JPS603351B2 - Hot-melt water-soluble adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a hot-melt water-soluble adhesive, particularly a modified polypinyl alcohol (hereinafter referred to as modified PVA) which is a saponified product of a copolymer of isoprobenyl acetate and vinyl acetate. It relates to a heat-melting and water-soluble adhesive.

Advantages of hot-melt adhesives include the fact that they are solvent-free, have low toxicity, provide a good work environment, and are non-drying, requiring short set times and high work efficiency. It is used as an adhesive for making boxes, attaching labels, etc.

On the other hand, in view of the shortage of wood and pulp and the effective use of resources, there is a demand for the collection and reuse of waste paper.

However, since conventional hot-melt adhesives are insoluble in water, non-welding adhesives remain in the waste paper as small lumps during the waste paper recycling process, and may adhere to rolls during paper making or cause pinholes. Waste paper using conventional hot-melt adhesives is not recovered because it causes paper breakage and adhesives with poor thermal stability decompose and become colored after repeated reuse.
A water-soluble resin such as polypynyl alcohol (hereinafter referred to as PVA) may be used as a heat-melting adhesive that can be used to recover waste paper, and may be dissolved and removed in water during the waste paper recycling process. However, PVA melts under heat, and no matter how high the temperature is tried, the melt viscosity is extremely high and decomposition occurs, making it impossible to coat the surface to be adhered. In order to eliminate this drawback, if it is applied in the form of an aqueous solution, coating becomes possible, but drying is required and productivity is significantly lower than with hot-melt adhesives.

There has also been a proposal to use PVA with a low degree of polymerization as a hot-melt adhesive (Tokusei No. 77632/1987), but even PVA with a degree of polymerization of 500 or less and a degree of saponification of 50-90 mol% still has a high melt viscosity. It cannot be used as a hot-melt adhesive unless a large amount of a specific plasticizer is used.

The present invention solves these drawbacks of PVA, and uses modified PVA which is a saponified copolymer containing vinyl acetate and isoprobenyl acetate with an average degree of polymerization of 1000 or less.
This is a water-soluble hot-melt adhesive that has the characteristics of a low melting point, low melt viscosity, and good water-removal properties.

Modified PVA, which is the main component of the present invention, is a saponified copolymer of isoprobenyl acetate and vinyl acetate, and the amount of isoprobenyl acetate contained in the polymer is 1 mol% relative to vinyl acetate. Preferably it is 5 to 30 mol%.

If it is less than 1 mol %, the modified PVA obtained by saponification has only slightly better heat meltability than conventional PVA, which is not preferable.

Further, the average degree of polymerization of the modified PVA needs to be 1000 or less, since the lower the melt viscosity is.

If the degree of polymerization is less than 1000, the melting temperature and melt viscosity are too high, and even if a large amount of plasticizer is added, a hot melt adhesive cannot be obtained. Next, partial saponification with a degree of saponification of 50 mol % or more or complete saponification may be used, but partial saponification is preferable when the degree of polymerization is 500 or more. If the degree of saponification is 50 mol% or less, the heat meltability is good but the water solubility is poor. These copolymers may be produced by any method such as solution polymerization, suspension polymerization, or bulk polymerization of the monomers, but especially in the case of solution polymerization, the solvent is not particularly limited, but a solution in methanol is used. Polymerization is most preferred from post-processes such as saponification.

Saponification is carried out by the usual methods of saponifying PVA, preferably in methanol solution. This is because isoprobenyl acetate has an extremely large chain transfer constant compared to vinyl acetate, so there is no need to use other chain transfer agents during solution polymerization in methanol, which has a relatively low chain transfer constant. This is because even if the /methanol ratio is high, products with a low degree of polymerization can be easily obtained and productivity is excellent. Normally, in order to produce a low polymerization degree product of PVA with a polymerization degree of 500 or less, a method is used in which vinyl acetate is polymerized in methanol solution and a chain transfer agent such as aldehydes, halogenated hydrocarbons, or mercaptans is added and saponified. Alternatively, there is a method in which vinyl acetate is polymerized in a chain transfer agent, and then the chain transfer agent is expelled and the saponification is carried out by replacing it with a methanol solution. However, the former method causes discoloration to yellow or brown during saponification and severe decomposition during hot melting. occurs concurrently.

The same is true in the latter case; furthermore, expulsion of the solvent requires a large amount of time and heat, and a significant increase in viscosity due to expulsion of the solvent requires equipment with a large amount of power, resulting in a decrease in productivity and This causes a rise in production costs. On the other hand, in the case of producing the modified PVA of the present invention, it is not necessary to use a chain transfer agent as described above in a methanol solution, and a product with good thermal stability can be obtained, and there is no need to replace the solvent. Although the hot-melt adhesive of the present invention can be made of modified PVA alone, it is preferable to add a plasticizer or a fluxing agent.

The combined use of a plasticizer has the effect of further lowering the melting temperature, and its combined use is particularly desirable in the case of modified PVA with a degree of polymerization of 500 or more and a degree of saponification of 90 mol% or more. Examples of plasticizers include glycerin, . Ethylene glycol, diethylene glycol, triethylene glycol, trimethy.
Commonly used substances include propane polyoxyethylene glycol, sorbitol, mannitol, and the like, and non-volatile substances are selected depending on the melting temperature. The amount of plasticizer is 10 to 10 parts by weight based on the modified PVA. Fluxing agents include substances used in ordinary hot-melt adhesives, such as polyethylene, polypropylene, polyvinyl acetate, vinyl acetate copolymers such as ethylene-vinyl acetate copolymers, rosin and rosin derivatives, and petroleum. resin, styrene-butadiene rubber, etc.

The combined use of rattan has the effect of improving adhesion. The amount of fluxing agent must be 10 parts by weight or less based on the modified PVA, and if it is less than 10 parts by weight, it will not be possible to obtain a water-soluble adhesive.

Note that all parts described in the specification are based on weight. below,
The invention will be explained by examples.

Example 1 9 parts of pinyl acetate, 20 parts of isoprobenyl acetate,
Methanol 9 melon Azobisisobutyronitrile 0.8
After the polymerization, the vinyl acetate monomer resulting from the polymerization was removed by a conventional method.

The isoprobenyl acetate content in this copolymer is 15
It was mol%. Next, the solution was adjusted to 35% methanol and saponified with 1'100 molar equivalent of caustic soda at 35 mol% to obtain modified PVA with a degree of polymerization of 612 and a degree of saponification of 90.4 mol%. The melting point of this modified PVA was 98°C.
Next, 15 parts of glycerin was blended with the modified PVAIO base material to prepare a hot-melt adhesive.

The melt viscosity of this composition (measured with a Shimadzu Koka flow tester) was 180 qo and 700 pS. This composition also dissolves in water at room temperature. Next, 400 evenings/unit area
After coating one side of that paperboard with the composition melted at 180 qo (coating amount: 60 q/end), another sheet of paper was placed on top of the paperboard, and the paper board was further passed between press rolls heated to 180 qC. Pasted together.

The adhesive strength of this paperboard was measured using an Autograph manufactured by Shimadzu Corporation, and the paper broke at room temperature, and the strength at this time was 670 μm/skin.

Example 2 Isoprobenyl acetate 10 was prepared in the same manner as in Example 1.
Mol% of isoprobenyl acetate-vinyl acetate copolymer was obtained and saponified by a conventional method to give a degree of polymerization of 460 and a degree of saponification of 77.
．． 0 mol % of modified M'A was obtained.

The melting point of this modified PVA was 105°C, and the simple melt viscosity was 1000 ps at 180°C. Next, an adhesive composition having the following composition was prepared.

Modified PVA of the Invention IO Ikarito Rosin Modified Product 4 Shogun Polyethylene Glycol #300 25 parts The melting point of this composition was 90oo, and the melt viscosity was 500 ps at 180°C. When the adhesive strength was measured under the same conditions as in Example 1, the paper was torn.

Example 3 In a similar manner to Example 1, isoprobenyl acetate 2
Modified PV with a degree of polymerization of 0 mol%, a degree of polymerization of 290, and a degree of saponification of 83 mol%
I got an A.

This modified PVA had a melting point of 90° C., a melt viscosity of 18 pS, and a sinusoidal ratio pS. Similarly, when the adhesive strength was measured, the paper was found to be torn. Comparative Example In Example 2, modified PVA was replaced with a polymerization degree of 420 and a saponification degree of approximately . 3 mol% normal PV
An adhesive composition similar to Example 2 was prepared using A.

Claims (1)

[Claims] 1 Degree of polymerization 100 obtained by saponifying 50 mol% or more of a vinyl acetate copolymer containing 1 mol% or more of isopropenyl acetate
A hot-melt water-soluble adhesive mainly composed of modified polyvinyl alcohol with a molecular weight of 0 or less.