JPH10265755A - Water-resistant adhesive for corrugated board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject adhesive having excellent water-resistant adhesivity and initial adhesivity and keeping the adhesivity even under application of heat and vibration during the passage through a hot plate of a corrugated board bonding apparatus by dispersing an acrylic resin emulsion and starch in water. SOLUTION: This adhesive is produced by dispersing (A) an acrylic resin emulsion and (B) starch in water. The component A is an aqueous emulsion of a synthetic resin composed mainly of a copolymer of a (meth)acrylic acid ester and styrene, etc. The component B is e.g. tapioca starch or acetylated tapioca starch. The amount of the component B is preferably 10-150 pts.wt. based on 100 pts.wt. of the synthetic resin in the component A. A corrugated board exhibiting excellent water-resistance can be produced by the use of the adhesive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an adhesive for producing water-resistant corrugated cardboard.

[0002]

2. Description of the Related Art Conventionally, starch paste has been used as an adhesive used for cardboard. The method of producing this starch paste is
From the early two-tank system stain-hole method, the manufacturing process has been streamlined and the one-tank system premix method has been shifted to the one-tank system no-carrier method. Although there are changes in the manufacturing method,
The starch paste itself is composed of gelatinized starch called a carrier part and ungelatinized starch called a main part.

When cardboard is manufactured using the above starch paste, if the cardboard is wet with water, the liner in the cardboard tends to peel off from the core. In order to prevent this peeling and improve the water resistance, a melamine resin, a ketone resin, a phenol resin, an amino resin, a urea resin, or the like is added to the starch paste.

However, these condensation resins containing formaldehyde tend to emit formalin odor,
Even when the above resins were added, the resulting adhesive did not have sufficient water-resistant adhesive strength.

Although it is conceivable to use a synthetic resin-based adhesive alone as a cardboard adhesive without using starch, it is not possible to obtain sufficient initial adhesiveness, and the current speed of the cardboard manufacturing process cannot be improved. Could not respond to.

[0006] In order to improve these points, it is known to add a rubber-based latex such as styrene-butadiene-based latex and calcium carbonate to starch (see JP-A-62-273275). By using this adhesive, sufficient normal state adhesiveness was obtained, and the water-resistant adhesive strength and initial adhesiveness were improved to some extent.

[0007]

However, the inventors of the present invention have studied that the water-resistant adhesive strength and the initial adhesiveness are not sufficiently improved, and cannot sufficiently cope with the current speed of the cardboard manufacturing process. It became clear.

[0008] Styrene / butadiene latex exhibits a glass transition point of -20 to 0 ° C. Although its melting point does not appear clearly, it softens at temperatures above the glass transition point, exhibits rubber-like elasticity close to that of a liquid, and adhesion depends on its adhesive strength. In addition to the adhesive force decreasing with increasing temperature, such adhesive layers are known to deform in a stress and time dependent manner. By the way, the styrene-butadiene-based latex solidifies and adheres at a temperature lower than the glass transition point. Therefore, in order to solidify the adhesive composed of the styrene-butadiene-based latex, the styrene-butadiene-based latex needs to have a temperature below the glass transition point, that is, -20 to 0. It is necessary to cool to below ℃. For general use, it is preferable to solidify at room temperature. Therefore, it is conceivable to crosslink the styrene / butadiene latex. However, even in this case, there is a problem that the solidification after two to three days is not sufficient.

For this reason, if the amount of heat and vibration applied during the production of the corrugated cardboard is not adjusted, the adhesive surface may peel off.

Accordingly, an object of the present invention is to provide not only excellent adhesiveness in a normal state but also excellent waterproof adhesive strength and initial adhesiveness.
It is an object of the present invention to provide a corrugated cardboard water-resistant adhesive which maintains its adhesiveness even when subjected to heat or vibration while passing through a hot plate of a corrugated cardboard bonding apparatus.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the present invention, an acrylic emulsion and starch are dispersed in water.

Further, 10 to 150 parts by weight of starch can be added to 100 parts by weight of the synthetic resin in the acrylic emulsion.

Further, tapioca starch or acetylated tapioca starch can be used as the starch.

The acrylic emulsion used as a water-resistant adhesive for corrugated boards generally has a glass transition point of 17 ° C. to 25 ° C. in the range of room temperature. Therefore, when heat is applied to a temperature exceeding the glass transition point, the acrylic emulsion exhibits rubber-like elasticity, and exhibits an adhesive function by its cohesive force. Thereafter, when cooled, the acrylic emulsion becomes a glass transition point or less at room temperature, solidifies and adheres.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. The water-resistant adhesive for cardboard according to the present invention comprises an acrylic emulsion and starch dispersed in water.

The acrylic emulsion is a copolymer of acrylate or methacrylate and styrene, or an acrylate or methacrylate, styrene, and other general-purpose vinyl monomer components copolymerizable with each other. Is a resin obtained by emulsifying a synthetic resin containing a copolymer containing as a main component in water.

The acrylate or methacrylate includes methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, Examples thereof include butyl methacrylate, pentyl methacrylate, and hexyl methacrylate, but are not particularly limited. The acrylate or methacrylate used as the copolymer may be used alone or in combination of two or more.

Further, as the above-mentioned vinyl monomer, resins other than the above-mentioned acrylate or methacrylate, such as monomers for general-purpose resins, can be used. Specific examples include ethylene, propylene, vinyl acetate, acrylonitrile, methacrylonitrile, acrylamide and the like.

If necessary, acrylic acid or a salt thereof or methacrylic acid or a salt thereof may be added to the acrylic emulsion as a monomer within a range that does not affect the water resistance of the obtained water-resistant adhesive for corrugated cardboard and copolymerized. You may.

The glass transition point of the above-mentioned acrylic emulsion is approximately room temperature of 17 to 25 ° C., and by setting the glass transition point or higher, fusion between the micelles of the acrylic emulsion can be achieved.

As the starch, any starch such as ordinary starch and chemically treated starch can be used. Examples include corn starch, processed starch, acetylated tapioca starch and the like. Commercially available processed starches include OHP-100 (manufactured by Oji Cornstarch), tapioca starch, and acetylated tapioca starch manufactured by Sanwa Starch Industries.

Starch generally has a granular structure having a diameter of 10 to 20 μm, that is, a secondary structure. When a certain temperature is reached in the presence of water, water is rapidly incorporated into the particles, and the starch swells largely in a spherical form to have a viscosity. Is expressed. Generally, when the temperature is increased in the presence of water in an amount of at least two to three times the amount of starch, the starch swells to exhibit a viscosity, and then gelatinizes and the grains disappear. When the particles disappear, the solution becomes a dispersion solution of amylose and amylopectin, which are primary structures, and the viscosity decreases. During this time, an endothermic phenomenon called starch gelatinization is observed. When such a change is measured using a viscometer manufactured by Plavender, which is a starch viscometer, the swelling onset temperature of corn starch is 71 to 75 ° C, and the swelling onset temperature of tapioca starch or acetylated tapioca starch is 62. ° C. When 2% by weight of borax is added to tapioca starch or acetylated tapioca starch,
Becomes From these, if tapioca starch or acetylated tapioca starch is used among the above-mentioned starches, the swelling start temperature can be further reduced, and the heating time can be shortened, that is, the molding speed can be increased. Therefore, in consideration of the swelling start temperature and the glass transition point of the acrylic emulsion, the temperature at which the obtained water-resistant adhesive for corrugated board exerts the adhesive force can be further reduced.

The above-mentioned borax is mainly composed of sodium borate, and by adding this to an adhesive, the apparent molecular weight of the gelatinized starch molecules is increased to increase the adhesive force and to adsorb to ungelatinized starch particles. Promotes gelatinization of starch. For this reason, the adhesive effect of the water-resistant adhesive for cardboard can be improved. That is, in the initial bonding, the acrylic emulsion adhesive is concentrated by the rapid absorption of water by the starch to favorably exert its viscosity,
In addition to the latent heat of vaporization of water which coexists with the heat received from the time the adhesive layer of the adhesive is formed to the time it is cooled, the gelatinization endotherm of the starch advantageously acts to protect the adhesive layer.

With respect to the amounts of the acrylic emulsion, starch and borax, 10 to 150 parts by weight of starch are preferably mixed with 100 parts by weight of the synthetic resin in the acrylic emulsion, and 20 to 120 parts by weight are mixed. Is preferred. When the amount of starch is less than 10 parts by weight, the amount of starch to be gelatinized is small, so that the water absorption capacity is reduced and the initial adhesive strength of the adhesive is reduced. Poor adhesion is observed. This poor adhesion is considered to be due to the promotion of brittleness of the adhesive layer due to the mixture of ungelatinized starch in the adhesive layer.

When the starch is used in an amount of 10 to 150 parts by weight, gelatinization of the starch and viscosity increase of the resin are easily caused at the same time, and the adhesive ability can be improved.

In the water-resistant adhesive for cardboard, borax can be dispersed in water in addition to the acrylic emulsion and starch. The amount of the borax to be added is preferably 1 to 3 parts by weight, more preferably 1.5 to 2.5 parts by weight, based on 100 parts by weight of the starch. When the amount of borax is less than 1 part by weight, the effect of borax is not exhibited, which is not preferable. When the amount exceeds 3 parts by weight, no particular problem occurs, but no significant effect is exhibited as compared with the case of 3 parts by weight.

The concentration of the suspension of the acrylic emulsion, starch and borax in water is preferably 40 to 55% by weight, and more preferably 40 to 50% by weight. If the amount is less than 40% by weight, the amount of water to be evaporated by the corrugator increases, which hinders adhesion. On the other hand, if it exceeds 55% by weight, it cannot be obtained because it is not within the range of viscosity that can be handled by pumping or the like. Considering the stability of the mixture, it is easy to maintain the concentration at the time of acquisition, but adding dry starch to the emulsion may cause the emulsion to be destroyed. Is not a good idea. The concentration of a commercially available emulsion is generally 45 to 55% by weight.

If necessary, a thickener for an aqueous emulsion of a synthetic resin may be added to the water-resistant adhesive for cardboard. Thereby, the viscosity is 400 to 1500 cps,
When the water-resistant adhesive for corrugated cardboard is used for 17 to 30 seconds in the number of seconds of the cup, the suitability for the corrugator is improved.

By using the water-resistant adhesive for cardboard as described above, sufficient initial adhesiveness can be exhibited, and it is possible to sufficiently cope with the current speed of the cardboard manufacturing process. The water-resistant adhesive strength after immersion in water for 60 minutes is 7 kgf / 4.
It became 2.5 cm ² or more, and it became possible to express excellent water resistance.

As described above, since ungelatinized starch is used and there is no contact with alkali, no gelatinized starch is contained inside. Conventional adhesives depend, at least in part, on the viscosity and adhesiveness of gelatinized starch, so that the viscosity and adhesive performance change over time due to the progress of gelatinization and aging, which is a characteristic property of gelatinized starch. It could not be avoided. However, the water-resistant adhesive for cardboard did not change in viscosity over time, and its adhesive performance did not change for 20 days or more.
For this reason, it is possible to supply a water-resistant adhesive for corrugated cardboard having a stable viscosity and adhesive strength irrespective of a change with time in viscosity due to aging, which is a peculiar defect of starch gelatinized by such a formulation.

[0031]

Embodiments of the present invention will be described below. Examination of Adhesiveness According to Types of Starch [Examples 1 to 3] A 2 liter polybeaker equipped with a constant-speed stirrer and a thermometer was fixed in a 42 ° C constant temperature bath, and water, borax, starch at 40 ° C were stirred with stirring. An adhesive was prepared by adding the acrylic emulsion and the thickener in the amounts shown in Table 1. As the starch, corn starch, processed starch, and acetylated tapioca starch were used, and as the emulsion, an acrylic emulsion (Nik Carbide Industries, Ltd .: Nik)
asol Rx533L, glass transition point 17 ° C, melting point 1
20 ° C.) and 1% by weight of a thickener for emulsion (Nikaso, manufactured by Nippon Carbide Industry Co., Ltd.)
IRx922L, resin content 30% by weight). The viscosity of each of the obtained adhesives was measured. “BV” in Table 1 is
Using a B-type viscometer, rotor no. The values measured at 3, 60 rpm are shown. "FV" indicates the number of seconds measured by Ford cup viscosity. Further, using each of the obtained adhesives, an adhesion test was performed by the following method. Table 1 shows the results. The adhesive strength in Table 1 indicates a value obtained by converting the force (kgf) required for peeling the paper per 42.5 cm ² .

Adhesion test The obtained adhesive was applied to the top of a single step (50 × 85 mm) of A flute to which a core of 200 g / m ² basis weight was bonded.
The water-resistant base paper having a basis weight of 290 g / m ² (50 mm × 85
mm) and bonded together at 175 ° C. for 5 seconds. The application amount of the adhesive at this time was 7 to 9 g / m ^{2 in} terms of dry weight. The adhesive strength of the obtained cardboard was measured by the following method.

Initial adhesive strength After heating at 175 ° C. for 5 seconds, immediately follow JIS Z 0
According to the method described in No. 402, a peeling test was carried out using an initial adhesion test measuring device described in JP-A-7-5097.

A normal adhesion strength A peeling test was performed in accordance with JIS Z 0402 “Corrugated cardboard adhesion test method”.

Waterproof adhesive strength for 60 minutes The obtained cardboard was immersed in water at 20 ° C. for 60 minutes, then pulled up and used as it was for the above-mentioned measurement of the normal adhesive strength.

Comparative Example 1 An experiment was conducted in the same manner as in Example 1 except that only the above-mentioned acrylic emulsion was used.
Table 1 shows the results. In addition, the viscosity and the adhesive strength were measured according to the above methods. The adhesive strength in Table 1 indicates the force (kgf) required for peeling off paper 42.5.
The value converted per cm ² is shown.

[0037]

[Table 1]

As a result , acetylated tapioca starch was the best for initial adhesion and 60 minutes of water-resistant adhesion, and corn starch, processed starch and acetylated tapioca starch were good for normal adhesion.

Examination of the amount of starch and the type of emulsion [Examples 4 to 7] Acetylated tapioca starch was used as the starch, and the emulsion was an acrylic emulsion (Nikasol Rx53 manufactured by Nippon Carbide Industry Co., Ltd.).
3L) (in Table 2, it is indicated as "acryl")
According to the method described in Example 1, the amounts shown in Table 2 were added to produce adhesives. Table 2 shows the results. In addition, the viscosity and the adhesive strength were measured according to the above methods. Further, the adhesive strength in Table 2 indicates a value obtained by converting the force (kgf) required for peeling per 42.5 cm ² of paper.

Comparative Example 2 An experiment was conducted in the same manner as in Example 1 except that only the acrylic emulsion was used. Table 3 shows the results. In addition, the viscosity and the adhesive strength were measured according to the above methods. The adhesive strength in Table 3 indicates the force (kgf) required for peeling.
Is converted to 42.5 cm ² of paper.

[Comparative Examples 3 to 7]
B type latex (commercially available product, concentration: 50% by weight, glass transition point: -1 ° C) (in Table 3, denoted as "SB")
Was used in the same manner as in Example 1 to produce an adhesive. Table 3 shows the results. In addition, the viscosity and the adhesive strength were measured according to the above methods. Also, the adhesive strength in Table 3 indicates the force (k
gf) is converted per 42.5 cm ² of paper.

[0042]

[Table 2]

[0043]

[Table 3]

As a result, when an acrylic emulsion was used, good adhesive strength was obtained irrespective of the concentration of the acetylated tapioca starch. It was found that when the SB latex was used as the emulsion, the normal adhesion was the same, but the initial adhesion strength and the water-resistant adhesion for 60 minutes were inferior to those using the acrylic emulsion.

[0045] According to the method described in strength test in Example 1 of laminated sheet according to the exemplary tests were prepared adhesive according manufacturing glue formulation of Table 4. In addition, what was shown above was used for each component. Further, as a water-proofing agent, a modified ketone resin: HRSA-1 (manufactured by Hornen Corporation; solid content: 40% by weight) was used. The viscosity was measured by the above method.

[0046]

[Table 4]

Example 8 The adhesive (glue formulation C) obtained according to the above-described glue formulation was provided to an actual corrugated board manufacturing machine. The adhesive strength of the obtained cardboard sheet was measured by the above method. Table 5 shows the results.
The adhesive strength in Table 5 indicates a value obtained by converting the force (kgf) required for peeling to 42.5 cm ² of paper. In Table 5, "SF" indicates a single facer side, and "DF" indicates a double facer side.

[Comparative Examples 8 to 9] The adhesives (glue formulations A and B) obtained in accordance with the above-mentioned glue formulation were provided to a corrugated board manufacturing machine. The adhesive strength of the obtained cardboard sheet was measured by the above method. Table 5 shows the results. The adhesive strength in Table 5 indicates a value obtained by converting the force (kgf) required for peeling to 42.5 cm ² of paper. Further, when the adhesive based on the glue formulation B was used, the adhesion was poor on the single side, so the experiment was stopped.

[0049]

[Table 5]

Result The corrugated cardboard sheet manufactured using the starch-based water-resistant adhesive made of the conventional glue formulation A had a water-resistant adhesive strength of 3 kg for 60 minutes.
f / 42.5 cm ² , but when the adhesive made of the paste formulation C according to the present invention was used, the water-resistant adhesive strength for 60 minutes was 7 kgf / 42.5 cm ² or more, which was good. Was. Further, the initial bonding was satisfactory at a laminating speed of 150 m, and the normal bonding strength showed a result equivalent to that of the conventional starch-based water-resistant adhesive.

[0051]

According to the present invention, the use of the above-mentioned water-resistant adhesive for corrugated board exerts a sufficient initial adhesiveness, so that it can sufficiently cope with the current speed of the corrugated board manufacturing process.

Further, since it has a sufficient normal state adhesiveness, it is possible to sufficiently maintain the adhesive strength of a cardboard manufactured using the water-resistant adhesive for cardboard.

Further, the water-resistant adhesive strength after immersion in water for 60 minutes becomes 7 kgf / 42.5 cm ² or more, and the cardboard manufactured using this water-resistant adhesive for cardboard can exhibit excellent water resistance. Now you can.

Furthermore, since gelatinized starch and alkali are not used at all, a sizing agent having a stable viscosity and adhesive force is completely independent of a change with time in viscosity due to aging which is a peculiar disadvantage of gelatinized starch. Can be supplied.

Further, since it is possible to make the glue in one tank, it is possible to save labor by shortening the time required for the glue and reducing the number of steps.

Claims (3)

[Claims] 1. A water-resistant adhesive for corrugated cardboard comprising an acrylic emulsion and starch dispersed in water. 2. Synthetic resin 1 in an acrylic emulsion
The water-resistant adhesive for cardboard according to claim 1, wherein 10 to 150 parts by weight of starch is added to 00 parts by weight. 3. The water-resistant adhesive for cardboard according to claim 1, wherein the starch is tapioca starch or acetylated tapioca starch.