(Meth)acrylic resin composition, inkjet printing substrate, (meth)acrylic resin laminate, key holder, strap, stand, and card

Abstract

Provided is a (meth)acrylic resin composition that can provide a (meth)acrylic resin laminate that can form an inkjet printing layer having higher inkjet printing adhesion and better inkjet printing resolution without providing a primer layer on the surface of a substrate for inkjet printing. [Solution] A (meth)acrylic resin composition containing a (meth)acrylic polymer (P) containing repeating units derived from methyl methacrylate and repeating units derived from an acrylic acid ester (a), and one or more ascorbic acids selected from the group consisting of ascorbic acid and ascorbic acid derivatives, preferably one or more ascorbic acids selected from the group consisting of reductone compounds and their oxidized products.

Description

[Technical Field]

[0001] The present invention relates to a (meth)acrylic resin composition, a substrate for inkjet printing, a (meth)acrylic resin laminate, a key holder, a strap, a stand, and a card. [Background technology]

[0002] Transparent resins such as (meth)acrylic resins, polycarbonate-based resins, and styrene-based resins have excellent transparency and mechanical properties, and are used in a wide range of applications, such as decorative items, display items such as signboards and advertisements, and displays. In particular, (meth)acrylic resins have been increasingly adopted for the above applications in recent years because they can produce clean cut surfaces during laser cutting and emit little odor.

[0003] The main uses of the decorative articles described above include key holders, straps, stands, and cards. Specifically, images such as letters, numbers, symbols, patterns, and characters are printed by inkjet printing on the surface of a sheet-shaped molded product ((meth)acrylic resin sheet) made of a (meth)acrylic resin composition cut to a work size, and then the product is cut into the shape of the final product using a laser cutting machine according to the printed shape and processed into a predetermined shape to be commercialized as a key holder, strap, stand, or card.

[0004] For applications in decorative items such as key holders, straps, stands, and cards, a substrate is required that has high adhesion (inkjet printing adhesion) to an inkjet printing layer formed from an inkjet printing ink so that the inkjet printing layer does not peel off from the (meth)acrylic resin laminate. In addition, when images such as letters, numbers, symbols, patterns, and characters are printed on the surface of a (meth)acrylic resin sheet, a substrate having high printing resolution is required so that the color and shape of the printed image can be clearly seen.

[0005] As a technique for improving the inkjet printing adhesion of a (meth)acrylic resin sheet, for example, Patent Document 1 discloses a UV ink fixing structure in which an adhesive primer layer is provided on the surface of a substrate such as a (meth)acrylic resin. Patent Document 2 discloses a substrate for inkjet printing made of an acrylic copolymer having a specific amount of repeating units derived from methyl methacrylate and a specific amount of repeating units derived from an acrylic ester.

[0006] As an example of a (meth)acrylic resin composition containing a reductone compound, Patent Document 3 discloses a method for polymerizing poly(methyl methacrylate) characterized by carrying out bulk polymerization or suspension polymerization in the presence of a redox catalyst system comprising a peroxygen compound selected from the group consisting of peroxyesters and diacyl peroxides and 6-O-alkanoyl-L-ascorbic acid as a reducing agent. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-52378 [Patent Document 2] Japanese Patent Application Publication No. 2019-214200 [Patent Document 3] Japanese Patent Application Publication No. 56-93706 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the technique disclosed in Patent Document 1 requires the provision of an additional primer layer, which has problems such as a decrease in the transparency inherent in (meth)acrylic resins and an increase in costs. Furthermore, the inkjet printing substrate disclosed in Patent Document 2 leaves room for further improvement in inkjet printing adhesion and inkjet printing resolution.

[0009] Patent Document 3 does not mention the use of the polymethyl methacrylate as a substrate for inkjet printing. However, since the polymethyl methacrylate disclosed in Patent Document 3 is not copolymerized with any (meth)acrylic acid ester other than methyl methacrylate, when used as a substrate for inkjet printing, the inkjet printing adhesion and inkjet printing resolution are inferior, as shown in Comparative Example 1 below.

[0010] The present invention has been made to solve the above-mentioned problems. Specifically, an object of the present invention is to provide a (meth)acrylic resin composition capable of forming a substrate for inkjet printing that can achieve higher inkjet printing adhesion and better inkjet printing resolution without providing a primer layer on an inkjet printing layer formed from an inkjet printing ink, and to provide a substrate for inkjet printing, a (meth)acrylic resin laminate, a key holder, a strap, a stand, and a card that use the (meth)acrylic resin composition. [Means for solving the problem]

[0011] As a result of extensive investigations to solve the above problems, the present inventors have found that the above problems can be solved by including a specific ascorbic acid in a (meth)acrylic resin composition constituting a substrate for inkjet printing.

[0012] [1] A (meth)acrylic resin composition comprising a (meth)acrylic polymer (P) containing a repeating unit derived from methyl methacrylate and a repeating unit derived from an acrylic acid ester (a), and one or more ascorbic acids selected from the group consisting of ascorbic acid and ascorbic acid derivatives. [2] The (meth)acrylic resin composition according to [1], wherein the ascorbic acid compound is one or more compounds selected from the group consisting of reductone compounds and their oxidized products. [3] The (meth)acrylic resin composition according to [1] or [2], wherein the content of the ascorbic acid compound in the (meth)acrylic resin composition is 0.001 ppm or more and 10,000 ppm or less. [4] The (meth)acrylic resin composition according to [2] or [3], wherein the reductone compound is at least one selected from the group consisting of (iso)ascorbic acid, salts thereof, and derivatives thereof. [5] The (meth)acrylic resin composition according to any one of [1] to [4], wherein the content of repeating units derived from methyl methacrylate in the (meth)acrylic polymer (P) is 70% by mass or more and 99% by mass or less. [6] The (meth)acrylic resin composition according to any one of [1] to [5], wherein the content of repeating units derived from the acrylic acid ester (a) in the (meth)acrylic polymer (P) is 1% by mass or more and 30% by mass or less. [7] The (meth)acrylic resin composition according to any one of [1] to [6], which is produced by bulk polymerization. [8] A substrate for inkjet printing, comprising the (meth)acrylic resin composition according to any one of [1] to [7]. [9] A (meth)acrylic resin laminate comprising the substrate for inkjet printing according to [8] and an inkjet printing layer formed on the surface of the substrate for inkjet printing.

[10] The (meth)acrylic resin laminate according to [9], wherein the inkjet printed layer is formed by curing an energy ray-curable composition.

[11] A key holder comprising the (meth)acrylic resin laminate according to [9] or

[10] .

[12] A strap comprising the (meth)acrylic resin laminate according to [9] or

[10] .

[13] A stand comprising the (meth)acrylic resin laminate according to [9] or

[10] .

[14] A card comprising the (meth)acrylic resin laminate according to [9] or

[10] .

[15] A method for producing a (meth)acrylic resin composition according to any one of [1] to [7], comprising a step of bulk polymerizing a polymerizable composition containing a (meth)acrylic polymer (P) including a repeating unit derived from methyl methacrylate and a repeating unit derived from an acrylic acid ester (a), and one or more ascorbic acids selected from the group consisting of ascorbic acid and ascorbic acid derivatives.

[16] The method for producing a (meth)acrylic resin composition according to

[15] , wherein the ascorbic acid compound is one or more compounds selected from the group consisting of reductone compounds and their oxidized products. [Effects of the Invention]

[0013] An inkjet printing substrate using the (meth)acrylic resin composition of the present invention can obtain high inkjet printing adhesion to an inkjet printing layer formed from an inkjet printing ink without providing a primer layer, and can also obtain excellent inkjet printing resolution. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below. However, the following description is an example of an embodiment of the present invention, and the present invention is not limited to the following description as long as it does not deviate from the gist of the present invention.

[0015] In the present invention, the term "monomer" refers to an unpolymerized compound, and the term "repeating unit" refers to a unit derived from a monomer formed by polymerization of the monomer. The repeating unit may be a unit formed directly by a polymerization reaction, or may be a unit in which a part of the unit is converted into a different structure by treating the polymer. "(Meth)acrylate", "(meth)acrylic acid", "(meth)acrylic", and "(iso)ascorbic acid" respectively mean at least one selected from "acrylate" and "methacrylate", at least one selected from "acrylic acid" and "methacrylic acid", at least one selected from "acrylic" and "methacrylic", and at least one selected from "ascorbic acid" and "isoascorbic acid". Additionally, "mass %" indicates the number of parts by weight of a particular component. Unless otherwise specified, in this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits, and "A to B" means A or more and B or less.

[0016] <Inkjet printing substrate> The substrate for inkjet printing of the present invention is a substrate for inkjet printing made of the (meth)acrylic resin composition of the present invention, which contains a (meth)acrylic polymer (P) including a repeating unit derived from methyl methacrylate and a repeating unit derived from an acrylic acid ester (a), and an ascorbic acid compound described below.

[0017] The inkjet printing substrate of the present invention is made of the (meth)acrylic resin composition of the present invention, and can achieve high inkjet printing adhesion and excellent inkjet printing resolution without providing a primer layer, and is therefore suitable for applications such as decorative items, signs for display and advertisements, and displays, etc. Among decorative items, the substrate is particularly suitable for applications such as key holders, straps, stands, and cards.

[0018] <(Meth)acrylic resin composition> The (meth)acrylic resin composition of the present invention is suitably used as a constituent component of the inkjet printing substrate of the present invention, and contains a (meth)acrylic polymer (P) containing a repeating unit derived from methyl methacrylate and a repeating unit derived from an acrylic acid ester (a), which will be described later, and an ascorbic acid compound, which will be described later. The (meth)acrylic resin composition contains the (meth)acrylic polymer (P) and an ascorbic acid compound described below, and thereby can constitute a substrate for inkjet printing that exhibits high inkjet printing adhesion and excellent inkjet printing resolution without providing a primer layer.

[0019] The (meth)acrylic resin composition of the present invention may be constituted of 100% by mass of the (meth)acrylic polymer (P) other than the ascorbic acid compound. When the (meth)acrylic resin composition of the present invention contains components other than the (meth)acrylic polymer (P) and ascorbic acids, the (meth)acrylic resin composition of the present invention preferably contains 80% by mass or more of the (meth)acrylic polymer (P) relative to 100% by mass of the total mass of the (meth)acrylic resin composition. When the content of the (meth)acrylic polymer (P) in the (meth)acrylic resin composition of the present invention is 80% by mass or more, the (meth)acrylic polymer (P) can maintain good mechanical strength and weather resistance in addition to the transparency inherent to the (meth)acrylic polymer (P).

[0020] <(Meth)acrylic polymer (P)> The (meth)acrylic polymer (P) is a constituent component of the (meth)acrylic resin composition of the present invention. From the viewpoint of achieving good inkjet printing adhesion, the (meth)acrylic polymer (P) contains repeating units derived from methyl methacrylate (hereinafter referred to as "MMA units") and repeating units derived from an acrylate ester (a) (described below) (hereinafter referred to as "acrylate ester (a) units").

[0021] The MMA unit is a component that imparts transparency, heat resistance, and surface hardness to the inkjet printing substrate of the present invention.

[0022] The acrylic acid ester (a) unit is a component that imparts high inkjet printing adhesion and excellent inkjet printing resolution to the inkjet printing substrate of the present invention without providing a primer layer. Examples of the acrylic acid ester (a), from the viewpoint of improving inkjet printing adhesion and inkjet printing resolution, include acrylic acid esters having a hydrocarbon group having 1 to 18 carbon atoms on the ester side chain, or acrylic acid esters having an aromatic hydrocarbon group on the ester side chain, or acrylic acid esters having an alicyclic hydrocarbon group having 3 to 20 carbon atoms on the ester side chain, acrylic acid esters having an alkoxy group or alkylalkoxy group having 1 to 9 carbon atoms on the ester side chain, acrylic acid esters having a hydroxyl group on the ester side chain, and acrylic acid esters having a carboxylic acid group on the ester side chain. Specifically, examples thereof include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, t-butyl acrylate, i-butyl acrylate, n-butyl acrylate, i-amyl acrylate, n-pentyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, i-decyl acrylate, lauryl acrylate, stearyl acrylate, cyclohexyl acrylate, bornyl acrylate, norbornyl acrylate, isobornyl acrylate, adamantyl acrylate, dimethyladamantyl acrylate, methylcyclohexyl acrylate, norbornylmethyl acrylate, menthyl acrylate, fenchyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, cyclodecyl acrylate, 4-t-butylcyclohexyl acrylate, trimethylcyclohexyl acrylate, phenyl acrylate, benzyl acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, Examples of acrylic acid esters include cyclic trimethylolpropane formal acrylate, 3,3,5-trimethylcyclohexyl acrylate, methoxyethyl acrylate, methoxypolyethylene glycol acrylate, ethoxyethoxyethyl acrylate, ethoxydiethylene glycol acrylate, 2-ethylhexyl diglycol acrylate, methoxydipropylene glycol acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate, phenoxyethyl acrylate, phenoxypolyethylene glycol acrylate, phenoxydiethylene glycol acrylate, m-phenoxybenzyl acrylate, 1-naphthalenemethyl acrylate, methylphenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl-2-hydroxyethyl phthalate, and 2-acryloyloxyethyl succinate. These acrylic acid esters (a) may be used alone or in combination of two or more. Among these acrylic acid esters (a), from the viewpoint of achieving good inkjet printing adhesion, acrylic acid esters having a hydrocarbon group having 1 to 13 carbon atoms on the ester side chain are more preferred, and 2-ethylhexyl acrylate, n-butyl acrylate, methyl acrylate, and ethyl acrylate are even more preferred.

[0023] The lower limit of the content of MMA units in the (meth)acrylic polymer (P) is not particularly limited, but from the viewpoint of improving the transparency, heat resistance, and surface hardness of the inkjet printing substrate, it is preferably 70% by mass or more, more preferably 80% by mass or more, and particularly preferably 85% by mass or more, relative to the total mass (100% by mass) of the (meth)acrylic polymer (P). On the other hand, the upper limit of the content of MMA units is not particularly limited, but from the viewpoint of ensuring the content of acrylic acid ester (a) units and improving the inkjet printing adhesion and inkjet printing resolution of the inkjet printing substrate, it is preferably 99% by mass or less, more preferably 97% by mass or less, and particularly preferably 95% by mass or less, relative to the total mass (100% by mass) of the (meth)acrylic polymer (P). The above upper and lower limits can be combined arbitrarily.

[0024] The lower limit of the content of the acrylic acid ester (a) units in the (meth)acrylic polymer (P) is not particularly limited, but from the viewpoint of improving the inkjet printing adhesion and inkjet printing resolution of the inkjet printing substrate, it is preferably 1% by mass or more, more preferably 3% by mass or more, and particularly preferably 5% by mass or more, relative to the total mass (100% by mass) of the (meth)acrylic polymer (P). On the other hand, the upper limit of the content of the acrylic acid ester (a) units is not particularly limited, but from the viewpoint of ensuring the content of the MMA units and maintaining good transparency, heat resistance, and surface hardness of the inkjet printing substrate, it is preferably 30% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less, relative to the total mass (100% by mass) of the (meth)acrylic polymer (P). The above upper and lower limits can be combined arbitrarily.

[0025] Furthermore, the (meth)acrylic polymer (P) may contain repeating units derived from vinyl monomers other than the MMA unit and the acrylic acid ester (a) unit, as long as the performance of the inkjet printing substrate of the present invention is not impaired. Specific examples of the other vinyl monomers include methacrylic acid esters other than methyl methacrylate, unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and itaconic acid, acid anhydrides such as maleic anhydride and itaconic anhydride, maleimide derivatives such as N-phenylmaleimide and N-cyclohexylmaleimide, vinyl esters such as vinyl acetate and vinyl benzoate, nitrogen-containing monomers such as vinyl chloride, vinylidene chloride, and derivatives thereof, methacrylamide, and acrylonitrile, epoxy group-containing monomers such as (meth)acrylic acid glycidyl acrylate, and aromatic compounds having an ethylenically unsaturated bond in the molecule such as styrene and α-methylstyrene. These other monomers may be used alone or in combination of two or more.

[0026] <Ascorbic acids> The ascorbic acids are one or more selected from the group consisting of ascorbic acid and ascorbic acid derivatives, and are constituent components of the (meth)acrylic resin composition of the present invention. That is, in the present invention, the term "ascorbic acids" collectively refers to ascorbic acid and a wide variety of derivatives of ascorbic acid. The (meth)acrylic resin composition of the present invention contains an ascorbic acid compound, and therefore the inkjet printing substrate of the present invention using the (meth)acrylic resin composition of the present invention exhibits excellent inkjet printing adhesion and inkjet printing resolution without providing a primer layer. Ascorbic acid and ascorbic acid derivatives are 1 C(OH)=C(OH)C(=O)R 2 They are classified into reductone compounds that have a reductone structure and non-reductone compounds that do not have a reductone structure.

[0027] The reason why the (meth)acrylic resin composition of the present invention, when it contains an ascorbic acid, results in good inkjet printing adhesion and inkjet printing resolution is not clear, but it is thought that when an ascorbic acid is present in the polymerization reaction system for obtaining the (meth)acrylic polymer (P), the ascorbic acid is localized on the surface of the polymerizable raw material (S1) described below during the polymerization reaction and is oxidized, thereby generating radicals locally and promoting specific polymerization reactions and curing reactions on the surface of the polymerizable raw material (S1), thereby achieving good inkjet printing adhesion and inkjet printing resolution.

[0028] <Reductone compounds> Reductone compounds and their oxidized products are one embodiment of the ascorbic acids according to the present invention. "Reductone compounds" are R 1 C(OH)=C(OH)C(=O)R 2 It refers to compounds having the structure (reductone structure) and their salts. 1 and R 2 may each independently represent any organic substituent, or may be joined together to form a ring structure. 1 C(OH)=C(OH)-C(=O)R 2 Examples of compounds having this structure (a partial structure in which a carbonyl group is bonded next to an enediol group) include glycinic acid and its derivatives, reductic acid and its derivatives, (iso)ascorbic acid and its isomers and derivatives, etc. The reductone compounds include oxidized forms (deprotonated reductones: R 1 C(=O)-C(=O)-C(=O)R 2 Among these, at least one selected from (iso)ascorbic acid, its isomers, derivatives, salts thereof, and oxidized forms thereof is preferred because of its low cost, low toxicity, low environmental impact, and high safety.

[0029] (Iso)ascorbic acid and its isomers and derivatives are not particularly limited, and examples include L-ascorbic acid or isoascorbic acid and its sugar derivatives (e.g., γ-lactoascorbic acid, glucoascorbic acid, fucoascorbic acid, glucoheptoascorbic acid, and maltoascorbic acid), and L-ascorbic acid or isoascorbic acid and its ester derivatives (e.g., L-ascorbyl 5-palmitate, L-ascorbyl 6-palmitate, L-ascorbyl 5,6-dipalmitate, L-ascorbyl 5-stearate, L-ascorbyl 6-stearate, L-ascorbyl 5,6-distearate, L-ascorbyl 5-phosphate, L-ascorbyl 6-phosphate, and 5,6-L-ascorbyl diphosphate). Furthermore, salts of (iso)ascorbic acid and its isomers and derivatives include salts of the above-mentioned compounds (e.g., alkali metal salts, ammonium salts, or salts known in the art), such as sodium ascorbic acid and potassium ascorbic acid, as well as magnesium L-ascorbyl phosphate. Among these, at least one of the reductone compounds and their oxidized forms is preferably at least one selected from (iso)ascorbic acid, its salts, and their oxidized forms. As the salt of (iso)ascorbic acid, an alkali metal salt is preferred, and a sodium salt is more preferred. If necessary, a mixture of these reductone compounds can be used.

[0030] <Non-reductone compounds> The non-reductone compound is one embodiment of the ascorbic acid compound according to the present invention. Non-reductone compounds are compounds in which the hydroxyl group of a reductone compound is replaced with another substituent, R 1 C(OH)=C(OH)C(=O)R 2 It does not have a reductone structure. The non-reductone compounds are not particularly limited, but examples thereof include 3-cetyl ether-L-ascorbyl, 2,6-dipalmitic acid-L-ascorbyl, and 2,3,5,6-tetraisopalmitic acid-L-ascorbyl.

[0031] <Ascorbic acid content> The content of ascorbic acids in the (meth)acrylic resin composition of the present invention is preferably 0.001 ppm or more and 10,000 ppm or less, based on 100% by mass of the total mass of the (meth)acrylic resin composition. The content of ascorbic acids in the (meth)acrylic resin composition can be determined by the method described in the Examples section below.

[0032] From the viewpoint of obtaining excellent inkjet printing adhesion and inkjet printing resolution, the content of ascorbic acids in the (meth)acrylic resin composition of the present invention is more preferably 0.01 ppm or more, even more preferably 0.1 ppm or more, and particularly preferably 1 ppm or more. Furthermore, from the viewpoint of maintaining the inherent high heat resistance of the (meth)acrylic resin composition, the content of ascorbic acids in the (meth)acrylic resin composition of the present invention is more preferably 5000 ppm or less, even more preferably 2000 ppm or less, and particularly preferably 1000 ppm or less. The above-mentioned preferred upper and lower limits can be combined arbitrarily.

[0033] As described below, ascorbic acids can be contained in the acrylic resin composition of the present invention by adding them to the polymerizable raw material (S1) that is the raw material for producing the (meth)acrylic resin composition.

[0034] The reductone compounds and their oxidized products and non-reductone compounds listed above are examples of the ascorbic acids according to the present invention, but the ascorbic acids according to the present invention are not limited to the above compounds, and other compounds may also be used. The ascorbic acids may be used alone or in combination of two or more. That is, one or more types of reductone compounds and their oxidized products may be used, one or more types of non-reductone compounds may be used, or one or more types of reductone compounds and their oxidized products may be used in combination with one or more types of non-reductone compounds.

[0035] The ascorbic acid compound can be added to the polymerizable raw material (S1) described below so that the content of the ascorbic acid compound in the (meth)acrylic resin composition of the present invention falls within the above-mentioned range. A solvent may be used when adding the ascorbic acid compound. Examples of the solvent include water and alcohols such as ethanol, ethylene glycol, propylene glycol, and glycerin.

[0036] As is clear from the analysis results of the content ratio of ascorbic acids in the examples given below, ascorbic acids, particularly reductone compounds, are reducing substances and are therefore oxidized to their oxidized forms under heating conditions during the production of the (meth)acrylic resin composition described below. Therefore, even if a reductone compound is added to the polymerizable raw material (S1), the resulting (meth)acrylic resin composition and inkjet printing substrate will contain a portion of the reductone compound as its oxidized form.

[0037] <Polymerizable raw material (S1)> The polymerizable raw material (S1) is a raw material for the polymerizable composition (S2) according to the present invention. The polymerizable raw material (S1) is a monomer composition containing methyl methacrylate and an acrylic acid ester (a).

[0038] The polymerizable raw material (S1) may contain a polymer (P1) containing MMA units as a main component in advance. Here, "contains as a main component" means that the polymer contains 85.0% by mass or more of the MMA unit, with the total mass of the polymer being 100% by mass. The polymer (P1) is a homopolymer of methyl methacrylate or a copolymer containing, relative to the total mass of the polymer (P1), 70% by mass or more and less than 99% by mass of MMA units and more than 1% by mass and not more than 30% by mass of repeating units derived from other monomers copolymerizable with methyl methacrylate. The other monomer copolymerizable with methyl methacrylate can be the same as the above-mentioned "acrylic acid ester (a)" and "other vinyl monomer other than MMA units and acrylic acid ester (a) units."

[0039] <Polymerizable composition (S2)> The polymerizable composition (S2) is a raw material for the inkjet printing substrate of the present invention. The polymerizable composition (S2) can contain the polymerizable raw material (S1), an ascorbic acid, and further a known polymerization initiator and chain transfer agent.

[0040] By including the polymer, the polymerizable composition (S2) becomes a viscous liquid (also called "syrup"), and therefore the polymerization time can be shortened and productivity can be improved.

[0041] As a method for obtaining the above-mentioned polymerizable composition (S2), for example, the following two methods can be mentioned. (Method 1) A method of dissolving the polymer in a monomer mixture containing methyl methacrylate, the methyl methacrylate, another monomer copolymerizable with the methyl methacrylate, and an ascorbic acid. (Method 2) A method in which a known radical polymerization initiator is added to a monomer mixture containing methyl methacrylate, or 70% by mass or more but less than 99% by mass of methyl methacrylate, more than 1% by mass but less than 30% by mass of another monomer copolymerizable with the methyl methacrylate, and an ascorbic acid, to polymerize a portion of the mixture, and then a predetermined amount of at least one monomer selected from methyl methacrylate and the monomer copolymerizable with the methyl methacrylate is added.

[0042] The radical polymerization initiator used when polymerizing the monomer mixture to obtain the polymerizable composition (S2) is not particularly limited, and examples thereof include azo polymerization initiators such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, and 2,2'-azobis-(2,4-dimethylvaleronitrile); and organic peroxide polymerization initiators such as lauroyl peroxide, diisopropyl peroxydicarbonate, benzoyl peroxide, bis(4-t-butylcyclohexyl) peroxydicarbonate, t-butyl peroxyneodecanoate, and t-hexyl peroxypivalate. These initiators can be used alone or in combination of two or more as needed. The amount of radical polymerization initiator added is preferably 0.05 to 1% by mass relative to 100% by mass of the monomer mixture.

[0043] The polymerization temperature during radical polymerization can be appropriately determined depending on the purpose, and is set appropriately within the range of 10 to 150° C. depending on the type of radical polymerization initiator used. Furthermore, the polymerizable composition (S2) can be polymerized under multi-stage temperature conditions as needed.

[0044] Examples of radical polymerization methods include bulk polymerization, suspension polymerization, emulsion polymerization, and dispersion polymerization, and among these, bulk polymerization is preferred from the viewpoint of productivity.

[0045] <Other additives> The polymerizable composition (S2) may contain various additives that have been conventionally used, if necessary, such as surfactants, leveling agents, colorants such as dyes and pigments, antioxidants, ultraviolet absorbers, heat stabilizers, flame retardants, plasticizers, release agents, solvents, and additives for imparting functions.

[0046] The amount of the additive added is determined appropriately within a range that does not impair the physical properties of the resulting inkjet printing substrate, and can be 10 parts by mass or less relative to 100 parts by mass of the polymerizable composition (S2).

[0047] <Method of manufacturing substrate for inkjet printing> The substrate for inkjet printing of the present invention, which is made of the (meth)acrylic resin composition of the present invention, can be produced by heating and polymerizing the polymerizable composition (S2). The method for producing the substrate for inkjet printing of the present invention is not particularly limited, and the substrate for inkjet printing of the present invention can be produced using, for example, a known cast polymerization method such as a cell casting method or a continuous casting method, or an extrusion molding method or an injection molding method. From the viewpoint that the obtained substrate for inkjet printing has excellent printing adhesion and heat resistance, the cast polymerization method is particularly preferred.

[0048] The cast polymerization method is a method in which the peripheries of two inorganic glass plates or metal plates (SUS plates) arranged opposite each other are sealed with gaskets such as soft resin tubes to form a mold, and then the polymerizable composition (S2) described above is poured into the mold, polymerized and cured by bulk polymerization, and the cured product is peeled off from the mold to obtain a sheet-like molded product made of the (meth)acrylic resin composition of the present invention, which is used as a substrate for inkjet printing.

[0049] Examples of molds used in the cell casting method include two plate-like bodies such as inorganic glass plates, chrome-plated metal plates, and stainless steel plates, arranged opposite each other at a predetermined distance, with a soft resin gasket placed on the edges of the bodies to form a sealed space between the plates and the gasket.

[0050] An example of a mold used in the continuous casting method is one in which a sealed space is formed by the opposing surfaces of a pair of endless belts running in the same direction at the same speed and soft resin gaskets running at the same speed as the endless belts on both side edges of the endless belts.

[0051] The gap of the mold is adjusted as appropriate depending on the diameter of the soft resin gasket described above so that a resin plate of the desired thickness can be obtained, but is generally 1 to 30 mm.

[0052] The polymerization method when using the cast polymerization method is not particularly limited, and for example, a known polymerization method used in the production of an acrylic polymer or a styrene resin can be used. Specifically, a so-called bulk polymerization method using a monomer as a polymerization solvent can be carried out under radical polymerization conditions.

[0053] The radical polymerization initiator added to the polymerizable composition (S2) for radical polymerization is not particularly limited, and examples thereof include azo polymerization initiators such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, and 2,2'-azobis-(2,4-dimethylvaleronitrile); and organic peroxide polymerization initiators such as lauroyl peroxide, diisopropyl peroxydicarbonate, benzoyl peroxide, bis(4-t-butylcyclohexyl) peroxydicarbonate, t-butyl peroxyneodecanoate, and t-hexyl peroxypivalate. These initiators can be used alone or in combination of two or more as needed. The amount of radical polymerization initiator added is preferably 0.05 to 1% by mass relative to 100% by mass of the polymerizable composition (S2). In addition to the radical polymerization initiator, additives such as a mold release agent, an ultraviolet absorber, a heat stabilizer, a light stabilizer, and a colorant may also be added as needed.

[0054] The polymerization temperature is not particularly limited, but is preferably 40 to 180° C., more preferably 50 to 150° C. The polymerization time may be appropriately determined depending on the progress of polymerization and curing.

[0055] <Inkjet printing ink> The type of ink for inkjet printing that can be used for the substrate for inkjet printing of the present invention is not particularly limited, and an energy ray-curable composition that cures from a liquid state to a solid state within seconds upon irradiation with active energy rays and forms a film of an inkjet printing layer can be used. Examples of active energy rays include electron beams, ultraviolet rays, and visible light, with ultraviolet rays being preferred from the viewpoint of equipment costs and productivity. Examples of light sources for active energy rays include ultraviolet LED lamps, fluorescent ultraviolet lamps, ultra-high pressure mercury lamps, high pressure mercury lamps, medium pressure mercury lamps, low pressure mercury lamps, metal halide lamps, Ar lasers, He—Cd lasers, solid-state lasers, xenon lamps, high frequency induction mercury lamps, and sunlight.

[0056] The inkjet printing ink can use a known energy ray-curable composition containing at least one photopolymerizable monomer selected from a known monofunctional monomer, a known polyfunctional monomer, and a known oligomer, and a known photopolymerization initiator. The energy ray-curable composition can contain, as necessary, a sensitizer, a pigment, a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a plasticizer, a solvent, an antifoaming agent, a dispersant, a leveling agent, a surfactant, etc. Commercially available inkjet printing inks include, for example, LH-100, LUS-120, and LUS-350 (manufactured by Mimaki Engineering Co., Ltd.) and ECO-UV ink (manufactured by Roland DG Corporation).

[0057] <Acrylic resin laminate and method for producing the same> The acrylic resin laminate of the present invention is a resin laminate comprising the inkjet printing substrate of the present invention and an inkjet printing layer formed adjacent to the surface of the inkjet printing substrate. Examples of a method for producing the acrylic resin laminate of the present invention include a method in which images such as letters, numbers, symbols, patterns, and characters are printed collectively on the surface of the inkjet printing substrate of the present invention using the inkjet printing ink to form a film of the inkjet printing ink, and then the film is irradiated with active energy rays such as ultraviolet rays and cured to form an inkjet printing layer on the surface of the inkjet printing substrate.

[0058]

[0043] Examples of a method for printing the inkjet printing ink on the surface of the inkjet printing substrate of the present invention include a method in which an inkjet printing ink is ejected from an ejection head of an inkjet printer onto the surface of the inkjet printing substrate to form a film.

[0059] The acrylic resin laminate of the present invention has sufficiently good adhesion between the inkjet printing layer formed from the inkjet printing ink and the inkjet printing substrate, without providing a primer layer on the surface of the inkjet printing substrate, and can form an inkjet printing layer that is less likely to bleed and has good printing resolution.

[0060] <Key holders, stands, straps, cards> The acrylic resin laminate of the present invention, on which the above-mentioned images of letters, numbers, symbols, patterns, characters, etc. are printed, is cut into the shape of the final product using cutting means such as a laser processing machine according to the shape of the image, thereby obtaining the key holder, stand, strap, and card of the present invention.

[0061] The inkjet printing substrate, acrylic resin laminate, key holder, stand, strap and card of the present invention can ensure sufficiently good adhesion between the inkjet printing layer formed from the inkjet printing ink and the inkjet printing substrate without providing a primer layer, and can form an inkjet printing layer with good printing resolution. That is, since the inkjet printing substrate and acrylic resin laminate of the present invention have the above-mentioned characteristics, they are particularly suitable for key chains for bundling keys, straps for mobile phones and the like, stands on which images of characters or the like are printed, and cards. [Example]

[0062] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0063] <Compound abbreviation> The abbreviations for the compounds used in the following Examples and Comparative Examples are as follows: MMA: Methyl methacrylate (Mitsubishi Chemical Corporation) BA: n-butyl acrylate (Mitsubishi Chemical Corporation) MA: Methyl acrylate (Mitsubishi Chemical Corporation) AA: L-ascorbic acid (Fujifilm Wako Pure Chemical Industries, Ltd.) IAA: Isoascorbic acid (Tokyo Chemical Industry Co., Ltd.) AS: 6-stearate-L-ascorbyl (Tokyo Chemical Industry Co., Ltd.) AP: 6-L-ascorbyl palmitate (Tokyo Chemical Industry Co., Ltd.) AC: 3-Cetyl ether-L-ascorbyl (Nikko Chemicals Co., Ltd.) ADP: 2,6-dipalmitic acid-L-ascorbyl (Tokyo Chemical Industry Co., Ltd.) GMH: Glucose monohydrate (manufactured by Sanei Sugar Chemical Co., Ltd.) TPP: Triphenylphosphine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) RL: Rongalite (Kanto Chemical Co., Ltd.)

[0064] <Evaluation method> Evaluations in the following examples and comparative examples were carried out by the following methods.

[0065] (1) Content of acrylic ester (a) units and MMA units The content ratio of the acrylic acid ester (a) unit and the MMA unit of the (meth)acrylic polymer (P) in the (meth)acrylic resin composition was measured according to the following method. Five mg of the inkjet printing substrate was pyrolyzed at 500°C using a pyrolysis apparatus (trade name: Double Shot Pyrolyzer PY-2020D, manufactured by Frontier Labs). The generated decomposition gas was introduced into a separation column (trade name: HP-WAX, inner diameter: 0.32 mm, column length: 30 m, film thickness: 0.25 μm, manufactured by Agilent Technologies) attached to a gas chromatography measurement apparatus (trade name: HP6890, manufactured by Agilent Technologies) equipped with an FID detector. The column measurement temperature program was as follows: after holding at 50°C for 5 minutes, the temperature was increased to 200°C at a rate of 10°C / min, and then held at 200°C for 10 minutes. Acrylic acid ester (a) was separated from the generated decomposition gas using He (1.2 ml / min, linear velocity 40 cm / sec) as a carrier gas. The content (unit: mass %) of the acrylate (a) unit was calculated from a calibration curve obtained using a model polymer prepared in advance. The content (unit: mass %) of MMA units in the (meth)acrylic resin composition was calculated according to the following formula. Content of MMA units (mass%) = 100 - content of acrylic ester (a) units (mass%)

[0066] (2) Ascorbic acid content The content of L-ascorbic acid and its oxidized form (dehydrogenated form) in the (meth)acrylic resin composition was measured according to the following method. Other ascorbic acids can also be analyzed by a similar method. The inkjet printing substrate was roughly crushed using air nippers, packed into a sample tube (made of polycarbonate), and crushed using a freeze crusher (trade name: Freezer / Mill 6750, manufactured by SPEX). 1 mL of LC-MS eluent (50 mM ammonium formate aqueous solution: acetonitrile = 30:70) was added to 0.25 g of the resulting fine powder, and the mixture was immersed for 45 minutes to extract L-ascorbic acid and its oxidized products. The supernatant was filtered through a 0.2 μm PTFE filter, and 10 μL of the filtrate was introduced into a separation column (product name: HILICpak VT-50 2D, inner diameter: 2.0 mm, column length: 150 mm, particle size: 5 μm, manufactured by Resonaq) attached to a liquid chromatography measuring device (product name: LC-20, manufactured by Shimadzu Corporation) equipped with a PDA detector (product name: SPD-M20A, manufactured by Shimadzu Corporation) and a mass spectrometer (product name: LCMS-2020, manufactured by Shimadzu Corporation, ionization mode: ESI-Negative). The column temperature was set to 30°C, and L-ascorbic acid and its oxidized products were separated using an eluent of 50 mM aqueous ammonium formate:acetonitrile=30:70 (0.2 mL / min). The content (unit: ppm) of L-ascorbic acid and its oxidized form in the (meth)acrylic resin composition was calculated from a calibration curve obtained from standards (L-ascorbic acid and its oxidized form, dehydroascorbic acid). L-ascorbic acid was quantified from the area of ​​the corresponding chromatogram at 268 nm using a PDA detector, and its oxidized form was quantified from the sum of the areas of the corresponding chromatograms at m / z = 173 (monomer) and m / z = 347 (dimer) using a mass spectrometer.

[0067] (3) Inkjet printing adhesion The inkjet printing adhesion of the inkjet printing substrate was evaluated based on the results of a peel test using a cross-cut method in accordance with JIS K5600-5-6. First, using an inkjet printer (UJF-6042 manufactured by Mimaki Engineering Co., Ltd.), a color image was printed on the inkjet printing substrate obtained in the examples and comparative examples using an inkjet printing ink (LH-100 manufactured by Mimaki Engineering Co., Ltd.). Next, the resulting printed portion was subjected to a peel test using a cross-cut method in accordance with JIS K5600-5-6. Based on the peel test results, the inkjet printing adhesion was evaluated according to the following criteria. <Evaluation criteria> AA: The area ratio of peeled printed area is less than 5% A: The area ratio of peeled printed area is 5% or more but less than 15% B: The area ratio of the peeled part of the printed part is 15% or more but less than 35% C: The area ratio of the peeled part of the printed part is 35% or more

[0068] (4) Ink wetting and spreading (printing resolution) As an index of the inkjet printing resolution of the inkjet printing substrate, 20 mg of inkjet printing ink (LH-100 manufactured by Mimaki Engineering Co., Ltd.) was dropped onto the inkjet printing substrate obtained in the Examples and Comparative Examples and allowed to stand. The ink area and outline were confirmed 30 minutes after dropping. The ink area was calculated using the following formula. From these results, the ink wetting and spreading properties were evaluated according to the following criteria. <Calculating the ink area> If the outline of the ink droplet is a perfect circle: Pi x radius of the ink droplet x radius of the ink droplet If the outline of the ink droplet is irregular and distorted (approximating an ellipse): Pi x major axis of the ink droplet x minor axis of the ink droplet <Evaluation criteria> AA: The area of ​​the ink droplet is 130 mm 2 Less than perfect circle with clean outline A: The area of ​​the ink droplet is 130 mm 2 More than 180mm 2 Less than perfect circle with clean outline B: The area of ​​the ink droplet is 180 mm 2 irregular or distorted shape

[0069] <Production Example 1> (1) Production of syrup (A) 98 parts by mass of MMA and 2 parts by mass of BA were fed into a reactor (polymerization vessel) equipped with a condenser, thermometer, and stirrer, and after bubbling with nitrogen gas, the temperature of the monomer composition in the reactor was raised to 80°C. When the temperature of the monomer composition reached 80°C, 0.1 parts by mass of 2,2'-azobis-(2,4-dimethylvaleronitrile) as a radical polymerization initiator and 0.07 parts by mass of 1-dodecanethiol as a chain transfer agent were added per 100 parts by mass of the monomer composition, and the temperature of the monomer composition in the reactor was further raised to 100°C and maintained at that temperature for 11 minutes. The reactor was then cooled to room temperature to obtain syrup (A) containing 25% by mass of solids.

[0070] <Production Example 2> (2) Production of syrup (B) 100 parts by mass of MMA was supplied to a reactor (polymerization vessel) equipped with a condenser, thermometer, and stirrer, and nitrogen gas was bubbled through. The temperature of the monomer composition in the reactor was then raised to 80°C. When the temperature of the monomer composition reached 80°C, 0.1 parts by mass of 2,2'-azobis-(2,4-dimethylvaleronitrile) as a radical polymerization initiator and 0.07 parts by mass of 1-dodecanethiol as a chain transfer agent were added per 100 parts by mass of the monomer composition. The temperature of the monomer composition in the reactor was then raised to 100°C and maintained at this temperature for 11 minutes. The reactor was then cooled to room temperature to obtain a syrup (B) containing 25% by mass of solids.

[0071] Example 1 (1) Preparation of polymerizable composition (S2) 9 parts by mass of BA was added to 91 parts by mass of the syrup (A) produced in Production Example 1 to obtain a polymerizable raw material (S1), and 0.3 parts by mass of t-hexyl peroxypivalate as a polymerization initiator and 20 ppm of L-ascorbic acid were further added and mixed to obtain a polymerizable composition (S2).

[0072] (2) Casting polymerization A mold for cast polymerization was prepared by placing two stainless steel plates facing each other and sealing their periphery with a soft resin gasket. After pouring the polymerizable composition (S2) into the mold, the distance between the opposing stainless steel plates was adjusted to 4.1 mm. The mold was then heated in an 80°C water bath for 1 hour and then in an air oven at 130°C for 1 hour, thereby polymerizing and curing the mixture in the mold. The mold was then air-cooled, and the stainless steel plates were removed to obtain a 3 mm-thick sheet-like molded product made of the (meth)acrylic resin composition, which was used as a substrate for inkjet printing. The evaluation results of the resulting substrate for inkjet printing are shown in Table 1.

[0073] <Comparative Example 1> (3) Preparation of polymerizable composition (S2) To 100 parts by mass of the syrup (B) produced in Production Example 2, 0.3 parts by mass of t-hexyl peroxypivalate as a polymerization initiator and 200 ppm of L-ascorbic acid were added and mixed to obtain a polymerizable composition (S2).

[0074] (4) Casting polymerization A mold for cast polymerization was prepared by placing two stainless steel plates facing each other and sealing their periphery with a soft resin gasket. After pouring the polymerizable composition (S2) into the mold, the distance between the opposing stainless steel plates was adjusted to 4.1 mm. The mold was then heated in an 80°C water bath for 1 hour and then in an air oven at 130°C for 1 hour, thereby polymerizing and curing the mixture in the mold. The mold was then air-cooled, and the stainless steel plates were removed to obtain a 3 mm-thick sheet-like molded product made of the (meth)acrylic resin composition, which was used as a substrate for inkjet printing. The evaluation results of the resulting substrate for inkjet printing are shown in Table 2.

[0075] <Examples 2 to 10 and Comparative Examples 2 to 5> A sheet-like molded article made of a (meth)acrylic resin composition was prepared as a substrate for inkjet printing under the same production conditions as in Example 1, except that the type of acrylic acid ester (a) and the type and amount of ascorbic acid or other reducing agent added were changed as shown in Tables 1 and 2. The evaluation results of the obtained substrate for inkjet printing are shown in Tables 1 and 2. The content of ascorbic acids in the (meth)acrylic resin composition was evaluated only in Examples 1 to 4 and Comparative Examples 1 and 2.

[0076] [Table 1]

[0077] [Table 2]

[0078] The following can be seen from Tables 1 and 2: The (meth)acrylic resin composition contains the (meth)acrylic polymer (P) obtained in Examples 1 to 8, which contains MMA units and repeating units derived from the acrylic acid ester (a), and at least one of a reductone compound and its oxidized product as ascorbic acids. An inkjet printing substrate made of this (meth)acrylic resin composition is excellent in inkjet printing adhesion and printing resolution. The (meth)acrylic resin compositions of Examples 9 and 10 contain, as ascorbic acids, non-reductone compounds in which the hydroxyl group of a reductone compound has been substituted with another substituent, and the inkjet printing substrates made of these (meth)acrylic resin compositions are slightly inferior to the inkjet printing substrates of Examples 1 to 8, but are superior to the inkjet printing substrates of the comparative examples in inkjet printing adhesion and printing resolution, especially printing resolution. The inkjet printing substrates obtained in Comparative Examples 1 to 5 were inferior in inkjet printing adhesion and printing resolution because the (meth)acrylic polymer (P) in the (meth)acrylic resin composition did not contain an acrylic acid ester (a) unit or did not contain ascorbic acids.

Claims

1. A (meth)acrylic resin composition comprising: a (meth)acrylic polymer (P) containing a repeating unit derived from methyl methacrylate and a repeating unit derived from an acrylic acid ester (a); and one or more ascorbic acids selected from the group consisting of ascorbic acid and ascorbic acid derivatives.

2. 2. The (meth)acrylic resin composition according to claim 1, wherein the ascorbic acid compound is one or more compounds selected from the group consisting of reductone compounds and their oxidized products.

3. The (meth)acrylic resin composition according to claim 1, wherein the ascorbic acid compound contained in the (meth)acrylic resin composition has a content of 0.001 ppm or more and 10,000 ppm or less.

4. 3. The (meth)acrylic resin composition according to claim 2, wherein the reductone compound is at least one selected from the group consisting of (iso)ascorbic acid, salts thereof, and derivatives thereof.

5. The (meth)acrylic resin composition according to claim 1, wherein the (meth)acrylic polymer (P) contains repeating units derived from methyl methacrylate in an amount of 70% by mass or more and 99% by mass or less.

6. The (meth)acrylic resin composition according to claim 1, wherein the (meth)acrylic polymer (P) contains repeating units derived from the acrylic acid ester (a) in an amount of 1% by mass or more and 30% by mass or less.

7. The (meth)acrylic resin composition according to claim 1 , which is produced by bulk polymerization.

8. A substrate for inkjet printing, comprising the (meth)acrylic resin composition according to any one of claims 1 to 7.

9. A (meth)acrylic resin laminate comprising the substrate for inkjet printing according to claim 8 and an inkjet printing layer formed on the surface of the substrate for inkjet printing.

10. The (meth)acrylic resin laminate according to claim 9 , wherein the inkjet print layer is formed by curing an energy ray-curable composition.

11. A key holder comprising the (meth)acrylic resin laminate according to claim 9.

12. A strap comprising the (meth)acrylic resin laminate according to claim 9.

13. A stand comprising the (meth)acrylic resin laminate according to claim 9.

14. A card comprising the (meth)acrylic resin laminate according to claim 9.

15. 8. A method for producing the (meth)acrylic resin composition according to any one of claims 1 to 7, comprising a step of bulk polymerizing a polymerizable composition containing a (meth)acrylic polymer (P) including a repeating unit derived from methyl methacrylate and a repeating unit derived from the acrylic acid ester (a), and one or more ascorbic acids selected from the group consisting of ascorbic acid and ascorbic acid derivatives.

16. The method for producing a (meth)acrylic resin composition according to claim 15, wherein the ascorbic acid compound is one or more compounds selected from the group consisting of reductone compounds and their oxidized products.

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