.); "Desmodur IL"; Desmodur HL "(both manufactured by Bayer AG)," Coronate EH "(manufactured by Nippon Polyurethane Industry Co., Ltd.) and other polyisocyanate compounds having an isocyanurate ring;" Sumidur L "(Sumitomo Bayer Urethane Co., Ltd.) Adduct polyisocyanate compounds such as "Coronate L" and "Coronate L-55E" (both manufactured by Nippon Polyurethane). These can be used alone or in combination of two or more. Also, a so-called blocked isocyanate obtained by reacting an isocyanate group of these compounds with a masking agent having active hydrogen and inactivating them may be used.

The polyfunctional epoxy compound is not particularly limited as long as it is a compound having two or more epoxy groups per molecule. Specific examples include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, bisphenol A / epichlorohydrin type epoxy resin, N, N, N ', N'-tetraglycidyl-
m-xylenediamine, 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N-diglycidylaniline, N, N-diglycidyltoluidine and the like.

The polyfunctional melamine compound is not particularly limited as long as it has at least two methylol groups, alkoxymethyl groups or imino groups per molecule. Specific examples include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexabutoxymethylmelamine, hexapentyloxymethylmelamine, and the like.

The metal crosslinking agent is not particularly limited. Specific examples include metals such as aluminum, zinc, cadmium, nickel, cobalt, copper, calcium, barium, titanium, manganese, iron, lead, zirconium, chromium, tin, acetylacetone, methyl acetoacetate, ethyl acetoacetate, and lactic acid. Metal chelate compounds coordinated with ethyl, methyl salicylate, and the like.

As the aziridine compound, N, N'-hexamethylene-1,6-bis (1-aziridinecarboxamide), trimethylolpropane-tri-β-aziridinylpropionate, bisisophthaloyl-1 − (2-
Methylaziridine), tri-1-aziridinyl phosphoxide, N, N′-diphenylethane-4,4′-bis (1-aziridinecarboxamide) and the like.

A crosslinking system using a functional group-containing monomer as a carboxyl group-containing monomer and a polyfunctional epoxy compound as a crosslinking agent is most preferred. The amount of the cross-linking agent is not particularly limited, but is preferably 0.05 to 15% by mass based on the pressure-sensitive adhesive polymer (nonvolatile content). If the amount is less than 0.05% by mass, the crosslinking is insufficient, the crosslinking density is low, and the cohesive strength may be insufficient.
If it exceeds 15% by mass, the crosslink density may be too high and the adhesive strength may be low. A more preferred lower limit is 0.1.
% By mass, and the upper limit is 10% by mass.

The pressure-sensitive adhesive composition containing the pressure-sensitive adhesive polymer and the crosslinking agent may optionally contain a tackifier. As the tackifier, (polymerized) rosin,
(Polymerization) Rosin ester type, terpene type, terpene phenol type, coumarone type, coumarone indene type, styrene resin type, xylene resin type, phenol resin type, petroleum resin type and the like can be mentioned. These can be used alone or in combination of two or more.

Although the amount of the tackifier is not particularly limited,
Usually, 5-1 to 100 parts by mass of the polymer for adhesive is used.
Preferably it is 00 parts by mass. If the amount of the tackifier is less than 5 parts by mass, the effect of improving the adhesive strength by the tackifier may not be exhibited. On the other hand, when the addition amount of the tackifier is more than 100 parts by mass, the tack may be reduced and the adhesive strength may be reduced. More preferably, it is in the range of 10 to 50 parts by mass.

If necessary, conventionally known additives such as fillers, pigments, diluents, antioxidants, ultraviolet absorbers and ultraviolet stabilizers are further added to the pressure-sensitive adhesive composition. You may. One or two of these additives may be used.
More than species can be used. The amount of these additives
What is necessary is just to set suitably so that desired physical property may be obtained.

Polymer for pressure-sensitive adhesive, crosslinking agent, if necessary
The pressure-sensitive adhesive composition prepared by mixing the above various additives, solvents and the like can be suitably used for the production of various pressure-sensitive adhesive products such as pressure-sensitive adhesive sheets, pressure-sensitive labels, pressure-sensitive adhesive tapes and double-sided tapes. Such a pressure-sensitive adhesive product is produced without a substrate or by forming a layer of a pressure-sensitive adhesive composition on a substrate and subjecting it to a crosslinking reaction.

As the base material, conventionally known papers such as high-quality paper, kraft paper, crepe paper, glassine paper, etc .; synthetic paper formed from polypropylene or the like and an inorganic filler; polyethylene, polypropylene, polyester, polystyrene, polyethylene terephthalate Plastics such as phthalate, polyvinyl chloride, and cellophane; fiber products such as woven and nonwoven fabrics; The shape of the substrate includes, for example, a film, a sheet, a tape, a plate, and a foam, but is not particularly limited.

By applying the pressure-sensitive adhesive composition to one surface of the substrate by a known method, a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive tape, a pressure-sensitive adhesive label or the like can be obtained. Further, by applying the pressure-sensitive adhesive composition to a release paper or the like in which a release agent is applied to a sheet-like material such as paper, synthetic paper, or a plastic film, an adhesive layer without a base material (single-layer structure) is obtained. It can be used as a double-sided tape without a base material. Alternatively, a double-sided tape may be formed by applying the same or different pressure-sensitive adhesive composition to both surfaces of the substrate.

The method for applying the pressure-sensitive adhesive composition to the substrate is not particularly limited, and a known method such as a roll coating method, a spray coating method, or a dipping method can be employed. In this case, any of a method of directly applying the pressure-sensitive adhesive composition to the substrate, a method of applying the pressure-sensitive adhesive composition to release paper or the like, and then transferring the coated material onto the substrate can be adopted.

After applying the pressure-sensitive adhesive composition, it is dried to form a pressure-sensitive adhesive layer on the substrate. The drying temperature is not particularly limited, but since the crosslinking reaction proceeds during heating and drying, it is preferable to dry at a temperature at which the crosslinking reaction proceeds promptly depending on the type of the crosslinking agent. In some applications, the pressure-sensitive adhesive composition may be directly applied to an adherend.

On the surface of the pressure-sensitive adhesive layer formed on the substrate,
For example, release paper may be attached. The surface of the pressure-sensitive adhesive layer can be suitably protected and preserved. The release paper is peeled off from the surface of the pressure-sensitive adhesive layer when the pressure-sensitive adhesive product is used. If a pressure-sensitive adhesive layer is formed on one surface of a base material such as a sheet or a tape, a known release agent may be applied to the back surface of the base material to form a release agent layer. By winding the pressure-sensitive adhesive sheet (tape) into a roll with the pressure-sensitive adhesive layer inside, the pressure-sensitive adhesive layer comes into contact with the release agent layer on the back of the base material, so that the surface of the pressure-sensitive adhesive layer is protected and protected. Will be saved.

[0051]

The present invention will be described in detail with reference to the following examples, but the scope of the present invention is not limited to these examples. Hereinafter, unless otherwise specified, “%” indicates “% by mass” and “parts” indicates “parts by mass”.

Example 1 A thermometer, a stirrer, an inert gas inlet tube, a reflux condenser, and a dropping funnel equipped with a dropping funnel were used for synthesizing a polymer for an adhesive.
In a one-necked flask, a mixture 4 comprising 219 parts of butyl acrylate, 219 parts of 2-ethylhexyl acrylate, 30 parts of acrylic acid, and 12 parts of 2-hydroxyethyl acrylate
180 parts of 80 parts, 120 parts of vinyl acetate and 600 parts of ethyl acetate were charged, and the temperature was raised to 80 ° C. under a stream of nitrogen gas. When the temperature reached 80 ° C., 0.27 parts of azobisisobutyronitrile (AIBN) was added. Then, polymerization for the initial charge was started. After 30 minutes from the start of polymerization, 420 parts of the remaining monomer, 0.63 part of AIBN and 20 parts of ethyl acetate
Were added over 1.5 hours, and at the end of the addition, 100 parts of ethyl acetate were added to the reactor. When the reaction was further continued for 90 minutes, a mixture consisting of 1.8 parts of AIBN and 50 parts of ethyl acetate was added as a booster in five portions every 30 minutes, and the reaction was continued for another 2 hours. At the end of the polymerization, 230 parts of ethyl acetate was added and cooled.

The polymer solution No. 1 has a non-volatile content of 39.1% and a viscosity of 4200 mPa · s (25
C, B-type viscometer, the same applies hereinafter). The weight average molecular weight (Mw) of the polymer is 50.9 × 10 ⁴ (GPC measurement:
Standard polystyrene equivalent). In addition, the reaction solution was sampled from the reactor, and the time-dependent change in the polymerization rate was measured by GC-M.
It was examined by S (gas chromatography mass spectroscopy) and shown in Table 1.

The conditions for measuring the molecular weight by GPC are as follows. The sample concentration was 0.2%, and the injection volume was 200 microliter / time. GPC measuring device: Liquid Chromatography Model 510
(Waters) Detector: M410 differential refractometer Column: Ultra Styragel Linear (7.8 mm × 30 c)
m) Ultra Styragel 100A (7.8 mm × 30 cm) Ultra Styragel 500A (7.8 mm × 30 cm) Solvent: THF (tetrahydrofuran) Comparative Example 1 The synthesis of a polymer for a pressure-sensitive adhesive for comparison was carried out by dropping a monomer having a uniform composition. went. In a four-necked flask equipped with a thermometer, a stirrer, an inert gas inlet tube, a reflux condenser, and a dropping funnel, 219 parts of butyl acrylate, 2-acrylic acid,
219 parts of ethylhexyl, 30 parts of acrylic acid, 180 parts of 600 parts of a monomer mixture composed of 12 parts of 2-hydroxyethyl acrylate and 120 parts of vinyl acetate, and 420 parts of ethyl acetate were charged, and the temperature was increased under a nitrogen gas stream. When the temperature reached 80 ° C., 0.27 parts of azobisisobutyronitrile (AIBN) was added to initiate polymerization of the initial charge. After 30 minutes from the start of the polymerization, 420 parts of the remaining monomer, 0.63 part of AIBN and 18 parts of ethyl acetate
Was added over 1.5 hours, and at the end of the addition, 100 parts of ethyl acetate were added to the reactor. When the reaction was further continued for 90 minutes, a mixture consisting of 1.8 parts of AIBN and 50 parts of ethyl acetate was added as a booster in five portions every 30 minutes, and the reaction was continued for another 2 hours. At the end of the polymerization, 150 parts of ethyl acetate was added and cooled.

The obtained polymer solution N for comparative pressure-sensitive adhesive was obtained.
o. 2 has a non-volatile content of 36.8% and a viscosity of 5200 mPa ·
s. The weight average molecular weight (Mw) of the polymer is 5
6.1 × 10 ⁴ (GPC measurement: standard polystyrene conversion)
Met. Further, similarly to the example, the time change of the polymerization rate was G
It was examined by C-MS and shown in Table 1.

[0056]

[Table 1]

The monomer remaining after 90 minutes of aging in Table 1 was mostly vinyl acetate in both Example 1 and Comparative Example 1. In Example 1, 1.8% of the residual vinyl acetate was present.
(The value when the total amount of the used monomers is 100%), and in Comparative Example 1, it was 7.2%. In Example 1, it was considered that the amount of vinyl acetate could be reduced since vinyl acetate was initially charged, and the final polymerization rate could be increased to 97.8%.

Example 2 A thermometer, a stirrer, an inert gas inlet tube, a reflux condenser, and a dropping funnel were used for synthesizing a polymer for an adhesive.
In a one-necked flask, 180 parts of a mixture of 340 parts of butyl acrylate, 136.2 parts of methyl methacrylate, 24 parts of maleic anhydride, and 540 parts of acrylic acid, 60 parts of vinyl acetate, and 60 parts of ethyl acetate 315 parts,
45 parts of toluene was charged, and the temperature was increased under a stream of nitrogen gas.
When the temperature reached 0 ° C., 0.48 parts of a peroxide-based initiator (trade name “Niper BMT-K40”, manufactured by NOF CORPORATION) was added, and polymerization for the initial charge was started. 1 from the start of polymerization
After 5 minutes, a mixture of 360 parts of the remaining monomer, 0.72 parts of Niper BMT-K40 and 20 parts of ethyl acetate was added dropwise over 1.5 hours, and 85 parts of ethyl acetate was added to the reactor when the addition was completed. Was added. When the content was further reacted for 90 minutes, the viscosity of the content increased, so that 248.2 parts of toluene and 45.4 parts of ethyl acetate were added as diluting solvents, and an azo-based polymerization initiator (trade name “ABN-E”) was added as a booster. ": A mixture consisting of 1.8 parts of Nippon Hydrazine Industry Co., Ltd.) and 41.7 parts of toluene was added in five portions every 30 minutes, and the reaction was continued for 4 hours. At the end of the polymerization, 28 parts of toluene was added, followed by cooling.

The conversion was 95.4%. The obtained polymer solution for adhesive No. The nonvolatile content of 3 is 39.4%,
The viscosity was 4050 mPa · s (25 ° C., B-type viscometer, the same applies hereinafter). The weight average molecular weight (Mw) of the polymer is 1.1 × 10 ⁴ (GPC measurement: standard polystyrene conversion)
Met.

The adhesive polymer solution No. 10 of 3
2.7 parts of a 3% ethyl acetate solution of a polyfunctional epoxy compound (trade name "TETRAD-C": manufactured by Mitsubishi Gas Chemical Company: 100% active ingredient) is used as a cross-linking agent for 0 part (present).
5 parts of the pressure-sensitive adhesive composition No. 1 was prepared.

As a substrate, a polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc., thickness 25 μm)
And the pressure-sensitive adhesive composition No. 1 has a thickness of 25μ after drying
m, and dried at 100 ° C. for 3 minutes. Thereafter, a release paper (manufactured by San-A Kaken Co., Ltd., trade name: K-80HS) is adhered to the surface of the pressure-sensitive adhesive to protect the pressure-sensitive adhesive.
An adhesive film (adhesive product) was obtained. This adhesive product was cut into a predetermined size to prepare a test piece. The release paper was peeled off when performing various measurement tests.

Comparative Example 2 A pressure-sensitive adhesive film was produced in the same manner as in Example 2, except that the composition of the pressure-sensitive adhesive polymer was changed as shown in Table 2.

Comparative Example 3 A pressure-sensitive adhesive film was prepared in the same manner as in Example 2 except that the composition of the polymer for a pressure-sensitive adhesive was changed as shown in Table 2, and a mixture of all monomers was dropped over 1.5 hours. Manufactured.

The pressure-sensitive adhesive films obtained in Example 2 and Comparative Examples 2-3 were laminated on an ABS plate (thickness: 3 mm) with a heating roll at 140 ° C. After cooling, the following characteristics were evaluated.

[Cooling and Heating Cycle] A thermo-hygrostat (PL-2)
F: manufactured by Tabaispec)
After leaving at -20 ° C for 4 hours, leaving at 80 ° C for 4 hours as one cycle, 10 cycles were repeated. AB
The adhesion between the S plate and the adhesive film was observed. The film was evaluated as ○ when there was no abnormality such as peeling, as Δ when the film was partially peeled, and as X when the film was significantly peeled. The results are shown in Table 2.

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[Table 2]

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According to the present invention, when 70% by mass or more of vinyl acetate is initially charged, the polymerization rate can be increased, and the amount of residual monomers and low molecular weight vinyl acetate can be reduced. As a result, it was possible to provide an adhesive product having an excellent balance between adhesive force and cohesive force and low temperature sensitivity.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09J 157/00 C09J 157/00 F term (Reference) 4J011 AA02 BB07 4J040 DE022 DF01 DF041 DF051 DF06 DG02 EB13 EC00 EF28 EH01 GA05 GA07 HA066 HD43 JB09 LA01 LA06 MA09 MA10 MA16 MB02 MB03 MB05 QA02 4J100 AG04Q AJ01R AJ02R AJ08R AK32R AL03P AL04P AL05P AL08P AL09R BC04P CA04 CA05 FA34 JA05

Claims (4)

[Claims] 1. A method for producing a polymer for a pressure-sensitive adhesive by radically polymerizing a monomer component essentially containing at least one alkyl (meth) acrylate and vinyl acetate. 70-100% by mass of
And a part of monomers other than vinyl acetate are first charged into a reactor to initiate polymerization, and then the remaining monomer components are charged into the reactor and polymerized. Method. 2. The polymerization method according to claim 1, wherein the monomer component further contains a functional group-containing monomer having a functional group capable of reacting with a functional group of a crosslinking agent. 3. A pressure-sensitive adhesive composition comprising the pressure-sensitive adhesive polymer obtained by the polymerization method according to claim 1. 4. A pressure-sensitive adhesive product comprising a pressure-sensitive adhesive layer obtained from the pressure-sensitive adhesive composition according to claim 3.