JPS626595B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water-soluble or water-dispersible hot melt adhesive, and more particularly to a hot melt adhesive suitable for bookbinding, packaging, paper tubes, heat-sensitive and rewetting tapes, labels, etc. Polyvinyl alcohol (hereinafter abbreviated as PVA) is a typical adhesive used in an aqueous solution;
A process of dissolving the PVA is required, and a process of heating and drying after adhesion is required. Moreover,
Due to the molecular structure of PVA, the intermolecular bonding force of the hydroxyl groups is strong, and the melting point and decomposition point are close to each other, making it difficult to melt. Therefore, ordinary PVA cannot be used as a hot melt adhesive. be. On the other hand, ethylene-vinyl acetate copolymer resin, so-called EVA resin, is currently used as a hot melt adhesive, but this resin is hydrophobic and insoluble in water. This is a major obstacle when recovering waste paper that has been bonded with a hot melt adhesive made of EVA resin. That is, EVA
Since the resin is insoluble in water, the waste paper does not fall apart when it is collected, and hot melt adhesive that remains unbroken can clog the screens at various points in the waste paper collection process, causing trouble. It causes Furthermore, problems such as finely crushed hot melt adhesive entering the waste paper, remelting during heating and drying and adhering to the roll, and creating spots on the surface of the waste paper product occur. The Ministry of International Trade and Industry has set out a policy to increase the waste paper recovery rate from the current 40% to over 50% from the perspective of pollution and resource reuse. Once used, waste paper recovery becomes extremely complex and difficult. Further, modified PVA with a degree of polymerization of 300 to 3000 and a degree of saponification of 85 mol% or more is known from Japanese Patent Publication No. 46-42015, which is a highly saponified copolymer of saturated branched fatty acid vinyl and vinyl acetate. However, such modified PVA is insoluble in water and has too high a melting point and melt viscosity, making it undesirable as a hot melt adhesive. In addition, one of the present applicants developed a water-soluble and heat-melting PVA-based hot melt adhesive made of a low saponification product of low polymerization degree polyvinyl acetate, and filed an application earlier (Japanese Patent Application Laid-Open No. No. 96831, No. 51-96832
issue). In line with the above national policy, the present inventors developed a hot melt adhesive that is water-soluble or water-dispersible and can be applied with a roll or nozzle applicator, and is primarily used for bonding paper products, such as bookbinding. The present invention was developed as a result of continued research to develop an adhesive that can be used for packaging and does not cause problems during waste paper collection. That is, the present invention has the general formula CH ₂ =CHOCOC
_{Intrinsic viscosity ( acetone _ _} In solvent at 30℃ concentration unit g/100
Measured in ml. Same below. ) A water-soluble or water-dispersible hot-melt adhesive made of a partially saponified product obtained by saponifying 45 to 80 mol% of the polyvinyl acetate portion of a polyvinyl acetate copolymer of 0.09 to 0.27. The hot melt adhesive of the present invention has the above-mentioned PVA
Water-soluble or water-based adhesives that have better heat resistance, cold resistance, and moisture resistance than hot melt adhesives, and have improved compatibility with thermoplastic resins and plastics, which are well known as additive components of hot melt adhesives. It is a dispersible hot melt adhesive. The saturated branched fatty acid vinyl used in the preparation of the hot melt adhesive of the present invention has the general formula CH ₂ =
CHOCOC R ₁ R ₂ R ₃ (wherein R ₁ , R ₂ and R ₃ represent an alkyl group). _R1 , _R2
The sum of the carbon numbers of the alkyl groups of R ₃ is 3 to 12, especially 6 to 12, considering the water solubility of the partially saponified product obtained and the compatibility with thermoplastic resins and plasticizers.
It is preferable that The hot melt adhesive of the present invention is prepared by copolymerizing such saturated branched fatty acid vinyl and vinyl acetate in a specific ratio to obtain a polyvinyl acetate copolymer, and partially saponifying the obtained polyvinyl acetate copolymer. be done. Copolymerization of saturated branched fatty acid vinyl and vinyl acetate is a process in which saturated branched fatty acid vinyl is
It is necessary to use 0.5-10% by weight, preferably 2-6% by weight. If the amount of saturated branched fatty acid vinyl is less than 0.5% by weight, the effect of copolymerization will be reduced, while if it exceeds 10% by weight, the water solubility of the partially saponified product obtained will be extremely reduced, which is not suitable. For copolymerization, a radical catalyst such as azobisisobutyronitrile is used, and the polymerization solvent has a chain transfer constant of 20×10 ^-4 at the polymerization temperature.
This can be carried out using the above-mentioned solvents, such as ethyl alcohol, isopropyl alcohol, and isobutyl alcohol. To adjust the hot melt adhesive of the present invention, adhesive properties,
In view of coating properties, the intrinsic viscosity of the polyvinyl acetate copolymer obtained is 0.09 to 0.27, preferably 0.14 to 0.21.
It is necessary that If the intrinsic viscosity is less than 0.09, the intermolecular cohesive force will be insufficient, making it unsuitable for use as an adhesive. On the other hand, if it exceeds 0.27, the melting temperature and melt viscosity will be too high, making it impossible to use a normal hot melt adhesive applicator, and as a result, it will be impossible to apply the adhesive to the object to be adhered, making it unsuitable. be. In addition, the degree of polymerization AC of polyvinyl acetate (hereinafter abbreviated as PVAc) having an intrinsic viscosity [η] of 0.09 to 0.27 is 50 to 300 when calculated from the following viscosity formula. logAC=1.613 log[η]×10 ⁻⁴ /7.94 The polyvinyl acetate copolymer obtained as described above is saponified by a known method. The hot melt adhesive of the present invention is made of a partially saponified polyvinyl acetate copolymer, and the saponification reaction is schematically shown by the following formula. As can be seen from the above formula, PVAc is produced by saponification reaction.
The acetate group in the part is decomposed and changes to a hydroxyl group,
The branched fatty acid group of the branched fatty acid vinyl moiety does not undergo the saponification reaction due to its steric hindrance and preferentially remains. The partially saponified product constituting the hot melt adhesive of the present invention is 45 to 80 mol%, preferably 55 to 80 mol% of the PVAc moiety of the polyvinyl acetate copolymer, by a saponification reaction.
70 mol% is changed to hydroxyl group. Generally, the proportion converted to hydroxyl groups is called the degree of saponification, and therefore, expressed as the degree of saponification, the degree of saponification of the PVAc moiety is 45 to 80 mol%, preferably 55 to 70 mol%. If the degree of saponification is less than 45 mol %, the water solubility of the partially saponified product tends to be extremely reduced, which is not preferred as a water-soluble or water-dispersible adhesive. If the degree of saponification exceeds 80 mol%, the melting point and melt viscosity of the partially saponified product will become extremely high, making hot melt coating difficult, which is not preferable. Table 1 shows the effects of the degree of polymerization and degree of saponification on the performance of the adhesive.

[Table] As is clear from Table 1, if the degree of polymerization is too high (Test samples No. 4 and 5), the adhesive will not dissolve in water, making it impossible to achieve the object of the present invention. Furthermore, as the degree of polymerization and saponification increases (sample Nos. 3, 4, and 5), the melt viscosity increases, making it difficult to melt and apply as a hot melt adhesive. The above-mentioned special public service in 1977
The copolymerized modified PVA described in Publication No. 42015 cannot be used for the purpose of the present invention because both the degree of polymerization and the degree of saponification are high. On the other hand, the adhesives of samples No. 1 and 2 of the present invention are particularly preferable because they have appropriate melting temperatures and viscosity, and are also water-soluble. Such adhesives are used for bookbinding,
It exhibited excellent coating and adhesion properties as a hot melt adhesive for labels, etc., and did not cause any trouble when recovering waste paper. The partially saponified product obtained as described above can of course be used alone as a water-soluble or water-dispersible hot melt adhesive as described above, but it also has properties such as heat resistance, cold resistance, and moisture resistance. In order to improve workability, it is preferable to add thermoplastic resins, tackifiers, waxes, plasticizers, fillers, antioxidants, etc. which are generally used as hot melt adhesive components. Examples of thermoplastic resins that can be used include polyethylene, polypropylene, ethylene-propylene copolymer, polyvinyl acetate, ethylene-vinyl acetate copolymer and its derivatives, ethylene-acrylic acid copolymer, and ethylene-acrylic acid ester copolymer. Polymers, ethylene-vinyl acetate-organic acid copolymers, ethylene-propylene-organic acid copolymers and derivatives thereof, polyesters, polyamides, butyl rubber, styrene-butadiene copolymers, styrene-isoprene copolymers, etc. . Examples of tackifiers that can be used include rosin, modified rosin and its derivatives, polyterpene resin, terpene phenol resin, aliphatic hydrocarbon resin, alicyclic hydrocarbon resin, aromatic hydrocarbon resin, styrene resin, xylene resin, coumaron-indene resin, vinyltoluene-a-methylstyrene copolymer, and the like. Examples of waxes that can be used include paraffin wax, microcrystalline wax, low molecular weight polyethylene wax, and oxidized polyethylene wax. Examples of plasticizers that can be used include polyhydric alcohols such as glycerin, trimethylolpropane, pentaerythritol, sorbitol, and mannitol, and modified products thereof; ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, and diethylene glycol; Glycols such as propylene glycol, tripropylene glycol, polypropylene glycol and their modified products, urea and ethylene urea,
Examples include urea derivatives such as propylene urea, phthalate esters such as DOP and DBP, and phosphate esters such as TCP and TPP. Further, examples of fillers that can be used include calcium carbonate, barium sulfate, zinc oxide, magnesium oxide, titanium oxide, and hydrated silicic acid. Furthermore, phenol-based, amine-based, phosphoric acid-based, and other antioxidants may be appropriately blended. The above thermoplastic resins, tackifiers, waxes, plasticizers, fillers, and antioxidants can be used alone or in combination of two or more. When the water-soluble or water-dispersible hot melt adhesive of the present invention is used for book binding, sealing of cardboard or cartons, pressure-sensitive tape, label, or rewetting tape, and then is recovered as waste paper, in the recovery and recycling process. There are no problems caused by adhesives. In addition, even in recycled products, there are no small pieces of adhesive left, and unlike recycled products made from waste paper using traditional hot melt adhesives, spots may develop due to the residual adhesive when heated. There's nothing to do. Furthermore, the adhesive of the present invention has excellent adhesion properties, particularly heat resistance, cold resistance, and moisture resistance, and also has low evaporation during melting, an appropriate melt viscosity, and excellent sinterability. Furthermore, since it has good thermal stability, it exhibits excellent performance as a hot melt adhesive. Hereinafter, the present invention will be explained in more detail with reference to Examples. Note that "parts" in the examples mean "parts by weight." Example 1, Comparative Example 1 Vinyl balsatric acid (manufactured by Ciel Chemical, trade name
VeoVa, ) 20g and vinyl acetate 480g were polymerized with 500g of ethyl alcohol at 70°C for 4 hours using 0.55g of azobisisobutyronitrile (AIBN) as an initiator. As a result, the intrinsic viscosity of an acetone solution at 30°C with a polymerization yield of 92% [η] = 0.173 (concentration unit g/
100ml) of copolymer was obtained. When this polymerization solution was desolvented at 140°C under reduced pressure, a transparent glass-like lump was obtained. This copolymer was more easily softened than vinyl acetate homopolymer. After dissolving this copolymer in methyl alcohol and adjusting the concentration to 63% by weight, 1.8 milliequivalents of caustic soda was added to 1 mole of PVAc portion and saponified at 40°C for 2 hours, resulting in the copolymer components. A modified PVA in which 65 mol% of the PVAc moiety was saponified was obtained. The obtained modified PVA melts at about 150-160℃,
The melt viscosity at 180℃ is 48000 centipoise and 30
A cloudy dispersion occurred in water at ℃. 100 parts each of this modified PVA (Example 1) and a low degree of polymerization, low saponified PVA (Comparative Example 1) having almost the same intrinsic viscosity, and the various components shown in Table 2 were heated at 170°C in the proportions shown in Table 2. and their compatibility was observed. The results are shown in Table 2. In Example 1, they were compatible over a wide range, and the compatibility was greatly improved compared to Comparative Example 1.

[Table] Example 2, Comparative Example 2 Trimethyl vinyl acetate 40g, vinyl acetate 460g
0.45g of AIBN in 500g of isopropyl alcohol
Polymerization was carried out at 80°C for 3.5 hours using as an initiator. As a result, a copolymer with a polymerization yield of 93% and an intrinsic viscosity [η] of an acetone solution at 30°C of 0.105 (concentration unit g/100ml) was obtained. After removing the solvent from this polymerization solution in the same manner as in Example 1, it was dissolved in methyl alcohol to a concentration of 65% by weight.
When milliequivalents of caustic soda was added and the mixture was saponified at 40°C for 2 hours, a modified PVA in which 68 mol% of the PVAc moiety in the copolymer component was saponified was obtained. The obtained modified PVA melts at 140-150 °C and 180 °C
The melt viscosity in °C was 35,000 centipoise. In addition, cloudy dispersion occurred in water at 30°C. This modified PVA ([η] = 0.105) and low polymerization degree low saponified PVA with almost the same intrinsic viscosity
([η]=0.103) was mixed with the components shown in Table 3 in the proportions shown in Table 3 to obtain an adhesive. In addition, the mixing temperature is 170℃.
I did it at

[Table] Good binding was obtained when the adhesives of Example 2 and Comparative Example 2 were used as hot melt adhesives for perfect binding. Furthermore, the results of measuring the adhesive strength when using this adhesive were as shown in Table 4. In addition, the above adhesive strength is 5cm
This shows the adhesive strength when two sheets of paper are peeled off from a sample cut into width. When each of the above-mentioned bound books was put into a waste paper recycling dissociator with water and stirred for 20 minutes, the adhesive was finely dispersed and no solid adhesive was found in both cases. This dissociated product was made into paper and heated to 180°C, but no spots due to residue appeared.

[Table] * indicates that paper layer destruction occurred.
Example 3, Comparative Example 3 20 g of vinyl 1,2-dimethyl-1-isopropylpropanecarboxylate and 480 g of vinyl acetate were polymerized in 500 g of isobutyl alcohol using 0.55 g of AIBN as an initiator at 70° C. for 4.5 hours. the result,
A copolymer with a polymerization yield of 94% and an intrinsic viscosity [η] of an acetone solution at 30°C of 0.21 (concentration unit g/100ml) was obtained. This polymerization solution was deliquified in the same manner as in Example 1, and then dissolved in methyl alcohol to a concentration of 68% by weight. Next, 2 milliequivalents of caustic soda was added to 1 mole of PVAc, and the mixture was thoroughly stirred. When saponified at 40℃ for 2 hours, PVAc in the copolymer component was
A modified PVA in which 58 mol% of the portion was saponified was obtained. The resulting modified PVA melts at 140-150 °C and
It was dispersed and dissolved in water at ℃. The above modified PVA ([η] = 0.21) and the same low degree of polymerization and low saponified PVA ([η] =
0.21) was mixed with the components shown in Table 5 in the proportions shown in Table 5 to obtain an adhesive.

[Table] The adhesives of Example 3 and Comparative Example 3 were applied as hot melt adhesives to corrugated board (K liner) in the form of a bead at a room temperature of 20°C and an adhesive temperature of 180°C, with an open time of 2 seconds. I did the crimp. This adhesive was left for a day and night at each measurement temperature shown in Table 6, and then peeled off with fingers at that temperature to observe the adhesiveness. The results were as shown in Table 6.

[Table] When each of the above-mentioned glued cardboard boxes was put into a waste paper recycling dissociator with water and stirred for 20 minutes, the adhesive was finely dispersed and no solid adhesive was found in both cases. Example 4, Comparative Example 4 Ethyl alcohol was added to the polymerization solution obtained by polymerization in the same manner as in Example 1, and after removing unreacted vinyl acetate by azeotropy, the concentration of the copolymer was reduced to 48%.
Then, add 7 milliequivalents of caustic soda to 1 mole of PVAc and heat at 40°C with thorough stirring.
It was saponified for 2 hours. As a result, modified PVA in which 57 mol% of the PVAc moiety in the copolymer component was saponified was obtained. The obtained modified PVA melts at 135-145 °C and 180
The melt viscosity in °C was 30,000 centipoise. In addition, when the mixture was forcibly stirred in water at 30°C, it became cloudy and dispersed. This modified PVA ([η] = 0.173 and the low degree of polymerization and low saponification PVA ([η] =
0.175) was mixed with the components shown in Table 7 in the proportions shown in Table 7 to obtain an adhesive.

【table】

[Table] The adhesives of Example 4 and Comparative Example 4 were heated to 180°C, poured onto a smooth mold release surface to a diameter of about 5 cm, and solidified. After this adhesive was left for one week under various conditions shown in Table 8, its hardness was measured to see the degree of softening due to moisture absorption. The results were as shown in Table 8. In addition, 20℃
The initial hardness of both was 95.

[Table] Hardness is based on a spring hardness meter.
(JIS K6301 compliant)
Example 5 10 g of 1,1,3,3-tetramethylbutanecarboxylic acid and 490 g of vinyl acetate were mixed in 500 g of isopropyl alcohol with 0.45 g of AIBN as an initiator.
Polymerization was carried out at 80°C for 4 hours. As a result, the polymerization yield was 94
%, and the intrinsic viscosity of an acetone solution at 30° C. was 0.13 (concentration unit: g/100 ml). Isopropyl alcohol and unreacted vinyl acetate were removed from the thus obtained polymerization solution at 80° C. under reduced pressure to obtain a transparent glassy copolymer. After dissolving this copolymer in methyl alcohol and adjusting the concentration to 65%, 1.8 milliequivalents of caustic soda was added to 1 mole of PVAc moiety and saponified at 40°C for 2 hours. A modified PVA in which 65 mol% of the PVAc moiety was saponified was obtained. The obtained modified PVA melts at 130-140 °C and 180 °C
Melt viscosity at 30℃ is 12000 centipoise
It was dissolved and dispersed in water. To 100 parts of this modified PVA, 30 parts of a propylene oxide 6 mole adduct of Sorbivit and 10 parts of ethylene glycol were added, melted and mixed at 170°C, and the adhesive was thinly rolled onto kraft paper at 180°C using a hot melt adhesive. This kraft paper was cut to a width of 5 cm to form a tape, and when the tape was applied to cardboard while heating it from the back with an iron, it showed good adhesion. In addition, this tape is put into a waste paper recycling machine with water,
After stirring for 10 minutes, the adhesive was finely dispersed and no solid adhesive was found.

Claims (1)

[Claims] 1 saturated branched fatty acid vinyl represented by the general formula CH ₂ =CHOCOC R ₁ , R ₂ , R ₃ (wherein R ₁ , R ₂ , R ₃ represent an alkyl group) is 0.5% relative to vinyl acetate.
Intrinsic viscosity obtained by ~10% by weight copolymerization (measured in acetone solvent at 30°C, concentration unit g/100ml) 0.09
A water-soluble or water-dispersible hot melt adhesive comprising a partially saponified product obtained by saponifying 45 to 80 mol% of the polyvinyl acetate portion of a polyvinyl acetate copolymer with a polyvinyl acetate of 0.27 to 0.27.