JPH09310055A - Releasable adhesive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition capable of not lowering bond strength, excellent in blocking resistance, releasable when required, comprising a synthetic rubber latex as an essential component composed of a neutralized substance of a polymer soluble in alkali water as a protective colloid. SOLUTION: This composition comprises a synthetic rubber latex as an essential component using a neutralized substance of an alkali-soluble polymer as a protective colloid. The polymer is preferably a homopolymer of an ethylenically unsaturated carboxylic acid, a copolymer of ethylenically unsaturated carboxylic acids or a copolymer of an ethylenically unsaturated carboxylic acid and a copolymerizable another ethylenically unsaturated monomer. The weight-average molecular weight of the polymer is 1,000-20,000, preferably 2,000-15,000. The amount of the protective colloid used is 5-100 pts.wt., preferably 10-50 pts.wt. based on 100 pts.wt. of the synthetic rubber latex (solid content).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel peelable adhesive composition, and more particularly to an adhesive composition which is temporarily adhered by pressure but can be easily peeled off when necessary.

[0002]

2. Description of the Related Art Conventionally, a sealed letter system has been generally used as a mailing means for confidential information such as personal information. However, from the viewpoint of cost reduction, in recent years, a postcard method having confidentiality has been put into practical use and has been rapidly spread. This postcard method with confidentiality folds a form sheet on which various information such as advertising information and personal information is printed, hides the information by adhering the overlapped parts, and then mails it as a postcard, and the recipient This is a method of reading hidden information by peeling off the overlapped portions.
The postcard method having such confidentiality is a method that uses a pseudo-adhesion method that allows the adhesive portion to be peeled off when necessary. Recently, it has been considered to apply this pseudo adhesive method to various forms as well as confidential postcards.

In the pseudo adhesive system, a pressure sensitive type peelable adhesive is mainly used. The pressure-sensitive peelable adhesive does not adhere at a low linear pressure of about several kg / cm, which is the case when the substrates coated with this adhesive are superposed (that is, they have excellent blocking resistance). ), Which is adhered by applying a high linear pressure of, for example, 100 kg / cm (that is, has a cold seal property), and when the adhered substrates are separated from each other, a characteristic of smoothly separating at the adhesive interface Have.

As an adhesive component of the peelable adhesive for this purpose, a modified natural rubber latex obtained by graft-polymerizing a vinyl-based monomer such as styrene or methyl methacrylate to a natural rubber latex is known (Japanese Patent Laid-Open No. 4-428).
No. 3). A peelable adhesive containing this modified natural rubber latex as an adhesive component is excellent in blocking resistance and cold sealability, but since the weather resistance of the natural rubber part is inferior, the adhesive strength decreases with time, Further, it has a drawback that the adhesive strength is lowered by exposure to ozone. Furthermore, since the quality stability of natural rubber latex varies from lot to lot, peelable adhesives containing modified natural rubber latex produced on the basis of this vary in lot-to-lot adhesive strength, resulting in product quality There is a problem with stability.

As a method of solving the drawbacks such as dust,
A peelable adhesive using synthetic rubber latex instead of natural rubber latex has been proposed (JP-A-7-15).
7736). However, a peelable adhesive containing synthetic rubber latex as an adhesive component has a problem that it is inferior in blocking resistance and cold sealability.

[0006]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a peelable adhesive composition which is excellent in blocking resistance and cold seal property without the adhesive strength being deteriorated with time or by exposure to ozone. There is a point to do.

[0007]

Means for Solving the Problems As a result of intensive research aimed at achieving the above object, the present inventors have adhered a synthetic rubber latex containing a neutralized product of an alkaline water-soluble polymer as a protective colloid. They have found that they can be used as components, and have completed the present invention based on this finding.

That is, the present invention relates to a peelable adhesive composition comprising a synthetic rubber latex containing a neutralized product of an alkali-soluble polymer as a protective colloid as an essential component.

The alkali-soluble polymer is a homopolymer of ethylenically unsaturated carboxylic acid, a copolymer of ethylenically unsaturated carboxylic acids with each other, or another ethylenically unsaturated copolymerizable with ethylenically unsaturated carboxylic acid. It is a copolymer with a monomer.

As the ethylenically unsaturated carboxylic acid,
Ethylenically unsaturated monocarboxylic acids such as (meth) acrylic acid and crotonic acid; ethylenically unsaturated polyvalent carboxylic acids such as fumaric acid, maleic acid, itaconic acid, butenetricarboxylic acid; monoethyl maleate, monomethyl itaconate, etc. Partial esters of ethylenically unsaturated polycarboxylic acids and the like can be mentioned. Of these ethylenically unsaturated carboxylic acids, ethylenically unsaturated monocarboxylic acids are preferred.

Examples of the ethylenically unsaturated monomer copolymerizable with the ethylenically unsaturated carboxylic acid include the above-mentioned ethylenically unsaturated carboxylic acid, methyl (meth) acrylate, ethyl (meth) acrylate and (meth) Propyl acrylate,
N-Amyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, (meth)
2-ethylhexyl acrylate, (meth) acrylic acid n
Ethylenically unsaturated carboxylic acid ester monomers such as octyl, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate; styrene, α
-Aromatic vinyl monomers such as methylstyrene, vinyltoluene, pt-butyltoluene, chlorostyrene;
Cyano group-containing ethylenically unsaturated monomers such as (meth) acrylonitrile; glycidyl esters of ethylenically unsaturated acids such as glycidyl (meth) acrylate; glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether; (meth) acrylamide , (Meth) acrylamide monomers such as N-methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-butoxymethylmethacrylamide; 1,3-butadiene, isoprene, 2,3-dimethyl-1 Conjugated diene monomers such as 3-butadiene and 1,3-pentadiene; halogenated vinyl monomers such as vinyl chloride; and carboxylic acid vinyl esters such as vinyl acetate. These monomers may be used alone or in combination of two or more. Among these monomers, the ethylenically unsaturated carboxylic acid ester monomer is preferable.

As the alkali-soluble polymer, a copolymer of the ethylenically unsaturated carboxylic acid and the ethylenically unsaturated monomer is preferable, and in this case, a preferable copolymerization ratio of both is 5:95 to. It is 80:20.

The neutralized product of the alkali-soluble polymer used in the present invention is obtained by neutralizing the alkali-soluble polymer with an alkali, and the degree of neutralization is usually 50% or more, preferably 70% or more. is there.

The alkali-soluble polymer used in the present invention is
The weight average molecular weight is usually 1,000 to 20,000.
It is 0, preferably 2,000 to 15,000. When the weight average molecular weight is less than 1,000, blocking resistance is poor. On the other hand, when the weight average molecular weight is more than 20,000, the viscosity of the obtained synthetic rubber latex increases, and it becomes impossible to obtain an adhesive composition having an appropriate viscosity and concentration. The weight average molecular weight is a value obtained by the method described below.

The alkali-soluble polymer can be obtained by known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization and dispersion polymerization. There is no particular limitation on the polymerization initiator, the molecular weight modifier, etc. used in the polymerization, and the addition method of the monomers and the like, the polymerization temperature, etc. are not limited.

The alkali used for neutralizing the alkali-soluble polymer is ammonia; amines such as methylamine, ethylamine, isopropylamine, dimethylamine, N, N-dimethylethanolamine, diisopropylamine, trimethylamine and triethanolamine; water. Examples thereof include hydroxides of alkali metals such as sodium oxide and potassium hydroxide. Of these, water-soluble is preferable, and ammonia is particularly preferable.

The glass transition temperature of the neutralized alkali-soluble polymer is usually +20 to + 200 ° C., preferably +30.
To + 150 ° C, more preferably +50 to + 150 ° C. When the glass transition temperature is less than + 20 ° C, the blocking resistance of the coating film of the peelable adhesive composition is poor, while
If it exceeds + 200 ° C, the adhesive strength of the peelable adhesive composition decreases and the peeling feeling after adhesion becomes not smooth.

The polymerizable monomer used in the synthesis of the synthetic rubber latex used in the present invention is not particularly limited, but α-methylstyrene, vinyltoluene, p-
Aromatic vinyl monomers such as t-butyltoluene and chlorostyrene; methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-amyl (meth) acrylate, (meth) acrylic Isoamyl acid,
N-Hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, (meth) acrylic acid (Meth) acrylic ester type monomers such as glycidyl; cyano group-containing ethylenically unsaturated monomers such as (meth) acrylonitrile; glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether; (meth) acryloamide, N- Methylol (meth) acrylamide, N-
(Meth) acrylamide monomers such as butoxymethyl (meth) acrylamide; 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-
Examples thereof include conjugated diene monomers such as pentadiene. Among these polymerizable monomers, a conjugated diene monomer, an aromatic vinyl monomer, a cyano group-containing ethylenically unsaturated monomer, a (meth) acrylic acid ester-based monomer and the like are preferable. These polymerizable monomers may be used alone or in combination of two or more.

As typical examples of the obtained synthetic rubber latex, polybutadiene, polyisoprene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, (meth) acrylic acid ester-butadiene copolymer, (meth) acrylic acid ester. Copolymer, styrene-
Examples thereof include (meth) acrylic acid ester copolymers.

The synthetic rubber latex of the present invention uses a neutralized product of an alkali-soluble polymer as a protective colloid. The amount of the neutralized product of the alkali-soluble polymer contained in the synthetic rubber latex is 1% of the synthetic rubber latex (solid content).
5 to 100 parts by weight, preferably 10 to 100 parts by weight
˜50 parts by weight. If the amount of the neutralized product of the alkali-soluble polymer is less than 5 parts by weight, the blocking resistance of the coating film of the peelable adhesive composition is inferior, and the adhesive strength changes with time.
Or it will decrease due to exposure to ozone. on the other hand,
When it exceeds 100 parts by weight, the adhesive strength of the peelable adhesive composition is lowered, and the peeling feeling after adhesion is not smooth.

The synthetic rubber latex used in the present invention can be produced by a known emulsion polymerization method. One of the methods is, for example, a polymerizable monomer in the presence of a neutralized product of an alkali-soluble polymer. The method of emulsion-polymerizing a monomer is mentioned. In this case, the amount of the neutralized alkali-soluble polymer is usually 5 to 100 parts by weight, preferably 10 to 50 parts by weight, based on 100 parts by weight of the polymerizable monomer. When the amount of the neutralized product of the alkali-soluble polymer is less than 5 parts by weight, the emulsified state is poor and the coating film of the peelable adhesive composition obtained is inferior in blocking resistance and the adhesive strength is deteriorated over time. Or, it will decrease due to ozone exposure. On the other hand, if the amount exceeds 100 parts by weight, the adhesive strength of the peelable adhesive composition obtained decreases, and the feeling of peeling after adhesion is not smooth, which is not preferable.

Another method is to carry out emulsion polymerization using a low-molecular weight emulsifier usually used in emulsion polymerization and add the alkali-soluble polymer neutralized product to the system. In this case, Before or after this addition, it is preferable to remove, from the latex, one of the low molecular weight emulsifiers, which is in a free state without being adsorbed to the polymer, by means such as dialysis. Thus, removal of the low molecular weight emulsifier is preferable from the viewpoint of the adhesive property over time, in view of the characteristics of the obtained adhesive composition.

Examples of the low molecular weight emulsifier include low molecular weight emulsifiers generally used in emulsion polymerization. For example, sulfuric acid esters of higher alcohols such as sodium lauryl sulfate and sodium dodecyl sulfate; dodecylbenzene sulfone. Alkylbenzene sulfonates such as sodium acidate; polyoxyethylene alkylallyl sulphates such as sodium polyoxyethylene phenyl ether sulfate; anionic surfactants such as polyphosphates; alkyl ester type of polyethylene glycol, alkyl phenyl ether type or Examples thereof include nonionic surfactants such as alkyl ether type.

Among these production methods, various methods of the peelable adhesive composition obtained by emulsion polymerization of a polymerizable monomer in the presence of a neutralized product of an alkali-soluble polymer and productivity at the time of synthesis It is suitable in terms of the above.

The polymerization initiator used in the polymerization is not particularly limited, and examples thereof include water-soluble initiators such as potassium persulfate, sodium persulfate, ammonium persulfate and hydrogen peroxide; benzoyl peroxide, di- Oil-soluble initiators such as t-butyl peroxide, 2,2-azobis-2,4-dimethylvaleronitrile and azobisisobutyronitrile; redox initiators in which peroxide is combined with a reducing agent such as sodium bisulfite. And so on.

The glass transition temperature of the polymer in the synthetic rubber latex thus obtained is usually -50 to 0 ° C, preferably -40 to -10 ° C.
It is. When the glass transition temperature of the polymer is lower than −50 ° C., the blocking resistance of the coating film of the peelable adhesive composition is poor, and the adhesive strength is deteriorated with time or due to environmental changes such as ozone exposure. Resulting in. On the other hand, 0 ℃
If it exceeds the range, the adhesive strength of the peelable adhesive composition decreases and the peeling feeling after adhesion becomes not smooth.

The peelable adhesive composition of the present invention generally contains a fine particulate filler as a component other than the synthetic rubber latex. Examples of the filler include inorganic fillers such as synthetic silica, kaolin clay, calcium carbonate, talc, titanium oxide and mica; organic fillers such as starch, polystyrene particles and polyester particles. The fine particulate filler has an average particle diameter of 0.01 to 30 μm, preferably 1 to 20 μm. These fillers can be blended alone or in combination of two or more, and a combination of synthetic silica and starch is preferable from the viewpoint of the balance between adhesive performance, printing performance and cost.

The amount of the fine particulate filler used is usually 50 to 3 with respect to 100 parts by weight of the solid content of the synthetic rubber latex.
00 parts by weight, preferably 100 to 250 parts by weight,
The adhesive strength can be adjusted to an appropriate value by the compounding ratio.

Further, the peelable adhesive composition of the present invention comprises
Known dispersants, thickeners, defoamers, pH adjusters, pressure-sensitive adhesives and the like can be contained within a range that does not impair the effects of the invention.

When the peelable adhesive composition of the present invention is applied to a substrate such as a postcard or various forms, 0.5 to 10.0 g / m ^{2 in} terms of solid content is applied. The surfaces coated with the peelable adhesive composition were overlapped with each other, and then 100 to 8
By applying a linear pressure of about 00 kg / cm, the coated surfaces adhere to each other.

[0031]

EXAMPLES The present invention will be described in more detail below with reference to production examples and examples, but the present invention is not limited thereto. The parts and% in the production examples and examples are based on weight, and the methods for measuring various physical properties in the production examples and examples are as follows.

(Glass Transition Temperature) Synthetic rubber latex was cast on a glass plate with a frame and dried at 20 ° C. for 48 hours to obtain a film. A scanning differential calorimeter (Model RDC220, manufactured by Seiko Denshi KK) was used for this film. The initial temperature was -100 ° C, and the temperature rising rate was 10 ° C / min.

(Acid Value) Alkali-Soluble Polymer (Unneutralized) Emulsion 2 g of phenolphthalein indicator was added to 1 g of solid content and titrated with 0.1N potassium hydroxide aqueous solution until neutralization. It is calculated as the mg of the required solid content of potassium hydroxide.

[0034] was applied (evaluation sheet of creating) test adhesive composition so that the coating amount of 5 g / m ² by dry weight using a commercially available wood free paper Meyer bar having a basis weight of 106 g / m ² Then, it dried at 120 degreeC for 30 second, and created the evaluation sheet.

(Initial Adhesion Force) The adhesive sheets of the evaluation sheet obtained by the above-mentioned production method were brought into contact with each other, and a linear pressure of 500 kg / cm was applied between the metal and metal roll nips to perform pressure bonding. This is cut into a width of 25 mm and a length of 170 mm, and 20
The T-type peel strength was measured at a pulling rate of 100 mm / min using a Tensilon type tensile tester in an environment of ° C and 65% relative humidity.

(Adhesion with Time) The evaluation sheet obtained by the above-mentioned preparation method was pressure-bonded by the same method as in the case of the evaluation of the initial adhesion, and then for 7 days or 14 in an environment of 20 ° C. and 65% relative humidity. After leaving for a day, T at a speed of 100 mm / min was measured with a Tensilon type tensile tester as in the initial adhesive strength evaluation.
The mold peel strength was measured.

(Ozone resistance to adhesion) The evaluation sheet obtained by the above-mentioned preparation method was exposed to ozone having a concentration of 2 ppm at 40 ° C. for 2 hours, and then subjected to the Tensilon tensile tester in the same manner as the initial adhesion evaluation. The T-type peel strength was measured at a speed of 100 mm / min.

(Peeling Feeling) The evaluation sheet obtained by the above-mentioned preparation method was pressure-bonded in the same manner as in the initial adhesive strength test, and then judged by the feeling when peeled by hand, and is shown by the following ◯ to ×. . ◯: Peeling off smoothly Δ: Slight lack of smoothness ×: No smoothness

(Blocking resistance) Adhesive-coated surfaces of the evaluation sheet obtained by the above-mentioned preparation method were put together to obtain 50
After being left for 30 minutes under a pressure of 500 g / m ² under an environment of ° C and a relative humidity of 80%, the degree of adhesion (blocking) was determined, and the results are shown by ◯ to × below. ◯: No adhesion (no blocking occurs at all). Δ: Adhesion but peeling without resistance (somewhat blocking) ×: Adhesion and peeling resistance is large (blocking occurred completely)

Production Example 1 (Production of Alkali-Soluble Polymer Neutralized Product) 23 parts of methacrylic acid, 51 parts of methyl methacrylate, 26 parts of ethyl acrylate, octyl thioglycolate 8
Parts, polymerizable surfactant (polyoxyethylene alkylpropenyl ether sulfate ammonium salt) 0.3
And 50 parts of deionized water were mixed to obtain a monomer emulsion. On the other hand, 200 parts of ion-exchanged water was charged into a nitrogen-substituted reactor equipped with a stirrer and heated to 80 ° C., and after adding 2 parts of potassium persulfate and 38 parts of ion-exchanged water to the reactor,
The monomer emulsion was continuously added to the reactor maintained at 80 ° C. for 1 hour to cause a reaction. After the addition of the monomer emulsion, the reaction was continued for another hour to obtain an unneutralized emulsion of the alkali-soluble polymer (a). Further, 14 parts of 28% ammonia water was added to the emulsion of the unneutralized product of the alkali-soluble polymer (a) to obtain a 25% aqueous solution of the neutralized product of the alkali-soluble polymer. The degree of neutralization is such that almost 100% of the acid groups in the polymer are neutralized. In addition, alkali-soluble polymer neutralized products (b) and (c) were obtained in the same manner as above except that the monomer composition was changed as shown in Table 1.

The resulting alkali-soluble polymer (a)
The physical properties of the neutralized product (c) are shown in Table 1. Incidentally, only the acid value is that of an unneutralized product.

[0042]

[Table 1]

Production Example 2 [Production of Synthetic Rubber Latexes (A) to (E) of the Present Invention] In a flask equipped with a stirrer and purged with nitrogen, the monomers shown in Table 2 were added.
186 parts of soft water, 0.2 part of t-dodecyl mercaptan, 0.4 part of diisopropylxanthogen sulfide and a neutralized product of an alkali-soluble polymer were added and mixed, and the mixture was mixed at 45 ° C.
After the temperature was raised to 5.0%, 5.0 parts of a 2% aqueous solution of potassium persulfate was added, and stirring was continued for 15 hours while maintaining the temperature at 45 ° C. to complete the polymerization reaction. After the reaction, the unreacted monomer is removed by distillation under reduced pressure, and the pH is adjusted with aqueous ammonia to obtain a synthetic rubber latex (A) having a solid content concentration of 42% and a pH of 7.
(E) was obtained.

Production Example 3 [Production of Synthetic Rubber Latex (F) of Comparative Example] In a flask equipped with a stirrer and purged with nitrogen, the monomers shown in Table 2 were added.
96 parts of soft water, 0.4 part of t-dodecyl mercaptan, 1.0 part of sodium polyoxyethylene nonylphenyl ether sulfate, naphthalenesulfonic acid formalin condensate 1.
5 parts and 1.0 part of sodium sulfate were added and mixed, and 45
After the temperature was raised to 0 ° C., 5.0 parts of a 2% aqueous solution of potassium persulfate was added, and stirring was continued for 15 hours while maintaining the temperature at 45 ° C. to complete the polymerization reaction. After the reaction, the same operation as in Production Example 2 was carried out to obtain a synthetic rubber latex (F) having a solid content concentration of 42% and a pH of 7.

[0045]

[Table 2]

Production Example 4 [Production of Modified Natural Rubber Latex (G) of Comparative Example] For comparison, 172.4 parts of graft modified natural rubber latex (Musashino Chemical Co., trade name: Coretex MG10) ( Solid content 100 parts),
Synthetic silica 40 parts, corn starch 160 parts, dispersant 4
And 490 parts of ion-exchanged water were added with stirring and mixing to obtain a modified natural rubber latex (G) having a solid content of 35%.

Example 1 Each copolymer latex 238.1 obtained in the above production example
25 parts of synthetic silica (Shionogi Seiyaku Co., Ltd., trade name: Carplex # 80) per 25 parts
Department, cornstarch (manufactured by Japan Food Processing Co., Ltd.) 100
Parts, dispersant (naphthalenesulfonic acid formalin condensate)
2 parts and 293 parts of ion-exchanged water were added with stirring and mixing to obtain an adhesive composition having a solid content of 35%. After applying such a coating amount of 5 g / m ² by dry weight using a Meyer bar with this adhesive woodfree paper having a basis weight of 106 g / m ^2,
It dried at 120 degreeC for 30 second, and created the evaluation sheet. The adhesive composition-coated surfaces of this evaluation sheet were aligned, and a linear pressure of 500 kg / cm was applied between the metal and the metal roll nip.
Was applied and pressure-bonded, and the adhesive strength and the peel strength were tested. Table 3 shows the evaluation results.

[0048]

[Table 3] * Fracture occurred between the substrate and the adhesive layer, or cohesive failure of the adhesive layer occurred. ** I could not crimp.

The embodiments of the present invention will be listed below. (1) A peelable adhesive composition comprising a synthetic rubber latex containing a neutralized product of an alkali-soluble polymer as a protective colloid as an essential component. (2) The peelable adhesive composition according to item (1), wherein the polymer in the synthetic rubber latex has a glass transition temperature of -50 to 0 ° C. (3) The peelable adhesive composition according to item (1), wherein the polymer in the synthetic rubber latex has a glass transition temperature of -40 to -10 ° C. (4) The peelable adhesive composition according to item (1), (2) or (3), wherein the neutralized alkali-soluble polymer has a glass transition temperature of +20 to + 200 ° C. (5) The peelable adhesive composition according to the above (1), (2) or (3), wherein the alkali-soluble polymer neutralized product has a glass transition temperature of +30 to + 150 ° C. (6) The amount of the neutralized alkali-soluble polymer used is 5 to 100 parts by weight relative to 100 parts by weight of synthetic rubber (solid content), (1), (2), (3), (4) ) Or the releasable adhesive composition according to (5). (7) The amount of the neutralized alkali-soluble polymer used is 10 to 50 parts by weight based on 100 parts by weight of synthetic rubber (solid content), (1), (2), (3), (4). ) Or the releasable adhesive composition according to (5).

[0050]

EFFECTS OF THE INVENTION According to the present invention, a highly stable peelable adhesive composition having excellent blocking resistance and cold sealability, whose adhesive strength does not decrease with time or due to environmental changes such as ozone exposure, is obtained. be able to.

Claims (1)

[Claims] 1. A peelable adhesive composition comprising a synthetic rubber latex containing a neutralized product of an alkali-soluble polymer as a protective colloid as an essential component.