Title 17, California Code of Regulations, section 94508 of the California Air Resources Board (CARB) defines low vapor pressure volatile organic compounds (LVP-VOC), which include low vapor pressure solvents (and/or low vapor pressure coupling co-solvents (i.e. a co-solvent used in a multi-solvent system)), as a chemical “compound” or “mixture” that contains at least one carbon atom and meets one of the following;

- (A) has a vapor pressure less than 0.1 mm Hg at 20° C., as determined by CARB Method 310 (CARB Method 310 as Amended Aug. 1, 2022 see: https://ww2.arb.ca.gov/sites/default/files/2022-10/CARB_Method310_MLD_SAS_0801202 2.pdf accessed Mar. 12, 2024); or
- (B) is a chemical “compound” with more than 12 carbon atoms, or a chemical “mixture” comprised solely of “compounds” with more than 12 carbon atoms, as verified by formulation data, and the vapor pressure and boiling point are unknown; or
- (C) is a chemical “compound” with a boiling point greater than 216° C., as determined by CARB Method 310; or
- (D) is the weight percent of a chemical “mixture” that boils above 216° C., as determined by CARB Method 310.

A chemical “compound” as used above means a molecule of definite chemical formula and isomeric structure, and a chemical “mixture” as used above means a substance comprised of two or more chemical “compounds.”

Paint Remover Composition

Provided herein are paint remover compositions that better comply with EPA and California regulations by including low vapor pressure solvents and water in the disclosed paint remover. In view of currently known paint remover compositions, the compositions disclosed herein further have increased water concentrations and decreased organic solvent levels (particularly decreased volatile organic solvents) and advantageously/unexpectedly exhibit improved paint removal times coupled with desired shelf-life stability (i.e., no observable phase separation after predetermined periods of time at predetermined temperature(s)). The paint remover compositions disclosed herein are suitable for chemically stripping paint of various kinds on various surfaces including but not limited to automotive paints and wall paints applied to, for example, porous and non-porous surfaces.

The disclosed paint remover compositions are preferably a miscible, single-phase paint remover composition is a liquid at ambient temperature and exhibits no visibly observable phase separation 28 days post-mixing/formulating at a temperature of 50° C. This property is particularly important for shelf-life and efficacy purpose as paint remover compositions that separate into one or more phases disadvantageously require frequent mixing by a user.

The paint remover composition (single-phase paint remover composition) includes (a) tetrahydrofuran ((THF) (CAS No. 109-99-9)) (e.g., as a primary organic solvent) at a sufficient concentration to remove paint, i.e. from 15 wt % to 49.5 wt %, more preferably 25 wt % to 49.5 wt %, and most preferably 35 wt % to 49.5 wt %;; (b) a low vapor pressure (LVP) coupling co-solvent (e.g., secondary organic solvent) present at an effective amount to maintain miscibility of the single-phase paint remover composition and to remove paint; (c) an amine with a molar volume of <100 cm³/mol; and (d) water at a concentration of greater than 18 wt % of an overall concentration of the single-phase paint remover composition.

The solvent systems used in the disclosed paint remover compositions (single-phase paint remover composition) advantageously provide for fast and complete removal of cross-linked multi-layer coating systems, such as those found on motor vehicles. In certain aspects of the paint remover composition, and more particularly a single-phase paint remover composition, wherein the LVP coupling co-solvent is present at a concentration of 1 wt % to 15 wt % of the overall concentration of the single-phase paint remover paint remover composition, and more particularly a single-phase paint remover composition, more preferably 1.5 wt % to 10 wt % of the overall concentration of the single-phase paint remover composition, and most preferably 2.5 wt % to 5 wt % of the overall concentration of the single-phase paint remover composition. The LVP coupling co-solvent is an alkanediol present in the paint remover in above-mentioned concentrations, more preferably a 1,2-alkanediol present in the paint remover in above-mentioned concentrations. In certain aspects of the paint remover composition, and more particularly a single-phase paint remover composition, the LVP coupling co-solvent is a hexanediol, pentanediol, or a combination thereof present in the paint remover in above-mentioned concentrations, and in preferred embodiments, the LVP coupling co-solvent is 1,2-hexanediol (CAS No. 6920-22-5), 1,2-pentanediol (CAS No, 5343-92-0), or a combination thereof present in the paint remover in above-mentioned concentrations. In certain aspects of the paint remover composition, and more particularly a single-phase paint remover composition, the LVP coupling co-solvent is 1,2-pentanediol present in the paint remover in above-mentioned concentrations. In certain aspects of the paint remover composition, and more particularly a single-phase paint remover composition, the LVP coupling co-solvent is 1,2-hexanediol present in the paint remover in above-mentioned concentrations. Moreover and as further evidenced by the Working Examples, there is an unexpected synergy between THF and the LVP coupling co-solvent when present in the concentrations disclosed herein and when water at a concentration of greater than 18 wt % of an overall concentration of the single-phase paint remover compositions. In particular, paint removal times are unexpectedly improved especially when compared with other organic solvent/paint remover systems having less water therein.

While the above-mentioned alkanediols are particularly effective in the disclosed paint removers herein, alkanediols are expensive to produce. Thus, leading to expensive manufacturing costs downstream as well as increased end-user expense when preparing compositions/formulations having the above-mentioned alkanediols therein.

To reduce production costs, while further maintaining paint remover efficacy exhibited by formulations solely using the above-mentioned alkanediols as LVP co-solvents (and/or while achieving similar paint removal times), an effective secondary co-solvent (a tertiary organic solvent in the composition) was identified, which can be further added to the disclosed paint remover compositions and advantageously allows for lower alkanediol concentrations in the disclosed paint removers. Moreover and as further evidenced by the Working Examples, there is an unexpected synergy between THF, the LVP coupling co-solvent, and the secondary co-solvent when present in the concentrations disclosed herein and when water at a concentration of greater than 18 wt % of an overall concentration of the single-phase paint remover compositions. In particular, paint removal times are unexpectedly improved especially in view of comparative formulations having other organic solvent/paint remover systems that include less water therein.

In this aspect, the single-phase paint remover composition, further includes a secondary co-solvent (a tertiary organic solvent in the composition) present at a concentration of 1 wt % to 7 wt % of the overall concentration of the single-phase paint remover composition and more preferably 2 wt % to 4 wt % of the overall concentration of the single-phase paint remover composition. In this aspect, the secondary co-solvent is water miscible, and/or the secondary co-solvent is a glycol, a glycol ether, or a combination thereof present in the paint remover in above-mentioned concentrations and more preferably the secondary co-solvent is an alkylene glycol, an alkylene glycol ether, or a combination thereof present in the paint remover in above-mentioned concentrations. In certain aspects, the secondary co-solvent is propylene glycol (CAS No. 57-55-6), diethylene glycol monobutyl ether (CAS No. 112-34-5), or a combination thereof.

In certain aspects of the paint remover composition, and more particularly a single-phase paint remover composition, the secondary co-solvent is propylene glycol, and in certain aspects is present in the paint remover composition and is at a concentration of 5 wt % or less of the overall concentration of the paint remover composition and more preferably at a concentration of 2.5 wt % or less overall concentration of the paint remover composition. In certain aspects and when the LVP coupling co-solvent concentration in the paint remover composition is 3 wt % or less (and more preferably 2.5 wt % or less), the secondary co-solvent (e.g., propylene glycol) is present is present at a concentration of 5 wt % or below of the overall concentration of the paint remover composition and more preferably at a concentration of 2.5 wt % or below overall concentration of the paint remover composition to further aid in miscibility of the components within the paint remover composition as well as to improve paint removal times. In certain aspects, propylene glycol is present in the paint remover at a concentration ranging from 0.5 wt % to 7 wt % of the overall concentration of the paint remover composition, preferably 1.5 wt % to 6 wt % of the overall concentration of the paint remover composition, more preferably from 2.0 wt % to 5.5 wt % of the overall concentration of the paint remover composition, and even more preferably from 2.5 wt % to 5.0 wt % of the overall concentration of the paint remover composition. In certain aspects, the ratio of THF to LVP in the paint remover composition is from 20:1 to 5:1, more preferably from 20:1 to 8:1, and most preferably from 20:1 to 10:1 relative to one another.

In certain aspects of the paint remover composition, and more particularly a single-phase paint remover composition, the secondary co-solvent is diethylene glycol monobutyl ether. In certain aspects and when the LVP coupling co-solvent is present and at a concentration in the paint remover composition is 3 wt % or less (and more preferably 2.5 wt % or less), the secondary co-solvent (e.g., diethylene glycol monobutyl ether) is present in the paint remover compositions and has a concentration of 5 wt % or less of the overall concentration of the paint remover composition and more preferably at a concentration of 2.5 wt % or less overall concentration of the paint remover composition to further aid in miscibility of the components within the paint remover composition as well as to improve paint removal times. In certain aspects, diethylene glycol monobutyl ether is present in the paint remover at a concentration ranging from 0.5 wt % to 7 wt % of the overall concentration of the paint remover composition, preferably 1.5 wt % to 6 wt % of the overall concentration of the paint remover composition, more preferably from 2.0 wt % to 5.5 wt % of the overall concentration of the paint remover composition, and even more preferably from 2.5 wt % to 5.0 wt % of the overall concentration of the paint remover composition.

In view of the above disclosures, when both the LVP coupling co-solvent and the secondary co-solvent are present in the single-phase paint remover composition, the LVP coupling co-solvent and the secondary co-solvent are present at a ratio ranging from 2:1 to 1:2 relative to one another, more preferably 1.5:1 to 1:1.5 relative to one another, and most preferably 1:1 relative to one another. In certain instances, when the 2:1 to 1:2 ratios of LVP coupling co-solvent and the secondary co-solvent are exceeded phase separation of the remover will occur upon aging/stored for prolonged time periods and paint removal times are insufficient/undesirable.

As alluded to above, water is present in the disclosed paint removers at rather high concentrations especially when compared to conventional paint removers. In particular, water is present in the single phase paint remover composition at concentration ranging from 18 wt % to 40 wt % of the overall concentration of the single-phase paint remover composition, more preferably 20 wt % to 30 wt % of the overall concentration of the single-phase paint remover composition, and most preferably 20 wt % to 27.5 wt % of the overall concentration of the single-phase paint remover composition.

Likewise, an amine/amine containing component is present in the disclosed paint remover. The molar volume of the amine may be <100 cm³/mol and more preferably may be <30 cm³/mol. In certain aspects, the amine/amine containing component is present in the remover composition at concentration ranging from 2.5 wt % to 20 wt % of the overall concentration of the single-phase paint remover composition, more preferably 5 wt % to 20 wt % of the overall concentration of the single-phase paint remover composition, and most preferably 10 wt % to 20 wt % of the overall concentration of the single-phase paint remover composition. The amine is selected from the group consisting of ammonia (CAS No. 7664-41-7) and/or aqua ammonia (CAS No. 1336-21-6), hydroxylamine (CAS No. 5470 Nov. 1), dimethylamine (CAS No. 124-40-3), ethanolamine (CAS No. 141-43-5), pyrrolidine (CAS No. 123-75-1), and a combination thereof.

Other components may be present in the formulation for paint removal. Non-limiting examples of other such components include, but are not limited to, dye, paraffin wax (present in a sufficient amount to act as a solvent evaporation retarder), antioxidant, surfactant, thickener, fumed silica, corrosion inhibitor, ammonia, peroxide inhibitor (including but not limited to butylated hydroxytoluene), or a combination thereof. The composition may further comprise a cellulosic thickener. Non-limiting examples of cellulosic thickeners are hydroxypropyl methyl cellulose, hydroxypropyl cellulose, and a combination thereof, The composition may comprise an amine containing corrosion inhibitor.

In addition to the above mentioned amines/amine containing components, the disclosed paint removers may further include amine containing corrosion inhibitors. These amine containing corrosion inhibitors include, but are not limited to, primary, secondary, tertiary or quaternary amines, aliphatic, cycloaliphatic or aromatic amines, polyamines, amine salts, such as amine-mineral acid salts, amine-nitrites, amine-carboxylates, amine-phosphates, amine-borates, alkanolamines or alkanolamine-borate complexes, amine-metal complexes, amine containing heterocycles, azoles, and mixtures thereof.

In certain aspects, the above-mentioned other components, cellulosic inhibitors, and/or amine containing corrosion inhibitors, alone or in combination, may be added in a range of 0 weight % to 25 weight %, more preferably 0.01 weight % to 12.5 weight %. In certain aspects of the paint remover composition, and more particularly a single-phase paint remover composition, has a viscosity ranging from 1,000 cP to 20,000 cP at 20° C., more preferably 3,000 cP to 15,000 cP at 20° C., most preferably 5,000 cP to 10,000 cP at 20° C. Viscosities in these ranges provide for the ideal balance of application properties, including but not limited to, spreadability, coverage and vertical cling.

A method of making the disclosed paint remover/single-phase paint remover composition comprising: (a) admixing tetrahydrofuran (THF) at a sufficient concentration to remove paint, i.e. from 15 wt % to 49.5 wt %, more preferably 25 wt % to 49.5 wt %, and most preferably 35 wt % to 49.5 wt %, with a: (i) a low vapor pressure (LVP) coupling co-solvent present at an effective amount to maintain miscibility of the single-phase paint remover composition and to remove paint; (ii) an amine with a molar volume of <100 cm³/mol; and (iii) water at a concentration of greater than 18 wt % of an overall concentration of the single-phase paint remover composition; and (b) forming the disclosed paint remover/single-phase paint remover composition.

Method of Removing Paint

Also disclosed is a method of removing paint including (a) applying the single-phase paint remover composition disclosed herein to a painted surface for a predetermined time period; and (b) after step (a), removing paint from the painted surface by wiping, scraping, blasting or rinsing. As alluded to above, the disclosed paint remover compositions are suitable for chemically stripping paint of various kinds on various surfaces. The paints include, for example, automotive paints having a plurality of layers (i.e., a primer layer, a base/pigment layer, and a top coat/clear layer) and/or wall paints. In certain aspects, the paints that will be removed have been applied to, for example, porous (sheetrock/gypsum board) and/or non-porous surfaces (metal or glass substrates).

In certain aspects of the method of removing paint, the predetermined time period ranges for 5 minutes to 300 minutes, more preferably 5 minutes to 120 minutes, and most preferably 5 minutes to 30 minutes. In certain aspects and either during the predetermined time period or directly after the predetermined time period, at least 50% of the paint has been removed from the painted surface when observed visually, at least 65% of the paint has been removed from the painted surface when observed visually, at least 75% of the paint has been removed from the painted surface when observed visually, at least 90% of the paint has been removed from the painted surface when observed visually, at least 95% of the paint has been removed from the painted surface when observed visually, at least 97.5% of the paint has been removed from the painted surface when observed visually, at least 99% of the paint has been removed from the painted surface when observed visually, or at least 100% of the paint has been removed from the painted surface when observed visually,

WORKING EXAMPLES

Table 1 shows a base formula that that omits any alkanediol, LVP coupling co-solvent. As shown in FIG. 1, the base formula was unstable exhibiting phase separation within five (5) minutes after mixing and viscosity decreases after initial mixing. Frequent mixing was necessary to avoid phase separation was shaken until homogenous.

TABLE 1

Base formula for evaluation of LVP coupling solvents

V1.02-base

Ingredient (wt %)
formula

Tetrahydrofuran
49.5

Surfactant¹
1

Paraffin wax
0.25

Hydroxypropyl
1

methyl cellulose

DI water
28.25

28-30% Aqua
15

ammonia

Surfadone LP-100²
5

¹Nonionic alcohol ethoxylate surfactant

²Surfadone LP-100 is n-octylpyrrolidone commercially available from Ashland

Table 2 and FIGS. 1 and 2 show the base formulation (100) (shown in Table 1) including various different LVP coupling co-solvents at various concentrations (i.e., 5% and/or 10% by wt) added thereto. In view of Table 1, only water concentrations were varied to account for the added LVP coupling co-solvent(s). After preparing and mixing (homogeneously mixing) the formulas shown in Table 2 and a further shown in the photographs in FIGS. 1 and 2, formula stability was evaluated after storage on a flat surface for 24 hrs at room temperature. As shown in FIG. 1 and Table 2, formulations with 5 wt % 1, 2 hexanediol (LVP couple co-solvent) and formulations with 5 wt % 1,2 pentanediol (LVP couple co-solvent) exhibited no phase separation, while all other formulations exhibited phase separation at 5 wt %.

TABLE 2

Evaluation of post-addition of 5% and 10% LVP

coupling solvents to base formula V1.02

Coupling Solvent
5%
10%
Observations

Butyl Carbitol
2 phase
1 phase (240)
10%-moderate clarity,

(110)

third highest viscosity

Dowanol DPnB
2 phase
2 phase (250)

(120)

Hexyl Cellosolve
2 phase
2 phase (260)

(130)

Hexyl Carbitol
2 phase
2 phase (270)

(140)

Benzyl alcohol
2 phase
2 phase (280)

(150)

Dowanol EPh
2 phase
2 phase (290)

(160)

Dowanol EPh6
2 phase
1 phase (300)
10%-most clear,

(170)

third highest viscosity

Hexylene glycol
2 phase
2 phase (310)

(2-Methyl-2,4-
(180)

pentanediol)

Octiol (1,2-
2 phase
1 phase
10%-Opaque,

Octanediol)
(190)
(loose) (320)
lowest viscosity

Hexiol (1,2-
1 phase
N/A
5%-hazy, second highest

Hexanediol)
(200)

viscosity

Pentiol (1,2-
1 phase
N/A
5%-moderate clarity, highest

Pentanediol)
(210)

viscosity

Ethylhexyl
2 phase
2 phase (330)
5%-slightly yellow;

glycerine (EHG)
(220)

10%-very yellow

Propylene glycol
2 phase
2 phase (340)

(230)

Tables 3 and 4 depict additional exemplary formulations (V1.17, V.1.3, V1.16) having 5 wt % of 1,2-pentanediol (LVP couple co-solvent) and exemplary formulation V1.15 having 10 wt % diethylene glycol monobutyl ether (LVP couple co-solvent) as well as the paint removal times when compared with a comparative example (i.e., “Comp. 1” in Table 4, which is the paint remover formula of Example 2 in U.S. Pat. No. 11,827,812).

TABLE 3

Comparison of Coupling solvent and water Levels on Stripping Time

Ingredient (wt %)
V1.17
V1.13
V1.16
V1.15

Tetrahydrofuran
49.5
49.5
49.5
49.5

Surfactant
1
1
1
1

Paraffin wax
0.15
0.15
0.15
0.15

Hydroxypropyl
1.25
1.25
1.25
1.25

methyl cellulose

DI water
20.6
15.6
10.6
10.6

28-30% Aqua
15
15
15
15

ammonia

1,2-Pentanediol
5
5
5
—

Surfadone LP-100
—
5
10
—

Diethylene glycol
—
—
—
10

monobutyl ether

Additives
2.5
2.5
2.5
2.5

TABLE 4

Comparison of Time (min) to Strip paint from 2017 Nissan Ultima hood

Total

H₂O:

Coupling
Total
Coupling

solvent
water
solvent
Spot 1
Spot 2

Ex.
(wt. %)
(wt. %)
ratio
(min)
(min)
Layers stripped

Comp. 1
—
3.5%
N/A
285
292
Clear/base/some primer

V1.17
5
25.1%
5.02
153
156
Clear/base/primer

V1.13
10
20.1%
2.01
168
168
Clear/base/primer

V1.15
15
15.1%
1.01
189
204
Clear/base/primer

V1.16
10
20.1%
2.01
168
171
Clear/base/primer

*Comp. 1 is paint remover formula according to Example 2 of U.S. Pat. No. 11,827,812.

Table 4 demonstrates unexpectedly that formulas with increased water levels and decreased coupling solvent levels demonstrate shorter time to strip automotive paint.

Tables 5 and 6 depict additional exemplary formulations (V1.40) having 5 wt % of 1,2-pentanediol and exemplary formulations V1.44 (having 2.5 wt % of 1,2-pentanediol (LVP couple co-solvent) and 2.5 wt % diethylene glycol monobutyl ether (secondary co-solvent)) and V1.45 (having 2.5 wt % of 1,2-pentanediol (LVP couple co-solvent), and 2.5 wt % propylene glycol (secondary co-solvent)) as well as the paint removal times when compared with a comparative example (i.e., “Comp. 1” in Table 4, which is the paint remover formula of Example 2 in U.S. Pat. No. 11,827,812). Comparative examples (V1.38, V1.39, V1.41, V1.43, and V1.46) are further shown in Table 5. Stability data of each formulation in Table 5 is shown in Table 6. Only formulations V1.40, V1.44, V1.45, and V1.54 exhibited the desired stability (i.e., no phase separation) post-storage for twenty-eight (28) days at 50° C. (with no intermittent mixing, etc. during storage).