JPH04145181A - Water-soluble hot-melt adhesive - Google Patents

Abstract

PURPOSE:To provide the subject adhesive composed of a composition of starch and a PVA resin containing oxyalkylene group, having excellent adhesive power, dissolution speed in water and antiblocking property and suitable for the bonding of cellulosic materials such as paper ware, package, bookbinding and wood working. CONSTITUTION:The objective adhesive is composed of a composition of (A) a PVA resin containing oxyalkylene group (preferably a resin containing 5-300 oxyalkylene groups and produced by saponifying a copolymer of a vinyl ester and an unsaturated monomer having oxyalkylene group) and (B) starch (preferably corn starch). Preferably, the components A and B form a sea-island structure and the average particle diameter of the dispersed starch is <=10mum.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention is applicable to hot melt adhesives, particularly paper cartons, packaging, bookbinding,
This invention relates to water-soluble hot melt adhesives that have strong adhesion to cellulose materials in adhesive applications such as woodworking.

``Prior art'' Compared to other adhesives, hot melt adhesives can be applied to a wide range of adherends, have a very fast adhesion speed, are not toxic or fire-hazardous, and are economically advantageous. For this reason, it has been increasingly used in recent years for applications such as bookbinding, packaging, woodworking, shoemaking, and textile adhesion, especially for cellulose-based materials.However, water pollution In today's world, where the conservation of natural resources is a major issue, the reuse of paper products is being actively used as one of the solutions.

In order to reuse paper products as waste paper, they must be heated and stirred in water to loosen them back to their original fiber state. In the case of hydrophobic resins such as ethylene-vinyl acetate copolymer and polyethylene, which have been widely used as hot melt adhesives, it takes a long time to recycle them, and the quality of recycled paper deteriorates. A problem has arisen. Therefore, recently, polyvinyl alcohol resins that can be removed by dissolving in water have attracted much attention as hot melt adhesives.

[Problems to be Solved by the Invention] However, polyvinyl alcohol resins that have water dissolution properties have a high thermal softening temperature and are hard due to the strength of the hydrogen bonds of the hydroxyl groups included in their molecular structure. Because of these properties, it cannot be used alone as a hot melt adhesive, and must be used by adding a large amount of plasticizer to avoid lowering the heat softening temperature and melt viscosity.

However, adhesives that contain a large amount of plasticizer tend to bleed over time, resulting in a decrease in adhesive strength, or blocking occurs, causing particles to form clumps during storage or transportation, making handling difficult. It has its drawbacks.

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

As a countermeasure against this problem, the present inventors developed a hot melt adhesive made of a polyvinyl alcohol resin containing an oxyalkylene group. The adhesive can be used as a hot melt adhesive without adding a large amount of plasticizer, and has excellent adhesive strength and
The water dissolution rate was greatly improved. However, it was found that the anti-blocking properties were somewhat poor, and that it remained an issue to solve this drawback.

[Means for Solving the Problems] However, as a result of extensive research in order to solve the above problems, the present inventors have developed a water-soluble hot melt produced from a composition of an oxyalkylene group-containing polyvinyl alcohol resin and starch. The inventors discovered that an adhesive could achieve the purpose and completed the present invention.

The water-soluble hot-melt adhesive produced from the composition of the oxyalkylene group-containing polyvinyl alcohol resin and starch of the present invention does not need to contain a particularly large amount of plasticizer, and has excellent adhesive strength, water dissolution rate, and resistance. Its feature is that it has very good blocking properties.

The present invention will be explained in detail below.

The oxyalkylene group-containing polyvinyl alcohol resin used in the present invention has the general formula % [where R1 and R* are hydrogen or an alkyl group, and X is hydrogen (however, R1 and R1 are not hydrogen at the same time), alkyl basis,
It has a structure represented by an organic residue such as an alkyl ester group, an alkylamido group, or a sulfonic acid group, where n is an integer from 1 to 300. X is usually hydrogen.

The number n is advantageously from 2 to 300, particularly preferably from 5 to 30.
About 0 oxyalkylene groups are practical, and polyoxypropylene groups, polyoxybutylene groups, etc. are effective.

The vinyl alcohol resin having an oxyalkylene group can be produced by any method. Examples include: (1) a method in which vinyl ester is polymerized in the presence of polyoquine alkylene and then saponified; (2) a method in which an unsaturated monomer having an oxyalkylene group and a vinyl ester are copolymerized and then saponified; is practical from the viewpoint of resin production and performance.

The method (2) will be explained in detail below.

Examples of the unsaturated monomer having an oxyalkylene group include the following. However, the present invention is not limited to these.

Methacrylic acid ester type [where R is hydrogen or a methyl group, A is an alkylene group, substituted alkylene group, phenylene group, substituted phenylene group, m is an integer of 0 or 1 or more, and n is an integer of 1 to 100] Polyoxyethylene (meth)acrylate,
Examples include polyquine propylene (meth)acrylate.

[where R'' is hydrogen or an alkyl group, or the same as above], and polyoxyethylene (meth)acrylamide, polyoxypropylene (meth)acrylamide, polyoxyethylene (1-(meth)acrylamide) 1,1-dimethylpropyl) ester and the like.

It is a methalyl alcohol type [R, R', R'', n is the same as above], and examples thereof include polyoxyethylene (meth)allyl ether, polyoxypropylene (meth)allyl ether, and the like.

(A, R', R'', m, and n are the same as above), such as polyoxypropylene vinyl ether.

Among such monomers, (meth)alcohol type monomers are preferably used.

As vinyl esters, vinyl formate, vinyl acetate, vinyl trifluoroacetate, vinyl propionate, vinyl butyrate, vinyl caprate, vinyl laurate, vinyl persate, vinyl palmitate, vinyl stearate, etc. are used alone or in combination. However, vinyl acetate is practically preferred.

In the present invention, during such polymerization, a small amount of a general monomer other than the unsaturated monomer having an oxyalkylene group and vinyl ester as described above is present within a range that does not impair water solubility. It's okay. Examples of these monomers are shown below.

Ethylenically unsaturated carboxylic acid alkyl esters, etc. Methyl crotonate, ethyl crotonate, methyl itaconate, ethyl itaconate, methyl sorbate, methyl sorbate, monoalkyl maleate, dialkyl maleate, alkyl oleate, ( Meta)
Methyl acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, (
Examples include pentyl meth)acrylate, hepdyl (meth)acrylate, octyl (meth)acrylate, denyl (meth)acrylate, hexadecyl (meth)acrylate, and octadecyl (meth)acrylate.

Allyl esters of saturated carboxylic acids, allyl stearate, allyl laurate, allyl yam oil fatty acid, allyl ocdylate, allyl butyrate, etc.

Ethylene, propylene, α-hexene, α-octene,
α-decene, α-dodecene, α-hexadecene, α-octadecene, etc.

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

Alkyl vinyl ether probyl vinyl ether, butyl vinyl ether, hexyl vinyl ether, octyl vinyl ether, decyl vinyl ether, dodecyl vinyl ether, tetradecyl vinyl ether, hexadecyl vinyl ether, octadecyl vinyl ether, etc.

Alkyl allyl ether propyl allyl ether, butyl allyl ether, hexyl allyl ether, octyl allyl ether, decyl allyl ether, dodecyl allyl ether, tetradecyl vinyl ether, hexadecyl allyl ether, octadecyl allyl ether, etc.

In addition, (meth)acrylamide, (meth)acrylonitrile, styrene, vinyl chloride, etc. can also be used.

Copolymerization is not particularly limited and any known polymerization method may be used, but solution polymerization is usually carried out using an alcohol such as methanol, ethanol or isopropyl alcohol as a solvent. Of course, emulsion polymerization and suspension polymerization are also possible. In such solution polymerization, the method of charging monomers is to first charge the entire amount of vinyl ester and a portion of the oxyalkylene group-containing unsaturated monomer, start polymerization, and then add the remaining unsaturated monomers during the polymerization period. Any method may be used, such as a method of adding the moesha' in the mixture continuously or in parts, or a method of adding the moesha' all at once. The copolymerization reaction is carried out using a known radical polymerization catalyst such as azobisisobutyronitrile, acetyl peroxide, hendiyl peroxide, and lauroyl peroxide. Further, the reaction temperature is selected from a range of about 50° C. to boiling point.

Saponification is carried out by dissolving the copolymer in alcohol and in the presence of an alkali catalyst. Examples of the alcohol include methanol, ethanol, butanol, and the like.

The concentration of copolymer in alcohol is selected from the range 20-50% by weight. As the saponification catalyst, it is necessary to use an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, potassium methylate, or an alkali catalyst such as alcoholade. It is necessary that the amount of such catalyst used is 1 to 100 millimole equivalents based on the vinyl ester.

The preferred degree of saponification is selected from the range of 30 to 100 mol%, particularly preferably 50 to 100 mol%.

In addition, the method is not limited to the above method, for example, polyvinyl alcohol (
It is also possible to carry out a method in which an alkylene oxide is subjected to an addition reaction with a partially saponified product or a completely saponified product.

Although the content of the oxyalkylene group-containing polyvinyl alcohol of the present invention is not particularly limited, it is usually 1 to 50% by weight, more preferably 5 to 40% by weight based on the entire resin. Further, the practical viscosity of a 4% aqueous solution at 20°C is 2 to 20 cps.

Examples of starches used in the present invention include raw starches such as corn starch, potato starch, serr starch, rice starch, kissaba starch, zago starch, tapioca starch, sorghum starch, rice starch, bean starch, arrowroot starch, bracken starch, lotus starch, and water chestnut starch: Physically modified starch (α-starch, fractionated amylose, moist heat treated starch, etc.), enzymatically modified starch (hydrolyzed dextrin, enzymatically decomposed dextrin, amylose, etc.), chemically modified starch (acid-treated starch, hypochlorous acid oxidized starch, (dialdehyde starch, etc.), chemically modified starch derivatives (esterified starch, etherified starch, cationized starch, crosslinked starch, etc.). Among chemically modified starch derivatives, esterified starches include acetate esterified starch, succinate esterified starch, nitrate esterified starch, phosphate esterified starch, urea phosphate esterified starch, xanthate esterified starch, and acetoacetic acid esterified starch. Examples of etherified starch such as esterified starch include allyl etherified starch, methyl etherified starch, carboquine methyl etherified starch,
Hydroxyethyl etherified starch, etc., hydroxypropyl etherified starch, cationized starch, such as a reaction product of starch and 2-diethylaminoethyl chloride, a reaction product of starch and 2,3-epoxypropyltrimethylammonium chloride, etc., as a crosslinked starch Examples of starch include polyaldehyde crosslinked starch, epichlorohydrin crosslinked starch, phosphoric acid crosslinked starch, acrolein crosslinked starch, etc. Corn starch is particularly practical.

In carrying out the present invention, the mixing ratio of the polyoxyalkylene group-containing polyvinyl alcohol resin and starch is 90:10 to 20:80, particularly 80:2 by weight.
It is set within the range of 0 to 5050. If the proportion of starch is too high, the adhesive strength will be insufficient as a hot melt adhesive, making it unusable. On the other hand, if the amount is too low, the anti-blocking effect will be poor and the biodegradability of the dissolved water will be poor.

The adhesive composition of the present invention is prepared by thoroughly blending the oxyalkylene group-containing polyvinyl alcohol resin and starch in the above ratio, and then heating the mixture to 130 to 180°C to melt each acid. The melt thus prepared can be directly applied to paper using a coater or the like, or it can be extruded to form blocks, slaps, strings, threads, sticks, flakes, pellets, sheets, films, etc. It can also be molded into powder form and then remelted and applied at the time of use.

In such an adhesive composition, polyvinyl alkyl group-containing vinyl alcohol/starch forms a sea-island structure, and the starch preferably has a dispersed average particle size of 10 μm or less, and when the starch has a dispersed average particle size of 10 μm or more, The excellent effects of the adhesive cannot be fully exhibited.

Although the adhesive can be blended with a plasticizer such as polyhydric alcohol, the oxyalkylene group-containing polyvinyl alcohol resin alone can be sufficiently melted without using a plasticizer.
The use of plasticizers may deteriorate the quality of the adhesive, so it is better not to use them.

In addition, if necessary, other additives such as rosins, rosin esters, pinene polymers, water-added petroleum resins, etc. may be used as tackifiers and antioxidants that are compatible with the resin.
Appropriate amounts of fillers, waxes, etc. may be added.

The hot melt adhesive thus obtained is used, in particular, for paper cartons, packaging, bookbinding, woodworking, etc.

[Operation] The water-soluble hot-melt adhesive of the present invention has excellent adhesive strength, water-soluble release strength, and blocking resistance, and is particularly suitable for adhesion to cellulose materials such as paper cartons, packaging, bookbinding, and woodworking. It is useful as an agent, and is extremely advantageous industrially in preventing water pollution and protecting natural resources.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

"%" and "part" are based on weight unless otherwise specified.

Examples 1 to 5 70 parts of oxoalkylene group-containing polyvinyl alcohol obtained by saponifying a copolymer of an oxyalkylene group-containing unsaturated monomer and vinyl acetate as shown in Table 1 and 30 parts of corn starch were mixed together. After blending, the mixture was heated to 160° C. to form a molten state and extruded into a film using an extruder to obtain a sample with a thickness of 200 μm and a size of 35×60 am.

Next, this film was used to heat seal and adhere kraft paper at 180°C. The peel strength, blocking property, and water dissolution rate of this adhesive were measured. The above results are summarized in Table 1.

Control Example ■ An experiment was conducted in the same manner as in Example 1 except that starch was not added. The results are shown in Table 1.

Comparative Example 2 Polyvinyl alcohol 70 consisting of a saponification degree of 90 mol% and an aqueous solution viscosity of 10 centiboise at 20°C was used in place of the oxyalkylene group-containing polyvinyl alcohol resin.
After adding 30 parts of glycerin to the mixture and blending well, an experiment was conducted according to Example 1.

The results are shown in Table 1.

The evaluation method is as follows.

・Peel strength: 20°C, 65%RH, after being left for 5 hours, using Shimadzu Autograph S-100 model, tensile speed 30cm/
Measurement of peel strength at 20°C and 65% anti-blocking film.
R0110097cm'' The state of peeling was observed after being left under pressure for 5 hours.

Not blocked at all. Slightly blocked. Broken film blocked on the entire surface. Water dissolution rate. The dissolution rate of a 20°C water sample was observed using a sample of ○△ x 30 x 50 mm while stirring in a 100 μm thick sample.

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

Claims (1)

[Claims] 1. A water-soluble hot melt adhesive comprising a composition of an oxyalkylene group-containing polyvinyl alcohol resin and starch. 2. The water-soluble hot melt adhesive according to claim 1, wherein the starch is corn starch. 3. The water-soluble hot melt adhesive according to claim 1, wherein the polyoxyalkylene group-containing polyvinyl alcohol resin and the starch form a sea-island structure, and the starch has a dispersed average particle size of 10 μm or less.