Description

PAINT REMOVERS CONTAINING HYDROXYPROPYL GUAR Technical Field [0001] The present invention relates to paint remover compositions containing hydroxypropyl guar having high degree of substitution and having thickening function. Background Art [0002] Paint removers are chemical compositions used to remove or to help removing paints, varnishes, enamels and various coatings which are used to protect and improve the appearance of surfaces. [0003] The chemical removal of these coatings, perfected during the years by the identification of increasingly efficient composition, is more and more widespread both in industrial and household applications and has largely replaced the more traditional physical methods, which use high temperatures to degrade the coating layer and lead to the formation of toxic vapours, and the purely mechanical methods involving the abrasion of the coatings with brushes or the use of moving abrading surfaces and a lot of skilled handiwork. [0004] The most common types of chemical paint removers contains an organic solvent as an essential component or, more frequently, a mixture of organic solvents, beside various additives which are included to improve the stripping performance. [0005] A general review on paint remover formulations can be found in JAIC, 32

(1993), 43-57 (T. Wollbrinck). [0006] The organic solvent penetrates the coating layer causing its swelling and separation from the substrate. [0007] The most used organic solvents are methylene chloride, toluene, N- methylpyrrolidone, glycol ethers, methanol. [0008] Among these, methylene chloride is the most employed; recently, more eco-compatible solvents, like limonene and glycol ethers, have entered into numerous paint remover formulations. [0009] Paint removers usually also contain a thickener that helps the composition adherence and permanence on the surfaces, and particularly on vertical

surfaces, thus allowing the solvent to perform its function on the underlying layer. As a consequence, thickeners increase the time of contact of the paint remover with the surface from where paint must be removed and moreover they reduce the evaporation of volatile components, drastically reducing the solvent dispersion into air. Many solvent based paint removers contain, as thickeners, cellulose derivatives, such as hydroxypropyl cellulose and hydroxypropyl methyl cellulose having high degree of substitution.

[0010] These cellulose derivatives are widely used thanks to their compatibility with solvents and to their good thickening power.

[0011] It has now been found that hydroxypropyl guar having degree of molar substitution from 2.0 to 4 and Brookfield viscosity at 2% by weight in water from 5,000 to 30,000 mPa*s (20 rpm, 20 ⁰ C) can be used as thickening agents in paint remover compositions in place of cellulose derivatives.

[0012] These specific hydroxyalkyl guar having high degree of substitution are perfectly suited to confer stability to the paint remover over time and its perfect adhesion on the surface to be treated.

[0013] In the Italian patent application VA2005A000039, the Applicant described ceramic vehicles consisting of at least 89% by weight of water and glycols (that is alcohols having at least two hydroxyl functionalities) and hydroxy alkyl guar thickeners having molar substitution comprised between 1.4 and 3.

[0014] VA2005A000039 nonetheless does not describe hydroxyalkyl guar having high molar susbtitution in compositions containing glycol ethers or other organic solvents.

Disclosure of Invention

[0015] It is a fundamental object of the invention a composition suitable as paint remover, having Brookfield viscosity from 800 to 30,000 mPa*s comprising: a) from 0.5 to 10% by weight of hydroxypropyl guar having molar substitution comprised between 2.0 and 4 and Brookfield viscosity at 25°C in water comprised between 5,000 and 30,000 mPa*s; b) from 80 to 99.5% by weight of a solvent or a mixture of solvents selected from the group consisting of chlorinated aliphatic hydrocarbons, aromatic

hydrocarbons, limonene, cyclic or alicyclic aliphatic ketones, cyclic or alicyclic aliphatic ethers, N-methyl pyrrolidone, dibasic carboxylic acid esters, water miscible mono-hydroxylated alcohols, water, wherein the amount of water is comprised between 0 and 60% by weight.

[0016] According to a preferred embodiment of this invention, the paint remover composition solvent or mixture of solvents consists of: i) from 0 to 95% by weight of chlorinated aliphatic hydrocarbons, aromatic hydrocarbons, limonene, cyclic or alicyclic aliphatic ketones, dibasic carboxylic acid esters, and mixtures thereof; ii) from 0 to 99.5% by weight of cyclic or alicyclic aliphatic ethers, N-methyl pyrrolidone and mixture thereof; iii) from 0 to 60% by weight of water, water miscible mono-hydroxylated aliphatic alcohols chosen among methanol, ethanol, isopropanol, t-butanol and mixture thereof, and the sum of ii) and iii) makes up at least 5% by weight of the solvent or mixture of solvents.

[0017] Hydroxypropyl guar (HPG) is widely used in many industrial applications, where mainly its thickening property and its characteristic of rheology modifier for aqueous solution are exploited.

[0018] According to a particular aspect of the present invention, hydroxypropyl guar having high degree of molar substitution, that is having molar substitution comprised between 2.0 and 4.0, is particularly useful also to thicken non-aqueous paint remover compositions (with the term "nonaqueous" we mean containing less than 5% by weight of water), containing suitable amounts of one or more water miscible mono- hydroxylated aliphatic alcohols, such as methanol, ethanol, isopropanol, t- butanol and mixture thereof.

[0019] In the present text, with the expression "molar substitution" (MS), we mean the molar substitution of hydroxypropyl guar measured by ¹ H-NMR.

[0020] Hydroxypropyl guar is obtained by chemical reaction of propylene oxide in the presence of basic catalysts (for example sodium hydroxide) on the hydroxyl groups of the galactomannan polysaccharide, which is commercially known as guar gum or guar.

[0021] The normally commercialised hydroxypropyl guar has a molar substitution comprised between 0.3 and 1.2 and it is not suited for the realisation of the

present invention; hydroxypropyl guar having a molar substitution comprised between 2.0 and 4.0 is made commercially available by Lamberti SpA under the trade name Esacol ®.

[0022] The choice of the solvents to be used for the realisation of the invention depends on the kind of coatings to be removed and on their attitude to dissolve hydroxypropyl guar having high substitution degree; due consideration is also made to the fact that the solubility of hydroxypropyl guar having high substitution degree is very similar to the solubility of hydroxypropyl cellulose having high substitution degree.

[0023] Also, the paint remover efficiency of the compositions of the present invention is very similar to the paint remover efficiency of compositions containing hydroxypropyl cellulose having high substitution degree, when the compositions possess the same viscosity and same solvent formulation.

[0024] The efficiency of the paint remover compositions of the present invention has been evaluated according to the method described in ASTM standard method D6189-97.

[0025] Among the chlorinated aliphatic hydrocarbons useful for the realisation of the present invention we cite methylene chloride, 1 ,1 ,1-trichloroethane, 1 ,2-dichloro ethane; among the aromatic hydrocarbons: toluene, xylene, and commercial mixtures of aromatic hydrocarbons; among the cyclic or alicyclic aliphatic ketones: acetone and methyl ethyl ketone; among the cyclic or alicyclic ethers: 1 ,3-dioxolane, dibutyl ether, methyl-, ethyl-, and butyl- cellosolve, methyl- ethyl- and butyl-carbitol, propylene glycol monomethyl- monoethyl- and monobutyl- ether, dipropylene glycol monomethylether acetate, propylene glycol monomethylether acetate, dimethoxymethane.

[0026] Among the dibasic carboxylic acid esters useful for the realisation of the invention we cite the methyl esters of adipic and succinic acid, that can be used in relevant amounts in the compositions of the present invention because they reduce the amount of methylene chloride and of other solvent which are presently little appreciated for eco-toxicological reasons.

[0027] Paint removers containing ethanol are used for shellac lacquers, those containing methyl ethyl ketones for nitrocellulose compositions, and so on, according to what is well known to the man skilled in the art.

[0028] Other organic or inorganic compounds, such as formic acid, acetic acid, oxalic acid, ammonium hydroxide, monoethanolamine, can be used as activating additives in the compositions of the invention.

[0029] The paint remover compositions can further contain the normally known additives, such as waxes and paraffins, surfactants, corrosion inhibitors, chelants, and sequestering agents. The total amounts of activators and additives normally represents from 0 to 10% by weight of the compositions of the present invention.

[0030] The paint remover compositions of the invention are useful for the paint removal from metal, wood or brick surfaces; they efficiently remove a great variety of coatings, such as alkyd, polyurethane and acrylic lacquers, vinyl dispersions, aqueous varnishes, shellac, nitrocellulose lacquers...

[0031] According to a particularly advantageous aspect of the present invention, the preparation of the paint remover compositions does not necessitate specific procedures connected with the use of hydroxypropyl guar.

[0032] According to the Applicant knowledge, the compositions of the invention are not described in the state of the art, nor the use of hydroxypropyl guar as thickener and stabiliser of paint remover composition is known.

[0033] It is therefore a further object of the present invention the use of hydroxypropyl guar having molar substitution comprised between 2.0 and 4.0, preferably, between 2.5 and 3.5, as thickener and stabiliser in paint removers.

[0034] The invention is also directed to a method for removing paints from metal, wood or brick surfaces comprising the following steps: I) a paint remover composition is prepared having Brookfield viscosity from 800 to 30,000 mPa*s comprising: a) from 0.5 to 10 by weight of hydroxypropyl guar having molar substitution comprised between 2.0 and 4 and Brookfield viscosity at 25 in water comprised between 5,000 and 30,000 mPa*s; b) from 80 to 99.5% by weight of a solvent or a mixture of solvents selected from the group consisting of chlorinated aliphatic hydrocarbons, aromatic

hydrocarbons, limonene, cyclic or alicyclic aliphatic ketones, cyclic or alicyclic aliphatic ethers, N-methyl pyrrolidone, dibasic carboxylic acid esters, water miscible mono-hydroxylated alcohols, water, and mixtures thereof, wherein the amount of water is comprised between 0 and 60% by weight; II) the paint remover composition is applied on the surface to be treated and left acting for 5-120 minutes; III) the coating and the paint remover composition is mechanically removed from the surface.

[0035] Paint remover compositions according to preferred embodiments and particular aspects of the present invention can advantageously be used as the paint remover composition of step I); additives and activators, such as those described above, may optionally be present in the paint remover composition of step I), in a 10% by weight maximum percentage.

[0036] Preferably the mechanical removal of step III) is performed with a plastic spatula, to avoid any damage of the surface, or even by washing with water. In the following examples the preparation of some paint remover according to the invention is reported.

[0037] Examples 1-3 [0038] At room temperature the following ingredients are mixed:

2 g hydroxypropyl guar (see Table 1)

198 g N-methyl pyrrolidone

[0039] The compositions described in Table 1 are obtained. [0040]

Table 1

[0041] MS= molar substitution HPG [0042] Vac = Brookfield viscosity HPG 2% in water (mPa*s, 20 rpm, 20 ⁰ C) [0043] V3h = Brookfield viscosity of the composition after 3h (mPa*s, 20 rpm,

20 ⁰ C)

[0044] ^* = Comparative example [0045]

[0046] The composition of Example 1 (comparative), even after 48 hours at ambient temperature, does not show any detectable thickening.

[0047] Example 4-6 [0048] A mixture S1 is made from:

• 20 parts by weight of toluene 30 parts by weight of methanol

• 23 parts by weight of methyl ethyl ketone 25 parts by weight of acetone

[0049] At room temperature the following ingredients are mixed for three hours: 2 g hydroxypropyl guar (see Table 2) 98 g mixture S1

[0050] [0051]

Table 2

[0052] MS= molar substitution HPG [0053] Vac = Brookfield viscosity HPG 2% in water (mPa*s, 20 rpm, 20 ⁰ C) [0054] V3h = Brookfield viscosity of the composition after 3h (mPa*s , 20 rpm,

20 ⁰ C)

[0055] ^• = Comparative example [0056] [0057] Examples 7-8 [0058] A mixture S2 is made from: 22.5 parts by weight of water

• 14 parts by weight of N-methyl-pyrrolidone 45 parts by weight of dibutylether

• 8 parts by weight of butyl carbitol (diethylene glycol monobutyl ether) 8.5 parts by weight of sodium dodecylbenzene sulfonate

• 0.8 parts by weight of cellulose fibre.

[0059] At room temperature the following ingredients are mixed for three hours:

1 g thickener (see Table 3) 99 g mixture S2

[0060]

Table 3

Example Thickener MS Th Vac v _2d

7* Klucel H ^** 5.0 32,600 6,200

8 HPG 3.0 15,000 5,200

[0061] MS Th= molar substitution thickener [0062] Vac = Brookfield viscosity HPG 2% in water (mPa*s, 20 rpm, 20 ⁰ C) [0063] V2d = Brookfield viscosity of the composition after 2 days (mPa*s , 20 rpm,

20 ⁰ C)

[0064] ^* = Comparative example [0065] ** =®, hydroxypropyl cellulose from Aqualon [0066] [0067] Examples 9-10 [0068] At room temperature the following ingredients are mixed for three hours:

• 1 g thickener (see Table 4) 99 g N-methyl-pyrrolidone.

[0069] The compositions described in Table 4 are obtained. [0070] [0071] [0072] [0073]

Table 4

[0074] MS Th= molar substitution thickener [0075] V3h = Brookfield viscosity of the composition after 3 hours (mPa*s, 20 rpm,

20°C)

[0076] ^* = Comparative example [0077] ** =®, hydroxypropyl cellulose from Aqualon