ANCHOR COAT AGENT

Abstract

Provided is an anchor coating agent which is excellent in storage stability and can form an anchor coat layer excellent in inkjet printability, coating film durability, and hiding power. The present invention relates to an anchor coating agent containing a white pigment, an ionic salt, and an aqueous resin having an acid value of 50 mgKOH/g or less.

Claims

1. An anchor coating agent comprising a white pigment, an ionic salt, and an aqueous resin having an acid value of 50 mgKOH/g or less.

2. The anchor coating agent according to claim 1, wherein the white pigment is titanium oxide.

3. The anchor coating agent according to claim 1, wherein the ionic salt is a dissociable metal salt.

4. The anchor coating agent according to claim 3, wherein the ionic salt is a calcium salt.

5. The anchor coating agent according to claim 1, wherein the aqueous resin having an acid value of 50 mg KOH/g or less has a glass transition temperature of 70° C. or lower.

6. The anchor coating agent according to claim 1, which is used for coating a surface of a linerboard or corrugated cardboard.

Description

DESCRIPTION OF EMBODIMENTS

[0076] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0077] Unless otherwise specified, “%” means “mass %” and “part(s)” means “part(s) by mass”.

[0078] The raw materials used in the following examples and comparative examples to prepare anchor coating agents are listed below.

<White Pigment>

[0079] Titanium oxide (TITANIX JR-809 available from Tayca Corporation, average particle size: 230 nm)

<Dispersant>

[0080] Tego Dispers 750W (available from Evonik, solids content: 40%)

<Aqueous Resin>

[0081] Acrylic resin emulsion (P-1) (available from Nippon Carbide Industries Co., Inc., FX2043, acid value: 10 mg KOH/g, glass transition temperature: 10° C., solids content: 50 mass %, aqueous medium: water)

[0082] Other acrylic resin emulsions were prepared by the following procedure.

[0083] To a mixture of monomers consisting of 1.5 parts by mass of acrylic acid, 68.5 parts by mass of methyl methacrylate, and 30 parts by mass of butyl acrylate were added 3 parts by mass of Aqualon HS-10 (available from DKS Co. Ltd.) as a surfactant and an aqueous solution obtained by dissolving 0.3 parts by mass of potassium persulfate in 46 parts by mass of distilled water. The mixture was emulsified in advance with a stirrer. A polymerization vessel equipped with a stirrer, a condenser, a thermometer, and a nitrogen introduction tube was charged with 20 parts by mass of distilled water and then purged with nitrogen. When the temperature of the vessel was raised to 80° C., the above emulsion of the monomers was added dropwise over three hours and the resulting mixture was further reacted for two hours, whereby the polymerization was completed. Here, a small amount of potassium persulfate was added at the late stage of the polymerization to consume the residual monomers. To the obtained emulsion was added sodium hydroxide to adjust the pH of the emulsion to 7. Thereafter, distilled water was added so that the solids concentration was 50 mass %. Thereby, an acrylic resin emulsion (P-2) (acid value: 10 mg KOH/g, glass transition temperature: 30° C., solids content: 50 mass %, aqueous medium: water) was obtained.

[0084] The composition of the monomer mixture in the synthesis of the acrylic resin emulsion (P-2) was changed to a composition containing 1.5 parts by mass of acrylic acid, 89.5 parts by mass of methyl methacrylate, and 9 parts by mass of butyl acrylate to obtain an acrylic resin emulsion (P-3) (acid value: 10 mg KOH/g, glass transition temperature: 70° C., solids content: 50%, aqueous medium: water).

[0085] The composition of the monomer mixture in the synthesis of the acrylic resin emulsion (P-2) was changed to a composition containing 1.5 parts by mass of acrylic acid, 40 parts by mass of methyl methacrylate, and 58.5 parts by mass of butyl acrylate to obtain an acrylic resin emulsion (P-4) (acid value: 10 mg KOH/g, glass transition temperature: −10° C., solids content: 50 mass %, aqueous medium: water).

[0086] The composition of the monomer mixture in the synthesis of the acrylic resin emulsion (P-2) was changed to a composition containing 4 parts by mass of acrylic acid, 53 parts by mass of methyl methacrylate, and 43 parts by mass of butyl acrylate to obtain an acrylic resin emulsion (P-5) (acid value: 30 mg KOH/g, glass transition temperature: 10° C., solids content: 50 mass %, aqueous medium: water).

[0087] The composition of the monomer mixture in the synthesis of the acrylic resin emulsion (P-2) was changed to a composition containing 9.0 parts by mass of acrylic acid, 44.7 parts by mass of methyl methacrylate, and 46.3 parts by mass of butyl acrylate to obtain an acrylic resin emulsion (P-6) (acid value: 70 mg KOH/g, glass transition temperature: 10° C., solids content: 50 mass %, aqueous medium: water).

<Polyolefin Wax>

[0088] Polyethylene wax (available from Mitsui Chemicals, Inc., CHEMIPEARL W-400)

<Ionic Salt>

[0089] Calcium chloride

Example 1

[0090] Titanium oxide, a dispersant, and water in proportions shown in Table 1 were stirred and mixed, followed by kneading using a bead mill according to a common method. The resulting kneaded product was further kneaded with the acrylic resin emulsion (P-1), polyethylene wax, and calcium chloride, so that an anchor coating agent was obtained.

Examples 2 to 7 and Comparative Examples 1 to 3

[0091] Anchor coating agents were obtained by the same procedure as in Example 1, except that the formulation was changed to those shown in Table 1.

(Storage Stability Evaluation)

[0092] The anchor coating agents obtained in Examples 1 to 7 and Comparative Examples 1 to 3 each were stored in an airtight container at 40° C. for seven days to determine the presence or absence of viscosity increase, separation, and sedimentation. The anchor coating agent was evaluated by the following criteria.

[0093] Excellent: almost no viscosity increase, separation, or sedimentation was observed.

[0094] Good: more viscosity increase, separation, and/or sedimentation than Excellent was/were observed.

[0095] Acceptable: more viscosity increase, separation, and/or sedimentation than Good was/were observed at levels that caused no operational problems.

[0096] Poor: there was difficulty in use due to a large viscosity increase, a large amount of separation, and/or sedimentation.

<Formation of Anchor Coat Layer>

[0097] One surface of a linerboard (K Liner, basis weight 140 g/m.sup.2, brown liner) was coated with the anchor coating agent obtained in each of Examples 1 to 7 and Comparative Examples 1 to 3 using a hand proofer (165 lines) such that the solids content was 5 g/m.sup.2. The anchor coating agent was dried with a dryer, whereby an anchor coat layer was formed.

(Inkjet Printability Evaluation)

[0098] On each of the anchor coat layers formed using the anchor coating agents obtained in Examples 1 to 7 and Comparative Examples 1 to 3 were printed 0.3-mm thin lines by an inkjet printer (available from Seiko Epson Corporation, PX105) using an inkjet ink (available from Seiko Epson Corporation, IC4CL69). Thickening of the lines due to bleeding was visually observed to evaluate the inkjet printability based on the following criteria.

[0099] Good: the printing was clear and there was no bleeding.

[0100] Acceptable: there was slight bleeding in the printing, but the thickening was not twice or more the original thickness.

[0101] Poor: partial bleeding and twice or more thickening were observed in the printing.

[0102] Unacceptable: there was difficulty in use because there were many lines with bleeding and twice or more thickening.

(Coating Film Resistance Evaluation)

[0103] Linerboards having the respective anchor coat layers formed using the anchor coating agents obtained in Examples 1 to 7 and Comparative Examples 1 to 3 each were cut to 2.5 cm×25 cm to obtain a sample piece.

[0104] Using a color fastness rubbing tester (available from Tester Sangyo Co., Ltd.), a surface (coated with the anchor coat layer) of the obtained sample piece was rubbed twice with a 200-g weight in a reciprocating manner using as a protective sheet a cotton cloth on which 5 drops of water were dropped.

[0105] Thereafter, the surface of the sample piece was visually observed, and the coating film durability was evaluated based on the following criteria.

[0106] Excellent: no coating was transferred.

[0107] Good: the white pigment slightly adhered to the protective sheet. The white pigment of the anchor coat layer was transferred in a small amount.

[0108] Acceptable: the white pigment adhered to the entire surface of the protective sheet. The white pigment of the anchor coat layer was transferred, and part of the linerboard was visible.

[0109] Poor: the white pigment adhered strongly to the entire surface of the protective sheet. The white pigment of the anchor coat layer was transferred and most of the linerboard was visible.

(Hiding Power Evaluation)

[0110] The anchor coat layers formed using the anchor coating agents obtained in Examples 1 to 7 and Comparative Examples 1 to 3 were visually observed, and the hiding power thereof was evaluated based on the following criteria.

[0111] Excellent: the coating film was white enough that the underlying linerboard was invisible.

[0112] Good: the coating film was white, but the underlying linerboard was not completely covered.

[0113] Acceptable: the coating film was a little white, and the brown color of the underlying linerboard was visible.

[0114] Poor: the coating film was transparent, and the underlying linerboard was visible therethrough.

TABLE-US-00001 TABLE 1 Examples Comparative Examples 1 2 3 4 5 6 7 1 2 3 Titanium oxide 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 — (parts by mass) Dispersant (parts by mass) 12.5 12.5 12.5 12.5 — 12.5 12.5 12.5 12.5 — Water (parts by mass) 10.5 10.5 10.5 10.5 23.0 10.5 10.5 10.5 15.5 73.0 Acrylic resin emulsion P-1 20.0 — — 10.0 20.0 — — — — 20.0 (parts by mass) P-2 — 20.0 — — — — — — — — P-3 — — 20.0 — — — — — — — P-4 — — — — — 20.0 — — — — P-5 — — — — — — 20.0 — — — P-6 — — — — — — — 20.0 20.0 — Polyethylene-based wax 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 (parts by mass) Calcium chloride (parts 5.0 5.0 5.0 15.0 5.0 5.0 5.0 5.0 — 5.0 by mass) Total (parts by mass) 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Storage stability evaluation Excellent Excellent Good Good Acceptable Good Good Poor Excellent Excellent Inkjet printability evaluation Good Good Good Good Good Good Good Acceptable Unacceptable Good Coating surface resistance Excellent Good Good Good Excellent Excellent Excellent Excellent Excellent Excellent Hiding property evaluation Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Poor

[0115] As shown in Table 1, the anchor coating agents of Examples 1 to 7 each were confirmed to be excellent in storage stability and to successfully form an anchor coat layer excellent in inkjet printability, coating film durability, and hiding power.

[0116] In particular, in Examples 1, 2, and 7 in which 5 to 15 mass % as a solids content of an aqueous resin having an acid value of 20 mg KOH/g or less and a glass transition temperature of 40° C. or lower was used, the anchor coating agent was confirmed to be particularly excellent in storage stability. Also, the anchor coating agent in Example 5 was confirmed to have sufficient storage stability without a dispersant.

[0117] In Examples 1 and 5 to 7 in which an aqueous resin having a glass transition temperature of 20° C. or lower was used, an anchor coat layer having particularly excellent coating film durability was confirmed to be successfully formed.

[0118] In contrast, Comparative Example 1 in which an aqueous resin having a predetermined acid value was not used was inferior in storage stability. Comparative Example 2 in which an ionic salt was not used was inferior in inkjet printability. Comparative Example 3 in which a white pigment was not used was inferior in hiding power.

INDUSTRIAL APPLICABILITY

[0119] The present invention can provide an anchor coating agent which is excellent in storage stability and can form an anchor coat layer excellent in ink-jet printability, coating film durability, and hiding power.