JP3214851B2 - Water soluble hot melt adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a hot-melt adhesive, particularly a water-soluble adhesive having strong adhesive strength to fibrous materials in adhesive applications such as paper containers, packaging, bookbinding and woodworking. Related to hot melt adhesives.

[Prior art] Compared with other adhesives, hot-melt adhesives can be applied to a wide range of adherends, have extremely high bonding speed, have no danger of toxicity and fire, are economically advantageous, etc. For these reasons, they have been increasingly used in recent years for applications such as bookbinding, packaging, woodworking, shoemaking, and textile bonding, especially for fibrous materials. However,
At present, when water pollution and protection of natural resources have become major issues, reuse of paper products has been actively pursued as one of the solutions.

In order to reuse paper products as waste paper, they must be heated and agitated in water to loosen them to their original fibrous state. In the case of hydrophobic resins such as ethylene-vinyl acetate copolymer and polyethylene, which have been widely used as hot melt adhesives in the past, it takes a long time to regenerate or the quality of regenerated paper decreases. The problem has arisen. Therefore, recently, a polyvinyl alcohol-based resin that can be dissolved and removed in water has attracted much attention as a hot melt adhesive.

[Problems to be Solved by the Invention] However, a polyvinyl alcohol-based resin having water dissolving and removing properties has a high thermal softening temperature and is hard due to the strength of hydrogen bond of a hydroxyl group contained in its molecular structure. Due to its properties, it cannot be used alone as a hot-melt adhesive, but must be used after blending a large amount of a plasticizer to lower the heat softening temperature and melt viscosity.

However, adhesives containing a large amount of plasticizer tend to cause bleeding of the plasticizer over time, resulting in a decrease in adhesive strength, blocking, and the accumulation of particles during storage or transportation, which makes particles difficult to handle. Has disadvantages.

Therefore, it can be used as a hot-melt adhesive without adding a large amount of plasticizer, and the development of an adhesive with further improved dissolution and removal properties in water is extremely industrially advantageous in preventing pollution of water and protecting natural resources. .

As a countermeasure, the present inventors have developed a hot melt adhesive composed of a polyvinyl alcohol resin to which an oxyalkylene group is bonded. The adhesive can be used as a hot melt adhesive without blending a large amount of a plasticizer, and the adhesive strength and the rate of dissolution in water have been greatly improved. However, the blocking resistance was somewhat poor, and it was found that solving such a drawback was left as an issue.

Means for Solving the Problems However, as a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a water-soluble solution produced from a composition of a polyvinyl alcohol-based resin having an oxyalkylene group bonded thereto and starch. The present inventors have found that a water-soluble hot-melt adhesive can achieve the object and completed the present invention.

The water-soluble hot-melt adhesive prepared from the composition of the polyvinyl alcohol-based resin having an oxyalkylene group bonded thereto and starch according to the present invention does not require the addition of a particularly large amount of a plasticizer, and has an adhesive force and a water dissolution rate. And blocking resistance are very excellent.

 Hereinafter, the present invention will be described in detail.

As the polyvinyl alcohol-based resin to which the oxyalkylene group used in the present invention is bonded, a general formula [Where R ¹ and R ² are hydrogen or an alkyl group, X is hydrogen, an alkyl group, an alkyl ester group, an alkylamide group, or a sulfonate group, and n represents an integer of 1 to 30]. It has. X is usually hydrogen.

The number of n is practically an oxyalkylene group of 2 to 300, particularly preferably about 5 to 300, and a polyoxyethylene group, a polyoxypropylene group, a polyoxybutylene group or the like is effective.

The polyvinyl alcohol-based resin having an oxyalkylene group bonded thereto can be produced by any method. For example, a method of polymerizing a vinyl ester in the presence of a polyoxyalkylene and saponifying, a method of copolymerizing an unsaturated monomer having an oxyalkylene group with a vinyl ester, and a method of saponifying, etc. Practical in terms of manufacturing and performance.

 The following method is specifically described.

Examples of the unsaturated monomer having an oxyalkylene group are as follows. However, the present invention is not limited to only these.

(Meth) acrylic ester type general formula Wherein R is hydrogen or a methyl group, R ¹ and R ² are hydrogen or an alkyl group, A is an alkylene group, a substituted alkylene group, a phenylene group, a substituted phenylene group, m is an integer of 0 or 1 or more, and n is An integer of 1 to 100], such as polyoxyethylene (meth) acrylate and polyoxypropylene (meth) acrylate.

(Meth) acrylamide type Wherein R ³ is hydrogen or an alkyl group or A, R, R ¹ , R ² , m, and n are the same as those described above.], Polyoxyethylene (meth) acrylamide, polyoxypropylene (meth) acrylamide, polyoxyethylene (1- (meth) Acrylamide-1,1-dimethylpropyl) ester and the like.

(Meth) allyl alcohol type general formula [R, R ¹ , R ² , and n are the same as those described above], and examples thereof include polyoxyethylene (meth) allyl ether and polyoxypropylene (meth) allyl ether.

Vinyl ether type general formula [A, R ¹ , R ² , m, and n are the same as those described above] and include polyoxypropylene vinyl ether and the like.

Among these monomers, the (meth) alcohol type is preferably used.

As vinyl esters, vinyl formate, vinyl acetate,
Vinyl trifluoroacetate, vinyl propionate, vinyl butyrate, vinyl caprate, vinyl laurate, vinyl versatate, vinyl palmitate, vinyl stearate and the like are used alone or in combination, but in practice vinyl acetate is preferred. .

In the present invention, at the time of such polymerization, the unsaturated monomer having an oxyalkylene group as described above, and other general monomers other than vinyl ester are present in a small amount as long as the water solubility is not impaired. May be. These monomers are exemplified below.

Ethylenic unsaturated carboxylic acid alkyl esters, etc.Methyl crotonate, ethyl crotonate, methyl itaconate, ethyl itaconate, methyl sorbate, ethyl sorbate, monoalkyl maleate, dialkyl maleate, alkyl oleate,
Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, ( Meta)
Decyl acrylate, hexadecyl (meth) acrylate,
Octadecyl (meth) acrylate and the like can be mentioned.

Allyl esters of saturated carboxylic acids: Allyl stearate, allyl laurate, allyl coconut oil, allyl octylate, allyl butyrate and the like.

α-olefin ethylene, propylene, α-hexene, α-octene, α-decene, α-dodecene, α-hexadecene, α
-Octadecene and the like.

Ethylenically unsaturated carboxylic acids (meth) acrylic acid, crotonic acid, (anhydride) maleic acid, fumaric acid, itaconic acid, and alkali metal salts and ammonium salts thereof.

Alkyl vinyl ether Propyl vinyl ether, butyl vinyl ether, hexyl vinylyl ether, octyl vinyl ether, decyl vinyl ether, dodecyl vinyl ether, tetradecyl vinyl ether, hexadecyl vinyl ether, octadecyl vinyl ether and the like.

Alkyl allyl ether propyl allyl ether, butyl allyl ether, hexyl allyl ether, octyl allyl ether, decyl allyl ether, dodecyl allyl ether, tetradecyl allyl ether, hexadecyl allyl ether, octadecyl allyl ether, and the like.

In addition, (meth) acrylamide, (meth) acrylonitrile, styrene, vinyl chloride and the like can be used.

The copolymerization is not particularly limited, and any known polymerization method can be used arbitrarily. Usually, solution polymerization using an alcohol such as methanol, ethanol or isopropyl alcohol as a solvent is performed. Of course, emulsion polymerization and suspension polymerization are also possible. In such a solution polymerization, as a method of charging the monomer, first, the entire amount of the vinyl ester and a part of the unsaturated monomer having the oxyalkylene group are charged,
Any method may be used, such as a method in which polymerization is started and the remaining unsaturated monomer is continuously or dividedly added during the polymerization period, or a method in which the former is charged at once. The copolymerization reaction is carried out using a known radical polymerization catalyst such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide and lauroyl peroxide. The reaction temperature is selected from the range of 50 ° C. to the boiling point.

The saponification is performed by dissolving the copolymer in an alcohol and in the presence of an alkali catalyst. Examples of the alcohol include methanol, ethanol, and butanol.

The concentration of the copolymer in the alcohol is selected from the range of 20 to 50% by weight. Sodium hydroxide as a saponification catalyst,
It is necessary to use an alkali catalyst such as an alkali metal hydroxide or an alcoholate such as potassium hydroxide, sodium methylate, sodium ethylate or potassium methylate. It is necessary to use the catalyst in an amount of 1 to 100 mmole equivalent to the vinyl ester.

The preferred degree of saponification is 30 to 100 mol%, particularly preferably 5
It is selected from the range of 0 to 100 mol%.

The method is not limited to the above method, and a method of adding an alkylene oxide to polyvinyl alcohol (partially saponified product or completely saponified product) can be used.

Thus, the content of the oxyalkylene group in the polyvinyl alcohol of the present invention is not particularly limited, but is usually 1 to 50% by weight, more preferably 5 to 40% by weight based on the whole resin. is there. The practical viscosity of the 4% aqueous solution at 20 ° C. is 2 to 20 cps.

Examples of the starch used in the present invention include corn starch, potato starch, sweet potato starch, wheat starch, kissava starch, sago starch, tapioca starch, sorghum starch, rice starch, bean starch, kudzu starch, raw starch, ash starch, and raw starch. Starch: physically modified starch (α-
Starch, fractionated amylose, heat-moisture treated starch, etc., enzyme-modified starch (hydrolyzed dextrin, enzyme-decomposed dextrin, amylose, etc.), chemically degraded starch (acid-treated starch, hypochlorite oxidized starch, dialdehyde starch, etc.), chemical Modified starch derivatives (esterified starch, etherified starch, cationized starch, cross-linked starch, etc.) and the like. Among the chemically modified starch derivatives, the esterified starch includes acetate esterified starch, succinic esterified starch, nitrated esterified starch, phosphorylated esterified starch, urea phosphorylated esterified starch, xanthated esterified starch, and acetoacetic acid. As etherified starch such as esterified starch, allyl etherified starch, methyl etherified starch, carboxymethyl etherified starch, hydroxyethyl etherified starch, etc., hydroxypropyl etherified starch, and cationized starch include starch and 2- Examples of crosslinked starch such as a reactant of diethylaminoethyl chloride and a reactant of starch and 2,3-epoxypropyltrimethylammonium chloride include formaldehyde crosslinked starch and shrimp Hydrin crosslinked starch, phosphoric acid crosslinked starch, acrolein-crosslinked starch and the like, in particular corn starch practical.

In carrying out the present invention, the mixing ratio of the polyvinyl alcohol-based resin and the starch to which the polyoxyalkylene group is bonded is 90:10 to 20:80 by weight, particularly 80:20 to 50:50.
Is set within the range. If the proportion of starch is too large, the adhesive strength of the hot-melt adhesive becomes insufficient, and it becomes unusable. On the other hand, when the amount is too small, the effect of preventing blocking is poor, and the biodegradability of dissolved water is poor.

The adhesive composition of the present invention is prepared by thoroughly blending the polyvinyl alcohol resin to which the oxyalkylene group is bonded and the starch in the above ratio, and then heating the mixture to 130 to 180 ° C. to melt each composition, so that the adhesive composition is prepared. However, the melt thus prepared can be directly applied to paper with a coater or the like, or the melt can be extruded once, and then the block, slug, string, thread, stick, flake, pellet,
After molding into a sheet, film, powder or the like, it can be re-melted and applied at the time of use.

In such an adhesive composition, polyoxyalkylene-bonded polyvinyl alcohol / starch forms a sea-island structure, and the dispersion average particle diameter of starch is preferably 10 μm or less, and the starch dispersion average particle diameter is 10 μm or more. In some cases, the excellent effects of the adhesive cannot be sufficiently exerted.

The adhesive may contain a plasticizer such as a polyhydric alcohol.However, even without using a plasticizer, the polyvinyl alcohol-based resin to which the oxyalkylene group is bonded can be sufficiently melted alone. It is better not to use it, as it may deteriorate the quality of the agent.

Also, if necessary, other additives such as rosins, rosin esterified compounds, pinene polymers, water-added petroleum resins and the like are suitable for tackifiers, antioxidants, fillers, waxes having good compatibility with the resins. You may add and use it.

The hot melt adhesive thus obtained is particularly suitable for paper containers,
Used as packaging, bookbinding, woodworking, etc.

[Action] The water-soluble hot-melt adhesive of the present invention has excellent adhesive strength, water-dissolving and removability, and blocking resistance, and is particularly useful for fibrous materials such as paper containers, packaging, bookbinding, and woodworking. And is extremely industrially advantageous in preventing water pollution and protecting natural resources.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.
“%” And “parts” are based on weight unless otherwise specified.

Examples 1 to 5 Polyvinyl alcohol 70 bonded to an oxyalkylene group obtained by saponifying a copolymer of an unsaturated monomer having an oxyalkylene group and vinyl acetate as shown in Table 1
Parts and 30 parts of corn starch after blending well
The mixture was heated to 160 ° C. to be in a molten state and extruded into a film by an extruder to obtain a sample having a thickness of 200 μm and 35 × 60 mm.

Next, using this film, kraft paper was heat-sealed at 180 ° C. The peel strength, blocking property and water dissolution rate of this adhesive were measured. Table 1 summarizes the above results.

Comparative Example 1 An experiment was carried out in the same manner as in Example 1 except that no starch was blended. Table 1 shows the results.

Comparative Example 2 Polyvinyl alcohol having a saponification degree of 90 mol% and an aqueous solution viscosity of 10 centipoise at 20 ° C. instead of the polyvinyl alcohol-based resin having an oxyalkylene group bonded thereto
After adding 30 parts of glycerin to 70 parts and blending well, an experiment was conducted according to Example 1 below.

 Table 1 shows the results.

 The evaluation method is as follows.

・ Peel strength: Measured at a pull rate of 30 cm / min using Autograph Model S-100 manufactured by Shimadzu Corporation after leaving it for 5 hours at 20 ° C. and 65% RH. ・ Blocking resistance Two sample films were stacked. This is 20 ℃, 65% R
H, the peeling state after standing for 5 hours under a pressure of 100 g / cm ² was observed.

○ No blocking at all △ Slightly blocked × Blocked over the entire surface ×× Film breakage ・ Water dissolution rate A 100 μm thick, 30 × 50 mm sample was placed in water at 20 ° C. and the dissolution rate of the sample was observed with stirring. did.

○ Dissolved in 3 minutes or less △ Dissolved in 3 to 5 minutes × Dissolved for 5 minutes or more [Effect] The water-soluble hot-melt adhesive of the present invention has extremely excellent adhesive strength, water dissolution rate, and blocking resistance, and is particularly intended for fibrous materials such as paper containers, packaging, bookbinding, and woodworking. It is useful as an adhesive, and is extremely industrially advantageous in preventing water pollution and protecting natural resources.

Continuation of the front page (56) References JP-A-60-42475 (JP, A) JP-A-49-58129 (JP, A) JP-A-57-165472 (JP, A) JP-A-54-26831 (JP) JP-A-58-38772 (JP, A) JP-A-48-73442 (JP, A) JP-A-56-14544 (JP, A) JP-A-61-36386 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C09J 1/00-201/10 C08L 1/00-101/16

Claims (3)

(57) [Claims] An oxyalkylene group-bonded polyvinyl alcohol resin represented by the following general formula and a starch composition, and the mixing ratio of the polyvinyl alcohol resin and starch is 90: Water soluble hot melt adhesive that is 10-20: 80. [Where R ¹ and R ² are hydrogen or an alkyl group, X is any of hydrogen, an alkyl group, an alkyl ester group, an alkylamide group, and a sulfonate group, and n represents an integer of 1 to 30]. ] 2. A water-soluble hot melt adhesive according to claim 1, wherein the starch is corn starch. 3. The water-soluble hot melt according to claim 1, wherein the polypinyl alcohol resin to which the oxyalkylene group is bonded and the starch form a sea-island structure, and the dispersion average particle size of the starch is 10 μm or less. adhesive.