Adhesive compositions, articles, laminated pressboards

Abstract

To provide: a styrene-free adhesive composition which can obtain sufficient adhesiveness between substrates and hardly causes peeling at the adhesive layer; and an article and a laminated press board using the adhesive composition.SOLUTION: There are provided: an adhesive composition which comprises at least one curable resin selected from the group consisting of an unsaturated polyester resin and a vinylester resin, an ethylenically unsaturated monomer other than styrene and optionally comprises an inorganic filler, wherein the ratio of the inorganic filler to the total of the curable resin, the ethylenically unsaturated monomer and the inorganic filler is 20 mass% or less; and an article and a laminated press board having a cured product of the adhesive composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to adhesive compositions, articles, and laminated pressboards. [Background technology]

[0002] Adhesive compositions are sometimes applied to substrates such as pressboards to bond the substrates together and obtain articles such as laminated pressboards. Adhesives containing various raw materials such as casein, starch, epoxy resin, unsaturated polyester resin, and phenolic resin are used for laminating pressboards (for example, Patent Documents 1 and 2). In adhesives containing curable resins, monomers having ethylenically unsaturated bonds may be used in combination (for example, Patent Document 3). In addition, inorganic fillers may be added to the adhesive composition to improve mechanical properties, thermal properties, processability, and impart functionality (for example, Patent Document 3, Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 59-211208 [Patent Document 2] Patent No. 6020364 [Patent Document 3] Japanese Patent Publication No. 2021-147448 [Non-patent literature]

[0004] [Non-Patent Document 1] "Network Polymers" Vol.36 No.6 (2015), pp.299-308. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In recent years, there has been a demand for styrene-free adhesive compositions. The inventors of this invention investigated various resins for styrene-free adhesive compositions and found that curable resins such as unsaturated polyester resins and vinyl ester resins are useful. However, while heat resistance is required for adhesive compositions depending on the application, the inventors' research has revealed that when inorganic fillers are added for heat resistance, styrene-free adhesive compositions containing these curable resins tend to delaminate in the adhesive layer that joins the substrates together. The present invention provides a styrene-free adhesive composition that provides sufficient adhesion between substrates and is less prone to peeling in the adhesive layer; and articles and laminated pressboards using the adhesive composition. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] An adhesive composition comprising; at least one curable resin selected from the group consisting of unsaturated polyester resins and vinyl ester resins; an ethylenically unsaturated monomer other than styrene; and optionally comprising an inorganic filler; wherein the proportion of the inorganic filler is 20% by mass or less with respect to the total of the curable resin, the ethylenically unsaturated monomer and the inorganic filler. [2] The adhesive composition of [1], wherein the viscosity measured with a B-type viscometer at 23°C and 30 rpm is 7000 mPa·s or less. [3] The adhesive composition of [1] or [2], which does not contain the inorganic filler. [4] An article comprising two or more substrates; an adhesive for bonding the two or more substrates together; wherein at least one of the adhesives is a cured product of any of the adhesive compositions of [1] to [3]. [5] A laminated pressboard comprising: a plurality of pressboards; and at least one adhesive layer for bonding the plurality of pressboards together; wherein at least one of the adhesive layers is a cured product of any of the adhesive compositions of [1] to [3]. [Effects of the Invention]

[0007] According to the present invention, there are provided a styrene-free adhesive composition in which sufficient adhesiveness between base materials is obtained and peeling in the adhesive layer hardly occurs; and an article and a laminated press board using the adhesive composition.

Brief Description of the Drawings

[0008] [Figure 1] FIG. 1 is a photograph of a jig used for measuring the peeling occurrence rate in an example. [Figure 2] FIG. 2 is a photograph of the jig of FIG. 1 taken from another angle. [Figure 3] FIG. 3 is a photograph showing the state when peeling occurred in the adhesive layer during the measurement of the peeling occurrence rate in an example. [Figure 4] FIG. 4 is a photograph showing the state when peeling did not occur in the adhesive layer but occurred in the paper layer during the measurement of the peeling occurrence rate in an example.

Modes for Carrying Out the Invention

[0009] In this specification, "~" indicating a numerical range means that the numerical values described before and after it are included as the lower limit value and the upper limit value. The lower limit value and the upper limit value of the numerical range disclosed in this specification can be arbitrarily combined to form a new numerical range.

[0010] <Adhesive Composition> The adhesive composition of the present invention contains at least one curable resin selected from the group consisting of an unsaturated polyester resin and a vinyl ester resin; and an ethylenically unsaturated monomer other than styrene. Further, the adhesive composition of the present invention optionally contains an inorganic filler. The adhesive composition of the present invention may further contain a curing agent as needed, and may further contain a curing accelerator as needed. Also, the adhesive composition of the present invention may further contain other components other than the curable resin, the ethylenically unsaturated monomer, the inorganic filler, the curing agent, and the curing accelerator as long as the effects of the invention are not impaired.

[0011] (Synthetic resin) The adhesive composition of the present invention contains at least one selected from the group consisting of unsaturated polyester resins and vinyl ester resins as a synthetic resin. Therefore, even in the case of a styrene-free adhesive composition, properties required in practice for adhesives, such as heat resistance and corrosion resistance, are likely to be fully exhibited.

[0012] The unsaturated polyester resin is not particularly limited as long as it is a polycondensate obtained by polycondensing a polyhydric alcohol, an unsaturated polybasic acid, and at least one selected from saturated polybasic acids and monobasic acids as required. The unsaturated polybasic acid is a polybasic acid having an ethylenic unsaturated bond. The saturated polybasic acid is a polybasic acid having no ethylenic unsaturated bond. The unsaturated polyester resin may be used alone or in combination of two or more.

[0013] The polyhydric alcohol serving as a raw material of the unsaturated polyester resin is not particularly limited as long as it is a compound having two or more hydroxyl groups. Among them, ethylene glycol, propylene glycol, butanediol, diethylene glycol, dipropylene glycol, triethylene glycol, pentanediol, hexanediol, neopentanediol, tetraethylene glycol, polyethylene glycol, neopentyl glycol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, bisphenol A, glycerin, ethylene oxide adduct of bisphenol A, and propylene oxide adduct of bisphenol A are preferable, and ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, hydrogenated bisphenol A, ethylene oxide adduct of bisphenol A, and propylene oxide adduct of bisphenol A are more preferable. The polyhydric alcohol may be used alone or in combination of two or more.

[0014] The unsaturated polybasic acid used as a raw material for unsaturated polyester resin is not particularly limited as long as it is a compound having an ethylenically unsaturated bond and two or more carboxyl groups, or an acid anhydride thereof. Examples include maleic acid, maleic anhydride, fumaric acid, citraconic acid, itaconic acid, and chloromaleic acid. Among these, maleic anhydride, fumaric acid, citraconic acid, itaconic acid, and chloromaleic acid are preferred from the viewpoint of heat resistance and mechanical strength of the cured product, and maleic anhydride and fumaric acid are more preferred. Unsaturated polybasic acids may be used individually or in combination of two or more.

[0015] The saturated polybasic acids that can be used as raw materials for unsaturated polyester resins are not particularly limited as long as they are compounds that do not have ethylenically unsaturated bonds and have two or more carboxyl groups, or their acid anhydrides. For example, halogenated phthalic anhydrides such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, tetrachlorophthalic anhydride, and tetrabromophthalic anhydride, aromatic saturated polybasic acids such as nitrophthalic acid, and their acid anhydrides; aliphatic saturated polybasic acids such as succinic acid, adipic acid, sebacic acid, oxalic acid, malonic acid, azelaic acid, glutaric acid, and hexahydrophthalic anhydride, and their acid anhydrides. Among these, phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, and adipic acid are preferred from the viewpoint of heat resistance and mechanical strength of the cured product, and phthalic anhydride, isophthalic acid, and terephthalic acid are more preferred. A saturated polybasic acid may be used alone or in combination of two or more.

[0016] Monobasic acids that can be used as raw materials for unsaturated polyester resins include dicyclopentadiene malate, benzoic acid and its derivatives, and cinnamic acid and its derivatives. Among these, dicyclopentadiene malate is preferred. Dicyclopentadiene malate can be synthesized from maleic anhydride and dicyclopentadiene. When monobasic acids are used, the viscosity of the unsaturated polyester resin tends to decrease. A single monobasic acid may be used alone, or two or more may be used in combination.

[0017] The mass-average molecular weight (Mw) of the unsaturated polyester resin is not particularly limited. The Mw of the unsaturated polyester resin is preferably 2,000 to 25,000, more preferably 3,000 to 20,000, and even more preferably 3,500 to 10,000. When Mw is within the above numerical range, the film-forming properties of the adhesive composition are good. In this specification, "mass-average molecular weight (Mw)" and "number-average molecular weight (Mn)" are defined as values ​​obtained by measuring at room temperature (23°C) under the following conditions using gel permeation chromatography (GPC) and using a standard polystyrene calibration curve. Equipment: Showa Denko Corporation's Shodex(registered trademark) GPC-101 Column: LF-804 manufactured by Showa Denko Corporation Column temperature: 40℃ Sample: 0.2% by mass of the sample in a tetrahydrofuran solution. Flow rate: 1mL / min Eluent: Tetrahydrofuran Detector: RI-71S

[0018] The degree of unsaturation of the unsaturated polyester resin is preferably 50 to 100 mol%, more preferably 60 to 100 mol%, and even more preferably 70 to 100 mol%. When the degree of unsaturation is within the above numerical range, the film-forming properties of the adhesive composition are good. The degree of unsaturation of an unsaturated polyester resin can be calculated using the following formula, based on the number of moles of unsaturated polybasic acid and saturated polybasic acid used as raw materials. Degree of unsaturation (mol %) = {(moles of unsaturated polybasic acid × number of unsaturated groups in unsaturated polybasic acid) / (moles of unsaturated polybasic acid + moles of saturated polybasic acid)} × 100

[0019] Unsaturated polyester resins can be produced using the above-mentioned raw materials by known synthesis methods. Various conditions in the synthesis of unsaturated polyester resins can be appropriately set depending on the raw materials used and their amounts. For example, an esterification reaction can be carried out under pressure or reduced pressure at a temperature of 140 to 230°C in an inert gas stream such as nitrogen gas. In esterification reactions, an esterification catalyst may be used as needed. Examples of esterification catalysts include manganese acetate, dibutyltin oxide, stannous oxalate, zinc acetate, and cobalt acetate. The esterification catalyst may be used alone or in combination of two or more types.

[0020] Examples of commercially available unsaturated polyester resins include Showa Denko Corporation's "Rigolac (registered trademark)" and DIC Material Corporation's "Sandoma (registered trademark)" and "Aqualight (registered trademark)".

[0021] (Vinyl ester resin) Vinyl ester resins are typically compounds having an ethylenically unsaturated bond, obtained by a ring-opening reaction between the epoxy group of an epoxy compound having two or more epoxy groups and the carboxyl group of an unsaturated monobasic acid. The unsaturated monobasic acid has both an ethylenically unsaturated bond and a carboxyl group. Such vinyl ester resins are described, for example, in the Polyester Resin Handbook (Nikkan Kogyo Shimbun, published 1988). Vinyl ester resin may be used alone or in combination of two or more types.

[0022] The epoxy compound used as a raw material for vinyl ester resin is not particularly limited as long as it is a compound having two or more epoxy groups. For example, at least one selected from the group consisting of bisphenol-type epoxy compounds, hydrogenated bisphenol-type epoxy compounds, and novolacphenol-type epoxy compounds can be used. These epoxy compounds further improve the mechanical strength and corrosion resistance of the cured product.

[0023] Examples of bisphenol-type epoxy compounds include the following compounds. Compounds obtained by reacting bisphenol compounds such as bisphenol A, bisphenol F, bisphenol S, and tetrabromobisphenol A with epichlorohydrin or methylepichlorohydrin. A compound obtained by reacting a compound obtained by glycidyl etherifying one or more bisphenol compounds with a condensate of one or more of the bisphenol compounds and epichlorohydrin or methylepichlorohydrin.

[0024] Examples of hydrogenated bisphenol-type epoxy compounds include the following compounds. Compounds obtained by reacting glycidyl ether of hydrogenated bisphenol A with bisphenol compounds such as bisphenol A, bisphenol F, bisphenol S, and tetrabromobisphenol A.

[0025] Examples of novolacphenol-type epoxy compounds include the following compounds. Compounds obtained by reacting phenol novolac or cresol novolac with epichlorohydrin or methylepichlorohydrin.

[0026] Among epoxy compounds, bisphenol A type epoxy compounds are preferred from the viewpoint of chemical resistance.

[0027] The unsaturated monobasic acid used as a raw material for vinyl ester resin is not particularly limited as long as it is a monocarboxylic acid having an ethylenically unsaturated bond. For example, at least one selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, and cinnamic acid is preferred, with acrylic acid and methacrylic acid being more preferred, and methacrylic acid being particularly preferred. The vinyl ester resin obtained by the reaction of methacrylic acid with an epoxy compound has high hydrolysis resistance to acids and alkalis, which can further improve the corrosion resistance of the cured product.

[0028] When the unsaturated monobasic acid is used in the ring-opening reaction between the epoxy compound and the unsaturated monobasic acid, the amount of unsaturated monobasic acid used is preferably 0.3 to 1.5 equivalents, more preferably 0.4 to 1.2 equivalents, and even more preferably 0.5 to 1.0 equivalents, per equivalent of epoxy groups in the epoxy compound. When the amount of unsaturated monobasic acid used is within the above numerical range, sufficient hardness of the cured product is easily obtained.

[0029] Vinyl ester resins can be synthesized by various synthesis methods. For example, one method involves dissolving an epoxy compound and an unsaturated monobasic acid in a solvent as needed, in the presence of an esterification catalyst, and reacting them at, for example, 70 to 150°C, preferably 80 to 140°C, and more preferably 90 to 130°C.

[0030] After synthesizing vinyl ester resins, unreacted unsaturated monobasic acids may remain. Such unreacted unsaturated monobasic acids are included in the ethylenically unsaturated monomers described later.

[0031] A commercially available styrene-free vinyl ester resin may be used. Commercially available styrene-free vinyl ester resins are not limited to those mentioned above, but examples include "Lipoxy®" from Showa Denko K.K. and "Exdoma®" from DIC Material Co., Ltd.

[0032] The adhesive composition of the present invention may further contain other curable resins other than unsaturated polyester resins and vinyl ester resins, as long as the effects of the invention are not impaired. Other curable resins are not particularly limited. Examples include urethane (meth)acrylate, epoxy resins, phenolic resins, and formaldehyde resins.

[0033] (Ethylene-unsaturated monomer) The ethylenically unsaturated monomers other than styrene are not particularly limited as long as they are polymerizable monomers having a carbon-carbon double bond in their molecule. Examples of ethylenically unsaturated monomers include, Vinyl compounds such as vinyl acetate, methoxystyrene, divinylbenzene, vinylnaphthalene, and acenaphthylene; Diene compounds such as butadiene, 2,3-dimethylbutadiene, isoprene, and chloroprene; (Meth)allyls such as di(meth)allyl phthalate and tri(meth)allyl isocyanurate; Methyl (meth)acrylate, hydroxyethyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, furfuryl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, phenyl (meth) )Acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, allyl (meth)acrylate, isobornyl (meth)acrylate, ethylene glycol monomethyl ether (meth)acrylate, ethylene glycol monoethyl ether (meth)acrylate, ethylene glycol monobutyl ether (meth)acrylate, ethylene glycol monohexyl ether (meth)acrylate, ethylene glycol mono-2-ethylhexyl ether (meth)acrylate, diethylene glycol monomethyl ether (meth)acrylate, diethylene glycol monoethyl ether (meth)acrylate, diethylene glycol monobutyl ether (meth)acrylate, diethylene glycol monohexyl ether (meth)acrylate, diethylene glycol mono-2-ethylhexyl ether (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, propylene glycol Di(meth)acrylate, neopentyl glycol di(meth)acrylate, polytetramethylene ether glycol (PTMG) di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 2-hydroxy-1,3-dimethacryloyloxypropane, 2,2-bis[4-(methacryloylethoxy)phenyl]propane, 2,2-bis[4-(methacryloxydiethoxy)phenyl]propane, 2,(meth)acrylates such as 2-bis[4-(methacryloxypolyethoxy)phenyl]propane, tetraethylene glycol diacrylate, bisphenol AEO-modified (n=2) diacrylate, isocyanuric acid EO-modified (n=3) diacrylate, pentaerythritol di(meth)acrylate monostearate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, tricyclodecanol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, etc. (meth)acrylamides such as (meth)acrylamide, N,N'-dimethyl(meth)acrylamide, and N,N'-diisopropyl(meth)acrylamide; Diethyl citraconate and other unsaturated dicarboxylic acid diesters; Monomaleimide compounds such as N-phenylmaleimide; N-(meth)acryloylphthalimide is one example. Among these, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, phenyl (meth)acrylate, and benzyl (meth)acrylate are preferred from the viewpoint of the physical properties of the cured product and surface drying properties, and methyl (meth)acrylate and hydroxyethyl (meth)acrylate are more preferred. Ethylene-unsaturated monomers may be used individually or in combination of two or more.

[0034] (Inorganic filler) The inorganic fillers of any component are not particularly limited, but examples include aluminum oxide, aluminum hydroxide, titanium oxide, silica sand, calcium carbonate, kaolin (clay), glass powder, talc, and fused silica.

[0035] (Hardening agent) A curing agent is a compound used to initiate the curing reaction of an adhesive composition. The curing agent should be appropriately selected depending on the type of curable resin, the usage conditions of the adhesive composition, the reaction conditions, etc. Examples of curing agents include thermal radical polymerization initiators and photoradical polymerization initiators. Examples of thermal radical polymerization initiators include various organic peroxides. For example, diacyl peroxides such as benzoyl peroxide; peroxyesters such as tert-butyl peroxybenzoate; hydroperoxides such as cumene hydroperoxide; dialkyl peroxides such as dicumyl peroxide; ketone peroxides such as methyl ethyl ketone peroxide and acetylacetone peroxide; peroxyketals such as 1,1-dialkylperoxycyclohesane; alkyl peresters such as alkyl peroxydecanoate; and peroxycarbonates such as peroxydicarbonate. Examples of photoradical polymerization initiators include NOF Corporation's "Permec®," Mitsui Chemicals Fine Industries, Inc.'s "Triganox®," and Arkema Yoshitomi Co., Ltd.'s "Luperox®."

[0036] (Other ingredients) Other components may be appropriately selected depending on the intended use and application of the adhesive composition. Examples include various additives such as curing accelerators, solvents, colorants, fibers, coupling agents, waxes, and thixotropes. However, other components are not limited to these examples.

[0037] Curing accelerators can be used to improve the curing speed of adhesive compositions. Examples of curing accelerators include amines such as aniline, N,N-substituted aniline, N,N-substituted-p-toluidine, and 4-(N,N-substituted amino)benzaldehyde, as well as cobalt compounds such as 2-ethylhexanoate and naphthenate. Specifically, examples include aniline, N,N-dimethylaniline, N,N-diethylaniline, p-toluidine, N,N-dimethyl-p-toluidine, N,N-bis(2-hydroxyethyl)-p-toluidine, 4-(N,N-dimethylamino)benzaldehyde, 4-[N,N-bis(2-hydroxyethyl)amino]benzaldehyde, 4-(N-methyl-N-hydroxyethylamino)benzaldehyde, N,N-bis(2-hydroxypropyl)-p-toluidine, N-ethyl-m-toluidine, triethanolamine, m-toluidine, diethylenetriamine, pyridine, phenylmorpholine, piperidine, N,N-bis(hydroxyethyl)aniline, and diethanolaniline. The hardening accelerator may be used alone or in combination of two or more types.

[0038] Solvents are used as needed to ensure uniform mixing of each component in the adhesive composition. Their content is not particularly limited and can be adjusted appropriately considering workability, viscosity, etc. The type of solvent is selected appropriately depending on the type of resin, application, etc. Examples include aliphatic hydrocarbons, aromatic hydrocarbons, ethers, ketones, esters, and linear carbonate esters. The solvent may be used alone or in combination of two or more types.

[0039] (composition) According to the inventors' research, curable resins such as unsaturated polyester resins and vinyl ester resins have weak interaction with inorganic fillers, making them prone to separation of the resin and inorganic filler before curing. Therefore, when the adhesive composition is applied in this manner, the adhesive layer becomes partially rich in inorganic fillers, and delamination is likely to occur starting from these points. Therefore, in the adhesive composition of the present invention, the proportion of inorganic filler is set to 20% by mass or less relative to the total of the curable resin, ethylenically unsaturated monomer, and inorganic filler. As a result, peeling of the adhesive layer is less likely to occur.

[0040] The total proportion of the curable resin, ethylenically unsaturated monomer, and inorganic filler is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 95 to 100% by mass, based on 100% by mass of the adhesive composition. When this proportion falls within the above numerical range, it is easier to ensure sufficient amounts of components such as curing agents and additives.

[0041] The proportion of curable resin is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 40 to 60% by mass, based on 100% by mass of the adhesive composition. When the proportion of curable resin is above the lower limit of the above numerical range, adhesion is easily obtained. When the proportion of curable resin is below the upper limit of the above numerical range, properties due to the inorganic filler of any component or other components are easily obtained.

[0042] The proportion of ethylenically unsaturated monomers is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 40 to 60% by mass, based on 100% by mass of the adhesive composition. If the proportion of ethylenically unsaturated monomers is above the lower limit of the above numerical range, the viscosity of the adhesive composition tends to decrease. If the proportion of ethylenically unsaturated monomers is below the upper limit of the above numerical range, the properties of the arbitrary inorganic filler and other components are easily obtained.

[0043] The proportion of inorganic filler is preferably 0 to 20% by mass, more preferably 0 to 15% by mass, and even more preferably 0 to 10% by mass, based on 100% by mass of the adhesive composition, and it is most preferable that the adhesive composition does not contain inorganic filler. If the proportion of inorganic filler is above the lower limit of the above numerical range, the adhesion will not deteriorate easily even in a heat-resistant environment. If the proportion of inorganic filler is below the upper limit of the above numerical range, the substrates will not easily peel off at the adhesive layer in articles to which substrates have been joined.

[0044] (Properties) The viscosity of the adhesive composition, measured with a Type B viscometer at 23°C and 30 rpm, is preferably 7000 mPa·s or less, more preferably 3000 mPa·s or less, and even more preferably 1500 mPa·s or less, from the viewpoint of curability and workability. The lower limit of this viscosity is preferably 10 mPa·s or more, more preferably 50 mPa·s or more, and even more preferably 100 mPa·s or more, from the viewpoint of curability and workability.

[0045] (Preparation method) The adhesive composition can be prepared by mixing the above-mentioned curable resin and ethylenically unsaturated monomer. It can also be prepared by optionally mixing inorganic fillers and curing agents. A pre-mixed mixture of the curable resin and ethylenically unsaturated monomer may also be used. Furthermore, other components besides the curable resin, ethylenically unsaturated monomer, inorganic filler, and curing agent may be mixed together, provided that they do not impair the effects of the invention.

[0046] (Mechanism of action) The adhesive composition described above contains at least one curable resin selected from the group consisting of unsaturated polyester resins and vinyl ester resins. Therefore, even if the adhesive composition is styrene-free, good adhesion between substrates can be easily obtained. Furthermore, because the proportion of the optional inorganic filler is not excessive, even if the interaction between the curable resin and the inorganic filler is weak, inorganic filler-rich areas are less likely to occur. As a result, it is thought that the number of points where delamination begins will be reduced. Therefore, a styrene-free adhesive composition is provided that provides sufficient adhesion between substrates and is less prone to peeling in the adhesive layer.

[0047] <Application> The adhesive composition of the present invention can be used as an adhesive after curing. The substrate to be bonded is not particularly limited, but wood-based materials such as pressboard are considered preferable. The curing conditions for bonding the substrates together may be thermal curing or photocuring, and are not particularly limited. They can be appropriately changed depending on the type and amount of curable resin.

[0048] (Goods) The adhesive composition of the present invention can be applied to bonding two or more substrates. According to the adhesive composition of the present invention, an article is provided which comprises two or more substrates; an adhesive for bonding the two or more substrates to each other; and at least one of the adhesives being a cured product of the adhesive composition of the present invention.

[0049] The base material for the article is not particularly limited, but examples include pressboard, wood, plywood, and hardboard. For example, the article can be used in various applications such as furniture, building materials, and household wood products, where pieces of wood are bonded together with the adhesive composition of the present invention.

[0050] In the case of an article having three or more substrates, multiple adhesives may be present. If multiple adhesives are present, at least one of them may be a cured product of the adhesive composition of the present invention. That is, all adhesives may be cured products of the adhesive composition of the present invention, or some of the adhesives may be cured products of the adhesive composition of the present invention.

[0051] (Laminated press board) When pressboard is used as a base material, a laminated pressboard is provided as an example of an article, comprising: a plurality of pressboards; and at least one adhesive layer for bonding the plurality of pressboards to each other; wherein at least one of the adhesive layers is a cured product of the adhesive composition of the present invention.

[0052] Pressboard is used as an electrical insulating material inside high-voltage, high-power substations. Pressboard can be made from general wood pulp, and the type of wood pulp is not particularly limited. Furthermore, wood pulp that has been beaten to enhance the interfiber bonding between pulp fibers may be used. The freeness of the wood pulp, according to JIS P 8121-2:2012, is preferably 200-500 mlCSF, and more preferably 250-450 mlCSF. When using two or more types of raw pulp, the freeness may be adjusted to the above numerical range by mixing separately beaten pulps, or by beating pre-mixed pulps. The method of beating the pulp is not particularly limited, and a general beating machine such as a refiner may be used.

[0053] In addition to pressboard made from wood pulp, heat-resistant pressboard made primarily from whole aromatic materials may also be used.

[0054] The thickness of the pressboard is not particularly limited, but for example, 0.5 to 13 mm is preferred, 1.0 to 10 mm is more preferred, and 2.0 to 8 mm is even more preferred. When the thickness of the pressboard is within the above numerical range, it is easy to obtain a pressboard laminate with excellent insulation properties and uniform density. The thickness of the pressboard is measured in accordance with JIS C 2305-2:2010.

[0055] The density of pressboard is 0.90-1.35 g / cm³ 3 Preferably, 0.95 to 1.30 g / cm³ 3 More preferably, 1.00 to 1.30 g / cm³ 3 This is even more preferable. When the density of the pressboard is within the aforementioned numerical range, it is easier to obtain a pressboard laminate that has excellent mechanical strength, excellent insulation, excellent adhesive strength, and can suppress the decrease in adhesive strength over time. The density of pressboard is calculated from the thickness and basis weight measured in accordance with JIS C 2305:2010.

[0056] The surface of the pressboard may be subjected to surface treatments such as embossing or smoothing treatments such as calendering, as needed. Furthermore, the front, back, or both sides of the pressboard may be subjected to surface treatments as required by the application. For example, depending on the application, surface treatment liquids such as surface sizing agents, water-resistant agents, flame retardants, and fire-retardants may be applied.

[0057] When manufacturing pressboard, a standard paper machine can be used. While there are no particular limitations on the type of paper machine, examples include continuous paper machines such as screenmills, cylinder machines, and inclined paper machines, or multi-layer paper machines combining these types. The paper-making sheets are laminated in a wet state without drying, and depending on the basis weight of each sheet, 10 to 300 layers are laminated. Pressboard is obtained by pressing and integrating these laminates. The laminate is subjected to a pressure of 10 to 100 kgf / cm² under conditions of 80 to 200°C. 2 They are fused together by being pressed under pressure for several minutes to several hours.

[0058] A laminated pressboard is made by laminating at least two or more pressboards with an adhesive layer consisting of a cured adhesive composition. Laminated pressboards can be manufactured by applying an adhesive composition to the surface of a pressboard, then layering another pressboard on top and bonding them together. Preferably, the adhesive composition is applied evenly to the entire bonding surface of the pressboard using a roller. In addition to a roller, it may also be applied using a brush, spray, or other application method, and the application method is not particularly limited. From the viewpoint of adhesion, it is preferable to dry the pressboards to remove moisture before applying the adhesive.

[0059] The amount of adhesive composition to be applied is not particularly limited, but from the viewpoint of forming an adhesive layer between the press boards and eliminating direct contact between the press boards to increase adhesive strength, 100 g / m² is recommended. 2 The above is preferable, 200g / m 2 The above is preferable. The upper limit of the application amount is not particularly limited. It can be set appropriately considering production costs and economics.

[0060] After layering the pressboard and adhesive layer so that the outermost surface is the pressboard, the temperature is set to 10°C to 60°C, more preferably 10°C to 40°C, and the pressure is set to 5 to 50 kgf / cm². 2It is preferable to press the material for several hours to one day under these conditions. After that, it may be dried at 10°C to 60°C (more preferably 10°C to 40°C) for several days. When pressboard laminates are produced under these conditions, it is easy to obtain pressboard laminates with excellent adhesive strength and electrical properties. It is preferable that the curing of the adhesive composition (rapid increase in viscosity) begins after the predetermined pressing pressure mentioned above is reached.

[0061] When a pressboard laminate has multiple adhesive layers, all of the adhesive layers may be cured products of the adhesive composition of the present invention, or some of the adhesive layers may be cured products of the adhesive composition of the present invention. When some of the multiple adhesive layers are cured products of the adhesive composition of the present invention, at least one selected from the group consisting of epoxy resins, phenolic resins, formaldehyde resins, casein compounds, and modified products thereof may be used in combination.

[0062] Applications of laminated pressboard include, for example, electrical insulation components for power transformers and reactors, as well as non-electrical applications such as furniture, building materials, and household woodworking tools. However, the applications of laminated pressboard are not limited to these examples. [Examples]

[0063] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description.

[0064] <Raw materials> (Resin components) • Resin component A1: A mixture of 50% by mass of unsaturated polyester resin and 50% by mass of methacrylic acid esters (DIC Material Corporation product "Aqualight®") • Resin component A2: A mixture of 50% by mass of bisphenol vinyl ester resin and 50% by mass of methacrylic acid esters (Showa Denko Corporation product "Lipoxy®") • Resin component A3: A mixture of unsaturated polyester resin: 50% by mass and styrene: 50% by mass (DIC Material Corporation product "Sandoma®")

[0065] (Inorganic filler) · Talc (particle size 9 μm, oil absorption 40 ml / 100 g) · Aluminum hydroxide (particle size 10 μm, oil absorption 35 ml / 100 g)

[0066] <Example 1> (Manufacture of press board) 100 g equivalent of wood pulp that had been beaten to a freeness of 350 ml CSF in advance was prepared in terms of absolute dry weight and dispersed in 20 L of water to obtain a slurry. After stirring the slurry in a pulper for 30 minutes, wet paper with a single leaf basis weight of about 100 g / m 2 was set and formed, and 50 sheets of this wet paper were laminated without drying. Then, it was hot pressed under the conditions of 140 °C and 40 kgf / cm 2 for 40 minutes to integrate the drying of the wet paper laminate, and a press board with a thickness of 5 mm and a density of 1.0 g / cm 3 was obtained.

[0067] (Preparation of adhesive composition) 85 parts by mass of resin component A1 and 15 parts by mass of talc were stirred and mixed for 30 minutes. Next, a cobalt octylate solvent solution (containing 50% by mass of the main component cobalt 2-ethylhexanoate) was added as a curing accelerator to a concentration of 0.2% by mass and stirred for 10 minutes. Then, the viscosity was measured using a B-type viscometer. After the viscosity measurement, further, a cumene hydroperoxide mixture (containing 80% by mass of cumene hydroperoxide as the main component) was mixed as a curing agent to a concentration of 0.35% by mass to obtain the adhesive composition of Example 1.

[0068] (Manufacture of laminated press board) The adhesive composition of Example 1 was applied to the entire surface of the press board using a roller so that the coating amount was 400 g / m 2 , and the press boards were bonded together. Then, it was pressurized at room temperature at 10 kgf / cm 2 for 3 hours to cure the resin, and a laminated press board with a thickness of 10 mm was obtained.

[0069] <Examples 2 to 5, Comparative Examples 1 to 3, Reference Example 1> An adhesive composition was prepared in the same manner as in Example 1, except that the composition of the resin components and inorganic fillers was changed as shown in Tables 1 and 2, to obtain a laminated pressboard.

[0070] <Rating> (Adhesiveness) Adhesion was evaluated by measuring the rate of delamination in the adhesive layer. The method for measuring the rate of delamination was as follows: Five sections (20 mm wide, 240 mm long) were taken from each example of laminated pressboard. The adhesion failure (presence or absence of adhesive layer delamination) confirmation test was performed as follows: A metal jig with a pointed tip (10 mm wide tip) was attached to the Tensilon universal testing machine as shown in Figures 1 and 2, and the adhesion failure was judged by the way cracks formed in the section when a wedge was driven into the adhesive layer at a speed of 5 mm / min. The test was performed at two locations at both ends of each of the five sections, for a total of n=10, and the rate of adhesion layer delamination was determined. As shown by the arrow in Figure 3, if there is adhesion failure, a crack occurs in the center of the adhesive layer, and the adhesive layer splits to the left and right. On the other hand, as shown by the arrow in Figure 4, if there is no adhesion failure and no delamination of the adhesive layer, cracks appear in the pressboard. In this test, it was evaluated that there was no practical problem if the rate of adhesion layer delamination was 20% or less.

[0071] (heat resistance) Heat resistance was evaluated by measuring the rate of strength reduction. The method for measuring the rate of strength reduction was as follows: Cut sections (10 mm wide, 100 mm long) of each example of laminated pressboard were impregnated with insulating oil (product name: High-Pressure Insulating Oil A, manufactured by ENEOS Corporation), and a heat degradation test (120°C, 90 days) was conducted. The rate of strength reduction was calculated from the ratio of the initial bending strength to the bending strength after 90 days at 120°C. The test method for the rate of strength reduction was carried out in accordance with JIS C 2324-2 Section 9. In this test, a rate of strength reduction of 20% or less was considered to be practically acceptable.

[0072] [Table 1]

[0073] [Table 2]

[0074] In Examples 1 to 5, although the adhesive compositions were styrene-free, they showed a peeling rate comparable to or lower than that of the adhesive composition in Reference Example 1, which contains styrene. Examples 1 to 5 confirmed that sufficient adhesion can be obtained even with styrene-free adhesive compositions, and that peeling of the adhesive layer is less likely to occur. Furthermore, in Examples 1-5, the rate of strength reduction after the heat degradation test was lower than in Comparative Examples 1-3, indicating superior heat resistance. [Industrial applicability]

[0075] According to the present invention, a styrene-free adhesive composition is provided that provides sufficient adhesion between substrates and is less prone to peeling in the adhesive layer; as well as articles and laminated pressboards using the adhesive composition.

Claims

1. An adhesive composition, Curable resin and Ethylene-unsaturated monomers other than styrene, Includes, The curable resin is a vinyl ester resin, Furthermore, it optionally contains inorganic fillers, The proportion of the inorganic filler is 20% by mass or less relative to the total of the curable resin, the ethylenically unsaturated monomer, and the inorganic filler. The proportion of the curable resin is 40 to 60% by mass relative to 100% by mass of the adhesive composition. An adhesive composition in which the total proportion of the curable resin, the ethylenically unsaturated monomer, and the inorganic filler is 95 to 100% by mass relative to 100% by mass of the adhesive composition.

2. The adhesive composition according to claim 1, wherein the viscosity measured with a B-type viscometer at 23°C and 30 rpm is 7000 mPa·s or less.

3. The adhesive composition according to claim 1 or 2, wherein it does not contain the inorganic filler.

4. Two or more substrates, An adhesive for bonding the two or more substrates together, It has, An article wherein at least one of the adhesives is a cured product of the adhesive composition according to claim 1 or 2.

5. Multiple pressboards, The plurality of press boards are bonded together by at least one adhesive layer, It has, A laminated press board in which at least one of the adhesive layers is a cured product of the adhesive composition according to claim 1 or 2.

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