JPS6310748B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pressure-sensitive adhesive that has excellent adhesion to cellulose substrates such as paper, cloth, and wood. Rubber-based pressure-sensitive adhesives have long been used as adhesive tapes for packaging materials such as cardboard. Most conventional packaging adhesive tapes have natural rubber or synthetic cis-1,4-polyisoprene rubber as an elastomer component. In recent years, styrene-diene block copolymers have attracted attention as elastomer components for adhesive tapes, and are already being applied in some areas, but their practical use is severely limited due to insufficient adhesion to paper. There is. In addition, recently, the surface condition of corrugated paper has varied widely due to the recycling of waste paper and the variety of types and amounts of fillers mixed into paper.
Even with conventional adhesive tapes whose main elastomer component is natural rubber, their adhesion has become a problem in some cases, and pressure-sensitive adhesives with excellent adhesion to cellulose substrates such as paper and wood are now available. Highly desired. Attempts have been made to solve this problem by using softeners such as tackifying resins and oils, but no sufficient improvement has yet been achieved. The present inventors conducted various studies in search of a new material for the purpose of improving adhesion to cellulose substrates, and
As a result of repeated efforts, it was discovered that by using a low molecular weight isoprene rubber with a specific structure as a component of a pressure-sensitive adhesive, it was possible to obtain a pressure-sensitive adhesive with improved adhesion to cellulose substrates. This led to the completion of the present invention. That is, the present invention comprises an elastomer, a tackifier resin, and a modified liquid rubber obtained by adding a maleimide derivative having a tertiary amino group or a hydroxyl group to a liquid isoprene rubber, and the amount of the tackifier resin and the modified liquid rubber used is is an elastomer
10 to 250 parts by weight and 5 to 100 parts by weight, respectively
60 parts by weight of pressure sensitive adhesive. Particularly when the modified rubber is a liquid isoprene rubber containing 0.5 to 20 moles of N-(hydroxyalkyl)-maleimide or N-(dialkylaminoalkane)-maleimide per 100 moles of monomer units. It was acknowledged that the project had achieved its objectives beyond the initial expectations. Examples of the elastomer used in the present invention include natural rubber (NR), synthetic cis-1,4-polyisoprene rubber (IR), styrene-isoprene random copolymer (SIR), polybutadiene rubber (BR),
Styrene-butadiene random copolymer (SBR)
Synthetic rubber such as styrene-isoprene block copolymer, styrene-butadiene block copolymer, ethylene-vinyl acetate copolymer, ethylene-
Examples include thermoplastic rubbers such as acrylic ester copolymers, ethylene-methacrylic esters, and modified rubbers thereof. Among these, isoprene-based solid rubbers such as natural rubber (NR), synthetic cis-1,4-polyisoprene rubber (IR), and styrene-isoprene block copolymer are preferred from the viewpoint of adhesiveness. An example of the styrene-isoprene block copolymer is represented by the following general formula. (S-I) _o , (S-I) _o -S and I- (S-
I) _o Here, S means a polystyrene block, I means a polyisoprene block, and n means an integer of 1 or more. Typical tackifier resins used in the present invention include terpene resins, terpene-phenol resins, rosin resins, aromatic hydrocarbon petroleum resins, coumaron-indene resins, and phenol resins. It will be done. These tackifier resins may be used alone or in combination of two or more. If the amount of the tackifier resin used is too large or too small, the tackiness and adhesion of the pressure sensitive adhesive will deteriorate. Therefore, the amount of the tackifying resin used is preferably 10 to 250 parts by weight, particularly 30 to 150 parts by weight, based on 100 parts by weight of the elastomer component. Furthermore, the modified liquid isoprene rubber used in the present invention is a modified liquid isoprene rubber obtained by adding a maleimide derivative containing a functional group having a tertiary amino group or a hydroxyl group at the N-1 position represented by the following general formula to a liquid isoprene rubber. It's rubber. general formula However, in the formula, R ₁ , R ₂ , R ₃ and R ₄ represent hydrogen or a lower alkyl group, which may be the same or different. Q represents a lower alkyl group, aryl group, or aralkyl group, and A represents OH or

[Formula] is represented, and R ₅ and R ₆ represent a lower alkyl group, an aryl group, or an aralkyl group. The liquid isoprene rubber is a homopolymer of isoprene or a copolymer of isoprene and a diene such as butadiene or piperidine.
Even if the copolymer is a random copolymer,
It may also be a block copolymer. In the present invention, if the molecular weight of the liquid isoprene rubber is too small, the modified isoprene rubber tends to bleed or migrate in the pressure-sensitive adhesive, and the performance of the adhesive changes significantly over time.
On the other hand, if the molecular weight becomes too large, the viscosity of the system used to prepare the modified isoprene rubber will become too high, and the resulting modified liquid isoprene rubber will have poor fluidity, resulting in poor workability. Therefore, the molecular weight of the liquid isoprene rubber is preferably 8,000 to 100,000, particularly 12,000 to 75,000. Note that molecular weight here means viscosity average molecular weight (M _v ), and using intrinsic viscosity ([η]) measured in a toluene solution at 30°C, [η] = 1.21 × 10 ^-4 M _v ^0.7
7 . If the amount of vinyl bonds in the liquid isoprene rubber is too large, gelation will easily occur when preparing the modified liquid isoprene rubber, and the glass transition point of the obtained modified liquid isoprene rubber will become high. The viscosity of the modified liquid isoprene rubber itself increases, resulting in poor workability and poor low-temperature performance of the resulting pressure-sensitive adhesive. Therefore, the amount of vinyl bonds in the liquid isoprene rubber is preferably 30% or less, particularly 20% or less. Note that the vinyl bond amount is determined by infrared absorption spectroscopy. In addition, when using a copolymer of isoprene and other dienes as the liquid isoprene rubber,
If the content of isoprene is too small, the reaction during modification will be difficult to proceed, and the pressure-sensitive adhesive finally obtained will have low adhesive performance. From this point of view and from the point of view of the manufacturing method of liquid isoprene rubber, it is preferable that the content of isoprene is 20% by weight or more, particularly 60% by weight or more, and even more preferably 100% by weight. This particular liquid isoprene rubber is
Although it can be produced by various methods, it is preferably produced by an anionic polymerization method. Among these, living polymerization using a lithium-based catalyst such as metallic lithium or organic lithium such as methyllithium, propyllithium, butyllithium, or distyrenyllithium is effective for easily controlling the molecular weight and producing a microstructure with a small amount of vinyl bonds. Therefore, it is also easy to produce a copolymer, so it is preferably employed. The polymerization solvent is preferably used because it is easy to control the polymerization, and n-butane, isobentane,
An inert hydrocarbon such as n-hexane, n-heptane, benzene, toluene or xylene is used, but there is no problem even if it is not used depending on the case. Such liquid isoprene rubber can be prepared by reacting the maleimide derivative itself and applying it as a modified liquid rubber to a pressure-sensitive adhesive without any problem, but it is not advantageous in terms of reactivity or economic efficiency. First, the general formula for liquid isoprene rubber is (In the formula, R ₁ , R ₂ , R ₃ and R ₄ each represent hydrogen or a lower alkyl group) or a derivative thereof (hereinafter simply abbreviated as maleic anhydride) is added, i.e. Maleation reaction is carried out, and then the resulting maleic anhydride modified rubber has the general formula

[Formula] (wherein R ₅ , R ₆ and Q represent lower alkyl, aryl group, or aralkyl group), or general formula NH ₂ -Q-OH (wherein Q is lower alkyl, (representing an aryl group or an aralkyl group), that is, an amidation reaction, and finally the amidated product of the maleic anhydride-modified liquid rubber obtained is subjected to an imidization reaction by dehydration etc. to substantially convert the maleic acid into It is preferable to use a modified liquid rubber added with an imide derivative. Any known method can be adopted for the reaction between liquid isoprene rubber and maleic anhydride, that is, the maleation reaction. For example, by mixing and stirring liquid isoprene rubber and maleic anhydride under heating. A method in which the reaction is carried out is preferably employed. For this reaction, it is also possible to use a catalyst such as a peroxide or an azo compound, and it is also possible to use an inert hydrocarbon solvent such as hexane, toluene or benzene. It is also possible to carry out the reaction in the presence of an antigelation agent such as acetylacetone or acetylacetone. The reaction temperature is preferably 100 to 250°C, and the reaction time is preferably 1 to 20 hours. The amount of maleic anhydride used is determined by determining the amount of maleimide derivative added in the maleimide derivative addition modified liquid rubber compared to the isoprene monomer or diene monomer (i.e., isoprene monomer and butadiene or piperylene, etc.) of the liquid isoprene rubber. The amount may be within a range of 0.5 to 20 mol % based on the diene monomer (diene monomer). The maleic anhydride-modified liquid isoprene rubber thus obtained is subjected to a reaction with an amino compound selected from the group consisting of diaminoamines or aminoalcohols, that is, an imidization reaction such as an amidation reaction and a subsequent dehydration reaction. be done. The diaminoamine used here has the general formula

[Formula] (In the formula, R ₅ and R ₆ represent a lower alkyl group, an aryl group, or an aralkyl group, and Q represents a lower alkyl group, an aryl group, or an aralkyl group. These may be the same or different. ), and typical examples include dimethylaminoethylamine, diethylaminoethylamine, diisopropylaminoethylamine, dimethylaminopropylamine, diethylaminopropylamine, dimethylaminobutylamine, diethylaminobutylamine, and the like. Among them, dialkylaminopropylamine is preferred. Amino alcohols have the general formula H ₂ N—
It is represented by R—OH (in the formula, R represents an alkyl group having 1 to 20 carbon atoms, an aryl group, or an aralkyl group), and typical examples include ethanolamine,
1-aminopropan-2-ol, 2-aminopropan-1-ol, 1-aminobutan-2-ol, 2-aminobutan-1-ol, 3-aminobutan-1-ol, 1-amino-2-methylpropane -2-ol, 1-aminopentane-4
Examples include aminoalkyl alcohols such as -ol or 1-aminopentan-5-ol, or aminoaralkyl alcohols such as aminophenol, aminocresol, aminoxylenol, or aminonaphthol. Among them, aminoalkyl alcohol is preferred. In this reaction, especially in the amidation reaction, it is necessary to pay sufficient attention to the reaction temperature. In other words, the acid anhydride group in maleic anhydride-modified liquid isoprene rubber easily reacts with diaminoamine or amino alcohol to form a semi-amidated product, but if the reaction temperature is too high at this time, gelation reaction or other reactions may occur. Undesirable side reactions occur. Therefore, the reaction temperature should be kept low until the amide is completed during the second half of addition of diaminoamine or aminoalcohol, specifically from room temperature to 130°C.
Particularly preferably, it is necessary to carry out the reaction at a temperature of 50 to 100°C. On the other hand, the dehydration reaction of imidization subsequent to amidation needs to be carried out at a higher temperature than the amidation reaction. If the temperature is too low at this time, imidization will not occur, and carboxyl groups will remain in the modified liquid isoprene rubber that is finally prepared, resulting in decreased adhesion to paper when used as a pressure-sensitive adhesive. This often leads to undesirable results. From this point of view, this dehydration reaction must be carried out at a temperature of 150-220°C, preferably 150-180°C. During this dehydration reaction, a dehydrating agent such as sulfuric acid, phosphoric acid, or phosphorus pentoxide may be used to accelerate the reaction, or a means of distilling off the water produced under reduced pressure may be used. good. The amount of diaminoamine or amino alcohol used is in most cases about the same number of moles to three times the number of moles of maleic anhydride added in the maleic anhydride-modified liquid isoprene rubber. In this way, a modified liquid rubber is obtained in which a maleimide derivative, that is, N-(dihydrocarbylamino)-maleimide or N-(hydroxyhydrocarbyl)-maleimide is added to liquid isoprene rubber. It will be done. In the present invention, if the amount of maleimide having a tertiary amino group or hydroxyl group added to the modified liquid isoprene rubber is too small, good adhesion to paper, which is the objective of the present invention, cannot be obtained; If it is too high, the viscosity becomes too high during the maleation reaction during modification, and in extreme cases, it becomes hard, resinous, and loses fluidity, which is undesirable. Therefore, in the case of isoprene or a copolymer of liquid isoprene rubber, the amount added is preferably 0.5 to 20 mol, particularly 1 to 10 mol, per 100 mol of the diene monomer. In the present invention, the amount of the modified liquid isoprene rubber used is suitably 5 to 60 parts by weight, particularly 10 to 40 parts by weight, per 100 parts by weight of the elastomer. If the amount used is too small or too large, good adhesion to cellulose substrates such as paper, cloth or wood cannot be obtained. In the present invention, in addition to the elastomer, tackifying resin, and modified liquid isoprene rubber, fillers, softeners, anti-aging agents, etc. may be added as necessary, and modified liquid isoprene rubber may be added to improve creep resistance. Crosslinking agents for isoprene rubber, such as isocyanate compounds or dihalogen compounds, may be added. In the present invention, the pressure-sensitive adhesive can be prepared by mixing the essential components of an elastomer, a tackifying resin, and a modified liquid isoprene rubber using a hot melt method, or by mixing the essential components in a solution state using an appropriate solvent. Manufactured by The pressure-sensitive adhesive thus obtained is coated on plastic film, cellophane paper, wood-free paper, kraft paper, cloth, etc. under heat or in a solution state to be put to practical use as an adhesive tape. The pressure-sensitive adhesive of the present invention not only has excellent adhesive strength, but also has excellent adhesive strength and cohesive strength, and also has excellent high-temperature and low-temperature performance. Therefore, it is used in the production of adhesive tapes, adhesive labels, and adhesive plasters. EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples in any way. In addition, in Examples and Comparative Examples, "parts" means "parts by weight" unless otherwise specified.
means. Examples 1 to 2 and Comparative Examples 1 to 5 Liquid polyisoprene rubber (with a molecular weight of 21,000 and a vinyl bond content of 7% (1,4 bond content of 92%)) was produced by anionic polymerization of isoprene using a lithium-based polymerization catalyst. (abbreviated as LIR in Table 2) was prepared.
100 parts of the liquid polyisoprene rubber was reacted with 6 parts of maleic anhydride under heating at 180°C to obtain maleic anhydride modification in which 4.2 moles of maleic anhydride was added per 100 moles of isoprene monomer in the liquid polyisoprene rubber. A liquid polyisoprene rubber (abbreviated as M-LIR in Table 2) was obtained. Next, isopropanolamine is added to the modified liquid polyisoprene rubber in an amount twice the molar amount of the added maleic anhydride to carry out a semi-amidation reaction, followed by a dehydration reaction at 160°C under reduced pressure to form N-
(2-Hydroxyisopropyl) - modified liquid polyisoprene rubber with maleimide added (second
In the table, it is abbreviated as OH-M-LIR. ) was obtained. Also,
Separately, 1.03 times the mole of dimethylaminopropylamine is added to the maleic anhydride added to the maleic anhydride-modified liquid polyisoprene rubber,
After half amidation, dehydration reaction was performed under reduced pressure at 160°C to obtain N-(dimethylaminopropane)-
Modified liquid polyisoprene rubber added with maleimide (abbreviated as NH ₂ -M-LIR in Table 2)
I got it. On the other hand, for comparison, a modified liquid polyisoprene rubber (EM-LIR) in which maleic acid monoester was added was prepared by reacting the maleic anhydride modified liquid polyisoprene rubber with methanol. Liquid polyisoprene rubber thus prepared, maleic anhydride liquid modified polyisoprene rubber, N-(2-hydroxyisopropyl)-maleimide modified liquid polyisoprene rubber, N-
(dimethylaminepropane) - A toluene solution of a pressure-sensitive adhesive compound was prepared using the maleimide-modified liquid polyisoprene rubber and the maleic acid monoester-modified liquid polyisoprene rubber in the formulation shown in Table 1, and the toluene solution was prepared. was coated on one side of release-treated kraft paper, and then dried to obtain an adhesive tape.

[Table] The adhesive tape thus obtained was subjected to an adhesion test. The test method was to attach adhesive tape in the form of a 25 mm x 100 mm strip to the kraft paper surface.
In the state shown in the figure, a load of 200 g was applied, and the time until peeling was measured, and this time was taken as the adhesive strength of the adhesive tape to the kraft paper. The results of the adhesion test are shown in Table 2. In addition, in the figure, A is the load, B is the kraft paper,
C indicates an adhesive tape paste, and D indicates an adhesive tape base material.

[Table] As is clear from Table 2, N-(2-hydroxyisopropyl)maleimide or N-
(dimethylaminopropane) - modified liquid polyisoprene rubber with maleimide added, i.e.
Adhesive tapes made using modified liquid isoprene-based rubbers to which maleimide having hydroxyl groups or tertiary amino groups such as OH-M-LIR and NH ₂ -M-LIR are added are unmodified liquid rubbers such as LIR and anhydrous maleimide. It has superior adhesion to kraft paper compared to adhesive tapes made of modified liquid rubber to which acids or maleic esters have been added. Example 3 and Comparative Example 6 A modified liquid in which N-(2-hydroxyisopropyl)-maleimide used in Example 1 was added to a pressure-sensitive adhesive having the formulation shown in Table 3 and containing natural rubber as an elastomer component. We investigated the effects of modification using isoprene rubber. The pressure-sensitive adhesive was prepared as a toluene solution and coated on cellophane paper to make an adhesive tape, and the adhesive force test of Example 1 was carried out in the same manner as in Example 1, except that the load was 400 g. The results are shown in Table 3.

【table】

[Table] As is clear from Table 3, the pressure sensitive adhesive using modified liquid isoprene rubber to which maleimide having a hydroxyl group is added has excellent adhesive strength to paper.

[Brief explanation of the drawing]

FIG. 1 shows a constant load peel test method used in Examples and Comparative Examples. In the figure, A is the load, B is the kraft paper, C is the adhesive tape, and D is the adhesive tape base material.

Claims (1)

[Scope of Claims] 1. A pressure-sensitive adhesive comprising an elastomer, a tackifier resin, and a modified liquid rubber obtained by adding a maleimide derivative having a tertiary amino group or a hydroxyl group to a liquid isoprene rubber. 2. The pressure-sensitive adhesive according to claim 1, wherein the elastomer is a styrene-isoprene block copolymer. 3. The pressure-sensitive adhesive according to claim 1, wherein the maleimide derivative is N-(hydroxyisopropyl)-maleimide. 4. The pressure-sensitive adhesive according to claim 1, wherein the maleimide derivative is N-(dimethylaminopropane)-maleimide.