The Inﬂuence of Battery Acid on the Destruction of Acrylic Coatings of Car Bodies

: Renovation coatings of car bodies undergo destruction under the inﬂuence of operational factors. Like ultraviolet radiation, erosion, and aggressive media (among others, battery acid). This article concerns the evaluation of the inﬂuence of battery acid on the destruction of acrylic coatings previously non-aged, as well as aged climatically for 2 years. Ageing of the coatings with battery acid contributed to a degradation increase of their chemical structure. It was supported by a considerable increase in the polar component of surface free energy (SFE) of the coatings. In the case of prior climate ageing, the increase in the polar component was even higher. Moreover, the coating’s ability to absorb battery acid increased, which induced blistering. The DSC method revealed that the action of battery acid caused more intense oxidation of coating material, and as a result, the brittleness increased, leading to chipping of the coating surface layers. This led to the increase in surface roughness, measured using an interferometric method. The coatings previously climatically aged for 2 years presented higher values of surface roughness parameters than the non-aged ones. The increase in the surface roughness contributed to a substantial decrease in the gloss of coatings. A sharp difference in colour escalating with the lengthening of the ageing period was also observed using the spectrophotometric method.


Introduction
Acrylic coatings have found a widespread and sustained application as decorativeprotective coatings of modern car bodies. Scientific development in the area of paints and varnishes for coatings of car bodies is presently focused on environmentally friendly coating materials. For this reason, volatile organic compounds (VOC) have been eliminated (or significantly reduced) from paint and lacquer formulas in the last 10 years. Moreover, approximately every five years, these formulas have undergone changes which primarily improve the quality of coatings. Therefore, conducting complete and long-lasting operational examinations on representative samples of coatings, which may last even 10 to 15 years, has no substantive grounds. What concerns the currently used new generations of coatings (nanocoatings especially) is necessary to test them in accelerated mode, enabling their quick operational life prediction in expected conditions [1][2][3][4][5][6].
Despite the progress in the fields of the production and application of polymer coating materials, problems still exist concerning their use for reliable and long-lasting protection of car bodies against operational environment influence. Coating life predicting is also a complicated question, since the complexity of the ENVIRONMENT-COATING-SUBSTRATE system results in a gap of an appropriate theoretical basis, as the component parts of the system and the relationships between them undergo constant changes. The changes concern the operational environment's aggressiveness as well as kinds of materials used for polymer coatings and also for substrates [6][7][8][9][10][11][12][13].
The kinetics of the destruction of polymer coatings resulting from operational environment influence (in the form of climatic factors and environment pollution) is not generating oxidative degradation [5,50,51]. Environmental factors embrace, among others, components such as mechanical factors, causing mechanical degradation [51], as well as aggressive media in the form of acids, alkalies, or/and salts, contributing to the hydrolytic degradation of coating materials [31].
Destruction of coatings, caused by polymer material degradation, leads to the decrease in protective effectiveness of the coatings, which is tantamount to their operational life shortening [24,25,52].
Ultraviolet radiation, which is part of the spectrum of sun radiation (UV-A range of wave length 315-400 nm), is the primary destructive factor in polymer ageing. It generates a photodegradation process of the superficial layers of polymer coatings of a radical nature, which is promoted by their structural defects in the form of pores and/or cracks. Oxidative ageing development of coating material has been documented in FTIR examinations by the intensity increase of the carbonyl group (C=O) band [1,5,24,25,32,34]. For example, in the case of acrylic coatings aged in a climatic station for one year, the band's intensity increase was stated for wavenumbers γ, equal to 1724 and 1690 cm −1 , both corresponding to carbonyl stretching frequency (carbonyl valence vibrations) [16]. Oxidized external sublayers of the topcoats show increased brittleness, which contributes to their chipping and the formation of pits, leading to an increase in the coating's roughness [15,24,25].
In the pits formed on the coating's surface, organic impurities and moisture settle, creating favourable conditions for the development of microorganisms in the form of viruses, bacteria, algae, and mould fungi. Products of their metabolism initiate the development of biological corrosion of polymer coatings [45]. It results in the generation of craters in coatings (reaching the substrate), as well as superficial etchings [1,2].
The coating's increased resistance to operational factors, including ultraviolet radiation, is achieved by nanoparticles' introduction to their structure, e.g., aluminium trioxide, titanium dioxide, or silicon dioxide [5,32,44,49]. It should be stressed that nanoparticles effectively fill nano-and micropores existing in polymer coatings, increasing their tightness, which limits aggressive media migration [15,25].
Coating-forming material is most frequently modified with nanoparticles of silicon dioxide (called silica) of a mass share from 3.5% [15] to 18% [5]. It is important that addition of nanofillers to the topcoat material only very slightly influences its transparency. For this reason, it is advisable to introduce nanofillers into paints for topcoats in order to improve the operational life of protective-decorative (multilayer) polymer coating systems [5,6,15,32].
During their service life, coatings of car bodies are often subjected to the influence of different operating fluids, e.g., diesel fuel, petrol, battery acid, or windscreen washing fluid [51].
The author of the presented paper in the work [16] discussed the destructive effects of diesel fuel contact with polymer coatings. Exposing the examined acrylic coating to diesel fuel resulted in ageing of the coating material, which included physical and chemical properties changes, such as thickness, hardness (acc. Buchholz), surface topography and roughness, gloss, and colour. The development of the ageing process in coatings under the influence of diesel fuel also resulted in a decrease of the contact angle θ C characterizing coating susceptibility to wetting with water. Thereby, the contact area of water drops with the coating surface increased, which led to the increased absorbability of water by the coating material.
In turn, in the presented paper, on the basis of carried out investigations, the effects are discussed of the influence of another operating fluid, i.e., battery acid, on acrylic coatings applied for car renovation.

Materials
An evaluation of the influence of battery acid on coatings was carried out on the example of acrylic coating systems, which are commonly used in body and paint workshops for the renovation of protective-decorative coatings applied on car bodies. Samples of the coatings were sprayed on surfaces of steel plates of dimensions 160 × 80 × 2 mm 3 . The plates were cut from sheets of non-alloy structural steel S 235 JRG 2 (acc. PN-EN 10025-1:2007 [53]). Before undercoat application, the surfaces of the steel plates were prepared with P80 abrasive paper and then degreased with extraction solvent.
Samples of coating systems were obtained by air spraying of three successive kinds of polymer coatings, which were as follows: the acrylic base coating, the acrylic interlayer coating (red), and the top layer made of the acrylic lacquer.
The intermediate coating was pigmented with iron red, made of iron trioxide (Fe 2 O 3 ) nanoparticles of dimensions d ≤ 60 nm.
After application, the coating systems were acclimatized for 10 days in the environment of a relative humidity equal to 65% ± 5% and a temperature of 20 ± 2 • C (according to the standard PN-EN 23270:1993 [54]). Then, preliminary examinations of their physical and chemical properties were carried out.
Subsequently, the examinations were made concerning the results of battery acid influence on the surface of coating systems. In the course of these examinations, cotton cosmetic pads soaked with battery acid were put on the surface of the examined coatings. The maximum period of coating exposure to battery acid action was 336 h. Two kinds of coating systems were subjected to battery acid action, specifically, the unaged climatically acrylic coatings (C0) and the acrylic coatings (C2) aged before (acc. PN-EN ISO 2810:2005 [55]) at a climatic station for the period of 2 years. The state of the coating surfaces subjected to battery acid action was evaluated after the lapse of the following periods: 48, 168, and 336 h.

Research Methodstsnle
Surface changes of acrylic coating systems (hereafter called "acrylic coatings") under the influence of battery acid were evaluated on the grounds of the examination results of their physical and chemical properties. The following properties were taken into account: thickness, hardness, surface topography and roughness, gloss, colour, and contact angle θ C of wetting the surface with aggressive media (diiodomethane and water), as well as resistance to oxidation.
The state of the coating surfaces was analysed based on their R a and R z roughness parameters and topography pictures. R a and R z parameters and the topography of acrylic coating surface were examined with a Taylor Hobson white-light interference microscope, Talysurf CCI 6000 (Taylor Hobson Precision, Leicester, UK), enabling optical measurements (acc. standards PN-M-04251:1987 [56] and PN-EN ISO 8501-1:2008 [57]).
Physical destruction of aged acrylic coatings was investigated using a Hitachi FESEM SU-70 (Hitachi, Tokyo, Japan).
Changes in chemical structure of acrylic topcoats that were aged at the climatic station were assessed using an infrared spectrophotometric method with a Jasco Inc. spectrophotometer FT/IR 6200 (Jasco Inc., Easton, MA, USA). The apparatus was controlled with a computer program, Spectra Manager, enabling mathematical and graphical processing of the obtained spectra. IR spectra were recorded with the help of a reflection method, using a single reflection ATR attachment of spectral range IRν = 4000-600 cm −1 and a resolution of 4 cm −1 .
Oxidation resistance of the coatings, which determines their thermal resistance, was examined using a LABSystem SETARAM TG-DTA/DSC apparatus (SETARAM Instrumentation, Caluire, France) were carried out by applying a dynamic method with a linear temperature increase, in the environment of oxygen as an oxidizing agent. Polymer samples, each of mass 3.0 ± 0.5 mg, were heated in a platinum melting pot from 20 to 400 • C at the heating rate of 10 • C/min and the oxygen flow rate of 60 mL/min. Based on obtained DSC curves, the temperature of oxidation onset of acrylic material was extrapolated. Measurement conditions were the same for all the samples, which enabled a comparison between DSC characteristics of the unaged coatings and coatings aged with battery acid. The thicknesses of the coatings were measured using an Elcometer 456CFN ultrameter (Elcometer, Aalen, Germany) (acc. PN-EN ISO 2808:2008 [58]), and their mean value was 115 ± 1 µm.
The Erichsen hardness tester (Erichsen, Ann Arbor, MI, USA) was used for measurements of the hardness of the coatings (acc. PN-EN ISO 2815:2004 [59]).
Contact angle θ C was determined with the help of a Goniometr 190 (Rame-Hart Instrument, Succasunna, NJ, USA) equipped with a camera and using MicroScan software.
The colour of the coatings was evaluated based on examination results obtained using a Konica Minolta CM-700d spectrophotometer (Konica Minolta, Tokyo, Japan).
Method of acrylic coatings ageing under the influence of the natural climatic conditions.
Climatic ageing of the coatings (acc. PN-EN ISO 2810:2005 [55]) took place on special racks where samples of the coatings were fastened after prior acclimatization. The racks with the samples were exposed for 24 months in a climatic station, situated on the grounds of the Mechanical Department in the University of Technology and Humanities in Radom (Central Poland).
The average annual climatic conditions during ageing of the coatings in the period of 2018-2019 were as follows [61,62]: Method of acrylic coatings ageing under the influence of battery acid Effects were investigated of the ageing of acrylic coatings under the influence of a sulphuric acid water solution of pH = 8, which is characteristic for battery acid used in cars. The maximum period of battery acid influence on the acrylic coatings was 336 h. For this purpose, cotton pads soaked with battery acid were applied on the surface of the coatings. The evaluation of the state of coating surfaces was done after 48, 96, 168, and 336 h of ageing.

Evaluation of the Destruction of Acrylic Coatings Aged in Natural Climatic Conditions
IR spectroscopic investigations (FTIR) were carried out in order to evaluate the chemical destruction of acrylic coatings aged at the climatic station for the period of 2 years. Obtained results, presented in Figure 1 in the form of infrared transmittance spectra, showed a dependence between transmittance (T) of infrared radiation and wavenumber (ν). We documented changes in the chemical structure of the coatings, which was evidenced by the increase of the carbonyl groups (C=O) content, as it was stated in the band with the peak of the wave number ν = 1724 cm −1 . This band corresponds to the carbonyl groups' stretching frequency (carbonyl valence vibrations). The increase of this band intensity documents the development of the ageing oxidation of the acrylic material.
SEM examination of the surface condition of the acrylic coatings showed that, as the ageing period increases, the destruction degree of the surface increases too (Table 1a-d).
As observed, climatic ageing leads to the chipping of filler and pigment particles from the surface of the coatings (Table 1c). Microcracks (Table 1b), craters (Table 1c), and etchings (Table 1c) appeared on the surface. The microcracks, which had a shape of parallel bands, probably formed areas of silver cracks, which arose because of the destructive influence of UV radiation (Table 1d).
Coatings 2021, 11, x FOR PEER REVIEW with the peak of the wave number ν = 1724 cm −1 . This band corresponds to the c groups' stretching frequency (carbonyl valence vibrations). The increase of this b tensity documents the development of the ageing oxidation of the acrylic materia SEM examination of the surface condition of the acrylic coatings showed tha ageing period increases, the destruction degree of the surface increases too (Tabl As observed, climatic ageing leads to the chipping of filler and pigment particles f surface of the coatings (Table 1c). Microcracks (Table 1b), craters (Table 1c), and e (Table 1c) appeared on the surface. The microcracks, which had a shape of paralle probably formed areas of silver cracks, which arose because of the destructive in of UV radiation (Table 1d).   with the peak of the wave number ν = 1724 cm −1 . This band corresponds to the carbonyl groups' stretching frequency (carbonyl valence vibrations). The increase of this band intensity documents the development of the ageing oxidation of the acrylic material. SEM examination of the surface condition of the acrylic coatings showed that, as the ageing period increases, the destruction degree of the surface increases too (Table 1a-d).
As observed, climatic ageing leads to the chipping of filler and pigment particles from the surface of the coatings (Table 1c). Microcracks (Table 1b), craters (Table 1c), and etchings (Table 1c) appeared on the surface. The microcracks, which had a shape of parallel bands, probably formed areas of silver cracks, which arose because of the destructive influence of UV radiation (Table 1d).  Acrylic coatings previously aged at the climatic station showed substantial destruction under the influence of accelerated acid rain ageing, which generated changes in their surface topography. Topography examples of coatings subjected to accelerated ageing with acid rain (water solution of sulphuric acid of pH = 5) are presented in Table 2. It is visible that changes in topography increased with the increase in the ageing period. This was caused by the increase of the coating's susceptibility to plastic deformation, which was associated with blistering [16].  Acrylic coatings previously aged at the climatic station showed substantial destruction under the influence of accelerated acid rain ageing, which generated changes in their surface topography. Topography examples of coatings subjected to accelerated ageing with acid rain (water solution of sulphuric acid of pH = 5) are presented in Table 2. It is visible that changes in topography increased with the increase in the ageing period. This was caused by the increase of the coating's susceptibility to plastic deformation, which was associated with blistering [16]. Acrylic coatings previously aged at the climatic station showed substantial destruction under the influence of accelerated acid rain ageing, which generated changes in their surface topography. Topography examples of coatings subjected to accelerated ageing with acid rain (water solution of sulphuric acid of pH = 5) are presented in Table 2. It is visible that changes in topography increased with the increase in the ageing period. This was caused by the increase of the coating's susceptibility to plastic deformation, which was associated with blistering [16].

Assessment of the Contact Angle θc of Acrylic Coatings' Surfaces
The operational life of protective acrylic coatings, which protect the surfaces of technical objects against the negative influence of environmental factors, depends strongly on the hydrophilicity of their surfaces, determining wettability of coatings with water. It should be stressed that, on hydrophilic surfaces, water drops fully spread, and the contact angle θ C = 0 • . In contrast, hydrophobic coatings of contact angle θ C = 90 • -180 • are the most advantageous with regard to their protective properties. Of course, in the case when the angle θ C = 180 • , the polymer coating is fully non-wettable with water.
Permeation of aggressive media (aqueous solutions of acids, alkali, and salts) into the polymer material of coatings equally depends on their surfaces' susceptibility to wetting with water. The lower value of contact angle θ C, the higher is the wettability of the coatings' surface with aggressive media; therefore, the surface contact with their drops is bigger, which results in higher absorptivity of coatings with these media.

Assessment of the Contact Angle θc of Acrylic Coatings' Surfaces
The operational life of protective acrylic coatings, which protect the surfaces of technical objects against the negative influence of environmental factors, depends strongly on the hydrophilicity of their surfaces, determining wettability of coatings with water. It should be stressed that, on hydrophilic surfaces, water drops fully spread, and the contact angle θC = 0°. In contrast, hydrophobic coatings of contact angle θC = 90°-180° are the most advantageous with regard to their protective properties. Of course, in the case when the angle θC = 180°, the polymer coating is fully non-wettable with water.
Permeation of aggressive media (aqueous solutions of acids, alkali, and salts) into the polymer material of coatings equally depends on their surfaces' susceptibility to wetting with water. The lower value of contact angle θC, the higher is the wettability of the coatings' surface with aggressive media; therefore, the surface contact with their drops is bigger, which results in higher absorptivity of coatings with these media.
Carried out investigations have indicated that the influence of battery acid on surfaces of acrylic coatings changed the values of their contact angle θC. In order to measure the value of contact angle θC for the surface of acrylic coatings, distilled water and diiodomethane were used as model measuring liquids. The values of free surface energy (SFE) and the polar and dispersive components for these liquids are known and presented in Table 3. Ten drops (of a volume of 5 mL each) of the liquids were applied in sequence with a micropipette to the surfaces of all acrylic coatings tested. Then, the value of contact angle ΘC for each of the 10 drops was measured. The influence of battery acid on the surfaces of acrylic coatings contributed to their contact angle θC decrease, in the case of water as well as diiodomethane (Table 4). Carried out investigations have indicated that the influence of battery acid on surfaces of acrylic coatings changed the values of their contact angle θ C . In order to measure the value of contact angle θ C for the surface of acrylic coatings, distilled water and diiodomethane were used as model measuring liquids. The values of free surface energy (SFE) and the polar and dispersive components for these liquids are known and presented in Table 3. Ten drops (of a volume of 5 mL each) of the liquids were applied in sequence with a micropipette to the surfaces of all acrylic coatings tested. Then, the value of contact angle Θ C for each of the 10 drops was measured. The influence of battery acid on the surfaces of acrylic coatings contributed to their contact angle θ C decrease, in the case of water as well as diiodomethane (Table 4). Coatings aged climatically for 2 years and then aged with battery acid for 336 h showed a decrease of the contact angle θ C value by 16%, whereas coatings aged only with battery acid for 336 h showed a decrease of the contact angle θ C value by 14%. These results document the increase of acrylic coatings hydrophilicity under the influence of ageing with battery acid, which is tantamount to the increase of the contact area of an aggressive medium drop with the coating surface. Therefore, the increase of coating susceptibility to absorb water (together with impurities) was observed, which migrates to the steel substrate and contributes to development of substrate corrosion.
Moreover, as a result of soaking of acrylic coatings with battery acid, their capacity for plastic deformation increases, which may result in microblisters development (Table 1c,d).
Subjecting acrylic coatings to battery acid action also caused an increase in their surface free energy (SFE) ( Table 5). The coatings after battery acid action showed a value of the SFE polar component 40% higher than non-aged coatings, which testify to a bigger chemical degradation of aged coatings. In the case of the coatings climatically aged beforehand and then subjected to battery acid action, the value increment of the SFE polar component was higher by 58%. Table 5. Surface free energy (SFE) of the acrylic coatings (description acc. Table 4).

Assessment of the Thickness of Acrylic Coatings
Battery acid action caused a thickness increase of 10% of the coatings previously aged climatically for 2 years. However, the thickness of the non-aged climatically coatings practically did not change after battery acid action.
The influence of battery acid action on the thickness of acrylic coatings is presented in Figure 2, while mathematical models of the thickness characteristics are presented in Table 6.    The reason that the thickness of the coating increases ( Figure 2) after being subjected to battery acid is probably highly linked to the increase in the porosity of the aged coatings and their soaking in battery acid, because earlier examinations of polymer coatings aged with aggressive media showed the generation of micro-and nanopores in coating material [24,25], the dimensions of which increased with the increase of the ageing period. These pores developed in the coatings that were soaking with aggressive media, which contributed to their thickness increase (as a result of coating swelling). The same process very likely occurred in the case of the coatings described in the present article, which were soaked in battery acid.
Moreover, coatings aged with battery acid show increased susceptibility to blistering ( Table 2) and cracking (Table 1). With ageing period, these pores, together with microcracks, form paths in the coating material, which conduct aggressive media to the metallic substrate, which causes its corrosion.

Evaluation of the Oxidative Resistance of Acrylic Coatings
Oxidative resistance of acrylic coatings was determined using differential scanning calorimetry (DSC). Based on obtained DSC curves (Figures 3 and 4), the following values of temperature were determined: oxidation onset temperature T g , exothermic peak temperature T 1 , endothermic peak temperature T 2 , and the thermal degradation end temperature T k of acrylic coatings.
Coatings 2021, 11, x FOR PEER REVIEW temperature; whereas, for the coatings aged with battery acid for 336 h, the exo peak occurs at temperature t = 368 °C, which is lower by 1.6% in comparison w temperature for non-aged coatings.
It should be noted that ageing of the acrylic coatings with battery acid contr the increase of their oxidation intensity, which was supported by the increase of t thermic band area (of the peak corresponding to temperature of t = 368 °C) in com with the non-aged coating. Moreover, a mass loss in the temperature range Tp curred. In the case of non-aged coatings, the mass loss ran to 20%. Oxidation pr occurring in the coatings in the time of ageing with battery acid for 336 h contrib the increase of their mass loss by up to 27%. It was stimulated by intensive devel of oxidation in the coatings aged with battery acid (Table 7).

Assessment of the Hardness of Acrylic Coatings
Results of Buchholz hardness tests of acrylic coatings subjected to battery acid ac are shown in Figure 5, while mathematical models of hardness characteristics are sented in Table 8. DSC examinations also bring information about the nature of reactions running during the thermal degradation of acrylic coatings. Reactions of rearrangement and oxidation trigger exothermic peaks; whereas, endothermic peaks refer mainly to depolymerisation processes running in the acrylic material.
Results of DSC measurements showed that oxidation of non-aged acrylic coatings runs the most intensively at temperature t = 374 • C, corresponding to the exothermic peak temperature; whereas, for the coatings aged with battery acid for 336 h, the exothermic peak occurs at temperature t = 368 • C, which is lower by 1.6% in comparison with this temperature for non-aged coatings.
It should be noted that ageing of the acrylic coatings with battery acid contribute to the increase of their oxidation intensity, which was supported by the increase of the exothermic band area (of the peak corresponding to temperature of t = 368 • C) in comparison with the non-aged coating. Moreover, a mass loss in the temperature range T p -T k occurred. In the case of non-aged coatings, the mass loss ran to 20%. Oxidation processes occurring in the coatings in the time of ageing with battery acid for 336 h contributed to the increase of their mass loss by up to 27%. It was stimulated by intensive development of oxidation in the coatings aged with battery acid (Table 7). Table 7. Thermal properties of the acrylic coatings.

Symbol of the Coating
Characteristic Values of Temperature (on DSC Curve) (at Heating Rate of 10 • C/min in Oxygen Atmosphere) ( • C)

Mass Loss in Temperature Range
T p -T k (on TG Curve)

Assessment of the Hardness of Acrylic Coatings
Results of Buchholz hardness tests of acrylic coatings subjected to battery acid action are shown in Figure 5, while mathematical models of hardness characteristics are presented in Table 8.

Assessment of the Hardness of Acrylic Coatings
Results of Buchholz hardness tests of acrylic coatings subjected to battery acid are shown in Figure 5, while mathematical models of hardness characteristics a sented in Table 8.   Changes in the chemical structure of acrylic coatings under the influence of battery acid (Points 3.2 and 3.4) contributed to their Buchholz hardness decrease. It was also found that the rate of hardness loss of acrylic coatings, aged climatically for 2 years, was higher than of unaged coatings, which resulted in the decrease of the aged coatings' resistance to scratching and erosion [23][24][25].

Assessment of Surface Roughness Parameters of Acrylic Coatings
Results from investigations of battery acid's influence on acrylic coatings indicated that coatings previously aged climatically for 2 years show higher values of surface roughness parameters than non-aged coatings. This is associated with the higher susceptibility of the climatically aged coatings to have fragments chipping from superficial layers. This is caused by the higher oxidation degree of acrylic resin in the case of climatically aged coatings, since the spectroscopic IR investigations proved the increased content of carbonyl groups in the coatings aged climatically compared with the non-aged coatings (Point 3.1). Ageing with battery acid also increased the oxidation degree of the acrylic coatings, which was documented by DSC examination (Point 3.4).
The characteristics of surface roughness parameters R a and R z of acrylic coatings subjected to battery acid action are shown in Figures 6 and 7, while mathematical models of characteristics of R a and R z roughness parameters are presented in Tables 9 and 10. coatings, since the spectroscopic IR investigations proved the increased content of carbonyl groups in the coatings aged climatically compared with the non-aged coatings (Point 3.1). Ageing with battery acid also increased the oxidation degree of the acrylic coatings, which was documented by DSC examination (Point 3.4).
The characteristics of surface roughness parameters Ra and Rz of acrylic coatings subjected to battery acid action are shown in Figures 6 and 7, while mathematical models of characteristics of Ra and Rz roughness parameters are presented in Tables 9 and 10.

Assessment of the Gloss of Acrylic Coatings
The results of gloss measurements showed that the influence of battery acid on acrylic coatings caused a substantial decrease in their gloss. The reason lies in the surface roughness increase of the coatings with increase of the period of battery acid action. It should be stressed that acrylic coatings previously aged climatically for 2 years showed a bigger loss of the gloss than non-aged ones. The coatings aged climatically showed significant destruction of their surface in the form of microcrackings, craters, and etchings (silver cracks), which influenced the surface topography, resulting in a gloss decrease. The coatings that were not aged climatically also showed a change in their surface topography (Points 3.1 and 3.6), resulting in a gloss decrease as well.
Battery acid's influence on the gloss of acrylic coatings at different angles (α) of light incidence are presented in Figures 8-10 (Figure 8 at α = 20 • , Figure 9 at α = 60 • , and Figure 10 at α = 85 • ), while mathematical models of gloss characteristics are given in Tables 11-13.

Assessment of the Colour of Acrylic Coatings
The degree of colour change of acrylic coatings was assessed according to criterion ∆E with the help of a Konica Minolta CM-700d apparatus, which is commonly used fo this purpose in scientific research. ∆E is a standard measurement, created by the Interna tional Commission on Illumination (ICI), that quantifies the difference between two col ours. The measurements showed substantial colour changes (visible even with unaided eye) as the colour parameter ∆E reached a value over 5 (Table 14).
The reason for the colour change was the fading of the pigment (iron red) under the influence of battery acid. Previous two-year climatic ageing caused colour fading, primar ily as a result of the sun's ultraviolet radiation.

Conclusions
The results of the examinations presented in this paper enable the following state ments about the influence of two-year climatic ageing and battery acid action for a period of 336 h on acrylic coatings' properties: 1. Climatic ageing of acrylic coatings for a period of 2 years caused their oxidation which was documented by spectroscopic IR investigations. SEM examination of the surface condition of the acrylic coatings showed that, as the ageing period increases, the destruction degree of the surface increases too (Table 1a-

Assessment of the Colour of Acrylic Coatings
The degree of colour change of acrylic coatings was assessed according to criterion ∆E with the help of a Konica Minolta CM-700d apparatus, which is commonly used for this purpose in scientific research. ∆E is a standard measurement, created by the International Commission on Illumination (ICI), that quantifies the difference between two colours. The measurements showed substantial colour changes (visible even with unaided eye) as the colour parameter ∆E reached a value over 5 (Table 14). The reason for the colour change was the fading of the pigment (iron red) under the influence of battery acid. Previous two-year climatic ageing caused colour fading, primarily as a result of the sun's ultraviolet radiation.

Conclusions
The results of the examinations presented in this paper enable the following statements about the influence of two-year climatic ageing and battery acid action for a period of 336 h on acrylic coatings' properties: 1.
Climatic ageing of acrylic coatings for a period of 2 years caused their oxidation, which was documented by spectroscopic IR investigations. SEM examination of the surface condition of the acrylic coatings showed that, as the ageing period increases, the destruction degree of the surface increases too (Table 1a-d). As observed, climatic ageing leads to the chipping of filler and pigment particles from the surface of the coatings and to microcracks, craters, and the appearance of etchings on the surface. The microcracks, which had a shape of parallel bands, probably formed areas of silver cracks, which arose because of the destructive influence of UV.

2.
Battery acid action for 336 h caused an increase in oxidation intensity in the acrylic material, which was documented by the results of the DSC examinations. The development of oxidation processes in the acrylic material contributed to the decrease of its Buchholz hardness. The rate of hardness loss of acrylic coatings (previously climatically aged for 2 years) in the course of ageing with battery acid was higher than that of climatically unaged ones.

3.
A slight increase in thickness of both kinds of coatings (non-aged and aged climatically) was also observed. The reasons for this phenomenon could be seen in the coating swelling as a result of soaking with battery acid. The tendency of acrylic coatings to absorb battery acid increases with ageing time progression. This was also confirmed by the contact angle θ C decrease in the case of water drops by a dozen percentage points for the coatings aged climatically. Therefore, the susceptibility to blistering of the coating aged with battery acid increased.

4.
Ageing of the coatings also contributed to a degradation increase of their chemical structure. This was indicated by an increase in the free surface energy (SFE) of the coatings. Acrylic coatings after ageing with battery acid demonstrated a polar component higher by 40%, which proved greater chemical degradation of these coatings, compared to non-aged coatings. Conversely, in the case of the coatings previously aged climatically, an increase of the polar component was higher and equal to 58%. 5.
The contact angle decreased by over 16% in the case of water. Therefore, the susceptibility to water absorption of coatings aged with battery acid increased, which caused blistering. 6.
The influence of ageing factors on the coatings contributed to their surface roughness increase. The coatings previously climatically aged for 2 years presented higher values of surface roughness parameters than the non-aged coatings. This was associated with a higher susceptibility of the climatically aged coatings to chipping. It was caused by a higher oxidation degree of acrylic resin due to climatic ageing. Spectroscopic IR investigations proved an increased content of carbonyl groups in the climatically aged coatings compared with the non-aged coatings.

7.
There was a substantial decrease of the gloss of coatings, which was caused by the increase in the surface roughness due to coating material chipping. The roughness increased with the lengthening of the period of battery acid action. It should be stressed that acrylic coatings previously aged climatically for 2 years showed greater gloss loss than the non-aged coatings. 8.
Substantial changes of coating colour were assessed according to the accepted criterion ∆E. The colour parameter ∆E of each examined coating reached a value over five. Colour changes were also visible with an unaided eye. 9.
As general results from the above conclusions, battery acid action caused destruction (blistering, surface roughness increase, gloss loss, and colour change) of the examined coatings. The destruction increased in the case of the coatings previously aged climatically.