Base paper for release paper and release paper

Abstract

The present invention provides a base paper for release paper in which the sealing layer can be easily separated and easily recycled. [Solution] The present invention relates to a base paper for release paper, wherein a sealing layer is laminated on at least one side of a base paper, and the sealing layer is a resin layer formed from a sealing layer forming composition mainly composed of a water-based polyurethane resin. Furthermore, in the release paper of the present invention, the release layer is laminated on the side of the release paper base paper opposite to the side of the sealing layer on which the base paper is provided.

Description

[Technical Field]

[0001] This invention relates to base paper for release paper and release paper. [Background technology]

[0002] Release paper is used as a backing to protect the adhesive surface of adhesive labels, adhesive stickers, adhesive tapes, etc., from the adhesion of dirt and other debris. The surface that comes into contact with the adhesive surface is coated with a release agent such as silicone resin. Conventional release paper is manufactured by coating the surface of a base paper such as polyethylene laminate paper, glassine paper, clay coated paper, or clear coated paper with a release agent. However, these release agents are used after being diluted with organic solvents such as toluene, which poses a problem of environmental damage. Therefore, in recent years, there has been a growing demand for water-based emulsion type silicone resins and solvent-free silicone resins.

[0003] Furthermore, since silicone resin used as a release agent is very expensive, it is necessary for the base paper for release paper to minimize the penetration of the silicone resin coating liquid into the base paper in order to enable the uniform application of a small amount of silicone resin coating liquid. However, in recent years, from the perspective of resource conservation, recyclability has also become a requirement.

[0004] To suppress the penetration of release agents such as silicone resin, a release paper base in which polyethylene is laminated to the base paper is preferable. However, it has the disadvantage that it is difficult to separate the release paper after use, making it unsuitable for recycling.

[0005] To improve upon the above drawbacks, a base paper for release paper is known, comprising a sealing layer containing at least a pigment component and an adhesive component on at least one surface of the base paper, wherein the median diameter (D50) of the pigment component measured by laser diffraction using a scattering particle size distribution analyzer is 2.0 to 7.0 μm, the adhesive component contains at least synthetic resin latex, and the amount of synthetic resin latex blended with 100 parts by mass of the pigment component (absolutely dry) is 8 to 20 parts by mass (absolutely dry) (see Patent Document 1).

[0006] Furthermore, there is a known release paper for adhesive labels characterized by having a tightness of 0.9 to 1.1 when an underlayer containing a tackifier with a softening point of 170°C or lower, a sealing layer containing a water-soluble resin, and a release agent layer are sequentially formed on the surface of ordinary paper made from wood pulp with a freeness of 350 to 500 ml CSF (see Patent Document 2).

[0007] Furthermore, there is a known release paper characterized by sequentially providing a sealing layer made of a water-soluble resin, an intermediate layer made of a water-soluble resin, and a release layer on at least one surface of a base paper made of pulp with a beaten degree of 20 to 44°SR (see Patent Document 3).

[0008] Furthermore, an acrylate-based latex containing a copolymer of ethyl acrylate and butyl acrylate is added to a water-dispersible paper substrate at a solid content of 0.5 to 10 g / m². 2 Apply to form a sealing layer, and then apply solvent-free silicone at a solid content equivalent of 0.3 to 3 g / m² on top of the sealing layer. 2 Release paper is known that is characterized by having a release layer formed by coating (see Patent Document 4). [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2016-223036 [Patent Document 2] Japanese Patent Publication No. 2005-010513 [Patent Document 3] Japanese Patent Publication No. 2002-166504 [Patent Document 4] Japanese Patent Application Publication No. 06-305087 [Overview of the project] [Problems that the invention aims to solve]

[0010] The present invention provides a novel base paper for release paper that does not use conventional polyolefin resins such as ethylene, and in which the sealing layer can be easily disintegrated and easily recycled. [Means for solving the problem]

[0011] As a result of diligent research to solve the aforementioned problems, the inventors of the present invention discovered that the problems could be solved by using a specific resin in the sealing layer, and thus completed the present invention.

[0012] In other words, the present invention relates to a base paper for release paper, wherein a sealing layer is laminated on at least one surface of a base paper, and the sealing layer is a resin layer formed from a sealing layer forming composition mainly composed of a water-based urethane resin. This invention relates to a release paper in which a release layer is laminated on the surface opposite to the surface of the sealing layer on which the base paper is provided, of the aforementioned release paper base paper. [Effects of the Invention]

[0013] By using the release paper base paper of the present invention, the decomposition properties of the sealing layer are good, so the base paper can be easily reused. [Brief explanation of the drawing]

[0014] [Figure 1] This figure schematically shows a cross-section of a release liner and a base paper for release liner according to one embodiment of the present invention. [Modes for carrying out the invention]

[0015] Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. 1. Note that the scope of the present invention is not limited to the release paper shown in FIG. 1. As shown in FIG. 1, the base paper 1 for release paper of the present invention is a base paper 1 for release paper formed by laminating a blocking layer 3 on at least one surface 2b of a base paper 2, and the blocking layer 3 is a resin layer formed from a composition for forming a blocking layer mainly composed of an aqueous polyurethane resin.

[0016] The base paper 2 used for the base paper 1 for release paper of the present invention is mainly composed of wood pulp fibers. As the wood pulp fibers, chemical pulps such as softwood kraft pulp, hardwood kraft pulp, and sulfite pulp, mechanical pulps such as stone ground pulp, thermomechanical pulp, and refiner ground pulp, and recycled pulp obtained from newspapers, coated paper, fine paper, etc. can be appropriately blended and used. In addition, non-wood pulps such as kenaf, hemp, and bamboo, and fiber materials other than cellulose fibers such as glass fibers and polyethylene fibers may be blended with the base paper 2 as needed.

[0017] When forming the base paper 2, internal additives such as sizing agents, paper strength enhancers, fixing agents, yield improvers, and dyes, and internal fillers such as talc, kaolin, titanium dioxide, aluminum hydroxide, and calcium carbonate can be added, or during the papermaking process, paper strength improvers such as starch and polyvinyl alcohol, surface sizing agents, and dyes can be applied using a size press, gate roll, etc. Appropriate surface treatment may be performed.

[0018] The base paper 2 preferably has a thickness of 40 μm or more and 300 μm or less. When the thickness of the base paper 2 is less than 40 μm, the occurrence of wrinkles increases during the production of the release paper. On the other hand, when the thickness of the base paper 2 exceeds 300 μm, the rigidity becomes too high and the handleability decreases.

[0019] The basis weight of the base paper 2 is preferably 40 g / m 2 or more and 200 g / m 2 or less, more preferably 50 g / m 2 or more and 160 g / m 2The following is more preferable: The basis weight of the base paper 2 is 40 g / m². 2 If the basis weight is less than 200 g / m², the paper strength will be weak and the paper may not be suitable for processing. On the other hand, the basis weight of base paper 2 is 200 g / m². 2 Exceeding this limit may result in poor handling.

[0020] The water-based polyurethane resin used in forming the sealing layer 3 of the present invention refers to a polyurethane resin that is soluble in water or emulsifiable in water. A water-soluble aqueous polyurethane resin refers to a urethane resin having hydrophilic groups. This water-soluble aqueous polyurethane resin is also called a self-emulsifying aqueous polyurethane resin. Examples of this water-soluble aqueous polyurethane resin include polyurethane resins having hydrophilic groups (anionic hydrophilic groups, cationic hydrophilic groups, or nonionic hydrophilic groups) in the molecule, and polyurethane resins to which hydrophilic segments have been added.

[0021] Furthermore, the water-emulsifiable water-based polyurethane resin refers to a polyurethane resin in which the polyurethane resin is encapsulated by a surfactant, making it dispersible in water. The water-emulsifiable water-based polyurethane resin is also called a forced-emulsification type water-based polyurethane resin. Generally, the water-emulsifiable water-based polyurethane resin is a hydrophobic polyurethane resin.

[0022] The surfactant used to obtain the water-based polyurethane resin that can be emulsified in water is one or more selected from anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, polymeric surfactants, and reactive surfactants. Specifically, examples of the anionic surfactant include higher fatty acids, resin acids, acidic fatty alcohols, sulfate esters, higher alkyl sulfonates, alkylallyl sulfonates, sulfonated castor oil, and sulfosuccinate esters. Furthermore, specific examples of the nonionic surfactant include known reaction products of ethylene oxide and long-chain fatty alcohols or phenols.

[0023] The polyurethane resin contained in the aqueous polyurethane resin is formed by reacting a polyurethane raw material composition containing a polyol component, an isocyanate component, and a crosslinking agent. The polyurethane resin can be produced by known methods for producing polyurethane resins. Among the aqueous polyurethane resins, polycarbonate-based polyurethane resins are preferred from the viewpoint of durability, abrasion resistance, and hydrolysis resistance. The polycarbonate-based polyurethane can be obtained, for example, by a polyaddition reaction using a polycarbonate-based diol and a polyisocyanate.

[0024] Specific examples of polyol components used to constitute the aqueous polyurethane resin include polyether polyols and polyester polyols.

[0025] As the polyether polyol, a polyether polyol obtained by ring-opening polymerization of alkylene oxide is preferred. As the alkylene oxide, specific examples include propylene oxide (PO), ethylene oxide (EO), butylene oxide, etc., which may be used individually or in combination of two or more. As the polyether polyol, polytetramethylene ether glycol, polypropylene glycol, etc., are preferred.

[0026] Examples of the aforementioned polyester polyols include those obtained by polycondensing an aliphatic carboxylic acid such as malonic acid, succinic acid, or adipic acid, or an aromatic carboxylic acid such as phthalic acid, with a polyhydric alcohol such as ethylene glycol, diethylene glycol, or propylene glycol.

[0027] The isocyanate component used to constitute the aforementioned aqueous polyurethane resin is generally selected appropriately from isocyanates used in the production of urethane by reacting them with polyols. Specifically, examples include aromatic isocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and isocyanate-terminated prepolymers.

[0028] Examples of the isocyanate component include, specifically, diphenylmethane diisocyanate (4,4'-MDI), polymeric MDI (crude MDI), urethane-modified MDI, urea-modified MDI, allophanate-modified MDI, biuret-modified MDI, carbodiimide-modified MDI, uretonimine-modified MDI, uretdione-modified MDI, isocyanurate-modified MDI, aromatic isocyanates such as 2,4-tolylene diisocyanate (2,4-TDI) and 2,6-tolylene diisocyanate (2,6-TDI), aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate (HDI), alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated TDI, and hydrogenated MDI, and isocyanate-terminated prepolymers obtained by prepolymerizing these. The exemplified isocyanate components can be used individually or in combination of two or more. As the isocyanate component, isocyanate group-terminated prepolymers are preferred.

[0029] The aforementioned crosslinking agents are used to improve the physical properties of water-based polyurethane resins, and specific examples include isocyanate-based crosslinking agents, carbodiimide-based crosslinking agents, and oxazoline-based crosslinking agents.

[0030] When manufacturing water-based polyurethane resins, it is preferable to use a catalyst. The catalyst is not particularly limited as long as it is generally usable for manufacturing polyurethane resins, and specific examples include amine-based catalysts such as triethylenediamine and diethanolamine, and metal catalysts such as bismuth catalysts.

[0031] In addition to the polyol component, isocyanate component, catalyst, and crosslinking agent used to constitute the aqueous polypolyurethane resin, other additives may be added to the sealing layer-forming composition of the present invention as needed. Specifically, examples of these other additives include plasticizers, foam stabilizers, fillers, antioxidants, defoaming agents, compatibilizers, colorants, stabilizers, and ultraviolet absorbers, which are additives that can be commonly used in the manufacture of polyurethane foam. The amount of these other additives added may be appropriately selected within a range that does not impair the effects of the present invention.

[0032] The aforementioned water-based polyurethane resin can also be appropriately selected from commercially available products. Specific examples of commercially available products include Rackcoat WN157M (manufactured by Seiko Chemicals Co., Ltd., a water-based polycarbonate polyurethane).

[0033] The sealing layer 3 preferably has a thickness of 0.5 μm or more and 50 μm or less, and more preferably has a thickness of 5 μm or more and 50 μm or less. If the thickness of the sealing layer 3 is less than 0.5 μm, it becomes difficult to suppress the penetration of the release agent into the base paper 2. On the other hand, if the thickness of the sealing layer 3 exceeds 50 μm, it becomes unnecessarily thick and impractical.

[0034] Various additives and fillers such as clay, silica, calcium carbonate, titanium dioxide, and zinc oxide may be added to the sealing layer 3 as desired, provided that the effects of the present invention are not impaired.

[0035] There are no particular limitations on the method for forming the sealing layer 3 on one or both sides of the base paper 2. Examples include conventionally known methods such as applying a sealing layer-forming composition mainly composed of the water-based urethane resin and drying it to form the sealing layer 3, or laminating the base paper 2 and the sealing layer 3 via an adhesive.

[0036] Examples of the release agent that can be used for the release paper of the present invention include, for example, silicone resins, fluorine compounds, amino alkyd compounds, polyester compounds, etc. Among them, silicone resins are preferably mentioned. Specific examples of the silicone resin include solventless silicone resins, solvent-based silicone resins, water-based emulsion silicone resins, solventless UV-curable silicone resins, and the like.

[0037] The release paper of the present invention is, for example, 0.5 to 2.0 g / m on the surface 3b of the blocking layer 3 provided with the base paper 2 of the base paper 1 for release paper, which is opposite to the surface 3a. 2 It can be obtained by applying a release agent so as to obtain a release layer 4. Further, as a method for applying the release agent to the base paper 1 for release paper, various coating devices such as a blade coater, an air knife coater, a rod blade coater, a bar blade coater, a gravure coater, etc. can be appropriately selected and used.

[0038] In addition, the 75° gloss of the surface 4b of the release layer 4 of the release paper of the present invention is preferably 70 to 90%, and more preferably 75 to 85%. If the 75° gloss is less than 70%, a uniform coating surface of the release agent cannot be obtained. Further, if the 75° gloss exceeds 90%, the release layer 4 becomes excessively thick, and the adhesion between the base paper 1 for release paper and the release layer 4 becomes insufficient.

Examples

[0039] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples in any way.

Examples

[0040] Coated and dried the high-quality paper 2 with a water-based urethane resin 1 (solid content 35%) so that the solid content was 3 g / m to obtain a base paper 1a for release paper. Also, coated and dried a water-based urethane resin 2 (solid content 32%) so that the solid content was 10 g / m to obtain a base paper 1b for release paper. 2 2 A black marker test liquid (an inspection liquid used to determine if the silicone coating is missing) was applied over the sealing layer 3. Those that did not penetrate to the back of each release paper base 1a and 1b were judged to have a sealing effect, while those that penetrated to the back of each release paper base 1a and 1b were judged to have no sealing effect. As a result, release paper base 1a and 1b were judged to have a sealing effect.

[0041] Release agents (products A, B, C, CZ, and D) were applied to the sealing layer 3 of release paper bases 1a and 1b in the solid content amounts shown in Table 1, and dried at 120°C to obtain release papers 10-1 to 10-8. Comparative release papers 11-1 to 11-5 were obtained in the same manner as release papers 10-1 to 10-8, except that polyethylene was used as the sealing layer 3. The adhesion and release strength of release papers 1-1 to 1-8 and comparative release papers 11-1 to 11-5 were evaluated. The release agents (products A, B, C, CZ, and D) use silicone resin. Adhesion was assessed by rubbing each release paper 10 times with the pad of a finger. If the release layer 4 did not peel off the sealing layer 3, it was judged to have good adhesion (○). If the release layer 4 peeled off the sealing layer 3, it was judged to have poor adhesion (×). We measured the peeling force of the release paper that exhibited good adhesion. The peeling force was measured in accordance with IS Z 0237. The results are shown in Table 1.

[0042] [Table 1] PU1: Water-based polyurethane resin 1 PU2: Water-based polyurethane resin 2 PE: Polyethylene

[0043] It has been confirmed that the release papers 10-1 to 10-8 of the present invention have equivalent performance to conventional comparative release papers 11-1 to 11-5, in which the resin constituting the sealing layer 3 is polyethylene. From the above, it has been determined that the base paper and release papers for release papers of the present invention can be used in the same way as release papers currently on the market. [Industrial applicability]

[0044] The release paper base paper of the present invention can be used for release papers such as those used for various types of seals.

Claims

1. A base paper for release paper, comprising a base paper with a sealing layer laminated on at least one surface thereof, wherein the sealing layer is a resin layer formed from a sealing layer-forming composition mainly composed of a water-based polyurethane resin.

2. A release paper according to claim 1, wherein the release layer is laminated on the side opposite to the side of the sealing layer on which the base paper is provided.

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