Patent Description:
The present invention relates to a paint-protective coating material and an acrylic coating composition.

For purposes such as prevention of surface damage in transporting, storing, aging and constructing articles having paint layers (or painted articles, e.g., painted automobiles and their components, or metal plates such as painted steel plates and molded articles therefrom), techniques are known such as adhering protective sheets to the paint layers for protection. A paint-protective sheet used for such purposes is generally constructed as an adhesively single-faced substrate-supported pressure-sensitive adhesive (PSA) sheet having a PSA layer on one face of a substrate sheet (support substrate) so that it can provide protection when adhered via the PSA to an adherend (an object to be protected). After the protective role is completed, the paint-protective sheet is removed (peeled away) from the adherend. Technical literatures related to paint-protective sheets include <CIT>. In this context, <NPL> describes the effect of copolymer composition on the dynamic mechanical and thermal behavior of butyl acrylate-acrylonitrile copolymers. Moreover, <CIT> discloses acrylic emulsions for use as water-based strippable paints; <CIT> relates to a strippable water-based coating composition that is capable of forming a coating film excellent in water resistance, strength, acid rain resistance, weather resistance, and strippability; and <CIT> discloses temporary coating films.

When protecting non-flat objects (especially objects having complex three-dimensional shapes such as automobile body shells), it is difficult to increase efficiency in suitable application of paint-protective sheets to the objects. In case of improper application of a paint-protective sheet to an object to be protected, for instance, when the applied paint-protective sheet has wrinkles, the wind may blow into the wrinkles while the post-application object is being stored or transported, thereby peeling off the paint-protective sheet and compromising the intended protection purpose.

On the other hand, it has been suggested to form a protective coat by directly applying a liquid protective coating composition onto the paint layer of an object to be protected and drying the liquid composition on the paint layer. Literatures related to this type of art include <CIT>. However, unlike the aforementioned paint-protective sheet, the protective coat thus formed from a liquid composition is free of a substrate; thus, for removal from the paint layer after serving the protective role, it tends to lack sufficient removability and workability.

An objective of this invention is thus to provide a paint-protective coating material that is formed from a liquid coating composition and comes with good removability and workability in removal from a paint layer. Another related objective is to provide a coating composition suited for forming the paint-protective coating material and a method for forming the paint-protective coating material.

This Description provides a paint-protective coating material (or abbreviated to a "coating material" hereinafter) formed from an acrylic coating composition comprising an acrylic polymer as base polymer. The acrylic polymer-forming monomers include a monomer (mT) having a homopolymer glass transition temperature (Tg) of <NUM> or higher and a monomer (mL) having a homopolymer Tg of - <NUM> or lower. The monomer (mT) includes at least acrylonitrile. In the monomers, the monomer (mT) and the monomer (mL) have a molar ratio (mT/mL) of <NUM> or higher and <NUM> or lower. The coating material has a storage modulus at <NUM> (or "G'(<NUM>)" hereinafter) of <NUM> MPa or higher and <NUM> MPa or lower, and has a storage modulus at <NUM> (or "G'(<NUM>)" hereinafter) of <NUM> MPa or higher. Such a paint-protective coating material can bring about good removability from paint layers and good removal workability for removal efficiency.

This Description provides an acrylic coating composition for forming a paint-protective coating material (or abbreviated to a "coating composition" hereinafter) that forms a paint-protective coating material having a storage modulus at <NUM> of <NUM> MPa or higher and <NUM> MPa or lower and also having a storage modulus at <NUM> of <NUM> MPa or higher. The coating composition comprises an acrylic polymer as base polymer. The acrylic polymer-forming monomers include a monomer (mT) having a homopolymer Tg of <NUM> or higher and a monomer (mL) having a homopolymer Tg of -<NUM> or lower. Here, the monomer (mT) includes at least acrylonitrile. In the monomers, the monomer (mT) and the monomer (mL) have a molar ratio (mT/mL) of <NUM> or higher and <NUM> or lower. Such a coating composition can form a paint-protective coating material that shows good removability from paint layers and good removal workability.

In some embodiments of the art disclosed herein (including the paint-protective coating material, acrylic coating composition, paint protection method and so on disclosed herein; the same applies, hereinafter), the acrylic polymer preferably has a glass transition temperature calculated based on the monomer composition (or a "calculated Tg" hereinafter) of -<NUM> or higher and -<NUM> or lower. According to the acrylic polymer having a calculated Tg in the range, the resulting paint-protective coating material is likely to satisfy the G'(<NUM>) and G'(<NUM>) described above.

In some preferable embodiments, the acrylonitrile content of the monomers is above <NUM> % by mole (mol%). This can bring about a paint-protective coating material that combines good removability from paint layers and good removal workability at a higher level with good balance.

In some embodiments of the art disclosed herein, the coating composition may further comprise <NUM> part to <NUM> parts by weight of an inorganic powder to <NUM> parts by weight of the acrylic polymer. According to a paint-protective coating material formed from a coating composition having such a composition, with the inorganic powder blocking light such as UV rays, photodegradation can be inhibited in the paint-protective coating material itself as well as in the paint layer protected with the paint-protective coating material. The inorganic powder preferably comprises titanium dioxide.

The coating composition can be in aqueous emulsion form where the acrylic polymer is dispersed in an aqueous solvent. Such an aqueous emulsion-based coating composition is preferable from the standpoint of environmental hygiene, etc. For instance, it is suited for reducing amounts of organic solvents used and emitted.

This Description provides a paint protection method comprising preparing a coating composition that comprises an acrylic polymer as base polymer, applying the coating composition to a paint layer of an object to be protected, and drying the coating composition to form a paint-protective coating material that temporarily protects the paint layer. The acrylic polymer-forming monomers include a monomer (mT) having a homopolymer Tg of <NUM> or higher and a monomer (mL) having a homopolymer Tg of -<NUM> or lower. Here, the monomer (mT) includes at least acrylonitrile. In the monomers, the monomer (mT) and the monomer (mL) have a molar ratio (mT/mL) of <NUM> or higher and <NUM> or lower. Here, the paint-protective coating material has a storage modulus at <NUM> of <NUM> MPa or higher and <NUM> MPa or lower and a storage modulus at <NUM> of <NUM> MPa or higher. According to the paint protection method, the paint layer can be suitably protected with the paint-protective coating material. The paint-protective coating material can bring about good removability from paint layers and good removal workability.

In some preferable embodiments, the coating composition is applied with a slot die. By drying the slot-die coated coating composition, a paint-protective coating material can be efficiently formed on the paint layer.

In some embodiments of the art disclosed herein, the coating composition preferably has a viscosity V<NUM> of <NUM> Pa•s or higher and <NUM> Pa•s or lower, determined at <NUM> rpm using a BH viscometer. The coating composition preferably has a viscosity V<NUM> of <NUM> Pa•s or higher at a shear rate of <NUM> sec-<NUM>, determined using a cone plate rheometer. The coating composition showing such viscometric properties has applicability suited for slot-die coating. Accordingly, it can be preferably used in an embodiment where it is slot-die coated onto a paint layer of an object to be protected; and by drying the composition, a paint-protective coating material can be efficiently formed on the paint layer.

The scope of invention for which patent protection is being sought by this application includes suitable combinations of the respective elements described in this Description.

Preferable embodiments of the present invention are described below. Matters necessary to practice this invention other than those specifically referred to in this Description can be understood by a person skilled in the art based on the disclosure about implementing the invention in this Description and common technical knowledge at the time the application was filed. The present invention can be practiced based on the contents disclosed in this Description and common technical knowledge in the subject field.

In the following drawings, components or units having the same functions may be described with the same symbols allocated and the redundant description may be omitted or simplified. The embodiments illustrated in the drawings are schematic in order to clearly describe the present invention and the drawings do not accurately represent the size or scale of products actually provided.

As used herein, the term "acrylic polymer" refers to a polymerization product of monomers that include at least one species of monomer selected from the group consisting of a monomer having at least one (meth)acryloyl group per molecule and (meth)acrylonitrile. Hereinafter, the monomer having at least one (meth)acryloyl group per molecule and (meth)acrylonitrile are comprehensively referred to as "acrylic monomers" as well. Accordingly, as used herein, an acrylic polymer is defined as a polymer comprising a monomeric unit derived from an acrylic monomer. Typical examples of the acrylic polymer include a polymer whose acrylic monomer content accounts for more than <NUM> % by weight (preferably more than <NUM> % by weight, e.g., more than <NUM> % by weight) of the acrylic polymer-forming monomers.

As used herein, the term "(meth)acryloyl" comprehensively refers to acryloyl and methacryloyl. Similarly, the terms "(meth)acrylate," "(meth)acryl" and "(meth)acrylonitrile" comprehensively refer to acrylate and methacrylate, acryloyl and methacryloyl, and acrylonitrile and methacrylonitrile, respectively.

The acrylic coating composition in the art disclosed herein comprises an acrylic polymer as base polymer. Here, the term "base polymer" refers to a component accounting for more than <NUM> % by weight (typically <NUM> % by weight or more, e.g., <NUM> % by weight or more, possibly <NUM> % by weight or more, or even <NUM> % by weight) of the polymer in the acrylic coating composition. The base polymer in a paint-protective coating material also means the same.

The acrylic polymer-forming monomers include at least acrylonitrile. The inclusion of acrylonitrile in the monomers helps bring about a paint-protective coating material that combines well-balanced removability from paint layers and removal workability as well as an acrylic coating composition capable of forming the coating material. Besides acrylonitrile, other monomers possibly included in the monomers are not particularly limited and can be suitably selected to obtain a desirable paint-protective coating material.

A favorable example of the non-acrylonitrile monomers possibly included in the monomers is an alkyl (meth)acrylate. By selecting a species and an amount used, the alkyl (meth)acrylate may help adjust the storage modulus, tensile properties, the SP value described later, etc. For the alkyl (meth)acrylate, solely one species or a combination of two or more species can be used.

As the alkyl (meth)acrylate, for instance, a compound represented by the following formula (<NUM>) can be preferably used:.

Here, R<NUM> in the formula (<NUM>) is a hydrogen atom or a methyl group. R<NUM> in the formula (<NUM>) is an acyclic alkyl group having <NUM> to <NUM> carbon atoms. Hereinafter, such a range of the number of carbon atoms may be indicated as "C<NUM>-<NUM>. " The acyclic alkyl group can be linear or branched.

Specific examples of the alkyl (meth)acrylate wherein R<NUM> is a C<NUM>-<NUM> acyclic alkyl group are not particularly limited. Examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, <NUM>-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate and eicosyl (meth)acrylate.

The acrylic polymer-forming monomers may include, as the non-acrylonitrile monomer, a non-alkyl-(meth)acrylate monomer (a monomer that is not an alkyl (meth)acrylate). Examples of such monomers include functional group-containing monomers such as carboxy group-containing monomers, hydroxy (OH) group-containing monomers, acid anhydride group-containing monomers, amide group-containing monomers, amino group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, keto group-containing monomers, monomers having nitrogen atom-containing rings (N-containing rings), alkoxysilyl group-containing monomers and imide group-containing monomers. Proper use of functional group-containing monomers can increase the cohesive strength of acrylic polymer. The functional group-containing monomers may also help adjust the storage modulus, tensile properties, the SP value described later, etc..

Examples of carboxy group-containing monomers include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid and isocrotonic acid. Among them, AA and MAA are preferable.

Examples of hydroxy group-containing monomers include hydroxyalkyl (meth)acrylates such as <NUM>-hydroxyethyl (meth)acrylate, <NUM>-hydroxypropyl (meth)acrylate, <NUM>-hydroxypropyl (meth)acrylate, <NUM>-hydroxybutyl (meth)acrylate and <NUM>-hydroxybutyl (meth)acrylate; polypropylene glycol mono(meth)acrylate; and N-hydroxyethyl (meth)acrylamide. Particularly preferable hydroxy group-containing monomers include hydroxyalkyl (meth)acrylates having linear alkyl groups with two to four carbon atoms.

Examples of amide group-containing monomers include (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N-butyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methylolpropane (meth)acrylamide, N-methoxymethyl (meth)acrylamide and N-butoxymethyl (meth)acrylamide.

Examples of amino group-containing monomers include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate and t-butylaminoethyl (meth)acrylate.

Examples of epoxy group-containing monomers include glycidyl (meth)acrylate, methylglycidyl (meth)acrylate and allyl glycidyl ether.

Examples of cyano group-containing monomers include methacrylonitrile and <NUM>-cyanoethyl (meth)acrylate.

Examples of keto group-containing monomers include diacetone (meth)acrylamide, diacetone (meth)acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetoacetate and vinyl acetoacetate.

Examples of monomers having N-containing rings include N-vinyl-<NUM>-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam and N-(meth)acryloyl morpholine.

Examples of alkoxysilyl group-containing monomers include (<NUM>-(meth)acryloxypropyl)trimethoxysilane, (<NUM>-(meth)acryloxypropyl)triethoxysilane, (<NUM>-(meth)acryloxypropyl)methyldimethoxysilane and (<NUM>-(meth)acryloxypropyl)methyldiethoxysilane.

Examples of imide group-containing monomers include cyclohexylmaleimide and isopropylmaleimide.

For an increase in cohesive strength and like purpose, the acrylic polymer-forming monomers may include other comonomers besides the monomers described above. Examples of the other comonomers include vinyl ester-based monomers such as vinyl acetate, vinyl propionate and vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrenes (α-methylstyrene, etc.) and vinyltoluene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate and isobomyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as aryl (meth)acrylates (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylate (e.g., phenoxyethyl (meth)acrylate) and arylalkyl (meth)acrylate (e.g., benzyl (meth)acrylate); olefinic monomers such as ethylene, propylene, isoprene, butadiene and isobutylene; chlorine-containing monomers such as vinyl chloride and vinylidene chloride; isocyanate group-containing monomers such as <NUM>-(meth)acryloyloxyethylisocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate and ethyl carbitol (meth)acrylate; vinyl ether-based monomers such as methyl vinyl ether and ethyl vinyl ether; and a polyfunctional monomer having two or more (e.g., three or more) polymerizable functional groups (e.g. (meth)acryloyl groups) per molecule, such as <NUM>,<NUM>-hexanediol di(meth)acrylate and trimethylolpropane tri(meth)acrylate.

The acrylic polymer-forming monomers include a monomer (mT) having a homopolymer Tg of <NUM> or higher and a monomer (mL) having a homopolymer Tg of -<NUM> or lower. Here, the monomer (mT) includes at least acrylonitrile (homopolymer Tg: <NUM>). Accordingly, the acrylic polymer is a polymerization product of monomers that comprise the monomer (mL) and monomer (mT) comprising at least acrylonitrile and may further comprise other monomers. As for the homopolymer Tg values of the respective monomers, similar to the homopolymer glass transition temperatures used for determining the calculated Tg described later, values given in known documents are used. When no homopolymer Tg values are given in known documents, values obtained by the method according to <CIT> are used.

The monomer (mT) may increase the acrylic polymer's calculated Tg and help enhance the cohesive strength and high-temperature properties (e.g. less lowering of storage modulus in a high temperature range, removability at high temperatures, etc.). As the monomer (mT), acrylonitrile can be used alone or in combination with other monomer(s) having a homopolymer Tg of <NUM> or higher. For the other monomer(s) having a homopolymer Tg of <NUM> or higher, the corresponding species can be suitably selected among, for instance, the aforementioned various monomers while not limited to these. The other monomer(s) can be used with acrylonitrile, solely as one species or in a combination of two or more species. The maximum homopolymer Tg of each monomer used as the monomer (mT) is not particularly limited. For instance, it can be <NUM> or lower, <NUM> or lower, or even <NUM> or lower.

Non-limiting specific examples of the non-acrylonitrile monomer possibly used as the monomer (mT) include acrylic acid, methacrylic acid, methyl methacrylate, methacrylonitrile, acryloylmorpholine, acrylamide, isobomyl acrylate, isobomyl methacrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, adamantyl acrylate and tert-butyl methacrylate. Favorable examples include acrylic acid and methyl methacrylate.

The acrylonitrile content of monomer (mT) can be, for instance, <NUM> mol% or higher. From the standpoint of readily obtaining favorable physical properties of the coating material, it is suitably <NUM> mol% or higher, or preferably <NUM> mol% or higher. In some embodiments, the acrylonitrile content of monomer (mT) can be above <NUM> mol%, above <NUM> mol%, above <NUM> mol%, above <NUM> mol%, or even <NUM> mol%. In some embodiments, the acrylonitrile content of monomer (mT) can be <NUM> mol% or lower, <NUM> mol% or lower, <NUM> mol% or lower, or even <NUM> mol% or lower.

The acrylonitrile content of all the acrylic polymer-forming monomers can be, for instance, <NUM> mol% or higher. From the standpoint of readily obtaining favorable physical properties of the coating material, it is suitably <NUM> mol% or higher (e.g., <NUM> mol% or higher), preferably <NUM> mol% or higher, possibly <NUM> mol% or higher, or even <NUM> mol% or higher. The art disclosed herein can be preferably implemented in an embodiment where the acrylonitrile content of all the acrylic polymer-forming monomers is above <NUM> mol%. From the standpoint of the flexibility of the paint-protective coating material, the acrylonitrile content is suitably <NUM> mol% or lower, or preferably below <NUM> mol%. In some embodiments, the acrylonitrile content can be <NUM> mol% or lower, or even <NUM> mol% or lower. The art disclosed herein can also be implemented in an embodiment where the acrylonitrile content is <NUM> mol% or lower, <NUM> mol% or lower, or even <NUM> mol% or lower.

The monomer (mL) may lower the acrylic polymer's calculated Tg and help enhance the low-temperature properties (e.g., cracking resistance at low temperatures, breaking/tearing resistance during removal from paint layers at low temperatures, etc.) of the paint-protective coating material. As the monomer (mL), a species having a homopolymer Tg of -<NUM> or lower can be used. It can be selected among, but not limited to, for instance, the aforementioned various monomers. For the monomer (mL), solely one species or a combination of two or more species can be used. Non-limiting specific examples of monomers usable as the monomer (mL) include n-butyl acrylate (BA), <NUM>-ethylhexyl acrylate (2EHA), isooctyl acrylate, isononyl acrylate, isoamyl acrylate, <NUM>-hydroxybutyl acrylate (4HBA), methoxyethyl acrylate, ethyl carbitol acrylate and ethoxy diethyleneglycol acrylate.

The minimum homopolymer Tg of each monomer used as the monomer (mL) is not particularly limited. It can be, for instance, -<NUM> or higher, -<NUM> or higher, or -<NUM> or higher. In some embodiments, as the monomer (mL), a monomer having a homopolymer Tg in the range of -<NUM> or higher and -<NUM> or lower can be preferably used. Of the monomer (mL), the ratio of monomer whose homopolymer Tg is in the range of -<NUM> or higher and -<NUM> or lower can be, for instance, <NUM> mol% or higher, <NUM> mol% or higher, <NUM> mol% or higher, <NUM> mol% or higher, or even <NUM> mol%.

In the monomers, the molar ratio (mT/mL) between the monomer (mT) and the monomer (mL) is suitably <NUM> or higher and <NUM> or lower. With the acrylic polymer formed from monomers having such a composition, the resulting paint-protective coating material is likely to satisfy the aforementioned G'(<NUM>) and G'(<NUM>). In some embodiments, the ratio mT/mL is preferably below <NUM>, more preferably <NUM> or lower, possibly <NUM> or lower, <NUM> or lower, or even <NUM> or lower. In some embodiments, the ratio mT/mL is preferably <NUM> or higher, or more preferably above <NUM>. This can bring about a paint-protective coating material that combines good removability from paint layers and good removal workability at a higher level with good balance. The ratio mT/mL can also be <NUM> or higher, <NUM> or higher, or even <NUM> or higher.

The acrylic polymer-forming monomers may further include other monomer(s) besides the monomers (mT) and (mL), that is, a monomer having a homopolymer glass transition temperature of higher than -<NUM> and lower than <NUM> (or a monomer (mI) hereinafter). As the monomer (mI), a species having a homopolymer glass transition temperature in the range can be selected among for instance, the aforementioned various monomers while it is not limited to these. For the monomer (mI), solely one species or a combination of two or more species can be used. Non-limiting specific examples of monomers usable as the monomer (mI) include ethyl acrylate (EA), ethyl methacrylate, methyl acrylate (MA), n-butyl methacrylate, isobutyl methacrylate, <NUM>-hydroxyethyl acrylate, <NUM>-hydroxyethyl methacrylate, <NUM>-hydroxypropyl acrylate, <NUM>- hydroxypropyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, vinyl acetate and N-vinyl-<NUM>-pyrrolidone.

The amount of monomer (mi) used can be suitably selected in the range up to the amount (mol%) obtained by subtracting the amounts (mol%) of monomers (mT) and (mL) from the amount of all monomers (<NUM> mol%). Of all monomers, the amount of monomer (mi) used is suitably no more than <NUM> mol%, preferably no more than <NUM> mol%, or more preferably no more than <NUM> mol%. The art disclosed herein can be preferably practiced in an embodiment where the amount of monomer (mi) used is <NUM> mol% or greater and below <NUM> mol% of all monomers, for instance, <NUM> mol% or greater and below <NUM> mol%. Here, that the amount of monomer (mi) used is <NUM> mol% of all monomers means that no monomer (mi) is used at least intentionally.

While no particular limitations are imposed, the calculated Tg of the acrylic polymer can be, for instance, -<NUM> or higher. In some embodiments, from the standpoint of the removability of the paint-protective coating material in a high temperature range (e.g., around <NUM>), it is suitably -<NUM> or higher, preferably -<NUM> or higher, possibly -<NUM> or higher, or even -<NUM> or higher. From the standpoint of the removal workability (e.g., reduction of failed removal due to chipping and tearing of the paint-protective coating material) when removing the paint-protective coating material from paint layers in a low-temperature environment such as outdoors in winter, in some embodiments, the acrylic polymer's calculated Tg is suitably <NUM> or lower, preferably -<NUM> or lower (e.g., -<NUM> or lower), possibly -<NUM> or lower, or even -<NUM> or lower. When the protected object provided with the paint-protective coating material is exposed to changes in temperature, it is also advantageous that the acrylic polymer's calculated Tg is not excessively high in view of reducing cracking in the paint-protective coating material caused by a difference in linear expansion coefficient compared to the protected object, etc..

Here, the acrylic polymer's calculated Tg refers to the Tg value determined by the Fox equation based on the composition of the monomers used in synthesizing the polymer. As shown below, the Fox equation is a relational expression between the Tg of a copolymer and glass transition temperatures Tgi of homopolymers of the respective monomers constituting the copolymer.

In the Fox equation, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi the weight fraction (copolymerization ratio by weight) of a monomer i in the copolymer, and Tgi the glass transition temperature (unit: K) of homopolymer of the monomer i.

As the glass transition temperatures of homopolymers used for determining the calculated Tg value, values found in publicly known documents are used. For example, with respect to the monomers listed below, as the glass transition temperatures of homopolymers of the monomers, the following values are used:.

With respect to the glass transition temperatures of homopolymers of monomers other than those listed above, values given in "<NPL>) are used. When no homopolymer Tg values are given in known documents, values obtained by the method according to <CIT> are used. In particular, to a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet and a condenser, are added <NUM> parts by weight of monomer, <NUM> part by weight of azobisisobutyronitrile, and <NUM> parts by weight of ethyl acetate as a polymerization solvent, and the mixture is stirred for one hour under a nitrogen gas flow. After oxygen is removed in this way from the polymerization system, the mixture is heated to <NUM> and the reaction is carried out for <NUM> hours. Then, it is cooled to room temperature, and a homopolymer solution having <NUM> % by mass solids content is obtained. Then, this homopolymer solution is applied onto a release liner by flow coating and allowed to dry to prepare a test sample (a sheet of homopolymer) of about <NUM> thickness. This test sample is cut out into a disc of <NUM> diameter and is placed between parallel plates; and while applying a shear strain at a frequency of <NUM> using a rheometer (model name ARES available from TA Instruments, Japan), the viscoelasticity is measured in the shear mode over a temperature range of -<NUM> to <NUM> at a heating rate of <NUM>/min; and the peak temperature of the tan δ curve is taken as the Tg of the homopolymer.

In some embodiments, the acrylic polymer's SP value is suitably greater than <NUM> (unit: (cal/cm<NUM>)<NUM>/<NUM>; the same applies hereinafter), preferably <NUM> or greater, or more preferably <NUM> or greater. As used herein, the SP value refers to the solubility parameter value determined from the basic structure of the compound by the method proposed by Fedors. Such an acrylic polymer's SP value can be far from (typically far above) the SP value of the paint layer to be protected. For instance, the paint layer can be a urethane-based paint layer formed upon reaction between an acrylic polyol resin and a polyisocyanate resin. With the acrylic polymer's SP value being far from the paint layer's SP value, the paint-protective coating material comprising the acrylic polymer tends to be less interactive with the paint layer. This is advantageous in view of reducing paint layer deformation caused by the paint-protective coating material as well as reducing failed removal and the rising removal workload due to the paint-protective coating material adhered too tightly to the paint layer. In some embodiments, the acrylic polymer's SP value can be <NUM> or higher, <NUM> or higher, or even <NUM> or higher. The maximum SP value of the acrylic polymer is not particularly limited. For instance, it is suitably <NUM> or lower, possibly <NUM> or lower, <NUM> or lower, below <NUM>, or even below <NUM>.

The method for obtaining an acrylic polymer from monomers as those described above is not particularly limited. Known polymerization methods can be suitably employed, such as emulsion polymerization, solution polymerization, bulk polymerization, and suspension polymerization. It is also possible to employ photopolymerization involving irradiation of light such as UV (typically carried out in the presence of a photopolymerization initiator) and active energy ray irradiation polymerization such as radiation polymerization involving irradiation of radioactive rays such as β rays and γ rays. In some preferable embodiments, the acrylic polymer is obtained by emulsion polymerization of monomers having an aforementioned composition. As the monomer supply method in emulsion polymerization, a suitable method can be employed among the all-at-once method where all the starting monomer mixture is supplied in one portion, gradual supply method, portion-wise supply method, etc. An emulsion of some or all of the monomers pre-mixed with water and emulsifier can be supplied to the polymerization vessel.

The polymerization temperature can be suitably selected in accordance with the monomer species, the solvent species, and the polymerization initiator species used, etc. The polymerization temperature is suitably about <NUM> or higher, preferably about <NUM> or higher, more preferably about <NUM> or higher; it can also be about <NUM> or higher, about <NUM> or higher, or even about <NUM> or higher. The polymerization temperature is suitably about <NUM> or lower (typically about <NUM> or lower), or preferably about <NUM> or lower (e.g. about <NUM> or lower). In emulsion polymerization, the polymerization temperature is preferably about <NUM> or lower (e.g. about <NUM> or lower).

The solvent (polymerization solvent) used for solution polymerization can be suitably selected among heretofore known organic solvents. For instance, aromatic compounds (typically aromatic hydrocarbons) such as toluene, acetic acid esters such as ethyl acetates, aliphatic and alicyclic hydrocarbons such as hexane and cyclohexane are preferably used.

In the polymerization, a known or commonly used thermal polymerization initiator or photopolymerization initiator can be used in accordance with the polymerization method and polymerization conditions. For the polymerization initiator, solely one species or a combination of two or more species can be used.

While no particular limitations are imposed, as the thermal polymerization initiator, it is possible to use, for example, an azo-based initiator, peroxide-based initiator or redox-based initiator by the combination of a peroxide and a reducing agent.

Examples of azo-based initiators include <NUM>,<NUM>'-azobisisobutyronitrile, <NUM>,<NUM>'-azobis[N-(<NUM>-carboxyethyl)-<NUM>-methylpropionamidine] hydrate, <NUM>,<NUM>'-azobis(<NUM>-methylpropionamidine) disulfate salt, <NUM>,<NUM>'-azobis(<NUM>-methylpropionamidine) dihydrochloride, <NUM>,<NUM>'-azobis(<NUM>-methylpropionamidine) dihydrochloride, <NUM>,<NUM>'-azobis[<NUM>-(<NUM>-methyl-<NUM>-imidazolin-<NUM>-yl)propane] dihydrochloride and <NUM>,<NUM>'-azobis(N,N'-dimethylene isobutylamidine) dihydrochloride.

Examples of peroxide-based initiators include persulfates such as potassium persulfate and ammonium persulfate; benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, dicumyl peroxide, dilauroyl peroxide, di-n-octanoyl peroxide, di(<NUM>-methylbenzoyl) peroxide, t-butyl peroxybenzoate, t-butyl peroxyisobutyrate, t-hexyl peroxypivalate, t-butyl peroxypivalate, di(<NUM>-ethylhexyl) peroxydicarbonate, di(<NUM>-t-butylcyclohexyl) peroxydicarbonate, di-sec-butyl peroxydicarbonate, t-butyl peroxyneodecanoate, <NUM>,<NUM>,<NUM>,<NUM>-tetramethyl butylperoxy-<NUM>-ethylhexanoate, <NUM>,<NUM>-bis(t-butylperoxy)-<NUM>,<NUM>,<NUM>-trimethylcyclohexane, <NUM>,<NUM>-bis(t-butylperoxy)cyclododecane, <NUM>,<NUM>-bis(t-hexylperoxy)cyclohexane and hydrogen peroxide.

Examples of redox-based initiators include a combination of a peroxide and ascorbic acid (combination of hydrogen peroxide water and ascorbic acid, etc.), a combination of a peroxide and an iron(II) salt (combination of hydrogen peroxide water and an iron(II) salt, etc.), and a combination of a persulfate salt and sodium hydrogen sulfite.

The photopolymerization initiator is not particularly limited. It is possible to use, for instance, ketal-based photopolymerization initiators, acetophenone-based photopolymerization initiators, benzoin ether-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, α-ketol photopolymerization initiators, aromatic sulphonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzylic photopolymerization initiators, benzophenone-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators.

The polymerization initiator can be used in a usual amount in accordance with the polymerization method, embodiment of polymerization, etc., and there are no particular limitations to the amount. For instance, relative to <NUM> parts by weight of monomers to be polymerized, about <NUM> part to <NUM> parts by weight (typically about <NUM> part to <NUM> parts by weight, e.g. about <NUM> part to <NUM> part by weight) of polymerization initiator can be used.

For the polymerization, as necessary, various heretofore known chain transfer agents (which can be considered also as a molecular weight-adjusting agent or polymerization degree-adjusting agent) can be used. For the chain transfer agent, solely one species or a combination of two or more species can be used. As the chain transfer agent, mercaptans can be used, such as n-dodecyl mercaptan, t-dodecyl mercaptan and thioglycolic acid. Alternatively, a chain transfer agent free of sulfur atoms (a sulfur-free chain transfer agent) can be used as well. Specific examples of the sulfur-free chain transfer agent include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenoids such as α-pinene and terpinolene; styrenes such as α-methylstyrene and α-methylstyrene dimer; compounds having benzylidenyl groups such as dibenzylidene acetone, cinnamyl alcohol and cinnamyl aldehyde; hydroquinones such as hydroquinone and naphthohydroquinone; quinones such as benzoquinone and naphthoquinone; olefins such as <NUM>,<NUM>-dimethyl-<NUM>-butene and <NUM>,<NUM>-cyclooctadiene; alcohols such as phenol, benzyl alcohol and allyl alcohol; and benzyl hydrogens such as diphenylbenzene and triphenylbenzene.

When using a chain transfer agent, it can be used in an amount of, for instance, about <NUM> part to <NUM> part by weight to <NUM> parts by weight of the monomers. The art disclosed herein can also be preferably implemented in an embodiment that uses no chain transfer agent.

Emulsion polymerization is usually carried out in the presence of an emulsifier. The emulsifier used in the emulsion polymerization is not particularly limited; known anionic emulsifiers, nonionic emulsifiers and the like can be used. These emulsifiers can be used singly as one species or in a combination of two or more species.

Non-limiting examples of anionic emulsifiers include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecyl benzene sulfonate, sodium polyoxyethylene lauryl sulfate, sodium polyoxyethylene alkyl ether sulfates, ammonium polyoxyethylene alkyl phenyl ether sulfates, sodium polyoxyethylene alkyl phenyl ether sulfates, and sodium polyoxyethylene alkyl sulfosuccinates. Non-limiting examples of non-ionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene aliphatic acid esters, and polyoxyethylene-polyoxypropylene block polymers. Reactive functional group-containing emulsifiers (reactive emulsifiers) can be used as well. Examples of reactive emulsifiers include a radically polymerizable emulsifier having a structure of an aforementioned anionic emulsifier or nonionic emulsifier with a radically polymerizable group such as propenyl group and ally ether group introduced therein.

In the emulsion polymerization, the emulsifier can be used in an amount of, for instance, <NUM> part by weight or greater, <NUM> part by weight or greater, or <NUM> part by weight or greater, or even <NUM> parts by weight or greater, relative to <NUM> parts by weight of the monomers. In some embodiments, the amount of emulsifier used is usually suitably <NUM> parts by weight or less to <NUM> parts by weight of the monomers, preferably <NUM> parts by weight or less, or possibly even <NUM> parts by weight or less.

Emulsion polymerization can also be carried out in the presence of a protective colloid. Examples of the protective colloid include polyvinyl alcohols such as a partially-saponified polyvinyl alcohol, fully-saponified polyvinyl alcohol and modified polyvinyl alcohol; cellulose derivatives such as hydroxyethyl cellulose, hydroxypropyl cellulose and carboxymethyl cellulose; and natural polysaccharides such as guar gum. The partially saponified polyvinyl alcohol has a saponification degree typically below <NUM> mol%, possibly below <NUM> mol%, or even below <NUM> mol%. The minimum saponification degree of the partially saponified polyvinyl alcohol is not particularly limited. From the standpoint of the emulsion stability, etc., it is suitably <NUM> mol% or higher, preferably <NUM> mol% or higher, or more preferably <NUM> mol% or higher (e.g., <NUM> mol% or higher). Examples of the modified polyvinyl alcohol include an anionic modified polyvinyl alcohol having an anionic group such as a carboxy group and a sulfonic acid group; and a cationic modified polyvinyl alcohol having a cationic group such as a quaternary ammonium salt. For instance, the modified polyvinyl alcohol has a saponification degree below <NUM> mol%, possibly below <NUM> mol%, below <NUM> mol%, or even below <NUM> mol%. The minimum saponification degree of the modified polyvinyl alcohol can be, for instance, <NUM> mol% or higher. From the standpoint of the emulsion stability, etc., it is suitably <NUM> mol% or higher, preferably <NUM> mol% or higher, or more preferably <NUM> mol% or higher (e.g., <NUM> mol% or higher). For the protective colloid, solely one species or a combination of two or more species can be used.

The amount of protective colloid used to <NUM> parts by weight of monomers is suitably <NUM> part by weight or greater, preferably <NUM> part by weight or greater (e.g., <NUM> part by weight or greater) and suitably <NUM> parts by weight or less, or preferably <NUM> parts by weight or less (e.g., <NUM> parts by weight or less, or <NUM> parts by weight or less). The use of the protective colloid is preferably combined with an aforementioned emulsifier, but not limited to this. The protective colloid can be used without using an emulsifier. For instance, emulsion polymerization can be carried out in the following embodiment: water and a protective colloid are placed into a polymerization vessel; monomers are partially or entirely pre-mixed and emulsified with water and an emulsifier; and the resulting emulsion is supplied to the polymerization vessel. When using an anionic protective colloid (e.g., anionic polyvinyl alcohol) and an emulsifier together, from the standpoint of the polymerization stability and like, as the emulsifier, it is preferable to use one, two or more species selected from the group of anionic emulsifiers and nonionic emulsifiers.

In some preferable embodiments, emulsion polymerization is carried out in the presence of an anionic modified polyvinyl alcohol. Aqueous acrylic polymer emulsions obtained by such emulsion polymerization tend to bring about thickening effect upon addition of thickeners. With the use of such an aqueous acrylic polymer emulsion, an acrylic coating composition can be favorably prepared, showing good viscometric properties suited for slot-die coating. Favorable examples of the anionic modified polyvinyl alcohol include sulfonic acid-modified polyvinyl alcohols and carboxylated polyvinyl alcohols. For instance, a sulfonic acid-modified polyvinyl alcohol and/or a carboxylated polyvinyl alcohol can be preferably used. An anionic modified polyvinyl alcohol can be used in combination with an emulsifier.

The acrylic coating composition disclosed herein comprises an aforementioned acrylic polymer as base polymer. The form of the acrylic coating composition is not particularly limited. For instance, it can be an aqueous emulsion-based composition in which the acrylic polymer is dispersed in an aqueous solvent, a solvent-based composition in which the acrylic polymer is dissolved in an organic solvent, etc. From the standpoint of the environmental hygiene, an aqueous emulsion-based coating composition is preferable. The following mainly describes the aqueous emulsion-based coating composition; however, the acrylic coating composition disclosed herein is not to be limited to the aqueous emulsion type.

In the aqueous emulsion-based coating composition, the aqueous solvent is water or a solvent mixture comprising water as the primary component (a component accounting for more than <NUM> % by weight). The other solvent(s) forming the solvent mixture besides water can be one, two or more species selected from various water-miscible organic solvents (lower alcohols, etc.). In the aqueous solvent in this description, the water content is typically <NUM> % by weight or higher, or preferably <NUM> % to <NUM> % by weight.

The coating composition disclosed herein can include various additives as desired. Examples of the additives include known thickener, thixotropic agent, dispersing agent, defoaming agent and inorganic powder. For instance, by adding various additives to an aqueous emulsion (polymerization reaction mixture) of acrylic polymer obtained by emulsion polymerization as described above, an aqueous emulsion-based coating composition cam be prepared. Alternatively, as the coating composition, aqueous emulsion of the acrylic polymer can be used as is or after pH adjustment (e.g. pH adjusted to about <NUM> to <NUM> by addition of ammonia water) and/or concentration adjustment (e.g. NV adjusted to about <NUM> % to <NUM> % by weight by addition of water).

Inorganic powder is included in the coating composition to form an inorganic powder-containing coating material. According to such a coating material, with the inorganic powder blocking light such as UV rays, photodegradation can be inhibited in the coating material itself as well as in the paint layer protected with the coating material. As the inorganic powder, oxides such as titanium dioxide, zinc oxide, magnesium oxide, alumina and silica; carbonates such as calcium carbonate; sulfates such as barium sulfate; and the like can be used. Inorganic powder capable of coloring the paint-protective coating material in white is preferable. With the white-colored paint-protective coating material, for instance, the temperature rise in sunlight can be reduced to better inhibit degradation of the coating material and the paint layer.

The amount of inorganic powder used to <NUM> parts by weight of acrylic polymer can be, for instance, <NUM> part by weight or greater. From the standpoint of the light-blocking effect, it is suitably <NUM> part by weight or greater, preferably <NUM> parts by weight or greater, more preferably <NUM> parts by weight or greater, possibly <NUM> parts by weight or greater, <NUM> parts by weight or greater, <NUM> parts by weight or greater, or even <NUM> parts by weight or greater. The amount of inorganic powder used to <NUM> parts by weight of acrylic polymer can be, for instance, <NUM> parts by weight or less. From the standpoint of the coating material's strength and ease of coating, it is suitably <NUM> parts by weight or less, advantageously <NUM> parts by weight or less, preferably <NUM> parts by weight or less, possibly <NUM> parts by weight or less, or even <NUM> parts by weight or less.

In some preferable embodiments, the inorganic power comprises at least titanium dioxide (TiO<NUM>). Titanium dioxide can also be used in combination with one, two or more species of other inorganic powder (e.g., calcium carbonate). The type of titanium dioxide is not particularly limited. For instance, titanium dioxide in any crystal form such as rutile, anatase and brookite can be used. In particular, rutile titanium dioxide is preferable. Titanium dioxide having coated particle surfaces can be used as well. The coating material of the titanium dioxide particles is not particularly limited. For instance, it can be an inorganic oxide such as silica, alumina and zinc oxide. Favorable examples include highly weather-resistant titanium dioxide (typically rutile titanium dioxide) having particle surfaces coated with Si-Al<NUM>O<NUM>, etc..

The amount of titanium dioxide used to <NUM> parts by weight of acrylic polymer can be, for instance, <NUM> part by weight or greater. From the standpoint of the light-blocking effect, it is suitably <NUM> part by weight or greater, preferably <NUM> part by weight or greater, more preferably <NUM> parts by weight or greater, or possibly even <NUM> parts by weight or greater. The amount of titanium dioxide used to <NUM> parts by weight of acrylic polymer is, for instance, possibly <NUM> parts by weight or less, suitably <NUM> parts by weight or less, preferably <NUM> parts by weight or less, possibly <NUM> parts by weight or less, or even <NUM> parts by weight or less.

The mean particle diameter of the inorganic powder is not particularly limited. For instance, from the standpoint of obtaining good light-blocking effect, the inorganic powder has a mean particle diameter of preferably <NUM> or greater, more preferably <NUM> or greater, possibly <NUM> or greater, or even <NUM> or greater. On the other hand, from the standpoint of the dispersity in resins, the mean particle diameter of the inorganic powder is suitably <NUM> or less, preferably <NUM> or less, more preferably <NUM> or less (e.g., <NUM> or less), possibly <NUM> or less, <NUM> or less, or even <NUM> or less. For instance, it is preferable to use titanium dioxide particles having a mean particle diameter of about <NUM> to <NUM>.

Thickener may help adjust the viscometric properties of the coating composition. As the thickener, known thickeners can be used such as urethane-based thickeners, cellulose-based thickeners, polyether-based thickeners and acrylic thickeners. For the thickener, solely one species or a combination of two or more species can be used.

Examples of commercial urethane-based thickeners include product names RHEOBYK-H 3300VF, RHEOBYK-T <NUM> and RHEOBYK-L <NUM> available from BYK; product names ADEKA NOL UH-450VF, ADEKA NOL UH-<NUM>, ADEKA NOL UH-<NUM>, ADEKA NOL UH-<NUM>, ADEKA NOL UH-<NUM>, ADEKA NOL UH-756VF and ADEKA NOL UH-814N available from ADEKA; and product names SN-THICKENER <NUM>, SN-THICKENER 621N, SN-THICKENER 625N, SN-THICKENER 627N and SN-THICKENER 660T available from San Nopco, Ltd. In some embodiments, as the urethane-based thickener, a urethane associative thickener can be preferably used. Favorable examples of the urethane associative thickener include product names RHEOBYK-H 3300VF, RHEOBYK-T <NUM> and RHEOBYK-L <NUM> available from BYK; and product names ADEKA NOL UH-450VF and ADEKA NOL UH-<NUM> available from ADEKA.

Examples of cellulose-based thickeners include hydroxyethyl cellulose, carboxymethyl cellulose and methyl cellulose. Examples of commercial products include product name SANHEC L available from Sansho Co.

Examples of polyether-based thickeners include polyethylene glycol, polyether dialkyl esters, polyether dialkyl ethers and epoxidized polyether. Examples of commercial products include product name POLYOX WSRN-<NUM> available from Dow Chemical Company.

Examples of acrylic thickeners include acrylate-based polymers such as sodium polyacrylate. Examples of commercial products include product names PRIMAL ASE-<NUM>, PRIMAL TT-<NUM> and PRIMAL RM-<NUM> available from Rohm and Haas Company; and product names SN-THICKENER <NUM>, SN-THICKENER <NUM>, SN-THICKENER <NUM>, SN-THICKENER <NUM> and SN-THICKENER <NUM> available from San Nopco, Ltd.

The amount of thickener used is not particularly limited and can be suitably adjusted to obtain desirable viscometric properties. From the standpoint of reducing excessive influence on physical properties of the coating material, in some embodiments, the amount of thickener used to <NUM> parts by weight of acrylic polymer is suitably <NUM> parts by weight or less, preferably <NUM> parts by weight or less, more preferably <NUM> parts by weight or less (e.g., <NUM> parts by weight or less), possibly <NUM> parts by weight or less, or even <NUM> parts by weight or less. The minimum amount of thickener used is not particularly limited. For instance, to <NUM> parts by weight of acrylic polymer, it can be <NUM> part by weight or greater, <NUM> part by weight or greater, or even <NUM> part by weight or greater.

Thixotropic agent may help adjust the viscometric properties of the coating composition. As the thixotropic agent, an inorganic material can be used, for instance, bentonite, modified bentonite, montmorillonite, hectorite, etc. For the thixotropic agent, solely one species or a combination of two or more species can be used.

The amount of thixotropic agent used is not particularly limited and can be suitably adjusted to obtain desirable viscometric properties. From the standpoint of reducing excessive influence on physical properties of the coating material, in some embodiments, the amount of thixotropic agent used to <NUM> parts by weight of acrylic polymer is suitably <NUM> parts by weight or less, preferably <NUM> parts by weight or less, possibly <NUM> parts by weight or less, <NUM> parts by weight or less, or even <NUM> parts by weight or less. The minimum amount of thixotropic agent used is not particularly limited. For instance, to <NUM> parts by weight of acrylic polymer, it can be <NUM> part by weight or greater, <NUM> part by weight or greater, or even <NUM> part by weight or greater.

The thixotropic agent may also serve as a thickener. These thickener and thixotropic agent can be used together, or just one of them can be used. When using a thickener and thixotropic agent together, their combined amount used to <NUM> parts by weight of acrylic polymer can be, for instance, <NUM> parts by weight or less, <NUM> parts by weight or less, <NUM> parts by weight or less, <NUM> parts by weight or less, or even <NUM> parts by weight or less; and <NUM> part by weight or greater, <NUM> part by weight or greater, or <NUM> part by weight or greater.

As for the method for applying the coating composition onto the paint layer of the obj ect to be protected, it is possible to employ application with a coater such as a die coater and spray coater as well as roller coating, dip coating, etc. The die coating can be carried out by a coating system including a robot arm equipped with a slit die. For instance, by controlling the robot arm to extrude the coating composition into continuous liquid film (in ribbon form) while allowing the slit die to move along the shape of the object to be protected, even when the object has a non-flat shape (e.g., a complex three-dimensional shape such as an automobile body shell), the coating composition can be applied efficiently and precisely onto the object.

From the standpoint of increasing the efficiency and precision of coating material formation, the applied coating composition is preferably dried with heat. The drying temperature can be, for instance, about <NUM> to <NUM> and is typically preferably about <NUM> to <NUM>.

While no particular limitations are imposed, from the standpoint of the ease of application and coating thickness management, etc., the non-volatile content (NV) of the coating composition is suitably about <NUM> % to <NUM> % by weight or preferably about <NUM> % to <NUM> % by weight. The NV can be adjusted through the amount of solvent (e.g., aqueous solvent) used. For instance, the NV of the coating composition can be adjusted through adjustment of the amount of water used in emulsion polymerization or addition of water after completion of emulsion polymerization.

The thickness of the paint-protective coating material is not particularly limited. From the standpoint of enhancing the protective effect, it is suitably <NUM> or greater. From the standpoint of the strength and removal workability, it is preferably <NUM> or greater, or more preferably <NUM> or greater (e.g., <NUM> or greater). The thickness of the coating material can be adjusted through the applied amount and NV of the coating composition. From the standpoint of the drying efficiency and sagging prevention of the applied composition, the thickness of the paint-protective coating material is suitably <NUM> or less, preferably <NUM> or less, or more preferably <NUM> or less.

In some embodiments, determined at <NUM> rpm using a BH viscometer, the coating composition has a viscosity V<NUM> of suitably <NUM> Pa•s or higher, preferably <NUM> Pa•s or higher, or more preferably <NUM> Pa•s or higher. With increasing viscosity V<NUM> determined at such a low shear rate, the anti-sag properties of the coating composition applied on the object to be protected tends to improve. On the other hand, from the standpoint of the defoaming properties and leveling properties of the coating composition, the coating composition's viscosity V<NUM> is suitably <NUM> Pa•s or lower, preferably <NUM> Pa•s or lower, or more preferably <NUM> Pa•s or lower (e.g., <NUM> Pa•s or lower).

Determined at <NUM> rpm using a BH viscometer, the coating composition has a viscosity V<NUM> which is not particularly limited and can be, for instance, about <NUM> Pa•s to <NUM> Pa•s. When the viscosity V<NUM> is in this range, an aforementioned V<NUM> value is likely to be obtained. The BH viscosity (viscosity determined with a BH viscometer) of the coating composition is determined according to the method described later in Examples.

In some embodiments, determined using a cone plate rheometer, the coating composition has a viscosity V<NUM> at a shear rate of <NUM> sec-<NUM> of preferably <NUM> Pa•s or higher, more preferably <NUM> Pa•s or higher, possibly <NUM> Pa•s or higher, <NUM> Pa•s or higher, or even <NUM> Pa•s or higher. When the viscosity V<NUM> determined at such a high shear rate is at least the prescribed values, the slot-die applicability (die-coating properties) can be increased. The maximum viscosity V<NUM> is not particularly limited. From the standpoint of the ease of combining with defoaming properties and ease of fluid feeding, it is suitably <NUM> Pa•s or lower, preferably <NUM> Pa•s or lower, possibly <NUM> Pa•s or lower, or even <NUM> Pa•s or lower. The rheometer viscosity (viscosity determined with a rheometer) of the coating composition is determined according to the method described later in Examples.

The paint-protective coating material disclosed herein can be formed using a coating composition as those described above. For instance, the coating composition is applied (preferably slot-die coated) onto a paint layer of an object to be protected and allowed to dry. By this, for instance, as shown in <FIG>, a paint-protective coating material <NUM> formed from the coating composition can be formed on a paint layer <NUM> of an object <NUM> to be protected.

The paint-protective coating material has a storage modulus at <NUM> (G'(<NUM>)) of <NUM> MPa or higher, preferably <NUM> MPa or higher, possibly <NUM> MPa or higher, or even <NUM> MPa or higher. The coating material having a G'(<NUM>) of at least the prescribed values tends to be less susceptible to tearing and excessive elongation while being peeled off the paint layer in a room temperature range. This is advantageous in view of increasing the removability. According to the present invention, G'(<NUM>) is suitably about <NUM> MPa or lower. From the standpoint of reducing marking on paint layers, it is also advantageous that G'(<NUM>) is not excessively high. It is also preferable in view of removal workability because it facilitates the initial action to start removing the coating material from the paint layer (e.g., scratching an edge of the coating material with a fingernail, etc., for lifting from the paint layer). In some embodiments, G'(<NUM>) can be <NUM> MPa or lower, <NUM> MPa or lower, <NUM> MPa or lower, <NUM> MPa or lower, or even <NUM> MPa or lower.

The paint-protective coating material has a storage modulus at <NUM> (G'(<NUM>)) of suitably <NUM> MPa or higher, or preferably <NUM> MPa or higher. The coating material having a G'(<NUM>) of at least the prescribed values can be suitably removed from paint layers without excessive softening even at a temperature higher than room temperature, such as when the protected object provided with the coating material is placed outdoors in summer. From the standpoint of enhancing the removability at high temperatures, in some embodiments, G'(<NUM>) is advantageously <NUM> MPa or higher, preferably <NUM> MPa or higher, possibly <NUM> MPa or higher, or even <NUM> MPa or higher. The maximum G'(<NUM>) is not particularly limited. From the standpoint of obtaining an aforementioned G' (<NUM>) value, it is suitably <NUM> MPa or lower, preferably <NUM> MPa or lower, possibly <NUM> MPa or lower, or even <NUM> MPa or lower. In some embodiments, G'(<NUM>) can also be <NUM> MPa or lower, or even <NUM> MPa or lower. From the standpoint of reducing marking on paint layers, it is also advantageous that G'(<NUM>) is not excessively high.

The storage moduli of the paint-protective coating material at <NUM>, <NUM> and other temperatures are determined according to the method described later in Examples.

In some embodiments of the paint-protective coating material disclosed herein, determined as the tan δ peak temperature in viscoelastic analysis, the coating material has a glass transition temperature (or "RSA-Tg" hereinafter) of suitably <NUM> or higher, preferably <NUM> or higher, or more preferably <NUM> or higher. RSA-Tg can be, for instance, <NUM> or lower, <NUM> or lower, or even <NUM> or lower (e.g., <NUM> or lower). The paint-protective coating material having an RSA-Tg value in these ranges is likely to satisfy the aforementioned G'(<NUM>) and G'(<NUM>) values.

Determined as the temperature corresponding to the inflection point of loss modulus G" in viscoelastic analysis, the coating material according to some embodiments has a glass transition temperature (or "RSA-Tg(G")" hereinafter) of suitably <NUM> or higher, preferably <NUM> or higher, or more preferably <NUM> or higher. RSA-Tg(G") can be, for instance, <NUM> or lower, <NUM> or lower, or even <NUM> or lower (e.g., <NUM> or lower). The paint-protective coating material having an RSA-Tg(G") value in these ranges is likely to satisfy the aforementioned G'(<NUM>) and G'(<NUM>) values. Examples A1 to A10 described later had the following RSA-Tg(G") values: <NUM> (A1), <NUM> (A2), <NUM> (A3), <NUM> (A4), <NUM> (A5), <NUM> (A6), <NUM> (A7), <NUM> (A8), <NUM> (A9) and <NUM> (A10).

Determined by the tensile test described later in Examples, the paint-protective coating material disclosed herein has a breaking strength of suitably <NUM> N/<NUM> or greater, or preferably <NUM> N/<NUM> or greater.

Determined by the tensile test described later in Examples, the paint-protective coating material disclosed herein has an yield strength of suitably <NUM> N/<NUM> or greater and <NUM> N/<NUM> or less, or preferably <NUM> N/<NUM> or greater and <NUM> N/<NUM> or less.

Determined by the tensile test described later in Examples, the paint-protective coating material disclosed herein has an elongation at break (break elongation) of suitably <NUM> % or higher, or preferably <NUM> % or higher. For instance, the maximum break elongation is suitably <NUM> % or lower. Such coating material can suitably deform during removal from paint layers for stress distribution; and therefore, the coating material can be inhibited from breaking due to local stress concentration.

From the standpoint of the workability during removal from paint layers, the paint-protective coating material combines well-balanced breaking strength, yield strength and break elongation (e.g. scoring at least <NUM> point on all test grades described later in Examples) is preferable.

This Description provides a paint protection method comprising the following: preparing a coating composition comprising an acrylic polymer as base polymer, applying the coating composition onto a paint layer of an object to be protected, and drying the coating composition to form a paint-protective coating material that temporarily protects the paint layer.

An embodiment of the paint protection method is described with reference to <FIG>. In particular, an acrylic coating composition disclosed herein is prepared (step S10). The coating composition is applied (e.g., slot-die coated) onto a paint layer of an object to be protected (step S20). The applied coating composition is allowed to dry to form a paint-protective coating material that temporarily protects the paint layer (step S30). By thus providing the coating material onto the paint layer, the paint layer can be protected from damage and degradation. The coating material after serving the protective role is removed (e.g., peeled away) from the paint layer when desired (step S40).

(<NUM>) A paint protection method, the method comprising.

(<NUM>) The paint protection method according to (<NUM>) above, wherein the paint-protective coating material is the paint-protective coating material according to any of (<NUM>) to (<NUM>) above.

(<NUM>) The paint protection method according to (<NUM>) or (<NUM>) above, that uses, as the acrylic coating composition, the acrylic coating composition according to any of (<NUM>) to (<NUM>) above.

(<NUM>) The paint protection method according to any of (<NUM>) to (<NUM>) above, wherein the acrylic coating composition is applied with a slot die.

Several working examples relating to the present invention are described below, but the present invention is not intended to be limited to these examples. In the description below, "parts" and "%" are by weight unless otherwise specified. The amounts of the respective materials used are based on active ingredients unless otherwise noted.

Were mixed <NUM> parts (<NUM> mol%) of n-butyl acrylate (BA), <NUM> parts (<NUM> mol%) of acrylonitrile (AN), <NUM> part of n-lauryl mercaptan, <NUM> parts of sodium polyoxyethylene lauryl sulfate (product name LATEMUL E118B available from Kao Corporation) and <NUM> parts of ion-exchanged water. While purging with nitrogen, the mixture was emulsified with an emulsifying machine (homomixer) to prepare a monomer emulsion.

Into a reaction vessel equipped with a condenser, nitrogen inlet, thermometer and stirrer, was placed <NUM> parts of ion-exchanged water. To this, was added <NUM> part of an anionic modified polyvinyl alcohol (product name GOHSENX L-<NUM> available from Nihon Gosei Kako, Ltd. ; saponification degree: <NUM>-<NUM> mol%), dissolved at room temperature while purging with nitrogen, and then heated to <NUM>. To this, was added, as a polymerization initiator, <NUM> part of <NUM>,<NUM>'-azobis[N-(<NUM>-carboxyethyl)-<NUM>-methylpropion amidine] hydrate (product name VA-<NUM> available from Wako Pure Chemical industries, Ltd. While keeping the liquid temperature around <NUM> in the reaction vessel, was added the monomer emulsion over three hours to carry out polymerization reaction. After completion of addition of the monomer emulsion, the reaction mixture was maintained and allowed to cure at the same temperature for three more hours. The system was allowed to cool to room temperature and then with addition of <NUM> % ammonium water, it was adjusted to pH <NUM> to obtain an aqueous emulsion of acrylic polymer. The aqueous emulsion was used as the acrylic coating composition according to this Example.

The monomer species and amounts used were changed as shown in Table <NUM>. Otherwise in the same manner as Example A1, were obtained aqueous acrylic polymer emulsions (acrylic coating compositions) according to the respective Examples.

Was horizontally held a painted steel plate with the painted face up, the steel plate coated with an acid epoxy crosslinked acrylic paint (product name KINO1210TW available from Kansai Paint Co. Onto the painted face of the painted steel plate, using an applicator available from TP Giken Co. , was applied the coating composition according to each Example and allowed to dry at <NUM> for three minutes to form film (a paint-protective coating material). The coating composition was applied in an amount to obtain a thickness of <NUM> by non-volatiles. At room temperature, the resulting film was peeled from the painted steel plate and cut into a <NUM> wide and <NUM> long strip to prepare a measurement sample for tensile testing.

In an environment at <NUM> and <NUM> %RH, the measurement sample was set in a tensile tester (system name TENSILON available from Shimadzu Corporation). Tensile tests were carried out at a reference line of <NUM> at a tensile speed of <NUM>/min to determine the breaking strength (N/<NUM>), yield strength (N/<NUM>) and break elongation.

Table <NUM> shows the results classified based on the following grades:.

The resulting test points on the breaking strength, yield strength and break elongation were combined. Based on the total score, the removal workability at room temperature was evaluated according to the three grades shown below. The results are shown in Table <NUM>.

Using the coating composition according to each Example, similar to the film preparation for the tensile testing, <NUM> thick film was formed on the painted steel plate. At room temperature, the resulting film was peeled from the painted steel plate. Several sheets of this film were layered and united into one body with pressure applied to prepare an approximately <NUM> thick laminate film. Of the laminate film, was punched out a disc of <NUM> diameter and placed between parallel plates. While applying a shear strain at a frequency of <NUM> using a rheometer (model name ARES G2 available from TA Instruments, Inc. ), the viscoelasticity was measured in the shear mode over a temperature range of - <NUM> to <NUM> at a heating rate of <NUM>/min. At the respective temperatures, the storage moduli G' were determined. The results are shown in Table <NUM>.

By the viscoelastic analysis, the tan δ peak temperature was determined. Table <NUM> shows the temperature as RSA-Tg.

To the painted steel plate, using an applicator available from TP Giken Co. , was applied the coating composition according to each Example and allowed to dry at <NUM> for three minutes to form film (a paint-protective coating material). Subsequently, the painted steel plate was placed into an incubator at <NUM>; at this temperature, the film was removed from the painted steel plate and the removability was evaluated according to the following two grades.

As shown in Table <NUM>, the films formed from the coating compositions of Examples A1 to A6 were all removed from the paint layers with good workability and were removable from the paint layers even at <NUM>. On the other hand, with respect to the films formed from the coating compositions of Examples A7 to A9 with the base polymer-forming monomers having a molar ratio (mT/mL) below <NUM> or above <NUM> and the film formed from the coating composition of Example A10 with acrylonitrile-free monomers, removal workability was not combined with removability at <NUM>.

To the acrylic coating composition of Example A1 prepared in Experiment <NUM>, for <NUM> parts of acrylic polymer in the composition, were added <NUM> parts of titanium dioxide (product name TIPAQUE CR-<NUM>, rutile titanium dioxide available from Ishihara Sangyo Kaisha, Ltd. ; mean particle diameter <NUM>), <NUM> parts of calcium carbonate (product name SOFTON <NUM> available from Shiraishi Calcium Kaisha, Ltd. ), <NUM> part of dispersing agent (product name DISPERBYK-<NUM> available from BYK), <NUM> part of a defoaming agent (product name DISPARLON AQ7533 available from Kusumoto Chemicals, Ltd. ) and <NUM> part of thixotropic agent (product name OPTIGEL WX available from BYK), and was further added water to adjust the NV to <NUM> %. Accordingly, was obtained the acrylic coating composition according to this Example.

The amounts of calcium carbonate, dispersing agent and thixotropic agent were changed as shown in Table <NUM>. Otherwise in the same manner as Example B1, were obtained acrylic coating compositions according to the respective Examples.

Were further added the thickener species in the amounts shown in Table <NUM>. Otherwise in the same manner as Example B2, were obtained acrylic coating compositions according to the respective Examples.

Were further added the thickener species in the amounts shown in Table <NUM> and no thixotropic agent was used. Otherwise in the same manner as Example B2, were obtained acrylic coating compositions according to the respective Examples.

Were further added the thickener species in the amounts shown in Table <NUM> and no thixotropic agent was used. Otherwise in the same manner as Example B1, were obtained acrylic coating compositions according to the respective Examples.

The thickeners shown in abbreviations in Table <NUM> are as follows:.

The coating compositions according to Examples B1 to B14 and the coating composition of Example A1 were subjected to the following measurements and evaluations. The results are shown in Table <NUM>.

At <NUM>, using a BH viscometer with a No. <NUM> rotor, the viscosity was measured at <NUM> rpm and at <NUM> rpm. From the results, the Ti value (ratio of viscosity at <NUM> rpm to viscosity at <NUM> rpm) was determined.

Using a rheometer (RheoStress <NUM> available from Haake Technik GmbH) with a cone-type rotor (cone diameter: <NUM>; cone angle: <NUM>°), at <NUM>, from the viscosity measured while continuously changing the shear rate from <NUM> sec-<NUM> to <NUM> sec-<NUM>, the viscosity at <NUM> sec-<NUM>, <NUM> sec-<NUM>, <NUM> sec-<NUM> and <NUM> sec-<NUM> were determined.

It is noted that with respect to the coating compositions of Examples B1, B6 and B13, films were formed from these compositions in the same manner as Experiment <NUM> and their storage moduli G'(<NUM>) were determined to be all in the range of <NUM> MPa or higher and <NUM> MPa or lower as follows: <NUM> MPa (Ex. B1), <NUM> MPa (Ex. B6) and <NUM> MPa (Ex. These films all had storage moduli G'(<NUM>) ≥ <NUM> MPa as follows: <NUM> MPa (Ex. B1), <NUM> MPa (Ex. B6) and <NUM> MPa (Ex.

Was horizontally held a painted steel plate with the painted face up, the steel plate coated with an acid epoxy crosslinked acrylic paint (product name KINO 1210TW available from Kansai Paint Co. In an environment at <NUM>, onto the painted face of the painted steel plate, using an applicator available from TP Giken Co. , was applied the coating composition according to each Example in a <NUM> wide border to a thickness of <NUM> by non-volatiles (i.e., <NUM> in wet film thickness). Immediately after the application, the painted steel plate was allowed to stand vertically and left for one minute. Subsequently, the state of the applied material (the composition applied onto the painted steel plate) was visually inspected. According to the results, anti-sag properties were evaluated based on the three grades shown below. The higher the score is, the better the anti-sag properties are.

A coating head (SCDM-<NUM>/<NUM> available from Nordson Corporation; <NUM> wide) was adjusted to a shim thickness of <NUM>. Into the coating head, was fed the coating composition according to each Example at an extrusion rate of <NUM><NUM>/min. While doing this, the width of liquid film extruded from the <NUM> × <NUM> slit was measured at a location <NUM> down the slit exit (downward). According to the value, die-coating properties were evaluated on the three grades shown below. It can be said that the higher the score is, the better the die-coating properties are. It is noted that when the liquid film continuity was broken in the width direction (e.g., when the liquid film was forked in two or more parts, etc.), it received a <NUM>-point grade regardless of the overall width.

In an environment at <NUM>, into a <NUM> volume beaker, <NUM> of each coating composition was placed, stirred at <NUM> rpm for <NUM> minutes using a disper, and then left standing. At <NUM> minutes of standing, was measured the liquid level H<NUM> (distance from the bottom of the beaker to the liquid surface; the same applies hereinafter). Relative to the initial (pre-stirring) liquid level H<NUM>, defoaming properties were evaluated according to the three grades shown below. The results are shown in Table <NUM>. The higher the score is, the better the defoaming properties are.

The coating compositions of Examples B1 to B11 all received <NUM>-point or higher grades in evaluations of die-coating properties and defoaming properties. These coating compositions showed practical defoaming properties and are suitable for die-coating formation of paint-protective coating materials on paint layers.

Although specific embodiments of the present invention have been described in detail above, these are merely for illustrations and do not limit the scope of the claims. The art according to the claims includes various modifications and changes made to the specific embodiments illustrated above.

Claim 1:
A paint-protective coating material formed from an acrylic coating composition comprising an acrylic polymer as base polymer, wherein
the acrylic polymer is formed from monomers comprising a monomer (mT) having a homopolymer glass transition temperature of <NUM> or higher and a monomer (mL) having a homopolymer glass transition temperature of -<NUM> or lower, with the monomer (mT) comprising at least acrylonitrile,
in the monomers, the monomer (mT) and the monomer (mL) have a molar ratio (mT/mL) of <NUM> or higher and <NUM> or lower, and
the paint-protective coating material has a storage modulus at <NUM> of <NUM> MPa or higher and <NUM> MPa or lower and a storage modulus at <NUM> of <NUM> MPa or higher, wherein the storage modulus at <NUM> and the storage modulus at <NUM> are determined as indicated in the description.