WO2001014492A1

WO2001014492A1 - Acrylic waterborne pressure sensitive adhesive composition with alkaline ph

Info

Publication number: WO2001014492A1
Application number: PCT/US2000/022362
Authority: WO
Inventors: Akiyoshi Mori; Motoyuki Takagi
Original assignee: National Starch And Chemical Investment Holding Corporation
Priority date: 1999-08-20
Filing date: 2000-08-15
Publication date: 2001-03-01
Also published as: JP2001055550A; AU2807901A

Abstract

To provide an acrylic waterborne pressure sensitive adhesive composition improved at least in one characteristic, such as high adhesion, less reduction of adhesion due to secular deterioration, etc. An acrylic waterborne pressure sensitive adhesive composition prepared by subjecting to emulsion polymerization in the presence of an aqueous medium a monomer mixture of 65 to 99.5 wt.% of (A) (meth)acrylic acid ester represented by the general formula (I): CH2 = C(R1)COOR2 (wherein R1 is hydrogen or methyl group and R2 is an alkyl group of 1 - 18 carbon atoms optionally having substituent (s)), and 0.1 to 5 wt.% of at least a member selected from (B) a monomer containing carboxyl group(s), (C) a monomer containing amide group(s), and (D) a monomer containing hydroxyl group(s), and adjusting pH of the resulting aqueous resin composition to 5 - 11 with (E) a non-volatile alkaline material. In addition, it is preferably an acrylic waterborne pressure sensitive adhesive composition in which 0 to 30 wt parts of (F) tackifier is added against 100 wt parts of the monomer mixture.

Description

ACRYLIC WATERBORNE PRESSURE SENSITIVE ADHESIVE COMPOSIΗON WITH ALKALINE PH

5 Detailed description of the invention

The present invention concerns an acrylic waterborne pressure sensitive adhesive composition, more specifically an acrylic waterborne pressure sensitive adhesive composition having high adhesion, less secular deterioration of adhesion and high coating 0 stability, used for papers, metals such as stainless steel, etc. and plastics such as polyethylene, etc.

While adhesives have so far been widely used for PSA tapes, PSA sheets, PSA paper labels, etc., aqueous adhesives not using any organic solvent are now attracting attention with growing public 5 interest in problems of global environment and safety of the human body in recent years. As a waterborne pressure sensitive adhesive composition, acrylic waterborne pressure sensitive adhesive composition is being studied, and improvement of adhesion to various adherents by the addition of tackifier, etc. is realized, but there still 0 remain problems of insufficient coating stability and low water resistance and humidity resistance (refer to Japanese Laid-Open Patent Publication No. S63-256672 and Japanese Laid-Open Patent Publication No. S58-185668).

As an acrylic waterborne pressure sensitive adhesive 5 composition having high adhesion, water resistance and coating stability, an acrylic waterborne pressure sensitive adhesive composition is disclosed which is prepared by polymerizing an acrylic monomer mixture containing polymerizable monomers and having at least one kind of functional group selected from carboxyl group(s), amide group(s), and hydroxyl group(s) in the presence of a tackifier dissolved therein, with an anionic surfactant having copolymerizable double bonds, and adjusting pH of the resultant aqueous resin with ammonia water (refer to Japanese Laid-Open Patent Publication No. H8-231937). However, there is no description at all about secular deterioration of adhesion of this acrylic waterborne pressure sensitive adhesive composition, and it is also insufficient in the coating stability required for an adhesive.

The present invention, with a view of solving such problems and achieving the requirement of providing an acrylic waterborne pressure sensitive adhesive composition improved, as compared with any conventional acrylic waterborne pressure sensitive adhesive composition, at least in one of the characteristics of high adhesion against papers, metals such as stainless steel, etc. and plastics and less secular deterioration of adhesion to various aherents, while preserving performances of an adhesive in respect of retaining power, ooze, etc. According to one of the essences of the present invention, a new acrylic waterborne pressure sensitive adhesive composition is provided, which is an acrylic waterborne pressure sensitive adhesive composition prepared by subjecting to emulsion polymerization in the presence of an aqueous medium a monomer mixture of 65 to 99.5wt% of (A) (meth)acrylic acid ester represented by the general formula: CH2 = C(R1 )COOR2 (I) (wherein R1 is hydrogen or methyl group and R2 is an alkyl group of 1 - 18 carbon atoms optionally having substituent (s)), and 0.1 to 5wt% of at least a member selected from (B) a monomer containing carboxyl group(s), (C) a monomer containing amide group(s), and (D) a monomer containing hydroxyl group(s), and adjusting pH of the resulting aqueous resin composition to 5 - 11 with (E) a non-volatile alkaline material, and this is particularly suitable as a waterborne pressure sensitive adhesive composition used for papers, metals and plastics.

In the description of the present specification, a state not containing any solvent is used as reference for weight parts and wt%, unless otherwise specified.

In the present invention, "aqueous" refers to a state in which a resin exists in an aqueous medium, which means a state in which the resin is dissolved and/or not dissolved in the aqueous medium.

Moreover, in the present invention, "aqueous medium" refers to common water such as distilled water or ion-exchanged water, etc. for example, but it may contain organic solvents which are either water soluble or dispersible in water and only minutely reactive with resin materials related to the present invention such as monomer, etc., it may also contain acetone, ethyl acetate, alcohols, etc. for example. It may further contain monomers, oligomers, prepolymers and/or resins, etc. which are either water soluble or dispersible in water, and it may still further contain emulsifying agents, polymerizable emulsifying agents, polymerization initiators, reducing agents, chain transfer agents and/or various kinds of additives, etc. which are usually used when manufacturing aqueous resin or water-soluble resin as described later. in the present invention, (A)"(meth)acrylic acid ester represented by the general formula (I)" constitutes the main component of the acrylic waterborne pressure sensitive adhesive composition according to the present invention, and itself has an excellent adhesive function performance at room temperature. In this specification, acrylic acid and metacrylic acid are also generically designated as "ester (meth)acrylic acid ester".

As such "(A) (meth)acrylic acid ester", one may mention methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i- propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, n- hexyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, n- nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, n- dodecyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, etc., for example.

Esepecially, preferable as (A)(meth)acrylic acid ester are methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate and butyl (meth)acrylate.

Those (A)(meth)acrylic acid esters can be used either alone or in combination with one another. in the present invention, the monomeric mixture shall preferably contain 65 to 99.9 wt% of (meth)acrylic acid ester. In the adhesive composition according to the present invention, "(B) monomer containing carboxyl group(s)", "(C) monomer containing amide group(s)", and "(D) monomer containing hydroxyl group(s)" are believed to control a reduction in adhesion due to passage of time i.e. secular deterioration of the adhesive composition according to the present invention, in combination with an adjustment of pH made by using "(E) non-volatile alkaline material" to be described later.

In the "(B) monomer containing carboxyl group(s)", the secular deterioration of adhesion due to reaction between the carboxyl group(s) in the waterborne pressure sensitive adhesive composition and the metallic ions in the paper base material is controlled because, thanks to the use of (E) non-volatile alkaline material especially, the salt formed does not volatilize with the evaporation of water content, but the waterborne pressure sensitive adhesive composition according to the present invention is not subject to any particular restraint by those reasons.

In the adhesive composition according to the present invention, "(B) monomer containing carboxyl group(s)" is a compound having carboxyl group(s) and ethylenic double bond(s), as exemplified by acrylic acid, metacrylic acid, itaconic acid, maleic acid, fumaric acid, half esters of maleic acid, etc., and especially acrylic acid, metacrylic acid, itaconic acid, and maleic acid are preferable.

Those "(B) monomers containing carboxyl group(s)" can be used alone or in combination with one another. In the present invention, "(C) monomer containing amide group(s)" refers to a compound having amide group(s) and ethylenic double bond(s), the nitrogen of the amide group possibly having substituent(s), including, for example, (d ) (meth)acrylamides such as (meth)acrylamide, N- propyl(meth)acrylamide, etc.:

(c2) vinyl compounds of chainlike amide such as N- vinylbutanamide, N-vinylhexanamide, etc.

(c3) vinyl compounds of annular amide such as N-vinyl- pyrrolidone, N-vinylcaprolactam, etc.

Especially, (meth)acrylamides such as (meth)acrylamide, N- propyl(meth)acrylamide, etc. are preferable.

Those (C) monomers containing amide group(s) can be used either alone or in combination with one another. In the present invention, "(D) monomer containing hydroxyl group(s)" refers to a compound having hydroxyl group(s) and ethylenic double bond(s), including, for example,

2-hydroxylethyl (meth)acrylate, 4-hydroxylbutyl

(meth)acrylate, 2-hydroxylpropyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, etc. and, especially, 2- hydroxylethyl (meth)acrylate and 4-hydroxylbutyl (meth)acrylate are preferable as (D).

Those (D) monomers containing hydroxyl group(s) can be used either alone or in combination with one another. In the present invention, the monomeric mixture shall preferably contain 0.1 to 5 wt% of at least one kind selected from among (B)monomer containing carboxyl group(s), (C)monomer containing amide group(s), and (D)monomer containing hydroxyl group(s), more preferably 0.5 to 3 wt% and still more preferably 0.5 to 2 wt%.

Those (B) monomers containing carboxyl group(s), (C) monomers containing amide group(s), and (D) monomers containing hydroxyl group(s) can be used either alone or in combination with one another. In the waterborne pressure sensitive adhesive composition according to the present invention, the said monomeric mixture may contain 0 to 30 wt% of monomers other than (A) ~ (D) copolymerizable with (A) - (D).

Here, "monomers other than (A) - (D)" are not subject to any particular restriction as long as they have such functions as controlling the glass transition temperature (Tg) of the resin obtained by polymerization of the said monomer mixture and providing it with adhesion, etc. and have no negative influences on the characteristics of the target waterborne pressure sensitive adhesive composition. As such "monomers other than (A) ~ (D)", one may enumerate, for example,

(ml ) vinyl compounds such as vinyl acetate, vinyl propionate, etc.

(m2) aromatic vinyl compounds such as stylene, vinyl toluene, α-methyl stylene, etc. (m3) vinyl compounds having cyano group(s) such as acrylonitrile, methacrylonitrile, etc.

(m4) silane coupling agents having ethylenic double bond(s) such as γ-(meth)acryloxy propyltrimethoxy silane, etc. (m5) compounds having epoxy group(s) such as glycidyl

(meth)acrylate, etc.

(m6) alkenes such as ethylene, propylene, butylene, isoprene, etc.

(m7) vinyl chloride compounds such as vinyl chloride, vinylene chloride, vinylidene chloride, etc.

(m8) compounds having methylol group(s) such as N- methylol (meth)acrylamide, etc.

(m9) multifunctional monomers such as diallyl phthalate, triallyl isocyanurate, divinylbenzene, etc. Those "monomers other than (A) - (D)" can be used either alone or in combination with one another.

In the waterborne pressure sensitive adhesive composition according to the present invention, a monomer mixture, containing at least one kind of monomer selected from said (A) and (B) to (D) and containing "monomers other than (A) ~ (D)" as required, is emulsion polymerized, in an aqueous medium, by a normal method, and by using a polymerization initiator and an emulsifying agent as required, to obtain aqueous resin composition. The polymerization initiator may also be used in combination with a reducing agent and a chain transfer agent as required. The polymerization reaction conditions such as reaction temperature, reaction time, composition and concentration of the monomer mixture in the aqueous medium, type, concentration and agitating speed, etc. of the polymerization initiator, the reducing agent, the chain transfer agent and emulsifying agent may be selected as required, depending on the characteπstics of the target waterborne pressure sensitive adhesive composition.

Here "polymerization initiator" used in the present invention refers to a compound capable of causing polymerization of the monomer mixture with an addition in small quantity, preferably one which can be used in an aqueous medium. One may enumerate, for example; persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate: organic peroxides such as t-butyl hydroperoxide, t-butyl peroxide benzoate, etc. hydrogen peroxide, etc..

Especially, ammonium persulfate, sodium persulfate, and potassium persulfa^te are preferable.

Moreover, "chain transfer agent" refers to a compound capable of controlling the molecular weight of the said aqueous resin and controlling the cohesion as characteristic of an adhesive, as exemplified by n-dodecyl mercaptan, t-dodecyl mercaptan, n-butyl mercaptan, 2-mercaptoethanol, etc.

Furthermore, "emulsifying agent" refers to a surfactant used for forming emulsion of aqueous medium and monomeric mixture, preferably a surfactant not having any negative influences on the polymerization reaction, and may be a compound selected from the group consisting of compounds having sulfonic group(s), sulfonate group(s) or sulfate group(s) and their mixtures. Ordinary surfactant may also be used other than the above. One may enumerate, for example, anionic surfactants such as higher fatty acid salt, alkyl aryl sulfonate, alkyl sulfonate, alkyl sulfate, polyoxyethylene alkyl sulfate, polyoxyethylene alkyl ether sulfate, alkyl sulfo succinate, etc. and nonionic surfactants such as polyoxy ethylene alkyl ether, polyoxy ethylene alkyl phenol ether, sorbitan higher fatty esters, polyoxyalkyl aryl ether, oxyethylene oxypropylene block copolymer, etc.

For emulsion polymerization, a polymerizable emulsifying agent can be used as emulsifying agent.

Here "polymerizable emulsifying agent" refers to a compound capable of functioning as emulsifying agent having polymerizable unsaturated bond(s) and capable of forming an emulsion of aqueous medium and monomer mixture, preferably an ethylenic unsaturated monomer selected from the group consisting of ethylenic unsaturated monomers having sulfonic group(s), sulfonate group(s), sulfate group(s) or ethyleneoxy group(s) and their mixtures. Moreover, the sulfonic group(s) or sulfonate group(s) of the said polymerizable emulsifying agent may be in the form of salt and, as counter cation of sulfonic group or sulfonate group, ammonium ion or alkaline metallic ion is preferable, especially ammonium ion, potassium ion, and sodium ion are preferable. As products realized by containing such polymerizable emulsifying agent, one may enumerate, for example, ELEMINOL JS-2 of Sanyo Chemical Industries, Ltd , AQUALON HS-10 (commercial name), AQUALON RN20 (commercial name), etc of Dai-ichi Kogyo Seiyaku Co , Ltd , LATEMUL S180A (commercial name), etc of Kao Corporation It is preferable to use 0 1 to 5 wt parts of those emulsifying agents for 100 wt parts of said monomer mixture realized by containing at least one kind of monomer selected from (A) and (B) ~ (D) and possibly containing "monomers other than (A) - (D)" It is more preferable to use 0 5 to 3 wt parts and it is particularly preferable to use 1 to 3 wt parts

In the waterborne pressure sensitive adhesive composition according to the present invention, the pH of an aqueous resin composition prepared by the said emulsion polymerization is adjusted to be in the range from 5 to 11 , by using (E) non-volatile alkaline material, to obtain the target acrylic waterborne pressure sensitive adhesive composition This adjustment of pH is necessary because, usually, the waterborne pressure sensitive adhesive composition after polymerization reaction presents acidity with addition of a polymerization initiator and, as required, a chain transfer agent

It is preferable to adjust pH of the aqueous resin composition to 5 to 11 , and it is more preferable to adjust it to 7 to 9

Here "(E) non-volatile alkaline material" is a material which is non-volatile at normal temperature and normal pressure, dissolves in water and presents a pH value no less than 7, and one may enumerate, for example, hydroxide of alkaline metals such as potassium hydroxide, sodium hydroxide, etc and hydroxide of alkaline earth metals such as magnesium hydroxide, calcium hydroxide, etc Especially, potassium hydroxide and sodium hydroxide are preferable Those (E) non-volatile alkaline materials can be used either alone or in combination with one another, and the (E) non-volatile alkaline material can be used either as a solution in a water medium or directly as it is

In the case where volatile ammonia (ammonia water) is used in place of the (E) non-volatile alkaline material, it is impossible to reveal a desirable characteristic of controlling secular deterioration of adhesion, as demonstated by the waterborne pressure sensitive adhesive composition according to the present invention This may be attributed to the following reason Ammonia forms a salt with carboxyl group(s) but the ammonia itself volatilizes together with evaporation of water, and it is believed that the carboxyl group is regenerated from the salt once formed On the other hand, a non-volatile alkaline material does not volatilize even with the evaporation of water after the formation of a salt with carboxyl group(s) and, therefore, no regeneration of the carboxyl group takes place and the carbonate once formed remains in the adhesive layer in the form of a salt For that reason, it is believed that reaction with the multivalent metal ions contained in the paper base material is controlled, thus preventing reduction of adhesion due to secular deterioration However, the waterborne pressure sensitive adhesive composition according to the present invention is not subject to any particular restriction for such reasons.

In the acrylic waterborne pressure sensitive adhesive composition according to the present invention, the preference is a waterborne pressure sensitive adhesive composition further containing, in the said pH controlled aqueous resin composition, 0 to 30 wt parts of (F) tackifier for 100 wt parts of monomer mixture containing at least one kind of monomer selected from said (A) and (B) - (C) and possibly containing "monomers other than (A) ~ (D)". Here, (F) tackifier refers to a tackifier normally used for a waterborne pressure sensitive adhesive composition, and has the function of improving the adhesion to various kinds of adherents.

As "(F) tackifier", one may enumerate, for example; terpene resin, rosin resin, petroleum resin with C5 to C9, xylene resin, phenolic resin, chroman resin, etc. and, especially, terpene resin and rosin resin are preferable.

They can be selected and used either alone or in combination with one another, as required.

In the waterborne pressure sensitive adhesive composition according to the present invention, it is preferable to add 0 to 30 wt parts of (F) tackifier for 100 wt parts of monomer mixture, containing at least one kind of monomer selected from said (A) and (B) ~ (D) and possibly containing "monomers other than (A) - (D)", and it is more preferable to add 10 to 20 wt parts. To the waterborne pressure sensitive adhesive composition according to the present invention may further be added additives generally used for ordinary acrylic waterborne pressure sensitive adhesive composition, such as wetting agent, anti-foam agent, thickening agent, antioxidant, UV absorbent, radical trapping agent, dispersant, pigment and antiseptic agent, etc., as required.

Those additives may be selected as required depending on the characteristics of the target waterborne pressure sensitive adhesive composition, and used either alone or in combination with one another. Moreover, the present invention provides a manufacturing process of said acrylic waterborne pressure sensitive adhesive composition according to the present invention. Namely, the acrylic waterborne pressure sensitive adhesive composition according to the present invention can be manufactured by subjecting to emulsion polymerization a monomer mixture comprising (A) (meth)acrylic acid ester and at least a member selected from (B) a monomer containing carboxyl group(s), (C) a monomer containing amide group(s), (C) a monomer containing amide group(s), and (D) a monomer containing hydroxyl group(s), and adjusting pH of the resulting aqueous resin composition to 5 - 11 with (E) a non-volatile alkaline material. Furthermore, in this manufacturing process, it is preferabale to add (F) a tackifier. The monomer composition may contain monomers other than (A) ~ (D).

The acrylic waterborne pressure sensitive adhesive composition according to the present invention can improve at least one of the characteristics of adhesion and reduction of adhesion due to secular deterioration, because pH of the aqueous resin composition, prepared by subjecting to emulsion polymerization a monomer mixture comprising (A) (meth)acrylic acid ester and at least a member selected from (B) a monomer containing carboxyl group(s), (C) a monomer containing amide group(s), and (D) a monomer containing hydroxyl group(s), is adjusted by using (E) a non-volatile alkaline material.

Working Example

The present invention will be described concretely and in detail by using Working Examples and Comparative Example hereafter, but those Working Examples and Comparative Examples represent only a mode of the present invention, and the present invention is in no way restricted by those examples.

In the description of Working Examples, a state not containing any solvent is used as reference for weight parts and wt%, unless otherwise specified.

Working Example 1 :

(1 ) Manufacture of an acrylic waterborne pressure sensitive adhesive composition

430 wt parts of distilled water and, as emulsifying agent, 0.7 wt parts of sodium dodecyl benzenesulfonate which was an anionic surfactant were poured into a reactor provided with an agitator, a reflux condenser, 2 dripping tanks and a thermometer, and the mixture was heated to 75°C while being agitated. To this mixture was added an aqueous solution prepared by dissolving 3% of monomer emulsifying agent (1 ) and 3 wt parts of ammoniuum persulfate in 30 wt parts of distilled water and, after an initial period reaction, an aqueous solution, prepared by dissolving the remaining portion of the monomer emulsifying agent (1 ) and 2 wt parts of ammoniuum persulfate in 25 wt parts of distilled water, was dripped from separate dripping tanks in 3 hours and 3.5 hours respectively while maintaining the temperature of the mixture at 75°C.

Here, the monomer emulsifying agent (1 ) was obtained by blending the following components:

(A1 ) 2-ethylhexyl acrylate (hereinafter referred to as "2HEA") - 840 wt parts (A2) methyl methacrylate (hereinafter referred to as "MMA")

~ 150 wt parts (B1 ) acrylic acid (hereinafter referred to as "AA")

- 10 wt parts γ-methacryloxypropyltrimethoxysilane (hereinafter referred to as "A174") -- 0.3 wt parts sodium dodecylbenzenesulfonate (anionic surfactant) -- 22.8 wt parts n-dodecyl mercaptan (chain transfer agent) (hereinafter referred to as "n-DM") -- 0.8 wt parts distilled water -- 200 wt parts After the dripping was over, the waterborne pressure sensitive adhesive composition obtained by agitating for 2 hours while maintaining the temperature of the reacting mixture at 75°C was cooled, and to this composition were added aqueous solution of potassium hydroxide as (E) non- volatile alkaline material and 185 wt parts of aqueous emulsion type tackifier of (F1 ) special rosin ester to adjust the solid content to 45%, the viscosity to 2000 to 4000 cps (30°C, the measuring method is described below)and pH to approx.7 to 8, and were further added 6 wt parts of wetting agent, 2 wt parts of anti-form agent and thickening agent to obtain the acrylic waterborne pressure sensitive adhesive composition of Working Example 1.

The properties of the acrylic waterborne pressure sensitive adhesive composition of Working Example 1 obtained as above were as follows: Viscosity of waterborne pressure sensitive adhesive composition: 2060 cps (30°C) pH of waterborne pressure sensitive adhesive composition: 7.5

The viscosity of aqueous adhesive was measured with a B type viscosimeter by turning the No. 4 rotor at a speed of 60 rpm at 30°C.

Moreover, the pH of waterborne pressure sensitive adhesive composition was measured by using a pH meter.

(2) Evaluation of waterborne pressure sensitive adhesive composition (a) Preparation of sample pieces for evaluation of aqueous adhesive

PSA paper label of waterborne pressure sensitive adhesive composition of Working Example 1 was prepared by coating the waterborne pressure sensitive adhesive composition of Working Example 1 on mold releasing paper in a way to have a coating volume of approximately 15 g/m² and, after 2 minutes of drying at 105°C, pasting wood-free paper on it. The width of this PSA paper label was adjusted to 25 mm to be used as PSA paper label sample (hereinafter referred to as sample piece), and the adhesion of the waterborne pressure sensitive adhesive composition according to the present invention was evaluated by using this sample piece.

(b) Evaluation of adhesion

The evaluation of adhesion was made on stainless steel and polyethylene, by using the same method as that described in JIS Z 0237.

The evaluation of adhesion on stainless steel was made as follows:

Said sample piece was pasted on the adherent or a stainless steel (SUS304) sheet (30 mm x 125 mm x 3 mm), in an atmosphere of 20°C with 65%RH, by using a 2 kg rubber roller and at a pasting speed of 300 mm/min (hereinafter referred to as "SUS evaluation sample). After 30 minutes of storage of the SUS evaluation sample at room temperature (20°C) under the condition of 65%RH, the force necessary for peeling the sample piece from the SUS evaluation sample was measured by using the 180°C peeling method. In the present specification, the force measured here is defined as SUS adhesion, which was 1260 gf/25 cm with the adhesive of Working Example 1. The larger this value the stronger the adhesion. Moreover, reduction of adhesion due to wet heat aging of waterborne pressure sensitive adhesive composition was checked. Another SUS evaluation sample was stored for 7 days at 50°C under the condition of 95%RH and, after one day of curing at 20°C, 65%RH, the force necessary for peeling the sample piece from the SUS evaluation sample was measured by using the 180° peeling method. The force measured here is defined as SUS aging adhesion, which was 980 gf/25 cm with the adhesive of Working Example 1. It is believed that the smaller the difference between this value and the value of SUS adhesion, the smaller the secular deterioration of adhesion.

The evaluation of adhesion on polyethylene was made by using the same method except that, in the said measurement of SUS adhesion, a polyethylene (Nippon Testpanel Osaka Co., Ltd.) sheet (30 mm x 125 mm x 3 mm) was used instead of a stainless steel sheet. Namely, after the said sample was pasted on the polyethylene sheet (hereinafter referred to as "PE evaluation sample), the force necessary for peeling the sample piece from the PE evaluation sample was measured in the same way as with the SUS evaluation sample. The force at that time is defined as PE adhesion, which was 690 gf/25 cm with the adhesive of Working Example 1. Furthermore, after another PE evaluation sample was submitted to wet heat treatment in the same way as with the SUS evaluation sample, the force necessary for peeling the sample piece from the PE evaluation sample was measured by using the 180° peeling method The force at that time is defined as PE aging adhesion, which was 460 gf/25 cm with the adhesive of Working Example 1

(c) Evaluation of hold and ooze

Hold and ooze basically required of an adhesive composition was evaluated on the waterborne pressure sensitive adhesive composition of Working Example 1

The hold was evaluated by using the same method as that indicated in JIS Z 0237, on a test piece prepared by the same method as that indicated in JIS Z 0237, after holding the test piece for 2 hours at 40°C under the condition of 65%RH The evaluation was made as for 200 mm or over, for 100 to 200 mm, f or 50 to 100 mm, and x for 0 to 50 mm The waterborne pressure sensitive adhesive composition of Working Example 1 was evaluated as

The evaluation of ooze was made by die cutting the PSA paper label (10 cm x 14 cm), pressing it for 30 minutes at 30°C with a pressure of 30 kg/cm2, and the measuring the weight of the paste which was squeezed out from the end of the die cutter The evaluation was made as f or a weight of squeeze-out paste per kg on the entire circumference of the label of 5 g/km or under, f o r 5 to 10 g/km, and * for 0 to 10 g/km or over. The waterborne pressure sensitive adhesive composition of Working Example 1 was evaluated as .

Table 1 summarizes the results of evaluation of the waterborne pressure sensitive adhesive composition of Working Example 1.

Working Example 2:

The waterborne pressure sensitive adhesive composition of Working Example 2 was obtained by using the same method as that indicated in Working Example 1 , except that 10 wt parts of (C1) acrylamide (hereinafter referred to as "AAm") was used instead of 10 wt parts of (B1 ) acrylic acid in Working Example 1.

The properties, adhesion, etc. of the waterborne pressure sensitive adhesive composition of Working Example 2 were evaluated by using the same method as that indicated in Working Example 1.

The results of this evaluation are given in Table 1.

Working Example 3: The waterborne pressure sensitive adhesive composition of

Working Example 3 was obtained by using the same method as that indicated in Working Example 1 , except that 140 wt parts of (A2) methyl methacrylate was used instead of 150 wt parts of (A2) methyl methacrylate, that 20 wt parts of (C1 ) acrylamide was used instead of 10 wt parts of (B1 ) acrylic acid, and that 1.6 wt parts of n-dodecyl mercaptan was used instead of 0.8 wt parts of n-dodecyl mercaptan in Working Example 1.

The properties, adhesion, etc. of the waterborne pressure sensitive adhesive composition of Working Example 3 were evaluated by using the same method as that indicated in Working Example 1. The results of this evaluation are given in Table 1.

Working Example 4:

The waterborne pressure sensitive adhesive composition of Working Example 4 was obtained by using the same method as that indicated in Working Example 1 , except that 10 wt parts of (D1 ) 2- hydroxyethyl acrylate (hereinafter referred to as "HEA") was used instead of 10 wt parts of (B1 ) acrylic acid in Working Example 1.

The properties, adhesion, etc. of the waterborne pressure sensitive adhesive composition of Working Example 4 were evaluated by using the same method as that indicated in Working Example 1. The results of this evaluation are given in Table 1.

Comparative Example 1 : The waterborne pressure sensitive adhesive composition of

Comparative Example 1 was obtained by using the same method as that indicated in Working Example 1 , except that adjustment of pH was made by using ammonia water instead of adjusting pH by using an aqueous solution of potassium hydroxide as (E) non-volatile alkaline material in Working Example 1. The properties, adhesion, etc. of the waterborne pressure sensitive adhesive composition of Comparative Example 1 were evaluated by using the same method as that indicated in Working Example 1. The results of this evaluation are given in Table 1.

Comparative Example 2:

The waterborne pressure sensitive adhesive composition of Comparative Example 2 was obtained by using the same method as that indicated in Working Example 1 , except that 10 wt parts of (B1 ) acrylic acid was not used at all, that 160 wt parts of (A2) methyl methacrylate was used instead of 150 wt parts of (A2) methyl methacrylate and that adjustment of pH was made by using ammonia water instead of adjusting pH by using aqueous solution of potassium hydroxide as (E) non volatile alkaline material in Working Example 1. The waterborne pressure sensitive adhesive composition of

Comparative Example 2 gelatinized after the emulsion polymerization and could not be evaluated.

Comparative Example 3: The waterborne pressure sensitive adhesive composition of

Comparative Example 3 was obtained by using the same method as that indicated in Working Example 1 , except that 10 wt parts of (D1 ) 2- hydroxyethyl acrylate was used instead of 10 wt parts of (B1 ) acrylic acid, and that adjustment of pH was made by using ammonia water instead of adjusting pH by using aqueous solution of potassium hydroxide as (E) non volatile alkaline material in Working Example 1

The properties, adhesion, etc of the waterborne pressure sensitive adhesive composition of Comparative Example 3 were evaluated by using the same method as that indicated in Working Example 1 The results of this evaluation are given in Table 1

Table 1

a) The unit of numerical values is wt part b) The unit is the cps value at 30°C

g o eva uation could be made In Table 1 ,

(A1 ) and (A2) are (A) (meth)acrylic acid ester", (A1 ) being 2- ethylhexyl acrylate, and (A2) being methyl methacrylate. (B1 ) is acrylic acid as (B) a monomer containing carboxyl group(s).

(C1 ) is acrylamide as (C) a monomer containing amide group(s).

(D1 ) is 2-hydroxylethyl acrylate as (D) a monomer containing hydroxyl group(s).

(G1 ) is aqueous emulsion type tackifier as (G) special rosin ester of resin provided with cohesion (Arakawa Chemical Industries, Ltd., Super Ester E730-55 (commercial name).

From Table 1 , the waterborne pressure sensitive adhesive composition of the Working Examples is understood to have been improved in adhesion after aging and more controlled in secular deterioration, compared with the waterborne pressure sensitive adhesive composition of the References.

The acrylic waterborne pressure sensitive adhesive composition according to the present invention, prepared by subjecting to emulsion polymerization a monomer mixture comprising (meth)acrylic acid ester and at least one kind of monomer containing carboxyl group(s), monomer containing amide group(s), and (D) a monomer containing hydroxyl group(s), and adjusting pH of an aqueous resin composition by using a non-volatile alkaline material, has high adhesion and excellent control on reduction of adhesion due to secular deterioration, and can be preferably used especially in various kinds of paper base material.

From what has been described above, it is possible to extend the warranty period of adhesive products by using the acrylic waterborne pressure sensitive adhesive composition according to the present invention.

Claims

What is claimed is:

1. An acrylic waterborne pressure sensitive adhesive composition prepared by subjecting to emulsion polymerization in the presence of an aqueous medium a monomer mixture of 65 to 99.5wt% of (A) (meth)acrylic acid ester represented by the general formula:

CH2 = C(R1 )COOR2 (I) (wherein R1 is hydrogen or methyl group and R2 is an alkyl group of 1 - 18 carbon atoms optionally having substituent (s)), and 0.1 to 5wt% of at least a member selected from (B) a monomer containing carboxyl group(s), (C) a monomer containing amide group(s), and (D) a monomer containing hydroxyl group(s), and adjusting pH of the resulting aqueous resin composition to 5 - 11 with (E) a non-volatile alkaline material.

2. The acrylic waterborne pressure sensitive adhesive composition as defined in Claim 1 , comprising 0 to 30 wt parts of (F) tackifier to 100 wt parts of the monomer mixture.

3. The acrylic waterborne pressure sensitive adhesive composition as defined in Claim 1 or 2, wherein the (E) non- volatile alkaline material is an alkaline metal hydroxide.