JP2003020463A - Hot-melt adhesive and bonding method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot-melt adhesive for the use in a paper field such as bookbinding, box-making and bag-making processes and free from the problems of widely used ethylene-vinyl acetate copolymer comprising the difficulty in the regeneration treatment of waste paper in water owing to the hydrophobic nature of the resin in spite of its excellent adhesivity, workability and flexibility. SOLUTION: The heat-sensitive adhesive consists of a starch paste liquid containing 10-100 pts.wt. of a starch plasticizer based on 100 pts.wt. of starch and having a viscosity of 100-200,000 cPs at 30 deg.C and 50% concentration. The adhesive can be used as a water-soluble hot-melt adhesive giving high adhesive force and water-dissolution rate after the preliminary drying treatment.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to starch-based hot melt adhesives. More specifically, it relates to a heat-sensitive adhesive which is a water-soluble heat-sensitive adhesive, is applied to a substrate, is pre-dried to form a heat-sensitive film on the substrate, and is then heat-bonded. Since this adhesive has a large adhesive force and a high dissolution rate in water, it is suitable as an adhesive for reusing used paper and for temporarily fixing fibers, which requires easy peelability of an adherend with water and high-speed water solubility. Alternatively, it is used as an adhesive for a collapsible cigarette filter, which is easily disintegrated by rainwater or the like when it is discarded in the environment after smoking.

[0002]

Hot melt adhesives are substances that are 100% solids at room temperature and do not contain or require volatile solvents. Although this adhesive is a solid substance at room temperature, it is melted by heating to become a liquid or liquid and is used in this form. Upon cooling, the adhesive becomes solid again and its cohesive force gives it adhesive strength. In this regard, hot melt adhesives differ from other types of adhesives that adhere via the solid state by evaporation or removal of solvent. Hot melt adhesives can be more cost and time efficient in the bonding process than these adhesives because the evaporation process required in water or solvent based adhesive systems is unnecessary. Also, it can be applied to a wide range of adherends, the adhesion speed is very fast,
Since it has no toxicity or danger, it is widely used for applications such as bookbinding, packaging, woodworking, shoemaking, and fabric bonding. As a hot melt adhesive, it is required to satisfy performances such as adhesiveness, meltability, heat resistance, cold resistance, and flexibility, and generally ethylene-vinyl acetate copolymer, polyethylene, polypropylene, polyamide, polyester are used. Used as a base polymer.

The protection of natural resources is being called for as an environmental problem,
Recycling such as recycling of used paper has been actively carried out. However, for example, most of the hot-melt adhesives for bookbinding are water-insoluble thermoplastic resins mainly composed of ethylene-vinyl acetate copolymer, so that in the used paper recycling process,
Adhesive released from the fiber portion of the paper remains as a lump or film, which adheres to the surface of the recycled paper, causing spots and irregularities, and adversely affecting the printability of the ink. Occurs. The hot melt adhesive for corrugated board has the same problem. Therefore, development of a water-soluble hot melt adhesive is desired.

In accordance with these requirements, many patents have been published that use partially saponified polyvinyl alcohol as a hot melt adhesive. For example, JP-A-58-1043
Japanese Patent Publication No. 8 describes a method for producing a polyvinyl alcohol-based hot melt adhesive. That is, the degree of polymerization 2
Polyvinyl acetate of 00 or less is dissolved in an aliphatic alcohol having 1 to 4 carbon atoms, an alkali is added, and a saponification degree is 30 to 80.
After partially saponifying to mol%, it is possible to remove the solvent and saponification by-products by heating and obtain a partially saponified polyvinyl alcohol melt, and mix the obtained partially saponified polyvinyl alcohol melt with a flux. Have been described. However, since polyvinyl alcohol has a strong hydrogen bond of a hydroxyl group in terms of its molecular structure, it has a high melting temperature, and its melting point is close to its melting point, so that oxidative decomposition occurs during melting. Therefore, in most cases, it is used as a hot melt adhesive having a low polymerization degree and partially saponified polyvinyl alcohol mixed with a plasticizer and a tackifier. However, although they have good water dispersibility,
Since it does not dissolve easily in water, the problem that the adhesive dispersed in the used paper recycling process is mixed into recycled paper has not been solved. In addition, there is a problem that workability is poor when applied by a coater or screen printing. As described above, the current situation is that there is no hot melt adhesive that is effective in recycling used paper resources and has excellent coating properties.

[0005]

Means for Solving the Problems As a result of intensive investigations by the present inventors on a water-soluble heat-sensitive adhesive capable of solving the above-mentioned problems, it was found that a starch paste solution containing a starch plasticizer has an adhesive strength and They have found that they can be used as water-soluble hot melt adhesives with a high water dissolution rate, and have completed the present invention.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The starch that can be used in the present invention may be unprocessed starch, but ether and / or esterified starch is preferable for stabilizing the viscosity of the paste solution. Examples of the etherification method include alkylation such as methylation, hydroxyalkylation such as hydroxypropylation, carboxymethylation, and cationization. Examples of the esterification method include fatty acid esterification such as acetic acid ester, sulfuric acid ester, phosphoric acid ester and the like. The degree of substitution thereof may be such that the aging of starch is suppressed, and 0.001 to
It is 0.5. When used as an adhesive, starch, which has a low viscosity when heated and melted, has good fluidity to an adherend and good adhesion. Examples of low-viscosity starch include roasted dextrin, enzyme-modified dextrin, acid-treated starch, and oxidized starch, but are not limited thereto. Further, it may be crosslinked.

The starch plasticizer is not particularly limited as long as it can gelatinize starch and impart plasticity to the gelatinized product. For example, urea, thiourea, paratoluenesulfonamide, melamine, guanidine, etc., and polyols. Among these, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, hexamethylene glycol, glycerin,
Examples thereof include polyhydric alcohols such as diglycerin, polyglycerin, trimethylolpropane, pentaerythritol, sorbitol and mannitol. Of these, urea and polyethylene glycol are preferred. These can be used alone or in combination of two or more.

The amount of the plasticizer used is 10 to 100 parts by mass, more preferably 100 parts by mass of starch per 100 parts by mass of starch.
It is suitable to use 20 to 70 parts by mass of the plasticizer per part by mass, from the viewpoint that the starch can be sufficiently gelatinized and appropriate fluidity can be imparted to the gelatinized product. Also,
If necessary, additives such as antiseptics, antiblocking agents, and inorganic substances may be added.

The method for preparing the paste solution is only required to completely gelatinize the starch. Specifically, a method of gelatinizing by heating the starch slurry to a temperature above the gelatinization starting temperature, a method of gelatinizing by adding an alkali such as sodium hydroxide to the starch slurry, and the like can be mentioned. The plasticizer may be added at any time. The viscosity of the paste solution can be freely adjusted, but it is 100-20 at 30 ° C.
Those of 0000 cps are preferably used.

The method of using the heat-sensitive adhesive of the present invention is to coat the base material by a coater, screen printing or the like and then pre-dry it to form a film-shaped hot melt adhesive layer on the base material. Then, bring it into close contact with the base material
Heat at ˜160 ° C. for several seconds to bond.

The heat-sensitive adhesive of the present invention can be used as a bookbinding adhesive, a box-making adhesive, and a water-soluble adhesive.
It can be used as an adhesive for wrapping paper. Since the heat-sensitive adhesive of the present invention is water-soluble and also has a high water-dissolution rate, even if waste paper using the heat-sensitive adhesive of the present invention is treated in a conventional recycling process, the conventional adhesive Had a drawback, that is, the adhesive released from the fiber portion of the paper remains as a lump or film, which adheres to the surface of the recycled paper, causing spots and irregularities, and It is possible to reproduce without causing problems such as adversely affecting printability. Further, since it is a starch paste solution, it has excellent coatability. It can also be used as an adhesive for temporarily fixing fibers in sewn clothing, and after sewing, the adhesive can be removed by washing with water. When it is used as a binder for a tobacco filter, it becomes a disintegrating tobacco filter and easily disintegrates due to rainwater when it is discarded in the environment after smoking.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. <Example 1> Oxidized hydroxypropyl starch (degree of substitution: 0.
05) 1900 parts by mass of water was added to 900 parts by mass and stirred. Heated above 80 ° C. until the slurry was completely glued. After cooling to 60 ° C., 400 parts by mass of urea was added and dissolved to obtain a heat-sensitive adhesive. The viscosity at 30 ° C is 3
It was 0000 cps. The viscosity stability was good even after one month. <Example 2> A heat-sensitive adhesive was obtained in the same manner as in Example 1 except that acid-treated hydroxypropyl starch (substitution degree: 0.10) was used instead of the oxidized hydroxypropyl starch. Three
The viscosity at 0 ° C. was 4000 cps. The viscosity stability was good even after one month. <Example 3> 1900 parts by mass of water and 400 parts by mass of urea were added to 900 parts by mass of oxidized starch acetate (degree of substitution 0.09) and stirred. The heat-sensitive adhesive was obtained by heating the slurry at 80 ° C. or higher until the paste was completely glued. The viscosity at 30 ° C is 20
It was 000 cps. The viscosity stability was good even after one month. <Example 4> To 450 parts by mass of water, 23 parts by mass of sodium hydroxide was added and dissolved by stirring. Oxidized cross-linked hydroxypropyl starch (degree of substitution 0.01) was added to gelatinize. After neutralization to pH 4 with dilute nitric acid, 200 parts by mass of urea dissolved in 100 parts by mass of water was added to obtain a heat-sensitive adhesive. The viscosity at 30 ° C. was 50,000 cps. The viscosity stability was good even after one month. <Example 5> Hydroxypropylated dextrin (substitution degree 0.002) instead of oxidized hydroxypropyl starch
A heat-sensitive adhesive was obtained in the same manner as in Example 1 except that was used. The viscosity at 30 ° C. was 200 cps. The viscosity stability was good even after one month. <Example 6> A heat-sensitive adhesive was obtained in the same manner as in Example 1 except that 45 parts by mass of polyethylene glycol (molecular weight: 400) was added simultaneously with urea. The viscosity at 30 ° C is
It was 28,000 cps. The viscosity stability was good even after one month.

<Example 7> The heat-sensitive adhesives obtained in Examples 1 to 6 were applied to plywood using a Mayer bar and then air-dried. A cotton cloth was applied to this plywood and heat-bonded with an iron at 160 ° C. for 5 seconds, and the peel strength was measured. The method for measuring the peel strength is as follows.

<Peeling strength measuring method>
After leaving it at 0 ° C and 65RH% for 24 hours, it was cut into a width of 2.5 cm and pulled by an autograph (pulling speed 100 mm /
min) Peel strength was determined.

<Example 8> The plywood adhered in Examples 1 to 6 was immersed in water at 25 ° C and the peeled state of the cotton cloth was observed. The results are shown in Table 1.

Comparative Example 1 A commercially available ethylene-vinyl acetate copolymer hot melt adhesive was melted by heating to give Example 7.
And the test of Example 8 was conducted, and the results are shown in Table 1. <Comparative Example 2> A commercially available urethane hot melt adhesive was heated and melted to perform the tests of Examples 7 and 8, and the results are shown in Table 1.

[0017]

[Table 1]

[0018]

As described above, the hot melt adhesive of the present invention can be applied by a coater, screen printing, etc.
It has high adhesive strength, is water-soluble, and has a high water-dissolution rate. For example, it is suitable as an adhesive for reusing used paper and temporarily fixing fibers, which requires easy peelability and water solubility of the adherend due to water.
Alternatively, it is extremely useful as an adhesive for a collapsible cigarette filter, which is easily disintegrated by rainwater or the like when it is discarded in the environment after smoking.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 4J004 AA04 AB05 BA02 CA02 CB01                       FA08                 4J040 BA121 BA122 GA05 GA07                       GA08 HB10 HB11 HC19 HD16                       JB01 JB03 KA25 KA31 MA08                       MA09 MB02 NA07 NA10 PA30                       PA33

Claims (4)

[Claims] 1. A starch paste solution containing starch 10 as a starch plasticizer.
A heat-sensitive adhesive characterized in that it contains 10 to 100 parts by weight per 0 parts by weight, and has a viscosity of 100 to 200,000 cps at 30 ° C. and a concentration of 50%. 2. The starch used in the starch paste solution is an etherified starch and / or an esterified starch.
The heat-sensitive adhesive described. 3. The heat-sensitive adhesive according to claim 1, wherein the starch plasticizer is urea and / or polyol. 4. A bonding method, which comprises applying the adhesive according to claim 1 on a base material, predrying the same to form a heat-sensitive film layer, and then heat-bonding it to an object to be bonded.