JPH0112794B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a polyvinyl alcohol (hereinafter abbreviated as PVA) adhesive composition, particularly an adhesive composition for manufacturing corrugated board. A so-called stain hole type adhesive is widely used as an adhesive for corrugated board, in which gelatinized starch is used as a dispersion medium (carrier part) and starch powder (main part) is dispersed therein. The adhesive is supplied to the corrugated top of the core, and when heated in contact with the liner on a corrugating machine, it rapidly gelatinizes and exhibits adhesive strength to the paper surface. However, with the recent increase in the market for the use of corrugated cardboard, corrugating machines are becoming larger and faster in order to improve productivity. Also, vegetables, fruits,
Depending on the contents of the cardboard packaging, such as fish, the container needs to be water resistant, so water-resistant cardboard is manufactured by applying waterproof treatment to the cardboard, or by pre-treating the core base paper to make it waterproof. In response to these market demands, the performance of conventional stain-hole adhesives using raw starch is no longer sufficient, and it is no longer necessary to use modified starch or high amylose starch for both the carrier and main parts. In addition, in order to impart water resistance, methods such as adding various waterproofing agents to these materials have been used. However, even with these improved adhesives, the adhesive strength is insufficient for highly processed base papers, and the water resistance is still insufficient, so that in many cases they cannot satisfy market demands. One of the solutions to this problem is to add PVA to some or all of the starch-based powders mentioned above for the purpose of imparting water resistance.
Attempts have been made to replace the PVA powder with PVA powder, but the present inventors' investigation revealed that when replacing such PVA powder, the initial adhesion strength of the adhesive is insufficient, resulting in a reduction in the lamination speed. A solution is needed. However, as a result of intensive research to solve this problem, the present inventors found that (A) PVA resin powder that is sparingly soluble in cold water and soluble or swellable in hot water, and (B) ethylene content of 5. The adhesive composition prepared by mixing ~40% by weight of ethylene-vinyl acetate copolymer emulsion has significantly improved initial adhesive strength and can sufficiently withstand high-speed adhesive bonding, and has not only normal adhesive strength but also water-resistant adhesive strength. Since it has remarkable performance such as large size, it has been found that it is extremely useful as a water-resistant corrugated board adhesive with excellent productivity and workability, and the present invention has been completed. Components (A) and (B) of the adhesive composition of the present invention will be specifically explained below. As the PVA resin of the component (A), completely saponified PVA with a degree of polymerization of about 1000 to 2000 is suitable, but it is not necessarily limited to this, and although it is sparingly soluble in cold water, it In particular, any PVA that can be rapidly dissolved or swelled during heating and pressurization during the bonding process may be used regardless of its degree of polymerization or saponification. It takes
PVA can also be prepared by heat-treating water-soluble PVA to limit its water solubility to a certain range. In addition, it is not necessarily limited to PVA itself, but it is also partially acetalized or etherified, or other types of monomers such as crotonic acid, acrylic acid, maleic acid, itaconic acid or their alkyl esters, alkyl vinyl ethers, Modified PVAs obtained by copolymerization or graft polymerization with α-olefins are also available.
PVA can be used in the same manner as long as its adhesive properties are not significantly impaired. There are no particular restrictions on the shape of these powders, and any shape may be used as long as it does not significantly impair the fluidity of the dispersion, but it is desirable that the particle size be as uniform and fine as possible, and usually 150 to 350 meshes, especially 100 meshes or less. It is preferable to use a material of about 100%. In addition, the amount of these used is 2 to 30% by weight based on the entire dispersion.
In particular, about 5 to 15% by weight is suitable. The above PVA resin powder may be mixed with component (B) as a powder, but it is usually used in the form of a dispersion liquid in which the PVA resin powder is dispersed in water or an aqueous solution of a water-soluble polymer substance. . As the medium in which the PVA resin powder is to be dispersed, not only water but also an aqueous solution of a water-soluble polymer substance can be used. These water-soluble polymer substances are used for the purpose of uniformly dispersing the PVA resin powder and imparting appropriate viscosity to the paste solution to improve workability. and PVA
Any material may be used as long as it has a certain degree of miscibility with the system resin when it is dissolved and does not significantly impair the stability of the dispersion. Examples of these include starch, modified starch, sodium polyacrylate, polyacrylamide, etc. Examples include water-soluble acrylic resins, cellulose derivatives such as alkyl celluloses and carboxyalkyl celluloses, proteins such as casein and gelatin, and PVA resins themselves may also be used. It is desirable to use these in amounts such that the viscosity of the dispersion at room temperature is about 300 to 1500 cp. Next, component (B) in the present invention is an ethylene-vinyl acetate copolymer emulsion (hereinafter abbreviated as EVA emulsion) with an ethylene content of 5 to 40% by weight.
It is. Although the initial adhesion strength is improved by using such EVA emulsion, the ethylene content is important, and if the ethylene content is other than 5 to 40% by weight,
The effects of the present invention cannot be obtained with EVA emulsion. There are no particular restrictions on the production of EVA emulsion, and any method can be used. For example, in an autoclave, surfactant, water-soluble protective colloid, PH buffer, water, catalyst, vinyl acetate monomer (a predetermined amount of
10~100%) and stir to emulsify. Next, after replacing the inside of the autoclave by pressurizing nitrogen gas,
Inject ethylene under pressure. Polymerization is initiated by heating, and the remaining vinyl acetate monomer (0 to 90% of the predetermined amount) and, if necessary, a further catalyst are added continuously, in portions, or all at once to continue polymerization. The injection of ethylene may be carried out all at once, in parts, or continuously. The EVA emulsion thus obtained can be used as it is, or after being diluted or concentrated as appropriate, or with the addition of a suitable thickener. In the EVA emulsion of component (B) of the present invention, as a third component, an unsaturated vinyl monomer having a glycidyl group such as glycidyl acrylate or glycidyl methacrylate, N-methylolacrylamide, or
- Methylol compounds such as methylolmethacrylamide and unsaturated vinyl monomers having N-methylol or alkoxyl groups such as their alkyl ethers of methyl, ethyl and butyl ethers, such as acrylic acid, itaconic acid, maleic acid and their esters; It is also possible to contain a small amount of an unsaturated vinyl monomer having a carboxyl group or a carboxylic acid ester group. In the present invention, the effect can be achieved with any EVA emulsion as long as the ethylene content is specified, but among EVA emulsions, 0.5 to 2.5% by weight of anionic surfactant and 4 to 2.5% by weight of anionic surfactant based on vinyl acetate. Use an EVA emulsion with an ethylene content of 20-29% by weight obtained by emulsion polymerization of ethylene and vinyl acetate in the presence of 7% by weight of a nonionic surfactant and 0.2-1% by weight of a water-soluble protective colloid. Its use is particularly preferred since it has the following advantages. For example, a large amount of pigment is mixed into the adhesive for corrugated board for the purpose of improving adhesive strength and coating properties, as well as increasing the amount and reducing costs. Especially when mixing emulsions and pigments, it is essential that so-called emulsion destruction such as gelation, thickening, and aggregation does not occur.
Since the above-mentioned improvement effect due to the addition of a pigment increases in proportion to the amount added, it can be said that an emulsion with a larger allowable amount of pigment is more useful. In the case of the commonly known EVA emulsion, at most 4
While the limit is to mix about twice as much pigment, this particular EVA emulsion is extremely stable without causing emulsion destruction even when mixed with 5 to 6 times as much pigment. Initial adhesion strength is particularly improved. Because it has good compatibility with water-soluble polymer substances or acrylic and styrene-butadiene emulsions, thickening, gelation, phase separation, etc. will not occur even if the mixed solution is left standing or stored for a long period of time. A stable adhesive for cardboard can be obtained. Examples of anionic surfactants used in producing such EVA emulsions include alkali salts of carboxylic acids and sulfonic acids, ammonium salts such as sodium laurate or sodium stearate, sodium dodecylbenzenesulfonate, sodium vinylsulfonate, and laurylsulfone. alkali salts of acidic alkyl phosphates, ammonium salts such as sodium diethylhexyl phosphate, alkali salts of acidic esters of alkanols and sulfuric acid, ammonium salts such as sodium lauric sulfate, alkali polyoxyethylene ethers and dialkyl sulfosuccinates. Various salts, ammonium salts and the like can be mentioned. In addition, nonionic surfactants include polyoxyethylene alkyl ether type, polyoxyethylene alkyl allyl ether type, polyoxyethylene alkyl ester type, sorbitan monoalkyl ester type, polyoxyethylene alkylimine type, and polyoxyethylene alkyl amide type. ,
Various types such as polyoxyethylene/polyoxypropylene condensation type, glyceride, and pentaerythritol ester types are mentioned. Furthermore, as water-soluble protective colloids, fully or partially saponified polyvinyl alcohol and its derivatives,
Examples include gelatin and cellulose derivatives, maleic acid or a half-ester copolymer of maleic acid and styrene, starch, dextrin derivatives, polyvinylpyrrolidone, polyacrylic acid amide, and the like. In particular, polyvinyl alcohols having an average degree of polymerization of 400 to 2,500 and an average degree of saponification of 83 to 97 mol% are preferably used. In this way, an adhesive is prepared by mixing both components (A) and (B), and the mixing ratio of both is 10 to 200% by weight (in terms of solid content) of (B) based on the PVA powder in (A). , preferably in a proportion of 20 to 50% by weight. The adhesive of the present invention is further mixed with a water-resistant agent such as urea-, melamine-formaldehyde initial condensate, N-methylol group-containing compound, glyoxal, dialdehyde starch, etc. to improve its water-resistant adhesive strength. In addition, when compounds such as boric acid and borax are added to the adhesive composition, which can act on the PVA resin at the bonding temperature to exhibit a significant thickening effect, the initial adhesive strength is further improved, and the inside of the paper layer is Its addition is desirable because it suppresses the penetration of the resin into the resin. Furthermore, if necessary, fillers such as starch powder, clay, calcium carbonate, and diatomaceous earth, pigments, synthetic resin emulsions other than EVA emulsions, and PH of alkali carbonates and alkali phosphates, etc.
Regulators, ethylene glycol, glycerin, etc.
A plasticizer effective for PVA may be added as appropriate. When producing corrugated board using the adhesive composition of the present invention, it is appropriate to adjust the amount of adhesive supplied to the bonded portion so that the solid content is usually about 8 to 25 g/m ² . The core supplied with adhesive is overlapped with the mating liner to be bonded, and then heated by a heating roll or the like, or preferably simultaneously pressurized to complete the bonding.
The heating and pressurizing conditions at that time are usually roll temperature 100~
It can be selected from a range of 200°C and a pressure of about 2 to 7 kg/cm ² . As already mentioned, the adhesive composition of the present invention can be particularly suitably applied in the production of water-resistant corrugated board, but it is not limited to such cases, but can be used in a wide range of applications where water resistance is strongly required. It can be effectively applied to adhesives. Next, the adhesive composition of the present invention will be explained in more detail by giving examples. Production of EVA emulsion and its performance In a stainless steel autoclave equipped with a magnetic stirrer, a water-soluble protective colloid, a nonionic surfactant, an anionic surfactant were added in the amounts shown in Table 1, and a PH buffer (secondary phosphorus An emulsion was prepared by adding 1.0 part of sodium chloride dodecahydrate), 100 parts of pure water, 0.15 part of Rongarit, and 20 parts of vinyl acetate monomer.
After purging with nitrogen, the temperature was raised and ethylene was injected, and 2 g of a 1% solution of a catalyst (ammonium persulfate) was added to initiate polymerization. While maintaining the ethylene pressure at 50 kg/cm ² , the remaining 80 parts of vinyl acetate monomer and the catalyst were continuously charged and polymerized for 5 hours. After the vinyl acetate monomer was completely charged, the injection of ethylene was stopped, and the polymerization was continued for 1.5 hours. Table 1 shows each performance of the obtained EVA emulsion. In Table 1, the contents of surfactants and water-soluble protective colloids are shown on a weight basis with respect to vinyl acetate. In addition, the following symbols were used. DBS; Sodium dodecylbenzenesulfonate RSN; Sodium lauryl sulfonate PON; Polyoxyethylene nonylphenyl ether (HLB15-19) EO/PO; Polyoxyethylene/polyoxypropylene block polymer (oxyethylene content 40
~60%, oxypropylene average molecular weight 1200~
2000) PVA; Polyvinyl alcohol (average saponification degree 87-89 mol%, polymerization degree 1400)

【table】

[Table] EVA emulsions as shown in Table 2 were produced according to the above method. Its performance is shown in Table 2.

[Table] Example 1, Control Example Using PVA with an average degree of polymerization of 1400, an average degree of saponification of 99.3 mol%, and a particle size of 200 to 350 mesh, A-flute double-sided corrugated cardboard sheets were laminated using a corrugating machine under the conditions shown below. . ◎Adhesive composition (viscosity is 1250cp at 40℃) (A) Component water 540 PVA powder 120Kg Clay 80Kg Borax 1Kg CMC 3Kg (B) Component EVA emulsion (E-1) (50% concentration)
60Kg Additive 80% methylolmelamine 20Kg ◎Base paper composition liner Basis weight 240g/m ^2Water resistant K liner core Basis weight 160g/m ^2Water resistant SCP core ◎Machine condition design speed 150m/min Press roll and corrugated roll Temperature: 160℃ Press roll pressure: 5Kg/m ² Also, as a control example, the use of component (B) in Example 1 was omitted, and the amount of water and CMC used was 1.7
A similar gluing operation was performed using Kg of adhesive (40°C, 1300cp). The performance of the obtained corrugated paperboard sheet is shown in Table 3.

[Table] During this lamination, a sheet with only the SF side laminated, that is, one and both sides of corrugated cardboard, was sampled and subjected to the following tests, and the initial adhesive strength, normal adhesive strength, and water-resistant adhesive strength were measured as follows. The results are shown in Table 4. An adhesive composition is applied to the corrugated top of a single-sided corrugated board at a solid content of 10 g/m ² , and a basis weight of 240
g/m ² liner and iron (pressure 50g/
cm ² , surface temperature 150℃). (1) Initial adhesive strength; after heating time of 3 seconds, 6 seconds, 9 seconds,
Immediately peel it off and observe how the core pulp transfers to the liner. Evaluation is made on a total of 5 levels: 100% indicates that the core pulp has completely transferred, 0% indicates no transfer, and 25%, 50%, and 75% are in between. (2) Normal adhesive strength: After heating the test piece for 10 seconds and controlling the humidity at 20°C and 65% relative humidity for 24 hours, measure the adhesive strength according to JISZ0402. (3) Water-resistant adhesive strength: After heating for 10 seconds, the test piece was immersed in water at 20℃ for 1 hour, and then JISZ0402
Measure the adhesive strength. Examples 2 to 5 Tests similar to those in Example 1 were conducted using adhesives as shown in Table 4. The results are shown in Table 4.

[Table] ●During the measurement, destruction of the base paper was observed.

Claims (1)

[Claims] 1. (A) A powder of a polyvinyl alcohol resin that is sparingly soluble in cold water and soluble or swellable in hot water, and (B) an ethylene content of 5 to 40% by weight based on the powder. An adhesive composition prepared by mixing 10 to 200% by weight of an ethylene-vinyl acetate copolymer emulsion in terms of solid content and a water-resistant agent. 2. The adhesive composition according to claim 1, wherein the polyvinyl alcohol resin powder of component (A) is dispersed in water or an aqueous solution of a water-soluble polymeric substance. 3 Component (B) is 0.5 to 2.5% by weight based on vinyl acetate
An ethylene-vinyl acetate copolymer obtained by emulsion polymerization of ethylene and vinyl acetate in the presence of an anionic surfactant, 4 to 7% by weight of a nonionic surfactant, and 0.2 to 1% by weight of a water-soluble protective colloid. The adhesive composition according to claim 1, which is a polymer emulsion. 4. The adhesive composition according to claim 3, wherein component (B) is an ethylene-vinyl acetate copolymer emulsion having an ethylene content of 20 to 29% by weight.