Coating composition and coating paper

Abstract

To provide a coating composition that can impart gas barrier properties to paper while reducing the environmental burden, and that does not impair the properties derived from paper.SOLUTION: The coating composition used for coating substrates made of paper contains naturally occurring polysaccharides and water.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a coating composition and a coated paper. [Background technology]

[0002] BACKGROUND ART Materials containing paper have traditionally been used as packaging materials.

[0003] Furthermore, paper-containing materials that have been given gas barrier properties against oxygen and the like are known. For example, Patent Document 1 describes a material in which a resin layer containing an ethylene-vinyl alcohol copolymer (EVOH) is laminated onto a paper substrate. Furthermore, Patent Document 2 describes a material in which a resin layer containing a polyvinyl alcohol resin (PVA) is laminated onto a paper substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-94574 [Patent Document 2] International Publication No. 2022 / 030519 Summary of the Invention [Problem to be solved by the invention]

[0005] However, coated paper with a resin layer formed using petroleum-derived materials such as EVOH and PVA does not decompose in nature and may place a burden on the environment.

[0006] Furthermore, even if the coated paper has a functional layer that exhibits gas barrier properties against oxygen and the like, it is desired that the paper still exhibit the properties (strength, flexibility, etc.) inherent in the original paper.

[0007] In view of the above circumstances, an object of the present invention is to provide a coating composition that can impart gas barrier properties to paper while reducing the environmental impact and without impairing the inherent properties of the paper. Another object of the present invention is to provide coated paper that can exhibit these properties. [Means for solving the problem]

[0008] The coating composition according to the present invention comprises: Used to coat paper substrates, It contains naturally occurring polysaccharides and water.

[0009] When used to coat paper substrates, the coating composition of the present invention can impart a layer with gas barrier properties to the paper while reducing the environmental impact due to the naturally occurring polysaccharides. Furthermore, the coating composition of the present invention can form a film by itself without being laminated to a substrate, and can impart gas barrier properties to coated paper produced in combination with a paper substrate with a smaller coating weight than a film produced by itself. Furthermore, the coating composition of the present invention can prevent the inherent properties of paper, such as strength and flexibility, from being impaired due to the naturally occurring polysaccharides that have a high affinity with paper.

[0010] In a preferred embodiment of the coating composition of the present invention, the polysaccharide is galactoxyloglucan, pullulan, or a water-soluble alginate such as sodium alginate, and the galactoxyloglucan is tamarind seed gum.

[0011] The coating composition of this embodiment can impart better gas barrier properties to paper.

[0012] In a more preferred embodiment of the present invention, the coating composition contains a plasticizer. The plasticizer is preferably selected from the group consisting of glycerin, diglycerin, triglycerin, trimethylolpropane, sugar alcohols having 4 to 6 carbon atoms, and polyoxyalkylene polyglyceryl ether. The content of the plasticizer is preferably 5% by mass or more and 45% by mass or less of the total mass of the polysaccharide and the plasticizer.

[0013] The coating composition of this embodiment can enhance flexibility, a property inherent to paper, by including a plasticizer, and the combination of galactoxyloglucan and a plasticizer can provide the paper with better gas barrier properties.

[0014] Next, the coated paper according to the present invention has: A substrate made of paper and a coating layer laminated on the substrate, The coating layer contains a naturally occurring polysaccharide.

[0015] Coated paper of this construction, which has a coating layer containing naturally occurring polysaccharides, can exhibit gas barrier properties and other inherent paper properties while reducing the environmental impact.

[0016] In a preferred embodiment of the coated paper of the present invention, the polysaccharide is galactoxyloglucan, pullulan, or a water-soluble alginate such as sodium alginate, and the galactoxyloglucan is tamarind seed gum.

[0017] Coated paper of this embodiment can exhibit better gas barrier properties.

[0018] In a more preferred embodiment of the coated paper of the present invention, the coating layer may contain a plasticizer. The plasticizer is preferably selected from the group consisting of glycerin, diglycerin, triglycerin, trimethylolpropane, sugar alcohols having 4 to 6 carbon atoms, and polyoxyalkylene polyglyceryl ether. The content of the plasticizer is preferably 5% to 45% by mass of the total mass of the polysaccharide and the plasticizer.

[0019] Coated paper of this configuration can exhibit flexibility, a property inherent to paper, due to the inclusion of a plasticizer in the coating layer. Furthermore, a coating layer containing galactoxyloglucan and a plasticizer can exhibit superior gas barrier properties. [Effects of the Invention]

[0020] As described above, the present invention can provide a coating composition that can reduce the environmental impact, impart gas barrier properties to paper, and not impair the inherent properties of the paper.The present invention also can provide coated paper that can exhibit these properties. DETAILED DESCRIPTION OF THE INVENTION

[0021] The coating composition according to an embodiment of the present invention will be described.

[0022] The coating composition according to this embodiment is used for coating a substrate made of paper and contains a naturally occurring polysaccharide and water. The coating composition may further contain a plasticizer.

[0023] Examples of the substrate include coated printing paper such as coated paper, unbleached wrapping paper such as unbleached kraft paper, and bleached wrapping paper such as bleached kraft paper. The substrate has a coated surface, which is the front or back surface to which the coating composition is applied. Both surfaces of the substrate may be coated. The substrate has a porous structure formed from cellulose fibers from the front surface to the back surface. The coated surface may be formed from the cellulose fibers. Furthermore, when the substrate is coated printing paper, the coated surface may be formed from a coating agent that can be penetrated by the coating composition containing water, a coating agent containing a polysaccharide such as starch, or a coating agent containing a pigment such as kaolin, talc, barium sulfate, or calcium carbonate, and has pores.

[0024] The basis weight of the substrate is, for example, 50 to 500 g / m 2 and 50 to 200 g / m 2 The basis weight of the substrate can be measured by the measurement method specified in JIS P 8124.

[0025] The naturally occurring polysaccharides refer to polysaccharides in which functional groups such as hydroxyl groups and amino groups have not been chemically converted. Examples of such chemical conversions include etherification, esterification, amidation, reduction, and oxidation. More specifically, the polysaccharides include those in which hydroxyl groups have not been converted to aldehyde groups or carboxyl groups by oxidation. Other examples include those in which hydroxyl groups or amino groups have not been chemically modified to have ester bonds or amide bonds by acetylation or the like, those in which hydroxyl groups have not been chemically modified to have ether bonds using a silane coupling agent or the like, and those that have not been graft-polymerized. The naturally occurring polysaccharides may be purified as needed.

[0026] Examples of such naturally occurring polysaccharides include galactoxyloglucans such as tamarind seed gum, pullulan, gum arabic, guar gum, xanthan gum, and water-soluble alginates. Examples of the water-soluble alginates include potassium alginate, sodium alginate, and ammonium alginate, which is a salt of alginic acid and ammonia. Among these, tamarind seed gum, pullulan, and sodium alginate are preferred.

[0027] The naturally occurring polysaccharides may be those obtained by partially decomposing the main chain or side chain of the above-mentioned polysaccharides through enzymatic degradation using a microbial enzyme, or those obtained by partially decomposing the main chain or side chain through acid degradation using an inorganic acid or an organic acid. Such partially decomposed polysaccharides are preferred because they are considered to have a lower environmental impact than petroleum-derived synthetic resins such as EVOH and PVA.

[0028] Examples of polysaccharides obtained by enzymatic hydrolysis include partial xyloglucan hydrolysates in which the galactose in the side chains of the galactoxyloglucan has been partially removed. The partial xyloglucan hydrolysates are obtained by partially removing the D-galactose in the side chains of the galactoxyloglucan. The partial xyloglucan hydrolysates are produced by enzymatically hydrolyzing the tamarind seed gum with β-galactosidase. The partial xyloglucan hydrolysates are preferably gelled by heating an aqueous solution containing 1% by mass of the partial xyloglucan hydrolysate to 30°C or higher, preferably 40°C or higher.

[0029] An example of a polysaccharide obtained by acid hydrolysis is an acid hydrolyzate of tamarind seed gum. It is preferable that such an acid hydrolyzate has a viscosity of 10 to 100 mPa·s in a 1.5% by mass aqueous solution at 25°C. The viscosity here refers to a value measured using a Brookfield viscometer (B-type viscometer) at a rotation speed of 30 rpm.

[0030] The naturally occurring polysaccharides are preferably derived from plants, microorganisms, or seaweed.

[0031] The coating composition may contain only one type of naturally occurring polysaccharide, or may contain two or more types of naturally occurring polysaccharide.

[0032] Examples of the plasticizer include glycerin, diglycerin, triglycerin, polyglycerin having a degree of polymerization of 3 to 20 (preferably 10 or less in terms of water solubility), glycols having a 1,2-dihydroxy structure such as propylene glycol and pentylene glycol, glycols having a 1,3-dihydroxy structure such as isoprene glycol, 1,3-butylene glycol, and trimethylolpropane, ether condensates of glycols such as dipropylene glycol, polyethylene glycol, and polyoxyalkylene polyglyceryl ether, sugar alcohols having 4 to 6 carbon atoms such as sorbitol, glucose, mannitol, and xylitol, and disaccharides such as trehalose. Among these, sorbitol, glycerin, diglycerin, triglycerin, trimethylolpropane, and polyoxyethylene polyglyceryl ether are preferred. The polyoxyalkylene polyglyceryl ether is preferably polyoxyethylene polyglyceryl ether having a degree of polymerization of 2 to 10. In this case, the amount of ethylene oxide added is preferably, for example, 1 mole or more and 10 moles or less. This ensures that the polyoxyethylene polyglyceryl ether and the polysaccharide are sufficiently compatible with each other. These may be used alone or in combination.

[0033] When the polysaccharide is a galactoxyloglucan such as tamarind seed gum, the plasticizer is preferably used in combination with the polysaccharide.

[0034] The coating composition preferably contains the naturally occurring polysaccharide in an amount of 0.5% to 50% by mass, more preferably 1% to 20% by mass, based on the total mass of the coating composition. When the naturally occurring polysaccharide is a galactoxyloglucan such as tamarind seed gum or the water-soluble alginate, the content is preferably 1% to 10% by mass, more preferably 1% to 5% by mass. When the naturally occurring polysaccharide is pullulan, the content may be 1% to 30% by mass, or even 1% to 20% by mass.

[0035] The coating composition preferably contains the plasticizer in an amount of 0.1% by mass to 10% by mass, more preferably 0.3% by mass to 5% by mass, and even more preferably 0.3% by mass to 3% by mass, based on the total mass of the coating composition.

[0036] The content of the plasticizer is preferably smaller than the content of the naturally occurring polysaccharide, and specifically, it is preferably 5% by mass or more and 45% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, relative to the total mass of the polysaccharide and the plasticizer.

[0037] The water may be ordinary tap water, but purified water such as distilled water or ion-exchanged water is preferred.

[0038] The coating composition may contain additives commonly used in the coating field, such as antifoaming agents, surface conditioners, preservatives, dispersants, inorganic fillers, and fibrous materials (e.g., cellulose nanofibers).

[0039] Next, the coated paper produced using the coating composition will be described.

[0040] The coated paper comprises a substrate made of the paper and a coating layer laminated on the substrate.

[0041] The coating layer is formed using the coating composition. Examples of the method for forming the coating layer include a method in which a coating film of the coating composition is formed on the substrate using a coating device, and excess water contained in the coating film is removed by heating and drying to form the coating layer.

[0042] The coating layer formed by such a method contains the naturally occurring polysaccharide and may further contain the plasticizer. The coating layer preferably contains the naturally occurring polysaccharide, such as tamarind seed gum, pullulan, or sodium alginate, which is a galactoxyloglucan, and more preferably contains the plasticizer. In particular, the coating layer preferably contains tamarind seed gum and the plasticizer.

[0043] The substrate may be impregnated with a portion of the naturally occurring polysaccharide and the plasticizer.

[0044] The coating amount of the polysaccharide in the coating layer is 1 g / m when the plasticizer is not contained. 2 It is preferable that the content is 2 g / m or more. 2 The coating amount of the polysaccharide in the coating layer is preferably 20 g / m or more when the plasticizer is not contained. 2 It may be less than 15 g / m 2 When the coating layer contains the plasticizer, the coating amount of the polysaccharide in the coating layer may be 1 g / m or less. 2 When the coating layer contains the plasticizer, the coating amount of the polysaccharide is preferably 15 g / m or more. 2 may be less than 12 g / m 2 or less, and even 10 g / m 2 It may be less than 8 g / m 2 It may be less than 5 g / m 2 It may be the following:

[0045] The coating amount of the plasticizer in the coating layer is, for example, 0.1 g / m 2 More than 10g / m 2 less than or equal to 0.1 g / m 2More than 5g / m 2 The content of the plasticizer in the coating layer is preferably smaller than the content of the naturally occurring polysaccharide, and specifically, it is preferably 5% by mass or more and 45% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, based on the total mass of the polysaccharide and the plasticizer.

[0046] The coated paper has an oxygen permeability of 100 cm 3 / m 2 The oxygen permeability may be less than 24h atm. The oxygen permeability can be measured at 23°C using gas chromatography according to JIS K 7126-1:2006. One reason why the coated paper exhibits such low oxygen permeability is that the polysaccharides, such as tamarind seed gum, form a film on the coated surface of the substrate, physically blocking the porous structure. In this physical blocking process, the polysaccharides have a sugar chain structure similar to that of the cellulose fibers constituting the substrate, which gives them a high affinity with the substrate and allows them to exhibit good adhesion to the substrate, i.e., high blocking properties for the porous structure of the substrate. Furthermore, the polysaccharides have a large number of hydroxyl groups in their molecules, making them highly polar, which is thought to inhibit the permeation of low-polarity molecules such as oxygen gas. In particular, tamarind seed gum, pullulan, and sodium alginate are thought to have such excellent blocking properties, thereby providing the coating layer with barrier properties against low-polarity gases such as oxygen. Such coated paper is suitable for use as packaging material for foods such as confectionery and seasonings, as well as for trays and paper containers.

[0047] Furthermore, the coating layer containing the polysaccharide and the plasticizer can have excellent conformability to the substrate. This allows the coating layer to suppress cracking due to expansion, contraction, or bending without impairing the flexibility of the substrate. Coated paper having such a coating layer is suitable as a packaging material for three-dimensionally shaped articles.

[0048] Although the embodiments have been shown above as examples, the coating composition and coated paper of the present invention are not limited to the configurations of the above-mentioned embodiments. Furthermore, the coating composition and coated paper of the present invention are not limited by the above-mentioned effects. The coating composition and coated paper of the present invention can be modified in various ways without departing from the gist of the present invention.

[0049] For example, the coated paper of the present invention may have other functional layers in addition to the coating layer that exhibits gas barrier properties, such as a moisture barrier layer. [Example]

[0050] The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples.

[0051] [Raw materials used] (polysaccharide) Tamarind seed gum (MP Gokyo Food & Chemical Co., Ltd.) Tamarind seed gum acid hydrolysate (MP Gokyo Food & Chemical Co., Ltd.) Pullulan ·Sodium alginate (chemically modified polysaccharides) Hydroxypropyl methylcellulose (petroleum-derived resin) Polyvinyl alcohol (plasticizer) Sorbitol Glycerin Diglycerin Triglycerin Polyoxyethylene polyglyceryl ether (EO addition amount: 4 moles) Trimethylolpropane (Paper substrate) Coated paper (basis weight 55 g / m 2 ) Bleached kraft paper (basis weight 50g / m 2 ) Unbleached kraft paper (basis weight 50g / m 2 )

[0052] [Manufacturing Example 1] Coating compositions were prepared according to the formulations shown in Tables 1 to 4. The prepared coating compositions were applied to a paper substrate using a bar coater and dried to form a coating layer, thereby obtaining coated paper.

[0053] [Evaluation method 1: Oxygen permeability] The oxygen permeability of each sample was measured by gas chromatography (at 23°C) according to JIS K 7126-1, and evaluated according to the following criteria. The results are shown in Tables 1 to 4. (Evaluation criteria) ○:100cm 3 / m 2 ·24h·Less than ATM ×:100cm 3 / m 2 ·24h · atm or more

[0054] [Evaluation method 2: Tensile properties] The tensile strength and tensile elongation at break of the coated paper and each of the other coated papers were measured according to the method described in JIS P 8113. The measurement conditions were a test piece width of 15 mm, a distance between the grippers of 90 mm, an elongation rate of 20 mm / min, a temperature of 23°C, and a humidity of 50%. The results are shown in Tables 2 to 4. [Evaluation method 3: Flexibility] The tensile elongation at break measured by Evaluation Method 2 was used and evaluated according to the following evaluation criteria. The results are shown in Tables 2 to 4. (Evaluation criteria) ○: Tensile elongation at break is greater than that of the substrate and is at least 1 time that of the substrate ×: Tensile elongation at break is less than that of the base material

[0055] [Table 1]

[0056] Each of Examples 1 to 3 in Table 1 has a coating layer containing tamarind seed gum, pullulan, and sodium alginate, and is coated with a coating weight of 3 to 10 g / m 2The paper in Comparative Example 1 showed good gas barrier properties within the coating amount range. On the other hand, Comparative Example 1 was coated paper that was not coated with a coating composition and therefore did not show gas barrier properties. These comparisons demonstrate that gas barrier properties can be imparted to a substrate by forming a coating layer on the substrate using a coating composition containing the above polysaccharide. Comparative Example 2 was formed with a coating layer containing hydroxypropyl methylcellulose, a chemically modified cellulose, but did not show the desired gas barrier properties. Comparative Example 3 was formed with a coating layer containing polyvinyl alcohol and showed the desired gas barrier properties, but polyvinyl alcohol is a petroleum-derived resin, which is not preferred.

[0057] [Table 2]

[0058] The coating composition used to prepare Examples 4 to 11 in Table 2 contains a plasticizer in addition to a polysaccharide. Examples 4 to 11 were prepared using this coating composition, with various changes to the coating amount and paper substrate. Each example did not impair the flexibility of the paper substrate and exhibited good gas barrier properties. Regarding the coating amount, the evaluation results for Example 1 showed that a coating composition containing no plasticizer required a coating amount of 5 g / m2 to impart gas barrier properties. 2 In contrast, the evaluation results of Example 4 show that the combined use of a plasticizer reduces the coating weight to 2 g / m 2 It can be seen that good gas barrier properties can be imparted with a coating amount of 1000. Furthermore, Examples 5, 6 and 9 exhibited appropriate flexibility and were superior in strength to the original paper substrate.

[0059] [Table 3]

[0060] Example 12 in Table 3 had a lower proportion of plasticizer than Example 5, but exhibited gas barrier properties and flexibility similar to those of Example 5.

[0061] [Table 4]

[0062] Table 4 shows the evaluation results of coated papers when the type of plasticizer combined with the polysaccharide was changed. Examples 13 to 17 showed good gas barrier properties. Furthermore, Examples 13, 14, and 17 showed gas barrier properties similar to Example 5, and also showed values ​​for tensile strength and tensile elongation at break equivalent to those of Example 5, indicating that they were excellent in strength and flexibility.

[0063] [Reference example] A coating composition was prepared by dissolving the components shown in Table 5 in water. The composition was applied to a plastic substrate using a bar coater or cast, dried, and the plastic substrate was peeled off to produce a film.

[0064] [Table 5]

[0065] The evaluation results of the Reference Examples in Table 5 show that in order to produce a film with the desired gas barrier properties, it is necessary to use a higher coating weight of polysaccharide than coated paper. In other words, it is clear that the combination of a paper substrate and a polysaccharide can produce coated paper with synergistic gas barrier properties. This is thought to be due to the high affinity of the polysaccharide, which fills the porous structure formed by cellulose fibers in the substrate, with the cellulose fibers, and the intermolecular interactions that result from the numerous hydroxyl groups present in both the polysaccharide and the cellulose fibers. These factors are thought to enable good gas barrier properties to be obtained in coated paper applications, even with a relatively low coating weight.

Claims

1. Used to coat paper substrates, A coating composition comprising a naturally occurring polysaccharide and water.

2. The coating composition of claim 1 , wherein the polysaccharide is galactoxyloglucan, pullulan, or a water-soluble alginate.

3. The coating composition of claim 2 , wherein the galactoxyloglucan is tamarind seed gum.

4. The coating composition according to claim 1 , further comprising a plasticizer.

5. 5. The coating composition according to claim 4, wherein the plasticizer is selected from the group consisting of glycerin, diglycerin, triglycerin, trimethylolpropane, sugar alcohols having 4 to 6 carbon atoms, and polyoxyalkylene polyglyceryl ethers.

6. The coating composition according to claim 4 , wherein the content of the plasticizer is 5% by mass or more and 45% by mass or less based on the total mass of the polysaccharide and the plasticizer.

7. A substrate made of paper and a coating layer laminated on the substrate, Coated paper, wherein the coating layer contains a naturally occurring polysaccharide.

8. 8. The coated paper of claim 7, wherein the polysaccharide is galactoxyloglucan, pullulan, or a water-soluble alginate.

9. 9. The coated paper of claim 8, wherein the galactoxyloglucan is tamarind seed gum.

10. 10. The coated paper according to claim 7, wherein the coating layer further comprises a plasticizer.

11. 11. The coated paper according to claim 10, wherein the plasticizer is selected from the group consisting of glycerin, diglycerin, triglycerin, trimethylolpropane, sugar alcohols having 4 to 6 carbon atoms, and polyoxyalkylene polyglyceryl ethers.

12. 11. The coated paper according to claim 10, wherein the content of the plasticizer is 5% by mass or more and 45% by mass or less, based on the total mass of the polysaccharide and the plasticizer.

Images