JPS6056176B2 - Method for modifying polyvinyl alcohol - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the modification of polyvinyl alcohol (hereinafter abbreviated as PVA) powder.

PVA is a typical water-soluble polymer, and its uses are wide-ranging, and proposals have been made for the development of various uses. One of these is adhesives for manufacturing corrugated cardboard.
This uses gelatinized starch as the dispersion medium (carrier part),
In so-called stain-hole adhesives in which starch powder (main part) is dispersed, part of the starch powder is replaced with PVA powder for the purpose of increasing adhesive strength, improving productivity, and imparting water resistance. There is something to replace it with. When the main part of the adhesive powder dispersed in the medium comes into contact with the core and liner heated on a corrugating machine, it rapidly becomes gelatinous and exhibits a strong adhesive force to the paper surface. However, the performance required for the PVA powder in the main part is that it is insoluble in hot water at room temperature to about 50°C, and that boric acid or The adhesive does not substantially react with borax and gel, and on the other hand, when bonding cardboard, it dissolves rapidly at temperatures above 100°C, and even if either of these properties is lacking, the adhesive remains in a stable slurry state. becomes difficult to obtain.

Starch powder has almost no problems like the ones mentioned above, but PVA powder is only partially dissolved in water, causing a significant increase in viscosity, and PVA powder tends to cause a crosslinking reaction with boric acid and borax, making it difficult to form a slurry. The use of PVA powder in stain-hole adhesives requires strict performance because the risk of loss of stability is very high.

As one such solution, a method has been proposed in which PVA powder is dispersed in methyl acetate or methanol and heat treated to reduce the solubility of the powder in water or the reactivity with boric acid and borax.

However, such heat treatment requires a temperature of at least 70°C, but in the above method, methyl acetate and methanol are low boiling point solvents, so they must be pressurized using an autoclave etc. must be processed by the system.

From the viewpoint of industrial implementation, pressurized system operation requires complicated process control and cannot be said to be an advantageous method. However, the present inventors have conducted extensive research into an industrially advantageous method for heat-treating PVA powder, and have found that quenching in a medium with a boiling point of 70°C or higher, which is a mixture of polyhydric alcohol or a non-solvent for PVA. By dispersing PVA powder with a degree of oxidation of 95 mol% or higher and heat-treating the powder at a temperature of 70°C or higher, the powder shows almost no solubility in hot water between room temperature and about 50°C, and is resistant to boric acid and borax. The present inventors have discovered that PVA powder, which hardly undergoes crosslinking reaction, can be produced under normal pressure, which is a remarkable effect, and has led to the completion of the present invention.

As mentioned above, the most important feature of the present invention is that the heat treatment is performed in a specific medium.

Since the boiling point of such a medium is 70°C or higher, it has the advantage of being able to be heat-treated at normal pressure, and the Stinhole adhesive that uses PVA powder modified by such heat treatment has a stable slurry. A very unique effect can be obtained. If the purpose is simply heat treatment in a normal pressure system, it is sufficient to use a medium with a boiling point of 70°C or higher, but other than the media specified in this application, water at room temperature to 50°C cannot be used. On the other hand, even if an insoluble PVA powder is obtained, a powder with reduced reactivity with boric acid and borax cannot be obtained, and it is not practical for use in adhesives.

Although it is not clear why the effects of the present application are obtained, the polyhydric alcohol used as a medium causes the redistribution of PVA crystals during heat treatment. It is thought that it exerts a specific action different from that of other media and contributes to a decrease in reactivity with boric acid and borax. In this application, polyhydric alcohols alone or in mixtures with PVA and non-solvents are used. Polyhydric alcohol is essentially a solvent for PVA, and if a polyhydric alcohol alone is subjected to heat treatment at too high a temperature, the PVA powder may dissolve during the treatment. Therefore, when processing at high temperatures, a PVA non-solvent is mixed to prevent the powder from dissolving. However, when using a non-solvent with a relatively low boiling point, if too large a quantity is used, it will be impossible to process in a normal pressure system.
Care must be taken to ensure that the boiling point of the mixed medium does not fall below 700C. Examples of the polyhydric alcohol used in the present invention include alkylene glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and butylene glycol, and glycerin.

Furthermore, as a non-solvent for PVA, any solvent can be used as long as it has the property of hardly dissolving PVA powder, but among such solvents, solvents that have good compatibility with polyhydric alcohols are usually used. Preferably used.

The above solvents include methanol, ethanol, n-propanol, IsO-propanol, n-butanol, IsO-propanol,
Examples include O-butanol, amyl alcohol, methyl acetate, ethyl acetate, acetone, ethylene glycol dimethyl ether, toluene, methylene chloride, etc., and depending on the type of polyhydric alcohol, one that is compatible with it may be appropriately selected. When polyhydric alcohol (4) and PVA non-solvent (B) are used together, the boiling point is 70'C.
If it can be maintained above, the mixing ratio cannot be unconditionally defined depending on the type of solvent, but it can be calculated by weight (CA)/
(B)=90/10~10/9 or preferably 80/20~
A range of 20/80 is suitable.

Among such mixed media, a combination of polyhydric alcohol and n-butanol and a mixture weight ratio of polyhydric alcohol/n-butanol are preferred.
The most effective heat treatment can be carried out when n-butanol of 80/20 to 20/80 is used.
When performing the heat treatment, the PVA powder may be dispersed in a medium and heated while stirring, and the heat treatment can be performed under normal pressure, making the process simple and practical.

PVA powder having a saponification degree of 95 mol% or more, preferably 97 to 100 mol%, is used. 9
If the PVA content is 5 mol% or less, no effect of heat treatment is observed.

A saponification degree of 99 mol% or more is suitable for use in corrugated board. Further, those having a particle size of about 200 mesh or less are usually used. The solid content concentration of the PVA powder to be dispersed is selected from a range of approximately 10 to 30% by weight. The heating temperature must be 70°C or higher, preferably 70-1
A temperature of about 60°C is selected. Moreover, the appropriate heating time is about 3 powders to 2 hours. After the heat treatment, the PVA powder is separated from the mixed solvent, and the medium adhering to the powder is appropriately washed with methyl acetate, methanol, etc., and dried to obtain the desired product.

To prepare an adhesive for corrugated board using the PVA powder obtained in this way, starch powder is mixed with an aqueous medium prepared by dissolving boric acid or borax in water or an aqueous solution of a water-soluble polymer, and an alkali such as sodium hydroxide. Disperse VA powder. Boric acid and borax are used to increase initial adhesion, and alkali is used to lower the gelatinization temperature of starch powder. The mixing weight ratio of PVA powder and starch powder is PVA/
Starch = 1/40 to 1/1, preferably 1/20 to 7/20
selected from the range. The amount of boric acid and borax used is 3 to 15% by weight of boric acid and 0.1 to 15% by weight of borax based on the starch powder.
It is about 5% by weight. Also, the alkali is 1 to starch powder.
~5% by weight is used. These auxiliaries can be added in advance to the aqueous medium in which the starch and PVA powder are to be dispersed, or added to an already prepared slurry of the powder, or mixed together with the powder and the auxiliary agent. This can be carried out by any method such as uniformly mixing the two in solid form in advance, or spraying a highly concentrated solution of the latter into the former and dispersing the mixture in an aqueous medium. Said PVA
Water or an aqueous solution of a water-soluble polymer substance can be used as the medium in which the powder and starch powder are to be dispersed. PVA. ．． #
It is sufficient that it has a certain degree of miscibility with the powder when it is dissolved, and that the stability of the solution is not significantly impaired by the above-mentioned compounds at room temperature and at the concentration used.
Examples of these include starch, dextrin, alkylcelluloses, carboxyalkylcelluloses, etc., but PVA itself can also be used if it is used at a relatively low concentration or if a variety that is as difficult to gel as possible is selected.

It is desirable to use these in amounts such that the viscosity of the slurry liquid at room temperature is about 300 to 100 μp.

If necessary, the dispersion may further contain fillers such as clay, calcium carbonate, diatomaceous earth, synthetic resin emulsions, pH regulators such as alkali carbonates, alkali phosphates, and the like. The solid content concentration of the slurry liquid is preferably about 15 to 3% by weight in consideration of workability and the like. When bonding the core and the liner using such an adhesive, it is appropriate to adjust the amount of adhesive supplied to the adhesive portion of the core so that the solid weight is usually about 3 to 6 f/d. It is. The core supplied with adhesive is polymerized with the mating liner to be bonded, and then heated with a heating roll or the like, or preferably simultaneously pressurized to complete the bonding, but the heating and pressure conditions at that time are normal. The temperature of the roll is selected from the range of 100 to 200°C and the pressure of about 2 to 7 atm. The adhesive can be suitably applied particularly when manufacturing corrugated cardboard, but is not limited to such cases, and can be effectively applied in a wide range of general cases where cardboard is bonded under heat.

Although the use of the PVA powder obtained by the present invention has mainly been explained for use in stain-hole type adhesives, it is limited to this application as long as the characteristics of the PVA obtained by the method of the present invention as described above can be effectively utilized. Not a thing,
For example, sizing agents for internal addition during paper making, binders for nonwoven fabrics for molded products such as films, fibers, and sheets by melt molding, hot melt adhesives, emulsifiers and suspensions for polymerizing vinyl monomers such as vinyl acetate and vinyl chloride. It can be used for various purposes such as agents.

Next, the method of the present invention will be explained in more detail by giving examples.

Example 1 n-butanol 70y1 ethylene glycol 30
PVA powder 15V with an average particle size of 200 mesh and a saponification degree of 99.5 mol% and a polymerization degree of 110 in a mixed medium consisting of
was dispersed, and heat treatment was performed at a temperature of 124° C. for 1 hour while stirring.

After the treatment, the PVA powder was separated, the surface of the powder was thoroughly washed with methanol, and the powder was vacuum dried at 8 CfC. The resulting PVA powder was tested for dissolution initiation temperature in cold water and reactivity with borax in the following manner.

1.Measurement method of melting start temperature A mixture of 340y of water and PVA6Of is charged into an aminograph measuring device, and the temperature is raised from 20°C at a rate of 1.5°C per minute until the temperature at which the viscosity change rapidly increases is dissolved. Let it be the starting temperature.

2. Testing method for reactivity with borax A sample mixture prepared by adding 0.3' of borax is subjected to the same procedure as above, and the temperature at which the viscosity change rapidly increases is measured.

As a result, the melting start temperature was 65.4°C, and the reactivity with borax was 60.1°C.

Next, the obtained PVA powder was used to bond cardboard as shown below.

Add 0.96k9 of starch, 0.17kg of sodium hydroxide, and 0.17k9 of borax to 10k9 of water to gelatinize the starch to form a carrier part, and mix and disperse the above-mentioned PVA powder 0.36k9 and starch powder 5k9 in 14k9 of water. The main part was prepared.

These were mixed to make an adhesive. A-flute SCP core with density 130 f/d and density 240 for double-sided corrugated board
The f/a C liner was adhered using a corrugating machine.

The temperature of the pressure roll was 150C, the pressure was 5 atm, and the amount of adhesive applied was 6 f/d. Double-sided adhesive strength measured with JISZO4O2 is 24kg/C7l! It was hot. Example 2~
8 An experiment was conducted according to Example 1 using the media shown in Table 1 instead of the medium in Example 1.

Claims (1)

[Claims] 1. Polyvinyl alcohol powder with a saponification degree of 95 mol% or more is dispersed in a medium with a boiling point of 70°C or higher, which is prepared by mixing a polyhydric alcohol or a non-solvent of polyvinyl alcohol, and A method for modifying polyvinyl alcohol, the method comprising heating the powder at a certain temperature. 2. The reforming method according to claim 1, wherein the medium is a mixed medium of polyhydric alcohol and n-butanol.