JPS5819681B2 - Polyvinyl alcohol - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a molded article, which is characterized by melt molding in a substantially anhydrous state using polyvinyl alcohol having good thermoplasticity and water resistance as a raw material.

Conventionally, as a method for manufacturing films or other molded products of polyvinyl alcohol (hereinafter abbreviated as PVA), a method has been used in which a concentrated aqueous solution of TVA is extruded in a molten state using a screw extruder. A drying process is essential to remove water from the molded product after molding.

As a result, the extrusion capacity and drying capacity are significantly reduced, limiting the production capacity and increasing the scale of the equipment.

Moreover, the removal of moisture causes an undesirable phenomenon in which the molded product shrinks.

On the other hand, in order to solve the above drawbacks, there is a method of adding only a plasticizer in a substantially anhydrous state, but there are restrictions on the amount of plasticizer added, and if a large amount is added, the melt viscosity during extrusion will decrease. However, the plasticizer oozes out and evaporates from the molded product, which is undesirable.

If the amount of plasticizer is at a level that does not cause oozing or volatilization, the melt viscosity during extrusion will not decrease that much and extrudability will be poor. On the other hand, if the extrusion temperature is raised to lower the melt viscosity, it will approach the decomposition temperature of PVA and the molded product will deteriorate. It comes to contain a large amount of colored, ungelled particles, and decomposition products, which significantly impairs transparency and makes it impractical.

Moreover, the molded product becomes inflexible and brittle.

In order to solve these drawbacks, the present inventors have conducted intensive research on the development of modified PVA with further improved thermoplasticity, and have found that (c) an alkyl vinyl ether represented by CH2=CHOR3 and (d) OH2= One or more aliphatic vinyl esters represented by OHOOOR4 (R3 and R4 are alkyl groups having 5 to 15 carbon atoms) and further (a) general formula CH2
=C(R1)OCOCH3(b) General formula OR2-OHR
One or more of the monomers (a) and (b) represented by 20000H3 (Rt, R2 is an alkyl group having 1 to 3 carbon atoms) are copolymerized with vinyl acetate, and the copolymer is saponified. modified polyvinyl alcohol (hereinafter referred to as modified PVA)
The present invention was based on the discovery that this material has good thermoplasticity and water resistance.

In the present invention, the above-mentioned modified PVA is replaced with ordinary PVA.
It has much better water resistance and flexibility than VA, and its softening point is very low, so it can be melt-extruded at low temperatures without adding a plasticizer or in the presence of a plasticizer. Films, hoses, and other molded products can be manufactured with extremely high efficiency.

It is generally known that modified PVA having a long chain saturated fatty acid group or a long chain alkyl group in its side chain is internally plasticized to some extent and has a lower softening point.

For example, Japanese Patent Publication No. 46-42015, British Patent No. 1, 12
No. 7,638 states that modified PVA having a long chain saturated branched fatty acid group or the longest alkyl group in the side chain has good thermoplasticity and water resistance.

However, the degree of decrease in the softening point of the modified PVA is not so large, and the heating temperature for extrusion molding is 200°C.
Must be above ℃.

At such temperatures, the modified PVA undergoes thermal decomposition like normal PVA, so the addition of heat stabilizers, plasticizers, etc. is essential, which limits its use, such as making it difficult to use for food packaging.

Further, if a large amount of long-chain saturated branched fatty acid groups or long-chain alkyl groups are introduced, a further reduction in the softening point can be expected, but in that case, the organic solvent resistance and gas shielding properties, which are characteristics of PVA, will be significantly impaired. However, this method has the disadvantage that a large amount of unreacted monomers are used for production, and recovery costs are high.

The present inventors have studied a method for producing internally plasticized modified polyvinylalconyl suitable for melt molding, and have used vinyl acetate and one or more monomers selected from monomers (c) and (d) having a long-chain alkyl group. , as well as the general t(a)CH2=C(
R1) OCOCH3 or (b) CH2=CH(R2)O
COCH3 (R1 and R2 are alkyl groups having 1 to 3 carbon atoms)
It was confirmed that the modified PVA obtained by saponifying a multi-component copolymer consisting of the monomers shown above has excellent internal plasticity and water resistance. It has been found that PVA has much more internal plasticity than modified PVA.

Monomers with long chain alkyl groups, i.e. 5 to 15 carbon atoms
Examples of the alkyl vinyl ether having an alkyl group R3 represented by CH2=CHOR3 include those in which R3 is a group such as octyl or lauryl.

Furthermore, it has an alkyl group R4 having 5 to 15 carbon atoms, and CH2
Examples of the fatty acid vinyl ester represented by =CHOCOR4 include those in which the fatty acid portion constituting the ester is valeric acid, caproic acid, caprylic acid, lauric acid, persatic acid, and the like.

Some of the drawings illustrate the relationship between the amount (mol %) of the modified moiety and the melting temperature of the products of the present invention, but for comparison, those of modified PVA having a long-chain alkyl group are also shown at the same time.

In the figure, the curve ■ is the product of the present invention, and the curve ■ is the comparative product.

The melting temperature was measured by differential thermal analysis, and the peak temperature of the endothermic peak corresponding to melting was determined as the melting temperature.

Looking at this figure, it can be seen that the product of the present invention has a lower melting temperature and superior thermoplasticity than the comparative product at the same rate of modification.

In the present invention, the general formula CH2=C(R1)OCOCH3 or CH2=C copolymerized with vinyl acetate
The amount of monomer of H(R2)OCOCH3 is 1 to 30 mol%
, preferably in the range of 5 to 20 mol%.

If it is less than 1 mol %, the melting temperature is almost different from that of ordinary PVA, making melt molding difficult.

On the other hand, if it exceeds 30 mol %, the melting temperature will be considerably lowered, but the degree of polymerization will be extremely low, and when a molded article is produced, the mechanical strength will be significantly reduced, making it impractical.

In addition, while the monomer contributes to the internal plasticization of PVA,
Since it has the disadvantage of impairing water resistance, it is not preferable to introduce it in a larger amount than necessary.

Next, the amount of monomer having a long chain alkyl group is 0.1 to 1
It is in the range of 0 mol%.

The monomer is introduced into the modified PVA of the present invention for the purpose of improving water resistance, and the amount introduced is determined depending on the degree of water resistance required.

In addition, the monomer CH2 introduced for the expression of internal plasticity
=C(R1)OCOCH3 or CH2=CH(R2
) It is also defined according to the amount of OCOCH3.

Therefore, although the amount of the monomer having a long-chain alkyl group to be introduced cannot be uniquely determined, it should be 0.1 mol % or more in order to achieve water resistance.

Also, the greater the amount introduced, the better the water resistance will be, but if too much is introduced, the degree of polymerization will drop significantly, reducing the strength of the molded product, and there will be a large amount of unreacted material, resulting in a large amount of cost for recovery. Therefore, the appropriate amount to be introduced is up to 10 mol%.

Further, the long chain alkyl group has 5 to 15 carbon atoms.

If the number of carbon atoms is 4 or less, the water resistance is insufficiently expressed, so the modified PVA loses water resistance.

The vinyl acetate copolymer used in the present invention can be saponified by a conventional method.

In this case, in addition to vinyl acetate, 0H2=0(R1)OCO
The ester moiety of CH3 or 0H2=OH(R2)OCOCH3 is also saponified.

The acetic acid groups may be eliminated by complete saponification, or some may be left by partial saponification, but from the viewpoint of water resistance, it is preferable to use less than 15 mol% of the total acetic acid groups, and when water resistance is strongly required. The content is preferably 3 mol% or less.

Furthermore, the modified PVA can be heat-treated as a molded article if necessary, and in that case, the method used for ordinary PVA can be adopted.

The modified PVA of the present invention can be melt-extruded at a temperature below the decomposition point of PVA without adding a plasticizer; By using the plasticizer used in polyvinyl alcohol, melt extrusion becomes easier and molding can be performed at lower temperatures.

Therefore, the combination of plasticizers is effective for applications where the use of PVA plasticizers as described above does not cause any problems.

The present invention will be explained below with reference to Examples.

Example 1 Vinyl acetate 109.5 parts, isopropenyl acetate-4
12.4 parts of lauryl vinyl ether, 20.0 parts of methanol, and 0.2 parts of azobisisobutyronitrile were added and polymerized at 60°C for 7 hours, then 55 parts of methanol
．． 6 parts of azobisisobutyronitrile and 0.4 parts of azobisisobutyronitrile were added, and the polymerization was further continued for 3 hours.

Unreacted vinyl acetate was expelled with methanol vapor, and caustic soda was added to the resulting paste at a molar ratio of 0.05.3
Saponified at 0°C and washed with methanol, 9.5 mol% of isopropenyl 1 alcohol unit, lauryl vinyl 1
A modified polyvinyl alcohol containing 0.92 mol % of vinyl and 0.75 mol % of residual acetic acid groups was obtained.

As a result of differential thermal analysis, this modified polyvinyl alcohol
It was found that it had an absorption peak due to melting at 81°C, which was 82°C lower than the 240°C of normal polyvinyl alcohol.

This modified PVA was heated to 1.80°C in an essentially anhydrous state with a water content of 1.0% or less, with a screw diameter of 30ml and a length of 600rrL/m (L/D=20) (7) in a test melt extruder. Supply, width 200 m1 FIL, slit width Q, 5. A film with a thickness of 50 μm was produced using a T-die of m/m.

This film was colorless and transparent, beautiful with very little fisheye, and flexible.

Further, this film was insoluble in water at room temperature and soluble in hot water at 801°C.

Example 2 In order to produce modified PVA with different amounts of modification, 2.5 parts of lauryl vinyl ether, 20.0 parts of methanol, and 0.2 to 0.3 parts of azobisisobutyronitrile were used. Five types of modified PVA with different amounts of modification were obtained in the same manner as in Example 1 by varying the ratio of vinyl acetate/isopropenyl acetate.

The amounts of modification (sum of impropenyl alcohol units and lauryl vinyl ether units) of these five types of modified PvA are 4.4, 9.2, 14.9, 19.0, and 25.9 mol%, respectively, and the residual acetic acid groups are respectively 0.71, 0.75°0.
78%, 0.82%, and 0.85% by mole.

The melting temperatures of these five types of modified PVA were investigated by absorption peaks by differential thermal analysis and were found to be 168 and 158°1, respectively.
The results are shown in curve I of the figure at 30.89.55°C.

Comparative Example 1 99.5 parts of vinyl acetate, 25 parts of lauryl vinyl ether.
Add 0 parts of methanol, 20.0 parts of methanol, and 0.2 parts of azobisisobutyronitrile, polymerize at 60°C for 10 hours, then add 55.6 parts of methanol and 0.4 parts of azobisisobutyronitrile. Then, polymerization was further carried out for 5 hours.

Caustic soda with a molar ratio of 0.05 was added to the paste obtained by expelling unreacted vinyl acetate, and the mixture was saponified at 30°C and washed with methanol to obtain lauryl vinyl ether 4.4
Modified privinyl alcohol with a mol% of residual acetic acid groups of 1.78 mol% was obtained.

As a result of differential thermal analysis, this modified polyvinyl alcohol
It was found that it had an absorption peak due to melting at 8°C, which was 32°C lower than the 240°C of ordinary polyvinyl alcohol.

This modified PVA was heated to 220° C. in a substantially anhydrous state with a moisture content of 1.0% or less using the same melt extruder and T-die as in Example 1 to produce a film with a thickness of about 50 μm.

This film had many yellow colored fish eyes, lacked flexibility, and was hard and brittle.

Comparative Example 2 In order to produce lauryl vinyl ether-modified PVA with different amounts of modification, modified PVA with different amounts of modification were prepared by varying the ratio of vinyl acetate and lauryl vinyl ether in Comparative Example 1.
Four types were obtained.

The amounts of lauryl vinyl ether in these modified PVAs were 4.4, 8.5, 12.7, and 20.5 mol%, and the residual acetate groups were 0.87, 0.90, and 1.65, respectively.
, 19.7 mol%.

According to differential thermal analysis, the melting temperatures of these four types of modified PVA were 208, 185, 160° and 129°C.

The results are shown in the curve ■ in the figure.

Comparing this curve (2) with the curve (2) of the product of the present invention, it can be seen that the product of the present invention has far superior thermoplasticity.

Example 3 Vinyl acetate 105.8 parts, isopropenyl acetate) 1
Modified polyvinyl alcohol was prepared in the same manner as in Example 1, except that the amount was changed to 2.4 parts and 6.2 parts of lauryl vinyl ether.

This modified PVA has isopropenyl alcohol units 8.
7 mol%, lauryl vinyl ether 2.1 mol%, and residual acetic acid group 0.82 mol%.

As a result of differential thermal analysis, this modified polyvinyl alcohol
It had an absorption peak at 8°C, which was 72°C lower than the 240°C of normal polyvinylfluorol.

Next, a film was produced from this modified PVA in the same manner as in Example 1, and a beautiful film was obtained that was colorless and transparent and had very few fish eyes.

Furthermore, this film was insoluble in water at room temperature and only swelled in boiling water.

Example 4 In Example 3, 12.4 parts of allyl acetate was used instead of isopropenyl acetate, 5.2 mol% of allyl alcohol units, and 1.8 parts of lauryl vinyl ether.
Modified polyvinyl alcohol containing 0.85 mol% of residual acetic acid groups was obtained.

The melting temperature of this modified polyvinyl alcohol was 172°C.

Example 5 In Example 3, 15.1 parts of vinyl persate was used instead of lauryl vinyl ate/l/l, and 8.5 parts of impropenyl alcohol units were used. A modified polyvinyl alcohol containing Q mol %, vinyl hassate 5.5 mol %, and residual acetic acid groups 1.53 mol % was obtained.

The melting temperature of this modified PVA was 163°C.

[Brief explanation of the drawing]

The figure shows the relationship between the amount of modification (mol %) and the melting temperature of the modified polyvinyl alcohol of the present invention.

Claims (1)

[Claims] 1(a) General formula (b) One or more monomers of (a) and (b) represented by the general formula (R2 = alkyl group having 1 to 3 carbon atoms) 1 to 30 mol% and (c) an alkyl vinyl ether represented by the general formula % formula % (3 (R3 - alkyl group having 5 to 15 carbon atoms)) and (d) general formula % formula % (R4 - alkyl group having 5 to 15 carbon atoms) 15 alkyl group) of fatty acid vinyl ester represented by (C), and (d)
Modified polyvinyl 7 alcohol obtained by saponifying a vinyl acetate copolymer obtained by copolymerizing 0.1 to 10 mol% of one or more selected from the following in a powder or pellet form in a substantially anhydrous state A method for producing polyvinyl alcohol-based molded products, which is characterized by melt molding.