JP6226912B2 - Release agent for tire inner surface - Google Patents

Description

  The present invention relates to a mold release agent for a tire inner surface. More specifically, the present invention relates to a mold release agent for a tire inner surface that exerts a mold release action by being interposed between a tire and a bladder during tire vulcanization molding.

In the tire manufacturing process, vulcanization molding of an unvulcanized green tire is usually performed by inflating a rubber bag called a bladder with hot water or steam inside the green tire and press-molding the unvulcanized green tire into a mold. Is done by. Usually, in order to perform this process smoothly, a release agent (a release agent for the tire inner surface) is applied in advance to the inner liner surface of the raw tire (hereinafter, the inner surface of the raw tire). The release agent for tire inner surface mainly has the performance to give good lubricity between the inner surface of the raw tire and the bladder (smoothness), and the ability to release the air that has entered the inner surface of the bladder and the raw tire and to bring them into close contact (air) (Permeability) is required, and when the bladder is contracted after the vulcanization is finished, a performance (releasability) that allows the bladder and the inner surface of the green tire to be smoothly peeled off is required. Therefore, a mixed composition of an oil-in-water emulsion of silicones that imparts releasability and a solid particle suspension that imparts smoothness and air permeability is applied as a mold release agent for the tire inner surface. Has been widely practiced.
Patent Document 1 discloses that a composition of an aqueous silicone emulsion and an inorganic powder containing mica having a primary average particle size of 55 to 95 μm is used as a release agent for the tire inner surface. In this example, since the inorganic powder is generally white, there is a problem that when the release agent for the tire inner surface is applied to the inner surface of the raw tire, the transparency is low and the appearance becomes whitish and cloudy. It was.
This problem can be solved to some extent by increasing the amount of silicone in the release agent for the tire inner surface. However, increasing the amount of silicone in the mold release agent also increases the amount of silicone that adheres to the tire bead obtained after vulcanization molding, and the high lubricity of silicone impedes braking of the tire. A new problem arises. In general, silicone has the highest price among the components constituting the release agent for the tire inner surface, and increasing the amount thereof is economically disadvantageous.
Moreover, in the release agent for tire inner surfaces of Patent Document 1, inorganic powder easily settles, and further improvement in dispersion stability over time as an agent has been desired.

JP 2005-193448 A

  The problem to be solved by the present invention is to provide a release agent for a tire inner surface that has good dispersion stability over time and is sufficiently transparent when adhered to a raw tire inner surface and vulcanized.

The present inventors have made intensive studies in order to solve the above problems, by including the specific polyhydric alcohol and a specific silicone component in the release agent for tire inner surface, conventional problems can be solved at a stroke The present invention has been found.

The release agent for tire inner surface according to the present invention includes an inorganic component made of powder, a silicone component, a surfactant, a polyhydric alcohol, and water,
The polyhydric alcohol is at least one selected from 3 to 8 valent alcohols, and the silicone component is a linear dimethylpolysiloxane having a viscosity at 25 ° C. of 100 to 100,000 cSt.
Here, it is preferable that at least one of the following requirements (1) to (3) is satisfied.
(1) The boiling point of the polyhydric alcohol is 200 ° C. or higher.
(2) The weight ratio of the total amount of the polyhydric alcohol and water is 35 to 90% by weight of the release agent for the tire inner surface, and the polyhydric alcohol is 10 to 60 of the total amount of the polyhydric alcohol and water. % By weight.
(3) The weight ratio of the inorganic component is 15 to 90% by weight, the weight ratio of the silicone component is 5 to 75% by weight, and the weight ratio of the surfactant with respect to the total amount of the inorganic component, the silicone component and the surfactant. Is 1 to 10% by weight.
The manufacturing method of the tire concerning the present invention includes the adhesion process which makes the above-mentioned mold release agent for tire inner surfaces adhere to a green tire inner surface, and the process of vulcanizing the green tire inner surface.

  The release agent for tire inner surface of the present invention has good dispersion stability over time. In addition, when the release agent for the tire inner surface is attached to the inner surface of the raw tire and vulcanized, the inner surface of the resulting tire is sufficiently transparent.

  Each component mix | blended with the mold release agent for tire inner surfaces of this invention is demonstrated, and the mold release agent for tire inner surfaces is explained in full detail.

[Inorganic component consisting of powder]
An inorganic component made of powder (hereinafter sometimes simply referred to as “inorganic component”) is a component mainly used to impart smoothness and air permeability.

Examples of inorganic components include, but are not limited to, smectites such as montmorillonite, beidellite, nontronite, saponite, hectorite, saconite, and stevensite; bentonite; vermiculite such as divermiculite and trivermiculite; halloysite, kaolinite Kaolin such as enderite, dickite, nacrite, chrysotile; talc, pyrophyllite, mica (mascobite, sericite), margarite, clintonite, muscovite, biotite, phlogopite, synthetic mica, fluoromica, paragolite , Phlogopite, repidolite, tetrasilic mica, teniolite and other phyllosilicates; antigolite and other jamon stones; donpasite, sudite, kukkaite, clinochlore, chamosite Chlorite, chlorite, such as nanlite; Sepiolite, Piolite-palyskite, such as palygorskite; (heavy) carbonates such as calcium carbonate, magnesium carbonate, barium carbonate; sulfates such as calcium sulfate, barium sulfate; silica, alumina, Metal oxides such as magnesium oxide, antimony trioxide, titanium oxide and iron oxide; metal hydroxides such as aluminum hydroxide, magnesium hydroxide and iron hydroxide; Bengala; diatomaceous earth; aluminum silicate; carbon black; be able to. These components may be used alone or in combination of two or more. It is preferable that the inorganic component is at least one selected from silica, mica and talc because it is inexpensive.
Although there is no limitation in particular about the average primary particle diameter of an inorganic component, 1-30 micrometers is preferable and 15-25 micrometers is more preferable. When the average primary particle size of the inorganic component is smaller than 1 μm,
When preparing the mold release agent for the tire inner surface, poor dispersion of the inorganic powder and insufficient air permeability may occur during tire vulcanization. On the other hand, when the average primary particle size of the inorganic component is larger than 30 μm, smoothness may be insufficient during tire vulcanization.

[Silicone component]
The silicone component is a main component that imparts releasability and lubricity to the release agent for the tire inner surface. Silicone is a general term for organopolysiloxanes is a concept including a silicone for oil. The silicone component contains these silicones.
Examples of the organopolysiloxane include dialkylpolysiloxanes such as dimethylpolysiloxane, diethylpolysiloxane, methylisopropylpolysiloxane, and methyldodecylpolysiloxane; methylphenylpolysiloxane, dimethylsiloxane / methylphenylsiloxane copolymer, dimethylsiloxane Alkylphenyl polysiloxanes such as diphenylsiloxane copolymers; alkylaralkyl polysiloxanes such as methyl (phenylethyl) polysiloxane and methyl (phenylpropyl) polysiloxane; 3,3,3-trifluoropropylmethyl polysiloxane Can do. These organopolysiloxanes may be used alone or in combination of two or more.

As the silicone component, from the viewpoint of releasability, silicone oil having a linear molecular structure, a low polymerization degree and fluidity at room temperature is preferable. The viscosity is not particularly limited, but the viscosity at 25 ° C. is preferably from 100 to 500,000 cSt, more preferably from 300 to 100,000 cSt, in terms of the balance between releasability and product stability.
As the silicone component, an emulsion of silicone may be used in the production of the release agent for the tire inner surface.

[Surfactant]
Surfactants not only disperse inorganic components in water, improve the dispersion stability of the release agent for the tire inner surface, but also repel the liquid when applying the release agent for the tire inner surface to the raw tire with a spray device etc. Provides preventing properties (wetting). The wettability can be adjusted by adjusting the blending amount.
The surfactant may be at least one selected from nonionic surfactants, anionic surfactants, cationic surfactants and amphoteric surfactants, and preferably nonionic surfactants and / or Or an anionic surfactant.

The nonionic surfactant is not particularly limited, but polyoxyalkylene such as polyoxyethylene alkyl ether / polyoxypropylene alkyl ether (alkyl may be any one of 1 to 3) is desirable. One or two or more nonionic surfactants may be used in combination.
The anionic surfactant is not particularly limited. For example, carboxylic acid type anionic surfactants and sulfonic acid type anionic surfactants are suitable. Particularly suitable are oxyethylene alkyl ether carboxylates and the like. As the sulfonic acid type anionic surfactant, alkane sulfonate, alkylbenzene sulfonate, dioctyl sulfosuccinate and the like are particularly suitable. These anionic surfactants may be used alone or in combination of two or more.

In order to improve dispersion stability and wettability, two or more surfactants may be used in combination, and examples thereof include a combination system of a nonionic surfactant and an anionic surfactant.
When the release agent for the tire inner surface contains a nonionic surfactant and an anionic surfactant, the respective weight ratios are not particularly limited, but there are reasons for the influence on foaming and the dispersion stability of inorganic components. Therefore, the nonionic surfactant / anionic surfactant (weight ratio) is preferably 75/25 to 99/1, more preferably 85/15 to 98/2, and 90/10 to 95 / 5 is particularly preferable.

〔water〕
Water can uniformly disperse the inorganic component contained in the tire inner surface release agent, and can evenly adhere the tire inner surface release agent to the raw tire inner surface. The water may be any of distilled water, ion exchange water, tap water, industrial water and the like.

[Polyhydric alcohol]
Polyhydric alcohol has high affinity with water, and when used with water, inorganic components are uniformly dispersed. Polyhydric alcohol suppresses sedimentation of inorganic components due to its moderate viscosity, improves the dispersion stability of the release agent for the tire inner surface over time, and uniformly attaches the release agent for the tire inner surface to the inner surface of the raw tire. Can be made. Moreover, when the release agent for the tire inner surface contains a polyhydric alcohol, when the release agent for the tire inner surface is adhered to the inner surface of the raw tire and vulcanized, the inner surface appearance of the obtained tire is sufficiently transparent. Become.
Although there is no limitation in particular about the valence (number of hydroxyl groups) of a polyhydric alcohol, Preferably it is 2-8, More preferably, it is 2-4, Most preferably, it is 2-3. Polyhydric alcohols with a valence greater than 8 are generally difficult to obtain.

Examples of the dihydric alcohol (polyhydric alcohol having 2 hydroxyl groups) include polyethylene glycols such as diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol and hexaethylene glycol; dipropylene glycol, tripropylene glycol and tetrapropylene. Polypropylene glycols such as glycol, pentapropylene glycol and hexapropylene glycol; polybutylene glycols such as dibutylene glycol, tributylene glycol, tetrabutylene glycol, pentabylene glycol and hexabutylene glycol; ethylene glycol, 1,2-propylene glycol 1,3-propylene glycol, 1,2-butanediol, 1,4-butanediol, 1,2, Pentanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-hexanediol, 1,5-hexanediol, 2,5-hexanediol, 1,7-heptanediol, 1,8-octane Diol, 1,2-octanediol, 1,9-nonanediol, 1,2-decanediol, 1,10-decanediol, 1,2-decanediol, 1,12-dodecanediol, 1,2-dodecanediol , 1,14-tetradecanediol, 1,2-tetradecanediol, 1,16-hexadecanediol, linear alkylene dihydric alcohols such as 1,2-hexadecanediol; 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol 2,4-dimethyl-2,4-dimethylpentanediol, 2,2-diethyl-1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, dimethyloloctane, 2- Ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2, Branched alkylene dihydric alcohols such as 4-diethyl-1,5-pentanediol; 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,2-cycloheptanediol, Examples thereof include cyclic alkylene dihydric alcohols such as tricyclodecane dimethanol.
Examples of the trihydric alcohol (polyhydric alcohol having 3 hydroxyl groups) include glycerin, trimethylolpropane, 1,2,6-hexanetriol, 3-methylpentane-1,3,5-triol, hydroxymethylhexanediol, A trimethylol octane etc. can be mentioned.

Examples of the 4- to 8-valent alcohol (polyhydric alcohol having 4 to 8 hydroxyl groups) include tetravalent alcohols such as pentaerythritol, diglycerin and ditrimethylolpropane; hexavalent alcohols such as dipentaerythritol, sorbitol and inositol; An octahydric alcohol such as pentaerythritol can be exemplified.
The boiling point (boiling temperature under one atmospheric pressure) of the polyhydric alcohol is not particularly limited, but is preferably 200 ° C. or higher, more preferably 210 ° C. or higher, particularly preferably 220 ° C. or higher, and most preferably 230 ° C. or higher. . When the boiling point of the polyhydric alcohol is less than 200 ° C., part of it is volatilized and lost during the vulcanization process, and the transparency of the inner surface appearance of the resulting tire may be lowered. There is no upper limit of the boiling point of the polyhydric alcohol, but it is preferably 400 ° C.

[Releasing agent for tire inner surface and manufacturing method thereof]
The mold release agent for a tire inner surface of the present invention is a composition comprising the inorganic component described above, a silicone component, a surfactant, a polyhydric alcohol, and water.
Since the release agent for tire inner surface of the present invention contains polyhydric alcohol, the dispersion stability over time is good, and when the release agent for tire inner surface is adhered to the inner surface of the raw tire and vulcanized In addition, the inner surface of the resulting tire is sufficiently transparent.

The weight ratio of the inorganic component, silicone component, surfactant, polyhydric alcohol, and water contained in the release agent for the tire inner surface is not particularly limited, but may be a blending ratio described below.
The weight ratio of the inorganic component is preferably 15 to 90% by weight, more preferably 35 to 80% by weight, and particularly preferably 55 to 70% by weight with respect to the total amount of the inorganic component, the silicone component and the surfactant. . When there are too few inorganic components, smoothness may deteriorate. Moreover, when there are too many inorganic components, powder may drop | omit from the molded tire inner surface and a tire storage location periphery may be soiled.

The weight ratio of the silicone component is preferably 5 to 75% by weight, more preferably 7 to 50% by weight, and particularly preferably 10 to 40% by weight with respect to the total amount of the inorganic component, the silicone component and the surfactant. . When there are too few silicone components, a mold release agent may deteriorate. Moreover, when there are too many silicone components, smoothness may deteriorate.
The weight ratio of the surfactant is preferably 1 to 10% by weight, more preferably 1 to 7.5% by weight, particularly preferably 2 to 5% by weight based on the total amount of the inorganic component, the silicone component and the surfactant. %. If the amount of the surfactant is too small, liquid repellency may occur on the inner surface of the raw tire during application, and the storage stability of the release agent for the inner surface of the tire may deteriorate. Moreover, when there are too many surfactants, the coating defect may generate | occur | produce by the deterioration of smoothness or foaming of the mold release agent for tire inner surfaces.

As described above, the polyhydric alcohol and water (hereinafter sometimes simply referred to as “solvent”) are components used to disperse the inorganic component as a common role. The weight ratio of the total amount of the solvent is not particularly limited, but is preferably 35 to 90% by weight, more preferably 40 to 70% by weight, and particularly preferably 45 to 60% with respect to the whole mold release agent for the tire inner surface. % By weight. When the amount of the solvent is too small, the inorganic component contained in the tire inner surface release agent may not be sufficiently dispersed, and a defective tire product may be generated. On the other hand, when there is too much solvent, time may be required for drying when the release agent for the tire inner surface is adhered. Moreover, the weight ratio of the inorganic component contained in the mold release agent for the tire inner surface is lowered, and the mold release property may be lowered.
The weight ratio of the polyhydric alcohol is not particularly limited, but is preferably 10 to 60% by weight, more preferably 20 to 55% by weight, and particularly preferably 30 to 30% with respect to the total amount of the solvent.
55% by weight. When the amount of polyhydric alcohol is too small, the dispersion stability with time may decrease. Moreover, when the release agent for the tire inner surface is adhered to the inner surface of the raw tire and vulcanized, the transparency of the inner surface appearance of the obtained tire may be lowered. On the other hand, when there is too much polyhydric alcohol, the air permeability deteriorates or the smoothness is insufficient due to the polyhydric alcohol occupying the voids between the individual particles of the inorganic component during tire vulcanization. Sometimes.

The mold release agent for tire inner surface of the present invention may contain additives such as thickeners, antifoaming agents, preservatives and the like as necessary in addition to the components described above.
About the manufacturing method of the mold release agent for tire inner surfaces of this invention, if the process of mixing an inorganic component, a silicone component, surfactant, and water is included, there will be no limitation in particular about a mixing order, the mixing equipment to be used, etc. .

〔tire〕
The tire of the present invention is a tire obtained by attaching the above-described release agent for the tire inner surface to the inner surface of the raw tire and vulcanizing it.
The tire of the present invention can be manufactured, for example, through an adhesion process and a vulcanization process described below.

[Adhesion process]
In the attaching step, first, a tire original form called a raw tire is prepared by combining and bonding necessary members such as a bead wire and a tire cord mainly with unvulcanized rubber.
Subsequently, the mold release agent for tire inner surfaces of this invention is made to adhere to this raw tire inner surface. As a method for attaching the release agent for the tire inner surface, spraying with an air gun or an airless gun is generally used, but a brush coating or a centrifugal coating machine may be used. The adhesion amount of the release agent for the tire inner surface varies depending on the use and size of the tire product, but is preferably 10 to 50 g / m ² after drying. Thereafter, until the release agent for the tire inner surface attached to the inner surface is sufficiently dried, the raw tire is left for several days if it is several tens of minutes to longer at room temperature.

[Vulcanization process]
Vulcanization is performed as follows on the dry green tire obtained in the adhesion step. First, the raw tire is placed in a metal mold, and a rubber bag called a bladder is pressed at high temperature with steam or the like from the inside to press the raw tire against the mold to obtain the final tire shape and tread. Vulcanize to form a pattern. The bladder surface temperature (mold temperature) during vulcanization is preferably 160 to 190 ° C., the pressure is preferably 12 to 30 kg / cm ² , and the vulcanization time is preferably 10 to 60 minutes. The tire of the present invention is advantageous in terms of aesthetics because the inner surface of the tire is not white and cloudy but transparent, as compared with the tire of the prior art.

Examples of the present invention and comparative examples will be described in detail below, but the scope of the present invention is not limited to these examples. Hereinafter, “parts” means “parts by weight”. The boiling point means a boiling temperature under one atmospheric pressure. The following Example 3 is referred to as Reference Example 3, and the following Example 4 is referred to as Reference Example 4.

[Example 1]
(Preparation of mold release agent)
Purified glycerin (purity: 98%, boiling point: 290 ° C.), which is a polyhydric alcohol, is uniformly dissolved in 53.5 parts of water, and then an oil-in-water emulsion of dimethylpolysiloxane (base oil viscosity) : About 10,000 mPa · s, solid content: 40%) 6 parts, mica powder 4 parts, talc powder 10 parts, carboxymethylcellulose (viscosity of 1% aqueous solution: 10 mPa · s) 0.5 part and sodium dodecylbenzenesulfonate 1 part was added and dissolved and dispersed uniformly using a homomixer to prepare a release agent. The obtained release agent was allowed to stand at room temperature for 10 hours. No sedimentation of the inorganic powder was observed, and the dispersion stability over time was good.

(Evaluation of release agent)
The obtained release agent was applied to an unvulcanized inner liner rubber sheet of 4 cm × 7 cm × 0.2 cm so that the coating amount after drying was 15 g / m ² . Next, a bladder rubber sheet of the same size was superposed on this unvulcanized rubber sheet, set on a desktop test press machine, and vulcanized by pressurizing at a mold temperature of 180 ° C. and a pressure of 20 kg / cm ² for 20 minutes.
The vulcanized rubber sheet was peeled off to obtain a vulcanized inner liner rubber sheet. This vulcanized inner liner rubber sheet was confirmed to have high transparency because the whiteness of mica and talc powder was suppressed by appearance due to the effect of glycerin.

(tire)
The release agent obtained above was applied to the inner surface of a 215 / 60R16 size raw tire so that the coating amount after drying was 15 g / m ² . Next, ten tires coated with a release agent were pressurized at a mold temperature of 180 ° C. and a pressure of 20 kg / cm ² for 20 minutes and vulcanized. The inner surface of the obtained tire was confirmed to have high transparency because the whiteness of mica and talc powder was suppressed.

[Example 2]
Mixing and dissolving 20 parts of a commercially available inner surface release agent for tires (RA-365P manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) in which necessary components as a release agent such as mica, talc, and silicone emulsion are mixed in advance in 55 parts of water Further, 25 parts of purified glycerin used in Example 1 was added to obtain a release agent. The dispersion stability over time of the obtained release agent was as good as in Example 1.
Using this release agent, the release agent was evaluated in the same manner as in Example 1 to produce a tire. In any case, the whiteness of the powder component contained in RA-365P was suppressed by glycerin, and it was confirmed that the transparency was high.

Example 3
A release agent was obtained in the same manner as in Example 1 except that the purified glycerin was changed to diethylene glycol (purity: 99%, boiling point: 244.3 ° C.) in Example 1. The dispersion stability over time of the obtained release agent was as good as in Example 1.
Using this release agent, the release agent was evaluated in the same manner as in Example 1 to produce a tire. In any case, the whiteness of mica and talc powder was suppressed by diethylene glycol, and it was confirmed that the transparency was high.

Example 4
A release agent was obtained in the same manner as in Example 1 except that the purified glycerin was changed to dipropylene glycol (boiling point: 232 ° C.) in Example 1. The dispersion stability over time of the obtained release agent was as good as in Example 1.
Using this release agent, the release agent was evaluated in the same manner as in Example 1 to produce a tire. In either case, the whiteness of mica and talc powder was suppressed by dipropylene glycol, and it was confirmed that the transparency was high.

[Comparative Example 1]
6 parts of oil-in-water emulsion of dimethylpolysiloxane (base oil viscosity: about 10,000 mPa · s, solid content: 40%), 7 parts of mica powder, 10 parts of talc powder with respect to 78.5 parts of water, 0.5 parts of carboxymethylcellulose (viscosity of 1% aqueous solution: 10 mPa · s) and 1 part of sodium dodecylbenzenesulfonate were added and uniformly dissolved and dispersed using a homomixer to prepare a comparative release agent. When the obtained comparative release agent was allowed to stand at room temperature for 10 hours, sedimentation of the inorganic powder was observed, and the dispersion stability over time was not good.
Using this comparative release agent, the release agent was evaluated in the same manner as in Example 1 to produce a tire. In any case, the rubber surface was not transparent but clouded due to the whiteness of mica and talc powder.

[Comparative Example 2]
25.0 parts of 2-propanol, which is a monohydric alcohol, is uniformly dissolved in 53.5 parts of water, and then an oil-in-water emulsion of dimethylpolysiloxane (base oil viscosity: about 10,000 mPa · s, solid content) : 40%) 6 parts, mica powder 4 parts, talc powder 10 parts, carboxymethylcellulose (viscosity of 1% aqueous solution: 10 mPa · s) 0.5 part and sodium dodecylbenzenesulfonate 1 part are added, and a homomixer is used. A release agent was prepared by uniformly dissolving and dispersing.
Using this comparative release agent, the release agent was evaluated in the same manner as in Example 1 to produce a tire. In any case, the rubber surface was not transparent but clouded due to the whiteness of mica and talc powder.

Claims (4)

Including an inorganic component made of powder, a silicone component, a surfactant, a polyhydric alcohol, and water,
The polyhydric alcohol is at least one selected from 3 to 8 alcohols,
A release agent for a tire inner surface, wherein the silicone component is a linear dimethylpolysiloxane having a viscosity of 100 to 100,000 cSt at 25 ° C.   The weight ratio of the total amount of the polyhydric alcohol and water is 35 to 90% by weight of the release agent for the tire inner surface, and the polyhydric alcohol is 10 to 60% by weight of the total amount of the polyhydric alcohol and water. The mold release agent for tire inner surfaces of Claim 1 which exists.   The weight ratio of the inorganic component is 15 to 90% by weight, the weight ratio of the silicone component is 5 to 75% by weight, based on the total amount of the inorganic component, the silicone component and the surfactant. The mold release agent for tire inner surfaces of Claim 1 or 2 whose weight ratio is 1 to 10 weight%. The manufacturing method of a tire including the adhesion process which adheres the mold release agent for tire inner surfaces in any one of Claims 1-3 to a green tire inner surface, and the process of vulcanizing a green tire inner surface.