JP2000169812A - Powdery heat-sensitive adhesive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject readily releasable water-soluble adhesive capable of freely selecting the particle diameter and having a high adhesive strength and a high water dissolution rate by adsorbing a starch plasticizer on a pregelatinized starch. SOLUTION: This adhesive is obtained by adsorbing (B) a starch plasticizer on (A) a pregelatinized starch. The aqueous solution of the component A preferably has 20-10,000 cP viscosity at 40% and 30 deg.C. The component B is preferably selected from urea, polyethylene glycol, polypropylene glycol, ethylene glycol, propylene glycol and glycerol. The amount of the component B used is preferably 10-100 pts.wt. based on 100 pts.wt. of the component A. The adhesive can be used for an adhesive for bookbinding, an adhesive for can manufacturing, an adhesive for packaging paper, or the like. A waste paper using the adhesive can be recycled without causing problems even by carrying out a recycling treatment according to a conventional method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a starch-based hot melt adhesive. More particularly, the present invention relates to a powdery heat-sensitive adhesive which is a water-soluble powdery heat-sensitive adhesive, in which a starch plasticizer is adsorbed to pregelatinized starch. Since this adhesive has a large adhesive strength and a high dissolution rate in water,
It is suitable as an adhesive for recycling waste paper and for temporarily fixing fibers, which require easy detachment of the adherend by water and high-speed water solubility. Alternatively, it is used as an adhesive for a disintegrating tobacco filter, which is easily disintegrated by rainwater when 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. The adhesive is a solid substance at room temperature, but is melted by heating to become a liquid or liquid and used in this form. Upon cooling, the adhesive becomes solid again and gains adhesion due to its cohesive strength. In this regard, hot melt adhesives differ from other types of adhesives that adhere through the solid state by evaporation or removal of solvents. Generally, hot melt adhesives are synthetic and natural resins and waxes,
Particularly petroleum-derived polymers such as polyethylene, ethylene-
Vinyl acetate, styrene block copolymer and polypropylene. Hot melt adhesives can be more cost and time efficient in the bonding process compared to these adhesives because they do not require an evaporation step as in water or solvent based adhesive systems. In addition, it can be applied to a wide range of adherends, has a very fast bonding speed, has no toxicity or danger, and is widely used in applications such as bookbinding, packaging, woodworking, shoemaking, and textile bonding. ing. Hot-melt adhesives are required to satisfy performances such as adhesiveness, meltability, heat resistance, cold resistance, and flexibility.Generally, ethylene-vinyl acetate copolymer, polyethylene, polypropylene, polyamide, and polyester are used. Used as base polymer.

[0003] Particularly, as an adhesive in the paper field such as bookbinding, box making, bag making, etc., ethylene having excellent adhesiveness, workability and flexibility is used.
-Vinyl acetate copolymer is widely used. But,
At present, it is difficult to recycle waste paper in water because the resin is hydrophobic. Recently, hot-melt adhesives made of water-soluble polyvinyl alcohol-based resins have attracted attention. As described in JP-A-51-88544, a hot melt adhesive composed of a polyvinyl alcohol-based resin includes:
It is described that a resin composition containing a phosphate compound in a polyvinyl alcohol-based resin is stable against thermal oxidation, and that such a resin composition is effective as a hot melt adhesive.

[0004]

The protection of natural resources has been called for as an environmental problem, and recycling such as recycling of waste paper has been actively carried out. However, most of the hot-melt adhesives for bookbinding are water-insoluble thermoplastic resins mainly composed of ethylene-vinyl acetate copolymer. It remains as a shape and adheres to the surface of the recycled paper, causing problems such as spots and irregularities and adversely affecting the printability of the ink. Therefore, development of a water-soluble hot melt adhesive is desired.

In accordance with these requirements, a number of patents have been published which use partially saponified polyvinyl alcohol as a hot melt adhesive. For example, JP-A-58-1043
No. 8 describes a method for producing a polyvinyl alcohol-based hot melt adhesive. That is, the degree of polymerization 2
Polyvinyl acetate of not more than 00 is dissolved in an aliphatic alcohol having 1 to 4 carbon atoms, and alkali is added thereto to obtain a saponification degree of 30 to 80.
It is possible to remove the solvent and the saponification by-product by heating after saponifying to a mole%, obtain a melt of partially saponified polyvinyl alcohol, and mix the obtained melt of partially saponified polyvinyl alcohol with a flux. Has been described. However, polyvinyl alcohol has problems such as high melting temperature due to strong hydrogen bonding of hydroxyl groups in molecular structure, and oxidative decomposition during melting due to its close melting point and melting point. For this reason, in most cases, it is used as a hot melt adhesive obtained by blending a plasticizer and a tackifier with a low polymerization degree and partially saponified polyvinyl alcohol.
However, although these have good water dispersibility, they do not readily dissolve in water, so the problem that the adhesive dispersed in the waste paper recycling step is mixed in the recycled paper has not been solved. Although starch has been used as an adhesive in aqueous systems for many years, they have not been used as a substrate or primary functional adhesive material in hot melt adhesives. This is mainly due to the fact that the starch does not normally melt in the absence of water or solvent, and therefore it is difficult to formulate a starch-based hot melt composition.

Recently, however, hot melt adhesives based on medium or high DS (substituted) starch esters have been disclosed in 1992.
Co-pending application no.
07 / 995,493. 1992
European Patent Publication No. 511916 on Nov. 4, 2001 shows that hydrogenated denbun hydrolysates are useful for forming hot melt adhesives. However, medium or high DS (degree of substitution) starch esters no longer exhibit water solubility and do not become water-soluble hot melt adhesives. Further, if the substitution degree is increased to this level, the cost becomes extremely high, which is not practical.

It is known that gelatinized products obtained by adding a polyol such as glycerin or urea to starch have thermoplasticity.
It can be used as a hot melt adhesive,
arch-based hotmelts for a
dhesive applications ”Tap
pi Journal, Vol 77, No. 9, 193
-195. However, since these contain water-insoluble synthetic plastics, they exhibit hydrophobicity and are no different from hydrophobic hot melt adhesives as a whole. Further, in this case, the starch is generally formed by mixing and gelatinizing starch together with a plasticizer and then removing water. Further, since polyol and urea have a property of not readily releasing water, it takes a long time for drying. Further, although such a mixture shows thermoplasticity, the film shows flexibility even at room temperature and is very difficult to be crushed. Further, the starch to which a plasticizer is added by such an addition method is liable to cause a remarkable decrease in adhesive strength.

The usual hot melt adhesive is often used in a molten state, but may be used in a powder form. For example, there are a method of dispersing and fusing to a shoji paper and a method of heat fusing to a crosspiece with an iron, and a case of using for bonding a base fabric. The general shape of the hot melt adhesive is a tile shape or a bar shape. Therefore, in order to use it in powder form, it is necessary to pulverize it. However, hot melt adhesives are sensitive to heat and generate heat due to friction when trying to pulverize,
It was extremely difficult to melt and pulverize. In an attempt to solve this problem, pulverization has been attempted using a method that generates less heat, but the throughput per unit time has been extremely reduced and the cost has been increased. As a solution to these problems, there is a powdery heat-sensitive adhesive in which 10 to 100 parts by weight of a starch plasticizer is impregnated with respect to 100 parts by weight of a low-viscosity starch. However, this is a fine particle having a particle diameter of several μm to several tens μm, which is almost the same as that of starch. There was a problem that it was too detailed.

[0009]

The present inventors have conducted intensive studies on a water-soluble heat-sensitive adhesive which can solve the above-mentioned problems. The present inventors have found that by changing the degree of pulverization of the pregelatinized starch as a raw material, it can be used as a water-soluble hot-melt adhesive having various particle diameters and a high dissolution rate in water, and completed the present invention.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The pregelatinized starch which can be used in the present invention is a porous one capable of adsorbing a starch plasticizer.
Examples of the production method include a method of gelatinizing and drying using a single or double dryer and a method of extruding by heating using an extruder. In any method, the particle size can be freely adjusted by pulverizing a film-like or lump-like product. Raw starch for alpha-modified starch includes raw starch and various starch derivatives. Starch having a low viscosity upon heating and melting when used as an adhesive has good fluidity to an adherend and good adhesion. Low-viscosity starches include, but are not limited to, roasted dextrin, acid-treated starch, oxidized starch, and the like. The viscosity range is 20% to 10000 cp at 40% concentration and 30 ° C.
s is preferred. Above this level, the fluidity during heating and melting is poor and the adhesive strength is weak. Below this, the pregelatinized starch tends to agglomerate and cannot maintain the powder state.
Particularly preferred viscosities are 100% to 6% at a concentration of 40% at 30C.
000 cps. More preferably 300 to 300
0 cps.

The plasticizer is not particularly limited as long as it can gelatinize starch and can impart plasticity to the gelatinized product. For example, urea, thiourea, p-toluenesulfonamide, melamine and the like, and polyols can be used. Examples include polyhydric alcohols such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, hexamethylene glycol, glycerin, diglycerin, polyglycerin, trimethylolpropane, pentaerythritol, sorbitol, and mannitol. Among them, urea, polyethylene glycol, polypropylene glycol and the like are preferable. The amount of the plasticizer to be used is preferably from 10 to 100 parts by weight per 100 parts by weight of starch from the viewpoint that the starch can be sufficiently gelatinized and the gelatinized product can have sufficient fluidity. . Further, it is preferable to use 20 to 70 parts by weight of a plasticizer per 100 parts by weight of starch, from the viewpoint of sufficiently gelatinizing the starch and imparting appropriate fluidity to the gelatinized product.

The water-soluble hot-melt adhesive of the present invention can be used as an adhesive for bookbinding,
It can be used for adhesives for box making and packaging paper. Since the hot-melt adhesive of the present invention is water-soluble and has a high water dissolution rate, even if the waste paper using the hot-melt adhesive of the present invention is treated in a conventional recycling process, the conventional adhesive can be used. The disadvantage that it had, that is, the adhesive detached from the fiber part of the paper remains as a lump or a film, which adheres to the surface of the recycled paper, causing spots and irregularities,
Reproduction can be performed without causing a problem such as adversely affecting the printability of the ink. Further, it can be used as an adhesive for temporarily fixing fibers of sewing clothes, and after sewing, the adhesive can be removed by washing with water. Further, when used as a binder for a tobacco filter, it becomes a disintegrating tobacco filter, and when it is disposed of in the environment after smoking, it is easily disintegrated by rainwater or the like. Further, the particle size can be freely adjusted by adjusting the particle size of the pregelatinized starch as a raw material, or by pulverizing after preparing the hot melt adhesive.

[0013]

EXAMPLES 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 40 parts by weight of urea and 5 parts by weight of polyethylene glycol (molecular weight: 200) were added to 100 parts by weight of methanol.
Stir and dissolve at 60 ° C. Next, 100 parts by weight of pregelatinized starch (viscosity: 2100 cps (40%, 30 ° C.), water: 5.6%, particle size: 100 to 250 μm) are added, and after sufficient stirring, methanol is distilled off under reduced pressure to obtain a powdery hot melt. An adhesive was obtained. The particle size was almost the same as the original pregelatinized starch. Therefore, the adhesive could be accurately applied to the bonding surface without being diffused.

Example 2 A powdery hot-melt adhesive was obtained in the same manner as in Example 1 except that polyethylene glycol (molecular weight: 400) was used instead of polyethylene glycol (molecular weight: 200). Example 3 A powdery hot-melt adhesive was obtained in the same manner as in Example 1 except that polyethylene glycol (molecular weight: 200) was used instead of polyethylene glycol (molecular weight: 200). Example 4 A powdery hot-melt adhesive was obtained in the same manner as in Example 1 except that polyethylene glycol (molecular weight: 2000) was used instead of polyethylene glycol (molecular weight: 200). Example 5 A powdery hot-melt adhesive was obtained in the same manner as in Example 1 except that polypropylene glycol (molecular weight: 1000) was used instead of polyethylene glycol (molecular weight: 200). Examples 6 to 8 Powdered hot-melt adhesives were obtained in the same manner as in Example 1 except that various pregelatinized starches having different viscosities were used.

Comparative Example 1 400 parts by weight of urea and 100 parts by weight of glycerin were added to 700 parts by weight of methanol, and the mixture was stirred and dissolved at 40 to 60 ° C.
Next, dextrin (viscosity 600 cps (40%, 30%)
C.), water 2.1%), 1000 parts by weight, and after sufficient stirring, methanol was distilled off under reduced pressure to obtain a powdery adhesive. This product had a particle diameter of 60 μm or less, and was not able to be spread accurately when the adhesive was applied to the bonding surface by a machine and accurately placed on a target portion. Comparative Example 2 400 parts by weight of urea and 100 parts by weight of glycerin were added to 700 parts by weight of methanol, and the mixture was stirred and dissolved at 40 to 60 ° C.
Next, pregelatinized starch (viscosity 20 cps (40%, 30%)
C.), water 4.3%), and 1000 parts by weight. After sufficiently stirring, methanol was distilled off under reduced pressure to obtain a powdery hot-melt adhesive.

Example 9 The hot-melt adhesives obtained in Examples 1 to 8 and Comparative Examples 1 and 2 were spread on a cotton cloth, uniformly dispersed, and continuously indirectly heated from above to adhere. After standing to cool, the cotton cloth was put on a plywood and heated and 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. Further, the adhered cotton cloth and the plywood were placed in water at 25 ° C. and slowly stirred to observe the peeling condition. The results are shown in Table 1.

[0017]

[Table 1] (Measurement method of peel strength) Bonded cotton cloth at 20 ° C, 65R
After being left at H% for 24 hours, it was cut into a width of 2.5 cm, and the peel strength was determined by pulling (pulling speed: 100 mm / min) by an autograph.

[0018]

As described above, the hot melt adhesive of the present invention can freely select the particle size, has a large adhesive strength, is water-soluble, and has a high water dissolution rate. For example, for waste paper recycling that requires easy peelability and water solubility of the adherend by water, suitable as an adhesive for temporary fixing of fibers, or easily disintegrated by rainwater when discarded in the environment after smoking, It is extremely useful as an adhesive for a disintegrating tobacco filter.

Claims (3)

[Claims] 1. A powdery heat-sensitive adhesive characterized in that a starch plasticizer is adsorbed on pregelatinized starch. 2. The aqueous solution of said pregelatinized starch is 40%,
The powdery heat-sensitive adhesive according to claim 1, which has a viscosity of 20 to 10000 cps at 0 ° C. 3. The starch plasticizer is urea, polyethylene glycol, polypropylene glycol, ethylene glycol,
The heat-sensitive adhesive powder according to claim 1, which is propylene glycol or glycerin.