JPH02163185A - Production of acrylic adhesive - Google Patents

Abstract

PURPOSE:To obtain readily a non-solvent, ion-crosslinking type acrylic adhesive having excellent adhesion retention by allowing a specific acrylic copolymer to react with a specific organometallic compound under heating in the absence of solvent. CONSTITUTION:After (A) an acrylic copolymer which bears reactive groups crosslinkable with metal ions in the side chains and has a melt viscosity of 5 X10<4> to 7X10<5>cps at 130 deg.C is combined with (B) an organometallic compound selected from metal chelates, metal alcoholates and carboxylates, they are heated, for example, in a nitrogen atmosphere up to 160 deg.C in the absence of solvent to effect the reactions whereby the subject adhesive is obtained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is an acrylic adhesive, in which an ionically crosslinked acrylic adhesive with particularly excellent adhesive retention and without the use of a solvent can be easily obtained. It relates to a manufacturing method that can be used.

(Prior art and its problems) As an acrylic adhesive, an acrylic copolymer copolymerized with an unsaturated carboxylic acid is made to contain metal ions,
A so-called ionically crosslinked pressure-sensitive adhesive in which an ionically crosslinked body is formed is known.

This ionic crosslinking type adhesive has a reversible property in that the ionic crosslinks dissociate when melted at high temperature and crosslink at room temperature, so aging to promote the crosslinking reaction is not necessary. It can also be applied in a high-temperature molten state, and at room temperature, due to crosslinking, it can provide excellent adhesive holding power, that is, the ability to maintain the adhesive state without peeling off due to external force after adhesion.

A method for manufacturing such an ionically crosslinked acrylic adhesive is to obtain a solution type adhesive by solution polymerizing an acrylic copolymer and then adding an organic or inorganic metal compound in the solution state. be. Such a solution type has an environmental problem in that the solvent must be volatilized and removed during the process of applying the adhesive to a film or the like.

There is also a method of solution polymerizing the acrylic copolymer, adding an organic or inorganic metal compound in a solution state, and then distilling off the solvent from the reaction system to obtain a solvent-free adhesive. In this method, the crosslinking reaction proceeds as the solvent is distilled off, resulting in extremely high viscosity in the system. There are problems in that it becomes impossible to completely distill off this licking solvent, and it becomes very difficult to remove the crosslinked adhesive from the reaction tank.

An object of the present invention is to provide a method for producing an ionically crosslinked acrylic adhesive that is easy to handle.

(Means for Solving the Problems) In order to achieve the above object, in the production method of the present invention, a specific acrylic copolymer and a specific metal compound are melt-kneaded without using a solvent. It has been found that the above problems can be solved by doing so, and the gist is that the side chain has a reactive group capable of crosslinking with a metal ion, and
Melt viscosity at 130℃ is 5 x 104 to 7 x 105 cps
It is characterized by adding an organometallic compound selected from a metal chelate compound, a metal alcoholade, and a carboxylic acid metal salt to an acrylic copolymer in the range of , and then reacting by heating and mixing without a solvent. It consists in a method for producing an acrylic adhesive.

The acrylic copolymer used in the present invention contains 60% by weight or more of acrylic ester and/or methacrylic ester. As the alcohol component constituting the ester, primary alcohols such as butyl alcohol, octyl alcohol, 2-ethylhexyl alcohol, and lauryl alcohol are usually used.

The copolymer may further contain a copolymerizable vinyl monomer such as vinyl acetate or vinyl chloride. In this case, the amount of vinyl monomer used is preferably 32% by weight or less based on the total raw materials of the copolymer component; if it exceeds 32% by weight, tack is likely to be insufficient. The acrylic acid and/or methacrylic ester needs to be copolymerized with a monomer having at least one reactive group capable of crosslinking with metal ions, and has the reactive groups shown in (a) to (e) below. Monomers can be suitably used.

(a) Monomers having a carboxyl group; acrylic acid, methacrylic acid, itaconic acid, maleic acid, etc.

(b) Monomers having hydroxyl groups: 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, etc.

(c) Monomers having an amide group; acrylamide, methacrylamide, N-methylolacrylamide, N-butyrolacrylamide, etc.

(d) Monomer having an amino group; N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminoethyl methacrylate, etc.

(e) Monomer having a phosphoric acid group: 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyacid phosphate, etc.

The above monomers may be contained one type or two or more types,
The amount used is 0.05 to 8.0% of the total raw materials of the copolymer component.
It can be suitably used in a range of about 0% by weight. Usage amount is 0.
If the amount is less than 1% by weight, no improvement in adhesive retention is observed, and the adhesive tends to ooze out onto the sides of the tape wound into a roll, which is disadvantageous. If it exceeds 8.0% by weight, the tack will be insufficient.

The acrylic copolymer consisting of the above components can be obtained by ordinary solution polymerization methods, etc., but the viscosity characteristics after solvent removal are as follows:
Melt viscosity at 130°C is 5 x 10 to 7 x 105 cp
A range of s, preferably a range of 10 x 10 to 5 x 105 cps can be suitably used. The melt viscosity can be measured using a normal B-type viscometer, and the melt viscosity is 5X1.
05cps ungrooved products tend to lack 5c force and have low adhesive holding power, and even if the amount of metal compound added is increased to increase cohesive strength, the balance of adhesive properties is poor, such as insufficient tack. There's a problem. Furthermore, if the pressure exceeds 7×10 5 cps, it tends to be difficult to copolymerize using the usual solution polymerization method, and it also tends to be difficult to apply the resulting pressure-sensitive adhesive.

In the present invention, it is necessary to add a specific organometallic compound to the acrylic copolymer having the above-mentioned melt viscosity and to react by heating and mixing. Examples of organometallic compounds include (i) metal chelate compounds, (11) metal flucorates, and (ii)
i) Carboxylic acid metal salts must be selected, and these metal compounds can be easily and uniformly dispersed in the polymer by melt-mixing without a solvent, and can easily react with the reactive groups in the acrylic copolymer. , can form a crosslinked structure.

When metal compounds other than the above (i) to (iii) are used, for example, inorganic metal compounds such as zinc oxide and calcium oxide, there is a problem that the compatibility with the acrylic copolymer is poor.

Here, (i) metal chelate compounds include β-diketones (2°4bentanedione, 2.4hebutanedione, etc.), ketoesters (methyl acetoacetate, ethyl acetoacetate, etc.), Droxycarboxylic acids (lactic acid ester, tartaric acid, etc.), keto alcohols (4-hydroxy-2-pentanone, 4-hydroxy-
2-heptanone, etc.), amino alcohols (monoethanolamine, jetanolamine, etc.), and metals that can form a chelate bond with these chelators, such as Na, Be, Mg, Ca, Cu, Pb, , Fe, C
Examples include chelate compounds formed from C, Nl, Zn, AI, Ti, Zr, and the like.

In addition, (ii) metal alcoholades include alkali metal alcoholades (lithium propinate, sodium methylate, cesium propinate, etc.), aluminum alcoholades (isopropylate, 5ec-butyrate, etc.), titanium alcoholades (tetraisopropyl titanate, Tetra n-butyl titanate, polytributyl titanate, etc.) can be used.

(1ii) Carboxylic acids of carboxylic acid metal salts include aliphatic carboxylic acids, aromatic carboxylic acids, oxalic acid, citric acid, rosin, hydrogenated rosin, etc., and metals include Na,
Be, Mg, Ca, Cu.

Sn, Pb, Fe, Mn, Co, Ni, Zn.

AI, Zr, etc. can be used.

As the amount of the organometallic compound added to the acrylic copolymer increases, the adhesive holding power improves, but the adhesive properties such as pole tack deteriorate, so the reactive groups in the acrylic copolymer The equivalent ratio is preferably in the range of 0.05 to 2.0.

In the present invention, it is necessary to heat and mix the above-mentioned acrylic copolymer and organometallic compound without a solvent to react. It can also be carried out continuously by kneading and discharging using a machine. It may be selected appropriately depending on the viscosity before and after crosslinking.

The adhesive obtained by the above method already has sufficient internal cohesive force due to ionic crosslinking, and can be used alone as an adhesive composition, but if necessary, a tackifier, Compounding agents such as plasticizers, stabilizers, fillers, etc. may be added.

Hereinafter, the present invention will be explained in detail with reference to Examples.

(Example) Examples 1 to 4 2-ethylhexyl acrylate 57% by weight butyl acrylate 4o horn acrylic acid
3. .

A 40% ethyl acetate solution of the copolymer having the above composition,
The solvent was removed under reduced pressure to obtain an acrylic copolymer having a melt viscosity at 130° C. (as measured by a B-type viscometer) of 2.3×10 5 cps.

Next, in a kneader with a heating mechanism, it was heated for 16 minutes in a nitrogen atmosphere.
The temperature was raised to 0°C, and an organic metal compound and additives having the composition shown in Table 1 were added to 100 parts by weight of the above acrylic copolymer, and the mixture was melt-kneaded for 1°C for 5 hours to obtain an adhesive. Na.

The obtained adhesive was coated onto a polyester film (PET, 38 μm) to a thickness of 20 μm using a hot melt coating device.
It was applied uniformly to a thickness of μm. Table 1 shows the results of evaluation of R-ball tack, holding power, and adhesion using the following methods using each film sample after coating.

Comparative Example 1 Film samples were obtained and evaluated in the same manner as in Examples 1 to 4, except that zinc oxide was used instead of the organometallic compound.

[Evaluation method] “Pole tack”; Each film sample was placed at a tilt angle of 30
Place two steel balls with different diameters ranging from 1/32 inch to 32/32 inch in diameter from a point 10 cm above the slope surface from the top of the film.
The maximum diameter of a steel ball that was rolled at an ambient temperature of 3° C. and came to rest within 10 cm below the slope from the top of the film was shown.

"Holding force": Each film sample (18mm x 2Qmm)
pasted on a stainless steel plate (SUS304) W f&, 2K
Pressure is applied once with a rubber roll weighing 1 kg, and after leaving it for 20 minutes at 40°C, hold the stainless steel plate vertically and apply a load of 1 kg to the bottom of the sample. In this case, measure the deviation length after 2 hours.

"Adhesive strength": After pasting each film sample (18 mm x 2 Q mm) on a stainless steel plate (SUS304), pressurize it with a 2 kg heavy rubber roll once and leave it for 20 minutes at 23 ° C.
A 180 degree peel test was conducted at a tensile rate of 300 mm/min under a cloud atmosphere at 23°C.

Here, the above characteristics are "pole tack" of 5 or more, "holding force" of 5 mm or less after 2 hours, and "adhesive force" of 4.
A tape that satisfies all the characteristics of 00 g/18'mm or more is considered good as an adhesive tape.

It can be seen from Table 1 that the adhesives of Examples 1 to 4 obtained according to the present invention have sufficient holding power and are also excellent in other adhesive properties. On the other hand, it can be seen that Comparative Example 1, in which no organometallic compound was used, had poor licking adhesive properties due to insufficient crosslinking of the acrylic copolymer. In addition, in the adhesive of Comparative Example 1, zinc oxide was not sufficiently dissolved and cloudiness was observed.

Examples 5 to 7, Comparative Examples 2 to 3 Acrylic copolymers having the compositions shown in Examples 1 to 4, each having a melt viscosity at 130°C shown in Table 2. Each sample was obtained in the same manner as in Examples 1 to 4 by adding zinc bisacetylacetonate in the parts by weight shown in Table 2 to 100 parts by weight of the above copolymer.

Next, the "pole tack", "holding force" and "adhesive force" were measured in the same manner as in Examples 1 to 4, and the results are shown in Table 2.

Table 2 shows that the adhesives of Examples 5 to 7 obtained according to the present invention have sufficient holding power and are also excellent in other adhesive properties. On the other hand, in Comparative Example 2, which used an acrylic copolymer with a low melt viscosity at 130°C, the holding power was insufficient, and in order to improve the holding power, the amount of the organometallic compound added was increased. It can be seen that Comparative Example 3 lacks tack.

(Effects of the Invention) As explained above, according to the method of the present invention, an ionically crosslinked acrylic adhesive with excellent adhesive holding power can be easily obtained, and it can be used for various adhesive applications. The sex is great.

Patent applicant: Mitsubishi Plastics Co., Ltd.

Claims (1)

[Claims] In addition to having a reactive group capable of crosslinking with metal ions in the side chain,
Melt viscosity at 130℃ is 5 x 10 to 7 x 10^5 cps
It is characterized by adding an organometallic compound selected from a metal chelate compound, a metal alcoholade, and a carboxylic acid metal salt to an acrylic copolymer in the range of , and then reacting by heating and mixing without a solvent. Method for manufacturing acrylic adhesive.